- Email: [email protected]
Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Review
Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism Zahra Bahadoran,1 Parvin Mirmiran,2 and Asghar Ghasemi3,* Nitric oxide (NO) contributes to carbohydrate metabolism and decreased NO bioavailability is involved in the development of type 2 diabetes mellitus (T2DM). NO donors may improve insulin signaling and glucose homeostasis in T2DM and insulin resistance (IR), suggesting the potential clinical importance of NO-based interventions. In this review, site-specific roles of the NO synthase (NOS)–NO pathway in carbohydrate metabolism are discussed. In addition, the metabolic effects of physiological low levels of NO produced by constitutive NOS (cNOS) versus pathological high levels of NO produced by inducible NOS (iNOS) in pancreatic b-cells, adipocytes, hepatocytes, and skeletal muscle cells are summarized. A better understanding of the NOS–NO system in the regulation of glucose homeostasis can hopefully facilitate the development of new treatments for T2DM.
NO and Carbohydrate Metabolism at a Glance NO, a ubiquitous signaling molecule and unique gasotransmitter, is involved in several physiological and pathological processes [1]. An overview of NO synthesis, the different NOS isoforms, and the concentration-dependent and dual (physiological and pathological) effects of NO are summarized in Box 1. Emerging data suggest that impaired NO homeostasis is involved in the development of IR and T2DM [2,3]. This idea is supported by human studies on polymorphisms in NOS genes [4–7] (Box 1), genetically modified animal models of the NOS–NO system [8–10] (Figure 1), and pharmacological investigations using NO donors (see Glossary) and NOS inhibitors [11–13]. The hypoglycemic properties of oral antidiabetic agents [e.g., metformin, thiazolidinediones (TZDs)] are also partly attributed to their capacity to modulate the NOS–NO system in pancreatic islets, skeletal muscle cells, hepatocytes, and adipocytes [14–16]. The physiological actions of NO in regulating carbohydrate metabolism are mostly attributed to low levels of NO produced by endothelial (eNOS) and neural (nNOS) NOS isoforms, whereas iNOS is mostly responsible for detrimental actions. In this review, we summarize current data on the role of the NOS–NO system in carbohydrate metabolism. Specifically, we discussed how the different NOS isoforms (eNOS/nNOS vs iNOS) are involved in glucose and insulin homeostasis in pancreatic b-cells, skeletal muscle, liver, and adipose tissue. The role of the NOS–NO system in the central regulation of glucose homeostasis is also discussed.
NO and Insulin Secretion All three NOS isoforms are expressed in pancreatic b-cells; nNOS is mainly localized in insulin secretory granules, and to a lesser extent in the mitochondrion and the nucleus [17]. Although the presence of eNOS in pancreatic b-cells has been reported [18], there are few data on eNOS’s function in b-cells [19]. iNOS is not detectable in b-cells at basal glucose levels and is expressed following exposure to higher glucose concentrations in the cytoplasm [20,21]. NO derived from cNOS acts as a mediator or negative feedback inhibitor of glucose-stimulated insulin secretion (GSIS) [21]. Stimulatory effect of cNOS-derived NO on GSIS is mediated by Ca+2 mobilization from the endoplasmic reticulum or mitochondrial pools; that is, by transient reversible increases in [Ca+2]i [22,23]. In addition, nNOS-derived NO increases glucokinase (GK) activity via S-nitrosylation of cysteine residues [24], a critical process that mediates GK dissociation from insulin secretory granules and potentiates insulin secretion [25] (Figure 2).
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
Highlights NO is involved in carbohydrate metabolism and disrupted NO pathways (i.e., decreased cNOSderived NO bioavailability or iNOS-induced overproduction of NO) leads to the development of T2DM. cNOS-derived NO improves insulin secretion and signaling, increases glucose uptake, and regulates hepatic glucose output. These physiological effects of NO are mainly mediated by the sGC–cGMP pathway. Cytokine-induced overactivity of iNOS leading to pathological levels of NO (micromolar) disturbs glucose and insulin homeostasis. NO-releasing drugs can restore disrupted NO signaling and improve carbohydrate metabolism in insulin resistance and T2DM. The clinical implications of NO donors encapsulated with common hypoglycemic agents like metformin might be considered as a future treatment for T2DM.
1Nutrition and Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran 2Department of Clinical Nutrition and Human Dietetics, Faculty of Nutrition Sciences and Food Technology, National Nutrition and Food Technology Research Institute, Shahid Beheshti University of Medical Sciences, Tehran, Iran 3Endocrine Physiology Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran
*Correspondence: [email protected], [email protected]
https://doi.org/10.1016/j.tem.2019.10.001 ª 2019 Elsevier Ltd. All rights reserved.
1
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Box 1. NOS–NO System and Carbohydrate Metabolism
Glossary
cNOS (eNOS and nNOS) isoforms and the iNOS isoform are involved in NO biosynthesis from L-arginine. Splice variants of the nNOS isoform (i.e., nNOSm, nNOSb, and mtNOS) have also been detected in skeletal muscle [36]. cNOS-derived NO (at low-nanomolar concentrations) mostly mediates physiological actions through activation of the sGC–cGMP pathway, whereas high concentrations (micromolar) of iNOS-induced NO mediate pathological effects, mostly through S-nitrosylation and nitration of proteins and the generation of peroxynitrite (ONOO).
AMP-activated protein kinase (AMPK): an energy sensor that regulates cellular metabolism; it is activated by a deficit in nutrient status and stimulates glucose uptake and lipid oxidation to produce energy. cGMP-dependent protein kinase or protein kinase G (PKG): a serine/threonine-specific protein kinase that is activated by cGMP. Glucose-inhibited (GI) and glucose-excited (GE) neurons: glucose-sensing neurons widely dispersed throughout the hypothalamus. GI neurons are activated in hypoglycemia via an interaction between AMPK and NO, which leads to chloride channel closure, membrane depolarization, and increased action potential frequency. GE neurons mainly utilize a glucose-sensing mechanism like that of the pancreatic b-cell, through KATP channels. KATP channel: an ATP-sensitive potassium channel and metabolic sensor that couples cellular metabolism to electrical activity. In pancreatic b-cells, the KATP channel regulates GSIS and is a target for sulfonylurea antidiabetic drugs. Macrophage metalloelastase (MMP12): a matrix metallopeptidase predominantly expressed by tissue mature macrophages; positively regulates iNOS expression and activity. Nitric oxide (NO) donors: pharmacologically active substances that release NO in vivo or in vitro; the most common NO donors include sodium nitroprusside (SNP), S-nitroso-N-acetyl-penicillamine (SNAP), 2-(N,N-diethylamino)diazenolate-2-oxide (DEANO), 3-morpholinosydnonimine (SIN-1), 1,1-diethyl-2-hydroxy-2-nitrosohydrazine (NONOate), 1-hydroxy-2-oxo-3-[Nmethyl-3-aminopropyl]-3-methyl1-triazene (NOC-7), and S-nitrosoglutathione (GSNO). NO scavengers: pharmacologically active substances that interfere with the toxic effects of excessive NO production while preserving some activity of NO that might be essential for normal biological function [e.g., 2-(4-carboxyphenyl)-4,5-dihydro-4,4,5,5-
Both decreased eNOS-derived NO bioavailability (i.e., decreased NOS expression and activity, uncoupling of NOS or NO scavenging by ROS) [2,93] and increased iNOS overexpression and activity occur in diabetes and IR [29]. Studies on eNOS gene polymorphisms in humans provide evidence on the critical roles of NO in carbohydrate metabolism [4]. The most common genetic variants of eNOS, considered risk factors for IR and T2DM, are an single nucleotide polymorphism (SNP) in the promoter region (T786C, rs2070744), an SNP in exon 7 (G894T, rs1799983), an SNP in intron 18 (IVS18-27A/C), and a variable number tandem repeat (VNTR) in intron 4 [4–7]. Use of NO donors (e.g., SNAP, SNP, SIN-1, NONOate), NOS substrates (L-arginine, L-citrulline), or NOS inhibitors (e.g., L-NMMA, L-NAME) is the most common pharmacological approach to determine how NO regulates glucose homeostasis (see text). Besides this, some part of the mechanisms by which antidiabetic drugs regulate carbohydrate metabolism are mediated by the NOS–NO system (e.g., modulation of NOS expression and activity). Metformin increases insulin secretion via AMPK-dependent iNOS/nNOS inhibition in pancreatic b-cells [14]. By contrast, in pancreatic islets, glibenclamide stimulates iNOS/nNOS, which decreases its ability to induce insulin secretion; metformin suppresses glibenclamide-induced NO production and augments glibenclamide-induced insulin release [14]. Metformin and troglitazone, as activators of the AMPK pathway, inhibit cytokine-induced iNOS expression and decrease iNOS protein turnover, normalize insulin-induced PI3K activity, and reverse IR in skeletal muscle cells and adipocytes [15].
In isolated pancreatic islets, increasing glucose concentration dose dependently increases the activity of cNOS and iNOS; however, cNOS activity is more rapidly adjusted to glucose concentration than iNOS activity [21]. Inhibition of cNOS activity in pancreatic islets potentiates GSIS and abolishes the negative peak that separates the first and second phases of insulin secretion, indicating negative feedback effect of NO on GSIS and its importance for the pattern of GSIS [21]. This negative feedback effect inhibits excessive insulin release in response to high glucose concentrations and protects b-cells [21,26]. One possible mechanism for the negative feedback effect of cNOS-derived NO on GSIS is the inhibition of phosphofructokinase and therefore glucose metabolism in pancreatic b-cells [27]. In addition to the production of NO (oxidating activity), nNOS has cytochrome c reductase activity (nonoxidating activity) [17]. nNOS inhibits GSIS by increasing NO production and stimulates GSIS by its nonoxidating activity; a balance between these two activities is essential for normal insulin secretion in response to glucose [17]. Protein inhibitor of nNOS (PIN) increases GSIS, an effect that is not related to the oxidating or nonoxidating activities of nNOS and is mediated by affecting the migration of insulin secretary granules [28]. mRNA/protein expression of iNOS is high in pancreatic islets of patients with T2DM, where inhibition of iNOS restores disrupted GSIS [29]. iNOS-derived NO mostly causes b-cell dysfunction, impaired insulin secretion, hyperglycemia, and the development of diabetes [21,26,29,30]. iNOS-derived NO, by a 30 ,50 -cGMP-independent mechanism inhibits insulin secretion [31] by inhibiting the mitochondrial electron transport chain (complexes I and II) and mitochondrial aconitase activity [32], S-nitrosylation of critical thiol groups involved in the secretory process [33], and tyrosine nitration and subsequent downregulation of GK [30]. Taking these findings together, the role of cNOS-derived NO as a mediator or negative feedback inhibitor of GSIS is controversial; however, the literature is in favor of an inhibitory effect of cNOS-derived NO on insulin secretion. This effect has physiological relevance to the normal pattern of insulin secretion. In addition, nNOS affects GSIS by mechanisms unrelated to NO synthesis (e.g., having
2
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Trends in Endocrinology and Metabolism
Figure 1. An Overview of Genetic Modifications of the Nitric Oxide Synthase (NOS)–NO System and Disrupted Glucose and Insulin Homeostasis in Animal Models. Impaired glucose and insulin homeostasis occur in both complete (eNOS/) and partial (eNOS+/) eNOSdeficient mice, whereas eNOS-overexpressed models (eNOS+) are resistant to chemically [streptozotocin (STZ) and alloxan (ALX)] and high-fat diet (HFD)-induced hyperinsulinemia. nNOS disruption in mice impairs glucose metabolism and results in insulin resistance (IR). Overexpression of iNOS (iNOS+) in skeletal muscle and liver induces IR, whereas iNOS-deficient models are resistant to HFD-induced IR.
cytochrome c reductase activity). While cNOS-derived NO mostly serves as a physiological negative feedback inhibitor of insulin secretion, iNOS-derived NO is mostly involved in pathological functions.
NO and Carbohydrate Metabolism in Skeletal Muscle All three NOS isoforms are expressed in skeletal muscle [34]. nNOS splice variants [nNOSm, nNOSb, and mitochondrial NOS (mtNOS)] are the most relevant isoforms involved in glucose uptake [35]. eNOS is highly expressed in the endothelium of vessels in skeletal muscle [36] and is responsible for 30% of glucose uptake in human skeletal muscles [37]. iNOS is hardly detectable in normal human skeletal muscle and expressed in response to inflammatory cytokines and oxidative stress [36].
Effects of cNOS-Derived NO on Skeletal Muscle Glucose Uptake The effects of cNOS-derived NO on skeletal muscle glucose uptake are mostly attributed to its mediatory role in response to insulin and contraction [38,39] and include increased blood flow, increased glucose transporter 4 (GLUT4) expression and translocation to membrane, and increased insulin transendothelial transport (ITT) (Figure 3). However, at least in fast-twitch glycolytic skeletal muscles, NOS inhibition has no effect on insulin- or contraction-induced glucose uptake, indicating that NO also has an insulin- and contraction-independent stimulatory effect on glucose uptake [40].
tetramethyl-1H-imidazolyl-1-oxy3-oxide (carboxy-PTIO)]. NO synthase (NOS) inhibitors: pharmacologically active substances that inhibit NOS enzymes and therefore NO production. The most common NOS inhibitors are L-arginine analogs [e.g., NGnitro-L-arginine methyl ester (LNAME), L-NG-monomethyl Larginine (L-NMMA), NG-methyl-Larginine (L-NMA), nitro-L-arginine (L-NNA)], which are competitive and nonselective inhibitors. Some NOS inhibitors are selective; for example, 7-nitroindazole (7-NI), a specific nNOS inhibitor, and aminoguanidine, a selective iNOS inhibitor. Peroxynitrite (ONOO): produced by the reaction of NO with the superoxide anion (O2d); a strong oxidant that reacts at a relatively slow rate with most biological molecules. The pathological effects of NO at toxic levels are partly attributed to peroxynitrite. S-Nitrosation: refers specifically to chemical reactions involving the addition of a nitrosonium ion (NO+) to a nucleophilic group, such as an amine or thiolate. S-Nitrosylation: refers to the direct addition of NO to a reactant (e.g., cysteine residues of a protein); in chemistry, it is defined as the coordination of NO to a metal center to form a metal nitrosyl complex. Soluble guanylyl cyclase (sGC): a heterodimeric (a and b subunits) heme protein of molecular mass 150 kDa; known as the primary receptor of NO that responds to NO binding by increasing cyclase activity, producing guanosine 30 ,50 -cGMP, and generating a signaling cascade.
Insulin activates vascular eNOS via the phosphoinositide 3-kinase (PI3K)–protein kinase B (PKB/Akt) pathway and causes NO release [41,42]; NO mediates insulin-induced capillary recruitment and increases blood flow, insulin delivery, and insulin-mediated glucose disposal [43]. In addition to eNOS-derived NO, nNOSm-derived NO has an important role in increasing blood flow, particularly during exercise [39]. Both insulin and muscle contraction activate nNOSm [via Akt- and AMP-activated protein kinase (AMPK)-dependent phosphorylation] and the resultant increased NO production promotes the expression and translocation of the GLUT4 and therefore glucose uptake [38]. NO increases GLUT4 gene expression by phosphorylation of a-AMPK and acetyl-CoA carboxylase and the translocation of phosphorylated a-AMPK to the nucleus [44]. NO increases GLUT4 translocation using the soluble guanylyl cyclase (sGC)–cGMP and cGMP-dependent protein kinase (PKG) pathway;
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
3
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Trends in Endocrinology and Metabolism
Figure 2. Nitric Oxide Synthase (NOS) Isoforms in Pancreatic b-Cells and the Role of Endogenous and Exogenous NO in Insulin Secretion. Physiological levels of endogenous nNOS-derived NO (1) stimulate Ca2+ mobilization from the endoplasmic reticulum and mitochondrion and increase the cytosolic free Ca2+ concentration, a critical step for glucose-stimulated insulin secretion, and (2) induce S-nitrosylation of glucokinase, an integral component of insulin granules, and regulate its localization and activity. (3) nNOS-derived NO in response to high levels of glucose may acts as a negative feedback signal for glucose-stimulated insulin secretion by the activation of KATP channels. (4) Pathological levels of iNOSinduced NO in response to toxic levels of glucose or inflammatory cytokines disturb glucose-stimulated insulin secretion by disturbing the glycolytic pathway and mitochondrial respiration. Abbreviations: RyR, ryanodine receptor; TCA, tricarboxylic acid; L-VDCC, L-type voltage-dependent calcium channel.
however, some cGMP–PKG-independent mechanisms (especially during skeletal muscle contraction) are also involved [39]. Potential cGMP-independent mechanisms are S-nitrosylation, S-glutathionylation, and tyrosine nitration of proteins involved in GLUT4 translocation [39]; the importance of these mechanisms is highlighted by knowing that the NO–sGC–cGMP pathway accounts for up to 50% of NO actions in skeletal muscle [36], and NO-induced sGC activity is lower in skeletal muscle than in most other tissues (15- vs 100–400-fold). Insulin delivery to muscle interstitial fluid, named ITT, is a rate-limiting step in the peripheral action of insulin [45]. NO increases ITT; this effect is sGC–cGMP-independent and occurs via the S-nitrosylation and decreased activity of protein-tyrosine phosphatase 1B (PTP1B) and the subsequently elimination of its inhibitory effect on insulin signaling and insulin transport [45].
Effects of iNOS-Derived and High Doses of Exogenous NO on Skeletal Muscle Glucose Uptake The mRNA expression and protein content of iNOS are higher in the skeletal muscle of patients with T2DM and IR [46–48]. Obesity-linked iNOS induction is mediated by increased expression and
4
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Figure 3. Nitric Oxide Synthase (NOS) Isoform Localization in Skeletal Muscle and the Role of NO in Insulin and Glucose Transport into Skeletal Muscle. (1) Both eNOS- and nNOSm-derived NO increase glucose disposal and insulin transendothelial transport. Insulin and skeletal muscle contraction stimulate nNOSm activity; nNOSm-derived NO increases (2) GLUT4 expression (by AMPK phosphorylation) and (3) GLUT4 translocation by phosphorylation and S-nitrosylation. (4) nNOSb and mtNOS are involved in skeletal muscle contraction and metabolism. iNOS-derived NO (5) disturbs insulininduced glucose uptake and (6) inhibits GLUT4 expression. Abbreviations: AMPK, 50 -AMP-activated protein kinase; CAT-1, cationic amino acid transporter-1; Cav-1, caveolin 1; DG, dystroglycan; GLUT, glucose transporter; IRS-1, insulin receptor substrate-1; mtNOS, mitochondrial NOS; PKB/Akt, protein kinase B; PDK1, 3-phosphoinositide-dependent protein kinase 1; PKG, protein kinase G; SG, sarcoglycan; sGC, soluble guanylyl cyclase; Syn, a1-syntrophin.
secretion of proinflammatory cytokines, including tumor necrosis factor alpha (TNF-a), interferongamma (IFN-g), interleukin-1b (IL-1b), and IL-6 in myocytes [49]. Increased circulating or intramyocellular free fatty acids have been also proposed as underlying mechanisms of obesity-induced iNOS in skeletal muscle [50]. Upregulation of iNOS in skeletal muscle is mediated by the activation of mitogen-activated protein kinase (MAPK) and its downstream pathways [extracellular regulated kinase (ERK1/ERK2), p38, in particular, c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK)], the transcription factor nuclear factor kappa B (NFkB), and the Janus kinase/signal transducer and activator of transcription (JAK–STAT) signaling pathway [48]. Accumulating evidence indicate that iNOS mediates high-fat diet (HFD)-induced IR in skeletal muscle [49,51,52]. iNOS-disrupted models are resistant to HFD-IR [52] and iNOS-knockout ob/ob mice have higher insulin sensitivity than iNOS+/+ ob/ob mice [51]. iNOS-derived NO or high doses of NO donors decrease GLUT4 gene expression and mitochondrial capacity in skeletal muscle [44,48]. Such pathological NO levels act in a sGC-independent manner [53], by the S-nitrosation and inactivation of proteins involved in the early steps of insulin signaling [i.e., insulin receptor beta (IRb), insulin receptor substrate-1 (IRS-1), and Akt [54]]. In addition, in skeletal muscle cells, iNOS-derived NO increases
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
5
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
proteasome-dependent degradation of IRS-1, which is involved in the development of T2DM and IR [51]. Furthermore, iNOS induction impairs insulin-dependent PI3K and Akt activation [51]. To sum up, cNOS-derived NO at physiological levels improves skeletal muscle insulin sensitivity and promotes glucose uptake via increased blood flow-dependent glucose delivery to skeletal muscle, increased GLUT4 expression and translocation, and increased ITT. By contrast, iNOS-derived NO at pathological levels (induced by obesity and inflammatory cytokines) impairs skeletal muscle insulin sensitivity and glucose uptake.
NO and Carbohydrate Metabolism in Adipose Tissue The predominant or probably the only cNOS isoform expressed in both white adipose tissue (WAT) and brown adipose tissue (BAT) seems to be eNOS [55,56]. In WAT, eNOS is activated by insulin (via the PI3K/Akt and MAPK/protein phosphatase-1 pathways) [57] and angiotensin II (by increasing intracellular calcium concentrations) [55]. In BAT, eNOS is located in the cytoplasm and nucleus of adipocytes and 70% of nuclear NOS activity is attributed to eNOS [58]. In BAT, eNOS expression is controlled by sympathetic fibers [56] and cold exposure and b3-adrenergic agonists enhance eNOS activity [58]. iNOS protein is found in both BAT and WAT [59] and is localized in adipocytes and other cells, such as macrophages [60]. NO mediates insulin-stimulated glucose uptake in both BAT and WAT and NOS blockade in these tissues can reduce insulin’s action on glucose uptake by more than 50% [61]. NO also increases glucose uptake in 3T3-L1 adipocytes through insulin-independent (without phosphorylation of IRS-1 and Akt) translocation of GLUT-4; this sGC-dependent effect of NO seems to be additive to effect of insulin [62]. Constitutive formation of NO by adipocyte eNOS is suggested to be important for normal glucose and insulin homeostasis in WAT [55]; support for this notion comes from data indicating that decreased eNOS phosphorylation, eNOS uncoupling, and decreased eNOS-derived NO in WAT contributes to the development of IR in obesity [63]. Beneficial effects of NO on glucose metabolism in WAT are achieved by mediating insulin-dependent and insulin-independent glucose uptake, and sGC and PKG (PKG1 and PKG2) are involved in these actions [55]. The effects of NO on brown adipocytes are illustrated in Figure 4. Unlike the physiological actions of adipocyte eNOS in glucose metabolism, high amounts of iNOS-derived NO in WAT are synthesized in response to inflammatory factors [e.g., approximately tenfold increase in iNOS expression in response to lipopolysaccharide (LPS)] [64] and initiate nitrosative stress and cause adipocyte dysfunction and glucose intolerance. The role of iNOS in impaired insulin sensitivity is further supported by data indicating that targeted disruption of the iNOS gene in obese ob/ob mice improves insulin sensitivity, glucose tolerance, and BAT function through enhanced expression of mitochondrion-related proteins, including peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1a), sirtuin-1 and -3, and uncoupling protein 1 (UCP-1) and -3 [8]. iNOS/ mice are also resistant to chronic hyperinsulinemiainduced IR in adipose tissue; such models display better glucose tolerance and improved insulin sensitivity than wild-type mice [9]. Similarly, deletion of the macrophage metalloelastase (MMP12) gene (regulator of iNOS) effectively prevents adipocyte iNOS expression/activity and IR in fat-fed mice [10]. A pathological level of NO in WAT and BAT, due to activated macrophage-induced iNOS stimulation [65], causes mitochondrial dysfunction, inhibition of preadipocyte differentiation, P53-dependent adipose tissue fibrosis, and increased protein levels of hypoxia-inducible factor 1 alpha (HIF-1a) [65]. It has, however, been reported that induction of iNOS by activated macrophages is not sufficient to induce IR. Unlike systemic iNOS inhibition, myeloid iNOS deficiency in mice did not decrease HFD-induced IR; in addition, improved carbohydrate metabolism after iNOS inhibition was identical in wild-type mice and mice with myeloid iNOS deficiency, indicating that iNOS inhibition in tissues other than macrophages protects against the development of IR in HFD-fed mice [60].
6
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Trends in Endocrinology and Metabolism
Figure 4. Role of Nitric Oxide (NO) in Carbohydrate Metabolism in Brown Adipose Tissue (BAT). (1) Endothelial NO synthase (eNOS)- and norepinephrine-stimulated inducible NOS (iNOS)-derived NO increases both basal and insulin-stimulated glucose uptake by increasing the translocation of glucose transporter 4 (GLUT4). (2) NO may also increase glucose uptake through the activation of mammalian target of rapamycin complex 2 (mTORC-2), an insulin-independent mediator of BAT glucose uptake. (3) Pathological levels of NO, mostly originated from macrophage-induced iNOS activity, may decrease glucose uptake by inhibition of GLUT4 translocation. Abbreviations: Akt, protein kinase B; PI3K, phosphoinositide 3-kinase; PPARg, peroxisome proliferator-activated receptor gamma; sGC, soluble guanylyl cyclase; UCP-1, uncoupling protein 1.
Since some physiological actions of NO in BAT are attributed to norepinephrine (NEP)-induced iNOS or sympathetic stimulated-iNOS (by cold or b3-adrenergic agonists) [58,66], it can be speculated that iNOS-derived NO in response to b3-adrenoceptor stimulation may also contribute to normal glucose metabolism in BAT (Figure 4). Taking these findings together, despite the existence of some ambiguous aspects and open questions, the following scenario might describe the role of the NOS–NO system in normal glucose metabolism in adipose tissue: eNOS-derived NO plays a key role in keeping adipose tissue more insulin sensitive and enhancing glucose disposal, whereas iNOS-derived NO, induced by obesity and inflammation, mostly contributes to the development of adipose tissue IR.
NO and Carbohydrate Metabolism in Liver The specific cellular localization of NOS isoforms in the liver provides crucial insights into the physiological role of NO. nNOS is normally expressed in Kupffer cells but not in hepatocytes [67]. eNOS is
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
7
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
uniformly distributed in hepatocytes, in the endothelium of the hepatic arteries, terminal hepatic venules, and sinusoids, and in the biliary epithelium [68]. Recently, a novel cNOS isoform was found in the mouse liver cell membrane that is stimulated by glucose [69]. iNOS is expressed in all of the main types of liver cells (hepatocytes, Kupffer and stellate cells) after sufficient exposure to stimuli (e.g., cytokines, LPS) [67]. In the normal liver, hepatocyte iNOS is mainly localized in the periportal zone of the liver acinus [68]. Although it has not yet been determined which cNOS isoform is mainly responsible for hepatic glucose metabolism, some evidence emphasizes a role for eNOS, since hepatic IR has been observed only in eNOS/, not in nNOS/, mice [70]. A membranous form of cNOS mediates glucose-induced GLUT4 synthesis and translocation as well as the expression of proinsulin genes I and II and insulin biosynthesis [69]. Physiological actions of NO on carbohydrate metabolism are achieved through extra- and intrahepatic pathways; in the extrahepatic pathway, NO acts mainly by controlling hepatic blood flow. NO acts as a potent vasodilator in the hepatic arterial circulation and also exerts a minor vasodilatory effect on the portal venous vascular bed [71]. It has been hypothesized that increased NO in the hepatic vasculature may also increase the surface area for glucose uptake [13]. Intrahepatic actions of NO include modulation of hepatic glucose output, which is mainly a result of changes in the expression and activity of enzymes involved in gluconeogenesis, glycogenolysis, and glycogenesis. Exogenous NO donation (low dose of NO-releasing compounds) and the supporting NO synthesis pathway [by administration of L-arginine or tetrahydrobiopterin (BH4)] also emphasize the critical role of hepatic NO in carbohydrate metabolism; these modulations decrease the expression of phosphoenolpyruvate carboxykinase (PEPCK) and subsequently suppress hepatic gluconeogenesis [72], and increase insulin sensitivity by releasing hepatic insulin sensitizing substance (HISS) [73]. NO concentrations required for 50% inhibition of hepatic gluconeogenesis have been determined in a range of 200–800 nM [12]. Cytokine-activated iNOS disturbs hepatic glucose metabolism by decreasing cAMP- and glucagonstimulated glycogenolysis; such pathological levels of NO inhibit the activity of GAPDH by S-nitrosylation [74]. Using liver-specific iNOS transgenic mice (L-iNOS-Tg; iNOS protein overexpressed by 5.2–6.1 times), Shinozaki et al. described mechanisms by which iNOS-derived NO contributes to hepatic IR [75]. They reported that insulin-stimulated phosphorylation of IRS-1 and IRS-2, Akt, glycogen synthase kinase-3b, forkhead box O1, and mammalian target of rapamycin (mTORC) are significantly disrupted in this model; in addition, increased activity of glycogen phosphorylase and decreased activity of glycogen synthase promote hyperglycemia [75]. NFkB and activator protein-1, key upregulators of iNOS transcription, are proposed as mediators of inflammation/obesity-induced hepatic IR [75]. Increased S-nitrosylation and subsequent inactivation of Akt [75], along with tyrosine nitration of key insulin signaling proteins in the liver (IRb, IRS-1 and IRS-2, Akt), also mediate the iNOSinduced development of hepatic IR [76].
Role of NO in Central Regulation of Glucose Homeostasis The interaction of the central nervous system (CNS) with peripheral organs is involved in glucose homeostasis and the defective crosstalk involved contributes to the development of T2DM [77]. The CNS [specifically, four hypothalamic nuclei; i.e., the arcuate nucleus (ARC), paraventricular nucleus (PVN), ventromedial nucleus of hypothalamus (VMH), and lateral hypothalamic nucleus (LHN)] has a vital role in glucose homoeostasis [78]. The hypothalamic NOS–NO system contributes to the central regulation of glucose homeostasis and nNOS is the predominantly involved isoform [79,80]. The central NOS–NO system regulates insulin secretion and its peripheral actions, and acute NOS blockade in the CNS causes hyperglycemia, peripheral IR, and decreased insulin secretion (Figure 5) [81]. Increased hypothalamic NO concentrations (using central injection of NO donors or lipid-induced activation of nNOS in the VMH) lead to hepatic IR and increased GSIS [82].
8
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Trends in Endocrinology and Metabolism
Figure 5. Nitric Oxide (NO) Actively Contributes to Glucose Sensing by the Brain. In the hypothalamic ventromedial nucleus of hypothalamus (VMH) neurons, neural NO synthase (nNOS)-derived NO is essential for the AMP-activated protein kinase (AMPK)-mediated counterregulatory response to hypoglycemia; in response to hypoglycemia and decreased ATP-to-ADP ratio in glucose-inhibited (GI) neurons, AMPK is activated and induces a series of sequential events including nNOS phosphorylation, increased NO production, sGC–cGMP signaling, amplification of AMPK, closure of cystic fibrosis transmembrane regulator (CFTR) chloride channels, and neural firing. Central actions of apelin, ghrelin, and leptin on glucose homeostasis are also NO dependent. Nonadrenergic noncholinergic (NANC) neurons containing nitrergic fibers in the vagus nerve can also link the CNS to pancreatic islets and skeletal muscle to modulate insulin secretion and actions. Abbreviations: AgRP, agouti-related peptide; ARC, arcuate nucleus; BAT, brown adipose tissue; GHS-R, ghrelin receptor; GK, glucokinase; GLUT, glucose transporter; LepR, leptin receptor; PMV, ventral premammillary nucleus.
Mechanisms by which the central NOS–NO system regulates pancreatic insulin release and mediates insulin’s actions in peripheral tissues are not yet clearly understood. It has been suggested that nonadrenergic noncholinergic (NANC) neurons, via nitrergic fibers in the vagus nerve, link the CNS to pancreatic islets and skeletal muscle to modulate insulin secretion and actions [81]. Insulin homeostasis can also be modulated by regulating the release of hypothalamic/pituitary hormones via NOdependent neural pathways [81]. Co-release of NO with acetylcholine and other neurotransmitters from vagal terminals is also responsible for linking the CNS to the regulation of hepatic gluconeogenesis [83]. NO is also involved in glucose sensing by the brain (Figure 5); the nNOS–NO system in VMH glucoseinhibited (GI) neurons is essential for the AMPK-mediated counterregulatory response to hypoglycemia [80]. Following the hypoglycemia-induced activation of AMPK, nNOS is phosphorylated and the resultant increased NO production stimulates sGC–cGMP signaling; cGMP amplifies AMPK activation and closes cystic fibrosis transmembrane regulator (CFTR) chloride channels, which induces neural firing [84]. VMH NO synthesis increases cerebral blood flow, leading to increased local nutrient availability under hypoglycemic conditions [80]. Increased glucose and leptin inhibit NO synthesis in VMH GI neurons via AMPK inhibition, whereas insulin stimulates NO production in VMH GI neurons via the PI3K pathway [85]. Insulin-induced hypoglycemia does not affect either eNOS or iNOS in VMH GI neurons [80]. It is unclear whether glucose sensing by glucose-excited (GE) neurons, responding to hyperglycemia via the GLUT2–GK–KATP channel pathway [86], is affected by NO.
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
9
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Central actions of apelin [87], ghrelin [88], and leptin [89] on glucose homeostasis are also NO dependent. Intracerebroventricular (ICV) injection of a low dose (0.002 fmol) of apelin improves glucose homeostasis in fed normal mice; this effect is NO dependent and is mediated, at least in part, via phosphorylation and increased activity of eNOS in the hypothalamus, as it is not observed in eNOS/ knockout mice [87]. ICV injection of a high dose (40 fmol) of apelin promotes IR in fasted normal mice, an effect aggravated in eNOS/ knockout mice [87]. Since the beneficial effects of apelin are not observed in mice fed a HFD, these data suggest that apelin-dependent basal NO production in the hypothalamus is essential for the maintenance of physiological glycemia and that high doses of central apelin may contribute to the transition from a normal to a diabetic state [87]. The orexigenic and metabolic actions (shifting fat oxidation into carbohydrate oxidation) of ghrelin, specifically in the ARC and PVN, are NO dependent [88]; ICV injection of L-NAME dose dependently attenuates ghrelin-induced increases in food intake and respiratory exchange ratio (RER) in both the ARC and the PVN [88]. It has been proposed that ghrelin activates its receptors (GHS-R 1a and b), and the AMPK–NO (probably eNOS-derived NO [90])–cGMP pathway mediates the actions of ghrelin in the hypothalamic regulation of energy balance [91,92]. Leptin receptors (LepR-b) and nNOS are coexpressed in the hypothalamus and 20% of hypothalamic LepR-b neurons have been estimated to contain nNOS [89]. Most LepR-nNOS neurons are located in the ventral premammillary nucleus (PMv), the DMH, and the ARC. Leptin’s action in glucose and insulin homeostasis is critically mediated via LepR-b-nNOS neurons; lack of nNOS in the PMv and ARC causes hyperglycemia and hyperinsulinemia [89].
Concluding Remarks and Perspectives Endogenous NOS-derived NO is involved in carbohydrate homeostasis and, depending on the NOS isoform, both physiological and pathological actions of NO have been reported. The site-specific actions are mostly dependent on the NOS isoform (cNOS and iNOS); nNOS in pancreatic b-cells and skeletal muscle cells and eNOS in adipocytes and hepatocytes are the predominant NOS isoforms mediating the physiological actions of NO in carbohydrate metabolism. cNOS-derived NO increases insulin secretion and improves insulin signaling and sensitivity, increases peripheral glucose uptake, and decreases hepatic glucose output. By contrast, iNOS-derived NO, produced in response to inflammatory stimuli, contributes to the development of IR. However, although it is mostly considered detrimental, further studies are needed to clarify the beneficial effects of iNOS-derived NO, if any, in carbohydrate metabolism. The roles of NO in brain glucose sensing and the central regulation of carbohydrate metabolism need further investigation (see Outstanding Questions). Exogenous NO donors at low and high doses have beneficial and detrimental effects on carbohydrate metabolism, respectively; these findings highlight the importance of considering NO concentration when carbohydrate metabolism is assessed, which is currently a hot topic arena under investigation. Interactions between NO and other gasotransmitters such as hydrogen sulfide in the regulation of carbohydrate metabolism also need to be assessed in future studies. In addition, the beneficial metabolic effects obtained from using NO donors/inhibitors in preclinical studies need to be translated into clinical settings in well-designed clinical trials. Some discrepant findings about the effect of NO on carbohydrate metabolism are a result of using nonspecific NOS inhibitors, using NO donors with differing pharmacokinetics and pharmacodynamics, and their off-target effects; these issues warrant further attention for future studies in the field. In addition, the cGMP-dependent and -independent effects of NO should be considered. Regarding the effect of NO on carbohydrate metabolism, one can predict that drugs targeting the NO pathway rank high in the future treatment of T2DM; data that support this idea are that metformin, as the first-line treatment for T2DM, exerts some of its antidiabetic effects by increasing eNOS activity. A NO–metformin hybrid drug may be a suggestion worth examining.
10
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
Outstanding Questions Considering that NO regulates carbohydrate metabolism in a concentration-dependent manner, what is the threshold concentration for its physiological vs pathological actions in different tissues? Response to this question would be critical were NO-releasing drugs to be considered as a potential treatment for T2DM and IR. Site-specific and NOS isoformdependent actions of NO on glucose and insulin homeostasis have been mostly reported in animals, but what about these effects in humans? Which actions of iNOS-derived NO on carbohydrate metabolism are physiological? The effect of iNOS-derived NO on carbohydrate metabolism is dependent on the nature of the enzyme induced, the subject tissue, and the concentration of the produced NO. Considering the importance of NO in the central regulation of glucose homeostasis, how does NO affect glucose sensing in brain and what is its significance in the development of diabetes?
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Acknowledgments This study was supported by Shahid Beheshti University of Medical Sciences (Grant No. 1-19626). The authors acknowledge Ms Niloofar Shiva for critical editing of the English grammar and syntax of the manuscript. References 1. Ghasemi, A. and Zahediasl, S. (2011) Is nitric oxide a hormone? Iran. Biomed. J. 15, 59–65 2. Tessari, P. et al. (2010) Nitric oxide synthesis is reduced in subjects with type 2 diabetes and nephropathy. Diabetes 59, 2152–2159 3. Natali, A. et al. (2013) Systemic inhibition of nitric oxide synthesis in non-diabetic individuals produces a significant deterioration in glucose tolerance by increasing insulin clearance and inhibiting insulin secretion. Diabetologia 56, 1183–1191 4. Moguib, O. et al. (2017) Endothelial nitric oxide synthase gene (T786C and G894T) polymorphisms in Egyptian patients with type 2 diabetes. J. Genet. Eng. Biotechnol. 15, 431–436 5. Thameem, F. et al. (2008) Endothelial nitric oxide synthase (eNOS) gene polymorphisms and their association with type 2 diabetes-related traits in Mexican Americans. Diab. Vasc. Dis. Res. 5, 109–113 6. Monti, L.D. et al. (2003) Endothelial nitric oxide synthase polymorphisms are associated with type 2 diabetes and the insulin resistance syndrome. Diabetes 52, 1270–1275 7. Tso, A.W. et al. (2006) Endothelial nitric oxide synthase G894T (Glu298Asp) polymorphism was predictive of glycemic status in a 5-year prospective study of Chinese subjects with impaired glucose tolerance. Metabolism 55, 1155–1158 8. Becerril, S. et al. (2010) Deletion of inducible nitricoxide synthase in leptin-deficient mice improves brown adipose tissue function. PLoS One 5, e10962 9. Kumar, D. et al. (2018) Chronic hyperinsulinemia promotes meta-inflammation and extracellular matrix deposition in adipose tissue: implications of nitric oxide. Mol. Cell. Endocrinol. 477, 15–28 10. Lee, J.-T. et al. (2014) Macrophage metalloelastase (MMP12) regulates adipose tissue expansion, insulin sensitivity, and expression of inducible nitric oxide synthase. Endocrinology 155, 3409–3420 11. McGrowdera, D. et al. (2006) Modulation of glucose uptake in adipose tissue by nitric oxide-generating compounds. J. Biosci. 31, 347–354 12. Horton, R.A. et al. (1994) Inhibition of hepatic gluconeogenesis by nitric oxide: a comparison with endotoxic shock. Biochem. J. 299, 735–739 13. Shepherd, A.I. et al. (2016) Effect of nitrate supplementation on hepatic blood flow and glucose homeostasis: a double-blind, placebo-controlled, randomized control trial. Am. J. Physiol. Gastrointest. Liver. Physiol. 311, G356–G364 14. Lundquist, I. et al. (2016) Metformin ameliorates dysfunctional traits of glibenclamide- and glucoseinduced insulin secretion by suppression of imposed overactivity of the islet nitric oxide synthase-NO system. PLoS One 11, e0165668 15. Pilon, G. et al. (2004) Inhibition of inducible nitricoxide synthase by activators of AMP-activated protein kinase a new mechanism of action of insulinsensitizing drugs. J. Biol. Chem. 279, 20767–20774 16. Fujita, Y. et al. (2010) Metformin suppresses hepatic gluconeogenesis and lowers fasting blood glucose levels through reactive nitrogen species in mice. Diabetologia 53, 1472–1481 17. Lajoix, A.-D. et al. (2001) A neuronal isoform of nitric oxide synthase expressed in pancreatic b-cells controls insulin secretion. Diabetes 50, 1311–1323
18. Nakada, S. et al. (2003) Constitutive nitric oxide synthases in rat pancreatic islets: direct imaging of glucose-induced nitric oxide production in betacells. Pflugers Arch 447, 305–311 19. Kurohane Kaneko, Y. and Ishikawa, T. (2013) Dual role of nitric oxide in pancreatic beta-cells. J. Pharmacol. Sci. 123, 295–300 20. Jimenez-Feltstrom, J. et al. (2005) Glucose stimulates the expression and activities of nitric oxide synthases in incubated rat islets: an effect counteracted by GLP1 through the cyclic AMP/PKA pathway. Cell Tissue Res. 319, 221–230 21. Henningsson, R. et al. (2002) Role of nitric oxide synthase isoforms in glucose-stimulated insulin release. Am. J. Physiol. Cell. Physiol. 283, C296–C304 22. Laffranchi, R. et al. (1995) Nitric oxide (nitrogen monoxide, NO) stimulates insulin secretion by inducing calcium release from mitochondria. Biochem. Biophys. Res. Commun. 217, 584–591 23. Willmott, N.J. et al. (1995) Nitric oxide induces intracellular Ca2+ mobilization and increases secretion of incorporated 5-hydroxytryptamine in rat pancreatic beta-cells. FEBS Lett 371, 99–104 24. Rizzo, M.A. and Piston, D.W. (2003) Regulation of beta cell glucokinase by S-nitrosylation and association with nitric oxide synthase. J. Cell Biol. 161, 243–248 25. Markwardt, M.L. et al. (2012) Association with nitric oxide synthase on insulin secretory granules regulates glucokinase protein levels. Mol. Endocrinol. 26, 1617–1629 26. Eckersten, D. and Henningsson, R. (2012) Nitric oxide (NO) – production and regulation of insulin secretion in islets of freely fed and fasted mice. Regul. Pept. 174, 32–37 27. Tsuura, Y. et al. (1998) Endogenous nitric oxide inhibits glucose-induced insulin secretion by suppression of phosphofructokinase activity in pancreatic islets. Biochem. Biophys. Res. Commun. 252, 34–38 28. Lajoix, A.D. et al. (2006) Protein inhibitor of neuronal nitric oxide synthase (PIN) is a new regulator of glucose-induced insulin secretion. Diabetes 55, 3279–3288 29. Muhammed, S.J. et al. (2012) Pancreatic beta-cell dysfunction, expression of iNOS and the effect of phosphodiesterase inhibitors in human pancreatic islets of type 2 diabetes. Diabetes Obes. Metab. 14, 1010–1019 30. Kim, J.Y. et al. (2010) Chronic ethanol consumptioninduced pancreatic b-cell dysfunction and apoptosis through glucokinase nitration and its downregulation. J. Biol. Chem. 285, 37251–37262 31. Tsuura, Y. et al. (1994) Nitric oxide opens ATPsensitive K+ channels through suppression of phosphofructokinase activity and inhibits glucoseinduced insulin release in pancreatic beta cells. J. Gen. Physiol. 104, 1079–1098 32. Corbett, J.A. et al. (1993) Nitric oxide mediates cytokine-induced inhibition of insulin secretion by human islets of Langerhans. Proc. Natl Acad. Sci. U. S. A. 90, 1731–1735 33. Panagiotidis, G. et al. (1995) Influence of nitric oxide synthase inhibition, nitric oxide and hydroperoxide on insulin release induced by various secretagogues. Br. J. Pharmacol. 114, 289–296
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
11
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
34. Frandsen, U. et al. (1996) Localization of nitric oxide synthase in human skeletal muscle. Biochem. Biophys. Res. Commun. 227, 88–93 35. McConell, G.K. and Kingwell, B.A. (2006) Does nitric oxide regulate skeletal muscle glucose uptake during exercise? Exerc. Sport. Sci. Rev. 34, 36–41 36. Stamler, J.S. and Meissner, G. (2001) Physiology of nitric oxide in skeletal muscle. Physiol. Rev. 81, 209–237 37. Baron, A.D. and Clark, M.G. (1997) Role of blood flow in the regulation of muscle glucose uptake. Annu. Rev. Nutr. 17, 487–499 38. Kellogg, D.L., III et al. (2017) Neuronal nitric oxide synthase mediates insulin- and oxidative stressinduced glucose uptake in skeletal muscle myotubes. Free Radic. Biol. Med. 110, 261–269 39. McConell, G.K. et al. (2012) Skeletal muscle nitric oxide signaling and exercise: a focus on glucose metabolism. Am. J. Physiol. Endocrinol. Metab. 303, E301–E307 40. Etgen, G.J., Jr. et al. (1997) Nitric oxide stimulates skeletal muscle glucose transport through a calcium/ contraction- and phosphatidylinositol-3-kinaseindependent pathway. Diabetes 46, 1915–1919 41. Vincent, M.A. et al. (2003) Molecular and physiologic actions of insulin related to production of nitric oxide in vascular endothelium. Curr. Diab. Rep. 3, 279–288 42. Montagnani, M. et al. (2001) Insulin-stimulated activation of eNOS is independent of Ca2+ but requires phosphorylation by Akt at Ser1179. J. Biol. Chem. 276, 30392–30398 43. Barrett, E.J. et al. (2011) Insulin regulates its own delivery to skeletal muscle by feed-forward actions on the vasculature. Am. J. Physiol. Endocrinol. Metab. 301, E252–E263 44. Lira, V.A. et al. (2007) Nitric oxide increases GLUT4 expression and regulates AMPK signaling in skeletal muscle. Am. J. Physiol. Endocrinol. Metab. 293, E1062–E1068 45. Wang, H. et al. (2013) Nitric oxide directly promotes vascular endothelial insulin transport. Diabetes 62, 4030–4042 46. Torres, S. et al. (2004) Inflammation and nitric oxide production in skeletal muscle of type 2 diabetic patients. J. Endocrinol. 181, 419–427 47. Krause, M. et al. (2012) Differential nitric oxide levels in the blood and skeletal muscle of type 2 diabetic subjects may be consequence of adiposity: a preliminary study. Metabolism 61, 1528–1537 48. Eghbalzadeh, K. et al. (2014) Skeletal muscle nitric oxide (NO) synthases and NO-signaling in ‘‘diabesity’’ – what about the relevance of exercise training interventions? Nitric Oxide 37, 28–40 49. Perreault, M. and Marette, A. (2001) Targeted disruption of inducible nitric oxide synthase protects against obesity-linked insulin resistance in muscle. Nat. Med. 7, 1138–1143 50. Martins, A.R. et al. (2012) Mechanisms underlying skeletal muscle insulin resistance induced by fatty acids: importance of the mitochondrial function. Lipids Health Dis. 11, 30 51. Sugita, H. et al. (2005) Inducible nitric-oxide synthase and NO donor induce insulin receptor substrate-1 degradation in skeletal muscle cells. J. Biol. Chem. 280, 14203–14211 52. Zanotto, T.M. et al. (2016) Blocking iNOS and endoplasmic reticulum stress synergistically improves insulin resistance in mice. Mol. Metab. 6, 206–218 53. Kapur, S. et al. (1997) Expression of nitric oxide synthase in skeletal muscle: a novel role for nitric oxide as a modulator of insulin action. Diabetes 46, 1691–1700
12
54. Carvalho-Filho, M.A. et al. (2005) S-Nitrosation of the insulin receptor, insulin receptor substrate 1, and protein kinase B/Akt: a novel mechanism of insulin resistance. Diabetes 54, 959–967 55. Engeli, S. et al. (2004) Regulation of the nitric oxide system in human adipose tissue. J. Lipid Res. 45, 1640–1648 56. Kikuchi-Utsumi, K. et al. (2002) Enhanced gene expression of endothelial nitric oxide synthase in brown adipose tissue during cold exposure. Am. J. Physiol. Regul. Integr. Comp. Physiol. 282, R623– R626 57. Ribie`re, C. et al. (2002) Insulin stimulates nitric oxide production in rat adipocytes. Biochem. Biophys. Res. Commun. 291, 394–399 58. Giordano, A. et al. (2002) Evidence for a functional nitric oxide synthase system in brown adipocyte nucleus. FEBS Lett. 514, 135–140 59. Kapur, S. et al. (2000) Nitric oxide: a new player in the modulation of energy metabolism. Int. J. Obes. Relat. Metab. Disord. 24 (Suppl. 4 ), S36–S40 60. Lu, M. et al. (2010) Inducible nitric oxide synthase deficiency in myeloid cells does not prevent dietinduced insulin resistance. Mol. Endocrinol. 24, 1413– 1422 61. Roy, D. et al. (1998) Insulin stimulation of glucose uptake in skeletal muscles and adipose tissues in vivo is NO dependent. Am. J. Physiol. 274, E692–E699 62. Tanaka, T. et al. (2003) Nitric oxide stimulates glucose transport through insulin-independent GLUT4 translocation in 3T3-L1 adipocytes. Eur. J. Endocrinol. 149, 61–67 63. Xia, N. et al. (2016) Uncoupling of endothelial nitric oxide synthase in perivascular adipose tissue of dietinduced obese mice. Arterioscler. Thromb. Vasc. Biol. 36, 78–85 64. Ribiere, C. et al. (1996) White adipose tissue nitric oxide synthase: a potential source for NO production. Biochem. Biophys. Res. Commun. 222, 706–712 65. Jang, J.E. et al. (2016) Nitric oxide produced by macrophages inhibits adipocyte differentiation and promotes profibrogenic responses in preadipocytes to induce adipose tissue fibrosis. Diabetes 65, 2516– 2528 66. Nisoli, E. et al. (1997) Inducible nitric oxide synthase in rat brown adipocytes: implications for blood flow to brown adipose tissue. Endocrinology 138, 676–682 67. Muriel, P. (2000) Regulation of nitric oxide synthesis in the liver. J. Appl. Toxicol. 20, 189–195 68. McNaughton, L. et al. (2002) Distribution of nitric oxide synthase in normal and cirrhotic human liver. Proc. Natl Acad. Sci. U. S. A. 99, 17161–17166 69. Bhattacharya, S. et al. (2013) The activation by glucose of liver membrane nitric oxide synthase in the synthesis and translocation of glucose transporter-4 in the production of insulin in the mice hepatocytes. PLoS One 8, e81935 70. Shankar, R.R. et al. (2000) Mice with gene disruption of both endothelial and neuronal nitric oxide synthase exhibit insulin resistance. Diabetes 49, 684–687 71. Eipel, C. et al. (2010) Regulation of hepatic blood flow: the hepatic arterial buffer response revisited. World J. Gastroenterol. 16, 6046–6057 72. Abudukadier, A. et al. (2013) Tetrahydrobiopterin has a glucose-lowering effect by suppressing hepatic gluconeogenesis in an endothelial nitric oxide synthase-dependent manner in diabetic mice. Diabetes 62, 3033–3043 73. Sadri, P. and Lautt, W.W. (1999) Blockade of hepatic nitric oxide synthase causes insulin resistance. Am. J. Physiol. Gastrointest. Liver Physiol. 277, G101–G108 74. Molina y Vedia, L. et al. (1992) Nitric oxide-induced S-nitrosylation of glyceraldehyde-3-phosphate
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
75.
76.
77. 78.
79. 80.
81. 82. 83. 84.
dehydrogenase inhibits enzymatic activity and increases endogenous ADP-ribosylation. J. Biol. Chem. 267, 24929–24932 Shinozaki, S. et al. (2011) Liver-specific inducible nitric-oxide synthase expression is sufficient to cause hepatic insulin resistance and mild hyperglycemia in mice. J. Biol. Chem. 286, 34959–34975 Charbonneau, A. and Marette, A. (2010) Inducible nitric oxide synthase induction underlies lipidinduced hepatic insulin resistance in mice: potential role of tyrosine nitration of insulin signaling proteins. Diabetes 59, 861–871 Tups, A. et al. (2017) Central regulation of glucose homeostasis. Compr. Physiol. 7, 741–764 Gu¨emes, A. and Georgiou, P. (2018) Review of the role of the nervous system in glucose homoeostasis and future perspectives towards the management of diabetes. Bioelectron. Med. 4, 9 Chachlaki, K. et al. (2017) Phenotyping of nNOS neurons in the postnatal and adult female mouse hypothalamus. J. Comp. Neurol. 525, 3177–3189 Fioramonti, X. et al. (2010) Ventromedial hypothalamic nitric oxide production is necessary for hypoglycemia detection and counterregulation. Diabetes 59, 519–528 Shankar, R. et al. (1998) Central nervous system nitric oxide synthase activity regulates insulin secretion and insulin action. J. Clin. Invest. 102, 1403–1412 Marsollier, N. et al. (2009) Deregulation of hepatic insulin sensitivity induced by central lipid infusion in rats is mediated by nitric oxide. PLoS One 4, e6649 Arble, D. and Sandoval, D. (2013) CNS control of glucose metabolism: response to environmental challenges. Front. Neurosci. 7, 20 Murphy, B.A. et al. (2009) AMP-activated protein kinase and nitric oxide regulate the glucose
85.
86. 87.
88.
89.
90. 91. 92. 93.
sensitivity of ventromedial hypothalamic glucoseinhibited neurons. Am. J. Physiol. Cell. Physiol. 297, C750–C758 Canabal, D.D. et al. (2007) Glucose, insulin, and leptin signaling pathways modulate nitric oxide synthesis in glucose-inhibited neurons in the ventromedial hypothalamus. Am. J. Physiol. Regul. Integr. Comp. Physiol. 292, R1418–R1428 Routh, V.H. (2010) Glucose sensing neurons in the ventromedial hypothalamus. Sensors (Basel) 10, 9002–9025 Duparc, T. et al. (2011) Central apelin controls glucose homeostasis via a nitric oxide-dependent pathway in mice. Antioxid. Redox Signal. 15, 1477– 1496 Abtahi, S. et al. (2017) Ghrelin enhances food intake and carbohydrate oxidation in a nitric oxide dependent manner. Gen. Comp. Endocrinol. 250, 9–14 Leshan, R.L. et al. (2012) Leptin action through hypothalamic nitric oxide synthase-1-expressing neurons controls energy balance. Nat. Med. 18, 820–823 Xu, X. et al. (2008) Molecular mechanisms of ghrelinmediated endothelial nitric oxide synthase activation. Endocrinology 149, 4183–4192 Gaskin, F.S. et al. (2003) Ghrelin-induced feeding is dependent on nitric oxide. Peptides 24, 913–918 Andersson, U. et al. (2004) AMP-activated protein kinase plays a role in the control of food intake. J. Biol. Chem. 279, 12005–12008 Lin, K.Y. et al. (2002) Impaired nitric oxide synthase pathway in diabetes mellitus: role of asymmetric dimethylarginine and dimethylarginine dimethylaminohydrolase. Circulation 106, 987–992
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
13
Trends in Endocrinology & Metabolism
Review
Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism Zahra Bahadoran,1 Parvin Mirmiran,2 and Asghar Ghasemi3,* Nitric oxide (NO) contributes to carbohydrate metabolism and decreased NO bioavailability is involved in the development of type 2 diabetes mellitus (T2DM). NO donors may improve insulin signaling and glucose homeostasis in T2DM and insulin resistance (IR), suggesting the potential clinical importance of NO-based interventions. In this review, site-specific roles of the NO synthase (NOS)–NO pathway in carbohydrate metabolism are discussed. In addition, the metabolic effects of physiological low levels of NO produced by constitutive NOS (cNOS) versus pathological high levels of NO produced by inducible NOS (iNOS) in pancreatic b-cells, adipocytes, hepatocytes, and skeletal muscle cells are summarized. A better understanding of the NOS–NO system in the regulation of glucose homeostasis can hopefully facilitate the development of new treatments for T2DM.
NO and Carbohydrate Metabolism at a Glance NO, a ubiquitous signaling molecule and unique gasotransmitter, is involved in several physiological and pathological processes [1]. An overview of NO synthesis, the different NOS isoforms, and the concentration-dependent and dual (physiological and pathological) effects of NO are summarized in Box 1. Emerging data suggest that impaired NO homeostasis is involved in the development of IR and T2DM [2,3]. This idea is supported by human studies on polymorphisms in NOS genes [4–7] (Box 1), genetically modified animal models of the NOS–NO system [8–10] (Figure 1), and pharmacological investigations using NO donors (see Glossary) and NOS inhibitors [11–13]. The hypoglycemic properties of oral antidiabetic agents [e.g., metformin, thiazolidinediones (TZDs)] are also partly attributed to their capacity to modulate the NOS–NO system in pancreatic islets, skeletal muscle cells, hepatocytes, and adipocytes [14–16]. The physiological actions of NO in regulating carbohydrate metabolism are mostly attributed to low levels of NO produced by endothelial (eNOS) and neural (nNOS) NOS isoforms, whereas iNOS is mostly responsible for detrimental actions. In this review, we summarize current data on the role of the NOS–NO system in carbohydrate metabolism. Specifically, we discussed how the different NOS isoforms (eNOS/nNOS vs iNOS) are involved in glucose and insulin homeostasis in pancreatic b-cells, skeletal muscle, liver, and adipose tissue. The role of the NOS–NO system in the central regulation of glucose homeostasis is also discussed.
NO and Insulin Secretion All three NOS isoforms are expressed in pancreatic b-cells; nNOS is mainly localized in insulin secretory granules, and to a lesser extent in the mitochondrion and the nucleus [17]. Although the presence of eNOS in pancreatic b-cells has been reported [18], there are few data on eNOS’s function in b-cells [19]. iNOS is not detectable in b-cells at basal glucose levels and is expressed following exposure to higher glucose concentrations in the cytoplasm [20,21]. NO derived from cNOS acts as a mediator or negative feedback inhibitor of glucose-stimulated insulin secretion (GSIS) [21]. Stimulatory effect of cNOS-derived NO on GSIS is mediated by Ca+2 mobilization from the endoplasmic reticulum or mitochondrial pools; that is, by transient reversible increases in [Ca+2]i [22,23]. In addition, nNOS-derived NO increases glucokinase (GK) activity via S-nitrosylation of cysteine residues [24], a critical process that mediates GK dissociation from insulin secretory granules and potentiates insulin secretion [25] (Figure 2).
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
Highlights NO is involved in carbohydrate metabolism and disrupted NO pathways (i.e., decreased cNOSderived NO bioavailability or iNOS-induced overproduction of NO) leads to the development of T2DM. cNOS-derived NO improves insulin secretion and signaling, increases glucose uptake, and regulates hepatic glucose output. These physiological effects of NO are mainly mediated by the sGC–cGMP pathway. Cytokine-induced overactivity of iNOS leading to pathological levels of NO (micromolar) disturbs glucose and insulin homeostasis. NO-releasing drugs can restore disrupted NO signaling and improve carbohydrate metabolism in insulin resistance and T2DM. The clinical implications of NO donors encapsulated with common hypoglycemic agents like metformin might be considered as a future treatment for T2DM.
1Nutrition and Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran 2Department of Clinical Nutrition and Human Dietetics, Faculty of Nutrition Sciences and Food Technology, National Nutrition and Food Technology Research Institute, Shahid Beheshti University of Medical Sciences, Tehran, Iran 3Endocrine Physiology Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran
*Correspondence: [email protected], [email protected]
https://doi.org/10.1016/j.tem.2019.10.001 ª 2019 Elsevier Ltd. All rights reserved.
1
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Box 1. NOS–NO System and Carbohydrate Metabolism
Glossary
cNOS (eNOS and nNOS) isoforms and the iNOS isoform are involved in NO biosynthesis from L-arginine. Splice variants of the nNOS isoform (i.e., nNOSm, nNOSb, and mtNOS) have also been detected in skeletal muscle [36]. cNOS-derived NO (at low-nanomolar concentrations) mostly mediates physiological actions through activation of the sGC–cGMP pathway, whereas high concentrations (micromolar) of iNOS-induced NO mediate pathological effects, mostly through S-nitrosylation and nitration of proteins and the generation of peroxynitrite (ONOO).
AMP-activated protein kinase (AMPK): an energy sensor that regulates cellular metabolism; it is activated by a deficit in nutrient status and stimulates glucose uptake and lipid oxidation to produce energy. cGMP-dependent protein kinase or protein kinase G (PKG): a serine/threonine-specific protein kinase that is activated by cGMP. Glucose-inhibited (GI) and glucose-excited (GE) neurons: glucose-sensing neurons widely dispersed throughout the hypothalamus. GI neurons are activated in hypoglycemia via an interaction between AMPK and NO, which leads to chloride channel closure, membrane depolarization, and increased action potential frequency. GE neurons mainly utilize a glucose-sensing mechanism like that of the pancreatic b-cell, through KATP channels. KATP channel: an ATP-sensitive potassium channel and metabolic sensor that couples cellular metabolism to electrical activity. In pancreatic b-cells, the KATP channel regulates GSIS and is a target for sulfonylurea antidiabetic drugs. Macrophage metalloelastase (MMP12): a matrix metallopeptidase predominantly expressed by tissue mature macrophages; positively regulates iNOS expression and activity. Nitric oxide (NO) donors: pharmacologically active substances that release NO in vivo or in vitro; the most common NO donors include sodium nitroprusside (SNP), S-nitroso-N-acetyl-penicillamine (SNAP), 2-(N,N-diethylamino)diazenolate-2-oxide (DEANO), 3-morpholinosydnonimine (SIN-1), 1,1-diethyl-2-hydroxy-2-nitrosohydrazine (NONOate), 1-hydroxy-2-oxo-3-[Nmethyl-3-aminopropyl]-3-methyl1-triazene (NOC-7), and S-nitrosoglutathione (GSNO). NO scavengers: pharmacologically active substances that interfere with the toxic effects of excessive NO production while preserving some activity of NO that might be essential for normal biological function [e.g., 2-(4-carboxyphenyl)-4,5-dihydro-4,4,5,5-
Both decreased eNOS-derived NO bioavailability (i.e., decreased NOS expression and activity, uncoupling of NOS or NO scavenging by ROS) [2,93] and increased iNOS overexpression and activity occur in diabetes and IR [29]. Studies on eNOS gene polymorphisms in humans provide evidence on the critical roles of NO in carbohydrate metabolism [4]. The most common genetic variants of eNOS, considered risk factors for IR and T2DM, are an single nucleotide polymorphism (SNP) in the promoter region (T786C, rs2070744), an SNP in exon 7 (G894T, rs1799983), an SNP in intron 18 (IVS18-27A/C), and a variable number tandem repeat (VNTR) in intron 4 [4–7]. Use of NO donors (e.g., SNAP, SNP, SIN-1, NONOate), NOS substrates (L-arginine, L-citrulline), or NOS inhibitors (e.g., L-NMMA, L-NAME) is the most common pharmacological approach to determine how NO regulates glucose homeostasis (see text). Besides this, some part of the mechanisms by which antidiabetic drugs regulate carbohydrate metabolism are mediated by the NOS–NO system (e.g., modulation of NOS expression and activity). Metformin increases insulin secretion via AMPK-dependent iNOS/nNOS inhibition in pancreatic b-cells [14]. By contrast, in pancreatic islets, glibenclamide stimulates iNOS/nNOS, which decreases its ability to induce insulin secretion; metformin suppresses glibenclamide-induced NO production and augments glibenclamide-induced insulin release [14]. Metformin and troglitazone, as activators of the AMPK pathway, inhibit cytokine-induced iNOS expression and decrease iNOS protein turnover, normalize insulin-induced PI3K activity, and reverse IR in skeletal muscle cells and adipocytes [15].
In isolated pancreatic islets, increasing glucose concentration dose dependently increases the activity of cNOS and iNOS; however, cNOS activity is more rapidly adjusted to glucose concentration than iNOS activity [21]. Inhibition of cNOS activity in pancreatic islets potentiates GSIS and abolishes the negative peak that separates the first and second phases of insulin secretion, indicating negative feedback effect of NO on GSIS and its importance for the pattern of GSIS [21]. This negative feedback effect inhibits excessive insulin release in response to high glucose concentrations and protects b-cells [21,26]. One possible mechanism for the negative feedback effect of cNOS-derived NO on GSIS is the inhibition of phosphofructokinase and therefore glucose metabolism in pancreatic b-cells [27]. In addition to the production of NO (oxidating activity), nNOS has cytochrome c reductase activity (nonoxidating activity) [17]. nNOS inhibits GSIS by increasing NO production and stimulates GSIS by its nonoxidating activity; a balance between these two activities is essential for normal insulin secretion in response to glucose [17]. Protein inhibitor of nNOS (PIN) increases GSIS, an effect that is not related to the oxidating or nonoxidating activities of nNOS and is mediated by affecting the migration of insulin secretary granules [28]. mRNA/protein expression of iNOS is high in pancreatic islets of patients with T2DM, where inhibition of iNOS restores disrupted GSIS [29]. iNOS-derived NO mostly causes b-cell dysfunction, impaired insulin secretion, hyperglycemia, and the development of diabetes [21,26,29,30]. iNOS-derived NO, by a 30 ,50 -cGMP-independent mechanism inhibits insulin secretion [31] by inhibiting the mitochondrial electron transport chain (complexes I and II) and mitochondrial aconitase activity [32], S-nitrosylation of critical thiol groups involved in the secretory process [33], and tyrosine nitration and subsequent downregulation of GK [30]. Taking these findings together, the role of cNOS-derived NO as a mediator or negative feedback inhibitor of GSIS is controversial; however, the literature is in favor of an inhibitory effect of cNOS-derived NO on insulin secretion. This effect has physiological relevance to the normal pattern of insulin secretion. In addition, nNOS affects GSIS by mechanisms unrelated to NO synthesis (e.g., having
2
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Trends in Endocrinology and Metabolism
Figure 1. An Overview of Genetic Modifications of the Nitric Oxide Synthase (NOS)–NO System and Disrupted Glucose and Insulin Homeostasis in Animal Models. Impaired glucose and insulin homeostasis occur in both complete (eNOS/) and partial (eNOS+/) eNOSdeficient mice, whereas eNOS-overexpressed models (eNOS+) are resistant to chemically [streptozotocin (STZ) and alloxan (ALX)] and high-fat diet (HFD)-induced hyperinsulinemia. nNOS disruption in mice impairs glucose metabolism and results in insulin resistance (IR). Overexpression of iNOS (iNOS+) in skeletal muscle and liver induces IR, whereas iNOS-deficient models are resistant to HFD-induced IR.
cytochrome c reductase activity). While cNOS-derived NO mostly serves as a physiological negative feedback inhibitor of insulin secretion, iNOS-derived NO is mostly involved in pathological functions.
NO and Carbohydrate Metabolism in Skeletal Muscle All three NOS isoforms are expressed in skeletal muscle [34]. nNOS splice variants [nNOSm, nNOSb, and mitochondrial NOS (mtNOS)] are the most relevant isoforms involved in glucose uptake [35]. eNOS is highly expressed in the endothelium of vessels in skeletal muscle [36] and is responsible for 30% of glucose uptake in human skeletal muscles [37]. iNOS is hardly detectable in normal human skeletal muscle and expressed in response to inflammatory cytokines and oxidative stress [36].
Effects of cNOS-Derived NO on Skeletal Muscle Glucose Uptake The effects of cNOS-derived NO on skeletal muscle glucose uptake are mostly attributed to its mediatory role in response to insulin and contraction [38,39] and include increased blood flow, increased glucose transporter 4 (GLUT4) expression and translocation to membrane, and increased insulin transendothelial transport (ITT) (Figure 3). However, at least in fast-twitch glycolytic skeletal muscles, NOS inhibition has no effect on insulin- or contraction-induced glucose uptake, indicating that NO also has an insulin- and contraction-independent stimulatory effect on glucose uptake [40].
tetramethyl-1H-imidazolyl-1-oxy3-oxide (carboxy-PTIO)]. NO synthase (NOS) inhibitors: pharmacologically active substances that inhibit NOS enzymes and therefore NO production. The most common NOS inhibitors are L-arginine analogs [e.g., NGnitro-L-arginine methyl ester (LNAME), L-NG-monomethyl Larginine (L-NMMA), NG-methyl-Larginine (L-NMA), nitro-L-arginine (L-NNA)], which are competitive and nonselective inhibitors. Some NOS inhibitors are selective; for example, 7-nitroindazole (7-NI), a specific nNOS inhibitor, and aminoguanidine, a selective iNOS inhibitor. Peroxynitrite (ONOO): produced by the reaction of NO with the superoxide anion (O2d); a strong oxidant that reacts at a relatively slow rate with most biological molecules. The pathological effects of NO at toxic levels are partly attributed to peroxynitrite. S-Nitrosation: refers specifically to chemical reactions involving the addition of a nitrosonium ion (NO+) to a nucleophilic group, such as an amine or thiolate. S-Nitrosylation: refers to the direct addition of NO to a reactant (e.g., cysteine residues of a protein); in chemistry, it is defined as the coordination of NO to a metal center to form a metal nitrosyl complex. Soluble guanylyl cyclase (sGC): a heterodimeric (a and b subunits) heme protein of molecular mass 150 kDa; known as the primary receptor of NO that responds to NO binding by increasing cyclase activity, producing guanosine 30 ,50 -cGMP, and generating a signaling cascade.
Insulin activates vascular eNOS via the phosphoinositide 3-kinase (PI3K)–protein kinase B (PKB/Akt) pathway and causes NO release [41,42]; NO mediates insulin-induced capillary recruitment and increases blood flow, insulin delivery, and insulin-mediated glucose disposal [43]. In addition to eNOS-derived NO, nNOSm-derived NO has an important role in increasing blood flow, particularly during exercise [39]. Both insulin and muscle contraction activate nNOSm [via Akt- and AMP-activated protein kinase (AMPK)-dependent phosphorylation] and the resultant increased NO production promotes the expression and translocation of the GLUT4 and therefore glucose uptake [38]. NO increases GLUT4 gene expression by phosphorylation of a-AMPK and acetyl-CoA carboxylase and the translocation of phosphorylated a-AMPK to the nucleus [44]. NO increases GLUT4 translocation using the soluble guanylyl cyclase (sGC)–cGMP and cGMP-dependent protein kinase (PKG) pathway;
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
3
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Trends in Endocrinology and Metabolism
Figure 2. Nitric Oxide Synthase (NOS) Isoforms in Pancreatic b-Cells and the Role of Endogenous and Exogenous NO in Insulin Secretion. Physiological levels of endogenous nNOS-derived NO (1) stimulate Ca2+ mobilization from the endoplasmic reticulum and mitochondrion and increase the cytosolic free Ca2+ concentration, a critical step for glucose-stimulated insulin secretion, and (2) induce S-nitrosylation of glucokinase, an integral component of insulin granules, and regulate its localization and activity. (3) nNOS-derived NO in response to high levels of glucose may acts as a negative feedback signal for glucose-stimulated insulin secretion by the activation of KATP channels. (4) Pathological levels of iNOSinduced NO in response to toxic levels of glucose or inflammatory cytokines disturb glucose-stimulated insulin secretion by disturbing the glycolytic pathway and mitochondrial respiration. Abbreviations: RyR, ryanodine receptor; TCA, tricarboxylic acid; L-VDCC, L-type voltage-dependent calcium channel.
however, some cGMP–PKG-independent mechanisms (especially during skeletal muscle contraction) are also involved [39]. Potential cGMP-independent mechanisms are S-nitrosylation, S-glutathionylation, and tyrosine nitration of proteins involved in GLUT4 translocation [39]; the importance of these mechanisms is highlighted by knowing that the NO–sGC–cGMP pathway accounts for up to 50% of NO actions in skeletal muscle [36], and NO-induced sGC activity is lower in skeletal muscle than in most other tissues (15- vs 100–400-fold). Insulin delivery to muscle interstitial fluid, named ITT, is a rate-limiting step in the peripheral action of insulin [45]. NO increases ITT; this effect is sGC–cGMP-independent and occurs via the S-nitrosylation and decreased activity of protein-tyrosine phosphatase 1B (PTP1B) and the subsequently elimination of its inhibitory effect on insulin signaling and insulin transport [45].
Effects of iNOS-Derived and High Doses of Exogenous NO on Skeletal Muscle Glucose Uptake The mRNA expression and protein content of iNOS are higher in the skeletal muscle of patients with T2DM and IR [46–48]. Obesity-linked iNOS induction is mediated by increased expression and
4
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Figure 3. Nitric Oxide Synthase (NOS) Isoform Localization in Skeletal Muscle and the Role of NO in Insulin and Glucose Transport into Skeletal Muscle. (1) Both eNOS- and nNOSm-derived NO increase glucose disposal and insulin transendothelial transport. Insulin and skeletal muscle contraction stimulate nNOSm activity; nNOSm-derived NO increases (2) GLUT4 expression (by AMPK phosphorylation) and (3) GLUT4 translocation by phosphorylation and S-nitrosylation. (4) nNOSb and mtNOS are involved in skeletal muscle contraction and metabolism. iNOS-derived NO (5) disturbs insulininduced glucose uptake and (6) inhibits GLUT4 expression. Abbreviations: AMPK, 50 -AMP-activated protein kinase; CAT-1, cationic amino acid transporter-1; Cav-1, caveolin 1; DG, dystroglycan; GLUT, glucose transporter; IRS-1, insulin receptor substrate-1; mtNOS, mitochondrial NOS; PKB/Akt, protein kinase B; PDK1, 3-phosphoinositide-dependent protein kinase 1; PKG, protein kinase G; SG, sarcoglycan; sGC, soluble guanylyl cyclase; Syn, a1-syntrophin.
secretion of proinflammatory cytokines, including tumor necrosis factor alpha (TNF-a), interferongamma (IFN-g), interleukin-1b (IL-1b), and IL-6 in myocytes [49]. Increased circulating or intramyocellular free fatty acids have been also proposed as underlying mechanisms of obesity-induced iNOS in skeletal muscle [50]. Upregulation of iNOS in skeletal muscle is mediated by the activation of mitogen-activated protein kinase (MAPK) and its downstream pathways [extracellular regulated kinase (ERK1/ERK2), p38, in particular, c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK)], the transcription factor nuclear factor kappa B (NFkB), and the Janus kinase/signal transducer and activator of transcription (JAK–STAT) signaling pathway [48]. Accumulating evidence indicate that iNOS mediates high-fat diet (HFD)-induced IR in skeletal muscle [49,51,52]. iNOS-disrupted models are resistant to HFD-IR [52] and iNOS-knockout ob/ob mice have higher insulin sensitivity than iNOS+/+ ob/ob mice [51]. iNOS-derived NO or high doses of NO donors decrease GLUT4 gene expression and mitochondrial capacity in skeletal muscle [44,48]. Such pathological NO levels act in a sGC-independent manner [53], by the S-nitrosation and inactivation of proteins involved in the early steps of insulin signaling [i.e., insulin receptor beta (IRb), insulin receptor substrate-1 (IRS-1), and Akt [54]]. In addition, in skeletal muscle cells, iNOS-derived NO increases
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
5
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
proteasome-dependent degradation of IRS-1, which is involved in the development of T2DM and IR [51]. Furthermore, iNOS induction impairs insulin-dependent PI3K and Akt activation [51]. To sum up, cNOS-derived NO at physiological levels improves skeletal muscle insulin sensitivity and promotes glucose uptake via increased blood flow-dependent glucose delivery to skeletal muscle, increased GLUT4 expression and translocation, and increased ITT. By contrast, iNOS-derived NO at pathological levels (induced by obesity and inflammatory cytokines) impairs skeletal muscle insulin sensitivity and glucose uptake.
NO and Carbohydrate Metabolism in Adipose Tissue The predominant or probably the only cNOS isoform expressed in both white adipose tissue (WAT) and brown adipose tissue (BAT) seems to be eNOS [55,56]. In WAT, eNOS is activated by insulin (via the PI3K/Akt and MAPK/protein phosphatase-1 pathways) [57] and angiotensin II (by increasing intracellular calcium concentrations) [55]. In BAT, eNOS is located in the cytoplasm and nucleus of adipocytes and 70% of nuclear NOS activity is attributed to eNOS [58]. In BAT, eNOS expression is controlled by sympathetic fibers [56] and cold exposure and b3-adrenergic agonists enhance eNOS activity [58]. iNOS protein is found in both BAT and WAT [59] and is localized in adipocytes and other cells, such as macrophages [60]. NO mediates insulin-stimulated glucose uptake in both BAT and WAT and NOS blockade in these tissues can reduce insulin’s action on glucose uptake by more than 50% [61]. NO also increases glucose uptake in 3T3-L1 adipocytes through insulin-independent (without phosphorylation of IRS-1 and Akt) translocation of GLUT-4; this sGC-dependent effect of NO seems to be additive to effect of insulin [62]. Constitutive formation of NO by adipocyte eNOS is suggested to be important for normal glucose and insulin homeostasis in WAT [55]; support for this notion comes from data indicating that decreased eNOS phosphorylation, eNOS uncoupling, and decreased eNOS-derived NO in WAT contributes to the development of IR in obesity [63]. Beneficial effects of NO on glucose metabolism in WAT are achieved by mediating insulin-dependent and insulin-independent glucose uptake, and sGC and PKG (PKG1 and PKG2) are involved in these actions [55]. The effects of NO on brown adipocytes are illustrated in Figure 4. Unlike the physiological actions of adipocyte eNOS in glucose metabolism, high amounts of iNOS-derived NO in WAT are synthesized in response to inflammatory factors [e.g., approximately tenfold increase in iNOS expression in response to lipopolysaccharide (LPS)] [64] and initiate nitrosative stress and cause adipocyte dysfunction and glucose intolerance. The role of iNOS in impaired insulin sensitivity is further supported by data indicating that targeted disruption of the iNOS gene in obese ob/ob mice improves insulin sensitivity, glucose tolerance, and BAT function through enhanced expression of mitochondrion-related proteins, including peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1a), sirtuin-1 and -3, and uncoupling protein 1 (UCP-1) and -3 [8]. iNOS/ mice are also resistant to chronic hyperinsulinemiainduced IR in adipose tissue; such models display better glucose tolerance and improved insulin sensitivity than wild-type mice [9]. Similarly, deletion of the macrophage metalloelastase (MMP12) gene (regulator of iNOS) effectively prevents adipocyte iNOS expression/activity and IR in fat-fed mice [10]. A pathological level of NO in WAT and BAT, due to activated macrophage-induced iNOS stimulation [65], causes mitochondrial dysfunction, inhibition of preadipocyte differentiation, P53-dependent adipose tissue fibrosis, and increased protein levels of hypoxia-inducible factor 1 alpha (HIF-1a) [65]. It has, however, been reported that induction of iNOS by activated macrophages is not sufficient to induce IR. Unlike systemic iNOS inhibition, myeloid iNOS deficiency in mice did not decrease HFD-induced IR; in addition, improved carbohydrate metabolism after iNOS inhibition was identical in wild-type mice and mice with myeloid iNOS deficiency, indicating that iNOS inhibition in tissues other than macrophages protects against the development of IR in HFD-fed mice [60].
6
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Trends in Endocrinology and Metabolism
Figure 4. Role of Nitric Oxide (NO) in Carbohydrate Metabolism in Brown Adipose Tissue (BAT). (1) Endothelial NO synthase (eNOS)- and norepinephrine-stimulated inducible NOS (iNOS)-derived NO increases both basal and insulin-stimulated glucose uptake by increasing the translocation of glucose transporter 4 (GLUT4). (2) NO may also increase glucose uptake through the activation of mammalian target of rapamycin complex 2 (mTORC-2), an insulin-independent mediator of BAT glucose uptake. (3) Pathological levels of NO, mostly originated from macrophage-induced iNOS activity, may decrease glucose uptake by inhibition of GLUT4 translocation. Abbreviations: Akt, protein kinase B; PI3K, phosphoinositide 3-kinase; PPARg, peroxisome proliferator-activated receptor gamma; sGC, soluble guanylyl cyclase; UCP-1, uncoupling protein 1.
Since some physiological actions of NO in BAT are attributed to norepinephrine (NEP)-induced iNOS or sympathetic stimulated-iNOS (by cold or b3-adrenergic agonists) [58,66], it can be speculated that iNOS-derived NO in response to b3-adrenoceptor stimulation may also contribute to normal glucose metabolism in BAT (Figure 4). Taking these findings together, despite the existence of some ambiguous aspects and open questions, the following scenario might describe the role of the NOS–NO system in normal glucose metabolism in adipose tissue: eNOS-derived NO plays a key role in keeping adipose tissue more insulin sensitive and enhancing glucose disposal, whereas iNOS-derived NO, induced by obesity and inflammation, mostly contributes to the development of adipose tissue IR.
NO and Carbohydrate Metabolism in Liver The specific cellular localization of NOS isoforms in the liver provides crucial insights into the physiological role of NO. nNOS is normally expressed in Kupffer cells but not in hepatocytes [67]. eNOS is
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
7
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
uniformly distributed in hepatocytes, in the endothelium of the hepatic arteries, terminal hepatic venules, and sinusoids, and in the biliary epithelium [68]. Recently, a novel cNOS isoform was found in the mouse liver cell membrane that is stimulated by glucose [69]. iNOS is expressed in all of the main types of liver cells (hepatocytes, Kupffer and stellate cells) after sufficient exposure to stimuli (e.g., cytokines, LPS) [67]. In the normal liver, hepatocyte iNOS is mainly localized in the periportal zone of the liver acinus [68]. Although it has not yet been determined which cNOS isoform is mainly responsible for hepatic glucose metabolism, some evidence emphasizes a role for eNOS, since hepatic IR has been observed only in eNOS/, not in nNOS/, mice [70]. A membranous form of cNOS mediates glucose-induced GLUT4 synthesis and translocation as well as the expression of proinsulin genes I and II and insulin biosynthesis [69]. Physiological actions of NO on carbohydrate metabolism are achieved through extra- and intrahepatic pathways; in the extrahepatic pathway, NO acts mainly by controlling hepatic blood flow. NO acts as a potent vasodilator in the hepatic arterial circulation and also exerts a minor vasodilatory effect on the portal venous vascular bed [71]. It has been hypothesized that increased NO in the hepatic vasculature may also increase the surface area for glucose uptake [13]. Intrahepatic actions of NO include modulation of hepatic glucose output, which is mainly a result of changes in the expression and activity of enzymes involved in gluconeogenesis, glycogenolysis, and glycogenesis. Exogenous NO donation (low dose of NO-releasing compounds) and the supporting NO synthesis pathway [by administration of L-arginine or tetrahydrobiopterin (BH4)] also emphasize the critical role of hepatic NO in carbohydrate metabolism; these modulations decrease the expression of phosphoenolpyruvate carboxykinase (PEPCK) and subsequently suppress hepatic gluconeogenesis [72], and increase insulin sensitivity by releasing hepatic insulin sensitizing substance (HISS) [73]. NO concentrations required for 50% inhibition of hepatic gluconeogenesis have been determined in a range of 200–800 nM [12]. Cytokine-activated iNOS disturbs hepatic glucose metabolism by decreasing cAMP- and glucagonstimulated glycogenolysis; such pathological levels of NO inhibit the activity of GAPDH by S-nitrosylation [74]. Using liver-specific iNOS transgenic mice (L-iNOS-Tg; iNOS protein overexpressed by 5.2–6.1 times), Shinozaki et al. described mechanisms by which iNOS-derived NO contributes to hepatic IR [75]. They reported that insulin-stimulated phosphorylation of IRS-1 and IRS-2, Akt, glycogen synthase kinase-3b, forkhead box O1, and mammalian target of rapamycin (mTORC) are significantly disrupted in this model; in addition, increased activity of glycogen phosphorylase and decreased activity of glycogen synthase promote hyperglycemia [75]. NFkB and activator protein-1, key upregulators of iNOS transcription, are proposed as mediators of inflammation/obesity-induced hepatic IR [75]. Increased S-nitrosylation and subsequent inactivation of Akt [75], along with tyrosine nitration of key insulin signaling proteins in the liver (IRb, IRS-1 and IRS-2, Akt), also mediate the iNOSinduced development of hepatic IR [76].
Role of NO in Central Regulation of Glucose Homeostasis The interaction of the central nervous system (CNS) with peripheral organs is involved in glucose homeostasis and the defective crosstalk involved contributes to the development of T2DM [77]. The CNS [specifically, four hypothalamic nuclei; i.e., the arcuate nucleus (ARC), paraventricular nucleus (PVN), ventromedial nucleus of hypothalamus (VMH), and lateral hypothalamic nucleus (LHN)] has a vital role in glucose homoeostasis [78]. The hypothalamic NOS–NO system contributes to the central regulation of glucose homeostasis and nNOS is the predominantly involved isoform [79,80]. The central NOS–NO system regulates insulin secretion and its peripheral actions, and acute NOS blockade in the CNS causes hyperglycemia, peripheral IR, and decreased insulin secretion (Figure 5) [81]. Increased hypothalamic NO concentrations (using central injection of NO donors or lipid-induced activation of nNOS in the VMH) lead to hepatic IR and increased GSIS [82].
8
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Trends in Endocrinology and Metabolism
Figure 5. Nitric Oxide (NO) Actively Contributes to Glucose Sensing by the Brain. In the hypothalamic ventromedial nucleus of hypothalamus (VMH) neurons, neural NO synthase (nNOS)-derived NO is essential for the AMP-activated protein kinase (AMPK)-mediated counterregulatory response to hypoglycemia; in response to hypoglycemia and decreased ATP-to-ADP ratio in glucose-inhibited (GI) neurons, AMPK is activated and induces a series of sequential events including nNOS phosphorylation, increased NO production, sGC–cGMP signaling, amplification of AMPK, closure of cystic fibrosis transmembrane regulator (CFTR) chloride channels, and neural firing. Central actions of apelin, ghrelin, and leptin on glucose homeostasis are also NO dependent. Nonadrenergic noncholinergic (NANC) neurons containing nitrergic fibers in the vagus nerve can also link the CNS to pancreatic islets and skeletal muscle to modulate insulin secretion and actions. Abbreviations: AgRP, agouti-related peptide; ARC, arcuate nucleus; BAT, brown adipose tissue; GHS-R, ghrelin receptor; GK, glucokinase; GLUT, glucose transporter; LepR, leptin receptor; PMV, ventral premammillary nucleus.
Mechanisms by which the central NOS–NO system regulates pancreatic insulin release and mediates insulin’s actions in peripheral tissues are not yet clearly understood. It has been suggested that nonadrenergic noncholinergic (NANC) neurons, via nitrergic fibers in the vagus nerve, link the CNS to pancreatic islets and skeletal muscle to modulate insulin secretion and actions [81]. Insulin homeostasis can also be modulated by regulating the release of hypothalamic/pituitary hormones via NOdependent neural pathways [81]. Co-release of NO with acetylcholine and other neurotransmitters from vagal terminals is also responsible for linking the CNS to the regulation of hepatic gluconeogenesis [83]. NO is also involved in glucose sensing by the brain (Figure 5); the nNOS–NO system in VMH glucoseinhibited (GI) neurons is essential for the AMPK-mediated counterregulatory response to hypoglycemia [80]. Following the hypoglycemia-induced activation of AMPK, nNOS is phosphorylated and the resultant increased NO production stimulates sGC–cGMP signaling; cGMP amplifies AMPK activation and closes cystic fibrosis transmembrane regulator (CFTR) chloride channels, which induces neural firing [84]. VMH NO synthesis increases cerebral blood flow, leading to increased local nutrient availability under hypoglycemic conditions [80]. Increased glucose and leptin inhibit NO synthesis in VMH GI neurons via AMPK inhibition, whereas insulin stimulates NO production in VMH GI neurons via the PI3K pathway [85]. Insulin-induced hypoglycemia does not affect either eNOS or iNOS in VMH GI neurons [80]. It is unclear whether glucose sensing by glucose-excited (GE) neurons, responding to hyperglycemia via the GLUT2–GK–KATP channel pathway [86], is affected by NO.
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
9
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Central actions of apelin [87], ghrelin [88], and leptin [89] on glucose homeostasis are also NO dependent. Intracerebroventricular (ICV) injection of a low dose (0.002 fmol) of apelin improves glucose homeostasis in fed normal mice; this effect is NO dependent and is mediated, at least in part, via phosphorylation and increased activity of eNOS in the hypothalamus, as it is not observed in eNOS/ knockout mice [87]. ICV injection of a high dose (40 fmol) of apelin promotes IR in fasted normal mice, an effect aggravated in eNOS/ knockout mice [87]. Since the beneficial effects of apelin are not observed in mice fed a HFD, these data suggest that apelin-dependent basal NO production in the hypothalamus is essential for the maintenance of physiological glycemia and that high doses of central apelin may contribute to the transition from a normal to a diabetic state [87]. The orexigenic and metabolic actions (shifting fat oxidation into carbohydrate oxidation) of ghrelin, specifically in the ARC and PVN, are NO dependent [88]; ICV injection of L-NAME dose dependently attenuates ghrelin-induced increases in food intake and respiratory exchange ratio (RER) in both the ARC and the PVN [88]. It has been proposed that ghrelin activates its receptors (GHS-R 1a and b), and the AMPK–NO (probably eNOS-derived NO [90])–cGMP pathway mediates the actions of ghrelin in the hypothalamic regulation of energy balance [91,92]. Leptin receptors (LepR-b) and nNOS are coexpressed in the hypothalamus and 20% of hypothalamic LepR-b neurons have been estimated to contain nNOS [89]. Most LepR-nNOS neurons are located in the ventral premammillary nucleus (PMv), the DMH, and the ARC. Leptin’s action in glucose and insulin homeostasis is critically mediated via LepR-b-nNOS neurons; lack of nNOS in the PMv and ARC causes hyperglycemia and hyperinsulinemia [89].
Concluding Remarks and Perspectives Endogenous NOS-derived NO is involved in carbohydrate homeostasis and, depending on the NOS isoform, both physiological and pathological actions of NO have been reported. The site-specific actions are mostly dependent on the NOS isoform (cNOS and iNOS); nNOS in pancreatic b-cells and skeletal muscle cells and eNOS in adipocytes and hepatocytes are the predominant NOS isoforms mediating the physiological actions of NO in carbohydrate metabolism. cNOS-derived NO increases insulin secretion and improves insulin signaling and sensitivity, increases peripheral glucose uptake, and decreases hepatic glucose output. By contrast, iNOS-derived NO, produced in response to inflammatory stimuli, contributes to the development of IR. However, although it is mostly considered detrimental, further studies are needed to clarify the beneficial effects of iNOS-derived NO, if any, in carbohydrate metabolism. The roles of NO in brain glucose sensing and the central regulation of carbohydrate metabolism need further investigation (see Outstanding Questions). Exogenous NO donors at low and high doses have beneficial and detrimental effects on carbohydrate metabolism, respectively; these findings highlight the importance of considering NO concentration when carbohydrate metabolism is assessed, which is currently a hot topic arena under investigation. Interactions between NO and other gasotransmitters such as hydrogen sulfide in the regulation of carbohydrate metabolism also need to be assessed in future studies. In addition, the beneficial metabolic effects obtained from using NO donors/inhibitors in preclinical studies need to be translated into clinical settings in well-designed clinical trials. Some discrepant findings about the effect of NO on carbohydrate metabolism are a result of using nonspecific NOS inhibitors, using NO donors with differing pharmacokinetics and pharmacodynamics, and their off-target effects; these issues warrant further attention for future studies in the field. In addition, the cGMP-dependent and -independent effects of NO should be considered. Regarding the effect of NO on carbohydrate metabolism, one can predict that drugs targeting the NO pathway rank high in the future treatment of T2DM; data that support this idea are that metformin, as the first-line treatment for T2DM, exerts some of its antidiabetic effects by increasing eNOS activity. A NO–metformin hybrid drug may be a suggestion worth examining.
10
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
Outstanding Questions Considering that NO regulates carbohydrate metabolism in a concentration-dependent manner, what is the threshold concentration for its physiological vs pathological actions in different tissues? Response to this question would be critical were NO-releasing drugs to be considered as a potential treatment for T2DM and IR. Site-specific and NOS isoformdependent actions of NO on glucose and insulin homeostasis have been mostly reported in animals, but what about these effects in humans? Which actions of iNOS-derived NO on carbohydrate metabolism are physiological? The effect of iNOS-derived NO on carbohydrate metabolism is dependent on the nature of the enzyme induced, the subject tissue, and the concentration of the produced NO. Considering the importance of NO in the central regulation of glucose homeostasis, how does NO affect glucose sensing in brain and what is its significance in the development of diabetes?
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
Acknowledgments This study was supported by Shahid Beheshti University of Medical Sciences (Grant No. 1-19626). The authors acknowledge Ms Niloofar Shiva for critical editing of the English grammar and syntax of the manuscript. References 1. Ghasemi, A. and Zahediasl, S. (2011) Is nitric oxide a hormone? Iran. Biomed. J. 15, 59–65 2. Tessari, P. et al. (2010) Nitric oxide synthesis is reduced in subjects with type 2 diabetes and nephropathy. Diabetes 59, 2152–2159 3. Natali, A. et al. (2013) Systemic inhibition of nitric oxide synthesis in non-diabetic individuals produces a significant deterioration in glucose tolerance by increasing insulin clearance and inhibiting insulin secretion. Diabetologia 56, 1183–1191 4. Moguib, O. et al. (2017) Endothelial nitric oxide synthase gene (T786C and G894T) polymorphisms in Egyptian patients with type 2 diabetes. J. Genet. Eng. Biotechnol. 15, 431–436 5. Thameem, F. et al. (2008) Endothelial nitric oxide synthase (eNOS) gene polymorphisms and their association with type 2 diabetes-related traits in Mexican Americans. Diab. Vasc. Dis. Res. 5, 109–113 6. Monti, L.D. et al. (2003) Endothelial nitric oxide synthase polymorphisms are associated with type 2 diabetes and the insulin resistance syndrome. Diabetes 52, 1270–1275 7. Tso, A.W. et al. (2006) Endothelial nitric oxide synthase G894T (Glu298Asp) polymorphism was predictive of glycemic status in a 5-year prospective study of Chinese subjects with impaired glucose tolerance. Metabolism 55, 1155–1158 8. Becerril, S. et al. (2010) Deletion of inducible nitricoxide synthase in leptin-deficient mice improves brown adipose tissue function. PLoS One 5, e10962 9. Kumar, D. et al. (2018) Chronic hyperinsulinemia promotes meta-inflammation and extracellular matrix deposition in adipose tissue: implications of nitric oxide. Mol. Cell. Endocrinol. 477, 15–28 10. Lee, J.-T. et al. (2014) Macrophage metalloelastase (MMP12) regulates adipose tissue expansion, insulin sensitivity, and expression of inducible nitric oxide synthase. Endocrinology 155, 3409–3420 11. McGrowdera, D. et al. (2006) Modulation of glucose uptake in adipose tissue by nitric oxide-generating compounds. J. Biosci. 31, 347–354 12. Horton, R.A. et al. (1994) Inhibition of hepatic gluconeogenesis by nitric oxide: a comparison with endotoxic shock. Biochem. J. 299, 735–739 13. Shepherd, A.I. et al. (2016) Effect of nitrate supplementation on hepatic blood flow and glucose homeostasis: a double-blind, placebo-controlled, randomized control trial. Am. J. Physiol. Gastrointest. Liver. Physiol. 311, G356–G364 14. Lundquist, I. et al. (2016) Metformin ameliorates dysfunctional traits of glibenclamide- and glucoseinduced insulin secretion by suppression of imposed overactivity of the islet nitric oxide synthase-NO system. PLoS One 11, e0165668 15. Pilon, G. et al. (2004) Inhibition of inducible nitricoxide synthase by activators of AMP-activated protein kinase a new mechanism of action of insulinsensitizing drugs. J. Biol. Chem. 279, 20767–20774 16. Fujita, Y. et al. (2010) Metformin suppresses hepatic gluconeogenesis and lowers fasting blood glucose levels through reactive nitrogen species in mice. Diabetologia 53, 1472–1481 17. Lajoix, A.-D. et al. (2001) A neuronal isoform of nitric oxide synthase expressed in pancreatic b-cells controls insulin secretion. Diabetes 50, 1311–1323
18. Nakada, S. et al. (2003) Constitutive nitric oxide synthases in rat pancreatic islets: direct imaging of glucose-induced nitric oxide production in betacells. Pflugers Arch 447, 305–311 19. Kurohane Kaneko, Y. and Ishikawa, T. (2013) Dual role of nitric oxide in pancreatic beta-cells. J. Pharmacol. Sci. 123, 295–300 20. Jimenez-Feltstrom, J. et al. (2005) Glucose stimulates the expression and activities of nitric oxide synthases in incubated rat islets: an effect counteracted by GLP1 through the cyclic AMP/PKA pathway. Cell Tissue Res. 319, 221–230 21. Henningsson, R. et al. (2002) Role of nitric oxide synthase isoforms in glucose-stimulated insulin release. Am. J. Physiol. Cell. Physiol. 283, C296–C304 22. Laffranchi, R. et al. (1995) Nitric oxide (nitrogen monoxide, NO) stimulates insulin secretion by inducing calcium release from mitochondria. Biochem. Biophys. Res. Commun. 217, 584–591 23. Willmott, N.J. et al. (1995) Nitric oxide induces intracellular Ca2+ mobilization and increases secretion of incorporated 5-hydroxytryptamine in rat pancreatic beta-cells. FEBS Lett 371, 99–104 24. Rizzo, M.A. and Piston, D.W. (2003) Regulation of beta cell glucokinase by S-nitrosylation and association with nitric oxide synthase. J. Cell Biol. 161, 243–248 25. Markwardt, M.L. et al. (2012) Association with nitric oxide synthase on insulin secretory granules regulates glucokinase protein levels. Mol. Endocrinol. 26, 1617–1629 26. Eckersten, D. and Henningsson, R. (2012) Nitric oxide (NO) – production and regulation of insulin secretion in islets of freely fed and fasted mice. Regul. Pept. 174, 32–37 27. Tsuura, Y. et al. (1998) Endogenous nitric oxide inhibits glucose-induced insulin secretion by suppression of phosphofructokinase activity in pancreatic islets. Biochem. Biophys. Res. Commun. 252, 34–38 28. Lajoix, A.D. et al. (2006) Protein inhibitor of neuronal nitric oxide synthase (PIN) is a new regulator of glucose-induced insulin secretion. Diabetes 55, 3279–3288 29. Muhammed, S.J. et al. (2012) Pancreatic beta-cell dysfunction, expression of iNOS and the effect of phosphodiesterase inhibitors in human pancreatic islets of type 2 diabetes. Diabetes Obes. Metab. 14, 1010–1019 30. Kim, J.Y. et al. (2010) Chronic ethanol consumptioninduced pancreatic b-cell dysfunction and apoptosis through glucokinase nitration and its downregulation. J. Biol. Chem. 285, 37251–37262 31. Tsuura, Y. et al. (1994) Nitric oxide opens ATPsensitive K+ channels through suppression of phosphofructokinase activity and inhibits glucoseinduced insulin release in pancreatic beta cells. J. Gen. Physiol. 104, 1079–1098 32. Corbett, J.A. et al. (1993) Nitric oxide mediates cytokine-induced inhibition of insulin secretion by human islets of Langerhans. Proc. Natl Acad. Sci. U. S. A. 90, 1731–1735 33. Panagiotidis, G. et al. (1995) Influence of nitric oxide synthase inhibition, nitric oxide and hydroperoxide on insulin release induced by various secretagogues. Br. J. Pharmacol. 114, 289–296
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
11
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
34. Frandsen, U. et al. (1996) Localization of nitric oxide synthase in human skeletal muscle. Biochem. Biophys. Res. Commun. 227, 88–93 35. McConell, G.K. and Kingwell, B.A. (2006) Does nitric oxide regulate skeletal muscle glucose uptake during exercise? Exerc. Sport. Sci. Rev. 34, 36–41 36. Stamler, J.S. and Meissner, G. (2001) Physiology of nitric oxide in skeletal muscle. Physiol. Rev. 81, 209–237 37. Baron, A.D. and Clark, M.G. (1997) Role of blood flow in the regulation of muscle glucose uptake. Annu. Rev. Nutr. 17, 487–499 38. Kellogg, D.L., III et al. (2017) Neuronal nitric oxide synthase mediates insulin- and oxidative stressinduced glucose uptake in skeletal muscle myotubes. Free Radic. Biol. Med. 110, 261–269 39. McConell, G.K. et al. (2012) Skeletal muscle nitric oxide signaling and exercise: a focus on glucose metabolism. Am. J. Physiol. Endocrinol. Metab. 303, E301–E307 40. Etgen, G.J., Jr. et al. (1997) Nitric oxide stimulates skeletal muscle glucose transport through a calcium/ contraction- and phosphatidylinositol-3-kinaseindependent pathway. Diabetes 46, 1915–1919 41. Vincent, M.A. et al. (2003) Molecular and physiologic actions of insulin related to production of nitric oxide in vascular endothelium. Curr. Diab. Rep. 3, 279–288 42. Montagnani, M. et al. (2001) Insulin-stimulated activation of eNOS is independent of Ca2+ but requires phosphorylation by Akt at Ser1179. J. Biol. Chem. 276, 30392–30398 43. Barrett, E.J. et al. (2011) Insulin regulates its own delivery to skeletal muscle by feed-forward actions on the vasculature. Am. J. Physiol. Endocrinol. Metab. 301, E252–E263 44. Lira, V.A. et al. (2007) Nitric oxide increases GLUT4 expression and regulates AMPK signaling in skeletal muscle. Am. J. Physiol. Endocrinol. Metab. 293, E1062–E1068 45. Wang, H. et al. (2013) Nitric oxide directly promotes vascular endothelial insulin transport. Diabetes 62, 4030–4042 46. Torres, S. et al. (2004) Inflammation and nitric oxide production in skeletal muscle of type 2 diabetic patients. J. Endocrinol. 181, 419–427 47. Krause, M. et al. (2012) Differential nitric oxide levels in the blood and skeletal muscle of type 2 diabetic subjects may be consequence of adiposity: a preliminary study. Metabolism 61, 1528–1537 48. Eghbalzadeh, K. et al. (2014) Skeletal muscle nitric oxide (NO) synthases and NO-signaling in ‘‘diabesity’’ – what about the relevance of exercise training interventions? Nitric Oxide 37, 28–40 49. Perreault, M. and Marette, A. (2001) Targeted disruption of inducible nitric oxide synthase protects against obesity-linked insulin resistance in muscle. Nat. Med. 7, 1138–1143 50. Martins, A.R. et al. (2012) Mechanisms underlying skeletal muscle insulin resistance induced by fatty acids: importance of the mitochondrial function. Lipids Health Dis. 11, 30 51. Sugita, H. et al. (2005) Inducible nitric-oxide synthase and NO donor induce insulin receptor substrate-1 degradation in skeletal muscle cells. J. Biol. Chem. 280, 14203–14211 52. Zanotto, T.M. et al. (2016) Blocking iNOS and endoplasmic reticulum stress synergistically improves insulin resistance in mice. Mol. Metab. 6, 206–218 53. Kapur, S. et al. (1997) Expression of nitric oxide synthase in skeletal muscle: a novel role for nitric oxide as a modulator of insulin action. Diabetes 46, 1691–1700
12
54. Carvalho-Filho, M.A. et al. (2005) S-Nitrosation of the insulin receptor, insulin receptor substrate 1, and protein kinase B/Akt: a novel mechanism of insulin resistance. Diabetes 54, 959–967 55. Engeli, S. et al. (2004) Regulation of the nitric oxide system in human adipose tissue. J. Lipid Res. 45, 1640–1648 56. Kikuchi-Utsumi, K. et al. (2002) Enhanced gene expression of endothelial nitric oxide synthase in brown adipose tissue during cold exposure. Am. J. Physiol. Regul. Integr. Comp. Physiol. 282, R623– R626 57. Ribie`re, C. et al. (2002) Insulin stimulates nitric oxide production in rat adipocytes. Biochem. Biophys. Res. Commun. 291, 394–399 58. Giordano, A. et al. (2002) Evidence for a functional nitric oxide synthase system in brown adipocyte nucleus. FEBS Lett. 514, 135–140 59. Kapur, S. et al. (2000) Nitric oxide: a new player in the modulation of energy metabolism. Int. J. Obes. Relat. Metab. Disord. 24 (Suppl. 4 ), S36–S40 60. Lu, M. et al. (2010) Inducible nitric oxide synthase deficiency in myeloid cells does not prevent dietinduced insulin resistance. Mol. Endocrinol. 24, 1413– 1422 61. Roy, D. et al. (1998) Insulin stimulation of glucose uptake in skeletal muscles and adipose tissues in vivo is NO dependent. Am. J. Physiol. 274, E692–E699 62. Tanaka, T. et al. (2003) Nitric oxide stimulates glucose transport through insulin-independent GLUT4 translocation in 3T3-L1 adipocytes. Eur. J. Endocrinol. 149, 61–67 63. Xia, N. et al. (2016) Uncoupling of endothelial nitric oxide synthase in perivascular adipose tissue of dietinduced obese mice. Arterioscler. Thromb. Vasc. Biol. 36, 78–85 64. Ribiere, C. et al. (1996) White adipose tissue nitric oxide synthase: a potential source for NO production. Biochem. Biophys. Res. Commun. 222, 706–712 65. Jang, J.E. et al. (2016) Nitric oxide produced by macrophages inhibits adipocyte differentiation and promotes profibrogenic responses in preadipocytes to induce adipose tissue fibrosis. Diabetes 65, 2516– 2528 66. Nisoli, E. et al. (1997) Inducible nitric oxide synthase in rat brown adipocytes: implications for blood flow to brown adipose tissue. Endocrinology 138, 676–682 67. Muriel, P. (2000) Regulation of nitric oxide synthesis in the liver. J. Appl. Toxicol. 20, 189–195 68. McNaughton, L. et al. (2002) Distribution of nitric oxide synthase in normal and cirrhotic human liver. Proc. Natl Acad. Sci. U. S. A. 99, 17161–17166 69. Bhattacharya, S. et al. (2013) The activation by glucose of liver membrane nitric oxide synthase in the synthesis and translocation of glucose transporter-4 in the production of insulin in the mice hepatocytes. PLoS One 8, e81935 70. Shankar, R.R. et al. (2000) Mice with gene disruption of both endothelial and neuronal nitric oxide synthase exhibit insulin resistance. Diabetes 49, 684–687 71. Eipel, C. et al. (2010) Regulation of hepatic blood flow: the hepatic arterial buffer response revisited. World J. Gastroenterol. 16, 6046–6057 72. Abudukadier, A. et al. (2013) Tetrahydrobiopterin has a glucose-lowering effect by suppressing hepatic gluconeogenesis in an endothelial nitric oxide synthase-dependent manner in diabetic mice. Diabetes 62, 3033–3043 73. Sadri, P. and Lautt, W.W. (1999) Blockade of hepatic nitric oxide synthase causes insulin resistance. Am. J. Physiol. Gastrointest. Liver Physiol. 277, G101–G108 74. Molina y Vedia, L. et al. (1992) Nitric oxide-induced S-nitrosylation of glyceraldehyde-3-phosphate
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
Please cite this article in press as: Bahadoran et al., Role of Nitric Oxide in Insulin Secretion and Glucose Metabolism, Trends in Endocrinology & Metabolism (2019), https://doi.org/10.1016/j.tem.2019.10.001
Trends in Endocrinology & Metabolism
75.
76.
77. 78.
79. 80.
81. 82. 83. 84.
dehydrogenase inhibits enzymatic activity and increases endogenous ADP-ribosylation. J. Biol. Chem. 267, 24929–24932 Shinozaki, S. et al. (2011) Liver-specific inducible nitric-oxide synthase expression is sufficient to cause hepatic insulin resistance and mild hyperglycemia in mice. J. Biol. Chem. 286, 34959–34975 Charbonneau, A. and Marette, A. (2010) Inducible nitric oxide synthase induction underlies lipidinduced hepatic insulin resistance in mice: potential role of tyrosine nitration of insulin signaling proteins. Diabetes 59, 861–871 Tups, A. et al. (2017) Central regulation of glucose homeostasis. Compr. Physiol. 7, 741–764 Gu¨emes, A. and Georgiou, P. (2018) Review of the role of the nervous system in glucose homoeostasis and future perspectives towards the management of diabetes. Bioelectron. Med. 4, 9 Chachlaki, K. et al. (2017) Phenotyping of nNOS neurons in the postnatal and adult female mouse hypothalamus. J. Comp. Neurol. 525, 3177–3189 Fioramonti, X. et al. (2010) Ventromedial hypothalamic nitric oxide production is necessary for hypoglycemia detection and counterregulation. Diabetes 59, 519–528 Shankar, R. et al. (1998) Central nervous system nitric oxide synthase activity regulates insulin secretion and insulin action. J. Clin. Invest. 102, 1403–1412 Marsollier, N. et al. (2009) Deregulation of hepatic insulin sensitivity induced by central lipid infusion in rats is mediated by nitric oxide. PLoS One 4, e6649 Arble, D. and Sandoval, D. (2013) CNS control of glucose metabolism: response to environmental challenges. Front. Neurosci. 7, 20 Murphy, B.A. et al. (2009) AMP-activated protein kinase and nitric oxide regulate the glucose
85.
86. 87.
88.
89.
90. 91. 92. 93.
sensitivity of ventromedial hypothalamic glucoseinhibited neurons. Am. J. Physiol. Cell. Physiol. 297, C750–C758 Canabal, D.D. et al. (2007) Glucose, insulin, and leptin signaling pathways modulate nitric oxide synthesis in glucose-inhibited neurons in the ventromedial hypothalamus. Am. J. Physiol. Regul. Integr. Comp. Physiol. 292, R1418–R1428 Routh, V.H. (2010) Glucose sensing neurons in the ventromedial hypothalamus. Sensors (Basel) 10, 9002–9025 Duparc, T. et al. (2011) Central apelin controls glucose homeostasis via a nitric oxide-dependent pathway in mice. Antioxid. Redox Signal. 15, 1477– 1496 Abtahi, S. et al. (2017) Ghrelin enhances food intake and carbohydrate oxidation in a nitric oxide dependent manner. Gen. Comp. Endocrinol. 250, 9–14 Leshan, R.L. et al. (2012) Leptin action through hypothalamic nitric oxide synthase-1-expressing neurons controls energy balance. Nat. Med. 18, 820–823 Xu, X. et al. (2008) Molecular mechanisms of ghrelinmediated endothelial nitric oxide synthase activation. Endocrinology 149, 4183–4192 Gaskin, F.S. et al. (2003) Ghrelin-induced feeding is dependent on nitric oxide. Peptides 24, 913–918 Andersson, U. et al. (2004) AMP-activated protein kinase plays a role in the control of food intake. J. Biol. Chem. 279, 12005–12008 Lin, K.Y. et al. (2002) Impaired nitric oxide synthase pathway in diabetes mellitus: role of asymmetric dimethylarginine and dimethylarginine dimethylaminohydrolase. Circulation 106, 987–992
Trends in Endocrinology & Metabolism, --, Vol. --, No. --
13