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Ethanol and Hippocampal Gene Expression: Linking in Ethanol Metabolism, Neurodegeneration, and Resistance to Oxidative Stress
C H A P T E R
48 Ethanol and Hippocampal Gene Expression: Linking in Ethanol Metabolism, Neurodegeneration, and Resistance to Oxidative Stress Mario Dı´az1, Vero´nica Casan˜as-Sa´nchez2, David Quinto-Alemany3 and Jose´ A. Pe´rez2 1
Departamento de Biologı´a Animal, Edafologı´a y Geologı´a & Unidad Asociada de Investigacio´n ULL-CSIC, “Fisiologı´a y Biofı´sica de la Membrana Celular en Patologı´as Neurodegenerativas y Tumorales”, Facultad de Ciencias, Seccio´n Biologı´a, Universidad de La Laguna, Tenerife, Spain 2Departamento de Bioquı´mica, Microbiologı´a, Biologı´a Celular y Gene´tica & Instituto Universitario de Enfermedades Tropicales y Salud Pu´blica de Canarias, Facultad de Ciencias, Seccio´n Biologı´a, Universidad de La Laguna, Tenerife, Spain 3Departamento de Biologı´a Animal, Edafologı´a y Geologı´a, Facultad de Ciencias, Seccio´n Biologı´a, Universidad de La Laguna, Tenerife, Spain
LIST OF ABBREVIATIONS AMPA CYP2E1 FAK GABA-A LTD LTP NMDA PKC ROS SOD CAT
α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid cytochrome P450 isoform 2E1 focal adhesion kinase gamma-aminobutyric acid A long-term depression long-term potentiation N-methyl-D-aspartate protein kinase C reactive oxygen species superoxide dismutase catalase
INTRODUCTION Ethanol is a very pleiotropic molecule and its effects extend to nearly all organs in an organism. Cell membranes are highly permeable to alcohol, and once alcohol enters the bloodstream it diffuses into nearly every cell in the body, including the brain. Ethanol is known to induce neurocognitive deficits and to provoke neuronal function impairments and, at high doses or long-
Neuroscience of Alcohol. DOI: https://doi.org/10.1016/B978-0-12-813125-1.00048-9
term consumption, to provoke injuries associated with neuronal degeneration (Givens, Williams, & Gill, 2000). There is general consensus on the participation of oxidative stress in the deleterious effects of ethanol and that ethanol-driven generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) are implicated in nerve tissue injury (Das & Vasudevan, 2007). However, given the pleotropic face of ethanol, the precise mechanisms underlying ethanol-induced neurological disorders are diverse and only partially understood (Harris, Trudell, & Mihic, 2008). Ethanol targets include a plethora of molecules from neurotransmitter receptors, kinases, signaling molecules, transcription factors, proto-oncogenes, and ion channels, among others (reviewed in Harris et al., 2008; Ryabinin, 1998). Further, recent evidence have demonstrated that ethanol drives changes in gene expression and transcriptional modulation, as well as in chromatin remodeling (Casan˜as-Sa´nchez, Perez, QuintoAlemany, & Dı´az, 2016; Chandrasekar, 2013; Hsieh & Gage, 2005; Jin et al., 2014; Moykkynen & Korpi, 2012; Nagy, Kolok, Dezso, Boros, & Szombathelyi, 2003). In
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© 2019 Elsevier Inc. All rights reserved.
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the brain, the hippocampus is particularly sensitive to ethanol. It is known that acute exposure to alcohol alters cognitive functions, such as working memory and spatial learning (Givens et al., 2000; White, Matthews, & Best, 2000). Studies addressing the effects of alcohol on human memory have shown that acute intoxication is more severe on the acquisition of new memories than for retrieval of already-formed (consolidated) memories, and that these effects of alcohol are similar to those reported after hippocampal damage (Ryabinin, 1998; White et al., 2000). Current evidence indicates that alcohol-mediated memory impairments are rather a “continuum of effects” (Collins et al., 2009) ranging from short-term memory deficits seen in lowdose acute exposures (i.e., moderate drinkers), to blackouts in chronic consumers (in some alcoholics), and permanent inability to form memories, as observed in alcoholic subjects with Wernicke Korsakoff syndrome (Sanvisens et al., 2017). In the past decade, a number of epidemiological studies have reported significantly reduced risks of cognitive decline or dementia (including Alzheimer’s disease) in light to moderate alcohol consumers in comparison to nondrinkers (and, obviously, to heavy drinkers) (Collins et al., 2009; Mukamal et al., 2003; NIAAA, 2000; Ruitenberg et al., 2002). The association of alcohol intake with dementia was boosted by the recognition that dementia shares risk factors with cardiovascular disease (Collins et al., 2009; Mukamal et al., 2006). Indeed, the relationship between alcohol intake and risk of dementia (Vascular dementia and Alzheimer disease) or cardiovascular disease (coronary heart disease or ischemic stroke) followed similar Ushaped dependences (Collins et al., 2009; Mukamal et al., 2006) with increased risks at higher alcohol intakes (Fig. 48.1). This U-shape relationship suggests that the effects of ethanol are hormetic (exhibit hormesis) and that beneficial or detrimental effects of ethanol are tightly correlated to the dose (Mattson, 2008). On the other hand, Bate and Williams (2011) demonstrated that pretreatment with low concentrations of ethanol (0.02% 0.08%) protected cortical and hippocampal neurons against Aβ-induced synapse damage. Interestingly, these authors also demonstrated that ethanol was able to protect neurons against the damage produced by presynaptic accumulation of α-synuclein (which are characteristic aggregates in Parkinson’s disease and dementia with Lewy bodies). However, the molecular mechanisms of ethanol-induced neuroprotection are largely unknown and only recently have started to be unraveled. Another intriguing aspect on the effects of low to moderate doses of ethanol is that its exposure brings about a degree of protection against other cell insults. This has been better demonstrated in experimental
FIGURE 48.1 The relationship between alcohol intake and risk of dementia in the Cardiovascular Health Study (Mukamal et al., 2006). Data gathered by Collins et al. (2009) were submitted to cuadratic polynomial fitting to show the U-shape relationship. The median of class categories was used as X-values. Former: Long-term abstainers.
ischemia-reperfusion injuries in animal models, where preadministration of low to moderate ethanol exposure prevents cardiovascular damage (Collins et al., 2009; Murry, Jennings, & Reimer, 1986). This phenomenon, namely “preconditioning,” allows tissues or cells to evolve towards a cytoprotective “phenotype” endowed with a higher tolerance against different insults (Murry et al., 1986). For instance, alcohol preconditioning effects on inflammatory neurotoxicity has been demonstrated in organotypic slices of rat hippocampusentorhinal cortex (two brain regions significantly affected in Alzheimer’s disease) in response to neuroinflammatory proteins HIV-1 gp120 neurotoxicity (Collins et al., 2009, 2010). Current hypothesis points to ethanol-induced changes in gene expression as putative mechanisms whereby it may not only exert some of its acute and chronic effects in the hippocampus, but also drive preconditioning in nerve cells. The changes in gene expression will be the focus of this chapter.
METABOLISM OF ETHANOL IN THE HIPPOCAMPUS Mounting evidence indicates that both chronic and acute alcohol consumption can cause brain oxidative damage. It is known that acetaldehyde resulting from ethanol metabolism, mediates many behavioral, neurochemical, and neurotoxic effects in the brain. However, systemic acetaldehyde derived from its peripheral metabolism (mainly from the liver) hardly penetrates into the brain due to the high aldehyde dehydrogenase
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(ALDH) activity in the endothelial cells at the bloodbrain barrier (Hipolito, Sanchez, Polache, & Granero, 2007). In the liver, ethanol is metabolized by ADH, catalase (CAT), and CYP2E1 (CYP450 isoform 2E1, a member of the superfamily). Conversely, in the brain, ADH is present at very low or negligible levels (Estonius, Svensson, & Hoog, 1996), and in vitro data indicate that CAT accounts for 60% of ethanol oxidation, whereas CYP2E1 accounts for an additional 20% (Zimatkin, Pronko, Vasiliou, Gonzalez, & Deitrich, 2006). Thus, because alcohol dehydrogenase activity is nearly negligible in the brain, the generation of acetaldehyde from ethanol occurs in situ and is mediated by catalase and CYP2E1 enzymes. In addition, catalytic activity of CYP2E1 on ethanol can produce ROS, which eventually causes damage to mitochondria, DNA modification, lipid peroxidation, and even cell death (Caro & Cederbaum, 2004). The mechanisms involved in ROS generation involve different cellular compartments and biochemical/chemical reactions which are shown in Fig. 48.2. CYP2E1 proteins are not uniformly expressed in brain regions, but rather are circumscribed to specific areas, including the hippocampus, substantia nigra, and cerebellum (Garcı´a-Sua´stegui et al., 2017; Shahabi, Andersson, & Nissbrandt, 2008). Ethanol is not only
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the substrate, but also a potent inducer, of CYP2E1 in the liver and brain, and current evidence suggests that ethanol toxicity and ethanol-related ROS generation is associated to elevated CYP2E1 levels in susceptible brain regions (Zhong et al., 2012). Indeed, earlier studies have shown that brain CYP2E1 was inducible by chronic (Roberts, Shoaf, Jeong, & Song, 1994) and acute (Yadav, Dhawan, Singh, Seth, & Parmar, 2006) ethanol treatment in rats. In the rat brain, chronic or acute ethanol treatment increases the amount of CYP2E1 proteins, mRNA levels, and activity in the hippocampus, cerebellum, and frontal cortex, but no significant changes were observed in other brain regions (Garcı´aSua´stegui et al., 2017; Zhong et al., 2012). Interestingly, in the study by Zhong et al. (2012), ethanol markedly increased the levels of CYP2E1 proteins and activity, but not the mRNA levels, in the brainstem after chronic ethanol treatment, indicating that posttranslational processing may also be involved in CYP2E1 induction. The elevated CYP2E1 levels were paralleled by ROS generation and neuronal damage in the hippocampus, cerebellum, and brainstem (Zhong et al., 2012). In summary, the hippocampus, cerebellum, and brainstem are susceptible regions to ethanol neurotoxicity. This selective sensitivity may be attributed to the cellular-specific, ethanol-induced, upregulation of
FIGURE 48.2 Ethanol oxidation by CYP2E1 in endoplasmic reticulum and CAT in peroxisomes results in an increase of ROS and oxidative stress. Ethanol is converted to acetaldehyde, which may enter the mitochondria and is oxidized to acetate by ALD or directly oxidized by CYP2E1 in the reticulum. O22radicals leave the mitochondria and endoplasmic reticulum and is converted into H2O2 by SOD isoforms in the cytoplasm and mitochondria. In the presence of iron ions (ferrous form), H2O2 gives rise to highly reactive OH radicals by virtue of the Fenton reaction. In addition, ethanol can increase the expression/activity of CYP2E1 resulting in an additional increase of ROS which starts a feedback cycle of ROS production. Increased ROS levels induce oxidative damage of lipids, proteins, DNA, and mitochondria. ALDH, aldehyde dehydrogenase; ETC, electron transport chain; OH, hydroxyl radical; ∙O22, superoxide anion radical; H2O2, hydrogen peroxide; Fe21, ferrous iron; MEOS, microsomal ethanol-oxidizing system.
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CYP2E1 or by posttranscriptional processing of CYP2E1, which in any case is paralleled by ROS generation to levels above neuronal ROS buffering capacities, eventually leading to neuronal degeneration.
CHRONIC AND LONG-TERM EFFECTS OF ETHANOL IN THE HIPPOCAMPUS Further to its effects on ROS generation, ethanol also affects several neurotransmitter systems in the brain. Compelling evidence indicates that an important site of ethanol actions is the glutamatergic neurotransmitter system, the main excitatory neurotransmitter in the brain. Ionotropic glutamate receptors form glutamate-gated ion channels and are classified into three main groups, AMPA receptors, kainate receptors, and NMDA receptors, with different locations and functions in neuronal synapse (Moykkynen & Korpi, 2012; Smart & Paoletti, 2012). The AMPA receptors normally mediate fast synaptic transmission and synaptic strength. NMDA receptors exhibit high calcium permeability and regulate intracellular signaling and synaptic plasticity. Finally, kainate receptors are present both in the presynaptic and postsynaptic membranes and have a modulatory role on neurotransmitter release. The three types are expressed in the hippocampus and are responsible for processes like LTP (long-term potentiation) and LTD (long-term depression), which are involved in synaptic plasticity, cognitive performance, and different types of memories (Nicoll & Roche, 2013). A number of studies have shown that ethanol is a potent inhibitor of ionotropic glutamate receptor function by decreasing current amplitude and by accelerating current desensitization (Carta, Ariwodola, Weiner, & Valenzuela, 2003; Moykkynen & Korpi, 2012), and LTP in vivo (Givens & McMahon, 1995), which ultimately alters neuronal plasticity. Of the different ionotropic glutamate receptors, NMDA receptors are regarded as the most sensitive to ethanol as they can be inhibited by clinically relevant concentrations of ethanol (20 mM). These inhibitory effects of ethanol occur almost immediately after ethanol enters the blood brain barrier, and appear to be mediated by interaction with specific binding sites of NMDA receptor subunits. However, chronic and prolonged ethanol exposition leads to a compensatory “upregulation” of NMDA receptors by modulation of gene expression (Jin et al., 2014; Moykkynen & Korpi, 2012). Not surprisingly, these alterations are supposed to contribute to the development of ethanol tolerance and dependence, as well as ethanol withdrawal syndrome (Nagy, 2004).
Ionotropic glutamate receptors are tetrameric proteins composed of different subunits, whose combinations determine their biophysical, physiological, and pharmacological properties. Recent papers on the effects of ethanol in in vitro and in vivo models have revealed alterations in the subunit composition of hippocampal glutamate receptors after long-term ethanol exposure. For instance, the NR2B subunit expression of the NMDA receptor has been demonstrated to be increased in cultured hippocampal and cortical neurons after 3 days of intermittent ethanol treatment (Nagy, 2004). mRNA and/or protein levels of NR2A and NR2B subunits were found elevated in rat hippocampus after in vivo chronic alcohol exposure (Follesa & Ticku, 1995; Nagy et al., 2003). In addition, in postmortem human brains from alcoholics, Jin et al. (2014) reported the significant increase in the mRNAs encoding for different subunits of AMPA receptors (GluA2 and GluA3), NMDA receptors (GluN1, GluN2A, GluN2C, GluN2D, and GluNA3), and kainate receptors (GluK2, GluK3, and GluK5) in the hippocampusdentate gyrus, but not in the prefrontal cortex. These results indicate that ethanol effectively affects the transcription levels of glutamate receptor subtypes in the brain, likely through different mechanisms (Chandrasekar, 2013), and more interestingly, that these changes are strictly circumscribed to specific brain regions. Assuming that these gene expression changes are translated into new subunits, it is expected that extensive remodeling of neurotransmission, signaling, and neuronal network excitability in the hippocampus occurs after chronic alcoholism. Further to its effect on glutamatergic systems, evidence accumulated over more than 30 years, demonstrates that ethanol effects on the central nervous system are intimately associated to its effects on GABAergic neurotransmission, the major inhibitory neurotransmitter in the brain. Substantial evidence supports the thesis that low to moderate (3 30 mmol/ L) ethanol concentrations enhance the inhibitory activity of GABA-A receptors (reviewed in Alfonso-Loeches & Guerri, 2011). GABA-A channels are pentameric ligand-gated chloride channels, in which the subunit composition determines the physiological and channel’s pharmacological properties, including its ethanol sensitivity. The majority of GABA-A receptors are composed of α-, β-, γ-, and δ-subunits (Olsen & Sieghart, 2008). A region in the transmembrane domains of the α/β subunits of the GABA-A receptor has been identified as the potential binding site for ethanol (Lobo & Harris, 2008), which might account for the acute inhibitory effects of alcohol intake. Nevertheless, the effects of ethanol strongly depend on the subunit composition of GABA-A receptors. GABA-A channels containing the α4, α5, or the δ
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subunit are of particular interest. These subunits are part of extrasynaptic GABA-A channels which give rise to tonic neuronal inhibition, resulting in decreased frequency of action potentials (Jin et al., 2011; Pavlov, Savtchenko, Kullmann, Semyanov, & Walker, 2009). Maximum sensitivity to ethanol appears to occur when the γ subunit (which is located outside of the synapse) was present (Alfonso-Loeches & Guerri, 2011). It is now widely accepted that activation of GABA-A channels containing these subunits have implications for cognitive functioning (Alfonso-Loeches & Guerri, 2011). As for glutamate receptors, chronic and long-term ethanol exposure also alters gene expression of GABA-A receptor subunits. Also, these changes occur in a brain region-specific manner in alcoholic subjects. Indeed, Jin et al. (2011) have shown a significant increase in the mRNAs encoding for α1, α4, α5, β1, and γ1 subunits in the hippocampal and dentate gyrus region of individuals suffering from alcoholism, whereas no changes in the dorsolateral prefrontal cortex were detected in postmortem human brains (Jin et al., 2011). These data further support the association of long-term changes in the GABA-A isoform expression and alcohol dependence (Lobo & Harris, 2008). Finally, studies have also demonstrated the existence of epigenetic changes after long-term alcohol consumption. Epigenetic modifications involve chromatin modifications, that is, histone acetylation, phosphorylation, and DNA methylation, which positively or negatively modulate transcriptional activity. Epigenetic modifications have been shown to play an important role in gene expression underlying the stability and plasticity of developing neuronal circuits (Hsieh & Gage, 2005). Chronic alcohol exposure in experimental animals have revealed decreased HDAC (Histone deacetylase) activity along with upregulation in histone acetylation (H3 and H4), CREBP (cAMPresponsive element binding protein), and neuropeptide Y (NPY), which are associated with the anxiolytic effects of alcohol exposure (Pandey, Ugale, Zhang, Tang, & Prakas, 2008). Interestingly, alterations in DNA methylation in the promoter regions of the α-synuclein gene have been observed in mesolimbic systems (Bonsch, Lenz, Kornhuber, & Bleich, 2005). Also, α-synuclein is involved in the regulation of dopamine biosynthesis and neurotransmission in the mesolimbic system, which plays a crucial role in reinforcing alcohol-seeking behavior (Perez et al., 2002). In agreement, an increased mRNA expression of α-synuclein in alcoholic subjects has been correlated with α-synuclein promoter DNA methylation and obsessive craving (Bonsch et al., 2004, 2005). These results suggest an association between the gene-specific DNA promoter hypermethylation and chronic alcohol consumption (Alfonso-Loeches & Guerri, 2011).
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ACUTE NONTOXIC ETHANOL INTAKE, HIPPOCAMPAL GENE EXPRESSION, AND ANTIOXIDANT POTENTIAL Epidemiological and prospective studies indicate that, at population levels, low to moderate alcohol consumption may be cardio-neuro-protective (reviewed in Collins et al., 2009). The mechanisms underlying these effects of ethanol are largely unknown. Some of these processes likely occur through changes in the ability of endogenous cytoprotective systems to cope with oxidative stress and also with the ability to modulate the transcriptional processes. Regarding brain tissues, seminal studies in cellular and animal models, showed that ethanol exposure under low exposure paradigms activated different signaling mechanisms, that is, selective activation of protein kinase C epsilon (PKCε) and focal adhesion kinase (FAK), which appear to be channeled through expression of heat-shock proteins (HSP) (Sivaswamy, Neafsey, & Collins, 2010). Furthermore, considerable research indicates that the increase of different HSPs (Heat-Shock Proteins, such HSP27, HSP70, HSP90), can be putative neuroprotective “effectors” (Reviewed in Collins et al., 2009, 2010). In this regard, a significant increase in inducible HSP70 and HSP27 proteins occurred in Hippocampal-Entorhinal cortex slices after B6 days of moderate alcohol exposure, which correlates with the onset of significant neuroprotection against gp120-induced (a proinflammatory glycoprotein from HIV-1) neurotoxicity (Collins, Wang, Achille, & Neafsey, 2005). Furthermore, in vitro studies in rat hippocampal cultures have shown that low to moderate ethanol exposure protects against neurotoxic protein aggregates, such amyloid peptides (Aβ) in Alzheimer’s disease, and improved the cognitive processes of learning and memory in 3xTgAD mice (Mun˜oz et al., 2015). Under this paradigm, it was shown that low concentrations of ethanol protect against synaptotoxicity induced by Aβ in hippocampal neurons (Belmadani, Kumar, Schipma, Collins, & Neafsey, 2004; Mun˜oz et al., 2015). Further, in mice, hippocampal cultures of ethanol protect against α-synuclein-induced toxicity, a hallmark in Parkinsons disease (Bate & Williams, 2011). Moreover, epidemiological studies have pointed out that low to moderate alcohol consumption is associated with a lower risk of incident dementia among older adults, being these individuals less likely to develop Alzheimer’s disease (Mukamal et al., 2003) (see Fig. 48.1). Ethanol is a prominent source of oxidative radicals in the brain (Das & Vasudevan, 2007). The high levels of peroxidable lipids and iron ions, together with the relatively low amounts of glutathione, make the brain particularly susceptible to nonenzymatic oxidation of
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cell components. However, recent experimental evidence has pointed out that different brain regions are capable of inducing the activation of antioxidant systems (Fig. 48.3) in response to an ethanol challenge, specifically at low to moderate concentrations (0.02% 0.1%). Indeed, work from our laboratory has demonstrated that 0.1% ethanol exposure to hippocampal-derived HT22 cells, modulates the expression of different genes belonging to the classical, glutathione/glutaredoxin and thioredoxin/peroxiredoxin antioxidant systems (Casan˜as-Sa´nchez et al., 2016). Among the different mRNAs up-regulated by ethanol we found: Sod1 (encoding for Cu/ZnSOD, the cytosolic superoxide dismutase isoform), Sod2 (encoding for MnSOD, the mitochondrial superoxide dismutase isoform), Gpx1 (encoding for GPx1, glutathione peroxidase 1), Gclc (encoding for the catalytic subunit GCLC, and responsible for de novo glutathione synthesis), and Txnrd1 (encoding for TXRD1, the cytoplasmic thioredoxin reductase isoform, the most abundantly expressed neurons) (Table 48.1). Further, in
consonance with the upregulation of Txnrd1, ethanol down-regulated the expression of Txnip, which is an endogenous inhibitor of thioredoxin (Yoshihara et al., 2014) and those of peroxiredoxins (Prdx1-5). Paralleling these changes, enzyme activities of total SOD, total glutathione peroxidase, and total thioredoxin reductase, were all increased (Fig. 48.4) (Casan˜as-Sa´nchez et al., 2016). In addition, ethanol exposure prevented glutamateinduced excitotoxicity in the same time-course as changes in gene expression (Fig. 48.5). These results were in agreement with previous results in the hippocampus of rats receiving acute intraperitoneal injections of ethanol (1.5 1.6 g/kg) showing significant increases in SOD and CAT activities (Enache et al., 2008) or in the rat cerebral cortex, hippocampus, and corpus striatum for glutathione peroxidase activity (Somani et al., 1996). We hypothesize that the transcriptional activation of critical enzymes of neuronal antioxidant systems, as well as that of inducible forms of HSP, underlie the efficient preconditioning effects of ethanol.
FIGURE 48.3
Organization of Classical, Thioredoxin/Peroxiredoxin, and Glutathione/Glutaredoxin antioxidant systems. For clarity the three systems were represented as separated pathways, although connections exist between them. For instance, reduced TRX may transfer the electrons in the two SH groups to oxidized PRDX, rendering reduced PRDX. TXNRD, thioredoxin reductase; TXN, thioredoxin; TXNIP, thioredoxin interacting protein; PRDX, peroxiredoxin; SRXN, sulfiredoxin; GPX, glutathione peroxidase; GSR, glutathione-S-reductase; GLRX, glutaredoxin; GST, glutathione-S-transferase; GSH, glutathione (reduced form); GSSG, glutathione (oxidized form).
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TABLE 48.1 Time-Course of Ethanol-Induced Changes in Gene Expression of Enzymes Belonging to the Three Antioxidant Systems in Hippocampal HT22 Cells
Thioredoxin/Peroxiredoxin
Generic
AOX system
GENE
6 Hr
24 Hr
30 Hr
48 Hr
Sod1 Sod2 Cat Txn1 Txn2 Txnip Txnrd1 Txnrd2 Txnrd3 Prdx2 Prdx3 Prdx4
Glutathione/ Glutaredoxin
Prdx5 Gclc Gsr Glrx1 Glrx2 Gpx1 Gpx4 Up-regulation
Down-regulation
Encoding genes: Sod1-2, superoxide dismutases 1 and 2; Cat, catalase; Txn1-2, thioredoxins 1 and 2; Txnip, thioredoxin interacting protein; Txnrd1-3, thioredoxin reductases 1-3; Prdx1-5, peroxiredoxins 1-5; Gclc, catalytic subunit of glutathione synthase; Gsr, glutathione-S-reductase; Glrx1-4, glutaredoxins 1 4.
FIGURE 48.4 Time-course of ethanol-induced changes in enzyme activities of antioxidant systems in mouse-derived hippocampal HT22 cells. t-SOD, total SOD; t-TXRND, total thioredoxin reductase; t-GPX, total glutathione peroxidase. Source: Adapted from Casan˜as-Sa´nchez V., Perez, J.A., Quinto-Alemany, D., & Dı´az M. (2016). Sub-toxic ethanol exposure modulates gene expression and enzyme activity of antioxidant systems to provide neuroprotection in hippocampal HT22 cells. Frontiers in Physiology, 7, 312.
In summary, we conclude that subtoxic exposure to ethanol may well be neuroprotective against oxidative insults (and perhaps other forms of cellular stress) in the cerebral cortex and hippocampus by triggering
transcriptional activation of antioxidant defenses and expression of inducible heat-shock proteins. These processes may well underlie the preconditioning effects of ethanol in the brain.
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FIGURE 48.5 Low doses of ethanol protect against glutamate-induced neurotoxicity. A representative experiment showing real-time changes in HT22 cell proliferation exposed to ethanol (1% or 0.1%) or ethanol (0.1%) 1 glutamate (20 mM) at the times indicated. Cell index is a parameter that measures cell proliferation/survival based on impedance measurements.
MINI-DICTIONARY OF TERMS Hormesis Any process in a cell or organism that exhibits a biphasic response to exposure to increasing amounts of a substance or condition. Thus, a generally favorable or beneficial biological response is characteristic of low exposures to the substance or other stressors, whereas unfavorable or detrimental effects are characteristic of higher amounts or condition levels, usually resulting in an inverted U-shaped dose-response. LTP Long-Term Potentiation consists on a rapidly induced and long-lasting form of synaptic plasticity linked to learning. It has been best studied in the hippocampus. Preconditioning A phenomenon that allows cells exposed to subtoxic or sublethal levels to toxicants or degree of injuries, not only to overcome the stress caused by them, but also to acquire protection against other kinds of insults. Oxidative stress A disturbance in the balance between the production of ROS and cellular antioxidant defenses. When antioxidant defenses are deficient, then ROS accumulate and may lead to cellular injury and even death. Hippocampus A brain structure belonging to the limbic system. In primates, including humans, it is located in the medial temporal lobe of the cerebral cortex. The hippocampus has a functional role in the consolidation of short-term memory to long-term memory, and also in the construction of spatial memory.
KEY FACTS • The effects of ethanol in hippocampal tissues are biphasic, provoking either detrimental or beneficial effects. • Chronic, long-term ethanol exposure or binge consumption causes severe damage in hippocampal neuronal and glial cells, usually accompanied by cell death. • Many of these deleterious effects are likely due to alcohol-induced generation of reactive oxygen species.
• Compensatory mechanisms involving changes in gene expression in the hippocampus usually parallel chronic, long-term ethanol exposure. • Conversely, acute, subtoxic exposure to ethanol triggers the transcriptional activation of antioxidant enzymes and heat-shock proteins, which protect hippocampal cells against oxidant stress and other insults. • These specific transcriptional activations likely underlie the preconditioning effects of ethanol.
SUMMARY POINTS • Ethanol exposure causes changes in gene expression in the hippocampus. • Chronic, long-term ethanol consumption affects neurotransmitter receptor functions and consolidation of hippocampal working memories. • Chronic, long-term ethanol exposure modulates neurotransmitter receptor gene expression in the hippocampus. • Exposure to acute low to moderate ethanol triggers the expression of different genes encoding for antioxidant enzymes and also heat-shock proteins. • Preconditioning effects of ethanol might be related to reinforcement of cellular antioxidant systems.
References Alfonso-Loeches, S., & Guerri, C. (2011). Molecular and behavioural aspects of the actions of alcohol on the adult and developing brain. Critical Reviews in Clinical Laboratory Sciences, 48, 19 47.
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REFERENCES
Bate, C., & Williams, A. (2011). Ethanol protects cultured neurons against amyloid-beta and alpha-synuclein-induced synapse damage. Neuropharmacology, 61, 1406 1412. Belmadani, A., Kumar, S., Schipma, M., Collins, M. A., & Neafsey, E. J. (2004). Inhibition of amyloid-beta-induced neurotoxicity and apoptosis by moderate ethanol preconditioning. NeuroReport, 15, 2093 2096. Bonsch, D., Lenz, B., Kornhuber, J., & Bleich, S. (2005). DNA hypermethylation of the alpha synuclein promoter in patients with alcoholism. NeuroReport, 16, 167 170. Bonsch, D., Reulbach, U., Bayerlein, K., Hillemacher, T., Kornhuber, J., & Bleich, S. (2004). Elevated alpha synuclein mRNA levels are associated with craving in patients with alcoholism. Biological Psychiatry, 56, 984 986. Caro, A. A., & Cederbaum, A. I. (2004). Oxidative stress, toxicology, and pharmacology of CYP2E1. Annual Review of Pharmacology and Toxicology, 44, 27 42. Carta, M., Ariwodola, O. J., Weiner, J. L., & Valenzuela, C. F. (2003). Alcohol potently inhibits the kainite receptor-dependent excitatory drive of hippocampal interneurons. Proceedings of the National Academy of Sciences USA, 100, 6813 6818. Casan˜as-Sa´nchez, V., Perez, J. A., Quinto-Alemany, D., & Dı´az, M. (2016). Sub-toxic ethanol exposure modulates gene expression and enzyme activity of antioxidant systems to provide neuroprotection in hippocampal HT22 cells. Frontiers in Physiology, 7, 312. Chandrasekar, R. (2013). Alcohol and NMDA receptor: Current research and future direction. Frontiers in Molecular Neuroscience, 6, 14. Collins, M. A., Neafsey, E. J., Mukamal, K. J., Gray, M. O., Parks, D. A., Das, D. K., & Korthuis, R. J. (2009). Alcohol in moderation, cardioprotection, and neuroprotection: Epidemiological considerations and mechanistic studies. Alcoholism: Clinical and Experimental Research, 33, 206 219. Collins, M. A., Neafsey, E. J., Wang, K., Achille, N. J., Mitchell, R. M., & Sivaswamy, S. (2010). Moderate ethanol preconditioning of rat brain cultures engenders neuroprotection against dementiainducing neuroinflammatory proteins: Possible signaling mechanisms. Molecular Neurobiology, 41, 420 425. Collins, M. A., Wang, K., Achille, N., & Neafsey, E. J. (2005). Moderate ethanol preconditioning of the brain as a neuroprotective strategy: Role for selective heat shock protein induction? Alcoholism: Clinical and Experimental Research, 29, 121A. Das, S. K., & Vasudevan, D. M. (2007). Alcohol-induced oxidative stress. Life Sciences, 81, 177 187. Enache, M., Van Waes, V., Vinner, E., Lhermitte, M., Maccari, S., & Darnaude´ry, M. (2008). Impact of an acute exposure to ethanol on the oxidative stress status in the hippocampus of prenatal restraint stress adolescent male rats. Brain Research, 1191, 55 62. Estonius, M., Svensson, S., & Hoog, J. O. (1996). Alcohol dehydrogenase in human tissues: Localisation of transcripts coding for five classes of the enzyme. FEBS Letters, 397, 338 342. Follesa, P., & Ticku, M. K. (1995). Chronic ethanol treatment differentially regulates NMDA receptor subunit mRNA expression in rat brain. Brain Research. Molecular Brain Research, 29, 99 106. Garcı´a-Sua´stegui, W. A., Ramos-Cha´vez, L. A., Rubio-Osornio, M., Calvillo-Velasco, M., Atzin-Me´ndez, J. A., Guevara, J., & SilvaAdaya, D. (2017). The role of CYP2E1 in the drug metabolism or bioactivation in the brain. Oxidative Medicine and Cellular Longevity, 2017, 4680732. Givens, B., & McMahon, K. (1995). Ethanol suppresses the induction of long-term potentiation in vivo. Brain Research, 688, 27 33. Givens, B., Williams, J. M., & Gill, T. M. (2000). Septohippocampal pathway as a site for the memory-impairing effects of ethanol. Hippocampus, 10, 111 121.
471
Harris, R. A., Trudell, J. R., & Mihic, S. J. (2008). Ethanol’s molecular targets. Science Signaling, 1, re7. Hipolito, L., Sanchez, M. J., Polache, A., & Granero, L. (2007). Brain metabolism of ethanol and alcoholism: An update. Current Drug Metabolism, 8, 716 727. Hsieh, J., & Gage, F. H. (2005). Chromatin remodeling in neural development and plasticity. Current Opinion in Cell Biology, 17, 664 671. Jin, Z., Bazov, I., Kononenko, O., Korpi, E. R., Bakalkin, G., & Birnir, B. (2011). Selective changes of GABA(A) channel subunit mRNAs in the hippocampus and orbitofrontal cortex but not in prefrontal cortex of human Alcoholics. Frontiers in Cellular Neuroscience, 5, 30. Jin, Z., Bhandage, A. K., Bazov, I., Kononenko, O., Bakalkin, G., Korpi, E. R., & Birnir, B. (2014). Selective increases of AMPA, NMDA, and kainate receptor subunit mRNAs in the hippocampus and orbitofrontal cortex but not in prefrontal cortex of human alcoholics. Frontiers in Cellular Neuroscience, 8, 11. Lobo, I. A., & Harris, R. A. (2008). GABA(A) receptors and alcohol. Pharmacology Biochemistry and Behavior, 90, 90 94. Mattson, M. P. (2008). Hormesis defined. Ageing Research Reviews, 7, 1 7. Moykkynen, T., & Korpi, E. R. (2012). Acute effects of ethanol on glutamate receptors. Basic & Clinical Pharmacology & Toxicology, 111, 4 13. Mukamal, K. J., Chung, H., Jenny, N. S., Kuller, L. H., Longstreth, W. T., Jr, . . . Siscovick, D. S. (2006). Alcohol consumption and risk of coronary heart disease in older adults: The Cardiovascular Health Study. Journal of American Geriatrics Society., 54(1), 30 37. Mukamal, K. J., Kuller, L. H., Fitzpatrick, A. L., Longstreth, W. T., Jr., Mittleman, M. A., & Siscovick, D. S. (2003). Prospective study of alcohol consumption and risk of dementia in older adults. JAMA, 289, 1405 1413. Mun˜oz, G., Urrutia, J. C., Burgos, C. F., Silva, V., Aguilar, F., Sama, M., . . . Aguayo, L. G. (2015). Low concentrations of ethanol protect against synaptotoxicity induced by Aβ in hippocampal neurons. Neurobiology of Aging, 36, 845 856. Murry, C. E., Jennings, R. B., & Reimer, K. A. (1986). Preconditioning with ischemia: A delay of lethal cell injury in ischemic myocardium. Circulation, 74, 1124 1136. Nagy, J. (2004). The NR2B subtype of NMDA receptor: A potential target for the treatment of alcohol dependence. Current Drug Targets. CNS and Neurological Disorders, 3, 169 179. Nagy, J., Kolok, S., Dezso, P., Boros, A., & Szombathelyi, Z. (2003). Differential alterations in the expression of NMDA receptor subunits following chronic ethanol treatment in primary cultures of rat cortical and hippocampal neurones. Neurochemistry International, 42, 35 43. National Institute on Alcohol Abuse and Alcoholism (NIAAA). (2000). Health risks and benefits of alcohol consumption. Alcohol Research & Health, 24, 5 11. Nicoll, R. A., & Roche, K. W. (2013). Long-term potentiation: Peeling the onion. Neuropharmacology, 74, 18 22. Olsen, R. W., & Sieghart, W. (2008). International union of pharmacology LXX. Subtypes of gamma-aminobutyric acid(A) receptors: Classification on the basis of subunit composition, pharmacology, and function. Update. Pharmacological Reviews, 60, 243 260. Pandey, S. C., Ugale, R., Zhang, H., Tang, L., & Prakas, A. (2008). Brain chromatin remodeling: A novel mechanism of alcoholism. Journal of Neuroscience, 28, 3729 3737. Pavlov, I., Savtchenko, L. P., Kullmann, D. M., Semyanov, A., & Walker, M. C. (2009). Outwardly rectifying tonically active GABAA receptors in pyramidal cells modulate neuronal offset, not gain. Journal of Neuroscience, 29, 15341 15350.
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Perez, R. G., Waymire, J. C., Lin, E., Liu, J. J., Guo, F., & Zigmond, M. J. (2002). A role for α-synuclein in the regulation of dopamine biosynthesis. Journal of Neuroscience, 22, 3090 3099. Roberts, B. J., Shoaf, S. E., Jeong, K. S., & Song, B. J. (1994). Induction of CYP2E1 in liver, kidney, brain and intestine during chronic ethanol administration and withdrawal: Evidence that CYP2E1 possesses a rapid phase half-life of 6 h or less. Biochemical and Biophysical Research Communications, 205, 1064 1071. Ruitenberg, A., Van Swieten, J. C., Witteman, J. C., Mehta, K. M., Van Duijn, C. M., Hofman, A., & Breteler, M. M. (2002). Alcohol consumption and risk of dementia: The Rotterdam Study. Lancet, 359(9303), 281 286. Ryabinin, A. E. (1998). Role of hippocampus in alcohol-induced memory impairment: Implications from behavioral and immediate early gene studies. Psychopharmacology, 139(1-2), 34 43. Sanvisens, A., Zuluaga, P., Fuster, D., Rivas, I., Tor, J., Marcos, M., . . . Muga, R. (2017). Long-term mortality of patients with an alcohol-related wernicke-korsakoff syndrome. Alcohol and Alcoholism, 52(4), 466 471. Shahabi, H. N., Andersson, D. R., & Nissbrandt, H. (2008). Cytochrome P450 2E1 in the substantia nigra: Relevance for dopaminergic neurotransmission and free radical production. Synaps, 62, 379 388. Sivaswamy, S., Neafsey, E. J., & Collins, M. A. (2010). Neuroprotective preconditioning of rat brain cultures with ethanol: Potential transduction by PKC isoforms and focal adhesion
kinase upstream of increases in effector heat shock proteins. European Journal of Neuroscience, 32, 1800-1182. Smart, T. G., & Paoletti, P. (2012). Synaptic neurotransmitter-gated receptors. Cold Spring Harbor Perspectives in Biology, 4, a009662. Somani, S. M., Husain, K., Diaz-Phillips, L., Lanzotti, D. J., Kareti, K. R., & Trammell, G. L. (1996). Interaction of exercise and ethanol on antioxidant enzymes in brain regions of the rat. Alcohol, 13, 603 610. White, A. M., Matthews, D. B., & Best, P. J. (2000). Ethanol, memory, and hippocampal function: A review of recent findings. Hippocampus, 10, 88 93. Yadav, S., Dhawan, A., Singh, R. L., Seth, P. K., & Parmar, D. (2006). Expression of constitutive and inducible cytochrome P450 2E1 in rat brain. Molecular and Cellular Biochemistry, 286, 171 180. Yoshihara, E., Masaki, S., Matsuo, Y., Chen, Z., Tian, H., & Yodoi, J. (2014). Thioredoxin/Txnip: Redoxisome, as a redox switch for the pathogenesis of diseases. Frontiers in Immunology, 4, 514. Zhong, Y., Dong, G., Luo, H., Cao, J., Wang, C., Wu, J., . . . Yue, J. (2012). Induction of brain CYP2E1 by chronic ethanol treatment and related oxidative stress in hippocampus cerebellum, and brainstem. Toxicology, 302, 275 284. Zimatkin, S. M., Pronko, S. P., Vasiliou, V., Gonzalez, F. J., & Deitrich, R. A. (2006). Enzymatic mechanisms of ethanol oxidation in the brain. Alcoholism: Clinical and Experimental Research, 30, 1500 1505.
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48 Ethanol and Hippocampal Gene Expression: Linking in Ethanol Metabolism, Neurodegeneration, and Resistance to Oxidative Stress Mario Dı´az1, Vero´nica Casan˜as-Sa´nchez2, David Quinto-Alemany3 and Jose´ A. Pe´rez2 1
Departamento de Biologı´a Animal, Edafologı´a y Geologı´a & Unidad Asociada de Investigacio´n ULL-CSIC, “Fisiologı´a y Biofı´sica de la Membrana Celular en Patologı´as Neurodegenerativas y Tumorales”, Facultad de Ciencias, Seccio´n Biologı´a, Universidad de La Laguna, Tenerife, Spain 2Departamento de Bioquı´mica, Microbiologı´a, Biologı´a Celular y Gene´tica & Instituto Universitario de Enfermedades Tropicales y Salud Pu´blica de Canarias, Facultad de Ciencias, Seccio´n Biologı´a, Universidad de La Laguna, Tenerife, Spain 3Departamento de Biologı´a Animal, Edafologı´a y Geologı´a, Facultad de Ciencias, Seccio´n Biologı´a, Universidad de La Laguna, Tenerife, Spain
LIST OF ABBREVIATIONS AMPA CYP2E1 FAK GABA-A LTD LTP NMDA PKC ROS SOD CAT
α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid cytochrome P450 isoform 2E1 focal adhesion kinase gamma-aminobutyric acid A long-term depression long-term potentiation N-methyl-D-aspartate protein kinase C reactive oxygen species superoxide dismutase catalase
INTRODUCTION Ethanol is a very pleiotropic molecule and its effects extend to nearly all organs in an organism. Cell membranes are highly permeable to alcohol, and once alcohol enters the bloodstream it diffuses into nearly every cell in the body, including the brain. Ethanol is known to induce neurocognitive deficits and to provoke neuronal function impairments and, at high doses or long-
Neuroscience of Alcohol. DOI: https://doi.org/10.1016/B978-0-12-813125-1.00048-9
term consumption, to provoke injuries associated with neuronal degeneration (Givens, Williams, & Gill, 2000). There is general consensus on the participation of oxidative stress in the deleterious effects of ethanol and that ethanol-driven generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) are implicated in nerve tissue injury (Das & Vasudevan, 2007). However, given the pleotropic face of ethanol, the precise mechanisms underlying ethanol-induced neurological disorders are diverse and only partially understood (Harris, Trudell, & Mihic, 2008). Ethanol targets include a plethora of molecules from neurotransmitter receptors, kinases, signaling molecules, transcription factors, proto-oncogenes, and ion channels, among others (reviewed in Harris et al., 2008; Ryabinin, 1998). Further, recent evidence have demonstrated that ethanol drives changes in gene expression and transcriptional modulation, as well as in chromatin remodeling (Casan˜as-Sa´nchez, Perez, QuintoAlemany, & Dı´az, 2016; Chandrasekar, 2013; Hsieh & Gage, 2005; Jin et al., 2014; Moykkynen & Korpi, 2012; Nagy, Kolok, Dezso, Boros, & Szombathelyi, 2003). In
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the brain, the hippocampus is particularly sensitive to ethanol. It is known that acute exposure to alcohol alters cognitive functions, such as working memory and spatial learning (Givens et al., 2000; White, Matthews, & Best, 2000). Studies addressing the effects of alcohol on human memory have shown that acute intoxication is more severe on the acquisition of new memories than for retrieval of already-formed (consolidated) memories, and that these effects of alcohol are similar to those reported after hippocampal damage (Ryabinin, 1998; White et al., 2000). Current evidence indicates that alcohol-mediated memory impairments are rather a “continuum of effects” (Collins et al., 2009) ranging from short-term memory deficits seen in lowdose acute exposures (i.e., moderate drinkers), to blackouts in chronic consumers (in some alcoholics), and permanent inability to form memories, as observed in alcoholic subjects with Wernicke Korsakoff syndrome (Sanvisens et al., 2017). In the past decade, a number of epidemiological studies have reported significantly reduced risks of cognitive decline or dementia (including Alzheimer’s disease) in light to moderate alcohol consumers in comparison to nondrinkers (and, obviously, to heavy drinkers) (Collins et al., 2009; Mukamal et al., 2003; NIAAA, 2000; Ruitenberg et al., 2002). The association of alcohol intake with dementia was boosted by the recognition that dementia shares risk factors with cardiovascular disease (Collins et al., 2009; Mukamal et al., 2006). Indeed, the relationship between alcohol intake and risk of dementia (Vascular dementia and Alzheimer disease) or cardiovascular disease (coronary heart disease or ischemic stroke) followed similar Ushaped dependences (Collins et al., 2009; Mukamal et al., 2006) with increased risks at higher alcohol intakes (Fig. 48.1). This U-shape relationship suggests that the effects of ethanol are hormetic (exhibit hormesis) and that beneficial or detrimental effects of ethanol are tightly correlated to the dose (Mattson, 2008). On the other hand, Bate and Williams (2011) demonstrated that pretreatment with low concentrations of ethanol (0.02% 0.08%) protected cortical and hippocampal neurons against Aβ-induced synapse damage. Interestingly, these authors also demonstrated that ethanol was able to protect neurons against the damage produced by presynaptic accumulation of α-synuclein (which are characteristic aggregates in Parkinson’s disease and dementia with Lewy bodies). However, the molecular mechanisms of ethanol-induced neuroprotection are largely unknown and only recently have started to be unraveled. Another intriguing aspect on the effects of low to moderate doses of ethanol is that its exposure brings about a degree of protection against other cell insults. This has been better demonstrated in experimental
FIGURE 48.1 The relationship between alcohol intake and risk of dementia in the Cardiovascular Health Study (Mukamal et al., 2006). Data gathered by Collins et al. (2009) were submitted to cuadratic polynomial fitting to show the U-shape relationship. The median of class categories was used as X-values. Former: Long-term abstainers.
ischemia-reperfusion injuries in animal models, where preadministration of low to moderate ethanol exposure prevents cardiovascular damage (Collins et al., 2009; Murry, Jennings, & Reimer, 1986). This phenomenon, namely “preconditioning,” allows tissues or cells to evolve towards a cytoprotective “phenotype” endowed with a higher tolerance against different insults (Murry et al., 1986). For instance, alcohol preconditioning effects on inflammatory neurotoxicity has been demonstrated in organotypic slices of rat hippocampusentorhinal cortex (two brain regions significantly affected in Alzheimer’s disease) in response to neuroinflammatory proteins HIV-1 gp120 neurotoxicity (Collins et al., 2009, 2010). Current hypothesis points to ethanol-induced changes in gene expression as putative mechanisms whereby it may not only exert some of its acute and chronic effects in the hippocampus, but also drive preconditioning in nerve cells. The changes in gene expression will be the focus of this chapter.
METABOLISM OF ETHANOL IN THE HIPPOCAMPUS Mounting evidence indicates that both chronic and acute alcohol consumption can cause brain oxidative damage. It is known that acetaldehyde resulting from ethanol metabolism, mediates many behavioral, neurochemical, and neurotoxic effects in the brain. However, systemic acetaldehyde derived from its peripheral metabolism (mainly from the liver) hardly penetrates into the brain due to the high aldehyde dehydrogenase
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(ALDH) activity in the endothelial cells at the bloodbrain barrier (Hipolito, Sanchez, Polache, & Granero, 2007). In the liver, ethanol is metabolized by ADH, catalase (CAT), and CYP2E1 (CYP450 isoform 2E1, a member of the superfamily). Conversely, in the brain, ADH is present at very low or negligible levels (Estonius, Svensson, & Hoog, 1996), and in vitro data indicate that CAT accounts for 60% of ethanol oxidation, whereas CYP2E1 accounts for an additional 20% (Zimatkin, Pronko, Vasiliou, Gonzalez, & Deitrich, 2006). Thus, because alcohol dehydrogenase activity is nearly negligible in the brain, the generation of acetaldehyde from ethanol occurs in situ and is mediated by catalase and CYP2E1 enzymes. In addition, catalytic activity of CYP2E1 on ethanol can produce ROS, which eventually causes damage to mitochondria, DNA modification, lipid peroxidation, and even cell death (Caro & Cederbaum, 2004). The mechanisms involved in ROS generation involve different cellular compartments and biochemical/chemical reactions which are shown in Fig. 48.2. CYP2E1 proteins are not uniformly expressed in brain regions, but rather are circumscribed to specific areas, including the hippocampus, substantia nigra, and cerebellum (Garcı´a-Sua´stegui et al., 2017; Shahabi, Andersson, & Nissbrandt, 2008). Ethanol is not only
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the substrate, but also a potent inducer, of CYP2E1 in the liver and brain, and current evidence suggests that ethanol toxicity and ethanol-related ROS generation is associated to elevated CYP2E1 levels in susceptible brain regions (Zhong et al., 2012). Indeed, earlier studies have shown that brain CYP2E1 was inducible by chronic (Roberts, Shoaf, Jeong, & Song, 1994) and acute (Yadav, Dhawan, Singh, Seth, & Parmar, 2006) ethanol treatment in rats. In the rat brain, chronic or acute ethanol treatment increases the amount of CYP2E1 proteins, mRNA levels, and activity in the hippocampus, cerebellum, and frontal cortex, but no significant changes were observed in other brain regions (Garcı´aSua´stegui et al., 2017; Zhong et al., 2012). Interestingly, in the study by Zhong et al. (2012), ethanol markedly increased the levels of CYP2E1 proteins and activity, but not the mRNA levels, in the brainstem after chronic ethanol treatment, indicating that posttranslational processing may also be involved in CYP2E1 induction. The elevated CYP2E1 levels were paralleled by ROS generation and neuronal damage in the hippocampus, cerebellum, and brainstem (Zhong et al., 2012). In summary, the hippocampus, cerebellum, and brainstem are susceptible regions to ethanol neurotoxicity. This selective sensitivity may be attributed to the cellular-specific, ethanol-induced, upregulation of
FIGURE 48.2 Ethanol oxidation by CYP2E1 in endoplasmic reticulum and CAT in peroxisomes results in an increase of ROS and oxidative stress. Ethanol is converted to acetaldehyde, which may enter the mitochondria and is oxidized to acetate by ALD or directly oxidized by CYP2E1 in the reticulum. O22radicals leave the mitochondria and endoplasmic reticulum and is converted into H2O2 by SOD isoforms in the cytoplasm and mitochondria. In the presence of iron ions (ferrous form), H2O2 gives rise to highly reactive OH radicals by virtue of the Fenton reaction. In addition, ethanol can increase the expression/activity of CYP2E1 resulting in an additional increase of ROS which starts a feedback cycle of ROS production. Increased ROS levels induce oxidative damage of lipids, proteins, DNA, and mitochondria. ALDH, aldehyde dehydrogenase; ETC, electron transport chain; OH, hydroxyl radical; ∙O22, superoxide anion radical; H2O2, hydrogen peroxide; Fe21, ferrous iron; MEOS, microsomal ethanol-oxidizing system.
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CYP2E1 or by posttranscriptional processing of CYP2E1, which in any case is paralleled by ROS generation to levels above neuronal ROS buffering capacities, eventually leading to neuronal degeneration.
CHRONIC AND LONG-TERM EFFECTS OF ETHANOL IN THE HIPPOCAMPUS Further to its effects on ROS generation, ethanol also affects several neurotransmitter systems in the brain. Compelling evidence indicates that an important site of ethanol actions is the glutamatergic neurotransmitter system, the main excitatory neurotransmitter in the brain. Ionotropic glutamate receptors form glutamate-gated ion channels and are classified into three main groups, AMPA receptors, kainate receptors, and NMDA receptors, with different locations and functions in neuronal synapse (Moykkynen & Korpi, 2012; Smart & Paoletti, 2012). The AMPA receptors normally mediate fast synaptic transmission and synaptic strength. NMDA receptors exhibit high calcium permeability and regulate intracellular signaling and synaptic plasticity. Finally, kainate receptors are present both in the presynaptic and postsynaptic membranes and have a modulatory role on neurotransmitter release. The three types are expressed in the hippocampus and are responsible for processes like LTP (long-term potentiation) and LTD (long-term depression), which are involved in synaptic plasticity, cognitive performance, and different types of memories (Nicoll & Roche, 2013). A number of studies have shown that ethanol is a potent inhibitor of ionotropic glutamate receptor function by decreasing current amplitude and by accelerating current desensitization (Carta, Ariwodola, Weiner, & Valenzuela, 2003; Moykkynen & Korpi, 2012), and LTP in vivo (Givens & McMahon, 1995), which ultimately alters neuronal plasticity. Of the different ionotropic glutamate receptors, NMDA receptors are regarded as the most sensitive to ethanol as they can be inhibited by clinically relevant concentrations of ethanol (20 mM). These inhibitory effects of ethanol occur almost immediately after ethanol enters the blood brain barrier, and appear to be mediated by interaction with specific binding sites of NMDA receptor subunits. However, chronic and prolonged ethanol exposition leads to a compensatory “upregulation” of NMDA receptors by modulation of gene expression (Jin et al., 2014; Moykkynen & Korpi, 2012). Not surprisingly, these alterations are supposed to contribute to the development of ethanol tolerance and dependence, as well as ethanol withdrawal syndrome (Nagy, 2004).
Ionotropic glutamate receptors are tetrameric proteins composed of different subunits, whose combinations determine their biophysical, physiological, and pharmacological properties. Recent papers on the effects of ethanol in in vitro and in vivo models have revealed alterations in the subunit composition of hippocampal glutamate receptors after long-term ethanol exposure. For instance, the NR2B subunit expression of the NMDA receptor has been demonstrated to be increased in cultured hippocampal and cortical neurons after 3 days of intermittent ethanol treatment (Nagy, 2004). mRNA and/or protein levels of NR2A and NR2B subunits were found elevated in rat hippocampus after in vivo chronic alcohol exposure (Follesa & Ticku, 1995; Nagy et al., 2003). In addition, in postmortem human brains from alcoholics, Jin et al. (2014) reported the significant increase in the mRNAs encoding for different subunits of AMPA receptors (GluA2 and GluA3), NMDA receptors (GluN1, GluN2A, GluN2C, GluN2D, and GluNA3), and kainate receptors (GluK2, GluK3, and GluK5) in the hippocampusdentate gyrus, but not in the prefrontal cortex. These results indicate that ethanol effectively affects the transcription levels of glutamate receptor subtypes in the brain, likely through different mechanisms (Chandrasekar, 2013), and more interestingly, that these changes are strictly circumscribed to specific brain regions. Assuming that these gene expression changes are translated into new subunits, it is expected that extensive remodeling of neurotransmission, signaling, and neuronal network excitability in the hippocampus occurs after chronic alcoholism. Further to its effect on glutamatergic systems, evidence accumulated over more than 30 years, demonstrates that ethanol effects on the central nervous system are intimately associated to its effects on GABAergic neurotransmission, the major inhibitory neurotransmitter in the brain. Substantial evidence supports the thesis that low to moderate (3 30 mmol/ L) ethanol concentrations enhance the inhibitory activity of GABA-A receptors (reviewed in Alfonso-Loeches & Guerri, 2011). GABA-A channels are pentameric ligand-gated chloride channels, in which the subunit composition determines the physiological and channel’s pharmacological properties, including its ethanol sensitivity. The majority of GABA-A receptors are composed of α-, β-, γ-, and δ-subunits (Olsen & Sieghart, 2008). A region in the transmembrane domains of the α/β subunits of the GABA-A receptor has been identified as the potential binding site for ethanol (Lobo & Harris, 2008), which might account for the acute inhibitory effects of alcohol intake. Nevertheless, the effects of ethanol strongly depend on the subunit composition of GABA-A receptors. GABA-A channels containing the α4, α5, or the δ
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subunit are of particular interest. These subunits are part of extrasynaptic GABA-A channels which give rise to tonic neuronal inhibition, resulting in decreased frequency of action potentials (Jin et al., 2011; Pavlov, Savtchenko, Kullmann, Semyanov, & Walker, 2009). Maximum sensitivity to ethanol appears to occur when the γ subunit (which is located outside of the synapse) was present (Alfonso-Loeches & Guerri, 2011). It is now widely accepted that activation of GABA-A channels containing these subunits have implications for cognitive functioning (Alfonso-Loeches & Guerri, 2011). As for glutamate receptors, chronic and long-term ethanol exposure also alters gene expression of GABA-A receptor subunits. Also, these changes occur in a brain region-specific manner in alcoholic subjects. Indeed, Jin et al. (2011) have shown a significant increase in the mRNAs encoding for α1, α4, α5, β1, and γ1 subunits in the hippocampal and dentate gyrus region of individuals suffering from alcoholism, whereas no changes in the dorsolateral prefrontal cortex were detected in postmortem human brains (Jin et al., 2011). These data further support the association of long-term changes in the GABA-A isoform expression and alcohol dependence (Lobo & Harris, 2008). Finally, studies have also demonstrated the existence of epigenetic changes after long-term alcohol consumption. Epigenetic modifications involve chromatin modifications, that is, histone acetylation, phosphorylation, and DNA methylation, which positively or negatively modulate transcriptional activity. Epigenetic modifications have been shown to play an important role in gene expression underlying the stability and plasticity of developing neuronal circuits (Hsieh & Gage, 2005). Chronic alcohol exposure in experimental animals have revealed decreased HDAC (Histone deacetylase) activity along with upregulation in histone acetylation (H3 and H4), CREBP (cAMPresponsive element binding protein), and neuropeptide Y (NPY), which are associated with the anxiolytic effects of alcohol exposure (Pandey, Ugale, Zhang, Tang, & Prakas, 2008). Interestingly, alterations in DNA methylation in the promoter regions of the α-synuclein gene have been observed in mesolimbic systems (Bonsch, Lenz, Kornhuber, & Bleich, 2005). Also, α-synuclein is involved in the regulation of dopamine biosynthesis and neurotransmission in the mesolimbic system, which plays a crucial role in reinforcing alcohol-seeking behavior (Perez et al., 2002). In agreement, an increased mRNA expression of α-synuclein in alcoholic subjects has been correlated with α-synuclein promoter DNA methylation and obsessive craving (Bonsch et al., 2004, 2005). These results suggest an association between the gene-specific DNA promoter hypermethylation and chronic alcohol consumption (Alfonso-Loeches & Guerri, 2011).
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ACUTE NONTOXIC ETHANOL INTAKE, HIPPOCAMPAL GENE EXPRESSION, AND ANTIOXIDANT POTENTIAL Epidemiological and prospective studies indicate that, at population levels, low to moderate alcohol consumption may be cardio-neuro-protective (reviewed in Collins et al., 2009). The mechanisms underlying these effects of ethanol are largely unknown. Some of these processes likely occur through changes in the ability of endogenous cytoprotective systems to cope with oxidative stress and also with the ability to modulate the transcriptional processes. Regarding brain tissues, seminal studies in cellular and animal models, showed that ethanol exposure under low exposure paradigms activated different signaling mechanisms, that is, selective activation of protein kinase C epsilon (PKCε) and focal adhesion kinase (FAK), which appear to be channeled through expression of heat-shock proteins (HSP) (Sivaswamy, Neafsey, & Collins, 2010). Furthermore, considerable research indicates that the increase of different HSPs (Heat-Shock Proteins, such HSP27, HSP70, HSP90), can be putative neuroprotective “effectors” (Reviewed in Collins et al., 2009, 2010). In this regard, a significant increase in inducible HSP70 and HSP27 proteins occurred in Hippocampal-Entorhinal cortex slices after B6 days of moderate alcohol exposure, which correlates with the onset of significant neuroprotection against gp120-induced (a proinflammatory glycoprotein from HIV-1) neurotoxicity (Collins, Wang, Achille, & Neafsey, 2005). Furthermore, in vitro studies in rat hippocampal cultures have shown that low to moderate ethanol exposure protects against neurotoxic protein aggregates, such amyloid peptides (Aβ) in Alzheimer’s disease, and improved the cognitive processes of learning and memory in 3xTgAD mice (Mun˜oz et al., 2015). Under this paradigm, it was shown that low concentrations of ethanol protect against synaptotoxicity induced by Aβ in hippocampal neurons (Belmadani, Kumar, Schipma, Collins, & Neafsey, 2004; Mun˜oz et al., 2015). Further, in mice, hippocampal cultures of ethanol protect against α-synuclein-induced toxicity, a hallmark in Parkinsons disease (Bate & Williams, 2011). Moreover, epidemiological studies have pointed out that low to moderate alcohol consumption is associated with a lower risk of incident dementia among older adults, being these individuals less likely to develop Alzheimer’s disease (Mukamal et al., 2003) (see Fig. 48.1). Ethanol is a prominent source of oxidative radicals in the brain (Das & Vasudevan, 2007). The high levels of peroxidable lipids and iron ions, together with the relatively low amounts of glutathione, make the brain particularly susceptible to nonenzymatic oxidation of
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cell components. However, recent experimental evidence has pointed out that different brain regions are capable of inducing the activation of antioxidant systems (Fig. 48.3) in response to an ethanol challenge, specifically at low to moderate concentrations (0.02% 0.1%). Indeed, work from our laboratory has demonstrated that 0.1% ethanol exposure to hippocampal-derived HT22 cells, modulates the expression of different genes belonging to the classical, glutathione/glutaredoxin and thioredoxin/peroxiredoxin antioxidant systems (Casan˜as-Sa´nchez et al., 2016). Among the different mRNAs up-regulated by ethanol we found: Sod1 (encoding for Cu/ZnSOD, the cytosolic superoxide dismutase isoform), Sod2 (encoding for MnSOD, the mitochondrial superoxide dismutase isoform), Gpx1 (encoding for GPx1, glutathione peroxidase 1), Gclc (encoding for the catalytic subunit GCLC, and responsible for de novo glutathione synthesis), and Txnrd1 (encoding for TXRD1, the cytoplasmic thioredoxin reductase isoform, the most abundantly expressed neurons) (Table 48.1). Further, in
consonance with the upregulation of Txnrd1, ethanol down-regulated the expression of Txnip, which is an endogenous inhibitor of thioredoxin (Yoshihara et al., 2014) and those of peroxiredoxins (Prdx1-5). Paralleling these changes, enzyme activities of total SOD, total glutathione peroxidase, and total thioredoxin reductase, were all increased (Fig. 48.4) (Casan˜as-Sa´nchez et al., 2016). In addition, ethanol exposure prevented glutamateinduced excitotoxicity in the same time-course as changes in gene expression (Fig. 48.5). These results were in agreement with previous results in the hippocampus of rats receiving acute intraperitoneal injections of ethanol (1.5 1.6 g/kg) showing significant increases in SOD and CAT activities (Enache et al., 2008) or in the rat cerebral cortex, hippocampus, and corpus striatum for glutathione peroxidase activity (Somani et al., 1996). We hypothesize that the transcriptional activation of critical enzymes of neuronal antioxidant systems, as well as that of inducible forms of HSP, underlie the efficient preconditioning effects of ethanol.
FIGURE 48.3
Organization of Classical, Thioredoxin/Peroxiredoxin, and Glutathione/Glutaredoxin antioxidant systems. For clarity the three systems were represented as separated pathways, although connections exist between them. For instance, reduced TRX may transfer the electrons in the two SH groups to oxidized PRDX, rendering reduced PRDX. TXNRD, thioredoxin reductase; TXN, thioredoxin; TXNIP, thioredoxin interacting protein; PRDX, peroxiredoxin; SRXN, sulfiredoxin; GPX, glutathione peroxidase; GSR, glutathione-S-reductase; GLRX, glutaredoxin; GST, glutathione-S-transferase; GSH, glutathione (reduced form); GSSG, glutathione (oxidized form).
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TABLE 48.1 Time-Course of Ethanol-Induced Changes in Gene Expression of Enzymes Belonging to the Three Antioxidant Systems in Hippocampal HT22 Cells
Thioredoxin/Peroxiredoxin
Generic
AOX system
GENE
6 Hr
24 Hr
30 Hr
48 Hr
Sod1 Sod2 Cat Txn1 Txn2 Txnip Txnrd1 Txnrd2 Txnrd3 Prdx2 Prdx3 Prdx4
Glutathione/ Glutaredoxin
Prdx5 Gclc Gsr Glrx1 Glrx2 Gpx1 Gpx4 Up-regulation
Down-regulation
Encoding genes: Sod1-2, superoxide dismutases 1 and 2; Cat, catalase; Txn1-2, thioredoxins 1 and 2; Txnip, thioredoxin interacting protein; Txnrd1-3, thioredoxin reductases 1-3; Prdx1-5, peroxiredoxins 1-5; Gclc, catalytic subunit of glutathione synthase; Gsr, glutathione-S-reductase; Glrx1-4, glutaredoxins 1 4.
FIGURE 48.4 Time-course of ethanol-induced changes in enzyme activities of antioxidant systems in mouse-derived hippocampal HT22 cells. t-SOD, total SOD; t-TXRND, total thioredoxin reductase; t-GPX, total glutathione peroxidase. Source: Adapted from Casan˜as-Sa´nchez V., Perez, J.A., Quinto-Alemany, D., & Dı´az M. (2016). Sub-toxic ethanol exposure modulates gene expression and enzyme activity of antioxidant systems to provide neuroprotection in hippocampal HT22 cells. Frontiers in Physiology, 7, 312.
In summary, we conclude that subtoxic exposure to ethanol may well be neuroprotective against oxidative insults (and perhaps other forms of cellular stress) in the cerebral cortex and hippocampus by triggering
transcriptional activation of antioxidant defenses and expression of inducible heat-shock proteins. These processes may well underlie the preconditioning effects of ethanol in the brain.
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FIGURE 48.5 Low doses of ethanol protect against glutamate-induced neurotoxicity. A representative experiment showing real-time changes in HT22 cell proliferation exposed to ethanol (1% or 0.1%) or ethanol (0.1%) 1 glutamate (20 mM) at the times indicated. Cell index is a parameter that measures cell proliferation/survival based on impedance measurements.
MINI-DICTIONARY OF TERMS Hormesis Any process in a cell or organism that exhibits a biphasic response to exposure to increasing amounts of a substance or condition. Thus, a generally favorable or beneficial biological response is characteristic of low exposures to the substance or other stressors, whereas unfavorable or detrimental effects are characteristic of higher amounts or condition levels, usually resulting in an inverted U-shaped dose-response. LTP Long-Term Potentiation consists on a rapidly induced and long-lasting form of synaptic plasticity linked to learning. It has been best studied in the hippocampus. Preconditioning A phenomenon that allows cells exposed to subtoxic or sublethal levels to toxicants or degree of injuries, not only to overcome the stress caused by them, but also to acquire protection against other kinds of insults. Oxidative stress A disturbance in the balance between the production of ROS and cellular antioxidant defenses. When antioxidant defenses are deficient, then ROS accumulate and may lead to cellular injury and even death. Hippocampus A brain structure belonging to the limbic system. In primates, including humans, it is located in the medial temporal lobe of the cerebral cortex. The hippocampus has a functional role in the consolidation of short-term memory to long-term memory, and also in the construction of spatial memory.
KEY FACTS • The effects of ethanol in hippocampal tissues are biphasic, provoking either detrimental or beneficial effects. • Chronic, long-term ethanol exposure or binge consumption causes severe damage in hippocampal neuronal and glial cells, usually accompanied by cell death. • Many of these deleterious effects are likely due to alcohol-induced generation of reactive oxygen species.
• Compensatory mechanisms involving changes in gene expression in the hippocampus usually parallel chronic, long-term ethanol exposure. • Conversely, acute, subtoxic exposure to ethanol triggers the transcriptional activation of antioxidant enzymes and heat-shock proteins, which protect hippocampal cells against oxidant stress and other insults. • These specific transcriptional activations likely underlie the preconditioning effects of ethanol.
SUMMARY POINTS • Ethanol exposure causes changes in gene expression in the hippocampus. • Chronic, long-term ethanol consumption affects neurotransmitter receptor functions and consolidation of hippocampal working memories. • Chronic, long-term ethanol exposure modulates neurotransmitter receptor gene expression in the hippocampus. • Exposure to acute low to moderate ethanol triggers the expression of different genes encoding for antioxidant enzymes and also heat-shock proteins. • Preconditioning effects of ethanol might be related to reinforcement of cellular antioxidant systems.
References Alfonso-Loeches, S., & Guerri, C. (2011). Molecular and behavioural aspects of the actions of alcohol on the adult and developing brain. Critical Reviews in Clinical Laboratory Sciences, 48, 19 47.
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REFERENCES
Bate, C., & Williams, A. (2011). Ethanol protects cultured neurons against amyloid-beta and alpha-synuclein-induced synapse damage. Neuropharmacology, 61, 1406 1412. Belmadani, A., Kumar, S., Schipma, M., Collins, M. A., & Neafsey, E. J. (2004). Inhibition of amyloid-beta-induced neurotoxicity and apoptosis by moderate ethanol preconditioning. NeuroReport, 15, 2093 2096. Bonsch, D., Lenz, B., Kornhuber, J., & Bleich, S. (2005). DNA hypermethylation of the alpha synuclein promoter in patients with alcoholism. NeuroReport, 16, 167 170. Bonsch, D., Reulbach, U., Bayerlein, K., Hillemacher, T., Kornhuber, J., & Bleich, S. (2004). Elevated alpha synuclein mRNA levels are associated with craving in patients with alcoholism. Biological Psychiatry, 56, 984 986. Caro, A. A., & Cederbaum, A. I. (2004). Oxidative stress, toxicology, and pharmacology of CYP2E1. Annual Review of Pharmacology and Toxicology, 44, 27 42. Carta, M., Ariwodola, O. J., Weiner, J. L., & Valenzuela, C. F. (2003). Alcohol potently inhibits the kainite receptor-dependent excitatory drive of hippocampal interneurons. Proceedings of the National Academy of Sciences USA, 100, 6813 6818. Casan˜as-Sa´nchez, V., Perez, J. A., Quinto-Alemany, D., & Dı´az, M. (2016). Sub-toxic ethanol exposure modulates gene expression and enzyme activity of antioxidant systems to provide neuroprotection in hippocampal HT22 cells. Frontiers in Physiology, 7, 312. Chandrasekar, R. (2013). Alcohol and NMDA receptor: Current research and future direction. Frontiers in Molecular Neuroscience, 6, 14. Collins, M. A., Neafsey, E. J., Mukamal, K. J., Gray, M. O., Parks, D. A., Das, D. K., & Korthuis, R. J. (2009). Alcohol in moderation, cardioprotection, and neuroprotection: Epidemiological considerations and mechanistic studies. Alcoholism: Clinical and Experimental Research, 33, 206 219. Collins, M. A., Neafsey, E. J., Wang, K., Achille, N. J., Mitchell, R. M., & Sivaswamy, S. (2010). Moderate ethanol preconditioning of rat brain cultures engenders neuroprotection against dementiainducing neuroinflammatory proteins: Possible signaling mechanisms. Molecular Neurobiology, 41, 420 425. Collins, M. A., Wang, K., Achille, N., & Neafsey, E. J. (2005). Moderate ethanol preconditioning of the brain as a neuroprotective strategy: Role for selective heat shock protein induction? Alcoholism: Clinical and Experimental Research, 29, 121A. Das, S. K., & Vasudevan, D. M. (2007). Alcohol-induced oxidative stress. Life Sciences, 81, 177 187. Enache, M., Van Waes, V., Vinner, E., Lhermitte, M., Maccari, S., & Darnaude´ry, M. (2008). Impact of an acute exposure to ethanol on the oxidative stress status in the hippocampus of prenatal restraint stress adolescent male rats. Brain Research, 1191, 55 62. Estonius, M., Svensson, S., & Hoog, J. O. (1996). Alcohol dehydrogenase in human tissues: Localisation of transcripts coding for five classes of the enzyme. FEBS Letters, 397, 338 342. Follesa, P., & Ticku, M. K. (1995). Chronic ethanol treatment differentially regulates NMDA receptor subunit mRNA expression in rat brain. Brain Research. Molecular Brain Research, 29, 99 106. Garcı´a-Sua´stegui, W. A., Ramos-Cha´vez, L. A., Rubio-Osornio, M., Calvillo-Velasco, M., Atzin-Me´ndez, J. A., Guevara, J., & SilvaAdaya, D. (2017). The role of CYP2E1 in the drug metabolism or bioactivation in the brain. Oxidative Medicine and Cellular Longevity, 2017, 4680732. Givens, B., & McMahon, K. (1995). Ethanol suppresses the induction of long-term potentiation in vivo. Brain Research, 688, 27 33. Givens, B., Williams, J. M., & Gill, T. M. (2000). Septohippocampal pathway as a site for the memory-impairing effects of ethanol. Hippocampus, 10, 111 121.
471
Harris, R. A., Trudell, J. R., & Mihic, S. J. (2008). Ethanol’s molecular targets. Science Signaling, 1, re7. Hipolito, L., Sanchez, M. J., Polache, A., & Granero, L. (2007). Brain metabolism of ethanol and alcoholism: An update. Current Drug Metabolism, 8, 716 727. Hsieh, J., & Gage, F. H. (2005). Chromatin remodeling in neural development and plasticity. Current Opinion in Cell Biology, 17, 664 671. Jin, Z., Bazov, I., Kononenko, O., Korpi, E. R., Bakalkin, G., & Birnir, B. (2011). Selective changes of GABA(A) channel subunit mRNAs in the hippocampus and orbitofrontal cortex but not in prefrontal cortex of human Alcoholics. Frontiers in Cellular Neuroscience, 5, 30. Jin, Z., Bhandage, A. K., Bazov, I., Kononenko, O., Bakalkin, G., Korpi, E. R., & Birnir, B. (2014). Selective increases of AMPA, NMDA, and kainate receptor subunit mRNAs in the hippocampus and orbitofrontal cortex but not in prefrontal cortex of human alcoholics. Frontiers in Cellular Neuroscience, 8, 11. Lobo, I. A., & Harris, R. A. (2008). GABA(A) receptors and alcohol. Pharmacology Biochemistry and Behavior, 90, 90 94. Mattson, M. P. (2008). Hormesis defined. Ageing Research Reviews, 7, 1 7. Moykkynen, T., & Korpi, E. R. (2012). Acute effects of ethanol on glutamate receptors. Basic & Clinical Pharmacology & Toxicology, 111, 4 13. Mukamal, K. J., Chung, H., Jenny, N. S., Kuller, L. H., Longstreth, W. T., Jr, . . . Siscovick, D. S. (2006). Alcohol consumption and risk of coronary heart disease in older adults: The Cardiovascular Health Study. Journal of American Geriatrics Society., 54(1), 30 37. Mukamal, K. J., Kuller, L. H., Fitzpatrick, A. L., Longstreth, W. T., Jr., Mittleman, M. A., & Siscovick, D. S. (2003). Prospective study of alcohol consumption and risk of dementia in older adults. JAMA, 289, 1405 1413. Mun˜oz, G., Urrutia, J. C., Burgos, C. F., Silva, V., Aguilar, F., Sama, M., . . . Aguayo, L. G. (2015). Low concentrations of ethanol protect against synaptotoxicity induced by Aβ in hippocampal neurons. Neurobiology of Aging, 36, 845 856. Murry, C. E., Jennings, R. B., & Reimer, K. A. (1986). Preconditioning with ischemia: A delay of lethal cell injury in ischemic myocardium. Circulation, 74, 1124 1136. Nagy, J. (2004). The NR2B subtype of NMDA receptor: A potential target for the treatment of alcohol dependence. Current Drug Targets. CNS and Neurological Disorders, 3, 169 179. Nagy, J., Kolok, S., Dezso, P., Boros, A., & Szombathelyi, Z. (2003). Differential alterations in the expression of NMDA receptor subunits following chronic ethanol treatment in primary cultures of rat cortical and hippocampal neurones. Neurochemistry International, 42, 35 43. National Institute on Alcohol Abuse and Alcoholism (NIAAA). (2000). Health risks and benefits of alcohol consumption. Alcohol Research & Health, 24, 5 11. Nicoll, R. A., & Roche, K. W. (2013). Long-term potentiation: Peeling the onion. Neuropharmacology, 74, 18 22. Olsen, R. W., & Sieghart, W. (2008). International union of pharmacology LXX. Subtypes of gamma-aminobutyric acid(A) receptors: Classification on the basis of subunit composition, pharmacology, and function. Update. Pharmacological Reviews, 60, 243 260. Pandey, S. C., Ugale, R., Zhang, H., Tang, L., & Prakas, A. (2008). Brain chromatin remodeling: A novel mechanism of alcoholism. Journal of Neuroscience, 28, 3729 3737. Pavlov, I., Savtchenko, L. P., Kullmann, D. M., Semyanov, A., & Walker, M. C. (2009). Outwardly rectifying tonically active GABAA receptors in pyramidal cells modulate neuronal offset, not gain. Journal of Neuroscience, 29, 15341 15350.
IV. PHARMACOLOGY, NEUROACTIVES, MOLECULAR, AND CELLULAR BIOLOGY
472
48. ETHANOL AND HIPPOCAMPAL GENE EXPRESSION: LINKING IN ETHANOL METABOLISM, NEURODEGENERATION, AND RESISTANCE
Perez, R. G., Waymire, J. C., Lin, E., Liu, J. J., Guo, F., & Zigmond, M. J. (2002). A role for α-synuclein in the regulation of dopamine biosynthesis. Journal of Neuroscience, 22, 3090 3099. Roberts, B. J., Shoaf, S. E., Jeong, K. S., & Song, B. J. (1994). Induction of CYP2E1 in liver, kidney, brain and intestine during chronic ethanol administration and withdrawal: Evidence that CYP2E1 possesses a rapid phase half-life of 6 h or less. Biochemical and Biophysical Research Communications, 205, 1064 1071. Ruitenberg, A., Van Swieten, J. C., Witteman, J. C., Mehta, K. M., Van Duijn, C. M., Hofman, A., & Breteler, M. M. (2002). Alcohol consumption and risk of dementia: The Rotterdam Study. Lancet, 359(9303), 281 286. Ryabinin, A. E. (1998). Role of hippocampus in alcohol-induced memory impairment: Implications from behavioral and immediate early gene studies. Psychopharmacology, 139(1-2), 34 43. Sanvisens, A., Zuluaga, P., Fuster, D., Rivas, I., Tor, J., Marcos, M., . . . Muga, R. (2017). Long-term mortality of patients with an alcohol-related wernicke-korsakoff syndrome. Alcohol and Alcoholism, 52(4), 466 471. Shahabi, H. N., Andersson, D. R., & Nissbrandt, H. (2008). Cytochrome P450 2E1 in the substantia nigra: Relevance for dopaminergic neurotransmission and free radical production. Synaps, 62, 379 388. Sivaswamy, S., Neafsey, E. J., & Collins, M. A. (2010). Neuroprotective preconditioning of rat brain cultures with ethanol: Potential transduction by PKC isoforms and focal adhesion
kinase upstream of increases in effector heat shock proteins. European Journal of Neuroscience, 32, 1800-1182. Smart, T. G., & Paoletti, P. (2012). Synaptic neurotransmitter-gated receptors. Cold Spring Harbor Perspectives in Biology, 4, a009662. Somani, S. M., Husain, K., Diaz-Phillips, L., Lanzotti, D. J., Kareti, K. R., & Trammell, G. L. (1996). Interaction of exercise and ethanol on antioxidant enzymes in brain regions of the rat. Alcohol, 13, 603 610. White, A. M., Matthews, D. B., & Best, P. J. (2000). Ethanol, memory, and hippocampal function: A review of recent findings. Hippocampus, 10, 88 93. Yadav, S., Dhawan, A., Singh, R. L., Seth, P. K., & Parmar, D. (2006). Expression of constitutive and inducible cytochrome P450 2E1 in rat brain. Molecular and Cellular Biochemistry, 286, 171 180. Yoshihara, E., Masaki, S., Matsuo, Y., Chen, Z., Tian, H., & Yodoi, J. (2014). Thioredoxin/Txnip: Redoxisome, as a redox switch for the pathogenesis of diseases. Frontiers in Immunology, 4, 514. Zhong, Y., Dong, G., Luo, H., Cao, J., Wang, C., Wu, J., . . . Yue, J. (2012). Induction of brain CYP2E1 by chronic ethanol treatment and related oxidative stress in hippocampus cerebellum, and brainstem. Toxicology, 302, 275 284. Zimatkin, S. M., Pronko, S. P., Vasiliou, V., Gonzalez, F. J., & Deitrich, R. A. (2006). Enzymatic mechanisms of ethanol oxidation in the brain. Alcoholism: Clinical and Experimental Research, 30, 1500 1505.
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