- Email: [email protected]
Statins attenuate sepsis
Evidence-based surgical hypothesis Statins attenuate sepsis Austin L. Spitzer, MD, and Hobart W. Harris, MD, MPH, San Francisco, Calif
Hypothesis. If (1) 3-hydroxy-3-methylglutaryl-coenzyme reductase inhibitors (statins) block the ratelimiting step in cholesterol synthesis and promote the expression of low-density lipoprotein receptors, (2) ‘‘Gram-negative sepsis’’ results from an abundant systemic response to bacterial lipopolysaccharide (endotoxin), (3) triglyceride-rich lipoproteins can bind endotoxin and low-density lipoprotein receptors enhance the uptake of both of these molecules, and (4) low-density lipoprotein receptor internalization of lipoproteins and endotoxin co-opts a common transcriptional regulatory system (NF-jB) that results in reduced cell vulnerability to inflammation, then statins, in addition to their lipid-lowering capacity, enhance endotoxin clearance from the circulation and attenuate the septic response. (Surgery 2006;139:283-7.) From the Departments of Surgery, University of California, San Francisco–East Bay and University of California, San Francisco
HYPERCHOLESTEROLEMIA HAS BEEN ASSOCIATED with increased mortality rate in a variety of chronic and acute disorders. The dietary intake of cholesterol is balanced with its de novo hepatic biosynthesis, and 3-hydroxy-3-methylglutaryl-coenzyme (HMGCoA) reductase is the rate-limiting enzymatic step. HMG-CoA reductase inhibitors, or statins, competitively inhibit HMG-CoA reductase and, in so doing, inhibit cholesterol biosynthesis. In addition to their cholesterol-lowering effects, statins appear to have independent anti-inflammatory effects. These effects appear to be mediated through interference of the synthesis of isoprenoid intermediates (mevalonate metabolites) and the limitation of the NF-jB–dependent regulation of inflammation.1 Statin pretreatment improved survival in a murine sepsis model, and statin therapy reduced both overall mortality and mortality rates that were attributable to bacteremia in a retrospective human study.2 Low-density lipoprotein (LDL) receptors are expressed ubiquitously and are a major site of cholesterol uptake and regulation; however, as cholesterol accumulates in cells, the number of LDL receptors decreases.3 In contrast, statins
Accepted for publication August 23, 2005. Reprint requests: Austin L. Spitzer, MD, Department of Surgery, University of California, San Francisco–East Bay, 1411 E 31st St, Oakland, CA 94602; E-mail: [email protected]. 0039-6060/$ - see front matter Ó 2006 Mosby, Inc. All rights reserved. doi:10.1016/j.surg.2005.08.029
promote the induction of LDL receptor messenger RNA4 and up-regulate LDL binding sites5 (Fig 1, A). Gram-negative sepsis results from an immunologic cascade after the systemic dissemination of bacterial lipopolysaccharide (LPS) or endotoxin. Although kinetics typically favor LPS binding to serum proteins that stimulate proinflammatory cellular activation pathways, LPS is also bound by triglyceride-rich lipoproteins (TRL) that may be internalized through the LDL receptor pathway. The appreciation of the pleiotropic nature of statins led us to postulate that these agents could exhibit anti-inflammatory activity because of their ability to expand LDL receptors, thereby promoting the increased internalization of lipoprotein bound endotoxin (TRL-LPS). We additionally propose that once internalized, TRL-LPS fragments interfere with proinflammatory cytokine signaling pathways and thus attenuate the systemic inflammatory response that is associated with sepsis. The vascular endothelium is integral in coordinating the inflammatory response to injury and sepsis, and the integrity of the endothelial surface is essential for maintaining homeostasis between the blood and surrounding tissues. As an autocrine, paracrine, and endocrine organ, the endothelium is responsible for the regulation of vasomotor tone, the maintenance of a nonthrombogenic surface, the adherence and activation of leukocytes, and the regulation of microvascular permeability. Like many of the body’s cells, the vascular endothelium acquires cholesterol for membrane synthesis primarily by receptor-mediated uptake of LDL, where it is then metabolized to SURGERY 283
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Fig 1, A, The role of statins in sepsis: 1, HMG-CoA reductase is the rate-limiting enzyme for cholesterol synthesis. 2, Statins competitively inhibit the binding of HMG-CoA at the catalytic site of HMG-CoA reductase, thereby reducing mevalonate synthesis. 3, Hypercholesterolemia reduces the capacity of endothelial cells to produce nitric oxide (NO), likely because of the reduced availability of L-arginine. Statins induce the transcriptional activation of the endothelial nitric oxide synthase (eNOS) gene in human cell lines and enhance endothelial function without reducing LDL cholesterol in primates. 4, Mevalonic acid, the precursor of cholesterol, destabilizes the messenger RNA for eNOS, which effectively reduces the synthesis of NO from L-arginine to L-citrulline. Thus, by limiting mevalonic acid synthesis, statins increase NO production. 5 and 6, Statins inhibit leukocyte-endothelium interactions and attenuate leukocyte infiltration. Pretreatment of rats with statins results in a 50% increase in the expression of eNOS and a 50% decrease in the expression of the adhesion molecule P-selectin in rat mesentery. Similarly, in human endothelial cells, statins promote the expression of eNOS and suppress leukocyte-endothelial interactions. In human cells that are stimulated with tumor necrosis factor (TNF), statins decrease intercellular adhesion molecule-1 (ICAM) messenger RNA levels and inhibit TNF–induced activation of NF-jB. Circulating levels of TNF are lower in patients with hypercholesterolemia who are taking statins versus control subjects. 7, Additionally, statins promote the expression of LDL receptors (LDLr), which enhance LPS clearance from the blood and thus attenuate inflammation.
cholesterol to be used by the cells for membrane synthesis. In vivo, normal circulating concentrations of lipoproteins down-regulate the expression of LDL receptors on vascular endothelial cells.6 Conversely, lipoprotein remnants, LDL, and oxidized LDL stimulate up-regulation of endothelial adhesion molecules and selectins to promote the generation of oxygen radicals, increase apoptosis, and reduce endothelium-dependent relaxation.
The vascular endothelium is a key target of LPS and is the first host tissue barrier to encounter circulating LPS that is shed from replicating or dying Gram-negative bacteria. Although much of the LPS-induced vascular damage can be explained by host responses to LPS, evidence exists for a direct role for LPS. Specifically, endothelial cells express Toll-like receptor--4 (TLR-4), an innate, immune pattern-recognition receptor that
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Fig 1, B, The role of lipopolysaccharide (LPS) in sepsis: 1, Binding of LPS to circulating LPS-binding protein (LBP) facilitates the transfer of LPS to soluble (sCD14) and membrane-bound CD14 and also to plasma lipoproteins, but the binding kinetics favor the CD14-mediated interaction. 2, The LPS signal is then transduced through the binding of the MD2/TLR-4 complex to the intracellular adaptor protein, MyD88, which binds and activates the protein kinase IRAK1 (not shown) and then the adaptor molecule TRAF6 (not shown). TRAF6 provokes the phosphorylation of inhibitory kappa B (IjB), which leads to the ubiquitin-dependent intranuclear translocation of NF-jB. 3, IjB is phosphorylated through a cascade of inducible protein kinases, ubiquitinated, and then degraded in the cytoplasm by the proteasome. 4 and 5, With removal of IjB, the nuclear localization sequence is unmasked, and NF-jB translocates to the nucleus, where it promotes transcription of inflammatory genes. After NF-jB activation, newly synthesized IjB can enter the nucleus, remove NF-jB from gene promoters, and export it back to the cytoplasm.
binds LPS.7 Endothelial cell activation is dependent on the cell surface assembly of a multiprotein recognition complex that consists of soluble CD14, MD-2, and TLR-48 (Fig 1, B). Although it was believed initially that LPS was cleared by resident hepatic macrophages (Kupffer cells) and then delivered to hepatocytes, more recently, hepatocytes have been reported to internalize LPS independent of Kupffer cells,9 and the rate at which hepatocytes internalize LPS increases markedly not only during sepsis10 but also with the infusion of lipoproteins.11 In addition to facilitating the removal of LPS from the circulation during sepsis, the liver also contributes to mobilizing the body’s fat stores through the synthesis and secretion
of TRL. This cytokine-mediated process, clinically termed the ‘‘lipemia of sepsis,’’ is a component of the innate immune response and has been implicated as a valuable component of an organism’s protection against sepsis through the binding and neutralization of LPS. Specifically, by mobilizing lipid stores, increased TRL not only fuel the heightened energy demands necessary to protect the host against systemic inflammation but also regulate the deleterious effects of LPS by inducing ‘‘cytokine tolerance’’ in hepatocytes. This cytokine tolerance correlates with lipoprotein-bound LPS internalization through LDL receptors12 and with the inhibition of the nuclear transcription factor, NF-jB.13 We reported previously that chylomicrons and
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Fig 1, C, The role of lipoprotein receptors in sepsis: 1, Although binding kinetics favor the CD14-mediated interaction between lipopolysaccharide (LPS) and leukocytes, as the concentration of lipoprotein increases, LPS-lipoprotein binding is increasingly favored. By binding to LPS, triglyceride-rich lipoproteins (TRL) help reduce the probability of LPS binding to CD14-bearing leukocytes and simultaneously increase the plasma clearance of LPS. The principles of classic receptor-ligand binding do not govern the interaction between lipoproteins and LPS, because there is no ‘‘LPS receptor’’ on the surface of lipoproteins. Instead, LPS is thought to dissolve into the phospholipid coat, with the ‘‘toxic’’ lipid A moiety buried in the phospholipid monolayer. The lipid A-phospholipid interaction effectively reduces the bioavailability of LPS, partially neutralizing its toxic effects. 2, Triglyceride-rich lipoprotein-bound LPS (TRL-LPS) inhibits the responsiveness of hepatocytes to proinflammatory cytokines in a manner that is related directly to the internalization of LPS. We think this inhibition also occurs in the vascular endothelium and follows internalization of TRL-LPS in a process that is regulated by the LDL receptor (LDLr). TRL-LPS complexes do not induce cytokine tolerance in hepatocytes from LDL receptor knock-out mice or when LDL receptor activity is inhibited with high-dose receptor-associated protein. TRL-LPS–mediated induction of cytokine tolerance to proinflammatory cytokines is a time- and dose-dependent process that requires functional LDL receptors. 3, In hepatocytes, LPS is internalized through LDL receptors and then traffics through the endosomal pathway, presumably resulting in its lysosomal degradation or detoxification. Some of the internalized TRL-LPS is excreted in bile, ‘‘escaping’’ lysosomal degradation. We think that a fraction of this escaped LPS directly inhibits cytokine-induced intracellular signaling. 4, Pretreatment of hepatocytes with TRL-LPS inhibits activation of NF-jB, and the mechanism of inhibition, although not established, may be associated with inhibition of IjB degradation. 5, Without phosphorylation of IjB, NF-jB essentially is ‘‘locked’’ in the cytosol and cannot translocate to the nucleus and bind to cognate promoters, which ultimately limits the inflammatory response.
very LDLs (integral to the lipemia of sepsis) can bind and neutralize LPS in a dose-dependent manner, increase LPS clearance from the plasma by liver parenchymal cells, and protect animals against LPS-induced lethality.11,14 Because endothelial cells
similarly express LDL receptors on their luminal surface, we suspected that they would also internalize lipid-bound LPS; indeed, endothelial cells that were pretreated with TRL-LPS demonstrated ‘‘cytokine tolerance’’ through the maintenance of
Surgery Volume 139, Number 3
membrane barrier integrity after proinflammatory insult with tumor necrosis factor-a or platelet-activating factor (Fig 1, C). We therefore hypothesize that part of the ability of statins to attenuate inflammation results from their ability to increase LDL receptors, which promotes the increased internalization of TRLLPS and results in the inhibition of NF-jB nuclear translocation, and, in so doing, attenuates the proinflammatory pathways.
REFERENCES 1. Steiner S, Speidl WS, Pleiner J, Seidinger D, Zorn G, Kaun C, et al. Simvastatin blunts endotoxin-induced tissue factor in vivo. Circulation 2005;111:1841-6. 2. Liappis AP, Kan VL, Rochester CG, Simon GL. The effect of statins on mortality in patients with bacteremia. Clin Infect Dis 2001;33:1352-7. 3. Russell DW, Yamamoto T, Schneider WJ, Slaughter CJ, Brown MS, Goldstein JL. cDNA cloning of the bovine low density lipoprotein receptor: feedback regulation of a receptor mRNA. Proc Natl Acad Sci USA 1983;80:7501-5. 4. Morikawa S, Umetani M, Nakagawa S, Yamazaki H, Suganami H, Inoue K, et al. Relative induction of mRNA for HMG CoA reductase and LDL receptor by five different HMG-CoA reductase inhibitors in cultured human cells. J Atheroscler Thromb 2000;7:138-44. 5. Li S, Dudczak R, Koller E, Baghestanian M, Ghannadan M, Minar E, et al. Effect of statins on lipoprotein receptor expression in cell lines from human mast cells and basophils. Eur J Clin Pharmacol 2003;59:507-16.
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6. Dehouck B, Dehouck M-P, Fruchart J-C, Cecchelli R. Upregulation of the low density lipoprotein receptor at the bloodbrain barrier: intercommunications between brain capillary endothelial cells and astrocytes. J Cell Biol 1994;126:465-73. 7. Faure E, Equils O, Sieling PA, Thomas L, Zhang FX, Kirschning CJ, et al. Bacterial lipopolysaccharide activates NF-lB through Toll-like receptor 4 (TLR-4) in cultured human dermal endothelial cells: differential expression of tlr-4 and tlr-2 in endothelial cells. J Biol Chem 2000;275: 11058-63. 8. Re F, Strominger JL. Separate functional domains of human MD-2 mediate toll-like receptor 4 binding and lipopolysaccharide responsiveness. J Immunol 2003;171:5272-6. 9. Mimura Y, Sakisaka S, Harada M, Sata M, Tanikawa K. Role of hepatocytes in direct clearance of lipopolysaccharide in rats. Gastroenterology 1995;109:1969-76. 10. Ghermay AP, Brady S, Havel RJ, Harris HW, Rapp JH. Sepsis increases endocytosis of endotoxin into hepatocytes. Surgery 1996;120:389-94. 11. Harris HW, Grunfield C, Feingold KR, Read TE, Kane JP, Jones AL, et al. Chylomicrons alter the fate of endotoxin, decreasing tumor necrosis factor release and preventing death. J Clin Invest 1993;91:1028-34. 12. Kasravi FB, Welch WJ, Peters-Lideu CA, Weisgraber KH, Harris HW. Induction of cytokine tolerance in rodent hepatocytes by chylomicron-bound LPS is low-density lipoprotein receptor dependent. Shock 2003;19:157-62. 13. Kumwenda ZL, Wong CB, Johnson JA, Gosnell JE, Welch WJ, Harris HW. Chylomicron-bound endotoxin selectively inhibits NF-jB activation in rat hepatocytes. Shock 2002; 18:182-8. 14. Harris HW, Grunfield C, Feingold KR, Rapp JH. Human very low density lipoproteins and chylomicrons can protect against endotoxin-induced death in mice. J Clin Invest 1990;86:696-702.
Hypothesis. If (1) 3-hydroxy-3-methylglutaryl-coenzyme reductase inhibitors (statins) block the ratelimiting step in cholesterol synthesis and promote the expression of low-density lipoprotein receptors, (2) ‘‘Gram-negative sepsis’’ results from an abundant systemic response to bacterial lipopolysaccharide (endotoxin), (3) triglyceride-rich lipoproteins can bind endotoxin and low-density lipoprotein receptors enhance the uptake of both of these molecules, and (4) low-density lipoprotein receptor internalization of lipoproteins and endotoxin co-opts a common transcriptional regulatory system (NF-jB) that results in reduced cell vulnerability to inflammation, then statins, in addition to their lipid-lowering capacity, enhance endotoxin clearance from the circulation and attenuate the septic response. (Surgery 2006;139:283-7.) From the Departments of Surgery, University of California, San Francisco–East Bay and University of California, San Francisco
HYPERCHOLESTEROLEMIA HAS BEEN ASSOCIATED with increased mortality rate in a variety of chronic and acute disorders. The dietary intake of cholesterol is balanced with its de novo hepatic biosynthesis, and 3-hydroxy-3-methylglutaryl-coenzyme (HMGCoA) reductase is the rate-limiting enzymatic step. HMG-CoA reductase inhibitors, or statins, competitively inhibit HMG-CoA reductase and, in so doing, inhibit cholesterol biosynthesis. In addition to their cholesterol-lowering effects, statins appear to have independent anti-inflammatory effects. These effects appear to be mediated through interference of the synthesis of isoprenoid intermediates (mevalonate metabolites) and the limitation of the NF-jB–dependent regulation of inflammation.1 Statin pretreatment improved survival in a murine sepsis model, and statin therapy reduced both overall mortality and mortality rates that were attributable to bacteremia in a retrospective human study.2 Low-density lipoprotein (LDL) receptors are expressed ubiquitously and are a major site of cholesterol uptake and regulation; however, as cholesterol accumulates in cells, the number of LDL receptors decreases.3 In contrast, statins
Accepted for publication August 23, 2005. Reprint requests: Austin L. Spitzer, MD, Department of Surgery, University of California, San Francisco–East Bay, 1411 E 31st St, Oakland, CA 94602; E-mail: [email protected]. 0039-6060/$ - see front matter Ó 2006 Mosby, Inc. All rights reserved. doi:10.1016/j.surg.2005.08.029
promote the induction of LDL receptor messenger RNA4 and up-regulate LDL binding sites5 (Fig 1, A). Gram-negative sepsis results from an immunologic cascade after the systemic dissemination of bacterial lipopolysaccharide (LPS) or endotoxin. Although kinetics typically favor LPS binding to serum proteins that stimulate proinflammatory cellular activation pathways, LPS is also bound by triglyceride-rich lipoproteins (TRL) that may be internalized through the LDL receptor pathway. The appreciation of the pleiotropic nature of statins led us to postulate that these agents could exhibit anti-inflammatory activity because of their ability to expand LDL receptors, thereby promoting the increased internalization of lipoprotein bound endotoxin (TRL-LPS). We additionally propose that once internalized, TRL-LPS fragments interfere with proinflammatory cytokine signaling pathways and thus attenuate the systemic inflammatory response that is associated with sepsis. The vascular endothelium is integral in coordinating the inflammatory response to injury and sepsis, and the integrity of the endothelial surface is essential for maintaining homeostasis between the blood and surrounding tissues. As an autocrine, paracrine, and endocrine organ, the endothelium is responsible for the regulation of vasomotor tone, the maintenance of a nonthrombogenic surface, the adherence and activation of leukocytes, and the regulation of microvascular permeability. Like many of the body’s cells, the vascular endothelium acquires cholesterol for membrane synthesis primarily by receptor-mediated uptake of LDL, where it is then metabolized to SURGERY 283
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Fig 1, A, The role of statins in sepsis: 1, HMG-CoA reductase is the rate-limiting enzyme for cholesterol synthesis. 2, Statins competitively inhibit the binding of HMG-CoA at the catalytic site of HMG-CoA reductase, thereby reducing mevalonate synthesis. 3, Hypercholesterolemia reduces the capacity of endothelial cells to produce nitric oxide (NO), likely because of the reduced availability of L-arginine. Statins induce the transcriptional activation of the endothelial nitric oxide synthase (eNOS) gene in human cell lines and enhance endothelial function without reducing LDL cholesterol in primates. 4, Mevalonic acid, the precursor of cholesterol, destabilizes the messenger RNA for eNOS, which effectively reduces the synthesis of NO from L-arginine to L-citrulline. Thus, by limiting mevalonic acid synthesis, statins increase NO production. 5 and 6, Statins inhibit leukocyte-endothelium interactions and attenuate leukocyte infiltration. Pretreatment of rats with statins results in a 50% increase in the expression of eNOS and a 50% decrease in the expression of the adhesion molecule P-selectin in rat mesentery. Similarly, in human endothelial cells, statins promote the expression of eNOS and suppress leukocyte-endothelial interactions. In human cells that are stimulated with tumor necrosis factor (TNF), statins decrease intercellular adhesion molecule-1 (ICAM) messenger RNA levels and inhibit TNF–induced activation of NF-jB. Circulating levels of TNF are lower in patients with hypercholesterolemia who are taking statins versus control subjects. 7, Additionally, statins promote the expression of LDL receptors (LDLr), which enhance LPS clearance from the blood and thus attenuate inflammation.
cholesterol to be used by the cells for membrane synthesis. In vivo, normal circulating concentrations of lipoproteins down-regulate the expression of LDL receptors on vascular endothelial cells.6 Conversely, lipoprotein remnants, LDL, and oxidized LDL stimulate up-regulation of endothelial adhesion molecules and selectins to promote the generation of oxygen radicals, increase apoptosis, and reduce endothelium-dependent relaxation.
The vascular endothelium is a key target of LPS and is the first host tissue barrier to encounter circulating LPS that is shed from replicating or dying Gram-negative bacteria. Although much of the LPS-induced vascular damage can be explained by host responses to LPS, evidence exists for a direct role for LPS. Specifically, endothelial cells express Toll-like receptor--4 (TLR-4), an innate, immune pattern-recognition receptor that
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Fig 1, B, The role of lipopolysaccharide (LPS) in sepsis: 1, Binding of LPS to circulating LPS-binding protein (LBP) facilitates the transfer of LPS to soluble (sCD14) and membrane-bound CD14 and also to plasma lipoproteins, but the binding kinetics favor the CD14-mediated interaction. 2, The LPS signal is then transduced through the binding of the MD2/TLR-4 complex to the intracellular adaptor protein, MyD88, which binds and activates the protein kinase IRAK1 (not shown) and then the adaptor molecule TRAF6 (not shown). TRAF6 provokes the phosphorylation of inhibitory kappa B (IjB), which leads to the ubiquitin-dependent intranuclear translocation of NF-jB. 3, IjB is phosphorylated through a cascade of inducible protein kinases, ubiquitinated, and then degraded in the cytoplasm by the proteasome. 4 and 5, With removal of IjB, the nuclear localization sequence is unmasked, and NF-jB translocates to the nucleus, where it promotes transcription of inflammatory genes. After NF-jB activation, newly synthesized IjB can enter the nucleus, remove NF-jB from gene promoters, and export it back to the cytoplasm.
binds LPS.7 Endothelial cell activation is dependent on the cell surface assembly of a multiprotein recognition complex that consists of soluble CD14, MD-2, and TLR-48 (Fig 1, B). Although it was believed initially that LPS was cleared by resident hepatic macrophages (Kupffer cells) and then delivered to hepatocytes, more recently, hepatocytes have been reported to internalize LPS independent of Kupffer cells,9 and the rate at which hepatocytes internalize LPS increases markedly not only during sepsis10 but also with the infusion of lipoproteins.11 In addition to facilitating the removal of LPS from the circulation during sepsis, the liver also contributes to mobilizing the body’s fat stores through the synthesis and secretion
of TRL. This cytokine-mediated process, clinically termed the ‘‘lipemia of sepsis,’’ is a component of the innate immune response and has been implicated as a valuable component of an organism’s protection against sepsis through the binding and neutralization of LPS. Specifically, by mobilizing lipid stores, increased TRL not only fuel the heightened energy demands necessary to protect the host against systemic inflammation but also regulate the deleterious effects of LPS by inducing ‘‘cytokine tolerance’’ in hepatocytes. This cytokine tolerance correlates with lipoprotein-bound LPS internalization through LDL receptors12 and with the inhibition of the nuclear transcription factor, NF-jB.13 We reported previously that chylomicrons and
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Fig 1, C, The role of lipoprotein receptors in sepsis: 1, Although binding kinetics favor the CD14-mediated interaction between lipopolysaccharide (LPS) and leukocytes, as the concentration of lipoprotein increases, LPS-lipoprotein binding is increasingly favored. By binding to LPS, triglyceride-rich lipoproteins (TRL) help reduce the probability of LPS binding to CD14-bearing leukocytes and simultaneously increase the plasma clearance of LPS. The principles of classic receptor-ligand binding do not govern the interaction between lipoproteins and LPS, because there is no ‘‘LPS receptor’’ on the surface of lipoproteins. Instead, LPS is thought to dissolve into the phospholipid coat, with the ‘‘toxic’’ lipid A moiety buried in the phospholipid monolayer. The lipid A-phospholipid interaction effectively reduces the bioavailability of LPS, partially neutralizing its toxic effects. 2, Triglyceride-rich lipoprotein-bound LPS (TRL-LPS) inhibits the responsiveness of hepatocytes to proinflammatory cytokines in a manner that is related directly to the internalization of LPS. We think this inhibition also occurs in the vascular endothelium and follows internalization of TRL-LPS in a process that is regulated by the LDL receptor (LDLr). TRL-LPS complexes do not induce cytokine tolerance in hepatocytes from LDL receptor knock-out mice or when LDL receptor activity is inhibited with high-dose receptor-associated protein. TRL-LPS–mediated induction of cytokine tolerance to proinflammatory cytokines is a time- and dose-dependent process that requires functional LDL receptors. 3, In hepatocytes, LPS is internalized through LDL receptors and then traffics through the endosomal pathway, presumably resulting in its lysosomal degradation or detoxification. Some of the internalized TRL-LPS is excreted in bile, ‘‘escaping’’ lysosomal degradation. We think that a fraction of this escaped LPS directly inhibits cytokine-induced intracellular signaling. 4, Pretreatment of hepatocytes with TRL-LPS inhibits activation of NF-jB, and the mechanism of inhibition, although not established, may be associated with inhibition of IjB degradation. 5, Without phosphorylation of IjB, NF-jB essentially is ‘‘locked’’ in the cytosol and cannot translocate to the nucleus and bind to cognate promoters, which ultimately limits the inflammatory response.
very LDLs (integral to the lipemia of sepsis) can bind and neutralize LPS in a dose-dependent manner, increase LPS clearance from the plasma by liver parenchymal cells, and protect animals against LPS-induced lethality.11,14 Because endothelial cells
similarly express LDL receptors on their luminal surface, we suspected that they would also internalize lipid-bound LPS; indeed, endothelial cells that were pretreated with TRL-LPS demonstrated ‘‘cytokine tolerance’’ through the maintenance of
Surgery Volume 139, Number 3
membrane barrier integrity after proinflammatory insult with tumor necrosis factor-a or platelet-activating factor (Fig 1, C). We therefore hypothesize that part of the ability of statins to attenuate inflammation results from their ability to increase LDL receptors, which promotes the increased internalization of TRLLPS and results in the inhibition of NF-jB nuclear translocation, and, in so doing, attenuates the proinflammatory pathways.
REFERENCES 1. Steiner S, Speidl WS, Pleiner J, Seidinger D, Zorn G, Kaun C, et al. Simvastatin blunts endotoxin-induced tissue factor in vivo. Circulation 2005;111:1841-6. 2. Liappis AP, Kan VL, Rochester CG, Simon GL. The effect of statins on mortality in patients with bacteremia. Clin Infect Dis 2001;33:1352-7. 3. Russell DW, Yamamoto T, Schneider WJ, Slaughter CJ, Brown MS, Goldstein JL. cDNA cloning of the bovine low density lipoprotein receptor: feedback regulation of a receptor mRNA. Proc Natl Acad Sci USA 1983;80:7501-5. 4. Morikawa S, Umetani M, Nakagawa S, Yamazaki H, Suganami H, Inoue K, et al. Relative induction of mRNA for HMG CoA reductase and LDL receptor by five different HMG-CoA reductase inhibitors in cultured human cells. J Atheroscler Thromb 2000;7:138-44. 5. Li S, Dudczak R, Koller E, Baghestanian M, Ghannadan M, Minar E, et al. Effect of statins on lipoprotein receptor expression in cell lines from human mast cells and basophils. Eur J Clin Pharmacol 2003;59:507-16.
Spitzer and Harris 287
6. Dehouck B, Dehouck M-P, Fruchart J-C, Cecchelli R. Upregulation of the low density lipoprotein receptor at the bloodbrain barrier: intercommunications between brain capillary endothelial cells and astrocytes. J Cell Biol 1994;126:465-73. 7. Faure E, Equils O, Sieling PA, Thomas L, Zhang FX, Kirschning CJ, et al. Bacterial lipopolysaccharide activates NF-lB through Toll-like receptor 4 (TLR-4) in cultured human dermal endothelial cells: differential expression of tlr-4 and tlr-2 in endothelial cells. J Biol Chem 2000;275: 11058-63. 8. Re F, Strominger JL. Separate functional domains of human MD-2 mediate toll-like receptor 4 binding and lipopolysaccharide responsiveness. J Immunol 2003;171:5272-6. 9. Mimura Y, Sakisaka S, Harada M, Sata M, Tanikawa K. Role of hepatocytes in direct clearance of lipopolysaccharide in rats. Gastroenterology 1995;109:1969-76. 10. Ghermay AP, Brady S, Havel RJ, Harris HW, Rapp JH. Sepsis increases endocytosis of endotoxin into hepatocytes. Surgery 1996;120:389-94. 11. Harris HW, Grunfield C, Feingold KR, Read TE, Kane JP, Jones AL, et al. Chylomicrons alter the fate of endotoxin, decreasing tumor necrosis factor release and preventing death. J Clin Invest 1993;91:1028-34. 12. Kasravi FB, Welch WJ, Peters-Lideu CA, Weisgraber KH, Harris HW. Induction of cytokine tolerance in rodent hepatocytes by chylomicron-bound LPS is low-density lipoprotein receptor dependent. Shock 2003;19:157-62. 13. Kumwenda ZL, Wong CB, Johnson JA, Gosnell JE, Welch WJ, Harris HW. Chylomicron-bound endotoxin selectively inhibits NF-jB activation in rat hepatocytes. Shock 2002; 18:182-8. 14. Harris HW, Grunfield C, Feingold KR, Rapp JH. Human very low density lipoproteins and chylomicrons can protect against endotoxin-induced death in mice. J Clin Invest 1990;86:696-702.