- Email: [email protected]
reperfusion injury and protection against reperfusion injury
Mechanism of Hepatic Ischemia/Reperfusion Injury and Protection Against Reperfusion Injury K.J. Kang
T
HE ISCHEMIA/REPERFUSION injury remains a problem after liver surgery or liver transplantation. Preservation injury is a major cause of primary nonfunction following liver transplantation. Sinusoidal endothelial cell (SEC) apoptosis is an outcome of cold ischemia/reperfusion injury. Investigators demonstrated a selective induction of apoptosis in sinusoidal and vascular endothelial cells within the liver following cold ischemia/warm reperfusion injury. Recent data also have indicated that platelet and leukocyte adhesion to the sinusoids mediate reperfusion injury by causing endothelial cell apoptosis. Ischemic preconditioning, namely, a short period of ischemia prior to a major ischemic insult, is highly protective to downregulate the caspase pathway and inhibit apoptotic cell death.1,2 Future research on ischemic livers should focus on mechanisms and mediators involved in apoptotic cell death, which may lead to innovative protective strategies and preservation solutions with important clinical implications. MECHANISM OF REPERFUSION INJURY AFTER WARM AND COLD ISCHEMIA
Ischemic liver injury is caused by a deficiency of oxygen, which occurs by hepatic vascular occlusion during liver resection or cold preservation before liver transplantation. Reperfusion after ischemia reoxygenates the liver; the introduction of oxygenated blood aggravates the hypoxic or ischemic insult. The mechanism of the ischemic injury involves the loss of mitochondrial respiration, leading to adenosine triphosphate (ATP) depletion and deterioration of energy-dependent metabolic pathways and transport processes. Hypothermia reduces the metabolic rate in tissues, therefore prolonging the period during which anoxic cells can retain essential metabolic functions. Cold preservation after harvesting the liver reduces the metabolic rate in the tissue, thereby prolonging the period during which anoxic cells retain essential metabolic functions. Hypothermia can induce cell injury, however, due to influx of sodium and chloride followed by secondary alterations of cellular calcium homeostasis and cell swelling. Cold preservation injury of the liver is also the result of angiogenic mechanisms. SECs are more susceptible to cold ischemia than hepatocytes. A short period of ischemia (30 minutes) produces apoptosis only of the SECs. A longer period of ischemia (1 hour) followed by reperfusion causes apoptosis
of both hepatocytes and SECs. The morphologic features of the SECs after cold preservation followed by reperfusion shows typical characteristics of apoptosis, including cytoplasmic blebbing, nuclear and cytoplasmic condensation, and typical apoptotic bodies in phagolysosomes. Two pathways activate effector caspases, which lead to apoptotic cell death. In the first one, death ligands such as tumor necrosis factor (TNF) or Fas activate receptors resulting in the formation of a death complex, which then activates caspase-8. In the second pathway, cellular stress leads to mitochondrial dysfunction with release of cytochrome C into the cytoplasm. Cytochrome C then binds to and triggers Apaf-1 followed by activation of caspase-9. A link between both pathways is the protein Bid, which can be activated by caspase-8, leading to a release of cytochrome C from mitochondria. Cytochrome C release can be blocked by anti-apoptotic Bcl-2 family members and promoted by proapoptotic members of this family such as Bax. Caspases and calpains are key cellular mediators of apoptosis after reperfusion. Overexpression of Bcl-2 and Bcl-x genes is resistant to this type of injury. Xanthine oxidase derived reactive oxygen intermediates (ROI) seems to play a pivotal role for the reperfusion injury.3 After extended periods of hypoxia or ischemia, intracellular reactive oxygen is produced, and xanthine oxidase as well as mitochondria contribute to the intracellular oxidant stress. Several articles revealing the mechanism of reperfusion injury support the observations that 50% to 80% of SECs and hepatocytes undergo apoptosis.4,5 as detected using TUNEL stain, DNA laddering, and caspase activities. But a recent article reported that oncotic necrosis and not apoptosis represents the predominant mode of cell death during hepatic ischemia-reperfusion.6 These authors used the similar assays however, more weighted to the morphologic criteria. They observed that the number of apoptotic hepatocytes and SECs was limited to less than 2% of all injured cells. There are several articles supporting the tenet that the TUNEL From the Department of Surgery, Keimyung University DongSan Medical Center, Taegu, Korea. Address reprint requests to Koo Jeong Kang, MD, Department of Surgery, Keimyung University Dong-San Medical Center, #194 Donsan Dong, Chunggu, Taegu, 700-712, Korea. E-mail: [email protected]
© 2002 by Elsevier Science Inc. 360 Park Avenue South, New York, NY 10010-1710
0041-1345/02/$–see front matter PII S0041-1345(02)03465-6
Transplantation Proceedings, 34, 2659 –2661 (2002)
2659
2660
stain does not discriminate apoptosis from necrosis.4,7 But many researchers have shown that the mechanism of cell death occurs through the apoptotic pathway. To establish preventive and therapeutic modalities, we must know the actual mechanisms of cell death—necrosis versus apoptosis. MEDIATORS OF REPERFUSION INJURY
The ischemia/reperfusion injury has been disseted into two distinct phases. The initial phase of injury is characterized by Kupffer cell induced oxidant stress. The later phase, which occurs more than 6 hours after reperfusion, includes direct damage by a complex cascade of inflammatory mediators released from recruited neutrophils. Initial Kupffer cell activation is a central hepatic pathophysiologic mechanism of the early reperfusion injury after warm and cold ischemia. Kupffer cells may be activated by subjecting them to hypoxia with subsequent reoxygenation. Activated Kupffer cell release of reactive oxygen species (ROS) into the vascular space induces a network of cytokines, which participate in both sinusoidal accumulation of granulocytes and microcirculatory failure. Neutrophils contribute to the ischemia/reperfusion injury in the rat liver via oxidant stress and mediator formation, events which seem to occur several hours after initiation of reflow. Experimental data indicate that a number of acute inflammatory mediators, namely TNF-␣, PAF, and chemokines cause neutrophil accumulation in the sinusoids. In vitro experiments using an isolated perfused rat liver model suggest that platelet as well as neutrophils induce SEC apoptosis upon reperfusion of the cold ischemic rat liver in a synergistic manner,8 an injury that is blocked by Kupffer cell inhibition. So, Kupffer cells, neutrophils, platelets, and the liberated factors from each of them interact during reperfusion producing the injury to SECs and hepatocytes. Meanwhile, CXC-chemokines and interleukin (IL)-8 are involved in the process of neutrophil recruitment. T cells resident in the liver also are involved in the cold ischemia-reperfusion injury unless dampened by IL-10, which decreases the release of T cell and macrophage-dependent cytokines. Transmigration of the neutrophils across the sinusoidal endothelial barrier requires adhesion molecules, ICAM-1, VCAM-1, and integrins. Cytokines, TNF-␣, IL-1, and TNF-␥ have been identified as the most potent stimuli. Also platelet endothelial cell adhesion molecule (PECAM-1) is critical for neutrophil transmigration in other sites but does not seem to play a role in the liver. Upregulation of the selectin family of adhesion molecules includes P-selectin, resulting in increased platelet and neutrophil adhesion to liver endothelial cells.9 The temporal succession of adhesion events leads to neutrophil rolling, arrest, and subsequent transmigration from the vascular lumen into the hepatic interstitium.10 Accumulation of activated neutrophils within the hepatic parenchyma causes hepatocyte damage through the release of oxidants and proteases or neutrophil-mediated heptocellular injury. The primary neutrophil oxidant-generating pathway involves NADPH oxidase.10 The activated enzyme
KANG
initiates a reperfusion injury by oxidizing NADPH. This released electron reduces molecular oxygen, forming O2⫺, a superoxide anion. Myeloperoxidase released from neutrophil granules converts H2O2 to hypochlorous acid (HOCl), another potent oxidant. The generation of O•2 , H2O2, HO⫺, and HOCl may directly damage hepatocytes facilitating protease-mediated hepatic injury. In addition to the generation of oxidants, activated neutrophils release a number of mediators from their granules, including proteases (elastase, cathepsin G, heparinase, and collagenase) and hydrolytic enzymes that may be directly cytotoxic to hepatocytes. Calpains (Ca2⫹-requiring cysteine proteases) mediate ischemic injury of the liver through modulation of apoptosis and necrosis, mediating both warm and cold ischemic injuries in rat liver.11 The regulatory mechanisms of initiation and progression of hepatic inflammatory responses induced by ischemia/reperfusion are not well-known, although significant entities appear to be IL-6, IL-10, and secretory leukocyte protease inhibitors (SLPI).12,13 Nuclear factor (NF-B) is a primary regulator of gene expression for a large number of proinflammatory cytokines and vascular adhesion molecules, and is activated during ischemia/reperfusion injury of the liver.14 Both IL-10 and SLPI prevent degradation of inhibitory proteins, IB proteins.15 In part due to the progressive effect of hepatic inflammatory response, NF-B is required for liver regeneration after transplantation. Microcirculatory failure is a potential mechanism of reperfusion injury, however, recent data show that sinusoidal plugging does not cause SEC injury nor affect sinusoidal perfusion. Instead of microcirculatory failure, an imbalance of vasoconstrictors and vasodilators is responsible for aggravating the reperfusion injury. These responses are mediated by NO, which ameliorates the injury,16 and endothelin-1, which causes sinusoidal constriction by contraction of Ito cells. Endothelin B receptors which occur in endothelial cells and induce NO-mediated vasorelaxation through activation of constitutive NO synthase; mediates-protection against anoxia-reoxygenation injury in the perfused rat liver.17 PREVENTIVE AND THERAPEUTIC STRATEGIES OF REPERFUSION INJURY
Numerous complex mechanisms seem to display benefecial effects against reperfusion injuries. But there may be much more sophisticated cell death process that can be elucidated. Ischemic preconditioning, a short period of ischemia before a sustained, ischemic insult, can ameliorate the reperfusion injury after warm and cold ischemia. The concept of ischemic preconditioning is based on the biological principle that tissue primed by various types of sublethal stress develops tolerance to subsequent lethal injury. Ischemic preconditioning protects against lethal ischemic stress through down-regulation of the apoptotic pathway.2 Nitric oxide, adenosine, and protein kinase C also have been implicated in the protective mechanisms of ischemic preconditioning. The possible mechanism may be associated with reduced sodium accumulation that decreases cell
REPERFUSION INJURY
killing,18 and protects against systemic disorders associated with hepatic ischemia/reperfusion through blockade of TNF-␣–induced P-selectin up-regulation.19 Evidence for a protective effect of ischemic preconditioning was recently provided in the human liver during hepatic resection.20 Hyperthermic preconditioning appears to exert an inhibitory effect on postischemic injury of the liver through the attenuation of microcirculatory disturbances, possibly mediated by HSP70 and heme oxygenase(HO)-1/HSP32 expression.21 Numerous exogenous factors induce HO-1, including ischemia, hypoxia, oxidative stress, and glutathione oxidation as well as heat. Pharmacologic preconditioning may induce a stress response that protects the liver against ischemia-reperfusion injury. The anticancer agent doxyrubicin has the potential to render the liver tolerant to reperfusion injury, possibly by increasing HSP72 and HSP73 in liver tissue22 and inducing HO-1.23 Hormonal preconditioning is also possibly via atrial natriuretic peptide (ANP), which protects the liver against a reperfusion injury.24 Potential roles of ANP include immune effects and protection of the liver against oxidant stress of activated Kupffer cell25 as well as vasodilating properties. Reactive oxygen species induce several pivotal mechanisms of ischemia and reperfusion injury. Numerous antioxidants have been considered as potential therapeutics. The endogenous antioxidant glutathione (GSH) is able to react spontaneously with hydroxygen peroxide, hypochlorous acid, and monochloramines formed by granulocytes, which attenuates the reperfusion injury in the liver.25 Because S-nitrosylated compounds (nitrosothiols; RS-NOs) function as NO reservoirs and preserve the antioxidant activities of NO, one S-nitosylated protease inhibitor, S-nitrso-␣1-protease inhibitor, exerts a cytoprotective effect on ischemia-reperfusion injuries. Additionally, we must develop simple methods to reduce the warm ischemic duration. Quick and meticulous surgery with an adequate Pringle maneuver can reduce the duration of warm ischemia and reduce bleeding and blood, leukocyte and platelet transfusions that may injure the liver. Reducing warm ischemic time and minimizing the inevitable inflammatory response during perioperative and intraoperative
2661
periods are easy methods that are critical for protection against reperfusion injuries. REFERENCES 1. Peralta C, Closa D, Hotter G, et al: Biochem Biophys Res Commun 229:264, 1996 2. Yadav SS, Sindram D, Perry DK, et al: Hepatology 30:1223, 1999 3. Jaeschke H: Chem Biol Interact 79:115, 1991 4. Cursio R, Gugenheim J, Ricci JE, et al: FASEB J 13:253, 1999 5. Kohli V, Selzner M, Madden JF, et al: Transplantation 67:1099, 1999 6. Gujral JS, Bucci TJ, Farhood A, et al: Hepatology 33:397, 2001 7. Lawson JA, Fisher MA, Simmons CA, et al: Toxicol Appl Pharmacol 156:179, 1999 8. Sindram D, Porte RJ, Hoffman MR, et al: Gastroenterology 118:183, 2000 9. Yadav SS, Howell DN, Steeber DA, et al: Hepatology 29: 1494, 1999 10. Lentsch AB, Kato A, Yoshidome H, et al: Hepatology 32:169, 2000 11. Kohli V, Madden JF, Bentley RC, et al: Gastroenterology 116:168, 1999 12. Camargo CA Jr., Madden JF, Gao W, et al: Hepatology 26:1513, 1997 13. Lentsch AB, Yoshidome H, Warner RL, et al: Gastroenterology 117:953, 1999 14. Zwacka RM, Zhang Y, Zhou W, et al: Hepatology 28:1022, 1998 15. Lentsch AB, Shanley TP, Sarma V, et al: J Clin Invest 100:2443, 1997 16. Wang Y, Mathews WR, Guido DM, et al: Shock 4:282, 1995 17. Taniai H, Suematsu M, Suzuki T, et al: Hepatology 33:894, 2001 18. Carini R, De Cesaris MG, Splendore R, et al: Hepatology 31:166, 2000 19. Peralta C, Fernandez L, Panes J, et al: Hepatology 33:100, 2001 20. Clavien PA, Yadav S, Sindram D, et al: Ann Surg 232:155, 2001 21. Terajima H, Enders G, Thiaener A, et al: Hepatology 31:407, 2000 22. Kume M, Yamamoto Y, Yamagami K, et al: Br J Surg 87:1168, 2000 23. Ito K, Ozasa H, Sanada K, et al: Hepatology 31:416, 2000 24. Gerbes AL, Vollmar AM, Kiemer AK, et al: Hepatology 28:1309, 1998 25. Bilzer M, Paumgartner G, Gerbes AL, et al: Gastroenterology 117:200, 1999
T
HE ISCHEMIA/REPERFUSION injury remains a problem after liver surgery or liver transplantation. Preservation injury is a major cause of primary nonfunction following liver transplantation. Sinusoidal endothelial cell (SEC) apoptosis is an outcome of cold ischemia/reperfusion injury. Investigators demonstrated a selective induction of apoptosis in sinusoidal and vascular endothelial cells within the liver following cold ischemia/warm reperfusion injury. Recent data also have indicated that platelet and leukocyte adhesion to the sinusoids mediate reperfusion injury by causing endothelial cell apoptosis. Ischemic preconditioning, namely, a short period of ischemia prior to a major ischemic insult, is highly protective to downregulate the caspase pathway and inhibit apoptotic cell death.1,2 Future research on ischemic livers should focus on mechanisms and mediators involved in apoptotic cell death, which may lead to innovative protective strategies and preservation solutions with important clinical implications. MECHANISM OF REPERFUSION INJURY AFTER WARM AND COLD ISCHEMIA
Ischemic liver injury is caused by a deficiency of oxygen, which occurs by hepatic vascular occlusion during liver resection or cold preservation before liver transplantation. Reperfusion after ischemia reoxygenates the liver; the introduction of oxygenated blood aggravates the hypoxic or ischemic insult. The mechanism of the ischemic injury involves the loss of mitochondrial respiration, leading to adenosine triphosphate (ATP) depletion and deterioration of energy-dependent metabolic pathways and transport processes. Hypothermia reduces the metabolic rate in tissues, therefore prolonging the period during which anoxic cells can retain essential metabolic functions. Cold preservation after harvesting the liver reduces the metabolic rate in the tissue, thereby prolonging the period during which anoxic cells retain essential metabolic functions. Hypothermia can induce cell injury, however, due to influx of sodium and chloride followed by secondary alterations of cellular calcium homeostasis and cell swelling. Cold preservation injury of the liver is also the result of angiogenic mechanisms. SECs are more susceptible to cold ischemia than hepatocytes. A short period of ischemia (30 minutes) produces apoptosis only of the SECs. A longer period of ischemia (1 hour) followed by reperfusion causes apoptosis
of both hepatocytes and SECs. The morphologic features of the SECs after cold preservation followed by reperfusion shows typical characteristics of apoptosis, including cytoplasmic blebbing, nuclear and cytoplasmic condensation, and typical apoptotic bodies in phagolysosomes. Two pathways activate effector caspases, which lead to apoptotic cell death. In the first one, death ligands such as tumor necrosis factor (TNF) or Fas activate receptors resulting in the formation of a death complex, which then activates caspase-8. In the second pathway, cellular stress leads to mitochondrial dysfunction with release of cytochrome C into the cytoplasm. Cytochrome C then binds to and triggers Apaf-1 followed by activation of caspase-9. A link between both pathways is the protein Bid, which can be activated by caspase-8, leading to a release of cytochrome C from mitochondria. Cytochrome C release can be blocked by anti-apoptotic Bcl-2 family members and promoted by proapoptotic members of this family such as Bax. Caspases and calpains are key cellular mediators of apoptosis after reperfusion. Overexpression of Bcl-2 and Bcl-x genes is resistant to this type of injury. Xanthine oxidase derived reactive oxygen intermediates (ROI) seems to play a pivotal role for the reperfusion injury.3 After extended periods of hypoxia or ischemia, intracellular reactive oxygen is produced, and xanthine oxidase as well as mitochondria contribute to the intracellular oxidant stress. Several articles revealing the mechanism of reperfusion injury support the observations that 50% to 80% of SECs and hepatocytes undergo apoptosis.4,5 as detected using TUNEL stain, DNA laddering, and caspase activities. But a recent article reported that oncotic necrosis and not apoptosis represents the predominant mode of cell death during hepatic ischemia-reperfusion.6 These authors used the similar assays however, more weighted to the morphologic criteria. They observed that the number of apoptotic hepatocytes and SECs was limited to less than 2% of all injured cells. There are several articles supporting the tenet that the TUNEL From the Department of Surgery, Keimyung University DongSan Medical Center, Taegu, Korea. Address reprint requests to Koo Jeong Kang, MD, Department of Surgery, Keimyung University Dong-San Medical Center, #194 Donsan Dong, Chunggu, Taegu, 700-712, Korea. E-mail: [email protected]
© 2002 by Elsevier Science Inc. 360 Park Avenue South, New York, NY 10010-1710
0041-1345/02/$–see front matter PII S0041-1345(02)03465-6
Transplantation Proceedings, 34, 2659 –2661 (2002)
2659
2660
stain does not discriminate apoptosis from necrosis.4,7 But many researchers have shown that the mechanism of cell death occurs through the apoptotic pathway. To establish preventive and therapeutic modalities, we must know the actual mechanisms of cell death—necrosis versus apoptosis. MEDIATORS OF REPERFUSION INJURY
The ischemia/reperfusion injury has been disseted into two distinct phases. The initial phase of injury is characterized by Kupffer cell induced oxidant stress. The later phase, which occurs more than 6 hours after reperfusion, includes direct damage by a complex cascade of inflammatory mediators released from recruited neutrophils. Initial Kupffer cell activation is a central hepatic pathophysiologic mechanism of the early reperfusion injury after warm and cold ischemia. Kupffer cells may be activated by subjecting them to hypoxia with subsequent reoxygenation. Activated Kupffer cell release of reactive oxygen species (ROS) into the vascular space induces a network of cytokines, which participate in both sinusoidal accumulation of granulocytes and microcirculatory failure. Neutrophils contribute to the ischemia/reperfusion injury in the rat liver via oxidant stress and mediator formation, events which seem to occur several hours after initiation of reflow. Experimental data indicate that a number of acute inflammatory mediators, namely TNF-␣, PAF, and chemokines cause neutrophil accumulation in the sinusoids. In vitro experiments using an isolated perfused rat liver model suggest that platelet as well as neutrophils induce SEC apoptosis upon reperfusion of the cold ischemic rat liver in a synergistic manner,8 an injury that is blocked by Kupffer cell inhibition. So, Kupffer cells, neutrophils, platelets, and the liberated factors from each of them interact during reperfusion producing the injury to SECs and hepatocytes. Meanwhile, CXC-chemokines and interleukin (IL)-8 are involved in the process of neutrophil recruitment. T cells resident in the liver also are involved in the cold ischemia-reperfusion injury unless dampened by IL-10, which decreases the release of T cell and macrophage-dependent cytokines. Transmigration of the neutrophils across the sinusoidal endothelial barrier requires adhesion molecules, ICAM-1, VCAM-1, and integrins. Cytokines, TNF-␣, IL-1, and TNF-␥ have been identified as the most potent stimuli. Also platelet endothelial cell adhesion molecule (PECAM-1) is critical for neutrophil transmigration in other sites but does not seem to play a role in the liver. Upregulation of the selectin family of adhesion molecules includes P-selectin, resulting in increased platelet and neutrophil adhesion to liver endothelial cells.9 The temporal succession of adhesion events leads to neutrophil rolling, arrest, and subsequent transmigration from the vascular lumen into the hepatic interstitium.10 Accumulation of activated neutrophils within the hepatic parenchyma causes hepatocyte damage through the release of oxidants and proteases or neutrophil-mediated heptocellular injury. The primary neutrophil oxidant-generating pathway involves NADPH oxidase.10 The activated enzyme
KANG
initiates a reperfusion injury by oxidizing NADPH. This released electron reduces molecular oxygen, forming O2⫺, a superoxide anion. Myeloperoxidase released from neutrophil granules converts H2O2 to hypochlorous acid (HOCl), another potent oxidant. The generation of O•2 , H2O2, HO⫺, and HOCl may directly damage hepatocytes facilitating protease-mediated hepatic injury. In addition to the generation of oxidants, activated neutrophils release a number of mediators from their granules, including proteases (elastase, cathepsin G, heparinase, and collagenase) and hydrolytic enzymes that may be directly cytotoxic to hepatocytes. Calpains (Ca2⫹-requiring cysteine proteases) mediate ischemic injury of the liver through modulation of apoptosis and necrosis, mediating both warm and cold ischemic injuries in rat liver.11 The regulatory mechanisms of initiation and progression of hepatic inflammatory responses induced by ischemia/reperfusion are not well-known, although significant entities appear to be IL-6, IL-10, and secretory leukocyte protease inhibitors (SLPI).12,13 Nuclear factor (NF-B) is a primary regulator of gene expression for a large number of proinflammatory cytokines and vascular adhesion molecules, and is activated during ischemia/reperfusion injury of the liver.14 Both IL-10 and SLPI prevent degradation of inhibitory proteins, IB proteins.15 In part due to the progressive effect of hepatic inflammatory response, NF-B is required for liver regeneration after transplantation. Microcirculatory failure is a potential mechanism of reperfusion injury, however, recent data show that sinusoidal plugging does not cause SEC injury nor affect sinusoidal perfusion. Instead of microcirculatory failure, an imbalance of vasoconstrictors and vasodilators is responsible for aggravating the reperfusion injury. These responses are mediated by NO, which ameliorates the injury,16 and endothelin-1, which causes sinusoidal constriction by contraction of Ito cells. Endothelin B receptors which occur in endothelial cells and induce NO-mediated vasorelaxation through activation of constitutive NO synthase; mediates-protection against anoxia-reoxygenation injury in the perfused rat liver.17 PREVENTIVE AND THERAPEUTIC STRATEGIES OF REPERFUSION INJURY
Numerous complex mechanisms seem to display benefecial effects against reperfusion injuries. But there may be much more sophisticated cell death process that can be elucidated. Ischemic preconditioning, a short period of ischemia before a sustained, ischemic insult, can ameliorate the reperfusion injury after warm and cold ischemia. The concept of ischemic preconditioning is based on the biological principle that tissue primed by various types of sublethal stress develops tolerance to subsequent lethal injury. Ischemic preconditioning protects against lethal ischemic stress through down-regulation of the apoptotic pathway.2 Nitric oxide, adenosine, and protein kinase C also have been implicated in the protective mechanisms of ischemic preconditioning. The possible mechanism may be associated with reduced sodium accumulation that decreases cell
REPERFUSION INJURY
killing,18 and protects against systemic disorders associated with hepatic ischemia/reperfusion through blockade of TNF-␣–induced P-selectin up-regulation.19 Evidence for a protective effect of ischemic preconditioning was recently provided in the human liver during hepatic resection.20 Hyperthermic preconditioning appears to exert an inhibitory effect on postischemic injury of the liver through the attenuation of microcirculatory disturbances, possibly mediated by HSP70 and heme oxygenase(HO)-1/HSP32 expression.21 Numerous exogenous factors induce HO-1, including ischemia, hypoxia, oxidative stress, and glutathione oxidation as well as heat. Pharmacologic preconditioning may induce a stress response that protects the liver against ischemia-reperfusion injury. The anticancer agent doxyrubicin has the potential to render the liver tolerant to reperfusion injury, possibly by increasing HSP72 and HSP73 in liver tissue22 and inducing HO-1.23 Hormonal preconditioning is also possibly via atrial natriuretic peptide (ANP), which protects the liver against a reperfusion injury.24 Potential roles of ANP include immune effects and protection of the liver against oxidant stress of activated Kupffer cell25 as well as vasodilating properties. Reactive oxygen species induce several pivotal mechanisms of ischemia and reperfusion injury. Numerous antioxidants have been considered as potential therapeutics. The endogenous antioxidant glutathione (GSH) is able to react spontaneously with hydroxygen peroxide, hypochlorous acid, and monochloramines formed by granulocytes, which attenuates the reperfusion injury in the liver.25 Because S-nitrosylated compounds (nitrosothiols; RS-NOs) function as NO reservoirs and preserve the antioxidant activities of NO, one S-nitosylated protease inhibitor, S-nitrso-␣1-protease inhibitor, exerts a cytoprotective effect on ischemia-reperfusion injuries. Additionally, we must develop simple methods to reduce the warm ischemic duration. Quick and meticulous surgery with an adequate Pringle maneuver can reduce the duration of warm ischemia and reduce bleeding and blood, leukocyte and platelet transfusions that may injure the liver. Reducing warm ischemic time and minimizing the inevitable inflammatory response during perioperative and intraoperative
2661
periods are easy methods that are critical for protection against reperfusion injuries. REFERENCES 1. Peralta C, Closa D, Hotter G, et al: Biochem Biophys Res Commun 229:264, 1996 2. Yadav SS, Sindram D, Perry DK, et al: Hepatology 30:1223, 1999 3. Jaeschke H: Chem Biol Interact 79:115, 1991 4. Cursio R, Gugenheim J, Ricci JE, et al: FASEB J 13:253, 1999 5. Kohli V, Selzner M, Madden JF, et al: Transplantation 67:1099, 1999 6. Gujral JS, Bucci TJ, Farhood A, et al: Hepatology 33:397, 2001 7. Lawson JA, Fisher MA, Simmons CA, et al: Toxicol Appl Pharmacol 156:179, 1999 8. Sindram D, Porte RJ, Hoffman MR, et al: Gastroenterology 118:183, 2000 9. Yadav SS, Howell DN, Steeber DA, et al: Hepatology 29: 1494, 1999 10. Lentsch AB, Kato A, Yoshidome H, et al: Hepatology 32:169, 2000 11. Kohli V, Madden JF, Bentley RC, et al: Gastroenterology 116:168, 1999 12. Camargo CA Jr., Madden JF, Gao W, et al: Hepatology 26:1513, 1997 13. Lentsch AB, Yoshidome H, Warner RL, et al: Gastroenterology 117:953, 1999 14. Zwacka RM, Zhang Y, Zhou W, et al: Hepatology 28:1022, 1998 15. Lentsch AB, Shanley TP, Sarma V, et al: J Clin Invest 100:2443, 1997 16. Wang Y, Mathews WR, Guido DM, et al: Shock 4:282, 1995 17. Taniai H, Suematsu M, Suzuki T, et al: Hepatology 33:894, 2001 18. Carini R, De Cesaris MG, Splendore R, et al: Hepatology 31:166, 2000 19. Peralta C, Fernandez L, Panes J, et al: Hepatology 33:100, 2001 20. Clavien PA, Yadav S, Sindram D, et al: Ann Surg 232:155, 2001 21. Terajima H, Enders G, Thiaener A, et al: Hepatology 31:407, 2000 22. Kume M, Yamamoto Y, Yamagami K, et al: Br J Surg 87:1168, 2000 23. Ito K, Ozasa H, Sanada K, et al: Hepatology 31:416, 2000 24. Gerbes AL, Vollmar AM, Kiemer AK, et al: Hepatology 28:1309, 1998 25. Bilzer M, Paumgartner G, Gerbes AL, et al: Gastroenterology 117:200, 1999