Markus Paxian

Recovery of hepatocellular ATP and “pericentral apoptosis” after hemorrhage and resuscitation

Progressive liver dysfunction contributes significantly to the development of multiple organ failure after trauma/hemorrhage. This study tested the relative impact of necrotic and apoptotic cell death in a graded model of hemorrhagic shock (mean arterial blood pressure=35±5 mmHg for 1, 2, or 3 h, followed by 2 h, 1 h, or no resuscitation, respectively) in rats. Prolonged periods of hemorrhagic hypotension (3 h) were paralleled by a profound decrease of hepatic ATP levels and occurrence of pericentral necrosis. Resuscitation after shorter periods of hemorrhagic hypotension resulted in restoration of tissue ATP whereas hepatocellular function as assessed by indocyanine green clearance remained depressed (49.9±1.6 mL/(min·kg) at baseline, 28.8± 1.2 mL/(min·kg) after 2 h of resuscitation; P<0.05). Under these conditions, induction of caspase activity and DNA fragmentation were observed in pericentral hepatocytes that could be prevented by the radical scavenger tempol. Pretreatment with z‐Val‐Ala‐Asp(O‐methyl)‐flouromethylketone prevented de novo expression of caspase‐generated cytokeratin 18, DNA fragmentation, and depression of hepatocellular indocyanine green clearance. These data suggest that prolonged low flow/hypoxia induces ATP depletion and pericentral necrosis and restoration of oxygen supply and ATP levels after shorter periods of low flow ischemia propagate programmed cell death or “pericentral apoptosis.”—Paxian, M., Bauer, I., Rensing, H., Jaeschke, H., Mautes, A. E. M., Kolb, S. A., Wolf, B., Stockhausen, A., Jeblick, S., Bauer, M. Recovery of hepatocellular ATP and “pericentral apoptosis” after hemorrhage and resuscitation. FASEB J. 17, 993–1002 (2003)

Prospective assessment of hepatic function and mechanisms of dysfunction in the critically ill.

Liver dysfunction affects a variety of metabolic pathways in the critically ill, but mechanisms remain poorly understood. We prospectively assessed markers of hepatic injury and function in sepsis and I/R injury in vivo and molecular mechanisms in human liver tissue ex vivo. Markers of hepatocellular injury, synthesis, and excretion, including plasma disappearance rate of indocyanine green (ICG), were measured in 48 patients with severe sepsis. Incidence of liver dysfunction was 42% as assessed by hyperbilirubinemia but 74% by impaired dye excretion. Conventional markers for liver injury failed to predict outcome, whereas dye excretion of less than 8% per minute predicted death with high sensitivity and specificity. Potential mechanisms were assessed via (a) gene expression analysis of transporter proteins for bilirubin and ICG in cultured human liver tissue, and (b) monitoring uptake and excretion of the dye after I/R injury in 12 patients receiving a biliary T-tube during liver transplantation. Ex vivo gene expression of transporters was differentially affected for bilirubin and ICG with upregulation of basolateral and downregulation of canalicular ICG transporters. Consistently, patients with unfavorable course after liver transplantation displayed almost complete cessation of biliary dye excretion, whereas uptake into the hepatocyte was reduced by only 40%. In conclusion, standard liver tests lack the required sensitivity to assess hepatic injury and function in the critically ill. Dye excretion better reflects excretory and/or microvascular dysfunction but still underestimates impaired canalicular transport. The observed differential susceptibility of the polar surfaces of human hepatocytes has potential implications for monitoring liver function and drug-induced liver injury.

Endothelin-1 and heme oxygenase-1 as modulators of sinusoidal tone in the stress-exposed rat liver☆

Heme oxygenase (HO)‐1 is up‐regulated after ischemia/reperfusion and contributes to maintenance of hepatic perfusion and integrity. Blockade of HO‐1 leads to an increased portal pressor response in the stress‐exposed liver. We tested whether the increase in portal pressure reflects unmasking of a concomitant up‐regulation of the vasoconstrictor endothelin (ET)‐1. Hemorrhagic shock induced messenger RNAs encoding HO‐1 (16‐fold) and ET‐1 (9‐fold) with a similar time course in the liver. At maximum induction of both mediators, rats received either vehicle or the endothelin ETA/B antagonist bosentan (10 mg/kg intravenously). Subsequently, the HO pathway was blocked in all animals by tin‐protoporphyrin (SnPP)‐IX (50 μmol/kg intravenously). Portal and sinusoidal hemodynamics were measured using microflow probes and intravital microscopy, respectively. Blockade of the HO pathway led to a significant increase in portal resistance (sham/SnPP‐IX, 0.17 ± 0.046 mm Hg · min · mL−1; shock/vehicle/SnPP‐IX, 0.57 ± 0.148 mm Hg · min · mL−1; P < 0.05) and a decrease in sinusoids conducting flow (shock/vehicle/SnPP‐IX: baseline, 28.3 ± 0.85 sinusoids/mm; 10 minutes after SnPP‐IX, 23.1 ± 1.09 sinusoids/mm; P < 0.05). Intravital microscopy showed narrowing of failing sinusoids colocalizing with stellate cells after blockade of the HO pathway. Blockade of ETA/B receptors attenuated the increase in portal resistance (shock/bosentan/SnPP‐IX, 0.29 ± 0.051 mm Hg · min · mL−1) and prevented sinusoidal perfusion failure (shock/bosentan/SnPP‐IX: baseline, 28.2 ± 0.97 sinusoids/mm; 10 minutes after SnPP‐IX, 28.8 ± 1.18 sinusoids/mm) as well as sinusoidal narrowing. In conclusion, a functional interaction of the up‐regulated vasodilatory HO system and the vasoconstrictor ET‐1 on the sinusoidal level exists under stress conditions. Both mediator systems affect sinusoidal diameter via direct action on hepatic stellate cells in vivo. (HEPATOLOGY2002;36:1453–1465).

Kupffer cells and neutrophils as paracrine regulators of the heme oxygenase-1 gene in hepatocytes after hemorrhagic shock.

Heme oxygenase (HO) plays a pivotal role for the maintenance of liver blood flow and hepatocellular integrity after hemorrhagic shock. We investigated the role of Kupffer cells and neutrophils as paracrine modulators of hepatocellular HO-1 gene expression in a rat model of hemorrhage and resuscitation. Male Sprague-Dawley rats (n = 6-10/group) were anesthetized (pentobarbital, 50 mg/kg intraperitonal) and subjected to hemorrhagic shock (mean arterial blood pressure: 35 mmHg for 60 min) or a sham protocol. Based on the time course of HO-1 gene expression, the effect of various antioxidants, Kupffer cell blockade [gadolinium chloride (GdCl3); 10 mg/kg; 24 h prior to hemorrhage or dichloromethylene diphosphonate (Cl2MDP); 1 mg/kg; 2 days prior to hemorrhage], or neutrophil depletion (vinblastine, 0.5 mg/kg, 5 days prior to hemorrhage) on induction of the HO-1 gene was assessed at 5 h of resuscitation, i.e., the time point of maximal induction. Kupffer cell blockade and antioxidants abolished HO-1 mRNA and protein induction after hemorrhage, while neutrophil depletion failed to affect hepatocellular HO-1 gene expression. In addition, Kupffer cell blockade aggravated hepatocellular injury. N-formyl-methionine-leucyl-phenylalanin (fMLP) induced a substantial influx of neutrophils into the liver but failed to induce hepatocellular HO-1 mRNA expression. These data suggest that Kupffer cells but not neutrophils induce an adaptive hepatocellular stress response after hemorrhage and resuscitation. Oxygen-free radicals released by Kupffer cells may serve as paracrine regulators of a hepatocellular stress gene which is necessary to maintain liver blood flow and integrity under stress conditions.

Perflubron emulsion improves hepatic microvascular integrity and mitochondrial redox state after hemorrhagic shock.

Hemorrhagic shock is associated with decreased systemic oxygen delivery, but also with impaired microvascular perfusion, which can result in diminished local oxygen availability even in the presence of adequate cardiac output after resuscitation. Beside surgical interventions to control blood loss, transfusion of stored packed red blood cells represents the current standard of care in the management of severe hemorrhagic shock. Because stored red blood cells are less deformable and show a higher O2 affinity that affects the O2 off-load to tissues, perfluorocarbon-based artificial oxygen carriers might improve local O2 delivery under these conditions. To test this, rats were subjected to hemorrhagic shock (1 h, mean arterial pressure [MAP] 30-35 mmHg) and were resuscitated with fresh whole blood, pentastarch, stored red blood cells, perflubron emulsion (2.7 and 5.4 g/kg body weight) together with pentastarch, or stored red blood cells together with 2.7 g/kg perflubron emulsion. Hepatic microcirculation, tissue oxygenation, and mitochondrial redox state were investigated by intravital microscopy. In addition, hepatocellular function and liver enzyme release were determined. After hemorrhagic shock and resuscitation with perflubron emulsion, volumetric sinusoidal blood flow was significantly increased compared with resuscitation with stored red blood cells. Furthermore, resuscitation with perflubron emulsion resulted in higher hepatic tissue PO2 and normalized mitochondrial redox potential, which was accompanied by lessened hepatocellular injury as well as improved liver function. These results indicate that, in this model of hemorrhagic shock, asanguineous fluid resuscitation with addition of perflubron emulsion is superior to stored blood or pentastarch alone with respect to increased local O2 availability on the cellular level. This effect is primarily due to improved restoration of hepatic microcirculatory integrity.

Perflubron Emulsion in Prolonged Hemorrhagic Shock: Influence on Hepatocellular Energy Metabolism and Oxygen-dependent Gene Expression

Background Liver dysfunction as a result of impaired oxygen availability frequently occurs following hemorrhage and contributes to delayed mortality. Artificial oxygen carriers may improve oxygen supply to vital organs while avoiding the need for allogeneic transfusion. Methods Rats were subjected to hemorrhagic hypotension (mean arterial pressure = 35–40 mmHg for 120 min) and were subsequently resuscitated with (1) stored whole rat blood, (2) pentastarch, or (3) pentastarch combined with perflubron emulsion (PFE; 2.7 or 5.4 g/kg body weight), a second-generation artificial oxygen carrier. Recovery of liver adenosine triphosphate, hepatocellular injury, and expression of glutamine synthetase 1, a gene that is induced by exposure of hepatocytes to low partial pressure of oxygen, were studied at 4 h of resuscitation. Results Stored whole blood or pentastarch failed to restore liver adenosine triphosphate concentrations after prolonged shock as compared to sham controls and resulted in increased gene expression of glutamine synthetase 1. Addition of 2.7 g PFE/kg restored liver adenosine triphosphate to control, whereas 5.4 g PFE/kg resulted in adenosine triphosphate concentrations significantly above control. Improved hepatocellular oxygen supply was also confirmed by restoration of the physiologic expression pattern of glutamine synthetase 1. Serum enzyme concentrations were highest after resuscitation with stored blood, whereas addition of PFE failed to further decrease enzyme concentrations as compared to pentastarch alone. Conclusions Resuscitation with PFE is superior to stored blood or asanguineous resuscitation with respect to restoration of hepatocellular energy metabolism. The improved hepatocellular oxygen availability is reflected in normalization of oxygen-dependent gene expression. However, improved oxygen availability failed to affect early hepatocellular injury.

Influence of heme-based solutions on stress protein expression and organ failure after hemorrhagic shock*

Objective:Hemoglobin-based oxygen carriers (e.g., diaspirin-cross-linked hemoglobin [DCLHb] and hemoglobin glutamer-200 [HbG]) may have potential in the treatment of hemorrhagic shock. The nitric oxide scavenging and direct vasoconstrictive side effects of free hemoglobin of currently available preparations may increase organ injury after shock in contrast to non-oxygen-carrying heme solutions (e.g., hemin arginate [HAR]). However, both classes of substances might induce the protective enzyme heme oxygenase (HO)-1, particularly in the liver. The aim of the study was to assess the role of pretreatment with DCLHb, HbG, or HAR on HO-1 expression and organ injury after hemorrhagic shock. Design:Prospective controlled laboratory study. Setting:Animal research laboratory at a university hospital. Subjects:Male Sprague-Dawley rats (200–300 g body weight, n = 5–12/group). Interventions:Twenty-four hours after different doses of DCLHb, HbG (each 1, 2, or 3 g/kg of body weight), or HAR (5, 25, or 75 mg/kg of body weight), the protein expression of HO-1 and heat shock protein-70 in liver, kidney, heart, lungs, and aorta was determined. Twenty-four hours after pretreatment with DCLHb, HbG, or HAR, rats were subjected to hemorrhage (mean arterial blood pressure, 35–40 mm Hg for 1 or 2 hrs)/resuscitation (5 or 4 hrs, respectively). Animals treated with Ringer’s solution (30 mL/kg of body weight) served as controls. In additional experiments, HO activity was blocked with tin mesoporphyrin-IX. Measurements and Main Results:DCLHb, HbG, and HAR dose-dependently induced HO-1 protein but not heat shock protein-70. Pretreatment with DCLHb or HbG shortened the onset of decompensation in shock (DCLHb, 40 ± 11 mins; HbG, 36 ± 4 mins) compared with vehicle (68 ± 4 mins, p < .05) and HAR pretreatment (81 ± 7 mins, p < .05). High doses of DCLHb pretreatment increased mortality (2 hrs of shock, 80%; p < .05 vs. vehicle or HAR). Pretreatment with HAR led to higher shed blood volumes (p < .05) and higher hepatocellular ATP levels (2 hrs of shock, p < .05 vs. DCLHb and HbG). Blockade of HO activity by tin mesoporphyrin-IX abolished the protection mediated by HAR. Conclusions:Although DCLHb, HbG, and HAR induce HO-1 in the absence of an unspecific stress response, only HAR pretreatment protects against shock-induced organ failure. Although the underlying mechanisms of positive HAR priming are not completely understood, the induction of HO-1 expression and the lack of nitric oxide scavenging through HAR may play an important role.

Inhibition of endothelin-1-mediated up-regulation of iNOS by bosentan ameliorates endotoxin-induced liver injury in cirrhosis.

ABSTRACT Endothelin-1 (ET-1) has been shown to regulate the expression of various genes in addition to its vasoconstrictor role in the liver. Elevated levels of ET-1 during cirrhosis play an important role in the observed microcirculatory dysfunction; however, its role as a transcription regulator remains unclear. This study aimed to determine the role of ET-1 in the hepatic gene expression of vasomediators after cirrhosis in response to LPS. Cirrhosis was induced by bile duct ligation (BDL) for 1 or 3 weeks in male Sprague-Dawley rats. Following 1 or 3 weeks of BDL or sham operation (sham), rats received an intravenous (i.v.) injection of bosentan, a dual-selective ETA/B receptor antagonist (30mg/kg bw) or saline, and an intraperitoneal (i.p.) injection of LPS (1 mg/kg bw). Plasma alanine aminotransferase (ALT) levels were significantly elevated in 1- and 3-week BDL animals. Six hours following LPS, the elevated ALT levels were markedly exacerbated in 3-week BDL animals, which were significantly ameliorated with bosentan treatment. LPS resulted in increased ET-1, inducible nitric oxide synthase (iNOS), and cyclooxygenase (COX)-2 mRNA expressions in both sham and BDL rats. Bosentan significantly inhibited the up-regulations of ET-1, iNOS, and COX-2 mRNA. Our data strongly suggest that ET-1 plays an important role in up-regulating the expression of iNOS, COX-2, and ET-1 itself in hepatic tissue following LPS challenge, which may contribute to the observed hepatocellular injury during endotoxemia in cirrhosis. Thus, due to significant increases in ET-1 levels during cirrhosis, ET-1 receptor blockade may prove to be of great therapeutic value in the treatment of cirrhotic patients exposed to secondary injuries such as endotoxemia.

Functional Link Between ETB Receptors and eNOS Maintain Tissue Oxygenation in the Normal Liver

Objective: Endothelins and their receptors play a crucial role in regulating liver microcirculation in pathophysiological conditions. The authors investigated the functional significance of the coupling of ETB receptors and eNOS in maintaining regional perfusion and tissue oxygenation in the normal liver.

Hepatic Redox Regulation of Transcription Factors Activator Protein-1 and Nuclear Factor-κB After Hemorrhagic Shock In Vivo

Ischemia and reperfusion result in a hepatocellular stress gene response, characterized by a zonal heterogeneity with pericentral hepatocytes being the primary target. In the present study, we assessed cell type-specific and zonal pattern of activation of redox-sensitive transcription factors nuclear factor-kappaB (NFkappaB) and activator protein-1 (AP-1) in a graded model of hemorrhage and their modulation by the antioxidants trolox and tempol. Hemorrhagic hypotension (35-40 mm Hg) up to 3 h without subsequent resuscitation led to an only moderate activation of NFkappaB and AP-1. In contrast, fluid resuscitation after 1 or 2 h of hemorrhage induced a profound activation of AP-1 within the first hour of reperfusion. Consistent with a regulation by oxygen free radicals, activation of AP-1 was substantially attenuated by antioxidants. The faint activation of NFkappaB with various intervals of hemorrhage was unaffected by antioxidants and did not exceed activation with sham operation. Immunohistochemistry for the AP-1 subunit c-Jun revealed a predominant expression in nuclei of pericentral and midzonal hepatocytes. These data suggest activation of AP-1 in hepatocytes most susceptible to injury and reprogramming of gene expression in low-flow ischemia. Whereas activation of NFkappaB is weak in this model and is not modulated by either reperfusion or antioxidants, regulation of AP-1 after hemorrhage and subsequent resuscitation seems to depend on oxygen free radical formation because it requires reperfusion and is inhibitable by antioxidants.