Hepatic release of endothelin-1 after warm ischemia. Reperfusion injury and its hemodynamic effect

Hepatic ischemia/reperfusion injury is diminished by atorvastatin in Wistar rats

BACKGROUND AND AIMS

Temporal occlusion of the hepatoduodenal ligament (HDL) is often used during liver surgeries in order to reduce blood loss, resulting in ischemia/reperfusion injury (I/R). The aim of the study was to investigate the effects of atorvastatin (ATOR) on hepatic I/R injury and on serum levels of tumor necrosis factor-alpha (TNF-α), endothelin-1 (ET-1), antithrombin III (ATIII) and intracellular adhesion molecule-1 (ICAM-1).

METHODS

Liver ischemia was induced in Wistar rats by clamping the HDL for 60 min, followed by either 60 or 180 min reperfusion. Rats received either vehicle or 10 mg/kg ATOR before hepatic I/R. Control group received sham surgery. Livers were examined for histological damage and serum AST, ALT, TNF-α, ET-1, ATIII and ICAM-1 concentrations were measured.

RESULTS

After I/R, AST and ALT were significantly elevated, ATIII levels were significantly depleted, both TNF-α and ICAM-1 levels increased and ET-1 was significantly elevated (at 180 min). ATOR pretreatment attenuated these alterations and diminished histological injury scores.

CONCLUSIONS

Our results show that ATOR protects the liver from I/R injury.

A novel mouse model of depletion of stellate cells clarifies their role in ischemia/reperfusion- and endotoxin-induced acute liver injury

BACKGROUND & AIMS

Hepatic stellate cells (HSCs) that express glial fibrillary acidic protein (GFAP) are located between the sinusoidal endothelial cells and hepatocytes. HSCs are activated during liver injury and cause hepatic fibrosis by producing excessive extracellular matrix. HSCs also produce many growth factors, chemokines and cytokines, and thus may play an important role in acute liver injury. However, this function has not been clarified due to unavailability of a model, in which HSCs are depleted from the normal liver.

METHODS

We treated mice expressing HSV-thymidine kinase under the GFAP promoter (GFAP-Tg) with 3 consecutive (3 days apart) CCl4 (0.16 μl/g; ip) injections to stimulate HSCs to enter the cell cycle and proliferate. This was followed by 10-day ganciclovir (40 μg/g/day; ip) treatment, which is expected to eliminate actively proliferating HSCs. Mice were then subjected to hepatic ischemia/reperfusion (I/R) or endotoxin treatment.

RESULTS

CCl4/ganciclovir treatment caused depletion of the majority of HSCs (about 64-72%), while the liver recovered from the initial CCl4-induced injury (confirmed by histology, serum ALT and neutrophil infiltration). The magnitude of hepatic injury due to I/R or endotoxemia (determined by histopathology and serum ALT) was lower in HSC-depleted mice. Their hepatic expression of TNF-α, neutrophil chemoattractant CXCL1 and endothelin-A receptor also was significantly lower than the control mice.

CONCLUSIONS

HSCs play an important role both in I/R- and endotoxin-induced acute hepatocyte injury, with TNF-α and endothelin-1 as important mediators of these effects.

Blockade of endothelin receptors with bosentan limits ischaemia/reperfusion-induced injury in rat ovaries

OBJECTIVE

To investigate the role of endothelin receptors in ovarian ischaemia/reperfusion (I/R) injury in rats using the endothelin receptor antagonist bosentan.

STUDY DESIGN

Group 1: sham operation; Group 2: sham operation and bosentan 60 mg/kg; Group 3: bilateral ovarian ischaemia; Group 4: 3-h period of ischaemia followed by 3h of reperfusion; Groups 5 and 6: bosentan 30 and 60 mg/kg, respectively, with bilateral ovarian ischaemia applied 30 min later; the bilateral ovaries were removed after 3h of ischaemia; Groups 7 and 8: 3h of bilateral ovarian ischaemia was applied, with bosentan 30 and 60 mg/kg, respectively, administered 2.5h after the induction of ischaemia; following the 3-h period of ischaemia, 3h of reperfusion was applied, after which the ovaries were removed.

RESULTS

Ischaemia and I/R decreased superoxide dismutase (SOD) activity and the level of glutathione (GSH) in ovarian tissue, but increased the level of malondialdehyde (MDA) significantly compared with the sham operation group. Bosentan 30 and 60 mg/kg before ischaemia and I/R decreased the MDA level and increased SOD activity and the GSH level in the experimental groups. The serum levels of the inflammatory cytokines interleukin (IL)-1β, IL-6 and tumour necrosis factor-α were also measured in the I/R injury model in rat ovaries. The levels of these cytokines were significantly higher in the ischaemia and I/R groups compared with the sham operation and sham operation plus bosentan groups. The histopathological findings also demonstrated the protective role of bosentan against I/R-induced injury in rat ovaries.

CONCLUSION

Administration of bosentan protects the ovaries against oxidative damage and I/R-induced injury.

Protective effects of branched-chain amino acids on hepatic ischemia-reperfusion-induced liver injury in rats: a direct attenuation of Kupffer cell activation

We determined whether there is a protective effect of branched-chain amino acid (BCAA) on hepatic ischemia-reperfusion (I/R)-induced acute liver injury. Wister rats were divided into the following four groups: simple laparotomy with vehicle; simple laparotomy with BCAA (1 g/kg body wt orally); I/R (30 min clamp) with vehicle; and I/R with BCAA. Serum liver function tests and the gene expression of adhesion molecules (intercellular adhesion molecule and vascular cell adhesion molecule) and vasoconstrictor-related genes (endothelin-1) in the liver were examined. In the in vivo study, portal venous pressure, leukocyte adhesion, and hepatic microcirculation were evaluated. Furthermore, Kupffer cells were isolated and cultured with various concentrations of BCAA in the presence or absence of lipopolysaccharide (LPS). Increased levels of liver function tests following I/R were significantly attenuated by BCAA treatment. The increased expression of adhesion molecules and endothelin-1 was also significantly attenuated by BCAA treatment. Moreover, increased portal venous pressure, enhanced leukocyte adhesion, and deteriorated hepatic microcirculation following I/R were all improved by BCAA treatment. In the experiment using isolated Kupffer cells, the expression of interleukin-6, interleukin-1β, and endothelin-1 in response to LPS stimulation was attenuated by BCAA in a dose-dependent fashion. These results indicate that perioperative oral administration of BCAA has excellent therapeutic potential to reduce I/R-induced liver injury. These beneficial effects may result from the direct attenuation of Kupffer cell activation under stressful conditions.

Decompression of the portal bed and twice-baseline portal inflow are necessary for the functional recovery of a "small-for-size" graft

BACKGROUND

In partial liver transplant, a reduction in the intrahepatic vascular bed produces a rise in the portal vein flow and the portal venous pressure gradient, leading to endothelial and, thereby, hepatocellular injury and death in a process known as "small-for-size" (SFS) syndrome.

OBJECTIVE

To demonstrate that a calibrated portocaval shunt prevents superfluous inflow in a porcine model of SFS transplant.

METHODS

Donor pigs (15-20 kg) underwent 70% hepatectomy. In 2 groups, a 6 mm (S6) (n = 6) or 12 mm (S12) (n = 6) Gore-Tex shunt was placed between the portal vein and infrahepatic inferior vena cava. In a third group, no portocaval shunt was placed (SFS) (n = 17). Grafts were stored for 5 hours at 4°C and then transplanted into recipients (30-35 kg).

RESULTS

Five-day survival was 29% in SFS, 100% in S6, and 0 in S12. Postreperfusion portal vein flow was 4-, 2-, and 1-times flow at baseline in SFS, S6, and S12, respectively. With respect to portal venous pressure gradient, both the 6- and 12-mm shunts effectively decompressed the portal bed. Aspartate aminotransferase and bilirubin rose and the Quick prothrombin time fell in all animals after reperfusion but improved significantly by day 5 in S6. Serum levels of endothelin-1 remained elevated in SFS and S12 but returned to baseline by 12 hours in S6: 2.76 (2.05-4.08) and 2.04 (1.97-2.12) versus 0.43 (0.26-0.50) pg/mL, respectively (P < 0.05 for both comparisons).

CONCLUSIONS

A calibrated portocaval shunt that maintains portal vein flow about twice its baseline value produces a favorable outcome after SFS liver transplantation, avoiding endothelial injury due to portal hyperperfusion or to hypoperfusion because of excess shunting.

Role of transcription factors in small intestinal ischemia-reperfusion injury and tolerance induced by ischemic preconditioning

BACKGROUND

Small intestinal ischemia-reperfusion (I/R) injury, a clinically important condition, induces severe organ damage. Ischemic preconditioning (IPC) produces tolerance to long-term I/R by inducing a short-term I/R. Herein, we have examined the reduction in the extent of injury by IPC.

METHODS

Small intestinal I/R injury was induced in rats by clamping the superior mesenteric artery (SMA) for 30 minutes followed by reperfusion for various 30 minutes. The IPC + I/R group underwent a short-term I/R (IPC) prior to long-term I/R. Nuclear factor-κB (NF-κB) activity was analyzed by an electrophoretic mobility shift assay and cytokine mRNA levels, by reverse transcription-polymerase chain reaction. Apoptosis-related genes were analyzed by Western blotting and immunohistochemistry, and apoptotic cells, by TUNEL staining.

RESULTS

The animals were subjected to 30 minutes of ischemia followed by 30 minutes of reperfusion. NF-κB activity increased in the I/R group and decreased in the IPC + I/R group. The IPC + I/R group showed decreased cytokine in mRNA levels. Expression of the proapoptotic gene caspase-3 was increased in the I/R and decreased in the IPC + I/R group. Expression of the antiapoptotic gene Bcl-xL was increased in the IPC + I/R group. The number of apoptotic cells was increased in the I/R and decreased in the IPC + I/R group.

CONCLUSION

Small intestinal I/R injury was reduced by IPC produced by clamping the SMA; thus, IPC may have potential clinical applications in the future.

Endothelin-1 aggravates hepatic ischemia/reperfusion injury during obstructive cholestasis in bile duct ligated mice

BACKGROUND

Cholestasis of the liver is known to be an important risk factor for surgical morbidity and mortality after major hepatectomy. However, the mechanism of liver injury in cholestatic liver is not fully understood. The goal of this study was to investigate the process of liver injury due to hepatic ischemia/reperfusion in obstructive cholestasis.

MATERIALS AND METHODS

Male C57BL/6 mice underwent common bile duct ligation and subsequently developed obstructive cholestasis. The mice were subjected to 90 min of partial hepatic ischemia followed by reperfusion.

RESULTS

The survival rate of the mice with cholestatic livers after hepatic ischemia/reperfusion was lower than that of the mice with normal livers. Biochemical and histological analyses showed that the cholestatic mice had a much higher degree of hepatocellular injury after reperfusion than the normal mice. Neutrophil accumulation after reperfusion was significantly decreased in the cholestatic livers; however, considerable microcirculatory disturbances were observed in cholestatic livers after reperfusion. Hepatic stellate cell activation and hepatic expression of endothelin-1 were evaluated by immunohistochemical staining in cholestatic livers after reperfusion. These observations were also associated with increased serum levels of endothelin-1.

CONCLUSIONS

Hepatic stellate cell activation and increased endothelin-1 production play a crucial role in hepatic ischemia/reperfusion injury in cholestatic liver.

Pharmacological strategies against cold ischemia reperfusion injury

IMPORTANCE OF THE FIELD

Good organ preservation is a determinant of graft outcome after revascularization. The necessity of increasing the quality of organ preservation, as well as of extending cold storage time, has made it necessary to consider the use of pharmacological additives.

AREAS COVERED IN THIS REVIEW

The complex physiopathology of cold-ischemia-reperfusion (I/R) injury--and in particular cell death, mitochondrial injury and endoplasmic reticulum stress--are reviewed. Basic principles of the formulation of the different preservation solutions are discussed.

WHAT THE READER WILL GAIN

Current strategies and new trends in static organ preservation using additives such as trimetazidine, polyethylene glycols, melatonin, trophic factors and endothelin antagonists in solution are presented and discussed. The benefits and mechanisms responsible for enhancing organ protection against I/R injury are also discussed. Graft preservation was substantially improved when additives were added to the preservation solutions.

TAKE HOME MESSAGE

Enrichment of preservation solutions by additives is clinically useful only for short periods. For longer periods of cold ischemia, the use of such additives becomes insufficient because graft function deteriorates as a result of ischemia. In such conditions, the preservation strategy should be changed by the use of machine perfusion in normothermic conditions.

Effect of pyrrolidine dithiocarbamate on hepatic vascular stress gene expression during ischemia and reperfusion

Pyrrolidine dithiocarbamate, an antioxidant and a potent inhibitor of nuclear factor-kappa B (NF-kappaB), is known to have protective effect against ischemia and reperfusion injury. This study examined the cytoprotective mechanism of pyrrolidine dithiocarbamate against the microcirculatory failure caused by hepatic ischemia and reperfusion. Rats were subjected to 60 min of hepatic ischemia followed by 5 h of reperfusion. Pyrrolidine dithiocarbamate (100 mg/kg) or the vehicle was administered intraperitoneally 24 h before ischemia. The level of serum aminotransferases and hepatic lipid peroxides significantly increased, and the glutathione contents fell in the ischemia/reperfusion group. Pyrrolidine dithiocarbamate prevented the increase in the level of serum enzymes and hepatic lipid peroxides, and the decrease in the glutathione contents. The NF-kappaB DNA-binding activity was inhibited by a pre-treatment with pyrrolidine dithiocarbamate. Ischemia and reperfusion significantly increased the mRNA expression of the endothelin-1 and endothelin ET(B) receptor, which was prevented by pyrrolidine dithiocarbamate. There were significant increases in the mRNA expressions of inducible nitric oxide synthase, tumor necrosis factor-alpha, and cyclooxygenase-2, in the livers after ischemia and reperfusion. These increases were attenuated by the pyrrolidine dithiocarbamate treatment. In a rat model of hepatic ischemia and reperfusion, our results suggest that the hepatoprotective actions of pyrrolidine dithiocarbamate may be mediated in part through the modulation of imbalanced expression of vascular stress genes.

Suprahepatic vena cava manipulative bleeding alleviates hepatic ischemia-reperfusion injury in rats

BACKGROUND

Little is known about time course and peak level of reactive oxygen species in suprahepatic vena cava after liver ischemia-reperfusion.

OBJECTIVE

To determine time course and peak level of reactive oxygen species in suprahepatic vena cava after liver ischemia-reperfusion. To focus on the effects of suprahepatic vena cava manipulative bleeding on the hepatic ischemia-reperfusion injury in rat model.

METHODS

In experiment Part I, blood was taken from suprahepatic vena cava and infrahepatic vena cava for malondialdehyde detection at different time points after reperfusion. Furthermore, we treated the experimental rats in Part II by suprahepatic vena cava manipulative bleeding or infrahepatic vena cava manipulative bleeding at 10 min after reperfusion.

RESULTS

In experiment Part I, malondialdehyde concentration in suprahepatic vena cava elevated obviously with time and peaked at 10 min after reperfusion. The numbers of accumulated polymorphonuclear neutrophils was significantly increased in ischemia-reperfusion group from 10 min after reperfusion, compared with sham-operated group. In Part II, 2% of body weight suprahepatic vena cava manipulative bleeding with blood transfusion at 10 min after reperfusion significantly decreased circulating malondialdehyde, tumour necrosis factor-alpha, endothelin-1, hyaluronic acid, alanine aminotransferase, aspartate aminotransferase levels and polymorphonuclear neutrophil infiltrations in the liver. The 7-day survival rate of this group was 68.75% (11/16) which was significantly higher than other groups.

CONCLUSIONS

We provided the first evidence that 2% of body weight suprahepatic vena cava manipulative bleeding with blood transfusion at 10 min after reperfusion significantly prevented liver ischemia-reperfusion injury.

Hepatic microcirculatory failure

Liver ischemia has been considered a frequent problem in medical practice, and can be associated to a number of surgical and clinical situations, such as massive hepatic resections, sepsis, liver trauma, circulatory shock and liver transplantation. After restoring blood flow, the liver is further subjected to an additional injury more severe than that induced by ischemia. On account of the complexity of mechanisms related to pathophysiology of ischemia and reperfusion (I/R) injury, this review deals with I/R effects on sinusoidal microcirculation, especially when steatosis is present. Alterations in hepatic microcirculation are pointed as a main factor to explain lower tolerance of fatty liver to ischemia-reperfusion insult. The employment of therapeutic strategies that interfere directly with vasoactive mediators (nitric oxide and endothelins) acting on the sinusoidal perfusion seem to be determinant for the protection of the liver parenchyma against I/R. These approaches could be very suitable to take advantage of marginal specimens as fatty livers, in which the microcirculatory disarrangements hamper its employment in liver transplantation.

Enhanced iNOS Gene Expression in the Steatotic Rat Liver after Normothermic Ischemia

BACKGROUND

Impaired hepatic microcirculation in the steatotic liver has been identified as a considerable factor for increased vulnerability after ischemia/reperfusion (I/R). Changes in regulation and synthesis of vasoactive mediators, such as nitric oxide (NO) and endothelin (ET-1), may result in functional impairment of postischemic sinusoidal perfusion. The aim of the current study was to assess the impact of I/R injury on postischemic gene expression of NO and ET-1 in steatotic livers.

MATERIALS AND METHODS

Male Sprague-Dawley rats with or without hepatic steatosis (induced by carbon tetrachloride treatment) were subjected to normothermic I/R injury. Steady-state mRNA levels were assessed using RT-PCR to study the expression of genes encoding ET-1, NO synthase (endothelial cell NO synthase and inducible NO synthase, iNOS). Immunohistochemistry was performed for detection of iNOS.

RESULTS

I/R injury was followed by increased iNOS gene expression (RT-PCR/immunohistochemistry) in animals with hepatic steatosis, predominately in hepatocytes with fatty degeneration. A mild increase in mRNA levels for ET-1 was found in steatotic rat livers. I/R induced a further increase in ET-1 gene expression in some but not all reperfused steatotic livers.

CONCLUSIONS

We show an enhanced gene expression of iNOS in postischemic steatotic rat livers. Hepatocytes with fatty degeneration appear to be the major source for NO generation. Furthermore, I/R may also induce ET-1 gene expression. Dysregulation of sinusoidal perfusion by NO and ET-1 is therefore likely to contribute to I/R injury of the steatotic liver.

Peroxisome proliferator-activated receptors ligands and ischemia-reperfusion injury

Peroxisome proliferator-activated receptors (PPARs) belong to a subfamily of transcription nuclear factors. Three isoforms of PPARs have been identified: alpha, beta/delta and gamma, encoded by different genes and distributed in various tissues. They play important roles in metabolic processes like regulation of glucose and lipid redistribution. They also have anti-atherogenic, anti-inflammatory as well as antihypertensive functions. There is good evidence that ligands of PPARs reduce tissue injury associated with ischemia and reperfusion. The potential utility of PPAR ligands in ischemia and reperfusion will be discussed in this review.

El preacondicionamiento isquémico del hígado: de las bases moleculares a la aplicación clínica

Ischemia-reperfusion injury is produced when an organ is deprived of blood flow (ischemia), which is then restored (reperfusion). In certain circumstances, this injury leads to irreversible organ damage. Several therapeutic strategies have been used to reduce the severity of this injury. One of these strategies is the application of brief and repetitive episodes of ischemia-reperfusion before prolonged ischemia-reperfusion (ischemic preconditioning). In the present article we review the molecular mechanisms through which ischemic preconditioning confers protection against ischemia-reperfusion injury. The application of ischemic preconditioning during liver surgery is discussed, both in normothermic situations such as liver resection and in situations of low temperature such as liver transplantation.

Role of endothelin-1 and cyclic nucleotides in ischemia/reperfusion-mediated microvascular leak

BACKGROUND

A consequence of ischemia/reperfusion (IR) is endothelial barrier dysfunction and intravascular volume loss. The purposes of our study are to explore the impact of: 1) cyclic guanosine monophosphate (cGMP) synthesis inhibition, 2) cyclic adenosine monophosphate (cAMP) synthesis inhibition, 3) treatment with endothelin-1, and 4) endothelin-1 (ET-1)-mediated cAMP changes on IR-induced fluid leak. We hypothesize that IR-mediated microvascular fluid leak results from increased cGMP activity and ET-1 decreases IR-induced fluid leak via cAMP.

METHODS

A micro-cannulation technique was used to determine fluid leak or hydraulic permeability (Lp) in rat mesenteric venules. Lp was measured during IR and after treatment with 1) cGMP synthesis inhibitor (LY83583,10 micromol/L) 2) cAMP synthesis inhibitor (2',5'dideoxyadenosine,10 micromol/L), 3) ET-1 (80 pM), and 4) cAMP synthesis inhibitor plus ET-1 (n=6 in each group; Lp represented as mean+/-standard error of the mean; units 10-cm/sec/cmH2O).

RESULTS

IR resulted in an increase in Lp (Lp=7.07+/-0.20) sevenfold above baseline (1.05+/-0.31) (p<or=0.001). Compared with IR alone, 1) pretreatment with cGMP synthesis inhibitor completely blocked IR-induced fluid leak (Lp=1.08+/-0.18) (p<or=0.001), 2) pretreatment with cAMP synthesis inhibitor attenuated fluid leak (Lp=3.92+/-0.20) (p<or=0.005), 3) treatment with ET-1 decreased fluid leak (Lp=5.38+/-0.28) (p<or=0.005), and 4) pretreatment with a cAMP inhibitor plus treatment with ET-1 reduced fluid leak nearly 50% compared with ET-1 alone (Lp=2.95+/-0.12) (p<or=0.005).

CONCLUSION

cGMP inhibition completely blocks fluid leak, pointing toward a central role as a mediator of IR-induced postcapillary venular leak. ET-1 mildly decreased leak. Furthermore, ET-1 may not exert its effects on microvascular fluid leak during IR via cAMP.

Advantage of ischemic preconditioning for hepatic resection in pigs

BACKGROUND

Ischemic preconditioning (IP) and intermittent inflow occlusion (IO) have provided beneficial outcomes in hepatic resection. However, comparison of these two procedures against warm hepatic ischemia-reperfusion injury has not been studied enough.

MATERIALS AND METHODS

Pigs that had undergone 65% hepatectomy were subjected to Control (120 min continuous ischemia, n = 6), IP (10 min ischemia and 10 min reperfusion, followed by 120 min continuous ischemia, n = 6), and IO (120 min ischemia in the form of eight successive periods of 15 min ischemia and 5 min reperfusion, n = 6). We evaluated hepatocyte injury by aspartate aminotransferase, lactate dehydrogenase and hepaplastin test, hepatic microcirculation by hepatic tissue blood flow (HTBF) and endothelin (ET)-1, inflammatory response by tumor necrosis factor-alpha (TNF-alpha), and histopathology after reperfusion.

RESULTS

IP prevented hepatocyte injury, HTBF disturbance, and hepatocyte necrosis in histopathology as well as IO. These two groups showed significantly better outcomes than Control. IP produced significantly less ET-1 and TNF-alpha than IO.

CONCLUSIONS

IP ameliorated hepatic warm ischemia-reperfusion injury. Furthermore, IP gained more advantages in preventing chemokine production such as ET-1 and inflammatory response over IO. IP could take the place of IO for hepatectomy.

Attenuation of proinflammatory gene expression and microcirculatory disturbances by endothelin A receptor blockade after orthotopic liver transplantation in pigs

BACKGROUND

Endothelin-1 (ET-1), a very potent mediator of vasoconstriction, leads to microcirculatory disturbances and release of proinflammatory cytokines under pathophysiologic conditions. Our aim was to evaluate the effect of a selective ET(A)-receptor antagonist (ET(A)-RA) on cold ischemia/reperfusion (I/R) injury in a pig model.

METHODS

Twenty pigs revealed orthotopic liver transplantation. The animals were randomized into 2 groups: control pigs received isotonic saline; the treated group received the selective ET(A)-RA BSF 208075 at the beginning of reperfusion. On postoperative days 4 and 7, animals were re-laparotomized to obtain tissue specimens. Liver tissue samples were collected and quantitative mRNA expression for prepro-ET-1, ET(A) receptor, pro-IL-1beta, pro-IL-6, pro-TNF-alpha, and endothelial nitric oxide synthase was analyzed using the TaqMan system. Additionally, immunohistochemical analysis for ET-1 was performed. Hepatic microcirculation was evaluated by laser Doppler flow measurement and partial pressure of oxygen and carbon dioxide measurements with the Paratrend sensor. Postischemic liver damage was monitored by measurement of liver enzymes and by histologic analysis using a semiquantitative scoring classification.

RESULTS

Treatment with the ET(A)-RA significantly reduced the severity of I/R injury evidenced by lower serum AST, ALT and GLDH. Analysis of partial pressure of oxygen and blood flow revealed a significant improvement of capillary perfusion and blood flow in the treated group and was associated with a relevant reduction of tissue injury. One hour after reperfusion, quantitative RT-PCR revealed significantly lower expression of prepro-ET-1, ET(A) receptor, endothelial nitric oxide synthase, pro-TNF-alpha, pro-IL-1beta and pro-IL-6 in the therapy group. Immunohistochemical analysis demonstrated significantly reduced ET-1 immunostaining after therapy. Histologic investigation suggested less tissue damage in treated animals.

CONCLUSIONS

Treatment with the selective ET(A)-RA BSF 208075 has protective effects on microcirculation after liver transplantation. ET(A)-RA not only affects the expression of vasoactive genes, but also decreases gene expression of proinflammatory cytokines such as TNF-alpha, IL-1beta and IL-6.

Endothelin activation and postoperative renal failure after human liver transplantation

Renal failure is an established risk factor for impaired patient outcome after orthotopic liver transplantation (OLT). As the endothelin pathway is known to be involved in the development of acute renal failure (ARF), we designed a study to clarify its role in ARF following OLT. Twenty consecutive patients with intact kidney function scheduled for their first OLT were prospectively studied. Plasma big endothelin-1 (ET-1) levels were measured before surgery, after graft reperfusion, and on the first and second postoperative day. According to postoperative glomerular filtration rate (GFR), patients were assigned to the acute renal dysfunction group (ARDF) and the non-ARDF group. Each patient's GFR was estimated according to the 4-variable formula used in the modification of diet in renal disease before surgery, daily within the first postoperative week, and at 1, 3, 12, and 24 months after surgery. Postoperative mean big ET-1 levels correlated significantly with the maximum percent decrease of GFR within 3 days after OLT (P < 0.01). The proportion of patients who developed ARDF was significantly correlated to mean postoperative big ET-1 quartiles (P < 0.01). In the ARDF group, the percent decrease of GFR within 24 months was significantly higher (P < 0.05) as compared to the non-ARDF group. In conclusion, patients who develop ARDF immediately after OLT do not fully recover to baseline regarding long-term kidney function. Short-term GFR was significantly correlated with postoperative big ET-1 plasma levels, suggesting renal dysfunction is mediated by the activated endothelin system.

Current Understanding of Gender Dimorphism in Hepatic Pathophysiology1

Studies have shown gender dimorphic response of the liver for various hepatic stresses including ischemia/reperfusion, hemorrhagic shock-resuscitation, hepatectomy, liver cirrhosis, endotoxemia, and chronic alcoholic consumption. The mechanisms responsible for the gender dimorphic response include differences in pro-inflammatory cytokine release, production of reactive oxygen species, and alteration in hepatic vasoregulatory action. These effects were shown to be modulated by circulating sex steroid levels. In this regard, modulation of sex steroid levels by agents/drugs has been proposed as a therapeutic option for preventing hepatic damage in various hepatic stress models. Further elucidation of precise mechanisms responsible for the gender-related differences in the hepatic pathophysiology is essential for the potential clinical application of sex hormone modulation therapy. In this article, current progress in our understanding the gender difference in the hepatic pathophysiology under the condition of hepatic stress is reviewed and discussed.

L-carnitine could not improve hepatic warm ischemia-reperfusion injury despite ameliorated blood flow

BACKGROUND

Carnitine is applied to ameliorate ischemia-reperfusion (I/R) injury of several organs. However, application to hepatic I/R injury is not frequently reported. The aim of this study was to elucidate the effect of exogenous carnitine administration to ameliorate the warm hepatic I/R injury.

MATERIALS AND METHODS

Male Wistar rats were divided into two groups, a carnitine group (Car);100 mg/kg of l-carnitine administration and a control group (C); vehicle administration. Thirty minutes after administration, the left hepatic lobes were given 60-min ischemia and then reperfused. Plasma alanine aminotransferase (ALT), aspartate aminotransferase (AST), glutamate dehydrogenase (GLDH), tumor necrosis factor (TNF)-alpha, and lipoperoxides (LPO) were measured. Hepatic adenosine triphosphate (ATP) concentration was also measured. The hepatic blood flow was estimated using a Laser Doppler. The presence of apoptosis in the livers was evaluated by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining.

RESULTS

In group Car, the blood flow of the left hepatic lobes was better recovered during the reperfusion period than in group C (P < 0.0001). Plasma levels of ALT, AST, GLDH, and TNF-alpha at 1 h after reperfusion were not significantly different between the groups. Although there were no statistical significances, ALT, AST, and TNF-alpha levels in group Car at 24 h after reperfusion tended to be higher than in group C. Plasma LPO levels were not different between the two groups. Also hepatic ATP concentration was not different between the two groups. TUNEL positive liver cells were visible only in group Car at 24 h after reperfusion, but not in the controls.

CONCLUSIONS

Although carnitine administration improved the hepatic blood flow during the reperfusion period, we could not demonstrate a protective effect to the hepatic warm I/R injury.

Improvement of postischemic hepatic microcirculation after endothelinA receptor blockade--endothelin antagonism influences platelet-endothelium interactions

Endothelin (ET) contributes to disturbances of hepatic microcirculation after ischemia/reperfusion (I/R) by causing vasoconstriction and enhancing leukocyte- and platelet-endothelium interactions. The aim of this study was to investigate a possible protective role of a selective endothelin(A) receptor antagonist (ET(A)-RA) in this setting. In a rat model, warm ischemia of the left lateral liver lobe was induced for 90 minutes under intraperitoneal anesthesia with xylazine and ketamine. Groups of rats consisted of sham-operated (SO, n=14), untreated ischemia (n=14), and treatment with BSF208075 (5 mg/kg body weight IV, n=14). The effect of the ET(A)-RA on I/R was assessed by in vivo microscopy 20 to 90 minutes after reperfusion; by measurement of local tissue Po(2), serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), and glutathione S-transferase alpha levels, and by histologic investigation. In the untreated group, sinusoidal constriction to 69.4+/-6.7% of diameters of SO rats was observed, leading to a significant decrease in perfusion rate (74.3+/-2.1% of SO) and liver tissue Po(2) (43.5+/-3.2% of SO) (P < 0.05). In addition, we found an increased percentage of stagnant leukocytes (142.9+/-11.9%) and platelets (450.1+/-62.3%) in sinusoids and in postsinusoidal venules (P < 0.05). Hepatocellular damage (AST and ALT increase to 1330+/-157 U/L and 750+/-125 U/L respectively; previously, 27.1+/-3.5 U/L and 28.5+/-3.6 U/L) was detected 6 hours after reperfusion (P < 0.05). Administration of the ET(A)-RA before reperfusion significantly reduced I/R injury. Sinusoidal diameters were maintained (108.5+/-6.6%), and perfusion rate (93.1+/-1.8%) and tissue Po(2) (95.3+/-5.7%) were significantly increased (P < 0.05). According to reduced leukocyte-endothelium interactions after therapy, both platelet rolling and adhesion were significantly reduced (P < 0.05). The number of stagnant platelets in sinusoids was 199.5+/-12.3% of 50 (P < 0.05). After treatment, hepatocellular damage was decreased (AST and ALT levels after 6 hours of reperfusion: 513+/-106 U/L and 309+/-84 U/L, respectively; P < 0.05), and histologic changes were reduced in the long term. Our results provide evidence that the new therapeutic approach with an ET(A)-RA is effective in reducing hepatic I/R injury. In addition to reduced leukocyte-endothelium interactions, the number of stagnant and rolling platelets in sinusoids and venules was significantly reduced. The reduction in microcirculatory damages is responsible for better organ outcome.

Effects of ETAReceptor Antagonism on Proinflammatory Gene Expression and Microcirculation Following Hepatic Ischemia/Reperfusion

BACKGROUND

The objective of this study was to investigate the effect of a specific endothelin(A) receptor antagonist (ET(A)-RA) on mRNA expression of genes encoding vasoactive mediators and proinflammatory cytokines and on the microhemodynamics (assessed by measurement of laser Doppler flow and tissue blood gases) following complete vascular exclusion of the porcine liver.

STUDY DESIGN

Sixteen adult German landrace pigs were subjected to 120 min of warm hepatic ischemia by total vascular exclusion. To avoid portal congestion, a passive porto-femoro/jugular bypass was implanted. The animals were divided into 2 groups: the control group received saline solution and the therapy group was given the selective ET(A)-RA BSF 208075. Hepatic microcirculation was evaluated by p(O(2)) and p(CO(2)) measurement with the Paratrend sensor and by laser Doppler flow measurement. Liver tissue samples were collected 1 h after reperfusion and quantitative mRNA expression for prepro-ET-1, pro-IL-1beta, pro-IL-6, pro-TNF-alpha, eNOS was analyzed using the TaqMan system. Additionally, immunohistochemical analysis using a semiquantitative score for ET-1 was performed. Postischemic liver damage was monitored by measurement of liver enzymes and assessed by histological analysis using a semiquantitative scoring classification.

RESULTS

Partial oxygen pressure in the hepatic tissue and laser Doppler flow were significantly improved in the therapy group. One hour after reperfusion, quantitative RT-PCR revealed significantly lower expression of prepro-ET-1, eNOS, pro-TNF-alpha, and pro-IL-6 in the therapy group compared to controls. Immunohistochemical analysis demonstrated significantly reduced ET-1 immunostaining after therapy. Furthermore, blockade of ET(A) receptors prevents tissue damage.

CONCLUSIONS

Treatment with the selective ET(A)-RA BSF 208075 has protective effects on microcirculation after 120 min liver ischemia and reperfusion. The authors were able to show that ET(A)-RA not only affects the expression of vasoactive genes, but also decreases gene expression of proinflammatory cytokines such as TNF-alpha and IL-6.

Assessment of hepatic ischemia-reperfusion injury by simultaneous measurement of tissue pO2, pCO2, and pH

INTRODUCTION

The objective of this study was to determine whether the simultaneous measurement of tissue pH, pCO(2), and pO(2) with a multiple-parameter fiberoptic sensor (Paratrend 7) can be used for continuous monitoring of hepatic microperfusion in a pig model of hepatic ischemia given endothelin(A) receptor antagonist (ET(A)-RA) or isotonic saline.

METHODS

Fourteen anesthetized swine were subjected to 2 h of hepatic vascular exclusion. The animals were randomized into two groups: control group (n = 7, saline solution iv) and therapy group (n = 7, ET(A)-RA). For evaluation of ischemia-reperfusion injury, the data of the multiple-parameter sensor (pO(2para), pCO(2para), and pH(para)) were compared with partial oxygen pressure in tissue (p(ti)O(2)), laser Doppler flow, and systemic hemodynamic, metabolic data, and time course of transaminases.

RESULTS

In the control group 30 and 60 min after reperfusion, the following values were measured: p(ti)O(2): 34.0 +/- 8.6 / 36.3 +/- 7.0 mm Hg (P < 0.05 vs. preop.: 49.8 +/- 12.1 mm Hg), laser Doppler area: 133.3 +/- 23.2 / 156.4 +/- 15.4 (P < 0.05 vs. preop.: 215.9 +/- 14.8). Animals in the therapy group revealed significantly improved values (p(ti)O(2): 54.0 +/- 8.6 / 58.1 +/- 7.8 mm Hg, laser Doppler: 210.2 +/- 38.5 / 225.2 +/- 21.3; P < 0.05). Using the Paratrend, also an improvement in the therapy group was seen 30 and 60 min after reperfusion. The values showed a strong correlation with p(ti)O(2) (r = 0.895; P < 0.05) and laser Doppler flow (r = 0.807; P < 0.05). In the treatment group, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and glutamate dehydrogenase (GLDH) were reduced 6 and 18 h after reperfusion, respectively, indicating hepatoprotection by the therapy (P < 0.05 vs. control).

CONCLUSIONS

The Paratrend sensor offers the opportunity to study postischemic organ hemodynamics through the simultaneous measurement of interstitial pH, pCO(2), and pO(2) in a small tissue region. This method offers a prognostic tool for the study of the effects of experimental vasoactive therapy on liver microcirculation and perspectives for continuous monitoring of human liver microperfusion after liver surgery and trauma.

REMOTE TRAUMA SENSITIZES HEPATIC MICROCIRCULATION TO ENDOTHELIN VIA CAVEOLIN INHIBITION OF eNOS ACTIVITY

This study addresses the microvascular mechanisms by which a remote, mild stress such as blunt trauma sensitizes the liver to injury. Rats received closed femur fracture (FFx), and 24 h later livers were isolated and perfused at a similar starting flow rate for assessment of vascular response to endothelin-1 (ET-1). Sinusoidal volumetric flow (QS), red blood cell velocity (VRBC), and sinusoidal diameter (Ds) were determined by intravital microscopy. Baseline portal resistance in livers from FFx rats was not changed. The FFx group showed a lower baseline VRBC (322.9 +/- 26.4 and 207.3 +/- 17.2 microm/s in sham and FFx,) and QS (28.4 +/- 4.2 and 17.6 +/- 2.1 pL/s in sham and FFx, P < 0.05). ET-1 caused a decrease in the VRBC in sham but no change after FFx. In contrast, Ds was unchanged by ET-1 in sham but decreased in FFx (10.3 +/- 0.4 to 10.7 +/- 0.5 vs. 10.6 +/- 0.4 to 9.0 +/- 0.4 microm at 10 min in sham and FFx groups, P < 0.05). The overall result of these changes was a greater decrease in sinusoidal flow in FFx compared with sham. There was no significant change in mRNA for ET-1, endothelin A (ETA) receptor, or iNOS (inducible nitric oxide synthase) in FFx compared with sham. However, endothelin B (ETB) receptor mRNA and eNOS (endothelial nitric oxide synthase) mRNA were increased in the FFx group (ETB, 54.81 +/- 8.08 in sham vs. 83.28 +/- 8.19 in FFx; eNOS, 56.11 +/- 2.53 in sham vs. 83.31 +/- 5.51 in FFx; P < 0.05) while the levels of these proteins remained unchanged. Caveolin-1 (cav-1) protein levels were elevated in FFx, and coimmunoprecipitation with both ETB and eNOS showed increased associations with these proteins, suggesting a possible inactivation of eNOS. The eNOS activity was also blunted in FFx animals in the presence of increased cav-1 expression. Taken together, these results demonstrate that remote trauma sensitizes the liver to the sinusoidal constrictor effect of ET-1. We propose that this hyperresponsiveness occurs as a result of uncoupling of the ETB receptor from eNOS activity mediated by interaction of eNOS and possibly the ETB receptor with increased caveolin-1. This vascular sensitization that occurs after FFx may contribute to the exacerbation of injury during subsequent stresses.

Role of kupffer cells in the vasoregulatory gene expression during hepatic ischemia/reperfusion

Hepatic microcirculatory failure is a major component of reperfusion injury in the liver. Recent data provided some evidence that endothelium-derived vasoconstrictors and vasodilators may be functionally important to the control of the total hepatic blood flow under these conditions of circulatory failure. Since Kupffer cells provide signals that regulate the hepatic response in ischemia/reperfusion (I/R), the aim of this study was to investigate the role of Kupffer cells in the I/R-induced imbalance of vasoregulatory gene expression. Rats were subjected to 60 min hepatic ischemia, followed by 5 h of reperfusion. The Kupffer cells were inactivated by gadolinium chloride (GdCl3, 7.5 mg/kg body weight, intravenously) 1 day prior to ischemia. Liver samples were obtained 5 hrs after reperfusion for RT-PCR analysis of the mRNA for genes of interest: endothelin-1 (ET-1), its receptors ETA and ETB, endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS) and heme oxygenase-1 (HO-1). ET-1 mRNA expression was increased by I/R. mRNA levels for ETA receptors showed no change, whereas ETB receptor transcripts increased in the I/R group. The increases in ET-1 and ETB mRNA were not prevented by the GdCl3 pretreatment. The mRNA levels for iNOS and eNOS significantly increased within the I/R group with no significant difference between the I/R group and the GdCl3-treated I/R group. HO-1 mRNA expression significantly increased in the I/R group and this increase was attenuated by GdCl3. In conclusion, we have demonstrated that an imbalance in hepatic vasoregulatory gene expression occurs during I/R. Our findings suggest that the activation of Kupffer cells is not required for I/R-induced hepatic microvascular dysfunction.

Endothelin-A receptor antagonist reduces microcirculatory disturbances and transplant dysfunction after partial liver transplantation

Endothelin-1 can induce microcirculatory disorders by mediating sinusoidal vasoconstriction, lowering the perfusion rate and promoting leukocyte adhesion, all of which may play a role in the pathogenesis of the damage sustained by partial liver transplants. In this pilot study, we investigated a selective endothelin-A receptor antagonist (Darusentan; Knoll GmbH, Ludwigshafen, Germany) for its potential influence on the microcirculation in the setting of partial liver transplantation. One hundred and forty isogeneic Lewis rats were divided into four groups: 1. partial liver transplantation (30% of the initial liver volume); 2. partial liver transplantation treated with Darusentan (1 mg/kg bodyweight intravenously) immediately before reperfusion; 3. full-size liver transplantation; and 4. sham operation. Subsequently, the liver microcirculation was evaluated by intravital microscopy, and survival, liver function, and morphology were followed up to the fourteenth day. Compared with full-size transplanted animals, rats subjected to partial liver transplantation without Darusentan (group I) displayed severe microcirculatory lesions characterized by a significantly decreased perfusion rate, increased leukocyte velocity, and increased leukocyte adhesion. Disintegration of endothelium and increased recruitment of Kupffer cells were frequent morphologic findings. The Darusentan-treated group II showed improved parameters of microcirculatory function and morphology as well as improved liver function. Microcirculatory disturbances play a key role in the pathogenesis of partial liver transplant dysfunction. Treatment with selective endothelin-A receptor antagonists represent a new therapeutic approach to improve the function of partial liver transplants by reducing microcirculatory lesions and their sequelae affecting sinusoidal endothelium and hepatocytes.

Impact of endothelin-1 on microcirculatory disturbance after partial hepatectomy under ischemia/reperfusion in thioacetamide-induced cirrhotic rats

BACKGROUND

Endothelin (ET)-1 contributes to hepatic ischemia and reperfusion (HIR) injury in normal liver. This study was conducted to clarify the role of ET-1 in HIR injury in cirrhotic state.

MATERIALS AND METHODS

Using thioacetamide-induced cirrhotic rats with spontaneous portosystemic shunt, we determined the changes in plasma aspartate aminotransferase (AST) levels, plasma and hepatic ET-1 values, 7-day survival rates, and hepatic oxygen saturation (SO(2)) by time-resolved spectroscopy as an indicator of hepatic microcirculation under intermittent or continuous total hepatic ischemia with subsequent partial hepatectomy.

RESULTS

Hepatic ET-1 levels in cirrhotic rats were significantly higher than those in noncirrhotic rats. Plasma and hepatic ET-1 levels at 1, 3 and 6 h of reperfusion after intermittent hepatic ischemia were significantly lower than those after continuous hepatic ischemia. In cirrhotic animals subjected to intermittent hepatic ischemia, the elevation of plasma AST levels at 1, 3 and 6 h of reperfusion and the decline in hepatic SO(2) at the end of 60-min hepatic ischemia and after reperfusion were significantly suppressed when compared with those subjected to continuous hepatic ischemia. Pretreatment with a nonselective endothelin receptor antagonist in continuous hepatic ischemia significantly ameliorated plasma AST levels and hepatic SO(2) values with less hepatic sinusoidal congestion, resulting in an improvement in the 7-day survival rate.

CONCLUSIONS

Continuous hepatic ischemia in the cirrhotic liver has disadvantages relating to microcirculatory derangement with more ET-1 production in partial hepatectomy. In liver surgery, pharmacological regulation of ET-1 production may lead to attenuation of reperfusion injuries for ischemically damaged cirrhotic liver.

Endothelin A receptor blockade reduces hepatic ischemia/reperfusion injury after warm ischemia in a pig model

It is well established that endothelin-1 (ET-1) is a very potent mediator of vasoconstriction that leads to microcirculatory disturbances. The aim of the study was to evaluate the effect of a selective endothelin A receptor antagonist on severe ischemia/reperfusion injury in a pig model. Fourteen pigs were subjected to 120 minutes of complete vascular exclusion of the liver with a passive bypass. The animals were randomized into two groups: a control group, which was given isotonic saline solution, and a therapy group, which received the selective endothelin A receptor antagonist BSF 208075 at the beginning of reperfusion. On postoperative days 4 and 7, animals were relaparotomized to obtain tissue specimens. Blood monitoring included aspartate aminotransferase (AST), alanine aminotransferase (ALT), glutamate dehydrogenase (GLDH), alkaline phosphatase, and ET-1. Partial oxygen tension (p(ti)O(2)) was measured by a Clarke-type electrode and blood flow by laser Doppler. A semiquantitative scoring index was used for assessment of histologic injury and for immunohistochemical analysis of ET-1. Treatment with the endothelin A receptor antagonist significantly reduced the severity of the ischemia/reperfusion injury, as evidenced by lower levels of AST, ALT, and GLDH. The dramatic increase in plasma ET-1 in the therapy group is clear evidence of effective receptor blockade. Analysis of p(ti)O(2) and blood flow revealed a significant improvement in capillary perfusion and blood flow in the treated group and was associated with relevant reduction of tissue injury. In summary, in the control group we observed serious microcirculatory disturbances and severe histologic damage in the liver after reperfusion. Treatment with a selective endothelin A receptor antagonist attenuated the ischemia/reperfusion injury in a porcine model of severe ischemia/reperfusion, as demonstrated by improved microcirculation, a reduction in histologic damage, and an decrease in liver enzymes.

Regulation of pro-inflammatory and anti-inflammatory cytokine responses by Kupffer cells in endotoxin-enhanced reperfusion injury after total hepatic ischemia

The effects of Kupffer cells on cytokine responses in endotoxin-enhanced reperfusion injury after total hepatic ischemia were investigated in this study. Male rats pretreated with either normal saline solution (NS group) or gadolinium chloride (GdCl(3)) to inhibit Kupffer cell function (GC group) were subjected to 60 min of hepatic ischemia. These animals received either normal saline solution or sublethal doses of endotoxin (1 mg/kg) at reperfusion. In the NS group, endotoxin administration induced an enhanced tumor necrosis factor-alpha (TNF-alpha) and interleukin-10 production 1 h after reperfusion with a subsequent peak of macrophage inflammatory protein-2 (MIP-2) levels, which resulted in a 7-day survival rate of 30%. Despite endotoxin administration, GdCl(3) pretreatment significantly suppressed TNF-alpha and increased interleukin-10 production 1 h after reperfusion, which led to a decline in MIP-2 production and amelioration of functional and structural liver damage with a 7-day survival rate of 80%. Augmented pro-inflammatory and anti-inflammatory cytokine responses by Kupffer cells were associated with endotoxin-enhanced reperfusion injury after hepatic ischemia. Kupffer cell blockade has a potential to attenuate the insult via modulation of cytokine responses.

Effects of the intermittent Pringle manoeuvre on hepatic gene expression and ultrastructure in a randomized clinical study

BACKGROUND

The intermittent Pringle manoeuvre during hepatectomy results in a better clinical outcome when the accumulated ischaemia time is less than 120 min. The aim of this study was to investigate hepatic gene expression related to microcirculatory modulation and ultrastructural changes in patients having the intermittent Pringle manoeuvre.

METHODS

Forty patients who underwent hepatectomy for liver tumours were randomly assigned to liver transection with intermittent Pringle manoeuvre (Pringle group, n = 20) or without the manoeuvre (control group, n = 20). The clinical data and hepatic expression of endothelin (ET) 1 and endothelial nitric oxide synthase (eNOS) combined with liver ultrastructure were compared.

RESULTS

The Pringle manoeuvre resulted in less blood loss (8.9 versus 12.4 ml/cm(2); P = 0.034), a shorter transection time (2.7 versus 4.1 min/cm(2); P = 0.015) and a lower serum bilirubin level on postoperative day 2 (26 versus 35 microm/l; P = 0.04). The hepatic messenger RNA content of ET-1 decreased by 38 per cent of the basal level in the Pringle group, whereas it increased by 28 per cent in the control group (P = 0.026). More patients in the control group showed swelling of mitochondria in hepatocytes and disruption of sinusoidal lining cells (12 of 20 patients versus three of 20 in the Pringle group; P = 0.008).

CONCLUSION

The intermittent Pringle manoeuvre results in less disturbance of the hepatic microcirculation and better preservation of liver sinusoids after hepatectomy.

Molecular mechanisms of hepatic ischemia-reperfusion injury and preconditioning

Ischemia-reperfusion injury is, at least in part, responsible for the morbidity associated with liver surgery under total vascular exclusion or after liver transplantation. The pathophysiology of hepatic ischemia-reperfusion includes a number of mechanisms that contribute to various degrees in the overall injury. Some of the topics discussed in this review include cellular mechanisms of injury, formation of pro- and anti-inflammatory mediators, expression of adhesion molecules, and the role of oxidant stress during the inflammatory response. Furthermore, the roles of nitric oxide in preventing microcirculatory disturbances and as a substrate for peroxynitrite formation are reviewed. In addition, emerging mechanisms of protection by ischemic preconditioning are discussed. On the basis of current knowledge, preconditioning or pharmacological interventions that mimic these effects have the greatest potential to improve clinical outcome in liver surgery involving ischemic stress and reperfusion.

Microvascular dysfunction induced by reperfusion injury and protective effect of ischemic preconditioning

Hepatic ischemia/reperfusion injury has immediate and deleterious effects on the outcome of patients after liver surgery. The precise mechanisms leading to the damage have not been completely elucidated. However, there is substantial evidence that the generation of oxygen free radicals and disturbances of the hepatic microcirculation are involved in this clinical syndrome. Microcirculatory dysfunction of the liver seems to be mediated by sinusoidal endothelial cell damage and by the imbalance of vasoconstrictor and vasodilator molecules, such as endothelin (ET), reactive oxygen species (ROS), and nitric oxide (NO). This may lead to no-reflow phenomenon with release of proinflammatory cytokines, sinusoidal plugging of neutrophils, oxidative stress, and as an ultimate consequence, hypoxic cell injury and parenchymal failure. An inducible potent endogenous mechanism against ischemia/reperfusion injury has been termed ischemic preconditioning. It has been suggested that preconditioning could inhibit the effects of different mediators involved in the microcirculatory dysfunction, including endothelin, tumor necrosis factor-alpha, and oxygen free radicals. In this review, we address the mechanisms of liver microcirculatory dysfunction and how ischemic preconditioning could help to provide new surgical and/or pharmacological strategies to protect the liver against reperfusion damage.

Endothelin receptor A blockade ameliorates hypothermic ischemia-reperfusion-related microhemodynamic disturbances during liver transplantation in the rat

BACKGROUND

The objective of this study was to investigate the effect of graft treatment with specific endothelin receptor antagonists (ET(A) and ET(B)) on the microhemodynamic disturbances which occur following ischemia/reperfusion injury during orthotopic liver transplantation (OLT) in the rat.

MATERIALS AND METHODS

OLT was performed in male Sprague-Dawley rats. An ET(A) receptor antagonist (BQ-610; 0.3 mg/kg) or ET(B) receptor antagonist IRL-1038 (20 nmol/kg) was administered intraportally into liver grafts in vitro at the beginning of 2- and 6-h cold storage (4 degrees C) using physiological saline. Sham-operated animals served as controls (Cont). Seven groups were studied: Cont; vehicle-2 h (saline treated); ET(B) antagonist-2 h; ET(A) antagonist-2 h; vehicle-6 h; ET(A) antagonist-6 h; and ET(B) antagonist-6 h. At 1 h after graft implantation, the liver microcirculation was investigated by intravital fluorescence microscopy.

RESULTS

In vehicle-treated livers, the hepatic microcirculation was markedly impaired compared with the Cont as manifested by a reduced lobular perfusion index, increased incidence of sinusoidal nonperfusion, elevated leukocyte adhesion in sinusoids and terminal hepatic venules, and increased hepatic venous resistance (23-fold; 6-h group). In addition, plasma liver enzymes were significantly elevated in the vehicle treated groups. Alterations to all these parameters were markedly reduced in the ET(A) receptor antagonist-treated liver grafts although there was still evidence of hepatic injury. The ET(B) receptor antagonist had little effect on the I/R-induced changes to the hepatic microcirculation.

CONCLUSIONS

Our results indicate that the ET(A) antagonism ameliorates hypothermic I/R-related microhemodynamic disturbances during OLT in the rat, suggesting that application of an ET(A) antagonist to liver grafts may have therapeutic potential in human liver transplantation.

Microcirculatory failure after rat liver transplantation is related to Kupffer cell-derived oxidant stress but not involved in early graft dysfunction

BACKGROUND

Microcirculatory failure, activation of Kupffer cells (KC), and the formation of reactive oxygen species (ROS) are considered pivotal mechanisms of reperfusion injury after orthotopic liver transplantation. However, the sequence of these events and their impact on early graft function remain controversial. We therefore investigated whether KC induce microcirculatory disturbances through ROS release and whether microcirculatory failure contributes to early graft function after liver transplantation.

METHODS

Donor livers of Lewis rats were pretreated either with saline or with gadolinium chloride (GdCl3), an inhibitor of KC function (n=8 each). Syngeneic OLT was performed after 24 hr of hypothermic preservation in University of Wisconsin solution.

RESULTS

Intravital microscopy revealed significantly higher sinusoidal perfusion rates in GdCl3-treated allografts (92+/-1.1% vs. 75.7+/-0.8%; P<0.001) compared with untreated controls; permanent leukocyte sticking in sinusoids (23.5+/-2.1 vs. 62.6+/-3.3 cells/lobule, P<0.001) and in postsinusoidal venules (153.1+/-10.4 vs. 446.6+/-46.4 cells/mm(2), P<0.001) were markedly attenuated in GdCl3-treated allografts. Improvement of microcirculatory parameters in GdCl3-treated livers was correlated with a significant reduction of plasma glutathione disulfide formation by KC-derived ROS (0.96+/-0.1 microM vs. 1.79+/-0.5 microM; P<0.01). Despite these beneficial effects, GdCl3-pretreatment failed to improve postischemic alanine aminotransferase release and bile flow.

CONCLUSIONS

Microcirculatory failure after liver transplantation is related to KC-derived oxidant stress but not involved in early graft dysfunction.

Altered endothelin receptor expression in prehepatic portal hypertension predisposes the liver to microcirculatory dysfunction in rats

BACKGROUND/AIMS

Endothelin (ET) is one of the most active vascular regulators in the liver. It is unknown how partial portal vein ligation (PPVL) induced prehepatic portal hypertension influences the response of the liver to ET and its agonists. Therefore, this study was conducted to determine the expression of ET receptors and its functional significance after PPVL.

METHODS

Competitive receptor binding study and semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) were performed using liver homogenates after 2 weeks of PPVL or sham operation in rats. Hepatic microcirculation was evaluated in vivo using intravital microscopy.

RESULTS

Although there was no significant difference in dissociation constant (Kd) and total amount of receptors (Bmax) between sham and PPVL, the proportion of ET(B) receptor was significantly increased in PPVL. RT-PCR analysis confirmed the up-regulation of ET(B) receptors demonstrated by the competitive receptor binding assay. In the functional study, infusion of ET(B) agonist (IRL 1620) in a low dosage did not change the hepatic microcirculation in sham but strongly constricted the sinusoids leading to a reduction of sinusoidal perfusion in PPVL.

CONCLUSIONS

These results suggest that prehepatic portal hypertension may predispose the hepatic microcirculation to dysregulation in stress conditions where ET is upregulated.

Protective role of an endothelin-converting enzyme inhibitor (FR901533) in hepatic ischemia/reperfusion injury

INTRODUCTION

There is evidence that endothelin (ET) contributes to disturbances of the hepatic microcirculation after warm ischemia/reperfusion (I/R) by causing vasoconstriction and by enhancing leukocyte endothelium interactions. The aim of this study was to investigate a possible protective role of the endothelin converting enzyme (ECE) inhibitor FR901533 in this setting.

METHODS

In an in vivo model (42 Wistar rats), hepatic ischemia was induced for 30 min by Pringle's maneuver. Sham operated (I), untreated ischemic (II), and treatment (III) groups with FR901533 (1 mg/kg bw iv) were investigated. The effect of FR901533 in I/R was assessed by in vivo microscopy (30-90 min after reperfusion), measurement of local tissue pO2 (30 and 60 min after reperfusion), and determination of AST/ALT levels (2 h, 6 h, and 2, 6, and 14 days after reperfusion).

RESULTS

In the untreated ischemic group (II) sinusoidal constriction to 76.3 +/- 4.2% of basic diameters was observed, leading to significant decreases in perfusion rate (82.3 +/- 3.6% of sham group) and in liver tissue pO(2) (43.5 +/- 3.2% of sham group) (P < 0.05). In addition, we found an increased percentage of stagnant leukocytes in sinusoids (138.3 +/- 9.8) and sticking leukocytes in postsinusoidal venules (155.2 +/- 3.3% of sham group) (P < 0.05). Hepatocellular damage (AST/ALT increase to 430.6 +/- 47.7 U/L/200.2 +/- 23.8 U/L, pre: 27.4 +/- 2.7 U/L/28.1 +/- 2.7 U/L) was detected 6 h after reperfusion (P < 0.05). Administration of the ECE inhibitor before ischemia significantly reduced I/R injury. Sinusoidal diameters were maintained (102.2 +/- 1.7%), while perfusion rate (93.1 +/- 1.8%) and tissue pO2 (105.3 +/- 2.7%) increased significantly (P < 0.05). Hepatocellular damage was decreased (AST/ALT levels after 6 h of reperfusion: 166.6 +/- 26.3 U/L/132.4 +/- 22.5 U/L, P < 0.05) and leukocyte sticking and rolling were significantly reduced (P < 0.05).

CONCLUSION

Our results provide evidence that the new therapeutic approach with an ECE inhibitor is effective in reducing hepatic I/R injury.

Bosentan, an endothelin antagonist, augments hepatic graft function by reducing graft circulatory impairment following ischemia/reperfusion injury

Endothelin is a potent hepatic vasoconstrictor. We evaluated the role of an endothelin antagonist in hepatic ischemia/reperfusion injury. Bosentan, a novel endothelin receptor antagonist, was infused directly into the portal vein prior to cold ischemia and immediately on reperfusion, in five porcine livers. Five other pigs underwent routine liver harvest and reperfusion without bosentan treatment. Hepatic vascular resistance and liver tissue blood flow, as measured by thermistor flow probes, were determined following reperfusion. Hepatocellular damage was assessed through hepatic venous levels of sorbitol dehydrogenase and lactate dehydrogenase. Endothelial cell damage was determined in sections immuno-stained for factor VIII. Graft function was determined through oxygen consumption, bile production, and response to bile acid challenge. Organs treated with bosentan demonstrated lower vascular resistance and enhanced tissue blood flow (P < 0.05) as compared to untreated organs. Portal vein inflow to hepatic tissue was significantly enhanced (4.4-fold) in the bosentan-treated organs (P < 0.05). No difference was observed in hepatocellular damage. Pathology scores for factor VIII immunohistochemical staining were 2.3-fold higher in the bosentan-treated livers as compared to untreated livers (P < 0.05). The bosentan-treated livers also demonstrated enhanced oxygen consumption, increased bile production, and augmented biliary response to a bile acid challenge (P < 0.05). These results indicate that administration of bosentan before and after ischemia/reperfusion reduces hepatic circulatory disturbances, diminishes endothelial cell damage, and augments hepatic graft function.

Assessment of hepatic ischaemia reperfusion injury by measuring intracellular tissue oxygenation using near infrared spectroscopy

AIMS/BACKGROUND

Hepatic ischaemia/reperfusion (I/R) injury is a major cause of liver damage during liver surgery and transplantation. The relationship between the severity of I/R injury and the degree of intracellular hypoxia has not been investigated.

METHODS

New Zealand white rabbits were used in 4 groups (n=6 each). At laparotomy, left lobe hepatic ischaemia was produced for 30, 45, or 60 min followed by 60 min reperfusion and compared with controls. Liver function, bile flow, and flow in the hepatic microcirculation (HM) were measured. Near infrared spectroscopy (NIRS) was used to monitor hepatic oxyhaemoglobin (HbO2), deoxyhaemoglobin (Hb), and cytochrome oxidase (Cyt Ox).

RESULTS

I/R injury produced deranged liver function tests, reduced bile flow, and reduced flow in the microcirculation in comparison with controls. During ischaemia, HbO2 and Cyt Ox were significantly reduced in comparison with controls. After reperfusion, a biphasic change in tissue oxygenation was observed, with an initial increase in HbO2 and Cyt Ox followed by a progressive reduction. The reduction in tissue oxygenation with ischaemia and reperfusion paralleled the ischaemia time. After I/R, the changes in Cyt Ox (intracellular oxygenation) significantly correlated with the parameters of hepatocellular injury to a higher degree than HbO2 (extracellular oxygenation).

CONCLUSION

This study shows the potential of monitoring the degree of I/R injury by measuring hepatic tissue intracellular oxygenation.

Pharmacologic graft protection without donor pretreatment in liver transplantation from non-heart-beating donors

BACKGROUND

Non-heart-beating donors (NHBDs) are considered potential sources of transplant organs in an effort to alleviate the problem of donor shortage in clinical liver transplantation. We investigated the possibility of pharmacologic protection of hepatic allograft function from NHBDs without donor pretreatment.

METHODS

Orthotopic liver transplantation was performed using pigs. In donors, cardiac arrest was induced by stopping the respirator. Forty-five minutes after cessation of the respirator, the liver was flushed with cold lactated Ringer's solution including heparin and with the University of Wisconsin (UW) solution, and then preserved for 8 hr at 4 degrees C in the UW solution. The pigs were divided into two groups: a control group and a treated group. In the treated group, an endothelin antagonist TAK-044 was added to the UW solutions (10 mg/L), and TAK-044 (10 mg/kg body weight) and a platelet activating factor antagonist E5880 (0.3 mg/kg body weight) were also administered to the recipients.

RESULTS

TAK-044 and E5880 treatment significantly increased the 7-day survival rate of the recipients (100% vs. 17%, P<0.05). In the treated group, portal venous pressure immediately after reperfusion of the graft was significantly lower than in the control group, and postoperative increase in serum concentrations of glutamic oxaloacetic transaminase and total bilirubin was attenuated. Moreover, the energy charge and adenosine triphosphate concentration of the liver were rapidly restored after reperfusion.

CONCLUSIONS

Pharmacologic modulation with TAK-044 and E5880 avoiding donor pretreatment can improve the viability of hepatic allografts procured from NHBDs.

Effects of exogenous endothelin-1 application on liver perfusion in native and transplanted porcine livers

PURPOSE

This study was designed to assess and differentiate the impact of progressivly increasing portal venous endothelin-1 (ET) plasma concentrations on hepatic micro- and macroperfusion of native porcine livers (Group A) and liver grafts after experimental transplantation (Group B).

METHODS

A standardized gradual increment in systemic ET plasma concentration (0-58 pg/ml) was induced by continuous ET-1 infusion into the portal vein in both groups (A: n = 10, B: n = 10). Control animals received only saline (n = 5, each group). Hepatic microcirculation (HMC) was quantified by thermodiffusion electrodes, hepatic artery flow (HAF), and portal venous flow (PVF) by Doppler flowmetry.

RESULTS

No changes in ET or perfusion parameters were observed in controls. The mean ET level after orthotopic liver transplantation (OLT) in Group B was elevated (baseline: 3.8 +/- 2.4 pg/ml) compared with Group A (2.8 +/- 1.9 pg/ml). With rising ET levels HAF decreased progressively in Group A from 205 +/- 97 (baseline) to 160 +/- 72 ml/min, and in Group B from 161 +/- 87 to 146 +/- 68 ml/min. PVF decreased in Group A from 722 +/- 253 to 370 +/- 198 ml/min, and in Group B from 846 +/- 263 to 417 +/- 203 ml/min. Baseline HMC in Group A was 86 +/- 15 and decreased significantly to 29 +/- 9 ml/100 g/min, and baseline MC in Group B was 90 +/- 22 and decreased to 44 +/- 32 ml/100 g/min. No significant alteration in systemic circulation was noted at the ET concentrations investigated.

CONCLUSIONS

Significant impairment of hepatic micro- and macrocirculation was detected after induction of systemic ET levels above 9.4 pg/ml both in native and in transplanted livers. Disturbance of HMC was caused predominantly by reduction of portal venous flow, while the effect of ET on HAF was less pronounced. Characteristics of flow impairment in transplanted and native livers were analogous after short cold ischemic graft storage (6 h).

The roles of platelet-activating factor and endothelin-1 in renal damage after total hepatic ischemia and reperfusion

BACKGROUND

This study was designed to verify the involvement of platelet-activating factor (PAF) in renal damage associated with hepatic ischemia and reperfusion (HIR) injury through the release of endothelin (ET)-1 and to determine the modulating effect of a specific PAF receptor antagonist on these insults in rats.

METHODS

Male rats pretreated with either normal saline as a vehicle (NS group) or intravenous TCV-309, a PAF receptor antagonist (TCV group), were subjected to 120 min of total hepatic ischemia under an extracorporeal portosystemic shunt. Plasma aspartate transaminase, creatinine, blood urea nitrogen, and ET-1 levels and the relative renal wet weight were determined under nonischemic conditions and at 1, 3, and 6 hr of reperfusion after hepatic ischemia. Changes in mean arterial blood pressure and renal tissue blood flow measurements in the kidney were determined throughout the experiment.

RESULTS

Increased plasma aspartate transaminase, creatinine, blood urea nitrogen, and ET-1 levels and the relative renal wet weight after HIR in the NS group were significantly suppressed by TCV-309 pretreatment. Mean arterial blood pressure and renal tissue blood flow after HIR in the TCV group were significantly improved when compared with those in the NS group. These effects resulted in attenuation of structural hepatic and renal damage with the improvement of 7-day survival (62%).

CONCLUSIONS

The present study demonstrates that renal damage as well as critical liver injury is produced after reperfusion following 120 min of total hepatic ischemia. A PAF receptor antagonist may be therapeutically useful to protect against these types of damage via indirect modulation of plasma ET-1 levels.