Hepatic tissue oxygenation as a predictive indicator of ischemia-reperfusion liver injury

Effects of Subnormothermic Regulated Hepatic Reperfusion on Mitochondrial and Transcriptomic Profiles in a Porcine Model

OBJECTIVE

We sought to investigate the biological effects of pre-reperfusion treatments of the liver after warm and cold ischemic injuries in a porcine donation after circulatory death model.

SUMMARY OF BACKGROUND DATA

Donation after circulatory death represents a severe form of liver ischemia and reperfusion injury that has a profound impact on graft function after liver transplantation.

METHODS

Twenty donor pig livers underwent 60 minutes of in situ warm ischemia after circulatory arrest and 120 minutes of cold static preservation prior to simulated transplantation using an ex vivo perfusion machine. Four reperfusion treatments were compared: Control-Normothermic (N), Control- Subnormothermic (S), regulated hepatic reperfusion (RHR)-N, and RHR-S (n = 5 each). The biochemical, metabolic, and transcriptomic profiles, as well as mitochondrial function were analyzed.

RESULTS

Compared to the other groups, RHR-S treated group showed significantly lower post-reperfusion aspartate aminotransferase levels in the reperfusion effluent and histologic findings of hepatocyte viability and lesser degree of congestion and necrosis. RHR-S resulted in a significantly higher mitochondrial respiratory control index and calcium retention capacity. Transcriptomic profile analysis showed that treatment with RHR-S activated cell survival and viability, cellular homeostasis as well as other biological functions involved in tissue repair such as cytoskeleton or cytoplasm organization, cell migration, transcription, and microtubule dynamics. Furthermore, RHR-S inhibited organismal death, morbidity and mortality, necrosis, and apoptosis.

CONCLUSION

Subnormothermic RHR mitigates IRI and preserves hepatic mitochondrial function after warm and cold hepatic ischemia. This organ resuscitative therapy may also trigger the activation of protective genes against IRI. Sub- normothermic RHR has potential applicability to clinical liver transplantation.

In vivo imaging of hepatic hemodynamics and light scattering property during ischemia-reperfusion in rats based on spectrocolorimetry

A red-green-blue camera-based imaging method is proposed for estimating spatial maps of concentrations of oxyhemoglobin (CHbO), deoxyhemoglobin (CHbR), total hemoglobin (CHbT), tissue oxygen saturation (StO2), and scattering power (b) in liver tissue. Hemodynamic responses to hepatic ischemia-reperfusion of in vivo rat liver tissues induced by portal triad occlusion were evaluated. Upon portal triad occlusion, this method yielded images of decreased CHbO, CHbT, StO2, and b, and increased CHbR followed by a progressive increase in CHbO and StO2 during reperfusion. Time courses of the changes in CHbO, CHbR, CHbT, and StO2 over different regions of interest (ROIs) revealed that ischemia results in an abrupt significant (P<0.05) reduction in CHbO, CHbT, and StO2 with a simultaneous increase in CHbR compared to the baseline level, indicative of the hemodynamic responses during hepatic ischemia-reperfusion. Upon reperfusion, there was a gradual increase in CHbO and StO2, and decrease in CHbR. The change in average scattering power b implies the presence of morphological alterations in the cellular and subcellular structures induced by ischemia or anoxia. This study shows the potential of monitoring spatiotemporal changes in hemodynamic parameters and morphological changes in studies of hepatic pathophysiology.

Changing paradigms in organ preservation and resuscitation

PURPOSE OF REVIEW

Shortage of donor organs has increased consideration for use of historically excluded grafts. Ex-vivo machine perfusion is an emerging technology that holds the potential for organ resuscitation and reconditioning, potentially increasing the quality and number of organs available for transplantation. This article aims to review the recent advances in machine perfusion and organ preservation solutions.

RECENT FINDINGS

Flow and pressure-based machine perfusion has shown improved kidney graft function and survival, especially among expanded criteria donors. Pressure-based machine perfusion is demonstrating promising results in preservation and resuscitation of liver, pancreas, heart, and also lung grafts. August 2014 marked Food and Drug Administration approval of XPS XVIVO Perfusion System (XVIVO Perfusion Inc., Englewood, Colorado, USA), a device for preserving and resuscitating lung allografts initially considered unsuitable for transplantation. Although there is no consensus among physicians about the optimal preservation solution, adding antiapoptotic and cell protective agents to preservation solutions is an interesting research area that offers potential to improve preservation.

SUMMARY

Ex-vivo machine perfusion of solid organs is a promising method that provides the opportunity for resuscitation and reconditioning of suboptimal grafts, expanding the number and quality of donor organs.

Ischaemia-reperfusion injury in liver transplantation--from bench to bedside

Ischaemia-reperfusion injury (IRI) in the liver, a major complication of haemorrhagic shock, resection and transplantation, is a dynamic process that involves the two interrelated phases of local ischaemic insult and inflammation-mediated reperfusion injury. This Review highlights the latest mechanistic insights into innate-adaptive immune crosstalk and cell activation cascades that lead to inflammation-mediated injury in livers stressed by ischaemia-reperfusion, discusses progress in large animal experiments and examines efforts to minimize liver IRI in patients who have received a liver transplant. The interlinked signalling pathways in multiple hepatic cell types, the IRI kinetics and positive versus negative regulatory loops at the innate-adaptive immune interface are discussed. The current gaps in our knowledge and the pathophysiology aspects of IRI in which basic and translational research is still required are stressed. An improved appreciation of cellular immune events that trigger and sustain local inflammatory responses, which are ultimately responsible for organ injury, is fundamental to developing innovative strategies for treating patients who have received a liver transplant and developed ischaemia-reperfusion inflammation and organ dysfunction.

Regulated hepatic reperfusion mitigates ischemia-reperfusion injury and improves survival after prolonged liver warm ischemia: a pilot study on a novel concept of organ resuscitation in a large animal model

BACKGROUND

Ischemia-reperfusion injury (IRI) can occur during hepatic surgery and transplantation. IRI causes hepatic mitochondrial and microcirculatory impairment, resulting in acute liver dysfunction and failure. We proposed a novel strategy of regulated hepatic reperfusion (RHR) to reverse the cellular metabolic deficit that incurred during organ ischemia by using a substrate-enriched, oxygen-saturated, and leukocyte-depleted perfusate delivered under regulated reperfusion pressure, temperature, and pH. We investigate the use of RHR in mitigating IRI after a prolonged period of warm ischemia.

METHODS

Using a 2-hour liver warm ischemia swine model, 2 methods of liver reperfusion were compared. The control group (n = 6) received conventional reperfusion with unmodified portal venous blood under unregulated reperfusion pressure, temperature, and pH. The experimental group (n = 6) received RHR. We analyzed the effects of RHR on post-reperfusion hemodynamic changes, liver function, and 7-day animal survival.

RESULTS

RHR resulted in 100% survival compared with 50% in the control group (p = 0.05). Post-reperfusion syndrome was not observed in the RHR group, but it occurred in 83% of the control group. RHR resulted in a lesser degree of change from baseline serum alanine aminotransferase levels, aspartate aminotransferase, and lactate dehydrogenase after reperfusion compared with the control group. Histopathologic evaluation showed minimal ischemic changes in the RHR group, whereas a considerable degree of coagulative hepatocellular necrosis was observed in the control group.

CONCLUSIONS

Regulated hepatic reperfusion mitigates IRI, facilitates liver function recovery, and improves survival after a prolonged period of hepatic warm ischemia. This novel strategy has potential applicability to clinical hepatic surgery and liver transplantation when marginal grafts are used.

The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-alpha, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.

Effects of hemodilution with a hemoglobin-based oxygen carrier (HBOC-201) on ischemia/reperfusion injury in a model of partial warm liver ischemia of the rat

BACKGROUND

Ischemia/reperfusion injury is an unavoidable complication in liver surgery and transplantation. Hemodilution with colloids can reduce postischemic injury but limits oxygen transport. Hemoglobin-based oxygen carriers have been evaluated as blood substitute and provide a plasma-derived oxygen transport. It was the aim of our study to evaluate the combined benefits of hemodilution with a better oxygen supply to reperfused liver tissue by the use of HBOC-201 (Hemopure).

MATERIAL AND METHODS

A model of partial warm liver ischemia in the rat was used. One group served as untreated control, the other groups were hemodiluted either with Ringer's lactate, Dextran-70, HBOC-201 or a mixture of Dextran and HBOC-201. After reperfusion, intravital microscopy studies were done and tissue pO(2) levels and transaminases measured. Statistical analysis was done by one- and two-way ANOVA, followed by pairwise comparison.

RESULTS

Hemodilution with Ringer's lactate did not show any improvement compared to the control group. Dextran and HBOC group were superior to the Ringer and control animals in all parameters studied. Leucocyte adherence in postsinusoidal venules improved from 569.03+/-171.87 and 364.52+/-167.32 in control and Ringer group to 131.68+/-58.34 and 68.44+/-20.31/mm(2) endothelium in Dextran and HBOC group (p<0.001). Concerning tissue pO(2) levels, HBOC (23.4+/-5.0 mmHg) proved to be superior to Dextran (7.9+/-4.4 mmHg; p=0.007).

CONCLUSION

HBOC was equivalent to Dextran in reducing I/R injury in the liver, but improved oxygenation of postreperfusion liver tissue.

Tezosentan, a novel endothelin receptor antagonist, markedly reduces rat hepatic ischemia and reperfusion injury in three different models

This study investigated the effects of dual endothelin (ET) receptor blockade in rat models of liver ischemia and reperfusion injury (IRI). Three models of IRI were used: (1) in vivo total hepatic warm ischemia with portal shunting for 60 minutes with control (saline) and treatment groups (15 mg/kg tezosentan intravenously prior to reperfusion), (2) ex vivo hepatic perfusion after 24 hours of cold storage in University of Wisconsin solution with control and treatment groups (10 mg/kg tezosentan in the perfusate), and (3) syngeneic liver transplantation (LT) after 24 hours of cold storage in University of Wisconsin solution with control and treatment groups (10 mg/kg tezosentan intravenously prior to reperfusion). Tezosentan treatment significantly improved serum transaminase and histology after IRI in all 3 models. This correlated with reduced vascular resistance, improved bile production, and an improved oxygen extraction ratio. Treatment led to a reduction in neutrophil infiltration and interleukin-1 beta and macrophage inflammatory protein 2 production. A reduction in endothelial cell injury as measured by purine nucleoside phosphorylase was seen. Survival after LT was significantly increased with tezosentan treatment (90% versus 50%). In conclusion, this is the first investigation to examine dual receptor ET blockade in 3 models of hepatic IRI and the first to use the parenterally administered agent tezosentan. The results demonstrate that in both warm and cold IRI tezosentan administration improves sinusoidal hemodynamics and is associated with improved tissue oxygenation and reduced endothelial cell damage. In addition, reduced tissue inflammation, injury, and leukocyte chemotactic signaling were seen. These results provide compelling data for the further investigation of the use of tezosentan in hepatic IRI.

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.

Near-infrared spectroscopic assessment of mitochondrial oxygenation status--comparison during normothermic extracorporeal liver perfusion by buffer only or buffer fortified with washed red blood cells: an experimental study

BACKGROUND

Use of marginal and non-heart-beating donors leads to an increased incidence of complications after clinical liver transplantation. Normothermic extracorporeal liver perfusion (NELP) may allow resuscitation and evaluation of such organs. Despite recent success in long-term liver preservation by NELP, no methods of organ evaluation have been defined. Mitochondrial cytochrome oxidase (Cyt Ox) levels reflect oxygen and substrate delivery, and hence ATP production at the cellular level. This study used near-infrared spectroscopy (NIRS) to measure Cyt Ox levels during NELP.

METHODS

Livers retrieved from New Zealand white rabbits were immediately perfused in an extracorporeal circuit with oxygenated buffer (group A, n = 4) or red blood cell (RBC)-fortified buffer (group B, n = 4). Perfusion was continued for 3 hours at 37 degrees C pH 7.4, and perfusate was gassed with 95%O2/5%CO2 at 1 liter per minute. Cyt Ox levels were monitored continuously by NIRS and bile output was measured.

RESULTS

Cyt Ox was reduced at the start of perfusion in both groups, but even more rapidly in the buffer-perfused group. After initial deterioration, Cyt Ox levels improved significantly (P < .05) with perfusion in the RBG-perfused group, but remained impaired in the buffer group 5.74 +/- 1.51 Deltamicromol/L and -25.77 +/- 21.94 Deltamicromol/L for groups B and A, respectively, at 180 minutes. Differences in bile output were not significant (19.33 +/- 9.50 and 25.00 +/- 16.81 micromol/min/100 g for groups B and A respectively).

CONCLUSIONS

Cyt Ox levels may offer better viability markers than bile output. NIRS is a practical method to measure tissue oxygenation, and RBC-based perfusion provided better oxygenation during NELP.

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.

Bile secretory function after warm hepatic ischemia-reperfusion injury in the rat

Hepatic ischemia-reperfusion (I-R) injury frequently is associated with cholestasis. However, the underlying mechanisms are not fully understood. The aim of the study is to assess bile secretory function in vivo in rats subjected to warm lobar hepatic ischemia at different times during reperfusion. A model of lobar 70% warm hepatic ischemia for 30 minutes was used with studies conducted at 1 and 6 hours and 1, 3, and 7 days after reperfusion. Bile secretory function was assessed after selective cannulation of bile ducts of ischemic (ILs) and nonischemic lobes (NILs). Serum activity of hepatic alanine and aspartate aminotransferase was slightly increased in rats subjected to I-R, whereas serum bile salt levels increased early during reperfusion, returning to control values after 7 days. ILs showed mild reversible leukocyte infiltration and no significant necrosis. Bile flow and bile salt excretion were significantly decreased in ILs during the first 24-hour reperfusion period compared with sham-operated rats and NILs. A marked reduction in glutathione (GSH) excretion occurred at 1 and 6 hours and 1 and 3 days, which returned to control values after 7 days. Total GSH and both reduced and oxidized GSH levels in liver homogenate and arterial blood GSH levels were unchanged at all times. Protein mass of multidrug resistance protein 2 and its function, assessed by the hepatic maximum secretory rate of ceftriaxone, did not show significant changes in ILs or NILs compared with sham-operated rats. Liver tissue gamma-glutamyl transpeptidase (GGT) and gamma-glutamylcysteine synthetase activities remained unchanged, whereas biliary GGT and cysteine secretory rates were significantly increased in ILs and NILs. Administration of acivicin, a GGT inhibitor, resulted in decreased secretion of this enzyme into bile and a parallel marked increase in biliary GSH secretion compared with untreated ischemic rats. In conclusion, warm hepatic I-R induces reversible cholestatic changes in ILs. GSH secretory rates from both ILs and NILs were markedly decreased during reperfusion. The reversibility of this effect after GGT inhibition, as well as increased release of active GGT into bile and cysteine biliary secretory rates, suggest increased GSH degradation in bile. These findings might be relevant for the I-R-induced clinical cholestasis, as well as cholangiocyte injury, seen after hepatic ischemia.

Effect of in situ hypothermic perfusion on intrahepatic pO2 and reactive oxygen species formation after partial hepatectomy under total hepatic vascular exclusion in pigs

AIM

This study examined attenuation of ischemia and reperfusion (I/R) induced liver injury during liver resections by hypothermic perfusion of the liver under total hepatic vascular exclusion (THVE).

METHOD

Reactive oxygen species (ROS) formation, microcirculatory integrity and endothelial cell damage were investigated. Left hemihepatectomy (LHX) was performed without in situ perfusion (control-LHX, n = 5) or with concomitant in situ perfusion with hypothermic (4 degrees C) Ringer-glucose (cold-LHX, n = 5) or normothermic (38 degrees C) Ringer-glucose (warm-LHX, n = 5). Glutathione (GSH) and malondialdehyde (MDA) concentrations, tissue pO2 levels and hyaluronic acid (HA) uptake capacity were determined.

RESULTS

After cold, warm and control-LHX, 24 h survival was 5/5, 0/5 and 3/5, respectively. GSH levels were best preserved after cold-LHX during reperfusion. MDA levels increased in all groups without significant differences between the groups during reperfusion. Tissue pO2 levels increased after cold-LHX whereas after warm-LHX and control-LHX, pO2 levels decreased during reperfusion. HA uptake capacity remained normal after cold-LHX. After warm-LHX and control-LHX, HA uptake capacity decreased after 6 h of reperfusion but recovered after 24 h of reperfusion in the control-LHX group.

CONCLUSION

Moderate hypothermic perfusion protects the liver from I/R injury during LHX under THVE. This protective effect depended on maintenance of liver microcirculation rather than a reduction in ROS formation.

The relationship of hepatic tissue oxygenation with nitric oxide metabolism in ischemic preconditioning of the liver

Ischemic preconditioning (IPC) may increase the hepatic tolerance of ischemic injury during liver surgery and transplantation via nitric oxide (NO) formation. This study investigates the effect of IPC on hepatic tissue oxygenation and the role of NO stimulation and inhibition on the preconditioning effect in the rat liver. Study groups had 1) sham laparotomy; 2) 45-min lobar liver ischemia and 2-h reperfusion (IR); 3) IPC with 5-min ischemia and 10-min reperfusion before IR; 4) L-arginine before IR; and 5) Nw-Nitro-L-arginine methyl ester (L-NAME) + IPC before IR. Hepatic tissue oxygenation was monitored by near-infrared spectroscopy. Plasma alanine aminotransferase and plasma nitrite/nitrate were measured. Following IR there was significant decrease in oxyhemoglobin and cytochrome oxidase and an increase in deoxyhemoglobin (PA redox state, PL-arginine did not attenuate the impairment in hepatic tissue oxygenation after IR (P>0.05 vs IR). In contrast, inhibition of NO synthesis blocked the effect of IPC and further impaired tissue oxygenation (decreased cytochrome oxidase CuA redox state and increased deoxyhemoglobin, both PL-arginine and increased by NO blockade with L-NAME (Plasma ALT, all P< 0.05 vs IR). Hepatic tissue oxygenation correlated significantly with ALT and plasma nitrite/nitrate. Ischemic preconditioning significantly improved hepatic intra cellular oxygenation and reduced hepatocellular injury. NO stimulation reduced hepatocellular injury, whereas inhibition of nitric oxide synthesis blocked the effect of IPC and reduced tissue oxygenation and increased hepatocellular injury.

Impact of inhibition of complement by sCR1 on hepatic microcirculation after warm ischemia

Recent observations provide evidence that complement is implicated as an important factor in the pathophysiology of ischemia/reperfusion injury (IRI). Here, we assessed the effects of complement inhibition on hepatic microcirculation by in vivo microscopy (IVM) using a rat model of warm hepatic ischemia clamping the left pedicle for 70 min. Ten animals received the physiological complement regulator soluble complement receptor type 1 (sCR1) intravenously 1 min prior to reperfusion. Controls were given an equal amount of Ringer's solution (n = 10). Microvascular perfusion and leukocyte adhesion were studied 30 to 100 min after reperfusion by IVM. Microvascular perfusion in hepatic sinusoids was significantly improved in the sCR1 group (80.6 +/- 0.6% of all observed sinusoids were perfused [sCR1] vs 67.3 +/- 1.2% [controls]). The number of adherent leukocytes was reduced in sinusoids (49.9 +/- 3.4 [sCR1] vs 312.3 +/- 14.2 in controls [adherent leukocytes per square millimeter of liver surface]; P < 0.001) as well as in postsinusoidal venules after sCR1 treatment (230.9 +/- 21.7 [sCR1] vs 1906.5 +/- 93.5 [controls] [adherent leukocytes per square millimeter of endothelial surface]; P < 0.001). Reflecting reduced hepatocyte injury, liver transaminases were decreased significantly upon sCR1 treatment compared to controls. Our results provide further evidence that complement plays a decisive role in warm hepatic IRI. Therefore, we conclude that complement inhibition by sCR1 is effective as a therapeutical approach to reduce microcirculatory disorders after reperfusion following warm organ ischemia.

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.

Effect of nitric oxide inhibition on rat liver ischemia reperfusion injury

Objective: to determine the role of nitric oxide (NO) in rat liver ischemia reperfusion we examined the effects of competitive NO synthesis inhibitor L-nitro-arginine-methyl-ester (L-NAME) and NO precursor L-arginin. Methods: 46 Sprague-Dawley rats were divided into five groups. Group 1, sham operated; group 2, 30-min ischemia administered; group 3, 60-min reperfusion administered after ischemia; group 4, 50 mg/kg L-NAME was given i.v. immediately before reperfusion; group 5, 50 mg/kg L-NAME+250 mg/kg L-arginin was given i.v. immediately before reperfusion. At the end of the experiment, liver was removed and superoxide dismutase (SOD), catalase, and malondialdehyde (MDA) were measured, transaminases SGOT and SGPT were measured in sera. Liver was also evaluated histopathologically. Results: transaminase levels were the highest in ischemia reperfusion group. Transaminases in this group were high compared with sham, ischemia, L-NAME and L-arginin groups (***P<0.001, ***P<0.001, *P<0.05, *P<0.05, respectively). SOD activity was 29.8+4 U/mg protein in L-arginin group. This level was the lowest level in all groups. SOD activity in L-arginin group was lower than that of sham and ischemia reperfusion groups (**P<0.01, *P<0.05, respectively). There were no significant differences in catalase activity and MDA levels among groups. Tissue damage was significant in ischemia and ischemia reperfusion groups. Tissue damages in these groups were greater than that of sham group (***P<0.001). In L-NAME treated group, tissue damage was similar to sham group, and significantly less than ischemia reperfusion group and L-arginin group (**P<0.01). Conclusion: even though there was significant tissue damage, we have not observed oxidative stress in the length of ischemia reperfusion period that we have performed. Mechanism of this damage seems to be independent from lipid peroxidation. NO supplementation decreased SOD, but did not cause further tissue damage. NO may dispose O(2)(-) by formation of peroxynitrite. L-NAME did not change lipid peroxidation, but clearly reduced reperfusion injury.

The effect of nitric oxide on ischemia-reperfusion injury in rat liver

A dual role for nitric oxide (NO) in ischemia-reperfusion (I/R) injury is still controversial. This study aims to investigate the role of NO in rat hepatic reperfusion injury. Ischemia was induced by total occlusion of hepatic artery and portal vein for 30 min, then the tissue was reperfused for 30 min. The animals in the L-NAME group (n=10) received N(G)nitro-L-arginine methyl ester (L-NAME) (15 mg/kg) intraperitoneally 60 min before ischemia. The ischemia group (n=10) was given an equal volume of saline solution. The control group comprised eight healthy rats which were not exposed to ischemia or reperfusion. An indicator of hepatic injury, plasma alanine amino transferase (ALT) enzyme activities, were increased in the L-NAME group as compared with the ischemia group (p<0.001). The level of serum nitrite, an index of NO production, and hepatic reduced glutathione (GSH) concentration were lower in the L-NAME group than in the ischemia group (p<0.001, p<0.01, respectively). Hepatic levels of malondialdehyde (MDA) and conjugated dienes (CD) were significantly increased in the L-NAME group as compared to the ischemia group (p<0.05, p<0.001, respectively). Our results confirm that L-NAME, an inhibitor of the enzyme NO synthase, increased the lipid peroxidation and possibly tissue injury, due to the inhibition of cytoprotective effects of NO in a rat hepatic I/R model.

Effect of graded hypoxia on hepatic tissue oxygenation measured by near infrared spectroscopy

BACKGROUND/AIMS

In liver transplantation ischaemia-reperfusion injury of the graft reduces hepatic tissue oxygenation which has prognostic value for patient survival. Near infrared spectroscopy (NIRS) can measure extracellular (haemoglobin oxygenation) and intracellular tissue oxygenation (cytochrome oxidase oxidation). However, it has not been validated for measuring hepatic tissue oxygenation in an experimental model with graded hypoxia.

METHODS

New Zealand White rabbits (2.9+/-0.3 kg, n=9) underwent laparotomy for liver exposure. Heart rate, blood pressure, temperature, arterial blood pH and blood gas partial pressures were monitored during the experiments. Near infrared spectroscopy probes were placed on the liver surface to record continuously hepatic oxyhaemoglobin, deoxyhaemoglobin and cytochrome oxidase oxidation. Graded hypoxia was achieved by stepwise reduction of the inspired oxygen from 15 to 4%. During recovery from hypoxia 30% oxygen was administered.

RESULTS

There was an immediate reduction of hepatic oxyhaemoglobin with hypoxia and a simultaneous increase of hepatic deoxyhaemoglobin. Hepatic oxyhaemoglobin showed a positive correlation with arterial oxygen pressure (r=0.77, p<0.001). Hepatic deoxyhaemoglobin showed a negative correlation with arterial oxygen pressure (r=-0.75, p<0.001). Hepatic cytochrome oxidase decreased significantly with an inspired oxygen of 10% or less and showed a positive correlation with arterial oxygen pressure (r= 0.90, p<0.001).

CONCLUSIONS

Near infrared spectroscopy is an effective method for monitoring hepatic extracellular and intracellular tissue oxygenation.

Prolonged continuous or intermittent vascular inflow occlusion during hemihepatectomy in pigs

OBJECTIVE

To assess ischemia and reperfusion (I/R) injury in a hemihepatectomy model in pigs after prolonged continuous or intermittent vascular inflow occlusion in the liver.

SUMMARY BACKGROUND DATA

Massive intraoperative blood loss during liver resections can be prevented by temporary vascular inflow occlusion, consequently leading to ischemia and reperfusion injury in the remnant liver. Previously, in a pig liver resection model in which only limited I/R injury was induced during brief (90 min) vascular inflow occlusion, the authors demonstrated reduced I/R injury after continuous (CNT) occlusion, compared to intermittent (INT). This liver resection study on pigs was undertaken to assess I/R injury after prolonged (120 min) CNT or INT occlusion.

METHODS

In pigs (37.0 +/- 1.5 kg), liver ischemia during 2 hours was CNT (n = 6) or INT (n = 6) (eight subsequent periods of 12 min ischemia and 3 min recirculation), followed by 6 hours of reperfusion. A left hemihepatectomy (45.5% +/- 1.4%) was performed within the first 12 minutes of ischemia. No hepatic pedicle clamping or liver resection was performed in control experiments (n = 6). Microvascular damage was assessed by hyaluronic acid (HA) uptake capacity of the liver (parameter of early sinusoidal endothelial cell damage) and restoration of intrahepatic tissue pO2 during reperfusion. Hepatocellular damage was tested by plasma concentrations of aspartate aminotransferase (AST), alanine aminotransferase, and lactate dehydrogenase (LDH).

RESULTS

Hyaluronic acid uptake after 6 hours of reperfusion, compared to preischemic uptake, was unaltered in the control group, but was significantly reduced in both resection groups. However, more HA was taken up after INT occlusion, compared to CNT (60.4% +/- 5.6% and 39.5% +/- 3.7%, respectively; ANOVA: p = 0.001). Intrahepatic tissue pO2 distribution after 6 hours of reperfusion more closely returned to preischemic configuration in the INT group than in the CNT group, indicating reduced microcirculatory disturbances after INT occlusion. Release of AST and LDH after 6 hours of reperfusion was significantly increased in both CNT and INT groups. Lower AST levels, however, were found after INT occlusion than after CNT occlusion (267.0 +/- 74.7 U/l and 603.3 +/- 132.4 U/l, respectively; p = 0.06).

CONCLUSIONS

Intermittent hepatic vascular inflow occlusion during prolonged liver ischemia in pigs resulted in less microcirculatory and hepatocellular injury, compared to continuous occlusion. Intermittent clamping is preferable when prolonged periods of vascular inflow occlusion are applied during liver resections.

Resuscitation with hypertonic saline dextran reduces endothelial cell swelling and improves hepatic microvascular perfusion and function after hemorrhagic shock

BACKGROUND

Hemorrhagic shock severely compromises hepatic microcirculation and function with tendency to promote hepatic insufficiency and multiple organ failure.

MATERIAL AND METHODS

The aim of the study was to evaluate the effects of small volume resuscitation on liver microcirculation (intravital fluorescence microscopy and electron microscopy) and function (arterial ketone body ratio (AKBR) and bile flow), in a rat model of traumatic-hemorrhagic shock. One hour after hemorrhage (MAP 40 mm Hg) the rats were resuscitated with HSD (7.2% NaCl/10% dextran 60, 10% of shed blood/2 min, n = 8); DEX (6% dextran 60, 100% of shed blood/5 min, n = 8); or RL (Ringer lactate, 400% of shed blood/20 min, n = 6).

RESULTS

HSD yielded a better recovery of sinusoidal perfusion (17.8 +/- 0.8% nonperfused sinusoids) than DEX (21.8 +/- 0. 7%, P < 0.05) and RL (23.9 +/- 0.9%, P < 0.01). Hemorrhagic shock produced a moderate increase of mean sinusoidal endothelial cell thickness, which was further enhanced by DEX and RL (P < 0.05 vs baseline), whereas HSD reduced the mean endothelial cell thickness toward baseline (P < 0.05 vs DEX and RL). Both AKBR and bile flow were profoundly reduced after 1 h shock. Resuscitation with DEX and RL produced a weak recovery, still remaining at shock level, while HSD infusion allowed a significant improvement of AKBR and bile flow (P < 0.05 vs shock).

CONCLUSION

Reduction of mean endothelial cell thickness after HSD is very likely the mechanism for the amelioration of sinusoidal perfusion, resulting in a significant improvement of hepatic energetic status and excretory function.

Effect of intermittent hepatic pedicle clamping on free radical generation in the rat liver

BACKGROUND

Intermittent hepatic pedicle clamping is thought to cause less hepatic reperfusion injury compared with continuous clamping. The mechanisms underlying this difference are unknown. We examined the relationship between intermittent ischemia/reperfusion and the production of free radicals using electron spin resonance spectrometry.

METHODS

Alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone was administered to rats as a spin trap agent. Continuous clamping (15, 30, or 60 minutes) or intermittent clamping (four cycles of 15-minute ischemia and 5 or 15 minutes of reperfusion) of hepatic pedicle was carried out. After reperfusion, free radical production in the liver was measured by an electron spin resonance spectrometer, and the level of hepatic injury was evaluated by measuring liver enzyme.

RESULTS

Longer periods of ischemia increased free radical production after reperfusion. There was no significant increase in free radical production or liver enzymes when the duration of ischemia was 15 minutes. Free radical production and liver damage were significantly less severe in intermittent pedicle clamping than in continuous clamping for 60 minutes, especially when the duration of the reperfusion between four cycles of ischemia was 15 minutes.

CONCLUSIONS

These results indicate that intermittent pedicle clamping lessens free radical production when compared with continuous clamping, although many free radicals are produced.

Recovery of blood flow and oxygen transport after temporary ischemia of rat liver

Hepatic tissue perfusion and O2 supply after ischemia are indispensable for recovery of cellular functions, but few studies have been performed regarding the recovery of tissue blood flow and O2 transport. After 5, 15, and 30 min of ischemia of rat livers, hepatic tissue perfusion, hepatic arterial and portal blood flow, plasma PO2, and O2 transport parameters were measured. Hepatic tissue blood flow and erythrocyte velocity in the sinusoids showed biphasic recoveries after temporal ischemia for 5, 15, and 30 min. The first peak in the flow appeared at 3-4 min after the initiation of tissue perfusion, and the second peak appeared at approximately 20 min, irrespective of the ischemic period. Hepatic blood flow during the initial increase contained relatively low O2-saturated blood compared with that in the second increase. Livers that had been subjected to a prior hepatic artery ligation only showed the first peak at approximately 4 min. The first increase in hepatic blood flow corresponded to the peak in the portal venous flow, and the second increase corresponded to that of the hepatic artery. These results suggested that hepatic microcirculation after temporary hepatic ischemia showed biphasic recoveries because of different restoration patterns of the portal vein and hepatic artery.

Inhibition of nitric oxide synthesis in ischemia/reperfusion of the rat liver is followed by impairment of hepatic microvascular blood flow

BACKGROUND

Recent studies provide evidence that nitric oxide (NO) has beneficial effects in hepatic ischemia/reperfusion injury. The purpose of this study was to evaluate whether nitric oxide is involved in the regulation of hepatic microvascular perfusion after warm hepatic ischemia. Therefore, we performed a study using in vivo fluorescence microscopy.

METHODS

Clamping of the left liver lobe was performed in male Wistar rats for the duration of 70 min. One experimental group (n=8) received L-NAME (Nw-nitro-L-arginine methyl ester hydrochloride), an NO-synthase inhibitor, 1 min prior to reperfusion. A second experimental group (n=8) received L-arginine (NO-substrate) continuously infused throughout the observation period. Controls (n=8) received equivalent volumes of an isotonic solution and underwent the same procedures. Hepatic microvascular blood flow and leukocyte-endothelial cell interaction was studied between 20 and 90 min after reperfusion using in vivo fluorescence microscopy.

RESULTS

Inhibition of NO-synthesis during reperfusion by application of L-NAME caused a marked decrease in sinusoidal blood flow velocity. Furthermore, we noted an increase of non-perfused sinusoids in this group. Treatment with L-arginine improved functional perfusion of hepatic acini and reduced significantly the number of adherent leukocytes in sinusoids and venules compared to control animals.

CONCLUSIONS

Our results provide further evidence that NO maintains postischemic hepatic microvascular perfusion and that inhibition of NO synthesis has detrimental effects on hepatic microhemodynamics during reperfusion.

Effect of the endothelin receptor antagonist bosentan on postischemic oxygen supply of the liver

Endothelin evokes strong and longlasting constriction of postischemic sinusoids, leading to microcirculatory disturbances and local hypoxia, thereby causing liver damage. The aim of the study was to avoid the constrictive response of sinusoids by blocking endothelin receptors. In an in vivo ischemia-reperfusion model (21 female Wistar rats, 250-300 g) with portal decompression by a splenocaval shunt, hepatic ischemia was induced for 30 min by cross clamping of the hepatoduodenal ligament. The endothelin receptor antagonist bosentan (10 mg/kg bw IV) was administered before ischemia. The effect of the receptor antagonist was assessed by serum levels of aspartate aminotransferase (ASAT) and alanine aminotransferase (ALAT) that were determined prior to ischemia, 2 and 6 h postoperatively. The local tissue pO2 was measured prior to inducing ischemia, 30 and 60 min after reperfusion. Application of 10 mg/kg bw endothelin receptor antagonist (ERA) intravenously did not influence the systemic blood pressure. The postischemic increase in serum ASAT and ALAT levels was diminished after receptor antagonist treatment (ASAT: p < .05). Local postischemic hepatic tissue pO2 was significantly decreased to 45% of basal values after 30 min and to 54.8% after 60 min of reperfusion (p < .05). Application of ERA results in a significant increase in local tissue pO2 to 110.9% of basal values after 30 min and to 90.7% after 60 min of reperfusion (p < .05). These data indicate that the endothelin receptor antagonist treatment results in a prevention of postischemic sinusoidal constriction avoiding hypoxia and leading to improved hepatocellular recovery.

Endothelin-1 is involved in the pathogenesis of ischemia/reperfusion liver injury by hepatic microcirculatory disturbances

Hepatic microcirculatory perturbation is observed after ischemia/reperfusion. Endothelin-1, a potent vasoconstrictive peptide, is known to modulate local circulation. This study was designed to examine whether endothelin-1 participates in the mechanism of microcirculatory disturbance and damage of the liver after ischemia/reperfusion. Ischemia in the median and left lateral lobes of the liver was induced for 60 min; it was followed by reperfusion for 24 hr. In some rats, endothelin-1 antiserum or control serum without endothelin-1-blocking activity was administered intravenously just before reperfusion. Rats were divided into three groups: an ischemia/reperfusion group that was injected with control serum, an endothelin-1 antiserum-treated group and a sham-operated group. Endothelin-1 concentrations in blood collected from the suprahepatic vena cava were measured before and after ischemia/reperfusion by use of a sandwich enzyme immunoassay. Index of blood volume in regional hepatic tissue and index of blood oxygenation in regional hepatic tissue were assessed with an organ reflectance spectrophotometry system before and at 5 min and 1, 2, and 24 hr after reperfusion. The endothelin-1 concentration in the ischemia/reperfusion group started to rise immediately at onset of reperfusion from basal values around 1 pg/ml and reached a value of 5 to 6 pg/ml 5 min after reperfusion; it was maintained at significantly high levels during the reperfusion period compared with the sham-operated group. Hepatic microcirculatory disturbance indicated by lowered index of blood volume in regional hepatic tissue and index of blood oxygenation in regional hepatic tissue levels was observed in the early phase of reperfusion in the ischemia/reperfusion group.(ABSTRACT TRUNCATED AT 250 WORDS)

Liver cytoprotection by prostaglandins

During the last decade intensive work on the relationships between the liver and the arachidonic acid cascade has greatly expanded our knowledge of this area of research. The liver has emerged as the major organ participating in the degradation and elimination of arachidonate products of systemic origin. The synthesis in the liver of arachidonate products derived from the cyclooxygenase, lipoxygenase and cytochrome P450 system pathways has been demonstrated. The participation of leukotriene B4 and cysteinyl-leukotrienes as mediators of liver damage and the possible therapeutic usefulness of prostaglandins (PGs) in acute liver injury has attracted the interest of clinicians. This article reviews the essential features regarding the role of arachidonate metabolites in liver disease and specially focuses on the cytoprotective effects on the liver displayed by PGE2, PGE1, PGI2 and synthetic PG analogs in experimental models of liver damage induced by ischemia-reperfusion injury, carbon tetrachloride, bacterial lipopolysaccharide and viral hepatitis and on the possible mechanisms underlying liver cytoprotection in these experimental models. The therapeutic usefulness of PGs in clinical practice is critically analyzed on the basis of available evidence in patients with fulminant hepatic failure and primary graft nonfunction following liver transplantation.