Role of cysteinyl-leukotrienes for portal pressure regulation and liver damage in cholestatic rat livers.

Kupffer cells (KCs) have a major role in liver injury, and cysteinyl-leukotrienes (Cys-LTs) are known to be involved as well. The KC-mediated pathways for the production and secretion of Cys-LT in cholestatic liver injury have not yet been elucidated. Here, we hypothesized that KC activation by Toll-like receptor ligands results in Cys-LT-mediated microcirculatory alterations and liver injury in acute cholestasis. We hypothesized further that this situation is associated with changes in the secretion and production of Cys-LT. One week after bile duct ligation (BDL), livers showed typical histological signs of cholestatic liver injury. Associated microcirculatory disturbances caused increased basal and maximal portal pressure following KC activation. These differences were determined in BDL livers compared with sham-operated livers in vivo (KC activation by LPS 4 mg/kg b.w.) and in isolated perfused organs (KC activation by Zymosan A, 150 µg/ml). Treatment with the 5-lipoxygenase inhibitor MK-886 alone did not alter portal perfusion pressure, lactate dehydrogenase (LDH) efflux, or bile duct proliferation in BDL animals. Following KC activation, portal perfusion pressure increased. The degree of cell injury was attenuated by MK-886 (3 µM) treatment as estimated by LDH efflux. In normal rats, a large amount of Cys-LT efflux was found in the bile. Only a minor amount was found in the effluent perfusate. In BDL livers, the KC-mediated Cys-LT efflux into the sinusoidal system increased, although the absolute Cys-LT level was still grossly lower than the biliary excretion in sham-operated livers. In conclusion, our results indicate that treatment with Cys-LT inhibitors might be a relevant target for attenuating cholestatic liver damage.

Portal pressure regulation following Kupffer cell activation: control of prostaglandin production by heme oxygenases.

BACKGROUND: Portal pressure (PP) results from the interplay of vasoconstrictors and vasodilators. Recently, we have shown that Kupffer cell (KC) activation increases PP. AIMS: The role of the vasodilating compounds nitric oxide (NO) and carbon monoxide (CO) was studied. The hypothesis of the present study was that these vasodilators counteract the PP increase following KC activation. METHODS: Livers of rats weighing 180-200 g were isolated and perfused. KCs were activated by zymosan A (cell wall particles from yeast; 150 µg/ml). The effects of NO and guanylate cyclase (GC) were evaluated by the NO synthase inhibitor N(G)-nitro-L-arginine methylester (L-NAME; 0.3 mM, and the GC inhibitor 4H-8-bromo-1,2,4-oxadiazolo(3,4-d)benz(b)(1,4)oxazin-1-one (NS-2028, 1.0 µM); the effects of the heme oxygenase (HO) derived compound CO were evaluated by direct administration of CO or inhibition of HO by zinc protoporphyrin IX (ZnPP IX, 1.0 µM). RESULTS: In isolated perfused rat livers, administration of L-NAME or NS-2028 further raised PP increase following KC activation. This effect could be reduced by the cGMP analogue 8-Br-cGMP. Inhibition of HO caused marked amplification of PP increase in zymosan-treated organs. CO prevented this PP increase cGMP independently. Interestingly, KC activation and simultaneous inhibition of HO augmented the production of prostaglandins D2 and F2α and of thromboxane A2. Accordingly, indomethacin blunted the increase of PP in zymosan/ZnPP-treated livers. CONCLUSIONS: NO restricts the initial PP increase after KC activation by GC-mediated cGMP. CO from heme degradation limits the increase of PP after KC activation eicosanoid dependently, but cGMP independently.

Tacrolimus preconditioning of rat liver allografts impacts glutathione homeostasis and early reperfusion injury.

OBJECTIVE: To characterize the immunosuppressant tacrolimus as a protective antioxidant in rat liver transplantation. METHODS: Livers of male Lewis rats underwent 24 h of hypothermic preservation in UW solution and were rinsed with tacrolimus or placebo directly before transplantation. Markers of liver injury, such as enzymes and bile flow, were determined during a 2 h reperfusion period. Concentrations of reduced (GSH) and oxidized (GSSG) glutathione were analyzed in plasma, bile, and liver tissue for estimation of oxidant stress caused by reactive oxygen species (ROS). RESULTS: Administration of tacrolimus (10 ng/mL) resulted in decreased ALT plasma levels (1740 ± 1169 U/l versus 3691 ± 1144 U/l; P < 0.05) at 2 h of reperfusion. While endogenous intracellular GSH concentrations remained unchanged, GSSG, the oxidation product of GSH, was markedly decreased at 2 h of reperfusion in preconditioned livers (47.0 ± 10.4 nm/g versus 71.8 ± 30.6 nm/g; P < 0.05). Correspondingly, GSSG bile concentrations (0.19 ± 0.04 mM versus 0.13 ± 0.04 mM; P < 0.05) as well as plasma GSSG levels (2.4 ± 0.3 mM versus 1.4 ± 0.2 mM; P < 0.05) were significantly increased upon reperfusion. These findings suggest that tacrolimus impacts post-ischemic GSH metabolism when administered as a rinse solution for liver allografts through an unknown pathway. CONCLUSION: Hepatocellular injury following transplantation was significantly decreased by preconditioning with tacrolimus. One possible mechanism of action is the detoxification of ROS through the preservation of cytosolic and extracellular GSH/GSSG ratios.

Treatment with the leukotriene inhibitor montelukast for 10 days attenuates portal hypertension in rat liver cirrhosis.

UNLABELLED: The mechanisms underlying intrahepatic vasoconstriction are not fully elucidated. Here we investigated the Kupffer cell (KC)-dependent increase in portal pressure by way of actions of vasoconstrictive cysteinyl leukotrienes (Cys-LTs). Liver cirrhosis was induced in rats by bile duct ligation (BDL for 4 weeks; controls: sham-operation) and thioacetamide application (18 weeks). Infusion of leukotriene (LT) C(4) or LTD(4) in isolated perfused livers (20 nM, BDL and sham) demonstrated that LTC(4) is a more relevant vasoconstrictor. In BDL animals the Cys-LT(1) receptor inhibitor montelukast (1 microM) reduced the maximal portal perfusion pressure following LTC(4) or LTD(4) infusion. The infusion of LTC(4) or D(4) in vivo (15 microg/kg b.w.) confirmed LTC(4) as the more relevant vasoconstrictor. Activation of KCs with zymosan (150 microg/mL) in isolated perfused BDL livers increased the portal perfusion pressure markedly, which was attenuated by LT receptor blockade (Ly171883, 20 microM). Cys-LTs in the effluent perfusate increased with KC activation but less with additional blockade of KCs with gadolinium chloride (10 mg/kg body weight, 48 and 24 hours pretreatment). KCs were isolated from normal rat livers and activated with zymosan or lipopolysaccharide at different timepoints. This resulted in an increase in Cys-LT production that was not influenced by preincubation with montelukast (1 microM). Infusion of LTC(4) (20 nM) and the thromboxane analog U46619 (0.1 microM) further enhanced portal pressure, indicating additive effects. Treatment with montelukast for 10 days resulted in an impressive reduction in the basal portal pressure and an attenuation of the KC-dependent increase in portal pressure. CONCLUSION: Activation of isolated KCs produced Cys-LTs. Infusion of Cys-LTs increased portal pressure and, vice versa, treatment with montelukast reduced portal pressure in rat liver cirrhosis. Therefore, montelukast may be of therapeutic benefit for patients with portal hypertension.

Intraperitoneal LPS amplifies portal hypertension in rat liver fibrosis.

Recent studies have shown that the risk of variceal bleeding in patients with liver cirrhosis increases with infections such as spontaneous bacterial peritonitis (SBP). In this study, we hypothesized that pretreatment with intraperitoneal LPS may escalate portal hypertension. In fibrotic livers (4 weeks after bile duct ligation, BDL), the activation of Kupffer cells (KCs) by zymosan (150 microg/ml) in the isolated non-recirculating liver perfusion system resulted in a transient increase in portal perfusion pressure. Pretreatment with intraperitoneal LPS (1 mg/kg body weight (b.w.) for 3 h) increased basal portal perfusion pressure, and prolonged the zymosan-induced increase from transient to a long-lasting increase that was sustained until the end of the experiments in BDL but not in sham-operated animals. Pretreatment with gadolinium chloride (10 mg/kg b.w.), MK-886 (0.6 mg/kg b.w.), Ly171883 (20 microM) or BM 13.177 (20 microM) reduced the maximal and long-lasting pressure increase in BDL animals by approximately 50-60%. The change in portal perfusion pressure was paralleled by a long-lasting production of cysteinyl leukotriene (Cys-LT) and thromboxane (TX) after LPS pretreatment. However, the response to vasoconstrictors was not altered by intraperitoneal LPS. Western blot analyses showed an increased Toll-like receptor (TLR)4 and MyD88 expression after LPS pretreatment. In vivo experiments confirmed that intraperitoneal LPS increased basal portal pressure, and extended the portal pressure increase produced by intraportal zymosan or by LPS infusion. In conclusion, upregulation of TLR4 and MyD88 expression in fibrotic livers confers hypersensitivity to LPS. This may lead to escalation of portal hypertension by production of TX and Cys-LT after endotoxin-induced KC activation. Therefore, LT inhibitors may represent a promising treatment option in addition to early administration of antibiotics in SBP.

Kupffer cell activation by hydrogen peroxide: a new mechanism of portal pressure increase.

This study aimed to investigate the effects of reactive oxygen species on the hepatic macrophages, the Kupffer cells (KC), and to identify the relevant targets of vasoconstrictors involved in the regulation of intrahepatic microcirculation and therefore portal pressure. The effects of hydrogen peroxide (H2O2), xanthine/xanthine oxidase or a thromboxane (TX) analogue (U46619; 0.1 microM) were tested in sham-operated and fibrotic livers (bile duct ligation over 4 weeks) during isolated rat liver perfusion and in vivo with or without additional KC blockade (gadolinium chloride, 10 mg kg(-1) body weight, 48 and 24 h, i.p.). To investigate downstream mechanisms, a TXA2 antagonist (BM 13.177; 20 microM) or a Rho kinase inhibitor (Y27632; 10 microM) was infused additionally. TXB2 efflux was measured by enzyme-linked immunosorbent assay. The phosphorylation state of moesin (p-moesin), as indicator for Rho kinase activity, was assessed by Western blot analyses. Portal pressure was dose-dependently increased by H2O2 (maximum, 0.5 mM) and, to a lower extent, by xanthine/xanthine oxidase together with catalase. The portal pressure increase by H2O2 was attenuated by previous KC blockade. TXA2 efflux increased after H2O2 infusion and was reduced by KC blockade. The TXA2 antagonist counteracted the H2O2-induced increase in portal pressure. The Rho kinase inhibitor attenuated portal pressure increase after TXA2 analogue or H2O2 infusion. Hepatic levels of p-moesin were increased after H2O2 infusion. Reactive oxygen species increased portal pressure via stimulation of TXA2 production by KCs and a subsequent Rho kinase-dependent contraction of the intrahepatic vasculature. In conclusion, the KCs that are well known to produce H2O2 could also be activated by H2O2. This vicious cycle may best be interrupted at the earliest time point.

Kupffer cell activation in normal and fibrotic livers increases portal pressure via thromboxane A(2).

BACKGROUND/AIMS: Cirrhotic patients show an increased risk of variceal bleeding upon bacterial infections. Kupffer cells (KC) constitute the first macrophage population to become activated by bacterial beta-glucans and endotoxins derived from the gut. We therefore investigated whether and how KC activation increases portal pressure. METHODS: KC in normal and fibrotic livers from bile duct ligated (BDL) rats were activated by the beta-glucan component of zymosan in vivo and during isolated rat liver perfusion. RESULTS: Activation of KC in normal livers resulted in a severalfold increase of portal pressure in vivo as well as in isolated perfused liver preparations. This increase and the accompanying 40-fold stimulation of hepatic prostaglandin F(2alpha)/D(2) and thromboxane A(2) (TxA(2)) production in isolated perfused livers were attenuated by KC blockade. The TxA(2) synthase inhibitor furegrelate and the TxA(2) receptor antagonist BM 13.177 reduced the increase of portal perfusion pressure supporting TxA(2) as pivotal vasoconstrictor released by activated KC. Importantly, a more pronounced vasopressor response in fibrotic livers was related to a raise in KC density and a 10-fold increase of TxA(2) production after KC activation. CONCLUSIONS: KC activated by beta-glucans increase portal pressure through the release of TxA(2). This vasopressor response is augmented in BDL induced fibrosis.

IL-22-mediated liver cell regeneration is abrogated by SOCS-1/3 overexpression in vitro.

The IL-10-like cytokine IL-22 is produced by activated T cells. In this study, we analyzed the role of this cytokine system in hepatic cells. Expression studies were performed by RT-PCR and quantitative PCR. Signal transduction was analyzed by Western blot experiments and ELISA. Cell proliferation was measured by MTS and [(3)H]thymidine incorporation assays. Hepatocyte regeneration was studied in in vitro restitution assays. Binding of IL-22 to its receptor complex expressed on human hepatic cells and primary human hepatocytes resulted in the activation of MAPKs, Akt, and STAT proteins. IL-22 stimulated cell proliferation and migration, which were both significantly inhibited by the phosphatidylinositol 3-kinase inhibitor wortmannin. IL-22 increased the mRNA expression of suppressor of cytokine signaling (SOCS)-3 and the proinflammatory cytokines IL-6, IL-8, and TNF-alpha. SOCS-1/3 overexpression abrogated IL-22-induced STAT activation and decreased IL-22-mediated liver cell regeneration. Hepatic IL-22 mRNA expression was detectable in different forms of human hepatitis, and hepatic IL-22 mRNA levels were increased in murine T cell-mediated hepatitis in vivo following cytomegalovirus infection, whereas no significant differences were seen in an in vivo model of ischemia-reperfusion injury. In conclusion, IL-22 promotes liver cell regeneration by increasing hepatic cell proliferation and hepatocyte migration through the activation of Akt and STAT signaling, which is abrogated by SOCS-1/3 overexpression.

Role of Kupffer cells in host defense and liver disease.

Kupffer cells (KC) constitute 80-90% of the tissue macrophages present in the body. They reside within the lumen of the liver sinusoids, and are therefore constantly exposed to gut-derived bacteria, microbial debris and bacterial endotoxins, known to activate macrophages. Upon activation KC release various products, including cytokines, prostanoides, nitric oxide and reactive oxygen species. These factors regulate the phenotype of KC themselves, and the phenotypes of neighboring cells, such as hepatocytes, stellate cells, endothelial cells and other immune cells that traffic through the liver. Therefore, KC are intimately involved in the liver's response to infection, toxins, ischemia, resection and other stresses. This review summarizes established basic concepts of KC function as well as their role in the pathogenesis of various liver diseases.

PI 3-kinase pathway is responsible for antiapoptotic effects of atrial natriuretic peptide in rat liver transplantation.

AIM: To investigate the in vivo effect of atrial natriuretic peptide (ANP) and its signaling pathway during orthotopic rat liver transplantation. METHODS: Rats were infused with NaCl, ANP (5 microg/kg), wortmannin (WM, 16 microg/kg), or a combination of both for 20 min. Livers were stored in UW solution (4 degrees C) for 24 h, transplanted and reperfused. Apoptosis was examined by caspase-3 activity and TUNEL staining. Phosphorylation of Akt and Bad was visualized by Western blotting and phospho-Akt-localization by confocal microscopy. RESULTS: ANP-pretreatment decreased caspase-3 activity and TUNEL-positive cells after cold ischemia, indicating antiapoptotic effects of ANP in vivo. The antiapoptotic signaling of ANP was most likely caused by phosphorylation of Akt and Bad, since pretreatment with PI 3-kinase inhibitor WM abrogated the ANP-induced reduction of caspase-3 activity. Interestingly, analysis of liver tissue by confocal microscopy showed translocation of phosphorylated Akt to the plasma membrane of hepatocytes evoked by ANP. CONCLUSION: ANP activates the PI-3-kinase pathway in the liver in vivo leading to phosphorylation of Bad, an event triggering antiapoptotic signaling cascade in ischemic liver.

Characterization of organic anion transporter regulation, glutathione metabolism and bile formation in the obese Zucker rat.

BACKGROUND/AIMS: Alterations in hepatobiliary transporters may render fatty livers more vulnerable against various toxic insults. METHODS: We therefore studied expression and function of key organic anion transporters and their transactivators in 8-week-old obese Zucker rats, an established model for non-alcoholic fatty liver disease. RESULTS: Compared to their heterozygous littermates, obese animals showed a significant reduction in canalicular bile salt secretion, which was paralleled by significantly diminished Oatp2 mRNA and protein levels together with reduced nuclear HNF3beta, while expression of bile salt export pump, organic anion transporter (Oatp) 1 and multidrug resistance-associated protein (Mrp) 4 were unchanged. Impaired bile salt-independent bile flow in obese rats was associated with a 50% reduction of biliary secretion of the Mrp 2 model-substrates glutathione disulfide and S-(2,4-dinitrophenyl)glutathione. In line Mrp2 protein expression was reduced by 50% in obese rats. CONCLUSIONS: Oatp2 and Mrp2 expression is decreased in fatty liver and may impair metabolism and biliary secretion of numerous xenobiotics. Reduction of bile salt secretion and absence of biliary GSH excretion may contribute to impaired bile flow and posthepatic disorders associated with biliary GSH depletion.

Suramin inhibits death receptor-induced apoptosis in vitro and fulminant apoptotic liver damage in mice.

Suramin is a polysulfonated derivative of urea and has been widely used both to treat infections and as a chemotherapeutic drug. Suramin has been shown to inhibit growth factor signaling pathways; however, its effect on apoptosis is unknown. Here we show that suramin inhibits apoptosis induced through death receptors in hepatoma and lymphoma cells. It also inhibits the proapoptotic effect of chemotherapeutic drugs. The antiapoptotic mechanism is specific to cell type and is caused by reduced activation, but not altered composition, of the death-inducing signaling complex (DISC), and by inhibition of the initiator caspases 8, 9 and 10. Suramin also shows similar effects in in vivo models: apoptotic liver damage induced by CD95 stimulation and endotoxic shock mediated by tumor-necrosis factor (TNF) are inhibited in mice, but necrotic liver damage is not inhibited in a rat model of liver transplantation. Thus, the antiapoptotic property of suramin in the liver may be therapeutically exploited.

ANP-induced decrease of iron regulatory protein activity is independent of HO-1 induction.

Atrial natriuretic peptide (ANP)-preconditioned livers are protected from ischemia-reperfusion injury. ANP-treated organs show increased expression of heme oxygenase (HO)-1. Because HO-1 liberates bound iron, the aim of our study was to determine whether ANP affects iron regulatory protein (IRP) activity and, thus, the levels of ferritin. Rat livers were perfused with Krebs-Henseleit buffer [+/-ANP, 8-bromo-cGMP (8-Br-cGMP), and tin protoporphyrin, 20 min], stored in University of Wisconsin solution (4 degrees C, 24 h), and reperfused (120 min). IRP activity was assessed by gel-shift assays, and ferritin, IRP phosphorylation, and PKC localization were assessed by Western blot. Control livers displayed decreased IRP activity at the end of ischemia but no change in ferritin content during ischemia and reperfusion. ANP-pretreated livers showed reduced IRP activity, an effect mimicked by 8-Br-cGMP. Ferritin levels were increased in ANP-pretreated organs. Simultaneous perfusion of livers with ANP and tin protoporphyrin did not reduce ANP-induced action, arguing against a role for HO-1 in changes in IRP activity. ANP and 8-Br-cGMP decreased membrane localization of PKC-alpha and PKC-epsilon, but this modulation of PKC seems unrelated to inhibition of IRP binding. This work shows the cGMP-mediated attenuation of IRP binding activity by ANP, which results in increased hepatic ferritin levels. This change in IRPs is independent of ANP-induced HO-1 and reduced PKC activation.

Intravenous administration of glutathione protects parenchymal and non-parenchymal liver cells against reperfusion injury following rat liver transplantation.

AIM: To investigated the effects of intravenous administration of the antioxidant glutathione (GSH) on reperfusion injury following liver transplantation. METHODS: Livers of male Lewis rats were transplanted after 24 h of hypothermic preservation in University of Wisconsin solution in a syngeneic setting. During a 2-h reperfusion period either saline (controls, n=8) or GSH (50 or 100 micromol/(h/kg), n=5 each) was continuously administered via the jugular vein. RESULTS: Two hours after starting reperfusion plasma ALT increased to 1457+/-281 U/L (mean+/-SE) in controls but to only 908+/-187 U/L (P<0.05) in animals treated with 100 microGSH/(h/kg). No protection was conveyed by 50 micromol GSH(h/kg). Cytoprotection was confirmed by morphological findings on electron microscopy: GSH treatment prevented detachment of sinusoidal endothelial cells (SEC) as well as loss of microvilli and mitochondrial swelling of hepatocytes. Accordingly, postischemic bile flow increased 2-fold. Intravital fluorescence microscopy revealed a nearly complete restoration of sinusoidal blood flow and a significant reduction of leukocyte adherence to sinusoids and postsinusoidal venules. Following infusion of 50 micromol and 100 micromol GSH/(h/kg), plasma GSH increased to 65+/-7 mol/L and 97+/-18 mol/L, but to only 20+/-3 mol/L in untreated recipients. Furthermore, plasma glutathione disulfide (GSSG) increased to 7.5+/-1.0 mol/L in animals treated with 100 micro(h/kg) GSH but did not raise levels of untreated controls (1.8+/-0.5 mol/L) following infusion of 50 microGSH/(h/kg) (2.2+/-0.2 mol/L). CONCLUSION: Plasma GSH levels above a critical level may act as a "sink" for ROS produced in the hepatic vasculature during reperfusion of liver grafts. Therefore, GSH can be considered a candidate antioxidant for the prevention of reperfusion injury after liver transplantation, in particular since it has a low toxicity in humans.

Selective retroinfusion of GSH and cariporide attenuates myocardial ischemia-reperfusion injury in a preclinical pig model.

OBJECTIVE: Reperfusion after ischemia may contribute to loss of myocardial function and increase in infarct size. Scavenging of reactive oxygen species (ROS) by glutathione (GSH) and inhibition of the sodium-proton-exchanger by cariporide are both capable of reducing myocardial reperfusion injury. We tested the efficacy of both agents applied regionally into the myocardium immediately before reperfusion. METHODS: Neonatal rat cardiomyocytes (NRCMs) were exposed to either hypoxia (H, 8 h)/reoxygenation (R, 1 h) or H2O2 (300 microM) in the presence or absence of GSH (10 mg/ml). In pigs (n=5 per group), percutaneous LAD occlusion was performed for 60 min. Application of GSH (250 mg/kg) and/or cariporide (1 mg/kg) was achieved by pressure-regulated retroinfusion of the anterior cardiac vein draining the ischemic area starting 5 min before reopening of the occluded LAD. Seven days later, subendocardial segment shortening (SES) was analyzed by sonomicrometry. Infarct size was determined by methylene-blue staining of the non-ischemic area and tetrazolium red staining of the viable myocardium in the area at risk (AAR). RESULTS: NRCM incubated with GSH (10 mg/ml) survived H/R or H2O2 (0.3 mM) to a larger extent than untreated cells. In pigs, infarct size of untreated hearts (51 +/- 6% of the AAR) was not significantly altered by GSH or cariporide retroinfusion alone (41 +/- 3% and 42 +/- 6%). In contrast, combined retroinfusion of cariporide and GSH significantly reduced infarct size (29 +/- 3%). SES of the infarcted area was improved only after cariporide/GSH retroinfusion as compared to untreated hearts. Additional systemic application of CD18-antibody IB4 (1.5 mg/kg) did not alter infarct size or SES in comparison to GSH/cariporide retroinfusion alone. CONCLUSION: Timely application of GSH scavenging ROS and cariporide targeting ion imbalance provides cardioprotection to the postischemic heart, which is superior to either treatment alone. The lack of an effect of additional IB4 treatment may indicate that GSH/cariporide retroinfusion itself affects leukocyte-dependent reperfusion injury.

Glutathione protects the rat liver against reperfusion injury after prolonged warm ischemia.

OBJECTIVE: To evaluate the potential of postischemic intravenous infusion of the endogenous antioxidant glutathione (GSH) to protect the liver from reperfusion injury following prolonged warm ischemia. BACKGROUND DATA: The release of reactive oxygen species (ROS) by activated Kupffer cells (KC) and leukocytes causes reperfusion injury of the liver after warm ischemia. Therefore, safe and cost-effective antioxidant strategies would appear a promising approach to prevent hepatic reperfusion injury during liver resection, but need to be developed. METHODS: Livers of male Lewis rats were subjected to 60, 90, or 120 minutes of normothermic ischemia. During a 120 minutes reperfusion period either GSH (50, 100 or 200 micromol/h/kg; n= 6-8) or saline (n= 8) was continuously administered via the jugular vein. RESULTS: Postischemic GSH treatment significantly prevented necrotic injury to hepatocytes as indicated by a 50-60% reduction of serum ALT and AST. After 1 hour of ischemia and 2 hours of reperfusion apoptotic hepatocytes were rare (0.50 +/- 0.10%; mean +/- SD) and not different in GSH-treated animals (0.65 +/- 0.20%). GSH (200 micromol GSH/h/kg) improved survival following 2 hours of ischemia (6 of 9 versus 3 of 9 rats; P < 0.05). Intravital fluorescence microscopy revealed a nearly complete restoration of sinusoidal blood flow. This was paralleled by a reduction of leukocyte adherence to sinusoids and postsinusoidal venules. Intravenous GSH administration resulted in a 10- to 40-fold increase of plasma GSH levels, whereas intracellular GSH contents were unaffected. Plasma concentrations of oxidized glutathione (GSSG) increased up to 5-fold in GSH-treated animals suggesting counteraction of the vascular oxidant stress produced by activated KC. CONCLUSIONS: Intravenous GSH administration during reperfusion of ischemic livers prevents reperfusion injury in rats. Because GSH is well tolerable also in man, this novel approach could be introduced to human liver surgery.

Atrial natriuretic peptide preconditioning protects against hepatic preservation injury by attenuating necrotic and apoptotic cell death.

BACKGROUND/AIMS: Preconditioning of livers with the atrial natriuretic peptide (ANP) markedly reduces hepatic ischemia-reperfusion injury. Aim of this study was to characterize the influence of ANP preconditioning on necrotic and apoptotic cell death and on proliferation. METHODS: Rat livers were perfused with Krebs-Henseleit buffer with or without ANP or its second messenger analogue 8-Bromo cyclic guanosine monophosphate (8-Br cGMP) for 20 min, stored in cold University of Wisconsin solution (24 h), and reperfused for up to 120 min. Apoptosis and necrosis were determined using biochemical and morphological criteria, proliferation was assessed by Ki67 histochemistry. RESULTS: Apoptosis peaked after 24 h of cold ischemia. Preconditioning with both ANP and 8-Br-cGMP significantly reduced caspase-3-like activity and the number of triphosphate nick-end labelling-positive cells. Reduction of apoptosis was significant for hepatocytes, but not for endothelial cells. After ischemia, degenerative cell changes were clearly reduced in ANP pretreated livers. After reperfusion, ANP preconditioning led to a significant reduction of necrotic hepatocytes and endothelial cells in periportal zones. Cell proliferation was not affected by preconditioning. CONCLUSIONS: ANP reduces necrotic and apoptotic cell death without affecting the proliferation status. The protection takes place mainly in the periportal area and seems to be most prominent against necrosis of hepatocytes and endothelial cells during reperfusion.

Rapid development of esophageal squamous cell carcinoma after liver transplantation for alcohol-induced cirrhosis.

Liver transplant recipients have an increased risk of developing de novo malignancies. It is generally accepted that chronic alcohol abuse is a contributive factor in the pathogenesis of several malignancies, in particular, of oropharyngeal squamous cell carcinoma (SCC). Thus, patients with end-stage alcohol-induced cirrhosis could be at risk of esophageal SCC following orthotopic liver transplantation (OLT). From January 1986 to December 1997 a total of 313 patients underwent OLT for various indications. Of these patients, 72 had alcohol-related cirrhosis. Oropharyngeal and esophageal malignancies after OLT were not observed in non-alcoholic patients. In contrast, these malignancies were diagnosed in three male patients who underwent transplantation for alcohol-induced cirrhosis (incidence 4.2%). Furthermore, all patients had a history of tobacco abuse. The tumors were located in the tongue of one patient and in the esophagus of two patients. While SCC of the tongue became apparent 5 years after OLT, esophageal SCC was detected 8 and 16 months after transplantation. Shortly before transplantation, endoscopy of the esophagus had not revealed evidence of pre-malignant dysplastic lesions in any of these patients. Thus, esophageal SCC may develop rapidly in patients undergoing transplantation for alcohol-related cirrhosis with a history of tobacco abuse before liver transplantation, which warrants careful post-transplant screening of these patients.

Kupffer-cell specific induction of heme oxygenase 1 (hsp32) by the atrial natriuretic peptide--role of cGMP.

BACKGROUND/AIMS: Pretreatment with atrial natriuretic peptide (ANP) attenuates ischemia-reperfusion injury of livers via cGMP. Heme oxygenase-1 (HO-1) is known as a protective mediator in ischemia-reperfusion injury. The aim of this study was to investigate whether ANP affects the expression of HO-1. METHODS: Rat livers were perfused with KH-buffer with/without ANP or 8-Br-cGMP, kept in UW solution (4 degrees C, 24 h), and reperfused. HO-1 mRNA and protein was determined by Northern and Western blot, in situ hybridization, and immunohistochemistry in livers or isolated liver cells. RESULTS: ANP significantly elevated HO-1 mRNA expression at the end of the preconditioning period and was without effects at the end of ischemia and during reperfusion. 8-Br-cGMP did not affect HO-1 mRNA expression. In situ hybridization as well as immunohistological double-staining revealed that Kupffer cells but not hepatocytes showed HO-1 mRNA and protein expression. Hepatocytes revealed no changes in HO-1 protein whereas Kupffer cells showed a marked increase in HO-1 protein after ANP treatment. Inhibition of HO-1 did not abrogate hepatoprotection conveyed by ANP. CONCLUSION: Our data show the potency of ANP to specifically induce HO-1 in Kupffer cells independently of cGMP. This increased expression of HO-1 is not involved in hepatoprotection conferred by ANP being in line with the knowledge that ANP mediates hepatoprotection via cGMP.

Induction of cellular resistance against Kupffer cell-derived oxidant stress: a novel concept of hepatoprotection by ischemic preconditioning.

Ischemic preconditioning (IP) triggers protection of the liver from prolonged subsequent ischemia. However, the underlying protective mechanisms are largely unknown. We investigated whether and how IP protects the liver against reperfusion injury caused by Kupffer cell (KC)-derived oxidants. IP before 90 minutes of warm ischemia of rat livers in vivo significantly reduced serum alanine aminotransferase (AST) levels and leukocyte adherence to sinusoids and postsinusoidal venules during reperfusion. This protective effect was mimicked by postischemic intravenous infusion of glutathione (GSH), an antioxidative strategy against KC-derived H(2)O(2). Interestingly, no additional protection was achieved by infusion of GSH to preconditioned animals. These findings and several additional experiments strongly suggest IP mediated antioxidative effects: IP prevented oxidant cell injury in isolated perfused rat livers after selective KC activation by zymosan. Moreover, IP prevented cell injury and pertubations of the intracellular GSH/GSSG redox system caused by direct infusion of H(2)O(2) (0.5 mmol/L). IP-mediated resistance against H(2)O(2) could neither be blocked by the adenosine A2a antagonist DMPX nor mimicked by A2a agonist CGS21680. In contrast, H(2)O(2) resistance was abolished by the p38 mitogen-activated protein kinase (p38 MAPK) inhibitor SB203580, but induced when p38 MAPK was directly activated by anisomycin. In conclusion, we propose a novel concept of hepatoprotection by IP: protection of liver cells by enhancing their resistance against KC-derived H(2)O(2). Activation of p38 MAPK and preservation of the intracellular GSH/oxidized glutathione (GSSG) redox system, but not adenosine A2a receptor stimulation, seems to be pivotal for the development of H(2)O(2) resistance in preconditioned livers.