Phosphodiesterases in the Liver as Potential Therapeutic Targets of Cirrhotic Portal Hypertension.

Liver cirrhosis is a frequent condition with high impact on patients' life expectancy and health care systems. Cirrhotic portal hypertension (PH) gradually develops with deteriorating liver function and can lead to life-threatening complications. Other than an increase in intrahepatic flow resistance due to morphological remodeling of the organ, a functional dysregulation of the sinusoids, the smallest functional units of liver vasculature, plays a pivotal role. Vascular tone is primarily regulated by the nitric oxide-cyclic guanosine monophosphate (NO-cGMP) pathway, wherein soluble guanylate cyclase (sGC) and phosphodiesterase-5 (PDE-5) are key enzymes. Recent data showed characteristic alterations in the expression of these regulatory enzymes or metabolite levels in liver cirrhosis. Additionally, a disturbed zonation of the components of this pathway along the sinusoids was detected. This review describes current knowledge of the pathophysiology of PH with focus on the enzymes regulating cGMP availability, i.e., sGC and PDE-5. The results have primarily been obtained in animal models of liver cirrhosis. However, clinical and histochemical data suggest that the new biochemical model we propose can be applied to human liver cirrhosis. The role of PDE-5 as potential target for medical therapy of PH is discussed.

Effects of Nuclear Factor-E2-related factor 2/Heme Oxygenase 1 on splanchnic hemodynamics in experimental cirrhosis with portal hypertension.

OBJECTIVE: We explored the effects of Nuclear Factor-E2-related factor 2 (Nrf2) and Heme Oxygenase 1 (HO-1) on splanchnic hemodynamics in portal hypertensive rats. METHODS: Experimental cirrhosis with portal hypertension was induced by intraperitoneal injection of carbon tetrachloride. The expression of proteins was examined by immunoblotting. Hemodynamic studies were performed by radioactive microspheres. The vascular perfusion system was used to measure the contractile response of mesentery arterioles in rats. RESULTS: Nrf2 expression in the nucleus and HO-1 expression in cytoplasm was significantly enhanced in portal hypertensive rats. Portal pressure, as well as regional blood flow, increased significantly in portal hypertension and can be blocked by tin protoporphyrin IX. The expression of endogenous nitric oxide synthase and vascular endothelial growth factors increased significantly compared to normal rats, while HO-1 inhibition decreased the expression of these proteins significantly. The contractile response of mesenteric arteries decreased in portal hypertension, but can be partially recovered through tin protoporphyrin IX treatment. CONCLUSIONS: The expression of Nrf2/HO-1 increased in mesenteric arteries of portal hypertensive rats, which was related to oxidative stress. HO-1was involved in increased portal pressure and anomaly splanchnic hemodynamics in portal hypertensive rats.

Hepatic dimethylarginine-dimethylaminohydrolase1 is reduced in cirrhosis and is a target for therapy in portal hypertension.

BACKGROUND & AIMS: Portal hypertension is characterized by reduced hepatic eNOS activity. Asymmetric-dimethylarginine (ADMA), an eNOS inhibitor, is elevated in cirrhosis and correlates with the severity of portal hypertension. Dimethylarginine dimethylaminohydrolase-1 (DDAH-1) is the key enzyme metabolizing hepatic ADMA. This study characterized DDAH-1 in cirrhosis, and explored hepatic DDAH-1 reconstitution through farnesoid X receptor (FXR) agonism and DDAH-1 gene therapy. METHODS: DDAH-1 immunohistochemistry was conducted on human cirrhosis and healthy liver tissue. Subsequently, sham-operated or bile-duct-ligated (BDL) cirrhosis rats were treated with the FXR agonist obeticholic acid (OA, 5 mg/kg) or vehicle for 5 days. Further, animals underwent hydrodynamic injection with DDAH-1-expressing plasmid or saline control, which resulted in the following groups: sham+saline, BDL+saline, BDL+DDAH-1-plasmid. Portal pressure (PP) measurements were performed. Plasma ALT was measured by COBAS INTEGRA, DDAH-1 expression by qPCR and Western blot, eNOS activity by radiometric assay. RESULTS: Immunohistochemistry and Western-blotting confirmed hepatic DDAH-1 was restricted to hepatocytes, and expression decreased significantly in cirrhosis. In BDL rats, reduced DDAH-1 expression was associated with elevated hepatic ADMA, reduced eNOS activity and high PP. OA treatment significantly increased DDAH-1 expression, reduced hepatic tissue ADMA, and increased liver NO generation. PP was significantly reduced in BDL+OA vs. BDL+vehicle (8±1 vs. 13.5±0.6 mmHg; p<0.01) with no change in the mean arterial pressure (MAP). Similarly, DDAH-1 hydrodynamic injection significantly increased hepatic DDAH-1 gene and protein expression, and significantly reduced PP in BDL+DDAH-1 vs. BDL+saline (p<0.01). CONCLUSIONS: This study demonstrates DDAH-1 is a specific molecular target for portal pressure reduction, through actions on ADMA-mediated regulation of eNOS activity. Our data support translational studies, targeting DDAH-1 in cirrhosis and portal hypertension.

G-protein-coupled receptor kinase interactor-1 (GIT1) is a new endothelial nitric-oxide synthase (eNOS) interactor with functional effects on vascular homeostasis.

Endothelial cell nitric-oxide (NO) synthase (eNOS), the enzyme responsible for synthesis of NO in the vasculature, undergoes extensive post-translational modifications that modulate its activity. Here we have identified a novel eNOS interactor, G-protein-coupled receptor (GPCR) kinase interactor-1 (GIT1), which plays an unexpected role in GPCR stimulated NO signaling. GIT1 interacted with eNOS in the endothelial cell cytoplasm, and this robust association was associated with stimulatory eNOS phosphorylation (Ser(1177)), enzyme activation, and NO synthesis. GIT1 knockdown had the opposite effect. Additionally, GIT1 expression was reduced in sinusoidal endothelial cells after liver injury, consistent with previously described endothelial dysfunction in this disease. Re-expression of GIT1 after liver injury rescued the endothelial phenotype. These data emphasize the role of GPCR signaling partners in eNOS function and have fundamental implications for vascular disorders involving dysregulated eNOS.

Droxidopa, an oral norepinephrine precursor, improves hemodynamic and renal alterations of portal hypertensive rats.

UNLABELLED: We aimed to evaluate the effects of droxidopa (an oral synthetic precursor of norepinephrine) on the hemodynamic and renal alterations of portal hypertensive rats. Sham, portal vein-ligated (PVL), and 4-week biliary duct-ligated (BDL) rats received a single oral dose of droxidopa (25-50 mg/kg) or vehicle and hemodynamic parameters were monitored for 2 hours. Two groups of BDL and cirrhotic rats induced by carbon tetrachloride (CCl(4) ) were treated for 5 days with droxidopa (15 mg/kg, twice daily, orally); hemodynamic parameters and blood and urinary parameters were assessed. The droxidopa effect on the Rho kinase (RhoK) / protein kinase B (AKT) / endothelial nitric oxide synthase (eNOS) pathways was analyzed by western blot in superior mesenteric artery (SMA). The acute administration of droxidopa in PVL and BDL rats caused a significant and maintained increase in arterial pressure and mesenteric arterial resistance, with a significant decrease of mesenteric arterial and portal blood flow, without changing portal pressure and renal blood flow. Two-hour diuresis greatly increased. Carbidopa (DOPA decarboxylase inhibitor) blunted all effects of droxidopa. Chronic droxidopa therapy in BDL rats produced the same beneficial hemodynamic effects observed in the acute study, did not alter liver function parameters, and caused a 50% increase in 24-hour diuresis volume (7.4 ± 0.9 mL/100g in BDL vehicle versus 11.8 ± 2.5 mL/100g in BDL droxidopa; P = 0.01). Droxidopa-treated rats also showed a decreased ratio of p-eNOS/eNOS and p-AKT/AKT and increased activity of RhoK in SMA. The same chronic treatment in CCl(4) rats caused similar hemodynamic effects and produced significant increases in diuresis volume and 24-hour natriuresis (0.08 ± 0.02 mmol/100g in CCl(4) vehicle versus 0.23 ± 0.03 mmol/100g in CCl(4) droxidopa; P = 0.014). CONCLUSION: Droxidopa might be an effective therapeutic agent for hemodynamic and renal alterations of liver cirrhosis and should be tested in cirrhosis patients.

Small liver remnants are more vulnerable to ischemia/reperfusion injury after extended hepatectomies: a case-control study.

BACKGROUND: There is evidence that small-for-size liver grafts are more vulnerable to ischemia/reperfusion injury after liver transplantation. We hypothesized that ischemic injury is more pronounced in small liver remnants after major hepatectomies. METHODS: Fifteen patients underwent extended hepatectomy with remnant liver mass less than 30% of standard liver weight (study group). These patients were matched with patients who underwent minor liver resection, with liver remnants equal to or more than 70% of standard liver weight (control group). Ischemia/reperfusion injury was assessed by tissue caspase-3 activity postoperatively as well as peak aspartate aminotransferase (AST) values and a-glutathione S-transferase (α-GST) levels adjusted for remnant liver weight. In addition, caspase-3 activity and adjusted serum markers of hepatocyte injury were correlated with the degree of postoperative portal hypertension. RESULTS: Caspase-3 activity was higher in patients with small liver remnants (22.66±6.57 vs. 12.60±4.06 count per high-power field, p<0.001). Serum markers of hepatocyte injury, when adjusted per gram of liver remnant, were found to be higher in the study group than in the control group (AST: 1.26±0.25 vs. 0.54±0.11 IU g(-1), p<0.001; α-GST: 0.14±0.02 vs. 0.08±0.01 IU g(-1), p<0.001). Tissue caspase-3 expression in the small liver remnant group correlated with both AST and α-GST levels adjusted per gram of liver remnant (r2=0.51, p=0.005 and r2=0.71, p<0.001, respectively). Significant correlations between postoperative portal hypertension and the same markers as well as caspase-3 activity were also demonstrated. CONCLUSION: Liver remnants less than 30% of standard liver weight are much more susceptible to ischemia/reperfusion injury than controls twice the size. Adjustment of serum markers of hepatocyte injury to the liver remnant weight depicts injury more accurately.

Arsenic-stimulated liver sinusoidal capillarization in mice requires NADPH oxidase-generated superoxide.

Environmental arsenic exposure, through drinking contaminated water, is a significant risk factor for developing vascular diseases and is associated with liver portal hypertension, vascular shunting, and portal fibrosis through unknown mechanisms. We found that the addition of low doses of arsenite to the drinking water of mice resulted in marked pathologic remodeling in liver sinusoidal endothelial cells (SECs), including SEC defenestration, capillarization, increased junctional PECAM-1 expression, protein nitration, and decreased liver clearance of modified albumin. Furthermore, the pathologic changes observed after in vivo exposure were recapitulated in isolated mouse SECs exposed to arsenic in culture. To investigate the role of NADPH oxidase-generated ROS in this remodeling, we examined the effect of arsenite in the drinking water of mice deficient for the p47 subunit of the NADPH oxidase and found that knockout mice were protected from arsenite-induced capillarization and protein nitration. Furthermore, ex vivo arsenic exposure increased SEC superoxide generation, and this effect was inhibited by addition of a Nox2 inhibitor and quenched by the cell-permeant superoxide scavenger. In addition, inhibiting either oxidant generation or Rac1-GTPase blocked ex vivo arsenic-stimulated SEC differentiation and dysfunction. Our data indicate that a Nox2-based oxidase is required for SEC capillarization and that it may play a central role in vessel remodeling following environmentally relevant arsenic exposures.

iNOS expression in vascular resident macrophages contributes to circulatory dysfunction of splanchnic vascular smooth muscle contractions in portal hypertensive rats.

Portal hypertension, a major complication of cirrhosis, is caused by both increased portal blood flow due to arterial vasodilation and augmented intrahepatic vascular resistance due to sinusoidal constriction. In this study, we examined the possible involvement of resident macrophages in the tone regulation of splanchnic blood vessels using bile duct ligated (BDL) portal hypertensive rats and an in vitro organ culture method. In BDL cirrhosis, the number of ED2-positive resident macrophages increased by two- to fourfold in the vascular walls of the mesenteric artery and extrahepatic portal vein compared with those in sham-operated rats. Many ED1-positive monocytes were also recruited into this area. The expression of inducible nitric oxide (NO) synthase (iNOS) mRNA was increased in the vascular tissues isolated from BDL rats, and accordingly, nitrate/nitrite production was increased. Immunohistochemistry revealed that iNOS was largely expressed in ED1-positive and ED2-positive cells. We further analyzed the effect of iNOS expression on vascular smooth muscle contraction using an in vitro organ culture system. iNOS mRNA expression and nitrate production significantly increased in vascular tissues (without endothelium) incubated with 1 µg/ml lipopolysaccharide (LPS) for 6 h. Immunohistochemistry indicated that iNOS was largely expressed in ED2-positive resident macrophages. α-Adrenergic-stimulated contractility of the mesenteric artery was greatly suppressed by LPS treatment and was restored by N(G)-nitro-L-arginine methyl ester (NO synthase inhibitor); in contrast, portal vein contractility was largely unaffected by LPS. Sodium nitroprusside (NO donor) and 8-bromo-cGMP showed greater contractile inhibition in the mesenteric artery than in the portal vein with decreasing myosin light chain phosphorylation. In the presence of an α-adrenergic agonist, the mesenteric artery cytosolic Ca(2+) level was greatly reduced by sodium nitroprusside; however, the portal vein Ca(2+) level was largely unaffected. These results suggest that the induction of iNOS in monocytes/macrophages contributes to a hypercirculatory state in the cirrhosis model rat in which the imbalance of the responsiveness of visceral vascular walls to NO (mesenteric artery >> portal vein) may account for the increased portal venous flow in portal hypertension.

Role of endothelial nitric oxide synthase in the development of portal hypertension in the carbon tetrachloride-induced liver fibrosis model.

Portal hypertension (PHT) is a complication of liver cirrhosis and directly increases mortality and morbidity by increasing the propensity of venous hemorrhage. There are two main underlying causations for PHT, increased hepatic resistance and systemic hyperdynamic circulation. Both are related to localized aberrations in endothelial nitric oxide synthase (eNOS) function and NO biosynthesis. This study investigates the importance of eNOS and systemic hyperdynamic-associated hyperemia to better understand the pathophysiology of PHT. Wild-type and eNOS(-/-) mice were given the hepatotoxin CCl(4) for 4-12 wk. Hepatic fibrosis was determined histologically following collagen staining. Portal venous pressure, hepatic resistance, and hyperemia were determined by measuring splenic pulp pressure (SPP), hepatic portal-venous perfusion pressure (HPVPP), abdominal aortic flow (Qao), and portal venous flow (Qpv). Hepatic fibrosis developed equally in wild-type and eNOS(-/-) CCl(4)-exposed mice. SPP, Qao, and Qpv increased rapidly in wild-type CCl(4)-exposed mice, but HPVPP did not. In eNOS(-/-) CCl(4) mice, Qao was not increased, SPP was partially increased, and HPVPP and Qpv were increased nonsignificantly. We concluded that the systemic hyperemia component of hyperdynamic circulation is eNOS dependent and precedes increased changes in hepatic resistance. Alternative mechanisms, possibly involving cyclooxygenase, may contribute. eNOS maintains normal hepatic resistance following CCl(4)-induced fibrosis. Consequently, increased portal pressure following chronic CCl(4) exposure is linked to hyperdynamic circulation in wild-type mice and increased hepatic resistance in eNOS(-/-) mice.

Vascular stasis, intestinal hemorrhage, and heightened vascular permeability complicate acute portal hypertension in cd39-null mice.

Vasoactive factors that regulate splanchnic hemodynamics include nitric oxide, catecholamines, and possibly extracellular nucleosides/nucleotides (adenosine, ATP). CD39/ectonucleoside triphosphate diphosphohydrolase-1 (NTPDase1) is the major vascular ectonucleotidase that hydrolyzes extracellular nucleotides. CD39 activity may be modulated by vascular injury, inflammation, and altered oxygen tension. Altered Cd39 expression by the murine hepatosplanchnic vasculature may impact hemodynamics and portal hypertension (PHT) in vivo. We noted that basal portal pressures (PPs) were comparable in wild-type and Cd39-null mice (n = 9). ATP infusions resulted in increments in PP in wild-type mice, but, in contrast, this significantly decreased in Cd39-null mice (n = 9) post-ATP in a nitric oxide-dependent manner. We then studied Cd39/NTPDase1 deletion in the regulation of portal hemodynamics, vascular integrity, and intestinal permeability in a murine model of PHT. Partial portal vein ligation (PPVL) was performed in Cd39-null (n = 44) and wild-type (n = 23) mice. Sequential measurements obtained after PPVL were indicative of comparable levels of PHT (ranges 14-29 mmHg) in both groups. There was one death in the wild-type group and eight in the Cd39-null group from intestinal bleeding (P = 0.024). Circulatory stasis in the absence of overt portal vein thrombosis, portal congestion, intestinal hemorrhage, and increased permeability were evident in all surviving Cd39-null mice. Deletion of Cd39 results in deleterious outcomes post-PPVL that are associated with significant microcirculatory derangements and major intestinal congestion with hemorrhage mimicking acute mesenteric occlusion. Absent Cd39/NTPDase1 and decreased generation of adenosine in the splanchnic circulation cause heightened vascular permeability and gastrointestinal hemorrhage in PPVL.

Defective endothelial nitric oxide synthase signaling is mediated by rho-kinase activation in rats with secondary biliary cirrhosis.

In liver cirrhosis, down-regulation of endothelial nitric oxide synthase (eNOS) has been implicated as a cause of increased intrahepatic resistance. We investigated whether Rho-kinase activation is one of the molecular mechanisms involved in defective eNOS signaling in secondary biliary cirrhosis. Liver cirrhosis was induced by bile duct ligation (BDL). We measured mean arterial pressure (MAP), portal venous pressure (PVP), and hepatic tissue blood flow (HTBF) during intravenous infusion of saline (control), 0.3, 1, or 2 mg/kg/hour fasudil for 60 minutes. In BDL rats, 1 and 2 mg/kg/hour fasudil significantly reduced PVP by 20% compared with controls but had no effect on HTBF. MAP was significantly reduced in response to 2 mg/kg/hour fasudil. In the livers of BDL rats, 1 and 2 mg/kg/hour fasudil significantly suppressed Rho-kinase activity and significantly increased eNOS phosphorylation, compared with controls. Fasudil significantly reduced the binding of serine/threonine Akt/PKB (Akt) to Rho-kinase and increased the binding of Akt to eNOS. These results show in secondary biliary cirrhosis that (1) Rho-kinase activation with resultant eNOS down-regulation is substantially involved in the pathogenesis of portal hypertension and (2) Rho-kinase might interact with Akt and subsequently inhibit the binding of Akt to eNOS.

[Clinical and morphological characteristics and some mechanisms of portal gastroduodenopathy in liver cirrhosis].

We have found out the clinical presentations and peculiarities of endoscopic and morphologic view of pathologies of mucous membrane of gastroduodenal zone caused by liver cirrhosis. We have examined 74 patients with liver cirrhosis of viral and nonviral etiology using the clinical, endoscopic, morphologic and immunohistochemical methods.We have found that during liver cirrhosis morphometric rates of epithelial cells of mucous coat of stomach that produce somatostatin and endothelin-1 decrease and morphometric rates of epithelial cells that produce nitrogen oxide synthase increase. We have also found out that during liver cirrhosis proliferate activity decrease and apoptosis of epithelial cell of mucous coat of stomach increase.

Role of nitric oxide synthase and cyclooxygenase in hyperdynamic splanchnic circulation of portal hypertension.

BACKGROUND: Nitric oxide (NO) and prostacyclin (PGI2) are both powerful vasoactive substances correlated with the hyperhemodynamics of portal hypertension (PHT), a common syndrome characterized by a pathological increase in portal venous pressure. The purpose of the present study was to evaluate the possible interaction between these two endothelial vasodilators, together with their respective roles in the hyperdynamic splanchnic circulation of PHT. METHODS: Ninety-six male Sprague-Dawley rats were randomly divided into three groups: intrahepatic portal hypertension (IHPH) induced by injection of CCl4 (n=31), prehepatic portal hypertension (PHPH) induced by partial stenosis of the portal vein (n=33), and sham-operated controls (SO) (n=32). Animals of each group received indomethacin (INDO), a cyclooxygenase (COX) inhibitor, either short-term (7 days) or long-term (15 days), with saline as control. Free portal pressure (FPP), together with the concentration of NO and PGI2 in serum were measured. The activity of constitutive nitric oxide synthase (cNOS) and inducible nitric oxide synthase (iNOS) in the abdominal aorta and small intestine were determined by spectrophotometry. RT-PCR was performed to measure the levels of cNOS and iNOS mRNA in the arteries and small intestines. RESULTS: Compared with SO rats, the concentrations of NO and PGI2 in PHT rats were elevated, which were consistent with the increased FPP (P<0.05). Although administration of INDO persistently decreased the concentration of PGI2 in serum (P<0.05), the long-term INDO-treated IHPH and PHPH groups had restored splanchnic hyperdynamic circulation, demonstrated by the enhanced FPP (P<0.05). Furthermore, the changes of dynamic circulatory state in both IHPH and PHPH rats were concomitant with the expression and activity of iNOS and the concentration of NO (P<0.05). Although the expression and activity of cNOS in abdominal aorta of PHT rats were higher than in SO rats (P<0.05), there was no difference in small intestinal tissues between PHT and SO rats (P>0.05). Moreover, the changes of iNOS activity and mRNA expression were more marked than cNOS in PHT rats, and there was no difference in expression and activity of cNOS between PHT rats treated by short- and long-term INDO (P>0.05). CONCLUSIONS: iNOS plays an important role in the hemodynamic abnormalities of PHT induced by overproduction of NO. There is a possible interaction between PGI2 and NO in hyperhemodynamics of PHT, but PGI2 may not be a mediator in the formation and development of the hyperdynamic circulatory state in PHT rats.

The soluble guanylate cyclase stimulator riociguat reduces fibrogenesis and portal pressure in cirrhotic rats.

In cirrhotic patients, portal hypertension (PHT) deteriorates survival, yet treatment options are limited. A major contributor to increased intrahepatic vasoconstriction in PHT is dysfunctional nitric-oxide signaling. Soluble guanylate cyclase (sGC) is the receptor of nitric-oxide and can be stimulated by riociguat. Riociguat is approved for pulmonary hypertension but has not been studied in liver cirrhosis. In this study we assessed the effects of riociguat on PHT and liver fibrosis in cholestatic (bile duct ligation, BDL) and toxic (carbon-tetrachloride, CCl4) rat models. In cirrhotic livers sGC expression was upregulated. In BDL rats, riociguat reduced liver fibrosis and decreased portal pressure without affecting systemic hemodynamics. In an early BDL disease stage, riociguat decreased bile duct proliferation, improved sinusoidal vascular dysfunction and inhibited angiogenesis. In advanced BDL riociguat exhibited anti-inflammatory effects. In CCl4 rats the beneficial effects of riociguat treatment were less pronounced and confined to an early disease stage. Similarly, in patients with cholestatic cirrhosis and PHT nitrates (that induce sGC activity) decreased portal pressure more effectively than in patients with non-cholestatic etiology. We also found an improvement of transaminases in patients with pulmonary hypertension receiving riociguat. Our findings support the clinical development of sGC stimulators in patients with cirrhotic PHT.

Case report of a modified Meso-Rex bypass as a treatment technique for late-onset portal vein cavernous transformation with portal hypertension after adult deceased-donor liver transplantation.

RATIONALE: Portal vein thrombosis is a complication after liver transplantation and cavernous transformation of the portal vein (CTPV) is a result of portal vein thrombosis, with symptoms of portal hypertension revealed by an enhanced CT scan. Meso-Rex bypass is an artificial shunt connecting the left portal vein to the superior mesenteric vein and is mainly used for idiopathic cavernomas. This technique is also used for post-transplant portal vein thrombosis in pediatric patients thereby bypassing obstructed sites of the extrahepatic portal vein. Here we report about an adult patient who was treated by connecting the cystic part of the portal vein to the splenic vein instead of the superior mesenteric vein. PATIENTS CONCERN: An adult male patient with post-liver transplantation portal vein cavernous transformation suffered from hypersplenism and elevated hepatic enzymes. DIAGNOSIS: The last follow up revealed irregular and obvious hypersplenism, and splenomegaly had occurred, while an enhanced CT scan revealed serious esophagogastric varices and CTPV in addition to occluded right and common PV trunks. INTERVENTION: The patient was treated by connecting the cystic part of the portal vein to the splenic vein instead of the superior mesenteric vein. OUTCOME: After the operation, a satisfactory velocity was confirmed 1 month postoperatively and the shunt still remained patent at the 6-month postoperation follow-up. LESSONS: A Meso-Rex bypass intervention connecting the left portal vein to the splenic vein instead of the superior mesenteric vein after liver transplantation in an adult patient with right and common portal vein occlusions has been successfully performed as an alternative approach.

Hepatic fibrosis, stellate cells, and portal hypertension.

Hepatic fibrogenesis is the common result of injury to the liver. It is believed to be a critical factor that leads to hepatic dysfunction and may be important in portal hypertension. The fibrogenic response is a complex process in which accumulation of extracellular matrix proteins, tissue contraction, and alteration in blood flow are prominent. A critical event in fibrogenesis is activation of resident perisinusoidal cells that are termed "hepatic stellate cells". Stellate cell activation is characterized by many important phenotypes, including enhanced extracellular matrix synthesis and prominent contractility. Given the central role of stellate cell activation in hepatic fibrogenesis (and portal hypertension), effective therapy for hepatic fibrogenesis is most likely will be directed at this event.

Antioxidant role of heme oxygenase-1 in prehepatic portal hypertensive rats.

AIM: To study the effect of bilirubin on the oxidative liver status and the activity and expression of heme oxygenase-1 (HO-1) in rat liver injury induced by prehepatic portal hypertension. METHODS: Wistar male rats, weighing 200-250 g, were divided at random into two groups: one group with prehepatic portal hypertension (PH) induced by regulated prehepatic portal vein ligation (PPVL) and the other group corresponded to sham operated rats. Portal pressure, oxidative stress parameters, antioxidant enzymes, HO-1 activity and expression and hepatic sinusoidal vasodilatation were measured. RESULTS: In PPVL rats oxidative stress was evidenced by a marked increase in thiobarbituric acid reactive substances (TBARS) content and a decrease in reduced glutathione (GSH) levels. The activities of liver antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) were also diminished while activity and expression of HO-1 were enhanced. Administration of bilirubin (5 mumol/kg body weight) 24 h before the end of the experiment entirely prevented all these effects. Pretreatment with Sn-protoporphyrin IX (Sn-PPIX) (100 mug/kg body weight, i.p.), a potent inhibitor of HO, completely abolished the oxidative stress and provoked a slight decrease in liver GSH levels as well as an increase in lipid peroxidation. Besides, carbon monoxide, another heme catabolic product, induced a significant increase in sinusoidal hepatic areas in PPVL group. Pretreatment of PPVL rats with Sn-PPIX totally prevented this effect. CONCLUSION: These results suggest a beneficial role of HO-1 overexpression in prehepatic portal hypertensive rats.

Prehepatic portal hypertension induces alterations in cytochrome oxidase activity in the rat adrenal gland.

One approach to assess neuroendocrine response to portal hypertension in short-term portal vein-stenosed rats consists in studying metabolic and functional activity patterns in adrenal glands using mitochondrial enzyme cytochrome c oxidase (COX) as a histochemical marker. Male Wistar rats were divided into two groups: a control group (Group I; n = 8), in which the animals did not undergo any operative intervention, and a triple calibrated portal vein stenosis group (TPVS) (Group II; n = 7). The sections of suprarenal glands were histochemically stained for COX and the optical densitometry was measured by a computer image analyzer attached to a microscope. In TPVS rats, COX activity in the adrenal gland cortex is lower than in control rats and affects the fascicular (52.30, 47.16-60.98, vs. 67.12, 60.31-73.89, p = .002), glomerular (49.68, 46.19-53.56 vs. 70.47, 64.64-73.51, p < .001), and reticular (47.35, 35.63-54.39, vs. 55.37, 49.76-58.97; p < .05) layers. In contrast, COX activity in the adrenal gland medulla is similar in TPVS rats and in control rats (29.91, 29.54-31.18, vs. 29.67, 28.95-30.23). The changes in adrenocortical COX activity in short-term-TPVS rats could constitute a pathogenic factor for both splanchnic and systemic hyperdynamic circulations, described in this experimental model of prehepatic portal hypertension.