Angiotensin receptor antagonists in portal hypertension: fog over paradise

Antagonism of sphingosine 1-phosphate receptor 2 causes a selective reduction of portal vein pressure in bile duct-ligated rodents

Sinusoidal vasoconstriction, in which hepatic stellate cells operate as contractile machinery, has been suggested to play a pivotal role in the pathophysiology of portal hypertension. We investigated whether sphingosine 1-phosphate (S1P) stimulates contractility of those cells and enhances portal vein pressure in isolated perfused rat livers with Rho activation by way of S1P receptor 2 (S1P(2) ). Rho and its effector, Rho kinase, reportedly contribute to the pathophysiology of portal hypertension. Thus, a potential effect of S1P(2) antagonism on portal hypertension was examined. Intravenous infusion of the S1P(2) antagonist, JTE-013, at 1 mg/kg body weight reduced portal vein pressure by 24% without affecting mean arterial pressure in cirrhotic rats induced by bile duct ligation at 4 weeks after the operation, whereas the same amount of S1P(2) antagonist did not alter portal vein pressure and mean arterial pressure in control sham-operated rats. Rho kinase activity in the livers was enhanced in bile duct-ligated rats compared to sham-operated rats, and this enhanced Rho kinase activity in bile duct-ligated livers was reduced after infusion of the S1P(2) antagonist. S1P(2) messenger RNA (mRNA) expression, but not S1P(1) or S1P(3) , was increased in bile duct-ligated livers of rats and mice and also in culture-activated rat hepatic stellate cells. S1P(2) expression, determined in S1P 2LacZ/+ mice, was highly increased in hepatic stellate cells of bile duct-ligated livers. Furthermore, the increase of Rho kinase activity in bile duct-ligated livers was observed as early as 7 days after the operation in wildtype mice, but was less in S1P 2-/- mice.

CONCLUSION

S1P may play an important role in the pathophysiology of portal hypertension with Rho kinase activation by way of S1P(2) . The S1P(2) antagonist merits consideration as a novel therapeutic agent for portal hypertension.

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.

Expression of angiotensin II receptor type 1 is reduced in advanced rat liver fibrosis

In this study, we assessed the hypothesis that the expression of angiotensin II receptor type 1 (AGTR1) in liver tissue changes with increasing fibrosis, which would influence the antifibrotic efficacy of AGTR1 blockers. Rats were treated with candesartancilexetil (CAN) initiated 8 or 15 days after bile duct occlusion (BDO). Four weeks after BDO, AGTR1 mRNA and protein were decreased compared to those in sham-operated animals depending on the amount of fibrosis. Starting CAN early, but not late, reduced mRNA of profibrotic TGF-beta, MMP2, and Smad2. However, CAN had no significant effect on collagen I, fibrosis, or intrahepatic resistance. In conclusion, progression of liver fibrosis reduces AGTR1 expression. Therefore, in our model, antifibrotic effects of CAN are insufficient to improve fibrosis or intrahepatic resistance. However, if AGTR1 blockade is started early, a decrease in essential profibrotic molecules is achieved. Hence, early initiation of therapy with AGTR1 blockers may be crucial for the prevention of cirrhosis.

Portal pressure response to losartan compared with propranolol in patients with cirrhosis

OBJECTIVES

Losartan, an angiotensin II receptor blocker, has portal hypotensive effects. This study evaluates the effect of losartan on portal pressure after 14 days and compares it with that of propranolol.

METHODS

A total of 39 individuals with cirrhosis were randomized into two groups of 19 and 20 patients each and were treated with losartan and propranolol, respectively. Hepatic venous pressure gradient was measured at baseline and on day 14 of therapy. Responders to therapy had hepatic venous pressure gradient reduction of >/=20% of baseline value.

RESULTS

With losartan, 15 of 19 (78.94%) patients were responders and with propranolol, nine of 20 (45%) patients were responders (p < 0.05). Although the hepatic venous pressure gradient reduction (i.e., percentage from baseline) with losartan (26.74 +/- 21.7%) was higher than with propranolol (14.52 +/- 32%), the difference was not significant. The reduction in hepatic venous pressure gradient with losartan was contributed mainly by a significant drop of wedge hepatic venous pressure from 32.42 +/- 6.61 mm of Hg to 28.31 +/- 5.09 mm of Hg (p < 0.05) compared to that with propranolol, which was from 34.55 +/- 5.41 mm of Hg to 32.75 +/- 8.13 mm of Hg (p > 0.05). Responders among alcohol-abusing patients were significantly higher with losartan (81.8%) compared to those on propranolol (27.2%; p < 0.05). In the losartan group, all seven nonascitic cirrhotic individuals, as compared with two of five in the propranolol group, responded to the drugs. During the study, no significant side effects were observed in either group (who were not receiving diuretics) or in follow-up with diuretics.

CONCLUSIONS

Losartan is as effective as propranolol in reducing portal pressure in cirrhotic patients who are not receiving diuretics. Losartan is also superior to propranolol for achieving target level hepatic venous gradient for prevention of variceal bleeding in nonascitic and alcohol-abusing cirrhotic patients.