Salvianolic acid B lowers portal pressure in cirrhotic rats and attenuates contraction of rat hepatic stellate cells by inhibiting RhoA signaling pathway

Abstract

The contraction of hepatic stellate cells (HSCs) has a critical role in the regulation of intrahepatic vascular resistance and portal hypertension. Previous studies have confirmed that salvianolic acid B (Sal B) is effective against liver fibrosis. In the present study, we evaluated the effect of Sal B on portal hypertension and on HSCs contractility. Liver cirrhosis was induced in rats by peritoneal injection of dimethylnitrosamine and the portal pressure was measured. HSCs contraction was evaluated by collagen gel contraction assay. Glycerol-urea gel electrophoresis was performed to determine the phosphorylation of myosin light chain 2 (MLC2). F-actin stress fiber polymerization was detected by fluorescein isothiocyanate-labeled phalloidin. Intracellular Ca2+ and RhoA signaling activation were also measured. Sal B effectively reduced the portal pressure in DMN-induced cirrhotic rats. It decreased the contraction by endothelin-1 (ET-1)-activated HSCs by ∼66.5% and caused the disassembly of actin stress fibers and MLC2 dephosphorylation. Although Sal B reduced ET-1-induced intracellular Ca2+ increase, blocking Ca2+ increase completely by BAPTA-AM, a Ca2+ chelator, barely affected the magnitude of contraction. Sal B decreased ET-1-induced RhoA and Rho-associated coiled coil-forming protein kinase (ROCK) II activation by 66.84% and by 76.79%, respectively, and inhibited Thr696 phosphorylation of MYPT1 by 80.09%. In vivo, Sal B lowers the portal pressure in rats with DMN-induced cirrhosis. In vitro, Sal B attenuates ET-1-induced HSCs contraction by inhibiting the activation of RhoA and ROCK II and the downstream MYPT1 phosphorylation at Thr696. We consider Sal B a potential candidate for the pharmacological treatment of portal hypertension.