Tetrandrine inhibits the activation of rat hepatic stellate cells via up-regulation of Smad 7

Aim To investigate the effect of lower concentrations of tetrandrine on culture-activation and transforming growth factor-β_1 (TGF-β_1)-stimulated activation of quiescent rat hepatic stellate cells (HSCs), and the possible relations between the underlying mechanism of the effect and TGF-β signaling via its receptors. Methods Freshly isolated HSCs from rat liver were subjected to treatment with lower concentrations of tetrandrine (0.4, 0.8, 1.6 and 3.2 μmol·L -1, respectively) at set point. The activation state of HSCs was determined by cell morphological features and detection of smooth muscle α-actin (α-SMA) using immunocytochemistry; HSCs were stimulated with TGF-β_1 (5 μg·L -1), in the presence or absence of an effective concentration of tetrandrine (1.6 μmol·L -1), which was determined formerly, and mRNA of TGF-β_1 and its typeⅠand typeⅡreceptors, Smad 3 and Smad 7 were analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR), while protein levers of α-SMA, Smad 3 and Smad 7 were evaluated by Western blot. Results Tetrandrine 0.4-3.2 μmol·L -1 prevented morphological transformation of HSCs from the quiescent state to the activated one, and the α-SMA expression was inhibited. Tetrandrine (1.6 μmol·L -1) also inhibited TGF-β_1-stimulated α-SMA expression in HSCs. The results of RT-PCR showed a decreased TGF-β_1 mRNA comparing to an up-regulation of Smad 7 mRNA, and the up-regulation of Smad 7 protein was also observed by Western blot, while the expressions of type Ⅰand type Ⅱ TGF-β_1 receptors and Smad 3 were changed by tetrandrine insignificantly. Conclusion Tetrandrine at lower concentrations has a significant inhibiting effect on culture-activation and TGF-β_1-stimulated activation of rat HSCs. This effect of tetrandrine may be associated with the up-regulation Smad 7 which in turn blocks TGF-β_1 expression and its downstream signaling.