Platyconic acid A, platycodi radix-derived saponin, suppresses TGF-β1-induced activation of hepatic stellate cells via blocking SMAD and activating the PPARγ signaling pathway

Abstract

Platycodi radix is a widely sold health food worldwide, which contains numerous phytochemicals that are beneficial to health. Previously, we reported that saponin from the roots of Platycodi radix-derived saponin inhibited toxicant-induced liver diseases. Nevertheless, the inhibitory effect of platyconic acid A (PA), the active component of Platycodi radix-derived saponin, on the anti-fibrotic activity involving the SMAD pathway remains unclear. We investigated the inhibitory effects of PA on TGF-1-induced activation of hepatic stellate cells (HSCs). PA inhibited TGF-1-enhanced cell proliferation, as well as expression of -SMA and collagen 1 in HSC-T6 cells. PA suppressed TGF-1-induced smad2/3 phosphorylation and smad binding elements 4 (SBE4) luciferase activity. Reversely, PA restored TGF-1-reduced expression of smad7 and peroxisome proliferator-activated receptor (PPAR)γ. PA also repressed TGF-1-induced phosphorylation of Akt and MAPKs. In summary, the results suggest that the inhibitory effect of PA on HSCs occurs through the blocking of SMAD-dependent and SMAD-independent pathways, leading to the suppression of -SMA and collagen 1 expression.