Taiwanese Green Propolis and Propolin G Protect the Liver from the Pathogenesis of Fibrosis via Eliminating TGF-β-Induced Smad2/3 Phosphorylation

Pathogenesis of fibrosis is a common process leading to chronic liver diseases and liver cirrhosis. New compounds for disease treatment and adjuvant therapy have been important issues in recent years. In this study, we isolated propolin G from Taiwanese green propolis (TGP) and investigated its antifibrotic effects by utilizing active hepatic stellate cells (HSCs) fibrosis model. Our results showed that TGP and propolin G inhibited alpha-SMA, collagen expression, and proliferation of HSC-T6 cells after TGF-beta treatment. They also reduced the accumulation of extracellular matrix (ECM) components such as collagen I alpha 1 (Col I alpha 1) through down-regulating JNK signaling. Subsequently, mRNA and protein expression of Smad2/3 but no other Smad members was specifically down-regulated in the presence of propolin G. This effect also significantly induced apoptosis-associated expression of cleaved caspase-3 and caspase-7 proteins for fibrotic cell clearance. In in vivo experiments, we found that propolin G and TGP can reduce plasma alanine aminotransferase (ALT) activation and perhaps lead to the prevention of alcohol-induced liver cirrhosis. Furthermore, TGP can significantly decrease the malondialdehyde (MDA) level but has no influence on plasma or hepatic superoxide dismutase (SOD) and glutathione peroxidase (GPx) levels, suggesting TGP protects the liver from alcohol-induced injury through antioxidant-independent pathways. In conclusion, this study provides a new perspective of propolin G and TGP on liver protection, and its application has potential for health management by daily supplement or adjuvant therapy in related diseases.