Amygdalin epimers exert discrepant anti-pulmonary fibrosis activity via inhibiting TGF-β1/Smad2/3 pathway

Idiopathic pulmonary fibrosis (IPF) represents a chronic and progressive tissue repair response that leads to irreversible scarring and lung remodeling. The decoction of bitter almond usually contains amygdalin epimers in traditional clinical application for lung disease. To reveal the differences of cytotoxicity and antifibrotic effect between amygdalin epimers, and potential mechanism is also explored. The cytotoxicity of amygdalin epimers were evaluated with MRC-5 cells in vitro. Their antifibrotic activities were evaluated in bleomycin-induced C57BL/6 mice and TGF-β1-induced MRC-5 cells. Here we demonstrated that L-amygdalin is more toxic of the amygdalin epimers in MRC-5 cells, and D-amygdalin is more effective in anti-pulmonary fibrosis among the amygdalin epimers in bleomycin-induced C57BL/6 mice. Herein, it was observed that D-amygdalin had a stronger inhibitory effect on inflammation than L-amygdalin, and had similar results in inhibiting the mRNA and protein expression levels of fibrosis-related biomarkers. The mechanism of anti-pulmonary fibrosis showed that amygdalin epimers suppressing expression of phosphorylation of Smads2/3, which implying deactivation of the TGF-β1induced Smads2/3 signal pathway. This study evaluates the amygdalin epimers cytotoxicity and antifibrotic effect, and its mechanisms were related to the TGF-β1/Smads2/3 signal pathway. It provides a reference for clinical safety and effectiveness of amygdalin epimers.