Apocynum leaf extract inhibits the progress of atherosclerosis in rats via the AMPK/mTOR pathway

Apocynum leaf extract is an extract of the dried leaves of Apocynum venetum (a member of the Apocynaceae family) that has many effects on the cardiovascular system. The aim of the present study was to evaluate the protective effects of apocynum leaf extract on the atherosclerosis in rats induced by high-fat diet combined with vitamin D3 intraperitoneal injection. The atherosclerosis in rats were induced with a high-fat diet and an intraperitoneal injection of VD3 once daily for three contiguous days at a total injection dose of 70 U/kg. At the end of the 18th week, serum total cholesterol (TC) and triglyceride (TG) contents were measured. Hydroxyproline content in the aorta were measured by the alkali hydrolysis method. The hematoxylin-eosin (HE) and immunohistochemical staining were applied to evaluate the morphological changes and the collagen I and α-smooth muscle actin expression. The protein expression and the mRNA level of AMPK and mTOR were detected by western blot analysis and reverse transcript PCR. After treatment with apocynum leaf extract, the serum total cholesterol and triglyceride concentration of the atherosclerotic rats were significantly decreased, both the Collagen I expression and the hydroxyproline content in the aorta were significantly reduced, and the α-SMA, a smooth muscle-specific marker, expression were also lower than the untreated atherosclerotic rats. Western blot analyses showed that the apocynum can marked increase the p-AMPK but decrease the mTOR protein expression. The apocynum leaf extract also exhibited higher AMPK and lower mTOR mRNA expression of the aorta in the atherosclerotic rats. We believe that the apocynum leaf extract can effectively reduce blood lipid levels in rats with atherosclerosis, delay atherosclerotic progression by inhibiting excessive collagen synthesis and inhibiting smooth muscle cell over-proliferation. The underlying mechanism may be related to the AMPK/mTOR signaling pathway activity. Our results contribute towards validation of the traditional use of apocynum leaf extract in the treatment of atherosclerosis.