Syringa pinnatifolia Hemsl. fraction protects against myocardial ischemic injury by targeting the p53-mediated apoptosis pathway

Peeled stems of Syringa pinnatifolia Hemsl. (SP) have been widely used to treat extra "He-Yi" induced myocardial ischemia for hundreds of years in Inner Mongolia, China and previous result showed that intragastric pretreatment with total extract (T) of SP has a protective effect against myocardial infarction (MI).This study aims to describe the pharmacological investigation and chemical characterization of the major (M) and minor (N) fractions obtained from T through column chromatography fractionation on macroporous resin and to explore whether the regulatory effects were linked to the p53-mediated apoptosis pathways.Left anterior descending (LAD) coronary artery-ligated mice and H9c2 cells cultured in serum-free medium under hypoxic conditions were treated with T, M, and N.Echocardiography was performed and biomarkers in serum were determined in mice, and pathological changes were observed through histopathology assay. Immunofluorescence staining and qRT-PCR were used to detect the expression levels of p53 in heart tissue. Flow cytometry was used to measure the level of apoptosis and caspase-3 activity in H9c2 cells. Western blot analysis was conducted to detect p53 and p53-mediated proteins apoptosis pathways of in both tissue and H9c2 cells.Both T and M have an equivalent cardioprotective effect whereas N is non-active. M decreased MI-induced myocardial compensatory expansion by decrease of left ventricular end-systolic diameter (LVESd) and left ventricular end-diastolic diameter (LVEDd) and prevented decreases in ejection fraction (EF) and fractional shortening (FS). The MI-induced increased levels of creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH), and hypersensitive C-reactive protein (hs-CRP) were decreased and the expanded infarction size was reduced. M could also improve cell viability and inhibit apoptosis in H9c2 cells under hypoxic conditions. Immunofluorescence and qRT-PCR assay showed that M suppressed p53 expression in the myocardium. Western blot analysis showed that M could prevent MI-induced activation of p53-mediated apoptosis pathway in both myocardium and H9c2 cells.The results demonstrated that M may protect against myocardial ischemia by improving cardiac function and inhibiting cardiomyocytes apoptosis. Overall, the present findings supported the clinical application of SP and enriched the research of anti-myocardial ischemia drug from traditional medicines.