Equivalent evaluation and biological ingredients of Syringa pinnatifolia against acute myocardial ischemia in mice

The peeled roots, stems, and twigs of Syringa pinnatifolia Hemsl., known as Shan-Chen-Xiang (SCX) in Chinese, has the traditional effects such as anti-Khii, clearing heat and relieving pain. It has been clinically applied for the treatment of heart failure and mental abnormalities, and gradually replaced agarwood in Mongolian medicine.The present study aims to evaluate whether the key subfraction C (C), a half composition in mass of total ethanol extract (T) of SCX, exerts an equivalent effect against acute myocardial ischemia (AMI) compared to fraction I (I), and what was the potential pharmacologically active constituents of SCX.Cardiac function, serum marker enzymes, and myocardial tissue pathology of infarcted mice with ligation of the anterior descending (LAD) branch of the left coronary artery were used to evaluate the anti-AMI effect of C and its equivalent potency to that of I. LCMS-IT-TOF was used to identify the main constituents in C and C-. The new and known compounds were isolated from C by a combination of mass spectrometry and bioactivity-guided fractionation methods, and structures were elucidated by extensive spectroscopic and chemical methods, including calculated 13C NMR data, calculated electronic circular dichroism, and single-crystal X-ray crystallography. The protective effect of isolates against oxidative injury induced by H2O2 in H9c2 cells was evaluated according to a previously reported protocol.The results of cardiac function, serum marker enzymes and myocardial tissue pathology observations (fosinopril as a positive drug) suggested that C (40 mg/kg, orally administered once a day for 7 days) possessed the anti-AMI effect and was equivalent to that of I, while C- did not show the positive effect. Then, 32 lignans were isolated from C, including the majors (8R,8'R,9S)-4,4'-dihydroxy-3,3',9-trimethoxy-9,9'-epoxylignan (24) and (8R,8'R,9R)-4,4'-dihydroxy-3,3',9-trimethoxy-9,9'-epoxylignan (25), which were confirmed by HPLC and LC-MS characterization. Among them, 15 ones were previously undescribed, including a pair of enantiomers (6a/6b), and 11 ones (1, 2, 6a/6b, 8, 10, 12, 16, 17, 24, and 25) exhibited protective effect against oxidative injury to H9c2 cells at different concentrations (ranged from 0.156 to 80 μM).C (40 mg/kg) exerts cardioprotective effect in mice, which was equivalent to that of I and T. Lignans, including both representative compounds (24, 25) and other undescribed molecules with low content, significantly contribute to the anti-AMI effect of SCX. However, the anti-AMI property assessment of SCX should not exclude the contribution from the representative sesquiterpenoid ZER. Hence, the exploration of the final potential substances in SCX requires further investigation.