New triterpenoid saponins isolated from the leaves of Astragalus membranaceus (Fisch.) Bge. and their neuroprotective effects.

Fifteen new triterpenoid saponins designated as huangqiyesaponin A-O (1-15), in addition to eleven previously identified compounds (16-26), were extracted from the leaves of Astragalus membranaceus (Fisch.) Bge. utilizing a 70% ethanol solution. The structural characterization of the isolated compounds was achieved through the application of 1D and 2D NMR spectroscopy, in combination with single crystal X-ray diffraction analysis. Additionally, d-galactose-stimulated HT22 mouse hippocampal neuronal cells were utilized to assess the potential neuroprotective effects of all isolated compounds. The findings indicated that compounds 5, 11, and 13-15 exhibited significant neuroprotective effects. To elucidate the signaling pathway associated with the neuroprotective effects of compounds 13 and 15, the protein expression levels of PINK1, parkin, P62, and LC3-II were evaluated through WB analysis. The results of the study indicated that the compounds 13 and 15 enhanced the proportion of LC3-II to LC3-I as well as the protein expressions of PINK1 and parkin while concurrently reducing the expression of P62 protein, suggesting that these compounds exert neuroprotective effects by promoting mitochondrial autophagy.