Cycloartane-type triterpenoids from Combretum quadrangulare Kurz with PCSK9 secretion inhibitory activities

Nine previously undescribed (1-9) and seven known (10-16) cycloartane-type triterpenoids were isolated and characterized from Combretum quadrangulare Kurz using physicochemical and spectroscopic methods. The absolute configurations of these compounds were determined through modified Mosher's method and quantum chemical calculation of electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectra. Their inhibitory activities against PCSK9 secretion were assessed, and a plausible structure-activity relationship was delineated. Compounds 2, 14, and 15 exhibited notable inhibitory effects on PCSK9 mRNA and protein levels, and significant PCSK9 mRNA inhibition was observed when co-treated with atorvastatin. Compound 15 showed the most potent activity, markedly enhancing LDL uptake compared to the negative control. In vivo pharmacokinetic studies confirmed that compound 15 exhibited higher distribution in the liver than plasma, where PCSK9 is predominantly synthesized. These findings emphasize the potential significance of the cycloartane-type triterpenoid scaffold in discovering PCSK9 inhibitors.