Novel triterpenoids from Alisma plantago-aquatica with influence on LDL uptake in HepG2 cells by inhibiting PCSK9

Abstract

BackgroundProprotein convertase subtilisin/kexin type 9 (PCSK9) has been regarded as an effective and exciting target in the treatment of atherosclerotic cardiovascular disease since 2003. Only two monoclonal antibodies have been approved in the market which, however, were also criticized for their high cost to $9000 per dose and delivery route. Exploration of natural new effective and cheaper small molecule alternatives with effective PCSK9 inhibition is feasible and desired. PurposeThe aim of the study was to explore natural small molecules with anti-hyperlipidemia activity through PCSK9 from Alisma plantago-aquatica. MethodA targeted isolation of triterpenoids from A. plantago-aquatica by LC-Orbitrap-QDa was conducted. The isolates were evaluated for their DiI-LDL uptake promoting activity with fluorescence intensity assayed in High-content Imaging System and PCSK9 inhibitory activity by Human PCSK9 Kit or western blot. The LDL uptake and PCSK9 level of target component in different concentrations and their mRNA level were further verified by corresponding kit, qPCR and western blot. ResultsSix novel triterpenoids, including three unusual nor-triterpenoids (1-3) and three protostane-type triterpenoids (4-6), along with thirty-four known ones, were isolated from A. plantago-aquatica. Compound 2 had the lowest number of carbon atoms than previous reported nor-PTs in this plant. The 17 triterpenoids showed relatively remarkable activities in promoting LDL uptake with relevant structure-activity relationships. And 6 triterpenoids may improve LDL uptake in HepG2 cells by inhibiting PCSK9, especially for alisol G (28) with PCSK9 inhibition reaching to 55.6%, which demonstrated to increase LDLR mRNA or protein, and simultaneously reduce PCSK9 mRNA or protein significantly. ConclusionThe protostane triterpenoids may serve as a new source for PCSK9 inhibitors.