Black Raspberry Extract Enhances LDL Uptake in HepG2 Cells by Suppressing PCSK9 Expression to Upregulate LDLR Expression

Black raspberry extract (BRE) has been widely used for treating prostate and urinary diseases and hyperlipidemia in Asia due to its significant lipid-lowering effects. The aim of this investigation was to evaluate the antihypercholesterolemia activity of BRE and the potential molecular mechanisms responsible for its antihypercholesterolemia activity by regulation of proprotein convertase subtilisin/kexin type 9 (PCSK9) expression in the human liver cell line HepG2. Reporter-based functional assay was used to identify herbal extracts that suppress PCSK9 expression in the HepG2 cells. Quantitative real-time polymerase chain reaction, Western blot analysis, and immunofluorescence staining were used to evaluate whether BRE modulates low-density lipoprotein receptor (LDLR) expression by repressing the hepatic expression of PCSK9. The LDLR activity of the HepG2 cells was determined using an LDL uptake assay. Our finding revealed that BRE modulates LDLR expression by suppressing the hepatic expression of PCSK9. We found that the combination of simvastatin and BRE caused the synergic induction of LDLR expression and LDL-C uptake, whereas simvastatin alone increased the expression of PCSK9 in the HepG2 cells. These results clearly demonstrated that the BRE from black raspberry suppressed simvastatin-induced PCSK9 expression and improved LDL-C uptake by hepatocytes through the induction of LDLR expression. These results suggest that the suppression of PCSK9 expression by BRE may potentiate the hypolipidemic effect of statins.