Inhibition of cholesterol biosynthesis in HepG2 cells by artichoke extracts is reinforced by glucosidase pretreatment

High-dose aqueous extracts from artichoke leaves were found to inhibit cholesterol biosynthesis from C-14-acetate rather moderately in HepG2 cells in contrast to primary cultured rat hepatocytes in which the inhibition was stronger. Preincubation of the extracts with several glycohydrolases revealed that pretreatment with beta-glucosidase considerably reinforced the inhibition. A significant reduction of acetate incorporation was found above extract concentrations of 0.01 mg/mL. and at 0.2 mg/mL. almost 60% inhibition was observed. Cytotoxic effects detected by the MTT-assay were restricted to higher concentrations of the extracts with and without beta-glucosidase pretreatment. Since cynaroside represents a major glucoside in artichoke extracts, both cynaroside and its aglycone luteolin were tested. It could be demonstrated that cynaroside is indeed one of the targets of beta-glucosidase and that the liberated luteolin is responsible for the inhibitory effect. Direct measurements of beta-glucosidase activity in rat hepatocytes and HepG2 cells revealed that endogenous enzyme activity in hepatocytes may be sufficient to convert cynaroside to its aglycone, while in HepG2 cells this may not be the case. These findings emphasize the importance of beta-glucosidase-dependent liberation of luteolin for the ability of artichoke extracts to inhibit hepatic cholesterol biosynthesis. Copyright (C) 2002 John Wiley Sons, Ltd.