Quercetin plays a cardiovascular protective role because of its antioxidant capacity and ability to modulate dyslipidemia. As alterations in hepatic lipid synthesis are crucial to the regulation of serum lipid levels, we investigated the quercetin effect on lipogenesis in rat liver cells. The effect of quercetin on the rate of synthesis of fatty acids, cholesterol, neutral lipids, phospholipids and very-low-density lipoproteins (VLDL) was investigated in rat hepatocyte suspensions following [1-(14)C]acetate incorporation into these lipid fractions. Enzyme activities of acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS) as well as diacylglycerol acyltransferase (DGAT) and 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMG-CoA-R), pace-setting steps of de novo fatty acid, triacylglycerol (TAG) and cholesterol synthesis respectively were assayed in digitonin-permeabilized hepatocytes. Within 30 min of quercetin addition to the hepatocytes, inhibition (IC50 approximately 25 microM) of fatty acid synthesis occurred. A reduction in label incorporation mainly into TAG was observed. Among neosynthesized fatty acids, palmitic acid formation was greatly reduced, suggesting that enzymatic step(s) of de novo fatty synthesis was affected. Only ACC activity was noticeably reduced, but no change in FAS activity was observed. DGAT activity was also inhibited. The decreased intracellular TAG content was paralleled by a reduction in acetate incorporation into VLDL-TAG. Conversely, cholesterol synthesis and HMG-CoA-R were not significantly affected by quercetin. In hepatocytes from normal rats, the quercetin-induced decrease in both de novo fatty acid and TAG synthesis, with a consequent reduction in VLDL-TAG formation, may represent a potential mechanism contributing to the reported hypotriacylglycerolemic effect of quercetin.
