Effects of Four Main Active Flavonoids of Nutt. on Oleic Acid-Induced Lipid Metabolism and Oxidative Stress in HepG2 Cells.

Background: Traditional Chinese medicines exhibit tremendous beneficial effects on the control of hyperlipidemia and hyperlipidemia-associated disorders. In the present study, we investigated the effects of four Nutt. extracts, including luteolin, marein, naringenin (NGN) and chlorogenic acid (CQA), on lipid accumulation and oxidative stress induced by oleic acid (OA) in HepG2 cells.

Methods: Oleic acid was employed to create a high-lipid milieu in a cellular setting using HepG2 cells. After treatment by luteolin, marein, NGN, and CQA, cell counting kit-8 assay was used for measuring cell viability. Lipid accumulation, lipid metabolism and oxidative stress were examined by means of enzyme-linked immunosorbent assay, Oil red O staining, quantitative real-time polymerase chain reaction (qRT-PCR) and 2',7'-dichlorodihydro fluorescein diacetate assays. Western blot and qRT-PCR assays were applied to determine the expression of genes and proteins, respectively.

Results: In OA-treated HepG2 cells, the administration of the four active flavonoids of Nutt. (luteolin, marein, NGN and CQA) enhanced cell viability ( < 0.05 or < 0.01); reduced lactate dehydrogenase releasing, lipid deposition and production of triglyceride, total cholesterol and low-density lipoprotein-cholesterol ( < 0.05 or < 0.01); and elevated high-density lipoprotein-cholesterol production ( < 0.05 or < 0.01 or < 0.001). Moreover, after luteolin, marein, NGN or CQA treatment, the expression of lipid metabolism-related genes including 3-hydroxy-3-methylglutaryl-CoA reductase (), low-density lipoprotein receptor () and apical sodium-dependent bile acid transporter () was downregulated ( < 0.01 or < 0.001) but the expression of cytochrome P450 family 7 subfamily A member 1 () was upregulated ( < 0.05 or < 0.01 or < 0.001) in OA-treated HepG2 cells. Similarly, luteolin, marein, NGN or CQA treatment greatly enhanced the anti-oxidant activities ( < 0.05 or < 0.01 or < 0.001) and decreased reactive oxygen species production ( < 0.01 or < 0.001) in OA-treated HepG2 cells. Sterol regulatory element-binding protein, a major transcription factor that moderates the biosynthesis of fatty acid, cholesterol and triglyceride, was also inhibited after luteolin, marein, NGN or CQA treatment ( < 0.05 or < 0.01 or < 0.001).

Conclusion: These findings demonstrated that luteolin, marein, NGN or CQA can effectively reduce OA-induced oxidative stress and lipid accumulation, corroborating their potential in hyperlipidemia treatment.