6-Ketocholestanol suppresses lipid accumulation by decreasing FASN gene expression through SREBP-dependent regulation in HepG2 cells.

Nuclear receptors, such as liver X receptors (LXRs) and sterol regulatory element-binding proteins (SREBPs), are key regulators of lipogenic genes, including fatty acid synthase (FASN). It has been reported that several oxycholesterols (OCs) act as LXR ligands; however, it is unclear whether all OC molecular species act as ligands. We previously demonstrated that the absorption rate of dietary 6-ketocholestanol (6-keto), an oxycholesterol, is the highest of all the OCs using thoracic lymph duct-cannulated rats. However, limited information is available about the physiological significance of 6-keto. In this study, we investigated whether treatment with 6-keto increases intracellular triacylglycerol (TAG) levels through up-regulation of lipogenic gene expression in HepG2 cells. 6-Keto treatment significantly reduced intracellular TAG levels through down-regulation of lipogenic genes including FASN. Although 6-keto significantly suppressed FASN gene promoter activities, the action was completely diminished when mutations were present in the SREBP promoter site. TO901317 (TO) significantly increased FASN gene promoter activities, whereas simultaneous treatment with TO and 6-keto significantly reduced this activity. We also compared the effects of several OCs that are oxidized at the carbon-6 and -7 in the B-ring of cholesterol on FASN gene promoter activities. Similar to 6-keto, 6α-OH and 6ß-OH significantly reduced the activity of the FASN gene promoter, which suggests that oxidation of carbon-6 in the B-ring may play an important role in the reduction of FASN expression. Our results indicate that 6-keto suppresses lipid accumulation by decreasing FASN gene expression through SREBP-dependent regulation in HepG2 cells.

The pathophysiological role of oxidized cholesterols in epicardial fat accumulation and cardiac dysfunction: a study in swine fed a high caloric diet with an inhibitor of intestinal cholesterol absorption, ezetimibe.

Oxidized cholesterols (oxycholesterols) in food have been recognized as strong atherogenic components, but their tissue distributions and roles in cardiovascular diseases remain unclear. To investigate whether accumulation of oxycholesterols is linked to cardiac morphology and function, and whether reduction of oxycholesterols can improve cardiac performance, domestic male swine were randomized to a control diet (C), high caloric diet (HCD) or HCD+Ezetimibe, an inhibitor of intestinal cholesterol absorption, group (HCD+E) and evaluated for: (1) distribution of oxycholesterol components in serum and tissues, (2) levels of oxycholesterol-related enzymes, (3) paracardial and epicardial coronary fat thickness, and (4) cardiac performance. Ezetimibe treatment for 8weeks attenuated increases in oxycholesterols in the HCD group almost completely in liver, but reduced only levels of 4ß-hydroxycholesterol in left ventricular (LV) myocardium. Ezetimibe treatment altered the expression of genes for cholesterol and fatty acid metabolism and decreased the expression of CYP3A46, which catabolizes cholesterol to 4ß-hydroxycholesterol, strongly in liver. An increase in epicardial fat thickness and impaired cardiac performance in the HCD group were improved by ezetimibe treatment, and the improvement was closely related to the reduction in levels of 4ß-hydroxycholesterol in LV myocardium. In conclusion, an increase in oxycholesterols in the HCD group was closely related to cardiac hypertrophy and dysfunction, as well as an increase in epicardial fat thickness. Ezetimibe may directly reduce oxycholesterol in liver and LV myocardium, and improve cardiac morphology and function.