Abstract
Background: Cytochrome P450 2B6 (CYP2B6) is a sexually dimorphic, anti-obesity CYP enzyme responsible for the metabolism of xeno- and endobiotics, including the metabolism of polyunsaturated fatty acids (PUFAs) into 9-hydroxyoctadecadienoic acid (9-HODE) and 9-hydroxyoctadecatrienoic acid (9-HOTrE). However, humanized CYP2B6 transgenic (hCYP2B6-Tg) mice are sensitive to diet-induced hepatic steatosis despite their resistance to obesity. The purpose of this study was to determine if 9-HODE, 9-HOTrE, or other factors contribute to the sexually dimorphic steatosis observed in hCYP2B6-Tg mice. Results: Cyp2b9/10/13-null (Cyp2b-null) mice were injected with either 9-HODE or 9-HOTrE for 2 days and were then subjected to a fasting period of 20 h to induce steatosis. Serum lipids were moderately increased, especially in females, after 9-HODE (triglycerides (TGs), very low-density lipoproteins (VLDLs)) and 9-HOTrE (high-density lipoproteins (HDLs), low-density lipoproteins (LDLs), cholesterol) treatment. No change in hepatic lipids and few changes in hepatic gene expression were observed in mice treated with either oxylipin, suggesting that these oxylipins had minimal to moderate effects. Therefore, to further investigate CYP2B6's role in steatosis, hCYP2B6-Tg and Cyp2b-null mice were subjected to a 20 h fast and compared. Both male and female hCYP2B6-Tg mice exhibited increased steatosis compared to Cyp2b-null mice. Serum cholesterol, triglycerides, HDLs, and VLDLs were increased in hCYP2B6-Tg males. Serum triglycerides and VLDLs were decreased in hCYP2B6-Tg females, suggesting the greater hepatic retention of lipids in females. Hepatic oxylipin profiles revealed eight perturbed oxylipins in female hCYP2B6-Tg mice and only one in males when compared to Cyp2b-null mice. RNA-seq also demonstrated greater effects in females in terms of the number of genes and gene ontology (GO) terms perturbed. There were only a few overlapping GO terms between sexes, and lipid metabolic processes were enriched in hCYP2B6-Tg male mice but were repressed in hCYP2B6-Tg females compared to Cyp2b-nulls. Conclusions: hCYP2B6-Tg mice are sensitive to fasting-mediated steatosis in males and females, although the responses are different. In addition, the oxylipins 9-HODE and 9-HOTrE are unlikely to be the primary cause of CYP2B6's pro-steatotic effects.