Sexually dimorphic effects of CYP2B6 in the development of fasting-mediated steatosis in mice: Effects are not mediated by the oxylipin products 9-HODE and 9-HOTrE
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-HODE and 9-HOTrE. However, hCYP2B6-Tg mice are sensitive to diet-induced hepatic steatosis despite their resistance to obesity. The purpose of this manuscript was determine if 9-HODE, 9-HOTrE, or other factors contribute to the sexually dimorphic steatosis observed in hCYP2B6-Tg mice. Cyp2b-null mice were injected with either 9-HODE or 9-HOTrE for 2 days then subjected to a fasting period of 20 hours to induce steatosis. Moderately increased serum lipids, especially in females, were observed after 9-HODE (TG, VLDL) and 9-HOTrE (HLD, LDL, cholesterol) treatment. No change in hepatic lipids and few changes in hepatic gene expression were observed in mice treated with either oxylipin, suggesting these oxylipins had little effect or their effects were extrahepatic. Therefore, to further investigate CYP2B6's role in steatosis, hCYP2B6-Tg and Cyp2b-null mice were subjected to a 20-hour fast and compared. Both male and female hCYP2B6-Tg mice exhibited increased steatosis compared to Cyp2b-null mice. Serum cholesterol, triglycerides, HDL, and VLDL were increased in hCYP2B6-Tg males. Serum triglycerides and VLDL were decreased in hCYP2B6-Tg females, suggesting greater hepatic retention of lipids.  Hepatic oxylipin profiles revealed 8 perturbed oxylipins in hCYP2B6-Tg mice and only 1 in males when compared to Cyp2b-null mice. RNA-seq also demonstrated greater effects in females in terms of number of genes and GO terms perturbed. There were only a few overlapping GO terms and lipid metabolic processes was enriched in hCYP2B6-Tg male mice but repressed in hCYP2B6-Tg females compared to Cyp2b-nulls. In conclusion, hCYP2B6-Tg mice are sensitive to steatosis in males and females although the responses are different. In addition, the oxylipins 9-HODE and 9-HOTrE are unlikely to be a major cause of CYP2B6's pro-steatotic effects. Overall design: Male and female Cypb-null and hCYP2B6-Tg mice were fasted for 20 hours prior to necropsy. Cyp2b-null mice were treated with 9-HODE or 9-HOTrE for 2 days followed by a 20-hour fast. RNA-seq was performed on RNA extracts frim the liver.