Heintz MM, McRee R, Kumar R, Baldwin WS. Gender differences in diet-induced nonalcoholic steatohepatitis (NASH) in Cyp2b-null mice. Society of Toxicology meeting, Anaheim, CA, March 2020.
Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease; however, it is the progression to nonalcoholic steatohepatitis (NASH) that is associated with most adverse outcomes. CYP2B metabolizes multiple xeno- and endobiotics, and male Cyp2b-null mice are diet-induced obese (DIO) with increases in NAFLD but little hepatic inflammation. However, this DIO-study was only performed for 10-weeks and recent research indicates that C57Bl/6 mice are recalcitrant to fibrosis and NASH development for up to 22-weeks. Therefore, to properly assess the role of Cyp2b in fatty liver dis-ease progression from NAFLD to NASH, we treated wildtype (WT) and Cyp2b-null mice with a normal diet (ND) or choline-deficient, L-amino acid-defined high fat diet (CDAHFD) for 8 weeks and determined metabolic and molecular changes. CDAHFD-fed WT female mice gained more weight and had greater liver (11%) and white adipose tissue (44%) mass than their Cyp2b-null coun-terparts, while males experienced diet-induced weight loss regardless of genotype. In both genders, hierarchical clustering of RNA-seq data demon-strates several genes involved in lipid metabolism, fibrosis, and inflammation responded differently in CDAHFD-fed Cyp2b-null mice compared to WT mice. Serum biomarkers of liver injury increased in both CDAHFD-fed female and male mice; however, CDAHFD-fed Cyp2b-null females exhibited significantly lower serum alanine aminotransferase, aspartate aminotransferase, and alka-line phosphatase concentrations compared to WT mice, indicating the loss of Cyp2b protected mice from liver injury in females. In contrast, males showed few differences in serum parameters related to genotype. Oil Red O staining and direct triglycerides measurements confirmed that CDAHFD-fed Cyp2b-null females were protected from fatty liver disease. CDAHFD-fed Cyp2b-null mice showed equivocal changes in fibrosis with some markers suggesting less inflammation probably due to glucocorticoid-mediated repression of im-mune responses. In contrast, CDAHFD-fed Cyp2b-null males had higher tri-glyceride levels. Results indicate that female Cyp2b-null mice are less suscep-tible to NASH than WT mice, while male Cyp2b-null mice are more susceptible to NAFLD with no changes in NASH development. Overall, this study indicates a minor role for Cyp2b in fatty liver disease progression that differs based on gender, with males being more susceptible to chemical inhibition of Cyp2b than females, who may be protected.