Role of CYP2B in Unsaturated Fatty Acid Metabolism, Obesity, and Non-Alcoholic Fatty Liver Disease
Date of Award
Doctor of Philosophy (PhD)
William S Baldwin
Obesity is closely linked to the development of nonalcoholic fatty liver disease (NAFLD). The prevalence of obesity is increasing in the United States, and the most recent 2017-2018 National Health and Nutrition Examination Survey recorded 42.4% of adults are obese. Cytochrome P450s (CYPs) play a primary role in phase I detoxification pathways, which in humans, includes over 90% of phase I-dependent metabolism of clinically used drugs, especially within CYP families 1-3. These enzymes also metabolize a vast number of environmental pollutants including industrial and agricultural chemicals, as well as endogenous compounds such as steroids, bile acids, and fatty acids. Hepatic CYP activity has been associated with fatty liver and the main regulator of CYP2B, the constitutive androstane receptor (CAR), has been identified as an anti-obesity transcription factor as its activation improved hepatic glucose and fatty acid metabolism in leptin-deficient mice. Thus, indicating a role for CAR in recognizing and Cyp2b in metabolizing hepatic lipids. Initial studies determined male Cyp2b-null mice are diet-induced obese with increased liver triglycerides. Cyp2b-null male mice fed a normal diet also showed hepatic gene expression and phospholipid profiles similar to wild-type mice fed a high fat diet (HFD), indicating progression to NAFLD even in the absence of a high-fat diet. Based on these results, we hypothesized that Cyp2bs are crucial in the hepatic metabolism and elimination of unsaturated fatty acids and continued to study the role of Cyp2b in the progression to nonalcoholic steatohepatitis (NASH) using our Cyp2b-null mouse model. Unexpectedly, the lack of Cyp2b in female mice was moderately protective from diet-induced NASH, while male Cyp2b-null mice were more susceptible to NAFLD, with few significant changes in NASH development. Therefore, murine Cyp2b enzymes are anti-obesogenic in males; however, there are some important interspecies differences between mouse and human CYPs. Therefore, PUFA metabolites of human CYP2B6 were identified from CYP2B6 containing baculosomes by LC-MS/MS. Results indicate human CYP2B6 primarily metabolizes PUFAs in the 9- and 13- positions with a preference for -linolenic acid in vitro. To increase relevance to humans, we produced a humanized CYP2B6 transgenic mouse and tested whether CYP2B6 could reverse diet-induced obesity when compared to Cyp2b-null mice. CYP2B6 partially reverses diet-induced obesity observed in Cyp2b-null mice, but with unexpected sexually dimorphic effects on obesity in females and fatty liver disease in males. Metabolic disease was also associated with oxylipin profiles and gene expression. Surprisingly, linoleic acid and arachidonic acid – based oxylipins were primarily altered in vivo; probably due to higher concentrations of these PUFAs in the mouse diet. Differential gene expression revealed changes in gene ontology terms associated with circadian rhythm, protein processing and lipid metabolism in humanized CYP2B6 transgenic mice. In conclusion, the changes in expression or inhibition of CYP2B6 may perturb lipid homeostasis, utilization, and metabolism and lead to adverse outcomes, primarily in males.
Heintz, Melissa, "Role of CYP2B in Unsaturated Fatty Acid Metabolism, Obesity, and Non-Alcoholic Fatty Liver Disease" (2020). All Dissertations. 2661.