Role of Cyt P450-Mediated Oxidation in Chemical-Induced Toxicity/Carcinogenicity

National Institute Of Environmental Health Sciences

Investigators

Linked publications & trials

Abstract

Global projections of obesity indicate that >1 billion adults (≥age 15) are overweight, (BMI >25kg/m2) and at least 400 million are obese (BMI >30kg/m2). Chronic diseases such as type-2 diabetes have also been associated with elevated BMI. In general, the etiology of most human diseases can be at least partially linked to environmental pollutants and lifestyle. We hypothesized that obese individuals may exhibit varied metabolism and responses to environmental agents. The overall purpose of the current research was to develop and characterize a genetically intact animal model that exhibits obesity as a result of consuming a high-fat/high calorie diet. Male mice were fed either a control diet or a high fat/high calorie diet as early as 5 weeks of age. Body weight and body fat measurements were obtained and complete necropsy was performed at 15, 20, and 30 weeks of age. The pathogenesis of obesity was assessed and characterized through the analysis of serum chemistry (glucose, cholesterol, triglycerides, insulin, and leptin), hematoxylin and eosin (H&E) and periodic acid schiff (PAS) evaluation of tissues, and hepatic and renal function. Significant increases in both body weight and body fat percentages were determined in male mice fed the high-fat/high calorie diet vs. age-matched littermates consuming control diet at 15, 20, and 30 weeks. In addition, serum cholesterol concentrations were significantly elevated in obese vs. lean mice. Obese animals also exhibited hyperglycemia, hyperinsulinemia and hyperleptinemia in association with significant insulin and leptin resistance. Lesions associated with obesity were also identified in the livers and kidneys of obese but not lean mice. Similar hepatic and renal lesions associated with obesity in mice were also characterized in humans suffering from non-alcoholic fatty liver disease and type 2-diabetes. These results demonstrated that consumption of high fat/high calorie diet leads to obesity and significantly increases the potential for the development of type 2 diabetes. Using this animal model, subsequent studies in this laboratory were designed to address the hypothesis that diet-induced obesity is associated with increased male infertility and obese male mice are more susceptible to the reproductive toxicity of environmental chemicals such as acrylamide (AA). Fertility of obese and lean male mice was compared by mating with untreated female mice. In late gestation, females were sacrificed and uterine content examined. Obesity resulted in significant reduction in plugs and pregnancies of control females partnered with obese vs. lean males. Serum leptin and insulin levels were each approximately 5-fold higher in obese vs. age-matched lean mice. Sperm from obese males exhibited decreased motility and reduced hyperactivated progression vs. lean mice. Treatment with AA exacerbated male infertility of obese and lean mice, however, this effect was more pronounced in obese mice. Further, females partnered with AA-treated obese male mice exhibited a further decrease in the % of live fetuses, while % resorptions increased. This work demonstrated that diet-induced obesity caused a significant reduction in male fertility and exacerbated AA-induced reproductive toxicity and germ cell mutagenicity. Because AA exhibited an exaggerated reproductive toxicity and germ cell mutagenicity in diet-induced obese vs. lean male mice. Further, because AA metabolism to glycidamide is a pre-requisite for these effects, current studies were undertaken to assess AA mechanism of action by comparing its metabolism in obese and lean male mice. Male C57Bl/6J mice were maintained on either a control or high fat (60% kcal fat) diet from 5 to 30 weeks of age. Mice fed high fat diet for 30 weeks showed significantly higher body weight and % body fat. AA was administered (po) to groups of obese and lean mice at 12.5, 25, or 50mg/5ml water/kg. Six hours after dosing, mice were euthanized and blood was collected to measure AA and GA-derived HGB adducts in RBCs. Liver, lung, and testes were removed for DNA adducts measurement. AA and GA-derived HGB and DNA adducts were measured using LC-ES/MS/MS analysis. In lean and obese mice AAVal adducts increased in a dose-dependent manner. AAVal was a credible measure of AA internal dose and indicated exposure was similar in obese and controls. While in both groups GAVal adducts increased in a dose-dependent manner, significantly higher levels were detected at all doses in obese mice. N3-GA-Gua and N7-GA-Ade adducts in liver, lung and testes were considerably higher in obese vs. lean mice. Therefore, increased AA metabolism to the epoxide intermediate, GA, and increased GA-DNA adducts may explain and contribute to the elevated sensitivity of obese mice to the reproductive toxicity and germ cell mutagenicity of AA. These data also support the premise that diet induced obesity renders humans more susceptible to environmental pollutants.