Azoxymethane Alters the Plasma Metabolome to a Greater Extent in Mice Fed a High Fat Diet Compared to AIN-93 Diet

OBJECTIVES: Consumption of a high fat diet (HFD) links obesity to colon cancer in humans. Consistent with this observation, our data show that a HFD (45% energy fat versus 16% energy fat in AIN-93 diet, AIN) promotes azoxymethane (AOM) induced colonic aberrant crypt foci (ACF) formation in a mouse cancer model. However, the underlying metabolic basis remains to be determined. We hypothesize that AOM treatment results in different plasma metabolomic responses in AOM mouse colon cancer model fed with a HFD compared to the AIN. METHODS: Four-week-old male C57BL/6 mice were fed the AIN or HFD in the context of with or without AOM treatment for 16 weeks. At the end of this study, plasma samples were extracted and derivatized by silylation and methyloximation then analyzed by time-of-flight mass spectrometry using an untargeted metabolomic technique. RESULTS: Untargeted metabolomic profiling showed that 53 of 144 identified metabolites were different between the 4 groups of mice (AIN only, AIN + AOM; HFD only, HFD + AOM). Sparse partial least squares discriminant analysis (two-dimensional plots) showed a separation between the HFD and HFD + AOM groups but not AIN and AIN + AOM groups. Major metabolites responsible for this separation were beta-sitosterol, dihydrocholesterol, alpha-tocopherol, methylphosphate, citric acid, cholesterol, isocitric acid, myristic acid, arachidonic acid, and nicotinamide. Importantly, the levels of dihydrocholesterol and cholesterol were inversely associated with AOM-induced colonic ACF formation. Functional pathway and enrichment analyses indicated that diets and AOM-induced colonic ACF modulated 5 metabolic pathways: (a) citrate cycle (TCA cycle), (b) arginine biosynthesis, (c) aminoacyl-tRNA biosynthesis, (d) alanine, aspartate and glutamate metabolism, (e) glyoxylate and dicarboxylate metabolism. CONCLUSIONS: Collectively, we demonstrate that AOM decreases dihydrocholesterol and cholesterol levels, and alters the composition of plasma metabolome to a greater extent in mice fed a HFD compared to the AIN. FUNDING SOURCES: This work was supported by U.S. Department of Agriculture, Agricultural Research Service, research project 3062-51000-056-00D.