ACYLCARNITINE AND AMINO ACID PROFILING IN PLASMA AND TISSUES OF NZO MICE AS A MODEL FOR OBESITY-INDUCED TYPE 2 DIABETES

Abstract

Metabolomics has identified biomarkers in human plasma with a predictive quality for type 2 diabetes (T2D) development. Amongst these markers are various acylcarnitine species, most prominently those derived from branched-chain amino acid (BCAA) breakdown. The metabolic perturbations in tissues underlying these changes in plasma are often unknown and hard to assess in humans. Thus, animal models are used to have access to the different tissues. In contrast to diet-induced obesity models or monogenetic mouse models of obesity and diabetes, the New Zealand Obese (NZO) mouse is a prototypical polygenic model for obesity, with a male-specific susceptibility to developing diabetes. We have used this model to study the metabolic alterations in obesity-induced diabetes for changes in tissue-specific acylcarnitine and amino acid profiles. Twelve male and 11 female NZO mice at an age of 8 weeks were fed a chemically-defined high carbohydrate diet for 12 weeks. Acylcarnitine and amino acid profiles were obtained from plasma, skeletal muscle, heart muscle, liver, kidney and adipose tissues, using a high-resolution LC-MS/MS method. This method covered around 35 amino acids and 43 acylcarnitine species originating from fatty acids and amino acids, as well as odd-numbered and dicarboxylic acylcarnitines. Furthermore, blood glucose, plasma insulin, non-esterified fatty acids (NEFA), triglyceride and urea concentrations were measured. Hierarchical cluster analysis of principle components derived from plasma samples revealed a grouping of normoglycemic females, normoglycemic males and hyperglycemic males and this originated mainly from differences in concentrations of acylcarnitines derived from BCAAs and odd-numbered short- and medium-chain fatty acids. Hyperglycemic males were characterized by high insulin levels and low levels of NEFAs. These findings largely match with findings in humans. Comparison of metabolite profiles in diabetic and non-diabetic male mice revealed the largest overlap of significant metabolite changes between plasma and liver, including longer-chain odd-numbered acylcarnitine species. In conclusion, the alterations in acylcarnitine and amino acid profiles in NZO mice largely overlap with findings in humans, suggesting similar underlying metabolic perturbations in this diabetes model as compared to humans. The metabolite profiling of individual tissues in this model suggests a specific role of the liver in the generation of odd-numbered fatty acylcarnitines.