Metabolomics for understanding of pathophysiology and drug action mechanism in metabolic diseases: adolescent obesity and metformin

Abstract

Metabolomics is a high-throughput method for assessing the pathophysiological state and for identifying novel biomarkers to understand molecular mechanisms of the disease. It has allowed the large-scale, simultaneous analysis of huge numbers of metabolites in biofluids particularly of metabolic diseases such as obesity and diabetes. The aim of this study was to investigate biomarkers affected by obesity and underlying molecular mechanisms of the anti-diabetic drug. For identifying urinary biomarkers to distinguish metabolomic characteristics between obesity and normal weight in adolescents, adolescent subjects were divided into non-obese (n = 91) and obese (n = 93) groups according to body mass index. Untargeted and targeted metabolomic profiling of urine was performed using high-performance liquid chromatography (LC)-quadrupole time-of-flight mass spectrometry (MS), and LC- and flow injection analysis-MS/MS systems, respectively. For identifying the novel underlying molecular mechanisms related to anti-diabetic effect of metformin, fourteen healthy male subjects were orally administered metformin (1000 mg) once. First morning urine samples were taken before and after administration to obtain metabolomic data. We then further investigated the anti-diabetic mechanism of metformin in vitro and in vivo. In adolescent obesity biomarker study, multivariate statistical analysis showed clear discrimination between the untargeted metabolomes of nonobese and obese groups. Seven endogenous metabolites were distinguished in the obese group, and inflammation-related metabolite markers showed strong predictive power for group classification. From targeted metabolomics, 45 metabolites mostly related to inflammation were significantly different in the obese group. In underlying mechanism study of metformin, the fluctuation of the metabolite cortisol indicated that the neuroendocrine system was involved in the anti-diabetic effect of metformin. And we found that metformin induced AMPK/liver X receptor alpha (LXRalpha) phosphorylation, followed by pro-opiomelanocortin (POMC) suppression in rats. Significantly different metabolome signatures were identified between normal weight and obese adolescents and before and after metformin treatment groups. These metabolomic studies demonstrated that inflammation-driven insulin resistance, ammonia toxicity, and oxidative stress may represent crucial metabolomic signatures in obese adolescents, and the anti-hyperglycemic effect of metformin is attributed to reduced POMC/adrenocorticotropic hormone (ACTH)/cortisol levels following AMPK/LXRalpha phosphorylation in the pituitaries.