2012 Annual Report
1a.Objectives (from AD-416):
Elevated fat levels within skeletal muscle cells (intramyocellular lipids) are highly correlated with muscle and whole-body insulin resistance, and more prevalent in obesity. The molecular links and metabolic shifts driving this association remain open to debate, but notably, reduced muscle mitochondrial fatty acid (FA) beta-oxidation is more prevalent among insulin-resistant/diabetic persons. Therefore, discovery of biomarkers reflective of the status of an individual’s muscle FA beta-oxidation activity or capacity would have tremendous prognostic and diagnostic value in terms of diabetes. Furthermore, characterization of metabolites associated with muscle mitochondrial fat metabolism should uncover candidate signaling factors which tie FA ß-oxidation to insulin signaling. We propose to identify, for the first time, specific biomarkers of muscle FA beta-oxidation using multiple metabolomic analytical platforms to compare metabolite profiles in samples derived from biological systems displaying disparate muscle fat combustion, including: isolated mitochondrial organelles and muscle cells catabolizing FA at different rates, a UCP3 transgenic animal model, and human subjects harboring a UCP3 truncation polymorphism. Pilot validation studies will test whether plasma metabolites and/or metabolite signatures identified in cell, animal, and human studies that track muscular FA beta-oxidation can be experimentally increased in obese, insulin-resistant subjects via a diet-exercise regimen designed to improve muscle fitness and FA combustion.
1b.Approach (from AD-416):
A comprehensive carnitine and acylcarnitine assay measuring >40 acylcarnitines will be employed to test samples derived from the following project aims:
Aim 1--Identify Metabolite Biomarkers of Muscle Fat Combustion in Organelle, Cell, and Animal Models Displaying Significantly Altered Fatty Acid beta-Oxidation. We will determine how metabolite profiles shift in models displaying increased muscle beta-oxidation (uncoupling protein 3-overexpressing muscle cell line and muscle UCP3-transgenic mice), and hypothesize that profiles in UCP3-overexpressing systems will reflect increased FA beta-oxidation. Complementary studies will identify tissue-specific metabolites generated by mitochondria in the course of palmitate catabolism in vitro, comparing muscle to liver and kidney preparations.
Aim 2--Identify Metabolite Biomarkers of Muscle Fat Combustion in Humans Harboring a UCP3 Missense Polymorphic Allele. We predict that subjects with this polymorphism (that yields a truncated UCP3 and 50% decreased whole-body fat combustion) will display a distinctive plasma metabolite profile indicative of reduced muscle FA oxidation, when compared to subjects without the polymorphism.
Aim 3--Determine Whether Metabolomic Profiles Reflective of Muscle Fat Combustion Predict Metabolic Health Changes Following Diet & Exercise Intervention in Obese Subjects. We hypothesize that biomarkers reflective of normal to increased muscle beta-oxidation will be increased, and markers indicative of poor muscle fat combustion reduced, in a cohort of sedentary obese subjects undergoing a 4 month diet-exercise protocol which will increase muscle fitness and improve insulin action.
This research contributes to objectives 3 and 6 of the in-house parent project. Studies that examine blood and tissue metabolites during exercise are geared to discovering unique muscle-specific patterns of metabolism, that may be dysregulated in obesity, pre-diabetes, and the type 2 diabetic states. The team has analyzed blood plasma before and during exercise in obese, pre-diabetic women and compared results of a comprehensive acylcarnitine metabolite panel to samples derived after the subjects lost weight and improved physical activity. The final results will be forthcoming in FY2013, and preliminary findings indicate that unique metabolites reflective of incomplete fatty acid combustion are increased by exercise.