Dynamic changes in fat oxidation in human primary myocytes mirror metabolic characteristics of the donor
Barbara Ukropcova, … , George A. Bray, Steven R. Smith
Barbara Ukropcova, … , George A. Bray, Steven R. Smith
Published July 1, 2005
Citation Information: J Clin Invest. 2005;115(7):1934-1941. https://doi.org/10.1172/JCI24332.
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Research Article Metabolism

Dynamic changes in fat oxidation in human primary myocytes mirror metabolic characteristics of the donor

Abstract

Metabolic flexibility of skeletal muscle, that is, the preference for fat oxidation (FOx) during fasting and for carbohydrate oxidation in response to insulin, is decreased during insulin resistance. The aim of this study was to test the hypothesis that the capacity of myotubes to oxidize fat in vitro reflects the donor’s metabolic characteristics. Insulin sensitivity (IS) and metabolic flexibility of 16 healthy, young male subjects was determined by euglycemic hyperinsulinemic clamp. Muscle samples were obtained from vastus lateralis, cultured, and differentiated into myotubes. In human myotubes in vitro, we measured suppressibility (glucose suppression of FOx) and adaptability (an increase in FOx in the presence of high palmitate concentration). We termed these dynamic changes in FOx metabolic switching. In vivo, metabolic flexibility was positively correlated with IS and maximal oxygen uptake and inversely correlated with percent body fat. In vitro suppressibility was inversely correlated with IS and metabolic flexibility and positively correlated with body fat and fasting FFA levels. Adaptability was negatively associated with percent body fat and fasting insulin and positively correlated with IS and metabolic flexibility. The interindividual variability in metabolic phenotypes was preserved in human myotubes separated from their neuroendocrine environment, which supports the hypothesis that metabolic switching is an intrinsic property of skeletal muscle.

Authors

Barbara Ukropcova, Michele McNeil, Olga Sereda, Lilian de Jonge, Hui Xie, George A. Bray, Steven R. Smith

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In vitro adaptability is an intrinsic characteristic of muscle cells. Th...
In vitro adaptability is an intrinsic characteristic of muscle cells. The capacity of muscle cells to increase FOx (measured by 14CO2 production) in the presence of high palmitate concentration (fold increase in 14CO2 = 14CO2 at 100 μM palmitate / 14CO2 at 0 μM palmitate) in vitro is correlated with flexible clinical phenotype [ΔRQ (clamp)] (A); insulin-sensitive clinical phenotype (IS is represented by the glucose disposal rate, measured by clamp) (B); VO2max in vivo (C); percent body fat, measured by dual energy X-ray absorptiometry (D); and fasting insulin levels on a standard diet (E). Muscle cells from 16 individuals were grown and differentiated into myotubes in 24-well plates. Myotubes were preincubated in glucose- and serum-free medium and incubated for 3 hours with 1 μCi/ml 14C-palmitate, in the presence or absence of 100 μm cold palmitate. After incubation, levels of 14CO2 and 14C-intermediate metabolites of FOx were determined. Assays were performed in duplicate, and data were normalized to protein content. Data were adjusted for basal 14CO2 production (14CO2 production at 1 μCi/ml labeled palmitate and 0 μM cold palmitate).