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 suppressibility is an intrinsic characteristic of muscle cells....
In vitro suppressibility is an intrinsic characteristic of muscle cells. The potential of glucose to suppress FOx (CO2) in vitro (% suppression of 14CO2 = [1 – (FOx at 5 mM glucose / FOx at 0 mM glucose)] × 100) is correlated with in vivo metabolic flexibility [as indicated by ΔRQ (clamp), an insulin-stimulated change in RQ, measured by indirect calorimetry during the clamp] (A); in vivo IS represented by glucose disposal rate, measured by clamp (B); percent body fat, measured by dual energy X-ray absorptiometry (C); and in vivo fasting FFA levels (D). 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, without glucose (to measure maximal FOx) or with 5 mM glucose (to measure suppressed FOx). After incubation, 14CO2 and 14C-intermediate metabolites of FOx were determined. Assays were performed in duplicates and data were normalized to protein content.