Abstracts for Oral Presentation

BACKGROUND: Based on in vivo studies, it has been proposed that mitochondrial content and oxidative capacity are good predictors of insulin sensitivity.but there is no direct experimental evidence to support this theory.To test this hypothesis, we developed a technique to pharmacologically stimulate mitochondrial biogenesis and oxidative capacity using in vitro cultures of human primary skeletal muscle cells.METHODS: Vastus lateralis myoblasts from 4 lean healthy subjects were cultured, pooled and differentiated into myotubes for 5 days.During differentiation.myotubes were either pulsed (PFI) or not pulsed (Control) with 0.5 p.M ionomycin and 4 p.M forskolin I h per day for the last 3 days of differentiation.All were continuously treated with 30 p.M palmitate to increase intramyocellular lipid content.Oleate and palmitate oxidation, mitochondrial content and enzyme activity, and insulin-stimulated glycogen storage were measured.RESULTS: Mitochondrial DNA copy number increased 4-fold in response to PFI treatment (p < 0.0 I), and mitotracker increased 2.5-fold (p < 0.01).Treatment with PFI promoted a 1.6-fold and 1.7-fold increase in oleate and palmitate oxidation.respectively, compared to control cells (p < 0.00 I).Citrate synthase and /3-hydroxy-acetyl-CoA dehydrogenase activities also increased by 1.2fold (p = 0.13) and 1.6-fold (p < 0.01), respectively.Stimulation of mitochondrial content and oxidative capacity with PFI treatment was accompanied by a l.3-fold and a 2-fold increase in both baseline (p < 0.001) and insulin-stimulated glycogen storage (p < 0.001), respectively.Change in insulin-mediated glycogen storage was tightly correlated with change in oxidative capacity (oleate oxidation: R2 = 0.76, P < 0.01; palmitate oxidation: R2 = 0.77, P < 0.01).CON-CLUSIONS: Our data demonstrates for the first time an in vitro functional relationship between increased mitochondrial oxidative capacity and insulin sensitivity.Pharmacological stimulation of mitochondrial biogenesis and/or oxidative capacity might be a promising treatment of insulin resistance.