Effects of Physiological Doses of Resveratrol and Quercetin on Glucose Metabolism in Primary Myotubes

Abstract

Phenolic compounds have emerged in recent years as an option to face insulin resistance and diabetes. The central aim of this study was: (1) to demonstrate that physiological doses of resveratrol (RSV) or quercetin (Q) can influence glucose metabolism in human myotubes, (2) to establish whether AMP-activated protein kinase (AMPK) and protein kinase B -PKB- (Akt) pathways are involved in this effect. In addition, the effects of these polyphenols on mitochondrial biogenesis and fatty acid oxidation were analysed. Myotubes from healthy donors were cultured for 24 h with either 0.1 μM of RSV or with 10 μM of Q. Glucose metabolism, such as glycogen synthesis, glucose oxidation, and lactate production, were measured with D[U-¹⁴C]glucose. β-oxidation using [1-¹⁴C]palmitate as well as the expression of key metabolic genes and proteins by Real Time PCR and Western blot were also assessed. Although RSV and Q increased pgc1α expression, they did not significantly change either glucose oxidation or β-oxidation. Q increased AMPK, insulin receptor substrate 1 (IRS-1), and AS160 phosphorylation in basal conditions and glycogen synthase kinase 3 (GSK3β) in insulin-stimulated conditions. RSV tended to increase the phosphorylation rates of AMPK and GSK3β. Both of the polyphenols increased insulin-stimulated glycogen synthesis and reduced lactate production in human myotubes. Thus, physiological doses of RSV or Q may exhibit anti-diabetic actions in human myotubes.

Keywords: glucose; human primary myotubes; quercetin; resveratrol.

Figure 1

Mitochondrial (a) and cytosolic (b) gene expression in human myotubes treated with 0.1 µM of resveratrol (RSV) and 10 µM of quercetin (Q) for 24 h. All of the data are presented as the mean ± SEM of two independent experiments (n = 6 per group). Comparisons between biological replicates of each treatment group and biological replicates of the control group were analysed by Student’s t-test. The asterisks represent differences versus the controls (* p < 0.05).

Figure 2

GLUT4 protein expression (a), glucose oxidation (b) and palmitate oxidation (c) in human myotubes treated with 0.1 µM of resveratrol (RSV) and 10 µM of quercetin (Q) for 24 h. All of the data are presented as the mean ± SEM of six (a) or three (b,c) biological replicates. Comparisons between each treatment group and the control group were analysed by Student’s t-test.

Figure 3

Protein expression of AMPK (a), IRS-1 (b), Akt (c), GSK3β (d), and AS160 (e) in human myotubes that were treated with 0.1 µM of resveratrol (RSV) and 10 µM of quercetin (Q) for 24 h in the presence or absence of insulin, with the exception of AMPK, which was measured only in basal conditions. Target protein bands are shown on the chart top as representative blot images. All of the data are presented as the mean ± SEM of six biological replicates. Comparisons between each treatment group and the control group were analysed by Student’s t-test. The asterisks represent differences versus the controls (* p < 0.05; ** p < 0.01).

Figure 3

Protein expression of AMPK (a), IRS-1 (b), Akt (c), GSK3β (d), and AS160 (e) in human myotubes that were treated with 0.1 µM of resveratrol (RSV) and 10 µM of quercetin (Q) for 24 h in the presence or absence of insulin, with the exception of AMPK, which was measured only in basal conditions. Target protein bands are shown on the chart top as representative blot images. All of the data are presented as the mean ± SEM of six biological replicates. Comparisons between each treatment group and the control group were analysed by Student’s t-test. The asterisks represent differences versus the controls (* p < 0.05; ** p < 0.01).

Figure 4

Glycogen synthesis (a) and lactate content in the media (b) in human myotubes treated with 0.1 µM of resveratrol (RSV) and 10 µM of quercetin (Q) for 24 h. Glycogen synthesis data are presented as the mean ± SEM of three biological replicates. The data of lactate content in the media are presented as the mean ± SEM of six biological replicates. Comparisons between each treatment group and the control group were analysed by Student’s t-test. The asterisks represent differences versus the controls (* p < 0.05; (*** p < 0.001)).