Quercetin But Not Quercitrin Ameliorates Tumor Necrosis Factor-Alpha-Induced Insulin Resistance in C2C12 Skeletal Muscle Cells

Skeletal muscle is a major site for glucose metabolism and its injury by cytokines can induce insulin resistance leading to type 2 diabetes. It has been suggested that quercetin may act as an anti-diabetic agent, however, the effects of quercetin on insulin resistance in skeletal muscle remain unknown. We aimed to investigate the role of quercetin and its glycoside, quercitrin in tumor necrosis factor-alpha (TNF-alpha) induced C2C12 skeletal muscle cell impairment. Quercetin, but not quercitrin moderately attenuated the effects of TNF-alpha and enhanced the basal and insulin stimulated uptake of glucose in a dose-dependent manner via the activation of the protein kinase B (Akt) and AMP-activated protein kinase (AMPK) pathways. Furthermore, the underlying mechanism also involved the suppression of nuclear factor-kappa B (NF-kappa B) signaling and the nitric oxide (NO)/inducible nitric oxide synthase (iNOS) system, downstream of AMPK transduction. In summary, quercetin exhibited its effect of improving glucose uptake and insulin sensitivity in skeletal muscle cells via the two independent signaling pathways of Akt and AMPK, and can be developed as a potential anti-diabetic agent.