An in vivo model for elucidation of the mechanism of tumor necrosis factor-α (TNF-α)-induced insulin resistance:: Evidence for differential regulation of insulin signaling by TNF-α

Tumor necrosis factor-alpha (TNF-alpha) has been shown to induce insulin resistance in cultured cells as well as in animal models. The aim of this study was to map the in vivo mechanism whereby TNF-alpha contributes to the pathogenesis of impaired insulin signaling, using obese and lean Zucker rats in which TNF-alpha activity was inhibited through adenovirus-mediated gene transfer. We employed a replication-incompetent adenovirus-5 (Ad5) vector to endogenously express a TNF inhibitor (TNFi) gene, which encodes a chimeric protein consisting of the extracellular domain of the human 55-kDa TNF receptor joined to a mouse IgG heavy chain. Control animals consisted of rats infected with the same titer of adenovirus carrying the lac-z complementary DNA, encoding for beta-galactosidase. There was a significant reduction in plasma insulin and free fatty acid levels in TNFi obese rats 2 days following Ad5 administration. The peripheral insulin sensitivity index was 50% greater, whereas hepatic glucose output was completely suppressed during hyperinsulinemic glucose clamps in TNFi obese animals, with no differences observed between the two lean groups.