Diosgenin ameliorates palmitate-induced endothelial dysfunction and insulin resistance via blocking IKKβ and IRS-1 pathways

Objective: We investigated whether diosgenin, a widely used steroidal sapogenin, exerted protection against palmitate (PA)-induced inflammation and insulin resistance in the endothelium. Methods: Human umbilical vein endothelial cells (HUVECs) were pretreated with diosgenin for 30 min, and then incubated with 100 mu mol/L PA for 30 min or 24 h with or without insulin. IKK beta, p65 phosphorylation, serine phosphorylation of insulin receptor substrate-1 (IRS-1) at S307, tyrosine phosphorylation of IRS-1, Akt and eNOS activation were determined by Western blot analysis. Levels of tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6), endothelin-1 (ET-1) and plasminogen activator inhibitor-1 (PAI-1) were measured with ELISA Kits. Intracellular nitric oxide (NO) was viewed with fluorescence microscopy. Effects of diosgenin on insulin-mediated vasodilation was investigated in the isolated rat aortic rings. Results: Diosgenin significantly reduced PA-enhanced IKK beta and NF-kappa B phosphorylation with inhibition of TNF-alpha and IL-6 production in endothelial cells at the concentrations of 0.1, 1 and 10 mu mol/L, well demonstrating its anti-inflammatory activity in an IKK beta/NF-kappa B-dependent fashion. Meanwhile, diosgenin attenuated PA-induced serine phosphorylation (S307) of IRS-1 and restored IRS-1 tyrosine phosphorylation in response to insulin. The beneficial modulation of serine/tyrosine phosphorylation of IRS-1 by diosgenin contributed to the improvement of insulin signaling along PI3K/Akt/eNOS pathways and thereby increased insulin-mediated NO production. Salicylate (5 mu mol/L), an inhibitor of IKK beta, showed similar activities as diosgenin. Diosgenin also remarkably inhibited ET-1 and PAI-1 production in the endothelial cells, and markedly restored the loss of insulin-mediated vasodilation in the presence of PA. Conclusion: The above-mentioned evidence suggests that diosgenin ameliorated endothelial dysfunction involved in insulin resistance through an IKK beta/IRS-1-dependent manner, shows potential application in the treatment for the cardiovascular diseases including atherosclerosis. (C) 2012 Elsevier Ireland Ltd. All rights reserved.