Modified Si-Miao-San extract inhibits inflammatory response and modulates insulin sensitivity in hepatocytes through an IKKβ/IRS-1/Akt-dependent pathway

Abstract

Aim of the study: Modified Si-Miao-San (mSMS) has showed anti-inflammatory potency and has been used in the clinic to treat metabolic disorders such as obesity and diabetes, but whether its anti-inflammatory activity contributes to improving insulin resistance remains to be determined. This study aims to investigate the mechanistic relationship between its anti-inflammatory activity and modulation of insulin sensitivity in free fatty acid-stimulated HepG2 cells.

Materials and methods: HepG2 cells were stimulated with palmitate (PA) and the effect of mSMS on insulin mediated-glycogen synthesis and triglyceride secretion was observed. The inhibition of mSMS on gene expression of proinflammatory cytokine tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and inhibitor of NF-κB kinase-β (IKKβ) activation was investigated. In addition, the effects of mSMS on insulin signaling transduction along insulin receptor substrates-1 (IRS-1)/Akt pathway were also evaluated. Furthermore, the effect of mSMS on glucose intolerance induced by conditioned-medium derived from activated macrophages was also assessed in normoglycemic mice.

Results: Treatment of hepatocytes with PA reduced insulin sensitivity and mSMS effectively increased insulin-mediated glycogen synthesis and restored insulin inhibition of triglyceride secretion. mSMS suppressed IKKβ activation and down-regulated TNF-α and IL-6 gene over-expression, demonstrating its anti-inflammatory activity in hepatocytes. PA-evoked inflammation impaired insulin signaling cascades and mSMS improved insulin signaling transduction by modification of Ser/Thr phosphorylation of IRS-1 and downstream Akt (T308), thereby improved insulin sensitivity in hepatocytes. mSMS also improved glucose intolerance induced by inflammatory cytokines in normoglycemic mice, which further demonstrated its modulation toward insulin sensitivity in vivo.

Conclusions: The results suggest that mSMS inhibited inflammatory response and improved insulin sensitivity in hepatocytes via an IKKβ/IRS-1/Akt-dependent pathway.