Homoplantaginin Modulates Insulin Sensitivity in Endothelial Cells by Inhibiting Inflammation

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Recent data have indicated that inflammation plays an important role in the development of insulin resistance. The present study aims at examining the activity of homoplantaginin, a flavonoid from a traditional Chinese medicine Salvia plebeia R. BR., on palmitic acid (PA)-induced insulin sensitivity and the underlying mechanisms of its anti-infammatory properties in the endothelial cells. Pre-treatment of homoplantaginin on human umbilical vein endothelial cells (HUVECs) significantly inhibited PA induced tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) mRNA expression, and inhibitory κB kinase beta (IKKβ) and nuclear factor-κB (NF-κB) p65 phosphorylation. To the PA-impaired insulin-dependent tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1) and decrease in nitric oxide (NO) production, pretreatment of homoplantaginin could effectively reverse the effects of PA. Additionally, homoplantaginin significantly modulated the Ser/Thr phosphorylation of IRS-1, improved phosphorylation of Akt and endothelial nitric oxide synthase (eNOS), and increased NO production in the presence of insulin. Taken together, our results demonstrated that homoplantaginin ameliorates endothelial insulin resistance by inhibiting inflammation and modulating cell signalling via the IKKβ/IRS-1/pAkt/peNOS pathway, suggesting it may be used for the prevention and treatment of endothelial dysfunction associated with insulin resistance.