Metformin inhibited homocysteine-induced upregulation of endothelin receptors through the Sirt1/NF-kappa B signaling pathway in vascular smooth muscle cells

摘要

Metformin (Met) can improve atherosclerosis (As). Abnormal endothelin receptors [including endothelin type A (ETA) or type B (ETB) receptor] in vascular smooth muscle cells (VSMCs) are involved in As. Hyperhomocysteinemia (HHcy) is an independent risk factor for As. The present study was designed to test our hypothesis that Met inhibits the upregulation of endothelin receptors induced by homocysteine (Hcy) in VSMCs. Rat superior mesenteric artery (SMA) without endothelium, as an in vitro model, was cultured in serum-free medium for 24 h in the presence of Hey with or without Met or nicotinamide (Nic). In vivo, rats received subcutaneous injections of Hcy in the presence or absence of Met or Nic for 3 weeks. Levels of protein expression were determined by Western blotting. The contractile responses to sarafotoxin 6c (an ETB receptor agonist) or ET-1 (an ETA/ETB receptor agonist) were studied using a sensitive myograph. The blood pressure of rats was measured using a noninvasive tail-cuff plethysmography method. The results showed that Met could significantly inhibit the Hcy-induced upregulation of endothelin receptors (including ETA and ETB receptor) protein expression and endothelin receptor-mediated vasoconstriction, and it recovered the Hcy-induced decrease in silent information regulator 1 (Sirt1) in a dosage-dependent manner in SMA. However, Nic (a Sirt1 inhibitor) recovered the levels of Met-inhibited endothelin receptors and acetylated p65. Furthermore, the in vivo results showed that Met not only significantly the inhibited HHcy-induced upregulation of endothelin receptors and acetylated p65 but also recovered the HHcy-induced decrease in Sirt1 in a dosage-dependent manner in SMA. In addition, Met significantly inhibited the HHcy-induced blood pressure elevation. However, these effects were reverted by Nic. In conclusion, these data demonstrated that Met inhibited the Hcy-induced increase in endothelin receptor expression by activating Sirt1 and then inhibiting NF-kappa B in VSMCs. These findings may provide insights into the mechanism underlying of Met-treated cardiovascular diseases induced by Hcy.