Vasoreactivity of isolated aortic rings from dyslipidemic and insulin resistant inducible nitric oxide synthase knockout mice.

Recent study from this lab indicated enhanced susceptibility of iNOS KO mice for diet induced obesity (DIO) and systemic insulin resistance (IR) as compared to C57BL/6 (WT) mice. The present study investigates aortic vasoreactivity in high fat diet (HFD) induced insulin resistant iNOS KO mice. WT and iNOS KO mice were fed with 45% HFD/10% LFD for ten weeks. Systemic IR was assessed via measurement of circulating lipids, glucose, and insulin; while phenylephrine (PE)/acetylcholine (ACh) induced responses were monitored in the isolated aortic rings. To understand the mechanism, qPCR or Western blotting experiments were performed in aorta and Ea.hy926 cells. After 10 weeks of HFD feeding, significant increase in the body weight/fat mass, augmented circulating lipids, glucose, insulin and inflammatory cytokines along with impaired acetylcholine induced aortic vasorelaxation and enhanced iNOS expression was observed in the aortic tissue of WT mice. In the aminoguanidine (AG, 20 mg/kg for 4 weeks) treated WT mice and also in iNOS KO mice, acetylcholine induced vasorelaxation was significantly preserved. Further, acetylcholine mediated vasorelaxation correlated with increased eNOS phosphorylation at Ser1177 residue in the iNOS KO mice and same was also observed in the iNOS silenced Ea.hy926 cells. Moreover, treatment of Ea.hy926 cells with palmitic acid or TNFα also caused a significant decrease in eNOS activity, which was reversed in iNOS silenced Ea.hy926 cells suggesting the role of iNOS in the reduction of eNOS activity. The study thus implies a critical role of iNOS in vascular diseases associated with dyslipidemia/IR.