Protective effect of inducible type nitric oxide synthase against intracellular oxidative stress caused by advanced glycation end-products in vascular smooth muscle cells from stroke-prone spontaneously hypertensive rats

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Abstract
A recent study demonstrated that free radicals were involved in the maintenance of hypertension in stroke-prone spontaneously hypertensive rats (SHRSP). However, the role of oxidative stress in hypertension and its related diseases in SHRSP remains unknown. On the other hand, advanced glycation end-products (AGEs) accumulate progressively in the vasculature with ageing, and have been identified to be as relevant mediators for various vascular complications. To elucidate whether nitric oxide (NO) produced by inducible type NO synthase (iNOS) in vascular smooth muscle cells (VSMC) taken from SHRSP and Wistar–Kyoto rats (WKY) attenuate AGEs-induced oxidative stress, we investigated the effect of NO donors and iNOS-induction in VSMC on intracellular oxidant level caused by AGEs. The cells preincubated with or without NO donor, S-nitroso-n-acetylpenicillamine (SNAP) or 3-morpholinosydnonimine (SIN-1), IL-1β and/or NG-monomethyl-L-arginine monoacetate (L-NMMA), were treated with AGEs, and the intracellular oxidant levels, total glutathione (GSH) levels, and γ-glutamylcysteine synthetase (GCS) mRNA were determined. We also determined the expression of an iNOS in VSMC from SHRSP and WKY. The intracellular oxidant level of VSMC was induced by AGEs in a dose-dependent manner. NO donor dose-dependently reduced AGEs-stimulated intracellular oxidant level. Treatment with IL-1β reduced the AGEs-stimulated intracellular oxidant level through increased NO production, whilst inhibition of NO production by L-NMMA reduced the inhibitory effect of IL-1β. We also confirmed that NO production as well as the expression of iNOS mRNA and the protein itself were significantly decreased in response to IL-1β in VSMC from SHRSP compared with WKY. We also confirmed that total GSH levels, decreased by AGEs, were restored by stimulation with IL-1β. Increased GSH synthesis was due to enhanced expression of the rate-limiting enzyme for GSH synthesis, GCS. These results indicate that NO release, produced by iNOS in VSMC in response to cytokines, might play a protective role against AGEs-stimulated oxidative stress in VSMC. This protective effect of NO is decreased in SHRSP compared to WKY.

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