Link between free radicals and protein kinase C in glucose-induced alteration of vascular dilation

Abstract

Development of vascular complications in diabetes has been linked to the quality of glucose regulation and characterized by endothelial dysfunction. The exact mechanism behind vascular complications in diabetes is poorly understood. However, alteration of nitric oxide (NO) biosynthesis or bioactivity is strongly implicated and the mechanism behind such alterations is still a subject for research investigations. In the present study, we tested the hypothesis that glucoseinduced attenuation of vascular relaxation involves protein kinase C (PKC)-linked generation of free radicals. Vascular relaxation to acetylcholine (ACh; 10 −9 -10 −5 M), isoproterenol (10 −9 -10 −5 M), or NO donor, sodium nitropruside (SNP; 10 −9 -10 −6 M) was determined in phenylephrine (PE, 10 −7 M) pre-constricted aortic rings from Sprague-Dawley rats in the presence or absence of 30 mM glucose (30 min), L-nitro-arginine methyl ester (L-NAME; 10 −4 M for 15 min), a NO synthase inhibitor, or xanthine (10 −5 M), a free radical generator. ACh dose-dependently caused relaxation that was attenuated by L-NAME, glucose, or xanthine. Pre-incubation (15 min) of the rings with vitamin C (10 −4 M), an antioxidant or calphostin C (10 −6 M), a PKC inhibitor, restored the ACh responses. However, high glucose had no significant effects on SNP or isoproterenolinduced relaxation. ACh-induced NO production by aortic ring was significantly reduced by glucose or xanthine. The reduced NO production was restored by pretreatment with vitamin C or calphostin C in the presence of glucose, but not xanthine. These data demonstrate that oxidants or PKC contribute to glucose-induced attenuation of vasorelaxation which could be mediated via impaired endothelial NO production and bioavailability. Thus, pathogenesis of glucose-induced vasculopathy involves PKC-coupled generation of oxygen free radicals which inhibit NO production and selectively inhibit NO-dependent relaxation.

Protein kinase C activation increases endothelial nitric oxide release in mesenteric arteries from orchidectomized rats

“…In this sense, it has been reported that PKC, depending on the tissue analysed, positively (Li et al 1998, Wedgwood et al 2001 or negatively (Mukherjee et al 2001, Yakubu et al 2004 regulates eNOS activity. PKC inhibition has also been reported to increase eNOS activity (Li et al 2005).…”

“…Endothelial NO is formed by eNOS (Förstermann et al 1991, Pollock et al 1991, 1993, which is regulated by multiple kinases (Dinerman et al 1994, Michell et al 2001. Several studies have reported that protein kinase C (PKC) could phosphorylate eNOS and modulate its activity, thereby leading to a decrease (Mukherjee et al 2001, Yakubu et al 2004 or increase (Li et al 1998, Wedgwood et al 2001) of endothelial NO production. In this sense, we observed that male sex hormone deprivation increased PKC activity of rat mesenteric arteries, and this positively modulates neuronal NO release in these arteries (BlancoRivero et al 2005a,b).…”

Alpha Lipoic Acid Treatment Improved Endothelium-dependent Relaxation in Diabetic Rat Aorta

“…In literature there are a number of contrary reports, showing increased relaxations and sensitivity of diabetic aorta to ISO 30) or no signiˆcant eŠect on ISO-induced relaxations. 31) Recently, it has also been reported that b-adrenoceptors induce vascular smooth muscle relaxation by acting through the NO-cGMP pathway and, when that is disrupted by endothelium removal or the presence of an NO synthase inhibitor, the cAMP pathway in smooth muscle is used. 32) To the best of our knowledge, there is no previous data on the eŠects of ALA on ACh-and ISO-induced relaxations in rat aorta.…”

The Methanol Seed Extract of Garcinia kola Attenuated Angiotensin II- and Lipopolyssacharide-Induced Vascular Smooth Muscle Cell Proliferation and Nitric Oxide Production

“…LPS mediates INOS expression through sequential activation of free radicals, protein kinase C (PKC) and protein tyrosine kinase (PTK) (6). PKC mediates essential cellular signals required for activation, proliferation, differentiation and survival and may be activated through a variety of agonists that may result in free radical generation (27). The GK extract significantly reduced ROS production indicating that the extract is a scavenger or prevents the activation pathway for the generation of ROS.…”