Diabetic-induced endothelial dysfunction in rat aorta: role of hydroxyl radicals

Abstract

AbstractŽ y . Objective: Previous studies suggest a role of superoxide anion radicals PO in impaired endothelium-dependent relaxation of 2 diabetic blood vessels; however, the role of secondary reactive oxygen species remains unclear. In the present study, we investigated a role of various potential reactive oxygen species in diabetic endothelial dysfunction. Methods: Thoracic aortic rings from 8-week streptozotocin-induced diabetic and age-matched control rats were mounted in isolated tissue baths. Endothelium-dependent relaxation to Ž . Ž . acetylcholine ACH and endothelium-independent relaxation to nitroglycerin NTG were assessed in precontracted rings. Results: ACH-induced relaxation was impaired in diabetic compared to control rings and was not improved with either indomethacin or daltroban. ACH-induced relaxation in both control and diabetic rings was completely blocked with the nitric oxide synthase inhibitors, Ž . L -nitroarginine methyl ester or L-nitroarginine L-NA . NTG-induced relaxation was insensitive to L-NA and was unaltered by diabetes.Ž . Pretreatment with superoxide dismutase SOD at activities which did not alter contractile tone failed to alter responses to ACH in diabetic rings. Similar results were obtained using either catalase or mannitol. In contrast, the combination of SOD plus catalase or Ž . DETAPAC, an inhibitor of metal-facilitated hydroxyl radical POH formation, markedly enhanced relaxation to ACH in diabetic but not in control rings. Neither the combination of SOD plus catalase nor DETAPAC altered the sensitivity or relaxation to NTG in control rings with or without endothelium. In diabetic rings with endothelium, both DETAPAC or SOD plus catalase increased sensitivity but not maximum relaxation to NTG. In diabetic rings without endothelium, relaxation and sensitivity to NTG were unaltered by either treatment. In L-NA-treated diabetic rings with endothelium, sensitivity and relaxation to NTG was unaltered by either DETAPAC or SOD plus catalase. Conclusion: Diabetic endothelium produces increases in both PO y and H O leading to enhanced intracellular production of 2 2 2 P OH. Thus, POH are implicated in diabetes-induced endothelial dysfunction.

Oxygen‐derived free radicals mediate endothelium‐dependent contractions in femoral arteries of rats with streptozotocin‐induced diabetes

“…Oxygen-derived free radicals play an important role in the occurrence of endothelium-dependent contractions in the basilar artery of the dog and the aorta of the spontaneously hypertensive rat Katusic et al, 1993;Yang et al, 2003aYang et al, , 2004aTang et al, 2007). Previous studies from our laboratory demonstrate that the calcium ionophore A23187 induces greater endothelium-dependent contractions in the femoral artery of diabetic rats than those of normoglycaemic animal (Shi et al, 2007), exemplifying the endothelial dysfunction caused by diabetes (Pieper and Gross, 1988;Heygate et al, 1995;Makimattila et al, 1996;Pieper et al, 1997;Vallejo et al, 2000). This prompted the investigation of the role of oxygen-derived free radicals in the endothelium-derived contracting factor-mediated responses of the femoral artery of rats with STZ-induced diabetes.…”

“…The effect of STZ-induced diabetes on nitric oxidemediated vasodilatation is still controversial; it has been reported as normal in the aorta (Head et al, 1987;Harris and MacLeod, 1988;Mulhern and Docherty, 1989), mesenteric artery (Harris and MacLeod, 1988) and femoral artery (Wigg et al, 2001), as blunted in aorta (Pieper et al, 1997;Vallejo et al, 2000), mesenteric artery (Heygate et al, 1995;Vallejo et al, 2000;Shi et al, 2007) and femoral artery (Shi et al, 2006) or augmented in aorta (Altan et al, 1989). The production of vasoconstrictor prostaglandins is augmented in diabetic animals (aorta , renal artery (Pflueger et al, 1999) and femoral artery (Shi et al, 2007)).…”

Endothelial dysfunction in diabetes

“…Oxygen-derived free radicals may impair endotheliumdependent vasodilatation through inactivation of NO or by serving as an EDCF (Rubanyi & Vanhoutte, 1986;Katusic & Vanhoutte, 1989). Acute administration of scavengers of superoxide anion, including superoxide dismutase (Hattori et al, 1991;Tesfamariam & Cohen, 1992;Pieper et al, 1996;Bohlen & Lash, 1993) and the combination of superoxide dismutase with catalase (Pieper et al, 1997) improved or normalized the abnormal endothelium-dependent responses in di erent models of diabetes and during high glucose exposure. Similarly, chronic treatment with probucol (Tesfamariam & Cohen, 1992), N-acetylcysteine (Pieper & Siebeneich, 1998b), vitamin E (Keegan et al, 1995;RoÈ sen et al, 1996) and vitamin C (Ting et al, 1996) prevented the development of endothelial dysfunction in clinical and experimental diabetes.…”

“…In an in vivo study of high glucose exposure of the mesenteric circulation, superoxide dismutase and catalase were equally or more e ective than cyclo-oxygenase inhibition in restoring the impaired ACh-induced vasodilatation, suggesting that the oxygen-derived radicals produced during prostanoid synthesis, rather than the prostanoids themselves, were responsible for the endothelial dysfunction (Bohlen & Lash, 1993). In some studies, hydroxyl radical scavengers restored endotheliumdependent vasodilatation, while superoxide dismutase had less or no e ect (Dai et al, 1993;Diederich et al, 1994;Pieper et al, 1997;Mayhan & Patel, 1998), suggesting a more important role of the hydroxyl radical in eliciting endothelial dysfunction.…”

Untitled

“…In addition to direct damage by reactive oxidative metabolites, however, alternative pathomechanisms have been proposed, but they have received little attention. For example, superoxide can be metabolized to H 2 O 2 , which can give rise to the production of more reactive intermediates, such as hydroxyl radical (• OH) [ 10 ] , which -among On the basis of the aforementioned fi ndings and because tyrosine kinases are known to be also important in the activation of eNOS by phosphorylation of eNOS Ser (1177) [ 6 ] we hypothesized that accumulation of o -Tyr in the vascular wall can contribute to impaired relaxation of arteries to insulin by interfering with the PI3K/Akt/eNOS/NO signaling pathway. Thus, we determined the eff ects of oral supplementation of o -Tyr on the vasomotor responses of isolated arteries to insulin and investigated the phosphorylation of eNOS in response to o -Tyr and p -Tyr treatment in cultured endothelial cells.…”