Diabetes‐induced nitrative stress in the retina, and correction by aminoguanidine

Abstract

Aminoguanidine inhibits the development of retinopathy in diabetic animals, but the mechanism remains unclear. Inasmuch as aminoguanidine is a relatively selective inhibitor of the inducible isoform of nitric oxide synthase (iNOS), we have investigated the effects of hyperglycemia on the retinal nitric oxide (NO) pathway in the presence and absence of aminoguanidine. In vivo studies utilized retinas from experimentally diabetic rats treated or without aminoguanidine for 2 months, and in vitro studies used bovine retinal endothelial cells and a transformed retinal glial cell line (rMC-1) incubated in 5 mM and 25 mM glucose with and without aminoguanidine (100 lg/mL). NO was detected as nitrite and nitrate, and nitrotyrosine and iNOS were detected using immunochemical methods. Retinal homogenates from diabetic animals had greater than normal levels of NO and iNOS (p < 0.05), and nitrotyrosine was greater than normal, especially in one band immunoprecipitated from retinal homogenates. Oral aminoguanidine significantly inhibited all of these increases. Nitrotyrosine was detected immunohistochemically only in the retinal vasculature of non-diabetic and diabetic animals. Retinal endothelial and rMC-1 cells cultured in high glucose increased NO and NT, and aminoguanidine inhibited both increases in rMC-1 cells, but only NT in endothelial cells. Hyperglycemia increases NO production in retinal cells, and aminoguanidine can inhibit this abnormality. Inhibition of diabetic retinopathy by aminoguanidine might be mediated in part by inhibition of sequelae of NO production.

Vascular endothelial growth factor in eye disease

“…10) (El-Remessy, 2003a;Graier et al, 1999;Graier et al, 1997;Graier et al, 1996) resulting in peroxynitrite formation. Research demonstrating increased levels of the peroxynitrite biomarker nitrotyrosine in retinas of diabetic patients and experimental animal models supports this concept and implies a role for peroxynitrite in the development of diabetic complications (Abu El-Asrar et al, 2004;Du et al, 2002;ElRemessy, 2003b;Kowluru and Odenbach, 2004;Obrosova et al, 2005). Studies in animal and tissue culture models have demonstrated that increased peroxynitrite formation is directly correlated with diabetes, high glucose-induced VEGF expression, and increased retinal vascular permeability (El-Remessy, 2003a;El-Remessy, 2003b;El-Remessy et al, 2006;El-Remessy et al, 2005).…”

“…The mechanisms by which oxidative stress contributes to VEGF overexpression are not fully understood. However, inhibiting nitric oxide synthase (NOS) has been shown to prevent signs of diabetic retinopathy in rats (Du et al, 2002;El-Remessy, 2003b;Kowluru et al, 2000), suggesting that formation of reactive nitrogen species plays a role in the pathology. Recent studies also indicate a role for peroxynitrite in diabetic retinopathy.…”

Functional Hyperemia and Mechanisms of Neurovascular Coupling in the Retinal Vasculature

“…29 Another change that occurs in the early stages of diabetic retinopathy in animal models of diabetes is an upregulation of inducible NOS (iNOS). iNOS increases are seen in both glial cells and neurons in the retina 92,108 and result in increased NO levels. 108,109 As described above, NO, in addition to acting on vessels to induce vasodilation, is a modulator of neurovascular coupling that suppresses flicker-evoked vasodilation.…”

“…Indeed, aminoguanidine has been shown to dramatically slow the progression of diabetic retinopathy in animal models of diabetes. [108][109][110][111][112] A human trial of aminoguanidine also demonstrates a slowing of diabetic retinopathy progression, although the trial was terminated early due to side effects of aminoguanidine when administered at high doses. 113 In addition to inhibiting iNOS, aminoguanidine also blocks formation of advanced glycation endproducts and its beneficial effect on diabetic retinopathy could be due to this effect on advanced glycation endproducts.…”

The contribution of hypertension to diabetic nephropathy and retinopathy: the role of inflammation and oxidative stress

“…92 Further corroborating the contribution of hypertension to retinal damage in diabetic SHR, we have demonstrated that anti-hypertensive treatment either with losartan (an AT1 receptor blocker, ARB) or with triple therapies (hydralazine, reserpine and hydrochlorothiazide) abolished these effects. 84 In the retina, a number of studies have shown that there is an increase in oxidative markers after the induction of DM, 67,[93][94][95] but the concomitance of diabetes and hypertension evoked earlier oxidative retinal damage characterized by an increase in nitrotyrosine and 8-OHdG in retinal tissue from short-term STZ-induced DM in SHRs. [96][97][98][99] These oxidative markers were the consequence of an increase in superoxide production and depletion of the gluthationereduced antioxidant system in the retinal tissue.…”