Nitrosative Stress in the Rat Retina at the Onset of Streptozotocin-Induced Diabetes

Abstract

Background/Aims. Nitric oxide is a multifunctional molecule that can modify proteins via nitrosylation; it can also initiate signaling cascades through the activation of soluble guanylate cyclase. Diabetic retinopathy is the leading cause of blindness, but its pathogenesis is unknown. Multiple mechanisms including oxidative-nitrosative stress have been implicated. Our main goal was to find significant changes in nitric oxide (NO) levels and determine their association with nitrosative stress in the rat retina at the onset of diabetes. Methods: Diabetes was induced by a single intraperitoneal administration of streptozotocin. The possible nitric oxide effects on the rat retina were evaluated by the presence of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d), a specific marker for NO-producing neurons, detected by histochemistry performed on whole retinas and retina sections. Immunohistochemistry was also performed on retina sections for iNOS, 3-nitrotyrosine (3-NT) and glial fibrillary acidic protein (GFAP). Retinal nitric oxide levels were assessed by measuring total nitrate/nitrite concentrations. Retinal cGMP levels were determined by radioimmunoassay. Western blots for nitrotyrosine (3-NT) and oxidized proteins were performed. Results: In the present study, we found increased activity of NADPH-diaphorase and iNOS immunoreactivity in the rat retina at the onset of diabetes; this increase correlated with a remarkable increase in NO levels as early as 7 days after the onset of diabetes. However, cGMP levels were not modified by diabetes, suggesting that NO did not activate its signaling cascade. Even so, Western blots revealed a progressive increase in nitrated proteins at 7 days after diabetes induction. Likewise, positive nitrotyrosine immunolabeling was observed in the photoreceptor layer, ganglion cell layer, inner nuclear layer and some Müller cell processes in the retinas of diabetic rats. In addition, levels of oxidized proteins were increased in the retina early after diabetes induction; these levels were reduced by the administration of L-NAME. In addition, stress in Müller cells was determined by immunoreactivity to the glial fibrillary acidic protein. Conclusions: Our findings indicated the occurrence of nitrosative stress at the onset of diabetes in the rat retina and emphasized the role of NO in retinal function and the pathogenesis of retinopathy.

Long-Term Functional and Structural Consequences of Primary Blast Overpressure to the Eye

“…A remarkable and unexpected finding from this study was the long-lived persistence of GFAP upregulation in blast-exposed retinas, even 8 months after a single exposure to ABO. GFAP upregulation is typically a signature that accompanies any insult to the retina, including neuronal degeneration and cell death in retinal degenerative diseases, 23,24 hyperglycemia insult in diabetic retinopathy, 50,51 and ischemic insult in ocular stroke. 52 The persistence of a gliotic response suggests that the local microenvironment of the retina was perturbed by blast exposure, belying the apparent ''normalcy'' of retinal layer thickness.…”

Identification of O-GlcNAcylation Modification in Diabetic Retinopathy and Crosstalk with Phosphorylation of STAT3 in Retina Vascular Endothelium Cells

“…Instances of diabetic retinopathy (DR) are increasing at an alarming rate, becoming a leading cause for visual impairment and blindness in diabetic patients worldwide [1,2]. Visual loss primarily occurs due to increased permeability of retinal vessels (diabetic macular edema) [3] and retinal neovascularization (proliferative diabetic retinopathy) [4,5].…”

Nitrosative Stress and Its Association with Cardiometabolic Disorders

“…Furthermore, the NO/soluble guanylate cyclase/guanosine cyclic monophosphate (cGMP) pathway is also involved in the modulation of visual information processing in the retina. However, in diabetic retinopathy, this pathway is impaired by S-nitrosylation, leading to visual loss and blindness [95]. The mechanisms initiated by hyperglycemia are not completely understood; however, the relationship between increased aldose reductase activity, NSS and PARP-1 activation has become a focus of interest in the diabetic lens, nerve and retina [96].…”