3-nitrotyrosine and Diabetic-Retinopathy

Macro- and microvascular disease are the most common causes of morbidity and mortality in patients with diabetes mellitus. Diabetic cardiovascular dysfunction represents a problem of great clinical importance underlying the development of various severe complications including retinopathy, nephropathy, neuropathy and increase the risk of stroke, hypertension and myocardial infarction. Hyperglycemic episodes, which complicate even well-controlled cases of diabetes, are closely associated with increased oxidative and nitrosative stress, which can trigger the development of diabetic complications. Hyperglycemia stimulates the production of advanced glycosylated end products, activates protein kinase C, and enhances the polyol pathway leading to increased superoxide anion formation. Superoxide anion interacts with nitric oxide, forming the potent cytotoxin peroxynitrite, which attacks various biomolecules in the vascular endothelium, vascular smooth muscle and myocardium, leading to cardiovascular dysfunction. The pathogenetic role of nitrosative stress and peroxynitrite, and downstream mechanisms including poly(ADP-ribose) polymerase (PARP) activation, is not limited to the diabetes-induced cardiovascular dysfunction, but also contributes to the development and progression of diabetic nephropathy, retinopathy and neuropathy. Accordingly, neutralization of peroxynitrite or pharmacological inhibition of PARP is a promising new approach in the therapy and prevention of diabetic complications. This review focuses on the role of nitrosative stress and downstream mechanisms including activation of PARP in diabetic complications and on novel emerging therapeutical strategies offered by neutralization of peroxynitrite and inhibition of PARP.

Topics: Animals; Cardiomyopathies; Diabetes Complications; Diabetic Angiopathies; Diabetic Nephropathies; Diabetic Neuropathies; Diabetic Retinopathy; Endothelium, Vascular; Humans; Nitric Oxide; Oxidative Stress; Peroxynitrous Acid; Poly(ADP-ribose) Polymerases; Superoxides; Tyrosine

To primarily explore the mechanism of captopril in oxidative stress and investigate the link between captopril alleviated oxidative damage and diabetic retinopathy (DR).. Human retinal microvascular endothelial cells (HRMECs) were used for in vitro experiments and cultured in a 5.5 mM or 30 mM glucose medium. Sprague-Dawley rats were used for in vivo experiments, and parts of the rats were established for diabetic groups by injected streptozotocin (n = 10, each group). Both experiments had a captopril-treated group. The levels of total cholesterol (TC), reactive oxygen species (ROS), nitric oxide (NO), and human 3-nitrotyrosine (3-NT) were detected in assay kits and ELISA. Western blotting was used to detect the expression of steroid regulatory element binding protein 2 (SREBP2), inducible nitric oxide synthase (iNOS), vascular endothelial growth factor (VEGF), and endothelial nitric oxide synthase (eNOS). Hematoxylin-eosin staining and Evans blue were used to describe retinal histopathology.. The levels of TC, ROS, NO, and 3-NT were increased in the higher glucose groups compared with the normal controls during in vivo and in vitro experiments. Western blotting showed a higher level of SREBP2, iNOS, and VEGF and a lower eNOS level in the higher glucose groups. These results were reversed by captopril. Captopril relieved diabetic retinal vascular leakage.. Our study suggested that captopril alleviates oxidative damage in DR due to creating lower peroxynitrite by decreasing ROS and NO, which may provide a visible direction for DR research.

Topics: Animals; Captopril; Cholesterol; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Disease Models, Animal; Endothelial Cells; Glucose; Humans; Male; Nitric Oxide; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; Oxidative Stress; Rats; Rats, Sprague-Dawley; Reactive Oxygen Species; Retina; Retinal Vessels; Streptozocin; Tyrosine; Vascular Endothelial Growth Factor A

In the development of diabetic retinopathy, retinal mitochondria are dysfunctional, and mitochondrial DNA (mtDNA) is damaged with increased base mismatches and hypermethylated cytosines. DNA methylation is also a potential source of mutation, and in diabetes, the noncoding region, the displacement loop (D-loop), experiences more methylation and base mismatches than other regions of the mtDNA. Our aim was to investigate a possible crosstalk between mtDNA methylation and base mismatches in the development of diabetic retinopathy. The effect of inhibition of Dnmts (by 5-aza-2'-deoxycytidine or Dnmt1-siRNA) on glucose-induced mtDNA base mismatches was investigated in human retinal endothelial cells by surveyor endonuclease digestion and validated by Sanger sequencing. The role of deamination factors on increased base mismatches was determined in the cells genetically modulated for mitochondrial superoxide dismutase (Sod2) or cytidine-deaminase (APOBEC3A). The results were confirmed in an in vivo model using retinal microvasculature from diabetic mice overexpressing Sod2. Inhibition of DNA methylation, or regulation of cytosine deamination, significantly inhibited an increase in base mismatches at the D-loop and prevented mitochondrial dysfunction. Overexpression of Sod2 in mice also prevented diabetes-induced D-loop hypermethylation and increase in base mismatches. The crosstalk between DNA methylation and base mismatches continued even after termination of hyperglycemia, suggesting its role in the metabolic memory phenomenon associated with the progression of diabetic retinopathy. Inhibition of DNA methylation limits the availability of methylated cytosine for deamination, suggesting a crosstalk between DNA methylation and base mismatches. Thus, regulation of DNA methylation, or its deamination, should impede the development of diabetic retinopathy by preventing formation of base mismatches and mitochondrial dysfunction.

Topics: Animals; APOBEC Deaminases; Base Pair Mismatch; Base Sequence; Cytosine; Diabetic Retinopathy; DNA Methylation; DNA, Mitochondrial; Endothelial Cells; Humans; Mice, Inbred C57BL; Nucleic Acid Conformation; Peroxynitrous Acid; Superoxide Dismutase; Tyrosine

Diabetic retinopathy (DR) is associated with nitrosative stress. The purpose of this study was to evaluate the beneficial effects of S-nitrosoglutathione (GSNO) eye drop treatment on an experimental model of DR.. Diabetes (DM) was induced in spontaneously hypertensive rats (SHR). Treated animals received GSNO eye drop (900 nM or 10 μM) twice daily in both eyes for 20 days. The mechanisms of GSNO effects were evaluated in human RPE cell line (ARPE-19).. In animals with DM, GSNO decreased inducible nitric oxide synthase (iNOS) expression and prevented tyrosine nitration formation, ameliorating glial dysfunction measured with glial fibrillary acidic protein, resulting in improved retinal function. In contrast, in nondiabetic animals, GSNO induced oxidative/nitrosative stress in tissue resulting in impaired retinal function. Nitrosative stress was present markedly in the RPE layer accompanied by c-wave dysfunction. In vitro study showed that treatment with GSNO under high glucose condition counteracted nitrosative stress due to iNOS downregulation by S-glutathionylation, and not by prevention of decreased GSNO and reduced glutathione levels. This posttranslational modification probably was promoted by the release of oxidized glutathione through GSNO denitrosylation via GSNO-R. In contrast, in the normal glucose condition, GSNO treatment promoted nitrosative stress by NO formation.. In this study, a new therapeutic modality (GSNO eye drop) targeting nitrosative stress by redox posttranslational modification of iNOS was efficient against early damage in the retina due to experimental DR. The present work showed the potential clinical implications of balancing the S-nitrosoglutathione/glutathione system in treating DR.

Topics: Analysis of Variance; Animals; Biomarkers; Cell Line; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Disease Models, Animal; Electroretinography; Glial Fibrillary Acidic Protein; Glutathione; Humans; Nitric Oxide Donors; Nitric Oxide Synthase Type II; Ophthalmic Solutions; Rats; Reactive Oxygen Species; Retina; S-Nitrosoglutathione; Tyrosine; Up-Regulation

To evaluate the role of melatonin, an antioxidant agent, in diabetic oxidative stress and vascular damage.. Diabetes was induced in 21 male Wistar rats by intraperitoneal (IP) administration of streptozotocin and then the rats were equally and randomly allocated to diabetic, melatonin, and vehicle groups. Seven healthy normal rats with similar features comprised the control group as the fourth group. All animals were followed for 12 weeks. The melatonin group received IP melatonin daily and the vehicle group received 2.5% ethanol IP at the last month. At the end of 12 weeks, the rats were killed and retinas were harvested. The retinas were investigated for the existence of hypoxia-inducible factor 1-α (HIF-1α), vascular endothelial growth factor A (VEGF-A), and pigment epithelium-derived factor (PEDF) by ELISA. Retinal oxidative stress is quantitated by measuring nitrotyrosine and malondialdehyde levels. Retinal immunohistochemistry with antibody against CD31 antigen was carried out on retinal cross-sections. For statistics, ANOVA test was used for multiple comparisons.. Hyperglycemia increased retinal oxidation as measured through levels of nitrotyrosine and malondialdehyde. Diabetic retinas are also associated with abnormal vascular changes such as dilatation and deformation. HIF-1α, VEGF-A, and PEDF were all increased because of diabetic injury. Melatonin showed a potential beneficial effect on retinopathy in diabetic rats. It decreased retinal nitrotyrosine and malondialdehyde levels, showing an antioxidative support. The vasculomodulator cytokines are decreased accordingly by melatonin therapy. Melatonin normalized retinal vascular changes as well.. Melatonin may show some advantage on diabetic vascular changes through decreasing oxidative stress and vessel-related cytokines.

Topics: Animals; Antioxidants; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 1; Diabetic Retinopathy; Enzyme-Linked Immunosorbent Assay; Eye Proteins; Hyperglycemia; Hypoxia-Inducible Factor 1, alpha Subunit; Injections, Intraperitoneal; Male; Malondialdehyde; Melatonin; Nerve Growth Factors; Oxidative Stress; Platelet Endothelial Cell Adhesion Molecule-1; Rats; Rats, Wistar; Retinal Vessels; Serpins; Tyrosine; Vascular Endothelial Growth Factor A

Oxidative stress is increased in the retina in diabetes, and it is considered to play an important role in the development of retinopathy. Findings indicate that obtusifolin has antioxidant properties. The purpose of this study was to examine the effect of obtusifolin on retinal capillary cell apoptosis and the development of pathology in diabetes. Retina was used from streptozotocin-induced diabetic rats receiving diets supplemented with or without obtusifolin (100, 200, and 400 mg/kg) for 11 months of diabetes. Capillary cell apoptosis (by terminal transferase-mediated dUTP nick-end labeling) and formation of acellular capillaries were investigated in the trypsin-digested retinal microvessels. The effect of obtusifolin administration on retinal 8-hydroxy-2'deoxyguanosine (8-OHdG) and nitrotyrosine levels was determined by enzyme-linked immunosorbent assay. Obtusifolin administration for the entire duration of diabetes inhibited capillary cell apoptosis and the number of acellular capillaries in the retina, despite similar severity of hyperglycemia in the four diabetic groups (with and without obtusifolin). Retinal 8-OHdG and nitrotyrosine levels were significantly increased, respectively, in diabetes, and obtusifolin administration inhibited these increases. Our results demonstrate that the long-term administration of obtusifolin has beneficial effects on the development of diabetic retinopathy via inhibition of accumulation of oxidatively modified DNA and nitrotyrosine in the retina. Obtusifolin represents an achievable adjunct therapy to help prevent vision loss in diabetic patients.

Topics: 8-Hydroxy-2'-Deoxyguanosine; Administration, Oral; Animals; Anthraquinones; Antioxidants; Apoptosis; Capillaries; Deoxyguanosine; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Hyperglycemia; Male; NF-kappa B; Oxidative Stress; Rats; Rats, Wistar; Retina; Tyrosine

To evaluate the role of rapamycin in the prevention of diabetic oxidative stress and the regulation of angiogenic factors.. Experimental animal study.. Diabetes was induced in 20 adult male Wistar rats by a single intraperitoneal administration of streptozotocin (60 mg/kg). Rats were randomly assigned into diabetic and rapamycin groups (n = 10). Ten healthy normal adult male rats of same age formed the control group. All groups were followed for 3 months. Rapamycin group received 1 mg/kg rapamycin via orogastric gavage during the last 4 weeks. At the end of 12 weeks, rats were sacrificed and biochemical oxidative stress markers (malondialdehyde and nitrotyrosine), together with vascular endothelial growth factor, hypoxia-inducible factor-1α, and pigment epithelium-derived factor, were measured in the retina. Blood biochemical analyses were also done.. In the diabetic group, retinal malondialdehyde and nitrotyrosine levels were increased in comparison with control and rapamycin groups (p < 0.05). Rapamycin suppressed oxidative stress and showed a beneficial effect. It also decreased all angiomodulator cytokines compared with the diabetic group (p < 0.05). Correspondingly, rapamycin also decreased plasma malondialdehyde levels compared with the diabetic group (p = 0.037).. Rapamycin may have a protective role against diabetes-induced oxidative retinal injury and may decrease angiomodulator cytokines.

Topics: Angiogenesis Modulating Agents; Animals; Anti-Bacterial Agents; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Eye Proteins; Hypoxia-Inducible Factor 1, alpha Subunit; Male; Malondialdehyde; Nerve Growth Factors; Oxidative Stress; Rats; Rats, Wistar; Serpins; Sirolimus; Tyrosine; Vascular Endothelial Growth Factor A

MicroRNAs (miRNAs) are known to participate in post-transcriptional regulation of gene expression and are involved in multiple pathogenic processes. Here, we identified miRNA expression changes in the retinas of Akita mice, a genetic model of type 1 diabetes, and investigated the potential role of miRNA in diabetic retinopathy.. Visual function of Akita and control mice was evaluated by electroretinography. MiRNA expression changes in the retinas of Akita mice were identified by miRNA-specific microarray and confirmed by quantitative RT-PCR (qRT-PCR). The potential downstream targets of identified miRNAs were predicted by bioinformatic analysis using web-based applications and confirmed by dual luciferase assay. The mRNA and protein changes of identified downstream targets were examined by qRT-PCR and Western blot analysis.. MiRNA-specific microarray and qRT-PCR showed that miR-200b was upregulated significantly in the Akita mouse retina. Sequence analysis and luciferase assay identified oxidation resistance 1 (Oxr1) as a downstream target gene regulated by miR-200b. In a human Müller cell line, MIO-M1, transfection of a miR-200b mimic downregulated Oxr1 expression. Conversely, transfection of MIO-M1 with a miR-200b inhibitor resulted in upregulated Oxr1. Furthermore, overexpression of recombinant Oxr1 attenuated oxidative stress marker, nitration of cellular proteins, and ameliorated apoptosis induced by 4-hydroxynonenal (4-HNE), an oxidative stressor. Similarly, transfection of a miR-200b inhibitor decreased, whereas transfection of miR-200b mimic increased the number of apoptotic cells following 4-HNE treatment.. These results suggested that miR-200b-regulated Oxr1 potentially has a protective role in diabetic retinopathy.

Topics: Animals; Apoptosis; Cells, Cultured; Diabetes Mellitus, Type 1; Diabetic Retinopathy; Disease Models, Animal; Down-Regulation; Mice; Mice, Inbred C57BL; MicroRNAs; Oligonucleotide Array Sequence Analysis; Orexin Receptors; Oxidative Stress; Real-Time Polymerase Chain Reaction; Receptors, Neuropeptide; Retina; RNA, Messenger; Transfection; Tyrosine

The present study was intended to investigate whether oxidative stress is the key regulator to alter neuroretinal biochemical homeostasis and in turn aggravate the process of diabetic retinopathy by inducing nitrosative stress in the retinal neurovascular unit.. Peripheral blood mononuclear cell reactive oxygen species level was measured by flow cytometry along with spectrophotometric detection of malondialdehyde (MDA) and glutamate from serum or plasma and a vitreous sample of study groups (i.e. subjects with proliferative diabetic retinopathy [PDR], type 2 diabetes without retinopathy [DNR] and healthy controls [HCs]). Further, nitrosative stress assessment was performed by spectrophotometric and enzyme-linked immunosorbent assay-based detection of serum and vitreous nitrite and nitrotyrosine concentrations, respectively.. The plasma glutamate level remains insignificant between subjects with PDR and DNR (p=0.505) or in HC (p=0.1344) individuals. However, serum MDA (p=0.0004), nitrite (p=0.0147) and nitrotyrosine (p=0.0129) were found to be strikingly higher among PDR subjects compared with the DNR group. Significantly increased levels of peripheral blood mononuclear cell reactive oxygen species (p<0.0001), vitreous glutamate (p=0.0009, p<0.0001), MDA (p=0.0058, p=0.0003), nitrite (p=0.0014, p<0.0001) and nitrotyrosine (p=0.0008, p<0.0001) were found in PDR subjects compared with DNR and HC subjects, respectively.. Our observation suggests that oxidative stress is associated with impairment in neuroretinal biochemical homeostasis among PDR subjects, which further augments retinal nitrosative stress and thus worsens the pathogenic process of retinopathy among PDR subjects.

Topics: Adult; Case-Control Studies; Diabetic Retinopathy; Female; Glutamic Acid; Humans; Leukocytes, Mononuclear; Male; Malondialdehyde; Middle Aged; Nitrites; Oxidative Stress; Reactive Oxygen Species; Retina; Tyrosine; Vitreous Body

Hypertension and diabetes are known risk factors for retinal microvascular damage. However, the combined effects of diabetes with early and established stages of hypertension on retinal microvascular degeneration remain incompletely understood.. Male spontaneously hypertensive rats (SHR) were compared to SHR with streptozotocin-induced diabetes (SHR+D) for 6 or 10 weeks and Wistar rats as controls.. Hypertension alone (the SHR group) or in combination with diabetes (the SHR+D group) for 6 weeks induced additive increases in total retinal cell death, compared to the Wistar controls. This increase was associated with significant increases in phosphorylated-Jun N-terminal kinase (pJNK) activation, phosphorylated-Akt inhibition, plasma and retinal lipid peroxides, and soluble intracellular adhesion molecule-1 (sICAM-1) levels. After 10 weeks, a similar trend was still observed in retinal nitrotyrosine, nuclear factor kappaB p65, and tumor necrosis factor-α expression, associated with exacerbated pJNK activation and formation of acellular capillaries.. In conclusion, combining diabetes and hypertension-potentiated retinal oxidative/inflammatory stress promoted imbalance between the JNK stress and survival Akt pathways resulting in accelerated retinal cell death and acellular capillary formation.

Topics: Animals; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Gene Expression; Hypertension; Inflammation; Intercellular Adhesion Molecule-1; Lipid Peroxidation; Male; MAP Kinase Kinase 4; NF-kappa B; Oxidative Stress; Phosphorylation; Proto-Oncogene Proteins c-akt; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Retina; Retinal Neovascularization; Tumor Necrosis Factor-alpha; Tyrosine

To simultaneously evaluate tyrosine nitrosylation and phosphorylation levels of vitreous interleukins of patients with diabetic retinopathy, in which abnormal tyrosine phosphorylation has been previously described.. Specific immunoprecipitation of interleukins IL-1α, IL-1β, IL-2 and IL-7 was carried out in samples obtained during vitrectomy performed for proliferative diabetic retinopathy in patients (n=12) and for macular hole in controls (n=12). Tyrosine nitrosylation and phosphorylation levels of the immunoprecipitated interleukins were analysed by Western blot with the respective specific antibodies and correlated. The results were also correlated with the total amount of immunoprecipitated interleukin protein. The mean phosphorylation/nitrosylation ratios of these proteins in vitreous humour of both the control group and diabetic patients were determined.. Diabetes was associated with decreased tyrosine nitrosylation of IL-1α, IL-1β and IL-7 and an increased tyrosine phosphorylation/nitrosylation ratio with respect to controls in IL-1α (1.58±0.22 vs. 2.74±0.39, respectively; p<0.05) and IL-7 (2.15±0.01 vs. 3.26±0.57, respectively; p<0.05). No significant changes were observed in nitrotyrosine or in the tyrosine phosphorylation/nitrosylation ratio of IL-2.. Proliferative diabetic retinopathy is associated with concomitant and simultaneous changes in both tyrosine phosphorylation and tyrosine nitrosylation status of specific pro-inflammatory interleukins present in the vitreous fluid such as IL-1α, IL-1β and IL-7. These changes could be related to the increase in pro-inflammatory activity detected in diabetes-induced retinopathy.

Topics: Aged; Blood Glucose; Blotting, Western; Chromatography, High Pressure Liquid; Diabetes Mellitus, Type 2; Diabetic Retinopathy; Female; Glycated Hemoglobin; Humans; Immunoprecipitation; Interleukin-1alpha; Interleukin-1beta; Interleukin-7; Male; Middle Aged; Nitric Oxide; Phosphorylation; Phosphotyrosine; Tyrosine; Vitreous Body

The risk of diabetic retinopathy is associated with the presence of both oxidative stress and toxic eicosanoids. Whether oxidative stress actually causes diabetic retinopathy via the generation of toxic eicosanoids, however, remains unknown. The aim of the present study was to determine whether tyrosine nitration of prostacyclin synthase (PGIS) contributes to retinal cell death in vitro and in vivo. Exposure of human retinal pericytes to heavily oxidized and glycated LDL (HOG-LDL), but not native forms of LDL (N-LDL), for 24 hours significantly increased pericyte apoptosis, accompanied by increased tyrosine nitration of PGIS and decreased PGIS activity. Inhibition of the thromboxane receptor or cyclooxygenase-2 dramatically attenuated HOG-LDL-induced apoptosis without restoring PGIS activity. Administration of superoxide dismutase (to scavenge superoxide anions) or L-N(G)-nitroarginine methyl ester (L-NAME, a nonselective nitric oxide synthase inhibitor) restored PGIS activity and attenuated pericyte apoptosis. In Akita mouse retinas, diabetes increased intraretinal levels of oxidized LDL and glycated LDL, induced PGIS nitration, enhanced apoptotic cell death, and impaired blood-retinal barrier function. Chronic administration of tempol, a superoxide scavenger, reduced intraretinal oxidized LDL and glycated LDL levels, PGIS nitration, and retina cell apoptosis, thereby preserving the integrity of blood-retinal barriers. In conclusion, oxidized LDL-mediated PGIS nitration and associated thromboxane receptor stimulation might be important in the initiation and progression of diabetic retinopathy.

Topics: Animals; Antioxidants; Apoptosis; Blood-Retinal Barrier; Cells, Cultured; Cyclic N-Oxides; Cyclooxygenase 2; Cytochrome P-450 Enzyme System; Diabetic Retinopathy; Glycation End Products, Advanced; Humans; Intramolecular Oxidoreductases; Lipoproteins, LDL; Mice; Mice, Inbred C57BL; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase Type II; Pericytes; Receptors, Thromboxane; Retina; Spin Labels; Superoxide Dismutase; Tight Junctions; Tyrosine

The pathophysiology of the early events leading to diabetic retinopathy is not fully understood. It has been suggested that Inflammatory processes are involved in the development of the disease; however, the concentrations of tissue retinal inflammatory mediators and their possible alteration in diabetic retinopathy have not been described. The aim of this work was to study T-helper cell cytokine and chemokine profiles, and tyrosine nitration in retinal tissue of diabetic rats.. Cytokines (interleukin IL-1a, IL-1b, IL-2, IL-4, IL-6, IL-10, TNFa, GM-CSF, IFN-g), chemokines (MIP-1a, MIP-2, MIP-3a, MCP-1, GRO/KC, RANTES, Fractalkine), and tyrosine nitration were measured in retinal homogenate obtained from Long-Evans rats after 5 months of experimental diabetes.. The T-helper type 1 cytokines IL-2 and INF-gamma, in addition to NO production (measured as nitrotyrosine), were found to be significantly elevated in diabetic rat retina homogenates. None of the other cytokines and chemokines studied were affected by the diabetic condition.. Immunoregulatory cytokines belonging to the Th-1 group (IL-2 and IFN-gamma) were increased in the retina of experimental diabetic rats. Moreover, the nitrotyrosine formation (as an expression of increased NO production) was significantly elevated in the diabetic retina, supporting the concept of an inflammatory element in the development of diabetic retinopathy.

Topics: Animals; Cataract; Chemokines; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Disease Models, Animal; Interferon-gamma; Interleukin-10; Interleukin-1alpha; Interleukin-1beta; Interleukin-2; Interleukin-4; Interleukin-6; Interleukin-8; Male; Nitric Oxide; Rats; Rats, Long-Evans; Retina; T-Lymphocytes, Helper-Inducer; Tumor Necrosis Factor-alpha; Tyrosine

The purpose of this study was to investigate the efficacy of tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl), a superoxide dismutase mimetic, in preventing early retinal molecular changes in a model that combines hypertension and diabetes.. Four-week-old spontaneously hypertensive rats (SHR) were rendered diabetic by streptozotocin. Diabetic SHR rats (DM-SHR) were randomized to receive or not receive tempol treatment. After 20 days of induction of diabetes, the rats were euthanatized, and their retinas were collected.. The early molecular markers of diabetic retinopathy (DR), glial fibrillary acidic protein, and fibronectin were evaluated by Western blot assays and showed an increase in DM-SHR compared with the SHR group. The oxidative balance, evaluated by superoxide production and nitric oxide end product levels estimated by a nitric oxide analyzer, and the counterpart antioxidative defense revealed an accentuated imbalance in DM-SHR compared with the SHR group. As a result, the product peroxynitrite, which was detected by immunohistochemistry for nitrotyrosine, was higher in the DM-SHR group. The retinal poly-ADP-ribose (PAR)-modified proteins, which reflect the activation of PAR polymerase (PARP), and the inducible nitric oxide synthase (iNOS) expressions were found to have increased in this group. Treatment with tempol reestablished the oxidative parameters and decreased the PAR-modified proteins, thus preventing extracellular matrix accumulation and glial reaction.. The administration of tempol prevented oxidative damage, decreased iNOS levels, and ameliorated the activation of PARP in the retinas of diabetic hypertensive rats. Consequently, the early molecular markers of DR, such as glial reaction (glial fibrillary acidic protein [GFAP]) and extracellular matrix accumulation (fibronectin), were prevented in tempol-treated rats.

Topics: Animals; Blotting, Western; Cyclic N-Oxides; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Fibronectins; Glial Fibrillary Acidic Protein; Glutathione; Hypertension; Immunoenzyme Techniques; Male; Neuroprotective Agents; Nitric Oxide Synthase Type II; Oxidation-Reduction; Oxidative Stress; Peroxynitrous Acid; Poly(ADP-ribose) Polymerases; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Spin Labels; Superoxide Dismutase; Tyrosine

Increased nitric oxide (NO) has been correlated with diabetic retinopathy. In this study we investigated the cell injury, production of NO in retinal pigment epithelial (RPE) cells exposed to increased glucose concentration, and its molecular mechanism involved. Cultured human RPE cells (ARPE-19) were exposed for 4 days with normal blood glucose concentration (5.5mM D-glucose), followed by exposure to either normal (5.5mM) or high (33 mM) concentrations of D-glucose for 48 h. To determine the cytotoxicity of high glucose, cell viability, ROS production and SOD activity were measured, respectively. The end product of NO (nitrite and nitrate) was determined by a colorimetric assay and nitrotyrosine levels were quantified by a competitive ELISA. The expression of iNOS and the activation of p38MAPK, ERK and JNK were analyzed by Western blot. Treatment of RPE cells with high glucose-induced a significant increased of iNOS, accompanied by an increase in cell damage, NO and nitrotyrosine levels. High glucose caused activation of p38MAPK and ERK, inhibition for p38MAPK and ERK abrogated the high glucose-induced increase in iNOS, cell injury and levels of NO and nitrotyrosine. High glucose causes increased cell damage and NO generation in RPE cells by a process of iNOS expression that requires the activation of p38MAPK and ERK.

Topics: Biomarkers; Cell Line; Diabetic Retinopathy; Enzyme Activation; Extracellular Signal-Regulated MAP Kinases; Glucose; Humans; L-Lactate Dehydrogenase; Mitogen-Activated Protein Kinases; Nitric Oxide; Nitric Oxide Synthase Type I; Nitric Oxide Synthase Type II; Nitric Oxide Synthase Type III; p38 Mitogen-Activated Protein Kinases; Reactive Nitrogen Species; Reactive Oxygen Species; Retinal Pigment Epithelium; Superoxide Dismutase; Tyrosine

Retinal microvascular cells play a crucial role in the pathogenesis of diabetic retinopathy. The endothelial effects of cloricromene, a novel coumarin derivative, on diabetic retinopathy induced by streptozotocin (STZ) in the rat were investigated.. Cloricromene (10 mg/kg intraperitoneally) was administered daily in diabetic rats, and 60 days later eyes were enucleated for localization of nitrotyrosine, ICAM-1, VEGF, ZO-1, occludin, claudin-5, and VE-cadherin by immunohistochemical analysis. The effect of treatment was also evaluated by TNFalpha, ICAM-1, VEGF, and eNOS protein levels measurement in the retina with the respective ELISA kits. Blood-retinal barrier (BRB) integrity was also evaluated by Evans blue.. Increased amounts of cytokines, adhesion molecule, and nitric oxide synthase were observed in retina. Cloricromene treatment significantly lowered retinal TNFalpha, ICAM-1, VEGF, and eNOS. Furthermore, immunohistochemical analysis for VEGF, ICAM-1, nitrotyrosine (a marker of peroxynitrite), and tight junctions revealed positive staining in the retina from STZ-treated rats. The degree of staining for VEGF, ICAM-1, nitrotyrosine, and tight junctions was markedly reduced in tissue sections obtained from diabetic rats treated with cloricromene. Treatment with cloricromene suppressed diabetes-related BRB breakdown by 45%.. This study provides the first evidence that the new coumarin derivative cloricromene attenuates the degree of inflammation preserving the BRB in diabetic rats.

Topics: Animals; Antigens, CD; Blood-Retinal Barrier; Blotting, Western; Cadherins; Chromonar; Claudin-5; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Enzyme-Linked Immunosorbent Assay; Immunohistochemistry; Injections, Intraperitoneal; Intercellular Adhesion Molecule-1; Male; Membrane Proteins; Nitric Oxide Synthase Type III; Occludin; Phosphoproteins; Platelet Aggregation Inhibitors; Rats; Rats, Sprague-Dawley; Tumor Necrosis Factor-alpha; Tyrosine; Vascular Endothelial Growth Factor A; Zonula Occludens-1 Protein

Renal protection against diabetes-induced pathogenic injuries by multiple exposures to low-dose radiation (LDR) was investigated to develop a novel approach to the prevention of renal disease for diabetic subjects. C57BL/6J mice were given multiple low-dose streptozotocin (STZ; 6 x 60 [corrected] mg/kg) to produce a type 1 diabetes. Two weeks after diabetes onset, some of diabetic mice and age-matched nondiabetic mice were exposed whole body to 25 mGy X-rays every other day for 2, 4, 8, 12, and 16 wk. Diabetes caused a significant renal dysfunction, shown by time-dependent increase in urinary microalbumin (Malb) and decrease in urinary creatinine (Cre), and pathological changes, shown by significant increases in renal structural changes and PAS-positive staining. However, diabetes-induced renal dysfunction and pathological changes were significantly, albeit partially, attenuated by multiple exposures to LDR. Furthermore, LDR protection against diabetes-induced renal dysfunction and pathological changes was associated with a significant suppression of diabetes-increased systemic and renal inflammation, shown by significant increases in serum and renal TNFalpha, ICAM-1, IL-18, MCP-1, and PAI-1 contents. To further explore the mechanism by which LDR prevents diabetes-induced renal pathological changes, renal oxidative damage was examined by Western blotting and immunohistochemical staining for 3-nitrotyrosine and 4-hydroxynonenal. Significant increase in oxidative damage was observed in diabetic mice, but not diabetic mice, with LDR. Renal fibrosis, examined by Western blotting of connective tissue growth factor and Masson's trichrome staining, was also evident in the kidneys of diabetic mice but not diabetic mice with LDR. These results suggest that multiple exposures to LDR significantly suppress diabetes-induced systemic and renal inflammatory response and renal oxidative damage, resulting in a prevention of the renal dysfunction and fibrosis.

Topics: Albuminuria; Aldehydes; Animals; Blotting, Western; Chemokine CCL2; Creatinine; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 1; Diabetic Retinopathy; Intercellular Adhesion Molecule-1; Interleukin-18; Male; Mice; Mice, Inbred C57BL; Nephritis; Random Allocation; Reverse Transcriptase Polymerase Chain Reaction; RNA; Serpin E2; Serpins; Tumor Necrosis Factor-alpha; Tyrosine

To assess the effect of docosahexanoic acid (DHA) and lutein (both compounds with anti-inflammatory and antioxidant properties) on experimental diabetic retinopathy.. Male Wistar rats were studied: non-diabetic controls, untreated diabetic controls, and diabetic rats were treated with DHA and lutein or the combination of DHA + insulin and lutein + insulin for 12 weeks. Oxidative stress and inflammatory markers, apoptosis, and functional tests were studied to confirm biochemical and functional changes in the retina of diabetic rats. Malondialdehyde (MDA), glutathione concentrations (GSH), and glutathione peroxidase activity (GPx) were measured as oxidative stress markers. TUNEL assay and caspase-3 immunohistochemistry and electroretinogram were performed.. Diabetes increases oxidative stress, nitrotyrosine concentrations, and apoptosis in the retina. At 12 weeks after onset of diabetes, total thickness of retinas of diabetic rats was significantly less than that in control rats. Specifically, the thickness of the outer and inner nuclear layers was reduced significantly in diabetic rats and demonstrated a loss of cells in the GCL. These retinal changes were avoided by the administration of insulin and DHA and lutein alone or in combination with insulin. Impairment of the electroretinogram (b-wave amplitude and latency time) was observed in diabetic rats. DHA and lutein prevented all these changes even under hyperglycemic conditions.. Lutein and DHA are capable of normalizing all the diabetes-induced biochemical, histological, and functional modifications. Specifically, the cell death mechanisms involved deserve further studies to allow the proposal as potential adjuvant therapies to help prevent vision loss in diabetic patients.

Topics: Animals; Anti-Inflammatory Agents, Non-Steroidal; Antioxidants; Apoptosis; Biomarkers; Blood Glucose; Caspase 3; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Docosahexaenoic Acids; Drug Therapy, Combination; Electroretinography; Enzyme-Linked Immunosorbent Assay; Fluorescent Antibody Technique, Indirect; Glutathione; Glutathione Peroxidase; In Situ Nick-End Labeling; Insulin; Lutein; Male; Malondialdehyde; Oxidative Stress; Rats; Rats, Wistar; Retina; Tyrosine

To investigate whether the micronutrients that were shown to reduce the risk of development of age-related macular degeneration in the Age-Related Eye Disease Study (AREDS) can have the same effect on the development of diabetic retinopathy in rats, and to understand the possible mechanisms.. Streptozotocin-induced diabetic rats received a powdered diet with or without supplemental micronutrients (ascorbic acid, vitamin E, beta-carotene, zinc, and copper). The retina was used after the rats had diabetes for 12 months to detect vascular histopathology and to measure the biochemical parameters and messenger RNA levels of the genes involved in oxidative and nitrative stress.. The AREDS-based micronutrients prevented a diabetes-induced increase in the number of retinal acellular capillaries. In the same rats, micronutrients inhibited increases in retinal oxidatively modified DNA and nitrotyrosine and decreases in manganese superoxide dismutase. Diabetes-induced alterations in the messenger RNA expression of mitochondrial electron transport complex III (coenzyme Q cytochrome-c reductase) and inducible nitric oxide synthase were also prevented.. Age-Related Eye Disease Study-based micronutrients inhibit the development of diabetic retinopathy in rodents by inhibiting oxidative and nitrative stress.. Micronutrients that slow down the onset and progression of age-related macular degeneration have the potential to inhibit the development of diabetic retinopathy.

Topics: Animals; Ascorbic Acid; beta Carotene; Body Weight; Copper; Deoxyadenosines; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Diet; Eating; Electron Transport Complex III; Glycated Hemoglobin; Immunoenzyme Techniques; Male; Micronutrients; Nitric Oxide Synthase Type II; Oxidative Stress; Polymerase Chain Reaction; Rats; Rats, Inbred Lew; Retinal Vessels; RNA, Messenger; Superoxide Dismutase; Tyrosine; Vitamin E; Zinc Oxide

Diabetic retinopathy, a retinal vascular disease, is inhibited in animals treated with aminoguanidine, an inhibitor of inducible nitric-oxide synthase. This treatment also reduces retinal protein nitration, which is greater in diabetic rat retina than nondiabetic retina. As an approach to understanding the molecular mechanisms of diabetic retinopathy, we sought the identity of nitrotyrosine-containing proteins in retina from streptozotocin-induced diabetic rats and in a rat retinal Müller cell line grown in high glucose (25 mM). Anti-nitrotyrosine immunoprecipitation products from rat retina and Müller cells were analyzed by LC-MS/MS. Ten nitrated proteins in diabetic rat retina and three nitrated proteins in Müller cells grown in high glucose were identified; three additional nitrotyrosine-containing proteins were tentatively identified from diabetic retina. The identified nitrotyrosine-containing proteins participate in a variety of processes including glucose metabolism, signal transduction, and transcription/translation. Among the nitrated proteins were insulin-responsive glucose transporter type 4 (GLUT-4), which has been implicated previously in the pathogenesis of diabetes mellitus; exocyst complex component Exo70, which functions in insulin-stimulated glucose uptake of GLUT-4-containing vesicles; and fibroblast growth factor receptor 2, which influences retinal vascularization via fibroblast growth factor signaling. Nitration of tyrosine phosphorylation sites were identified in five proteins, including GLUT-4, exocyst complex component Exo70, protein-tyrosine phosphatase eta, sensory neuron synuclein, and inositol trisphosphate receptor 3. Quantitation of nitration and phosphorylation at common tyrosine modification sites in GLUT-4 and protein-tyrosine phosphatase eta from diabetic and nondiabetic animals suggests that nitration reduced tyrosine phosphorylation approximately 2X in these proteins from diabetic retina. The present results provide new insights regarding tyrosine nitration and its potential role in the molecular mechanisms of diabetic retinopathy.

Topics: Amino Acid Sequence; Animals; Blotting, Western; Diabetic Retinopathy; Electrophoresis, Polyacrylamide Gel; Glucose Transporter Type 4; Immunoprecipitation; Male; Molecular Sequence Data; Nitrogen; Phosphorylation; Phosphotyrosine; Protein Structure, Tertiary; Protein Tyrosine Phosphatases; Proteins; Rats; Rats, Sprague-Dawley; Receptor, Fibroblast Growth Factor, Type 2; Tyrosine; Vesicular Transport Proteins

Oxidative damage and growth factors are implicated in the pathogenesis of retinopathy in diabetes. Recent studies have shown that two dietary carotenoids, lutein and zeaxanthin (Zx), that are specifically concentrated within ocular tissues, may play important roles in maintaining their integrity. This study is to evaluate the potential protective effects of Zx against retinal oxidative damage and growth factors in diabetes.. A group of rats received normal powdered diet or powdered diet supplemented with 0.02% or 0.1% Zx soon after induction of diabetes. Age-matched normal rats served as control subjects. At 2 months of diabetes, oxidative stress, vascular endothelial cell growth factor (VEGF), and intercellular adhesion molecule (ICAM)-1 were quantified in the retina.. Zx supplementation prevented diabetes-induced increase in retinal damage, and increases in VEGF and ICAM-1. The levels of lipid peroxide, oxidatively modified DNA, electron transport complex III, nitrotyrosine, and mitochondrial superoxide dismutase were similar in the retinas of Zx-treated diabetic rats and normal control rats, and these values were significantly different from those obtained from diabetic rats without any supplementation. In the same rats, Zx also prevented diabetes-induced increases in retinal VEGF and ICAM-1. Both 0.02% and 0.1% Zx had similar effects on diabetes-induced retinal abnormalities, and these effects were achieved without ameliorating the severity of hyperglycemia. However, Zx administration failed to prevent a diabetes-induced decrease in retinal GSH levels.. Zx significantly inhibits diabetes-induced retinal oxidative damage and elevation in VEGF and adhesion molecule, all abnormalities that are associated with the pathogenesis of diabetic retinopathy. The results suggest that Zx supplementation has the potential to inhibit the development of retinopathy in diabetic patients.

Topics: 8-Hydroxy-2'-Deoxyguanosine; Animals; Blood Glucose; Deoxyguanosine; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Diet; Electron Transport Complex III; Intercellular Adhesion Molecule-1; Male; Nitric Oxide Synthase Type II; Oxidative Stress; Rats; Rats, Inbred Lew; RNA, Messenger; Superoxide Dismutase; Tyrosine; Vascular Endothelial Growth Factor A; Xanthophylls; Zeaxanthins

This study was aimed at evaluating the potent and specific aldose reductase inhibitor fidarestat, on diabetes-associated cataract formation, and retinal oxidative-nitrosative stress, glial activation, and apoptosis. Control and streptozotocin-diabetic rats were treated with or without fidarestat (16 mg kg(-1)d(-1)) for 10 weeks after an initial 2-week period without treatment. Lens changes were evaluated by indirect ophthalmoscopy and portable slit lamp. Nitrotyrosine, poly(ADP-ribose), and glial fibrillary acidic protein expression were assessed by immunohistochemistry. The rate of apoptosis was quantified in flat-mounted retinas by TUNEL assay with immunoperoxidase staining. To dissect the effects of high glucose exposure in retinal microvascular cells, primary bovine retinal pericytes and endothelial cells were cultured in 5 or 30 mM glucose, with or without fidarestat (10 microM) for 3-14 days. Apoptosis was assessed by TUNEL assay, nitrotyrosine and poly(ADP-ribose) by immunocytochemistry, and Bax and Bcl-2 expression by Western blot analyses. Fidarestat treatment prevented diabetic cataract formation and counteracted retinal nitrosative stress, and poly(ADP-ribose) polymerase activation, as well as glial activation. The number of TUNEL-positive nuclei (mean +/- SEM) was increased approximately 4-fold in diabetic rats vs. controls (207+/-33 vs. 49+/-4, p<0.01), and this increase was partially prevented by fidarestat (106+/-34, p<0.05 vs. untreated diabetic group). The apoptotic cell number increased with the prolongation of exposure of both pericytes and endothelial cells to high glucose levels. Fidarestat counteracted nitrotyrosine and poly(ADP-ribose) accumulation and apoptosis in both cell types. Antiapoptotic effect of fidarestat in high glucose-exposed retinal pericytes was not associated with the inhibition of Bax or increase in Bcl-2 expression. In conclusion, the findings, i) support an important role for aldose reductase in diabetes-associated cataract formation, and retinal oxidative-nitrosative stress, glial activation, and apoptosis, and ii) provide a rationale for the development of aldose reductase inhibitors, and, in particular, fidarestat, for the prevention and treatment of diabetic ocular complications.

Topics: Aldehyde Reductase; Animals; Apoptosis; Apoptosis Regulatory Proteins; bcl-2-Associated X Protein; Blood Glucose; Blotting, Western; Cataract; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Glial Fibrillary Acidic Protein; Imidazolidines; Immunohistochemistry; In Situ Nick-End Labeling; Neuroglia; Ophthalmoscopy; Oxidative Stress; Poly(ADP-ribose) Polymerases; Rats; Retina; Streptozocin; Tyrosine

Apoptosis of retinal capillary cells is an early event in the pathogenesis of retinopathy in diabetes, and oxidative stress has been linked to accelerated apoptosis of retinal capillary cells. Mitochondria are the major endogenous source of superoxide, and superoxide is considered to be a causal link between elevated glucose and the major biochemical pathways postulated to be involved in the development of vascular complications in diabetes. The purpose of the present study is to determine the role of mitochondrial superoxide dismutase (MnSOD) in the development of diabetic retinopathy.. The effect of overexpression of MnSOD on glucose-induced endothelial cell oxidative stress, nitrosative stress, and apoptosis was determined by using bovine retinal endothelial cells. Furthermore, the effect of diabetes in rats (11 months' duration) on the activity and the mRNA expression of retinal MnSOD were also determined.. MnSOD activity in the nontransfected control retinal endothelial cells was 20% compared with the total SOD activity and was increased to 60% in the MnSOD-transfected cells. MnSOD overexpression prevented a glucose-induced increase in oxidative stress (8-hydroxy guanosine levels), nitrosative stress (nitrotyrosine formation), and apoptosis of retinal endothelial cells. MnSOD enzyme activity and its mRNA were decreased significantly in the retina obtained from the diabetic rats, and these abnormalities were prevented by long-term lipoic acid therapy.. The results of this study suggest a protective role for MnSOD in retinal capillary cell death and, ultimately, in the pathogenesis of retinopathy in diabetes. Understanding the role of MnSOD to modify the course of retinopathy could elucidate important molecular targets for future pharmacological interventions.

Topics: Animals; Apoptosis; Cattle; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Endothelium, Vascular; Gene Expression Regulation, Enzymologic; Guanosine; Mitochondria; Nitrosation; Oxidative Stress; Rats; Rats, Wistar; Retina; Retinal Vessels; RNA, Messenger; Superoxide Dismutase; Transfection; Tyrosine

To further investigate the effect of NO and its synthase on the retinal oxidative damages in diabetes.. Diabetic rat model was induced by injection with streptozotoc. Saline was injected in the controls. The retina was excised and studied 2 w and 20 w after the establishment of the experimental model and the controls. The distribution and content of 3-nitrotyrosine (3-NT) in the retina were analyzed by employing immunohistochemical method and icon manipulation technique. The proteins and mRNA expression of inducible nitric oxide synthetase (iNOS) and neuronal nitric oxide synthetase (nNOS) were determined by employing immunohistochemical method and RT-PCR technique.. The 3-NT expression in the retina of diabetic rats increased in the second week of diabetes. The positive cells only distributed in the ganglion cell layer, indicating that the retinal damage of diabetic rats first appeared in the ganglion cell layer. The NT expression increased significantly in the 20 week of diabetes and the positive cells distributed in the whole layers of retina, indicating that the retinal oxidative damages was in progress step by step and the production of NO increased with the progress of diabetes. Compared with the control, the iNOS expression increased and nNOS decreased in the 2 w of diabetes. The former increased further while the latter nearly disappeared in the 20 w, indicating that the increasing production of NO in the retina of diabetic rats was related with the decrease of nNOS expression and the increase of iNOS expression.. The diabetic retinal damages first appear in the ganglion cell layer. Later on, the function of the external retinal layers is impaired. The retinal damages at the early stage of diabetes mainly focus on the ganglion cell layer. In the diabetic rat models, the retinal damages are closely related with the increase of NO which results from the decrease of nNOS expression and increase of iNOS expression.

Topics: Animals; Diabetic Retinopathy; Immunohistochemistry; Male; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type I; Nitric Oxide Synthase Type II; Rats; Rats, Sprague-Dawley; Retinal Ganglion Cells; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Tyrosine

Clinical and experimental studies have shown that reinstitution of good glycemic control (GC) after a period of poor glycemic control (PC) does not produce immediate benefits on the progression of retinopathy, and hyperglycemia is sufficient to initiate the development of diabetic retinopathy. In this study, the effect of reinstitution of GC on hyperglycemia-induced increased oxidative stress and nitrative stress was evaluated in the retina of rats maintained in PC before initiation of GC. In diabetic rats, 2 or 6 months of PC (GHb >11.0%) was followed by 7 months of GC (GHb <5.5%). Reinstitution of GC after 2 months of PC inhibited elevations in retinal lipid peroxides and NO levels by approximately 50%, but failed to have any beneficial effects on nitrotyrosine formation. However, reversal of hyperglycemia after 6 months of PC had no significant effect on retinal oxidative stress and NO levels (P < 0.02 vs. normal). In the same rats, inducible nitric oxide synthase expression and nitrotyrosine levels remained elevated by >80% compared with normal rats or rats kept in GC for the duration. This suggests that oxidative and nitrative modifications in retina occur early in the course of development of retinopathy in diabetes. These abnormalities are not easily reversed by reinstitution of GC, and the duration of PC before initiation of GC influences the outcome of the reversal. Characterization of the abnormalities responsible for the resistance of retinopathy to arrest after reinstitution of GC will help identify potential future therapies to inhibit progression of diabetic retinopathy.

Topics: Animals; Blood Glucose; Diabetes Mellitus; Diabetic Retinopathy; Glutathione; Hyperglycemia; Insulin; Lipid Peroxides; Male; Nitrates; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Oxidative Stress; Rats; Rats, Wistar; Retina; Tyrosine

Oxidative stress is increased in the retina in diabetes, and long-term administration of antioxidants inhibits the development of retinopathy in diabetic rats. The purpose of this study is to determine how diabetes affects the activation of a redox-sensitive nuclear transcriptional factor in the retina, NF-kappaB, and its inhibition by antioxidants. Alloxan diabetic rats were assigned to receive standard diet or the diet supplemented with multiple antioxidants, including ascorbic acid, Trolox, dl alpha-tocopherol acetate, N-acetyl cysteine, beta-carotene, and selenium for up to 14 months. NF-kappaB activation, oxidative stress and nitric oxides were measured in the retina at 2, 8 and 14 months of diabetes. Retinal NF-kappaB was activated by about 60% at two months after induction of diabetes, remained activated for up to 14 months of diabetes, and the duration of diabetes had no effect on the intensity of NF-kappaB activation. Similarly, oxidative stress and nitric oxides were elevated by over 50% in the retina of rats diabetic for 14 months, and nitrotyrosine levels were elevated by over two folds. Administration of the antioxidants to the rats for the entire duration of diabetes inhibited activation of NF-kappaB and elevations in oxidative stress, nitric oxides and nitrotyrosine formation without ameliorating the severity of hyperglycemia. These in vivo results were confirmed by in vitro studies showing that high glucose activates NF-kappaB and elevates NO and lipid peroxides in both retinal endothelial cells and pericytes that can be inhibited by antioxidants. Thus, the results suggest that the activation of retinal NF-KB in diabetes is an early event in the development of retinopathy, and it remains active when the retinal capillary cell death is accelerating, and histopathology is developing. Beneficial effects of antioxidants on the development of diabetic retinopathy might involve inhibition of NF-kappaB activation and its downstream pathways in the retina.

Topics: alpha-Tocopherol; Animals; Antioxidants; Ascorbic Acid; beta Carotene; Chromans; Cysteine; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Glucose; Lipid Peroxides; Male; NF-kappa B; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Rats; Rats, Sprague-Dawley; Retina; Selenium; Tyrosine

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 microg/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.

Topics: Animals; Cattle; Cells, Cultured; Cyclic GMP; Diabetes Complications; Diabetes Mellitus; Diabetic Retinopathy; Endothelium, Vascular; Glucose; Guanidines; Hyperglycemia; Immunohistochemistry; Male; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Oxidative Stress; Peroxynitrous Acid; Rats; Rats, Sprague-Dawley; Retina; Streptozocin; Tyrosine

Ischemic proliferative retinopathy (e.g., diabetes mellitus, retinopathy of prematurity, or retinal vein occlusion) is a major cause of blindness worldwide. Apart from neovascularization, ischemic proliferative retinopathy leads to retinal degeneration. Apoptosis has been ascribed to be the leading mechanism in ischemic retinal degeneration. We showed recently that inducible nitric oxide synthase (iNOS) is expressed in the avascular retina in proliferative retinopathy in vivo and that iNOS expression in retinal glial cells is responsible for retinal neuronal cell death in vitro. Here we show that retinal apoptosis and subsequent degeneration occur in the murine model of ischemic proliferative retinopathy. Furthermore, because NO can have beneficial or detrimental effects in the retina, we analyzed the role of iNOS on retinal apoptosis in ischemic proliferative retinopathy. Using iNOS knock-out mice and iNOS inhibitor 1400W, we demonstrate in vivo that iNOS expression induces apoptosis locally in the inner nuclear layer of the avascular retina and that protein nitration may be involved in this process. These findings are the first evidence for retinal apoptosis in an animal model of ischemic proliferative retinopathy, demonstrating that iNOS plays a crucial role not only in retinal neovascular disease but also in retinal degeneration. We show that it is an ideal target to protect the hypoxic retina from degeneration and to improve its vascularization.

Topics: Aging; Amidines; Animals; Animals, Newborn; Apoptosis; Benzylamines; Cell Count; Crosses, Genetic; Diabetic Retinopathy; Disease Models, Animal; Drug Administration Routes; Enzyme Inhibitors; Immunohistochemistry; In Situ Nick-End Labeling; Ischemia; Mice; Mice, Inbred Strains; Mice, Knockout; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Oxygen; Proteins; Retina; Retinal Diseases; Retinal Vein Occlusion; Tyrosine