RESUMO
Retinal ischemia could provoke blindness. At present, there is no effective treatment against retinal ischemic damage. Strong evidence supports that glutamate is implicated in retinal ischemic damage. We investigated whether a brief period of global or ocular hypothermia applied 24 h before ischemia (i.e. hypothermic preconditioning, HPC) protects the retina from ischemia/reperfusion damage, and the involvement of glutamate in the retinal protection induced by HPC. For this purpose, ischemia was induced by increasing intraocular pressure to 120 mm Hg for 40 min. One day before ischemia, animals were submitted to global or ocular hypothermia (33°C and 32°C for 20 min, respectively) and fourteen days after ischemia, animals were subjected to electroretinography and histological analysis. Global or ocular HPC afforded significant functional (electroretinographic) protection in eyes exposed to ischemia/reperfusion injury. A marked alteration of the retinal structure and a decrease in retinal ganglion cell number were observed in ischemic retinas, whereas global or ocular HPC significantly preserved retinal structure and ganglion cell count. Three days after ischemia, a significant decrease in retinal glutamate uptake and glutamine synthetase activity was observed, whereas ocular HPC prevented the effect of ischemia on these parameters. The intravitreal injection of supraphysiological levels of glutamate induced alterations in retinal function and histology which were significantly prevented by ocular HPC. These results support that global or ocular HPC significantly protected retinal function and histology from ischemia/reperfusion injury, probably through a glutamate-dependent mechanism.
Assuntos
Ácido Glutâmico/efeitos adversos , Hipotermia Induzida , Traumatismo por Reperfusão/terapia , Doenças Retinianas/prevenção & controle , Células Ganglionares da Retina/patologia , Animais , Transporte Biológico , Contagem de Células , Temperatura Baixa , Eletrorretinografia , Glutamato-Amônia Ligase/metabolismo , Ácido Glutâmico/metabolismo , Injeções Intravítreas , Masculino , Ratos , Ratos Wistar , Recuperação de Função Fisiológica , Traumatismo por Reperfusão/metabolismo , Traumatismo por Reperfusão/patologia , Doenças Retinianas/metabolismo , Doenças Retinianas/patologia , Células Ganglionares da Retina/efeitos dos fármacos , Células Ganglionares da Retina/metabolismoRESUMO
Diabetic retinopathy is a leading cause of acquired blindness in adults, mostly affected by type 2 diabetes mellitus (T2DM). We have developed an experimental model of early T2DM in adult rats which mimics some features of human T2DM at its initial stages, and provokes significant retinal alterations. We investigated the effect of ischemic conditioning on retinal changes induced by the moderate metabolic derangement. For this purpose, adult male Wistar rats received a control diet or 30% sucrose in the drinking water, and 3 weeks after this treatment, animals were injected with vehicle or streptozotocin (STZ, 25mg/kg). Retinal ischemia was induced by increasing intraocular pressure to 120 mm Hg for 5 min; this maneuver started 3 weeks after vehicle or STZ injection and was weekly repeated in one eye, while control eyes were submitted to a sham procedure. Fasting and postprandial glycemia, and glucose, and insulin tolerance tests were analyzed. At 12 weeks of treatment, animals which received a sucrose-enriched diet and STZ showed significant differences in metabolic tests, as compared with control groups. Brief ischemia pulses in one eye and a sham procedure in the contralateral eye did not affect glucose metabolism in control or diabetic rats. Ischemic pulses reduced the decrease in the electroretinogram a-wave, b-wave, and oscillatory potential amplitude, and the increase in retinal lipid peroxidation, NOS activity, TNFα, Müller cells glial fibrillary acidic protein, and vascular endothelial growth factor levels observed in diabetic animals. In addition, ischemic conditioning prevented the decrease in retinal catalase activity induced by T2DM. These results indicate that induction of ischemic tolerance could constitute a fertile avenue for the development of new therapeutic strategies to treat diabetic retinopathy associated with T2DM.
Assuntos
Diabetes Mellitus Tipo 2/complicações , Diabetes Mellitus Tipo 2/fisiopatologia , Retinopatia Diabética/fisiopatologia , Retinopatia Diabética/terapia , Isquemia/fisiopatologia , Precondicionamento Isquêmico/métodos , Animais , Diabetes Mellitus Experimental/complicações , Diabetes Mellitus Experimental/fisiopatologia , Retinopatia Diabética/metabolismo , Modelos Animais de Doenças , Humanos , Isquemia/metabolismo , Masculino , Ratos , Ratos WistarRESUMO
Diabetic retinopathy (DR) is a leading cause of acquired blindness in adults, mostly affected by type 2 diabetes mellitus (T2DM). We have developed an experimental model of early T2DM in adult rats which mimics some features of human T2DM at its initial stages and provokes significant retinal alterations. The aim of this work was to analyze the effect of melatonin on retinal changes induced by the moderate metabolic derangement. For this purpose, adult male Wistar rats received a control diet or 30% sucrose in the drinking water. Three weeks after this treatment, animals were injected with vehicle or streptozotocin (STZ, 25 mg/kg). One day or 3 wk after vehicle or STZ injection, animals were subcutaneously implanted with a pellet of melatonin. Fasting and postprandial glycemia, and glucose, and insulin tolerance tests were analyzed. At 12 wk of treatment, animals which received a sucrose-enriched diet and STZ showed significant differences in metabolic tests, as compared with control groups. Melatonin, which did not affect glucose metabolism in control or diabetic rats, prevented the decrease in the electroretinogram a-wave, b-wave, and oscillatory potential amplitude, and the increase in retinal lipid peroxidation, NOS activity, TNFα, Müller cells glial fibrillary acidic protein, and vascular endothelial growth factor levels. In addition, melatonin prevented the decrease in retinal catalase activity. These results indicate that melatonin protected the retina from the alterations observed in an experimental model of DR associated with type 2 diabetes.
Assuntos
Diabetes Mellitus Tipo 2/tratamento farmacológico , Diabetes Mellitus Tipo 2/metabolismo , Retinopatia Diabética/tratamento farmacológico , Retinopatia Diabética/metabolismo , Melatonina/uso terapêutico , Animais , Catalase/metabolismo , Eletrorretinografia , Glucose/metabolismo , Imuno-Histoquímica , Masculino , Ratos , Ratos Wistar , Tiobarbitúricos/metabolismo , Fator de Necrose Tumoral alfa/metabolismoRESUMO
Diabetic retinopathy is a leading cause of acquired blindness in young, but also in elder adults, mostly affected by type 2 diabetes mellitus (T2DM). The aim of this work was to develop an experimental model of early human T2DM in adult rats, and to analyze retinal functional, morphological, and biochemical changes arising during the early stages of the moderate metabolic derangement. For this purpose, animals were divided in four groups: adult male Wistar rats receiving: tap water and citrate buffer i.p. (group 1), tap water with 30% sucrose and citrate buffer i.p. (group 2), tap water and 25mg/kg i.p streptozotocin (STZ, group 3), or 30% sucrose and STZ (group 4). Fasting and postprandial glycemia, fructosamine and serum insulin levels were assessed. In addition, i.p. glucose and insulin tolerance tests were performed. Retinal function (electroretinogram, ERG) and morphology (optical microscopy), retinal nitric oxide synthase (NOS) activity (using (3)H-arginine), lipid peroxidation (thiobarbituric acid reactive substances, TBARS), and TNFα levels (ELISA) were evaluated. At 6 and 12 weeks of treatment, animals which received a sucrose-enriched diet and STZ showed significant differences in most metabolic tests, as compared with the other groups. At 12 weeks of treatment, a significant decrease in the ERG a- and b- wave and oscillatory potential amplitudes, and a significant increase in retinal NOS activity, TBARS, TNFα, glial fibrillary acidic protein in Müller cells, and vascular endothelial growth factor levels were observed. These results indicate that the combination of diet-induced insulin resistance and a slight secretory impairment resulting from a low-dose STZ treatment mimics some features of human T2DM at its initial stages, and provokes significant retinal alterations.