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EGCG, a major component of green tea, has a number of properties which includes it being a powerful antioxidant. The purpose of this investigation was to deduce whether inclusion of EGCG in the drinking water of albino rats attenuates the effect of a light insult (2200 lx, for 24 h) to the retina. TUNEL-positive cells were detected in the outer nuclear layer of the retina, indicating the efficacy of the light insult in inducing photoreceptor degeneration. Moreover, Ret-P1 and the mRNA for rhodopsin located at photoreceptors were also significantly reduced as well as the amplitude of both the a- and b-waves of the electroretinogram was also reduced showing that photoreceptors in particular are affected by light. An increase in protein/mRNA of GFAP located primarily to Muller cells caused by light shows that other retinal components are also influenced by the light insult. However, antigens associated with bipolar (α-PKC), ganglion (Thy-1) and amacrine (GABA) cells, in contrast, appeared unaffected. The light insult also caused a change in the content of various proteins (caspase-3, caspase-8, PARP, Bad, and Bcl-2) involved in apoptosis. A number of the changes to the retina caused by a light insult were significantly attenuated when EGCG was in the drinking water. The reduction of the a- and b-waves and photoreceptor specific mRNAs/protein caused by light were significantly less. In addition, EGCG attenuated the changes caused by light to certain apoptotic proteins (especially at after 2 days) but did not appear to significantly influence the light-induced up-regulation of GFAP protein/mRNA. It is concluded that orally administered EGCG blunts the detrimental effect of light to the retina of albino rats where the photoreceptors are primarily affected.

Endothelins exert pathological effects in the eye and much interest centres on their role in causing retinal neuronal death in ischemic diseases like glaucoma. In the present study the influence of the non-selective endothelin antagonist, sulfisoxazole on raised intraocular pressure-induced ischemia to the rat retina was investigated. Moreover, in vitro studies on primary rat retinal cultures were undertaken to see whether sulfisoxazole is able to blunt the toxic effect of lipopolysaccharide (LPS) to retinal neurones. In order to determine whether sulfisoxazole provides protection to the retina the a- and b-wave amplitudes of the electroretinogram (ERG), the localisation of retinal choline acetyltransferase (ChAT), nitric oxide synthase (nNOS) and Thy-1 and the retinal mRNA levels of Thy-1 and FGF-2 were deduced in retinas subjected to ischemia in the absence or presence of sulfisoxazole. The results showed that the ischemia-induced changes to the a- and b-wave amplitudes of the ERG and changes associated with the localisation of ChAT, nNOS and Thy-1 to be significantly blunted by sulfisoxazole. However, while the ischemia-induced changes to Thy-1 and FGF-2 mRNAs were reduced by sulfisoxazole, the reduction was non-significant. The in vitro studies provided support for the protective effect of sulfisoxazole. Here, it was clearly shown that sulfisoxazole attenuated the elevation of nitric oxide (deduced by measuring nitrite) and the reduction in numbers of GABA-containing neurones caused by LPS. The present study provides evidence for the first time that endothelin antagonist can protect the retina from ischemic-like insults as occurs in glaucoma.

Carotid artery occlusion (two vessel occlusion; 2-VO) for 3 or 9 months causes a suppression of the electroretinogram. However, after 3 months the retinal morphology appears unaffected judging from the localisation of GABA, ChAT, αPKC, Thy-1 and GFAP immunoreactivities. Moreover, no difference in NMDA-R1, opsin or Thy-1 mRNA levels were detected. In contrast, after 9 months 2-VO photoreceptor degeneration occurred as indicated by thinning of the outer nuclear layer and reduced Ret-P1 immunoreactivity. All other immunoreactivities appeared normal. These findings were supported by analysis of retinal mRNA levels. We conclude that the major effect of prolonged 2-VO is photoreceptor degeneration.

The aim of this study was to examine whether the antioxidant epigallocatechin gallate (EGCG), a catechin-base flavonoid derived from green tea protects retina neurones in situ from ischemia/reperfusion and in vitro from an oxidative stress insult of hydrogen peroxide (H(2)O(2)). Similar results were obtained when rats were injected by two different regimes of EGCG. Ischemia was delivered by raising the intraocular pressure above the systolic blood pressure (120 mm Hg) generally for 45 min. The electroretinogram (ERG) was measured prior to ischemia and 5 days after reperfusion. Rats were killed 7 days after ischemia and processed for immunohistochemistry and for determining of mRNA and protein levels by RT-PCR and electrophoresis/western blotting, respectively. In addition, optic nerves 7 days after ischemia were subjected to protein analysis. Ischemia/reperfusion caused a significant reduction in the a- and b-wave amplitudes of the ERGs, a decrease in retinal ganglion cell and photoreceptor specific proteins and mRNAs, an increase in retinal caspase-3 mRNA and protein, an increase in retinal caspase-8 mRNA, an increase in retinal GFAP protein and mRNA and a decrease in optic nerve proteins associated with ganglion cell axons. All these changes were significantly counteracted by EGCG. Moreover, EGCG clearly blunted ischemia/reperfusion-induced changes in the localisation of retinal Thy-1 and ChAT immunoreactivities. EGCG also significantly reduced the apoptosis to retinal ganglion cells (RGC-5 cells) in culture caused by H(2)O(2). The results of the study demonstrate that EGCG provides protection to retinal neurones from oxidative stress and ischemia/reperfusion.

Glial-derived monocarboxylate lactate is thought to be an important energy source for neurons during brain activation or in hypoxia–ischemia. Treatment with α-cyano-4-hydroxycinnamate (4-CIN), a monocarboxylate transporter inhibitor, has been recently reported to exacerbate delayed neuronal damage in a rat model of cerebral ischemia, an effect ascribed to inhibition of lactate/pyruvate transport. Since monocarboxylate transporters are abundant in the retina, we examined the effect of 4-CIN administration on the outcome of high intraocular pressure-induced retinal ischemia in rats. Retinal ischemic damage was assessed by changes in the electroretinogram (ERG), the retinal localization of choline acetyltransferase (ChAT) and neuronal nitric oxide synthase (nNOS) immunoreactivities, and the loss of retinal mRNA for Thy-1. Intraperitoneal or intravitreal administration of 4-CIN had no effect on the ERG or the localization of ChAT and nNOS immunoreactivities in either the control retina or a retina subjected to ischemia/reperfusion. In addition, intravitreal injection of 4-CIN had no effect on ischemia-induced reduction of retinal mRNA levels for Thy-1. These results provide no evidence to support the view that blockade of lactate uptake and/or pyruvate entry into mitochondria for oxidative metabolism has an influence on the outcome of retinal ischemia/reperfusion.

Age- and sex-matched pigmented (Lister Hooded) and albino (Wistar) rats were used in this study. The retinas of the animals were subjected to pressure-induced ischaemia (35 min, 120 mmHg) and reperfusion (3 days) in precisely the same way. The b-wave of the electroretinogram (ERG) in the pigmented animals recovered to normal levels while those of the albino rats were reduced by more than 80%. Moreover, the choline acetyltransferase (ChAT) immunoreactivity associated with a sub-set of amacrine cells was almost completely obliterated in the retinas from the albino rats but unaffected in the retinas of the pigmented rats. Also, in certain areas of the retina from albino rats there was a suggestion that the calretinin-immunoreactivity was affected. This was never seen in the retinas of the pigmented animals. The GABA-immunoreactivity in the retina of both albino and pigmented rats appeared to be unaffected by ischaemia/reperfusion. The data presented show that retinas from albino rats are more susceptible to ischaemia/reperfusion than retinas from pigmented animals. The results also show that reduction of the b-wave of the ERG and changes in the nature of the ChAT immunoreactivity represent sensitive markers to detect the effect of ischaemia/reperfusion to the retina.

Studies on rat cortical cultures show that glutamate (10 μM) or hypoxia followed by reoxygenation causes damage to the cells as indexed by a release of lactate dehydrogenase (LDH). These effects could be counteracted by the N-methyl- d -aspartate (NMDA) antagonist MK-801 (2 μM) but not by the kainate/AMPA antagonist CNQX (100 μM). These data favour the view that the damage caused to the cells by glutamate and hypoxia/reperfusion is mediated via NMDA receptors. The damage to the cells could also be prevented by melatonin (100 μM). The melatonin effect is not mediated by specific receptors because it was not blunted by the melatonin antagonist, luzindole. Moreover, NMDA stimulated an accumulation of 45 Ca 2+ by cortical neurones, but although this effect was counteracted by MK-801, melatonin was ineffective, which showed that the neuroprotective effect of melatonin is not elicited by direct action with NMDA receptors. Ascorbate and iron stimulated the production of free radicals in a retinal cell preparation. Chelation of the iron with deferoxamine prevented this process as did melatonin while MK-801 had no effect. The combined findings suggest that melatonin counteracts the in vitro destructive effects of NMDA or hypoxia/reperfusion by preventing accumulation of excessive free radicals.