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Objectives:Central/branch retinal artery/vein occlusion, diabetes, glaucoma and, possibly, age related macular degeneration are conditions associated with retinal ischemia. All these diseases may lead to severe sequelae. Therefore, the management of retinal ischemia is critical.S-allyl-L-cysteine (SAC), an active organosulfur compound in aged garlic extract, has been reported to possess an antioxidative activity. To be specific, SAC exhibits its potent antioxidative effects scavenging superoxide radical, hydroxyl radicals and hydrogen peroxide. Another mechanism suggests that SAC prevents oxidized low-density lipoprotein (LDL)-induced endothelial cell injury.The using of SAC to attenuate a number of events that are implicated to occur in the pathogenesis of retinal ischemia or relevant glaucoma is therefore self-evident. The aims of the present study were to examine whether:(ⅰ) SAC has the protective effect on retina ischemia plus reperfusion (I/R); and (ⅱ) SAC protects the retina against I/R by downregulating the expression of hypoxia-inducible factor-1α(HIF-1α), vascular endothelium growth factor (VEGF) or matrix metalloproteinase-9 (MMP-9). Overall, this would provide evidence to support the view that therapies unrelated to lowering the IOP might be useful to improve physiological function, as well as reverse the pathological and molecular changes.Methods:In vivo, retinal ischemia was induced by raising intraocular pressure (IOP) to 120 mmHg for 60 minutes. In vitro, an ischaemic-like insult, namely oxidative stress or excitoxicity, was established by incubation of retinal ganglion cells (RGCs) with 500μM H2O2 or 100μM kainate for 24 hours. In the present study, SAC or vehicle was intravitreously administered 15 minutes before ischemia/reperfusion was induced. The physiological function is assessed in this study by measuring attenuation of the reduction of the electroretinogram (ERG) b-wave amplitude, an indexation of the retinal ischaemia. The pathological changes are estimated by loss of choline acetyltransferase (ChAT) immunolabelling amacrine cell bodies/neuronal processes, increased immunoreactivity of vimentin, a marker of Muller cells. Quantification of the changes in the levels of the mRNA and/or protein levels of HIF-la, VEGF or MMP-9 was also carried out by western blot, enzyme-linked immunosorbent assay, and real-time polymerase chain reaction.Results:Ischemia plus reperfusion in the rat caused severe retinal alterations, especially the inner retina. Retinal changes subjected to high IOP were characterized by decreased ERG b-wave amplitudes, loss of choline acetyltransferase immunolabelling amacrine cell bodies/neuronal processes, increased immunoreactivity of vimentin, a marker of Muller cells, as well as up-regulation of HIF-1α, VEGF or MMP-9 mRNA levels. The up-regulation of protein levels of HIF-1α, VEGF and MMP-9 was also seen in RGCs. Of clinical importance, ischemic/ischemic-like detrimental effects are dose-dependently (with the least effect at 25μM) and/or significantly (50μM and/or 100μM) blunted when SAC was applied 15 minutes before retinal ischemia.Conclusion:The present results have supported that SAC can significantly attenuate the detrimental effects of the ischemic insult to the retina as well as the oxidative stress and the excitotoxicity to RGCs. Thus, these pioneering evidences support the idea that SAC can protect against retinal ischemia by, at least in part, acting as an antioxidant, a glutamate antagonist as well as a down-regulator of the defined I/R-upregulated HIF-la, VEGF or MMP-9.
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