Neuroprotection by trans-resveratrol in rats with N-methyl-D-aspartate (NMDA)-induced retinal injury: Insights into the role of adenosine A1 receptors.

Adenosine A1 receptors (AA1R) have been shown to counteract N-methyl-D-aspartate (NMDA)-mediated glutamatergic excitotoxicity. In the present study, we investigated the role of AA1R in neuroprotection by trans-resveratrol (TR) against NMDA-induced retinal injury. In total, 48 rats were divided into the following four groups: normal rats pretreated with vehicle; rats that received NMDA (NMDA group); rats that received NMDA after pretreatment with TR; and rats that received NMDA after pretreatment with TR and 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), an AA1R antagonist. Assessment of general and visual behaviour was performed using the open field test and two-chamber mirror test, respectively, on Days 5 and 6 post NMDA injection. Seven days after NMDA injection, animals were euthanized, and eyeballs and optic nerves were harvested for histological parameters, whereas retinae were isolated to determine the redox status and expression of pro- and anti-apoptotic proteins. In the present study, the retinal and optic nerve morphology in the TR group was protected from NMDA-induced excitotoxic damage. These effects were correlated with the lower retinal expression of proapoptotic markers, lipid peroxidation, and markers of nitrosative/oxidative stress. The general and visual behavioural parameters in the TR group showed less anxiety-related behaviour and better visual function than those in the NMDA group. All the findings observed in the TR group were abolished by administration of DPCPX.

Effect of trans-resveratrol on glutamate clearance and visual behaviour in rats with glutamate induced retinal injury.

Glutamate-induced excitotoxic injury is widely described as a prominent pathophysiological mechanism in several neurodegenerative diseases including glaucoma. Glaucoma, the leading cause of irreversible blindness, is characterized by loss of retinal ganglion cells (RGC). Currently, the treatment focuses on lowering intraocular pressure (IOP) and no neuroprotective therapies are available. Since excessive glutamate-mediated neurotransmission underlies glaucomatous RGC apoptosis, enhancing synaptic glutamate clearance by glutamate transporters in glial cells is expected to protect against excitotoxic injury. Trans-resveratrol is known for its neuroprotective effects; however, its effects on the expression of glutamate transporters and glutamate clearance in retina remain unclear. Hence, in the current study, we investigated the protective effects of trans-resveratrol against glutamate-induced retinal injury in rats. Rats were intravitreally injected with glutamate alone or glutamate with trans-resveratrol as pre- and post-treatment. Animals were subjected to Open Field Test (OFT) on day six and a two-chamber mirror test on day seven post-injection. Subsequently, rats were sacrificed and retinal expression of excitatory amino acid transporter (EAAT)1 and EAAT2 gene and protein was determined using PCR and ELISA, respectively. Retinal glutamate concentration was measured using ELISA and retinal morphology was studied on H&E-stained retinal sections. It was observed that pre-treatment with trans-resveratrol causes gene expression for EAAT1 and EAAT2 to increase by 2.51 and 1.93 folds compared to glutamate-treated group (p < 0.001 and p < 0.01, respectively); while the same in trans-resveratrol post-treatment group showed a 1.58- and 1.44 folds upregulation (p < 0.05).The retinal EAAT1 and EAAT2 protein expression was significantly greater in trans-resveratrol pre-treatment group compared to glutamate-treated group (p < 0.05) but not in post-treatment group. Retinal glutamate concentration was1.64 folds greater in glutamate-treated group than the vehicle-treated group (p < 0.01) but the same was 1.27-fold lower in trans-resveratrol pre-treatment group compared to glutamate-treated group (p < 0.01). Corresponding to these findings, we observed preservation of retinal morphology and visual behaviour in trans-resveratrol pre-treatment group compared to glutamate-treated group. We did not observe similar effects of trans-resveratrol when it was given as post-treatment after glutamate administration. In conclusion, current study showed that pre-treatment with trans-resveratrol protects against glutamate induced changes in retinal morphology and visual behaviour by increasing the expression of EAAT1 and EAAT2 and increasing glutamate clearance in rat retinas. The results of this study may be relevant to disease conditions involving excitotoxic neuronal injury.

Intravitreal Trans-Resveratrol Ameliorates NMDA-Induced Optic Nerve and Retinal Injury.

PURPOSE: Retinal and optic nerve damage in glaucoma involves excitotoxicity via N-methyl-D-aspartate (NMDA) receptors. Since, trans-resveratrol (TR) is known to provide neuroprotection, we investigated its protective effects against NMDA-induced retinal and optic nerve injury. METHODS: Sprague Dawley rats were divided into four groups which received vehicle (PBS), NMDA, and TR 0.4 or TR 4 nmol 24 h prior to NMDA, unilaterally and intravitreally. Seven days post-injection, rats were euthanized; eyeballs were enucleated and subjected to hematoxylin and eosin and terminal transferase dUTP nick end labeling staining while optic nerves were isolated for toluidine blue staining. RESULTS: Retinal morphometry showed that ganglion cell layer (GCL) layer thickness within inner retina (IR), retinal cell count (RCC) per 100-µm length of GCL, RCC per 100-µm2 area of GCL, and RCC per 100 µm2 of IR were significantly higher in both TR-treated groups compared to the NMDA group. No differences were observed between the two dose groups. Optic nerve morphology was in accordance with the retinal morphology whereby TR-treated groups showed significantly lesser degenerative changes compared to NMDA-treated group. CONCLUSIONS: TR protects against NMDA-induced changes in retinal and optic nerve morphology by preventing retinal cell apoptosis.