Comparison of the neuroprotective effects of brimonidine tartrate and melatonin on retinal ganglion cells

Purpose We aimed to compare the neuroprotective effects of brimonidine tartrate (BRT) and melatonin (MEL) on retinal ganglion cells (RGCs) in a rat glaucoma model. Methods Thirty-six adult Wistar albino rats were allocated into six groups: control (C), glaucoma (G), BRT, MEL, G + BRT and G + MEL. After establishing the glaucoma model, intraocular pressure (IOP) of all animals measured at day 4 and day 30 was compared statistically with day 0 and day 4, respectively. Prior to sacrification at day 30 for histological evaluation and TUNEL analysis, retrograde labeling of non-apoptotic RGCs with 3% Fluorogold was performed and RGCs were evaluated under fluorescein microscope. Results IOP measurements at day 4 were significantly higher than basal measurements in all glaucoma groups. BRT alone induced a time-dependent decrease in IOP ( p < 0.05), while MEL alone failed to reduce IOP. However, both BRT and MEL reduced IOP in the presence of glaucoma at day 30 ( p < 0.05). BRT treatment significantly reversed the reduced non-apoptotic RGC counts ( p < 0.01) and increased TUNEL-positive RGCs ( p < 0.001) to control group levels in the presence of glaucoma. However, no statistical significance was found between groups G and G + MEL considering 3% Fluorogold-labeled cell counts and apoptotic index values. Conclusion Our study revealed that systemic administration of BRT also has an IOP reducing effect. MEL has no neuroprotective effect on RGCs; on the other hand, BRT acts as a neuroprotective agent against glaucomatous injury, when applied systemically.