Caspase Inhibitors Are Protective in NMDA-Mediated Retinal Ganglion Cell Death

Abstract

Purpose:: Excitotoxic neuronal cell death is a feature of numerous central nervous system and eye diseases, including glaucoma. Apoptosis is a major mechanism of cell death in glutamate-induced excitotoxicity and caspases as executors of apoptosis play an important role in the development of the respective diseases. Aim of this study was to characterize the caspases involved in excitotoxic retinal ganglion cell death induced by the glutamate receptor agonist N-methyl-D-Aspartate (NMDA) in Brown Norway rats.

Methods:: Animals were injected intravitreally with one of six caspase inhibitors (namely against caspase 1, 3, 4, 6, 8 and 9). Seven hours later, NMDA or PBS as a control were injected intravitreally into the respective eyes. The neuroprotective potential against NMDA-toxicity was assessed by retinal ganglion cell quantification. Additionally, wholemount TUNEL was performed.

Results:: Statistical analysis revealed significant neuroprotective effects for the inhibitors of caspases 3, 6, 8 and 9, but not for those of caspases 1 and 4. The inhibitors of caspases 6 and 9 showed greater neuroprotective potential than those of caspases 3 and 8, although cell death was not entirely averted in any case, indicating that caspase-mediated apoptosis is probably not the only mechanism of retinal ganglion cell death in our animal model. Results of ganglion cell countings were confirmed using whole mount TUNEL.

Conclusions:: Excitotoxic retinal ganglion cell death after NMDA injection is mediated mainly through apoptosis whereby extrinsic as well as intrinsic pathways of caspase activation play a role.

Keywords: apoptosis/cell death • cell survival • ganglion cells