Superoxide signaling and cell death in retinal ganglion cell axotomy: effects of metallocorroles.

Injury to retinal ganglion cell (RGC) axons within the optic nerve causes apoptosis of the soma. We previously demonstrated that in vivo axotomy causes elevation of superoxide anion within the RGC soma, and that this occurs 1-2 days before annexin-V positivity, a marker of apoptosis. Pegylated superoxide dismutase delivery to the RGC prevents the superoxide elevation and rescues the soma. Together, these results imply that superoxide is an upstream signal for apoptosis after axonal injury in RGCs. We then studied metallocorroles, potent superoxide dismutase mimetics, which we had shown to be neuroprotective in vitro and superoxide scavengers in vivo for RGCs. RGCs were retrograde labeled with the fluorescent dye 4Di-10Asp, and then axotomized by intraorbital optic nerve transection. Iron(III) 2,17-bis-sulfonato-5,10,15-tris(pentafluorophenyl)corrole (Fe(tpfc)(SO(3)H)(2)) (Fe-corrole) was injected intravitreally. Longitudinal imaging of RGCs was performed and the number of surviving RGCs enumerated. There was significantly greater survival of labeled RGCs with Fe-corrole, but the degree of neuroprotection was relatively less than that predicted by their ability to scavenge superoxide-This implies an unexpected complexity in signaling of apoptosis by reactive oxygen species.