Reduction of Rod Photoreceptor Cell Death in tubby Mutants by Inorganic Cerium Oxide Nanoparticles

Abstract

Purpose: : The tubby mutation in mice causes progressive rod cell death. By four week of age, half of the rod cell population has died. We showed that bright cyclic light (800 lux) accelerated the degeneration of rod cells in tubby mutants. This suggests that the defective rod cells may be hypersensitive to oxidative stress. Using a rat light damage model, we demonstrated that inorganic cerium oxide nanoparticles (nanoceria) prevented rod cell death. Presently we investigated if nanoceria could prevent rod cell death in this retinal degeneration model.

Methods: : Mice of genotypes tub/tub, tub/+, and wild type (C57BL/6J) were raised in cyclic light condition. Nanoceria or saline was delivered to tubby mutants starting at postnatal day 7 or 10 depending on routes of delivery. Three delivery routes were performed: intravitreal (IV), intraperitoneal (IP), and intracardial (IC). Protection from rod cell death was evaluated by electroretinography and retinal histology at 4 or 5 week of age. The degree of oxidative stress was determined in retinal sections using reactive oxygen species probes: dihydroethidium and dichlorofluorescein. We also measured gene expression for pro-apoptotic enzymes and anti-oxidative stress phase II enzymes in these experimental animals.

Results: : We showed that intravitreal and intracardial delivery of nanoceria prevented the death of a significant number of rod cells. The rod function in these animals concomitantly showed a significant increase as measured by a- and b-wave amplitudes compared to saline injected animals. We determined that three anti-oxidative stress phase II proteins or their activities were up regulated while two pro-apoptotic enzymes were down regulated in the nanoceria injected animals. We also demonstrated that oxidative stress markers were present in significantly higher amounts in tubby retinas than in wild type or heterozygous retinas.

Conclusions: : Mutations in any one of 144 genes cause retinal degeneration. Rather than developing individual therapies, we focus our strategy on a single node, oxidative stress, common to these blinding diseases. In support of this, we have demonstrated that the nanoceria prolong the functional life span of defective rod cells in the tubby mouse, thus preserving vision. Understanding the anti-apoptotic mechanism by which the nanoceria rescue photoreceptors will be important for their development as a therapy for retinal degeneration.

Keywords: cell survival • retinal degenerations: cell biology • oxidation/oxidative or free radical damage