Abstract
Purpose:
Oxidative stress is associated with the progression of many neurodegenerative diseases including Retinitis Pigmentosa. We have shown that a single application of nanoceria, catalytic scavengers of reactive oxygen species, at early ages can delay photoreceptor cell degeneration for at least 3 weeks in the P23H-1 rat model for autosomal dominant Retinitis Pigmentosa. However, the duration of the catalytic activity of nanoceria after intravitreal injection is still unclear. We have shown that nanoceria reduced the number of apoptotic photoreceptor cells 3 days after application and have extended the study to 21 days.
Methods:
We used heterozygous P23H-1 rats in our study. We administered 2 µl of either saline or nanoceria (344 ng) to each eye of these animals at postnatal day (P) 15. Eyes were collected at 3, 7, 14, and 21 days post injection for assessment of apoptosis. We quantified the number of apoptotic (TUNEL+) profiles in the outer nuclear layer (ONL) of 5 µm thick retinal sections using the ApopTag Plus Fluorescein In Situ Apoptosis Detection kit (Millipore #S7111).
Results:
The number of apoptotic photoreceptor cells in the P23H-1 rat retina paralleled the reported reduction of ONL thickness in this animal. We observed higher numbers of apoptotic cells in the ONL from P18 to P24. The number gradually declined thereafter. We observed reduction of apoptotic cells by 60%, 38%, 9%, and 7% at 3, 7, 14, 21days, respectively, after nanoceria injection vs saline.
Conclusions:
The process of apoptosis consists of initiation, commitment, and degradation phases. TUNEL assay detects cells that are at the degradation phase which is estimated to be about 3 hours. This provides a temporal snapshot of the health status of the cells in the tissue. We demonstrated that nanoceria were effective in preventing photoreceptor cell apoptosis up to 14 days after intravitreal injection. The anti-apoptotic effect was most striking 3 days after nanoceria application and was still impressive 7 days after injection. We observed small but measurable reduction even at 21 days post injection. We conclude that the catalytic activity of nanoceria becomes limited after 14 days in vivo. Nanoceria have regenerative properties in vitro but we do not know if these nanoparticles residing in the retina retain this property.
Keywords: 608 nanomedicine •
426 apoptosis/cell death •
634 oxidation/oxidative or free radical damage