Dose-Response To A Broad-Spectrum Antioxidant In The "ROP Rat"

Abstract

Purpose: : To evaluate a range of doses of antioxidants (AOs) on the neuro-vasculopathy of a rat model of retinopathy of prematurity (ROP). Oxidative damage may be involved in ROP because the retina has both the highest metabolic demands of any tissue in the body and because it captures light, a significant originator of free radicals. Promotion of mitochondrial homeostasis might, therefore, mitigate ROP.

Methods: : Dams of Penn et al. (1994) "50/10 model" rats (ROP rats, n=89) and room-air-reared controls (RAR rats, n=95) were fed isocaloric, AIN93G-based chows blended with an AO supplement at 0% (control), 0.5%, 1%, 4% and 15% concentrations. The supplement was designed to promote mitochondrial oxidative phosphorylation by retarding the accumulation of reactive oxygen species and supporting the normal action of vitamin cofactors that are operative in cellular metabolism. The 1% chow mimics in a rat dam a dose 10× to 100× typical intake of each AO in human. Dams were placed on the chows at gestational day 19 and remained on them until testing at P18-20. At test, retinal function in one eye of every rat was evaluated by electroretinography (ERG). After the ERG, the retina was flatmounted and vasculopathy was quantified by custom developed Mechanistic Oxygen-induced Retinopathy Evaluation (MOIRE) software. The fellow retina was prepared for qPCR of selected stress markers and neurovascular growth factors. Data were analyzed by ANOVA followed by Holm-Sidak pairwise post-hoc tests against the values in ROP rats on control chow.

Results: : The 15% chow was close to the LD50 and worsened every ERG parameter; it was thus excluded from further analyses. Significant improvements in photoreceptor response sensitivity and amplitude were found at intermediate AO concentrations (0.5-4%). The oscillatory potentials on the 1% chow were also improved. Avascular retina was reduced on the 0.5% chow, but neovascularization did not change with dose. mRNA expression of CHOP was reduced on 0.5-4% chows, and HIF-1 expression was likewise reduced on 0.5%. VEGF expression was not altered, although PEDF was reduced on 0.5-4%.

Conclusions: : Intermediate doses (0.5-1%) of AO were beneficial. The highest dose was toxic. None was a panacea. This may, in part, explain the mixed findings for AOs in ROP to date. Some of the pathology may have been mediated by defects in protein folding. Determination of which AOs reached the pups’ retinae is vital to further interpretation of these results.

Keywords: antioxidants • electroretinography: non-clinical • oxidation/oxidative or free radical damage