Increased Fundus Autofluorescence (FAF) in a Rat Model of Sodium Iodate (NaIO3) Induced Retinal Pigment Epithelium (RPE) Toxicity

Abstract

Purpose: : to determine if Fundus Autofluorescence (FAF) imaging can be used in a pre-clinical model of RPE damage. Specifically, we asked (1) if FAF changes reported in patients with RPE loss (eg, in "dry" AMD, retinitis pigmentosa (RP) or ocular inflammatory disease), can be detected in the rat eye; and (2) if the cellular correlates of the observed FAF changes can be determined using histological techniques. The overarching goal is to permit the reciprocal translation of clinical biomarkers and tissue analysis

Methods: : NaIO3, an RPE toxin, was injected systemically at 45-60mg/kg in adult Sprague Dawley rats. The Heidelberg Retinal Angiography II was used to image eyes at baseline (pre-NaIO3), and at intervals from 1 to 88 days thereafter. Images were obtained in all channels: red-free (RF), infra-red (810nm), fluorescein channel (488nm) and the ICG channel (790nm). Control animals were injected with saline. After imaging, dissected eyes were analysed by wholemount white-light and > 488nm long-pass fluorescence, and by cross-sectional analysis using H&E and immunohistochemistry for activated microglia (lectin SB4).

Results: : animals receiving NaIO3 developed a reticular pattern of FAF in the 488nm channel that appeared between the 3^rd and 7^th day. This pattern persisted, becoming somewhat granular in appearance, until approximately the 4^{th -} 6^th week when poorly delineated areas of hypofluorescence developed. Slightly darkened curvilinear shapes appeared in the RF channel that corresponded to some areas of hyperfluorescence. No change was observed in the 790 or IR channels. Wholemount analysis showed a speckled pattern of >488nm autofluorescence that was partly consistent with in vivo images. H&E at day 12 (the time point evaluated to date) showed folding and disruption of the outer retina with patchy loss of the photoreceptors and RPE. Activated microglia were detected in the peripapillary region.

Conclusions: : FAF can be useful in the rodent eye. NaIO3-induced toxicity leads to changes that mimic those observed clinically in patients with RPE disease such as AMD, RP or ocular inflammation. To our knowledge, this study is the first to confirm that FAF can be used in pre-clinical models of disease thereby permitting translation of clinical methods and basic science.

Keywords: age-related macular degeneration • imaging/image analysis: non-clinical • retinal pigment epithelium