Suppression of Complement C5 Activation in the Light-Induced Retinal Damage Model of African Green Monkeys

Abstract

Purpose : Complement proteins have been linked to ocular inflammatory and retinal degenerative diseases. Light induced damage (LD) in the eyes of African Green Monkeys (AGM) triggers inflammation and complement activation. This provides an effective model for testing the efficacy of drug candidates in reducing complement activity. The purpose of the current study was to examine the efficacy of anti-C5 monoclonal antibody and compare with its fragment antigen-binding (Fab) format in LD model.

Methods : AGM eyes were examined using color fundus photography, fluorescein angiography, and optical coherence tomography at baseline and 48 hours after light exposure. Twenty-five monkeys were randomized by weight into eight groups. Test articles were administered either intravitreally or intravenously 48 hours before light damage. Macular irradiation was performed for 2 hours with an energy density of 8000 mW/cm2. Animals were euthanized and their eyes enucleated 48 hours after light exposure. Immunohistochemistry for C3b and MAC proteins was performed on paraffinized sections to confirm complement deposition in light-damaged monkey eyes. The retinal and choroidal tissues from each dissection were lysed, and complement activation was measured using C3a ELISA and MAC Gyros immunoassay.

Results : In AGM LD model, complement C3b and MAC protein deposition were observed in the photoreceptor layer through IHC staining. An increase in complement activation in the retina and choroid tissue was observed following LD. In the AGM light damage model, both intravitreal C5 antibody and Fab fragment were found to suppress soluble C5b-9 production in the retina. Interestingly, only the full-length anti-C5 Ab, not the Fab fragment, could inhibit sC5b-9 production in the choroid. Systemic C5 antibody was shown to prevent complement activation in both the retina and choroid tissue in the AGM LD model.

Conclusions : The AGM light damage model is a useful model to assess the efficacy of anti-complement therapeutics. In this model, complement activity within the eye can be suppressed either by intravitreal or intravenous injection of an anti-C5 antibody. However, intravitreally administered Fab fragment is not able to inhibit sC5b-9 production in the choroid.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.