Polyphosphate protects against laser-induced choroidal neovascularization in mice by blocking complement activation and oxidative damage

Abstract

Purpose : The mechanisms underlying age-related macular degeneration (AMD) are incompletely understood. However, excess complement activation and oxidative stress are implicated. We recently reported that polyphosphate (polyP), a naturally occurring inorganic linear polymer, inhibits the terminal pathway of complement. The goal of this project is to evaluate the efficacy of administering polyP as a therapeutic agent in a laser-induced model of choroidal neovascularization (CNV) in mice and to explore the mechanisms of action of polyP in vitro.

Methods : Eyes of C57Bl6J mice were exposed to laser injuries that induce CNV. PolyP₁₃₀ or monoP (200 μM) was injected intravitreally immediately after laser injury. Fourteen days later, eyes were excised and dissected into eye cups. These were immunostained for endothelial cells and deposition of the terminal complement complex C5b-9, followed by flat mounting. Staining was quantified by confocal microscopy and computer analysis. Cultured retinal pigment epithelial cells (RPE) and choroid endothelial cells (CEC) were exposed to H₂O₂ or to human serum to induce complement activation. The effect of polyP and monoP on cell viability, catalase expression, and complement activation was assessed by nuclear staining, qRT-PCR, and deposition of C5b-9 detected by flow cytometry, respectively. Statistical analyses were performed with One Way ANOVA and Student’s t-test with significance at P < 0.05.

Results : Intravitreal injection of polyP₁₃₀ exhibited a significant reduction in C5b-9 deposition on the choroid following laser injury, with a reduction in CNV, as compared to monoP. PolyP and monoP protected the RPE and CEC from H₂O₂-induced loss of nuclear integrity and increased catalase expression in a concentration-dependent manner. PolyP also suppressed C5b-9 deposition on the cell surface.

Conclusions : In a murine model of wet AMD, polyP provided protection by reducing CNV and complement activation. This is in line with biochemical studies in which polyP interferes with the terminal pathway of complement. We further showed that polyP protects key cells associated with AMD from oxidative stress. Further in vivo validation and toxicity studies are ongoing, and the mechanisms by which polyP interferes with oxidative stress-induced injury are being explored.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.