The value of broad spectrum chemokine inhibitors in modulating microglia/macrophage-mediated inflammation in a model of atrophic AMD

Abstract

Purpose : Macrophage recruitment and activation is implicated in pathogenesis of retinal diseases such as atrophic AMD, where they accumulate amongst the ONL and subretinal space. Such recruitment is aided by the expression of chemokines, which furnish these cells with directional cues that augment their migration to areas of retinal injury. While these qualities make chemokines a potential therapeutic target in curtailing retinal inflammation, their wide variety and signalling redundancy pose challenges to broadly modulating their activity. Here, we examine the efficacy of the broad spectrum chemokine inhibitor (BSCI) NR58-3.14.3 – a suppressor of Ccl- and Cxcl- pathways – in reducing macrophage activity and photoreceptor death, using a light-induced model of outer-retinal atrophy and inflammation.

Methods : Photooxidative damage was induced in SD rats via exposure to 1000lx light for 24hrs, which were then euthanized at 0 or 7 days post-exposure (n=12 for each group). Prior to damage, NR58-3.14.3 was injected intravitreally. Retinas were harvested and evaluated for the effect of NR58-3.14.3 on the recruitment and cytokine expression profile of subretinal macrophages (FACS, qPCR, Immunohistochemistry), as well as photoreceptor degeneration (TUNEL). One-way ANOVA was used for statistics.

Results : Injection of NR58-3.14.3 reduced the accumulation of subretinal macrophages following exposure to light damage, at both 0 and 7 days post-exposure time-points , compared to PBS-injected controls <span style="line-height:20.8px">(P<0.05)</span>. NR58-3.14.3 also reduced the up-regulation of inflammatory markers including of Il6, Ccl3 and Ccl4 in recruited macrophages (P<0.05), which are promoters of their pathogenic activity in the retina. Finally, NR58-3.14.3 injected retinas displayed markedly reduced photoreceptor death following light damage, at both 0 and 7 days post-exposure (P<0.05).

Conclusions : Our findings indicate that NR58-3.14.3 is effective in inhibiting macrophage activity and cell death in light damage, and thus illustrates the potential of BSCIs as novel therapeutic agents in thwarting retinal inflammation. Although BSCIs may not be appropriate for all retinal inflammatory conditions, our results suggest that they may be beneficial for retinal dystrophies in which chemokine expression and subretinal macrophage recruitment are implicated, such as advanced AMD.