Connexin43 (Cx43) and the inflammasome pathway; Effective Therapeutic Targets in Serious Eye Disease
Colin R Green1,2, Brian Levy2, Lola Rotimi1, Ilva Rupenthal1, Helen Danesh-Meyer1, Cindy Guo3, Mohd Nasir bin Mat Nor3, Monica Acosta3
1.Department of Ophthalmology, University of Auckland and New Zealand National Eye Centre, Auckland, New Zealand
2.OcuNexus Therapeutics Inc., San Diego, California
3.School of Optometry and Vision Sciences, University of Auckland and New Zealand National Eye Centre, Auckland, New Zealand.
In chronic back of the eye disease the inflammasome pathway is triggered by extracellular release of ATP creating a perpetual cycle of inflammation. We set out to test whether ATP release is via the Cx43 gap junction hemichannel (HC), which forms a pathological pore, and whether it can be prevented by HC block. Two posterior segment HC modulating compounds have been developed, an intravitreal mimetic Peptide5 (MP) and an orally available (HCB1019) small molecule.
Numerous experiments both in vitro and in vivo were carried out to confirm the mechanism of action of topical, intravitreal and oral administration of HC blockers on the activated and recycling inflammasome pathway of inflammation. These include the effect of ATP release in endothelial hypoxia, blocking the inflammasome cycle (NLRP3) in a rat pain model and inhibiting inflammation and effect on cytokines and neuronal effects in a spinal contusion model. Animal models of DME (retinal ischemia-reperfusion) and dry AMD (bright light damage) were used to study the effects of HC block on these serious posterior segment diseases.
With injury Cx43 is increased. Endothelial hypoxic assays demonstrated ATP release which was significantly and specifically inhibited by HC block with Peptide5. A rat model of sciatic nerve constriction showed inflammasome activation (NLRP3) and chronic pain. Both NLRP3 and pain were significantly reduced by Peptide5. Spinal contusion models showed significant inhibition of TNFa and IL-1b levels, neuronal sparing and recovered locomotor function with Peptide5. A DME model treated with the HC blocker Peptide5 reduced vascular leak up to 86% (p<0.05) and showed significant neuronal sparing (p<0.05). Bright light Dry AMD model demonstrated that both the intravitreal peptide5 and systemically administered HCB1019 retained ERG function and preserved retinal structure. Untreated control animals had severe ERG impairment and thinning of the inner and outer nuclear layers.
ATP release is mediated by Cx43 overexpression and pathological opening of HCs, activating the inflammasome pathway. HC block in animal models significantly improves outcomes, preventing inflammation, edema, cell loss, microvascular dropout and haemorrhage. These data show potential to radically enhance treatment of chronic ocular disease through a novel and differentiated MOA.