Abstract
Purpose :
Open Connexin43 (Cx43) hemichannels release ATP which can activate, amplify and perpetuate the NLRP3 inflammasome pathway underlying chronic inflammatory diseases, including diabetic retinopathy, and cause a loss of vascular integrity. A spontaneously diabetic strain of Sprague Dawley (SD) rats has been shown to develop micro and macroaneurysms, with vessel leak confirmed with Evans blue dye perfusion, and concomitant attenuation of retinal function using electroretinography (ERG). Using an oral hemichannel blocker, Xiflam (tonabersat), we sought to evaluate the potential role of hemichannel block in the treatment of diabetic retinopathy.
Methods :
Diabetic rats with aneurysms, confirmed using optical coherence tomography (OCT), and reduced ERG activity at week 5 were split into two groups; one fed once daily with Xiflam (0.28mg/kg) for 14 days, one fed vehicle only (peanut butter). At week 8 animals were reassessed with OCT and ERG and retinas collected for immunohistochemical labelling with markers of Cx43, GFAP (astrocyte and Müller cell hyperreactivity) and Iba1 (microglia).
Results :
Diabetic rats had elevated blood glucose levels of 16.85±0.63mmol/L compared to normal SD rats (6.37mmol/L) (p<0.001), and lower mean body weight (179.6 vs 198.2g). Xiflam treated diabetic rats had fewer and smaller retinal aneurysms compared to untreated animals. There was reduced GFAP labelling in Müller cells but intense labelling in untreated animals (p<0.001), and reduced Iba1 positive cell numbers (p<0.001) and Cx43 (p<0.001), both back to normal levels. Retinal function (ERG mixed a-wave, mixed b-wave, Rod PIII, PII and cone PII amplitudes) was reduced (p<0.001 for intensities above 0.1 log cd.s/m2 for mixed a-wave and all intensities for mixed b-wave) at 5 weeks but restored to normal levels after Xiflam treatment; retinal function of untreated animals continued to decline.
Conclusions :
Cx43 hemichannel block is known to reduce the release of inflammatory cytokines in the inflammasome pathway, including VEGF. In this model of diabetes, oral Xiflam reduced aneurysms, reduced inflammation and promoted recovery of ERG activity. Targeting Cx43 hemichannels offers potential to break the inflammatory cycle and preserve vascular integrity in diabetic retinopathy, with implications for other chronic retinal diseases.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.