Nitroxide-based drugs have proven effective in modulating radical-induced oxidative stress by modulating antioxidant enzymes and genes that control distinct immune and anti-inflammatory responses. Due to their reasonable chemical stability and ability to shuttle between oxidised and reduced forms at physiologically relevant redox potentials, nitroxide-based radicals have also proven effective as biological probes of redox status. Herein, we investigated the potential of a unique nitroxide-based antioxidant and anti-inflammatory agent to protect the retina from experimentally induced degeneration. An established rat model of retinal degeneration was used, viz. laser-induced choroidal neovascularisation (CNV), to study the effects of the hybrid steroidal anti-inflammatory-antioxidant prednisolone 2,2,6,6-tetramethylpiperidine-1-oxyl(TEMPO) nitroxide compound. Full-field electroretinography (ERG) was used to assess retinal toxicity and determine any functional changes – a-wave, b-wave, c-wave, isolated cone b-wave and oscillatory potentials. Moreover, optical coherence tomography (OCT) was utilised to observe changes in retinal morphology and quantify changes in the outer nuclear layer. Structural changes were confirmed by histology. Vascular endothelial cell distribution at the CNV lesion site was investigated using isolectin B4 fluorescence histology, and the inflammatory response of microglia and Müller was investigated using IBA-1 and GFAP immunohistochemistry, respectively. The prednisolone-TEMPO (Pred-TEMPO) hybrid was not toxic in the retina. No changes in a-wave, b-wave, c-wave, isolated cone b-wave and oscillatory potentials were seen. No significant changes in all the electrophysiological parameters were seen after laser induction. Pred-TEMPO reduced laser-induced CNV lesion IB4-positive area compared to untreated control and prednisolone-treated rats. No changes were seen in the GFAP expression after treatment with pred-TEMPO; however, the microglial inflammatory response was significantly reduced in the pred-TEMPO treated animals compared to the vehicle. These findings demonstrate that nitroxide-based compounds are potential therapeutics for retinal degenerative diseases involving inflammatory and oxidative stress-mediated components, including age-related macular degeneration.
Protecting the retina from oxidative injury with a novel nitroxide-corticosteroid agent
Toto, R. (Author). 13 Feb 2025
Student thesis: Master's Thesis