Infliximab reduces Zaprinast-induced retinal degeneration in cultures of porcine retina

Background: cGMP-degrading phosphodiesterase 6 (PDE6) mutations cause around 4 to 5% of retinitis pigmentosa (RP), a rare form of retinal dystrophy. Growing evidence suggests that inflammation is involved in the progression of RP. The aims of this study were to corroborate the presence of high TNF alpha concentration in the eyes of RP patients and to evaluate whether the blockade of TNF alpha with Infliximab, a monoclonal anti-TNF alpha antibody, prevented retinal degeneration induced by PDE6 inhibition in cultures of porcine retina. Methods: Aqueous humor from 30 patients with RP and 13 healthy controls were used to quantify the inflammatory mediators IL-6, TNF alpha, IL-1 beta, IL-10 by a multiplex enzyme-linked immunosorbent assay (ELISA) system. Retinal explants from pig were exposed to Zaprinast, a PDE6 inhibitor, for 24 hours in the absence or the presence of Infliximab. Cell death was evaluated by TUNEL assay. The number and distribution of caspase-3 positive cells, indirect poly(ADP) ribose polymerase (PARP) activation and glial fibrillary acidic protein (GFAP) content were visualized by immunolabeling. Antioxidant total capacity, nitrites and thiobarbituric acid reactive substances (TBARS) formation were determined to evaluate antioxidant-oxidant status. Results: IL-6 and TNF alpha concentrations were higher in the aqueous humor of RP patients than in controls. Infliximab prevented retinal degeneration, as judging by the reduced presence of TUNEL-positive cells, the reduction of caspase-3 activation and also reduction of glial activation, in an ex vivo model of porcine retina. Additionally, Infliximab partially reduced oxidative stress in retinal explants exposed to Zaprinast. Conclusions: Inflammatory mediators IL-6 and TNF alpha were elevated in the aqueous humor of RP patients corroborating previous studies suggesting sustained chronic inflammation. Our study suggests that TNF alpha is playing an important role in cell death in an ex vivo model of retinal degeneration by activating different cell pathways at different cell layers of the retina that should be further studied.