Cytochrome P450 2C Epoxygenases Mediate Photochemical Stress-induced Death of Photoreceptors [Molecular Bases of Disease]

February 11th, 2014 by Chang, Q., Berdyshev, E., Bogaard, J., White, J. J., Chen, S., Shah, R., Mu, W., Grantner, R., Bettis, S., Grassi, M. A.

Degenerative loss of photoreceptors occurs in inherited and age-related retinal degenerative diseases. Chemical screen facilitates development of new testing routes for neuroprotection and mechanistic investigation. Herein, we conducted a mouse-derived photoreceptor (661W cells)-based high throughput screen of the FDA-approved Prestwick drug library to identify putative cytoprotective compounds against light-induced, synthetic visual chromophore-precipitated cell death. Different classes of hit compounds were identified, some of which target to known genes or pathways pathologically associated with retinitis pigmentosa. Sulfaphenazole (SFZ), a selective inhibitor of human cytochrome P450 (CYP) 2C9 isozyme, was identified as a novel and leading cytoprotective compound. Expression of CYP2C proteins was induced by light. Gene-targeted knockdown of CYP2C55, the homologous gene of CYP2C9, demonstrated viability rescue to light-induced cell death while stable expression of functional CYP2C9-GFP fusion protein further exacerbated light-induced cell death. Mechanistically, SFZ inhibited light-induced necrosis and mitochondrial stress-initiated apoptosis. Light elicited calcium influx, which was mitigated by SFZ. Light provoked release of arachidonic acid (AA) from membrane phospholipids and production of non-epoxyeicosatrienoic acid (EET) metabolites. Administration of SFZ further stimulated the production of non-EET metabolites, suggesting a metabolic shift of AA under inhibition of the CYP2C pathway. Together, our findings indicate that CYP 2C genes play a direct causative role in photochemical stress-induced death of photoreceptors and suggest that the CYP monooxygenase system is a risk factor for retinal photo damage, especially in individuals with Stargardt disease or age-related macular degeneration that deposit condensation products of retinoids.