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A.R. Wielgus, C.F. Chignell, D.–N. Hu, J.E. Roberts; Comparison of the potential phototoxicity of A2E with its precursor trans–retinal in human retinal pigment epithelial cells . Invest. Ophthalmol. Vis. Sci. 2004;45(13):736.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To compare the potential visible light induced toxicity in human retinal pigment epithelial (hRPE) cells of A2E (a major fluorophore of lipofuscin) with its precursor trans–retinal. Methods: A2E was synthesized and purified according to the procedure described by Parish et al. [Proc. Natl. Acad. Sci. USA, (1998) 95:14609–14613]. Changes of redox potential and evidence of lipid peroxidation induced by either A2E or trans–retinal in the presence and absence of visible light (λ>400nm) were monitored by GSH depletion and FOX assay, respectively. The amount of trans–retinal and A2E incorporated into the cells and total lipid content were determined by thin layer chromatography. Cell viability was estimated using MTS and LDH assays. Protein content was determined by the BCA method. Results: Human RPE cells that had incorporated trans–retinal had significant alteration of redox equilibrium of glutathione when irradiated with visible light. In comparison, although there was some oxidized glutathione formed with the equivalently irradiated A2E treated hRPE cells, total intracellular level of GSH changed only slightly and there was no detectable extracellular modification of either oxidized or reduced GSH. Lipid hydroperoxides induced by irradiation of A2E incorporated hRPE cells were negligible compared to those induced by trans–retinal. Conclusions: These studies support our previous conclusions (Roberts et al. Photochem. Photobiol. 2002; Pawlak et al. Photochem. Photobiol. 2003) that although A2E may be toxic in high concentrations, the phototoxic properties of A2E are insignificant when compared its precursor trans–retinal. The endogenous production of A2E may serve as a protective mechanism to prevent damage to the retina by unbound trans–retinal.
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