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Z. Wang, J. Dillon, R.J. Bennick, E.R. Gaillard; The Oxidation and Photooxidation of A2E Results in the Formation of Highly Reactive Carbonyl Compounds . Invest. Ophthalmol. Vis. Sci. 2005;46(13):258.
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Purpose: The thermal or photochemical oxidation of A2E leads to a number of products including those with molecular weights smaller than that of A2E. The purpose of this study is to determine if these smaller mass products are highly reactive aldehydes. Methods: A2E dissolved in ethanol was injected into water with 1% ethanol in the final solution. The solution was bubbled with oxygen and kept in the dark for one month or directly irradiated for 2 hours with Philips "special Blue" Bilirubin bulbs through a 1/4 inch sheet of plexiglass (exc > 400 nm). The reaction mixtures were mixed with p–nitrophenylhydrazine (p–NP) (1:5 molar A2E:p–NP) and kept in the dark for 30 minutes. The samples were subjected to ESI/MS analysis (ThermoElectron LCQ Advantage) and compared to reaction mixture without p–NP. Results: The oxidation products of A2E with molecular mass less than that of A2E react with p–NP forming products with increases in molecular weight corresponding to the formation of the p–nitrophenylhydrazones of the oxidation products. The major MS/MS fragmentations of these products consisted of the loss of the p–nitrophenylhydrazine fragment. The full mass spectra also indicated that the oxidation mixture contained a series of p–NP positive products with starting molecular weights greater than A2E. The MS/MS fragmentation of these products indicated that they resulted from the addition of oxygen and loss of hydrogen from A2E. The MS/MS fragmentation of these products suggested that the reactive carbonyl groups of these products are in the cyclohexenyl ring. Conclusions: The oxidation of A2E results in the cleavage of polyene double bonds and the concommitant formation of reactive aldehydes. The oxidative formation of these aldehydes in RPE cells will have lethal effects on cell viability. In addition, A2E oxidation products formed through oxygen addition and molecular hydrogen loss appear to have ketone groups in the cyclohexenyl ring.
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