Purchase this article with an account.
M. B. Rozanowska, R. Edge, E. T. Land, S. Navaratnam, T. G. Truscott, B. Rozanowski; Free Radical Interactions of Retinal Constituents - Retinaldehyde and Its Adducts With Phosphatidylethanolamine. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3258. doi: https://doi.org/.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To compare interactions of physiologically relevant free radicals with molecular constituents of photoreceptor outer segments, retinaldehyde (RAL) and RAL-phosphatidylethanolamine (RAL-PE) adducts, and to assess the damaging potential of semioxidized and semireduced retinoids.
RAL and synthesized RAL-PE were solubilized in aqueous solutions in Triton X-100 micelles. Pulse radiolysis was used to generate retinoid radical cations and anions, and oxygen-centred free radicals - hydroxyl, peroxyl, and superoxide radical. Time-resolved absorption spectroscopy was used to study interactions of oxygen-centred free radicals with retinoids, semireduced retinoids with oxygen and semioxidized retinoids with amino acids and ascorbate.
Interaction of both RAL and RAL-PE with carbon tetrachloride-derived peroxyl radical led to the formation of retinoid-derived cation radicals and other species, possibly radical adducts. RAL cation radicals were also formed upon interaction of RAL with hydroxyl radical. Neither RAL nor RAL-PE interacted with superoxide, but retinoid radical anions of both RAL and RAL-PE were scavenged in the presence of oxygen suggesting electron transfer from semi-reduced retinoid to oxygen forming the superoxide. Semioxidized retinoids were scavenged by tyrosine (bimolecular rate constants of 1.4x106 and 3.0x106 M-1s-1 for RAL-PE and RAL, respectively) and cysteine (2.2x107 and 2.9x107 M-1s-1 for RAL-PE and RAL, respectively). In compoarison with amino acids, ascorbate was scavenging retinoids at least 15 times more effectivetively (3.5x108 and 7.4x108 M-1s-1 for RAL-PE and RAL, respectively).
While binding of RAL to PE dramatically diminishes photochemical activity of RAL in RAL-PE adducts, they retain ability to scavenge free radicals. Moreover, the semioxidized RAL-PE adducts are less damaging to proteins than semioxidized RAL. Ascorbate can effectively protect amino acids from semioxidized retinoids. Altogether, PE seems to play a vital protective role in the retina by binding RAL and preventing RAL-mediated damage while retaining antioxidant properties of RAL.
This PDF is available to Subscribers Only