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Keiko Ueda, Ying Song, Joshua Dunaief, Janet R Sparrow; Iron promotes photooxidation of the retinaldehyde-adduct A2E.. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5785.
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© ARVO (1962-2015); The Authors (2016-present)
Hephaestin (Heph) and ceruloplasmin (Cp) are ferroxidase proteins that convert ferrous to ferric iron to enable cellular iron export. Iron dysregulation is well known to be associated with retinal degeneration. For instance, patients lacking the ferroxidase ceruloplasmin (Cp) as an autosomal recessive disorder, exhibit retinal iron accumulation and early-onset macular degeneration. Cp/Heph double-knockout (DKO) mice undergo age-dependent retinal iron accumulation that is most pronounced in RPE and they succumb to retinal degeneration. In this work we sought to determine whether iron accumulation impacts levels of bisretinoid lipofuscin in RPE.
Mice with mutations in Cp (Cp-/-) and in the Heph gene (Hephsla) on a C57BL/6J background were raised in cyclic light. Bisretinoids were quantified by reverse phase HPLC. For an A2E photooxidation assay, A2E (100 microM; DMSO/PBS) was incubated with the iron chelator deferiprone (50-200 microM) in PBS and was irradiated (430 ± 30 nm) for 30 seconds. A2E was then extracted and quantified by HPLC.
In Cp-/-; Hephsla/sla mice at 8-9 months of age, A2E levels were only 20% of heterozygous and wild-type mice. In Cp-/-; Hephsla/sla mice at 6 months of age, A2E was not detected. In an in vitro assay, chelation of iron by DFP protected A2E from photooxidation with the result that the photooxidation-associated consumption of A2E was reduced and higher A2E levels were observed.
Reduced levels of A2E were observed in the Cp/Heph DKO mice that are characterized by elevated intracellular iron. In addition, iron chelation protected against the photooxidation of A2E. Taken together these finding indicate that intracellular iron contributes to the photooxidation of bisretinoid. The photodegradation products of A2E consist of a mixture of aldehyde-bearing fragments that elicit cellular damage.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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