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J.B. O'Neill, J.V. Glenn, T.E. DeGooyer, X. Zhang, M.B. Boulton, K. Uchida, U. Chakravarthy, R.E. Hogg, T. Curtis, A.W. Stitt; Advanced Lipoxidation Endproducts (ALEs) and RPE Dysfunction – A Link to Age–Related Macular Degeneration (AMD)? . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2874.
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Advanced lipoxidation endproducts (ALEs) may play a causative role in disease, accumulating as heterogeneous chemical adducts on proteins during aging and at an accelerated rate in smokers. ALE modifications can alter protein structure and function although their pathogenic role in the retina is largely unknown. The aldehyde acrolein is formed during cellular oxidative stress and can bind to ε–amino group of lysine to form the ALE, acrolein–lysine adduct (FDP–lysine). In the present study we have evaluated presence of FDP–lysine (a defined ALE) in AMD patients and tested the effects of this protein–modification on retinal pigment epithelium (RPE) function.
FDP–lysine immunoreactivity was investigated in sera from a small cohort of patients with wet AMD and age/sex matched controls (n=20/group) using competitive ELISAs. FDP–lysine in the retina was also immunolocalised in post–mortem eyes from AMD patients. In a parallel in vitro study, confluent, quiescent RPE (ARPE–19) were exposed to FDP–lysine (10, 25 & 50 µM) for 7 days and assessed for apoptotic death by changes in annexin V or JC–1 under flow cytometric analysis. Alterations in antioxidant mRNAs were examined by real time RT–PCR and activation of transcriptional activity of NFΚB was quantified.
Serological data demonstrated significantly elevated levels of ALE in patients with AMD (P<0.005). Retinae from AMD patients also had elevated FDP–lysine–immunoreactivity compared to age–matched controls and this was localised to photoreceptor outer–segments, RPE, Bruch’s membrane and choroid. FDP–lysine–treated RPE did not show any evidence of apoptotic cell death after 7 days of treatment post confluency. Relative antioxidant gene expression in ARPE–19 was significantly reduced after FDP–lysine exposure. In response to increased FDP–lysine concentrations, NFΚB transcriptional activity was noticeably reduced in comparison to control (P<0.001).
Data suggests that levels of FDP–lysine are increased in serum and retina from patients with AMD. This ALE may have an important pathogenic role in outer retinal ageing by altering antioxidant defence mechanisms in RPE.
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