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Janet R. Sparrow, Kee Dong Yoon, Jilin Zhou, Kazunori Yamamoto; Molecular Links between RPE Bisretinoid Lipofuscin and Drusen. Invest. Ophthalmol. Vis. Sci. 2011;52(14):897.
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We have previously shown that photodegradation of A2E releases methylglyoxal (MG), a low molecular weight reactive dicarbonyl that initiates advanced glycation end-product (AGE)-modification of proteins and lipids. This finding is significant since AGE-modified proteins are present in drusen. Here we sought to understand the propensity for dicarbonyl products to form from RPE bisretinoids and to test for evidence that these dicarbonyl products of bisretinoid photooxidation and photocleavage, can impact the environment of the RPE cell in vitro.
Liquid chromatography (LC) coupled to positive electrospray ionization mass spectrometry (ESI-MS) was employed to analyze photocleavage products of A2E and all-trans-retinal dimer. ARPE-19 cells that were grown on a fibronectin substrate were allowed to accumulate A2E, were treated with aminoguanidine and irradiated at 430 nm. Fibronectin was immunoprecipitated from homogenates of the cells and substrate and fibronectin was probed for AGE-modification by ELISA.
Within the complex mixture of photo-degradation products generated by irradiation of A2E and all-trans-retinal dimer, we detected of methylglyoxal (72 Da) and glyoxal (GO; 58 Da) by trapping with 4-nitrophenylhydrazine (4-NPH) or aminoguanidine. AGE-fibronectin adducts were detected at sites of blue light (430 nm) irradiation; pretreatment of the cells with aminoguanidine attenuated this deposition.
Photodegradation of A2E and all-trans-retinal dimer releases MG and GO, low molecular weight reactive dicarbonyls that initiate AGE formation. Pre-treatment of cells with aminoguanidine a known scavenger of MG and GO and experimental therapeutic, reduced AGE-adduct formation on extracellular fibronectin. MG is already known to be generated by carbohydrate and lipid oxidation; the generation from bisretinoids represents a newly recognized source. It is significant that AGE-modified proteins are detected in drusen; drusen have been linked to AMD pathogenesis. These findings suggest a possible association between RPE bisretinoid lipofuscin photooxidation and drusen formation.
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