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C. Pfahler, N.H. Ansari, S. Previs, R.H. Nagaraj; Lysinimine is an obligatory intermediate in the formation of lysine–AGEs from glyoxal: Detection in human lens proteins. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1685.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Glyoxal is an alpha–dicarbonyl compound formed during protein glycation and oxidation of polyunsatutared fatty acids (PUFAs). Several specific advanced glycation end products (AGEs) of glyoxal reaction have been detected in tissues, including the lens. In this study we have investigated mechanisms of AGE formation from glyoxal focusing mainly on lysinimine, an initial condensation product of lysine and glyoxal. Methods: Formation of lysinimine and its conversion to AGEs was investigated in proteins incubated with glyoxal under physiological conditions. Lysinimine was detected as N6–hydroxyethylysine (HEL) after reduction by NaCNBH3 and it was quantified by RP–HPLC and post column derivatization with o–phthalaldehyde. Specific AGEs of glyoxal, GOLD, GALA, GOLA and CML were also similarly quantified in proteins after hydrolysis with either acid or a combination of enzymes. HEL and glyoxal–AGEs were also measured in clear and cataractous human lenses, and in organ cultured rat lenses that were subjected to oxidative stress (H2O2 and Fe2+). Results: During the 30–day incubation of proteins with glyoxal, lysinimine content rose rapidly within 24 hrs and then steeply declined, and was present at low levels during rest of the incubation. During this period, glyoxal–AGE levels steadily increased up to 14 days and then remained constant. When short–term glyoxal–modified proteins (10 hrs, 5 mM) were dialyzed and incubated for 21 days at 37 0C, synthesis of all AGEs occurred in the absence of glyoxal, but reduction with NaCNBH3 before dialysis prevented their synthesis. Human lenses showed significant amounts of lysinimine and glyoxal–AGEs but no correlations were found between lysinimine content and AGEs. Oxidative conditions promoted HEL formation in organ cultured rat lenses. Incubation with PUFA linoleic acid also produced lysinimine and glyoxal–AGEs in proteins. Conclusions: Our results suggest that lysine–AGE formation from glyoxal in proteins occurs through the formation of an obligatory lysinimine intermediate. Oxidation of PUFAs is likely a source of glyoxal. These reactions could play a role in the chemical modification of proteins during lens aging and cataract formation.
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