Methylglyoxal-derived hydroimidazolone advanced glycation end-products of human lens proteins.

PURPOSE To determine the concentrations of methylglyoxal-derived advanced glycation end-products (AGEs), the hydroimidazolones MG-H1 and -H2, in soluble human lens proteins and compare them with the concentrations of other methylglyoxal-derived AGEs and pentosidine. METHODS Lens protein samples were hydrolyzed enzymatically. AGEs were assayed without derivatization by HPLC with tandem mass spectrometry; the fluorescent AGEs argpyrimidine and pentosidine were assayed by fluorometric detection. MG-H1 and -H2 were resolved and assayed by fluorometric detection after derivatization with 6-aminoquinolyl-N-hydroxysuccimidylcarbamate (AQC). RESULTS The methylglyoxal-derived hydroimidazolones MG-H1 and -H2 were detected and quantified in human lens proteins. AGE concentrations (mean +/- SEM) were: MG-H1 4609 +/- 411 pmol/mg protein, MG-H2 3085 +/- 328 pmol/mg protein, argpyrimidine 205 +/- 19 pmol/mg protein, and pentosidine 0.693 +/- 0.104 pmol/mg protein. The concentration of MG-H1 in human lens protein correlated positively with donor age (correlation coefficient = 0.28, P < 0.05), the concentration of MG-H2 (correlation coefficient = 0.78, P < 0.001) and argpyrimidine (correlation coefficient = 0.42, P < 0.01). The concentrations of AGEs were increased in cataractous lenses in comparison with noncataractous lenses: the increases were MG-H1 85%, MG-H2 122%, argpyrimidine 255%, and pentosidine 183% (P < 0.001). Multiple logistic regression analysis showed a significant link of cataract to donor age (regression coefficient beta = 0.094, P = 0.026) and argpyrimidine (beta = 0.022, P = 0.002). CONCLUSIONS Methylglyoxal hydroimidazolones are quantitatively major AGEs of human lens proteins. These substantial modifications of lens proteins may stimulate further glycation, oxidation, and protein aggregation leading to the formation of cataract.