Identification of DNA adducts of methylglyoxal.
Methylglyoxal (MG) is a sugar degradation product, which is endogenously formed by fragmentation of triose phosphates during glycolysis, ketone body metabolism of acetone, and catabolism of threonine. Food, beverages, and medical products are important exogenous sources with concentrations of up to 100 microM MG. MG is a reactive dicarbonyl compound, which easily modifies amino groups of proteins (glycation reaction) and thereby induces proinflammatory responses. Moreover, increased mutation frequencies in mammalian cells after treatment with MG have been reported, which are caused by stable modifications of DNA bases. Thus far, two types of adducts have been identified, which are formed during the reaction of free guanine or 2'-deoxyguanosine with high MG concentrations. In this study, we investigated the prolonged exposure of DNA to physiological MG concentrations. DNA was incubated with MG, enzymatically hydrolyzed to release the free nucleosides, and then analyzed by LC-MS/MS. We detected four products, which were derived from the reaction of 2'-deoxyguanosine and 2'-deoxyadenosine with 1 and 2 equiv of MG each. The adducts with 1 equiv of MG were identified as N2-(1-carboxyethyl)-2'-deoxyguanosine (CEdG) and N6-(1-carboxyethyl)-2'-deoxyadenosine. LC-MS/MS was optimized for these compounds, and incubation of DNA was repeated using physiological concentrations of 10 microM MG. Thereby, CEdG proved to be the most sensitive and suitable marker for the reaction of DNA with MG (negative MRM mode, three mass transitions [M - 1](-) 338-->178, 338-->106, and 338-->149).