Preferential formation of N ω -(carboxyethyl)arginine from methylglyoxal and its accumulation in human lens proteins

Methylglyoxal (MGO), a highly reactive dicarbonyl compound generated mainly by glycolysis, is a major precursor of advanced glycation end products (AGEs). Although lysine-derived AGEs, such as Nε-(carboxyethyl)lysine (CEL), have been widely used as markers of MGO-mediated protein modification, increasing evidence suggests that MGO preferentially modifies arginine residues. However, the biochemical significance of arginine-derived AGEs remains poorly understood because of limited analytical and immunochemical methods for their detection. In this study, we investigated the formation and quantitative significance of Nω-(carboxyethyl)arginine (CEA), an underexplored MGO-derived arginine adduct. CEA was chemically synthesized and structurally characterized by NMR and mass spectrometry. Analysis of human tissues revealed that CEA accumulated at high levels in cataractous lenses, comparable to MG-H1 and higher than CEL levels. A monoclonal antibody specific for CEA was developed and validated using ELISA, showing no cross-reactivity with related AGEs. CEA was generated in a time-dependent manner in bovine serum albumin incubated with MGO, whereas CEL formation was minimal. CEA levels were higher than those of CEL in MGO-modified proteins, indicating its preferential formation under physiological conditions. These findings indicate that CEA is a reliable marker for evaluating MGO-mediated protein degeneration and dicarbonyl stress in vitro and in vivo.