N[superscript [var epsilon]]-(Carboxymethyl)lysine and 3-DG-Imidazolone Are Major AGE Structures in Protein Modification by 3-Deoxyglucosone

The levels of plasma 3-deoxyglucosone (3-DG) increase under hyperglycemic conditions and are associated with the pathogenesis of diabetic complications because of the high reactivity of 3-DG with proteins to form advanced glycation end products (AGE). To investigate potential markers for 3-DG-mediated protein modification in vitro and in vivo, we compared the yield of several 3-DG-derived AGE structures by immunochemical analysis and HPLC and measured their localization in human atherosclerotic lesions. When BSA was incubated with 3-DG at 37°C for up to 4 wk, the amounts of N[superscript [var epsilon]]-(carboxymethyl)lysine (CML) and 3-DG-imidazolone steeply increased with incubation time, whereas the levels of pyrraline and pentosidine increased slightly by day 28. In contrast, significants amount of pyrraline and pentosidine were also observed when BSA was incubated with 3-DG at 60°C to enhance AGE-formation. In atherosclerotic lesions, CML and 3-DG-imidazolone were found intracellularly in the cytoplasm of most foam cells and extracellularly in the atheromatous core. A weak-positive immunoreaction with pyrraline was found in the extracellular matrix and a few foam cells in aortic intima with atherosclerotic lesions. Our results provide the first evidence that CML and 3-DG-imidazolone are major AGE structures in 3-DG-modified proteins, and that 3-DG-imidazolone provides a better marker for protein modification by 3-DG than pyrraline.