Metabolization of the Advanced Glycation End Product N-ε-Carboxymethyllysine (CML) by Different Probiotic E. coli Strains.

N-ε-Carboxymethyllysine (CML) is formed during glycation reactions (synonym, Maillard reaction). CML is degraded by the human colonic microbiota, but nothing is known about the formation of particular metabolites. In the present study, six probiotic E. coli strains were incubated with CML in the presence or absence of oxygen in either minimal or nutrient-rich medium. CML was degraded by all strains only in the presence of oxygen. HPLC-MS/MS was applied for identification of metabolites of CML. For the first time, three bacterial metabolites of CML have been identified, namely N-carboxymethylcadaverine (CM-CAD), N-carboxymethylaminopentanoic acid (CM-APA), and the N-carboxymethyl-Δ1-piperideinium ion. During 48 h of incubation of CML with five different E. coli strains in minimal medium in the presence of oxygen, 37-66% of CML was degraded, while CM-CAD (1.5-8.4% of the initial CML dose) and CM-APA (0.04-0.11% of the initial CML dose) were formed linearly. Formation of the metabolites is enhanced when dipeptide-bound CML is applied, indicating that transport phenomena may play an important role in the "handling" of the compound by microorganisms.