Identification of N-epsilon-(2-propenal)lysine as a major urinary metabolite of malondialdehyde.

N-epsilon-(2-propenal)lysine (epsilon-PL) was identified as one of two major metabolites of malondialdehyde (MDA) excreted in rat and human urine. This compound is derived mainly but not exclusively from the diet, where it arises from a reaction between free MDA generated in the oxidative decomposition of polyunsaturated fatty acids and the epsilon-amino of the lysine residues of food proteins. It is released during protein digestion and represents the main form in which MDA is absorbed. It is excreted partially in unchanged form and partially as the acetylated derivative N-alpha-acetyl-N-epsilon-(2-propenal)lysine. Its administration to rats did not result in an increase in the excretion of free MDA in the urine. The findings that MDA in foods is absorbed mainly as epsilon-PL, and that this compound is not metabolized to free MDA in vivo, mitigate concern over the possible mutagenicity and carcinogenicity of MDA in the diet.