Detection of a lipid-lysine adduct family with an amide bond as the linkage: novel markers for lipid-derived protein modifications.

An amide-type adduct, hexanoyl-lysine (HEL) is generated from the reaction between n-6 fatty acid (FA)-derived lipid peroxide and lysine. Immunochemical and chemical methods can be used to detect the formation of HEL. For example, an ELISA kit using the monoclonal antibody to HEL is now commercially available. We recently identified propanoyl-lysine (propionyl-lysine, PRL) from the reaction of an n-3 FA and a lysine residue. The antibody to PRL has been prepared and characterized. Using these monoclonal antibodies, the localization of adducts in tissues has been confirmed. Moreover, both amide-type adducts, HEL and PRL, can be simultaneously measured using liquid chromatography mass spectrometry (LC/MS/MS) with isotope dilution methods. The LC/MS/MS analysis reveals the rigid amounts of the adducts in human urine. Both the chemical and immunochemical methods are useful for the estimation of amide-type adducts in vivo.