CARBOXYMETHYLETHANOLAMINE, A BIOMARKER OF PHOSPHOLIPID MODIFICATION DURING THE MAILLARD REACTION IN-VIVO

N-epsilon-(Carboxymethyl)lysine (CML) is a stable chemical modificatio n of proteins formed from both carbohydrates and lipids during autoxid ation reactions, We hypothesized that carboxymethyl lipids such as (ca rboxymethyl)phosphatidylethanolamine (carboxymethyl-PE) would also be formed in these reactions, and we therefore developed a gas chromatogr aphy-mass spectrometry assay for quantification of carboxymethylethano lamine (CME) following hydrolysis of phospholipids. In vitro, CME was formed during glycation of dioleoyl-PE under air and from linoleoylpal mitoyl-PE, but not from dioleoyl-PE, in the absence of glucose, In viv o, CME was detected in lipid extracts of red blood cell membranes, sim ilar to 0.14 mmol of CME/mol of ethanolamine, from control and diabeti c subjects, (n = 22, p > 0.5), Levels of CML in erythrocyte membrane p roteins were similar to 0.2 mmol/mol of lysine for both control and di abetic subjects (p > 0.5), For this group of diabetic subjects there w as no indication of increased oxidative modification of either lipid o r protein components of red cell membranes, CME was also detected in f asting urine at 2-3 nmol/mg of creatinine in control and diabetic subj ects (p = 0.085), CME inhibited detection of advanced glycation end pr oduct (AGE)-modified protein in a competitive enzyme-linked immunosorb ent assay using an anti-AGE antibody previously shown to recognize CML , suggesting that carboxymethyl-PE may be a component of AGE lipids de tected in AGE low density lipoprotein, Measurement of levels of CME in blood, tissues, and urine should be useful for assessing oxidative da mage to membrane lipids during aging and in disease.