NCarboxyethyllysine

Nε-(Carboxyethyl)lysine, commonly abbreviated CEL and also known as N-carboxyethyllysine, is an advanced glycation end product (AGE). It forms when the ε-amino group of lysine residues reacts with reactive carbonyl species, yielding a carboxyethyl-lysine adduct. CEL can be present in a protein-bound form within tissues and fluids, as well as as a free compound released during proteolysis.

Formation and occurrence: Endogenous formation of CEL occurs under conditions that promote glycation, such as hyperglycemia, oxidative stress, and aging. CEL is also generated during the heat processing of protein-rich foods, including baked and fried products, contributing to dietary AGE intake. Dietary exposure can influence circulating and tissue levels of CEL, which can be detected in plasma, serum, urine, and various tissues.

Detection and analysis: CEL is typically quantified by liquid chromatography–tandem mass spectrometry (LC-MS/MS) in biological samples. Analytical approaches may distinguish free CEL from protein-bound CEL after appropriate hydrolysis or digestion, and often incorporate isotope-labeled standards to ensure accuracy.

Significance: As a major AGE, CEL serves as a biomarker of glycation and the overall AGE burden. Elevated CEL levels have been reported in aging and in diabetes and may be associated with alterations in protein structure and function. While correlations exist between CEL and disease states, CEL is generally considered a marker of glycation rather than a proven causal factor in disease processes.