Measurement of Homocitrulline, A Carbamylation-derived Product, in Serum and Tissues by LC-MS/MS

Carbamylation corresponds to the non-enzymatic binding of isocyanic acid to protein amino groups and participates in protein molecular aging, characterized by the alteration of their structural and functional properties. Carbamylated proteins exert deleterious effects in vivo and are involved in the progression of various diseases, including atherosclerosis and chronic kidney disease. Therefore, there is a growing interest to evaluate the carbamylation rate of blood or tissue proteins, since carbamylation-derived products (CDPs) constitute valuable biomarkers in these contexts. Homocitrulline, formed by isocyanic acid covalently attaches to the ε-NH₂ group of lysine residue side chain, is the most characteristic CDP. Sensitive and specific quantification of homocitrulline requires mass spectrometry-based methods. This unit describes a liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for the quantification of homocitrulline, with special emphasis on pre-analytical steps that allow quantification of total or protein-bound homocitrulline in serum or tissue samples. © 2018 by John Wiley & Sons, Inc.