Semicarbazide-sensitive amine oxidase (SSAO) catalyzes formation of methylglyoxal (MG) from aminoacetone; MG then reacts with proteins to form advanced glycation end products or AGEs. Because of its potential to generate MG, SSAO may contribute to AGE-associated vascular complications of aging and diabetes. We developed a method to measure SSAO activity in bovine aortic smooth muscle cells (BASMC) based on the oxidation of 2',7'-dichlorofluorescin by hydrogen peroxide and horseradish peroxidase. The SSAO activity was completely inhibited by 10 mM semicarbazide. Argpyrimidine is a readily detectable fluorescent product of the reaction between MG and arginine. Cell lysates incubated with aminoacetone formed argpyrimidine in a reaction that was inhibited by 20 mM semicarbazide. Immunostaining of tissue sections showed that aminoacetone-treated rats (normal as well as diabetic) formed more argpyrimidine in aortic smooth muscle than untreated controls. We believe that SSAO can enhance AGE synthesis in the macrovasculature of diabetic individuals by production of MG. (C) 2002 Elsevier Science (USA). All rights reserved.