HPLC-UV method for evaluation of inhibitors of plasma amine oxidase using derivatization of an aliphatic aldehyde product with TRIS

Plasma amine oxidase (PAO), which is also designated as semicarbazide-sensitive amine oxidase (SSAO), copper-containing amine oxidase 3 (AOC3), or vascular adhesion protein-1 (VAP-1), catalyzes the oxidative deamination of primary amines to aldehydes using copper and a quinone as cofactors. Because it participates in the transmigration of inflammatory cells through the blood vessels into the tissue, PAO is attributed an important role in inflammatory diseases. Therefore, inhibitors of this enzyme could lead to new therapeutics for the treatment of inflammation-related conditions. Assays for the evaluation of PAO inhibitors usually measure the conversion of benzylamine to benzaldehyde by UV spectroscopy. We have developed a test system with the new substrate 6-(5-phenyl-2H-tetrazol-2-yl)hexan-1-amine, monitoring the formation of the enzyme product 6-(5-phenyl-2H-tetrazol-2-yl)hexanal by reversed phase HPLC with UV detection. Since this compound only eluted with poor peak shape due to hydrate formation in the aqueous mobile phase, it was derivatized with tris(hydroxymethyl)aminomethane (TRIS) under mild conditions to an oxazolidine prior HPLC analysis. The validation of the method revealed that the new substrate was bound with higher affinity to PAO and converted with higher velocity than the standard substrate benzylamine.