Assay of MAO Inhibition by Chromatographic Techniques (HPLC/HPLC-MS).

Abstract

Monoamine oxidase (MAO) enzymes (MAO A and B) catalyze the oxidative deamination of biogenic amines, neurotransmitters, and xenobiotic amines and contribute to the regulation of the contentof these activesubstances in mammalian organisms. The oxidation of biogenic amines by MAO produces hydrogen peroxide (H2O2) and aldehydes that represent risk factors for oxidative injury.The inhibitorsof MAO are useful as antidepressants and neuroprotective agents. Usually, the assays of MAO determine amine deamination products or measure the H2O2 released by using direct spectrophotometric or fluorimetric methods. Direct methods are more prone to interferences and can afford inaccurate results. Those limitations can beavoided by using chromatographic techniques. This work describesa chromatographic method to assay MAO A and MAOB activity by using kynuramine as a nonselective substrate and the subsequentanalysis of 4-hydroxyquinoline by RP-HPLC-DAD-fluorescence and mass spectrometry(MS). Alternatively, the assay uses the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxin as a substrate of MAO that is oxidized (bioactivated) to neurotoxic pyridinium cations which areanalyzed by HPLC. These methods are applied to assess the inhibition of MAO by bioactive β-carboline alkaloids occurring in foods, plants, and biological systems.