Semicarbazide-sensitive amine oxidase (SSAO) catalyzes the deamination of methylamine and aminoacetone to produce toxic aldehydes, i.e. formaldehyde and methylglyoxal, as well as hydrogen peroxide and ammonia. An increase of SSAO activity was detected by different laboratories in patients suffering from vascular disorders, i.e. diabetes and myocardial infarction. The enzyme has been suggested to play a role in vascular endothelial damage and atherogenesis. To date, there are no selective SSAO inhibitors. In the present study, 2-bromoethylamine (2-BrEA) was found to be a highly effective and selective inhibitor of SSAO obtained from different sources. The inhibition was irreversible and time dependent. It was competitive when the enzyme was not preincubated with the inhibitor, but became noncompetitive after incubation of the enzyme with 2-BrEA. The aldehyde trapping agent o-phenylenediamine was capable of preventing 2-BrEA-induced inhibition of SSAO activity. An aldehyde product was detected to be an initial product of 2-BrEA after it was incubated with SSAO. The inhibition, therefore, is mechanism-based. The SSAO inhibitory effects of eight structural analogues of 2-BrEA were assessed. It was concluded that a bromine atom at the beta position is quite important for exerting high potency of SSAO inhibition. The inhibition of SSAO activity by 2-BrEA was also demonstrated in vivo. It increased the urinary excretion of methylamine, an endogenous substrate for SSAO, in mice. 2-BrEA can be employed as a very useful tool in the investigation of SSAO.
