Identification of a furazolidone metabolite responsible for the inhibition of amino oxidases.

1 Furazolidone, a drug widely used in human and veterinary medicine, exhibits inhibition of monoamine oxidase activity, as observed in the tissues of a number of different animal species, including man. The aim of the current study was to determine which of the two possible metabolites, 3-amino-2-oxazolidone (AOZ) or beta-hydroxyethylhydrazine (HEH), a well-known carcinogenic compound, is involved in the toxicological effects reported. 2 A new spectrometric method was set up to differentiate intracellular HEH from AOZ inside cells. This method works well at low pH where both AOZ and HEH are free in solution and available to react with the chemical chromophore (DAB). 3 The results confirm that furazolidone has to be metabolized in the intact cell in order to exhibit mitochondrial monoamine oxidase inhibition, whereas AOZ itself is able to exert a reversible monoamine oxidase inhibition. AOZ also inhibits bovine serum amino oxidase. On the contrary, HEH gives irreversible inhibition of both enzymes. However, the reversible nature of the AOZ inhibition with respect to HEH suggests that the two metabolites act by different mechanisms which do not require the biotransformation of AOZ to HEH. 4 Cell lysates, previously incubated with AOZ, were directly analysed and the formation of HEH from AOZ was not detected, supporting the conclusion that the amino oxidase inhibition observed on treatment with furazolidone was attributable to AOZ and not to HEH.