Neurotoxicity of 3,4-methylenedioxymethamphetamine (MDMA) is still controversially discussed. Formation of reactive oxygen species e.g. based on elevated dopamine (DA) concentrations and DA quinone formation is discussed among others. Inhibition potential of MDMA metabolites regarding neurotransmitter degradation by catechol-O-methyltransferase and sulfotransferase was described previously. Their influence on monoamine oxidase (MAO) - the major DA degradation pathway - has not yet been studied in humans. Therefore the inhibition potential of MDMA and its metabolites on the deamination of the neurotransmitters DA and serotonin (5-HT) by MAO-A and B using recombinant human enzymes in vitro should be investigated. In initial studies, MDMA and MDA showed relevant inhibition (> 30%) towards MAO A for 5-HT and DA. No relevant effects towards MAO B were observed. Further investigation on MAO-A revealed MDMA as a competitive inhibitor of 5-HT and DA deamination with Ki 24.5 ±7.1μM and 18.6±4.3μM respectively and MDA as a mixed-type inhibitor with Ki 7.8±2.6μM and 8.4±3.2μM respectively. Although prediction of in vivo relevance needs to be done with care, relevant inhibitory effects at expected plasma concentrations after recreational MDMA consumption seems unlikely based on the obtained data.
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