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MDMA (ecstasy) inhibition of MAO type A and type B: comparisons with fenfluramine and fluoxetine (Prozac)
1Department of Biology, New York University, NY 10003.
Abstract:
3,4-Methylenedioxymethamphetamine (MDMA), a serotonin (5-HT) neurotoxin, has been shown to promote the release of serotonin (5-HT) and block its reuptake. The increased buildup of extracellular 5-HT should normally be degraded by monoamine oxidase (MAO). The effects of both enantiomers of MDMA were examined on MAO-A and monoamine oxidase-B (MAO-B) activity in rat brain homogenates. Both enantiomers competitively inhibited 5-HT catabolism by rat brain MAO-A. The Ki of MDMA for MAO-A was 22 mumol/L. A mixed type of inhibition by MDMA was observed for phenethylamine catabolism by MAO-B for both optical antipodes. Logistical analysis of concentration response curves for MDMA inhibition of MAO-A and MAO-B show an IC50 of 44 mumol/L for inhibition of MAO-A by MDMA. The IC50 value of MDMA inhibition of MAO-B was 370 mumol/L, showing a selective potency for MAO-A inhibition. The MAO inhibitory properties of fenfluramine (FEN) and fluoxetine (FLUOX) were compared to those of MDMA. The rank order potency of these drugs for MAO-A inhibition was MDMA > FLUOX > FEN, whereas for MAO-B inhibition, FLUOX > MDMA > FEN. A combination of FLUOX and MDMA at their respective IC50 did not inhibit MAO activity more than either drug alone at equivalent concentrations. These results indicate that the actions of FEN do not appear to involve MAO inhibition. MDMA (ecstasy) produced a preferential inhibition of MAO-A (IC50 = 44 mumol/L), which should increase extracellular 5-HT.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
3,4-Methylenedioxymethamphetamine (MDMA) preferentially inhibits monoamine oxidase-A (MAO-A), increasing extracellular serotonin (5-HT). This study investigated MDMA
Area of Science:
- Neuropharmacology
- Enzyme kinetics
- Drug metabolism
Background:
- 3,4-Methylenedioxymethamphetamine (MDMA) is known to affect serotonin (5-HT) levels by promoting its release and blocking reuptake.
- Extracellular serotonin is normally degraded by monoamine oxidase (MAO) enzymes, specifically MAO-A and MAO-B.
- Understanding MDMA's interaction with MAO is crucial for elucidating its neurochemical effects.
Purpose of the Study:
- To investigate the effects of both enantiomers of MDMA on MAO-A and MAO-B activity in rat brain homogenates.
- To compare the MAO inhibitory properties of MDMA with fenfluramine (FEN) and fluoxetine (FLUOX).
Main Methods:
- Enzyme inhibition assays were performed using rat brain homogenates.
- The effects of MDMA enantiomers on serotonin (5-HT) and phenethylamine catabolism by MAO-A and MAO-B were measured.
- Kinetic parameters (Ki, IC50) were determined, and drug potencies were compared.
Main Results:
- Both MDMA enantiomers competitively inhibited 5-HT catabolism by MAO-A (Ki = 22 µmol/L).
- MDMA exhibited mixed-type inhibition of phenethylamine catabolism by MAO-B.
- MDMA showed selective potency for MAO-A inhibition (IC50 = 44 µmol/L) over MAO-B (IC50 = 370 µmol/L).
Conclusions:
- MDMA preferentially inhibits MAO-A, which is expected to increase extracellular 5-HT levels.
- The rank order for MAO-A inhibition was MDMA > FLUOX > FEN.
- MDMA's actions do not appear to significantly involve MAO inhibition, unlike fenfluramine.