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Monoamine oxidase inhibitors (MAOIs) are a class of drugs that inhibit the activity of one or both monoamine oxidase enzymes: monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B). They are best known as effective antidepressants , especially for treatment-resistant depression and atypical depression . [ 1 ]
A few endogenous MAEs have been identified, including the trace amines β-phenylethylamine (PEA), tyramine, and tryptamine. [1] [11] At a concentration of 16 μM (1.6 × 10 −5 M), β-phenylethylamine has been shown to act as a MAE for norepinephrine (2.6-fold increase), dopamine (1.3-fold increase), and serotonin (2.3-fold increase) in the rat brainstem in vitro.
Monoamine oxidases (MAO) (EC 1.4.3.4) are a family of enzymes that catalyze the oxidation of monoamines, employing oxygen to clip off their amine group. [ 1 ] [ 2 ] They are found bound to the outer membrane of mitochondria in most cell types of the body.
In addition to its MRA activity, 4-MTDMA is a fairly potent monoamine oxidase A (MAO-A) inhibitor, with an IC 50 Tooltip half-maximal inhibitory concentration of 2,100 nM. [4] [5] Potent monoamine oxidase inhibition by amphetamines has been associated with dangerous and sometimes fatal toxicity in humans. [4] [5]
Monoamine oxidase A, also known as MAO-A, is an enzyme (E.C. 1.4.3.4) that in humans is encoded by the MAOA gene. [ 5 ] [ 6 ] This gene is one of two neighboring gene family members that encode mitochondrial enzymes which catalyze the oxidative deamination of amines , such as norepinephrine , serotonin and tyramine .
It is most efficacious as a releaser of norepinephrine, with an EC 50 of 109 nM (DA), 41.4 nM (NE), and 5,246 nM . [ 2 ] It also functions as a weak monoamine oxidase inhibitor (MAOI) ( IC 50 Tooltip half-maximal inhibitory concentration = 130 μM for MAO-A Tooltip monoamine oxidase A and 750 μM for MAO-B Tooltip monoamine oxidase B ).
Although it has been estimated that a single 300 mg dose of moclobemide inhibits 80% of monoamine oxidase-A (MAO-A) and 20-30% of MAO-B, [100] studies evaluating brain occupancy of MAO-A enzymes have shown dosages of 600 mg to only inhibit 74% of MAO-A enzymes [101] and dosages in the 900–1200 mg range to inhibit slightly less MAO-A than ...
Tryptolines are competitive selective inhibitors of the enzyme monoamine oxidase type A (). 5-Hydroxytryptoline and 5-methoxytryptoline (pinoline) are the most active monoamine oxidase inhibitors (MAOIs) with IC 50 s of 0.5 μM and 1.5 μM respectively.