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. They are also used to treat panic disorder, social anxiety disorder, Parkinson's disease, and several other disorders.
Monoamine oxidases (MAO) are a family of enzymes that catalyze the oxidation of monoamines, employing oxygen to clip off their amine group. They are found bound to the outer membrane of mitochondria in most cell types of the body. The first such enzyme was discovered in 1928 by Mary Bernheim in the liver and was named tyramine oxidase. The MAOs belong to the protein family of flavin-containing amine oxidoreductases.
Phenethylamine (PEA) is an organic compound, natural monoamine alkaloid, and trace amine, which acts as a central nervous system stimulant in humans. In the brain, phenethylamine regulates monoamine neurotransmission by binding to trace amine-associated receptor 1 (TAAR1) and inhibiting vesicular monoamine transporter 2 (VMAT2) in monoamine neurons. To a lesser extent, it also acts as a neurotransmitter in the human central nervous system. In mammals, phenethylamine is produced from the amino acid L-phenylalanine by the enzyme aromatic L-amino acid decarboxylase via enzymatic decarboxylation. In addition to its presence in mammals, phenethylamine is found in many other organisms and foods, such as chocolate, especially after microbial fermentation.
Myristicin is a naturally occurring compound found in common herbs and spices, such as nutmeg. It is an insecticide, and has been shown to enhance the effectiveness of other insecticides.
Tranylcypromine, sold under the brand name Parnate among others, is a monoamine oxidase inhibitor (MAOI). More specifically, tranylcypromine acts as nonselective and irreversible inhibitor of the enzyme monoamine oxidase (MAO). It is used as an antidepressant and anxiolytic agent in the clinical treatment of mood and anxiety disorders, respectively.
Harmala alkaloids are several alkaloids that increase effects of reward system neurotransmitter dopamine by acting as monoamine oxidase inhibitors (MAOIs). These alkaloids are found in the seeds of Peganum harmala, as well as leaves of tobacco and coffee beans. The alkaloids include harmine, harmaline, harmalol, and their derivatives, which have similar chemical structures, hence the name "harmala alkaloids". These alkaloids are of interest for their use in Amazonian shamanism, where they are derived from other plants. Harmine, once known as telepathine and banisterine, is a naturally occurring beta-carboline alkaloid that is structurally related to harmaline, and also found in the vine Banisteriopsis caapi. Tetrahydroharmine is also found in B. caapi and P. harmala. Dr. Alexander Shulgin has suggested that harmine may be a breakdown product of harmaline. Harmine and harmaline are reversible inhibitors of monoamine oxidase A (RIMAs). They can stimulate the central nervous system by inhibiting the metabolism of monoamine compounds such as serotonin and norepinephrine.
Rhodiola rosea is a perennial flowering plant in the family Crassulaceae. It grows naturally in wild Arctic regions of Europe, Asia, and North America, and can be propagated as a groundcover.
Iproniazid is a non-selective, irreversible monoamine oxidase inhibitor (MAOI) of the hydrazine class. It is a xenobiotic that was originally designed to treat tuberculosis, but was later most prominently used as an antidepressant drug. However, it was withdrawn from the market because of its hepatotoxicity. The medical use of iproniazid was discontinued in most of the world in the 1960s, but remained in use in France until its discontinuation in 2015.
Clorgiline (INN), or clorgyline (BAN), is a monoamine oxidase inhibitor (MAOI) structurally related to pargyline which is described as an antidepressant. Specifically, it is an irreversible and selective inhibitor of monoamine oxidase A (MAO-A). Clorgiline was never marketed, but it has found use in scientific research. It has been found to bind with high affinity to the σ1 receptor (Ki = 3.2 nM) and with very high affinity to the I2 imidazoline receptor (Ki = 40 pM).
Monoamine oxidase A, also known as MAO-A, is an enzyme that in humans is encoded by the MAOA gene. This gene is one of two neighboring gene family members that encode mitochondrial enzymes which catalyze the oxidative deamination of amines, such as dopamine, norepinephrine, and serotonin. A mutation of this gene results in Brunner syndrome. This gene has also been associated with a variety of other psychiatric disorders, including antisocial behavior. Alternatively spliced transcript variants encoding multiple isoforms have been observed.
Rasagiline is an irreversible inhibitor of monoamine oxidase-B used as a monotherapy to treat symptoms in early Parkinson's disease or as an adjunct therapy in more advanced cases.
3,4-Dimethoxyphenethylamine (DMPEA) is a chemical compound of the phenethylamine class. It is an analogue of the major human neurotransmitter dopamine where the 3- and 4-position hydroxy groups have been replaced with methoxy groups. It is also closely related to mescaline which is 3,4,5-trimethoxyphenethylamine.
Monoamine oxidase B, also known as MAO-B, is an enzyme that in humans is encoded by the MAOB gene.
Pheniprazine is an irreversible and nonselective monoamine oxidase inhibitor (MAOI) of the hydrazine chemical class that was used as an antidepressant in the 1960s. It was also used in the treatment of angina pectoris and schizophrenia. Pheniprazine has been largely discontinued due to toxicity concerns such as jaundice, amblyopia, and optic neuritis.
4-Benzylpiperidine is a drug and research chemical used in scientific studies. It acts as a monoamine releasing agent with 20- to 48-fold selectivity for releasing dopamine versus serotonin. It is most efficacious as a releaser of norepinephrine, with an EC50 of 109 nM (DA), 41.4 nM (NE) and 5246 nM (5-HT). It has a fast onset of action and a short duration. It also functions as a monoamine oxidase inhibitor (MAOI) with preference for MAO-A.
3-Fluoroamphetamine is a stimulant drug from the amphetamine family which acts as a monoamine releaser with similar potency to methamphetamine but more selectivity for dopamine and norepinephrine release over serotonin. It is self-administered by mice to a similar extent to related drugs such as 4-fluoroamphetamine and 3-methylamphetamine.
Herbacetin is a flavonol, a type of flavonoid.
Almoxatone (MD-780,236) is a selective and reversible inhibitor of MAO-B. It was patented as an antidepressant and antiparkinsonian agent but was never marketed.
Thiopropamine is a stimulant drug which is an analogue of amphetamine where the phenyl ring has been replaced by thiophene. It has similar stimulant effects to amphetamine but with around one third the potency. The N-methyl and thiophen-3-yl analogues are also known and are somewhat more potent, though still generally weaker than the corresponding amphetamines.
Substituted tryptamines, or serotonin analogues, are organic compounds which may be thought of as being derived from tryptamine itself. The molecular structures of all tryptamines contain an indole ring, joined to an amino (NH2) group via an ethyl (−CH2–CH2−) sidechain. In substituted tryptamines, the indole ring, sidechain, and/or amino group are modified by substituting another group for one of the hydrogen (H) atoms.
