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.
Monoamine neurotransmitters are neurotransmitters and neuromodulators that contain one amino group connected to an aromatic ring by a two-carbon chain (such as -CH2-CH2-). Examples are dopamine, norepinephrine and serotonin.
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.
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.
Tyramine, also known under several other names, is a naturally occurring trace amine derived from the amino acid tyrosine. Tyramine acts as a catecholamine releasing agent. Notably, it is unable to cross the blood-brain barrier, resulting in only non-psychoactive peripheral sympathomimetic effects following ingestion. A hypertensive crisis can result, however, from ingestion of tyramine-rich foods in conjunction with the use of monoamine oxidase inhibitors (MAOIs).
Selegiline, also known as L-deprenyl and sold under the brand names Eldepryl, Emsam, Selgin, among other names, is a medication which is used in the treatment of Parkinson's disease and major depressive disorder. It is provided in the form of a capsule or tablet taken by mouth or orally disintegrating tablets taken on the tongue for Parkinson's disease and as a patch applied to skin for depression.
Isocarboxazid is a non-selective, irreversible monoamine oxidase inhibitor (MAOI) of the hydrazine class used as an antidepressant. Along with phenelzine and tranylcypromine, it is one of only three classical MAOIs still available for clinical use in the treatment of psychiatric disorders in the United States, though it is not as commonly employed in comparison to the others.
Moclobemide, sold under the brand names Amira, Aurorix, Clobemix, Depnil and Manerix among others, is a reversible inhibitor of monoamine oxidase A (RIMA) drug primarily used to treat depression and social anxiety. It is not approved for use in the United States, but is approved in other Western countries such as Canada, the UK and Australia. It is produced by affiliates of the Hoffmann–La Roche pharmaceutical company. Initially, Aurorix was also marketed by Roche in South Africa, but was withdrawn after its patent rights expired and Cipla Medpro's Depnil and Pharma Dynamic's Clorix became available at half the cost.
Levomethamphetamine is the levorotatory (L-enantiomer) form of methamphetamine. Levomethamphetamine is a sympathomimetic vasoconstrictor that is the active ingredient in some over-the-counter (OTC) nasal decongestant inhalers in the United States.
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).
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.
Oxidative deamination is a form of deamination that generates α-keto acids and other oxidized products from amine-containing compounds, and occurs primarily in the liver. Oxidative deamination is stereospecific, meaning it contains different stereoisomers as reactants and products; this process is either catalyzed by L or D- amino acid oxidase and L-amino acid oxidase is present only in the liver and kidney. Oxidative deamination is an important step in the catabolism of amino acids, generating a more metabolizable form of the amino acid, and also generating ammonia as a toxic byproduct. The ammonia generated in this process can then be neutralized into urea via the urea cycle.
Benzofuranylpropylaminopentane is a drug with an unusual monoamine-release potentiating mechanism of action. It can loosely be grouped with the stimulant or antidepressant drug families, but its mechanism of action is quite different.
Monoamine oxidase B, also known as MAOB, is an enzyme that in humans is encoded by the MAOB gene.
Safinamide is a drug used as an add-on treatment for Parkinson's disease with "off" episodes; it has multiple modes of action, including the inhibition of monoamine oxidase B.
Bifemelane (INN) (Alnert, Celeport), or bifemelane hydrochloride (JAN), also known as 4-(O-benzylphenoxy)-N-methylbutylamine, is an antidepressant and cerebral activator that is widely used in the treatment of cerebral infarction patients with depressive symptoms in Japan, and in the treatment of senile dementia as well. It also appears to be useful in the treatment of glaucoma. Bifemelane acts as a monoamine oxidase inhibitor (MAOI) of both isoenzymes, with competitive (reversible) inhibition of MAO-A (Ki = 4.20 μM) (making it a reversible inhibitor of monoamine oxidase A (RIMA)) and non-competitive (irreversible) inhibition of MAO-B (Ki = 46.0 μM), and also acts (weakly) as a norepinephrine reuptake inhibitor. The drug has nootropic, neuroprotective, and antidepressant-like effects in animal models, and appears to enhance the cholinergic system in the brain.
Mofegiline (MDL-72,974) is a selective, irreversible inhibitor of monoamine oxidase B (MAO-B) and semicarbazide-sensitive amine oxidase (SSAO) which was under investigation for the treatment of Parkinson's disease and Alzheimer's disease, but was never marketed.
Moussa B. H. Youdim is an internationally renowned Israeli neuroscientist specializing in neurochemistry and neuropharmacology. He is the discoverer of both monoamine oxidase (MAO) B inhibitors l-deprenyl (Selegiline) and rasagiline (Azilect) as anti-Parkinson drugs which possess neuroprotective activities. He is currently professor emeritus at Technion - Faculty of Medicine and President of Youdim Pharmaceuticals.
Acetryptine (INN), also known as 5-acetyltryptamine (5-AT), is a drug described as an antihypertensive agent which was never marketed. Structurally, acetryptine is a substituted tryptamine, and is closely related to other substituted tryptamines like serotonin (5-hydroxytryptamine). It was developed in the early 1960s. The binding of acetryptine to serotonin receptors does not seem to have been well-investigated, although it was assessed at the 5-HT1A and 5-HT1D receptors and found to bind to them with high affinity. The drug may also act as a monoamine oxidase inhibitor (MAOI); specifically, as an inhibitor of MAO-A.
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