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Monoamine oxidase inhibitors (MAOIs) are chemicals which inhibit the activity of the monoamine oxidase enzyme family. They have a long history of use as medications prescribed for the treatment of depression. They are also used in the treatment of Parkinson's disease and several other disorders.
Mechanism of action
MAOIs act by inhibiting the activity of monoamine oxidase, preventing the breakdown of monoamine neurotransmitters and thereby increasing their availability. There are two isoforms of monoamine oxidase, MAO-A and MAO-B. MAO-A preferentially deaminates serotonin, melatonin, adrenaline, and noradrenaline. MAO-B preferentially deaminates phenylethylamine and trace amines. Dopamine is equally deaminated by both types.
The early MAOIs inhibit monoamine oxidase irreversibly. When they react with monoamine oxidase, they permanently deactivate it and the enzyme cannot function until it has been replaced by the body, which can take about two weeks. A few newer MAOIs (known as RIMAs) are reversible, meaning that they are able to detach from the enzyme to facilitate usual catabolism of the substrate.
The MAOIs are infamous for their numerous drug interactions, including the following kinds of substances:
- Substances that are metabolized by monoamine oxidase, as they can be boosted by up to several fold
- Substances that increase serotonin, noradrenaline, or dopamine activity as too much of any of these neurochemicals can result in severe acute consequences including serotonin syndrome, hypertensive crisis, and psychosis. Such substances include phenethylamines, amphetamines, tryptamines, lysergamides, and monoamine reuptake inhibitors
- Specific foods with high amounts of tyramine:
- Aged cheese (gouda, camembert, cheddar)
- Aged, smoked or pickled meats
- Aged or fermented soy and yeast products (soy sauce, teriyaki sauce)
- Overripe fruits
- San Pedro cactuses (Peyote cactus does not contain high amount of tyramine)
- Other monoamine oxidase inhibitors
- Phenelzine (common brand name Nardil)
- Tranylcypromine (common brand name Parnate)
- Isocarboxazid (common brand name Marplan)
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- McCabe-Sellers BJ, Staggs CG, and Bogle ML. Tyramine in foods and monoamine oxidase inhibitor drugs: A crossroad where medicine, nutrition, pharmacy and food industry converge; J Food Comp Anal. 2006; 19:S58. | http://naldc.nal.usda.gov/download/7351/PDF