Tyramine, found in several foods, is metabolized by MAO. Ingestion and absorption of tyramine causes extensive release of norepinephrine, which can rapidly increase blood pressure to the point of causing hypertensive crisis.
Tyramine is a common component in many foods, and is normally rapidly metabolized by MAO-A. Individuals not taking MAOIs may consume at least 2 grams of tyramine in a meal and not experience an increase in blood pressure, whereas those taking MAOIs such as tranylcypromine may experience a sharp increase in blood pressure following consumption of as little as 10 mg of tyramine, which can lead to hypertensive crisis.[9][8]
Of note, there has not been found to be a correlation between sex and age below 65 regarding incidence of adverse effects.[10]
Tranylcypromine is not associated with weight gain and has a low risk for hepatotoxicity compared to the hydrazine MAOIs.[10][7]
It is generally recommended that MAOIs be discontinued prior to anesthesia; however, this creates a risk of recurrent depression. In a retrospective observational cohort study, patients on tranylcypromine undergoing general anesthesia had a lower incidence of intraoperative hypotension, while there was no difference between patients not taking an MAOI regarding intraoperative incidence of bradycardia, tachycardia, or hypertension.[11] The use of indirect sympathomimetic drugs or drugs affecting serotonin reuptake, such as meperidine or dextromethorphan poses a risk for hypertension and serotonin syndrome respectively; alternative agents are recommended.[12][13] Other studies have come to similar conclusions.[10] Pharmacokinetic interactions with anesthetics are unlikely, given that tranylcypromine is a high-affinity substrate for CYP2A6 and does not inhibit CYP enzymes at therapeutic concentrations.[9]
Tranylcypromine abuse has been reported at doses ranging from 120–600 mg per day.[6][14][10] It is thought that higher doses have more amphetamine-like effects and abuse is promoted by the fast onset and short half-life of tranylcypromine.[10]
Cases of suicidal ideation and suicidal behaviours have been reported during tranylcypromine therapy or early after treatment discontinuation.[6]
Symptoms of tranylcypromine overdose are generally more intense manifestations of its usual effects.[6]
Interactions
In addition to contraindicated concomitant medications, tranylcypromine inhibits CYP2A6, which may reduce the metabolism and increase the toxicity of substrates of this enzyme, such as:[8]
Tranylcypromine acts as a nonselective and irreversible inhibitor of monoamine oxidase.[2] Regarding the isoforms of monoamine oxidase, it shows slight preference for the MAOBisoenzyme over MAOA.[9] This leads to an increase in the availability of monoamines, such as serotonin, norepinephrine, and dopamine, as well as a marked increase in the availability of trace amines, such as tryptamine, octopamine, and phenethylamine.[9][8] The clinical relevance of increased trace amine availability is unclear.
Tranylcypromine has also been shown to inhibit the histone demethylase, BHC110/LSD1. Tranylcypromine inhibits this enzyme with an IC50 < 2 μM, thus acting as a small molecule inhibitor of histone demethylation with an effect to derepress the transcriptional activity of BHC110/LSD1 target genes.[15] The clinical relevance of this effect is unknown.
Tranylcypromine has been found to inhibit CYP46A1 at nanomolar concentrations.[16] The clinical relevance of this effect is unknown.
Mechanism of tranylcypromine inhibition of MAO.[17]
Pharmacokinetics
Tranylcypromine reaches its maximum concentration (tmax) within 1–2 hours.[9] After a 20 mg dose, plasma concentrations reach at most 50-200 ng/mL.[9] While its half-life is only about 2 hours, its pharmacodynamic effects last several days to weeks due to irreversible inhibition of MAO.[9]
Metabolites of tranylcypromine include 4-hydroxytranylcypromine, N-acetyltranylcypromine, and N-acetyl-4-hydroxytranylcypromine, which are less potent MAO inhibitors than tranylcypromine itself.[9]Amphetamine was once thought to be a metabolite of tranylcypromine, but has not been shown to be.[9][18][8]
Tranylcypromine inhibits CYP2A6 at therapeutic concentrations.[8]
Tranylcypromine was originally developed as an analog of amphetamine.[2][9] Although it was first synthesized in 1948,[20] its MAOI action was not discovered until 1959. Precisely because tranylcypromine was not, like isoniazid and iproniazid, a hydrazine derivative, its clinical interest increased enormously, as it was thought it might have a more acceptable therapeutic index than previous MAOIs.[21]
The drug was introduced by Smith, Kline and French in the United Kingdom in 1960, and approved in the United States in 1961.[22] It was withdrawn from the market in February 1964 due to a number of patient deaths involving hypertensive crises with intracranial bleeding. However, it was reintroduced later that year with more limited indications and specific warnings of the risks.[23][9][8]
Research
Tranylcypromine is known to inhibit LSD1, an enzyme that selectively demethylates two lysines found on histone H3.[15][9][24] Genes promoted downstream of LSD1 are involved in cancer cell growth and metastasis, and several tumor cells express high levels of LSD1.[24] Tranylcypromine analogues with more potent and selective LSD1 inhibitory activity are being researched in the potential treatment of cancers.[24][25]
Tranylcypromine may have neuroprotective properties applicable to the treatment of Parkinson's disease, similar to the MAO-B inhibitors selegiline and rasagiline.[26][7] As of 2017, only one clinical trial in Parkinsonian patients has been conducted, which found some improvement initially and only slight worsening of symptoms after a 1.5 year followup.[7]
^ abcdefWilliams DA (2007). "Antidepressants". In Foye, William O., Lemke, Thomas L., Williams, David A. (eds.). Foye's Principles of Medicinal Chemistry. Hagerstwon, USA: Lippincott Williams & Wilkins. pp. 590–1. ISBN978-0-7817-6879-5.
^Baker GB, Urichuk LJ, McKenna KF, Kennedy SH (June 1999). "Metabolism of monoamine oxidase inhibitors". Cellular and Molecular Neurobiology. 19 (3): 411–26. doi:10.1023/a:1006901900106. PMID10319194. S2CID21380176.
^Baldessarini RJ (2005). "17. Drug therapy of depression and anxiety disorders". In Brunton LL, Lazo JS, Parker KL (eds.). Goodman & Gilman's The Pharmacological Basis of Therapeutics. New York: McGraw-Hill. ISBN978-0-07-142280-2.
^Blom-Peters L, Lamy M (1993). "Monoamine oxidase inhibitors and anesthesia: an updated literature review". Acta Anaesthesiologica Belgica. 44 (2): 57–60. PMID8237297.
^Le Gassicke J, Ashcroft GW, Eccleston D, Evans JI, Oswald I, Ritson EB (1 April 1965). "The Clinical State, Sleep and Amine Metabolism of a Tranylcypromine ('Parnate') Addict". The British Journal of Psychiatry. 111 (473): 357–364. doi:10.1192/bjp.111.473.357.
^Sherry RL, Rauw G, McKenna KF, Paetsch PR, Coutts RT, Baker GB (December 2000). "Failure to detect amphetamine or 1-amino-3-phenylpropane in humans or rats receiving the MAO inhibitor tranylcypromine". Journal of Affective Disorders. 61 (1–2): 23–9. doi:10.1016/s0165-0327(99)00188-3. PMID11099737.
^A US patent 4016204 A, Vithal Jagannath Rajadhyaksha, "Method of synthesis of trans-2-phenylcyclopropylamine", published 1977-04-05, assigned to Nelson Research & Development Company
^Burger A, Yost WL (1948). "Arylcycloalkylamines. I. 2-Phenylcyclopropylamine". Journal of the American Chemical Society. 70 (6): 2198–2201. doi:10.1021/ja01186a062.
^López-Muñoz F, Alamo C (2009). "Monoaminergic neurotransmission: the history of the discovery of antidepressants from 1950s until today". Current Pharmaceutical Design. 15 (14): 1563–86. doi:10.2174/138161209788168001. PMID19442174.
^ abcZheng YC, Yu B, Jiang GZ, Feng XJ, He PX, Chu XY, et al. (2016). "Irreversible LSD1 Inhibitors: Application of Tranylcypromine and Its Derivatives in Cancer Treatment". Current Topics in Medicinal Chemistry. 16 (19): 2179–88. doi:10.2174/1568026616666160216154042. PMID26881714.
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![Mechanism of tranylcypromine inhibition of MAO.[17]](http://upload.wikimedia.org/wikipedia/commons/thumb/3/30/Tranylcypromine-MAO-inhibiton.png/1200px-Tranylcypromine-MAO-inhibiton.png)
![Synthesis of tranylcypromine[19]](http://upload.wikimedia.org/wikipedia/commons/thumb/f/fb/Tranylcypromine-synth.png/2000px-Tranylcypromine-synth.png)
