Multiple tryptamine-derived drugs have been developed to treat migraines, while trace amine-associated receptors are being explored as a potential treatment target for neuropsychiatric disorders.[12][13][14]
Endogenous levels of tryptamine in the mammalian brain are less than 100 ng per gram of tissue.[4][9] However, elevated levels of trace amines have been observed in patients with certain neuropsychiatric disorders taking medications, such as bipolar depression and schizophrenia.[15]
Mammalian gut microbiome
Tryptamine is relatively abundant in the gut and feces of humans and rodents.[2][10]Commensal bacteria, including Ruminococcus gnavus and Clostridium sporogenes in the gastrointestinal tract, possess the enzyme tryptophan decarboxylase, which aids in the conversion of dietary tryptophan to tryptamine.[2] Tryptamine is a ligand for gut epithelial serotonin type 4 (5-HT4) receptors and regulates gastrointestinal electrolyte balance through colonic secretions.[10]
Metabolism
Biosynthesis
To yield tryptamine in vivo, tryptophan decarboxylase removes the carboxylic acid group on the α-carbon of tryptophan.[4] Synthetic modifications to tryptamine can produce serotonin and melatonin; however, these pathways do not occur naturally as the main pathway for endogenous neurotransmitter synthesis.[16]
Catabolism
Monoamine oxidases A and B are the primary enzymes involved in tryptamine metabolism to produce indole-3-acetaldehyde, however it is unclear which isoform is specific to tryptamine degradation.[17]
Figure
Conversion of tryptophan to tryptamine, followed by its degradation to indole-3-acetaldehyde.
Tryptamine produced by mutualistic bacteria in the human gut activates serotonin GPCRs ubiquitously expressed along the colonic epithelium.[10] Upon tryptamine binding, the activated 5-HT4 receptor undergoes a conformational change which allows its Gs alpha subunit to exchange GDP for GTP, and its liberation from the 5-HT4 receptor and βγ subunit.[10] GTP-bound Gs activates adenylyl cyclase, which catalyzes the conversion of ATP into cyclic adenosine monophosphate (cAMP).[10] cAMP opens chloride and potassium ion channels to drive colonic electrolyte secretion and promote intestinal motility.[11][34]
Tryptamine promotes intestinal motility by activating serotonin receptors in the gut to increase colonic secretions.
Tryptamine is an agonist of the trace amine-associated receptor 1 (TAAR1).[21] It is a potent TAAR1 full agonist in rats, a weak TAAR1 full agonist in mice, and a very weak TAAR1 partial agonist in humans.[21] Tryptamine may act as a trace neuromodulator in some species via activation of TAAR1 signaling.[21][51]
TAAR1 agonists are under investigation as a novel treatment for neuropsychiatric conditions like schizophrenia, drug addiction, and depression.[9] The TAAR1 is expressed in brain structures associated with dopamine systems, such as the ventral tegmental area (VTA) and serotonin systems in the dorsal raphe nuclei (DRN).[9] Additionally, the human TAAR1 gene is localized at 6q23.2 on the human chromosome, which is a susceptibility locus for mood disorders and schizophrenia.[21] Activation of TAAR1 suggests a potential novel treatment for neuropsychiatric disorders, as TAAR1 agonists produce antipsychotic-like, anti-addictive, and antidepressant-like effects in animals.[52][21]
TAAR1 affinities and activational potencies of tryptamines[21][22]
Notes: (1) EC50 and Ki values are in nanomolar (nM). (2) EC50 reflects the concentration required to elicit 50% of the maximum TAAR1 response. (3) The smaller the Ki value, the stronger the compound binds to the receptor.
In animals, tryptamine, alone and/or in combination with a monoamine oxidase inhibitor (MAOI), produces behavioral changes such as hyperlocomotion and reversal of reserpine-induced behavioral depression.[53][30][56][57] In addition, it produces effects like hyperthermia, tachycardia, myoclonus, and seizures or convulsions, among others.[53][30][56][57] Findings on tryptamine and the head-twitch response in rodents have been mixed, with some studies reporting no effect,[58][59] some studies reporting induction of head twitches by tryptamine,[60][61][62] and others reporting that tryptamine actually antagonized 5-hydroxytryptophan (5-HTP)-induced head twitches.[56][58] Another study found that combination of tryptamine with an MAOI dose-dependently produced head twitches.[63] Head twitches in rodents are a behavioral proxy of psychedelic-like effects.[64][65] Many of the effects of tryptamine can be reversed by serotonin receptor antagonists like metergoline, metitepine (methiothepin), and cyproheptadine.[30][56][57][53] Conversely, the effects of tryptamine in animals are profoundly augmented by MAOIs due to inhibition of its metabolism.[30][57][53]
Tryptamine seems to also elevate prolactin and cortisol levels in animals and/or humans.[57]
The LD50 values of tryptamine in animals include 100mg/kg i.p. in mice, 500mg/kg s.c. in mice, and 223mg/kg i.p. in rats.[66]
Tryptamine is metabolized by monoamine oxidase (MAO) to form indole-3-acetic acid (IAA).[57][30][56] Its metabolism is described as extremely rapid and its elimination half-life and duration as very short.[30][6][54][55] In addition, its duration is described as shorter than that of dimethyltryptamine (DMT).[53] Brain tryptamine levels are increased up to 300-fold by MAOIs in animals.[56] In addition, the effects of exogenous tryptamine are strongly augmented by monoamine oxidase inhibitors (MAOIs).[30][56]
Tryptamine is excreted in urine and its rate of urinary excretion has been reported to be pH-dependent.[55][67][68]
The endogenous monoamine neurotransmittersserotonin (5-hydroxytryptamine or 5-HT) and melatonin (5-methoxy-N-acetyltryptamine), as well as trace amines like N-methyltryptamine (NMT), N,N-dimethyltryptamine (DMT), and bufotenin (N,N-dimethylserotonin), are derivatives of tryptamine.
All tryptamine derivatives possess a modified 2-aminoethyl group and/or the addition of a substituent on the indole.
A variety of drugs, including both naturally occurring and pharmaceutical substances, are derivatives of tryptamine. These include the tryptamine psychedelics like psilocybin, psilocin, DMT, and 5-MeO-DMT; tryptamine stimulants, entactogens, psychedelics, and/or antidepressants like α-methyltryptamine (αMT) and α-ethyltryptamine (αET); triptan antimigraine agents like sumatriptan; certain antipsychotics like oxypertine; and the sleep aid melatonin.
Drugs very closely related to tryptamines, but technically not tryptamines themselves, include certain triptans like avitriptan and naratriptan; the antipsychotics sertindole and tepirindole; and the MAOI antidepressants pirlindole and tetrindole.
↑ 7.07.1"Tryptamine: a metabolite of tryptophan implicated in various neuropsychiatric disorders". Metab Brain Dis8 (1): 1–44. March 1993. doi:10.1007/BF01000528. PMID8098507.
↑ 9.09.19.29.39.4Berry, Mark D.; Gainetdinov, Raul R.; Hoener, Marius C.; Shahid, Mohammed (2017-12-01). "Pharmacology of human trace amine-associated receptors: Therapeutic opportunities and challenges" (in en). Pharmacology & Therapeutics180: 161–180. doi:10.1016/j.pharmthera.2017.07.002. ISSN0163-7258. PMID28723415.
↑"Central serotonin receptors as targets for drug research". J Med Chem30 (1): 1–12. January 1987. doi:10.1021/jm00384a001. PMID3543362. "Table II. Affinities of Selected Phenalkylamines for 5-HT1 and 5-HT2 Binding Sites".
↑ 40.040.1"The effects of non-medically used psychoactive drugs on monoamine neurotransmission in rat brain". European Journal of Pharmacology559 (2–3): 132–137. March 2007. doi:10.1016/j.ejphar.2006.11.075. PMID17223101.
↑ 44.044.144.2"Pharmacological studies with endogenous enhancer substances: beta-phenylethylamine, tryptamine, and their synthetic derivatives". Progress in Neuro-Psychopharmacology & Biological Psychiatry28 (3): 421–427. May 2004. doi:10.1016/j.pnpbp.2003.11.016. PMID15093948.
↑ 45.045.145.2"Enhancer regulation/endogenous and synthetic enhancer compounds: a neurochemical concept of the innate and acquired drives". Neurochem Res28 (8): 1275–1297. August 2003. doi:10.1023/a:1024224311289. PMID12834268.
↑"Structure-activity studies leading to (-)1-(benzofuran-2-yl)-2-propylaminopentane, ((-)BPAP), a highly potent, selective enhancer of the impulse propagation mediated release of catecholamines and serotonin in the brain". Bioorg Med Chem9 (5): 1197–1212. May 2001. doi:10.1016/s0968-0896(01)00002-5. PMID11377178.
↑ 53.053.153.253.353.453.553.653.7Martin, W. R.; Sloan, J. W. (1977). "Pharmacology and Classification of LSD-like Hallucinogens". Drug Addiction II. Berlin, Heidelberg: Springer Berlin Heidelberg. pp. 305–368. doi:10.1007/978-3-642-66709-1_3. ISBN978-3-642-66711-4. "MARTIN and SLOAN (1970) found that intravenously infused tryptamine increased blood pressure, dilated pupils, enhanced the patellar reflex, and produced perceptual distortions. [...] Tryptamine, but not DMT, increases locomotor activity in the mouse, while both antagonize reserpine depression (V ANE et al., 1961). [...] In the rat, tryptamine causes backward locomotion, Straub tail, bradypnea and dyspnea, and clonic convulsions (TEDESCHI et al., 1959). [...] Tryptamine produces a variety of changes in the cat causing signs of sympathetic activation including mydriasis, retraction of nictitating membrane, piloerection, motor signs such as extension of limbs and convulsions and affective changes such as hissing and snarling (LAIDLAW, 1912). [...]"
↑ 54.054.154.254.354.4Shulgin, A. (1997). Tihkal: The Continuation. Transform Press. #53. T. ISBN978-0-9630096-9-2. https://books.google.com/books?id=jl_ik66IumUC. Retrieved 17 August 2024. "(with 250 mg, intravenously) "Tryptamine was infused intravenously over a period of up to 7.5 minutes. Physical changes included an increases in blood pressure, in the amplitude of the patellar reflex, and in pupillary diameter. The subjective changes are not unlike those seen with small doses of LSD. A point-by-point comparison between the tryptamine and LSD syndromes reveals a close similarity which is consistent with the hypothesis that tryptamine and LSD have a common mode of action.""
↑"Effects of 5,7-dihydroxytryptamine and 6-hydroxydopamine on head-twitch response induced by serotonin, p-chloroamphetamine, and tryptamine in mice". Psychopharmacology (Berl)95 (1): 124–131. 1988. doi:10.1007/BF00212780. PMID3133691.
↑Irons, Jane; Robinson, C. M.; Marsden, C. A. (1984). "5ht Involvement in Tryptamine Induced Behaviour in Mice". Neurobiology of the Trace Amines. Totowa, NJ: Humana Press. pp. 423–427. doi:10.1007/978-1-4612-5312-9_35. ISBN978-1-4612-9781-9.
↑Kozlenkov, Alexey; González-Maeso, Javier (2013). "Animal Models and Hallucinogenic Drugs". The Neuroscience of Hallucinations. New York, NY: Springer New York. pp. 253–277. doi:10.1007/978-1-4614-4121-2_14. ISBN978-1-4614-4120-5.