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The HTR of 5-HTP is is blocked by serotonin [[5-HT2A receptor|5-HT<sub>2A</sub> receptor]] [[receptor antagonist|antagonist]]s, which block the [[hallucinogen]]ic effects of serotonergic psychedelics in humans, is prevented by [[aromatic L-amino acid decarboxylase|aromatic <small>L</small>-amino acid decarboxylase]] (AAAD) [[aromatic L-amino acid decarboxylase inhibitor|inhibitor]]s, which convert 5-HTP into serotonin, and is potentiated by [[monoamine oxidase A]] (MAO-A) [[monoamine oxidase inhibitor|inhibitor]]s, which prevent the [[catabolism|degradation]] of serotonin and other [[endogenous]] [[substituted tryptamine|tryptamine]]s.<ref name="SchmidBohn2018">{{cite book | last=Schmid | first=Cullen L. | last2=Bohn | first2=Laura M. | title=5-HT2A Receptors in the Central Nervous System | chapter=βArrestins: Ligand-Directed Regulators of 5-HT2A Receptor Trafficking and Signaling Events | publisher=Springer International Publishing | publication-place=Cham | date=2018 | isbn=978-3-319-70472-2 | doi=10.1007/978-3-319-70474-6_2 | page=31–55}}</ref><ref name="KozlenkovGonzález-Maeso2013" /><ref name="JasterdelaFuenteRevengaGonzález-Maeso2022" /><ref name="SchmidBohn2010" /> In addition, the HTR of 5-HTP is abolished by [[indolethylamine N-methyltransferase|indolethylamine ''N''-methyltransferase]] (INMT) [[enzyme inhibitor|inhibitor]]s, which convert serotonin and other endogenous tryptamines into ''N''-[[methyl group|methylated]] tryptamines, such as [[N-Methylserotonin|''N''-methylserotonin]] (NMS; norbufotenin), [[bufotenin]] (5-hydroxy-''N'',''N''-dimethyltryptamine; 5-HO-DMT), and [[dimethyltryptamine|''N'',''N''-dimethyltryptamine]] (DMT).<ref name="KozlenkovGonzález-Maeso2013">{{cite book | last=Kozlenkov | first=Alexey | last2=González-Maeso | first2=Javier | title=The Neuroscience of Hallucinations | chapter=Animal Models and Hallucinogenic Drugs | publisher=Springer New York | publication-place=New York, NY | date=2013 | isbn=978-1-4614-4120-5 | doi=10.1007/978-1-4614-4121-2_14 | page=253–277}}</ref><ref name="HalberstadtGeyer2018">{{cite journal | vauthors = Halberstadt AL, Geyer MA | title = Effect of Hallucinogens on Unconditioned Behavior | journal = Curr Top Behav Neurosci | volume = 36 | issue = | pages = 159–199 | date = 2018 | pmid = 28224459 | pmc = 5787039 | doi = 10.1007/7854_2016_466 | url = }}</ref><ref name="SchmidBohn2010" /> These ''N''-methylated tryptamines are well-known for their psychedelic effects, whereas serotonin itself, without [[biotransformation]], does not seem to produce psychedelic effects.<ref name="KozlenkovGonzález-Maeso2013" /><ref name="KozlenkovGonzález-Maeso2013" /><ref name="SchmidBohn2010" /> 5-HTP has not been found to produce psychedelic effects in humans, which has been attributed to the high doses required to produce such effects.<ref name="KozlenkovGonzález-Maeso2013" /><ref name="JasterdelaFuenteRevengaGonzález-Maeso2022" /> The 5-HTP doses that produce the HTR in rodents are orders of magnitude higher than the doses of 5-HTP that have been used safely and therapeutically in humans.<ref name="JasterdelaFuenteRevengaGonzález-Maeso2022" />
The HTR of 5-HTP is is blocked by serotonin [[5-HT2A receptor|5-HT<sub>2A</sub> receptor]] [[receptor antagonist|antagonist]]s, which block the [[hallucinogen]]ic effects of serotonergic psychedelics in humans, is prevented by [[aromatic L-amino acid decarboxylase|aromatic <small>L</small>-amino acid decarboxylase]] (AAAD) [[aromatic L-amino acid decarboxylase inhibitor|inhibitor]]s, which convert 5-HTP into serotonin, and is potentiated by [[monoamine oxidase A]] (MAO-A) [[monoamine oxidase inhibitor|inhibitor]]s, which prevent the [[catabolism|degradation]] of serotonin and other [[endogenous]] [[substituted tryptamine|tryptamine]]s.<ref name="SchmidBohn2018">{{cite book | last=Schmid | first=Cullen L. | last2=Bohn | first2=Laura M. | title=5-HT2A Receptors in the Central Nervous System | chapter=βArrestins: Ligand-Directed Regulators of 5-HT2A Receptor Trafficking and Signaling Events | publisher=Springer International Publishing | publication-place=Cham | date=2018 | isbn=978-3-319-70472-2 | doi=10.1007/978-3-319-70474-6_2 | page=31–55}}</ref><ref name="KozlenkovGonzález-Maeso2013" /><ref name="JasterdelaFuenteRevengaGonzález-Maeso2022" /><ref name="SchmidBohn2010" /> In addition, the HTR of 5-HTP is abolished by [[indolethylamine N-methyltransferase|indolethylamine ''N''-methyltransferase]] (INMT) [[enzyme inhibitor|inhibitor]]s, which convert serotonin and other endogenous tryptamines into ''N''-[[methyl group|methylated]] tryptamines, such as [[N-Methylserotonin|''N''-methylserotonin]] (NMS; norbufotenin), [[bufotenin]] (5-hydroxy-''N'',''N''-dimethyltryptamine; 5-HO-DMT), and [[dimethyltryptamine|''N'',''N''-dimethyltryptamine]] (DMT).<ref name="KozlenkovGonzález-Maeso2013">{{cite book | last=Kozlenkov | first=Alexey | last2=González-Maeso | first2=Javier | title=The Neuroscience of Hallucinations | chapter=Animal Models and Hallucinogenic Drugs | publisher=Springer New York | publication-place=New York, NY | date=2013 | isbn=978-1-4614-4120-5 | doi=10.1007/978-1-4614-4121-2_14 | page=253–277}}</ref><ref name="HalberstadtGeyer2018">{{cite journal | vauthors = Halberstadt AL, Geyer MA | title = Effect of Hallucinogens on Unconditioned Behavior | journal = Curr Top Behav Neurosci | volume = 36 | issue = | pages = 159–199 | date = 2018 | pmid = 28224459 | pmc = 5787039 | doi = 10.1007/7854_2016_466 | url = }}</ref><ref name="SchmidBohn2010" /> These ''N''-methylated tryptamines are well-known for their psychedelic effects, whereas serotonin itself, without [[biotransformation]], does not seem to produce psychedelic effects.<ref name="KozlenkovGonzález-Maeso2013" /><ref name="KozlenkovGonzález-Maeso2013" /><ref name="SchmidBohn2010" /> 5-HTP has not been found to produce psychedelic effects in humans, which has been attributed to the high doses required to produce such effects.<ref name="KozlenkovGonzález-Maeso2013" /><ref name="JasterdelaFuenteRevengaGonzález-Maeso2022" /> The 5-HTP doses that produce the HTR in rodents are orders of magnitude higher than the doses of 5-HTP that have been used safely and therapeutically in humans.<ref name="JasterdelaFuenteRevengaGonzález-Maeso2022" />


The lack of the HTR and psychedelic effects with serotonin itself has been attributed to the fact that these effects appear to be dependent on activation of a population of [[intracellular]] 5-HT<sub>2A</sub> receptors expressed in [[cortex|cortical]] [[neuron]]s in the [[medial prefrontal cortex]] (mPFC) that lack the [[serotonin transporter]] (SERT).<ref name="Sapienza2023">{{cite journal | last=Sapienza | first=Jacopo | title=The Key Role of Intracellular 5-HT2A Receptors: A Turning Point in Psychedelic Research? | journal=Psychoactives | volume=2 | issue=4 | date=13 October 2023 | issn=2813-1851 | doi=10.3390/psychoactives2040018 | doi-access=free | pages=287–293}}</ref><ref name="VargasDunlapDong2023">{{cite journal | vauthors = Vargas MV, Dunlap LE, Dong C, Carter SJ, Tombari RJ, Jami SA, Cameron LP, Patel SD, Hennessey JJ, Saeger HN, McCorvy JD, Gray JA, Tian L, Olson DE | title = Psychedelics promote neuroplasticity through the activation of intracellular 5-HT2A receptors | journal = Science | volume = 379 | issue = 6633 | pages = 700–706 | date = February 2023 | pmid = 36795823 | pmc = 10108900 | doi = 10.1126/science.adf0435 | url = }}</ref> Serotonin itself is too [[hydrophilic]] to enter serotonergic neurons without the SERT, whereas serotonergic psychedelics and serotonin's ''N''-methylated [[structural analogue]]s are [[lipophilic]] and readily enter these neurons, in turn activating intracellular 5-HT<sub>2A</sub> receptors.<ref name="Sapienza2023" /><ref name="VargasDunlapDong2023" />
The lack of the HTR and psychedelic effects with serotonin itself has been attributed to the fact that these effects appear to be dependent on activation of a population of [[intracellular]] 5-HT<sub>2A</sub> receptors expressed in [[cortex|cortical]] [[neuron]]s in the [[medial prefrontal cortex]] (mPFC) that lack the [[serotonin transporter]] (SERT) and are inaccessible to serotonin.<ref name="Sapienza2023">{{cite journal | last=Sapienza | first=Jacopo | title=The Key Role of Intracellular 5-HT2A Receptors: A Turning Point in Psychedelic Research? | journal=Psychoactives | volume=2 | issue=4 | date=13 October 2023 | issn=2813-1851 | doi=10.3390/psychoactives2040018 | doi-access=free | pages=287–293}}</ref><ref name="VargasDunlapDong2023">{{cite journal | vauthors = Vargas MV, Dunlap LE, Dong C, Carter SJ, Tombari RJ, Jami SA, Cameron LP, Patel SD, Hennessey JJ, Saeger HN, McCorvy JD, Gray JA, Tian L, Olson DE | title = Psychedelics promote neuroplasticity through the activation of intracellular 5-HT2A receptors | journal = Science | volume = 379 | issue = 6633 | pages = 700–706 | date = February 2023 | pmid = 36795823 | pmc = 10108900 | doi = 10.1126/science.adf0435 | url = }}</ref> Serotonin itself is too [[hydrophilic]] to enter serotonergic neurons without the SERT, whereas serotonergic psychedelics and serotonin's ''N''-methylated [[metabolite]]s and [[structural analogue|analogue]]s are [[lipophilic]] and readily enter these neurons.<ref name="Sapienza2023" /><ref name="VargasDunlapDong2023" />


== See also ==
== See also ==

Revision as of 03:51, 11 September 2024

Not to be confused with 5-hydroxytryptamine.

5-Hydroxytryptophan
Skeletal formula
Ball-and-stick model
Names
IUPAC name
2-amino-3-(5-hydroxy-1H-indol-3-yl)propanoic acid
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.022.193 Edit this at Wikidata
KEGG
MeSH 5-Hydroxytryptophan
UNII
  • InChI=1S/C11H12N2O3/c12-9(11(15)16)3-6-5-13-10-2-1-7(14)4-8(6)10/h1-2,4-5,9,13-14H,3,12H2,(H,15,16)/t9-/m0/s1 checkY
    Key: LDCYZAJDBXYCGN-VIFPVBQESA-N checkY
  • InChI=1/C11H12N2O3/c12-9(11(15)16)3-6-5-13-10-2-1-7(14)4-8(6)10/h1-2,4-5,9,13-14H,3,12H2,(H,15,16)/t9-/m0/s1
    Key: LDCYZAJDBXYCGN-VIFPVBQEBZ
  • O=C(O)[C@@H](N)Cc2c1cc(O)ccc1[nH]c2
Properties
C11H12N2O3
Molar mass 220.228 g·mol−1
Density 1.484 g/mL
Melting point 298 to 300 °C (568 to 572 °F; 571 to 573 K)
Boiling point 520.6 °C (969.1 °F; 793.8 K)
Pharmacology
N06AX01 (WHO)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

5-Hydroxytryptophan (5-HTP), also known as oxitriptan, is a naturally occurring amino acid and chemical precursor as well as a metabolic intermediate in the biosynthesis of the neurotransmitter serotonin.

Uses

5-HTP is sold over the counter in the United States, France, Canada, Singapore, the Netherlands, and the United Kingdom as a dietary supplement for use as an antidepressant, appetite suppressant, and sleep aid. It is also marketed in many European countries for the indication of major depression under the trade names Cincofarm, Levothym, Levotonine, Oxyfan, Telesol, Tript-OH, and Triptum.[1]

A 2002 review concluded that although the data evaluated suggests that 5-HTP is more effective than placebo in the treatment of depression, the evidence was insufficient to be conclusive due to a lack of clinical data meeting the rigorous standards of the day.[2] More and larger studies using current methodologies are needed to determine if 5-HTP is truly effective in treating depression.[3][4] In small, controlled trials 5-HTP has also been reported to augment the antidepressant efficacy of the antidepressant clomipramine.[5][6][7] A 2020 meta-analysis found oral 5-HTP supplementation had a large effect size on depression symptom severity. However, the included studies were considered relatively weak and the methods and treatment duration varied between the seven studies examined.[8]

5-HTP use after MDMA

MDMA is an empathogenic-entactogenic and serotonergic psychotropic drug used primarily for recreational, though sometimes also therapeutic, purposes. Among users of MDMA, the serotonergic effects of the drug are often of particular interest and concern: After consuming MDMA, serotonin concentrations are greatly reduced in the brain. 5-HTP is necessary for serotonin production and its concentrations in the brain also decrease after taking MDMA.

Other usage

At high doses, or in combination with carbidopa, 5-HTP has been used to treat obesity (by promoting weight loss).[9][10]

In clinical trials of various design, 5-HTP has also been reported to treat fibromyalgia,[11] myoclonus,[12] migraine,[13] and cerebellar ataxia.[14] However, these clinical findings, as for all therapeutic findings with 5-HTP, are preliminary and need confirmation in larger trials.

Drawbacks

5-HTP's short half-life (<2h)[15] may inherently limit its therapeutic potential,[16] as systemic 5-HTP exposure levels will fluctuate substantially even with relatively frequent dosing. Such exposure fluctuations are usually associated with increased adverse event burdens resulting from Cmax (time to maximal systemic concentration) drug spikes, and decreased clinical efficacy resulting from sub-therapeutic exposure for large parts of the day, when taken as a single dose unit or at intervals significantly larger than Cmax. It has been proposed that 5-HTP dosage forms achieving prolonged delivery would be more effective,[16] as has been demonstrated many times with other pharmaceuticals with short durations of action.[17] For example, controlled release oxycodone (OxyContin) or morphine (MS-Contin) are intended to, via novel delivery mechanisms, permit pain relief for up to twelve hours with an active ingredient which only provides relief for 3–6 hours. However, the inherent variability amongst different people with respect to drug metabolism makes this task challenging.

Side effects

Potential side effects of 5-HTP include heartburn, stomach pain, nausea, vomiting, diarrhea, drowsiness, sexual problems, vivid dreams or nightmares, and muscle problems.[18]

Because 5-HTP has not been thoroughly studied in a clinical setting, possible side effects and interactions with other drugs are not well known. According to the US National Library of Medicine, 5-HTP has not been associated with serotonin syndrome or any serious adverse events in humans.[19] Across multiple studies, 5-HTP has also been reported to not cause any noticeable hematological or cardiovascular changes.[20] 5-HTP had also been associated with eosinophilia, but later studies have not found any causal connection.[21]

Interactions

When combined with antidepressants of the MAOI or SSRI class, very high parenteral doses of 5-HTP can cause acute serotonin syndrome in rats.[22][23] It is unclear if such findings have clinical relevance, as most drugs will cause serious adverse events or death in rodents at very high doses. In humans, 5-HTP has never been clinically associated with serotonin syndrome – although a case report suggests 5-HTP can precipitate mania when added to an MAOI.[24]

When combined with carbidopa (as a treatment for symptoms of Parkinson's disease), 5-HTP causes nausea and vomiting; however this can be alleviated via administration of granisetron.[25] As mentioned below under pharmacology, cases of scleroderma-like illness have been reported in patients using carbidopa and 5-HTP.[26]

Oral 5-HTP results in an increase in urinary 5-HIAA, a serotonin metabolite, indicating that 5-HTP is peripherally metabolized to serotonin, which is then metabolized. This might cause false positive results in tests looking for carcinoid syndrome.[27][28] Due to the conversion of 5-HTP into serotonin by the liver, there could be a risk of heart valve disease from serotonin's effect on the heart, as based on preclinical findings.[29][30] However, 5-HTP has not been associated with cardiac toxicity in humans.[21][20][19][31]

It has been suggested that 5-HTP may cause eosinophilia-myalgia syndrome (EMS), a serious condition which results in extreme muscle tenderness, myalgia, and blood abnormalities. However, there is evidence to show that EMS was likely caused by a contaminant in certain 5-HTP supplements.[32]

Production

5-HTP is produced from the amino acid tryptophan through the action of the enzyme tryptophan hydroxylase. Tryptophan hydroxylase is one of the biopterin-dependent aromatic amino acid hydroxylases. Production of 5-HTP is the rate-limiting step in 5-HT (serotonin) synthesis. 5-HTP is normally rapidly converted to 5-HT by amino acid decarboxylase.[33]

Absorption

After oral administration, 5-HTP is absorbed by the upper intestine.[15] The mode of absorption is not known, but presumably involves active transport via amino acid transporters. 5-HTP is adequately absorbed via oral cavity.[34] With a decarboxylase inhibitor, the bioavailability of 5-HTP can be higher than 50%.[35]

Pharmacology

The psychoactive action of 5-HTP is derived from its increase in production of serotonin in central nervous system tissue.[36]

Metabolic pathway from tryptophan to serotonin.
Metabolic pathway from tryptophan to serotonin.

Research shows that co-administration with carbidopa greatly increases plasma 5-HTP levels.[37] Other studies have indicated the risk of a scleroderma-like condition resulting from the combination of 5-HTP and carbidopa.[38]

Pharmacokinetics

5-HTP is rapidly absorbed with a tmax of ≈1.5 h, and rapidly eliminated with a half-life of ≈1.5 – 2 h. Co-administration of a decarboxylase inhibitor (e.g. carbidopa, benserazide) doubles the half-life of 5-HTP to ≈ 3 – 4 h,[39][15] and enhances exposure several-fold, depending on the dosing regimen.[15][40]

Metabolism

5-HTP is decarboxylated to serotonin (5-hydroxytryptamine or 5-HT) by the enzyme aromatic-L-amino-acid decarboxylase with the help of vitamin B6.[41] This reaction occurs both in nervous tissue and in the liver.[42] 5-HTP crosses the blood–brain barrier,[43] while 5-HT does not. Excess 5-HTP, especially when administered with vitamin B6, is thought to be metabolized and excreted.[44][45]

5-HTP AAAD Serotonin
 
PLP
 
 


Regulatory status

There are currently no approved drug products containing 5-HTP approved by the FDA.[46] All available 5-HTP products are nutraceuticals and are as such not regulated or verified for purity, integrity, or clinical efficacy or safety, mandating caution regarding human consumption.[47]

As of 25 August 2020, Hungary added 5-HTP to the controlled psychoactive substances list, prohibiting production, sale, import, storage and use, becoming the first country to do so.[48]

5-HTP slow-release

5-HTP's short half-life is impractical for chronic drug therapy. Research conducted at Duke University in mice have demonstrated that 5-HTP when administered as slow-release appears to gain drug properties.[49] Slow-release delivery attenuates or abolishes the peaks and valleys in 5-HTP exposure during treatment.[50] Slow-release delivery of 5-HTP markedly improved the safety profile of 5-HTP and conferred stable plasma exposure of 5-HTP and strong and sustained enhancement of brain serotonin function.[49] This discovery indicates that 5-HTP slow-release medications represent a new avenue for treatment of brain disorders responsive to serotonergic enhancement.

Dietary sources

See also: Tryptophan § Dietary sources

Though 5-HTP is found in food only in insignificant quantities, it is a chemical involved intermediately in the metabolism of tryptophan, an amino acid found in all unfractionated foods, with lower total amino acid content correlating with increased tryptophan absorption.[51]

The seeds of the Griffonia simplicifolia, a climbing shrub native to West Africa and Central Africa, are used as an herbal supplement for their 5-HTP content.[52][53][54] In one 2010 trial, Griffonia simplicifolia extract appeared to increase satiety in overweight women.[55]

Research

Psychedelic effects

5-HTP robustly produces the head-twitch response (HTR) in rodents when administered at relatively high doses.[56][57][58][59] Similarly, intracerebroventricular injection of serotonin, but not peripheral administration of serotonin, produces the HTR.[57][56][59] The HTR is induced by serotonergic psychedelics like lysergic acid diethylamide (LSD) and psilocybin and is a behavioral proxy of psychedelic effects.[60][56]

The HTR of 5-HTP is is blocked by serotonin 5-HT2A receptor antagonists, which block the hallucinogenic effects of serotonergic psychedelics in humans, is prevented by aromatic L-amino acid decarboxylase (AAAD) inhibitors, which convert 5-HTP into serotonin, and is potentiated by monoamine oxidase A (MAO-A) inhibitors, which prevent the degradation of serotonin and other endogenous tryptamines.[57][56][58][59] In addition, the HTR of 5-HTP is abolished by indolethylamine N-methyltransferase (INMT) inhibitors, which convert serotonin and other endogenous tryptamines into N-methylated tryptamines, such as N-methylserotonin (NMS; norbufotenin), bufotenin (5-hydroxy-N,N-dimethyltryptamine; 5-HO-DMT), and N,N-dimethyltryptamine (DMT).[56][61][59] These N-methylated tryptamines are well-known for their psychedelic effects, whereas serotonin itself, without biotransformation, does not seem to produce psychedelic effects.[56][56][59] 5-HTP has not been found to produce psychedelic effects in humans, which has been attributed to the high doses required to produce such effects.[56][58] The 5-HTP doses that produce the HTR in rodents are orders of magnitude higher than the doses of 5-HTP that have been used safely and therapeutically in humans.[58]

The lack of the HTR and psychedelic effects with serotonin itself has been attributed to the fact that these effects appear to be dependent on activation of a population of intracellular 5-HT2A receptors expressed in cortical neurons in the medial prefrontal cortex (mPFC) that lack the serotonin transporter (SERT) and are inaccessible to serotonin.[62][63] Serotonin itself is too hydrophilic to enter serotonergic neurons without the SERT, whereas serotonergic psychedelics and serotonin's N-methylated metabolites and analogues are lipophilic and readily enter these neurons.[62][63]

See also

References

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