Chemistry:AM404
AM404, also known as N-arachidonoylphenolamine,[1][2] is an active metabolite of paracetamol (acetaminophen), responsible for all or part of its analgesic action[3] and anticonvulsant effects.[4] Chemically, it is the amide formed from 4-aminophenol and arachidonic acid. AM404 is one of the AM cannabinoids discovered by Alexandros Makriyannis and his team.
Pharmacokinetics
AM404 is found in the brains of animals and cerebrospinal fluid of humans taking paracetamol. It is produced from 4-aminophenol by the action of FAAH.[5][6]
It is also generated in vitro from 4-aminophenol by peripheral sensory neurons.[7]
Pharmacodynamics
AM404 is a weak agonist of cannabinoid receptors CB1 and CB2, an inhibitor of endocannabinoid transporter, a potent activator of TRPV1,[5] and a very potent inhibitor of Nav1.8 and 1.7.[7] It weakly inhibits cyclooxygenases (COX).[8] The endocannbinoid system, TRPV1, and COX are involved in pain and thermoregulatory pathways.[8] Nav1.8 and 1.7 are involved in peripheral pain perception.[7]
CB1 and CB2
AM404 is a weak agonist of cannabinoid receptors CB1 and CB2.[5]
Endocannabinoid concentration
It is established that AM404 increases concentrations of the endogenous cannabinoid anandamide within the synaptic cleft, contributing to its analgesic activity.[8] This has been well characterised as involving endocannabinoid transporter inhibition, but the precise transporter responsible is yet to be determined.[8][9][10]
AM404 was originally reported to be an endogenous cannabinoid reuptake inhibitor, preventing the transport of anandamide and other related compounds back from the synaptic cleft, much in the same way that common selective serotonin reuptake inhibitor (SSRI) antidepressants prevent the reuptake of serotonin. Earlier work on the mechanism of AM404 suggested that the inhibition of fatty acid amide hydrolase (FAAH) by AM404 was responsible for all of its attributed reuptake properties, since intracellular FAAH hydrolysis of anandamide changes the intra/extracellular anandamide equilibrium.[10] However, this is not the case, as newer research on FAAH knockout mice has found that brain cells internalize anandamide through a selective transport mechanism which is independent of FAAH activity.[9] It is this mechanism which is inhibited by AM404.
TRPV1
AM404 is also a TRPV1 agonist[11] and inhibitor of cyclooxygenase COX-1 and COX-2, thus attenuating prostaglandin synthesis.
The anticonvulsant action of AM404 is mediated through TRPV1, according to Suemaru et al. (2018),[12] rebutting a previous explanation involving CB1 receptors.[4]
Sodium channels
AM404 has also been reported to inhibit voltage-gated sodium channels in the peripheral nervous system, with much greater potency than its effects at previously proposed targets. Specifically, it inhibits Nav1.8 and 1.7 channels at nanomolar concentrations in vitro.[7] AM404 injected into the hind paw of rats increase the pain threshold for the treated paw, but not the untreated paw, confirming the peripheral nature of this effect. It also lowers pain responses in a few other in vivo models when injected directly into the affected area. Other tested metabolites of paracetamol do not block pain-sensing sodium channels in vitro.[13]
See also
- VDM-11 (2-methyl analogue)
References
- ↑ "Oral acetaminophen-induced spinal 5-hydroxytriyptamine release produces analgesic effects in the rat formalin test". Biomedicine & Pharmacotherapy 146. February 2022. doi:10.1016/j.biopha.2021.112578. PMID 34959121.
- ↑ "Novel bioactive metabolites of dipyrone (metamizol)". Bioorganic & Medicinal Chemistry 20 (1): 101–107. January 2012. doi:10.1016/j.bmc.2011.11.028. PMID 22172309.
- ↑ "The analgesic activity of paracetamol is prevented by the blockade of cannabinoid CB1 receptors". European Journal of Pharmacology 531 (1–3): 280–281. February 2006. doi:10.1016/j.ejphar.2005.12.015. PMID 16438952.
- ↑ 4.0 4.1 "Acetaminophen inhibits status epilepticus in cultured hippocampal neurons". NeuroReport 22 (1): 15–18. January 2011. doi:10.1097/WNR.0b013e3283413231. PMID 21037491.
- ↑ 5.0 5.1 5.2 "Acetaminophen from liver to brain: New insights into drug pharmacological action and toxicity". Pharmacological Research 109: 119–31. July 2016. doi:10.1016/j.phrs.2016.02.020. PMID 26921661.
- ↑ "First evidence of the conversion of paracetamol to AM404 in human cerebrospinal fluid". J Pain Res 10: 2703–2709. 2017. doi:10.2147/JPR.S143500. PMID 29238213.
- ↑ 7.0 7.1 7.2 7.3 "The analgesic paracetamol metabolite AM404 acts peripherally to directly inhibit sodium channels". Proceedings of the National Academy of Sciences of the United States of America 122 (23). June 2025. doi:10.1073/pnas.2413811122. PMID 40465624.
- ↑ 8.0 8.1 8.2 8.3 "Conversion of acetaminophen to the bioactive N-acylphenolamine AM404 via fatty acid amide hydrolase-dependent arachidonic acid conjugation in the nervous system". The Journal of Biological Chemistry 280 (36): 31405–31412. September 2005. doi:10.1074/jbc.M501489200. PMID 15987694.
- ↑ 9.0 9.1 "Anandamide transport is independent of fatty-acid amide hydrolase activity and is blocked by the hydrolysis-resistant inhibitor AM1172". Proceedings of the National Academy of Sciences of the United States of America 101 (23): 8756–8761. June 2004. doi:10.1073/pnas.0400997101. PMID 15138300.
- ↑ 10.0 10.1 "Evidence against the presence of an anandamide transporter". Proceedings of the National Academy of Sciences of the United States of America 100 (7): 4269–4274. April 2003. doi:10.1073/pnas.0730816100. PMID 12655057. Bibcode: 2003PNAS..100.4269G.
- ↑ "The anandamide transport inhibitor AM404 activates vanilloid receptors". European Journal of Pharmacology 396 (1): 39–42. May 2000. doi:10.1016/s0014-2999(00)00207-7. PMID 10822052.
- ↑ "TRPV1 mediates the anticonvulsant effects of acetaminophen in mice". Epilepsy Research 145: 153–159. September 2018. doi:10.1016/j.eplepsyres.2018.06.016. PMID 30007240.
- ↑ "Does Paracetamol Block Peripheral Pain?" (in en). 11 June 2025. https://conexiant.com/neurology/articles/paracetamol-metabolite-blocks-pain-at-source/.
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