Fatty-acid amide hydrolase 1

Function

FAAH is an integral membrane hydrolase with a single N-terminal transmembrane domain. In vitro, FAAH has esterase and amidase activity. In vivo, FAAH is the principal catabolic enzyme for a class of bioactive lipids called the fatty acid amides (FAAs). Members of the FAAs include:

• Anandamide (N-arachidonoylethanolamine), an endocannabinoid
• 2-arachidonoylglycerol (2-AG), an endocannabinoid.
• Other N-acylethanolamines, such as N-oleoylethanolamine and N-palmitoylethanolamine
• The sleep-inducing lipid oleamide
• The N-acyltaurines, which are agonists of the transient receptor potential (TRP) family of calcium channels.

FAAH knockout mice display highly elevated (15-fold) levels of N-acylethanolamines and N-acyltaurines in various tissues. Because of their significantly elevated anandamide levels, FAAH KOs have an analgesic phenotype, showing reduced pain sensation in the hot plate test, the formalin test, and the tail flick test. Finally, because of their impaired ability to degrade anandamide, FAAH KOs also display supersensitivity to exogenous anandamide, a cannabinoid receptor (CB) agonist. (Humans have two fatty-acid amide hydrolase genes, the other being FAAH2, while rodents only have FAAH. This is likely to complicate translations between human and rodent biology.)

Due to the ability of FAAH to regulate nociception, it is currently viewed as an attractive drug target for the treatment of pain.

Studies in cells and animals and genetic studies in humans have shown that inhibiting FAAH may be a useful strategy to treat anxiety disorders, as inhibition produce analgesic, anxiolytic, neuroprotective, and anti-inflammatory effects by elevated N-acylethanolamines (NAE's) and their activation of cannabinoid receptors.

Inhibitors

PLEASE DO NOT ADD UNSOURCED INFORMATION TO THIS SECTION, AND PLEASE MOVE THE SECTION TOWARD SECONDARY SOURCES. IN ALL CASES, BE CAREFUL TO REFLECT SPECIFICALLY WHAT IS SAID IN THE PUBLICATION. PRIMARY SOURCES SHOULD BE ACCOMPANIED BY STATEMENTS LIKE, "In one report…" RATHER THAN STATING A FIRM CONCLUSION BASED ON ONE PRIMARY SOURCE. MOREOVER, TERMS LIKE "SELECTIVE", STATED PERFUNCTORILY, ARE NEAR MEANINGLESS; SOME DATA NEEDS BE STATED, AND/OR A COMPARISON TO OTHER MORE ESTABLISHED AGENTS.

Activation of the cannabinoid receptor CB1 or CB2 in different tissues, including skin, inhibit FAAH, and thereby increases endocannabinoid levels.

Based on the hydrolytic mechanism of fatty acid amide hydrolase, a large number of irreversible and reversible inhibitors of this enzyme have been developed.

Some of the more significant compounds are listed below;

• AM374, palmitylsulfonyl fluoride, one of the first FAAH inhibitors developed for in vitro use, but too reactive for research in vivo
• ARN2508, derivative of flurbiprofen, dual FAAH / COX inhibitor
• BIA 10-2474 (Bial-Portela & Ca. SA, Portugal) has been linked to severe adverse events affecting 5 patients in a drug trial in Rennes, France, and at least one death, in January 2016. Many other pharmaceutical companies have previously taken other FAAH inhibitors into clinical trials without reporting such adverse events.
• BMS-469908
• CAY-10402
• JNJ-245
• JNJ-1661010
• JNJ-28833155
• JNJ-40413269
• JNJ-42119779
• JNJ-42165279 in clinical trials against social anxiety and depression, trials suspended as a precautionary measure following serious adverse event with BIA 10-2474
• LY-2183240
• Cannabidiol
• MK-3168
• MK-4409
• MM-433593
• OL-92
• OL-135
• PF-622
• PF-750
• PF-3845
• PF-04862853
• Redafamdastat (JZP-150; PF-04457845) – "exquisitely selective" for FAAH over other serine hydrolases, but failed in clinical trials against osteoarthritis
• RN-450
• SA-47
• SA-73
• SSR-411298 well tolerated in clinical trials but insufficient efficacy against depression, subsequently trialled against cancer pain as an adjunctive treatment.
• ST-4068, reversible inhibitor of FAAH
• TK-25
• URB524
• URB597 (KDS-4103, Kadmus Pharmaceuticals), is an irreversible inactivator with a carbamate-based mechanism, and appears in one report as a somewhat selective, though it also inactivates other serine hydrolases (e.g., carboxylesterases) in peripheral tissues.
• URB694
• URB937
• VER-156084 (Vernalis)
• V-158866 (Vernalis) in clinical trials for neuropathic pain following spinal injury, and spasticity associated with multiple sclerosis. Structure not revealed though Vernalis holds several patents in the area.

Inhibition and binding

Structural and conformational properties that contribute to enzyme inhibition and substrate binding imply an extended bound conformation, and a role for the presence, position, and stereochemistry of a delta cis double bond.

Enhancement of FAAH activity

Insulin medication increases the production and activity of FAAH.

Genetic variants

rs324420

The FAAH gene contains a single nucleotide polymorphism (SNP) called rs324420. The variant allele, C385A, is associated with a higher sensitivity of FAAH to proteolytic degradation and a shorter half-life compared to the standard C variant. As a result, carriers of the A variant has increased N-acylethanolamine (NAE) levels and anandamide (AEA) signaling at the cannabinoid receptors. The A variant may be responsible for lower levels of the FAAH protein seen in high-performing athletes, providing increased physical and mental fitness. However, among elite Polish athletes, the A variant is under-represented regardless of metabolic characteristics of their sport disciplines; this seems to suggest an opposite role for the A variant.

A 2017 study found a strong correlation between national percentage of very happy people (as measured by the World Values Survey) and the presence of the rs324420 C385A allele in citizens' genetic make-up.

The C385A allele was initially provisionally linked to drug abuse and dependence but this was not borne out in subsequent studies. According to later studies, carriers of the A allele are more likely to try cannabis, but less likely to become dependent.

{{vanchor|FAAH-OUT}} microdeletion

Main article: Jo Cameron

FAAH-OUT is a pseudogene downstream of the FAAH coding region. It expresses a long non-coding RNA (lncRNA) that increases the expression of FAAH. In 2019, a Scottish woman named Jo Cameron was found to have both a previously unreported microdeletion mutation in FAAH-OUT and a rs324420 C385A mutation. The result is extreme disruption of FAAH function leading to elevated anandamide levels. She was immune to anxiety, unable to experience fear, and insensitive to pain. The frequent burns and cuts suffered due to her hypoalgesia healed quicker than average with little or no scarring.

• Her son, who shares the FAAH-OUT deletion but has no C385A mutation, has a lesser degree of pain insensitivity.

A 2023 study looks further into the functions of FAAH-OUT using transcriptomic analyses of cell models, some created anew using CRISPR-Cas9, others obtained from the 2019 patient. The study confirms that FAAH-OUT increases the expression of FAAH, both via its lncRNA product and through an intronic enhancer called FAAH-AMP. Loss of FAAH-OUT also changes the expression of a wide network of genes beyond FAAH itself. For example, although the pain insensitivity is mostly due to loss of FAAH function (via increased endocannabinoid levels and reduced ACKR3 expression), lack of depression and anxiety is instead due to a non-canonical Wnt pathway upregulating BDNF. The increased wound healing is due to both pathways: loss of FAAH function increases N-acyltaurine levels; the non-canonical Wnt pathway is also beneficial to healing.

Assays

The enzyme is typically assayed making use of a radiolabelled anandamide substrate, which generates free labelled ethanolamine, although alternative LC-MS methods have also been described.

Structures

The first crystal structure of FAAH was published in 2002 (PDB code 1MT5). Structures of FAAH with drug-like ligands were first reported in 2008, and include non-covalent inhibitor complexes and covalent adducts.

Regulation

In slime molds

The slime mold Dictyostelium discoideum produces a semispecific FAAH inhibitor. By controlling the levels of FAAH activity, they modulate endogenous N-acylethanolamine levels.

Enzyme classification

In the Enzyme Commission numbering scheme, "fatty acid amide hydrolase" is . The number applies to all enzymes that have the chemical activity; in humans it covers both the genes FAAH and FAAH2. The systematic name is "fatty acylamide amidohydrolase". Recorded synonyms include "oleamide hydrolase", "anandamide amidohydrolase".

References

References

1. "UniProt".
2. (September 1993). "Enzymatic synthesis and degradation of anandamide, a cannabinoid receptor agonist". Biochemical Pharmacology.
3. (November 1996). "Molecular characterization of an enzyme that degrades neuromodulatory fatty-acid amides". Nature.
4. (March 1997). "Molecular characterization of human and mouse fatty acid amide hydrolases". Proceedings of the National Academy of Sciences of the United States of America.
5. (November 2002). "Structural adaptations in a membrane enzyme that terminates endocannabinoid signaling". Science.
6. (October 1999). "Fatty acid amide hydrolase competitively degrades bioactive amides and esters through a nonconventional catalytic mechanism". Biochemistry.
7. (July 2001). "Supersensitivity to anandamide and enhanced endogenous cannabinoid signaling in mice lacking fatty acid amide hydrolase". Proceedings of the National Academy of Sciences of the United States of America.
8. (November 2000). "The fatty acid amide hydrolase (FAAH)". Chemistry and Physics of Lipids.
9. (November 2004). "Assignment of endogenous substrates to enzymes by global metabolite profiling". Biochemistry.
10. (June 1995). "Chemical characterization of a family of brain lipids that induce sleep". Science.
11. (August 2006). "A FAAH-regulated class of N-acyl taurines that activates TRP ion channels". Biochemistry.
12. (October 2004). "The endogenous cannabinoid system and its role in nociceptive behavior". Journal of Neurobiology.
13. (December 2006). "A second fatty acid amide hydrolase with variable distribution among placental mammals". The Journal of Biological Chemistry.
14. (February 2014). "Inhibition of fatty acid amide hydrolase (FAAH) as a novel therapeutic strategy in the treatment of pain and inflammatory diseases in the gastrointestinal tract". European Journal of Pharmaceutical Sciences.
15. (June 2014). "The endocannabinoid system as a potential therapeutic target for pain modulation". Balkan Medical Journal.
16. (August 2015). "Full Fatty Acid Amide Hydrolase Inhibition Combined with Partial Monoacylglycerol Lipase Inhibition: Augmented and Sustained Antinociceptive Effects with Reduced Cannabimimetic Side Effects in Mice". The Journal of Pharmacology and Experimental Therapeutics.
17. (November 2013). "Amygdala FAAH and anandamide: mediating protection and recovery from stress". Trends in Pharmacological Sciences.
18. (September 2016). "The endocannabinoid system and Post Traumatic Stress Disorder (PTSD): From preclinical findings to innovative therapeutic approaches in clinical settings". Pharmacological Research.
19. (August 2021). "N-Palmitoyl Serinol Stimulates Ceramide Production through a CB1-Dependent Mechanism in In Vitro Model of Skin Inflammation". International Journal of Molecular Sciences.
20. (April 2009). "Pharmacotherapeutic modulation of the endocannabinoid signalling system in psychiatric disorders: drug-discovery strategies". International Review of Psychiatry.
21. (July 2009). "Fatty acid amide hydrolase as a potential therapeutic target for the treatment of pain and CNS disorders". Expert Opinion on Drug Discovery.
22. (January 2010). "FAAH and MAGL inhibitors: therapeutic opportunities from regulating endocannabinoid levels". Current Opinion in Investigational Drugs.
23. (2010). "Discovery and development of endocannabinoid-hydrolyzing enzyme inhibitors". Current Topics in Medicinal Chemistry.
24. (August 2011). "Fatty acid amide hydrolase inhibitors--progress and potential". CNS & Neurological Disorders Drug Targets.
25. (May 2013). "Latest advances in the discovery of fatty acid amide hydrolase inhibitors". Expert Opinion on Drug Discovery.
26. (February 2014). "Elevating endocannabinoid levels: pharmacological strategies and potential therapeutic applications". The Proceedings of the Nutrition Society.
27. (2015). "Fatty acid amide hydrolase inhibitors: a patent review (2009-2014)". Expert Opinion on Therapeutic Patents.
28. (2016). "More Details Emerge on Fateful French Drug Trial". [[Science (magazine).
29. (April 2013). "Chemical probes of endocannabinoid metabolism". Pharmacological Reviews.
30. (May 2011). "Discovery and molecular basis of potent noncovalent inhibitors of fatty acid amide hydrolase (FAAH)". Proceedings of the National Academy of Sciences of the United States of America.
31. (December 2015). "Preclinical Characterization of the FAAH Inhibitor JNJ-42165279". ACS Medicinal Chemistry Letters.
32. (17 January 2016). "Janssen Research & Development, LLC Voluntarily Suspends Dosing in Phase 2 Clinical Trials of Experimental Treatment for Mood Disorders". Janssen.com.
33. (December 2005). "Identification of a high-affinity binding site involved in the transport of endocannabinoids". Proceedings of the National Academy of Sciences of the United States of America.
34. (December 2012). "Multiple mechanisms involved in the large-spectrum therapeutic potential of cannabidiol in psychiatric disorders". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences.
35. (2015). "Endocannabinoids".
36. {{ClinicalTrialsGov. NCT00822744. An Eight-week Study of SSR411298 as Treatment for Major Depressive Disorder in Elderly Patients (FIDELIO)
37. "Clinical trials for SSR411298.". EU Clinical Trials Register.
38. (November 2007). "Novel mechanistic class of fatty acid amide hydrolase inhibitors with remarkable selectivity". Biochemistry.
39. (August 2009). "Fatty acid amide hydrolase inhibitors. Surprising selectivity of chiral azetidine ureas". Bioorganic & Medicinal Chemistry Letters.
40. {{ClinicalTrialsGov. NCT01748695. A Safety, Tolerability and Efficacy Study of V158866 in Central Neuropathic Pain Following Spinal Cord Injury
41. "Azetidine derivatives as FAAH inhibitors".
42. (January 2012). "Fatty acid amide hydrolase inhibitors. 3: tetra-substituted azetidine ureas with in vivo activity". Bioorganic & Medicinal Chemistry Letters.
43. (January 1999). "Trifluoromethyl ketone inhibitors of fatty acid amide hydrolase: a probe of structural and conformational features contributing to inhibition". Bioorganic & Medicinal Chemistry Letters.
44. (2010). "Effect of anaesthesia and cardiopulmonary bypass on blood endocannabinoid concentrations during cardiac surgery". British Journal of Anaesthesia.
45. (May 2023). "Association of ''FAAH'' rs324420 (C385A) Polymorphism with High-Level Performance in Volleyball Players". Genes.
46. (August 2017). "Genetic variants associated with physical and mental characteristics of the elite athletes in the Polish population". Scandinavian Journal of Medicine & Science in Sports.
47. (2017-04-01). "A Genetic Component to National Differences in Happiness". Journal of Happiness Studies.
48. (April 2013). "Inhibition of FAAH and activation of PPAR: new approaches to the treatment of cognitive dysfunction and drug addiction". Pharmacology & Therapeutics.
49. (September 2023). "Molecular basis of FAAH-OUT-associated human pain insensitivity". Brain.
50. (28 March 2019). "At 71, She's Never Felt Pain or Anxiety. Now Scientists Know Why.". The New York Times.
51. (28 March 2019). "Scientists find genetic mutation that makes woman feel no pain". The Guardian.
52. (2009). "Ligand-Macromolecular Interactions in Drug Discovery".
53. (January 2013). "Quantitative LC-MS/MS analysis of arachidonoyl amino acids in mouse brain with treatment of FAAH inhibitor". Analytical Biochemistry.
54. (September 2008). "Structure-guided inhibitor design for human FAAH by interspecies active site conversion". Proceedings of the National Academy of Sciences of the United States of America.
55. (February 2013). "Identification of N-acylethanolamines in Dictyostelium discoideum and confirmation of their hydrolysis by fatty acid amide hydrolase". Journal of Lipid Research.
56. "KEGG ENZYME: 3.5.1.99".