Pharmacological Activity of Fatty Acid Amides Is Regulated, but Not Mediated, by Fatty Acid Amide Hydrolase in Vivo
- 1The Skaggs Institute for Chemical Biology and Departments of Cell Biology and Chemistry, The Scripps Research Institute, La Jolla, California (G.H., B.F.C.); and 2Department of Pharmacology and Toxicology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia (A.H.L., G.G.)
- Dr. Benjamin F. Cravatt, 10550 N. Torrey Pines Rd., La Jolla, CA 92037. E-mail:cravatt{at}scripps.edu
Abstract
Fatty acid amides (FAAs) represent a class of neuromodulatory lipids that includes the endocannabinoid anandamide and the sleep-inducing substance oleamide. Both anandamide and oleamide produce behavioral effects indicative of cannabinoid activity, but only anandamide binds the cannabinoid (CB1) receptor in vitro. Accordingly, oleamide has been proposed to induce its behavioral effects by serving as a competitive substrate for the brain enzyme fatty acid amide hydrolase (FAAH) and inhibiting the degradation of endogenous anandamide. To test the role that FAAH plays as a mediator of oleamide activity in vivo, we have compared the behavioral effects of this FAA in FAAH(+/+) and (−/−) mice. In both genotypes, oleamide produced hypomotility, hypothermia, and ptosis, all of which were enhanced in FAAH(−/−) mice, were unaffected by the CB1 antagonistN-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-di-chlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride (SR141716A) and occurred in CB1(−/−) mice. Additionally, oleamide displayed negligible binding to the CB1 receptor in brain extracts from either FAAH(+/+) or (−/−) mice. In contrast, anandamide exhibited a 15-fold increase in apparent affinity for the CB1 receptor in brains from FAAH(−/−) mice, consistent with its pronounced CB1-dependent behavioral effects in these animals. Contrary to both oleamide and anandamide, monoacylglycerol lipids exhibited equivalent hydrolytic stability and pharmacological activity in FAAH(+/+) and (−/−) mice. Collectively, these results indicate that FAAH is a key regulator, but not mediator of FAA activity in vivo. More generally, these findings suggest that FAAs represent a family of signaling lipids that, despite sharing similar chemical structures and a common pathway for catabolism, produce their behavioral effects through distinct receptor systems in vivo.
Footnotes
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This work was supported by the National Institute of Mental Health (58542, to B.F.C.) and National Institute on Drug Abuse (13173 and 15197 to B.F.C. and 03672 and 09789 to A.H.L.) of the National Institutes of Health, the Baxter Foundation, the Helen L. Dorris Institute for the Study of Neurological and Psychiatric Disorders of Children and Adolescents, and the Skaggs Institute for Chemical Biology.
- Abbreviations:
- 2-AG
- 2-arachidonoylglycerol
- CB1
- cannabinoid
- FAA
- fatty acid amide
- MAG
- monoacylglycerol
- PEA
- N-palmitoylethanolamine
- OEA
- N-oleoylethanolamine
- FAAH
- fatty acid amide hydrolase
- %MPE
- percentage of maximum possible effect
- PMSF
- phenylmethylsulfonyl fluoride
- 2-OG
- 2-oleoylglycerol
- GABA
- γ-aminobutyric acid
- SR141716A
- N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-di-chlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride
- WIN 55,212-2
- (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpho-linylmethyl) pyrrolo-[1,2,3-d,e]-1,4-benzoxazin-6-yl]-1-naphth-alenyl-methanonemesylate
- CP 55,940
- (1R,3R,4R)-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-4-(3-hydroxypropyl)cyclohexan-1-ol
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- Received February 6, 2002.
- Accepted March 6, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
