Abstract
Inhibition of the metabolism of the endocannabinoids, anandamide (AEA) and 2-arachidonyl glycerol (2-AG), by their primary metabolic enzymes, fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), respectively, has the potential to increase understanding of the physiological functions of the endocannabinoid system. To date, selective inhibitors of FAAH, but not MAGL, have been developed. The purpose of this study was to determine the selectivity and efficacy of N-arachidonyl maleimide (NAM), a putative MAGL inhibitor, for modulation of the effects of 2-AG. Our results showed that NAM unmasked 2-AG activity in a tetrad of in vivo tests sensitive to the effects of cannabinoids in mice. The efficacy of 2-AG (and AEA) to produce hypothermia was reduced compared with Δ9-tetrahydrocannabinol; however, 2-AG differed from AEA by its lower efficacy for catalepsy. All tetrad effects were partially CB1 receptor-mediated because they were attenuated (but not eliminated) by SR141716A [N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-H-pyrazole-3-carboxamide HCl] and in CB1-/- mice. In vitro, NAM increased endogenous levels of 2-AG in the brain. Furthermore, NAM raised the potency of 2-AG, but not AEA, in agonist-stimulated guanosine 5′-O-(3-[35S]thio)triphosphate binding assay, a measure of G-protein activation. These results suggest that NAM is an MAGL inhibitor with in vivo and in vitro efficacy. NAM and other MAGL inhibitors are valuable tools to elucidate the biological functions of 2-AG and to examine the consequences of dysregulation of this endocannabinoid. In addition, NAM's unmasking of 2-AG effects that are only partially reversed by SR141716A offers support for the existence of non-CB1, non-CB2 cannabinoid receptors.
Footnotes
-
This work was supported by the National Institutes of Health Grants DA016644, DA03672, and DA09789 (to J.L.W.), DA05274 (to D.E.S.), DA14277 (to L.J.S.-S.), and DA05488 (to R.K.R.).
-
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
-
doi:10.1124/jpet.108.141382.
-
ABBREVIATIONS: CNS, central nervous system; AEA, anandamide; 2-AG, 2-arachidonylglycerol; FAAH, fatty acid amide hydrolase; MAGL, monoacylglycerol lipase; URB597, (3′-(aminocarbonyl)[1,1′-biphenyl]-3-yl)-cyclohexylcarbamate; URB602, [1,1′-biphenyl]-3-yl-carbamic acid, cyclohexyl ester; MAFP, methyl arachidonyl fluorophosphonate; NAM, N-arachidonyl maleimide; SR141716A, N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-H-pyrazole-3-carboxamide HCl; SR144528, N-((1S)-endo-1,3,3-trimethyl bicyclo heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide); WIN 55,212-2, R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo-[1,2,3-de]-1, 4-benzoxazinyl]-(1-naphthalenyl)methanone mesylate; GTPγS, guanosine 5′-3-O-(thio)triphosphate; [35S]GTPγS, guanosine 5′-O-(3-[35S]thio)triphosphate; BSA, bovine serum albumin; ANOVA, analysis of variance; THC, Δ9-tetrahydrocannabinol; GPR, G protein-coupled receptor.
- Received May 22, 2008.
- Accepted August 4, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|