ARACHIDONOYLSEROTONIN AND OTHER NOVEL INHIBITORS OF FATTY-ACID AMIDE HYDROLASE

Fatty acid amide hydrolase (FAAH) catalyzes the hydrolysis of bioactiv e fatty acid amides and esters such as the endogenous cannabinoid rece ptor ligands, anandamide (N-arachidonoyl-ethanolamine) and 2-arachidon oylglycerol, and the putative sleep inducing factor cis-9-octadecenoam ide (oleamide). Most FAAH blockers developed to date also inhibit cyto solic phospholipase A(2) (cPLA(2)) and/or bind to the CB1 cannabinoid receptor subtype. Here we report the finding of four novel FAAH inhibi tors, two of which, malhamensilipin A and grenadadiene, were screened out of a series of thirty-two different algal natural products, and tw o others, arachidonoylethylene glycol (AEG) and arachidonoyl-serotonin (AA-5-HT) were selected out of five artificially functionalized polyu nsaturated fatty acids. When using FAAH preparations from mouse neurob lastoma N18TG2 cells and [C-14]anandamide as a substrate, the IC(50)s for these compounds ranged from 12.0 to 26 mu M, the most active compo und being AA-5-HT. This substance was also active on FAAH from rat bas ophilic leukaemia (RBL-2H3) cells (IC50 = 5.6 mu M), and inhibited [14 C]anandamide hydrolysis by both N18TG2 and RBL-2H3 intact cells withou t affecting [C-14]anandamide uptake. While AEG behaved as a competitiv e inhibitor and was hydrolyzed to arachidonic acid (AA) by FAAH prepar ations, AA-5-HT was resistant to FAAH-catalyzed hydrolysis and behaved as a tight-binding, albeit non-covalent, mixed inhibitor. AA-5-HT did not interfere with cPLA(2)-mediated, ionomycin or antigen-induced rel ease of [H-3]AA from RBL-2H3 cells, nor with cPLA(2) activity in cell- free experiments. Finally, AA-5-HT did not activate CB1 cannabinoid re ceptors since it acted as a very weak ligand in in vitro binding assay s, and, at 10-15 mg/kg body weight, it was not active in the 'open fie ld', 'hot plate' and rectal hypothermia tests carried out in mice. Con versely AEG behaved as a cannabimimetic substance in these tests as we ll as in the 'ring' immobility test where AA-5-HT was also active. AA- 5-HT is the first FAAH inhibitor reported to date which is inactive bo th against cPLA(2) and at CB1 receptors, whereas AEG represents a new type of cannabinoid receptor agonist. (C) 1998 Academic Press.