No abstract

The endocannabinoid system includes two G-protein coupled cannabinoid receptors (CB1 and CB2), their endogenous lipid ligands (endocannabinoids), and the enzymes and transporters that help regulate cannabinergic tone ( 1 ). Endocannabinoid signaling is ubiquitous in mammals, being particularly critical in brain , where it modulates neurotransmitter release and exhibits neuroprotective effects ( 2, 3 ). Although the fi rst two endocannabinoids identifi ed, N -arachidonoylethanolamine (anandamide, AEA) and 2-arachidonoylglycerol (AG), have been extensively characterized, the (patho)physiological impact of endocannabinoid signaling has prompted the search for additional endocannabinoids and their related metabolites/ biosynthetic precursors, creating an evolving network of chemical species collectively termed the endocannabinoid metabolome, few of which have been functionally annotated ( 1,(3)(4)(5)(6)(7)(8)(9). Although the translational and diagnostic aspects of endocannabinoid signaling are well appreciated ( 10, 11 ), factors that infl uence and regulate the endocannabinoid metabolome profi le among various tissues and compartments remains incompletely described and understood ( 1, 10 ), as are the metabolome's relationship to lipid pathways outside of the endocannabinoid signaling system ( 3, 9 ). Abstract

The endocannabinoid system's biological significance continues to grow as novel endocannabinoid metabolites are discovered. Accordingly, a myopic view of the system that focuses solely on one or two endocannabinoids, such as anandamide or 2-arachidonoyl glycerol, is insufficient to describe the biological responses to perturbations of the system. Rather, the endocannabinoid metabolome as a whole must be analyzed. The work described here is based on liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry. This method has been validated to quantify, in a single chromatographic run, the levels of 15 known or suspected metabolites of the endocannabinoid system in the rat brain and is applicable to other biological matrixes. We have obtained an endocannabinoid profile specifically for the frontal cortex of the rat brain and have determined anandamide level differences following the administration of the fatty acid amide hydrolase inhibitor AM374.

Cannabinoid (CB)1 receptor inverse agonists inhibit food intake in animals and humans but also potentiate emesis. It is not clear whether these effects result from inverse agonist properties or from the blockade of endogenous cannabinoid signaling. Here, we examine the effect of a neutral CB1 antagonist, AM4113, on food intake, weight gain, and emesis. Neutral antagonist and binding properties were confirmed in HEK-293 cells transfected with human CB1 or CB2 receptors. AM4113 had no effect on forskolin-stimulated cAMP production at concentrations up to 630 nM. The Ki value of AM4113 (0.80 +/- 0.44 nM) in competitive binding assays with the CB1/2 agonist [3H]CP55,940 was 100-fold more selective for CB1 over CB2 receptors. We determined that AM4113 antagonized CB1 receptors in brain by blocking hypothermia induced by CP55,940. AM4113 (0-20 mg/kg) significantly reduced food intake and weight gain in rat. Compared with AM251, higher doses of AM4113 were needed to produce similar effects on food intake and body weight. Unlike AM251 (5 mg/kg), a highly anorectic dose of AM4113 (10 mg/kg) did not significantly potentiate vomiting induced by the emetic morphine-6-glucoronide. We show that a centrally active neutral CB1 receptor antagonist shares the appetite suppressant and weight loss effects of inverse agonists. If these compounds display similar properties in humans, they could be developed into a new class of antiobesity agents.