Anandamide studies

CP 55940 (79) and nabilone (80) are synthetic ligands for the cannabiaoid receptor. However, the identification of the eicosanoid, anandamide (81), as an endogenous cannabimimetic has provided an important tool to study cannabiaoid receptor function. 

Endocannabinoids are endogenous mediators acting via the binding to, and activation of, cannabinoid receptors, CBX and CB2 [1]. iV-arachidonoy 1-ethanol-amine (AEA, anandamide) and 2-arachidonoyl-glycerol (2-AG) (Fig. 1) are the two most studied endocannabinoids. In the nervous system, endocannabinoids act as... 

Endocannabinoids. Figure 1 Chemical structures of the two most studied endocannabinoids, anandamide and 2-arachidonoylglycerol, of Cannabis sativa psychoactive principle, A9-tetrahydrocannabinol, and of the CB-i receptor antagonist/inverse agonist, rimonabant. 

The best studied of the endocarmabinoids are anandamide (A -arachidonyl-ethanolamine, AEA)(1) and 2-arachidonylglycerol (2-AG)(2). Anandamide was first identified from porcine brain extracts by Devane and co-workers in 1992 [13], while 2-AG was first reported in 1995 to have been isolated from canine gut [14] and rat brain [15]. More recently, noladin ether (2-arachidonyl-glyceryl ether, 2-AGE)(3) [16], virodhamine (D-arachidonyl-ethanolamine)(4) [17] and A-arachidonyl-dopamine (NADA)(5) [18] were proposed as endogenous ligands for the cannabinoid receptors. In a subsequent publication, the authors failed to detect noladin ether in mammalian brains and questioned the relevance of this compound as an endocarmabinoid [19]. Anandamide, noladin ether and NADA have functional selectivity for CBi receptors, virodhamine is CB2 selective and 2-AG is essentially non-selective. 

The biosyntheses of anandamide and 2-AG have been studied in depth [10]. These compounds appear to be synthesised on demand in response to certain stimuli, rather than being stored in cells. Little is known regarding the biosynthesis of noladin ether, virodhamine or NADA. 

FAAH was originally purified and cloned from rat liver microsomes and is able to catalyse the hydrolysis of anandamide and 2-AG, in addition to other long-chain fatty acid amides [25]. Studies into the structure and role of this enzyme have generated interest in the potential therapeutic applications of FAAH inhibitors [26-28]. FAAH knock-out mouse brains contained 15-fold higher levels of anandamide than their wild-type counterparts and these animals have also been shown to be more responsive to exogenously administered anandamide [29]. These animals also showed a reduced response to painful stimuli, supporting the hypothesis that FAAH inhibition may provide novel analgesics. Levels of 2-AG were not elevated in the FAAH knock-out animals, apparently due to the existence of alternative metabolic fates for this compound [30]. 

The first substrate analogue inhibitors of FAAH were reported in 1994. The anandamide analogues prepared represented three elasses of putative transition-state inhibitors a-trifluoromethyl ketones, a-ketoesters and a-ketoamides [62], In the initial sereening studies, it was found that the trifluoromethyl ketone eompounds tested were effeetive inhibitors of AEA hydrolysis. A selected set of a-keto esters also inhibited hydrolysis, while a-keto amides were ineffective. In particular, arachidonyl trifluoromethyl ketone (32), gave almost 100% inhibition of anandamide hydrolysis. A detailed investigation of the structural requirements for FAAH inhibition with a-trifluoromethyl ketones has been carried out by Roger and co-workers [63]. 

Since the discovery of anandamide in 1992, a number of studies have examined its pharmacological properties. Although its roles are still elusive, a plethora of data supports the initial postulate that anandamide is the major endogenous cannabinoid ligand. As mentioned earlier, anandamide binds to CB1 from brain preparations and displaces various well-... 

Anandamide, in vivo, was shown to produce the four characteristic effects of cannabimimetics, namely, analgesia, hypothermia, hypoactiv-ity, and catalepsy (Smith, 1994 Fride, 1993 Crawley, 1993). These four effects are not unique to cannabimimetics when they are produced together, however, they are highly predictive of cannabimimetic activity (Martin, 1991). Anandamide was found to be less potent than delta-9-THC in producing these behavioral effects in mice (Fride, 1993). It has quicker onset and shorter duration of action, the latter because of rapid catabolism. Cross-tolerance studies, in which pretreatment of mice with delta-9-THC produced tolerance to most of the pharmacological effects of anandamide and vice versa, indicate that both drugs act on the same receptor (Jarbe, 1998). 

All the foregoing pharmacological effects of anandamide, in conjunction with the well-documented existence of specific systems for its biosynthesis, catabolism, and cellular reuptake to be discussed shortly, suggest that anandamide is indeed the endogenous cannabinoid ligand. The other two less studied A -acylethanolamide endocannabinoids and also 2-AG may serve similar functions. The differential roles of each of these four endocannabinoids are still unclear. 

Mulet, X. and Drummond, C.J. (2011) Anandamide andanalogous endocannabinoids a lipid self-assembly study. Soft Matter, 7, 5319—5328. 

Adams IB, Compton DR, Martin BR. (1998). Assessment of anandamide interaction with the cannabinoid brain receptor SR 141716A antagonism studies in mice and autoradiographic analysis of receptor binding in rat brain. J Pharmacoi Exp Ther. 284(3) 1209-17. 

Functional interactions between the nicotinic and cannabinoid systems have been proposed (Cohen et al. 2002) and several studies have tested the applicability of these ideas to nicotine discrimination. However cannabinoid agonists acting at cannabinoid CBi and CB2 receptors have failed to generalise with nicotine (Zaniewska et al. 2006). Results with the anandamide uptake and fatty acid amide hydrolase inhibitors AM-404 and URB 597, that elevate brain concentrations of endogenous cannabinoids, were also negative. Furthermore, neither the CBi receptor... 

Some people claim that the effects of low doses of salvinorin are similar to Cannabis and have suggested the possibility that like THC, salvinorin A might bind to the anandamide receptor site (CBl). This site had not been looked at in the NovaScreen study, so in 1998, Siebert submitted a sample of salvinorin A to Dr. Raphael... 

Cannabis, or marijuana, has been used for centuries for both symptomatic and prophylactic treatment of migraine. It was highly esteemed as a headache remedy by the most prominent physicians of the age between 1874 and 1942, remaining part of the Western pharmacopoeia for this indication even into the mid-20th century. Current ethnobotanical and anecdotal references continue to refer to its efficacy for this malady, and biochemical studies of THC and anandamide have provided a scientific basis for such treatment (Russo, 1998). 

Best studied, among these ligands, are the lipid derivatives anandamide (AEA) (Devane etal., 1992) and 2-arachidonoylglycerol (2-AG) (Mechoulam et al., 1995 Sugiura et al., 1995), which differ from classical and peptide neurotransmitters in... 

Consistent with a role for anandamide as an endogenous neuroprotectant in the adult brain, it has been hypothesized that the endocannabinoid system promotes neuroprotection in the developing brain (Fride, 2008 Fride and Shohami, 2002). Several studies support this hypothesis (i) activation of CB1 receptors in 7-day-old rats by WIN55,212-2 prevented neuronal loss (Martinez-... 

Anandamide is rapidly hydrolysed enzymatically to arachidonic acid and ethanol-amine by a fatty acid amide hydrolase (FAAH) [50], The molecular characterization, cloning and expression of FAAH have been reported in a recent study [51]. FAAH can be blocked with either the general serine protease inhibitor phenyl methy(sulphonyl fluoride [38] or with the highly efficient methyl arachidonyl fluorophsphonate [52], The non-steroidal antiinflammatory ibuprofen in therapeutic doses, but not aspirin, sulindac or acetaminophen, also inhibits anandamide metabolism [53], This observation may have therapeutic implications. 

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