Methyl arachidonyl fluorophosphonate: a potent irreversible inhibitor of anandamide amidase

Spinal phospholipase A2 in inflammatory hyperalgesia: role of group IVA cPLA2

Current work has shown the importance of spinal cyclooxygenase (COX) products in facilitatory processes leading to tissue injury induced hyperalgesia. This cascade must originate with free arachidonic acid (AA) released by the activity of spinal phospholipase A2s (PLA2). In the present work, we studied the role of PLA2s in spinal sensitization. We first demonstrate the presence of constitutive mRNA in the spinal cord for PLA2 Groups IB, IIA, IIC, IVA, V and VI by reverse transcription-polymerase chain reaction (RT-PCR) and sequencing. Using quantitative-PCR, we found that Group IVA cPLA2 and Group VI iPLA2 are the predominant PLA2 messages in the spinal cord. Western blotting and activity assays specific for Group IVA cPLA2 and Group VI iPLA2 verified the presence of these enzymes. PLA2 activity in spinal cord homogenates was suppressed by methyl arachidonyl fluorophosphonate (MAFP) and arachidonyl trifluoromethylketone (AACOCF3), mixed inhibitors of Group IVA cPLA2 and Group VI iPLA2 as well as by bromoenol lactone (BEL), a Group VI iPLA2 inhibitor. The spinal expression of PLA2 mRNA or protein was not altered in the face of peripheral inflammation. Secondly, we showed that intrathecal (i.t.) administration of MAFP and AACOCF3, but not BEL, dose-dependently prevented thermal hyperalgesia induced by intraplantar carrageenan as well as formalin-induced flinching. Finally, i.t. injection of AACOCF3, at antihyperalgesic doses, decreased the release of prostaglandin E2 (PGE2) into spinal dialysate evoked by i.t. NMDA, while i.t. injection of BEL had no effect. Taken together, this work points to a role for constitutive Group IVA cPLA2 in spinal nociceptive processing.

PGE2 release is independent of upregulation of Group V phospholipase A2 during long-term stimulation of P388D1 cells with LPS

P388D1 cells release arachidonic acid (AA) and produce prostaglandin E2 (PGE2) upon long-term stimulation with lipopolysaccharide (LPS). The cytosolic Group IVA (GIVA) phospholipase A2 (PLA2) has been implicated in this pathway. LPS stimulation also results in increased expression and secretion of a secretory PLA2, specifically GV PLA2. To test whether GV PLA2 contributes to PGE2 production and whether GIVA PLA2 activation increases the expression of GV PLA2, we utilized the specific GIVA PLA2 inhibitor pyrrophenone and second generation antisense oligonucleotides (AS-ONs) designed to specifically inhibit expression and activity of GV PLA2. Treatment of P388D1 cells with antisense caused a marked decrease in basal GV PLA2 mRNA and prevented the LPS-induced increase in GV PLA2 mRNA. LPS-stimulated cells release active GV PLA2 into the medium, which is inhibited to background levels by antisense treatment. However, LPS-induced PGE2 release by antisense-treated cells and by control cells are not significantly different. Collectively, the results suggest that the upregulation of GV PLA2 during long-term LPS stimulation is not required for PGE2 production by P388D1 cells. Experiments employing pyrrophenone suggested that GIVA PLA2 is the dominant player involved in AA release, but it appears not to be involved in the regulation of LPS-induced expression of GV PLA2 or cyclooxygenase-2.

Anandamide transport: A critical review

Anandamide (AEA) uptake has been described over the last decade to occur by facilitated diffusion, but a protein has yet to be isolated. In some cell types, it has recently been suggested that AEA, an uncharged hydrophobic molecule, passively diffuses through the plasma membrane in a process that is not protein-mediated. Since that observation, recent kinetics studies (using varying assay conditions) have both supported and denied the presence of an AEA transporter. In this review, we analyze the current literature exploring the mechanism of AEA uptake and endeavor to explain the reasons for the divergent views. One of the main variables among laboratories is the incubation time of the cells with AEA. Initial kinetics (at time points <1 min depending upon the cell type) isolate events that occur at the plasma membrane and are most useful to study saturability of uptake and effects of purported transport inhibitors upon uptake. Results with longer incubation times reflect events not only at the plasma membrane but also interactions at intracellular sites that may include enzyme(s), other proteins, or specialized lipid-binding domains. Furthermore, at long incubation times, antagonists to AEA receptors reduce AEA uptake. Another complicating factor in AEA transport studies is the nonspecific binding to plastic culture dishes. The magnitude of this effect may exceed AEA uptake into cells. Likewise, AEA may be released from plastic culture dishes (without cells) in such a manner as to mimic efflux from cells. AEA transport protocols using BSA, similar to the method used for fatty acid uptake studies, are gaining acceptance. This may improve AEA solution stability and minimize binding to plastic, although some groups report that BSA interferes with uptake. In response to criticisms that many transport inhibitors also inhibit the fatty acid amide hydrolase (FAAH), new compounds have recently been synthesized. Following their characterization in FAAH+/+ and FAAH-/- cells and transgenic mice, several inhibitors have been shown to have physiological activity in FAAH-/- mice. Their targets are now being characterized with the possibility that a protein transporter for AEA may be characterized.

The endocannabinoid arachidonyl ethanolamide (anandamide) increases pulmonary arterial pressure via cyclooxygenase-2 products in isolated rabbit lungs

Several cannabinoids elicit systemic vasodilation, mainly via CB1 cannabinoid and vanilloid receptors. However, effects in the pulmonary circulation are unknown. Using the isolated, ventilated, buffer-perfused rabbit lung, we have shown that the endocannabinoids arachidonyl ethanolamide (anandamide) and 2-arachidonyl glycerol (2-AG) dose-dependently increase pulmonary arterial pressure (+19.9 +/- 3.4 mmHg, 5 microM, and +39.5 +/- 10.8 mmHg, 0.4 microM, respectively). 2-AG induced lung edema. The CB1 receptor antagonist AM-251 (0.1 and 5 microM) and the VR1 vanilloid receptor antagonist capsazepine (10 microM) failed to reduce anandamide's effects. The metabolically stable anandamide and 2-AG analogs R-methanandamide and noladin ether, Delta9-tetrahydrocannabinol, and the synthetic cannabinoid HU-210, which is no arachidonic acid product, were without effect. The unspecific cyclooxygenase (COX) inhibitor aspirin (100 microM, P < 0.001) and the specific COX-2 inhibitor nimesulide (10 microM, P < 0.01) completely prevented pulmonary hypertension after 5 microM anandamide. COX-2 RNA was detected in rabbit lungs. The synthetic thromboxane receptor antagonist SQ 29,548 was without effect, but the specific EP1 prostanoid receptor antagonist SC-19220 (100 microM) inhibited the pressure increase after anandamide (P < 0.05). PCR analysis detected fatty acid amidohydrolase (FAAH), an enzyme that degrades endocannabinoids, in rabbit lung tissue. Furthermore, the specific FAAH inhibitor methyl arachidonyl fluorophosphonate (0.1 microM) blocked pressure effects of anandamide (P < 0.01). Finally, anandamide (99 +/- 55 pmol/g) and 2-AG (19.6 +/- 8.4 nmol/g) were found in native lungs. We conclude that anandamide increases pulmonary arterial pressure via COX-2 metabolites following enzymatic degradation by FAAH into arachidonic acid products.

Endocannabinoids Part I: molecular basis of endocannabinoid formation, action and inactivation and development of selective inhibitors

The discovery of specific receptors for Delta9-tetrahydrocannabinol, the major psychoactive component of marijuana, opened new horizons for the possible therapeutic exploitation of Cannabis sativa and the cannabinoids. Endogenous ligands of cannabinoid receptors, the 'endocannabinoids', were found and the molecular mechanisms underlying their biological effects and the regulation of their levels are now being identified. Cause/effect relationships between alterations of cannabinoid receptor/endocannabinoid levels in tissues and the symptoms of various pathological states are starting to be revealed. These studies may open the way to the possible use of substances that manipulate endocannabinoid levels and actions, such as inhibitors of the biosynthesis and inactivation and receptor antagonists, as cannabinoid-based therapeutic agents with little or no psychotropic side effect, thus potentially fulfilling an ambition nurtured for almost two centuries.

Discovery of a potent, selective, and efficacious class of reversible alpha-ketoheterocycle inhibitors of fatty acid amide hydrolase effective as analgesics

Fatty acid amide hydrolase (FAAH) degrades neuromodulating fatty acid amides including anandamide (endogenous cannabinoid agonist) and oleamide (sleep-inducing lipid) at their sites of action and is intimately involved in their regulation. Herein we report the discovery of a potent, selective, and efficacious class of reversible FAAH inhibitors that produce analgesia in animal models validating a new therapeutic target for pain intervention. Key to the useful inhibitor discovery was the routine implementation of a proteomics-wide selectivity screen against the serine hydrolase superfamily ensuring selectivity for FAAH coupled with systematic in vivo examinations of candidate inhibitors.

Heterocyclic sulfoxide and sulfone inhibitors of fatty acid amide hydrolase

A novel series of heterocyclic sulfoxides and sulfones was prepared and examined as potential inhibitors of fatty acid amide hydrolase (FAAH), the enzyme responsible for inactivation of neuromodulating fatty acid amides including anandamide and oleamide.

A spectrophotometric assay for fatty acid amide hydrolase suitable for high-throughput screening

Signalling via the endocannabinoids anandamide and 2-arachidonylglycerol appears to be terminated largely through the action of the enzyme fatty acid amide hydrolase (FAAH). In this report, we describe a simple spectrophotometric assay to detect FAAH activity in vitro using the ability of the enzyme to hydrolyze oleamide and measuring the resultant production of ammonia with a NADH/NAD+-coupled enzyme reaction. This dual-enzyme assay was used to determine Km and Vmax values of 104 microM and 5.7 nmol/min/mgprotein, respectively, for rat liver FAAH-catalyzed oleamide hydrolysis. Inhibitor potency was determined with the resultant rank order of methyl arachidonyl fluorophosphonate>phenylmethylsulphonyl fluoride>anandamide. This assay system was also adapted for use in microtiter plates and its ability to detect a known inhibitor of FAAH demonstrated, highlighting its potential for use in high-throughput screening.

Analogs of the dihydroceramide desaturase inhibitor GT11 modified at the amide function: synthesis and biological activities

Dihydroceramide desaturase is the last enzyme in the biosynthesis of ceramide de novo. The cyclopropene-containing sphingolipid GT11 is a competitive inhibitor of dihydroceramide desaturase. The biological effects of chemical modification of the GT11 amide linkage are reported in this article. Either N-methyl substitution or replacement of the amide alpha-carbonyl methylene by oxygen result in inactive compounds. In contrast, both urea (3) and thiourea (4) analogs of GT11, as well as three alpha-ketoamides (5-7), did inhibit the desaturation of N-octanoylsphinganine to N-octanoylsphingosine, although with significantly lower potency than GT11. Furthermore, the alpha-ketoamides 5-7 inhibit the acidic ceramidase with similar potencies (IC50 52-83 microM). Inhibition of the neutral/alkaline ceramidase by these compounds requires around 20-fold higher concentrations. Structure-activity relationships and the biological interest of these compounds are discussed.

The biosynthesis, fate and pharmacological properties of endocannabinoids

The finding of endogenous ligands for cannabinoid receptors, the endocannabinoids, opened a new era in cannabinoid research. It meant that the biological role of cannabinoid signalling could be finally studied by investigating not only the pharmacological actions subsequent to stimulation of cannabinoid receptors by their agonists, but also how the activity of these receptors was regulated under physiological and pathological conditions by varying levels of the endocannabinoids. This in turn meant that the enzymes catalysing endocannabinoid biosynthesis and inactivation had to be identified and characterized, and that selective inhibitors of these enzymes had to be developed to be used as (1) probes to confirm endocannabinoid involvement in health and disease, and (2) templates for the design of new therapeutic drugs. This chapter summarizes the progress achieved in this direction during the 12 years following the discovery of the first endocannabinoid.

N-cyclohexanecarbonylpentadecylamine: a selective inhibitor of the acid amidase hydrolysing N-acylethanolamines, as a tool to distinguish acid amidase from fatty acid amide hydrolase

Anandamide ( N-arachidonoylethanolamine) and other bioactive N-acylethanolamines are degraded to their corresponding fatty acids and ethanolamine. This hydrolysis is mostly attributed to catalysis by FAAH (fatty acid amide hydrolase), which exhibits an alkaline pH optimum. In addition, we have identified another amidase which catalyses the same reaction exclusively at acidic pH values [Ueda, Yamanaka and Yamamoto (2001) J. Biol. Chem. 276, 35552-35557]. In attempts to find selective inhibitors of this acid amidase, we screened various derivatives of palmitic acid, 1-hexadecanol, and 1-pentadecylamine with N-palmitoylethanolamine as substrate. Here we show that N-cyclohexanecarbonylpentadecylamine inhibits the acid amidase from rat lung with an IC50 of 4.5 microM, without inhibiting FAAH at concentrations up to 100 microM. The inhibition was reversible and non-competitive. This compound also inhibited the acid amidase in intact alveolar macrophages. With the aid of this inhibitor, it was revealed that rat basophilic leukaemia cells possess the acid amidase as well as FAAH. Thus the inhibitor may be a useful tool to distinguish the acid amidase from FAAH in various tissues and cells and to elucidate the physiological role of the enzyme.

Reversible Inhibitors of Fatty Acid Amide Hydrolase That Promote Analgesia: Evidence for an Unprecedented Combination of Potency and Selectivity

Fatty acid amide hydrolase (FAAH) is the primary catabolic regulator of several bioactive lipid amides in vivo, including the endogenous cannabinoid anandamide and the sleep-inducing substance oleamide. Inhibitors of FAAH are considered a potential therapeutic approach for the treatment of several nervous system disorders, including pain, anxiety, and insomnia. However, for FAAH inhibitors to achieve clinical utility, they must not only display efficacy in vivo but also selectivity for this enzyme relative to the numerous other serine hydrolases present in mammalian proteomes. Here, we report a general strategy for evaluating the pharmacological activity and target specificity of FAAH inhibitors and its implementation to develop the first class of selective reversible inhibitors of this enzyme that are highly efficacious in vivo. Using a series of functional proteomics, analytical chemistry, and behavioral pharmacology assays, we have identified a class of alpha-keto-heterocycles that show unprecedented selectivity for FAAH relative to other mammalian hydrolases, and, when administered to rodents, raise central nervous system levels of anandamide and promote cannabinoid receptor 1-dependent analgesia in several assays of pain sensation. These studies provide further evidence that FAAH may represent an attractive therapeutic target and describe a general route by which inhibitors of this enzyme can be optimized to achieve exceptional potency, selectivity, and efficacy in vivo.

Dexamethasone promotes toxicity in U937 cells exposed to otherwise nontoxic concentrations of peroxynitrite: pivotal role for lipocortin 1-mediated inhibition of cytosolic phospholipase A2

Pretreatment with dexamethasone (Dex) was not toxic for U937 cells but caused a rapid lethal response upon subsequent exposure to otherwise nontoxic concentrations of peroxynitrite. This effect was not associated with enhanced formation of hydrogen peroxide taking place after peroxynitrite and was shown previously to play a pivotal role in the ensuing lethal response. Further analyses revealed that although Dex did not affect cytosolic phospholipase A(2) (cPLA(2)) expression, it markedly reduced the extent of arachidonic acid (AA) release mediated by peroxynitrite-dependent stimulation of cPLA(2). This event, as well as the enhanced toxicity, was abolished by mifepristone, a glucocorticoid receptor antagonist. The outcome of various approaches, using phospholipase A(2) inhibitors, cPLA(2) antisense oligonucleotide-transfected cells, and supplementation with exogenous AA, led to the demonstration that inhibition of cPLA(2) activity is causally linked to the increased susceptibility to peroxynitrite caused by Dex. Finally, the effects of Dex were shown to be mediated by enhanced expression of lipocortin 1 (LC1), a cPLA(2) inhibitory protein. These results indicate that Dex promotes toxicity in U937 cells exposed to otherwise nontoxic concentrations of peroxynitrite and that this event is causally linked to enhanced expression of LC1 leading to inhibition of cPLA(2). Thus, the increased lethal response arises because of LC1-dependent impairment of the AA-induced cytoprotective mechanism triggered by peroxynitrite.

Monoglyceride lipase-like enzymatic activity is responsible for hydrolysis of 2-arachidonoylglycerol in rat cerebellar membranes

2-Arachidonoylglycerol (2-AG) is an endogenous cannabinoid that binds to CB1 and CB2 cannabinoid receptors, inducing cannabimimetic effects. However, the cannabimimetic effects of 2-AG are weak in vivo due to its rapid enzymatic hydrolysis. The enzymatic hydrolysis of 2-AG has been proposed to mainly occur by monoglyceride lipase (monoacylglycerol lipase). Fatty acid amide hydrolase (FAAH), the enzyme responsible for the hydrolysis of N-arachidonoylethanolamide (AEA), is also able to hydrolyse 2-AG. In the present study, we investigated the hydrolysis of endocannabinoids in rat cerebellar membranes and observed that enzymatic activity towards 2-AG was 50-fold higher than that towards AEA. Furthermore, various inhibitors for 2-AG hydrolase activity were studied in rat cerebellar membranes. 2-AG hydrolysis was inhibited by methyl arachidonylfluorophosphonate, hexadecylsulphonyl fluoride and phenylmethylsulphonyl fluoride with ic(50) values of 2.2 nM, 241 nM and 155 microM, respectively. Potent FAAH inhibitors, such as OL-53 and URB597, did not inhibit the hydrolysis of 2-AG, suggesting that 2-AG is inactivated in rat cerebellar membranes by an enzyme distinct of FAAH. The observation that the hydrolysis of 1(3)-AG and 2-AG occurred at equal rates supports the role of MGL in 2-AG inactivation. This enzyme assay provides a useful method for future inhibition studies of 2-AG degrading enzyme(s) in brain membrane preparation having considerably higher MGL-like activity when compared to FAAH activity.

Characterization of an anandamide degradation system in prostate epithelial PC-3 cells: synthesis of new transporter inhibitors as tools for this study

The response of anandamide is terminated by a carrier-mediated transport followed by degradation catalyzed by the cloned enzyme fatty acid amidohydrolase (FAAH). In this study, we provide biochemical data showing an anandamide uptake process and the expression of FAAH in human prostate. Anandamide was accumulated in PC-3 cells by a saturable and temperature-dependent process. Kinetic studies of anandamide uptake, determined in the presence of cannabinoid and vanilloid antagonists, revealed apparent parameters of KM=4.7+/-0.2 microm and Vmax=3.3+/-0.3 pmol min-1 (10(6) cells)-1. The accumulation of anandamide was moderately inhibited by previously characterized anandamide transporter inhibitors (AM404, UCM707 and VDM11) but was unaffected by inhibitors of other lipid transport systems (phloretin or verapamil) and moderately affected by the FAAH inhibitor methyl arachidonyl fluorophosphonate. The presence of FAAH in human prostate epithelial PC-3 cells was confirmed by analyzing its expression by Western blot and measuring FAAH activity. To further study the structural requirements of the putative carrier, we synthesized a series of structurally different compounds 1-8 and evaluated their capacity as uptake inhibitors. They showed different inhibitory capacity in PC-3 cells, with (9Z,12Z)-N-(fur-3-ylmethyl)octadeca-9,12-dienamide (4, UCM119) being the most efficacious, with maximal inhibition and IC50 values of 49% and 11.3+/-0.5 microM, respectively. In conclusion, PC-3 cells possess a complete inactivation system for anandamide formed by an uptake process and the enzyme FAAH. These results suggest a possible physiological function of anandamide in the prostate, reinforcing the role of endocannabinoid system as a neuroendocrine modulator. British Journal of Pharmacology (2004) 141, 457-467. doi:10.1038/sj.bjp.0705628

An optimized approach to study endocannabinoid signaling: evidence against constitutive activity of rat brain adenosine A1 and cannabinoid CB1 receptors

At nanomolar concentrations, SR141716 and AM251 act as specific and selective antagonists of the cannabinoid CB1 receptor. In the micromolar range, these compounds were shown to inhibit basal G-protein activity, and this is often interpreted to implicate constitutive activity of the CB1 receptors in native tissue. We show here, using [35S]GTPgammaS binding techniques, that micromolar concentrations of SR141716 and AM251 inhibit basal G-protein activity in rat cerebellar membranes, but only in conditions where tonic adenosine A1 receptor signaling is not eliminated. Unlike lipophilic A1 receptor antagonists (potency order DPCPX>>N-0840 approximately cirsimarin>caffeine), adenosine deaminase (ADA) was not fully capable in eliminating basal A1 receptor-dependent G-protein activity. Importantly, all antagonists reduced basal signal to the same extent (20%), and the response evoked by the inverse agonist DPCPX was not reversed by the neutral antagonist N-0840. These data indicate that rat brain A1 receptors are not constitutively active, but that an ADA-resistant adenosine pool is responsible for tonic A1 receptor activity in brain membranes. SR141716 and AM251, at concentrations fully effective in reversing CB1-mediated responses (10-6 m), did not reduce basal G-protein activity, indicating that CB1 receptors are not constitutively active in these preparations.4 At higher concentrations (1-2.5 x 10-5 m), both antagonists reduced basal G-protein activity in control and ADA-treated membranes, but had no effect when A1 receptor signaling was blocked with DPCPX. Moreover, the CB1 antagonists right-shifted A1 agonist dose-response curves without affecting maximal responses, suggesting competitive mode of antagonist action. The CB1 antagonists did not affect muscarinic acetylcholine or GABAB receptor signaling. When further optimizing G-protein activation assay for the labile endocannabinoid 2-arachidonoylglycerol (2-AG), we show, by using HPLC, that pretreatment of cerebellar membranes with methyl arachidonoyl fluorophosphonate (MAFP) fully prevented enzymatic degradation of 2-AG and concomitantly enhanced the potency of 2-AG. In contrast to previous claims, MAFP exhibited no antagonist activity at the CB1 receptor.6 The findings establish an optimized method with improved signal-to-noise ratio to assess endocannabinoid-dependent G-protein activity in brain membranes, under assay conditions where basal adenosinergic tone and enzymatic degradation of 2-AG are fully eliminated.

Cellular accumulation of anandamide: consensus and controversy

The endocannabinoids N-arachidonylethanolamine (AEA or anandamide) and 2-arachidonylglycerol (2-AG) are hypothesized to function in the brain as interneuronal signaling molecules. Prevailing models of the actions of these molecules require that they traverse cellular plasma membranes twice; first, following cellular synthesis and second, prior to enzymatic hydrolysis. The transmembrane movement of AEA has been studied in multiple laboratories with a primary focus on its cellular accumulation following extracellular administration. Although there are areas of consensus among laboratories regarding AEA accumulation, several aspects are very unclear. In particular, there is a lack of consensus in the literature regarding the importance of AEA hydrolysis by fatty acid amide hydrolase in maintaining the driving force for accumulation. Furthermore, evidence for and against a transmembrane carrier protein has been published. We have reviewed the available literature and present a working model of the processes that are involved in the cellular accumulation of AEA. It is our hypothesis that transmembrane movement of AEA is regulated by concentration gradient between extracellular and intracellular free AEA. Furthermore, it is our view that a significant portion of the intracellular AEA in most cells is sequestered either by a protein or lipid compartment and that AEA sequestered in this manner does not equilibrate directly with the extracellular pool. Finally, we discuss the available data that have been presented in support of a transmembrane carrier protein for AEA.

Inhibition of Platelet-Activating Factor (PAF) Acetylhydrolase by Methyl Arachidonyl Fluorophosphonate Potentiates PAF Synthesis in Thrombin-Stimulated Human Coronary Artery Endothelial Cells

We have previously demonstrated that thrombin stimulation of endothelial cells results in increased membrane-associated, Ca(2+)-independent phospholipase A2 (iPLA2) activity, accelerated hydrolysis of membrane plasmalogen phospholipids, and production of several biologically active phospholipid metabolites, including prostacyclin and platelet-activating factor (PAF) that is abolished by pretreatment with the iPLA2-selective inhibitor bromoenol lactone. This study was designed to further investigate the role of alternative PLA2 inhibitors, including methyl arachidonyl fluorophosphonate (MAFP, an inhibitor of cytosolic PLA2 isoforms), on phospholipid turnover and PAF production from thrombin-stimulated human coronary artery endothelial cells (HCAECs). Paradoxically, pretreatment of HCAEC with MAFP (5-25 microM) resulted in a significant increase in PAF production in both unstimulated and thrombin-stimulated cells that was found to be a direct result of inhibition of PAF acetylhydrolase (PAF-AH) activity. Pretreatment with MAFP did not significantly inhibit HCAEC PLA2 activity, possibly due to the localization of PLA2 activity in the membrane fraction rather than the cytosol. Bromoenol lactone did not inhibit PAF-AH activity, even at concentrations as high as 20 microM. We conclude that MAFP augments thrombin-stimulated PAF production by inhibition of PAF catabolism without affecting membrane-associated iPLA2 activity.

Arachidonylsulfonyl derivatives as cannabinoid CB1 receptor and fatty acid amide hydrolase inhibitors

Arachidonylsulfonyl fluoride (3), reported here for the first time, is similar in potency to its known methyl arachidonylfluorophosphonate (2) analogue as an inhibitor of mouse brain fatty acid amide hydrolase activity (IC(50) 0.1 nM) and cannabinoid CB1 agonist [3H]CP 55,940 binding (IC(50) 304-530 nM). Interestingly, 3 is much more selective than 2 as an inhibitor for fatty acid amide hydrolase relative to acetylcholinesterase, butyrylcholinesterase and neuropathy target esterase. N-(2-Hydroxyethyl)arachidonylsulfonamide (4) is at least 2500-fold less potent than N-(2-hydroxyethyl)arachidonamide (anandamide) (1) at the CB1 agonist site.

Molecular identification of a functional homologue of the mammalian fatty acid amide hydrolase in Arabidopsis thaliana

N-Acylethanolamines (NAEs) are endogenous constituents of plant and animal tissues, and in vertebrates their hydrolysis terminates their participation as lipid mediators in the endocannabinoid signaling system. The membrane-bound enzyme responsible for NAE hydrolysis in mammals has been identified at the molecular level (designated fatty acid amide hydrolase, FAAH), and although an analogous enzyme activity was identified in microsomes of cotton seedlings, no molecular information is available for this enzyme in plants. Here we report the identification, the heterologous expression (in Escherichia coli), and the biochemical characterization of an Arabidopsis thaliana FAAH homologue. Candidate Arabidopsis DNA sequences containing a characteristic amidase signature sequence (PS00571) were identified in plant genome data bases, and a cDNA was isolated by reverse transcriptase-PCR using Arabidopsis genome sequences to develop appropriate oligonucleotide primers. The cDNA was sequenced and predicted to encode a protein of 607 amino acids with 37% identity to rat FAAH within the amidase signature domain (18% over the entire length). Residues determined to be important for FAAH catalysis were conserved between the Arabidopsis and rat protein sequences. In addition, a single transmembrane domain near the N terminus was predicted in the Arabidopsis protein sequence, similar to that of the rat FAAH protein. The putative plant FAAH cDNA was expressed as an epitope/His-tagged fusion protein in E. coli and solubilized from cell lysates in the nonionic detergent, dodecyl maltoside. Affinity-purified recombinant protein was indeed active in hydrolyzing a variety of naturally occurring N-acylethanolamine types. Kinetic parameters and inhibition data for the recombinant Arabidopsis protein were consistent with these properties of the enzyme activity characterized previously in plant and animal systems. Collectively these data now provide support at the molecular level for a conserved mechanism between plants and animals for the metabolism of NAEs.

Esters, Retroesters, and a Retroamide of Palmitic Acid: Pool for the First Selective Inhibitors of N-Palmitoylethanolamine- Selective Acid Amidase

Cyclohexyl hexadecanoate, hexadecyl propionate, and N-(3-hydroxypropionyl)pentadecanamide, respectively ester, retroester, and retroamide derivatives of N-palmitoylethanolamine, represent the first selective inhibitors of "N-palmitoylethanolamine hydrolase" described so far. These compounds are devoid of affinity for CB(1) and CB(2) receptors and characterized by high percentages of inhibition of N-palmitoylethanolamine-selective acid amidase (84.0, 70.5, and 76.7% inhibition at 100 microM, respectively) with much lower inhibitory effect on either fatty acid amide hydrolase or the uptake of anandamide.

Fatty acid amide hydrolase: an emerging therapeutic target in the endocannabinoid system

The medicinal properties of exogenous cannabinoids have been recognized for centuries and can largely be attributed to the activation in the nervous system of a single G-protein-coupled receptor, CB1. However, the beneficial properties of cannabinoids, which include relief of pain and spasticity, are counterbalanced by adverse effects such as cognitive and motor dysfunction. The recent discoveries of anandamide, a natural lipid ligand for CB1, and an enzyme, fatty acid amide hydrolase (FAAH), that terminates anandamide signaling have inspired pharmacological strategies to augment endogenous cannabinoid ('endocannabinoid') activity with FAAH inhibitors, which might exhibit superior selectivity in their elicited behavioral effects compared with direct CB1 agonists.

A high-throughput-compatible assay for determining the activity of fatty acid amide hydrolase

Fatty acid amide hydrolase (EC 3.5.1.4.) is the enzyme responsible for the rapid degradation of lipid-derived chemical messengers such as anandamide, oleamide, and 2-arachidonoylglycerol. The pharmacological characterization of this enzyme in vivo has been hampered by the lack of selective and bioavailable inhibitors. We have developed a simple, radioactive, high-throughput-compatible assay for this enzyme based on the differential absorption of the substrate and its products to activated charcoal. The assay was validated using known inhibitors. It may be applied for the identification of new inhibitors from a compound library.

Design, synthesis, and structure-activity relationships of alkylcarbamic acid aryl esters, a new class of fatty acid amide hydrolase inhibitors

Fatty acid amide hydrolase (FAAH), an intracellular serine hydrolase enzyme, participates in the deactivation of fatty acid ethanolamides such as the endogenous cannabinoid anandamide, the intestinal satiety factor oleoylethanolamide, and the peripheral analgesic and anti-inflammatory factor palmitoylethanolamide. In the present study, we report on the design, synthesis, and structure-activity relationships (SAR) of a novel class of potent, selective, and systemically active inhibitors of FAAH activity, which we have recently shown to exert potent anxiolytic-like effects in rats. These compounds are characterized by a carbamic template substituted with alkyl or aryl groups at their O- and N-termini. Most compounds inhibit FAAH, but not several other serine hydrolases, with potencies that depend on the size and shape of the substituents. Initial SAR investigations suggested that the requirements for optimal potency are a lipophilic N-alkyl substituent (such as n-butyl or cyclohexyl) and a bent O-aryl substituent. Furthermore, the carbamic group is essential for activity. A 3D-QSAR analysis on the alkylcarbamic acid aryl esters showed that the size and shape of the O-aryl moiety are correlated with FAAH inhibitory potency. A CoMSIA model was constructed, indicating that whereas the steric occupation of an area corresponding to the meta position of an O-phenyl ring improves potency, a region of low steric tolerance on the enzyme active site exists corresponding to the para position of the same ring. The bent shape of the O-aryl moieties that best fit the enzyme surface closely resembles the folded conformations observed in the complexes of unsaturated fatty acids with different proteins. URB524 (N-cyclohexylcarbamic acid biphenyl-3-yl ester, 9g) is the most potent compound of the series (IC(50) = 63 nM) and was therefore selected for further optimization.

Evidence against the presence of an anandamide transporter

On the basis of temperature dependency, saturability, selective inhibition, and substrate specificity, it has been proposed that an anandamide transporter exists. However, all of these studies have examined anandamide accumulation at long time points when downstream effects such as metabolism and intracellular sequestration are operative. In the current study, we have investigated the initial rates (<1 min) of anandamide accumulation in neuroblastoma and astrocytoma cells in culture and have determined that uptake is not saturable with increasing concentrations of anandamide. However, anandamide hydrolysis, after uptake in neuroblastoma cells, was saturable at steady-state time points (5 min), suggesting that fatty acid amide hydrolase (FAAH) may be responsible for observed saturation of uptake at long time points. In general, arvanil, olvanil, and N-(4-hydroxyphenyl)arachidonylamide (AM404) have been characterized as transport inhibitors in studies using long incubations. However, we found these "transport inhibitors" did not inhibit anandamide uptake in neuroblastoma and astrocytoma cells at short time points (40 sec or less). Furthermore, we confirmed that these inhibitors in vitro were actually inhibitors of FAAH. Therefore, the likely mechanism by which the transport inhibitors raise anandamide levels to exert pharmacological effects is by inhibiting FAAH, and they should be reevaluated in this context. Immunofluorescence has indicated that FAAH staining resides mainly on intracellular membranes of neuroblastoma cells, and this finding is consistent with our observed kinetics of anandamide hydrolysis. In summary, these data suggest that anandamide uptake is a process of simple diffusion. This process is driven by metabolism and other downstream events, rather than by a specific membrane-associated anandamide carrier.

Anandamide inhibits nuclear factor-kappaB activation through a cannabinoid receptor-independent pathway

Anandamide (arachidonoylethanolamine, AEA), an endogenous agonist for both the cannabinoid CB(1) receptor and the vanilloid VR1 receptor, elicits neurobehavioral, anti-inflammatory, immunomodulatory, and proapoptotic effects. Because of the central role of nuclear factor-kappaB (NF-kappaB) in the inflammatory process and the immune response, we postulated that AEA might owe some of its effects to the suppression of NF-kappaB. This study shows that AEA inhibits tumor necrosis factor-alpha (TNFalpha)-induced NF-kappaB activation by direct inhibition of the IkappaB kinase (IKK)beta and, to a lesser extent, the IKKalpha subunits of kappaB inhibitor (IkappaB) kinase complex, and that IKKs inhibition by AEA correlates with inhibition of IkappaBalpha degradation, NF-kappaB binding to DNA, and NF-kappaB-dependent transcription in TNFalpha-stimulated cells. AEA also prevents NF-kappaB-dependent reporter gene expression induced by mitogen-activated protein kinase kinase kinase and NF-kappaB-inducing kinase. The NF-kappaB inhibitory activity of AEA was independent of CB(1) and CB(2) activation in TNFalpha-stimulated 5.1 and A549 cell lines, which do not express vanilloid receptor 1, and was not mediated by hydrolytic products formed through the activity of the enzyme fatty acid amide hydrolase. Chemical modification markedly affected AEA inhibitory activity on NF-kappaB, suggesting rather narrow structure-activity relationships and the specific interaction with a molecular target. Substitution of the alkyl moiety with less saturated fatty acids generally reduced or abolished activity. However, replacement of the ethanolamine "head" with a vanillyl group led to potent inhibition of TNFalpha-induced NF-kappaB-dependent transcription. These findings provide new mechanistic insights into the anti-inflammatory and proapoptotic activities of AEA, and should foster the synthesis of improved analogs amenable to pharmaceutical development as anti-inflammatory agents.

Intrathecally applied flurbiprofen produces an endocannabinoid-dependent antinociception in the rat formalin test

It is generally accepted that the phospholipase-A2-cyclooxygenase-prostanoids-cascade mediates spinal sensitization and hyperalgesia. However, some observations are not in line with this hypothesis. The aim of the present work was to investigate whether different components of this cascade exhibit nociceptive or antinociceptive effects in the rat formalin test. Intrathecal (i.th.) injection of prostaglandin E2 (PGE2) induced a dose-dependent antinociceptive effect on the formalin-induced nociception. Furthermore, thimerosal, which inhibits the reacylation of arachidonic acid thereby enhancing arachidonic acid levels, had an antinociceptive effect rather than the expected pronociceptive effect when given i.th. While the phospholipase A2 inhibitor methyl arachidonyl fluorophosphonate (MAFP; i.th.) had a significant antinociceptive effect, its analogue palmitoyl trifluoromethyl ketone (PTFMK; i.th.) had no significant effect on the formalin-induced nociception. However, MAFP, but not PTFMK, showed a cannabinoid CB1 agonistic effect as shown by the inhibition of electrically evoked contractions of the vas deferens isolated from CB1 wild-type mice but not of that from CB1 knockout mice. The antinociceptive effect of MAFP was completely reversed by the CB1 receptor antagonist AM-251 (i.th.), thus attributing such effect to its CB1 agonistic effect. Moreover, the antinociceptive effect of the cyclooxygenase inhibitor, flurbiprofen (i.th.) was reversed by the co-administration of AM-251, but not by PGE2. Finally. the combination of phenylmethylsulfonyl fluoride (PMSF; intraperitoneal), which inhibits the degradation of anandamide through the inhibition of fatty acid amidohydrolase, with thimerosal (i.th.) produced a profound CB1-dependent antinociception. The present results show that endocannabinoids play a major role in mediating flurbiprofen-induced antinociception at the spinal level.

Recent advances in the synthesis of endocannabinoid related ligands

The chemical strategies used for the synthesis of various ligands related to the endocannabinoid system namely anandamide (AEA), 2-arachidonylglycerol (2-Ara-Gl), CB1/(vanilloid receptors) VR1, anandamide membrane transporter (AMT) and fatty acid amide hydrolase (FAAH) are described in this review. In general, the chemical synthesis of analogs with changes in the head group of AEA was quite straightforward involving the conversion of an acid to an amide or an ester. Analogs which had modifications in the end pentyl chain were more difficult to synthesize and required multistep synthetic sequences to prepare the target compounds. A facile total synthesis of 2-Ara-Gl was reported and an HPLC procedure for its identification and quantification was developed, but because of the instability of 2-Ara-Gl another synthesis was developed so that it can be stored as the more stable phenylboronate ester. Similarly the chemical synthesis of various ligands in the remaining areas of CB1/VR1, AMT and FAAH are described. A summary of the present state of knowledge about the SAR in each area is presented to help in the design and synthesis of novel ligands for the future.

Cannabinergic ligands

The understanding of the pharmacology surrounding the cannabinergic system has seen many advances since the discovery of the CB1 receptor in the mammalian brain and the CB2 receptor in the periphery. Among these advances is the discovery of the endogenous ligands arachidonoylethanolamide (anandamide) and 2-arachidonoylglycerol amide (2-AG), which are selective agonists for the CB1 and CB2 receptors, respectively. These endogenous neuromodulators involved in the cannabinergic system are thought to be produced on demand and are metabolized by the enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAG lipase). Recently, we characterized a reuptake system that facilitates the transport of anandamide across the cell membrane and subsequently developed selective inhibitors of this transport, which have been found to have therapeutic potential as analgesic and peripheral vasodilators. The cannabinergic proteins currently being explored, which include the CB1 and CB2 receptors, FAAH and the anandamide transporter, are excellent targets for the development of therapeutically useful drugs for a range of conditions including pain, loss of appetite, immunosuppression, peripheral vascular disease and motor disorders. As cannabinoid research has progressed, various potent and selective cannabimimetic ligands, targeting these four cannabinoid proteins, have been designed and synthesized. Many of these ligands serve as important molecular probes, providing structural information regarding the binding sites of the cannabinergic proteins, as well as pharmacological tools, which have been playing pivotal roles in research aimed at understanding the biochemical and physiological aspects of the endocannabinoid system. This review will focus on some of the current cannabinergic ligands and probes and their pharmacological and therapeutic potential.

Experimental parkinsonism alters endocannabinoid degradation: implications for striatal glutamatergic transmission

Cannabinoid receptors and their endogenous ligands have been recently identified in the brain as potent inhibitors of neurotransmitter release. Here we show that, in a rat model of Parkinson's disease induced by unilateral nigral lesion with 6-hydroxydopamine (6-OHDA), the striatal levels of anandamide, but not that of the other endocannabinoid 2-arachidonoylglycerol, were increased. Moreover, we observed a decreased activity of the anandamide membrane transporter (AMT) and of the anandamide hydrolase [fatty acid amide hydrolase (FAAH)], whereas the binding of anandamide to cannabinoid receptors was unaffected. Spontaneous glutamatergic activity recorded from striatal spiny neurons was higher in 6-OHDA-lesioned rats. Inhibition of AMT by N-(4-hydroxyphenyl)-arachidonoylamide (AM-404) or by VDM11, or stimulation of the cannabinoid CB1 receptor by HU-210 reduced glutamatergic spontaneous activity in both naive and 6-OHDA-lesioned animals to a similar extent. Conversely, the FAAH inhibitors phenylmethylsulfonyl fluoride and methyl-arachidonoyl fluorophosphonate were much more effective in 6-OHDA-lesioned animals. The present study shows that inhibition of anandamide hydrolysis might represent a possible target to decrease the abnormal cortical glutamatergic drive in Parkinson's disease.

Cannabinoid CB1 receptor as a target for chlorpyrifos oxon and other organophosphorus pesticides

Binding of the endocannabinoid anandamide or of Delta(9)-tetrahydrocannabinol to the agonist site of the cannabinoid receptor (CB1) is commonly assayed with [3H]CP 55,940. Potent long-chain alkylfluorophosphonate inhibitors of agonist binding suggest an additional, important and closely-coupled nucleophilic site, possibly undergoing phosphorylation. We find that the CB1 receptor is also sensitive to inhibition in vitro and in vivo by several organophosphorus pesticides and analogs. Binding of [3H]CP 55,940 to mouse brain CB1 receptor in vitro is inhibited 50% by chlorpyrifos oxon at 14 nM, chlorpyrifos methyl oxon at 64 nM and paraoxon, diazoxon and dichlorvos at 1200-4200 nM. Some 15 other organophosphorus pesticides and analogs are less active in vitro. The plant defoliant tribufos inhibits CB1 in vivo, without cholinergic poisoning signs, by 50% at 50 mg/kg intraperitoneally with a recovery half-time of 3-4 days, indicating covalent derivatization. [3H-ethyl]Chlorpyrifos oxon may be suitable for radiolabeling and characterization of this proposed nucleophilic site.

Endocannabinoid hydrolases

Endocannabinoids (endogenous ligands of cannabinoid receptors) such as anandamide (N-arachidonoylethanolamine) and 2-arachidonoylglycerol (2-AG) are inactivated upon enzymatic hydrolysis. Recent progress in the enzymological and molecular biological studies on the 'endocannabinoid hydrolases' is reviewed in this article. Anandamide is hydrolyzed to arachidonic acid and ethanolamine by a membrane-bound amidase generally referred to as fatty acid amide hydrolase (FAAH). This enzyme has a broad substrate specificity, hydrolyzing oleamide (an endogenous sleep-inducing factor) and 2-AG as well as anandamide. cDNA cloning revealed that FAAH is composed of 579 amino acids and belongs to the amidase signature family. A serine residue functioning as a catalytic nucleophile and several other catalytically important residues were identified in its primary structure. Furthermore, recent generation and analysis of the FAAH gene-deficient mice demonstrated the central role of this enzyme in the metabolism of anandamide. Alternatively, an amidase, which is distinct from FAAH but also hydrolyzing anandamide and other N-acylethanolamines at acidic pH, was identified in human megakaryoblastic cells and rat organs such as lung and spleen. As for the 2-AG hydrolysis, in addition to the known monoacylglycerol lipase, other esterases and FAAH may be involved.

Activation of N-acylethanolamine-releasing phospholipase D by polyamines

N-acylethanolamines including anandamide (an endogenous ligand of cannabinoid receptors) are biosynthesized from N-acyl-phosphatidylethanolamine (PE) by a phosphodiesterase of the phospholipase D type. The enzyme partially purified from the particulate fraction of rat heart hydrolyzed N-palmitoyl-PE to N-palmitoylethanolamine with a specific activity of 50 nmol/min per mg protein at 37 degrees C in the presence of 10 mM CaCl2. We found that the enzyme was highly activated in dose-dependent manner by polyamines like spermine, spermidine, and putrescine. Spermine was the most potent with an EC50 value around 0.1 mM, and increased the specific enzyme activity 27 fold up to 53 nmol/min per mg protein. However, a synergistic effect of spermine and the known activator (Ca2+ or Triton X-100) was not observed. The spermine-stimulated enzyme was also active with N-arachidonoyl-PE (a precursor of anandamide). Thus, polyamines may function as endogenous activators to control the biosynthesis of anandamide and other N-acylethanolamines.

The spinal phospholipase-cyclooxygenase-prostanoid cascade in nociceptive processing

Intrathecal phospholipase A2 (PLA2) and cyclooxygenase-2 (COX-2), but not COX-1, inhibitors attenuate facilitated pain states generated by peripheral injury/inflammation and by direct activation of spinal glutamate and substance P receptors. These results are consistent with the constitutive expression of PLA2 and COX-2 in spinal cord, the spinal release of prostaglandins by persistent afferent input, and the effects of prostaglandins on spinal excitability. Whereas the acute actions of COX-2 inhibitors are clearly mediated by constitutively expressed spinal COX-2, studies of spinal COX-2 expression indicate that it is upregulated by neural input and circulating cytokines. Given the intrathecal potency of COX-2 inhibitors, the comparable efficacy of intrathecal versus systemic COX-2 inhibitors in hyperalgesic states not associated with inflammation, and the onset of antihyperalgesic activity prior to COX-2 upregulation, it is argued that a principal antihyperalgesic mechanism of COX-2 inhibitors lies with modulation of constitutive COX-2 present at the spinal level.

Selective inhibitors of fatty acid amide hydrolase relative to neuropathy target esterase and acetylcholinesterase: toxicological implications

Fatty acid amide hydrolase (FAAH) plays an important role in nerve function by regulating the action of endocannabinoids (e.g., anandamide) and hydrolyzing a sleep-inducing factor (oleamide). Several organophosphorus pesticides and related compounds are shown in this study to be more potent in vivo inhibitors of mouse brain FAAH than neuropathy target esterase (NTE), raising the question of the potential toxicological relevance of FAAH inhibition. These FAAH-selective compounds include tribufos and (R)-octylbenzodioxaphosphorin oxide with delayed neurotoxic effects in mice and hens plus several organophosphorus pesticides (e.g., fenthion) implicated as delayed neurotoxicants in humans. The search for a highly potent and selective inhibitor for FAAH relative to NTE for use as a toxicological probe culminated in the discovery that octylsulfonyl fluoride inhibits FAAH by 50% at 2 nM in vitro and 0.2 mg/kg in vivo and NTE is at least 100-fold less sensitive in each case. More generally, the studies revealed 12 selective in vitro inhibitors for FAAH (mostly octylsulfonyl and octylphosphonyl derivatives) and 9 for NTE (mostly benzodioxaphosphorin oxides and organophosphorus fluoridates). The overall in vivo findings with 16 compounds indicate the expected association of AChE inhibition with acute or cholinergic syndrome and >70% brain NTE inhibition with delayed neurotoxic action. Surprisingly, 75-99% brain FAAH inhibition does not lead to any overt neurotoxicity or change in behavior (other than potentiation of exogenous anandamide action). Thus, FAAH inhibition in mouse brain does not appear to be a primary target for organophosphorus pesticide-induced neurotoxic action (cholinergic or intermediate syndrome or delayed neurotoxicity).

Endocannabinoid structure-activity relationships for interaction at the cannabinoid receptors

Anandamide (N -arachidonoylethanolamine) was the first ligand to be identified as an endogenous ligand of the G-protein coupled cannabinoid CB1 receptor. Subsequently, two other fatty acid ethanolamides, N -homo- gamma -linolenylethanolamine and N -7,10,13,16-docosatetraenylethanolamine were identified as endogenous cannabinoid ligands. A fatty acid ester, 2-arachidonoylglycerol (2-AG), and a fatty acid ether, 2-arachidonyl glyceryl ether also have been isolated and shown to be endogenous cannabinoid ligands. Recent studies have postulated the existence of carrier-mediated anandamide transport that is essential for termination of the biological effects of anandamide. A membrane bound amidohydrolase (fatty acid amide hydrolase, FAAH), located intracellularly, hydrolyzes and inactivates anandamide and other endogenous cannabinoids such as 2-AG. 2-AG has also been proposed to be an endogenous CB2 ligand. Structure-activity relationships (SARs) for endocannabinoid interaction with the CB receptors are currently emerging in the literature. This review considers cannabinoid receptor SAR developed to date for the endocannabinoids with emphasis upon the conformational implications for endocannabinoid recognition at the cannabinoid receptors.

The fatty acid amide hydrolase (FAAH)

The fatty acid amide hydrolase (FAAH), is the enzyme responsible for the hydrolysis of anandamide, an endocannabinoid. The FAAH knockout, the assays for FAAH, the activity of its substrates, its reversibility and its cloning from rat, mouse, human, and pig are covered in this review. The conserved regions of FAAH are described in terms of sequence and function, including the domains that contains the serine catalytic nucleophile, the hydrophobic domain important for self-association, the proline rich domain region which may be important for subcellular localization and the fatty acid chain binding domain. The FAAH mouse promoter region was characterized in terms of its transcription start site and its activity in different cell types. The distribution of FAAH in the major organs in the body is described as well as regional distribution in the brain and its correlation with cannabinoid receptors. Since FAAH is recognized as a drug target, a large number of inhibitors have been synthesized and tested since 1994 and these are reviewed in terms of reversibility, potency, and specificity for FAAH.

Purification and characterization of an acid amidase selective for N-palmitoylethanolamine, a putative endogenous anti-inflammatory substance

N-Arachidonoylethanolamine (anandamide) is cannabimimetic, and N-palmitoylethanolamine is anti-inflammatory and immunosuppressive. We found an amidase that is more active with the latter than the former in contrast to the previously known anandamide amidohydrolase for which N-palmitoylethanolamine is a poor substrate. Proteins solubilized by freezing and thawing from the 12,000 x g pellet of various rat organs hydrolyzed [(14)C]N-palmitoylethanolamine to palmitic acid and ethanolamine. The specific enzyme activity was higher in the order of lung > spleen > small intestine > thymus > cecum, and high activity was found in peritoneal and alveolar macrophages. The enzyme with a molecular mass of 31 kDa was purified from rat lung to a specific activity of 1.8 micromol/min/mg protein. Relative reactivities of the enzyme with various N-acylethanolamines (100 microm) were as follows: N-palmitoylethanolamine, 100%; N-myristoylethanolamine, 48%; N-stearoylethanolamine, 21%; N-oleoylethanolamine, 20%; N-linoleoylethanolamine, 13%; anandamide, 8%. The enzyme was the most active at pH 5 and was activated 7-fold by Triton X-100. The enzyme was almost insensitive to methyl arachidonyl fluorophosphonate, which inhibited anandamide amidohydrolase potently. Thus, the new enzyme referred to as N-palmitoylethanolamine hydrolase was clearly distinguishable from anandamide amidohydrolase.

Fatty acid amide hydrolase: biochemistry, pharmacology, and therapeutic possibilities for an enzyme hydrolyzing anandamide, 2-arachidonoylglycerol, palmitoylethanolamide, and oleamide

Fatty acid amide hydrolase (FAAH) is responsible for the hydrolysis of a number of important endogenous fatty acid amides, including the endogenous cannabimimetic agent anandamide (AEA), the sleep-inducing compound oleamide, and the putative anti-inflammatory agent palmitoylethanolamide (PEA). In recent years, there have been great advances in our understanding of the biochemical and pharmacological properties of the enzyme. In this commentary, the structure and biochemical properties of FAAH and the development of potent and selective FAAH inhibitors are reviewed, together with a brief discussion on the therapeutic possibilities for such compounds in the treatment of inflammatory pain and ischaemic states.

Proteins regulating the biosynthesis and inactivation of neuromodulatory fatty acid amides

Fatty acid amides (FAAs) represent a growing family of biologically active lipids implicated in a diverse range of cellular and physiological processes. At present, two general types of fatty acid amides, the N-acylethanolamines (NAEs) and the fatty acid primary amides (FAPAs), have been identified as potential physiological neuromodulators/neurotransmitters in mammals. Representative members of these two subfamilies include the endocannabinoid NAE anandamide and the sleep-inducing FAPA oleamide. In this Chapter, molecular mechanisms proposed for the biosynthesis and inactivation of FAAs are critically evaluated, with an emphasis placed on the biochemical and cell biological properties of proteins thought to mediate these processes.

Role of Fatty Acid Amide Hydrolase in the Transport of the Endogenous Cannabinoid Anandamide

A facilitated transport process that removes the endogenous cannabinoid anandamide from extracellular spaces has been identified. Once transported into the cytoplasm, fatty acid amide hydrolase (FAAH) is responsible for metabolizing the accumulated anandamide. We propose that FAAH contributes to anandamide uptake by creating and maintaining an inward concentration gradient for anandamide. To explore the role of FAAH in anandamide transport, we examined anandamide metabolism and uptake in RBL-2H3 cells, which natively express FAAH, as well as wild-type HeLa cells that lack FAAH. RBL-2H3 and FAAH-transfected HeLa cells demonstrated a robust ability to metabolize anandamide compared with vector-transfected HeLa cells. This activity was reduced to that observed in wild-type HeLa cells upon the addition of the FAAH inhibitor methyl arachidonyl fluorophosphonate. Anandamide uptake was reduced in a dose-dependent manner by various FAAH inhibitors in both RBL-2H3 cells and wild-type HeLa cells. Anandamide uptake studies in wild-type HeLa cells showed that only FAAH inhibitors structurally similar to anandamide decreased anandamide uptake. Because there is no detectable FAAH activity in wild-type HeLa cells, these FAAH inhibitors are probably blocking uptake via actions on a plasma membrane transport protein. Phenylmethylsulfonyl fluoride, a FAAH inhibitor that is structurally unrelated to anandamide, inhibited anandamide uptake in RBL-2H3 cells and FAAH-transfected HeLa cells, but not in wild-type HeLa cells. Furthermore, expression of FAAH in HeLa cells increased maximal anandamide transport 2-fold compared with wild-type HeLa cells. These results suggest that FAAH facilitates anandamide uptake but is not solely required for transport to occur.

Fatty Acid Amide Hydrolase Inhibition by Neurotoxic Organophosphorus Pesticides

Organophosphorus (OP) compound-induced inhibition of acetylcholinesterase (AChE) and neuropathy target esterase explains the rapid onset and delayed neurotoxic effects, respectively, for OP insecticides and related compounds but apparently not a third or intermediate syndrome with delayed onset and reduced limb mobility. This investigation tests the hypothesis that fatty acid amide hydrolase (FAAH), a modulator of endogenous signaling compounds affecting sleep (oleamide) and analgesia (anandamide), is a sensitive target for OP pesticides with possible secondary neurotoxicity. Chlorpyrifos oxon inhibits 50% of the FAAH activity (IC50 at 15 min, 25 degrees C, pH 9.0) in vitro at 40--56 nM for mouse brain and liver, whereas methyl arachidonyl phosphonofluoridate, ethyl octylphosphonofluoridate (EOPF), oleyl-4H-1,3,2-benzodioxaphosphorin 2-oxide (oleyl-BDPO), and dodecyl-BDPO give IC50s of 0.08--1.1 nM. These BDPOs and EOPF inhibit mouse brain FAAH in vitro with > or =200-fold higher potency than for AChE. Five OP pesticides inhibit 50% of the brain FAAH activity (ED50) at <30 mg/kg 4 h after ip administration to mice; while inhibition by chlorpyrifos, diazinon, and methamidophos occurs near acutely toxic levels, profenofos and tribufos are effective at asymptomatic doses. Two BDPOs (dodecyl and phenyl) and EOPF are potent inhibitors of FAAH in vivo (ED50 0.5--6 mg/kg). FAAH inhibition of > or =76% in brain depresses movement of mice administered anandamide at 30 mg/kg ip, often leading to limb recumbency. Thus, OP pesticides and related inhibitors of FAAH potentiate the cannabinoid activity of anandamide in mice. More generally, OP compound-induced FAAH inhibition and the associated anandamide accumulation may lead to reduced limb mobility as a secondary neurotoxic effect.

The activity of anandamide at vanilloid VR1 receptors requires facilitated transport across the cell membrane and is limited by intracellular metabolism

The endogenous ligand of CB(1) cannabinoid receptors, anandamide, is also a full agonist at vanilloid VR1 receptors for capsaicin and resiniferatoxin, thereby causing an increase in cytosolic Ca(2+) concentration in human VR1-overexpressing (hVR1-HEK) cells. Two selective inhibitors of anandamide facilitated transport into cells, VDM11 and VDM13, and two inhibitors of anandamide enzymatic hydrolysis, phenylmethylsulfonyl fluoride and methylarachidonoyl fluorophosphonate, inhibited and enhanced, respectively, the VR1-mediated effect of anandamide, but not of resiniferatoxin or capsaicin. The nitric oxide donor, sodium nitroprusside, known to stimulate anandamide transport, enhanced anandamide effect on the cytosolic Ca(2+) concentration. Accordingly, hVR1-HEK cells contain an anandamide membrane transporter inhibited by VDM11 and VDM13 and activated by sodium nitroprusside, and an anandamide hydrolase activity sensitive to phenylmethylsulfonyl fluoride and methylarachidonoyl fluorophosphonate, and a fatty acid amide hydrolase transcript. These findings suggest the following. (i) Anandamide activates VR1 receptors by acting at an intracellular site. (ii) Degradation by fatty acid amide hydrolase limits anandamide activity on VR1; and (iii) the anandamide membrane transporter inhibitors can be used to distinguish between CB(1) or VR1 receptor-mediated actions of anandamide. By contrast, the CB(1) receptor antagonist SR141716A inhibited also the VR1-mediated effect of anandamide and capsaicin on cytosolic Ca(2+) concentration, although at concentrations higher than those required for CB(1) antagonism.

The cellular uptake of anandamide is coupled to its breakdown by fatty-acid amide hydrolase

Anandamide is an endogenous compound that acts as an agonist at cannabinoid receptors. It is inactivated via intracellular degradation after its uptake into cells by a carrier-mediated process that depends upon a concentration gradient. The fate of anandamide in those cells containing an amidase called fatty-acid amide hydrolase (FAAH) is hydrolysis to arachidonic acid and ethanolamine. The active site nucleophilic serine of FAAH is inactivated by a variety of inhibitors including methylarachidonylfluorophosphonate (MAFP) and palmitylsulfonyl fluoride. In the current report, the net uptake of anandamide in cultured neuroblastoma (N18) and glioma (C6) cells, which contain FAAH, was decreased by nearly 50% after 6 min of incubation in the presence of MAFP. Uptake in laryngeal carcinoma (Hep2) cells, which lack FAAH, is not inhibited by MAFP. Free anandamide was found in all MAFP-treated cells and in control Hep2 cells, whereas phospholipid was the main product in N18 and C6 control cells when analyzed by TLC. The intracellular concentration of anandamide in N18, C6, and Hep2 cells was up to 18-fold greater than the extracellular concentration of 100 nm, which strongly suggests that it is sequestered within the cell by binding to membranes or proteins. The accumulation of anandamide and/or its breakdown products was found to vary among the different cell types, and this correlated approximately with the amount of FAAH activity, suggesting that the breakdown of anandamide is in part a driving force for uptake. This was shown most clearly in Hep2 cells transfected with FAAH. The uptake in these cells was 2-fold greater than in vector-transfected or untransfected Hep2 cells. Therefore, it appears that FAAH inhibitors reduce anandamide uptake by cells by shifting the anandamide concentration gradient in a direction that favors equilibrium. Because inhibition of FAAH increases the levels of extracellular anandamide, it may be a useful target for the design of therapeutic agents.

The fatty acid amide hydrolase (FAAH)

The topic of this review is fatty acid amide hydrolase (FAAH), one of the best-characterized enzymes involved in the hydrolysis of bioactive lipids such as anandamide, 2-arachidonoylglycerol (2-AG), and oleamide. Herein, we discuss the nomenclature, the various assays that have been developed, the relative activity of the various substrates and the reversibility of the enzyme reactions catalyzed by FAAH. We also describe the cloning of the enzyme from rat and subsequent cDNA isolation from mouse, human, and pig. The proteins and the mRNAs from different species are compared. Cloning the enzyme permitted the purification and characterization of recombinant FAAH. The conserved regions of FAAH are described in terms of sequence and function, including the amidase domain which contains the serine catalytic nucleophile, the hydrophobic domain important for self association, and the proline rich domain region, which may be important for subcellular localization. The distribution of FAAH in the major organs of the body is described as well as regional distribution in the brain and its correlation with cannabinoid receptors. Since FAAH is recognized as a drug target, a large number of inhibitors have been synthesized and tested since 1994 and these are reviewed in terms of reversibility, potency, and specificity for FAAH and cannabinoid receptors.

Conformational requirements for endocannabinoid interaction with the cannabinoid receptors, the anandamide transporter and fatty acid amidohydrolase

Anandamide (N-arachidonoylethanolamine) has been identified as an endogenous ligand of the G-protein coupled cannabinoid CB(1) receptor. Recent studies have postulated the existence of carrier-mediated anandamide transport which is involved in the termination of the biological effects of anandamide. A membrane bound amidohydrolase (fatty acid amide hydrolase, FAAH), located intracellulary, hydrolyzes and inactivates anandamide and other endogenous cannabinoids such as 2-arachidonoylglycerol (2-AG). Structure-activity relationships (SARs) for endocannabinoid interaction with the CB receptors, the anandamide transporter and FAAH are currently emerging in the literature. This review considers the divergences between these SARs and focuses upon the conformational implications for endocannabinoid recognition at each of these biological targets.