High-performance liquid chromatographic determination of anandamide amidase activity in rat brain microsomes

( R)- N-(1-Methyl-2-hydroxyethyl)-13-( S)-methyl-arachidonamide (AMG315): A Novel Chiral Potent Endocannabinoid Ligand with Stability to Metabolizing Enzymes

The synthesis of potent metabolically stable endocannabinoids is challenging. Here we report a chiral arachidonoyl ethanolamide (AEA) analogue, namely, (13 S,1' R)-dimethylanandamide (AMG315, 3a), a high affinity ligand for the CB1 receptor ( K_i of 7.8 ± 1.4 nM) that behaves as a potent CB1 agonist in vitro (EC₅₀ = 0.6 ± 0.2 nM). (13 S,1' R)-dimethylanandamide is the first potent AEA analogue with significant stability for all endocannabinoid hydrolyzing enzymes as well as the oxidative enzymes COX-2. When tested in vivo using the CFA-induced inflammatory pain model, 3a behaved as a more potent analgesic when compared to endogenous AEA or its hydrolytically stable analogue AM356. This novel analogue will serve as a very useful endocannabinoid probe.

The monoacylglycerol lipase inhibitor JZL184 attenuates LPS-induced increases in cytokine expression in the rat frontal cortex and plasma: differential mechanisms of action

BACKGROUND AND PURPOSE

JZL184 is a selective inhibitor of monoacylglycerol lipase (MAGL), the enzyme that preferentially catabolizes the endocannabinoid 2-arachidonoyl glycerol (2-AG). Here, we have studied the effects of JZL184 on inflammatory cytokines in the brain and plasma following an acute immune challenge and the underlying receptor and molecular mechanisms involved.

EXPERIMENTAL APPROACH

JZL184 and/or the CB₁ receptor antagonist, AM251 or the CB₂ receptor antagonist, AM630 were administered to rats 30 min before lipopolysaccharide (LPS). 2 h later cytokine expression and levels, MAGL activity, 2-AG, arachidonic acid and prostaglandin levels were measured in the frontal cortex, plasma and spleen.

KEY RESULTS

JZL184 attenuated LPS-induced increases in IL-1β, IL-6, TNF-α and IL-10 but not the expression of the inhibitor of NFkB (IκBα) in rat frontal cortex. AM251 attenuated JZL184-induced decreases in frontal cortical IL-1β expression. Although arachidonic acid levels in the frontal cortex were reduced in JZL184-treated rats, MAGL activity, 2-AG, PGE₂ and PGD₂ were unchanged. In comparison, MAGL activity was inhibited and 2-AG levels enhanced in the spleen following JZL184. In plasma, LPS-induced increases in TNF-α and IL-10 levels were attenuated by JZL184, an effect partially blocked by AM251. In addition, AM630 blocked LPS-induced increases in plasma IL-1β in the presence, but not absence, of JZL184.

CONCLUSION AND IMPLICATIONS

Inhibition of peripheral MAGL in rats by JZL184 suppressed LPS-induced circulating cytokines that in turn may modulate central cytokine expression. The data provide further evidence for the endocannabinoid system as a therapeutic target in treatment of central and peripheral inflammatory disorders.

2012 Division of medicinal chemistry award address. Trekking the cannabinoid road: a personal perspective

My involvement with the field of cannabinoids spans close to 3 decades and covers a major part of my scientific career. It also reflects the robust progress in this initially largely unexplored area of biology. During this period of time, I have witnessed the growth of modern cannabinoid biology, starting from the discovery of its two receptors and followed by the characterization of its endogenous ligands and the identification of the enzyme systems involved in their biosynthesis and biotransformation. I was fortunate enough to start at the beginning of this new era and participate in a number of the new discoveries. It has been a very exciting journey. With coverage of some key aspects of my work during this period of "modern cannabinoid research," this Award Address, in part historical, intends to give an account of how the field grew, the key discoveries, and the most promising directions for the future.

Endocannabinoid enzyme engineering: soluble human thio-monoacylglycerol lipase (sol-S-hMGL)

In the mammalian central nervous system, monoacylglycerol lipase (MGL) is principally responsible for inactivating the endocannabinoid signaling lipid 2-arachidonoylglycerol (2-AG) and modulates cannabinoid-1 receptor (CB1R) desensitization and signal intensity. MGL is also a drug target for diseases in which CB1R stimulation may be therapeutic. To inform the design of human MGL (hMGL) inhibitors, we have engineered a Leu(Leu(169);Leu(176))-to-Ser(Ser(169);Ser(176)) double hMGL mutant (sol-hMGL) which exhibited enhanced solubility properties, and we further mutated this variant by substituting its catalytic-triad Ser(122) with Cys (sol-S-hMGL). The hMGL variants hydrolyzed both 2-AG and a fluorogenic reporter substrate with comparable affinities. Our results suggest that the hMGL cysteine mutant maintains the same overall architecture as wild-type hMGL. The results also underscore the superior nucleophilic nature of the reactive catalytic Ser(122) residue as compared to that of Cys(122) in the sol-S-hMGL mutant and suggest that the nucleophilic character of the Cys(122) residue is not commensurately enhanced within the three dimensional architecture of hMGL. The interaction of the sol-hMGL variants with the irreversible inhibitors AM6580 and N-arachidonylmaleimide (NAM) and the reversible inhibitor AM10212 was profiled. LC/MS analysis of tryptic digests from sol-S-hMGL directly demonstrate covalent modification of this variant by NAM and AM6580, consistent with enzyme thiol alkylation and carbamoylation, respectively. These data provide insight into hMGL catalysis, the key role of the nucleophilic character of Ser(122), and the mechanisms underlying hMGL inhibition by different classes of small molecules.

A scintillation proximity assay for fatty acid amide hydrolase compatible with inhibitor screening

Scintillation proximity assay (SPA) is a homogenous and versatile technology for the simple and sensitive detection of the interaction of protein targets with their ligands. Herein, we described a SPA assay developed to identify compounds that bind to human fatty acid amide hydrolase (FAAH). This SPA assay utilizes the specific binding of [(3)H]-R(+)-methanandamide ((3)H-MAEA), a competitive nonhydrolyzed FAAH inhibitor, to FAAH expressing microsomes and evaluates its displacement by FAAH inhibitors. In contrast to the classical SPA radioligand binding assay which detects bound ligand, in our assay the released radiolabel is detected through its interaction with the SPA beads. This novel SPA assay has been validated and demonstrated to be simple, sensitive, and amenable to high-throughput screening.

A novel monoacylglycerol lipase inhibitor with analgesic and anti-inflammatory activity

A variety of long chain 1,2-diamines and related compounds were synthesized and tested for their activity on fatty acid amide hydrolase (FAAH) and monoacyglycerol lipase (MGL). (2S,9Z)-Octadec-9-ene-1,2-diamine selectively inhibits MGL (K(i) 21.8 microM) without significantly affecting FAAH. This compound exhibited interesting in vivo analgesic and anti-inflammatory properties, suggesting that selective inhibitors of MGL may be valuable novel agents for the treatment of inflammatory pain.

Development of novel tail-modified anandamide analogs

To explore the hydrophobic groove subsite within the CB1 cannabinoid receptor we have designed and synthesized a group of tail-substituted anandamide analogs. Our design involves the introduction of aryl or heterocyclic ring as terminal substituents that are connected to the last cis-arachidonyl double bond through aliphatic chains of variable lengths. Our results indicate that there are strict stereochemical requirements for the interaction of such analogs with the CB1 receptor. The optimal pharmacophore includes the phenyl, p-substituted phenyl, or 3-furyl substituents attached to the cis-double bond through a four methylene chain.

Ligands that target cannabinoid receptors in the brain: from THC to anandamide and beyond

A major finding--that (-)-trans-Delta(9)-tetrahydrocannabinol (Delta(9)-THC) is largely responsible for the psychotropic effects of cannabis--prompted research in the 1970s and 1980s that led to the discovery that this plant cannabinoid acts through at least two types of cannabinoid receptor, CB(1) and CB(2), and that Delta(9)-THC and other compounds that target either or both of these receptors as agonists or antagonists have important therapeutic applications. It also led to the discovery that mammalian tissues can themselves synthesize and release agonists for cannabinoid receptors, the first of these to be discovered being arachidonoylethanolamide (anandamide) and 2-arachidonoylglycerol. These 'endocannabinoids' are released onto their receptors in a manner that appears to maintain homeostasis within the central nervous system and sometimes either to oppose or to mediate or exacerbate the unwanted effects of certain disorders. This review provides an overview of the pharmacology of cannabinoid receptors and their ligands. It also describes actual and potential clinical uses both for cannabinoid receptor agonists and antagonists and for compounds that affect the activation of cannabinoid receptors less directly, for example by inhibiting the enzymatic hydrolysis of endocannabinoids following their release.

Full mass spectrometric characterization of human monoacylglycerol lipase generated by large-scale expression and single-step purification

The serine hydrolase monoacylglycerol lipase (MGL) modulates endocannabinoid signaling in vivo by inactivating 2-arachidonoylglycerol (2-AG), the main endogenous agonist for central CB1 and peripheral CB2 cannabinoid receptors. To characterize this key endocannabinoid enzyme by mass spectrometry-based proteomics, we first overexpressed recombinant hexa-histidine-tagged human MGL (hMGL) in Escherichia coli and purified it in a single chromatographic step with high yield (approximately 30 mg/L). With 2-AG as substrate, hMGL displayed an apparent V max of 25 micromol/(microg min) and K m of 19.7 microM, an affinity for 2-AG similar to that of native rat-brain MGL (rMGL) (Km=33.6 microM). hMGL also demonstrated a comparable affinity (Km approximately 8-9 microM) for the novel fluorogenic substrate, arachidonoyl, 7-hydroxy-6-methoxy-4-methylcoumarin ester (AHMMCE), in a sensitive, high-throughput fluorometric MGL assay. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) unequivocably demonstrated the mass (34,126 Da) and purity of this hMGL preparation. After in-solution tryptic digestion, hMGL full proteomic characterization was carried out, which showed (1) an absence of intramolecular disulfide bridges in the functional, recombinant enzyme and (2) the post-translational removal of the enzyme's N-terminal methionine. Availability of sufficient quantities of pure, well-characterized hMGL will enable further molecular and structural profiling of this key endocannabinoid-system enzyme.

Conformationally constrained analogues of 2-arachidonoylglycerol

Novel monocyclic analogues of 2-arachidonoylglycerol (2-AG) were designed in order to explore the pharmacophoric conformations of this endocannabinoid ligand at the key cannabinergic proteins. All 2-arachidonoyl esters of 1,2,3-cyclohexanetriol [meso-7 (AM5504), (+/-)-8 (AM5503), and meso-9 (AM5505)] were synthesized by regioselective acylation of 2,3-dihydroxycyclohexanone followed by selective reductions. The optically active isomers (+)-8 (AM4434) and (-)-8 (AM4435) were synthesized from (2S,3S)- and (2R,3R)-2,3-dihydroxycyclohexanone, respectively, via a chemoenzymatic route. These head group constrained and conformationally restricted analogues of 2-AG as well as the 1-keto precursors were evaluated as substrates for the endocannabinoid deactivating hydrolytic enzymes monoacylglycerol lipase (MGL) and fatty acid amide hydrolase (FAAH), and also were tested for their affinities for CB1 and CB2 cannabinoid receptors. The observed biochemical differences between these ligands can help define the conformational requirements for 2-AG activity at each of the above endocannabinoid protein targets.

A novel scintillation proximity assay for fatty acid amide hydrolase compatible with inhibitor screening

A binding assay for human fatty acid amide hydrolase (FAAH) using the scintillation proximity assay (SPA) technology is described. This SPA uses the specific interactions of [3H]R(+)-methanandamide (MAEA) and FAAH expressing microsomes to evaluate the displacement activity of FAAH inhibitors. We observed that a competitive nonhydrolyzed FAAH inhibitor, [3H]MAEA, bound specifically to the FAAH microsomes. Coincubation with an FAAH inhibitor, URB-597, competitively displaced the [3H]MAEA on the FAAH microsomes. The released radiolabel was then detected through an interaction with the SPA beads. The assay is specific for FAAH given that microsomes prepared from cells expressing the inactive FAAH-S241A mutant or vector alone had no significant ability to bind [3H]MAEA. Furthermore, the binding of [3H]MAEA to FAAH microsomes was abolished by selective FAAH inhibitors in a dose-dependent manner, with IC50 values comparable to those seen in a functional assay. This novel SPA has been validated and demonstrated to be simple, sensitive, and amenable to high-throughput screening.

High-Throughput Screening for the Discovery of Inhibitors of Fatty Acid Amide Hydrolase Using a Microsome-Based Fluorescent Assay

Fatty acid amide hydrolase (FAAH) is a membrane-associated enzyme that catalyzes the hydrolysis of several endogenous bioactive lipids, including anandamide (AEA), N-palmitoylethanolamine (PEA), oleamide, and N-oleoylethanolamine (OEA). These fatty acid amides participate in many physiological activities such as analgesia, anxiety, sleep modulation, anti inflammatory responses, and appetite suppression. Because FAAH plays an essential role in controlling the tone and activity of these endogenous bioactive lipids, this enzyme has been implicated to be a drug target for the therapeutic management of pain, anxiety, and other disorders. In an effort to discover FAAH inhibitors, the authors have previously reported the development of a novel fluorescent assay using purified FAAH microsomes as an enzyme source and a fluorogenic substrate, arachidonyl 7-amino, 4-methyl coumarin amide (AAMCA). Herein, the authors have adapted this assay to a high-throughput format and have screened a large library of small organic compounds, identifying a number of novel FAAH inhibitors. These data further verify that this fluorescent assay is sufficiently robust, efficient, and low-cost for the identification of FAAH inhibitory molecules and open this class of enzymes for therapeutic exploration.

Modulators of endocannabinoid enzymic hydrolysis and membrane transport

Tissue concentrations of the endocannabinoids N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) are regulated by both synthesis and inactivation. The purpose of this review is to compile available data regarding three inactivation processes: fatty acid amide hydrolase, monoacylglycerol lipase, and cellular membrane transport. In particular, we have focused on mechanisms by which these processes are modulated. We describe the in vitro and in vivo effects of inhibitors of these processes as well as available evidence regarding their modulation by other factors.

High affinity electrophilic and photoactivatable covalent endocannabinoid probes for the CB1 receptor

We have designed and synthesized the first two high affinity covalent anandamide probes for the CB1 receptor by introducing either an electrophilic isothiocyanato or a photoactivatable azido group at the terminal carbon of the arachidonic acid moiety. The headgroup of these anandamide analogues was optimized by using a cyclopropylamide substituent to impart optimal CB1 affinity. Both 20-isothiocyanato-eicosa-5,8,11,14-tetraenoic acid cyclopropylamide (1, AM3677) and 20-azido-eicosa-5,8,11,14-tetraenoic acid cyclopropylamide (2, AM3661) exhibited high selectivities for the CB1 receptor with K(i) values of 1.3 and 0.9 nM, respectively. Using suitable experimental conditions, both ligands were shown to covalently label the CB1 receptor with high efficiency. These two covalent probes for the endocannabinoid CB1 binding site open the door for exploring the ligand binding motifs involved in the activation of the CB1 receptor by its endogenous ligand, anandamide.

Cell signaling by endocannabinoids and their congeners: questions of selectivity and other challenges

The major endocannabinoids, anandamide (N-arachidonoylethanolamide, 20:4n-6 N-acylethanolamine) and 2-arachidonoylglycerol (2-AG) are structurally and functionally similar, but they are produced by different metabolic pathways and their levels must therefore be regulated by different mechanisms. Both endocannabinoids are accompanied by cannabinoid receptor-inactive, saturated and mono- or di-unsaturated congeners which can influence their metabolism and function. Here we review published data on the presence and production of anandamide and 2-AG and their congeners in mammalian cells and discuss this information in terms of their proposed signaling functions.

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.

Simultaneous measurement of anandamide and 2-arachidonoylglycerol by polymyxin B-selective adsorption and subsequent high-performance liquid chromatography analysis: increase in endogenous cannabinoids in the sera of patients with endotoxic shock

Anandamide (ANA) and 2-arachidonoylglycerol (2-AG), two endogenous cannabinoids, can be generated by activated macrophages and platelets, respectively, in the context of endotoxic shock, and are proposed to play a crucial role in the induction of the shock-related hypotension. Taking advantage of our recently discovered function of polymyxin B (PMB) binding to ANA and 2-AG, we developed a new method for measuring ANA and 2-AG by applying PMB-immobilized beads to selectively adsorb them in biological fluids, instead of organic solvent extraction. The eluate from beads can be directly fractionated by reverse-phase high-performance liquid chromatography (HPLC), and the fractionations corresponding to authentic ANA and 2-AG are collected and derivatized with fluorogenic reagent and subsequently quantified by HPLC with fluorometric detection. The calibration graphs of ANA and 2-AG were linear over a range of 1 to 500 pmol/ml. The limits of detection for ANA and 2-AG were 20 and 50 fmol, respectively. Intraassay precision was 2.24-4.25 and 3.47-5.44%, and interassay was 4.05-6.14 and 4.92-7.28% for ANA and 2-AG, respectively. Using this method, we first determined a 4-fold and 3-fold higher level of ANA and 2-AG, respectively, in the sera of patients with endotoxic shock than in normal serum. This finding should help in elucidating the role of the endogenous cannabinoids in the hypotension of human endotoxic shock. This method is rapid, sensitive, and reliable for simultaneously quantifying ANA and 2-AG in biological fluids, and has potential for clinical usage.

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.

Novel and sensitive method for the detection of anandamide by the use of its dansyl derivative

The dansyl ester of anandamide was prepared and showed intense fluorescence on silica gel thin-layer chromatography when viewed under long-wavelength ultraviolet light (detection limit, 15 fmol). A high-performance liquid chromatography method for the quantitation of anandamide was developed using a C18 column (250 x 4.6 mm) with gradient elution (1% acetic acid-methanol) and detection at 255 nm. The method was applied to the measurement of anandamide in media from cultured hepatocytes. Sample preparation involved extraction with a C18 cartridge, derivatization with dansyl chloride, thin-layer chromatography, and quantitation. The detection limit in hepatocyte media is 4.3 nmol at a signal-to-noise ratio of three.

Polymyxin B binds to anandamide and inhibits its cytotoxic effect

Anandamide (ANA), an endogenous cannabinoid, can be generated by activated macrophages during endotoxin shock and is thought to be a paracrine contributor to hypotension. We discovered that ANA in saline/ethanol solution and in serum was efficiently adsorbed in a polymyxin B (PMB)-immobilized beads column and eluted with ethanol. We confirmed the direct binding of PMB to ANA by using surface plasmon resonance. The adsorption of ANA by PMB may abolish the diverse effects of ANA such as hypotension, immunosuppression, and cytotoxicity, and may suggest a new therapeutic strategy for endotoxin shock.

Structure-activity relationships of anandamide, an endogenous cannabinoid ligand

Identification of arachidonylethanolamide (anandamide) as an endogenous cannabinoid is one of the most important developments in cannabinoid research in recent years. In a relatively short period of time thereafter, pharmacological and biochemical studies have confirmed initial speculations that anandamide is a neuromodulator and significantly advanced our understanding of cannabinoid biochemistry. Moreover, the discovery of anandamide has led to the identification of two heretofore unknown proteins associated with cannabinoid physiology: 1) Anandamide Amidohydrolase (AAH), an enzyme responsible for the hydrolytic breakdown of anandamide and 2) the Anandamide Transporter (ANT), a carrier protein involved in the transport of anandamide across the cell membrane. Evidence obtained so far suggests that these two proteins, in combination, are responsible for the termination of the biological actions of anandamide. Also, the discovery of anandamide has revealed a novel class of more selective cannabimimetic agents possessing a somewhat different pharmacological profile of potential therapeutic value. A number of such analogs have now been reported many of which possess markedly improved cannabinoid receptor affinity and metabolic stability compared to those of the parent ligand. Generally, anandamide and all known analogs exhibit significant selectivity for the CB1 receptor and modest to very low affinity for CB2. For this reason, this group of compounds can be considered as CB1 ligands. The purpose of this review is to summarize the structure-activity relationships (SAR) of anandamide for the CB1 cannabinoid receptor and to define the structural requirements for the substrates and the inhibitors of anandamide amidohydrolase and the anandamide transporter.

Substrate specificity and stereoselectivity of rat brain microsomal anandamide amidohydrolase

Anandamide amidohydrolase (AAH) catalyzes the hydrolysis of arachidonylethanolamide (anandamide), an endogenous cannabinoid receptor ligand. To delineate the structural requirements of AAH substrates, rat brain microsomal AAH hydrolysis of a series of anandamide congeners was studied using two reverse-phase high-performance liquid chromatography (RP-HPLC) assays developed in our laboratory. Arachidonamide (1) was found to be the best substrate with an apparent Km of 2.34 mM and a Vmax of 2.89 nmol/min/mg of protein. Although anandamide (2) has a similar Km value, its Vmax is approximately one-half that of arachidonamide. N, N-Bis(2-hydroxyethyl)arachidonamide (3) was not hydrolyzed, suggesting specificity for unsubstituted or mono-N-substituted arachidonamides. Analogues with a methyl group at the 1'-position of the ethanolamido headgroup were also found to have greater resistance to enzymatic turnover and therefore increased metabolic stability. The enzyme exhibited high stereoselectivity as the rate of hydrolysis of (R)-alpha-methanandamide (2.4%) (anandamide = 100%) was about 10-fold lower than that of its (S)-enantiomer (23%). In contrast, (R)-beta-methanandamide was 6-times more susceptible (121%) than the (S)-beta-enantiomer (21%). Interestingly, an inverse correlation was shown between AAH stereoselectivity and the brain cannabinoid receptor affinity as the enantiomers with high receptor affinity displayed low susceptibility to hydrolysis by AAH. Metabolic stability is also imparted to analogues with a short hydrocarbon headgroup as well as to those possessing 2-monomethyl or 2,2-dimethyl substituents. 2-Arachidonylglycerol and racemic 1-arachidonylglycerol were shown to be excellent AAH substrates. To identify AAH inhibitors, hydrolysis of anandamide was also studied in the presence of a select group of cannabimimetics. Of these, (-)-Delta8-THC and SR141716A, a biarylpyrazole CB1 antagonist, were found to inhibit enzymatic activity. These newly defined enzyme recognition parameters should provide a foundation for the rational development of stable, therapeutically useful anandamide analogues with high receptor affinity.

A sensitive and specific radiochromatographic assay of fatty acid amide hydrolase activity

A radiochromatographic method has been set up in order to determine fatty acid amide hydrolase (FAAH) activity, based on reversed-phase high-performance liquid chromatography and on-line scintillation counting. The reaction products were separated using a C18 column eluted with methanol-water-acetic acid and quantitated with an external standard. Baseline separation of the acid product from the substrate was completed in less than 4 min, with a detection limit of 2.5 fmol arachidonic acid at a signal to noise ratio of 4:1. The method enabled to determine the kinetic constants (i.e., apparent Km of 2.0 +/- 0.2 microM and Vmax of 800 +/- 75 pmol. min-1. mg protein-1 toward anandamide) and the substrate specificity of human brain FAAH, as well as the extent of enzyme inhibition by some anandamide congeners. The femtomole sensitivity and the accuracy of the method allow detection and characterization of the activity of FAAH in very minute tissue samples or in samples where the enzymatic activity is very low.

Inhibition of anandamide hydrolysis by the enantiomers of ibuprofen, ketorolac, and flurbiprofen

The endogenous cannabimimetic anandamide is hydrolyzed by a fatty acid amide hydrolase to yield arachidonic acid and ethanolamine. In the present study, the regional distribution of the activity and its sensitivity to inhibition by the enantiomers of ibuprofen, ketorolac, and flurbiprofen has been investigated. The rate of [3H]anandamide hydrolysis was found in both 7-week-old and 90-week-old rats to be in the order hippocampus > cerebral cortex > cerebellum > striatum approximately midbrain, with higher rates of hydrolysis for the 7-week-old rats than for the 90-week-old rats. In whole brain (minus cerebellum), the R(-)-enantiomer of ibuprofen was a mixed-type inhibitor of anandamide hydrolysis and was approximately 2-3 times more potent than the S(+)-enantiomer, IC50 values of 230 and 750 microM, respectively, being found. A similar pattern of inhibition of anandamide hydrolysis was seen when intact C6 rat glioma cells were used. Ketorolac inhibited rat brain anandamide hydrolysis, with IC50 values of 50, 440, and 80 microM being found for the R-, S-, and R,S-forms, respectively. The IC50 value for R-flurbiprofen (60 microM) was similar to the IC50 value for the S-enantiomer (50 microM). These data demonstrate that there is no dramatic enantiomeric selectivity of NSAID compounds as inhibitors of fatty acid amide hydrolase enzyme(s) responsible for the hydrolysis of anandamide. The enantiomers of flurbiprofen and R-ketorolac are the most potent NSAID inhibitors of fatty acid amide hydrolase yet reported.

Novel analogues of arachidonylethanolamide (anandamide): affinities for the CB1 and CB2 cannabinoid receptors and metabolic stability

Several analogues of the endogenous cannabinoid receptor ligand arachidonylethanolamide (anandamide) were synthesized and evaluated in order to study (a) the structural requirements for high-affinity binding to the CB1 and CB2 cannabinoid receptors and (b) their hydrolytic stability toward anandamide amidase. The series reported here was aimed at exploring structure-activity relationships (SAR) primarily with regard to stereoelectronic requirements of ethanolamido headgroup for interaction with the cannabinoid receptor active site. Receptor affinities, reported as Ki values, were obtained by a standard receptor binding assay using [3H]CP-55,940 as the radioligand, while stability toward the amidase was evaluated by comparing the Ki of each analogue in the presence and absence of phenylmethanesulfonyl fluoride (PMSF), a serine protease blocker and inhibitor of anandamide amidase. Introduction of a methyl group in the 1'- and 2'-positions or substitution of the ethanolamido headgroup with a butylamido group gave analogues with vastly improved biochemical stability. This is accomplished in some cases with increased receptor affinity. Conversely, oxazolyl and methyloxazolyl headgroups led to low-affinity analogues. Substitution of the hydroxyl group with electronegative substituents such as fluoro, chloro, allyl, and propargyl groups significantly increased receptor affinity but did not influence the biochemical stability. The 2'-chloro analogue of anandamide was found to have the highest affinity for CB1. Additionally, reversing the positions of the carbonyl and NH in the amido group produces retro-anandamides possessing considerably higher metabolic stability. Replacement of the arachidonyl tail with oleyl or linoleyl results in analogues with low affinities for both receptors. All of the analogues in this study showed high selectivity for the CB1 receptor over the peripheral CB2 receptor. The most potent analogues were tested for their ability to stimulate the binding of [35S]GTPgammaS to G-proteins and were shown to be potent cannabimimetic agonists. The results are discussed in terms of pharmacophoric features affecting receptor affinity and enzymatic stability.

Biochemistry of the endogenous ligands of cannabinoid receptors

In 1992 the discovery of the first endogenous ligand of cannabinoid receptors, anandamide, provided conclusive support to the hypothesis that an "endogenous cannabinoid regulatory system" exists in mammalian nervous tissue. Anandamide (N-arachidonoyl-ethanolamine) was the first of a series of long-chain fatty acid derivatives, including two other polyunsaturated N-acylethanolamines and 2-arachidonoyl-glycerol, found to exert cannabimimetic properties in either central or peripheral tissues. Here we review the current knowledge on the biochemical bases of the formation and inactivation of endogenous cannabinoid ligands as well as of their interaction with cannabinoid receptor subtypes.

Determination of anandamide amidase activity using ultraviolet-active amine derivatives and reverse-phase high-performance liquid chromatography

Anandamide amidase catalyzes the hydrolysis of anandamide (AEA) to arachidonic acid (AA) and ethanolamine (EA). Recently, we published a method for determining anandamide amidase activity based on the measurement of arachidonic acid with direct UV detection at 204 nm. However, this method cannot be used to determine the hydrolysis of non-UV-active AEA analogs. It also cannot be used to study AEA amidase inhibitors that contain the arachidonic acid tail, and which are also enzyme substrates. Here we report a novel, more general method for measuring amidase activity by o-phthaldialdehyde (OPA) precolumn derivatization and reverse-phase high-performance liquid chromatography (HPLC). The hydrolysis product, ethanolamine, after separation from protein was derivatized with OPA to form a UV-active isoindole derivative which was then detected at 230 nm. The detection limit for derivatized ethanolamine was 1.0 pmol and retention times were typically less than 8 min. Our new method can detect non-UV-active analogs through derivatization of the amine product. It can thus be used after careful selection of the HPLC conditions in competition experiments between AEA and AEA analogs possessing different head groups. The most effective competitive inhibitor tested was (R)-N-(1-methyl-2-hydroxyethyl)arachidonylamide (AM356), which is resistant to enzymatic hydrolysis and yet inhibits AEA hydrolysis in a competition experiment by 43%. Moreover, this method offers several advantages over existing methodologies using radioisotopes or solvent extraction procedures. Our work to date has shown that small structural changes in the AEA molecule can result in significant variation in both affinity and turnover rate for each analog with respect to AEA amidase.

Formation of N-acyl-phosphatidylethanolamines and N-acetylethanolamines: proposed role in neurotoxicity

The formation of N-acyl-phosphatidylethanolamine (NAPE) and N-acylethanolamine (NAE), including anandamide, in mammals in relation to neurotoxicity is discussed. Data on the characterization of the NAPE-forming N-acyltransferase, the NAPE-hydrolyzing phospholipase D, and the NAE-hydrolyzing amidase are reviewed. We suggest that NAPE and NAE, including anandamide, are formed in neurons in response to the high intracellular calcium concentrations that occur in injured neurons, e.g. due to glutamate excitotoxicity. NAPE may have functions of its own besides being a precursor for NAE. The formation of both of these lipids may serve as a cytoprotective response, whether mediated by physical interactions with membranes or enzymes, or mediated by activation of cannabinoid receptors. This suggestion implies that NAPE and NAE may have pathophysiological roles in the brain. Whether these lipids also have physiological roles is uncertain.

Fatty acid sulfonyl fluorides inhibit anandamide metabolism and bind to the cannabinoid receptor

Arachidonoyl ethanolamide (anandamide) is an endogenous ligand for cannabinoid receptors (CB1, CB2) and a putative neurotransmitter. Phenylmethylsulfonyl fluoride (PMSF) is an inhibitor of the enzyme (an amidase) which hydrolyzes anandamide to arachidonic acid and ethanolamine. We report here that fatty acid sulfonyl fluorides are potent inhibitors of anandamide metabolism. In order to investigate the SAR of these anandamide amidase inhibitors we tested a series of fatty acid (C12 to C20) sulfonyl fluorides both as inhibitors of anandamide degradation and as ligands for the central cannabinoid receptor (CB1). AM374 (palmitylsulfonyl fluoride, C16) was approximately 20 times more potent than PMSF and 50 times more potent than arachidonyltrifluoromethyl ketone in preventing the hydrolysis of anandamide in brain homogenates. AM374 was over a thousand-fold more effective than PMSF in inhibiting the amidase in cultured cells. The C12 to C18 sulfonyl fluoride analogs were equipotent as inhibitors of the amidase and the reverse reaction (the synthase) with nanomolar IC50 values. These compounds generally showed decreasing affinity for the CB1 receptor as the chain length increased; thus, C12 sulfonylfluoride had an IC50 of 18 nM and C20 sulfonylfluoride had an IC50 of 78 microM. The C14, C16, and C18 sulfonyl fluorides showed high selectivity for the amidase over the CB1 receptor and thus are potentially useful selective anandamide amidase inhibitors.

Novel inhibitors of brain, neuronal, and basophilic anandamide amidohydrolase

Mammalian brain as well as mouse neuroblastoma (N18TG2) and rat basophilic leukaemia (RBL) cells were previously shown to contain "anandamide amidohydrolase', a membrane-bound enzyme sensitive to serine and cysteine protease inhibitors and catalyzing the hydrolysis of the endogenous cannabimimetic metabolite, anandamide (arachidonoyl-ethanolamide). With the aim of developing novel inhibitors of this enzyme, we synthesized three arachidonic acid (AA) analogues, i.e. arachidonoyl-diazo-methyl-ketone (ADMK), ara-chidonoyl-chloro-methyl-ketone (ACMK) and O-acetyl-arachidonoyl-hydroxamate (AcAHA), by adding to the fatty acid moiety three functional groups previously used to synthesize irreversible inhibitors of serine and cysteine proteases. The three compounds were purified and characterized by proton nuclear magnetic resonance and electron impact mass spectrometry. Their effect was tested on anandamide amidohydrolase partially purified from N18TG2 and RBL-1 cells and porcine brain. Pre-treatment of the enzyme with each compound produced a significant inhibition, with ADMK being the most potent (IC50 = 3, 2 and 6 microM) and AcAHA the weakest (IC50 = 34, 15 and 25 microM) inhibitors. The inactivated enzyme regained its full activity when chromatographed by anion-exchange chromatography, suggesting that none of the compounds inhibited the amidohydrolase in a covalent manner. Accordingly, Lineweaver-Burk profiles showed competitive inhibition by each compound. Conversely, the irreversible inhibitor of cytosolic phospholipase As, methyl-arachidonoyl-fluoro-phosphonate (MAFP), covalently inhibited the amidohydrolase. MAFP was active at concentrations 10(3) times lower than those reported for phospholipase A2 inhibition, and is the most potent anandamide amidohydrolase inhibitor so far described (IC50 = 1-3 nM). MAFP, ADMK and ACMK, probably by inhibiting anandamide degradation, produced an apparent increase of the in vitro formation of anandamide from its biosynthetic precursor N-arachidonoyl-phosphatidyl-ethanolamine.