Methyl arachidonyl fluorophosphonate: a potent irreversible inhibitor of anandamide amidase

Exceptionally potent inhibitors of fatty acid amide hydrolase: the enzyme responsible for degradation of endogenous oleamide and anandamide

The development of exceptionally potent inhibitors of fatty acid amide hydrolase (FAAH), the enzyme responsible for the degradation of oleamide (an endogenous sleep-inducing lipid), and anandamide (an endogenous ligand for cannabinoid receptors) is detailed. The inhibitors may serve as useful tools to clarify the role of endogenous oleamide and anandamide and may prove to be useful therapeutic agents for the treatment of sleep disorders or pain. The combination of several features-an optimal C12-C8 chain length, pi-unsaturation introduction at the corresponding arachidonoyl Delta(8,9)/Delta(11,12) and oleoyl Delta(9,10) location, and an alpha-keto N4 oxazolopyridine with incorporation of a second weakly basic nitrogen provided FAAH inhibitors with K(i)s that drop below 200 pM and are 10(2)-10(3) times more potent than the corresponding trifluoromethyl ketones.

Azido- and isothiocyanato-substituted aryl pyrazoles bind covalently to the CB1 cannabinoid receptor and impair signal transduction

3-Azidophenyl- and 3-isothiocyanatophenyl-and 2-(5'-azidopentyl)- and 2-(5'-isothiocyanatopentyl)pyrazoles were synthesized to determine whether these compounds could behave as covalently binding ligands for the CB1 cannabinoid receptor in rat brain membranes. Heterologous displacement of [3H]CP55940 indicated that the apparent affinity of these compounds for the CB1 receptor was similar to that of the parent compound, SR141716A, with the exception of the 3-isothiocyanato derivatives, which showed a 10-fold loss of affinity. The 3-azidophenyl and 3-isothiocyanatophenyl compounds behaved as antagonists against the cannabinoid agonist desacetyllevonantradol in activation of G proteins [guanosine 5'-O-(y-[35S]thio)triphosphate ([35S]GTPgammaS) binding] and regulation of adenylyl cyclase. The 2-(5'-azidopentyl)- and 2-(5'-isothiocyanatopentyl)pyrazoles were poor antagonists for [35S]GTPgammaS binding, and both compounds failed to antagonize the cannabinoid regulation of adenylyl cyclase. After incubation with the isothiocyanato analogues or UV irradiation of the azido analogues, the 3-substituted aryl pyrazoles formed covalent bonds with the CB1 receptor as evidenced by the loss of specific binding of [3H]CP55940. In the case of the isothiocyanato analogues, the log concentration-response curve for cannabinoid-stimulated [35S]GTPgammaS binding was shifted to the right, indicating that loss of receptors compromised signal transduction capability. These irreversibly binding antagonists might be useful tools for the investigation of tolerance and receptor down-regulation in both in vitro and in vivo studies.

Biochemistry and pharmacology of the endocannabinoids arachidonylethanolamide and 2-arachidonylglycerol

The purpose of this review is to discuss the cellular synthesis and inactivation of two putative endogenous ligands of the cannabinoid receptor, N-arachidonylethanolamine (AEA) and 2-arachidonylglycerol (2-AG). Both ligands are synthesized by neurons and brain tissue in response to increased intracellular calcium concentrations. Both ligands are substrates for fatty acid amide hydrolase (FAAH). Both AEA and 2-AG bind to the neuronal form of the cannabinoid receptor (CB1). AEA binds the receptor with moderate affinity and has the characteristics of a partial agonist, whereas, 2-AG binds with low affinity but exhibits full efficacy. Two possible physiological roles of the endocannabinoids and the CB1 receptor are discussed: the regulation of gestation and the regulation of gastrointestinal motility.

Anandamide amidohydrolase (fatty acid amide hydrolase)

Anandamide (N-arachidonoylethanolamine) loses its cannabimimetic activity when it is hydrolyzed to arachidonic acid and ethanolamine by the catalysis of an enzyme referred to as anandamide amidohydrolase or fatty acid amide hydrolase. Cravatt's group and our group cloned cDNA of the enzyme from rat, human, mouse and pig, and the primary structures revealed that the enzymes belong to an amidase family characterized by the amidase signature sequence. The recombinant enzyme acted not only as an amidase for anandamide and oleamide, but also as an esterase for 2-arachidonoylglycerol. The reversibility of the enzymatic anandamide hydrolysis and synthesis was also confirmed with a purified recombinant enzyme. Several fatty acid derivatives like methyl arachidonyl fluorophosphonate potently inhibited the enzyme. The enzyme was distributed widely in mammalian organs such as liver, small intestine and brain. However, the anandamide hydrolyzing enzyme found in human megakaryoblastic cells was catalytically distinct from the previously known enzyme.

Activity-based protein profiling: the serine hydrolases

With the postgenome era rapidly approaching, new strategies for the functional analysis of proteins are needed. To date, proteomics efforts have primarily been confined to recording variations in protein level rather than activity. The ability to profile classes of proteins on the basis of changes in their activity would greatly accelerate both the assignment of protein function and the identification of potential pharmaceutical targets. Here, we describe the chemical synthesis and utility of an active-site directed probe for visualizing dynamics in the expression and function of an entire enzyme family, the serine hydrolases. By reacting this probe, a biotinylated fluorophosphonate referred to as FP-biotin, with crude tissue extracts, we quickly and with high sensitivity detect numerous serine hydrolases, many of which display tissue-restricted patterns of expression. Additionally, we show that FP-biotin labels these proteins in an activity-dependent manner that can be followed kinetically, offering a powerful means to monitor dynamics simultaneously in both protein function and expression.

Identification of two serine residues involved in catalysis by fatty acid amide hydrolase

Fatty acid amide hydrolase is an integral membrane protein that hydrolyzes a novel and growing class of neuromodulatory fatty acid molecules, including anandamide, 2-arachidonyl glycerol, and oleamide. This activity is inhibited by serine and cysteine reactive agents, suggesting that the active site contains a serine or cysteine residue. Therefore serine and cysteine residues were mutated to alanine and the effects on activity were determined. Mutants were prepared using site-directed mutagenesis methods and expressed in COS-7 cells. Serine mutations S217A and S241A completely abolished enzymatic activity. Mutants S152A and C249A had no effect on activity, while S218A showed a slight decrease in activity. To confirm these results biochemically, the mutant enzymes were reacted with the irreversible inhibitor [(14)C]-diisopropyl fluorophosphate. All of the mutants except S217A and S241A were labeled. We therefore confirm that fatty acid amide hydrolase is a serine hydrolase and propose that both Ser-217 and Ser-241 are essential for enzyme activity.

Equilibrium in the hydrolysis and synthesis of cannabimimetic anandamide demonstrated by a purified enzyme

Anandamide, an endogenous ligand for cannabinoid receptors, loses its biological activities when it is hydrolyzed to arachidonic acid and ethanolamine by anandamide amidohydrolase. We overexpressed a recombinant rat enzyme with a hexahistidine tag in a baculovirus-insect cell expression system, and purified the enzyme with the aid of a Ni-charged resin to a specific activity as high as 5.7 micromol/min/mg protein. The purified recombinant enzyme catalyzed not only the hydrolysis of anandamide and palmitoylethanolamide, but also their reverse synthetic reactions. In order to attain an equilibrium of the anandamide hydrolysis and its reverse reaction within 10 min, we utilized a large amount of the purified enzyme. The equilibrium constant ([arachidonic acid][ethanolamine])/([anandamide][water]) was calculated as 4x10(-3) (37 degrees C, pH 9.0). These experimental results with a purified enzyme preparation quantitatively confirmed the reversibility of the enzyme reaction previously observed with crude enzyme preparations.

Discovery and characterization of endogenous cannabinoids

The characterization of cannabinoid receptors and signal transduction mechanisms provided the impetus for the searching for endogenous ligands for this system. The result was a family of fatty acid derivatives that interact with cannabinoid receptors to varying degrees. The two ligands that have received the most attention are anandamide (AN) and 2-arachidonolyl-glycerol (Ara-Gl). They are both present in central as well as peripheral tissues. Mechanisms for the synthesis and metabolism of AN have been described. Presently, the physiological stimuli for production and release of AN are unknown. As a result, elucidation of its physiological role remains elusive. However, it seems reasonable to conclude that both AN and 2-Ara-Gl interact with cannabinoid receptors in both peripheral and central tissue to produce a wide range of effects. Administration of these ligands to laboratory animals produce effects that are quite similar to those elicited by delta9-tetrahydrocannabinol (THC), the psychoactive constituent in marijuana. Nevertheless, there are some pharmacological differences between the plant-derived THC and the endogenous cannabinoids that could be due to either pharmadynamic or pharmacokinetics dissimilarities. Extensive structure-activity relationship studies have provided some vital insights into the actions of the endogenous ligands. First and foremost, systematic structural alterations in AN have additional support that it is acting at the cannabinoid receptors in a fashion similar to that of THC. Development of metabolically stable analogs of AN, as well as those with greater receptor affinity, have helped substantiate AN and THC similarities. Nevertheless, pharmacological differences remain between the endogenous and exogenous ligands. Whether these differences are due to the nature of their interaction with the cannabinoid receptors, activation of unique signaling pathways, interactions with non-cannabinoid receptors, or pharmacokinetic considerations remain to be resolved.

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.

N-acylphosphatidylethanolamine-hydrolysing phospholipase D lacks the ability to transphosphatidylate

The N-acylphosphatidylethanolamine-hydrolysing phospholipase D (NAPE-PLD) generates N-acylethanolamines, including N-arachidonoyl-ethanolamine (anandamide), that may be neuroprotective and analgesic. The properties of NAPE-PLD from rat heart and brain microsomes are investigated and compared to those of other PLDs. NAPE-PLD is inhibited by the fatty acid aminohydrolase inhibitor MAFP in high concentrations (> or = 100 microM) while PMSF in high concentrations (10 mM) tends to stabilise NAPE-PLD activity. Oleate inhibits NAPE-PLD but the enzyme is not affected by PIP2, alpha-synuclein or mastoparan. Furthermore, it is for the first time reported that NAPE-PLD is not capable of catalysing a transphosphatidylation reaction like most other known PLDs.

An acid amidase hydrolyzing anandamide as an endogenous ligand for cannabinoid receptors

Anandamide loses its cannabimimetic activities upon hydrolysis to arachidonic acid and ethanolamine. So far the anandamide hydrolyzing activity widely distributed in mammalian organs has been attributed exclusively to an enzyme referred to as anandamide amidohydrolase with an optimum pH around 9. We found another enzyme hydrolyzing anandamide in a human megakaryoblastic cell line (CMK). The enzyme present in the 12,000 x g pellet of the cell homogenate was solubilized by freeze-thaw. The solubilized enzyme showed an optimal pH around 5, and was almost inactive at alkaline pH. The enzyme activity was increased by the addition of dithiothreitol. In contrast, anandamide amidohydrolase of RBL-1 cells was mostly insoluble even after freeze-thaw, showed an optimal pH at 9, and was not affected by dithiothreitol. Furthermore, the enzyme of CMK cells was much less sensitive to phenylmethylsulfonyl fluoride and methyl arachidonoyl fluorophosphonate potently inhibiting anandamide amidohydrolase, and effectively hydrolyzed palmitoylethanolamide, which was a poor substrate for anandamide amidohydrolase. Thus, the enzyme of CMK cells is distinguishable from anandamide amidohydrolase.

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.

Induction of cyclo-oxygenase-2 expression by methyl arachidonyl fluorophosphonate in murine J774 macrophages: roles of protein kinase C, ERKs and p38 MAPK

1. Methyl arachidonyl fluorophosphonate (MAFP), an inhibitor of phospholipase A2 (PLA2), has been widely used to assess the roles of PLA2 in various cell functions. Here, we report on a novel action of this compound at concentrations similar to those used for PLA2 inhibition. 2. The murine macrophage J774 released a large amount of prostaglandin E2 (PGE2) by MAFP (1-30 microM), which was abolished by indomethacin and NS-398 but not by valeryl salicylate, and results from increased cyclo-oxygenase-2 (COX-2) protein levels and gene expression. 3. This PGE2 release was blocked by inhibitors of tyrosine kinase (genistein), protein kinase C (PKC) (Ro 31-8220, Go 6976 or LY 379196), mitogen-activated protein kinase kinase (MEK) (PD 098059) or p38 mitogen-activated protein kinase (MAPK) (SB 203580). 4. Consistent with these results, MAFP caused membrane translocation of PKCbetaI and betaII isoforms and activated extracellular signal-regulated kinase (ERK) and p38 MAPK. 5. In accordance with these effects of MAFP, PKC activator phorbol 12-myristate 13-acetate (PMA) increased PGE2 release and caused activation of PKCbeta, ERKs and p38 MAPK. 6. This is the first report that the PLA2 inhibitor, MAFP, can induce COX-2 gene expression and PGE2 synthesis via the PKC-, ERK- and p38 MAPK-dependent pathways. Thus, the use of MAFP as a PLA2 inhibitor should be treated with caution.

Enzymes of porcine brain hydrolyzing 2-arachidonoylglycerol, an endogenous ligand of cannabinoid receptors

Anandamide and 2-arachidonoylglycerol (2-AG) are two endogenous ligands for the cannabinoid receptors, and their cannabimimetic activities are lost when they are hydrolyzed enzymatically. Cytosol and particulate fractions of porcine brain exhibited a high 2-AG hydrolyzing activity of 100 nmol/min/mg protein. Most of the activity could be attributed to a monoacylglycerol lipase-like enzyme that did not hydrolyze anandamide. It was separated by hydroxyapatite chromatography from anandamide amidohydrolase, which is also capable of hydrolyzing 2-AG as well as anandamide. Thus, porcine brain has at least two enzymes capable of hydrolyzing 2-AG. The 2-AG hydrolase activities of both the cytosolic and particulate enzymes were irreversibly and time-dependently inhibited by methyl arachidonyl fluorophosphonate with IC50 values as low as 2-3 nM.

Trifluoromethyl ketone inhibitors of fatty acid amide hydrolase: a probe of structural and conformational features contributing to inhibition

The examination of a series of trifluoromethyl ketone inhibitors of Fatty Acid Amide Hydrolase (FAAH, oleamide hydrolase, anandamide amidohydrolase) is detailed in efforts that define structural and conformational properties that contribute to enzyme inhibition and substrate binding. The results imply an extended bound conformation, highlight a role for the presence, position, and stereochemistry of a delta cis double bond, and suggest little apparent role for C11-C18/C22 of the fatty acid amide substrates.

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.

The CB1 cannabinoid receptor in the brain

The CB1 cannabinoid receptor in brain is a G-protein-coupled receptor that exists as a protein possessing seven transmembrane helices that span the membrane. The intracellular surface is able to interact with f1p4oteins of the Gi/o family to regulate effector proteins, including adenylate cyclase, Ca2+ channels, and K+ channels, and to stimulate the mitogen-activated protein kinase pathway. The CB1 cannabinoid receptor recognizes three classes of agonist ligands: cannabinoid, eicosanoid, and aminoalkylindole. These agonist subtypes may interact with the CB1 cannabinoid receptor by some common points of association, yet may have subtle differences in the way that they interact with the receptor protein. This may be evident in the allosteric regulation by monovalent cations and individual agonists. The juxtamembrane region of the C-terminal is able to activate G-proteins. It is proposed that conformational changes in the receptor induced by agonist ligands may alter the conformation or exposure of the juxtamembrane C-terminal region extending from helix VII.

Arachidonoylserotonin and other novel inhibitors of fatty acid amide hydrolase

Fatty acid amide hydrolase (FAAH) catalyzes the hydrolysis of bioactive fatty acid amides and esters such as the endogenous cannabinoid receptor ligands, anandamide (N-arachidonoyl-ethanolamine) and 2-arachidonoylglycerol, and the putative sleep inducing factor cis-9-octadecenoamide (oleamide). Most FAAH blockers developed to date also inhibit cytosolic phospholipase A2 (cPLA2) and/or bind to the CB1 cannabinoid receptor subtype. Here we report the finding of four novel FAAH inhibitors, two of which, malhamensilipin A and grenadadiene, were screened out of a series of thirty-two different algal natural products, and two others, arachidonoylethylene glycol (AEG) and arachidonoyl-serotonin (AA-5-HT) were selected out of five artificially functionalized polyunsaturated fatty acids. When using FAAH preparations from mouse neuroblastoma N18TG2 cells and [14C]anandamide as a substrate, the IC50s for these compounds ranged from 12.0 to 26 microM, the most active compound being AA-5-HT. This substance was also active on FAAH from rat basophilic leukaemia (RBL-2H3) cells (IC50 = 5.6 microM), and inhibited [14C]anandamide hydrolysis by both N18TG2 and RBL-2H3 intact cells without affecting [14C]anandamide uptake. While AEG behaved as a competitive inhibitor and was hydrolyzed to arachidonic acid (AA) by FAAH preparations, AA-5-HT was resistant to FAAH-catalyzed hydrolysis and behaved as a tight-binding, albeit non-covalent, mixed inhibitor. AA-5-HT did not interfere with cPLA2-mediated, ionomycin or antigen-induced release of [3H]AA from RBL-2H3 cells, nor with cPLA2 activity in cell-free experiments. Finally, AA-5-HT did not activate CB1 cannabinoid receptors since it acted as a very weak ligand in in vitro binding assays, and, at 10-15 mg/kg body weight, it was not active in the 'open field', 'hot plate' and rectal hypothermia tests carried out in mice. Conversely AEG behaved as a cannabimimetic substance in these tests as well as in the 'ring' immobility test where AA-5-HT was also active. AA-5-HT is the first FAAH inhibitor reported to date which is inactive both against cPLA2 and at CB1 receptors, whereas AEG represents a new type of cannabinoid receptor agonist.

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.

'Endocannabinoids' and other fatty acid derivatives with cannabimimetic properties: biochemistry and possible physiopathological relevance

The only endogenous substances isolated and characterised so far that are capable of mimicking the pharmacological actions of the active principle of marijuana, (-)-Delta9-tetrahydrocannabinol, are amides and esters of fatty acids. Some of these compounds, like anandamide (N-arachidonoylethanolamine) and 2-arachidonoylglycerol, act as true 'endogenous cannabinoids' by binding and functionally activating one or both cannabinoid receptor subtypes present on nervous and peripheral cell membranes. The metabolic pathways and molecular mode of actions of these metabolites, as well as their possible implication in physiopathological responses, are reviewed here.

Cannabinoid receptors and their endogenous agonists

Marijuana has been in use for over 4000 years as a therapeutic and as a recreational drug. Within the past decade, two cannabinoid receptor types have been identified, their signal transduction characterized, and an endogenous lipid agonist isolated from mammalian tissues. The CB1 cannabinoid receptor is widely distributed in mammalian tissues, with the highest concentrations found in brain neurons. CB1 receptors are coupled to modulation of adenylate cyclase and ion channels. The CB2 receptor is found in cells of the immune system and is coupled to inhibition of adenylate cyclase. Both receptor types selectively bind delta 9-THC, the active principle in marijuana, and anandamide (arachidonylethanolamide), an endogenous cannabimimetic eicosanoid. Progress is being made in the development of novel agonists and antagonists with receptor subtype selectivity, mice with genetic deletion of the cannabinoid receptors, and receptor-specific antibodies, which should help in providing a better understanding of the physiological role of the cannabinoid receptors.

Anandamide amidase inhibition enhances anandamide-stimulated nitric oxide release in invertebrate neural tissues

Anandamide, an endogenous cannabinoid signaling molecule, in a concentration dependent manner, initiates the release of nitric oxide (NO) from leech and mussel ganglia. SR 141716A, a cannabinoid antagonist, blocks the anandamide stimulated release of NO from these tissues. Methyl arachidonyl fluorophosphonate (MAFP), a specific anandamide amidase inhibitor, when administered to either ganglia with anandamide (10-6 M) did not increase the peak level of NO release but did significantly extend NO release from 12 to 18 min (P<0.05). Lower levels of anandamide (10-8 and 10-7 M) do not stimulate the release of significant amounts of NO from these tissues. However, in the presence of MAFP (2.5 nM), the lower anandamide concentrations were able to release significant peak amounts of NO. In mussel neural tissues, the peak NO release increased from 2.2+/-1.3 nM to 8.6+/-2.1 nM. Taken together, the results indirectly demonstrate the presence of anandamide amidase in these tissues, suggesting that the enzyme may serve as an endogenous regulator of anandamide action.

Pharmacological evidence for anandamide amidase in human cardiac and vascular tissues

The present report demonstrates the presence of antianandamide and anticannabinoid receptor 1 immunopositive material on the saphenous vascular endothelium. The endogenous cannabinoid, anandamide, in a dose-dependent manner stimulated the release of nitric oxide (NO) from saphenous vein, internal thoracic artery and right atrium tissue segments in vitro. This process can be antagonized by the nitric oxide synthase (NOS) inhibitor, N-omega-nitro-L-arginine methyl ester (L-NAME) (10(-4) M; 3.4+/-0.9 nM NO; P<0.01 compared to anandamide alone), as well as by the cannabinoid receptor I antagonist SR 141716A (2.9+/-1.0 nM NO; P<0.01). Furthermore, in the presence of varying concentrations of methylarachidonylfluorophosphonate, an anandamide amidase inhibitor, 10(-8) M anandamide stimulates a higher peak level of NO that remains elevated for a longer period of time (P<0.05) compared to anandamide alone, demonstrating the presence of anandamide amidase in human vascular tissues. Morphine, as anandamide, can stimulate the release of NO from right atria. This process can be inhibited by the opiate receptor antagonist naloxone and the NOS inhibitor L-NAME. As expected SR 141716A (10(-6) M; 26+3.8 NO nM in the presence of 10(-7) M morphine) did not antagonize morphine's ability to release NO. Taken together, the data demonstrate that cannabinoid signalling is involved with the regulation of the microvascular environment.

Structural requirements for 5-HT2A and 5-HT1A serotonin receptor potentiation by the biologically active lipid oleamide

Oleamide is an endogenous fatty acid primary amide that possesses sleep-inducing properties in animals and that has been shown to effect serotonergic receptor responses and block gap junction communication. Herein, the potentiation of the 5-HT1A receptor response is disclosed, and a study of the structural features of oleamide required for potentiation of the 5-HT2A and 5-HT1A response to serotonin (5-HT) is described. Of the naturally occurring fatty acids, the primary amide of oleic acid (oleamide) is the most effective at potentiating the 5-HT2A receptor response. The structural features required for activity were found to be highly selective. The presence, position, and stereochemistry of the delta9-cis double bond is required, and even subtle structural variations reduce or eliminate activity. Secondary or tertiary amides may replace the primary amide but follow a well defined relationship requiring small amide substituents, suggesting that the carboxamide serves as a hydrogen bond acceptor but not donor. Alternative modifications at the carboxamide as well as modifications of the methyl terminus or the hydrocarbon region spanning the carboxamide and double bond typically eliminate activity. A less extensive study of the 5-HT1A potentiation revealed that it is more tolerant and accommodates a wider range of structural modifications. An interesting set of analogs was identified that inhibit rather than potentiate the 5-HT2A, but not the 5-HT1A, receptor response, further suggesting that such analogs may permit the selective modulation of serotonin receptor subtypes and even have opposing effects on the different subtypes.

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.

Alternative pathways of anandamide biosynthesis in rat testes

We have investigated the biosynthesis of long-chain N-acylethanolamines (NAEs) from endogenous substrates in rat testes membranes with special emphasis on anandamide (20:4n-6 NAE), a cannabinoid receptor agonist. Incubation of various membrane preparations with 5 mM Ca2+ produced both N-acyl phosphatidylethanolamine (N-acyl PE) and NAE with primarily (approximately 85%) N-palmitoyl groups (16:0 NAE) and less than 2% 20:4n-6 NAE. In contrast, incubation of these membranes with 5 mM EGTA and 10 mM ethanolamine had little effect on N-acyl PE composition but yielded NAEs whose major constituent (32-37%) was anandamide. Incubations with [1,1,2,2,-2H4]ethanolamine in media containing 40% H2(18)O showed that the Ca(2+)-independent NAE synthesis occurred by direct condensation of ethanolamine with free fatty acids present in the membrane preparation. This biosynthetic activity occurred at ethanolamine concentrations as low as 50 microM and exhibited substrate selectivity for arachidonate which increased with increasing ethanolamine concentrations. The results of inhibitor experiments suggest that the Ca(2+)-independent NAE synthesis was catalyzed by the NAE amidohydrolase acting in reverse. This condensation reaction could be important in agonist-induced anandamide synthesis for cell signalling through cannabinoid receptors.

Anandamide amidohydrolase reacting with 2-arachidonoylglycerol, another cannabinoid receptor ligand

Two endogenous ligands for cannabinoid receptors, anandamide (arachidonylethanolamide) and 2-arachidonoylglycerol, lose their biological activities by enzymatic hydrolysis. A cDNA for a rat liver enzyme hydrolyzing anandamide as well as oleamide was overexpressed in COS-7 cells. When the particulate fraction was allowed to react with 2-arachidonoylglycerol, arachidonic acid was produced. In contrast, this hydrolytic reaction did not occur with the control cells. The hydrolysis of 2-arachidonoylglycerol proceeded about 4-fold faster than the anandamide hydrolysis with a Km value as low as 6 microM and an optimal pH of 10. Phenylmethylsulfonyl fluoride and methyl arachidonyl fluorophosphonate inhibited the hydrolysis of both anandamide and 2-arachidonoylglycerol in parallel. Furthermore, the hydrolysis of [14C]2-arachidonoylglycerol was inhibited by anandamide dose-dependently. These results suggest that anandamide and 2-arachidonoylglycerol can be inactivated by the same enzyme.

The cloned rat hydrolytic enzyme responsible for the breakdown of anandamide also catalyzes its formation via the condensation of arachidonic acid and ethanolamine

Anandamide amidase is the hydrolytic enzyme responsible for the breakdown of anandamide, an endogenous cannabimimetic, to arachidonate and ethanolamine. Another enzymatic activity called anandamide synthase catalyzes the reverse reaction, that is the condensation of arachidonate and ethanolamine. Using a recently cloned rat fatty acid amidohydrolase (FAAH), we tested the hypothesis that the synthase and the amidase activities are catalyzed by the same enzyme. Untransfected and vector transfected (pcDNA3) COS-7 cells did not express detectable levels of either the amidase or synthase. However, when COS-7 cells were transiently transfected with a rat FAAH pcDNA3 construct, both amidase and synthase were concomitantly expressed. These results indicate that the enzymatic formation of anandamide from arachidonic acid and ethanolamine can be mediated by anandamide amidase acting in the reverse direction. The FAAH transfected cells expressed higher levels of enzyme than either rat brain homogenates or neuroblastoma cells in culture. Furthermore, the reaction rate for the amidase in FAAH transfected COS-7 cells, neuroblastoma cells and brain homogenate was always greater than the synthase reaction. These studies raise the question if this synthase reaction serves any physiological role, especially in view of the evidence that anandamide can be formed by a different pathway.

Evidence that methyl arachidonyl fluorophosphonate is an irreversible cannabinoid receptor antagonist

1. Methyl arachidonyl fluorophosphonate (MAFP) (1 microM) significantly attenuated the ability of WIN 55,212-2, CP 55,940, (-)-delta 9-tetrahydrocannabinol (THC), nabilone and (R)-(+)-arachidonoyl-1'-hydroxy-2'-propylamide (methanandamide) to inhibit electrically-evoked isometric contractions of the myenteric plexus-longitudinal muscle preparation of guinea-pig small intestine. 2. The sizes of the maximal responses to WIN 55,212-2 and CP 55,940 decreased significantly in the presence of 1 microM MAFP. 3. MAFP (1 microM) essentially abolished the inhibitory effects on the twitch response of the highest concentration of methanandamide used (3.162 microM). The dextral shift it induced in the log concentration-response curve of nabilone was non-parallel. In contrast, the dextral shift in the log concentration-response curve of THC produced by MAFP did not deviate significantly from parallelism and was relatively small with a mean value of 3.45 and 95% confidence limits of 1.19 and 13.08. 4. MAFP (1 microM) did not attenuate the effects of normorphine or clonidine on the twitch response of the myenteric plexus-longitudinal muscle preparation or affect the contractile response of this preparation to acetylcholine. 5. When administered by itself at concentrations of 1 to 1000 nM, MAFP had no detectable effect on the twitch response of the myenteric plexus-longitudinal muscle preparation. 6. These results support the hypothesis that MAFP is an irreversible cannabinoid CB1 receptor antagonist that possesses some degree of selectivity.