Characterization of the fatty acid amide hydrolase inhibitor cyclohexyl carbamic acid 3'-carbamoyl-biphenyl-3-yl ester (URB597): effects on anandamide and oleoylethanolamide deactivation

Fatty acid amide hydrolase: from characterization to therapeutics

Fatty acid amide hydrolase (FAAH) is an integral membrane enzyme within the amidase-signature family that terminates the action of several endogenous lipid messengers, including oleamide and the endocannabinoid anandamide. The hydrolysis of such messengers leads to molecules devoid of biological activity, and, therefore, modulates a number of neurobehavioral processes in mammals, including pain, sleep, feeding, and locomotor activity. Investigations into the structure and function of FAAH, its biological and therapeutic implications, as well as a description of different families of FAAH inhibitors are the topic of this review.

The N-acylethanolamine-hydrolyzing acid amidase (NAAA)

Bioactive N-acylethanolamines, including the endocannabinoid anandamide and anti-inflammatory N-palmitoylethanolamine, are hydrolyzed to fatty acids and ethanolamine in animal tissues by the catalysis of fatty acid amide hydrolase (FAAH). We recently cloned cDNA of N-acylethanolamine-hydrolyzing acid amidase (NAAA), another enzyme catalyzing the same reaction, from human, rat, and mouse. NAAA reveals no sequence homology with FAAH and belongs to the choloylglycine hydrolase family. The most striking catalytic property of NAAA is pH optimum at 4.5-5, which is consistent with its immunocytochemical localization in lysosomes. In rat, NAAA is highly expressed in lung, spleen, thymus, and intestine. Notably, the expression level of NAAA is exceptionally high in rat alveolar macrophages. The primary structure of NAAA exhibits 33-35% amino acid identity to that of acid ceramidase, a lysosomal enzyme hydrolyzing ceramide to fatty acid and sphingosine. NAAA actually showed a low, but detectable ceramide-hydrolyzing activity, while acid ceramidase hydrolyzed N-lauroylethanolamine. Thus, NAAA is a novel lysosomal hydrolase, which is structurally and functionally similar to acid ceramidase. These results suggest a unique role of NAAA in the degradation of N-acylethanolamines.

Modulation of the endocannabinoid system: therapeutic potential against cocaine dependence

Dependence on cocaine is still a main unresolved medical and social concern, and in spite of research efforts, no pharmacological therapy against cocaine dependence is yet available. Recent studies have shown that the endocannabinoid system participates in specific stages and aspects of drug dependence in general, and some of this evidence suggests an involvement of the cannabinoid system in cocaine effects. For example, cocaine administration has been shown to alter brain endocannabinoid levels, and the endocannabinoid system has been involved in long-term modifications of brain processes that might play a role in neuro/behavioral effects of psychostimulant drugs like cocaine. Human studies show that marijuana dependence is frequently associated with cocaine dependence, and that the cannabinoid receptor CNR1 gene polymorphism might be related to cocaine addiction. This article will review the main papers in the field showing how a modulation of different components of the cannabinoid system might interact with some of the neurobiological/behavioral effects of cocaine related to its reinforcing effects, evaluated in preclinical models or in clinical settings. The goal of this review will be to provide insights into the complex picture of cocaine abuse and addiction, and to extrapolate from such endocannabinoid-cocaine interactions useful information to test the therapeutic potential of cannabinoid ligands and endocannabinoid-level enhancers against cocaine dependence for future preclinical/clinical trials.

The endogenous cannabinoid anandamide has effects on motivation and anxiety that are revealed by fatty acid amide hydrolase (FAAH) inhibition

Converging evidence suggests that the endocannabinoid system is an important constituent of neuronal substrates involved in brain reward processes and emotional responses to stress. Here, we evaluated motivational effects of intravenously administered anandamide, an endogenous ligand for cannabinoid CB1-receptors, in Sprague-Dawley rats, using a place-conditioning procedure in which drugs abused by humans generally produce conditioned place preferences (reward). Anandamide (0.03-3 mg/kg intravenous) produced neither conditioned place preferences nor aversions. However, when rats were pre-treated with the fatty acid amide hydrolase (FAAH) inhibitor URB597 (cyclohexyl carbamic acid 3'-carbamoyl-3-yl ester; 0.3 mg/kg intraperitoneal), which blocks anandamide's metabolic degradation, anandamide produced dose-related conditioned place aversions. In contrast, URB597 alone showed no motivational effects. Like URB597 plus anandamide, the synthetic CB1-receptor ligand WIN 55,212-2 (50-300 microg/kg, intravenous) produced dose-related conditioned place aversions. When anxiety-related effects of anandamide and URB597 were evaluated in a light/dark box, both a low anandamide dose (0.3 mg/kg) and URB597 (0.1 and 0.3 mg/kg) produced anxiolytic effects when given alone, but produced anxiogenic effects when combined. A higher dose of anandamide (3 mg/kg) produced anxiogenic effects and depressed locomotor activity when given alone and these effects were potentiated after URB597 treatment. Finally, anxiogenic effects of anandamide plus URB597 and development of place aversions with URB597 plus anandamide were prevented by the CB1-receptor antagonist AM251 (3 mg/kg intraperitoneal). Thus, additive interactions between the effects of anandamide on brain reward processes and on anxiety may account for its aversive effects when intravenously administered during FAAH inhibition with URB597.

Inhibition of fatty acid amide hydrolase produces analgesia by multiple mechanisms

1 The reversible fatty acid amide hydrolase (FAAH) inhibitor OL135 reverses mechanical allodynia in the spinal nerve ligation (SNL) and mild thermal injury (MTI) models in the rat. The purpose of this study was to investigate the role of the cannabinoid and opioid systems in mediating this analgesic effect. 2 Elevated brain concentrations of anandamide (350 pmol g(-1) of tissue vs 60 pmol g(-1) in vehicle-treated controls) were found in brains of rats given OL135 (20 mg kg(-1)) i.p. 15 min prior to 20 mg kg(-1) i.p. anandamide. 3 Predosing rats with OL135 (2-60 mg kg(-1) i.p.) 30 min before administration of an irreversible FAAH inhibitor (URB597: 0.3 mg kg(-1) intracardiac) was found to protect brain FAAH from irreversible inactivation. The level of enzyme protection was correlated with the OL135 concentrations in the same brains. 4 OL135 (100 mg kg(-1) i.p.) reduced by 50% of the maximum possible efficacy (MPE) mechanical allodynia induced by MTI in FAAH(+/+)mice (von Frey filament measurement) 30 min after dosing, but was without effect in FAAH(-/-) mice. 5 OL135 given i.p. resulted in a dose-responsive reversal of mechanical allodynia in both MTI and SNL models in the rat with an ED(50) between 6 and 9 mg kg(-1). The plasma concentration at the ED(50) in both models was 0.7 microM (240 ng ml(-1)). 6 In the rat SNL model, coadministration of the selective CB(2) receptor antagonist SR144528 (5 mg kg(-1) i.p.), with 20 mg kg(-1) OL135 blocked the OL135-induced reversal of mechanical allodynia, but the selective CB(1) antagonist SR141716A (5 mg kg(-1) i.p.) was without effect. 7 In the rat MTI model neither SR141716A or SR144528 (both at 5 mg kg(-1) i.p.), or a combination of both antagonists coadministered with OL135 (20 mg kg(-1)) blocked reversal of mechanical allodynia assessed 30 min after dosing. 8 In both the MTI model and SNL models in rats, naloxone (1 mg kg(-1), i.p. 30 min after OL135) reversed the analgesia (to 15% of control levels in the MTI model, to zero in the SNL) produced by OL135.

Role of endocannabinoids in alcohol consumption and intoxication: studies of mice lacking fatty acid amide hydrolase

Endocannabinoid signaling plays the important role in regulation of ethanol intake. Fatty acid amide hydrolase (FAAH) is a key membrane protein for metabolism of endocannabinoids, including anandamide, and blockade of FAAH increases the level of anandamide in the brain. To determine if FAAH regulates ethanol consumption, we studied mutant mice with deletion of the FAAH gene. Null mutant mice showed higher preference for alcohol and voluntarily consumed more alcohol than wild-type littermates. There was no significant difference in consumption of sweet or bitter solutions. To determine the specificity of FAAH for ethanol intake, we studied additional ethanol-related behaviors. There were no differences between null mutant and wild-type mice in severity of ethanol-induced acute withdrawal, conditioned taste aversion to alcohol, conditioned place preference, or sensitivity to hypnotic effect of ethanol. However, null mutant mice showed shorter duration of loss of righting reflex induced by low doses of ethanol (3.2 and 3.4 g/kg) and faster recovery from motor incoordination induced by ethanol. All three behavioral phenotypes (increased preference for ethanol, decreased sensitivity to ethanol-induced sedation, and faster recovery from ethanol-induced motor incoordination) seen in mutant mice were reproduced in wild-type mice by injection of a specific inhibitor of FAAH activity--URB597. These data suggest that increased endocannabinoid signaling increased ethanol consumption owing to decreased acute ethanol intoxication.

Rapid screening for potentially relevant polymorphisms in the human fatty acid amide hydrolase gene using Pyrosequencing

INTRODUCTION

Fatty acid amides such as the endocannabinoid anandamide serve as mammalian lipid transmitters in various physiological and pathophysiological processes including inflammation. They are rapidly degraded by the fatty acid amide hydrolase (FAAH). Non-functional FAAH resulted in reduced inflammatory and nociceptive responses. Evidence suggests that human genetic FAAH variants modulate pain and addiction but their clinical role is still poorly known. We therefore developed reliable high-throughput screening assays for FAAH polymorphisms to facilitate research of their clinical role.

MATERIALS AND METHODS

Six simplex Pyrosequencing assays were developed for FAAH polymorphisms dbSNP rs932816, rs4141964, rs324420, rs324419, rs2295633 and rs12029329 spanning the whole FAAH gene. They are frequent or have been functionally associated. Assays were established and validated in DNA samples from 350 healthy unrelated Caucasians.

RESULTS

In all 350 DNA samples the six FAAH polymorphisms were identified correctly as verified by control samples obtained by conventional sequencing. The observed frequencies of homozygous, heterozygous and non-carriers of the minor alleles were in agreement with the Hardy-Weinberg equilibrium. Minor allelic frequencies were: rs932816G>A=0.26, rs4141964C>T=0.37, rs324420C>A=0.20, rs324419C>T=0.15, rs2295633G>A=0.35 and rs12029329G>C=0.25. SNPs were in high linkage except between rs324419 and rs12029329. One single haploblock was identified, spanning either the whole gene range or excluding rs12029329 in the 3' region, depending on the statistical procedure of haloblock assignment.

CONCLUSION

The presently developed Pyrosequencing assays allow for quick and reliable detection of FAAH genotypes and may facilitate investigations of FAAH genetic functional associations.

Microglia produce and hydrolyze palmitoylethanolamide

Microglial cell activation and migration play an important role in neuroinflammation propagation. While it is known that the lipid transmitter palmitoylethanolamide (PEA) regulates microglial migration by interacting with a cannabinoid-like receptor, the production and inactivation of this lipid by microglia has never been addressed directly. Here we show that the mouse microglial cell line BV-2 produces and hydrolyzes PEA. The carbamate compound URB602 inhibits PEA hydrolysis in BV-2 cell homogenates and increases PEA levels in intact cells, whereas the FAAH inhibitor URB597 and serine-hydrolase inhibitor MAFP do not affect PEA levels in intact cells. This unique pharmacological profile of inhibitors on PEA hydrolysis suggests the involvement of a previously undescribed enzyme that degrades PEA. This enzyme expressed by microglia constitutes a promising target for controlling the propagation of neuroinflammation.

Effects of the fatty acid amide hydrolase inhibitor URB597 on the sleep-wake cycle, c-Fos expression and dopamine levels of the rat

Our group has described previously that the endogenous cannabinoid anandamide induces sleep. The hydrolysis of this lipid involves the activity of the fatty acid amide hydrolase (FAAH), which additionally catalyzes the degradation of the satiety factor oleoylethanolamide and the analgesic-inducing lipid palmitoylethanolamide. It has been demonstrated that the inhibition of the FAAH by URB597 increases levels of anandamide, oleoylethanolamide and palmitoylethanolamide in the brain of rats. In order to determinate the physiological properties of the FAAH inhibition on the sleep modulation, we report the pharmacological effects on the sleep-wake cycle of the rat after i.c.v. administrations of URB597, oleoylethanolamide or palmitoylethanolamide (10, 20 microg/5 microl). Separate unilateral i.c.v. injections of 3 compounds during the lights-on period, increased wakefulness and decreased slow wave (SW) sleep in rats in a dose-dependent fashion. We additionally found out that, compared to controls, c-Fos immunoreactivity in hypothalamus and dorsal raphe nucleus was increased in rats that received URB597, oleoylethanolamide or palmitoylethanolamide (10, 20 microg/5 microl, i.c.v.). Next, we found that after an injection of the compounds, levels of dopamine were increased whereas extracellular levels of levodopa (l-DOPA) were decreased. These findings indicate that that inhibition of the FAAH, via URB597, modulates waking. These effects were mimicked separately by the administration of oleoylethanolamide or palmitoylethanolamide. The alertness induced by the compounds tested here activated wake-promoting brain regions and they also induced the release of dopamine. Our results suggest that FAAH activity as well as two molecules that are catalyzed by this enzyme, oleoylethanolamide and palmitoylethanolamide, participate in the regulation of the waking state. Alternative approaches to treat sleep disorders such as excessive somnolence might consider the use of the URB597, oleoylethanolamide or palmitoylethanolamide since all compounds enhance waking.

Evaluation of fatty acid amide hydrolase inhibition in murine models of emotionality

RATIONALE

Manipulations of the endocannabinoid/fatty acid amide hydrolase (FAAH) signaling systems result in conflicting and paradoxical effects in rodent models of emotional reactivity.

OBJECTIVES

In the present study, we tested the hypothesis that the inhibition of FAAH would elicit significant effects in murine models used to screen anxiolytic and antidepressant drugs.

MATERIALS AND METHODS

FAAH (-/-) mice and wild-type mice treated with FAAH inhibitors (URB597 and OL-135) were evaluated in standard behavioral screening models for antidepressant (i.e., tail suspension and forced-swim tests) and anxiolytic (i.e., elevated plus maze) agents. The doses of URB597 and OL-135 selected were based on their ability to augment the pharmacological effects (i.e., analgesia, catalepsy, and hypothermia) of exogenously administered anandamide.

RESULTS

FAAH (-/-) mice, anandamide-injected FAAH (-/-) mice, or wild-type mice injected with FAAH inhibitors or anandamide failed to exhibit significant effects in standard tests of emotional reactivity, although the antidepressant desipramine and the anxiolytic agent midazolam were active in the appropriate assays. FAAH- (-/-) and URB597-treated mice finally displayed significant effects in the tail suspension test when substantial methodological changes were made (i.e., altered ambient light and increased sample sizes).

CONCLUSIONS

Although FAAH suppression can elicit significant effects under some instances in which consequential procedural modifications are made, the present results indicate that the pharmacological inhibition or genetic deletion of FAAH is ineffective in standard mouse models of emotional reactivity. It remains to be established whether the effects of FAAH inhibition in these modified tasks are predictive of their efficacy in treating emotional disorders.

Interactions between endocannabinoids and stress-induced decreased sensitivity to natural reward

Since endocannabinoids modulate reward processing and the stress response, we tested the hypothesis that endocannabinoids regulate stress-induced decreased sensitivity to natural reward. Restraint was used to produce stress-induced reductions in sucrose consumption and preference in male mice. Central cannabinoid receptor (CB(1)) signaling was modulated pharmacologically prior to the application of stress. The preference for sucrose over water was significantly decreased in mice exposed to restraint. Treatment of mice with a cannabinoid receptor agonist (CP55940) or fatty acid amide hydrolase inhibitor (URB597) attenuated, while the CB(1) receptor antagonist/inverse agonist, rimonabant (SR141716), enhanced, stress-induced decreases in sucrose preference. These data are consistent with a tonically active, stress-inhibitory role for the CB(1) receptor. Mice treated with 10 daily episodes of restraint showed reduced sucrose preference that was unaffected by CP55940 and URB597. However, rimonabant produced a greater reduction in sucrose preference on day 10 compared to day 1. These data suggest that on day 10, endocannabinoid signaling is maximally activated and essential for reward sensitivity. The findings of the present study indicate that the CB(1)/endocannabinoid signaling system is an important allostatic mediator that both modulates the responses of mice to stress and is itself modulated by stress.

Identification of a novel endocannabinoid-hydrolyzing enzyme expressed by microglial cells

The endocannabinoids (eCBs) anandamide and 2-arachidonoyl glycerol (2-AG) are inactivated by a two-step mechanism. First, they are carried into cells, and then anandamide is hydrolyzed by fatty acid amide hydrolase (FAAH) and 2-AG by monoacylglycerol lipase (MGL). Here we provide evidence for a previously undescribed MGL activity expressed by microglial cells. We found that the mouse microglial cell line BV-2 does not express MGL mRNA and yet efficiently hydrolyzes 2-AG. URB597 (3'-carbamoyl-biphenyl-3-yl-cyclohexylcarbamate) reduces this hydrolysis by 50%, suggesting the involvement of FAAH. The remaining activity is blocked by classic MGL inhibitors [[1,1-biphenyl]-3-yl-carbamic acid, cyclohexyl ester (URB602) and MAFP (methylarachidonyl fluorophosphate)] and is unaffected by inhibitors of COXs (cyclooxygenases), LOXs (lipooxygenases), and DGLs (diacylglycerol lipases), indicating the involvement of a novel MGL activity. Accordingly, URB602 leads to selective accumulation of 2-AG in intact BV-2 cells. Although MGL expressed in neurons is equally distributed between the cytosolic, mitochondrial, and nuclear fractions, the novel MGL activity expressed by BV-2 cells is enriched in mitochondrial and nuclear fractions. A screen for novel inhibitors of eCB hydrolysis identified several compounds that differentially block MGL, FAAH, and the novel MGL activity. Finally, we provide evidence for expression of the novel MGL by mouse primary microglia in culture. Our results suggest the presence of a novel, pharmacologically distinct, MGL activity that controls 2-AG levels in microglia.

The fatty acid amide hydrolase inhibitor URB597 (cyclohexylcarbamic acid 3'-carbamoylbiphenyl-3-yl ester) reduces neuropathic pain after oral administration in mice

Fatty acid amide hydrolase (FAAH) is an intracellular serine hydrolase that catalyzes the cleavage of bioactive fatty acid ethanolamides, such as the endogenous cannabinoid agonist anandamide. Genetic deletion of the faah gene in mice elevates brain anandamide levels and amplifies the antinociceptive effects of this compound. Likewise, pharmacological blockade of FAAH activity reduces nocifensive behavior in animal models of acute and inflammatory pain. In the present study, we investigated the effects of the selective FAAH inhibitor URB597 (KDS-4103, cyclohexylcarbamic acid 3'-carbamoylbiphenyl-3-yl ester) in the mouse chronic constriction injury (CCI) model of neuropathic pain. Oral administration of URB597 (1-50 mg/kg, once daily) for 4 days produced a dose-dependent reduction in nocifensive responses to thermal and mechanical stimuli, which was prevented by a single i.p. administration of the cannabinoid CB(1) receptor antagonist rimonabant (1 mg/kg). The antihyperalgesic effects of URB597 were accompanied by a reduction in plasma extravasation induced by CCI, which was prevented by rimonabant (1 mg/kg i.p.) and attenuated by the CB(2) antagonist SR144528 (1 mg/kg i.p.). Oral dosing with URB597 achieved significant, albeit transient, drug levels in plasma, inhibited brain FAAH activity, and elevated spinal cord anandamide content. The results provide new evidence for a role of the endocannabinoid system in pain modulation and reinforce the proposed role of FAAH as a target for analgesic drug development.

Endocannabinoids and the regulation of their levels in health and disease

PURPOSE OF REVIEW

Endocannabinoids are defined as endogenous agonists of cannabinoid receptors, that is, of the two G-protein-coupled receptors for the Cannabis psychoactive principle Delta-tetra-hydrocannabinol. Two such endogenous mediators have been most thoroughly studied so far: anandamide and 2-arachidonoylglycerol. Here we review the mechanisms for the regulation of their levels under physiological and pathological conditions, and recent findings on their role in disease.

RECENT FINDINGS

It is becoming increasingly clear that, although both anandamide and 2-arachidonoyl-glycerol are produced and degraded 'on demand', the levels of these two compounds appear to be regulated in different, and sometimes even opposing, ways, often using redundant molecular mechanisms. Alterations of endocannabinoid levels have been found in both animal models of pain, neurological and neurodegenerative states, gastrointestinal disorders and inflammatory conditions, and in blood, cerebrospinal fluid and bioptic samples from patients with various diseases.

SUMMARY

Endocannabinoid levels appear to be transiently elevated as an adaptive reaction to re-establish normal homeostasis when this is acutely and pathologically perturbed. In some chronic conditions, however, this system also contributes to the progress or symptoms of the disorder. As a consequence, new therapeutic drugs are being designed from both stimulants and blockers of endocannabinoid action.

Predominant expression of lysosomal N-acylethanolamine-hydrolyzing acid amidase in macrophages revealed by immunochemical studies

Bioactive N-acylethanolamines, including anandamide (an endocannabinoid), N-palmitoylethanolamine (an anti-inflammatory substance), and N-oleoylethanolamine (an anorexic substance) are enzymatically hydrolyzed to fatty acids and ethanolamine. Fatty acid amide hydrolase plays a major role in this reaction. In addition, we cloned cDNA of an isozyme termed "N-acylethanolamine-hydrolyzing acid amidase (NAAA)" [K. Tsuboi, Y.-X. Sun, Y. Okamoto, N. Araki, T. Tonai, N. Ueda, Molecular characterization of N-acylethanolamine-hydrolyzing acid amidase, a novel member of the choloylglycine hydrolase family with structural and functional similarity to acid ceramidase, J. Biol. Chem. 280 (2005) 11082-11092]. Previous biochemical analyses suggested the expression of NAAA in macrophage cells and various rat tissues including lung and brain. To clarify the physiological significance of NAAA, here we immunochemically studied NAAA for the first time. We developed an antibody specific for rat NAAA, and by Western blotting revealed that NAAA is glycosylated and subjected to specific proteolysis. In alveolar macrophages isolated from rat lung, NAAA was immunocytochemically localized in lysosomes. In the whole lung tissue, only alveolar macrophages were immunostained for NAAA. Conformably, the mRNA and protein levels and activity of NAAA in alveolar macrophages were much higher than those in the whole lung tissue. In brain, intraventricular macrophages were positively stained with anti-NAAA antibody, while microglia appeared to be negative. These results strongly suggested the importance of macrophages as an expression site of NAAA in rat tissues.

The cannabinoid system and its pharmacological manipulation--a review, with emphasis upon the uptake and hydrolysis of anandamide

Although cannabis has been used both recreationally and for medicinal purposes since ancient times, it was not until the 1990s that the receptors responsible for many of the actions of Delta(9)-tetrahydrocannabinol, the main psychoactive ingredient of cannabis, were cloned. Since then, our knowledge of the endogenous cannabinoid system, its physiology, pharmacology and therapeutic potential have expanded enormously. In the present review, the cannabinoid system is described, with particular emphasis on the mechanisms of removal and metabolism of the endocannabinoid signalling molecule anandamide. The current literature shows that cells can accumulate anandamide, and that this process can be disrupted pharmacologically, but that the nature of the mechanism(s) involved remains a matter of some debate. The main enzyme for the hydrolysis of anandamide, fatty acid amide hydrolase, is well characterized, and molecules selectively inhibiting this enzyme have potential therapeutic utility in a number of areas, in particular for the treatment of pain conditions.

Determination of anandamide and other fatty acyl ethanolamides in human serum by electrospray tandem mass spectrometry

We developed a new selective liquid chromatography-electrospray ionization-tandem mass spectrometry method for the identification and quantification of anandamide (AEA), an endogenous cannabinoid receptor ligand, and other bioactive fatty acid ethanolamides (FAEs) in biological samples. Detection limit (0.025 pmol for AEA and 0.1 pmol for palmitoylethanolamide (PEA) and oleoylethanolamide (OEA)) and quantification limit (0.2 pmol for AEA and 0.4 pmol for OEA and PEA) were in the high fmol to low pmol range for all analytes. Linear correlations (r(2)=0.99) were observed in the calibration curves for standard AEA over the range of 0.025-25 pmol and for standard PEA and OEA over the range of 0.1-500 pmol. This method provides a time-saving and sensitive alternative to existing methods for the analysis of FAEs in biological samples.

Enhancement of endocannabinoid signalling during adolescence: Modulation of impulsivity and long-term consequences on metabolic brain parameters in early maternally deprived rats

Pharmacological modulation of the endocannabinoid system is a novel but poorly explored field for potential therapy. Early maternal deprivation represents an animal model for specific aspects of neuropsychiatric disorders. This study explored whether a pharmacological manipulation of the endocannabinoid system at adolescence may restore altered phenotypes resulting from early maternal deprivation. Wistar male rats, maternally deprived for 24 h on postnatal day (PND) 9, were administered the fatty-acid amide hydrolase (FAAH) inhibitor URB597 (0, 0.1 or 0.5 mg/kg/day) for six days during adolescence (PND 31-43), while tested in the intolerance-to-delay task. Deprived (DEP) adolescent rats showed a trend for higher impulsivity levels and an increased locomotor response to novelty when compared to non-deprived (NDEP) controls. The low dose of URB597 effectively decreased impulsive behaviour specifically in DEP subjects. Moreover, long-term metabolic brain changes, induced by drug treatment during adolescence, were detected in DEP animals using proton magnetic resonance spectroscopy ((1)H MRS). Significant changes were only found within the hippocampus: N-acetyl-aspartate and total creatine were up-regulated by the low dose; glutamate and glutamate plus glutamine were conversely down-regulated by the higher dose. In summary, administration of URB597 during adolescence increased self-control behaviour and produced enduring brain biochemical modifications, in a model for neuropsychiatric disorders.

Effects of the FAAH inhibitor, URB597, and anandamide on lithium-induced taste reactivity responses: a measure of nausea in the rat

RATIONALE

The endogenous cannabinoid system plays a vital role in the control of nausea and emesis. Because of the rapid breakdown and hydrolysis of endocannabinoids, such as anandamide, the therapeutic effects may be enhanced by prolonging their duration of action.

OBJECTIVE

The present experiment evaluated the potential of various doses of URB597, a fatty acid amide hydrolase (FAAH) inhibitor, alone and in combination with systemic administration of anandamide to modulate the establishment of lithium-induced conditioned taste reactivity responses in rats.

MATERIALS AND METHODS

In experiment 1, on the conditioning day, rats first received an injection of 0.3 mg/kg URB597, 0.15 mg/kg URB597, or vehicle and then received a second injection of anandamide (5 mg/kg) or vehicle, before a 3-min exposure of 0.1% saccharin by intraoral infusion. Immediately after the saccharin exposure, the rats were injected with lithium chloride. On each of three test days, rats received a 3-min intraoral infusion of saccharin solution, and the taste reactivity responses were videotaped and monitored. In experiment 2, the effects of pretreatment with the CB(1) antagonist, AM-251, on URB597 and anandamide-induced suppressed aversion was evaluated.

RESULTS

Administration of URB597 alone and in combination with anandamide reduced active rejection reactions elicited by a LiCl-paired saccharin solution; both effects were reversed by pretreatment with AM-251, suggesting that they were CB(1) receptor mediated.

CONCLUSIONS

The results suggest that prolonging the action of anandamide by pretreatment with the FAAH inhibitor, URB597, suppresses lithium-induced nausea in the rat.

Analgesic effects of fatty acid amide hydrolase inhibition in a rat model of neuropathic pain

Cannabinoid-based medicines have therapeutic potential for the treatment of pain. Augmentation of levels of endocannabinoids with inhibitors of fatty acid amide hydrolase (FAAH) is analgesic in models of acute and inflammatory pain states. The aim of this study was to determine whether local inhibition of FAAH alters nociceptive responses of spinal neurons in the spinal nerve ligation model of neuropathic pain. Electrophysiological studies were performed 14-18 d after spinal nerve ligation or sham surgery, and the effects of the FAAH inhibitor cyclohexylcarbamic acid 3-carbamoyl biphenyl-3-yl ester (URB597) on mechanically evoked responses of spinal neurons and levels of endocannabinoids were determined. Intraplantar URB597 (25 microg in 50 microl) significantly (p < 0.01) attenuated mechanically evoked responses of spinal neurons in sham-operated rats. Effects of URB597 were blocked by the cannabinoid 1 receptor (CB1) antagonist AM251 [N-1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide] (30 microg in 50 microl) and the opioid receptor antagonist naloxone. URB597 treatment increased levels of anandamide, 2-arachidonyl glycerol, and oleoyl ethanolamide in the ipsilateral hindpaw of sham-operated rats. Intraplantar URB597 (25 microg in 50 microl) did not, however, alter mechanically evoked responses of spinal neurons in spinal nerve ligated (SNL) rats or hindpaw levels of endocannabinoids. Intraplantar injection of a higher dose of URB597 (100 microg in 50 microl) significantly (p < 0.05) attenuated evoked responses of spinal neurons in SNL rats but did not alter hindpaw levels of endocannabinoids. Spinal administration of URB597 attenuated evoked responses of spinal neurons and elevated levels of endocannabinoids in sham-operated and SNL rats. These data suggest that peripheral FAAH activity may be altered or that alternative pathways of metabolism have greater importance in SNL rats.

The endogenous cannabinoid anandamide produces delta-9-tetrahydrocannabinol-like discriminative and neurochemical effects that are enhanced by inhibition of fatty acid amide hydrolase but not by inhibition of anandamide transport

Anandamide is an endogenous ligand for brain cannabinoid CB(1) receptors, but its behavioral effects are difficult to measure due to rapid inactivation. Here we used a drug-discrimination procedure to test the hypothesis that anandamide, given i.v. or i.p., would produce discriminative effects like those of delta-9-tetrahydrocannabinol (THC) in rats when its metabolic inactivation was inhibited. We also used an in vivo microdialysis procedure to investigate the effects of anandamide, given i.v. or i.p., on dopamine levels in the nucleus accumbens shell in rats. When injected i.v., methanandamide (AM-356), a metabolically stable anandamide analog, produced clear dose-related THC-like discriminative effects, but anandamide produced THC-like discriminative effects only at a high 10-mg/kg dose that almost eliminated lever-press responding. Cyclohexyl carbamic acid 3'-carbamoyl-biphenyl-3-yl ester (URB-597), an inhibitor of fatty acid amide hydrolase (FAAH), the main enzyme responsible for metabolic inactivation of anandamide, produced no THC-like discriminative effects alone but dramatically potentiated discriminative effects of anandamide, with 3 mg/kg anandamide completely substituting for the THC training dose. URB-597 also potentiated the ability of anandamide to increase dopamine levels in the accumbens shell. The THC-like discriminative-stimulus effects of anandamide after URB-597 and methanandamide were blocked by the CB1 receptor antagonist rimonabant, but not the vanilloid VR1 receptor antagonist capsazepine. Surprisingly, the anandamide transport inhibitors N-(4-hydroxyphenyl)-eicosa-5,8,11,14-tetraenamide (AM-404) and N-(3-furylmethyl)eicosa-5,8,11,14-tetraenamide (UCM-707) did not potentiate THC-like discriminative effects of anandamide or its dopamine-elevating effects. Thus, anandamide has THC-like discriminative and neurochemical effects that are enhanced after treatment with a FAAH inhibitor but not after treatment with transport inhibitors, suggesting brain area specificity for FAAH versus transport/FAAH inactivation of anandamide.

The acetaminophen-derived bioactive N-acylphenolamine AM404 inhibits NFAT by targeting nuclear regulatory events

AM404 is a synthetic TRPV1/CB(1) hybrid ligand with inhibitory activity on the anandamide transporter and is used for the pharmacological manipulation of the endocannabinoid system. It has been recently described that acetaminophen is metabolised in the brain to form the bioactive N-acylphenolamine AM404 and therefore, we have evaluated the effect of this metabolite in human T cells, discovering that AM404 is a potent inhibitor of TCR-mediated T-cell activation. Moreover, we found that AM404 specifically inhibited both IL-2 and TNF-alpha gene transcription and TNF-alpha synthesis in CD3/CD28-stimulated Jurkat T cells in a FAAH independent way. To further characterize the biochemical inhibitory mechanisms of AM404, we examined the signaling pathways that regulate the activation of the transcription factors NF-kappaB, NFAT and AP-1 in Jurkat cells. We found that AM404 inhibited both the binding to DNA and the transcriptional activity of endogenous NFAT and the transcriptional activity driven by the over expressed fusion protein Gal4-NFAT (1-415). However, AM404 did not affect early steps in NFAT signaling such as CD3-induced calcium mobilization and NFAT1 dephosphorylation. The NFAT inhibitory activity of AM404 seems to be quite specific since this compound did not interfere with the signaling pathways leading to AP-1 or NF-kappaB activation. These findings provide new mechanistic insights into the immunological effects of AM404 which in part could explain some of the activities ascribed to the widely used acetaminophen.

Anxiolytic-like properties of the anandamide transport inhibitor AM404

The endocannabinoids anandamide and 2-arachidonoyglycerol (2-AG) may contribute to the regulation of mood and emotion. In this study, we investigated the impact of the endocannabinoid transport inhibitor AM404 on three rat models of anxiety: elevated plus maze, defensive withdrawal and separation-induced ultrasonic vocalizations. AM404 (1-5 mg kg(-1), intraperitoneal (i.p.)) exerted dose-dependent anxiolytic-like effects in the three models. These behavioral effects were associated with increased levels of anandamide, but not 2-AG, in the prefrontal cortex and were prevented by the CB(1) cannabinoid antagonist rimonabant (SR141716A), suggesting that they were dependent on anandamide-mediated activation of CB(1) cannabinoid receptors. We also evaluated whether AM404 might influence motivation (in the conditioned place preference (CPP) test), sensory reactivity (acoustic startle reflex) and sensorimotor gating (prepulse inhibition (PPI) of the startle reflex). In the CPP test, AM404 (1.25-10 mg kg(-1), i.p.) elicited rewarding effects in rats housed under enriched conditions, but not in rats kept in standard cages. Moreover, AM404 did not alter reactivity to sensory stimuli or cause overt perceptual distortion, as suggested by its lack of effect on startle or PPI of startle. These results support a role of anandamide in the regulation of emotion and point to the anandamide transport system as a potential target for anxiolytic drugs.

Effects of endocannabinoid neurotransmission modulators on brain stimulation reward

RATIONALE

The endogenous cannabinoid system is responsive to the neurobiological actions of Delta9-tetrahydrocannabinol (THC) and other cannabinoid ligands. While numerous studies have focused on the behavioral and pharmacological effects of THC and cannabinoid agonists in experimental animals, most recent work focuses on compounds that modulate endocannabinoid neurotransmission. However, the relevant studies concerning the ability of endocannabinoid modulators to modify reward processes in experimental animals remain rather scarce.

OBJECTIVES

The present study examined the effects of drugs modulating endocannabinoid neurotransmission on brain reward function using the rate-frequency curve shift paradigm of intracranial self-stimulation (ICSS).

METHODS

Animals were implanted with electrodes into the medial forebrain bundle (MFB). After brain stimulation reward thresholds stabilized, rats received intraperitoneal injections of the fatty acid amide hydrolase (FAAH) inhibitors phenylmethylsulfonyl fluoride (PMSF) (0, 15, 30, and 60 mg/kg) and URB-597 (0, 0.3, 1, and 3 mg/kg) and the selective anandamide reuptake inhibitor OMDM-2 (0, 3, 10, and 30 mg/kg).

RESULTS

The highest dose of URB-597 and OMDM-2 significantly increased the threshold frequency required for MFB ICSS, while PMSF increased the threshold frequency in all doses tested. The cannabinoid 1 (CB1) receptor antagonist SR141716A reversed the actions of URB-597 and OMDM-2, but not PMSF, without affecting reward thresholds by itself.

CONCLUSIONS

These results indicate that under the present experimental conditions endocannabinoid modulators do not exhibit reinforcing properties, but rather have inhibitory influence on reward processes. The anhedonic effects of URB-597 and OMDM-2, but not PMSF, observed at the highest doses in this study are probably mediated through direct CB1 receptor stimulation.

Pharmacological profile of the selective FAAH inhibitor KDS-4103 (URB597)

In the present article, we review the pharmacological properties of KDS-4103 (URB597), a highly potent and selective inhibitor of the enzyme fatty-acid amide hydrolase (FAAH), which catalyzes the intracellular hydrolysis of the endocannabinoid anandamide. In vitro, KDS-4103 inhibits FAAH activity with median inhibitory concentrations (IC(50)) of 5 nM in rat brain membranes and 3 nM in human liver microsomes. In vivo, KDS-4103 inhibits rat brain FAAH activity after intraperitoneal (i.p.) administration with a median inhibitory dose (ID(50)) of 0.15 mg/kg. The compound does not significantly interact with other cannabinoid-related targets, including cannabinoid receptors and anandamide transport, or with a broad panel of receptors, ion channels, transporters and enzymes. By i.p. administration to rats and mice KDS-4103 elicits significant, anxiolytic-like, antidepressant-like and analgesic effects, which are prevented by treatment with CB1 receptor antagonists. By contrast, at doses that significantly inhibit FAAH activity and substantially raise brain anandamide levels, KDS-4103 does not evoke classical cannabinoid-like effects (e.g., catalepsy, hypothermia, hyperphagia), does not cause place preference, and does not produce generalization to the discriminative effects of the active ingredient of cannabis, Delta9-tetrahydrocannabinol (Delta9-THC). These findings suggest that KDS-4103 acts by enhancing the tonic actions of anandamide on a subset of CB(1) receptors, which may normally be engaged in controlling emotions and pain. KDS-4103 is orally available in rats and cynomolgus monkeys. Sub-chronic repeated dose studies (1,500 mg/kg, per os) in these two species have not demonstrated systemic toxicity. Likewise, no toxicity was noted in bacterial cytotoxicity tests in vitro and in the Ames test. Furthermore, no deficits were observed in rats on the rotarod test after acute i.p. treatment with KDS-4103 at doses up to 5 mg/kg or in a functional observation battery after oral doses up to 1,500 mg/kg. The results suggest that KDS-4103 will offer a novel approach with a favorable therapeutic window for the treatment of anxiety, depression and pain.

Non-cannabinoid CB1, non-cannabinoid CB2 antinociceptive effects of several novel compounds in the PPQ stretch test in mice

The analgesic and anti-hyperalgesic effects of cannabinoid- and vanilloid-like compounds, plus the fatty acid amide hydrolase (FAAH) inhibitor Cyclohexylcarbamic acid 3'-carbamoyl-biphenyl-3-yl ester (URB597), and acetaminophen, were evaluated in the phenyl-p-quinone (PPQ) pain model, using different routes of administration in combination with opioid and cannabinoid receptor antagonists. All the compounds tested produced analgesic effects. Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and (R)-(+)-arachidonyl-1'-hydroxy-2'-propylamide ((R)-methanandamide) were active by three routes of administration: i.p., s.c. and, p.o. Delta(9)-THC produced ED(50)s of 2.2 mg/kg (0.3-15.6) i.p., 9 mg/kg (4.3-18.9) s.c., and 6.4 mg/kg (5.5-7.6) p.o. Similarly, (R)-methanandamide yielded ED(50)s of 2.9 mg/kg (1-8) i.p., 11 mg/kg (7-17) s.c., and 11 mg/kg (0.9-134) p.o. N-vanillyl-arachidonyl-amide (arvanil) was active by two routes, producing ED(50)s of 4.7 mg/kg (3.0-7.4) s.c. and 0.06 mg/kg (0.02-0.2) i.p. Palmitoylethanolamide, URB597, and acetaminophen were active i.p., resulting in ED(50)s of 3.7 mg/kg (3.2-4.2), 22.9 mg/kg (11.1-47.2), and 160 mg/kg (63-405), respectively. None of the cannabinoid or opioid receptor antagonists tested blocked the compounds evaluated, with two exceptions: the antinociceptive effects of Delta(9)-THC and URB597 were completely blocked by SR141716A, a cannabinoid CB(1) receptor antagonist. Western immunoassays performed using three opioid receptor antibodies, a cannabinoid CB(1) receptor antibody and a transient receptor potential vanilloid type 1(TRPV(1)) receptor antibody, yielded no change in receptor protein levels after short-term arvanil, (R)-methanandamide or Delta(9)-THC administration. These data suggest that all the compounds tested, except Delta(9)-THC and URB597, produced analgesia via a non-cannabinoid CB(1), non-cannabinoid CB(2) pain pathway not yet identified.

Anandamide administration alone and after inhibition of fatty acid amide hydrolase (FAAH) increases dopamine levels in the nucleus accumbens shell in rats

Although endogenous cannabinoid systems have been implicated in the modulation of the rewarding effects of abused drugs and food, little is known about the direct effects of endogenous ligands for cannabinoid receptors on brain reward processes. Here we show for the first time that the intravenous administration of anandamide, an endogenous ligand for cannabinoid receptors, and its longer-lasting synthetic analog methanandamide, increase the extracellular dopamine levels in the nucleus accumbens shell of awake, freely moving rats, an effect characteristic of most drugs abused by humans. Anandamide produced two distinctly different effects on dopamine levels: (1) a rapid, transient increase that was blocked by the cannabinoid CB1 receptor antagonist rimonabant, but not by the vanilloid VR1 receptor antagonist capsazepine, and was magnified and prolonged by the fatty acid amide hydrolase (FAAH) enzyme inhibitor, URB597; (2) a smaller delayed and long-lasting increase, not sensitive to CB1, VR1 or FAAH blockade. Both effects were blocked by infusing either tetrodotoxin (TTX, 1 microm) or calcium-free Ringer's solution through the microdialysis probe, demonstrating that they were dependent on the physiologic activation of dopaminergic neurotransmission. Thus, these results indicate that anandamide, through the activation of the mesolimbic dopaminergic system, participates in the signaling of brain reward processes.

Cannabidiol, a constituent ofCannabis sativa, modulates sleep in rats

Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and cannabidiol (CBD) are two major constituents of Cannabis sativa. Delta(9)-THC modulates sleep, but no clear evidence on the role of CBD is available. In order to determine the effects of CBD on sleep, it was administered intracerebroventricular (icv) in a dose of 10 microg/5 microl at the beginning of either the lights-on or the lights-off period. We found that CBD administered during the lights-on period increased wakefulness (W) and decreased rapid eye movement sleep (REMS). No changes on sleep were observed during the dark phase. Icv injections of CBD (10 microg/5microl) induced an enhancement of c-Fos expression in waking-related brain areas such as hypothalamus and dorsal raphe nucleus (DRD). Microdialysis in unanesthetized rats was carried out to characterize the effects of icv administration of CBD (10 microg/5 microl) on extracellular levels of dopamine (DA) within the nucleus accumbens. CBD induced an increase in DA release. Finally, in order to test if the waking properties of CBD could be blocked by the sleep-inducing endocannabinoid anandamide (ANA), animals received ANA (10 microg/2.5 microl, icv) followed 15 min later by CBD (10 microg/2.5 microl). Results showed that the waking properties of CBD were not blocked by ANA. In conclusion, we found that CBD modulates waking via activation of neurons in the hypothalamus and DRD. Both regions are apparently involved in the generation of alertness. Also, CBD increases DA levels as measured by microdialysis and HPLC procedures. Since CBD induces alertness, it might be of therapeutic value in sleep disorders such as excessive somnolence.

Inactivation of N-acyl phosphatidylethanolamine phospholipase D reveals multiple mechanisms for the biosynthesis of endocannabinoids

N-Acyl ethanolamines (NAEs) constitute a large and diverse class of signaling lipids that includes the endogenous cannabinoid anandamide. Like other lipid transmitters, NAEs are thought to be biosynthesized and degraded on-demand rather than being stored in vesicles prior to signaling. The identification of enzymes involved in NAE metabolism is therefore imperative to achieve a complete understanding of this lipid signaling system and control it for potential therapeutic gain. Recently, an N-acyl phosphatidylethanolamine phospholipase D (NAPE-PLD) was identified as a candidate enzyme involved in the biosynthesis of NAEs. Here, we describe the generation and characterization of mice with a targeted disruption in the NAPE-PLD gene [NAPE-PLD(-/-) mice]. Brain tissue from NAPE-PLD(-/-) mice showed more than a 5-fold reduction in the calcium-dependent conversion of NAPEs to NAEs bearing both saturated and polyunsaturated N-acyl chains. However, only the former group of NAEs was decreased in level in NAPE-PLD(-/-) brains, and these reductions were most dramatic for NAEs bearing very long acyl chains (>or=C20). Further studies identified a calcium-independent PLD activity in brains from NAPE-PLD(-/-) mice that accepted multiple NAPEs as substrates, including the anandamide precursor C20:4 NAPE. The illumination of distinct enzymatic pathways for the biosynthesis of long chain saturated and polyunsaturated NAEs suggests a strategy to control the activity of specific subsets of these lipids without globally affecting the function of the NAE family as a whole.

Endocannabinoids potently protect the newborn brain against AMPA-kainate receptor-mediated excitotoxic damage

Brain lesions induced in newborn mice or rats by the glutamatergic agonists ibotenate (acting on NMDA and metabotropic receptors) or S-bromowillardiine (acting on AMPA-kainate receptors) mimic some aspects of white matter cysts and transcortical necrosis observed in human perinatal brain damage associated with cerebral palsy. Exogenous and endogenous cannabinoids have received increasing attention as potential neuroprotective agents in a number of neurodegenerative disorders of the adult. One recent study showed neuroprotection by the cannabinoid agonist WIN-55212 in a newborn rat model of acute severe asphyxia. The present study was designed to assess the neuroprotective effects of the endogenous cannabinoid anandamide using a well-defined rodent model of neonatal excitotoxic brain lesions. In this model, anandamide provided dose-dependent and long-lasting protection of developing white matter and cortical plate reducing the size of lesions induced by S-bromowillardiine. Anandamide had only marginal neuroprotective effect against ibotenate-induced cortical grey matter lesions. Anandamide-induced neuroprotection against AMPA-kainate receptor-mediated brain lesions were blocked by a CB1 antagonist but not by a CB2 antagonist. Furthermore, anandamide effects were mimicked by a CB1 agonist but not by a CB2 agonist. Real-time PCR confirmed the expression of CB1 receptors, but not CB2 receptors, in the untreated newborn neocortex. Finally, neuroprotective effects of anandamide in white matter involved increased survival of preoligodendrocytes and better preservation of myelination. The present study provides experimental support for the role of endocannabinoids as a candidate therapy for excitotoxic perinatal brain lesions.

Evaluation of the role of nicotinic acetylcholine receptor subtypes and cannabinoid system in the discriminative stimulus effects of nicotine in rats

Male Wistar rats were trained to discriminate (-)-nicotine (0.4 mg/kg) from saline under a two-lever, fixed-ratio 10 schedule of water reinforcement. During test sessions the following drugs were coadministered with saline (substitution studies) or nicotine (0.025-0.4 mg/kg; combination studies): the alpha4beta2 nicotinic acetylcholine receptor subtype antagonist dihydro-beta-erythroidine (DHbetaE), the non-selective nicotinic acetylcholine receptor subtype antagonist mecamylamine, the alpha7 nicotinic acetylcholine receptor subtype antagonist methyllycaconitine (MLA), the alpha4beta2 nicotinic acetylcholine receptor subtype agonist 5-iodo-3-(2(S)-azetidinylmethoxy)pyridine (5-IA), the cannabinoid CB1 receptor antagonist/partial agonist rimonabant, the cannabinoid CB2 receptor antagonist N-[(1S)-endo-1,3,3-trimethylbicyclo-[2.2.1]heptan-2-yl]5-(4-chloro-3-methyl-phenyl)-1-(4-methybenzyl)pyrazole-3-carboxamide (SR 144528), the cannabinoid CB1/2 receptor agonists (-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)-phenyl]-trans-4-(3-hydroxy-propyl)cyclohexanol (CP 55,940) or R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]-pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-(1-naphthalenyl)-methanone mesylate (WIN 55,212-2), the endogenous cannabinoid agonist and non-competitive alpha7 nicotinic acetylcholine receptor subtype antagonist anandamide, the anandamide uptake and fatty acid amide hydrolase inhibitor N-(4-hydroxyphenyl)-5Z,8Z,11Z,14Z-eicosatetraenamide (AM-404), the fatty acid amide hydrolase inhibitor cyclohexylcarbamic acid 3'-carbamoyl-biphenyl-3-yl ester (URB 597), AM-404+anandamide or URB 597+anandamide. 5-IA (0.01 mg/kg) fully substituted for nicotine, while other drugs were inactive. In combination studies, DHbetaE and mecamylamine dose-dependently attenuated the discriminative stimulus effects of nicotine and the full substitution of 5-IA, while MLA, rimonabant, SR 144528, CP 55,940, WIN 55,212-2, and URB 597 did not alter the nicotine cue. Pretreatment with AM-404+anandamide or URB 597+anandamide weakly enhanced nicotine-lever responding. Our pharmacological analyses demonstrates that the expression of nicotine discrimination is under the control of nicotinic acetylcholine receptor subtypes composed of alpha4beta2 (but not of alpha7) subunits. Furthermore, we excluded the involvement of either cannabinoid CB1 and CB2 receptors or increases in the endocannabinoid tone in the nicotine discrimination.

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.

Inhibitors of fatty acid amide hydrolase reduce carrageenan-induced hind paw inflammation in pentobarbital-treated mice: comparison with indomethacin and possible involvement of cannabinoid receptors

The in vivo effect of inhibitors of fatty acid amide hydrolase (FAAH) upon oedema volume and FAAH activity was evaluated in the carrageenan induced hind paw inflammation model in the mouse. Oedema was measured at two time points, 2 and 4 h, after intraplantar injection of carrageenan to anaesthetised mice. Intraperitoneal (i.p.) injections of the FAAH inhibitor URB597 (0.1, 0.3, 1 and 3 mg kg(-1)) 30 min prior to carrageenan administration, dose-dependently reduced oedema formation. At the 4 h time point, the ED(50) for URB597 was approximately 0.3 mg kg(-1). Indomethacin (5 mg kg(-1) i.p.) completely prevented the oedema response to carrageenan. The antioedema effects of indomethacin and URB597 were blocked by 3 mg kg(-1) i.p. of the CB(2) receptor antagonist SR144528. The effect of URB597 was not affected by pretreatment with the peroxisome proliferator-activated receptor gamma antagonist bisphenol A diglycidyl ether (30 mg kg(-1) i.p.) or the TRPV1 antagonist capsazepine (10 mg kg(-1) i.p.), when oedema was assessed 4 h after carrageenan administration. The CB(1) receptor antagonists AM251 (3 mg kg(-1) i.p.) and rimonabant (0.5 mg kg(-1) i.p.) gave inconsistent effects upon the antioedema effect of URB597. FAAH measurements were conducted ex vivo in the paws, spinal cords and brains of the mice. The activities of FAAH in the paws and spinal cords of the inflamed vehicle-treated mice were significantly lower than the corresponding activities in the noninflamed mice. PMSF treatment almost completely inhibited the FAAH activity in all three tissues, as did the highest dose of URB597 (3 mg kg(-1)) in spinal cord samples, whereas no obvious changes were seen ex vivo for the other treatments. In conclusion, the results show that in mice, treatment with indomethacin and URB597 produce SR144528-sensitive anti-inflammatory effects in the carrageenan model of acute inflammation.

Endocannabinoids in the intact retina: 3H-anandamide uptake, fatty acid amide hydrolase immunoreactivity and hydrolysis of anandamide

There is much evidence for an endocannabinoid system in the retina. However, neither the distribution of endocannabinoid uptake, the regulation of endocannabinoid levels, nor the role of endocannabinoid metabolism have been investigated in the retina. Here we focused on one endocannabinoid, anandamide (AEA), and its major hydrolyzing enzyme, fatty acid amide hydrolase (FAAH), in the goldfish retina. Immunoblots of FAAH immunoreactivity (IR) in goldfish retina, brain and rat retina, and brain homogenates showed a single band at 61 kDa that was blocked by preadsorption with peptide antigen. Specific FAAH IR (blocked by preadsorption) was most prominent over Müller cells and cone inner segments. Weaker label was observed over some amacrine cells, rare cell bodies in the ganglion cell layer, and in four lamina in the inner plexiform layer. FAAH activity assays showed that goldfish-retinal and brain homogenates hydrolyzed AEA at rates comparable to rat brain homogenate, and the hydrolysis was inhibited by methyl arachidonyl fluorophosphonate (MAFP) and N-(4 hydroxyphenyl)-arachidonamide (AM404), with IC50s of 21 nM and 1.5 μM, respectively. Cellular 3H-AEA uptake in the intact retina was determined by in vitro autoradiography. Silver-grain accumulation at 20°C was most prominent over cone photoreceptors and Müller cells. Uptake was significantly reduced when retinas were incubated at 4°C, or preincubated with 100 nM MAFP or 10 μM AM404. There was no differential effect of blocking conditions on the distribution of silver grains over cones or Müller cells. The codistribution of FAAH IR and 3H-AEA uptake in cones and Müller cells suggests that the bulk clearance of AEA in the retina occurs as a consequence of a concentration gradient created by FAAH activity. We conclude that endocannabinoids are present in the goldfish retina and underlay the electrophysiological effects of cannabinoid ligands previously shown on goldfish cones and bipolar cells.

Synthesis and Structure-Activity Relationships of FAAH Inhibitors: Cyclohexylcarbamic Acid Biphenyl Esters with Chemical Modulation at the Proximal Phenyl Ring

Fatty acid amide hydrolase (FAAH) is a serine hydrolase that catalyzes the intracellular hydrolysis of fatty acid ethanolamides such as anandamide and oleoylethanolamide. Targeting this enzyme may have important therapeutic potentials owing to the multiple physiological roles of these amides. Cyclohexylcarbamic acid biphenyl-3-yl ester (URB524) was one of the most promising FAAH inhibitors so far described. We report the modulation of the electronic and steric features of the proximal phenyl ring of this compound by introducing a series of substituents at the ortho and para positions. pIC50 values were found to correlate with molecular features thought to be involved in the recognition step such as steric hindrance and hydrogen-bonding ability. Derivatives with small polar groups at the para position of the proximal phenyl ring were slightly better FAAH inhibitors than the parent compound URB524.

Up-regulation of anandamide levels as an endogenous mechanism and a pharmacological strategy to limit colon inflammation

Direct stimulation of cannabinoid CB1 receptors exerts a protective function in animal models of inflammatory bowel diseases (IBDs). However, it is not known whether endocannabinoids are up-regulated during IBDs in animals or humans, nor whether pharmacological elevation of endocannabinoid levels can be exploited therapeutically in these disorders. In this study we addressed these questions. Colon inflammation was induced in mice and rats with 2,4-dinitrobenzene- and 2,4,6-trinitrobenzene sulfonic acids (DNBS and TNBS), respectively. DNBS-treated mice were treated chronically (for 3 or 7 days) with inhibitors of anandamide enzymatic hydrolysis (N-arachidonoyl-serotonin, AA-5-HT) or reuptake (VDM11), 10 or 5 mg/kg, s.c., or with 5-amino-salicilic acid (5-ASA, 1.4 mg/kg, i.r.). Endocannabinoids (anandamide and 2-arachidonoylglycerol, 2-AG) were quantified in mouse colon, or in rat colon mucosa and submucosa, and in bioptic samples from the colon of patients with untreated ulcerative colitis, by liquid chromatography-mass spectrometry. A strong elevation of anandamide, but not 2-AG, levels was found in the colon of DNBS-treated mice, in the colon submucosa of TNBS-treated rats, and in the biopsies of patients with ulcerative colitis. VDM-11 significantly elevated anandamide levels in the colon of DNBS-treated mice and concomitantly abolished inflammation, whereas AA-5-HT did not affect endocannabinoid levels and was significantly less efficacious at attenuating colitis. 5-ASA also increased anandamide levels and abolished colitis. Thus, anandamide is elevated in the inflamed colon of patients with ulcerative colitis, as well as in animal models of IBDs, to control inflammation, and elevation of its levels with inhibitors of its cellular reuptake might be used in the treatment of IBDs.

Antidepressant-like activity and modulation of brain monoaminergic transmission by blockade of anandamide hydrolysis

Although anecdotal reports suggest that cannabis may be used to alleviate symptoms of depression, the psychotropic effects and abuse liability of this drug prevent its therapeutic application. The active constituent of cannabis, delta9-tetrahydrocannabinol, acts by binding to brain CB1 cannabinoid receptors, but an alternative approach might be to develop agents that amplify the actions of endogenous cannabinoids by blocking their deactivation. Here, we show that URB597, a selective inhibitor of the enzyme fatty-acid amide hydrolase, which catalyzes the intracellular hydrolysis of the endocannabinoid anandamide, exerts potent antidepressant-like effects in the mouse tail-suspension test and the rat forced-swim test. Moreover, URB597 increases firing activity of serotonergic neurons in the dorsal raphe nucleus and noradrenergic neurons in the nucleus locus ceruleus. These actions are prevented by the CB1 antagonist rimonabant, are accompanied by increased brain anandamide levels, and are maintained upon repeated URB597 administration. Unlike direct CB1 agonists, URB597 does not exert rewarding effects in the conditioned place preference test or produce generalization to the discriminative effects of delta9-tetrahydrocannabinol in rats. The findings support a role for anandamide in mood regulation and point to fatty-acid amide hydrolase as a previously uncharacterized target for antidepressant drugs.

Endocannabinoids at the spinal level regulate, but do not mediate, nonopioid stress-induced analgesia

Recent work in our laboratories has demonstrated that an opioid-independent form of stress-induced analgesia (SIA) is mediated by endogenous cannabinoids [Hohmann et al., 2005. Nature 435, 1108]. Non-opioid SIA, induced by a 3-min continuous foot shock, is characterized by the mobilization of two endocannabinoid lipids--2-arachidonoylglycerol (2-AG) and anandamide--in the midbrain periaqueductal gray (PAG). The present studies were conducted to examine the contributions of spinal endocannabinoids to nonopioid SIA. Time-dependent increases in levels of 2-AG, but not anandamide, were observed in lumbar spinal cord extracts derived from shocked relative to non-shocked rats. Notably, 2-AG accumulation was of smaller magnitude than that observed previously in the dorsal midbrain following foot shock. 2-AG is preferentially degraded by monoacylglycerol lipase (MGL), whereas anandamide is hydrolyzed primarily by fatty-acid amide hydrolase (FAAH). This metabolic segregation enabled us to manipulate endocannabinoid tone at the spinal level to further evaluate the roles of 2-AG and anandamide in nonopioid SIA. Intrathecal administration of the competitive CB1 antagonist SR141716A (rimonabant) failed to suppress nonopioid SIA, suggesting that supraspinal rather than spinal CB1 receptor activation plays a pivotal role in endocannabinoid-mediated SIA. By contrast, spinal inhibition of MGL using URB602, which selectively inhibits 2-AG hydrolysis in the PAG, enhanced SIA through a CB1-selective mechanism. Spinal inhibition of FAAH, with either URB597 or arachidonoyl serotonin (AA-5-HT), also enhanced SIA through a CB1-mediated mechanism, presumably by increasing accumulation of tonically released anandamide. Our results suggest that endocannabinoids in the spinal cord regulate, but do not mediate, nonopioid SIA.

Identification and functional characterization of brainstem cannabinoid CB2 receptors

The presence and function of CB2 receptors in central nervous system (CNS) neurons are controversial. We report the expression of CB2 receptor messenger RNA and protein localization on brainstem neurons. These functional CB2 receptors in the brainstem were activated by a CB2 receptor agonist, 2-arachidonoylglycerol, and by elevated endogenous levels of endocannabinoids, which also act at CB1 receptors. CB2 receptors represent an alternative site of action of endocannabinoids that opens the possibility of nonpsychotropic therapeutic interventions using enhanced endocannabinoid levels in localized brain areas.

Application of 3D-QSAR in the Rational Design of Receptor Ligands and Enzyme Inhibitors

Quantitative structure-activity relationships (QSARs) are frequently employed in medicinal chemistry projects, both to rationalize structure-activity relationships (SAR) for known series of compounds and to help in the design of innovative structures endowed with desired pharmacological actions. As a difference from the so-called structure-based drug design tools, they do not require the knowledge of the biological target structure, but are based on the comparison of drug structural features, thus being defined ligand-based drug design tools. In the 3D-QSAR approach, structural descriptors are calculated from molecular models of the ligands, as interaction fields within a three-dimensional (3D) lattice of points surrounding the ligand structure. These descriptors are collected in a large X matrix, which is submitted to multivariate analysis to look for correlations with biological activity. Like for other QSARs, the reliability and usefulness of the correlation models depends on the validity of the assumptions and on the quality of the data. A careful selection of compounds and pharmacological data can improve the application of 3D-QSAR analysis in drug design. Some examples of the application of CoMFA and CoMSIA approaches to the SAR study and design of receptor or enzyme ligands is described, pointing the attention to the fields of melatonin receptor ligands and FAAH inhibitors.

Cannabinoid agonists but not inhibitors of endogenous cannabinoid transport or metabolism enhance the reinforcing efficacy of heroin in rats

Accumulating evidence suggests that the endogenous cannabinoid system is involved in the reinforcing effects of heroin. In rats intravenously self-administering heroin, we investigated effects of cannabinoid CB1 receptor agonists and compounds that block transport or metabolism of the endogenous cannabinoid anandamide. The natural cannnabinoid CB1 receptor agonist delta-9-tetrahydrocannabinol (THC, 0.3-3 mg/kg i.p.) did not alter self-administration of heroin under a fixed-ratio one (FR1) schedule, except at a high 3 mg/kg dose which decreased heroin self-administration. Under a progressive-ratio schedule, however, THC dose-dependently increased the number of 50 mug/kg heroin injections self-administered per session and the maximal ratio completed (break-point), with peak increases at 1 mg/kg THC. In addition, 1 mg/kg THC increased break-points and injections self-administered over a wide range of heroin injection doses (25-100 microg/kg), indicating an increase in heroin's reinforcing efficacy and not its potency. The synthetic cannabinoid CB1 receptor agonist WIN55,212-2 (0.3-3 mg/kg i.p.) had effects similar to THC under the progressive-ratio schedule. In contrast, AM-404 (1-10 mg/kg i.p.), an inhibitor of transport of anandamide, and URB-597 (0.01-0.3 mg/kg i.p.), an inhibitor of the enzyme fatty acid amide hydrolase (FAAH) that degrades anandamide, or their combination, did not increase reinforcing efficacy of heroin at any dose tested. Thus, activation of cannabinoid CB1 receptors facilitates the reinforcing efficacy of heroin and this appears to be mediated by interactions between cannabinoid CB1 receptors and mu-opioid receptors and their signaling pathways, rather than by an opioid-induced release of endogenous cannabinoids.

The therapeutic potential of drugs that target cannabinoid receptors or modulate the tissue levels or actions of endocannabinoids

There are at least 2 types of cannabinoid receptor, CB(1) and CB(2), both G protein coupled. CB(1) receptors are expressed predominantly at nerve terminals and mediate inhibition of transmitter release, whereas CB(2) receptors are found mainly on immune cells, their roles including the modulation of cytokine release and of immune cell migration. Endogenous agonists for cannabinoid receptors also exist. These "endocannabinoids" are synthesized on demand and removed from their sites of action by cellular uptake and intracellular enzymic hydrolysis. Endocannabinoids and their receptors together constitute the endocannabinoid system. This review summarizes evidence that there are certain central and peripheral disorders in which increases take place in the release of endocannabinoids onto their receptors and/or in the density or coupling efficiency of these receptors and that this upregulation is protective in some disorders but can have undesirable consequences in others. It also considers therapeutic strategies by which this upregulation might be modulated to clinical advantage. These strategies include the administration of (1) a CB(1) and/or CB(2) receptor agonist or antagonist that does or does not readily cross the blood brain barrier; (2) a CB(1) and/or CB(2) receptor agonist intrathecally or directly to some other site outside the brain; (3) a partial CB(1) and/or CB(2) receptor agonist rather than a full agonist; (4) a CB(1) and/or CB(2) receptor agonist together with a noncannabinoid, for example, morphine or codeine; (5) an inhibitor or activator of endocannabinoid biosynthesis, cellular uptake, or metabolism; (6) an allosteric modulator of the CB(1) receptor; and (7) a CB(2) receptor inverse agonist.

Involvement of N-acylethanolamine-hydrolyzing acid amidase in the degradation of anandamide and other N-acylethanolamines in macrophages

Bioactive N-acylethanolamines including the endocannabinoid anandamide are known to be hydrolyzed to fatty acids and ethanolamine by fatty acid amide hydrolase (FAAH). In addition, we recently cloned an isozyme termed "N-acylethanolamine-hydrolyzing acid amidase (NAAA)", which is active only at acidic pH [Tsuboi, Sun, Okamoto, Araki, Tonai, Ueda, J. Biol. Chem. 285 (2005) 11082-11092]. However, physiological roles of NAAA remained unclear. Here, we examined a possible contribution of NAAA to the degradation of various N-acylethanolamines in macrophage cells. NAAA mRNA as well as FAAH mRNA was detected in several macrophage-like cells, including RAW264.7, and mouse peritoneal macrophages. The homogenates of RAW264.7 cells showed both the NAAA and FAAH activities which were confirmed with the aid of their respective specific inhibitors, N-cyclohexanecarbonylpentadecylamine (CCP) and URB597. As analyzed with intact cells, RAW264.7 cells and peritoneal macrophages degraded anandamide, N-palmitoylethanolamine, N-oleoylethanolamine, and N-stearoylethanolamine. Pretreatment of the cells with CCP or URB597 partially inhibited the degradation, and a combination of the two compounds caused more profound inhibition. In contrast, the anandamide hydrolysis in mouse brain appeared to be principally attributable to FAAH despite the expression of NAAA in the brain. These results suggested that NAAA and FAAH cooperatively degraded various N-acylethanolamines in macrophages.

Inhibition of fatty-acid amide hydrolase enhances cannabinoid stress-induced analgesia: sites of action in the dorsolateral periaqueductal gray and rostral ventromedial medulla

Recent research in our laboratory has demonstrated that stress activates an endogenous cannabinoid mechanism that suppresses sensitivity to pain [Nature 435 (2005) 1108]. In this work, CB(1) antagonists administered systemically blocked stress-induced analgesia induced by brief, continuous foot-shock. The present studies were conducted to examine the role of cannabinoid CB(1) receptors in the brainstem rostral ventromedial medulla (RVM) and midbrain dorsolateral periaqueductal gray (PAG) in cannabinoid stress-induced analgesia (SIA). Pharmacological blockade of vanilloid TRPV1 receptors with capsazepine, administered systemically, did not alter cannabinoid SIA, suggesting that cannabinoid SIA was not dependent upon TRPV1. Microinjection of the competitive CB(1) antagonist rimonabant (SR141716A) into either the RVM or dorsolateral PAG suppressed stress antinociception in this model. Rimonabant was maximally effective following microinjection into the dorsolateral PAG. The fatty-acid amide hydrolase (FAAH) inhibitor arachidonoyl serotonin (AA-5-HT) was subsequently used to block hydrolysis of endocannabinoids and enhance SIA. Systemic and site-specific injections of AA-5-HT into either the dorsolateral PAG or RVM induced CB(1)-mediated enhancements of SIA. Palmitoyltrifluoromethylketone, a potent inhibitor of FAAH and phospholipase A2 activity, administered systemically, exerted similar effects. In all conditions, the antinociceptive effects of each FAAH inhibitor were completely blocked by coadministration of the CB(1) antagonist rimonabant. The present results provide evidence that a descending cannabinergic neural system is activated by environmental stressors to modulate pain sensitivity in a CB(1)-dependent manner.

The endocannabinoid system in the physiology and pathophysiology of the gastrointestinal tract

Numerous investigations have recently demonstrated the important roles of the endocannabinoid system in the gastrointestinal (GI) tract under physiological and pathophysiological conditions. In the GI tract, cannabinoid type 1 (CB1) receptors are present in neurons of the enteric nervous system and in sensory terminals of vagal and spinal neurons, while cannabinoid type 2 receptors are located in immune cells. Activation of CB1 receptors was shown to modulate several functions in the GI tract, including gastric secretion, gastric emptying and intestinal motility. Under pathophysiological conditions induced experimentally in rodents, the endocannabinoid system conveys protection to the GI tract (e.g. from inflammation and abnormally high gastric and enteric secretions). Such protective activities are largely in agreement with anecdotal reports from folk medicine on the use of Cannabis sativa extracts by subjects suffering from various GI disorders. Thus, the endocannabinoid system may serve as a potentially promising therapeutic target against different GI disorders, including frankly inflammatory bowel diseases (e.g. Crohn's disease), functional bowel diseases (e.g. irritable bowel syndrome) and secretion- and motility-related disorders. As stimulation of this modulatory system by CB1 receptor agonists can lead to unwanted psychotropic side effects, an alternative and promising avenue for therapeutic applications resides in the treatment with CB1 receptor agonists that are unable to cross the blood-brain barrier, or with compounds that inhibit the degradation of endogenous ligands (endocannabinoids) of CB1 receptors, hence prolonging the activity of the endocannabinoid system.

Effect of repeated systemic administration of selective inhibitors of endocannabinoid inactivation on rat brain endocannabinoid levels

Several selective inhibitors of endocannabinoid inactivation via either the fatty acid amide hydrolase (FAAH) or the putative endocannabinoid transporter have been developed so far. Here, we have studied the effect in rats of a subchronic intraperitoneal treatment with three recently developed selective inhibitors of endocannabinoid uptake (VDM-11, UCM-707 and OMDM-2) or with a selective FAAH inhibitor (N-arachidonoyl-serotonin, AA-5-HT), on the brain levels of anandamide and 2-arachidonoylglycerol (2-AG) measured by means of isotope dilution LC-MS 1, 5 and 12 h after the last treatment. OMDM-2 was the most efficacious compound at enhancing the levels of anandamide at all time points, with a maximal effect (1.9-fold enhancement) after 5h. This compound also enhanced 2-AG levels by approximately 1.3-fold, but only 5 and 12h from administration. VDM-11 slightly, albeit significantly, enhanced anandamide levels (1.3-fold) only at 1h from administration and 2-AG levels (1.3-fold) only after 5h. Finally, UCM-707 only affected 2-AG levels (by two-fold) at only 1h from administration. FAAH inhibition by AA-5-HT significantly enhanced the levels of both anandamide (between 1.3- and 1.5-fold, maximal effect after 1 h) and 2-AG (between 1.3- and 1.6-fold, maximal effect after 12 h) at all time points. Brains from rats treated with AA-5-HT did never exhibit enhanced levels of serotonin, thus pointing to the metabolic stability of this FAAH inhibitor. These data indicate that: (1) the pharmacological effects reported so far for the four compounds under study in animal models of diseases may be due to enhancement of both anandamide and 2-AG levels; (2) 2-AG seems to need a longer time after the last administration in order to be augmented; (3) OMDM-2 and AA-5-HT should be regarded as enhancers of endocannabinoid levels suitable for use in vivo.