The fatty-acid amide hydrolase inhibitor URB597 does not affect triacylglycerol hydrolysis in rat tissues

The effects of chronic FAAH inhibition on myocardial lipid metabolism in normotensive and DOCA-salt hypertensive rats

AIMS

There is significant evidence that the endocannabinoid system (ECS) takes part in the regulation of the cardiovascular system in hypertension. It is quite well established that hypertension causes several changes in the heart metabolism, but it is still unknown whether the ECS affects this process. Therefore, we investigated the influence of prolonged ECS activation on myocardial lipid metabolism in deoxycorticosterone acetate (DOCA)-salt hypertensive rats by chronic fatty acid amide hydrolase (FAAH) inhibition.

MATERIALS AND METHODS

We examined the uptake and oxidation of palmitic acid during the heart perfusion as well as intramyocardial and plasma lipid contents using gas liquid chromatography. Total, plasmalemmal and intracellular expressions of selected proteins were estimated by the Western blot technique. Moreover, the left ventricle's morphology, including myocardial vessels density, was measured using immunohistochemistry.

KEY FINDINGS

We demonstrated that hypertension induced cardiomyocytes and myocardial blood vessels hypertrophy, followed by a reduction in myocardial palmitate oxidation. Interestingly, prolonged activation of the ECS in the normotensive rats induced cardiomyocyte enlargement and intensified fatty acids metabolism. We have also shown that FAAH inhibition improved morphology of coronary blood vessels and only partially maintained its effect on lipid metabolism in the DOCA-salt hearts (i.e. elevated plasma and intramyocardial TAG contents as well as plasmalemmal FAT/CD36 and total FATP1 expressions).

SIGNIFICANCE

This study revealed that chronic FAAH inhibition has no protective effects on the heart lipid metabolism in hypertension.

Identification of novel third-generation synthetic cannabinoids in products by ultra-performance liquid chromatography and time-of-flight mass spectrometry

Synthetic cannabinoids are a group of compounds that are structurally diverse and are commonly found in various herbal incense and potpourri blends, which are sold in convenience stores, smoke shops and over the Internet. During the past few years, multiple state and federal legislations have been enacted controlling various subsets of these compounds that have been detected in compound categories generally considered the first and second product generations. As shown in previous studies, as compounds become controlled, new compounds emerge and become prevalent. We report on the emergence and prevalence of five different compounds (A796,260, MAM-2201, UR-144, URB597 and XLR-11) in the state of Indiana through their qualitative detection in solid-dosage herbal products via rapid solvent extraction and ultra-performance liquid chromatography with time-of-flight mass spectrometry (UPLC/ToF). We demonstrate the use of UPLC/ToF to be a suitable tool in the identification of these substances in a crime laboratory or forensic laboratory setting, which ultimately enables a laboratory to design assays for the detection of specific analytes in biological specimens in regard to regional trends and prevalence.

Inhibition of FAAH and activation of PPAR: new approaches to the treatment of cognitive dysfunction and drug addiction

Enhancing the effects of endogenously-released cannabinoid ligands in the brain might provide therapeutic effects more safely and effectively than administering drugs that act directly at the cannabinoid receptor. Inhibitors of fatty acid amide hydrolase (FAAH) prevent the breakdown of endogenous ligands for cannabinoid receptors and peroxisome proliferator-activated receptors (PPAR), prolonging and enhancing the effects of these ligands when they are naturally released. This review considers recent research on the effects of FAAH inhibitors and PPAR activators in animal models of addiction and cognition (specifically learning and memory). These studies show that FAAH inhibitors can produce potentially therapeutic effects, some through cannabinoid receptors and some through PPAR. These effects include enhancing certain forms of learning, counteracting the rewarding effects of nicotine and alcohol, relieving symptoms of withdrawal from cannabis and other drugs, and protecting against relapse-like reinstatement of drug self-administration. Since FAAH inhibition might have a wide range of therapeutic actions but might also share some of the adverse effects of cannabis, it is noteworthy that at least one FAAH-inhibiting drug (URB597) has been found to have potentially beneficial effects but no indication of liability for abuse or dependence. Although these areas of research are new, the preliminary evidence indicates that they might lead to improved therapeutic interventions and a better understanding of the brain mechanisms underlying addiction and memory.

Covalent inhibitors of fatty acid amide hydrolase: a rationale for the activity of piperidine and piperazine aryl ureas

Recently, covalent drugs have attracted great interest in the drug discovery community, with successful examples that have demonstrated their therapeutic effects. Here, we focus on the covalent inhibition of the fatty acid amide hydrolase (FAAH), which is a promising strategy in the treatment of pain and inflammation. Among the most recent and potent FAAH inhibitors (FAAHi), there are the cyclic piperidine and piperazine aryl ureas. FAAH hydrolyzes efficiently the amide bond of these compounds, forming a covalent enzyme-inhibitor adduct. To rationalize this experimental evidence, we performed an extensive computational analysis centered on piperidine-based PF750 (1) and piperazine-based JNJ1661010 (2), two potent lead compounds used to generate covalent inhibitors as clinical candidates. We found that FAAH induces a distortion of the amide bond of the piperidine and piperazine aryl ureas. Quantum mechanics/molecular mechanics ΔE(LUMO-HOMO) energies indicate that the observed enzyme-induced distortion of the amide bond favors the formation of a covalent FAAH-inhibitor adduct. These findings could help in the rational structure-based design of novel covalent FAAHi.

Ethanolamine is a novel STAT-3 dependent cardioprotective agent

Ethanolamine is a biogenic amine found naturally in the body as part of membrane lipids and as a metabolite of the cardioprotective substances, sphingosine-1-phosphate (S1P) and anandamide. In the brain, ethanolamine, formed from the breakdown of anandamide protects against ischaemic apoptosis. However, the effects of ethanolamine in the heart are unknown. Signal transducer and activator of transcription 3 (STAT-3) is a critical prosurvival factor in ischaemia/reperfusion (I/R) injury. Therefore, we investigated whether ethanolamine protects the heart via activation of STAT-3. Isolated hearts from wildtype or cardiomyocyte specific STAT-3 knockout (K/O) mice were pre-treated with ethanolamine (Etn) (0.3 mmol/L) before I/R insult. In vivo rat hearts were subjected to 30 min ischaemia/2 h reperfusion in the presence or absence of 5 mg/kg S1P and/or the FAAH inhibitor, URB597. Infarct size was measured at the end of each protocol by triphenyltetrazolium chloride staining. Pre-treatment with ethanolamine decreased infarct size in isolated mouse or rat hearts subjected to I/R but this infarct sparing effect was lost in cardiomyocyte specific STAT-3 deficient mice. Pre-treatment with ethanolamine increased nuclear phosphorylated STAT-3 [control 0.75 ± 0.08 vs. Etn 1.50 ± 0.09 arbitrary units; P < 0.05]. Our findings suggest a novel cardioprotective role for ethanolamine against I/R injury via activation of STAT-3.

A second generation of carbamate-based fatty acid amide hydrolase inhibitors with improved activity in vivo

The fatty acid ethanolamides are a class of signaling lipids that include agonists at cannabinoid and alpha type peroxisome proliferator-activated receptors (PPARalpha). In the brain, these compounds are primarily hydrolyzed by the intracellular serine enzyme fatty acid amide hydrolase (FAAH). O-aryl carbamate FAAH inhibitors such as URB597 are being evaluated clinically for the treatment of pain and anxiety, but interactions with carboxylesterases in liver might limit their usefulness. Here we explore two strategies aimed at overcoming this limitation. Lipophilic N-terminal substitutions, which enhance FAAH recognition, yield potent inhibitors but render such compounds susceptible to attack by broad-spectrum hydrolases and inactive in vivo. By contrast, polar electron-donating O-aryl substituents, which decrease carbamate reactivity, yield compounds, such as URB694, that are highly potent FAAH inhibitors in vivo and less reactive with off-target carboxylesterases. The results suggest that an approach balancing inhibitor reactivity with target recognition produces FAAH inhibitors that display significantly improved drug-likeness.

Anandamide increases the differentiation of rat adipocytes and causes PPARgamma and CB1 receptor upregulation

Anandamide (N-arachidonoylethanolamine, AEA) or its metabolites participate in energy balance mainly through feeding modulation. In addition, AEA has been found to increase 3T3-L1 adipocyte differentiation process. In this study, the effect of AEA, R(+)-methanandamide (R(+)-mAEA), URB597, and indomethacin on primary rat adipocyte differentiation was evaluated by a flow cytometry method and by Oil Red-O staining. Reverse transcription-PCR and western blotting analysis were performed in order to study the effect of AEA on peroxisome proliferator-activated receptor (PPAR)gamma2, cannabinoid receptors (CBRs), fatty acid amidohydrolase (FAAH), and cyclooxygenase-2 (COX-2) expression, during the differentiation process. AEA increased adipocyte differentiation in primary cell cultures in a concentration- and time-dependent manner and induced PPARgamma2 gene expression, confirming findings with 3T3-L1 cell line. CB1R, FAAH, and COX-2 expression was also increased while CB2R expression was decreased. Inhibition of FAAH and COX-2 attenuated the AEA-induced differentiation. Our findings indicate that AEA regulates energy homeostasis not only by appetite modulation but may also regulate adipocyte differentiation and phenotype.

Structure-property relationships of a class of carbamate-based fatty acid amide hydrolase (FAAH) inhibitors: chemical and biological stability

Cyclohexylcarbamic acid aryl esters are a class of fatty acid amide hydrolase (FAAH) inhibitors, which includes the reference compound URB597. The reactivity of their carbamate fragment is involved in pharmacological activity and may affect their pharmacokinetic and toxicological properties. We conducted in vitro stability experiments in chemical and biological environments to investigate the structure-stability relationships in this class of compounds. The results show that electrophilicity of the carbamate influences chemical stability, as suggested by the relation between the rate constant of alkaline hydrolysis (log k(pH9)) and the energy of the lowest unoccupied molecular orbital (LUMO). Introduction of small electron-donor substituents at conjugated positions of the O-aryl moiety increased the overall hydrolytic stability of the carbamate group without affecting FAAH inhibitory potency, whereas peripheral non-conjugated hydrophilic groups, which favor FAAH recognition, helped decrease oxidative metabolism in the liver.

The endocannabinoid system as a target for the treatment of cannabis dependence

The endocannabinoid system modulates neurotransmission at inhibitory and excitatory synapses in brain regions relevant to the regulation of pain, emotion, motivation, and cognition. This signaling system is engaged by the active component of cannabis, Delta9-tetrahydrocannabinol (Delta9-THC), which exerts its pharmacological effects by activation of G protein-coupled type-1 (CB1) and type-2 (CB2) cannabinoid receptors. During frequent cannabis use a series of poorly understood neuroplastic changes occur, which lead to the development of dependence. Abstinence in cannabinoid-dependent individuals elicits withdrawal symptoms that promote relapse into drug use, suggesting that pharmacological strategies aimed at alleviating cannabis withdrawal might prevent relapse and reduce dependence. Cannabinoid replacement therapy and CB1 receptor antagonism are two potential treatments for cannabis dependence that are currently under investigation. However, abuse liability and adverse side-effects may limit the scope of each of these approaches. A potential alternative stems from the recognition that (i) frequent cannabis use may cause an adaptive down-regulation of brain endocannabinoid signaling, and (ii) that genetic traits that favor hyperactivity of the endocannabinoid system in humans may decrease susceptibility to cannabis dependence. These findings suggest in turn that pharmacological agents that elevate brain levels of the endocannabinoid neurotransmitters, anandamide and 2-arachidonoylglycerol (2-AG), might alleviate cannabis withdrawal and dependence. One such agent, the fatty-acid amide hydrolase (FAAH) inhibitor URB597, selectively increases anandamide levels in the brain of rodents and primates. Preclinical studies show that URB597 produces analgesic, anxiolytic-like and antidepressant-like effects in rodents, which are not accompanied by overt signs of abuse liability. In this article, we review evidence suggesting that (i) cannabis influences brain endocannabinoid signaling and (ii) FAAH inhibitors such as URB597 might offer a possible therapeutic avenue for the treatment of cannabis withdrawal.

Synthesis and quantitative structure-activity relationship of fatty acid amide hydrolase inhibitors: modulation at the N-portion of biphenyl-3-yl alkylcarbamates

Alkylcarbamic acid biphenyl-3-yl esters are a class of fatty acid amide hydrolase (FAAH) inhibitors that comprises cyclohexylcarbamic acid 3'-carbamoylbiphenyl-3-yl ester (URB597), a compound with analgesic, anxiolytic-like and antidepressant-like properties in rat and mouse models. Here, we extended the structure-activity relationships (SARs) for this class of compounds by replacing the cyclohexyl ring of the parent compound cyclohexylcarbamic acid biphenyl-3-yl ester (URB524) (FAAH IC50 = 63 nM) with a selected set of substituents of different size, shape, flexibility, and lipophilicity. Docking experiments and linear interaction energy (LIE) calculations indicated that the N-terminal group of O-arylcarbamates fits within the lipophilic region of the substrate-binding site, mimicking the arachidonoyl chain of anandamide. Significant potency improvements were observed for the beta-naphthylmethyl derivative 4q (IC50 = 5.3 nM) and its 3'-carbamoylbiphenyl-3-yl ester 4z (URB880, IC50 = 0.63 nM), indicating that shape complementarity and hydrogen bonds are crucial to obtain highly potent inhibitors.

The complications of promiscuity: endocannabinoid action and metabolism

In this review, we present our understanding of the action and metabolism of endocannabinoids and related endogenous molecules. It is clear that the interactions between the multiple endocannabinoid-like molecules (ECLs) are highly complex, both at the level of signal transduction and metabolism. Thus, ECLs are a group of ligands active at 7-transmembrane and nuclear receptors, as well as transmitter-gated and ion channels. ECLs and their metabolites can converge on common endpoints (either metabolic or signalling) through contradictory or reinforcing pathways. We highlight the complexity of the endocannabinoid system, based on the promiscuous nature of ECLs and their metabolites, as well as the synthetic modulators of the endocannabinoid system.

Enhancement of endocannabinoid signaling and the pharmacotherapy of depression

Cannabinoids are well known modulators of mood and emotional behavior. Current research supports a role for endocannabinoid signaling in the treatment of depression. Changes in levels of the cannabinoid CB(1) receptor or the endogenous CB(1) receptor ligands, anandamide and 2-AG, are observed both in humans suffering from depression and in animal models of depression, and experimental manipulation of CB(1) receptor signaling has also been shown to affect emotional reactivity in rodents. Importantly, inhibitors of anandamide inactivation have demonstrated efficacy in enhancing stress-coping and mood-related behavior. This article will review these areas of research, highlighting the potential of endocannabinoid metabolism modulators as therapeutics for the treatment of depression.

The pharmacology of the cannabinoid system--a question of efficacy and selectivity

Our knowledge of the function of the cannabinoid system in the body has been aided by the availability of pharmacological agents that affect its function. This has been achieved by the design of agents that either directly interact with the receptor (agonists and antagonist/inverse agonists) and agents that indirectly modulate the receptor output by changing the levels of the endogenous cannabinoids (endocannabinoids). In this review, examples of the most commonly used receptor agonists, antagonists/inverse agonists, and indirectly acting agents (anandamide uptake inhibitors, fatty acid amide hydrolase inhibitors, monoacylglycerol lipase inhibitors) are given, with particular focus upon their selectivity and, in the case of the directly acting compounds, efficacy. Finally, the links between the endocannabinoid and cyclooxygenase pathways are explored, in particular, with respect to agents whose primary function is to inhibit cyclooxygenase activity, but which also interact with the endocannabinoid system.

The 'specific' tyrosine kinase inhibitor genistein inhibits the enzymic hydrolysis of anandamide: implications for anandamide uptake

BACKGROUND AND PURPOSE

The cellular uptake of anandamide is reduced by inhibitors of fatty acid amide hydrolase (FAAH) and by agents disrupting endocytotic mechanisms. However, it is not clear if these events occur over the same time frame and if they occur to the same extent in different cells. We have therefore investigated the effects of such compounds in three cell lines of different origins using different assay incubation times and temperatures.

EXPERIMENTAL APPROACH

FAAH activity and cellular uptake of anandamide was measured using anandamide, radio-labelled either in the ethanolamine or arachidonoyl part of the molecule.

KEY RESULTS

The FAAH inhibitor URB597 inhibited the uptake of anandamide into C6 glioma, RBL2H3 basophilic leukaemia cells and P19 embryonic carcinoma cells at incubation time 4 min. However, a time-dependent and temperature-sensitive residual uptake remained after URB597 treatment. The combination of progesterone and nystatin reduced the uptake, but also decreased the amount of anandamide retained by the wells. Genistein inhibited anandamide uptake in a manner that was not additive to that of URB597. However, genistein was a potent competitive inhibitor of FAAH (K(i) value 8 microM).

CONCLUSIONS AND IMPLICATIONS

The reduction of anandamide uptake by genistein can be explained by its ability to inhibit FAAH with a potency which overlaps that for inhibition of tyrosine kinase. The FAAH- resistant but time-dependent uptake of anandamide is seen in all three cell lines studied and is thus presumably a generally occurring process.

Fatty acid amide hydrolase inhibitors display broad selectivity and inhibit multiple carboxylesterases as off-targets

Fatty acid amide hydrolase (FAAH) is the primary regulator of several bioactive lipid amides including anandamide. Inhibitors of FAAH are potentially useful for the treatment of pain, anxiety, depression, and other nervous system disorders. However, FAAH inhibitors must display selectivity for this enzyme relative to the numerous other serine hydrolases present in the human proteome in order to be therapeutically acceptable. Here we employed activity-based protein profiling (ABPP) to assess the selectivity of FAAH inhibitors in multiple rat and human tissues. We discovered that some inhibitors, including carbamate compounds SA-47 and SA-72, and AM404 are exceptionally selective while others, like URB597, BMS-1, OL-135, and LY2077855 are less selective, displaying multiple off-targets. Since proteins around 60kDa constitute the major off-targets for URB597 and several other FAAH inhibitors with different chemical structures, we employed the multi-dimensional protein identification technology (MudPIT) approach to analyze their identities. We identified multiple carboxylesterase isozymes as bona fide off-targets of FAAH inhibitors. Consistently, enzymatic assay confirmed inhibition of carboxylesterase activities in rat liver by FAAH inhibitors. Since carboxylesterases hydrolyze a variety of ester-containing drugs and prodrugs, we speculate that certain FAAH inhibitors, by inhibiting carboxylesterases, might have drug-drug interactions with other medicines if developed as therapeutic agents.