Substrate specificity and stereoselectivity of rat brain microsomal anandamide amidohydrolase

Deletion of fatty acid amide hydrolase reduces lyso-sulfatide levels but exacerbates metachromatic leukodystrophy in mice

An inherited deficiency of arylsulfatase A (ASA) causes the lysosomal storage disease metachromatic leukodystrophy (MLD) characterized by massive intralysosomal storage of the acidic glycosphingolipid sulfatide and progressive demyelination. Lyso-sulfatide, which differs from sulfatide by the lack of the N-linked fatty acid also accumulates in MLD and is considered a key driver of pathology although its concentrations are far below sulfatide levels. However, the metabolic origin of lyso-sulfatide is unknown. We show here that ASA-deficient murine macrophages and microglial cells express an endo-N-deacylase that cleaves the N-linked fatty acid from sulfatide. An ASA-deficient astrocytoma cell line devoid of this activity was used to identify the enzyme by overexpressing 13 deacylases with potentially matching substrate specificities. Hydrolysis of sulfatide was detected only in cells overexpressing the enzyme fatty acid amide hydrolase (FAAH). A cell-free assay with recombinant FAAH confirmed the novel role of this enzyme in sulfatide hydrolysis. Consistent with the in vitro data, deletion of FAAH lowered lyso-sulfatide levels in a mouse model of MLD. Regardless of the established cytotoxicity of lyso-sulfatide and the anti-inflammatory effects of FAAH inhibition seen in mouse models of several neurological diseases, genetic inactivation of FAAH did not mitigate, but rather exacerbated the disease phenotype of MLD mice. This unexpected finding was reflected by worsening of rotarod performance, increase of anxiety-related exploratory activity, aggravation of peripheral neuropathy and reduced life expectancy. Thus, we conclude that FAAH has a protective function in MLD and may represent a novel therapeutic target for treatment of this fatal condition.

Metabolic studies of synaptamide in an immortalized dopaminergic cell line

INTRODUCTION

Synaptamide, the N-acylethanolamine of docosahexaenoic acid (DHA), is structurally similar to the endocannabinoid N-arachidonoylethanolamine, anandamide. It is an endogenous ligand at the orphan G-protein coupled receptor 110 (GPR110; ADGRF1), and induces neuritogenesis and synaptogenesis in hippocampal and cortical neurons, as well as neuronal differentiation in neural stem cells.

PURPOSE

Our goal was to characterize the metabolic fate (synthesis and metabolism) of synaptamide in a dopaminergic cell line using immortalized fetal mesencephalic cells (N27 cells). Both undifferentiated and differentiating N27 cells were used in this study in an effort to understand synaptamide synthesis and metabolism in developing and adult cells.

METHODS

Radiotracer uptake and hydrolysis assays were conducted in N27 cells incubated with [1-¹⁴C]DHA or with one of two radioisotopomers of synaptamide: [α,β-¹⁴C₂]synaptamide and [1-¹⁴C-DHA]synaptamide.

RESULTS

Neither differentiated nor undifferentiated N27 cells synthesized synaptamide from radioactive DHA, but both rapidly incorporated radioactivity from exogenous synaptamide into membrane phospholipids, regardless of which isotopomer was used. Pharmacological inhibition of fatty acid amide hydrolase (FAAH) reduced formation of labeled phospholipids in undifferentiated but not differentiated cells.

CONCLUSIONS

In undifferentiated cells, synaptamide uptake and metabolism is driven by its enzymatic hydrolysis (fatty acid amide hydrolase; FAAH), but in differentiating cells, the process seems to be FAAH independent. We conclude that differentiated and undifferentiated N27 cells utilize synaptamide via different mechanisms. This observation could be extrapolated to how different mechanisms may be in place for synaptamide uptake and metabolism in developing and adult dopaminergic cells.

Structure-Activity Relationships of Central Nervous System Penetration by Fatty Acid Amide Hydrolase (FAAH)-Targeted Thyromimetic Prodrugs

Thyroid hormone (TH) action is of clinical interest in treating demyelinating diseases of the central nervous system (CNS). Two amide prodrugs of sobetirome, a potent thyroid hormone agonist, were previously shown to significantly improve CNS selective distribution of the parent drug through hydrolysis in the CNS by fatty acid amide hydrolase (FAAH). This concept is elaborated upon here with a series of 29 amide prodrugs targeting FAAH. We identify that conservative aliphatic modifications such as the N-methyl (4), N-ethyl (5), N-fluoroethyl (15), and N-cyclopropyl (18) substantially favor selective CNS distribution of the parent drug in mice. Additionally, lead compounds exhibit moderate to good rates of hydrolysis at FAAH in vitro suggesting both enzymatic and physicochemical properties are important parameters for optimization. Both 4 and 15 were orally bioavailable while retaining appreciable CNS parent drug delivery following an oral dose. The pharmacokinetic parameters of 4 over 24 h postdose (i.v. and p.o.) were determined.

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

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

Targeting Fatty-Acid Amide Hydrolase with Prodrugs for CNS-Selective Therapy

The blood-brain barrier (BBB) can be a substantial impediment to achieving therapeutic levels of drugs in the CNS. Certain chemical functionality such as the carboxylic acid is a general liability for BBB permeability preventing significant CNS distribution of a drug from a systemic dose. Here, we report a strategy for CNS-selective distribution of the carboxylic acid containing thyromimetic sobetirome using prodrugs targeted to fatty-acid amide hydrolase (FAAH), which is expressed in the brain. Two amide prodrugs of sobetirome were shown to be efficient substrates of FAAH with Vmax/KM values comparable to the natural endocannabinoid FAAH substrate anandamide. In mice, a systemic dose of sobetirome prodrug leads to a substantial ∼60-fold increase in brain distribution (Kp) of sobetirome compared to an equimolar systemic dose of the parent drug. The increased delivery of sobetirome to the brain from the prodrug was diminished by both pharmacological inhibition and genetic deletion of FAAH in vivo. The increased brain exposure of sobetirome arising from the prodrug corresponds to ∼30-fold increased potency in brain target engagement compared to the parent drug. These results suggest that FAAH-targeted prodrugs can considerably increase drug exposure to the CNS with a concomitant decrease in systemic drug levels generating a desirable distribution profile for CNS acting drugs.

Development of fragment-based n-FABS NMR screening applied to the membrane enzyme FAAH

Despite the recognized importance of membrane proteins as pharmaceutical targets, the reliable identification of fragment hits that are able to bind these proteins is still a major challenge. Among different ¹⁹F NMR spectroscopic methods, n-fluorine atoms for biochemical screening (n-FABS) is a highly sensitive technique that has been used efficiently for fragment screening, but its application for membrane enzymes has not been reported yet. Herein, we present the first successful application of n-FABS to the discovery of novel fragment hits, targeting the membrane-bound enzyme fatty acid amide hydrolase (FAAH), using a library of fluorinated fragments generated based on the different local environment of fluorine concept. The use of the recombinant fusion protein MBP-FAAH and the design of compound 11 as a suitable novel fluorinated substrate analogue allowed n-FABS screening to be efficiently performed using a very small amount of enzyme. Notably, we have identified 19 novel fragment hits that inhibit FAAH with a median effective concentration (IC₅₀) in the low mM-μM range. To the best of our knowledge, these results represent the first application of a ¹⁹F NMR fragment-based functional assay to a membrane protein.

Inhibition of Fatty Acid Amidohydrolase, the Enzyme Responsible for the Metabolism of the Endocannabinoid Anandamide, by Analogues of Arachidonoyl-serotonin

Arachidonoyl-serotonin inhibits in a mixed-type manner the metabolism of the endocannabinoid anandamide by the enzyme fatty acid amidohydrolase. In the present study, compounds related to arachidonoyl-serotonin have been synthesised and investigated for their ability to inhibit anandamide hydrolysis by this enzyme in rat brain homogenates. Removal of the 5-hydroxy from the serotonin head group of arachidonoyl-serotonin produced a compound (N-arachidonoyltryptamine) that was a 2.3-fold weaker inhibitor of anandamide hydrolysis, but which also produced its inhibition by a mixed-type manner (Ki(slope) 1.3 microM; Ki(intercept) 44 microM). Replacement of the amide linkage in this compound by an ester group further reduced the potency. In contrast, replacement of the arachidonoyl side chain by a linolenoyl side chain did not affect the observed potency. N-(Fur-3-ylmethyl) arachidonamide (UCM707), N-(fur-3-ylmethyl)linolenamide and N-(fur-3-ylmethyl)oleamide inhibited anandamide hydrolysis with pI50 values of 4.53, 5.36 and 5.25, respectively. The linolenamide derivative was also found to be a mixed-type inhibitor. It is concluded that the 5-hydroxy group of arachidonoyl-serotonin contributes to, but is not essential for, inhibitory potency at fatty acid amidohydrolase.

Full inhibition of spinal FAAH leads to TRPV1-mediated analgesic effects in neuropathic rats and possible lipoxygenase-mediated remodeling of anandamide metabolism

Neuropathic pain elevates spinal anandamide (AEA) levels in a way further increased when URB597, an inhibitor of AEA hydrolysis by fatty acid amide hydrolase (FAAH), is injected intrathecally. Spinal AEA reduces neuropathic pain by acting at both cannabinoid CB1 receptors and transient receptor potential vanilloid-1 (TRPV1) channels. Yet, intrathecal URB597 is only partially effective at counteracting neuropathic pain. We investigated the effect of high doses of intrathecal URB597 on allodynia and hyperalgesia in rats with chronic constriction injury (CCI) of the sciatic nerve. Among those tested, the 200 µg/rat dose of URB597 was the only one that elevated the levels of the FAAH non-endocannabinoid and anti-inflammatory substrates, oleoylethanolamide (OEA) and palmitoylethanolamide (PEA), and of the endocannabinoid FAAH substrate, 2-arachidonoylglycerol, and fully inhibited thermal and tactile nociception, although in a manner blocked almost uniquely by TRPV1 antagonism. Surprisingly, this dose of URB597 decreased spinal AEA levels. RT-qPCR and western blot analyses demonstrated altered spinal expression of lipoxygenases (LOX), and baicalein, an inhibitor of 12/15-LOX, significantly reduced URB597 analgesic effects, suggesting the occurrence of alternative pathways of AEA metabolism. Using immunofluorescence techniques, FAAH, 15-LOX and TRPV1 were found to co-localize in dorsal spinal horn neurons of CCI rats. Finally, 15-hydroxy-AEA, a 15-LOX derivative of AEA, potently and efficaciously activated the rat recombinant TRPV1 channel. We suggest that intrathecally injected URB597 at full analgesic efficacy unmasks a secondary route of AEA metabolism via 15-LOX with possible formation of 15-hydroxy-AEA, which, together with OEA and PEA, may contribute at producing TRPV1-mediated analgesia in CCI rats.

Role of endocannabinoids and cannabinoid-1 receptors in cerebrocortical blood flow regulation

Background

Endocannabinoids are among the most intensively studied lipid mediators of cardiovascular functions. In the present study the effects of decreased and increased activity of the endocannabinoid system (achieved by cannabinoid-1 (CB1) receptor blockade and inhibition of cannabinoid reuptake, respectively) on the systemic and cerebral circulation were analyzed under steady-state physiological conditions and during hypoxia and hypercapnia (H/H).

Methodology/Principal Findings

In anesthetized spontaneously ventilating rats the CB1-receptor antagonist/inverse agonist AM-251 (10 mg/kg, i.v.) failed to influence blood pressure (BP), cerebrocortical blood flow (CoBF, measured by laser-Doppler flowmetry) or arterial blood gas levels. In contrast, the putative cannabinoid reuptake inhibitor AM-404 (10 mg/kg, i.v.) induced triphasic responses, some of which could be blocked by AM-251. Hypertension during phase I was resistant to AM-251, whereas the concomitant CoBF-increase was attenuated. In contrast, hypotension during phase III was sensitive to AM-251, whereas the concomitant CoBF-decrease was not. Therefore, CoBF autoregulation appeared to shift towards higher BP levels after CB1-blockade. During phase II H/H developed due to respiratory depression, which could be inhibited by AM-251. Interestingly, however, the concomitant rise in CoBF remained unchanged after AM-251, indicating that CB1-blockade potentially enhanced the reactivity of the CoBF to H/H. In accordance with this hypothesis, AM-251 induced a significant enhancement of the CoBF responses during controlled stepwise H/H.

Conclusion/Significance

Under resting physiological conditions CB1-receptor mediated mechanisms appear to have limited influence on systemic or cerebral circulation. Enhancement of endocannabinoid levels, however, induces transient CB1-independent hypertension and sustained CB1-mediated hypotension. Furthermore, enhanced endocannabinoid activity results in respiratory depression in a CB1-dependent manner. Finally, our data indicate for the first time the involvement of the endocannabinoid system and CB1-receptors in the regulation of the cerebral circulation during H/H and also raise the possibility of their contribution to the autoregulation of CoBF.

Highly selective inhibitors of monoacylglycerol lipase bearing a reactive group that is bioisosteric with endocannabinoid substrates

The endocannabinoids 2-arachidonoyl glycerol (2-AG) and N-arachidonoyl ethanolamine (anandamide) are principally degraded by monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), respectively. The recent discovery of O-aryl carbamates such as JZL184 as selective MAGL inhibitors has enabled functional investigation of 2-AG signaling pathways in vivo. Nonetheless, JZL184 and other reported MAGL inhibitors still display low-level cross-reactivity with FAAH and peripheral carboxylesterases, which can complicate their use in certain biological studies. Here, we report a distinct class of O-hexafluoroisopropyl (HFIP) carbamates that inhibits MAGL in vitro and in vivo with excellent potency and greatly improved selectivity, including showing no detectable cross-reactivity with FAAH. These findings designate HFIP carbamates as a versatile chemotype for inhibiting MAGL and should encourage the pursuit of other serine hydrolase inhibitors that bear reactive groups resembling the structures of natural substrates.

Acute Immobilization Stress Modulate GABA Release from Rat Olfactory Bulb: Involvement of Endocannabinoids-Cannabinoids and Acute Stress Modulate GABA Release

We studied the effects of cannabinoids and acute immobilization stress on the regulation of GABA release in the olfactory bulb. Glutamate-stimulated 3H-GABA release was measured in superfused slices. We report that cannabinoids as WIN55, 212-2, methanandamide, and 2-arachidonoylglycerol were able to inhibit glutamate- and KCl-stimulated 3H-GABA release. This effect was blocked by the CB1 antagonist AM281. On the other hand, acute stress was able per se to increase endocannabinoid activity. This effect was evident since the inhibition of stimulated GABA release by acute stress was reversed with AM281 and tetrahydrolipstatin. Inhibition of the endocannabinoid transport or its catabolism showed reduction of GABA release, antagonized by AM281 in control and stressed animals. These results point to endocannabinoids as inhibitory modulators of GABA release in the olfactory bulb acting through an autocrine mechanism. Apparently, stress increases the endocannabinoid system, modulating GABAergic synaptic function in a primary sensory organ.

Endocannabinoid signaling in neurotoxicity and neuroprotection

The cannabis plant and products produced from it, such as marijuana and hashish, have been used for centuries for their psychoactive properties. The mechanism for how Delta(9)-tetrahydrocannabinol (THC), the active constituent of cannabis, elicits these neurological effects remained elusive until relatively recently, when specific G-protein coupled receptors were discovered that appeared to mediate cellular actions of THC. Shortly after discovery of these specific receptors, endogenous ligands (endocannabinoids) were identified. Since that time, an extensive number of papers have been published on the endocannabinoid signaling system, a widespread neuromodulatory mechanism that influences neurotransmission throughout the nervous system. This paper summarizes presentations given at the 12th International Neurotoxicology Association meeting that described the potential role of endocannabinoids in the expression of neurotoxicity. Dr. Raphael Mechoulam first gave an overview of the discovery of exogenous and endogenous cannabinoids and their potential for neuroprotection in a variety of conditions. Dr. Larry Parsons then described studies suggesting that endocannabinoid signaling may play a selective role in drug reinforcement. Dr. Carey Pope presented information on the role that endocannabinoid signaling may have in the expression of cholinergic toxicity following anticholinesterase exposures. Together, these presentations highlighted the diverse types of neurological insults that may be modulated by endocannabinoids and drugs/toxicants which might influence endocannabinoid signaling pathways.

Synthesis and evaluation of paracetamol esters as novel fatty acid amide hydrolase inhibitors

Fatty acid amide hydrolase (FAAH) is the key hydrolytic enzyme for the endogenous cannabinoid receptor ligand anandamide. The synthesis and evaluation for their FAAH inhibitory activities of a series of 18 paracetamol esters are described. Structure-activity relationship studies indicated that the ester (33) with a 2-(4-(2-(trifluoromethyl)pyridin-4-ylamino)phenyl)acetic acid substituent was the most potent analogue in this series. The compound inhibited FAAH activity in a competitive manner with a K(i) value of 0.16 microM. The compound was also able to inhibit the FAAH activity in rat basophilic leukemia cells as assessed by measuring either the hydrolysis of anandamide, the FAAH-dependent cellular accumulation of anandamide, or the FAAH-dependent recycling of tritium to the cell membranes. The compound also inhibited the activity of monoacylglycerol lipase (MGL), the enzyme responsible for the hydrolysis of the endogenous cannabinoid receptor ligand 2-arachidonoylglycerol, with an IC(50) value of 1.9 microM. It is concluded that the compound may be a useful template for the design of potent novel inhibitors of FAAH.

X-ray crystallographic analysis of alpha-ketoheterocycle inhibitors bound to a humanized variant of fatty acid amide hydrolase

Three cocrystal X-ray structures of the alpha-ketoheterocycle inhibitors 3-5 bound to a humanized variant of fatty acid amide hydrolase (FAAH) are disclosed and comparatively discussed alongside those of 1 (OL-135) and its isomer 2. These five X-ray structures systematically probe each of the three active site regions key to substrate or inhibitor binding: (1) the conformationally mobile acyl chain-binding pocket and membrane access channel responsible for fatty acid amide substrate and inhibitor acyl chain binding, (2) the atypical active site catalytic residues and surrounding oxyanion hole that covalently binds the core of the alpha-ketoheterocycle inhibitors captured as deprotonated hemiketals mimicking the tetrahedral intermediate of the enzyme-catalyzed reaction, and (3) the cytosolic port and its uniquely important imbedded ordered water molecules and a newly identified anion binding site. The detailed analysis of their key active site interactions and their implications on the interpretation of the available structure-activity relationships are discussed providing important insights for future design.

Structural basis for human monoglyceride lipase inhibition

Monoglyceride lipase (MGL) is a serine hydrolase that hydrolyses 2-arachidonoylglycerol (2-AG) into arachidonic acid and glycerol. 2-AG is an endogenous ligand of cannabinoid receptors, involved in various physiological processes in the brain. We present here the first crystal structure of human MGL in its apo form and in complex with the covalent inhibitor SAR629. MGL shares the classic fold of the alpha/beta hydrolase family but depicts an unusually large hydrophobic occluded tunnel with a highly flexible lid at its entry and the catalytic triad buried at its end. Structures reveal the configuration of the catalytic triad and the shape and nature of the binding site of 2-AG. The bound structure of SAR629 highlights the key interactions for productive binding with MGL. The shape of the tunnel suggests a high druggability of the protein and provides an attractive template for drug discovery.

Synthesis, in vitro and in vivo evaluation, and radiolabeling of aryl anandamide analogues as candidate radioligands for in vivo imaging of fatty acid amide hydrolase in the brain

Fatty acid amide hydrolyase (FAAH) is one of the main enzymes responsible for terminating the signaling of endocannabinoids in the brain. Imaging FAAH in vivo using PET or SPECT is important to deeper understanding of its role in neuropsychiatric disorders. However, at present, no radioligand is available for mapping the enzyme in vivo. Here, we synthesized 18 aryl analogues of anandamide, FAAH's endogenous substrate, and in vitro evaluated their potential as metabolic trapping tracers. Interaction studies with recombinant FAAH revealed good to very good interaction of the methoxy substituted aryl anandamide analogues 17, 18, 19, and 20 with FAAH and they were identified as competing substrates. Compounds 17 and 18 did not display significant binding to CB1 and CB2 cannabinoid receptors and stand out as potential candidate metabolic trapping tracers. They were successfully labeled with 11C in good yields and high radiochemical purity and displayed brain uptake in C57BL/6J mice. Radioligands [11C]-17 and [11C]-18 merit further investigation in vivo.

Apparent affinity estimates of rimonabant in combination with anandamide and chemical analogs of anandamide in rhesus monkeys discriminating Delta9-tetrahydrocannabinol

RATIONALE

Anandamide and Delta(9)-tetrahydrocannabinol (Delta(9)-THC) sometimes produce different discriminative stimulus effects and, therefore, appear to differ in their mechanism of action. In order to understand the widespread use of cannabis and the therapeutic potential of cannabinoids, mechanisms responsible for behavioral effects need to be identified.

OBJECTIVE

Drug discrimination was used to compare the mechanism of action of Delta(9)-THC, anandamide, and two structural analogs of anandamide in rhesus monkeys.

MATERIALS AND METHODS

Monkeys discriminated Delta(9)-THC (0.1 mg/kg i.v.) from vehicle. Delta(9)-THC, anandamide, methanandamide, and arachidonylcyclopropylamide (ACPA) were administered i.v. alone and in combination with at least one dose of rimonabant. Schild analysis and single-dose apparent affinity estimates were used to estimate the potency of rimonabant as an antagonist of each cannabinoid; these values were compared to examine whether the same receptors mediated discriminative stimulus effects.

RESULTS

Delta(9)-THC, ACPA, methanandamide, and anandamide produced greater than 96% of responses on the Delta(9)-THC lever. The ED(50) values were 0.024 mg/kg for Delta(9)-THC, 0.14 mg/kg for ACPA, 0.28 mg/kg for methanandamide, and 1.7 mg/kg for anandamide. The duration of action of Delta(9)-THC was 4-6 h and longer than the duration of action ACPA, methanandamide, and anandamide (i.e., each less than 50 min). Rimonabant surmountably antagonized the discriminative stimulus effects of each agonist, and the apparent affinity estimates (pA (2) and pK (B) values) were 6.24-6.83.

CONCLUSIONS

Rimonabant can produce surmountable antagonism of the behavioral effects of not only Delta(9)-THC but also anandamide, methanandamide, and ACPA, and the interactions appear simple, competitive, and reversible. These cannabinoid agonists act at the same receptors to produce discriminative stimulus effects.

The case for the development of novel analgesic agents targeting both fatty acid amide hydrolase and either cyclooxygenase or TRPV1

Although the dominant approach to drug development is the design of compounds selective for a given target, compounds targeting more than one biological process may have superior efficacy, or alternatively a better safety profile than standard selective compounds. Here, this possibility has been explored with respect to the endocannabinoid system and pain. Compounds inhibiting the enzyme fatty acid amide hydrolase (FAAH), by increasing local endocannabinoid tone, produce potentially useful effects in models of inflammatory and possibly neuropathic pain. Local increases in levels of the endocannabinoid anandamide potentiate the actions of cyclooxygenase inhibitors, raising the possibility that compounds inhibiting both FAAH and cyclooxygenase can be as effective as non-steroidal anti-inflammatory drugs but with a reduced cyclooxygenase inhibitory 'load'. An ibuprofen analogue active in models of visceral pain and with FAAH and cyclooxygenase inhibitory properties has been identified. Another approach, built in to the experimental analgesic compound N-arachidonoylserotonin, is the combination of FAAH inhibitory and transient receptor potential vanilloid type 1 antagonist properties. Although finding the right balance of actions upon the two targets is a key to success, it is hoped that dual-action compounds of the types illustrated in this review will prove to be useful analgesic drugs.

Radiosynthesis, in vitro and in vivo evaluation of 123I-labeled anandamide analogues for mapping brain FAAH

Fatty acid amide hydrolase (FAAH) is one of the main enzymes responsible for terminating the signaling of endocannabinoids, including anandamide. This paper is the first report of the synthesis, [123I]-labeling and in vitro and in vivo evaluation of anandamide analogues as potential metabolic trapping radioligands for in vivo evaluation of brain FAAH. N-(2-iodoethyl)linoleoylamide (2) and N-(2-iodoethyl)arachidonylamide (4) were synthesized with good yields (75% and 86%, respectively) in a two steps procedure starting from their respective acids. In vitro analyses, performed using recombinant rat FAAH and [3H]-anandamide, demonstrated interaction of 2 and 4 with FAAH (IC50 values of 5.78 microM and 3.14 microM, respectively). [123I]-2 and [123I]-4 were synthesized with radiochemical yields of 21% and 12%, respectively, and radiochemical purities were > 90%. Biodistribution studies in mice demonstrated brain uptake for both tracers (maximum values of 1.23%ID/g at 3 min pi for [123I]-2 and 0.58%ID/g at 10 min pi for [123I]-4). However, stability studies demonstrated the sensitivity of both tracers to dehalogenation.

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

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

Optimization of the central heterocycle of alpha-ketoheterocycle inhibitors of fatty acid amide hydrolase

The synthesis and evaluation of a refined series of alpha-ketoheterocycles based on the oxazole 2 (OL-135) incorporating systematic changes in the central heterocycle bearing a key set of added substituents are described. The nature of the central heterocycle, even within the systematic and minor perturbations explored herein, significantly influenced the inhibitor activity: 1,3,4-oxadiazoles and 1,2,4-oxadiazoles 9 > tetrazoles, the isomeric 1,2,4-oxadiazoles 10, 1,3,4-thiadiazoles > oxazoles including 2 > 1,2-diazines > thiazoles > 1,3,4-triazoles. Most evident in these trends is the observation that introduction of an additional heteroatom at position 4 (oxazole numbering, N > O > CH) substantially increases activity that may be attributed to a reduced destabilizing steric interaction at the FAAH active site. Added heterocycle substituents displaying well-defined trends may be utilized to enhance the inhibitor potency and, more significantly, to enhance the inhibitor selectivity. These trends, exemplified herein, emerge from both enhancements in the FAAH activity and simultaneous disruption of binding affinity for competitive off-target enzymes.

Studies of anandamide accumulation inhibitors in cerebellar granule neurons: comparison to inhibition of fatty acid amide hydrolase

The endocannabinoid, N-arachidonylethanolamine (AEA) is accumulated by neurons via a process that has been characterized biochemically but not molecularly. Inhibitors of AEA accumulation have been characterized individually but have not been compared in a single study. Our purpose was to compare the potency of five previously described compounds (AM404, AM1172, VDM11, OMDM-2, and UCM707) both as inhibitors of AEA and N-palmitoylethanolamine (PEA) accumulation by cerebellar granule neurons and as inhibitors of AEA hydrolysis. The compounds all inhibited AEA accumulation; AM404, VDM11 and OMDM-2 with IC(50) values of approximately 5 microM, whereas AM1172 and UCM707 exhibited IC(50) values of 24 and 30 microM, respectively. The compounds also inhibited PEA accumulation; AM404 being the most potent with an IC(50) of 6 microM, whereas the other compounds had IC(50) values in the range of 30-70 microM. All of the compounds potently inhibited AEA hydrolysis by brain membranes; the K(I) values for AM404, VDM11, and UCM707 were less than 1 microM; AM1172 and OMDM-2 exhibited K(I) values of 3 and 10 microM, respectively. The IC(50) values for inhibition of AEA accumulation were compared to the IC(50) values for PEA accumulation and AEA hydrolysis using linear regression. None of the regressions were significant. These data indicate that inhibition of AEA accumulation by neurons is not a result of the inhibition of endocannabinoid hydrolysis and is a process different from the accumulation of PEA. These studies support the hypothesis that the cellular AEA accumulation beyond simple equilibrium between intracellular and extracellular concentrations occurs because AEA binds to an intracellular protein that is not FAAH but that also recognizes the AEA uptake inhibitors.

Optimization of alpha-ketooxazole inhibitors of fatty acid amide hydrolase

A series of alpha-ketooxazoles containing conformational constraints in the flexible C2 acyl side chain of 2 (OL-135) and representative oxazole C5 substituents were prepared and examined as inhibitors of fatty acid amide hydrolase (FAAH). Exceptionally potent and selective FAAH inhibitors emerged from the series (e.g., 6, Ki = 200 and 260 pM for rat and rhFAAH). With simple and small C5 oxazole substituents, each series bearing a biphenylethyl, phenoxyphenethyl, or (phenoxymethyl)phenethyl C2 side chain was found to follow a well-defined linear relationship between -log Ki and Hammett sigmap of a magnitude (rho = 2.7-3.0) that indicates that the substituent electronic effect dominates, confirming its fundamental importance to the series and further establishing its predictive value. Just as significantly, the nature of the C5 oxazole substituent substantially impacts the selectivity of the inhibitors whereas the effect of the C2 acyl chain was more subtle but still significant even in the small series examined. Combination of these independent features, which display generalized trends across a range of inhibitor series, simultaneously improves FAAH potency and selectivity and can provide exquisitely selective and potent FAAH inhibitors.

Endocannabinoid metabolism and uptake: novel targets for neuropathic and inflammatory pain

Cannabinoid CB1 and CB2 receptors are located at key sites involved in the relaying and processing of noxious inputs. Both CB1 and CB2 receptor agonists have analgesic effects in a range of models of inflammatory and neuropathic pain. Importantly, clinical trials of cannabis-based medicines indicate that the pre-clinical effects of cannabinoid agonists may translate into therapeutic potential in humans. One of the areas of concern with this pharmacological approach is that CB1 receptors have a widespread distribution in the brain and that global activation of CB1 receptors is associated with adverse side effects. Studies of the endogenous cannabinoids (endocannabinoids) have demonstrated that they are present in most tissues and that in some pain states, such as neuropathic pain, levels of endocannabinoids are elevated at key sites involved in pain processing. An alternative approach that can be used to harness the potential therapeutic effects of cannabinoids is to maximise the effects of the endocannabinoids, the actions of which are terminated by re-uptake and metabolism by various enzymes, including fatty acid amide hydrolase (FAAH), monoacylglycerol lipase (MAGL) and cyclooxygenase type 2 (COX2). Preventing the metabolism, or uptake, of endocannabinoids elevates levels of these lipid compounds in tissue and produces behavioural analgesia in models of acute pain. Herein we review recent studies of the effects of inhibition of metabolism of endocannabinoids versus uptake of endocannabinoids on nociceptive processing in models of inflammatory and neuropathic pain.

Conformationally constrained analogues of 2-arachidonoylglycerol

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

Structure-activity relationships of alpha-ketooxazole inhibitors of fatty acid amide hydrolase

A systematic study of the structure-activity relationships of 2b (OL-135), a potent inhibitor of fatty acid amide hydrolase (FAAH), is detailed targeting the C2 acyl side chain. A series of aryl replacements or substituents for the terminal phenyl group provided effective inhibitors (e.g., 5c, aryl = 1-napthyl, Ki = 2.6 nM), with 5hh (aryl = 3-ClPh, Ki = 900 pM) being 5-fold more potent than 2b. Conformationally restricted C2 side chains were examined, and many provided exceptionally potent inhibitors, of which 11j (ethylbiphenyl side chain) was established to be a 750 pM inhibitor. A systematic series of heteroatoms (O, NMe, S), electron-withdrawing groups (SO, SO2), and amides positioned within and hydroxyl substitutions on the linking side chain were investigated, which typically led to a loss in potency. The most tolerant positions provided effective inhibitors (12p, 6-position S, Ki = 3 nM, or 13d, 2-position OH, Ki = 8 nM) comparable in potency to 2b. Proteome-wide screening of selected inhibitors from the systematic series of >100 candidates prepared revealed that they are selective for FAAH over all other mammalian serine proteases.

Characterization of the vasorelaxation to methanandamide in rat gastric arteries

In the present study, the relaxant effect of the cannabinoid methanandamide was explored in rat gastric arteries. Since in some vessels cannabinoids have been shown to release calcitonin gene-related peptide (CGRP) from perivascular nerves, the influence of methanandamide was compared with that of exogenous CGRP. Methanandamide and CGRP elicited concentration-dependent, endothelium-independent relaxations. Methanandamide-induced relaxations were unaffected by the CB1 receptor antagonist AM251, the CB2 receptor antagonists AM630 and SR144528, and combined pre-exposure to AM251 and SR144528. Pre-exposure to O-1918, an antagonist of a novel nonCB1/nonCB2 cannabinoid receptor, did not influence the relaxations to methanandamide. Capsaicin or capsazepine treatment slightly inhibited methanandamide-induced relaxations. Preincubation with 30 mmol/L extracellular K+ or 3 mmol/L TEA had no significant effect on the responses elicited by methanandamide, but reduced CGRP-induced relaxations. Relaxation to 10(-5) mol/L methanandamide was significantly blunted by Bay K8644 and by preincubation with nifedipine. Furthermore, 10(-5) mol/L methanandamide significantly inhibited CaCl2-induced contractions in norepinephrine-stimulated vessels previously depleted of intra- and extracellular Ca2+. Finally, preincubation with 10(-5) mol/L methanandamide almost completely abolished high K+-induced contractions. These findings suggest that the vasorelaxant action of methanandamide in rat gastric arteries is not mediated by stimulation of known cannabinoid receptors and only partly related to stimulation of TRPV1 receptors on perivascular nerves. At high concentrations, methanandamide might induce relaxation by reducing calcium entry into the smooth muscle cells.

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.

Potent and selective alpha-ketoheterocycle-based inhibitors of the anandamide and oleamide catabolizing enzyme, fatty acid amide hydrolase

A study of the structure-activity relationships (SAR) of 2f (OL-135), a potent inhibitor of fatty acid amide hydrolase (FAAH), is detailed, targeting the 5-position of the oxazole. Examination of a series of substituted benzene derivatives (12-14) revealed that the optimal position for substitution was the meta-position with selected members approaching or exceeding the potency of 2f. Concurrent with these studies, the effect of substitution on the pyridine ring of 2f was also examined. A series of small, nonaromatic C5-substituents was also explored and revealed that the K(i) follows a well-defined correlation with the Hammett sigma(p) constant (rho = 3.01, R2 = 0.91) in which electron-withdrawing substituents enhance potency, leading to inhibitors with K(i)s as low as 400 pM (20n). Proteomic-wide screening of the inhibitors revealed that most are exquisitely selective for FAAH over all other mammalian proteases, reversing the 100-fold preference of 20a (C5 substituent = H) for the enzyme TGH.

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 endocannabinoid system as an emerging target of pharmacotherapy

The recent identification of cannabinoid receptors and their endogenous lipid ligands has triggered an exponential growth of studies exploring the endocannabinoid system and its regulatory functions in health and disease. Such studies have been greatly facilitated by the introduction of selective cannabinoid receptor antagonists and inhibitors of endocannabinoid metabolism and transport, as well as mice deficient in cannabinoid receptors or the endocannabinoid-degrading enzyme fatty acid amidohydrolase. In the past decade, the endocannabinoid system has been implicated in a growing number of physiological functions, both in the central and peripheral nervous systems and in peripheral organs. More importantly, modulating the activity of the endocannabinoid system turned out to hold therapeutic promise in a wide range of disparate diseases and pathological conditions, ranging from mood and anxiety disorders, movement disorders such as Parkinson's and Huntington's disease, neuropathic pain, multiple sclerosis and spinal cord injury, to cancer, atherosclerosis, myocardial infarction, stroke, hypertension, glaucoma, obesity/metabolic syndrome, and osteoporosis, to name just a few. An impediment to the development of cannabinoid medications has been the socially unacceptable psychoactive properties of plant-derived or synthetic agonists, mediated by CB(1) receptors. However, this problem does not arise when the therapeutic aim is achieved by treatment with a CB(1) receptor antagonist, such as in obesity, and may also be absent when the action of endocannabinoids is enhanced indirectly through blocking their metabolism or transport. The use of selective CB(2) receptor agonists, which lack psychoactive properties, could represent another promising avenue for certain conditions. The abuse potential of plant-derived cannabinoids may also be limited through the use of preparations with controlled composition and the careful selection of dose and route of administration. The growing number of preclinical studies and clinical trials with compounds that modulate the endocannabinoid system will probably result in novel therapeutic approaches in a number of diseases for which current treatments do not fully address the patients' need. Here, we provide a comprehensive overview on the current state of knowledge of the endocannabinoid system as a target of pharmacotherapy.

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

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

Caged vanilloid ligands for activation of TRPV1 receptors by 1- and 2-photon excitation

Nociceptive neurons in the peripheral nervous system detect noxious stimuli and report the information to the central nervous system. Most nociceptive neurons express the vanilloid receptor, TRPV1, a nonselective cation channel gated by vanilloid ligands such as capsaicin, the pungent essence of chili peppers. Here, we report the synthesis and biological application of two caged vanilloids: biologically inert precursors that, when photolyzed, release bioactive vanilloid ligands. The two caged vanilloids, Nb-VNA and Nv-VNA, are photoreleased with quantum efficiency of 0.13 and 0.041, respectively. Under flash photolysis conditions, photorelease of Nb-VNA and Nv-VNA is 95% complete in approximately 40 micros and approximately 125 micros, respectively. Through 1-photon excitation with ultraviolet light (360 nm), or 2-photon excitation with red light (720 nm), the caged vanilloids can be photoreleased in situ to activate TRPV1 receptors on nociceptive neurons. The consequent increase in intracellular free Ca(2+) concentration ([Ca(2+)](i)) can be visualized by laser-scanning confocal imaging of neurons loaded with the fluorescent Ca(2+) indicator, fluo-3. Stimulation results from TRPV1 receptor activation, because the response is blocked by capsazepine, a selective TRPV1 antagonist. In Ca(2+)-free extracellular medium, photoreleased vanilloid can still elevate [Ca(2+)](i), which suggests that TRPV1 receptors also reside on endomembranes in neurons and can mediate Ca(2+) release from intracellular stores. Notably, whole-cell voltage clamp measurements showed that flash photorelease of vanilloid can activate TRPV1 channels in <4 ms at 22 degrees C. In combination with 1- or 2-photon excitation, caged vanilloids are a powerful tool for probing morphologically distinct structures of nociceptive sensory neurons with high spatial and temporal precision.

Endocannabinoid signaling dynamics probed with optical tools

Intercellular signaling dynamics critically influence the functional roles that the signals can play. Small lipids are synthesized and released from neurons, acting as intercellular signals in regulating neurotransmitter release, modulating ion channels on target cells, and modifying synaptic plasticity. The repertoire of biological effects of lipids such as endocannabinoids (eCBs) is rapidly expanding, yet lipid signaling dynamics have not been studied. The eCB system constitutes a powerful tool for bioassaying the dynamics of lipid signaling. The eCBs are synthesized in, and released from, postsynaptic somatodendritic domains that are readily accessible to whole-cell patch electrodes. The dramatic effects of these lipid signals are detected electrophysiologically as CB1-dependent alterations in conventional synaptic transmission, which therefore serve as a sensitive reporter of eCB actions. We used electrophysiological recording, photolytic release of caged glutamate and a newly developed caged AEA (anandamide), together with rapid [Ca2+]i measurements, to investigate the dynamics of retrograde eCB signaling between CA1 pyramidal cells and GABAergic synapses in rat hippocampus in vitro. We show that, at 22 degrees C, eCB synthesis and release must occur within 75-190 ms after the initiating stimulus, almost an order of magnitude faster than previously thought. At 37 degrees C, the time could be < 50 ms. Activation of CB1 and downstream processes constitute a significant fraction of the total delay and are identified as major rate-limiting steps in retrograde signaling. Our findings imply that lipid messenger dynamics are comparable with those of metabotropic neurotransmitters and can modulate neuronal interactions on a similarly fast time scale.

Identification of an unusual naturally occurring apolar fatty acid amide in mammalian brain and a method for its quantitative determination

Fatty acid amides (FAAs), such as the N-acylamides, N-acylethanolamides, N-acyldopamines and N-acylamino acids, are now emerging as an important new class of lipid-signalling molecules. This paper provides evidence, based on high-performance liquid chromatography/electrospray ionisation mass spectrometry (HPLC/ESI-MS/MS), gas chromatography/mass spectrometry (GC/MS) and 1H-NMR, of the occurrence in mouse and bovine brain extracts of a compound characterised by a mass spectrum attributable to a FAA not previously described, namely, the isopropyl-amide of stearic acid (SIPA). A highly sensitive GC/MS method was developed for quantification of naturally occurring SIPA and, also, for purposes of comparison, that of palmitoylethanolamide (PEA), a structurally related compound commonly determined in animal tissues. The results obtained show that SIPA levels in mouse brain are 8-10-fold higher than those of PEA. Moreover, SIPA was found in human neuroblastoma cell (SHSY-5Y) extracts, at significantly higher levels following exposure of the cells to the mitochondrial inhibitor rotenone. All this evidence not only shows surprisingly that SIPA may be found naturally in mammalian biological extracts despite the unusual functional group (i.e. isopropylamide) implicated, but also raises many important questions concerning its biological origin.

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.

Influence of the degree of unsaturation of the acyl side chain upon the interaction of analogues of 1-arachidonoylglycerol with monoacylglycerol lipase and fatty acid amide hydrolase

Little is known as to the structural requirements of the acyl side chain for interaction of acylglycerols with monoacylglycerol lipase (MAGL), the enzyme chiefly responsible for the metabolism of the endocannabinoid 2-arachidonoylglycerol (2-AG) in the brain. In the present study, a series of twelve analogues of 1-AG (the more stable regioisomer of 2-AG) were investigated with respect to their ability to inhibit the metabolism of 2-oleoylglycerol by cytosolic and membrane-bound MAGL. In addition, the ability of the compounds to inhibit the hydrolysis of anandamide by fatty acid amide hydrolase (FAAH) was investigated. For cytosolic MAGL, compounds with 20 carbon atoms in the acyl chain and 2-5 unsaturated bonds inhibited the hydrolysis of 2-oleoylglycerol with similar potencies (IC50 values in the range 5.1-8.2 microM), whereas the two compounds with a single unsaturated bond were less potent (IC50 values 19 and 21 microM). The fully saturated analogue 1-monoarachidin did not inhibit the enzyme, whereas the lower side chain analogues 1-monopalmitin and 1-monomyristin inhibited the enzyme with IC50 values of 12 and 32 microM, respectively. The 22-carbon chain analogue of 1-AG was also potent (IC50 value 4.5 microM). Introduction of an alpha-methyl group for the C20:4, C20:3, and C22:4 compounds did not affect potency in a consistent manner. For the FAAH and the membrane-bound MAGL, there was no obvious relationship between the degree of unsaturation of the acyl side chain and the ability to inhibit the enzymes. It is concluded that increasing the number of unsaturated bonds on the acyl side chain of 1-AG from 1 to 5 has little effect on the affinity of acylglycerols for cytosolic MAGL.

Characterization of the sulfhydryl-sensitive site in the enzyme responsible for hydrolysis of 2-arachidonoyl-glycerol in rat cerebellar membranes

We have previously reported that the endocannabinoid, 2-arachidonoyl-glycerol (2-AG), is hydrolyzed in rat cerebellar membranes by monoglyceride lipase (MGL)-like enzymatic activity. The present study shows that, like MGL, 2-AG-degrading enzymatic activity is sensitive to inhibition by sulfhydryl-specific reagents. Inhibition studies of this enzymatic activity by N-ethylmaleimide analogs revealed that analogs with bulky hydrophobic N-substitution were more potent inhibitors than hydrophilic or less bulky agents. Interestingly, the substrate analog N-arachidonylmaleimide was found to be the most potent inhibitor. A comparison model of MGL was constructed to get a view on the cysteine residues located near the binding site. These findings support our previous conclusion that the 2-AG-degrading enzymatic activity in rat cerebellar membranes corresponds to MGL or MGL-like enzyme and should facilitate further efforts to develop potent and more selective MGL inhibitors.

Induction of cyclooxygenase-2 by anandamide in cerebral microvascular endothelium

Anandamide (AEA), an endogenous cannabinoid receptor agonist, is a potent vasodilator in the cerebral microcirculation. AEA is converted to arachidonic acid (AA) by fatty acid amidohydrolase (FAAH), and the conversion of AA to prostaglandins has been proposed as a potential mechanism for the vasodilation. Although AEA stimulated prostaglandin production by mouse cerebral microvascular endothelial cells, no [(3)H]prostaglandins were produced when these cells were incubated with [3H]AEA. Incubation with R(+)-methanandamide (MAEA), a stable analogue of AEA that is not a substrate for FAAH, produced a similar increase in PGE2 production as AEA. The PGE2 production induced by either AEA or MAEA was completely inhibited by NS-398, a selective cyclooxygenase (COX)-2 inhibitor, suggesting that COX-2 was induced. AEA and MAEA increased the expression of COX-2 protein in a time-dependent manner. This increase occurred as early as 1 h and reached maximum at 2 h. Induction of COX-2 protein by AEA was partially inhibited by AM-251, a selective cannabinoid receptor-1 antagonist. Furthermore, AEA increased COX-2 promoter activity approximately twofold above baseline in a fragment ranging from -1432 to +59, the full-length of the COX-2 promoter, and the increase in COX-2 promoter activity produced by AEA was partially inhibited by AM-251. These results indicate that AEA increased COX-2 expression at the transcriptional level through, at least in part, a cannabinoid receptor-1-mediated mechanism in cerebral microvascular endothelium.

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

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

Heterocyclic sulfoxide and sulfone inhibitors of fatty acid amide hydrolase

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

Structural requirements for cannabinoid receptor probes

The discovery and cloning of CB1 and CB2, the two known G(i/o) protein-coupled cannabinoid receptors, as well as the isolation and characterization of two families of endogenous cannabinergic ligands represented by arachidonoylethanolamide (anandamide) and 2-arachidonoylglycerol (2-AG), have opened new horizons in this newly discovered field of biology. Furthermore, a considerable number of cannabinoid analogs belonging to structurally diverse classes of compounds have been synthesized and tested, thus providing substantial information on the structural requirements for cannabinoid receptor recognition and activation. Experiments with site-directed mutated receptors and computer modeling studies have suggested that these diverse classes of ligands may interact with the receptors through different binding motifs. The information about the exact binding site may be obtained with the help of suitably designed molecular probes. These ligands either interact with the receptors in a reversible fashion (reversible probes) or alternatively attach at or near the receptor active site with the formation of covalent bonds (irreversible probes). This review focuses on structural requirements of cannabinoid receptor ligands and highlights their pharmacological and therapeutic potential.

Inverse agonism and neutral antagonism at cannabinoid CB1 receptors

There are at least two types of cannabinoid receptor, CB1 and CB2, both G protein coupled. CB1 receptors are expressed predominantly at nerve terminals and mediate inhibition of transmitter release whereas CB2 receptors are found mainly on immune cells, one of their roles being to modulate cytokine release. Endogenous cannabinoid receptor agonists also exist and these "endocannabinoids" together with their receptors constitute the "endocannabinoid system". These discoveries were followed by the development of a number of CB1- and CB2-selective antagonists that in some CB1 or CB2 receptor-containing systems also produce "inverse cannabimimetic effects", effects opposite in direction from those produced by cannabinoid receptor agonists. This review focuses on the CB1-selective antagonists, SR141716A, AM251, AM281 and LY320135, and discusses possible mechanisms by which these ligands produce their inverse effects: (1) competitive surmountable antagonism at CB1 receptors of endogenously released endocannabinoids, (2) inverse agonism resulting from negative, possibly allosteric, modulation of the constitutive activity of CB1 receptors in which CB1 receptors are shifted from a constitutively active "on" state to one or more constitutively inactive "off" states and (3) CB1 receptor-independent mechanisms, for example antagonism of endogenously released adenosine at A1 receptors. Recently developed neutral competitive CB1 receptor antagonists, which are expected to produce inverse effects through antagonism of endogenously released endocannabinoids but not by modulating CB1 receptor constitutive activity, are also discussed. So too are possible clinical consequences of the production of inverse cannabimimetic effects, there being convincing evidence that released endocannabinoids can have "autoprotective" roles.

The anandamide membrane transporter. Structure–activity relationships of anandamide and oleoylethanolamine analogs with phenyl rings in the polar head group region

A new series of anandamide and N-oleoylethanolamine analogs, most of which with aromatic moieties in the head group region, has been synthesized and evaluated as inhibitors of anandamide uptake. Some of them efficaciously inhibit the uptake process with K(i) values in the low micromolar range (2.4-21.2microM). Strict structural requisites are needed to observe a significant inhibition and in no case inhibition of fatty acid amidohydrolase overlaps with inhibition of anandamide uptake.

Mandelamide hydrolase from Pseudomonas putida: characterization of a new member of the amidase signature family

A recently discovered enzyme in the mandelate pathway of Pseudomonas putida, mandelamide hydrolase (MAH), catalyzes the hydrolysis of mandelamide to mandelic acid and ammonia. Sequence analysis suggests that MAH is a member of the amidase signature family, which is widespread in nature and contains a novel Ser-cis-Ser-Lys catalytic triad. Here we report the expression in Escherichia coli, purification, and characterization of both wild-type and His(6)-tagged MAH. The recombinant enzyme was stable, exhibited a pH optimum of 7.8, and was able to hydrolyze both enantiomers of mandelamide with little enantiospecificity. The His-tagged variant showed no significant change in kinetic constants. Phenylacetamide was found to be the best substrate, with changes in chain length or replacement of the phenyl group producing greatly decreased values of k(cat)/K(m). As with another member of this family, fatty acid amide hydrolase, MAH has the uncommon ability to hydrolyze esters and amides at similar rates. MAH is even more unusual in that it will only hydrolyze esters and amides with little steric bulk. Ethyl and larger esters and N-ethyl and larger amides are not substrates, suggesting that the MAH active site is very sterically hindered. Mutation of each residue in the putative catalytic triad to alanine resulted in total loss of activity for S204A and K100A, while S180A exhibited a 1500-fold decrease in k(cat) and significant increases in K(m) values. Overall, the MAH data are similar to those of fatty acid amide hydrolase and support the suggestion that there are two distinct subgroups within the amidase signature family.

RNA interference suggests a primary role for monoacylglycerol lipase in the degradation of the endocannabinoid 2-arachidonoylglycerol

The endogenous cannabinoid 2-arachidonoylglycerol (2-AG) is produced by neurons and other cells in a stimulus-dependent manner and undergoes rapid biological inactivation through transport into cells and catalytic hydrolysis. The enzymatic pathways responsible for 2-AG degradation are only partially understood. We have shown previously that overexpression of monoacylglycerol lipase (MGL), a cytosolic serine hydrolase that cleaves 1- and 2-monoacylglycerols to fatty acid and glycerol, reduces stimulus-dependent 2-AG accumulation in primary cultures of rat brain neurons. We report here that RNA interference-mediated silencing of MGL expression greatly enhances 2-AG accumulation in HeLa cells. After stimulation with the calcium ionophore ionomycin, 2-AG levels in MGL-silenced cells were comparable with those found in cells in which 2-AG degradation had been blocked using methyl arachidonyl fluorophosphonate, a nonselective inhibitor of 2-AG hydrolysis. The results indicate that MGL plays an important role in the degradation of endogenous 2-AG in intact HeLa cells. Furthermore, immunodepletion experiments show that MGL accounts for at least 50% of the total 2-AG-hydrolyzing activity in soluble fractions of rat brain, suggesting that this enzyme also contributes to 2-AG deactivation in the central nervous system.

Anandamide transport is independent of fatty-acid amide hydrolase activity and is blocked by the hydrolysis-resistant inhibitor AM1172

The endogenous cannabinoid anandamide is removed from the synaptic space by a high-affinity transport system present in neurons and astrocytes, which is inhibited by N-(4-hydroxyphenyl)-arachidonamide (AM404). After internalization, anandamide is hydrolyzed by fatty-acid amide hydrolase (FAAH), an intracellular membrane-bound enzyme that also cleaves AM404. Based on kinetic evidence, it has recently been suggested that anandamide internalization may be mediated by passive diffusion driven by FAAH activity. To test this possibility, in the present study, we have investigated anandamide internalization in wild-type and FAAH-deficient (FAAH(-/-)) mice. Cortical neurons from either mouse strain internalized [(3)H]anandamide through a similar mechanism, i.e., via a rapid temperature-sensitive and saturable process, which was blocked by AM404. Moreover, systemic administration of AM404 to either wild-type or FAAH(-/-) mice enhanced the hypothermic effects of exogenous anandamide, a response that was prevented by the CB(1) cannabinoid antagonist rimonabant (SR141716A). The results indicate that anandamide internalization in mouse brain neurons is independent of FAAH activity. In further support of this conclusion, the compound N-(5Z, 8Z, 11Z, 14Z eicosatetraenyl)-4-hydroxybenzamide (AM1172) blocked [(3)H]anandamide internalization in rodent cortical neurons and human astrocytoma cells without acting as a FAAH substrate or inhibitor. AM1172 may serve as a prototype for novel anandamide transport inhibitors with increased metabolic stability.