Fatty acid amide hydrolase: a gate-keeper of the endocannabinoid system

Need for Methods to Investigate Endocannabinoid Signaling

Endocannabinoids (eCBs) are endogenous lipids able to bind to cannabinoid receptors, the primary molecular targets of the cannabis (Cannabis sativa) active principle Δ⁹-tetrahydrocannabinol. During the last 20 years, several N-acylethanolamines and acylesters have been shown to act as eCBs, and a complex array of receptors, metabolic enzymes, and transporters (that altogether form the so-called "eCB system") has been shown to finely tune their manifold biological activities. It appears now urgent to develop methods and protocols that allow to assay in a specific and quantitative manner the distinct components of the eCB system and that can properly localize them within the cell. A brief overview of eCBs and of the proteins that bind, transport, and metabolize these lipids is presented here, in orderto put in a better perspective, the relevance of methodologies that help to disclose molecular details of eCB signaling in health and disease. Proper methodological approaches form also the basis for a more rationale and effective drug design and therapeutic strategy to combat human disorders.

Radiometric Assay of FAAH Activity

Fatty acid amide hydrolase (FAAH) is an intracellular enzyme responsible for the hydrolysis of endogenous anandamide (AEA), a reaction that terminates the biological effects of this lipid mediator. The final products of AEA cleavage are arachidonic acid and ethanolamine. In the method described herein, FAAH activity is measured through the use of the radioactive substrate [¹⁴C-ethanolamine]-AEA and subsequent quantification of the reaction product [¹⁴C]-ethanolamine.

A NIR fluorescent probe for fatty acid amide hydrolase bioimaging and its application in development of inhibitors

Fatty acid amide hydrolase (FAAH) is primarily responsible for the inactivation of fatty acid ethanolamide (FAE) and is involved in a variety of biological functions related to diseases of the nervous system. Herein, we developed a highly selective and sensitive FAAH-activated near-infrared fluorescent probe named DAND and achieved the real-time detection and imaging of FAAH activity in complex biosystems. Moreover, a visual high-throughput screening method was established using DAND, piperine was identified as a novel inhibitor of FAAH. Based on the interaction of piperine with FAAH, a more potent FAAH inhibitor (11f) was designed and synthesized which possessed an IC₅₀ value of 0.65 μM. Furthermore, 11f could attenuate the liposaccharide (LPS)-induced activation of BV2 cells, exhibiting an excellent anti-inflammatory activity. These results indicated that DAND could be used as a promising molecular tool for exploring FAAH activity and for rapidly screening potential FAAH inhibitors. In addition, piperine and its derivatives could serve as potential candidate drugs for the treatment of neurodegenerative diseases in the future.

In Silico and In Vitro Analysis of Major Cannabis-Derived Compounds as Fatty Acid Amide Hydrolase Inhibitors

Accumulated evidence suggests that enhancing the endocannabinoid (eCB) tone, in particular of anandamide (N-arachidonoylethanolamine, AEA), has therapeutic potential in many human diseases. Fatty acid amide hydrolase (FAAH) is a membrane-bound enzyme principally responsible for the degradation of AEA, and thus it represents a relevant target to increase signaling thereof. In recent years, different synthetic and natural compounds have been developed and tested on rat FAAH, but little is known of their effect on the human enzyme. Here, we sought to investigate six major cannabis-derived compounds to compare their action on rat and human FAAHs. To this aim, we combined an in silico analysis of their binding mode and affinity, with in vitro assays of their effect on enzyme activity. This integrated approach allowed to disclose differences in efficacy towards rat and human FAAHs, and to highlight the role of key residues involved in the inhibition of both enzymes. This study suggests that the therapeutic efficacy of compounds targeted towards FAAH should be always tested in vitro on both rat and human enzymes.

The Impact of Controlled Ovarian Stimulation Hormones on the Metabolic State and Endocannabinoid System of Human Cumulus Cells

Different Follicle Stimulating Hormone (FSH) formulation and Luteinizing Hormone (LH) are used in Assisted Reproductive Technology (ART) to induce follicles development and oocytes maturation, but it is still under debate which protocol is to be preferred. In the present study, the different effects on cumulus cells (CCs) of three controlled ovarian stimulation (COS) protocols, based on urinary FSH, recombinant FSH, or human Menopausal Gonadotropin (hMG) administration, were assessed. CCs were obtained from 42 normal-responders women undergoing COS, randomly divided into three groups according to the used gonadotropin formulation. Differences were found in the expression of genes belonging to the endocannabinoid system (the receptors CNR1, CNR2 and TRPV1, and the enzymes involved in the metabolisms of anandamide, NAPE-PLD and FAAH, and 2-acylglycerol, DAGL and MAGL); consistently, changes in lipid (PPARα, and FASN) and carbohydrate (GLUT1 and GLUT9) metabolisms, in CCs’ macromolecules composition (highlighted by Fourier Transform Infrared Microspectroscopy, FTIRM), and in the number of retrieved oocytes were found. For the first time, statistically significant evidence on the differences related to each COS protocol on the endocannabinoid system, metabolism and macromolecular composition of CCs was found, representing a proof of concept to be further confirmed in a larger cohort of patients.

Advances in the discovery of fatty acid amide hydrolase inhibitors: what does the future hold?

INTRODUCTION

Fatty acid amide hydrolase (FAAH) is a membrane-bound enzyme, that inactivates endogenous signaling lipids of the fatty acid amide family, including the endocannabinoid anandamide (N-arachidonoylethanolamine, AEA). The latter compound has been shown to regulate a number of important pathophysiological conditions in humans, like feeding, obesity, immune response, reproductive events, motor coordination, and neurological disorders. Hence, direct manipulation of the endocannabinoid tone is thought to have therapeutic potential. A new opportunity to develop effective drugs may arise from multi-target directed ligand (MTDL) strategies, which brings the concept that a single compound can recognize different targets involved in the cascade of pathophysiological events.

AREAS COVERED

This review reports the latest advances in the development of new single targeted and dual-targeted FAAH inhibitors over the past 5 years.

EXPERT OPINION

In recent years, several FAAH inhibitors have been synthesized and investigated, yet to date none of them has reached the market as a systemic drug. Due to the diligence of inherent redundancy and robustness in many biological networks and pathways, multitarget inhibitors present a new prospect in the pharmaceutical industry for treatment of complex diseases.

The endocrine disruptor DEHP and the ECS: analysis of a possible crosstalk

Studies of the last decade associated the environmental contamination by di-(2-ethylhexyl)-phthalate (DEHP) with obesity and endocrine malfunction. DEHP was found to interact with several receptors - among them are receptors of the endocannabinoid system (ECS) with high expression levels in adipose tissue. Furthermore, the correlation for BMI and body fat to the serum endocannabinoid level raises the question if the obesogenic and endocrine-disrupting DEHP effects are mediated via the ECS. We therefore characterized the ECS in a human cell model of adipogenesis using the SGBS preadipocytes to subsequently investigate if DEHP exposure affects the intrinsic ECS. The receptors of the ECS and the endocannabinoid-metabolizing enzymes were upregulated during normal adipogenesis, accompanied by an increasing secretion of the adipokines adiponectin and leptin. DEHP affected the secretion of both adipokines but not the ECS, suggesting DEHP to alter the endocrine function of adipocytes without the involvement of the intrinsic ECS.

Expression and Function of the Endocannabinoid Modulating Enzymes Fatty Acid Amide Hydrolase and N-Acylphosphatidylethanolamine-Specific Phospholipase D in Endometrial Carcinoma

Background: The concentrations of three N-acylethanolamines (NAEs), anandamide (AEA), N-oleoylethanolamide (OEA), and N-palmitylethanolamide (PEA) are increased in the endometria of women with endometrial cancer (EC). It is widely accepted that plasma levels of these three NAEs are regulated by the actions of the rate-limiting enzymes N-acylphoshatidylethanolamine-specific phospholipase D (NAPE-PLD) and fatty acid amide hydrolase (FAAH), which are synthesizing and degradative, respectively. The expression and activity of these enzymes have not previously been studied in EC.

Methods: FAAH activity in peripheral blood lymphocytes, and transcript and protein expression for FAAH and NAPE-PLD in EC tissues were measured using enzyme, quantitative RT-PCR, and histomorphometry (of immunoreactive tissue sections), respectively. Samples were from 6 post-menopausal women with atrophic endometria (controls) and 34 women with histologically diagnosed EC. Concentrations of the three NAEs also measured in plasma and tissues were correlated with lymphocytic FAAH activity and the NAPE-PLD and FAAH transcript and protein levels.

Results: Peripheral lymphocyte FAAH activity was unaffected in women with EC compared to controls. The FAAH transcript expression level was significantly (p < 0.0001) 75% lower in EC whilst NAPE-PLD levels were not significantly (p = 0.798) increased. In line with the transcript data, a significant (p < 0.0001) tumor type-dependent 70–90% decrease in FAAH protein and significant 4- to 14-fold increase in NAPE-PLD protein (p < 0.0001) was observed in the malignant tissue with more advanced disease having lower FAAH and higher NAPE-PLD expression than less advanced disease. Correlation analyses also confirmed that tissue NAE concentrations were inversely related to FAAH expression and directly correlated to NAPE-PLD expression and the NAPE-PLD/FAAH ratio.

Conclusion: These data support our previous observation of tissue levels of AEA, OEA, and PEA and a role for NAE metabolism in the pathogenesis of EC.

The Potential of Cannabinoid-Based Treatments in Tourette Syndrome

Novel pharmacological treatments are needed for Tourette syndrome. Our goal was to examine the current evidence base and biological rationale for the use of cannabis-derived medications or medications that act on the cannabinoid system in Tourette syndrome. We conducted a comprehensive literature search of PubMed for randomized controlled trials or clinical trials of cannabis-derived medications in Tourette syndrome. Data regarding the population, intervention, safety profile, and outcomes for each trial were extracted and reported and the evidence supporting use of individual cannabis-derived medications was critiqued. There is a strong biological rationale regarding how cannabis-derived medications could affect tic severity. Anecdotal case reports and series have noted that many patients report that their tics improve after using cannabis. However, only two small randomized, placebo-controlled trials of Δ⁹-tetrahydrocannabinol have been published; these suggested possible benefits of cannabis-derived agents for the treatment of tics. Trials examining other agents active on the cannabinoid system for tic disorders are currently ongoing. Cannabinoid-based treatments are a promising avenue of new research for medications that may help the Tourette syndrome population. However, given the limited research available, the overall efficacy and safety of cannabinoid-based treatments is largely unknown. Further trials are needed to examine dosing, active ingredients, and optimal mode of administration of cannabis-derived compounds, assuming initial trials suggest efficacy. Clinical use for refractory patients should at the very least be restricted to adult populations, given the uncertain efficacy and risk of developmental adverse effects that cannabinoids may have in children. Even in adult populations, cannabis-derived medications are associated with significant issues such as the effects they have on driving safety and the fact that they cause positive urine drug screens that can affect employment.

Cannabinoid Receptor 2 Agonist Prevents Local and Systemic Inflammatory Bone Destruction in Rheumatoid Arthritis

Cannabinoid receptor 2 (CB2) has been implicated as an important clinical regulator of inflammation and malignant osteolysis. Here, we observed that CB2 expression was markedly higher in the collagen-induced arthritis (CIA) mice synovium and bone tissues than in the noninflamed synovium and bone tissues. The CB2 selective agonist (JWH133) but not antagonist (SR144528) suppressed CIA in mice without toxic effects, as demonstrated by the decreased synovial hyperplasia, inflammatory responses, cartilage damage, and periarticular and systemic bone destruction. JWH133 treatment decreased the infiltration of pro-inflammatory M1-like macrophages and repolarized macrophages from the M1 to M2 phenotype. Similarly, activation of CB2 increased the expression of anti-inflammatory cytokine interleukin (IL)-10 and reduced the expression of pro-inflammatory cytokines, including tumor necrosis factor-α (TNF-α), IL-1β, and IL-6. In addition, JWH133 treatment attenuated osteoclast formation and osteoclastic bone resorption, and reduced the expression of receptor activators of the nuclear factor-κB (NF-κB) ligand (RANKL), matrix metallopeptidase-9 (MMP-9), tartrate-resistant acid phosphatase (TRAP), cathepsin K (CTSK), and nuclear factor of activated T-cells 1 (NFAT-1) in CIA mice and osteoclast precursors, which were obviously blocked by pretreatment with SR144528. Mechanistically, JWH133 inhibited RANKL-induced NF-κB activation in the osteoclast precursors. We found that JWH133 ameliorates pathologic bone destruction in CIA mice via the inhibition of osteoclastogenesis and modulation of inflammatory responses, thereby highlighting its potential as a treatment for human rheumatoid arthritis. © 2018 American Society for Bone and Mineral Research.

Crosstalk Between Nitric Oxide and Endocannabinoid Signaling Pathways in Normal and Pathological Placentation

Endocannabinoids are a group of endogenous lipid mediators that act as ligands of cannabinoid and vanilloid receptors, activating multiple signal transduction pathways. Together with enzymes responsible for their synthesis and degradation, these compounds constitute the endocannabinoid system (ECS), which is involved in different physiological processes in reproduction. The placenta, which is essential for the success of gestation and optimal fetal growth, undergoes constant tissue remodeling. ECS members are expressed in trophoblast cells, and current evidence suggests that this system is involved in placental development, apoptosis, and syncytialization. Impairment of endocannabinoid signaling has been associated with several pathological conditions such as intrauterine growth restriction and preeclampsia. Both clinical entities are characterized by dysregulation on vascular perfusion where nitrergic system performs a pivotal role. Nitric oxide (NO) is a potent local vasodepressor that exerts a critical role in the regulation of hemodynamic flow, contributing to the maintenance of low vascular resistance in the feto-placental circulation. NO production could be affected by different factors and growing evidence suggests that the endocannabinoid mediators may regulate nitrergic signaling. Herein, we review emerging knowledge supporting ECS-mediated regulation of NO production in normal placentation. Finally, we discuss how alterations in these systems could affect homoeostasis and contribute to the occurrence of placental-mediated pregnancy complications. Given the impact on women and perinatal heath, we will focus on current knowledge regarding the effects of ECS on nitrergic system in normal and pathological placentation.

Anandamide Revisited: How Cholesterol and Ceramides Control Receptor-Dependent and Receptor-Independent Signal Transmission Pathways of a Lipid Neurotransmitter

Anandamide is a lipid neurotransmitter derived from arachidonic acid, a polyunsaturated fatty acid. The chemical differences between anandamide and arachidonic acid result in a slightly enhanced solubility in water and absence of an ionisable group for the neurotransmitter compared with the fatty acid. In this review, we first analyze the conformational flexibility of anandamide in aqueous and membrane phases. We next study the interaction of the neurotransmitter with membrane lipids and discuss the molecular basis of the unexpected selectivity of anandamide for cholesterol and ceramide from among other membrane lipids. We show that cholesterol behaves as a binding partner for anandamide, and that following an initial interaction mediated by the establishment of a hydrogen bond, anandamide is attracted towards the membrane interior, where it forms a molecular complex with cholesterol after a functional conformation adaptation to the apolar membrane milieu. The complex is then directed to the anandamide cannabinoid receptor (CB1) which displays a high affinity binding pocket for anandamide. We propose that cholesterol may regulate the entry and exit of anandamide in and out of CB1 by interacting with low affinity cholesterol recognition sites (CARC and CRAC) located in transmembrane helices. The mirror topology of cholesterol binding sites in the seventh transmembrane domain is consistent with the delivery, extraction and flip-flop of anandamide through a coordinated cholesterol-dependent mechanism. The binding of anandamide to ceramide illustrates another key function of membrane lipids which may occur independently of protein receptors. Interestingly, ceramide forms a tight complex with anandamide which blocks the degradation pathway of both lipids and could be exploited for anti-cancer therapies.

The Endogenous Cannabinoid System: A Budding Source of Targets for Treating Inflammatory and Neuropathic Pain

A great need exists for the development of new medications to treat pain resulting from various disease states and types of injury. Given that the endogenous cannabinoid (that is, endocannabinoid) system modulates neuronal and immune cell function, both of which play key roles in pain, therapeutics targeting this system hold promise as novel analgesics. Potential therapeutic targets include the cannabinoid receptors, type 1 and 2, as well as biosynthetic and catabolic enzymes of the endocannabinoids N-arachidonoylethanolamine and 2-arachidonoylglycerol. Notably, cannabinoid receptor agonists as well as inhibitors of endocannabinoid-regulating enzymes fatty acid amide hydrolase and monoacylglycerol lipase produce reliable antinociceptive effects, and offer opioid-sparing antinociceptive effects in myriad preclinical inflammatory and neuropathic pain models. Emerging clinical studies show that 'medicinal' cannabis or cannabinoid-based medications relieve pain in human diseases such as cancer, multiple sclerosis, and fibromyalgia. However, clinical data have yet to demonstrate the analgesic efficacy of inhibitors of endocannabinoid-regulating enzymes. Likewise, the question of whether pharmacotherapies aimed at the endocannabinoid system promote opioid-sparing effects in the treatment of pain reflects an important area of research. Here we examine the preclinical and clinical evidence of various endocannabinoid system targets as potential therapeutic strategies for inflammatory and neuropathic pain conditions.

1-Heteroarylpropan-2-ones as inhibitors of fatty acid amide hydrolase: Studies on structure-activity relationships and metabolic stability

The serine hydrolase fatty acid amide hydrolase (FAAH) catalyzes the degradation of the endocannabinoid anandamide, which possesses analgesic and anti-inflammatory effects. A new series of 1-heteroarylpropan-2-ones was synthesized and evaluated for FAAH inhibition. Structure-activity relationship studies revealed that 1H-benzotriazol-1-yl, 1H-7-azabenzotriazol-1-yl, 1H-tetrazol-1-yl and 2H-tetrazol-2-yl substituents have the highest impact on inhibitory potency. Furthermore, attempts were made to increase the limited metabolic stability of the ketone functionality of these compounds towards metabolic reduction by introduction of shielding alkyl substituents in proximity of this serine reactive group.

The endocannabinoid system in the baboon (Papio spp.) as a complex framework for developmental pharmacology

INTRODUCTION

The consumption of marijuana (exogenous cannabinoid) almost doubled in adults during last decade. Consumption of exogenous cannabinoids interferes with the endogenous cannabinoid (or "endocannabinoid" (eCB)) system (ECS), which comprises N-arachidonylethanolamide (anandamide, AEA), 2-arachidonoyl glycerol (2-AG), endocannabinoid receptors (cannabinoid receptors 1 and 2 (CB1R and CB2R), encoded by CNR1 and CNR2, respectively), and synthesizing/degrading enzymes (FAAH, fatty-acid amide hydrolase; MAGL, monoacylglycerol lipase; DAGL-α, diacylglycerol lipase-alpha). Reports regarding the toxic and therapeutic effects of pharmacological compounds targeting the ECS are sometimes contradictory. This may be caused by the fact that structure of the eCBs varies in the species studied.

OBJECTIVES

First: to clone and characterize the cDNAs of selected members of ECS in a non-human primate (baboon, Papio spp.), and second: to compare those cDNA sequences to known human structural variants (single nucleotide polymorphisms and haplotypes).

MATERIALS AND METHODS

Polymerase chain reaction-amplified gene products from baboon tissues were transformed into Escherichia coli. Amplicon-positive clones were sequenced, and the obtained sequences were conceptually translated into amino-acid sequences using the genetic code.

RESULTS

Among the ECS members, CNR1 was the best conserved gene between humans and baboons. The phenotypes associated with mutations in the untranslated regions of this gene in humans have not been described in baboons. One difference in the structure of CNR2 between humans and baboons was detected in the region with the only known clinically relevant polymorphism in a human receptor. All of the differences in the amino-acid structure of DAGL-α between humans and baboons were located in the hydroxylase domain, close to phosphorylation sites. None of the differences in the amino-acid structure of MAGL observed between baboons and humans were located in the area critical for enzyme function.

CONCLUSION

The evaluation of the data, obtained in non-human primate model of cannabis-related developmental exposure should take into consideration possible evolutionary-determined species-specific differences in the CB1R expression, CB2R transduction pathway, and FAAH and DAGLα substrate-enzyme interactions.

1-(5-Carboxyindazol-1-yl)propan-2-ones as dual inhibitors of cytosolic phospholipase A2α and fatty acid amide hydrolase: bioisosteric replacement of the carboxylic acid moiety

Indazole-5-carboxylic acids with 3-aryloxy-2-oxopropyl residues in position 1 were previously reported to be potent dual inhibitors of cytosolic phospholipase A₂α (cPLA₂α) and fatty acid amide hydrolase (FAAH). In continuation of our structure-activity studies on cPLA₂α and FAAH inhibitors, a number of derivatives of these substances characterized by bioisosteric replacement of the carboxylic acid functionality by inverse amides, sulfonylamides, carbamates and ureas were prepared. The biological evaluation of the obtained compounds showed that the carboxylic acid functionality of the lead compounds is of special importance for a pronounced inhibition of cPLA₂α and FAAH.

The endocannabinoid system in the human granulosa cell line KGN

Ovarian steroidogenesis is embedded in a sensitive network of regulatory mechanisms crucial for human fertility. The endocannabinoid system (ECS) represents an intrinsic modulating system involved in the regulation of endocrine functions. In the present study we characterized the ECS in the human granulosa cell line KGN and its impact on gonadotropin sensitivity and steroid hormone synthesis under basal and FSH-stimulated conditions. Expression studies were performed and estradiol was measured. CB1, CB2, DAGL, FAAH, GPR55, MAGL, NAPE-PLD and TRPV1 were expressed without FSH-dependent effects. Treatment with selective cannabinoid receptor agonists reduced basal but not FSH-stimulated estradiol and CYP19. Progesterone was not altered by ECS manipulation. CB1 agonist changed the expression of miRNAs associated with granulosa cell function, e.g. miR-23a, miR-24, miR-181a and miR-320a. Present data indicate a modulating role of the intrinsic ovarian ECS in the regulation of estradiol synthesis.

Assay of FAAH Activity

Fatty acid amide hydrolase (FAAH) is an intracellular enzyme responsible for the hydrolysis of endogenous anandamide (AEA), a reaction that terminates the biological effects of this lipid mediator. The final products of this reaction are arachidonic acid and ethanolamine. In the method described herein, FAAH activity is measured through the use of a radioactive substrate by quantification of reaction products, that is, [(14)C]-ethanolamine from [(14)C-ethanolamine]-AEA.

Need for Methods to Investigate Endocannabinoid Signaling

Endocannabinoids (eCBs) are endogenous lipids able to activate cannabinoid receptors, the primary molecular targets of the cannabis (Cannabis sativa) active principle Δ(9)-tetrahydrocannabinol. During the last 20 years, several N-acylethanolamines and acylesters have been shown to act as eCBs, and a complex array of receptors, metabolic enzymes, and transporters (that altogether form the so-called eCB system) has been shown to finely tune their manifold biological activities. It appears now urgent to develop methods and protocols that allow to assay in a specific and quantitative manner the distinct components of the eCB system, and that can properly localize them within the cell. A brief overview of eCBs and of the proteins that bind, transport, and metabolize these lipids is presented here, in order to put in a better perspective the relevance of methodologies that help to disclose molecular details of eCB signaling in health and disease. Proper methodological approaches form also the basis for a more rationale and effective drug design and therapeutic strategy to combat human disorders.

Harnessing the pyrroloquinoxaline scaffold for FAAH and MAGL interaction: definition of the structural determinants for enzyme inhibition

The pharmacogenic pyrroloquinoxaline scaffold has been exploited for developing piperazine and 4-aminopiperidine carboxamides/carbamates as inhibitors of the endocannabinoids’ catabolic enzymes fatty acid amide hydrolase and monoacylglycerol lipase.

Structure-activity relationship studies on 1-heteroaryl-3-phenoxypropan-2-ones acting as inhibitors of cytosolic phospholipase A2α and fatty acid amide hydrolase: replacement of the activated ketone group by other serine traps

Cytosolic phospholipase A2α (cPLA2α) and fatty acid amide hydrolase (FAAH) are serine hydrolases. cPLA2α is involved in the generation of pro-inflammatory lipid mediators, FAAH terminates the anti-inflammatory effects of endocannabinoids. Therefore, inhibitors of these enzymes may represent new drug candidates for the treatment of inflammation. We have reported that certain 1-heteroarylpropan-2-ones are potent inhibitors of cPLA2α and FAAH. The serine reactive ketone group of these compounds, which is crucial for enzyme inhibition, is readily metabolized resulting in inactive alcohol derivatives. In order to obtain metabolically more stable inhibitors, we replaced this moiety by α-ketoheterocyle, cyanamide and nitrile serine traps. Investigations on activity and metabolic stability of these substances revealed that in all cases an increased metabolic stability was accompanied by a loss of inhibitory potency against cPLA2α and FAAH, respectively.

The endocannabinoid system and its therapeutic implications in rheumatoid arthritis

Since the discovery of the endogenous receptor for Δ(9)-tetrahydrocannabinol, a main constituent of marijuana, the endocannabinoid system (comprising cannabinoid receptors and their endogenous ligands, as well as the enzymes involved in their metabolic processes) has been implicated as having multiple regulatory functions in many central and peripheral conditions, including rheumatoid arthritis (RA). RA is an immune-mediated inflammatory disease that is associated with the involvement of many kinds of cells (such as fibroblastlike synoviocytes [FLSs], osteoclasts, T cells, B cells, and macrophages) and molecules (such as interleukin-1β, tumor necrosis factor-α, interleukin-6, matrix metalloproteinases [MMPs], and chemokines). Increasing evidence suggests that the endocannabinoid system, especially cannabinoid receptor 2 (CB2), has an important role in the pathophysiology of RA. Many members of the endocannabinoid system are reported to inhibit synovial inflammation, hyperplasia, and cartilage destruction in RA. In particular, specific activation of CB2 may relieve RA by inhibiting not only the production of autoantibodies, proinflammatory cytokines, and MMPs, but also bone erosion, immune response mediated by T cells, and the proliferation of FLSs. In this review, we will discuss the possible functions of the endocannabinoid system in the modulation of RA, which may be a potential target for treatment.

Regulation of cannabinoid receptor gene expression and endocannabinoid levels in lymphocyte subsets by interferon-β: a longitudinal study in multiple sclerosis patients

Evidence suggests the involvement of the cannabinoid system in the pathogenesis of multiple sclerosis (MS). We studied cannabinoid receptor (CB)1 and CB2 receptor gene expression in B, natural killer (NK) and T cells from MS patients before and after 1 year of interferon beta therapy, and compared these levels to those of healthy controls. We also measured the production of the endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG) and the gene expression of the endocannabinoid-degrading enzyme fatty acid amide hydrolase (FAAH) in these cells. Prior to interferon therapy, MS patients showed significantly elevated CB2 expression in B cells, but not in T or NK cells. These levels decreased gradually within 6 months to 1 year of interferon treatment. CB1 expression was elevated in all cell subsets, but only reached statistical significance in T cells; all levels decreased progressively over time. Before treatment, AEA but not 2-AG levels were significantly elevated in the three cell populations; after 1 year of treatment, all values decreased to control levels. The expression of FAAH was unchanged. The different expression of cannabinoid receptor genes and the increased level of AEA in lymphocytes point to a possible role of the cannabinoid system in MS immune response and its modulation by interferon.

Endocannabinoids, related compounds and their metabolic routes

Endocannabinoids are lipid mediators able to bind to and activate cannabinoid receptors, the primary molecular targets responsible for the pharmacological effects of the Δ⁹-tetrahydrocannabinol. These bioactive lipids belong mainly to two classes of compounds: N-acylethanolamines and acylesters, being N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG), respectively, their main representatives. During the last twenty years, an ever growing number of fatty acid derivatives (endocannabinoids and endocannabinoid-like compounds) have been discovered and their activities biological is the subject of intense investigations. Here, the most recent advances, from a therapeutic point of view, on endocannabinoids, related compounds, and their metabolic routes will be reviewed.

Physical activity and the endocannabinoid system: an overview

Recognized as a "disease modifier", physical activity (PA) is increasingly viewed as a more holistic, cost-saving method for prevention, treatment and management of human disease conditions. The traditional view that PA engages the monoaminergic and endorphinergic systems has been challenged by the discovery of the endocannabinoid system (ECS), composed of endogenous lipids, their target receptors, and metabolic enzymes. Indeed, direct and indirect evidence suggests that the ECS might mediate some of the PA-triggered effects throughout the body. Moreover, it is now emerging that PA itself is able to modulate ECS in different ways. Against this background, in the present review we shall discuss evidence of the cross-talk between PA and the ECS, ranging from brain to peripheral districts and highlighting how ECS must be tightly regulated during PA, in order to maintain its beneficial effects on cognition, mood, and nociception, while avoiding impaired energy metabolism, oxidative stress, and inflammatory processes.

Prior stimulation of the endocannabinoid system prevents methamphetamine-induced dopaminergic neurotoxicity in the striatum through activation of CB2 receptors

Methamphetamine toxicity is associated with cell death and loss of dopamine neuron terminals in the striatum similar to what is found in some neurodegenerative diseases. Conversely, the endocannabinoid system (ECS) has been suggested to be neuroprotective in the brain, and new pharmacological tools have been developed to increase their endogenous tone. In this study, we evaluated whether ECS stimulation could reduce the neurotoxicity of high doses of methamphetamine on the dopamine system. We found that methamphetamine alters the levels of the major endocannabinoids, anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) in the striatum, suggesting that the ECS participates in the brain responses to methamphetamine. Δ(9)-tetrahydrocannabinol (THC), a cannabis-derived agonist of both CB1 and CB2 cannabinoid receptors, or inhibitors of the main enzymes responsible for the degradation of AEA and 2-AG (URB597 and JZL184, respectively), blunted the decrease in striatal protein levels of tyrosine hydroxylase induced by methamphetamine. In addition, antagonists of CB2, but not of CB1, blocked the preventive effects of URB597 and JZL184, suggesting that only the former receptor subtype is engaged in neuroprotection exerted by ECS stimulation. Finally, we found that methamphetamine increases striatal levels of the cytokine tumor necrosis factor alpha, an effect that was blocked by ECS stimulation. Altogether, our results indicate that stimulation of ECS prior to the administration of an overdose of methamphetamine considerably reduces the neurotoxicity of the drug through CB2 receptor activation and highlight a protective function for the ECS against the toxicity induced by drugs and other external insults to the brain. This article is part of the Special Issue entitled 'CNS Stimulants'.

Endocannabinoids as biomarkers of human reproduction

BACKGROUND

Infertility is a condition of the reproductive system that affects ∼10-15% of couples attempting to conceive a baby. More than half of all cases of infertility are a result of female conditions, while the remaining cases can be attributed to male factors, or to a combination of both. The search for suitable biomarkers of pregnancy outcome is a challenging issue in human reproduction, aimed at identifying molecules with predictive significance of the reproductive potential of male and female gametes. Among the various candidates, endocannabinoids (eCBs), and in particular anandamide (AEA), represent potential biomarkers of human fertility disturbances. Any perturbation of the balance between synthesis and degradation of eCBs will result in local changes of their tone in human female and male reproductive tracts, which in turn regulates various pathophysiological processes, oocyte and sperm maturation included.

METHODS

PubMed and Web of Science databases were searched for papers using relevant keywords like 'biomarker', 'endocannabinoid', 'infertility', 'pregnancy' and 'reproduction'.

RESULTS

In this review, we discuss different studies on the measurements of AEA and related eCBs in human reproductive cells, tissues and fluids, where the local contribution of these bioactive lipids could be critical in ensuring normal sperm fertilizing ability and pregnancy.

CONCLUSION

Based on the available data, we suggest that the AEA tone has the potential to be exploited as a novel diagnostic biomarker of infertility, to be used in association with assays of conventional hormones (e.g. progesterone, β-chorionic gonadotrophin) and semen analysis. However further quantitative research of its predictive capacity is required.

ω-Heteroarylalkylcarbamates as inhibitors of fatty acid amide hydrolase (FAAH)

A series of heteroaryl-substituted alkylcarbamates have been synthesized and evaluated for their inhibitory potency against fatty acid amide hydrolase (FAAH).

Anandamide levels fluctuate in the bovine oviduct during the oestrous cycle

Mammalian oviduct acts as a reservoir for spermatozoa and provides an environment in which they may compete for the opportunity to fertilize the oocyte. Whilst in the oviduct spermatozoa undergo capacitation essential for fertilization. Sperm-oviduct interaction is essential for sperm capacitation and is a tightly regulated process influenced by the local microenvironment. Previously we reported that the endocannabinoid anandamide (AEA) regulates sperm release from epithelial oviductal cells by promoting sperm capacitation. The aims of this work were to measure the AEA content and to characterize the main AEA metabolic pathway in the bovine oviduct and determine how these change through the oestrous cycle. In this study, the levels of AEA and two other N-acylethanolamines, N-oleoylethanolamine and N-palmitoylethanolamine, were measured in bovine oviduct collected during different stages of oestrous cycle by ultra high performance liquid chromatography tandem mass spectrometry. Results indicated that intracellular oviductal epithelial levels of all three N-acylethanolamines fluctuate during oestrous cycle. Anandamide from oviductal fluid also varied during oestrous cycle, with the highest values detected during the periovulatory period. Endocannabinoid levels from ipsilateral oviduct to ovulation were higher than those detected in the contralateral one, suggesting that levels of oviductal AEA may be regulated by ovarian hormones. The expression and localization of N-acylethanolamines metabolizing enzymes in bovine oviduct were also determined by RT-PCR, Western blot, and immunohistochemistry but no change was found during the oestrous cycle. Furthermore, nanomolar levels of AEA were detected in follicular fluids, suggesting that during ovulation the mature follicle may contribute to oviductal AEA levels to create an endocannabinoid gradient conducive to the regulation of sperm function for successful fertilization.

In vitro and in vivo models of Huntington's disease show alterations in the endocannabinoid system

In this study, we analyzed the components of the endocannabinoid system (ECS) in R6/2 mice, a widely used model of Huntington's disease (HD). We measured the endogenous content of N-arachidonoylethanolamine and 2-arachidonoylglycerol and the activity of their biosynthetic enzymes (N-acyl-phosphatidylethanolamine-hydrolyzing phospholipase D and diacylglycerol lipase, respectively) and hydrolytic enzymes [fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase, respectively] and of their target receptors (type 1 cannabinoid receptor, type 2 cannabinoid receptor, and transient receptor potential vanilloid-1) in the brains of wild-type and R6/2 mice of different ages, as well as in the striatum and cortex of 12-week-old animals. In addition, we measured FAAH activity in lymphocytes of R6/2 mice. In the whole brains of 12-week-old R6/2 mice, we found reductions in N-acyl-phosphatidylethanolamine-hydrolyzing phospholipase D activity, diacylglycerol lipase activity and cannabinoid receptor binding, mostly associated with changes in the striatum but not in the cortex, as well as an increase in 2-arachidonoylglycerol content as compared with wild-type littermates, without any other change in ECS elements. Then, our analysis was extended to HD43 cells, an inducible cellular model of HD derived from rat ST14A cells. In both induced and noninduced conditions, we demonstrated a fully functional ECS. Overall, our data suggest that the ECS is differently affected in mouse and human HD, and that HD43 cells are suitable for high-throughput screening of FAAH-oriented drugs affecting HD progression.

Modulating the endocannabinoid system in human health and disease--successes and failures

The discovery of the endocannabinoid system, comprising the G-protein coupled cannabinoid 1 and 2 receptors (CB1/2), their endogenous lipid ligands or endocannabinoids, and synthetic and metabolizing enzymes, has triggered an avalanche of experimental studies implicating the endocannabinoid system in a growing number of physiological/pathological functions. These studies have also suggested that modulating the activity of the endocannabinoid system holds therapeutic promise for a broad range of diseases, including neurodegenerative, cardiovascular and inflammatory disorders; obesity/metabolic syndrome; cachexia; chemotherapy-induced nausea and vomiting; and tissue injury and pain, amongst others. However, clinical trials with globally acting CB1 antagonists in obesity/metabolic syndrome, and other studies with peripherally-restricted CB1/2 agonists and inhibitors of the endocannabinoid metabolizing enzyme in pain, have introduced unexpected complexities, suggesting that a better understanding of the pathophysiological role of the endocannabinoid system is required to devise clinically successful treatment strategies.

Modulation of neuropathic-pain-related behaviour by the spinal endocannabinoid/endovanilloid system

Neuropathic pain refers to chronic pain that results from injury to the nervous system. The mechanisms involved in neuropathic pain are complex and involve both peripheral and central phenomena. Although numerous pharmacological agents are available for the treatment of neuropathic pain, definitive drug therapy has remained elusive. Recent drug discovery efforts have identified an original neurobiological approach to the pathophysiology of neuropathic pain. The development of innovative pharmacological strategies has led to the identification of new promising pharmacological targets, including glutamate antagonists, microglia inhibitors and, interestingly, endogenous ligands of cannabinoids and the transient receptor potential vanilloid type 1 (TRPV1). Endocannabinoids (ECs), endovanilloids and the enzymes that regulate their metabolism represent promising pharmacological targets for the development of a successful pain treatment. This review is an update of the relationship between cannabinoid receptors (CB1) and TRPV1 channels and their possible implications for neuropathic pain. The data are focused on endogenous spinal mechanisms of pain control by anandamide, and the current and emerging pharmacotherapeutic approaches that benefit from the pharmacological modulation of spinal EC and/or endovanilloid systems under chronic pain conditions will be discussed.

Latest advances in the discovery of fatty acid amide hydrolase inhibitors

INTRODUCTION

Fatty acid amide hydrolase (FAAH) is the major catabolic enzyme of the endocannabinoid N-arachidonoylethanolamine (anandamide) that, with different degrees of efficiency, also hydrolyzes other endogenous fatty acid ethanolamides. FAAH is increasingly being considered a relevant therapeutic target, especially in models of inflammatory pain. The opportunity to selectively increase the endocannabinoid tone only in those tissues where such an enhancement can be beneficial might result in a therapeutic benefit with more limited side effects, compared to the use of direct agonists of anandamide-binding receptors. Thus the research for selective FAAH inhibitors has become a hot topic in current drug discovery.

AREAS COVERED

This review highlights the advances in the development of different compounds belonging to different chemical families that have been proposed as FAAH inhibitors. Several classes of inhibitors have been reported so far, and they may be classified into two major classes: reversible and irreversible compounds. These inhibitors are reviewed herein with an emphasis on their potency and selectivity.

EXPERT OPINION

In recent years, tremendous efforts have been made to develop the FAAH inhibitors, and consequently many novel chemical templates have been discovered. It is still a major challenge to identify the first inhibitor of FAAH suitable for clinical exploitation that satisfies the requirements of potency, selectivity versus proteins related to anandamide activity as well as other potential off-targets, reversibility versus irreversibility, and efficacy toward rat versus human FAAH.

Elevated anandamide and related N-acylethanolamine levels occur in the peripheral blood of women with ectopic pregnancy and are mirrored by changes in peripheral fatty acid amide hydrolase activity

BACKGROUND

Studies from knockout mice suggest that perturbations in oviductal endocannabinoid levels, endocannabinoid receptors, or endocannabinoid degrading enzyme [fatty acid amide hydrolase (FAAH)] expression result in infertility secondary to physical trapping of embryos. Similar observations have been made in ectopic pregnant women together with a suggestion that the endocannabinoid receptor gene polymorphism 1359G/A (rs1049353) is associated with ectopic pregnancy. These observations led to the hypothesis that ectopic pregnancy is associated with a perturbation in levels of endocannabinoids and FAAH activity and that such changes are associated with impaired tubal function.

AIMS

The objective of the study was to quantify the plasma levels of endocannabinoids (anandamide, oleoylethanolamide, and palmitoylethanolamide) and evaluate blood endocannabinoid metabolizing enzyme activities FAAH and N-acyl-phosphatidyl-ethanolamine phospholipase D (NAPE-PLD) in ectopic pregnancy and normal pregnant controls and relate that to β-human chorionic gonadotropin (β-hCG) levels. Additionally, we wanted to examine the effect of endocannabinoids on cilia beat frequency in Fallopian tube epithelial cells ex vivo.

PARTICIPANTS AND METHODS

Whole blood collected from ectopic and normal pregnancies was used for quantification of plasma endocannabinoid levels by ultra-HPLC-tandem mass spectrometry of FAAH and NAPE-PLD enzyme activities by radiometric assays, and β-hCG by immunoassay. Fallopian tube epithelial cells from healthy volunteers were treated with endocannabinoids and cilia beat frequency analyzed using a high-speed digital camera and CiliaFA software.

RESULTS

FAAH activity (P < .05) but not NAPE-PLD activity was significantly reduced in ectopic pregnancies. All 3 endocannabinoids levels were significantly higher (P < .05) in ectopic pregnancy. There was no correlation between endocannabinoids, enzyme activity, and β-hCG levels. Oleoylethanolamide (P < .05), but not methanandamide or palmitoylethanolamide, significantly decreased cilia beat frequency in Fallopian tube epithelial cells.

CONCLUSION

Elevated endocannabinoid levels and reduced FAAH activity are associated with ectopic pregnancy and may modulate tubal function, suggesting dysfunctional endocannabinoid action in ectopic implantation. Oleoylethanolamide may play a critical role in embryo-tubal transport.

Epigenetic mechanisms and endocannabinoid signalling

The endocannabinoid system, composed of endogenous lipids, their target receptors and metabolic enzymes, has been implicated in multiple biological functions in health and disease, both in the central nervous system and in peripheral organs. Despite the exponential growth of experimental evidence on the key role of endocannabinoid signalling in basic cellular processes, and on its potential exploitation for therapeutic interventions, much remains to be clarified about the respective regulatory mechanisms. Epigenetics refers to a set of post-translational modifications that regulate gene expression without causing variation in DNA sequence, endowed with a major impact on signal transduction pathways. The epigenetic machinery includes DNA methylation, histone modifications, nucleosome positioning and non-coding RNAs. Due to the reversibility of epigenetic changes, an emerging field of interest is the possibility of an 'epigenetic therapy' that could possibly be applied also to endocannabinoids. Here, we review current knowledge of epigenetic regulation of endocannabinoid system components under both physiological and pathological conditions, as well as the epigenetic changes induced by endocannabinoid signalling.

Analysis of fatty acid amide hydrolase activity in plants

N-Acylethanolamines (NAEs) are fatty acid derivatives amide-linked to ethanolamine. NAEs vary in chain lengths and numbers of double bonds and generally reflect the fatty acids found in membrane lipids in the tissues in which they reside. NAEs are present naturally in trace amounts and occur in a wide range of organisms including plants, animals, and microbes. Some NAE types are known to be involved in the endocannabinoid signaling system of vertebrates, and in plants they may play important regulatory roles in several physiological processes, such as root growth, seedling development, stress responses, and pathogen interactions. The biological effects of NAEs are terminated through their hydrolysis into the ethanolamine and free fatty acid by a membrane enzyme known as the fatty acid amide hydrolase (FAAH). Thus, FAAH represents an important target to better understand the function of these lipid mediators in numerous cellular processes. FAAH has been extensively characterized in mammalian and plant systems, and they share a conserved Ser-Ser-Lys catalytic mechanism. Here we describe procedures and experimental conditions to assay and characterize recombinant and endogenous FAAH enzymatic activity derived from plant tissues.

Rat and human fatty acid amide hydrolases: overt similarities and hidden differences

Fatty acid amide hydrolase (FAAH) is a membrane protein that plays a relevant role in the metabolism of fatty acid amides and esters. It degrades important neurotransmitters such as oleamide and anandamide, and it has been involved in a number of human pathological conditions, representing therefore a valuable target for biochemical and pharmacological research. In this study, we have investigated in vitro the structure-function relationship of rat and human FAAHs. In particular circular dichroism, fluorescence spectroscopy and light scattering measurements have been performed, in order to characterize the structural features of the two proteins, both in the presence and absence of the irreversible inhibitor methoxyarachidonyl-fluorophosphonate. The results demonstrate that the structural dynamics of the two FAAHs are different, despite their high sequence homology and overall similarity in temperature-dependence. Additionally, membrane binding and kinetic assays of both FAAHs indicate that also the functional properties of the two enzymes are different in their interaction with lipid bilayers and with exogenous inhibitors. These findings suggest that pre-clinical studies of FAAH-dependent human diseases based only on animal models should be interpreted with caution, and that the efficacy of new drugs targeted to FAAH should be tested in vitro, on both rat and human enzymes.

Acute reduction of anandamide-hydrolase (FAAH) activity is coupled with a reduction of nociceptive pathways facilitation in medication-overuse headache subjects after withdrawal treatment

OBJECTIVES

We investigated (1) a possible relationship between the functional activity of the endocannabinoid system and the facilitation of pain processing in migraineurs with medication-overuse headache, and (2) the effect of withdrawal treatment on both.

BACKGROUND

The endocannabinoid system antinociception effect includes prevention of nociceptive pathways sensitization. The sensitization of the pain pathways has been demonstrated to be pivotal in the development and maintenance of chronic form of migraine, including medication-overuse headache.

METHODS

We used the temporal summation threshold of the nociceptive withdrawal reflex to explore the spinal cord pain processing, and the platelet activity of the enzyme fatty acid amide hydrolase to detect the functional state of the endocannabinoid system in 27 medication-overuse headache subjects before and 10 and 60 days after a standard withdrawal treatment and compared results with those of 14 controls.

RESULTS

A significantly reduced temporal summation threshold and increased related pain sensation was found in subjects before withdrawal treatment when compared with controls. A significant fatty acid amide hydrolase activity reduction coupled with a significant improvement (reduction) in facilitation of spinal cord pain processing (increase in temporal summation threshold and reduction in related pain sensation) was found in medication-overuse headache subjects at both 10 and 60 days after withdrawal treatment when compared with medication-overuse headache subjects before withdrawal treatment.

CONCLUSIONS

We demonstrated a marked facilitation in spinal cord pain processing in medication-overuse headache before withdrawal treatment when compared with controls. Furthermore, the acute reduction of the fatty acid amide hydrolase activity coupled with a reduction of the facilitation in pain processing immediately (10 days) after withdrawal treatment and its persistence 60 days after withdrawal treatment could represent the consequence of a mechanism devoted to acutely reduce the degradation of endocannabinoids and aimed to increase the activity of the endocannabinoid system that results in an antinociceptive effect.

Impact of embedded endocannabinoids and their oxygenation by lipoxygenase on membrane properties

N-Arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol are the best characterized endocannabinoids. Their biological activity is subjected to metabolic control whereby a dynamic equilibrium among biosynthetic, catabolic, and oxidative pathways drives their intracellular concentrations. In particular, lipoxygenases can generate hydroperoxy derivatives of endocannabinoids, endowed with distinct activities within cells. The in vivo interaction between lipoxygenases and endocannabinoids is likely to occur within cell membranes; thus, we sought to ascertain whether a prototypical enzyme like soybean (Glycine max) 15-lipoxygenase-1 is able to oxygenate endocannabinoids embedded in synthetic vesicles and how these substances could affect the binding ability of the enzyme to different lipid bilayers. We show that (i) embedded endocannabinoids increase membrane fluidity; (ii) 15-lipoxygenase-1 preferentially binds to endocannabinoid-containing bilayers; and that (iii) 15-lipoxygenase-1 oxidizes embedded endocannabinoids and thus reduces fluidity and local hydration of membrane lipids. Together, the present findings reveal further complexity in the regulation of endocannabinoid signaling within the central nervous system, disclosing novel control by oxidative pathways.

The novel reversible fatty acid amide hydrolase inhibitor ST4070 increases endocannabinoid brain levels and counteracts neuropathic pain in different animal models

The effect of the enol carbamate 1-biphenyl-4-ylethenyl piperidine-1-carboxylate (ST4070), a novel reversible inhibitor of fatty acid amide hydrolase (FAAH), was investigated for acute pain sensitivity and neuropathic pain in rats and mice. Brain enzymatic activity of FAAH and the endogenous levels of its substrates, anandamide (AEA; N-arachidonoylethanolamine), 2-arachidonoylglycerol (2-AG), and N-palmitoylethanolamine (PEA), were measured in control and ST4070-treated mice. ST4070 (10, 30, and 100 mg/kg) was orally administered to assess mechanical nociceptive thresholds and allodynia by using the Randall-Selitto and von Frey tests, respectively. Neuropathy was induced in rats by either the chemotherapeutic agent vincristine or streptozotocin-induced diabetes, whereas the chronic constriction injury (CCI) model was chosen to evaluate neuropathy in mice. ST4070 produced a significant increase of nociceptive threshold in rats and counteracted the decrease of nociceptive threshold in the three distinct models of neuropathic pain. In diabetic mice, ST4070 inhibited FAAH activity and increased the brain levels of AEA and PEA, without affecting that of 2-AG. The administration of ST4070 generated long-lasting pain relief compared with pregabalin and the FAAH inhibitors 1-oxo-1[5-(2-pyridyl)-2-yl]-7-phenylheptane (OL135) and cyclohexylcarbamic acid 3'-carbamoylbiphenyl-3-ylester (URB597) in CCI neuropathic mice. The antiallodynic effects of ST4070 were prevented by pretreatment with cannabinoid type 1 and cannabinoid type 2 receptor antagonists and by the selective peroxisome proliferator-activated receptor α antagonist [(2S)-2-[[(1Z)-1-methyl-3-oxo-3-[4-(trifluoromethyl)phenyl]-1-propenyl]amino]-3-[4-[2-(5-methyl-2-phenyl-4-oxazolyl)ethoxy]phenyl]propyl]-carbamic acid ethyl ester (GW6471). The administration of ST4070 generated long-lasting neuropathic pain relief compared with pregabalin and the FAAH inhibitors OL135 and URB597. Taken together, the reversible FAAH inhibitor ST4070 seems to be a promising novel therapeutic agent for the management of neuropathic pain.

Inhibiting fatty acid amide hydrolase normalizes endotoxin-induced enhanced gastrointestinal motility in mice

BACKGROUND AND PURPOSE

Gastrointestinal (GI) motility is regulated in part by fatty acid ethanolamides (FAEs), including the endocannabinoid (EC) anandamide (AEA). The actions of FAEs are terminated by fatty acid amide hydrolase (FAAH). We investigated the actions of the novel FAAH inhibitor AM3506 on normal and enhanced GI motility.

EXPERIMENTAL APPROACH

We examined the effect of AM3506 on electrically-evoked contractility in vitro and GI transit and colonic faecal output in vivo, in normal and FAAH-deficient mice treated with saline or LPS (100 µg·kg(-1), i.p.), in the presence and absence of cannabinoid (CB) receptor antagonists. mRNA expression was measured by quantitative real time-PCR, EC levels by liquid chromatography-MS and FAAH activity by the conversion of [(3)H]-AEA to [(3)H]-ethanolamine in intestinal extracts. FAAH expression was examined by immunohistochemistry.

KEY RESULTS

FAAH was dominantly expressed in the enteric nervous system; its mRNA levels were higher in the ileum than the colon. LPS enhanced ileal contractility in the absence of overt inflammation. AM3506 reversed the enhanced electrically-evoked contractions of the ileum through CB(1) and CB(2) receptors. LPS increased the rate of upper GI transit and faecal output. AM3506 normalized the enhanced GI transit through CB(1) and CB(2) receptors and faecal output through CB(1) receptors. LPS did not increase GI transit in FAAH-deficient mice.

CONCLUSIONS AND IMPLICATIONS

Inhibiting FAAH normalizes various parameters of GI dysmotility in intestinal pathophysiology. Inhibition of FAAH represents a new approach to the treatment of disordered intestinal motility.

Cannabinoid receptor expression in HIV encephalitis and HIV-associated neuropathologic comorbidities

AIMS

Cannabinoids have been proposed for treating various neurodegenerative disorders and as adjunct therapy for HIV+ patients with neurologic sequelae. The expression of cannabinoid receptors (CB1 and CB2) has been reported in neurodegenerative diseases and in simian immunodeficiency virus encephalitis, yet the receptor expression in the central nervous system of HIV+ individuals is not known.

METHODS

An anti-CB1 antibody and two anti-CB2 antibodies were employed for immunohistochemistry in the cerebral cortex and white matter of HIV encephalitis (HIVE) and HIV-associated comorbidities, as well as control brains (HIV- and HIV+).

RESULTS

By quantitative image analysis, we observed that CB1 was increased in HIVE brains and those with comorbidities, while CB2 was significantly increased in the white matter of HIVE. Morphologically, CB1 was present in neurones, and both CB1 and CB2 were present in meningeal macrophages and subpial glia in all brains. In HIVE, CB1 was found in white matter microglia and perivascular cells, while CB2 was increased in microglia, astrocytes and perivascular macrophages. Double immunofluorescence with cell-specific markers and immunoblots on primary cultured microglia and astrocytes substantiated the glial localization of the cannabinoid receptors and specificity of the antibodies.

CONCLUSIONS

Our study indicates that cannabinoid receptor expression occurs in glia in HIVE brains, and this may have ramifications for the potential use of cannabinoid ligands in HIV-infected patients.

The endogenous cannabinoid system in the gut of patients with inflammatory bowel disease

Activation of cannabinoid receptors (CBs) by endocannabinoids impacts on a number of gastrointestinal functions. Recent data indicate that CB1 agonists improve 2,4-dinitrobenzene sulfonic acid-induced colitis in mice, thus suggesting a role for the endocannabinoid agonist anandamide (AEA) in protecting the gut against inflammation. We here examined the gut endocannabinoid system in inflammatory bowel disease (IBD) patients, and investigated the ex vivo and in vitro effects of the non-hydrolysable AEA analog methanandamide (MAEA) on the mucosal proinflammatory response. The content of AEA, but not of 2-arachidonoyl-glycerol and N-palmitoylethanolamine, was significantly lower in inflamed than uninflamed IBD mucosa, and this was paralleled by lower activity of the AEA-synthesizing enzyme N-acyl-phosphatidylethanolamine-specific phospholipase D and higher activity of the AEA-degrading enzyme fatty acid amide hydrolase. MAEA significantly downregulated interferon-γ and tumor necrosis factor-α secretion by both organ culture biopsies and lamina propria mononuclear cells. Although these results are promising, further studies are needed to determine the role of cannabinoid pathways in gut inflammation.

Is lipid signaling through cannabinoid 2 receptors part of a protective system?

The mammalian body has a highly developed immune system which guards against continuous invading protein attacks and aims at preventing, attenuating or repairing the inflicted damage. It is conceivable that through evolution analogous biological protective systems have been evolved against non-protein attacks. There is emerging evidence that lipid endocannabinoid signaling through cannabinoid 2 (CB₂) receptors may represent an example/part of such a protective system/armamentarium. Inflammation/tissue injury triggers rapid elevations in local endocannabinoid levels, which in turn regulate signaling responses in immune and other cells modulating their critical functions. Changes in endocannabinoid levels and/or CB₂ receptor expressions have been reported in almost all diseases affecting humans, ranging from cardiovascular, gastrointestinal, liver, kidney, neurodegenerative, psychiatric, bone, skin, autoimmune, lung disorders to pain and cancer, and modulating CB₂ receptor activity holds tremendous therapeutic potential in these pathologies. While CB₂ receptor activation in general mediates immunosuppressive effects, which limit inflammation and associated tissue injury in large number of pathological conditions, in some disease states activation of the CB₂ receptor may enhance or even trigger tissue damage, which will also be discussed alongside the protective actions of the CB₂ receptor stimulation with endocannabinoids or synthetic agonists, and the possible biological mechanisms involved in these effects.