Unraveling the complexities of cannabinoid receptor 2 (CB2) immune regulation in health and disease

It has become clear that the endocannabinoid system is a potent regulator of immune responses, with the cannabinoid receptor 2 (CB2) as the key component due to its high expression by all immune subtypes. CB2 has been shown to regulate immunity by a number of mechanisms including development, migration, proliferation, and effector functions. In addition, CB2 has been shown to modulate the function of all immune cell types examined to date. CB2 is a G_i-protein-coupled receptor and thus exhibits a complex pharmacology allowing both stimulatory and inhibitory signaling that depends on receptor expression levels, ligand concentration, and cell lineage specificities. Here, we discuss both in vitro and in vivo experimental evidence that CB2 is a potent regulator of immune responses making it a prime target for the treatment of inflammatory diseases.     

Pharmacotherapeutic targeting of the endocannabinoid signaling system: drugs for obesity and the metabolic syndrome

Endogenous signaling lipids ("endocannabinoids") functionally related to Delta(9)-tetrahydrocannabinol, the psychoactive ingredient of marijuana (Cannabis), are important biomediators and metabolic regulators critical to mammalian (patho)physiology. The growing family of endocannabinoids, along with endocannabinoid biosynthetic and inactivating enzymes, transporters, and at least two membrane-bound, G-protein coupled receptors, comprise collectively the mammalian endocannabinoid signaling system. The ubiquitous and diverse regulatory actions of the endocannabinoid system in health and disease have supported the regulatory approval of natural products and synthetic agents as drugs that alter endocannabinoid-system activity. More recent data support the concept that the endocananbinoid system may be modulated for therapeutic gain at discrete pharmacological targets with safety and efficacy. Potential medications based on the endocannabinoid system have thus become a central focus of contemporary translational research for varied indications with important unmet medical needs. One such indication, obesity, is a global pandemic whose etiology has a pathogenic component of endocannabinoid-system hyperactivity and for which current pharmacological treatment is severely limited. Application of high-affinity, selective CB1 cannabinoid receptor ligands to attenuate endocannabinoid signaling represents a state-of-the-art approach for improving obesity pharmacotherapy. To this intent, several selective CB1 receptor antagonists with varied chemical structures are currently in advanced preclinical or clinical trials, and one (rimonabant) has been approved as a weight-management drug in some markets. Emerging preclinical data suggest that CB1 receptor neutral antagonists may represent breakthrough medications superior to antagonists/inverse agonists such as rimonabant for therapeutic attenuation of CB1 receptor transmission. Since obesity is a predisposing condition for the cluster of cardiovascular and metabolic derangements collectively known as the metabolic syndrome, effective endocannabinoid-modulatory anti-obesity therapeutics would also help redress other major health problems including type-2 diabetes, atherothrombosis, inflammation, and immune disorders. Pressing worldwide healthcare needs and increasing appreciation of endocannabinoid biology make the rational design and refinement of targeted CB1 receptor modulators a promising route to future medications with significant therapeutic impact against overweight, obesity, obesity-related cardiometabolic dysregulation, and, more generally, maladies having a reward-supported appetitive component.     

The endocannabinoid system as a novel target for the treatment of liver fibrosis

The cannabinoid system comprises specific G protein-coupled receptors (CB1 and CB2), exogenous (marijuana-derived cannabinoids) and endogenous (endocannabinoids) ligands, and a machinery dedicated to endocannabinoid synthesis and degradation. Studies over two decades have extensively documented the crucial role of the cannabinoid system in the regulation of a variety of pathophysiological conditions. However, its role in liver pathology has only been recently unravelled, probably given the low expression of CB1 and CB2 in the normal liver. We have recently demonstrated that CB1 and CB2 receptors display opposite effects in the regulation of liver fibrogenesis during chronic liver injury. Indeed, both receptors are up-regulated in the liver of cirrhotic patients, and expressed in liver fibrogenic cells. Moreover, CB1 receptors are profibrogenic and accordingly, the CB1 antagonist rimonabant reduces fibrosis progression in three experimental models. In keeping with these results, daily cannabis smoking is a risk factor for fibrosis progression in patients with chronic hepatitis C. In contrast, CB2 display antifibrogenic effects, by a mechanism involving reduction of liver fibrogenic cell accumulation. These results may offer new perspectives for the treatment of liver fibrosis, combining CB2 agonist and CB1 antagonist therapy.     

Inhibition of cyclooxygenase-2 potentiates retrograde endocannabinoid effects in hippocampus

In hippocampal pyramidal cells, a rise in Ca(2+) releases endocannabinoids that activate the presynaptic cannabinoid receptor (CB1R) and transiently reduce GABAergic transmission-a process called depolarization-induced suppression of inhibition (DSI). The mechanism that limits the duration of endocannabinoid action in intact cells is unknown. Here we show that inhibition of cyclooxygenase-2 (COX-2), not fatty acid amide hydrolase (FAAH), prolongs DSI, suggesting that COX-2 limits endocannabinoid action.     

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

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

Endocannabinoid control of food intake and energy balance

Marijuana and its major psychotropic component, Delta(9)-tetrahydrocannabinol, stimulate appetite and increase body weight in wasting syndromes, suggesting that the CB(1) cannabinoid receptor and its endogenous ligands, the endocannabinoids, are involved in controlling energy balance. The endocannabinoid system controls food intake via both central and peripheral mechanisms, and it may also stimulate lipogenesis and fat accumulation. Here we discuss the multifaceted regulation of energy homeostasis by endocannabinoids, together with its applications to the treatment of eating disorders and metabolic syndromes.     

Cannabinoid receptors and pain

Mammalian tissues contain at least two types of cannabinoid receptor, CB(1) and CB(2), both coupled to G proteins. CB(1) receptors are expressed mainly by neurones of the central and peripheral nervous system whereas CB(2) receptors occur centrally and peripherally in certain non-neuronal tissues, particularly in immune cells. The existence of endogenous ligands for cannabinoid receptors has also been demonstrated. The discovery of this 'endocannabinoid system' has prompted the development of a range of novel cannabinoid receptor agonists and antagonists, including several that show marked selectivity for CB(1) or CB(2) receptors. It has also been paralleled by a renewed interest in cannabinoid-induced antinociception. This review summarizes current knowledge about the ability of cannabinoids to produce antinociception in animal models of acute pain as well as about the ability of these drugs to suppress signs of tonic pain induced in animals by nerve damage or by the injection of an inflammatory agent. Particular attention is paid to the types of pain against which cannabinoids may be effective, the distribution pattern of cannabinoid receptors in central and peripheral pain pathways and the part that these receptors play in cannabinoid-induced antinociception. The possibility that antinociception can be mediated by cannabinoid receptors other than CB(1) and CB(2) receptors, for example CB(2)-like receptors, is also discussed as is the evidence firstly that one endogenous cannabinoid, anandamide, produces antinociception through mechanisms that differ from those of other types of cannabinoid, for example by acting on vanilloid receptors, and secondly that the endocannabinoid system has physiological and/or pathophysiological roles in the modulation of pain.     

Role of endogenous cannabinoids in synaptic signaling

Research of cannabinoid actions was boosted in the 1990s by remarkable discoveries including identification of endogenous compounds with cannabimimetic activity (endocannabinoids) and the cloning of their molecular targets, the CB1 and CB2 receptors. Although the existence of an endogenous cannabinoid signaling system has been established for a decade, its physiological roles have just begun to unfold. In addition, the behavioral effects of exogenous cannabinoids such as delta-9-tetrahydrocannabinol, the major active compound of hashish and marijuana, await explanation at the cellular and network levels. Recent physiological, pharmacological, and high-resolution anatomical studies provided evidence that the major physiological effect of cannabinoids is the regulation of neurotransmitter release via activation of presynaptic CB1 receptors located on distinct types of axon terminals throughout the brain. Subsequent discoveries shed light on the functional consequences of this localization by demonstrating the involvement of endocannabinoids in retrograde signaling at GABAergic and glutamatergic synapses. In this review, we aim to synthesize recent progress in our understanding of the physiological roles of endocannabinoids in the brain. First, the synthetic pathways of endocannabinoids are discussed, along with the putative mechanisms of their release, uptake, and degradation. The fine-grain anatomical distribution of the neuronal cannabinoid receptor CB1 is described in most brain areas, emphasizing its general presynaptic localization and role in controlling neurotransmitter release. Finally, the possible functions of endocannabinoids as retrograde synaptic signal molecules are discussed in relation to synaptic plasticity and network activity patterns.     

Blockade of cannabinoid receptors reduces inflammation, leukocyte accumulation and neovascularization in a model of sponge-induced inflammatory angiogenesis

Objective

Angiogenesis depends on a complex interaction between cellular networks and mediators. The endocannabinoid system and its receptors have been shown to play a role in models of inflammation. Here, we investigated whether blockade of cannabinoid receptors may interfere with inflammatory angiogenesis.

Materials and methods

Polyester-polyurethane sponges were implanted in C57Bl/6j mice. Animals received doses (3 and 10 mg/kg/daily, s.c.) of the cannabinoid receptor antagonists SR141716A (CB1) or SR144528 (CB2). Implants were collected at days 7 and 14 for cytokines, hemoglobin, myeloperoxidase, and N-acetylglucosaminidase measurements, as indices of inflammation, angiogenesis, neutrophil and macrophage accumulation, respectively. Histological and morphometric analysis were also performed.

Results

Cannabinoid receptors expression in implants was detected from day 4 after implantation. Treatment with CB1 or CB2 receptor antagonists reduced cellular influx into sponges at days 7 and 14 after implantation, although CB1 receptor antagonist were more effective at blocking leukocyte accumulation. There was a reduction in TNF-α, VEGF, CXCL1/KC, CCL2/JE, and CCL3/MIP-1α levels, with increase in CCL5/RANTES. Both treatments reduced neovascularization. Dual blockade of cannabinoid receptors resulted in maximum inhibition of inflammatory angiogenesis.

Conclusions

Blockade of cannabinoid receptors reduced leukocyte accumulation, inflammation and neovascularization, suggesting an important role of endocannabinoids in sponge-induced inflammatory angiogenesis both via CB1 and CB2 receptors.     

Stress regulates endocannabinoid-CB1 receptor signaling

The CB1 cannabinoid receptor is a G protein coupled receptor that is widely expressed throughout the brain. The endogenous ligands for the CB1 receptor (endocannabinoids) are N-arachidonylethanolamine and 2-arachidonoylglycerol; together the endocannabinoids and CB1R subserve activity dependent, retrograde inhibition of neurotransmitter release in the brain. Deficiency of CB1 receptor signaling is associated with anhedonia, anxiety, and persistence of negative memories. CB1 receptor-endocannabinoid signaling is activated by stress and functions to buffer or dampen the behavioral and endocrine effects of acute stress. Its role in regulation of neuronal responses is more complex. Chronic variable stress exposure reduces endocannabinoid-CB1 receptor signaling and it is hypothesized that the resultant deficiency in endocannabinoid signaling contributes to the negative consequences of chronic stress. On the other hand, repeated exposure to the same stress can sensitize CB1 receptor signaling, resulting in dampening of the stress response. Data are reviewed that support the hypothesis that CB1 receptor signaling is stress responsive and that maintaining robust endocannabinoid/CB1 receptor signaling provides resilience against the development of stress-related pathologies.     

Expression of the endocannabinoid system in the bi-potential HEL cell line: commitment to the megakaryoblastic lineage by 2-arachidonoylglycerol

The role of the endocannabinoid system in haematopoietic cells is not completely understood. We investigated whether human erythroleukemia (HEL) cells were able to bind, metabolise and transport the main endocannabinoids, anandamide (AEA) and 2-arachidonoylglycerol (2-AG). We also investigated whether AEA or 2-AG could modulate HEL differentiation. Although able to internalise both endocannabinoids, HEL cells had the machinery to metabolise 2-AG only, since they were devoid of the enzymes needed to synthesise and degrade AEA. Nonetheless, the intracellular transport of exogenous AEA might be required to activate the vanilloid receptors, with yet unknown implications for vascular biology. On the contrary, 2-AG appeared to play a role in lineage determination. Indeed, 2-AG itself drove HEL cells towards megakaryocytic differentiation, as it enhanced expression of beta3 integrin subunit, a megakaryocyte/platelet surface antigen, and glycoprotein VI, a late marker of megakaryocytes; in parallel, it reduced the amount of messenger RNA encoding for glycophorin A, a marker of erythroid phenotype. All these effects were mediated by activation of CB(2) cannabinoid receptors that triggered an extracellular signal-regulated kinase-dependent signalling cascade. In addition, classical inducers of megakaryocyte differentiation reduced 2-AG synthesis (although they did not affect the binding efficiency of CB(2) receptors), suggesting that levels of this endocannabinoid may be critical for committing HEL cells towards the megakaryocytic lineage.     

Up-regulation of the endocannabinoid system in the uterus of leptin knockout (ob/ob) mice and implications for fertility

The levels of the endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG) are under the negative control of leptin in the rodent hypothalamus. As leptin and endocannabinoids play opposite roles in the control of reproduction, we have investigated whether the impaired fertility typical of leptin-defective ob/ob mice is due, in part, to enhanced uterine endocannabinoid levels. We found that levels of both anandamide and 2-AG in the uterus of ob/ob mice are significantly elevated with respect to wild-type littermates, due to reduced hydrolase activity in the case of anandamide, and to reduced monoacylglycerol lipase and enhanced diacylglycerol lipase activity in the case of 2-AG. Furthermore, the process mediating endocannabinoid cellular uptake was also impaired in ob/ob mice, whereas the levels of cannabinoid and anandamide receptors were not modified. Although ineffective in wild-type mice, treatment of ob/ob mice with leptin re-established endocannabinoid levels and enzyme activities back to the values observed in wild-type littermates. Finally, treatment of ob/ob females with the CB1 receptor antagonist SR141716A did not improve their fertility, and inhibition of endocannabinoid inactivation with the endocannabinoid uptake inhibitor OMDM-1 in wild-type females did not result in impaired fertility.     

Reduced endocannabinoid immune modulation by a common cannabinoid 2 (CB2) receptor gene polymorphism: possible risk for autoimmune disorders

Immune system responsiveness results from numerous factors, including endogenous cannabinoid signaling in immunocytes termed the "immunocannabinoid" system. This system can be an important signaling pathway for immune modulation. To assess the immunomodulating role of the cannabinoid 2 (CB2) receptor, we sought polymorphisms in the human gene, identified a common dinucleotide polymorphism, and investigated its effect on endocannabinoid-induced inhibition of T lymphocyte proliferation. The CB2 cDNA 188-189 GG/GG polymorphism predicts the substitution of glutamine at amino acid position 63 by arginine. T lymphocytes from CB2 188-189 GG/GG homozygotes had approximately twofold reduction of endocannabinoid-induced inhibition of proliferation compared with cells from CB2 188-189 AA/AA homozygotes. In GG/GG subjects, the reduced endocannabinoid inhibitory response was highly significant for N-arachidonylglycine and nearly significant for 2-arachidonylglycerol, and a specific CB2 receptor antagonist partially blocked these effects. Also, patients with autoimmune diseases had an increased prevalence of the homozygous GG/GG genotype. Collectively, these results demonstrate reduced endogenous fatty acid amide immunomodulatory responses in individuals with the CB2 188-189 GG/GG genotype and suggest that this CB2 gene variation may be a risk factor for autoimmunity. The results also support the proposition that the CB2 receptor may represent a novel pharmacological target for selective agonists designed to suppress autoreactive immune responses while avoiding CB1 receptor-mediated cannabinoid adverse effects.     

Depolarization-induced suppression of excitation in murine autaptic hippocampal neurones

Depolarization-induced suppression of excitation and inhibition (DSE and DSI) appear to be important forms of short-term retrograde neuronal plasticity involving endocannabinoids (eCB) and the activation of presynaptic cannabinoid CB1 receptors. We report here that CB1-dependent DSE can be elicited from autaptic cultures of excitatory mouse hippocampal neurones. DSE in autaptic cultures is both more robust and elicited with a more physiologically relevant stimulus than has been thus far reported for conventional hippocampal cultures. An additional requirement for autaptic DSE is filled internal calcium stores. Pharmacological experiments favour a role for 2-arachidonyl glycerol (2-AG) rather than arachidonyl ethanolamide (AEA) or noladin ether as the relevant endocannabinoid to elicit DSE. In particular, the latter two compounds fail to reversibly inhibit EPSCs, a quality inconsistent with the role of bona fide eCB mediating DSE. Δ⁹-Tetrahydrocannabinol (Δ⁹-THC) fails to inhibit EPSCs, yet readily occludes both DSE and EPSC inhibition by a synthetic CB1 agonist, WIN 55212-2. With long-term exposure (∼18 h), Δ⁹-THC also desensitizes CB1 receptors. Lastly, a functional endocannabinoid transporter is necessary for the expression of DSE.     

Association between lipid accumulation and the cannabinoid system in Huh7 cells expressing HCV genes

Evidence from clinical and laboratory studies has accumulated indicating that the activation of the cannabinoid system is crucial for steatosis, especially in non-alcoholic fatty liver disease. However, the association between hepatitis C virus (HCV) infection and the cannabinoid system has not been well investigated and it is unclear whether steatosis in chronic hepatitis C develops via activation of the endocannabinoid/cannabinoid receptor signaling pathway. In this study, we examined the expression of a cannabinoid receptor (CB1) and the lipid accumulation in the hepatic Huh7 cell line, expressing HCV genes. We utilized Huh7/Rep-Feo-1b cells stably expressing HCV non-structural proteins (NS) 3, NS4, NS5A, and NS5B, as well as Tet-On Core-2 cells, in which the HCV core protein expression is inducible. Significantly higher levels of stored triglycerides were found in Huh7/Rep-Feo-1b cells compared to Huh7 cells. Also, triglyceride accumulation and CB1 receptor expression were down-regulated in Huh7/Rep-Feo-1b cells after HCV reduction by IFNα. Moreover, lipid accumulation appeared to increase after CB1 agonist treatment, while it decreased after CB1 antagonist treatment, although significant differences were not found compared to untreated cells. In Tet-On Core-2 cells, induction of HCV core protein expression did not affect CB1 expression or triglyceride accumulation. The results of this study in cultured cells suggest that HCV infection may activate the cannabinoid system and precede steatosis, but the core protein by itself may not have any effect on the cannabinoid system.     

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.     

Cannabis and cannabinoids: pharmacology and rationale for clinical use

It is now known that there are at least two types of cannabinoid receptors. These are CB1 receptors, present mainly on central and peripheral neurones, and CB2 receptors, present mainly on immune cells. Endogenous cannabinoid receptor agonists ('endocannabinoids') have also been identified. The discovery of this 'endogenous cannabinoid system' has led to the development of selective CB1 and CB2 receptor ligands and fueled renewed interest in the clinical potential of cannabinoids. Two cannabinoid CB1 receptor agonists are already used clinically, as antiemetics or as appetite stimulants. These are D 9 - tetrahydrocannabinol (THC) and nabilone. Other possible uses for CB1 receptor agonists include the suppression of muscle spasm/spasticity associated with multiple sclerosis or spinal cord injury, the relief of chronic pain and the management of glaucoma and bronchial asthma. CB1 receptor antagonists may also have clinical applications, e. g. as appetite suppressants and in the management of schizophrenia or disorders of cognition and memory. So too may CB2 receptor ligands and drugs that activate cannabinoid receptors indirectly by augmenting endocannabinoid levels at cannabinoid receptors. When taken orally, THC seems to undergo variable absorption and to have a narrow 'therapeutic window' (dose range in which it is effective without producing significant unwanted effects). This makes it difficult to predict an oral dose that will be both effective and tolerable to a patient and indicates a need for better cannabinoid formulations and modes of administration. For the therapeutic potential of cannabis or CB1 receptor agonists to be fully exploited, it will be important to establish objectively and conclusively (a) whether these agents have efficacy against selected symptoms that is of clinical significance and, if so, whether the benefits outweigh the risks, (b) whether cannabis has therapeutic advantages over individual cannabinoids, (c) whether there is a need for additional drug treatments to manage any of the disorders against which cannabinoids are effective, and (d) whether it will be possible to develop drugs that have reduced psychotropic activity and yet retain the ability to act through CB1 receptors to produce their sought-after effects.     

Impaired expression of indoleamine 2, 3-dioxygenase in monocyte-derived dendritic cells in response to Toll-like receptor-7/8 ligands

The endogenous cannabinoid system plays an important role in regulating the immune system. Modulation of endogenous cannabinoids represents an attractive alternative for the treatment of inflammatory disorders. This study investigated the effects of URB597, a selective inhibitor of fatty acid amide hydrolase (FAAH), the enzyme catalysing degradation of the endogenous cannabinoid anandamide, and AM404, an inhibitor of anandamide transport, on lipopolysaccharide (LPS)-induced increases in plasma cytokine levels in rats. Both URB597 and AM404 potentiated the LPS-induced increase in plasma tumour necrosis factor-alpha (TNF-alpha) levels. The peroxisome proliferator-activated receptor gamma (PPARgamma) antagonist, GW9662, attenuated the AM404-induced augmentation of TNF-alpha levels. Furthermore, the selective cannabinoid CB1 and CB2 receptor antagonists, AM251 and AM630 respectively, and the transient receptor potential vanilloid receptor-1 (TRPV1) antagonist, SB366791, reduced LPS-induced TNF-alpha plasma levels both alone and in combination with AM404. In contrast, AM404 inhibited LPS-induced increases in circulating interleukin-1beta (IL-1beta) and IL-6. AM251 attenuated the immunosuppressive effect of AM404 on IL-1beta. None of the antagonists altered the effect of AM404 on LPS-induced IL-6. Moreover, AM251, AM630 and SB366791, administered alone, inhibited LPS-induced increases in plasma IL-1beta and IL-6 levels. In conclusion, inhibition of endocannabinoid degradation or transport in vivo potentiates LPS-induced increases in circulating TNF-alpha levels, an effect which may be mediated by PPARgamma and is also reduced by pharmacological blockade of CB1, CB2 and TRPV1. The immunosuppressive effect of AM404 on IL-1beta levels is mediated by the cannabinoid CB1 receptor. Improved understanding of endocannabinoid-mediated regulation of immune function has fundamental physiological and potential therapeutic significance.     

Overactivity of the intestinal endocannabinoid system in celiac disease and in methotrexate-treated rats

The endocannabinoid system is upregulated in both human inflammatory bowel diseases and experimental models of colitis. In this study, we investigated whether this upregulation is a marker also of celiac disease-induced atrophy. The levels of the cannabinoid CB(1) receptor, of the endocannabinoids, anandamide, and 2-arachidonoyl-glycerol (2-AG), and of the anti-inflammatory mediator palmitoylethanolamide (PEA) were analyzed in bioptic samples from the duodenal mucosa of celiac patients at first diagnosis assessed by the determination of antiendomysial antibodies and histological examination. Samples were analyzed during the active phase of atrophy and after remission and compared to control samples from non-celiac patients. The levels of anandamide and PEA were significantly elevated (approx. 2- and 1.8-fold, respectively) in active celiac patients and so were those of CB(1) receptors. Anandamide levels returned to normal after remission with a gluten-free diet. We also analyzed endocannabinoid and PEA levels in the jejunum of rats 2, 3, and 7 days after treatment with methotrexate, which causes inflammatory features (assessed by histopathological analyses and myeloperoxidase activity) similar to those of celiac patients. In both muscle/serosa and mucosa layers, the levels of anandamide, 2-AG, and PEA peaked 3 days after treatment and returned to basal levels at remission, 7 days after treatment. Thus, intestinal endocannabinoid levels peak with atrophy and regress with remission in both celiac patients and methotrexate-treated rats. The latter might be used as a model to study the role of the endocannabinoid system in celiac disease.