Biosynthesis and inactivation of the endocannabinoid 2-arachidonoylglycerol in circulating and tumoral macrophages

Involvement of cannabinoid receptors in gut motility and visceral perception

From a historical perspective to the present day, all the evidence suggests that activation of cannabinoid receptors (CBRs) is beneficial for gut discomfort and pain, which are symptoms related to dysmotility and visceral perception. CBRs comprise G-protein coupled receptors that are predominantly in enteric and central neurones (CB1R) and immune cells (CB2R). In the last decade, evidence obtained from the use of selective agonists and inverse agonists/antagonists indicates that manipulation of CB1R can alter (1) sensory processing from the gut, (2) brain integration of brain-gut axis, (3) extrinsic control of the gut and (4) intrinsic control by the enteric nervous system. The extent to which activation of CB1R is most critical at these different levels is related to the region of the GI tract. The upper GI tract is strongly influenced by CB1R activation on central vagal pathways, whereas intestinal peristalsis can be modified by CB1R activation in the absence of extrinsic input. Actions at multiple levels make the CB1R a target for the treatment of functional bowel disorders, such as IBS. Since low-grade inflammation may act as a trigger for occurrence of IBS, CB2R modulation could be beneficial, but there is little supporting evidence for this yet. The challenge is to accomplish CBR activation while minimizing adverse effects and abuse liabilities. Potential therapeutic strategies involve increasing signaling by endocannabinoids (EC). The pathways involved in the biosynthesis, uptake and degradation of EC provide opportunities for modulation of CB1R and some recent evidence with inhibitors of EC uptake and metabolism suggest that these could be exploited for therapeutic gain.

Further evidence for the existence of a specific process for the membrane transport of anandamide

Indirect evidence for the existence of a specific protein-mediated process for the cellular uptake of endocannabinoids has been reported, but recent results suggested that such a process, at least for AEA [ N -arachidonoylethanolamine (anandamide)], is facilitated uniquely by its intracellular hydrolysis by FAAH (fatty acid amide hydrolase) [Glaser, Abumrad, Fatade, Kaczocha, Studholme and Deutsch (2003) Proc. Natl. Acad. Sci. U.S.A. 100, 4269-4274]. In the present study, we show that FAAH alone cannot account for the facilitated diffusion of AEA across the cell membrane. In particular, (i) using a short incubation time (90 s) to avoid AEA hydrolysis by FAAH, AEA accumulation into rat basophilic leukaemia or C6 cells was saturable at low microM concentrations of substrate and non-saturable at higher concentrations; (ii) time-dependent and, at low microM concentrations of substrate, saturable AEA accumulation was observed also using mouse brain synaptosomes; (iii) using synaptosomes prepared from FAAH-deficient mice, saturable AEA accumulation was still observed, although with a lower efficacy; (iv) when 36 AEA and N -oleoylethanolamine analogues, most of which with phenyl rings in the polar head group region, were tested as inhibitors of AEA cellular uptake, strict structural and stereochemical requirements were needed to observe significant inhibition, and in no case the inhibition of FAAH overlapped with the inhibition of AEA uptake; and (v) AEA biosynthesis by cells and sensory neurons was followed by AEA release, and this latter process, which cannot be facilitated by FAAH, was still blocked by an inhibitor of AEA uptake. We suggest that at least one protein different from FAAH is required to facilitate AEA transport across the plasma membrane in a selective and bi-directional way.

Inhibition of monoacylglycerol lipase and fatty acid amide hydrolase by analogues of 2-arachidonoylglycerol

The pharmacology of monoacylglycerol lipase (MAGL) is not well understood. In consequence, the abilities of a series of analogues of 2-arachidonoylglycerol (2-AG) to inhibit cytosolic 2-oleoylglycerol and membrane-bound anandamide hydolysis by MAGL and fatty acid amide hydrolase (FAAH), respectively, have been investigated. 2-AG and its 1-regioisomer (1-AG) interacted with MAGL with similar affinities (IC(50) values 13 and 17 mum, respectively). Shorter homologues of 2-AG (2-linoleoylglycerol and 2-oleoylglycerol) had affinities for MAGL similar to 2-AG. This pattern was also seen when the arachidonoyl side chain of arachidonoyl trifluoromethylketone was replaced by an oleoyl side chain. Arachidonoyl serinol (IC(50) value 73 microM) was a weaker inhibitor of MAGL than 2-AG. The IC(50) values of noladin ether towards MAGL and FAAH were 36 and 3 microM, respectively. Arachidonoyl glycine interacted with FAAH (IC(50) value 4.9 microM) but only weakly interacted with MAGL (IC(50) value >100 microM). alpha-Methyl-1-AG had similar potencies towards MAGL and FAAH (IC(50) values of 11 and 33 microM, respectively). O-2203 (1-(20-cyano-16,16-dimethyl-eicosa-5,8,11,14-tetraenoyl) glycerol) and O-2204 (2-(20-hydroxy-16,16-dimethyl-eicosa-5,8,11,14-tetraenoyl) glycerol) were slightly less potent, but again affected both enzymes equally. alpha-Methyl-1-AG, O-2203 and O-2204 interacted only weakly with cannabinoid CB(1) receptors expressed in CHO cells (K(i) values 1.8, 3.7 and 3.2 microM, respectively, compared with 0.24 microM for 1-AG) and showed no evidence of central cannabinoid receptor activation in vivo at doses up to 30 mg kg(-1) i.v. It is concluded that compounds like alpha-Methyl-1-AG, O-2203 and O-2204 may be useful as leads for the discovery of selective MAGL inhibitors that lack direct effects upon cannabinoid receptors.

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

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

The endocannabinoid system and its therapeutic exploitation

The term 'endocannabinoid' - originally coined in the mid-1990s after the discovery of membrane receptors for the psychoactive principle in Cannabis, Delta9-tetrahydrocannabinol and their endogenous ligands - now indicates a whole signalling system that comprises cannabinoid receptors, endogenous ligands and enzymes for ligand biosynthesis and inactivation. This system seems to be involved in an ever-increasing number of pathological conditions. With novel products already being aimed at the pharmaceutical market little more than a decade since the discovery of cannabinoid receptors, the endocannabinoid system seems to hold even more promise for the future development of therapeutic drugs. We explore the conditions under which the potential of targeting the endocannabinoid system might be realized in the years to come.

2-arachidonoylglycerol, an endogenous cannabinoid receptor ligand, induces the migration of EoL-1 human eosinophilic leukemia cells and human peripheral blood eosinophils

2-arachidonoylglycerol (2-AG) is an endogenous cannabinoid receptor ligand. To date, two types of cannabinoid receptors have been identified: the CB1 receptor, abundantly expressed in the brain, and the CB2 receptor, expressed in various lymphoid tissues such as the spleen. The CB1 receptor has been assumed to play an important role in the regulation of synaptic transmission, whereas the physiological roles of the CB2 receptor remain obscure. In this study, we examined whether the CB2 receptor is present in human eosinophils and found that the CB2 receptor is expressed in human peripheral blood eosinophils. In contrast, human neutrophils do not contain a significant amount of the CB2 receptor. We then examined the effect of 2-AG on the motility of eosinophils. We found that 2-AG induces the migration of human eosinophilic leukemia EoL-1 cells. The migration evoked by 2-AG was abolished in the presence of SR144528, a CB2 receptor antagonist, or by pretreatment of the cells with pertussis toxin, suggesting that the CB2 receptor and Gi/o are involved in the 2-AG-induced migration. The migration of EoL-1 cells induced by 2-AG was suggested to be a result of chemotaxis. In contrast to 2-AG, neither anandamide nor free arachidonic acid elicited the migration. Finally, we examined the effect of 2-AG on human peripheral blood eosinophils and neutrophils and found that 2-AG induces migration of eosinophils but not neutrophils. These results suggest that the CB2 receptor and its endogenous ligand 2-AG may be closely involved in allergic inflammation accompanied by the infiltration of eosinophils.

Immunosuppressive activity of endovanilloids: N-arachidonoyl-dopamine inhibits activation of the NF-kappa B, NFAT, and activator protein 1 signaling pathways

Endogenous N-acyl dopamines such as N-arachidonoyldopamine (NADA) and N-oleoyldopamine have been recently identified as a new class of brain neurotransmitters sharing endocannabinoid and endovanilloid biological activities. As endocannabinoids show immunomodulatory activity, and T cells play a key role in the onset of several diseases that affect the CNS, we have evaluated the immunosuppressive activity of NADA and N-oleoyldopamine in human T cells, discovering that both compounds are potent inhibitors of early and late events in TCR-mediated T cell activation. Moreover, we found that NADA specifically inhibited both IL-2 and TNF-alpha gene transcription in stimulated Jurkat T cells. To further characterize the inhibitory mechanisms of NADA at the transcriptional level, we examined the DNA binding and transcriptional activities of NF-kappaB, NF-AT, and AP-1 transcription factors in Jurkat cells. We found that NADA inhibited NF-kappaB-dependent transcriptional activity without affecting either degradation of the cytoplasmic NF-kappaB inhibitory protein, IkappaBalpha, or DNA binding activity. However, phosphorylation of the p65/RelA subunit was clearly inhibited by NADA in stimulated cells. In addition, NADA inhibited both binding to DNA and the transcriptional activity of NF-AT and AP-1, as expected from the inhibition of NF-AT1 dephosphorylation and c-Jun N-terminal kinase activation in stimulated T cells. Finally, overexpression of a constitutively active form of calcineurin demonstrated that this phosphatase may represent one of the main targets of NADA. These findings provide new mechanistic insights into the anti-inflammatory activities of NADA and highlight their potential to design novel therapeutic strategies to manage inflammatory diseases.

Cultured rat microglial cells synthesize the endocannabinoid 2-arachidonylglycerol, which increases proliferation via a CB2 receptor-dependent mechanism

Microglia, as phagocytes and antigen-presenting cells in the central nervous system, are activated in such disease processes as stroke and multiple sclerosis. Because peripheral macrophages are capable of producing endocannabinoids, we have examined endocannabinoid production in a macrophage-colony stimulating factor (M-CSF)-dependent rat microglial cell line (RTMGL1) using reversed phase high-pressure liquid chromatography and liquid chromatography-mass spectroscopy. We determined that cultured microglial cells produce the endocannabinoid 2-arachidonylglycerol (2-AG) as well as anandamide in smaller quantities. When 2-AG, but not anandamide, is added exogenously, RTMGL1 microglia increase their proliferation. This increased proliferation is blocked by an antagonist of the CB(2) receptor N-[(1S)endo-1,3,3-trimethyl bicyclo heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide (SR144528) and mimicked by the CB(2) receptor-specific agonist 1,1-dimethylbutyl-1-deoxy-Delta(9)-tetrahydrocannabinol (JWH133). Accompanying the increase in proliferation seen with 2-AG is an increase in active ERK1 that is also blocked with SR144528. The RTMGL1 microglial cells, which exist in a primed state, express the CB(1) and CB(2) receptors as demonstrated by reverse transcription-polymerase chain reaction and immunostaining. The CB(2) receptor in untreated cells is expressed both at the cell surface and internally, and exposure of the cells to 2-AG significantly increases receptor internalization. These data suggest that 2-AG activation of CB(2) receptors may contribute to the proliferative response of microglial cells, as occurs in neurodegenerative disorders.

Distinct Expression Profiles of the Peripheral Cannabinoid Receptor in Lymphoid Tissues Depending on Receptor Activation Status

Using two distinct anti-CB2 receptor Abs, we investigated the expression patterns of the peripheral cannabinoid receptor CB2 in human secondary lymphoid organs. Immunohistochemical analysis using an N-terminal specific anti-CB2 Ab revealed high protein expression in the germinal centers (GCs) of secondary follicles. A C-terminal specific anti-CB2 Ab, which only recognizes a nonphosphorylated inactive receptor, showed positivity in the mantle zones (MZs) and marginal zones (MGZs) of the secondary follicles where resting cells reside, and in the primary follicles. In contrast, no positivity was observed in GCs using the C-terminal Ab, suggesting that active CB2 receptors are mainly present on cells in the GCs. Dual immunohistochemical analysis revealed that B lymphocytes express the CB2 protein abundantly. In contrast to B cells in the MZ or MGZ, CB2-expressing cells in the GCs coexpress the costimulatory membrane protein CD40, which is mainly expressed in the GCs and at very low levels in the MZs and MGZs and the proliferation marker Ki-67. Using the human Raji B cell line as a model, we demonstrate in a transwell assay that moderate migration occurs upon stimulation of the CB2 receptor with the endocannabinoid 2-arachidonoylglycerol, which is enhanced by CD40 costimulation. Our findings, that GC-related cells express active CB2 and that CB2-dependent migration requires CD40 costimulation, suggest that CB2 is involved in B cell activation.

Cannabinoids and neuroinflammation

Growing evidence suggests that a major physiological function of the cannabinoid signaling system is to modulate neuroinflammation. This review discusses the anti-inflammatory properties of cannabinoid compounds at molecular, cellular and whole animal levels, first by examining the evidence for anti-inflammatory effects of cannabinoids obtained using in vivo animal models of clinical neuroinflammatory conditions, specifically rodent models of multiple sclerosis, and second by describing the endogenous cannabinoid (endocannabinoid) system components in immune cells. Our aim is to identify immune functions modulated by cannabinoids that could account for their anti-inflammatory effects in these animal models.

Cannabinoid pharmacology in the cardiovascular system: potential protective mechanisms through lipid signalling

Cannabinoids include not only plant-derived compounds (of which delta9-tetrahydrocannabinol is the primary psychoactive ingredient of cannabis), but also synthetic agents and endogenous substances termed endocannabinoids which include anandamide (2-arachidonoylethanolamide) and 2-arachidonoylglycerol. Cannabinoids act on specific, G-protein-coupled, receptors which are currently divided into two types, CB1 and CB2. Relatively selective agonists and antagonists for these receptors have been developed, although one agent (SR141716A) widely used as an antagonist at CB1 receptors has non-cannabinoid receptor-mediated effects at concentrations which are often used to define the presence of the CB1 receptor. Both cannabinoid receptors are primarily coupled to Gi/o proteins and act to inhibit adenylyl cyclase. Stimulation of CB1 receptors also modulates the activity of K+ and Ca2+ channels and of protein kinase pathways including protein kinase B (Akt) which might mediate effects on apoptosis. CB, receptors may activate the extracellular signal-regulated kinase cascade through ceramide signalling. Cannabinoid actions on the cardiovascular system have been widely interpreted as being mediated by CB1 receptors although there are a growing number of observations, particularly in isolated heart and blood vessel preparations, that suggest that other cannabinoid receptors may exist. Interestingly, the currently identified cannabinoid receptors appear to be related to a wider family of lipid receptor, those for the lysophospholipids, which are also linked to Gi/o protein signalling. Anandamide also activates vanilloid VR1 receptors on sensory nerves and releases the vasoactive peptide, calcitonin gene-related peptide (CGRP), which brings about vasodilatation through its action on CGRP receptors. Current evidence suggests that endocannabinoids have important protective roles in pathophysiological conditions such as shock and myocardial infarction. Therefore, their cardiovascular effects and the receptors mediating them are the subject of increasing investigative interest.

The endocannabinoid system: a general view and latest additions

After the discovery, in the early 1990s, of specific G-protein-coupled receptors for marijuana's psychoactive principle Delta(9)-tetrahydrocannabinol, the cannabinoid receptors, and of their endogenous agonists, the endocannabinoids, a decade of investigations has greatly enlarged our understanding of this altogether new signalling system. Yet, while the finding of the endocannabinoids resulted in a new effort to reveal the mechanisms regulating their levels in the brain and peripheral organs under physiological and pathological conditions, more endogenous substances with a similar action, and more molecular targets for the previously discovered endogenous ligands, anandamide and 2-arachidonoylglycerol, or for some of their metabolites, were being proposed. As the scenario becomes subsequently more complicated, and the experimental tasks to be accomplished correspondingly more numerous, we briefly review in this article the latest 'additions' to the endocannabinoid system together with earlier breakthroughs that have contributed to our present knowledge of the biochemistry and pharmacology of the endocannabinoids.

In vivo pharmacological actions of two novel inhibitors of anandamide cellular uptake

Two inhibitors of the cellular uptake of the endocannabinoid anandamide, (R)-N-oleoyl-(1'-hydroxybenzyl)-2'-ethanolamine and (S)-N-oleoyl-(1'-hydroxybenzyl)-2'-ethanolamine (OMDM-1 and OMDM-2, respectively), were recently synthesized, and their in vitro pharmacological activity described. Here we have assessed their activity in two typical pharmacological responses of cannabimimetic compounds. We first examined whether these compounds exert any effect per se on locomotion and pain perception in rats, and/or enhance the effects of anandamide on these two processes. We compared the effects of the novel compounds with those produced by a previously developed selective inhibitor, N-arachidonoyl-(2-methyl-4-hydroxyphenyl)amine (VDM-11). When assayed alone, OMDM-1 and OMDM-2 (1-10 mg/kg, i.p.) did not affect any of the five motor parameters under investigation, although the former compound exhibited a trend for the inhibition of ambulation, fast movements, and speed in rats. OMDM-2 and, to a lesser extent, VDM-11 (5 mg/kg, i.p.) enhanced the motor-inhibitory effects of a noneffective dose (2 mg/kg, i.p.) of anandamide, while OMDM-1 did not. In a typical test of acute analgesia, OMDM-2 and VDM-11 (1-10 mg/kg, i.p.), but not OMDM-1, significantly enhanced the time spent by rats on a "hot plate." However, the same compounds (5 mg/kg, i.p.) did not enhance the analgesic effect of a subeffective dose (2 mg/kg, i.p.) of anandamide, whereas OMDM-1 exerted a strong trend towards potentiation (P=0.06). We next explored the possible use of the two novel compounds in a pathological condition. Thus, we determined if, like other previously developed anandamide reuptake inhibitors, OMDM-1 and OMDM-2 inhibit spasticity in an animal model of multiple sclerosis-the chronic relapsing experimental allergic encephalomyelitis in mice. As previously shown with a higher dose of VDM-11, both novel compounds (5 mg/kg, i.v.) significantly reduced spasticity of the hindlimb in mice with chronic relapsing experimental allergic encephalomyelitis. We suggest that OMDM-1 and, particularly, OMDM-2 are useful pharmacological tools for the study of the (patho)physiological role of the anandamide cellular uptake process, and represent unique templates for the development of new antispastic drugs.

Lipopolysaccharide induces anandamide synthesis in macrophages via CD14/MAPK/phosphoinositide 3-kinase/NF-kappaB independently of platelet-activating factor

Macrophage-derived endocannabinoids have been implicated in endotoxin (lipopolysaccharide (LPS))-induced hypotension, but the endocannabinoid involved and the mechanism of its regulation by LPS are unknown. In RAW264.7 mouse macrophages, LPS (10 ng/ml) increases anandamide (AEA) levels >10-fold via CD14-, NF-kappaB-, and p44/42-dependent, platelet-activating factor-independent activation of the AEA biosynthetic enzymes, N-acyltransferase and phospholipase D. LPS also induces the AEA-degrading enzyme fatty acid amidohydrolase (FAAH), and inhibition of FAAH activity potentiates, whereas actinomycin D or cycloheximide blocks the LPS-induced increase in AEA levels and N-acyltransferase and phospholipase D activities. In contrast, cellular levels of the endocannabinoid 2-arachidonoylglycerol (2-AG) are unaffected by LPS but increased by platelet-activating factor. LPS similarly induces AEA, but not 2-AG, in mouse peritoneal macrophages where basal AEA levels are higher, and the LPS-stimulated increase in AEA is potentiated in cells from FAAH-/- as compared with FAAH+/+ mice. Intravenous administration of 107 LPS-treated mouse macrophages to anesthetized rats elicits hypotension, which is much greater in response to FAAH-/- than FAAH+/+ cells and is susceptible to inhibition by SR141716, a cannabinoid CB1 receptor antagonist. We conclude that AEA and 2-AG synthesis are differentially regulated in macrophages, and AEA rather than 2-AG is a major contributor to LPS-induced hypotension.

Uptake and metabolism of [3H]anandamide by rabbit platelets. Lack of transporter?

Anandamide is an endogenous ligand for cannabinoid receptor and its protein-mediated transport across cellular membranes has been demonstrated in cells derived from brain as well as in cells of the immune system. This lipid is inactivated via intracellular degradation by a fatty acid amidohydrolase (FAAH). In the present study, we report that rabbit platelets, in contrast to human platelets, do not possess a carrier-mediated mechanism for the transport of [3H]anandamide into the cell, i.e. cellular uptake was not temperature dependent and its accumulation was not saturable. This endocannabinoid appears to enter the cell by simple diffusion. Once taken up by rabbit platelets, [3H]anandamide was rapidly metabolized into compounds which were secreted into the medium. Small amounts of free arachidonic acid as well as phospholipids were amongst the metabolic products. FAAH inhibitors did not decrease anandamide uptake, whereas these compounds inhibited anandamide metabolism. In conclusion, anandamide is rapidly taken up by rabbit platelets and metabolized mainly into water-soluble metabolites. Interestingly, the present study also suggests the absence of a transporter for anandamide in these cells.

Inhibition of C6 glioma cell proliferation by anandamide, 1-arachidonoylglycerol, and by a water soluble phosphate ester of anandamide: variability in response and involvement of arachidonic acid

It has previously been shown that the endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG) inhibit the proliferation of C6 glioma cells in a manner that can be prevented by a combination of capsazepine (Caps) and cannabinoid (CB) receptor antagonists. It is not clear whether the effect of 2-AG is due to the compound itself, due to the rearrangement to form 1-arachidonoylglycerol (1-AG) or due to a metabolite. Here, it was found that the effects of 2-AG can be mimicked with 1-AG, both in terms of its potency and sensitivity to antagonism by Caps and CB receptor antagonists. In order to determine whether the effect of Caps could be ascribed to actions upon vanilloid receptors, the effect of a more selective vanilloid receptor antagonist, SB366791 was investigated. This compound inhibited capsaicin-induced Ca(2+) influx into rVR1-HEK293 cells with a pK(B) value of 6.8+/-0.3. The combination of SB366791 and CB receptor antagonists reduced the antiproliferative effect of 1-AG, confirming a vanilloid receptor component in its action. 1-AG, however, showed no direct effect on Ca(2+) influx into rVR1-HEK293 cells indicative of an indirect effect upon vanilloid receptors. Identification of the mechanism involved was hampered by a large inter-experimental variation in the sensitivity of the cells to the antiproliferative effects of 1-AG. A variation was also seen with anandamide, which was not a solubility issue, since its water soluble phosphate ester showed the same variability. In contrast, the sensitivity to methanandamide, which was not sensitive to antagonism by the combination of Caps and CB receptor antagonists, but has similar physicochemical properties to anandamide, did not vary between experiments. This variation greatly reduces the utility of these cells as a model system for the study of the antiproliferative effects of anandamide. Nevertheless, it was possible to conclude that the antiproliferative effects of anandamide were not solely mediated by either its hydrolysis to produce arachidonic acid or its CB receptor-mediated activation of phospholipase A(2) since palmitoyltrifluoromethyl ketone did not prevent the response to anandamide. The same result was seen with the fatty acid amide hydrolase inhibitor palmitoylethylamide. Increasing intracellular arachidonic acid by administration of arachidonic acid methyl ester did not affect cell proliferation, and the modest antiproliferative effect of umbelliferyl arachidonate was not prevented by a combination of Caps and CB receptor antagonists.

Endocannabinoid signalling in the blood of patients with schizophrenia

AIM

To test the hypothesis that schizophrenia might be associated with alterations of the endogenous cannabinoid system in human blood.

RESULTS

Blood from 20 healthy volunteers and 12 patients with schizophrenia, 5 of which both before and after a successful antipsychotic treatment, was analysed for: 1) the amounts of the endocannabinoid anandamide; 2) the levels of cannabinoid CB1 and CB2 receptor mRNAs, and 3) the levels of the mRNA encoding the enzyme fatty acid amide hydrolase (FAAH), responsible for anandamide degradation. The amounts of anandamide were significantly higher in the blood of patients with acute schizophrenia than in healthy volunteers (7.79 +/- 0.50 vs. 2.58 +/- 0.28 pmol/ml). Clinical remission was accompanied by a significant decrease of the levels of anandamide (3.88 +/- 0.72 pmol/ml) and of the mRNA transcripts for CB2 receptors and FAAH.

CONCLUSION

These findings indicate that endocannabinoid signalling might be altered during the acute phase of schizophrenia not only in the central nervous system but also in the blood. These changes might be related to the several immunological alterations described in schizophrenia.

Endocannabinoids and related fatty acid amides, and their regulation, in the salivary glands of the lone star tick

The salivary glands and saliva from the lone star tick Amblyomma americanum (L.) were analyzed for the presence of the two endogenous agonists of cannabinoid receptors, N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol (2-AG), as well as of the anandamide congener, N-palmitoylethanolamine (PEA), an anti-inflammatory and analgesic mediator that is inactive at cannabinoid receptors. Two very sensitive mass-spectrometric techniques were used for this purpose. Both 2-AG and PEA, as well as other N-acylethanolamines (NAEs), were identified in salivary glands, but anandamide was below detection. The levels of 2-AG were considerably higher in the salivary glands of partially fed than replete females. Ex vivo gland stimulation with arachidonic acid increased the levels of 2-AG, but not of PEA or other NAEs, and caused the formation of anandamide and of the potent analgesic compound N-arachidonoylglycine. Instead, the amounts of anandamide, 2-AG and PEA were not influenced by treatment of salivary glands with dopamine, which stimulates saliva secretion. The possible biosynthetic precursors of anandamide, PEA and other NAEs were also detected in salivary glands, whereas only PEA was detected in tick saliva. These data demonstrate for the first time that the salivary glands of an obligate ectoparasite species can make endocannabinoids and/or related congeners with analgesic and anti-inflammatory activity, which possibly participate in the inhibition of the host defense reactions.

2-arachidonoylglycerol induces the migration of HL-60 cells differentiated into macrophage-like cells and human peripheral blood monocytes through the cannabinoid CB2 receptor-dependent mechanism

2-Arachidonoylglycerol is an endogenous ligand for the cannabinoid receptors (CB1 and CB2) and has been shown to exhibit a variety of cannabimimetic activities in vitro and in vivo. Recently, we proposed that 2-arachidonoylglycerol is the true endogenous ligand for the cannabinoid receptors, and both receptors (CB1 and CB2) are primarily 2-arachidonoylglycerol receptors. The CB1 receptor is assumed to be involved in the attenuation of neurotransmission. On the other hand, the physiological roles of the CB2 receptor, which is abundantly expressed in several types of leukocytes such as macrophages, still remain unknown. In this study, we examined the effects of 2-arachidonoylglycerol on the motility of HL-60 cells differentiated into macrophage-like cells. We found that 2-arachidonoylglycerol induces the migration of differentiated HL-60 cells. The migration induced by 2-arachidonoylglycerol was blocked by treatment of the cells with either SR144528, a CB2 receptor antagonist, or pertussis toxin, suggesting that the CB2 receptor and Gi/Go are involved in the 2-arachidonoylglycerol-induced migration. Several intracellular signaling molecules such as Rho kinase and mitogen-activated protein kinases were also suggested to be involved. In contrast to 2-arachidonoylglycerol, anandamide, another endogenous cannabinoid receptor ligand, failed to induce the migration. The 2-arachidonoylglycerol-induced migration was also observed for two other types of macrophage-like cells, the U937 cells and THP-1 cells, as well as human peripheral blood monocytes. These results strongly suggest that 2-arachidonoylglycerol induces the migration of several types of leukocytes such as macrophages/monocytes through a CB2 receptor-dependent mechanism thereby stimulating inflammatory reactions and immune responses.

Cannabinoid modulation of peripheral autonomic and sensory neurotransmission

Cannabinoids are cell membrane-derived signalling molecules that are released from nerves, blood cells and endothelial cells, and have diverse biological effects. They act at two distinct types of G-protein-coupled receptors, cannabinoid CB(1) and CB(2) receptors. Cannabinoid CB(1) receptors are highly localised in the central nervous system and are also found in some peripheral tissues, and cannabinoid CB(2) receptors are found outside the central nervous system, in particular in association with immune tissues. Novel actions of cannabinoids at non-CB(1) non-CB(2) cannabinoid-like receptors and vanilloid VR1 receptors have also recently been described. There is growing evidence that, among other roles, cannabinoids can act at prejunctional sites to modulate peripheral autonomic and sensory neurotransmission, and the present article is aimed at providing an overview of this. Inhibitory cannabinoid CB(1) receptors are expressed on the peripheral terminals of autonomic and sensory nerves. The role of cannabinoid receptor ligands in modulation of sensory neurotransmission is complex, as certain of these (anandamide, an "endocannabinoid", and N-arachidonoyl-dopamine, an "endovanilloid") also activate vanilloid VR1 receptors (coexpressed with cannabinoid CB(1) receptors), which excites sensory nerves and causes a release of sensory neurotransmitter. The fact that the activities of anandamide and N-arachidonoyl-dopamine span two distinct receptor families raises important questions about cannabinoid/vanilloid nomenclature, and as both compounds are structurally related to the archetypal vanilloid capsaicin, all three are arguably members of the same family of signalling molecules. Anandamide is released from nerves, but unlike classical neurotransmitters, it is not stored in and released from nerve vesicles, but is released on demand from the nerve cell membrane. In the central nervous system, cannabinoids function as retrograde signalling molecules, inhibiting via presynaptic cannabinoid CB(1) receptors the release of classical transmitter following release from the postsynaptic cell. At the neuroeffector junction, it is more likely that cannabinoids are released from prejunctional sites, as the neuroeffector junction is wide in some peripheral tissues and cannabinoids are rapidly taken up and inactivated. Understanding the actions of cannabinoids as modulators of peripheral neurotransmission is relevant to a variety of biological systems and possibly their disorders.

Novel selective and metabolically stable inhibitors of anandamide cellular uptake

Novel aromatic analogues of N-oleoylethanolamine and N-arachidonoylethanolamine (anandamide, AEA) were synthesized and, based on the capability of similar compounds to interact with proteins of the endocannabinoid and endovanilloid signaling systems, were tested on: (i) cannabinoid CB(1) and CB(2) receptors; (ii) vanilloid VR1 receptors; (iii) anandamide cellular uptake (ACU); and (iv) the fatty acid amide hydrolase (FAAH). The (R)- and, particularly, the (S)-1'-(4-hydroxybenzyl) derivatives of N-oleoylethanolamine and AEA (OMDM-1, OMDM-2, OMDM-3, and OMDM-4) inhibited to a varied extent ACU in RBL-2H3 cells (K(i) ranging between 2.4 and 17.7 micro M), the oleoyl analogues (OMDM-1 and OMDM-2, K(i) 2.4 and 3.0 micro M, respectively) being 6- to 7-fold more potent than the arachidonoyl analogues (OMDM-3 and OMDM-4). These four compounds exhibited: (i) poor affinity for either CB(1) (K(i)> or = 5 micro M) or CB(2) (K(i)>10 micro M) receptors in rat brain and spleen membranes, respectively; (ii) almost no activity at vanilloid receptors in the intracellular calcium assay carried out with intact cells over-expressing the human VR1 (EC(50)> or = 10 micro M); and (iii) no activity as inhibitors of FAAH in N18TG2 cell membranes (K(i)>50 micro M). The oleoyl- and arachidonoyl-N'-(4-hydroxy-3-methoxybenzyl)hydrazines (OMDM-5 and OMDM-6), inhibited ACU (K(i) 4.8 and 7.0 micro M, respectively), and were more potent as VR1 agonists (EC(50) 75 and 50nM, respectively), weakly active as CB(1) receptor ligands (K(i) 4.9 and 3.2 micro M, respectively), and inactive as CB(2) ligands (K(i)>5 micro M) as well as on FAAH (K(i)> or = 40 micro M). In conclusion, we report two novel potent and selective inhibitors of ACU (OMDM-1 and OMDM-2) and one "hybrid" agonist of CB(1) and VR1 receptors (OMDM-6). Unlike other compounds of the same type, OMDM-1, OMDM-2, and OMDM-6 were very stable to enzymatic hydrolysis by rat brain homogenates.

Therapeutic potential of cannabinoids in CNS disease

The major psychoactive constituent of Cannabis sativa, delta(9)-tetrahydrocannabinol (delta(9)-THC), and endogenous cannabinoid ligands, such as anandamide, signal through G-protein-coupled cannabinoid receptors localised to regions of the brain associated with important neurological processes. Signalling is mostly inhibitory and suggests a role for cannabinoids as therapeutic agents in CNS disease where inhibition of neurotransmitter release would be beneficial. Anecdotal evidence suggests that patients with disorders such as multiple sclerosis smoke cannabis to relieve disease-related symptoms. Cannabinoids can alleviate tremor and spasticity in animal models of multiple sclerosis, and clinical trials of the use of these compounds for these symptoms are in progress. The cannabinoid nabilone is currently licensed for use as an antiemetic agent in chemotherapy-induced emesis. Evidence suggests that cannabinoids may prove useful in Parkinson's disease by inhibiting the excitotoxic neurotransmitter glutamate and counteracting oxidative damage to dopaminergic neurons. The inhibitory effect of cannabinoids on reactive oxygen species, glutamate and tumour necrosis factor suggests that they may be potent neuroprotective agents. Dexanabinol (HU-211), a synthetic cannabinoid, is currently being assessed in clinical trials for traumatic brain injury and stroke. Animal models of mechanical, thermal and noxious pain suggest that cannabinoids may be effective analgesics. Indeed, in clinical trials of postoperative and cancer pain and pain associated with spinal cord injury, cannabinoids have proven more effective than placebo but may be less effective than existing therapies. Dronabinol, a commercially available form of delta(9)-THC, has been used successfully for increasing appetite in patients with HIV wasting disease, and cannabinoid receptor antagonists may reduce obesity. Acute adverse effects following cannabis usage include sedation and anxiety. These effects are usually transient and may be less severe than those that occur with existing therapeutic agents. The use of nonpsychoactive cannabinoids such as cannabidiol and dexanabinol may allow the dissociation of unwanted psychoactive effects from potential therapeutic benefits. The existence of other cannabinoid receptors may provide novel therapeutic targets that are independent of CB(1) receptors (at which most currently available cannabinoids act) and the development of compounds that are not associated with CB(1) receptor-mediated adverse effects. Further understanding of the most appropriate route of delivery and the pharmacokinetics of agents that act via the endocannabinoid system may also reduce adverse effects and increase the efficacy of cannabinoid treatment. This review highlights recent advances in understanding of the endocannabinoid system and indicates CNS disorders that may benefit from the therapeutic effects of cannabinoid treatment. Where applicable, reference is made to ongoing clinical trials of cannabinoids to alleviate symptoms of these disorders.

Endocannabinoids and their actions

Endocannabinoids are a new class of lipid mediators, which includes amides and esters of long-chain polyunsaturated fatty acids. Anandamide (I) and 2-arachidonoylglycerol (II) are the main endogenous agonists of cannabinoid receptors, able to mimic several pharmacological effects of delta 9-tetrahydrocannabinol (III), the active principle of Cannabis sativa preparations such as hashish and marijuana. The pathways leading to the synthesis and release of anandamide and 2-arachidonoylglycerol from neuronal and nonneuronal cells are rather uncertain. Instead, evidence has accumulated showing that the activity of these compounds at their specific receptors is limited by cellular uptake through a specific membrane transporter, followed by intracellular degradation by a fatty acid amide hydrolase. Here, the endocannabinoids and the endocannabinoid-like compounds most relevant for human physiology will be discussed, along with the synthetic and degradative pathways of anandamide and 2-arachidonoylglycerol and their molecular targets on the cell surface. The main actions of the endocannabinoids in human cells and tissues will also be reviewed, focusing on the activities most recently discovered in the central nervous system and in the periphery.

Plant-derived, synthetic and endogenous cannabinoids as neuroprotective agents. Non-psychoactive cannabinoids, 'entourage' compounds and inhibitors of N-acyl ethanolamine breakdown as therapeutic strategies to avoid pyschotropic effects

There is good evidence that plant-derived and synthetic cannabinoids possess neuroprotective properties. These compounds, as a result of effects upon CB(1) cannabinoid receptors, reduce the release of glutamate, and in addition reduce the influx of calcium following NMDA receptor activation. The major obstacle to the therapeutic utilization of such compounds are their psychotropic effects, which are also brought about by actions on CB(1) receptors. However, synthesis of the endogenous cannabinoids anandamide and 2-arachidonoylglycerol, which also have neuroprotective properties, are increased under conditions of severe inflammation and ischemia, raising the possibility that compounds that prevent their metabolism may be of therapeutic utility without having the drawback of producing psychotropic effects. In this review, the evidence indicating neuroprotective actions of plant-derived, synthetic and endogenous cannabinoids is presented. In addition, the pharmacological properties of endogenous anandamide-related compounds that are not active upon cannabinoid receptors, but which are also produced during conditions of severe inflammation and ischemia and may contribute to a neuroprotective action are reviewed.

Cell signaling by endocannabinoids and their congeners: questions of selectivity and other challenges

The major endocannabinoids, anandamide (N-arachidonoylethanolamide, 20:4n-6 N-acylethanolamine) and 2-arachidonoylglycerol (2-AG) are structurally and functionally similar, but they are produced by different metabolic pathways and their levels must therefore be regulated by different mechanisms. Both endocannabinoids are accompanied by cannabinoid receptor-inactive, saturated and mono- or di-unsaturated congeners which can influence their metabolism and function. Here we review published data on the presence and production of anandamide and 2-AG and their congeners in mammalian cells and discuss this information in terms of their proposed signaling functions.

Chemical stability of 2-arachidonylglycerol under biological conditions

Recent evidence indicates that 2-arachidonylglycerol (2-AG) is a potent and specific ligand for the central and peripheral cannabinoid receptors. Therefore, the chemical stability of this molecule under biological conditions is of interest. A method for the isolation and detection of 2-AG using HPLC with evaporative light scattering detection is described. The method provides an extraction recovery from aqueous media of 78%, and a limit of detection of 60 ng on column. Incubation of 2-AG in culture medium or biological buffers indicated that it is stable to oxidation and ester hydrolysis for up to 6 h at 37 degrees C. However, gradual disappearance of the compound was noted due to adherence to glass and plastic surfaces. During incubation in RPMI culture medium, 2-AG rearranged to 1(3)-arachidonylglycerol (1(3)-AG) in a first order process with a half-life of 10 min in the absence of serum and 2.3 min in the presence of 10% fetal calf serum. Further studies indicated that the acyl migration reaction is base catalyzed (k(cat)=78,000/min M), and that the reaction is affected slightly by changes in buffer (Tris) concentration and not at all by changes in ionic strength. The results indicate that 2-AG is readily converted to 1(3)-AG under conditions commonly used to study receptor-ligand interactions, findings that have significant implications for the interpretation of relative ligand potency between the two isomers.

Cannabinoid modulation of sensory neurotransmission via cannabinoid and vanilloid receptors: roles in regulation of cardiovascular function

Capsaicin-sensitive sensory nerves are widely distributed in the cardiovascular system. They are activated by a variety of physical and chemical stimuli, characteristically by capsaicin acting via the vanilloid receptor VR1, and have a role in the regulation of peripheral vascular resistance and maintenance of homeostasis via their afferent and efferent functions. Cannabinoids, a recently discovered family of extracellular signalling molecules, can act at cannabinoid (CB) receptors expressed on sensory nerves, to cause inhibition of sensory neurotransmitter release. There is recent evidence, however, that anandamide, an endogenous cannabinoid, can activate VR1, coexpressed with CB receptors on the same sensory nerve terminals, causing a release of sensory neurotransmitter, vasorelaxation and hypotension. Hence, anandamide can elicit opposite actions, inhibition via CB receptors and excitation via VR1, on sensory neurotransmission. The possible biological significance of this is discussed.

Regulation of anandamide tissue levels by N-arachidonylglycine

N-arachidonylglycine (NAGly), the carboxylic analog of the endocannabinoid anandamide, occurs in rat and bovine brain as well as in peripheral sites and shows activity against tonic, formalin-induced pain. It was also observed, using cell membrane preparations, that it inhibits the hydrolytic activity of fatty acid amide hydrolase (FAAH) on anandamide (N-arachidonylethanolamide). These data suggested that it may serve as an endogenous regulator of tissue anandamide concentrations. In this report, we show findings derived from mass spectrometric analyses, indicating that blood levels of anandamide in rats given 10 mg/kg p.o. of NAGly were increased significantly by more than 9-fold when compared with vehicle-treated controls. In vitro evidence in RAW 264.7 cells using a deuterium-labeled NAGly demonstrated that it was not a precursor or source of arachidonic acid for the observed 50% rise in anandamide levels, suggesting that the increase was due to some effect other than increased biosynthesis of anandamide. Moreover, the findings presented here suggest that NAGly can serve as a model for the design of agents to provide pharmacological control of tissue anandamide concentrations.

Acute neuronal injury, excitotoxicity, and the endocannabinoid system

The endocannabinoid system is a valuable target for drug discovery, because it is involved in the regulation of many cellular and physiological functions. The endocannabinoid system constitutes the endogenous lipids anandamide, 2-arachidonoylglycerol and noladin ether, and the cannabinoid CB1 and CB2 receptors as well as the proteins for their inactivation. It is thought that (endo)cannabinoid-based drugs may potentially be useful to reduce the effects of neurodegeneration. This paper reviews recent developments in the endocannabinoid system and its involvement in neuroprotection. Exogenous (endo)cannabinoids have been shown to exert neuroprotection in a variety of in vitro and in vivo models of neuronal injury via different mechanisms, such as prevention of excitotoxicity by CB1-mediated inhibition of glutamatergic transmission, reduction of calcium influx, and subsequent inhibition of deleterious cascades, TNF-alpha formation, and anti-oxidant activity. It has been suggested that the release of endogenous endocannabinoids during neuronal injury might be a protective response. However, several observations indicate that the role of the endocannabinoid system as a general endogenous protection system is questionable. The data are critically reviewed and possible explanations are given.

Presence and regulation of the endocannabinoid system in human dendritic cells

Cannabinoid receptors and their endogenous ligands, the endocannabinoids, have been detected in several blood immune cells, including monocytes/macrophages, basophils and lymphocytes. However, their presence in dendritic cells, which play a key role in the initiation and development of the immune response, has never been investigated. Here we have analyzed human dendritic cells for the presence of the endocannabinoids, anandamide and 2-arachidonoylglycerol (2-AG), the cannabinoid CB1 and CB2 receptors, and one of the enzymes mostly responsible for endocannabinoid hydrolysis, the fatty acid amide hydrolase (FAAH). By using a very sensitive liquid chromatography-atmospheric pressure chemical ionization-mass spectrometric (LC-APCI-MS) method, lipids extracted from immature dendritic cells were shown to contain 2-AG, anandamide and the anti-inflammatory anandamide congener, N-palmitoylethanolamine (PalEtn) (2.1 +/- 1.0, 0.14 +/- 0.02 and 8.2 +/- 3.9 pmol x 10(-7) cells, respectively). The amounts of 2-AG, but not anandamide or PalEtn, were significantly increased following cell maturation induced by bacterial lipopolysaccharide (LPS) or the allergen Der p 1 (2.8- and 1.9-fold, respectively). By using both RT-PCR and Western immunoblotting, dendritic cells were also found to express measurable amounts of CB1 and CB2 receptors and of FAAH. Cell maturation did not consistently modify the expression of these proteins, although in some cell preparations a decrease of the levels of both CB1 and CB2 mRNA transcripts was observed after LPS stimulation. These findings demonstrate for the first time that the endogenous cannabinoid system is present in human dendritic cells and can be regulated by cell activation.

From cannabis to cannabinergics: new therapeutic opportunities

The molecular basis of cannabinoid activity is better understood since the discovery of the CB(1) receptor in the mammalian brain and the CB(2) receptor in peripheral tissues. Subsequently, an endogenous CB(1) receptor ligand, arachidonylethanolamide (anandamide), was isolated from porcine brain and shown to be metabolized by the enzyme arachidonylethanolamide amidohydrolase or fatty acid amide hydrolase. Recently, we have characterized a reuptake system for the transport of anandamide across the cell membrane, and have shown that selective inhibition of this transporter is associated with analgesia and peripheral vasodilation. The four cannabinoid system proteins, including the CB(1) and CB(2) receptors, fatty acid amide hydrolase, and the anandamide transporter, are excellent targets for the development of novel medications for various conditions, including pain, immunosuppression, peripheral vascular disease, appetite enhancement or suppression, and motor disorders. During the last decade, numerous selective ligands for each of these proteins were designed and synthesized. Many of these agents serve as important molecular probes, providing structural information about their binding sites, as well as pharmacological tools imparting information about the roles of their targets in physiological and disease states. All of the above compounds that modulate the functions of the endocannabinoid system can be collectively described under the term cannabinergics, regardless of chemical classification or type of resultant pharmacological action.

Endocannabinoid hydrolases

Endocannabinoids (endogenous ligands of cannabinoid receptors) such as anandamide (N-arachidonoylethanolamine) and 2-arachidonoylglycerol (2-AG) are inactivated upon enzymatic hydrolysis. Recent progress in the enzymological and molecular biological studies on the 'endocannabinoid hydrolases' is reviewed in this article. Anandamide is hydrolyzed to arachidonic acid and ethanolamine by a membrane-bound amidase generally referred to as fatty acid amide hydrolase (FAAH). This enzyme has a broad substrate specificity, hydrolyzing oleamide (an endogenous sleep-inducing factor) and 2-AG as well as anandamide. cDNA cloning revealed that FAAH is composed of 579 amino acids and belongs to the amidase signature family. A serine residue functioning as a catalytic nucleophile and several other catalytically important residues were identified in its primary structure. Furthermore, recent generation and analysis of the FAAH gene-deficient mice demonstrated the central role of this enzyme in the metabolism of anandamide. Alternatively, an amidase, which is distinct from FAAH but also hydrolyzing anandamide and other N-acylethanolamines at acidic pH, was identified in human megakaryoblastic cells and rat organs such as lung and spleen. As for the 2-AG hydrolysis, in addition to the known monoacylglycerol lipase, other esterases and FAAH may be involved.

Cardiovascular effects of cannabinoids

The prototypic endocannabinoid, anandamide, and synthetic analogues have been shown to elicit pressor and depressor effects, bradycardia, vasorelaxation, and inhibition of neurotransmission in the central and peripheral nervous systems. Cannabinoid-mediated inhibition of neurotransmission is mediated by inhibition of voltage-gated Ca(2+) channels and adenylyl cyclase and activation of inwardly rectifying K(+) channels. The precise mechanisms underlying the vasorelaxant actions of cannabinoids are currently unclear, but might involve both receptor-dependent and -independent and endothelium-dependent and -independent pathways. Mechanisms proposed have included the release of endothelial autacoids, activation of myoendothelial gap junctions, activation of the Na(+) pump, activation of K(+) channels, inhibition of Ca(2+) channels, and activation of vanilloid receptors, leading to the release of sensory neurotransmitters. Pathophysiologically, the vasodilator actions of endocannabinoids have been implicated in the hypotension associated with both septic and haemorrhagic shock, but their physiological significance remains to be determined.

Effect of the cannabinoid receptor ligand, WIN 55,212-2, on superoxide anion and TNF-alpha production by human mononuclear cells

Cannabinoids are known to downregulate immune response but the role for cannabinoid receptors in cannabinoid-induced immunosuppression is still unclear. To address this question, the interference of CB1 and CB2 receptor antagonists with the inhibition of TNF-alpha production by synthetic cannabinoid WIN 55,212-2 was studied using human peripheral blood mononuclear cells (PBMC) in vitro. CB2 (SR 144528) but not CB1 (SR 141716A) receptor antagonist dose dependently interfered with WIN 55,212-2-induced inhibition of TNF-alpha synthesis. Also, WIN 55,212-2 decreased fMLP-induced reactive oxygen species generation in lipopolysaccharide (LPS)-primed PBMC. However, the high concentrations of cannabinoid receptor ligands needed to achieve significant effects suggest that the observed effects may be in part cannabinoid receptor independent.

Cellular transport of anandamide, 2-arachidonoylglycerol and palmitoylethanolamide--targets for drug development?

The endogenous cannabinoid anandamide (AEA) is transported into cells by a temperature-sensitive process of facilitated diffusion. This uptake process has been characterised both biochemically and pharmacologically, and shown to be regulated at least in part by the intracellular metabolism of the accumulated AEA by fatty acid amide hydrolase. In this review, the properties of this transport process are briefly reviewed together with the corresponding transport mechanisms for the related endogenous compounds 2-arachidonoylglycerol and palmitoylethanolamide. In addition, the possibility that these transport mechanisms can be targets for therapeutic strategies aimed at prolonging the effects of the endocannabinoids is discussed.

CB(1) and CB(2) receptor-mediated signalling: a focus on endocannabinoids

The discovery that the major psychoactive component of marijuana activated two G-protein coupled receptors prompted the search for the endogenous cannabinoid ligands now termed endocannabinoids. To date three putative ligands have been isolated, all consisting of arachidonic acid linked to a polar head group. Both synthetic and endogenous cannabinoids have been the focus of extensive study over the past few years. The signalling events produced by endocannabinoids as compared with Delta(9) -THC and synthetic cannabinoids contain many similarities. However, as research focuses more on endogenous ligands the divergence between these classes of compounds grows. This review focuses upon the developments in endocannabinoid signal transduction from receptor-mediated activation of common G-protein linked effector pathways through downstream regulation of gene transcription.

Endocannabinoids, hormone-cytokine networks and human fertility

Anandamide (N -arachidonoylethanolamine, AEA) is a major endocannabinoid, shown to impair mouse pregnancy and embryo development and to induce apoptosis in blastocysts. Here, we review the roles of AEA, of the AEA-binding cannabinoid (CB) receptors, of the selective AEA membrane transporter (AMT), and of the AEA-hydrolyzing enzyme fatty acid amide hydrolase (FAAH), in human gestation. In particular, we discuss the interplay between the endocannabinoid system and the hormone-cytokine array involved in the control of human pregnancy, showing that the endocannabinoids take part in the immunological adaptation occurring during early pregnancy. In this line, we discuss the critical role of FAAH in human peripheral lymphocytes, showing that the expression of this enzyme is regulated by progesterone, Th1 and Th2 cytokines, which also regulate fertility. Moreover, we show that AEA and the other endocannabinoid, 2-arachidonoylglycerol, inhibit the release of the fertility-promoting cytokine leukemia inhibitory factor from human lymphocytes. Taken together, low FAAH and consistently high blood levels of AEA, but not CB receptors or AMT, can be early (<8 weeks of gestation) markers of spontaneous abortion, potentially useful as diagnostic tools for large-scale, routine monitoring of gestation in humans.

Biosynthesis and degradation of anandamide and 2-arachidonoylglycerol and their possible physiological significance

N -arachidonoylethanolamine (anandamide) was the first endogenous cannabinoid receptor ligand to be discovered. Dual synthetic pathways for anandamide have been proposed. One is the formation from free arachidonic acid and ethanolamine, and the other is the formation from N -arachidonoyl phosphatidylethanolamine (PE) through the action of a phosphodiesterase. These pathways, however, do not appear to be able to generate a large amount of anandamide, at least under physiological conditions. The generation of anandamide from free arachidonic acid and ethanolamine is catalyzed by a degrading enzyme anandamide amidohydrolase/fatty acid amide hydrolase operating in reverse and requires large amounts of substrates. As for the second pathway, arachidonic acids esterified at the 1-position of glycerophospholipids, which are mostly esterified at the 2-position, are utilized for the formation of N -arachidonoyl PE, a stored precursor form of anandamide. In fact, the actual levels of anandamide in various tissues are generally low except in a few cases. 2-Arachidonoylglycerol (2-AG) was the second endogenous cannabinoid receptor ligand to be discovered. 2-AG is a degradation product of arachidonic acid-containing glycerophospholipids such as inositol phospholipids. Several investigators have demonstrated that 2-AG is produced in a variety of tissues and cells upon stimulation. 2-AG acts as a full agonist at the cannabinoid receptors (CB1 and CB2). Evidence is gradually accumulating and indicates that 2-AG is the most efficacious endogenous natural ligand for the cannabinoid receptors. In this review, we summarize the tissue levels, biosynthesis, degradation and possible physiological significance of two endogenous cannabimimetic molecules, anandamide and 2-AG.

Endocannabinoids in the immune system and cancer

The present review focuses on the role of the endogenous cannabinoid system in the modulation of immune response and control of cancer cell proliferation. The involvement of cannabinoid receptors, endogenous ligands and enzymes for their biosynthesis and degradation, as well as of cannabinoid receptor-independent events is discussed. The picture arising from the recent literature appears very complex, indicating that the effects elicited by the stimulation of the endocannabinoid system are strictly dependent on the specific compounds and cell types considered. Both the endocannabinoid anandamide and its congener palmitoylethanolamide, exert a negative action in the onset of a variety of parameters of the immune response. However, 2-arachidonoylglycerol appears to be the true endogenous ligand for peripheral cannabinoid receptors, although its action as an immunomodulatory molecule requires further characterization. Modulation of the endocannabinoid system interferes with cancer cell proliferation either by inhibiting mitogenic autocrine/paracrine loops or by directly inducing apoptosis; however, the proapoptotic effect of anandamide is not shared by other endocannabinoids and suggests the involvement of non-cannabinoid receptors, namely the VR1 class of vanilloid receptors. In conclusion, further investigations are needed to elucidate the function of endocannabinoids as immunosuppressant and antiproliferative/cytotoxic agents. The experimental evidence reviewed in this article argues in favor of the therapeutic potential of these compounds in immune disorders and cancer.

The fatty acid amide hydrolase (FAAH)

The fatty acid amide hydrolase (FAAH), is the enzyme responsible for the hydrolysis of anandamide, an endocannabinoid. The FAAH knockout, the assays for FAAH, the activity of its substrates, its reversibility and its cloning from rat, mouse, human, and pig are covered in this review. The conserved regions of FAAH are described in terms of sequence and function, including the domains that contains the serine catalytic nucleophile, the hydrophobic domain important for self-association, the proline rich domain region which may be important for subcellular localization and the fatty acid chain binding domain. The FAAH mouse promoter region was characterized in terms of its transcription start site and its activity in different cell types. The distribution of FAAH in the major organs in the body is described as well as regional distribution in the brain and its correlation with cannabinoid receptors. Since FAAH is recognized as a drug target, a large number of inhibitors have been synthesized and tested since 1994 and these are reviewed in terms of reversibility, potency, and specificity for FAAH.

Activation of PAF receptors results in enhanced synthesis of 2-arachidonoylglycerol (2-AG) in immune cells

The endocannabinoid signaling system is believed to play a down-regulatory role in the control of cell functions. However, little is known about the factors activating endocannabinoid synthesis and which of two known endocannabinoids, 2-arachidonoylglycerol (2-AG) or N-arachidonoylethanolamine (20:4n-6 NAE, anandamide), is of physiological importance. We approached these questions by studying a possible link between cell activation with 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet-activating factor, PAF) and the generation of 2-AG and anandamide in human platelets and mouse P388D1 macrophages. Human platelets responded to stimulation with the production of various 1- and 2-monoacylglycerols, including 2-AG, whereas stimulation of P388D1 macrophages induced the rapid and selective generation of 2-AG, which was immediately released into the medium. The effect of PAF was receptor mediated, as PAF receptor antagonist BN52021 blocked the effect. The treatment did not change the content of anandamide in either macrophages or platelet-rich plasma. The inhibitors of PI- and PC-specific phospholipases C (U73122 and D609) as well as PI3-kinase inhibitor (wortmannin) attenuated PAF-induced 2-AG production in macrophages. These data suggest a direct role for the endocannabinoid system in controlling immune cell activation status and indicate that 2-AG rather than anandamide is the endocannabinoid rapidly produced in response to proinflammatory stimulation of immune cells.

Anandamide induces cardiovascular and respiratory reflexes via vasosensory nerves in the anaesthetized rat

1. We tested the hypothesis that sensory nerves innervating blood vessels play a role in the local and systemic regulation of the cardiovascular and respiratory (CVR) systems. We measured CVR reflexes evoked by administration of anandamide (86 - 863 nmoles) and capsaicin (0.3 - 10 nmoles) into the hindlimb vasculature of anaesthetized rats. 2. Anandamide and capsaicin each caused a rapid dose-dependent reflex fall in blood pressure and an increase in ventilation when injected intra-arterially into the hindlimb. 3. Action of both agonists at the vanilloid receptor (VR1) on perivascular sensory nerves was investigated using capsazepine (1 mg kg(-1) i.a.) a competitive VR1 antagonist, ruthenium red (1 mg kg(-1) i.a.), a non-competitive antagonist at VR1, or a desensitizing dose of capsaicin (200 nmoles i.a.). The cannabinoid receptor antagonist SR141716 (1 mg kg(-1) i.a.) was used to determine agonist activity at the CB(1) receptor. 4. Capsazepine, ruthenium red, or acute VR1 desensitization by capsaicin-pretreatment, markedly attenuated the reflex CVR responses evoked by anandamide and capsaicin (P< 0.05; paired Student's t-test). Blockade of CB(1) had no significant effect on the responses to anandamide. 5. Local sectioning of the femoral and sciatic nerves attenuated CVR responses to anandamide and capsaicin (P< 0.05). Vagotomy or carotid sinus sectioning had no significant effect on anandamide- or capsaicin-induced responses. 6. These data demonstrate that both the endogenous cannabinoid, anandamide, and the vanilloid, capsaicin, evoke CVR reflexes when injected intra-arterially into the rat hindlimb. These responses appear to be mediated reflexly via VR1 located on sensory nerve endings within the hindlimb vasculature.

Long-term inhibition of nitric oxide synthase potentiates effects of anandamide in the rat mesenteric bed

In rat isolated mesenteric beds, anandamide induced a concentration-dependent reduction (0.01-50 microM) of the contractile responses elicited by bolus administration of noradrenaline. The anandamide-induced reductions of noradrenaline responses were unmodified by the in vitro exposure to the nitric oxide synthase (NOS) inhibitor, 100 microM L-N(G)-nitro-L-arginine methyl ester (L-NAME), whereas they were significantly potentiated after the long-term in vivo administration of L-NAME (70 mg/kg/day during 4 weeks). Responses to anandamide were not potentiated and even reduced in mesenteric beds from rats made hypertensive by aortic coarctation. In mesenteric beds isolated from either untreated or in vivo L-NAME treated rats, concentration-response curves to anandamide were significantly attenuated by the non-selective K+ channel blocker tetraethylammonium (TEA) but were not modified by either endothelium removal, or the soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one (ODQ) or the cannabinoid receptor antagonists 6-iodo-2-methyl-1-[2-(4-morpholinyl)ethyl]-1H-indol-3-yl] (4-methoxyphenyl) methanone (AM630) and 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-4-morpholinyl-1H-pyrazole-3-carboxamide (AM281). On the other hand, the vanilloid receptor agonist (E)-N-[4-hydroxy-3-methoxyphenyl)methyl]-8-methyl-6-nonenamide (capsaicin) induced a concentration-dependent inhibition of noradrenaline-induced vasoconstriction, and the vanilloid receptor antagonist N-[2-(4-chlorophenyl)ethyl]-1,3,4,5-tetrahydro-7,8-dihydroxy-2H-2-benzazepine-2-carbothioamide (capsazepine) caused a significant reduction of anandamide-induced responses in mesenteric beds isolated from both control and chronic L-NAME treated rats. The non-metabolizable analogue of anandamide, methanandamide, produced higher reductions of noradrenaline responses than anandamide in mesenteric beds isolated from controls but not from the L-NAME treated rats. Moreover, in mesenteric beds from untreated but not from L-NAME treated rats, the effects of anandamide were significantly potentiated by the inhibitor of endocannabinoid degradation, 200 microM phenylmethylsulphonyl fluoride (PMSF), and by the inhibitor of anandamide uptake, 5 microM (all Z)-N-(4-hydroxyphenyl)-5,8,11,14-eicosatetraenamide (AM404). It is concluded that long-term inhibition of NOS potentiates anandamide-induced relaxations probably through changes in either endocannabinoid metabolism or uptake. A possible compensatory role for endocannabinoids in vascular function in situations in which nitric oxide (NO) synthesis is long-term impaired arises from the present results.

Lipopolysaccharide downregulates fatty acid amide hydrolase expression and increases anandamide levels in human peripheral lymphocytes

Lipopolysaccharide (LPS) increases the levels of the endogenous cannabinoid anandamide (N-arachidonoylethanolamine, AEA) in rat macrophages, but the mechanism responsible for this effect has not been elucidated. Here we demonstrate that LPS enhances the levels of AEA (fourfold over controls) also in human lymphocytes. We show that in these cells LPS inhibits the activity of the AEA-degrading enzyme fatty acid amide hydrolase (FAAH), by downregulating the gene expression at transcriptional level. Lymphocytes have also a specific AEA transporter and a functional CB1 cannabinoid receptor, which were not modulated by LPS. The effect of this endotoxin on FAAH was not mediated by AEA-induced activation of cannabinoid receptors. Conversely, the stimulatory action of LPS on AEA levels might be due to inhibition of FAAH, as suggested by the observation that an increase of AEA amounts was also induced by an irreversible FAAH inhibitor. These results suggest that lymphocytes take part in regulating the peripheral endocannabinoid system and endocannabinoid homeostasis.

Fatty acid amide hydrolase: biochemistry, pharmacology, and therapeutic possibilities for an enzyme hydrolyzing anandamide, 2-arachidonoylglycerol, palmitoylethanolamide, and oleamide

Fatty acid amide hydrolase (FAAH) is responsible for the hydrolysis of a number of important endogenous fatty acid amides, including the endogenous cannabimimetic agent anandamide (AEA), the sleep-inducing compound oleamide, and the putative anti-inflammatory agent palmitoylethanolamide (PEA). In recent years, there have been great advances in our understanding of the biochemical and pharmacological properties of the enzyme. In this commentary, the structure and biochemical properties of FAAH and the development of potent and selective FAAH inhibitors are reviewed, together with a brief discussion on the therapeutic possibilities for such compounds in the treatment of inflammatory pain and ischaemic states.

Effects of cannabinoids on LPS-stimulated inflammatory mediator release from macrophages: involvement of eicosanoids

Delta(9)-Tetrahydrocannabinol (Delta(9)-THC) is the major psychoactive component of marijuana and elicits pharmacological actions via cannabinoid receptors. Anandamide (AEA) and 2-arachidonoyl-glycerol (2-AG) are endogenous ligands for cannabinoid receptors, which because of their structural similarities to arachidonic acid (AA), AEA, and 2-AG could serve as substrates for lipoxygenases and cyclooxygenases (COXs) that metabolize polyunsaturated fatty acids to potent bioactive molecules. In this study, we have compared the effects of Delta(9)-THC, AEA, 2-AG, and another cannabinoid agonist, indomethacin morpholinylamide (IMMA), on lipopolysaccharide (LPS)-induced NO, IL-6, and PGE(2) release from J774 macrophages. Delta(9)-THC, IMMA, and AEA diminish LPS-induced NO and IL-6 production in a concentration-dependent manner. 2-AG inhibits the production of IL-6 but slightly increases iNOS-dependent NO production. Delta(9)-THC and IMMA also inhibit LPS-induced PGE(2) production and COX-2 induction, while AEA and 2-AG have no effects. These discrepant results of 2-AG on iNOS and COX-2 induction might be due to its bioactive metabolites, AA and PGE(2), whose incubation cause the potentiation of both iNOS and COX-2 induction. On the contrary, the AEA metabolite, PGE(2)-ethanolamide, influences neither the LPS-induced NO nor IL-6 production. Taken together, direct cannabinoid receptor activation leads to anti-inflammatory action via inhibition of macrophage function. The endogenous cannabinoid, 2-AG, also serves as a substrate for COX-catalyzing PGE(2) production, which in turn modulates the action of CB2.

The vanilloid receptor (VR1)-mediated effects of anandamide are potently enhanced by the cAMP-dependent protein kinase

The endogenous cannabinoid receptor ligand, anandamide (AEA), is a full agonist of the vanilloid receptor type 1 (VR1) for capsaicin. Here, we demonstrate that the potency and efficacy of AEA at VR1 receptors can be significantly increased by the concomitant activation of protein kinase A (PKA). In human embryonic kidney (HEK) cells over-expressing human VR1, AEA induces a rise in cytosolic Ca(2+) concentration that is mediated by this receptor. The EC(50) for this effect was decreased five-fold in the presence of forskolin (FRSK, 1-5 microM) or the cAMP analogue, 8-Br-cAMP (10-100 microM). The effects of 8-Br-cAMP and FRSK were blocked by a selective PKA inhibitor. The FRSK (10 nM) also potently enhanced the sensory neurone- and VR1-mediated constriction by AEA of isolated guinea-pig bronchi, and this effect was abolished by a PKA inhibitor. In rat dorsal root ganglia slices, AEA-induced release of substance P, an effect mediated by VR1 activation, was enhanced three-fold by FRSK (10 nM). Thus, the ability of AEA to stimulate sensory VR1, with subsequent neuropeptide release, appears to be regulated by the state of activation of PKA. This observation supports the hypothesis that endogenous AEA might stimulate VR1 under certain pathophysiological conditions.

Hu 210: a potent tool for investigations of the cannabinoid system

The synthetic compound HU 210 displays a multiplicity of biochemical, pharmacological, and behavioral effects, most of which have been demonstrated to be dependent on a selective agonistic activity at CB(1) and CB(2) cannabinoid receptors and to involve the main neurotransmitter systems. Results obtained in various studies suggest a potential clinical application of this highly potent drug (e.g., as antipyretic, antiinflammatory, analgesic, antiemetic, and antipsychotic agent) as well as its usefulness in research aimed to develop a better understanding of the involvement of the endogenous cannabinoid system in a number of physiopathological functions.