(-)-Delta9-tetrahydrocannabinol antagonizes the peripheral cannabinoid receptor-mediated inhibition of adenylyl cyclase

Sch35966 is a potent, selective agonist at the peripheral cannabinoid receptor (CB2) in rodents and primates

BACKGROUND AND PURPOSE

The peripheral cannabinoid receptor (CB(2)) is expressed on peripheral immune cells and is thought to have a role in the immunosuppressive effects of cannabinoids. Historically, there have been few potent, CB(2)-selective agonists to assess the contribution of CB(2) to this phenomenon. The studies presented here describe the synthesis of 8,10-bis[(2,2-dimethyl-1-oxopropyl)oxy]-11-methyl-1234-tetrahydro-6H-benzo[beta]quinolizin-6-one (Sch35966), which binds with low nanomolar potency to CB(2) in both primates and rodents.

EXPERIMENTAL APPROACH

The affinity, potency and efficacy of Sch35966 and other cannabinoid ligands at CB(2) was assessed using competition binding assays vs [(3)H]CP55,940, [(35)S]GTPgammaS exchange, cAMP accumulation and cell chemotaxis assays.

KEY RESULTS

We showed that Sch35966 has >450-fold selectivity for CB(2) binding vs the central cannabinoid receptor (CB(1)) in primates (humans and cynomolgus monkeys) and rodents (rats and mice). Sch35966 is an agonist as it effectively inhibited forskolin-stimulated cAMP synthesis in CHO-hCB(2) cells, stimulated [(35)S]GTPgammaS exchange and directed chemotaxis in cell membranes expressing CB(2). In all species examined, Sch35966 was more potent, more efficacious and more selective than JWH-015 (a commonly used CB(2)-selective agonist).

CONCLUSIONS AND IMPLICATIONS

Taken together, the data show that Sch35966 is a potent and efficacious CB(2)-selective agonist in rodents and primates.

Anandamide protects from low serum-induced apoptosis via its degradation to ethanolamine

Anandamide (AEA) is a lipid molecule belonging to the family of endocannabinoids. Various studies report neuroprotective activity of AEA against toxic insults, such as ischemic conditions and excitotoxicity, whereas some show that AEA has pro-apoptotic effects. Here we have shown that AEA confers a protective activity in N18TG2 murine neuroblastoma cells subjected to low serum-induced apoptosis. We have demonstrated that the protection from apoptosis by AEA is not mediated via the CB1 receptor, the CB2 receptor, or the vanilloid receptor 1. Interestingly, breakdown of AEA by fatty acid amide hydrolase is required for the protective effect of AEA. Furthermore, the ethanolamine (EA) generated in this reaction is the metabolite responsible for the protective response. The elevation in the levels of reactive oxygen species during low serum-induced apoptosis is not affected by AEA or EA. On the other hand, AEA and EA reduce caspase 3/7 activity, and AEA attenuates the cleavage of PARP-1. Taken together, our results demonstrate a role for AEA and EA in the protection against low serum-induced apoptosis.

2-Arachidonoylglycerol Enhances the Phagocytosis of Opsonized Zymosan by HL-60 Cells Differentiated into Macrophage-Like Cells

2-Arachidonoylglycerol is an endogenous ligand for the cannabinoid receptors (CB1 and CB2). While evidence is accumulating that the CB1 receptor plays important regulatory roles in various nervous tissues and cells, the physiological roles of the CB2 receptor, which is abundantly expressed in the immune system, are yet to be determined. In this study, we examined in detail the effect of 2-arachidonoylglycerol on the phagocytosis of opsonized zymosan by HL-60 cells that had differentiated into macrophage-like cells. We found that the addition of 2-arachidonoylglycerol augmented the phagocytosis of opsonized zymosan by the differentiated HL-60 cells. The effect was observed from 1 nM and increased with increasing concentrations of 2-arachidonoylglycerol. Treatment of the cells with SR144528 or pertussis toxin abolished the effect of 2-arachidonoylglycerol, indicating that the CB2 receptor and Gi/o are involved in the augmented phagocytosis. Phosphatidylinositol 3-kinase and extracellular signal-regulated kinase were also suggested to be involved; treatment of the cells with wortmannin or PD98059 abrogated the 2-arachidonoylglycerol-augmented phagocytosis. These results strongly suggest that 2-arachidonoylglycerol, derived from stimulated inflammatory cells, has an important role in augmenting the phagocytosis of invading microorganisms by macrophages/monocytes thereby stimulating inflammatory reactions and immune responses.

The cannabinoid CB2 receptor inverse agonist JTE-907 suppresses spontaneous itch-associated responses of NC mice, a model of atopic dermatitis

JTE-907, N-(benzo[1,3]dioxol-5-ylmethyl)-7-methoxy-2-oxo-8-pentyloxy-1,2-dihydroquinoline-3-carboxamide, is a selective cannabinoid CB2 receptor antagonist/inverse agonist. The anti-pruritic activity of JTE-907 was studied in NC mice with chronic dermatitis, a model of atopic dermatitis. The oral dose of JTE-907 (1 and 10 mg/kg/day), an immunosuppressant agent tacrolimus (1 mg/kg/day) and a glucocorticoid betamethasone 17-valerate (1 mg/kg/day) for 20 days suppressed the spontaneous scratching and cutaneous nerve activity of NC mice. JTE-907 (10, but not 1, mg/kg) and tacrolimus, but not betamethasone, tended to alleviate the dermatitis. Betamethasone inhibited the body weight gain. These results suggest that JTE-907 suppresses spontaneous itch-associated responses of NC mice without adverse effects such as weight loss.

Effects on cell viability

Cannabinoids are known to control the cell survival/death decision, leading to different outcomes that depend on the nature of the target cell and its proliferative or differentiation status. Cannabinoids induce growth arrest or apoptosis in a number of transformed cells in culture. They do so by modulating key cell signalling pathways involved in the control of tumour cell fate. The best-characterised example is cannabinoid-induced apoptosis of glioma cells, which occurs via sustained ceramide accumulation, extracellular signal-regulated kinase activation and Akt inhibition. In addition, cannabinoid administration inhibits the angiogenesis and slows the growth of different types of tumours in laboratory animals. By contrast, most of the experimental evidence indicates that cannabinoids protect normal neurons and glial cells from apoptosis as induced by toxic insults such as glutamatergic overstimulation, ischaemia and oxidative damage. It is therefore very likely that cannabinoids regulate cell survival and cell death pathways differently in tumour and non-tumour cells. Regarding immune cells, cannabinoids affect proliferation and survival in a complex and still obscure manner that depends on the experimental setting. The findings reviewed here might set the basis for the use of cannabinoids in the treatment of cancer and neurodegenerative diseases.

[Endogenous cannabinoid receptor ligands--anandamide and 2-arachidonoylglycerol]

Marijuana has been used as a traditional medicine and a pleasure-inducing drug for thousands of years around the world, especially in Asia. Delta(9)-tetrahydrocannabinol, major psychoactive component of marijuana, has been shown to interact with specific cannabinoid receptors, thereby eliciting a variety of pharmacological responses in experimental animals and human. In 1990, the gene encoding a cannabinoid receptor (CB1) was cloned. This prompted the search for endogenous ligands. In 1992, N-arachidonoylethanolamine (anandamide) was isolated from pig brain as an endogenous ligand, and in 1995, 2-arachidonoylglycerol was isolated from rat brain and canine gut as another endogenous ligand. Both anandamide and 2-arachidonoylglycerol exhibit various cannabimimetic activities. The results of structure-activity relationship experiments, however, revealed that 2-arachidonoylglycerol, but not anandamide, is the intrinsic natural ligand for the cannabinoid receptor. 2-arachidonoylglycerol is a degradation product of inositol phospholipids that links the function of the cannabinoid receptors with the enhanced inositol phospholipid turnover in stimulated tissues and cells. The possible physiological roles of cannabinoid receptors and 2-arachidonoylglycerol in various mammalian tissues such as those of the nervous and inflammatory cells are demonstrated. Furthermore, the future development of therapeutic drugs coming from this endocannabinoid system are discussed.

Chronic exposure to Delta9-tetrahydrocannabinol downregulates oxytocin and oxytocin-associated neurophysin in specific brain areas

Cannabinoids are widely abused drugs. Our goal was to identify genes modulated by Delta9-tetrahydrocannabinol (Delta9-THC) treatment. We found that chronic administration of Delta9-THC (1.5 mg/kg/day, i.p.; 7 days) to rats, downregulates the expression of oxytocin-neurophysin (OT-NP) mRNA and of OT and oxytocin-associated NP (NPOT) immunoreactivity in nucleus accumbens (NAc) and ventral tegmental area (VTA), brain areas involved in reward and addiction. Real-time PCR revealed a 60% and 53% reduction of OT-NP mRNA in NAc and VTA, respectively, under chronic treatment, while no changes were observed in NAc after 24 h. Immunohistochemistry showed a large decrease in number of OT and NPOT-stained fibers in NAc (by 59% and 52%, respectively) and VTA (by 50% and 56%, respectively). No changes in cell staining were observed in the paraventricular nucleus and supraoptic nucleus. As OT is known to inhibit development of drug tolerance and attenuate withdrawal symptoms, we suggest that OT downregulation could play a role during the establishment of the chronic effects of Delta9-THC.

Plant cannabinoids: a neglected pharmacological treasure trove

Most of the cannabinoids in Cannabis sativa L. have not been fully evaluated for their pharmacological activity. A publication in this issue presents evidence that a plant cannabinoid, Delta(9)-tetrahydrocannabivarin is a potent antagonist of anandamide, a major endogenous cannabinoid. It seems possible that many of the non-psychoactive constituents of this plant will be of biological interest.

Pharmacological actions of cannabinoids

Mammalian tissues express at least two types of cannabinoid receptor, CB1 and CB2, both G protein coupled. CB1 receptors are expressed predominantly at nerve terminals where they mediate inhibition of transmitter release. CB2 receptors are found mainly on immune cells, one of their roles being to modulate cytokine release. Endogenous ligands for these receptors (endocannabinoids) also exist. These are all eicosanoids; prominent examples include arachidonoylethanolamide (anandamide) and 2-arachidonoyl glycerol. These discoveries have led to the development of CB1- and CB2-selective agonists and antagonists and of bioassays for characterizing such ligands. Cannabinoid receptor antagonists include the CB1-selective SR141716A, AM251, AM281 and LY320135, and the CB2-selective SR144528 and AM630. These all behave as inverse agonists, one indication that CB1 and CB2 receptors can exist in a constitutively active state. Neutral cannabinoid receptor antagonists that seem to lack inverse agonist properties have recently also been developed. As well as acting on CB1 and CB2 receptors, there is convincing evidence that anandamide can activate transient receptor potential vanilloid type 1 (TRPV1) receptors. Certain cannabinoids also appear to have non-CB1, non-CB2, non-TRPV1 targets, for example CB2-like receptors that can mediate antinociception and "abnormal-cannabidiol" receptors that mediate vasorelaxation and promote microglial cell migration. There is evidence too for TRPV1-like receptors on glutamatergic neurons, for alpha2-adrenoceptor-like (imidazoline) receptors at sympathetic nerve terminals, for novel G protein-coupled receptors for R-(+)-WIN55212 and anandamide in the brain and spinal cord, for novel receptors for delta9-tetrahydrocannabinol and cannabinol on perivascular sensory nerves and for novel anandamide receptors in the gastro-intestinal tract. The presence of allosteric sites for cannabinoids on various ion channels and non-cannabinoid receptors has also been proposed. In addition, more information is beginning to emerge about the pharmacological actions of the non-psychoactive plant cannabinoid, cannabidiol. These recent advances in cannabinoid pharmacology are all discussed in this review.

The effects of Delta9-tetrahydrocannabinol in rat mesenteric vasculature, and its interactions with the endocannabinoid anandamide

1 Delta9-tetrahydrocannabinol (THC) produces varying effects in mesenteric arteries: vasorelaxation (third-order branches, G3), modest vasorelaxation (G2), no effect (G1) and vasoconstriction (the superior mesenteric artery, G0). 2 In G3, vasorelaxation to THC was inhibited by pertussis toxin, but was unaffected by the CB1 receptor antagonist, AM251 (1 microM), incubation with the TRPV1 receptor agonist capsaicin (10 microM, 1 h), the TRPV1 receptor antagonist capsazepine (10 microM) or de-endothelialisation. 3 In G3, vasorelaxation to THC was inhibited by high K+ buffer, and by the following K+ channel inhibitors: charybdotoxin (100 nM), apamin (500 nM) and barium chloride (30 microM), but not by 4-aminopyridine, glibenclamide or tertiapin. 4 In G3, THC (10 and 100 microM) inhibited the contractile response to Ca2+ in a Ca2+-free, high potassium buffer, indicating that THC blocks Ca2+ influx. 5 In G0, the vasoconstrictor responses to THC were inhibited by de-endothelialisation and SR141716A (100 nM), but not by the endothelin (ET(A)) receptor antagonist FR139317 (1 microM).THC (1 and 10 microM) antagonised vasorelaxation to anandamide in G3 but not G0. THC did not antagonise the noncannabinoid verapamil, capsaicin or the CB1 receptor agonist CP55,940. 6 THC (10 and 100 microM) inhibited endothelium-derived relaxing factor (EDHF)-mediated responses to carbachol in a manner similar to the gap junction inhibitor 18alpha-glycyrrhetinic acid. 7 These data show that THC causes vasorelaxation through activation of K+ channels and inhibition of Ca2+ channels, and this involves non-CB1, non-TRPV1 but G-protein-coupled receptors. In G0, THC does not cause relaxation and at high concentrations causes contractions. Importantly, THC antagonises the effects of anandamide, possibly through inhibition of EDHF activity.

Evidence for the Involvement of the Cannabinoid CB2 Receptor and Its Endogenous Ligand 2-Arachidonoylglycerol in 12-O-Tetradecanoylphorbol-13-acetate-induced Acute Inflammation in Mouse Ear

2-Arachidonoylglycerol is an endogenous ligand for the cannabinoid receptors. Two types of cannabinoid receptors have been identified to date. The CB1 receptor is abundantly expressed in the brain, and assumed to be involved in the attenuation of neurotransmission. On the other hand, the physiological roles of the CB2 receptor, mainly expressed in several types of inflammatory cells and immunocompetent cells, have not yet been fully elucidated. In this study, we investigated possible pathophysiological roles of the CB2 receptor and 2-arachidonoylglycerol in acute inflammation in mouse ear induced by the topical application of 12-O-tetradecanoylphorbol-13-acetate. We found that the amount of 2-arachidonoylglycerol was markedly augmented in inflamed mouse ear. In contrast, the amount of anandamide, another endogenous cannabinoid receptor ligand, did not change markedly. Importantly, 12-O-tetradecanoylphorbol-13-acetate-induced ear swelling was blocked by treatment with SR144528, a CB2 receptor antagonist, suggesting that the CB2 receptor is involved in the swelling. On the other hand, the application of AM251, a CB1 receptor antagonist, exerted only a weak suppressive effect. The application of SR144528 also reduced the 12-O-tetradecanoylphorbol-13-acetate-induced production of leukotriene B(4) and the infiltration of neutrophils in the mouse ear. Interestingly, the application of 2-arachidonoylglycerol to the mouse ear evoked swelling, which was abolished by treatment with SR144528. Nitric oxide was suggested to be involved in the ear swelling induced by 2-arachidonoylglycerol. These results suggest that the CB2 receptor and 2-arachidonoylglycerol play crucial stimulative roles during the course of inflammatory reactions.

2-arachidonoylglycerol, an endogenous cannabinoid receptor ligand, induces rapid actin polymerization in HL-60 cells differentiated into macrophage-like cells

Delta9-Tetrahydrocannabinol, a major psychoactive constituent of marijuana, interacts with specific receptors, i.e. the cannabinoid receptors, thereby eliciting a variety of pharmacological responses. To date, two types of cannabinoid receptors have been identified: the CB1 receptor, which is abundantly expressed in the nervous system, and the CB2 receptor, which is predominantly expressed in the immune system. Previously, we investigated in detail the structure-activity relationship of various cannabinoid receptor ligands and found that 2-AG (2-arachidonoylglycerol) is the most efficacious agonist. We have proposed that 2-AG is the true natural ligand for both the CB1 and CB2 receptors. Despite the potential physiological importance of 2-AG, not much information is available concerning its biological activities towards mammalian tissues and cells. In the present study, we examined the effect of 2-AG on morphology as well as the actin filament system in differentiated HL-60 cells, which express the CB2 receptor. We found that 2-AG induces rapid morphological changes such as the extension of pseudopods. We also found that it provokes a rapid actin polymerization in these cells. Actin polymerization induced by 2-AG was abolished when cells were treated with SR144528, a CB2 receptor antagonist, and pertussis toxin, suggesting that the response was mediated by the CB2 receptor and G(i/o). A phosphoinositide 3-kinase, Rho family small G-proteins and a tyrosine kinase were also suggested to be involved. Reorganization of the actin filament system is known to be indispensable for a variety of cellular events; it is possible that 2-AG plays physiologically essential roles in various inflammatory cells and immune-competent cells by inducing a rapid actin rearrangement.

New perspectives in the studies on endocannabinoid and cannabis: 2-arachidonoylglycerol as a possible novel mediator of inflammation

2-Arachidonoylglycerol is an endogenous ligand for the cannabinoid receptors. To date, two types of cannabinoid receptors (CB1 and CB2) have been identified. The CB1 receptor is assumed to be involved in the attenuation of synaptic transmission. On the other hand, the physiological roles of the CB2 receptor, which is abundantly expressed in several types of inflammatory cells and immunocompetent cells, have not yet been fully elucidated. Recently, we investigated in detail possible physiological roles of the CB2 receptor and 2-arachidonoylglycerol in inflammation. We found that 2-arachidonoylglycerol induces the activation of p42/44 and p38 mitogen-activated protein kinases and c-Jun N-terminal kinase; actin rearrangement and morphological changes; augmented production of chemokines in HL-60 cells; and the migration of HL-60 cells differentiated into macrophage-like cells, human monocytes, natural killer cells, and eosinophils. We also found that the level of 2-arachidonoylglycerol in mouse ear is markedly elevated following treatment with 12-O-tetradecanoylphorbol 13-acetate, which induces acute inflammation. Notably, the inflammation induced by 12-O-tetradecanoylphorbol 13-acetate was blocked by treatment with SR144528, a CB2-receptor antagonist. Similar results were obtained with an allergic inflammation model in mice. These results strongly suggest that 2-arachidonoylglycerol plays essential roles in the stimulation of various inflammatory reactions in vivo.

Comparison of cannabinoid ligands affinities and efficacies in murine tissues and in transfected cells expressing human recombinant cannabinoid receptors

Affinities and efficacies of several reference cannabinoid ligands were investigated at central and peripheral cannabinoid receptors in three different species (rat, mouse, and human). The tested compounds belong to different chemical classes such as classical and non-classical terpene derivatives (Delta(8)-THC, Delta(9)-THC, HU 210, CP 55,940, CP 55,244, CP 55,243 and CP 47,947), aminoalkylindole (WIN 55,212-2, WIN 55,212-3) and diarylpyrazole cannabinoids (SR 141716A, SR 144528). As cannabinoid receptors have been shown to be mainly coupled to Gi/o type G- proteins, and by using the [(35)S]-GTPgammaS nucleotide binding modulation, we characterized the functional activity of these ligands which can act as agonists (positive intrinsic activity), partial agonists (partial positive intrinsic activity), antagonists (no intrinsic activity), or inverse agonists (negative intrinsic activity). To our knowledge, some derivatives (Delta(8)-THC, WIN 55,212-3, CP 55,243 and CP 47,947) have never been characterized in [(35)S]-GTPgammaS binding assays and up to now, this study represents the largest survey of reference cannabinoids performed in unique experimental conditions and in the same laboratory.

Bioisosteric Replacements of the Pyrazole Moiety of Rimonabant: Synthesis, Biological Properties, and Molecular Modeling Investigations of Thiazoles, Triazoles, and Imidazoles as Potent and Selective CB1 Cannabinoid Receptor Antagonists

Series of thiazoles, triazoles, and imidazoles were designed as bioisosteres, based on the 1,5-diarylpyrazole motif that is present in the potent CB(1) receptor antagonist rimonabant (SR141716A, 1). A number of target compounds was synthesized and evaluated in cannabinoid (hCB(1) and hCB(2)) receptor assays. The thiazoles, triazoles, and imidazoles elicited in vitro( )()CB(1) antagonistic activities and in general exhibited considerable CB(1) vs CB(2) receptor subtype selectivities, thereby demonstrating to be cannabinoid bioisosteres of the original diarylpyrazole class. Some key representatives in the imidazole series showed potent pharmacological in vivo activities after oral administration in both a CB agonist-induced hypotension model and a CB agonist-induced hypothermia model. Molecular modeling studies showed a close three-dimensional structural overlap between the key compound 62 and rimonabant. A structure-activity relationship (SAR) study revealed a close correlation between the biological results in the imidazole and pyrazole series.

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.

Synthesis, Biological Properties, and Molecular Modeling Investigations of Novel 3,4-Diarylpyrazolines as Potent and Selective CB1 Cannabinoid Receptor Antagonists

A series of novel 3,4-diarylpyrazolines was synthesized and evaluated in cannabinoid (hCB(1) and hCB(2)) receptor assays. The 3,4-diarylpyrazolines elicited potent in vitro CB(1) antagonistic activities and in general exhibited high CB(1) vs CB(2) receptor subtype selectivities. Some key representatives showed potent pharmacological in vivo activities after oral dosing in both a CB agonist-induced blood pressure model and a CB agonist-induced hypothermia model. Chiral separation of racemic 67, followed by crystallization and an X-ray diffraction study, elucidated the absolute configuration of the eutomer 80 (SLV319) at its C(4) position as 4S. Bioanalytical studies revealed a high CNS-plasma ratio for the development candidate 80. Molecular modeling studies showed a relatively close three-dimensional structural overlap between 80 and the known CB(1) receptor antagonist rimonabant (SR141716A). Further analysis of the X-ray diffraction data of 80 revealed the presence of an intramolecular hydrogen bond that was confirmed by computational methods. Computational models and X-ray diffraction data indicated a different intramolecular hydrogen bonding pattern in the in vivo inactive compound 6. In addition, X-ray diffraction studies of 6 revealed a tighter intermolecular packing than 80, which also may contribute to its poorer absorption in vivo. Replacement of the amidine -NH(2) moiety with a -NHCH(3) group proved to be the key change for gaining oral biovailability in this series of compounds leading to the identification of 80.

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.

Synthesis and characterization of NESS 0327: a novel putative antagonist of the CB1 cannabinoid receptor

The compound N-piperidinyl-[8-chloro-1-(2,4-dichlorophenyl)-1,4,5,6-tetrahydrobenzo [6,7]cyclohepta[1,2-c]pyrazole-3-carboxamide] (NESS 0327) was synthesized and evaluated for binding affinity toward cannabinoid CB1 and CB2 receptor. NESS 0327 exhibited a stronger selectivity for CB1 receptor compared with N-piperidinyl-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR 141716A), showing a much higher affinity for CB1 receptor (Ki = 350 +/- 5 fM and 1.8 +/- 0.075 nM, respectively) and a higher affinity for the CB2 receptor (Ki = 21 +/- 0.5 nM and 514 +/- 30 nM, respectively). Affinity ratios demonstrated that NESS 0327 was more than 60,000-fold selective for the CB1 receptor, whereas SR 141716A only 285-fold. NESS 0327 alone did not produce concentration-dependent stimulation of guanosine 5'-O-(3-[35S]thio)-triphosphate ([35S]GTPgammaS) binding in rat cerebella membranes. Conversely, NESS 0327 antagonized [R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrolol [1,2,3-de]-1,4-benzoxazin-yl]-(1-naphthalenyl)methanone mesylate] (WIN 55,212-2)-stimulated [35S]GTPgammaS binding. In functional assay, NESS 0327 antagonized the inhibitory effects of WIN 55,212-2 on electrically evoked contractions in mouse isolated vas deferens preparations with pA2 value of 12.46 +/- 0.23. In vivo studies indicated that NESS 0327 antagonized the antinociceptive effect produced by WIN 55,212-2 (2 mg/kg s.c.) in both tail-flick (ID50 = 0.042 +/- 0.01 mg/kg i.p.) and hot-plate test (ID50 = 0.018 +/- 0.006 mg/kg i.p.). These results indicated that NESS 0327 is a novel cannabinoid antagonist with high selectivity for the cannabinoid CB1 receptor.

Integrity of extracellular loop 1 of the human cannabinoid receptor 1 is critical for high-affinity binding of the ligand CP 55,940 but not SR 141716A

Like other G-protein coupled receptors with hydrophobic ligands, the human cannabinoid receptor 1 (CB1) is thought to bind its ligands within the transmembrane region of the receptor. However, for some of these receptors the extracellular loops (ECs) have also been shown to play a role in ligand recognition and selectivity. We have taken a mutagenesis approach to examine the role of the amino terminus, EC1, and EC3 of CB1 in ligand binding. Eight mutant receptors, each with a dipeptide insertion, were constructed, expressed, and evaluated for binding to the cannabinoid ligands (-)-cis-3[2-hydroxy-4-(1',1'-dimethylheptyl)phenyl]-trans-4-(3-hydroxypropyl)cyclohexanol (CP 55,940) and N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride (SR 141716A). Mutants with insertions in the membrane distal region of the amino terminus or EC3 maintained affinity for both ligands. Those with insertions in the membrane proximal region of the amino terminus or EC1 exhibited a loss of affinity for CP 55,940 while retaining wild-type affinity for SR 141716A. Representative mutants were analyzed for agonist-induced inhibition of cyclic AMP accumulation, and the results indicated that G-protein coupling remained intact. Alanine substitution mutants were made to address whether it was the perturbation of the overall structure of the region or the displacement of particular side chains that was responsible for the loss of CP 55,940 binding. We conclude that a structurally intact EC1, but not the comparably short EC3, is essential for high-affinity CP 55,940 binding.

Pharmacological characterisation of cannabinoid receptors inhibiting interleukin 2 release from human peripheral blood mononuclear cells

The effects of a range of cannabinoid receptor agonists and antagonists on phytohaemagglutinin-induced secretion of interleukin-2 from human peripheral blood mononuclear cells were investigated. The nonselective cannabinoid receptor agonist WIN55212-2 ((R)-(+)-[2,3-dihydro-5-methyl-3-[4-morpholinylmethyl]pyrrolo[1,2,3-de]1,4-benzoxazin-6-yl](1-naphthyl) methanone mesylate) and the selective cannabinoid CB(2) receptor agonist JWH 015 ((2-methyl-1-propyl-1H-indol-3-yl)-1-napthalenylmethanone) inhibited phytohaemagglutinin (10 microg/ml)-induced release of interleukin-2 in a concentration-dependent manner (IC(1/2max), WIN55212-2=8.8 x 10(-7) M, 95% confidence limits (C.L.)=2.2 x 10(-7)-3.5 x 10(-6) M; JWH 015=1.8 x 10(-6) M, 95% C.L.=1.2 x 10(-6)-2.9 x 10(-6) M, n=5). The nonselective cannabinoid receptor agonists CP55,940 ((-)-3-[2-hydroxy-4-(1,1-dimethyl-hepthyl)-phenyl]4-[3-hydroxypropyl]cyclo-hexan-1-ol), Delta(9)-tetrahydrocannabinol and the selective cannabinoid CB(1) receptor agonist ACEA (arachidonoyl-2-chloroethylamide) had no significant (P>0.05) inhibitory effect on phytohaemagglutinin-induced release of interleukin-2. Dexamethasone significantly (P<0.05) inhibited phytohaemagglutinin-induced release of interleukin-2 in a concentration-dependent manner (IC(1/2max)=1.3 x 10(-8) M, 95% C.L.=1.4 x 10(-9)-3.2 x 10(-8) M). The cannabinoid CB(1) receptor antagonist SR141716A (N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride) (10(-6) M) did not antagonise the inhibitory effect of WIN55212-2 whereas the cannabinoid CB(2) receptor antagonist SR144528 (N-(1,S)-endo-1,3,3-trimethyl bicyclo(2,2,1)heptan-2-yl)-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide) antagonised the inhibitory effect of WIN55212-2 (pA(2)=6.3+/-0.1, n=5). In addition, CP55,940 (10(-6) M) and Delta(9)-tetrahydrocannabinol (10(-6) M) also antagonised the inhibitory effects of WIN55212-2 (pA(2)=6.1+/-0.1, n=5 and pA(2)=6.9+/-0.2, n=5). In summary, WIN55,212-2 and JWH 015 inhibited interleukin-2 release from human peripheral blood mononuclear cells via the cannabinoid CB(2) receptor. In contrast, CP55,940 and Delta(9)-tetrahydrocannabinol behaved as partial agonists/antagonists in these cells.

Evidence for a physiological role of endocannabinoids in the modulation of seizure threshold and severity

The anticonvulsant effect of cannabinoids has been shown to be mediated through activation of the cannabinoid CB(1) receptor. This study was initiated to evaluate the effects of endogenously occurring cannabinoids (endocannabinoids) on seizure severity and threshold. The anticonvulsant effect of the endocannabinoid, arachidonylethanolamine (anandamide), was evaluated in the maximal electroshock seizure model using male CF-1 mice and was found to be a fully efficacious anticonvulsant (ED(50)=50 mg/kg i.p.). The metabolically stable analog of anandamide, (R)-(20-cyano-16,16-dimetyldocosa-cis-5,8,11,14-tetraenoyl)-1'-hydroxy-2'-propylamine (O-1812), was also determined to be a potent anticonvulsant in the maximal electroshock model (ED(50)=1.5 mg/kg i.p.). Furthermore, pretreatment with the cannabinoid CB(1) receptor specific antagonist N-(piperidin-1-yl-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamidehydrochloride (SR141716A) completely abolished the anticonvulsant effect of anandamide as well as O-1812 (P< or =0.01, Fisher exact test), indicating a cannabinoid CB(1) receptor-mediated anticonvulsant mechanism for both endocannabinoid compounds. Additionally, the influence of cannabinoid CB(1) receptor endogenous tone on maximal seizure threshold was assessed using SR141716A alone. Our data show that SR141716A (10 mg/kg i.p.) significantly reduced maximal seizure threshold (CC(50)=14.27 mA) compared to vehicle-treated animals (CC(50)=17.57 mA) (potency ratio=1.23, lower confidence limit=1.06, upper confidence limit=1.43), indicating the presence of an endogenous cannabinoid tone that modulates seizure activity. These data demonstrate that anandamide and its analog, O-1812, are anticonvulsant in a whole animal model and further implicate the cannabinoid CB(1) receptor as a major endogenous site of seizure modulation.

Cannabinoids and cell fate

Cannabinoids recently have been shown to control the cell survival/death decision. Thus, cannabinoids induce growth arrest or apoptosis in a number of transformed neural and non-neural cells in culture. In addition, cannabinoid administration induces regression of malignant gliomas in rodents by a mechanism that may involve sustained ceramide generation and extracellular signal-regulated kinase activation. In contrast, most of the experimental evidence indicates that cannabinoids may protect normal neurons from toxic insults, such as glutamatergic overstimulation, ischaemia, and oxidative damage. Regarding immune cells, low doses of cannabinoids may enhance proliferation, whereas high doses of cannabinoids usually induce growth arrest or apoptosis. The potential therapeutic applications of these findings are discussed.

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.

Autocrine and paracrine regulation of lymphocyte CB2 receptor expression by TGF-beta

The marijuana-derived cannabinoid Delta(9)-tetrahydrocannabinol (THC) has been shown to be immunosuppressive. We report that THC induces the immunosuppressive cytokine TGF-beta by human peripheral blood lymphocytes (PBL). The ability of THC to stimulate TGF-beta production was blocked by the CB2 receptor specific antagonist SR144528 but not by the CB1 specific antagonist AM251. Furthermore, our data suggest that TGF-beta actively regulates lymphocyte CB2 receptor expression in an autocrine and paracrine manner. Whereas the addition of recombinant TGF-beta to PBL cultures downregulated CB2 receptor expression, anti-TGF-beta antibody treatment increased CB2 receptor expression. We conclude that one mechanism by which THC contributes to immune suppression is by stimulating an enhanced production of lymphocyte TGF-beta.

The potent emetogenic effects of the endocannabinoid, 2-AG (2-arachidonoylglycerol) are blocked by delta(9)-tetrahydrocannabinol and other cannnabinoids

Cannabinoids, including the endogenous cannabinoid or endocannabinoid, anandamide, modulate several gastrointestinal functions. To date, the gastrointestinal effects of the second putative endocannabinoid 2-arachidonoylglycerol (2-AG) have not been studied. In the present study using a shrew (Cryptotis parva) emetic model, 2-AG (0.25-10 mg/kg, i.p.) potently and dose-dependently increased vomiting frequency (ED(50) = 1.13 mg/kg) and the number of animals vomiting (ED(50) = 0.48 mg/kg). In contrast, neither anandamide (2.5-20 mg/kg) nor methanandamide (5-10 mg/kg) induced a dose-dependent emetogenic response, but both could partially block the induced emetic effects. Delta(9)-Tetrahydrocannabinol and its synthetic analogs reduced 2-AG-induced vomiting with the rank order potency: CP 55,940 > WIN 55,212-2 > Delta(9)-tetrahydrocannabinol. The nonpsychoactive cannabinoid, cannabidiol, was inactive. Nonemetic doses of SR 141716A (1-5 mg/kg) also blocked 2-AG-induced vomiting. The 2-AG metabolite arachidonic acid also caused vomiting. Indomethacin, a cyclooxygenase inhibitor, blocked the emetogenic effects of both arachidonic acid and 2-AG. CP 55,940 also blocked the emetic effects of arachidonic acid. 2-AG (0.25-10 mg/kg) reduced spontaneous locomotor activity (ED(50) = 11 mg/kg) and rearing frequency (ED(50) = 4.3 mg/kg) in the shrew, whereas such doses of both anandamide and methanandamide had no effect on locomotor parameters. The present study indicates that: 1) 2-AG is an efficacious endogenous emetogenic cannabinoid involved in vomiting circuits, 2) the emetic action of 2-AG and the antiemetic effects of tested cannabinoids are mediated via CB(1) receptors, and 3) the emetic effects of 2-AG occur in lower doses relative to its locomotor suppressant actions.

Molecular targets for cannabidiol and its synthetic analogues: effect on vanilloid VR1 receptors and on the cellular uptake and enzymatic hydrolysis of anandamide

1. (-)-Cannabidiol (CBD) is a non-psychotropic component of Cannabis with possible therapeutic use as an anti-inflammatory drug. Little is known on the possible molecular targets of this compound. We investigated whether CBD and some of its derivatives interact with vanilloid receptor type 1 (VR1), the receptor for capsaicin, or with proteins that inactivate the endogenous cannabinoid, anandamide (AEA). 2. CBD and its enantiomer, (+)-CBD, together with seven analogues, obtained by exchanging the C-7 methyl group of CBD with a hydroxy-methyl or a carboxyl function and/or the C-5' pentyl group with a di-methyl-heptyl (DMH) group, were tested on: (a) VR1-mediated increase in cytosolic Ca(2+) concentrations in cells over-expressing human VR1; (b) [(14)C]-AEA uptake by RBL-2H3 cells, which is facilitated by a selective membrane transporter; and (c) [(14)C]-AEA hydrolysis by rat brain membranes, which is catalysed by the fatty acid amide hydrolase. 3. Both CBD and (+)-CBD, but not the other analogues, stimulated VR1 with EC(50)=3.2 - 3.5 microM, and with a maximal effect similar in efficacy to that of capsaicin, i.e. 67 - 70% of the effect obtained with ionomycin (4 microM). CBD (10 microM) desensitized VR1 to the action of capsaicin. The effects of maximal doses of the two compounds were not additive. 4. (+)-5'-DMH-CBD and (+)-7-hydroxy-5'-DMH-CBD inhibited [(14)C]-AEA uptake (IC(50)=10.0 and 7.0 microM); the (-)-enantiomers were slightly less active (IC(50)=14.0 and 12.5 microM). 5. CBD and (+)-CBD were also active (IC(50)=22.0 and 17.0 microM). CBD (IC(50)=27.5 microM), (+)-CBD (IC(50)=63.5 microM) and (-)-7-hydroxy-CBD (IC(50)=34 microM), but not the other analogues (IC(50)>100 microM), weakly inhibited [(14)C]-AEA hydrolysis. 6. Only the (+)-isomers exhibited high affinity for CB(1) and/or CB(2) cannabinoid receptors. 7. These findings suggest that VR1 receptors, or increased levels of endogenous AEA, might mediate some of the pharmacological effects of CBD and its analogues. In view of the facile high yield synthesis, and the weak affinity for CB(1) and CB(2) receptors, (-)-5'-DMH-CBD represents a valuable candidate for further investigation as inhibitor of AEA uptake and a possible new therapeutic agent.

Cannabinoid receptors and the regulation of immune response

Cannabinoid research underwent a tremendous increase during the last 10 years. This progress was made possible by the discovery of cannabinoid receptors and the endogenous ligands for these receptors. Cannabinoid research is developing in two major directions: neurobehavioral properties of cannabinoids and the impact of cannabinoids on the immune system. Recent studies characterized the cannabinoid-induced response as a very complex process because of the involvement of multiple signalling pathways linked to cannabinoid receptors or effects elicited by cannabinoids without receptor participation. The objective of this review is to present this complexity as it applies to immune response. The functional properties of cannabinoid receptors, signalling pathways linked to cannabinoid receptors and the modulation of immune response by cannabinoid receptor ligands are discussed. Special attention is given to 'endocannabinoids' as immunomodulatory molecules.

Inhibition of nitric oxide production in RAW264.7 macrophages by cannabinoids and palmitoylethanolamide

We have investigated the inhibition of lipopolysaccharide stimulated nitric oxide production in RAW264.7 macrophages by the cannabinoids and the putative cannabinoid CB(2)-like receptor ligand, palmitoylethanolamide. (R)-(+)-[2, 3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo-[1,2,3-de]-1, 4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate ((+)-WIN55212) and, to a lesser extent (-)-cis-3-[2-hydroxy-4-(1, 1-dimethylheptyl)phenyl]-trans-4-(3-hydroxy-propyl)cyclohexan++ +-1-ol (CP55940), significantly inhibited lipopolysaccharide stimulated nitric oxide production. The level of inhibition was found to be dependent on the concentration of lipopolysaccharide used to induce nitric oxide production. Palmitoylethanolamide significantly inhibited nitric oxide production induced by lipopolysaccharide. The inhibition of nitric oxide production by (+)-WIN55212 but not palmitoylethanolamide was significantly attenuated in the presence of the cannabinoid CB(2) receptor antagonist, N-[(1S)-endo-1,3, 3-trimethyl bicyclo [2.2.1] heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazo le- 3-carboxamide (SR144528). (+)-WIN55212 produced a pertussis toxin-sensitive parallel rightward shift in the log concentration-response curve for lipopolysaccharide, causing a fivefold increase in the EC(50) value for lipopolysaccharide with no change in the E(max) value. (-)-WIN55212 had no effect on the log concentration-response curve for lipopolysaccharide. Palmitoylethanolamide did not produce a rightward shift in the lipopolysaccharide concentration-response curve. However, it did produce a pertussis toxin-insensitive reduction in the E(max) value. The results suggest that the inhibition of lipopolysaccharide mediated nitric oxide release by (+)-WIN55212 in murine macrophages is mediated by cannabinoid CB(2) receptors. In contrast, the inhibition by palmitoylethanolamide does not appear to be mediated by cannabinoid receptors.

Cannabinoid receptor ligands: clinical and neuropharmacological considerations, relevant to future drug discovery and development

This review highlights some important advances that have taken place in cannabinoid research over the last four years. It focuses on novel ligands that are of interest either as experimental tools or as lead compounds for therapeutic agents and possible clinical applications for some of these ligands. The molecular targets for these compounds are various components of the system of endogenous cannabinoids (endocannabinoids) and receptors that together constitute the 'endocannabinoid system'. These are CB(1) cannabinoid receptors that are present mainly on central and peripheral neurones, CB(2) cannabinoid receptors that are expressed predominantly by immune cells, the biochemical mechanisms responsible for the tissue uptake or metabolism of endocannabinoids and vanilloid receptors. Other cannabinoid receptor types may also exist. Recently developed ligands include potent and selective agonists for CB(1) and CB(2) receptors, a potent CB(2)-selective antagonist/inverse agonist and inhibitors of endocannabinoid uptake or metabolism. Future research should be directed at characterising the endocannabinoid system more completely and at obtaining more conclusive clinical data about the possible beneficial effects of cannabinoids as well as their adverse effects. There is also a need for improved cannabinoid formulations/modes of administration in the clinic and advances in this area should be facilitated by the recent development of a potent water-soluble CB(1)/CB(2) receptor agonist. A growing number of strategies for separating sought-after therapeutic effects of cannabinoid receptor agonists from the unwanted consequences of CB(1) receptor activation are now emerging and these are discussed at the end of this review.

The CB1 cannabinoid receptor is coupled to the activation of protein kinase B/Akt

Cannabinoids exert most of their effects in the central nervous system through the CB(1) cannabinoid receptor. This G-protein-coupled receptor has been shown to be functionally coupled to inhibition of adenylate cyclase, modulation of ion channels and activation of extracellular-signal-regulated kinase. Using Chinese hamster ovary cells stably transfected with the CB(1) receptor cDNA we show here that Delta(9)-tetrahydrocannabinol (THC), the major active component of marijuana, induces the activation of protein kinase B/Akt (PKB). This effect of THC was also exerted by the endogenous cannabinoid anandamide and the synthetic cannabinoids CP-55940 and HU-210, and was prevented by the selective CB(1) antagonist SR141716. Pertussis toxin and wortmannin blocked the CB(1) receptor-evoked activation of PKB, pointing to the sequential involvement of a G(i)/G(o) protein and phosphoinositide 3'-kinase. The functionality of the cannabinoid-induced stimulation of PKB was proved by the increased phosphorylation of glycogen synthase kinase-3 serine 21 observed in cannabinoid-treated cells and its prevention by SR141716 and wortmannin. Cannabinoids activated PKB in the human astrocytoma cell line U373 MG, which expresses the CB(1) receptor, but not in the human promyelocytic cell line HL-60, which expresses the CB(2) receptor. Data indicate that activation of PKB may be responsible for some of the effects of cannabinoids in cells expressing the CB(1) receptor.

Neuropharmacology and therapeutic potential of cannabinoids

Mammalian tissues contain at least two types of cannabinoid receptor, CB₁, found mainly on neurones and CB₂, found mainly in immune cells. Endogenous ligands for these receptors have also been identified. These endocannabinoids and their receptors constitute the endogenous cannabinoid system. Two cannabinoid receptor agonists, Δ⁹-tetrahydrocannabinol and nabilone, are used clinically as anti-emetics or to boost appetite. Additional therapeutic uses of cannabinoids may include the suppression of some multiple sclerosis and spinal injury symptoms, the management of pain, bronchial asthma and glaucoma, and the prevention of neurotoxicity. There are also potential clinical applications for CB₁ receptor antagonists, in the management of acute schizophrenia and cognitive/memory dysfunctions and as appetite suppressants. Future research is likely to be directed at characterizing the endogenous cannabinoid system more completely, at obtaining more conclusive clinical data about cannabinoids with regard to both beneficial and adverse effects, at developing improved cannabinoid formulations and modes of administration for use in the clinic and at devising clinical strategies for separating out the sought-after effects of CB₁ receptor agonists from their psychotropic and other unwanted effects.

Presence and functional regulation of cannabinoid receptors in immune cells

In the last 30 years studies on drug-abusing humans and animals injected with cannabinoids, as well as in vitro models employing immune cell cultures, have demonstrated that marijuana and cannabinoids are immunomodulators. Both types of cannabinoid receptors, CB1 and CB2, have been found in immune cells, suggesting they are important in mediating the effects of cannabinoids on the immune system. This article reviews the data on the function and distribution of cannabinoid receptors in the immune system and their involvement in the immunomodulatory effect of these substances.

The peripheral cannabinoid receptor, Cb2, in retrovirally-induced leukemic transformation and normal hematopoiesis

Following retroviral insertional mutagenesis we recently identified the gene encoding the peripheral cannabinoid receptor (Cb2) near a common virus integration site (VIS), Evi11. In 13 out of 105 Cas-Br-M murine leukemia virus (MuLV) induced leukemias retroviral integrations occured either in the 5' or 3' part of the Cb2 gene. The Cb2 receptor protein is 44% homologous to the central cannabinoid receptor Cb1, which belongs to the superfamily of seven transmembrane (7TM) receptors. Cb1 is mainly expressed in brain, whereas Cb2 encodes the hematopoietic form. Besides the natural cannabinoids, delta9-tetrahydrocannabinol (delta9-THC) and cannabinol, and the many synthetic agonists that have been generated, e.g CP55,940 or WIN55,212-2, several endogenous ligands have recently been identified. These include the arachidonic acid derivatives anandamide and 2-arachidonylglycerol as well as the fatty acid palmitoylethanolamide. Although in the past many studies described growth inhibitory effects of cannabinoid agonists on the in vitro proliferation of hematopoietic cells, recent studies demonstrated that activation of Cb2 may have growth stimulatory effects on blood precursor cells. We demonstrated that many murine hematopoietic growth factor (HGF) dependent cell lines also require the presence of anandamide for optimal growth in serum free culture. Thus, the Cb2 receptor may be an important regulator of normal hematopoietic growth and development. These results strengthen our finding that Cb2 is a proto-oncogene and may implicate a growth advantage for leukemia cells that aberrantly express Cb2. Here we briefly review the mechanisms and application of retroviral insertional mutagenesis in leukemic transformation in mice and discuss the role of the peripheral cannabinoid receptor in leukemia development and normal hematopoiesis.

Inhibition of adenylyl cyclase isoforms V and VI by various Gbetagamma subunits

An intriguing development in the G-protein signaling field has been the finding that not only the Galpha subunit, but also Gbetagamma subunits, affect a number of downstream target molecules. One of the downstream targets of Gbetagamma is adenylyl cyclase, and it has been demonstrated that a number of isoforms of adenylyl cyclase can be either inhibited or stimulated by Gbetagamma subunits. Until now, adenylyl cyclase type I has been the only isoform reported to be inhibited by free Gbetagamma. Here we show by transient cotransfection into COS-7 cells of either adenylyl cyclase V or VI, together with Ggamma2 and various Gbeta subunits, that these two adenylyl cyclase isozymes are markedly inhibited by Gbetagamma. In addition, we show that Gbeta1 and Gbeta5 subunits differ in their activity. Gbeta1 transfected alone markedly inhibited adenylyl cylcase V and VI (probably by recruiting endogenous Ggamma subunits). On the other hand, Gbeta5 produced less inhibition of these isozymes, and its activity was enhanced by the addition of Ggamma2. These results demonstrate that adenylyl cyclase types V and VI are inhibited by Gbetagamma dimers and that Gbeta1 and Gbeta5 subunits differ in their capacity to regulate these adenylyl cyclase isozymes.

An entourage effect: inactive endogenous fatty acid glycerol esters enhance 2-arachidonoyl-glycerol cannabinoid activity

2-Arachidonoyl-glycerol (2-Ara-GI) has been isolated from various tissues and identified as an endogenous ligand for both cannabinoid receptors, CB1 and CB2. Here we report that in spleen, as in brain and gut, 2-Ara-GI is accompanied by several 2-acyl-glycerol esters, two major ones being 2-linoleoyl-glycerol (2-Lino-Gl) and 2-palmitoyl-glycerol (2-Palm-Gl). These two esters do not bind to the cannabinoid receptors, nor do they inhibit adenylyl cyclase via either CB1 or CB2; however, they significantly potentiate the apparent binding of 2-Ara-Gl and its apparent capacity to inhibit adenylyl cyclase. Together these esters also significantly potentiate 2-Ara-Gl inhibition of motor behavior, immobility on a ring, analgesia on a hot plate and hypothermia caused by 2-Ara-Gl in mice. 2-Lino-Gl, but not 2-Palm-GI, significantly inhibits the inactivation of 2-Ara-Gl by neuronal and basophilic cells. These data indicate that the biological activity of 2-Ara-Gl can be increased by related, endogenous 2-acyl-glycerols, which alone show no significant activity in any of the tests employed. This effect ('entourage effect') may represent a novel route for molecular regulation of endogenous cannabinoid activity.

Complex pharmacology of natural cannabinoids: evidence for partial agonist activity of delta9-tetrahydrocannabinol and antagonist activity of cannabidiol on rat brain cannabinoid receptors

Delta9-tetrahydrocannabinol (delta9-THC), cannabinol and cannabidiol are three important natural cannabinoids from the Marijuana plant (Cannabis sativa). Using [35S]GTP-gamma-S binding on rat cerebellar homogenate as an index of cannabinoid receptor activation we show that: delta9-THC does not induce the maximal effect obtained by classical cannabinoid receptor agonists such as CP55940. Moreover at high concentration delta9-THC exhibits antagonist properties. Cannabinol is a weak agonist on rat cerebellar cannabinoid receptors and cannabidiol behaves as an antagonist acting in the micromolar range.

Differential modulation of adenylyl cyclases I and II by various G beta subunits

The accepted dogma concerning the regulation of adenylyl cyclase (AC) activity by G beta gamma dimers states that the various isoforms of AC respond differently to the presence of free G beta gamma. It has been demonstrated that AC I activity is inhibited and AC II activity is stimulated by G beta gamma subunits. This result does not address the possible differences in modulation that may exist among the different G beta gamma heterodimers. Six isoforms of G beta and 12 isoforms of G gamma have been cloned to date. We have established a cell transfection system in which G beta and G gamma cDNAs were cotransfected with either AC isoform I or II and the activity of these isoforms was determined. We found that while AC I activity was inhibited by both G beta 1/gamma 2 and G beta 5/gamma 2 combinations, AC II responded differentially and was stimulated by G beta 1/gamma 2 and inhibited by G beta 5/gamma 2. This finding demonstrates differential modulatory activity by different combinations of G beta gamma on the same AC isoform and demonstrates another level of complexity within the AC signaling system.

Pharmacology of cannabinoid CB1 and CB2 receptors

There are at least two types of cannabinoid receptors, CB1 and CB2, both coupled to G-proteins. CB1 receptors are present in the central nervous system and CB1 and CB2 receptors in certain peripheral tissues. The existence of endogenous cannabinoid receptor agonists has also been demonstrated. These discoveries have led to the development of selective cannabinoid CB1 and CB2 receptor ligands. This review focuses on the classification, binding properties, effector systems and distribution of cannabinoid receptors. It also describes the various cannabinoid receptor agonists and antagonists now available and considers the main in vivo and in vitro bioassay methods that are generally used.

Cannabinol derivatives: binding to cannabinoid receptors and inhibition of adenylylcyclase

Several derivatives of cannabinol and the 1,1-dimethylheptyl homolog (DMH) of cannabinol were prepared and assayed for binding to the brain and the peripheral cannabinoid receptors (CB1 and CB2), as well as for activation of CB1- and CB2-mediated inhibition of adenylylcyclase. The DMH derivatives were much more potent than the pentyl (i.e., cannabinol) derivatives. 11-Hydroxycannabinol (4a) was found to bind potently to both CB1 and CB2 (Ki values of 38.0 +/- 7.2 and 26.6 +/- 5.5 nM, respectively) and to inhibit CB1-mediated adenylylcyclase with an EC50 of 58.1 +/- 6.2 nM but to cause only 20% inhibition of CB2-mediated adenylylcyclase at 10 microM. It behaves as a specific, though not potent, CB2 antagonist. 11-Hydroxycannabinol-DMH (4b) is a very potent agonist for both CB1 and CB2 (Ki values of 100 +/- 50 and 200 +/- 40 pM; EC50 of adenylylcyclase inhibition 56.2 +/- 4.2 and 207.5 +/- 27.8 pM, respectively).

Synthesis of prostaglandin E2 ethanolamide from anandamide by cyclooxygenase-2

Because of its structural similarity to polyunsaturated fatty acids, anandamide could serve as substrate for enzymes such as lipoxygenases and cyclooxygenases, which metabolize polyunsaturated fatty acids to potent bioactive metabolites. Here the ability of recombinant human cyclooxygenase-1 (hCOX-1) and cyclooxygenase-2 (hCOX-2) to metabolize anandamide was studied. Baculovirus-expressed and -purified hCOX-2, but not hCOX-1, effectively oxygenated anandamide. Reverse phase high pressure liquid chromatography analysis of the products derived from 1-14C-labeled anandamide showed that the products formed are similar to those formed with arachidonic acid as substrate. The major prostanoid product derived from anandamide was determined by mass spectrometry to be prostaglandin E2 ethanolamide. Incubation of anandamide with lysates and the intact cell line expressing COX-2 but not that of COX-1 produced prostaglandin E2 ethanolamide. These results demonstrate the existence of a COX-2-mediated pathway for anandamide metabolism, and the metabolites formed represent a novel class of prostaglandins.

Structural requirements for binding of anandamide-type compounds to the brain cannabinoid receptor

In order to establish the structural requirements for binding to the brain cannabinoid receptor (CB1), we have synthesized numerous fatty acid amides, ethanolamides, and some related simple derivatives and have determined their Ki values. A few alpha-methyl- or alpha, alpha-dimethylarachidonoylalkylamides were also examined. In the 20:4, n-6 series, the unsubstituted amide is inactive; N-monoalkylation, at least up to a branched pentyl group, leads to significant binding. N,N-Dialkylation, with or without hydroxylation on one of the alkyl groups, leads to elimination of activity. Hydroxylation of the N-monoalkyl group at the omega carbon atom retains activity. In the 20x, n-6 series, x has to be either 3 or 4; the presence of only two double bonds leads to inactivation. In the n-3 series, the limited data reported suggest that the derived ethanolamides are either inactive or less active than comparable compounds in the n-6 series. Alkylation or dialkylation of the alpha carbon adjacent to the carbonyl group retains the level of binding in the case of anandamide (compounds 48, 49); however, alpha-monomethylation or alpha,alpha-dimethylation of N-propyl derivatives (50-53) potentiates binding and leads to the most active compounds seen in the present work (Ki values of 6.9 +/- 0.7 to 8.4 +/- 1.1 nM). We have confirmed that the presence of a chiral center on the N-alkyl substituent may lead to enantiomers which differ in their levels of binding (compounds 54, 57 and 55, 56).

Biosynthesis, uptake, and degradation of anandamide and palmitoylethanolamide in leukocytes

Anandamide (arachidonoylethanolamide, AnNH) and palmitoylethanolamide (PEA) have been proposed as the physiological ligands, respectively, of central and peripheral cannabinoid receptors. Both of these receptors are expressed in immune cells, including macrophages and mast cells/basophils, where immunomodulatory and/or anti-inflammatory actions of AnNH and PEA have been recently reported. We now provide biochemical grounds to these actions by showing that the biosynthesis, uptake, and degradation of AnNH and PEA occur in leukocytes. On stimulation with ionomycin, J774 macrophages and RBL-2H3 basophils produced AnNH and PEA, probably through the hydrolysis of the corresponding N-acylphosphatidylethanolamines, also found among endogenous phospholipids. Immunological challenge of RBL-2H3 cells also caused AnNH and PEA release. The chemical structure and the amounts of AnNH and PEA produced upon ionomycin stimulation were determined by means of double radiolabeling experiments and isotope dilution gas chromatography/electron impact mass spectrometry. Both cell lines rapidly sequestered the two amides from the culture medium through temperature-dependent, saturable and chemically inactivable mechanisms. Once uptaken by basophils, AnNH and PEA compete for the same inactivating enzyme which catalyzes their hydrolysis to ethanolamine. This enzyme was found in both microsomal and 10,000 x g fractions of RBL cell homogenates, and exhibited similar inhibition and temperature/pH dependence profiles but a significantly higher affinity for PEA with respect to neuronal "anandamide amidohydrolase." The finding of biosynthetic and inactivating mechanisms for AnNH and PEA in macrophages and basophils supports the previously proposed role as local modulators of immune/inflammatory reactions for these two long chain acylethanolamides.

Metabolic stimulation of mouse spleen lymphocytes by low doses of delta9-tetrahydrocannabinol

The present work was undertaken to study the metabolic response of mouse spleen lymphocytes to physiologically relevant doses of delta9-tetrahydrocannabinol (THC), the major active component of marijuana. At those concentrations (i.e. nanomolar range), THC induced a 2-2.5-fold stimulation of both glucose oxidation to CO2 and phospholipid synthesis from glucose. This stimulation was (i) dose-dependent up to 1 microM THC, (ii) mimicked by the synthetic cannabinoid HU-210, (iii) prevented by forskolin and pertussis toxin, and (iv) unaffected by the CB1 receptor antagonist SR141716A. THC was also able to antagonize the forskolin-induced elevation of intracellular cAMP concentration. In contrast, at non-physiological, cytotoxic doses (i.e. micromolar range) THC markedly depressed glucose metabolism in lymphocytes by a cannabinoid receptor-independent pathway. Results thus indicate that physiologically relevant doses of THC induce a metabolic stimulation of lymphocytes that seems to be mediated by a cannabinoid receptor-dependent pathway.