Effects of Peripheral Cannabinoid Receptor Ligands on Motility and Polarization in Neutrophil-like HL60 Cells and Human Neutrophils

Controlling 2-arachidonoylglycerol metabolism as an anti-inflammatory strategy

The endocannabinoid system is implicated in, and regulates, several physiological processes, ranging from food intake and energy balance to pain and inflammation. 2-Arachidonoylglycerol (2-AG) is a full agonist at the cannabinoid receptors which classically mediate its effects. The activity of this bioactive lipid is dependent on its endogenous levels, which are tightly controlled by several hydrolases, monoacylglycerol lipase and α/β-hydrolase domain 6 and 12. Moreover, 2-AG is also a substrate of cyclooxygenase-2, and this reaction leads to the formation of prostaglandin glycerol esters, the effects of which remain to be fully elucidated. In this review we discuss the multiple mechanisms by which 2-AG controls inflammation and the therapeutic potential of 2-AG metabolism inhibitors.

Orphan G protein receptor GPR55 as an emerging target in cancer therapy and management

G protein-coupled receptors (GPCRs) modulate a vast array of cellular processes. The current review gives an overview of the general characteristics of GPCRs and their role in physiological conditions. In addition, it describes the current knowledge of the physiological and pathophysiological functions of GPR55, an orphan GPCR, and how it can be exploited as a therapeutic target to combat various cancers.

Cannabinoid receptor 2: potential role in immunomodulation and neuroinflammation

An accumulating body of evidence suggests that endocannabinoids and cannabinoid receptors type 1 and 2 (CB(1), CB(2)) play a significant role in physiologic and pathologic processes, including cognitive and immune functions. While the addictive properties of marijuana, an extract from the Cannabis plant, are well recognized, there is growing appreciation of the therapeutic potential of cannabinoids in multiple pathologic conditions involving chronic inflammation (inflammatory bowel disease, arthritis, autoimmune disorders, multiple sclerosis, HIV-1 infection, stroke, Alzheimer's disease to name a few), mainly mediated by CB(2) activation. Development of CB(2) agonists as therapeutic agents has been hampered by the complexity of their intracellular signaling, relative paucity of highly selective compounds and insufficient data regarding end effects in the target cells and organs. This review attempts to summarize recent advances in studies of CB(2) activation in the setting of neuroinflammation, immunomodulation and HIV-1 infection.

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

OBJECTIVE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

2-Arachidonoyl-glycerol- and arachidonic acid-stimulated neutrophils release antimicrobial effectors against E. coli, S. aureus, HSV-1, and RSV

The endocannabinoid 2-AG is highly susceptible to its hydrolysis into AA, which activates neutrophils through de novo LTB(4) biosynthesis, independently of CB activation. In this study, we show that 2-AG and AA stimulate neutrophils to release antimicrobial effectors. Supernatants of neutrophils activated with nanomolar concentrations of 2-AG and AA indeed inhibited the infectivity of HSV-1 and RSV. Additionally, the supernatants of 2-AG- and AA-stimulated neutrophils strongly impaired the growth of Escherichia coli and Staphylococcus aureus. This correlated with the release of a large amount (micrograms) of α-defensins, as well as a limited amount (nanograms) of LL-37. All the effects of AA and 2-AG mentioned above were prevented by inhibiting LTB(4) biosynthesis or by blocking BLT(1). Importantly, neither CB(2) receptor agonists nor antagonists could mimic nor prevent the effects of 2-AG, respectively. In fact, qPCR data show that contaminating eosinophils express ∼100-fold more CB(2) receptor mRNA than purified neutrophils, suggesting that CB(2) receptor expression by human neutrophils is limited and that contaminating eosinophils are likely responsible for the previously documented CB(2) expression by freshly isolated human neutrophils. The rapid conversion of 2-AG to AA and their subsequent metabolism into LTB(4) promote 2-AG and AA as multifunctional activators of neutrophils, mainly exerting their effects by activating the BLT(1). Considering that nanomolar concentrations of AA or 2-AG were sufficient to impair viral infectivity, this suggests potential physiological roles for 2-AG and AA as regulators of host defense in vivo.

Regulation of MMP-9 by a WIN-binding site in the monocyte-macrophage system independent from cannabinoid receptors

The cannabinoid system is known to be involved in the regulation of inflammatory processes. Therefore, drugs targeting cannabinoid receptors are considered as candidates for anti-inflammatory and tissue protective therapy. We demonstrated that the prototypical cannabinoid agonist R(+)WIN55,212-2 (WIN) reduced the secretion of matrix metalloproteinase-9 (MMP-9) in a murine model of cigarette-smoke induced lung inflammation. In experiments using primary cells and cell lines of the monocyte-macrophage-system we found that binding of the cannabinoid-receptor agonist WIN to a stereo-selective, specific binding site in cells of the monocyte-macrophage-system induced a significant down-regulation of MMP-9 secretion and disturbance of intracellular processing, which subsequently down-regulated MMP-9 mRNA expression via a ERK1/2-phosphorylation-dependent pathway. Surprisingly, the anti-inflammatory effect was independent from classical cannabinoid receptors. Our experiments supposed an involvement of TRPV1, but other yet unidentified sites are also possible. We conclude that cannabinoid-induced control of MMP-9 in the monocyte-macrophage system via a cannabinoid-receptor independent pathway represents a general option for tissue protection during inflammation, such as during lung inflammation and other diseases associated with inflammatory tissue damage.

CB₂: therapeutic target-in-waiting

CB₂ cannabinoid receptor agonists hold promise as a new class of therapeutics for indications as diverse as pain, neuroinflammation, immune suppression and osteoporosis. These potential indications are supported by strong preliminary data from multiple investigators using diverse preclinical models. However, clinical trials for CB₂ agonists, when they have been reported have generally been disappointing. This review considers possible explanations for the mismatch between promising preclinical data and disappointing clinical data. We propose that a more careful consideration of CB₂ receptor pharmacology may help move CB₂ agonists from "promising" to "effective" therapeutics.

Activation of cannabinoid receptor 2 attenuates leukocyte-endothelial cell interactions and blood-brain barrier dysfunction under inflammatory conditions

Previous studies have shown that modulation of the receptor-mediated cannabinoid system during neuroinflammation can produce potent neuroprotective and anti-inflammatory effects. However, in this context, little is known about how selective activation of the cannabinoid type-2 receptor (CB2R) affects the activated state of the brain endothelium and blood-brain barrier (BBB) function. Using human brain tissues and primary human brain microvascular endothelial cells (BMVECs), we demonstrate that the CB2R is highly upregulated during inflammatory insult. We then examined whether the CB2R agonists could attenuate inflammatory responses at the BBB using a mouse model of LPS-induced encephalitis and highly selective CB2R agonists. Visualization by intravital microscopy revealed that administration of JWH133 [(6aR,10aR)-3-(1,1-dimethylbutyl)-6a,7,10,10a-tetrahydro-6,6,9-trimethyl-6H-dibenzo[b,d]pyran] or a novel resorcinol-based compound, O-1966 (1-[4-(1,1-dimethyl-heptyl)-2,6-dimethoxy-phenyl]-3-methyl-cyclohexanol), greatly attenuated leukocyte adhesion in surface pial vessels and in deep ascending cortical postcapillary venules. BBB permeability assessments with small and large fluorescent tracers showed that CB2R agonists were effective at preventing barrier leakiness after LPS administration. To determine whether the effects by CB2R agonists on barrier protection are not only due to the CB2R modulation of immune cell function, we tested the agonists in vitro with barrier-forming primary BMVECs. Remarkably, the addition of CB2R agonist increased transendothelial electrical resistance and increased the amount of tight junction protein present in membrane fractions. Furthermore, CB2R agonists decreased the induction of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 surface expression in BMVECs exposed to various proinflammatory mediators. Together, these results suggest that pharmacological CB2R ligands offer a new strategy for BBB protection during neuroinflammation.

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

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

Cannabinoid receptor 2 is critical for the homing and retention of marginal zone B lineage cells and for efficient T-independent immune responses

The endocannabinoid system has emerged as an important regulator of immune responses, with the cannabinoid receptor 2 (CB2) and its principle ligand 2-archidonoylglycerol playing a major role. How CB2 regulates B cell functions is not clear, even though they express the highest levels of CB2 among immune cell subsets. In this study, we show that CB2-deficient mice have a significant reduction in the absolute number of marginal zone (MZ) B cells and their immediate precursor, transitional-2 MZ precursor. The loss of MZ lineage cells in CB2(-/-) mice was shown to be B cell intrinsic using bone marrow chimeras and was not due to a developmental or functional defect as determined by B cell phenotype, proliferation, and Ig production. Furthermore, CB2(-/-) B cells were similar to wild type in their apoptosis, cell turnover, and BCR and Notch-2 signaling. We then demonstrated that CB2(-/-) MZ lineage B cells were less efficient at homing to the MZ and that their subsequent retention was also regulated by CB2. CB2(-/-) mice immunized with T-independent Ags produced significantly less Ag-specific IgM. This study demonstrates that CB2 positively regulates T-independent immune responses by controlling the localization and positioning of MZ lineage cells to the MZ.

GPR55 regulates cannabinoid 2 receptor-mediated responses in human neutrophils

The directional migration of neutrophils towards inflammatory mediators, such as chemokines and cannabinoids, occurs via the activation of seven transmembrane G protein coupled receptors (7TM/GPCRs) and is a highly organized process. A crucial role for controlling neutrophil migration has been ascribed to the cannabinoid CB(2) receptor (CB(2)R), but additional modulatory sites distinct from CB(2)R have recently been suggested to impact CB(2)R-mediated effector functions in neutrophils. Here, we provide evidence that the recently de-orphanized 7TM/GPCR GPR55 potently modulates CB(2)R-mediated responses. We show that GPR55 is expressed in human blood neutrophils and its activation augments the migratory response towards the CB(2)R agonist 2-arachidonoylglycerol (2-AG), while inhibiting neutrophil degranulation and reactive oxygen species (ROS) production. Using HEK293 and HL60 cell lines, along with primary neutrophils, we show that GPR55 and CB(2)R interfere with each other's signaling pathways at the level of small GTPases, such as Rac2 and Cdc42. This ultimately leads to cellular polarization and efficient migration as well as abrogation of degranulation and ROS formation in neutrophils. Therefore, GPR55 limits the tissue-injuring inflammatory responses mediated by CB(2)R, while it synergizes with CB(2)R in recruiting neutrophils to sites of inflammation.

Pleiotropic effects of prostaglandin E2 in hematopoiesis; prostaglandin E2 and other eicosanoids regulate hematopoietic stem and progenitor cell function

Eicosanoids have been implicated in the physiological regulation of hematopoiesis with pleiotropic effects on hematopoietic stem cells and various classes of lineage restricted progenitor cells. Herein we review the effects of eicosanoids on hematopoiesis, focusing on new findings implicating prostaglandin E(2) in enhancing hematopoietic stem cell engraftment by enhancing stem cell homing, survival and self-renewal. We also describe a role for cannabinoids in hematopoiesis. Lastly, we discuss the yin and yang of various eicosanoids in modulating hematopoietic stem and progenitor cell functions and summarize potential strategies to take advantage of these effects for therapeutic benefit for hematopoietic stem cell transplantation.

HIV-1 infection and alcohol abuse: neurocognitive impairment, mechanisms of neurodegeneration and therapeutic interventions

Clinical studies indicate that alcohol dependence has an additive effect on cognitive deficits associated with HIV-1 infection. Findings in humans and animal models suggest that alcohol, similar to HIV-1, induces inflammatory processes in the brain leading to neurodegeneration. The causes of HIV-1-associated neurotoxicity are comparable to those mediating alcohol-induced neuronal injury. This review aims to present the mechanisms of the combined effects of HIV-1 and alcohol abuse in the brain and to discuss neuroprotective therapies. Oxidative stress, overproduction of pro-inflammatory factors, impairment of blood-brain barrier and glutamate associated neurotoxicity appear to play important roles in alcohol driven neurodegeneration. Diminution of neuroinflammation constitutes a logical approach for prevention of HIV-1 and alcohol mediated neurodegeneration. Agonists of cannabinoid receptor 2 (CB₂) possess potent anti-inflammatory and neuroprotective properties. We address multifaceted beneficial effects of CB₂ activation in the setting of HIV-1 brain infection and alcohol abuse.

Chronic Δ-9-tetrahydrocannabinol administration increases lymphocyte CXCR4 expression in rhesus macaques

Cannabinoids have been reported to produce various immunomodulatory effects, which could potentially impact the host response to bacterial or viral infection. We have recently demonstrated that chronic Δ-9-tetrahydrocannabinol (THC; 0.32 mg/kg i.m., BID) decreased early mortality in rhesus macaques infected with simian immunodeficiency virus (SIV). However, the possibility that prolonged THC administration affects lymphocyte counts, phenotype, and proliferation indices has not been addressed. We examined expression of proliferative and phenotypic markers in circulating lymphocytes of male young adult rhesus macaques chronically-treated with THC (i.m. twice daily 0.32 mg/kg) for 12 months. Chronic THC administration did not alter lymphocyte subtypes, naïve and memory subsets, proliferation, or apoptosis of T lymphocytes when compared to time-matched vehicle-treated controls. However, chronic THC increased T lymphocyte CXCR4 expression on both CD4+ and CD8+ T lymphocytes compared to control. These results show that chronic THC administration produces changes in T cell phenotype, which can potentially contribute to host immunomodulation to infectious challenges.

Cannabinoid Receptor 2 Deficiency in Haematopoietic cells Aggravates Early Atherosclerosis in LDL Receptor Deficient Mice

OBJECTIVE

The cannabinoid receptor 2 (CB2) has been implicated to play a role in various inflammatory processes. Since atherosclerosis is currently considered a chronic inflammatory disease, we studied the effect of haematopoietic CB2 deficiency on atherosclerosis development.

METHODS AND RESULTS

To investigate the effect of CB2 deficiency in immune cells on atherogenesis in vivo, a bone marrow transplantation was performed in irradiated LDL receptor deficient mice (LDLr(-/-)), using CB2 deficient (CB2(-/-)) or wildtype (WT) donor mice. After 12 weeks on a high fat-high cholesterol diet, en face analysis showed that atherosclerosis in the aortic arch was significantly increased in CB2(-/-) transplanted animals (6.40 ± 3.21%) as compared to WT transplanted mice (3.85 ± 1.61%). Although the total lesion area in the aortic root was not significantly different between WT and CB2(-/-) transplanted mice (0.45 ± 0.13 mm(2) and 0.51 ± 0.17 mm(2), respectively), CB2(-/-) transplanted mice showed a significantly larger plaque area (0.13 ± 0.07 mm(2)) than WT transplanted mice (0.08 ± 0.05 mm(2)) in the aortic valve in which atherogenesis is in an earlier stage than in the other aortic valves.

CONCLUSIONS

Lack of endocannabinoid signaling via the CB2 receptor aggravates early atherosclerosis development in LDLr(-/-) mice, suggesting that CB2 specific activation may prevent the development of atherosclerosis.

Detecting constitutive activity and protean agonism at cannabinoid-2 receptor

Since the cannabinoid system is involved in regulating several physiological functions such as locomotor activity, cognition, nociception, food intake, and inflammatory reaction, it has been the subject of intense study. Research on the pharmacology of this system has enormously progressed in the last 20years. One intriguing aspect that emerged from this research is that cannabinoid receptors (CBs) express a high level of constitutive activity. Investigation on this particular aspect of receptor pharmacology has largely focused on CB1, the CB subtype highly expressed in several brain regions. More recently, research on constitutive activity on the other CB subtype, CB2, was stimulated by the increasing interest on its potential as target for the treatment of various pathologies (e.g., pain and inflammation). There are several possible implications of constitutive activity on the therapeutic action of both agonists and antagonists, and consequently, it is important to have valuable methods to study this aspect of CB2 pharmacology. In the present chapter, we describe three methods to study constitutive activity at CB2: two classical methods relying on the detection of changes in cAMP level and GTPγS binding and a new one based on cell impedance measurement. In addition, we also included a section on detection of protean agonism, which is an interesting pharmacological phenomenon strictly linked to constitutive activity.

The endocannabinoid 2-arachidonoyl-glycerol activates human neutrophils: critical role of its hydrolysis and de novo leukotriene B4 biosynthesis

Although endocannabinoids are important players in nociception and obesity, their roles as immunomodulators remain elusive. The main endocannabinoids described to date, namely 2-arachidonoyl-glycerol (2-AG) and arachidonyl-ethanolamide (AEA), induce an intriguing profile of pro- and anti-inflammatory effects. This could relate to cell-specific cannabinoid receptor expression and/or the action of endocannabinoid-derived metabolites. Importantly, 2-AG and AEA comprise a molecule of arachidonic acid (AA) in their structure and are hydrolyzed rapidly. We postulated the following: 1) the released AA from endocannabinoid hydrolysis would be metabolized into eicosanoids; and 2) these eicosanoids would mediate some of the effects of endocannabinoids. To confirm these hypotheses, experiments were performed in which freshly isolated human neutrophils were treated with endocannabinoids. Unlike AEA, 2-AG stimulated myeloperoxidase release, kinase activation, and calcium mobilization by neutrophils. Although 2-AG did not induce the migration of neutrophils, it induced the release of a migrating activity for neutrophils. 2-AG also rapidly (1 min) induced a robust biosynthesis of leukotrienes, similar to that observed with AA. The effects of 2-AG were not mimicked nor prevented by cannabinoid receptor agonists or antagonists, respectively. Finally, the blockade of either 2-AG hydrolysis, leukotriene (LT) B(4) biosynthesis, or LTB(4) receptor 1 activation prevented all the effects of 2-AG on neutrophil functions. In conclusion, we demonstrated that 2-AG potently activates human neutrophils. This is the consequence of 2-AG hydrolysis, de novo LTB(4) biosynthesis, and an autocrine activation loop involving LTB(4) receptor 1.

Pharmacology, signaling and physiological relevance of the G protein-coupled receptor 55

According to The European Monitoring Centre for Drugs and Drug Addiction (EMCDDA), ∼70 million European adults have consumed cannabis on at least one occasion. Cannabis consumption leads to a variety of psychoactive effects due to the presence of the constituent Δ(9)-tetrahydrocannabinol (Δ(9)-THC). Δ(9)-THC interacts with the endocannabinoid system (ECS), which consists of the seven transmembrane spanning (7TM)/G protein-coupled receptors (GPCRs) CB(1) and CB(2), their respective ligands (endocannabinoids), and enzymes involved in their biosynthesis and degradation. This system plays a critical role in many physiological processes such as learning and memory, appetite control, pain sensation, motor coordination, lipogenesis, modulation of immune response, and the regulation of bone mass. Therefore, a huge effort has been spent trying to fully elucidate the composition and function of the ECS. The G protein-coupled receptor 55 (GPR55) was recently proposed as a novel component of this system; however, its classification as a cannabinoid receptor has been significantly hampered by its complex pharmacology, signaling, and cellular function. GPR55 is phylogenetically distinct from the traditional cannabinoid receptors, but in some experimental paradigms, it is activated by endocannabinoids, phytocannabinoids, and synthetic cannabinoid ligands. However, the most potent compound appears to be a lysophospholipid known as lysophosphatidylinositol (LPI). Here, we provide a comprehensive evaluation of the current pharmacology and signaling of GPR55 and review the proposed role of this receptor in a number of physiological and pathophysiological processes.

Eicosanoid regulation of hematopoiesis and hematopoietic stem and progenitor trafficking

Hematopoietic stem cell (HSC) transplantation is a potentially curative treatment for numerous hematological malignancies. The transplant procedure as performed today takes advantage of HSC trafficking; either egress of HSC from the bone marrow to the peripheral blood, that is, mobilization, for acquisition of the hematopoietic graft, and/or trafficking of HSC from the peripheral blood to bone marrow niches in the recipient patient, that is HSC homing. Numerous studies, many of which are reviewed herein, have defined hematopoietic regulatory mechanisms mediated by the 20-carbon lipid family of eicosanoids, and recent evidence strongly supports a role for eicosanoids in regulation of hematopoietic trafficking, adding a new role whereby eicosanoids regulate hematopoiesis. Short-term exposure of HSC to the eicosanoid prostaglandin E(2) increases CXCR4 receptor expression, migration and in vivo homing of HSC. In contrast, cannabinoids reduce hematopoietic progenitor cell (HPC) CXCR4 expression and induce HPC mobilization when administered in vivo. Leukotrienes have been shown to alter CD34(+) cell adhesion, migration and regulate HSC proliferation, suggesting that eicosanoids have both opposing and complimentary roles in the regulation of hematopoiesis. As numerous FDA approved compounds regulate eicosanoid signaling or biosynthesis, the utility of eicosanoid-based therapeutic strategies to improve hematopoietic transplantation can be rapidly evaluated.

Characterizing cannabinoid CB2 receptor ligands using DiscoveRx PathHunter beta-arrestin assay

The authors have characterized a set of cannabinoid CB(2) receptor ligands, including triaryl bis sulfone inverse agonists, in a cell-based receptor/beta-arrestin interaction assay (DiscoveRx PathHunter). The results were compared with results using a competitive ligand binding assay, and with effects on forskolin-stimulated cAMP levels (PerkinElmer LANCE). The authors show good correlation between the 3 assay systems tested, with the beta-arrestin protein complementation assay exhibiting a more robust signal than the cAMP assay for cannabinoid CB(2) agonists. Further assay validation shows that DiscoveRx PathHunter HEK293 CB(2) beta-arrestin assay can be carried out from cryopreserved cell suspensions, eliminating variations caused by the need for multiple cell pools during live cell screening campaigns. These results, and the authors' results evaluating a test set of random library compounds, validate the use of ligand-induced interaction between the human cannabinoid CB(2) receptor and beta-arrestin as an appropriate and valuable screening platform for compounds specific for the cannabinoid CB(2) receptor.

The emerging role of the endocannabinoid system in cardiovascular disease

Endocannabinoids are endogenous bioactive lipid mediators present both in the brain and various peripheral tissues, which exert their biological effects via interaction with specific G-protein-coupled cannabinoid receptors, the CB(1) and CB(2). Pathological overactivation of the endocannabinoid system (ECS) in various forms of shock and heart failure may contribute to the underlying pathology and cardiodepressive state by the activation of the cardiovascular CB(1) receptors. Furthermore, tonic activation of CB(1) receptors by endocannabinoids has also been implicated in the development of various cardiovascular risk factors in obesity/metabolic syndrome and diabetes, such as plasma lipid alterations, abdominal obesity, hepatic steatosis, inflammation, and insulin and leptin resistance. In contrast, activation of CB(2) receptors in immune cells exerts various immunomodulatory effects, and the CB(2) receptors in endothelial and inflammatory cells appear to limit the endothelial inflammatory response, chemotaxis, and inflammatory cell adhesion and activation in atherosclerosis and reperfusion injury. Here, we will overview the cardiovascular actions of endocannabinoids and the growing body of evidence implicating the dysregulation of the ECS in a variety of cardiovascular diseases. We will also discuss the therapeutic potential of the modulation of the ECS by selective agonists/antagonists in various cardiovascular disorders associated with inflammation and tissue injury, ranging from myocardial infarction and heart failure to atherosclerosis and cardiometabolic disorders.

CB(2) cannabinoid receptor activation is cardioprotective in a mouse model of ischemia/reperfusion

Preventive treatment with cannabinoid agonists has been reported to reduce the infarct size in a mouse model of myocardial ischemia/reperfusion. Here we investigated the possible cardioprotective effect of selective CB(2) cannabinoid receptor activation during ischemia. We performed left coronary artery ligature in C57Bl/6 mice for 30 min, followed by 24 h of reperfusion. Five minutes before reperfusion, mice received intraperitoneal injection of the CB(2) selective agonist JWH-133 (20 mg/kg) or vehicle. Infarct size was assessed histologically and by cardiac troponin I (cTnI) ELISA. Immunohistochemical analysis of leukocyte infiltration, oxidative stress in situ quantification, real-time RT-PCR analysis of inflammatory mediators as well as western blots for kinase phosphorylation was also performed. In addition, we studied chemotaxis and integrin expression of human neutrophils in vitro. JWH-133 significantly reduced the infarct size (I/area at risk: 19.27%+/-1.91) as compared to vehicle-treated mice (31.77%+/-2.7). This was associated with a reduction of oxidative stress and neutrophil infiltration in the infarcted myocardium, whereas activation of ERK 1/2 and STAT-3 was increased. Preinjection of PI3K inhibitor LY294002, MEK 1/2 inhibitor U0126 and JAK-2 inhibitor AG-490 partially abrogated the JWH-133 mediated infarct size reduction. No changes in cardiac CXCL1, CXCL2, CCL3, TNF-alpha, and ICAM-1 expression levels were found. Furthermore, JWH-133 inhibited the TNF-alpha induced chemotaxis and integrin CD18/CD11b (Mac-1) upregulation on human neutrophils. Our data suggest that JWH-133 administration during ischemia reduces the infarct size in a mouse model of myocardial ischemia/reperfusion through a direct cardioprotective activity on cardiomyocytes and neutrophils.

Endocannabinoid functions controlling neuronal specification during brain development

Endocannabinoids (eCBs) regulate a broad range of physiological functions in the postnatal brain and are implicated in the neuropathogenesis of psychiatric and metabolic diseases. Accumulating evidence indicates that eCB signaling also serves key functions during neurodevelopment; and is inherently involved in the control of neurogenesis, neural progenitor proliferation, lineage segregation, and the migration and phenotypic specification of immature neurons. Recent advances in developmental biology define fundamental eCB-driven cellular mechanisms that also contribute to our understanding of the molecular substrates of prenatal drug, in particular cannabis, actions. Here, we summarize known organizing principles of eCB-signaling systems in the developing telencephalon, and outline the sequence of decision points and underlying signaling pathways upon CB1 cannabinoid receptor activation that contribute to neuronal diversification in the developing brain. Finally, we discuss how these novel principles affect the formation of complex neuronal networks.

CB2 receptor-mediated migration of immune cells: it can go either way

Though many studies have examined the role of CB2 receptors in immune cell migration, it has been difficult to form definitive conclusions about the physiopathological role of these receptors in regulating immune responses and how this might be pharmacologically targeted for therapy. Do cannabinoids promote inflammation through the recruitment of immune cells, or reduce inflammation by interfering with the action of other chemoattractants? Is therapeutic intervention with an agonist or antagonist more appropriate for the reduction of inflammation? In this review, we will summarize the progress that has been made in answering these questions and outline current hypotheses.

Inhibition of human neutrophil chemotaxis by endogenous cannabinoids and phytocannabinoids: evidence for a site distinct from CB1 and CB2

Here, we show a novel pharmacology for inhibition of human neutrophil migration by endocannabinoids, phytocannabinoids, and related compounds. The endocannabinoids virodhamine and N-arachidonoyl dopamine are potent inhibitors of N-formyl-l-methionyl-l-leucyl-l-phenylalanine-induced migration of human neutrophils, with IC(50) values of 0.2 and 8.80 nM, respectively. The endocannabinoid anandamide inhibits human neutrophil migration at nanomolar concentrations in a biphasic manner. The phytocannabinoid (-)-cannabidiol is a partial agonist, being approximately 40 fold more potent than (+)-cannabidiol; abnormal-cannabidiol is a full agonist. Furthermore, the abnormal-cannabidiol (CBD) analog trans-4-[3-methyl-6-(1-methylethenyl)-2-cyclohexen-1-yl]-5-methyl-1,3-benzenediol (O-1602) inhibits migration, with an IC(50) value of 33 nM. This reported profile of agonist efficacy and potency parallels with the pharmacology of the novel "abnormal-cannabidiol" receptor or a related orphan G protein-coupled receptor, which are already known to modulate cell migration. Although having no effect alone, N-arachidonoyl l-serine attenuated inhibition of human neutrophil migration induced by anandamide, virodhamine, and abnormal-CBD. Our data also suggest that there is cross-talk/negative co-operativity between the cannabinoid CB(2) receptor and this novel target: CB(2) receptor antagonists significantly enhance the inhibition observed with anandamide and virodhamine. This study reveals that certain endogenous lipids, phytocannabinoids, and related ligands are potent inhibitors of human neutrophil migration, and it implicates a novel pharmacological target distinct from cannabinoid CB(1) and CB(2) receptors; this target is antagonized by the endogenous compound N-arachidonoyl l-serine. Furthermore, our findings have implications for the potential pharmacological manipulation of elements of the endocannabinoid system for the treatment of various inflammatory conditions.

Involvement of cannabinoid receptor CB2 in dectin-1-mediated macrophage phagocytosis

Cannabinoid receptors are expressed in macrophages, but little is known of their roles. We here examined their involvement in phagocytosis. The presence of 2-arachidonylglycerol, an endocannabinoid, augmented the phagocytosis of zymosan by mouse macrophages, while the phagocytosis of Escherichia coli, Staphylococcus aureus, apoptotic cells or latex beads remained unaffected. An agonist of the cannabinoid receptors CB1 and CB2 also stimulated the phagocytosis of zymosan. The stimulatory effect of 2-arachidonylglycerol was abolished when phagocytosis reactions were carried out in the presence of an antagonist of CB2 but not of CB1. Furthermore, the phagocytosis of zymosan in the presence of 2-arachidonylglycerol was severely inhibited by the addition of a beta-glucan-containing carbohydrate or antibody neutralizing dectin-1, a beta-glucan-recognizing phagocytosis receptor. These results suggested that the activation of CB2 in macrophages leads to the stimulation of dectin-1-mediated phagocytosis.

Biology and therapeutic potential of cannabinoid CB2 receptor inverse agonists

Evidence has emerged suggesting a role for the cannabinoid CB2 receptor in immune cell motility. This provides a rationale for a novel and generalized immunoregulatory role for cannabinoid CB2 receptor-specific compounds. In support of this possibility, we will review the biology of a class of cannabinoid CB2 receptor-specific inverse agonist, the triaryl bis-sulfones. We will show that one candidate, Sch.414319, is potent and selective for the cannabinoid CB2 receptor, based on profiling studies using biochemical assays for 45 enzymes and 80 G-protein coupled receptors and ion channels. We will describe initial mechanistic studies using this optimized triaryl bis-sulfone, showing that the compound exerts a broad effect on cellular protein phosphorylations in human monocytes. This profile includes the down regulation of a required phosphorylation of the monocyte-specific actin bundling protein L-plastin. We suggest that this observation may provide a mechanism for the observed activity of Sch.414319 in vivo. Our continued analysis of the in vivo efficacy of this compound in diverse disease models shows that Sch.414319 is a potent modulator of immune cell mobility in vivo, can modulate bone damage in antigen-induced mono-articular arthritis in the rat, and is uniquely potent at blocking experimental autoimmune encephalomyelitis in the rat.

Temporal variation in CB2R levels following T lymphocyte activation: Evidence that cannabinoids modulate CXCL12-induced chemotaxis

Cannabinoids have long been proposed to affect the immune system, especially as one of the cannabinoid receptors, the cannabinoid receptor-2 (CB(2)R) has been found almost exclusively on immune cells. Here, using human in vitro activated peripheral blood-derived T lymphocytes we investigated the long-term changes in cannabinoid receptor protein expression following cellular activation and the effects of cannabinoids on migration. We report that resting T lymphocytes do not detectably express either the cannabinoid receptor-1 (CB(1)R) or CB(2)R at the protein level. However, CB(2)R protein expression is upregulated in a biphasic manner in T lymphocytes following activation by superantigen. The cannabinoids 2-AG and JWH-133 were found to elicit activation of downstream biochemical effectors (as assessed by the phosphorylation of the ERK1/2 MAP kinases). Neither 2-AG nor JWH-133 induced chemotaxis in day 5 activated T lymphocytes, when receptor expression was at its highest. Interestingly, both 2-AG and JWH-133 inhibited CXCL12-induced chemotaxis, suggesting a modulatory role for cannabinoids in activated T lymphocytes.

Targeting the CB2 receptor for immune modulation

Early work on the biology of the components of Cannabis sativa showed evidence for a potential influence on immune regulation. With the discovery of a peripheral cannabinoid receptor associated with immune cells, many laboratories have sought to link the immunoregulatory activities of cannabinoid compounds with this receptor, hoping that such compounds would lack the psychoactive effects of marijuana and other nonspecific cannabinoid agonists. In this report, the authors investigate the role of the cannabinoid CB2 receptor in immune regulation, with particular emphasis on compounds shown to regulate immune cell recruitment. The authors conclude by using the immune cell recruitment model to rationalise cannabinoid CB2 receptor-specific effects in modulating immune disease, particularly the increasing evidence for its role in experimental autoimmune encephalomyelitis and in influencing bone density.

Human receptors patched and smoothened partially transduce hedgehog signal when expressed in Drosophila cells

In humans, dysfunctions of the Hedgehog receptors Patched and Smoothened are responsible for numerous pathologies. However, signaling mechanisms involving these receptors are less well characterized in mammals than in Drosophila. To obtain structure-function relationship information on human Patched and Smoothened, we expressed these human receptors in Drosophila Schneider 2 cells. We show here that, as its Drosophila counterpart, human Patched is able to repress the signaling pathway in the absence of Hedgehog ligand. In response to Hedgehog, human Patched is able to release Drosophila Smoothened inhibition, suggesting that human Patched is expressed in a functional state in Drosophila cells. We also provide experiments showing that human Smo, when expressed in Schneider cells, is able to bind the alkaloid cyclopamine, suggesting that it is expressed in a native conformational state. Furthermore, contrary to Drosophila Smoothened, human Smoothened does not interact with the kinesin Costal 2 and thus is unable to transduce the Hedgehog signal. Moreover, cell surface fluorescent labeling suggest that human Smoothened is enriched at the Schneider 2 plasma membrane in response to Hedgehog. These results suggest that human Smoothened is expressed in a functional state in Drosophila cells, where it undergoes a regulation of its localization comparable with its Drosophila homologue. Thus, we propose that the upstream part of the Hedgehog pathway involving Hedgehog interaction with Patched, regulation of Smoothened by Patched, and Smoothened enrichment at the plasma membrane is highly conserved between Drosophila and humans; in contrast, signaling downstream of Smoothened is different.