Inhibition of the cyclic AMP signaling cascade and nuclear factor binding to CRE and kappaB elements by cannabinol, a minimally CNS-active cannabinoid

The Development of Cannabinoids as Therapeutic Agents in the United States

Cannabis is one of the oldest and widely used substances in the world. Cannabinoids within the cannabis plant, known as phytocannabinoids, mediate cannabis' effects through interactions with the body's endogenous cannabinoid system. This endogenous system, the endocannabinoid system, has important roles in physical and mental health. These roles point to the potential to develop cannabinoids as therapeutic agents while underscoring the risks related to interfering with the endogenous system during nonmedical use. This scoping narrative review synthesizes the current evidence for both the therapeutic and adverse effects of the major (i.e., Δ9-tetrahydrocannabinol and cannabidiol) and lesser studied minor phytocannabinoids, from nonclinical to clinical research. We pay particular attention to the areas where evidence is well established, including analgesic effects after acute exposures and neurocognitive risks after acute and chronic use. In addition, drug development considerations for cannabinoids as therapeutic agents within the United States are reviewed. The proposed clinical study design considerations encourage methodological standards for greater scientific rigor and reproducibility to ultimately extend our knowledge of the risks and benefits of cannabinoids for patients and providers. SIGNIFICANCE STATEMENT: This work provides a review of prior research related to phytocannabinoids, including therapeutic potential and known risks in the context of drug development within the United States. We also provide study design considerations for future cannabinoid drug development.

The effects of subacute exposure to a water-soluble cannabinol compound in male mice

Background

Cannabinol (CBN) is one of the many cannabinoids present in Cannabis sativa and has been explored as a potential treatment for sleeplessness. The purpose of this study was to determine the physiological and behavioral effects of subacute exposure to therapeutic and low pharmacological levels of a mechanically formed, stabilized water-soluble cannabinol nano-emulsion (CBNight™).

Methods

Sixty-two male mice were randomly assigned to one of six treatment groups given CBNight™ at dosages designed to deliver 0mg (control) to 4 mg/kg of CBN daily via oral gavage for 14 days. In-cage behavior was observed at 30 minutes and at 2, 4, 8, and 16 hours after each dose. After 14 days, the mice were sacrificed and necropsied. Organs were weighed and inspected for gross abnormalities, and blood was collected via cardiac puncture for clinical chemistry.

Results

No dosage-dependent adverse effects on behavior, body mass, or blood chemistry were observed, except that the highest doses of CBNight™ were associated with significantly lower eosinophil counts.

Conclusions

The commercially available, water-soluble CBN compound employed in this study does not appear to cause adverse effects in mice; rather, it appears to be well tolerated at pharmacological levels. The findings of eosinopenia at higher doses of CBN and lack of hepatotoxicity at any dosage employed in this study have not been reported to date.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42238-022-00153-w.

Detection of Cannabinoid Receptor Expression by Endometriotic Lesions in Women with Endometriosis as an Alternative to Opioid-Based Pain Medication

Emerging information suggests a potential role of medicinal cannabis in pain medication in addition to enhancing immune functions. Endometriosis is a disease of women of reproductive age associated with infertility and reproductive failure as well as chronic pain of varying degrees depending on the stage of the disease. Currently, opioids are being preferred over nonsteroidal anti-inflammatory drugs (NSAID) due to the latter’s side effects. However, as the opioids are becoming a source of addiction, additional pain medication is urgently needed. Cannabis offers an alternative therapy for treating the pain associated with endometriosis. Information on the use and effectiveness of cannabis against endometriotic pain is lacking. Moreover, expression of receptors for endocannabinoids by the ovarian endometriotic lesions is not known. The goal of this study was to examine whether cannabinoid receptors 1 and 2 (CB1 and CB2) are expressed by ovarian endometriotic lesions. Archived normal ovarian tissues, ovaries with endometriotic lesions, and normal endometrial tissues were examined for the presence of endometrial stromal cells using CD10 (a marker of endometrial stromal cells). Expression of CB1 and CB2 were determined by immunohistochemistry, immunoblotting, and gene expression studies. Intense expression for CB1 and CB2 was detected in the epithelial cells in ovarian endometriotic lesions. Compared with stroma in ovaries with endometriotic lesions, the expression of CB1 and CB2 was significantly higher in the epithelial cells in endometriotic lesions in the ovary ( $P<0.0001$ and $P<0.05$ , respectively). Immunoblotting and gene expression assays showed similar patterns for CB1 and CB2 protein and CNR1 (gene encoding CB1) and CNR2 (gene encoding CB2) gene expression. These results suggest that ovarian endometriotic lesions express CB1 and CB2 receptors, and these lesions may respond to cannabinoids as pain medication. These results will form a foundation for a clinical study with larger cohorts.

“The Two Sides of the Same Coin”—Medical Cannabis, Cannabinoids and Immunity: Pros and Cons Explained

Cannabis, as a natural medicinal remedy, has long been used for palliative treatment to alleviate the side effects caused by diseases. Cannabis-based products isolated from plant extracts exhibit potent immunoregulatory properties, reducing chronic inflammatory processes and providing much needed pain relief. They are a proven effective solution for treatment-based side effects, easing the resulting symptoms of the disease. However, we discuss the fact that cannabis use may promote the progression of a range of malignancies, interfere with anti-cancer immunotherapy, or increase susceptibility to viral infections and transmission. Most cannabis preparations or isolated active components cause an overall potent immunosuppressive impact among users, posing a considerable hazard to patients with suppressed or compromised immune systems. In this review, current knowledge and perceptions of cannabis or cannabinoids and their impact on various immune-system components will be discussed as the “two sides of the same coin” or “double-edged sword”, referring to something that can have both favorable and unfavorable consequences. We propose that much is still unknown about adverse reactions to its use, and its integration with medical treatment should be conducted cautiously with consideration of the individual patient, effector cells, microenvironment, and the immune system.

Phytocannabinoid Pharmacology: Medicinal Properties of Cannabis sativa Constituents Aside from the "Big Two"

Plant-based therapies date back centuries. Cannabis sativa is one such plant that was used medicinally up until the early part of the 20th century. Although rich in diverse and interesting phytochemicals, cannabis was largely ignored by the modern scientific community due to its designation as a schedule 1 narcotic and restrictions on access for research purposes. There was renewed interest in the early 1990s when the endocannabinoid system (ECS) was discovered, a complex network of signaling pathways responsible for physiological homeostasis. Two key components of the ECS, cannabinoid receptor 1 (CB1) and cannabinoid receptor 2 (CB2), were identified as the molecular targets of the phytocannabinoid Δ⁹-tetrahydrocannabinol (Δ⁹-THC). Restrictions on access to cannabis have eased worldwide, leading to a resurgence in interest in the therapeutic potential of cannabis. Much of the focus has been on the two major constituents, Δ⁹-THC and cannabidiol (CBD). Cannabis contains over 140 phytocannabinoids, although only a handful have been tested for pharmacological activity. Many of these minor cannabinoids potently modulate receptors, ionotropic channels, and enzymes associated with the ECS and show therapeutic potential individually or synergistically with other phytocannabinoids. The following review will focus on the pharmacological developments of the next generation of phytocannabinoid therapeutics.

Cannabinoids, Inner Ear, Hearing, and Tinnitus: A Neuroimmunological Perspective

Cannabis has been used for centuries for recreational and therapeutic purposes. Whereas, the recreative uses are based on the psychotropic effect of some of its compounds, its therapeutic effects range over a wide spectrum of actions, most of which target the brain or the immune system. Several studies have found cannabinoid receptors in the auditory system, both at peripheral and central levels, thus raising the interest in cannabinoid signaling in hearing, and especially in tinnitus, which is affected also by anxiety, memory, and attention circuits where cannabinoid effects are well described. Available studies on animal models of tinnitus suggest that cannabinoids are not likely to be helpful in tinnitus treatment and could even be harmful. However, the pharmacology of cannabinoids is very complex, and most studies focused on neural CB1R-based responses. Cannabinoid effects on the immune system (where CB2Rs predominate) are increasingly recognized as essential in understanding nervous system pathological responses, and data on immune cannabinoid targets have emerged in the auditory system as well. In addition, nonclassical cannabinoid targets (such as TRP channels) appear to play an important role in the auditory system as well. This review will focus on neuroimmunological mechanisms for cannabinoid effects and their possible use as protective and therapeutic agents in the ear and auditory system, especially in tinnitus.

The endocannabinoid signaling pathway as an emerging target in pharmacotherapy, earmarking mitigation of destructive events in rheumatoid arthritis

Rheumatoid arthritis is an inflammatory autoimmune disease, characterized by synovial proliferation, destruction to articular cartilage and severe pain. The cannabinoids obtained from Cannabis sativa exhibited their actions via cannabinoid-1 and -2 receptors, which also provides a platform for endocannabinoids to act. The endocannabinoid system comprises endocannabinoid molecules involved in signaling processes, along with G-protein coupled receptors and enzymes associated with ligand biosynthesis, activation and degradation. The action of endocannabinoid system in immune system regulation, via primary CB2 activation, followed by inhibition of production of pro-inflammatory cytokines, auto-antibodies and MMPs, FLSs proliferation and T-cell mediated immune response, are elaborated as potential therapeutic regimes in rheumatoid arthritis. The involvement of endocannabinoid system in immune cells like, B cells, T cells and macrophages, as well as regulatory actions on sensory noniceptors to ameliorate pain is significantly highlighted in the review, elaborating the actions of endocannabinoid signaling in mitigating the disease events. The review also focuses on enhancement of endocannabinoid tone, either by inhibiting the degradation enzymes, like FAAH, MAGL, COX, CytP450, LOX, etc. or by retarding cellular uptake processes. Moreover, the review portrays the optimizing role of endocannabinoid system, in abbreviating the symptoms and complications of rheumatoid arthritis in patients and mitigating inflammation, pain and immune mediated effects significantly.

Pharmacological potential of varinic-, minor-, and acidic phytocannabinoids

While natural Δ9-tetrahidrocannabinol (Δ9THC), cannabidiol (CBD), and their therapeutic potential have been extensively researched, some cannabinoids have been less extensively investigated. The present article compiles data from the literature that highlight the health benefits and therapeutic potential of lesser known phytocannabinoids, which we have divided into varinic, acidic, and "minor" (i.e., cannabinoids that are not present in high quantities in common varieties of Cannabis sativa L). A growing interest in these compounds, which are enriched in some cannabis varieties, has already resulted in enough preclinical information to show that they are promising therapeutic agents for a variety of diseases. Every phytocannabinoid has a "preferential" mechanism of action, and often targets the cannabinoid receptors, CB1 and/or CB2. The recent resolution of the structure of cannabinoid receptors demonstrates the atypical nature of cannabinoid binding, and that different binding modes depend on the agonist or partial agonist/inverse agonist, which allows for differential signaling, even acting on the same cannabinoid receptor. In addition, other players and multiple signaling pathways may be targeted/engaged by phytocannabinoids, thereby expanding the mechanistic possibilities for therapeutic use.

Can Hemp Help? Low-THC Cannabis and Non-THC Cannabinoids for the Treatment of Cancer

Cannabis has been used to relieve the symptoms of disease for thousands of years. However, social and political biases have limited effective interrogation of the potential benefits of cannabis and polarised public opinion. Further, the medicinal and clinical utility of cannabis is limited by the psychotropic side effects of ∆⁹-tetrahydrocannabinol (∆⁹-THC). Evidence is emerging for the therapeutic benefits of cannabis in the treatment of neurological and neurodegenerative diseases, with potential efficacy as an analgesic and antiemetic for the management of cancer-related pain and treatment-related nausea and vomiting, respectively. An increasing number of preclinical studies have established that ∆⁹-THC can inhibit the growth and proliferation of cancerous cells through the modulation of cannabinoid receptors (CB1R and CB2R), but clinical confirmation remains lacking. In parallel, the anti-cancer properties of non-THC cannabinoids, such as cannabidiol (CBD), are linked to the modulation of non-CB1R/CB2R G-protein-coupled receptors, neurotransmitter receptors, and ligand-regulated transcription factors, which together modulate oncogenic signalling and redox homeostasis. Additional evidence has also demonstrated the anti-inflammatory properties of cannabinoids, and this may prove relevant in the context of peritumoural oedema and the tumour immune microenvironment. This review aims to document the emerging mechanisms of anti-cancer actions of non-THC cannabinoids.

µ-opioid receptor, β-endorphin, and cannabinoid receptor-2 are increased in the colonic mucosa of irritable bowel syndrome patients

BACKGROUND AND AIMS

The gut immune, cannabinoid, and opioid systems constitute an integrated network contributing to visceral sensation and pain modulation. We aimed to assess the expression of the µ-opioid receptor (MOR), its ligand β-endorphin (β-END), and cannabinoid receptor-2 (CB2 ) in patients with irritable bowel syndrome (IBS) and asymptomatic controls (AC) and their correlation with sex and symptom perception.

METHODS

Mucosal biopsies were obtained from the left colon of 31 IBS patients (45% women) with predominant constipation (IBS-C, 9) or diarrhea (IBS-D, 10) or with mixed bowel habits (IBS-M, 12) and 32 AC (44% women) and processed for qRT-PCR, Western blotting, and immunohistochemistry.

KEY RESULTS

µ-opioid receptor and CB2 mRNA and protein expression and β-END protein levels were increased in patients with IBS compared to AC (all Ps=0.021). A significant sex by IBS interaction was found in relation to CB2 mRNA expression (P = .003) with women showing a markedly higher expression to men (P = .035). In contrast, in AC, men had higher expression than women (P = .033). β-END, MOR, and CB2 immunoreactivities (IR) were localized to CD4+T cells including EMR-1+ eosinophils and CD31+ T cells but not to mast cells.

CONCLUSIONS

The increased expression of MOR, β-END, and CB2 in the mucosa of IBS patients, where they are localized to immune cells, suggests that opioid and cannabinoid systems play an immune-related compensatory role in visceral pain in IBS patients. Further work is necessary to support this hypothesis.

Emerging drugs and therapeutics for systemic sclerosis

INTRODUCTION

Treatment of systemic sclerosis (SSc) is challenging despite advances in medical therapeutics for other rheumatologic diseases. Significant disease modifying therapy is lacking for most patients with SSc, due to the heterogeneous multisystem nature of SSc and its complex pathophysiology. The emergence of organ based management strategies has provided guidance in patient care as well as research and drug development. Areas covered: Design and development of new compounds focused on the underlying fibrotic disease processes have been sparse. Therefore, organ based strategies with targeted approaches have been directed towards the most devastating and life threatening features of systemic sclerosis. These include pulmonary arterial hypertension, interstitial lung disease, peripheral vasculopathy and skin thickening. In this context, new treatment regimens using older drugs as well as discovery of novel compounds based on recent insights of the disease pathophysiology are discussed. Expert opinion: Systemic sclerosis is a heterogeneous rare disease that carries a high burden of morbidity and mortality. Organ based management strategies have improved the natural history of systemic sclerosis using targeted interventions or strategies, particularly vascular features. However, more research is required to better understand disease mechanisms, including an ultimate unifying pathway that explains the multisystem nature of systemic sclerosis.

Cannabinoid receptor subtype 2 (CB2R) agonist, GW405833 reduces agonist-induced Ca(2+) oscillations in mouse pancreatic acinar cells

Emerging evidence demonstrates that the blockade of intracellular Ca(2+) signals may protect pancreatic acinar cells against Ca(2+) overload, intracellular protease activation, and necrosis. The activation of cannabinoid receptor subtype 2 (CB2R) prevents acinar cell pathogenesis in animal models of acute pancreatitis. However, whether CB2Rs modulate intracellular Ca(2+) signals in pancreatic acinar cells is largely unknown. We evaluated the roles of CB2R agonist, GW405833 (GW) in agonist-induced Ca(2+) oscillations in pancreatic acinar cells using multiple experimental approaches with acute dissociated pancreatic acinar cells prepared from wild type, CB1R-knockout (KO), and CB2R-KO mice. Immunohistochemical labeling revealed that CB2R protein was expressed in mouse pancreatic acinar cells. Electrophysiological experiments showed that activation of CB2Rs by GW reduced acetylcholine (ACh)-, but not cholecystokinin (CCK)-induced Ca(2+) oscillations in a concentration-dependent manner; this inhibition was prevented by a selective CB2R antagonist, AM630, or was absent in CB2R-KO but not CB1R-KO mice. In addition, GW eliminated L-arginine-induced enhancement of Ca(2+) oscillations, pancreatic amylase, and pulmonary myeloperoxidase. Collectively, we provide novel evidence that activation of CB2Rs eliminates ACh-induced Ca(2+) oscillations and L-arginine-induced enhancement of Ca(2+) signaling in mouse pancreatic acinar cells, which suggests a potential cellular mechanism of CB2R-mediated protection in acute pancreatitis.

CB2 Cannabinoid receptors as a therapeutic target-what does the future hold?

The past decades have seen an exponential rise in our understanding of the endocannabinoid system, comprising CB1 and CB2 cannabinoid receptors, endogenous cannabinoids (endocannabinoids), and the enzymes that synthesize and degrade endocannabinoids. The primary focus of this review is the CB2 receptor. CB2 receptors have been the subject of considerable attention, primarily due to their promising therapeutic potential for treating various pathologies while avoiding the adverse psychotropic effects that can accompany CB1 receptor-based therapies. With the appreciation that CB2-selective ligands show marked functional selectivity, there is a renewed opportunity to explore this promising area of research from both a mechanistic as well as a therapeutic perspective. In this review, we summarize our present knowledge of CB2 receptor signaling, localization, and regulation. We discuss the availability of genetic tools (and their limitations) to study CB2 receptors and also provide an update on preclinical data on CB2 agonists in pain models. Finally, we suggest possible reasons for the failure of CB2 ligands in clinical pain trials and offer possible ways to move the field forward in a way that can help reconcile the inconsistencies between preclinical and clinical data.

Mutant huntingtin impairs immune cell migration in Huntington disease

In Huntington disease (HD), immune cells are activated before symptoms arise; however, it is unclear how the expression of mutant huntingtin (htt) compromises the normal functions of immune cells. Here we report that primary microglia from early postnatal HD mice were profoundly impaired in their migration to chemotactic stimuli, and expression of a mutant htt fragment in microglial cell lines was sufficient to reproduce these deficits. Microglia expressing mutant htt had a retarded response to a laser-induced brain injury in vivo. Leukocyte recruitment was defective upon induction of peritonitis in HD mice at early disease stages and was normalized upon genetic deletion of mutant htt in immune cells. Migration was also strongly impaired in peripheral immune cells from pre-manifest human HD patients. Defective actin remodeling in immune cells expressing mutant htt likely contributed to their migration deficit. Our results suggest that these functional changes may contribute to immune dysfunction and neurodegeneration in HD, and may have implications for other polyglutamine expansion diseases in which mutant proteins are ubiquitously expressed.

Bone marrow transplantation confers modest benefits in mouse models of Huntington's disease

Huntington's disease (HD) is caused by an expanded polyglutamine tract in the protein huntingtin (htt). Although HD has historically been viewed as a brain-specific disease, htt is expressed ubiquitously, and recent studies indicate that mutant htt might cause changes to the immune system that could contribute to pathogenesis. Monocytes from HD patients and mouse models are hyperactive in response to stimulation, and increased levels of inflammatory cytokines and chemokines are found in pre-manifest patients that correlate with pathogenesis. In this study, wild-type (WT) bone marrow cells were transplanted into two lethally irradiated transgenic mouse models of HD that ubiquitously express full-length htt (YAC128 and BACHD mice). Bone marrow transplantation partially attenuated hypokinetic and motor deficits in HD mice. Increased levels of synapses in the cortex were found in HD mice that received bone marrow transplants. Importantly, serum levels of interleukin-6, interleukin-10, CXC chemokine ligand 1, and interferon-γ were significantly higher in HD than WT mice but were normalized in mice that received a bone marrow transplant. These results suggest that immune cell dysfunction might be an important modifier of pathogenesis in HD.

Cannabinoids and the immune system: an overview

Cannabinoids can influence the immune network. Data on the impact of exogenous cannabinoid ligands on immune function serve not only to understand how the endocannabinoid system modulates immune phenomena associated with infection or inflammation, but also to identify therapeutic targets for immune diseases. Cannabinoids can modulate immune reactions in the periphery but also in the brain, influence T cell subset balance and cytokine expression and play a role in the balance between neuroinflammation and neurodegeneration. Immune cells can synthesize endocannabinoids and also be influenced by cannabinoid analogues. Cannabinoid receptors show different expression on immune cells depending on activation status and stimuli. The complexity of relation between cannabinoid ligands of various classes and cannabinoid receptors brought the need to refine the simple conceptual frame of agonist-antagonists and offered potential implications for understanding interactions in pathological conditions. The immune influence of cannabinoid ligands is not fully elucidated. However, aspects of their immunomodulatory effects provide the basis for a context-dependent targeted therapeutic approach, thus leading to the possibility for the use of cannabinoids in the treatment of inflammatory disease.

Cannabinoids and experimental models of multiple sclerosis

The inflammatory response is a hallmark in the development of autoimmune-mediated neurodegenerative diseases of the central nervous system (CNS). Research on these pathological phenomena is being extensively undertaken and experimental autoimmune encephalomyelitis (EAE) serves as a valuable animal model. Studies from this model have generated interesting insights into biological effects of cannabinoids and may, at least to a certain extent, reflect the cannabinoid-mediated protective mechanisms also in human diseases with similar characteristics, such as multiple sclerosis (MS). Cannabinoids are involved in regulation of the immune system. These effects comprise modulation of inflammatory reaction through components of the innate and adaptive immune responses. Cannabinoids also confer neuroprotection and assist neuroregeneration, thus maintaining a balance within the delicate CNS microenvironment and restoring function following pathological condition, commonly driven by neuroinflammation. Continued studies of cannabinoid actions in EAE pathogenesis should be beneficial for the better understanding of the mechanisms governing such a vast array of physiological effects and in development of new therapeutic strategies for the treatment of human neuroinflammatory and neurodegenerative diseases.

Endocannabinoids and immune regulation

Cannabinoid pharmacology has made important advances in recent years after the discovery of the cannabinoid receptors. These discoveries have added to our understanding of exogenous and endogenous cannabinoid signaling along with exploring the various pathways of their biosynthesis, molecular structure, inactivation, and anatomical distribution of their receptors throughout the body. The endocannabinoid system is involved in immunoregulation and neuroprotection. In this article, we have reviewed the possible mechanisms of the regulation of the immune response by endocannabinoids which include modulation of immune response in different cell types, effect on cytokine network, induction of apoptosis in immune cells and downregulation of innate and adaptive immune response. Studies from our laboratory have suggested that administration of endocannabinoids or use of inhibitors of enzymes that breakdown the endocannabinoids, leads to immunosuppression and recovery from immune-mediated injury to organs such as the liver. Thus, manipulation of endocannabinoids in vivo may constitute a novel treatment modality against inflammatory disorders.

The profile of immune modulation by cannabidiol (CBD) involves deregulation of nuclear factor of activated T cells (NFAT)

Cannabidiol (CBD) is a cannabinoid compound derived from Cannabis Sativa that does not possess high affinity for either the CB1 or CB2 cannabinoid receptors. Similar to other cannabinoids, we demonstrated previously that CBD suppressed interleukin-2 (IL-2) production from phorbol ester plus calcium ionophore (PMA/Io)-activated murine splenocytes. Thus, the focus of the present studies was to further characterize the effect of CBD on immune function. CBD also suppressed IL-2 and interferon-gamma (IFN-gamma) mRNA expression, proliferation, and cell surface expression of the IL-2 receptor alpha chain, CD25. While all of these observations support the fact that CBD suppresses T cell function, we now demonstrate that CBD suppressed IL-2 and IFN-gamma production in purified splenic T cells. CBD also suppressed activator protein-1 (AP-1) and nuclear factor of activated T cells (NFAT) transcriptional activity, which are critical regulators of IL-2 and IFN-gamma. Furthermore, CBD suppressed the T cell-dependent anti-sheep red blood cell immunoglobulin M antibody forming cell (anti-sRBC IgM AFC) response. Finally, using splenocytes derived from CB1(-/-)/CB2(-/-) mice, it was determined that suppression of IL-2 and IFN-gamma and suppression of the in vitro anti-sRBC IgM AFC response occurred independently of both CB1 and CB2. However, the magnitude of the immune response to sRBC was significantly depressed in CB1(-/-)/CB2(-/-) mice. Taken together, these data suggest that CBD suppresses T cell function and that CB1 and/or CB2 play a critical role in the magnitude of the in vitro anti-sRBC IgM AFC response.

Differential modulation of AP-1- and CRE-driven transcription by cannabinoid agonists emphasizes functional selectivity at the CB1 receptor

BACKGROUND AND PURPOSE

Long-term adaptations to pharmacological stimuli frequently originate from modulation of complex intracellular signalling pathways. We previously reported that HU210 and CP55940, two CB1 cannabinoid receptor agonists, induced opposite effects on TH expression. Herein, we characterized their influence on cAMP response element (CRE) and activator protein 1 (AP-1)-mediated regulation of gene transcription.

EXPERIMENTAL APPROACH

The activity of the agonists was examined on transfected N1E-115 cells in which expression of the luciferase reporter gene was controlled by transcription promoters consisting of repeats of either CRE or AP-1 elements. In addition, the implication of classical signalling pathways was investigated using a variety of kinase inhibitors.

KEY RESULTS

Consistent with the CB1-mediated reduction of cAMP accumulation, both ligands decreased CRE-driven luciferase expression with similar potencies. HU210 also exhibited a concentration-dependent reduction of luciferase activity in cells engineered to examine AP-1-controlled transcription, whereas such response was not obtained with CP55940. Responses were all inhibited by SR141716A and were modified in Pertussis toxin-treated cells, suggesting agonist-selective regulations of distinct Gi/o-dependent mechanisms through CB1 receptor activation. Finally, PKC inhibitors efficiently inhibited the paradoxical effect of HU210 on AP-1-mediated transcription, indicating selective regulation of PKC-dependent responses.

CONCLUSIONS AND IMPLICATIONS

Together, our results demonstrate that two cannabinoid ligands, commonly used as reference agonists acting on the same receptor with similar affinities, differentially modulate gene transcription through distinct controls of AP-1. This could reflect activation of distinct subsets of Gi/o-proteins, supporting the concept of functional selectivity at CB1 receptors.

Suppressive effects of cannabidiol on antigen-specific antibody production and functional activity of splenocytes in ovalbumin-sensitized BALB/c mice

Cannabidiol (CBD) and cannabis-based medicines are potential therapeutic agents. Because the immune system has been widely demonstrated to be affected by psychoactive cannabinoids, such as Delta(9)-tetrahydrocannabinol, the objective of the present studies is to investigate the immunomodulatory effect of CBD, the major non-psychoactive cannabinoid in marijuana. BALB/c mice were intraperitoneally administered with a single dose of CBD (5-20 mg/kg) prior to ovalbumin (OVA) sensitization, and the serum production of antigen-specific antibodies was measured 7 days post OVA sensitization. The serum level of OVA-specific IgM was significantly attenuated by a high dose of CBD (20 mg/kg), and OVA-specific IgG(1) and IgG(2a) by all 3 doses of CBD. Concordantly, splenocytes of mice administered with CBD (5 or 20 mg/kg) produced less IL-2, IL-4 and IFN-gamma than those of vehicle-treated controls, upon ex vivo stimulation with phorbol ester plus calcium ionophore. Likewise, T-cell mitogen (concanavalin A)-induced proliferation of splenocytes was also markedly suppressed in mice administered with CBD. Furthermore, the observed ex vivo effects of CBD on cytokine production and T-cell proliferation were confirmed in splenocytes directly exposed to CBD (1-8 microM) in vitro, indicating a direct effect by CBD. Taken together, the results demonstrated that CBD markedly suppressed antigen-specific antibody production in OVA-sensitized mice, and suggest that CBD-mediated suppression of humoral immunity could be mediated by the impaired functions of splenocytes.

Cannabinoid signalling in TNF-α induced IL-8 release

The molecular events mediating the immunomodulatory properties of cannabinoids have remained largely unresolved. We have therefore investigated the molecular mechanism(s) through which R-(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl] pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-napthanlenyl) methanone (WIN55212-2) modulate production of interleukin-8 (IL-8) in HT-29 cells. Release of IL-8 induced by tumor necrosis factor-alpha (TNF-alpha) was determined by enzyme-linked immunosorbent assay (ELISA). Changes in expression of inhibitory kappa B (IkappaB) were monitored by Western blotting and activation of nuclear factor-kappa B (NF-kappaB) was determined in electrophoretic mobility shift assay (EMSAs). TNF-alpha induced release of IL-8 was inhibited by WIN55212-2 which also blocked the degradation of IkappaB-alpha and activation of NF-kappaB induced by TNF-alpha. These data provide strong evidence that WIN55212-2 may modulate IL-8 release by negatively regulating the signaling cascade leading to the activation of NF-kappaB. These findings highlight a potential mechanism for the immunomodulatory properties of cannabinoids and contribute towards acquiring a clear understanding of the role of cannabinoids in inflammation.

Effects on the immune system

Marijuana and other exogenous cannabinoids alter immune function and decrease host resistance to microbial infections in experimental animal models and in vitro. Two modes of action by which delta9-tetrahydrocannabinol (THC) and other cannabinoids affect immune responses have been proposed. First, cannabinoids may signal through the cannabinoid receptors CB1 and CB2. Second, at sites of direct exposure to high concentrations of cannabinoids, such as the lung, membrane perturbation may be involved. In addition, endogenous cannabinoids or endocannabinoids have been identified and have been proposed as native modulators of immune functions through cannabinoid receptors. Exogenously introduced cannabinoids may disturb this homoeostatic immune balance. A mode by which cannabinoids may affect immune responses and host resistance maybe by perturbing the balance of T helper (Th)1 pro-inflammatory versus Th2 anti-inflammatory cytokines. While marijuana and various cannabinoids have been documented to alter immune functions in vitro and in experimental animals, no controlled longitudinal epidemiological studies have yet definitively correlated immunosuppressive effects with increased incidence of infections or immune disorders in humans. However, cannabinoids by virtue of their immunomodulatory properties have the potential to serve as therapeutic agents for ablation of untoward immune responses.

2-Arachidonoylglycerol stimulates activator protein-1-dependent transcriptional activity and enhances epidermal growth factor-induced cell transformation in JB6 P+ cells

2-Arachidonoylglycerol (2-AG) is the most abundant endocannabinoid, and it plays a critical role in cannabinoid receptor-mediated cell signaling. Although 2-AG was shown to induce ERK activation via the cannabinoid receptor 1 (CB1), only a nonspecific CB receptor agonist and antagonist was used in those studies. Whether cannabinoid receptor 2 (CB2) is involved in 2-AG-induced ERK activation is still unclear. Moreover, whether 2-AG is involved in mediation of AP-1 activity and cell transformation is also not known. In the present study, we show that 2-AG stimulates AP-1-dependent transcriptional activity and enhances epidermal growth factor-induced cell transformation in mouse epidermal JB6 P+ Cl41 cells. Using JB6 P+ C141 cells, stably transfected with an AP-1 luciferase reporter, we found that 10 microm 2-AG induced up to a 3-fold stimulation of AP-1 transcriptional activity. The AP-1 stimulation appeared to be mediated by ERK but not JNK or p38 kinase. PD98059, a specific inhibitor of MEK1, almost completely blocked 2-AG-induced ERK phosphorylation and AP-1 activation. Using CB1/2-/- murine embryonic fibroblasts, we present the first direct evidence that both cannabinoid receptors 1 and 2 (CB1/2) are involved in 2-AG-induced ERK activation. 2-AG could not stimulate ERK phosphorylation or Fyn kinase activity in dominant negative Fyn. In addition, the Fyn inhibitor PP2 blocked 2-AG-induced Fyn kinase activity and ERK phosphorylation and activity. Small interfering RNA Fyn also suppressed 2-AG-induced ERK phosphorylation. Interestingly, 2-AG enhanced epidermal growth factor-induced AP-1 DNA binding and cell transformation. Taken together, our data provide direct evidence suggesting that 2-AG may have a novel role in cell transformation and carcinogenesis in a signaling pathway involving CB1/2 and activation of Fyn, ERKs, and AP-1.

Arachidonylethanolamide Induces Apoptosis of Human Glioma Cells through Vanilloid Receptor-1

The anti-tumor properties of cannabinoids have recently been evidenced, mainly with delta9-tetrahydrocannabinol (THC). However, the clinical application of this drug is limited by possible undesirable side effects due to a broad expression of cannabinoid receptors (CB1 and CB2). An attractive field of research therefore is to identify molecules with more selective tumor targeting. This is particularly important for malignant gliomas, considering their poor prognosis and their location in the brain. Here we investigated whether the most potent endogenous cannabinoid, arachidonylethanolamide (AEA), could be a candidate. We observed that AEA induced apoptosis in long-term and recently established glioma cell lines via aberrantly expressed vanilloid receptor-1 (VR1). In contrast with their role in THC-mediated death, both CB1 and CB2 partially protected glioma against AEA-induced apoptosis. These data show that the selective targeting of VR1 by AEA or more stable analogues is an attractive research area for the treatment of glioma.

Cannabinoids inhibit the activation of ERK MAPK in PMA/Io-stimulated mouse splenocytes

The mechanism of action of immune suppression by cannabinoids involves suppression of interleukin-2 (IL-2) production in phorbol ester plus calcium ionophore (PMA/Io)-stimulated lymphocytes. This decrease in IL-2 was due to inhibition of activator protein-1 (AP-1) and nuclear factor of activated T cells (NF-AT) transcription factors, both of which depend on proteins that are regulated by the extracellular signal-regulated kinase subgroup of the mitogen-activated protein kinases (ERK MAPK). Thus, the objective of the present study was to characterize the effects of cannabinoid compounds on ERK MAPK under conditions where IL-2 expression was suppressed. Using the MEK inhibitor PD098059 in order to assess the role of ERK MAPK in PMA/Io-stimulated splenocytes (SPLC), it was determined that IL-2 production and expression of c-fos and c-jun nuclear protein expression depended on activation of ERK MAPK. In response to PMA/Io, expression of nuclear phosphorylated ERK MAPK was rapidly induced, peaked at approximately 15 min, and was sustained for up to 240 min. Pretreatment with cannabinol (CBN) inhibited expression of phosphorylated ERK MAPK at several time points up to 240 min post cellular activation. Furthermore, WIN-55212-2, a synthetic cannabinoid, inhibited expression of phosphorylated ERK MAPK at 240 min post cellular activation. CBN did not induce activation of ERK MAPK in the absence of PMA/Io. Collectively, these studies suggest that cannabinoid-induced inhibition of IL-2 in PMA/Io-stimulated splenocytes might be due, in part, to inhibition of ERK MAPK activation.

Evidence for cannabinoid receptor-dependent and -independent mechanisms of action in leukocytes

Cannabinoids exhibit immunosuppressive actions that include inhibition of interleukin-2 production in response to a variety of T cell activation stimuli. Traditionally, the effects of these compounds have been attributed to cannabinoid receptors CB1 and CB2, both of which are expressed in mouse splenocytes. Therefore, N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorphenyl)-4-methyl-H-pyrazole-3 carboxyamidehydrochloride (SR141716A), a CB1 antagonist, and N-[(1S)-endo-1,3,3,-trimethyl-bicyclo[2,2,1]heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide (SR144528), a CB2 antagonist, were used to investigate the role of cannabinoid receptors in the cannabinoid-induced inhibition of phorbol ester plus calcium ionophore (PMA/Io)-stimulated interleukin-2 production by mouse splenocytes. PMA/Io-stimulated interleukin-2 production was inhibited by cannabinol, cannabidiol, and both WIN 55212-2 stereoisomers with a rank order potency of R-(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-napthanlenyl) methanone mesylate (WIN 55212-2) approximately cannabidiol > S-(-)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-napthanlenyl) methanone mesylate (WIN 55212-3) approximately cannabinol. Cannabinoid-induced inhibition of PMA/Io-stimulated interleukin-2 was not attenuated by the presence of both SR144528 and SR141716A. Using pertussis toxin to address the role of G protein-coupled receptors in this response, it was determined that pertussis toxin treatment did not attenuate cannabinol-induced inhibition of PMA/Io-stimulated interleukin-2. With the demonstration that cannabinoid-induced inhibition of PMA/Io-stimulated interleukin-2 was not mediated via CB1 or CB2, alternative targets of cannabinoids in T cells were examined. Specifically, it was demonstrated that cannabinoids elevated intracellular calcium concentration in resting splenocytes and that the cannabinol-induced elevation in intracellular calcium concentration was attenuated by treatment with both SR144528 and SR141716A. Interestingly, pretreatment of splenocytes with agents that elevate intracellular calcium concentration inhibited PMA/Io-stimulated interleukin-2 production, suggesting that an elevation in intracellular calcium concentration might be involved in the mechanism of interleukin-2 inhibition. These studies suggest that immune modulation produced by cannabinoids involves multiple mechanisms, which might be both cannabinoid receptor-dependent and -independent.

Attenuation of the ovalbumin-induced allergic airway response by cannabinoid treatment in A/J mice

T cells are sensitive to modulation by cannabinoids as evidenced by their ability to inhibit expression of cytokines, including interleukin (IL)-2 and IL-4. Because T cells play a key role in the pathophysiology of allergic asthma by expressing T helper cell (Th)2 cytokines, the objective of the present studies was to examine the effect of cannabinoids on immunologic and pathologic features associated with the allergic airway response induced by ovalbumin (Ova). A/J mice were systemically sensitized with Ova and subsequently challenged with aerosolized Ova. The steady-state mRNA expression of IL-2 and Th2 cytokines (IL-4, IL-5, and IL-13) was markedly increased in the lungs of Ova-sensitized mice 24 h after a single Ova challenge. Concordantly, the level of total and Ova-specific serum immunoglobulin (Ig)E and intraepithelial mucosubstances in the axial intrapulmonary airway of Ova-sensitized mice was robustly elevated 96 h after the second Ova challenge. Cannabinol (CBN) or Delta(9)-tetrahydrocannabinol (Delta(9)-THC; 50 mg/kg, ip), administered daily for 3 consecutive days before sensitization and then before challenge, significantly attenuated the elevation of IL-2, IL-4, IL-5, and IL-13 steady-state mRNA expression elicited by Ova challenge in the lungs. In addition, the elevation of serum IgE and the mucus overproduction induced by Ova challenge was also markedly attenuated by CBN or Delta(9)-THC administration in Ova-sensitized mice. These results suggest that plant-derived immunomodulatory cannabinoids exhibit potential therapeutic utility in the treatment of allergic airway disease by inhibiting the expression of critical T cell cytokines and the associated inflammatory response.

Norepinephrine increases I kappa B alpha expression in astrocytes

The neurotransmitter norepinephrine (NE) can inhibit inflammatory gene expression in glial cells; however, the mechanisms involved are not clear. In primary astrocytes, NE dose-dependently increased the expression of inhibitory I kappa B alpha protein accompanied by an increase in steady state levels of I kappa B alpha mRNA. Maximal increases were observed at 30-60 min for the mRNA and at 4 h for protein, and these effects were mediated by NE binding to beta-adrenergic receptors. NE activated a 1.3-kilobase I kappa B alpha promoter transfected into astrocytes or C6 glioma cells, and this activation was prevented by a beta-antagonist and by protein kinase A inhibitors but not by an NF kappa B inhibitor. NE increased I kappa B alpha protein in both the cytosolic and the nuclear fractions, suggesting an increase in nuclear uptake of I kappa B alpha. I kappa B alpha was detected in the frontal cortex of normal adult rats, and its levels were reduced if central NE levels were depleted by lesion of the locus ceruleus. The reduction of brain I kappa B alpha levels was paralleled by increased inflammatory responses to lipopolysaccharide. These results demonstrate that I kappa B alpha expression is regulated by NE at both transcriptional and post-transcriptional levels, which could contribute to the observed anti-inflammatory properties of NE in vitro and in vivo.

Delta(9)-tetrahydrocannabinol-induced apoptosis in the thymus and spleen as a mechanism of immunosuppression in vitro and in vivo

Delta(9)-tetrahydrocannabinol (THC), the main psychoactive component of marijuana has been shown to suppress the immune response. However, the exact mechanism of THC-induced immunosuppression remains unclear. In the current study, we tested the hypothesis that exposure to THC leads to the induction of apoptosis in lymphocyte populations. Splenocytes of C57BL/6 mice cultured in the presence of 10 microM or greater concentrations of THC showed significantly reduced proliferative response to mitogens, including anti-CD3 monoclonal antibodies (mAbs), concanavalin A (Con A), and lipopolysaccharide (LPS) in vitro. Thymocytes and naive and activated splenocytes exposed to 10 microM or 20 microM THC showed significantly increased levels of apoptosis. Treatment with CB2 antagonist inhibited THC-induced apoptosis in thymocytes and activated splenocytes. Administration of 10 mg/kg body weight of THC into C57BL/6 mice led to thymic and splenic atrophy as early as 6 h after treatment. This effect could be partially inhibited by treatment with a caspase inhibitor in vivo. THC exposure led to reductions in the numbers of all subpopulations of splenocytes and thymocytes examined. Functional studies revealed that splenocytes from THC-treated mice had significantly reduced proliferative response to anti-CD3 mAbs, Con A, and LPS in vitro. Finally, thymocytes and splenocytes exposed to THC in vivo exhibited apoptosis upon in vitro culture. Together, these results suggest that in vivo exposure to THC can lead to significant suppression of the immune response by induction of apoptosis.

Targeting CB2 cannabinoid receptors as a novel therapy to treat malignant lymphoblastic disease

In the current study, we examined whether ligation of CB2 receptors would lead to induction of apoptosis in tumors of immune origin and whether CB2 agonist could be used to treat such cancers. Exposure of murine tumors EL-4, LSA, and P815 to delta-9-tetrahydrocannabinol (THC) in vitro led to a significant reduction in cell viability and an increase in apoptosis. Exposure of EL-4 tumor cells to the synthetic cannabinoid HU-210 and the endogenous cannabinoid anandamide led to significant induction of apoptosis, whereas exposure to WIN55212 was not effective. Treatment of EL-4 tumor-bearing mice with THC in vivo led to a significant reduction in tumor load, increase in tumor-cell apoptosis, and increase in survival of tumor-bearing mice. Examination of a number of human leukemia and lymphoma cell lines, including Jurkat, Molt-4, and Sup-T1, revealed that they expressed CB2 receptors but not CB1. These human tumor cells were also susceptible to apoptosis induced by THC, HU-210, anandamide, and the CB2-selective agonist JWH-015. This effect was mediated at least in part through the CB2 receptors because pretreatment with the CB2 antagonist SR144528 partially reversed the THC-induced apoptosis. Culture of primary acute lymphoblastic leukemia cells with THC in vitro reduced cell viability and induced apoptosis. Together, the current data demonstrate that CB2 cannabinoid receptors expressed on malignancies of the immune system may serve as potential targets for the induction of apoptosis. Also, because CB2 agonists lack psychotropic effects, they may serve as novel anticancer agents to selectively target and kill tumors of immune origin.

Cannabinol enhancement of interleukin-2 (IL-2) expression by T cells is associated with an increase in IL-2 distal nuclear factor of activated T cell activity

It has been demonstrated previously that cannabinol (CBN) differentially modulates interleukin-2 (IL-2) protein secretion by T cells with a corresponding change in extracellular signal-regulated kinase activity. The objective of the present studies was to further investigate the molecular mechanism by which CBN enhances IL-2 gene expression using the EL4 T cell line. We demonstrate here that steady-state IL-2 mRNA expression was significantly enhanced by CBN in a concentration-dependent manner in EL4 cells activated with suboptimal concentrations of phorbol-12-myristate-13-acetate (2-10 nM). Concordantly, a marked increase was observed in nuclear factor of activated T cells (NF-AT) DNA binding activity to the IL-2 distal NF-AT site, but not to nuclear factor for immunoglobulin kappa chain in B cells or activator protein 1 motifs. Transient transfection of EL4 cells with a reporter gene under the control of multiple IL-2 distal NF-AT motifs exhibited increased transcriptional activity by CBN in suboptimally activated cells. In addition, the CBN-mediated enhancement of IL-2 protein secretion and the transcriptional activity of the IL-2 distal NF-AT reporter gene was abrogated by the calcium/calmodulin-dependent protein kinase inhibitor KN93, but not by the CB2 receptor antagonist SR144528. Enhancement of IL-2 was also demonstrated with CP55940, Delta(9)-tetrahydrocannabinol, and cannabidiol, thus suggesting that the phenomenon is not unique to CBN. Collectively, these results suggest that increased IL-2 secretion by CBN is mediated through the enhancement of IL-2 gene transcription by activation of NF-AT in a CB1/CB2-independent manner.

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.

Modulation of CREB and NF-kappaB signal transduction by cannabinol in activated thymocytes

Cannabinoid compounds inhibit the cAMP signalling cascade in leukocytes. One of these compounds, cannabinol (CBN) has been shown to inhibit interleukin-2 (IL-2) expression and the activation of cAMP response element binding protein (CREB) and nuclear factor for immunoglobulin kappa chain in B cells (NF-kappaB) following phorbol-12-myristate-13 acetate (PMA) plus ionomycin (Io) treatment of thymocytes. Therefore, the objective of the present studies was to determine the role of cAMP and protein kinase A (PKA) in the CBN-mediated inhibition of IL-2, CREB, and NF-kappaB in PMA/Io-activated thymocytes. The inhibition of CREB/ATF-1 phosphorylation, or cAMP response element (CRE) or kappaB DNA binding activity produced by CBN in PMA/Io-activated thymocytes, could not be reversed by DBcAMP costimulation. Furthermore, DBcAMP failed to reverse the concentration-dependent inhibition of IL-2 protein secretion by CBN. Pretreatment of thymocytes with H89 produced a modest inhibition of PMA/Io-induced CREB/ATF-1 phosphorylation and CRE DNA binding activity but H89 had no effect on protein binding to a kappaB motif. Additionally, H89 modestly inhibited PMA/Io-induced IL-2 secretion. In light of the modest involvement of the cAMP pathway in CBN-mediated inhibition of CREB and IL-2 in PMA/Io-activated thymocytes, PD098059 (PD), the MEK inhibitor, was utilized to determine the role of ERK MAP kinases in thymocytes. ERKs play a critical role in IL-2 production but not for CREB phsophorylation. Collectively, these findings suggest that CBN may modulate several signalling pathways in activated T cells.

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.

The effects of cannabinoids on the brain

Cannabinoids have a long history of consumption for recreational and medical reasons. The primary active constituent of the hemp plant Cannabis sativa is delta9-tetrahydrocannabinol (delta9-THC). In humans, psychoactive cannabinoids produce euphoria, enhancement of sensory perception, tachycardia, antinociception, difficulties in concentration and impairment of memory. The cognitive deficiencies seem to persist after withdrawal. The toxicity of marijuana has been underestimated for a long time, since recent findings revealed delta9-THC-induced cell death with shrinkage of neurons and DNA fragmentation in the hippocampus. The acute effects of cannabinoids as well as the development of tolerance are mediated by G protein-coupled cannabinoid receptors. The CB1 receptor and its splice variant CB1A, are found predominantly in the brain with highest densities in the hippocampus, cerebellum and striatum. The CB2 receptor is found predominantly in the spleen and in haemopoietic cells and has only 44% overall nucleotide sequence identity with the CB1 receptor. The existence of this receptor provided the molecular basis for the immunosuppressive actions of marijuana. The CB1 receptor mediates inhibition of adenylate cyclase, inhibition of N- and P/Q-type calcium channels, stimulation of potassium channels, and activation of mitogen-activated protein kinase. The CB2 receptor mediates inhibition of adenylate cyclase and activation of mitogen-activated protein kinase. The discovery of endogenous cannabinoid receptor ligands, anandamide (N-arachidonylethanolamine) and 2-arachidonylglycerol made the notion of a central cannabinoid neuromodulatory system plausible. Anandamide is released from neurons upon depolarization through a mechanism that requires calcium-dependent cleavage from a phospholipid precursor in neuronal membranes. The release of anandamide is followed by rapid uptake into the plasma and hydrolysis by fatty-acid amidohydrolase. The psychoactive cannabinoids increase the activity of dopaminergic neurons in the ventral tegmental area-mesolimbic pathway. Since these dopaminergic circuits are known to play a pivotal role in mediating the reinforcing (rewarding) effects of the most drugs of abuse, the enhanced dopaminergic drive elicited by the cannabinoids is thought to underlie the reinforcing and abuse properties of marijuana. Thus, cannabinoids share a final common neuronal action with other major drugs of abuse such as morphine, ethanol and nicotine in producing facilitation of the mesolimbic dopamine system.

Inhibition of the cAMP signaling cascade via cannabinoid receptors: a putative mechanism of immune modulation by cannabinoid compounds

Immune modulation by cannabinoids has been widely established over the past three decades. In spite of this, the mechanism of action responsible for immune modulation and other well described biological effects attributed to cannabinoid compounds has been elusive. The identification and cloning of two novel G protein coupled receptors, CB1 and CB2, both of which bind cannabimimetic agents has served as the basis for a putative mechanism of action. CB1, which is also referred to as the central cannabinoid receptor is the primary form expressed within the central nervous system (CNS). Conversely, the peripheral cannabinoid receptor, CB2, does not appear to be expressed within the CNS but is the predominant form of the receptor expressed within the immune system. Both CB1 and CB2 negatively regulate adenylate cyclase activity through a pertussis toxin sensitive GTP-binding protein. Recent investigations addressing the mechanism by which cannabinoids disrupt leukocyte function have demonstrated that in the presence of cannabinoids the cAMP signaling cascade is markedly inhibited as evidenced by decreased adenylate cyclase and protein kinase A activity and decreased DNA binding by cAMP response element binding proteins. The focus of this discussion will be on the effects cannabinoids elicit on events within the cAMP cascade and related signaling pathways critical to the regulation of cytokine genes.