Functional consequences of nonsynonymous single nucleotide polymorphisms in the CB2 cannabinoid receptor. Pharmacogenet Genomics. 2010;20:157-166. [PMID: 20124950 DOI: 10.1097/fpc.0b013e3283367c6b]

Immunomodulatory function of cannabinoid receptor 2 and its agonist osteogenic growth peptide in health and cancer: a study in mice and humans

Colon carcinoma is among the most prevalent malignant tumors, with inflammation being the primary risk factor. Cannabinoid receptor 2 (CB2/CNR2) has complex immunomodulatory functions. Therefore, we investigated the role of osteogenic growth peptide (OGP), an endogenous selective CB2 agonist, in colon carcinogenesis and immune modulation in transgenic mice (ApcMin/+).We injected 8-week-old (progression phase) or five-week-old (initiation phase) ApcMin/+ mice with OGP or vehicle weekly for 8 weeks or 4 weeks, respectively. During the progression phase, OGP-treated mice displayed significantly fewer tumors in the large intestine and smaller tumors in the small intestine. During the initiation phase, OGP significantly attenuated adenomagenesis in both the small and large intestine, decreased IL-6 and IL-4 levels, increased splenic anti-tumor CD8+ T cells, and diminished populations of tumor-promoting myeloid-derived suppressor cells. Further, we used exomic analyses of UKBiobank patients to determine the relationship between CNR2 polymorphisms and tumor-associated myeloid cells in humans. We found that the common CNR2-Q63R polymorphism is associated with monocyte count. Our results suggest that CB2 activation via OGP attenuates tumorigenesis and adenoma growth by modulating immune cells, corroborated by a significant association between CNR2 polymorphisms and monocytopoiesis in humans.

The endocannabinoid system's genetic polymorphisms in sickle cell anemia patients

Sickle cell anemia (SCA) is a monogenic blood disease with complex and multifactorial pathophysiology. The endocannabinoid system (ECS) could be a candidate for modulating SCA complications, such as priapism, as it has demonstrated an essential role in hematopoiesis, platelet aggregation, and immune responses. We evaluated the association of ECS-related single nucleotide polymorphisms (SNP) (FAAH rs324420, MAGL rs604300, CNR1 rs7766029, and CNR2 rs35761398) with priapism in a Brazilian SCA cohort. The study involved 138 SCA patients (n = 80 with priapism and n = 58 without priapism). SCA was detected with HPLC, and the Hb SS genotype was confirmed with PCR-RE. Alpha thalassemia mutations were detected with Multiplex-PCR, and SNP genotyping was performed using TaqMan genotyping assays. We observed a lower frequency of -α3.7kb-thalassemia mutation in patients with priapism than in patients without this complication (p < 0.001), and in adjusted multivariate analyses TT-CC genotype of CNR2 rs35761398 was associated with a lower chance of developing priapism (OR = 0.386 [0.175-0.854], p = 0.019) and a lower risk of it over time (HR = 0.634 [0.402-0.987], p = 0.049). The SCA ischemic priapism is related to unbalanced vasodilation/vasoconstriction pathways, such as decreased RhoA/Rho-kinase (ROCK) signaling. Since activating the type 2 cannabinoid receptor (CB2) decreases RhoA activation, we suggest a novel approach to SCA priapism involving CB2.

Single nucleotide polymorphisms in the cannabinoid CB2 receptor: Molecular pharmacology and disease associations

Preclinical evidence implicating cannabinoid receptor 2 (CB2) in various diseases has led researchers to question whether CB2 genetics influence aetiology or progression. Associations between conditions and genetic loci are often studied via single nucleotide polymorphism (SNP) prevalence in case versus control populations. In the CNR2 coding exon, ~36 SNPs have high overall population prevalence (minor allele frequencies [MAF] ~37%), including non-synonymous SNP (ns-SNP) rs2501432 encoding CB2 63Q/R. Interspersed are ~27 lower frequency SNPs, four being ns-SNPs. CNR2 introns also harbour numerous SNPs. This review summarises CB2 ns-SNP molecular pharmacology and evaluates evidence from ~70 studies investigating CB2 genetic variants with proposed linkage to disease. Although CNR2 genetic variation has been associated with a wide variety of conditions, including osteoporosis, immune-related disorders, and mental illnesses, further work is required to robustly validate CNR2 disease links and clarify specific mechanisms linking CNR2 genetic variation to disease pathophysiology and potential drug responses.

Immunomodulatory effects of cannabinoids against viral infections: a review of its potential use in SARS-CoV2 infection

The COVID-19 pandemic is a global health crisis affecting millions of people worldwide. Along with vaccine development, there is also a priority to discover new drugs and treatments. One approach involves modulating the immune system to manage inflammation and cytokine storms. Patients with a high severity of complications exhibit a high level of inflammatory cytokines, particularly IL-6, in the airways and other infected tissues. Several studies have reported the function of the endocannabinoid system in regulating inflammation and different immune responses. Cannabinoids are a class of natural chemicals found in the Cannabis plant. Recently, the anti-inflammatory properties of cannabinoids and their mediatory immunosuppression mechanisms through the endocannabinoid system have engrossed scientists in the health field for infectious conditions. Research suggests that the immune system can regulate cytokine activation through cannabinoid receptors, particularly with Cannabidiol (CBD), the second most prevalent compound in cannabis. While CBD has been deemed safe by the World Health Organization and shows no signs of abuse potential, excessive CBD use may lead to respiratory depression. CBD shows promise in reducing immune cell recruitment and cytokine storms in organs affected by SARS-CoV2. However, before clinical use, it's crucial to evaluate cannabinoid-based medications' active ingredient concentrations and potential interactions with other drugs, along with associated side effects. Indication-based dosing, consistent formulations, and ensuring purity and potency are essential. This review highlights cannabinoids' effects on COVID-19 management and prognosis, drawing from preclinical and clinical studies.

A Military Community Cohort Study Reveals Single Nucleotide Polymorphisms in Inflammation Mediator Genes That Associate With Type 2 Diabetes

INTRODUCTION

Type 2 diabetes mellitus (T2DM) is a prevalent metabolic disorder characterized by hyperglycemia of varying degrees. Genetic and lifestyle variations are known to influence the onset and severity of T2DM. Among the genetic variations reported to confer susceptibility to the disease are certain single nucleotide polymorphisms (SNPs). Here, we report the analysis of 18 such SNPs in a military community cohort of 716 subjects, comprising 477 diabetic and 239 control subjects. The population studied included active-duty military personnel, veterans, and their families. The SNPs analyzed in this work occur in nine different genes, comprising six interleukin (IL) genes (IL1A, IL1B, IL4, IL6, IL10, and IL18), fatty acid amide hydrolase (FAAH) gene, and cannabinoid receptors 1 and 2 genes (CNR1, CNR2). The products of these genes are players in different conditions, including inflammation, a process linked with diabetes.

MATERIALS AND METHODS

The T2DM and control (no diabetes) DNA samples were acquired from an archived sample repository (Center for Advanced Molecular Detection, 59th Medical Wing, U.S. Air Force, Joint Base San Antonio [JBSA]-Lackland, TX). The blood samples had been previously collected from gender- and race-mixed cohorts under a protocol approved by the 59th Medical Wing Institutional Review Board. Single nucleotide polymorphism (SNP) genotyping was done by real-time Polymerase Chain Reaction (PCR) using TaqMan assay reagents. The statistical analysis software 9.3 (SAS 9.3) was used for statistical analyses to reveal associations between the SNP genotypes and T2DM.

RESULTS

Out of the 18 SNPs analyzed, six showed statistically significant association with T2DM in the overall cohort (P < .05). The odds ratio for these associations varied from 1.57 to 3.16. The rs16944 T/T homozygous genotype (IL1B) showed the strongest association with T2DM, with P = .005. In the White cohort, five of these six SNPs and one other, rs806368 (cannabinoid receptor 1), associate with T2DM. However, the gender-specific analysis of the White cohort revealed only two SNP associations with T2DM in the female cohort, rs16944 (IL1B) and rs2295632 (FAAH), both also showing association in the overall mixed cohort. Likewise, four SNPs showed T2DM association in the White male cohort, with rs187238 (IL18) being uniquely significant in this group.

CONCLUSIONS

The IL1B SNP rs16944 showed consistent statistically significant association with T2DM and therefore is likely a promising biomarker for T2DM. We note, however, that this association in a generic sense may be with the inflammatory process that accompanies T2DM and not per se with T2DM.

Cannabis Pharmacogenomics: A Path to Personalized Medicine

Cannabis and related compounds have created significant research interest as a promising therapy in many disorders. However, the individual therapeutic effects of cannabinoids and the incidence of side effects are still difficult to determine. Pharmacogenomics may provide the answers to many questions and concerns regarding the cannabis/cannabinoid treatment and help us to understand the variability in individual responses and associated risks. Pharmacogenomics research has made meaningful progress in identifying genetic variations that play a critical role in interpatient variability in response to cannabis. This review classifies the current knowledge of pharmacogenomics associated with medical marijuana and related compounds and can assist in improving the outcomes of cannabinoid therapy and to minimize the adverse effects of cannabis use. Specific examples of pharmacogenomics informing pharmacotherapy as a path to personalized medicine are discussed.

Cannabinoids and Multiple Sclerosis: A Critical Analysis of Therapeutic Potentials and Safety Concerns

Multiple sclerosis (MS) is a complicated condition in which the immune system attacks myelinated axons in the central nervous system (CNS), destroying both myelin and axons to varying degrees. Several environmental, genetic, and epigenetic factors influence the risk of developing the disease and how well it responds to treatment. Cannabinoids have recently sparked renewed interest in their therapeutic applications, with growing evidence for their role in symptom control in MS. Cannabinoids exert their roles through the endogenous cannabinoid (ECB) system, with some reports shedding light on the molecular biology of this system and lending credence to some anecdotal medical claims. The double nature of cannabinoids, which cause both positive and negative effects, comes from their actions on the same receptor. Several mechanisms have been adopted to evade this effect. However, there are still numerous limitations to using cannabinoids to treat MS patients. In this review, we will explore and discuss the molecular effect of cannabinoids on the ECB system, the various factors that affect the response to cannabinoids in the body, including the role of gene polymorphism and its relation to dosage, assessing the positive over the adverse effects of cannabinoids in MS, and finally, exploring the possible functional mechanism of cannabinoids in MS and the current and future progress of cannabinoid therapeutics.

Cannabinoid CB2 Receptors in Neurodegenerative Proteinopathies: New Insights and Therapeutic Potential

Some of the most prevalent neurodegenerative disorders, including Alzheimer's and Parkinson's disease, are proteinopathies characterized by the accumulation of specific protein aggregates in the brain. Such misfolded protein aggregates can trigger modulation of the innate and adaptive immune systems and subsequently lead to chronic neuroinflammation that drives the onset and progression of neurodegenerative diseases. Since there is still no effective disease-modifying treatment, new therapeutic targets for neurodegenerative proteinopathies have been sought. The endocannabinoid system, and in particular the cannabinoid CB2 receptors, have been extensively studied, due to their important role in neuroinflammation, especially in microglial cells. Several studies have shown promising effects of CB2 receptor activation on reducing protein aggregation-based pathology as well as on attenuating inflammation and several dementia-related symptoms. In this review, we discuss the available data on the role of CB2 receptors in neuroinflammation and the potential benefits and limitations of specific agonists of these receptors in the therapy of neurodegenerative proteinopathies.

Cannabinoids in rheumatology: Friend, foe or a bystander?

OBJECTIVES

Cannabinoids have gained popularity recently with special emphasis on their use for chronic pain. Although NICE guidelines advise against their usage for management of chronic pain, almost all rheumatologists encounter a few patients in their daily practice who either use them or are curious about them. We reviewed the mechanism of action of cannabinoids, current knowledge about their role in rheumatology and potential drug interactions with common drugs used in Rheumatology. We attempted to answer the question "If cannabinoids are friend, foe or just a mere bystander?"

METHODS

We adhered to a search strategy for writing narrative reviews as per available guidelines. We searched PubMed with the search terms "Cannabinoids", "Rheumatology" and "Chronic pain" for published articles and retrieved 613 articles. The abstracts and titles of these articles were screened to identify relevant studies focusing on mechanism of actions, adverse effects and drug interactions. We also availed the services of a musculoskeletal librarian.

RESULTS

Despite the NHS guidelines against the usage of cannabinoids and associated significant stigma, cannabinoids are increasingly used for the management of pain in rheumatology without prescription. Cannabinoids act through two major receptors CB1 and CB2, which are important modulators of the stress response with potential analgesic effects. Their role in various rheumatological diseases including Rheumatoid arthritis, Osteoarthritis and Fibromyalgia have been explored with some benefits. However, in addition to the adverse effects, cannabinoids also have some potential interactions with common drugs used in rheumatology, which many users are unaware of.

CONCLUSION

While the current studies and patient reported outcomes suggest cannabinoids to be a "friend" of rheumatology, their adverse events and drug interactions prove to be a "Foe". We were unable to arrive at a definite answer for our question posed, however on the balance of probabilities we can conclude cannabinoids to be a "foe". Under these circumstances, a disease and drug focussed research is need of the hour to answer the unresolved question.

Characterization of cannabinoid receptors expressed in Ewing sarcoma TC-71 and A-673 cells as potential targets for anti-cancer drug development

AIMS

Characterizing cannabinoid receptors (CBRs) expressed in Ewing sarcoma (EWS) cell lines as potential targets for anti-cancer drug development.

MAIN METHODS

CBR affinity and function were examined by competitive binding and G-protein activation, respectively. Cannabinoid-mediated cytotoxicity and cell viability were evaluated by LDH, and trypan blue assays, respectively.

KEY FINDINGS

qRT-PCR detected CB1 (CB1R) and CB2 receptor (CB2R) mRNA in TC-71 cells. However, binding screens revealed that CBRs expressed exhibit atypical properties relative to canonical receptors, because specific binding in TC-71 could only be demonstrated by the established non-selective CB1/CB2R radioligand [³H]WIN-55,212-2, but not CB1/CB2R radioligand [³H]CP-55,940. Homologous receptor binding demonstrated that [³H]WIN-55,212-2 binds to a single site with nanomolar affinity, expressed at high density. Further support for non-canonical CBRs expression is provided by subsequent binding screens, revealing that only 9 out of 28 well-characterized cannabinoids with high affinity for canonical CB1 and/or CB2Rs were able to displace [³H]WIN-55,212-2, whereas two ligands enhanced [³H]WIN-55,212-2 binding. Five cannabinoids producing the greatest [³H]WIN-55,212-2 displacement exhibited high nanomolar affinity (K_i) for expressed receptors. G-protein modulation and adenylyl cyclase assays further indicate that these CBRs exhibit distinct signaling/functional profiles compared to canonical CBRs. Importantly, cannabinoids with the highest affinity for non-canonical CBRs reduced TC-71 viability and induced cytotoxicity in a time-dependent manner. Studies in a second EWS cell line (A-673) showed similar atypical binding properties of expressed CBRs, and cannabinoid treatment produced cytotoxicity.

SIGNIFICANCE

Cannabinoids induce cytotoxicity in EWS cell lines via non-canonical CBRs, which might be a potential therapeutic target to treat EWS.

Functional variation (Q63R) in the cannabinoid CB2 receptor may affect the severity of COVID-19: a human study and molecular docking

Evidence supports a role of host genetic diversity in the clinical course of coronavirus disease 2019 (COVID-19). Variation in the cannabinoid CB2 receptor gene (CNR2) could affect the regulatory action of endocannabinoids on the immune system, resulting in an increased risk of various inflammatory diseases. The present study investigated the relationship between the CNR2-Q63R variant and COVID-19 severity. A total of 200 Iranian COVID-19 patients were enrolled in the study and genotyped using a TaqMan assay. The co-dominant, dominant, recessive, over-dominant, and additive inheritance models were analyzed using SNPStats software. In silico molecular docking was also performed to simulate the effects of the Q63R variation on CB2 binding with a ligand and with the G-protein. A significant difference in the Q63R allele and genotype distribution was found between expired and discharged COVID-19 patients in co-dominant, recessive, and additive inheritance models. The molecular docking results showed that the predicted structure of mutant CB2 (63R type) could not bind to the G-protein in the correct position. The data indicated that the Q63R variation in the CNR2 gene may affect the severity of COVID-19. Identification of genes related to susceptibility and severity of COVID-19 may lead to specific targets for drug repurposing or development.

The CB2 cannabinoid receptor as a therapeutic target in the central nervous system

INTRODUCTION

Targeting CB2 cannabinoid receptor (CB2r) represents a promising approach for the treatment of central nervous system disorders. These receptors were identified in peripheral tissues, but also in neurons in the central nervous system. New findings have highlighted the interest to target these central receptors to obtain therapeutic effects devoid of the classical cannabinoid side-effects.

AREAS COVERED

In this review, we searched PubMed (January 1991-May 2021), ClinicalTrials.gov and Cochrane Library databases for articles, reviews and clinical trials. We first introduce the relevance of CB2r as a key component of the endocannabinoid system. We discuss CB2r interest as a possible novel target in the treatment of pain. This receptor has raised interest as a potential target for neurodegenerative disorders treatment, as we then discussed. Finally, we underline studies revealing a novel potential CB2r interest in mental disorders treatment.

EXPERT OPINION

In spite of the interest of targeting CB2r for pain, clinical trials evaluating CB2r agonist analgesic efficacy have currently failed. The preferential involvement of CB2r in preventing the development of chronic pain could influence the failure of clinical trials designed for the treatment of already established pain syndromes. Specific trials should be designed to target the prevention of chronic pain development.

Biased Coupling to β-Arrestin of Two Common Variants of the CB2 Cannabinoid Receptor

β-arrestins are partners of the G protein-coupled receptors (GPCRs), regulating their intracellular trafficking and signaling. Development of biased GPCR agonists, selectively targeting either G protein or β-arrestin pathways, are in the focus of interest due to their therapeutic potential in different pathological conditions. The CB₂ cannabinoid receptor (CB₂R) is a GPCR involved in various functions in the periphery and the central nervous system. Two common occurring variants of CB₂R, harboring Q63R or L133I missense mutations, have been implicated in the development of a diverse set of disorders. To evaluate the effect of these mutations, we characterized the binding profile of these mutant CB₂ receptors to G proteins and β-arrestin2. Although their ability to inhibit cAMP signaling was similar, the Q63R mutant had increased, whereas the L133I mutant receptor had decreased β-arrestin2 binding. In line with these observations, the variants also had altered intracellular trafficking. Our results show that two common variants of the CB₂ receptor have biased signaling properties, which may contribute to the pathogenesis of the associated disorders and may offer CB₂R as a target for further development of biased receptor activation strategies.

Cannabinoid Receptor Type 2: A Possible Target in SARS-CoV-2 (CoV-19) Infection?

In late December 2019, a novel coronavirus (SARS-CoV-2 or CoV-19) appeared in Wuhan, China, causing a global pandemic. SARS-CoV-2 causes mild to severe respiratory tract inflammation, often developing into lung fibrosis with thrombosis in pulmonary small vessels and causing even death. COronaVIrus Disease (COVID-19) patients manifest exacerbated inflammatory and immune responses, cytokine storm, prevalence of pro-inflammatory M1 macrophages and increased levels of resident and circulating immune cells. Men show higher susceptibility to SARS-CoV-2 infection than women, likely due to estrogens production. The protective role of estrogens, as well as an immune-suppressive activity that limits the excessive inflammation, can be mediated by cannabinoid receptor type 2 (CB2). The role of this receptor in modulating inflammation and immune response is well documented in fact in several settings. The stimulation of CB2 receptors is known to limit the release of pro-inflammatory cytokines, shift the macrophage phenotype towards the anti-inflammatory M2 type and enhance the immune-modulating properties of mesenchymal stromal cells. For these reasons, we hypothesize that CB2 receptor can be a therapeutic target in COVID-19 pandemic emergency.

Evaluation of common variants in the CNR2 gene and its interaction with abdominal obesity for osteoporosis susceptibility in Chinese post-menopausal females

Objectives

The objective of this study was to investigate the association of four single-nucleotide polymorphisms (SNPs) of the cannabinoid receptor 2 (CNR2) gene, gene-obesity interaction, and haplotype combination with osteoporosis (OP) susceptibility.

Methods

Chinese patients with OP were recruited between March 2011 and December 2015 from our hospital. In this study, a total of 1267 post-menopausal female patients (631 OP patients and 636 control patients) were selected. The mean age of all subjects was 69.2 years (sd 15.8). A generalized multifactor dimensionality reduction (GMDR) model and logistic regression model were used to examine the interaction between SNP and obesity on OP. For OP patient-control haplotype analyses, the SHEsis online haplotype analysis software (http://analysis.bio-x.cn/) was employed.

Results

The logistic regression model revealed that the C allele of rs2501431 and the G allele of rs3003336 were associated with increased OP risk, compared with those with wild genotype. However, no significant correlations were found when analyzing the association of rs4237 and rs2229579 with OP risk. The GMDR analysis suggested that the interaction model composed of two factors, rs3003336 and abdominal obesity (AO), was the best model with statistical significance (p-value from sign test (P_sign) = 0.012), indicating a potential gene-environment interaction between rs3003336 and AO. Overall, the two-locus models had a cross-validation consistency of 10/10 and had a testing accuracy of 0.641. Abdominally obese subjects with the AG or GG genotype have the highest OP risk, compared with subjects with the AA genotype and normal waist circumference (WC) (odds ratio (OR) 2.23, 95% confidence interval (CI) 1.54 to 3.51). Haplotype analysis also indicated that the haplotype containing the rs3003336-G and rs2501431-C alleles was associated with a statistically increased OP risk.

Conclusion

Our results suggested that the C allele of rs2501431 and the G allele of rs3003336 of the CNR2 gene, interaction between rs3003336 and AO, and the haplotype containing the rs3003336-G and rs2501431-C alleles were all associated with increased OP risk.

Cite this article: Bone Joint Res 2019;8:544–549.

Cannabinoid Actions on Neural Stem Cells: Implications for Pathophysiology

With the increase of life expectancy, neurodegenerative disorders are becoming not only a health but also a social burden worldwide. However, due to the multitude of pathophysiological disease states, current treatments fail to meet the desired outcomes. Therefore, there is a need for new therapeutic strategies focusing on more integrated, personalized and effective approaches. The prospect of using neural stem cells (NSC) as regenerative therapies is very promising, however several issues still need to be addressed. In particular, the potential actions of pharmacological agents used to modulate NSC activity are highly relevant. With the ongoing discussion of cannabinoid usage for medical purposes and reports drawing attention to the effects of cannabinoids on NSC regulation, there is an enormous, and yet, uncovered potential for cannabinoids as treatment options for several neurological disorders, specifically when combined with stem cell therapy. In this manuscript, we review in detail how cannabinoids act as potent regulators of NSC biology and their potential to modulate several neurogenic features in the context of pathophysiology.

Pharmacogenetics of Cannabinoids

Although the application of medical marijuana and cannabinoid drugs is controversial, it is a part of modern-day medicine. The list of diseases in which cannabinoids are promoted as a treatment is constantly expanding. Cases of significant improvement in patients with a very poor prognosis of glioma or epilepsy have already been described. However, the occurrence of side effects is still difficult to estimate, and the current knowledge of the therapeutic effects of cannabinoids is still insufficient. In our opinion, the answers to many questions and concerns regarding the medical use of cannabis can be provided by pharmacogenetics. Knowledge based on proteins and molecules involved in the transport, action, and metabolism of cannabinoids in the human organism leads us to predict candidate genes which variations are responsible for the presence of the therapeutic and side effects of medical marijuana and cannabinoid-based drugs. We can divide them into: receptor genes-CNR1, CNR2, TRPV1, and GPR55, transporters-ABCB1, ABCG2, SLC6A, biotransformation, biosynthesis, and bioactivation proteins encoded by CYP3A4, CYP2C19, CYP2C9, CYP2A6, CYP1A1, COMT, FAAH, COX2, ABHD6, ABHD12 genes, and also MAPK14. This review organizes the current knowledge in the context of cannabinoids pharmacogenetics according to individualized medicine and cannabinoid drugs therapy.

Cannabinoid Receptor 2 Functional Variant Contributes to the Risk for Pediatric Inflammatory Bowel Disease

GOALS

We conducted a case-control association analysis to establish the role of a common CB2 functional variant, Q63R, in the susceptibility to inflammatory bowel disease (IBD).

BACKGROUND

Endocannabinoids may limit intestinal inflammation through cannabinoid receptor 1 and/or 2 (CB1, CB2).

STUDY

We genotyped 217 pediatric IBD patients [112 Crohn's disease (CD), 105 ulcerative colitis (UC)] and 600 controls for the CB2-Q63R variant by Taqman assay. Data were collected from clinical records on age at diagnosis, disease activity, duration and location, extraintestinal manifestations, therapy, clinical relapses, and need for surgery.

RESULTS

We found a significant association of the CB2-R63 variant with IBD (allele frequencies, P=0.04; genotype distributions, P=0.0006), in particular with CD (allele frequencies, P=0.002; genotype distributions, P=0.00005) and with UC only for genotype distributions (P=0.03). RR carriers showed an increased risk for developing IBD [odds ratio (OR)=1.82; P=0.0002 for IBD; OR=2.02; P=10 for CD; OR=1.63; P=0.02 for UC at 95% confidence interval]. Upon genotype-phenotype evaluation, RR patients showed an increased frequency of moderate-to-severe disease activity at diagnosis in the case of both CD and UC (P=0.01 and P=0.02, respectively) and also an earlier clinical relapse in UC (P=0.04). In UC, all the clinical features related to the CB2 risk allele were still significantly associated with the variant when analyzed using a multivariate logistic regression model (P=0.001).

CONCLUSIONS

The CB2-Q63R variant contributes to the risk for pediatric IBD, in particular CD. The R63 variant is associated with a more severe phenotype in both UC and CD. Taken together, our data point toward the involvement of the CB2 receptor in the pathogenesis and clinical features of pediatric IBD.

Effects of cannabinoid receptor type 2 in respiratory syncytial virus infection in human subjects and mice

An accumulating body of evidence suggests that the endocannabinoid system plays a significant role in pathophysiological processes and impacts disease severity. Here we investigate the possible role of a cannabinoid receptor type 2 (CB2) functional variant in determining disease severity and the potential pharmacological therapeutic effects of CB2 activation in viral respiratory infection. The common missense variant (CAA/CGG; Q63R) of the gene-encoding CB2 receptor (CNR2) was evaluated in 90 inpatient and 90 outpatient children with acute respiratory tract infection (ARTI). The frequency distribution of respiratory syncytial virus (RSV)-the main cause of severe cases of bronchiolitis and pneumonia in children-was studied in all collected samples. The mechanism through which CB2 affects clinical outcomes in case of RSV infection was studied in Balb/c mice model using AM630 as a CB2 antagonist. The potential therapeutic effect of CB2 activation during RSV infection was studied using a selective agonist, JWH133. The CB2 Q63R variation was associated with increased risk of hospitalization in children with ARTI. Children carrying the QQ genotype were more prone to developing severe ARTI (OR = 3.275, 95% CI: 1.221–8.705; p = 0.019). Of all the children enrolled in the study, 83 patients (46.1%) were found positive for RSV infection. The associated risk of developing severe ARTI following RSV infection increased more than two-fold in children carrying the Q allele (OR = 2.148, 95% CI: 1.092–4.224; p = 0.026). In mice, the blockade of CB2 by AM630 during RSV infection enhanced the influx of BAL cells and production of cytokines/chemokines while exaggerating lung pathology. CB2 activation by JWH133 reduces the influx of BAL cells and production of cytokines/chemokines while alleviating lung pathology. Collectively, CB2 is associated with RSV severity during infancy and may serve as a therapeutic target in RSV infection through the alleviation of virus-associated immunopathology.

Cannabinoid receptor 2-63 RR variant is independently associated with severe necroinflammation in HIV/HCV coinfected patients

OBJECTIVE

This is the first study to analyze the impact of the rs35761398 variant of the CNR2 gene leading to the substitution of GLN (Q) of codon 63 of the cannabinoid receptor 2 (CB2) with ARG (R) on the clinical presentation of chronic hepatitis in HIV/HCV coinfected patients.

METHODS

Enrolled in this study were 166 consecutive HIV/HCV coinfected patients, naïve for HCV treatment. A pathologist unaware of the patients' condition graded liver fibrosis, necroinflammation (Ishak) and steatosis. All patients were screened for the CB2 rs35761398 polymorphism.

RESULTS

Of the 166 HIV/HCV coinfected patients, 72.9% were males, 42.5% were infected with HCV-genotype-3 and 60.2% had been intravenous drug users. The median age was 40.6 years and the immunological condition good (median CD4+ cells/mm3 = 507, IQR: 398.0-669.5). Thirty-five (21.1%) patients were naive for ART and 131(78.9%) were on ART. The CB2-RR variant was detected in 45.8% of patients, QR in 38.6% and QQ in 15.7%. Patients with CB2-RR showed a necroinflammation score (HAI) ≥9 more frequently than those with CB2-QQ or CB2-QR (32.9% vs. 11.5% and 14.1%, respectively, p≤0.001). In the multivariate analysis, the CB2-RR variant (p = 0.03) and liver fibrosis were both identified as independent predictors of the entity of liver necroinflammation (p = 0.0001).

CONCLUSION

This study shows interesting interplay between the CB2-RR variant and liver necroinflammation in chronic hepatitis patients with HIV/HCV coinfection, an observation of clinical value that coincides with the interest in the use of the CB2 agonists and antagonists in clinical practice emerging from the literature.

CB2-63 polymorphism and immune-mediated diseases associated with HCV chronic infection

AIMS

To evaluate whether CB2 variants are associated with the presence of immune-mediated disorders (IMDs) in patients with chronic HCV infection.

METHODS

One hundred and sixty-eight anti-HCV/HCV-RNA-positive patients were enrolled, 81 with signs of IMDs and 87 without. In the IMDs group, 22 (27.2%) showed ANA positivity (titers ≥1:160), 3 (3.7%) SMA positivity (titers ≥1:160), 24 (29.6%) had cryoglobulinemia, 25 (30.9%) autoimmune thyroiditis, 4 (4.9%) psoriasis, 2 (2.5%) B-cell non-Hodgkin lymphoma and 1 (1.2%) autoimmune hemolytic anemia. All patients were screened for the CNR2 rs35761398 single nucleotide polymorphism using a TaqMan Assay.

RESULTS

Compared with the 87 patients without IMDs, the 81 with IMDs were more frequently females (65% vs. 45%, p=0.01), but no significant difference was found in the initial demographic, epidemiological, serological, biochemical or virological data. Instead, the prevalence of patients with the CB2-63 RR variant was significantly higher in the IMD than in the non-IMD group (49.4% vs. 24.1%, p=0.001). A logistic regression analysis including the CB2-63 receptor (RR vs. QR or QQ), age and sex identified the CB2-63 RR as the only independent predictor of IMDs (p=0.005).

CONCLUSIONS

The data suggest a significant, previously unknown, independent association between the CB2-63 RR variant and IMDs in anti-HCV-positive patients. The study was approved by the Ethics Committee of the Azienda Ospedaliera Universitaria of the Second University of Naples (n° 214/2012).

Crosstalk between endocannabinoid and immune systems: a potential dysregulation in depression?

BACKGROUND

The endocannabinoid (eCB) system, an endogenous lipid signaling system, appears to be dysregulated in depression. The role of endocannabinoids (eCBs) as potent immunomodulators, together with the accumulating support for a chronic low-grade inflammatory profile in depression, suggests a compelling hypothesis for a fundamental impairment in their intercommunication, in depression.

OBJECTIVE

We aim to review previous literature on individual associations between the immune and eCB systems and depression. It will focus on peripheral and central mechanisms of crosstalk between the eCB and immune systems. A potential dysregulation in this crosstalk will be discussed in the context of depression.

RESULTS

Investigations largely report a hypoactivity of the eCB system and increased inflammatory markers in individuals with depression. Findings depict a multifaceted communication whereby immunocompetent and eCB-related cells can both influence the suppression and enhancement of the other's activity in both the periphery and central nervous system. A dysregulation of the eCB system, as seen in depression, appears to be associated with central and peripheral concentrations of inflammatory agents implicated in the pathophysiology of this illness.

CONCLUSION

The eCB and immune systems have been individually associated with and implicated in pathogenic mechanisms of depression. Both systems tightly regulate the other's activity. As such, a dysregulation in this crosstalk has potential to influence the onset and maintenance of this neuropsychiatric illness. However, few studies have investigated both systems and depression conjointly. This review highlights the demand to consider joint eCB-immune interactions in the pathoetiology of depression.

Cannabinoid receptor gene polymorphisms and bone mineral density in Korean postmenopausal women

OBJECTIVE

We investigated the association between single nucleotide polymorphisms in cannabinoid receptor (CNR) genes and bone mineral density (BMD) in Korean postmenopausal women.

METHODS

Seven polymorphisms (rs2023239, rs806379, rs12720071, rs1049353, rs806368, rs2180619, and rs7766029) in the cannabinoid receptor type 1 (CNR1) gene and 16 polymorphisms (rs2501432, rs2502992, rs2501431, rs3003336, rs4649124, rs2502993, rs2229579, rs2229580, rs2229581, rs2229583, rs2229584, rs2229585, rs2229586, rs4237, rs7530595, and rs16828926) in the cannabinoid receptor type 2 (CNR2) gene were analyzed in 405 Korean postmenopausal women. Serum levels of bone turnover markers, osteoprotegerin (OPG), and soluble receptor activator of nuclear factor-κB ligand (sRANKL) were measured, and BMD at the lumbar spine and femoral neck was examined.

RESULTS

The CNR2 rs2501431, rs3003336, rs2229579, and rs4237 polymorphisms in CNR genes were associated with lumbar spine BMD. Women with the AA genotype of rs3003336 and rs4237 polymorphisms had significantly lower lumbar spine BMD compared with women with the non-AA genotype. Lumbar spine BMD in women with the TT genotype of CNR2 rs2501431 and rs2229579 polymorphisms was significantly lower than that in women with the non-TT genotype. Significantly higher odds for osteoporosis of the lumbar spine and/or femoral neck were observed in women with the TT genotype of rs2229579 polymorphisms (odds ratio, 3.43; 95% CI, 1.28-9.19) and with the AA genotype of rs4237 polymorphisms (odds ratio, 1.74; 95% CI, 1.03-2.95) compared with those not carrying the genotypes. The adjusted serum levels of bone turnover markers, OPG, sRANKL, or sRANKL × 1,000-to-OPG ratios were not associated with CNR gene polymorphisms.

CONCLUSIONS

Our results suggest that rs2501431, rs3003336, rs2229579, and rs4237 polymorphisms in CNR genes may be genetic factors affecting BMD in Korean postmenopausal women.

Evaluation of common variants in CNR2 gene for bone mineral density and osteoporosis susceptibility in postmenopausal women of Han Chinese

Postmenopausal osteoporosis is a major health problem with important genetic factors in postmenopausal women. We thoroughly evaluated the relationship of CNR2 polymorphisms with osteoporosis in a cohort of 1032 osteoporosis patients and 2089 healthy controls from Han Chinese postmenopausal women. Statistically significant differences, depending on different genotypes, were presented.

INTRODUCTION

Osteoporosis is a major health problem in postmenopausal women, which is a multifactorial disease in which genetic determinants are modulated by hormonal, environmental, and nutritional factors. An important clinical risk factor in the pathogenesis of osteoporosis is the presence of genetic polymorphism in susceptibility genes. The aim of our study was to investigate whether CNR2 gene, which attributes to osteoporosis susceptibility in some populations, is associated with bone mineral density (BMD) or osteoporosis in Han Chinese postmenopausal women.

METHODS

We examine 39 SNPs covering the region of CNR2 gene in 3121 Han Chinese postmenopausal women, consisting of 1032 osteoporosis patients and 2089 healthy controls, to evaluate the association with BMD and osteoporosis.

RESULTS

We found that rs4237 and rs2501431 were significantly associated with BMD and osteoporosis (corrected p = 0.020085 and 0.017199) in our sample, and the TT genotype of rs2501431 and the AA genotype of rs4237 had lower lumbar spine BMD and femoral neck BMD compared with the other genotypes. Additionally, analyses by haplotypes indicated that two haplotype blocks, containing rs4237 and rs2501431 respectively, in the CNR2 gene significantly associated with BMD and osteoporosis (both global permutation p < 0.001), and a risk haplotype (ATTT) in the block of rs3003336-rs2501431-rs2502992-rs2501432 had almost 4-fold increase in the cases.

CONCLUSIONS

Our results provide further supportive evidence for an important role of CNR2 gene in the etiology of osteoporosis and suggest that it may be a genetic risk factor for BMD and osteoporosis in Han Chinese postmenopausal women.

The Cannabinoid Receptor 2 Q63R Variant Modulates the Relationship between Childhood Obesity and Age at Menarche

Background

The ovary is an important site where gene variants modulate pubertal timing. The cannabinoid receptor 2 (CB2) is expressed in the ovary, plays a role in folliculogenesis and ovulation, and can be modulated by estrogens. Obesity is strictly associated with early menarche and is characterized by sex hormone and endocannabinoid derangement.

Aim

In this study, we investigated the role of the CB2 receptor in determining the age at menarche in obese girls.

Methods

We studied a cohort of 240 obese girls (age 11.9±3 years; BMI z-score 2.8±0.8). The age at menarche (if it had already occurred) was recorded at the time of the visit or via phonecall. The CNR2 rs35761398 polymorphism, which leads to the CB2 Q63R variant, was detected by the TaqMan assay.

Results

In total, 105 patients were homozygous for the R63-coding allele (RR), 113 were QR and 22 were QQ. Variance analysis revealed a significantly earlier age of menarche in subjects carrying the Q63 allele, which was also found after adjusting for BMI z-score (11±1.2 vs. 11.6±1.2 years, p = 0.0003). Logistic regression analysis demonstrated that patients homozygous for the Q allele had a 2.2-fold higher risk (odds ratio = 2.2; CI1.1–3.4; p = 0.02) of presenting with an early menarche (age at menarche <12 years).

Conclusion

We demonstrated for the first time the association between the CB2 Q63R functional variant and the age at menarche in a cohort of Italian obese girls.

Role of genetic polymorphisms in hepatitis C virus chronic infection

AIM: To analyze the host genetics factors influencing the clinical course and the response to antiviral treatment in patients with chronic hepatitis C (CHC).

METHODS: We conducted an electronic search on the PubMed and MEDLINE (2000-2014) databases and Cochrane library (2000-2014). A total of 73 articles were retrieved and their data were extensively evaluated and discussed by the authors and then analyzed in this review article.

RESULTS: Several studies associated polymorphisms in the interleukin 28B gene on chromosome 19 (19q13.13) with a spontaneous viral clearance in acute hepatitis C and with the response to pegylated interferon (Peg-IFN)-based treatment in chronic hepatitis C patients. Other investigations demonstrated that inosine triphosphate pyrophosphatase genetic variants protect hepatitis C virus-genotype-1 CHC patients from ribavirin-induced anemia, and other studies that a polymorphism in the patatin-like phospholipase domain-containing protein 3 was associated with hepatic steatosis in CHC patients. Although not conclusive, some investigations suggested that the vitamin D-associated polymorphisms play an important role in the achievement of sustained virologic response in CHC patients treated with Peg-IFN-based antiviral therapy. Several other polymorphisms have been investigated to ascertain their possible impact on the natural history and on the response to treatment in patients with CHC, but the data are preliminary and warrant confirmation.

CONCLUSION: Several genetic polymorphisms seem to influence the clinical course and the response to antiviral treatment in patients with CHC, suggesting individualized follow up and treatment strategies.

Cannabinoid receptor 2-63 QQ variant is associated with persistently normal aminotransferase serum levels in chronic hepatitis C

BACKGROUND AND AIM

To evaluate in anti-HCV-positive patients the clinical impact of the rs35761398 variant of the CNR2 gene leading to the substitution of Gln (Q) of codon 63 of the cannabinoid receptor 2 (CB2) with Arg (R).

PATIENTS AND METHODS

253 consecutive anti-HCV-/HCV-RNA-positive patients were enrolled, of whom 53 were HCV carriers with persistently normal ALT (PNALT group) and 200 had a history of steadily abnormal serum ALT values (abnormal ALT group). All patients were naive for antiviral therapy and were screened for the CNR2 rs35761398 polymorphism by a TaqMan assay.

RESULTS

Subjects in the PNALT group, compared with those in the abnormal ALT group were older (58.5±12 vs. 50.7±12.4 years, p = 0.001), more frequently female (66% vs. 42%, p = 0.003), with lower body mass index (BMI) (24.5±3.1 vs. 26.6±4.6, p = 0.003), and more frequently with HCV genotype 2 (43.1% vs 17.7%, p = 0.0002) and CB2-63 QQ variant (34% vs. 11%, p = 0.0001). Considering all 253 patients, no difference in the demographic, biochemical, or virological data was observed between patients in the different CB2-63 variants. The logistic regression analysis identified CB2-63 QQ, HCV genotype 2, older age and lower BMI as independent predictors of PNALT (p<0.00001).

DISCUSSION

The CB2-63 QQ variant in HCV patients was independently associated with the PNALT status.

What we know and do not know about the cannabinoid receptor 2 (CB2)

It has been well appreciated that the endocannabinoid system can regulate immune responses via the cannabinoid receptor 2 (CB2), which is primarily expressed by cells of the hematopoietic system. The endocannabinoid system is composed of receptors, ligands and enzymes controlling the synthesis and degradation of endocannabinoids. Along with endocannabinoids, both plant-derived and synthetic cannabinoids have been shown to bind to and signal through CB2 via G proteins leading to both inhibitory and stimulatory signals depending on the biological process. Because no cannabinoid ligand has been identified that only binds to CB2, the generation of mice deficient in CB2 has greatly expanded our knowledge of how CB2 contributes to immune cell development and function in health and disease. In regards to humans, genetic studies have associated CB2 with a variety of human diseases. Here, we review the endocannabinoid system with an emphasis on CB2 and its role in the immune system.

Association between a polymorphism in cannabinoid receptor 2 and severe necroinflammation in patients with chronic hepatitis C

BACKGROUND & AIMS

The cannabinoid receptor 2 (CB2) has been implicated in liver disease. The single-nucleotide polymorphism rs35761398 in cannabinoid receptor 2 gene (CNR2), which encodes the CB2, substitutes glutamine (Q) 63 with arginine (R), and reduces the function of the gene product. We investigated the effects of CNR2 rs35761398 in patients with hepatitis C virus (HCV) infection.

METHODS

We studied 169 consecutive patients with asymptomatic chronic hepatitis (tested positive for anti-HCV and HCV RNA) at 2 liver units in southern Italy. First, liver biopsy samples were collected from July 2009 through December 2011. All patients were naive to antiviral therapy; CNR2 genotype was determined by polymerase chain reaction analysis.

RESULTS

Patients with the CB2-63 QQ variant had higher serum levels of aminotransferase than those with the CB2-63 QR or RR variants; they also had higher histologic activity index (HAI) scores (8.6 ± 3.8) than patients without the CB2-63 RR variant (5.3 ± 3.6; P < .005) or those with the CB2-63 QR variant (5.8 ± 3.3; P < .001). Patients with the different variants of CNR2 did not differ in fibrosis stage or steatosis score. Moderate or severe chronic hepatitis (HAI score, >8) was identified more frequently (55.5%) in patients with the CB2-63 QQ variant than in those with the 63 QR (20%; P < .005) or RR variants (17.4%; P < .005). In logistic regression analysis, the CB2-63 QQ variant and fibrosis score were independent predictors of moderate or severe chronic hepatitis (HAI score, >8; P < .0001).

CONCLUSIONS

The CB2-63 QQ variant of CNR2 is associated with more severe inflammation and hepatocellular necrosis in patients with HCV infection.

Pharmacogenetics of the G protein-coupled receptors

Pharmacogenetics investigates the influence of genetic variants on physiological phenotypes related to drug response and disease, while pharmacogenomics takes a genome-wide approach to advancing this knowledge. Both play an important role in identifying responders and nonresponders to medication, avoiding adverse drug reactions, and optimizing drug dose for the individual. G protein-coupled receptors (GPCRs) are the primary target of therapeutic drugs and have been the focus of these studies. With the advance of genomic technologies, there has been a substantial increase in the inventory of naturally occurring rare and common GPCR variants. These variants include single-nucleotide polymorphisms and insertion or deletions that have potential to alter GPCR expression of function. In vivo and in vitro studies have determined functional roles for many GPCR variants, but genetic association studies that define the physiological impact of the majority of these common variants are still limited. Despite the breadth of pharmacogenetic data available, GPCR variants have not been included in drug labeling and are only occasionally considered in optimizing clinical use of GPCR-targeted agents. In this chapter, pharmacogenetic and genomic studies on GPCR variants are reviewed with respect to a subset of GPCR systems, including the adrenergic, calcium sensing, cysteinyl leukotriene, cannabinoid CB1 and CB2 receptors, and the de-orphanized receptors such as GPR55. The nature of the disruption to receptor function is discussed with respect to regulation of gene expression, expression on the cell surface (affected by receptor trafficking, dimerization, desensitization/downregulation), or perturbation of receptor function (altered ligand binding, G protein coupling, constitutive activity). The large body of experimental data generated on structure and function relationships and receptor-ligand interactions are being harnessed for the in silico functional prediction of naturally occurring GPCR variants. We provide information on online resources dedicated to GPCRs and present applications of publically available computational tools for pharmacogenetic studies of GPCRs. As the breadth of GPCR pharmacogenomic data becomes clearer, the opportunity for routine assessment of GPCR variants to predict disease risk, drug response, and potential adverse drug effects will become possible.

Chronic HCV infection and inflammation: Clinical impact on hepatic and extra-hepatic manifestations

The liver has a central role in regulating inflammation by its capacity to secrete a number of proteins that control both local and systemic inflammatory responses. Chronic inflammation or an exaggerated inflammatory response can produce detrimental effects on target organs. Chronic hepatitis C virus (HCV) infection causes liver inflammation by complex and not yet well-understood molecular pathways, including direct viral effects and indirect mechanisms involving cytokine pathways, oxidative stress and steatosis induction. An increasing body of evidence recognizes the inflammatory response in chronic hepatitis C as pathogenically linked to the development of both liver-limited injury (fibrosis, cirrhosis and hepatocellular carcinoma) and extrahepatic HCV-related diseases (lymphoproliferative disease, atherosclerosis, cardiovascular and brain disease). Defining the complex mechanisms of HCV-induced inflammation could be crucial to determine the global impact of infection, to estimate progression of the disease, and to explore novel therapeutic approaches to avert HCV-related diseases. This review focuses on HCV-related clinical conditions as a result of chronic liver and systemic inflammatory states.

Cannabinoid receptor type 2 functional variant influences liver damage in children with non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) comprises a spectrum of disease ranging from simple steatosis to inflammatory steatohepatitis (NASH) with different degrees of fibrosis that can ultimately progress to cirrhosis. Accumulating evidence suggests the involvement of the endocannabinoid-system in liver disease and related complications. In particular, hepatoprotective properties for Cannabinoid Receptor type 2 (CB2) have been shown both through experimental murine models of liver injury and association study between a CB2 functional variant, Q63R, and liver enzymes in Italian obese children with steatosis.

Here, in order to clarify the role of CB2 in severity of childhood NAFLD, we have investigated the association of the CB2 Q63R variant, with histological parameters of liver disease severity in 118 Italian children with histologically-proven NAFLD.

CB2 Q63R genotype was assigned performing a TaqMan assay and a general linear model analysis was used to evaluate the association between the polymorphism and the histological parameters of liver damage.

We have found that whereas CB2 Q63R variant is not associated with steatosis or fibrosis, it is associated with the severity of the inflammation (p = 0.002) and the presence of NASH (p = 0.02).

Our findings suggest a critical role for CB2 Q63R variant in modulating hepatic inflammation state in obese children and in the consequent increased predisposition of these patients to liver damage.

Cannabinoid receptors: nomenclature and pharmacological principles

The CB1 and CB2 cannabinoid receptors are members of the G protein-coupled receptor (GPCR) family that are pharmacologically well defined. However, the discovery of additional sites of action for endocannabinoids as well as synthetic cannabinoid compounds suggests the existence of additional cannabinoid receptors. Here we review this evidence, as well as the current nomenclature for classifying a target as a cannabinoid receptor. Basic pharmacological definitions, principles and experimental conditions are discussed in order to place in context the mechanisms underlying cannabinoid receptor activation. Constitutive (agonist-independent) activity is observed with the overexpression of many GPCRs, including cannabinoid receptors. Allosteric modulators can alter the pharmacological responses of cannabinoid receptors. The complex molecular architecture of each of the cannabinoid receptors allows for a single receptor to recognize multiple classes of compounds and produce an array of distinct downstream effects. Natural polymorphisms and alternative splice variants may also contribute to their pharmacological diversity. As our knowledge of the distinct differences grows, we may be able to target select receptor conformations and their corresponding pharmacological responses. Importantly, the basic biology of the endocannabinoid system will continue to be revealed by ongoing investigations.

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.

Brain CB₂ Receptors: Implications for Neuropsychiatric Disorders

Although previously thought of as the peripheral cannabinoid receptor, it is now accepted that the CB₂ receptor is expressed in the central nervous system on microglia, astrocytes and subpopulations of neurons. Expression of the CB₂ receptor in the brain is significantly lower than that of the CB₁ receptor. Conflicting findings have been reported on the neurological effects of pharmacological agents targeting the CB₂ receptor under normal conditions. Under inflammatory conditions, CB₂ receptor expression in the brain is enhanced and CB₂ receptor agonists exhibit potent anti-inflammatory effects. These findings have prompted research into the CB₂ receptor as a possible target for the treatment of neuroinflammatory and neurodegenerative disorders. Neuroinflammatory alterations are also associated with neuropsychiatric disorders and polymorphisms in the CB₂ gene have been reported in depression, eating disorders and schizophrenia. This review will examine the evidence to date for a role of brain CB₂ receptors in neuropsychiatric disorders.