An amino-terminal variant of the central cannabinoid receptor resulting from alternative splicing

No Evidence for Endocannabinoid-Induced G Protein Subtype Selectivity at Human and Rodent Cannabinoid CB1 Receptors

Introduction: The endocannabinoid system (ECS) is a widespread neurotransmitter system. A key characteristic of the ECS is that there are multiple endogenous ligands (endocannabinoids). Of these, the most extensively studied are arachidonoyl ethanolamide (AEA) and 2-arachidonoyl-glycerol (2-AG), both act as agonists at the cannabinoid CB1 receptor. In humans, three CB1 variants have been identified: hCB1, considered the most abundant G protein-coupled receptor in the brain, alongside the less abundant and studied variants, hCB1a and hCB1b. CB1 exhibits a preference for coupling with inhibitory Gi/o proteins, although its interactions with specific members of the Gi/o family remain poorly characterized. This study aimed to compare the AEA and 2-AG-induced activation of various G protein subtypes at CB1. Furthermore, we compared the response of human CB1 (hCB1, hCB1a, hCB1b) and explored species differences by examining rodent receptors (mCB1, rCB1). Materials and Methods: Activation of individual G protein subtypes in HEK293 cells transiently expressing CB1 was measured with G protein dissociation assay utilizing TRUPATH biosensors. The performance of the TRUPATH biosensors was evaluated using Z-factor analysis. Pathway potencies and efficacies were analyzed using the operational analysis of bias to determine G protein subtype selectivity for AEA and 2-AG. Results: Initial screening of TRUPATH biosensors performance revealed variable sensitivities within our system. Based on the biosensor performance, the G protein subtypes pursued for further characterization were Gi1, Gi3, GoA, GoB, GZ, G12, and G13. Across all pathways, AEA demonstrated partial agonism, whereas 2-AG exhibited full or high-efficacy agonism. Notably, we provide direct evidence that the hCB1 receptor couples to G12 and G13 proteins. Our findings do not indicate any evidence of G protein subtype selectivity. Similar observations were made across the human receptor variants (hCB1, hCB1a, hCB1b), as well as at mCB1 and rCB1. Discussion: There was no evidence suggesting G protein subtype selectivity for AEA and 2-AG at CB1, and this finding remained consistent across human receptor variants and different species.

Exploring the evolutionary trajectory and functional landscape of cannabinoid receptors: A comprehensive bioinformatic analysis

The bioinformatic analysis of cannabinoid receptors (CBRs) CB1 and CB2 reveals a detailed picture of their structure, evolution, and physiological significance within the endocannabinoid system (ECS). The study highlights the evolutionary conservation of these receptors evidenced by sequence alignments across diverse species including humans, amphibians, and fish. Both CBRs share a structural hallmark of seven transmembrane (TM) helices, characteristic of class A G-protein-coupled receptors (GPCRs), which are critical for their signalling functions. The study reports a similarity of 44.58 % between both CBR sequences, which suggests that while their evolutionary paths and physiological roles may differ, there is considerable conservation in their structures. Pathway databases like KEGG, Reactome, and WikiPathways were employed to determine the involvement of the receptors in various signalling pathways. The pathway analyses integrated within this study offer a detailed view of the CBRs interactions within a complex network of cannabinoid-related signalling pathways. High-resolution crystal structures (PDB ID: 5U09 for CB1 and 5ZTY for CB2) provided accurate structural information, showing the binding pocket volume and surface area of the receptors, essential for ligand interaction. The comparison between these receptors' natural sequences and their engineered pseudo-CBRs (p-CBRs) showed a high degree of sequence identity, confirming the validity of using p-CBRs in receptor-ligand interaction studies. This comprehensive analysis enhances the understanding of the structural and functional dynamics of cannabinoid receptors, highlighting their physiological roles and their potential as therapeutic targets within the ECS.

Cardiotoxic effects of common and emerging drugs: role of cannabinoid receptors

Drug-induced cardiotoxicity has become one of the most common and detrimental health concerns, which causes significant loss to public health and drug resources. Cannabinoid receptors (CBRs) have recently achieved great attention for their vital roles in the regulation of heart health and disease, with mounting evidence linking CBRs with the pathogenesis and progression of drug-induced cardiotoxicity. This review aims to summarize fundamental characteristics of two well-documented CBRs (CB1R and CB2R) from aspects of molecular structure, signaling and their functions in cardiovascular physiology and pathophysiology. Moreover, we describe the roles of CB1R and CB2R in the occurrence of cardiotoxicity induced by common drugs such as antipsychotics, anti-cancer drugs, marijuana, and some emerging synthetic cannabinoids. We highlight the 'yin-yang' relationship between CB1R and CB2R in drug-induced cardiotoxicity and propose future perspectives for CBR-based translational medicine toward cardiotoxicity curation and clinical monitoring.

The Cannabinoid Receptor Type 1 Positive Allosteric Modulator ZCZ011 Attenuates Naloxone-Precipitated Diarrhea and Weight Loss in Oxycodone-Dependent Mice

Opioid use disorder reflects a major public health crisis of morbidity and mortality in which opioid withdrawal often contributes to continued use. However, current medications that treat opioid withdrawal symptoms are limited by their abuse liability or lack of efficacy. Although cannabinoid 1 (CB1) receptor agonists, including Δ9-tetrahydrocannabinol, ameliorate opioid withdrawal in both clinical and preclinical studies of opioid dependence, this strategy elicits cannabimimetic side effects as well as tolerance and dependence after repeated administration. Alternatively, CB1 receptor positive allosteric modulators (PAMs) enhance CB1 receptor signaling and show efficacy in rodent models of pain and cannabinoid dependence but lack cannabimimetic side effects. We hypothesize that the CB1 receptor PAM ZCZ011 attenuates naloxone-precipitated withdrawal signs in opioid-dependent mice. Accordingly, male and female mice given an escalating dosing regimen of oxycodone, a widely prescribed opioid, and challenged with naloxone displayed withdrawal signs that included diarrhea, weight loss, jumping, paw flutters, and head shakes. ZCZ011 fully attenuated naloxone-precipitated withdrawal-induced diarrhea and weight loss and reduced paw flutters by approximately half, but its effects on head shakes were unreliable, and it did not affect jumping behavior. The antidiarrheal and anti-weight loss effects of ZCZ0111 were reversed by a CB1 not a cannabinoid receptor type 2 receptor antagonist and were absent in CB1 (-/-) mice, suggesting a necessary role of CB1 receptors. Collectively, these results indicate that ZCZ011 completely blocked naloxone-precipitated diarrhea and weight loss in oxycodone-dependent mice and suggest that CB1 receptor PAMs may offer a novel strategy to treat opioid dependence. SIGNIFICANCE STATEMENT: Opioid use disorder represents a serious public health crisis in which current medications used to treat withdrawal symptoms are limited by abuse liability and side effects. The CB1 receptor positive allosteric modulator (PAM) ZCZ011, which lacks overt cannabimimetic behavioral effects, ameliorated naloxone-precipitated withdrawal signs through a CB1 receptor mechanism of action in a mouse model of oxycodone dependence. These results suggest that CB1 receptor PAMs may represent a viable strategy to treat opioid withdrawal.

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.

Alternative Pre-mRNA Splicing of the Mu Opioid Receptor Gene, OPRM1: Insight into Complex Mu Opioid Actions

Most opioid analgesics used clinically, including morphine and fentanyl, as well as the recreational drug heroin, act primarily through the mu opioid receptor, a class A Rhodopsin-like G protein-coupled receptor (GPCR). The single-copy mu opioid receptor gene, OPRM1, undergoes extensive alternative splicing, creating multiple splice variants or isoforms via a variety of alternative splicing events. These OPRM1 splice variants can be categorized into three major types based on the receptor structure: (1) full-length 7 transmembrane (TM) C-terminal variants; (2) truncated 6TM variants; and (3) single TM variants. Increasing evidence suggests that these OPRM1 splice variants are pharmacologically important in mediating the distinct actions of various mu opioids. More importantly, the OPRM1 variants can be targeted for development of novel opioid analgesics that are potent against multiple types of pain, but devoid of many side-effects associated with traditional opiates. In this review, we provide an overview of OPRM1 alternative splicing and its functional relevance in opioid pharmacology.

Endogenous opioid and cannabinoid systems modulate the muscle pain: A pharmacological study into the peripheral site

The participation of the peripheral opioid and cannabinoid endogenous systems in modulating muscle pain and inflammation has not been fully explored. Thus, the aim of this study was to investigate the involvement of these endogenous systems during muscular-tissue hyperalgesia induced by inflammation. Hyperalgesia was induced by carrageenan injection into the tibialis anterior muscles of male Wistar rats. We padronized an available Randal-Sellito test adaptation to evaluate nociceptive behavior elicited by mechanical insult in muscles. Western blot analysis was performed to evaluate the expression levels of opioid and cannabinoid receptors in the dorsal root ganglia. The non-selective opioid peptide receptor antagonist (naloxone) and the selective mu opioid receptor MOP (clocinnamox) and kappa opioid receptor KOP (nor-binaltorphimine) antagonists were able to intensify carrageenan-induced muscular hyperalgesia. On the other hand, the selective delta opioid receptor (DOP) antagonist (naltrindole) did not present any effect on nociceptive behavior. Moreover, the selective inhibitor of aminopeptidases (Bestatin) provoked considerable dose-dependent analgesia when intramuscularly injected into the hyperalgesic muscle. The CB₁ receptor antagonist (AM251), but not the CB₂ receptor antagonist (AM630), intensified muscle hyperalgesia. All irreversible inhibitors of anandamide hydrolase (MAFP), the inhibitor for monoacylglycerol lipase (JZL184) and the anandamide reuptake inhibitor (VDM11) decreased carrageenan-induced hyperalgesia in muscular tissue. Lastly, MOP, KOP and CB₁ expression levels in DRG were baseline even after muscular injection with carrageenan. The endogenous opioid and cannabinoid systems participate in peripheral muscle pain control through the activation of MOP, KOP and CB₁ receptors.

Neuromolecular Mechanisms of Cannabis Action

Most of our current understanding of the neuromolecular mechanisms of Cannabis action focusses on two plant cannabinoids, THC and CBD. THC acts primarily through presynaptic CB cannabinoid receptors to regulate neurotransmitter release in the brain, spinal cord and peripheral nerves. CBD action, on the other hand, is probably mediated through multiple molecular targets.

On the Role of Central Type-1 Cannabinoid Receptor Gene Regulation in Food Intake and Eating Behaviors

Different neuromodulatory systems are involved in long-term energy balance and body weight and, among these, evidence shows that the endocannabinoid system, in particular the activation of type-1 cannabinoid receptor, plays a key role. We here review current literature focusing on the role of the gene encoding type-1 cannabinoid receptors in the CNS and on the modulation of its expression by food intake and specific eating behaviors. We point out the importance to further investigate how environmental cues might have a role in the development of obesity as well as eating disorders through the transcriptional regulation of this gene in order to prevent or to treat these pathologies.

Cannabinoid Receptor 1 Inhibition in Chronic Kidney Disease: A New Therapeutic Toolbox

Chronic kidney disease (CKD) concerns millions of individuals worldwide, with few therapeutic strategies available to date. Recent evidence suggests that the endocannabinoid system (ECS) could be a new therapeutic target to prevent CKD. ECS combines receptors, cannabinoid receptor type 1 (CB1R) and type 2 (CB2R), and ligands. The most prominent receptor within the kidney is CB1R, its endogenous local ligands being anandamide and 2-arachidonoylglycerol. Therefore, the present review focuses on the therapeutic potential of CB1R and not CB2R. In the normal kidney, CB1R is expressed in many cell types, especially in the vasculature where it contributes to the regulation of renal hemodynamics. CB1R could also participate to water and sodium balance and to blood pressure regulation but its precise role remains to decipher. CB1R promotes renal fibrosis in both metabolic and non-metabolic nephropathies. In metabolic syndrome, obesity and diabetes, CB1R inhibition not only improves metabolic parameters, but also exerts a direct role in preventing renal fibrosis. In non-metabolic nephropathies, its inhibition reduces the development of renal fibrosis. There is a growing interest of the industry to develop new CB1R antagonists without central nervous side-effects. Experimental data on renal fibrosis are encouraging and some molecules are currently under early-stage clinical phases (phases I and IIa studies). In the present review, we will first describe the role of the endocannabinoid receptors, especially CB1R, in renal physiology. We will next explore the role of endocannabinoid receptors in both metabolic and non-metabolic CKD and renal fibrosis. Finally, we will discuss the therapeutic potential of CB1R inhibition using the new pharmacological approaches. Overall, the new pharmacological blockers of CB1R could provide an additional therapeutic toolbox in the management of CKD and renal fibrosis from both metabolic and non-metabolic origin.

Development and Validation of CRISPR Activator Systems for Overexpression of CB1 Receptors in Neurons

Gene therapy approaches using viral vectors for the overexpression of target genes have been for several years the focus of gene therapy research against neurological disorders. These approaches deliver robust expression of therapeutic genes, but are typically limited to the delivery of single genes and often do not manipulate the expression of the endogenous locus. In the last years, the advent of CRISPR-Cas9 technologies have revolutionized many areas of scientific research by providing novel tools that allow simple and efficient manipulation of endogenous genes. One of the applications of CRISPR-Cas9, termed CRISPRa, based on the use of a nuclease-null Cas9 protein (dCas9) fused to transcriptional activators, enables quick and efficient increase in target endogenous gene expression. CRISPRa approaches are varied, and different alternatives exist with regards to the type of Cas9 protein and transcriptional activator used. Several of these approaches have been successfully used in neurons in vitro and in vivo, but have not been so far extensively applied for the overexpression of genes involved in synaptic transmission. Here we describe the development and application of two different CRISPRa systems, based on single or dual Lentiviral and Adeno-Associated viral vectors and VP64 or VPR transcriptional activators, and demonstrate their efficiency in increasing mRNA and protein expression of the Cnr1 gene, coding for neuronal CB1 receptors. Both approaches were similarly efficient in primary neuronal cultures, and achieved a 2–5-fold increase in Cnr1 expression, but the AAV-based approach was more efficient in vivo. Our dual AAV-based VPR system in particular, based on Staphylococcus aureus dCas9, when injected in the hippocampus, displayed almost complete simultaneous expression of both vectors, high levels of dCas9 expression, and good efficiency in increasing Cnr1 mRNA as measured by in situ hybridization. In addition, we also show significant upregulation of CB1 receptor protein in vivo, which is reflected by an increased ability in reducing neurotransmitter release, as measured by electrophysiology. Our results show that CRISPRa techniques could be successfully used in neurons to target overexpression of genes involved in synaptic transmission, and can potentially represent a next-generation gene therapy approach against neurological disorders.

Cannabinoid receptor CNR1 expression and DNA methylation in human prefrontal cortex, hippocampus and caudate in brain development and schizophrenia

Beyond being one the most widely used psychoactive drugs in the world, cannabis has been identified as an environmental risk factor for psychosis. Though the relationship between cannabis use and psychiatric disorders remains controversial, consistent association between early adolescent cannabis use and the subsequent risk of psychosis suggested adolescence may be a particularly vulnerable period. Previous findings on gene by environment interactions indicated that cannabis use may only increase the risk for psychosis in the subjects who have a specific genetic vulnerability. The type 1 cannabinoid receptor (CB1), encoded by the CNR1 gene, is a key component of the endocannabinoid system. As the primary endocannabinoid receptor in the brain, CB1 is the main molecular target of the endocannabinoid ligand, as well as tetrahydrocannabinol (THC), the principal psychoactive ingredient of cannabis. In this study, we have examined mRNA expression and DNA methylation of CNR1 in human prefrontal cortex (PFC), hippocampus, and caudate samples. The expression of CNR1 is higher in fetal PFC and hippocampus, then drops down dramatically after birth. The lifespan trajectory of CNR1 expression in the DLPFC differentially correlated with age by allelic variation at rs4680, a functional polymorphism in the COMT gene. Compared with COMT methionine¹⁵⁸ carriers, Caucasian carriers of the COMT valine¹⁵⁸ allele have a stronger negative correlation between the expression of CNR1 in DLPFC and age. In contrast, the methylation level of cg02498983, which is negatively correlated with the expression of CNR1 in PFC, showed the strongest positive correlation with age in PFC of Caucasian carriers of COMT valine¹⁵⁸. Additionally, we have observed decreased mRNA expression of CNR1 in the DLPFC of patients with schizophrenia. Further analysis revealed a positive eQTL SNP, rs806368, which predicted the expression of a novel transcript of CNR1 in human DLPFC, hippocampus and caudate. This SNP has been associated with addiction and other psychiatric disorders. THC or ethanol are each significantly associated with dysregulated expression of CNR1 in the PFC of patients with affective disorder, and the expression of CNR1 is significantly upregulated in the PFC of schizophrenia patients who completed suicide. Our results support previous studies that have implicated the endocannabinoid system in the pathology of schizophrenia and provided additional insight into the mechanism of increasing risk for schizophrenia in the adolescent cannabis users.

Molecular Mechanism and Cannabinoid Pharmacology

Since antiquity, Cannabis has provoked enormous intrigue for its potential medicinal properties as well as for its unique pharmacological effects. The elucidation of its major cannabinoid constituents, Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD), led to the synthesis of new cannabinoids (termed synthetic cannabinoids) to understand the mechanisms underlying the pharmacology of Cannabis. These pharmacological tools were instrumental in the ultimate discovery of the endogenous cannabinoid system, which consists of CB1 and CB2 cannabinoid receptors and endogenously produced ligands (endocannabinoids), which bind and activate both cannabinoid receptors. CB1 receptors mediate the cannabimimetic effects of THC and are highly expressed on presynaptic neurons in the nervous system, where they modulate neurotransmitter release. In contrast, CB2 receptors are primarily expressed on immune cells. The endocannabinoids are tightly regulated by biosynthetic and hydrolytic enzymes. Accordingly, the endocannabinoid system plays a modulatory role in many physiological processes, thereby generating many promising therapeutic targets. An unintended consequence of this research was the emergence of synthetic cannabinoids sold for human consumption to circumvent federal laws banning Cannabis use. Here, we describe research that led to the discovery of the endogenous cannabinoid system and show how knowledge of this system benefitted as well as unintentionally harmed human health.

Allosteric modulators restore orthosteric agonist binding to mutated CB1 receptors

OBJECTIVES

To determine if diminished orthosteric agonist binding due to mutations in extracellular loops 1 or 2 of the cannabinoid receptor 1 (CB₁ ) can be overcome by an allosteric modulator and restore agonist binding.

METHODS

Binding assays were performed using a range of concentrations of orthosteric compound, in the presence or absence of a set concentration of the allosteric modulator PSNCBAM-1 to determine the EC₅₀ in its absence or presence.

KEY FINDINGS

Single mutations in extracellular loop 1 or 2 of CB₁ showed weak or no binding of agonist CP55940 to the receptor. Interestingly, upon addition of the allosteric modulator PSNCBAM-1, this binding was restored typically to wild-type CB₁ levels. In a few cases, the allosteric modulator ORG27569 was compared with PSNCBAM-1 for CP55940 binding and it also restored binding. Further, wild-type levels of inverse agonist bound the CB₁ mutants in the absence of modulator, suggesting the mutants were originally folded like the wild type.

CONCLUSIONS

Based on our findings, we provide evidence of a therapeutic application for allosteric modulators in situations where a mutation in the receptor may hinder its function. By utilizing allosteric modulators, restoration of orthosteric binding may be possible.

Roles of the Hepatic Endocannabinoid and Apelin Systems in the Pathogenesis of Liver Fibrosis

Hepatic fibrosis is the consequence of an unresolved wound healing process in response to chronic liver injury and involves multiple cell types and molecular mechanisms. The hepatic endocannabinoid and apelin systems are two signalling pathways with a substantial role in the liver fibrosis pathophysiology-both are upregulated in patients with advanced liver disease. Endogenous cannabinoids are lipid-signalling molecules derived from arachidonic acid involved in the pathogenesis of cardiovascular dysfunction, portal hypertension, liver fibrosis, and other processes associated with hepatic disease through their interactions with the CB₁ and CB₂ receptors. Apelin is a peptide that participates in cardiovascular and renal functions, inflammation, angiogenesis, and hepatic fibrosis through its interaction with the APJ receptor. The endocannabinoid and apelin systems are two of the multiple cell-signalling pathways involved in the transformation of quiescent hepatic stellate cells into myofibroblast like cells, the main matrix-producing cells in liver fibrosis. The mechanisms underlying the control of hepatic stellate cell activity are coincident despite the marked dissimilarities between the endocannabinoid and apelin signalling pathways. This review discusses the current understanding of the molecular and cellular mechanisms by which the hepatic endocannabinoid and apelin systems play a significant role in the pathophysiology of liver fibrosis.

The endocannabinoid system: Overview of an emerging multi-faceted therapeutic target

The endocannabinoids anandamide (AEA) and 2-arachidonoylglyerol (2-AG) are endogenous lipid mediators that exert protective roles in pathophysiological conditions, including cardiovascular diseases. In this brief review, we provide a conceptual framework linking endocannabinoid signaling to the control of the cellular and molecular hallmarks, and categorize the key components of endocannabinoid signaling that may serve as targets for novel therapeutics. The emerging picture not only reinforces endocannabinoids as potent regulators of cellular metabolism but also reveals that endocannabinoid signaling is mechanistically more complex and diverse than originally thought.

Endocannabinoids in the Islets of Langerhans: the ugly, the bad, and the good facts

The endocannabinoid system (ECS) regulates cellular homeostasis and whole-body metabolism. There is an autonomous ECS in the endocrine pancreas, including the cannabinoid 1 receptor (CB₁R) that is present in β-cells. Here, we discuss conflicts that have arisen with regard to the function(s) of the ECs in the endocrine pancreas and that have caused confusion when defining the role of the ECS in islets of Langerhans, especially the role(s) of CB₁R in β-cells. We also discuss the latest data published concerning the ECS in islets. CB₁R in particular is not simply a negative modulator of insulin secretion as it is also involved in intra-islet inflammation during high fat-high sugar intake and it is a negative regulator of β-cell viability and turnover. We also discuss the feasibility of using CB₁R as a target for the treatment of diabetes.

Cannabinoid Receptors and the Endocannabinoid System: Signaling and Function in the Central Nervous System

The biological effects of cannabinoids, the major constituents of the ancient medicinal plant Cannabis sativa (marijuana) are mediated by two members of the G-protein coupled receptor family, cannabinoid receptors 1 (CB1R) and 2. The CB1R is the prominent subtype in the central nervous system (CNS) and has drawn great attention as a potential therapeutic avenue in several pathological conditions, including neuropsychological disorders and neurodegenerative diseases. Furthermore, cannabinoids also modulate signal transduction pathways and exert profound effects at peripheral sites. Although cannabinoids have therapeutic potential, their psychoactive effects have largely limited their use in clinical practice. In this review, we briefly summarized our knowledge of cannabinoids and the endocannabinoid system, focusing on the CB1R and the CNS, with emphasis on recent breakthroughs in the field. We aim to define several potential roles of cannabinoid receptors in the modulation of signaling pathways and in association with several pathophysiological conditions. We believe that the therapeutic significance of cannabinoids is masked by the adverse effects and here alternative strategies are discussed to take therapeutic advantage of cannabinoids.

Discovery and characterization of two novel CB1 receptor splice variants with modified N-termini in mouse

Numerous studies have been carried out in the mouse model, investigating the role of the cannabinoid receptor type 1 (CB1). However, mouse CB1 (mCB1) receptor differs from human CB1 (hCB1) receptor in 13 amino acid residues. Two splice variants, hCB1a and hCB1b, diverging in their amino-termini, have been reported to be unique for hCB1 and, via different signaling properties, contribute to CB1 receptor physiology and pathophysiology. We hypothesized that splice variants also exist for the mCB1 receptor and have different signaling properties. On murine hippocampal cDNA, we identified two novel mCB1 receptor splice variants generated by splicing of introns with 117 bp and 186 bp in the N-terminal domain, corresponding to deletions of 39 or 62 amino acids, respectively. The mRNAs for the splice variants mCB1a and mCB1b are expressed at low levels in different brain regions. Western blot analysis of protein extracts from stably transfected HEK293 cells indicates a strongly reduced glycosylation because of the absence of two glycosylation sites in mCB1b. On-cell western analysis in these stable lines revealed increased internalization of mCB1a and mCB1b upon stimulation with the agonist WIN55,212-2 as compared to mCB1. Results also point toward an increased affinity to SR141716 for mCB1a, as well as slightly enhanced inhibition of neurotransmission compared to mCB1. In mCB1b, agonist-induced MAPK phosphorylation was decreased compared to mCB1 and mCB1a. Identification of mouse CB1 receptor splice variants may help to explain differences found between human and mouse endocannabinoid systems and improve the understanding of CB1 receptor signaling and trafficking in different species.

CB1 and CB2 Receptor Pharmacology

The CB1 and CB2 cannabinoid receptors (CB1R, CB2R) are members of the G protein-coupled receptor (GPCR) family that were identified over 20 years ago. CB1Rs and CB2Rs mediate the effects of Δ9-tetrahydrocannabinol (Δ9-THC), the principal psychoactive constituent of marijuana, and subsequently identified endogenous cannabinoids (endocannabinoids) anandamide and 2-arachidonoyl glycerol. CB1Rs and CB2Rs have both similarities and differences in their pharmacology. Both receptors recognize multiple classes of agonist and antagonist 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. This chapter will discuss their pharmacological characterization, distribution, phylogeny, and signaling pathways. In addition, the effects of extended agonist exposure and how that affects signaling and expression patterns of the receptors are considered.

The emerging role of the endocannabinoid system in the pathogenesis and treatment of kidney diseases

Endocannabinoids (eCBs) are endogenous lipid ligands that bind to cannabinoid receptors that also mediate the effects of marijuana. The eCB system is comprised of eCBs, anandamide, and 2-arachidonoyl glycerol, their cannabinoid-1 and cannabinoid-2 receptors (CB1 and CB2, respectively), and the enzymes involved in their biosynthesis and degradation. It is present in both the central nervous system and peripheral organs including the kidney. The current review focuses on the role of the eCB system in normal kidney function and various diseases, such as diabetes and obesity, that directly contributes to the development of renal pathologies. Normally, activation of the CB1 receptor regulates renal vascular hemodynamics and stimulates the transport of ions and proteins in different nephron compartments. In various mouse and rat models of obesity and type 1 and 2 diabetes mellitus, eCBs generated in various renal cells activate CB1 receptors and contribute to the development of oxidative stress, inflammation, and renal fibrosis. These effects can be chronically ameliorated by CB1 receptor blockers. In contrast, activation of the renal CB2 receptors reduces the deleterious effects of these chronic diseases. Because the therapeutic potential of globally acting CB1 receptor antagonists in these conditions is limited due to their neuropsychiatric adverse effects, the recent development of peripherally restricted CB1 receptor antagonists may represent a novel pharmacological approach in treating renal diseases.

Targeted proteomics of cannabinoid receptor CB1 and the CB1b isoform

Cannabinoid receptors (CBR), including CB1 and CB2 have been therapeutic targets for a number of conditions. Recently, splice variants of the CB1R have been identified in humans. The isoforms differ in their N-terminus sequence and pharmacological activity relative to the CB1R, as a result, the differentiation between the CB1 receptor and its isoform is required. As a result, a selected reaction monitoring mass spectrometry (SRM-MS) method was developed for the quantitation of CB1 and the CB1b isoform in CHO cells transduced with CB1 and CB1b. The SRM-MS protocol was assessed with isotopically labeled peptide standards and had high reproducibility of intra-day assay (CVs from 1.9 to 4.3% for CB1 and 0.5 to 5.9% for CB1b) and inter-day assay (CVs from 1.2 to 5.2% for CB1 and 1.2 to 6.1% for CB1b).

Human CB1 Receptor Isoforms, present in Hepatocytes and β-cells, are Involved in Regulating Metabolism

Therapeutics aimed at blocking the cannabinoid 1 (CB1) receptor for treatment of obesity resulted in significant improvements in liver function, glucose uptake and pancreatic β-cell function independent of weight loss or CB1 receptor blockade in the brain, suggesting that peripherally-acting only CB1 receptor blockers may be useful therapeutic agents. Neuropsychiatric side effects and lack of tissue specificity precluded clinical use of first-generation, centrally acting CB1 receptor blockers. In this study we specifically analyzed the potential relevance to diabetes of human CB1 receptor isoforms in extraneural tissues involved in glucose metabolism. We identified an isoform of the human CB1 receptor (CB1b) that is highly expressed in β-cells and hepatocytes but not in the brain. Importantly, CB1b shows stronger affinity for the inverse agonist JD-5037 than for rimonabant compared to CB1 full length. Most relevant to the field, CB1b is a potent regulator of adenylyl cyclase activity in peripheral metabolic tissues. CB1b blockade by JD-5037 results in stronger adenylyl cyclase activation compared to rimonabant and it is a better enhancer of insulin secretion in β-cells. We propose this isoform as a principal pharmacological target for the treatment of metabolic disorders involving glucose metabolism.

Spontaneous Cannabinoid Receptor 2 (CB2) Expression in the Cochlea of Adult Albino Rat and Its Up-Regulation after Cisplatin Treatment

We provide evidence for the presence of cannabinoid CB₂ receptors in some cellular types of the cochlea of the adult albino rat. Cannabinoids and their receptors are increasingly being studied because of their high potential for clinical use. As a hyperspecialized portion of the peripheral nervous system, study of the expression and function of cannabinoid receptors in the hearing organ is of high interest. Stria vascularis and inner hair cells express CB₂ receptor, as well as neurites and cell bodies of the spiral ganglion. Cellular types such as supporting cells and outer hair cells, in which the expression of other types of functional receptors has been reported, do not significantly express CB₂ receptors in this study. An up-regulation of CB₂ gene expression was detected after an ototoxic event such as cisplatin treatment, probably due to pro-inflammatory events triggered by the drug. That fact suggests promising potential of CB₂ receptor as a therapeutic target for new treatments to palliate cisplatin-induced hearing loss and other ototoxic events which triggers inflammatory pathways.

Genomic structure and expression of the human serotonin 2A receptor gene (HTR2A) locus: identification of novel HTR2A and antisense (HTR2A-AS1) exons

Background

The serotonin 2A receptor is widely implicated in genetic association studies and remains an important drug target for psychiatric, neurological, and cardiovascular conditions. RNA sequencing redefined the architecture of the serotonin 2A receptor gene (HTR2A), revealing novel mRNA transcript isoforms utilizing unannotated untranslated regions of the gene. Expression of these untranslated regions is modulated by common single nucleotide polymorphisms (SNPs), namely rs6311. Previous studies did not fully capture the complexity of the sense- and antisense-encoded transcripts with respect to novel exons in the HTR2A gene locus. Here, we comprehensively catalogued exons and RNA isoforms for both HTR2A and HTR2A-AS1 using RNA-Seq from human prefrontal cortex and multiple mouse tissues. We subsequently tested associations between expression of newfound gene features and common SNPs in humans.

Results

We find that the human HTR2A gene spans ~66 kilobases and consists of 7, rather than 4 exons. Furthermore, the revised human HTR2A-AS1 gene spans ~474 kilobases and consists of 18, rather than 3 exons. Three HTR2A exons directly overlap with HTR2A-AS1 exons, suggesting potential for complementary nucleotide interactions. The repertoire of possible mouse Htr2a splice isoforms is remarkably similar to humans and we also find evidence for overlapping sense-antisense transcripts in the same relative positions as the human transcripts. rs6311 and SNPs in high linkage disequilibrium are associated with HTR2A-AS1 expression, in addition to previously described associations with expression of the extended 5’ untranslated region of HTR2A.

Conclusions

Our proposed HTR2A and HTR2A-AS1 gene structures dramatically differ from current annotations, now including overlapping exons on the sense and anti-sense strands. We also find orthologous transcript isoforms expressed in mice, providing opportunities to elucidate the biological roles of the human isoforms using a model system. Associations between rs6311 and expression of HTR2A and HTR2A-AS1 suggest this polymorphism is capable of modulating the expression of the sense or antisense transcripts. Still unclear is whether these SNPs act directly on the expression of the sense or antisense transcripts and whether overlapping exons are capable of interacting through complimentary base-pairing. Additional studies are necessary to determine the extent and nature of interactions between the SNPs and the transcripts prior to interpreting these findings in the context of phenotypes associated with HTR2A.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-015-0325-6) contains supplementary material, which is available to authorized users.

Alternative Splicing of G Protein-Coupled Receptors: Relevance to Pain Management

Drugs that target G protein-coupled receptors (GPCRs) represent the primary treatment strategy for patients with acute and chronic pain; however, there is substantial individual variability in both the efficacy and adverse effects associated with these drugs. Variability in drug responses is due, in part, to individuals' diversity in alternative splicing of pain-relevant GPCRs. G protein-coupled receptor alternative splice variants often exhibit distinct tissue distribution patterns, drug-binding properties, and signaling characteristics that may impact disease pathology as well as the extent and direction of analgesic effects. We review the importance of GPCRs and their known splice variants to the management of pain.

Species differences in cannabinoid receptor 2 and receptor responses to cocaine self-administration in mice and rats

The discovery of functional cannabinoid receptors 2 (CB2Rs) in brain suggests a potential new therapeutic target for neurological and psychiatric disorders. However, recent findings in experimental animals appear controversial. Here we report that there are significant species differences in CB2R mRNA splicing and expression, protein sequences, and receptor responses to CB2R ligands in mice and rats. Systemic administration of JWH133, a highly selective CB2R agonist, significantly and dose-dependently inhibited intravenous cocaine self-administration under a fixed ratio (FR) schedule of reinforcement in mice, but not in rats. However, under a progressive ratio (PR) schedule of reinforcement, JWH133 significantly increased breakpoint for cocaine self-administration in rats, but decreased it in mice. To explore the possible reasons for these conflicting findings, we examined CB2R gene expression and receptor structure in the brain. We found novel rat-specific CB2C and CB2D mRNA isoforms in addition to CB2A and CB2B mRNA isoforms. In situ hybridization RNAscope assays found higher levels of CB2R mRNA in different brain regions and cell types in mice than in rats. By comparing CB2R-encoding regions, we observed a premature stop codon in the mouse CB2R gene that truncated 13 amino-acid residues including a functional autophosphorylation site in the intracellular C-terminus. These findings suggest that species differences in the splicing and expression of CB2R genes and receptor structures may in part explain the different effects of CB2R-selective ligands on cocaine self-administration in mice and rats.

Cannabinoids: new promising agents in the treatment of neurological diseases

Nowadays, Cannabis sativa is considered the most extensively used narcotic. Nevertheless, this fame obscures its traditional employ in native medicine of South Africa, South America, Turkey, Egypt and in many regions of Asia as a therapeutic drug. In fact, the use of compounds containing Cannabis and their introduction in clinical practice is still controversial and strongly limited by unavoidable psychotropic effects. So, overcoming these adverse effects represents the main open question on the utilization of cannabinoids as new drugs for treatment of several pathologies. To date, therapeutic use of cannabinoid extracts is prescribed in patients with glaucoma, in the control of chemotherapy-related vomiting and nausea, for appetite stimulation in patients with anorexia-cachexia syndrome by HIV, and for the treatment of multiple sclerosis symptoms. Recently, researcher efforts are aimed to employ the therapeutic potentials of Cannabis sativa in the modulation of cannabinoid receptor activity within the central nervous system, particularly for the treatment of neurodegenerative diseases, as well as psychiatric and non-psychiatric disorders. This review evaluates the most recent available data on cannabinoids utilization in experimental and clinical studies, and highlights their beneficial effects in the prevention of the main neurological diseases and for the clinical treatment of symptoms with them correlated.

Neurophysiological evidence for the presence of cannabinoid CB1 receptors in the laterodorsal tegmental nucleus

Marijuana, which acts within the endocannabinoid (eCB) system as an agonist of the cannabinoid type 1 receptor (CB1R), exhibits addictive properties and has powerful actions on the state of arousal of an organism. The laterodorsal tegmental nucleus (LDT), as a component of the reticular activating system, is involved in cortical activation and is important in the development of drug addiction-associated behaviours. Therefore, eCBs might exert behavioural effects by actions on the LDT; however, it is unknown whether eCBs have actions on neurons in this nucleus. Accordingly, whole-cell voltage- and current-clamp recordings were conducted from mouse brain slices, and responses of LDT neurons to the CB1R agonist WIN-2 were monitored. Our results showed that WIN-2 decreased the frequency of spontaneous and miniature inhibitory postsynaptic currents (sIPSCs and mIPSCs). Ongoing activity of endogenous eCBs was confirmed as AM251, a potent CB1R antagonist, elicited sIPSCs. WIN-2 reduced the firing frequency of LDT neurons. In addition, our RT-PCR studies confirmed the presence of CB1R transcript in the LDT. Taken together, we conclude that CB1Rs are functionally active in the LDT, and their activation changes the firing frequency and synaptic activity of neurons in this nucleus. Therefore, endogenous eCB transmission could play a role in processes involving the LDT, such as cortical activation and motivated behaviours and, further, behavioural actions of marijuana are probably mediated, in part, via cellular actions within the LDT induced by this addictive and behavioural state-altering drug.

Endocannabinoids are Involved in Male Vertebrate Reproduction: Regulatory Mechanisms at Central and Gonadal Level

Endocannabinoids (eCBs) are natural lipids regulating a large array of physiological functions and behaviors in vertebrates. The eCB system is highly conserved in evolution and comprises several specific receptors (type-1 and type-2 cannabinoid receptors), their endogenous ligands (e.g., anandamide and 2-arachidonoylglycerol), and a number of biosynthetic and degradative enzymes. In the last few years, eCBs have been described as critical signals in the control of male and female reproduction at multiple levels: centrally, by targeting hypothalamic gonadotropin-releasing-hormone-secreting neurons and pituitary, and locally, with direct effects on the gonads. These functions are supported by the extensive localization of cannabinoid receptors and eCB metabolic enzymes at different levels of the hypothalamic-pituitary-gonadal axis in mammals, as well as bonyfish and amphibians. In vivo and in vitro studies indicate that eCBs centrally regulate gonadal functions by modulating the gonadotropin-releasing hormone-gonadotropin-steroid network through direct and indirect mechanisms. Several proofs of local eCB regulation have been found in the testis and male genital tracts, since eCBs control Sertoli and Leydig cells activity, germ cell progression, as well as the acquisition of sperm functions. A comparative approach usually is a key step in the study of physiological events leading to the building of a general model. Thus, in this review, we summarize the action of eCBs at different levels of the male reproductive axis, with special emphasis, where appropriate, on data from non-mammalian vertebrates.

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.

The pentafluorosulfanyl group in cannabinoid receptor ligands: synthesis and comparison with trifluoromethyl and tert-butyl analogues

Competitive CB₁ receptor antagonists carrying an aromatic SF₅ group in position 3 of a pyrazole ring were synthesised and compared with their CF₃ and tert-butyl analogues. Results confirmed that an aromatic SF₅ group can be used as a bioisosteric analogue of a CF₃ group and possibly of a bulky aliphatic group too.

Co-expression of the human cannabinoid receptor coding region splice variants (hCB₁) affects the function of hCB₁ receptor complexes

The human type 1 cannabinoid (hCB1) receptor is expressed at high levels in the central nervous system. mRNA variants of the coding region of this receptor, human cannabinoid hCB1a and hCB1b receptors, have been identified, their biological function remains unclear. The present study demonstrated that the three human cannabinoid hCB1 coding region variants are expressed in the human and monkey (Macaca fascicularis) brain. Western blot analyses of homogenates from different regions of the monkey brain demonstrated that proteins with the expected molecular weights of the cannabinoid CB1, CB1a and CB1b receptors were co-expressed throughout the brain. Given the co-localization of these receptors, we hypothesized that physical interactions between the three splice variants may affect cannabinoid pharmacology. The human cannabinoid hCB1, hCB1a, and hCB1b receptors formed homodimers and heterodimers, as determined by BRET in transiently transfected HEK 293A cells. We found that the co-expression of the human cannabinoid hCB1 and each of the splice variants increased cell surface expression of the human cannabinoid hCB1 receptor and increased Gi/o-dependent ERK phosphorylation in response to cannabinoid agonists. Therefore, the human cannabinoid hCB1 coding region splice variants play an important physiological role in the activity of the endocannabinoid system.

Dissociation of the pharmacological effects of THC by mTOR blockade

The potential therapeutic benefits of cannabinoid compounds have raised interest in understanding the molecular mechanisms that underlie cannabinoid-mediated effects. We previously showed that the acute amnesic-like effects of delta9-tetrahydrocannabinol (THC) were prevented by the subchronic inhibition of the mammalian target of rapamycin (mTOR) pathway. In the present study, we assess the relevance of the mTOR pathway in other acute and chronic pharmacological effects of THC. The rapamycin derivative temsirolimus, an inhibitor of the mTOR pathway approved by the Food and Drug Administration, prevents both the anxiogenic- and the amnesic-like effects produced by acute THC. In contrast, THC-induced anxiolysis, hypothermia, hypolocomotion, and antinociception are not sensitive to the mTOR inhibition. In addition, a clear tolerance to THC-induced anxiolysis, hypothermia, hypolocomotion, and antinociception was observed after chronic treatment, but not to its anxiogenic- and amnesic-like effects. Temsirolimus pre-treatment prevented the amnesic-like effects of chronic THC without affecting the downregulation of CB1 receptors (CB1R) induced by this chronic treatment. Instead, temsirolimus blockade after chronic THC cessation did not prevent the residual cognitive deficit produced by chronic THC. Using conditional knockout mice lacking CB1R in GABAergic or glutamatergic neurons, we found that GABAergic CB1Rs are mainly downregulated under chronic THC treatment conditions, and CB1-GABA-KO mice did not develop cognitive deficits after chronic THC exposure. Therefore, mTOR inhibition by temsirolimus allows the segregation of the potentially beneficial effects of cannabinoid agonists, such as the anxiolytic and antinociceptive effects, from the negative effects, such as anxiogenic- and amnesic-like responses. Altogether, these results provide new insights for targeting the endocannabinoid system in order to prevent possible side effects.

Cannabinoid CB1 receptor is expressed in chromophobe renal cell carcinoma and renal oncocytoma

OBJECTIVE

To analyze the mRNA and protein expression of cannabinoid receptors CB1 and CB2 in chromophobe renal cell carcinoma (ChRCC) and renal oncocytoma (RO).

DESIGN AND METHODS

Fresh and formalin-fixed tissue samples of ChRCC and RO were analyzed by using real-time quantitative RT-PCR and immunohistochemical techniques (n=40).

RESULTS

Quantitative RT-PCR analysis showed that CB1 mRNA was underexpressed by 12-fold in ChRCC and had a variable expression in RO. CB1 protein showed intense positive immunostaining in both neoplasms. Both CB2 mRNA and protein were not expressed in tumor and non tumor renal tissue.

CONCLUSION

This distinct immunoprofile may eventually be used as an additional tool with practical interest in the differential diagnosis of renal tumors.

Endocannabinoids and endovanilloids: a possible balance in the regulation of the testicular GnRH signalling

Reproductive functions are regulated both at central (brain) and gonadal levels. In this respect, the endocannabinoid system (eCS) has a very influential role. Interestingly, the characterization of eCS has taken many advantages from the usage of animal models different from mammals. Therefore, this review is oriented to summarize the main pieces of evidence regarding eCS coming from the anuran amphibian Rana esculenta, with particular interest to the morphofunctional relationship between eCS and gonadotropin releasing hormone (GnRH). Furthermore, a novel role for endovanilloids in the regulation of a testicular GnRH system will be also discussed.

Endocannabinoids and obesity

A safe and effective antiobesity drug is needed to combat the global obesity epidemic. The discovery of cannabinoids from medicinal herbs has revealed the endocannabinoid system (ECS) in animals and humans, which regulates various physiological activities such as feeding, thermogenesis, and body weight (BW). Although cannabinoid receptors 1 (CB1) antagonists have shown antiobesity efficacies in animal models and in the clinic, they failed to establish as a treatment due to their psychological side effects. Recent studies indicate that CB1 in various peripheral tissues may mediate some of the therapeutic effects of CB1 antagonists, such as improved lipid and glucose homeostasis. It rationalizes the development of compounds with limited brain penetration, for minimizing the side effects while retaining the therapeutic efficacies. A survey of the literature has revealed some controversies about how the ECS affects obesity. This review summarizes the research progresses and discusses some future perspectives.

The role of CB1 in immune modulation by cannabinoids

There is clear evidence that CB(2), historically referred to as the peripheral cannabinoid receptor, mediates many of the immune modulatory effects of cannabinoids. However, cannabinoid receptors cannot be classified simply as central or peripheral since CB(2) has been shown to play a role in the central nervous system (CNS) and CB(1) mediates many immune system effects. Although Cnr1 mRNA and CB(1) protein expression is lower than Cnr2 mRNA or CB(2) protein expression in cells of the immune system, several studies have shown direct modulation of immune function via CB(1) by endogenous and exogenous cannabinoids in T cells, innate cells, and to a lesser extent, B cells. In addition, indirect, but CB(1)-dependent, mechanisms of immune modulation exist. In fact, the mechanism by which cannabinoids attenuate neuroinflammation via CB(1) is likely a combination of immune suppression and neuroprotection. Although many studies demonstrate that agonists for CB(1) are immune suppressive and anti-inflammatory, CB(1) antagonists also exhibit anti-inflammatory properties. Overall, the data demonstrate that many of the immune modulatory effects of cannabinoids are mediated via CB(1).

Differential signalling in human cannabinoid CB1 receptors and their splice variants in autaptic hippocampal neurones

BACKGROUND AND PURPOSE

Cannabinoids such as Δ(9) - tetrahydrocannabinol, the major psychoactive component of marijuana and hashish, primarily act via cannabinoid CB(1) and CB(2) receptors to produce characteristic behavioural effects in humans. Due to the tractability of rodent models for electrophysiological and behavioural studies, most of the studies of cannabinoid receptor action have used rodent cannabinoid receptors. While CB(1) receptors are relatively well-conserved among mammals, human CB(1) (hCB(1) ) differs from rCB(1) and mCB(1) receptors at 13 residues, which may result in differential signalling. In addition, two hCB(1) splice variants (hCB(1a) and hCB(1b) ) have been reported, diverging in their amino-termini relative to hCB(1) receptors. In this study, we have examined hCB(1) signalling in neurones.

EXPERIMENTAL APPROACH

hCB(1) , hCB(1a) hCB(1b) or rCB(1) receptors were expressed in autaptic cultured hippocampal neurones from CB(1) (-/-) mice. Such cells express a complete endogenous cannabinoid signalling system. Electrophysiological techniques were used to assess CB(1) receptor-mediated signalling. KEY RESULTS Expressed in autaptic hippocampal neurones cultured from CB(1) (-/-) mice, hCB(1) , hCB(1a) and hCB(1b) signal differentially from one another and from rodent CB(1) receptors. Specifically, hCB(1) receptors inhibit synaptic transmission less effectively than rCB(1) receptors.

CONCLUSIONS AND IMPLICATIONS

Our results suggest that cannabinoid receptor signalling in humans is quantitatively very different from that in rodents. As the problems of marijuana and hashish abuse occur in humans, our results highlight the importance of studying hCB(1) receptors. They also suggest further study of the distribution and function of hCB(1) receptor splice variants, given their differential signalling and potential impact on human health.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids in Biology and Medicine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7.

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.

Contributions of endocannabinoid signaling to psychiatric disorders in humans: genetic and biochemical evidence

The endocannabinoid signaling system is a widespread, neuromodulatory system in brain and is also widely utilized in the periphery to modulate metabolic functions and the immune system. Preclinical data demonstrate that endocannabinoid signaling is an important stress buffer and modulates emotional and cognitive functions. These data suggest the hypothesis that endocannabinoid signaling could be dysfunctional in a number of mental disorders. Genetic polymorphisms in the human genes for two important proteins of the endocannabinoid signaling system, the CB1 cannabinoid receptor (CB1R) and fatty acid amide hydrolase (FAAH), have been explored in the context of normal and pathological conditions. In the case of the gene for FAAH, the mechanistic relationships among the common genetic polymorphism, the expression of the FAAH protein, and its likely impact on endocannabinoid signaling are understood. However, multiple polymorphisms in the gene for the CB1R occur and are associated with human phenotypic differences without an understanding of the functional relationships among the gene, mRNA, protein, and protein function. The endocannabinoid ligands are found in the circulation, and several studies have identified changes in their concentrations under various conditions. These data are reviewed for the purpose of generating hypotheses and to encourage further studies in this very interesting and important area.

The cannabinoid type-1 receptor carboxyl-terminus, more than just a tail

The cannabinoid type-1 (CB(1)) receptor is a G protein-coupled receptor that binds the main active ingredient of marijuana, Δ(9)-tetrahydrocannabinol, and has been implicated in several disease states, including drug addiction, anxiety, depression, obesity, and chronic pain. In the two decades since the discovery of CB(1), studies at the molecular level have centered on the transmembrane core. This interest has now expanded as we discover that other regions of CB(1), including the CB(1) carboxyl-terminus, have critical structures that are important for CB(1) activity and regulation. Following the recent description of the three dimensional structure of the full-length CB(1) carboxyl-terminal tail [Biopolymers (2009) vol. 91, pp. 565-573], several residues and structural motifs including two α-helices (termed H8 and H9) have been postulated to interact with common G protein-coupled receptor accessory proteins, such as G-proteins and β-arrestins. This discourse will focus on the CB(1) carboxyl-terminus; our current understanding of the structural features of this region, evidence for its interaction with proteins, and the impact of structure on the binding and regulatory function of CB(1) accessory proteins. The involvement of the carboxyl-terminus in the receptor life cycle including activation, desensitization, and internalization will be highlighted.

Evaluation of the role of striatal cannabinoid CB1 receptors on movement activity of parkinsonian rats induced by reserpine

It has been observed cannabinoid CB1 receptor signalling and the levels of endocannabinoid ligands significantly increased in the basal ganglia and cerebrospinal fluids of Parkinson's disease (PD) patients. These evidences suggest that the blocking of cannabinoid CB1 receptors might be beneficial to improve movement disorders as a sign of PD. In this study, a dose-response study of the effects of intrastriatal injection of a cannabinoid CB1 receptor antagonist, AM251 and agonist, ACPA, on movement activity was performed by measuring the catalepsy of reserpinized and non-PD (normal) rats with bar test. Also the effect of co-administration the most effective dose of AM251 and several doses of ACPA were assessed. AM251 decreases the reserpine induced catalepsy in dose dependent manner and ACPA causes catalepsy in normal rats in dose dependant manner as well. AM251 significantly reverse the cataleptic effect in all three groups (1, 10, 100 ng/rat) that received ACPA. These results support this theory that cannabinoid CB1 receptor antagonists might be useful to alleviate movement disorder in PD. Also continuance of ACPA induced catalepsy in rats after AM251 injection can indicate that other neurotransmitters or receptors interfere in ACPA induced catalepsy. Based on the present finding there is an incomplete overlapping between cannabinoid CB1 receptor agonist and antagonist effects.

Role of the cannabinoid system in pain control and therapeutic implications for the management of acute and chronic pain episodes

Cannabis extracts and synthetic cannabinoids are still widely considered illegal substances. Preclinical and clinical studies have suggested that they may result useful to treat diverse diseases, including those related with acute or chronic pain. The discovery of cannabinoid receptors, their endogenous ligands, and the machinery for the synthesis, transport, and degradation of these retrograde messengers, has equipped us with neurochemical tools for novel drug design. Agonist-activated cannabinoid receptors, modulate nociceptive thresholds, inhibit release of pro-inflammatory molecules, and display synergistic effects with other systems that influence analgesia, especially the endogenous opioid system. Cannabinoid receptor agonists have shown therapeutic value against inflammatory and neuropathic pains, conditions that are often refractory to therapy. Although the psychoactive effects of these substances have limited clinical progress to study cannabinoid actions in pain mechanisms, preclinical research is progressing rapidly. For example, CB(1)mediated suppression of mast cell activation responses, CB(2)-mediated indirect stimulation of opioid receptors located in primary afferent pathways, and the discovery of inhibitors for either the transporters or the enzymes degrading endocannabinoids, are recent findings that suggest new therapeutic approaches to avoid central nervous system side effects. In this review, we will examine promising indications of cannabinoid receptor agonists to alleviate acute and chronic pain episodes. Recently, Cannabis sativa extracts, containing known doses of tetrahydrocannabinol and cannabidiol, have granted approval in Canada for the relief of neuropathic pain in multiple sclerosis. Further double-blind placebo-controlled clinical trials are needed to evaluate the potential therapeutic effectiveness of various cannabinoid agonists-based medications for controlling different types of pain.