Are CB2 Receptors a New Target for Schizophrenia Treatment?
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ABSTRACT:
SUBMITTER: Cortez IL
PROVIDER: S-EPMC7673393 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Cannabinoids suppress behavioural responses to noxious stimulation and suppress nociceptive transmission through activation of CB1 and CB2 receptor subtypes. CB1 receptors are expressed at high levels in the central nervous system (CNS), whereas CB2 receptors are found predominantly, but not exclusively, outside the CNS. CB2 receptors are also upregulated in the CNS and dorsal root ganglia by pathological pain states. Here, we review behavioural, neurochemical and electrophysiological data, which identify cannabinoid CB2 receptors as a therapeutic target for treating pathological pain states with limited centrally, mediated side effects. The development of CB2-selective agonists (with minimal affinity for CB1) as well as mutant mice lacking CB2 receptors has provided pharmacological and genetic tools required to evaluate the effectiveness of CB2 agonists in suppressing persistent pain states. This review will examine the efficacy of cannabinoid CB2-selective agonists in suppressing acute, inflammatory and neuropathic nociception following systemic and local routes of administration. Data derived from behavioural, neurochemical and neurophysiological approaches are discussed to better understand the relationship between antinociceptive effects induced by CB2-selective agonists in behavioural studies and neural mechanisms of pain suppression. Finally, the therapeutic potential and possible limitations of CB2-based pharmacotherapies for pathological pain states induced by tissue and nerve injury are discussed.
| S-EPMC2219541 | biostudies-other
Project description:Cannabinoid type-1 (CB1) and type-2 (CB2) receptors belong to the family of G protein-coupled receptors and mediate biological effects of phyto-derived and endogenous cannabinoids. Whereas functions of CB1 receptor have been extensively studied, the CB2 receptor has emerged over the last few years as a critical player in regulation of inflammation, pain, atherosclerosis and osteoporosis. Therefore, although still at a preclinical stage, the development of selective CB2 molecules has gained of interest as new targets in drug discovery. Recent data have unravelled a key role of CB2 receptors during chronic and acute liver injury, including fibrogenesis associated to chronic liver diseases, ischaemia-reperfusion-induced liver injury, and hepatic encephalopathy associated to acute liver failure. This review summarizes the latest advances on the recently identified role of CB2 receptors in the pathophysiology of liver diseases.
| S-EPMC2219531 | biostudies-other
Project description:The endocannabinoid system (ECS) is ubiquitous in most human tissues, and involved in the regulation of mental health. Consequently, its dysregulation is associated with neuropsychiatric and neurodegenerative disorders. Together, the ECS and the expanded endocannabinoidome (eCBome) are composed of genes coding for CB1 and CB2 cannabinoid receptors (CB1R, CB2R), endocannabinoids (eCBs), and the metabolic enzyme machinery for their synthesis and catabolism. The activation of CB1R is associated with adverse effects on the central nervous system (CNS), which has limited the therapeutic use of drugs that bind this receptor. The discovery of the functional neuronal CB2R raised new possibilities for the potential and safe targeting of the ECS for the treatment of CNS disorders. Previous studies were not able to detect CB2R mRNA transcripts in brain tissue and suggested that CB2Rs were absent in the brain and were considered peripheral receptors. Studies done on the role of CB2Rs as a potential therapeutic target for treating different disorders revealed the important putative role of CB2Rs in certain CNS disorders, which requires further clinical validation. This review addresses recent advances on the role of CB2Rs in neuropsychiatric and neurodegenerative disorders, including, but not limited to, anxiety, depression, schizophrenia, Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD) and addiction.
| S-EPMC8778243 | biostudies-literature
Project description:Cannabinoids have been always identified as harmful drugs because of their negative effects on male and female reproduction. The discovery of the 'endocannabinoid system (ECS)', composed of bioactive lipids (endocannabinoids), their receptors and their metabolic enzymes, and the generation of mouse models missing cannabinoid receptors or other elements of the ECS, has enabled a wealth of information on the significance of endocannabinoid signalling in multiple reproductive events: Sertoli cell survival, spermatogenesis, placentation, fertilization, preimplantation embryo development, implantation and postimplantation embryonic growth. These studies have also opened new perspectives in clinical applications, pointing to the ECS as a new target for correcting infertility and for improving reproductive health in humans. This review will focus on the involvement of type-2 cannabinoid (CB2) receptors in reproductive biology, covering both the male and female sides. It will also discuss the potential relevance of the immunological activity of CB2 at the maternal/foetal interface, as well as the distinctiveness of CB2 versus type-1 cannabinoid (CB1) receptors that might be exploited for a receptor subtype-specific regulation of fertility. In this context, the different signalling pathways triggered by CB1 and CB2 (especially those controlling the intracellular tone of nitric oxide), the different activation of CB1 and CB2 by endogenous agonists (like anandamide and 2-arachidonoylglycerol) and the different localization of CB1 and CB2 within membrane subdomains, termed 'lipid rafts', will be discussed. It is hoped that CB2-dependent endocannabinoid signalling might become a useful target for correcting infertility, in both men and women.
| S-EPMC2219526 | biostudies-other
Project description:Background and purposeHeteromerization of GPCRs is key to the integration of extracellular signals and the subsequent cell response via several mechanisms including heteromer-selective ligand binding, trafficking and/or downstream signalling. As the lysophosphatidylinositol GPCR 55 (GPR55) has been shown to affect the function of the cannabinoid receptor subtype 2 (CB2 receptor) in human neutrophils, we investigated the possible heteromerization of CB2 receptors with GPR55.Experimental approachThe direct interaction of human GPR55 and CB2 receptors heterologously expressed in HEK293 cells was assessed by co-immunoprecipitation and bioluminescence resonance energy transfer assays. The effect of cross-talk on signalling was investigated at downstream levels by label-free real-time methods (Epic dynamic mass redistribution and CellKey impedance assays), ERK1/2-MAPK activation and gene reporter assays.Key resultsGPR55 and CB2 receptors co-localized on the surface of HEK293 cells, co-precipitated in membrane extracts and formed heteromers in living HEK293 cells. Whereas heteromerization led to a reduction in GPR55-mediated activation of transcription factors (nuclear factor of activated T-cells, NF-?B and cAMP response element), ERK1/2-MAPK activation was potentiated in the presence of CB2 receptors. CB2 receptor-mediated signalling was also affected by co-expression with GPR55. Label-free assays confirmed cross-talk between the two receptors.Conclusions and implicationsHeteromers, unique signalling units, form in HEK293 cells expressing GPR55 and CB2 receptors. The signalling by agonists of either receptor was governed (i) by the presence or absence of the partner receptors (with the consequent formation of heteromers) and (ii) by the activation state of the partner receptor.
| S-EPMC4294047 | biostudies-literature
Project description:The therapeutic and psychoactive properties of cannabinoids have long been recognized. The type 2 receptor for cannabinoids (CB2) has emerged as an important therapeutic target in several pathologies, as it mediates beneficial effects of cannabinoids while having little if any psychotropic activity. Difficulties associated with the development of CB2-based therapeutic agents have been related to its intricate pharmacology, including the species specificity and functional selectivity of the CB2-initiated responses. We postulated that a plasmalemmal or subcellular location of the receptor may contribute to the differential signaling pathways initiated by its activation. To differentiate between these two, we used extracellular and intracellular administration of CB2 ligands and concurrent calcium imaging in CB2-expressing U2OS cells. We found that extracellular administration of anandamide was ineffective, whereas 2-arachidonoyl glycerol (2-AG) and WIN55,212-2 triggered delayed, CB2-dependent Ca(2+) responses that were Gq protein-mediated. When microinjected, all agonists elicited fast, transient, and dose-dependent elevations in intracellular Ca(2+) concentration upon activation of Gq-coupled CB2 receptors. The CB2 dependency was confirmed by the sensitivity to AM630, a selective CB2 antagonist, and by the unresponsiveness of untransfected U2OS cells to 2-AG, anandamide, or WIN55,212-2. Moreover, we provide functional and morphological evidence that CB2 receptors are localized at the endolysosomes, while their activation releases Ca(2+) from inositol 1,4,5-trisphosphate-sensitive- and acidic-like Ca(2+) stores. Our results support the functionality of intracellular CB2 receptors and their ability to couple to Gq and elicit Ca(2+) signaling. These findings add further complexity to CB2 receptor pharmacology and argue for careful consideration of receptor localization in the development of CB2-based therapeutic agents.
| S-EPMC4144709 | biostudies-literature
Project description:Amongst the various demyelinating diseases that affect the central nervous system, those induced by an inflammatory response stand out because of their epidemiological relevance. The best known inflammatory-induced demyelinating disease is multiple sclerosis, but the immune response is a common pathogenic mechanism in many other less common pathologies (e.g., acute disseminated encephalomyelitis and acute necrotizing haemorrhagic encephalomyelitis). In all such cases, modulation of the immune response seems to be a logical therapeutic approach. Cannabinoids are well known immunomodulatory molecules that act through CB1 and CB2 receptors. While activation of CB1 receptors has a psychotropic effect, activation of CB2 receptors alone does not. Therefore, to bypass the ethical problems that could result from the treatment of inflammation with psychotropic molecules, considerable effort is being made to study the potential therapeutic value of activating CB2 receptors. In this review we examine the current knowledge and understanding of the utility of cannabinoids as therapeutic molecules for inflammatory-mediated demyelinating pathologies. Moreover, we discuss how CB2 receptor activation is related to the modulation of immunopathogenic states.
| S-EPMC2219542 | biostudies-other
Project description:There are two well characterized cannabinoid receptors (CBRs), CB1-Rs and CB2-Rs, with other candidates, such as GPR55, PPARs and vanilloid TRPV1 (VR1) receptors, which are either activated by cannabinoids and/or endocannabinoids (eCBs). The neuronal and functional expression of CB2-Rs in the brain has been much less well characterized in comparison with the expression of the ubiquitous CB1-Rs. CB2-Rs were previously thought to be predominantly expressed in immune cells in the periphery and were traditionally referred to as peripheral CB2-Rs. We and others have now demonstrated the expression of CB2-Rs in neuronal, glial and endothelial cells in the brain, and this warrants a re-evaluation of the CNS effects of CB2-Rs. In the present review we summarize our current understanding of CNR2 genomic structure, its polymorphic nature, subtype specificity, from mice to human subjects, and its variants that confer vulnerabilities to neuropsychiatric disorders beyond neuro-immuno-cannabinoid activity.
| S-EPMC3388033 | biostudies-literature
Project description:BACKGROUND:Because of their low levels of expression and the inadequacy of current research tools, CB2 cannabinoid receptors (CB2R) have been difficult to study, particularly in the brain. This receptor is especially relevant in the context of neuroinflammation, so novel tools are needed to unveil its pathophysiological role(s). METHODS:We have generated a transgenic mouse model in which the expression of enhanced green fluorescent protein (EGFP) is under the control of the cnr2 gene promoter through the insertion of an Internal Ribosomal Entry Site followed by the EGFP coding region immediately 3' of the cnr2 gene and crossed these mice with mice expressing five familial Alzheimer's disease (AD) mutations (5xFAD). RESULTS:Expression of EGFP in control mice was below the level of detection in all regions of the central nervous system (CNS) that we examined. CB2R-dependent-EGFP expression was detected in the CNS of 3-month-old AD mice in areas of intense inflammation and amyloid deposition; expression was coincident with the appearance of plaques in the cortex, hippocampus, brain stem, and thalamus. The expression of EGFP increased as a function of plaque formation and subsequent microgliosis and was restricted to microglial cells located in close proximity to neuritic plaques. AD mice with CB2R deletion exhibited decreased neuritic plaques with no changes in IL1? expression. CONCLUSIONS:Using a novel reporter mouse line, we found no evidence for CB2R expression in the healthy CNS but clear up-regulation in the context of amyloid-triggered neuroinflammation. Data from CB2R null mice indicate that they play a complex role in the response to plaque formation.
| S-EPMC5968596 | biostudies-literature
Project description:Recently, A-836339 [2,2,3,3-tetramethylcyclopropanecarboxylic acid [3-(2-methoxyethyl)-4,5-dimethyl-3H-thiazol-(2Z)-ylidene]amide] (1) was reported to be a selective CB2 agonist with high binding affinity. Here we describe the radiosynthesis of [11C]A-836339 ([11C]1) via its desmethyl precursor as a candidate radioligand for imaging CB2 receptors with positron-emission tomography (PET). Whole body and the regional brain distribution of [11C]1 in control CD1 mice demonstrated that this radioligand exhibits specific uptake in the CB2-rich spleen and little specific in vivo binding in the control mouse brain. However, [11C]1 shows specific cerebral uptake in the lipopolysaccharide (LPS)-induced mouse model of neuroinflammation and in the brain areas with Abeta amyloid plaque deposition in a mouse model of Alzheimer's disease (APPswe/PS1dE9 mice). These data establish a proof of principle that CB2 receptors binding in the neuroinflammation and related disorders can be measured in vivo.
| S-EPMC2903661 | biostudies-literature