Lipopolysaccharide and cyclic AMP regulation of CB(2) cannabinoid receptor levels in rat brain and mouse RAW 264.7 macrophages

Alcohol activates cannabinoid receptor 1 and 2 in a model of pathogen induced pulmonary inflammation

Alcohol use disorder (AUD) is defined as patterns of alcohol misuse and affects over 30 million people in the US. AUD is a systemic disease with the epidemiology of acute lung injury and excessive alcohol use established in the literature. However, the distinct mechanisms by which alcohol induces the risk of pulmonary inflammation are less clear. A compelling body of evidence shows that cannabinoid receptors (CB1R and CB2R) play a relevant role in AUD. For this study, we investigated the role of CBR signaling in pulmonary immune activation. Using a human macrophage cell line, we evaluated the expression of CBR1 and CBR2 after cells were exposed to EtOH, +/- cannabinoid agonists and antagonists by flow cytometry. We also evaluated the expression of cannabinoid receptors from the lungs of adolescent mice exposed to acute binge EtOH +/- cannabinoid agonists and antagonists at both resting state and after microbial challenge via western blot, rt-PCR, cytokine analysis, and histology. Our results suggest that EtOH exposure modulates the expression of CBR1 and CBR2. Second, EtOH may contribute to the release of DAMPs and other proinflammatory cytokines, Finally, microbial challenge induces pulmonary inflammation in acute binge EtOH-exposed mice, and this observed immune activation may be CBR-dependent. We have shown that adolescent binge drinking primes the lung to subsequent microbial infection in adulthood and this response can be mitigated with cannabinoid antagonists. These novel findings may provide a framework for developing potential novel therapeutics in AUD research.

Angiotensinergic effect of β-Caryophyllene on Lipopolysaccharide- induced systemic inflammation

Renin-Angiotensin System (RAS) is a peptidergic system, canonically known for its role in blood pressure regulation. Furthermore, a non-canonical RAS regulates pathophysiological phenomena, such as inflammation since it consists of two main axes: the pro-inflammatory renin/(pro)renin receptor ((P)RR) axis, and the anti-inflammatory angiotensin-converting enzyme 2 (ACE2)/Angiotensin-(1-7) (Ang-(1-7))/Mas Receptor (MasR) axis. Few phytochemicals have shown to exert angiotensinergic and anti-inflammatory effects through some of these axes; nevertheless, anti-inflammatory drugs, such as phytocannabinoids have not been studied regarding this subject. Among phytocannabinoids, β-Caryophyllene stands out as a dietary phytocannabinoid with antiphlogistic activity that possess a unique sesquiterpenoid structure. Although its cannabinergic effect has been studied, its angiotensinergic effect reminds underexplored. This study aims to explore the angiotensinergic effect of β-Caryophyllene on inflammation and stress at a systemic level. After intranasal Lipopolysaccharide (LPS) installation and oral treatment with β-Caryophyllene, the concentration and activity of key RAS elements in the serum, such as Renin, ACE2 and Ang-(1-7), along with the stress hormone corticosterone and pro/anti-inflammatory cytokines, were measured in mice serum. The results show that β-Caryophyllene treatment modified RAS levels by increasing Renin and Ang-(1-7), alongside the reduction of pro-inflammatory cytokines and corticosterone levels. These results indicate that β-Caryophyllene exhibits angiotensinergic activity in favor of anti-inflammation.

Neurotrophic Factors in Cannabis-induced Psychosis: An Update

BACKGROUND

Cannabis is the most widely used illicit substance. Numerous scientific evidence confirm the strong association between cannabis and psychosis. Exposure to cannabis can induce the development of psychosis and schizophrenia in vulnerable individuals. However, the neurobiological processes underlying this relationship are unknown. Neurotrophins are a class of proteins that serve as survival factors for central nervous system (CNS) neurons. In particular, Nerve Growth Factor (NGF) plays an important role in the survival and function of cholinergic neurons while Brain Derived Neurotrophic Factor (BDNF) is involved in synaptic plasticity and the maintenance of midbrain dopaminergic and cholinergic neurons. Glial Cell Derived Neurotrophic Factor (GDNF) promotes the survival of midbrain dopaminergic neurons and Neuregulin 1 (NrG- 1) contributes to glutamatergic signals regulating the N-methyl-D-aspartate (NMDA). They have a remarkable influence on the neurons involved in the Δ-9-THC (tethra-hydro-cannabinol) action, such as dopaminergic and glutamatergic neurons, and can play dual roles: first, in neuronal survival and death, and, second, in activity-dependent plasticity.

METHODS

In this brief update, reviewing in a narrative way the relevant literature, we will focus on the effects of cannabis on this class of proteins, which may be implicated, at least in part, in the mechanism of the psychostimulant-induced neurotoxicity and psychosis.

CONCLUSION

Since altered levels of neurotrophins may participate in the pathogenesis of psychotic disorders which are common in drug users, one possible hypothesis is that repeated cannabis exposure can cause psychosis by interfering with neurotrophins synthesis and utilization by CNS neurons.

GPR55 activation prevents amphetamine-induced conditioned place preference and decrease the amphetamine-stimulated inflammatory response in the ventral hippocampus in male rats

Inflammatory response in the Central Nervous System (CNS) induced by psychostimulants seems to be a crucial factor in the development and maintenance of drug addiction. The ventral hippocampus (vHp) is part of the reward system involved in substance addiction and expresses abundant G protein-coupled receptor 55 (GPR55). This receptor modulates the inflammatory response in vitro and in vivo, but there is no information regarding its anti-inflammatory effects and its impact on psychostimulant consumption. The aim of the present study was to investigate whether vHp GPR55 activation prevents both the inflammatory response induced by amphetamine (AMPH) in the vHp and the AMPH-induced conditioned place preference (A-CPP). Wistar adult male rats with a bilateral cannula into the vHp or intact males were subjected to A-CPP (5 mg/kg). Upon the completion of A-CPP, the vHp was dissected to evaluate IL-1β and IL-6 expression through RT-PCR, Western blot and immunofluorescence. Our results reveal that AMPH induces both A-CPP and an increase of IL-1β and IL-6 in the vHp. The GPR55 agonist lysophosphatidylinositol (LPI, 10 μM) infused into the vHp prevented A-CPP and the AMPH-induced IL-1β increase. CID 16020046 (CID, 10 μM), a selective GPR55 antagonist, abolished LPI effects. To evaluate the effect of the inflammatory response, lipopolysaccharide (LPS, 5 μg/μl) was infused bilaterally into the vHp during A-CPP acquisition. LPS strengthened A-CPP and increased IL-1β/IL-6 mRNA and protein levels in the vHp. LPS also increased CD68, Iba1, GFAP and vimentin expression. All LPS-induced effects were blocked by LPI. Our results suggest that GPR55 activation in the vHp prevents A-CPP while decreasing the local neuro-inflammatory response. These findings indicate that vHp GPR55 is a crucial factor in preventing the rewarding effects of AMPH due to its capacity to interfere with proinflammatory responses in the vHp.

WIN55212-2 Modulates Intracellular Calcium via CB1 Receptor-Dependent and Independent Mechanisms in Neuroblastoma Cells

The CB1 cannabinoid receptor (CB1R) and extracellular calcium (eCa2+)-stimulated Calcium Sensing receptor (CaSR) can exert cellular signaling by modulating levels of intracellular calcium ([Ca2+]i). We investigated the mechanisms involved in the ([Ca2+]i) increase in N18TG2 neuroblastoma cells, which endogenously express both receptors. Changes in [Ca2+]i were measured in cells exposed to 0.25 or 2.5 mM eCa2+ by a ratiometric method (Fura-2 fluorescence) and expressed as the difference between baseline and peak responses (ΔF340/380). The increased ([Ca2+]i) in cells exposed to 2.5 mM eCa2+ was blocked by the CaSR antagonist, NPS2143, this inhibition was abrogated upon stimulation with WIN55212-2. WIN55212-2 increased [Ca2+]i at 0.25 and 2.5 mM eCa2+ by 700% and 350%, respectively, but this increase was not replicated by CP55940 or methyl-anandamide. The store-operated calcium entry (SOCE) blocker, MRS1845, attenuated the WIN55212-2-stimulated increase in [Ca2+]i at both levels of eCa2+. Simultaneous perfusion with the CB1 antagonist, SR141716 or NPS2143 decreased the response to WIN55212-2 at 0.25 mM but not 2.5 mM eCa2+. Co-perfusion with the non-CB1/CB2 antagonist O-1918 attenuated the WIN55212-2-stimulated [Ca2+]i increase at both eCa2+ levels. These results are consistent with WIN55212-2-mediated intracellular Ca2+ mobilization from store-operated calcium channel-filled sources that could occur via either the CB1R or an O-1918-sensitive non-CB1R in coordination with the CaSR. Intracellular pathway crosstalk or signaling protein complexes may explain the observed effects.

Microglial Endocannabinoid Signalling in AD

Chronic inflammation in Alzheimer's disease (AD) has been recently identified as a major contributor to disease pathogenesis. Once activated, microglial cells, which are brain-resident immune cells, exert several key actions, including phagocytosis, chemotaxis, and the release of pro- or anti-inflammatory mediators, which could have opposite effects on brain homeostasis, depending on the stage of disease and the particular phenotype of microglial cells. The endocannabinoids (eCBs) are pleiotropic bioactive lipids increasingly recognized for their essential roles in regulating microglial activity both under normal and AD-driven pathological conditions. Here, we review the current literature regarding the involvement of this signalling system in modulating microglial phenotypes and activity in the context of homeostasis and AD-related neurodegeneration.

Identification of an Orally Bioavailable, Brain-Penetrant Compound with Selectivity for the Cannabinoid Type 2 Receptor

Modulation of the endocannabinoid system (ECS) is of great interest for its therapeutic relevance in several pathophysiological processes. The CB2 subtype is largely localized to immune effectors, including microglia within the central nervous system, where it promotes anti-inflammation. Recently, a rational drug design toward precise modulation of the CB2 active site revealed the novelty of Pyrrolo[2,1-c][1,4]benzodiazepines tricyclic chemotype with a high conformational similarity in comparison to the existing leads. These compounds are structurally unique, confirming their chemotype novelty. In our continuing search for new chemotypes as selective CB2 regulatory molecules, following SAR approaches, a total of 17 selected (S,E)-11-[2-(arylmethylene)hydrazono]-PBD analogs were synthesized and tested for their ability to bind to the CB1 and CB2 receptor orthosteric sites. A competitive [³H]CP-55,940 binding screen revealed five compounds that exhibited >60% displacement at 10 μM concentration. Further concentration-response analysis revealed two compounds, 4k and 4q, as potent and selective CB2 ligands with sub-micromolar activities (K_i = 146 nM and 137 nM, respectively). In order to support the potential efficacy and safety of the analogs, the oral and intravenous pharmacokinetic properties of compound 4k were sought. Compound 4k was orally bioavailable, reaching maximum brain concentrations of 602 ± 162 ng/g (p.o.) with an elimination half-life of 22.9 ± 3.73 h. Whether administered via the oral or intravenous route, the elimination half-lives ranged between 9.3 and 16.7 h in the liver and kidneys. These compounds represent novel chemotypes, which can be further optimized for improved affinity and selectivity toward the CB2 receptor.

Cannabinoid receptor type 2 agonist JWH-133 decreases cathepsin B secretion and neurotoxicity from HIV-infected macrophages

HIV-associated neurocognitive disorders (HAND) are prevalent despite combined antiretroviral therapy (cART), affecting 52% of people living with HIV. Our laboratory has demonstrated increased expression of cathepsin B (CATB) in postmortem brain tissue with HAND. Increased secretion of CATB from in vitro HIV-infected monocyte-derived macrophages (MDM) induces neurotoxicity. Activation of cannabinoid receptor type 2 (CB2R) inhibits HIV-1 replication in macrophages and the neurotoxicity induced by viral proteins. However, it is unknown if CB2R agonists affect CATB secretion and neurotoxicity in HIV-infected MDM. We hypothesized that HIV-infected MDM exposed to CB2R agonists decrease CATB secretion and neurotoxicity. Primary MDM were inoculated with HIV-1ADA and treated with selective CB2R agonists JWH-133 and HU-308. HIV-1 p24 and CATB levels were determined from supernatants using ELISA. MDM were pre-treated with a selective CB2R antagonist SR144528 before JWH-133 treatment to determine if CB2R activation is responsible for the effects. Neuronal apoptosis was assessed using a TUNEL assay. Results show that both agonists reduce HIV-1 replication and CATB secretion from MDM in a time and dose-dependent manner and that CB2R activation is responsible for these effects. Finally, JWH-133 decreased HIV/MDM-CATB induced neuronal apoptosis. Our results suggest that agonists of CB2R represent a potential therapeutic strategy against HIV/MDM-induced neurotoxicity.

Anti-Inflammatory Activity of a CB2 Selective Cannabinoid Receptor Agonist: Signaling and Cytokines Release in Blood Mononuclear Cells

The endocannabinoid system (ECS) exerts immunosuppressive effects, which are mostly mediated by cannabinoid receptor 2 (CBR2), whose expression on leukocytes is higher than CBR1, mainly localized in the brain. Targeted CBR2 activation could limit inflammation, avoiding CBR1-related psychoactive effects. Herein, we evaluated in vitro the biological activity of a novel, selective and high-affinity CBR2 agonist, called JT11, studying its potential CBR2-mediated anti-inflammatory effect. Trypan Blue and MTT assays were used to test the cytotoxic and anti-proliferative effect of JT11 in Jurkat cells. Its pro-apoptotic activity was investigated analyzing both cell cycle and poly PARP cleavage. Finally, we evaluated its impact on LPS-induced ERK1/2 and NF-kB-p65 activation, TNF-α, IL-1β, IL-6 and IL-8 release in peripheral blood mononuclear cells (PBMCs) from healthy donors. Selective CB2R antagonist SR144528 and CBR2 knockdown were used to further verify the selectivity of JT11. We confirmed selective CBR2 activation by JT11. JT11 regulated cell viability and proliferation through a CBR2-dependent mechanism in Jurkat cells, exhibiting a mild pro-apoptotic activity. Finally, it reduced LPS-induced ERK1/2 and NF-kB-p65 phosphorylation and pro-inflammatory cytokines release in human PBMCs, proving to possess in vitro anti-inflammatory properties. JT11 as CBR2 ligands could enhance ECS immunoregulatory activity and our results support the view that therapeutic strategies targeting CBR2 signaling could be promising for the treatment of chronic inflammatory diseases.

Cannabinoid receptor 2 is necessary to induce toll-like receptor-mediated microglial activation

The tight regulation of microglia activity is key for precise responses to potential threats, while uncontrolled and exacerbated microglial activity is neurotoxic. Microglial toll-like receptors (TLRs) are indispensable for sensing different types of assaults and triggering an innate immune response. Cannabinoid receptor 2 (CB2) signaling is a key pathway to control microglial homeostasis and activation, and its activation is connected to changes in microglial activity. We aimed to investigate how CB2 signaling impacts TLR-mediated microglial activation. Here, we demonstrate that deletion of CB2 causes a dampened transcriptional response to prototypic TLR ligands in microglia. Loss of CB2 results in distinct microglial gene expression profiles, morphology, and activation. We show that the CB2-mediated attenuation of TLR-induced microglial activation is mainly p38 MAPK-dependent. Taken together, we demonstrate that CB2 expression and signaling are necessary to fine-tune TLR-induced activation programs in microglia.

First In Class (S,E)-11-[2-(Arylmethylene)Hydrazono]-PBD Analogs As Selective CB2 Modulators Targeting Neurodegenerative Disorders

Newly designed pyrrolo[2,1-c][1,4]benzodiazepines tricyclic skeleton has shown potential clusters of cannabinoid receptors CB1/CB2 selective ligands. CB2 plays a critical role in microglial-derived neuroinflammation, where it modulates cell proliferation, migration, and differentiation into M1 or M2 phenotypes. Beginning with computer-based docking studies accounting the recently discovered X-ray crystal structure of CB2, we designed a series of PBD analogs as potential ligands of CB2 and tested their binding affinities. Interestingly, computational studies and theoretical binding affinities of several selected (S,E)-11-[2-(arylmethylene)hydrazono]-PBD analogs, have revealed the presence of potential selectivity in binding attraction towards CB1 and CB2. Reported here is the discovery of the first representatives of this series of selective binding to CB2. Preliminary data showed that this class of molecules display potential binding efficacy towards the cannabinoid receptors tested. Intriguingly, initial cannabinoid binding assay showed a selective binding affinity of 4g and 4h showed K _i of 0.49 and 4.7 μM towards CB2 receptors while no binding was observed to CB1. The designed leads have shown remarkable stability pattern at the physiological pH magnifying their therapeutic values. We hypothesize that the PBD tricyclic structure offers the molecule an appropriate three-dimensional conformation to fit snugly within the active site of CB2 receptors, giving them superiority over the reported CB2 agonists/inverse agonists. Our findings suggested that the attachment of heterocyclic ring through the condensation of diazepine hydrazone and S- or N-heterocyclic aldehydes enhances the selectivity of CB2 over CB1.

CB1 Cannabinoid Receptors Stimulate Gβγ-GRK2-Mediated FAK Phosphorylation at Tyrosine 925 to Regulate ERK Activation Involving Neuronal Focal Adhesions

CB₁ cannabinoid receptors (CB₁) are abundantly expressed in the nervous system where they regulate focal adhesion kinase (FAK) and the mitogen-activated protein kinases (MAPK) extracellular signal-regulated kinase 1 and 2 (ERK1/2). However, the role of CB₁-stimulated FAK 925 tyrosine phosphorylation (Tyr-P) in regulating ERK1/2 activation remains undefined. Here, immunoblotting analyses using antibodies against FAK phospho-Tyr 925 and ERK2 phospho-Tyr 204 demonstrated CB₁-stimulated FAK 925 Tyr-P and ERK2 204 Tyr-P (0–5 min) which was followed by a decline in Tyr-P (5–20 min). CB₁ stimulated FAK-Grb2 association and Ras-mediated ERK2 activation. The FAK inhibitors Y11 and PF 573228 abolished FAK 925 Tyr-P and partially inhibited ERK2 204 Tyr-P. FAK 925 Tyr-P and ERK2 204 Tyr-P were adhesion-dependent, required an intact actin cytoskeleton, and were mediated by integrins, Flk-1 vascular endothelial growth factor receptors, and epidermal growth factor receptors. FAK 925 Tyr-P and ERK2 204 Tyr-P were blocked by the Gβγ inhibitor gallein, a GRK2 inhibitor, and GRK2 siRNA silencing, suggesting Gβγ and GRK2 participate in FAK-mediated ERK2 activation. Together, these studies indicate FAK 925 Tyr-P occurs concurrently with CB₁-stimulated ERK2 activation and requires the actin cytoskeleton and G_i/oβγ-GRK2-mediated cross-talk between CB₁, integrins, and receptor tyrosine kinases (RTKs).

Activation of cannabinoid 2 receptor relieves colonic hypermotility in a rat model of irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a common disease with intestinal dysmotility, whose mechanism remains elusive. The endocannabinoid system is emerging as an important modulator of gastrointestinal (GI) motility in multiple diseases, but its involvement in IBS is unknown. We aimed to determine whether cannabinoid 2 (CB2) receptor modulates intestinal motility associated with stress-induced IBS.

METHODS

A rat IBS model was established by chronic water avoidance stress (WAS). Colonic pathological alterations were detected histologically and intestinal motility was assessed by intestinal transit time (ITT) and fecal water content (FWC). Visceral sensitivity was determined by visceromotor response (VMR) to colorectal distension (CRD). Real-time PCR, western blot, and immunostaining were performed to identify colonic CB2 receptor expression. Colonic muscle strip contractility was studied by isometric transducers and nitric oxide (NO) was detected by the Griess test. The effects of AM1241, a selective agonist of CB2 receptors, on colonic motility were examined.

KEY RESULTS

After 10 days of WAS exposure, ITT was decreased and FWC elevated while VMR magnitude in response to CRD was significantly enhanced. Colon CB2 protein and mRNA levels increased and density of CB2-positive macrophages in the mucosa and enteric neurons in the myenteric plexus was higher than in controls. Pharmacological enhancement of CB2 activity by AM1241 relieved colonic hypermotility in WAS rats in a concentration-dependent manner via inhibition of p38 phosphorylation and elevation of NO production.

CONCLUSION

CB2 receptor may exert an important inhibitory effect in stress-induced colonic hypermotility by modulating NO synthesis through p38 mitogen-activated protein kinase signaling. AM1241 could be used as a potential drug to treat disorders with colonic hypermotility.

Cannabinoid CB1 and CB2 Receptors, and Monoacylglycerol Lipase Gene Expression Alterations in the Basal Ganglia of Patients with Parkinson's Disease

Previous studies suggest that the endocannabinoid system plays an important role in the neuropathological basis of Parkinson's disease (PD). This study was designed to detect potential alterations in the cannabinoid receptors CB1 (CB1r) and CB2 (A isoform, CB2Ar), and in monoacylglycerol lipase (MAGL) gene expression in the substantia nigra (SN) and putamen (PUT) of patients with PD. Immunohistochemical studies were performed to identify precise CB2r cellular localization in the SN of control and PD patients. To ensure the validity and reliability of gene expression data, the RNA integrity number (RIN) was calculated. CB1r, CB2Ar, and MAGL gene expressions were evaluated by real-time polymerase chain reaction (real-time PCR) using Taqman assays. Immunohistochemical experiments with in situ proximity ligation assay (PLA) were used to detect the precise cellular localization of CB2r in neurons, astrocytes, and/or microglia. All RIN values from control and PD postmortem brain samples were > 6. CB1r gene expression was unchanged in the SN but significantly higher in the PUT of patients with PD. CB2Ar gene expression was significantly increased (4-fold) in the SN but decreased in the PUT, whereas MAGL gene expression was decreased in the SN and increased in the PUT. Immunohistochemical analyses revealed that CB2r co-localize with astrocytes but not with neurons or microglial cells in the SN. The results of the present study suggest that CB1r, CB2r, and MAGL are closely related to the neuropathological processes of PD. Therefore, the pharmacological modulation of these targets could represent a new potential therapeutic tool for the management of PD.

Discovery of a fluorinated 4-oxo-quinoline derivative as a potential positron emission tomography radiotracer for imaging cannabinoid receptor type 2

The cannabinoid receptor type 2 (CB2) is part of the endocannabinoid system and has gained growing attention in recent years because of its important role in neuroinflammatory/neurodegenerative diseases. Recently, we reported on a carbon-11 labeled 4-oxo-quinoline derivative, designated RS-016, as a promising radiotracer for imaging CB2 using PET. In this study, three novel fluorinated analogs of RS-016 were designed, synthesized, and pharmacologically evaluated. The results of our efforts led to the identification of N-(1-adamantyl)-1-(2-(2-fluoroethoxy)ethyl)-8-methoxy-4-oxo-1,4-dihydroquinoline-3-carboxamide (RS-126) as the most potent candidate for evaluation as a CB2 PET ligand. [(18) F]RS-126 was obtained in ≥ 99% radiochemical purity with an average specific radioactivity of 98 GBq/μmol at the end of the radiosynthesis. [(18) F]RS-126 showed a logD7.4 value of 1.99 and is stable in vitro in rat and human plasma over 120 min, whereas 55% intact parent compound was found in vivo in rat blood plasma at 10 min post injection. In vitro autoradiographic studies with CB2-positive rat spleen tissue revealed high and blockable binding which was confirmed in in vivo displacement experiments with rats by dynamic PET imaging. Ex vivo biodistribution studies confirmed accumulation of [(18) F]RS-126 in rat spleen with a specificity of 79% under blocking conditions. The moderate elevated CB2 levels in LPS-treated mice brain did not permit the detection of CB2 by [(18) F]RS-126 using PET imaging. In summary, [(18) F]RS-126 demonstrated high specificity toward CB2 receptor in vitro and in vivo and is a promising radioligand for imaging CB2 receptor expression. Cannabinoid receptor type 2 (CB2) is an interesting target for PET imaging. Specific binding of [(18) F]RS-126 in CB2-positive spleen tissue (white arrow head) was confirmed in in vivo displacement experiments with rats. Time activity curve of [(18) F]RS-126 in the spleen after the addition of GW405833 (CB2 specific ligand, green) demonstrates faster radiotracer elimination (blue) compared to the tracer only (red).

Interaction between Cannabinoid System and Toll-Like Receptors Controls Inflammation

Since the discovery of the endocannabinoid system consisting of cannabinoid receptors, endogenous ligands, and biosynthetic and metabolizing enzymes, interest has been renewed in investigating the promise of cannabinoids as therapeutic agents. Abundant evidence indicates that cannabinoids modulate immune responses. An inflammatory response is triggered when innate immune cells receive a danger signal provided by pathogen- or damage-associated molecular patterns engaging pattern-recognition receptors. Toll-like receptor family members are prominent pattern-recognition receptors expressed on innate immune cells. Cannabinoids suppress Toll-like receptor-mediated inflammatory responses. However, the relationship between the endocannabinoid system and innate immune system may not be one-sided. Innate immune cells express cannabinoid receptors and produce endogenous cannabinoids. Hence, innate immune cells may play a role in regulating endocannabinoid homeostasis, and, in turn, the endocannabinoid system modulates local inflammatory responses. Studies designed to probe the interaction between the innate immune system and the endocannabinoid system may identify new potential molecular targets in developing therapeutic strategies for chronic inflammatory diseases. This review discusses the endocannabinoid system and Toll-like receptor family and evaluates the interaction between them.

The cyclic AMP signaling pathway: Exploring targets for successful drug discovery (Review)

During development of disease, complex intracellular signaling pathways regulate an intricate series of events, including resistance to external toxins, the secretion of cytokines and the production of pathological phenomena. Adenosine 3′,5′-cyclic monophosphate (cAMP) is a nucleotide that acts as a key second messenger in numerous signal transduction pathways. cAMP regulates various cellular functions, including cell growth and differentiation, gene transcription and protein expression. This review aimed to provide an understanding of the effects of the cAMP signaling pathway and the associated factors on disease occurrence and development by examining the information from a new perspective. These novel insights aimed to promote the development of novel therapeutic approaches and aid in the development of new drugs.

Preclinical evaluation of SMM-189, a cannabinoid receptor 2-specific inverse agonist

Cannabinoid receptor 2 agonists and inverse agonists are emerging as new therapeutic options for a spectrum of autoimmune-related disease. Of particular interest, is the ability of CB2 ligands to regulate microglia function in neurodegenerative diseases and traumatic brain injury. We have previously reported the receptor affinity of 3',5'-dichloro-2,6-dihydroxy-biphenyl-4-yl)-phenyl-methanone (SMM-189) and the characterization of the beneficial effects of SMM-189 in the mouse model of mild traumatic brain injury. Herein, we report the further characterization of SMM-189 as a potent and selective CB2 inverse agonist, which acts as a noncompetitive inhibitor of CP 55,940. The ability of SMM-189 to regulate microglial activation, in terms of chemokine expression and cell morphology, has been determined. Finally, we have determined that SMM-189 possesses acceptable biopharmaceutical properties indicating that the triaryl class of CB2 inverse agonists are viable compounds for continued preclinical development for the treatment of neurodegenerative disorders and traumatic brain injury.

Cannabinoid CB2 Receptors in a Mouse Model of Aβ Amyloidosis: Immunohistochemical Analysis and Suitability as a PET Biomarker of Neuroinflammation

In Alzheimer's disease (AD), one of the early responses to Aβ amyloidosis is recruitment of microglia to areas of new plaque. Microglial receptors such as cannabinoid receptor 2 (CB2) might be a suitable target for development of PET radiotracers that could serve as imaging biomarkers of Aβ-induced neuroinflammation. Mouse models of amyloidosis (J20APPswe/ind and APPswe/PS1ΔE9) were used to investigate the cellular distribution of CB2 receptors. Specificity of CB2 antibody (H60) was confirmed using J20APPswe/ind mice lacking CB2 receptors. APPswe/PS1ΔE9 mice were used in small animal PET with a CB2-targeting radiotracer, [11C]A836339. These studies revealed increased binding of [11C]A836339 in amyloid-bearing mice. Specificity of the PET signal was confirmed in a blockade study with a specific CB2 antagonist, AM630. Confocal microscopy revealed that CB2-receptor immunoreactivity was associated with astroglial (GFAP) and, predominantly, microglial (CD68) markers. CB2 receptors were observed, in particular, in microglial processes forming engulfment synapses with Aβ plaques. In contrast to glial cells, neuron (NeuN)-derived CB2 signal was equal between amyloid-bearing and control mice. The pattern of neuronal CB2 staining in amyloid-bearing mice was similar to that in human cases of AD. The data collected in this study indicate that Aβ amyloidosis without concomitant tau pathology is sufficient to activate CB2 receptors that are suitable as an imaging biomarker of neuroinflammation. The main source of enhanced CB2 PET binding in amyloid-bearing mice is increased CB2 immunoreactivity in activated microglia. The presence of CB2 immunoreactivity in neurons does not likely contribute to the enhanced CB2 PET signal in amyloid-bearing mice due to a lack of significant neuronal loss in this model. However, significant loss of neurons as seen at late stages of AD might decrease the CB2 PET signal due to loss of neuronally-derived CB2. Thus this study in mouse models of AD indicates that a CB2-specific radiotracer can be used as a biomarker of neuroinflammation in the early preclinical stages of AD, when no significant neuronal loss has yet developed.

Cannabinoid receptor 2 protects against acute experimental sepsis in mice

The systemic inflammatory response syndrome can be self-limited or can progress to severe sepsis and septic shock. Despite significant advances in the understanding of the molecular and cellular mechanisms of septic shock, it is still one of the most frequent and serious problems confronting clinicians in the treatments. And the effects of cannabinoid receptor 2 (CB2R) on the sepsis still remain undefined. The present study was aimed to explore the role and mechanism of CB2R in acute sepsis model of mice. Here, we found that mice were more vulnerable for lipopolysaccharide- (LPS-) induced death and inflammation after CB2R deletion (CB2R^−/−). CB2R agonist, GW405833, could significantly extend the survival rate and decrease serum proinflammatory cytokines in LPS-treated mice. GW405833 dose-dependently inhibits proinflammatory cytokines release in splenocytes and peritoneal macrophages as well as splenocytes proliferation, and these effects were partly abolished in CB2R^−/− splenocytes but completely abolished in CB2R^−/− peritoneal macrophages. Further studies showed that GW405833 inhibits LPS-induced phosphorylation of ERK1/2 and STAT3 and blocks IκBα degradation and NF-κB p65 nuclear translocation in macrophages. All data together showed that CB2R provides a protection and is a potential therapeutic target for the sepsis.

Mutant huntingtin impairs immune cell migration in Huntington disease

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

Marine cyanobacterial fatty acid amides acting on cannabinoid receptors

Striking cAMP: certain fatty acid amides from marine cyanobacteria can mimic the endocannabinoids. Serinolamide B, a new analogue identified from a Guamanian sample, and malyngamide B, a representative member of a large class of cyanobacterial metabolites, can decrease forskolin-induced cAMP accumulation through the cannabinoid receptors.

Cannabinoid CB(2) receptors modulate ERK-1/2 kinase signalling and NO release in microglial cells stimulated with bacterial lipopolysaccharide

BACKGROUND AND PURPOSE

Cannabinoid (CB) receptor agonists have potential utility as anti-inflammatory drugs in chronic immune inflammatory diseases. In the present study, we characterized the signal transduction pathways affected by CB(2) receptors in quiescent and lipopolysaccharide (LPS)-stimulated murine microglia.

EXPERIMENTAL APPROACH

We examined the effects of the synthetic CB(2) receptor ligand, JWH-015, on phosphorylation of MAPKs and NO production.

KEY RESULTS

Stimulation of CB(2) receptors by JWH-015 activated JNK-1/2 and ERK-1/2 in quiescent murine microglial cells. Furthermore, CB(2) receptor activation increased p-ERK-1/2 at 15 min in LPS-stimulated microglia. Surprisingly, this was reduced after 30 min in the presence of both LPS and JWH-015. The NOS inhibitor L-NAME blocked the ability of JWH-015 to down-regulate the LPS-induced p-ERK increase, indicating that activation of CB(2) receptors reduced effects of LPS on ERK-1/2 phosphorylation through NO. JWH-015 increased LPS-induced NO release at 30 min, while at 4 h CB(2) receptor stimulation had an inhibitory effect. All the effects of JWH-015 were significantly blocked by the CB(2) receptor antagonist AM 630 and, as the inhibition of CB(2) receptor expression by siRNA abolished the effects of JWH-015, were shown to be mediated specifically by activation of CB(2) receptors.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrate that CB(2) receptor stimulation activated the MAPK pathway, but the presence of a second stimulus blocked MAPK signal transduction, inhibiting pro-inflammatory LPS-induced production of NO. Therefore, CB(2) receptor agonists may promote anti-inflammatory therapeutic responses in activated microglia.

Prevention of paclitaxel-induced neuropathy through activation of the central cannabinoid type 2 receptor system

BACKGROUND

Peripheral neuropathy is a major dose-limiting toxicity of chemotherapy, especially after multiple courses of paclitaxel. The development of paclitaxel-induced neuropathy is associated with the activation of microglia followed by the activation and proliferation of astrocytes, and the expression and release of proinflammatory cytokines in the spinal dorsal horn. Cannabinoid type 2 (CB(2)) receptors are expressed in the microglia in neurodegenerative disease models.

METHODS

To explore the potential of CB(2) agonists for preventing paclitaxel-induced neuropathy, we designed and synthesized a novel CB(2)-selective agonist, namely, MDA7. The effect of MDA7 in preventing paclitaxel-induced allodynia was assessed in rats and in CB(2)(+/+) and CB(2)(-/-) mice. We hypothesized that the CB(2) receptor functions in a negative-feedback loop and that early MDA7 administration can blunt the neuroinflammatory response to paclitaxel and prevent mechanical allodynia through interference with specific signaling pathways.

RESULTS

We found that MDA7 prevents paclitaxel-induced mechanical allodynia in rats and mice in a dose- and time-dependent manner without compromising paclitaxel's antineoplastic effect. MDA7's neuroprotective effect was absent in CB(2)(-/-) mice and was blocked by CB(2) antagonists, suggesting that MDA7's action directly involves CB(2) receptor activation. MDA7 treatment was found to interfere with early events in the paclitaxel-induced neuroinflammatory response as evidenced by relatively reduced toll-like receptor and CB(2) expression in the lumbar spinal cord, reduced levels of extracellular signal-regulated kinase 1/2 activity, reduced numbers of activated microglia and astrocytes, and reduced secretion of proinflammatory mediators in vivo and in in vitro models.

CONCLUSIONS

Our findings suggest an innovative therapeutic approach to prevent chemotherapy-induced neuropathy and may permit more aggressive use of active chemotherapeutic regimens with reduced long-term sequelae.

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

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

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

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

Prospects for cannabinoid therapies in basal ganglia disorders

Cannabinoids are promising medicines to slow down disease progression in neurodegenerative disorders including Parkinson's disease (PD) and Huntington's disease (HD), two of the most important disorders affecting the basal ganglia. Two pharmacological profiles have been proposed for cannabinoids being effective in these disorders. On the one hand, cannabinoids like Δ(9) -tetrahydrocannabinol or cannabidiol protect nigral or striatal neurons in experimental models of both disorders, in which oxidative injury is a prominent cytotoxic mechanism. This effect could be exerted, at least in part, through mechanisms independent of CB(1) and CB(2) receptors and involving the control of endogenous antioxidant defences. On the other hand, the activation of CB(2) receptors leads to a slower progression of neurodegeneration in both disorders. This effect would be exerted by limiting the toxicity of microglial cells for neurons and, in particular, by reducing the generation of proinflammatory factors. It is important to mention that CB(2) receptors have been identified in the healthy brain, mainly in glial elements and, to a lesser extent, in certain subpopulations of neurons, and that they are dramatically up-regulated in response to damaging stimuli, which supports the idea that the cannabinoid system behaves as an endogenous neuroprotective system. This CB(2) receptor up-regulation has been found in many neurodegenerative disorders including HD and PD, which supports the beneficial effects found for CB(2) receptor agonists in both disorders. In conclusion, the evidence reported so far supports that those cannabinoids having antioxidant properties and/or capability to activate CB(2) receptors may represent promising therapeutic agents in HD and PD, thus deserving a prompt clinical evaluation.

Reduced infarct size and accumulation of microglia in rats treated with WIN 55,212-2 after neonatal stroke

Cannabinoids have emerged as brain protective agents under neurodegenerative conditions. Many neuroprotective actions of cannabinoids depend on the activation of specific receptors, cannabinoid receptor type 1 (CB1R) and type 2 (CB2R). The aim of the present study was to determine whether the CB2R and CB1R agonist WIN 55,212-2 (WIN) protects neonatal brain against focal cerebral ischemia-reperfusion and whether anti-inflammatory mechanisms play a role in protection. Seven-day-old rats were subjected to 90-min middle cerebral artery occlusion (MCAO), and injured rats were identified by diffusion-weighted MRI during the occlusion. After reperfusion, rats were subcutaneously administered 1 mg/kg of WIN or vehicle twice daily until sacrifice. MCAO led to increased mRNA expression of CB2R (but not CB1R), chemokine receptors (CCR2 and CX3CR1), and cytokines (IL-1β and TNFα), as well as increased protein expression of chemokines MCP-1 and MIP-1α and microglial activation 24 h after MCAO. WIN administration significantly reduced microglial activation at this point and attenuated infarct volume and microglial accumulation and proliferation in the injured cortex 72 h after MCAO. Cumulatively, our results show that the cannabinoid agonist WIN protects against neonatal focal stroke in part due to inhibitory effects on microglia.

4-Oxo-1,4-dihydropyridines as selective CB2 cannabinoid receptor ligands: structural insights into the design of a novel inverse agonist series

Growing evidence shows that CB(2) receptor is an attractive therapeutic target. Starting from a series of 4-oxo-1,4-dihydroquinoline-3-carboxamide as selective CB(2) agonists, we describe here the medicinal chemistry approach leading to the development of CB(2) receptor inverse agonists with a 4-oxo-1,4-dihydropyridine scaffold. The compounds reported here show high affinity and potency at the CB(2) receptor while showing only modest affinity for the centrally expressed CB(1) cannabinoid receptor. Further, we found that the functionality of this series is controlled by its C-6 substituent because agonists bear a methyl or a tert-butyl group and inverse agonists, a phenyl or 4-chlorophenyl group, respectively. Finally, in silico studies suggest that the C-6 substituent could modulate the conformation of W6.48 known to be critical in GPCR activation.

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.

The cannabinoid CB2 receptor as a target for inflammation-dependent neurodegeneration

Endocannabinoids are released following brain injury and may protect against excitotoxic damage during the acute stage of injury. Brain injury also activates microglia in a secondary inflammatory phase of more widespread damage. Most drugs targeting the acute stage are not effective if administered more than 6 hours after injury. Therefore, drugs targeting microglia later in the neurodegenerative cascade are desirable. We have found that cannabinoid CB2 receptors are up-regulated during the activation of microglia following brain injury. Specifically, CB2-positive cells appear in the rat brain following both hypoxia-ischemia (HI) and middle cerebral artery occlusion (MCAO). This may regulate post-injury microglial activation and inflammatory functions. In this paper we review in vivo and in vitro studies of CB2 receptors in microglia, including our results on CB2 expression post-injury. Taken together, studies show that CB2 is up-regulated during a process in which microglia become primed to proliferate, and then become fully reactive. In addition, CB2 activation appears to prevent or decrease microglial activation. In a rodent model of Alzheimer's disease microglial activation was completely prevented by administration of a selective CB2 agonist. The presence of CB2 receptors in microglia in the human Alzheimer's diseased brain suggests that CB2 may provide a novel target for a range of neuropathologies. We conclude that the administration of CB2 agonists and antagonists may differentially alter microglia-dependent neuroinflammation. CB2 specific compounds have considerable therapeutic appeal over CB1 compounds, as the exclusive expression of CB2 on immune cells within the brain provides a highly specialised target, without the psychoactivity that plagues CB1 directed therapies.

Evidence that MDMA ('ecstasy') increases cannabinoid CB2 receptor expression in microglial cells: role in the neuroinflammatory response in rat brain

3,4-Methylenedioxymethamphetamine (MDMA, 'ecstasy') produces selective long-lasting serotonergic neurotoxicity in rats. The drug also produces acute hyperthermia which modulates the severity of the neurotoxic response. In addition, MDMA produces signs of neuroinflammation reflected as microglial activation and an increase in the release of interleukin-1beta, the latter of which appears to be a consequence of the hyperthermic response and to be implicated in the neurotoxicity induced by the drug. Over-expression of the cannabinoid CB2 receptor in microglia during non-immune and immune pathological conditions is thought to be aimed at controlling the production of neurotoxic factors such as proinflammatory cytokines. Our objective was to study the pattern of CB2 receptor expression following MDMA and to examine the effect of JWH-015 (a CB2 agonist) on the MDMA-induced neuroinflammatory response as well as 5-hydroxytryptamine (5-HT) neurotoxicity. Adult Dark Agouti rats were given MDMA (12.5 mg/kg, i.p.) and killed 3 h or 24 h later for the determination of CB2 receptor expression. JWH-015 was given 48 h, 24 h and 0.5 h before MDMA and 1 h and/or 6 h later and animals were killed for the determination of microglial activation (3 h and 24 h) and 5-HT neurotoxicity (7 days). MDMA increased CB2 receptor expression shortly after administration and these receptors were found in microglia. JWH-015 decreased MDMA-induced microglial activation and interleukin-1beta release and slightly decreased MDMA-induced 5-HT neurotoxicity. In conclusion, CB2 receptor activation reduces the neuroinflammatory response following MDMA and provides partial neuroprotection against the drug.

Cannabinoids as therapeutic agents for ablating neuroinflammatory disease

Cannabinoids have been reported to alter the activities of immune cells in vitro and in vivo. These compounds may serve as ideal agents for adjunct treatment of pathological processes that have a neuroinflammatory component. As highly lipophilic molecules, they readily access the brain. Furthermore, they have relatively low toxicity and can be engineered to selectively target cannabinoid receptors. To date, two cannabinoid receptors have been identified, characterized and designated CB(1) and CB(2). CB(1) appears to be constitutively expressed within the CNS while CB(2) apparently is induced during inflammation. The inducible nature of expression of CB(2) extends to microglia, the resident macrophages of the brain that play a critical role during early stages of inflammation in that compartment. Thus, the cannabinoid-cannabinoid receptor system may prove therapeutically manageable in ablating neuropathogenic disorders such as Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, HIV encephalitis, closed head injury, and granulomatous amebic encephalitis.

Cannabinoid CB2 receptors in the enteric nervous system modulate gastrointestinal contractility in lipopolysaccharide-treated rats

Enhanced intestinal transit due to lipopolysaccharide (LPS) is reversed by cannabinoid (CB)2 receptor agonists in vivo, but the site and mechanism of action are unknown. We have tested the hypothesis that CB2 receptors are expressed in the enteric nervous system and are activated in pathophysiological conditions. Tissues from either saline- or LPS-treated (2 h; 65 microg/kg ip) rats were processed for RT-PCR, Western blotting, and immunohistochemistry or were mounted in organ baths where electrical field stimulation was applied in the presence or absence of CB receptor agonists. Whereas the CB2 receptor agonist JWH133 did not affect the electrically evoked twitch response of the ileum under basal conditions, in the LPS-treated tissues JWH133 was able to reduce the enhanced contractile response in a concentration-dependent manner. Rat ileum expressed CB2 receptor mRNA and protein under physiological conditions, and this expression was not affected by LPS treatment. In the myenteric plexus, CB2 receptors were expressed on the majority of neurons, although not on those expressing nitric oxide synthase. LPS did not alter the distribution of CB2 receptor expression in the myenteric plexus. In vivo LPS treatment significantly increased Fos expression in both enteric glia and neurons. This enhanced expression was significantly attenuated by JWH133, whose action was reversed by the CB2 receptor antagonist AM630. Taking these facts together, we conclude that activation of CB2 receptors in the enteric nervous system of the gastrointestinal tract dampens endotoxin-induced enhanced intestinal contractility.

Cannabinoid CB2 receptors in human brain inflammation

The presence of functional cannabinoid CB2 receptors in the CNS has provoked considerable controversy over the past few years. Formerly considered as an exclusively peripheral receptor, it is now accepted that it is also present in limited amounts and distinct locations in the brain of several animal species, including humans. Furthermore, the inducible nature of these receptors under neuroinflammatory conditions, in contrast to CB1, makes them attractive targets for the development of novel therapeutic approaches. In fact, the undesired psychoactive effects caused by CB1 activation have largely limited the clinical use of cannabinoid-related compounds that act on these receptors. In this review some recent findings on the antiinflammatory properties of CB2 receptors are presented, as well as new perspectives that have been obtained based on studies of human postmortem brain samples. In addition, various working hypotheses are also proposed and discussed.