Cannabinoid CB2 receptor: a new target for controlling neural cell survival?

Endocannabinoids and Cancer

A large body of evidence shows that cannabinoids, in addition to their well-known palliative effects on some cancer-associated symptoms, can reduce tumour growth in animal models of cancer. They do so by modulating key cell signalling pathways involved in the control of cancer cell proliferation and survival. In addition, cannabinoids inhibit angiogenesis and cell proliferation in different types of tumours in laboratory animals. By contrast, little is known about the biological role of the endocannabinoid system in cancer physio-pathology, and several studies suggest that it may be over-activated in cancer. In this review, we discuss our current understanding of cannabinoids as antitumour agents, focusing on recent advances in the molecular mechanisms of action, including resistance mechanisms and opportunities for combination therapy approaches.

Ligand-based homology modelling of the human CB2 receptor SR144528 antagonist binding site: a computational approach to explore the 1,5-diaryl pyrazole scaffold

SR144528 docking mode into the LBHM of the human CB₂ receptor antagonist binding site.

Identification of CB₂ receptors in human nigral neurons that degenerate in Parkinson's disease

It is well-demonstrated that cannabinoid CB2 receptors located in glial cells are up-regulated in neurodegenerative disorders serving as a target to control glial influences to neurons. Recent evidence indicates that CB2 receptors may be also located in certain neuronal subpopulations and serve as a marker of neuronal losses. We investigated this possibility in the post-mortem substantia nigra of Parkinson's disease (PD) patients and controls. Immunostaining for the CB2 receptor was found in tyrosine hydroxylase-positive neurons in the substantia nigra, a fact confirmed with double-staining analyses. The signal was found in controls but also in PD patients, in which CB2 receptor labelling was significantly lower, in parallel to the losses of these neurons experienced in the disease. These data show for the first time that CB2 receptors are located in tyrosine hydroxylase-containing neurons in the substantia nigra at levels significantly lower in PD patients compared to controls.

Cannabinoid receptor 2 agonist attenuates pain related behavior in rats with chronic alcohol/high fat diet induced pancreatitis

Background

Chronic Pancreatitis (CP) is a complex and multifactorial syndrome. Many contributing factors result in development of dysfunctional pain in a significant number of patients. Drugs developed to treat a variety of pain states fall short of providing effective analgesia for patients with chronic pancreatitis, often providing minimal to partial pain relief over time with significant side effects. Recently, availability of selective pharmacological tools has enabled great advances in our knowledge of the role of the cannabinoid receptors in pathophysiology. In particular, cannabinoid receptor 2 (CB2) has emerged as an attractive target for management of chronic pain, as demonstrated in several studies with inflammatory and neuropathic preclinical pain models. In this study, the analgesic efficacy of a novel, highly selective CB2 receptor agonist, LY3038404 HCl, is investigated in a chronic pancreatitis pain model, induced with an alcohol/high fat (AHF) diet.

Results

Rats fed the AHF diet developed visceral pain-like behaviors detectable by week 3 and reached a maximum at week 5 that persists as long as the diet is maintained. Rats with AHF induced chronic pancreatitis were treated with LY3038404 HCl (10 mg/kg, orally, twice a day for 9 days). The treated animals demonstrated significantly alleviated pain related behaviors after 3 days of dosing, including increased paw withdrawal thresholds (PWT), prolonged abdominal withdrawal latencies (ABWL), and decreased nocifensive responses to noxious 44°C hotplate stimuli. Terminal histological analysis of pancreatic tissue sections from the AHF chronic pancreatitis animals demonstrated extensive injury, including a global pancreatic gland degeneration (cellular atrophy), vacuolization (fat deposition), and fibrosis. After the LY3038404 HCl treatment, pancreatic tissue was significantly protected from severe damage and fibrosis. LY3038404 HCl affected neither open field exploratory behaviors nor dark/light box preferences as measures of higher brain and motor functions.

Conclusion

LY3038404 HCl, a potent CB2 receptor agonist, possesses tissue protective and analgesic properties without effects on higher brain function. Thus, activation of CB2 receptors is suggested as a potential therapeutic target for visceral inflammation and pain management.

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.

Role of CB2 receptors and cGMP pathway on the cannabinoid-dependent antiepileptic effects in an in vivo model of partial epilepsy

This study aimed at providing an insight on the possible role of cannabinoid (CB) type 2 receptors (CB2R) and cGMP pathway in the antiepileptic activity of WIN 55,212-2, (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl) pyrrolo[1,2,3-de]-1,4-benzoxazin-6-Yl]-1-naphthalenylmethanone, a non-selective CB agonist, in the maximal dentate activation (MDA) model of partial epilepsy in adult male rats. We evaluated the activity of a CB2 antagonist/inverse agonist AM630, [6-iodo-2-methyl-1-[2-(4-morpholinyl)ethyl]-1H-indol-3-yl](4-methoxyphenyl)methanone or 6-iodopravadoline, alone or in co-administration with WIN 55,212-2. Also, in the MDA model it was investigated the co-treatment of WIN 55,212-2 and 1H-[1,2,4]Oxadiazole[4,3-a]quinoxalin-1-one (ODQ), a specific inhibitor of the nitric oxide (NO)-activated soluble guanylyl cyclase (sGC), the cGMP producing enzyme. The WIN 55,212-2-dependent (21mg/kg) antiepileptic effects were significantly increased by the co-administration with AM630 and by the co-treatment with ODQ (10mg/kg). Whereas, the administration of AM630 (2mg/kg), alone exerts no effects on hippocampal hyperexcitability. Our data show that pharmacological blockade of CB2 receptors and of sGC seems to cooperate with WIN in its antiepileptic action. These findings shed light on CB signaling mechanisms, hinting that the modulation of the effects of CB agonist in the hyperexcitability phenomena may be exerted both by targeting CB receptors and their possible downstream effectors, such as nitrergic-dependent cGMP pathway.

Early phytocannabinoid chemistry to endocannabinoids and beyond

Isolation and structure elucidation of most of the major cannabinoid constituents--including Δ(9)-tetrahydrocannabinol (Δ(9)-THC), which is the principal psychoactive molecule in Cannabis sativa--was achieved in the 1960s and 1970s. It was followed by the identification of two cannabinoid receptors in the 1980s and the early 1990s and by the identification of the endocannabinoids shortly thereafter. There have since been considerable advances in our understanding of the endocannabinoid system and its function in the brain, which reveal potential therapeutic targets for a wide range of brain disorders.

Detection of cannabinoid receptors CB1 and CB2 within basal ganglia output neurons in macaques: changes following experimental parkinsonism

Although type 1 cannabinoid receptors (CB₁Rs) are expressed abundantly throughout the brain, the presence of type 2 cannabinoid receptors (CB₂Rs) in neurons is still somewhat controversial. Taking advantage of newly designed CB₁R and CB₂R mRNA riboprobes, we demonstrate by PCR and in situ hybridization that transcripts for both cannabinoid receptors are present within labeled pallidothalamic-projecting neurons of control and MPTP-treated macaques, whereas the expression is markedly reduced in dyskinetic animals. Moreover, an in situ proximity ligation assay was used to qualitatively assess the presence of CB₁Rs and CB₂Rs, as well as CB₁R–CB₂R heteromers within basal ganglia output neurons in all animal groups (control, parkinsonian and dyskinetic macaques). A marked reduction in the number of CB₁Rs, CB₂Rs and CB₁R–CB₂R heteromers was found in dyskinetic animals, mimicking the observed reduction in CB₁R and CB₂R mRNA expression levels. The fact that chronic levodopa treatment disrupted CB₁R–CB₂R heteromeric complexes should be taken into consideration when designing new drugs acting on cannabinoid receptor heteromers.

Functions of the CB1 and CB 2 receptors in neuroprotection at the level of the blood-brain barrier

The cannabinoid (CB) receptors are the main targets of the cannabinoids, which include plant cannabinoids, endocannabinoids and synthetic cannabinoids. Over the last few years, accumulated evidence has suggested a role of the CB receptors in neuroprotection. The blood-brain barrier (BBB) is an important brain structure that is essential for neuroprotection. A link between the CB receptors and the BBB is thus likely, but this possible connection has only recently gained attention. Cannabinoids and the BBB share the same mechanisms of neuroprotection and both protect against excitotoxicity (CB1), cell death (CB1), inflammation (CB2) and oxidative stress (possibly CB independent)-all processes that also damage the BBB. Several examples of CB-mediated protection of the BBB have been found, such as inhibition of leukocyte influx and induction of amyloid beta efflux across the BBB. Moreover, the CB receptors were shown to improve BBB integrity, particularly by restoring the tightness of the tight junctions. This review demonstrated that both CB receptors are able to restore the BBB and neuroprotection, but much uncertainty about the underlying signaling cascades still exists and further investigation is needed.

Changes in endocannabinoid receptors and enzymes in the spinal cord of SOD1(G93A) transgenic mice and evaluation of a Sativex(®) -like combination of phytocannabinoids: interest for future therapies in amyotrophic lateral sclerosis

AIMS

Cannabinoids afford neuroprotection in SOD1(G93A) mutant mice, an experimental model of amyotrophic lateral sclerosis (ALS). However, these mice have been poorly studied to identify alterations in those elements of the endocannabinoid system targeted by these treatments. Moreover, we studied the neuroprotective effect of the phytocannabinoid-based medicine Sativex(®) in these mice.

METHODS

First, we analyzed the endocannabinoid receptors and enzymes in the spinal cord of SOD1(G93A) transgenic mice at a late stage of the disease. Second, 10-week-old transgenic mice were daily treated with an equimolecular combination of Δ(9) -tetrahydrocannabinol- and cannabidiol-enriched botanical extracts (20 mg/kg for each phytocannabinoid).

RESULTS

We found a significant increase of CB2 receptors and NAPE-PLD enzyme in SOD1(G93A) transgenic males and only CB2 receptors in females. Pharmacological experiments demonstrated that the treatment of these mice with the Sativex(®) -like combination of phytocannabinoids only produced weak improvements in the progression of neurological deficits and in the animal survival, particularly in females.

CONCLUSIONS

Our results demonstrated changes in endocannabinoid signaling, in particular a marked up-regulation of CB2 receptors, in SOD1(G93A) transgenic mice, and provide support that Sativex(®) may serve as a novel disease-modifying therapy in ALS.

Prior stimulation of the endocannabinoid system prevents methamphetamine-induced dopaminergic neurotoxicity in the striatum through activation of CB2 receptors

Methamphetamine toxicity is associated with cell death and loss of dopamine neuron terminals in the striatum similar to what is found in some neurodegenerative diseases. Conversely, the endocannabinoid system (ECS) has been suggested to be neuroprotective in the brain, and new pharmacological tools have been developed to increase their endogenous tone. In this study, we evaluated whether ECS stimulation could reduce the neurotoxicity of high doses of methamphetamine on the dopamine system. We found that methamphetamine alters the levels of the major endocannabinoids, anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) in the striatum, suggesting that the ECS participates in the brain responses to methamphetamine. Δ(9)-tetrahydrocannabinol (THC), a cannabis-derived agonist of both CB1 and CB2 cannabinoid receptors, or inhibitors of the main enzymes responsible for the degradation of AEA and 2-AG (URB597 and JZL184, respectively), blunted the decrease in striatal protein levels of tyrosine hydroxylase induced by methamphetamine. In addition, antagonists of CB2, but not of CB1, blocked the preventive effects of URB597 and JZL184, suggesting that only the former receptor subtype is engaged in neuroprotection exerted by ECS stimulation. Finally, we found that methamphetamine increases striatal levels of the cytokine tumor necrosis factor alpha, an effect that was blocked by ECS stimulation. Altogether, our results indicate that stimulation of ECS prior to the administration of an overdose of methamphetamine considerably reduces the neurotoxicity of the drug through CB2 receptor activation and highlight a protective function for the ECS against the toxicity induced by drugs and other external insults to the brain. This article is part of the Special Issue entitled 'CNS Stimulants'.

Endocannabinoid-hydrolysing enzymes in the post-mortem cerebellum of humans affected by hereditary autosomal dominant ataxias

OBJECTIVES

Spinocerebellar ataxias (SCAs) are characterized by a loss of balance and motor coordination due to degeneration of the cerebellum and its afferent and efferent connections. We recently found important changes in cannabinoid CB1 and CB2 receptors in the post-mortem cerebellum of patients affected by different SCAs.

METHODS

We wanted to further explore this issue by analysing the two major endocannabinoid-hydrolysing enzymes, fatty acid amide hydrolase (FAAH) and monoacyl glycerol lipase (MAGL), in the post-mortem cerebellum of SCA patients and control subjects.

RESULTS

Immunoreactivity for the FAAH and MAGL enzymes was found in the granular layer, in Purkinje cells, in neurons of the dentate nucleus and in areas of white matter in the cerebellum of patients at levels frequently notably higher than those in control subjects. Using double-labelling procedures, we found co-localization of FAAH and MAGL with calbindin, supporting the presence of these enzymes in Purkinje neurons.

CONCLUSIONS

Degradative endocannabinoid enzymes are significantly increased in the cerebellum of SCA patients, which would presumably lead to reduced endocannabinoid levels. The identification of these enzymes in Purkinje neurons suggests a relationship with the pathogenesis of SCAs and suggests that the endocannabinoid system could provide potential therapeutic targets for the treatment of disease progression in SCAs.

Changes in CB(1) and CB(2) receptors in the post-mortem cerebellum of humans affected by spinocerebellar ataxias

BACKGROUND AND PURPOSE

Spinocerebellar ataxias (SCAs) are a family of chronic progressive neurodegenerative diseases, clinically and genetically heterogeneous, characterized by loss of balance and motor coordination due to degeneration of the cerebellum and its afferent and efferent connections. Unlike other motor disorders, the possible role of changes in the endocannabinoid system in the pathogenesis of SCAs has not been investigated.

EXPERIMENTAL APPROACH

The status of cannabinoid receptor type 1 (CB1 ) and cannabinoid receptor type 2 (CB2 ) receptors in the post-mortem cerebellum of SCA patients and controls was investigated using immunohistochemical procedures.

KEY RESULTS

Immunoreactivity for the CB1 receptor, and also for the CB2 receptor, was found in the granular layer, Purkinje cells, neurons of the dentate nucleus and areas of white matter in the cerebellum of SCA patients at levels notably higher than controls. Double-labelling procedures demonstrated co-localization of CB1 and, in particular, CB2 receptors with calbindin, supporting the presence of these receptors in Purkinje neurons. Both receptors also co-localized with Iba-1 and glial fibrillary acidic protein in the granular layer and white matter areas, indicating that they are present in microglia and astrocytes respectively.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrate that CB1 and CB2 receptor levels are significantly altered in the cerebellum of SCA patients. Their identification in Purkinje neurons, which are the main cells affected in SCAs, as well as the changes they experienced, suggest that alterations in endocannabinoid receptors may be related to the pathogenesis of SCAs. Therefore, the endocannabinoid system could provide potential therapeutic targets for the treatment of SCAs and its progression.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-6.

Neuroprotective effects of the cannabinoid agonist HU210 on retinal degeneration

Cannabinoids have been demonstrated to exert neuroprotective effects on different types of neuronal insults. Here we have addressed the therapeutic potential of the synthetic cannabinoid HU210 on photoreceptor degeneration, synaptic connectivity and functional activity of the retina in the transgenic P23H rat, an animal model for autosomal dominant retinitis pigmentosa (RP). In P23H rats administered with HU210 (100 μg/kg, i.p.) from P24 to P90, ERG recordings showed an amelioration of vision loss, as compared to vehicle-administered animals. Under scotopic conditions, the maximum a-wave amplitudes recorded at P60 and P90 were higher in HU210-treated animals, as compared to the values obtained in untreated animals. The scotopic b-waves were significantly higher in treated animals than in untreated rats at P30, P60 and P90. This attenuation of visual deterioration correlated with a delay in photoreceptor degeneration and the preservation of retinal cytoarchitecture. HU210-treated animals had 40% more photoreceptors than untreated animals. Presynaptic and postsynaptic elements, as well as the synaptic contacts between photoreceptors and bipolar or horizontal cells, were also preserved in HU210-treated P23H rats. These results indicate that HU210 preserves cone and rod structure and function, together with their contacts with postsynaptic neurons, in P23H rats. These data suggest that cannabinoids are potentially useful to delay retinal degeneration in RP patients.

Marijuana use and brain immune mechanisms

The recreational smoking of marijuana, or Cannabis sativa, has become widespread, including among adolescents. Marijuana contains a class of compounds known as phytocannabinoids that include cannabidiol (CBD) and Δ(9)-tetrahydrocannabinol (THC). THC is the major psychoactive component in marijuana, but also exhibits immunosuppressive activity. CBD, while not psychotropic, also modulates immune function, but its mechanism of action appears to differ from that of THC. Since both compounds are highly lipophilic, they readily passage the blood-brain barrier and access the central nervous system. Since CBD is not psychotropic, it has been considered as a candidate therapeutic compound for ablating neuropathological processes characterized by hyperinflammation. However, an unresolved question centers around the impact of these compounds on immune-competent cells within the CNS in relation to susceptibility to infection. There are accumulating data indicating that THC inhibits the migratory capability of macrophage-like cells resident in the CNS, such as microglia, toward nodes of microbial invasion. Furthermore, phytocannabinoids have been reported to exert developmental and long-term effects on the immune system suggesting that exposure to these substances during an early stage in life has the potential to alter the fundamental neuroimmune response to select microbial agents in the adult.

J, Viana RB, Baetas AC, Orestes E, Andrade MA, Honório KM, da Silva ABF. Understanding the molecular aspects of tetrahydrocannabinol and cannabidiol as antioxidants

An antioxidant mechanism of tetrahydrocannabinol (THC) and cannabidiol (CBD) were compared with a simplified model of α-tocopherol, butylhydroxytoluene and hydroxytoluene in order to understand the antioxidant nature of THC and CBD molecules using DFT. The following electronic properties were evaluated: frontier orbitals nature, ionization potential, O-H bond dissociation energy (BDE_OH), stabilization energy, and spin density distribution. An important factor that shows an influence in the antioxidant property of THC is the electron abstraction at the phenol position. Our data indicate that the decrease of the HOMO values and the highest ionization potential values are related to phenol, ether, and alkyl moieties. On the other hand, BDE_OH in molecules with the cyclohexenyl group at ortho position of phenol are formed from lower energies than the molecules with an ether group at the meta position. In the light of our results, the properties calculated here predict that THC has a sightly higher antioxidant potential than CBD.

Radiofluorination and biological evaluation of N-aryl-oxadiazolyl-propionamides as potential radioligands for PET imaging of cannabinoid CB2 receptors

Background

The level of expression of cannabinoid receptor type 2 (CB₂R) in healthy and diseased brain has not been fully elucidated. Therefore, there is a growing interest to assess the regional expression of CB₂R in the brain. Positron emission tomography (PET) is an imaging technique, which allows quantitative monitoring of very low amounts of radiolabelled compounds in living organisms at high temporal and spatial resolution and, thus, has been widely used as a diagnostic tool in nuclear medicine. Here, we report on the radiofluorination of N-aryl-oxadiazolyl-propionamides at two different positions in the lead structure and on the biological evaluation of the potential of the two tracers [¹⁸F]1 and [¹⁸F]2 as CB₂ receptor PET imaging agents.

Results

High binding affinity and specificity towards CB₂ receptors of the lead structure remained unaffected by the structural changes such as the insertion of the aliphatic and aromatic fluorine in the selected labelling sites of 1 and 2. Aliphatic and aromatic radiofluorinations were optimized, and [¹⁸F]1 and [¹⁸F]2 were achieved in radiochemical yields of ≥30% with radiochemical purities of ≥98% and specific activities of 250 to 450 GBq/μmol. Organ distribution studies in female CD1 mice revealed that both radiotracers cross the blood–brain barrier (BBB) but undergo strong peripheral metabolism. At 30 min after injection, unmetabolized [¹⁸F]1 and [¹⁸F]2 accounted for 60% and 2% as well as 68% and 88% of the total activity in the plasma and brain, respectively. The main radiometabolite of [¹⁸F]2 could be identified as the free acid [¹⁸F]10, which has no affinity towards the CB₁ and CB₂ receptors but can cross the BBB.

Conclusions

N-aryl-oxadiazolyl-propionamides can successfully be radiolabelled with ¹⁸F at different positions. Fluorine substitution at these positions did not affect affinity and specificity towards CB₂R. Despite a promising in vitro behavior, a rather rapid peripheral metabolism of [¹⁸F]1 and [¹⁸F]2 in mice and the generation of brain permeable radiometabolites hamper the application of these radiotracers in vivo. However, it is expected that future synthetic modification aiming at a replacement of metabolically susceptible structural elements of [¹⁸F]1 and [¹⁸F]2 will help to elucidate the potential of this class of compounds for CB₂R PET studies.

Critical appraisal of the potential use of cannabinoids in cancer management

Cannabinoids have been attracting a great deal of interest as potential anticancer agents. Originally derived from the plant Cannabis sativa, there are now a number of endo-, phyto- and synthetic cannabinoids available. This review summarizes the key literature to date around the actions, antitumor activity, and mechanisms of action for this broad range of compounds. Cannabinoids are largely defined by an ability to activate the cannabinoid receptors – CB₁ or CB₂. The action of the cannabinoids is very dependent on the exact ligand tested, the dose, and the duration of exposure. Some cannabinoids, synthetic or plant-derived, show potential as therapeutic agents, and evidence across a range of cancers and evidence in vitro and in vivo is starting to be accumulated. Studies have now been conducted in a wide range of cell lines, including glioma, breast, prostate, endothelial, liver, and lung. This work is complemented by an increasing body of evidence from in vivo models. However, many of these results remain contradictory, an issue that is not currently able to be resolved through current knowledge of mechanisms of action. While there is a developing understanding of potential mechanisms of action, with the extracellular signal-regulated kinase pathway emerging as a critical signaling juncture in combination with an important role for ceramide and lipid signaling, the relative importance of each pathway is yet to be determined. The interplay between the intracellular pathways of autophagy versus apoptosis is a recent development that is discussed. Overall, there is still a great deal of conflicting evidence around the future utility of the cannabinoids, natural or synthetic, as therapeutic agents.

Cannabinoid receptor CB2 modulates axon guidance

Navigation of retinal projections towards their targets is regulated by guidance molecules and growth cone transduction mechanisms. Here, we present in vitro and in vivo evidences that the cannabinoid receptor 2 (CB2R) is expressed along the retino-thalamic pathway and exerts a modulatory action on axon guidance. These effects are specific to CB2R since no changes were observed in mice where the gene coding for this receptor was altered (cnr2 (-/-)). The CB2R induced morphological changes observed at the growth cone are PKA dependent and require the presence of the netrin-1 receptor, Deleted in Colorectal Cancer. Interfering with endogenous CB2R signalling using pharmacological agents increased retinal axon length and induced aberrant projections. Additionally, cnr2 (-/-) mice showed abnormal eye-specific segregation of retinal projections in the dorsal lateral geniculate nucleus (dLGN) indicating CB2R's implication in retinothalamic development. Overall, this study demonstrates that the contribution of endocannabinoids to brain development is not solely mediated by CB1R, but also involves CB2R.

Radiolabeling and in vitro /in vivo evaluation of N-(1-adamantyl)-8-methoxy-4-oxo-1-phenyl-1,4-dihydroquinoline-3-carboxamide as a PET probe for imaging cannabinoid type 2 receptor

The cannabinoid type 2 (CB2) receptor plays an important role in neuroinflammatory and neurodegenerative diseases such as multiple sclerosis, amyotrophic lateral sclerosis, and Alzheimer’s disease and is therefore a very promising target for therapeutic approaches as well as for imaging. Based on the literature, we identified one 4-oxoquinoline derivative(designated KD2) as the lead structure. It was synthesized, radiolabeled and evaluated as a potential imaging tracer for CB2. [11C]KD2 was obtained in 99% radiochemical purity.Moderate blood–brain barrier (BBB) passage was predicted for KD2 from an in vitro transport assay with P-glycoprotein-transfected Madin Darby canine kidney cells. No efflux of KD2 by P-glycoprotein was detected. In vitro autoradiography of rat and mouse spleen slices demonstrated that [11C]KD2 exhibits high specific binding towards CB2. High spleen uptake of [11C]KD2 was observed in dynamic positron emission tomography(PET) studies with Wistar rats and its specificity was confirmed by displacement study with a selective CB2 agonist, GW405833. A pilot autoradiography study with post-mortem spinal cord slices from amyotrophic lateral sclerosis (ALS)patients with [11C]KD2 suggested the presence of CB2 receptors under disease conditions. Specificity of [11C]KD2 binding could also be demonstrated on these human tissues. In conclusion, [11C]KD2 shows good in vitro and in vivo properties as a potential PET tracer for CB2.

Selective cannabinoid receptor type 2 (CB2) agonists: optimization of a series of purines leading to the identification of a clinical candidate for the treatment of osteoarthritic pain

A focused screening strategy identified thienopyrimidine 12 as a cannabinoid receptor type 2 agonist (hCB2) with moderate selectivity over the hCB1 receptor. This initial hit suffered from poor in vitro metabolic stability and high in vivo clearance. Structure-activity relationships describe the optimization and modification to a new more polar series of purine CB2 agonists. Examples from this novel scaffold were found to be highly potent and fully efficacious agonists of the human CB2 receptor with excellent selectivity against CB1, often having no CB1 agonist activity at the highest concentration measured (>100 μM). Compound 26 is a centrally penetrant molecule which possesses good biopharmaceutical properties, is highly water-soluble, and demonstrates robust oral activity in rodent models of joint pain. In addition, the peripherally restricted molecule 22 also demonstrated significant efficacy in the same analgesic model of rodent inflammatory pain.

Cannabidiol for neurodegenerative disorders: important new clinical applications for this phytocannabinoid?

Cannabidiol (CBD) is a phytocannabinoid with therapeutic properties for numerous disorders exerted through molecular mechanisms that are yet to be completely identified. CBD acts in some experimental models as an anti-inflammatory, anticonvulsant, anti-oxidant, anti-emetic, anxiolytic and antipsychotic agent, and is therefore a potential medicine for the treatment of neuroinflammation, epilepsy, oxidative injury, vomiting and nausea, anxiety and schizophrenia, respectively. The neuroprotective potential of CBD, based on the combination of its anti-inflammatory and anti-oxidant properties, is of particular interest and is presently under intense preclinical research in numerous neurodegenerative disorders. In fact, CBD combined with Δ(9)-tetrahydrocannabinol is already under clinical evaluation in patients with Huntington's disease to determine its potential as a disease-modifying therapy. The neuroprotective properties of CBD do not appear to be exerted by the activation of key targets within the endocannabinoid system for plant-derived cannabinoids like Δ(9)-tetrahydrocannabinol, i.e. CB(1) and CB(2) receptors, as CBD has negligible activity at these cannabinoid receptors, although certain activity at the CB(2) receptor has been documented in specific pathological conditions (i.e. damage of immature brain). Within the endocannabinoid system, CBD has been shown to have an inhibitory effect on the inactivation of endocannabinoids (i.e. inhibition of FAAH enzyme), thereby enhancing the action of these endogenous molecules on cannabinoid receptors, which is also noted in certain pathological conditions. CBD acts not only through the endocannabinoid system, but also causes direct or indirect activation of metabotropic receptors for serotonin or adenosine, and can target nuclear receptors of the PPAR family and also ion channels.

Modulating the endocannabinoid system in human health and disease--successes and failures

The discovery of the endocannabinoid system, comprising the G-protein coupled cannabinoid 1 and 2 receptors (CB1/2), their endogenous lipid ligands or endocannabinoids, and synthetic and metabolizing enzymes, has triggered an avalanche of experimental studies implicating the endocannabinoid system in a growing number of physiological/pathological functions. These studies have also suggested that modulating the activity of the endocannabinoid system holds therapeutic promise for a broad range of diseases, including neurodegenerative, cardiovascular and inflammatory disorders; obesity/metabolic syndrome; cachexia; chemotherapy-induced nausea and vomiting; and tissue injury and pain, amongst others. However, clinical trials with globally acting CB1 antagonists in obesity/metabolic syndrome, and other studies with peripherally-restricted CB1/2 agonists and inhibitors of the endocannabinoid metabolizing enzyme in pain, have introduced unexpected complexities, suggesting that a better understanding of the pathophysiological role of the endocannabinoid system is required to devise clinically successful treatment strategies.

Antibody testing for brain immunohistochemistry: brain immunolabeling for the cannabinoid CB₂ receptor

The question of whether cannabinoid CB₂ receptors are expressed on neurons in the brain and under what circumstances they are expressed is controversial in cannabinoid neuropharmacology. While some studies have reported that CB₂ receptors are not detectable on neurons under normal circumstances, other studies have reported abundant neuronal expression. One reason for these apparent discrepancies is the reliance on incompletely validated CB₂ receptor antibodies and immunohistochemical procedures. In this study, we demonstrate some of the methodological problems encountered using three different commercial CB₂ receptor antibodies. We show that (1) the commonly used antibodies that were confirmed by many of the tests used for antibody validation still failed when examined using the knockout control test; (2) the coherence between the labeling patterns provided by two antibodies for the same protein at different epitopes may be misleading and must be validated using both low- and high-magnification microscopy; and (3) although CB₂ receptor antibodies may label neurons in the brain, the protein that the antibodies are labeling is not necessarily CB₂. These results showed that great caution needs to be exercised when interpreting the results of brain immunohistochemistry using CB₂ receptor antibodies and that, in general, none of the tests for antibody validity that have been proposed, apart from the knockout control test, are reliable.

The pseudokinase tribbles homologue-3 plays a crucial role in cannabinoid anticancer action

Δ(9)-Tetrahydrocannabinol (THC), the major active ingredient of marijuana, and other cannabinoids inhibit tumor growth in animal models of cancer. This effect relies, at least in part, on the up-regulation of several endoplasmic reticulum stress-related proteins including the pseudokinase tribbles homologue-3 (TRIB3), which leads in turn to the inhibition of the AKT/mTORC1 axis and the subsequent stimulation of autophagy-mediated apoptosis in tumor cells. Here, we took advantage of the use of cells derived from Trib3-deficient mice to investigate the precise mechanisms by which TRIB3 regulates the anti-cancer action of THC. Our data show that RasV(12)/E1A-transformed embryonic fibroblasts derived from Trib3-deficient mice are resistant to THC-induced cell death. We also show that genetic inactivation of this protein abolishes the ability of THC to inhibit the phosphorylation of AKT and several of its downstream targets, including those involved in the regulation of the AKT/mammalian target of rapamycin complex 1 (mTORC1) axis. Our data support the idea that THC-induced TRIB3 up-regulation inhibits AKT phosphorylation by regulating the accessibility of AKT to its upstream activatory kinase (the mammalian target of rapamycin complex 2; mTORC2). Finally, we found that tumors generated by inoculation of Trib3-deficient cells in nude mice are resistant to THC anticancer action. Altogether, the observations presented here strongly support that TRIB3 plays a crucial role on THC anti-neoplastic activity. This article is part of a Special Issue entitled Lipid Metabolism in Cancer.

Evaluation of (Z)-2-((1-benzyl-1H-indol-3-yl)methylene)-quinuclidin-3-one analogues as novel, high affinity ligands for CB1 and CB2 cannabinoid receptors

A small library of N-benzyl indolequinuclidinone (IQD) analogs has been identified as a novel class of cannabinoid ligands. The affinity and selectivity of these IQDs for the two established cannabinoid receptor subtypes, CB1 and CB2, was evaluated. Compounds 8 (R=R(2)=H, R(1)=F) and 13 (R=COOCH3, R(1)=R(2)=H) exhibited high affinity for CB2 receptors with Ki values of 1.33 and 2.50 nM, respectively, and had lower affinities for the CB1 receptor (Ki values of 9.23 and 85.7 nM, respectively). Compound 13 had the highest selectivity of all the compounds examined, and represents a potent cannabinoid ligand with 34-times greater selectivity for CB2R over CB1R. These findings are significant for future drug development, given recent reports demonstrating beneficial use of cannabinoid ligands in a wide variety of human disease states including drug abuse, depression, schizophrenia, inflammation, chronic pain, obesity, osteoporosis and cancer.

Using the endocannabinoid system as a neuroprotective strategy in perinatal hypoxic-ischemic brain injury

One of the most important causes of brain injury in the neonatal period is a perinatal hypoxic-ischemic event. This devastating condition can lead to long-term neurological deficits or even death. After hypoxic-ischemic brain injury, a variety of specific cellular mechanisms are set in motion, triggering cell damage and finally producing cell death. Effective therapeutic treatments against this phenomenon are still unavailable because of complex molecular mechanisms underlying hypoxic-ischemic brain injury. After a thorough understanding of the mechanism underlying neural plasticity following hypoxic-ischemic brain injury, various neuroprotective therapies have been developed for alleviating brain injury and improving long-term outcomes. Among them, the endocannabinoid system emerges as a natural system of neuroprotection. The endocannabinoid system modulates a wide range of physiological processes in mammals and has demonstrated neuroprotective effects in different paradigms of acute brain injury, acting as a natural neuroprotectant. The aim of this review is to study the use of different therapies to induce long-term therapeutic effects after hypoxic-ischemic brain injury, and analyze the important role of the endocannabinoid system as a new neuroprotective strategy against perinatal hypoxic-ischemic brain injury.

Chronic activation of cannabinoid receptors in vitro does not compromise mouse islet function

We have demonstrated previously that mouse and human islets express ECS (endocannabinoid system) elements, and that short-term activation of islet cannabinoid CB1r and CB2r (cannabinoid type 1 and 2 receptors respectively) stimulates insulin secretion in vitro. There is evidence that the ECS is overactive in Type 2 diabetes, impairing glucose homoeostasis, but little is known about whether it is implicated in islet dysfunction. Therefore the aim of the present study was to investigate the effect of chronic exposure of isolated mouse islets to cannabinoid receptor agonists on islet gene expression and function. Quantitative RT-PCR (reverse transcription-PCR) indicated that mRNAs encoding synthesis [NAPE-PLD (N-acyl-phosphatidyl ethanolamide-hydrolysing phospholipase D)] and degradation [FAAH (fatty acid amide hydrolase)] of the endocannabinoid AEA (anandamide) were the most abundant ECS elements in mouse islets, with much lower levels of CB1r, CB2r, DAGL (diacylglycerol lipase) and MAGL (monoacylglycerol lipase) mRNAs. Maintenance of islets for up to 7 days in the presence of the CB1r agonist ACEA [N-(2-chloroethyl)-5Z,8Z,11Z,14Z-eiscosatetraenamide] or the CB2r agonist JWH015 [(2-methyl-1propyl-1H-indol3-yl)-1-napthalenylmethanone] did not compromise islet viability, as assessed by islet morphology and caspase activities, but there were some changes in mRNAs encoding ECS components. Neither glucose-stimulated insulin secretion nor acute insulin secretory responses to ACEA or JWH015 at 16 mM glucose were substantially modified by a 48 h or 7 day pre-exposure to these cannabinoid receptor agonists, but the stimulation of secretion at 3 mM glucose by 100 nM ACEA was significantly reduced after prolonged treatment with ACEA. Despite JWH015-induced reductions in islet glucagon content at 48 h and 7 days, there were no reductions in arginine-induced glucagon secretion from islets pre-exposed to JWH015 or ACEA. These data indicate that treatment of islets with agonists of CB1r and CB2r for up to 7 days does not have any major impact on islet function, suggesting that the impairments in glucose homoeostasis observed following overactivation of the ECS should be sought in relation to insulin resistance rather than β-cell dysfunction.

Local delivery of cannabinoid-loaded microparticles inhibits tumor growth in a murine xenograft model of glioblastoma multiforme

Cannabinoids, the active components of marijuana and their derivatives, are currently investigated due to their potential therapeutic application for the management of many different diseases, including cancer. Specifically, Δ⁹-Tetrahydrocannabinol (THC) and Cannabidiol (CBD) – the two major ingredients of marijuana – have been shown to inhibit tumor growth in a number of animal models of cancer, including glioma. Although there are several pharmaceutical preparations that permit the oral administration of THC or its analogue nabilone or the oromucosal delivery of a THC- and CBD-enriched cannabis extract, the systemic administration of cannabinoids has several limitations in part derived from the high lipophilicity exhibited by these compounds. In this work we analyzed CBD- and THC-loaded poly-ε-caprolactone microparticles as an alternative delivery system for long-term cannabinoid administration in a murine xenograft model of glioma. In vitro characterization of THC- and CBD-loaded microparticles showed that this method of microencapsulation facilitates a sustained release of the two cannabinoids for several days. Local administration of THC-, CBD- or a mixture (1∶1 w:w) of THC- and CBD-loaded microparticles every 5 days to mice bearing glioma xenografts reduced tumour growth with the same efficacy than a daily local administration of the equivalent amount of those cannabinoids in solution. Moreover, treatment with cannabinoid-loaded microparticles enhanced apoptosis and decreased cell proliferation and angiogenesis in these tumours. Our findings support that THC- and CBD-loaded microparticles could be used as an alternative method of cannabinoid delivery in anticancer therapies.

Spice drugs are more than harmless herbal blends: a review of the pharmacology and toxicology of synthetic cannabinoids

"K2" and "Spice" drugs (collectively hereafter referred to as Spice) represent a relatively new class of designer drugs that have recently emerged as popular alternatives to marijuana, otherwise characterized as "legal highs". These drugs are readily available on the Internet and sold in many head shops and convenience stores under the disguise of innocuous products like herbal blends, incense, or air fresheners. Although package labels indicate "not for human consumption", the number of intoxicated people presenting to emergency departments is dramatically increasing. The lack of validated and standardized human testing procedures and an endless supply of potential drugs of abuse are primary reasons why researchers find it difficult to fully characterize clinical consequences associated with Spice. While the exact chemical composition and toxicology of Spice remains to be determined, there is mounting evidence identifying several synthetic cannabinoids as causative agents responsible for psychoactive and adverse physical effects. This review provides updates of the legal status of common synthetic cannabinoids detected in Spice and analytical procedures used to test Spice products and human specimens collected under a variety of clinical circumstances. The pharmacological and toxicological consequences of synthetic cannabinoid abuse are also reviewed to provide a future perspective on potential short- and long-term implications.

Lead discovery, chemistry optimization, and biological evaluation studies of novel biamide derivatives as CB2 receptor inverse agonists and osteoclast inhibitors

N,N'-((4-(Dimethylamino)phenyl)methylene)bis(2-phenylacetamide) was discovered by using 3D pharmacophore database searches and was biologically confirmed as a new class of CB(2) inverse agonists. Subsequently, 52 derivatives were designed and synthesized through lead chemistry optimization by modifying the rings A-C and the core structure in further SAR studies. Five compounds were developed and also confirmed as CB(2) inverse agonists with the highest CB(2) binding affinity (CB(2)K(i) of 22-85 nM, EC(50) of 4-28 nM) and best selectivity (CB(1)/CB(2) of 235- to 909-fold). Furthermore, osteoclastogenesis bioassay indicated that PAM compounds showed great inhibition of osteoclast formation. Especially, compound 26 showed 72% inhibition activity even at the low concentration of 0.1 μM. The cytotoxicity assay suggested that the inhibition of PAM compounds on osteoclastogenesis did not result from its cytotoxicity. Therefore, these PAM derivatives could be used as potential leads for the development of a new type of antiosteoporosis agent.

Cannabinoids, multiple sclerosis and neuroprotection

The cannabinoid signaling system participates in the control of cell homeostasis in the CNS, which explains why, in different neurodegenerative diseases including multiple sclerosis (MS), alterations in this system have been found to serve both as a pathogenic factor (malfunctioning of this system has been found at early phases of these diseases) and as a therapeutic target (the management of this system has beneficial effects). MS is an autoimmune disease that affects the CNS and it is characterized by inflammation, demyelination, remyelination, gliosis and axonal damage. Although it has been considered mainly as an inflammatory disorder, recent studies have recognized the importance of axonal loss both in the progression of the disorder and in the appearance of neurological disability, even in early stages of the disease. In recent years, several laboratories have addressed the therapeutic potential of cannabinoids in MS, given the experience reported by some MS patients who self-medicated with marijuana. Most of these studies focused on the alleviation of symptoms (spasticity, tremor, anxiety and pain) or on the inflammatory component of the disease. However, recent data also revealed the important neuroprotective action that could be exerted by cannabinoids in this disorder. The present review will be precisely centered on this neuroprotective potential, which is based mainly on antioxidant, anti-inflammatory and anti-excitotoxic properties, exerted through the activation of CB1 or CB2 receptors or other unknown mechanisms.

Targeting the endocannabinoid system for gastrointestinal diseases: future therapeutic strategies

Cannabinoids extracted from the marijuana plant (Cannabis sativa) and synthetic cannabinoids have numerous effects on gastrointestinal (GI) functions. Recent experimental data support an important role for cannabinoids in GI diseases. Genetic studies in humans have proven that defects in endocannabinoid metabolism underlie functional GI disorders. Mammalian cells have machinery, the so-called endocannabinoid system (ECS), to produce and metabolize their own cannabinoids in order to control homeostasis of the gut in a rapidly adapting manner. Pharmacological manipulation of the ECS by cannabinoids, or by drugs that raise the levels of endogenous cannabinoids, have shown beneficial effects on GI pathophysiology. This review gives an introduction into the functions of the ECS in the GI tract, highlights the role of the ECS in GI diseases and addresses its potential pharmacological exploitation.

Activation of the CB2 receptor system reverses amyloid-induced memory deficiency

Cannabinoid type 2 (CB(2)) agonists are neuroprotective and appear to play modulatory roles in neurodegenerative processes in Alzheimer's disease. We have studied the effect of 1-((3-benzyl-3-methyl-2,3-dihydro-1-benzofuran-6-yl) carbonyl) piperidine (MDA7)-a novel selective CB(2) agonist that lacks psychoactivity-on ameliorating the neuroinflammatory process, synaptic dysfunction, and cognitive impairment induced by bilateral microinjection of amyloid-β (Aβ)(1-40) fibrils into the hippocampal CA1 area of rats. In rats injected with Aβ(1-40) fibrils, compared with the administration of intraperitoneal saline for 14 days, treatment with 15 mg/kg of intraperitoneal MDA7 daily for 14 days (1) ameliorated the expression of CD11b (microglia marker) and glial fibrillary acidic protein (astrocyte marker), (2) decreased the secretion of interleukin-1β, (3) decreased the upsurge of CB(2) receptors, (4) promoted Aβ clearance, and (5) restored synaptic plasticity, cognition, and memory. Our findings suggest that MDA7 is an innovative therapeutic approach for the treatment of Alzheimer's disease.

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.

Endocannabinoid modulation of dopaminergic motor circuits

There is substantial evidence supporting a role for the endocannabinoid system as a modulator of the dopaminergic activity in the basal ganglia, a forebrain system that integrates cortical information to coordinate motor activity regulating signals. In fact, the administration of plant-derived, synthetic or endogenous cannabinoids produces several effects on motor function. These effects are mediated primarily through the CB(1) receptors that are densely located in the dopamine-enriched basal ganglia networks, suggesting that the motor effects of endocannabinoids are due, at least in part, to modulation of dopaminergic transmission. On the other hand, there are profound changes in CB(1) receptor cannabinoid signaling in the basal ganglia circuits after dopamine depletion (as happens in Parkinson's disease) and following l-DOPA replacement therapy. Therefore, it has been suggested that endocannabinoid system modulation may constitute an important component in new therapeutic approaches to the treatment of motor disturbances. In this article we will review studies supporting the endocannabinoid modulation of dopaminergic motor circuits.

Latest advances in novel cannabinoid CB(2) ligands for drug abuse and their therapeutic potential

The field of cannabinoid (CB) drug research is experiencing a challenge as the CB(1) antagonist Rimonabant, launched in 2006 as an anorectic/anti-obesity drug, was withdrawn from the European market due to the complications of suicide and depression as side effects. There is interest in developing CB(2) drugs without CB(1) psychotropic side effects for drug-abuse treatment and therapeutic medication. The CB(1) receptor was discovered predominantly in the brain, whereas the CB(2) is mainly expressed in peripheral cells and tissues, and is involved in immune signal transduction. Conversely, the CB(2) receptor was recently detected in the CNS, for example, in the microglial cells and the neurons. While the CB(2) neurons activity remains controversial, the CB(2) receptor is an attractive therapeutic target for neuropathic pain, immune system, cancer and osteoporosis without psychoactivity. This review addresses CB drug abuse and therapeutic potential with a focus on the most recent advances on new CB(2) ligands from the literature as well as patents.

Design, synthesis, and pharmacological characterization of indol-3-ylacetamides, indol-3-yloxoacetamides, and indol-3-ylcarboxamides: potent and selective CB2 cannabinoid receptor inverse agonists

In our search for new cannabinoid receptor modulators, we describe herein the design and synthesis of three sets of indole-based ligands characterized by an acetamide, oxalylamide, or carboxamide chain, respectively. Most of the compounds showed affinity for CB2 receptors in the nanomolar range, with K(i) values spanning 3 orders of magnitude (377-0.37 nM), and moderate to good selectivity over CB1 receptors. Their in vitro functional activity as inverse agonists was confirmed in vivo in the formalin test of acute peripheral and inflammatory pain in mice, in which compounds 10a and 11e proved to be able to reverse the effect of the CB2 selective agonist COR167.

Sativex-like combination of phytocannabinoids is neuroprotective in malonate-lesioned rats, an inflammatory model of Huntington's disease: role of CB1 and CB2 receptors

We have investigated whether a 1:1 combination of botanical extracts enriched in either Δ(9)-tetrahydrocannabinol (Δ(9)-THC) or cannabidiol (CBD), which are the main constituents of the cannabis-based medicine Sativex, is neuroprotective in Huntington's disease (HD), using an experimental model of this disease generated by unilateral lesions of the striatum with the mitochondrial complex II inhibitor malonate. This toxin damages striatal neurons by mechanisms that primarily involve apoptosis and microglial activation. We monitored the extent of this damage and the possible preservation of the striatal parenchyma by treatment with a Sativex-like combination of phytocannabinoids using different histological and biochemical markers. Results were as follows: (i) malonate increased the volume of edema measured by in vivo NMR imaging and the Sativex-like combination of phytocannabinoids partially reduced this increase; (ii) malonate reduced the number of Nissl-stained cells, while enhancing the number of degenerating cells stained with FluoroJade-B, and the Sativex-like combination of phytocannabinoids reversed both effects; (iii) malonate caused a strong glial activation (i.e., reactive microglia labeled with Iba-1, and astrogliosis labeled with GFAP) and the Sativex-like combination of phytocannabinoids attenuated both responses; and (iv) malonate increased the expression of inducible nitric oxide synthase and the neurotrophin IGF-1, and both responses were attenuated after the treatment with the Sativex-like combination of phytocannabinoids. We also wanted to establish whether targets within the endocannabinoid system (i.e., CB(1) and CB(2) receptors) are involved in the beneficial effects induced in this model by the Sativex-like combination of phytocannabinoids. This we did using selective antagonists for both receptor types (i.e., SR141716 and AM630) combined with the Sativex-like phytocannabinoid combination. Our results indicated that the effects of this combination are blocked by these antagonists and hence that they do result from an activation of both CB(1) and CB(2) receptors. In summary, this study provides preclinical evidence in support of a beneficial effect of the cannabis-based medicine Sativex as a neuroprotective agent capable of delaying signs of disease progression in a proinflammatory model of HD, which adds to previous data obtained in models priming oxidative mechanisms of striatal injury. However, the interest here is that, in contrast with these previous data, we have now obtained evidence that both CB(1) and CB(2) receptors appear to be involved in the effects produced by a Sativex-like phytocannabinoid combination, thus stressing the broad-spectrum properties of Sativex that may combine activity at the CB(1) and/or CB(2) receptors with cannabinoid receptor-independent actions.

Towards the use of cannabinoids as antitumour agents

Various reports have shown that cannabinoids (the active components of marijuana and their derivatives) can reduce tumour growth and progression in animal models of cancer, in addition to their well-known palliative effects on some cancer-associated symptoms. This Opinion article discusses our current understanding of cannabinoids as antitumour agents, focusing on recent insights into the molecular mechanisms of action, including emerging resistance mechanisms and opportunities for combination therapy approaches. Such knowledge is required for the optimization of preclinical cannabinoid-based therapies and for the preliminary clinical testing that is currently underway.

The fatty acid amide hydrolase inhibitor URB597 exerts anti-inflammatory effects in hippocampus of aged rats and restores an age-related deficit in long-term potentiation

BACKGROUND

Several factors contribute to the deterioration in synaptic plasticity which accompanies age and one of these is neuroinflammation. This is characterized by increased microglial activation associated with increased production of proinflammatory cytokines like interleukin-1β (IL-1β). In aged rats these neuroinflammatory changes are associated with a decreased ability of animals to sustain long-term potentiation (LTP) in the dentate gyrus. Importantly, treatment of aged rats with agents which possess anti-inflammatory properties to decrease microglial activation, improves LTP. It is known that endocannabinoids, such as anandamide (AEA), have anti-inflammatory properties and therefore have the potential to decrease the age-related microglial activation. However, endocannabinoids are extremely labile and are hydrolyzed quickly after production. Here we investigated the possibility that inhibiting the degradation of endocannabinoids with the fatty acid amide hydrolase (FAAH) inhibitor, URB597, could ameliorate age-related increases in microglial activation and the associated decrease in LTP.

METHODS

Young and aged rats received subcutaneous injections of the FAAH inhibitor URB597 every second day and controls which received subcutaneous injections of 30% DMSO-saline every second day for 28 days. Long-term potentiation was recorded on day 28 and the animals were sacrificed. Brain tissue was analyzed for markers of microglial activation by PCR and for levels of endocannabinoids by liquid chromatography coupled to tandem mass spectrometry.

RESULTS

The data indicate that expression of markers of microglial activation, MHCII, and CD68 mRNA, were increased in the hippocampus of aged, compared with young, rats and that these changes were associated with increased expression of the proinflammatory cytokines interleukin (IL)-1β and tumor necrosis factor-α (TNFα) which were attenuated by treatment with URB597. Coupled with these changes, we observed an age-related decrease in LTP in the dentate gyrus which was partially restored in URB597-treated aged rats. The data suggest that enhancement of levels of endocannabinoids in the brain by URB597 has beneficial effects on synaptic function, perhaps by modulating microglial activation.

Cannabinoid receptors CB1 and CB2 form functional heteromers in brain

Exploring the role of cannabinoid CB(2) receptors in the brain, we present evidence of CB(2) receptor molecular and functional interaction with cannabinoid CB(1) receptors. Using biophysical and biochemical approaches, we discovered that CB(2) receptors can form heteromers with CB(1) receptors in transfected neuronal cells and in rat brain pineal gland, nucleus accumbens, and globus pallidus. Within CB(1)-CB(2) receptor heteromers expressed in a neuronal cell model, agonist co-activation of CB(1) and CB(2) receptors resulted in a negative cross-talk in Akt phosphorylation and neurite outgrowth. Moreover, one specific characteristic of CB(1)-CB(2) receptor heteromers consists of both the ability of CB(1) receptor antagonists to block the effect of CB(2) receptor agonists and, conversely, the ability of CB(2) receptor antagonists to block the effect of CB(1) receptor agonists, showing a bidirectional cross-antagonism phenomenon. Taken together, these data illuminate the mechanism by which CB(2) receptors can negatively modulate CB(1) receptor function.

Exogenous and endogenous cannabinoids suppress inhibitory neurotransmission in the human neocortex

Activation of CB(1) receptors on axon terminals by exogenous cannabinoids (eg, Δ(9)-tetrahydrocannabinol) and by endogenous cannabinoids (endocannabinoids) released by postsynaptic neurons leads to presynaptic inhibition of neurotransmission. The aim of this study was to characterize the effect of cannabinoids on GABAergic synaptic transmission in the human neocortex. Brain slices were prepared from neocortical tissues surgically removed to eliminate epileptogenic foci. Spontaneous GABAergic inhibitory postsynaptic currents (sIPSCs) were recorded in putative pyramidal neurons using patch-clamp techniques. To enhance the activity of cannabinoid-sensitive presynaptic axons, muscarinic receptors were continuously stimulated by carbachol. The synthetic cannabinoid receptor agonist WIN55212-2 decreased the cumulative amplitude of sIPSCs. The CB(1) antagonist rimonabant prevented this effect, verifying the involvement of CB(1) receptors. WIN55212-2 decreased the frequency of miniature IPSCs (mIPSCs) recorded in the presence of tetrodotoxin, but did not change their amplitude, indicating that the neurotransmission was inhibited presynaptically. Depolarization of postsynaptic pyramidal neurons induced a suppression of sIPSCs. As rimonabant prevented this suppression, it is very likely that it was due to endocannabinods acting on CB(1) receptors. This is the first demonstration that an exogenous cannabinoid inhibits synaptic transmission in the human neocortex and that endocannabinoids released by postsynaptic neurons suppress synaptic transmission in the human brain. Interferences of cannabinoid agonists and antagonists with synaptic transmission in the cortex may explain the cognitive and memory deficits elicited by these drugs.

Intrathecal cannabilactone CB(2)R agonist, AM1710, controls pathological pain and restores basal cytokine levels

Spinal glial and proinflammatory cytokine actions are strongly implicated in pathological pain. Spinal administration of the anti-inflammatory cytokine interleukin (IL)-10 abolishes pathological pain and suppresses proinflammatory IL-1β and tumor necrosis factor alpha (TNF-α). Drugs that bind the cannabinoid type-2 receptor (CB(2)R) expressed on spinal glia reduce mechanical hypersensitivity. To better understand the CB(2)R-related anti-inflammatory profile of key anatomical nociceptive regions, we assessed mechanical hypersensitivity and protein profiles following intrathecal application of the cannabilactone CB(2)R agonist, AM1710, in 2 animal models; unilateral sciatic nerve chronic constriction injury (CCI), and spinal application of human immunodeficiency virus-1 glycoprotein 120 (gp120), a model of peri-spinal immune activation. In CCI animals, lumbar dorsal spinal cord and corresponding dorsal root ganglia (DRG) were evaluated by immunohistochemistry for expression of IL-10, IL-1β, phosphorylated p38-mitogen-activated-kinase (p-p38MAPK), a pathway associated with proinflammatory cytokine production, glial cell markers, and degradative endocannabinoid enzymes, including monoacylglycerol lipase (MAGL). AM1710 reversed bilateral mechanical hypersensitivity. CCI revealed decreased IL-10 expression in dorsal spinal cord and DRG, while AM1710 resulted in increased IL-10, comparable to controls. Adjacent DRG and spinal sections revealed increased IL-1β, p-p38MAPK, glial markers, and/or MAGL expression, while AM1710 suppressed all but spinal p-p38MAPK and microglial activation. In spinal gp120 animals, AM1710 prevented bilateral mechanical hypersensitivity. For comparison to immunohistochemistry, IL-1β and TNF-α protein quantification from lumbar spinal and DRG homogenates was determined, and revealed increased DRG IL-1β protein levels from gp120, that was robustly prevented by AM1710 pretreatment. Cannabilactone CB(2)R agonists are emerging as anti-inflammatory agents with pain therapeutic implications.

Cannabinoids ameliorate disease progression in a model of multiple sclerosis in mice, acting preferentially through CB1 receptor-mediated anti-inflammatory effects

Multiple sclerosis (MS) is an autoimmune disease that affects the CNS and it is characterized by inflammation, demyelination, remyelination, gliosis and axonal damage that occur mainly in the spinal cord. Cannabinoids have been proposed as promising therapeutic agents in MS given their capability to alleviate specific MS symptoms (e.g., spasticity, pain). Although MS has been considered mainly an inflammatory disorder, recent evidence, however, revealed the importance of neurodegenerative events, opening the possibility that cannabinoid agonists, given their cytoprotective properties, may also serve to reduce oligodendrocyte death and axonal damage in MS. Thus, the treatment with WIN55,512-2, a potent CB(1) and CB(2) agonist, was reported to be effective to ameliorate tremor and spasticity in mice with chronic relapsing experimental autoimmune encephalomyelitis, a murine model of MS, but also to delay disease progression in this and other murine models of MS. The purpose of this investigation was to further explore the mechanism(s) underlying the amelioration in disease progression caused by WIN55,212-2. We have particularly focused on anti-glutamatergic and anti-inflammatory effects of this cannabinoid agonist. In this study, we used mice treated with myelin oligodendrocyte glycoprotein (MOG) that induces a progressive pattern of EAE and conducted the pharmacological experiments in early stages of the disease. As expected, the administration of WIN55,512-2 (5 mg/kg, i.p) had a positive effect in reducing neurological disability and improving motor coordination of EAE mice. Levels of glutamate and GABA in the spinal cord and also in the brainstem of EAE mice were similar to control animals, and, accordingly, they were not altered by the treatment with WIN55,212-2. However, EAE mice showed some subtle alterations in mRNA levels for the glutamate transporter GLT1 and, to a lesser extent, GLAST too, changes that were altered by the treatment with WIN55,212-2 in the spinal cord, but not in the brainstem. Regarding to inflammatory responses, EAE mice showed a marked up-regulation in mRNA levels for COX-2, inducible NOS and TNF-α in the spinal cord and the brainstem, these responses being attenuated after the treatment with WIN55,212-2. We also observed the presence of cell aggregates in the spinal cord of EAE mice that were significantly attenuated by the treatment with WIN55,212-2. Immunohistochemical analysis (with Iba-1 and Cd11b) of these aggregates indicated that they corresponded to microglia (resident macrophages) and peripheral macrophages. Lastly, experiments conducted with selective antagonists for the CB(1) (e.g. rimonabant) or CB(2) (e.g. AM-630) receptors revealed that WIN55,212-2 effects in EAE mice were mediated by the activation of CB(1) but not CB(2) receptors, as reflected the reversion of positive effects of this cannabinoid on neurological decline, TNF-α generation and accumulation of cell aggregates in the spinal cord with rimonabant, but not with AM-630. This was concordant with the lack of positive effects on neurological decline observed in EAE mice when they received HU-308, a selective CB(2) receptor agonist, instead WIN55,212-2. In summary, the treatment of EAE mice with the cannabinoid agonist WIN55,512-2 reduced their neurological disability and the progression of the disease. This effect was exerted through the activation of CB(1) receptors, which would exert a positive influence in the reduction of inflammatory events linked to the pathogenesis of this disease.