Activation of cannabinoid 2 receptors protects against cerebral ischemia by inhibiting neutrophil recruitment

The cannabinoid 2 receptor agonist β-caryophyllene modulates the inflammatory reaction induced by Mycobacterium bovis BCG by inhibiting neutrophil migration

OBJECTIVE AND DESIGN

β-Caryophyllene (BCP) is a sesquiterpene that binds to the cannabinoid 2 (CB₂) receptor and exerts anti-inflammatory effects. In this study, we investigated the anti-inflammatory effect of BCP and another CB₂ agonist, GP1a in inflammatory experimental model induced by Mycobacterium bovis (BCG).

METHODS

C57Bl/6 mice were pretreated orally with BCP (0.5-50 mg/kg) or intraperitonealy with GP1a (10 mg/kg) 1 h before the induction of pleurisy or pulmonary inflammation by BCG. The direct action of CB₂ agonists on neutrophils function was evaluated in vitro.

RESULTS

β-Caryophyllene (50 mg/kg) impaired BCG-induced neutrophil accumulation in pleurisy without affecting mononuclear cells or the production of TNF-α and CCL2/MCP-1. However, BCP inhibited CXCL1/KC, leukotriene B₄ (LTB₄), IL-12, and nitric oxide production. GP1a had a similar effect to BCP. Preincubation of neutrophils with BCP (10 µM) impaired chemotaxis toward LTB₄ and adhesion to endothelial cells stimulated with TNF-α, and both, BCP and GP1a, impaired LTB₄-induced actin polymerization.

CONCLUSION

These results suggest that the CB₂ receptor may represent a new target for modulating the inflammatory reaction induced by mycobacteria.

Cannabinoid 2 receptor activation reduces leukocyte adhesion and improves capillary perfusion in the iridial microvasculature during systemic inflammation

BACKGROUND

Leukocyte adhesion to the endothelium and decreased microvascular blood flow causing microcirculatory dysfunction are hallmarks of systemic inflammation. We studied the impact of cannabinoid receptor activation on the iridial microcirculation, which is accessible non-invasively in vivo, in systemic inflammation induced by endotoxin challenge.

METHODS

40 Lewis rats were used in the experiments. Endotoxemia was induced by 2 mg/kg i.v. lipopolysaccharide (LPS). Cannabinoid receptors (CBRs) were stimulated by i.v. administration of WIN 55212-2 (WIN; 1 mg/kg). CB1R antagonist (AM281; 2.5 mg/kg i.v.) or CB2R antagonist (AM630; 2.5 mg/kg i.v.) treatment prior to WIN was applied to identify the anti-inflammatory effects underlying each CBR subtype. Leukocyte-endothelial interactions were examined in rat iridial microvas culature by intravital microscopy at baseline and 1 and 2 h post-LPS. Additionally, systemic (mean arterial pressure, heart rate) and local (laser Doppler flow) hemodynamic variables were measured prior to and during cannabinoid treatments.

RESULTS

Endotoxemia resulted in severe inflammation as shown by significantly increased numbers of adherent leukocytes at 1 and 2 h observation time post-LPS challenge and decreased microcirculatory blood flow at 2 h within the iridial microcirculation. WIN treatment significantly reduced leukocyte adhesion in iridial microvessels with a diameter greater and less than 25 μm during endotoxemia (p <  0.05). Pre-treatment of animals by CB1R antagonist, AM281, did not affect WIN effects on LPS-induced leukocyte adhesion. When pre-treated with the CB2R antagonist, AM630, a reversal of the WIN-induced reduction in leukocyte adhesion was noticed in vessels with a diameter of less than 25 μm (p <  0.05). Cannabinoid treatment significantly increased the local iridial microcirculatory blood flow 2 hours after systemic LPS administration (p <  0.05).

CONCLUSIONS

Systemic administration of the CBR agonist, WIN, decreased leukocyte-adhesion and improved iridial microvascular blood flow. This effect is most likely mediated by CB2R activation. Our findings indicate that the iris microvasculature can serve as a model to study the microcirculation during systemic inflammation and help to identify potential therapies to treat microcirculatory dysfunction in diseases such as sepsis.

Post-ischemic treatment of WIB801C, standardized Cordyceps extract, reduces cerebral ischemic injury via inhibition of inflammatory cell migration

ETHNOPHARMACOLOGICAL RELEVANCE

Anti-inflammatory therapy has been intensively investigated as a potential strategy for treatment of cerebral stroke. However, despite many positive outcomes reported in animal studies, anti-inflammatory treatments have not proven successful in humans as yet. Although immunomodulatory activity and safety of Cordyceps species (Chinese caterpillar fungi) have been proven in clinical trials and traditional Asian prescriptions for inflammatory diseases, its anti-ischemic effect remains elusive.

AIM OF THE STUDY

In the present study, therefore, we investigated the potential therapeutic efficacy of WIB801C, the standardized extract of Cordyceps militaris, for treatment of cerebral ischemic stroke.

MATERIALS AND METHODS

The anti-chemotactic activity of WIB801C was assayed in cultured rat microglia/macrophages. Sprague-Dawley rats were subjected to ischemic stroke via either transient (1.5-h tMCAO and subsequent 24-h reperfusion) or permanent middle cerebral artery occlusion (pMCAO for 24-h without reperfusion). WIB801C was orally administered twice at 3- and 8-h (50mg/kg each) after the onset of MCAO. Infarct volume, edema, blood brain barrier and white matter damages, neurological deficits, and long-term survival rates were investigated. The infiltration of inflammatory cells into ischemic lesions was assayed by immunostaining.

RESULTS

WIB801C significantly decreased migration of cultured microglia/macrophages. This anti-chemotactic activity of WIB-801C was not mediated via adenosine A3 receptors, although cordycepin, the major ingredient of WIB801C, is known as an adenosine receptor agonist. Post-ischemic treatment with WIB801C significantly reduced the infiltration of ED-1-and MPO-positive inflammatory cells into ischemic lesions in tMCAO rats. WIB801C-treated rats exhibited significantly decreased infarct volume and cerebral edema, less white matter and blood-brain barrier damages, and improved neurological deficits. WIB801C also improved survival rates over 34 days after ischemia onset. A significant reduction in infarct volume and neurobehavioral deficits by WIB801C was also observed in rats subjected to pMCAO.

CONCLUSIONS

In summary, post-ischemic treatment of WIB801C reduced infiltration of inflammatory cells into ischemic lesions via inhibition of chemotaxis, which confers long-lasting histological and neurological protection in ischemic brain. WIB801C may be a promising anti-ischemic drug candidate with clinically relevant therapeutic time window and safety.

Role of neutrophils in atherogenesis: an update

BACKGROUND

The role of neutrophils in the beginning and the progression of the atherosclerotic process did not receive much attention until the last years. On the contrary, recent data, in both the experimental animals and humans, suggest important effects of these cells with possible clinical consequences.

MATERIALS AND METHODS

This narrative review was based on the papers found on PubMed and MEDLINE up to July 2015. The search terms used were 'neutrophil, atherosclerosis' in combination with 'recruitment, chemokine, plaque destabilization and pathophysiology'.

RESULTS

Different models demonstrate the presence and the actions of neutrophils in the early steps of the atherogenesis confirming the fundamental role of these cells in the response of the innate immune system to different pathogens (in this context the modified lipoproteins). However, also the late phases of the atherosclerotic process, in particular the destabilization of a mature plaque, seem to be modulated by the neutrophils, possibly through the interaction with recently discovered biological systems such as the endocannabinoids.

CONCLUSIONS

The understanding of the mechanisms involved in the modulation exerted by neutrophils in atherosclerosis is pivotal in terms of the complete definition of the overall picture. This approach will certainly give us new targets and new pharmacological opportunities for the anti-inflammatory strategy of the cardiovascular prevention.

CB2 receptor activation prevents glial-derived neurotoxic mediator production, BBB leakage and peripheral immune cell infiltration and rescues dopamine neurons in the MPTP model of Parkinson's disease

The cannabinoid (CB2) receptor type 2 has been proposed to prevent the degeneration of dopamine neurons in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice. However, the mechanisms underlying CB2 receptor-mediated neuroprotection in MPTP mice have not been elucidated. The mechanisms underlying CB2 receptor-mediated neuroprotection of dopamine neurons in the substantia nigra (SN) were evaluated in the MPTP mouse model of Parkinson's disease (PD) by immunohistochemical staining (tyrosine hydroxylase, macrophage Ag complex-1, glial fibrillary acidic protein, myeloperoxidase (MPO), and CD3 and CD68), real-time PCR and a fluorescein isothiocyanate-labeled albumin assay. Treatment with the selective CB2 receptor agonist JWH-133 (10 μg kg(-1), intraperitoneal (i.p.)) prevented MPTP-induced degeneration of dopamine neurons in the SN and of their fibers in the striatum. This JWH-133-mediated neuroprotection was associated with the suppression of blood-brain barrier (BBB) damage, astroglial MPO expression, infiltration of peripheral immune cells and production of inducible nitric oxide synthase, proinflammatory cytokines and chemokines by activated microglia. The effects of JWH-133 were mimicked by the non-selective cannabinoid receptor WIN55,212 (10 μg kg(-1), i.p.). The observed neuroprotection and inhibition of glial-mediated neurotoxic events were reversed upon treatment with the selective CB2 receptor antagonist AM630, confirming the involvement of the CB2 receptor. Our results suggest that targeting the cannabinoid system may be beneficial for the treatment of neurodegenerative diseases, such as PD, that are associated with glial activation, BBB disruption and peripheral immune cell infiltration.

Cannabinoids to treat spinal cord injury

Spinal cord injury (SCI) is a devastating condition for which there is no standard treatment beyond rehabilitation strategies. In this review, we discuss the current knowledge on the use of cannabinoids to treat this condition. The endocannabinoid system is expressed in the intact spinal cord, and it is dramatically upregulated after lesion. Endogenous activation of this system counteracts secondary damage following SCI, and treatments with endocannabinoids or synthetic cannabinoid receptor agonists promote a better functional outcome in experimental models. The use of cannabinoids in SCI is a new research field and many questions remain open. Here, we discuss caveats and suggest some future directions that may help to understand the role of cannabinoids in SCI and how to take advantage of this system to regain functions after spinal cord damage.

Cannabinoid receptor-specific mechanisms to alleviate pain in sickle cell anemia via inhibition of mast cell activation and neurogenic inflammation

Sickle cell anemia is a manifestation of a single point mutation in hemoglobin, but inflammation and pain are the insignia of this disease which can start in infancy and continue throughout life. Earlier studies showed that mast cell activation contributes to neurogenic inflammation and pain in sickle mice. Morphine is the common analgesic treatment but also remains a major challenge due to its side effects and ability to activate mast cells. We, therefore, examined cannabinoid receptor-specific mechanisms to mitigate mast cell activation, neurogenic inflammation and hyperalgesia, using HbSS-BERK sickle and cannabinoid receptor-2-deleted sickle mice. We show that cannabinoids mitigate mast cell activation, inflammation and neurogenic inflammation in sickle mice via both cannabinoid receptors 1 and 2. Thus, cannabinoids influence systemic and neural mechanisms, ameliorating the disease pathobiology and hyperalgesia in sickle mice. This study provides 'proof of principle' for the potential of cannabinoid/cannabinoid receptor-based therapeutics to treat several manifestations of sickle cell anemia.

Tissue plasminogen activator followed by antioxidant-loaded nanoparticle delivery promotes activation/mobilization of progenitor cells in infarcted rat brain

Inherent neuronal and circulating progenitor cells play important roles in facilitating neuronal and functional recovery post stroke. However, this endogenous repair process is rather limited, primarily due to unfavorable conditions in the infarcted brain involving reactive oxygen species (ROS)-mediated oxidative stress and inflammation following ischemia/reperfusion injury. We hypothesized that during reperfusion, effective delivery of antioxidants to ischemic brain would create an environment without such oxidative stress and inflammation, thus promoting activation and mobilization of progenitor cells in the infarcted brain. We administered recombinant human tissue-type plasminogen activator (tPA) via carotid artery at 3 h post stroke in a thromboembolic rat model, followed by sequential administration of the antioxidants catalase (CAT) and superoxide dismutase (SOD), encapsulated in biodegradable nanoparticles (nano-CAT/SOD). Brains were harvested at 48 h post stroke for immunohistochemical analysis. Ipsilateral brain slices from animals that had received tPA + nano-CAT/SOD showed a widespread distribution of glial fibrillary acidic protein-positive cells (with morphology resembling radial glia-like neural precursor cells) and nestin-positive cells (indicating the presence of immature neurons); such cells were considerably fewer in untreated animals or those treated with tPA alone. Brain sections from animals receiving tPA + nano-CAT/SOD also showed much greater numbers of SOX2- and nestin-positive progenitor cells migrating from subventricular zone of the lateral ventricle and entering the rostral migratory stream than in t-PA alone treated group or untreated control. Further, animals treated with tPA + nano-CAT/SOD showed far fewer caspase-positive cells and fewer neutrophils than did other groups, as well as an inhibition of hippocampal swelling. These results suggest that the antioxidants mitigated the inflammatory response, protected neuronal cells from undergoing apoptosis, and inhibited edema formation by protecting the blood-brain barrier from ROS-mediated reperfusion injury. A longer-term study would enable us to determine if our approach would assist progenitor cells to undergo neurogenesis and to facilitate neurological and functional recovery following stroke and reperfusion injury.

New horizons for newborn brain protection: enhancing endogenous neuroprotection

Intrapartum-related events are the third leading cause of childhood mortality worldwide and result in one million neurodisabled survivors each year. Infants exposed to a perinatal insult typically present with neonatal encephalopathy (NE). The contribution of pure hypoxia-ischaemia (HI) to NE has been debated; over the last decade, the sensitising effect of inflammation in the aetiology of NE and neurodisability is recognised. Therapeutic hypothermia is standard care for NE in high-income countries; however, its benefit in encephalopathic babies with sepsis or in those born following chorioamnionitis is unclear. It is now recognised that the phases of brain injury extend into a tertiary phase, which lasts for weeks to years after the initial insult and opens up new possibilities for therapy.There has been a recent focus on understanding endogenous neuroprotection and how to boost it or to supplement its effectors therapeutically once damage to the brain has occurred as in NE. In this review, we focus on strategies that can augment the body's own endogenous neuroprotection. We discuss in particular remote ischaemic postconditioning whereby endogenous brain tolerance can be activated through hypoxia/reperfusion stimuli started immediately after the index hypoxic-ischaemic insult. Therapeutic hypothermia, melatonin, erythropoietin and cannabinoids are examples of ways we can supplement the endogenous response to HI to obtain its full neuroprotective potential. Achieving the correct balance of interventions at the correct time in relation to the nature and stage of injury will be a significant challenge in the next decade.

Non-Selective Cannabinoid Receptor Antagonists, Hinokiresinols Reduce Infiltration of Microglia/Macrophages into Ischemic Brain Lesions in Rat via Modulating 2-Arachidonolyglycerol-Induced Migration and Mitochondrial Activity

Growing evidence suggests that therapeutic strategies to modulate the post-ischemic inflammatory responses are promising approaches to improve stroke outcome. Although the endocannabinoid system has been emerged as an endogenous therapeutic target to regulate inflammation after stroke insult, the downstream mechanisms and their potentials for therapeutic intervention remain controversial. Here we identified trans- and cis-hinokiresinols as novel non-selective antagonists for two G-protein-coupled cannabinoid receptors, cannabinoid receptor type 1 and type 2. The Electric Cell-substrate Impedance Sensing and Boyden chamber migration assays using primary microglial cultures revealed that both hinokiresinols significantly inhibited an endocannabinoid, 2-arachidonoylglycerol-induced migration. Hinokiresinols modulated 2-arachidonoylglycerol-induced mitochondrial bioenergetics in microglia as evidenced by inhibition of ATP turnover and reduction in respiratory capacity, thereby resulting in impaired migration activity. In rats subjected to transient middle cerebral artery occlusion (1.5-h) followed by 24-h reperfusion, post-ischemic treatment with hinokiresinols (2 and 7-h after the onset of ischemia, 10 mg/kg) significantly reduced cerebral infarct and infiltration of ED1-positive microglial/macrophage cells into cerebral ischemic lesions in vivo. Co-administration of exogenous 2-AG (1 mg/kg, i.v., single dose at 2 h after starting MCAO) abolished the protective effect of trans-hinokiresionol. These results suggest that hinokiresinols may serve as stroke treatment by targeting the endocannabinoid system. Alteration of mitochondrial bioenergetics and consequent inhibition of inflammatory cells migration may be a novel mechanism underlying anti-ischemic effects conferred by cannabinoid receptor antagonists.

Cannabinoids in Neurodegenerative Disorders and Stroke/Brain Trauma: From Preclinical Models to Clinical Applications

Cannabinoids form a singular family of plant-derived compounds (phytocannabinoids), endogenous signaling lipids (endocannabinoids), and synthetic derivatives with multiple biological effects and therapeutic applications in the central and peripheral nervous systems. One of these properties is the regulation of neuronal homeostasis and survival, which is the result of the combination of a myriad of effects addressed to preserve, rescue, repair, and/or replace neurons, and also glial cells against multiple insults that may potentially damage these cells. These effects are facilitated by the location of specific targets for the action of these compounds (e.g., cannabinoid type 1 and 2 receptors, endocannabinoid inactivating enzymes, and nonendocannabinoid targets) in key cellular substrates (e.g., neurons, glial cells, and neural progenitor cells). This potential is promising for acute and chronic neurodegenerative pathological conditions. In this review, we will collect all experimental evidence, mainly obtained at the preclinical level, supporting that different cannabinoid compounds may be neuroprotective in adult and neonatal ischemia, brain trauma, Alzheimer's disease, Parkinson's disease, Huntington's chorea, and amyotrophic lateral sclerosis. This increasing experimental evidence demands a prompt clinical validation of cannabinoid-based medicines for the treatment of all these disorders, which, at present, lack efficacious treatments for delaying/arresting disease progression, despite the fact that the few clinical trials conducted so far with these medicines have failed to demonstrate beneficial effects.

Downstream effects of endocannabinoid on blood cells: implications for health and disease

Endocannabinoids (eCBs), among which N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG) are the most biologically active members, are polyunsaturated lipids able to bind cannabinoid, vanilloid and peroxisome proliferator-activated receptors. Depending on the target engaged, these bioactive mediators can regulate different signalling pathways, at both central and peripheral levels. The biological action of eCBs is tightly controlled by a plethora of metabolic enzymes which, together with the molecular targets of these substances, form the so-called "endocannabinoid system". The ability of eCBs to control manifold peripheral functions has received a great deal of attention, especially in the light of their widespread distribution in the body. In particular, eCBs are important regulators in blood, where they modulate haematopoiesis, platelet aggregation and apoptosis, as well as chemokine release and migration of immunocompetent cells. Here, we shall review the current knowledge on the pathophysiological roles of eCBs in blood. We shall also discuss the involvement of eCBs in those disorders affecting the haematological system, including cancer and inflammation. Knowledge gained to date underlines a fundamental role of the eCB system in blood, thus suggesting that it may represent a therapeutic promise for a broad range of diseases involving impaired hematopoietic cell functions.

A CB2-Selective Cannabinoid Suppresses T-Cell Activities and Increases Tregs and IL-10

We have previously shown that agonists selective for the cannabinoid receptor 2 (CB2), including O-1966, inhibit the Mixed Lymphocyte Reaction (MLR), an in vitro correlate of organ graft rejection, predominantly through effects on T-cells. Current studies explored the mechanism of this immunosuppression by O-1966 using mouse spleen cells. Treatment with O-1966 dose-relatedly decreased levels of the active nuclear forms of the transcription factors NF-κB and NFAT in wild-type T-cells, but not T-cells from CB2 knockout (CB2R k/o) mice. Additionally, a gene expression profile of purified T-cells from MLR cultures generated using a PCR T-cell activation array showed that O-1966 decreased mRNA expression of CD40 ligand and CyclinD3, and increased mRNA expression of Src-like-adaptor 2 (SLA2), Suppressor of Cytokine Signaling 5 (SOCS5), and IL-10. The increase in IL-10 was confirmed by measuring IL-10 protein levels in MLR culture supernatants. Further, an increase in the percentage of regulatory T-cells (Tregs) was observed in MLR cultures. Pretreatment with anti-IL-10 resulted in a partial reversal of the inhibition of proliferation and blocked the increase of Tregs. Additionally, O-1966 treatment caused a dose-related decrease in the expression of CD4 in MLR cultures from wild-type, but not CB2R k/o, mice. These data support the potential of CB2-selective agonists as useful therapeutic agents to prolong graft survival in transplant patients, and strengthens their potential as a new class of immunosuppressive agents with broader applicability.

Complexity of the cell-cell interactions in the innate immune response after cerebral ischemia

In response to brain ischemia a cascade of signals leads to the activation of the brain innate immune system and to the recruitment of blood borne derived cells to the ischemic tissue. These processes have been increasingly shown to play a role on stroke pathogenesis. Here, we discuss the key features of resident microglia and different leukocyte subsets implicated in cerebral ischemia with special emphasis of neutrophils, monocytes and microglia. We focus on how leukocytes are recruited to injured brain through a complex interplay between endothelial cells, platelets and leukocytes and describe different strategies used to inhibit their recruitment. Finally, we discuss the possible existence of different leukocyte subsets in the ischemic tissue and the repercussion of different myeloid phenotypes on stroke outcome. The knowledge of the nature of these heterogeneous cell-cell interactions may open new lines of investigation on new therapies to promote protective immune responses and tissue repair after cerebral ischemia or to block harmful responses. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

Regulation of inflammation by cannabinoids, the endocannabinoids 2-arachidonoyl-glycerol and arachidonoyl-ethanolamide, and their metabolites

2-Arachidonoyl-glycerol (2-AG) and arachidonyl-ethanolamide (AEA) are endocannabinoids that have been implicated in many physiologic disorders, including obesity, metabolic syndromes, hepatic diseases, pain, neurologic disorders, and inflammation. Their immunomodulatory effects are numerous and are not always mediated by cannabinoid receptors, reflecting the presence of an arachidonic acid (AA) molecule in their structure, the latter being the precursor of numerous bioactive lipids that are pro- or anti-inflammatory. 2-AG and AEA can thus serve as a source of AA but can also be metabolized by most eicosanoid biosynthetic enzymes, yielding additional lipids. In this regard, enhancing endocannabinoid levels by using endocannabinoid hydrolysis inhibitors is likely to augment the levels of these lipids that could regulate inflammatory cell functions. This review summarizes the metabolic pathways involved in the biosynthesis and metabolism of AEA and 2-AG, as well as the biologic effects of the 2-AG and AEA lipidomes in the regulation of inflammation.

The HIF-1/glial TIM-3 axis controls inflammation-associated brain damage under hypoxia

Inflammation is closely related to the extent of damage following cerebral ischaemia, and the targeting of this inflammation has emerged as a promising therapeutic strategy. Here, we present that hypoxia-induced glial T-cell immunoglobulin and mucin domain protein (TIM)-3 can function as a modulator that links inflammation and subsequent brain damage after ischaemia. We find that TIM-3 is highly expressed in hypoxic brain regions of a mouse cerebral hypoxia-ischaemia (H/I) model. TIM-3 is distinctively upregulated in activated microglia and astrocytes, brain resident immune cells, in a hypoxia-inducible factor (HIF)-1-dependent manner. Notably, blockade of TIM-3 markedly reduces infarct size, neuronal cell death, oedema formation and neutrophil infiltration in H/I mice. Hypoxia-triggered neutrophil migration and infarction are also decreased in HIF-1α-deficient mice. Moreover, functional neurological deficits after H/I are significantly improved in both anti-TIM-3-treated mice and myeloid-specific HIF-1α-deficient mice. Further understanding of these insights could serve as the basis for broadening the therapeutic scope against hypoxia-associated brain diseases.

Nutritional or pharmacological activation of HCA(2) ameliorates neuroinflammation

Neuroinflammation is a pathology common to many neurological diseases, including multiple sclerosis (MS) and stroke. However, therapeutic attempts to modulate neuroinflammation have proved difficult. Neuroinflammatory cells express HCA2, a receptor for the endogenous neuroprotective ketone body β-hydroxybutyrate (BHB) as well as for the drugs dimethyl fumarate (DMF) and nicotinic acid, which have established efficacy in the treatment of MS and experimental stroke, respectively. This review summarizes the evidence that HCA2 is involved in the therapeutic effects of DMF, nicotinic acid, and ketone bodies in reducing neuroinflammation. Furthermore, we discuss the mechanisms underlying the beneficial effects of HCA2 activation in neuroinflammatory diseases and the therapeutic potential of recently developed synthetic ligands of HCA2.

Cannabinoids in experimental stroke: a systematic review and meta-analysis

Cannabinoids (CBs) show promise as neuroprotectants with some agents already licensed in humans for other conditions. We systematically reviewed CBs in preclinical stroke to guide further experimental protocols. We selected controlled studies assessing acute administration of CBs for experimental stroke, identified through systematic searches. Data were extracted on lesion volume, outcome and quality, and analyzed using random effect models. Results are expressed as standardized mean difference (SMD) with 95% confidence intervals (CIs). In all, 144 experiments (34 publications) assessed CBs on infarct volume in 1,473 animals. Cannabinoids reduced infarct volume in transient (SMD -1.41 (95% CI -1.71), -1.11) P<0.00001) and permanent (-1.67 (-2.08, -1.27), P<0.00001) ischemia and in all subclasses: endocannabinoids (-1.72 (-2.62, -0.82), P=0.0002), CB1/CB2 ligands (-1.75 (-2.19, -1.31), P<0.00001), CB2 ligands (-1.65 (-2.09, -1.22), P<0.00001), cannabidiol (-1.20 (-1.63, -0.77), P<0.00001), Δ(9)-tetrahydrocannabinol (-1.43 (-2.01, -0.86), P<0.00001), and HU-211 (-2.90 (-4.24, -1.56), P<0.0001). Early and late neuroscores significantly improved with CB use (-1.27 (-1.58, -0.95), P<0.00001; -1.63 (-2.64, -0.62), P<0.002 respectively) and there was no effect on survival. Statistical heterogeneity and publication bias was present, median study quality was 4 (range 1 to 6/8). Overall, CBs significantly reduced infarct volume and improve functional outcome in experimental stroke. Further studies in aged, female and larger animals, with other co-morbidities are required.

Very-late-antigen-4 (VLA-4)-mediated brain invasion by neutrophils leads to interactions with microglia, increased ischemic injury and impaired behavior in experimental stroke

Neuronal injury from ischemic stroke is aggravated by invading peripheral immune cells. Early infiltrates of neutrophil granulocytes and T-cells influence the outcome of stroke. So far, however, neither the timing nor the cellular dynamics of neutrophil entry, its consequences for the invaded brain area, or the relative importance of T-cells has been extensively studied in an intravital setting. Here, we have used intravital two-photon microscopy to document neutrophils and brain-resident microglia in mice after induction of experimental stroke. We demonstrated that neutrophils immediately rolled, firmly adhered, and transmigrated at sites of endothelial activation in stroke-affected brain areas. The ensuing neutrophil invasion was associated with local blood-brain barrier breakdown and infarct formation. Brain-resident microglia recognized both endothelial damage and neutrophil invasion. In a cooperative manner, they formed cytoplasmic processes to physically shield activated endothelia and trap infiltrating neutrophils. Interestingly, the systemic blockade of very-late-antigen-4 immediately and very effectively inhibited the endothelial interaction and brain entry of neutrophils. This treatment thereby strongly reduced the ischemic tissue injury and effectively protected the mice from stroke-associated behavioral impairment. Behavioral preservation was also equally well achieved with the antibody-mediated depletion of myeloid cells or specifically neutrophils. In contrast, T-cell depletion more effectively reduced the infarct volume without improving the behavioral performance. Thus, neutrophil invasion of the ischemic brain is rapid, massive, and a key mediator of functional impairment, while peripheral T-cells promote brain damage. Acutely depleting T-cells and inhibiting brain infiltration of neutrophils might, therefore, be a powerful early stroke treatment.

Cannabinoid Signaling and Neuroinflammatory Diseases: A Melting pot for the Regulation of Brain Immune Responses

The concept of the central nervous system (CNS) as an immune-privileged site, essentially due to the presence of the blood brain barrier, appears to be overly simplistic. Indeed, within healthy CNS immune activities are permitted and are required for neuronal function and host defense, not only due to the presence of the resident innate immune cells of the brain, but also by virtue of a complex cross-talk of the CNS with peripheral immune cells. Nonetheless, long-standing and persisting neuroinflammatory responses are most often detrimental and characterize several neuroinflammatory diseases, including multiple sclerosis, Alzheimer's disease and amyotrophic lateral sclerosis. A growing body of evidence suggests that Cannabis sativa-derived phytocannabinoids, as well as synthetic cannabinoids, are endowed with significant immunoregulatory and anti-inflammatory properties, both in peripheral tissues and in the CNS, through the activation of cannabinoid receptors. In this review, the immunomodulatory effects of cannabinoid signaling on the most relevant brain immune cells will be discussed. In addition, the impact of cannabinoid regulation on the overall integration of the manifold brain immune responses will also be highlighted, along with the implication of these compounds as potential agents for the management of neuroinflammatory disorders.

Genetic Manipulation of the Endocannabinoid System

The physiological and pathophysiological functions of the endocannabinoid system have been studied extensively using transgenic and targeted knockout mouse models. The first gene deletions of the cannabinoid CB(1) receptor were described in the late 1990s, soon followed by CB(2) and FAAH mutations in early 2000. These mouse models helped to elucidate the fundamental role of endocannabinoids as retrograde transmitters in the CNS and in the discovery of many unexpected endocannabinoid functions, for example, in the skin, bone and liver. We now have knockout mouse models for almost every receptor and enzyme of the endocannabinoid system. Conditional mutant mice were mostly developed for the CB(1) receptor, which is widely expressed on many different neurons, astrocytes and microglia, as well as on many cells outside the CNS. These mouse strains include "floxed" CB(1) alleles and mice with a conditional re-expression of CB(1). The availability of these mice made it possible to decipher the function of CB(1) in specific neuronal circuits and cell populations or to discriminate between central and peripheral effects. Many of the genetic mouse models were also used in combination with viral expression systems. The purpose of this review is to provide a comprehensive overview of the existing genetic models and to summarize some of the most important discoveries that were made with these animals.

Cannabinoid receptor type 2 agonist attenuates apoptosis by activation of phosphorylated CREB-Bcl-2 pathway after subarachnoid hemorrhage in rats

Early brain injury (EBI) which comprises of vasogenic edema and apoptotic cell death is an important component of subarachnoid hemorrhage (SAH) pathophysiology. This study evaluated whether cannabinoid receptor type 2 (CB2R) agonist, JWH133, attenuates EBI after SAH and whether CB2R stimulation reduces pro-apoptotic caspase-3 via up-regulation of cAMP response element-binding protein (CREB)-Bcl-2 signaling pathway. Male Sprague-Dawley rats (n=123) were subjected to SAH by endovascular perforation. Rats received vehicle or JWH133 at 1h after SAH. Neurological deficits and brain water content were evaluated at 24h after SAH. Western blot was performed to quantify phosphorylated CREB (pCREB), Bcl-2, and cleaved caspase-3 levels. Neuronal cell death was evaluated with terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end-labeling staining. Additionally, CREB siRNA was administered to manipulate the proposed pathway. JWH133 (1.0mg/kg) improved neurological deficits and reduced brain water content in left hemisphere 24h after SAH. JWH133 significantly increased activated CREB (pCREB) and Bcl-2 levels and significantly decreased cleaved caspase-3 levels in left hemisphere 24h after SAH. CREB siRNA reversed the effects of treatment. TUNEL positive neurons in the cortex were reduced with JWH133 treatment. Thus, CB2R stimulation attenuated EBI after SAH possibly through activation of pCREB-Bcl-2 pathway.

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.

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

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

Cancer risks from diabetes therapies: evaluating the evidence

Epidemiological studies have identified positive associations between diabetes, obesity and cancer. Insulin, metformin and thiazolidinediones (TDZs) are among the major diabetes therapies that improve glycaemic control by acting via molecular targets including the insulin receptor and insulin-like growth factor pathways, adenosine monophosphate-activated kinase and peroxisome proliferator-activated receptor γ. It is well-established that clinical application of insulin and TDZs is associated with weight gain, but the potential of these therapies to promote tumourigenesis is less well-studied. In addition, although anti-tumour properties of metformin have been proposed, recently published data do not support a protective effect of metformin against cancer in diabetic patients. Given that diabetes and cancer each account for 8% and 13% of global deaths and there is a substantial financial burden incurred by both disorders, developing diabetes therapies that are safe, efficacious and cost-effective has never been more desirable. This timely review examines recent progress in delineating the molecular mechanisms responsible for the anti-diabetic actions of insulin, metformin and TZDs and considers evidence implicating these therapies in cell transformation and tumourigenesis. In addition, since the endocannabinoid signalling system (ECS) is now considered a therapeutic target and biomarker candidate for hyperglycaemia, obesity and cell growth, a brief section covering recent scientific advances regarding the ECS, particularly its functions in regulating glucose metabolism and cell survival, is also included in this review.

Cannabinoid type 2 receptor stimulation attenuates brain edema by reducing cerebral leukocyte infiltration following subarachnoid hemorrhage in rats

Early brain injury (EBI), following subarachnoid hemorrhage (SAH), comprises blood-brain barrier (BBB) disruption and consequent edema formation. Peripheral leukocytes can infiltrate the injured brain, thereby aggravating BBB leakage and neuroinflammation. Thus, anti-inflammatory pharmacotherapies may ameliorate EBI and provide neuroprotection after SAH. Cannabinoid type 2 receptor (CB2R) agonism has been shown to reduce neuroinflammation; however, the precise protective mechanisms remain to be elucidated. This study aimed to evaluate whether the selective CB2R agonist, JWH133 can ameliorate EBI by reducing brain-infiltrated leukocytes after SAH. Adult male Sprague-Dawley rats were randomly assigned to the following groups: sham-operated, SAH with vehicle, SAH with JWH133 (1.0mg/kg), or SAH with a co-administration of JWH133 and selective CB2R antagonist SR144528 (3.0mg/kg). SAH was induced by endovascular perforation, and JWH133 was administered 1h after surgery. Neurological deficits, brain water content, Evans blue dye extravasation, and Western blot assays were evaluated at 24h after surgery. JWH133 improved neurological scores and reduced brain water content; however, SR144528 reversed these treatment effects. JWH133 reduced Evans blue dye extravasation after SAH. Furthermore, JWH133 treatment significantly increased TGF-β1 expression and prevented an SAH-induced increase in E-selectin and myeloperoxidase. Lastly, SAH resulted in a decreased expression of the tight junction protein zonula occludens-1 (ZO-1); however, JWH133 treatment increased the ZO-1 expression. We suggest that CB2R stimulation attenuates neurological outcome and brain edema, by suppressing leukocyte infiltration into the brain through TGF-β1 up-regulation and E-selectin reduction, resulting in protection of the BBB after SAH.

The cannabinoid CB2 receptor agonist GW405833 does not ameliorate brain damage induced by hypoxia-ischemia in rats

The cannabinoid CB2 receptor has been under investigation as a potential target for neuroprotection with the suppression of neuroinflammation as the proposed mechanism of action. Several studies have now reported that CB2 agonists are neuroprotective in models of cerebral ischemia. However, these studies have tended to measure brain infarctions in rodents 1-3 days after drug administration and have not assessed behavioral outcomes. As it has been shown that apparent protection soon after injury is not necessarily correlated with improved outcome after several weeks, we tested the CB2 selective agonist GW405833 in a model of cerebral hypoxia-ischemia, and assessed histological and behavioral outcomes 15 days after injury. Many putatively neuroprotective drugs have failed to translate from promising preclinical results to clinical success. We designed our experiments to not only stringently test CB2 mediated neuroprotection, but also to test several drug administration regimens to maximize the chance of detecting any therapeutic effect. However, GW405833 failed to provide neuroprotection in any of our experiments. These results challenge how far the results of earlier studies into CB2 mediated neuroprotection as measured at early time points may be extrapolated to later time points or to other models.

Hydroxycarboxylic acid receptor 2 mediates dimethyl fumarate's protective effect in EAE

Taken orally, the drug dimethyl fumarate (DMF) has been shown to improve functional outcomes for patients with MS; however, it is unclear how DMF mediates a protective effect. DMF and, more so, its active metabolite, monomethyl fumarate, are known agonists of the hydroxycarboxylic acid receptor 2 (HCA₂), a G protein-coupled membrane receptor. Here, we evaluated the contribution of HCA₂ in mediating the protective effect afforded by DMF in EAE, a mouse model of MS. DMF treatment reduced neurological deficit, immune cell infiltration, and demyelination of the spinal cords in wild-type mice, but not in Hca2⁻/⁻ mice, indicating that HCA₂ is required for the therapeutic effect of DMF. In particular, DMF decreased the number of infiltrating neutrophils in a HCA₂-dependent manner, likely by interfering with neutrophil adhesion to endothelial cells and chemotaxis. Together, our data indicate that HCA₂ mediates the therapeutic effects of DMF in EAE. Furthermore, identification of HCA₂ as a molecular target may help to optimize MS therapy.

Cannabinoids inhibit T-cells via cannabinoid receptor 2 in an in vitro assay for graft rejection, the mixed lymphocyte reaction

Cannabinoids are known to have anti-inflammatory and immunomodulatory properties. Cannabinoid receptor 2 (CB2) is expressed mainly on leukocytes and is the receptor implicated in mediating many of the effects of cannabinoids on immune processes. This study tested the capacity of Δ(9)-tetrahydrocannabinol (Δ(9)-THC) and of two CB2-selective agonists to inhibit the murine Mixed Lymphocyte Reaction (MLR), an in vitro correlate of graft rejection following skin and organ transplantation. Both CB2-selective agonists and Δ(9)-THC significantly suppressed the MLR in a dose dependent fashion. The inhibition was via CB2, as suppression could be blocked by pretreatment with a CB2-selective antagonist, but not by a CB1 antagonist, and none of the compounds suppressed the MLR when splenocytes from CB2 deficient mice were used. The CB2 agonists were shown to act directly on T-cells, as exposure of CD3(+) cells to these compounds completely inhibited their action in a reconstituted MLR. Further, the CB2-selective agonists completely inhibited proliferation of purified T-cells activated by anti-CD3 and anti-CD28 antibodies. T-cell function was decreased by the CB2 agonists, as an ELISA of MLR culture supernatants revealed IL-2 release was significantly decreased in the cannabinoid treated cells. Together, these data support the potential of this class of compounds as useful therapies to prolong graft survival in transplant patients.

N2 neutrophils, novel players in brain inflammation after stroke: modulation by the PPARγ agonist rosiglitazone

BACKGROUND AND PURPOSE

Neutrophils have been traditionally recognized as major mediators of a deleterious inflammatory response in acute ischemic stroke, but their potential as a therapeutic target remains unexplored. Recent evidence indicates that neutrophils may acquire different phenotypes and contribute to resolution of inflammation through the release of anti-inflammatory mediators. Thus, similar to M2 macrophages, neutrophils have been proposed to shift toward an N2 phenotype, a polarization that is peroxisome proliferator-activated receptor-γ dependent in macrophages. We hypothesize that peroxisome proliferator-activated receptor-γ activation with rosiglitazone induces changes in neutrophilic mobilization and phenotype that might influence stroke outcome.

METHODS

Brain sections and cell suspensions were prepared from mice exposed to permanent distal middle cerebral artery occlusion. Double immunostaining with stereological counting of brain sections and flow-cytometry analysis of brain cell suspensions were performed.

RESULTS

Rosiglitazone accelerated neutrophil infiltration to the ischemic core, concomitantly to neuroprotection. Some neutrophils (≈31%) expressed M2 markers, namely Ym1 and CD206 (mannose receptor). After treatment with the peroxisome proliferator-activated receptor-γ agonist rosiglitazone, most neutrophils (≈77%) acquired an N2 phenotype. Interestingly, rosiglitazone increased neutrophil engulfment by microglia/macrophages, a clearance that preferentially affected the N2 subset.

CONCLUSIONS

We present the first evidence of neutrophil reprogramming toward an N2 phenotype in brain inflammation, which can be modulated by activation of the peroxisome proliferator-activated receptor-γ nuclear receptor. We also show that N2 polarization is associated with an increased neutrophil clearance, thus suggesting that this switch is a crucial event for resolution of inflammation that may participate in neuroprotection.

Aging aggravates ischemic stroke-induced brain damage in mice with chronic peripheral infection

Ischemic stroke is confounded by conditions such as atherosclerosis, diabetes, and infection, all of which alter peripheral inflammatory processes with concomitant impact on stroke outcome. The majority of the stroke patients are elderly, but the impact of interactions between aging and inflammation on stroke remains unknown. We thus investigated the influence of age on the outcome of stroke in animals predisposed to systemic chronic infection. Th1-polarized chronic systemic infection was induced in 18-22 month and 4-month-old C57BL/6j mice by administration of Trichuris muris (gut parasite). One month after infection, mice underwent permanent middle cerebral artery occlusion and infarct size, brain gliosis, and brain and plasma cytokine profiles were analyzed. Chronic infection increased the infarct size in aged but not in young mice at 24 h. Aged, ischemic mice showed altered plasma and brain cytokine responses, while the lesion size correlated with plasma prestroke levels of RANTES. Moreover, the old, infected mice exhibited significantly increased neutrophil recruitment and upregulation of both plasma interleukin-17α and tumor necrosis factor-α levels. Neither age nor infection status alone or in combination altered the ischemia-induced brain microgliosis. Our results show that chronic peripheral infection in aged animals renders the brain more vulnerable to ischemic insults, possibly by increasing the invasion of neutrophils and altering the inflammation status in the blood and brain. Understanding the interactions between age and infections is crucial for developing a better therapeutic regimen for ischemic stroke and when modeling it as a disease of the elderly.

Cannabinoids: well-suited candidates for the treatment of perinatal brain injury

Perinatal brain injury can be induced by a number of different damaging events occurring during or shortly after birth, including neonatal asphyxia, neonatal hypoxia-ischemia and stroke-induced focal ischemia. Typical manifestations of these conditions are the presence of glutamate excitoxicity, neuroinflammation and oxidative stress, the combination of which can potentially result in apoptotic-necrotic cell death, generation of brain lesions and long-lasting functional impairment. In spite of the high incidence of perinatal brain injury, the number of clinical interventions available for the treatment of the affected newborn babies is extremely limited. Hence, there is a dramatic need to develop new effective therapies aimed to prevent acute brain damage and enhance the endogenous mechanisms of long-term brain repair. The endocannabinoid system is an endogenous neuromodulatory system involved in the control of multiple central and peripheral functions. An early responder to neuronal injury, the endocannabinoid system has been described as an endogenous neuroprotective system that once activated can prevent glutamate excitotoxicity, intracellular calcium accumulation, activation of cell death pathways, microglia activation, neurovascular reactivity and infiltration of circulating leukocytes across the blood-brain barrier. The modulation of the endocannabinoid system has proven to be an effective neuroprotective strategy to prevent and reduce neonatal brain injury in different animal models and species. Also, the beneficial role of the endocannabinoid system on the control of the endogenous repairing responses (neurogenesis and white matter restoration) to neonatal brain injury has been described in independent studies. This review addresses the particular effects of several drugs that modulate the activity of the endocannabinoid system on the progression of different manifestations of perinatal brain injury during both the acute and chronic recovery phases using rodent and non-rodent animal models, and will provide a complete description of the known mechanisms that mediate such effects.

Cerebroprotective effects of TAK-937, a novel cannabinoid receptor agonist, in permanent and thrombotic focal cerebral ischemia in rats: therapeutic time window, combination with t-PA and efficacy in aged rats

Some occluded arteries of acute ischemic stroke (AIS) patients are not recanalized, even if thrombolytic therapy is performed. Considering such clinical settings, we examined the potential cerebroprotective efficacy of TAK-937, a novel cannabinoid receptor agonist, in young adult and aged rats with a permanent middle cerebral artery occlusion (MCAO) model and conducted a combination study with TAK-937 and tissue type plasminogen activator (t-PA) in a rat thrombotic MCAO model. TAK-937 significantly reduced infarct volume when it was administered 3 and 5h after permanent MCAO in young adult rats. A thrombotic MCAO was induced by photo-irradiation of the middle cerebral artery with Rose Bengal administration and a permanent MCAO was produced by thermoelectric coagulation of occluded arteries. TAK-937 (10, 30 and 100μg/kg/h) was intravenously infused 1, 3, 5, or 8-24h after MCAO. t-PA (3 or 10mg/kg) was intravenously administered 1, 1.5 or 2h after MCAO. Infarct volume was determined using a 2,3,5-triphenyltetrazolium chloride staining method 24 or 48h after MCAO. The combined treatment of TAK-937 with t-PA significantly reduced the cerebral infarction compared with t-PA treatment alone in a rat thrombotic MCAO model. TAK-937 reduced infarct volume of aged rats as well, when it was administered 1h after permanent MCAO. These results suggest that TAK-937 exerts protective effects regardless of age and has a wide therapeutic time window in permanent occlusion. Furthermore, combined treatment of TAK-937 with t-PA would provide more therapeutic efficacy compared to t-PA treatment alone.

Cannabinoid receptor 2: potential role in immunomodulation and neuroinflammation

An accumulating body of evidence suggests that endocannabinoids and cannabinoid receptors type 1 and 2 (CB(1), CB(2)) play a significant role in physiologic and pathologic processes, including cognitive and immune functions. While the addictive properties of marijuana, an extract from the Cannabis plant, are well recognized, there is growing appreciation of the therapeutic potential of cannabinoids in multiple pathologic conditions involving chronic inflammation (inflammatory bowel disease, arthritis, autoimmune disorders, multiple sclerosis, HIV-1 infection, stroke, Alzheimer's disease to name a few), mainly mediated by CB(2) activation. Development of CB(2) agonists as therapeutic agents has been hampered by the complexity of their intracellular signaling, relative paucity of highly selective compounds and insufficient data regarding end effects in the target cells and organs. This review attempts to summarize recent advances in studies of CB(2) activation in the setting of neuroinflammation, immunomodulation and HIV-1 infection.

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.

Trisubstituted Sulfonamides: a New Chemotype for Development of Potent and Selective CB2 Receptor Inverse Agonists

An extensive exploration of the SAR of a trisubstituted sulfonamides series led to the identification of 39, which is a potent and selective CB₂ receptor inverse agonist (CB₂Ki = 5.4 nM, and CB₁Ki = 500 nM). The functional properties measured by cAMP assays indicated that the selected compounds were CB₂ inverse agonists with high potency values (34, EC₅₀ = 8.2 nM, and 39, EC₅₀ = 2.5 nM). Furthermore, an osteoclastogenesis bioassay indicated that trisubstituted sulfonamide compounds showed great inhibition of osteoclast formation.

Treatment with Evasin-3 reduces atherosclerotic vulnerability for ischemic stroke, but not brain injury in mice

Neutrophilic inflammation might have a pathophysiological role in both carotid plaque rupture and ischemic stroke injury. Here, we investigated the potential benefits of the CXC chemokine-binding protein Evasin-3, which potently inhibits chemokine bioactivity and related neutrophilic inflammation in two mouse models of carotid atherosclerosis and ischemic stroke, respectively. In the first model, the chronic treatment with Evasin-3 as compared with Vehicle (phosphate-buffered saline (PBS)) was investigated in apolipoprotein E-deficient mice implanted of a 'cast' carotid device. In the second model, acute Evasin-3 treatment (5 minutes after cerebral ischemia onset) was assessed in mice subjected to transient left middle cerebral artery occlusion. Although CXCL1 and CXCL2 were upregulated in both atherosclerotic plaques and infarcted brain, only CXCL1 was detectable in serum. In carotid atherosclerosis, treatment with Evasin-3 was associated with reduction in intraplaque neutrophil and matrix metalloproteinase-9 content and weak increase in collagen as compared with Vehicle. In ischemic stroke, treatment with Evasin-3 was associated with reduction in ischemic brain neutrophil infiltration and protective oxidants. No other effects in clinical and histological outcomes were observed. We concluded that Evasin-3 treatment was associated with reduction in neutrophilic inflammation in both mouse models. However, Evasin-3 administration after cerebral ischemia onset failed to improve poststroke outcomes.

Cannabinoid receptor 2 signaling in peripheral immune cells modulates disease onset and severity in mouse models of Huntington's disease

Peripheral immune cells and brain microglia exhibit an activated phenotype in premanifest Huntington's disease (HD) patients that persists chronically and correlates with clinical measures of neurodegeneration. However, whether activation of the immune system contributes to neurodegeneration in HD, or is a consequence thereof, remains unclear. Signaling through cannabinoid receptor 2 (CB(2)) dampens immune activation. Here, we show that the genetic deletion of CB(2) receptors in a slowly progressing HD mouse model accelerates the onset of motor deficits and increases their severity. Treatment of mice with a CB(2) receptor agonist extends life span and suppresses motor deficits, synapse loss, and CNS inflammation, while a peripherally restricted CB(2) receptor antagonist blocks these effects. CB(2) receptors regulate blood interleukin-6 (IL-6) levels, and IL-6 neutralizing antibodies partially rescue motor deficits and weight loss in HD mice. These findings support a causal link between CB(2) receptor signaling in peripheral immune cells and the onset and severity of neurodegeneration in HD, and they provide a novel therapeutic approach to treat HD.

2-Arachidonoyl-glycerol- and arachidonic acid-stimulated neutrophils release antimicrobial effectors against E. coli, S. aureus, HSV-1, and RSV

The endocannabinoid 2-AG is highly susceptible to its hydrolysis into AA, which activates neutrophils through de novo LTB(4) biosynthesis, independently of CB activation. In this study, we show that 2-AG and AA stimulate neutrophils to release antimicrobial effectors. Supernatants of neutrophils activated with nanomolar concentrations of 2-AG and AA indeed inhibited the infectivity of HSV-1 and RSV. Additionally, the supernatants of 2-AG- and AA-stimulated neutrophils strongly impaired the growth of Escherichia coli and Staphylococcus aureus. This correlated with the release of a large amount (micrograms) of α-defensins, as well as a limited amount (nanograms) of LL-37. All the effects of AA and 2-AG mentioned above were prevented by inhibiting LTB(4) biosynthesis or by blocking BLT(1). Importantly, neither CB(2) receptor agonists nor antagonists could mimic nor prevent the effects of 2-AG, respectively. In fact, qPCR data show that contaminating eosinophils express ∼100-fold more CB(2) receptor mRNA than purified neutrophils, suggesting that CB(2) receptor expression by human neutrophils is limited and that contaminating eosinophils are likely responsible for the previously documented CB(2) expression by freshly isolated human neutrophils. The rapid conversion of 2-AG to AA and their subsequent metabolism into LTB(4) promote 2-AG and AA as multifunctional activators of neutrophils, mainly exerting their effects by activating the BLT(1). Considering that nanomolar concentrations of AA or 2-AG were sufficient to impair viral infectivity, this suggests potential physiological roles for 2-AG and AA as regulators of host defense in vivo.

Interleukin-17 in post-stroke neurodegeneration

Stroke is a leading cause of physical disability with neurodegenerative sequelae such as dementia and depression causing significant excess morbidity. Stroke severity can be exacerbated by apoptotic cell death in ischemic tissue, of which inflammatory activity is a key determinant. Studies have identified harmful and beneficial sets of T lymphocytes that infiltrate the brain post-stroke and their activation signals, suggesting that they might be targeted for therapeutic benefit. Animal models and human studies implicate interleukin(IL)-17 and its congeners (e.g. IL-23, IL-21) as mediators of tissue damage in the delayed phase of the inflammatory cascade and the involvement of T lymphocytes in propagating IL-17 release. In this review, we highlight the current understanding of IL-17 secreting cells, including sets of CD4(+) αβ and CD4(-) γδ T lymphocytes, as potentially important mediators of brain pathology post-stroke. Interactions between the IL-17 axis and innate pathways, positive feedback mechanisms that prolong or amplify IL-17, and IL-17 regulatory pathways may offer intervention targets to enhance recovery, prevent long-term decline, and improve quality of life.

Targeting cannabinoid receptor CB(2) in cardiovascular disorders: promises and controversies

Cardiovascular disease is the leading cause of death and disability worldwide, which can be largely attributed to atherosclerosis, a chronic inflammation of the arteries characterized by lesions containing immune and smooth muscle cells, lipids and extracellular matrix. In recent years, the lipid endocannabinoid system has emerged as a new therapeutic target in variety of disorders associated with inflammation and tissue injury, including those of the cardiovascular system. The discovery that Δ-9-tetrahydrocannabinol (Δ9-THC), the main active constituent of marijuana, inhibited atherosclerotic plaque progression via a cannabinoid 2 (CB(2) ) receptor-dependent anti-inflammatory mechanism, and that certain natural and synthetic cannabinoid ligands could modulate the myocardial or cerebral ischaemia-reperfusion-induced tissue damage, have stimulated impetus for a growing number of studies investigating the implication of CB(2) receptors in atherosclerosis, restenosis, stroke, myocardial infarction and heart failure. The aim of this review is to update on recent findings and controversies on the role of CB(2) receptors in cardiovascular disease. Particular emphasis will be placed on novel insights in the potential cellular targets of CB(2) stimulation in cardiovascular system (e.g. endothelial and vascular smooth muscle cells, cardiomyocytes, infiltrating and/or resident monocytes/macrophages and leukocytes, etc.), their interplay and intracellular signalling mechanisms identified, as well as on experimental and clinical studies.

Neutralization of the IL-17 axis diminishes neutrophil invasion and protects from ischemic stroke

The devastating effect of ischemic stroke is attenuated in mice lacking conventional and unconventional T cells, suggesting that inflammation enhances tissue damage in cerebral ischemia. We explored the functional role of αβ and γδ T cells in a murine model of stroke and distinguished 2 different T cell–dependent proinflammatory pathways in ischemia-reperfusion injury. IFN-γ produced by CD4+ T cells induced TNF-α production in macrophages, whereas IL-17A secreted by γδ T cells led to neutrophil recruitment. The synergistic effect of TNF-α and IL-17A on astrocytes resulted in enhanced secretion of CXCL-1, a neutrophil chemoattractant. Application of an IL-17A–blocking antibody within 3 hours after stroke induction decreased infarct size and improved neurologic outcome in the murine model. In autoptic brain tissue of patients who had a stroke, we detected IL-17A–positive lymphocytes, suggesting that this aspect of the inflammatory cascade is also relevant in the human brain. We propose that selective targeting of IL-17A signaling might provide a new therapeutic option for the treatment of stroke.

Connexin 36 promotes cortical spreading depolarization and ischemic brain damage

Cortical spreading depolarization (CSD) promotes the progression of neuronal injury after cerebral ischemia. However, the mechanisms of propagation of postischemic CSD events are still unclear. In this study we characterized the role of the main neuronal gap junction protein connexin 36 (Cx36) in generating postischemic CSDs. In Cx36-deficient mice and controls we occluded the distal middle cerebral artery. To detect CSD events we recorded the direct current and laser Doppler flow. In addition, locomotor function and the infarct size were determined. Cx36-deficient mice had significantly fewer and shorter CSD events than wild-type controls. Additionally, Cx36 deletion is neuroprotective, leading to a better functional outcome and decreased infarct size after ischemia. These results suggest a detrimental role for Cx36 after ischemia, possibly by promoting CSD.

Cannabinoid receptor subtypes 1 and 2 mediate long-lasting neuroprotection and improve motor behavior deficits after transient focal cerebral ischemia

The endocannabinoid system is crucially involved in the regulation of brain activity and inflammation. We have investigated the localization of cannabinoid CB1 and CB2 receptors in adult rat brains before and after focal cerebral ischemia due to endothelin-induced transient occlusion of the middle cerebral artery (eMCAO). Using immunohistochemistry, both receptor subtypes were identified in cortical neurons. After eMCAO, neuronal cell death was accompanied by reduced neuronal CB1 and CB2 receptor-linked immunofluorescence. In parallel, CB1 receptor was found in activated microglia/macrophages 3 days post eMCAO and in astroglia cells at days 3 and 7. CB2 receptor labeling was identified in activated microglia/macrophages or astroglia 3 and 7d ays post ischemia, respectively. In addition, immune competent CD45-positive cells were characterized by pronounced CB2 receptor staining 3 and 7 days post eMCAO. KN38-72717, a potent and selective CB1 and CB2 receptor agonist, revealed a significant, dose-dependent and long-lasting reduction of cortical lesion sizes due to eMCAO, when applied consecutively before, during and after eMCAO. In addition, severe motor deficits of animals suffering from eMCAO were significantly improved by KN38-7271. KN38-7271 remained effective, even if its application was delayed up to 6h post eMCAO. Finally, we show that the endocannabinoid system assembles a comprehensive machinery to defend the brain against the devastating consequences of cerebral ischemia. In summary, this study underlines the therapeutic potential of CB1 and/or CB2 receptor agonists against neurodegenerative diseases or injuries involving acute or chronic imbalances of cerebral blood flow and energy consumption.