Evidence that 2-arachidonoylglycerol but not N-palmitoylethanolamine or anandamide is the physiological ligand for the cannabinoid CB2 receptor. Comparison of the agonistic activities of various cannabinoid receptor ligands in HL-60 cells

High Times for Painful Blues: The Endocannabinoid System in Pain-Depression Comorbidity

Depression and pain are two of the most debilitating disorders worldwide and have an estimated cooccurrence of up to 80%. Comorbidity of these disorders is more difficult to treat, associated with significant disability and impaired health-related quality of life than either condition alone, resulting in enormous social and economic cost. Several neural substrates have been identified as potential mediators in the association between depression and pain, including neuroanatomical reorganization, monoamine and neurotrophin depletion, dysregulation of the hypothalamo-pituitary-adrenal axis, and neuroinflammation. However, the past decade has seen mounting evidence supporting a role for the endogenous cannabinoid (endocannabinoid) system in affective and nociceptive processing, and thus, alterations in this system may play a key role in reciprocal interactions between depression and pain. This review will provide an overview of the preclinical evidence supporting an interaction between depression and pain and the evidence supporting a role for the endocannabinoid system in this interaction.

Omega-3 PUFAs Lower the Propensity for Arachidonic Acid Cascade Overreactions

A productive view of the benefits from omega-3 (n-3) nutrients is that the dietary essential omega-6 (n-6) linoleic acid has a very narrow therapeutic window which is widened by n-3 nutrients. The benefit from moderate physiological actions of the arachidonic acid cascade can easily shift to harm from excessive pathophysiological actions. Recognizing the factors that predispose the cascade to an unwanted overactivity gives a rational approach for arranging beneficial interactions between the n-3 and n-6 essential nutrients that are initial components of the cascade. Much detailed evidence for harmful cascade actions was collected by pharmaceutical companies as they developed drugs to decrease those actions. A remaining challenge is to understand the factors that predispose the cascade toward unwanted outcomes and create the need for therapeutic interventions. Such understanding involves recognizing the similar dynamics for dietary n-3 and n-6 nutrients in forming the immediate precursors of the cascade plus the more vigorous actions of the n-6 precursor, arachidonic acid, in forming potent mediators that amplify unwanted cascade outcomes. Tools have been developed to aid deliberate day-to-day quantitative management of the propensity for cascade overactivity in ways that can decrease the need for drug treatments.

Promising cannabinoid-based therapies for Parkinson's disease: motor symptoms to neuroprotection

Parkinson’s disease (PD) is a slow insidious neurological disorder characterized by a loss of dopaminergic neurons in the midbrain. Although several recent preclinical advances have proposed to treat PD, there is hardly any clinically proved new therapeutic for its cure. Increasing evidence suggests a prominent modulatory function of the cannabinoid signaling system in the basal ganglia. Hence, use of cannabinoids as a new therapeutic target has been recommended as a promising therapy for PD. The elements of the endocannabinoid system are highly expressed in the neural circuit of basal ganglia wherein they bidirectionally interact with dopaminergic, glutamatergic, and GABAergic signaling systems. As the cannabinoid signaling system undergoes a biphasic pattern of change during progression of PD, it explains the motor inhibition typically observed in patients with PD. Cannabinoid agonists such as WIN-55,212-2 have been demonstrated experimentally as neuroprotective agents in PD, with respect to their ability to suppress excitotoxicity, glial activation, and oxidative injury that causes degeneration of dopaminergic neurons. Additional benefits provided by cannabinoid related compounds including CE-178253, oleoylethanolamide, nabilone and HU-210 have been reported to possess efficacy against bradykinesia and levodopa-induced dyskinesia in PD. Despite promising preclinical studies for PD, use of cannabinoids has not been studied extensively at the clinical level. In this review, we reassess the existing evidence suggesting involvement of the endocannabinoid system in the cause, symptomatology, and treatment of PD. We will try to identify future threads of research that will help in the understanding of the potential therapeutic benefits of the cannabinoid system for treating PD.

Inhibition of monoacylglycerol lipase mediates a cannabinoid 1-receptor dependent delay of kindling progression in mice

Endocannabinoids, including 2-arachidonoylglycerol (2-AG), activate presynaptic cannabinoid type 1 receptors (CB1R) on inhibitory and excitatory neurons, resulting in a decreased release of neurotransmitters. The event-specific activation of the endocannabinoid system by inhibition of the endocannabinoid degrading enzymes may offer a promising strategy to selectively activate CB1Rs at the site of excessive neuronal activation with the overall goal to prevent the development epilepsy. The aim of this study was to investigate the impact of monoacylglycerol lipase (MAGL) inhibition on the development and progression of epileptic seizures in the kindling model of temporal lobe epilepsy. Therefore, we selectively blocked MAGL by JZL184 (8mg/kg, i.p.) in mice to analyze the effects of increased 2-AG levels on kindling acquisition and to exclude an anticonvulsive potential. Our results showed that JZL184 treatment significantly delayed the development of generalized seizures (p=0.0066) and decreased seizure (p<0.0001) and afterdischarge duration (p<0.001) in the kindling model of temporal lobe epilepsy, but caused only modest effects in fully kindled mice. Moreover, we proved that JZL184 treatment had no effects in conditional CB1R knockout mice lacking expression of the receptor in principle neurons of the forebrain. In conclusion, the data demonstrate that indirect CB1R agonism delays the development of generalized epileptic seizures but has no relevant acute anticonvulsive effects. Furthermore, we confirmed that the effects of JZL184 on kindling progression are CB1R mediated. Thus, the data indicate that the endocannabinoid 2-AG might be a promising target for an anti-epileptogenic approach.

Endocannabinoid signaling at the periphery: 50 years after THC

In 1964, the psychoactive ingredient of Cannabis sativa, Δ(9)-tetrahydrocannabinol (THC), was isolated. Nearly 30 years later the endogenous counterparts of THC, collectively termed endocannabinoids (eCBs), were discovered: N-arachidonoylethanolamine (anandamide) (AEA) in 1992 and 2-arachidonoylglycerol (2-AG) in 1995. Since then, considerable research has shed light on the impact of eCBs on human health and disease, identifying an ensemble of proteins that bind, synthesize, and degrade them and that together form the eCB system (ECS). eCBs control basic biological processes including cell choice between survival and death and progenitor/stem cell proliferation and differentiation. Unsurprisingly, in the past two decades eCBs have been recognized as key mediators of several aspects of human pathophysiology and thus have emerged to be among the most widespread and versatile signaling molecules ever discovered. Here some of the pioneers of this research field review the state of the art of critical eCB functions in peripheral organs. Our community effort is aimed at establishing consensus views on the relevance of the peripheral ECS for human health and disease pathogenesis, as well as highlighting emerging challenges and therapeutic hopes.

Palmitoylethanolamide inhibits glutamate release in rat cerebrocortical nerve terminals

The effect of palmitoylethanolamide (PEA), an endogenous fatty acid amide displaying neuroprotective actions, on glutamate release from rat cerebrocortical nerve terminals (synaptosomes) was investigated. PEA inhibited the Ca²⁺-dependent release of glutamate, which was triggered by exposing synaptosomes to the potassium channel blocker 4-aminopyridine. This release inhibition was concentration dependent, associated with a reduction in cytosolic Ca²⁺ concentration, and not due to a change in synaptosomal membrane potential. The glutamate release-inhibiting effect of PEA was prevented by the Cav2.1 (P/Q-type) channel blocker ω-agatoxin IVA or the protein kinase A inhibitor H89, not affected by the intracellular Ca²⁺ release inhibitors dantrolene and CGP37157, and partially antagonized by the cannabinoid CB1 receptor antagonist AM281. Based on these results, we suggest that PEA exerts its presynaptic inhibition, likely through a reduction in the Ca²⁺ influx mediated by Cav2.1 (P/Q-type) channels, thereby inhibiting the release of glutamate from rat cortical nerve terminals. This release inhibition might be linked to the activation of presynaptic cannabinoid CB1 receptors and the suppression of the protein kinase A pathway.

Endocannabinoid Catabolic Enzymes Play Differential Roles in Thermal Homeostasis in Response to Environmental or Immune Challenge

Cannabinoid receptor agonists, such as Δ(9)-THC, the primary active constituent of Cannabis sativa, have anti-pyrogenic effects in a variety of assays. Recently, attention has turned to the endogenous cannabinoid system and how endocannabinoids, including 2-arachidonoylglycerol (2-AG) and anandamide, regulate multiple homeostatic processes, including thermoregulation. Inhibiting endocannabinoid catabolic enzymes, monoacylglycerol lipase (MAGL) or fatty acid amide hydrolase (FAAH), elevates levels of 2-AG or anandamide in vivo, respectively. The purpose of this experiment was to test the hypothesis that endocannabinoid catabolic enzymes function to maintain thermal homeostasis in response to hypothermic challenge. In separate experiments, male C57BL/6J mice were administered a MAGL or FAAH inhibitor, and then challenged with the bacterial endotoxin lipopolysaccharide (LPS; 2 mg/kg ip) or a cold (4 °C) ambient environment. Systemic LPS administration caused a significant decrease in core body temperature after 6 h, and this hypothermia persisted for at least 12 h. Similarly, cold environment induced mild hypothermia that resolved within 30 min. JZL184 exacerbated hypothermia induced by either LPS or cold challenge, both of which effects were blocked by rimonabant, but not SR144528, indicating a CB1 cannabinoid receptor mechanism of action. In contrast, the FAAH inhibitor, PF-3845, had no effect on either LPS-induced or cold-induced hypothermia. These data indicate that unlike direct acting cannabinoid receptor agonists, which elicit profound hypothermic responses on their own, neither MAGL nor FAAH inhibitors affect normal body temperature. However, these endocannabinoid catabolic enzymes play distinct roles in thermoregulation following hypothermic challenges.

Chronic activation of CB2 cannabinoid receptors in the hippocampus increases excitatory synaptic transmission

KEY POINTS

The effects of cannabinoids are primarily mediated by two types of cannabinoid receptors, CB1 receptors in the nervous system and CB2 receptors in the immune system. Recent evidence indicates that CB2 receptors are also widely expressed in the brain and involved in neuropsychiatric functions, such as schizophrenia-like behaviours, anxiety, memory, vomiting and pain. The cellular mechanisms by which CB2 receptors regulate neuronal functions are unknown. We show that chronic activation of CB2 receptors in the hippocampus for 7-10 days increases excitatory synaptic transmission, whereas short-term activation of CB2 receptors has little effect on synaptic activity. This study reveals a novel role of CB2 receptors in the brain, which is clearly distinct from that of CB1 receptors, and thus, will help us to understand better the diverse effects of cannabinoids in the nervous system.

ABSTRACT

The roles of CB1 cannabinoid receptors in regulating neuronal activity have been extensively characterized. Although early studies show that CB1 receptors are present in the nervous system and CB2 cannabinoid receptors are in the immune system, recent evidence indicates that CB2 receptors are also expressed in the brain. Activation or blockade of CB2 receptors in vivo induces neuropsychiatric effects, but the cellular mechanisms of CB2 receptor function are unclear. The aim of this study is to determine how activation of CB2 receptors present in the hippocampus regulates synaptic function. Here, we show that when organotypic cultures of rodent hippocampal slices were treated with a CB2 receptor agonist (JWH133 or GP1a) for 7-10 days, quantal glutamate release became more frequent and spine density was increased via extracellular signal-regulated kinases. Chronic intraperitoneal injection of JWH133 into mice also increased excitatory synaptic transmission. These effects were blocked by a CB2 receptor antagonist (SR144528) or absent from hippocampal slices of CB2 receptor knock-out mice. This study reveals a novel cellular function of CB2 cannabinoid receptors in the hippocampus and provides insights into how cannabinoid receptor subtypes diversify the roles of cannabinoids in the brain.

Endocannabinoids and the Immune System in Health and Disease

Endocannabinoids are bioactive lipids that have the potential to signal through cannabinoid receptors to modulate the functional activities of a variety of immune cells. Their activation of these seven-transmembranal, G protein-coupled receptors sets in motion a series of signal transductional events that converge at the transcriptional level to regulate cell migration and the production of cytokines and chemokines. There is a large body of data that supports a functional relevance for 2-arachidonoylglycerol (2-AG) as acting through the cannabinoid receptor type 2 (CB2R) to inhibit migratory activities for a diverse array of immune cell types. However, unequivocal data that supports a functional linkage of anandamide (AEA) to a cannabinoid receptor in immune modulation remains to be obtained. Endocannabinoids, as typical bioactive lipids, have a short half-life and appear to act in an autocrine and paracrine fashion. Their immediate effective action on immune function may be at localized sites in the periphery and within the central nervous system. It is speculated that endocannabinoids play an important role in maintaining the overall "fine-tuning" of the immune homeostatic balance within the host.

Inhibitors of Fatty Acid Amide Hydrolase and Monoacylglycerol Lipase: New Targets for Future Antidepressants

Cannabis and analogs of Δ⁹-tetrahydrocannabinol have been used for therapeutic purposes, but their therapeutic use remains limited because of various adverse effects. Endogenous cannabinoids have been discovered, and dysregulation of endocannabinoid signaling is implicated in the pathophysiology of major depressive disorder (MDD). Recently, endocannabinoid hydrolytic enzymes such as fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) have become new therapeutic targets in the treatment of MDD. Several FAAH or MAGL inhibitors are reported to have no cannabimimetic side effects and, therefore, are new potential therapeutic options for patients with MDD who are resistant to first-line antidepressants (selective serotonin and serotonin-norepinephrine reuptake inhibitors). In this review, we focus on the possible relationships between MDD and the endocannabinoid system as well as the inhibitors' therapeutic potential. MAGL inhibitors may reduce inflammatory responses through activation of cannabinoid receptor type 2. In the hypothalamic-pituitary-adrenal axis, repeated FAAH inhibitor administration may be beneficial for reducing circulating glucocorticoid levels. Both FAAH and MAGL inhibitors may contribute to dopaminergic system regulation. Recently, several new inhibitors have been developed with strong potency and selectivity. FAAH inhibitor, MAGL inhibitor, or dual blocker use would be promising new treatments for MDD. Further pre-clinical studies and clinical trials using these inhibitors are warranted.

Palmitoylethanolamide regulates development of intestinal radiation injury in a mast cell-dependent manner

BACKGROUND

Mast cells and neuroimmune interactions regulate the severity of intestinal radiation mucositis, a dose-limiting toxicity during radiation therapy of abdominal malignancies.

AIM

Because endocannabinoids (eCB) regulate intestinal inflammation, we investigated the effect of the cannabimimetic, palmitoylethanolamide (PEA), in a mast competent (+/+) and mast cell-deficient (Ws/Ws) rat model.

METHODS

Rats underwent localized, fractionated intestinal irradiation, and received daily injections with vehicle or PEA from 1 day before until 2 weeks after radiation. Intestinal injury was assessed noninvasively by luminol bioluminescence, and, at 2 weeks, by histology, morphometry, and immunohistochemical analysis, gene expression analysis, and pathway analysis.

RESULTS

Compared with +/+ rats, Ws/Ws rats sustained more intestinal structural injury (p = 0.01), mucosal damage (p = 0.02), neutrophil infiltration (p = 0.0003), and collagen deposition (p = 0.004). PEA reduced structural radiation injury (p = 0.02), intestinal wall thickness (p = 0.03), collagen deposition (p = 0.03), and intestinal inflammation (p = 0.02) in Ws/Ws rats, but not in +/+ rats. PEA inhibited mast cell-derived cellular immune response and anti-inflammatory IL-6 and IL-10 signaling and activated the prothrombin pathway in +/+ rats. In contrast, while PEA suppressed nonmast cell-derived immune responses, it increased anti-inflammatory IL-10 and IL-6 signaling and decreased activation of the prothrombin pathway in Ws/Ws rats.

CONCLUSIONS

These data demonstrate that the absence of mast cells exacerbate radiation enteropathy by mechanisms that likely involve the coagulation system, anti-inflammatory cytokine signaling, and the innate immune system; and that these mechanisms are regulated by PEA in a mast cell-dependent manner. The eCB system should be explored as target for mitigating intestinal radiation injury.

Microinjection of 2-arachidonoyl glycerol into the rat ventral hippocampus differentially modulates contextually induced fear, depending on a persistent pain state

The endogenous cannabinoid (endocannabinoid) system plays a key role in the modulation of aversive and nociceptive behaviour. The components of the endocannabinoid system are expressed throughout the hippocampus, a brain region implicated in both conditioned fear and pain. In light of evidence that pain can impact on the expression of fear-related behaviour, and vice versa, we hypothesised that exogenous administration of the endocannabinoid 2-arachidonoyl glycerol (2-AG) into the ventral hippocampus (vHip) would differentially regulate fear responding in the absence vs. the presence of formalin-evoked nociceptive tone. Fear-conditioned rats showed significantly increased freezing and a reduction in formalin-evoked nociceptive behaviour upon re-exposure to a context previously paired with footshock. Bilateral microinjection of 2-AG into the vHip significantly reduced contextually induced freezing in non-formalin-treated rats, and reduced formalin-evoked nociceptive behaviour in non-fear-conditioned rats. In contrast, 2-AG microinjection had no effect on fear responding in formalin-treated rats, and no effect on nociceptive behaviour in fear-conditioned rats. The inhibitory effect of 2-AG on fear-related behaviour, but not pain-related behaviour, was blocked by co-administration of the cannabinoid receptor 1 (CB1) antagonist/inverse agonist rimonabant. Tissue levels of the endocannabinoids N-arachidonoylethanolamide (anandamide, AEA) and 2-AG were similar in the vHip of fear-conditioned rats receiving formalin injection and the vHip of fear-conditioned rats receiving saline injection. However, the levels of AEA and 2-AG were significantly lower in the contralateral ventrolateral periaqueductal grey of formalin-treated fear-conditioned rats than in that of their saline-treated counterparts. These data suggest that 2-AG-CB1 receptor signalling in the vHip has an anti-aversive effect, and that this effect is abolished in the presence of a persistent pain state.

No more pain upon Gq-protein-coupled receptor activation: role of endocannabinoids

Marijuana has been used to relieve pain for centuries. The analgesic mechanism of its constituents, the cannabinoids, was only revealed after the discovery of cannabinoid receptors (CB1 and CB2) two decades ago. The subsequent identification of the endocannabinoids, anandamide and 2-arachidonoylglycerol (2-AG), and their biosynthetic and degradation enzymes discloses the therapeutic potential of compounds targeting the endocannabinoid system for pain control. Inhibitors of the anandamide and 2-AG degradation enzymes, fatty acid amide hydrolase and monoacylglycerol lipase, respectively, may be superior to direct cannabinoid receptor ligands as endocannabinoids are synthesized on demand and rapidly degraded, focusing action at generating sites. Recently, a promising strategy for pain relief was revealed in the periaqueductal gray (PAG). It is initiated by Gq-protein-coupled receptor (Gq PCR) activation of the phospholipase C-diacylglycerol lipase enzymatic cascade, generating 2-AG that produces inhibition of GABAergic transmission (disinhibition) in the PAG, thereby leading to analgesia. Here, we introduce the antinociceptive properties of exogenous cannabinoids and endocannabinoids, involving their biosynthesis and degradation processes, particularly in the PAG. We also review recent studies disclosing the Gq PCR-phospholipase C-diacylglycerol lipase-2-AG retrograde disinhibition mechanism in the PAG, induced by activating several Gq PCRs, including metabotropic glutamatergic (type 5 metabotropic glutamate receptor), muscarinic acetylcholine (M1/M3), and orexin 1 receptors. Disinhibition mediated by type 5 metabotropic glutamate receptor can be initiated by glutamate transporter inhibitors or indirectly by substance P, neurotensin, cholecystokinin and capsaicin. Finally, the putative role of 2-AG generated after activating the above neurotransmitter receptors in stress-induced analgesia is discussed.

CB2 Cannabinoid receptors as a therapeutic target-what does the future hold?

The past decades have seen an exponential rise in our understanding of the endocannabinoid system, comprising CB1 and CB2 cannabinoid receptors, endogenous cannabinoids (endocannabinoids), and the enzymes that synthesize and degrade endocannabinoids. The primary focus of this review is the CB2 receptor. CB2 receptors have been the subject of considerable attention, primarily due to their promising therapeutic potential for treating various pathologies while avoiding the adverse psychotropic effects that can accompany CB1 receptor-based therapies. With the appreciation that CB2-selective ligands show marked functional selectivity, there is a renewed opportunity to explore this promising area of research from both a mechanistic as well as a therapeutic perspective. In this review, we summarize our present knowledge of CB2 receptor signaling, localization, and regulation. We discuss the availability of genetic tools (and their limitations) to study CB2 receptors and also provide an update on preclinical data on CB2 agonists in pain models. Finally, we suggest possible reasons for the failure of CB2 ligands in clinical pain trials and offer possible ways to move the field forward in a way that can help reconcile the inconsistencies between preclinical and clinical data.

Differential activation of intracellular versus plasmalemmal CB2 cannabinoid receptors

The therapeutic and psychoactive properties of cannabinoids have long been recognized. The type 2 receptor for cannabinoids (CB₂) has emerged as an important therapeutic target in several pathologies, as it mediates beneficial effects of cannabinoids while having little if any psychotropic activity. Difficulties associated with the development of CB₂-based therapeutic agents have been related to its intricate pharmacology, including the species specificity and functional selectivity of the CB₂-initiated responses. We postulated that a plasmalemmal or subcellular location of the receptor may contribute to the differential signaling pathways initiated by its activation. To differentiate between these two, we used extracellular and intracellular administration of CB₂ ligands and concurrent calcium imaging in CB₂-expressing U2OS cells. We found that extracellular administration of anandamide was ineffective, whereas 2-arachidonoyl glycerol (2-AG) and WIN55,212-2 triggered delayed, CB₂-dependent Ca²⁺ responses that were Gq protein-mediated. When microinjected, all agonists elicited fast, transient, and dose-dependent elevations in intracellular Ca²⁺ concentration upon activation of Gq-coupled CB₂ receptors. The CB₂ dependency was confirmed by the sensitivity to AM630, a selective CB₂ antagonist, and by the unresponsiveness of untransfected U2OS cells to 2-AG, anandamide, or WIN55,212-2. Moreover, we provide functional and morphological evidence that CB₂ receptors are localized at the endolysosomes, while their activation releases Ca²⁺ from inositol 1,4,5-trisphosphate-sensitive- and acidic-like Ca²⁺ stores. Our results support the functionality of intracellular CB₂ receptors and their ability to couple to Gq and elicit Ca²⁺ signaling. These findings add further complexity to CB₂ receptor pharmacology and argue for careful consideration of receptor localization in the development of CB₂-based therapeutic agents.

Harnessing the anti-inflammatory potential of palmitoylethanolamide

Palmitoylethanolamide (PEA) is a peroxisome proliferator-activated receptor alpha (PPAR-α) ligand that exerts anti-inflammatory, analgesic and neuroprotective actions. PEA is synthetized from phospholipids through the sequential actions of N-acyltransferase and N-acylphosphatidylethanolamine-preferring phospholipase D (NAPE-PLD), and its actions are terminated by its hydrolysis by two enzymes, fatty acid amide hydrolase (FAAH) and N-acylethanolamine-hydrolysing acid amidase (NAAA). Here, we review the impact of PEA administration in inflammatory and neurodegenerative settings and the differential role of FAAH and NAAA in controlling PEA levels. Recent studies with NAAA inhibitors put forth this enzyme as capable of increasing PEA levels in vivo in inflammatory processes, and identified it as an interesting target for drug discovery research. Thus, PEA hydrolysis inhibitors could constitute potential therapeutic alternatives in chronic inflammatory and neurodegenerative diseases.

The endocannabinoid/endovanilloid N-arachidonoyl dopamine (NADA) and synthetic cannabinoid WIN55,212-2 abate the inflammatory activation of human endothelial cells

Although cannabinoids, such as Δ(9)-tetrahydrocannabinol, have been studied extensively for their psychoactive effects, it has become apparent that certain cannabinoids possess immunomodulatory activity. Endothelial cells (ECs) are centrally involved in the pathogenesis of organ injury in acute inflammatory disorders, such as sepsis, because they express cytokines and chemokines, which facilitate the trafficking of leukocytes to organs, and they modulate vascular barrier function. In this study, we find that primary human ECs from multiple organs express the cannabinoid receptors CB1R, GPR18, and GPR55, as well as the ion channel transient receptor potential cation channel vanilloid type 1. In contrast to leukocytes, CB2R is only minimally expressed in some EC populations. Furthermore, we show that ECs express all of the known endocannabinoid (eCB) metabolic enzymes. Examining a panel of cannabinoids, we demonstrate that the synthetic cannabinoid WIN55,212-2 and the eCB N-arachidonoyl dopamine (NADA), but neither anandamide nor 2-arachidonoylglycerol, reduce EC inflammatory responses induced by bacterial lipopeptide, LPS, and TNFα. We find that endothelial CB1R/CB2R are necessary for the effects of NADA, but not those of WIN55,212-2. Furthermore, transient receptor potential cation channel vanilloid type 1 appears to counter the anti-inflammatory properties of WIN55,212-2 and NADA, but conversely, in the absence of these cannabinoids, its inhibition exacerbates the inflammatory response in ECs activated with LPS. These data indicate that the eCB system can modulate inflammatory activation of the endothelium and may have important implications for a variety of acute inflammatory disorders that are characterized by EC activation.

Targeting the cannabinoid system for pain relief?

Marijuana has been used to relieve pain for centuries, but its analgesic mechanism has only been understood during the past two decades. It is mainly mediated by its constituents, cannabinoids, through activating central cannabinoid 1 (CB1) receptors, as well as peripheral CB1 and CB2 receptors. CB2-selective agonists have the benefit of lacking CB1 receptor-mediated CNS side effects. Anandamide and 2-arachidonoylglycerol (2-AG) are two intensively studied endogenous lipid ligands of cannabinoid receptors, termed endocannabinoids, which are synthesized on demand and rapidly degraded. Thus, inhibitors of their degradation enzymes, fatty acid amide hydrolase and monoacylglycerol lipase (MAGL), respectively, may be superior to direct cannabinoid receptor ligands as a promising strategy for pain relief. In addition to the antinociceptive properties of exogenous cannabinoids and endocannabinoids, involving their biosynthesis and degradation processes, we also review recent studies that revealed a novel analgesic mechanism, involving 2-AG in the periaqueductal gray (PAG), a midbrain region for initiating descending pain inhibition. It is initiated by Gq-protein-coupled receptor (GqPCR) activation of the phospholipase C (PLC)-diacylglycerol lipase (DAGL) enzymatic cascade, generating 2-AG that produces inhibition of GABAergic transmission (disinhibition) in the PAG, thereby leading to analgesia. This GqPCR-PLC-DAGL-2-AG retrograde disinhibition mechanism in the PAG can be initiated by activating type 5 metabotropic glutamate receptor (mGluR5), muscarinic acetylcholine (M1/M3), and orexin (OX1) receptors. mGluR5-mediated disinhibition can be initiated by glutamate transporter inhibitors, or indirectly by substance P, neurotensin, cholecystokinin, capsaicin, and AM404, the bioactive metabolite of acetaminophen in the brain. The putative role of 2-AG generated after activating the above neurotransmitter receptors in stress-induced analgesia is also discussed.

Endocannabinoid system and pain: an introduction

The endocannabinoid (EC) system consists of two main receptors: cannabinoid type 1 receptor cannabinoid receptors are found in both the central nervous system (CNS) and periphery, whereas the cannabinoid type 2 receptor cannabinoid receptor is found principally in the immune system and to a lesser extent in the CNS. The EC family consists of two classes of well characterised ligands; the N-acyl ethanolamines, such as N-arachidonoyl ethanolamide or anandamide (AEA), and the monoacylglycerols, such as 2-arachidonoyl glycerol. The various synthetic and catabolic pathways for these enzymes have been (with the exception of AEA synthesis) elucidated. To date, much work has examined the role of EC in nociceptive processing and the potential of targeting the EC system to produce analgesia. Cannabinoid receptors and ligands are found at almost every level of the pain pathway from peripheral sites, such as peripheral nerves and immune cells, to central integration sites such as the spinal cord, and higher brain regions such as the periaqueductal grey and the rostral ventrolateral medulla associated with descending control of pain. EC have been shown to induce analgesia in preclinical models of acute nociception and chronic pain states. The purpose of this review is to critically evaluate the evidence for the role of EC in the pain pathway and the therapeutic potential of EC to produce analgesia. We also review the present clinical work conducted with EC, and examine whether targeting the EC system might offer a novel target for analgesics, and also potentially disease-modifying interventions for pathophysiological pain states.

Quantitative metabolic profiling of lipid mediators

Lipids are heterogeneous biological molecules that possess multiple physiological roles including cell structure, homeostasis, and restoration of tissue functionality during and after inflammation. Lipid metabolism constitutes a network of pathways that are related at multiple biosynthetic hubs. Disregulation of lipid metabolism can lead to pathophysiological effects and multiple lipid mediators have been described to be involved in physiological processes, (e.g. inflammation). Accordingly, a thorough description of these pathways may shed light on putative relations in multiple complex diseases, including chronic obstructive pulmonary disease, asthma, Alzheimer's disease, multiple sclerosis, obesity, and cancer. Due to the structural complexity of lipids and the low abundance of many lipid mediators, mass spectrometry is the most commonly employed method for analysis. However, multiple challenges remain in the efforts to analyze every lipid subfamily. In this review, the biological role of sphingolipids, glycerolipids, oxylipins (e.g. eicosanoids), endocannabinoids, and N-acylethanolamines in relation to health and disease and the state-of-the-art analyses are summarized. The characterization and understanding of these pathways will increase our ability to examine for interrelations among lipid pathways and improve the knowledge of biological mechanisms in health and disease.

Cannabinoid Receptor 2 (CB2) Plays a Role in the Generation of Germinal Center and Memory B Cells, but Not in the Production of Antigen-Specific IgG and IgM, in Response to T-dependent Antigens

The cannabinoid receptor 2 (CB2) has been reported to modulate B cell functions including migration, proliferation and isotype class switching. Since these processes are required for the generation of the germinal center (GC) and antigen-specific plasma and memory cells following immunization with a T-dependent antigen, CB2 has the capacity to alter the quality and magnitude of T-dependent immune responses. To address this question, we immunized WT and CB2^−/− mice with the T-dependent antigen 4-hydroxy-3-nitrophenylacetyl (NP)-chicken-gamma-globulin (CGG) and measured GC B cell formation and the generation of antigen-specific B cells and serum immunoglobulin (Ig). While there was a significant reduction in the number of splenic GC B cells in CB2^−/− mice early in the response there was no detectable difference in the number of NP-specific IgM and IgG₁ plasma cells. There was also no difference in NP-specific IgM and class switched IgG₁ in the serum. In addition, we found no defect in the homing of plasma cells to the bone marrow (BM) and affinity maturation, although memory B cell cells in the spleen were reduced in CB2^−/− mice. CB2-deficient mice also generated similar levels of antigen-specific IgM and IgG in the serum as WT following immunization with sheep red blood cells (sRBC). This study demonstrates that although CB2 plays a role in promoting GC and memory B cell formation/maintenance in the spleen, it is dispensable on all immune cell types required for the generation of antigen-specific IgM and IgG in T-dependent immune responses.

The actions and metabolism of lysophosphatidylinositol, an endogenous agonist for GPR55

Lysophosphatidylinositol (LPI) is a subspecies of lysophospholipid and is assumed to be not only a degradation product of phosphatidylinositol (PI), but also a bioactive lysophospholipid mediator. However, not much attention has been directed toward LPI compared to lysophosphatidic acid (LPA), since the receptor for LPI has not been identified. During screening for an agonist for the orphan G protein coupled receptor GPR55, we identified LPI, 2-arachidonoyl LPI in particular, as an agonist for GPR55. Our efforts to identify an LPI receptor facilitated research on LPI as a lipid messenger. In addition, we also found that DDHD1, previously identified as phosphatidic acid-preferring phospholipase A1, was one of the synthesizing enzymes of 2-arachidonoyl LPI. Here, we summarized the background for discovering the LPI receptor, and the actions/metabolism of LPI. We also referred to the biosynthesis of PI, a 1-stearoyl-2-arachidonoyl species, since the molecule is the precursor of 2-arachidonoyl LPI. Furthermore, we discussed physiological and/or pathophysiological processes involving LPI and GPR55, including the relevance of LPI-GPR55 and cannabinoids, since GPR55 was previously postulated to be another cannabinoid receptor. Although there is no doubt that GPR55 is the LPI receptor, we should re-consider whether or not GPR55 is in fact another cannabinoid receptor.

Why do cannabinoid receptors have more than one endogenous ligand?

The endocannabinoid system was revealed following the understanding of the mechanism of action of marijuana's major psychotropic principle, Δ(9)-tetrahydrocannabinol, and includes two G-protein-coupled receptors (GPCRs; the cannabinoid CB1 and CB2 receptors), their endogenous ligands (the endocannabinoids, the best studied of which are anandamide and 2-arachidonoylglycerol (2-AG)), and the proteins that regulate the levels and activity of these receptors and ligands. However, other minor lipid metabolites different from, but chemically similar to, anandamide and 2-AG have also been suggested to act as endocannabinoids. Thus, unlike most other GPCRs, cannabinoid receptors appear to have more than one endogenous agonist, and it has been often wondered what could be the physiological meaning of this peculiarity. In 1999, it was proposed that anandamide might also activate other targets, and in particular the transient receptor potential of vanilloid type-1 (TRPV1) channels. Over the last decade, this interaction has been shown to occur both in peripheral tissues and brain, during both physiological and pathological conditions. TRPV1 channels can be activated also by another less abundant endocannabinoid, N-arachidonoyldopamine, but not by 2-AG, and have been proposed by some authors to act as ionotropic endocannabinoid receptors. This article will discuss the latest discoveries on this subject, and discuss, among others, how anandamide and 2-AG differential actions at TRPV1 and cannabinoid receptors contribute to making this signalling system a versatile tool available to organisms to fine-tune homeostasis.

Full inhibition of spinal FAAH leads to TRPV1-mediated analgesic effects in neuropathic rats and possible lipoxygenase-mediated remodeling of anandamide metabolism

Neuropathic pain elevates spinal anandamide (AEA) levels in a way further increased when URB597, an inhibitor of AEA hydrolysis by fatty acid amide hydrolase (FAAH), is injected intrathecally. Spinal AEA reduces neuropathic pain by acting at both cannabinoid CB1 receptors and transient receptor potential vanilloid-1 (TRPV1) channels. Yet, intrathecal URB597 is only partially effective at counteracting neuropathic pain. We investigated the effect of high doses of intrathecal URB597 on allodynia and hyperalgesia in rats with chronic constriction injury (CCI) of the sciatic nerve. Among those tested, the 200 µg/rat dose of URB597 was the only one that elevated the levels of the FAAH non-endocannabinoid and anti-inflammatory substrates, oleoylethanolamide (OEA) and palmitoylethanolamide (PEA), and of the endocannabinoid FAAH substrate, 2-arachidonoylglycerol, and fully inhibited thermal and tactile nociception, although in a manner blocked almost uniquely by TRPV1 antagonism. Surprisingly, this dose of URB597 decreased spinal AEA levels. RT-qPCR and western blot analyses demonstrated altered spinal expression of lipoxygenases (LOX), and baicalein, an inhibitor of 12/15-LOX, significantly reduced URB597 analgesic effects, suggesting the occurrence of alternative pathways of AEA metabolism. Using immunofluorescence techniques, FAAH, 15-LOX and TRPV1 were found to co-localize in dorsal spinal horn neurons of CCI rats. Finally, 15-hydroxy-AEA, a 15-LOX derivative of AEA, potently and efficaciously activated the rat recombinant TRPV1 channel. We suggest that intrathecally injected URB597 at full analgesic efficacy unmasks a secondary route of AEA metabolism via 15-LOX with possible formation of 15-hydroxy-AEA, which, together with OEA and PEA, may contribute at producing TRPV1-mediated analgesia in CCI rats.

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.

The role of endocannabinoids in pain modulation

The endocannabinoid system (ES) is comprised of cannabinoid (CB) receptors, their endogenous ligands (endocannabinoids), and proteins responsible for their metabolism. Endocannabinoids serve as retrograde signaling messengers in GABAergic and glutamatergic synapses, as well as modulators of postsynaptic transmission, that interact with other neurotransmitters. Physiological stimuli and pathological conditions lead to differential increases in brain endocannabinoids that regulate distinct biological functions. Furthermore, endocannabinoids modulate neuronal, glial, and endothelial cell function and exert neuromodulatory, anti-excitotoxic, anti-inflammatory, and vasodilatory effects. Analgesia is one of the principal therapeutic targets of cannabinoids. Cannabinoid analgesia is based on the suppression of spinal and thalamic nociceptive neurons, but peripheral sites of action have also been identified. The chronic pain that occasionally follows peripheral nerve injury differs fundamentally from inflammatory pain and is an area of considerable unmet therapeutic need. Over the last years, considerable progress has been made in understanding the role of the ES in the modulation of pain. Endocannabinoids have been shown to behave as analgesics in models of both acute nociception and clinical pain such as inflammation and painful neuropathy. The framework for such analgesic effects exists in the CB receptors, which are found in areas of the nervous system important for pain processing and in immune cells that regulate the neuro-immune interactions that mediate the inflammatory hyperalgesia. The purpose of this review is to present the available research and clinical data, up to date, regarding the ES and its role in pain modulation, as well as its possible therapeutic perspectives.

Fatty Acid modulation of the endocannabinoid system and the effect on food intake and metabolism

Endocannabinoids and their G-protein coupled receptors (GPCR) are a current research focus in the area of obesity due to the system's role in food intake and glucose and lipid metabolism. Importantly, overweight and obese individuals often have higher circulating levels of the arachidonic acid-derived endocannabinoids anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) and an altered pattern of receptor expression. Consequently, this leads to an increase in orexigenic stimuli, changes in fatty acid synthesis, insulin sensitivity, and glucose utilisation, with preferential energy storage in adipose tissue. As endocannabinoids are products of dietary fats, modification of dietary intake may modulate their levels, with eicosapentaenoic and docosahexaenoic acid based endocannabinoids being able to displace arachidonic acid from cell membranes, reducing AEA and 2-AG production. Similarly, oleoyl ethanolamide, a product of oleic acid, induces satiety, decreases circulating fatty acid concentrations, increases the capacity for β -oxidation, and is capable of inhibiting the action of AEA and 2-AG in adipose tissue. Thus, understanding how dietary fats alter endocannabinoid system activity is a pertinent area of research due to public health messages promoting a shift towards plant-derived fats, which are rich sources of AEA and 2-AG precursor fatty acids, possibly encouraging excessive energy intake and weight gain.

Antiepileptic action of N-palmitoylethanolamine through CB1 and PPAR-α receptor activation in a genetic model of absence epilepsy

N-palmitoylethanolamine (PEA), an endogenous fatty acid ethanolamide, plays a key role in the regulation of the inflammatory response and pain through, among others, activation of nuclear peroxisome proliferator-activated receptors (PPAR-α). Endogenous cannabinoids play a protective role in several central nervous system (CNS) disorders, particularly those associated with neuronal hyperexcitability. We investigated the effects of PEA and the role of PPAR-α in absence epilepsy using the WAG/Rij rat model. PEA, anandamide (AEA), a PPAR-α antagonist (GW6471) and a synthetic CB1 receptor antagonist/inverse agonist (SR141716) were administered to WAG/Rij rats in order to evaluate the effects on epileptic spike-wave discharges (SWDs) on EEG recordings. We studied also the effects of PEA co-administration with SR141716 and GW6471 and compared these effects with those of AEA to evaluate PEA mechanism of action and focusing on CB1 receptors and PPAR-α. Both PEA and AEA administration significantly decreased SWDs parameters (absence seizures). In contrast, GW6471 was devoid of effects while SR141716 had pro-absence effects. The co-administration of SR141716 with PEA or AEA completely blocked the anti-absence effects of these compounds. GW6471 antagonized PEA's effects whereas it did not modify AEA's effects. Furthermore, we have also measured PEA, AEA and 2-AG (2-arachidonoylglycerol) brain levels identifying significant differences between epileptic and control rats such as decreased PEA levels in both thalamus and cortex that might contribute to absence epilepsy. Our data demonstrate that PEA has anti-absence properties in the WAG/Rij rat model and that such properties depend on PPAR-α and indirect activation of CB1 receptors. This article is part of the Special Issue entitled 'New Targets and Approaches to the Treatment of Epilepsy'.

Consequences of essential fatty acids

Essential fatty acids (EFA) are nutrients that form an amazingly large array of bioactive mediators that act on a large family of selective receptors. Nearly every cell and tissue in the human body expresses at least one of these receptors, allowing EFA-based signaling to influence nearly every aspect of human physiology. In this way, the health consequences of specific gene-environment interactions with these nutrients are more extensive than often recognized. The metabolic transformations have similar competitive dynamics for the n-3 and n-6 homologs when converting dietary EFA from the external environment of foods into the highly unsaturated fatty acid (HUFA) esters that accumulate in the internal environment of cells and tissues. In contrast, the formation and action of bioactive mediators during tissue responses to stimuli tend to selectively create more intense consequences for n-6 than n-3 homologs. Both n-3 and n-6 nutrients have beneficial actions, but many common health disorders are undesired consequences of excessive actions of tissue n-6 HUFA which are preventable. This review considers the possibility of preventing imbalances in dietary n-3 and n-6 nutrients with informed voluntary food choices. That action may prevent the unintended consequences that come from eating imbalanced diets which support excessive chronic actions of n-6 mediators that harm human health. The consequences from preventing n-3 and n-6 nutrient imbalances on a nationwide scale may be very large, and they need careful evaluation and implementation to avoid further harmful consequences for the national economy.

Cannabinoid receptors: nomenclature and pharmacological principles

The CB1 and CB2 cannabinoid receptors are members of the G protein-coupled receptor (GPCR) family that are pharmacologically well defined. However, the discovery of additional sites of action for endocannabinoids as well as synthetic cannabinoid compounds suggests the existence of additional cannabinoid receptors. Here we review this evidence, as well as the current nomenclature for classifying a target as a cannabinoid receptor. Basic pharmacological definitions, principles and experimental conditions are discussed in order to place in context the mechanisms underlying cannabinoid receptor activation. Constitutive (agonist-independent) activity is observed with the overexpression of many GPCRs, including cannabinoid receptors. Allosteric modulators can alter the pharmacological responses of cannabinoid receptors. The complex molecular architecture of each of the cannabinoid receptors allows for a single receptor to recognize multiple classes of compounds and produce an array of distinct downstream effects. Natural polymorphisms and alternative splice variants may also contribute to their pharmacological diversity. As our knowledge of the distinct differences grows, we may be able to target select receptor conformations and their corresponding pharmacological responses. Importantly, the basic biology of the endocannabinoid system will continue to be revealed by ongoing investigations.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Cannabinoid receptors in submandibular acinar cells: functional coupling between saliva fluid and electrolytes secretion and Ca2+ signalling

Cannabinoid receptors (CBRs) belong to the G protein-coupled receptor superfamily, and activation of CBRs in salivary cells inhibits agonist-stimulated salivation and modifies saliva content. However, the role of different CBR subtypes in acinar cell physiology and in intracellular signalling remains unclear. Here, we uncover functional CB(1)Rs and CB(2)Rs in acinar cells of rat submandibular gland and their essential role in saliva secretion. Pharmacological activation of CB(1)Rs and CB(2)Rs in the submandibular gland suppressed saliva outflow and modified saliva content produced by the submandibular gland in vivo. Using Na(+)-selective microelectrodes to record secretory Na(+) responses in the lumen of acini, we observed a reduction in Na(+) transport following the activation of CBRs, which was counteracted by the selective CB(1)R antagonist AM251. In addition, activation of CB(1)Rs or CB Rs caused inhibition of Na(+)-K(+) 2 -ATPase activity in microsomes derived from the gland tissue as well as in isolated acinar cells. Using a Ca(2+) imaging technique, we showed that activation of CB(1)Rs and CB(2)Rs alters [Ca(2+)](cyt) signalling in acinar cells by distinct pathways, involving Ca(2+) release from the endoplasmic reticulum (ER) and store-operated Ca(2+) entry (SOCE), respectively. Our data demonstrate the expression of CB(1)Rs and CB(2)Rs in acinar cells, and their involvement in the regulation of salivary gland functioning.

Mechanisms of osteoclastogenesis inhibition by a novel class of biphenyl-type cannabinoid CB(2) receptor inverse agonists

The cannabinoid CB(2) receptor is known to modulate osteoclast function by poorly understood mechanisms. Here, we report that the natural biphenyl neolignan 4'-O-methylhonokiol (MH) is a CB(2) receptor-selective antiosteoclastogenic lead structure (K(i) < 50 nM). Intriguingly, MH triggers a simultaneous G(i) inverse agonist response and a strong CB(2) receptor-dependent increase in intracellular calcium. The most active inverse agonists from a library of MH derivatives inhibited osteoclastogenesis in RANK ligand-stimulated RAW264.7 cells and primary human macrophages. Moreover, these ligands potently inhibited the osteoclastogenic action of endocannabinoids. Our data show that CB(2) receptor-mediated cAMP formation, but not intracellular calcium, is crucially involved in the regulation of osteoclastogenesis, primarily by inhibiting macrophage chemotaxis and TNF-α expression. MH is an easily accessible CB(2) receptor-selective scaffold that exhibits a novel type of functional heterogeneity.

Cannabinoid receptor 2 is critical for the homing and retention of marginal zone B lineage cells and for efficient T-independent immune responses

The endocannabinoid system has emerged as an important regulator of immune responses, with the cannabinoid receptor 2 (CB2) and its principle ligand 2-archidonoylglycerol playing a major role. How CB2 regulates B cell functions is not clear, even though they express the highest levels of CB2 among immune cell subsets. In this study, we show that CB2-deficient mice have a significant reduction in the absolute number of marginal zone (MZ) B cells and their immediate precursor, transitional-2 MZ precursor. The loss of MZ lineage cells in CB2(-/-) mice was shown to be B cell intrinsic using bone marrow chimeras and was not due to a developmental or functional defect as determined by B cell phenotype, proliferation, and Ig production. Furthermore, CB2(-/-) B cells were similar to wild type in their apoptosis, cell turnover, and BCR and Notch-2 signaling. We then demonstrated that CB2(-/-) MZ lineage B cells were less efficient at homing to the MZ and that their subsequent retention was also regulated by CB2. CB2(-/-) mice immunized with T-independent Ags produced significantly less Ag-specific IgM. This study demonstrates that CB2 positively regulates T-independent immune responses by controlling the localization and positioning of MZ lineage cells to the MZ.

Targeting CB(2) receptor as a neuroinflammatory modulator in experimental autoimmune encephalomyelitis

During immune mediated demyelinating lesions, the endocannabinoid system is involved in the pathogenesis of both neuroinflammation and neurodegeneration through different mechanisms. Here, we explored the cellular distribution of cannabinoid 2 receptor (CB(2)R) in the central nervous system (CNS) and detected the level of CB(2)R expression during experimental autoimmune encephalomyelitis (EAE) by RT-PCR, Western blot and immunostaining. Our results show that CB(2)R was expressed in neurons, microglia and astrocytes. During EAE, the expression of CB(2)R in spinal cord rose slowly at days 9 and 17 post immunization (p.i.), and elevated rapidly at day 28 p.i., while the expression of CB(2)R in spleen elevated rapidly and got a plateau at days 17 and 28 p.i. Only the increase of CB(2)R expression in spinal cord demonstrated a significant difference when compared to control mice immunized with complete Freund's adjuvant (CFA). The selective CB(2)R antagonist (SR144528) exacerbated EAE clinical severity accompanied by weight loss. SR144528 inhibited the expression of CB(2)R, but increased the expression of CB(1)R in brain, spinal cord and spleen. The administration of SR144528 declined interferon-γ, IL-17, IL-4, IL-10, IL-1β, IL-6 and tumor necrosis factor-α, but increased CX3CL1 in brain and/or spinal cord. In contrast, IL-17 and MCP-1 were increased, while CX3CL1 was decreased in splenic mononuclear cells as compared to vehicle controls. These results indicate that manipulation of CB(2)R may have therapeutic value in MS, but its complexity remains to be considered and studied for further clinical application.

GPR55 regulates cannabinoid 2 receptor-mediated responses in human neutrophils

The directional migration of neutrophils towards inflammatory mediators, such as chemokines and cannabinoids, occurs via the activation of seven transmembrane G protein coupled receptors (7TM/GPCRs) and is a highly organized process. A crucial role for controlling neutrophil migration has been ascribed to the cannabinoid CB(2) receptor (CB(2)R), but additional modulatory sites distinct from CB(2)R have recently been suggested to impact CB(2)R-mediated effector functions in neutrophils. Here, we provide evidence that the recently de-orphanized 7TM/GPCR GPR55 potently modulates CB(2)R-mediated responses. We show that GPR55 is expressed in human blood neutrophils and its activation augments the migratory response towards the CB(2)R agonist 2-arachidonoylglycerol (2-AG), while inhibiting neutrophil degranulation and reactive oxygen species (ROS) production. Using HEK293 and HL60 cell lines, along with primary neutrophils, we show that GPR55 and CB(2)R interfere with each other's signaling pathways at the level of small GTPases, such as Rac2 and Cdc42. This ultimately leads to cellular polarization and efficient migration as well as abrogation of degranulation and ROS formation in neutrophils. Therefore, GPR55 limits the tissue-injuring inflammatory responses mediated by CB(2)R, while it synergizes with CB(2)R in recruiting neutrophils to sites of inflammation.

Anti-inflammatory cannabinoids in diet: Towards a better understanding of CB(2) receptor action?

The endocannabinoid system is an ancient lipid signaling network which in mammals modulates neuronal functions, inflammatory processes, and is involved in the aetiology of certain human lifestyle diseases, such as Crohn's disease, atherosclerosis and osteoarthritis. The system is able to downregulate stress-related signals that lead to chronic inflammation and certain types of pain, but it is also involved in causing inflammation-associated symptoms, depending on the physiological context. The cannabinoid type-2 (CB(2)) receptor, which unlike the CB(1) receptor does not induce central side effects, has been shown to be a promising therapeutic target. While CB(1) receptor antagonists/inverse agonists are of therapeutic value, also CB(2) receptor ligands including agonists are of pharmacological interest. Although the endocannabinoid system is known to be involved in the regulation of energy homoeostasis and metabolism (mainly via CB(1) receptors) there was hitherto no direct link between food intake and cannabinoid receptor activation. Our recent finding that beta-caryophyllene, a ubiquitous lipohilic plant natural product, selectively binds to the CB(2) receptor and acts as a full agonist is unexpected. Maybe even more unexpected is that oral administration of this dietary compound exerts potent anti-inflammatory effects in wild type mice but not in CB(2) receptor (Cnr2(-/-)) knockout mice. Like other CB(2) ligands also beta-caryophyllene inhibits the pathways triggered by activation of the toll-like receptor complex CD14/TLR4/MD2, which typically lead to the expression of proinflammatory cytokines (IL-1beta, IL-6; IL-8 and TNFalpha) and promotes a TH(1) immune response. In this addendum, the CB(2) receptor-dependent effect of beta-caryophyllene on LPS-triggered activation of the kinases Erk1/2 and JNK1/2 are further discussed with respect to the possibility that both CB(2) inverse agonists and agonists, independent of their G-protein signaling, may block LPS-triggered activation of MAPKs, leading to inhibition of proinflammatory cytokine expression and attenuation of inflammation.

Crystal structure of a soluble form of human monoglyceride lipase in complex with an inhibitor at 1.35 Å resolution

A high-resolution structure of a ligand-bound, soluble form of human monoglyceride lipase (MGL) is presented. The structure highlights a novel conformation of the regulatory lid-domain present in the lipase family as well as the binding mode of a pharmaceutically relevant reversible inhibitor. Analysis of the structure lacking the inhibitor indicates that the closed conformation can accommodate the native substrate 2-arachidonoyl glycerol. A model is proposed in which MGL undergoes conformational and electrostatic changes during the catalytic cycle ultimately resulting in its dissociation from the membrane upon completion of the cycle. In addition, the study outlines a successful approach to transform membrane associated proteins, which tend to aggregate upon purification, into a monomeric and soluble form.

Administration of 2-arachidonoylglycerol ameliorates both acute and chronic experimental autoimmune encephalomyelitis

BACKGROUND AND PURPOSE

Experimental autoimmune encephalomyelitis (EAE) is a widely used model of multiple sclerosis (MS) and both conditions have been reported to exhibit reduced endocannabinoid activity. The purpose of this study was to address the effect of exogenously administered 2-arachidonoylglycerol (2AG), an endocannabinoid receptor ligand, on acute phase and chronic disability in EAE.

EXPERIMENTAL APPROACH

Acute and chronic EAE models were induced in susceptible mice and 2AG-treatment was applied for 14 days from day of disease induction.

KEY RESULTS

2AG-treatment ameliorated acute phase of disease with delay of disease onset in both EAE models and reduced disease mortality and long-term (70 days post-induction) clinical disability in chronic EAE. Reduced axonal pathology in the chronic EAE- (p<0.0001) and increased activation and ramification of microglia in the 2AG-treated acute EAE- (p<0.05) model were noticed. The latter was accompanied by a 2- to 4-fold increase of the M2-macrophages in the perivascular infiltrations (p<0.001) of the 2AG-treated animals in the acute (day 22), although not the chronic (day 70), EAE model. Expression of cannabinoid receptors 1 (CB1R) and 2 (CB2R) was increased in 2AG-treated animals of acute EAE vs. controls (p<0.05). In addition, ex vivo viability assays exhibited reduced proliferation of activated lymph node cells when extracted from 2AG-treated EAE animals, whereas a dose-dependent response of activated lymphocytes to 2AG-treatment in vitro was noticed.

CONCLUSION AND IMPLICATIONS

Our data indicate for the first time that 2AG treatment may provide direct (via CBRs) and immune (via M2 macrophages) mediated neuroprotection in EAE.

Chemoenzymatic Synthesis of 2-Arachidonoylglycerol, An Endogenous Ligand for Cannabinoid Receptors

A simple and efficient synthesis of 2-arachidonoyl glycerol, an endogenous agonist for cannabinoid receptors was achieved using Novozym 435, immobilized lipase from Candida Antarctica.

Cannabinoids: potential targets for bladder dysfunction

Cannabinoids are the active chemical components of Cannabis sativa (marijuana). The medical use of cannabis goes back over 5,000 years. Cannabinoids produce a very wide array of central and peripheral effects, some of which may have beneficial clinical applications. The discovery of cannabinoid receptors has spawned great interest within the pharmaceutical industry with the hopes of capitalizing on the beneficial effects of cannabis without the unwanted psychotropic effects on the central and peripheral nervous system. This chapter presents an overview of the pharmacology of cannabinoids and their derivatives. It reviews the current literature on central and peripheral cannabinoid receptors as related to effects on the lower urinary tract and the role of these receptors in normal and abnormal urinary tract function. An objective evaluation of the published results of clinical trials of cannabis extracts for the treatment of bladder dysfunction resulting from multiple sclerosis is also presented. It is clear that cannabinoid receptors are present in the lower urinary tract as well as spinal and higher centers involved in lower urinary tract control. Systemic cannabinoids have effects on the lower urinary tract that may be able to become clinically useful; however, a much greater understanding of the mechanisms of cannabinoid receptors in control of the human lower urinary tract is necessary to facilitate development of novel cannabinoid drugs for treatment of pelvic disorders.

CB2: a cannabinoid receptor with an identity crisis

CB(2) was first considered to be the 'peripheral cannabinoid receptor'. This title was bestowed based on its abundant expression in the immune system and presumed absence from the central nervous system. However, multiple recent reports question the absence of CB(2) from the central nervous system. For example, it is now well accepted that CB(2) is expressed in brain microglia during neuroinflammation. However, the extent of CB(2) expression in neurons has remained controversial. There have been studies claiming either extreme-its complete absence to its widespread expression-as well as everything in between. This review will discuss the reported tissue distribution of CB(2) with a focus on CB(2) in neurons, particularly those in the central nervous system as well as the implications of that presence. As CB(2) is an attractive therapeutic target for pain management and immune system modulation without overt psychoactivity, defining the extent of its presence in neurons will have a significant impact on drug discovery. Our recommendation is to encourage cautious interpretation of data that have been presented for and against CB(2)'s presence in neurons and to encourage continued rigorous study.