The endocannabinoid system: current pharmacological research and therapeutic possibilities

Crosstalk between the endocannabinoid and mid-brain dopaminergic systems: Implication in dopamine dysregulation

Endocannabinoids (eCBs) and the expanded endocannabinoid system (ECS)-"endocannabinoidome", consists of the endogenous ligands, eCBs, their canonical and non-canonical receptor subtypes, and their synthesizing and metabolizing enzymes. This system modulates a wide range of body functions and acts as a retrograde signaling system within the central nervous system (CNS) by inhibition of classical transmitters, and plays a vital modulatory function on dopamine, a major neurotransmitter in the CNS. Dopamine is involved in different behavioral processes and contributes to different brain disorders-including Parkinson's disease, schizophrenia, and drug addiction. After synthesis in the neuronal cytosol, dopamine is packaged into synaptic vesicles until released by extracellular signals. Calcium dependent neuronal activation results in the vesicular release of dopamine and interacts with different neurotransmitter systems. The ECS, among others, is involved in the regulation of dopamine release and the interaction occurs either through direct or indirect mechanisms. The cross-talk between the ECS and the dopaminergic system has important influence in various dopamine-related neurobiological and pathologic conditions and investigating this interaction might help identify therapeutic targets and options in disorders of the CNS associated with dopamine dysregulation.

Lipid-based formulations to increase cannabidiol bioavailability: In vitro digestion tests, pre-clinical assessment and clinical trial

Herein, medium-chain triglycerides (MCT), glyceryl monolinoleate (GML), and a self-emulsifying drug delivery system (SEDDS) for cannabidiol (CBD) delivery were compared using in vitro and in vivo (mouse and human) studies. In vitro digestion tests showed that SEDDS yielded the highest CBD recovery in the aqueous phase (86 ± 2%), followed by GML (13 ± 2%) and MCT (5.6% ± 0.8%). In vivo tests (mouse) revealed that SEDDS promoted the highest CBD exposure, exhibiting an area under the plasma concentration-time curve (AUC_0-6h) 1.48 times greater than GML and 3.97 times greater than that of the MCT formulation. A single-dose, open-label, crossover study performed in 11 volunteers showed that SEDDS increased CBD AUC_0-12h by 1.12 and 1.48 times in relation to GML and MCT, respectively. The in vitro-in vivo correlation was r² 0.75 for mice and r² 0.66 for humans. The AUC correlation between mice and humans was 0.98. Collectively, these results indicate that the lipid profile substantially influences CBD delivery and highlights the potential of the SEDDS and GML formulations as candidate solutions for increasing CBD AUC and bioavailability.

Chain Substituted Cannabilactones with Selectivity for the CB2 Cannabinoid Receptor

In earlier work, we reported a novel class of CB2 selective ligands namely cannabilactones. These compounds carry a dimethylheptyl substituent at C3, which is typical for synthetic cannabinoids. In the current study with the focus on the pharmacophoric side chain at C3 we explored the effect of replacing the C1'-gem-dimethyl group with the bulkier cyclopentyl ring, and, we also probed the chain's length and terminal carbon substitution with bromo or cyano groups. One of the analogs synthesized namely 6-[1-(1,9-dihydroxy-6-oxo-6H-benzo[c]chromen-3-yl) cyclopentyl] hexanenitrile (AM4346) has very high affinity (Ki = 4.9 nM) for the mouse CB2 receptor (mCB2) and 131-fold selectivity for that target over the rat CB1 (rCB1). The species difference in the affinities of AM4346 between the mouse (m) and the human (h) CB2 receptors is reduced when compared to our first-generation cannabilactones. In the cyclase assay, our lead compound was found to be a highly potent and efficacious hCB2 receptor agonist (EC50 = 3.7 ± 1.5 nM, E(max) = 89%). We have also extended our structure-activity relationship (SAR) studies to include biphenyl synthetic intermediates that mimic the structure of the phytocannabinoid cannabinodiol.

Lipocalin-Type Prostaglandin D Synthase Is a Novel Phytocannabinoid-Binding Protein

Lipocalin-type prostaglandin D synthase (L-PGDS; EC:5.3.99.2) is an enzyme with dual functional roles as a prostaglandin D₂ -synthesizing enzyme and as an extracellular transporter for diverse lipophilic compounds in the cerebrospinal fluid (CSF). Transport of hydrophobic endocannabinoids is mediated by serum albumin in the blood and intracellularly by the fatty acid binding proteins, but no analogous transport mechanism has yet been described in CSF. L-PGDS has been reported to promiscuously bind a wide variety of lipophilic ligands and is among the most abundant proteins found in the CSF. Here, we examine the binding of several classes of endogenous and synthetic ligands to L-PGDS. Endocannabinoids exhibited low affinity toward L-PGDS, while cannabinoid metabolites and synthetic cannabinoids displayed higher affinities for L-PGDS. These results indicate that L-PGDS is unlikely to function as a carrier for endocannabinoids in the CSF, but it may bind and transport a subset of cannabinoids.

The Fatty Acid Amide Hydrolase Inhibitor URB937 Ameliorates Radiation-Induced Lung Injury in a Mouse Model

Radiation-induced lung injury (RILI) is a potentially life-threatening complication of radiotherapy. In the current study, we examined the potential protective effects of URB937, an inhibitor of fatty acid amide hydrolase using a mouse model of RILI. Briefly, male C57BL/6 mice received 16Gy irradiation to the thoracic region and then intraperitoneal injection of either URB937 (1 mg/kg) or vehicle every 2 days for 30 days. The extent of the lung injury was evaluated histologically at the end of the drug treatment as well as 3 months after the cessation of the treatment. The data showed URB937 attenuated radiation-induced lung injury and increased endocannabinoid concentration in lung tissue. Treatment with URB937 decreased leukocyte migration and inflammatory cytokines in bronchoalveolar lavage fluid and plasma at day 30. Histopathological examination revealed URB937 could restore lung structure and restrain inflammatory cell and fibroblast accumulation caused by irradiation in lung tissue. URB937 also decreased radiation-induced pro-inflammatory (e.g., interleukin-1β, interleukin-6, tumor necrosis factor-α) and pro-fibrotic cytokines (e.g., transforming growth factor-β1) level in lung tissue, as well as lipid peroxidation in the lungs. Mouse survival examined in a separate group of experimental subjects indicated that URB937 could prolong animal survival. Experiments using a mouse bearing Lewis lung carcinoma cells showed that URB937 does not affect irradiation-induced inhibition of tumor growth. These results suggest that inhibiting fatty acid amide hydrolase could ameliorate RILI without compromising the efficacy of irradiation on tumor control.

2-Arachidonoylglycerol metabolism is differently modulated by oligomeric and fibrillar conformations of amyloid beta in synaptic terminals

Alzheimer's disease (AD) is the most prevalent disorder of senile dementia mainly characterized by amyloid-beta peptide (Aβ) deposits in the brain. Cannabinoids are relevant to AD as they exert several beneficial effects in many models of this disease. Still, whether the endocannabinoid system is either up- or down-regulated in AD has not yet been fully elucidated. Thus, the aim of the present paper was to analyze endocannabinoid 2-arachidonoylglycerol (2-AG) metabolism in cerebral cortex synaptosomes incubated with Aβ oligomers or fibrils. These Aβ conformations were obtained by "aging" the 1-40 fragment of the peptide under different agitation and time conditions. A diminished availability of 2-AG resulting from a significant decrease in diacylglycerol lipase (DAGL) activity was observed in the presence of large Aβ_1-40 oligomers along with synaptosomal membrane damage, as judged by transmission electron microscopy and LDH release. Conversely, a high availability of 2-AG resulting from an increase in DAGL and lysophosphatidic acid phosphohydrolase activities occurred in the presence of Aβ_1-40 fibrils although synaptosomal membrane disruption was also observed. Interestingly, neither synaptosomal mitochondrial viability assayed by MTT reduction nor membrane lipid peroxidation assayed by TBARS formation measurements were altered by Aβ_1-40 oligomers or fibrils. These results show a differential effect of Aβ_1-40 peptide on 2-AG metabolism depending on its conformation.

The effect of FAAH, MAGL, and Dual FAAH/MAGL inhibition on inflammatory and colorectal distension-induced visceral pain models in Rodents

BACKGROUND

Recent studies showed that the pharmacological inhibition of endocannabinoid degrading enzymes such as fatty acid amide hydrolase (FAAH) and monoacyl glycerol lipase (MAGL) elicit promising analgesic effects in a variety of nociceptive models without serious side effects. However, the full spectrum of activities is not observed upon inhibition of either FAAH or MAGL enzymes alone and thus dual FAAH and MAGL inhibitors have been described. Visceral pain is strongly associated with inflammation and distension of the gut. Thus, we explored the comparable effects of FAAH, MAGL, and dual FAAH/MAGL inhibitors on inflammatory and mechanically evoked visceral pain models.

METHODS

Visceral inflammatory and distension-induced pain were assessed with the 0.6% acetic acid writhing test in mice and colorectal distension (CRD) test in rats, respectively. The selective FAAH inhibitor PF 3845, MAGL inhibitor JZL 184, dual inhibitor JZL 195, and the cannabis analog CP 55,940 were given systemically 30 min prior to nociceptive testing.

KEY RESULTS

PF 3845 (5, 10, and 20 mg/kg), JZL 184 (5, 10, and 20 mg/kg), and JZL 195 (5, 10, and 20 mg/kg) elicit dose-dependent antinociceptive in the acetic acid writhing test. In the CRD model, while JZL 195 (5, 10, or 20 mg/kg) and PF3845 (10, 20, and 40 mg/kg) produced dose-dependent antinociceptive effects comparable to those of CP 55,940 (0.1, 0.3, or 1 mg/kg), JZL 184 (10, 20, and 40 mg/kg) alone did not alter the visceromotor response (VMR).

CONCLUSIONS & INFERENCES

The selective FAAH inhibitor and dual FAAH/MAGL inhibitors were effective in both inflammatory and mechanically evoked visceral pain, while the MAGL inhibitor elicited an analgesic effect in inflammatory, but not in distension-induced, visceral pain.

A novel near-infrared fluorescence imaging probe that preferentially binds to cannabinoid receptors CB2R over CB1R

The type 2 cannabinoid receptors (CB2R) have gained much attention recently due to their important regulatory role in a host of pathophysiological processes. However, the exact biological function of CB2R and how this function might change depending on disease progression remains unclear and could be better studied with highly sensitive and selective imaging tools for identifying the receptors. Here we report the first near infrared fluorescence imaging probe (NIR760-XLP6) that binds preferentially to CB2R over the type 1 cannabinoid receptors (CB1R). The selectivity of the probe was demonstrated by fluorescence microscopy using DBT-CB2 and DBT-CB1 cells. Furthermore, in mouse tumor models, NIR760-XLP6 showed significantly higher uptake in DBT-CB2 than that in DBT-CB1 tumors. These findings indicate that NIR760-XLP6 is a promising imaging tool for the study of CB2R regulation.

Interplay between synaptic endocannabinoid signaling and metaplasticity in neuronal circuit function and dysfunction

Synaptic neuromodulation acts across different functional domains to regulate cognitive processing and behavior. Recent challenges are related to elucidating the molecular and cellular mechanisms through which neuromodulatory pathways act on multiple time scales to signal state-dependent contingencies at the synaptic level or to stabilise synaptic connections during behavior. Here, we present a framework with the synaptic neuromodulators endocannabinoids (eCBs) as key players in dynamic synaptic changes. Modulation of various molecular components of the eCB pathway yields interconnected functional activation states of eCB signaling (prior, tonic, and persistent), which may contribute to metaplastic control of synaptic and behavioral functions in health and disease. The emerging picture supports aberrant metaplasticity as a contributor to cognitive dysfunction associated with several pathological states in which eCB signaling, or other neuromodulatory pathways, are deregulated.

Cannabinoid Regulation of Brain Reward Processing with an Emphasis on the Role of CB1 Receptors: A Step Back into the Future

Over the last decades, the endocannabinoid system has been implicated in a large variety of functions, including a crucial modulation of brain-reward circuits and the regulation of motivational processes. Importantly, behavioral studies have shown that cannabinoid compounds activate brain reward mechanisms and circuits in a similar manner to other drugs of abuse, such as nicotine, alcohol, cocaine, and heroin, although the conditions under which cannabinoids exert their rewarding effects may be more limited. Furthermore, there is evidence on the involvement of the endocannabinoid system in the regulation of cue- and drug-induced relapsing phenomena in animal models. The aim of this review is to briefly present the available data obtained using diverse behavioral experimental approaches in experimental animals, namely, the intracranial self-stimulation paradigm, the self-administration procedure, the conditioned place preference procedure, and the reinstatement of drug-seeking behavior procedure, to provide a comprehensive picture of the current status of what is known about the endocannabinoid system mechanisms that underlie modification of brain-reward processes. Emphasis is placed on the effects of cannabinoid 1 (CB1) receptor agonists, antagonists, and endocannabinoid modulators. Further, the role of CB1 receptors in reward processes is investigated through presentation of respective genetic ablation studies in mice. The vast majority of studies in the existing literature suggest that the endocannabinoid system plays a major role in modulating motivation and reward processes. However, much remains to be done before we fully understand these interactions. Further research in the future will shed more light on these processes and, thus, could lead to the development of potential pharmacotherapies designed to treat reward-dysfunction-related disorders.

Role of cannabinoids in the treatment of pain and (painful) spasticity

Both the discovery of the endocannabinoid system (ECS) and its role in the control of pain and habituation to stress, as well as the significant analgesic and antihyperalgesic effects in animal studies, suggest the usefulness of cannabinoids in pain conditions. However, in human experimental or clinical trials, no convincing reduction of acute pain, which may be caused by a pronociceptive, ECS-triggered mechanism on the level of the spinal cord, has been demonstrated. In contrast, in chronic pain and (painful) spasticity, an increasing number of randomized, double-blind, placebo-controlled studies have shown the efficacy of cannabinoids, which is combined with a narrow therapeutic index. Patients with unsatisfactory response to other methods of pain therapy and who were characterized by failed stress adaptation particularly benefited from treatment with cannabinoids. None of the attempts to overcome the disadvantage of the narrow therapeutic index, either by changing the route of application or by formulating balanced cannabinoid preparations, have resulted in a major breakthrough. Therefore, different methods of administration and other types of cannabinoids, such as endocannabinoid modulators, should be tested in future trials.

Endocannabinoid signaling in midbrain dopamine neurons: more than physiology?

Different classes of neurons in the CNS utilize endogenous cannabinoids as retrograde messengers to shape afferent activity in a short- and long-lasting fashion. Transient suppression of excitation and inhibition as well as long-term depression or potentiation in many brain regions require endocannabinoids to be released by the postsynaptic neurons and activate presynaptic CB1 receptors. Memory consolidation and/or extinction and habit forming have been suggested as the potential behavioral consequences of endocannabinoid-mediated synaptic modulation. HOWEVER, ENDOCANNABINOIDS HAVE A DUAL ROLE: beyond a physiological modulation of synaptic functions, they have been demonstrated to participate in the mechanisms of neuronal protection under circumstances involving excessive excitatory drive, glutamate excitotoxicity, hypoxia-ischemia, which are key features of several neurodegenerative disorders. In this framework, the recent discovery that the endocannabinoid 2-arachidonoyl-glycerol is released by midbrain dopaminergic neurons, under both physiological synaptic activity to modulate afferent inputs and pathological conditions such as ischemia, is particularly interesting for the possible implication of these molecules in brain functions and dysfunctions. Since dopamine dysfunctions underlie diverse neuropsychiatric disorders including schizophrenia, psychoses, and drug addiction, the importance of better understanding the correlation between an unbalanced endocannabinoid signal and the dopamine system is even greater. Additionally, we will review the evidence of the involvement of the endocannabinoid system in the pathogenesis of Parkinson's disease, where neuroprotective actions of cannabinoid-acting compounds may prove beneficial.The modulation of the endocannabinoid system by pharmacological agents is a valuable target in protection of dopamine neurons against functional abnormalities as well as against their neurodegeneration.

Dual blockade of FAAH and MAGL identifies behavioral processes regulated by endocannabinoid crosstalk in vivo

Delta(9)-tetrahydrocannabinol (THC), the psychoactive component of marijuana, and other direct cannabinoid receptor (CB1) agonists produce a number of neurobehavioral effects in mammals that range from the beneficial (analgesia) to the untoward (abuse potential). Why, however, this full spectrum of activities is not observed upon pharmacological inhibition or genetic deletion of either fatty acid amide hydrolase (FAAH) or monoacylglycerol lipase (MAGL), enzymes that regulate the two major endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG), respectively, has remained unclear. Here, we describe a selective and efficacious dual FAAH/MAGL inhibitor, JZL195, and show that this agent exhibits broad activity in the tetrad test for CB1 agonism, causing analgesia, hypomotilty, and catalepsy. Comparison of JZL195 to specific FAAH and MAGL inhibitors identified behavioral processes that were regulated by a single endocannabinoid pathway (e.g., hypomotility by the 2-AG/MAGL pathway) and, interestingly, those where disruption of both FAAH and MAGL produced additive effects that were reversed by a CB1 antagonist. Falling into this latter category was drug discrimination behavior, where dual FAAH/MAGL blockade, but not disruption of either FAAH or MAGL alone, produced THC-like responses that were reversed by a CB1 antagonist. These data indicate that AEA and 2-AG signaling pathways interact to regulate specific behavioral processes in vivo, including those relevant to drug abuse, thus providing a potential mechanistic basis for the distinct pharmacological profiles of direct CB1 agonists and inhibitors of individual endocannabinoid degradative enzymes.

Cannabinoids against pain. Efficacy and strategies to reduce psychoactivity: a clinical perspective

The clinical use of cannabinoids is currently a topic of interest not exclusively, but most importantly, concerning different areas of pain therapy. One of the major obstacles in developing clinically acceptable compounds is the cannabimimetic side-effect profile of delta-9-tetrahydrocannabinol (THC) and other cannabinoids. This article gives a brief overview of the endocannabinoid system, its components and functions and explains the current approaches to avoiding cannabimimetic side effects by separating them from the therapeutic effects. One of these approaches is the addition of cannabidiol (CBD) as well as the use of preparations suitable for oromucosal application. Also cannabinoids, which primarily stimulate peripheral cannabinoid-1 (CB1) receptors or selectively cannabinoid-2 (CB2) receptors, can further separate analgesic activity from cannabimimetic activity. Local or topical modes of application are another attempt aiming in the same direction. Modulating the endogenous cannabinoid tone (via the inhibition of endocannabinoid-metabolising enzymes) is another strategy. The combination of THC in low, non-psychoactive doses with opioids has a synergistic effect and reduces opioid tolerance effects. Available data from these approaches are summarised and their more and less promising aspects are discussed.

Basic neuroanatomy and neuropharmacology of cannabinoids

Humans have used Cannabis sativa (marijuana) for at least 12,000 years, but researchers have only recently described an endogenous cannabinoid system. The endocannabinoid system modulates an array of physiological and psychological functions. Endocannabinoids are widely distributed throughout the body, including the central nervous system (CNS). This article gives a basic overview of endocannabinoid neuroanatomy and function. Several endocannabinoids have been discovered to date, and their roles are being elucidated. Two G-protein coupled cannabinoid receptors, CB1R and CB2R, have been identified, although other candidate receptors exist, including ion channel and nuclear receptors that might be components of the endocannabinoid system. It appears that cannabinoids are dysregulated in a number of psychiatric disorders and might be involved in their pathogenesis. There is now evidence that manipulation of the endocannabinoid system could be a therapeutic target for a variety of conditions.

Inhibition of fatty acid amide hydrolase and cyclooxygenase-2 increases levels of endocannabinoid related molecules and produces analgesia via peroxisome proliferator-activated receptor-alpha in a model of inflammatory pain

The antinociceptive effects of the endocannabinoids (ECs) are enhanced by inhibiting catabolic enzymes such as fatty acid amide hydrolase (FAAH). The physiological relevance of the metabolism of ECs by other pathways, such as cyclooxygenase-2 (COX2) is less clear. To address this question we compared the effects of local inhibition of FAAH versus COX2 (URB597 and nimesulide, respectively) on inflammatory hyperalgesia and levels of endocannabinoids and related molecules in the hindpaw. Inflammatory hyperalgesia was measured following intraplantar injection of carrageenan. Effects of intraplantar injection of URB597 (25 microg and 100 microg) or nimesulide (50 microg) on hyperalgesia and hindpaw levels of anandamide (AEA), 2-arachidonoylglycerol (2AG) and N-palmitoylethanolamine (PEA) were determined. Although both doses of URB597 increased levels of AEA and 2AG in the carrageenan inflamed hindpaw, only the lower dose of URB597 attenuated hyperalgesia (P<0.05). Nimesulide attenuated both hyperalgesia and hindpaw oedema (P<0.001, P<0.01, respectively) and increased levels of PEA (P<0.05) in the hindpaw. Since both AEA and PEA are ligands for peroxisome proliferator-activated receptor-alpha (PPARalpha), the effects of the PPARalpha antagonist GW6471 on nimesulide- and URB597-mediated effects were studied. GW6471, but not a PPARgamma antagonist, blocked the inhibitory effects of nimesulide and URB597 on hyperalgesia. Our data suggest that both COX2 and FAAH play a role in the metabolism of endocannabinoids and related molecules. The finding that PPARalpha antagonism blocked the inhibitory effects of nimesulide and URB597 suggests that PPARalpha contributes to their antinociceptive effects in the carrageenan model of inflammatory hyperalgesia.

New tetrazole-based selective anandamide uptake inhibitors

A new series of 1,5- and 2,5-disubstituted tetrazoles have been synthesized and evaluated as inhibitors of anandamide cellular uptake. Some of them inhibit the uptake process with a relatively high potency (IC(50)=2.3-5.1microM) and selectively over other proteins involved in endocannabinoid action and metabolism.

The endocannabinoid system in cancer-potential therapeutic target?

Endogenous arachidonic acid metabolites with properties similar to compounds of Cannabis sativa Linnaeus, the so-called endocannabinoids, have effects on various types of cancer. Although endocannabinoids and synthetic cannabinoids may have pro-proliferative effects, predominantly inhibitory effects on tumor growth, angiogenesis, migration and metastasis have been described. Remarkably, these effects may be selective for the cancer cells, while normal cells and tissues are spared. Such apparent tumor cell selectivity makes the endocannabinoid system an attractive potential target for cancer therapy. In this review we discuss various means by which the endocannabinoid system may be targeted in cancer and the current knowledge considering the regulation of the endocannabinoid system in malignancy.

Agonist-dependent cannabinoid receptor signalling in human trabecular meshwork cells

BACKGROUND AND PURPOSE

Trabecular meshwork (TM) is an ocular tissue involved in the regulation of aqueous humour outflow and intraocular pressure (IOP). CB1 receptors (CB1) are present in TM and cannabinoid administration decreases IOP. CB1 signalling was investigated in a cell line derived from human TM (hTM).

EXPERIMENTAL APPROACH

CB1 signalling was investigated using ratiometric Ca2+ imaging, western blotting and infrared In-Cell Western analysis.

KEY RESULTS

WIN55212-2, a synthetic aminoalkylindole cannabinoid receptor agonist (10-100 microM) increased intracellular Ca2+ in hTM cells. WIN55,212-2-mediated Ca2+ increases were blocked by AM251, a CB1 antagonist, but were unaffected by the CB2 antagonist, AM630. The WIN55,212-2-mediated increase in [Ca2+]i was pertussis toxin (PTX)-insensitive, therefore, independent of Gi/o coupling, but was attenuated by a dominant negative Galpha(q/11) subunit, implicating a Gq/11 signalling pathway. The increase in [Ca2+]i was dependent upon PLC activation and mobilization of intracellular Ca2+ stores. A PTX-sensitive increase in extracellular signal-regulated kinase (ERK1/2) phosphorylation was also observed in response to WIN55,212-2, indicative of a Gi/o signalling pathway. CB1-Gq/11 coupling to activate PLC-dependent increases in Ca2+ appeared to be specific to WIN55,212-2 and were not observed with other CB1 agonists, including CP55,940 and methanandamide. CP55940 produced PTX-sensitive increases in [Ca2+]i at concentrations>or=15 microM, and PTX-sensitive increases in ERK1/2 phosphorylation.

CONCLUSIONS AND IMPLICATIONS

This study demonstrates that endogenous CB1 couples to both Gq/11 and Gi/o in hTM cells in an agonist-dependent manner. Cannabinoid activation of multiple CB1 signalling pathways in TM tissue could lead to differential changes in aqueous humour outflow and IOP.

5-Lipoxygenase and anandamide hydrolase (FAAH) mediate the antitumor activity of cannabidiol, a non-psychoactive cannabinoid

It has been recently reported that cannabidiol (CBD), a non-psychoactive cannabinoid, is able to kill glioma cells, both in vivo and in vitro, independently of cannabinoid receptor stimulation. However, the underlying biochemical mechanisms were not clarified. In the present study, we performed biochemical analysis of the effect of CBD both in vivo, by using glioma tumor tissues excised from nude mice, and in vitro, by using U87 glioma cells. In vivo exposure of tumor tissues to CBD significantly decreased the activity and content of 5-lipoxygenase (LOX, by approximately 40%), and of its end product leukotriene B4 ( approximately 25%). In contrast cyclooxygenase (COX)-2 activity and content, and the amount of its end product prostaglandin E2, were not affected by CBD. In addition, in vivo treatment with CBD markedly stimulated ( approximately 175%) the activity of fatty acid amide hydrolase (FAAH), the main anandamide-degrading enzyme, while decreasing anandamide content ( approximately 30%) and binding to CB1 cannabinoid receptors ( approximately 25%). In vitro pre-treatment of U87 glioma cells with MK-886, a specific 5-LOX inhibitor, significantly enhanced the antimitotic effect of CBD, whereas the pre-treatment with indomethacin (pan-COX inhibitor) or celecoxib (COX-2 inhibitor), did not alter CBD effect. The study of the endocannabinoid system revealed that CBD was able to induce a concentration-dependent increase of FAAH activity in U87 cells. Moreover, a significantly reduced growth rate was observed in FAAH-over-expressing U87 cells, compared to wild-type controls. In conclusion, the present investigation indicates that CBD exerts its antitumoral effects through modulation of the LOX pathway and of the endocannabinoid system, suggesting a possible interaction of these routes in the control of tumor growth.

New 1,2,3,4-tetrahydropyrrolo[3,4-b]indole derivatives as selective CB2 receptor agonists

The preparation and evaluation of a novel class of CB2 agonists based on a 1,2,3,4-tetrahydropyrrolo[3,4-b]indole moiety are reported. They showed binding affinities up to 4.2 nM toward CB2 with sub-nanomolar EC(50) values. They also showed moderate to good (>350-fold) selectivity over the CB1 receptor.

The complications of promiscuity: endocannabinoid action and metabolism

In this review, we present our understanding of the action and metabolism of endocannabinoids and related endogenous molecules. It is clear that the interactions between the multiple endocannabinoid-like molecules (ECLs) are highly complex, both at the level of signal transduction and metabolism. Thus, ECLs are a group of ligands active at 7-transmembrane and nuclear receptors, as well as transmitter-gated and ion channels. ECLs and their metabolites can converge on common endpoints (either metabolic or signalling) through contradictory or reinforcing pathways. We highlight the complexity of the endocannabinoid system, based on the promiscuous nature of ECLs and their metabolites, as well as the synthetic modulators of the endocannabinoid system.

Obesity in neurobiology

Obesity reflects an imbalance between energy uptake and expenditure that is mediated by behavior. Obesity is a growing epidemic and a major risk factor for neurobiological diseases like stroke, dementia, intracranial hypertension and sleep disorders. Conversely, obesity can also be induced by neurobiological disorders and drugs. The etiology of obesity is complex and includes biology, behavior and environment. Physicians are faced with the need to manage obesity while strategies for prevention and sustained weight reduction are limited. Present treatment options comprise lifestyle modification, diet, pharmacotherapy and bariatric surgery. Considerable headway has been made into elucidating the neurobiological underpinnings of obesogenic behavior. There is now a growing understanding of the metabolic, hormonal and behavioral circuitries that contribute to the complex and redundant system for energy balance. Changing the net balance of this system to prevent or reduce obesity requires multimodal and long-term interventions.

Strategies to improve ingestive behaviour with reference to critical illness

The complex interplay between neural and endocrine responses following food intake regulates ingestive behaviour and ultimately determines subsequent energy intake. These processes include cognitive, gastrointestinal-derived and metabolic mechanisms. Such physiological responses to the ingestion of food initiate short- to medium-term inhibition of intake (satiety). However, in clinical states in which systemic inflammation is evident there is a more profound satiety response and a clear absence of motivation to eat that is evident as loss of appetite. These negative influences on energy intake can contribute to poor nutritional status, and consequently poor physical function, and impact on rehabilitation and recovery. Cytokine mediators of the inflammatory response directly influence feeding behaviour at the hypothalamic nuclei and may explain the lack of motivation and desire for food. However, additional detrimental effects on appetite are brought about because of alterations in intermediary metabolism present in inflammation-induced catabolism. This process forms part of the host response to inflammation and may explain symptoms, such as early satiety, frequently reported in many patient groups. In clinical states, and cancer in particular, pharmacological strategies have been employed to ameliorate the inflammatory response in an attempt to improve energy intake. Some success of this approach has been reported following administration of substrates such as EPA. Novel strategies to improve intake through administration of anti-cytokine drugs such as thalidomide may also be of benefit. However, drugs that oppose the actions of neurotransmitter pathways involved in central induction of satiety, such as 5-hydroxytryptamine, have failed to improve intake but appear to enhance enjoyment of food. Such findings indicate that therapeutic nutritional targets can only be achieved where novel pharmacological therapies can be supported by more innovative and integrated dietary management strategies. Many of these strategies remain to be elucidated.

The pharmacology of the cannabinoid system--a question of efficacy and selectivity

Our knowledge of the function of the cannabinoid system in the body has been aided by the availability of pharmacological agents that affect its function. This has been achieved by the design of agents that either directly interact with the receptor (agonists and antagonist/inverse agonists) and agents that indirectly modulate the receptor output by changing the levels of the endogenous cannabinoids (endocannabinoids). In this review, examples of the most commonly used receptor agonists, antagonists/inverse agonists, and indirectly acting agents (anandamide uptake inhibitors, fatty acid amide hydrolase inhibitors, monoacylglycerol lipase inhibitors) are given, with particular focus upon their selectivity and, in the case of the directly acting compounds, efficacy. Finally, the links between the endocannabinoid and cyclooxygenase pathways are explored, in particular, with respect to agents whose primary function is to inhibit cyclooxygenase activity, but which also interact with the endocannabinoid system.

Enhancement of endocannabinoid signalling during adolescence: Modulation of impulsivity and long-term consequences on metabolic brain parameters in early maternally deprived rats

Pharmacological modulation of the endocannabinoid system is a novel but poorly explored field for potential therapy. Early maternal deprivation represents an animal model for specific aspects of neuropsychiatric disorders. This study explored whether a pharmacological manipulation of the endocannabinoid system at adolescence may restore altered phenotypes resulting from early maternal deprivation. Wistar male rats, maternally deprived for 24 h on postnatal day (PND) 9, were administered the fatty-acid amide hydrolase (FAAH) inhibitor URB597 (0, 0.1 or 0.5 mg/kg/day) for six days during adolescence (PND 31-43), while tested in the intolerance-to-delay task. Deprived (DEP) adolescent rats showed a trend for higher impulsivity levels and an increased locomotor response to novelty when compared to non-deprived (NDEP) controls. The low dose of URB597 effectively decreased impulsive behaviour specifically in DEP subjects. Moreover, long-term metabolic brain changes, induced by drug treatment during adolescence, were detected in DEP animals using proton magnetic resonance spectroscopy ((1)H MRS). Significant changes were only found within the hippocampus: N-acetyl-aspartate and total creatine were up-regulated by the low dose; glutamate and glutamate plus glutamine were conversely down-regulated by the higher dose. In summary, administration of URB597 during adolescence increased self-control behaviour and produced enduring brain biochemical modifications, in a model for neuropsychiatric disorders.

Rimonabant: endocannabinoid inhibition for the metabolic syndrome

Rimonabant is the first drug to target the endocannabinoid (CB) pathway by inhibiting the actions of anandamide and 2-archidonyl-glycerol on CB1 receptors. This review gives an overview of rimonabant and the CB system and how this system relates to obesity. Rimonabant blocks the central effects of this neurotransmitter pathway involved in obesity and weight control and also blocks the direct effects of CBs on adipocyte and hepatocyte metabolism. Blockade of CB1 receptors leads to a decrease in appetite and also has direct actions in adipose tissue and the liver to improve glucose, fat and cholesterol metabolism so improving insulin resistance, triglycerides and high-density lipoprotein cholesterol (HDL-C) and in some patients, blood pressure. The Rimonabant in Obesity (RIO) trials have shown that rimonabant induces weight loss > 5% in 30-40% of patients and > 10% in 10-20% above both a dietary run-in and long-term hypocaloric management over a 2 year period with a low level of drug-related side effects. Rimonabant therapy is associated with an extra 8-10% increase in HDL-C and a 10-30% reduction in triglycerides and improvements in insulin resistance, glycaemic control in patients with diabetes and also adipokines and cytokines including C-reactive protein over hypocaloric diet therapy. In addition rimonabant abolishes the weight gain associated with smoking cessation and improves the chances of quitting smoking. Thus rimonabant has major effects on both the metabolic syndrome and cardiovascular risk factors thus has the potential to reduce the risks of type 2 diabetes and cardiovascular disease associated with the cardiometabolic phenotype.

2-Arachidonoylglycerol (2-AG) membrane transport: history and outlook

Only a few studies have addressed the transport of 2-arachidonoylglycerol (2-AG), a naturally occurring agonist for cannabinoid receptors. Based upon saturation kinetics, these early reports have proposed that 2-AG enters the cell by a specific 2-AG transporter, via the putative anandamide transporter, or by simple diffusion. In this review, the uptake of 2-AG is discussed in light of the recent advances that have been made for anandamide transport, where the mechanism appears to be rate-limited diffusion through the membrane. Endocannabinoids may be a distinct class of agonists since they are hydrophobic and neutral, exhibiting similar biophysical properties to some anesthetics that freely diffuse through the membrane.

Synthesis of a potential photoactivatable anandamide analog

A potential photoreactive analog of anandamide was synthesized via selective hydrogenation of a skipped tetrayne intermediate. This compound might be a useful tool to search for new cannabinoid receptors.