Inhibitory effects of certain enantiomeric cannabinoids in the mouse vas deferens and the myenteric plexus preparation of guinea-pig small intestine

Effects of Cannabinoids on Intestinal Motility, Barrier Permeability, and Therapeutic Potential in Gastrointestinal Diseases

Cannabinoids and their receptors play a significant role in the regulation of gastrointestinal (GIT) peristalsis and intestinal barrier permeability. This review critically evaluates current knowledge about the mechanisms of action and biological effects of endocannabinoids and phytocannabinoids on GIT functions and the potential therapeutic applications of these compounds. The results of ex vivo and in vivo preclinical data indicate that cannabinoids can both inhibit and stimulate gut peristalsis, depending on various factors. Endocannabinoids affect peristalsis in a cannabinoid (CB) receptor-specific manner; however, there is also an important interaction between them and the transient receptor potential cation channel subfamily V member 1 (TRPV1) system. Phytocannabinoids such as Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) impact gut motility mainly through the CB1 receptor. They were also found to improve intestinal barrier integrity, mainly through CB1 receptor stimulation but also via protein kinase A (PKA), mitogen-associated protein kinase (MAPK), and adenylyl cyclase signaling pathways, as well as by influencing the expression of tight junction (TJ) proteins. The anti-inflammatory effects of cannabinoids in GIT disorders are postulated to occur by the lowering of inflammatory factors such as myeloperoxidase (MPO) activity and regulation of cytokine levels. In conclusion, there is a prospect of utilizing cannabinoids as components of therapy for GIT disorders.

Goods and Bads of the Endocannabinoid System as a Therapeutic Target: Lessons Learned after 30 Years

The cannabis derivative marijuana is the most widely used recreational drug in the Western world and is consumed by an estimated 83 million individuals (∼3% of the world population). In recent years, there has been a marked transformation in society regarding the risk perception of cannabis, driven by its legalization and medical use in many states in the United States and worldwide. Compelling research evidence and the Food and Drug Administration cannabis-derived cannabidiol approval for severe childhood epilepsy have confirmed the large therapeutic potential of cannabidiol itself, Δ9-tetrahydrocannabinol and other plant-derived cannabinoids (phytocannabinoids). Of note, our body has a complex endocannabinoid system (ECS)-made of receptors, metabolic enzymes, and transporters-that is also regulated by phytocannabinoids. The first endocannabinoid to be discovered 30 years ago was anandamide (N-arachidonoyl-ethanolamine); since then, distinct elements of the ECS have been the target of drug design programs aimed at curing (or at least slowing down) a number of human diseases, both in the central nervous system and at the periphery. Here a critical review of our knowledge of the goods and bads of the ECS as a therapeutic target is presented to define the benefits of ECS-active phytocannabinoids and ECS-oriented synthetic drugs for human health. SIGNIFICANCE STATEMENT: The endocannabinoid system plays important roles virtually everywhere in our body and is either involved in mediating key processes of central and peripheral diseases or represents a therapeutic target for treatment. Therefore, understanding the structure, function, and pharmacology of the components of this complex system, and in particular of key receptors (like cannabinoid receptors 1 and 2) and metabolic enzymes (like fatty acid amide hydrolase and monoacylglycerol lipase), will advance our understanding of endocannabinoid signaling and activity at molecular, cellular, and system levels, providing new opportunities to treat patients.

Tricyclic Pyrazole-Based Compounds as Useful Scaffolds for Cannabinoid CB1/CB2 Receptor Interaction

Cannabinoids comprise different classes of compounds, which aroused interest in recent years because of their several pharmacological properties. Such properties include analgesic activity, bodyweight reduction, the antiemetic effect, the reduction of intraocular pressure and many others, which appear correlated to the affinity of cannabinoids towards CB₁ and/or CB₂ receptors. Within the search aiming to identify novel chemical scaffolds for cannabinoid receptor interaction, the CB₁ antagonist/inverse agonist pyrazole-based derivative rimonabant has been modified, giving rise to several tricyclic pyrazole-based compounds, most of which endowed of high affinity and selectivity for CB₁ or CB₂ receptors. The aim of this review is to present the synthesis and summarize the SAR study of such tricyclic pyrazole-based compounds, evidencing, for some derivatives, their potential in the treatment of neuropathic pain, obesity or in the management of glaucoma.

Analogues of cannabinoids as multitarget drugs in the treatment of Alzheimer's disease

Given that neuronal degeneration in Alzheimer's disease (AD) is caused by the combination of multiple neurotoxic insults, current directions in the research of novel therapies to treat this disease attempts to design multitarget strategies that could be more effective than the simply use of acetylcholinesterase inhibitors; currently, the most used therapy for AD. One option, explored recently, is the synthesis of new analogues of cannabinoids that could competitively inhibit the acetylcholinesterase (AChE) enzyme and showing the classic neuroprotective profile of cannabinoid compounds. In this work, molecular docking has been used to design some cannabinoid analogues with such multitarget properties, based on the similarities of donepezil and Δ⁹-tetrahydrocannabinol. The analogues synthesized, compounds 1 and 2, demonstrated to have two interesting characteristics in different in vitro assays: competitive inhibition of AChE and competitive antagonism at the CB₁/CB₂ receptors. They are highly lipophilic, highlighting that they could easily reach the CNS, and apparently presented a low toxicity. These results open the door to the synthesis of new compounds for a more effective treatment of AD.

New cannabinoid receptor antagonists as pharmacological tool

Synthesis and pharmacological evaluation of a new series of cannabinoid receptor antagonists of indazole ether derivatives have been performed. Pharmacological evaluation includes radioligand binding assays with [³H]-CP55940 for CB1 and CB2 receptors and functional activity for cannabinoid receptors on isolated tissue. In addition, functional activity of the two synthetic cannabinoids antagonists 18 (PGN36) and 17 (PGN38) were carried out in the osteoblastic cell line MC3T3-E1 that is able to express CB2R upon osteogenic conditions. Both antagonists abolished the increase in collagen type I gene expression by the well-known inducer of bone activity, the HU308 agonist. The results of pharmacological tests have revealed that four of these derivatives behave as CB2R cannabinoid antagonists. In particular, the compounds 17 (PGN38) and 18 (PGN36) highlight as promising candidates as pharmacological tools.

The effects of varying Mg2+ ion concentrations on contractions to the cotransmitters ATP and noradrenaline in the rat vas deferens

The vas deferens responds to a single electrical pulse with a biphasic contraction caused by cotransmitters ATP and noradrenaline. Removing Mg²⁺ (normally 1.2 mM) from the physiological salt solution (PSS) enhances the contraction. This study aimed to determine the effect of Mg²⁺ concentration on nerve cotransmitter-mediated contractions. Rat vasa deferentia were sequentially bathed in increasing (0, 1.2, 3 mM) or decreasing (3, 1.2, 0 mM) Mg²⁺ concentrations. At each concentration a single field pulse was applied, and the biphasic contraction recorded. Contractions to exogenous noradrenaline 10 μM and ATP 100 μM were also determined. The biphasic nerve-mediated contraction was elicited by ATP and noradrenaline as NF449 (10 μM) and prazosin (100 nM) completely prevented the respective peaks. Taking the contractions in normal PSS (Mg²⁺ 1.2 mM) as 100%, lowering Mg²⁺ to 0 mM enhanced the ATP peak to 170 ± 7% and raising Mg²⁺ to 3 mM decreased it to 39 ± 3%; the noradrenaline peak was not affected by lowering Mg²⁺ to 0 mM (97 ± 3%) but was decreased to 63 ± 4% in high Mg²⁺ (3 mM). Contractions to exogenous ATP, but not noradrenaline, were increased in Mg²⁺ 0 mM and both were inhibited with Mg²⁺ 3 mM. Changing Mg²⁺ concentration affects the contractions elicited by the cotransmitters ATP and noradrenaline. The greatest effects were to potentiate the contraction to ATP in Mg²⁺ 0 mM and to inhibit the contraction to both ATP and noradrenaline in high Mg²⁺. Future publications should clearly justify any decision to vary the magnesium concentration from normal (1.2 mM) values.

Development of Oxygen-Bridged Pyrazole-Based Structures as Cannabinoid Receptor 1 Ligands

In this work, the synthesis of the cannabinoid receptor 1 neutral antagonists 8-chloro-1-(2,4-dichlorophenyl)-N-piperidin-1-yl-4,5-dihydrobenzo-1H-6-oxa-cyclohepta[1,2-c]pyrazole-3-carboxamide 1a and its deaza N-cyclohexyl analogue 1b has led to a deepening of the structure-activity studies of this class of compounds. A series of novel 4,5-dihydrobenzo-oxa-cycloheptapyrazoles analogues of 1a,b, derivatives 1c–j, was synthesized, and their affinity towards cannabinoid receptors was determined. Representative terms were evaluated using in vitro tests and isolated organ assays. Among the derivatives, 1d and 1e resulted in the most potent CB₁ receptor ligands (K_iCB₁ = 35 nM and 21.70 nM, respectively). Interestingly, both in vitro tests and isolated organ assays evidenced CB₁ antagonist activity for the majority of the new compounds, excluding compound 1e, which showed a CB₁ partial agonist behaviour. CB₁ antagonist activity of 1b was further confirmed by a mouse gastrointestinal transit assay. Significant activity of the new CB₁ antagonists towards food intake was showed by preliminary acute assays, evidencing the potentiality of these new derivatives in the treatment of obesity.

Indazolylketones as new multitarget cannabinoid drugs

Multitarget cannabinoids could be a promising therapeutic strategic to fight against Alzheimer's disease. In this sense, our group has developed a new family of indazolylketones with multitarget profile including cannabinoids, cholinesterase and BACE-1 activity. A medicinal chemistry program that includes computational design, synthesis and in vitro and cellular evaluation has allowed to us to achieve lead compounds. In this work, the synthesis and evaluation of a new class of indazolylketones have been performed. Pharmacological evaluation includes functional activity for cannabinoid receptors on isolated tissue. In addition, in vitro inhibitory assays in AChE/BuChE enzymes and BACE-1 have been carried out. Furthermore, studies of neuroprotective effects in human neuroblastoma SH-SY5Y cells and studies of the mechanisms of survival/death in lymphoblasts of patients with Alzheimer's disease have been achieved. The results of pharmacological tests have revealed that some of these derivatives (5, 6) behave as CB2 cannabinoid agonists and simultaneously show BuChE and/or BACE-1 inhibition.

Novel derivatives of 1,2,3-triazole, cannabinoid-1 receptor ligands modulate gastrointestinal motility in mice

Cannabinoid-1 (CB1) receptors are broadly distributed in the central and peripheral nervous systems; among others, they are located in the enteric nervous system. In the gastrointestinal (GI) system, they participate in regulation of intestinal motility or ion transport. The aim of our study was to assess the effect of 1,2,3-triazole derivatives (compound 1: 2-[4,5-bis(2,4-dichlorophenyl)-2H-1,2,3-triazol-2-yl]-N-(2-fluorobenzyl)acetamide, compound 2: 2-[4,5-bis(2,4-dichlorophenyl)-2H-1,2,3-triazol-2-yl]-N-(4-fluorobenzyl)acetamide, compound 3: N-benzyl-2-[4-(4-chlorophenyl)-5-(2,4-dichlorophenyl)-2H-1,2,3-triazol-2-yl]acetamide]), characterized in vitro as CB1 antagonists with high CB1 over CB2 selectivity, in the mouse GI tract. The action of compounds 1-3 was assessed in vitro (electrical field stimulated smooth muscle contractility of the mouse ileum and colon) and in vivo (whole GI transit time). Compound 1 decreased ileal (10^-6 M) and colonic (10^-7-10^-6 M) smooth muscles contractility. Moreover, it prolonged whole GI transit. Compound 2 (10^-10-10^-8 M) slightly increased the amplitude of muscle contractions in the ileum, but at a higher concentration (10^-6 M), the amplitude was decreased. Compound 2 reduced colonic contractility but accelerated GI transit. Compound 3 decreased the amplitude of intestinal muscle contractions in the ileum (10^-6 M) and colon (10^-10-10^-6 M). Moreover, it increased the GI transit time in vivo. Triazole derivatives possess easily modifiable structure and interesting pharmacological action in the GI tract; further, alterations may enhance their efficacy at CB receptors and provide low side effect profile in clinical conditions.

The Cannabinoid Receptor Interacting Proteins 1 of zebrafish are not required for morphological development, viability or fertility

The Cannabinoid Receptor Interacting Protein 1 (Cnrip1) was discovered as an interactor with the intracellular region of Cannabinoid Receptor 1 (CB1R, also known as Cnr1 or CB1). Functional assays in mouse show cannabinoid sensitivity changes and Cnrip1 has recently been suggested to control eye development in Xenopus laevis. Two Cnrip1 genes are described in zebrafish, cnrip1a and cnrip1b. In situ mRNA hybridisation revealed accumulation of mRNA encoding each gene primarily in brain and spinal cord, but also elsewhere. For example, cnrip1b is expressed in forming skeletal muscle. CRISPR/Cas9 genome editing generated predicted null mutations in cnrip1a and cnrip1b. Each mutation triggered nonsense-mediated decay of the respective mRNA transcript. No morphological or behavioural phenotype was observed in either mutant. Moreover, fish lacking both Cnrip1a and Cnrip1b both maternally and zygotically are viable and fertile and no phenotype has so far been detected despite strong evolutionary conservation over at least 400 Myr.

In vitro and non-invasive in vivo effects of the cannabinoid-1 receptor agonist AM841 on gastrointestinal motor function in the rat

BACKGROUND

Cannabinoids have been traditionally used for the treatment of gastrointestinal (GI) symptoms, but the associated central effects, through cannabinoid-1 receptors (CB1R), constitute an important drawback. Our aims were to characterize the effects of the recently developed highly potent long-acting megagonist AM841 on GI motor function and to determine its central effects in rats.

METHODS

Male Wistar rats were used for in vitro and in vivo studies. The effect of AM841 was tested on electrically induced twitch contractions of GI preparations (in vitro) and on GI motility measured radiographically after contrast administration (in vivo). Central effects of AM841 were evaluated using the cannabinoid tetrad. The non-selective cannabinoid agonist WIN 55,212-2 (WIN) was used for comparison. The CB1R (AM251) and CB2R (AM630) antagonists were used to characterize cannabinoid receptor-mediated effects of AM841.

KEY RESULTS

AM841 dose-dependently reduced in vitro contractile activity of rat GI preparations via CB1R, but not CB2R or opioid receptors. In vivo, AM841 acutely and potently reduced gastric emptying and intestinal transit in a dose-dependent and AM251-sensitive manner. The in vivo GI effects of AM841 at 0.1 mg/kg were comparable to those induced by WIN at 5 mg/kg. However, at this dose, AM841 did not induce any sign of the cannabinoid tetrad, whereas WIN induced significant central effects.

CONCLUSIONS & INFERENCES

The CB1R megagonist AM841 may potently depress GI motor function in the absence of central effects. This effect may be mediated peripherally and may be useful in the treatment of GI motility disorders.

Combining rimonabant and fentanyl in a single entity: preparation and pharmacological results

Based on numerous pharmacological studies that have revealed an interaction between cannabinoid and opioid systems at the molecular, neurochemical, and behavioral levels, a new series of hybrid molecules has been prepared by coupling the molecular features of two wellknown drugs, ie, rimonabant and fentanyl. The new compounds have been tested for their affinity and functionality regarding CB₁ and CB₂ cannabinoid and μ opioid receptors. In [³⁵S]-GTPγS (guanosine 5′-O-[gamma-thio]triphosphate) binding assays from the post-mortem human frontal cortex, they proved to be CB₁ cannabinoid antagonists and μ opioid antagonists. Interestingly, in vivo, the new compounds exhibited a significant dual antagonist action on the endocannabinoid and opioid systems.

Cannabinoids may worsen gastric dysmotility induced by chronic cisplatin in the rat

BACKGROUND

Although cannabinoids have traditionally been used for the treatment and/or prevention of nausea and/or emesis, anorexia and weight loss induced by clinical use of antineoplastic drugs, their efficacy and safety in long-term treatments are still controversial. Our aim was to analyze the effects of the non-selective cannabinoid agonist WIN 55 212-2 (WIN) on gastrointestinal (GI) dysmotility and other adverse effects induced by repeated cisplatin administration in the rat.

METHODS

Male Wistar rats received two intraperitoneal injections once a week for 4 weeks: the first one was WIN, at non-psychoactive doses (0.5 or 1 mg kg(-1)), its vehicle or saline; the second one was cisplatin (2 mg kg(-1)) or saline. Radiographic techniques were used to determine the acute (after first dose), chronic (after last dose), and residual (1 week after treatment finalization) effects of cisplatin and/or WIN on GI motility. Bodyweight gain, food ingestion, and mechanical sensitivity were also tested.

KEY RESULTS

Weekly cisplatin induced mechanical allodynia, which WIN prevented, as well as weight gain reduction and anorexia, which WIN did not. Gastric emptying was dose-dependently delayed by cisplatin and this effect was enhanced upon chronic treatment. WIN aggravated cisplatin-induced gastric dysmotility. One week after treatment finalization, only minor alterations of GI motor function were found in rats treated with cisplatin, WIN or both.

CONCLUSIONS & INFERENCES

WIN weekly administered at low doses prevents neuropathy, but does not prevent anorexia or weight loss and aggravates gastric dysmotility induced by cisplatin. Cannabinoids should be handled with caution if chronically administered during chemotherapy.

Cannabinoids and muscular pain. Effectiveness of the local administration in rat

BACKGROUND

Pain associated with musculoskeletal disorders can be difficult to control and the incorporation of new approaches for its treatment is an interesting challenge. Activation of cannabinoid (CB) receptors decreases nociceptive transmission in acute, inflammatory and neuropathic pain states; however, although the use of cannabis derivatives has been recently accepted as a useful alternative for the treatment of spasticity and pain in patients with multiple sclerosis, the effects of CB receptor agonists in muscular pain have hardly been studied.

METHODS

Here, we characterized the antinociceptive effect of non selective and selective CB agonists by systemic and local administration, in two muscular models of pain, masseter and gastrocnemius, induced by hypertonic saline (HS) injection. Drugs used were: the non-selective agonist WIN 55,212-2 and two selective agonists, ACEA (CB 1) and JWH 015 (CB 2); AM 251 (CB 1) and AM 630 (CB 2) were used as selective antagonists.

RESULTS

In the masseter pain model, both systemic (intraperitoneal) and local (intramuscular) administration of CB 1 and CB 2 agonists reduced the nociceptive behaviour induced by HS, whereas in the gastrocnemius model the local administration was more effective than systemic.

CONCLUSIONS

Our results provide evidence that both, CB 1 and CB 2 receptors can contribute to muscular antinociception and, interestingly, suggest that the local administration of CB agonists could be a new and useful pharmacological strategy in the treatment of muscular pain, avoiding adverse effects induced by systemic administration.

Description of a bivalent cannabinoid ligand with hypophagic properties

A series of bivalent cannabinoid ligands is proposed. The synthesis of double amides based on the rimonabant structure separated by an alkyl chain and the evaluation of their affinities for cannabinoid receptors are reported. The data of 4d confirmed that a bivalent structure is a suitable scaffold for CB1 cannabinoid receptor binding. The compound 4d was selected for in vitro and in vivo pharmacological evaluations. Moreover, intraperitoneal administration of 4d to food-deprived rats resulted in a dose-dependent inhibition of feeding that was maintained up to 240 min.

Cannabinoid agonist WIN 55,212-2 prevents the development of paclitaxel-induced peripheral neuropathy in rats. Possible involvement of spinal glial cells

Spinal glial activation contributes to the development and maintenance of chronic pain states, including neuropathic pain of diverse etiologies. Cannabinoid compounds have shown antinociceptive properties in a variety of neuropathic pain models and are emerging as a promising class of drugs to treat neuropathic pain. Thus, the effects of repeated treatment with WIN 55,212-2, a synthetic cannabinoid agonist, were examined throughout the development of paclitaxel-induced peripheral neuropathy. Painful neuropathy was induced in male Wistar rats by intraperitoneal (i.p.) administration of paclitaxel (1mg/kg) on four alternate days. Paclitaxel-treated animals received WIN 55,212-2 (1mg/kg, i.p.) or minocycline (15 mg/kg, i.p.), a microglial inhibitor, daily for 14 days, simultaneous with the antineoplastic. The development of hypersensitive behaviors was assessed on days 1, 7, 14, 21 and 28 following the initial administration of drugs. Both the activation of glial cells (microglia and astrocytes) at day 29 and the time course of proinflammatory cytokine release within the spinal cord were also determined. Similar to minocycline, repeated administration of WIN 55,212-2 prevented the development of thermal hyperalgesia and mechanical allodynia in paclitaxel-treated rats. WIN 55,212-2 treatment also prevented spinal microglial and astrocytic activation evoked by paclitaxel at day 29 and attenuated the early production of spinal proinflammatory cytokines (interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α). Our results confirm changes in the reactivity of glial cells during the development of peripheral neuropathy induced by paclitaxel and support a preventive effect of WIN 55,212-2, probably via glial cells reactivity inactivation, on the development of this neuropathy.

Chromenopyrazoles: non-psychoactive and selective CB₁ cannabinoid agonists with peripheral antinociceptive properties

The unwanted psychoactive effects of cannabinoid receptor agonists have limited their development as medicines. These CB₁-mediated side effects are due to the fact that CB₁ receptors are largely expressed in the central nervous system (CNS). As it is known that CB₁ receptors are also located peripherally, there is growing interest in targeting cannabinoid receptors located outside the brain. A library of chromenopyrazoles designed analogously to the classical cannabinoid cannabinol were synthesized, characterized, and tested for cannabinoid activity. Radioligand binding assays were used to determine their affinities at CB₁ and CB₂ receptors. Structural features required for CB₁/CB₂ affinity and selectivity were explored by molecular modeling. Some compounds in the chromenopyrazole series were observed to be selective CB₁ ligands. These modeling studies suggest that full CB₁ selectivity over CB₂ can be explained by the presence of a pyrazole ring in the structure. The functional activities of selected chromenopyrazoles were evaluated in isolated tissues. In vivo behavioral tests were then carried out on the most effective CB₁ cannabinoid agonist, 13 a. Chromenopyrazole 13 a did not induce modifications in any of the tested parameters on the mouse cannabinoid tetrad, thus discounting CNS-mediated effects. This lack of agonistic activity in the CNS suggests that this compound does not readily cross the blood-brain barrier. Moreover, 13 a can induce antinociception in a rat peripheral model of orofacial pain. Taking into account the negative results obtained with the hot-plate test, the antinociception induced by 13 a in the orofacial test could be mediated through peripheral mechanisms.

Discovery of Potent Dual PPARα Agonists/CB1 Ligands

This letter describes the synthesis and in vitro and in vivo evaluation of dual ligands targeting the cannabinoid and peroxisome proliferator-activated receptors (PPAR). These compounds were obtained from fusing the pharmacophores of fibrates and the diarylpyrazole rimonabant, a cannabinoid receptor antagonist. They are the first examples of dual compounds with nanomolar affinity for both PPARα and cannabinoid receptors. Besides, lead compound 2 proved to be CB1 selective. Unexpectedly, the phenol intermediates tested were equipotent (compound 1 as compared to 2) or even more potent (compound 3 as compared with 4). This discovery opens the way to design new dual ligands.

Cannabinoid/agonist WIN 55,212-2 reduces cardiac ischaemia–reperfusion injury in Zucker diabetic fatty rats: role of CB2 receptors and iNOS/eNOS

BACKGROUND

Diabetes increases cardiac damage after myocardial ischaemia. Cannabinoids can protect against myocardial ischaemia/reperfusion injury. The aim of this study was to examine the cardioprotective effect of the cannabinoid agonist WIN 55,212-2 (WIN) against ischaemia/reperfusion injury in an experimental model of type 2 diabetes. We performed these experiments in the Zucker diabetic fatty rat, and focused on the role of cannabinoid receptors in modulation of cardiac inducible nitric oxide synthase (iNOS)/endothelial-type nitric oxide synthase (eNOS) expression.

METHODS

Male 20-week-old Zucker diabetic fatty rats were treated with vehicle, WIN, the selective CB1 or CB2 receptor antagonists AM251 and AM630, respectively, AM251 + WIN or AM630 + WIN. Hearts were isolated from these rats, and the cardiac functional response to ischaemia/reperfusion injury was evaluated. In addition, cardiac iNOS and eNOS expression were determined by western blot.

RESULTS

WIN significantly improved cardiac recovery after ischaemia/ reperfusion in the hearts from Zucker diabetic fatty rats by restoring coronary perfusion pressure and heart rate to preischaemic levels. Additionally, WIN decreased cardiac iNOS expression and increased eNOS expression after ischaemia/reperfusion in diabetic hearts. WIN-induced cardiac functional recovery was completely blocked by the CB2 antagonist AM630. However, changes in NOS isoenzyme expression were not affected by the CB antagonists.

CONCLUSIONS

This study shows a cardioprotective effect of a cannabinoid agonist on ischaemia/reperfusion injury in an experimental model of a metabolic disorder. The activation mainly of CB2 receptors and the restoration of iNOS/eNOS cardiac equilibrium are mechanisms involved in this protective effect. These initial studies have provided the basis for future research in this field.

Cannabinoid-induced delayed gastric emptying is selectively increased upon intermittent administration in the rat: role of CB1 receptors

BACKGROUND

Cannabinoids acutely administered depress central, cardiovascular and gastrointestinal functions. These effects might be modified upon repeated administration. Compared to the effects induced by daily administration, those induced by intermittent administration are less known. The effect of intermittent treatment with the CB1/CB2 cannabinoid agonist WIN55,212-2 (WIN) was studied in the rat.

METHODS

Male rats received saline, vehicle or WIN at 0.5 (low-WIN) or 5 (high-WIN) mg kg(-1) week(-1) for 4 weeks. WIN effects on the central nervous system (cannabinoid tetrad tests), cardiovascular function and gastrointestinal motor function were evaluated after the first and last doses, and, where appropriate, 1 week after the last dose. To determine the involvement of CB1 receptors in the chronic effect of WIN, the CB1 receptor antagonist/inverse agonist AM251 (1 mg kg(-1)) was used.

KEY RESULTS

High- (but not low-) WIN induced the four signs of the cannabinoid tetrad, and reduced gastrointestinal motility, but did not alter cardiovascular parameters. Upon chronic intermittent administration, tolerance did not clearly develop to WIN effects. Quite the opposite, depression of gastric emptying was intensified. No effect was long-lasting. Repeated administration of AM251 was more efficacious than single administration to block WIN chronic central effects, but the opposite occurred regarding lower intestinal motility.

CONCLUSIONS & INFERENCES

Upon intermittent administration, hypersensitization may develop to some effects (particularly delayed gastric emptying) induced by cannabinoid agonists. CB1 antagonists/inverse agonists may show different efficacy upon repeated or single administration to block cannabinoid-induced central and gastrointestinal effects. Thus, cannabinoid effects are dependent on the pattern of drug administration.

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.

Regulation of hippocampal cannabinoid CB1 receptor actions by adenosine A1 receptors and chronic caffeine administration: implications for the effects of Δ9-tetrahydrocannabinol on spatial memory

The cannabinoid CB(1) receptor-mediated modulation of γ-aminobutyric acid (GABA) release from inhibitory interneurons is important for the integrity of hippocampal-dependent spatial memory. Although adenosine A(1) receptors have a central role in fine-tuning excitatory transmission in the hippocampus, A(1) receptors localized in GABAergic cells do not directly influence GABA release. CB(1) and A(1) receptors are the main targets for the effects of two of the most heavily consumed psychoactive substances worldwide: Δ(9)-tetrahydrocannabinol (THC, a CB(1) receptor agonist) and caffeine (an adenosine receptor antagonist). We first tested the hypothesis that an A(1)-CB(1) interaction influences GABA and glutamate release in the hippocampus. We found that A(1) receptor activation attenuated the CB(1)-mediated inhibition of GABA and glutamate release and this interaction was manifested at the level of G-protein activation. Using in vivo and in vitro approaches, we then investigated the functional implications of the adenosine-cannabinoid interplay that may arise following chronic caffeine consumption. Chronic administration of caffeine in mice (intraperitoneally, 3 mg/kg/day, for 15 days, >12 h before trials) led to an A(1)-mediated enhancement of the CB(1)-dependent acute disruptive effects of THC on a short-term spatial memory task, despite inducing a reduction in cortical and hippocampal CB(1) receptor number and an attenuation of CB(1) coupling with G protein. A(1) receptor levels were increased following chronic caffeine administration. This study shows that A(1) receptors exert a negative modulatory effect on CB(1)-mediated inhibition of GABA and glutamate release, and provides the first evidence of chronic caffeine-induced alterations on the cannabinoid system in the cortex and hippocampus, with functional implications in spatial memory.

Differential effects of CB(1) neutral antagonists and inverse agonists on gastrointestinal motility in mice

BACKGROUND

Cannabinoid type 1 (CB(1)) receptors are involved in the regulation of gastrointestinal (GI) motility and secretion. Our aim was to characterize the roles of the CB(1) receptor on GI motility and secretion in vitro and in vivo by using different classes of CB(1) receptor antagonists.

METHODS

Immunohistochemistry was used to examine the localization of CB(1) receptor in the mouse ileum and colon. Organ bath experiments on mouse ileum and in vivo motility testing comprising upper GI transit, colonic expulsion, and whole gut transit were performed to characterize the effects of the inverse agonist/antagonist AM251 and the neutral antagonist AM4113. As a marker of secretory function we measured short circuit current in vitro using Ussing chambers and stool fluid content in vivo in mouse colon. We also assessed colonic epithelial permeability in vitro using FITC-labeled inulin.

KEY RESULTS

In vivo, the inverse agonist AM251 increased upper GI transit and whole gut transit, but it had no effect on colonic expulsion. By contrast, the neutral antagonist AM4113 increased upper GI transit, but unexpectedly reduced both colonic expulsion and whole gut transit at high, but not lower doses.

CONCLUSIONS & INFERENCES

Cannabinoid type 1 receptors regulate small intestinal and colonic motility, but not GI secretion under physiological conditions. Cannabinoid type 1 inverse agonists and CB(1) neutral antagonists have different effects on intestinal motility. The ability of the neutral antagonist not to affect whole gut transit may be important for the future development of CB(1) receptor antagonists as therapeutic agents.

The cannabinoid antagonist SR144528 enhances the acute effect of WIN 55,212-2 on gastrointestinal motility in the rat

BACKGROUND

In the absence of pathology, cannabinoid-induced depression of gastrointestinal (GI) motility is thought to be mediated primarily by CB1 receptors, whereas the role of CB2 receptors is still unclear. The aim of this work was to radiographically analyze the acute effect of the mixed cannabinoid agonist WIN 55,212-2 (WIN) on GI motor function in the rat, focusing on the involvement of CB1 and CB2 receptors.

METHODS

Male Wistar rats received different doses of WIN and both psychoactivity (cannabinoid tetrad) and GI motility (radiographic analysis) were tested. The duration of WIN effect on GI motility was also radiographically analyzed. Finally, the involvement of the different cannabinoid receptors on WIN-induced alterations of GI motility was analyzed by the previous administration of selective CB1 (AM251) and CB2 (SR144528 or AM630) antagonists. After administration of contrast medium, alterations in GI motility were quantitatively evaluated in serial radiographs by assigning a compounded value to each region of the GI tract.

KEY RESULTS

Low, analgesic doses of WIN delayed intestinal transit, but high, psychoactive doses were required to delay gastric emptying. Acute WIN effects on GI motility were confined to the first few hours after administration. AM251 partially counteracted the effect of WIN on GI motility. Surprisingly, SR144528 (but not AM630) enhanced WIN-induced delayed gastric emptying.

CONCLUSIONS & INFERENCES

X-ray analyses confirm that cannabinoids inhibit GI motility via CB1 receptors; in addition, cannabinoids could influence motility through interaction with a SR144528-sensitive site. Further studies are needed to verify if such site of action is the CB2 receptor.

Characteristics of tolerance in the guinea pig ileum produced by chronic in vivo exposure to opioid versus cannabinoid agonists

Few studies have compared the nature of tolerance that develops following chronic opioid treatment with that which develops after chronic cannabinoid exposure in the same tissue and species. The degree and character of tolerance induced by 7 twice daily injections of morphine or 5 daily injections of the cannabinoid receptor agonist, WIN-55,212-2, was examined by comparing the ability of DAMGO, 2-chloroadenosine (CADO) and WIN-55,212-2 to inhibit neurogenic contractions of the longitudinal muscle/myenteric plexus preparation (LM/MP) and the ability of nicotine to elicit contractions in the LM/MP. Chronic morphine treatment resulted in subsensitivity to all inhibitory agonists (rightward shift in IC(50) values of 4-5-fold) and an increased responsiveness to the excitatory effect of nicotine while chronic WIN-55,212-2 exposure resulted in subsensitivity only to WIN-55,212-2 and a reduction in maximum response to both WIN-55,212-2 and DAMGO but no change in responsiveness to CADO. Chronic WIN-55,212-2 treatment significantly reduced CB(1) but not MOR receptor protein abundance while chronic morphine treatment did not change either. Assessment of the distribution of MOR and CB(1) receptors in myenteric neurons revealed distinct individual receptor expression as well as co-localization which was unaffected by either cannabinoid or opioid treatment. Thus, in contrast to the heterologous tolerance that develops after opioid treatment, tolerance in the LM/MP following chronic in vivo WIN-55,212-2 exposure appears to be homologous in character and is accompanied by a selective decrease in CB(1) receptor protein abundance. The data suggest that the cellular basis of tolerance differs between the two systems.

Novel selective antagonist of the cannabinoid CB1 receptor, MJ15, with prominent anti-obesity effect in rodent models

MJ15, a novel cannabinoid CB(1) receptor selective antagonist was discovered. In receptor binding assays, MJ15 displayed a high affinity for rat cannabinoid CB(1) receptor (K(i)=27.2 pM, and IC(50)=118.9 pM), but a much lower affinity for rat cannabinoid CB(2) receptor (only 46% inhibition at 10 microM). At the cellular level, the IC(50) values against activation of cannabinoid CB(1) and CB(2) receptors induced by Win55212-2 in specially designed EGFP-CB(1)_U2OS and EGFP-CB(2)_U2OS cells were 0.11 microM and >10 microM, respectively. In addition, MJ15 dose-dependently blocked Win55212-2 mediated increase of intracellular Ca(2+) levels in hippocampal cells and reversed the inhibitory effects of cannabinoid CB(1) receptor agonist on forskolin-stimulated adenylyl cyclase activity in CHO cells expressing the human cannabinoid CB(1) receptor. In animal experiments, MJ15 demonstrated remarkable effects from 20 to 40 mg/kg, including promoted the small intestine peristalsis in ICR mice and inhibited food intake and body weight increase in diet-induced obesity (DIO) rat and mouse. 40 mg/kg MJ15 significantly reduced food intake at initial 2 weeks of treatment, prevented the increase of body weight and adipose by 46% and 28% respectively in DIO rats, and reduced body weight and adipose gain by 70% and 23% respectively in early onset obesity DIO mice after 4 weeks treatment. Meanwhile, dyslipidemia were ameliorated in both models. Taken together the in vitro and in vivo data, MJ15 is demonstrated to be a potent and selective cannabinoid CB(1) receptor antagonist and holds a prominent potency in obesity and dyslipidemia treatment.

Pharmacological characterization of cannabinoid receptor activity in the rat-isolated ileum myenteric plexus-longitudinal muscle preparation

BACKGROUND AND PURPOSE

Cannabinoid effects on intestinal transit are commonly evaluated in rats. We characterized the cannabinoid receptors mediating the inhibitory effect of 5-(1,1-dimethylheptyl)-2-[5-hydroxy-2-(3-hydroxypropyl)-cyclohexyl]-phenol (CP 55,940), (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate (WIN 55,212-2), arachidonylethanolamide (AEA) and Delta(9)-tetrahydrocannabinol (Delta(9)-THC) on contractions of the rat ileum myenteric plexus-longitudinal muscle (MPLM) preparation.

EXPERIMENTAL APPROACH

The interaction of each agonist was examined with the CB(1) and CB(2) receptor antagonist rimonabant and SR 144,528 respectively, on contractions elicited by electrical field stimulation (EFS) or exogenous ACh. The interaction of AEA with capsazepine, a TRPV(1) receptor antagonist, was also investigated.

KEY RESULTS

EFS with single and trains of pulses evoked neurogenic ACh-mediated twitch and rebound contractions respectively. The rank order of potency for inhibition was CP 55,940 = WIN 55,212-2 > AEA > Delta(9)-THC and AEA > WIN 55,212-2 =Delta(9)-THC = CP 55,940 respectively. The stereoisomer WIN 55,212-3 was without effect. Rimonabant antagonized the inhibition of the twitches with pK(B) values of around 8.60, but only antagonized rebound contractions induced by WIN 55,212-2, AEA and Delta(9)-THC, with pA(2) values of around 6.80. Rimonabant increased the twitches but inhibited the rebound contractions. Contractions to exogenous ACh were not altered. These observations extended to the guinea pig ileum MPLM.

CONCLUSIONS AND IMPLICATIONS

The rat MPLM contains CB(1) receptors and at least two non-CB(1)-non-CB(2)-non-TRPV(1) receptors attenuating EFS-evoked ACh-mediated contractions in an EFS frequency-dependent pre-synaptic and stereo-specific manner. Augmentation of the twitches by rimonabant may be through antagonism of an endocannabinoid tone or inverse agonism, whereas inhibition of the rebound contractions involved partial agonism.

Anti-inflammatory properties of CB1-receptor antagonist involves beta2 adrenoceptors

Antagonists of the cannabinoid receptor 1 (CB1) impart anti-inflammatory activity even though, paradoxically, CB2 receptors are more predominant on cells of the immune system. We attempted to understand the mechanism of this activity by using an acute model of lipopolysaccharide-induced inflammation/stress in both rat and mouse, with selective antagonists to CB1 receptors. We demonstrate that the ability of a CB1 antagonist to inhibit release of proinflammatory cytokines is not dependent on either adrenal-derived catecholamines or corticosteroids or input from the pituitary or thymus glands but does involve the spleen. Furthermore, we show that the anti-inflammatory activity is retained without communication from the central nervous system following ganglionic blockade, suggesting a peripheral site of action. Finally, we show that the anti-inflammatory activity can be inhibited with the use of a selective beta2-adrenoceptor antagonist.

Molecules Acting on CB1 Receptor and their Effects on Morphine Withdrawal In Vitro

Several pharmacological studies indicate that CB1 cannabinoid receptors (CB1Rs) are present in guinea pig ileum (GPI) and their activation reduce the acetylcholine (Ach) release. Dependence can be induced and measured in vitro by using GPI and the contraction due to opioid withdrawal is caused by acetylcholine release.

Design of molecules acting on the CB1Rs are widely studied and the large availaibility of CB1Rs agonists and antagonists provides powerful tools to determine the role of these receptors in mediating some of physiological and pharmacological effects in the myenteric neurones.

Given the relationship between CB1Rs/Opioid Withdrawal/Ach system, in the present paper we have designed six new CB1Rs agonists named A-F and evaluated their role in mediating morphine withdrawal in GPI. Also, a comparative study was performed by using the CB1Rs synthetic cannabinoid WIN 55,212-2 and CP 55,940. The results of our experiments indicate that both WIN 55,212-2 and CP 55,940 (1x10^-8-5x10^-8-1x10^-7 M) were able to reduce morphine withdrawal in a concentration-dependent manner. Very similar results were obtained with the new CB1Rs agonists (A-F) used at same concentrations. The results of our experiments indicate that CB1Rs are involved in the control of morphine withdrawal in vitro thus confirming an important functional interaction between the cannabinoid and opioid system.

Selective lack of tolerance to delayed gastric emptying after daily administration of WIN 55,212-2 in the rat

The use of cannabinoids to treat gastrointestinal (GI) motor disorders has considerable potential. However, it is not clear if tolerance to their actions develops peripherally, as it does centrally. The aim of this study was to examine the chronic effects of the cannabinoid agonist WIN 55,212-2 (WIN) on GI motility, as well as those in the central nervous and cardiovascular systems. WIN was administered for 14 days, at either non-psychoactive or psychoactive doses. Cardiovascular parameters were measured in anaesthetized rats, whereas central effects and alterations in GI motor function were assessed in conscious animals using the cannabinoid tetrad and non-invasive radiographic methods, respectively. Tests were performed after first (acute effects) and last (chronic effects) administration of WIN, and 1 week after discontinuing treatment (residual effects). Food intake and body weight were also recorded throughout treatment. Blood pressure and heart rate remained unchanged after acute or chronic administration of WIN. Central activity and GI motility were acutely depressed at psychoactive doses, whereas non-psychoactive doses only slightly reduced intestinal transit. Most effects were reduced after the last administration. However, delayed gastric emptying was not and could, at least partially, account for a concomitant reduction in food intake and body weight gain. The remaining effects of WIN administration in GI motility were blocked by the CB1 antagonist AM 251, which slightly accelerated motility when administered alone. No residual effects were found 1 week after discontinuing cannabinoid treatment. The different systems show differential sensitivity to cannabinoids and tolerance developed at different rates, with delayed gastric emptying being particularly resistant to attenuation upon chronic treatment.

Science signals a new understanding of marihuana

Some recent scientific advances in the study of the cannabinoids are outlined. The mode of action of marihuana and the cannabinoids has now been described. They belong to a new class of drug that acts on a hitherto undescribed neuro-physiological system. An endogenous neurotransmitter or neuromodulator for this system has been isolated, identified and named "anandamide". These findings throw new light and imbue new confidence for the future of the therapeutic application of compounds derived from and related to the cannabinoids and anandamide. An outline is also provided of the current knowledge and future potential of cannabinoids in therapeutics. The effect of the current legal classification of the cannabinoids on the research and development of these compounds is discussed.

Antinociceptive effect of the cannabinoid agonist, WIN 55,212-2, in the orofacial and temporomandibular formalin tests

Orofacial pain disorders are frequent in the general population and their pharmacological treatment is not always adequately resolved. Cannabinoids have demonstrated their analgesic effect in several pain conditions, both in animal models and in clinical situations. The aim of the present study was to evaluate the cannabinoid-mediated antinociception in two inflammatory models of orofacial pain (orofacial and temporomandibular joint (TMJ) formalin test) and to compare it with a spinal inflammatory model (paw formalin test). WIN 55,212-2 (0.5, 1mg/kg), a synthetic cannabinoid agonist, was intraperitoneally (i.p.) administered prior to formalin and significantly reduced the nociceptive behavioural responses in these inflammatory tests. To elucidate which subtype of receptor could be involved in such effect, two selective cannabinoid antagonists were administered prior to WIN. SR141716A (1mg/kg i.p.), the CB1 receptor-selective antagonist, was able to prevent the cannabinoid-induced analgesia in all three models, whereas SR144528 (1mg/kg i.p.), the CB2 receptor-selective antagonist, only prevented it in the paw formalin test. A comparison with the antinociceptive effects of morphine (2.5, 5, 10mg/kg, i.p.), indomethacin (2.5, 5mg/kg, i.p.) and ketamine (25, 50mg/kg, i.p.) was also performed. Morphine displayed a dose-dependent reduction of acute and inflammatory pain in all three models, whereas indomethacin and ketamine only attenuated inflammatory pain at the highest tested doses. These results indicate that the cannabinoid-induced antinociception in the orofacial region is mediated by activation of CB1 cannabinoid receptor. Moreover WIN was as effective as morphine and more effective than indomethacin and ketamine, in oral inflammatory pain.

Modulation of excitatory synaptic transmission by Delta 9-tetrahydrocannabinol switches from agonist to antagonist depending on firing rate

Delta(9)-tetrahydrocannabinol (THC), the principal psychoactive ingredient in marijuana, acts as a partial agonist on presynaptic cannabinoid type 1 (CB1) receptors to inhibit neurotransmitter release. Here, we report that THC inhibits excitatory neurotransmission between cultured rat hippocampal neurons in a manner highly sensitive to stimulus rate. THC (1 microM) inhibited excitatory postsynaptic currents (EPSCs) and whole-cell I(Ca) evoked at 0.1 Hz but at 0.5 Hz THC had little effect. The cannabinoid receptor full agonists [(R)-(+)-[2,3-dihydro-5-methyl-3[(4-morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-naphthalenyl)methanone mesylate salt] (Win55212-2) (100 nM) and 2-arachidonylglycerol (1 microM) inhibited EPSCs independent of stimulation at 0.1 or 0.5 Hz. THC occupied CB1 receptors at 0.5 Hz, but the receptors failed to couple to presynaptic Ca(2+) channels. Consequently, 1 microM THC blocked the inhibition of EPSC amplitude by Win55212-2 when EPSCs were evoked at 0.5 Hz. A depolarizing prepulse to 0 mV reversed THC inhibition of I(Ca), but reversal of the inhibition produced by Win55212-2 required a pulse to +80 mV, suggesting that the voltage-dependent reversal of Gbetagamma inhibition of voltage-gated Ca(2+) channels accounts for the frequency-dependence of cannabinoid action. THC blocked depolarization-induced suppression of EPSCs evoked at 0.5 Hz, indicating that it inhibited retrograde endocannabinoid signaling in a frequency-dependent manner. Thus, THC displayed a state-dependent switching from agonist to antagonist that may account for its complex actions in vivo.

Development of novel tail-modified anandamide analogs

To explore the hydrophobic groove subsite within the CB1 cannabinoid receptor we have designed and synthesized a group of tail-substituted anandamide analogs. Our design involves the introduction of aryl or heterocyclic ring as terminal substituents that are connected to the last cis-arachidonyl double bond through aliphatic chains of variable lengths. Our results indicate that there are strict stereochemical requirements for the interaction of such analogs with the CB1 receptor. The optimal pharmacophore includes the phenyl, p-substituted phenyl, or 3-furyl substituents attached to the cis-double bond through a four methylene chain.

Synthesis and Cannabinoid Activity of a Variety of 2,3-Substituted 1-Benzo[b]thiophen Derivatives and 2,3-Substituted Benzofuran: Novel Agonists for the CB1 Receptor

An exploratory chemical effort has been undertaken to develop a novel series of compounds as selective CB1 agonists. It is hoped that compounds of this type will have clinical utility in pain control and cerebral ischaemia following stroke or traumatic head injury. We report here medicinal chemistry studies directed towards the investigation of several classes of 1-benzo[b]thiophen and benzofuran derivatives as novel CB1 agonists. We have discovered a novel series of compounds, which contain a 1-benzo[b]thiophen or a benzofuran group as the central aromatic group. Our investigation of this series of compounds has enhanced our understanding of the importance of binding sites within the CB1 receptor for favourable CB1 potency. Our understanding of these factors allowed us to modify the structure of a 1-benzothiophen derivative and improve its potency at the CB1 receptor.

Discovery of 1,1-dioxo-1,2,6-thiadiazine-5-carboxamide derivatives as cannabinoid-like molecules with agonist and antagonist activity

A series of new 2-substituted 1,1-dioxo-1,2,6-thiadiazine-5-carboxylate derivatives have been prepared from monosubstituted sulfamides in order to obtain N-substituted 1,1-dioxo-1,2,6-thiadiazine-5-carboxamides as novel cannabinoid derivatives, analogues of Rimonabant (SR141716A). Their potential functional activity on cannabinoid receptors has been evaluated in vitro and in vivo in mice, showing that two compounds (37 and 39) behave as cannabinoid agonists in vitro. Their potency is lower than that of the reference compound, WIN 55,212-2, but their efficacy is similar to that of this cannabinoid agonist, although no in vivo activity is observed. Another derivative (38) behaves as a cannabinoid antagonist both in vitro and in vivo, being its efficacy and potency similar to that of the well-known antagonist SR141716A.

Analgesic properties of oleoylethanolamide (OEA) in visceral and inflammatory pain

Oleoylethanolamide (OEA) is a natural fatty acid amide that mainly modulates feeding and energy homeostasis by binding to peroxisome proliferator-activated receptor-alpha (PPAR-alpha) [Rodríguez de Fonseca F, Navarro M, Gómez R, Escuredo L, Navas F, Fu J, et al. An anorexic lipid mediator regulated by feeding. Nature 2001;414:209-12; Fu J, Gaetani S, Oveisi F, Lo Verme J, Serrano A, Rodríguez de Fonseca F, et al. Oleoylethanolamide regulates feeding and body weight through activation of the nuclear receptor PPAR-alpha. Nature 2003;425:90-3]. Additionally, it has been proposed that OEA could act via other receptors, including the vanilloid receptor (TRPV1) [Wang X, Miyares RL, Ahern GP. Oleoylethanolamide excites vagal sensory neurones, induces visceral pain and reduces short-term food intake in mice via capsaicin receptor TRPV1. J Physiol 2005;564:541-7.] or the GPR119 receptor [Overton HA, Babbs AJ, Doel SM, Fyfe MC, Gardner LS, Griffin G, et al. Deorphanization of a G protein-coupled receptor for oleoylethanolamide and its use in the discovery of small-molecule hypophagic agents. Cell Metab 2006;3:167-175], suggesting that OEA might subserve other physiological roles, including pain perception. We have evaluated the effect of OEA in two types of nociceptive responses evoked by visceral and inflammatory pain in rodents. Our results suggest that OEA has analgesic properties reducing the nociceptive responses produced by administration of acetic acid and formalin in two experimental animal models. Additional research was performed to investigate the mechanisms underlying this analgesic effect. To this end, we evaluated the actions of OEA in mice null for the PPAR-alpha receptor gene and compared its actions with those of PPAR-alpha receptor wild-type animal. We also compared the effect of MK-801 in order to evaluate the role of NMDA receptor in this analgesia. Our data showed that OEA reduced visceral and inflammatory responses through a PPAR-alpha-activation independent mechanism. Co-administration of subanalgesic doses of MK-801 and OEA produced an analgesic effect, suggesting the participation of glutamatergic transmission in the antinociceptive effect of OEA. This study represents a novel approach to the examination of the effectiveness of OEA in nociceptive responses and provides a framework for understanding its biological functions and endogenous targets in visceral and inflammatory pain.

The cannabinoid CB1 receptor regulates bone formation by modulating adrenergic signaling

We have recently reported that in bone the cannabinoid CB1 receptor is present in sympathetic terminals. Here we show that traumatic brain injury (TBI), which in humans enhances peripheral osteogenesis and fracture healing, acutely stimulates bone formation in a distant skeletal site. At this site we demonstrate i) a high level of the main endocannabinoid, 2-arachidonoylglycerol (2-AG), and expression of diacylglycerol lipases, enzymes essential for 2-AG synthesis; ii) that the TBI-induced increase in bone formation is preceded by elevation of the 2-AG and a decrease in norepinephrine (NE) levels. The TBI stimulation of bone formation was absent in CB1-null mice. In wild-type animals it could be mimicked, including the suppression of NE levels, by 2-AG administration. The TBI- and 2-AG-induced stimulation of osteogenesis was restrained by the beta-adrenergic receptor agonist isoproterenol. NE from sympathetic terminals is known to tonically inhibit bone formation by activating osteoblastic beta2-adrenergic receptors. The present findings further demonstrate that the sympathetic control of bone formation is regulated through 2-AG activation of prejunctional CB1. Elevation of bone 2-AG apparently suppresses NE release from bone sympathetic terminals, thus alleviating the inhibition of bone formation. The involvement of osteoblastic CB2 signaling in this process is minimal, if any.

WIN 55,212-2 prevents mechanical allodynia but not alterations in feeding behaviour induced by chronic cisplatin in the rat

Anorexia, nausea/emesis and peripheral sensorial neuropathy are frequent adverse effects associated with chemotherapy. Cannabinoids have been proposed to alleviate these effects, but their preventive properties in long-term experimental models have not been tested. This study was conducted to determine whether or not a cannabinoid agonist (WIN-55,212-2) can prevent anorexia, pica (an indirect marker of nausea in non-vomiting species, consisting of the ingestion of non-nutritive substances such as kaolin) and mechanical allodynia (a marker of peripheral neuropathy) induced by the antineoplastic drug cisplatin chronically administered. Isolated rats with free access to food and kaolin received either saline, cannabinoid vehicle, WIN-55,212-2 (1-2 mg kg(-1)), cisplatin (1-2 mg kg(-1)), or both drugs once per week for five consecutive weeks. Modifications in temperature, body weight gain, food and kaolin intake, and the threshold for mechanical allodynia were recorded. Additionally, the acute psychoactive effects of the cannabinoid (hypomotility, hypothermia, analgesia and catalepsia) were assayed by means of the cannabinoid tetrad. WIN 55,212-2 prevented the development of mechanical allodynia but not anorexia, pica and reduction in weight gain induced by chronic cisplatin. The effect of WIN 55,212-2 was evident even at a dose lacking activity in the cannabinoid tetrad. The preventive effect on cisplatin-induced mechanical allodynia exerted by the cannabinoid could be due to a neuroprotective role, as has been suggested for other conditions. The present results support the interest in the evaluation of cannabinoids for treatment of patients suffering or likely to suffer neuropathic pain.

Cannabinoid signalling in TNF-α induced IL-8 release

The molecular events mediating the immunomodulatory properties of cannabinoids have remained largely unresolved. We have therefore investigated the molecular mechanism(s) through which R-(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl] pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-napthanlenyl) methanone (WIN55212-2) modulate production of interleukin-8 (IL-8) in HT-29 cells. Release of IL-8 induced by tumor necrosis factor-alpha (TNF-alpha) was determined by enzyme-linked immunosorbent assay (ELISA). Changes in expression of inhibitory kappa B (IkappaB) were monitored by Western blotting and activation of nuclear factor-kappa B (NF-kappaB) was determined in electrophoretic mobility shift assay (EMSAs). TNF-alpha induced release of IL-8 was inhibited by WIN55212-2 which also blocked the degradation of IkappaB-alpha and activation of NF-kappaB induced by TNF-alpha. These data provide strong evidence that WIN55212-2 may modulate IL-8 release by negatively regulating the signaling cascade leading to the activation of NF-kappaB. These findings highlight a potential mechanism for the immunomodulatory properties of cannabinoids and contribute towards acquiring a clear understanding of the role of cannabinoids in inflammation.

Effects of cannabinoids on neurotransmission

The CB1 cannabinoid receptor is widely distributed in the central and peripheral nervous system. Within the neuron, the CB1 receptor is often localised in axon terminals, and its activation leads to inhibition of transmitter release. The consequence is inhibition of neurotransmission via a presynaptic mechanism. Inhibition of glutamatergic, GABAergic, glycinergic, cholinergic, noradrenergic and serotonergic neurotransmission has been observed in many regions of the central nervous system. In the peripheral nervous system, CB1 receptor-mediated inhibition of adrenergic, cholinergic and sensory neuroeffector transmission has been frequently observed. It is characteristic for the ubiquitous operation of CB1 receptor-mediated presynaptic inhibition that antagonistic components of functional systems (for example, the excitatory and inhibitory inputs of the same neuron) are simultaneously inhibited by cannabinoids. Inhibition of voltage-dependent calcium channels, activation of potassium channels and direct interference with the synaptic vesicle release mechanism are all implicated in the cannabinoid-evoked inhibition of transmitter release. Many presynaptic CB1 receptors are subject to an endogenous tone, i.e. they are constitutively active and/or are continuously activated by endocannabinoids. Compared with the abundant data on presynaptic inhibition by cannabinoids, there are only a few examples for cannabinoid action on the somadendritic parts of neurons in situ.

A cannabinoid agonist, WIN 55,212-2, reduces neuropathic nociception induced by paclitaxel in rats

Paclitaxel is an effective antineoplastic drug treatment used as an anti-tumoral therapy. Unfortunately its use is associated with unwanted side effects, which include the development of peripheral neuropathies and neuropathic pain, greatly affecting the quality of life of patients. It is well known that agonists of the cannabinoid receptor are able to reduce hyperalgesia and allodynia that develop after nerve injury. Our aim was to evaluate the efficacy of the cannabinoid agonist WIN 55,212-2 to reduce the thermal hyperalgesia and the tactile allodynia induced by administration of paclitaxel in rats. Present results demonstrate that WIN 55,212-2 (1 mg/kg i.p.) significantly reduced the heat (P<0.0001) and the mechanical (P=0.0003) withdrawal thresholds, the dose being smaller than that required to reach similar effects in the sciatic nerve constriction model (1.5 mg/kg). When the cannabinoid tetrad test was evaluated to measure behavioral modifications, it was found that WIN 55,212-2 (1mg/kg) did not induce changes either in body temperature or in immobility time, and only a reduction in spontaneous motility was recorded. This effect was antagonized by SR 141716A, suggesting the involvement of the CB1 receptor, although the participation of CB2 receptors cannot be excluded from this study. When WIN 55,212-2 was administered intraplantar, no differences were observed between the injected paw and the contralateral paw, suggesting that systemic mechanisms are needed to reach effectiveness. From these results we suggest that cannabinoids may be an interesting alternative to reduce neuropathic symptoms induced by paclitaxel, however more work is required to assess this possibility.

Effects of cannabinoid receptor activation on rabbit bisected vas deferens strips

1. In the present study, the effects of anandamide and WIN 55,212-2, cannabinoid receptor agonists, were investigated on electrical field stimulation (EFS)-induced biphasic twitch responses obtained from the epididymal and prostatic portions of rabbit vas deferens strips. 2. Anandamide and WIN 55,212-2 dose-dependently inhibited both the first and second phases of the EFS-induced twitch responses recorded from epididymal and prostatic portions of the vas deferens over the concentration range 10(-9) to 3 x 10(-6) mol/L. 3. The cannabinoid CB1 receptor antagonist AM 251 (10(-6) mol/L) and the cannabinoid CB2 receptor antagonist AM 630 (10(-6) mol/L) had no effect on the inhibitory action of anandamide on the biphasic twitch responses in the prostatic and epididymal portions of the rabbit vas deferens. 4. In both the prostatic and epididymal portions of the rabbit vas deferens, AM 251 significantly, but not completely, reversed the inhibitory effect of WIN 55,212-2 on the first phase of the twitch response. In contrast, AM 630 did not have any effect on the inhibitory action of WIN 55,212-2 in the rabbit vas deferens strips. 5. The inhibitory effects of anandamide or WIN 55,212-2 on EFS-induced twitch responses of both the prostatic and epididymal portions of the rabbit vas deferens were not altered in the presence of 10(-5) mol/L naloxone. 6. These results suggest that cannabinoid receptors may have a modulatory role in the regulation of sympathetic transmission in the rabbit vas deferens. However, further investigation is required to characterize the receptors involved.

Acute delta9-tetrahydrocannabinol-induced deficits in reversal learning: neural correlates of affective inflexibility

Despite concerns surrounding the possible adverse effects of marijuana on complex cognitive function, the processes contributing to the observed cognitive deficits are unclear, as are the causal relationships between these impairments and marijuana exposure. In particular, marijuana-related deficits in cognitive flexibility may affect the social functioning of the individual and may contribute to continued marijuana use. We therefore examined the ability of rats to perform affective and attentional shifts following acute administration of Delta(9)-tetrahydrocannabinol (THC), the primary psychoactive marijuana constituent. Administration of 1 mg/kg THC produced marked impairments in the ability to reverse previously relevant associations between stimulus features and reward presentation, while the ability to transfer attentional set between dimensional stimulus properties was unaffected. Concurrent in situ hybridization analysis of regional c-fos and ngfi-b expression highlighted areas of the prefrontal cortex and striatum that were recruited in response to both THC administration and task performance. Furthermore, the alterations in mRNA expression in the orbitofrontal cortex and striatum were associated with the ability to perform the reversal discriminations. These findings suggest that marijuana use may produce inelasticity in updating affective associations between stimuli and reinforcement value, and that this effect may arise through dysregulation of orbitofrontal and striatal circuitry.

Evaluation of the effect of age on cannabinoid receptor functionality and expression in guinea-pig ileum longitudinal muscle–myenteric plexus preparations

Cannabinoid drugs exert a wide range of biological effects and are currently under study for their multiple potential therapeutic uses. Cannabinoids reduce gastrointestinal (GI) motility and this is mediated by the CB1 cannabinoid receptor (CB1R) present in the myenteric neurones. GI motility can also be affected by a variety of pathophysiological situations, including ageing. The purpose of this work was to study the influence of age on the functionality and expression of CB1R in the myenteric plexus. Ileal longitudinal muscle-myenteric plexus (LMMP) preparations from young, adult and old guinea-pigs were used in two sets of experiments: in vitro assessment of the inhibitory cannabinoid effect upon electrically stimulated contractions and immunohistochemical quantification of myenteric neurones expressing CB1R. LMMP preparations responded to the synthetic cannabinoid WIN 55,212-2, and the endogenous cannabinoid ligand anandamide in an age-independent manner. The total number of CB1R-immunoreactive (IR) myenteric neurones, which included at least part of the motor neurones to the longitudinal smooth muscle, decreased in proportion to the general neuronal population; however, the proportion of CB1R-IR neurones was preserved in old animals. These data may justify the preservation of the effectiveness of the cannabinoids in the isolated guinea-pig ileum. This age-related independency of CB1R expression and effect on GI motility could be of interest if cannabinoids are to be used therapeutically.