Neurobehavioral activity in mice of N-vanillyl-arachidonyl-amide

A type II cannabis extract and a 1:1 blend of Δ(9)-tetrahydrocannabinol and cannabidiol display distinct antinociceptive profiles and engage different endocannabinoid targets when administered into the subarachnoid space

Introduction: Cannabis extracts are being increasingly used to mitigate chronic pain. Current guidelines for their prescription rely on Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) content as well as the ratio of these major cannabinoids present in the blend. Here we assessed whether these descriptors were representative of product effectiveness to produce a desired outcome such as analgesia. Methods: In this study, we used a rat model of diabetic neuropathy and assessed the reduction in mechanical allodynia following intrathecal injection of pure THC, pure CBD, a 1:1 mix of these compounds and a "balanced" chemotype II cannabis extract. Engagement of endocannabinoid targets by different treatments was investigated using CB1 (AM251) and CB2 (AM630) receptor antagonists as well as a TRPV1 channel blocker (capsazepine). Results: Antinociceptive responses induced by an equivalent amount of THC administered in its pure form, as a THC:CBD mix or as a "balanced" extract were distinct. Furthermore, the 1:1 THC:CBD mix and the balanced extract had not only different response profiles but their relative engagement of CB1, CB2 receptors and TRPV1 channels was distinct. Discussion: These findings indicate that antinociceptive responses and targets engaged by blended cannabinoids are composition-specific, and cannot be simply inferred from THC and CBD contents. This information may have implications in relation to the way medicinal cannabis products are prescribed.

Comparison of the Anticancer Effects of Arvanil and Olvanil When Combined with Cisplatin and Mitoxantrone in Various Melanoma Cell Lines-An Isobolographic Analysis

Due to the unique structures of arvanil and olvanil, the drugs combine certain properties of both cannabinoids and vanilloids, which makes them able to stimulate both TPRV1 and CB1 receptors and causes them to be interesting agents in the setting of carcinoma treatment. The aim of this study was to investigate the cytotoxic and anti-proliferative effects of arvanil and olvanil when administered alone and in combination with cisplatin (CDDP) and mitoxantrone (MTX), using various primary (A375, FM55P) and metastatic (SK-MEL 28, FM55M2) human malignant melanoma cell lines. The results indicate that both arvanil and olvanil inhibited (dose-dependently) the viability and proliferation of various malignant melanoma cells, as demonstrated by MTT and BrdU assays. The safety profile of both arvanil and olvanil tested in human keratinocytes (HaCaT) and normal human melanocytes (HEMa-LP) revealed that neither arvanil nor olvanil caused significant cytotoxicity in HaCaT and HEMa-LP cell lines in LDH and MTT assays. Isobolographically, it was found that both arvanil and olvanil exerted additive interactions with MTX and antagonistic interactions with CDDP in the studied malignant melanoma cell lines. In conclusion, the combinations of arvanil or olvanil with MTX may be considered as a part of melanoma multi-drug therapy; however, the combination of these compounds with CDDP should be carefully considered due to the antagonistic interactions observed in the studied malignant melanoma cell lines.

Affinin and hexahydroaffinin: Chemistry and toxicological profile

The present work aimed to determine the safety parameters of two new alkamides, affinin and hexahydroaffinin, with antinociceptive activity. To predict the preliminary acute toxicity, we used the acute and subchronic toxicity (50 mg/kg, orally [po]) in Swiss Webster mice. Genotoxicity assayed via analysis of cell micronuclei of the femoral bone marrow in mice; at the same time, metabolic parameters determined from peripheral blood samples. Furthermore, to discard the neuropharmacological effects, we assessed the ambulatory activity in mice to determine the possible effects in the central nervous system. Finally, we used capsaicin as a positive control of alkamides. According to our results, hexahydroaffinin (LD50  ≥ 5,000 mg/kg, po) is significantly less noxious than affinin (LD50 = 1,442.2 mg/kg, po) or capsaicin (LD50 = 489.9 mg/kg, po). In subchronic administration, we did not observe any changes in hematological or biochemical parameters in any compound analyzed from peripheral blood samples. Finally, the data from the genotoxicity assay showed micronuclei formation in 28%, 5%, and 3% of mice in the capsaicin, affinin, and hexahydroaffinin groups, respectively. With the results obtained in the present investigation, we suggest that affinin and hexahydroaffinin are not only useful candidates for possible new drugs but also safe compounds.

Bile acid composition regulates GPR119-dependent intestinal lipid sensing and food intake regulation in mice

OBJECTIVES

Lipid mediators in the GI tract regulate satiation and satiety. Bile acids (BAs) regulate the absorption and metabolism of dietary lipid in the intestine, but their effects on lipid-regulated satiation and satiety are completely unknown. Investigating this is challenging because introducing excessive BAs or eliminating BAs strongly impacts GI functions. We used a mouse model (Cyp8b1^-/- mice) with normal total BA levels, but alterations in the composition of the BA pool that impact multiple aspects of intestinal lipid metabolism. We tested two hypotheses: BAs affect food intake by (1) regulating production of the bioactive lipid oleoylethanolamide (OEA), which enhances satiety; or (2) regulating the quantity and localisation of hydrolysed fat in small intestine, which controls gastric emptying and satiation.

DESIGN

We evaluated OEA levels, gastric emptying and food intake in wild-type and Cyp8b1^-/- mice. We assessed the role of the fat receptor GPR119 in these effects using Gpr119^-/- mice.

RESULTS

Cyp8b1^-/- mice on a chow diet showed mild hypophagia. Jejunal OEA production was blunted in Cyp8b1^-/- mice, thus these data do not support a role for this pathway in the hypophagia of Cyp8b1^-/- mice. On the other hand, Cyp8b1 deficiency decreased gastric emptying, and this was dependent on dietary fat. GPR119 deficiency normalised the gastric emptying, gut hormone levels, food intake and body weight of Cyp8b1^-/- mice.

CONCLUSION

BAs regulate gastric emptying and satiation by determining fat-dependent GPR119 activity in distal intestine.

Dual-Acting Compounds Targeting Endocannabinoid and Endovanilloid Systems-A Novel Treatment Option for Chronic Pain Management

Compared with acute pain that arises suddenly in response to a specific injury and is usually treatable, chronic pain persists over time, and is often resistant to medical treatment. Because of the heterogeneity of chronic pain origins, satisfactory therapies for its treatment are lacking, leading to an urgent need for the development of new treatments. The leading approach in drug design is selective compounds, though they are often less effective and require chronic dosing with many side effects. Herein, we review novel approaches to drug design for the treatment of chronic pain represented by dual-acting compounds, which operate at more than one biological target. A number of studies suggest the involvement of the cannabinoid and vanilloid receptors in pain. Interestingly cannabinoid system is in interrelation with other systems that comprise lipid mediators: prostaglandins, produced by COX enzyme. Therefore, in the present review, we summarize the role of dual-acting molecules (FAAH/TRPV1 and FAAH/COX-2 inhibitors) that interact with endocannabinoid and endovanillinoid systems and act as analgesics by elevating the endogenously produced endocannabinoids and dampening the production of pro-inflammatory prostaglandins. The plasticity of the endocannabinoid system (ECS) and the ability of a single chemical entity to exert an activity on two receptor systems has been developed and extensively investigated. Here, we review up-to-date pharmacological studies on compounds interacting with FAAH enzyme together with TRPV1 receptor or COX-2 enzyme respectively. Multi-target pharmacological intervention for treating pain may lead to the development of original and efficient treatments.

Sensory nerves contribute to cutaneous vasodilator response to cathodal stimulation in healthy rats

Cutaneous current-induced vasodilation (CIV) in response to galvanic current application is an integrative model of neurovascular interaction that relies on capsaicin-sensitive fiber activation. The upstream and downstream mechanisms related to the activation of the capsaicin-sensitive fibers involved in CIV are not elucidated. In particular, the activation of cutaneous transient receptor potential vanilloid type-1 (TRPV1) channels and/or acid-sensing ion channels (ASIC) (activators mechanisms) and the release of calcitonin gene-related peptide (CGRP) and substance P (SP) (effector mechanisms) have been tested. To assess cathodal CIV, we measured cutaneous blood flow using laser Doppler flowmetry for 20min following cathodal current application (240s, 100μA) on the skin of the thigh in anesthetized healthy rats for 20min. CIV was studied in rats treated with capsazepine and amiloride to inhibit TRPV1 and ASIC channels, respectively; CGRP8-37 and SR140333 to antagonize CGRP and neurokinin-1 (NK1) receptors, respectively; compared to their respective controls. Cathodal CIV was attenuated by capsazepine (12±2% vs 54±6%, P<0.001), amiloride (19±8% vs 61±6%, P<0.01), CGRP8-37 (15±6% vs 61±6%, P<0.001) and SR140333 (9±5% vs 54±6%, P<0.001) without changing local acidification. This is the first integrative study performed in healthy rats showing that cutaneous vasodilation in response to cathodal stimulation is initiated by activation of cutaneous TRPV1 and ASIC channels likely through local acidification. The involvement of CGRP and NK1 receptors suggests that cathodal CIV is the result of CGRP and SP released through activated capsaicin-sensitive fibers. Therefore cathodal CIV could be a valuable method to assess sensory neurovascular function in the skin, which would be particularly relevant to evaluate the presence of small nerve fiber disorders and the effectiveness of treatments.

Fatty acid amide hydrolase-dependent generation of antinociceptive drug metabolites acting on TRPV1 in the brain

The discovery that paracetamol is metabolized to the potent TRPV1 activator N-(4-hydroxyphenyl)-5Z,8Z,11Z,14Z-eicosatetraenamide (AM404) and that this metabolite contributes to paracetamol’s antinociceptive effect in rodents via activation of TRPV1 in the central nervous system (CNS) has provided a potential strategy for developing novel analgesics. Here we validated this strategy by examining the metabolism and antinociceptive activity of the de-acetylated paracetamol metabolite 4-aminophenol and 4-hydroxy-3-methoxybenzylamine (HMBA), both of which may undergo a fatty acid amide hydrolase (FAAH)-dependent biotransformation to potent TRPV1 activators in the brain. Systemic administration of 4-aminophenol and HMBA led to a dose-dependent formation of AM404 plus N-(4-hydroxyphenyl)-9Z-octadecenamide (HPODA) and arvanil plus olvanil in the mouse brain, respectively. The order of potency of these lipid metabolites as TRPV1 activators was arvanil = olvanil>>AM404> HPODA. Both 4-aminophenol and HMBA displayed antinociceptive activity in various rodent pain tests. The formation of AM404, arvanil and olvanil, but not HPODA, and the antinociceptive effects of 4-aminophenol and HMBA were substantially reduced or disappeared in FAAH null mice. The activity of 4-aminophenol in the mouse formalin, von Frey and tail immersion tests was also lost in TRPV1 null mice. Intracerebroventricular injection of the TRPV1 blocker capsazepine eliminated the antinociceptive effects of 4-aminophenol and HMBA in the mouse formalin test. In the rat, pharmacological inhibition of FAAH, TRPV1, cannabinoid CB1 receptors and spinal 5-HT₃ or 5-HT_1A receptors, and chemical deletion of bulbospinal serotonergic pathways prevented the antinociceptive action of 4-aminophenol. Thus, the pharmacological profile of 4-aminophenol was identical to that previously reported for paracetamol, supporting our suggestion that this drug metabolite contributes to paracetamol’s analgesic activity via activation of bulbospinal pathways. Our findings demonstrate that it is possible to construct novel antinociceptive drugs based on fatty acid conjugation as a metabolic pathway for the generation of TRPV1 modulators in the CNS.

Regulation of GPR119 receptor activity with endocannabinoid-like lipids

The GPR119 receptor plays an important role in the secretion of incretin hormones in response to nutrient consumption. We have studied the ability of an array of naturally occurring endocannabinoid-like lipids to activate GPR119 and have identified several lipid receptor agonists. The most potent receptor agonists identified were three N-acylethanolamines: oleoylethanolamine (OEA), palmitoleoylethanolamine, and linoleylethanolamine (LEA), all of which displayed similar potency in activating GPR119. Another lipid, 2-oleoylglycerol (2-OG), also activated GPR119 receptor but with significantly lower potency. Endogenous levels of endocannabinoid-like lipids were measured in intestine in fasted and refed mice. Of the lipid GPR119 agonists studied, the intestinal levels of only OEA, LEA, and 2-OG increased significantly upon refeeding. Intestinal levels of OEA and LEA in the fasted mice were low. In the fed state, OEA levels only moderately increased, whereas LEA levels rose drastically. 2-OG was the most abundant of the three GPR119 agonists in intestine, and its levels were radically elevated in fed mice. Our data suggest that, in lean mice, 2-OG and LEA may serve as physiologically relevant endogenous GPR119 agonists that mediate receptor activation upon nutrient uptake.

Spinal anandamide produces analgesia in neuropathic rats: possible CB(1)- and TRPV1-mediated mechanisms

The endocannabinoid anandamide (AEA) activates also transient receptor potential vanilloid-1 (TRPV1) channels. However, no data exist on the potential role of spinal TRPV1 activation by AEA in neuropathic pain. We tested the effect of: 1) AEA (5-100 μg), alone or in the presence of an inhibitor of its hydrolysis, and 2) elevated levels of endogenous AEA (following inhibition of AEA hydrolysis), in CCI rats, and the involvement of TRPV1 or cannabinoid CB(1) receptors in the observed effects. Levels of AEA in the spinal cord of CCI rats were measured following all treatments. AEA (50 μg) displayed anti-allodynic and anti-hyperalgesic effects which were abolished by previous antagonism of TRPV1, but not CB(1), receptors. Depending on the administered dose, the selective inhibitor of AEA enzymatic hydrolysis, URB597 (10-100 μg), reduced thermal and tactile nociception via CB(1) or CB(1)/TRPV1 receptors. The anti-nociceptive effects of co-administered per se ineffective doses of AEA (5 μg) and URB597 (5 μg) was abolished by antagonism of CB(1), but not TRPV1, receptors. Spinal AEA levels were increased after CCI, slightly increased further by URB597, 10 μg i.t., and strongly elevated by URB597, 100 μg. Injection of AEA (50 μg) into the lumbar spinal cord led to its dramatic elevation in this tissue, whereas, when a lower dose was used (5 μg) AEA endogenous levels were elevated only in the presence of URB597 (5 μg). We suggest that spinal AEA reduces neuropathic pain via CB(1) or TRPV1, depending on its local concentration.

Differential effects of TRPV1 receptor ligands against nicotine-induced depression-like behaviors

BACKGROUND

The contributions of brain cannabinoid (CB) receptors, typically CB1 (CB type 1) receptors, to the behavioral effects of nicotine (NC) have been reported to involve brain transient receptor potential vanilloid 1 (TRPV1) receptors, and the activation of candidate endogenous TRPV1 ligands is expected to be therapeutically effective. In the present study, the effects of TRPV1 ligands with or without affinity for CB1 receptors were examined on NC-induced depression-like behavioral alterations in a mouse model in order to elucidate the "antidepressant-like" contributions of TRPV1 receptors against the NC-induced "depression" observed in various types of tobacco abuse.

RESULTS

Repeated subcutaneous NC treatments (NC group: 0.3 mg/kg, 4 days), like repeated immobilization stress (IM) (IM group: 10 min, 4 days), caused depression-like behavioral alterations in both the forced swimming (reduced swimming behaviors) and the tail suspension (increased immobility times) tests, at the 2 h time point after the last treatment. In both NC and IM groups, the TRPV1 agonists capsaicin (CP) and olvanil (OL) administered intraperitoneally provided significant antidepressant-like attenuation against these behavioral alterations, whereas the TRPV1 antagonist capsazepine (CZ) did not attenuate any depression-like behaviors. Furthermore, the endogenous TRPV1-agonistic CB1 agonists anandamide (AEA) and N-arachidonyldopamine (NADA) did not have any antidepressant-like effects. Nevertheless, a synthetic "hybrid" agonist of CB1 and TRPV1 receptors, arvanil (AR), caused significant antidepressant-like effects. The antidepressant-like effects of CP and OL were antagonized by the TRPV1 antagonist CZ. However, the antidepressant-like effects of AR were not antagonized by either CZ or the CB1 antagonist AM 251 (AM).

CONCLUSIONS

The antidepressant-like effects of TRPV1 agonists shown in the present study suggest a characteristic involvement of TRPV1 receptors in NC-induced depression-like behaviors, similar to those caused by IM. The strong antidepressant-like effects of the potent TRPV1 plus CB1 agonist AR, which has been reported to cause part of its TRPV1-mimetic and cannabimimetic effects presumably via non-TRPV1 or non-CB1 mechanisms support a contribution from other sites of action which may play a therapeutically important role in the treatment of NC abuse.

Thermoregulatory phenotype of the Trpv1 knockout mouse: thermoeffector dysbalance with hyperkinesis

This study aimed at determining the thermoregulatory phenotype of mice lacking transient receptor potential vanilloid-1 (TRPV1) channels. We used Trpv1 knockout (KO) mice and their genetically unaltered littermates to study diurnal variations in deep body temperature (T(b)) and thermoeffector activities under basal conditions, as well as thermoregulatory responses to severe heat and cold. Only subtle alterations were found in the basal T(b) of Trpv1 KO mice or in their T(b) responses to thermal challenges. The main thermoregulatory abnormality of Trpv1 KO mice was a different pattern of thermoeffectors used to regulate T(b). On the autonomic side, Trpv1 KO mice were hypometabolic (had a lower oxygen consumption) and hypervasoconstricted (had a lower tail skin temperature). In agreement with the enhanced skin vasoconstriction, Trpv1 KO mice had a higher thermoneutral zone. On the behavioral side, Trpv1 KO mice preferred a lower ambient temperature and expressed a higher locomotor activity. Experiments with pharmacological TRPV1 agonists (resiniferatoxin and anandamide) and a TRPV1 antagonist (AMG0347) confirmed that TRPV1 channels located outside the brain tonically inhibit locomotor activity. With age (observed for up to 14 months), the body mass of Trpv1 KO mice exceeded that of controls, sometimes approaching 60 g. In summary, Trpv1 KO mice possess a distinct thermoregulatory phenotype, which is coupled with a predisposition to age-associated overweight and includes hypometabolism, enhanced skin vasoconstriction, decreased thermopreferendum, and hyperkinesis. The latter may be one of the primary deficiencies in Trpv1 KO mice. We propose that TRPV1-mediated signals from the periphery tonically suppress the general locomotor activity.

The hypothermic response to bacterial lipopolysaccharide critically depends on brain CB1, but not CB2 or TRPV1, receptors

Hypothermia occurs in the most severe cases of systemic inflammation, but the mechanisms involved are poorly understood. This study evaluated whether the hypothermic response to bacterial lipopolysaccharide (LPS) is modulated by the endocannabinoid anandamide(AEA) and its receptors: cannabinoid-1 (CB1), cannabinoid-2 (CB2) and transient receptor potential vanilloid-1 (TRPV1). In rats exposed to an ambient temperature of 22◦C, a moderate dose of LPS (25 - 100 μg kg−1 I.V.) induced a fall in body temperature with a nadir at ∼100 minpostinjection. This response was not affected by desensitization of intra-abdominal TRPV1 receptors with resiniferatoxin (20 μg kg - 1 I.P.), by systemic TRPV1 antagonism with capsazepine(40mg kg−1 I.P.), or by systemic CB2 receptor antagonism with SR144528 (1.4 mg kg−1 I.P.).However, CB1 receptor antagonism by rimonabant (4.6mg kg−1 I.P.) or SLV319 (15mg kg−1 I.P.)blocked LPS hypothermia. The effect of rimonabant was further studied. Rimonabant blocked LPS hypothermia when administered I.C.V. at a dose (4.6 μg) that was too low to produce systemic effects. The blockade of LPS hypothermia by I.C.V. rimonabant was associated with suppression of the circulating level of tumour necrosis factor-α. In contrast to rimonabant,the I.C.V. administration of AEA (50 μg) enhanced LPS hypothermia. Importantly, I.C.V. AEAdid not evoke hypothermia in rats not treated with LPS, thus indicating that AEA modulates LPS-activated pathways in the brain rather than thermo effector pathways. In conclusion, the present study reveals a novel, critical role of brain CB1 receptors in LPS hypothermia. Brain CB1 receptors may constitute a new therapeutic target in systemic inflammation and sepsis.

N-palmitoyl-vanillamide (palvanil) is a non-pungent analogue of capsaicin with stronger desensitizing capability against the TRPV1 receptor and anti-hyperalgesic activity

N-acyl-vanillamide (NAVAM) analogues of the natural pungent principle of capsicum, capsaicin, were developed several years ago as potential non-pungent analgesic compounds. N-oleoyl-vanillamide (olvanil) and N-arachidonoy-vanillamide (arvanil), in particular, were described in several publications and patents to behave as potent anti-hyperalgesic compounds in experimental models of chronic and inflammatory pain, and to activate both "capsaicin receptors", i.e. the transient receptor potential of vanilloid type-1 (TRPV1) channel, and, either directly or indirectly, cannabinoid receptors of type-1. Here we report the biochemical and pharmacological characterization of a so far neglected NAVAM, N-palmitoyl-vanillamide (palvanil), and propose its possible use instead of capsaicin, as a possible topical analgesic. Palvanil exhibited a kinetics of activation of human recombinant TRPV1-mediated intracellular calcium elevation significantly slower than that of capsaicin (t(1/2)=21s and 8s, respectively at 1μM). Slow kinetics of TRPV1 agonists were previously found to be associated with stronger potencies as TRPV1 desensitizing agents, which in turn are usually associated with lower pungency and stronger anti-hyperalgesic activity. Accordingly, palvanil desensitized the human recombinant TRPV1 to the effect of capsaicin (10nM) with significantly higher potency than capsaicin (IC(50)=0.8nM and 3.8nM, respectively), this effect reaching its maximum more rapidly (50 and 250min, respectively). Palvanil was also more potent than capsaicin at desensitizing the stimulatory effect of TRPV1 by low pH together with anandamide, which mimics conditions occurring during inflammation. In the eye-wiping assay carried out in mice, palvanil was not pungent and instead caused a strong and long-lasting inhibition of capsaicin-induced eye-wiping. Finally, intraplantar palvanil inhibited the second phase of the nociceptive response to formalin in mice. In conclusion, palvanil appears to be a non-pungent analogue of capsaicin with stronger desensitizing effects on TRPV1 and hence potentially higher anti-hyperalgesic activity.

Midcervical vagotomy precludes respiratory response to novel anti-inflammatory and anti-tumour drug arvanil in rats

Arvanil is a metabolically stable hybrid between anandamide and capsaicin. The present study was designed to test the role of the vagal pathway in post-arvanil respiratory and blood pressure responses. Respiratory and pressure changes evoked by an intravenous injection of arvanil were investigated in 21 urethane-chloralose anaesthetised and spontaneously breathing rats. In control neurally intact rats the effects of arvanil were checked to establish the appropriate dose of the drug. In the experimental group rats were challenged with arvanil while intact, following bilateral midcervical vagotomy and after subsequent supranodose vagotomy. In all neurally intact animals bolus injection of 0.8 mg/kg of arvanil into the right femoral vein induced a significant increase of tidal volume (+1+/-0.11 ml; P<0.01) and diaphragm activity (+1.72+/-0.1 arbitrary units; P<0.01) as well as hypertension (+31.9+/-2.9 mm Hg; P<0.001) and a fall in respiratory rate (-24.7+/-0.4 breath/min; P<0.001). Bilateral midcervical vagotomy precluded the alteration of respiratory parameters but did not eliminate blood pressure response. Arvanil-induced increase in mean arterial blood pressure still persisted after supranodose vagotomy. Results indicated that the respiratory effects evoked by arvanil administered via the peripheral circulation require intact midcervical vagi. Supranodose vagotomy failed to eliminate the hypertension evoked by arvanil.

Conformationally constrained fatty acid ethanolamides as cannabinoid and vanilloid receptor probes

To investigate if certain acylethanolamides bind to both cannabinoid (CB(1) and CB(2)) and vanilloid TRPV1 receptors because of their conformational flexibility, we introduced a methylene lock on their ethanolamine "head", thereby generating a cyclopropane ring with two stereogenic centers and chiral cis/trans diastereomers with different topology of presentation to binding sites. After resolution by chiral-phase HPLC, diastereo- and enantiopure arachidonoyl-, oleoyl-, and palmitoylcyclopropanolamides were tested in assays of CB(1), CB(2), and TRPV1 activity. Diastereodifferentiation between pairs of cis-trans isomers was observed only for TRPV1 activity, with poor enantiodifferentiation. Methylenation introduced (i) CB(1) receptor affinity in oleoylethanolamide while increasing in a diastereoselective way its activity at TRPV1 and (ii) strong diastereoselective activity at TRPV1, but not cannabinoid, receptors in the otherwise inactive palmitoylethanolamide. These results show that the N-alkyl group of acylethanolamides has a different role in their interaction with cannabinoid and vanilloid receptors and that acylcyclopropanolamides qualify as CB(1)/TRPV1 "hybrids" of potential therapeutic utility.

Body-temperature maintenance as the predominant function of the vanilloid receptor TRPV1

Agonists of the transient receptor potential vanilloid type 1 (TRPV1), such as capsaicin, cause pain and a drop in body temperature (hypothermia). Conversely, antagonists of TRPV1 block pain behaviors in rodent models of inflammation, osteoarthritis and cancer. Efforts that evaluate TRPV1 antagonists in on-target challenge models have uncovered that TRPV1 blockade elicits an increase in body temperature (hyperthermia) from rodents to primates, revealing the intimate relationship between the role of TRPV1 in pain and body-temperature maintenance. This evolutionarily conserved function of TRPV1 in body-temperature maintenance became a hurdle for clinical development of one antagonist, AMG 517. However, several other TRPV1 antagonists are currently being evaluated in the clinic and soon-to-be-published results should shed light on the potential of managing antagonist-induced hyperthermia while developing them as therapeutics.

The role of TRPV1 receptors in the antinociceptive effect of anandamide at spinal level

While it is well known that the endogenous cannabinoid receptor ligand anandamide also activates the transient receptor potential vanilloid1 (TRPV1) receptors, there has been no in vivo study indicating the role of the TRPV1 receptors in the antinociceptive effect of anandamide at spinal level. The goal of this study was to determine the effect of inhibition of TRPV1 receptors by capsazepine on the antinociceptive potency of anandamide after intrathecal administration. Anandamide alone (1, 30 or 100 microg) dose-dependently decreased carrageenan-induced thermal hyperalgesia, however, the highest dose caused temporary excitation and vocalization, suggesting the pain-inducing potential of anandamide. Capsazepine (10 or 20 microg) by itself did not change the pain sensitivity markedly, but the lower dose increased it, and the higher dose decreased the antinociceptive effect of 30 microg anandamide. Furthermore, both doses of capsazepine decreased the efficacy of the largest dose of anandamide. These results show that TRPV1 receptor activation plays a substantial role in the antinociceptive effects of anandamide at spinal level. The effect of the inhibition on TRPV1 receptors depended on the dose applied. We presume that coactivation of the cannabinoid and TRPV1 receptors by anandamide provides elevated antinociception through the release of antinociceptive endogenous ligands at spinal level.

An optimized GC-MS method detects nanomolar amounts of anandamide in mouse brain

The endocannabinoids anandamide and 2-arachidonoylglycerol, as well as several anandamide-related N-acylethanolamines, belong to a family of lipid transmitter that regulate fundamental physiological processes, including neurotransmission and neuroinflammation. Their precise quantification in biological matrices can be achieved by gas chromatography-mass spectrometry (GC-MS), but this method typically requires multiple time-consuming purification steps such as solid-phase extraction followed by HPLC. Here we report a novel solid-phase extraction procedure allowing for single-step, and thus higher throughput, purification of endocannabinoids and N-acylethanolamines before GC-MS quantification. We determined the minimal amount of mouse brain tissue required to reliably detect endocannabinoids and N-acylethanolamines when using this approach and provide direct evidence for quantification accuracy by using radioactive and deuterated standards spiked into mouse brain samples. Using this method, we found that mouse brain contains much higher levels of anandamide (>1 nmol/g tissue) than previously reported, whereas levels of 2-arachidonoylglycerol and other N-acylethanolamines are well within the range of previous reports. In addition, we show that mouse brain amounts of endocannabinoids and N-acylethanolamines differ depending on animal gender as well as on whether the tissue was fixed or not. Our study shows that endocannabinoid and N-acylethanolamine levels quantified in mouse brain by GC-MS depend closely on tissue amount and preparation as well as on animal gender and that, depending on such parameters, anandamide levels could be underestimated.

Arvanil, anandamide and N-arachidonoyl-dopamine (NADA) inhibit emesis through cannabinoid CB1 and vanilloid TRPV1 receptors in the ferret

Cannabinoid (CB) agonists suppress nausea and vomiting (emesis). Similarly, transient receptor potential vanilloid-1 (TRPV1) receptor agonists are anti-emetic. Arvanil, N-(3-methoxy-4-hydroxy-benzyl)-arachidonamide, is a synthetic 'hybrid' agonist of CB1 and TRPV1 receptors. Anandamide and N-arachidonoyl-dopamine (NADA) are endogenous agonists at both these receptors. We investigated if arvanil, NADA and anandamide were anti-emetic in the ferret and their mechanism of action. All compounds reduced the episodes of emesis in response to morphine 6 glucuronide. These effects were attenuated by AM251, a CB1 antagonist that was pro-emetic per se, and TRPV1 antagonists iodoresiniferatoxin and AMG 9810, which were without pro-emetic effects. Similar sensitivity to arvanil and NADA was found for prodromal signs of emesis. We analysed the distribution of TRPV1 receptors in the ferret brainstem and, for comparison, the co-localization of CB1 and TRPV1 receptors in the mouse brainstem. TRPV1 immunoreactivity was largely restricted to the nucleus of the solitary tract of the ferret, with faint labeling in the dorsal motor nucleus of the vagus and sparse distribution in the area postrema. A similar distribution of TRPV1, and its extensive co-localization with CB1, was observed in the mouse. Our findings suggest that CB1 and TRPV1 receptors in the brainstem play a major role in the control of emesis by agonists of these two receptors. While there appears to be an endogenous 'tone' of CB1 receptors inhibiting emesis, this does not seem to be the case for TRPV1 receptors, indicating that endogenously released endocannabinoids/endovanilloids inhibit emesis preferentially via CB1 receptors.

Capsaicin and nitric oxide synthase inhibitor interact to evoke a hypothermic synergy

The present study investigated the effect of a drug combination of capsaicin and L-NAME on hypothermia in rats. Capsaicin administration (0.1, 0.25, 0.5, 1 and 2mg/kg, i.m.) caused a significant hypothermia. L-NAME (50mg/kg, i.p.), a nonspecific nitric oxide synthase (NOS) inhibitor, was ineffective. For combined administration, progressively increasing doses of capsaicin (0.1, 0.25, 0.5, 1 and 2mg/kg, i.p.) were given with a non-hypothermic dose of L-NAME (50mg/kg, i.p.). Experiments revealed that L-NAME (50mg/kg, i.p.) enhanced the hypothermic response to capsaicin (0.25, 0.5, 1, and 2mg/kg, i.m.). Comparison of the graded dose-effect curves for capsaicin alone and capsaicin plus L-NAME revealed a significant difference (P<0.05), thus indicating synergy for the drug interaction. To determine if L-NAME acted centrally, a fixed dose of L-NAME (1mg/rat, i.c.v.) was given with graded doses of capsaicin (0.25, 0.5, 1, and 2mg/kg, i.m.). L-NAME (1mg/rat, i.c.v.) only enhanced the hypothermia at a single dose of capsaicin (0.5mg/kg, i.m.). The super-additive hypothermia produced by the concurrent administration of capsaicin and L-NAME (50mg/kg, i.p.) is the first evidence of synergy for a drug combination of capsaicin and a NOS inhibitor. The synergy is apparent only when L-NAME is given systemically, thus indicating that the inhibition of peripheral NO production enhances the hypothermic response to capsaicin.

Non-cannabinoid CB1, non-cannabinoid CB2 antinociceptive effects of several novel compounds in the PPQ stretch test in mice

The analgesic and anti-hyperalgesic effects of cannabinoid- and vanilloid-like compounds, plus the fatty acid amide hydrolase (FAAH) inhibitor Cyclohexylcarbamic acid 3'-carbamoyl-biphenyl-3-yl ester (URB597), and acetaminophen, were evaluated in the phenyl-p-quinone (PPQ) pain model, using different routes of administration in combination with opioid and cannabinoid receptor antagonists. All the compounds tested produced analgesic effects. Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and (R)-(+)-arachidonyl-1'-hydroxy-2'-propylamide ((R)-methanandamide) were active by three routes of administration: i.p., s.c. and, p.o. Delta(9)-THC produced ED(50)s of 2.2 mg/kg (0.3-15.6) i.p., 9 mg/kg (4.3-18.9) s.c., and 6.4 mg/kg (5.5-7.6) p.o. Similarly, (R)-methanandamide yielded ED(50)s of 2.9 mg/kg (1-8) i.p., 11 mg/kg (7-17) s.c., and 11 mg/kg (0.9-134) p.o. N-vanillyl-arachidonyl-amide (arvanil) was active by two routes, producing ED(50)s of 4.7 mg/kg (3.0-7.4) s.c. and 0.06 mg/kg (0.02-0.2) i.p. Palmitoylethanolamide, URB597, and acetaminophen were active i.p., resulting in ED(50)s of 3.7 mg/kg (3.2-4.2), 22.9 mg/kg (11.1-47.2), and 160 mg/kg (63-405), respectively. None of the cannabinoid or opioid receptor antagonists tested blocked the compounds evaluated, with two exceptions: the antinociceptive effects of Delta(9)-THC and URB597 were completely blocked by SR141716A, a cannabinoid CB(1) receptor antagonist. Western immunoassays performed using three opioid receptor antibodies, a cannabinoid CB(1) receptor antibody and a transient receptor potential vanilloid type 1(TRPV(1)) receptor antibody, yielded no change in receptor protein levels after short-term arvanil, (R)-methanandamide or Delta(9)-THC administration. These data suggest that all the compounds tested, except Delta(9)-THC and URB597, produced analgesia via a non-cannabinoid CB(1), non-cannabinoid CB(2) pain pathway not yet identified.

Inhibitors of fatty acid amide hydrolase reduce carrageenan-induced hind paw inflammation in pentobarbital-treated mice: comparison with indomethacin and possible involvement of cannabinoid receptors

The in vivo effect of inhibitors of fatty acid amide hydrolase (FAAH) upon oedema volume and FAAH activity was evaluated in the carrageenan induced hind paw inflammation model in the mouse. Oedema was measured at two time points, 2 and 4 h, after intraplantar injection of carrageenan to anaesthetised mice. Intraperitoneal (i.p.) injections of the FAAH inhibitor URB597 (0.1, 0.3, 1 and 3 mg kg(-1)) 30 min prior to carrageenan administration, dose-dependently reduced oedema formation. At the 4 h time point, the ED(50) for URB597 was approximately 0.3 mg kg(-1). Indomethacin (5 mg kg(-1) i.p.) completely prevented the oedema response to carrageenan. The antioedema effects of indomethacin and URB597 were blocked by 3 mg kg(-1) i.p. of the CB(2) receptor antagonist SR144528. The effect of URB597 was not affected by pretreatment with the peroxisome proliferator-activated receptor gamma antagonist bisphenol A diglycidyl ether (30 mg kg(-1) i.p.) or the TRPV1 antagonist capsazepine (10 mg kg(-1) i.p.), when oedema was assessed 4 h after carrageenan administration. The CB(1) receptor antagonists AM251 (3 mg kg(-1) i.p.) and rimonabant (0.5 mg kg(-1) i.p.) gave inconsistent effects upon the antioedema effect of URB597. FAAH measurements were conducted ex vivo in the paws, spinal cords and brains of the mice. The activities of FAAH in the paws and spinal cords of the inflamed vehicle-treated mice were significantly lower than the corresponding activities in the noninflamed mice. PMSF treatment almost completely inhibited the FAAH activity in all three tissues, as did the highest dose of URB597 (3 mg kg(-1)) in spinal cord samples, whereas no obvious changes were seen ex vivo for the other treatments. In conclusion, the results show that in mice, treatment with indomethacin and URB597 produce SR144528-sensitive anti-inflammatory effects in the carrageenan model of acute inflammation.

Involvement of cannabinoid receptors in the regulation of neurotransmitter release in the rodent striatum: a combined immunochemical and pharmacological analysis

Despite the profound effect of cannabinoids on motor function, and their therapeutic potential in Parkinson's and Huntington's diseases, the cellular and subcellular distributions of striatal CB1 receptors are not well defined. Here, we show that CB1 receptors are primarily located on GABAergic (vesicular GABA transporter-positive) and glutamatergic [vesicular glutamate transporter-1 (VGLUT-1)- and VGLUT-2-positive] striatal nerve terminals and are present in the presynaptic active zone, in the postsynaptic density, as well as in the extrasynaptic membrane. Both the nonselective agonist WIN552122 [(R)-(+)-[2,3-dihydro-5-methyl-3[(4-morpholinyl)methyl] pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-naphthalenyl)methanone mesylate salt] (EC50, 32 nM) and the CB1-selective agonist ACEA [N-(2-chloroethyl)-5Z,8Z,11Z,14Z-eicosatetraenamide] inhibited [3H]GABA release from rat striatal slices. The effect of these agonists was prevented by the CB1-selective antagonists SR141716A [N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide] (1 microM) and AM251 [1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide trifluoroacetate salt] (1 microM), indicating that cannabinoids inhibit the release of GABA via activation of presynaptic CB1 receptors. Cannabinoids modulated glutamate release via both CB1 and non-CB1 mechanisms. Cannabinoid agonists and antagonists inhibited 25 mM K+-evoked [3H]glutamate release and sodium-dependent [3H]glutamate uptake. Partial involvement of CB1 receptors is suggested because low concentrations of SR141716A partly and AM251 fully prevented the effect of WIN552122 and CP55940 [5-(1,1-dimethylheptyl)-2-[5-hydroxy-2-(3-hydroxypropyl)cyclohexyl]phenol]. However, the effect of CB1 agonists and antagonists persisted in CB1 knock-out mice, indicating the involvement of non-CB1,CB1-like receptors. In contrast, cannabinoids did not modulate [3H]dopamine release or [3H]dopamine and [3H]GABA uptake. Our results indicate distinct modulation of striatal GABAergic and glutamatergic transmission by cannabinoids and will facilitate the understanding of the role and importance of the cannabinoid system in normal and pathological motor function.

Iodinated N-Acylvanillamines: Potential “Multiple-Target” Anti-Inflammatory Agents Acting via the Inhibition of T-Cell Activation and Antagonism at Vanilloid TRPV1 Channels

Synthetic N-acylvanillamines were designed and developed as metabolically stable compounds with pharmacological potential in analgesia and inflammation because of their interaction with cannabinoid receptors and the vanilloid receptor (TRPV1). Here, we show that arvanil inhibits early events in T-cell receptor (TCR)-mediated T-cell activation, such as calcium mobilization and nuclear factor of activated T-cell activation, and in late events in TCR-mediated activation, such as interleukin (IL)-2 gene transcription, IL-2R expression, and cell-cycle progression. Arvanil also prevents tumor necrosis factor-alpha-induced nuclear factor-kappaB (NF-kappaB) activation by direct inhibition of IkappaBalpha degradation, NF-kappaB binding to DNA, and NF-kappaB-dependent transcription. Aromatic iodination meta to the phenolic hydroxyl (on the 6'-carbon atom) converts arvanil and olvanil from TRPV1 agonists into antagonists. However, this structural modification did not affect the immunosuppressive and proapoptotic activity of these compounds. In summary, we described here novel activities of arvanil on T-cell functions and the development of two novel inhibitors of neurogenic inflammation (6'-I-olvanil and 6'-I-arvanil) endowed with a unique combination of TRPV1 antagonistic-, immunosuppressive-, and NF-kappaB-inhibitory properties. Our findings provide new mechanistic insights into the biological activities of N-alkylvanillamines and should foster the synthesis of improved analogs amenable to pharmaceutical development as analgesic and anti-inflammatory agents.

Cannabinoids and prefrontal cortical function: Insights from preclinical studies

Marijuana use has been associated with disordered cognition across several domains influenced by the prefrontal cortex (PFC). Here, we review the contribution of preclinical research to understanding the effects of cannabinoids on cognitive ability, and the mechanisms by which cannabinoids may affect the neurochemical processes in the PFC that are associated with these impairments. In rodents, acute administration of cannabinoid agonists produces deficits in working memory, attentional function and reversal learning. These effects appear to be largely dependent on CB1 cannabinoid receptor activation. Preclinical studies also indicate that the endogenous cannabinoid system may tonically regulate some mnemonic processes. Effects of cannabinoids on cognition may be mediated via interaction with neurochemical processes in the PFC and hippocampus. In the PFC, cannabinoids may alter dopaminergic, cholinergic and serotonergic transmission. These mechanisms may underlie cognitive impairments observed following marijuana intake in humans, and may also be relevant to other disorders of cognition. Preclinical research will further enhance our understanding of the interactions between the cannabinoid system and cognitive functioning.

First “hybrid” ligands of vanilloid TRPV1 and cannabinoid CB2receptors and non-polyunsaturated fatty acid-derived CB2-selective ligands

12-Phenylacetyl-ricinoleoyl-vanillamide (phenylacetylrinvanil, PhAR, IDN5890), is an ultra-potent agonist of human vanilloid TRPV1 receptors also endowed with moderate affinity for human cannabinoid CB(2) receptors. To improve its CB(2) affinity and temper its potency at TRPV1, the modification of the polar headgroup and the lipophilic 12-acylgroup of PhAR was pursued. Replacement of the vanillyl headgroup of PhAR with various aromatic or alkyl amino groups decreased activity at TRPV1 receptors, although the dopamine, cyclopropylamine, 1'-(R)- and 1'-(S)-methyl-ethanolamine, and ethanolamine derivatives retained significant potency (EC(50) 31-126 nM). Within these compounds, the 12-phenylacetylricinoleyl cyclopropylamide and ethanolamide were the strongest ligands at CB(2) receptors, with K(i) of 22 and 44 nM, and 14- and >20-fold selectivity over cannabinoid CB(1) receptors, respectively. The propyl- and allyl-derivatives also exhibited high affinity at CB(2) receptors (K(i)=40 and 22 nM, with 40 and >80-fold selectivity over CB(1) receptors, respectively), but no activity at TRPV1 receptors. The cyclopropyl- and allyl-derivatives behaved as CB(2) inverse agonists in the GTP-gamma-S binding assay. Addition of para-methoxy, -tert-butyl or -chlorine groups to the 12-phenylacetyl moiety of PhAR produced compounds that retained full potency at TRPV1 receptors, but with improved selectivity over CB(2) or CB(1) receptors. Thus, the manipulation of PhAR led to the development of the first CB(2)/TRPV1 dual ligands and of an entirely new class of inverse agonists at CB(2) receptors. Both types of compounds might find application in the treatment of inflammation, and represent new molecular probes to investigate the endocannabinoid-endovanilloid signalling system.

Effects of cannabinoids on hypothalamic and reproductive function

Marijuana and cannabinoids have been shown to exert profound effects on hypothalamic regulatory functions and reproduction in both experimental animals and humans. Here we review the role of (endo)cannabinoids in the regulation of appetite and food intake. There is converging evidence that the hypothalamic endocannabinoid system changes after leptin treatment. Cannabinoid administration decreases heat production by altering hypothalamic neurotransmitter production. Experimental and human data have also shown that the endocannabinoid system is involved in the regulation of reproductive function at both central and peripheral levels. We discuss also the role of fatty acid amide hydrolase (FAAH) in gestation, and in particular the regulation of the activity of FAAH by progesterone and leptin. We show that endocannabinoids inhibit the release of leukaemia inhibitory factor (LIF) from peripheral T lymphocytes. Taken together, endocannabinoids not only help to maintain neuroendocrine homeostasis, but also take part in immunological changes occurring during early pregnancy.

Vascular effects of anandamide and N-acylvanillylamines in the human forearm and skin microcirculation

The endocannabinoid anandamide is an emerging potential signalling molecule in the cardiovascular system. Anandamide causes vasodilatation, bradycardia and hypotension in animals and has been implicated in the pathophysiology of endotoxic, haemorrhagic and cardiogenic shock, but its vascular effects have not been studied in man. Human forearm blood flow and skin microcirculatory flow were recorded using venous occlusion plethysmography and laser-Doppler perfusion imaging (LDPI), respectively. Each test drug was infused into the brachial artery or applied topically on the skin followed by a standardized pin-prick to disrupt the epidermal barrier. Anandamide failed to affect forearm blood flow when administered intra-arterially at infusion rates of 0.3-300 nmol min(-1). The highest infusion rate led to an anandamide concentration of approximately 1 microM in venous blood as measured by mass spectrometry. Dermal application of anandamide significantly increased skin microcirculatory flow and coapplication of the transient receptor potential vanilloid 1 (TRPV1) antagonist capsazepine inhibited this effect. The TRPV1 agonists capsaicin, olvanil and arvanil all induced concentration-dependent increases in skin blood flow and burning pain when administered dermally. Coapplication of capsazepine inhibited blood flow and pain responses to all three TRPV1 agonists. This study shows that locally applied anandamide is a vasodilator in the human skin microcirculation. The results are consistent with this lipid being an activator of TRPV1 on primary sensory nerves, but do not support a role for anandamide as a circulating vasoactive hormone in the human forearm vascular bed.

Capsaicin evokes hypothermia independent of cannabinoid CB1 and CB2 receptors

The present study investigated a potential role for cannabinoid CB(1) and CB(2) receptors in capsaicin-evoked hypothermia. Capsaicin (1 mg/kg, s.c.) caused rapid and significant hypothermia in rats. Pretreatment with SR 141716A (1, 2.5 and 5 mg/kg, i.p.), a CB(1) antagonist, or SR 144528 (1, 2.5 and 5 mg/kg, i.p.), a CB(2) antagonist, did not affect capsaicin-induced hypothermia. In separate experiments, the hypothermia caused by WIN 55212-2 (5 mg/kg, i.m.), a cannabinoid agonist, was not significantly altered by capsazepine (10 and 30 mg/kg, i.p.) or SB 366791 (2 mg/kg, i.p.), a novel TRPV1 antagonist. These data suggest that capsaicin causes hypothermia by a CB(1)- and CB(2)-independent mechanism, and that WIN 55212-2 causes hypothermia by a TRPV1-independent mechanism.

Capsaicin exhibits neuroprotective effects in a model of transient global cerebral ischemia in Mongolian gerbils

1. Capsaicin, the irritant principle of hot peppers, is a vanilloid agonist known to activate the transient receptor potential channel vanilloid subfamily member 1 (VR1), recently reported to be involved in neurodegeneration. The present study investigated the role of VR1 in a model of global cerebral ischemia in gerbils. 2. Over the dose range tested, capsaicin (0.01, 0.025, 0.05, 0.2 and 0.6 mg kg(-1)), given 5 min after recirculation, dose-dependently antagonized the ischemia-induced electroencephalographic total spectral power decrease and restored relative frequency band distribution evaluated 7 days after ischemia. 3. Capsaicin, at all tested doses, fully prevented ischemia-induced hyperlocomotion evaluated 1 day after ischemia. 4. Capsaicin dose-dependently antagonized ischemia-induced memory impairment evaluated in a passive avoidance task, 3 days after ischemia. 5. Capsaicin showed a dose-dependent hypothermic effect evaluated for 2 h after recirculation. 6. At 7 days after ischemia, a progressive survival of pyramidal cells in the CA1 subfield in capsaicin-treated gerbils, with a maximum of 80%, at a dose of 0.2 mg kg(-1), was obtained. 7. The selective VR1 antagonist, capsazepine (0.01 mg kg(-1)), reversed capsaicin-induced protective effects, in a competitive manner. 8. These results suggest that the neuroprotective effect of capsaicin may be attributable, at least in part, to VR1 desensitization and provide a valuable target for development of interventional pharmacological strategies.

Endocannabinoids Part I: molecular basis of endocannabinoid formation, action and inactivation and development of selective inhibitors

The discovery of specific receptors for Delta9-tetrahydrocannabinol, the major psychoactive component of marijuana, opened new horizons for the possible therapeutic exploitation of Cannabis sativa and the cannabinoids. Endogenous ligands of cannabinoid receptors, the 'endocannabinoids', were found and the molecular mechanisms underlying their biological effects and the regulation of their levels are now being identified. Cause/effect relationships between alterations of cannabinoid receptor/endocannabinoid levels in tissues and the symptoms of various pathological states are starting to be revealed. These studies may open the way to the possible use of substances that manipulate endocannabinoid levels and actions, such as inhibitors of the biosynthesis and inactivation and receptor antagonists, as cannabinoid-based therapeutic agents with little or no psychotropic side effect, thus potentially fulfilling an ambition nurtured for almost two centuries.

Arvanil, a hybrid endocannabinoid and vanilloid compound, behaves as an antihyperkinetic agent in a rat model of Huntington's disease

The present study was designed to examine whether arvanil (N-arachidonoyl-vanillyl-amide), an endocannabinoid/vanilloid structural "hybrid", might provide symptom relief in the rat model of Huntington's disease (HD) generated by bilateral intrastriatal application of 3-nitropropionic acid (3-NP), where previous evidence suggests that hybrid cannabinoid/vanilloid compounds might be effective. As expected, arvanil did reduce ambulation, stereotypic activity, and number of hole entries, and increased the inactivity, in control rats. It was also active in 3-NP-lesioned rats, where, despite its lowering effects on stereotypic activity and number of hole entries, arvanil reduced the hyperkinesia (increased ambulation) typical of these rats, and also increased the inactivity, these two effects being more moderate than those found in control rats. Arvanil caused its antihyperkinetic effects in 3-NP-lesioned rats presumably by enhancing excitatory transmission at the globus pallidus, since it increased glutamate content in this region. This contrasts with its effects in control rats where arvanil enhanced GABA transmission at the globus pallidus. In summary, arvanil does alleviate hyperkinesia typical of HD, although it also affects locomotion in normal rats. Nevertheless, considering the lack of efficacious pharmacological treatments in this basal ganglia disorder, our findings might provide the basis for the development of more specific drugs against HD.

The endocannabinoid system and its therapeutic exploitation

The term 'endocannabinoid' - originally coined in the mid-1990s after the discovery of membrane receptors for the psychoactive principle in Cannabis, Delta9-tetrahydrocannabinol and their endogenous ligands - now indicates a whole signalling system that comprises cannabinoid receptors, endogenous ligands and enzymes for ligand biosynthesis and inactivation. This system seems to be involved in an ever-increasing number of pathological conditions. With novel products already being aimed at the pharmaceutical market little more than a decade since the discovery of cannabinoid receptors, the endocannabinoid system seems to hold even more promise for the future development of therapeutic drugs. We explore the conditions under which the potential of targeting the endocannabinoid system might be realized in the years to come.

A new strategy to block tumor growth by inhibiting endocannabinoid inactivation

Endocannabinoid signaling has been shown to be enhanced in several cancer tissues and malignant cells, and studies in cell lines have shown that this up-regulation might serve the purpose of providing transformed cells with a further means to inhibit their proliferation. Here we investigated the effect of inhibitors of endocannabinoid degradation on the growth of rat thyroid tumor xenografts induced in athymic mice. VDM-11, a selective inhibitor of endocannabinoid cellular re-uptake, and arachidonoyl-serotonin (AA-5-HT), a selective blocker of endocannabinoid enzymatic hydrolysis, both inhibited the growth in vivo of tumor xenografts induced by the subcutaneous injection of rat thyroid transformed (KiMol) cells. This effect was accompanied by significantly enhanced endocannabinoid concentrations in the tumors excised at the end of the in vivo experiments. Endocannabinoids, as well as VDM-11 and AA-5-HT, inhibited the growth in vitro of the transformed rat thyroid cells used to induce the tumors in vivo, and their effect was reversed at least in part by the cannabinoid CB1 receptor antagonist SR141716A. This compound, however, when administered alone, did not enhance, but instead slightly inhibited, the growth of rat thyroid transformed cells both in vitro and in tumor xenografts induced in vivo. These findings indicate that endocannabinoids tonically control tumor growth in vivo by both CB1-mediated and non-CB1-mediated mechanisms and that, irrespective of the molecular mechanism of their anti-proliferative action, inhibitors of their inactivation might be used for the development of novel anti-cancer drugs.

A comparison of the discriminative stimulus effects of delta(9)-tetrahydrocannabinol and O-1812, a potent and metabolically stable anandamide analog, in rats

Efforts to determine whether Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and anandamide elicit similar discriminative stimulus effects have yielded conflicting results. The difficulty in establishing a discriminative cue to anandamide may be due to its metabolic instability. Rats were trained to discriminate either Delta(9)-THC or O-1812, a metabolically stable anandamide analog, from vehicle to avoid this issue. O-1812 and Delta(9)-THC substituted for each other; however, both drugs were more potent in the O-1812-trained rats. Further, O-1812 only substituted for Delta(9)-THC at response rate decreasing doses. The CB(1) antagonist, SR141716A, blocked the discriminative stimulus effects of both drugs but augmented their rate effects. O-1839, a VR(1) agonist, failed to substitute for either cannabinoid. These results suggest that the discriminative stimulus effects of Delta(9)-THC and O-1812 are similar, but subtle differences also exist.

Effects of the vanilloid agonist olvanil and antagonist capsazepine on rat behaviors

Vanilloid receptors (VR) are molecular integrators of painful chemical and physical stimuli. Olvanil is an agonist of the vanilloid receptor; capsazepine is a competitive VR antagonist. The authors were interested in investigated the effects of these compounds on anxiety-like behaviors in rats using the elevated plus maze. In addition, the authors examined the effects of olvanil on the Porsolt swim test. Doses of 0, 0.2, 1.0 and 5.0 mg/kg olvanil, respectively, yielded percent open arm entries at 5 min of 25+/-10.1, 19.3+/-7.1, 14.9+/-5.9 and 0+/-0. We demonstrated a drug effect by showing that the mean of the 0.2, 1 and 5 mg/kg doses was significantly lower than the 0 mg/kg dose at P<.05. In addition, the authors examined the effect of olvanil on the ability of rats to perform in the Porsolt swim test. Float time for rats was tested with 0.1 or 2 mg/kg olvanil and differences between the float times for the lower and higher doses were significant at P<.05. In addition, the effects of various doses of the vanilloid antagonist capsazepine was examined on elevated plus maze behavior. Doses of 0, 1, 5 and 10 mg/kg yielded percent time in the open arms at 5 min of 1.46+/-1.38, 15.05+/-10.42, 11.54+/-10.57, and 14.56+/-7.86. The mean of the 1, 5 and 10 mg/kg doses was significantly greater than the percent time in the open arms for the vehicle, consistent with a drug effect. The results suggest that the vanilloid agonists and antagonists may impact on behaviors involving anxiety and affect. However, it cannot be ruled that the findings could be due to nonspecific motor effect.

The CB1/VR1 agonist arvanil induces apoptosis through an FADD/caspase-8-dependent pathway

1. Arvanil (N-arachidonoylvanillamine), a nonpungent capsaicin-anandamide hybrid molecule, has been shown to exert biological activities through VR1/CB1-dependent and -independent pathways. We have found that arvanil induces dose-dependent apoptosis in the lymphoid Jurkat T-cell line, but not in peripheral blood T lymphocytes. Apoptosis was assessed by DNA fragmentation through cell cycle and TUNEL analyses. 2. Arvanil-induced apoptosis was initiated independently of any specific phase of the cell cycle, and it was inhibited by specific caspase-8 and -3 inhibitors and by the activation of protein kinase C. In addition, kinetic analysis by Western blots and fluorimetry showed that arvanil rapidly activates caspase-8, -7 and -3, and induces PARP cleavage. 3. The arvanil-mediated apoptotic response was greatly inhibited in the Jurkat-FADDDN cell line, which constitutively expresses a negative dominant form of the adapter molecule Fas-associated death domain (FADD). This cell line does not undergo apoptosis in response to Fas (CD95) stimulation. 4. Using a cytofluorimetric approach, we have found that arvanil induced the production of reactive oxygen species (ROS) in both Jurkat-FADD+ and Jurkat-FADDDN cell lines. However, ROS accumulation only plays a residual role in arvanil-induced apoptosis. 5. These results demonstrate that arvanil-induced apoptosis is essentially mediated through a mechanism that is typical of type II cells, and implicates the death-inducing signalling complex and the activation of caspase-8. This arvanil-apoptotic activity is TRPV1 and CB-independent, and can be of importance for the development of potential anti-inflammatory and antitumoral drugs.

Halogenation of a capsaicin analogue leads to novel vanilloid TRPV1 receptor antagonists

1. The C-5 halogenation of the vanillyl moiety of resiniferatoxin, an ultrapotent agonist of vanilloid TRPV1 receptors, results in a potent antagonist for these receptors. Here, we have synthesized a series of halogenated derivatives of 'synthetic capsaicin' (nonanoyl vanillamide=nordihydrocapsaicin) differing for the nature (iodine, bromine-chlorine) and the regiochemistry (C-5, C-6) of the halogenation. 2. The activity of these compounds was investigated on recombinant human TRPV1 receptors overexpressed in HEK-293 cells. None of the six compounds exerted any significant agonist activity, as assessed by measuring their effect on TRPV1-mediated calcium mobilization. Instead, all compounds antagonized, to various extents, the effect of capsaicin in this assay. 3. All 6-halo-nordihydrocapsaicins behaved as competitive antagonists against human TRPV1 according to the corresponding Schild's plots, and were more potent than the corresponding 5-halogenated analogues. The iodo-derivatives were more potent than the bromo- and chloro-derivatives. 4. Using human recombinant TRPV1, 6-iodo-nordihydrocapsaicin (IC(50)=10 nM against 100 nM capsaicin) was about four times more potent than the prototypical TRPV1 antagonist, capsazepine, and was tested against capsaicin also on native TRPV1 in: (i) rat dorsal root ganglion neurons in culture; (ii) guinea-pig urinary bladder; and (iii) guinea-pig bronchi. In all cases, except for the guinea-pig bronchi, the compound was significantly more potent than capsazepine as a TRPV1 antagonist. 5. In conclusion, 6-iodo-nordihydrocapsaicin, a stable and easily prepared compound, is a potent TRPV1 antagonist and a convenient replacement for capsazepine in most of the in vitro preparations currently used to assess the activity of putative vanilloid receptor agonists.

Post-ischemic treatment with cannabidiol prevents electroencephalographic flattening, hyperlocomotion and neuronal injury in gerbils

The potential activity of cannabidiol, a non-psychoactive constituent of marijuana, in preventing damage caused by cerebral ischemia was studied. Cannabidiol (1.25-20 mg/kg) was given 5 min after 10 min bilateral carotid occlusion in freely-moving awake gerbils. Seven days after ischemia, it antagonized the electroencephalographic flattening of total spectral power, with a dose-dependent bell-shaped curve; the neuroprotective effect was greatest with 5 mg/kg. One day after ischemia cannabidiol completely antagonized ischemia-induced hyperlocomotion, at all doses. Rectal temperature did not change during the first hour after occlusion. Histological examination showed complete survival of CA1 neurons in cannabidiol-treated gerbils. These findings suggest a potential therapeutic role of cannabidiol in cerebral ischemia, though the clear mechanism of action remains to be elucidated.

Neuroprotection by the endogenous cannabinoid anandamide and arvanil against in vivo excitotoxicity in the rat: role of vanilloid receptors and lipoxygenases

Type 1 vanilloid receptors (VR1) have been identified recently in the brain, in which they serve as yet primarily undetermined purposes. The endocannabinoid anandamide (AEA) and some of its oxidative metabolites are ligands for VR1, and AEA has been shown to afford protection against ouabain-induced in vivo excitotoxicity, in a manner that is only in part dependent on the type 1 cannabinoid (CB1) receptor. In the present study, we assessed whether VR1 is involved in neuroprotection by AEA and by arvanil, a hydrolysis-stable AEA analog that is a ligand for both VR1 and CB1. Furthermore, we assessed the putative involvement of lipoxygenase metabolites of AEA in conveying neuroprotection. Using HPLC and gas chromatography/mass spectroscopy, we demonstrated that rat brain and blood cells converted AEA into 12-hydroxy-N-arachidoylethanolamine (12-HAEA) and 15-hydroxy-N-arachidonoylethanolamine (15-HAEA) and that this conversion was blocked by addition of the lipoxygenase inhibitor nordihydroguaiaretic acid. Using magnetic resonance imaging we show the following: (1) pretreatment with the reduced 12-lipoxygenase metabolite of AEA, 12-HAEA, attenuated cytotoxic edema formation in a CB1 receptor-independent manner in the acute phase after intracranial injection of the Na+/K+-ATPase inhibitor ouabain; (2) the reduced 15-lipoxygenase metabolite, 15-HAEA, enhanced the neuroprotective effect of AEA in the acute phase; (3) modulation of VR1, as tested using arvanil, the VR1 agonist capsaicin, and the antagonist capsazepine, leads to neuroprotective effects in this model, and arvanil is a potent neuroprotectant, acting at both CB1 and VR1; and (4) the in vivo neuroprotective effects of AEA are mediated by CB1 but not by lipoxygenase metabolites or VR1.

Effect of arvanil (N-arachidonoyl-vanillyl-amine), a nonpungent anandamide-capsaicin hybrid, on ion currents in NG108-15 neuronal cells

The effects of arvanil (N-arachidonoyl-vanillyl-amine), a structural hybrid between capsaicin and anandamide, on ion currents in a mouse neuroblastoma and rat glioma hybrid cell line, NG108-15, were examined with the aid of the whole-cell voltage-clamp technique. Arvanil (0.2-50 microM) caused an inhibition of voltage-dependent L-type Ca(2+) current (I(Ca,L)) in a concentration-dependent manner. Arvanil produced no change in the overall shape of the current-voltage relationship of I(Ca,L). The IC(50) value of arvanil-induced inhibition of I(Ca,L) was 2 microM. Arvanil (5 microM) could shift the steady-state inactivation curve of I(Ca,L) to a more negative potential by approximately -15mV. No effect of arvanil (20 microM) on delayed rectifier K(+) current (I(K(DR))) was observed; however, capsaicin (20 microM), glyceryl nonivamide (20 microM) and capsinolol (20 microM) suppressed it significantly. Arvanil (20 microM) caused a slight reduction in the amplitude of erg (ether-à-go-go-related)-mediated K(+) current (I(K(erg))) without modifying the activation curve of this current, while capsaicin and glyceryl nonivamide were more effective in suppressing I(K(erg)). Under current-clamp configuration, arvanil decreased the firing frequency of action potentials. Arvanil-mediated inhibition of I(Ca,L) appeared to be independent of its binding to either vanilloid or cannabinoid receptors. The channel-blocking properties of arvanil may, at least in part, contribute to the underlying mechanisms by which it affects neuronal or neuroendocrine function.

Cannabinoid pharmacology: implications for additional cannabinoid receptor subtypes

Delta(9)-Tetrahydrocannabinol (delta(9)-THC), the primary psychoactive constituent of marijuana (Cannabis sativa), is known to bind to two cannabinoid receptors: CB(1) receptors, located primarily in the brain, and CB(2) receptors, located primarily in the periphery. Recent research has suggested that other cannabinoids, including anandamide and WIN 55212-2, may also act at novel non-CB(1), non-CB(2) cannabinoid receptor(s). Anandamide produces a number of in vivo pharmacological effects in CB(1) knockout mice that are not produced by delta(9)-THC and cannot be explained by anandamide's rapid metabolism. In addition, in vitro anandamide and WIN 55212-2 stimulate [35S]GTPgammaS binding in both CB(1) knockout and wildtype mice while delta(9)-THC stimulates this binding only in wildtype mice. Although anandamide and vanilloid agonists share pharmacological effects, anandamide's actions in CB(1) knockout mice do not appear to be mediated by vanilloid VR(1) receptors. While not yet conclusive, these results suggest the possibility of additional cannabinoid receptors in the brain and periphery.