Plant cannabinoids: a neglected pharmacological treasure trove

Most of the cannabinoids in Cannabis sativa L. have not been fully evaluated for their pharmacological activity. A publication in this issue presents evidence that a plant cannabinoid, Delta(9)-tetrahydrocannabivarin is a potent antagonist of anandamide, a major endogenous cannabinoid. It seems possible that many of the non-psychoactive constituents of this plant will be of biological interest.

Evidence that the plant cannabinoid Delta9-tetrahydrocannabivarin is a cannabinoid CB1 and CB2 receptor antagonist

Delta9-tetrahydrocannabivarin (THCV) displaced [(3)H]CP55940 from specific binding sites on mouse brain and CHO-hCB(2) cell membranes (K(i)=75.4 and 62.8 nM, respectively).THCV (1 microM) also antagonized CP55940-induced stimulation of [(35)S]GTPgammaS binding to these membranes (apparent K(B)=93.1 and 10.1 nM, respectively). In the mouse vas deferens, the ability of Delta9-tetrahydrocannabinol (THC) to inhibit electrically evoked contractions was antagonized by THCV, its apparent K(B)-value (96.7 nM) approximating the apparent K(B)-values for its antagonism of CP55940- and R-(+)-WIN55212-induced stimulation of [(35)S]GTPgammaS binding to mouse brain membranes. THCV also antagonized R-(+)-WIN55212, anandamide, methanandamide and CP55940 in the vas deferens, but with lower apparent K(B)-values (1.5, 1.2, 4.6 and 10.3 nM, respectively).THCV (100 nM) did not oppose clonidine, capsaicin or (-)-7-hydroxy-cannabidiol-dimethylheptyl-induced inhibition of electrically evoked contractions of the vas deferens. Contractile responses of the vas deferens to phenylephrine hydrochloride or beta,gamma-methylene-ATP were not reduced by 1microM THCV or R-(+)-WIN55212, suggesting that THCV interacts with R-(+)-WIN55212 at prejunctional sites. At 32 microM, THCV did reduce contractile responses to phenylephrine hydrochloride and beta,gamma-methylene-ATP, and above 3 microM it inhibited electrically evoked contractions of the vas deferens in an SR141716A-independent manner. In conclusion, THCV behaves as a competitive CB(1) and CB(2) receptor antagonist. In the vas deferens, it antagonized several cannabinoids more potently than THC and was also more potent against CP55940 and R-(+)-WIN55212 in this tissue than in brain membranes. The bases of these agonist- and tissue-dependent effects remain to be established.

Inhibition of fatty acid amide hydrolase and monoacylglycerol lipase by the anandamide uptake inhibitor VDM11: evidence that VDM11 acts as an FAAH substrate

There is some dispute concerning the extent to which the uptake inhibitor VDM11 (N-(4-hydroxy-2-methylphenyl) arachidonoyl amide) is capable of inhibiting the metabolism of the endocannabinoid anandamide (AEA) by fatty acid amide hydrolase (FAAH). In view of a recent study demonstrating that the closely related compound AM404 (N-(4-hydroxyphenyl)arachidonylamide) is a substrate for FAAH, we re-examined the interaction of VDM11 with FAAH. In the presence of fatty acid-free bovine serum albumin (BSA, 0.125% w v(-1)), both AM404 and VDM11 inhibited the metabolism of AEA by rat brain FAAH with similar potencies (IC(50) values of 2.1 and 2.6 microM, respectively). The compounds were about 10-fold less potent as inhibitors of the metabolism of 2-oleoylglycerol (2-OG) by cytosolic monoacylglycerol lipase (MAGL). The potency of VDM11 towards FAAH was dependent upon the assay concentration of fatty acid-free bovine serum albumin (BSA). Thus, in the absence of fatty acid-free BSA, the IC(50) value for inhibition of FAAH was reduced by a factor of about two (from 2.9 to 1.6 microM). A similar reduction in the IC(50) value for the inhibition of membrane bound MAGL by both this compound (from 14 to 6 microM) and by arachidonoyl serinol (from 24 to 13 microM) was seen. An HPLC assay was set up to measure 4-amino-m-cresol, the hypothesised product of FAAH-catalysed VDM11 hydrolysis. 4-Amino-m-cresol was eluted with a retention time of approximately 2.4 min, but showed a time-dependent degradation to compounds eluting at peaks of approximately 5.6 and approximately 8 min. Peaks with the same retention times were also found following incubation of the membranes with VDM11, but were not seen when the membranes were preincubated with the FAAH inhibitors URB597 (3'-carbamoyl-biphenyl-3-yl-cyclohexylcarbamate) and CAY10401 (1-oxazolo[4,5-b]pyridin-2-yl-9-octadecyn-1-one) prior to addition of VDM11. The rate of metabolism of VDM11 was estimated to be roughly 15-20% of that for anandamide. It is concluded that VDM11 is an inhibitor of FAAH under the assay conditions used here, and that the inhibition may at least in part be a consequence of the compound acting as an alternative substrate.

UCM707, an inhibitor of the anandamide uptake, behaves as a symptom control agent in models of Huntington's disease and multiple sclerosis, but fails to delay/arrest the progression of different motor-related disorders

To date, UCM707, (5Z,8Z,11Z,14Z)-N-(3-furylmethyl)eicosa-5,8,11,14-tetraenamide, has the highest potency and selectivity in vitro and in vivo as inhibitor of the endocannabinoid uptake. This may enable this compound to potentiate endocannabinoid transmission, with minimal side effects, in the treatment of several neurological disorders. In the present study, we examined whether the treatment with UCM707 produced beneficial effects, as other cannabinoid-related compounds have already shown, to alleviate motor deterioration or to delay/arrest neurodegeneration, in several models of neurological diseases such as Huntington's disease (HD), Parkinson's disease (PD) and multiple sclerosis (MS). UCM707 exhibited a notable anti-hyperkinetic activity in a rat model of HD generated by bilateral intrastriatal application of 3-nitropropionic acid. This effect was possibly associated with an amelioration of GABA and glutamate deficits induced by the toxin in the globus pallidus and the substantia nigra, respectively. However, UCM707 did not protect against the death of GABAergic neurons that occurs in rats with striatal atrophy generated by unilateral application of malonate, another animal model of HD, which is more useful to test neuroprotective strategies. In addition, UCM707 did not provide neuroprotection in rats with unilateral lesions of the nigrostriatal dopaminergic neurons caused by 6-hydroxydopamine, a rat model of PD. This was possibly due to the fact that UCM707 is devoid of anti-oxidant properties since another uptake inhibitor, AM404, that has these properties acted as a protective agent. Lastly, UCM707 was also unable to inhibit the development of the neurological impairment of rats with experimental autoimmune encephalomyelitis (EAE), an acute model of MS. However, UCM707, like other endocannabinoid uptake inhibitors reported previously, significantly reduced spasticity of the hindlimbs in a chronic relapsing EAE mice, a chronic model of MS. In summary, UCM707 might be a promising compound in HD to alleviate motor symptoms, which represents an important goal considering the current lack of efficient pharmacological treatments in this basal ganglia disorder. However, the compound was unable to delay neurodegeneration in this disorder and also in PD. In addition, UCM707 did not produce any neurological recovery from inflammatory attack in an EAE rat model of MS, although it retained the classic anti-spastic action shown by other uptake inhibitors in the EAE mouse model of this disease.

The endogenous cannabinoid, anandamide, induces cell death in colorectal carcinoma cells: a possible role for cyclooxygenase 2

BACKGROUND AND AIMS

Cyclooxygenase 2 (COX-2) is upregulated in most colorectal cancers and is responsible for metabolism of the endogenous cannabinoid, anandamide, into prostaglandin-ethanolamides (PG-EAs). The aims of this study were to determine whether anandamide and PG-EAs induce cell death in colorectal carcinoma (CRC) cells, and whether high levels of COX-2 in CRC cells could be utilised for their specific targeting for cell death by anandamide.

METHODS

We determined the effect of anandamide on human CRC cell growth by measuring cell growth and cell death, whether this was dependent on COX-2 protein expression or enzyme activity, and the potential involvement of PG-EAs in induction of cell death.

RESULTS

Anandamide inhibited the growth of CRC cell lines HT29 and HCA7/C29 (moderate and high COX-2 expressors, respectively) but had little effect on the very low COX-2 expressing CRC cell line, SW480. Induction of cell death in HT29 and HCA7/C29 cell lines was partially rescued by the COX-2 selective inhibitor NS398. Cell death induced by anandamide was neither apoptosis nor necrosis. Furthermore, inhibition of fatty acid amide hydrolase potentiated the non-apoptotic cell death, indicating that anandamide induced cell death was mediated via metabolism of anandamide by COX-2, rather than its degradation into arachidonic acid and ethanolamine. Interestingly, both PGE2-EA and PGD2-EA induced classical apoptosis.

CONCLUSIONS

These findings suggest anandamide may be a useful chemopreventive/therapeutic agent for colorectal cancer as it targets cells that are high expressors of COX-2, and may also be used in the eradication of tumour cells that have become resistant to apoptosis.

Effect of anandamide uptake inhibition in the production of nitric oxide and in the release of cytokines in astrocyte cultures

Astrocytes play a key role regulating aspects of inflammation in the central nervous system (CNS). Several enzymes, such as the inducible nitric oxide synthase (iNOS) or the cyclooxygenase-2 (COX-2), along with different inflammatory mediators such as the free radical nitric oxide (NO) or proinflammatory cytokines, have been proposed to be involved in the cell damage associated with neuroinflammation. Recent studies suggest that the endogenous cannabinoid system (ECS) may be involved in the regulation of neuroinflammation. Cannabinoid agonists decrease neurotoxicity and release of proinflammatory factors from activated glial cells and anandamide itself is able to promote antiinflammatory responses in astrocytes via CB1 cannabinoid receptors. The present study is aimed at studying whether UCM707, a potent and selective anandamide uptake inhibitor, is able to inhibit the production of proinflammatory mediators by LPS-stimulated astrocytes. Our findings indicate that UCM707 is able to reduce NO release, iNOS expression, and the production of the proinflammatory cytokines tumoral necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) in a significant manner, while producing a slight increase in IL-6 levels. These effects can be reproduced by administration of the synthetic agonist HU210 and partially or totally blocked by administration of CB1 or CB2 selective antagonists, further supporting the involvement of the ECS. These results confirm the ability of UCM707 to reinforce the beneficial effects induced by anandamide and make it an attractive candidate for the management of those pathologies with neuroinflammation as one of their hallmarks.

Cannabinoid antagonist AM 281 reduces mortality rate and neurologic dysfunction after cecal ligation and puncture in rats

OBJECTIVES

The purpose of this study was to examine whether anandamide, an endogenous cannabinoid receptor ligand, is involved in the pathogenesis of septic encephalopathy.

DESIGN

Prospective, controlled study.

SUBJECTS

Male Wistar rats (7 wks old) were randomly divided into four groups as follows: group 1, control (0.5 mL of saline injected subcutaneously); group 2, sham (surgical abdominal incision and suturing were performed, but ligation and puncture of the cecum were omitted); group 3, cecal ligation and puncture (CLP); group 4, CLP + AM 281 ([N-morpholin-4-yl]-5-[2,4-yl]-5-[2,4-dichlorophenyl]-4-methyl-1H-pyrazole-3-carboxamide) as the cannabinoid receptor antagonist (1 mg/kg intraperitoneally).

INTERVENTIONS

Sepsis was induced by CLP under pentobarbital anesthesia (10 mg/kg intraperitoneally) with 1% isoflurane. A 2-Fr high-fidelity micromanometer catheter was inserted into the left ventricle via the right carotid artery to assess hemodynamics. Each of the rats was neurologically assessed at 30 mins and 12, 24, and 48 hrs after the treatment. The cytoplasmic levels of caspase-3 in the hippocampi were assayed before surgery and at 30 mins and 24 and 48 hrs after surgery using Western blotting techniques. To examine the effects of AM 281 on neurologic function and mortality rate, we set another control group treated solely with AM 281. Selective inducible nitric oxide synthase inhibitor, L-N6-(1-iminoethyl)-lysine (4 mg/kg), was injected intraperitoneally immediately after CLP to produce the CLP + L-N6-(1-iminoethyl)-lysine group to exclude the influence of depressed hemodynamics on neurologic impairment.

MEASUREMENTS AND MAIN RESULTS

It was found that administration of AM 281 could prevent the hemodynamic changes induced by sepsis. Reflex responses, including the pinna, corneal, paw or tail flexion, and righting reflexes, and the escape response significantly decreased in the CLP and CLP + L-N6-(1-iminoethyl)-lysine groups at 48 hrs after the surgery. In contrast, no changes in these reflex responses were found between the CLP + AM 281 and control and sham groups. In addition, no effects of the administration of AM 281 on neurologic function and mortality rate in the control group were found. Tissue caspase-3 levels were elevated at 48 hrs after CLP in the CLP alone group (means +/- sd: control, 3.9 +/- 0.4; sham, 4.2 +/- 0.4; CLP, 7.1 +/- 1.0 [p < .01]; CLP + AM 281, 4.0 +/- 0.5 densitometric units). In addition, administration of AM 281 also decreased the mortality rate (p < .05).

CONCLUSIONS

Administration of AM 281 prevented the hemodynamic changes and development of neurologic dysfunction occurring in association with septic shock, and could decrease the mortality rate in experimentally induced septic shock in rats. Although further studies are necessary to determine whether endogenous cannabinoids cause septic encephalopathy in rats directly or via their effects on systemic hemodynamics, the beneficial effects of AM 281 on these rats might have significant therapeutic implications in cases of septic encephalopathy.

Selective inhibition of 2-AG hydrolysis enhances endocannabinoid signaling in hippocampus

The functions of 2-arachidonoylglycerol (2-AG), the most abundant endocannabinoid found in the brain, remain largely unknown. Here we show that two previously unknown inhibitors of monoacylglycerol lipase, a presynaptic enzyme that hydrolyzes 2-AG, increase 2-AG levels and enhance retrograde signaling from pyramidal neurons to GABAergic terminals in the hippocampus. These results establish a role for 2-AG in synaptic plasticity and point to monoacylglycerol lipase as a possible drug target.

Cyclooxygenation of the arachidonoyl side chain of 1-arachidonoylglycerol and related compounds block their ability to prevent anandamide and 2-oleoylglycerol metabolism by rat brain in vitro

In the present study, the abilities of cyclooxygenated derivatives of 1-arachidonoylglycerol and related compounds to prevent the metabolism of [3H]2-oleoylglycerol and [3H]anandamide by cytosolic and membrane fractions, respectively, have been investigated. For each compound, nine concentrations (range 0.2-100 microM) were tested. 1-Arachidonoylglycerol inhibited the hydrolysis of [3H]2-oleoylglycerol with a pI50 value of 5.17+/-0.04 (maximum attainable inhibition 88%). In contrast, the 1-glyceryl esters of prostaglandin D2, E2 and F2alpha were very weak inhibitors of this hydrolysis. Similarly, prostaglandin D2, prostaglandin D2 ethanolamide and prostaglandin D2 serinol amide produced <20% inhibition of [3H]2-oleoylglycerol metabolism at any concentration tested, in contrast to previous data with arachidonic acid, anandamide and arachidonoyl serinol which are all able to inhibit metabolism of this substrate under the assay conditions used here. A similar pattern was seen for all the compounds with respect to the inhibition of [3H]anandamide hydrolysis by the membrane fractions. Thus, cyclooxygenation of the arachidonoyl side chain greatly reduces the ability of 1-arachidonoylglycerol and related compounds to inhibit the hydrolysis of [3H]2-oleoylglycerol and [3H]anandamide.

Sex-linked differences in the vasorelaxant effects of anandamide in vascular mesenteric beds: role of oestrogens

Anandamide (0.01 to 10 microM) caused greater concentration-dependent reductions of the contractile-induced responses to noradrenaline in female than in male mesenteric vascular beds isolated from adult Sprague-Dawley rats. Greater relaxant responses in females were also induced by the vanilloid TRPV1 receptor agonist capsaicin (0.01 to 10 microM), whereas no sex differences were observed for the relaxations caused by either acetylcholine or sodium nitroprusside. The effect of anandamide in either sex was reduced by the vanilloid TRPV1 receptor antagonist capsazepine but not by the cannabinoid CB1 receptor antagonist N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyrazole-carboxamide (SR141716A). In males, the anandamide-induced relaxations were potentiated by in vitro exposure during 5 min to 0.5 microM 17beta-oestradiol and unmodified by the protein synthesis inhibitor cycloheximide. The vasorelaxant effects of anandamide in female rats were decreased by ovariectomy. This decrease was prevented by in vivo treatment with 17beta-oestradiol-3-benzoate (450 microg/kg i.m., once a week during 3 weeks) and counteracted by in vitro exposure to oestrogen. In vivo treatment with 17beta-oestradiol also potentiated anandamide-induced responses in males. In conclusion, this study shows an oestrogen-dependent sensitivity to the vanilloid TRPV1 receptor-mediated vasorelaxant effects of anandamide in the mesenteric vasculature of Sprague-Dawley rats, that could be mediated by both genomic and non-genomic mechanisms.

Anandamide transport inhibitor AM404 and structurally related compounds inhibit synaptic transmission between rat hippocampal neurons in culture independent of cannabinoid CB1 receptors

N-(hydroxyphenyl)-arachidonamide (AM404) is an inhibitor of endocannabinoid transport. We examined the effects of AM404 on glutamatergic synaptic transmission using network-driven increases in intracellular Ca2+ concentration ([Ca2+] spikes) as an assay. At a concentration of 1 microM AM404 inhibited [Ca2+]i spiking by 73+/-8%. The cannabinoid CB1 receptor antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride (SR141716A), the vanilloid VR1 receptor antagonist capsazepine (CPZ), and treatment with pertussis toxin failed to block AM404-mediated inhibition. AM404 (3 microM) inhibited action-potential-evoked Ca2+ influx by 58+/-3% but failed to affect calcium influx evoked by depolarization with 30 mM K+, suggesting that the inhibition of electrically evoked [Ca2+]i increases and that [Ca2+]i spiking was due to inhibition of Na+ channels. Palmitoylethanolamide (PMEA), capsaicin (CAP) and (5Z,8Z,11Z,14Z)-N-(4-hydroxy-2-methylphenyl)-5,8,11,14-eicosatetraenamide (VDM11), compounds structurally similar to AM404, inhibited [Ca2+]i spiking by 34+/-10%, 42+/-18% and 67+/-12%, respectively. Thus, AM404 and related compounds inhibit depolarization-induced Ca2+ influx independent of cannabinoid receptors, suggesting caution when using these agents as pharmacological probes to study synaptic transmission.

AM404, an inhibitor of anandamide reuptake decreases Fos-immunoreactivity in the spinal cord of neuropathic rats after non-noxious stimulation

Cannabinoids like anandamide are involved in pain transmission. In this study we evaluated the effects of administrating N-(4-hydroxyphenyl)-5Z,8Z,11Z,14Z-eicosatetraenamide (AM404), an inhibitor of anandamide reuptake and monitoring the expression of c-fos, a marker of activated neurons in an experimental model of neuropathic pain (sciatic nerve tying). Fos expression was monitored 14 days after tying of sciatic nerve and 2 h after non-noxious stimulation. We showed that non-noxious stimulation increased Fos-positivity in the dorsal superficial laminae of the lumbar spinal cord of tied animals but not in the control animals. AM404 significantly reduced Fos induction in tied animals. Co-administration of cannabinoid CB1 receptor, cannabinoid CB2 receptor and transient receptor potential vanilloid type 1 (TRPV-1) antagonists reduced the effect of AM404 and this reduction was higher using cannabinoid CB1 receptor antagonist. These results suggest that AM404 could be a useful drug to reduce neuropathic pain and that cannabinoid CB1 receptor, cannabinoid CB2 receptor and vanilloid TRPV-1 receptor are involved.

2-Arachidonoylglycerol

Endocannabinoids have been implicated in cancer. Increasing endogenous 2-arachidonoylglycerol (2-AG) by blocking its metabolism inhibits invasion of androgen-independent prostate cancer (PC-3 and DU-145) cells. Noladin ether (a stable 2-AG analog) and exogenous CB1 receptor agonists possess similar effects. Conversely, reducing endogenous 2-AG by inhibiting its synthesis or blocking its binding to CB1 receptors with antagonists increases the cell invasion. 2-AG and noladin ether decrease protein kinase A activity in these cells, indicating coupling of the CB1 receptor to downstream effectors. The results suggest that cellular 2-AG, acting through the CB1 receptor, is an endogenous inhibitor of invasive prostate cancer cells.

Sensorimotor gating in mice is disrupted after AM404, an anandamide reuptake and degradation inhibitor

RATIONALE

Prepulse inhibition (PPI) represents a normal sensorimotor gating response that is typically impaired in schizophrenic patients. It is known that cannabinoid CB1 agonists reduce sensorimotor gating in rats, suggesting that the CB1 receptor and the cannabinoid system are involved in sensorimotor gating.

OBJECTIVE

The objective was to study the effects of AM404, an anandamide reuptake and degradation inhibitor, on PPI and startle response in Swiss mice. METHODS. AM404 was injected either acutely (0, 2.5 and 5 mg/kg i.p.) or chronically (5 mg/kg daily, 7 days). The PPI protocol was based on standard methodologies using acoustic stimuli (pulse 120 dB; prepulses 70 dB and 80 dB). SR141716A, a CB1 antagonist, was employed for further confirmation of the involvement of CB1 receptors.

RESULTS

Acute AM404 (5 mg/kg) disrupted PPI (70-dB prepulse, P<0.05) and enhanced the startle response after the 2.5-mg/kg dose (P<0.01). Chronic AM404 disrupted PPI after both 70-dB (P<0.01) and 80-dB prepulses (P<0.05). These effects were blocked after SR141716A cotreatment.

CONCLUSIONS

The data indicate that AM404 (5 mg/kg) acts as a psychodysleptic, altering PPI through stimulation of cannabinoid CB1 receptors, pointing to a possible "psychosis-like" state after enhancement of anandamide bioavailability. The startle response was enhanced only following a lower AM404 dose (2.5 mg/kg), indicating that AM404 induced hyperreactivity at a dose that did not affect PPI, further reinforcing a selective disruption of PPI.

Reversible, temperature-dependent, and AM404-inhibitable adsorption of anandamide to cell culture wells as a confounding factor in release experiments

Relatively little is known about the process whereby the endocannabinoid anandamide (AEA) is released from cells. A simple way of studying this process is to sample the appearance in the medium of tritium following preloading of cells with [(3)H]AEA under conditions where its metabolism is prevented. However, this approach may be complicated by the ability of AEA to be adsorbed reversibly to the cell culture wells. In the present study, it is found that cell culture wells adsorb almost half of the added AEA in a manner prevented by fatty acid-free bovine serum albumin, and by the prototypical uptake inhibitors AM404 and VDM11 with IC(50) values of 3 and 1 microM, respectively. After incubation followed by washing of the plates, AEA is released into the medium from the wells by a first order process (K approximately 0.1 min(-1)) that is temperature-dependent and increased by AM404 and fatty acid-free bovine serum albumin. When assays were run with 0.15% fatty acid-free bovine serum albumin during the loading, washing and release phases of the assay, the release from the well was greatly reduced and a first order, temperature-sensitive release from C6 glioma cells could be unmasked. It is concluded that the reversible adsorption of AEA by cell culture wells can be a confounding factor in release experiments.

Behavioral and molecular changes elicited by acute administration of SR141716 to Delta9-tetrahydrocannabinol-tolerant rats: an experimental model of cannabinoid abstinence

Whether chronic cannabinoid consumption produces a dependent state comparable to that occurring with other drugs (e.g. the appearance of withdrawal signs when consumption is interrupted), and whether chronic cannabinoid consumption increases the risk of consuming other drugs of greater addictive power, are probably the two questions relating to cannabinoid addiction that provoke the most controversy. The present study was designed to further explore these two questions in laboratory animals. Firstly, we examined the effects of an acute challenge with SR141716 (an antagonist for the cannabinoid CB(1) receptor) in Delta(9)-tetrahydrocannabinol (Delta(9)-THC)-tolerant rats. This antagonist has been reported to precipitate a cannabinoid withdrawal syndrome. Thus, the administration of SR141716 to Delta(9)-THC-tolerant rats reduced inactivity in the open-field test and enhanced responses as tremor, turning and retropulsion-these responses that were only slightly enhanced in control rats. The administration of SR141716 increased the plasma prolactin and the corticosterone concentration in controls, but these increases were much lesser in Delta(9)-THC-tolerant rats. In addition, CRF-mRNA levels in the paraventricular hypothalamic nucleus, while reduced in SR141716-treated controls, were significantly increased in Delta(9)-THC-tolerant rats. The analysis of endocannabinoids also revealed that the administration of SR141716, which was mostly inactive in control rats, was able to reverse the changes in anandamide or 2-arachidonoylglycerol concentrations found in Delta(9)-THC-tolerant rats, in the striatum, limbic forebrain, diencephalon, cerebellum and brainstem, but not in the midbrain and hippocampus. As a second objective, we evaluated whether Delta(9)-THC-tolerant rats were more vulnerable to morphine in a self-administration paradigm. The Delta(9)-THC-tolerant and control rats self-administered morphine to a similar extent, in concordance with the similar values of dopaminergic activity in limbic and motor regions. In summary, our data indicate that Delta(9)-THC-tolerant rats were not more vulnerable to the reinforcing properties of morphine. However, they responded to the blockade of CB(1) receptors by exhibiting slightly but possibly relevant differences in behavioral, endocrine and molecular parameters compared to the response in non-tolerant rats. This is indicative of the existence of a withdrawal syndrome in cannabinoid-tolerant rats that is mild compared with abstinence in opioid-dependent rats.

Modulation of trigeminal sensory neuron activity by the dual cannabinoid-vanilloid agonists anandamide, N-arachidonoyl-dopamine and arachidonyl-2-chloroethylamide

1. Peripheral cannabinoids have been shown to suppress nociceptive neurotransmission in a number of behavioral and neurophysiological studies. It is not known, however, whether cannabinoids exert this action through direct interactions with nociceptors in the periphery and/or if other processes are involved. To gain a better understanding of the direct actions of cannabinoid-vanilloid agonists on sensory neurons, we examined the effects of these compounds on trigeminal ganglion (TG) neurons in vitro. 2. AEA (EC(50)=11.0 microM), NADA (EC(50)=857 nM) and arachidonyl-2-chloroethylamide ACEA (EC(50)=14.0 microM) each evoked calcitonin gene-related peptide (CGRP) release from TG neurons. The TRPV1 antagonists iodo-resiniferatoxin (I-RTX) and capsazepine (CPZ) each obtunded AEA-, NADA-, ACEA- and capsaicin (CAP)-evoked CGRP release with individually equivalent IC(50)'s for each of the compounds (I-RTX IC(50) range=2.6-4.0 nM; CPZ IC(50) range=523-1140 microM). 3. The pro-inflammatory mediator prostaglandin E(2) significantly increased the maximal effect of AEA-evoked CGRP release without altering the EC(50). AEA, ACEA and CAP stimulated cAMP accumulation in TG neurons in a calcium- and TRPV1-dependent fashion. Moreover, the protein kinase inhibitor staurosporine significantly inhibited AEA- and CAP-evoked CGRP release. 4. The pungency of AEA, NADA, ACEA and CAP in the rat eye-wipe assay was also assessed. Interestingly, when applied intraocularly, NADA or CAP each produced nocifensive responses, while AEA or ACEA did not. 5. Finally, the potential inhibitory effects of these cannabinoids on TG nociceptors were evaluated. Neither AEA nor ACEA decreased CAP-evoked CGRP release. Furthermore, neither of the cannabinoid receptor type 1 antagonists SR141716A nor AM251 had any impact on either basal or CAP-evoked CGRP release. AEA also did not inhibit 50 mM K(+)-evoked CGRP release and did not influence bradykinin-stimulated inositol phosphate accumulation. 6. We conclude that the major action of AEA, NADA and ACEA on TG neurons is excitatory, while, of these, only NADA is pungent. These findings are discussed in relation to our current understanding of interactions between the cannabinoid and vanilloid systems and nociceptive processing in the periphery.

The endogenous cannabinoid system and the treatment of marijuana dependence

The active principle of marijuana, Delta9-tetrahydrocannabinol (Delta9-THC), exerts its pharmacological effects by binding to selective receptors present on the membranes of neurons and other cells. These cannabinoid receptors are normally engaged by a family of lipid mediators, called endocannabinoids, which are thought to participate in the regulation of a diversity of brain functions, including pain, mood, appetite and memory. Marijuana use may lead to adaptive changes in endocannabinoid signaling, and these changes might contribute to effects of marijuana as well as to the establishment of marijuana dependence. In the present article, I outline current views on how endocannabinoid substances are produced, released, and deactivated in the brain. In addition, I review recent progress on the development of pharmacological agents that interfere with endocannabinoid deactivation and discuss their potential utility in the treatment of marijuana dependence and other aspects of drug abuse.

In vivo pharmacological actions of two novel inhibitors of anandamide cellular uptake

Two inhibitors of the cellular uptake of the endocannabinoid anandamide, (R)-N-oleoyl-(1'-hydroxybenzyl)-2'-ethanolamine and (S)-N-oleoyl-(1'-hydroxybenzyl)-2'-ethanolamine (OMDM-1 and OMDM-2, respectively), were recently synthesized, and their in vitro pharmacological activity described. Here we have assessed their activity in two typical pharmacological responses of cannabimimetic compounds. We first examined whether these compounds exert any effect per se on locomotion and pain perception in rats, and/or enhance the effects of anandamide on these two processes. We compared the effects of the novel compounds with those produced by a previously developed selective inhibitor, N-arachidonoyl-(2-methyl-4-hydroxyphenyl)amine (VDM-11). When assayed alone, OMDM-1 and OMDM-2 (1-10 mg/kg, i.p.) did not affect any of the five motor parameters under investigation, although the former compound exhibited a trend for the inhibition of ambulation, fast movements, and speed in rats. OMDM-2 and, to a lesser extent, VDM-11 (5 mg/kg, i.p.) enhanced the motor-inhibitory effects of a noneffective dose (2 mg/kg, i.p.) of anandamide, while OMDM-1 did not. In a typical test of acute analgesia, OMDM-2 and VDM-11 (1-10 mg/kg, i.p.), but not OMDM-1, significantly enhanced the time spent by rats on a "hot plate." However, the same compounds (5 mg/kg, i.p.) did not enhance the analgesic effect of a subeffective dose (2 mg/kg, i.p.) of anandamide, whereas OMDM-1 exerted a strong trend towards potentiation (P=0.06). We next explored the possible use of the two novel compounds in a pathological condition. Thus, we determined if, like other previously developed anandamide reuptake inhibitors, OMDM-1 and OMDM-2 inhibit spasticity in an animal model of multiple sclerosis-the chronic relapsing experimental allergic encephalomyelitis in mice. As previously shown with a higher dose of VDM-11, both novel compounds (5 mg/kg, i.v.) significantly reduced spasticity of the hindlimb in mice with chronic relapsing experimental allergic encephalomyelitis. We suggest that OMDM-1 and, particularly, OMDM-2 are useful pharmacological tools for the study of the (patho)physiological role of the anandamide cellular uptake process, and represent unique templates for the development of new antispastic drugs.

The ingestion of Ginkgo biloba extract (EGb 761) inhibits arachidonic acid-mediated platelet aggregation and thromboxane B2 production in healthy volunteers

Twelve non-diabetic volunteers (age = 39 +/- 13 years, BMI = 23.5 +/- 3.5) undertook a randomized double-blind placebo-controlled crossover study in which they ingested either 120 mg of EGb 761 or a placebo daily for 3 months and then switched to the other test capsules for the next 3 months. Platelet aggregation in platelet-rich plasma (PRP) was performed at the end of each 3-month arm, with or without 1-min incubation with graded doses of EGb 761. In the placebo cycles, AA-stimulated TXB2 production was 2581 +/-1337 pg/10(6) platelets (range 897-5485) compared to 1668 +/- 992 pg/10(6) platelets (range 6-1668) in the EGb 761 cycles (p < 0.005). Incubation of PRP with EGb 761 (150 microg/ml) completely inhibited platelet aggregation accompanied by inhibition of TXB2 synthesis in all subjects both in the placebo (<200 pg TXB2/10(6) platelets) and EGb 761 cycles (< 120 TXB2/10(6) platelets) (p < 0.0001). These results support EGb 761-mediated inhibition of platelet TXB2 synthesis in vivo.

Effects of d-003, a new substance purified from sugar cane wax, on platelet aggregation and plasma levels of arachidonic acid metabolites in healthy volunteers

D-003 is a mixture of very high molecular weight aliphatic acids purified from sugar cane wax showing cholesterol-lowering and antiplatelet effects proven in experimental and clinical studies. Experimental evidence indicates that inhibition of platelet aggregation induced by D-003 is associated with a reduction of thromboxane B2 (TxB2) and an increase of prostacyclin (Pgl2) serum levels. This double-blinded, randomized, placebo-controlled study was undertaken to investigate whether D-003 (20 mg/day) modifies serum levels of TxB2 and Pgl2 and inhibits platelet aggregation in human healthy volunteers. Thirty-one subjects were randomized to placebo or D-003 at 20 mg/day for 14 days. Serum levels of TxB2 and Pgl2 and platelet aggregation to arachidonic acid (AA) (1.75 mM) and collagen (1 microg/ml) were assessed. D-003 (20 mg/day) significantly reduced (p < 0.001) TxB2by 36.4% and increased Pgl2 serum levels by 31% compared with baseline, and these changes were different from placebo. As expected, D-003 significantly inhibited (p < 0.001) platelet aggregation to AA (81.9-65.6%) and to collagen (75.3-62.3%). No subject withdrew from the study. No drug-related disturbances were observed. We conclude that D-003 at 20 mg/day for 14 days significantly inhibited platelet aggregation to AA and collagen and reduced TxB2 and increased Pgl2 serum levels. These results are consistent with those observed in experimental models, indicating that the antiplatelet effect of D-003 is associated with the observed changes on the levels of AA metabolites. Further studies, however, should explore the mechanism involved in this action in greater depth.

Fatty acid-binding proteins inhibit hydration of epoxyeicosatrienoic acids by soluble epoxide hydrolase

Epoxyeicosatrienoic acids (EETs) are potent regulators of vascular homeostasis and are bound by cytosolic fatty acid-binding proteins (FABPs) with K(d) values of approximately 0.4 microM. To determine whether FABP binding modulates EET metabolism, we examined the effect of FABPs on the soluble epoxide hydrolase (sEH)-mediated conversion of EETs to dihydroxyeicosatrienoic acids (DHETs). Kinetic analysis of sEH conversion of racemic [(3)H]11,12-EET yielded K(m) = 0.45 +/- 0.08 microM and V(max) = 9.2 +/- 1.4 micromol min(-1) mg(-)(1). Rat heart FABP (H-FABP) and rat liver FABP were potent inhibitors of 11,12-EET and 14,15-EET conversion to DHET. The resultant inhibition curves were best described by a substrate depletion model, with K(d) = 0.17 +/- 0.01 microM for H-FABP binding to 11,12-EET, suggesting that FABP acts by reducing EET availability to sEH. The EET depletion by FABP was antagonized by the co-addition of arachidonic acid, oleic acid, linoleic acid, or 20-hydroxyeicosatetraenoic acid, presumably due to competitive displacement of FABP-bound EET. Collectively, these findings imply that FABP might potentiate the actions of EETs by limiting their conversion to DHET. However, the effectiveness of this process may depend on metabolic conditions that regulate the levels of competing FABP ligands.

Endocannabinoids protect the rat isolated heart against ischaemia

1 The purpose of this study was to determine whether endocannabinoids can protect the heart against ischaemia and reperfusion. 2 Rat isolated hearts were exposed to low-flow ischaemia (0.5-0.6 ml min(-1)) and reperfusion. Functional recovery as well as CK and LDH overflow into the coronary effluent were monitored. Infarct size was determined at the end of the experiments. Phosphorylation levels of p38, ERK1/2, and JNK/SAPK kinases were measured by Western blots. 3 None of the untreated hearts recovered from ischaemia during the reperfusion period. Perfusion with either 300 nM palmitoylethanolamide (PEA) or 300 nM 2-arachidonoylglycerol (2-AG), but not anandamide (up to 1 micro M), 15 min before and throughout the ischaemic period, improved myocardial recovery and decreased the levels of coronary CK and LDH. PEA and 2-AG also reduced infarct size. 4 The CB(2)-receptor antagonist, SR144528, blocked completely the cardioprotective effect of both PEA and 2-AG, whereas the CB(1)-receptor antagonist, SR141716A, blocked partially the effect of 2-AG only. In contrast, both ACEA and JWH015, two selective agonists for CB(1)- and CB(2)- receptors, respectively, reduced infarct size at a concentration of 50 nM. 5 PEA enhanced the phosphorylation level of p38 MAP kinase during ischaemia. PEA perfusion doubled the baseline phosphorylation level of ERK1/2, and enhanced its increase upon reperfusion. The cardioprotective effect of PEA was completely blocked by the p38 MAP kinase inhibitor, SB203580, and significantly reduced by the ERK1/2 inhibitor, PD98059, and the PKC inhibitor, chelerythrine. 6 In conclusion, endocannabinoids exert a strong cardioprotective effect in a rat model of ischaemia-reperfusion that is mediated mainly through CB(2)-receptors, and involves p38, ERK1/2, as well as PKC activation.

Design, synthesis, and biological evaluation of new inhibitors of the endocannabinoid uptake: comparison with effects on fatty acid amidohydrolase

A new series of arachidonic acid derivatives were synthesized and evaluated as inhibitors of the endocannabinoid uptake. Most of them are able to inhibit anandamide uptake with IC(50) values in the low micromolar range (IC(50) = 0.8-24 microM). In general, the compounds had only weak effects upon CB(1), CB(2), and VR(1) receptors (K(i) > 1000-10000 nM). In addition, there was no obvious relationship between the abilities of the compounds to affect anandamide uptake and to inhibit anandamide metabolism by fatty acid amidohydrolase (FAAH; IC(50) = 30-113 microM). This indicates that the compounds do not exert their effects secondarily to FAAH inhibition. It is hoped that these compounds, particularly the most potent in this series (compound 5, UCM707, with IC(50) values for anandamide uptake and FAAH of 0.8 and 30 microM, respectively), will provide useful tools for the elucidation of the role of the anandamide transporter system in vivo.

Modifications of the ethanolamine head in N-palmitoylethanolamine: synthesis and evaluation of new agents interfering with the metabolism of anandamide

The endogenous fatty acid amide anandamide (AEA) has, as a result of its actions on cannabinoid and vanilloid receptors, a number of important pharmacological properties including effects on nociception, memory processes, spasticity, and cell proliferation. Inhibition of the metabolism of AEA, catalyzed by fatty acid amide hydrolase (FAAH), potentiates the actions of AEA in vivo and therefore may be a useful target for drug development. In the present study, we have investigated whether substitution of the headgroup of the endogenous alternative FAAH substrate palmitoylethanolamide (PEA) can result in the identification of novel compounds preventing AEA metabolism. Thirty-seven derivatives of PEA were synthesized, with the C16 long chain of palmitic acid kept intact, and comprising 20 alkylated, 12 aromatic, and 4 halogenated amides. The ability of the PEA derivatives to inhibit FAAH-catalyzed hydrolysis of [(3)H]AEA was investigated using rat brain homogenates as a source of FAAH. Inhibition curves were analyzed to determine the potency of the inhibitable fraction (pI(50) values) and the maximal attained inhibition for the compound, given that solubility in an aqueous environment is a major issue for these compounds. In the alkylamide family, palmitoylethylamide and palmitoylallylamide were inhibitors of AEA metabolism with pI(50) values of 5.45 and 5.47, respectively. Halogenated derivatives (Cl and Br) exhibit pI(50) values of approximately 5.5 but rather low percentages of maximal inhibition. The -OH group of the ethyl head chain of N-palmitoylethanolamine was not necessary for interaction with FAAH. Amides containing aromatic moieties were less potent inhibitors of AEA metabolism. Compounds containing amide and ester bonds, 13 and 37, showed pI(50) values of 4.99 and 5.08, respectively. None of the compounds showed obvious affinity for CB(1) or CB(2) receptors expressed on Chinese hamster ovary (CHO) cells. It is concluded that although none of the compounds were dramatically more potent than PEA itself at reducing the metabolism of AEA, the lack of effect of the compounds at CB(1) and CB(2) receptors makes them useful templates for development of possible therapeutic FAAH inhibitors.