Biochemistry and pharmacology of arachidonylethanolamide, a putative endogenous cannabinoid

Endocannabinoid Degradation Enzyme Inhibitors as Potential Antipsychotics: A Medicinal Chemistry Perspective

The endocannabinoid system (ECS) plays a very important role in numerous physiological and pharmacological processes, such as those related to the central nervous system (CNS), including learning, memory, emotional processing, as well pain control, inflammatory and immune response, and as a biomarker in certain psychiatric disorders. Unfortunately, the half-life of the natural ligands responsible for these effects is very short. This perspective describes the potential role of the inhibitors of the enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MGL), which are mainly responsible for the degradation of endogenous ligands in psychic disorders and related pathologies. The examination was carried out considering both the impact that the classical exogenous ligands such as Δ⁹-tetrahydrocannabinol (THC) and (-)-trans-cannabidiol (CBD) have on the ECS and through an analysis focused on the possibility of predicting the potential toxicity of the inhibitors before they are subjected to clinical studies. In particular, cardiotoxicity (hERG liability), probably the worst early adverse reaction studied during clinical studies focused on acute toxicity, was predicted, and some of the most used and robust metrics available were considered to select which of the analyzed compounds could be repositioned as possible oral antipsychotics.

The Endocannabinoid System as a Target for Neuroprotection/Neuroregeneration in Perinatal Hypoxic-Ischemic Brain Injury

The endocannabinoid (EC) system is a complex cell-signaling system that participates in a vast number of biological processes since the prenatal period, including the development of the nervous system, brain plasticity, and circuit repair. This neuromodulatory system is also involved in the response to endogenous and environmental insults, being of special relevance in the prevention and/or treatment of vascular disorders, such as stroke and neuroprotection after neonatal brain injury. Perinatal hypoxia-ischemia leading to neonatal encephalopathy is a devastating condition with no therapeutic approach apart from moderate hypothermia, which is effective only in some cases. This overview, therefore, gives a current description of the main components of the EC system (including cannabinoid receptors, ligands, and related enzymes), to later analyze the EC system as a target for neonatal neuroprotection with a special focus on its neurogenic potential after hypoxic-ischemic brain injury.

Biosynthesis of N-Docosahexanoylethanolamine from Unesterified Docosahexaenoic Acid and Docosahexaenoyl-Lysophosphatidylcholine in Neuronal Cells

We investigated the synthesis of N-docosahexaenoylethanolamine (synaptamide) in neuronal cells from unesterified docosahexaenoic acid (DHA) or DHA-lysophosphatidylcholine (DHA-lysoPC), the two major lipid forms that deliver DHA to the brain, in order to understand the formation of this neurotrophic and neuroprotective metabolite of DHA in the brain. Both substrates were taken up in Neuro2A cells and metabolized to N-docosahexaenoylphosphatidylethanolamine (NDoPE) and synaptamide in a time- and concentration-dependent manner, but unesterified DHA was 1.5 to 2.4 times more effective than DHA-lysoPC at equimolar concentrations. The plasmalogen NDoPE (pNDoPE) amounted more than 80% of NDoPE produced from DHA or DHA-lysoPC, with 16-carbon-pNDoPE being the most abundant species. Inhibition of N-acylphosphatidylethanolamine-phospholipase D (NAPE-PLD) by hexachlorophene or bithionol significantly decreased the synaptamide production, indicating that synaptamide synthesis is mediated at least in part via NDoPE hydrolysis. NDoPE formation occurred much more rapidly than synaptamide production, indicating a precursor–product relationship. Although NDoPE is an intermediate for synaptamide biosynthesis, only about 1% of newly synthesized NDoPE was converted to synaptamide, possibly suggesting additional biological function of NDoPE, particularly for pNDoPE, which is the major form of NDoPE produced.

N-Docosahexaenoylethanolamine: A neurotrophic and neuroprotective metabolite of docosahexaenoic acid

N-Docosahexaenoylethanolamine (synaptamide) is an endocannabinoid-like metabolite endogenously synthesized from docosahexaenoic acid (DHA, 22:6n-3), the major omega-3 polyunsaturated fatty acid present in the brain. Although its biosynthetic mechanism has yet to be established, there is a closely linked relationship between the levels of synaptamide and its precursor DHA in the brain. Synaptamide at nanomolar concentrations promotes neurogenesis, neurite outgrowth and synaptogenesis in developing neurons. Synaptamide also attenuates the lipopolysaccharide-induced neuroinflammatory response and reduces the deleterious effects of ethanol on neurogenic differentiation of neural stem cells (NSCs). These actions are mediated by a specific target receptor of synaptamide GPR110 (ADGRF1), a G-protein coupled receptor that is highly expressed in NSCs and the brain during development. Synaptamide binding to GPR110 induces cAMP production and phosphorylation of protein kinase A (PKA) and the cAMP response element binding protein (CREB). This signaling pathway leads to the expression of neurogenic and synaptogenic genes and suppresses the expression of proinflammatory genes. The GPR110-dependent cellular effects of synaptamide are recapitulated in animal models, suggesting that synaptamide-derived mechanisms may have translational implications. The synaptamide bioactivity transmitted by newly deorphanized GPR110 provides a novel target for neurodevelopmental and neuroprotective control as well as new insight into mechanisms for DHA's beneficial effects on the central nervous system.

Endocannabinoid dynamics gate spike-timing dependent depression and potentiation

Synaptic plasticity is a cardinal cellular mechanism for learning and memory. The endocannabinoid (eCB) system has emerged as a pivotal pathway for synaptic plasticity because of its widely characterized ability to depress synaptic transmission on short- and long-term scales. Recent reports indicate that eCBs also mediate potentiation of the synapse. However, it is not known how eCB signaling may support bidirectionality. Here, we combined electrophysiology experiments with mathematical modeling to question the mechanisms of eCB bidirectionality in spike-timing dependent plasticity (STDP) at corticostriatal synapses. We demonstrate that STDP outcome is controlled by eCB levels and dynamics: prolonged and moderate levels of eCB lead to eCB-mediated long-term depression (eCB-tLTD) while short and large eCB transients produce eCB-mediated long-term potentiation (eCB-tLTP). Moreover, we show that eCB-tLTD requires active calcineurin whereas eCB-tLTP necessitates the activity of presynaptic PKA. Therefore, just like glutamate or GABA, eCB form a bidirectional system to encode learning and memory.

The Endocannabinoid Signaling System in the CNS: A Primer

The purpose of this chapter is to provide an introduction to the mechanisms for the regulation of endocannabinoid signaling through CB1 cannabinoid receptors in the central nervous system. The processes involved in the synthesis and degradation of the two most well-studied endocannabinoids, 2-arachidonoylglycerol and N-arachidonylethanolamine are outlined along with information regarding the regulation of the proteins involved. Signaling mechanisms and pharmacology of the CB1 cannabinoid receptor are outlined, as is the paradigm of endocannabinoid/CB1 receptor regulation of neurotransmitter release. The reader is encouraged to appreciate the importance of the endocannabinoid/CB1 receptor signaling system in the regulation of synaptic activity in the brain.

Mechanisms of exercise-induced hypoalgesia

The purpose of this study was to examine opioid and endocannabinoid mechanisms of exercise-induced hypoalgesia (EIH). Fifty-eight men and women (mean age = 21 years) completed 3 sessions. During the first session, participants were familiarized with the temporal summation of heat pain and pressure pain protocols. In the exercise sessions, following double-blind administration of either an opioid antagonist (50 mg naltrexone) or placebo, participants rated the intensity of heat pulses and indicated their pressure pain thresholds and pressure pain ratings before and after 3 minutes of submaximal isometric exercise. Blood was drawn before and after exercise. Results indicated that circulating concentrations of 2 endocannabinoids, N-arachidonylethanolamine and 2-arachidonoylglycerol, as well as related lipids oleoylethanolamide, palmitoylethanolamide, N-docosahexaenoylethanolamine, and 2-oleoylglycerol, increased significantly (P < .05) following exercise. Pressure pain thresholds increased significantly (P < .05), whereas pressure pain ratings decreased significantly (P < .05) following exercise. Also, temporal summation ratings were significantly lower (P < .05) following exercise. These changes in pain responses did not differ between the placebo and naltrexone conditions (P > .05). A significant association was found between EIH and docosahexaenoylethanolamine. These results suggest involvement of a nonopioid mechanism in EIH following isometric exercise.

PERSPECTIVE

Currently, the mechanisms responsible for EIH are unknown. This study provides support for a potential endocannabinoid mechanism of EIH following isometric exercise.

TRPV1 mediates cellular uptake of anandamide and thus promotes endothelial cell proliferation and network-formation

Anandamide (N-arachidonyl ethanolamide, AEA) is an endogenous cannabinoid that is involved in various pathological conditions, including cardiovascular diseases and tumor-angiogenesis. Herein, we tested the involvement of classical cannabinoid receptors (CBRs) and the Ca(2+)-channel transient receptor potential vanilloid 1 (TRPV1) on cellular AEA uptake and its effect on endothelial cell proliferation and network-formation. Uptake of the fluorescence-labeled anandamide (SKM4-45-1) was monitored in human endothelial colony-forming cells (ECFCs) and a human endothelial-vein cell line (EA.hy926). Involvement of the receptors during AEA translocation was determined by selective pharmacological inhibition (AM251, SR144528, CID16020046, SB366791) and molecular interference by TRPV1-selective siRNA-mediated knock-down and TRPV1 overexpression. We show that exclusively TRPV1 contributes essentially to AEA transport into endothelial cells in a Ca(2+)-independent manner. This TRPV1 function is a prerequisite for AEA-induced endothelial cell proliferation and network-formation. Our findings point to a so far unknown moonlighting function of TRPV1 as Ca(2+)-independent contributor/regulator of AEA uptake. We propose TRPV1 as representing a promising target for development of pharmacological therapies against AEA-triggered endothelial cell functions, including their stimulatory effect on tumor-angiogenesis.

Neuronal substrates and functional consequences of prenatal cannabis exposure

Cannabis remains one of the world's most widely used substance of abuse amongst pregnant women. Trends of the last 50 years show an increase in popularity in child-bearing women together with a constant increase in cannabis potency. In addition, potent herbal "legal" highs containing synthetic cannabinoids that mimic the effects of cannabis with unknown pharmacological and toxicological effects have gained rapid popularity amongst young adults. Despite the surge in cannabis use during pregnancy, little is known about the neurobiological and psychological consequences in the exposed offspring. In this review, we emphasize the importance of maternal programming, defined as the intrauterine presentation of maternal stimuli to the foetus, in neurodevelopment. In particular, we focus on cannabis-mediated maternal adverse effects, resulting in direct central nervous system alteration or sensitization to late-onset chronic and neuropsychiatric disorders. We compare clinical and preclinical experimental studies on the effects of foetal cannabis exposure until early adulthood, to stress the importance of animal models that permit the fine control of environmental variables and allow the dissection of cannabis-mediated molecular cascades in the developing central nervous system. In sum, we conclude that preclinical experimental models confirm clinical studies and that cannabis exposure evokes significant molecular modifications to neurodevelopmental programs leading to neurophysiological and behavioural abnormalities.

The contractile effect of anandamide in the guinea-pig small intestine is mediated by prostanoids but not TRPV1 receptors or capsaicin-sensitive nerves

Although exogenous and endogenous cannabinoid receptor agonists have well-documented inhibitory effects on gastrointestinal motility, a TRPV1 receptor-mediated excitatory action of anandamide (arachidonoyl ethanolamide, AEA) in the guinea-pig ileum strip has also been described. We used in vitro capsaicin desensitization for assessing the possible participation of sensory neurons in the contractile effect of anandamide on the guinea-pig whole ileum, as well as autonomic drugs and a cyclooxygenase inhibitor for characterizing this response. Isolated organ experiments were used with isotonic recording. Contractions induced by anandamide (1 or 10 μM) were strongly inhibited by tetrodotoxin, indomethacin or atropine plus a tachykinin NK(1) receptor antagonist, but weakly to moderately reduced by atropine alone and partly diminished by the fatty acid amide hydrolase inhibitor URB 597. Neither capsaicin pre-treatment nor the TRPV1 receptor antagonist BCTC, the ganglionic blocking drug hexamethonium or cannabinoid (CB1 or CB2 ) receptor antagonists, influenced the effect of anandamide. It is concluded that the capsaicin-insensitive, neuronal excitatory effect of anandamide in the intestine is most probably mediated by cyclooxygenase products. Such a mechanism may also play a role at other sites in the mammalian body.

Peripheral antinociceptive effect of anandamide and drugs that affect the endocannabinoid system on the formalin test in normal and streptozotocin-diabetic rats

Diabetes is often associated with painful neuropathy. The current treatments are symptomatic and ineffective. Cannabinoids have been proposed as promising drugs for chronic pain treatment and its antinociceptive effect has already been related in nerve injury models of neuropathic pain, but little has been investigated in painful diabetic neuropathy models. Thus, the current study aims to investigate the potential antinociceptive effect of drugs that alter endocannabinoid system when injected subcutaneously into the dorsal surface of the ipsilateral hind paw in chemical hyperalgesia induced by formalin in both normoglycemic (Ngl) and streptozotocin-diabetic (Dbt) rats. Diabetic rats exhibited exaggerated flinching behaviors during first and second phases of the formalin test, indicating the presence of hyperalgesia. AM404, an anandamide (AEA) re-uptake inhibitor, AEA (an agonist of CB1/CB2 receptors) or ACEA (a selective CB1 receptor agonist) induced antinociception in both phases of formalin test in Ngl and Dbt rats. In both groups, the antinociceptive effect of ACEA was prevented by AM251, a CB1 inverse agonist while the antinociceptive effect of AEA was prevented by AM251 or AM630, a CB2 receptor antagonist. In Ngl rats, the antinociceptive effect of AM404 was prevented by AM251 or capsazepine only during first phase of the formalin test while in Dbt rats, this effect was blocked by pretreatment with AM251 (both phases) or AM630 (second phase). Taken together, these results demonstrated broad-spectrum antinociceptive properties of cannabinoids in a model of painful diabetic neuropathy. Peripheral activation of both cannabinoid receptors seems to mediate the antinociceptive effect of exogenous or endogenous anandamide.

Modulation of endocannabinoid-mediated long-lasting disinhibition of striatal output by cholinergic interneurons

The frequency and duration of glutamatergic inputs to the striatum are strong determinants of the net effect of retrograde endocannabinoid (eCB) signaling, and key factors in determining if long-term depression (LTD) has a net disinhibitory or inhibitory action in striatum. Low to moderate frequency stimulation in the dorsolateral striatum elevates eCB levels to an extent that primarily depresses transmitter release at inhibitory synapses, leading to a long-lasting disinhibition (DLL) of synaptic output. The aim of this study was to further characterize the basic features of endocannabinoid-mediated DLL of striatal output induced by moderate frequency stimulation (5 Hz, 60 s). DLL was inhibited in slices treated with the group 1 metabotropic glutamate receptor (mGluR) antagonists MPEP (40 μM) and CPCCOEt (40 μM), the dopamine D2 receptor antagonist sulpiride (5 μM), the L-type calcium channel blocker nifedipine (20 μM), the nicotinic receptor antagonist mecamylamine (10 μM), the muscarinic agonist oxotremorine sesquifumarate (10 μM), and strychnine (0.1 μM). Strychnine did not block DLL induced by WIN55,212-2 (250 nM), showing that glycine receptor-mediated modulation of eCB signaling occurs upstream from CB(1)R activation. Scopolamine (10 μM) restored DLL in strychnine-treated slices, suggesting that inhibition of glycine receptors on cholinergic interneurons could modulate eCB signaling by enhancing muscarinic receptor activation and reducing the opening of L-type calcium channels in response to depolarization. These data suggests that similar activation points are required for stimulation-induced DLL as for LTD at excitatory striatal synapses, and that cholinergic interneurons are key modulators of stimulation-induced eCB signaling in the striatum.

Behavioral effects of fatty acid amide hydrolase inhibition on morphine withdrawal symptoms

Chronic morphine exposure causes tolerance and dependence. The cessation of morphine consumption induces a withdrawal syndrome that may involve cannabinoids and is characterized by undesirable psychological and physical signs. The present study examined whether augmentation of the endocannabinoid system by inhibition of fatty acid amide hydrolase could suppress the morphine withdrawal syndrome in morphine-addicted rats. Morphine dependency was induced by 7 consecutive days of morphine injection. The morphine-addicted rats received URB597 (1, 0.5, 0.3, 0.1, 0.03 mg/kg), a fatty acid amide hydrolase inhibitor, before the precipitation of morphine withdrawal syndromes by naloxone. Withdrawal symptoms including jumping, teeth chattering, paw tremor, wet dog shakes, face grooming, penis licking, standing, rearing, sniffing and percent of weight loss were recorded during 30 min after naloxone injection. The results showed that the morphine withdrawal precipitated rats had significantly more withdrawal symptoms than naive control rats and the administration of URB597 (all doses except 0.03 mg/kg) reduced most of the morphine withdrawal symptoms. We conclude that the administration of URB597 modulated morphine withdrawal symptoms. This finding shows that endocannabinoids interact with the opioid system during the morphine withdrawal period and that potentiation of the endogenous cannabinoid system by URB597 may be a new target strategy for the management of morphine addiction.

Endocannabinoid signalling: has it got rhythm?

Endogenous cannabinoid signalling is widespread throughout the body, and considerable evidence supports its modulatory role in many fundamental physiological processes. The daily and seasonal cycles of the relationship of the earth and sun profoundly affect the terrestrial environment. Terrestrial species have adapted to these cycles in many ways, most well studied are circadian rhythms and hibernation. The purpose of this review was to examine literature support for three hypotheses: (i) endocannabinoid signalling exhibits brain region-specific circadian rhythms; (ii) endocannabinoid signalling modulates the rhythm of circadian processes in mammals; and (iii) changes in endocannabinoid signalling contribute to the state of hibernation. The results of two novel studies are presented. First, we report the results of a study of healthy humans demonstrating that plasma concentrations of the endocannabinoid, N-arachidonylethanolamine (anandamide), exhibit a circadian rhythm. Concentrations of anandamide are threefold higher at wakening than immediately before sleep, a relationship that is dysregulated by sleep deprivation. Second, we investigated differences in endocannabinoids and congeners in plasma from Marmota monax obtained in the summer and during the torpor state of hibernation. We report that 2-arachidonoylglycerol is below detection in M. monax plasma and that concentrations of anandamide are not different. However, plasma concentrations of the anorexigenic lipid oleoylethanolamide were significantly lower in hibernation, while the concentrations of palmitoylethanolamide and 2-oleoylglycerol were significantly greater in hibernation. We conclude that available data support a bidirectional relationship between endocannabinoid signalling and circadian processes, and investigation of the contribution of endocannabinoid signalling to the dramatic physiological changes that occur during hibernation is warranted.

Examining the roles of cannabinoids in pain and other therapeutic indications: a review

IMPORTANCE OF THE FIELD

In recent times, our knowledge of cannabinoids and the endocannabinoid system has greatly advanced. With expanding knowledge, synthetic cannabinoids - including nabilone, dronabinol and a combination of synthetic Delta9-THC and cannabidiol - have been developed and tested for benefit in a variety of therapeutic indications.

AREAS COVERED IN THIS REVIEW

The aim of this article is to provide a summative review of the vast amount of clinical trial data now available on these agents.

WHAT THE READER WILL GAIN

To locate clinical trials for review, a literature search was performed using PubMed between the dates of 25 May and 30 June 2009. Search parameters were set to isolate only human randomized controlled trials (RCTs) published between 1990 and 2009. Keywords consistently used for each search include: cannabinoids, marijuana, THC, nabilone and dronabinol. Preferential selection was given to the best-designed trials, focusing on placebo-controlled, double-blind RCTs with the largest patient populations, if available.

TAKE HOME MESSAGE

As efficacy and tolerability of these agents remain questionable, it is important that cannabinoids not be considered 'first-line' therapies for conditions for which there are more supported and better-tolerated agents. Instead, these agents could be considered in a situation of treatment failure with standard therapies or as adjunctive agents where appropriate.

Endogenous cannabinoids induce fever through the activation of CB1 receptors

BACKGROUND AND PURPOSE

The effects of centrally administered cannabinoids on body core temperature (Tc) and the contribution of endogenous cannabinoids to thermoregulation and fever induced by lipopolysaccharide (LPS) (Sigma Chem. Co., St. Louis, MO, USA) were investigated.

EXPERIMENTAL APPROACH

Drug-induced changes in Tc of male Wistar rats were recorded over 6 h using a thermistor probe (Yellow Springs Instruments 402, Dayton, OH, USA) inserted into the rectum.

KEY RESULTS

Injection of anandamide [(arachidonoylethanolamide (AEA); Tocris, Ellisville, MO, USA], 0.01-1 microg i.c.v. or 0.1-100 ng intra-hypothalamic (i.h.), induced graded increases in Tc (peaks 1.5 and 1.6 degrees C at 4 h after 1 microg i.c.v. or 10 ng i.h.). The effect of AEA (1 microg, i.c.v.) was preceded by decreases in tail skin temperature and heat loss index (values at 1.5 h: vehicle 0.62, AEA 0.48). Bell-shaped curves were obtained for the increase in Tc induced by the fatty acid amide hydrolase inhibitor [3-(3-carbamoylphenyl)phenyl] N-cyclohexylcarbamate (Cayman Chemical Co., Ann Arbor, MI, USA) (0.001-1 ng i.c.v.; peak 1.9 degrees C at 5 h after 0.1 ng) and arachidonyl-2-chloroethylamide (ACEA; Tocris) (selective CB(1) agonist; 0.001-1 microg i.c.v.; peak 1.4 degrees C 5 h after 0.01 microg), but (R,S)-(+)-(2-Iodo-5-nitrobenzoyl)-[1-(1-methyl-piperidin-2-ylmethyl)-1H-indole-3-yl] methanone (Tocris) (selective CB(2) agonist) had no effect on Tc. AEA-induced fever was unaffected by i.c.v. pretreatment with 6-Iodo-2-methyl-1-[2-(4-morpholinyl)ethyl]-1H-indole-3-yl](4-methoxyphenyl) methanone (Tocris) (selective CB(2) antagonist), but reduced by i.c.v. pretreatment with N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251; Tocris) (selective CB(1) antagonist). AM251 also reduced the fever induced by ACEA or LPS.

CONCLUSIONS AND IMPLICATIONS

The endogenous cannabinoid AEA induces an integrated febrile response through activation of CB(1) receptors. Endocannabinoids participate in the development of the febrile response to LPS constituting a target for antipyretic therapy.

Acute ethanol treatment prevents endocannabinoid-mediated long-lasting disinhibition of striatal output

Recent research has suggested that the neuronal circuit adaptations elicited by drugs of abuse share common features with traditional learning models, and that drugs of abuse cause long-term changes in behavior by altering synaptic function and plasticity. Especially, the endocannabinoid (eCB) system appears to be involved in the neuronal circuitry regulating ethanol (EtOH) preference in rodent. The aim of this study was to evaluate if acute EtOH exposure could modulate eCB-mediated plasticity in the dorsolateral striatum. Our data show that EtOH (20-50 mM) prevents eCB-mediated long-lasting disinhibition (DLL) of striatal output induced by a single stimulation train delivered at 5 Hz for 60 s, and reduces long-term depression (LTD) induced by low-frequency stimulation at inhibitory synapses. Acute EtOH-treatment also prevents DLL induced by the L-type calcium channel activator 2,5-dimethyl-4-[2-(phenylmethyl)benzoyl]-1H-pyrrole-3-carboxylic acid methylester (FPL64176; 500 nM), or by the cannabinoid 1 receptor (CB(1)R) agonist WIN55,212-2 (300 nM), indicating that EtOH affects eCB-signaling at a stage that is downstream from eCB production and release. Importantly, high-frequency stimulation, or a higher concentration of WIN55,212-2 (1 muM), induces EtOH-insensitive depression of striatal output, suggesting that EtOH affects CB(1)R-mediated signaling in a synapse-specific manner. Maintaining the balance between excitation and inhibition is vital for neuronal networks, and EtOH-mediated modulation of eCB-signaling might thus affect the stability and the fine-tuning of neuronal circuits in the striatum. Our data suggest that changes in eCB-signaling could be involved in the physiological response to acute alcohol intoxication.

Antidepressant-like activity of the fatty acid amide hydrolase inhibitor URB597 in a rat model of chronic mild stress

BACKGROUND

The endocannabinoid anandamide may be involved in the regulation of emotional reactivity. In particular, it has been shown that pharmacological inhibition of the enzyme fatty acid amide hydrolase (FAAH), which catalyzes the intracellular hydrolysis of anandamide, elicits anxiolytic-like and antidepressant-like effects in rodents.

METHODS

We investigated the impact of chronic treatment with the selective FAAH inhibitor, URB597 (also termed KDS-4103), on the outcomes of the chronic mild stress (CMS) in rats, a behavioral model with high isomorphism to human depression.

RESULTS

Daily administration of URB597 (.3 mg kg(-1), intraperitoneal [IP]) for 5 weeks corrected the reduction in body weight gain and sucrose intake induced by CMS. The antidepressant imipramine (20 mg kg(-1), once daily, IP) produced a similar response, whereas lower doses of URB597 were either marginally effective (.1 mg kg(-1)) or ineffective (.03 mg kg(-1)). Treatment with URB597 (.3 mg kg(-1)) resulted in a profound inhibition of brain FAAH activity in both CMS-exposed and control rats. Furthermore, the drug regimen increased anandamide levels in midbrain, striatum, and thalamus.

CONCLUSIONS

URB597 exerts antidepressant-like effects in a highly specific and predictive animal model of depression. These effects may depend on the ability of URB597 to enhance anandamide signaling in select regions of the brain.

Anandamide protects from low serum-induced apoptosis via its degradation to ethanolamine

Anandamide (AEA) is a lipid molecule belonging to the family of endocannabinoids. Various studies report neuroprotective activity of AEA against toxic insults, such as ischemic conditions and excitotoxicity, whereas some show that AEA has pro-apoptotic effects. Here we have shown that AEA confers a protective activity in N18TG2 murine neuroblastoma cells subjected to low serum-induced apoptosis. We have demonstrated that the protection from apoptosis by AEA is not mediated via the CB1 receptor, the CB2 receptor, or the vanilloid receptor 1. Interestingly, breakdown of AEA by fatty acid amide hydrolase is required for the protective effect of AEA. Furthermore, the ethanolamine (EA) generated in this reaction is the metabolite responsible for the protective response. The elevation in the levels of reactive oxygen species during low serum-induced apoptosis is not affected by AEA or EA. On the other hand, AEA and EA reduce caspase 3/7 activity, and AEA attenuates the cleavage of PARP-1. Taken together, our results demonstrate a role for AEA and EA in the protection against low serum-induced apoptosis.

Pharmacological profile of the selective FAAH inhibitor KDS-4103 (URB597)

In the present article, we review the pharmacological properties of KDS-4103 (URB597), a highly potent and selective inhibitor of the enzyme fatty-acid amide hydrolase (FAAH), which catalyzes the intracellular hydrolysis of the endocannabinoid anandamide. In vitro, KDS-4103 inhibits FAAH activity with median inhibitory concentrations (IC(50)) of 5 nM in rat brain membranes and 3 nM in human liver microsomes. In vivo, KDS-4103 inhibits rat brain FAAH activity after intraperitoneal (i.p.) administration with a median inhibitory dose (ID(50)) of 0.15 mg/kg. The compound does not significantly interact with other cannabinoid-related targets, including cannabinoid receptors and anandamide transport, or with a broad panel of receptors, ion channels, transporters and enzymes. By i.p. administration to rats and mice KDS-4103 elicits significant, anxiolytic-like, antidepressant-like and analgesic effects, which are prevented by treatment with CB1 receptor antagonists. By contrast, at doses that significantly inhibit FAAH activity and substantially raise brain anandamide levels, KDS-4103 does not evoke classical cannabinoid-like effects (e.g., catalepsy, hypothermia, hyperphagia), does not cause place preference, and does not produce generalization to the discriminative effects of the active ingredient of cannabis, Delta9-tetrahydrocannabinol (Delta9-THC). These findings suggest that KDS-4103 acts by enhancing the tonic actions of anandamide on a subset of CB(1) receptors, which may normally be engaged in controlling emotions and pain. KDS-4103 is orally available in rats and cynomolgus monkeys. Sub-chronic repeated dose studies (1,500 mg/kg, per os) in these two species have not demonstrated systemic toxicity. Likewise, no toxicity was noted in bacterial cytotoxicity tests in vitro and in the Ames test. Furthermore, no deficits were observed in rats on the rotarod test after acute i.p. treatment with KDS-4103 at doses up to 5 mg/kg or in a functional observation battery after oral doses up to 1,500 mg/kg. The results suggest that KDS-4103 will offer a novel approach with a favorable therapeutic window for the treatment of anxiety, depression and pain.

Investigational therapies in the treatment of obesity

Obesity is a major public health concern and environmental factors are involved in its development. The hypothalamus is a primary site for the integration of signals for the regulation of energy homeostasis. Dysregulation of these pathways can lead to weight loss or gain. Some drugs in development can have favourable effects on body weight, acting on some of these pathways and leading to responses resulting in weight loss. Strategies for the management of weight reduction include exercise, diet, behavioural therapy, drug therapy and surgery. Investigational antiobesity medications can modulate energy homeostasis by stimulating catabolic or inhibiting anabolic pathways. Investigational drugs stimulating catabolic pathways consist of leptin, agonists of melanocortin receptor-4, 5-HT and dopamine; bupropion, growth hormone fragments, cholecystokinin subtype 1 receptor agonist, peptide YY3-36, oxyntomodulin, ciliary neurotrophic factor analogue, beta3-adrenergic receptor agonists, adiponectin derivatives and glucagon-like peptide-1. On the other hand, investigational drugs inhibiting anabolic pathways consist of the ghrelin receptor, neuropeptide Y receptor and melanin-concentrating hormone-1 antagonists; somatostatin analogues, peroxisome proliferator-activated receptor-gamma and -beta/delta antagonists, gastric emptying retardation agents, pancreatic lipase inhibitors, topiramate and cannabinoid-1 receptor antagonists. These differing approaches are reviewed and commented on in this article.

Lipids and drugs of abuse

Drug abuse continues to take an enormous economic and social toll on the world. Among the costs are reduced productivity, increased need for medical services and stress on families. Treatments that allow affected individuals to reduce compulsive drug use are lacking and novel approaches to their development will likely come from increased understanding of the consequences of chronic exposure to reinforcing drugs. The purpose of this review is to explore the role of lipids in drug abuse and to present a rationale for an increased focus on the interactions between drugs of abuse and lipids in the brain. Small molecular weight lipids function as neuromodulators in the brain and, as such, play a role in the synaptic plasticity that occurs following exposure to drugs of abuse. In addition, the membrane lipid bilayer consists of lipid subdomains and emerging evidence suggests that protein function can be altered by transient associations with these subdomains. Finally, lipidomics is a very new field devoted to the exploration of changes in cellular lipid constituents during phenotypic alterations. Enhanced research in all of these areas will likely provide useful insights into and, perhaps, therapeutic targets for the treatment of drug abuse.

Molecular biology of cannabinoid receptors

To date, two cannabinoid receptors have been isolated by molecular cloning. The CB1 and CB2 cannabinoid receptors are members of the G protein-coupled receptor family. There is also evidence for additional cannabinoid receptor subtypes. The CB1 and CB2 receptors recognize endogenous and exogenous cannabinoid compounds, which fall into five structurally diverse classes. Mutagenesis and molecular modeling studies have identified several key amino acid residues involved in the selective recognition of these ligands. Numerous residues involved in receptor activation have been elucidated. Regions of the CB1 receptor mediating desensitization and internalization have also been discovered. The known genetic structures of the CB1 and CB2 receptors indicate polymorphisms and multiple exons that maybe involved in tissue and species-specific regulation of these genes. The cannabinoid receptors are regulated during chronic agonist exposure, and gene expression is altered in disease states. There is a complex molecular architecture of the cannabinoid receptors that allows a single receptor to recognize multiple classes of compounds and produce an array of distinct downstream effects.

Decrease in prostaglandin level is a prerequisite for the expression of cannabinoid withdrawal: A quasi abstinence approach

Cannabinoid withdrawal has been indicated in both human and animal subjects. One of pathways proposed to facilitate cannabinoid action is the arachidonic acid cascade. Previously, we have shown that prostaglandin attenuated the expression of withdrawal signs in tetrahydrocannabinol-dependent mice. It follows that the cascade might participate in the expression of cannabinoid withdrawal. We utilized a quasi abstinence approach (the induction of a state of cannabinoid withdrawal without giving any cannabinoid substances in a naïve animal) to describe the relationship between the change in prostaglandin level, an end product of the arachidonic acid cascade, and the expression of cannabinoid withdrawal. Administration of 10 mg/kg diclofenac, a prostaglandin synthesis inhibitor, i.p. 30 min before SR 141716A induced cannabinoid withdrawal signs in naïve mice, which were comparable to the true abstinence in cannabinoid-tolerant mice. In turn, 10 mg/kg Delta(8)-THC i.p., given 15 min prior to SR 141716A, blocked the expression of these signs. These results suggested that the decrease in prostaglandin level is a prerequisite for the expression of cannabinoid withdrawal.

On the importance of anandamide structural features for its interactions with DPPC bilayers: effects on PLA2 activity

The acylethanolamide anandamide (AEA) occurs in a variety of mammalian tissues and, as a result of its action on cannabinoid receptors, exhibits several cannabimimetic activities. Moreover, some of its effects are mediated through interaction with an ion channel-type vanilloid receptor. However, the chemical features of AEA suggest that some of its biological effects could be related to physical interactions with the lipidic part of the membrane. The present work studies the effect of AEA-induced structural modifications of the dipalmitoylphosphatidylcholine (DPPC) bilayer on phospholipase A2 (PLA2) activity, which is strictly dependent on lipid bilayer features. This study, performed by 2-dimethylamino-(6-lauroyl)-naphthalene fluorescence, demonstrates that the effect of AEA on PLA2 activity is concentration-dependent. In fact, at low AEA/DPPC molar ratios (from R = 0.001 to R = 0.04), there is an increase of the enzymatic activity, which is completely inhibited for R = 0.1. X-ray diffraction data indicate that the AEA affects DPPC membrane structural properties in a concentration-dependent manner. Because the biphasic effect of increasing AEA concentrations on PLA2 activity is related to the induced modifications of membrane bilayer structural properties, we suggest that AEA-phospholipid interactions may be important to produce, at least in part, some of the similarly biphasic responses of some physiological activities to increasing concentrations of AEA.

Induction of cyclooxygenase-2 by anandamide in cerebral microvascular endothelium

Anandamide (AEA), an endogenous cannabinoid receptor agonist, is a potent vasodilator in the cerebral microcirculation. AEA is converted to arachidonic acid (AA) by fatty acid amidohydrolase (FAAH), and the conversion of AA to prostaglandins has been proposed as a potential mechanism for the vasodilation. Although AEA stimulated prostaglandin production by mouse cerebral microvascular endothelial cells, no [(3)H]prostaglandins were produced when these cells were incubated with [3H]AEA. Incubation with R(+)-methanandamide (MAEA), a stable analogue of AEA that is not a substrate for FAAH, produced a similar increase in PGE2 production as AEA. The PGE2 production induced by either AEA or MAEA was completely inhibited by NS-398, a selective cyclooxygenase (COX)-2 inhibitor, suggesting that COX-2 was induced. AEA and MAEA increased the expression of COX-2 protein in a time-dependent manner. This increase occurred as early as 1 h and reached maximum at 2 h. Induction of COX-2 protein by AEA was partially inhibited by AM-251, a selective cannabinoid receptor-1 antagonist. Furthermore, AEA increased COX-2 promoter activity approximately twofold above baseline in a fragment ranging from -1432 to +59, the full-length of the COX-2 promoter, and the increase in COX-2 promoter activity produced by AEA was partially inhibited by AM-251. These results indicate that AEA increased COX-2 expression at the transcriptional level through, at least in part, a cannabinoid receptor-1-mediated mechanism in cerebral microvascular endothelium.

Food for thought: endocannabinoid modulation of lipogenesis

An emerging body of evidence implicates peripheral and central endocannabinoid pathways in the regulation of feeding behavior and body weight. A report in this issue of the JCI demonstrates the presence of a common endocannabinoid-regulated molecular pathway for peripheral lipogenic and central appetitive regulation. This pathway involves the activation of the transcription factor SREBP-1c and its associated enzymes, acetyl-CoA carboxylase-1 and fatty acid synthase, in the liver and hypothalamus. Activation of cannabinoid receptor 1 (CB(1)) in liver plays a key role in increased serum lipid production, fatty liver, and possibly diet-induced obesity. Conversely, stimulation of these receptors in the hypothalamus may lead to an increase in food consumption. Thus, targeting both of these pathways with CB(1) antagonists could promote sustained weight loss and favorable serum lipid profiles in obese patients.

Metabolism of anandamide in cerebral microvascular endothelial cells

Anandamide (N-arachidonoylethanolamine, AEA), an endogenous cannabinoid receptor agonist, causes potent vasodilation in the cerebral circulation through an endothelial-dependent or -independent mechanism. We have investigated the processing of [3H]AEA in cultured mouse cerebral microvascular endothelial cells (MEC) in order to better understand its mechanism of action in the cerebral vasculature. These cells took up anandamide very quickly, reaching a maximum value in 5 min and remaining at that level for at least 8 h. Analysis of the cell lipids demonstrated that, in addition to free anandamide, radioactivity was incorporated into phosphatidylcholine (PC), phosphatidylinositol (PI), and phosphatidylethanolamine (PE) in a time-dependent manner. Analysis of the hydrolyzed cell lipids indicated that anandamide was converted to arachidonic acid, a process that was inhibited by the selective fatty acid amide hydrolase inhibitor oleyl trifluoromethyl ketone (OTMK). Phospholipase A2 (PLA2) hydrolysis of the PC, PI, and PE fractions indicated that the arachidonic acid formed from anandamide was esterified predominately into sn-2 position of the endothelial phospholipids. Furthermore, anandamide and arachidonic acid were released when the cells were incubated with A23187. These results suggest that the biological activity of anandamide might be regulated by its rapid uptake and calcium-dependent release in endothelial cells, and conversion of anandamide to arachidonic acid might serve as an inactivation process in the cerebral microcirculation.

Waterborne Lead Exposure Affects Brain Endocannabinoid Content in Male but not Female Fathead Minnows (Pimephales promelas)

There are several similarities between the behavioral and neurochemical effects of lead (Pb2+) and the cannabinoids. Both Pb2+ exposure and cannabinoid treatment decrease exploratory behavior. Pb2+-induced hyperactivity has been observed in rats and fish. By comparison, cannabinoids increase locomotor activity at higher doses in rats. Moreover, Pb2+ exposure produces learning and memory impairments as do the cannabinoids. Many of the behavioral effects of Pb2+ are thought to be due, in part, to the ability of Pb2+ to either inhibit or mimic the actions of calcium (Ca2+). At low concentrations, Pb2+ enhances basal release of neurotransmitter from presynaptic terminals by increasing intracellular free Ca2+ concentrations. Pb2+ also decreases evoked neurotransmitter release due to blockade of voltage-gated Ca2+ channels. Interestingly, the endocannabinoids (eCBs) including N-arachidonylethanolamine (AEA) and 2-arachidonylglycerol (2-AG) are synthesized in response to increases in intracellular Ca2+ and activate the CB1 receptor that inhibits voltage-gated Ca2+ channels. We tested the hypothesis that waterborne Pb2+ exposure significantly affects whole-brain eCB content in adult male and female fathead minnows (Pimephales promelas). Waterborne Pb2+ exposure (1.0 ppm) resulted in a time-dependent accumulation of Pb2+ in bone in both males and females. Brain AEA and 2-AG content were significantly greater in females compared to males. Pb2+ exposure increased brain AEA content in males at 7 and 14 days of exposure and increased brain 2-AG content at 14 days. Pb2+ exposure had no effect on either brain AEA or 2-AG content in females at any of the time points examined. As eCBs serve as activity-dependent retrograde inhibitors of neurotransmitter release, the increase in brain eCB content would accentuate Pb2+-induced decreases in evoked neurotransmitter release in male but not female fathead minnows.

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.

Evidence against the presence of an anandamide transporter

On the basis of temperature dependency, saturability, selective inhibition, and substrate specificity, it has been proposed that an anandamide transporter exists. However, all of these studies have examined anandamide accumulation at long time points when downstream effects such as metabolism and intracellular sequestration are operative. In the current study, we have investigated the initial rates (<1 min) of anandamide accumulation in neuroblastoma and astrocytoma cells in culture and have determined that uptake is not saturable with increasing concentrations of anandamide. However, anandamide hydrolysis, after uptake in neuroblastoma cells, was saturable at steady-state time points (5 min), suggesting that fatty acid amide hydrolase (FAAH) may be responsible for observed saturation of uptake at long time points. In general, arvanil, olvanil, and N-(4-hydroxyphenyl)arachidonylamide (AM404) have been characterized as transport inhibitors in studies using long incubations. However, we found these "transport inhibitors" did not inhibit anandamide uptake in neuroblastoma and astrocytoma cells at short time points (40 sec or less). Furthermore, we confirmed that these inhibitors in vitro were actually inhibitors of FAAH. Therefore, the likely mechanism by which the transport inhibitors raise anandamide levels to exert pharmacological effects is by inhibiting FAAH, and they should be reevaluated in this context. Immunofluorescence has indicated that FAAH staining resides mainly on intracellular membranes of neuroblastoma cells, and this finding is consistent with our observed kinetics of anandamide hydrolysis. In summary, these data suggest that anandamide uptake is a process of simple diffusion. This process is driven by metabolism and other downstream events, rather than by a specific membrane-associated anandamide carrier.

Arachidonic acid release and prostaglandin F(2alpha) formation induced by anandamide and capsaicin in PC12 cells

Anandamide, an endogenous agonist of cannabinoid receptors, activates various signal transduction pathways. Anandamide also activates vanilloid VR(1) receptor, which was a nonselective cation channel with high Ca(2+) permeability and had sensitivity to capsaicin, a pungent principle in hot pepper. The effects of anandamide and capsaicin on arachidonic acid metabolism in neuronal cells have not been well established. We examined the effects of anandamide and capsaicin on arachidonic acid release in rat pheochromocytoma PC12 cells. Both agents stimulated [3H]arachidonic acid release in a concentration-dependent manner from the prelabeled PC12 cells even in the absence of extracellular CaCl(2). The effect of anandamide was neither mimicked by an agonist nor inhibited by an antagonist for cannabinoid receptors. The effects of anandamide and capsaicin were inhibited by phospholipase A(2) inhibitors, but not by an antagonist for vanilloid VR(1) receptor. In PC12 cells preincubated with anandamide or capsaicin, [3H]arachidonic acid release was marked and both agents were no more effective. Co-addition of anandamide or capsaicin synergistically enhanced [3H]arachidonic acid release by mastoparan in the absence of CaCl(2). Anandamide stimulated prostaglandin F(2alpha) formation. These findings suggest that anandamide and capsaicin stimulated arachidonic acid metabolism in cannabinoid receptors- and vanilloid VR(1) receptor-independent manner in PC12 cells. The possible mechanisms are also discussed.

From cannabis to cannabinergics: new therapeutic opportunities

The molecular basis of cannabinoid activity is better understood since the discovery of the CB(1) receptor in the mammalian brain and the CB(2) receptor in peripheral tissues. Subsequently, an endogenous CB(1) receptor ligand, arachidonylethanolamide (anandamide), was isolated from porcine brain and shown to be metabolized by the enzyme arachidonylethanolamide amidohydrolase or fatty acid amide hydrolase. Recently, we have characterized a reuptake system for the transport of anandamide across the cell membrane, and have shown that selective inhibition of this transporter is associated with analgesia and peripheral vasodilation. The four cannabinoid system proteins, including the CB(1) and CB(2) receptors, fatty acid amide hydrolase, and the anandamide transporter, are excellent targets for the development of novel medications for various conditions, including pain, immunosuppression, peripheral vascular disease, appetite enhancement or suppression, and motor disorders. During the last decade, numerous selective ligands for each of these proteins were designed and synthesized. Many of these agents serve as important molecular probes, providing structural information about their binding sites, as well as pharmacological tools imparting information about the roles of their targets in physiological and disease states. All of the above compounds that modulate the functions of the endocannabinoid system can be collectively described under the term cannabinergics, regardless of chemical classification or type of resultant pharmacological action.

Putative neuroprotective actions of N-acyl-ethanolamines

N-Acyl-ethanolamines (NAEs) and their precursors, N-acyl-ethanolamine phospholipids (NAPEs), are present in the mammalian brain at levels of a few hundred picomoles/gram tissue and a few nanomoles/gram tissue, respectively. NAE-containing arachidonic acid is called anandamide, and it has attracted particular attention since it is a partial agonist for the cannabinoid receptors, for which 2-arachidonoylglycerol is the full agonist. In addition, anandamide may also activate the vanilloid receptor. Anandamide usually amounts to 1-10% of NAEs, as the vast majority of N-acyl groups are saturated and monounsaturated fatty acids. Formation of NAPE and NAE is catalyzed by an N-acyltransferase and an NAPE-hydrolyzing phospholipase D, respectively, two enzymes that have been characterized only preliminary. Interestingly, NAPEs and NAEs accumulate in the brain in response to neurodegenerative insults at a time when other phospholipids are subjected to rapid degradation. This is an important biosynthetic aspect of NAPE and NAE, as NAEs may be neuroprotective by a number of different mechanisms involving both receptor activation and non-receptor-mediated effects, e.g. by binding to cannabinoid receptors and interfering with ceramide turnover, respectively.

Fatty acid amide hydrolase localization in the human central nervous system: an immunohistochemical study

Recent discoveries have opened new fields for research on the biochemistry and pharmacology of cannabinoids. Among them, and most importantly, are the characterization and molecular cloning of central and peripheral cannabinoid receptors as well as the isolation of the first putative endogenous ligands that bind to them, anandamide and 2-arachidonylglycerol. The enzyme that degrades these so-called "endocannabinoids" is an integral membrane protein, fatty acid amide hydrolase. Its distribution and biochemistry in rat brain suggest that it plays a critical role in the regulation of the endocannabinoid system. However, few data exist regarding its distribution and mechanism of action in human tissues. To that end, we have studied its cellular distribution in the human central nervous system by immunohistochemistry. Using an affinity-purified antibody, we report that fatty acid amide hydrolase is localized to specific and well-delimited cell populations, including cortical pyramidal neurons, subcortical white matter astrocytes, striatal and striatoefferent projecting neurons, hypothalamic and midbrain nuclei, granular and molecular layers of the cerebellum, Purkinje neurons, dentate cerebellar nucleus, inferior olivary nuclei and others. This distribution resembles that of the central cannabinoid receptors as well as that of the enzyme distribution in the rat brain. In summary, the cellular localization of the degradative enzyme of the endogenous cannabinoid ligands in human central nervous system reveals its presence on both neuronal and glial elements and shows a significant overlapping with that of central cannabinoid receptors, mainly in areas related with motor control, confirming the notion that the endocannabinoid system plays a critical role in the control of movement.

Anandamide and diet: inclusion of dietary arachidonate and docosahexaenoate leads to increased brain levels of the corresponding N-acylethanolamines in piglets

Endogenous ligands of cannabinoid receptors have been discovered recently and include some N-acylethanolamines (NAEs; e.g., N-arachidonoylethanolamine) and some 2-acylglycerols (e.g., sn-2-arachidonoylglycerol). Previously, we found these compounds to be active biologically when administered per os in large quantities to mice. In the present work, piglets were fed diets with and without 20:4n-6 and 22:6n-3 fatty acid precursors of NAEs, in levels similar to those found in porcine milk, during the first 18 days of life, and corresponding brain NAEs were assessed. In piglets fed diets containing 20:4n-6 and 22:6n-3, there were increases in several biologically active NAEs in brain homogenates-20:4n-6 NAE (4-fold), 20:5n-3 NAE (5-fold), and 22:5n-3 and 22:6n-3 NAE (9- to 10-fold). These results support a mechanism we propose for dietary long-chain polyunsaturated fatty acids influences on brain biochemistry with presumed functional sequelae. This paradigm will enable targeted investigations to determine whether and why specific populations such as infants, elderly, or persons suffering from certain clinical conditions may benefit from dietary long-chain polyunsaturated fatty acids.

The activity of anandamide at vanilloid VR1 receptors requires facilitated transport across the cell membrane and is limited by intracellular metabolism

The endogenous ligand of CB(1) cannabinoid receptors, anandamide, is also a full agonist at vanilloid VR1 receptors for capsaicin and resiniferatoxin, thereby causing an increase in cytosolic Ca(2+) concentration in human VR1-overexpressing (hVR1-HEK) cells. Two selective inhibitors of anandamide facilitated transport into cells, VDM11 and VDM13, and two inhibitors of anandamide enzymatic hydrolysis, phenylmethylsulfonyl fluoride and methylarachidonoyl fluorophosphonate, inhibited and enhanced, respectively, the VR1-mediated effect of anandamide, but not of resiniferatoxin or capsaicin. The nitric oxide donor, sodium nitroprusside, known to stimulate anandamide transport, enhanced anandamide effect on the cytosolic Ca(2+) concentration. Accordingly, hVR1-HEK cells contain an anandamide membrane transporter inhibited by VDM11 and VDM13 and activated by sodium nitroprusside, and an anandamide hydrolase activity sensitive to phenylmethylsulfonyl fluoride and methylarachidonoyl fluorophosphonate, and a fatty acid amide hydrolase transcript. These findings suggest the following. (i) Anandamide activates VR1 receptors by acting at an intracellular site. (ii) Degradation by fatty acid amide hydrolase limits anandamide activity on VR1; and (iii) the anandamide membrane transporter inhibitors can be used to distinguish between CB(1) or VR1 receptor-mediated actions of anandamide. By contrast, the CB(1) receptor antagonist SR141716A inhibited also the VR1-mediated effect of anandamide and capsaicin on cytosolic Ca(2+) concentration, although at concentrations higher than those required for CB(1) antagonism.

Cannabinoid receptor activation and elevated cyclic AMP reduce glutamate neurotoxicity

Cannabinoid receptor activation in vivo reduces ischemic injury, a phenomenon that has not been successfully reproduced in vitro. Because cyclic adenosine monophosphate (cAMP) levels are radically elevated during ischemic reperfusion, but cannabinoid receptor activation reduces cAMP levels, we hypothesized that cannabinoids might prevent in vitro glutamate toxicity if reperfusion was simulated by cAMP supplementation after glutamate removal. Although neuronal cultures were unaffected by the single addition of either cannabinoid or dibutyryl cAMP (dbcAMP), glutamate toxicity was reduced by 20% when cannabinoid was present during glutamate exposure and either dbcAMP or forskolin was added after glutamate removal. Further studies revealed that cannabinoid receptor activation reduces glutamate toxicity by attenuating calcium influx through N- and P/Q-type calcium channels. The effect of glutamate exposure on neuronal cAMP levels was also examined. Glutamate exposure significantly reduced neuronal cAMP levels, although suppression was even greater when cannabinoid was present. Because neurological outcome after ischemia is poor when cAMP levels during reperfusion are low, it is hypothesized that cAMP elevation after glutamate exposure may offset excitotoxic and/or cannabinoid receptor-induced cAMP depletion. Cannabinoids protect against ischemic injury in vivo, but only reduce toxicity in vitro when cAMP levels are elevated, possibly suggesting that cAMP elevation during reperfusion reduces brain injury by off-setting the effect of Gi/o protein-coupled systems on adenylate cyclase.

The cellular uptake of anandamide is coupled to its breakdown by fatty-acid amide hydrolase

Anandamide is an endogenous compound that acts as an agonist at cannabinoid receptors. It is inactivated via intracellular degradation after its uptake into cells by a carrier-mediated process that depends upon a concentration gradient. The fate of anandamide in those cells containing an amidase called fatty-acid amide hydrolase (FAAH) is hydrolysis to arachidonic acid and ethanolamine. The active site nucleophilic serine of FAAH is inactivated by a variety of inhibitors including methylarachidonylfluorophosphonate (MAFP) and palmitylsulfonyl fluoride. In the current report, the net uptake of anandamide in cultured neuroblastoma (N18) and glioma (C6) cells, which contain FAAH, was decreased by nearly 50% after 6 min of incubation in the presence of MAFP. Uptake in laryngeal carcinoma (Hep2) cells, which lack FAAH, is not inhibited by MAFP. Free anandamide was found in all MAFP-treated cells and in control Hep2 cells, whereas phospholipid was the main product in N18 and C6 control cells when analyzed by TLC. The intracellular concentration of anandamide in N18, C6, and Hep2 cells was up to 18-fold greater than the extracellular concentration of 100 nm, which strongly suggests that it is sequestered within the cell by binding to membranes or proteins. The accumulation of anandamide and/or its breakdown products was found to vary among the different cell types, and this correlated approximately with the amount of FAAH activity, suggesting that the breakdown of anandamide is in part a driving force for uptake. This was shown most clearly in Hep2 cells transfected with FAAH. The uptake in these cells was 2-fold greater than in vector-transfected or untransfected Hep2 cells. Therefore, it appears that FAAH inhibitors reduce anandamide uptake by cells by shifting the anandamide concentration gradient in a direction that favors equilibrium. Because inhibition of FAAH increases the levels of extracellular anandamide, it may be a useful target for the design of therapeutic agents.

Loss of cannabinoid-stimulated guanosine 5'-O-(3-[(35)S]Thiotriphosphate) binding without receptor down-regulation in brain regions of anandamide-tolerant rats

The endogenous cannabinoid anandamide has been reported to produce well-defined behavioral tolerance, but studies on the possible mechanisms underlying this process are few and often contradictory. The present study was designed to survey the cellular events involved in anandamide tolerance, in terms of the effects on receptor number, coupling with G proteins, and activation of the cyclic AMP (cAMP) cascade. Chronic treatment of rats with anandamide (20 mg/kg i.p. for 15 days) resulted in behavioral tolerance without any change in cannabinoid receptor binding in the brain regions studied (striatum, cortex, hippocampus, and cerebellum), suggesting that receptor down-regulation was not involved in the development of anandamide behavioral tolerance. In contrast, prolonged exposure to anandamide significantly reduced agonist-stimulated guanosine 5'-O:-(3-[(35)S]thiotriphosphate) binding in the same areas, with losses of >50%, suggesting that receptor desensitization may be part of the molecular mechanism underlying this tolerance. Finally, concerning the cAMP cascade-the most well-known intracellular signaling pathways activated by CB(1) receptors-in the brain regions from rats tolerant to anandamide, we found no alteration in cAMP levels or in protein kinase A activity. We propose that anandamide, unlike Delta(9)-tetrahydrocannabinol and other cannabinoids, does not alter the receptor system at multiple levels but that desensitization of the CB(1) receptor might account for behavioral tolerance to the drug.

Endocannabinoids and fatty acid amides in cancer, inflammation and related disorders

The long history of the medicinal use of Cannabis sativa and, more recently, of its chemical constituents, the cannabinoids, suggests that also the endogenous ligands of cannabinoid receptors, the endocannabinoids, and, particularly, their derivatives may be used as therapeutic agents. Studies aimed at correlating the tissue and body fluid levels of endogenous cannabinoid-like molecules with pathological conditions have been started and may lead to identify those diseases that can be alleviated by drugs that either mimic or antagonize the action of these substances, or modulate their biosynthesis and degradation. Hints for the therapeutic applications of endocannabinoids, however, can be obtained also from our previous knowledge of marijuana medicinal properties. In this article, we discuss the anti-tumor and anti-inflammatory activity of: (1) the endocannabinoids anandamide (arachidonoylethanolamide) and 2-arachidonoyl glycerol; (2) the bioactive fatty acid amides palmitoylethanolamide and oleamide; and (3) some synthetic derivatives of these compounds, such as the N-acyl-vanillyl-amines. Furthermore, the possible role of cannabimimetic fatty acid derivatives in the pathological consequences of cancer and inflammation, such as cachexia, wasting syndrome, chronic pain and local vasodilation, will be examined.

The movement of N-arachidonoylethanolamine (anandamide) across cellular membranes

This review presents and explores the hypothesis that N-arachidonoylethanolamine (AEA, also called anandamide) is transported across cellular membranes by a process that is protein-mediated. Support for this hypothesis comes from experiments demonstrating that cellular accumulation of extracellularly applied AEA is saturable, time and temperature dependent and exhibits selective inhibition by various structural analogs of AEA. The accumulation of AEA is cell specific; data is presented demonstrating that several cell types, including the bovine adrenal zona glomerulosa cell, exhibit very high capacity for AEA accumulation while others, such as the HeLa cell, have a very low capacity. The transport process has the characteristics of facilitated diffusion; it is bi-directional, not dependent on either ATP or extracellular sodium and exhibits the trans effect of flux coupling. Several important questions remain to be answered regarding the carrier, including its molecular structure and its role in the release and inactivation of endogenously produced AEA.

2-Arachidonoylglycerol and the cannabinoid receptors

2-Arachidonoylglycerol (2-AG) is a unique molecular species of monoacylglycerol isolated from rat brain and canine gut as an endogenous cannabinoid receptor ligand (Sugiura, T., Kondo, S., Sukagawa, A., Nakane, S., Shinoda, A., Itoh, K., Yamashita, A., Waku, K., 1995. 2-Arachidonoylglycerol: a possible endogenous cannabinoid receptor ligand in brain. Biochem. Biophys. Res. Commun. 215, 89-97; Mechoulam, R., Ben-Shabat, S., Hanus, L., Ligumsky, M., Kaminski, N. E., Schatz, A.R., Gopher, A., Almog, S., Martin, B.R., Compton, D.R., Pertwee, R.G., Giffin, G., Bayewitch, M., Brag, J., Vogel, Z., 1995. Identification of an endogenous 2-monoglyceride, present in canine gut, that binds to cannabinoid receptors. Biochem. Pharmacol. 50, 83-90). 2-AG binds to the cannabinoid receptors (CB1 and CB2) and exhibits a variety of cannabimimetic activities in vitro and in vivo. Recently, we found that 2-AG induces Ca(2+) transients in NG108-15 cells, which express the CB1 receptor, and in HL-60 cells, which express the CB2 receptor, through a cannabinoid receptor- and Gi/Go-dependent mechanism. Based on the results of structure-activity relationship experiments, we concluded that 2-AG but not anandamide is the natural ligand for both the CB1 and the CB2 receptors and both receptors are primarily 2-AG receptors. Evidences are gradually accumulating that 2-AG is a physiologically essential molecule, although further detailed studies appear to be necessary to determine relative importance of 2-AG and anandamide in various animal tissues. In this review, we described mainly our previous and current experimental results, as well as those of others, concerning the tissue levels, bioactions and metabolism of 2-AG.

Pathways and mechanisms of N-acylethanolamine biosynthesis: can anandamide be generated selectively?

Long-chain N-acylethanolamines (NAEs) and their precursors, N-acylethanolamine phospholipids, are ubiquitous trace constituents of animal and human cells, tissues and body fluids. Their cellular levels appear to be tightly regulated and they accumulate as the result of injury. Saturated and monounsaturated congeners which represent the vast majority of cellular NAEs can have cytoprotective effects while polyunsaturated NAEs, especially 20:4n-6 NAE (anandamide), elicit physiological effects by binding to and activating cannabinoid receptors. It is the purpose of this article to review published data on the pathways and mechanisms of NAE biosynthesis in mammals and to evaluate this information for its physiological significance. The generation and turnover of NAE via N-acyl PE through the transacylation-phosphodiesterase pathway may represent a novel cannabinoid receptor-independent signalling system, analogous to and possibly related to ceramide-mediated cell signalling.

N-Acylethanolamines and precursor phospholipids - relation to cell injury

The present review focuses on the relationship between formation of N-acylethanolamine phospholipids (NAPEs) and N-acyletransferase (NAEs) catalyzed by N-acyltranferase and NAPE-hydrolyzing phospholipase D, respectively, and cell injury in tissues like brain, heart, and testis. A number of mechanisms are proposed by which these two groups of lipids may have cytoprotective properties. The mechanisms may involve activation of cannabinoid receptors, as well as non-receptor-mediated effects such as stabilization of membrane bilayers, antioxidant mechanisms, inhibition of calcium leakage from mitochondria, and direct inhibition of ceramidase. Anandamide (20:4-NAE) is formed as a minor component along with other NAEs during cell injury. Whether 20:4-NAE has a separate physiological role is at present not known, but some data suggest that 20:4-NAE may be formed, e.g. in the uterus, by a more selective mechanism without being accompanied by a vast majority of saturated and monounsaturated NAEs.