Stereoselective modulatory actions of oleamide on GABA(A) receptors and voltage-gated Na(+) channels in vitro: a putative endogenous ligand for depressant drug sites in CNS

Brain Metabolomics in Fragile X-Associated Tremor/Ataxia Syndrome (FXTAS)

The course of pathophysiological mechanisms involved in fragile X-associated tremor/ataxia syndrome (FXTAS) remains largely unknown. Previous proteomics and metabolomics studies conducted in blood samples collected from FMR1 premutation carriers with FXTAS reported abnormalities in energy metabolism, and precursors of gluconeogenesis showed significant changes in plasma expression levels in FMR1 premutation carriers who developed FXTAS. We conducted an analysis of postmortem human brain tissues from 44 donors, 25 brains with FXTAS, and 19 matched controls. We quantified the metabolite relative abundance in the inferior temporal gyrus and the cerebellum using untargeted mass spectrometry (MS)-based metabolomics. We investigated how the metabolite type and abundance relate to the number of cytosine-guanine-guanine (CGG) repeats, to markers of neurodegeneration, and to the symptoms of FXTAS. A metabolomic analysis identified 191 primary metabolites, the data were log-transformed and normalized prior to the analysis, and the relative abundance was compared between the groups. The changes in the relative abundance of a set of metabolites were region-specific with some overlapping results; 22 metabolites showed alterations in the inferior temporal gyrus, while 21 showed differences in the cerebellum. The relative abundance of cytidine was decreased in the inferior temporal gyrus, and a lower abundance was found in the cases with larger CGG expansions; oleamide was significantly decreased in the cerebellum. The abundance of 11 metabolites was influenced by changes in the CGG repeat number. A histological evaluation found an association between the presence of microhemorrhages in the inferior temporal gyrus and a lower abundance of 2,5-dihydroxypyrazine. Our study identified alterations in the metabolites involved in the oxidative-stress response and bioenergetics in the brains of individuals with FXTAS. Significant changes in the abundance of cytidine and oleamide suggest their potential as biomarkers and therapeutic targets for FXTAS.

Garcinia oligantha: A comprehensive overview of ethnomedicine, phytochemistry and pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Garcinia oligantha Merr. is an ethnomedicine plant mainly distributed in Guangdong and Hainan, China. It has the effects of heat-clearing and detoxicating, which has been used by local ethnic minorities to treat a variety of diseases, including inflammation, internal heat, toothache and scald.

THE AIM OF THE REVIEW

This review summarizes and discusses the progress of the chemical compounds and biological activities of G. oligantha that have been studied in recent years to provide the direction for the prospective research and applications of G. oligantha.

MATERIALS AND METHODS

The relevant literature about G. oligantha was accessible from ancient Chinese medical books and records, theses, as well as major scientific databases such as Google Scholar, PubMed, Web of Science, ScienceDirect, SciFinder, Baidu Scholar and China National Knowledge Infrastructure (CNKI).

RESULTS

To date, more than 150 chemical compounds were isolated from this plant, including xanthones, volatile oil, fatty acid, benzofurane derivative and biphenyl compounds. Xanthones are the main bioactive compounds that exhibit diverse biological effects, such as antitumor, analgesic, anti-inflammatory, antioxidative, neuroprotective, antimalarial and antibacterial effects, which are consistent with its traditional uses as a folk medicine. Modern pharmacological studies show that these compounds participate in a variety of signaling pathways underlying different pathophysiologies, making them a valuable medicinal resource.

CONCLUSION

G. oligantha is an ethnomedicine with a long history. However, due to regional and cultural constraints, the popularisation and use of ethnomedicine are still limited. Modern pharmacological and chemical research suggest that G. oligantha contains a variety of bioactive compounds and showed diverse biological functions, which is worthy of comprehensive and in-depth research. This review summarizes and discusses the recent progress in studies on G. oligantha, looking forward to promote further research and sustainable development of folk medicinal plants.

Oleamide Reduces Mitochondrial Dysfunction and Toxicity in Rat Cortical Slices Through the Combined Action of Cannabinoid Receptors Activation and Induction of Antioxidant Activity

The potential treatment of neurodegenerative disorders requires the development of novel pharmacological strategies at the experimental level, such as the endocannabinoid-based therapies. The effects of oleamide (OEA), a fatty acid primary amide with activity on cannabinoid receptors, was tested against mitochondrial toxicity induced by the electron transport chain complex II inhibitor, 3-nitropropionic acid (3-NP), in rat cortical slices. OEA prevented the 3-NP-induced loss of mitochondrial function/cell viability at a concentration range of 5 nM-25 µM, and this protective effect was observed only when the amide was administered as pretreatment, but not as post-treatment. The preservation of mitochondrial function/cell viability induced by OEA in the toxic model induced by 3-NP was lost when the slices were pre-incubated with the cannabinoid receptor 1 (CB1R) selective inhibitor, AM281, or the cannabinoid receptor 2 (CB2R) selective inhibitor, JTE-907. The 3-NP-induced inhibition of succinate dehydrogenase (mitochondrial Complex II) activity was recovered by 25 nM OEA. The amide also prevented the increased lipid peroxidation and the changes in reduced/oxidized glutathione (GSH/GSSG) ratio induced by 3-NP. The cell damage induced by 3-NP, assessed as incorporation of cellular propidium iodide, was mitigated by OEA. Our novel findings suggest that the neuroprotective properties displayed by OEA during the early stages of damage to cortical cells involve the converging activation of CB1R and CB2R and the increase in antioxidant activity, which combined may emerge from the preservation of the functional integrity of mitochondria.

Serotonin 2A receptors and cannabinoids

Accumulating evidence has proven that both exogenous cannabinoids as well as imbalances in the endocannabinoid system are involved in the onset and development of mental disorders such as anxiety, depression, or schizophrenia. Extensive recent research in this topic has mainly focused on the molecular mechanisms by which cannabinoid agonists may contribute to the pathophysiology of these disorders. Initially, serotonin neurotransmitter garnered most attention due to its relationship to mood disorders and mental diseases, with little attention to specific receptors. To date, the focus has redirected toward the understanding of different serotonin receptors, through a demonstration of its versatile pharmacology and synergy with different modulators. Serotonin 2A receptors are a good example of this phenomenon, and the complex signaling that they trigger appears of high relevance in the context of mental disorders, especially in schizophrenia. This chapter will analyze most relevant attributes of serotonin 2A receptors and the endocannabinoid system, and will highlight the evidence toward the functional bidirectional interaction between these elements in the brain as well as the impact of the endocannabinoid system dysregulation on serotonin 2A receptors functionality.

In Vitro Bioassay-Guided Identification of Anticancer Properties from Moringa oleifera Lam. Leaf against the MDA-MB-231 Cell Line

Moringa oleifera Lam. (MO) is a medicinal plant distributed across the Middle East, Asia, and Africa. MO has been used in the traditional treatment of various diseases including cancer. This study aimed to perform bioassay-guided fractionation and identification of bioactive compounds from MO leaf against MDA-MB-231 breast cancer cells. MO leaf was sequentially extracted with hexane, ethyl acetate (EtOAc), and ethanol. The most effective extract was subjected to fractionation. MO extract and its derived fractions were continuously screened for anti-cancer activities. The strongest fraction was selected for re-fractionation and identification of bioactive compounds using LC-ESI-QTOF-MS/MS analysis. The best anticancer activities were related to the fraction no. 7-derived crude EtOAc extract. This fraction significantly reduced cell viability and clonogenic growth and increased cells apoptosis. Moreover, sub-fraction no. 7.7-derived fraction no. 7 was selected for the identification of bioactive compounds. There were 10 candidate compounds tentatively identified by LC-ESI-QTOF-MS. Three of identified compounds (7-octenoic acid, oleamide, and 1-phenyl-2-pentanol) showed anticancer activities by inducing cell cycle arrest and triggering apoptosis through suppressed Bcl-2 expression which subsequently promotes activation of caspase 3, indicators for the apoptosis pathway. This study identified 10 candidate compounds that may have potential in the field of anticancer substances.

Antiepileptic and Neuroprotective Effects of Oleamide in Rat Striatum on Kainate-Induced Behavioral Seizure and Excitotoxic Damage via Calpain Inhibition

Oleamide was first known as a sleep-inducing fatty acid amide, and later shown to have wide range of neuropharmacological effects upon different neurochemical systems. However, the effects of oleamide on brain damage have scarcely been studied, and the molecular mechanisms and sites of its action remain elusive. Kainic acid (KA) has been used to produce an epileptic animal model that mimics human temporal lobe epilepsy and to induce calpain-activated excitotoxicity, which occurs in numerous neurodegenerative disorders. In this study, we examined whether oleamide protects against the KA-induced excitotoxic brain damage accompanied by behavioral seizure activity and neuronal cell death. Moreover, whether these effects of oleamide were mediated by calpain activity-related cellular mechanisms was investigated. KA-induced epileptic rats were produced by an intrastriatal injection of KA (5 nmole). Oral administration of oleamide (0.5, 2, and 10 mg/kg) 30 min prior to the KA injection showed dose-dependent inhibition of the KA-induced behavioral seizure activities that were monitored starting from 60 to 180 min post-surgery. Further repetitive oral administration of oleamide (once per day) for the next 4 consecutive days post-KA injection produced significant neuroprotection against the disrupted neuronal integrity that resulted from KA-induced excitotoxic damage that was also demonstrated by staining of striatal tissue sections with cresyl violet, hematoxylin/eosin, and fluoro-Jade B. In addition, oleamide blocked the KA-induced cleavage of cyclin-dependent kinase-5 coactivator (Cdk5-p35) and collapsin response mediator protein-2, which are believed to be mediated by calpain activation in striatal tissues dissected from KA-induced epileptic rats. Oleamide also reversed the KA-induced reduction in expression of an endogenous calpain inhibitory protein, calpastatin, and a marker of synaptic activity, synapsin-II. The hypothesis that oleamide could induce direct calpain inhibition was further investigated using in vitro calpain assays in both brain tissue and a cell-free and calpain-overexpressed neuronal cell system. These findings together suggest that oleamide has protective effects against excitotoxicity-induced neuronal death and behavioral seizure, partly via its direct calpain inhibitory activity.

Passiflora incarnata attenuation of neuropathic allodynia and vulvodynia apropos GABA-ergic and opioidergic antinociceptive and behavioural mechanisms

Background

Passiflora incarnata is widely used as an anxiolytic and sedative due to its putative GABAergic properties. Passiflora incarnata L. methanolic extract (PI-ME) was evaluated in an animal model of streptozotocin-induced diabetic neuropathic allodynia and vulvodynia in rats along with antinociceptive, anxiolytic and sedative activities in mice in order to examine possible underlying mechanisms.

Methods

PI-ME was tested preliminary for qualitative phytochemical analysis and then quantitatively by proximate and GC-MS analysis. The antinociceptive property was evaluated using the abdominal constriction assay and hot plate test. The anxiolytic activity was performed in a stair case model and sedative activity in an open field test. The antagonistic activities were evaluated using naloxone and/or pentylenetetrazole (PTZ). PI-ME was evaluated for prospective anti-allodynic and anti-vulvodynic properties in a rat model of streptozotocin induced neuropathic pain using the static and dynamic testing paradigms of mechanical allodynia and vulvodynia.

Results

GC-MS analysis revealed that PI-ME contained predominant quantities of oleamide (9-octadecenamide), palmitic acid (hexadecanoic acid) and 3-hydroxy-dodecanoic acid, among other active constituents. In the abdominal constriction assay and hot plate test, PI-ME produced dose dependant, naloxone and pentylenetetrazole reversible antinociception suggesting an involvement of opioidergic and GABAergic mechanisms. In the stair case test, PI-ME at 200 mg/kg increased the number of steps climbed while at 600 mg/kg a significant decrease was observed. The rearing incidence was diminished by PI-ME at all tested doses and in the open field test, PI-ME decreased locomotor activity to an extent that was analagous to diazepam. The effects of PI-ME were antagonized by PTZ in both the staircase and open field tests implicating GABAergic mechanisms in its anxiolytic and sedative activities. In the streptozotocin-induced neuropathic nociceptive model, PI-ME (200 and 300 mg/kg) exhibited static and dynamic anti-allodynic effects exemplified by an increase in paw withdrawal threshold and paw withdrawal latency. PI-ME relieved only the dynamic component of vulvodynia by increasing flinching response latency.

Conclusions

These findings suggest that Passiflora incarnata might be useful for treating neuropathic pain. The antinociceptive and behavioural findings inferring that its activity may stem from underlying opioidergic and GABAergic mechanisms though a potential oleamide-sourced cannabimimetic involvement is also discussed.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-016-1048-6) contains supplementary material, which is available to authorized users.

Fatty acid amide signaling molecules

Key studies leading to the discovery and definition of the role of endogenous fatty acid amide signaling molecules are summarized.

Properties of gap junction blockers and their behavioural, cognitive and electrophysiological effects: animal and human studies

Gap junctions play an important role in brain physiology. They synchronize neuronal activity and connect glial cells participating in the regulation of brain metabolism and homeostasis. Gap junction blockers (GJBs) include various chemicals that impair gap junction communication, disrupt oscillatory neuronal activity over a wide range of frequencies, and decrease epileptic discharges. The behavioural and clinical effects of GJBs suggest that gap junctions can be involved in the regulation of locomotor activity, arousal, memory, and breathing. Severe neuropsychiatric side effects suggest the involvement of gap junctions in mechanisms of consciousness. Unfortunately, the available GJBs are not selective and can bind to targets other than gap junctions. Other problems in behavioural studies include the possible adverse effects of GJBs, for example, retinal toxicity and hearing disturbances, changes in blood-brain transport, and the metabolism of other drugs. Therefore, it is necessary to design experiments properly to avoid false, misleading or uninterpretable results. We review the pharmacological properties and electrophysiological, behavioural and cognitive effects of the available gap junction blockers, such as carbenoxolone, glycyrrhetinic acid, quinine, quinidine, mefloquine, heptanol, octanol, anandamide, fenamates, 2-APB, several anaesthetics, retinoic acid, oleamide, spermine, aminosulfonates, and sodium propionate. It is concluded that despite a number of different problems, the currently used gap junction blockers could be useful tools in pharmacology and neuroscience.

Effect of oleamide on pentylenetetrazole-induced seizures in rats

Oleamide exhibits antiepileptic activity and significantly decreases the degree of pentylenetetrazole-induced seizures.

Biosynthesis, degradation and pharmacological importance of the fatty acid amides

The identification of two biologically active fatty acid amides, N-arachidonoylethanolamine (anandamide) and oleamide, has generated a great deal of excitement and stimulated considerable research. However, anandamide and oleamide are merely the best-known and best-understood members of a much larger family of biologically occurring fatty acid amides. In this review, we will outline which fatty acid amides have been isolated from mammalian sources, detail what is known about how these molecules are made and degraded in vivo, and highlight their potential for the development of novel therapeutics.

The complications of promiscuity: endocannabinoid action and metabolism

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

Ethanolamine and related amino alcohols increase basal and evoked release of [3H]-D-aspartic acid from synaptosomes by enhancing the filling of synaptic vesicles

This research examines the effects of ethanolamine and other amino alcohols on the dynamics of acridine orange (AO), oxonol V, and [3H]-D-aspartic acid in synaptic preparations isolated from mammalian brain. Ethanolamine concentration-dependently enhanced AO release from synaptosomes. Similar effects were observed with methylethanolamine and dimethylethanolamine, but not choline. The enhancement of AO efflux by ethanolamine was independent of extrasynaptosomal calcium (in contrast to KCl-induced AO efflux), was unaffected by tetrodotoxin and did not involve depolarization of the synaptosomal plasma membrane. KCl was unable to release AO from synaptosomes following exposure to ethanolamine, however ethanolamine and other amino alcohols were found to enhance both basal and KCl-evoked release of [3H]-D-aspartic acid from synaptosomes. Using isolated synaptic vesicles we demonstrate that amino alcohols are able to 1) abolish the ATP-dependent intravesicular proton concentration (i.e. stimulate efflux of AO) in a similar way to carbonyl cyanide m-chlorophenylhydrazone (CCCP), 2) increase the ATP-supported transvesicular membrane potential (i.e. quench oxonol V fluorescence) in contrast to CCCP and 3) enhance intravesicular uptake of [3H]-D-aspartic acid. These results suggest that positively charged, membrane impermeant amino alcohol species are generated within synaptic vesicles as they sequester protons. Cationic forms of these amino alcohols boost the transvesicular electrical potential which increases transmitter uptake into synaptic vesicles and facilitates enhancement of basal and evoked release of transmitter. Our data suggest a potential role for ethanolamine and related amino alcohols in the regulation of synaptic vesicle filling. These findings may also have relevance to neuropathophysiological states involving altered production of ethanolamine.

Oleamide: A Fatty Acid Amide Signaling Molecule in the Cardiovascular System?

Oleamide (cis-9,10-octadecenoamide), a fatty acid primary amide discovered in the cerebrospinal fluid of sleep-deprived cats, has a variety of actions that give it potential as a signaling molecule, although these actions have not been extensively investigated in the cardiovascular system. The synthetic pathway probably involves synthesis of oleoylglycine and then conversion to oleamide by peptidylglycine alpha-amidating monooxygenase (PAM); breakdown of oleamide is by fatty acid amide hydrolase (FAAH). Oleamide interacts with voltage-gated Na(+) channels and allosterically with GABA(A) and 5-HT(7) receptors as well as having cannabinoid-like actions. The latter have been suggested to be due to potentiation of the effects of endocannabinoids such as anandamide by inhibiting FAAH-mediated hydrolysis. This might underlie an "entourage effect" whereby co-released endogenous nonagonist congeners of endocannabinoids protect the active molecule from hydrolysis by FAAH. However, oleamide has direct agonist actions at CB(1) cannabinoid receptors and also activates the TRPV1 vanilloid receptor. Other actions include inhibition of gap-junctional communication, and this might give oleamide a role in myocardial development. Many of these actions are absent from the trans isomer of 9,10-octadecenoamide. One of the most potent actions of oleamide is vasodilation. In rat small mesenteric artery the response does not involve CB(1) cannabinoid receptors but another pertussis toxin-sensitive, G protein-coupled receptor, as yet unidentified. This receptor is sensitive to rimonabant and O-1918, an antagonist at the putative "abnormal-cannabidiol" or endothelial "anandamide" receptors. Vasodilation is mediated by endothelium-derived nitric oxide, endothelium-dependent hyperpolarization, and also through activation of TRPV1 receptors. A physiological role for oleamide in the heart and circulation has yet to be demonstrated, as has production by cells of the cardiovascular system, but this molecule has a range of actions that could give it considerable modulatory power.

Receptor-independent actions of cannabinoids on cell membranes: Focus on endocannabinoids

Cannabinoids are a structurally diverse group of mostly lipophilic molecules that bind to cannabinoid receptors. In fact, endogenous cannabinoids (endocannabinoids) are a class of signaling lipids consisting of amides and esters of long-chain polyunsaturated fatty acids. They are synthesized from lipid precursors in plasma membranes via Ca(2+) or G-protein-dependent processes and exhibit cannabinoid-like actions by binding to cannabinoid receptors. However, endocannabinoids can produce effects that are not mediated by these receptors. In pharmacologically relevant concentrations, endocannabinoids modulate the functional properties of voltage-gated ion channels including Ca(2+) channels, Na(+) channels, various types of K(+) channels, and ligand-gated ion channels such as serotonin type 3, nicotinic acetylcholine, and glycine receptors. In addition, modulatory effects of endocannabinoids on other ion-transporting membrane proteins such as transient potential receptor-class channels, gap junctions and transporters for neurotransmitters have also been demonstrated. Furthermore, functional properties of G-protein-coupled receptors for different types of neurotransmitters and neuropeptides are altered by direct actions of endocannabinoids. Although the mechanisms of these effects are currently not clear, it is likely that these direct actions of endocannabinoids are due to their lipophilic structures. These findings indicate that additional molecular targets for endocannabinoids exist and that these targets may represent novel sites for cannabinoids to alter either the excitability of the neurons or the response of the neuronal systems. This review focuses on the results of recent studies indicating that beyond their receptor-mediated effects, endocannabinoids alter the functions of ion channels and other integral membrane proteins directly.

Oleic acid derived metabolites in mouse neuroblastoma N18TG2 cells

Oleamide is an endogenous sleep-inducing lipid that has been isolated from the cerebrospinal fluid of sleep-deprived mammals. Oleamide is the best-understood member of the primary fatty acid amide family. One key unanswered question regarding oleamide and all other primary acid amides is the pathway by which these molecules are produced. One proposed pathway involves oleoyl-CoA and N-oleoylglycine as intermediates: oleic acid --> oleoyl-CoA --> N-oleoylglycine --> oleamide. The first and third reactions are known reactions, catalyzed by acyl-CoA synthetase and peptidylglycine alpha-amidating monooxygenase (PAM). Oleoyl-CoA formation from oleic acid has been demonstrated in vitro and in vivo while, to date, N-oleoylglycine cleavage to oleamide has been established only in vitro. PAM catalyzes the final step in alpha-amidated peptide biosynthesis, and its proposed role in primary fatty acid amide biosynthesis has been controversial. Mouse neuroblastoma N(18)TG(2) cells are an excellent model system for the study of oleamide biosynthesis because these cells convert [(14)C]-oleic acid to [(14)C]-oleamide and express PAM in a regulated fashion. We report herein that growth of the N(18)TG(2) cells in the presence of [(14)C]-oleic acid under conditions known to stimulate PAM expression generates an increase in [(14)C]-oleamide or in the presence of a PAM inhibitor generates [(14)C]-N-oleoylglycine. This represents the first identification of N-oleoylglycine from a biological source. In addition, N(18)TG(2) cell growth in the presence of N-oleoylglycine yields oleamide. These results strongly indicate that N-oleoylglycine is an intermediate in oleamide biosynthesis and provide further evidence that PAM does have a role in primary fatty acid amide production in vivo.

Inhibition of voltage-sensitive sodium channels by the cannabinoid 1 receptor antagonist AM 251 in mammalian brain

The cannabinoid 1 receptor antagonist AM 251 is known to block the inhibitory effects of endocannabinoids and synthetic cannabinoid agonists on transmitter release through an action at presynaptic cannabinoid 1 receptors in brain. We examined the ability of AM 251 to inhibit sodium channel-dependent functions and the binding of [3H]batrachotoxinin A 20-alpha-benzoate to sodium channels in mouse brain synaptic preparations. Depolarization of synaptoneurosomes by the sodium channel site 2-specific neurotoxin veratridine, which is abolished by tetrodotoxin, was found to be inhibited in a concentration-dependent fashion by AM 251 (IC50=8.9 microM). Veratridine-dependent (tetrodotoxin suppressible) release, of L-glutamic acid and GABA from synaptosomes was also reduced by AM 251 [IC50s=8.5 microM (L-glutamic acid), 9.2 microM (GABA)]. The binding of the radioligand [3H]batrachotoxinin A 20-alpha-benzoate to site 2 on sodium channels was displaced by AM 251 (IC50=11.2 microM). Scatchard analysis of binding showed that at its IC50, AM 251 increased (by 2.3 times) the KD of radioligand without altering Bmax, suggesting a competitive mechanism of inhibition by AM 251. Kinetic experiments indicated that AM 251 inhibits equilibrium binding by allosterically accelerating the dissociation of the [3H]-batrachotoxinin A 20-alpha-benzoate:sodium channel complex. Our data suggest that micromolar concentrations of AM 251 are capable of reducing neuronal excitability and inhibiting release of excitatory and inhibitory transmitters through blockade of voltage-sensitive sodium channels in brain.

The sleep lipid oleamide may represent an endogenous anticonvulsant: an in vitro comparative study in the 4-aminopyridine rat brain-slice model

cis-Oleamide (cOA) is a putative endocannabinoid, which modulates GABA(A) receptors, Na+ channels and gap-junctions (important targets for clinical and experimental anticonvulsants). Here we address the hypothesis that cOA possesses seizure limiting properties and might represent an endogenous anticonvulsant. Field potentials were recorded from the rat hippocampus and visual cortex. The effects of cOA, were compared to carbamazepine (CBZ), pentobarbital (PB) and carbenoxolone (CRX) on 4-Aminopyridine(4AP)-induced epileptiform discharges. CBZ (100 microM), PB (50 microM) and CRX (100 microM), but not cOA (64 microM), significantly attenuated the duration of the evoked epileptiform discharges in CA1. Interictal activity in CA3 was significantly depressed by CRX and cOA (irreversible by AM251), increased by CBZ and remained unaffected by PB. CBZ, PB and CRX abolished spontaneous ictal events and attenuated evoked ictal discharges in the visual cortex. cOA did not abolish spontaneous ictal events, but significantly (albeit weakly) reduced the duration of evoked ictal events. cOA and CRX, in contrast to CBZ or PB, caused a significant delay in the development of the evoked (tonic phase) epileptiform discharges. The weak effects of cOA seem independent of cannabinoid (CB1) receptors. Enzymatic cleavage and lack of specific antagonists for cOA confound simple interpretations of its actions in slices. Its high lipophilicity, imposing a permeability barrier, may also explain the lack of anticonvulsant activity. The effects of cOA may well be masked by release of the endogenous ligand upon ictal depolarisation as we demonstrate here for established endocannabinoids. cOA does not possess profound antiepileptic actions in our hands compared to CBZ, PB or CRX.

Differential effects of the sleep-inducing lipid oleamide and cannabinoids on the induction of long-term potentiation in the CA1 neurons of the rat hippocampus in vitro

Cannabinoids have been shown to impair cognition in vivo and block long-term potentiation (LTP), a candidate experimental model of learning and memory in vitro, via cannabinoid receptor (CB1) activation. cis-Oleamide (cOA) is an endogenous sleep-inducing lipid with putative cannabinomimetic properties. We hypothesise that cOA is cannabinomimetic and perform a comparative study with synthetic and endogenous cannabinoids on their effects on synaptic conditioning via two different patterns of stimulation in the hippocampal slice. CB1 agonists, R(+)-WIN55212-2 and anandamide, but not cOA blocked high frequency stimulation (HFS)-LTP. R(+)-WIN55212-2 and cOA (stereoselectively) attenuated responses to theta-burst-LTP, while anandamide did not. The anandamide transport inhibitor, AM404, attenuated HFS-LTP, an effect reversed by the CB1 receptor antagonist SR141716A but not mimicked by the vanilloid receptor agonist capsaicin. TFNO, an inhibitor of fatty acid amide hydrolase (FAAH), the enzyme responsible for degrading anandamide, failed to block HFS-LTP alone or in combination with cOA. On the contrary, this combination was as effective as cOA on its own in attenuating theta-burst-LTP. cOA effects on theta-burst-LTP were prevented in the presence of the GABA(A) receptor blocker picrotoxin, but not by pretreatment with SR141716A. These findings suggest that cOA neither directly activates CB1 receptors nor acts via the proposed "entourage" effect [Nature 389 (1997) 25] to increase titres of anandamide through FAAH inhibition. The selective effects of cOA on theta-burst-conditioning may reflect modulation of GABAergic transmission. Anandamide uptake inhibition, but not blockade of FAAH, effectively increases synaptic concentrations of endocannabinoids.

A rapid assay for the brevetoxin group of sodium channel activators based on fluorescence monitoring of synaptoneurosomal membrane potential

A functional pharmacologically-based assay for the brevetoxin group of sodium channel activators was developed using synaptoneurosomes isolated from the brains of CD1 mice. The assay can detect the depolarizing effect of brevetoxin congeners PbTx-2 and PbTx-3 as enhancements of the veratridine-dependent increase in fluorescence of the voltage-sensitive fluorescent probe rhodamine 6G. The assay is relatively rapid and can detect brevetoxin activity in the nanomolar range. The synaptoneurosomal assay has been used to analyse mussel tissue extracts spiked with PbTx-2, and composite toxicity, expressed as PbTx-3 equivalents in extracts of oysters naturally exposed to brevetoxins. In this latter context, the synaptoneurosomal technique was shown to compare favorably with the cytotoxicity assay, the receptor binding assay and HPLC/MS. Our results support the concept that this membrane potential assay detects brevetoxins based on their interaction with sodium channels.

Selective effect of oleamide, an endogenous sleep-inducing lipid amide, on pentylenetetrazole-induced seizures in mice

The anti-seizure effect of oleamide, an endogenous sleep-inducing fatty acid amide, was studied in mice. Oleamide, in the dose range 43.7-700.0 mg kg(-1), significantly and dose-dependently inhibited the seizures induced by pentylenetetrazole. However, oleamide showed no inhibitory action on the seizures induced by picrotoxin, strychnine, caffeine or semicarbazide. These results provide the first evidence for the anti-seizure effect of oleamide, and suggest that this effect may be selective to the seizure model induced by pentylenetetrazole.

Sodium channel inhibition by anandamide and synthetic cannabimimetics in brain

Anandamide is a prominent member of the endocannabinoids, a group of diffusible lipid molecules which influences neuronal excitability. In this context, endocannabinoids are known to modulate certain presynaptic Ca(2+) and K(+) channels, either through cannabinoid (CB1) receptor stimulation and second messenger pathway activation or by direct action. We investigated the susceptibility of voltage-sensitive sodium channels to anandamide and other cannibimimetics using both biochemical and electrophysiological approaches. Here we report that anandamide, AM 404 and WIN 55,212-2 inhibit veratridine-dependent depolarization of synaptoneurosomes (IC(50)s, respectively 21.8, 9.3 and 21.1 microM) and veratridine-dependent release of L-glutamic acid and GABA from purified synaptosomes [IC(50)s: 5.1 microM (L-glu) and 16.5 microM (GABA) for anandamide; 1.6 microM (L-glu) and 3.3 microM (GABA) for AM 404, and 12.2 (L-glu) and 14.4 microM (GABA) for WIN 55,212-2]. The binding of [3H]batrachotoxinin A 20-alpha-benzoate to voltage-sensitive sodium channels was also inhibited by low to mid micromolar concentrations of anandamide, AM 404 and WIN 55,212-2. In addition, anandamide (10 microM), AM 404 (10 microM) and WIN 55,212-2 (1 microM) were found to markedly block TTX-sensitive sustained repetitive firing in cortical neurones without altering primary spikes, consistent with a state-dependent mechanism. None of the inhibitory effects we demonstrate on voltage-sensitive sodium channels are attenuated by the potent CB1 antagonist AM 251 (1-2 microM). Anandamide's action is reversible and its effects are enhanced by fatty acid amidohydrolase inhibition. We propose that voltage-sensitive sodium channels may participate in a novel signaling pathway involving anandamide. This mechanism has potential to depress synaptic transmission in brain by damping neuronal capacity to support action potentials and reducing evoked release of both excitatory and inhibitory transmitters.

A rapid and sensitive assay for paralytic shellfish poison (PSP) toxins using mouse brain synaptoneurosomes

A membrane potential assay using mouse brain synaptoneurosomes was evaluated for the determination of paralytic shellfish poison (PSP) toxin content of mussels and other bivalve species important to the shellfish industry. The assay relies on the ability of PSP toxins to block veratridine-induced depolarization of synaptoneurosomes. Changes in the membrane potential of synaptoneurosomes were monitored using the voltage-sensitive fluorescent probe rhodamine 6G. Standard saxitoxin was found to be a potent inhibitor of the membrane depolarizing effects of the sodium channel activator veratridine (I(50) ca. 4 nM). Likewise, shellfish extracts containing PSP toxins inhibited veratridine-induced depolarization. Neither saxitoxin or shellfish extracts had any discernible effect on the resting membrane potential of synaptoneurosomes. When synaptoneurosomal results for extracts of mussels (n=120) and other shellfish (n=29) were correlated with official mouse toxicity assay data there was very good agreement (r(2)=0.84 and 0.86, respectively), indicating that the in vitro assay has utility for a variety of commercially relevant shellfish species. Our investigation suggests that the mouse synaptoneurosome assay is of similar sensitivity to the official CD1 mouse toxicity assay. The synaptoneurosome fraction can be prepared quickly (approx. 40 min) and an individual assay takes less than 7 min. Since 20 such assays can be performed using material from a single CD1 mouse brain, there is considerable opportunity for reducing the number of animals required in conventional PSP monitoring while retaining the same animal system.

The sleep hormone oleamide modulates inhibitory ionotropic receptors in mammalian CNS in vitro

1. We examine the sensitivity of GABA(A) and glycine receptors (same ionotropic superfamily) to oleamide. We address subunit-dependence/modulatory mechanisms and analogies with depressant drugs. 2. Oleamide modulated human GABA(A) currents (alpha(1)beta(2)gamma(2L)) in oocytes (EC(50), 28.94+/-s.e.mean of 1.4 microM; Maximum 216%+/-35 of control, n=4). Modulation of human alpha1 glycine homo-oligomers (significant), was less marked, with a lower EC(50) (P<0.05) than GABA receptors (EC(50), 22.12+/-1.4 microM; Maximum 171%+/-30, n=11). 3. Only the hypnogenic cis geometric isomer enhanced glycine currents (without altering slope or maximal current, it reduced the glycine EC(50) from 322 to 239 microM: P<0.001). Modulation was not voltage-dependent or associated with a shift in E(r). 4. beta 1 containing GABA(A) receptors (insensitive to many depressant drugs) were positively modulated by oleamide. Oleamide efficacy was circa 2x greater at alpha(1)beta(1)gamma(2L) than alpha(1)beta(2)gamma(2L) (P=0.007). Splice variation in gamma subunits did not alter oleamide sensitivity. 5. cis-9,10-Octadecenoamide had no effect on the equilibrium binding of [(3)H]-muscimol or [(3)H]-EBOB to mouse brain membranes. It does not directly mimic GABA, or operate as a neurosteroid-, benzodiazepine- or barbiturate-like modulator of GABA(A)-receptors. 6. The transport of [(3)H]-GABA into mouse brain synaptoneurosomes was unaffected by high micromolar concentrations of cis-9,10-octadecenoamide. Oleamide does not enhance GABA-ergic currents or prolong IPSCs by inhibiting GABA transport. 7. Oleamide is a non-selective modulator of inhibitory ionotropic receptors. The sleep lipid exerts its effects indirectly, or at a novel recognition site on the GABA(A) complex.

Cannabinoid receptor-inactive N-acylethanolamines and other fatty acid amides: metabolism and function

Although it is now generally accepted that long-chain N-acylethanolamines and their precursors, N-acylethanolamine phospholipids, exist as trace constituents in virtually all vertebrate cells and tissues, their possible biological functions are just emerging. While anandamide (N-arachidonoylethanolamine) has received much attention due to its ability to bind to and activate cannabinoid receptors, the saturated and monounsaturated N-acylethanolamines, which usually represent the vast majority, are cannabinoid receptor-inactive but appear to interact with endocannabinoids and to have other signaling functions as well. Also, primary fatty acid amides, including the amide of oleic acid, which acts as a sleep-inducing agent, do not interact with cannabinoid receptors but are catabolically related to endocannabinoids. Here we review published information on the occurrence, metabolism, and possible signaling functions of the cannabinoid receptor-inactive N-acylethanolamines and primary fatty acid amides.

Effect of oleamide on Ca(2+) signaling in human bladder cancer cells

The effect of oleamide, a sleep-inducing endogenous lipid in animal models, on intracellular free levels of Ca(2+) ([Ca(2+)](i)) in non-excitable and excitable cells was examined by using fura-2 as a fluorescent dye. [Ca(2+)](i) in pheochromocytoma cells, renal tubular cells, osteoblast-like cells, and bladder cancer cells were increased on stimulation of 50 microM oleamide. The response in human bladder cancer cells (T24) was the greatest and was further explored. Oleamide (10-100 microM) increased [Ca(2+)](i) in a concentration-dependent fashion with an EC(50) of 50 microM. The [Ca(2+)](i) signal comprised an initial rise and a sustained plateau and was reduced by removing extracellular Ca(2+) by 85 +/- 5%. After pre-treatment with 10-100 microM oleamide in Ca(2+)-free medium, addition of 3 mM Ca(2+) increased [Ca(2+)](i) in a manner dependent on the concentration of oleamide. The [Ca(2+)](i) increase induced by 50 microM oleamide was reduced by 100 microM La(3+) by 40%, but was not altered by 10 microM nifedipine, 10 microM verapamil, and 50 microM Ni(2+). In Ca(2+)-free medium, pre-treatment with thapsigargin (1 microM), an endoplasmic reticulum Ca(2+) pump inhibitor, abolished 50 microM oleamide-induced [Ca(2+)](i) increases; conversely, pretreatment with 50 microM oleamide reduced 1 microM thapsigargin-induced [Ca(2+)](i) increases by 50 +/- 3%. Suppression of the activity of phospholipase C with 2 microM U73122 failed to alter 50 microM oleamide-induced Ca(2+) release. Linoleamide (10-100 microM), another sleep-inducing lipid with a structure similar to that of oleamide, also induced an increase in [Ca(2+)](i). Together, it was shown that oleamide induced significant [Ca(2+)](i) increases in cells by a phospholipase C-independent release of Ca(2+) from thapsigargin-sensitive stores and by inducing Ca(2+) entry.

Effect of oleamide on sleep and its relationship to blood pressure, body temperature, and locomotor activity in rats

Oleamide (cis-9,10-octadecenoamide) is a brain lipid that has recently been isolated from the cerebral fluid of sleep-deprived cats. Intracerebroventricular and intraperitoneal administration of oleamide induces sleep in rats. However, it is unclear whether oleamide's hypnogenic effects are mediated, in part, by its actions on blood pressure and core body temperature. Here we show that systemic administration of oleamide (10 and 20 mg/kg) in rats increased slow-wave sleep 2, without affecting blood pressure and heart rate. In addition, oleamide decreased body temperature and locomotor activity in a dose-dependent manner. These latter effects were not correlated in time with the observed increases in slow-wave sleep. These data suggest that the hypnogenic effects of oleamide are not related to changes in blood pressure, heart rate, or body temperature.

Insecticidal arylalkylbenzhydrolpiperidines: novel inhibitors of voltage-sensitive sodium and calcium channels in mammalian brain

Using preparations derived from whole mouse brain, we have demonstrated that insecticidal arylalkylbenzhydrolpiperidines inhibit the depolarization of synaptoneurosomes as measured by rhodamine 6G fluorescence and block 22Na+ uptake into synaptosomes, when veratridine is used as the activator. These insecticides also have the ability to potently displace the binding of [3H]batrachotoxinin A 20-alpha-benzoate ([3H]BTX-B) to neuronal sodium channels in a concentration-dependent manner. The study compounds can be classified as competitive inhibitors of radioligand binding, since they decrease the affinity of [3H]BTX-B for site 2 without affecting the concentration of sites labelled by this radioligand. Our kinetic analyses revealed that at its IC50, the 4-carbomethoxyaminobenzyl-piperidine analogue reduces the rate of association of [3H]BTX-B with site 2, whereas higher concentrations were required to accelerate dissociation of the [3H]BTX-B:sodium channel complex. These results indicate an ability to interact with both non-activated and persistently activated states of the voltage-sensitive sodium channel, but higher affinity for the former. Such a profile also implies that inhibition of [3H]BTX-B binding to site 2 occurs via an allosteric mechanism. In addition, arylalkylbenzhydrolpiperidines interact with presynaptic voltage-sensitive calcium channels, since we demonstrate that they inhibit increases in [free Ca++] and 45Ca++ uptake when evoked by high KC1 concentration in mouse brain synaptosomal preparations. Such effects generally occur at concentrations that are higher than those required to inhibit sodium channels. Blockade of sodium and calcium channels may therefore contribute to the in vivo neurological effects observed in rodents exposed to these insecticides.

Fatty acid amide hydrolase: biochemistry, pharmacology, and therapeutic possibilities for an enzyme hydrolyzing anandamide, 2-arachidonoylglycerol, palmitoylethanolamide, and oleamide

Fatty acid amide hydrolase (FAAH) is responsible for the hydrolysis of a number of important endogenous fatty acid amides, including the endogenous cannabimimetic agent anandamide (AEA), the sleep-inducing compound oleamide, and the putative anti-inflammatory agent palmitoylethanolamide (PEA). In recent years, there have been great advances in our understanding of the biochemical and pharmacological properties of the enzyme. In this commentary, the structure and biochemical properties of FAAH and the development of potent and selective FAAH inhibitors are reviewed, together with a brief discussion on the therapeutic possibilities for such compounds in the treatment of inflammatory pain and ischaemic states.

alpha-Keto heterocycle inhibitors of fatty acid amide hydrolase: carbonyl group modification and alpha-substitution

Two sets of novel analogues of the recently disclosed alpha-keto heterocycle inhibitors of fatty acid amide hydrolase (FAAH), the enzyme responsible for regulation of endogenous oleamide and anandamide, were synthesized and evaluated in order to clarify a role of the electrophilic carbonyl group and structural features important for their activity. Both the electrophilic carbonyl and the degree of alpha-substitution markedly affect inhibitor potency.

Fatty acid amide hydrolase substrate specificity

Fatty acid amide hydrolase (FAAH), also referred to as oleamide hydrolase and anandamide amidohydrolase, is a serine hydrolase responsible for the degradation of endogenous oleamide and anandamide, fatty acid amides that function as chemical messengers. FAAH hydrolyzes a range of fatty acid amides, and the present study examines the relative rates of hydrolysis of a variety of natural and unnatural fatty acid primary amide substrates using pure recombinant rat FAAH.

A simple polar deacetylated caloporoside derivative is a positive modulator of the GABA(A) chloride channel complex in cortical mammalian neurones

Synthesis of octyl-O-beta-D-mannopyranoside, a caloporoside analogue was achieved by the activation of 2,3,4,6-rerra-O-benzyl-1-O-1',3'2'-dioxaphosphacyclohexane-a lpha,beta-D-mannopyranosyl-2-oxide with TMSOTf (Trimethyl silyl triflate) and subsequent debenzylation. At 100 microM the molecule significantly and reversibly increased the magnitude of GABA(A) currents evoked in cultured rat pyramidal neurones whilst concomitantly reducing the incidence of spontaneous synaptic activity. These results contradict earlier proposals that such molecules bind to the TBPS (tert-Butylbicyclophosphorothionate) site to block the chloride channel.