Isolation, identification and synthesis of an endogenous arachidonic amide that inhibits calcium channel antagonist 1,4-dihydropyridine binding

Effects of cannabinoids on ligand-gated ion channels

Phytocannabinoids such as Δ⁹-tetrahydrocannabinol and cannabidiol, endocannabinoids such as N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol, and synthetic cannabinoids such as CP47,497 and JWH-018 constitute major groups of structurally diverse cannabinoids. Along with these cannabinoids, CB1 and CB2 cannabinoid receptors and enzymes involved in synthesis and degradation of endocannabinoids comprise the major components of the cannabinoid system. Although, cannabinoid receptors are known to be involved in anti-convulsant, anti-nociceptive, anti-psychotic, anti-emetic, and anti-oxidant effects of cannabinoids, in recent years, an increasing number of studies suggest that, at pharmacologically relevant concentrations, these compounds interact with several molecular targets including G-protein coupled receptors, ion channels, and enzymes in a cannabinoid-receptor independent manner. In this report, the direct actions of endo-, phyto-, and synthetic cannabinoids on the functional properties of ligand-gated ion channels and the plausible mechanisms mediating these effects were reviewed and discussed.

Chemical Composition of the Red Sea Green Algae Ulva lactuca: Isolation and In Silico Studies of New Anti-COVID-19 Ceramides

Coronavirus disease 2019 (COVID-19) is the disease caused by the virus SARS-CoV-2 responsible for the ongoing pandemic which has claimed the lives of millions of people. This has prompted the scientific research community to act to find treatments against the SARS-CoV-2 virus that include safe antiviral medicinal compounds. The edible green algae U. lactuca. is known to exhibit diverse biological activities such as anti-influenza virus, anti-Japanese encephalitis virus, immunomodulatory, anticoagulant, antioxidant and antibacterial activities. Herein, four new ceramides in addition to two known ones were isolated from Ulva lactuca. The isolated ceramides, including Cer-1, Cer-2, Cer-3, Cer-4, Cer-5 and Cer-6 showed promising antiviral activity against SARS-CoV-2 when investigated using in silico approaches by preventing its attachment to human cells and/or inhibiting its viral replication. Cer-4 and Cer-5 were the most effective in inhibiting the human angiotensin converting enzyme (hACE)-spike protein complex which is essential for the virus to enter the human host. In addition to this, Cer-4 also showed an inhibition of the SARS-CoV-2 protease (M^pro) that is responsible for its viral replication and transcription. In this study, we also used liquid chromatography coupled to electrospray ionization high-resolution mass spectroscopy (LC-ESI-HRMS) to identify several metabolites of U. lactuca, including metabolites such as fatty acids, their glyceride derivatives, terpenoids, sterols and oxysterols from the organic extract. Some of these metabolites also possessed promising antiviral activity, as previously reported.

Cannabinoids and Endocannabinoid System Changes in Intestinal Inflammation and Colorectal Cancer

Despite the multiple preventive measures and treatment options, colorectal cancer holds a significant place in the world's disease and mortality rates. The development of novel therapy is in critical need, and based on recent experimental data, cannabinoids could become excellent candidates. This review covered known experimental studies regarding the effects of cannabinoids on intestinal inflammation and colorectal cancer. In our opinion, because colorectal cancer is a heterogeneous disease with different genomic landscapes, the choice of cannabinoids for tumor prevention and treatment depends on the type of the disease, its etiology, driver mutations, and the expression levels of cannabinoid receptors. In this review, we describe the molecular changes of the endocannabinoid system in the pathologies of the large intestine, focusing on inflammation and cancer.

Effects of the endogenous cannabinoid anandamide on voltage-dependent sodium and calcium channels in rat ventricular myocytes

BACKGROUND AND PURPOSE

The endocannabinoid anandamide (N-arachidonoyl ethanolamide; AEA) exerts negative inotropic and antiarrhythmic effects in ventricular myocytes.

EXPERIMENTAL APPROACH

Whole-cell patch-clamp technique and radioligand-binding methods were used to analyse the effects of anandamide in rat ventricular myocytes.

KEY RESULTS

In the presence of 1-10 μM AEA, suppression of both Na(+) and L-type Ca(2+) channels was observed. Inhibition of Na(+) channels was voltage and Pertussis toxin (PTX) - independent. Radioligand-binding studies indicated that specific binding of [(3) H] batrachotoxin (BTX) to ventricular muscle membranes was also inhibited significantly by 10 μM metAEA, a non-metabolized AEA analogue, with a marked decrease in Bmax values but no change in Kd . Further studies on L-type Ca(2+) channels indicated that AEA potently inhibited these channels (IC50 0.1 μM) in a voltage- and PTX-independent manner. AEA inhibited maximal amplitudes without affecting the kinetics of Ba(2+) currents. MetAEA also inhibited Na(+) and L-type Ca(2+) currents. Radioligand studies indicated that specific binding of [(3) H]isradipine, was inhibited significantly by metAEA. (10 μM), changing Bmax but not Kd .

CONCLUSION AND IMPLICATIONS

Results indicate that AEA inhibited the function of voltage-dependent Na(+) and L-type Ca(2+) channels in rat ventricular myocytes, independent of CB1 and CB2 receptor activation.

Modulation of T-type calcium channels by bioactive lipids

T-type calcium channels (T-channels/CaV3) have unique biophysical properties allowing a calcium influx at resting membrane potential of most cells. T-channels are ubiquitously expressed in many tissues and contribute to low-threshold spikes and burst firing in central neurons as well as to pacemaker activities in cardiac cells. They also emerged as potential targets to treat cancer and hypertension. Regulation of these channels appears complex, and several studies have indicated that CaV3.1, CaV3.2, and CaV3.3 currents are directly inhibited by multiple endogenous lipids independently of membrane receptors or intracellular pathways. These bioactive lipids include arachidonic acid and ω3 poly-unsaturated fatty acids; the endocannabinoid anandamide and other N-acylethanolamides; the lipoamino-acids and lipo-neurotransmitters; the P450 epoxygenase metabolite 5,6-epoxyeicosatrienoic acid; as well as similar molecules with 18-22 carbons in the alkyl chain. In this review, we summarize evidence for direct effects of these signaling molecules, the molecular mechanisms underlying the current inhibition, and the involved chemical features. The impact of this modulation in physiology and pathophysiology is discussed with a special emphasis on pain aspects and vasodilation. Overall, these data clearly indicate that T-current inhibition is an important mechanism by which bioactive lipids mediate their physiological functions.

Blockade of β-cell K(ATP) channels by the endocannabinoid, 2-arachidonoylglycerol

The endocannabinoid system has been demonstrated to be active in the pancreatic β-cell. However the effects of the endocannabinoids (ECs) on insulin secretion are not well defined and may vary depending on the metabolic state of the β-cell. Specifically it is not known whether the effects of the ECs occur by activation of the cannabinoid receptors or via their direct interaction with the ion channels of the β-cell. To begin to delineate the effects of ECs on β-cell function, we examined how the EC, 2-AG influences β-cell ion channels in the absence of glucose stimulation. The mouse insulinoma cell line R7T1 was used to survey the effects of 2-AG on the high voltage activated (HVA) calcium, the delayed rectifier (K(v)), and the ATP-sensitive K (K(ATP)) channels by whole cell patch clamp recording. At 2mM glucose, 2-AG inhibited the HVA calcium (the majority of which are L-type channels), K(v), and K(ATP) channels. The channel exhibiting the most sensitivity to 2-AG blockade was the K(ATP) channel, where the IC(50) for 2-AG was 1 μM. Pharmacological agents revealed that the blockade of all these channels was independent of cannabinoid receptors. Our results provide a mechanism for the previous observations that CB1R agonists increase insulin secretion at low glucose concentrations through CB1R independent blockade of the K(ATP) channel.

International Union of Basic and Clinical Pharmacology. LXXIX. Cannabinoid receptors and their ligands: beyond CB₁ and CB₂

There are at least two types of cannabinoid receptors (CB(1) and CB(2)). Ligands activating these G protein-coupled receptors (GPCRs) include the phytocannabinoid Δ(9)-tetrahydrocannabinol, numerous synthetic compounds, and endogenous compounds known as endocannabinoids. Cannabinoid receptor antagonists have also been developed. Some of these ligands activate or block one type of cannabinoid receptor more potently than the other type. This review summarizes current data indicating the extent to which cannabinoid receptor ligands undergo orthosteric or allosteric interactions with non-CB(1), non-CB(2) established GPCRs, deorphanized receptors such as GPR55, ligand-gated ion channels, transient receptor potential (TRP) channels, and other ion channels or peroxisome proliferator-activated nuclear receptors. From these data, it is clear that some ligands that interact similarly with CB(1) and/or CB(2) receptors are likely to display significantly different pharmacological profiles. The review also lists some criteria that any novel "CB(3)" cannabinoid receptor or channel should fulfil and concludes that these criteria are not currently met by any non-CB(1), non-CB(2) pharmacological receptor or channel. However, it does identify certain pharmacological targets that should be investigated further as potential CB(3) receptors or channels. These include TRP vanilloid 1, which possibly functions as an ionotropic cannabinoid receptor under physiological and/or pathological conditions, and some deorphanized GPCRs. Also discussed are 1) the ability of CB(1) receptors to form heteromeric complexes with certain other GPCRs, 2) phylogenetic relationships that exist between CB(1)/CB(2) receptors and other GPCRs, 3) evidence for the existence of several as-yet-uncharacterized non-CB(1), non-CB(2) cannabinoid receptors; and 4) current cannabinoid receptor nomenclature.

Dual modulation of CNS voltage-gated calcium channels by cannabinoids: Focus on CB1 receptor-independent effects

The neuromodulatory effects of cannabinoids in the central nervous system have mainly been associated with G-protein coupled cannabinoid receptor (CB1R) mediated inhibition of voltage-gated calcium channels (VGCCs). Numerous studies show, however, that cannabinoids can also modulate VGCCs independent of CB1R activation. Nevertheless, despite the fact that endocannabinoids have a nearly equal efficacy for direct and CB1R-mediated effects on VGCC, the role of the direct cannabinoid-VGCC interaction has been largely underestimated. In this review, we summarize recent studies on the modulation of different types of VGCCs by cannabinoids, highlight the evidence for and implications of the CB1R-independent modulation, and put forward the concept, that direct interaction of cannabinoids and VGCCs is as important in regulation of VGCCs function as the CB1R-mediated effects.

Effects of anandamide and noxious heat on intracellular calcium concentration in nociceptive drg neurons of rats

As an endogenous agonist at the cannabinoid receptor CB1 and the capsaicin-receptor TRPV1, anandamide may exert both anti- and pronociceptive actions. Therefore we studied the effects of anandamide and other activators of both receptors on changes in free cytosolic calcium ([Ca(2+)](i)) in acutely dissociated small dorsal root ganglion neurons (diameter: < or =30 microm). Anandamide (10 microM) increased [Ca(2+)](i) in 76% of the neurons. The EC(50) was 7.41 microM, the Hill slope was 2.15 +/- 0.43 (mean +/- SE). This increase was blocked by the competitive TRPV1-antagonist capsazepine (10 microM) and in Ca(2+)-free extracellular solution. Neither exclusion of voltage-gated sodium channels nor additional blockade of voltage-gated calcium channels of the L-, N-, and/or T-type, significantly reduced the anandamide-induced [Ca(2+)](i) increase or capsaicin-induced [Ca(2+)](i) transients (0.2 microM). The CB1-agonist HU210 (10 microM) inhibited the anandamide-induced rise in [Ca(2+)](i). Conversely, the CB1-antagonist AM251 (3 microM) induced a leftward shift of the concentration-response relationship by approximately 4 microM (P < 0.001; Hill slope, 2.17 +/- 0.75). Intracellular calcium transients in response to noxious heat (47 degrees C for 10 s) were highly correlated with the anandamide-induced [Ca(2+)](i) increases (r = 0.84, P < 0.001). Heat-induced [Ca(2+)](i) transients were facilitated by preincubation with subthreshold concentrations of anandamide (3 microM), an effect that was further enhanced by 3 microM AM251. Although anandamide acts on both TRPV1 and CB1 receptors in the same nociceptive DRG neurons, its pronociceptive effects dominate. Anandamide triggers an influx of calcium through TRPV1 but no intracellular store depletion. It facilitates the heat responsiveness of TRPV1 in a calcium-independent manner. These effects of anandamide differ from those of the classical exogenous TRPV1-agonist capsaicin and suggest a primarily modulatory mode of action of anandamide.

Characterization of the vasorelaxation to methanandamide in rat gastric arteries

In the present study, the relaxant effect of the cannabinoid methanandamide was explored in rat gastric arteries. Since in some vessels cannabinoids have been shown to release calcitonin gene-related peptide (CGRP) from perivascular nerves, the influence of methanandamide was compared with that of exogenous CGRP. Methanandamide and CGRP elicited concentration-dependent, endothelium-independent relaxations. Methanandamide-induced relaxations were unaffected by the CB1 receptor antagonist AM251, the CB2 receptor antagonists AM630 and SR144528, and combined pre-exposure to AM251 and SR144528. Pre-exposure to O-1918, an antagonist of a novel nonCB1/nonCB2 cannabinoid receptor, did not influence the relaxations to methanandamide. Capsaicin or capsazepine treatment slightly inhibited methanandamide-induced relaxations. Preincubation with 30 mmol/L extracellular K+ or 3 mmol/L TEA had no significant effect on the responses elicited by methanandamide, but reduced CGRP-induced relaxations. Relaxation to 10(-5) mol/L methanandamide was significantly blunted by Bay K8644 and by preincubation with nifedipine. Furthermore, 10(-5) mol/L methanandamide significantly inhibited CaCl2-induced contractions in norepinephrine-stimulated vessels previously depleted of intra- and extracellular Ca2+. Finally, preincubation with 10(-5) mol/L methanandamide almost completely abolished high K+-induced contractions. These findings suggest that the vasorelaxant action of methanandamide in rat gastric arteries is not mediated by stimulation of known cannabinoid receptors and only partly related to stimulation of TRPV1 receptors on perivascular nerves. At high concentrations, methanandamide might induce relaxation by reducing calcium entry into the smooth muscle cells.

Effects of chronic nitric oxide synthase inhibition on the cardiovascular responses to cannabinoids in vivo and in vitro

BACKGROUND AND PURPOSE

Since the vasorelaxant potency of the endocannabinoid anandamide is enhanced in perfused mesenteric vascular beds from rats made hypertensive by chronic inhibition of NO synthase (L-NAME in drinking water), we hypothesized that in vivo, anandamide-induced vasodilatation would be similarly enhanced in L-NAME-treated animals.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats were given L-NAME in drinking water (7.5 mg kg(-1) day(-1)) for 4 weeks. Relaxant effects of anandamide were measured in perfused mesenteric vascular beds and in isolated small mesenteric arteries. Renal, mesenteric and hindquarters haemodynamic responses to anandamide, methanandamide, the synthetic cannabinoid agonist WIN-55212-2 and the cannabinoid receptor antagonist AM251 were assessed in conscious, chronically-instrumented rats.

KEY RESULTS

Vasorelaxant responses to anandamide were enhanced in the perfused mesentery but not in isolated mesenteric resistance vessels. In vivo, anandamide caused vasodilatation only in the hindquarters vascular bed and only in control rats. Methanandamide caused a late-onset (40 min after administration) tachycardia, mesenteric and hindquarters vasoconstriction, and renal vasodilatation, which did not differ between control and L-NAME-treated rats. AM251 had no effect on resting blood pressure in control or L-NAME-treated rats and WIN55212-2 caused pressor and renal and mesenteric vasoconstrictor responses, with hindquarters vasodilatation in both groups of animals.

CONCLUSIONS AND IMPLICATIONS

The results provide no in vivo evidence for enhanced vasodilator responses to cannabinoids, or up-regulation of endocannabinoids or their receptor activity, following chronic NO synthase inhibition.

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.

Effect of an unstirred layer on the membrane permeability of anandamide

To study the effect of an unstirred layer (UL), we have investigated the exchange efflux kinetics of anandamide at 0 degrees C, pH 7.3, from albumin-free as well as from albumin-filled human red blood cell ghosts to media of various BSA concentrations ([BSA](o)). The rate constant (k(m)) of unidirectional flux from the outer membrane leaflet to BSA in the medium increased with the square root of [BSA](o) in accordance with the existence of a UL, which is a water layer adjacent to the membrane that is not subject to the same gross mixing that takes place in the rest of the medium. From k(m), it is possible to calculate the rate constant of anandamide dissociation from BSA (k(1)) if we know the membrane binding of anandamide, the equilibrium dissociation constant of BSA-anandamide complexes, and the diffusion constant of anandamide. We estimated k(1) to be 3.33 +/- 0.27 s(-1). The net flux of [(3)H]anandamide is balanced by an equal and opposite movement of nonradioactive anandamide in exchange efflux experiments. This means that our results are also valid for uptake. We show that for anandamide with rapid membrane translocation, UL causes a significant resistance to cellular uptake. Depicting the rate of anandamide uptake as a function of equilibrium water phase concentrations results in a parabolic uptake dependence. Such apparent "saturation kinetics" is often interpreted as indicating the involvement of transport proteins. The validity of such an interpretation is discussed.

Anandamide as an intracellular messenger regulating ion channel activity

The endocannabinoid anandamide (N-arachidonoylethanolamine) was proposed to be an extracellular retrograde messenger, which regulates excitability of neurons by cannabinoid CB1 receptor-dependent inhibition of neurotransmitter release. Recent findings indicate that the neuromodulatory actions of anandamide might be more complex. Anandamide has been shown to directly modulate various ion channels, such as alpha7-nicotinic acetylcholine receptors, T-type Ca2+ channels, voltage-gated and background K+-channels and Transient Receptor Potential Vanilloid type 1 (TRPV1) channels. The binding site of anandamide at some of these ion channels appears to be intracellular or at the bilayer interface. This rises the intriguing possibility that anandamide, prior to its release into the synaptic cleft, may regulate ion homeostasis and excitability of neurons as an intracellular modulator of ion channels independent of its action at cannabinoid CB1 receptors. This possibility might extend the concept of anandamide as an endocannabinoid retrograde messenger and may have profound implications for its role in neurotransmission and neuronal function. Here, we will review the evidence for this hypothesis.

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

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

Differential effects of endogenous and synthetic cannabinoids on voltage-dependent calcium fluxes in rabbit T-tubule membranes: comparison with fatty acids

The effects of cannabinoid receptor ligands including 2-arachidonoylglycerol, R-methanandamide, Delta9-THC (Delta9-tetrahydrocannabinol), WIN 55,212-2 [4,5-dihydro-2-methyl-4(4-morpholinylmethyl)-1-(1-naphthalenylcarbonyl)-6H-pyrrolo[3,2,1ij]quinolin-6-one], CP 55,940 ([1alpha,2beta-(R)-5alpha]-(-)-5-(1,1-dimethyl)-2-[5-hydroxy-2-(3-hydroxypropyl) cyclohexyl-phenol]) and a series of fatty acids on depolarization-induced Ca2+ effluxes mediated by voltage-dependent Ca2+ channels were investigated comparatively in transverse tubule membrane vesicles from rabbit skeletal muscle. Vesicles were loaded with 45Ca2+ and membrane potentials were generated by establishing potassium gradients across the vesicle using the ionophore valinomycin. Endocannabinoids, 2-arachidonoylglycerol and R-methanandamide (all 10 microM), inhibited depolarization-induced Ca2+ effluxes and specific binding of [3H]PN 200-110 (isradipine) to transverse tubule membranes. On the other hand, synthetic cannabinoids, including CP 55,940, WIN 55,212-2, and Delta9-THC (all 10 microM), were ineffective. Additional experiments using endocannabinoid metabolites suggested that whereas ethanolamine and glycerol were ineffective, arachidonic acid inhibited Ca2+ effluxes and specific binding of [3H]PN 200-110. Further studies indicated that only those fatty acids containing two or more double bonds were effective in inhibiting depolarization-induced Ca2+ effluxes and specific binding of [3H]PN 200-110. These results indicate that endocannabinoids, but not synthetic cannabinoids, directly inhibit the function of voltage-dependent calcium channels (VDCCs) and modulate the specific binding of calcium channel ligands of the dihydropyridine (DHP) class.

Endothelium-independent relaxation to cannabinoids in rat-isolated mesenteric artery and role of Ca2+ influx

(1) Three cannabinoid receptor agonists, anandamide (CB(1) receptor-selective) and the aminoalkyl-indoles, JWH 015(2-methyl-1-propyl-1H-indol-3-yl)-1-napthalenylmethanone; (CB(2) receptor-selective), R-(+)-WIN 55,212-2 (R-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolol[1,2,3-de]-1,4-benzoxazin-6-yl]-1-napthalenylmethanone; slightly CB(2) receptor-selective), as well as the enantiomer S-(-)-WIN 55,212-3(S-(-)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolol[1,2,3-de]-1,4-benzoxazin-6-yl]-1-napthalenylmethanone; inactive at cannabinoid receptors), induced endothelium-independent relaxation of methoxamine-precontracted isolated small mesenteric artery of rat. KCL (60 mM) precontraction did not affect relaxation to the aminoalkylindoles, but reduced that to anandamide. (2) SR14176A (N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide; 3 micro M; CB(1) receptor antagonist) inhibited relaxation only to JWH 015 and anandamide. Neither AM 251 (N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide; CB(1) antagonist) nor SR 144528 (N-[(1S)-endo-1,3,3-trimethyl bicyclo[2.2.1] heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide; CB(2) antagonist; both at 3 micro M) affected any of the relaxations. (3) Vanilloid receptor desensitisation with capsaicin reduced anandamide relaxation; addition of SR 141716A (3 micro M) then caused further inhibition. SR 141716A did not affect capsaicin-induced relaxation. (4) The aminoalkylindoles inhibited CaCl(2)-induced contractions in methoxamine-stimulated vessels previously depleted of intracellular Ca(2+). These inhibitory effects were greatly reduced or abolished in ionomycin-(a calcium ionophore) contracted vessels. Anandamide also caused vanilloid receptor-independent, SR 141716A- (3 micro M) insensitive, inhibition of CaCl(2) contractions. (5) In conclusion, the aminoalkylindoles JWH 015, R-(+)-WIN 55,212-2 and S-(-)-WIN 55,212-3 relax rat small mesenteric artery mainly by inhibiting Ca(2+) influx into vascular smooth muscle. Anandamide causes vasorelaxation by activating vanilloid receptors, but may also inhibit Ca(2+) entry. Relaxation to JWH 015 and anandamide was sensitive to SR 141716A, but there is no other evidence for the involvement of CB(1) or CB(2) receptors in responses to these compounds.

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

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

Acute neuronal injury, excitotoxicity, and the endocannabinoid system

The endocannabinoid system is a valuable target for drug discovery, because it is involved in the regulation of many cellular and physiological functions. The endocannabinoid system constitutes the endogenous lipids anandamide, 2-arachidonoylglycerol and noladin ether, and the cannabinoid CB1 and CB2 receptors as well as the proteins for their inactivation. It is thought that (endo)cannabinoid-based drugs may potentially be useful to reduce the effects of neurodegeneration. This paper reviews recent developments in the endocannabinoid system and its involvement in neuroprotection. Exogenous (endo)cannabinoids have been shown to exert neuroprotection in a variety of in vitro and in vivo models of neuronal injury via different mechanisms, such as prevention of excitotoxicity by CB1-mediated inhibition of glutamatergic transmission, reduction of calcium influx, and subsequent inhibition of deleterious cascades, TNF-alpha formation, and anti-oxidant activity. It has been suggested that the release of endogenous endocannabinoids during neuronal injury might be a protective response. However, several observations indicate that the role of the endocannabinoid system as a general endogenous protection system is questionable. The data are critically reviewed and possible explanations are given.

Anandamide receptors

Anandamide (N -arachidonoyl-ethanolamine, AEA) was the first endogenous ligand of cannabinoid receptors to be discovered. Yet, since early studies, AEA appeared to exhibit also some effects that were not mediated by cannabinoid CB(1) or CB(2) receptors. Indeed, AEA exerts some behavioral actions also in mice with genetically disrupted CB(1) receptors, whereas in vitro it is usually a partial agonist at these receptors and a weak activator of CB(2) receptors. Nevertheless, several pharmacological effects of AEA are mediated by CB(1) receptors, which, by being coupled to G-proteins, can be seen as AEA "metabotropic" receptors. Furthermore, at least two different, and as yet uncharacterized, G-protein-coupled AEA receptors have been suggested to exist in the brain and vascular endothelium, respectively. AEA is also capable of directly inhibiting ion currents mediated by L-type Ca(2+) channels and TASK-1 K(+) channels. However, to date the only reasonably well characterized, non-cannabinoid site of action for AEA is the vanilloid receptor type 1 (VR1), a non-selective cation channel gated also by capsaicin, protons and heat. VR1 might be considered as an AEA "ionotropic" receptor and, under certain conditions, mediates effects ranging from vasodilation, broncho-constriction, smooth muscle tone modulation and nociception to stimulation of hippocampal pair-pulse depression, inhibition of tumor cell growth and induction of apoptosis.

Biosynthesis and degradation of anandamide and 2-arachidonoylglycerol and their possible physiological significance

N -arachidonoylethanolamine (anandamide) was the first endogenous cannabinoid receptor ligand to be discovered. Dual synthetic pathways for anandamide have been proposed. One is the formation from free arachidonic acid and ethanolamine, and the other is the formation from N -arachidonoyl phosphatidylethanolamine (PE) through the action of a phosphodiesterase. These pathways, however, do not appear to be able to generate a large amount of anandamide, at least under physiological conditions. The generation of anandamide from free arachidonic acid and ethanolamine is catalyzed by a degrading enzyme anandamide amidohydrolase/fatty acid amide hydrolase operating in reverse and requires large amounts of substrates. As for the second pathway, arachidonic acids esterified at the 1-position of glycerophospholipids, which are mostly esterified at the 2-position, are utilized for the formation of N -arachidonoyl PE, a stored precursor form of anandamide. In fact, the actual levels of anandamide in various tissues are generally low except in a few cases. 2-Arachidonoylglycerol (2-AG) was the second endogenous cannabinoid receptor ligand to be discovered. 2-AG is a degradation product of arachidonic acid-containing glycerophospholipids such as inositol phospholipids. Several investigators have demonstrated that 2-AG is produced in a variety of tissues and cells upon stimulation. 2-AG acts as a full agonist at the cannabinoid receptors (CB1 and CB2). Evidence is gradually accumulating and indicates that 2-AG is the most efficacious endogenous natural ligand for the cannabinoid receptors. In this review, we summarize the tissue levels, biosynthesis, degradation and possible physiological significance of two endogenous cannabimimetic molecules, anandamide and 2-AG.

Exogenous anandamide protects rat brain against acute neuronal injury in vivo

The endocannabinoid anandamide [N-arachidonoylethanolamine (AEA)] is thought to function as an endogenous protective factor of the brain against acute neuronal damage. However, this has never been tested in an in vivo model of acute brain injury. Here, we show in a longitudinal pharmacological magnetic resonance imaging study that exogenously administered AEA dose-dependently reduced neuronal damage in neonatal rats injected intracerebrally with the Na(+)/K(+)-ATPase inhibitor ouabain. At 15 min after injury, AEA (10 mg/kg) administered 30 min before ouabain injection reduced the volume of cytotoxic edema by 43 +/- 15% in a manner insensitive to the cannabinoid CB(1) receptor antagonist SR141716A. At 7 d after ouabain treatment, 64 +/- 24% less neuronal damage was observed in AEA-treated (10 mg/kg) rats compared with control animals. Coadministration of SR141716A prevented the neuroprotective actions of AEA at this end point. In addition, (1) no increase in AEA and 2-arachidonoylglycerol levels was detected at 2, 8, or 24 hr after ouabain injection; (2) application of SR141716A alone did not increase the lesion volume at days 0 and 7; and (3) the AEA-uptake inhibitor, VDM11, did not affect the lesion volume. These data indicate that there was no endogenous endocannabinoid tone controlling the acute neuronal damage induced by ouabain. Although our data seem to question a possible role of the endogenous cannabinoid system in establishing a brain defense system in our model, AEA may be used as a structural template to develop neuroprotective agents.

The endocannabinoid nervous system: unique opportunities for therapeutic intervention

The active principle in marijuana, Delta(9)-tetrahydrocannabinol (THC), has been shown to have wide therapeutic application for a number of important medical conditions, including pain, anxiety, glaucoma, nausea, emesis, muscle spasms, and wasting diseases. Delta(9)-THC binds to and activates two known cannabinoid receptors found in mammalian tissue, CB1 and CB2. The development of cannabinoid-based therapeutics has focused predominantly on the CB1 receptor, based on its predominant and abundant localization in the CNS. Like most of the known cannabinoid agonists, Delta(9)-THC is lipophilic and relatively nonselective for both receptor subtypes. Clinical studies show that nonselective cannabinoid agonists are relatively safe and provide therapeutic efficacy, but that they also induce psychotropic side effects. Recent studies of the biosynthesis, release, transport, and disposition of anandamide are beginning to provide an understanding of the role of lipid transmitters in the CNS. This review attempts to link current understanding of the basic biology of the endocannabinoid nervous system to novel opportunities for therapeutic intervention. This new knowledge may facilitate the development of cannabinoid receptor-targeted therapeutics with improved safety and efficacy profiles.

Cellular signal transduction by anandamide and 2-arachidonoylglycerol

Anandamide (arachidonylethanolamide) and 2-arachidonoylglycerol mediate many of their actions via either CB(1) or CB(2) cannabinoid receptor subtypes. These agonist-receptor interactions result in activation of G proteins, particularly those of the G(i/o) family. Signal transduction pathways that are regulated by these G proteins include inhibition of adenylyl cyclase, regulation of ion currents (inhibition of voltage-gated L, N and P/Q Ca(2+)-currents; activation of K(+) currents); activation of focal adhesion kinase (FAK), mitogen activated protein kinase (MAPK) and induction of immediate early genes; and stimulation of nitric oxide synthase (NOS). Other effects of anandamide and/or 2-arachidonoylglycerol that are not mediated via cannabinoid receptors include inhibition of L-type Ca(2+) channels, stimulation of VR(1) vanilloid receptors, transient changes in intracellular Ca(2+), and disruption of gap junction function. Cardiovascular regulation by anandamide appears to occur by a variety of receptor-mediated and non-receptor-mediated mechanisms. This review will describe and evaluate each of these signal transduction pathways and mechanisms.

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

We studied the cannabimimetic properties of N-vanillyl-arachidonoyl-amide (arvanil), a potential agonist of cannabinoid CB(1) and capsaicin VR(1) receptors, and an inhibitor of the facilitated transport of the endocannabinoid anandamide. Arvanil and anandamide exhibited similar affinities for the cannabinoid CB(1) receptor, but arvanil was less efficacious in inducing cannabinoid CB(1) receptor-mediated GTPgammaS binding. The K(i) of arvanil for the vanilloid VR(1) receptor was 0.28 microM. Administered i.v. to mice, arvanil was 100 times more potent than anandamide in producing hypothermia, analgesia, catalepsy and inhibiting spontaneous activity. These effects were not attenuated by the cannabinoid CB(1) receptor antagonist N-(piperidin-1-yl)-5-(4-chloro-phenyl)-1-(2, 4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide.HCl (SR141716A). Arvanil (i.t. administration) induced analgesia in the tail-flick test that was not blocked by either SR141716A or the vanilloid VR(1) antagonist capsazepine. Conversely, capsaicin was less potent as an analgesic (ED(50) 180 ng/mouse, i.t.) and its effects attenuated by capsazepine. The analgesic effect of anandamide (i.t.) was also unaffected by SR141716A but was 750-fold less potent (ED(50) 20.5 microg/mouse) than capsaicin. These data indicate that the neurobehavioral effects exerted by arvanil are not due to activation of cannabinoid CB(1) or vanilloid VR(1) receptors.

Endogenous cannabinoid anandamide directly inhibits voltage-dependent Ca(2+) fluxes in rabbit T-tubule membranes

The effect of the endogenous cannabinoid, anandamide on Ca(2+) flux responses mediated by voltage-dependent Ca(2+) channels was studied in transverse tubule membrane vesicles from rabbit skeletal muscle. Vesicles were loaded with 45Ca(2+) and membrane potentials were generated by establishing K(+) gradients across the vesicle using the ionophore, valinomycin. Anandamide, in the range of 1-100 microM, inhibited depolarization-induced efflux responses. Anandamide also functionally modulated the effects of nifedipine (1-10 microM) and Bay K 8644 (1 microM) on Ca(2+) flux responses. Pretreatment with the specific cannabinoid receptor antagonist, SR141716A (1 microM), pertussis toxin (5 microg/ml), the amidohydrolase inhibitor, phenylmethylsulfonyl fluoride (0.2 mM) or the cyclooxygenase inhibitor, indomethacin (5 microM) did not alter the inhibition of efflux responses by anandamide. Arachidonic acid (10-100 microM) also effectively inhibited 45Ca(2+) efflux from membrane vesicles. In radioligand binding studies, it was found that both anandamide and arachidonic acid inhibited the specific binding of [3H]PN 200-110 to transverse tubule membranes with IC(50) values of 4.4+/-0. 7 and 13.4+/-3.5 microM, respectively. These results indicate that anandamide, independent of cannabinoid receptor activation, directly inhibits the function of voltage-dependent calcium channels and modulates the specific binding of calcium channel ligands of the dihydropyridine class.

Functional CB1 cannabinoid receptors in human vascular endothelial cells

Cannabinoid CB1 receptor mRNA was detected using reverse transcription-polymerase chain reaction (RT-PCR) in endothelial cells from human aorta and hepatic artery and in the ECV304 cell line derived from human umbilical vein endothelial cells. CB1 receptor-binding sites were detected by the high-affinity antagonist radioligand [(125)I]AM-251. In ECV304 cells, both the highly potent synthetic cannabinoid agonist HU-210 and the endogenous ligand anandamide induce activation of mitogen-activated protein (MAP) kinase, and the effect of HU-210 was completely blocked, whereas the effect of anandamide was partially inhibited by SR141716A, a selective CB1 receptor antagonist. Transfection of ECV304 cells with CB1 receptor antisense, but not sense, oligonucleotides caused the same pattern of inhibition as SR141716A. This provides more definitive evidence for the involvement of CB1 receptors in MAP kinase activation and suggests that anandamide may also activate MAP kinase via an additional, CB1 receptor-independent, SR141716A-resistant mechanism. The MAP kinase activation by anandamide in ECV304 cells requires genistein-sensitive tyrosine kinases and protein kinase C (PKC), and anandamide also activates p38 kinase and c-Jun kinase. These findings indicate that CB1 receptors located in human vascular endothelium are functionally coupled to the MAP kinase cascade. Activation of protein kinase cascades by anandamide may be involved in the modulation of endothelial cell growth and proliferation.

Substrate specificity and stereoselectivity of rat brain microsomal anandamide amidohydrolase

Anandamide amidohydrolase (AAH) catalyzes the hydrolysis of arachidonylethanolamide (anandamide), an endogenous cannabinoid receptor ligand. To delineate the structural requirements of AAH substrates, rat brain microsomal AAH hydrolysis of a series of anandamide congeners was studied using two reverse-phase high-performance liquid chromatography (RP-HPLC) assays developed in our laboratory. Arachidonamide (1) was found to be the best substrate with an apparent Km of 2.34 mM and a Vmax of 2.89 nmol/min/mg of protein. Although anandamide (2) has a similar Km value, its Vmax is approximately one-half that of arachidonamide. N, N-Bis(2-hydroxyethyl)arachidonamide (3) was not hydrolyzed, suggesting specificity for unsubstituted or mono-N-substituted arachidonamides. Analogues with a methyl group at the 1'-position of the ethanolamido headgroup were also found to have greater resistance to enzymatic turnover and therefore increased metabolic stability. The enzyme exhibited high stereoselectivity as the rate of hydrolysis of (R)-alpha-methanandamide (2.4%) (anandamide = 100%) was about 10-fold lower than that of its (S)-enantiomer (23%). In contrast, (R)-beta-methanandamide was 6-times more susceptible (121%) than the (S)-beta-enantiomer (21%). Interestingly, an inverse correlation was shown between AAH stereoselectivity and the brain cannabinoid receptor affinity as the enantiomers with high receptor affinity displayed low susceptibility to hydrolysis by AAH. Metabolic stability is also imparted to analogues with a short hydrocarbon headgroup as well as to those possessing 2-monomethyl or 2,2-dimethyl substituents. 2-Arachidonylglycerol and racemic 1-arachidonylglycerol were shown to be excellent AAH substrates. To identify AAH inhibitors, hydrolysis of anandamide was also studied in the presence of a select group of cannabimimetics. Of these, (-)-Delta8-THC and SR141716A, a biarylpyrazole CB1 antagonist, were found to inhibit enzymatic activity. These newly defined enzyme recognition parameters should provide a foundation for the rational development of stable, therapeutically useful anandamide analogues with high receptor affinity.

'Endocannabinoids' and other fatty acid derivatives with cannabimimetic properties: biochemistry and possible physiopathological relevance

The only endogenous substances isolated and characterised so far that are capable of mimicking the pharmacological actions of the active principle of marijuana, (-)-Delta9-tetrahydrocannabinol, are amides and esters of fatty acids. Some of these compounds, like anandamide (N-arachidonoylethanolamine) and 2-arachidonoylglycerol, act as true 'endogenous cannabinoids' by binding and functionally activating one or both cannabinoid receptor subtypes present on nervous and peripheral cell membranes. The metabolic pathways and molecular mode of actions of these metabolites, as well as their possible implication in physiopathological responses, are reviewed here.

Cannabinoid receptors and their endogenous agonists

Marijuana has been in use for over 4000 years as a therapeutic and as a recreational drug. Within the past decade, two cannabinoid receptor types have been identified, their signal transduction characterized, and an endogenous lipid agonist isolated from mammalian tissues. The CB1 cannabinoid receptor is widely distributed in mammalian tissues, with the highest concentrations found in brain neurons. CB1 receptors are coupled to modulation of adenylate cyclase and ion channels. The CB2 receptor is found in cells of the immune system and is coupled to inhibition of adenylate cyclase. Both receptor types selectively bind delta 9-THC, the active principle in marijuana, and anandamide (arachidonylethanolamide), an endogenous cannabimimetic eicosanoid. Progress is being made in the development of novel agonists and antagonists with receptor subtype selectivity, mice with genetic deletion of the cannabinoid receptors, and receptor-specific antibodies, which should help in providing a better understanding of the physiological role of the cannabinoid receptors.

Chemical requirements for inhibition of gap junction communication by the biologically active lipid oleamide

Oleamide is an endogenous fatty acid primary amide that possesses sleep-inducing properties in animals and has been shown to effect serotonergic systems and block gap junction communication in a structurally specific manner. Herein, the structural features of oleamide required for inhibition of the gap junction-mediated chemical and electrical transmission in rat glial cells are defined. The effective inhibitors fall into two classes of fatty acid primary amides of which oleamide and arachidonamide are the prototypical members. Of these two, oleamide constitutes the most effective, and its structural requirements for inhibition of the gap junction are well defined. It requires a chain length of 16-24 carbons of which 16-18 carbons appears optimal, a polarized terminal carbonyl group capable of accepting but not necessarily donating a hydrogen bond, a Delta9 cis double bond, and a hydrophobic methyl terminus. Within these constraints, a range of modifications are possible, many of which may be expected to improve in vivo properties. A select set of agents has been identified that serves both as oleamide agonists and as inhibitors of fatty acid amide hydrolase, which is responsible for the rapid inactivation of oleamide.

Arachidonylethanolamide (anandamide) binds with low affinity to dihydropyridine binding sites in brain membranes

The purpose of this study was to explore the hypothesis that the dihydropyridine (DHP) binding site of the L-type calcium channel is a high affinity binding site for the cannabimimetic arachidonylethanolamide (AEA). Binding affinities were determined from competition isotherms using the DHP analog [3H]PN-200. AEA competed for [3H]PN-200 binding with a K(I) of 40 +/- 4 microM. Inclusion of phenylmethylsulfonyl fluoride to inhibit an amidohydrolase that converts AEA to arachidonic acid had little effect on the K(I) of AEA (48 +/- 6 microM). Arachidonic acid had a slightly higher K(I) (120 +/- 11 microM) and other N-acylethanolamides examined (linolenylethanolamide, dihomo-gamma-linolenylethanolamide, docosatetraenylethanolamide, and palmitoylethanolamide) had no effect on [3H]PN-200 binding at concentrations as high as 10 microM. Our conclusions are that AEA binds to the DHP binding site with relatively low affinity and its conversion to arachidonic acid is not required for binding.

Inhibition by 2-arachidonoylglycerol, a novel type of possible neuromodulator, of the depolarization-induced increase in intracellular free calcium in neuroblastoma x glioma hybrid NG108-15 cells

2-Arachidonoylglycerol was found to inhibit the depolarization-induced increase in [Ca2+]i in NG108-15 cells differentiated with prostaglandin E1 and theophylline in a dose-dependent manner. Such an effect appears to be rather specific to polyunsaturated fatty acid-containing monoacylglycerols such as 2-arachidonoylglycerol. Neither 2-palmitoylglycerol nor free arachidonic acid exhibited appreciable inhibitory activity. These observations raise the possibility that 2-arachidonoylglycerol attenuates the increase in [Ca2+]i, thereby modulating several neural functions in this type of cell.

Human fetal membranes inhibit calcium L-channel activated uterine contractions

OBJECTIVE

Paracrine signals among fetal membranes, decidua, and uterus play an important role in the initiation of parturition in women. In previous work we demonstrated that fetal membranes inhibit uterine contractions. In the current study we test the hypothesis that the fetal membranes decrease uterine contractions by inhibition of the uterine calcium L-channel.

STUDY DESIGN

Our dual-chamber fetal membrane-uterine muscle in vitro model was used in this study. Rat uterine muscle strips were anchored into the maternal sides of the chambers. Fetal membranes (or Parafilm controls) were added to the chamber in a removable cassette. Uterine contractions were stimulated with the specific calcium L-channel agonist Bay K 8644.

RESULTS

When uterine muscle was exposed to full-thickness fetal membranes (amnion-chorion with attached decidua) or to the intact fetal components (chorion-amnion) or to chorion alone, the Bay K 8644 dose-response curve was significantly shifted to the right. When uterine muscle was exposed to amnion alone or to the decidua alone, the Bay K 8644 dose-response curve was not shifted. Fetal membranes, did not cause a shift in the ionomycin (a calcium ionophore) dose-response curve.

CONCLUSION

These results support the hypothesis and provide evidence that human fetal membranes, most likely chorion, release an endogenous calcium L-channel inhibitor.

Isotope dilution mass spectrometric measurements indicate that arachidonylethanolamide, the proposed endogenous ligand of the cannabinoid receptor, accumulates in rat brain tissue post mortem but is contained at low levels in or is absent from fresh tissue

Arachidonylethanolamide (AEA) isolated from porcine brain binds to cannabinoid receptors, mimics cannabinoid pharmacologic effects, and has been proposed as an endogenous cannabinoid receptor ligand. Demonstration of co-distribution of AEA and cannabinoid receptors in various brain regions could provide supportive evidence for this role. We have performed isotope dilution mass spectrometric measurements of AEA and have demonstrated AEA production by rat tissue homogenates in vitro from exogenous arachidonate and ethanolamine. No detectable endogenous AEA (<3.5 pmol/g of tissue) was observed in fresh rat brain, whether or not inhibitors of AEA hydrolysis were present during tissue processing. AEA (>1 nmol/g) was produced during saponification of brain phospholipid extracts. This appears not to reflect hydrolysis of N-arachidonylethanolamine phospholipid precursors of AEA, because Streptomyces chromfucsis phospholipase D, which is active against NAPE, failed to generate AEA from brain phospholipids despite substantial conversion of phospholipids to phosphatidic acid. Such experiments suggested that the abundance of N-arachidonylethanolamine phospholipid in fresh rat brain may be less than 1 in 10(6) phospholipid molecules. AEA generated during saponification of tissue phospholipids appears to arise from base-catalyzed aminolysis of arachidonate-containing glycerolipids, because AEA was produced from synthetic (1-stearoyl, 2-arachidonoyl)-phosphatidylethanolamine under saponification conditions, and the amount produced increased 300-fold when free ethanolamine was included in the hydrolysis solution. Although AEA was not detectable (<0.17 pmol/mg of protein) in fresh rat brain, AEA accumulated post mortem to levels of 126 pmol/mg of brain protein. These findings do not exclude the possibility that AEA is rapidly synthesized and degraded locally in vivo, but they indicate that the AEA content of fresh rat brain and of NAPE precursors from which AEA might be derived are exceedingly low and that AEA can be produced artifactually from biological materials.

Effects of topical anandamides on intraocular pressure in normotensive rabbits

A series of anandamide-type compounds were synthesized and studied for their effect on the intraocular pressure (IOP) of normotensive pigmented rabbits. Each test compound was dissolved in an aqueous 2-hydroxypropyl-beta-cyclodextrin solution and administered (31.25 - 62.5 micrograms) unilaterally to the eye. The most promising anandamides caused a statistically significant reduction of IOP in treated eyes, usually preceded by an initial transient elevation of IOP, compared to saline controls. In the contralateral untreated eyes, only a marginal or short hypotensive response was observed. Indomethacin pre-treatment (12.5 mg, s.c.) eliminated the IOP response to administered anandamides and arachidonic acid.

Effects of anandamide and arachidonic acid on specific binding of (+) -PN200-110, diltiazem and (-) -desmethoxyverapamil to L-type Ca2+ channel

We examined the effects of anandamide (N-arachidonoylethanolamine) on the binding of three types of Ca2+ channel antagonists for L-type Ca2+ channel, i.e., 1,4-dihydropyridine, 1,5-benzothiazepine and phenylalkylamine, to rabbit skeletal muscle membranes. Anandamide inhibited the binding of all three ligands. Arachidonic acid, a putative metabolite or a precursor of anandamide, inhibited 1,4-dihydropyridine binding, whereas it augmented both 1,5-benzothiazepine and phenylalkylamine binding. The involvement of prostaglandins synthesized from arachidonic acid was considered to be minor. These findings indicate that both anandamide and arachidonic acid interact not only with 1,4-dihydropyridine but also with 1,5-benzothiazepine and phenylalkylamine binding sites as a common feature of unsaturated lipids.

Partial purification and characterization of the porcine brain enzyme hydrolyzing and synthesizing anandamide

Anandamide (arachidonylethanolamide) is known as an endogenous agonist for cannabinoid receptors. An amidohydrolase, which hydrolyzed anandamide, was solubilized from the microsomal fraction of porcine brain with 1% Triton X-100. The enzyme was partially purified by Phenyl-5PW hydrophobic chromatography to a specific activity of approximately 0.37 mumol/min/mg of protein at 37 degrees C. As assayed with 14C-labeled substrates, the apparent Km value for anandamide was 60 microM, and anandamide was more active than ethanolamides of linoleic, oleic, and palmitic acids. Ceramidase and protease activities were not detected in our enzyme preparation. The purified enzyme also synthesized anandamide from free arachidonic acid in the presence of a high concentration of ethanolamine with a specific activity of about 0.16 mumol/min/mg of protein at 37 degrees C. On the basis of cochromatographies, pH dependence, heat inactivation, and effects of inhibitors such as arachidonyl trifluoromethyl ketone, p-chloromercuribenzoic acid, diisopropyl fluorophosphate, and phenylmethylsulfonyl fluoride, it was suggested that the anandamide amidohydrolase and synthase activities were attributable to a single enzyme protein.