Pharmacological evidence for anandamide amidase in human cardiac and vascular tissues

CannabinEYEds: The Endocannabinoid System as a Regulator of the Ocular Surface Nociception, Inflammatory Response, Neovascularization and Wound Healing

The endocannabinoid system (ECS) is a complex regulatory system, highly conserved among vertebrates. It has been widely described in nearly all human tissues. In the conjunctiva and cornea, the ECS is believed to play a pivotal role in the modulation of the local inflammatory state as well as in the regulation of tissue repair and fibrosis, neo-angiogenesis and pain perception. This review aims to summarize all the available data on ECS expression and its function in ocular surface structures to provide a specific insight concerning its modulation in dry eye disease, and to propose directions for future research.

Residual Effects of THC via Novel Measures of Brain Perfusion and Metabolism in a Large Group of Chronic Cannabis Users

Given the known vascular effects of cannabis, this study examined the neurophysiological factors that may affect studies of brain activity in cannabis users. We conducted a systematic evaluation in 72 h abstinent, chronic cannabis users (N=74) and nonusing controls (N=101) to determine the association between prolonged cannabis use and the following neurophysiological indicators: (1) global and regional resting cerebral blood flow (CBF), (2) oxygen extraction fraction (OEF), and (3) cerebral metabolic rate of oxygen (CMRO₂). We found that cannabis users had greater global OEF and CMRO₂ compared with nonusers. Regionally, we found higher CBF in the right pallidum/putamen of the cannabis users compared with nonusers. Global resting CBF and regional CBF of right superior frontal cortex correlated positively with creatinine-normalized Δ9-tetrahydrocannabinol (THC) levels. These findings demonstrate residual effects of cannabis use whereby global and regional brain metabolism are altered in those with prolonged cannabis exposure. These neurophysiological alterations should be considered in both research and clinical applications.

Cannabinoid signaling in health and disease

Cannabis sativa has long been used for medicinal purposes. To improve safety and efficacy, compounds from C. sativa were purified or synthesized and named under an umbrella group as cannabinoids. Currently, several cannabinoids may be prescribed in Canada for a variety of indications such as nausea and pain. More recently, an increasing number of reports suggest other salutary effects associated with endogenous cannabinoid signaling including cardioprotection. The therapeutic potential of cannabinoids is therefore extended; however, evidence is limited and mechanisms remain unclear. In addition, the use of cannabinoids clinically has been hindered due to pronounced psychoactive side effects. This review provides an overview on the endocannabinoid system, including known physiological roles, and conditions in which cannabinoid receptor signaling has been implicated.

Isoniazid metabolism and hepatotoxicity

Isoniazid (INH) is highly effective for the management of tuberculosis. However, it can cause liver injury and even liver failure. INH metabolism has been thought to be associated with INH-induced liver injury. This review summarized the metabolic pathways of INH and discussed their associations with INH-induced liver injury.

Ligand activation of cannabinoid receptors attenuates hypertrophy of neonatal rat cardiomyocytes

: Endocannabinoids are bioactive amides, esters, and ethers of long-chain polyunsaturated fatty acids. Evidence suggests that activation of the endocannabinoid pathway offers cardioprotection against myocardial ischemia, arrhythmias, and endothelial dysfunction of coronary arteries. As cardiac hypertrophy is a convergence point of risk factors for heart failure, we determined a role for endocannabinoids in attenuating endothelin-1-induced hypertrophy and probed the signaling pathways involved. The cannabinoid receptor ligand anandamide and its metabolically stable analog, R-methanandamide, suppressed hypertrophic indicators including cardiomyocyte enlargement and fetal gene activation (ie, the brain natriuretic peptide gene) elicited by endothelin-1 in isolated neonatal rat ventricular myocytes. The ability of R-methanandamide to suppress myocyte enlargement and fetal gene activation was mediated by CB2 and CB1 receptors, respectively. Accordingly, a CB2-selective agonist, JWH-133, prevented only myocyte enlargement but not brain natriuretic peptide gene activation. A CB1/CB2 dual agonist with limited brain penetration, CB-13, inhibited both hypertrophic indicators. CB-13 activated AMP-activated protein kinase (AMPK) and, in an AMPK-dependent manner, endothelial nitric oxide synthase (eNOS). Disruption of AMPK signaling, using compound C or short hairpinRNA knockdown, and eNOS inhibition using L-NIO abolished the antihypertrophic actions of CB-13. In conclusion, CB-13 inhibits cardiomyocyte hypertrophy through AMPK-eNOS signaling and may represent a novel therapeutic approach to cardioprotection.

Triphasic blood pressure responses to cannabinoids: do we understand the mechanism?

The cannabinoids comprise three major classes of substances, including compounds derived from the cannabis plant (e.g. Δ(9) -tetrahydrocannabinol and the chemically related substances CP55940 and HU210), endogenously formed (e.g. anandamide) and synthetic compounds (e.g. WIN55212-2). Beyond their psychotropic effects, cannabinoids have complex effects on blood pressure, including biphasic changes of Δ(9) -tetrahydrocannabinol and WIN55212-2 and an even triphasic effect of anandamide. The differing pattern of blood pressure changes displayed by the three types of compounds is not really surprising since, although they share an agonistic effect at cannabinoid CB(1) and CB(2) receptors, some compounds have additional effects. In particular, anandamide is known for its pleiotropic effects, and there is overwhelming evidence that anandamide influences blood pressure via (i) CB(1) receptors, (ii) TRPV1 receptors, (iii) endothelial cannabinoid receptors and (iv) degradation products. This review is dedicated to the description of the effects of externally added cannabinoids on cardiovascular parameters in vivo. First, the cardiovascular effects of cannabinoids in anaesthetized animals will be highlighted since most data have been generated in experiments of that type. The text will follow the three phases of anandamide on blood pressure, and we will check to which extent cardiovascular changes elicited by other cannabinoids show overlap with those effects or differ. The second part will be dedicated to the cardiovascular effects of the cannabinoids in conscious animals. In the third part, cardiovascular effects in humans will be discussed, and similarities and differences with respect to the data from animals will be examined.

Endocannabinoid system in cardiovascular disorders - new pharmacotherapeutic opportunities

The long history of Cannabis sativa had its development stimulated and oriented for medicine after the discovery and chemical characterization of its main active ingredient, the 9-tetrahydrocannabinol (9-THC). Consequently, a binding site for 9-THC was identified in rat brains and the first cannabinoid receptor (CB1) was cloned, followed by the CB2 and by the discover of two endogenous agonists: anandamide and 2-arachidonoyl glycerol. Cannabinoid receptors, endocannabinoids and the enzymes that catalyze its synthesis and degradation constitute the endocannabinoid system (ECS), which plays an important role in the cardiovascular system. In vivo experiments with rats have demonstrated the action of anandamide and 2-AG on the development of atherosclerotic plaque, as well as an effect on heart rate, blood pressure, vasoactivity and energy metabolism (action in dyslipidemia and obesity). Recent studies with an antagonist of CB1 receptors showed that the modulation of ECS can play an important role in reducing cardiovascular risk in obese and dyslipidemic patients. Similarly, studies in rats have demonstrated the action of CB2 receptors in adhesion, migration, proliferation and function of immune cells involved in the atherosclerotic plaque formation process. The evidence so far gathered shows that the modulation of ECS (as agonism or antagonism of its receptors) is an enormous potential field for research and intervention in multiple areas of human pathophysiology. The development of selective drugs for the CB1 and CB2 receptors may open a door to new therapeutic regimens.This review article aims to address the key findings and evidences on the modulation of ECS, in order to prospect future forms of therapeutic intervention at the cardiovascular level. A recent, emerging, controversial and of undoubted scientific interest subject, which states as a potential therapeutic target to reach in the 21^st century.

Cannabinoids and endocannabinoids in metabolic disorders with focus on diabetes

The cannabinoid receptors for Δ(9)-THC, and particularly, the CB(1) receptor, as well as its endogenous ligands, the endocannabinoids anandamide and 2-arachidonoylglycerol, are deeply involved in all aspects of the control of energy balance in mammals. While initially it was believed that this endocannabinoid signaling system would only facilitate energy intake, we now know that perhaps even more important functions of endocannabinoids and CB(1) receptors in this context are to enhance energy storage into the adipose tissue and reduce energy expenditure by influencing both lipid and glucose metabolism. Although normally well controlled by hormones and neuropeptides, both central and peripheral aspects of endocannabinoid regulation of energy balance can become dysregulated and contribute to obesity, dyslipidemia, and type 2 diabetes, thus raising the possibility that CB(1) antagonists might be used for the treatment of these metabolic disorders. On the other hand, evidence is emerging that some nonpsychotropic plant cannabinoids, such as cannabidiol, can be employed to retard β-cell damage in type 1 diabetes. These novel aspects of endocannabinoid research are reviewed in this chapter, with emphasis on the biological effects of plant cannabinoids and endocannabinoid receptor antagonists in diabetes.

The molecules: mechanisms of arterial vasodilatation observed in the splanchnic and systemic circulation in portal hypertension

A hyperdynamic splanchnic and systemic circulation is typical of cirrhotic patients and has been observed in all experimental forms of portal hypertension. The hyperdynamic circulation is most likely initiated by arterial vasodilatation, leading to central hypovolemia, sodium retention, and an increased intravascular volume. Arterial vasodilatation is regulated by a complex interplay of various vasodilator molecules and factors that influence the production of those vasodilator molecules. Nitric oxide (NO) has been recognized as the most important vasodilator molecule that mediates the excessive arterial vasodilatation observed in portal hypertension. The aims of this review are (1) to categorize NO synthase isoforms involved in NO overproduction; (2) to explain the mechanisms of endothelial NO synthase up-regulation; and (3) to summarize other molecules involved in the arterial vasodilatation.

Cannabinoids as therapeutic agents in cardiovascular disease: a tale of passions and illusions

In addition to their classical known effects, such as analgesia, impairment of cognition and learning and appetite enhancement, cannabinoids have also been related to the regulation of cardiovascular responses and implicated in cardiovascular pathology. Elevated levels of endocannabinoids have been related to the extreme hypotension associated with various forms of shock as well as to the cardiovascular abnormalities that accompany cirrhosis. In contrast, cannabinoids have also been associated with beneficial effects on the cardiovascular system, such as a protective role in atherosclerosis progression and in cerebral and myocardial ischaemia. In addition, it has also been suggested that the pharmacological manipulation of the endocannabinoid system may offer a novel approach to antihypertensive therapy. During the last decades, the tremendous increase in the understanding of the molecular basis of cannabinoid activity has encouraged many pharmaceutical companies to develop more potent synthetic cannabinoid analogues and antagonists, leading to an explosion of basic research and clinical trials. Consequently. not only the synthetic THC dronabinol (Marinol) and the synthetic THC analogue nabilone (Cesamet) have been approved in the United States, but also the standardized cannabis extract (Sativex) in Canada. At least three strategies can be foreseen in the future clinical use of cannabinoid-based drugs: (a) the use of CB(1) receptor antagonists, such as the recently approved rimonabant (b) the use of CB(2)-selective agonists, and (c) the use of inhibitors of endocannabinoid degradation. In this context, the present review examines the effects of cannabinoids and of the pharmacological manipulation of the endocannabinoid system, in cardiovascular pathophysiology.

Cannabinoid agonists induce relaxation in the bovine ophthalmic artery: evidences for CB1 receptors, nitric oxide and potassium channels

Glaucoma pathophysiology appears to involve vascular deficits, which may contribute to initiation and progression of the disease. Anandamide, the endogenous cannabinoid ligand, and WIN55212-2, a synthetic cannabinoid agonist, are able to evoke concentration-dependent relaxations in bovine ophthalmic artery rings, precontracted with 5-hydroxytryptamine (5-HT) (1 microM). Endothelium removal reduces cannabinoid agonist potency and efficacy. The selective cannabinoid 1 (CB1) receptor antagonists SR141716A (100 nM) and AM251 (100 nM) cause a shift to the right in the concentration-response curves to anandamide and WIN55212-2 in arterial rings both in the presence and in the absence of endothelium. In endothelium-intact arteries, the nitric oxide synthase inhibitor, N(G)-monomethyl-L-arginine (L-NMMA, 300 microM), completely blocked the anandamide- and WIN55212-2-relaxant responses; by contrast, the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP, 100 microM) induced an increase in vasorelaxant responses to cannabinoid agonists. Relaxations to anandamide and WIN55212-2 were inhibited by iberiotoxin (IbTX, 200 nM), a blocker of large conductance, Ca2+-activated K+ channel (BK(Ca)), and by 4-aminopyridine (4-AP; 1 mM), a blocker of delayed rectifier K+ channel, whereas the blockade of K(ATP) channels by glibenclamide (5 microM) and of small conductance Ca2+-activated K+ channels (SK(Ca)) by apamin (100 nM) did not produce any effects. These data suggest that anandamide and WIN55212-2 relax the bovine ophthalmic artery by involving CB1 the cannabinoid receptor-sensitive pathway. In endothelium-intact arteries, relaxation occurs through activation of nitric oxide synthase cyclic GMP and Ca2+-activated K+ channels. They also cause endothelium-independent relaxation by involving potassium channel opening.

Endocannabinoid system and its role in energy regulation

Endocannabinoids are endogenous agonists for the two types of cannabinoid receptors identified to date, the CB₁ and CB₂ receptors. CB₁ receptors and tissue concentrations of endocannabinoids sufficient to activate them are present in the brain structures controlling energy intake (i.e., the hypothalamus, nucleus accumbens and nodose ganglion), as well as in all peripheral organs mostly involved in the regulation of energy homeostasis (i.e., the duodenum, small and large intestine, adipose tissue, skeletal muscle, pancreas and liver). Several peripheral neuropeptides and hormones involved in energy balance, and type of diet, regulate endocannabinoid levels, whereas endocannabinoids, in turn, regulate the expression and release of hypothalamic mediators involved in nutrient intake. Dysregulation of the endocannabinoid system might contribute to the development of eating disorders and explain why CB₁ receptor blockers are efficacious at reducing not only food intake but also the metabolic consequences of visceral adiposity and obesity.

The hyperdynamic circulation of chronic liver diseases: from the patient to the molecule

The hyperdynamic circulatory syndrome observed in chronic liver diseases is a great example of research that originated from clinical observations and progressed in the last 50 years from the patient to the experimental laboratory. Our knowledge has evolved from the patient to the molecule, using experimental models that serve as a source for understanding the complex pathophysiological mechanisms that govern this complex syndrome. We now know that progressive vasodilatation is central to the detrimental effects observed in multiple organs. Although nitric oxide has been shown to be the primary vasodilator molecule in these effects, other molecules also participate in the complex mechanisms of vasodilatation. This review summarizes three major areas: first, clinical observation in patients; second, experimental models used to study the hyperdynamic circulatory syndrome; and third, the vasodilator molecules that play roles in vascular abnormalities observed in portal hypertension.

Role of CGRP and GABA in the hypotensive effect of intrathecally administered anandamide to anesthetized rats

In urethane-anesthetized rats the intrathecal (i.t.) injection of 100 nmol anandamide produced a hypotensive effect (-19.3+/-1.6 mm Hg; n=6) that was mimicked by i.t. administration of 0.25 nmol calcitonin gene-related peptide (CGRP; -26.2+/-1.8 mm Hg, n=4). Both effects were antagonized either by the CGRP receptor antagonist CGRP(8-37) (5 nmol; i.t.) or by the gamma-aminobutyric acid (GABA)(A) receptor antagonist bicuculline (8.8 nmol, i.t) or by the GABA(B) receptor antagonist 2-hydroxy saclofen (110 nmol; i.t.). On the contrary, blockade of spinal CGRP receptors by CGRP(8-37) did not modify the hypotensive response to either the GABA(A)-receptor agonist muscimol (8.8 nmol; i.t.) or the GABA(B)-receptor agonist baclofen (100 nmol; i.t). This result suggests a unidirectional effect of CGRP on the GABAergic system. The response to anandamide remained unaltered after acute inhibition of nitric oxide (NO) synthase activity by either i.t. (1 micromol) or i.v. (10 mg/kg) injection of N(G)-nitro-L-arginine methyl ester (L-NAME), but increased significantly after long-term L-NAME administration (70 mg/kg/day; four weeks; p.o.), thus suggesting compensatory changes in cardiovascular homeostasis. It is proposed that the hypotensive effect of anandamide in urethane-anesthetized rats could involve the release of CGRP followed by the release of GABA in the spinal cord. NO does not appear to have a direct participation in the spinal mechanisms involved in the decrease of the blood pressure caused by anandamide.

Cardiovascular pharmacology of cannabinoids

Cannabinoids and their synthetic and endogenous analogs affect a broad range of physiological functions, including cardiovascular variables, the most important component of their effect being profound hypotension. The mechanisms of the cardiovascular effects of cannabinoids in vivo are complex and may involve modulation of autonomic outflow in both the central and peripheral nervous systems as well as direct effects on the myocardium and vasculature. Although several lines of evidence indicate that the cardiovascular depressive effects of cannabinoids are mediated by peripherally localized CB1 receptors, recent studies provide strong support for the existence of as-yet-undefined endothelial and cardiac receptor(s) that mediate certain endocannabinoid-induced cardiovascular effects. The endogenous cannabinoid system has been recently implicated in the mechanism of hypotension associated with hemorrhagic, endotoxic, and cardiogenic shock, and advanced liver cirrhosis. Furthermore, cannabinoids have been considered as novel antihypertensive agents. A protective role of endocannabinoids in myocardial ischemia has also been documented. In this chapter, we summarize current information on the cardiovascular effects of cannabinoids and highlight the importance of these effects in a variety of pathophysiological conditions.

Cannabinoids acting on CB1 receptors decrease contractile performance in human atrial muscle

Cannabinoids elicit hypotension mainly via activated CB(1) receptors and show complex cardiovascular actions. Effects on human heart muscle have not been studied yet. Isolated human atrial heart muscle preparations were stimulated by electrical field with 1 Hz to contract isometrically at optimal length and were challenged with the endogenous cannabinoid arachidonyl ethanolamide (anandamide), the metabolically stable analogue R-methanandamide, and the potent synthetic CB(1) receptor agonist HU-210. Anandamide dose-dependently decreased systolic force (82.2 +/- 4.8% and 60.8 +/- 6.8% of maximal systolic force for 0.1 and 1 microM, respectively, P < 0.05). The selective CB(1) receptor antagonist AM-251 (1 microM, P < 0.05), but not the CB(2) receptor antagonist, AM-630 (1 microM), the nitric oxide synthase inhibitor N omega-nitro-l-arginine methyl ester (l-NAME) (500 microM), or the cyclooxygenase inhibitor indomethacin (100 microM), prevented the effect. Contrary to indomethacin, l-NAME alone showed negative inotropic effects (72.1 +/- 3.54%, P < 0.001). The R-methanandamide (1 microM: 50.4 +/- 3.5%, P < 0.001) and HU-210 (1 microM: 60.1 +/- 3.8%, P < 0.001) had similar negative inotropic effects. The existence of CB(1) receptors on heart muscle was verified using Western blot analysis and immunofluorescence staining. The conclusion is that anandamide, R-methanandamide, and HU-210 decrease contractile performance in human atrial muscle via CB(1) receptors.

Cardiovascular effects of cannabinoids

The prototypic endocannabinoid, anandamide, and synthetic analogues have been shown to elicit pressor and depressor effects, bradycardia, vasorelaxation, and inhibition of neurotransmission in the central and peripheral nervous systems. Cannabinoid-mediated inhibition of neurotransmission is mediated by inhibition of voltage-gated Ca(2+) channels and adenylyl cyclase and activation of inwardly rectifying K(+) channels. The precise mechanisms underlying the vasorelaxant actions of cannabinoids are currently unclear, but might involve both receptor-dependent and -independent and endothelium-dependent and -independent pathways. Mechanisms proposed have included the release of endothelial autacoids, activation of myoendothelial gap junctions, activation of the Na(+) pump, activation of K(+) channels, inhibition of Ca(2+) channels, and activation of vanilloid receptors, leading to the release of sensory neurotransmitters. Pathophysiologically, the vasodilator actions of endocannabinoids have been implicated in the hypotension associated with both septic and haemorrhagic shock, but their physiological significance remains to be determined.

Substantial species differences in relation to formation and degradation of N-acyl-ethanolamine phospholipids in heart tissue: an enzyme activity study

The formation of N-acyl-ethanolamines (NAEs), including the cannabinoid receptor ligand anandamide, and their precursors N-acyl-ethanolamine phospholipids (NAPEs) are catalyzed by NAPE-hydrolyzing phospholipase D (NAPE-PLD) and N-acyl-transferase, respectively. NAPE and NAE are suggested to have beneficial effects on the heart, but in the literature there are indications of species differences in the activity of these enzymes. We have examined heart microsomes from rats, mice, guinea pigs, rabbits, frogs, cows, dogs, cats, mini pigs and human beings for activities of these two enzymes. N-Acyl-transferase activity was very high in dogs and cats (>13 pmol/min/mg protein) whereas it was very low to barely detectable in the other species (<3 pmol/min/mg protein). NAPE-PLD activity was very high in rats and guinea pigs (>45 pmol/min/mg protein) whereas it was 9 pmol/min/mg protein in frogs and below that in the other species. The ratio of activity between the two enzymes varied from 0.002 to 15 in the investigated species. The activity of the two enzymes in rat hearts as opposed to rat brain did not change during development. These results indicate that there may be substantial species differences in the generation of anandamide and other NAEs as well as NAPEs in heart tissues.

Cardiovascular pharmacology of anandamide

The fatty acid amide anandamide produces hypotension and a decrease in systemic vascular resistance in vivo. A drop in blood pressure is also seen with synthetic cannabinoid (CB) receptor agonists. The hypotensive responses to anandamide and synthetic cannabinoids are absent in CB1 receptor gene knockout mice. In isolated arteries and perfused vascular beds, anandamide induces vasodilator responses, which cannot be mimicked by synthetic cannabinoids. Instead, vanilloid receptors on perivascular sensory nerves play a key role in these effects of anandamide. Activation of vanilloid receptors by anandamide triggers the release of sensory neuropeptides such as the vasodilator calcitonin gene-related peptide (CGRP). Anandamide is detected in blood and in many cells of the cardiovascular system, and macrophage-derived anandamide may be involved in several hypotensive clinical conditions. Interestingly, cannabinoid and vanilloid receptors display an overlap in ligand recognition properties, and the frequently used CB1 receptor antagonist SR141716A also inhibits vanilloid receptor-mediated responses. The presence of anandamide in endothelial cells, neurones and activated macrophages (monocytes), and its ability to activate CB and vanilloid receptors make this lipid a potential bioregulator in the cardiovascular system.

Opioids are non-competitive inhibitors of nitric oxide synthase in T47D human breast cancer cells

Opioids and nitric oxide (NO) interact functionally in different systems. NO-generating agents decrease the activity of opioid agonists, prevent opioid tolerance, and are used in opioid withdrawal syndromes. There exist, however, few reports indicating a direct interaction of the two systems. T47D human breast cancer cells in culture express opioid receptors, and opioid agonists inhibit their growth, while they release high amounts of the NO-related molecules NO(2-)/NO(3-)to the culture medium. We have used this system to assay a possible direct interaction of opiergic and nitric oxide systems. Our results show that delta- or mu-acting opioid agonists do not modify the release of NO(2-)/NO(3-). In contrast, kappa-acting opioid agonists (ethylketocyclazocine, and alpha(S1)-casomorphine) decrease the release of NO(2-)/NO(3-), in a time- and dose-dependent manner. The general opioid antagonist diprenorphine (10(-6) M) produce a similar NO(2-)/NO(3-)release inhibition, indicating a possible non-opioid-receptor mediated phenomenon. In addition, ethylketocyclazocine, alpha(S1)-casomorphin and diprenorphine directly inhibit NOS activity: agonists, interact with both calcium-dependent and independent NOS-isoforms, while the antagonist diprenorphine modifies only the activity of the calcium-dependent fraction of the enzyme. Analysis of this interaction revealed that opioids modify the dimeric active form of NOS, through binding to the reductase part of the molecule, acting as non-competitive inhibitors of the enzyme. This interaction opens interesting new possibilities for tumor biology and breast cancer therapy.

Endocannabinoids acting at vascular CB1 receptors mediate the vasodilated state in advanced liver cirrhosis

Advanced cirrhosis is associated with generalized vasodilation of unknown origin, which contributes to mortality. Cirrhotic patients are endotoxemic, and activation of vascular cannabinoid CB1 receptors has been implicated in endotoxin-induced hypotension. Here we show that rats with biliary cirrhosis have low blood pressure, which is elevated by the CB1 receptor antagonist SR141716A. The low blood pressure of rats with CCl4-induced cirrhosis was similarly reversed by SR141716A, which also reduced the elevated mesenteric blood flow and portal pressure. Monocytes from cirrhotic but not control patients or rats elicited SR141716A-sensitive hypotension in normal recipient rats and showed significantly elevated levels of anandamide. Compared with non-cirrhotic controls, in cirrhotic human livers there was a three-fold increase in CB1 receptors on isolated vascular endothelial cells. These results implicate anandamide and vascular CB1 receptors in the vasodilated state in advanced cirrhosis and indicate a novel approach for its management.

Evidence for an endocannabinoid system in the central nervous system of the leech Hirudo medicinalis

In invertebrates, like Hydra and sea urchins, evidence for a functional cannabinoid system was described. The partial characterization of a putative CB1 cannabinoid receptor in the leech Hirudo medicinalis led us to investigate the presence of a complete endogenous cannabinoid system in this organism. By using gas chromatography-mass spectrometry, we demonstrate the presence of the endocannabinoids anandamide (N-arachidonoylethanolamine, 21.5+/-0.7 pmol/g) and 2-arachidonoyl-glycerol (147.4+/-42.7 pmol/g), and of the biosynthetic precursor of anandamide, N-arachidonylphosphatidyl-ethanolamine (16.5+/-3.3 pmol/g), in the leech central nervous system (CNS). Anandamide-related molecules such as N-palmitoylethanolamine (32.4+/-1.6 pmol/g) and N-linolenoylethanolamine (5.8 pmol/g) were also detected. We also found an anandamide amidase activity in the leech CNS cytosolic fraction with a maximal activity at pH 7 and little sensitivity to typical fatty acid amide hydrolase (FAAH) inhibitors. Using an antiserum directed against the amidase signature sequence, we focused on the identification and the localization of the leech amidase. Firstly, leech nervous system protein extract was subjected to Western blot analysis, which showed three immunoreactive bands at ca. approximately 42, approximately 46 and approximately 66 kDa. The former and latter bands were very faint and were also detected in whole homogenates from the coelenterate Hydra vulgaris, where the presence of CB1-like receptors, endocannabinoids and a FAAH-like activity was reported previously. Secondly, amidase immunocytochemical detection revealed numerous immunoreactive neurons in the CNS of three species of leeches. In addition, we observed that leech amidase-like immunoreactivity matches to a certain extent with CB1-like immunoreactivity. Finally, we also found that stimulation by anandamide of this receptor leads, as in mammals, to inhibition of cAMP formation, although this effect appeared to be occurring through the previously described anandamide-induced and CB1-mediated activation of nitric oxide release. Taken together, these results suggest the existence of a complete and functional cannabinoid system in leeches.

2-arachidonyl-glycerol stimulates nitric oxide release from human immune and vascular tissues and invertebrate immunocytes by cannabinoid receptor 1

The pharmacological physiological effects of the endogenous cannabinomimetic (endocannabinoid) anandamide have been well characterized. Another endocannabinoid, 2-arachidonoyl-glycerol (2-AG), has been less-widely studied. 2-AG occurs in vertebrate and invertebrate tissues and binds to both cannabinoid receptors (CB1 and CB2). In the current study, 2-AG was found to cause human monocytes and immunocytes from Mytilus edulis to become round and immobile, which may correlate with decreased production of cytokines and adhesion molecules, i.e. an immunosuppressive response. In addition, exposure of these cells to 2-AG results in nitric oxide (NO) release, which is blocked by the nitric oxide synthase inhibitor, l-NAME and a CB1 antagonist, but not by a CB2 antagonist. The results obtained in the human vascular system were similar to those obtained in immune cells. Treatment of human saphenous veins and atria with 2-AG stimulated basal NO release, which was antagonized by l-NAME and a CB1 antagonist. Taken together these results indicate that 2-AG exerts immune and vascular actions similar to those observed with anandamide.

Influence of cannabinoids on the delayed rectifier in freshly dissociated smooth muscle cells of the rat aorta

The influence of the cannabinoids anandamide, methanandamide and WIN 55212-2 on the delayed rectifier K(+) current (I(K(V))) in rat arterial myocytes was investigated. Anandamide caused a concentration-dependent reduction of total peak and late K(+) current (I(K)). The maximal effect (about 50% inhibition of I(K)) was reached with 3 microM, and half-maximal current block was observed at 0.6 microM. Blockade was voltage-independent. Inhibition of I(K) by the cannabinoid was associated with a characteristic increase in the rate of current relaxation. Methanandamide (10 microM), a metabolically more stable analogue of anandamide, decreased I(K) with a similar time course. Current traces in the presence of the drug also showed an acceleration of inactivation. The presence of TEA did not impair the inhibition by anandamide or methanandamide, but inhibition was prevented by pre-exposure to 4-AP, showing that both cannabinoids inhibited I(K(V)) while having no influence on Ca(2+)-dependent K(+) current (I(K(Ca))). The CB(1) receptor antagonist SR141716A (10 microM) did not influence the action of anandamide or methanandamide. Arachidonic acid (1 microM) increased I(K) considerably. However, in the presence of TEA it caused a decrease of I(K(V)) with a characteristic increase in the rate of current relaxation. WIN 55212-2 (20 microM) caused similar inhibition of I(K). Internally applied anandamide (10 microM) or methanandamide (10 microM) was ineffective at influencing I(K). In the dialyzed cells, the additional external application of a cannabinoid promptly initiated inhibition. The results show that anandamide, methanandamide and WIN 55212-2 affect I(K(V)) in a cannabinoid receptor-independent way similar to that of arachidonic acid, which, unlike the cannabinoids, additionally increases a Ca(2+)-activated K(+) current. It is suggested that cannabinoids might bind to an external site on or near the K(v) channel of the vascular smooth muscle cells.

Basal nitric oxide limits immune, nervous and cardiovascular excitation: human endothelia express a mu opiate receptor

Nitric oxide (NO) is a major signaling molecule in the immune, cardiovascular and nervous systems. The synthesizing enzyme, nitric oxide synthase (NOS) occurs in three forms: endothelial (e), neuronal (n) and inducible (i) NOS. The first two are constitutively expressed. We surmise that in many tissues there is a basal level of NO and that the actions of several signaling molecules initiate increases in cNOS-derived NO to enhance momentary basal levels that exerts inhibitory cellular actions, via cellular conformational changes. It is our contention that much of the literature concerning the actions of NO really deal with i-NOS-derived NO. We make the case that cNOS is responsible for a basal or 'tonal' level of NO; that this NO keeps particular types of cells in a state of inhibition and that activation of these cells occurs through disinhibition. Furthermore, naturally occurring signaling molecules such as morphine, anandamide, interleukin-10 and 17-beta-estradiol appear to exert, in part, their beneficial physiological actions, i.e., immune and endothelial down regulation by the stimulation of cNOS. In regard to opiates, we demonstrate the presence of a human endothelial mu opiate receptor by RT-PCR and sequence determination, further substantiating the role of opiates in vascular coupling to NO release. Taken together, cNOS derived NO enhances basal NO actions, i.e., cellular activation state, and these actions are further enhanced by iNOS derived NO.

The endothelial component of cannabinoid-induced relaxation in rabbit mesenteric artery depends on gap junctional communication

1. We have shown that the endocannabinoid anandamide and its stable analogue methanandamide relax rings of rabbit superior mesenteric artery through endothelium-dependent and -independent mechanisms that are unaffected by blockade of NO synthase and cyclooxygenase. 2. The endothelium-dependent component of the responses was attenuated by the gap junction inhibitor 18alpha-glycyrrhetinic acid (18alpha-GA; 50 microM), and a synthetic connexin-mimetic peptide homologous to the extracellular Gap 27 sequence of connexin 43 (43Gap 27, SRPTEKTIFII; 300 microM). By contrast, the corresponding connexin 40 peptide (40Gap 27, SRPTEKNVFIV) was inactive. 3. The cannabinoid CB1 receptor antagonist SR141716A (10 microM) also attenuated endothelium-dependent relaxations but this inhibition was not observed with the CB1 receptor antagonist LY320135 (10 microM). Furthermore, SR141716A mimicked the effects of 43Gap 27 peptide in blocking Lucifer Yellow dye transfer between coupled COS-7 cells (a monkey fibroblast cell line), whereas LY320135 was without effect, thus suggesting that the action of SR141716A was directly attributable to effects on gap junctions. 4. The endothelium-dependent component of cannabinoid-induced relaxation was also attenuated by AM404 (10 microM), an inhibitor of the high-affinity anandamide transporter, which was without effect on dye transfer. 5. Taken together, the findings suggest that cannabinoids derived from arachidonic acid gain access to the endothelial cytosol via a transporter mechanism and subsequently stimulate relaxation by promoting diffusion of an to adjacent smooth muscle cells via gap junctions. 6. Relaxations of endothelium-denuded preparations to anandamide and methanandamide were unaffected by 43Gap 27 peptide, 18alpha-GA, SR141716A, AM404 and indomethacin and their genesis remains to be established.