There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Probability Distributions.- Linear Models for Regression.- Linear Models for Classification.- Neural Networks.- Kernel Methods.- Sparse Kernel Machines.- Graphical Models.- Mixture Models and EM.- Approximate Inference.- Sampling Methods.- Continuous Latent Variables.- Sequential Data.- Combining Models.

Pattern Recognition and Machine Learning

Two types of cannabinoid receptor have been discovered so far, CB(1) (2.1: CBD:1:CB1:), cloned in 1990, and CB(2) (2.1:CBD:2:CB2:), cloned in 1993. Distinction between these receptors is based on differences in their predicted amino acid sequence, signaling mechanisms, tissue distribution, and sensitivity to certain potent agonists and antagonists that show marked selectivity for one or the other receptor type. Cannabinoid receptors CB(1) and CB(2) exhibit 48% amino acid sequence identity. Both receptor types are coupled through G proteins to adenylyl cyclase and mitogen-activated protein kinase. CB(1) receptors are also coupled through G proteins to several types of calcium and potassium channels. These receptors exist primarily on central and peripheral neurons, one of their functions being to inhibit neurotransmitter release. Indeed, endogenous CB(1) agonists probably serve as retrograde synaptic messengers. CB(2) receptors are present mainly on immune cells. Such cells also express CB(1) receptors, albeit to a lesser extent, with both receptor types exerting a broad spectrum of immune effects that includes modulation of cytokine release. Of several endogenous agonists for cannabinoid receptors identified thus far, the most notable are arachidonoylethanolamide, 2-arachidonoylglycerol, and 2-arachidonylglyceryl ether. It is unclear whether these eicosanoid molecules are the only, or primary, endogenous agonists. Hence, we consider it premature to rename cannabinoid receptors after an endogenous agonist as is recommended by the International Union of Pharmacology Committee on Receptor Nomenclature and Drug Classification. Although pharmacological evidence for the existence of additional types of cannabinoid receptor is emerging, other kinds of supporting evidence are still lacking.

https://pharmrev.aspetjournals.org/content/pharmrev/54/2/161.full.pdf

International Union of Pharmacology. XXVII. Classification of Cannabinoid Receptors

http://www.back-in-business-physiotherapy.com/images/files/DescendingControl.pdf

Descending control of pain.

The endogenous cannabinoid receptor agonist anandamide is a powerful vasodilator of isolated vascular preparations, but its mechanism of action is unclear. Here we show that the vasodilator response to anandamide in isolated arteries is capsaicin-sensitive and accompanied by release of calcitonin-gene-related peptide (CGRP). The selective CGRP-receptor antagonist 8-37 CGRP, but not the cannabinoid CB1 receptor blocker SR141716A, inhibited the vasodilator effect of anandamide. Other endogenous (2-arachidonylglycerol, palmitylethanolamide) and synthetic (HU 210, WIN 55,212-2, CP 55,940) CB1 and CB2 receptor agonists could not mimic the action of anandamide. The selective 'vanilloid receptor' antagonist capsazepine inhibited anandamide-induced vasodilation and release of CGRP. In patch-clamp experiments on cells expressing the cloned vanilloid receptor (VR1), anandamide induced a capsazepine-sensitive current in whole cells and isolated membrane patches. Our results indicate that anandamide induces vasodilation by activating vanilloid receptors on perivascular sensory nerves and causing release of CGRP. The vanilloid receptor may thus be another molecular target for endogenous anandamide, besides cannabinoid receptors, in the nervous and cardiovascular systems.

Vanilloid receptors on sensory nerves mediate the vasodilator action of anandamide

https://www.cell.com/trends/neurosciences/pdf/S0166-2236(98)01283-1.pdf

Endocannabinoids: endogenous cannabinoid receptor ligands with neuromodulatory action.

Anandamide was the first brain metabolite shown to act as a ligand of “central” CB1 cannabinoid receptors. Here we report that the endogenous cannabinoid potently and selectively inhibits the proliferation of human breast cancer cells in vitro. Anandamide dose-dependently inhibited the proliferation of MCF-7 and EFM-19 cells with IC50 values between 0.5 and 1.5 μM and 83–92% maximal inhibition at 5–10 μM. The proliferation of several other nonmammary tumoral cell lines was not affected by 10 μM anandamide. The anti-proliferative effect of anandamide was not due to toxicity or to apoptosis of cells but was accompanied by a reduction of cells in the S phase of the cell cycle. A stable analogue of anandamide (R)-methanandamide, another endogenous cannabinoid, 2-arachidonoylglycerol, and the synthetic cannabinoid HU-210 also inhibited EFM-19 cell proliferation, whereas arachidonic acid was much less effective. These cannabimimetic substances displaced the binding of the selective cannabinoid agonist [3H]CP 55,940 to EFM-19 membranes with an order of potency identical to that observed for the inhibition of EFM-19 cell proliferation. Moreover, anandamide cytostatic effect was inhibited by the selective CB1 receptor antagonist SR 141716A. Cell proliferation was arrested by a prolactin mAb and enhanced by exogenous human prolactin, whose mitogenic action was reverted by very low (0.1–0.5 μM) doses of anandamide. Anandamide suppressed the levels of the long form of the prolactin receptor in both EFM-19 and MCF-7 cells, as well as a typical prolactin-induced response, i.e., the expression of the breast cancer cell susceptibility gene brca1. These data suggest that anandamide blocks human breast cancer cell proliferation through CB1-like receptor-mediated inhibition of endogenous prolactin action at the level of prolactin receptor.

/pdf/the-endogenous-cannabinoid-anandamide-inhibits-human-breast-48ignla63w.pdf

The endogenous cannabinoid anandamide inhibits human breast cancer cell proliferation

We reported previously that synthetic amides of polyunsaturated fatty acids with bioactive amines can result in substances that interact with proteins of the endogenous cannabinoid system (ECS). Here we synthesized a series of N-acyl-dopamines (NADAs) and studied their effects on the anandamide membrane transporter, the anandamide amidohydrolase (fatty acid amide hydrolase, FAAH) and the two cannabinoid receptor subtypes, CB(1) and CB(2). NADAs competitively inhibited FAAH from N18TG2 cells (IC(50)=19-100 microM), as well as the binding of the selective CB(1) receptor ligand, [(3)H]SR141716A, to rat brain membranes (K(i)=250-3900 nM). The arachidonoyl (20:4 omega 6), eicosapentaenoyl (20:5 omega 3), docosapentaenoyl (22:5 omega 3), alpha-linolenoyl (18:3 omega 3) and pinolenoyl (5c,9c,12c 18:3 omega 6) homologues were also found to inhibit the anandamide membrane transporter in RBL-2H3 basophilic leukaemia and C6 glioma cells (IC(50)=17.5-33 microM). NADAs did not inhibit the binding of the CB(1)/CB(2) receptor ligand, [(3)H]WIN55,212-2, to rat spleen membranes (K(i)>10 microM). N-arachidonyl-dopamine (AA-DA) exhibited 40-fold selectivity for CB(1) (K(i)=250 nM) over CB(2) receptors, and N-docosapentaenoyl-dopamine exhibited 4-fold selectivity for the anandamide transporter over FAAH. AA-DA (0.1-10 microM) did not displace D1 and D2 dopamine-receptor high-affinity ligands from rat brain membranes, thus suggesting that this compound has little affinity for these receptors. AA-DA was more potent and efficacious than anandamide as a CB(1) agonist, as assessed by measuring the stimulatory effect on intracellular Ca(2+) mobilization in undifferentiated N18TG2 neuroblastoma cells. This effect of AA-DA was counteracted by the CB(1) antagonist SR141716A. AA-DA behaved as a CB(1) agonist in vivo by inducing hypothermia, hypo-locomotion, catalepsy and analgesia in mice (1-10 mg/kg). Finally, AA-DA potently inhibited (IC(50)=0.25 microM) the proliferation of human breast MCF-7 cancer cells, thus behaving like other CB(1) agonists. Also this effect was counteracted by SR141716A but not by the D2 antagonist haloperidol. We conclude that NADAs, and AA-DA in particular, may be novel and useful probes for the study of the ECS.

N-acyl-dopamines: novel synthetic CB 1 cannabinoid-receptor ligands and inhibitors of anandamide inactivation with cannabimimetic activity in vitro and in vivo

Biosynthesis, Uptake, and Degradation of Anandamide and Palmitoylethanolamide in Leukocytes

The stimulus-induced biosynthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG) in intact mouse J774 macrophages and the inactivation of 2-AG by the same cells or by rat circulating macrophages was studied. By using gas chromatography-mass spectrometry, we found that ionomycin (5 µm) and lipopolysaccharide (LPS, 200 µg·mL−1) cause a 24-fold and 2.5-fold stimulation of 2-AG levels in J774 cells, respectively, thus providing unprecedented evidence that this cannabimimetic metabolite can be synthesized by macrophages. In J774 cells, LPS also induced a 7.8-fold increase of the levels of the other endocannabinoid, anandamide, and, in rat circulating macrophages, an almost twofold increase of 2-AG levels. Extracellular [3H]2-AG was cleared from the medium of intact J774 macrophages (t1/2 = 19–28 min) and esterified to phospholipids, diacylglycerols and triglycerides or hydrolyzed to [3H]arachidonic acid and glycerol. These catabolic processes were attenuated differentially by various enzyme inhibitors. Rat circulating macrophages were shown to contain enzymatic activities for the hydrolysis of 2-AG, including: (a) fatty acid amide hydrolase (FAAH), the enzyme responsible for anandamide breakdown and previously shown to catalyse also 2-AG hydrolysis, and (b) a 2-AG hydrolase activity different from FAAH and down-regulated by LPS. High levels of FAAH mRNA were found in circulating macrophages but not platelets, which, however, contain a 2-AG hydrolase. Both platelets and macrophages were shown to express the mRNA for the CB1 cannabinoid receptor. A macrophage 2-AG hydrolase with apparent Km = 110 µm and Vmax = 7.9 nmol·min−1·(mg protein)−1 was partially characterized in J774 cells and found to exhibit an optimal pH of 6–7 and little or no sensitivity to typical FAAH inhibitors. These findings demonstrate for the first time that macrophages participate in the homeostasis of the hypotensive and immunomodulatory endocannabinoid 2-AG through metabolic mechanisms that are subject to regulation.

Dominique Melck

Papers

Endocannabinoids: endogenous cannabinoid receptor ligands with neuromodulatory action.

The endogenous cannabinoid anandamide inhibits human breast cancer cell proliferation

N-acyl-dopamines: novel synthetic CB 1 cannabinoid-receptor ligands and inhibitors of anandamide inactivation with cannabimimetic activity in vitro and in vivo

Biosynthesis, Uptake, and Degradation of Anandamide and Palmitoylethanolamide in Leukocytes

Biosynthesis and inactivation of the endocannabinoid 2-arachidonoylglycerol in circulating and tumoral macrophages.