BackgroundMicroglia provide continuous immune surveillance of the CNS and upon activation rapidly change phenotype to express receptors that respond to chemoattractants during CNS damage or infection. These activated microglia undergo directed migration towards affected tissue. Importantly, the molecular species of chemoattractant encountered determines if microglia respond with pro- or anti-inflammatory behaviour, yet the signaling molecules that trigger migration remain poorly understood. The endogenous cannabinoid system regulates microglial migration via CB2 receptors and an as yet unidentified GPCR termed the 'abnormal cannabidiol' (Abn-CBD) receptor. Abn-CBD is a synthetic isomer of the phytocannabinoid cannabidiol (CBD) and is inactive at CB1 or CB2 receptors, but functions as a selective agonist at this Gi/o-coupled GPCR. N-arachidonoyl glycine (NAGly) is an endogenous metabolite of the endocannabinoid anandamide and acts as an efficacious agonist at GPR18. Here, we investigate the relationship between NAGly, Abn-CBD, the unidentified 'Abn-CBD' receptor, GPR18, and BV-2 microglial migration.ResultsUsing Boyden chamber migration experiments, yellow tetrazolium (MTT) conversion, In-cell Western, qPCR and immunocytochemistry we show that NAGly, at sub-nanomolar concentrations, and Abn-CBD potently drive cellular migration in both BV-2 microglia and HEK293-GPR18 transfected cells, but neither induce migration in HEK-GPR55 or non-transfected HEK293 wildtype cells. Migration effects are blocked or attenuated in both systems by the 'Abn-CBD' receptor antagonist O-1918, and low efficacy agonists N-arachidonoyl-serine and cannabidiol. NAGly promotes proliferation and activation of MAP kinases in BV-2 microglia and HEK293-GPR18 cells at low nanomolar concentrations - cellular responses correlated with microglial migration. Additionally, BV-2 cells show GPR18 immunocytochemical staining and abundant GPR18 mRNA. qPCR demonstrates that primary microglia, likewise, express abundant amounts of GPR18 mRNA.ConclusionsNAGly is the most effective lipid recruiter of BV-2 microglia currently reported and its effects mimic those of Abn-CBD. The data generated from this study supports the hypothesis that GPR18 is the previously unidentified 'Abn-CBD' receptor. The marked potency of NAGly acting on GPR18 to elicit directed migration, proliferation and perhaps other MAPK-dependent phenomena advances our understanding of the lipid-based signaling mechanisms employed by the CNS to actively recruit microglia to sites of interest. It offers a novel research avenue for developing therapeutics to elicit a self-renewing population of neuroregenerative microglia, or alternatively, to prevent the accumulation of misdirected, pro-inflammatory microglia which contribute to and exacerbate neurodegenerative disease.

BACKGROUND AND PURPOSEEndometriosis is a disorder in which the endometrium forms growths outside the uterus and is associated with chronic pain. Recent evidence suggests that endometrial motility plays a role in the aetiology of endometriosis. The endocannabinoid system regulates cellular migration. Given the growing involvement of the endocannabinoids in reproduction, we investigated the role of the endocannabinoid system in migration of endometrial cells. EXPERIMENTAL APPROACHMigration of the human endometrial HEC-1B cells was assayed. Standard PCR techniques were used to determine the presence of the GPCR, GPR18, in HEC-1B cells, and p44/42 MAPK was assayed in stably transfected HEK293-GPR18 cells to determine receptor specificity for known cannabinoid agonists and antagonists. N-arachidonoyl ethanolamine (AEA) metabolism was measured, using HPLC/MS/MS for lipid analysis. KEY RESULTS AEA, D 9-tetrahydrocannabinol (D 9 -THC) and N-arachidonoyl glycine (NAGly) induce migration of HEC-1B cells through cannabinoid CB1 receptor-independent mechanisms. MAPK activation in HEK293-GPR18 cells revealed novel pharmacology for known CB1 and CB2 receptor ligands at GPR18 receptors, including D 9 -THC, which activates MAPK at nanomolar concentrations, whereas WIN 55212-2, CP55940, JWH-133 and JWH-015, and arachidonyl-1-hydroxy-2-propylamide (R1-methanandamide) had no effect. Moreover, HEC-1B migration and MAPK activation by NAGly and D 9 -THC were antagonized by Pertussis toxin, AM251 and cannabidiol. CONCLUSIONS AND IMPLICATIONSAn understanding of the function and regulation of GPR18 and its molecular interactions with endogenous ligands, and how phytocannabinoids play a role with GPR18 signalling is vital if we are to comprehensively assess the function of the cannabinoid signalling system in human health and disease. LINKED ARTICLESThis article is commented on by Alexander, pp. 2411-2413 of this issue and is part of a themed section on Cannabinoids in Biology and Medicine. To view Alexander visit http://dx

Background Cannabinoids are known to reduce intestinal inflammation. Atypical cannabinoids produce pharmacological effects via unidentified targets. We were interested whether the atypical cannabinoid O-1602, reportedly an agonist of the putative cannabinoid receptor GPR55, reduces disease severity of dextran sulfate sodium (DSS) and trinitrobenzene sulfonic acid (TNBS)-induced colitis in C57BL/6N and CD1 mice. Methods DSS (2.5% and 4%) was supplied in drinking water for one week while TNBS (4 mg) was applied as a single intrarectal bolus. Results Both treatments caused severe colitis. Injection of O-1602 (5 mg/kg i.p.) significantly reduced macroscopic and histological colitis scores, and myeloperoxidase activity. The protective effect was still present in cannabinoid receptor 1 (CB1) and 2 (CB2) double knockout mice and mice lacking the GPR55 gene. To investigate a potential mechanism underlying the protection by O-1602 we performed neutrophil chemotactic assays. O-1602 concentration-dependently inhibited migration of murine neutrophils to keratinocyte-derived chemokine (KC), N-formyl-methionyl-leucyl-phenylalanine (fMLP) and the N-formyl-peptide receptor ligand WKYMVm. The inhibitory effect of O-1602 was preserved in neutrophils from CB1/CB2 double knockout and GPR55 knockout mice. No differences were seen in locomotor activity between O-1602-treated and control mice indicating lack of central sedation by this compound. Conclusions Our data demonstrate that O-1602 is protective against experimentally induced colitis and inhibits neutrophil recruitment independently of CB1, CB2 and GPR55 receptors. Thus, atypical cannabinoids represent a novel class of therapeutics that may be useful for the treatment of inflammatory bowel diseases.

A family of endogenous lipids, structurally analogous to the endogenous cannabinoid, N-arachidonoyl ethanolamine (Anandamide), and called N-acyl amides have emerged as a family of biologically active compounds at TRP receptors. N-acyl amides are constructed from an acyl group and an amine via an amide bond. This same structure can be modified by changing either the fatty acid or the amide to form potentially hundreds of lipids. More than 70 N-acyl amides have been identified in nature. We have ongoing studies aimed at isolating and characterizing additional members of the family of N-acyl amides in both central and peripheral tissues in mammalian systems. Here, using a unique in-house library of over 70 N-acyl amides we tested the following three hypotheses: (1) Additional N-acyl amides will have activity at TRPV1-4, (2) Acute peripheral injury will drive changes in CNS levels of N-acyl amides, and (3) N-acyl amides will regulate calcium in CNS-derived microglia. Through these studies, we have identified 20 novel N-acyl amides that collectively activate (stimulating or inhibiting) TRPV1-4. Using lipid extraction and HPLC coupled to tandem mass spectrometry we showed that levels of at least 10 of these N-acyl amides that activate TRPVs are regulated in brain after intraplantar carrageenan injection. We then screened the BV2 microglial cell line for activity with this N-acyl amide library and found overlap with TRPV receptor activity as well as additional activators of calcium mobilization from these lipids. Together these data provide new insight into the family of N-acyl amides and their roles as signaling molecules at ion channels, in microglia, and in the brain in the context of inflammation.

Here, we show a novel pharmacology for inhibition of human neutrophil migration by endocannabinoids, phytocannabinoids, and related compounds. The endocannabinoids virodhamine and N-arachidonoyl dopamine are potent inhibitors of N-formyl-L-methionyl-L-leucyl-L-phenylalanine-induced migration of human neutrophils, with IC 50 values of 0.2 and 8.80 nM, respectively. The endocannabinoid anandamide inhibits human neutrophil migration at nanomolar concentrations in a biphasic manner. The phytocannabinoid (Ϫ)-cannabidiol is a partial agonist, being ϳ40 fold more potent than (ϩ)-cannabidiol; abnormal-cannabidiol is a full agonist. Furthermore, the abnormal-cannabidiol (CBD) analog) inhibits migration, with an IC 50 value of 33 nM. This reported profile of agonist efficacy and potency parallels with the pharmacology of the novel "abnormal-cannabidiol" receptor or a related orphan G protein-coupled receptor, which are already known to modulate cell migration. Although having no effect alone, Narachidonoyl L-serine attenuated inhibition of human neutrophil migration induced by anandamide, virodhamine, and abnormal-CBD. Our data also suggest that there is crosstalk/negative co-operativity between the cannabinoid CB 2 receptor and this novel target: CB 2 receptor antagonists significantly enhance the inhibition observed with anandamide and virodhamine. This study reveals that certain endogenous lipids, phytocannabinoids, and related ligands are potent inhibitors of human neutrophil migration, and it implicates a novel pharmacological target distinct from cannabinoid CB 1 and CB 2 receptors; this target is antagonized by the endogenous compound N-arachidonoyl L-serine. Furthermore, our findings have implications for the potential pharmacological manipulation of elements of the endocannabinoid system for the treatment of various inflammatory conditions. The endocannabinoid system comprises two known receptors (CB 1 and CB 2 ); a family of endogenous ligands (endocannabinoids); and specific molecular machinery for the synthesis, transport, and inactivation of these ligands (Pertwee and Ross, 2002). The most studied endocannabinoids are arachidonoylethanolamide (AEA), also known as anandamide, and 2-arachidonoyl glycerol (2-AG), both of which are synthesized on demand, and they are rapidly hydrolyzed by the enzymes fatty acid amide hydrolase and monoacyl glycerol lipase, respectively (Fowler et al., 2005). There are a number of additional endocannabinoids; these include N-arachidonoyl