Cannabinoid and Vanilloid Effects of R(+)-Methanandamide in the Hemisected Meningeal Preparation

Interplay between cannabinoids and the neuroimmune system in migraine

Migraine is a common and complex neurological disorder that has a high impact on quality of life. Recent advances with drugs that target the neuropeptide calcitonin gene-related peptide (CGRP) have helped, but treatment options remain insufficient. CGRP is released from trigeminal sensory fibers and contributes to peripheral sensitization, perhaps in part due to actions on immune cells in the trigeminovascular system. In this review, we will discuss the potential of cannabinoid targeting of immune cells as an innovative therapeutic target for migraine treatment. We will cover endogenous endocannabinoids, plant-derived phytocannabinoids and synthetically derived cannabinoids. The focus will be on six types of immune cells known to express multiple cannabinoid receptors: macrophages, monocytes, mast cells, dendritic cells, B cells, and T cells. These cells also contain receptors for CGRP and as such, cannabinoids might potentially modulate the efficacy of current CGRP-targeting drugs. Unfortunately, to date most studies on cannabinoids and immune cells have relied on cell cultures and only a single preclinical study has tested cannabinoid actions on immune cells in a migraine model. Encouragingly, in that study a synthetically created stable chiral analog of an endocannabinoid reduced meningeal mast cell degranulation. Likewise, clinical trials evaluating the safety and efficacy of cannabinoid-based therapies for migraine patients have been limited but are encouraging. Thus, the field is at its infancy and there are significant gaps in our understanding of the impact of cannabinoids on immune cells in migraine. Future research exploring the interactions between cannabinoids and immune cells could lead to more targeted and effective migraine treatments.

Effects of the Dual FAAH/MAGL Inhibitor AKU-005 on Trigeminal Hyperalgesia in Male Rats

The inhibition of endocannabinoid hydrolysis by enzymatic inhibitors may interfere with mechanisms underlying migraine-related pain. The dual FAAH/MAGL inhibitor AKU-005 shows potent inhibitory activity in vitro. Here, we assessed the effect of AKU-005 in a migraine animal model based on nitroglycerin (NTG) administration. Male rats were treated with AKU-005 (0.5 mg/kg, i.p.) or vehicle 3 h after receiving NTG (10 mg/kg, i.p.) or NTG vehicle. One hour later, rats were subjected to the open field test followed by the orofacial formalin test. At the end of the test, we collected serum samples for assessing calcitonin gene-related peptide (CGRP) levels as well as meninges, trigeminal ganglia, and brain areas to assess mRNA levels of CGRP and pro-inflammatory cytokines, and endocannabinoid and related lipid levels. AKU-005 reduced NTG-induced hyperalgesia during the orofacial formalin test but did not influence NTG-induced changes in the open field test. It significantly reduced serum levels of CGRP, CGRP, and pro-inflammatory cytokine mRNA levels in the meninges, trigeminal ganglia, and central areas. Surprisingly, AKU-005 caused no change in endocannabinoids and related lipids in the regions evaluated. The present findings suggest that AKU-005 may have anti-migraine effects by reducing CGRP synthesis and release and the associated inflammatory events. This effect, however, does not seem mediated via an interference with the endocannabinoid pathway.

Inhibiting Endocannabinoid Hydrolysis as Emerging Analgesic Strategy Targeting a Spectrum of Ion Channels Implicated in Migraine Pain

Migraine is a disabling neurovascular disorder characterized by severe pain with still limited efficient treatments. Endocannabinoids, the endogenous painkillers, emerged, alternative to plant cannabis, as promising analgesics against migraine pain. In this thematic review, we discuss how inhibition of the main endocannabinoid-degrading enzymes, monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), could raise the level of endocannabinoids (endoCBs) such as 2-AG and anandamide in order to alleviate migraine pain. We describe here: (i) migraine pain signaling pathways, which could serve as specific targets for antinociception; (ii) a divergent distribution of MAGL and FAAH activities in the key regions of the PNS and CNS implicated in migraine pain signaling; (iii) a complexity of anti-nociceptive effects of endoCBs mediated by cannabinoid receptors and through a direct modulation of ion channels in nociceptive neurons; and (iv) the spectrum of emerging potent MAGL and FAAH inhibitors which efficiently increase endoCBs levels. The specific distribution and homeostasis of endoCBs in the main regions of the nociceptive system and their generation ‘on demand’, along with recent availability of MAGL and FAAH inhibitors suggest new perspectives for endoCBs-mediated analgesia in migraine pain.

Dual action of the cannabinoid receptor 1 ligand arachidonyl-2′-chloroethylamide on calcitonin gene-related peptide release

Background

Based on the current understanding of the role of neuropeptide signalling in migraine, we explored the therapeutic potential of a specific cannabinoid agonist. The aim of the present study was to examine the effect of the synthetic endocannabinoid (eCB) analogue, arachidonyl-2′-chloroethylamide (ACEA), on calcitonin gene-related peptide (CGRP) release in the dura and trigeminal ganglion (TG), as cannabinoids are known to activate G_i/o-coupled cannabinoid receptors type 1 (CB1), resulting in neuronal inhibition.

Methods

The experiments were performed using the hemi-skull model and dissected TGs from male Sprague-Dawley rats. CGRP release was induced by either 60 mM K⁺ (for depolarization-induced stimulation) or 100 nM capsaicin (for transient receptor potential vanilloid 1 (TRPV1) -induced stimulation) and measured using an enzyme-linked immunosorbent assay. The analysis of CGRP release data was combined with immunohistochemistry in order to study the cellular localization of CB1, cannabinoid receptor type 2 (CB2), CGRP and receptor activity modifying protein 1 (RAMP1), a subunit of the functional CGRP receptor, in the TG.

Results

CB1 was predominantly expressed in neuronal somas in which colocalization with CGRP was observed. Furthermore, CB1 exhibited colocalization with RAMP1 in neuronal Aδ-fibres but was not clearly expressed in the CGRP-immunoreactive C-fibres. CB2 was mainly expressed in satellite glial cells and did not show substantial colocalization with either CGRP or RAMP1. Without stimulation, 140 nM ACEA per se caused a significant increase in CGRP release in the dura but not TG, compared to vehicle. Furthermore, 140 nM ACEA did not significantly modify neither K⁺- nor capsaicin-induced CGRP release. However, when the TRPV1 blocker AMG9810 (1 mM) was coapplied with ACEA, K⁺-induced CGRP release was significantly attenuated in the TG and dura.

Conclusions

Results from the present study indicate that ACEA per se does not exhibit antimigraine potential due to its dual agonistic properties, resulting in activation of both CB1 and TRPV1, and thereby inhibition and stimulation of CGRP release, respectively.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10194-022-01399-8.

Dual Inhibition of FAAH and MAGL Counteracts Migraine-like Pain and Behavior in an Animal Model of Migraine

The endocannabinoid system exerts an important role in pain processing and modulation. Modulation of the system with hydrolase inhibitors of anandamide (AEA) or 2-arachidonyl glycerol (2-AG) has proved effective in reducing migraine-like features in animal models of migraine. Here, we investigated the effect of dual inhibition of the AEA and 2-AG catabolic pathways in the nitroglycerin-based animal model of migraine. The dual inhibitor JZL195 was administered to rats 2 h after nitroglycerin or vehicle injection. Rats were then exposed to the open field test and the orofacial formalin test. At the end of the tests, they were sacrificed to evaluate calcitonin gene-related peptide (CGRP) serum levels and gene expression of CGRP and cytokines in the cervical spinal cord and the trigeminal ganglion. The dual inhibitor significantly reduced the nitroglycerin-induced trigeminal hyperalgesia and pain-associated behavior, possibly via cannabinoid 1 receptors-mediated action, but it did not change the hypomotility and the anxiety behaviors induced by nitroglycerin. The decreased hyperalgesia was associated with a reduction in CGRP and cytokine gene expression levels in central and peripheral structures and reduced CGRP serum levels. These data suggest an antinociceptive synergy of the endocannabinoid action in peripheral and central sites, confirming that this system participates in reduction of cephalic pain signals.

Emerging Roles for Ion Channels in Ovarian Cancer: Pathomechanisms and Pharmacological Treatment

Ovarian cancer (OC) is the deadliest gynecologic cancer, due to late diagnosis, development of platinum resistance, and inadequate alternative therapy. It has been demonstrated that membrane ion channels play important roles in cancer processes, including cell proliferation, apoptosis, motility, and invasion. Here, we review the contribution of ion channels in the development and progression of OC, evaluating their potential in clinical management. Increased expression of voltage-gated and epithelial sodium channels has been detected in OC cells and tissues and shown to be involved in cancer proliferation and invasion. Potassium and calcium channels have been found to play a critical role in the control of cell cycle and in the resistance to apoptosis, promoting tumor growth and recurrence. Overexpression of chloride and transient receptor potential channels was found both in vitro and in vivo, supporting their contribution to OC. Furthermore, ion channels have been shown to influence the sensitivity of OC cells to neoplastic drugs, suggesting a critical role in chemotherapy resistance. The study of ion channels expression and function in OC can improve our understanding of pathophysiology and pave the way for identifying ion channels as potential targets for tumor diagnosis and treatment.

Receptor mechanisms mediating the anti-neuroinflammatory effects of endocannabinoid system modulation in a rat model of migraine

Calcitonin gene-related peptide (CGRP), substance P and dural mast cells are main contributors in neurogenic inflammation underlying migraine pathophysiology. Modulation of endocannabinoid system attenuates migraine pain, but its mechanisms of action remain unclear. We investigated receptor mechanisms mediating anti-neuroinflammatory effects of endocannabinoid system modulation in in vivo migraine model and ex vivo hemiskull preparations in rats. To induce acute model of migraine, a single dose of nitroglycerin was intraperitoneally administered to male rats. Moreover, isolated ex vivo rat hemiskulls were prepared to study CGRP and substance P release from meningeal trigeminal afferents. We used methanandamide (cannabinoid agonist), rimonabant (cannabinoid receptor-1 CB1 antagonist), SR144528 (CB2 antagonist) and capsazepine (transient receptor potential vanilloid-1 TRPV1 antagonist) to explore effects of endocannabinoid system modulation on the neurogenic inflammation, and possible involvement of CB1, CB2 and TRPV1 receptors during endocannabinoid effects. Methanandamide attenuated nitroglycerin-induced CGRP increments in in vivo plasma, trigeminal ganglia and brainstem and also in ex vivo hemiskull preparations. Methanandamide also alleviated enhanced number and degranulation of dural mast cells induced by nitroglycerin. Rimonabant, but not capsazepine or SR144528, reversed the attenuating effects of methanandamide on CGRP release in both in vivo and ex vivo experiments. Additionally, SR144528, but not rimonabant or capsazepine, reversed the attenuating effects of methanandamide on dural mast cells. However, neither nitroglycerin nor methanandamide changed substance P levels in both in vivo and ex vivo experiments. Methanandamide modulates CGRP release in migraine-related structures via CB1 receptors and inhibits the degranulation of dural mast cells through CB2 receptors. Selective ligands targeting CB1 and CB2 receptors may provide novel and effective treatment strategies against migraine.

Stimulation of rat cranial dura mater with potassium chloride causes CGRP release into the cerebrospinal fluid and increases medullary blood flow

Primary headaches may be accompanied by increased intracranial blood flow induced by the release of the potent vasodilator calcitonin gene-related peptide (CGRP) from activated meningeal afferents. We aimed to record meningeal and medullary blood flow simultaneously and to localize the sites of CGRP release in rodent preparations in vivo and ex vivo. Blood flow in the exposed rat parietal dura mater and the medulla oblongata was recorded by laser Doppler flowmetry, while the dura was stimulated by topical application of 60mM potassium chloride (KCl). Samples of jugular venous plasma and cerebrospinal fluid (CSF) collected from the cisterna magna were analysed for CGRP concentrations using an enzyme immunoassay. In a hemisected rat skull preparation lined with dura mater the CGRP releasing effect of KCl superfusion was examined. Superfusion of the dura mater with KCl decreased meningeal blood flow unless alpha-adrenoceptors were blocked by phentolamine, whereas the medullary blood flow was increased. The same treatment caused increased CGRP concentrations in jugular plasma and CSF and induced significant CGRP release in the hemisected rat skull preparation. Anaesthesia of the trigeminal ganglion by injection of lidocaine reduced increases in medullary blood flow and CGRP concentration in the CSF upon meningeal KCl application. CGRP release evoked by depolarisation of meningeal afferents is accompanied by increased blood flow in the medulla oblongata but not the dura mater. This discrepancy can be explained by the smooth muscle depolarising effect of KCl and the activation of sympathetic vasoconstrictor mechanisms. The medullary blood flow response is most likely mediated by CGRP released from activated central terminals of trigeminal afferents. Increased blood supply of the medulla oblongata and CGRP release into the CSF may also occur in headaches accompanying vigorous activation of meningeal afferents.

Endovanilloids are potential activators of the trigeminovascular nocisensor complex

Background

In the dura mater encephali a significant population of trigeminal afferents coexpress the nociceptive ion channel transient receptor potential vanilloid type 1 (TRPV1) receptor and calcitonin gene-related peptide (CGRP). Release of CGRP serves the central transmission of sensory information, initiates local tissue reactions and may also sensitize the nociceptive pathway. To reveal the possible activation of meningeal TRPV1 receptors by endogenously synthetized agonists, the effects of arachidonylethanolamide (anandamide) and N-arachidonoyl-dopamine (NADA) were studied on dural vascular reactions and meningeal CGRP release.

Methods

Changes in meningeal blood flow were measured with laser Doppler flowmetry in a rat open cranial window preparation following local dural applications of anandamide and NADA. The release of CGRP evoked by endovanilloids was measured with ELISA in an in vitro dura mater preparation.

Results

Topical application of NADA induced a significant dose-dependent increase in meningeal blood flow that was markedly inhibited by pretreatments with the TRPV1 antagonist capsazepine, the CGRP antagonist CGRP_8–37, or by prior systemic capsaicin desensitization. Administration of anandamide resulted in minor increases in meningeal blood flow that was turned into vasoconstriction at the higher concentration. In the in vitro dura mater preparation NADA evoked a significant increase in CGRP release. Cannabinoid CB1 receptors of CGRP releasing nerve fibers seem to counteract the TRPV1 agonistic effect of anandamide in a dose-dependent fashion, a result which is confirmed by the facilitating effect of CB1 receptor inhibition on CGRP release and its reversing effect on the blood flow.

Conclusions

The present findings demonstrate that endovanilloids are potential activators of meningeal TRPV1 receptors and, consequently the trigeminovascular nocisensor complex that may play a significant role in the pathophysiology of headaches. The results also suggest that prejunctional CB1 receptors may modulate meningeal vascular responses.

Chemical mediators of migraine: preclinical and clinical observations

Migraine is a neurovascular disorder, and although the pathophysiology of migraine has not been fully delineated, much has been learned in the past 50 years. This knowledge has been accompanied by significant advancements in the way migraine is viewed as a disease process and in the development therapeutic options. In this review, we will focus on 4 mediators (nitric oxide, histamine, serotonin, and calcitonin gene-related peptide) which have significantly advanced our understanding of migraine as a disease entity. For each mediator we begin by reviewing the preclinical data linking it to migraine pathophysiology, first focusing on the vascular mechanisms, then the neuronal mechanisms. The preclinical data are then followed by a review of the clinical data which support each mediator's role in migraine and highlights the pharmacological agents which target these mediators for migraine therapy.

TRPV1, TRPA1, and CB1 in the isolated vagus nerve--axonal chemosensitivity and control of neuropeptide release

Vagal sensory afferents innervating airways and abdominal tissues express TRPV1 and TRPA1, two depolarizing calcium permeable ion channels playing a major role in sensing environmental irritants and endogenous metabolites which cause neuropeptide release and neurogenic inflammation. Here we have studied axonal chemosensitivity and control of neuropeptide release from the isolated rat and mouse vagus nerve by using prototypical agonists of these transduction channels - capsaicin, mustard oil and the specific endogenous activators, anandamide (methyl arachidonyl ethanolamide, mAEA), and acrolein, respectively. Capsaicin evoked iCGRP release from the rat vagus nerve with an EC₅₀ of 0.12 μM. Co-application of mAEA had a dual effect: nanomolar concentrations of mAEA (0.01 μM) significantly reduced capsaicin-evoked iCGRP release while concentrations ≥ 1 μM mAEA had sensitizing effects. Only 100 μM mAEA directly augmented iCGRP release by itself. In the mouse, 310 μM mAEA increased release in wildtype and TRPA1-/- mice which could be inhibited by capsazepine (10 μM) and was completely absent in TRPV1-/- mice. CB1-/- and CB1/CB2 double -/- mice equally displayed increased sensitivity to mAEA (100 μM) and a sensitizing effect to capsaicin, in contrast to wildtypes. Acrolein and mustard oil (MO)--at μM concentrations--induced a TRPA1-dependent iCGRP release; however, millimolar concentrations of mustard oil (>1mM) evoked iCGRP release by activating TRPV1, confirming recent evidence for TRPV1 agonism of high mustard oil concentrations. Taken together, we present evidence for functional expression of excitatory TRPV1, TRPA1, and inhibitory CB1 receptors along the sensory fibers of the vagus nerve which lend pathophysiological relevance to the axonal membrane and the control of neuropeptide release that may become important in cases of inflammation or neuropathy. Sensitization and possible ectopic discharge may contribute to the development of autonomic dysregulation in visceral tissues that are innervated by the vagus nerve.

Calcitonin gene-related peptide receptor antagonists for migraine

IMPORTANCE OF THE FIELD

Migraine is a highly prevalent disabling condition, and the current treatment options are not satisfactory. The role of calcitonin gene-related peptide (CGRP) in migraine pathophysiology is well established. CGRP receptor antagonists address this new target and have the potential to improve therapy for both responders and non-responders to previous options.

AREAS COVERED IN THIS REVIEW

This review describes CGRP, its receptors and their role in the pathophysiology of migraine. CGRP receptor antagonists are a recent development; all reported antagonists are reported in chronological order. The experimental evidence, as well as all clinical trials since the first proof-of-concept study in 2004, is discussed.

WHAT THE READER WILL GAIN

An overview of the CGRP system and why it provides an attractive drug target for headache. The main focus is on the currently presented CGRP receptor antagonists and clinical evidence for this new therapeutic option.

TAKE HOME MESSAGE

CGRP receptor antagonists will provide an additional and valuable therapeutic option for the treatment of headaches.