Wiping Out CGRP: Potential Cardiovascular Risks

Is selective 5-HT1F receptor agonism an entity apart from that of the triptans in antimigraine therapy?

Migraine is a neurovascular disorder that involves activation of the trigeminovascular system and cranial vasodilation mediated by release of calcitonin gene-related peptide (CGRP). The gold standard for acute migraine treatment are the triptans, 5-HT1B/1D/(1F) receptor agonists. Their actions are thought to be mediated through activation of: (i) 5-HT1B receptors in cranial blood vessels with subsequent cranial vasoconstriction; (ii) prejunctional 5-HT1D receptors on trigeminal fibers that inhibit trigeminal CGRP release; and (iii) 5-HT1B/1D/1F receptors in central nervous system involved in (anti)nociceptive modulation. Unfortunately, coronary arteries also express 5-HT1B receptors whose activation would produce coronary vasoconstriction; hence, triptans are contraindicated in patients with cardiovascular disease. In addition, since migraineurs have an increased cardiovascular risk, it is important to develop antimigraine drugs devoid of vascular (side) effects. Ditans, here defined as selective 5-HT1F receptor agonists, were developed on the basis that most of the triptans activate trigeminal 5-HT1F receptors, which may explain part of the triptans' antimigraine action. Amongst the ditans, lasmiditan: (i) fails to constrict human coronary arteries; and (ii) is effective for the acute treatment of migraine in preliminary Phase III clinical trials. Admittedly, the exact site of action is still unknown, but lasmiditan possess a high lipophilicity, which suggests a direct action on the central descending antinociceptive pathways. Furthermore, since 5-HT1F receptors are located on trigeminal fibers, they could modulate CGRP release. This review will be particularly focussed on the similarities and differences between the triptans and the ditans, their proposed sites of action, side effects and their cardiovascular risk profile.

The Biology of Monoclonal Antibodies: Focus on Calcitonin Gene-Related Peptide for Prophylactic Migraine Therapy

Calcitonin gene-related peptide (CGRP) is 37-amino-acid neuropeptide, crucially involved in migraine pathophysiology. Four monoclonal antibodies (mAbs) targeting the CGRP pathway are currently under evaluation for the prevention of episodic and chronic migraine: eptinezumab (ALD403), fremanezumab (TEV-48125), galcanezumab (LY2951742), and erenumab (AMG334). As reviewed in this article, all 4 antibodies have been proven effective, tolerable, and safe as migraine prophylactic treatments in phase II clinical trials. The mean decrease in migraine days per month was between 3.4 and 6.3 days/month after 8 to 12 weeks of treatment, and the placebo subtracted benefit ranged from 1 to 2.18 days. Notably, up to 32% of subjects experienced total migraine freedom after drug administration. Substance class-specific adverse events and treatment-related serious adverse event did not occur. Further long-term and large-scale trials are currently under way to verify the safety and efficacy profile of mAbs. In particular, the potential risk of vascular adverse events and the role of anti-drug antibodies deserve special attention. Anti-CGRP peptide and anti-CGRP receptor antibodies are the first effective treatments, which were specifically developed for the prevention of migraine. Their site of action in migraine prevention is most likely peripheral due to large molecule size, which prevents the penetration through the blood-brain barrier and thereby shows that peripheral components play a pivotal role in the pathophysiology of a CNS disease.

Migraine

Migraine is a chronic paroxysmal neurological disorder characterised by multiphase attacks of head pain and a myriad of neurological symptoms. The underlying genetic and biological underpinnings and neural networks involved are coming sharply into focus. This progress in the fundamental understanding of migraine has led to novel, mechanism-based and disease-specific therapeutics. In this Seminar, the clinical features and neurobiology of migraine are reviewed, evidence to support available treatment options is provided, and emerging drug, device, and biological therapies are discussed.

The role of anti-CGRP antibodies in the pathophysiology of primary headaches

Calcitonin gene-related peptide (CGRP), a potent vasodilator and pain-signaling neuropeptide, is a validated therapeutic target for migraine and cluster headache. Four anti-CGRP monoclonal antibodies (mAbs) have been developed, representing the first specific, mechanism-based, migraine prophylactic treatment. CGRP mAbs demonstrated good efficacy coupled to excellent tolerability and safety in 5 phase II clinical trials. Notably, CGRP mAbs induced complete migraine remission in a patients' subset. To date, more than 20 phase III trials using CGRP mAbs for of episodic and chronic migraine and cluster headache prevention are ongoing. Future investigations will shed light on migraine endophenotypes predictive of good CGRP mAbs responsiveness and provide answers on their long-term cardiovascular safety.

Protective effects of PACAP in ischemia

Pituitary adenylate cyclase activating polypeptide (PACAP) is an ubiquitous peptide involved, among others, in neurodevelopment, neuromodulation, neuroprotection, neurogenic inflammation and nociception. Presence of PACAP and its specific receptor, PAC1, in the trigeminocervical complex, changes of PACAP levels in migraine patients and the migraine-inducing effect of PACAP injection strongly support the involvement of PACAP/PAC1 receptor in migraine pathogenesis. While antagonizing PAC1 receptor is a promising therapeutic target in migraine, the diverse array of PACAP's functions, including protection in ischemic events, requires that the cost-benefit of such an intervention is well investigated by taking all the beneficial effects of PACAP into account. In the present review we summarize the protective effects of PACAP in ischemia, especially in neuronal ischemic injuries, and discuss possible points to consider when developing strategies in migraine therapy interfering with the PACAP/PAC1 receptor system.

Calcitonin gene-related peptide (receptor) antibodies: an exciting avenue for migraine treatment

Specific prophylactic migraine treatments are urgently needed because of the unmet needs of many migraine patients. Antibodies targeting calcitonin gene-related peptide (CGRP) or its receptor have recently shown efficacy in episodic and chronic migraine and will be available soon.

Side effects associated with current and prospective antimigraine pharmacotherapies

INTRODUCTION

Migraine is a neurovascular disorder. Current acute specific antimigraine pharmacotherapies target trigeminovascular 5-HT1B/1D, 5-HT1F and CGRP receptors but, unfortunately, they induce some cardiovascular and central side effects that lead to poor treatment adherence/compliance. Therefore, new antimigraine drugs are being explored. Areas covered: This review considers the adverse (or potential) side effects produced by current and prospective antimigraine drugs, including medication overuse headache (MOH) produced by ergots and triptans, the side effects observed in clinical trials for the new gepants and CGRP antibodies, and a section discussing the potential effects resulting from disruption of the cardiovascular CGRPergic neurotransmission. Expert opinion: The last decades have witnessed remarkable developments in antimigraine therapy, which includes acute (e.g. triptans) and prophylactic (e.g. β-adrenoceptor blockers) antimigraine drugs. Indeed, the triptans represent a considerable advance, but their side effects (including nausea, dizziness and coronary vasoconstriction) preclude some patients from using triptans. This has led to the development of the ditans (5-HT1F receptor agonists), the gepants (CGRP receptor antagonists) and the monoclonal antibodies against CGRP or its receptor. The latter drugs represent a new hope in the antimigraine armamentarium, but as CGRP plays a role in cardiovascular homeostasis, the potential for adverse cardiovascular side effects remains latent.

Calcitonin Gene-Related Peptide Antagonists and Therapeutic Antibodies

The calcitonin gene-related peptide (CGRP) receptor is composed of the calcitonin receptor-like receptor (CLR, a class B GPCR) and a single-pass membrane protein known as receptor activity modifying protein type 1 (RAMP1). The levels of the CGRP peptide increase during a migraine attack and infusion of CGRP can provoke a migraine attack. Consequently, there is much interest in inhibiting the actions of CGRP as a way to control migraine. Here we describe the development of small molecule antagonists designed to bind to the CGRP receptor to block its action by preventing binding of the CGRP peptide. We also describe the development of antibody drugs, designed to bind either to the CGRP receptor to block its action, or to bind directly to the CGRP peptide. The field has been very active, with one antibody drug approved and three antibody drugs in phase III clinical trial. Initial programs on the development CGRP antagonists were frustrated by liver toxicity but the current outlook is very promising with five small molecule antagonists in various stages of clinical trial.

CGRP, a target for preventive therapy in migraine and cluster headache: Systematic review of clinical data

Introduction

Migraine and cluster headache are challenging to manage, with no tailored preventive medications available. Targeting the calcitonin gene-related peptide (CGRP) pathway to treat these headaches may be the first focused therapeutic option to date, with the potential for promising efficacy.

Methods

We systematically searched PubMed and clinicaltrials.gov for randomized controlled trials investigating the preventive potential of monoclonal antibodies against the CGRP pathway in the treatment of migraine and cluster headache.

Results

The literature search returned a total of 136 records, of which 32 were eligible for review.

Discussion

Clinical data from phase II and III trials of the four monoclonal antibodies targeting the CGRP pathway: Eptinezumab, erenumab, fremanezumab, and galcanezumab, collectively show a positive effect in the preventive treatment of episodic and chronic migraine. Multiple phase II and III trials are under way to further determine the efficacy and safety of this new drug class. It may be particularly important to assess the cardiovascular effects of long-term CGRP blockade. Phase III trials are also currently in progress for the preventive treatment of cluster headache.

Conclusion

Efficacy of anti-CGRP monoclonal antibodies spells a promising future for the many patients suffering from migraine, and possibly also for the smaller but severely-affected population with cluster headache.

Gender aspects of CGRP in migraine

Background

Migraine is two to three times more prevalent in women than in men, but the mechanisms involved in this gender disparity are still poorly understood. In this respect, calcitonin gene-related peptide (CGRP) plays a key role in migraine pathophysiology and, more recently, the functional interactions between ovarian steroid hormones, CGRP and the trigeminovascular system have been recognized and studied in more detail.

Aims

To provide an overview of CGRP studies that have addressed gender differences utilizing animal and human migraine preclinical research models to highlight how the female trigeminovascular system responds differently in the presence of varying ovarian steroid hormones.

Conclusions

Gender differences are evident in migraine. Several studies indicate that fluctuations of ovarian steroid hormone (mainly estrogen) levels modulate CGRP in the trigeminovascular system during different reproductive milestones. Such interactions need to be considered when conducting future animal and human experiments, since these differences may contribute to the development of gender-specific therapies.

Phase I, Randomized, Double-blind, Placebo-controlled, Single-dose, and Multiple-dose Studies of Erenumab in Healthy Subjects and Patients With Migraine

Monoclonal antibodies (mAbs) targeting calcitonin gene-related peptide (CGRP) signaling are being explored as prophylactic treatments for migraine. Erenumab (AMG 334) is the first potent, selective, and competitive human mAb antagonist of the CGRP receptor. We report the data from two phase I studies assessing the safety, pharmacokinetics (PK), and pharmacodynamics of single and multiple administrations of erenumab in healthy subjects and patients with migraine. The results indicate that the PK profile of erenumab is nonlinear from 1 mg to 70 mg and the linear portion of the clearance from 70 mg to 210 mg is consistent with other human immunoglobulin G2 antibodies. Single doses of erenumab resulted in >75% inhibition of capsaicin-induced dermal blood flow, with no apparent dose-dependency for erenumab ≥21 mg. Erenumab was generally well tolerated, with an acceptable safety profile, supporting further clinical development of erenumab for migraine prevention.

Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of the CGRP Binding Monoclonal Antibody LY2951742 (Galcanezumab) in Healthy Volunteers

Background: Calcitonin gene-related peptide (CGRP) is pivotal in the pathophysiology of migraine headaches and represents a promising target for migraine treatment. The humanized monoclonal antibody galcanezumab (LY2951742) binds to CGRP and may be effective in migraine prophylaxis.

Objectives: The primary objective was to evaluate the safety and tolerability of single and multiple doses of galcanezumab in humans. Secondary objectives included assessing the pharmacokinetics and evaluating target engagement.

Methods: A double-blind, randomized, placebo-controlled study (NCT 01337596) with single escalating and multiple subcutaneous (SC) doses of galcanezumab was performed in healthy male volunteers. Single doses of 1, 5, 25, 75, 200, and 600 mg of galcanezumab (n = 7/dose) or placebo (n = 2/dose) were injected SC in six consecutive cohorts of nine subjects each. One cohort of nine subjects received multiple (4) 150 mg doses of galcanezumab or placebo every other week. Target engagement was evaluated by measuring inhibition of capsaicin-induced increase in dermal blood flow (DBF).

Findings: Sixty-three subjects were randomized and included in the safety analyses. Galcanezumab was well tolerated in single doses (1–600 mg SC) and consecutive doses (150 mg SC). There was no dose-dependent difference in type or frequency of treatment-emergent adverse events, and no clinically meaningful difference when compared with placebo. Pharmacokinetics were linear. Galcanezumab induced a robust, dose-dependent, and durable inhibition of capsaicin-induced increase in DBF, supporting the continued clinical development of galcanezumab for prophylaxis in migraine patients.

The role of α1- and α2-adrenoceptor subtypes in the vasopressor responses induced by dihydroergotamine in ritanserin-pretreated pithed rats

Background

Dihydroergotamine (DHE) is an acute antimigraine agent that displays affinity for dopamine D₂-like receptors, serotonin 5-HT_1/2 receptors and α₁/α₂-adrenoceptors. Since activation of vascular α₁/α₂-adrenoceptors results in systemic vasopressor responses, the purpose of this study was to investigate the specific role of α₁- and α₂-adrenoceptors mediating DHE-induced vasopressor responses using several antagonists for these receptors.

Methods

For this purpose, 135 male Wistar rats were pithed and divided into 35 control and 100 pretreated i.v. with ritanserin (100 μg/kg; to exclude the 5-HT₂ receptor-mediated systemic vasoconstriction). Then, the vasopressor responses to i.v. DHE (1–3100 μg/kg, given cumulatively) were determined after i.v. administration of some α₁/α₂-adrenoceptor antagonists.

Results

In control animals (without ritanserin pretreatment), the vasopressor responses to DHE were: (i) unaffected after prazosin (α₁; 30 μg/kg); (ii) slightly, but significantly, blocked after rauwolscine (α₂; 300 μg/kg); and (iii) markedly blocked after prazosin (30 μg/kg) plus rauwolscine (300 μg/kg). In contrast, after pretreatment with ritanserin, the vasopressor responses to DHE were: (i) attenuated after prazosin (α₁; 10 and 30 μg/kg) or rauwolscine (α₂; 100 and 300 μg/kg); (ii) markedly blocked after prazosin (30 μg/kg) plus rauwolscine (300 μg/kg); (iii) attenuated after 5-methylurapidil (α_1A; 30–100 μg/kg), L-765,314 (α_1B; 100 μg/kg), BMY 7378 (α_1D; 30–100 μg/kg), BRL44408 (α_2A; 100–300 μg/kg), imiloxan (α_2B; 1000–3000 μg/kg) or JP-1302 (α_2C; 1000 μg/kg); and (iv) unaffected after the corresponding vehicles (1 ml/kg).

Conclusion

These results suggest that the DHE-induced vasopressor responses in ritanserin-pretreated pithed rats are mediated by α₁- (probably α_1A, α_1B and α_1D) and α₂- (probably α_2A, α_2B and α_2C) adrenoceptors. These findings could shed light on the pharmacological profile of the vascular side effects (i.e. systemic vasoconstriction) produced by DHE and may lead to the development of more selective antimigraine drugs devoid vascular side effects.

Blocking CGRP in migraine patients - a review of pros and cons

Migraine is the most prevalent neurological disorder worldwide and it has immense socioeconomic impact. Currently, preventative treatment options for migraine include drugs developed for diseases other than migraine such as hypertension, depression and epilepsy. During the last decade, however, blocking calcitonin gene-related peptide (CGRP) has emerged as a possible mechanism for prevention of migraine attacks. CGRP has been shown to be released during migraine attacks and it may play a causative role in induction of migraine attacks. Here, we review the pros and cons of blocking CGRP in migraine patients. To date, two different classes of drugs blocking CGRP have been developed: small molecule CGRP receptor antagonists (gepants), and monoclonal antibodies, targeting either CGRP or the CGRP receptor. Several trials have been conducted to test the efficacy and safety of these drugs. In general, a superior efficacy compared to placebo has been shown, especially with regards to the antibodies. In addition, the efficacy is in line with other currently used prophylactic treatments. The drugs have also been well tolerated, except for some of the gepants, which induced a transient increase in transaminases. Thus, blocking CGRP in migraine patients is seemingly both efficient and well tolerated. However, CGRP and its receptor are abundantly present in both the vasculature, and in the peripheral and central nervous system, and are involved in several physiological processes. Therefore, blocking CGRP may pose a risk in subjects with comorbidities such as cardiovascular diseases. In addition, long-term effects are still unknown. Evidence from animal studies suggests that blocking CGRP may induce constipation, affect the homeostatic functions of the pituitary hormones or attenuate wound healing. However, these effects have so far not been reported in human studies. In conclusion, this review suggests that, based on current knowledge, the pros of blocking CGRP in migraine patients exceed the cons.

Anti-CGRP Monoclonal Antibodies: the Next Era of Migraine Prevention?

OPINION STATEMENT

Migraine is a very disabling disorder with severe impact on patients' lives and substantive costs to society in terms of healthcare costs and lost productivity. Prevention is a key component of migraine therapy, and while numerous preventive options exist, each is burdened by either troublesome side effects or insufficient efficacy. All migraine preventives currently in clinical use were licensed for other purposes and, by chance, have efficacy against migraine. As our understanding of migraine has evolved, calcitonin gene-related peptide (CGRP) has moved to the forefront as a neuropeptide central to migraine pathophysiology. Six small molecule CGRP receptor antagonists were shown to be effective for acute treatment of migraine; two were stopped for hepatotoxicity or one for formulation concern issues and one is now in phase III. Monoclonal antibodies against CGRP or the CGRP receptor have a longer duration of action and have been investigated for migraine prevention. Four are in development and three have completed phase II and one phase III trials; every reported study has been positive. Furthermore, no safety issues have arisen to date, including hepatic or cardiovascular effects, and initial tolerability appears to be excellent. Monoclonal antibodies antagonizing the CGRP pathway represent a novel approach to prevention: a mechanism-specific migraine-targeted therapy. While we must await the results of all the phase III trials, cautious excitement seems warranted as we enter a new era of better tolerated, well-understood, bespoke migraine treatment for this common and disabling neurological disorder.

Pharmacological analysis of the inhibition produced by moxonidine and agmatine on the vasodepressor sensory CGRPergic outflow in pithed rats

Calcitonin gene-related peptide (CGRP) plays a role in several (patho)physiological functions, and modulation of its release is considered a therapeutic target. In this respect, electrical spinal (T₉--T₁₂) stimulation of the perivascular sensory outflow in pithed rats produces vasodepressor responses mediated by CGRP release. This study investigated the role of imidazoline I₁ and I₂ receptors in the inhibition by moxonidine and agmatine of these vasodepressor responses. Male Wistar pithed rats (pretreated i.v. with 25mg/kg gallamine and 2mg/kg⋅min hexamethonium) received i.v. continuous infusions of methoxamine (20μg/kg⋅min) followed by physiological saline (0.02ml/min), moxonidine (1, 3, 10 or 30μg/kg⋅min) or agmatine (1000 or 3000μg/kg⋅min). Under these conditions, electrical stimulation (0.56-5.6Hz; 50V; 2ms) of the spinal cord (T₉-T₁₂) produced frequency-dependent vasodepressor responses which were: (i) unchanged during saline infusion; and (ii) inhibited during the above infusions of moxonidine or agmatine. Moreover, using i.v. administrations, the inhibition by 3μg/kg⋅min moxonidine or 3000μg/kg⋅min agmatine (which failed to inhibit the vasodepressor responses by α-CGRP; 0.1-1µg/kg) was: (i) unaltered after saline (1ml/kg), rauwolscine (300μg/kg; α₂-adrenoceptor antagonist) or BU224 (300μg/kg; imidazoline I₂ receptor antagonist); and (ii) reversed after AGN 192403 (3000μg/kg; imidazoline I₁ receptor antagonist). This reversion was relatively more pronounced after AGN 192403 plus rauwolscine. These blocking doses of antagonists lacked any effects on the electrically-induced vasodepressor responses. Therefore, the inhibition of the vasodepressor sensory CGRPergic outflow by moxonidine and agmatine is mainly mediated by prejunctional imidazoline I₁ receptors on perivascular sensory nerves.

Animal models of pain and migraine in drug discovery

Preclinical research activities in relation to pain typically involve the 'holy trinity' of nociceptive, inflammatory and neuropathic pain for purposes of target validation and defining target product profiles of novel analgesic compounds. For some reason it seems that headache or migraine are rarely considered as additional entities to explore. Frontline medications used in the treatment of, for example, inflammatory pain, neuropathic pain and migraine (NSAIDs versus pregabalin/duloxetine versus triptans) reveal distinct differences in pathophysiology that partially explain this approach. Nevertheless, for many patients enduring chronic pain, regardless of aetiology, high unmet needs remain. By focusing more on commonalities shared between neuropathic pain and headache disorders such as migraine, drug discovery efforts could be spread more efficiently across a larger indication area. Here, some of the most commonly used models and methods employed within 'pain and migraine' drug development will be presented. Recent advances within these disciplines suggest that, with the addition of a few extra carefully chosen ancillary models and/or endpoints, the relative value in terms of resources used, reciprocal flow of information and net worth of a 'typical' package could be increased substantially for the pain and migraine fields.

Olcegepant blocks neurogenic and non-neurogenic CGRPergic vasodepressor responses and facilitates noradrenergic vasopressor responses in pithed rats

BACKGROUND AND PURPOSE

Olcegepant (BIBN4096BS) is a selective non-peptide CGRP receptor antagonist with acute antimigraine properties. Since systemic vascular tone is modulated by perivascular (primary sensory CGRPergic and sympathetic) nerves, this randomized study investigated in pithed rats the effect of acute i.v. treatment with olcegepant on the neurogenic and non-neurogenic: (i) CGRPergic vasodepressor responses; and (ii) noradrenergic vasopressor responses. The pithed rat is an experimental model predictive of systemic (cardio) vascular side effects.

EXPERIMENTAL APPROACH

Seventy-five male Wistar rats (divided into 15 groups, n = 5 each) were pithed, artificially ventilated and prepared for: (i) spinal stimulation (T₉ -T₁₂ ; 0.56-5.6 Hz) of the sensory CGRPergic vasodepressor outflow or i.v. bolus injections (0.1-1 μg·kg^-1 ) of α-CGRP, substance P or acetylcholine, which induced frequency-dependent or dose-dependent vasodepressor responses; or (ii) spinal stimulation (T₇ -T₉ ; 0.03-3 Hz) of the sympathetic vasopressor outflow or i.v. bolus injections (0.03-3 μg·kg^-1 ) of noradrenaline, which produced frequency-dependent or dose-dependent vasopressor responses.

KEY RESULTS

Olcegepant (1000 and 3000 μg·kg^-1 , i.v.) dose-dependently blocked the vasodepressor responses to sensory nerve stimulation or i.v. α-CGRP, without affecting those to substance P or acetylcholine. Whereas it potentiated the vasopressor responses to sympathetic nerve stimulation or i.v. noradrenaline.

CONCLUSIONS AND IMPLICATIONS

Olcegepant (i.v.) selectively blocked the neurogenic and non-neurogenic CGRPergic vasodepressor responses. This blockade by olcegepant potentiated the neurogenic and non-neurogenic noradrenergic vasopressor responses in pithed rats, an effect that might result in an increased vascular resistance and, consequently, in a prohypertensive action.

CGRP and its receptors

The calcitonin gene-related peptide (CGRP) neuropeptide system is an important but still evolving target for migraine. A fundamental consideration for all of the current drugs in clinical trials and for ongoing development in this area is the identity, expression pattern, and function of CGRP receptors because this knowledge informs safety and efficacy considerations. In recent years, only the calcitonin receptor-like receptor/receptor activity-modifying protein 1 (RAMP1) complex, known as the CGRP receptor, has generally been considered relevant. However, CGRP is capable of activating multiple receptors and could have more than one endogenous receptor. The recent identification of the CGRP-responsive calcitonin receptor/RAMP1 complex (AMY₁ receptor - amylin subtype 1 receptor) in the trigeminovascular system warrants a deeper consideration of the molecular identity of CGRP receptor(s) involved in the pathophysiology, and thus potential treatment of migraine. This perspective considers some of the issues and implications.

CGRP receptor antagonist activity of olcegepant depends on the signalling pathway measured

Background Calcitonin gene-related peptide (CGRP) is a neuropeptide that acts in the trigeminovascular system and is believed to play an important role in migraine. CGRP activates two receptors that are both present in the trigeminovascular system; the CGRP receptor and the amylin 1 (AMY₁) receptor. CGRP receptor antagonists, including olcegepant (BIBN4096BS) and telcagepant (MK-0974), can treat migraine. This study aimed to determine the effectiveness of these antagonists at blocking CGRP receptor signalling in trigeminal ganglia (TG) neurons and transfected CGRP and AMY₁ receptors in Cos7 cells, to better understand their mechanism of action. Methods CGRP stimulation of four intracellular signalling molecules relevant to pain (cAMP, CREB, p38 and ERK) were examined in rat TG neurons and compared to transfected CGRP and AMY₁ receptors in Cos7 cells. Results In TG neurons, olcegepant displayed signal-specific differences in antagonism of CGRP responses. This effect was also evident in transfected Cos7 cells, where olcegepant blocked CREB phosphorylation more potently than expected at the AMY₁ receptor, suggesting that the affinity of this antagonist can be dependent on the signalling pathway activated. Conclusions CGRP receptor antagonist activity appears to be assay-dependent. Thus, these molecules may not be as selective for the CGRP receptor as commonly reported.

Heteroreceptors Modulating CGRP Release at Neurovascular Junction: Potential Therapeutic Implications on Some Vascular-Related Diseases

Calcitonin gene-related peptide (CGRP) is a 37-amino-acid neuropeptide belonging to the calcitonin gene peptide superfamily. CGRP is a potent vasodilator with potential therapeutic usefulness for treating vascular-related disease. This peptide is primarily located on C- and Aδ-fibers, which have extensive perivascular presence and a dual sensory-efferent function. Although CGRP has two major isoforms (α-CGRP and β-CGRP), the α-CGRP is the isoform related to vascular actions. Release of CGRP from afferent perivascular nerve terminals has been shown to result in vasodilatation, an effect mediated by at least one receptor (the CGRP receptor). This receptor is an atypical G-protein coupled receptor (GPCR) composed of three functional proteins: (i) the calcitonin receptor-like receptor (CRLR; a seven-transmembrane protein), (ii) the activity-modifying protein type 1 (RAMP1), and (iii) a receptor component protein (RCP). Although under physiological conditions, CGRP seems not to play an important role in vascular tone regulation, this peptide has been strongly related as a key player in migraine and other vascular-related disorders (e.g., hypertension and preeclampsia). The present review aims at providing an overview on the role of sensory fibers and CGRP release on the modulation of vascular tone.

Pro-nociceptive migraine mediator CGRP provides neuroprotection of sensory, cortical and cerebellar neurons via multi-kinase signaling

Background Blocking the pro-nociceptive action of CGRP is one of the most promising approaches for migraine prophylaxis. The aim of this study was to explore a role for CGRP as a neuroprotective agent for central and peripheral neurons. Methods The viability of isolated rat trigeminal, cortical and cerebellar neurons was tested by fluorescence vital assay. Engagement of Nrf2 target genes was analyzed by qPCR. The neuroprotective efficacy of CGRP in vivo was tested in mice using a permanent cerebral ischemia model. Results CGRP prevented apoptosis induced by the amino acid homocysteine in all three distinct neuronal populations. Using a set of specific kinase inhibitors, we show the role of multi-kinase signaling pathways involving PKA and CaMKII in neuronal survival. Forskolin triggered a very similar signaling cascade, suggesting that cAMP is the main upstream trigger for multi-kinase neuroprotection. The specific CGRP antagonist BIBN4096 reduced cellular viability, lending further support to the proposed neuroprotective function of CGRP. Importantly, CGRP was neuroprotective against permanent ischemia in mice. Conclusion Our data show an unexpected 'positive' role for the endogenous pro-nociceptive migraine mediator CGRP, suggesting more careful examination of migraine prophylaxis strategy based on CGRP antagonism although it should be noted that homocysteine induced apoptosis in primary neuronal cell culture might not necessarily reproduce all the features of cell loss in the living organism.