The trigeminovascular system and migraine: studies characterizing cerebrovascular and neuropeptide changes seen in humans and cats

Exploration of purinergic receptors as potential anti-migraine targets using established pre-clinical migraine models

BACKGROUND

The current understanding of mechanisms behind migraine pain has been greatly enhanced with the recent therapies targeting calcitonin gene-related peptide and its receptor. The clinical efficacy of calcitonin gene-related peptide-blocking drugs indicates that, at least in a considerable proportion of patients, calcitonin gene-related peptide is a key molecule in migraine pain. There are several receptors and molecular pathways that can affect the release of and response to calcitonin gene-related peptide. One of these could be purinergic receptors that are involved in nociception, but these are greatly understudied with respect to migraine.

OBJECTIVE

We aimed to explore purinergic receptors as potential anti-migraine targets.

METHODS

We used the human middle meningeal artery as a proxy for the trigeminal system to screen for possible anti-migraine candidates. The human findings were followed by intravital microscopy and calcitonin gene-related peptide release measurements in rodents.

RESULTS

We show that the purinergic P2Y13 receptor fulfills all the features of a potential anti-migraine target. The P2Y13 receptor is expressed in both the human trigeminal ganglion and middle meningeal artery and activation of this receptor causes: a) middle meningeal artery contraction in vitro; b) reduced dural artery dilation following periarterial electrical stimulation in vivo and c) a reduction of CGRP release from both the dura and the trigeminal ganglion in situ. Furthermore, we show that P2X3 receptor activation of the trigeminal ganglion causes calcitonin gene-related peptide release and middle meningeal artery dilation.

CONCLUSION

Both an agonist directed at the P2Y13 receptor and an antagonist of the P2X3 receptor seem to be viable potential anti-migraine therapies.

Dynamic changes in CGRP, PACAP, and PACAP receptors in the trigeminovascular system of a novel repetitive electrical stimulation rat model: Relevant to migraine

Migraine is the seventh most disabling disorder globally, with prevalence of 11.7% worldwide. One of the prevailing mechanisms is the activation of the trigeminovascular system, and calcitonin gene-related peptide (CGRP) is an important therapeutic target for migraine in this system. Recent studies suggested an emerging role of pituitary adenylate cyclase-activating peptide (PACAP) in migraine. However, the relation between CGRP and PACAP and the role of PACAP in migraine remain undefined. In this study, we established a novel repetitive (one, three, and seven days) electrical stimulation model by stimulating dura mater in conscious rats. Then, we determined expression patterns in the trigeminal ganglion and the trigeminal nucleus caudalis of the trigeminovascular system. Electrical stimulation decreased facial mechanical thresholds, and the order of sensitivity was as follows: vibrissal pad >inner canthus >outer canthus (P < 0.001). The electrical stimulation group exhibited head-turning and head-flicks (P < 0.05) nociceptive behaviors. Importantly, electrical stimulation increased the expressions of CGRP, PACAP, and the PACAP-preferring type 1 (PAC1) receptor in both trigeminal ganglion and trigeminal nucleus caudalis (P < 0.05). The expressions of two vasoactive intestinal peptide (VIP)-shared type 2 (VPAC1 and VPAC2) receptors were increased in the trigeminal ganglion, whereas in the trigeminal nucleus caudalis, their increases were peaked on Day 3 and then decreased by Day 7. PACAP was colocalized with NEUronal Nuclei (NeuN), PAC1, and CGRP in both trigeminal ganglion and the trigeminal nucleus caudalis. Our results demonstrate that the repetitive electrical stimulation model can simulate the allodynia during the migraine chronification, and PACAP plays a role in the pathogenesis of migraine potentially via PAC1 receptor.

Gepants for the treatment of migraine

INTRODUCTION

Migraine is the most common of all neurological disorders. A breakthrough in migraine treatment emerged in the early nineties with the introduction of 5-HT1B/D receptor agonists called triptans. Triptans are used as the standard of care for acute migraine; however, they have significant limitations such as incomplete and inconsistent pain relief, high rates of headache recurrence, class- specific side effects and cardiovascular contraindications. First- and second-generation calcitonin gene-related peptide (CGRP) receptor antagonists, namely gepants, is a class of drugs primarily developed for the acute treatment of migraine. CGRP is the most evaluated target for migraine treatments that are in development.

AREAS COVERED

This article reviews the available data for first- and second-generation CGRP receptor antagonists, the role of CGRPs in human physiology and migraine pathophysiology and the possible mechanism of action and safety of CGRP-targeted drugs.

EXPERT OPINION

Available data suggest that second generation of gepants has clinical efficacy similar to triptans and lasmiditan (5-HT1F receptor agonist) and has improved tolerability. Future studies will assess their safety, especially in specific populations such as patients with cardiovascular disease and pregnant women.

Primary headache disorders: Five new things

Purpose of review

To review 5 new areas in primary headache disorders, especially migraine and cluster headache.

Recent findings

Calcitonin gene-related peptide (CGRP) receptor antagonists (gepants-rimegepant and ubrogepant) and serotonin 5-HT_1F receptor agonists (ditans-lasmiditan) have completed phase 3 clinical trials and will soon offer novel, effective, well-tolerated nonvasoconstrictor options to treat acute migraine. CGRP preventive treatment is being revolutionized after the licensing of 3 monoclonal antibodies (MABs), erenumab, fremanezumab, and galcanezumab, with eptinezumab to follow, especially designed for migraine; they are effective and well tolerated. For patients seeking a nondrug therapy, neuromodulation approaches, single-pulse transcranial magnetic stimulation, noninvasive vagus nerve stimulation (nVNS), and external trigeminal nerve stimulation, represent licensed, well-tolerated approaches to migraine treatment. For the acute treatment of episodic cluster headache, nVNS is effective, well tolerated, and licensed; nVNS is effective and well tolerated in preventive treatment of cluster headache. The CGRP MAB galcanezumab was effective and well tolerated in a placebo-controlled trial in the preventive treatment of episodic cluster headache. Sphenopalatine ganglion stimulation has been shown to be effective and well tolerated in 2 randomized sham-controlled studies on chronic cluster headache. Understanding the premonitory (prodromal) phase of migraine during which patients experience symptoms such as yawning, tiredness, cognitive dysfunction, and food cravings may help explain apparent migraine triggers in some patients, thus offering better self-management.

Summary

Headache medicine has made remarkable strides, particularly in understanding migraine and cluster headache in the past 5 years. For the most common reason to visit a neurologist, therapeutic advances offer patients reduced disability and neurologists a rewarding, key role in improving the lives of those with migraine and cluster headache.

How to integrate monoclonal antibodies targeting the calcitonin gene-related peptide or its receptor in daily clinical practice

BACKGROUND

Migraine is a major public health issue associated with significant morbidity, considerable negative impact on quality of life, and significant socioeconomic burden. Preventive treatments are required to reduce the occurrence and the severity of acute attacks and to minimize the use of abortive medications and the associate risk of drug-related adverse events, as well as the onset of medication-overuse headache and chronification of migraine. We performed a review of all available evidence on the safety and efficacy of monoclonal antibodies targeting the calcitonin gene-related peptide or its receptor for the preventive treatment of migraine to provide evidence-based guidance on their use in clinical practice. Monoclonal antibodies targeting the calcitonin gene-related peptide or its receptor are mechanism-specific drugs for the preventive treatment of migraine. Double-blind randomized clinical trials have shown that monoclonal antibodies targeting the calcitonin gene-related peptide or its receptor are effective across all the spectrum of migraine patients who require prevention and have a good safety and tolerability profile. Nevertheless, high costs limit the affordability of those drugs at the moment.

CONCLUSIONS

Specificity, long half-life, efficacy, tolerability, and ease of use make monoclonal antibodies targeting the calcitonin gene-related peptide or its receptor an appealing treatment option for migraine prevention. Optimal strategies to manage treatment over time still need to be clarified with real-life data.

CGRP and the Trigeminal System in Migraine

OBJECTIVE

The goal of this narrative review is to provide an overview of migraine pathophysiology, with an emphasis on the role of calcitonin gene-related peptide (CGRP) within the context of the trigeminovascular system.

BACKGROUND

Migraine is a prevalent and disabling neurological disease that is characterized in part by intense, throbbing, and unilateral headaches. Despite recent advances in understanding its pathophysiology, migraine still represents an unmet medical need, as it is often underrecognized and undertreated. Although CGRP has been known to play a pivotal role in migraine for the last 2 decades, this has now received more interest spurred by the early clinical successes of drugs that block CGRP signaling in the trigeminovascular system.

DESIGN

This narrative review presents an update on the role of CGRP within the trigeminovascular system. PubMed searches were used to find recent (ie, 2016 to November 2018) published articles presenting new study results. Review articles are also included not as primary references but to bring these to the attention of the reader. Original research is referenced in describing the core of the narrative, and review articles are used to support ancillary points.

RESULTS

The trigeminal ganglion neurons provide the connection between the periphery, stemming from the interface between the primary afferent fibers of the trigeminal ganglion and the meningeal vasculature and the central terminals in the trigeminal nucleus caudalis. The neuropeptide CGRP is abundant in trigeminal ganglion neurons, and is released from the peripheral nerve and central nerve terminals as well as being secreted within the trigeminal ganglion. Release of CGRP from the peripheral terminals initiates a cascade of events that include increased synthesis of nitric oxide and sensitization of the trigeminal nerves. Secreted CGRP in the trigeminal ganglion interacts with adjacent neurons and satellite glial cells to perpetuate peripheral sensitization, and can drive central sensitization of the second-order neurons. A shift in central sensitization from activity-dependent to activity-independent central sensitization may indicate a mechanism driving the progression of episodic migraine to chronic migraine. The pathophysiology of cluster headache is much more obscure than that of migraine, but emerging evidence suggests that it may also involve hypersensitivity of the trigeminovascular system. Ongoing clinical studies with therapies targeted at CGRP will provide additional, valuable insights into the pathophysiology of this disorder.

CONCLUSIONS

CGRP plays an essential role in the pathophysiology of migraine. Treatments that interfere with the functioning of CGRP in the peripheral trigeminal system are effective against migraine. Blocking sensitization of the trigeminal nerve by attenuating CGRP activity in the periphery may be sufficient to block a migraine attack. Additionally, the potential exists that this therapeutic strategy may also alleviate cluster headache as well.

The effect of orofacial complete Freund's adjuvant treatment on the expression of migraine-related molecules

Background

Migraine is a neurovascular primary headache disorder, which causes significant socioeconomic problems worldwide. The pathomechanism of disease is enigmatic, but activation of the trigeminovascular system (TS) appears to be essential during the attack. Migraine research of recent years has focused on neuropeptides, such as calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase-activating polypeptide 1–38 (PACAP1–38) as potential pathogenic factors and possible therapeutic offensives. The goal of present study was to investigate the simultaneous expression of CGRP and precursor of PACAP1–38 (preproPACAP) in the central region of the TS in a time-dependent manner following TS activation in rats.

Methods

The right whisker pad of rats was injected with 50 μl Complete Freund’s Adjuvant (CFA) or saline. A mechanical allodynia test was performed with von Frey filaments before and after treatment. Transcardial perfusion of the animals was initiated 24, 48, 72 and 120 h after injection, followed by the dissection of the nucleus trigeminus caudalis (TNC). After preparation, the samples were stored at − 80 °C until further use. The relative optical density of CGRP and preproPACAP was analyzed by Western blot. One-way ANOVA and Kruskal-Wallis followed by Tukey post hoc test were used to evaluate the data. Regression analysis was applied to explore the correlation between neuropeptides expression and hyperalgesia.

Results

Orofacial CFA injection resulted in significant CGRP and preproPACAP release in the TNC 24, 48, 72 and 120 h after the treatment. The level of neuropeptides reached its maximum at 72 h after CFA injection, corresponding to the peak of facial allodynia. Negative, linear correlation was detected between the expression level of neuropeptides and value of mechanonociceptive threshold.

Conclusion

This is the first study which suggests that the expression of CGRP and preproPACAP simultaneously increases in the central region of activated TS and it influences the formation of mechanical hyperalgesia. Our results contribute to a better understanding of migraine pathogenesis and thereby to the development of more effective therapeutic approaches.

Calcitonin Gene-Related Peptide Modulators - The History and Renaissance of a New Migraine Drug Class

Several lines of evidence pointed to an important role for CGRP in migraine. These included the anatomic colocalization of CGRP and its receptor in sensory fibers innervating pain-producing meningeal blood vessels, its release by trigeminal stimulation, the observation of elevated CGRP in the cranial circulation during migraine with normalization concomitant with headache relief by sumatriptan, and translational studies with intravenous (IV) CGRP that evoked migraine only in migraineurs. The development of small molecule CGRP receptor antagonists (CGRP-RAs) that showed clinical antimigraine efficacy acutely and prophylactically in randomized placebo-controlled clinical trials subsequently gave definitive pharmacological proof of the importance of CGRP in migraine. More recently, CGRP target engagement imaging studies using a CGRP receptor PET ligand [¹¹ C]MK-4232 demonstrated that there was no brain CGRP receptor occupancy at clinically effective antimigraine doses of telcagepant, a prototypic CGRP-RA. Taken together, these data indicated that (1) the therapeutic site of action of the CGRP-RAs was peripheral not central; (2) that IV CGRP had most likely evoked migraine through an action at sites outside the blood-brain barrier; and (3) that migraine pain was therefore, at least in part, peripheral in origin. The evolution of CGRP migraine science gave impetus to the development of peripherally acting drugs that could modulate CGRP chronically to prevent frequent episodic and chronic migraine. Large molecule biologic antibody (mAb) approaches that are given subcutaneously to neutralize circulating CGRP peptide (fremanezumab, galcanezumab) or block CGRP receptors (erenumab) have shown consistent efficacy and tolerability in multicenter migraine prevention trials and are now approved for clinical use. Eptinezumab, a CGRP neutralizing antibody given IV, shows promise in late stage clinical development. Recently, orally administered next-generation small molecule CGRP-RAs have been shown to have safety and efficacy in acute treatment (ubrogepant and rimegepant) and prevention (atogepant) of migraine, giving additional CGRP-based therapeutic options for migraine patients.

Once-monthly galcanezumab for the prevention of migraine in adults: an evidence-based descriptive review and potential place in therapy

In the last 15 years relevant efforts have been made to demonstrate that calcitonin gene-related peptide (CGRP) antagonism is a valuable and druggable mechanism for treatment or prevention of migraine. Galcanezumab is one of the antibodies developed and studied to prevent migraine by targeting CGRP. The scope of this review is to report data currently available on galcanezumab. According to available data, galcanezumab is safe and efficacious in preventing migraine in episodic migraine patients, also reducing disability and functional impairment due to the disorder. In September 2018, galcanezumab was approved in the USA for the prevention of migraine in adults. The placement of galcanezumab into the current therapeutic scenario will be a revolution for migraine patients, and probably in a less near future also for patients affected by other primary headaches.

TRP Channels and Migraine: Recent Developments and New Therapeutic Opportunities

Migraine is the second-most disabling disease worldwide, and the second most common neurological disorder. Attacks can last many hours or days, and consist of multiple symptoms including headache, nausea, vomiting, hypersensitivity to stimuli such as light and sound, and in some cases, an aura is present. Mechanisms contributing to migraine are still poorly understood. However, transient receptor potential (TRP) channels have been repeatedly linked to the disorder, including TRPV1, TRPV4, TRPM8, and TRPA1, based on their activation by pathological stimuli related to attacks, or their modulation by drugs/natural products known to be efficacious for migraine. This review will provide a brief overview of migraine, including current therapeutics and the link to calcitonin gene-related peptide (CGRP), a neuropeptide strongly implicated in migraine pathophysiology. Discussion will then focus on recent developments in preclinical and clinical studies that implicate TRP channels in migraine pathophysiology or in the efficacy of therapeutics. Given the use of onabotulinum toxin A (BoNTA) to treat chronic migraine, and its poorly understood mechanism, this review will also cover possible contributions of TRP channels to BoNTA efficacy. Discussion will conclude with remaining questions that require future work to more fully evaluate TRP channels as novel therapeutic targets for migraine.

Recent Advances in Pharmacotherapy for Migraine Prevention: From Pathophysiology to New Drugs

Migraine is a common and disabling neurological disorder, with a significant socioeconomic burden. Its pathophysiology involves abnormalities in complex neuronal networks, interacting at different levels of the central and peripheral nervous system, resulting in the constellation of symptoms characteristic of a migraine attack. Management of migraine is individualised and often necessitates the commencement of preventive medication. Recent advancements in the understanding of the neurobiology of migraine have begun to account for some parts of the symptomatology, which has led to the development of novel target-based therapies that may revolutionise how migraine is treated in the future. This review will explore recent advances in the understanding of migraine pathophysiology, and pharmacotherapeutic developments for migraine prevention, with particular emphasis on novel treatments targeted at the calcitonin gene-related peptide (CGRP) pathway.

Neuroimaging clues of migraine aura

While migraine headaches can be provoked, or predicted by the presence of an aura or premonitory symptoms, the prediction or elicitation of the aura itself is more problematic. Therefore, imaging studies directly examining the aura phenomenon are sparse. There are however interictal imaging studies that can shed light on the pathophysiology of the migraine with aura (MWA) cascade. Here, we review findings pointing to the involvement of cortical spreading depression (CSD) and neuroinflammation in MWA. Whether asymptomatic CSD also happens in some migraine without aura is still under debate. In addition, new evidence points to glial activation in MWA, indicating the involvement of astrocytes in the neuroinflammatory cascade that follows CSD, as well as dural macrophages, supporting the involvement of the trigeminovascular system in migraine pain.

Neurovascular mechanisms of migraine and cluster headache

Vascular theories of migraine and cluster headache have dominated for many years the pathobiological concept of these disorders. This view is supported by observations that trigeminal activation induces a vascular response and that several vasodilating molecules trigger acute attacks of migraine and cluster headache in susceptible individuals. Over the past 30 years, this rationale has been questioned as it became clear that the actions of some of these molecules, in particular, calcitonin gene-related peptide and pituitary adenylate cyclase-activating peptide, extend far beyond the vasoactive effects, as they possess the ability to modulate nociceptive neuronal activity in several key regions of the trigeminovascular system. These findings have shifted our understanding of these disorders to a primarily neuronal origin with the vascular manifestations being the consequence rather than the origin of trigeminal activation. Nevertheless, the neurovascular component, or coupling, seems to be far more complex than initially thought, being involved in several accompanying features. The review will discuss in detail the anatomical basis and the functional role of the neurovascular mechanisms relevant to migraine and cluster headache.

Perivascular neurotransmitters: Regulation of cerebral blood flow and role in primary headaches

In order to understand the nature of the relationship between cerebral blood flow (CBF) and primary headaches, we have conducted a literature review with particular emphasis on the role of perivascular neurotransmitters. Primary headaches are in general considered complex polygenic disorders (genetic and environmental influence) with pathophysiological neurovascular alterations. Identified candidate headache genes are associated with neuro- and gliogenesis, vascular development and diseases, and regulation of vascular tone. These findings support a role for the vasculature in primary headache disorders. Moreover, neuronal hyperexcitability and other abnormalities have been observed in primary headaches and related to changes in hemodynamic factors. In particular, this relates to migraine aura and spreading depression. During headache attacks, ganglia such as trigeminal and sphenopalatine (located outside the blood-brain barrier) are variably activated and sensitized which gives rise to vasoactive neurotransmitter release. Sympathetic, parasympathetic and sensory nerves to the cerebral vasculature are activated. During migraine attacks, altered CBF has been observed in brain regions such as the somatosensory cortex, brainstem and thalamus. In regulation of CBF, the individual roles of neurotransmitters are partly known, but much needs to be unraveled with respect to headache disorders.

CGRP Antagonists for the Treatment of Chronic Migraines: a Comprehensive Review

PURPOSE OF REVIEW

The purpose of the following review is to summarize the most recent understanding of migraine pathophysiology, as well as of basic and clinical science pharmacologic literature regarding the development of calcitonin gene receptor peptide (CGRP) antagonists as a novel therapeutic modality for the treatment of migraine headaches. A review is provided of erenumab, the first of its class FDA approved CGRP antagonist.

RECENT FINDINGS

Despite its high prevalence, the occurrence and treatment of migraine headaches is poorly understood. Erenumab and CGRP antagonists as a whole significantly reduce the average number of migraine days experienced in migraine sufferers. CGRP antagonists appear to significantly improve treatment outcomes in patients who suffer from episodic and chronic migraines. Erenumab is the first CGRP antagonist to be FDA approved for public use; however, further development of biologics in this class is underway.

CGRP-based Migraine Therapeutics: How Might They Work, Why So Safe, and What Next?

Migraine is a debilitating neurological condition that involves the neuropeptide calcitonin gene-related peptide (CGRP). An exciting development is the recent FDA approval of the first in an emerging class of CGRP-targeted drugs designed to prevent migraine. Yet despite this efficacy, there are some fundamental unanswered questions, such as where and how CGRP works in migraine. Preclinical data suggest that CGRP acts via both peripheral and central mechanisms. The relevance of peripheral sites is highlighted by the clinical efficacy of CGRP-blocking antibodies, even though they do not appreciably cross the blood-brain barrier. The most likely sites of action are within the dura and trigeminal ganglia. Furthermore, it would be foolish to ignore perivascular actions in the dura since CGRP is the most potent vasodilatory peptide. Ultimately, the consequence of blocking CGRP or its receptor is reduced peripheral neural sensitization. Underlying their efficacy is the question of why the antibodies have such an excellent safety profile so far. This may be due to the presence of a second CGRP receptor and vesicular release of a large bolus of peptides. Finally, despite the promise of these drugs, there are unmet gaps because they do not work for all patients; so what next? We can expect advances on several fronts, including CGRP receptor structures that may help development of centrally-acting antagonists, combinatorial treatments that integrate other therapies, and development of drugs that target other neuropeptides. This is truly an exciting time for CGRP and the migraine field with many more discoveries on the horizon.

Plasma Calcitonin Gene-Related Peptide: A Potential Biomarker for Diagnosis and Therapeutic Responses in Pediatric Migraine

Background: Plasma calcitonin gene-related peptide (CGRP) plays a key role in the migraine pathophysiology. This study aimed to investigate its role in predicting diagnosis and outcome of pharmacotherapy in pediatric migraine. Methods: We prospectively recruited 120 subjects, who never took migraine-preventive agents in a pediatric clinic, including 68 patients with migraine, 30 with non-migraine headache (NM), and 22 non-headache (NH) age-matched controls. Short-term therapeutic response was measured for at least 2 weeks after the start of therapy. Responders were defined with >50% headache reduction. Plasma CGRP concentrations were measured by ELISA. Results: In the migraine group, more patients required acute therapy, as compared to the NM group (62/68, 91% vs. 5/30, 15%, p = 0.001). The mean plasma CGRP level in migraineurs either during (291 ± 60 pg/ml) or between (240 ± 48) attacks was higher than in NM patients (51 ± 5 pg/ml, p = 0.006 and 0.018, respectively) and NH controls (53 ± 6 pg/ml, p = 0.016 and 0.045, respectively). Forty-seven patients (69%) needed preventive treatments and had higher plasma CGRP levels (364 ± 62 pg/ml, n = 47) than those not (183 ± 54 pg/ml, n = 21) (p = 0.031). Topiramate responders had higher plasma CGRP levels than non-responders (437 ± 131 pg/ml, n = 14 vs. 67 ± 19 pg/ml, n = 6, p = 0.021). Survival curves of plasma CGRP levels also showed those with higher CGRP levels responded better to topiramate. Differences were not found in the other preventives. Conclusion: The plasma CGRP level can differentiate migraine from non-migraine headache. It may also serve as a reference for the therapeutic strategy since it is higher in patients requiring migraine prevention and responsive to short-term topiramate treatment. These results are clinically significant, especially for the young children who cannot clearly describe their headache symptoms and may provide new insights into the clinical practice for the diagnosis and treatment of pediatric migraine.

Bioactive Lipids in Cancer, Inflammation and Related Diseases : Acute and Chronic Mild Traumatic Brain Injury Differentially Changes Levels of Bioactive Lipids in the CNS Associated with Headache

Headache is a common complaint after mild traumatic brain injury (mTBI). Changes in the CNS lipidome were previously associated with acrolein-induced headache in rodents. mTBI caused similar headache-like symptoms in rats; therefore, we tested the hypothesis that mTBI might likewise alter the lipidome. Using a stereotaxic impactor, rats were given either a single mTBI or a series of 4 mTBIs 48 h apart. 72 h later for single mTBI and 7 days later for repeated mTBI, the trigeminal ganglia (TG), trigeminal nucleus (TNC), and cerebellum (CER) were isolated. Using HPLC/MS/MS, ~80 lipids were measured in each tissue and compared to sham controls. mTBI drove widespread alterations in lipid levels. Single mTBI increased arachidonic acid and repeated mTBI increased prostaglandins in all 3 tissue types. mTBI affected multiple TRPV agonists, including N-arachidonoyl ethanolamine (AEA), which increased in the TNC and CER after single mTBI. After repeated mTBI, AEA increased in the TG, but decreased in the TNC. Common to all tissue types in single and repeated mTBI was an increase the AEA metabolite, N-arachidonoyl glycine, a potent activator of microglial migration. Changes in the CNS lipidome associated with mTBI likely play a role in headache and in long-term neurodegenerative effects of repeated mTBI.

Role of CGRP in Migraine

Migraine is a common neurological disorder that afflicts up to 15% of the adult population in most countries, with predominance in females. It is characterized by episodic, often disabling headache, photophobia and phonophobia, autonomic symptoms (nausea and vomiting), and in a subgroup an aura in the beginning of the attack. Although still debated, many researchers consider migraine to be a disorder in which CNS dysfunction plays a pivotal role while various parts of the trigeminal system are necessary for the expression of associated symptoms.Treatment of migraine has in recent years seen the development of drugs that target the trigeminal sensory neuropeptide calcitonin gene-related peptide (CGRP) or its receptor. Several of these drugs are now approved for use in frequent episodic and in chronic migraine. CGRP-related therapies offer considerable improvements over existing drugs, as they are the first to be designed specifically to act on the trigeminal pain system: they are more specific and have little or no adverse effects. Small molecule CGRP receptor antagonists, gepants, are effective for acute relief of migraine headache, whereas monoclonal antibodies against CGRP (Eptinezumab, Fremanezumab, and Galcanezumab) or the CGRP receptor (Erenumab) effectively prevent migraine attacks. The neurobiology of CGRP signaling is briefly summarized together with key clinical evidence for the role of CGRP in migraine headache, including the efficacy of CGRP-targeted treatments.

A phase 3, long-term, open-label safety study of Galcanezumab in patients with migraine

BACKGROUND

Galcanezumab, a humanized monoclonal antibody that selectively binds to the calcitonin gene-related peptide, has demonstrated in previous Phase 2 and Phase 3 clinical studies (≤6-month of treatment) a reduction in the number of migraine headache days and improved patients' functioning. This study evaluated the safety and tolerability, as well as the effectiveness of galcanezumab for up to 12 months of treatment in patients with migraine.

METHODS

Patients diagnosed with episodic or chronic migraine, 18 to 65 years old, that were not exposed previously to galcanezumab, were randomized to receive galcanezumab 120 mg or 240 mg, administered subcutaneously once monthly for a year. Safety and tolerability were evaluated by frequency of treatment-emergent adverse events (TEAEs), serious adverse events (SAEs), and adverse events (AEs) leading to study discontinuation. Laboratory values, vital signs, electrocardiograms, and suicidality were also analyzed. Additionally, overall change from baseline in the number of monthly migraine headache days, functioning, and disability were assessed.

RESULTS

One hundred thirty five patients were randomized to each galcanezumab dose group. The majority of patients were female (> 80%) and on average were 42 years old with 10.6 migraine headache days per month at baseline. 77.8% of the patients completed the open-label treatment phase, 3.7% of patients experienced an SAE, and 4.8% discontinued due to AEs. TEAEs with a frequency ≥ 10% of patients in either dose group were injection site pain, nasopharyngitis, upper respiratory tract infection, injection site reaction, back pain, and sinusitis. Laboratory values, vital signs, or electrocardiograms did not show anyclinically meaningful differences between galcanezumab dosesOverall mean reduction in monthly migraine headache days over 12 months for the galcanezumab dose groups were 5.6 (120 mg) and 6.5 (240 mg). Level of functioning was improved and headache-related disability was reduced in both dose groups.

CONCLUSION

Twelve months of treatment with self-administered injections of galcanezumab was safe and associated with a reduction in the number of monthly migraine headache days. Safety and tolerability of the 2 galcanezumab dosing regimens were comparable.

TRIAL REGISTRATION

ClinicalTrials.gov as NCT02614287 , posted November 15, 2015. These data were previously presented as a poster at the International Headache Congress 2017: PO-01-184, Late-Breaking Abstracts of the 2017 International Headache Congress. (2017). Cephalalgia, 37(1_suppl), 319-374.

Peripherally administered calcitonin gene-related peptide induces spontaneous pain in mice: implications for migraine

Migraine is the third most common disease in the world (behind dental caries and tension-type headache) with an estimated global prevalence of 15%, yet its etiology remains poorly understood. Recent clinical trials have heralded the potential of therapeutic antibodies that block the actions of the neuropeptide calcitonin gene-related peptide (CGRP) or its receptor to prevent migraine. Calcitonin gene-related peptide is believed to contribute to trigeminal nerve hypersensitivity and photosensitivity in migraine, but a direct role in pain associated with migraine has not been established. In this study, we report that peripherally administered CGRP can act in a light-independent manner to produce spontaneous pain in mice that is manifested as a facial grimace. As an objective validation of the orbital tightening action unit of the grimace response, we developed a squint assay using a video-based measurement of the eyelid fissure, which confirmed a significant squint response after CGRP injection, both in complete darkness and very bright light. These indicators of discomfort were completely blocked by preadministration of a monoclonal anti-CGRP-blocking antibody. However, the nonsteroidal anti-inflammatory drug meloxicam failed to block the effect of CGRP. Interestingly, an apparent sex-specific response to treatment was observed with the antimigraine drug sumatriptan partially blocking the CGRP response in male, but not female mice. These results demonstrate that CGRP can induce spontaneous pain, even in the absence of light, and that the squint response provides an objective biomarker for CGRP-induced pain that is translatable to humans.

Basic Considerations for the Use of Monoclonal Antibodies in Migraine

BACKGROUND

Migraine impacts more than 36 million people in the United States and 1 billion people worldwide. Despite the increasing availability of acute and preventive therapies, there is still tremendous unmet need. Potential treatments in development include monoclonal antibodies (mAbs). Appropriate use of these “biologic” treatments will necessitate an understanding of the aspects that distinguish them from traditional medications.

AIM

Many drug classes are prescribed for migraine treatment, but all have limitations. Recently, calcitonin gene-related peptide (CGRP) activity has shown a significant promise as a target for preventive therapy. In this review, we provide an overview of the potential role of CGRP mAbs in migraine, with a focus on their design, pharmacokinetics, safety, and immunogenicity.

CONCLUSIONS

The CGRP mAbs are an innovative new therapy for migraine and address the need for effective and tolerable preventive options. MAbs, including those that target CGRP or its receptor, bind to a target with high specificity and affinity and lead to few off-target adverse effects, although mechanism-based adverse reactions may occur. Unlike other therapeutic antibodies used to treat neurologic disease, CGRP mAbs do not have a target within the immune system and have been designed to avoid altering the immune system. The safety and efficacy of mAbs against CGRP or its receptors are being investigated in clinical development programs, and the first of these therapies has received regulatory approval in the United States.

Erenumab in the treatment of migraine

Migraine is a highly prevalent neurological pain syndrome, and its management is limited due to side effects posed by current preventive therapies. Calcitonin gene-related peptide (CGRP) plays a crucial role in the pathogenesis of migraine. In recent years, research has been dedicated to the development of monoclonal antibodies against CGRP and CGRP receptors for the treatment of migraine. This review will focus on the first US FDA-approved CGRP-receptor monoclonal antibody developed for the prevention of migraine: erenumab. Two Phase II trials (one for episodic migraine and one for chronic migraine) and two Phase III trials for episodic migraine have been published demonstrating the efficacy and safety of erenumab in the prevention of migraine.

What Are We Missing in the Diagnostic Criteria for Migraine?

PURPOSE OF REVIEW

This review is intended to examine how the diagnostic criteria for migraine have evolved over the past 45 years and to evaluate the strengths and weaknesses of the current diagnostic criteria promulgated by the International Classification of Headache Disorders (ICHD).

RECENT FINDINGS

The ICHD is a comprehensive and systematic classification system for headache disorders. As the pathophysiology of migraine is more fully elucidated and more sophisticated diagnostic technologies are developed (e.g., the identification of biomarkers), the current diagnostic criteria for migraine will likely be further refined. The ICHD has allowed for more precise research study design in the field of headache medicine. The current diagnostic criteria for migraine outlined in the 3rd version of the ICHD are far more sensitive and specific than the clinical criteria proposed in 1962. In future iterations, dividing episodic and chronic migraine into subtypes based on frequency (i.e., low frequency vs high frequency; near-daily vs daily) potentially could assist in guiding clinical management. In addition, a better understanding of aura, vestibular migraine, migrainous infarction, and hemiplegic migraine likely will lead to more refined diagnostic criteria for those entities.

The association between migraine and physical exercise

BACKGROUND

There is an unmet need of pharmacological and non-pharmacological treatment options for migraine patients. Exercise can be used in the treatment of several pain conditions, including. However, what exact role exercise plays in migraine prevention is unclear. Here, we review the associations between physical exercise and migraine from an epidemiological, therapeutical and pathophysiological perspective.

METHODS

The review was based on a primary literature search on the PubMed using the search terms "migraine and exercise".

RESULTS

Low levels of physical exercise and high frequency of migraine has been reported in several large population-based studies. In experimental studies exercise has been reported as a trigger factor for migraine as well as migraine prophylaxis. Possible mechanisms for how exercise may trigger migraine attacks, include acute release of neuropeptides such as calcitonin gene-related peptide or alternation of hypocretin or lactate metabolism. Mechanisms for migraine prevention by exercise may include increased beta-endorphin, endocannabinoid and brain-derived neurotrophic factor levers in plasma after exercise.

CONCLUSION

In conclusion, it seems that although exercise can trigger migraine attacks, regular exercise may have prophylactic effect on migraine frequency. This is most likely due to an altered migraine triggering threshold in persons who exercise regularly. However, the frequency and intensity of exercise that is required is still an open question, which should be addressed in future studies to delineate an evidence-based exercise program to prevent migraine in sufferers.

Antigens and Antibodies in Disease With Specifics About CGRP Immunology

Growth in knowledge about calcitonin gene-related peptide (CGRP) in the pathophysiology of migraine brought CGRP antagonism to headache medicine. Failures in development of small molecule CGRP receptor antagonists and increasing knowledge and use of monoclonal antibodies (mAbs) in medicine led to the breakthrough development of large molecule anti-CGRP mAbs: eptinezumab, erenumab, fremanezumab, and galcanezumab. This specifics about CGRP immunology aims to outline: (1) knowledge needed for CGRP antagonism and (2) developmental issues of specific CGRP antagonists for provider use. This clinically oriented review documents IgG structure and function; state of the art of monoclonal IgG production and ligand-antigen-antibodies in migraine therapeutics contributing to immunogenic risks and off-target toxicities. Specifics to CGRP ligand, receptor, antagonism, and molecules, small and large, complete this review. Completion will facilitate assessment of the similarities, differences, and application of the forthcoming anti-CGRP receptor and ligand antagonists for patients.

TRP Channels as Potential Targets for Sex-Related Differences in Migraine Pain

Chronic pain is one of the most debilitating human diseases and represents a social and economic burden for our society. Great efforts are being made to understand the molecular and cellular mechanisms underlying the pathophysiology of pain transduction. It is particularly noteworthy that some types of chronic pain, such as migraine, display a remarkable sex dimorphism, being up to three times more prevalent in women than in men. This gender prevalence in migraine appears to be related to sex differences arising from both gonadal and genetic factors. Indeed, the functionality of the somatosensory, immune, and endothelial systems seems modulated by sex hormones, as well as by X-linked genes differentially expressed during development. Here, we review the current data on the modulation of the somatosensory system functionality by gonadal hormones. Although this is still an area that requires intense investigation, there is evidence suggesting a direct regulation of nociceptor activity by sex hormones at the transcriptional, translational, and functional levels. Data are being accumulated on the effect of sex hormones on TRP channels such as TRPV1 that make pivotal contributions to nociceptor excitability and sensitization in migraine and other chronic pain syndromes. These data suggest that modulation of TRP channels' expression and/or activity by gonadal hormones provide novel pathways for drug intervention that may be useful for targeting the sex dimorphism observed in migraine.

New strategies for the treatment and prevention of primary headache disorders

The primary headache disorders, which include migraine, cluster headache and tension-type headache, are among the most common diseases and leading causes of disability worldwide. The available treatment options for primary headache disorders have unsatisfactory rates of efficacy, tolerability and patient adherence. In this Review, we discuss promising new approaches for the prevention of primary headache disorders, such as monoclonal antibodies targeting calcitonin gene-related peptide (CGRP) or its receptor, and small-molecule CGRP receptor antagonists. Neuromodulation approaches employing noninvasive or implantable devices also show promise for treating primary headache disorders. Noninvasive treatments, such as transcranial magnetic stimulation and transcutaneous peripheral nerve stimulation, are delivered by devices that patients can self-administer. Implantable devices targeting the occipital nerves, sphenopalatine ganglion or high cervical spinal cord are placed using percutaneous and/or surgical procedures, and are powered either wirelessly or by surgically implanted batteries. These new and emerging treatments have the potential to address unmet patient needs and reduce headache-associated disability.

Vascular Contributions to Migraine: Time to Revisit?

Migraine is one of the most prevalent and disabling neurovascular disorders worldwide. However, despite the increase in awareness and research, the understanding of migraine pathophysiology and treatment options remain limited. For centuries, migraine was considered to be a vascular disorder. In fact, the throbbing, pulsating quality of the headache is thought to be caused by mechanical changes in vessels. Moreover, the most successful migraine treatments act on the vasculature and induction of migraine can be accomplished with vasoactive agents. However, over the past 20 years, the emphasis has shifted to the neural imbalances associated with migraine, and vascular changes have generally been viewed as an epiphenomenon that is neither sufficient nor necessary to induce migraine. With the clinical success of peripherally-acting antibodies that target calcitonin gene-related peptide (CGRP) and its receptor for preventing migraine, this neurocentric view warrants a critical re-evaluation. This review will highlight the likely importance of the vasculature in migraine.

Current understanding of meningeal and cerebral vascular function underlying migraine headache

BACKGROUND

The exact mechanisms underlying the onset of a migraine attack are not completely understood. It is, however, now well accepted that the onset of the excruciating throbbing headache of migraine is mediated by the activation and increased mechanosensitivity (i.e. sensitization) of trigeminal nociceptive afferents that innervate the cranial meninges and their related large blood vessels.

OBJECTIVES

To provide a critical summary of current understanding of the role that the cranial meninges, their associated vasculature, and immune cells play in meningeal nociception and the ensuing migraine headache.

METHODS

We discuss the anatomy of the cranial meninges, their associated vasculature, innervation and immune cell population. We then debate the meningeal neurogenic inflammation hypothesis of migraine and its putative contribution to migraine pain. Finally, we provide insights into potential sources of meningeal inflammation and nociception beyond neurogenic inflammation, and their potential contribution to migraine headache.

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.

Efficacy and safety of galcanezumab for the prevention of episodic migraine: Results of the EVOLVE-2 Phase 3 randomized controlled clinical trial

Introduction Galcanezumab is a humanized monoclonal antibody binding calcitonin gene-related peptide, used for migraine prevention. Methods A global, double-blind, 6-month study of patients with episodic migraine was undertaken with 915 intent-to-treat patients randomized to monthly galcanezumab 120 mg (n = 231) or 240 mg (n = 223) or placebo (n = 461) subcutaneous injections. Primary endpoint was overall mean change from baseline in monthly migraine headache days. Key secondary endpoints were ≥50%,  ≥ 75%, and 100% response rates; monthly migraine headache days with acute migraine medication use; Patient Global Impression of Severity rating; the Role Function-Restrictive score of the Migraine-Specific Quality of Life Questionnaire. Results Mean monthly migraine headache days were reduced by 4.3 and 4.2 days by galcanezumab 120 and 240 mg, respectively, and 2.3 days by placebo. The group differences (95% CIs) versus placebo were 2.0 (-2.6, -1.5) and 1.9 (-2.4, -1.4), respectively. Both doses were superior to placebo for all key secondary endpoints. Injection site pain was the most common treatment-emergent adverse event, reported at similar rates in all treatment groups. Both galcanezumab doses had significantly more injection site reactions and injection site pruritus, and the 240 mg group had significantly more injection site erythema versus placebo. Conclusions Galcanezumab 120 or 240 mg given once monthly was efficacious, safe, and well tolerated. Study identification EVOLVE-2; NCT02614196; https://clinicaltrials.gov/ct2/show/NCT02614196 . Trial Registration NCT02614196.

Characterization of the trigeminovascular actions of several adenosine A2A receptor antagonists in an in vivo rat model of migraine

BACKGROUND

Migraine is considered a neurovascular disorder, but its pathophysiological mechanisms are not yet fully understood. Adenosine has been shown to increase in plasma during migraine attacks and to induce vasodilation in several blood vessels; however, it remains unknown whether adenosine can interact with the trigeminovascular system. Moreover, caffeine, a non-selective adenosine receptor antagonist, is included in many over the counter anti-headache/migraine treatments.

METHODS

This study used the rat closed cranial window method to investigate in vivo the effects of the adenosine A_2A receptor antagonists with varying selectivity over A₁ receptors; JNJ-39928122, JNJ-40529749, JNJ-41942914, JNJ-40064440 or JNJ-41501798 (0.3-10 mg/kg) on the vasodilation of the middle meningeal artery produced by either CGS21680 (an adenosine A_2A receptor agonist) or endogenous CGRP (released by periarterial electrical stimulation).

RESULTS

Regarding the dural meningeal vasodilation produced neurogenically or pharmacologically, all JNJ antagonists: (i) did not affect neurogenic vasodilation but (ii) blocked the vasodilation produced by CGS21680, with a blocking potency directly related to their additional affinity for the adenosine A₁ receptor.

CONCLUSIONS

These results suggest that vascular adenosine A_2A (and, to a certain extent, also A₁) receptors mediate the CGS21680-induced meningeal vasodilation. These receptors do not appear to modulate prejunctionally the sensory release of CGRP. Prevention of meningeal arterial dilation might be predictive for anti-migraine drugs, and since none of these JNJ antagonists modified per se blood pressure, selective A_2A receptor antagonism may offer a novel approach to antimigraine therapy which remains to be investigated in clinical trials.

Dihydroergotamine inhibits the vasodepressor sensory CGRPergic outflow by prejunctional activation of α2-adrenoceptors and 5-HT1 receptors

BACKGROUND

Dihydroergotamine (DHE) is an antimigraine drug that produces cranial vasoconstriction and inhibits trigeminal CGRP release; furthermore, it inhibits the vasodepressor sensory CGRPergic outflow, but the receptors involved remain unknown. Prejunctional activation of α_2A/2C-adrenergic, serotonin 5-HT_1B/1F, or dopamine D₂-like receptors results in inhibition of this CGRPergic outflow. Since DHE displays affinity for these receptors, this study investigated the pharmacological profile of DHE-induced inhibition of the vasodepressor sensory CGRPergic outflow.

METHODS

Pithed rats were pretreated i.v. with hexamethonium (2 mg/kg·min) followed by continuous infusions of methoxamine (20 μg/kg·min) and DHE (3.1 μg/kg·min). Then, stimulus-response curves (spinal electrical stimulation; T₉-T₁₂) or dose-response curves (i.v. injections of α-CGRP) resulted in frequency-dependent or dose-dependent decreases in diastolic blood pressure.

RESULTS

DHE inhibited the vasodepressor responses to electrical stimulation (0.56-5.6 Hz), without affecting those to i.v. α-CGRP (0.1-1 μg/kg). This inhibition by DHE (not produced by the methoxamine infusions): (i) was abolished by pretreatment with the combination of the antagonists rauwolscine (α₂-adrenoceptor; 310 μg/kg) plus GR127935 (5-HT_1B/1D; 31 μg/kg); and (ii) remained unaffected after rauwolscine (310 μg/kg), GR127935 (31 μg/kg) or haloperidol (D₂-like; 310 μg/kg) given alone, or after the combination of rauwolscine plus haloperidol or GR127935 plus haloperidol at the aforementioned doses.

CONCLUSION

DHE-induced inhibition of the vasodepressor sensory CGRPergic outflow is mainly mediated by prejunctional rauwolscine-sensitive α₂-adrenoceptors and GR127935-sensitive 5-HT_1B/1D receptors, which correlate with α_2A/2C-adrenoceptors and 5-HT_1B receptors, respectively. These findings suggest that DHE-induced inhibition of the perivascular sensory CGRPergic outflow may facilitate DHE's vasoconstrictor properties resulting in an increased vascular resistance.

Phase 1, randomized, parallel-group, double-blind, placebo-controlled trial to evaluate the effects of erenumab (AMG 334) and concomitant sumatriptan on blood pressure in healthy volunteers

OBJECTIVES

The aim of this study was to assess the effects of concomitant administration of erenumab and sumatriptan on resting blood pressure, pharmacokinetics, safety, and tolerability in healthy subjects.

METHODS

In this phase 1, parallel-group, one-way crossover, double-blind, placebo-controlled study, healthy adult subjects were randomized (1:2) to receive either intravenous placebo and subcutaneous sumatriptan 12 mg (i.e. two 6-mg injections separated by 1 hour) or intravenous erenumab 140 mg and subcutaneous sumatriptan 12 mg. Blood pressure was measured pre-dose and at prespecified times post-dose. The primary endpoint was individual time-weighted averages of mean arterial pressure, measured from 0 hours to 2.5 hours after the first dose of sumatriptan. Pharmacokinetic parameters for sumatriptan were evaluated by calculating geometric mean ratios (erenumab and sumatriptan/placebo and sumatriptan). Adverse events and anti-erenumab antibodies were also evaluated.

RESULTS

A total of 34 subjects were randomized and included in the analysis. Least squares mean (standard error) time-weighted averages of mean arterial pressure were 87.4 (1.0) mmHg for the placebo and sumatriptan group and 87.4 (1.2) mmHg for the erenumab and sumatriptan group. Mean difference in mean arterial pressure between groups was -0.04 mmHg (90% confidence interval: -2.2, 2.1). Geometric mean ratio estimates for maximum plasma concentration of sumatriptan was 0.95 (90% confidence interval: 0.82, 1.09), area under the plasma concentration-time curve (AUC) from time 0 to 6 hours was 0.98 (90% confidence interval: 0.93, 1.03), and AUC from time 0 to infinity was 1.00 (90% confidence interval: 0.96, 1.05). No clinically relevant safety findings for co-administration of sumatriptan and erenumab were identified.

CONCLUSION

Co-administration of erenumab and sumatriptan had no additional effect on resting blood pressure or on pharmacokinetics of sumatriptan. Trial registration: ClinicalTrials.gov, NCT02741310.

Animal Models of Chronic Migraine

PURPOSE OF REVIEW

Chronic migraine (CM) is a recalcitrant subtype of migraine which causes high degrees of disability, poor treatment responses, and frequent recurrences in sufferers. However, the pathophysiological mechanisms underlying the development and chronification of migraine attacks remain incompletely understood. A validated animal model could help to decipher the pathogenic mechanism of the disease, facilitating the development of possible therapeutic strategies for CM. In this review, we aimed to summarize current animal models of CM and discuss the validity of these models.

RECENT FINDINGS

Several methods have been available to induce recurrent headache-like behaviors or biochemical changes in rodents, including repeated dural application of inflammatory soup, chronic systemic infusion of nitroglycerin, repeated administration of acute migraine abortive treatment to simulate medication overuse headache, or genetic modification. These models exhibit some features that are believed to be associated with migraine; however, none of the model can recapitulate all the clinical phenotypes found in humans and each has its own weakness. The complex features of CM increase the difficulty of constructing a proper animal model. Nonetheless, currently available models are valid to certain degrees. Future directions might consider simulating the spontaneity and chronicity of migraine by combining known genetic substrates and allostatic loads into the same model.

Calcitonin Gene-Related Peptide-Targeted Therapies for Migraine and Cluster Headache: A Review

Calcitonin gene-related peptide (CGRP) is a signaling neuropeptide released from activated trigeminal sensory afferents in headache and facial pain disorders. There are a handful of CGRP-targeted therapies currently in phase 3 studies for migraine acute treatment or prevention. Currently, 4 monoclonal antibodies targeting either the CGRP ligand or receptor are being studied for migraine prevention: ALD403 (eptinezumab), AMG 334 (erenumab), LY2951742 (galcanezumab), and TEV-48125 (fremanezumab). Meanwhile, 1 small-molecule CGRP receptor antagonist (ubrogepant, MK-1602) is currently in phase 3 studies for the acute treatment of migraine. Two of these anti-CGRP monoclonal antibodies are in clinical trials for cluster headache prevention as well. Several other small-molecular CGRP receptor antagonists are in earlier stages of development for acute migraine treatment or prevention. In this review, we will discuss the growing body of clinical trials studying CGRP-targeted therapies for migraine and cluster headache.

CGRP – a target for acute therapy in migraine: Clinical data

Background

A better understanding of the mechanisms underlying the migraine attack has reinforced the concept that migraine is a complex brain disease, and has paved the way for the development of new migraine specific acute treatments. In recent years, targeting the calcitonin gene-related peptide and its receptors has been one of the most promising pharmacological strategies for both acute and preventive treatment of migraine.

Findings

Randomized double-blind placebo-controlled trials have demonstrated the superiority of small molecule calcitonin gene-related peptide receptor antagonists (gepants) over placebo in treating acute migraine attacks measured as the two-hour pain free endpoint. Gepants also improved migraine associated symptoms, such as nausea, photophobia and phonophobia. Two of the class have had their development stopped because of hepatotoxicity, which is emerging as being due to metabolites. Gepants have a good tolerability and can be safely used in patients with stable cardiovascular disease.

Conclusion

Exciting results have been obtained targeting the calcitonin gene-related peptide pathway to abort acute migraine attacks, thus reinforcing the relevance of mechanism-based treatments specific for migraine.

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 Treatment: Current Acute Medications and Their Potential Mechanisms of Action

Migraine is a common and disabling primary headache disorder with a significant socioeconomic burden. The management of migraine is multifaceted and is generally dichotomized into acute and preventive strategies, with several treatment modalities. The aims of acute pharmacological treatment are to rapidly restore function with minimal recurrence, with the avoidance of side effects. The choice of pharmacological treatment is individualized, and is based on the consideration of the characteristics of the migraine attack, the patient's concomitant medical problems, and treatment preferences. Notwithstanding, a good understanding of the pharmacodynamic and pharmacokinetic properties of the various drug options is essential to guide therapy. The current approach and concepts relevant to the acute pharmacological treatment of migraine will be explored in this review.