Premonitory and nonheadache symptoms induced by CGRP and PACAP38 in patients with migraine

Hypersensitivity to calcitonin gene-related peptide in chronic migraine

OBJECTIVE

To investigate if calcitonin gene-related peptide infusion induces migraine-like attacks in chronic migraine patients.

METHODS

Fifty-eight patients with chronic migraine, either with or without headache on the experimental day, were assessed for the incidence of migraine-like attacks after an intravenous infusion with calcitonin gene-related peptide 1.5 µg/min over 20 min. The primary endpoint was the incidence of migraine-like attacks after calcitonin gene-related peptide. Exploratory endpoints were the association between the incidence of migraine-like attacks and presence of headache on the experimental day, and headache frequency in the past month. Migraine-like attack data was compared to a historic cohort of 91 episodic migraine patients without headache on the experimental day. Total tenderness score, pressure-pain threshold and supra-threshold pressure pain at baseline were investigated in relation to incidence of migraine-like attacks and presence of headache on the experimental day.

RESULTS

In total, 83% of the 58 chronic migraine patients developed migraine-like attacks after calcitonin gene-related peptide infusion. Migraine-like attacks were found in 92% of chronic migraine patients with headache on the experimental day compared to 65% of chronic migraine patients without headache on the experimental day (p = 0.035). No differences were observed in total tenderness score and pressure-pain threshold between chronic migraine patients with and without headache on the experimental day. The incidence of migraine-like attacks following calcitonin gene-related peptide in chronic migraine patients without headache (65%) was equal to the historic cohort of 91 episodic migraine patients without headache (67%) on the experimental day.

CONCLUSIONS

Chronic migraine patients are hypersensitive to calcitonin gene-related peptide. The potency of calcitonin gene-related peptide as a migraine inductor is increased in chronic migraine patients with ongoing headache. We suggest that calcitonin gene-related peptide, besides being a migraine trigger also acts as a modulator of nociceptive transmission in the trigeminal system.

A phase 2, randomized, double-blind, placebo-controlled trial of AMG 301, a pituitary adenylate cyclase-activating polypeptide PAC1 receptor monoclonal antibody for migraine prevention

Objective

To assess the safety and efficacy of AMG 301, an inhibitor of the pituitary adenylate cyclase-activating polypeptide (PACAP)-1 (PAC1) receptor, for prevention of migraine.

Methods

In a double-blind trial, patients were randomized 4:3:3 to placebo, AMG 301 210 mg every 4 weeks, or AMG 301 420 mg every 2 weeks for 12 weeks. Effect on monthly migraine days and other secondary measures were assessed over weeks 9–12. Safety and tolerability were assessed.

Results

Of 343 randomized patients (mean age, 41.8–42.5 years), the majority were women (85.4–90.4%), white (94.1–96.2%), and had episodic migraine (62.5–67.9%). A total of 305 patients completed treatment (placebo, n = 124; AMG 301 210 mg, n = 94; AMG 301 420 mg, n = 87). Least squares mean reduction at week 12 in monthly migraine days from baseline was −2.5 (0.4) days for placebo and −2.2 (0.5) days for both AMG 301 treatment groups. No difference between AMG 301 and placebo on any measure of efficacy was observed; mean (95% confidence interval) treatment difference versus placebo for monthly migraine days for AMG 301 210 mg, 0.3 (−0.9 to 1.4); AMG 301 420 mg, 0.3 (−0.9 to 1.4). The incidence of adverse events was similar across groups.

Conclusion

AMG 301 offered no benefit over placebo for migraine prevention; further studies may be necessary to fully understand the role of PACAP isoforms and its receptors in migraine pathophysiology.

Study Registration

ClinicalTrials.gov: NCT03238781

Hypersensitivity to Calcitonin Gene-Related Peptide in Post-Traumatic Headache

OBJECTIVE

To demonstrate that calcitonin gene-related peptide (CGRP) induces headache exacerbation with migraine-like features in patients with persistent post-traumatic headache (PTH) attributed to mild traumatic brain injury (TBI).

METHODS

A randomized, double-blind, placebo-controlled, two-way crossover study was conducted. Analyses were intention-to-treat. Eligible patients were aged 18 to 65 years and had a history of persistent PTH after mild TBI for at least 12 months. Patients were randomized to receive an intravenous infusion of 1.5μg/min of CGRP or placebo (isotonic saline) over 20 minutes on two separate experimental days. A 12-hour observational period was used to evaluate the following outcomes: (1) difference in incidence of headache exacerbation with migraine-like features and (2) difference in area under the curve for headache intensity scores.

RESULTS

Thirty patients (mean age = 37 years, 25 women [83%]) were randomized and completed the study. During the 12-hour observational period, 21 of 30 patients (70%) developed headache exacerbation with migraine-like features after CGRP, compared with 6 patients (20%) after placebo (p < 0.001). The baseline-corrected area under the curve for headache intensity scores was significantly larger after CGRP, compared with placebo (p < 0.001).

INTERPRETATION

Patients with persistent PTH are hypersensitive to CGRP, which underscores its pathophysiological importance. Furthermore, CGRP-targeted therapies might provide a novel mechanism-based treatment option for patients with persistent PTH. ANN NEUROL 2020;88:1220-1228.

Premonitory symptoms in glyceryl trinitrate triggered migraine attacks: a case-control study

ABSTRACT

Spontaneous and pharmacologically provoked migraine attacks are frequently preceded by nonheadache symptoms called premonitory symptoms. Here, we systematically evaluated premonitory symptoms in migraine patients and healthy controls after glyceryl trinitrate (GTN) infusion. In women with migraine without aura (n = 34) and age-matched female controls (n = 24), we conducted systematically a semistructured interview assessing 21 possible premonitory symptoms every 15 minutes in the 5 hours after GTN infusion (0.5 µg/kg/min over 20 minutes). Migraine-like headaches occurred in 28/34 (82.4%) migraineurs (GTN responders). After GTN, 26/28 (92.9%) responders, 6/6 (100%) nonresponders, and 13/24 (54.2%) controls reported at least one possible premonitory symptom. Concentration difficulties (P = 0.011), yawning (P = 0.009), nausea (P = 0.028), and photophobia (P = 0.001) were more frequently reported by those migraineurs who developed a migraine-like attack vs healthy controls. Importantly, concentration difficulties were exclusively reported by those who developed a migraine-like attack. Thus, our findings support the view that GTN is able to provoke the naturally occurring premonitory symptoms and show that yawning, nausea, photophobia, and concentration difficulties are most specific for an impending GTN-induced migraine-like headache. We suggest that these symptoms may also be helpful as early warning signals in clinical practice with concentration difficulties exclusively reported by those who develop a migraine-like attack.

Vascular actions of peripheral CGRP in migraine-like photophobia in mice

BACKGROUND

Calcitonin gene-related peptide is recognized as a key player in migraine, yet the mechanisms and sites of calcitonin gene-related peptide action remain unknown. The efficacy of calcitonin gene-related peptide-blocking antibodies as preventative migraine drugs supports a peripheral site of action, such as the trigeminovasculature. Given the apparent disconnect between the importance of vasodilatory peptides in migraine and the prevailing opinion that vasodilation is an epiphenomenon, the goal of this study was to test whether vasodilation plays a role in calcitonin gene-related peptide-induced light aversive behavior in mice.

METHODS

Systemic mean arterial pressure and light aversive behavior were measured after intraperitoneal administration of calcitonin gene-related peptide and vasoactive intestinal peptide in wild-type CD1 mice. The functional significance of vasodilation was tested by co-administration of a vasoconstrictor (phenylephrine, endothelin-1, or caffeine) with calcitonin gene-related peptide to normalize blood pressure during the light aversion assay.

RESULTS

Both calcitonin gene-related peptide and vasoactive intestinal peptide induced light aversion that was associated with their effect on mean arterial pressure. Notably, vasoactive intestinal peptide caused relatively transient vasodilation and light aversion. Calcitonin gene-related peptide-induced light aversion was still observed even with normalized blood pressure. However, two of the agents, endothelin-1 and caffeine, did reduce the magnitude of light aversion.

CONCLUSION

We propose that perivascular calcitonin gene-related peptide causes light-aversive behavior in mice by both vasomotor and non-vasomotor mechanisms.

Migraine and Two-Pore-Domain Potassium Channels

Migraine is a common, disabling neurological disorder with a genetic, environmental, and hormonal component with an annual prevalence estimated at ~15%. It is characterized by attacks of severe, usually unilateral and throbbing headache, and can be accompanied by nausea, vomiting, and photophobia. Migraine is clinically divided into two main subtypes: migraine with aura, when it is preceded by transient neurological disturbances due to cortical spreading depression (CSD), and migraine without aura. Activation and sensitization of trigeminal sensory neurons, leading to the release of pro-inflammatory peptides, is likely a key component in headache pain initiation and transmission in migraine. In the present review, we will focus on the function of two-pore-domain potassium (K_2P) channels, which control trigeminal sensory neuron excitability and their potential interest for developing new drugs to treat migraine.

Biochemical Modulation and Pathophysiology of Migraine

BACKGROUND

Migraine is a common disabling neurological disorder where attacks have been recognized to consist of more than headache. The premonitory, headache, and postdromal phases are the various phases of the migraine cycle, where aura can occur before, during, or after the onset of pain. Migraine is also associated with photosensitivity and cranial autonomic symptoms, which includes lacrimation, conjunctival injection, periorbital edema, ptosis, nasal congestion, and rhinorrhoea. This review will present the current understanding of migraine pathophysiology and the relationship to the observed symptoms.

EVIDENCE ACQUISITION

The literature was reviewed with specific focus on clinical, neurophysiological, functional imaging, and preclinical studies in migraine including the studies on the role of calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase activating polypeptide (PACAP).

RESULTS

The phases of the migraine cycle have been delineated by several studies. The observations of clinical symptoms help develop hypotheses of the key structures involved and the biochemical and neuronal pathways through which the effects are mediated. Preclinical studies and functional imaging studies have provided evidence for the role of multiple cortical areas, the diencephalon, especially the hypothalamus, and certain brainstem nuclei in the modulation of nociceptive processing, symptoms of the premonitory phase, aura, and photophobia. CGRP and PACAP have been found to be involved in nociceptive modulation and through exploration of CGRP mechanisms, new successful treatments have been developed.

CONCLUSIONS

Migraine is a complex neural disorder and is important to understand when seeing patients who present to neuro-ophthalmology, especially with the successful translation from preclinical and clinical research leading to successful advances in migraine management.

Two-Hour CGRP Infusion Causes Gastrointestinal Hyperactivity: Possible Relevance for CGRP Antibody Treatment

OBJECTIVE

The monoclonal antibodies against calcitonin gene-related peptide (CGRP) or its receptor are new antimigraine drugs from which many patients already benefit. Very few side effects have been reported from the antibody trials, including very few gastrointestinal (GI) side effects. The current data derive from a double-blind cross-over study of CGRP infusion for 2 hours. We present the GI side effects of the infusion and raise the question if underreporting of GI symptoms in CGRP antibody trials has occurred. We also discuss why constipation may be more likely with CGRP receptor blockade than with CGRP neutralizing antibodies.

METHODS

Thirty healthy volunteers were recruited to receive a 2-hour infusion of CGRP 1.5 µg/minutes on 2 different days. The participants were pretreated with sumatriptan tablets (2 × 50 mg) 1 day and with placebo the other day. During the infusion, the participants were asked about side effects including a detailed description about their GI symptoms. Clinical observations like flatulence, rumbling, and use of bedpan were also noted. After the infusion, the participants filled out a questionnaire about side effects at home until 12-hour after the infusion start. The study was conducted at the Danish Headache Center at Rigshospitalet Glostrup in the period February 2018 to July 2018.

RESULTS

On both study days 93% (27/29 participants) experienced symptoms from the GI system during the infusion. Rumbling, stomach pain, nausea, diarrhea, and an urge to defecate were the most commonly experienced GI side effects. There was no difference in symptoms between placebo and sumatriptan pretreatment.

CONCLUSION

We conclude that a 2-hour infusion of CGRP causes frequent and sometimes severe symptoms from the GI system. The symptoms are not antagonized by sumatriptan. More attention should be paid to constipation as a possible side effect of CGRP receptor antagonists.

Imaging the Premonitory Phase of Migraine

Migraine is a common and disabling brain disorder with a broad and heterogeneous phenotype, involving both pain and painless symptoms. Over recent years, more clinical and research attention has been focused toward the premonitory phase of the migraine attack, which can start up to days before the onset of head pain. This early phase can involve symptomatology, such as cognitive and mood change, yawning, thirst and urinary frequency and sensory sensitivities, such as photophobia and phonophobia. In some patients, these symptoms can warn of an impending headache and therefore offer novel neurobiological insights and therapeutic potential. As well as characterization of the phenotype of this phase, recent studies have attempted to image this early phase using functional neuroimaging and tried to understand how the symptoms are mediated, how a migraine attack may be initiated, and how nociception may follow thereafter. This review will summarize the recent and evolving findings in this field and hypothesize a mechanism of subcortical and diencephalic brain activation during the start of the attack, including that of basal ganglia, hypothalamus, and thalamus prior to headache, which causes a top-down effect on brainstem structures involved in trigeminovascular nociception, leading ultimately to headache.

Calcitonin gene-related peptide (CGRP): role in migraine pathophysiology and therapeutic targeting

Introduction: The neuropeptide calcitonin gene-related peptide (CGRP) is recognized as a critical player in migraine pathophysiology. Excitement has grown regarding CGRP because of the development and clinical testing of drugs targeting CGRP or its receptor. While these drugs alleviate migraine symptoms in half of the patients, the remaining unresponsive half of this population creates an impetus to address unanswered questions that exist in this field.Areas covered: We describe the role of CGRP in migraine pathophysiology and CGRP-targeted therapeutics currently under development and in use. We also discuss how a second CGRP receptor may provide a new therapeutic target.Expert opinion: CGRP-targeting drugs have shown a remarkable safety profile. We speculate that this may reflect the redundancy of peptides within the CGRP family and a second CGRP receptor that may compensate for reduced CGRP activity. Furthermore, we propose that an inherent safety feature of peptide-blocking antibodies is attributed to the fundamental nature of peptide release, which occurs as a large bolus in short bursts of volume transmission. These facts support the development of more refined CGRP therapeutic drugs, as well as drugs that target other neuropeptides. We believe that the future of migraine research is bright with exciting advances on the horizon.

Redefining migraine phases - a suggestion based on clinical, physiological, and functional imaging evidence

Migraine is defined by attacks of headache with a specific length and associated symptoms such as photophobia, phonophobia and nausea. It is long recognized that migraine is more than just the attacks and that migraine should be understood as a cycling brain disorder with at least 4 phases: interictal, preictal, ictal and postictal. However, unlike the pain phase, the other phases are less well defined, which renders studies focusing on these phases susceptible to bias. We herewith review the available clinical, electrophysiological, and neuroimaging data and propose that the preictal phase should be defined as up to 48 hours before the headache attack and the postictal phase as up to 24 hours following the ictal phase. This would allow future studies to specifically investigate these migraine phases and to make study results more comparable.

Circulating Biomarkers in Migraine: New Opportunities for Precision Medicine

Background:

Migraine is the most common neurological disorder and the second most disabling human condition, whose pathogenesis is favored by a combination of genetic, epigenetic, and environmental factors. In recent years, several efforts have been made to identify reliable biomarker(s) useful to monitor disease activity and/or ascertain the response to a specific treatment.

Objective:

To review the current evidence on the potential biological markers associated with migraine.

Methods:

A structured search of peer-reviewed research literature was performed by searching major publications databases up to December 2017.

Results:

Several circulating biomarkers have been proposed as diagnostic or therapeutic tools in migraine, mostly related to migraine’s inflammatory pathophysiological aspects. Nonetheless, their detection is still a challenge for the scientific community, reflecting, at least in part, disease complexity and clinical diagnostic limitations. At the present time, calcitonin generelated peptide (CGRP) represents probably the most promising candidate as a diagnostic and/or therapeutic biomarker, as its plasma levels are elevated during migraine attack and decrease during successful treatment. Other molecules (including some neuropeptides, cytokines, adipokines, or vascular activation markers) despite promising, do not possess the sufficient prerequisites to be considered as migraine biomarkers.

Conclusion:

The characterization of migraine-specific biomarkers would be fundamental in a perspective of precision medicine, enabling risk assessment and tailored treatments. However, speculating on the clinical validity of migraine biomarkers may be premature and controlled clinical trials are presently needed to investigate both the diagnostic and therapeutic value of these biomarkers in migraine.

Effects of fremanezumab on the use of acute headache medication and associated symptoms of migraine in patients with episodic migraine

BACKGROUND

Fremanezumab, a fully humanized monoclonal antibody targeting calcitonin gene-related peptide, has demonstrated efficacy for the preventive treatment of migraine in adults.

OBJECTIVE

To evaluate the effect of fremanezumab treatment on acute headache medication use and migraine-associated symptoms in patients with episodic migraine.

METHODS

In the Phase 3 HALO trial, patients with episodic migraine were randomized to receive subcutaneous fremanezumab monthly (225 mg at baseline, weeks 4 and 8), fremanezumab quarterly (675 mg at baseline, placebo at weeks 4 and 8), or placebo over a 12-week period. The secondary endpoint was change from baseline in the monthly number of days with use of any acute headache mediation or migraine-specific acute headache medication; exploratory endpoints were change from baseline in the monthly number of days with nausea or vomiting, photophobia, or phonophobia.

RESULTS

Of 875 patients randomized, 865 were included in the analysis (monthly, n = 287; quarterly, n = 288; placebo, n = 290). Baseline mean ± standard deviation days with: Any acute headache medication use (monthly: 7.7 ± 3.4; quarterly: 7.8 ± 3.7; placebo: 7.7 ± 3.6), migraine-specific acute headache medication use (6.1 ± 3.1; 6.6 ± 3.1; 7.1 ± 3.0), nausea or vomiting (4.5 ± 3.6; 4.9 ± 3.7; 4.5 ± 3.3) and photophobia and phonophobia (5.5 ± 4.1; 6.3 ± 4.1; 6.0 ± 3.9) were similar among treatment arms. Fremanezumab reduced the number of days of acute headache medication use ([least-squares mean change vs. placebo] monthly: -1.4 [95% confidence interval: -1.84, -0.89], p < 0.001; quarterly: -1.3 [-1.76, -0.82], p < 0.001) and migraine-specific acute headache medication use (monthly: -2.2 [-2.80, -1.56], p < 0.001; quarterly: -2.2 [-2.81, -1.58], p < 0.001) compared with placebo. Fremanezumab also reduced nausea or vomiting, photophobia, and phonophobia compared with placebo.

CONCLUSIONS

Fremanezumab reduced the need for acute headache medications, including migraine-specific medications, while treating migraine-associated symptoms in patients with episodic migraine.

TRIAL REGISTRATION

Clinicaltrials.gov NCT02629861.

CGRP in Animal Models of Migraine

With the approval of calcitonin gene-related peptide (CGRP) and CGRP receptor monoclonal antibodies by the Federal Drug Administration, a new era in the treatment of migraine patients is beginning. However, there are still many unknowns in terms of CGRP mechanisms of action that need to be elucidated to allow new advances in migraine therapies. CGRP has been studied both clinically and preclinically since its discovery. Here we review some of the preclinical data regarding CGRP in animal models of migraine.

CGRP in Human Models of Migraine

Over the past three decades, calcitonin gene-related peptide (CGRP) has emerged as a key molecule. Provocation experiments have demonstrated that intravenous CGRP infusion induces migraine-like attacks in migraine with and without aura patients. In addition, these studies have revealed a heterogeneous CGRP response, i.e., some migraine patients develop migraine-like attacks after CGRP infusion, while others do not. The role of CGRP in human migraine models has pointed to three potential sites of CGRP-induced migraine: (1) vasodilation via cyclic adenosine monophosphate (cAMP) and possibly cyclic guanosine monophosphate (cGMP); (2) activation of trigeminal sensory afferents, and (3) modulation of deep brain structures. In the future, refined human experimental studies will continue to unveil the role of CGRP in migraine pathogenesis.

Animal models of migraine and experimental techniques used to examine trigeminal sensory processing

Background

Migraine is a common debilitating condition whose main attributes are severe recurrent headaches with accompanying sensitivity to light and sound, nausea and vomiting. Migraine-related pain is a major cause of its accompanying disability and can encumber almost every aspect of daily life.

Main body

Advancements in our understanding of the neurobiology of migraine headache have come in large from basic science research utilizing small animal models of migraine-related pain. In this current review, we aim to describe several commonly utilized preclinical models of migraine. We will discuss the diverse array of methodologies for triggering and measuring migraine-related pain phenotypes and highlight briefly specific advantages and limitations therein. Finally, we will address potential future challenges/opportunities to refine existing and develop novel preclinical models of migraine that move beyond migraine-related pain and expand into alternate migraine-related phenotypes.

Conclusion

Several well validated animal models of pain relevant for headache exist, the researcher should consider the advantages and limitations of each model before selecting the most appropriate to answer the specific research question. Further, we should continually strive to refine existing and generate new animal and non-animal models that have the ability to advance our understanding of head pain as well as non-pain symptoms of primary headache disorders.

The Migraine Premonitory Phase

PURPOSE OF REVIEW

The premonitory phase of migraine is defined as the presence of nonpainful symptomatology occurring hours to days before the onset of headache. Symptoms can include neck stiffness, yawning, thirst, and increased frequency of micturition. Clinical recognition of these symptoms is important to ensure early and effective attack management. Further understanding of the clinical phenotype and neurobiological mediation of these symptoms is important in the advancement of therapeutics research in both acute and preventive treatments of migraine.

RECENT FINDINGS

Since 2014, functional imaging studies have been conducted during the premonitory stage of migraine and have provided novel insights into the early neurobiology and anatomy of the earliest stage of the migraine attack. These studies have shown early involvement of subcortical brain areas including the hypothalamus, substantia nigra, dorsal pons, and various limbic cortical areas, including the anterior cingulate cortex during the premonitory phase. More recent work has revealed altered hypothalamic-brainstem functional connectivity during migraine, which starts before the onset of pain. These exciting findings have provided functional correlation of the symptoms experienced by patients and changes seen on functional brain imaging.

SUMMARY

This article focuses on the prevalence, phenotype, and proposed neurobiology of premonitory symptomatology in migraineurs as well as the scope of future research.

PACAP27 induces migraine-like attacks in migraine patients

Introduction

Pituitary adenylate cyclase-activating polypeptide (PACAP) is found in two functional isoforms, namely PACAP38 and PACAP27. The migraine-inducing properties of PACAP38 are well studied. However, it is not known whether the lesser-known and under-studied protein isoform, PACAP27, can also induce migraine attacks. Here, we studied the effect of human PACAP27 infusion on induction of migraine in a provocation model.

Methods

In a crossover study, 20 migraine without aura patients were randomly assigned to receive human PACAP27 (10 picomol/kg/min) or saline (placebo) infusion over 20 min. We recorded the migraine and associated symptoms.

Results

All patients completed the study. PACAP27 provoked migraine-like attacks in 11 patients (55%) and two developed attacks after placebo (10%) ( p = 0.022). The headache intensity and duration after PACAP27 was significantly greater compared to placebo ( p = 0.003).

Conclusion

PACAP27 triggers migraine attacks without aura. These novel data strengthen the role of PACAP and its receptors in migraine pathogenesis.

Pathophysiological Mechanisms in Migraine and the Identification of New Therapeutic Targets

Migraine is a strongly disabling disease characterized by a unilateral throbbing headache lasting for up to 72 h for each individual attack. There have been many theories on the pathophysiology of migraine throughout the years. Currently, the neurovascular theory dominates, suggesting clear involvement of the trigeminovascular system. The most recent data show that a migraine attack most likely originates in the hypothalamus and activates the trigeminal nucleus caudalis (TNC). Although the mechanisms are unknown, activation of the TNC leads to peripheral release of calcitonin gene-related protein (CGRP), most likely from C-fibers. During the past year monoclonal antibodies against CGRP or the CGRP receptor have emerged as the most promising targets for migraine therapy, and at the same time established the strong involvement of CGRP in the pathophysiology of migraine. The viewpoint presented here focuses further on the activation of the CGRP receptor on the sensory Aδ-fiber, leading to the sensation of pain. The CGRP receptor activates adenylate cyclase, which leads to an increase in cyclic adenosine monophosphate (cAMP). We hypothesize that cAMP activates the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, triggering an action potential sensed as pain. The mechanisms behind migraine pain on a molecular level, particularly their importance to cAMP, provide clues to potential new anti-migraine targets. In this article we focus on the development of targets related to the CGRP system, and further include novel targets such as the pituitary adenylate cyclase-activating peptide (PACAP) system, the serotonin 5-HT_1F receptor, purinergic receptors, HCN channels, adenosine triphosphate-sensitive potassium channels (K_ATP), and the glutaminergic system.

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.

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.

Pharmacologic Characterization of ALD1910, a Potent Humanized Monoclonal Antibody against the Pituitary Adenylate Cyclase-Activating Peptide

Migraine is a debilitating disease that affects almost 15% of the population worldwide and is the first cause of disability in people under 50 years of age, yet its etiology and pathophysiology remain incompletely understood. Recently, small molecules and therapeutic antibodies that block the calcitonin gene-related peptide (CGRP) signaling pathway have reduced migraine occurrence and aborted acute attacks of migraine in clinical trials and provided prevention in patients with episodic and chronic migraine. Heterogeneity is present within each diagnosis and patient's response to treatment, suggesting migraine as a final common pathway potentially activated by multiple mechanisms, e.g., not all migraine attacks respond to or are prevented by anti-CGRP pharmacological interventions. Consequently, other unique mechanisms central to migraine pathogenesis may present new targets for drug development. Pituitary adenylate cyclase-activating peptide (PACAP) is an attractive novel target for treatment of migraines. We generated a specific, high-affinity, neutralizing monoclonal antibody (ALD1910) with reactivity to both PACAP38 and PACAP27. In vitro, ALD1910 effectively antagonizes PACAP38 signaling through the pituitary adenylate cyclase-activating peptide type I receptor, vasoactive intestinal peptide receptor 1, and vasoactive intestinal peptide receptor 2. ALD1910 recognizes a nonlinear epitope within PACAP and blocks its binding to the cell surface. To test ALD1910 antagonistic properties directed against endogenous PACAP, we developed an umbellulone-induced rat model of neurogenic vasodilation and parasympathetic lacrimation. In vivo, this model demonstrates that the antagonistic activity of ALD1910 is dose-dependent, retaining efficacy at doses as low as 0.3 mg/kg. These results indicate that ALD1910 represents a potential therapeutic antibody to address PACAP-mediated migraine.

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.

Pediatric vs. Adult Prodrome and Postdrome: A Window on Migraine Pathophysiology?

Few studies have been conducted on the prodromal and postdromal phases of the migraine attack in children and adolescents. Using a questionnaire, we found that 67% of 103 children and adolescents with migraine reported at least one prodromal symptom, with a mean number per subject of 1.8 (median 2.2). The most frequently reported prodromal symptoms were face changes, fatigue and irritability. In pediatric patients selected as having prodrome, fatigue, mood change and neck stiffness were the most frequently reported prodromal symptoms. Using a different design, Laurell et al. found that 71% of 137 pediatric patients reported at least one prodromal symptom with a mean number per subject of 1.9 ± 2.0. Studying postdrome was fraught with unexpected difficulties as our preliminary research showed. Patients reported 2 groups of symptoms occurring during the resolution phase of the headache: symptoms whose onset was before headache cessation and were persisting after it, and symptoms whose onset was after headache cessation. We referred to the former as persistent symptoms and to the latter as true postdromes. Ninety-one per cent of patients reported persistent symptoms, with a mean of 6.0 and a median of 2, asthenia, pallor, cognitive difficulties, anorexia, somnolence, and nausea being the more frequently reported. True postdromes were reported by 82% of patients, with a mean of 2.6 and a median of 2, thirst, somnolence, visual disturbances, food craving, paraesthesias, and ocular pain being the most frequent reported. Interestingly, several prodromal and postdromal symptoms are also encountered during the aura classic and/or accompany the headache phase. Functional imaging in migraine has showed that the activations in areas such as hypothalamus or brainstem may begin before headache onset and/or persist after headache relief. Thus, one may wonder whether prodromal and postdromal symptoms may indicate the involvement of the limbic system, dopaminergic pathways, the hypothalamus and the brainstem. Differences between children, adolescents and adults might contribute to the understanding of migraine neurobiology.

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.

Migraine induction with calcitonin gene-related peptide in patients from erenumab trials

BACKGROUND

Migraine prevention with erenumab and migraine induction by calcitonin gene-related peptide (CGRP) both carry notable individual variance. We wanted to explore a possible association between individual efficacy of anti-CGRP treatment and susceptibility to migraine induction by CGRP.

METHODS

Thirteen migraine patients, previously enrolled in erenumab anti-CGRP receptor monoclonal antibody trials, received CGRP in a double-blind, placebo-controlled, randomized cross-over design to investigate their susceptibility to migraine induction. A standardized questionnaire was used to assess the efficacy of previous antibody treatment. The patients were stratified into groups of high responders and poor responders. Primary outcomes were incidence of migraine-like attacks and area under the curve of headache intensity after infusion of CGRP and placebo. All interviews and experiments were performed in laboratories at the Danish Headache Center, Copenhagen, Denmark.

RESULTS

Ten high responders and three poor responders were included. CGRP induced migraine-like attacks in ten (77%) patients, whereof two were poor responders, compared to none after placebo (p = 0.002). The area under the curve for headache intensity was greater after CGRP, compared to placebo, at 0-90 min (p = 0.009), and 2-12 h (p = 0.014). The median peak headache intensity score was 5 (5-9) after CGRP, compared to 2 (0-4) after placebo (p = 0.004).

CONCLUSIONS

Patients with an excellent effect of erenumab are highly susceptible to CGRP provocation. If an association is evident, CGRP provocation could prove a biomarker for predicting antibody treatment efficacy.

TRIAL REGISTRATION

Retrospectively registered at clinicaltrials.gov with identifier: NCT03481400 .

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.

PACAP38 and PAC1 receptor blockade: a new target for headache?

Pituitary adenylate cyclase activating polypeptide-38 (PACAP38) is a widely distributed neuropeptide involved in neuroprotection, neurodevelopment, nociception and inflammation. Moreover, PACAP38 is a potent inducer of migraine-like attacks, but the mechanism behind this has not been fully elucidated.

Migraine is a neurovascular disorder, recognized as the second most disabling disease. Nevertheless, the antibodies targeting calcitonin gene-related peptide (CGRP) or its receptor are the only prophylactic treatment developed specifically for migraine. These antibodies have displayed positive results in clinical trials, but are not effective for all patients; therefore, new pharmacological targets need to be identified.

Due to the ability of PACAP38 to induce migraine-like attacks, its location in structures previously associated with migraine pathophysiology and the 100-fold selectivity for the PAC₁ receptor when compared to VIP, new attention has been drawn to this pathway and its potential role as a novel target for migraine treatment. In accordance with this, antibodies against PACAP38 (ALD 1910) and PAC₁ receptor (AMG 301) are being developed, with AMG 301 already in Phase II clinical trials. No results have been published so far, but in preclinical studies, AMG 301 has shown responses comparable to those observed with triptans. If these antibodies prove to be effective for the treatment of migraine, several considerations should be addressed, for instance, the potential side effects of long-term blockade of the PACAP (receptor) pathway. Moreover, it is important to investigate whether these antibodies will indeed represent a therapeutic advantage for the patients that do not respond the CGRP (receptor)-antibodies.

In conclusion, the data presented in this review indicate that PACAP38 and PAC₁ receptor blockade are promising antimigraine therapies, but results from clinical trials are needed in order to confirm their efficacy and side effect profile.

Transport of the pituitary adenylate cyclase-activating polypeptide across the blood-brain barrier: implications for migraine

Background

Pituitary adenylate cyclase-activating polypeptide (PACAP) is widely distributed in the nervous system and is involved in migraine pathophysiology. Understanding the function of the blood-brain barrier (BBB) in relation to PACAP is important to the understand the mechanisms behind PACAP-induced migraine attacks, but also to develop antimigraine drugs targeting the PACAP receptors Here, we aim to review the transport ability of PACAP across the BBB.

Methods

We performed a systematic literature search on PubMed to identify studies reporting original data on PACAP and BBB. The search was finalized in July 2017.

Results

The literature search identified 96 papers of which 11 contained relevant data. In addition, two papers were known to be relevant and were included. A total of 13 papers studies were included in the final analysis. Preclinical studies (n = 10) suggest the existence of specific PACAP transport systems across the BBB, while human PACAP studies failed to show vasodilator effect of PACAP on the cerebral arteries from the lumen (n = 3).

Conclusion

PACAP38 is transported over the BBB actively, while PACAP27 cross the BBB by diffusion over the membrane, but after crossing the endothelial membrane both isoforms are either rapidly degraded or efflux back from brain to blood. Thus, a direct central action of the PACAPs is unlikely. This is supported by studies showing selective PACAP effect on extra-cerebral arteries.

Redox Mechanisms in Migraine: Novel Therapeutics and Dietary Interventions

SIGNIFICANCE

Migraine represents the third most prevalent and the seventh most disabling human disorder. Approximately 30% of migraine patients experience transient, fully reversible, focal neurological symptoms (aura) preceding the attack. Recent Advances: Awareness of the hypothesis that migraine actually embodies a spectrum of illnesses-ranging from episodic to chronic forms-is progressively increasing and poses novel challenges for clarifying the underlying pathophysiological mechanisms of migraine as well as for the development of novel therapeutic interventions. Several theories have evolved to the current concept that a combination of genetic, epigenetic, and environmental factors may play a role in migraine pathogenesis, although their relative importance is still being debated.

CRITICAL ISSUES

One critical issue that deserves a particular attention is the role of oxidative stress in migraine. Indeed, potentially harmful oxidative events occur during the migraine attack and long-lasting or frequent migraine episodes may increase brain exposure to oxidative events that can lead to chronic transformation. Moreover, a wide variety of dietary, environmental, physiological, behavioral, and pharmacological migraine triggers may act through oxidative stress, with clear implications for migraine treatment and prophylaxis. Interestingly, almost all current prophylactic migraine agents exert antioxidant effects.

FUTURE DIRECTIONS

Increasing awareness of the role of oxidative stress and/or decreased antioxidant defenses in migraine pathogenesis and progression to a chronic condition lays the foundations for the design of novel prophylactic approaches, which, by reducing brain oxidative phenomena, could favorably modify the clinical course of migraine. Antioxid. Redox Signal. 28, 1144-1183.

PACAP38: Emerging Drug Target in Migraine and Cluster Headache

Here, we review the role of pituitary adenylate cyclase-activating peptide-38 (PACAP38) in migraine and cluster headache (CH). Mounting evidence implicates signaling molecule PACAP38 in the pathophysiology of migraine. Human provocation studies show PACAP38 induces migraine attacks in migraine patients without aura and marked and sustained dilation of extracerebral arteries. PACAP38 selectively targets the PAC₁ receptor making this receptor a promising candidate for targeted migraine therapy. Randomized clinical trials are warranted to pursue this possible treatment pathway. PACAP38 provocation studies in CH could elucidate possible involvement of PACAP38 in CH pathophysiology and predict efficacy of PACAP38 antagonists in this primary headache.

PACAP38 in human models of primary headaches

Background

To review the role of PACAP38 in human models of primary headaches, discuss possible mechanisms of PACAP38-induced migraine, and outline future directions.

Discussion

Experimental studies have established PACAP38 as a potent pharmacological “trigger” molecule of migraine-like attacks. These studies have also revealed a heterogeneous PACAP38 migraine response in migraine without aura patients. In addition, findings from brain imaging studies have demonstrated neuronal and vascular changes in migraine patients both ictally and interictally after PACAP38 infusion.

Conclusion

Human migraine models have shed light on the importance of PACAP38 in the pathophysiology of primary headaches. These studies have also pointed to the PAC₁ receptor and the PACAP38 molecule itself as target sites for drug testing. Future research should seek to understand the mechanisms underlying PACAP38-induced migraine. The results from an ongoing proof of concept randomized clinical trial may reveal the therapeutic potential of anti-PAC₁ receptor antibodies for migraine prevention.

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.

Induction of Migraine-Like Photophobic Behavior in Mice by Both Peripheral and Central CGRP Mechanisms

The neuropeptide calcitonin gene-related peptide (CGRP) is a key player in migraine. Although migraine can be treated using CGRP antagonists that act peripherally, the relevant sites of CGRP action remain unknown. To address the role of CGRP both within and outside the CNS, we used CGRP-induced light-aversive behavior in mice as a measure of migraine-associated photophobia. Peripheral (intraperitoneal) injection of CGRP resulted in light-aversive behavior in wild-type CD1 mice similar to aversion seen previously after central (intracerebroventricular) injection. The phenotype was also observed in C57BL/6J mice, although to a lesser degree and with more variability. After intraperitoneal CGRP, motility was decreased in the dark only, similar to motility changes after intracerebroventricular CGRP. In addition, as with intracerebroventricular CGRP, there was no general increase in anxiety as measured in an open-field assay after intraperitoneal CGRP. Importantly, two clinically effective migraine drugs, the 5-HT1B/D agonist sumatriptan and a CGRP-blocking monoclonal antibody, attenuated the peripheral CGRP-induced light aversion and motility behaviors. To begin to address the mechanism of peripheral CGRP action, we used transgenic CGRP-sensitized mice that have elevated levels of the CGRP receptor hRAMP1 subunit in nervous tissue (nestin/hRAMP1). Surprisingly, sensitivity to low light was not seen after intraperitoneal CGRP injection, but was seen after intracerebroventricular CGRP injection. These results suggest that CGRP can act in both the periphery and the brain by distinct mechanisms and that CGRP actions may be transmitted to the CNS via indirect sensitization of peripheral nerves.

SIGNIFICANCE STATEMENT

The neuropeptide calcitonin gene-related peptide (CGRP) is a central player in migraine pathogenesis, yet its site(s) of action remains unknown. Some preclinical studies have pointed to central sites in the brain and brainstem. However, a peripheral site of action is indicated by the ability of intravenous CGRP to trigger migraine in humans and the efficacy of CGRP receptor antagonists that evidently do no penetrate the CNS in effective amounts. Resolving this issue is particularly important given recent clinical trials showing that anti-CGRP monoclonal antibodies can reduce and even prevent migraine attacks. In this study, we report that CGRP can act in both the brain and the periphery of the mouse to cause migraine-like photophobia by apparently distinct mechanisms.

CGRP in human models of primary headaches

Objective To review the role of CGRP in human models of primary headaches and to discuss methodological aspects and future directions. Discussion Provocation experiments demonstrated a heterogeneous CGRP migraine response in migraine patients. Conflicting CGRP plasma results in the provocation experiments are likely due to assay variation; therefore, proper validation and standardization of an assay is needed. To what extent CGRP is involved in tension-type headache and cluster headache is unknown. Conclusion Human models of primary headaches have elucidated the role of CGRP in headache pathophysiology and sparked great interest in developing new treatment strategies using CGRP antagonists and antibodies. Future studies applying more refined human experimental models should identify biomarkers of CGRP-induced primary headache and reveal whether CGRP provocation experiments could be used to predict efficacy of CGRP antagonists in migraine patients.