Animal Models of Chronic Migraine: From the Bench to Therapy

PURPOSE OF REVIEW

Chronic migraine is a disabling progressive disorder without effective management approaches. Animal models have been developed and used in chronic migraine research. However, there are several problems with existing models. Therefore, we aimed to summarize and analyze existing animal models to facilitate translation from basic to clinical.

RECENT FINDINGS

The most commonly used models are the inflammatory soup induction model and the nitric oxide donor induction model. In addition, KATP openers have also been used in model induction. Based on the above models, some molecular targets have been identified, such as glutamate receptors. However, each model has its shortcomings and characteristics, and there are still some common problems that need to be solved, such as spontaneous headache, evaluation criteria after model establishment, and identification methods. In this review, we summarized and highlighted the advantages and limitations of the currently commonly used animal models of chronic migraine with a special focus on drug discovery and current therapeutic strategies, and discussed the directions that can be worked on in the future.

Unravelling the Genetic Landscape of Hemiplegic Migraine: Exploring Innovative Strategies and Emerging Approaches

Migraine is a severe, debilitating neurovascular disorder. Hemiplegic migraine (HM) is a rare and debilitating neurological condition with a strong genetic basis. Sequencing technologies have improved the diagnosis and our understanding of the molecular pathophysiology of HM. Linkage analysis and sequencing studies in HM families have identified pathogenic variants in ion channels and related genes, including CACNA1A, ATP1A2, and SCN1A, that cause HM. However, approximately 75% of HM patients are negative for these mutations, indicating there are other genes involved in disease causation. In this review, we explored our current understanding of the genetics of HM. The evidence presented herein summarises the current knowledge of the genetics of HM, which can be expanded further to explain the remaining heritability of this debilitating condition. Innovative bioinformatics and computational strategies to cover the entire genetic spectrum of HM are also discussed in this review.

Migraine: Advances in the Pathogenesis and Treatment

This article presents a comprehensive review on migraine, a prevalent neurological disorder characterized by chronic headaches, by focusing on their pathogenesis and treatment advances. By examining molecular markers and leveraging imaging techniques, the research identifies key mechanisms and triggers in migraine pathology, thereby improving our understanding of its pathophysiology. Special emphasis is given to the role of calcitonin gene-related peptide (CGRP) in migraine development. CGRP not only contributes to symptoms but also represents a promising therapeutic target, with inhibitors showing effectiveness in migraine management. The article further explores traditional medical treatments, scrutinizing the mechanisms, benefits, and limitations of commonly prescribed medications. This provides a segue into an analysis of emerging therapeutic strategies and their potential to enhance migraine management. Finally, the paper delves into neuromodulation as an innovative treatment modality. Clinical studies indicating its effectiveness in migraine management are reviewed, and the advantages and limitations of this technique are discussed. In summary, the article aims to enhance the understanding of migraine pathogenesis and present novel therapeutic possibilities that could revolutionize patient care.

Mouse Models of Familial Hemiplegic Migraine for Studying Migraine Pathophysiology

Migraine, an extremely disabling neurological disorder, has a strong genetic component. Since monogenic mi-graines (resulting from mutations or changes in a single gene) may help researchers discover migraine pathophysiology, transgenic mice models harboring gene mutations identified in Familial Hemiplegic Migraine (FHM) patients have been gen-erated. Studies in these FHM mutant mice models have shed light on the mechanisms of migraine and may aid in the identifi-cation of novel targets for treatment. More specifically, the studies shed light on how gene mutations, hormones, and other factors impact the pathophysiology of migraine. The models may also be of relevance to researchers outside the field of mi-graine as some of their aspects are relevant to pain in general. Additionally, because of the comorbidities associated with mi-graine, they share similarities with the mutant mouse models of epilepsy, stroke, and perhaps depression. Here, we review the experimental data obtained from these mutant mice and focus on how they can be used to investigate the pathophysiology of migraine, including synaptic plasticity, neuroinflammation, metabolite alterations, and molecular and behavioral mecha-nisms of pain.

Mechanisms of migraine as a chronic evolutive condition

Understanding the mechanisms of migraine remains challenging as migraine is not a static disorder, and even in its episodic form migraine remains an "evolutive" chronic condition. Considerable progress has been made in elucidating the pathophysiological mechanisms of migraine, associated genetic factors that may influence susceptibility to the disease, and functional and anatomical changes during the progression of a migraine attack or the transformation of episodic to chronic migraine. Migraine is a life span neurological disorder that follows an evolutive age-dependent change in its prevalence and even clinical presentations. As a disorder, migraine involves recurrent intense head pain and associated unpleasant symptoms. Migraine attacks evolve over different phases with specific neural mechanisms and symptoms being involved during each phase. In some patients, migraine can be transformed into a chronic form with daily or almost daily headaches. The mechanisms behind this evolutive process remain unknown, but genetic and epigenetic factors, inflammatory processes and central sensitization may play an important role.

Genetic mouse models of migraine

Mouse models of rare monogenic forms of migraine provide a unique experimental system to study the cellular and circuit mechanisms of the primary brain dysfunctions causing a migraine disorder. Here, we discuss the migraine-relevant phenotypes and the migraine-relevant functional alterations in the brain of five genetic mouse models of migraine, four of which carry mutations derived from patients with familial hemiplegic migraine (FHM) and the fifth carry a mutation from patients with both phenotypically normal MA and familial advanced sleep phase syndrome (FASPS). We focus on the latter mouse model, in which a ubiquitous serine-threonine kinase is mutated, and on two mouse models of pure FHM, in which a voltage-gated calcium channel controlling neurotransmitter release at most brain synapses and a Na/K ATPase that is expressed mainly in astrocytes in the adult brain are mutated, respectively. First, we describe the behavioral phenotypes of the genetic animal models and review the evidence that an increased susceptibility to experimentally induced cortical spreading depression (CSD) is a key migraine-relevant phenotype common to the five models. Second, we review the synaptic alterations in the cerebral cortex of the genetic models of migraine and discuss the mechanisms underlying their increased susceptibility to CSD. Third, we review the alterations in the trigeminovascular pain pathway and discuss possible implications for migraine pain mechanisms. Finally, we discuss the insights into migraine pathophysiology obtained from the genetic models of migraine, in particular regarding the mechanisms that make the brain of migraineurs susceptible to the ignition of “spontaneous” CSDs. Although the reviewed functional studies support the view of migraine as a disorder of the brain characterized by dysfunctional regulation of the excitatory/inhibitory balance in specific neuronal circuits, much work remains to be done in the genetic mouse models e.g. to identfy the relevant dysfunctional circuits and to establish whether and how the alterations in the function of specific circuits (in the cerebral cortex and/or other brain areas) are state-dependent and may, in certain conditions, favor CSD ignition and the migraine attack.

Migraine: Experimental Models and Novel Therapeutic Approaches

Migraine is a disorder affecting an increasing number of subjects. Currently, this disorder is not entirely understood, and limited therapeutic solutions are available. Migraine manifests as a debilitating headache associated with an altered sensory perception that may compromise the quality of life. Animal models have been developed using chemical, physical or genetic modifications, to evoke migraine-like hallmarks for the identification of novel molecules for the treatment of migraine. In this context, experimental models based on the use of chemicals as nitroglycerin or inflammatory soup were extensively used to mimic the acute state and the chronicity of the disorder. This manuscript is aimed to provide an overview of murine models used to investigate migraine pathophysiology. Pharmacological targets as 5-HT and calcitonin gene-related peptide (CGRP) receptors were evaluated for their relevance in the development of migraine therapeutics. Drug delivery systems using nanoparticles may be helpful for the enhancement of the brain targeting and bioavailability of anti-migraine drugs as triptans. In conclusion, the progresses in migraine management have been reached with the development of emerging agonists of 5-HT receptors and novel antagonists of CGRP receptors. The nanoformulations may represent a future perspective in which already known anti-migraine drugs showed to better exert their therapeutic effects.

Trigeminovascular calcitonin gene-related peptide function in Cacna1a R192Q-mutated knock-in mice

Familial hemiplegic migraine type 1 (FHM1) is a rare migraine subtype. Whereas transgenic knock-in mice with the human pathogenic FHM1 R192Q missense mutation in the Cacna1a gene reveal overall neuronal hyperexcitability, the effects on the trigeminovascular system and calcitonin gene-related peptide (CGRP) receptor are largely unknown. This gains relevance as blockade of CGRP and its receptor are therapeutic targets under development. Hence, we set out to test these effects in FHM1 mice. We characterized the trigeminovascular system of wild-type and FHM1 mice through: (i) in vivo capsaicin- and CGRP-induced dural vasodilation in a closed-cranial window; (ii) ex vivo KCl-induced CGRP release from isolated dura mater, trigeminal ganglion and trigeminal nucleus caudalis; and (iii) peripheral vascular function in vitro . In mutant mice, dural vasodilatory responses were significantly decreased compared to controls. The ex vivo release of CGRP was not different in the components of the trigeminovascular system between genotypes; however, sumatriptan diminished the release in the trigeminal ganglion, trigeminal nucleus caudalis and dura mater but only in wild-type mice. Peripheral vascular function was similar between genotypes. These data suggest that the R192Q mutation might be associated with trigeminovascular CGRP receptor desensitization. Novel antimigraine drugs should be able to revert this complex phenomenon.

Emerging drugs for migraine treatment: an update

Introduction: Migraine is a very frequent and disabling neurological disorder. The current treatment options are old, generally poorly tolerated and not migraine-specific, reflecting the low priority of migraine research and highlighting the vast unmet need in its management. Areas covered: Advancement in the understanding of migraine pathophysiological mechanisms and identification of novel potentially meaningful targets have resulted in a multitude of emerging acute and preventive treatments. Here we review the known putative migraine pathophysiological mechanisms in order to understand the rationale of the most promising novel treatments targeting the Calcitonin-Gene-Related Peptide receptor and ligand and the 5 hydroxytryptamine (5-HT)1F receptor. Key findings on the phase II and phase III clinical trials on these treatments will be summarized. Furthermore, a critical analysis on failed trials of potentially meaningful targets such the nitric oxide and the orexinergic pathways will be conducted. Future perspective will be outlined. Expert opinion: The recent approval of Erenumab and Fremanezumab is a major milestone in the therapy of migraine since the approval of triptans. Several more studies are needed to fully understand the clinical potential, long-term safety and cost-effectiveness of these therapies. This paramount achievement should stimulate the development of further research in the migraine field.

Pathophysiology of Migraine: A Disorder of Sensory Processing

Plaguing humans for more than two millennia, manifest on every continent studied, and with more than one billion patients having an attack in any year, migraine stands as the sixth most common cause of disability on the planet. The pathophysiology of migraine has emerged from a historical consideration of the "humors" through mid-20th century distraction of the now defunct Vascular Theory to a clear place as a neurological disorder. It could be said there are three questions: why, how, and when? Why: migraine is largely accepted to be an inherited tendency for the brain to lose control of its inputs. How: the now classical trigeminal durovascular afferent pathway has been explored in laboratory and clinic; interrogated with immunohistochemistry to functional brain imaging to offer a roadmap of the attack. When: migraine attacks emerge due to a disorder of brain sensory processing that itself likely cycles, influenced by genetics and the environment. In the first, premonitory, phase that precedes headache, brain stem and diencephalic systems modulating afferent signals, light-photophobia or sound-phonophobia, begin to dysfunction and eventually to evolve to the pain phase and with time the resolution or postdromal phase. Understanding the biology of migraine through careful bench-based research has led to major classes of therapeutics being identified: triptans, serotonin 5-HT1B/1D receptor agonists; gepants, calcitonin gene-related peptide (CGRP) receptor antagonists; ditans, 5-HT1F receptor agonists, CGRP mechanisms monoclonal antibodies; and glurants, mGlu5 modulators; with the promise of more to come. Investment in understanding migraine has been very successful and leaves us at a new dawn, able to transform its impact on a global scale, as well as understand fundamental aspects of human biology.

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.

Animal models of monogenic migraine

Migraine is a highly prevalent and disabling neurological disorder with a strong genetic component. Rare monogenic forms of migraine, or syndromes in which migraine frequently occurs, help scientists to unravel pathogenetic mechanisms of migraine and its comorbidities. Transgenic mouse models for rare monogenic mutations causing familial hemiplegic migraine (FHM), cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), and familial advanced sleep-phase syndrome (FASPS), have been created. Here, we review the current state of research using these mutant mice. We also discuss how currently available experimental approaches, including epigenetic studies, biomolecular analysis and optogenetic technologies, can be used for characterization of migraine genes to further unravel the functional and molecular pathways involved in migraine.

Modulation of nociceptive dural input to the trigeminocervical complex through GluK1 kainate receptors

Migraine is a common and disabling neurologic disorder, with important psychiatric comorbidities. Its pathophysiology involves activation of neurons in the trigeminocervical complex (TCC). Kainate receptors carrying the glutamate receptor subunit 5 (GluK1) are present in key brain areas involved in migraine pathophysiology. To study the influence of kainate receptors on trigeminovascular neurotransmission, we determined the presence of GluK1 receptors within the trigeminal ganglion and TCC with immunohistochemistry. We performed in vivo electrophysiologic recordings from TCC neurons and investigated whether local or systemic application of GluK1 receptor antagonists modulated trigeminovascular transmission. Microiontophoretic application of a selective GluK1 receptor antagonist, but not of a nonspecific ionotropic glutamate receptor antagonist, markedly attenuated cell firing in a subpopulation of neurons activated in response to dural stimulation, consistent with selective inhibition of postsynaptic GluK1 receptor-evoked firing seen in all recorded neurons. In contrast, trigeminovascular activation was significantly facilitated in a different neuronal population. The clinically active kainate receptor antagonist LY466195 attenuated trigeminovascular activation in all neurons. In addition, LY466195 demonstrated an N-methyl-d-aspartate receptor-mediated effect. This study demonstrates a differential role of GluK1 receptors in the TCC, antagonism of which can inhibit trigeminovascular activation through postsynaptic mechanisms. Furthermore, the data suggest a novel, possibly presynaptic, modulatory role of trigeminocervical kainate receptors in vivo. Differential activation of kainate receptors suggests unique roles for this receptor in pro- and antinociceptive mechanisms in migraine pathophysiology.

Breath powered nasal delivery: a new route to rapid headache relief

The nose offers an attractive noninvasive alternative for drug delivery. Nasal anatomy, with a large mucosal surface area and high vascularity, allows for rapid systemic absorption and other potential benefits. However, the complex nasal geometry, including the narrow anterior valve, poses a serious challenge to efficient drug delivery. This barrier, plus the inherent limitations of traditional nasal delivery mechanisms, has precluded achievement of the full potential of nasal delivery. Breath Powered bi-directional delivery, a simple but novel nasal delivery mechanism, overcomes these barriers. This innovative mechanism has now been applied to the delivery of sumatriptan. Multiple studies of drug deposition, including comparisons of traditional nasal sprays to Breath Powered delivery, demonstrate significantly improved deposition to superior and posterior intranasal target sites beyond the nasal valve. Pharmacokinetic studies in both healthy subjects and migraineurs suggest that improved deposition of sumatriptan translates into improved absorption and pharmacokinetics. Importantly, the absorption profile is shifted toward a more pronounced early peak, representing nasal absorption, with a reduced late peak, representing predominantly gastrointestinal (GI) absorption. The flattening and “spreading out” of the GI peak appears more pronounced in migraine sufferers than healthy volunteers, likely reflecting impaired GI absorption described in migraineurs. In replicated clinical trials, Breath Powered delivery of low-dose sumatriptan was well accepted and well tolerated by patients, and onset of pain relief was faster than generally reported in previous trials with noninjectable triptans. Interestingly, Breath Powered delivery also allows for the potential of headache-targeted medications to be better delivered to the trigeminal nerve and the sphenopalatine ganglion, potentially improving treatment of various types of headache. In brief, Breath Powered bi-directional intranasal delivery offers a new and more efficient mechanism for nasal drug delivery, providing an attractive option for improved treatment of headaches by enabling or enhancing the benefits of current and future headache therapies.

Monoclonal antibodies for migraine: preventing calcitonin gene-related peptide activity

Calcitonin gene-related peptide (CGRP) is a well-studied neuropeptide of relevance for migraine pathophysiology. Jugular levels of CGRP are increased during migraine attacks, and intravenous CGRP administration induces migraine-like headache in most individuals with migraine. Several CGRP receptor antagonists (CGRP-RAs) were shown to be effective for the acute treatment of migraine, validating the target for the treatment of migraine. However, for a number of reasons, including issues of liver toxicity with chronic use, the development of CGRP-RAs has yet to produce a viable clinical therapeutic. Development of monoclonal antibodies (mAbs) targeting the CGRP pathway is an alternative approach that should avoid many of the issues seen with CGRP-RAs. The exquisite target specificity, prolonged half-lives, and reduced potential for hepatotoxicity and drug-drug interactions make mAbs suitable for the preventive treatment of migraine headaches. This manuscript provides an overview of the role of CGRP in the pathophysiology of migraine, followed by a review of the clinical development of CGRP-RAs. Some basic concepts on antibodies are then discussed along with the publicly disclosed information on the development of mAbs targeting the CGRP pathway.

Calcitonin gene-related peptide and migraine with aura: A systematic review

Background

Calcitonin gene-related peptide (CGRP) is a key molecule in migraine pathophysiology. Most studies have focused on CGRP in relation to migraine without aura (MO). About one-third of migraine patients have attacks with aura (MA), and this is a systematic review of the current literature on CGRP and MA.

Methods

We performed a systematic literature search on MEDLINE for reports of CGRP and MA, covering basic science, animal and human studies as well as randomized clinical trials.

Results

The literature search identified 594 citations, of which 38 contained relevant, original data. Plasma levels of CGRP in MA patients are comparable to MO, but CGRP levels varied among studies. A number of animal studies, including knock-ins of familial hemiplegic migraine (FHM) genes, have examined the relationship between CGRP and cortical spreading depression. In patients, CGRP does not trigger migraine in FHM, but is a robust trigger of migraine-like headache both in MA and MO patients. The treatment effect of CGRP antagonists are well proven in the treatment of migraine, but no studies have studied the effect specifically in MA patients.

Conclusion

This systematic review indicates that the role of CGRP in MA is less studied than in MO. Further studies of the importance of CGRP for auras and migraine are needed.

Animal migraine models for drug development: status and future perspectives

Migraine is number seven in WHO's list of all diseases causing disability and the third most costly neurological disorder in Europe. Acute attacks are treatable by highly selective drugs such as the triptans but there is still a huge unmet therapeutic need. Unfortunately, drug development for headache has almost come to a standstill partly because of a lack of valid animal models. Here we review previous models with emphasis on optimal characteristics of a future model. In addition to selection of animal species, the method of induction of migraine-like changes and the method of recording responses elicited by such measures are crucial. The most naturalistic way of inducing attacks is by infusion of endogenous signaling molecules that are known to cause migraine in patients. The most valid response is recording of neural activity in the trigeminal system. The most useful headache related responses are likely to be behavioral, allowing multiple experiments in each individual animal. Distinction is made between acute and prophylactic models and how to validate each of them. Modern insight into neurobiological mechanisms of migraine is so good that it is only a question of resources and efforts that determine when valid models with ability to predict efficacy in migraine will be available.

The mechanism of functional up-regulation of P2X3 receptors of trigeminal sensory neurons in a genetic mouse model of familial hemiplegic migraine type 1 (FHM-1)

A knock-in (KI) mouse model of FHM-1 expressing the R192Q missense mutation of the Cacna1a gene coding for the α1 subunit of Ca_V2.1 channels shows, at the level of the trigeminal ganglion, selective functional up-regulation of ATP -gated P2X3 receptors of sensory neurons that convey nociceptive signals to the brainstem. Why P2X3 receptors are constitutively more responsive, however, remains unclear as their membrane expression and TRPV1 nociceptor activity are the same as in wildtype (WT) neurons. Using primary cultures of WT or KI trigeminal ganglia, we investigated whether soluble compounds that may contribute to initiating (or maintaining) migraine attacks, such as TNFα, CGRP, and BDNF, might be responsible for increasing P2X3 receptor responses. Exogenous application of TNFα potentiated P2X3 receptor-mediated currents of WT but not of KI neurons, most of which expressed both the P2X3 receptor and the TNFα receptor TNFR2. However, sustained TNFα neutralization failed to change WT or KI P2X3 receptor currents. This suggests that endogenous TNFα does not regulate P2X3 receptor responses. Nonetheless, on cultures made from both genotypes, exogenous TNFα enhanced TRPV1 receptor-mediated currents expressed by a few neurons, suggesting transient amplification of TRPV1 nociceptor responses. CGRP increased P2X3 receptor currents only in WT cultures, although prolonged CGRP receptor antagonism or BDNF neutralization reduced KI currents to WT levels. Our data suggest that, in KI trigeminal ganglion cultures, constitutive up-regulation of P2X3 receptors probably is already maximal and is apparently contributed by basal CGRP and BDNF levels, thereby rendering these neurons more responsive to extracellular ATP.

TNFα levels and macrophages expression reflect an inflammatory potential of trigeminal ganglia in a mouse model of familial hemiplegic migraine

Latent changes in trigeminal ganglion structure and function resembling inflammatory conditions may predispose to acute attacks of migraine pain. Here, we investigated whether, in trigeminal sensory ganglia, cytokines such as TNFα might contribute to a local inflammatory phenotype of a transgenic knock-in (KI) mouse model of familial hemiplegic migraine type-1 (FHM-1). To this end, macrophage occurrence and cytokine expression in trigeminal ganglia were compared between wild type (WT) and R192Q mutant Ca_V2.1 Ca²⁺ channel (R192Q KI) mice, a genetic model of FHM-1. Cellular and molecular characterization was performed using a combination of confocal immunohistochemistry and cytokine assays. With respect to WT, R192Q KI trigeminal ganglia were enriched in activated macrophages as suggested by their morphology and immunoreactivity to the markers Iba1, CD11b, and ED1. R192Q KI trigeminal ganglia constitutively expressed higher mRNA levels of IL1β, IL6, IL10 and TNFα cytokines and the MCP-1 chemokine. Consistent with the report that TNFα is a major factor to sensitize trigeminal ganglia, we observed that, following an inflammatory reaction evoked by LPS injection, TNFα expression and macrophage occurrence were significantly higher in R192Q KI ganglia with respect to WT ganglia. Our data suggest that, in KI trigeminal ganglia, the complex cellular and molecular environment could support a new tissue phenotype compatible with a neuroinflammatory profile. We propose that, in FHM patients, this condition might contribute to trigeminal pain pathophysiology through release of soluble mediators, including TNFα, that may modulate the crosstalk between sensory neurons and resident glia, underlying the process of neuronal sensitisation.

Calcium channels and migraine

Missense mutations in CACNA1A, the gene that encodes the pore-forming α1 subunit of human voltage-gated Ca(V)2.1 (P/Q-type) calcium channels, cause a rare form of migraine with aura (familial hemiplegic migraine type 1: FHM1). Migraine is a common disabling brain disorder whose key manifestations are recurrent attacks of unilateral headache that may be preceded by transient neurological aura symptoms. This review, first, briefly summarizes current understanding of the pathophysiological mechanisms that are believed to underlie migraine headache, migraine aura and the onset of a migraine attack, and briefly describes the localization and function of neuronal Ca(V)2.1 channels in the brain regions that have been implicated in migraine pathogenesis. Then, the review describes and discusses i) the functional consequences of FHM1 mutations on the biophysical properties of recombinant human Ca(V)2.1 channels and native Ca(V)2.1 channels in neurons of knockin mouse models carrying the mild R192Q or severe S218L mutations in the orthologous gene, and ii) the functional consequences of these mutations on neurophysiological processes in the cerebral cortex and trigeminovascular system thought to be involved in the pathophysiology of migraine, and the insights into migraine mechanisms obtained from the functional analysis of these processes in FHM1 knockin mice. This article is part of a Special Issue entitled: Calcium channels.