Migraine can be induced by sildenafil without changes in middle cerebral artery diameter

Provocation of attacks to discover migraine signaling mechanisms and new drug targets: early history and future perspectives - a narrative review

INTRODUCTION

The development of several experimental migraine provocation models has significantly contributed to an understanding of the signaling mechanisms of migraine. The early history of this development and a view to the future are presented as viewed by the inventor of the models.

METHODS

Extensive knowledge of the literature was supplemented by scrutiny of reference lists.

RESULTS

Early studies used methodologies that were not blinded. They suggested that histamine and nitroglycerin (Glyceryl trinitrate, GTN) could induce headache and perhaps migraine. The development of a double blind, placebo-controlled model, and the use of explicit diagnostic criteria for induced migraine was a major step forward. GTN, donor of nitric oxide (NO), induced headache in people with- and without migraine as well as delayed migraine attacks in those with migraine. Calcitonin gene-related peptide (CGRP) did the same, supporting the development of CGRP antagonists now widely used in patients. Likewise, pituitary adenylate cyclase activating peptide (PACAP) provoked headache and migraine. Recently a PACAP antibody has shown anti migraine activity in a phase 2 trial. Increase of second messengers activated by NO, CGRP and PACAP effectively induced migraine. The experimental models have also been used in other types of headaches and have been combined with imaging and biochemical studies. They have also been used for drug testing and in genetic studies.

CONCLUSION

Conclusion. Human migraine provocation models have informed about signaling mechanisms of migraine leading to new drugs and drug targets. Future use of these models in imaging-, biochemistry- and genetic studies as well as in the further study of animal models is promising.

Molecular nociceptive mechanisms in migraine: The migraine cascade

OBJECTIVE

This review will explore the categorization of migraine-provoking molecules, their cellular actions, site of action and potential drug targets based on the migraine cascade model.

METHODS

Personal experience and literature.

RESULTS

Migraine impacts over 1 billion people worldwide but is underfunded in research. Recent progress, particularly through the human and animal provocation model, has deepened our understanding of its mechanisms. This model have identified endogenous neuropeptides such as calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase-activating peptide (PACAP) that induces controlled migraine-like attacks leading to significant discoveries of their role in migraine. This knowledge led to the development of CGRP-inhibiting drugs; a groundbreaking migraine treatment now accessible globally. Also a PACAP-inhibiting drug was effective in a recent phase II trial. Notably, rodent studies have shed light on pain pathways and the mechanisms of various migraine-inducing substances identifying novel drug targets. This is primarily done by using selective inhibitors that target specific signaling pathways of the known migraine triggers leading to the hypothesized cellular cascade model of migraine.

CONCLUSION

The model of migraine presents numerous opportunities for innovative drug development. The future of new migraine treatments is limited only by the investment from pharmaceutical companies.

Induction of cGMP-mediated migraine attacks is independent of CGRP receptor activation

BACKGROUND

The cAMP and cGMP pathways are implicated in the initiation of migraine attacks, but their interactions remain unclear. Calcitonin gene-related peptide (CGRP) triggers migraine attacks via cAMP, whereas the phosphodiesterase-5 inhibitor sildenafil induces migraine attacks via cGMP. Our objective was to investigate whether sildenafil could induce migraine attacks in individuals with migraine pre-treated with the CGRP-receptor antibody erenumab.

METHODS

In this randomized, double-blind, placebo-controlled, cross-over study, adults with migraine without aura received a single subcutaneous injection of 140 mg erenumab on day 1. They were then randomized to receive sildenafil 100 mg or placebo on two experimental days, each separated by at least one week, between days 8 and 21. The primary endpoint was the difference in the incidence of migraine attacks between sildenafil and placebo during the 12-h observation period after administration.

RESULTS

In total, 16 participants completed the study. Ten participants (63%) experienced a migraine attack within 12 h after sildenafil administration compared to three (19%) after placebo (p = 0.016). The median headache intensity was higher after sildenafil than after placebo (area under the curve (AUC) for the 12-h observation period, p = 0.026). Furthermore, sildenafil induced a significant decrease in mean arterial blood pressure (AUC, p = 0.026) and a simultaneous increase in heart rate (AUC, p < 0.001) during the first hour after administration compared to placebo.

CONCLUSION

These findings provide evidence that migraine induction via the cGMP pathway can occur even under CGRP receptor blockade.

TRIAL REGISTRATION

ClinicalTrials.gov: Identifier NCT05889455.

Headache Attributed to a Substance or Its Withdrawal

Identification of substances that may cause or trigger headache is important to start effective treatment early to prevent unnecessary suffering, deterioration in quality of life, and the development of chronic pain. Treatment in case of medication overuse and other chronic headache should be decisive and effective. Drug withdrawal and introduction of effective prophylactic medication for the underlying headache disorder should be the primary treatment strategy. Typical headache-inducing substances are nitric oxide, phosphodiesterase, cocaine, alcohol, histamine, carbon oxide, and calcitonin gene-related peptide. The withdrawal of caffeine, estrogen, and opioids is most often associated with the development of headache.

Migraine headache and aura induced by hypoxia

Migraine, a common neurological disorder, impacts over a billion individuals globally. Its complex aetiology involves various signalling cascades. Hypoxia causes headaches such as high-altitude headache and acute mountain sickness which share phenotypical similarities with migraine. Epidemiological data indicate an increased prevalence of migraine with and without aura in high-altitude populations. Experimental studies have further shown that hypoxia can induce migraine attacks. This review summarizes evidence linking hypoxia to migraine, delves into potential pathophysiological mechanisms and highlights research gaps.

A Comprehensive Investigation of Risk Association Between the -786 T > C, + 884 G > A, VNTR, rs743506, rs3918226 of eNOS and Susceptibility of Migraine: A Updated Meta-Analysis Utilizing Trial Sequential Analysis

With a feature of complex pathogenic mechanisms, migraine is a well-known common neurovascular disorder. Multiple genes are responsible for hindering the susceptibility of pain threshold one of which is the eNOS gene and its variants. Multiple independent observational studies with case-control design produced conflicting findings, which can be attributed to a variety of factors including varying sample sizes, demographic stratification, technique application, etc. Therefore, in the present study we aimed to find out the precise risk between the selected variant of eNOS and the risk of migraine and its clinical subtypes using a meta-analysis approach. To find the association between the risk variants of the eNOS gene and migraine, a PRISMA-based systematic literature review strategy was utilized to search via online resources including PubMed and Google Scholar. Using several genetic models, odds ratios with 95% confidence intervals were computed to pool the data. To access heterogeneity, Cochran's Q Test and I2 statistics were utilized, while Begg's and Egger's tests were used to determine publication bias. A p-value of 0.05 or below was deemed statistically significant for all two-sided tests. The present meta-analysis was able to find out the significant protective association between rs743506 and migraine after using dominant (OR: 0.66, CI [0.49-0.86]), over-dominant (OR: 0.56, CI [0.42-0.75]), codominant model (OR: 0.58, CI[0.43-0.77]). Only significant risk association was found between rs1799983, rs3918226, and risk of migraine with aura after utilizing recessive and codominant models i.e., HR vs HW and HR vs HT. The present meta-analysis showed that rs743506 showed a protective association in comparison to rs1799983, rs3918226 which showed significant risk in the MA group. Also, TSA showed non-significant results and therefore, in conclusion, more studies are required to establish risk.

Arterial Spin Labeling in Migraine: A Review of Migraine Categories and Mimics

Migraine is a complex headache characterized by changes in functional connectivity and cerebral perfusion. The perfusion changes represent a valuable domain for targeted drug therapy. Arterial spin labeling is a noncontrast imaging technique of quantifying cerebral perfusion changes in the migraine setting. In this narrative review, we will discuss the pathophysiology of the different categories of migraine, as defined by the International Classification of Headache Disorders-3 and describe a category-based approach to delineating perfusion changes in migraine on arterial spin labeling images. We will also discuss the use of arterial spin labeling to differentiate migraine from stroke and/or seizures in the adult and pediatric populations. Our systematic approach will help improve the understanding of the complicated vascular changes that occur during migraines and identify potential areas of future research.

Association between dietary potassium intake and severe headache or migraine in US adults: a population-based analysis

Background

Migraine is a prevalent neurovascular headache disorder. The link between dietary potassium and blood pressure has been established. We sought to delineate the relationship between dietary potassium intake and the prevalence of migraines.

Methods

We conducted a cross-sectional analysis using data from the National Health and Nutrition Examination Survey (NHANES) spanning 1999-2004, comprising 10,254 participants aged ≥20 years. Participants who reported severe headaches or migraine in the self-report questionnaire were identified as migraineurs. A 24-h dietary recall methodology was used to assess dietary potassium intake. Multivariate regression analysis and restricted cubic spline (RCS) modeling were utilized to elucidate the relationship between dietary potassium and migraines.

Results

Among the 10,254 participants, 20.1% were identified with migraine or severe headaches. The adjusted odds ratio (OR) for migraine occurrence in the Q2 dietary potassium intake (1771-2,476 mg/d) was 0.84 (95% CI: 0.73-0.97, p = 0.021) compared to the lowest quartile (Q1, ≤ 1771 mg/d). The relationship between dietary potassium and migraine exhibited an L-shaped pattern (non-linear, p = 0.016) with an inflection at approximately 1439.3 mg/d. In the subgroup analysis, when compared to Q1, who had the lowest dietary potassium intake, the adjusted OR for Q2 in females, those in the medium-high household income group, and with a Body Mass Index (BMI) ≥ 25 kg/m2 were as follows: (OR, 0.82; 95% CI, 0.69-0.98), (OR, 0.79; 95% CI, 0.66-0.95), and (OR, 0.78; 95% CI, 0.66-0.93), respectively. No significant interaction was observed across groups after adjusting for all possible covariates.

Conclusion

The relationship between dietary potassium intake and migraine prevalence among US adults appears to follow an L-shaped curve.

Emerging experimental drugs in clinical trials for migraine: observations and key talking points

INTRODUCTION

There have been significant advances in the treatment of migraine. In response to the clinical success of monoclonal antibodies targeting calcitonin gene-related peptide, there is interest in the clinical trial outcomes of alternative emerging drugs that act on novel targets associated with migraine pathophysiology. As approximately 50% of patients do not respond to CGRP therapies, there is significant value in future drug innovation. Emerging drugs in clinical trials for the treatment of migraine aim to fill this need.

AREAS COVERED

The emerging drugs that will be discussed in this review include zavegepant, lasmiditan, delta opioid receptor agonists, neuronal nitric oxide synthase inhibitors, monoclonal antibodies targeting pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptor, dual orexin receptor antagonists, metabotropic glutamate receptor 5 antagonists, and inducers of ketosis.

EXPERT OPINION

When considering the preclinical and clinical research related to the emerging drug classes discussed in this review, most therapies are derived from highly supported targets of migraine pathogenesis. Although the individual drugs discussed in this review may be of dubious clinical value, the importance of the therapeutic targets on which they act cannot be understated. Future research is necessary to appropriately target the pathways elucidated by preclinical studies.

Future targets for migraine treatment beyond CGRP

BACKGROUND

Migraine is a disabling and chronic neurovascular headache disorder. Trigeminal vascular activation and release of calcitonin gene-related peptide (CGRP) play a pivotal role in the pathogenesis of migraine. This knowledge has led to the development of CGRP(-receptor) therapies. Yet, a substantial proportion of patients do not respond to these treatments. Therefore, alternative targets for future therapies are warranted. The current narrative review provides a comprehensive overview of the pathophysiological role of these possible non-CGRP targets in migraine.

FINDINGS

We covered targets of the metabotropic receptors (pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal peptide (VIP), amylin, and adrenomedullin), intracellular targets (nitric oxide (NO), phosphodiesterase-3 (PDE3) and -5 (PDE5)), and ion channels (potassium, calcium, transient receptor potential (TRP), and acid-sensing ion channels (ASIC)). The majority of non-CGRP targets were able to induce migraine-like attacks, except for (i) calcium channels, as it is not yet possible to directly target channels to elucidate their precise involvement in migraine; (ii) TRP channels, activation of which can induce non-migraine headache; and (iii) ASICs, as their potential in inducing migraine attacks has not been investigated thus far. Drugs that target its receptors exist for PACAP, NO, and the potassium, TRP, and ASIC channels. No selective drugs exist for the other targets, however, some existing (migraine) treatments appear to indirectly antagonize responses to amylin, adrenomedullin, and calcium channels. Drugs against PACAP, NO, potassium channels, TRP channels, and only a PAC₁ antibody have been tested for migraine treatment, albeit with ambiguous results.

CONCLUSION

While current research on these non-CGRP drug targets has not yet led to the development of efficacious therapies, human provocation studies using these targets have provided valuable insight into underlying mechanisms of migraine headaches and auras. Further studies are needed on these alternative therapies in non-responders of CGRP(-receptor) targeted therapies with the ultimate aim to pave the way towards a headache-free future for all migraine patients.

Assessment of morphometric parameters of middle cerebral artery using CT angiography in a tertiary care hospital

PURPOSE

Middle cerebral artery (MCA) favors secondaries and emboli deposition. Also, with an increase in incidence of MCA aneurysms, majorly at the M1 division point, actual standardized measurement of MCA is necessary. Thus, main aim of the study is assessment of the MCA morphometry using CT Angiography in Indian population.

METHODS

CT cerebral Angiography datasets of 289 patients (180 males and 109 females) were assessed for the MCA morphometry (Average age - 49.29 ± 16.16 years, Range- 11 to 85 years). The cases involving aneurysms and infarcts were excluded. The total length of MCA, length of M1 segment and diameter were measured and the results were statistically analysed.

RESULTS

The mean total length of MCA, length of M1 segment and diameter were 24.02 ± 1.22 mm, 14.32 ± 1.27 mm, 3.33 ± 0.62 mm, respectively. The mean length of M1 segment on the right and left sides was 14.19 ± 1.39 mm and 14.44 ± 1.12 mm, respectively and the difference was statistically significant (p ≤ 0.05). The mean diameter on the right and left sides was 3.32 ± 0.62 mm and 3.33 ± 0.62 mm, respectively and the difference was not statistically significant (p = 0.832). The M1 segment length was maximum in patients over 60 years and diameter was maximum in young patients (20-40 years). The mean length of M1 segment in early bifurcation (4.4 ± 0.65 mm), bifurcation (14.32 ± 1.27 mm) and trifurcation (14.15 ± 1.43 mm) was also noted.

CONCLUSION

The MCA measurements will be useful for surgeons to minimize errors in handling cases of intracranial aneurysms or infarcts and provide the best possible outcome to the patients.

Shared and independent roles of CGRP and PACAP in migraine pathophysiology

The neuropeptides calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase-activating polypeptide (PACAP) have emerged as mediators of migraine pathogenesis. Both are vasodilatory peptides that can cause migraine-like attacks when infused into people and migraine-like symptoms when injected into rodents. In this narrative review, we compare the similarities and differences between the peptides in both their clinical and preclinical migraine actions. A notable clinical difference is that PACAP, but not CGRP, causes premonitory-like symptoms in patients. Both peptides are found in distinct, but overlapping areas relevant to migraine, most notably with the prevalence of CGRP in trigeminal ganglia and PACAP in sphenopalatine ganglia. In rodents, the two peptides share activities, including vasodilation, neurogenic inflammation, and nociception. Most strikingly, CGRP and PACAP cause similar migraine-like symptoms in rodents that are manifested as light aversion and tactile allodynia. Yet, the peptides appear to act by independent mechanisms possibly by distinct intracellular signaling pathways. The complexity of these signaling pathways is magnified by the existence of multiple CGRP and PACAP receptors that may contribute to migraine pathogenesis. Based on these differences, we suggest PACAP and its receptors provide a rich set of targets to complement and augment the current CGRP-based migraine therapeutics.

Migraine and obesity: what is the real direction of their association?

INTRODUCTION

In recent decades, studies have addressed the issue of how migraine and obesity are related and have suggested obesity as a risk factor for migraine headache. However, the exact direction of this relationship remains under debate. In this review, the authors summarize the evidence that have suggested migraine as a risk factor for obesity and overweightness.

AREAS COVERED

This article reviews the results of the previous research published on PubMed and Scopus databases (from 2000 to 2020) concerning the association between migraine and obesity to determine the actual direction of their association. Special attention has been given to the common mechanistic pathways involved in the pathophysiology of migraine and obesity.

EXPERT OPINION

The majority of research conducted thus far has considered obesity as a risk factor for migraine. However, because of the cross-sectional design of available research, we cannot be certain of the proposed direction of this association. There is evidence supporting the hypothesis that obesity can serve as a consequence of migraine through the effects of neuropeptides, inflammatory mediators, adipokines, gut microbiota and modifications in eating behavior and lifestyle. However, the real direction of the relationship between migraine and obesity should be further investigated in large prospective studies.

The anatomy of head pain

Pain-sensitive structures in the head and neck, including the scalp, periosteum, meninges, and blood vessels, are innervated predominantly by the trigeminal and upper cervical nerves. The trigeminal nerve supplies most of the sensation to the head and face, with the ophthalmic division (V1) providing innervation to much of the supratentorial dura mater and vessels. This creates referral patterns for pain that may be misleading to clinicians and patients, as described by studies involving awake craniotomies and stimulation with electrical and mechanical stimuli. Most brain parenchyma and supratentorial vessels refer pain to the ipsilateral V1 territory, and less commonly the V2 or V3 region. The upper cervical nerves provide innervation to the posterior scalp, while the periauricular region and posterior fossa are territories with shared innervation. Afferent fibers that innervate the head and neck send nociceptive input to the trigeminocervical complex, which then projects to additional pain processing areas in the brainstem, thalamus, hypothalamus, and cortex. This chapter discusses the pain-sensitive structures in the head and neck, including pain referral patterns for many of these structures. It also provides an overview of peripheral and central nervous system structures responsible for transmitting and interpreting these nociceptive signals.

Migraine Pathophysiology Revisited: Proposal of a New Molecular Theory of Migraine Pathophysiology and Headache Diagnostic Criteria

Various explanations for the pathophysiology of migraines have been proposed; however, none of these provide a complete explanation. The author critically reviews previous theories and proposes a new molecular theory of migraine pathophysiology. The diagnosis of primary headaches is generally based on clinical histories and symptoms only because there is no reliable diagnostic examination. The author proposes a new classification system and set of diagnostic criteria for headaches based on molecular markers.

Calcitonin Gene-Related Peptide (CGRP) and Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) in Migraine Pathogenesis

Migraine is a prevalent and debilitating neurologic disorder. Advancements in understanding the underlying pathophysiological mechanisms are spearheading the effort to introduce disease-specific treatment options. In recent years this effort has largely focused on alteration of endogenous neuropeptide signaling, namely the peptides calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase-activating polypeptide (PACAP). Human studies into the pathophysiological underpinnings of CGRP and PACAP in migraine are manifold and here we review the works investigating these neuropeptides in patients suffering from migraine in order to elucidate the background for developing new treatment options for this vastly disabling disorder.

ATP-Sensitive Potassium Channels in Migraine: Translational Findings and Therapeutic Potential

Globally, migraine is a leading cause of disability with a huge impact on both the work and private life of affected persons. To overcome the societal migraine burden, better treatment options are needed. Increasing evidence suggests that ATP-sensitive potassium (KATP) channels are involved in migraine pathophysiology. These channels are essential both in blood glucose regulation and cardiovascular homeostasis. Experimental infusion of the KATP channel opener levcromakalim to healthy volunteers and migraine patients induced headache and migraine attacks in 82-100% of participants. Thus, this is the most potent trigger of headache and migraine identified to date. Levcromakalim likely induces migraine via dilation of cranial arteries. However, other neuronal mechanisms are also proposed. Here, basic KATP channel distribution, physiology, and pharmacology are reviewed followed by thorough review of clinical and preclinical research on KATP channel involvement in migraine. KATP channel opening and blocking have been studied in a range of preclinical migraine models and, within recent years, strong evidence on the importance of their opening in migraine has been provided from human studies. Despite major advances, translational difficulties exist regarding the possible anti-migraine efficacy of KATP channel blockage. These are due to significant species differences in the potency and specificity of pharmacological tools targeting the various KATP channel subtypes.

A single dose of exenatide had no effect on blood flow velocity in the middle cerebral artery in elderly healthy volunteers: Randomized, placebo-controlled, double-blind clinical trial

Background and aims

Glucagon-like peptide 1 (GLP-1) receptor agonists (GLP-1RA) are widely used for the treatment of type 2 diabetes, and recent studies indicate that they may be cardio- and neuroprotective. The safety and effect of a single dose of exenatide, a short-acting GLP-1RA, on cerebral and peripheral arterial function remain unknown.

Methods

In this randomized, double-blind pilot trial, we assigned elderly healthy volunteers without diabetes and no previous history of stroke to receive a single dose of subcutaneous exenatide (5 μg) or placebo. Primary outcome was immediate changes over time in blood flow velocity of the middle cerebral arteries (V_MCA) assessed by repeated transcranial Doppler measurements. Secondary outcomes were changes in peripheral arterial function with finger plethysmography, ankle-brachial index (ABI), and inflammatory- and endothelial-specific biomarkers.

Results

Healthy volunteers (13 women and 17 men) were included: (mean ± standard deviation) age: 62 ± 8 years; body weight: 79.6 ± 12.7 kg; V_MCA: 65.3 ± 10.7 cm/s; fasting plasma glucose: 5.5 ± 0.5 mmol/L; HbA1c: 33.9 ± 4.1 mmol/mol (5.3 ± 0.38%). No differences between exenatide and placebo group were seen regarding V_MCA (p = 0.058), systolic ABI (p = 0.71), plethysmography (p = 0.45), tumor necrosis factor (p = 0.33), interleukin-6 (p = 0.11), interleukin-1β (p = 0.34), vascular cell adhesion molecule 1 (p = 0.73), intercellular adhesion molecule 1 (p = 0.74), or E-selectin (p = 0.31). No severe adverse events were observed.

Conclusion

A single dose of exenatide did not change cerebral blood flow velocity or peripheral vessel function in elderly healthy volunteers. The medication was safe to use in persons without diabetes allowing us to investigate this drug further in search of the neuroprotective mechanisms.

Clinical Trial Registration

https://clinicaltrials.gov, Identifier NCT02838589.

The headache and aura-inducing effects of sildenafil in patients with migraine with aura

INTRODUCTION

It has not been established if migraine headache and migraine aura share common pathophysiological mechanisms. Sildenafil, a phosphodiesterase-5 inhibitor, causes cGMP accumulation and provokes migraine-like headache in patients with migraine without aura. We investigated if sildenafil induced aura and migraine-like headache in patients with migraine with aura.

METHODS

In a randomized, double-blinded, placebo-controlled crossover study, 16 patients with migraine with aura (of whom 11 patients exclusively had attacks of migraine with aura) received 100 mg sildenafil or placebo on two separate days. The development, duration, and characteristics of aura and headache were recorded using a questionnaire. The primary outcome was the incidence of migraine aura.

RESULTS

Aura symptoms were induced in three patients (19%) after sildenafil and none after placebo (P < 0.001). After administration of sildenafil, 12 patients (75%) developed headache compared with two patients (12.5%) after placebo (Fisher's exact test, P < 0.001). The headache in nine patients (56%) after sildenafil and one patient (6%) after placebo fulfilled the criteria for migraine-like attacks (Fisher's exact test, P = 0.002). All patients, who fulfilled the criteria for migraine-like attacks, reported that the attack mimicked the headache phase during their usual migraine attacks.

DISCUSSION

Sildenafil have a moderate migraine headache-inducing and a modest aura-inducing effect in patients with migraine with aura, even in those who exclusively experienced attacks of migraine with aura in their spontaneous attacks. These findings suggest that accumulation of cGMP by PDE5-inhibition do not play any significant role in the initiation of migraine aura and refute the hypothesis of sildenafil being a tool for pharmacological provocation of this phenomenon. These findings further support dissociation between the aura and the headache phase.Trial registration: ClinicalTrials.gov - NCT02795351.

Involvement of adenosine signaling pathway in migraine pathophysiology: A systematic review of clinical studies

OBJECTIVE

To systematically review clinical studies investigating the involvement of adenosine and its receptors in migraine pathophysiology.

BACKGROUND

Adenosine is a purinergic signaling molecule, clinically used in cardiac imaging during stress tests. Headache is a frequent adverse event after intravenous adenosine administration. Migraine headache relief is reported after intake of adenosine receptor antagonist, caffeine. These findings suggest a possible involvement of adenosine signaling in migraine pathophysiology and its potential as a drug target.

METHODS

A search through PubMed and EMBASE was undertaken for clinical studies investigating the role of adenosine and its receptors in migraine, published until September 2021.

RESULTS

A total of 2510 studies were screened by title and abstract. Of these, seven clinical studies were included. The main findings were that adenosine infusion induced headache, and plasma adenosine levels were elevated during ictal compared to interictal periods in migraine patients.

CONCLUSION

The present systematic review emphasizes a potentially important role of adenosine signaling in migraine pathogenesis. Further randomized and placebo-controlled clinical investigations applying adenosine receptors modulators in migraine patients are needed to further understand the adenosine involvement in migraine.

Effect of KATP channel blocker glibenclamide on PACAP38-induced headache and hemodynamic

OBJECTIVE

To determine whether glibenclamide, a non-selective adenosine 5'-triphosphate-sensitive K⁺ (K_ATP) channel blocker, attenuates pituitary adenylate cyclase-activating polypeptide-38 (PACAP38)-induced headache and vascular changes in healthy volunteers.

METHODS

In a double-blind, randomized, placebo controlled and crossover design, 22 healthy volunteers were assigned to receive an intravenous infusion of 10 picomole/kg/min pituitary adenylate cyclase-activating polypeptide-38 over 20 minutes followed by oral administration of 10 mg glibenclamide or placebo. The primary endpoint was the difference in incidence of headache (0-12 hours) between glibenclamide and placebo. The secondary endpoints were a difference in area under the curve for headache intensity scores, middle cerebral artery velocity (V_meanMCA), superficial temporal artery diameter, radial artery diameter, heart rate, mean arterial blood pressure and facial skin blood flow between the two study days.

RESULTS

Twenty participants completed the study. We found no difference in the incidence of pituitary adenylate cyclase-activating polypeptide-38-induced headache after glibenclamide (19/20, 95%) compared to placebo (18/20, 90%) (P = 0.698). The area under the curve for headache intensity, middle cerebral artery velocity, superficial temporal artery diameter, radial artery diameter, facial skin blood flow, heart rate and mean arterial blood pressure did not differ between pituitary adenylate cyclase-activating polypeptide-38-glibenclamide day compared to pituitary adenylate cyclase-activating polypeptide-38-placebo day (P > 0.05).

CONCLUSIONS

Posttreatment with 5'-triphosphate-sensitive K₊ channel inhibitor glibenclamide did not attenuate pituitary adenylate cyclase-activating polypeptide-38-induced headache and hemodynamic changes in healthy volunteers. We suggest that pituitary adenylate cyclase-activating polypeptide-38-triggered signaling pathway could be mediated by specific isoforms of sulfonylurea receptor subunits of 5'-triphosphate-sensitive K₊ channels and other types of potassium channels.

Migraine

Migraine is a common, chronic, disorder that is typically characterized by recurrent disabling attacks of headache and accompanying symptoms, including aura. The aetiology is multifactorial with rare monogenic variants. Depression, epilepsy, stroke and myocardial infarction are comorbid diseases. Spreading depolarization probably causes aura and possibly also triggers trigeminal sensory activation, the underlying mechanism for the headache. Despite earlier beliefs, vasodilation is only a secondary phenomenon and vasoconstriction is not essential for antimigraine efficacy. Management includes analgesics or NSAIDs for mild attacks, and, for moderate or severe attacks, triptans or 5HT_1B/1D receptor agonists. Because of cardiovascular safety concerns, unreliable efficacy and tolerability issues, use of ergots to abort attacks has nearly vanished in most countries. CGRP receptor antagonists (gepants) and lasmiditan, a selective 5HT1_F receptor agonist, have emerged as effective acute treatments. Intramuscular onabotulinumtoxinA may be helpful in chronic migraine (migraine on ≥15 days per month) and monoclonal antibodies targeting CGRP or its receptor, as well as two gepants, have proven effective and well tolerated for the preventive treatment of migraine. Several neuromodulation modalities have been approved for acute and/or preventive migraine treatment. The emergence of new treatment targets and therapies illustrates the bright future for migraine management.

Opening of BKCa channels causes migraine attacks: a new downstream target for the treatment of migraine

ABSTRACT

Migraine is a common and frequently disabling neurological disorder, but the initiating migraine mechanisms are still poorly understood. Potassium channel opening may cause migraine, and we therefore examined the migraine-inducing effect of MaxiPost, a large (big)-conductance calcium-activated potassium (BKCa) channel opener, on migraine induction and cephalic vasodilation in individuals with migraine. Twenty-six patients with migraine without aura were randomly allocated to receive an infusion of MaxiPost or placebo on 2 study days separated by at least 1 week. The primary endpoint was the difference in incidence of migraine attacks after MaxiPost compared with placebo. The secondary endpoints were the difference in incidence of headaches and the difference in area under the curve for headache intensity scores (0-12 hours), for middle cerebral artery blood flow velocity (VMCA) (0-2 hours), and for superficial temporal artery and radial artery diameter. Twenty-two patients completed the study. Twenty-one of 22 (95%) developed migraine attacks after MaxiPost compared with none after placebo (P < 0.0001); the difference of incidence is 95% (95% confidence interval 86%-100%). The incidence of headache over the 12-hour observation period was higher after MaxiPost day (n = 22) than after placebo (n = 7) (P < 0.0001). We found a significant increase of VMCA and superficial temporal and radial arteries' diameter. Because BKCa channel opening initiates migraine attacks, we suggest that BKCa channel blockers could be potential candidates for novel antimigraine drugs.

Intradural artery dilation during experimentally induced migraine attacks

The middle meningeal artery is a proposed surrogate marker for activation of trigeminal nociceptors during migraine. Previous studies focused on the extracranial part of the artery; hence, vasoreactivity in the intradural arteries during migraine is unknown. Thirty-four patients with migraine without aura were given sildenafil on one day and calcitonin gene-related peptide on another in double-blind crossover fashion. Patients were scanned with 3.0 T MR angiography before drug administration and again 6 hours later during induced attacks of migraine. We measured circumference of the intradural segment of the middle meningeal artery before and during induced migraine attacks. The middle cerebral and superficial temporal arteries were also examined. Fourteen patients had attacks during the second scan after both study drugs and 11 had a migraine after either one or the other, resulting in a total of 39 attacks included in the final analysis. Mean circumference of the intradural middle meningeal artery at baseline was 3.18 mm with an increase of 0.11 mm during attacks (P = 0.005), corresponding to a relative dilation of 3.6% [95% CI: 1.4%-5.7%]. Middle cerebral artery dilated by 9.4% [95% CI: 7.1%-11.7%] and superficial temporal artery by 2.3% [95% CI: 0.2%-4.4%]. Our study shows that the intradural middle meningeal artery and the middle cerebral artery are dilated during migraine induced by calcitonin gene-related peptide as well as sildenafil. We propose that intradural vasculature is affected by migraine-driven activation of trigeminal afferents during migraine attacks.

Cerebrovascular Reactivity Measures Are Associated With Post-traumatic Headache Severity in Chronic TBI; A Retrospective Analysis

OBJECTIVE

To characterize the relationship between persistent post-traumatic headache (pPTH) and traumatic cerebrovascular injury (TCVI) in chronic traumatic brain injury (TBI). Cerebrovascular reactivity (CVR), a measure of the cerebral microvasculature and endothelial cell function, is altered both in individuals with chronic TBI and migraine headache disorder (Amyot et al., 2017; Lee et al., 2019b). The pathophysiologies of pPTH and migraine are believed to be associated with chronic microvascular dysfunction. We therefore hypothesize that TCVI may contribute to the underlying migraine-like mechanism(s) of pPTH.

MATERIALS AND METHODS

22 moderate/severe TBI participants in the chronic stage (>6 months) underwent anatomic and functional magnetic resonance imaging (fMRI) scanning with hypercapnia gas challenge to measure CVR as well as the change in CVR (ΔCVR) after single-dose treatment of a specific phosphodiesterase-5 (PDE-5) inhibitor, sildenafil, which potentiates vasodilation in response to hypercapnia in impaired endothelium, as part of a Phase2a RCT of sildenafil in chronic TBI (NCT01762475). CVR and ΔCVR measures of each participant were compared with the individual's pPTH severity measured by the headache impact test-6 (HIT-6) survey.

RESULTS

There was a moderate correlation between HIT-6 and both CVR and ΔCVR scores [Spearman's correlation = -0.50 (p = 0.018) and = 0.46 (p = 0.03), respectively], indicating that a higher headache burden is associated with decreased endothelial function in our chronic TBI population.

CONCLUSION

There is a correlation between PTH and CVR in chronic moderate-severe TBI. This relationship suggests that chronic TCVI may underlie the pathobiology of pPTH. Further, our results suggest that novel treatment strategies that target endothelial function and vascular health may be beneficial in refractory pPTH.

Migraine: disease characterisation, biomarkers, and precision medicine

Migraine is a disabling neurological disorder, diagnosis of which is based on clinical criteria. A shortcoming of these criteria is that they do not fully capture the heterogeneity of migraine, including the underlying genetic and neurobiological factors. This complexity has generated momentum for biomarker research to improve disease characterisation and identify novel drug targets. In this Series paper, we present the progress that has been made in the search for biomarkers of migraine within genetics, provocation modelling, biochemistry, and neuroimaging research. Additionally, we outline challenges and future directions for each biomarker modality. We also discuss the advances made in combining and integrating data from multiple biomarker modalities. These efforts contribute to developing precision medicine that can be applied to future patients with migraine.

Effect of Adrenomedullin on Migraine-Like Attacks in Patients With Migraine: A Randomized Crossover Study

OBJECTIVE

To determine whether the IV infusion of adrenomedullin, a potent vasodilator belonging to calcitonin family of peptides, provokes attacks of migraine in patients.

METHODS

Twenty patients with migraine without aura participated in a placebo-controlled and double-blind clinical study. In a randomized crossover design, the patients received an IV infusion of human adrenomedullin (19.9 pmol/kg/min) or placebo (saline) administrated via an automated IV pump (20 minutes). The patients participated in 2 study days with a washout period of minimum of 7 days. The primary outcome of the study was predefined as a difference in migraine incidence (0-12 hours), and the secondary outcomes were the area under curve (AUC_0-12 hours) for the headache intensity score and AUC_{0-90 minutes} for mean arterial blood pressure (MAP), flushing, and heart rate (HR).

RESULTS

Eleven patients with migraine without aura (55%) fulfilled migraine attacks criteria after adrenomedullin infusion compared to only 3 patients who reported attack (15%) after placebo (p = 0.039). We found that patients reported in a period of 0 to 12 hours stronger headache intensity after adrenomedullin compared to placebo infusion (p = 0.035). AUC_{0-90 minutes} value for HR and flushing (p < 0.05) was significant and for MAP (p = 0.502) remained unchanged. Common reported adverse events were facial flushing, heat sensation, and palpitation (p < 0.001).

CONCLUSION

Our data implicate adrenomedullin in migraine pathogenesis. This suggests that adrenomedullin or its receptors are novel therapeutic targets for the treatment of migraine. However, we cannot discount the possibility that adrenomedullin may be acting through the canonical calcitonin gene-related peptide receptor.

TRIAL REGISTRATION INFORMATION

ClinicalTrials.gov Identifier: NCT04111484.

Opening of ATP sensitive potassium channels causes migraine attacks with aura

Migraine afflicts more than one billion individuals worldwide and is a leading cause of years lived with disability. In about a third of individuals with migraine aura occur in relation to migraine headache. The common pathophysiological mechanisms underlying migraine headache and migraine aura are yet to be identified. Based on recent data, we hypothesized that levcromakalim, an ATP-sensitive potassium channel opener, would trigger migraine attacks with aura in migraine with aura patients.

Phase 1 study to access safety, tolerability, pharmacokinetics, and pharmacodynamics of kynurenine in healthy volunteers

The kynurenine pathway (KP) is the main path for tryptophan metabolism, and it represents a multitude of potential sites for drug discovery in neuroscience, including pain, stroke, and epilepsy. L‐kynurenine (LKYN), the first active metabolite in the pathway, emerges to be a prodrug targeting glutamate receptors. The safety, tolerability, pharmacokinetics, and pharmacodynamics of LKYN in humans have not been previously investigated. In an open‐label, single ascending dose study, six participants received an intravenous infusion of 50, 100, and 150 µg/kg LKYN and new six participants received an intravenous infusion of 0.3, 0.5, 1, and 5 mg/kg LKYN. To compare the pharmacological effects between species, we investigated in vivo the vascular effects of LKYN in rats. In humans, LKYN was safe and well‐tolerated at all dose levels examined. After infusion, LKYN plasma concentration increased significantly over time 3.23 ± 1.12 µg/mL (after 50 µg/kg), 4.04 ± 1.1 µg/mL (after 100 µg/kg), and 5.25 ± 1.01 µg/mL (after 150 µg/kg) (p ≤ 0.001). We observed no vascular changes after infusion compared with baseline. In rats, LKYN had no effect on HR and MAP and caused no dilation of dural and pial arteries. This first‐in‐human study of LKYN showed that LKYN was safe and well‐tolerated after intravenous infusion up to 5 mg/kg over 20 minutes. The lack of change in LKYN metabolites in plasma suggests a relatively slow metabolism of LKYN and no or little feed‐back effect of LKYN on its synthesis. The therapeutic potential of LKYN in stroke and epilepsy should be explored in future studies in humans.

Infusion of Pituitary Adenylate Cyclase-Activating Polypeptide-38 in Patients with Rosacea Induces Flushing and Facial Edema that Can Be Attenuated by Sumatriptan

BACKGROUND

The pathogenesis of rosacea is incompletely understood. Signaling neuropeptides, including PACAP, a regulator of vasodilation and edema, are upregulated in rosacea skin. Here, we evaluated PACAP38-induced rosacea features and examined whether a 5-HT_1B/1D receptor agonist could reduce these features.

METHODS

A total of 35 patients with erythematotelangiectatic rosacea received an intravenous infusion of 10 pmol/kg/minute of PACAP38 followed by an intravenous infusion of 4 mg sumatriptan or placebo (saline) on two study days in a double-blind, randomized, placebo-controlled, and cross-over trial.

RESULTS

PACAP38 increased facial skin blood flow by 90%, dilated the superficial temporal artery by 56%, and induced prolonged flushing and facial edema. Compared with placebo, sumatriptan reduced PACAP38-induced facial skin blood flow for 50 minutes (P = 0.023), constricted the superficial temporal artery for 80 minutes (P = 0.010), and reduced duration of flushing (P = 0.001) and facial edema (P < 0.001).

CONCLUSIONS

We established a clinical experimental model of rosacea features and showed that sumatriptan was able to attenuate PACAP38-induced rosacea flushing and edema. Findings support a key role of PACAP38 in rosacea flushing pathogenesis. It remains unknown whether PACAP38 inhibition can improve rosacea.

TRIAL REGISTER

The trial was registered at ClinicalTrials.govNCT03878784 in March 2019.

Early treatment with sumatriptan prevents PACAP38-induced migraine: A randomised clinical trial

OBJECTIVE

To determine whether early treatment with sumatriptan can prevent PACAP38-induced migraine attacks.

METHODS

A total of 37 patients with migraine without aura were enrolled between July 2018 to December 2019. All patients received an intravenous infusion of 10 picomole/kg/min of PACAP38 over 20 min followed by an intravenous infusion of 4 mg sumatriptan or placebo over 10 min on two study days in a randomised, double-blind, placebo-controlled, crossover study.

RESULTS

Of 37 patients enrolled, 26 (70.3%) completed the study and were included in analyses. Of the 26 patients, four (15%) developed a PACAP38-induced migraine attack on sumatriptan and 11 patients (42%) on placebo (p = 0.016). There were no differences in area under the curve for headache intensity between sumatriptan (mean AUC 532) and placebo (mean AUC 779) (p = 0.35). Sumatriptan significantly constricted the PACAP38-dilated superficial temporal artery immediately after infusion (T30) compared with infusion of placebo (p < 0.001).Conclusions and relevance: Early treatment with intravenously administered sumatriptan prevented PACAP38-induced migraine. Prevention of migraine attacks was associated with vasoconstriction by sumatriptan in the earliest phases of PACAP provocation. These results suggest that sumatriptan prevents PACAP38-induced migraine by modulation of nociceptive transmission within the trigeminovascular system.Trial Registration: ClinicalTrials.gov (NCT03881644).

Opening of BKCa channels alters cerebral hemodynamic and causes headache in healthy volunteers

Introduction

Preclinical data implicate large conductance calcium-activated potassium (BKCa) channels in the pathogenesis of headache and migraine, but the exact role of these channels is still unknown. Here, we investigated whether opening of BKCa channels would cause headache and vascular effects in healthy volunteers.

Methods

In a randomized, double-blind, placebo-controlled, cross-over study, 21 healthy volunteers aged 18–39 years were randomly allocated to receive an intravenous infusion of 0.05 mg/min BKCa channel opener MaxiPost and placebo on two different days. The primary endpoints were the difference in incidence of headache and the difference in area under the curve (AUC) for headache intensity scores (0–12 hours) and for middle cerebral artery blood flow velocity (VMCA) (0–2 hours) between MaxiPost and placebo. The secondary endpoints were the differences in area under the curve for superficial temporal artery and radial artery diameter (0–2 hours) between MaxiPost and placebo.

Results

Twenty participants completed the study. Eighteen participants (90%) developed headache after MaxiPost compared with six (30%) after placebo ( p = 0.0005); the difference of incidence is 60% (95% confidence interval 36–84%). The area under the curve for headache intensity (AUC0–12 hours, p = 0.0003), for mean VMCA (AUC0–2 hours, p = 0.0001), for superficial temporal artery diameter (AUC0–2 hours, p = 0.003), and for radial artery diameter (AUC0–2 hours, p = 0.03) were significantly larger after MaxiPost compared to placebo.

Conclusion

MaxiPost caused headache and dilation in extra- and intracerebral arteries. Our findings suggest a possible role of BKCa channels in headache pathophysiology in humans. ClinicalTrials.gov, ID: NCT03887325.

Secondary headache attributed to exposure to or overuse of a substance

BACKGROUND

Secondary headaches attributed to exposure to or the overuse of a substance are classified under chapter eight in the International Classification of Headache Disorders 3rd edition. Three distinct sub-chapters consider: 1. Headache attributed to exposure to a substance, 2. Medication overuse headache, and 3. Headache attributed to substance withdrawal. Headache attributed to exposure to a substance refers to a headache with onset immediately or within hours after the exposure, while medication overuse headache is a headache occurring on 15 or more days per month that has developed as a consequence of regular usage of acute headache medication(s) for more than three consecutive months in a patient with a pre-existing primary headache disorder. The withdrawal of caffeine, oestrogen, and opioids is most often associated with the development of headache.

DISCUSSION

Despite the current headache classification, there is no certainty of a causal relationship between the use of any substance and the development of headache. Some substances are likely to provoke headache in patients that suffer from a primary headache disorder like migraine, tension-type headache or cluster headache, while others were described to cause headache even in people that generally do not get headaches. Toxic agents, such as carbon monoxide (CO) are difficult to investigate systematically, while other substances such as nitric oxide (NO) were specifically used to induce headache experimentally. If a patient with an underlying primary headache disorder develops a headache, in temporal relation to exposure to a substance, which is significantly worse than the usual headache it is considered secondary. This is even more the case if the headache phenotype is different from the usually experienced headache characteristics. Medication overuse headache is a well-described, distinct disease entity with only marginally understood pathophysiology and associated psychological factors. Managing medication overuse headache patients includes education, detoxification, prophylactic treatments and treating comorbidities, which is reflected in available guidelines. Viewing medication overuse headache as a separate entity helps clinicians and researchers better recognise, treat and study the disorder.

CONCLUSION

Identification of substances that may cause or trigger secondary headache is important in order to educate patients and health care professionals about potential effects of these substances and prevent unnecessary suffering, as well as deterioration in quality of life. Treatment in case of medication overuse and other chronic headache should be decisive and effective.

Migraine and aura triggered by normobaric hypoxia

BACKGROUND

For future experimental studies or the development of targeted pharmaceutical agents, a deeper insight into the pathophysiology of migraine is of utmost interest. Reliable methods to trigger migraine attacks including aura are desirable to study this complex disease in vivo.

METHODS

To investigate hypoxia as a trigger for migraine and aura, we exposed volunteers diagnosed with migraine, with (n = 16) and without aura (n = 14), to hypoxia utilizing a hypoxic chamber adjusted to a FiO₂ of 12.6%. The occurrence of headache, migraine, aura, and accompanying symptoms were registered and vital signs were collected for 6 hours under hypoxia and 2 hours of follow-up. A binary logistic regression analysis examined the probability of triggering headaches, migraines, aura, photo- and phonophobia.

FINDINGS

Of 30 participants, 24 (80.0%) developed headaches and 19 (63.3%) migraine, five (16.7%) reported aura. Two patients that developed aura never experienced aura symptoms before in their life. The increase of mean heart frequency was higher in patients developing headaches or migraine. Mean SpO₂ during hypoxia was 83.39%.

CONCLUSION

Hypoxia was able to trigger migraine attacks and aura independently of any pharmacological agent.

Low frequency activation of the sphenopalatine ganglion does not induce migraine-like attacks in migraine patients

Introduction

Cephalic autonomic symptoms occur in 27‒73% of migraine patients during attacks. The role of parasympathetic activation in migraine attack initiation remains elusive. Low frequency stimulation of the sphenopalatine ganglion increases parasympathetic outflow. In this study, we hypothesized that low frequency stimulation of the sphenopalatine ganglion would provoke migraine-like attacks in migraine patients.

Methods

In a double-blind randomized sham-controlled crossover study, 12 migraine patients with a sphenopalatine ganglion neurostimulator received low frequency or sham stimulation for 30 min on two separate days. We recorded headache characteristics, cephalic autonomic symptoms, ipsilateral mechanical perception and pain thresholds, mean blood flow velocity in the middle cerebral artery (VMCA) and diameter of the superficial temporal artery during and after stimulation.

Results

Five patients (42%) reported a migraine-like attack after low frequency stimulation compared to six patients (50%) after sham ( p = 1.000). We found a significant increase in mechanical detection thresholds during low frequency stimulation compared to baseline ( p = 0.007). Occurrence of cephalic autonomic symptoms and changes in mechanical perception thresholds, VMCA and diameter of the superficial temporal artery showed no difference between low frequency stimulation compared to sham ( p = 0.533).

Conclusion

Low frequency stimulation of the sphenopalatine ganglion did not induce migraine-like attacks or autonomic symptoms in migraine patients. These data suggest that increased parasympathetic outflow by the sphenopalatine ganglion neurostimulator does not initiate migraine-like attacks. Study protocol: ClinicalTrials.gov registration number NCT02510742

Two-hour infusion of vasoactive intestinal polypeptide induces delayed headache and extracranial vasodilation in healthy volunteers

BACKGROUND

In recent years, vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptides (PACAPs) have gained special interest in headache science. VIP and PACAPs (two isoforms, PACAP27 and PACAP38) are related in structure and function, as are their receptors, but they show differences in vasodilating- and headache-inducing properties. Intravenous infusion of PACAP27 or PACAP38, but not VIP, induces a long-lasting dilation of cranial arteries and delayed headache. The relationship between the long-lasting cranial vasodilation and headache development is not fully clarified.

METHODS

In a double-blinded, placebo-controlled, crossover study in 12 healthy volunteers, diameter changes of cranial arteries, occurrence of headache and the parasympathetic system were examined before, during and after a 2-hour continuous intravenous infusion of VIP and placebo. Primary endpoints were the differences in area under the curve for the superficial temporal artery diameter and headache intensity scores, as well as in headache incidence, between VIP and placebo.

RESULTS

The superficial temporal artery diameter was significantly larger on the VIP day compared to placebo (p < 0.001) and the dilation lasted for more than 2 h. The incidence of headache was higher (p = 0.003) on the VIP day compared to the placebo day. The difference in headache intensity scores was more evident in the post-infusion period (120-200 min, p = 0.034) and in the post-hospital phase (4-12 h, p = 0.025). Cranial parasympathetic activity, measured through the production of tears, was higher during VIP compared to placebo (p = 0.033).

CONCLUSION

Continuous intravenous infusion of VIP over 2 h induced a long-lasting cranial vasodilation, activation of the cranial parasympathetic system, and delayed mild headaches in healthy volunteers.Trial Registration: The study is registered at ClinicalTrials.gov (NCT03989817).

Targeting BKCa Channels in Migraine: Rationale and Perspectives

Large (big)-conductance calcium-activated potassium (BK_Ca) channels are expressed in migraine-related structures such as the cranial arteries, trigeminal ganglion and trigeminal spinal nucleus, and they play a substantial role in vascular tonus and neuronal excitability. Using synthetic BK_Ca channels openers was associated with headache as a frequent adverse effect in healthy volunteers. Additionally, BK_Ca channels are downstream molecules in migraine signalling pathways that are activated by several compounds known to provoke migraine, including calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase-activating polypeptide (PACAP) and glyceryl trinitrate (GTN). Also, there is a high affinity and a close coupling between BK_Ca channels and ATP-sensitive potassium (K_ATP) channels, the role of which has recently been established in migraine pathophysiology. These observations raise the question as to whether direct BK_Ca channel activation can provoke migraine in migraine patients, and whether the BK_Ca channel could be a potential novel anti-migraine target. Hence, randomized and placebo-controlled clinical studies on BK_Ca channel openers or blockers in migraine patients are needed.

Tadalafil may improve cerebral perfusion in small-vessel occlusion stroke-a pilot study

New treatments for cerebral small-vessel disease are needed to reduce the risk of small-vessel occlusion stroke and vascular cognitive impairment. We investigated an approach targeted to the signalling molecule cyclic guanosine monophosphate, using the phosphodiesterase 5 inhibitor tadalafil, to explore if it improves cerebral blood flow and endothelial function in patients with cerebral small-vessel disease and stroke. In a randomized, double-blinded, placebo-controlled, cross-over pilot trial (NCT02801032), we included patients who had a previous (>6 months) small-vessel occlusion stroke. They received a single dose of either 20 mg tadalafil or placebo on 2 separate days at least 1 week apart. We measured the following: baseline MRI for lesion load, repeated measurements of blood flow velocity in the middle cerebral artery by transcranial Doppler, blood oxygen saturation in the cortical microvasculature by near-infrared spectroscopy, peripheral endothelial response by EndoPAT and endothelial-specific blood biomarkers. Twenty patients with cerebral small-vessel disease stroke (3 women, 17 men), mean age 67.1 ± 9.6, were included. The baseline mean values ± standard deviations were as follows: blood flow velocity in the middle cerebral artery, 57.4 ± 10.8 cm/s; blood oxygen saturation in the cortical microvasculature, 67.0 ± 8.2%; systolic blood pressure, 145.8 ± 19.5 mmHg; and diastolic blood pressure, 81.3 ± 9.1 mmHg. We found that tadalafil significantly increased blood oxygen saturation in the cortical microvasculature at 180 min post-administration with a mean difference of 1.57 ± 3.02%. However, we saw no significant differences in transcranial Doppler measurements over time. Tadalafil had no effects on peripheral endothelial function assessed by EndoPAT and endothelial biomarker results conflicted. Our findings suggest that tadalafil may improve vascular parameters in patients with cerebral small-vessel disease stroke, although the effect size was small. Increased oxygenation of cerebral microvasculature during tadalafil treatment indicated improved perfusion in the cerebral microvasculature, theoretically presenting an attractive new therapeutic target in cerebral small-vessel disease. Future studies of the effect of long-term tadalafil treatment on cerebrovascular reactivity and endothelial function are needed to evaluate general microvascular changes and effects in cerebral small-vessel disease and stroke.

Intravenous Endothelin-1 Infusion Does Not Induce Aura or Headache in Migraine Patients With Aura

OBJECTIVE

To investigate whether intravenously infused provokes migraine aura and migraine headache in migraine patients with aura.

BACKGROUND

Migraine with aura has been associated with endothelial dysfunction and increased stroke risk. The initiating mechanism of migraine aura symptoms is not known. Experimental provocation of migraine headache using vasoactive peptides has provided tremendous advances in the understanding of migraine pathophysiology but substances that can induce migraine aura have not been identified. Endothelin-1 (ET-1), an endogenous, potent vasoconstrictor peptide released from the vascular endothelium, has been proposed to trigger migraine aura. This hypothesis is based on reports of increased plasma ET-1 levels early during the migraine attacks and the observation that ET-1 applied to the cortical surface potently induces the cortical spreading depolarization, the underlying electrophysiological phenomenon of migraine aura, in animals. Further, endothelial damage due to, for example, carotid puncture and vascular pathology is known to trigger aura episodes.

METHODS

We investigated whether intravascular ET-1 would provoke migraine aura in patients. Using a two-way crossover, randomized, placebo-controlled, double-blind design, we infused high-dose (8 ng/kg/minutes for 20 minutes) intravenous ET-1 in patients with migraine with typical aura. The primary end-point was the difference in incidence of migraine aura between ET-1 and placebo. Experiments were carried out at a public tertiary headache center (Danish Headache Center, Rigshospitalet Glostrup, Denmark).

RESULTS

Fourteen patients received intravenous ET-1. No patients reported migraine aura symptoms or migraine headache during or up to 24 hours following the ET-1 infusion. Four patients reported mild to moderate headache only on the ET-1 day, 3 patients reported moderate headache on the placebo day, and 1 patient reported mild headache on both days. No serious adverse events occurred during or after infusion.

CONCLUSIONS

Provocation of migraine aura by procedures or conditions involving vascular irritation is unlikely to be mediated by ET-1.

Development of novel phosphodiesterase 5 inhibitors for the therapy of Alzheimer's disease

Nitric oxide (NO) is a gaseous molecule that plays a multifactorial role in several cellular processes. In the central nervous system, the NO dual nature in neuroprotection and neurotoxicity has been explored to unveil its involvement in Alzheimer's disease (AD). A growing body of research shows that the activation of the NO signaling pathway leading to the phosphorylation of the transcription factor cyclic adenine monophosphate responsive element binding protein (CREB) (so-called NO/cGMP/PKG/CREB signaling pathway) ameliorates altered neuroplasticity and memory deficits in AD animal models. In addition to NO donors, several other pharmacological agents, such as phosphodiesterase 5 (PDE5) inhibitors have been used to activate the pathway and rescue memory disorders. PDE5 inhibitors, including sildenafil, tadalafil and vardenafil, are marketed for the treatment of erectile dysfunction and arterial pulmonary hypertension due to their vasodilatory properties. The ability of PDE5 inhibitors to interfere with the NO/cGMP/PKG/CREB signaling pathway by increasing the levels of cGMP has prompted the hypothesis that PDE5 inhibition might be used as an effective therapeutic strategy for the treatment of AD. To this end, newly designed PDE5 inhibitors belonging to different chemical classes with improved pharmacologic profile (e.g. higher potency, improved selectivity, and blood-brain barrier penetration) have been synthesized and evaluated in several animal models of AD. In addition, recent medicinal chemistry effort has led to the development of agents concurrently acting on the PDE5 enzyme and a second target involved in AD. Both marketed and investigational PDE5 inhibitors have shown to reverse cognitive defects in young and aged wild type mice as well as transgenic mouse models of AD and tauopathy using a variety of behavioral tasks. These studies confirmed the therapeutic potential of PDE5 inhibitors as cognitive enhancers. However, clinical studies assessing cognitive functions using marketed PDE5 inhibitors have not been conclusive. Drug discovery efforts by our group and others are currently directed towards the development of novel PDE5 inhibitors tailored to AD with improved pharmacodynamic and pharmacokinetic properties. In summary, the present perspective reports an overview of the correlation between the NO signaling and AD, as well as an outline of the PDE5 inhibitors used as an alternative approach in altering the NO pathway leading to an improvement of learning and memory. The last two sections describe the preclinical and clinical evaluation of PDE5 inhibitors for the treatment of AD, providing a comprehensive analysis of the current status of the AD drug discovery efforts involving PDE5 as a new therapeutic target.

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.

Investigation of distinct molecular pathways in migraine induction using calcitonin gene-related peptide and sildenafil

Objective

Migraine displays clinical heterogeneity of attack features and attack triggers. The question is whether this heterogeneity is explained by distinct intracellular signaling pathways leading to attacks with distinct clinical features. One well-known migraine-inducing pathway is mediated by cyclic adenosine monophosphate and another by cyclic guanosine monophosphate. Calcitonin gene-related peptide triggers migraine via the cyclic adenosine monophosphate pathway and sildenafil via the cyclic guanosine monophosphate pathway. To date, no studies have examined whether migraine induction mediated via the cyclic adenosine monophosphate and cyclic guanosine monophosphate pathways yields similar attacks within the same patients.

Methods

Patients were subjected to migraine induction on two separate days using calcitonin gene-related peptide (1.5 µg/min for 20 minutes) and sildenafil (100 mg) in a double-blind, randomized, double-dummy, cross-over design. Data on headache intensity, characteristics and accompanying symptoms were collected until 24 hours after drug administration.

Results

Thirty-four patients were enrolled and 27 completed both study days. Seventeen patients developed migraine after both study drugs (63%; 95% CI: 42–81). Eight patients developed migraine on one day only (seven after sildenafil and one after calcitonin gene-related peptide). Two patients did not develop migraine on either day. Headache laterality, nausea, photophobia and phonophobia were similar between drugs in 77%, 65%, 100%, and 94%, respectively, of the 17 patients who developed attacks on both days.

Conclusion

A majority of patients developed migraine after both calcitonin gene-related peptide and sildenafil. This supports the hypothesis that the cyclic adenosine monophosphate and cyclic guanosine monophosphate intracellular signaling pathways in migraine induction converge in a common cellular determinator, which ultimately triggers the same attacks. Trial registration: ClinicalTrials.gov Identifier: NCT03143465.

The metabolic face of migraine - from pathophysiology to treatment

Migraine can be regarded as a conserved, adaptive response that occurs in genetically predisposed individuals with a mismatch between the brain's energy reserve and workload. Given the high prevalence of migraine, genotypes associated with the condition seem likely to have conferred an evolutionary advantage. Technological advances have enabled the examination of different aspects of cerebral metabolism in patients with migraine, and complementary animal research has highlighted possible metabolic mechanisms in migraine pathophysiology. An increasing amount of evidence - much of it clinical - suggests that migraine is a response to cerebral energy deficiency or oxidative stress levels that exceed antioxidant capacity and that the attack itself helps to restore brain energy homeostasis and reduces harmful oxidative stress levels. Greater understanding of metabolism in migraine offers novel therapeutic opportunities. In this Review, we describe the evidence for abnormalities in energy metabolism and mitochondrial function in migraine, with a focus on clinical data (including neuroimaging, biochemical, genetic and therapeutic studies), and consider the relationship of these abnormalities with the abnormal sensory processing and cerebral hyper-responsivity observed in migraine. We discuss experimental data to consider potential mechanisms by which metabolic abnormalities could generate attacks. Finally, we highlight potential treatments that target cerebral metabolism, such as nutraceuticals, ketone bodies and dietary interventions.

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.

Opening of ATP-sensitive potassium channels causes migraine attacks: a new target for the treatment of migraine

Migraine is one of the most disabling and prevalent of all disorders. To improve understanding of migraine mechanisms and to suggest a new therapeutic target, we investigated whether opening of ATP-sensitive potassium channels (KATP) would cause migraine attacks. In this randomized, double-blind, placebo-controlled, crossover study, 16 patients aged 18–49 years with one to five migraine attacks a month were randomly allocated to receive an infusion of 0.05 mg/min KATP channel opener levcromakalim and placebo on two different days (ClinicalTrials.gov number, NCT03228355). The primary endpoints were the difference in incidence of migraine attacks, headaches and the difference in area under the curve (AUC) for headache intensity scores (0–12 h) and for middle cerebral artery blood flow velocity (0–2 h) between levcromakalim and placebo. Between 24 May 2017 and 23 November 2017, 16 patients randomly received levcromakalim and placebo on two different days. Sixteen patients (100%) developed migraine attacks after levcromakalim compared with one patient (6%) after placebo (P = 0.0001); the difference of incidence is 94% [95% confidence interval (CI) 78–100%]. The incidence of headache over the 12 h observation period was higher but not significant after levcromakalim (n = 16) than after placebo (n = 7) (P = 0.016) (95% CI 16–71%). The AUC for headache intensity was significantly larger after levcromakalim compared to placebo (AUC0–12h, P < 0.0001). There was no change in mean middle cerebral artery blood flow velocity after levcromakalim compared to placebo (AUC0–2hP = 0.46). Opening of KATP channels caused migraine attacks in all patients. This suggests a crucial role of these channels in migraine pathophysiology and that KATP channel blockers could be potential targets for novel drugs for migraine.

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.