Lack of correlation between vasodilatation and pharmacologically induced immediate headache in healthy subjects

The human NTG model of migraine in drug discovery and development

INTRODUCTION

Various triggers can originate a migraine attack. In healthy volunteers and patients with migraine, the nitroglycerin (NTG) provocation model induces a headache that resembles migraine in pain characteristics and vascular manifestations. This headache is reversible and treatable in monitored conditions, providing an opportunity to test novel antimigraine medications in early clinical development.

AREAS COVERED

This perspective covers the main characteristics and applications of the human NTG model of migraine with effective and ineffective antimigraine therapies.

EXPERT OPINION

The NTG model represents a potential de-risking strategy to test novel hypotheses for antimigraine mechanisms in humans. Considering previous studies conducted with effective and ineffective antimigraine therapies, the sensitivity of the model was 71% while the specificity was 100%. The probability that following an analgesic effect, that compound would truly be efficacious in individuals with migraine was 100%. Following a negative result, the probability that such compound would truly be ineffective in patients with individuals was 33%. A clinical trial testing the analgesic properties of novel compounds after a sublingual and/or intravenous NTG challenge in migraine patients may support a subsequent phase 2 trial for the treatment of migraine.

Migraine attacks are of peripheral origin: the debate goes on

BACKGROUND

Despite the pervasiveness of migraine, the underlying pathophysiological mechanisms initiating migraine attacks are far from well understood and are matter of scientific debate.

OBJECTIVE

In this narrative review, we discuss key evidence for that suggest a peripheral origin or central origin and provide directions for future studies that may provide further clarification.

DISCUSSION

Migraine pathogenesis is considered to involve the trigeminovascular system, a term that encompasses the trigeminal nerve and its axonal projections to the intracranial blood vessels. Beyond any doubt both peripheral and central mechanisms are involved in migraine pathogenesis, but an unresolved question is the how the initial activation occurs in a migraine attack. Evidence favoring a peripheral origin of migraine attacks, i.e., initial events occur outside of the blood-brain barrier, include the importance of sensitization of perivascular sensory afferents early on in a migraine attack. Evidence favoring a central origin include the occurrence of prodromal symptoms, migraine aura, and activation of structures within the central nervous system early in and during a migraine attack.

CONCLUSIONS

Both peripheral and central mechanisms are likely involved in a migraine attack, e.g., peripheral nociceptive input is necessary for pain transmission and cortical activity is necessary for pain perception. Yet, the debate of whether migraine attacks are initiated a peripheral or central site remains unresolved. The increased focus on prodromal symptoms and on the development of a human model of migraine aura will possibly provide key arguments needed to answer this question in the near future. Until then, we cannot draw firm conclusions and the debate goes on.

VIDEO LINK

Video recording of the debate held at the 1st International Conference on Advances in Migraine Sciences (ICAMS 2022, Copenhagen, Denmark) is available at: https://www.youtube.com/watch?v=NC0nlcKohz0 .

Cerebral hemodynamics in the different phases of migraine and cluster headache

Headache is one of the most common ailments; migraine is one of the most prevalent and disabling neurological disorders and cluster headache presents as one of the most excruciating pain disorders. Both are complex disorder characterized by recurrent episodes of headache. A key feature is that various triggers can set off an attack providing the opportunity to explore disease mechanisms by experimentally inducing attacks. This review summarizes neuroimaging and hemodynamic studies in human in provoked and spontaneous attacks of migraine and cluster headache. Cerebral hemodynamics during different phases of the migraine attack demonstrate alterations in cerebral blood flow and perfusion, vessel caliber, cortical and sub-cortical function, underscoring that migraine pathophysiology is highly complex. Migraine attacks might begin in diencephalic and brainstem areas, whereas migraine aura is a cortical phenomenon. In cluster headache pathophysiology, the hypothalamus might also play a pivotal role, whereas the pattern of cerebral blood flood differs from migraine. For both disorders, alterations of arterial blood vessel diameter might be more an epiphenomenon of the attack than a causative trigger. Studying cerebral hemodynamics in provocation models are important in the search for specific biomarkers in the hope to discover future targets for more specific and effective mechanism-based anti-headache treatment.

Sildenafil and calcitonin gene-related peptide dilate intradural arteries: A 3T MR angiography study in healthy volunteers

Background

Sildenafil and calcitonin gene-related peptide are vasoactive substances that induce migraine attacks in patients. The intradural arteries are thought to be involved, but these have never been examined in vivo. Sildenafil is the only migraine-inducing compound for which cephalic, extracranial artery dilation is not reported. Here, we investigate the effects of sildenafil and calcitonin gene-related peptide on the extracranial and intradural parts of the middle meningeal artery.

Methods

In a double-blind, randomized, three-way crossover, placebo-controlled head-to-head comparison study, MR-angiography was recorded in healthy volunteers at baseline and twice after study drug (sildenafil/ calcitonin gene-related peptide/saline) administration. Circumferences of extracranial and intradural middle meningeal artery segments were measured using semi-automated analysis software. The area under the curve for circumference change was compared using paired t-tests between study days.

Results

Twelve healthy volunteers completed the study. The area under the curveBaseline-120min was significantly larger on both the sildenafil and the calcitonin gene-related peptide day in the intradural middle meningeal artery (calcitonin gene-related peptide, p = 0.013; sildenafil, p = 0.027) and the extracranial middle meningeal artery (calcitonin gene-related peptide, p = 0.0003; sildenafil, p = 0.021), compared to placebo. Peak intradural middle meningeal artery dilation was 9.9% (95% CI [2.9–16.9]) after sildenafil (T30min) and 12.5% (95% CI [8.1–16.8]) after calcitonin gene-related peptide (T30min). Peak dilation of the extracranial middle meningeal artery after calcitonin gene-related peptide (T30min) was 15.7% (95% CI [11.2–20.1]) and 18.9% (95% CI [12.8–24.9]) after sildenafil (T120min).

Conclusion

An important novel finding is that both sildenafil and calcitonin gene-related peptide dilate intradural arteries, supporting the notion that all known pharmacological migraine triggers dilate cephalic vessels. We suggest that intradural artery dilation is associated with headache induced by calcitonin gene-related peptide and sildenafil.

Carbon monoxide inhalation induces headache but no migraine in patients with migraine without aura

INTRODUCTION

Carbon monoxide is an endogenously produced signaling gasotransmitter known to cause headache and vasodilation. We hypothesized that inhalation of carbon monoxide would induce migraine-like attacks in migraine without aura patients.

METHODS

In a randomized, double-blind, placebo-controlled crossover design, 12 migraine patients were allocated to inhalation of carbon monoxide (carboxyhemoglobin 22%) or placebo on two separate days. Headache and migraine characteristics were recorded during hospital (0-2 hours) and post-hospital (2-13 hours) phases.

RESULTS

Six patients (50%) developed migraine-like attacks after carbon monoxide compared to two after placebo (16.7%) ( p = 0.289). The median time to onset of migraine-like attacks after carbon monoxide inhalation was 7.5 h (range 3-12) compared to 11.5 h (range 11-12) after placebo. Nine out of 12 patients (75%) developed prolonged headache after carbon monoxide. The area under the curve for headache score (0-13 hours) was increased after carbon monoxide compared with placebo ( p = 0.033).

CONCLUSION

Carbon monoxide inhalation did not provoke more migraine-like attacks in migraine patients compared to placebo, but induced more headache in patients compared to placebo. These data suggest that non-toxic concentrations of carbon monoxide had low potency in migraine induction and that the carbon monoxide inhalation model is not suitable to study migraine.

Human models of migraine - short-term pain for long-term gain

Migraine is a complex disorder characterized by recurrent episodes of headache, and is one of the most prevalent and disabling neurological disorders. A key feature of migraine is that various factors can trigger an attack, and this phenomenon provides a unique opportunity to investigate disease mechanisms by experimentally inducing migraine attacks. In this Review, we summarize the existing experimental models of migraine in humans, including those that exploit nitric oxide, histamine, neuropeptide and prostaglandin signalling. We describe the development and use of these models in the discovery of molecular pathways that are responsible for initiation of migraine attacks. Combining experimental human models with advanced imaging techniques might help to identify biomarkers of migraine, and in the ongoing search for new and better migraine treatments, human models will have a key role in the discovery of future targets for more-specific and more-effective mechanism-based antimigraine drugs.

Carbon monoxide inhalation induces headache in a human headache model

Introduction

Carbon monoxide (CO) is an endogenously produced signalling molecule that has a role in nociceptive processing and cerebral vasodilatation. We hypothesized that inhalation of CO would induce headache and vasodilation of cephalic and extracephalic arteries.

Methods

In a randomized, double-blind, placebo-controlled crossover design, 12 healthy volunteers were allocated to inhalation of CO (carboxyhemoglobin 22%) or placebo on two separate days. Headache was scored on a verbal rating scale from 0–10. We recorded mean blood velocity in the middle cerebral artery (VMCA) by transcranial Doppler, diameter of the superficial temporal artery (STA) and radial artery (RA) by high-resolution ultrasonography and facial skin blood flow by laser speckle contrast imaging.

Results

Ten volunteers developed headache after CO compared to six after placebo. The area under the curve for headache (0–12 hours) was increased after CO compared with placebo ( p = 0.021). CO increased VMCA ( p = 0.002) and facial skin blood flow ( p = 0.012), but did not change the diameter of the STA ( p = 0.060) and RA ( p = 0.433).

Conclusion

In conclusion, the study demonstrated that CO caused mild prolonged headache but no arterial dilatation in healthy volunteers. We suggest this may be caused by a combination of hypoxic and direct cellular effects of CO.

Alcohol-induced headaches: Evidence for a central mechanism?

Alcoholic drinks (ADs) have been reported as a migraine trigger in about one-third of the migraine patients in retrospective studies. Some studies found that ADs trigger also other primary headaches. The studies concerning the role of ADs in triggering various types of primary headaches published after the International Headache Society classification criteria of 1988 were reviewed, and the pathophysiological mechanisms were discussed. Many studies show that ADs are a trigger of migraine without aura (MO), migraine with aura (MA), cluster headache (CH), and tension-type headache (TH). While data on MO and CH are well delineated, those in MA and TH are discordant. There are sparse reports that ADs are also triggers of less frequent types of primary headache such as familial hemiplegic migraine, hemicrania continua, and paroxysmal hemicrania. However, in some countries, the occurrence of alcohol as headache trigger is negligible, perhaps determined by alcohol habits. The frequency estimates vary widely based on the study approach and population. In fact, prospective studies report a limited importance of ADs as migraine trigger. If ADs are capable of triggering practically all primary headaches, they should act at a common pathogenetic level. The mechanisms of alcohol-provoking headache were discussed in relationship to the principal pathogenetic theories of primary headaches. The conclusion was that vasodilatation is hardly compatible with ADs trigger activity of all primary headaches and a common pathogenetic mechanism at cortical, or more likely at subcortical/brainstem, level is more plausible.

Dural administration of inflammatory soup or Complete Freund's Adjuvant induces activation and inflammatory response in the rat trigeminal ganglion

Background

Migraine is a painful disorder with a huge impact on individual and public health. We hypothesize that migraine pain originates from a central mechanism that results secondarily in hypersensitivity in peripheral afferents associated with the cerebral and cranial blood vessels. It has previously been shown that application of inflammatory or algesic substances onto the dura mater or chemical stimulation of the dural receptive fields causes hypersensitivity to mechanical and thermal stimulation together with direct activation of the TG. We asked whether local inflammation of dura mater induces inflammatory activation in the trigeminal ganglion.

Methods

We performed topical administration of inflammatory soup (IS) or Complete Freund’s Adjuvant (CFA) onto an exposed area of the rat dura mater in vivo for 20 min. The window was closed and the rats were sacrificed after 4 h and up to 7 days. Myography was performed on middle meningeal arteries. The trigeminal ganglia were removed and processed for immunohistochemistry or Western blot.

Results

Both CFA and IS induced enhanced expression of pERK1/2, IL-1β and CGRP in the trigeminal ganglia. The pERK1/2 immunoreactivity was mainly seen in the satellite glial cells, while IL-1β reactivity was observed in the neuronal cytoplasm, close to the cell membrane, seemingly as sign of neuro-glial interaction. The CGRP expression in the neurons and nerve fibres was enhanced after the application of either inflammatory agent. Myography resulted in a strong vasoconstrictor response to IS, but not to CFA.

Conclusions

These results suggest that the application of IS or CFA onto the dura mater causes long-term activation of the TG and demonstrate the importance of the neuro-glial interaction in the activation of the trigeminovascular system.

Electronic supplementary material

The online version of this article (doi:10.1186/s10194-015-0564-y) contains supplementary material, which is available to authorized users.

Evaluation of ADMA-DDAH-NOS axis in specific brain areas following nitroglycerin administration: study in an animal model of migraine

BACKGROUND

Nitric oxide (NO) is known to play a key role in migraine pathogenesis, but modulation of NO synthesis has failed so far to show efficacy in migraine treatment. Asymmetric dimethylarginine (ADMA) is a NO synthase (NOS) inhibitor, whose levels are regulated by dimethylarginine dimethylaminohydrolase (DDAH). Systemic administration of nitroglycerin (or glyceryl trinitrate, GTN) is a NO donor that consistently induces spontaneous-like headache attacks in migraneurs. GTN administration induces an increase in neuronal NOS (nNOS) that is simultaneous with a hyperalgesic condition. GTN administration has been used for years as an experimental animal model of migraine. In order to gain further insights in the precise mechanisms involved in the relationships between NO synthesis and migraine, we analyzed changes induced by GTN administration in ADMA levels, DDHA-1 mRNA expression and the expression of neuronal and endothelial NOS (nNOS and eNOS) in the brain. We also evaluated ADMA levels in the serum.

METHODS

Male Sprague-Dawley rats were injected with GTN (10 mg/kg, i.p.) or vehicle and sacrificed 4 h later. Brain areas known to be activated by GTN administration were dissected out and utilized for the evaluation of nNOS and eNOS expression by means of western blotting. Cerebral and serum ADMA levels were measured by means of ELISA immunoassay. Cerebral DDAH-1 mRNA expression was measured by means of RT-PCR. Comparisons between experimental groups were performed using the Mann Whitney test.

RESULTS

ADMA levels and nNOS expression increased in the hypothalamus and medulla following GTN administration. Conversely, a significant decrease in DDAH-1 mRNA expression was observed in the same areas. By contrast, no significant change was reported in eNOS expression. GTN administration did not induce any significant change in serum levels of ADMA.

CONCLUSION

The present data suggest that ADMA accumulates in the brain after GTN administration via the inhibition of DDAH-1. This latter may represent a compensatory response to the excessive local availability of NO, released directly by GTN or synthetized by nNOS. These findings prompt an additional mediator (ADMA) in the modulation of NO axis following GTN administration and offer new insights in the pathophysiology of migraine.

PACAP-38 infusion causes sustained vasodilation of the middle meningeal artery in the rat: possible involvement of mast cells

BACKGROUND

In healthy human volunteers and in migraineurs, pituitary adenylate cyclase-activating polypeptide-38 (PACAP-38) infusion caused sustained vasodilation of the middle meningeal artery (MMA) and an immediate as well as a delayed headache. All the study subjects experienced facial flushing. Mast cells (MCs) might have a role in the long-lasting effect of PACAP-38 infusion. We hypothesized that in mast cell-depleted (MCD) rats the vascular responses to PACAP-38 would be lesser than in control rats because of a lack of vasodilatory products released during MC degranulation.

METHODS

MCs were depleted by chronic treatment with compound 48/80. The effect of 20 minutes' intravenous (i.v.) infusion of calcitonin gene-related peptide (CGRP), PACAP-38, PACAP(6-38) (PAC-1 receptor antagonist) and PACAP-27 on the diameter of the MMA and on mean arterial blood pressure (MABP) in control and MCD rats was recorded by using the genuine closed-cranial window (CCW) model. Vasoactive intestinal polypeptide (VIP) infusion was given only in control rats. A combination of the histamine H1 receptor antagonist mepyramine (4 mg kg(-1) i.v.) and the H2 receptor antagonist famotidine (1 mg kg(-1) i.v.) was given 10 minutes prior to PACAP-38 infusion. Increasing doses of PACAP-38, PACAP-27 and VIP were infused through the intracarotid artery (i.c.) in control and MCD rats to see the direct effects of these peptides on MMA diameter change.

RESULTS

There was no significant change in CGRP-induced MMA diameter increase in control and MCD rats, and the dilated MMA immediately returned back to baseline after stopping the infusion. The delayed MMA dilation induced by PACAP-38 was abolished in MCD and antihistamine (AH)-pretreated rats. Compared to PACAP-38, the PACAP-27 i.v. infusion gave smaller peak dilation of MMA in control rats. In MCD rats, PACAP-27 did not induce any significant dilation. VIP i.v. infusion reduced MABP but did not dilate MMA significantly. PACAP(6-38), which is a potent MC degranulator, also gave a significant delayed dilation of MMA. PACAP-38 i.c. responses (direct receptor mediated response) were not affected by MC depletion. Only the maximum response (% E max) value of PACAP-27 (i.c.) was significantly lower in MCD rats compared to control rats.

CONCLUSIONS

The delayed MMA dilatory responses to PACAP-38 infusion were attenuated in MCD and AH-pretreated rats, indicating a role of the MC mediator-histamine in PACAP-38-induced delayed dilation of MA.

Pearls and pitfalls in human pharmacological models of migraine: 30 years' experience

In vitro studies have contributed to the characterization of receptors in cranial blood vessels and the identification of new possible anti-migraine agents. In vivo animal models enable the study of vascular responses, neurogenic inflammation, peptide release and genetic predisposition and thus have provided leads in the search for migraine mechanisms. All animal-based results must, however, be validated in human studies because so far no animal models can predict the efficacy of new therapies for migraine.

Given the nature of migraine attacks, fully reversible and treatable, the headache- or migraine-provoking property of naturally occurring signaling molecules can be tested in a human model. If such an endogenous substance can provoke migraine in human patients, then it is likely, although not certain, that blocking its effect will be effective in the treatment of acute migraine attacks.

To this end, a human in vivo model of experimental headache and migraine in humans has been developed. Human models of migraine offer unique possibilities to study mechanisms responsible for migraine and to explore the mechanisms of action of existing and future anti-migraine drugs. The human model has played an important role in translational migraine research leading to the identification of three new principally different targets in the treatment of acute migraine attacks and has been used to examine other endogenous signaling molecules as well as genetic susceptibility factors. New additions to the model, such as advanced neuroimaging, may lead to a better understanding of the complex events that constitute a migraine attack, and better and more targeted ways of intervention.

Nitroglycerin-induced changes in facial skin temperature: 'cold nose' as a predictor of headache?

Nitroglycerin (NTG) often induces headaches when used to treat cardiac diseases. Such property of NTG has been widely used in modelling of migraine-like headaches. However, background reasons, predisposing to the development of NTG-headache, are less studied. The main aim of our study was to find, using NTG model, easily accessible markers of the vascular changes associated with headache. Because changes in the blood flow alter the local skin temperature (Tsk), we studied the relationship between the regional changes in the facial Tsk and NTG-induced headaches. Tsk was measured with infrared thermography in 11 healthy women during 3 h after sublingual NTG administration. NTG caused headache in five women, and four of them were the first-degree relatives of migraine patients. Notably, before NTG administration, subjects in the headache group had lower Tsk values, especially in the nose area, than women in the pain-free group (n = 6). NTG-induced headache was associated with a long-lasting increase of Tsk over the baseline. In sharp contrast, in the pain-free group, the Tsk reduced and returned rapidly to the baseline. Thus, the low baseline level and greater increase of regional Tsk correlated with the incidence of headache that supports a role of greater vascular changes in headache happening on the basis of the dissimilarities in vascular tone. An easily accessible phenomenon of 'cold nose' may indicate background vascular dysfunctions in individuals with predisposition to headache. Facial infrared thermography, coupled with NTG administration, suggests a novel temporally controlled approach for non-invasive investigation of vascular processes accompanying headaches.

Headache and mechanical sensitization of human pericranial muscles after repeated intake of monosodium glutamate (MSG)

Background

A single intake of monosodium glutamate (MSG) may cause headache and increased muscle sensitivity. We conducted a double-blinded, placebo-controlled, crossover study to examine the effect of repeated MSG intake on spontaneous pain, mechanical sensitivity of masticatory muscles, side effects, and blood pressure.

Methods

Fourteen healthy subjects participated in 5 daily sessions for one week of MSG intake (150 mg/kg) or placebo (24 mg/kg NaCl) (randomized, double-blinded). Spontaneous pain, pressure pain thresholds and tolerance levels for the masseter and temporalis muscles, side effects, and blood pressure were evaluated before and 15, 30, and 50 min after MSG intake. Whole saliva samples were taken before and 30 min after MSG intake to assess glutamate concentrations.

Results

Headache occurred in 8/14 subjects during MSG and 2/14 during placebo (P = 0.041). Salivary glutamate concentrations on Day 5 were elevated significantly (P < 0.05). Pressure pain thresholds in masseter muscle were reduced by MSG on Day 2 and 5 (P < 0.05). Blood pressure was significantly elevated after MSG (P < 0.040).

Conclusion

In conclusion, MSG induced mechanical sensitization in masseter muscle and adverse effects such as headache and short-lasting blood pressure elevation for which tolerance did not develop over 5 days of MSG intake.

The role of the neurovascular scalp structures in migraine

AIM

To review reports suggesting a role for neurovascular scalp structures in migraine.

MAIN DATA REPORTED

(A) Scalp periarterial nervous fibres contain all the main peptides and receptors involved in pain. (B) It is possible to interrupt or alleviate migraine pain with a prolonged compression of the main scalp arteries, which decreases blood flow through the pain-sensitized vessels and probably induces a temporary conduction block of periarterial nociceptive fibres. (C) Painful points are present on the scalp arteries of a considerable percentage of migraine sufferers. (D) It is possible to stop or alleviate pain by intervening on nociceptive periarterial fibres, as for example with the injection of lidocaine or 3-5 ml saline, and with percutaneous application of a capsaicin cream.

CONCLUSION

The data reported suggest a role for neurovascular scalp structures in at least some patients with migraine. It would be of interest to find a clinical distinction between patients according to the prevalence of an intracranial or extracranial peripheral pain mechanism. This could lead to more efficacious treatments.

Antidromic vasodilatation and the migraine mechanism

Despite the fact that an unprecedented series of new discoveries in neurochemistry, neuroimaging, genetics and clinical pharmacology accumulated over the last 20 years has significantly increased our current knowledge, the underlying mechanism of the migraine headache remains elusive. The present review article addresses, from early evidence that emerged at the end of the nineteenth century, the role of ‘antidromic vasodilatation’ as part of the more general phenomenon, currently defined as neurogenic inflammation, in the unique type of pain reported by patients suffering from migraine headaches. The present paper describes distinctive orthodromic and antidromic properties of a subset of somatosensory neurons, the vascular- and neurobiology of peptides contained in these neurons, and the clinical–pharmacological data obtained in recent investigations using provocation tests in experimental animals and human beings. Altogether, previous and recent data underscore that antidromic vasodilatation, originating from the activation of peptidergic somatosensory neurons, cannot yet be discarded as a major contributing mechanism of the throbbing head pain and hyperalgesia of migraine.