Characterisation of CGRP receptors in the human isolated middle meningeal artery

Pharmacology of erenumab in human isolated coronary and meningeal arteries: Additional effect of gepants on top of a maximum effect of erenumab

BACKGROUND AND PURPOSE

Multiple drugs targeting the calcitonin gene-related peptide (CGRP) receptor have been developed for migraine treatment. Here, the effect of the monoclonal antibody erenumab on CGRP-induced vasorelaxation was investigated in human isolated blood vessels, as well as the effect of combining erenumab with the small molecule drugs, namely rimegepant, olcegepant, or sumatriptan.

EXPERIMENTAL APPROACH

Concentration-response curves to CGRP, adrenomedullin or pramlintide were constructed in human coronary artery (HCA) and human middle meningeal artery (HMMA) segments, incubated with or without erenumab and/or olcegepant. pA2 or pKb values were calculated to determine the potency of erenumab in both tissues. To study whether acutely acting antimigraine drugs exerted additional CGRP-blocking effects on top of erenumab, HCA segments were incubated with a maximally effective concentration of erenumab (3 μM), precontracted with KCl and exposed to CGRP, followed by rimegepant, olcegepant, or sumatriptan in increasing concentrations.

KEY RESULTS

Erenumab shifted the concentration-response curve to CGRP in both vascular tissues. However, in HCA, the Schild plot slope was significantly smaller than unity, whereas this was not the case in HMMA, indicating different CGRP receptor mechanisms in these tissues. In HCA, rimegepant, olcegepant and sumatriptan exerted additional effects on CGRP on top of a maximal effect of erenumab.

CONCLUSIONS AND IMPLICATIONS

Gepants have additional effects on top of erenumab for CGRP-induced relaxation and could be effective in treating migraine attacks in patients already using erenumab as prophylaxis.

Blocking the CGRP Receptor: Differences across Human Vascular Beds

Multiple drugs targeting the calcitonin gene-related peptide (CGRP) receptor have been developed for the treatment of migraine. Here, the effect of the small-molecule CGRP receptor antagonist zavegepant (0.1 nM-1 µM) on CGRP-induced relaxation in isolated human coronary arteries (HCAs) was investigated. A Schild plot was constructed and a pA2 value was calculated to determine the potency of zavegepant. The potency and Schild plot slopes of atogepant, olcegepant, rimegepant, telcagepant, ubrogepant and zavegepant in HCAs and human middle meningeal arteries (HMMAs), obtained from our earlier studies, were compared. Zavegepant shifted the concentration-response curve to CGRP in HCAs. The corresponding Schild plot slope was not different from unity, resulting in a pA2 value of 9.92 ± 0.24. No potency difference between HCAs and HMMAs was observed. Interestingly, olcegepant, atogepant and rimegepant, with a Schild plot slope < 1 in HCAs, were all >1 log unit more potent in HMMAs than in HCAs, while telcagepant, ubrogepant and zavegepant, with a Schild plot slope not different from unity, showed similar (<1 log difference) potency across both tissues. As a Schild plot slope < 1 may point to the involvement of multiple receptors, it is important to further identify the receptors involved in the relaxation to CGRP in HCAs, which may be used to improve the cardiovascular safety of future antimigraine drugs.

New Insights on Metabolic and Genetic Basis of Migraine: Novel Impact on Management and Therapeutical Approach

Migraine is a hereditary disease, usually one-sided, sometimes bilateral. It is characterized by moderate to severe pain, which worsens with physical activity and may be associated with nausea and vomiting, may be accompanied by photophobia and phonophobia. The disorder can occur at any time of the day and can last from 4 to 72 h, with and without aura. The pathogenic mechanism is unclear, but extensive preclinical and clinical studies are ongoing. According to electrophysiology and imaging studies, many brain areas are involved, such as cerebral cortex, thalamus, hypothalamus, and brainstem. The activation of the trigeminovascular system has a key role in the headache phase. There also appears to be a genetic basis behind the development of migraine. Numerous alterations have been identified, and in addition to the genetic cause, there is also a close association with the surrounding environment, as if on the one hand, the genetic alterations may be responsible for the onset of migraine, on the other, the environmental factors seem to be more strongly associated with exacerbations. This review is an analysis of neurophysiological mechanisms, neuropeptide activity, and genetic alterations that play a fundamental role in choosing the best therapeutic strategy. To date, the goal is to create a therapy that is as personalized as possible, and for this reason, steps forward have been made in the pharmacological field in order to identify new therapeutic strategies for both acute treatment and prophylaxis.

Hypervigilance, Allostatic Load, and Migraine Prevention: Antibodies to CGRP or Receptor

Migraine involves brain hypersensitivity with episodic dysfunction triggered by behavioral or physiological stressors. During an acute migraine attack the trigeminal nerve is activated (peripheral sensitization). This leads to central sensitization with activation of the central pathways including the trigeminal nucleus caudalis, the trigemino-thalamic tract, and the thalamus. In episodic migraine the sensitization process ends with the individual act, but with chronic migraine central sensitization may continue interictally. Increased allostatic load, the consequence of chronic, repeated exposure to stressors, leads to central sensitization, lowering the threshold for future neuronal activation (hypervigilance). Ostensibly innocuous stressors are then sufficient to trigger an attack. Medications that reduce sensitization may help patients who are hypervigilant and help to balance allostatic load. Acute treatments and drugs for migraine prevention have traditionally been used to reduce attack duration and frequency. However, since many patients do not fully respond, an unmet treatment need remains. Calcitonin gene-related peptide (CGRP) is a vasoactive neuropeptide involved in nociception and in the sensitization of peripheral and central neurons of the trigeminovascular system, which is implicated in migraine pathophysiology. Elevated CGRP levels are associated with dysregulated signaling in the trigeminovascular system, leading to maladaptive responses to behavioral or physiological stressors. CGRP may, therefore, play a key role in the underlying pathophysiology of migraine. Increased understanding of the role of CGRP in migraine led to the development of small-molecule antagonists (gepants) and monoclonal antibodies (mAbs) that target either CGRP or the receptor (CGRP-R) to restore homeostasis, reducing the frequency, duration, and severity of attacks. In clinical trials, US Food and Drug Administration-approved anti-CGRP-R/CGRP mAbs were well tolerated and effective as preventive migraine treatments. Here, we explore the role of CGRP in migraine pathophysiology and the use of gepants or mAbs to suppress CGRP-R signaling via inhibition of the CGRP ligand or receptor.

Identifying New Antimigraine Targets: Lessons from Molecular Biology

Primary headaches are one of the most common conditions; migraine being most prevalent. Recent work on the pathophysiology of migraine suggests a mismatch in the communication or tuning of the trigeminovascular system, leading to sensitization and the release of calcitonin gene-related peptide (CGRP). In the current Opinion, we use the up-to-date molecular understanding of mechanisms behind migraine pain, to provide novel aspects on how to modify the system and for the development of future treatments; acute as well as prophylactic. We explore the distribution and the expression of neuropeptides themselves, as well as certain ion channels, and most importantly how they may act in concert as modulators of excitability of both the trigeminal C neurons and the Aδ neurons.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Anti-migraine Calcitonin Gene-Related Peptide Receptor Antagonists Worsen Cerebral Ischemic Outcome in Mice

Objective

Calcitonin gene–related peptide (CGRP) pathway inhibitors are emerging treatments for migraine. CGRP‐mediated vasodilation is, however, a critical rescue mechanism in ischemia. We, therefore, investigated whether gepants, small molecule CGRP receptor antagonists, worsen cerebral ischemia.

Methods

Middle cerebral artery was occluded for 12 to 60 minutes in mice. We compared infarct risk and volumes, collateral flow, and neurological deficits after pretreatment with olcegepant (single or 10 daily doses of 0.1–1mg/kg) or rimegepant (single doses of 10–100mg/kg) versus vehicle. We also determined their potency on CGRP‐induced relaxations in mouse and human vessels, in vitro.

Results

Olcegepant (1mg/kg, single dose) increased infarct risk after 12‐ to 20‐minute occlusions mimicking transient ischemic attacks (14/19 vs 6/18 with vehicle, relative risk = 2.21, p < 0.022), and doubled infarct volumes (p < 0.001) and worsened neurological deficits (median score = 9 vs 5 with vehicle, p = 0.008) after 60‐minute occlusion. Ten daily doses of 0.1 to 1mg/kg olcegepant yielded similar results. Rimegepant 10mg/kg increased infarct volumes by 60% after 20‐minute ischemia (p = 0.03); 100mg/kg caused 75% mortality after 60‐minute occlusion. In familial hemiplegic migraine type 1 mice, olcegepant 1mg/kg increased infarct size after 30‐minute occlusion (1.6‐fold, p = 0.017). Both gepants consistently diminished collateral flow and reduced reperfusion success. Olcegepant was 10‐fold more potent than rimegepant on CGRP‐induced relaxations in mouse aorta.

Interpretation

Gepants worsened ischemic stroke in mice via collateral dysfunction. CGRP pathway blockers might thus aggravate coincidental cerebral ischemic events. The cerebrovascular safety of these agents must therefore be better delineated, especially in patients at increased risk of ischemic events or on prophylactic CGRP inhibition. ANN NEUROL 2020;88:771–784

Pharmacological treatment of migraine: CGRP and 5-HT beyond the triptans

Migraine is a highly disabling neurovascular disorder characterized by a severe headache (associated with nausea, photophobia and/or phonophobia), and trigeminovascular system activation involving the release of calcitonin-gene related peptide (CGRP). Novel anti-migraine drugs target CGRP signaling through either stimulation of 5-HT1F receptors on trigeminovascular nerves (resulting in inhibition of CGRP release) or direct blockade of CGRP or its receptor. Lasmiditan is a highly selective 5-HT1F receptor agonist and, unlike the triptans, is devoid of vasoconstrictive properties, allowing its use in patients with cardiovascular risk. Since lasmiditan can actively penetrate the blood-brain barrier, central therapeutic as well as side effects mediated by 5-HT1F receptor activation should be further investigated. Other novel anti-migraine drugs target CGRP signaling directly. This neuropeptide can be targeted by the monoclonal antibodies eptinezumab, fremanezumab and galcanezumab, or by CGRP-neutralizing L-aptamers called Spiegelmers. The CGRP receptor can be targeted by the monoclonal antibody erenumab, or by small-molecule antagonists called gepants. Currently, rimegepant and ubrogepant have been developed for acute migraine treatment, while atogepant is studied for migraine prophylaxis. Of these drugs targeting CGRP signaling directly, eptinezumab, erenumab, fremanezumab, galcanezumab, rimegepant and ubrogepant have been approved for clinical use, while atogepant is in the last stage before approval. Although all of these drugs seem highly promising for migraine treatment, their safety should be investigated in the long-term. Moreover, the exact mechanism(s) of action of these drugs need to be elucidated further, to increase both safety and efficacy and to increase the number of responders to the different treatments, so that all migraine patients can satisfactorily be treated.

Targeting CGRP for migraine treatment: mechanisms, antibodies, small molecules, perspectives

INTRODUCTION

Calcitonin Gene-Related Peptide (CGRP) has gradually emerged as a suitable therapeutic target to treat migraine. Considering the social and economic burden of migraine, it is fundamental to optimize the disease management with efficacious and safe treatments. In this scenario, drugs targeting GCRP, monoclonal antibodies (MoAbs) and gepants, represent new therapeutic strategies.

AREAS COVERED

In the present work, the authors aim at appraising the main insights and implications of treatments targeting CGRP by reviewing pathophysiology and clinical information.

EXPERT OPINION

Anti-CGRP MoAbs are the first migraine-specific preventive treatments representing a suitable option especially for difficult-to-treat patients. They can be safely administered for long periods even in association with preventatives acting on different targets. Gepants are a safe alternative to triptans for the acute management of migraine and are currently being tested for prevention, thus representing the first transitional molecules for disease therapy. In the future, it might be possible to adapt the treatment according to patients' characteristics and disease phenotype even combining the two treatments targeting the CGRP pathway.

Calcitonin Gene-Related Peptide (CGRP) and Cluster Headache

Cluster headache (CH) is a severe primary headache with a prevalence of 1/1000 individuals, and a predominance in men. Calcitonin gene-related peptide (CGRP) is a potent vasodilator, originating in trigeminal neurons and has a central role in CH pathophysiology. CGRP and the CGRP receptor complex have recently taken center stage as therapeutic targets for primary headaches, such as migraine. Multiple CGRP and CGRP receptor monoclonal antibodies, as well as small molecule antagonists (gepants) are on their way constituting a new frontier of migraine and possibly CH medication. During a CH attack, there is an activation of the trigeminal-autonomic reflex with the release of CGRP, and inversely if CGRP is administered to a CH patient in an active disease phase, it triggers an attack. Increased levels of CGRP have been found in ipsilateral jugular vein blood during the active phase of CH. This process is hypothesized to have a key role in the intense pain perception and in the associated distinctive vasodilation. So far, clinical tests of CGRP antibodies have been inconclusive in CH patients. This review summarizes the current state of knowledge on the role of CGRP in CH pathology, and as a target for future treatments.

Characterisation of the calcitonin gene-related peptide receptor antagonists ubrogepant and atogepant in human isolated coronary, cerebral and middle meningeal arteries

BACKGROUND

Migraine has been associated with a dysfunctional activation of the trigeminovascular system. Calcitonin gene-related peptide, a neuropeptide released from the trigeminal nerve fibres, has an important role in the pathophysiology of migraine and is a current therapeutic target for migraine treatment.

METHODS

We examined the effects of two novel calcitonin gene-related peptide receptor antagonists, ubrogepant and atogepant, on the relaxations induced by α calcitonin gene-related peptide in human isolated middle meningeal, cerebral and coronary arteries. Furthermore, the contractile responses to atogepant and ubrogepant per se were studied and compared to the responses elicited by zolmitriptan in proximal and distal human coronary arteries.

RESULTS

In intracranial arteries, both blockers antagonized the calcitonin gene-related peptide-induced relaxations more potently when compared to the inhibition observed in distal human coronary arteries, with atogepant showing a higher potency. When analysing their antagonistic profile in HCA, ubrogepant showed a competitive antagonist profile, while atogepant showed a non-competitive one. Neither of the gepants had vasoconstrictor effect at any of the concentrations studied in human coronary arteries, whereas zolmitriptan elicited concentration-dependent contractions.

CONCLUSION

ubrogepant and atogepant differentially inhibit the calcitonin gene-related peptide-dependent vasodilatory responses in intracranial arteries when compared to distal human coronary arteries. Also, both gepants are devoid of vasoconstrictive properties in human coronary arteries.

Characterisation of vasodilatory responses in the presence of the CGRP receptor antibody erenumab in human isolated arteries

BACKGROUND

Migraine is associated with activation of the trigeminovascular system, release of calcitonin gene-related peptide (CGRP) and dilation of dural arteries. Novel treatments target calcitonin gene-related peptide or its receptor, which are present in all vascular beds, raising cardiovascular concerns. Erenumab is a human CGRP-receptor antibody approved for the prophylactic treatment of migraine.

METHODS

We characterised the relaxant responses to CGRP in the absence and presence of erenumab (1 μM) in isolated human middle meningeal, internal mammary and (proximal and distal) coronary arteries. Furthermore, in human internal mammary arteries from cardiovascularly-compromised patients, we assessed the pharmacological specificity of erenumab by investigating whether the vasodilatory responses to acetylcholine, sodium nitroprusside, pituitary adenylate cyclase activating polypeptide-38 (PACAP), vasoactive intestinal peptide and nicardipine, along with the vasoconstrictor responses to dihydroergotamine, were modified by erenumab.

RESULTS

Calcitonin gene-related peptide induced concentration-dependent vasodilatory responses in all vessels studied that were significantly antagonised by erenumab. In human internal mammary arteries from cardiovascularly-compromised patients, the responses to acetylcholine, sodium nitroprusside, PACAP, vasoactive intestinal peptide, nicardipine and dihydroergotamine were unaffected by erenumab.

CONCLUSION

Erenumab inhibits calcitonin gene-related peptide-induced vasodilatory responses in human middle meningeal arteries, human internal mammary arteries and human coronary arteries. Moreover, erenumab shows functional specificity as no interaction was observed with the relaxant responses to several vasodilators, nor the dihydroergotamine-dependent vasoconstrictor responses.

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.

Triptans and CGRP blockade - impact on the cranial vasculature

The trigeminovascular system plays a key role in the pathophysiology of migraine. The activation of the trigeminovascular system causes release of various neurotransmitters and neuropeptides, including serotonin and calcitonin gene-related peptide (CGRP), which modulate pain transmission and vascular tone. Thirty years after discovery of agonists for serotonin 5-HT1B and 5-HT1D receptors (triptans) and less than fifteen after the proof of concept of the gepant class of CGRP receptor antagonists, we are still a long way from understanding their precise site and mode of action in migraine. The effect on cranial vasculature is relevant, because all specific anti-migraine drugs and migraine pharmacological triggers may act in perivascular space. This review reports the effects of triptans and CGRP blocking molecules on cranial vasculature in humans, focusing on their specific relevance to migraine treatment.

Experimental inflammation following dural application of complete Freund's adjuvant or inflammatory soup does not alter brain and trigeminal microvascular passage

Background

Migraine is a paroxysmal, disabling primary headache that affects 16 % of the adult population. In spite of decades of intense research, the origin and the pathophysiology mechanisms involved are still not fully known. Although triptans and gepants provide effective relief from acute migraine for many patients, their site of action remains unidentified. It has been suggested that during migraine attacks the leakiness of the blood-brain barrier (BBB) is altered, increasing the passage of anti-migraine drugs. This study aimed to investigate the effect of experimental inflammation, following dural application of complete Freund’s adjuvant (CFA) or inflammatory soup (IS) on brain and trigeminal microvascular passage.

Methods

In order to address this issue, we induced local inflammation in male Sprague-Dawley-rats dura mater by the addition of CFA or IS directly on the dural surface. Following 2, 24 or 48 h of inflammation we calculated permeability-surface area product (PS) for [⁵¹Cr]-EDTA in the trigeminal ganglion (TG), spinal trigeminal nucleus, cortex, periaqueductal grey and cerebellum.

Results

We observed that [⁵¹Cr]-EDTA did not pass into the central nervous system (CNS) in a major way. However, [⁵¹Cr]-EDTA readily passed the TG by >30 times compared to the CNS. Application of CFA or IS did not show altered transfer constants.

Conclusions

With these experiments we show that dural IS/CFA triggered TG inflammation, did not increase the BBB passage, and that the TG is readily exposed to circulating molecules. The TG could provide a site of anti-migraine drug interaction with effect on the trigeminal system.

Electronic supplementary material

The online version of this article (doi:10.1186/s10194-015-0575-8) contains supplementary material, which is available to authorized users.

Meningeal blood flow is controlled by H2 S-NO crosstalk activating a HNO-TRPA1-CGRP signalling pathway

BACKGROUND AND PURPOSE

Meningeal blood flow is controlled by CGRP released from trigeminal afferents and NO mainly produced in arterial endothelium. The vasodilator effect of NO may be due to the NO-derived compound, nitroxyl (HNO), generated through reaction with endogenous H2 S. We investigated the involvement of HNO in CGRP release and meningeal blood flow.

EXPERIMENTAL APPROACH

Blood flow in exposed dura mater of rats was recorded by laser Doppler flowmetry. CGRP release from the dura mater in the hemisected rat head was quantified using an elisa. NO and H2 S were localized histochemically with specific sensors.

KEY RESULTS

Topical administration of the NO donor diethylamine-NONOate increased meningeal blood flow by 30%. Pretreatment with oxamic acid, an inhibitor of H2 S synthesis, reduced this effect. Administration of Na2 S increased blood flow by 20%, an effect abolished by the CGRP receptor antagonist CGRP8-37 or the TRPA1 channel antagonist HC030031 and reduced when endogenous NO synthesis was blocked. Na2 S dose-dependently increased CGRP release two- to threefold. Co-administration of diethylamine-NONOate facilitated CGRP release, while inhibition of endogenous NO or H2 S synthesis lowered basal CGRP release. NO and H2 S were mainly localized in arterial vessels, HNO additionally in nerve fibre bundles. HNO staining was lost after treatment with L-NMMA and oxamic acid.

CONCLUSIONS AND IMPLICATIONS

NO and H2 S cooperatively increased meningeal blood flow by forming HNO, which activated TRPA1 cation channels in trigeminal fibres, inducing CGRP release. This HNO-TRPA1-CGRP signalling pathway may be relevant to the pathophysiology of headaches.

CGRP receptor antagonists and antibodies against CGRP and its receptor in migraine treatment

Recently developed calcitonin gene-related peptide (CGRP) receptor antagonistic molecules have shown promising results in clinical trials for acute treatment of migraine attacks. Drugs from the gepant class of CGRP receptor antagonists are effective and do not cause vasoconstriction, one of the major limitations in the use of triptans. However their use had to be discontinued because of risk of liver toxicity after continuous exposure. As an alternative approach to block CGRP transmission, fully humanized monoclonal antibodies towards CGRP and the CGRP receptor have been developed for treatment of chronic migraine (attacks >15 days/month). Initial results from phase I and II clinical trials have revealed promising results with minimal side effects and significant relief from chronic migraine as compared with placebo. The effectiveness of these various molecules raises the question of where is the target site(s) for antimigraine action. The gepants are small molecules that can partially pass the blood-brain barrier (BBB) and therefore, might have effects in the CNS. However, antibodies are large molecules and have limited possibility to pass the BBB, thus effectively excluding them from having a major site of action within the CNS. It is suggested that the antimigraine site should reside in areas not limited by the BBB such as intra- and extracranial vessels, dural mast cells and the trigeminal system. In order to clarify this topic and surrounding questions, it is important to understand the localization of CGRP and the CGRP receptor components in these possible sites of migraine-related regions and their relation to the BBB.

Chemical mediators of migraine: preclinical and clinical observations

Migraine is a neurovascular disorder, and although the pathophysiology of migraine has not been fully delineated, much has been learned in the past 50 years. This knowledge has been accompanied by significant advancements in the way migraine is viewed as a disease process and in the development therapeutic options. In this review, we will focus on 4 mediators (nitric oxide, histamine, serotonin, and calcitonin gene-related peptide) which have significantly advanced our understanding of migraine as a disease entity. For each mediator we begin by reviewing the preclinical data linking it to migraine pathophysiology, first focusing on the vascular mechanisms, then the neuronal mechanisms. The preclinical data are then followed by a review of the clinical data which support each mediator's role in migraine and highlights the pharmacological agents which target these mediators for migraine therapy.

Effect of CGRP and sumatriptan on the BOLD response in visual cortex

To test the hypothesis that calcitonin gene-related peptide (CGRP) modulates brain activity, we investigated the effect of intravenous CGRP on brain activity in response to a visual stimulus. In addition, we examined if possible alteration in brain activity was reversed by the anti-migraine drug sumatriptan. Eighteen healthy volunteers were randomly allocated to receive CGRP infusion (1.5 μg/min for 20 min) or placebo. In vivo activity in the visual cortex was recorded before, during and after infusion and after 6 mg subcutaneous sumatriptan by functional magnetic resonance imaging (3 T). 77% of the participants reported headache after CGRP. We found no changes in brain activity after CGRP (P = 0.12) or after placebo (P = 0.41). Sumatriptan did not affect brain activity after CGRP (P = 0.71) or after placebo (P = 0.98). Systemic CGRP or sumatriptan has no direct effects on the BOLD activity in visual cortex. This suggests that in healthy volunteers both CGRP and sumatriptan may exert their actions outside of the blood–brain barrier.

Characterization of capsaicin induced responses in mice vas deferens: evidence of CGRP uptake

Calcitonin gene-related peptide (CGRP) is extensively distributed in primary afferent sensory nerves, including those innervating the genitourinary tract. Capsaicin can stimulate the release of CGRP from intracellular stores of these nerves, but this phenomenon has not been investigated in-depth in isolated preparations. The present study sets out to study and characterize the capsaicin as well as CGRP-induced responses in isolated mouse vas deferens. The effects of capsaicin and CGRP family of peptides were studied on electrically-induced twitch responses in the absence or presence of transient receptor potential cation channel vanilloid subfamily member 1 (TRPV1) antagonist and CGRP receptor antagonists. Twitch responses were attenuated by capsaicin (1nM-30nM) and CGRP family of peptides. The potency order was CGRP>intermedin-long (IMDL)~[Cys(Et)(2,7)]αCGRP~adrenomedullin (AM)>[Cys(ACM)(2,7)]αCGRP>amylin (AMY). These responses were disinhibited by the CGRP receptor antagonists and TRPV1 antagonists. The addition of CGRP receptor antagonists caused a transient potentiation of the twitch response and this potentiation was blocked by pretreatment with capsaicin and enhanced by incubation with exogenous CGRP. During the second consecutive cumulative concentration-response curve with capsaicin, the first phase of concentration-response curve disappeared and this was partially restored when the mouse vas deferens was preincubated with CGRP, suggesting the uptake of exogenous CGRP by nerves. Besides showing capsaicin-induced CGRP releases this study shows that exogenous CGRP can be taken up in vas deferens and can be re-released. CGRP uptake will add another dimension in understanding the homeostasis of this neuropeptide.

Calcitonin gene-related peptide inhibits chemokine production by human dermal microvascular endothelial cells

This study examined whether the sensory neuropeptide calcitonin gene-related peptide (CGRP) inhibits release of chemokines by dermal microvascular endothelial cells. Dermal blood vessels are associated with nerves containing CGRP, suggesting that CGRP-containing nerves may regulate cutaneous inflammation through effects on vessels. We examined CGRP effects on stimulated chemokine production by a human dermal microvascular endothelial cell line (HMEC-1) and primary human dermal microvascular endothelial cells (pHDMECs). HMEC-1 cells and pHDMECs expressed mRNA for components of the CGRP and adrenomedullin receptors and CGRP inhibited LPS-induced production of the chemokines CXCL8, CCL2, and CXCL1 by both HMEC-1 cells and pHDMECs. The receptor activity-modifying protein (RAMP)1/calcitonin receptor-like receptor (CL)-specific antagonists CGRP₈-₃₇ and BIBN4096BS, blocked this effect of CGRP in a dose-dependent manner. CGRP prevented LPS-induced IκBα degradation and NF-κB binding to the promoters of CXCL1, CXCL8 and CCL2 in HMEC-1 cells and Bay 11-7085, an inhibitor of NF-κB activation, suppressed LPS-induced production of CXCL1, CXCL8 and CCL2. Thus, the NF-κB pathway appears to be involved in CGRP-mediated suppression of chemokine production. Accordingly, CGRP treatment of LPS-stimulated HMEC-1 cells inhibited their ability to chemoattract human neutrophils and mononuclear cells. Elucidation of this pathway may suggest new avenues for therapeutic manipulation of cutaneous inflammation.

The relevance of preclinical research models for the development of antimigraine drugs: focus on 5-HT(1B/1D) and CGRP receptors

Migraine is a complex neurovascular syndrome, causing a unilateral pulsating headache with accompanying symptoms. The past four decades have contributed immensely to our present understanding of migraine pathophysiology and have led to the introduction of specific antimigraine therapies, much to the relief of migraineurs. Pathophysiological factors culminating into migraine headaches have not yet been completely deciphered and, thus, pose an additional challenge for preclinical research in the absence of any direct experimental marker. Migraine provocation experiments in humans use a head-score to evaluate migraine, as articulated by the volunteer, which cannot be applied to laboratory animals. Therefore, basic research focuses on different symptoms and putative mechanisms, one at a time or in combination, to validate the hypotheses. Studies in several species, utilizing different preclinical approaches, have significantly contributed to the two antimigraine principles in therapeutics, namely: 5-HT(1B/1D) receptor agonists (known as triptans) and CGRP receptor antagonists (known as gepants). This review will analyze the preclinical experimental models currently known for the development of these therapeutic principles, which are mainly based on the vascular and/or neurogenic theories of migraine pathogenesis. These include models based on the involvement of cranial vasodilatation and/or the trigeminovascular system in migraine. Clearly, the preclinical strategies should involve both approaches, while incorporating the newer ideas/techniques in order to get better insights into migraine pathophysiology.

Characterization of the calcitonin gene-related peptide receptor antagonist telcagepant (MK-0974) in human isolated coronary arteries

The sensory neuropeptide calcitonin gene-related peptide (CGRP) plays a role in primary headaches, and CGRP receptor antagonists are effective in migraine treatment. CGRP is a potent vasodilator, raising the possibility that antagonism of its receptor could have cardiovascular effects. We therefore investigated the effects of the antimigraine CGRP receptor antagonist telcagepant (MK-0974) [N-[(3R,6S)-6-(2,3-difluorophenyl)-2-oxo-1-(2,2,2-trifluoroethyl)azepan-3-yl]-4-(2-oxo-2,3-dihydro-1H-imidazo[4,5-b]pyridine-1-yl)piperidine-1-carboxamide] on human isolated coronary arteries. Arteries with different internal diameters were studied to assess the potential for differential effects across the coronary vascular bed. The concentration-dependent relaxation responses to human alphaCGRP were greater in distal coronary arteries (i.d. 600-1000 microm; E(max) = 83 +/- 7%) than proximal coronary arteries (i.d. 2-3 mm; E(max) = 23 +/- 9%), coronary arteries from explanted hearts (i.d. 3-5 mm; E(max) = 11 +/- 3%), and coronary arterioles (i.d. 200-300 microm; E(max) = 15 +/- 7%). Telcagepant alone did not induce contraction or relaxation of these coronary blood vessels. Pretreatment with telcagepant (10 nM to 1 microM) antagonized alphaCGRP-induced relaxation competitively in distal coronary arteries (pA(2) = 8.43 +/- 0.24) and proximal coronary arteries and coronary arterioles (1 microM telcagepant, giving pK(B) = 7.89 +/- 0.13 and 7.78 +/- 0.16, respectively). alphaCGRP significantly increased cAMP levels in distal, but not proximal, coronary arteries, and this was abolished by pretreatment with telcagepant. Immunohistochemistry revealed the expression and colocalization of the CGRP receptor elements calcitonin-like receptor and receptor activity-modifying protein 1 in the smooth muscle cells in the media layer of human coronary arteries. These findings in vitro support the cardiovascular safety of CGRP receptor antagonists and suggest that telcagepant is unlikely to induce coronary side effects under normal cardiovascular conditions.

Effect of the calcitonin gene-related peptide (CGRP) receptor antagonist telcagepant in human cranial arteries

Introduction: Calcitonin gene-related peptide (CGRP) is a neuronal messenger in intracranial sensory nerves and is considered to play a significant role in migraine pathophysiology.

Materials and methods: We investigated the effect of the CGRP receptor antagonist, telcagepant, on CGRP-induced cranial vasodilatation in human isolated cerebral and middle meningeal arteries. We also studied the expression of the CGRP receptor components in cranial arteries with immunocytochemistry. Concentration response curves to αCGRP were performed in human isolated cerebral and middle meningeal arteries in the absence or presence of telcagepant. Arterial slices were stained for RAMP1, CLR and actin in a double immunofluorescence staining.

Results: In both arteries, we found that: (i) telcagepant was devoid of any contractile or relaxant effects per se; (ii) pretreatment with telcagepant antagonised the αCGRP-induced relaxation in a competitive manner; and (iii) immunohistochemistry revealed expression and co-localisation of CLR and RAMP1 in the smooth muscle cells in the media layer of both arteries.

Conclusions: Our findings provide morphological and functional data on the presence of CGRP receptors in cerebral and meningeal arteries, which illustrates a possible site of action of telcagepant in the treatment of migraine.

The middle meningial artery during a migraine attack: 3T magnetic resonance angiography study

We performed 3T magnetic resonance angiography (MRA) during a spontaneous migraine attack. The patient was a 42-year-old woman migraineur diagnosed by the IHS criteria. The change of the middle meningial artery (MMA) was measured on the axial brain images using MATLAB for three phases (attack-free period, during an attack, a period after medication). There were no dramatic changes of vasodilation in the MMA during the attack (2.0 mm), attack-free period (diameter 1.9 mm), or period after medication (1.7 mm), resembling extrapolations of observations in experimental animal models. This finding suggests that the dramatic vasomotion might not be associated with migraine pathophysiology.

The involvement of CGRP, adrenomedullin, and sensory nerves in remote vasomotor responses within the hamster cheek pouch microcirculation

Previous work from our laboratory demonstrated a role for sensory nerves in remote dilations to microapplied methacholine by blocking the response with CGRP8-37 and concluded CGRP was the neurotransmitter. Recently, a more specific CGRP receptor antagonist, BIBN4096BS, was developed. The goals of the present study are to characterize the effects of BIBN4096BS on vasomotor responses in the hamster cheek pouch microcirculation, and to verify the role of CGRP in remote dilations to capsaicin and methacholine and to test adrenomedullin as an alternative neurotransmitter. BIBN4096BS pretreatment inhibits dilation to CGRP while having no significant effect on baseline diameter, it shifts the EC(50) to superfused CGRP from 1.5+/-0.3 pM to 2.5+/-0.6 nM and it shifts the apparent EC(50) to capsaicin from 31.5 nM to 171 nM. Local and remote dilations caused by the microapplication of methacholine are not inhibited by 300 nM BIBN4096BS (Local: 9.7+/-1.2 versus 9.7+/-1.5; 500:5.5+/-0.4 versus 5.7+/-0.5; 1000:4.4+/-0.6 versus 4.8+/-0.5). Remote dilations to methacholine were significantly inhibited however when adrenomedullin receptor antagonist adrenomedullin-(26-52) was microapplied to the remote site. Perivascular neurons containing adrenomedullin can be detected with immunohistochemistry. The results, combined with previous work, suggest that adrenomedullin, and not CGRP, is involved in remote dilations to methacholine.

Current and prospective pharmacological targets in relation to antimigraine action

Migraine is a recurrent incapacitating neurovascular disorder characterized by unilateral and throbbing headaches associated with photophobia, phonophobia, nausea, and vomiting. Current specific drugs used in the acute treatment of migraine interact with vascular receptors, a fact that has raised concerns about their cardiovascular safety. In the past, alpha-adrenoceptor agonists (ergotamine, dihydroergotamine, isometheptene) were used. The last two decades have witnessed the advent of 5-HT(1B/1D) receptor agonists (sumatriptan and second-generation triptans), which have a well-established efficacy in the acute treatment of migraine. Moreover, current prophylactic treatments of migraine include 5-HT(2) receptor antagonists, Ca(2+) channel blockers, and beta-adrenoceptor antagonists. Despite the progress in migraine research and in view of its complex etiology, this disease still remains underdiagnosed, and available therapies are underused. In this review, we have discussed pharmacological targets in migraine, with special emphasis on compounds acting on 5-HT (5-HT(1-7)), adrenergic (alpha(1), alpha(2,) and beta), calcitonin gene-related peptide (CGRP(1) and CGRP(2)), adenosine (A(1), A(2), and A(3)), glutamate (NMDA, AMPA, kainate, and metabotropic), dopamine, endothelin, and female hormone (estrogen and progesterone) receptors. In addition, we have considered some other targets, including gamma-aminobutyric acid, angiotensin, bradykinin, histamine, and ionotropic receptors, in relation to antimigraine therapy. Finally, the cardiovascular safety of current and prospective antimigraine therapies is touched upon.

Neurovascular pharmacology of migraine

Migraine is a paroxysmal neurovascular disorder, which affects a significant proportion of the population. Since dilation of cranial blood vessels is likely to be responsible for the headache experienced in migraine, many experimental models for the study of migraine have focussed on this feature. The current review discusses a model that is based on the constriction of carotid arteriovenous anastomoses in anaesthetized pigs, which has during the last decades proven of great value in identifying potential antimigraine drugs acting via a vascular mechanism. Further, the use of human isolated blood vessels in migraine research is discussed. Thirdly, we describe an integrated neurovascular model, where dural vasodilatation in response to trigeminal perivascular nerve stimulation can be studied. Such a model not only allows an in-depth characterization of directly vascularly acting drugs, but also of drugs that are supposed to act via inhibition of vasodilator responses to endogenous neuropeptides, or of drugs that inhibit the release of these neuropeptides. We discuss the use of this model in a study on the influence of female sex hormones on migraine. Finally, the implementation of this model in mice is considered. Such a murine model allows the use of genetically modified animals, which will lead to a better understanding of the ion channel mutations that are found in migraine patients.

Increased expression in calcitonin-like receptor induced by aldosterone in cerebral arteries from spontaneously hypertensive rats does not correlate with functional role of CGRP receptor

OBJECTIVE

To analyze the effect of aldosterone on the expression of calcitonin gene-related peptide (CGRP) receptor components, calcitonin-like receptor (CL receptor) and receptor activity modifying protein 1 (RAMP1), as well as the effect of this mineralocorticoid on CGRP-mediated vasodilation in middle cerebral arteries from Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR).

RESULTS

CGRP 0.1 nM-0.1 microM induced a concentration-dependent relaxation that was nitric oxide independent and higher in SHR middle cerebral arteries. CL receptor and RAMP1 expression were similar in both strains. The relaxation to CGRP was not modified by aldosterone 1 microM in either strain, although aldosterone 1 microM increased expression of CL receptor without modifying RAMP1 in segments from SHR rats.

CONCLUSIONS

CGRP elicits greater vasodilation in middle cerebral arteries from SHR than WKY rats, that is nitric oxide independent, and by mechanism independent of CGRP receptor components expression. Although aldosterone increases the expression of CL receptor in SHR, it does not alter vasodilation to CGRP, since RAMP1 expression is not increased. These results indicate that the increase in CL receptor, without an increase in RAMP1, does not correlate with changes in functional role of the CGRP receptor.

Pharmacogenomics and migraine: possible implications

Pharmacogenomics is the science about how inherited factors influence the effects of drugs. Drug response is always a result of mutually interacting genes with important modifications from environmental and constitutional factors. Based on the genetic variability of pharmacokinetic and in some cases pharmacodynamic variability we mention possible implications for the acute and preventive treatment of migraine. Pharmacogenomics will most likely in the future be one part of our therapeutic armamentarium and will provide a stronger scientific basis for optimizing drug therapy on the basis of each patient’s genetic constitution.

Treatment of migraine attacks based on the interaction with the trigemino-cerebrovascular system

Primary headaches such as migraine are among the most prevalent neurological disorders, affecting up to one-fifth of the adult population. The scientific work in the last decade has unraveled much of the pathophysiological background of migraine, which is now considered to be a neurovascular disorder. It has been discovered that the trigemino-cerebrovascular system plays a key role in migraine headache pathophysiology by releasing the potent vasodilator calcitonin gene-related peptide (CGRP). This neuropeptide is released in parallel with the pain and its concentration correlates well with the intensity of the headache. The development of drugs of the triptan class has provided relief for the acute attacks but at the cost of, mainly cardiovascular, side effects. Thus, the intention to improve treatment led to the development of small CGRP receptor antagonists such as olcegepant (BIBN4096BS) and MK-0974 that alleviate the acute migraine attack without acute side events. The purpose of this review is to give a short overview of the pathological background of migraine headache and to illustrate the mechanisms behind the actions of triptans and the promising CGRP receptor blockers.

Novel migraine therapy with calcitonin gene-regulated peptide receptor antagonists

Primary headaches, for example, migraine and cluster headaches represent the most prevalent neurological disorders, affecting up to 15-20% of the adult population. There is a clear association between head pain and the release of calcitonin gene-related peptide (CGRP). In this review the role of CGRP in human cranial circulation is described and the role for specific CGRP antagonism elucidated. It is well known that triptans (5-HT(1B/1D) agonist) alleviate headache in part through normalisation of CGRP levels. The central role of CGRP in migraine pathophysiology has resulted in the development of small-molecule CGRP antagonists with no cardiovascular side effects. Such compounds have high selectivity for human CGRP receptors and are efficacious in the relief of acute migraine attacks. Research indicates that they effect the abluminal side of the blood-brain barrier and that they are not vasoconstrictive, providing a new dimension in therapy.

Pharmacological characterisation of capsaicin-induced relaxations in human and porcine isolated arteries

Capsaicin, a pungent constituent from red chilli peppers, activates sensory nerve fibres via transient receptor potential vanilloid receptors type 1 (TRPV1) to release neuropeptides like calcitonin gene-related peptide (CGRP) and substance P. Capsaicin-sensitive nerves are widely distributed in human and porcine vasculature. In this study, we examined the mechanism of capsaicin-induced relaxations, with special emphasis on the role of CGRP, using various pharmacological tools. Segments of human and porcine proximal and distal coronary arteries, as well as cranial arteries, were mounted in organ baths. Concentration response curves to capsaicin were constructed in the absence or presence of the CGRP receptor antagonist olcegepant (BIBN4096BS, 1 μM), the neurokinin NK₁ receptor antagonist L-733060 (0.5 μM), the voltage-sensitive calcium channel blocker ruthenium red (100 μM), the TRPV1 receptor antagonist capsazepine (5 μM), the nitric oxide synthetase inhibitor N^ω-nitro-l-arginine methyl ester HCl (l-NAME; 100 μM), the gap junction blocker 18α-glycyrrhetinic acid (10 μM), as well as the RhoA kinase inhibitor Y-27632 (1 μM). Further, we also used the K⁺ channel inhibitors 4-aminopyridine (1 mM), charybdotoxin (0.5 μM) + apamin (0.1 μM) and iberiotoxin (0.5 μM) + apamin (0.1 μM). The role of the endothelium was assessed by endothelial denudation in distal coronary artery segments. In distal coronary artery segments, we also measured levels of cyclic adenosine monophosphate (cAMP) after exposure to capsaicin, and in human segments, we also assessed the amount of CGRP released in the organ bath fluid after exposure to capsaicin. Capsaicin evoked concentration-dependent relaxant responses in precontracted arteries, but none of the above-mentioned inhibitors did affect these relaxations. There was no increase in the cAMP levels after exposure to capsaicin, unlike after (exogenously administered) α-CGRP. Interestingly, there were significant increases in CGRP levels after exposure to vehicle (ethanol) as well as capsaicin, although this did not induce relaxant responses. In conclusion, the capsaicin-induced relaxations of the human and porcine distal coronary arteries are not mediated by CGRP, NK₁, NO, vanilloid receptors, voltage-sensitive calcium channels, K⁺ channels or cAMP-mediated mechanisms. Therefore, these relaxant responses to capsaicin are likely to be attributed to a non-specific, CGRP-independent mechanism.

Effects of current and prospective antimigraine drugs on the porcine isolated meningeal artery

Vasoconstriction to agonists at serotonin (5-hydroxytryptamine; 5-HT) receptors and alpha-adrenoceptors, as well as vasodilatation induced by alpha-CGRP, have been well described in the porcine carotid circulation in vivo. The present study sets out to investigate the effects of current and prospective antimigraine drugs on porcine meningeal artery segments in vitro. Sumatriptan, ergotamine, dihydroergotamine, isometheptene and clonidine failed to contract the meningeal artery, but 5-HT, noradrenaline and phenylephrine induced concentration-dependent contractions. The contractions to 5-HT were competitively antagonized by the 5-HT(2A) receptor antagonist ketanserin, whilst those to noradrenaline were antagonized by alpha(1)-(prazosin), alpha(2)-(rauwolscine and yohimbine) and alpha(2C/2B)-(OPC-28326) adrenoceptor antagonists. Whilst dobutamine and salbutamol were ineffective, alpha-CGRP produced concentration-dependent relaxations that were antagonized by the CGRP(1) receptor antagonist olcegepant. In agreement with their lack of contractile effect, sumatriptan and ergotamine failed to influence forskolin-stimulated cyclic AMP accumulation in the porcine meningeal artery; in contrast, both compounds decreased forskolin-stimulated cyclic AMP accumulation in the human isolated saphenous vein, where they induced contractions. Finally, using RT-PCR, we could demonstrate the presence of mRNAs encoding for several 5-HT receptors (5-HT(1B), 5-HT(1D), 5-HT(1F), 5-HT(2A) and 5-HT(7)) and adrenoceptors (alpha(1A), alpha(1B), alpha(1D), alpha(2A), alpha(2B), alpha(2C), beta(1) and beta(2)), as well as that for the calcitonin receptor like receptor, a component of the CGRP(1) receptor. These results suggest that: (i) the porcine meningeal artery may not be involved in the vasoconstriction of the carotid vascular bed elicited by antimigraine drugs in anaesthetized pigs, and (ii) the mismatch between the presence of receptor mRNA and the lack of response to sumatriptan, dobutamine and salbutamol implies that mRNAs for the 5-HT(1B) receptor and beta(1)- and beta(2)-adrenoceptors are probably unstable, or that their density is too low for being translated as receptor protein in sufficient quantities.