Kayi Y. Chan

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.

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 αCGRP were greater in distal coronary arteries (i.d. 600–1000 μm; Emax = 83 ± 7%) than proximal coronary arteries (i.d. 2–3 mm; Emax = 23 ± 9%), coronary arteries from explanted hearts (i.d. 3–5 mm; Emax = 11 ± 3%), and coronary arterioles (i.d. 200–300 μm; Emax = 15 ± 7%). Telcagepant alone did not induce contraction or relaxation of these coronary blood vessels. Pretreatment with telcagepant (10 nM to 1 μM) antagonized αCGRP-induced relaxation competitively in distal coronary arteries (pA2 = 8.43 ± 0.24) and proximal coronary arteries and coronary arterioles (1 μM telcagepant, giving pKB = 7.89 ± 0.13 and 7.78 ± 0.16, respectively). αCGRP 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.

Pharmacological characterization of VIP and PACAP receptors in the human meningeal and coronary artery.

Objective: We pharmacologically characterized pituitary adenylate cyclase–activating polypeptides (PACAPs), vasoactive intestinal peptide (VIP) and the VPAC1, VPAC2 and PAC1 receptors in human meningeal (for their role in migraine) and coronary (for potential side effects) arteries. Methods: Concentration response curves to PACAP38, PACAP27, VIP and the VPAC1 receptor agonist ([Lys15,Arg16,Leu27]-VIP[1-7]-GRF[8-27]) were constructed in the absence or presence of the PAC1 receptor antagonist PACAP6-38 or the VPAC1 receptor antagonist, PG97269. mRNA expression was measured using qPCR. Results: PACAP38 was less potent than VIP in both arteries. Both peptides had lower potency and efficacy in meningeal than in coronary arteries, while mRNA expression of VPAC1 receptor was more pronounced in meningeal arteries. PACAP6-38 reduced the Emax of PACAP27, while PG97269 right-shifted the VIP-induced relaxation curve only in the coronary arteries. Conclusion: The direct vasodilatory effect of VIP and PACAP might be less relevant than the central effect of this compound in migraine pathogenesis.

Potential mechanisms of prospective antimigraine drugs: A focus on vascular (side) effects

Currently available drugs for the acute treatment of migraine, i.e. ergot alkaloids and triptans, are cranial vasoconstrictors. Although cranial vasoconstriction is likely to mediate-at least a part of-their therapeutic effects, this property also causes vascular side-effects. Indeed, the ergot alkaloids and the triptans have been reported to induce myocardial ischemia and stroke, albeit in extremely rare cases, and are contraindicated in patients with known cardiovascular risk factors. In view of these limitations, novel antimigraine drugs devoid of vascular (side) effects are being explored. Currently, calcitonin gene-related peptide (CGRP) receptor antagonists, which do not have direct vasoconstrictor effects, are under clinical development. Other classes of drugs, such as 5-HT(1F) receptor agonists, glutamate receptor antagonists, nitric oxide synthase inhibitors, VPAC/PAC receptor antagonists and gap junction modulators, have also been proposed as potential targets for acute antimigraine drugs. Although these prospective drugs do not directly induce vasoconstriction, they may well induce indirect vascular effects by inhibiting or otherwise modulating the responses to endogenous vasoactive substances. These indirect vascular effects might contribute to the therapeutic efficacy of the previously mentioned compounds, but may alternatively also lead to vascular side-effects. As described in the current review, some of the prospective antimigraine drugs with a proposed non-vascular mechanism of action may still have direct or indirect vascular effects.

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, α-adrenoceptor agonists (ergotamine, dihydroergotamine, isometheptene) were used. The last two decades have witnessed the advent of 5-HT1B/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-HT2 receptor antagonists, Ca2+ channel blockers, and β-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-HT1–7), adrenergic (α1, α2, and β), calcitonin gene-related peptide (CGRP1 and CGRP2), adenosine (A1, A2, and A3), 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.

Functional characterization of contractions to tegaserod in human isolated proximal and distal coronary arteries.

Tegaserod, a 5-HT(4) receptor agonist, has been used to treat idiopathic constipation and constipation-predominant irritable bowel disease. It has recently been suggested that tegaserod has an affinity for 5-HT(1B) receptors, which mediate vasoconstriction. As some patients have experienced cardiac ischemia during treatment with tegaserod, we assessed contractions to tegaserod in healthy and diseased human isolated coronary arteries and compared the results with those obtained using sumatriptan, an established 5-HT(1B) receptor agonist. Proximal and distal human coronary arteries were divided into sets of healthy and diseased tissues based on functional endothelial responses. Concentration-response curves to tegaserod and sumatriptan were constructed to assess their contractile potential. Tegaserods antagonist properties at 5-HT(1B) receptors were studied by constructing concentration-response curves to sumatriptan in the absence or presence of tegaserod (1 microM). Sumatriptan induced concentration-dependent contractions, which were greater in distal than in proximal coronary artery segments. In the proximal segments, tegaserod induced contractions only at concentrations of 10 microM or higher, while in distal segments contractions were generally absent. Tegaserod did not antagonize sumatriptan-induced contractions. There was no difference between the results obtained in healthy and diseased coronary arteries. In conclusion, tegaserod induced contractions in human proximal coronary arteries at concentrations 1000 times higher than C(max) (6 mg bid). Hence, tegaserod does not exhibit a relevant vasoconstrictor potential in the human coronary artery. Further, tegaserod did not behave as an antagonist at 5-HT(1B) receptors. Additional studies may be warranted to investigate the use of 5-HT(4) agonists in patients with cardiovascular risk factors.

Effects of ionotropic glutamate receptor antagonists on rat dural artery diameter in an intravital microscopy model

Background and purpose:  During migraine, trigeminal nerves may release calcitonin gene‐related peptide (CGRP), inducing cranial vasodilatation and central nociception; hence, trigeminal inhibition or blockade of craniovascular CGRP receptors may prevent this vasodilatation and abort migraine headache. Several preclinical studies have shown that glutamate receptor antagonists affect the pathophysiology of migraine. This study investigated whether antagonists of NMDA (ketamine and MK801), AMPA (GYKI52466) and kainate (LY466195) glutamate receptors affected dural vasodilatation induced by α‐CGRP, capsaicin and periarterial electrical stimulation in rats, using intravital microscopy.

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.

Dihydroergotamine and sumatriptan in isolated human coronary artery, middle meningeal artery and saphenous vein

Background Dihydroergotamine (DHE) and sumatriptan are contraindicated in patients with cardiovascular disease because of their vasoconstricting properties, which have originally been explored in proximal coronary arteries. Our aim was to investigate DHE and sumatriptan in the proximal and distal coronary artery, middle meningeal artery and saphenous vein. Methods Blood vessel segments were mounted in organ baths and concentration response curves for DHE and sumatriptan were constructed. Results In the proximal coronary artery, meningeal artery and saphenous vein, maximal contractions to DHE (proximal: 8 ± 4%; meningeal: 32 ± 7%; saphenous: 52 ± 11%) and sumatriptan (proximal: 17 ± 7%; meningeal: 61 ± 18%, saphenous: 37 ± 8%) were not significantly different. In the distal coronary artery, contractions to DHE (5 ± 2%) were significantly smaller than those to sumatriptan (17 ± 9%). At clinically relevant concentrations, mean contractions to DHE and sumatriptan were below 3% in proximal coronary arteries and below 6% in distal coronary arteries. Contractions in the meningeal artery and saphenous vein were higher (7%–38%). Conclusions Contractions to DHE in distal coronary arteries are smaller than those to sumatriptan, while at clinical concentrations they both induce only slight contractions. In meningeal arteries contractions to DHE and sumatriptan are significantly larger, showing their cranioselectivity. Contractions to DHE in the saphenous vein are higher than those in the arteries, confirming its venous contractile properties.

A human capsaicin model to quantitatively assess salivary CGRP secretion

Background Capsaicin induces the release of calcitonin gene-related peptide (CGRP) via the transient receptor potential channel V1 (TRPV1). The CGRP response after capsaicin application on the tongue might reflect the “activation state” of the trigeminal nerve, since trigeminal CGRP-containing vesicles are depleted on capsaicin application. We tested (i) the quantitative CGRP response after oral capsaicin application; (ii) the optimal concentration of red chili homogenate; and (iii) the day-to-day variability in this response. Methods Saliva was collected for two consecutive days after oral application of eight capsaicin dilutions (red chili homogenates) of increasing concentrations in 13 healthy individuals. Effects of homogenate concentration were assessed. Consecutively, saliva was sampled after application of vehicle and undiluted homogenates. Results CGRP secretion (pg/ml) increased dose-dependently with homogenate concentration (p < 0.001). CGRP levels were highest after application of nondiluted homogenate (vs. baseline: 13.3 (5.0) vs. 9.7 (2.9); p = 0.003, as was total CGRP secretion in five minutes (pg) with undiluted (vs. baseline): 89.2 (44.1) vs. 14.1 (2.8); p < 0.001. The dose-dependent response in CGRP was not affected by day (p = 0.14) or day*concentration (p = 0.60). Increase in CGRP (undiluted – baseline; pg/ml) did not differ between measurements on dose-finding (p = 0.67) and follow-up days (p = 0.46). Conclusion Oral application of red chili homogenate is well tolerated and causes a dose-dependent CGRP release in saliva, without day-to-day effects in this response. This model could be used to noninvasively study the activation state of the trigeminal nerve innervating salivary glands.