Direct evidence for central sites of action of zolmitriptan (311C90): an autoradiographic study in cat

Biological and small molecule strategies in migraine therapy with relation to the calcitonin gene-related peptide family of peptides

Migraine is one of the most common of neurological disorders with a global prevalence of up to 15%. One in five migraineurs have frequent episodic or chronic migraine requiring prophylactic treatment. In recent years, specific pharmacological treatments targeting calcitonin gene-related peptide (CGRP) signalling molecules have provided safe and effective treatments, monoclonal antibodies for prophylaxis and gepants for acute therapy. Albeit beneficial, it is important to understand the molecular mechanisms of these new drugs to better understand migraine pathophysiology and improve therapy. Here, we describe current views on the role of the CGRP family of peptides - CGRP, calcitonin, adrenomedullin, amylin - and their receptors in the trigeminovascular system. All these molecules are present within the trigeminovascular system but differ in expression and localization. It is likely that they have different roles, which can be utilized in providing additional drug targets.

Brain structure and function related to headache: Brainstem structure and function in headache

OBJECTIVE

To review and discuss the literature relevant to the role of brainstem structure and function in headache.

BACKGROUND

Primary headache disorders, such as migraine and cluster headache, are considered disorders of the brain. As well as head-related pain, these headache disorders are also associated with other neurological symptoms, such as those related to sensory, homeostatic, autonomic, cognitive and affective processing that can all occur before, during or even after headache has ceased. Many imaging studies demonstrate activation in brainstem areas that appear specifically associated with headache disorders, especially migraine, which may be related to the mechanisms of many of these symptoms. This is further supported by preclinical studies, which demonstrate that modulation of specific brainstem nuclei alters sensory processing relevant to these symptoms, including headache, cranial autonomic responses and homeostatic mechanisms.

REVIEW FOCUS

This review will specifically focus on the role of brainstem structures relevant to primary headaches, including medullary, pontine, and midbrain, and describe their functional role and how they relate to mechanisms of primary headaches, especially migraine.

Current and novel insights into the neurophysiology of migraine and its implications for therapeutics

Migraine headache and its associated symptoms have plagued humans for two millennia. It is manifest throughout the world, and affects more than 1/6 of the global population. It is the most common brain disorder, and is characterized by moderate to severe unilateral headache that is accompanied by vomiting, nausea, photophobia, phonophobia, and other hypersensitive symptoms of the senses. While there is still a clear lack of understanding of its neurophysiology, it is beginning to be understood, and it seems to suggest migraine is a disorder of brain sensory processing, characterized by a generalized neuronal hyperexcitability. The complex symptomatology of migraine indicates that multiple neuronal systems are involved, including brainstem and diencephalic systems, which function abnormally, resulting in premonitory symptoms, ultimately evolving to affect the dural trigeminovascular system, and the pain phase of migraine. The migraineur also seems to be particularly sensitive to fluctuations in homeostasis, such as sleep, feeding and stress, reflecting the abnormality of functioning in these brainstem and diencephalic systems. Implications for therapeutic development have grown out of our understanding of migraine neurophysiology, leading to major drug classes, such as triptans, calcitonin gene-related peptide receptor antagonists, and 5-HT1F receptor agonists, as well as neuromodulatory approaches, with the promise of more to come. The present review will discuss the current understanding of the neurophysiology of migraine, particularly migraine headache, and novel insights into the complex neural networks responsible for associated neurological symptoms, and how interaction of these networks with migraine pain pathways has implications for the development of novel therapeutics.

Pathophysiology of Migraine: A Disorder of Sensory Processing

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

Differences of Anti-Nociceptive Mechanisms of Migraine Drugs on the Trigeminal Pain Processing during and Outside Acute Migraine Attacks

The aim of this study was to investigate central anti-nociceptive mechanisms of i.v. acetylsalicylic acid (ASA) and oral zolmitriptan (ZOL) in migraine patients and healthy subjects using the ‘nociceptive’ blink reflex (nBR). Twenty-eight migraine patients received ASA ( n = 14, 1000 mg i.v) or ZOL ( n = 14, 5 mg p.o) during the acute migraine attack and interictally. Thirty healthy subjects received either ASA or ZOL vs. placebo using a double blind cross over design. nBR was recorded in all patients and subjects before, 60 and 90 min after treatment. ASA and ZOL did not inhibit nBR responses in healthy subjects. Both ASA and ZOL suppressed nBR responses (ASA by 68%, ZOL by 78%) only during the acute attack but not interictally. The data suggest, that the anti-nociceptive effects of migraine drugs on the trigeminal nociceptive processing are different during and outside an acute migraine attack.

A PET study with [11C]AZ10419369 to determine brain 5-HT1B receptor occupancy of zolmitriptan in healthy male volunteers

Aim

To investigate the occupancy at brain 5-hydroxytryptamine (5-HT) 1B receptors in human subjects after administration of the antimigraine drug zolmitriptan.

Methods

Positron emission tomography (PET) studies were undertaken using the radioligand [11C]AZ10419369 in eight control subjects at baseline and after administration of zolmitriptan orodispersible tablets. The subjects were examined after two consecutive administrations of 10 mg zolmitriptan, approximately 1 week apart. Two of the subjects were subsequently examined after administration of 5 mg zolmitriptan. One week after the last administration of zolmitriptan five of the subjects underwent additional PET measurements without drug pretreatment.

Results

After administration of 10 mg zolmitriptan, mean receptor occupancy was 4–5%. No consistent changes in 5-HT1B receptor binding were observed for subjects who received 5 mg zolmitriptan. There was a statistically significant negative relationship between binding potential ( BPND) and plasma concentration of zolmitriptan and the active metabolite 183C91, respectively. All of the five subjects who were examined 1 week after dosing with zolmitriptan showed higher BPND post drug administration compared with baseline.

Conclusion

This is the first demonstration of CNS 5-HT1B receptor occupancy of a triptan. The findings are consistent with the low receptor occupancy previously reported in PET studies with agonists at other G protein coupled receptors.

Pharmacokinetic evaluation of zolmitriptan for the treatment of migraines

INTRODUCTION

Migraine is a multifactorial neurovascular disorder characterized by recurrent episodes of disabling pain attacks, accompanied with gastrointestinal, neurological systems dysfunction. The pharmacologic treatment of migraine is classically divided in the management of the acute attack and preventive strategies. Acute treatments consist of triptan, ergot, opioid, antiemetic and NSAIDs.

AREAS COVERED

This article discusses pharmacodynamics and pharmacokinetics of zolmitriptan . The data were obtained by searching the following keywords in MEDLINE: zolmitriptan, pharmacokinetics, pharmacodynamics, triptans, migraine, menstrual-related migraine, cluster headache, relatively to the period 1989 - 2012.

EXPERT OPINION

Zolmitriptan has been considered effective treatment in the acute phase of migraine, menstrual-related migraine and cluster headache attacks. Pharmacokinetic parameters may vary as a consequence of gender differences, inter- and intra-subjects variability and delivery system. Zolmitriptan was developed with the aim of obtaining a lipophilic compound in order to be more rapidly absorbed and centrally active. Pharmacologically, pharmacokinetic parameters are responsible for its wide efficacy and the limited adverse effect profile.

mRNA expression of 5-hydroxytryptamine 1B, 1D, and 1F receptors and their role in controlling the release of calcitonin gene-related peptide in the rat trigeminovascular system

Triptans, a family of 5-hydroxytryptamine (5-HT) 1B, 1D, and 1F receptor agonists, are used in the acute treatment of migraine attacks. The site of action and subtypes of the 5-HT(1) receptor that mediate the antimigraine effect have still to be identified. This study investigated the mRNA expression of these receptors and the role of 5-HT(1) receptor subtypes in controlling the release of calcitonin gene-related peptide (CGRP) in rat dura mater, trigeminal ganglion (TG), and trigeminal nucleus caudalis (TNC). The mRNA for each receptor subtype was quantified by quantitative real-time polymerase chain reaction. A high potassium concentration was used to release CGRP from dura mater, isolated TG, and TNC in vitro. The immunoreactive CGRP (iCGRP) release was measured by enzyme-linked immunoassay. The mRNA transcripts of the 3 5-HT(1) receptor subtypes were detected in the trigeminovascular system. Sumatriptan inhibited iCGRP release by 31% in dura mater, 44% in TG, and 56% in TNC. This effect was reversed by a 5-HT(1B/1D) antagonist (GR127395). The 5-HT(1F) agonist (LY-344864) was effective in the dura mater (26% iCGRP inhibition), and the 5-HT(1D) agonist (PNU-142633) had a significant effect in the TNC (48%), whereas the 5-HT(1B) agonist (CP-94253) was unable to reduce the iCGRP release in all tissues studied. We found that sumatriptan reduced the iCGRP release via activation of 5-HT(1D) and 5-HT(1F) receptor subtypes. The 5-HT(1F) receptor agonist was effective only in peripheral terminals in dura mater, whereas the 5-HT(1D) agonist had a preferential effect on central terminals in the TNC.

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.

Autoradiographic Mapping of 5-HT(1B/1D) Binding Sites in the Rhesus Monkey Brain Using [carbonyl-C]zolmitriptan

Zolmitriptan is a serotonin 5-HT(1B/1D) receptor agonist that is an effective and well-tolerated drug for migraine treatment. In a human positron emission tomography study, [(11)C]zolmitriptan crossed the blood-brain barrier but no clear pattern of regional uptake was discernable. The objective of this study was to map the binding of [(11)C]zolmitriptan in Rhesus monkey brain using whole hemisphere in vitro autoradiography with [(11)C]zolmitriptan as a radioligand. In saturation studies, [(11)C]zolmitriptan showed specific (90%) binding to a population of high-affinity binding sites (Kd 0.95-5.06 nM). There was regional distribution of binding sites with the highest density in the ventral pallidum, followed by the external globus pallidus, substantia nigra, visual cortex, and nucleus accumbens. In competitive binding studies with 5-HT(1) receptor antagonists, [(11)C]zolmitriptan binding was blocked by selective 5-HT(1B) and 5-HT(1D) ligands in all target areas. There was no appreciable change in binding with the addition of a 5-HT(1A) receptor antagonist.

Zolmitriptan nasal spray in the acute treatment of cluster headache: a meta-analysis of two studies

OBJECTIVE

To conduct an individual subject meta-analysis of available controlled studies of zolmitriptan nasal spray in the acute treatment of cluster headache.

BACKGROUND

Two double-blind, placebo-controlled, randomized, crossover studies of zolmitriptan nasal spray in the acute treatment of cluster headache, with similar patient populations, protocol designs, doses, and clinical endpoints have been published.

METHODS

In both double-blind studies, each patient was to treat 3 attacks, 1 with placebo, 1 with zolmitriptan 5 mg, and 1 with zolmitriptan 10 mg in a randomized, crossover manner. Headache intensity was rated on a 5-point scale (none to very severe). The primary endpoint was headache relief at 30 minutes post dose: reduction from moderate, severe, or very severe pain to mild or none. A multilevel, random-effects, logistic regression model was used to analyze the data.

RESULTS

A total of 121 patients (100 male; 64.5% with episodic cluster headache) provided efficacy data for at least 1 attack. Zolmitriptan 5 mg and 10 mg were significantly more effective at providing headache relief at 30 minutes post treatment than placebo (odds ratio 3.48; 95% confidence interval 1.49-8.10 and odds ratio 8.68; 95% confidence interval: 3.35-22.5, respectively). For episodic cluster headache, response rates were 35.6%, 51.7%, and 73.7% for placebo, zolmitriptan 5 mg (odds ratio 2.5; P = .06 vs placebo), and 10 mg (odds ratio 9.9; P < .001 vs placebo), respectively. For chronic cluster headache, response rates were 17.2%, 41.9%, and 40.7% for placebo, zolmitriptan 5 mg (odds ratio 8.1; P = .035), and 10 mg (odds ratio 7.6; P = .046), respectively. Zolmitriptan was well tolerated in both studies with no serious adverse events reported.

CONCLUSION

Zolmitriptan nasal spray at a dose of 5 mg and 10 mg is efficacious in the acute treatment of episodic and chronic cluster headache.

Does sumatriptan cross the blood-brain barrier in animals and man?

Sumatriptan, a relatively hydrophilic triptan, based on several animal studies has been regarded to be unable to cross the blood–brain barrier (BBB). In more recent animal studies there are strong indications that sumatriptan to some extent can cross the BBB. The CNS adverse events of sumatriptan in migraine patients and normal volunteers also indicate a more general effect of sumatriptan on CNS indicating that the drug can cross the BBB in man. It has been discussed whether a defect in the BBB during migraine attacks could be responsible for a possible central effect of sumatriptan in migraine. This review suggests that there is no need for a breakdown in the BBB to occur in order to explain a possible central CNS effect of sumatriptan.

Spinal sumatriptan inhibits capsaicin-induced canine external carotid vasodilatation via 5-HT1B rather than 5-HT1D receptors

Migraine is a neurovascular disorder associated with trigeminal activation, vasodilatation and trigeminal release of calcitonin gene-related peptide (CGRP). The antimigraine properties of triptans may be due to: i) vasoconstriction of the carotid arterial bed via 5-HT(1B) receptors; and ii) inhibition of CGRP release from trigeminal nerves, via 5-HT(1B/1D) receptors. This study investigated the effects of intrathecally administered sumatriptan (a 5-HT(1B/1D) receptor agonist) and PNU-142633 (a 5-HT(1D) receptor agonist) on the canine external carotid vasodilator responses to capsaicin, alpha-CGRP and acetylcholine. For this purpose, 42 mongrel dogs were anaesthetised with sodium pentobarbitone and, subsequently, vagosympathectomized. The animals were prepared to measure arterial blood pressure, heart rate and external carotid blood flow; the thyroid artery was cannulated for infusion of agonists. 1-min intracarotid (i.c.) continuous infusions of capsaicin, alpha-CGRP and acetylcholine produced dose-dependent increases in external carotid blood flow without affecting arterial blood pressure or heart rate. These vasodilator responses remained unaffected after intrathecal (i.t.) administration of physiological saline (0.5 ml) or PNU-142633 (300-1000 microg); in contrast, i.t. sumatriptan (300-1000 microg) significantly inhibited the vasodilator responses to capsaicin, but not those to alpha-CGRP or acetylcholine. Furthermore, i.t. administration of SB224289 (a 5-HT(1B) receptor antagonist), but not of BRL15572 (a 5-HT(1D) receptor antagonist), abolished the above inhibition by sumatriptan. These results suggest that sumatriptan-induced inhibition of the external carotid vasodilatation to capsaicin involves a central mechanism mainly mediated by 5-HT(1B) receptors.

Migraine, allodynia, and implications for treatment

Allodynia--perception of pain from non-noxious stimuli--is a common clinical feature in various pain syndromes. The significance for migraine has increasingly been recognized and the pathophysiology has been investigated in detail. Allodynia is a marker for sensitization of central trigeminal neurons. Intensity and persistence of allodynic symptoms are a function of duration of migraine attacks, frequency of attacks, and migraine history. It has been hypothesized that treatment success with triptans may be severely impaired in the presence of allodynia. However, randomized controlled trials did not confirm that. Treatment with cyclooxygenase inhibitors and dihydroergotamine does not seem to be limited by allodynia; these medications may be able to reverse allodynia. Data on the new class of calcitonin-gene related-peptide antagonists are not yet available. Additional and more refined randomized controlled trials, focusing on methodological issues pertaining to the determination of allodynia, are warranted to resolve the true relationship between allodynia and treatment response. Regardless--based on available randomized controlled trials--the recommendation prevails to initiate abortive treatment as soon as possible after attack onset when pain is still mild.

EFNS guideline on the drug treatment of migraine - report of an EFNS task force

Migraine is one of the most frequent disabling neurological conditions with a major impact on the patients' quality of life. To give evidence-based or expert recommendations for the different drug treatment procedures of the different migraine syndromes based on a literature search and an consensus in an expert panel. All available medical reference systems were screened for all kinds of clinical studies on migraine with and without aura and on migraine-like syndromes. The findings in these studies were evaluated according to the recommendations of the EFNS resulting in level A,B, or C recommendations and good practice points. For the acute treatment of migraine attacks, oral non-steroidal anti-inflammatory drugs (NSAIDs) and triptans are recommended. The administration should follow the concept of stratified treatment. Before intake of NSAIDs and triptans, oral metoclopramide or domperidon is recommended. In very severe attacks, intravenous acetylsalicylic acid or subcutaneous sumatriptan are drugs of first choice. A status migrainosus can probably be treated by steroids. For the prophylaxis of migraine, betablockers (propranolol and metoprolol), flunarizine, valproic acid, and topiramate are drugs of first choice. Drugs of second choice for migraine prophylaxis are amitriptyline, naproxen, petasites, and bisoprolol.

Experimental migraine models and their relevance in migraine therapy

Although the understanding of migraine pathophysiology is incomplete, it is now well accepted that this neurovascular syndrome is mainly due to a cranial vasodilation with activation of the trigeminal system. Several experimental migraine models, based on vascular and neuronal involvement, have been developed. Obviously, the migraine models do not entail all facets of this clinically heterogeneous disorder, but their contribution at several levels (molecular, in vitro, in vivo) has been crucial in the development of novel antimigraine drugs and in the understanding of migraine pathophysiology. One important vascular in vivo model, based on an assumption that migraine headache involves cranial vasodilation, determines porcine arteriovenous anastomotic blood flow. Other models utilize electrical stimulation of the trigeminal ganglion/nerve to study neurogenic dural inflammation, while the superior sagittal sinus stimulation model takes into account the transmission of trigeminal nociceptive input in the brainstem. More recently, the introduction of integrated models, namely electrical stimulation of the trigeminal ganglion or systemic administration of capsaicin, allows studying the activation of the trigeminal system and its effect on the cranial vasculature. Studies using in vitro models have contributed enormously during the preclinical stage to characterizing the receptors in cranial blood vessels and to studying the effects of several putative antimigraine agents. The aforementioned migraine models have advantages as well as some limitations. The present review is devoted to discussing various migraine models and their relevance to antimigraine therapy.

Donitriptan, but not sumatriptan, inhibits capsaicin-induced canine external carotid vasodilatation via 5-HT1B rather than 5-HT1D receptors

BACKGROUND AND PURPOSE

It has been suggested that during a migraine attack capsaicin-sensitive trigeminal sensory nerves release calcitonin gene-related peptide (CGRP), resulting in cranial vasodilatation and central nociception; hence, trigeminal inhibition may prevent this vasodilatation and abort migraine headache. This study investigated the effects of the agonists sumatriptan (5-HT(1B/1D) water-soluble), donitriptan (5-HT(1B/1D) lipid-soluble), PNU-142633 (5-HT(1D) water-soluble) and PNU-109291 (5-HT(1D) lipid-soluble) on vasodilator responses to capsaicin, alpha-CGRP and acetylcholine in dog external carotid artery.

EXPERIMENTAL APPROACH

59 vagosympathectomized dogs were anaesthetized with sodium pentobarbitone. Blood pressure and heart rate were recorded with a pressure transducer, connected to a cannula inserted into a femoral artery. A precalibrated flow probe was placed around the common carotid artery, with ligation of the internal carotid and occipital branches, and connected to an ultrasonic flowmeter. The thyroid artery was cannulated for infusion of agonists.

KEY RESULTS

Intracarotid infusions of capsaicin, alpha-CGRP and acetylcholine dose-dependently increased blood flow through the carotid artery. These responses remained unaffected after intravenous (i.v.) infusions of sumatriptan, PNU-142633, PNU-109291 or physiological saline; in contrast, donitriptan significantly attenuated the vasodilator responses to capsaicin, but not those to alpha-CGRP or acetylcholine. Only sumatriptan and donitriptan dose-dependently decreased the carotid blood flow. Interestingly, i.v. administration of the antagonist, SB224289 (5-HT(1B)), but not of BRL15572 (5-HT(1D)), abolished the inhibition by donitriptan.

CONCLUSIONS AND IMPLICATIONS

Our results suggest that the inhibition produced by donitriptan of capsaicin-induced external carotid vasodilatation is mainly mediated by 5-HT(1B), rather than 5-HT(1D), receptors, probably by a central mechanism.

Multiple attack study on the available triptans in Italy versus placebo

The aim of the study is to evaluate the efficacy and tolerability of the five triptans that are commercially available in Italy (zolmitriptan 2.5 mg, rizatriptan 10 mg, sumatriptan 100 mg, almotriptan 12.5 mg and eletriptan 40 mg). The study was conducted in single-blind versus placebo and its duration was 18 months. At the Headache Centre of the 'Agostino Gemelli' Hospital in Rome we selected 42 patients, suffering from headache with and without aura (International Headache Society Committee on Headache Classification, 1988 Cephalalgia 8:1-96), whose headache frequency ranged between 1- and 4-monthly crises. For a total of 25 crises, for every five consecutive crises, a different triptan was taken. The end-points of the study were as follows: response at 2 h, 'pain free' at 2 h and 'sustained pain free' (at 24 h). The intra-patient consistency and the tolerability were also evaluated. Thirty patients completed the study and the statistical analysis was only applied to these patients. No substantial difference in terms of the efficacy of the triptans was noted; all triptans were well tolerated. These results suggest the possibility of testing different triptans in the same patient in order to identify the ideal drug for every patient.

Zolmitriptan:a new acute treatment for migraine

Zolmitriptan is a new oral acute treatment for migraine. It is a selective and potent agonist at the serotonin (5-HT)(1B/1D) receptor and was developed to improve on the oral bioavailability, tissue selectivity and CNS penetration of earlier compounds. Animal studies confirmed that these objectives had been attained. In man, zolmitriptan is rapidly absorbed after oral administration, with at least 75% of the eventual C(max) reached within 1 h. Oral bioavailability is approximately 40%. The elimination half-life of zolmitriptan is approximately 2.5 h and the primary route of elimination is metabolism, with one of the metabolites being pharmacologically active. A consistent 2-h headache response rate of 60-70% was observed at doses of 2.5 mg and above. Long-term treatment response is high (> 80%) and consistent. In addition, there is evidence from electrophysiology in migraineurs that zolmitriptan has a central action not shared by sumatriptan. Zolmitriptan is well-tolerated. The nature and incidence of the most frequently reported adverse events are similar to those of other 5-HT(1B/1D) agonists. Long-term zolmitriptan usage was associated with an improvement in quality of life. Zolmitriptan is a suitable first-line drug for acute treatment for migraine.

Distribution of Zolmitriptan into the CNS in Healthy Volunteers

OBJECTIVE

Triptans are highly effective in the treatment of migraine. Both central and peripheral mechanisms of action have been suggested. Until now, firm data about the passage of triptans into the CNS in humans have been lacking. The aim of the current study was to evaluate, using positron emission tomography (PET), the uptake and distribution of zolmitriptan into the CNS after intranasal administration.

SUBJECTS AND METHODS

Eight healthy volunteers, five males and three females (mean ages 23 and 26 years, respectively), were included. Radioactive [carbonyl-11C]zolmitriptan was infused intravenously for 5 minutes on two occasions: once alone, and once 30-40 minutes after intranasal administration of unlabelled zolmitriptan 5 mg. PET was used to measure the concentration of labelled zolmitriptan in the brain, from the start of the tracer infusion for 90 minutes. Regional cerebral blood volume was determined with [15O]carbon monoxide. In addition, an MRI scan was performed to obtain anatomical information. The PET images were analysed quantitatively for different areas of the brain, generating [11C]zolmitriptan time-activity data corrected for circulating tracer activity. The rate of uptake of intranasal zolmitriptan into the CNS was estimated by kinetic modelling using the PET data.

RESULTS

PET data from this study demonstrate a rapid dose-proportional uptake of [11C]zolmitriptan into the brain. Significant concentrations of [11C]zolmitriptan were found in all brain regions studied. Calculated CNS concentrations after intranasal zolmitriptan administration showed a gradual increase, reaching about 2 nM (0.5 microg/L) 30 minutes after administration and 3.5 nM (1.0 microg/L), or one-fifth of the plasma concentration, 1 hour after administration. Five minutes after zolmitriptan administration, the mean CNS concentration had already reached 0.5 nM, which is higher than in vitro values for initiation of the agonistic action on 5-HT(1B/1D) receptors.

CONCLUSION

This study demonstrates by direct measurements that zolmitriptan enters the brain parenchyma in humans, achieving an uptake rate and concentration compatible with a central mode of action.

Preclinical neuropharmacology of naratriptan

The basic CNS neuropharmacology of naratriptan is reviewed here. Naratriptan is a second-generation triptan antimigraine drug, developed at a time when CNS activity was thought not to be relevant to its therapeutic effect in migraine. It was, however, developed to be a more lipid-soluble, more readily absorbed and less readily metabolized variant on preexisting triptans and these variations conferred on it a higher CNS profile. Naratriptan is a 5-HT(1B/1D) receptor agonist with a highly selective action on migraine pain and nausea, without significant effect on other pain or even other trigeminal pain. Probable sites of therapeutic action of naratriptan include any or all of: the cranial vasculature; the peripheral terminations of trigeminovascular sensory nerves; the first-order synapses of the trigeminovascular sensory system; the descending pain control system; and the nuclei of the thalamus. Naratriptan may prevent painful dilatation of intracranial vessels or reverse such painful dilatation. Naratriptan can prevent the release of sensory peptides and inhibit painful neurogenic vasodilatation of intracranial blood vessels. At the first order synapse of the trigeminal sensory system, naratriptan can selectively suppress neurotransmission from sensory fibers from dural and vascular tissue, while sparing transmission from other trigeminal fibers, probably through inhibition of neuropeptide transmitter release. In the periaqueductal gray matter and in the nucleus raphe magnus, naratriptan selectively activates inhibitory neurons which project to the trigeminal nucleus and spinal cord and which exert inhibitory influences on trigeminovascular sensory input. Naratriptan has also a therapeutic effect on the nausea of migraine, possibly exerting its action at the level of the nucleus tractus solitarius via the same mechanisms by which it inhibits trigeminovascular nociceptive input. The incidence of naratriptan-induced adverse effects in the CNS is low and it is not an analgesic for pain other than that of vascular headache. In patients receiving selective serotonin uptake inhibitors (SSRIs) naratriptan may cause serotonin syndrome-like behavioral side effects. The mechanism of action involved in the production of behavioral and other CNS side effects of naratriptan is unknown.

Effects of acute or chronic administration of anti-migraine drugs sumatriptan and zolmitriptan on serotonin synthesis in the rat brain

Triptans are 5-HT1 receptor agonists used as anti-migraine drugs. They act primarily on meningeal blood vessels and on trigeminovascular afferents, but they may also exert central effects. We studied the regional effects of acute and chronic treatment with sumatriptan or zolmitriptan on the rate of serotonin (5-HT) synthesis in the rat brain, using the alpha-14C-methyl-L-tryptophan quantitative autoradiographic method. Sumatriptan at low (300 microg/kg, s.c.) and high (1 mg/kg) doses, as well as zolmitriptan (100 microg/kg), acutely decreased (15-40%, P < 0.05-0.001) 5-HT synthetic rate in many brain regions, including the dorsal raphe nucleus. Chronically, sumatriptan (21 days, approximately 300 microg/kg per day via osmotic minipumps) induced significant increases in the 5-HT synthesis rate in many projection areas but had no effect in the dorsal raphe nucleus. The acute effects on 5-HT synthesis rate would be compatible with activation of 5-HT1 autoreceptors that inhibit serotonin release. In contrast, the increased 5-HT synthesis rate observed after chronic sumatriptan might possibly result from a down-regulation/desensitization of 5-HT1 receptors and/or unmasking of excitatory triptan-sensitive 5-HT receptors. Overall, the present findings indicate that not only zolmitriptan but also sumatriptan affect brain serotonergic neurotransmission.

The 5-hydroxytryptamine1B/1D/1F receptor agonists eletriptan and naratriptan inhibit trigeminovascular input to the nucleus tractus solitarius in the cat

Migraine pain arises in the trigeminovascular system and is often associated with nausea and sometimes with vomiting. In this study, an in vivo cat model of trigeminovascular stimulation was used to determine first whether there is a functional connection between the trigeminovascular system and the nucleus tractus solitarius (NTS), which is involved in regulating vomiting, and second whether anti-migraine drugs have any effect on such a connection. Chloralose-anaesthetised cats (n=16) were prepared for single neuron recording. The superior sagittal sinus (SSS) was isolated and stimulated electrically. The brainstem near the obex was exposed and a metal microelectrode equipped with six glass barrels for microiontophoresis was placed in the NTS. Recordings were made from 44 NTS neurons which responded to SSS stimulation with A-delta latencies. Iontophoretic ejection (50 nA) of eletriptan or naratriptan suppressed the response in 75% (15/20) and 78% (11/14) of cells and caused an average suppression of cell firing of 42+/-5% (n=20) and 54+/-8% (n=14), respectively. This suppression could be antagonized by the concurrent ejection (20-50 nA) of the 5-HT(1B/1D) receptor antagonist GR127935. We conclude that activation of the trigeminovascular system excites cells in the NTS that can be inhibited by eletriptan and naratriptan through activation of 5-HT(1B/1D) receptors. It is possible that in patients having a migraine attack trigeminovascular activation triggers nausea and vomiting, and that the alleviation of these symptoms by anti-migraine compounds may be via an action at 5-HT(1B/1D) receptors in the NTS.

Activation of 5-HT1B/1D receptor in the periaqueductal gray inhibits nociception

It is considered that the site of action of the abortive antimigraine compounds acting at serotonin, 5-HT(1B/1D,) receptors (triptans) is the trigeminovascular system. We tested whether there is a non-trigeminal site of action. The 5-HT(1B/1D) agonist, naratriptan, was microinjected into the ventrolateral periaqueductal gray (vlPAG), and activity in the trigeminal nucleus caudalis (TNC) was monitored. Recordings were made from 20 nociceptive neurons in the dorsal horn of the TNC that received convergent input from the dura mater and face. Responses of neurons to dural, facial cutaneous and corneal stimulation were studied before and after injection of naratriptan. Naratriptan decreased the excitability to electrical stimulation of the dura mater as the A-fiber response decreased by 24 +/- 4.1% (p < 0.001) and the C-fiber response decreased by 42 +/- 8.2% (p < 0.001). Spontaneous activity was decreased by 38 +/- 7.5% (p < 0.001). After injection, the mechanical thresholds of the dura mater increased from (n = 14, p < 0.01). Responses to stimulation of the face and cornea were not altered by injection of naratriptan. These results suggest that 5-HT(1B/1D) receptor activation in the vlPAG activates descending pain-modulating pathways that inhibit dural, but not facial and corneal nociceptive input. These findings have implications for the understanding of the action of triptans in migraine and cluster headache, suggesting that brain loci other than the trigeminal nucleus may play a role in the clinical action of triptans.

The antimigraine 5-HT 1B/1D receptor agonists, sumatriptan, zolmitriptan and dihydroergotamine, attenuate pain-related behaviour in a rat model of trigeminal neuropathic pain

1. Peripheral lesion to the trigeminal nerve may induce severe pain states. Several lines of evidence have suggested that the antimigraine effect of the triptans with 5-HT(1B/1D) receptor agonist properties may result from inhibition of nociceptive transmission in the spinal nucleus of the trigeminal nerve by these drugs. On this basis, we have assessed the potential antinociceptive effects of sumatriptan and zolmitriptan, compared to dihydroergotamine (DHE), in a rat model of trigeminal neuropathic pain. 2. Chronic constriction injury was produced by two loose ligatures of the infraorbital nerve on the right side. Responsiveness to von Frey filament stimulation of the vibrissal pad was used to evaluate allodynia. 3. Two weeks after ligatures, rats with a chronic constriction of the right infraorbital nerve displayed bilateral mechanical hyper-responsiveness to von Frey filament stimulation of the vibrissal pad with a mean threshold of 0.38+/-0.04 g on the injured side and of 0.43+/-0.04 g on the contralateral (left) side (versus > or =12.5 g on both sides in the same rats prior to nerve constriction injury). 4. Sumatriptan at a clinically relevant dose (100 microg kg(-1), s.c.) led to a significant reduction of the mechanical allodynia-like behaviour on both the injured and the contralateral sides (peak-effects 6.3+/-1.1 g and 4.4+/-0.7 g, respectively). A more pronounced effect was obtained with zolmitriptan (100 microg kg(-1), s.c.) (peak-effects: 7.4+/-0.9 g and 3.2+/-1.3 g) whereas DHE (50-100 microg kg(-1), i.v.) was less active (peak-effect approximately 1.5 g). 5. Subcutaneous pretreatment with the 5-HT(1B/1D) receptor antagonist, GR 127935 (3 mg kg(-1)), prevented the anti-allodynia-like effects of triptans and DHE. Pretreatment with the 5-HT(1A) receptor antagonist, WAY 100635 (2 mg kg(-1), s.c.), did not alter the effect of triptans but significantly enhanced that of DHE (peak effect 4.3+/-0.5 g). 6. In a rat model of peripheral neuropathic pain, which consisted of a unilateral loose constriction of the sciatic nerve, neither sumatriptan (50-300 microg kg(-1)) nor zolmitriptan (50-300 microg kg(-1)) modified the thresholds for paw withdrawal and vocalization in response to noxious mechanical stimulation. 7. These results support the rationale for exploring the clinical efficacy of brain penetrant 5-HT(1B/1D) receptor agonists as analgesics to reduce certain types of trigeminal neuropathic pain in humans.

Review of zolmitriptan and its clinical applications in migraine

Preclinical studies have shown that zolmitriptan is a selective serotonin 5-HT(1B/1D) receptor agonist (triptan). Randomised, placebo-controlled, double-blind trials in patients with migraine have shown that zolmitriptan has good efficacy measured using 2 h response and pain-free rates. Migraine-associated symptoms, including nausea, photophobia and phonophobia, are also improved with zolmitriptan. Oral zolmitriptan (2.5 and 5 mg) has an onset of action within 45 min and efficacy is sustained in most patients who respond at 2 h. The orally-disintegrating zolmitriptan tablet has the advantage that it may be taken immediately, without the need for additional fluids, any time a migraine headache occurs. Patients may benefit in terms of improved efficacy from the convenience of the disintegrating tablet, since there is evidence that taking triptan therapy as early as possible in an attack is advantageous. For similar reasons, as well as improved efficacy, a nasal spray formulation is in development. Zolmitriptan is effective in the treatment of migraine associated with menses and migraine with aura. There is no tachyphylaxis following repeated doses for multiple attacks of migraine over a prolonged period of time. Compared to placebo, the incidence of persistent migraine headache is reduced by zolmitriptan and recurrent migraine headache occurs less frequently. Zolmitriptan has also shown efficacy in the treatment of persistent and/or recurrent migraine headache. Comparative clinical studies have shown overall that zolmitriptan has similar or superior efficacy to sumatriptan in the treatment of migraine. Specifically, zolmitriptan 2.5 mg was significantly more effective than sumatriptan 25 or 50 mg according to a number of end points, including headache response at 2 h. Oral zolmitriptan is also effective in the acute treatment of cluster headache. Zolmitriptan is generally well tolerated, with most adverse events being mild-to-moderate, transient and resolving without intervention or the need for treatment withdrawal. The consistent efficacy in treating all types of migraine and the choice of available formulations make zolmitriptan acceptable to patients and a suitable first-line therapy for the treatment of migraine.

Adenosine A1 receptor agonists inhibit trigeminovascular nociceptive transmission

There is a considerable literature to suggest that adenosine A1 receptor agonists may have anti-nociceptive effects, and we sought to explore the role of adenosine A1 receptors in a model of trigeminovascular nociceptive transmission. Cats were anaesthetized (alpha-chloralose 60 mg/kg, intraperitoneally), and prepared for physiological monitoring. The superior sagittal sinus (SSS) was stimulated electrically, and linked units were recorded in the trigeminocervical complex. Post-stimulus histograms were constructed to analyse the responses and the effect of drug administration. Blood was sampled from the external jugular vein to determine levels of calcitonin gene-related peptide (CGRP) release before and after drug administration. Intravenous administration of the highly selective adenosine A1 receptor agonist, GR79236 (3-100 microg/kg) had a dose-dependent inhibitory effect on SSS-evoked trigeminal activity. The maximal effect (80 +/- 6% reduction in probability of firing) was seen at 100 microg/kg. The neuronal inhibitory effect of GR79236 could be inhibited by the selective adenosine A1 receptor antagonist DPCPX (300 microg/kg; P < 0.05). SSS stimulation increased cranial CGRP levels from 33 +/- 2 pmol/l (n = 6) to 64 +/- 3 pmol/l, an effect substantially reduced by pre-treatment with GR79236 (30 microg/kg; P < 0.01). The selective low efficacy adenosine A1 receptor agonist, GR190178 (30-1000 microg/kg i.v.), also inhibited SSS-evoked neuronal activity in a dose-dependent fashion. In this model of trigeminovascular nociception, adenosine A1 receptor activation leads to neuronal inhibition without concomitant vasoconstriction, suggesting a novel avenue for the treatment of migraine and cluster headache.

Zolmitriptan versus a combination of acetylsalicylic acid and metoclopramide in the acute oral treatment of migraine: a double-blind, randomised, three-attack study

This multicentre, randomised, double-blind study compared oral zolmitriptan 2.5 mg with a combination of oral acetylsalicylic acid 900 mg and metoclopramide 10 mg as acute anti-migraine therapy for 3 migraine attacks. In total, 666 patients took at least one dose of study medication (326 took zolmitriptan and 340 took acetylsalicylic acid plus metoclopramide). The percentage of patients with a 2-hour headache response after the first dose for all 3 attacks (the primary end point) was 33.4% with zolmitriptan and 32.9% with acetylsalicylic acid plus metoclopramide [odds ratio 1.06, 95% confidence interval (CI) 0.77-1.47; p = 0.7228]. For the majority of secondary end points, the two treatments demonstrated comparable efficacy. However, post hoc analysis showed that significantly more patients receiving zolmitriptan were free of pain 2 h after the first dose in all 3 attacks compared with patients receiving acetylsalicylic acid plus metoclopramide (10.7 vs. 5.3%; odds ratio 2.19, 95% CI 1.23-4.03; p = 0.0095). In addition, post hoc analysis showed that the overall 2-hour pain-free response rate was consistently higher with zolmitriptan (34.6%) than with acetylsalicylic acid plus metoclopramide (27.9%) (odds ratio 1.40, 95% CI 1.09-1.78; p = 0.007). Both treatments reduced migraine-associated nausea, vomiting, phonophobia and photophobia. There were no important inter-group differences with respect to the onset of meaningful migraine relief, the frequency of headache recurrence, the usage or efficacy of a second dose of medication or the use of escape medication. However, at the last attack, the proportion of patients who expressed overall satisfaction with the treatment was significantly higher in the zolmitriptan group, i.e. 83.7%, versus 75.0% with acetylsalicylic acid plus metoclopramide (p = 0.0346). Both agents were well tolerated. Adverse events were reported by 40.8% (133/326) of zolmitriptan-treated patients and 29.1% (99/340) of those treated with acetylsalicylic acid plus metoclopramide. The incidence of withdrawals due to adverse events was very low with both zolmitriptan (0.9%) and the combination regimen (1.5%); the latter percentage included 1 patient who withdrew from the study due to phlebitis, which was classified as a serious adverse event. This study showed that zolmitriptan is effective and well tolerated for the acute treatment of moderate to severe migraine. Zolmitriptan was at least as effective as acetylsalicylic acid plus metoclopramide in achieving a 2-hour headache response, but significantly more effective than the combination therapy for other end points, including the 2-hour pain-free response.

Advances in pharmacological treatment of migraine

Migraine is a paroxysmal disorder with attacks of headache, nausea, vomiting, photo- and phonophobia and malaise. This review summarises new treatment options both for the therapy of the acute attack as well as for migraine prophylaxis. Analgesics like aspirin or non-steroidal anti-inflammatory drugs (NSAIDs) are effective in treating migraine attacks. Few controlled trials were performed for the use of ergotamine or dihydroergotamine. These trials indicate inferior efficacy compared with serotonin (5-HT(1B/D)) agonists (triptans). The triptans (almotriptan, eletriptan, frovatriptan, naratriptan, rizatriptan, sumatriptan and zolmitriptan), are highly effective. They improve headache as well as nausea, photo- and phonophobia. The different triptans show only minor differences in efficacy, headache recurrence and adverse effects. The knowledge of their different pharmacological profile allows a more specific treatment of the individual migraine characteristics. Migraine prophylaxis is recommended, when more than three attacks occur per month, if attacks do not respond to acute treatment or if side effects of acute treatment are severe. Substances with proven efficacy include the beta-blockers metoprolol and propranolol, the calcium channel blocker flunarizine, several 5-HT antagonists and amitriptyline. Recently anti-epileptic drugs (valproic acid, gabapentin, topiramate) were evaluated for the prophylaxis of migraine. The use of botulinum toxin is under investigation.

Serotonergic effects and extracellular brain levels of eletriptan, zolmitriptan and sumatriptan in rat brain

In vivo microdialysis was used to assess the central serotonergic effects and extracellular brain levels of the 5-HT(1B/1D) receptor agonists eletriptan, zolmitriptan and sumatriptan in rats after intravenous and intracerebral administration, while their binding affinities and functional potencies were determined at 5-HT(1B), 5-HT(1D) and 5-HT(1A) receptors. In vitro studies showed that all three triptans are high affinity, full agonists at 5-HT(1B/1D) receptors, but that sumatriptan is functionally less potent as a 5-HT(1B/1D) agonist than zolmitriptan and eletriptan. Local intracortical perfusion with the compounds via the dialysis probe decreased cortical 5-HT (5-hydroxytryptamine, serotonin) release with ED(50) values of approximately 0.1 microM for eletriptan and zolmitriptan and 0.5 microM for sumatriptan. At 3.2 mg/kg i.v., both eletriptan and zolmitriptan decreased 5-HT levels by about 35%, while sumatriptan had no effect, despite the fact that maximal sumatriptan concentrations in cortical dialysates were higher (8.8 nM at 20 min) than those of zolmitriptan (5.9 nM at 20 min) and eletriptan (2.6 nM at 40 min). The observation that eletriptan and zolmitriptan produce almost identical central serotonergic effects, after intracerebral as well as after systemic administration, is in agreement with their comparable functional 5-HT(1B/1D) receptor agonist potencies and their free levels in cortical dialysates after 3.2 mg/kg i.v. On the other hand, the lack of central serotonergic effects of 3.2 mg/kg i.v. sumatriptan is likely due to its weaker functional 5-HT(1B/1D) receptor agonist potency than eletriptan and zolmitriptan, rather than lower brain levels, consistent with sumatriptan's fivefold lower potency after intracerebral administration.

The pharmacology of headache

Headache is a common problem which besets most of us at some time or the other. The pharmacology of headache is complex in an overall sense but can be understood in terms of the anatomy and physiology of the pain-producing structures. Migraine can be used as a template to understand the activation of nociceptive systems in the head and thus their neurotransmitter mediation and modulation. In recent years, the role of serotonin (5-HT) in headache pharmacology has been unravelled in the context of both understanding its role in the nociceptive systems related to headache and by exploiting its 5-HT1 receptor subtypes in headache therapeutics. The pharmacology of the head pain systems, as they are known and as they might evolve, are explored in the context of both, the anatomy and physiology of trigeminovascular nociception and in the context of clinical questions, such as those of efficacy, headache recurrence and adverse events.

5-HT(1A) and 5-HT(1B/1D) receptors are involved in the modulation of the trigeminovascular system of the cat: a microiontophoretic study

Electrical stimulation of the superior sagittal sinus in the cat activated neurones in the trigeminal nucleus caudalis. The mean latency of these responses (10.1 ms) was consistent with activation of Adelta-fibres. Microiontophoretic ejection of either the selective serotonin(1A) (5-HT(1A)) agonist (+)8-OH-DPAT or the 5-HT(1B/1D) agonist alniditan resulted in the reversible suppression of the response to superior sagittal sinus stimulation of 29/46 and 18/20 trigeminal neurones, respectively. The response to sagittal sinus stimulation was suppressed by 39+/-5% (n=46) by (+)8-OH-DPAT and 65+/-5% (n=20) by alniditan. Microiontophoretic ejection of the selective 5-HT(1A) receptor antagonist WAY-100635 significantly antagonised the effect of (+)8-OH-DPAT (effect reduced by 30%, P<0.05). The ejection of GR-127935, a selective 5-HT(1B/1D), antagonist, significantly antagonised the effect of alniditan (effect reduced by 52%, P<0.02). In eight neurones the response to convergent facial receptive field stimulation was also tested in the presence of alniditan. Only 4/8 receptive field responses were suppressed by alniditan (compared to 8/8 sagittal sinus responses) and alniditan had significantly less quantitative effect on the response to receptive field stimulation than on the response to sagittal sinus stimulation in the same neurones (mean reduction 36+/-14% and 66+/-8%, respectively, P<0.05). These results suggest that pharmacological modulation of the trigeminovascular system can occur at the first central synapse and that, in addition to 5-HT(1B/1D) receptors, 5-HT(1A) receptors may be involved in the modulation of sensory neurotransmission in the trigeminovascular system.

Zolmitriptan stimulates a Ca(2+)-dependent K(+) current in C6 glioma cells stably expressing recombinant human 5-HT(1B) receptors

Stimulation of a Ca(2+)-dependent K(+) current by zolmitriptan, a 5-HT(1B/1D) receptor partial agonist, was investigated in C6 glioma cells stably expressing recombinant human 5-HT(1B) receptors. Outward K(+) currents (I(K)) were examined in non-transfected C6 glioma cells and in cells expressing cloned human 5-HT(1B) receptors using the patch-clamp technique in the whole-cell configuration. In C6 glioma cells expressing recombinant human 5-HT(1B) receptor, zolmitriptan increased I(K) in a concentration-dependent manner (maximum increase 16.3+/-7.8%, n=5, p<0.001) with a pD(2) value (geometric mean with 95% confidence intervals) of 7.03 (7.90-6.10). Zolmitriptan failed to elicit increases in I(K) in non-transfected C6 cells. In the presence of the mixed 5-HT(1B/1D) receptor antagonist, N-[4-methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2(-methyl-4(5-methyl-1 ,2,4)-oxadiazol-3-yl)[1,1-biphenyl]-4-carboxamide 2HCl (GR 127935, 0. 1 mcM), zolmitriptan (1 mcM) failed to significantly increase I(K) in C6 cells expressing human 5-HT(1B) receptors confirming that zolmitriptan-evoked responses were indeed mediated by human 5-HT(1B) receptors. In C6 cells expressing cloned human 5-HT(1B) receptors, zolmitriptan-induced increases in I(K) were prevented by the calcium chelator, EGTA (5 mM) when included in the patch pipette (maximum increase -3.3+/-4.2%, n=4, P=NS). The Ca(2+)-dependent K(+) channel blockers, iberiotoxin (0.1 mcM) and tetraethylammonium (TEA, 1 mM), abolished zolmitriptan-induced increases in I(K) (4.5+/-7.3%, n=4 and -0.8+/-1.7%, n=4, respectively, P=NS in each case) in C6 cells expressing human 5-HT(1B) receptors, confirming the involvement of Ca(2+)-dependent K(+) channels. In conclusion, the 5-HT(1B/1D) receptor partial agonist, zolmitriptan, stimulates I(K/Ca) in C6 glioma cells stably transfected with human 5-HT(1B) receptors suggesting an increase of hyperpolarizing current.

Comparison of the efficacy of zolmitriptan and sumatriptan: issues in migraine trial design

In this international, multicentre, double-blind, placebo-controlled, single attack study, 'triptan naive' migraine patients were randomized in an 8:8:1 ratio to receive zolmitriptan 5 mg, sumatriptan 100 mg or placebo. The all-treated analysis included 1058 patients who took study medication. The primary endpoint, complete headache response, was reported by 39%, 38% and 32% of patients treated with zolmitriptan, sumatriptan and placebo, respectively, with no significant difference between treatment groups. In patients with moderate headache at baseline, complete response was significantly greater following zolmitriptan than after placebo (48% vs. 27%; P=0.01); there was no significant difference between sumatriptan and placebo groups (40% vs. 27%). In patients with severe baseline headache (where a greater reduction in headache intensity is required for a headache response), there was no significant difference between any groups in complete headache response rates. For secondary endpoints, active treatment groups were significantly superior to placebo for: 1-, 2- and 4-h headache response (e.g. 2-h headache response rates: zolmitriptan 59%; sumatriptan 61%; placebo 44%; P < 0.01 vs. placebo); pain-free response rates at 2 and 4 h; alleviation of nausea and vomiting; use of escape medication and restoration of normal activity. The incidence of adverse events was similar between zolmitriptan and sumatriptan groups but was slightly lower in the placebo group. The lack of difference between active treatments and placebo for complete response probably reflects the high placebo response obtained, which is probably a result of deficiencies in trial design. For example, the randomization ratio may result in high expectation of active treatment. Thus, while ethically patient exposure to placebo should be minimized, this must be balanced against the scientific rationale underpinning study design.

Auditory evoked potentials in the assessment of central nervous system effects of antimigraine drugs

Because the "intensity dependence" of cortical auditory evoked potentials (IDAP) is under serotonergic control, it can be used to assess central antimigraine effects of 5HT1B/1D agonists. We measured IDAP before and 2 h after naratriptan (5 mg, n = 19) and zolmitriptan (5 mg, n = 19) in healthy volunteers. IDAP was expressed as the amplitude-stimulus intensity function ("ASF slope"). Naratriptan tended to increase ASF slope (mean difference 0.23 +/- 0.62 microV/10 dB, p = 0.06) while zolmitriptan (0.08 +/- 0.95 microV/10 dB, p = 0.35) did not. We assessed the suitability of IDAP for measuring central antimigraine drug effects using repeatability data (see companion paper). We calculated the trade-off between the size of the expected drug effects (ASF slope difference) and the necessary sample size. Because of poor repeatability 36 to 80 subjects are required to detect ASF slope changes in the 0.25-0.5 microV/10 dB range. These data can be used to design trials using IDAP.

Humanization of mouse 5-hydroxytryptamine1B receptor gene by homologous recombination: in vitro and in vivo characterization

We replaced the coding region of the murine 5-hydroxytryptamine (5-HT)1B receptor by the human 5-HT1B receptor using homologous recombination in embryonic stem cells and generated and characterized homozygous transgenic mice that express only the human (h) 5-HT1B receptor. The distribution patterns of h5-HT1B and murine (m) 5-HT1B receptor mRNA and binding sites in brain sections of transgenic and wild-type mice were identical as measured by in situ hybridization histochemistry and radioligand receptor autoradiography. When measured in parallel under identical conditions, the h5-HT1B receptor expressed in mouse brain had the same pharmacological characteristics as that in human brain. Stimulation by 5-HT1B agonists of [35S]guanosine-5'-O-(3-thio)triphosphate binding in brain sections demonstrated the functional coupling of the h5-HT1B receptor to G proteins in mouse brain. In tissue slices from various brain regions, electrically stimulated [3H]5-HT release was not modified by 5-HT1B agonists in tissue from either transgenic and wild-type mice; a 5-HT1B antagonist enhanced electrically stimulated [3H]5-HT release in wild-type mouse brain, but was ineffective in the transgenics. The centrally active 5-HT1A/5-HT1B agonist RU24969 induced hypothermia but did not increase locomotor activity in the transgenic mice. The ineffectiveness of RU24969 in the transgenic mice could be due to the lower affinity of the compound for the h5-HT1B receptor compared with the m5-HT1B receptor. The present study demonstrates a complete replacement of the mouse receptor by its human receptor homolog and a functional coupling to G proteins. However, modulation of [3H]5-HT release could not be shown. Furthermore, behavioral effects were not clearly observed, which may be due to a lack of appropriate tools.

Acute management of migraine: triptans and beyond

Migraine is a paroxysmal disorder characterized by attacks of headache, nausea, vomiting, photophobia and phonophobia, and malaise. This review summarizes new treatment options for the therapy of acute attacks. Sumatriptan was the first specific serotonin-1B/D agonist for the treatment of acute migraine attacks. Apart from the oral and subcutaneous formulation, it is also available as nasal spray and suppository. The other new migraine drugs zolmitriptan, naratriptan, rizatriptan and eletriptan differ in their pharmacological profiles, which translates into minor differences in efficacy, headache recurrence and side-effects. Importantly, in clinical practice individual patients may show a preference for one treatment over another. New drugs in migraine treatment include substance-P antagonists, nitric oxide synthetase inhibitors and calcitonin gene-related peptide antagonists.

Trigeminovascular nociceptive transmission involves N-methyl-D-aspartate and non-N-methyl-D-aspartate glutamate receptors

Interest in the fundamental mechanisms underlying headache, particularly the pathophysiology of migraine and cluster headache, has lead to the study of the physiology and pharmacology of the trigeminovascular system and its central ramifications. Cats were anaesthetized (60 mg/kg alpha-chloralose, i.p., along with halothane for all surgical procedures) and prepared for physiological monitoring. The animals were placed in a stereotaxic frame and ventilated. A midline craniotomy and C2 laminectomy were performed for access to the superior sagittal sinus and C2 dorsal horn, respectively. The sinus was isolated from the underlying cortex and stimulated electrically after the animals had been paralysed with gallamine (6 mg/kg, i.v.). Units linked to stimulation were recorded with a tungsten-in-glass microelectrode placed in the most caudal part of the trigeminal nucleus, the trigeminocervical complex. Signals from the neurons were amplified, filtered and passed to a microcomputer, where post-stimulus histograms were constructed on-line to analyse the responses to stimulation. Units responded to sagittal sinus stimulation with a typical latency of 8-10 ms. All units studied had a probability of firing of 0.6 or greater. Intravenous injection of the non-competitive N-methyl-D-aspartate receptor antagonist, dizocilpine maleate (4 mg/kg, i.v.), resulted in a substantial and prolonged blockade of firing of units in the trigeminocervical complex. Similarly, administration of the non-N-methyl-D-aspartate excitatory amino acid receptor blocker, GYKI 52466, lead to a dose-dependent inhibition of trigeminovascular-evoked responses in the trigeminocervical complex. These data demonstrate the participation of both N-methyl-D-aspartate- and non-N-methyl-D-aspartate-mediated mechanisms in transmission within the trigeminocervical complex, and suggest a clear preclinical role of glutamatergic mechanisms in primary headache syndromes, such as migraine and cluster headache.

Effects of zolmitriptan (Zomig) on central serotonergic neurotransmission as assessed by active oddball auditory event-related potentials in volunteers without migraine

In this randomized, double-blind, three-period crossover trial, 24 healthy volunteers without migraine received zolmitriptan 5 mg, dexfenfluramine 15 mg or placebo orally. At 2, 6, and 24 h postdose, auditory stimuli of 1000 Hz (nontarget tone) and 2000 Hz (target tone) were randomly and binaurally presented in an active oddball paradigm (4:1 ratio). Cortical auditory evoked responses were recorded for 500 msec poststimulus. Plasma concentrations of zolmitriptan and a 17-lead quantitative EEG were assessed at the same timepoints. Relative to placebo, zolmitriptan reduced the maximum absolute amplitude, amplitude difference (from nontarget tone noise) and area under the curve of the cortical auditory target tone event-related potential (P300 ERP). The most dramatic effect of zolmitriptan was to diminish the point estimate of noise during the 200-400 msec poststimulus epoch. The effect of zolmitriptan appeared concentration dependent. The latency of the P300 ERP was unaffected by zolmitriptan and there was no clinically significant effect on the EEG. Modification by zolmitriptan of the cortical electrical activity evoked by auditory stimuli confirms a central action of this drug in humans, which appears to affect cortical information processing without global alteration of the quantitative EEG.

Vasoconstriction in human isolated middle meningeal arteries: determining the contribution of 5-HT1B- and 5-HT1F-receptor activation

AIMS

Sumatriptan is a 5-HT1B/1D-receptor agonist which also has affinity for 5-HT1F-receptors. The vasoconstrictor effects of sumatriptan are thought to be 5-HT1B-receptor mediated and these receptors have been shown to be expressed in human cranial blood vessels. However, in the same tissue mRNA coding for 5-HT1F-receptors has also been identified and this study addresses the possibility of whether 5-HT1F-receptor activation contributes to vasoconstriction.

METHODS

The ability of two selective 5-HT1B/1D-receptor antagonists (GR125,743 and GR127,935) with no affinity for 5-HT1F-receptors, to inhibit sumatriptan evoked contractions in human isolated middle meningeal artery was investigated. Using a series of 5-HT1B/1D-receptor agonists (sumatriptan, zolmitriptan, CP122,288, L-741,519 and L-741,604), some with high affinity for 5-HTIF-receptors and the non-selective 5-HT-receptor agonists 5-HT and 5-CT, we compared the vasoconstrictor potency of these drugs in human isolated middle meningeal artery with their affinities at cloned human 5-HT1B-, 5-HT1D-and 5-HT1F-receptors expressed in CHO cell lines.

RESULTS

GR125,743 antagonized sumatriptan evoked contractions in a competitive manner (apparent pA2 9.1) and GR127,935 antagonized sumatriptan-induced responses in a non-competitive manner (reducing the maximum contraction to 27%). There was a significant correlation between vasoconstrictor potency and 5-HT1B-receptor affinity (r=0.93, P=0.002) but not with 5-HT1D- or 5-HT1F-receptor affinity (r=0.74, P=0.06; r= 0.31, P= 0.49, respectively).

CONCLUSIONS

These experiments show that in human middle meningeal artery vasoconstriction to sumatriptan-like agents is 5-HT1B-receptor mediated with little if any contribution from 5-HT1F-receptor activation.

Release of immunoreactive substance P in the brain stem upon stimulation of the cranial dura mater with low pH - inhibition by the serotonin (5-HT1) receptor agonist CP 93,129

1. The therapeutical benefit of serotonin (5-HT1) receptor agonists in the treatment of migraine headache has been attributed to their inhibitory effect on the release of pro-inflammatory neuropeptides from trigeminal afferents within the cranial meninges. The effect of 5-HT1 receptor agonists on the release of neuropeptides from central afferent terminals has not been examined so far. In the present study in the rat we therefore measured the effect of the 5-HT1B receptor agonist CP 93,129 on the stimulation-evoked release of immunoreactive substance P (ir-SP) in the spinal trigeminal nucleus. 2. To measure release of ir-SP, microprobes coated with antibody to substance P were inserted into the medulla oblongata at the level of the obex. The ipsilateral parietal dura mater encephali was exposed and stimulated with acid phosphate buffered Tyrode solution (pH 5.8). This chemical stimulus increased the release of ir-SP in the medullary dorsal horn. 3. Systemic (i.v.) administration of CP 93,129 (460 nmol kg(-1)) prior to stimulation suppressed the stimulation-evoked increase of release of ir-SP. Local administration of CP 93,129 (10 microM) to the dorsal surface of the medulla had no significant inhibitory effect on the release. 4. It is concluded that systemically applied 5-HT1 receptor agonists reduce the stimulation-evoked release of substance P from the central endings of meningeal afferents in the spinal trigeminal nucleus (medullary dorsal horn). This inhibitory effect may contribute to the antinociceptive effect of 5-HT1 receptor agonists in migraine.

The effects of 5-HT1A, 5-HT1B and 5-HT1D receptor agonists on trigeminal nociceptive neurotransmission in anaesthetized rats

Pre-clinical studies have suggested that one mechanism of antimigraine action of the 'triptan' 5-HT1B/1D receptor agonists may be through inhibition of central nociceptive transmission in the trigeminal dorsal horn. In anaesthetized rats, the 5-HT1B/1D receptor agonist, zolmitriptan (up to 3 mg kg(-1), i.v.), inhibited the action potential discharge of single trigeminal neurones to noxious electrical stimulation of the middle meningeal artery. In contrast, the selective 5-HT1B receptor agonist, CP-93,129 (3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one), and the 5-HT1A receptor selective agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) had no effect in this assay at up to 3 mg kg(-1), i.v.. Brain penetrant, triptan 5-HT1B/1D receptor agonists may therefore mediate their central trigeminal anti-nociceptive action in the rat via 5-HT1D, but not 5-HT1B or 5-HT1A, receptors.

Cranial vascular effects of zolmitriptan, a centrally active 5-HT1B/1D receptor partial agonist for the acute treatment of migraine

The anti-migraine drug zolmitriptan is a novel 5-HT1B/1D receptor partial agonist which, unlike sumatriptan, has been shown to cross the intact blood-brain barrier. In this study we examined whether or not the ability to access the cerebro-vascular intima affects the way in which a centrally-active 5-HT1B/1D receptor agonist influences cranial haemodynamics. The effects of zolmitriptan on carotid arterial blood flow distribution were studied in anaesthetised cats using radiolabelled microspheres. Zolmitriptan (10-1000 microg kg(-1) i.v.) selectively reduced arteriovenous-anastomotic (AVA) conductance producing a maximum decrease of 92.5+/-2.3%. The drug also produced a modest reduction in extra-cerebral conductance (23.9+/-6.5% maximum reduction at 30 microg kg(-1), i.v.), but was without effect on cerebral conductance. Using laser doppler flowmetry in anaesthetised cats, zolmitriptan (1-30 microg kg(-1), i.v.) produced dose-dependent decreases in ear microvascular conductance (15+/-5 to 60+/-6%) which mirrored decreases in carotid arterial conductance (12+/-11 to 61+/-5%). By contrast, zolmitriptan at doses up to 1000 microg kg(-1) was without effect on cerebral microvascular conductance. Although zolmitriptan crosses the blood-brain barrier and can therefore access the cerebro-vascular intima, this study suggests that this property does not adversely affect cerebrovascular function.

Zolmitriptan, a 5-HT1B/1D receptor agonist for the acute oral treatment of migraine: a multicentre, dose-range finding study

Zolmitriptan is a selective 5-HT1B/1D receptor agonist for acute oral migraine therapy. This randomized, placebo-controlled, parallel-group study investigated the efficacy and tolerability of oral zolmitriptan (5, 10, 15 and 20 mg) in the treatment of single acute migraine attacks. Of 1181 patients randomized, 840 were evaluable for the primary efficacy analysis. Headache response rates (a reduction in headache intensity from severe or moderate at baseline to mild or no pain at 2 hours post-treatment) were similar across the zolmitriptan dose groups (66%, 71%, 69% and 77% for 5 mg, 10 mg, 15 mg and 20 mg, respectively) and were significantly higher than that for placebo (19%; all groups P < 0.001). A headache response was reported at 1 hour by 40-50% of zolmitriptan recipients (16% placebo). At 2 hours post dose, 39-47% of zolmitriptan-treated patients were pain-free, compared with 1% of placebo recipients. Headache recurrence occurred in 21-29% (upper 95% CI 37.1) of zolmitriptan-treated patients and in 65% (95% CI 38.3, 85.8) of placebo recipients. Zolmitriptan was well tolerated at each dose. The most commonly reported adverse events were asthenia, dizziness, paraesthesia and feelings of heaviness. Most adverse events were of mild or moderate intensity and were transient. The frequency of adverse events was dose-related. Although, zolmitriptan 5 mg exhibited the most favourable efficacy and tolerability profile, the dose response data suggest that lower doses would also offer significant efficacy. Copyright 1998 Lippincott Williams & Wilkins

Serotonin inhibits trigeminal nucleus activity evoked by craniovascular stimulation through a 5HT1B/1D receptor: a central action in migraine?

The development of serotonin (5HT1B/1D) agonists as treatments for the acute attack of migraine has resulted in considerable interest in their mechanism of action and, to some extent, renewed interest in the role of serotonin (5-hydroxytryptamine; 5HT) in the disorder. The initial synthesis of this class of compounds was predicated on the clinical observation that intravenous 5HT terminated acute attacks of migraine. In this study the superior sagittal sinus was isolated in the alpha-chloralose (60 mg/kg i.p. and 20 mg/kg i.v. injection supplementary 2 hourly) anesthetized cat. The sinus was stimulated electrically (120V, 250 microsec duration, 0.3 Hz), and neurons of the trigeminocervical complex in the dorsal C2 spinal cord were monitored using electrophysiological methods. After baseline recordings in each animal, 5HT (15 microg/kg/min) was infused for 5 minutes in the presence of either vehicle (group A) or the 5HT1B/1D antagonist GR127935 (100 microg/kg i.v. injection; group B). The baseline probability of cell firing after sagittal sinus stimulation was 0.61 +/- 0.1 at a latency to the fastest peak of 11.1 +/- 0.4 msec. In group A, 5HT infusion alone had a small effect of increasing mean blood pressure (12 +/- 3 mm Hg), which in itself did not alter cell firing. In group A, 5HT alone had an inhibitory effect on evoked trigeminal activity, which developed 15 to 20 minutes after commencement of the infusion. The inhibition of cell firing lasted for 20 minutes, after which the activity returned to baseline. In group B, the combination of 5HT and GR127935 had no effect on trigeminal cell firing, although the small hypertensive effect was still present. These data indicate that 5HT inhibits evoked trigeminal nucleus firing via the 5HT1B/1D receptor at which GR127935 is an antagonist. It is likely that some part of the effect of 5HT in migraine relates to inhibition of trigeminal nucleus activity, just as it is likely that some part of the effect of the triptans is also mediated at this central site and may be complementary to their nonneuronal actions. Moreover, the data highlight the case for describing this class of headache as neurovascular headaches rather than vascular headaches, to recognize the implicit contribution of the trigeminovascular system to their pathophysiology.

Dimerization of sumatriptan as an efficient way to design a potent, centrally and orally active 5-HT1B agonist

A new bivalent ligand of formula 3 which results from the covalent coupling of two sumatriptan molecules with a p-xylyl spacer at the level of the sulfonamide nitrogen has been prepared and evaluated as a 5-HT1B/1D receptors agonist. In vitro experiments at 5-HT1B human cloned receptors (Ki = 0.64 nM; EC50 = 0.58 nM) and at the level of the contraction of the New Zealand white rabbit saphenous vein (pD2 = 6.6) demonstrate the superior potency of dimer 3 as a 5-HT1B receptor agonist when compared to sumatriptan or zolmitriptan. Interestingly enough, the new bivalent agonist 3 was found to induce hypothermia in the guineapig upon oral administration suggesting good oral activity and access to the brain.

Comparison of more and less lipophilic serotonin (5HT1B/1D) agonists in a model of trigeminovascular nociception in cat

The trigeminovascular system consists of bipolar neurons innervating pain-producing intracranial structures, such as the superior sagittal sinus (SSS), and projecting to the medullary and upper cervical dorsal horn second order neurons. Zolmitriptan is a newly developed 5HT1B/1D receptor agonist with both peripheral and central sites of action in the trigeminovascular system due to greater lipophilicity relative to the more hydrophilic antimigraine compound sumatriptan. Given that we have seen electrophysiological and autoradiographic binding data to suggest that the compound may inhibit activity at second-order neurons this study was designed to examine whether such an effect could be demonstrated in a population of trigeminal neurons using Fos immunohistochemistry. Cats were anesthetised with alpha-chloralose (60 mg/kg intraperitoneal then 20 mg/kg intravenous maintenance) with all surgery being conducted using halothane (1-3%). The animals were prepared for physiological monitoring, including blood pressure, heart rate, rectal temperature, and end-expiratory CO2. They were intubated, ventilated, and paralyzed with gallamine triethiodide (6 mg/kg i.v.). A midline craniotomy was performed to expose the sinus for electrical stimulation using hook electrodes. Twenty-four hours after completion of the surgical procedures the animal was ready for treatment. Vehicle, sumatriptan (85 micrograms/kg), or zolmitriptan (30 micrograms/kg) was administered and the SSS was stimulated (250 microseconds, 100 V at 0.3 Hz) for 1 h. Following an additional 1 h the animal was perfused and immunohistochemistry was used to detect the protein product of the immediate early gene c-Fos. We compared the dorsal horns of the medulla (trigeminal nucleus caudalis) and the C1 and C2 cervical spinal cords in control animals with those receiving zolmitriptan or sumatriptan. We noted a significant reduction in Fos expression after treatment with zolmitriptan but no effect with sumatriptan. Given that zolmitriptan accesses central neurons and that the method of stimulation we have employed would bypass peripheral trigeminal mechanisms it is likely that the reduction in second-order trigeminal neuronal activity was due to a direct inhibitory effect of the compound on those cells. These neurons form a possible site for the treatment of acute attacks of migraine.