Pharmacological opportunities and pitfalls in the therapy of migraine

Perivascular neurotransmitters: Regulation of cerebral blood flow and role in primary headaches

In order to understand the nature of the relationship between cerebral blood flow (CBF) and primary headaches, we have conducted a literature review with particular emphasis on the role of perivascular neurotransmitters. Primary headaches are in general considered complex polygenic disorders (genetic and environmental influence) with pathophysiological neurovascular alterations. Identified candidate headache genes are associated with neuro- and gliogenesis, vascular development and diseases, and regulation of vascular tone. These findings support a role for the vasculature in primary headache disorders. Moreover, neuronal hyperexcitability and other abnormalities have been observed in primary headaches and related to changes in hemodynamic factors. In particular, this relates to migraine aura and spreading depression. During headache attacks, ganglia such as trigeminal and sphenopalatine (located outside the blood-brain barrier) are variably activated and sensitized which gives rise to vasoactive neurotransmitter release. Sympathetic, parasympathetic and sensory nerves to the cerebral vasculature are activated. During migraine attacks, altered CBF has been observed in brain regions such as the somatosensory cortex, brainstem and thalamus. In regulation of CBF, the individual roles of neurotransmitters are partly known, but much needs to be unraveled with respect to headache disorders.

Pharmacological neuroimaging in headache and pain

PURPOSE OF REVIEW

The current review gives an overview about recent advances in neuroimaging studies with specific emphasis on pharmacological modulation of pain and headache. Further, we want to highlight how imaging methods have changed our understanding of chronic pain and discuss how pharmacological MRI could lead to new insights into underlying mechanisms of headache and pain.

RECENT FINDINGS

Several studies from different imaging laboratories have highlighted the outstanding role of imaging in getting a deeper insight regarding the central mechanisms of drugs. Neuroimaging techniques start to unravel how analgesic drugs, antidepressants or NSAIDs act on pain perception and in particular on central pain processes. Furthermore, the studies included in this review show how context dependent drugs act and how differently they reveal their action in the human brain.

SUMMARY

Imaging techniques give us the opportunity to gain a better understanding of drug processes in the central nervous system and help to understand where drugs reveal their therapeutic effect. While some substances work on the emotional-affective component of pain, others modulate sensory-discriminative pain pathways. Especially in the field of headache research, still a lot has to be done to understand how preventatives and acute medication modulate the human brain. Future studies should also replicate and extend recent findings.

Patient outcome in migraine prophylaxis: the role of psychopharmacological agents

INTRODUCTION

Migraine is a serious illness that needs correct treatment for acute attacks and, in addition, a treatment prophylaxis, since patients with migraine suffer during acute attacks and also between attacks.

METHODS

A systematic review of the most relevant clinical trials of migraine headache and its epidemiology, pathophysiology, comorbidity, and prophylactic treatment (medical and nonmedical) was carried out using "Medline" and "PsychINFO" from 1973 to 2009. Approximately 110 trials met our inclusion criteria and were included in the current review.

RESULTS

The most effective pharmacological treatment for migraine prophylaxis is propranolol and anticonvulsants such as topiramate, valproic acid, and amitriptyline. Nonmedical treatments such as acupuncture, biofeedback, and melatonin have also been proposed. Peripheral neurostimulation has been suggested for the treatment of chronic daily headache that does not respond to prophylaxis and for the treatment of drug-resistant primary headache. The majority of the pharmacological agents available today have limited efficacy and may cause adverse effects incompatible with long-term use.

LIMITATIONS

The review was limited by the highly variable and often insufficient reporting of the complex outcome data and by the fact that migraine prophylaxis trials typically use headache diaries to monitor the course of the disease. The results of the different studies were also presented in different ways, making comparison of the results difficult.

DISCUSSION

An adequate prophylaxis is crucial in reducing disability and preventing the evolution of the problem into a chronic progressive illness. The implications of the present findings were discussed.

Capillary endothelial Na(+), K(+), ATPase transporter homeostasis and a new theory for migraine pathophysiology

BACKGROUND

Cerebrospinal fluid sodium concentration ([Na(+)](csf)) increases during migraine, but the cause of the increase is not known.

OBJECTIVE

Analyze biochemical pathways that influence [Na(+)](csf) to identify mechanisms that are consistent with migraine.

METHOD

We reviewed sodium physiology and biochemistry publications for links to migraine and pain.

RESULTS

Increased capillary endothelial cell (CEC) Na(+), K(+), -ATPase transporter (NKAT) activity is probably the primary cause of increased [Na(+)](csf). Physiological fluctuations of all NKAT regulators in blood, many known to be involved in migraine, are monitored by receptors on the luminal wall of brain CECs; signals are then transduced to their abluminal NKATs that alter brain extracellular sodium ([Na(+)](e)) and potassium ([K(+)](e)).

CONCLUSIONS

We propose a theoretical mechanism for aura and migraine when NKAT activity shifts outside normal limits: (1) CEC NKAT activity below a lower limit increases [K(+)](e), facilitates cortical spreading depression, and causes aura; (2) CEC NKAT activity above an upper limit elevates [Na(+)](e), increases neuronal excitability, and causes migraine; (3) migraine-without-aura may arise from CEC NKAT over-activity without requiring a prior decrease in activity and its consequent spreading depression; (4) migraine triggers disturb, and treatments improve, CEC NKAT homeostasis; (5) CEC NKAT-induced regulation of neural and vasomotor excitability coordinates vascular and neuronal activities, and includes occasional pathology from CEC NKAT-induced apoptosis or cerebral infarction.

Botulinum Toxin—A Treatment for Migraine? A Systematic Review

Scalp injection of botulinum toxin type A (BT-A) into the superficial musculature has evoked interest in the management of migraine headache. In clinical trials, prevention of migraine attacks for 3 months or more has been seen in some patients following BT-A scalp injections. In the majority of pain syndromes where BT-A is effective, inhibition of muscle spasms appears to be an important component of its activity. A direct or independent and prolonged analgesic action unrelated to skeletal muscle relaxation is believed to underlie the prophylactic efficacy of BT-A in migraine; peripheral and central modulation of pain impulses by BT-A has also been proposed. A direct peripheral antinociceptive effect was not seen in three controlled studies of BT-A in normal human volunteers. Experimental evidence for BT-A-induced analgesia in rats is suggestive but dose-dependent and lasts only 2 weeks. In migraine patients, a consistent or dose-dependent response to BT-A treatment has not been seen. Peak responses to BT-A in migraine patients are seen at 8-12 weeks, whereas BT-A-affected nerve endings in mice fully recover function between 63 and 91 days; the difference in species limits the interpretation of this dissonance. As BT-A does not normally cross the intact blood-brain barrier, meningeal nociceptors appear unlikely to be influenced by scalp injections of BT-A; the possibility of antidromic transfer of BT-A in the trigeminovascular system should be considered. The extended period for which migraine prophylaxis might be required, the antigenic and headache-provoking potential of BT-A, the inability of BT-A to affect central neuronal processes significantly, including the aura of migraine, the possible placebo effect of needling, and purely subjective outcome measures in headache studies are additional concerns in evaluating this treatment strategy. The clinical utility of BT-A has not been compared against established migraine prophylactic agents. The efficacy of BT-A in preventing migraine headache attacks remains controversial and the underlying scientific rationale is debatable.

S+ -flurbiprofen but not 5-HT1 agonists suppress basal and stimulated CGRP and PGE2 release from isolated rat dura mater

Neurogenic inflammation of the meninges, expressed in plasma extravasation and vasodilatation, putatively contributes to certain types of headache. Both, non-steroidal antiinflammatory drugs (NSAIDs) and serotonin-1 (5-HT1) receptor agonists are similarly effective antimigraine drugs but their mechanism of action is unclear. The clinical observation that sumatriptan lowered plasma levels of calcitonin gene-related peptide (CGRP), found increased during migraine attacks, drew attention to a possible inhibition of pro-inflammatory neuropeptide release from trigeminal afferents. An isolated preparation of fluid-filled rat skull cavities was used to study effects of NSAIDs and 5-HT(1B/D) agonists on the dura stimulated by inflammatory mediators (bradykinin, histamine and serotonin, 10(-5)M each). The release of immunoreactive CGRP (iCGRP) and immunoreactive PGE(2) (iPGE(2)) was measured in 5-min samples of superfusates using enzyme immunoassays. S(+)-flurbiprofen (10(-6)M) strongly reduced the basal and stimulated iCGRP release and abolished iPGE(2) release; R(-)-flurbiprofen showed much less effect on iPGE(2) liberation and did not influence iCGRP release. The 5-HT(1B/D) agonists naratriptan and CP93,129 were ineffective on both iCGRP and iPGE(2) release. Inspite of its weak COX blocking effect, R(-)-flurbiprofen is reported to exert antinociceptive effects, although it has not been tested in migraine. Only the potent COX blocker S(+)-flurbiprofen also suppressed iCGRP release while the 5-HT(1B/D) agonists were ineffective. Thus, inhibition of meningeal neuropeptide secretion is not a common action principle of the drugs that could be essential for their antimigraine effects.

Possible role of alpha-adrenoceptor subtypes in acute migraine therapy

Even though the underlying mechanisms for the pathophysiology of migraine attacks are not completely understood, little doubt exists that the headache phase is explained by dilatation of cranial, extracerebral blood vessels. In this context, experimental models predictive for anti-migraine activity have shown that both triptans and ergot alkaloids, which abort migraine headache, produce vasoconstriction within the carotid circulation of different species. In contrast to the well-established role of serotonin (5-hydroxytryptamine; 5-HT) 5-HT1B receptors in the common carotid vascular bed, the role of alpha-adrenoceptors and their subtypes has been examined only relatively recently. Using experimental animal models and alpha1- and alpha2-adrenoceptor agonists (phenylephrine and BHT933, respectively) and antagonists (prazosin and rauwolscine, respectively), it was shown that activation of either receptor produces a cranioselective vasoconstriction. Subsequently, investigations employing relatively selective antagonists at alpha1- (alpha1A, alpha1B, alpha1D) and alpha2- (alpha2A, alpha2B, alpha2C) adrenoceptor subtypes revealed that specific receptors mediate the carotid haemodynamic responses in these animals. From these observations, together with the potential limited role of alpha1B- and alpha2C-adrenoceptors in the regulation of systemic haemodynamic responses, it is suggested that selective agonists at these receptors may provide a promising novel avenue for the development of acute anti-migraine drugs.

Molecular cloning and tissue distribution of mRNA encoding porcine 5-HT7 receptor and its comparison with the structure of other species

The effects of 5-hydroxytriptamine (5-HT, serotonin) are mediated via five main receptor types of which the 5-HT7 receptor is the most recently characterised member. The 5-HT7 receptor has been shown to participate in mediating cranial blood vessels dilatation that may result in migraine headache. We report here the cDNA cloning, sequencing and tissue distribution of porcine 5-HT7 receptor and illustrate its comparison with corresponding receptor of known species. Employing a combination of reverse transcriptase and inverse polymerase chain reaction we amplified and sequenced a full length cDNA from the porcine cerebral cortex. The deduced amino acid sequence comparison confirmed that the cloned porcine receptor belongs to 5-HT7 receptor as described for human and other species and showing overall homology of 92-96%. The expression of 5-HT7 receptor mRNA was observed in porcine central (cerebral cortex, trigeminal ganglion and cerebellum) as well as in peripheral (pulmonary and coronary arteries, superior vena cava and saphenous vein) tissues. The established cDNA sequence and tissue distribution of porcine 5-HT7 receptor will be helpful in exploring the role of this receptor in pathophysiological processes and to predict as a potential therapeutic target for antimigraine drug development.

Antiepileptic Drug Therapy in Migraine Headache

Severe migraine affects more than 28 million Americans. It is associated with episodic as well as long-term disability and suffering, yet it is underdiagnosed and undertreated. Acute treatments have advanced considerably, ignited by sumatriptan and the subsequent triptans; unfortunately migraine prevention has lagged far behind. There are no great migraine preventives! No migraine preventive agent studied in good randomized, double blind, placebo-controlled trials proved to be 50% better than placebo. Migraine trials typically focus on episodic migraine, a milder, gentler type of migraine that is selected for low frequency, lack of daily headaches, no preventive need, and previous failure to no more than a few preventive agents. These features are not typical of the usual migraine patient seen in most neurologic practices, thus the results of clinical trials may not carryover to real world situations. Treatment of frequent, chronic, or pervasive migraine is inadequate, and never has been studied in randomized controlled trials. Traditional migraine preventives, eg, beta-blockers, calcium channel blockers, and tricyclic antidepressants, are often ineffective in difficult or complicated populations. The antiepileptic drugs represent a category of pharmaceutics that target the neuronal instability and central hyperexcitability of migraine, and, through these actions, may be more effective than traditional preventives. Episodic migraine attacks are associated with peripheral and central sensitization; however, if attacks are frequent, severe, or long lasting, this sensitization may increase the risk of developing daily headaches. If antiepileptic drugs have an effect on central sensitization, perhaps mediated via glutamate inhibition or gamma-aminobutyric acid potentiation, it is appropriate to use these agents early in migraine treatment, particularly in the highly comorbid patient, possibly in conjunction with agents that antagonize the 5HT2 receptor. This report reviews the best currently available evidence on antiepileptic drugs in the prevention of episodic migraine, and tabulates potential drug-drug and cytochrome P450 interactions. All antiepileptic drugs presented are effective in migraine prevention. However, deciding on the best agent for each individual patient will require recognizing comorbidity and assessing antiepileptic drug pharmacodynamics, tolerability, and safety.