Antimigraine drug interactions with serotonin receptor subtypes in human brain

European Headache Federation (EHF) critical re-appraisal and meta-analysis of oral drugs in migraine prevention-part 2: flunarizine

OBJECTIVE

Novel disease-specific and mechanism-based treatments sharing good evidence of efficacy for migraine have been recently marketed. However, reimbursement by insurers depends on treatment failure with classic anti-migraine drugs. In this systematic review and meta-analysis, we aimed to identify and rate the evidence for efficacy of flunarizine, a repurposed, first- or second-line treatment for migraine prophylaxis.

METHODS

A systematic search in MEDLINE, Cochrane CENTRAL, and ClinicalTrials.gov was performed for trials of pharmacological treatment in migraine prophylaxis, following the Preferred Reporting Items for Systematic Reviews (PRISMA). Eligible trials for meta-analysis were randomized, placebo-controlled studies comparing flunarizine with placebo. Outcomes of interest according to the Outcome Set for preventive intervention trials in chronic and episodic migraine (COSMIG) were the proportion of patients reaching a 50% or more reduction in monthly migraine days, the change in monthly migraine days (MMDs), and Adverse Events (AEs) leading to discontinuation.

RESULTS

Five trials were eligible for narrative description and three for data synthesis and analysis. No studies reported the predefined outcomes, but one study assessed the 50% reduction in monthly migraine attacks with flunarizine as compared to placebo showing a benefit from flunarizine with a low or probably low risk of bias. We found that flunarizine may increase the proportion of patients who discontinue due to adverse events compared to placebo (risk difference: 0.02; 95% CI -0.03 to 0.06).

CONCLUSIONS

Published flunarizine trials predate the recommended endpoints for evaluating migraine prophylaxis drugs, hence the lack of an adequate assessment for these endpoints. Further, modern-day, large-scale studies would be valuable in re-evaluating the efficacy of flunarizine for the treatment of migraines, offering additional insights into its potential benefits.

Classics in Chemical Neuroscience: Amitriptyline

Amitriptyline was the second tricyclic antidepressant to appear on the market for major depressive disorder under the brand name Elavil in 1961. Since its emergence, amitriptyline has been an effective therapeutic in various disease states and disorders but has also been a concerning source of cardiotoxicity. Amitriptyline inhibits serotonin and norepinephrine reuptake as well as produces off-target activity at histaminergic, muscarinic, and various other receptors. Its role as a modulator of monoamines helped further establish the monoamine theory to understand various mood disorders, paving the way for the now more common selective serotonin/norepinephrine reuptake inhibitors. In this review, we will discuss amitriptyline's synthesis, manufacturing information, drug metabolism, pharmacology, adverse effects, and its history and importance in therapy to present amitriptyline as a true classic in chemical neuroscience.

Analysis of the effects of a tricyclic antidepressant on secondary sleep disturbance induced by chronic pain in a preclinical model

Chronic pain and sleep have a bidirectional relationship that promotes a vicious circle making chronic pain more difficult to treat. Therefore, pain and sleep should be treated simultaneously. In our previous study, we suggested that hyperactivation of ascending serotonergic neurons could cause secondary sleep disturbance in chronic pain. This study aimed to demonstrate the effects of a tricyclic antidepressant (amitriptyline) and a selective 5-hydroxy-tryptamine 2A (5-HT_2A) antagonist (MDL 100907) that adjust serotonergic transmission, on secondary sleep disturbance induced in a preclinical chronic pain model. We produced a chronic neuropathic pain model by partial sciatic nerve ligation in mice, analyzed their electroencephalogram (EEG) and electromyogram (EMG) using the SleepSign software, and evaluated the sleep condition of the pain model mice after administration of amitriptyline or MDL 100907. Amitriptyline improved thermal hyperalgesia and the amount of sleep, especially non-REM sleep. Time change of normalized power density of δ wave in the nerve ligation group with amitriptyline administration showed a normal pattern that was similar to sham mice. In addition, MDL 100907 normalized sleep condition similar to amitriptyline, without improvement in pain threshold. In conclusion, amitriptyline could improve sleep quantity and quality impaired by chronic pain. 5-HT_2A receptor antagonism could partially contribute to this sleep improvement, but is not associated with pain relief.

Sustained Hypoxia Elicits Competing Spinal Mechanisms of Phrenic Motor Facilitation

Acute intermittent hypoxia (AIH) induces phrenic long-term facilitation (pLTF), a form of spinal motor plasticity. Competing mechanisms give rise to phrenic motor facilitation (pMF; a general term including pLTF) depending on the severity of hypoxia within episodes. In contrast, moderate acute sustained hypoxia (mASH) does not elicit pMF. By varying the severity of ASH and targeting competing mechanisms of pMF, we sought to illustrate why moderate AIH (mAIH) elicits pMF but mASH does not. Although mAIH elicits serotonin-dependent pLTF, mASH does not; thus, mAIH-induced pLTF is pattern sensitive. In contrast, severe AIH (sAIH) elicits pLTF through adenosine-dependent mechanisms, likely from greater extracellular adenosine accumulation. Because serotonin- and adenosine-dependent pMF interact via cross talk inhibition, we hypothesized that pMF is obscured because the competing mechanisms of pMF are balanced and offsetting during mASH. Here, we demonstrate the following: (1) blocking spinal A2A receptors with MSX-3 reveals mASH-induced pMF; and (2) sASH elicits A2A-dependent pMF. In anesthetized rats pretreated with intrathecal A2A receptor antagonist injections before mASH (PaO2 = 40-54 mmHg) or sASH (PaO2 = 25-36 mmHg), (1) mASH induced a serotonin-dependent pMF and (2) sASH induced an adenosine-dependent pMF, which was enhanced by spinal serotonin receptor inhibition. Thus, competing adenosine- and serotonin-dependent mechanisms contribute differentially to pMF depending on the pattern/severity of hypoxia. Understanding interactions between these mechanisms has clinical relevance as we develop therapies to treat severe neuromuscular disorders that compromise somatic motor behaviors, including breathing. Moreover, these results demonstrate how competing mechanisms of plasticity can give rise to pattern sensitivity in pLTF.

SIGNIFICANCE STATEMENT

Intermittent hypoxia elicits pattern-sensitive spinal plasticity and improves motor function after spinal injury or during neuromuscular disease. Specific mechanisms of pattern sensitivity in this form of plasticity are unknown. We provide evidence that competing mechanisms of phrenic motor facilitation mediated by adenosine 2A and serotonin 2 receptors are differentially expressed, depending on the pattern/severity of hypoxia. Understanding how these distinct mechanisms interact during hypoxic exposures differing in severity and duration will help explain interesting properties of plasticity, such as pattern sensitivity, and may help optimize therapies to restore motor function in patients with neuromuscular disorders that compromise movement.

β-blockers and the risk of incident depression in the elderly

The hypothesis that β-blockers cause depression has been both confirmed and refuted in previous studies. However, in hardly any of these studies, depression was systematically and adequately assessed. The aim of this cohort study was to examine whether β-blockers, in general, highly lipid-soluble, nonselective, or serotonergic receptor-binding β-blockers, are associated with incident depression. Between 1993 and 2005, 5104 elderly persons were followed for incident depressions. Depressions were identified by regular interview and continuous monitoring of medical records. Cases were categorized as clinically relevant depressive symptoms or as depressive syndromes, the latter including Diagnostic and Statistical Manual of Mental Disorders-IV-defined depressive disorders. Pharmacies provided information on filled β-blockers. We used Cox regression with drug use as a time-dependent variable to analyze the data, adjusted for potential demographic covariates, activity of daily living, and (contra)indications for β-blockers. We found that use of β-blockers in general did not convey an increased risk of depressive symptoms (hazard ratio [HR], 0.76; 95% confidence interval [CI], 0.37-1.59) or depressive syndromes (HR, 0.99; 95% CI, 0.53-1.84). Highly lipid-soluble β-blockers, mostly propranolol in our study, were associated with depressive symptoms during the first 3 months of use (HR, 3.31; 95% CI, 1.03-10.6), but not with depressive syndromes. Nonselective or serotonergic receptor affinity was not associated with an increased risk of depressive symptoms or syndromes independent of high lipid solubility. We conclude that β-blockers in general do not convey an increased risk of depression. Lipophilic β-blockers are associated with an increased risk of depressive symptoms.

Interictal brain 5-HT1A receptors binding in migraine without aura: a 18F-MPPF-PET study

In this study we aimed to assess the brain distribution of 5-HT(1A) receptors in migraine patients without aura. Ten female migraine patients and 24 female healthy volunteers underwent magnetic resonance imaging and positron emission tomography using a radioligand antagonist of 5-HT(1A) receptors [4-(2'-methoxyphenyl)-1-[2'-(N-2-pirydynyl)-p-fluorobenzamido]-ethylpiperazine ((18)F-MPPF)]. A simplified reference tissue model was used to generate parametric images of 5-HT(1A) receptor binding potential (BP) values. Statistical Parametrical Mapping (SPM) analysis showed increased MPPF BP in posterior cortical areas and hippocampi bilaterally in patients compared with controls. Region of interest (ROI) analysis showed a non-significant trend in favour of a BP increase patients in cortical regions identified by the SPM analysis except in hippocampi, left parietal areas and raphe nuclei. During the interictal period of migraine patients without aura, the increase of MPPF BP in posterior cortical and limbic areas could reflect an increase in receptor density or a decrease of endogenous serotonin, which could explain their altered cortical excitability.

Current and prospective pharmacological targets in relation to antimigraine action

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

Molecular Mechanisms of Migraine

Migraine is a common complex disorder that affects a large portion of the population and thus incurs a substantial economic burden on society. The disorder is characterized by recurrent headaches that are unilateral and usually accompanied by nausea, vomiting, photophobia, and phonophobia. The range of clinical characteristics is broad and there is evidence of comorbidity with other neurological diseases, complicating both the diagnosis and management of the disorder. Although the class of drugs known as the triptans (serotonin 5-HT(1B/1D) agonists) has been shown to be effective in treating a significant number of patients with migraine, treatment may in the future be further enhanced by identifying drugs that selectively target molecular mechanisms causing susceptibility to the disease.Genetically, migraine is a complex familial disorder in which the severity and susceptibility of individuals is most likely governed by several genes that may be different among families. Identification of the genomic variants involved in genetic predisposition to migraine should facilitate the development of more effective diagnostic and therapeutic applications. Genetic profiling, combined with our knowledge of therapeutic response to drugs, should enable the development of specific, individually-tailored treatment.

Practical synthesis of chiral emopamil left hand as a bioactive motif

An asymmetric synthesis of (2S)-2-(2-isopropyl)-5-hydroxy-2-phenylpentanenitrile (emopamil left hand, 2) has been completed by use of the MAD (methyl aluminum bis(4-methyl-2,6-di-tert-butylphenoxide)-induced rearrangement of a chiral epoxyalcohol as the key reaction. The stereochemistry of the chiral quaternary center was confirmed by transformation of 2 to (S)-noremopamil. This method requires minimal purification procedures and affords high chemical and optical yields. Acid-catalyzed isomerization of an allylaldehyde and retro-aldol type racemization at the quaternary carbon of a nitrile-alcohol were encountered.

Platelet 3H ketanserin binding in migraine

Platelet 3H ketanserin binding was studied in 33 patients of migraine and 30 healthy controls. The binding characteristics: equilibrium dissociation constant (Kd) and maximal number of binding sites (Bmax) determined by Scatchard analysis revealed a significant decrease in Kd and no change in Bmax in migraine cases. No correlation was observed between the Kd and Bmax with the clinical features of migraine. The findings of the present study show that there is a decreased affinity of platelet 5-HT2 receptors in migraine.

The use of pindolol with fluoxetine in the treatment of major depression: final results from a double-blind, placebo-controlled trial

BACKGROUND

Preliminary reports have suggested that concomitant institution of pindolol and serotonin reuptake inhibitors robustly hastens clinical response; however, contradictory evidence from a randomized double-blind, controlled trial was recently reported by this group in a population of depressed patients who were prescribed fluoxetine and pindolol. Herein, we report final results from an extended sample size.

METHODS

Drug-free outpatients with a major depressive episode were randomized in a double-blind manner to one of two treatment conditions: fluoxetine (20 mg daily) with pindolol (7.5 to 10 mg daily) or fluoxetine (20 mg daily) with placebo. After 6 weeks, patients were followed for 3 more weeks in a single-blind manner, on fluoxetine and placebo pindolol.

RESULTS

Eighty-six patients completed at least 1 or more weeks on protocol, with 45 and 41 patients randomized to the pindolol and placebo groups respectively. After 2 weeks on protocol, partial remission (i.e., at least 50% decrease in depression rating scores from baseline) rates for pindolol (16%) and placebo (19%) groups were comparable. By the study's end, a partial remission was achieved, at least transiently, for 67% of the pindolol group and 80% of the placebo group. Pindolol treatment was associated with statistically significant reduction in blood pressure and pulse as compared to the control group. The two groups did not have overall differences in rates of attrition, time to response, and side effects.

CONCLUSIONS

In accord with our previously published findings, these extended results do not support the efficacy of pindolol in hastening clinical response to fluoxetine in a patient population with predominantly chronic and recurrent depression.

The effects of sumatriptan on pituitary secretion in man

Sumatriptan, a new antimigraine drug with high affinity and selectivity for certain 5-hydroxytryptamine (5-HT1D) receptor subtypes, was administered to 12 normal subjects, in order to investigate the effects of 5-HT receptor activation on anterior pituitary secretion. Sumatriptan increased plasma growth hormone (GH) levels from 2.5 +/- 0.5 mIU/l in basal conditions to 17.3 +/- 2.6 mIU/l 30 min after administration of the drug. After pre-treatment with cyproheptadine, an anti-serotoninergic drug known to inhibit GH secretion, the mean integrated sumatriptan-induced GH response decreased from 14.8 +/- 3.9 muI/l*hr to 3.7 +/- 1.7 mIU/l*hr. Sumatriptan administration did not have any effect on the secretion of the other anterior pituitary hormones. It is concluded that sumatriptan selectively increases GH secretion in man, but the exact nature of the receptors involved is not yet known.

On serotonin and migraine: a clinical and pharmacological review

Migraine patients have chronically low systemic 5-HT, predisposing them to develop migrainous headache once an attack has been initiated. Changes in platelet 5-HT content are not causally related, but reflect similar changes at a neuronal level. Stimulation of vascular 5-HT1 receptors, probably located in the vessel wall within the dural vascular bed, may alleviate the headache and associated symptoms, but does not interact with earlier mechanisms within the pathophysiological cascade. These receptors are of an as yet unidentified 5-HT1 subtype, closely resembling, but not identical to 5-HT1D receptors. Activation of these receptors results in vasoconstriction, inhibiting depolarization of sensory perivascular afferents within the trigemino-vascular system and thus stopping the headache. Additional inhibition of the release of vasoactive neuropeptides may be involved, but seems to be of only secondary clinical importance.

Molecular structural basis of ligand selectivity for 5-HT2 versus 5-HT1C cortical receptors

A molecular structural criterion of ligand selectivity for the 5-HT2 versus 5-HT1C receptor was hypothesized on the basis of radioligand binding data. Despite the large number of compounds which have been tested at both receptors, analysis of published data led to the identification of only five agents which are greater than 10-fold selective for the 5-HT2 versus the 5-HT1C receptor. Comparison of the two-dimensional structures revealed that, although these five compounds represent three distinct structural classes, they share a common structural feature located in the region hypothesized to be involved in receptor binding: a carbonyl or carboxyl oxygen interposed spatially between an aromatic ring and nitrogen atom. This structural feature was used to predict the relative selectivity of compounds that had not previously been analyzed at both the 5-HT2 and 5-HT1C receptors. All six drugs tested which contain the identified reactive carbonyl or carboxyl group were found to be selective for the 5-HT2 versus the 5-HT1C receptor with selectivity ratios ranging from 26 to 380. By contrast, three agents which are structurally similar but do not contain the reactive carbonyl or carboxyl group displayed equally high affinity for both receptor binding sites. Since the physiological roles of the 5-HT2 and 5-HT1C receptor are markedly different, it would be of potential clinical and scientific value to utilize this molecular structural feature to further identify chemical compounds which would selectively interact with only one of the two receptors.

Verapamil and migraine prophylaxis: mechanisms and efficacy

Calcium channel blockers have demonstrated efficacy in investigative use for prophylaxis of migraine and cluster headaches. In particular, verapamil, with its low side-effect profile, appears to be a promising alternative to the currently available agents for prophylactic treatment of chronic recurring headaches. Although its exact mechanisms of action in this application are unknown, verapamil exerts a vasodilatory effect on cerebral arteries and interacts with serotonergic systems involved in migraine pathogenesis. A review of studies from the past decade indicates that verapamil may be as effective as traditional therapies as prophylaxis for the major types of chronic recurring headache.

New vistas on 5-HT receptors and migraine

1. A number of serotonergic agents have been shown to be effective in the treatment of migraine. At the present time, migraine drug interactions have been analyzed most extensively at 5-hydroxytryptamine1D (5-HT1D), 5-HT2 and 5-HT3 receptor subtypes. 2. This review will summarize the current status of 5-HT receptor subtypes as they relate to anti-migraine agents. 3. The available data suggest that drug interactions with specific 5-HT receptor subtypes may be the basis for their efficacy in both the acute and prophylactic treatment of migraine.

Effects of Ca2+ channel ligands on [3H]QNB binding at m1 and m3 muscarinic receptors

1. The effects of Ca2+ channel ligands on [3H]QNB binding in m1- or m3-transfected Chinese hamster ovary (CHO) cells have been studied. 2. The IC50 values of Ca2+ channel ligands for the inhibition of [3H]QNB binding were between 10(-6) and 10(-4) M and the rank order of potency was HOE 166 greater than McN 6186 greater than nicardipine greater than tiamdipine greater than verapamil greater than diltiazem greater than Bay K 8644 greater than nifedipine at m1 and m3 receptors. 3. The results indicate that Ca2+ channel ligands employed in this experiment do not distinguish subtypes of muscarinic receptors.

Localization of 3H-dihydroergotamine-binding sites in the cat central nervous system: relevance to migraine

Dihydroergotamine (DHE) is the treatment of choice in aborting the acute attack of migraine. Although its efficacy has been known for 40 years, its mechanism of action is still disputed. Data regarding the site of action of dihydroergotamine may provide an insight into its mechanism of action and thus identify a locus of potentially abnormal pathophysiology in migraine. By using in vitro and ex vivo autoradiographic techniques, the localization of specific binding sites for 3H-dihydroergotamine in the cat brain has been examined. Binding was seen in the dorsal horn of the cervical spinal cord, in the medulla, associated with the nucleus of the tractus solitarius, area postrema, and descending spinal trigeminal nucleus, and in the mesencephalon and the cerebral cortex. The highest density of binding sites was found in the dorsal and medial raphe nuclei of the midbrain. Furthermore, these same brain regions were also labeled after intravenous administration of 3H-dihydroergotamine. It is important that the brain areas specifically labeled are key nuclei involved in cranial pain transmission, suggesting that dihydroergotamine may act at these central sites in migraine.

Serotonin and migraine

Migraine has long been considered as a "vascular headache" but clearly neurological mechanisms are involved. The pathophysiology appears to somehow involve serotonin, both peripherally and centrally, but its involvement may be just epiphenomenal. Adding to the enigma it is apparent that many of the presently available drugs for the treatment of migraine interact in one way or another with serotonin receptors. However, they tend to have a number of other unrelated actions and they are only of limited clinical value. Interestingly a promising new drug for the treatment of the acute attack, sumatriptan, has a very selective action as an agonist at a specific 5-HT1-like receptor sub-type, mediating vasoconstriction, which is localized on cranial blood vessels. Its action may, or may not, be independent of any involvement of serotonin in the genesis of migraine. Hopefully though, current attempts to determine sumatriptan's mechanism of action will shed further light on the pathology of migraine itself and the putative involvement of serotonin.

Pharmacology of migraine

Stabilization of serotonergic neurotransmission by depressing the activity of serotonergic neurons may be the common mode of action of drugs effective in migraine. By serotonin receptor agonism, by prolonging the biologic half-life of serotonin in the synaptic cleft (through blockade of its re-uptake or metabolic degradation), by an increase in its synthesis, by inhibiting the release of serotonin, or by activation of cyclic AMP (fig), a unitary expression for the action of these drugs can be formulated which is corroborated, for many of the drugs, by direct measurement of serotonergic neuronal firing rates. However, there are at least three serotonin receptor sites in brain at which drugs would be effective, as assessed by differential responsiveness to agonists and antagonists and by different types of postsynaptic responses: presynaptically, postsynaptically, and at the autoreceptor itself. The locus of action for the antimigraine drugs may be primarily at the raphe, upon the serotonin neurons per se, but it will probably prove to be more complex as more data are generated.

Drugs affecting serotonin neurons

Advances in serotonin pharmacology, the development of drugs that intervene at specific sites to modify serotonergic function, have accompanied advances in the understanding of physiologic roles of serotonin present in neurons and elsewhere and of serotonin receptors that are widely distributed in brain and many peripheral tissues. The pharmacologic advances have sometimes been stimulated by developments in serotonin physiology, such as the recognition of multiple serotonin receptor subtypes, and in other cases have been a major factor in providing new insights into physiologic roles of serotonin. Drugs that modify serotonin function have a variety of therapeutic applications currently and many more potential therapeutic uses to be explored in the future. Having drugs that act with high specificity or selectivity on particular enzymes in serotonin biosynthesis, on particular serotonin receptors, or at other sites such as uptake carriers for serotonin not only offers the hope of improved clinical therapy in diseases caused by abnormal serotonergic function or in which alteration of serotonergic function can alleviate symptoms, but also provides valuable pharmacologic tools for learning more about serotonin physiology and probing the functional status of serotonergic systems. The next few years promise to yield important new serotonergic drugs.

Antagonism of 5-hydroxytryptamine1A (5-HT1A) receptor-mediated modulation of adenylate cyclase activity by pindolol and propranolol isomers

The interactions of the stereoisomers of pindolol and propranolol with 5-hydroxytryptamine1A (5-HT1A) binding sites and adenylate cyclase activity were examined in rat hippocampus. (-)Pindolol and (-)propranolol displayed high affinity for 5-HT1A binding sites, and their affinities were not affected significantly by the addition of 10(-4) M GTP to the radioligand assay. The selective 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) decreased forskolin-stimulated adenylate cyclase activity. The (-)isomers of pindolol and propranolol did not affect basal or forskolin-stimulated activity but, at a concentration of 10(-5) M, they reversed the 8-OH-DPAT inhibition of the forskolin-stimulated cyclase activity. The (+)isomers were less potent in producing this effect. These data suggest that (-)pindolol and (-)propranolol are potent antagonists at 5-HT1A receptors in rat hippocampus.