Preclinical studies on the anti-migraine drug, sumatriptan

Pathophysiology of Migraine

OBJECTIVE

This article provides an overview of the current understanding of migraine pathophysiology through insights gained from the extended symptom spectrum of migraine, neuroanatomy, migraine neurochemistry, and therapeutics.

LATEST DEVELOPMENTS

Recent advances in human migraine research, including human experimental migraine models and functional neuroimaging, have provided novel insights into migraine attack initiation, neurochemistry, neuroanatomy, and therapeutic substrates. It has become clear that migraine is a neural disorder, in which a wide range of brain areas and neurochemical systems are implicated, producing a heterogeneous clinical phenotype. Many of these neural pathways are monoaminergic and peptidergic, such as those involving calcitonin gene-related peptide and pituitary adenylate cyclase-activating polypeptide. We are currently witnessing an exciting era in which specific drugs targeting these pathways have shown promise in treating migraine, including some studies suggesting efficacy before headache has even started.

ESSENTIAL POINTS

Migraine is a brain disorder involving both headache and altered sensory, limbic, and homeostatic processing. A complex interplay between neurotransmitter systems, physiologic systems, and pain processing likely occurs. Targeting various therapeutic substrates within these networks provides an exciting avenue for future migraine therapeutics.

Hypothetical biosynthetic pathways of pharmaceutically potential hallucinogenic metabolites in Myristicaceae, mechanistic convergence and co-evolutionary trends in plants and humans

The family Myristicaceae harbour mind-altering phenylpropanoids like myristicin, elemicin, safrole, tryptamine derivatives such as N,N-dimethyltryptamine (DMT) and 5-methoxy N,N-dimethyltryptamine (5-MeO-DMT) and β-carbolines such as 1-methyl-6-methoxy-dihydro-β-carboline and 2-methyl-6-methoxy-1,2,3,4-tetrahydro-β-carboline. This study aimed to systematically review and propose the hypothetical biosynthetic pathways of hallucinogenic metabolites of Myristicaceae which have the potential to be used pharmaceutically. Relevant publications were retrieved from online databases, including Google Scholar, PubMed Central, Science Direct and the distribution of the hallucinogens among the family was compiled. The review revealed that the biosynthesis of serotonin in plants was catalysed by tryptamine 5-hydroxylase (T5H) and tryptophan 5-hydroxylase (TPH), whereas in invertebrates and vertebrates only by tryptophan 5-hydroxylase (TPH). Indolethylamine-N-methyltransferase catalyses the biosynthesis of DMT in plants and the brains of humans and other mammals. Caffeic acid 3-O-methyltransferase catalyses the biosynthesis of both phenylpropanoids and tryptamines in plants. All the hallucinogenic markers exhibited neuropsychiatric effects in humans as mechanistic convergence. The review noted that DMT, 5-MeO-DMT, and β-carbolines were natural protectants against both plant stress and neurodegenerative human ailments. The protein sequence data of tryptophan 5-hydroxylase and tryptamine 5-hydroxylase retrieved from NCBI showed a co-evolutionary relationship in between animals and plants on the phylogenetic framework of a Maximum Parsimony tree. The review also demonstrates that the biosynthesis of serotonin, DMT, 5-MeO-DMT, 5-hydroxy dimethyltryptamine, and β-carbolines in plants, as well as endogenous secretion of these compounds in the brain and blood of humans and rodents, reflects co-evolutionary mutualism in plants and humans.

Neuroimaging in the pre-ictal or premonitory phase of migraine: a narrative review

BACKGROUND

The premonitory phase, or prodrome, of migraine, provides valuable opportunities to study attack initiation and for treating the attack before headache starts. Much that has been learned about this phase in recent times has come from the outcomes of functional imaging studies. This review will summarise these studies to date and use their results to provide some feasible insights into migraine neurobiology.

MAIN BODY

The ability to scan repeatedly a patient without radiation and with non-invasive imaging modalities, as well as the recognition that human experimental migraine provocation compounds, such as nitroglycerin (NTG) and pituitary adenylate cyclase activating polypeptide (PACAP), can trigger typical premonitory symptoms (PS) and migraine-like headache in patients with migraine, have allowed feasible and reproducible imaging of the premonitory phase using NTG. Some studies have used serial scanning of patients with migraine to image the migraine cycle, including the 'pre-ictal' phase, defined by timing to headache onset rather than symptom phenotype. Direct observation and functional neuroimaging of triggered PS have also revealed compatible neural substrates for PS in the absence of headache. Various imaging methods including resting state functional MRI (rsfMRI), arterial spin labelling (ASL), positron emission tomography (PET) and diffusion tensor imaging (DTI) have been used. The results of imaging the spontaneous and triggered premonitory phase have been largely consistent and support a theory of central migraine attack initiation involving brain areas such as the hypothalamus, midbrain and limbic system. Early dysfunctional pain, sensory, limbic and homeostatic processing via monoaminergic and peptidergic neurotransmission likely manifests in the heterogeneous PS phenotype.

CONCLUSION

Advances in human migraine research, including the use of functional imaging techniques lacking radiation or radio-isotope exposure, have led to an exciting opportunity to study the premonitory phase using repeated measures imaging designs. These studies have provided novel insights into attack initiation, migraine neurochemistry and therapeutic targets. Emerging migraine-specific therapies, such as those targeting calcitonin gene-related peptide (CGRP), are showing promise acutely when taken during premonitory phase to reduce symptoms and prevent subsequent headache. Therapeutic research in this area using PS for headache onset prediction and early treatment is likely to grow in the future.

Synthesis of novel sulfonamides with anti-Alzheimer and antioxidant capacities

A series of novel dopamine analogs incorporating urea and sulfonamide functional groups was synthesized from 3,4-dimethoxyphenethylamine. The reaction of 3,4-dimethoxyphenethylamine with N,N-dimethylcarbamoyl chloride, followed by the sulfonyl chlorination of the urea derivative, gave benzene-1-sulfonyl chloride 9, which was reacted with NH₃ (aq) or N-alkyl amines to give related sulfonamides. The O-demethylation reaction of the subsequent compounds with BBr₃ afforded four novel phenolic dopamine analogs including sulfonamide and urea in the same structure. The anticholinergic and antioxidant effects of the synthesized compounds were examined. Compound 13 exhibited inhibition at the micromolar level for both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). The IC₅₀ value of 13 was calculated as 298 ± 43 µM for AChE and 321 ± 29 µM for BChE. The antioxidant and antiradical effects of the molecules were investigated by five different methods. Among the synthesized compounds 10-18, the best antioxidant and antiradical activities belong to the phenolic compounds 15-18. Compounds 16 and 18 have a higher reducing power than the standards used, that is, butylated hydroxytoluene, butylated hydroxyanisole, Trolox, and α-tocopherol, for Fe³⁺ -Fe²⁺ and Cu²⁺ -Cu⁺ reducing activities. For the DPPH• radical scavenging method, compounds 16-18 have a much better scavenging power than the standard molecules. In addition, it has been determined by the induced-fit docking method that compound 13 is well-fitted in the active site of the enzymes. ADME studies reveal that the pharmacokinetic and physicochemical properties of all synthesized compounds are within an acceptable range.

Targeting the 5-HT system: Potential side effects

Targeting the serotonin (5-HT) system is no simple task: there are at least 15 5-HT receptors, in addition to a number of transporters and metabolizing enzymes. Multiple 5-HT receptor variants exist due to genetic variations and/or post translational modifications, splice variants or editing variants. Some receptors may form homo and heteromers. The 5-HT system is targeted by multiple drugs to treat a variety of diseases. Given the homology amongst the 5-HT and neighbouring receptor classes, only few drugs are actually selective for a single target. In fact, many 5-HT drugs act on a combination of targets, i.e. several receptors and/or transporters or enzymes. For instance, a number of antidepressants or antipsychotics act on 5-HT and other transmitter systems. Recently developed drugs may show target selectivity by design, based on the current state of knowledge, whereas many older compounds hit multiple targets since they were developed using phenotypic screens, as was done well into the 1980's. Ergot analogues, antipsychotics or antidepressants, fall into this category. As our knowledge developed over the last 25-30 years, some targets have very well-defined liabilities: for instance, 5HT_2B or 5-HT_2A receptor agonists, will produce valvulopathies or hallucinations, respectively, whereas 5-HT₃ receptor antagonists, may lead to constipation. This short review will be limited in scope as there are multiple targets and even more compounds to discuss. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Cortical spreading depolarisation-induced facial hyperalgesia, photophobia and hypomotility are ameliorated by sumatriptan and olcegepant

Cortical spreading depolarisation (CSD), the neural mechanism underlying migraine aura, may cause headache by sensitising the trigeminal system. Photophobia, the most bothersome accompanying symptom during migraine attacks, is more prevalent in migraine with aura than in migraine without aura. Whether CSD plays a role in developing photophobia remains unknown. Moreover, migraine-induced physical hypoactivity contributes to loss of productivity. We aimed to investigate the development of trigeminal sensitisation, photophobia and locomotive abnormality after KCl-induced CSD using 86 male C57BL/6 mice. Sham-operated mice were used as controls. We confirmed the presence of trigeminal sensitisation and photophobia at 24 h after CSD. CSD-subjected mice also exhibited significantly reduced locomotive activity in both light and dark zones. Hence, the CSD-induced hypomobility was likely to be independent of photophobia. The 5-HT1B/1D agonist, sumatriptan, corrected all these CSD-induced abnormalities. Moreover, dose dependency was demonstrated in the ameliorating effect of the calcitonin gene-related peptide (CGRP) receptor antagonist, olcegepant, on these abnormalities. Sumatriptan and olcegepant improved mouse locomotion with therapeutic lags ranging from 20 to 30 min. Collectively, CSD caused trigeminal sensitisation, photophobia and hypomobility that persisted for at least 24 h by a mechanism involving the 5-HT1B/1D and CGRP activity.

Nose-to-brain delivery of sumatriptan-loaded nanostructured lipid carriers: preparation, optimization, characterization and pharmacokinetic evaluation

OBJECTIVES

Migraine is a neurological disorder with unilateral pulsatile headache which can affect the functions of sufferers. Migraineurs experience some undesirable symptoms such as pain, nausea, vomiting and in some cases auras which make the oral delivery non-selective. The lipid nanoparticles are considered as good carriers for nose-to-brain drug delivery. The present study aimed to formulate and evaluate a sumatriptan-loaded nanostructured lipid carrier (NLC).

METHODS

A drug-loaded NLC was optimized using D-optimal design of experiment and then the characterization of the formulated NLC including particle size, zeta potential, electron microscopy, thermal analysis, drug loading efficiency and release kinetics were carried out. Pharmacokinetic evaluations were also performed during an in-vivo study on Sprague-Dawley rats and neuropharmacokinetic parameters such as drug targeting efficiency (DTE) and direct transport percentage (DTP) were calculated.

KEY FINDINGS

The optimization of experiments led to nanoparticles with 101 nm mean diameter and polydispersity index (PDI) of 0.27. The drug entrapment efficiency (EE) for optimized nanoparticle was found to be 91.00%. DTE and DTP of intranasal-administered NLC were calculated 258.02% and 61.23%, respectively.

CONCLUSIONS

Neuropharmacokinetic evaluation of intranasal NLC dispersion represents a suitable brain delivery system. The DTP of NLC formulation suggests the desirable entrance of sumatriptan into the brain.

Investigation of sumatriptan and ketorolac trometamol in the human experimental model of headache

BACKGROUND

Pituitary adenylate cyclase-activating polypeptide-38 (PACAP38) induces headache in healthy volunteers but the precise mechanisms by which PACAP38 leads to headache are unclear. We investigated the headache preventive effect of sumatriptan and ketorolac on PACAP38-induced headache in healthy volunteers. In addition, we explored contribution of vascular mechanisms to PACAP38-induced headache using high resolution magnetic resonance angiography.

METHODS

Thirty-four healthy volunteers were divided in two groups (A and B) and received infusion of PACAP38 (10 picomol/kg/min) over 20 min. Group A was pretreated with intravenous sumatriptan (4 mg) or ketorolac (30 mg) 20 min before infusion of PACAP38. Group B received infusion of sumatriptan or ketorolac as post-treatment 90 min after infusion of PACAP38. In both experiments, we used a randomized, double-blind, cross-over design. We recorded headache characteristics and circumference of extra-intracerebral arteries.

RESULTS

We found no difference in AUC _{(0-6 h)} of PACAP38-induced headache in group A, pretreated with sumatriptan or ketorolac (p = 0.297). There was no difference between sumatriptan and ketorolac in PACAP38-induced circumference change (AUC_{Baseline-110 min}) of MMA (p = 0.227), STA (p = 0.795) and MCA (p = 0.356). In group B, post-treatment with ketorolac reduced PACAP38-headache compared to sumatriptan (p < 0.001). Post-treatment with sumatriptan significantly reduced the circumference of STA (p = 0.039) and MMA (p = 0.015) but not of MCA (p = 0.981) compared to ketorolac. In an explorative analysis, we found that pre-treatment with sumatriptan reduced PACAP38-induced headache compared to no treatment (AUC_0-90min).

CONCLUSIONS

Post-treatment with ketorolac was more effective in attenuating PACAP38-induced headache compared to sumatriptan. Ketorolac exerted its effect without affecting PACAP38-induced arterial dilation, whereas sumatriptan post-treatment attenuated PACAP38-induced dilation of MMA and STA. Pre-treatment with sumatriptan attenuated PACAP38-induced headache without affecting PACAP38-induced arterial dilation. Our findings suggest that ketorolac and sumatriptan attenuated PACAP38-induced headache in healthy volunteers without vascular effects.

TRIAL REGISTRATION

Clinicaltrials.gov (NCT03585894). Registered 13 July 2018.

Ultra-rapid brain uptake of subcutaneous sumatriptan in the rat: Implication for cluster headache treatment

BACKGROUND

In spite of the substantial therapeutic efficacy of triptans, their site of action is still debated. Subcutaneous sumatriptan is the most efficacious symptomatic treatment for cluster headache (CH) patients, showing therapeutic onset within a few minutes after injection even in migraine patients. However, whether subcutaneous sumatriptan is able to reach the CNS within this short time frame is currently unknown.

METHODS

Here, by means of liquid chromatography/mass spectrometry, we investigated peripheral and brain distribution of subcutaneous sumatriptan soon after injection in rats at a dose equivalent to that used in patients. Tissue sumatriptan contents were compared to those of oxazepam, a prototypical lipophilic, neuroactive drug.

RESULTS

We report that sumatriptan accumulated within brain regions of relevance to migraine and CH pathogenesis such as the hypothalamus and the brainstem as soon as 1 and 5 minutes after injection. Notably, sumatriptan brain distribution was faster than that of oxazepam, reaching concentrations exceeding its reported binding affinity for 5HT1_B/D receptors, and in the range of those able to inhibit neurotransmitter release in vivo.

CONCLUSION

Our findings indicate that sumatriptan distributes within the CNS soon after injection, and are in line with prompt pain relief by parenteral sumatriptan in CH patients.

The inadequacy of the reductionist approach in discovering new therapeutic agents against complex diseases

For more than 20 years, drug discovery has relied on two assumptions, i.e. (i) a therapeutic response can be triggered by modulating the activity of a single gene product, and (ii) a compound uncovered by its activity on a recombinant protein in vitro can perform its activity in vivo. Drug discovery operates accordingly by using the concepts of targets and pipelines. The target, such as a gene product, is the intended point of therapeutic intervention, and compounds that modulate its activity in vitro follow a series of downstream developments. This reductionist approach has developed due to advances in combinatorial chemistry, robotics, molecular biology, and genomics. The expectation of this approach is that the frequency of drug discovery will dramatically increase, while its associated cost would decrease. However, the frequency of new drug discovery has decreased, while the associated costs have surged. We performed a retrospective study that examined how successful development programs have led to marketed drugs for all indications except anti-infective and anti-neoplastic agents. We concluded that the target and pipeline paradigms are limited and are actually causing the drug development industry to collectively fail to meet the critical medical needs. Impact statement The initial scope of this investigation was to build the set of human genes that are presumed to be the therapeutic intervention points of US FDA-approved drugs, in all therapeutics areas but oncology. The prerequisite for this study was the establishment of the non-redundant set of all active pharmaceutical ingredients for these disease areas. Pertaining to complex diseases, the main observation was that there is not a single instance in the history of drug discovery, where a compound, initially selected by means of a biochemical assay, achieved a significant therapeutic response. The whole field of Drug R&D faces an unacceptable lack of new treatments to address unmet medical needs. The conclusion is that complex biological assays have to be designed for the primary selection of candidate therapeutics.

Synthesis, biological evaluation and computational studies of novel iminothiazolidinone benzenesulfonamides as potent carbonic anhydrase II and IX inhibitors

A series of iminothiazolidinone-sulfonamide hybrids (2a-k) was synthesized by heterocyclization of sulfanilamide thioureas with methyl bromoacetate and characterized by spectroscopic techniques, mass and elemental analysis. The synthesized derivatives were screened against four relevant human (h) isoforms of carbonic anydrases (CAs, EC 4.2.1.1) I, II, IV and IX. These enzymes are involved in a variety of diseases, including glaucoma, retinitis pigmentosa, epilepsy, arthritis, and tumors. Derivatives 2a-2k exhibited the best inhibitory activity against the cytosolyc hCA II (KIs are reaching the sub-nanomolar range, 0.41-37.8 nM) and against the tumor-associated isoform hCA IX (KIs are spanning between 24.3 and 368.3 nM). The binding mode of the reported iminothiazolidinone benzenesulfonamides within hCA II and IX catalytic clefts was investigated by docking studies.

Migraine Treatment: Current Acute Medications and Their Potential Mechanisms of Action

Migraine is a common and disabling primary headache disorder with a significant socioeconomic burden. The management of migraine is multifaceted and is generally dichotomized into acute and preventive strategies, with several treatment modalities. The aims of acute pharmacological treatment are to rapidly restore function with minimal recurrence, with the avoidance of side effects. The choice of pharmacological treatment is individualized, and is based on the consideration of the characteristics of the migraine attack, the patient's concomitant medical problems, and treatment preferences. Notwithstanding, a good understanding of the pharmacodynamic and pharmacokinetic properties of the various drug options is essential to guide therapy. The current approach and concepts relevant to the acute pharmacological treatment of migraine will be explored in this review.

5-HT Receptor Nomenclature: Naming Names, Does It Matter? A Tribute to Maurice Rapport

The naming of 5-HT receptors has been challenging, especially in the early days when the concept of multiple receptors for a single neurotransmitter was considered to be unrealistic at best. Yet pharmacological (rank orders of potency in functional or biochemical settings) and transductional evidence (second messengers, electrophysiology) clearly indicated the existence of receptor families and subfamilies. The genetic revolution, with the cloning and study of recombinantly expressed receptors, and eventually the cloning of the human and other genomes have made such reservations obsolete. Further, the advances in structural biology, with the possibility to study ligand receptor complexes as crystals and/or using solution NMR have largely confirmed the complexity of the 5-HT receptor system: species differences, existence of multiple receptor active and inactive states, splice variants, editing variants, complexes with multiple interacting proteins and transduction bias. This is a short personal history on how advances in biochemistry, molecular biology, biophysics, imaging and medicinal chemistry, some lateral thinking, and a decent amount of collaborative spirit within the 5-HT receptor nomenclature committee and the 5-HT community at large have helped to better define the pharmacology of the 5-HT receptor family.

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.

Preliminary brain-targeting studies on intranasal mucoadhesive microemulsions of sumatriptan

The aim of this investigation was to prepare microemulsions containing sumatriptan (ST) and sumatriptan succinate (SS) to accomplish rapid delivery of drug to the brain in acute attacks of migraine and perform comparative in vivo evaluation in rats. Sumatriptan microemulsions (SME)/sumatriptan succinate microemulsions (SSME) were prepared using titration method and characterized for drug content, globule size and size distribution, and zeta potential. Biodistribution of SME, SSME, sumatriptan solution (SSS), and marketed product (SMP) in the brain and blood of Swiss albino rats following intranasal and intravenous (IV) administrations were examined using optimized technetium-labeled (^99mTc-labeled) ST formulations. The pharmacokinetic parameters, drug targeting efficiency (DTE), and direct drug transport (DTP) were derived. Gamma scintigraphy imaging of rat brain following IV and intranasal administrations were performed to ascertain the localization of drug. SME and SSME were transparent and stable with mean globule size 38±20 nm and zeta potential between -35 to -55 mV. Brain/blood uptake ratios at 0.5 hour following IV administration of SME and intranasal administrations of SME, SMME, and SSS were found to be 0.20, 0.50, 0.60, and 0.26, respectively, suggesting effective transport of drug following intranasal administration of microemulsions. Higher DTE and DTP for mucoadhesive microemulsions indicated more effective targeting following intranasal administration and best brain targeting of ST from mucoadhesive microemulsions. Rat brain scintigraphy endorsed higher uptake of ST into the brain. Studies conclusively demonstrated rapid and larger extent of transport of microemulsion of ST compared with microemulsion of SS, SMP, and SSS into the rat brain. Hence, intranasal delivery of ST microemulsion developed in this investigation can play a promising role in the treatment of acute attacks of migraine.

Cilostazol induces C-fos expression in the trigeminal nucleus caudalis and behavioural changes suggestive of headache with the migraine-like feature photophobia in female rats

Introduction

Research in development of new migraine therapeutics is hindered by the lack of suitable, predictive animal models. Cilostazol provokes headache in healthy humans and migraineurs by increasing intracellular cAMP levels. We aimed to investigate whether cilostazol could provoke headache-like behaviours and c-fos expression in rats. In order to evaluate the predictive validity of the model, we examined the response to the migraine specific drug sumatriptan.

Methods

The effect of cilostazol (125 mg/kg p.o.) in female Sprague Dawley rats was evaluated on a range of spontaneous behavioural parameters, light sensitivity and mechanical sensitivity thresholds. We also measured c-fos expression in the trigeminal nucleus caudalis.

Results

Cilostazol increased light sensitivity and grooming behaviour. These manifestations were not inhibited by sumatriptan. Cilostazol also induced c-fos expression in the trigeminal nucleus caudalis. Furthermore, trigeminal – but not hind paw hyperalgesia was observed.

Conclusion

The altered behaviours are suggestive of cilostazol induced headache with migraine-like features, but not specific. The presence of head specific hyperalgesia and the c-fos response in the trigeminal nucleus caudalis imply that the model involves trigeminal nociception. The model will be useful for studying mechanisms related to the cAMP pathway in headache, but its predictive properties appear to be more limited due to the lack of response to sumatriptan.

Nitroglycerin-Induced nNOS Increase in Rat Trigeminal Nucleus Caudalis is Inhibited by Systemic Administration of Lysine Acetylsalicylate but not of Sumatriptan

Systemic administration of nitroglycerin (NTG), a nitric oxide (NO) donor, in migraineurs triggers after several hours an attack of which the precise mechanisms are unknown. We found previously in rats that nitroglycerin (10 mg/kg s.c.) is able to increase significantly after 4 h the number of neuronal nitric oxide synthase (nNOS)-immunoreactive neurones in the cervical part of trigeminal nucleus caudalis. In the present experiments, we demonstrate that the 5-HT1B/D agonist sumatriptan (0.6 mg/kg s.c.) does not alter this phenomenon when given before NTG. By contrast, pretreatment with lysine acetylsalicylate (50 mg/kg i.m.) attenuates the NTG-induced nNOS expression in the superficial laminae of trigeminal nucleus caudalis. These findings suggest that effect of NTG on nNOS at a high dosage may involve the cycloxygenase pathway and that activation of the peripheral 5-HT1B/D receptors is not able to modify this effect. These data could help to better understand the role of NO in the pathogenesis of headaches and the action of antimigraine drugs.

Overview of migraine treatment

SUMMARY Migraine is ranked as the 19th top cause of disability worldwide by WHO. Despite advancements in migraine-specific acute treatment, only a minority of patients utilize these medications. Specific pharmacologic treatments consist of the ergot alkaloids and triptans (serotonin 5-HT1B/1D receptor agonists). Both classes are regarded as relatively safe and effective; however, there is a greater concern for vasoconstrictive effects with the ergots, which limits their use. Triptans transformed migraine therapy, setting in motion revolutionary research that heightened our understanding of migraine mechanisms. However, one in three migraineurs may be triptan nonresponders and there is a group of migraine patients that remains ‘refractory’ to conventional pharmacologic migraine therapy. This article discusses the approach to migraine management, reviews currently available acute and preventive pharmacologic and nonpharmacologic treatment options for migraine headache, as well as briefly focuses on novel and upcoming medicines presently under investigation.

Preparation and evaluation of tubular micelles of pluronic lecithin organogel for transdermal delivery of sumatriptan

The present work focuses on the preparation and evaluation of lecithin organogel system of thermoreversible polymer pluronic F127, which would enhance the stability and absorption of sumatriptan succinate across the skin. Formulations were developed with and without co-surfactant (pluronic F127). The prepared organogels were evaluated for its appearance, organoleptic characteristics, and feel upon application, homogeneity, occlusivenes, washability, pH, viscosity, spreadability, gel transition temperature of formulations. The formulations were also evaluated for drug content, in vitro drug diffusion properties and skin irritation testing. In vivo evaluation of formulations was carried out by hot plate and writhing test method, and finally the optimized formulation was subjected to stability studies. The developed formulations were easily washable, smooth in feel, and showed no clogging which indicate superior texture of system. Formulation, containing pluronic showed greater spreadability and higher drug diffusion rate as compared to pluronic free organogel. Drug content of organogel formulations was in the range of 94-97%. The pH of the formulations was 6.48 ± 0.5 and 6.98 ± 0.1, reflecting no risk of skin irritation. Pluronic not only enhances the stability of organogel by increasing the viscosity (from 6,541 ± 234.76 to 7,826 ± 155.65 poise) but also increases the release of drug from 67.39 ± 1.53% to 74.21 ± 1.7%. The sumatriptan exhibits higher and long lasting antinociceptive effect as indicated by the persistent increase in reaction time in hot plate and inhibited abdominal contraction in acetic acid-induced writhing test (p < 0.05). The prepared optimized formulation was found to be stable without any significant changes at room temperature.

Distribution of 5-HT(1B), 5-HT(1D) and 5-HT(1F) receptor expression in rat trigeminal and dorsal root ganglia neurons: relevance to the selective anti-migraine effect of triptans

Triptans, acting as serotonin, 5-HT(1B/1D/1F), receptor agonists, provide an effective and established treatment option in migraine and cluster headache. Clinical observations suggest a relatively specific effect of these compounds on primary headache disorders, but not in other pain syndromes. The mechanism of this specificity, however, is not well understood. Hence, we systematically studied primary sensory ganglia in rat to determine if the peripheral distribution of 5HT(1B/1D/1F) receptors showed any anatomical difference that would account for the specificity of clinical effect. Rat primary afferent and sensory ganglia neurons--trigeminal ganglia (Vg), and dorsal root ganglia (DRG): C(2), C(5), T(5), L(5)--were examined using paraffin-embedded, slide-bound tissue sections reacted with specific primary antibodies for rat 5-HT(1B, 1D) and (1F) receptors in a peroxidase-based immunohistochemical method. Immunoreactivity specific for all three serotonergic receptor subtypes was demonstrated in the five peripheral nervous system regions examined and quantitated. There was a good agreement for 5-HT(1B) and 5-HT(1D) receptors to that previously demonstrated in Vg and DRG L(5), while this was the first characterisation for 5-HT(1F) receptor in any of the five regions, as well as for 5-HT(1B) and 5HT(1D) receptors in DRG C(2), C(5) and T(5). In summary, all three 5-HT receptors are equally represented in Vg and the DRGs examined. We conclude that the triptans are theoretically able to bind to receptors at each level of the peripheral neuraxis without any apparent anatomical preference for the head.

Triptans, serotonin agonists, and serotonin syndrome (serotonin toxicity): a review

The US Food and Drug Administration (FDA) have suggested that fatal serotonin syndrome (SS) is possible with selective serotonin reuptake inhibitors (SSRIs) and triptans: this warning affects millions of patients as these drugs are frequently given simultaneously. SS is a complex topic about which there is much misinformation. The misconception that 5-HT1A receptors can cause serious SS is still widely perpetuated, despite quality evidence that it is activation of the 5-HT2A receptor that is required for serious SS. This review considers SS involving serotonin agonists: ergotamine, lysergic acid diethylamide, bromocriptine, and buspirone, as well as triptans, and reviews the experimental foundation underpinning the latest understanding of SS. It is concluded that there is neither significant clinical evidence, nor theoretical reason, to entertain speculation about serious SS from triptans and SSRIs. The misunderstandings about SS exhibited by the FDA, and shared by the UK Medicines and Healthcare products Regulatory Agency (in relation to methylene blue), are an important issue with wide ramifications.

The effects of chronic administration of sumatriptan and dipyrone on serotonergic system in the rat brain: an immunohistochemical study

OBJECTIVE

To investigate the effects of chronic high dose sumatriptan and dipyrone treatment on central serotonergic system in rats.

MATERIALS AND METHODS

Male Sprague-Dawley rats (seven per group) were daily injected with sumatriptan (3 mg/kg), dipyrone (400 mg/kg) or saline for 30 days. The brains of animals were surgically removed and immunohistochemically stained for serotonin. Serotonin-positive stained cells were counted automatically by using a computerized image analysis program. Statistical analysis carried out using one-way ANOVA followed by post hoc Tukey test.

RESULTS

A significant decrease in serotonin-positive cells in the brainstem was observed after chronic sumatriptan administration while chronic use of dipyrone induced a significant increase in serotonin-positive cells both in the cortex and midbrain.

CONCLUSION

Our data suggest that central serotonergic system might be modified by chronic use of sumatriptan and dipyrone.

The triptans

The migraine-specific triptans have revolutionized the treatment of migraine and are currently the drugs of choice to treat a migraine attack in progress. Over the past 15 years, triptans were released in rapid succession, with each one demonstrating some specific pharmacokinetic properties that may be translated into clinical advantages. Triptans share many similarities, but also have important differences from one another. Accordingly, herein we discuss the class of the triptans. We first define the trigeminovascular system and its importance in migraine pain, then discuss the mechanism of action of the triptans and contrast the evidence supporting the use of different triptans. We close with our view of the future and hopes for the next generation of antimigraine therapies.

Migraine in the triptan era: progresses achieved, lessons learned and future developments

Triptans, serotonin 5-HT1B/1D receptor agonists, more than revolutionizing the treatment of migraine, stimulated also ground breaking research that provided insights into the anatomy, physiology, and molecular pharmacology of migraine. This knowledge, in turn, is stimulating research on new mechanisms of action for the treatment of migraine. Accordingly, it is opportune to critically review the main advances in migraine science that happened in the triptan era. Herein we first review and conceptualize some of the progresses achieved in migraine science during the triptan era. We then review the class of the triptans - mechanism of action and clinical evidence. We close by briefly discussing the class of CGRP receptor antagonists, which is currently being developed for the acute treatment of migraine.

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.

Revisiting the efficacy of sumatriptan therapy during the aura phase of migraine

OBJECTIVE

To reexamine the efficacy of terminating migraine headache by administration of sumatriptan during the visual-aura phase of the attack. Background.- Although the antimigraine action of triptans is most effective soon after onset of the headache, treatment during the aura phase has been found to be ineffective.

METHODS

Nineteen subjects having migraine with aura were studied using a 4-way crossover, open-label design. Each patient was asked to treat 8 consecutive attacks with 100 mg of sumatriptan RT: 3 attacks treated at a timing of the patient's discretion (baseline); 1 attack treated 4 hours after onset of pain (late); 2 attacks treated within 1 hour of onset of pain (early); 2 attacks treated during the aura phase - before the onset of pain (aura). Pain level and cutaneous allodynia were reported by the patients at the onset of pain, at the time of treatment, and 2 and 24 hours after treatment.

RESULTS

Sumatriptan treatment during the aura preempted the development of headache in 34/38 (89%) attacks. The same patients were rendered pain-free in 30/38 (79%) of attacks treated within 1 hour of pain onset, and in 4/19 (21%) of attacks treated 4 hours after the onset of pain. The incidence of allodynia at the time of treatment was 2/38 (5%) in attacks treated during aura, 8/38 (21%) in attacks treated early, and 14/19 (74%) in attacks treated late.

CONCLUSION

Considering the discrepancy between the present and previous clinical studies, it is worthwhile revisiting the efficacy of preemptive triptan therapy during the aura phase of migraine attacks, using larger-scale, 3-way, crossover, placebo-controlled studies.

Intranasal mucoadhesive microemulsions of zolmitriptan: Preliminary studies on brain-targeting

The aim of this investigation was to prepare microemulsions containing zolmitriptan (ZT) for rapid drug delivery to the brain to treat acute attacks of migraine and to characterize microemulsions and evaluate biodistribution in rats. Zolmitriptan microemulsions (ZME) were prepared using the titration method and were characterized for globule size distribution and zeta potential. ZT was radiolabeled using (99m)Tc (technetium) and radiolabeled-drug formulations of ZT were used to carry out biodistribution of drug in the brain of Swiss albino rats after intranasal and intravenous administration. The pharmacokinetic parameters, drug targeting efficiency (%DTE) and direct nose-to-brain drug transport (%DTP) were calculated. Brain scintigraphy imaging in rats were also performed to ascertain the uptake of drug into the brain. ZME were transparent and stable with mean globule size of 35 +/- 25 nm and zeta potential of - 38- - 52 mV. (99m)Tc-labeled-drug formulations of ZT were found to be stable and suitable to perform in vivo studies. Following intranasal administrations of zolmitriptan mucoadhesive microemulsion (ZMME), ZME, Zolmitriptan solution (ZS) and intravenous administration of ZS, brain/blood uptake ratios at 0.50 h were found to be 0.70, 0.56, 0.27 and 0.13, respectively, indicating effective brain-targeting following intranasal administration of ZMME. Comparing intranasal administration of ZMME with intravenous administration of ZME, the %DTE and %DTP were found higher indicating effective drug transport following intranasal administration and highest brain-targeting following ZMME administration. Rat brain scintigrams showed substantial uptake of drug into the brain after intranasal administration of ZMME. Studies of this investigation conclusively demonstrated rapid and larger extent of transport into the rat brain following intranasal administration of ZMME and can play a promising role in the treatment of acute attacks of migraine.

History of the Use of Ergotamine and Dihydroergotamine in Migraine From 1906 and Onward

Dale showed in 1906 in a seminal work that ergot inhibits the pressor effect of adrenaline. Stoll at Sandoz isolated ergotamine from ergot in 1918. Based on the belief that migraine was due to increased sympathetic activity, ergotamine was first used in the acute treatment of migraine by Maier in Switzerland in 1925. In 1938 Graham and Wolff demonstrated the parallel decrease of temporal pulsations and headache after ergotamine i.v. This inspired the vascular theory of Wolff: an initial cerebral vasoconstriction followed by an extracranial vasodilation. Dihydroergotamine (DHE) was introduced as an adrenolytic agent in 1943. It is still in use parenterally and by the nasal route. Before the triptan era ergotamine and DHE had widespread use as the only specific antimigraine drugs. From 1950 the world literature on ergotamine was dominated by two adverse events: ergotamine overuse headache and the relatively rare overt ergotism. Recently, oral ergotamine, which has an oral bioavailability of < 1%, has been inferior to oral triptans in randomized clinical trials. A European Consensus in 2000 concluded that ergotamine is not a drug of first choice. In an American review of 2003 it was suggested that ergotamine may be considered in the treatment of selected patients with moderate to severe migraine.

Challenges in developing P2 purinoceptor-based therapeutics

Advances in the molecular cloning, expression and functional characterization of the P2 purinoceptor superfamily have provided a wealth of data to support a diverse functional role for ATP and related nucleotides in the regulation of tissue function. As with other receptor superfamilies, it is likely that distinct subtypes of each receptor will subserve discrete functions depending on tissue distribution and disease pathophysiology. At the present time, ATP is being evaluated as an anticancer agent and as an anaesthesia adjunct whereas UTP is studied as a novel treatment for cystic fibrosis. ARL67085 is a potent and selective P2T receptor antagonist that has potential as a novel antithrombotic agent. The key to exploiting the P2 purinoceptor area to enhance understanding of disease aetiology and concurrent therapeutic potential will be to focus efforts on the identification of novel pharmacophores that have potent and selective interactions with the various receptor subtypes as potential new leads. To this end, the use of high-throughput screening in conjunction with combinatorial chemical, conventional chemical and natural product library compound sources will be critical.

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.

5-HT(1B) receptors, ventral orbitofrontal cortex, and aggressive behavior in mice

RATIONALE

Systemic injections of 5-HT(1B) receptor agonists have been shown to have specific anti-aggressive effects in aggressive individuals. One site of action for these drugs is the 5-HT(1B) receptors in the ventral orbitofrontal cortex (VO PFC), an area that has been implicated in the inhibitory control of behavior and is a terminal region for 5-HT projections.

OBJECTIVE

To assess the anti-aggressive effects of the 5-HT(1B) receptor agonist CP-94,253 when microinjected into the VO PFC (0.1, 0.56, and 1.0 microg/0.2 microl) or into the infralimbic prefrontal cortex (IL PFC; 1.0 microg/0.2 microl) in separate groups of aggressive resident male mice. To confirm the 5-HT(1B) receptor as the critical site of action for the anti-aggressive effects, the 5-HT(1B/D) antagonist GR-127,935 was microinjected at 10.0 microg/0.2 microl into the VO PFC. After recovery from surgery, the anti-aggressive effects of microinjected CP-94,253 were studied during 5-min resident-intruder confrontations that were recorded and analyzed.

RESULTS

Microinjections of CP-94,253 (0.56 and 1.0 microg/0.2 microl) dose-dependently reduced the frequency of attack bites and sideways threats. This effect was behaviorally specific because non-aggressive motor activities were not significantly altered by the drug. In the IL vmPFC or in an area lateral to the VO PFC, CP-94,253 (1.0 microg/0.2 microl) did not have significant behavioral effects.

CONCLUSIONS

The results highlight the 5-HT(1B) receptors in the VO PFC as a particularly important site for the inhibition of species-typical aggressive behavior in male mice.

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.

Distribution of intranasal C-zolmitriptan assessed by positron emission tomography

Nine healthy volunteers aged 18-28 years were recruited into this open, single-centre, two-phase trial. In phase 1, two volunteers received a single dose of 11C-zolmitriptan 2.5 mg administered as a nasal spray and then underwent positron emission tomography (PET) scanning to determine the most appropriate times for scanning in phase 2. In phase 2, six volunteers received two doses and an additional volunteer one dose of 11C-zolmitriptan 2.5 mg intranasally. Volunteers underwent PET scanning over sectors covering one of the nasopharynx, lungs or abdomen, for up to 1.5 h postdose. The brain was also scanned and plasma zolmitriptan levels were measured. Almost 100% of the administered dose was detected in the nasopharynx immediately after dosing. This declined thereafter to about 50% at 20 min and to 35% at 80 min after dosing. Radioactivity appeared slowly in the upper abdomen, with 25% of given radioactivity detected at 20 min and persisting until 80 min after dosing. Minimal radioactivity was detected in the lungs. Radioactivity was detectable within brain tissue suggesting central penetration of zolmitriptan. Zolmitriptan in plasma had approached its maximum concentration by 15 min postdose. The data indicate initial absorption across the nasal mucosa contributing to an early systemic availability. 11C-Zolmitriptan administered intranasally was well tolerated.