MERTK in the rat trigeminal system: a potential novel target for cluster headache?

The trigeminal system is key to the pathophysiology of migraine and cluster headache, two primary headache disorders that share many features. Recently, MER proto-oncogene tyrosine kinase (MERTK), a cell surface receptor, was strongly associated with cluster headache through genetic studies. Further, the MERTK ligand galectin-3 has been found to be elevated in serum of migraine patients. In this study, MERTK and MERTK ligands were investigated in key tissue to better understand their potential implication in the pathophysiology of primary headache disorders. Immunohistochemistry was used to map MERTK and galectin-3 expression in rat trigeminal ganglia. RT-qPCR was used to assess MERTK gene expression in blood, and ELISA immunoassays were used for MERTK ligand quantification in serum from study participants with and without cluster headache. MERTK gene expression was elevated in blood samples from study participants with cluster headache compared to controls. In addition, MERTK ligand galectin-3 was found at increased concentration in the serum of study participants with cluster headache, whereas the levels of MERTK ligands growth arrest specific 6 and protein S unaffected. MERTK and galectin-3 were both expressed in rat trigeminal ganglia. Galectin-3 was primarily localized in smaller neurons and to a lesser extent in C-fibres, while MERTK was found in satellite glia cells and in the outer membrane of Schwann cells. Interestingly, a strong MERTK signal was found specifically in the region proximal to the nodes of Ranvier. The overexpression of MERTK and galectin-3 in tissue from study participants with cluster headache, as well as the presence of MERTK in rat peripheral satellite glia cells and Schwann cells in the trigeminal ganglia, further highlights MERTK signalling as an interesting potential future therapeutic target in primary headache.

Peptides, MAbs, Molecules, Mechanisms, and More: Taking a Stab at Cluster Headache.

BACKGROUND: Cluster headache is a highly disabling neurological disorder. PURPOSE: The purpose of this review is to highlight recent therapeutic advances in the treatment of cluster headache such as monoclonal antibodies as well as non-invasive vagus nerve stimulation, and examine future potential therapeutic targets. DISCUSSION: Several therapeutic agents currently in use may have underlying mechanisms important to cluster headache pathophysiology and have yet to be completely elucidated. The psychobiological aspects of cluster headache have a significant impact on patients, as well as pose limitations for treatment. Neuropeptides may play a role in underlying mechanisms in why cluster headache patients are frequent tobacco smokers. Alterations in the hypothalamic-pituitary-adrenal axis and neuroinflammation may play a role in suicidality. The circadian nature of cluster headache may generate the development of future treatment options. New understanding of mechanisms underlying post-traumatic headache may also provide insights into cluster headache pathophysiology. CONCLUSION: Molecular targets and neuromodulation advances have paved the way for a new generation of therapeutic agents in cluster headache. There are several other potential targets.

Linking Cigarette Smoking/Tobacco Exposure and Cluster Headache: A Pathogenesis Theory.

INTRODUCTION: To propose a hypothesis theory to establish a linkage between cigarette smoking and cluster headache pathogenesis. BACKGROUND: Cluster headache is a primary headache syndrome grouped under the trigeminal autonomic cephalalgias. What distinguishes cluster headache from all other primary headache conditions is its inherent connection to cigarette smoking. It is undeniable that tobacco exposure is in some manner related to cluster headache. The connection to tobacco exposure for cluster headache is so strong that even if an individual sufferer never smoked, then that individual typically had significant secondary smoke exposure as a child from parental smoking behavior and in many instances both scenarios exist. The manner by which cigarette smoking is connected to cluster headache pathogenesis is unknown at present. If this could be determined this may contribute to advancing our understanding of cluster headache pathophysiology. METHODS/RESULTS: Hypothesis statement. CONCLUSION: The hypothesis theory will include several principles: (1) the need of double lifetime tobacco exposure, (2) that cadmium is possibly the primary agent in cigarette smoke that leads to hypothalamic-pituitary-gonadal axis toxicity promoting cluster headache, (3) that the estrogenization of the brain and its specific sexually dimorphic nuclei is necessary to develop cluster headache with tobacco exposure, and (4) that the chronic effects of smoking and its toxic metabolites including cadmium and nicotine on the cortex are contributing to the morphometric and orexin alterations that have been previously attributed to the primary headache disorder itself.

PACAP38: Emerging Drug Target in Migraine and Cluster Headache.

Here, we review the role of pituitary adenylate cyclase-activating peptide-38 (PACAP38) in migraine and cluster headache (CH). Mounting evidence implicates signaling molecule PACAP38 in the pathophysiology of migraine. Human provocation studies show PACAP38 induces migraine attacks in migraine patients without aura and marked and sustained dilation of extracerebral arteries. PACAP38 selectively targets the PAC1 receptor making this receptor a promising candidate for targeted migraine therapy. Randomized clinical trials are warranted to pursue this possible treatment pathway. PACAP38 provocation studies in CH could elucidate possible involvement of PACAP38 in CH pathophysiology and predict efficacy of PACAP38 antagonists in this primary headache.

Expression of messenger molecules and receptors in rat and human sphenopalatine ganglion indicating therapeutic targets.

BACKGROUND: Migraine and Cluster Headache (CH) are two primary headaches with severe disease burden. The disease expression and the mechanisms involved are poorly known. In some attacks of migraine and in most attacks of CH, there is a release of vasoactive intestinal peptide (VIP) originating from parasympathetic cranial ganglia such as the sphenopalatine ganglion (SPG). Patients suffering from these diseases are often deprived of effective drugs. The aim of the study was to examine the localization of the botulinum toxin receptor element synaptic vesicle glycoprotein 2A (SV-2A) and the vesicular docking protein synaptosomal-associated protein 25 (SNAP25) in human and rat SPG. Additionally the expression of the neurotransmitters pituitary adenylate cyclase activating polypeptide (PACAP-38), nitric oxide synthase (nNOS), VIP and 5-hydroxttryptamine subtype receptors (5-HT1B,1D,1F) were examined. METHODS: SPG from adult male rats and from humans, the later removed at autopsy, were prepared for immunohistochemistry using specific antibodies against neurotransmitters, 5-HT1B,1D,1F receptors, and botulinum toxin receptor elements. RESULTS: We found that the selected neurotransmitters and 5-HT receptors were expressed in rat and human SPG. In addition, we found SV2-A and SNAP25 expression in both rat and human SPG. We report that all three 5-HT receptors studied occur in neurons and satellite glial cells (SGCs) of the SPG. 5-HT1B receptors were in addition found in the walls of intraganglionic blood vessels. CONCLUSIONS: Recent focus on the SPG has emphasized the role of parasympathetic mechanisms in the pathophysiology of mainly CH. The development of next generation's drugs and treatment of cranial parasympathetic symptoms, mediated through the SPG, can be modulated by treatment with BoNT-A and 5-HT receptor agonists.

Corticosteroids alter CGRP and melatonin release in cluster headache episodes.

BACKGROUND: Calcitonin gene-related peptide (CGRP) is a marker of trigeminal activation in acute cluster headache (CH). Melatonin production is altered in CH patients and may reflect hypothalamic dysfunction. We assessed the effects of short-term CH prevention with corticosteroids on CGRP and melatonin release in a prospective observational cohort study hypothesizing that corticosteroids influence the interictal activity of both systems indicated by the change of these biomarkers. METHODS: Episodic CH subjects (n = 9) in the bout and controls with multiple sclerosis (n = 6) received 1000 mg/d methylprednisolone (MPD) i.v. for three days followed by oral tapering with prednisone. We determined CGRP plasma levels in external jugular vein blood outside an attack and 6-sulfatoxymelatonin (aMT6s) - the stable metabolite of melatonin - in 12-hour day- and nighttime urine collection prior to and several times after MPD therapy and again when CH subjects were outside the bout in complete remission. CH patients recorded the frequency of attacks. RESULTS: In parallel to the reduction of headache frequency, administration of corticosteroids resulted in significantly decreased CGRP plasma levels and increased nocturnal aMT6s urine excretion in CH subjects. No significant changes were observed in controls. CONCLUSION: Corticosteroids alter CGRP plasma and aMT6s urine levels in a cluster bout. These changes may indicate an effect of corticosteroids on trigeminal activation and hypothalamic dysfunction.

Role of nitric oxide in cluster headache.

Nitric oxide (NO) is an important molecule in headache pathophysiology. NO regulates vascular tone and acts as a potent vasodilator, and thus participates in regulating blood flow. NO is also considered to play a role in processing sensory information and pain sensitization. In this article, we review the role of NO in one of the primary headache disorders, cluster headache (CH). The pathophysiology of CH is still not completely understood. A multifactorial genesis where NO is likely to be involved is probable. The level of NO production has been shown to correlate with disease activity in several inflammatory disorders, such as cystitis, multiple sclerosis, and cerebral lupus erythematosus. In this article, the issue of whether similar circumstances apply for CH and also the role of NO in the pathophysiology of CH in a wider perspective are discussed.

Central modulation in cluster headache patients treated with occipital nerve stimulation: an FDG-PET study.

BACKGROUND: Occipital nerve stimulation (ONS) has raised new hope for drug-resistant chronic cluster headache (drCCH), a devastating condition. However its mode of action remains elusive. Since the long delay to meaningful effect suggests that ONS induces slow neuromodulation, we have searched for changes in central pain-control areas using metabolic neuroimaging. METHODS: Ten drCCH patients underwent an 18FDG-PET scan after ONS, at delays varying between 0 and 30 months. All were scanned with ongoing ONS (ON) and with the stimulator switched OFF. RESULTS: After 6-30 months of ONS, 3 patients were pain free and 4 had a ≥ 90% reduction of attack frequency (responders). In all patients compared to controls, several areas of the pain matrix showed hypermetabolism: ipsilateral hypothalamus, midbrain and ipsilateral lower pons. All normalized after ONS, except for the hypothalamus. Switching the stimulator ON or OFF had little influence on brain glucose metabolism. The perigenual anterior cingulate cortex (PACC) was hyperactive in ONS responders compared to non-responders. CONCLUSIONS: Metabolic normalization in the pain neuromatrix and lack of short-term changes induced by the stimulation might support the hypothesis that ONS acts in drCCH through slow neuromodulatory processes. Selective activation in responders of PACC, a pivotal structure in the endogenous opioid system, suggests that ONS could restore balance within dysfunctioning pain control centres. That ONS is nothing but a symptomatic treatment might be illustrated by the persistent hypothalamic hypermetabolism, which could explain why autonomic attacks may persist despite pain relief and why cluster attacks recur shortly after stimulator arrest. PET studies on larger samples are warranted to confirm these first results.

Diminished nocturnal lipolysis in cluster headache: a sign of central sympathetic dysregulation?

BACKGROUND: It is unclear whether the autonomic symptoms during cluster headache (CH) attacks are of central or peripheral origin. A metabolic change such as altered lipolysis would reflect a central autonomic dysfunction. OBJECTIVE: To study nocturnal lipolysis in CH patients and healthy control subjects. METHODS: Microdialysis technique was used to measure glycerol levels, the end-product of lipolysis, in subcutaneous adipose tissue. Ten CH patients participated, of whom six were studied in remission as well as during symptomatic periods but between headache attacks. Fifteen healthy control subjects were studied. Mean glycerol, glucose, and lactate concentrations were calculated for three 2-hour intervals between 2400 and 0600 hours. RESULTS: Compared with healthy control subjects, symptomatic CH patients had lower glycerol levels during all three intervals (69, 61, and 73% of control levels; p < 0.05). CH patients in remission showed lower glycerol levels from 0200 to 0600 hours (68 and 63% of control levels; p < 0.05). There were no significant differences between the CH groups. Compared with healthy control subjects, patients in remission also showed a significantly different nocturnal temporal pattern, demonstrating declining glycerol levels during the first part of the night. CONCLUSIONS: Altered lipolysis was found in patients with CH, both in symptomatic periods and in remission. The altered lipolysis may be due to a reduced nocturnal sympathetic activity and consequently an indication of central sympathetic dysregulation and hypothalamic dysfunction.

Aspects on the pathophysiology of migraine and cluster headache.

The specific cause of migraine headache remains unknown. Current theories suggest that the initiation of a migraine attack involves a primary CNS dysfunction with subsequent activation of the trigeminovascular system. Studies in patients have revealed a clear association between headache and the release of the neuropeptide calcitonin gene-related peptide, probably from C fibres. In cluster headache and in a case of chronic paroxysmal headache there was in addition release of the parasympathetic neuropeptide vasoactive intestinal peptide, which was associated with headache, nasal congestion and rhinorrhea. Triptan administration, activating the 5-HT(1B/1D) receptors, caused the headache to subside and the neuropeptide release to normalise. These data suggest the involvement of sensory and parasympathetic mechanisms in the pathophysiology of primary headaches.

Deficient energy metabolism is associated with low free magnesium in the brains of patients with migraine and cluster headache.

We used phosphorus magnetic resonance spectroscopy to assess in vivo the brain cytosolic free magnesium concentration and the free energy released by the reaction of adenosine triphosphate (ATP) hydrolysis (DeltaG(ATPhyd)), the latter being an index of the cell's bioenergetics condition. We studied 78 patients with migraine in attack-free periods (7 with migraine stroke, 13 with migraine with prolonged aura, 37 with migraine with typical aura or basilar migraine, and 21 with migraine without aura), and 13 patients with cluster headache. In the occipital lobes of all subgroups of migraine and in cluster headache patients cytosolic free [Mg(2+)] as well as the free energy released by the reaction of ATP hydrolysis were significantly reduced. Among migraine patients, the level of free energy released by the reaction of ATP hydrolysis and the cytosolic free [Mg(2+)] showed a trend in keeping with the severity of clinical phenotype, both showing the lowest values in patients with migraine stroke and the highest in patients with migraine without aura. These results support our current hypothesis that the reduction in free [Mg(2+)] in tissues with mitochondrial dysfunction is secondary to the bioenergetics deficit, and are against a primary role of low brain cytosolic free [Mg(2+)] in causing the bioenergetics deficit in headache.

Pathophysiology of primary headaches.

The cerebral circulation is innervated by sympathetic, parasympathetic, and sensory nerves, which store a considerable number of neurotransmitters. The role of these has been evaluated in primary headaches. A clear association between head pain and the release of calcitonin gene-related peptide was demonstrated. In cluster headache and in a case of chronic paroxysmal headache there was in addition the release of vasoactive intestinal peptide, which was associated with the facial symptoms (nasal congestion, rhinorrhea). In parallel with sumatriptan treatment, head pain subsided and neuropeptide release normalized. These data show the involvement of sensory and parasympathetic mechanisms in the pathophysiology of primary headaches.

Cluster headache is not associated with signs of a systemic inflammation.

OBJECTIVE: To investigate whether there is clinical or biochemical evidence for a transient systemic inflammation during active periods of cluster headache. METHODS: Twenty-seven male and female consecutively selected patients with episodic cluster headache filled in questionnaires aiming at detecting any concurrent systemic vasculitic or rheumatoid disease. They were physically examined by both a neurologist and a rheumatologist independent of each other. Blood and urine samples were taken one to three times during an active cluster period and once in remission. The following analyses were performed: hemoglobin, erythrocyte sedimentation rate, C-reactive protein, complete blood counts including differential counts, creatinine, albumin, creatine kinase, electrophoreses of serum (with haptoglobin, orosomucoid, IgG, IgM), von Willebrand's factor, antinuclear antibodies, rheumatoid factor, cytoplasmic antineutrophil cytoplasmic autoantibodies, perinuclear antineutrophil cytoplasmic autoantibodies, and routine urinary tests. An age- and sex-matched control group of 99 consecutive patients attending the Outpatient Department of Neurology for symptoms/diseases other than severe headache completed the same questionnaire as the patient group. RESULTS: Only one patient with cluster headache showed clinical signs (livedo reticularis) that could have been due to an ongoing systemic vasculitis. Most symptoms were equally or even more prevalent in the control group than among the patients with cluster headache. However, cold feet were about twice as prevalent among female patients with cluster headache than in the control group. This was considered due to their smoking habits. Laboratory tests showed no statistically significant differences between the active cluster periods and remission. There were some slightly abnormal values in single laboratory tests, some of which were probably due to concurrent upper respiratory infections. The findings of laboratory tests for one patient could have been due to nephritis. All patients were negative for cytoplasmic antineutrophil cytoplasmic autoantibodies and perinuclear antineutrophil cytoplasmic autoantibodies. CONCLUSIONS: These results were taken as evidence that no systemic inflammation is present during the active cluster headache period. However, whether a local retro-orbital inflammation underlies the pathophysiology of cluster headache remains obscure.

Phosphorus magnetic resonance spectroscopy in cluster headache.

We performed in vivo MR spectroscopy phosphorus (31P-MRS) on the brain and skeletal muscles of 14 patients affected with cluster headache (CH). We examined patients in interictal periods, and also examined nine of them during the cluster period, although not during the attack. Brain 31P-MRS showed reduced phosphocreatine (PCr) levels, an increased ADP concentration (calculated from the creatine kinase equilibrium), a reduced phosphorylation potential, and a high relative rate of ATP biosynthesis (V/Vmax %). The inorganic phosphate (P(i)) content was increased during the cluster period. Ten of 13 patients also showed a slow rate of PCr recovery in muscle after the exercise. 31P-MRS in CH patients showed abnormalities of brain and skeletal muscle energy metabolism comparable with those seen in various types of migraine, thus leading us to suggest a similarity in biochemical pathogenic mechanisms between CH and migraine.

Clusterlike headache as a first sign of brain metastases of lung cancer.

We report on a patient with clusterlike headache and multiple brain metastases of lung cancer. Initially, cluster headache was suggested clinically by characteristic symptoms without any focal central nervous system signs. However, magnetic resonance imaging demonstrated multiple brain metastases. It is possible that tumor necrosis factor may have played a role in initiating the clusterlike headache.

Human in vivo evidence for trigeminovascular activation in cluster headache. Neuropeptide changes and effects of acute attacks therapies.

Cluster headache is a rare very severe disorder that is clinically well characterized with a relatively poorly understood pathophysiology. In this study patients with episodic cluster headache fulfilling the criteria of the International Headache Society were examined during an acute spontaneous attack of headache to determine the local cranial release of neuropeptides. Blood was sampled from the external jugular vein ipsilateral to the pain before and after treatment of the attack. Samples were assayed for calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), substance P and neuropeptide Y. Attacks were treated with either oxygen inhalation, sumatriptan or an opiate. Thirteen patients were studied of whom 10 were male and three female. All had well-established typical attacks of cluster headache when blood was sampled. During the attacks external jugular vein blood levels of CGRP and VIP were raised while there was no change in neuropeptide Y or substance P. Calcitonin gene-related peptide levels rose to 110 +/- 7 pmol/l (normal: < 40) while VIP levels rose to 20 +/- 3 pmol/l (normal: < 7). Treatment with both oxygen and subcutaneous sumatriptan reduced the CGRP level to normal, while opiate administration did not alter the peptide levels. These data demonstrate for the first time in vivo human evidence for activation of the trigeminovascular system and the cranial parasympathetic nervous system in an acute attack of cluster headache. Furthermore, it is shown that both oxygen and sumatriptan abort the attacks and terminate activity in the trigeminovascular system.

Opioid and sympathetic nervous system activity in cluster headache under verapamil or prednisone treatment.

This study was undertaken to evaluate the effect of treatment with prednisone or verapamil on plasma met-enkephalin (ME), neutrophil met-enkephalin containing peptides (NMECP) and free and conjugated plasma catecholamines (CA) in cluster headache (CH) patients. After obtaining a basal sample, patients were randomly selected to be treated with either verapamil (n = 5) or prednisone (n = 5). A second blood sample was obtained 10 days after starting treatment. At this time all patients were free of symptoms. ME (0.49 +/- 0.10 pmol/mL) and NMECP (35.1 +/- 2.4 pmol/mg protein) levels after prednisone treatment were significantly higher (P < 0.05) than in basal conditions (0.29 +/- 0.08 pmol/mL and 27.14 +/- 2.4 pmol/mg protein), while no differences were found in catecholamine levels. No differences in ME, NMECP or CA were found during verapamil treatment. Our results suggest that in CH the two drugs act through different mechanisms. The relief of the bout obtained with prednisone may be related to the opioid system stimulation observed in these patients.

Nostril capsaicin application as a model of trigeminal primary sensory neuronal activation.

Capsaicin was applied unilaterally to the nostril mucosa of 18 episodic cluster headache sufferers in remission. Plasma and saliva levels of substance P (SP), calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP) were measured by radioimmunoassay. Increase of salivary SP-LI and CGRP-LI as well as of plasma CGRP-LI occurred after capsaicin stimulation. Capsaicin-induced neurochemical changes in saliva and in plasma were compared to the changes observed during cluster headache attacks measured in a separate study. The comparative changes in SP, CGRP and VIP characterizing these two conditions suggest that trigeminal capsaicin-sensitive sensory neurones are unlikely to play any fundamental role in the mechanics of cluster headache.

Sensory neuropeptides (substance P, calcitonin gene-related peptide) and vasoactive intestinal polypeptide in human saliva: their pattern in migraine and cluster headache.

Substance P, calcitonin gene-related peptide and vasoactive intestinal polypeptide-like immunoreactivities have been evaluated in the saliva of 15 subjects suffering from migraine without aura and 16 control subjects. All three peptides were also measured in the symptomatic/non-symptomatic side saliva sampled from 10 cluster headache sufferers during the cluster period, 5 cluster headache sufferers out of the cluster period, as well as in the right and left side saliva of 18 control subjects. The most interesting result gives a clear difference in common migraine and cluster headache salivary vasoactive intestinal polypeptide-like immunoreactivity contents. In fact, these are enhanced during cluster headache attack and decreased during migraine attack when compared with the interictal period vasoactive intestinal polypeptide-like immunoreactivity levels. Another remarkable finding concerns the significant increase of substance P-like immunoreactivity and calcitonin gene-related peptide-like immunoreactivity levels, from basal values, in the saliva sampled during both migraine and cluster headache attacks. Control subjects showed a calcitonin gene-related peptide-like immunoreactivity and substance P-like immunoreactivity salivary contents significantly higher than migraine sufferers' saliva sampled in basal conditions. Conversely, calcitonin gene-related peptide-like immunoreactivities levels in controls were lower than in cluster headache sufferers' saliva obtained during intervals. Finally, during cluster headache attacks the enhancement of substance P-like immunoreactivity and vasoactive intestinal polypeptide-like immunoreactivity salivary contents interest the non-symptomatic side, whereas the symptomatic side salivary substance P-like immunoreactivity and vasoactive intestinal polypeptide-like immunoreactivity contents remain unchanged. These findings do not allow any final conclusion. However, this biochemical evaluation indicates relevant changes of the salivary neuropeptides in diseases, such as migraine and cluster headache, in which pain transmission is surely involved.

Cluster headache in the male: sex steroid pattern and gonadotropic response to luteinizing hormone releasing hormone.

Serum testosterone, dihydrotestosterone, delta 4-androstendione and 17 beta-estradiol, sex hormone binding globulin (SHBG) and gonadotropic response to luteinizing hormone releasing hormone (LHRH) were studied in 34 male subjects with episodic or chronic cluster headache (CH). The sex steroid free fractions and those bound to SHBG and albumin were determined by a simulatory computerized method based on the mass action law. Individual steroid values were dispersed over a wide range in CH patients. Total, free and carrier protein-bound testosterone levels were significantly diminished only in chronic CH, where luteinizing hormone (LH) peak values after intravenous administration of LHRH were also decreased. Basal and peak follicle stimulating hormone (FSH) levels were significantly increased in episodic and in chronic CH groups, in comparison to healthy controls.