Sieneke Labruijere

Activation of 5-hydroxytryptamine1B/1D/1F receptors as a mechanism of action of antimigraine drugs

Introduction: The introduction of the triptans (5-hydroxytryptamine (5-HT)1B/1D receptor agonists) was a great improvement in the acute treatment of migraine. However, shortcomings of the triptans have prompted research on novel serotonergic targets for the treatment of migraine. Areas covered: In this review the different types of antimigraine drugs acting at 5-HT receptors, their discovery and development are discussed. The first specific antimigraine drugs were the ergot alkaloids, consisting of ergotamine, dihydroergotamine and methysergide, which are agonists at 5-HT receptors, but can also bind α-adrenoceptors and dopamine receptors. In the 1990s, the triptans became available on the market. They are 5-HT1B/1D receptor agonists, showing fewer side effects due to their receptor specificity. In the last years, compounds that bind specifically to 5-HT1D, 5-HT1F and 5-HT7 receptors have been explored for their antimigraine potential. Furthermore, the serotonergic system seems to act in tight connection with the glutamatergic as well as the CGRP-ergic systems, which may open novel therapeutic avenues. Expert opinion: Although the triptans are very effective in treating migraine attacks, their shortcomings have stimulated the search for novel drugs. Currently, the focus is on 5-HT1F receptor agonists, which seem devoid of vascular side effects. Moreover, novel compounds that affect multiple transmitter and/or neuropeptide systems that are involved in migraine could be of therapeutic relevance.

Comparison of the vasodilator responses of isolated human and rat middle meningeal arteries to migraine related compounds

BackgroundMigraine attacks occur spontaneously in those who suffer from the condition, but migraine-like attacks can also be induced artificially by a number of substances. Previously published evidence makes the meninges a likely source of migraine related pain. This article investigates the effect of several vasodilators on meningeal arteries in order to find a connection between the effect of a substance on a meningeal vessel and its ability to artificially induce migraine.MethodsA myograph setup was used to test the vasodilator properties of the substances acetylcholine (ACh), sodium nitroprusside (SNP), sildenafil, prostaglandin E2 (PGE2), pituitary adenylate cyclase activating peptide-38 (PACAP-38), calcitonin gene-related peptide (CGRP) and NaCl buffer on meningeal arteries from human and rat. An unpaired t-test was used to statistically compare the mean Emax(%) at the highest concentration of each substance to the Emax(%) of NaCl buffer.ResultsIn the human experiments, all substances except PACAP-38 had an Emax (%) higher than the NaCl buffer, but the difference was only significant for SNP and CGRP. For the human samples, clinically tested antimigraine compounds (sumatriptan, telcagepant) were applied to the isolated arteries, and both induced a significant decrease of the effect of exogenously administrated CGRP. In experiments on rat middle meningeal arteries, pre-contracted with PGF2α, similar tendencies were seen. When the pre-contraction was switched to K+ in a separate series of experiments, CGRP and sildenafil significantly relaxed the arteries.ConclusionsStill no definite answer can be given as to why pain is experienced during an attack of migraine. No clear correlation was found between the efficacy of a substance as a meningeal artery vasodilator in human and the ability to artificially induce migraine or the mechanism of action. Vasodilatation could be an essential trigger, but only in conjunction with other unknown factors. The vasculature of the meninges likely contributes to the propagation of the migrainal cascade of symptoms, but more research is needed before any conclusions can be drawn about the nature of this contribution.

Analysis of the vascular responses in a murine model of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women of there productive age, but the exact pathophysiological mechanisms involved remain unclear. Cardiovascular disease risk is increased in PCOS patients and endothelial damage has been observed. We recently developed a mouse model of PCOS with reproductive and metabolic characteristics resembling those observed in women with PCOS. In this model we studied vascular function with particular emphasis on markers of vascular endothelial function. Animals were treated for 90 days with dihydrotestosterone (DHT; 27.5 mg/day) or placebo using subcutaneous continuous-release pellets. Aortas were isolated for isometric force recordings in organ baths to investigate endothelial and vascular smooth muscle characteristics. Lungs were used to analyze endothelial nitric oxide synthase (eNOS) expression and phosphorylation. Asymmetric dimethylarginine (ADMA) levels were investigated in serum to assess endothelial damage. Expression of androgen receptor (Ar) mRNA was studied in aortas. DHT treatment (compared with placebo) induced i) a significant decrease in acetylcholine-induced aortic relaxations, with no change in calcitonin gene related peptide- or sodium nitroprusside-induced relaxations, as well as 5-hydroxytryptamine-induced contractions; ii) no change in eNOS expression/phosphorylation in lungs or in plasma ADMA levels; and iii) a twofold increase in aortic AR expression. Our results suggest that, in DHT-exposed mice, hyperandrogenemia specifically decreases endothelium dependent vasorelaxation without deterioration of smooth muscle function. This study may initiate further investigations to elucidate underlying mechanism for the phenotype that is present in these animals, as well as in PCOS patients.

Long-lasting physiological antagonism of calcitonin gene-related peptide towards endothelin-1 in rat mesenteric arteries and human coronary arteries

Endothelin-1 causes long-lasting contraction via endothelin type A receptor (ETAR) in isolated rat mesenteric arteries (RMA) that cannot be readily terminated by removing the agonist, or by adding the ETAR antagonist BQ123 or the NO donor sodium nitroprusside. It could be terminated by adding calcitonin-gene related peptide (CGRP), most likely because CGRP causes ET-1/ETAR dissociation. Here we investigated this phenomenon in human coronary microarteries (HCMA). We simultaneously verified the effects of CGRP in RMA and HCMA towards other vasoconstrictors, i.e., the α1-adrenoceptor agonist phenylephrine, the thromboxane A2 analog U46619 (9,11-dideoxy-11α,9α-epoxy-methano-prostaglandin F2α) and KCl. Long-lasting contraction (remaining after washing away the agonist) was observed for ET-1 in RMA, but not HCMA. Constrictions to phenylephrine, U46619 or KCl did not last upon washing. When added on top of ET-1-initiated contraction in RMA, CGRP effectively counteracted vasoconstriction, i.e., it caused full relaxation. Inhibitory effects of CGRP were also observed when briefly exposing RMA and HCMA to CGRP 1h before the addition of ET-1. Similar inhibitory effects of transient CGRP pre-incubation were seen towards phenylephrine, U46619 or KCl in RMA and HCMA. In conclusion, our data imply that CGRP, like ET-1, causes long-lasting effects that remain apparent up to 1h after its removal from the organ bath. Thus, in addition to the reported dissociation of ET-1/ETAR complexes, CGRP causes long-lasting non-selective arterial smooth muscle relaxation that may add to the neuropeptide being a physiological antagonist of arterial effects of ET-1. Long-lasting, washout-resistant ET-1/ETAR interaction does not occur in HCMAs.

Dihydroergotamine and sumatriptan in isolated human coronary artery, middle meningeal artery and saphenous vein

Background Dihydroergotamine (DHE) and sumatriptan are contraindicated in patients with cardiovascular disease because of their vasoconstricting properties, which have originally been explored in proximal coronary arteries. Our aim was to investigate DHE and sumatriptan in the proximal and distal coronary artery, middle meningeal artery and saphenous vein. Methods Blood vessel segments were mounted in organ baths and concentration response curves for DHE and sumatriptan were constructed. Results In the proximal coronary artery, meningeal artery and saphenous vein, maximal contractions to DHE (proximal: 8 ± 4%; meningeal: 32 ± 7%; saphenous: 52 ± 11%) and sumatriptan (proximal: 17 ± 7%; meningeal: 61 ± 18%, saphenous: 37 ± 8%) were not significantly different. In the distal coronary artery, contractions to DHE (5 ± 2%) were significantly smaller than those to sumatriptan (17 ± 9%). At clinically relevant concentrations, mean contractions to DHE and sumatriptan were below 3% in proximal coronary arteries and below 6% in distal coronary arteries. Contractions in the meningeal artery and saphenous vein were higher (7%–38%). Conclusions Contractions to DHE in distal coronary arteries are smaller than those to sumatriptan, while at clinical concentrations they both induce only slight contractions. In meningeal arteries contractions to DHE and sumatriptan are significantly larger, showing their cranioselectivity. Contractions to DHE in the saphenous vein are higher than those in the arteries, confirming its venous contractile properties.

Methylation of Migraine-Related Genes in Different Tissues of the Rat

17ß-Estradiol, an epigenetic modulator, is involved in the increased prevalence of migraine in women. Together with the prophylactic efficacy of valproate, which influences DNA methylation and histone modification, this points to the involvement of epigenetic mechanisms. Epigenetic studies are often performed on leukocytes, but it is unclear to what extent methylation is similar in other tissues. Therefore, we investigated methylation of migraine-related genes that might be epigenetically regulated (CGRP-ergic pathway, estrogen receptors, endothelial NOS, as well as MTHFR) in different migraine-related tissues and compared this to methylation in rat as well as human leukocytes. Further, we studied whether 17ß-estradiol has a prominent role in methylation of these genes. Female rats (n = 35) were ovariectomized or sham-operated and treated with 17β-estradiol or placebo. DNA was isolated and methylation was assessed through bisulphite treatment and mass spectrometry. Human methylation data were obtained using the Illumina 450k genome-wide methylation array in 395 female subjects from a population-based cohort study. We showed that methylation of the Crcp, Calcrl, Esr1 and Nos3 genes is tissue-specific and that methylation in leukocytes was not correlated to that in other tissues. Interestingly, the interindividual variation in methylation differed considerably between genes and tissues. Furthermore we showed that methylation in human leukocytes was similar to that in rat leukocytes in our genes of interest, suggesting that rat may be a good model to study human DNA methylation in tissues that are difficult to obtain. In none of the genes a significant effect of estradiol treatment was observed.

Discovery techniques for calcitonin gene-related peptide receptor antagonists for potential antimigraine therapies.

Introduction: Calcitonin gene-related peptide (CGRP) exerts a key function in migraine pathophysiology through the trigeminovascular system. Influencing this system via CGRP receptor antagonists seems to be an important new option in treating migraine attacks. To characterize new compounds, models are used to study the vascular effects as well as their effects on the central nervous system. Areas covered: The authors review the clinical trials and many different in vitro and in vivo experimental models that have been used to investigate the effects and side effects in animals, healthy subjects and patients. These experimental models are essential, not only in characterizing new CGRP receptor antagonists, but also in gaining more insight into the pathophysiological mechanisms behind migraines. Expert opinion: Although triptans were a major breakthrough in migraine treatment, they are not effective for every patient and contraindicated in patients with cardiovascular disease. There is still a demand for other acute antimigraine acting drugs with CGRP receptor antagonists being the most promising candidates. CGRP plays a role in protection against ischemia, but CGRP receptor antagonists do not seem to affect this protection to a harmfull extent, when used incidentally as acute antimigraine treatment. In order for drug specificity to be increased, the site of action needs to be identified; this consequently may lead to a decrease in dosing with fewer side effects.

Trigeminovascular calcitonin gene-related peptide function in Cacna1a R192Q-mutated knock-in mice

Familial hemiplegic migraine type 1 (FHM1) is a rare migraine subtype. Whereas transgenic knock-in mice with the human pathogenic FHM1 R192Q missense mutation in the Cacna1a gene reveal overall neuronal hyperexcitability, the effects on the trigeminovascular system and calcitonin gene-related peptide (CGRP) receptor are largely unknown. This gains relevance as blockade of CGRP and its receptor are therapeutic targets under development. Hence, we set out to test these effects in FHM1 mice. We characterized the trigeminovascular system of wild-type and FHM1 mice through: (i) in vivo capsaicin- and CGRP-induced dural vasodilation in a closed-cranial window; (ii) ex vivo KCl-induced CGRP release from isolated dura mater, trigeminal ganglion and trigeminal nucleus caudalis; and (iii) peripheral vascular function in vitro. In mutant mice, dural vasodilatory responses were significantly decreased compared to controls. The ex vivo release of CGRP was not different in the components of the trigeminovascular system between genotypes; however, sumatriptan diminished the release in the trigeminal ganglion, trigeminal nucleus caudalis and dura mater but only in wild-type mice. Peripheral vascular function was similar between genotypes. These data suggest that the R192Q mutation might be associated with trigeminovascular CGRP receptor desensitization. Novel antimigraine drugs should be able to revert this complex phenomenon.

Endothelin-converting-enzyme 1 inhibition and CGRP receptor recycling in human coronary and middle meningeal arteries

Although best known for its role in the conversion of big endothelin to endothelin-1, endothelin-converting enzyme 1 (ECE-1) also regulates the resensitization of certain neuropeptide receptors, including the receptor for calcitonin gene-related peptide (CGRP) ( Padilla et al., 2007 ). We investigated the role of ECE-1 in the resensitization of responses to CGRP in human coronary (HCA) and middle meningeal (HMA) arteries using the potent and selective ECE-1 inhibitor, SM-19712. Segments of HCA (O 0.5–1 mm) and HMA (O 0.5–1 mm) were mounted in organ baths and concentration response curves (CRCs) to CGRP were constructed in the absence or presence of the ECE-1 inhibitor SM-19712. After the first CRC to CGRP the segments were washed and after 30-45 minutes a second CRC was constructed in the absence or presence of SM-19712 to investigate ECE-1-dependent CGRP resensitization. Furthermore, CRCs to big endothelin were constructed in the presence or absence of SM-19712. In both HCA and HMA, no differences were seen between the initial responses to CGRP in the absence or presence of SM-19712 (HCA Emax+SM19712 94±8%, Emax–SM19712 93±5%; pEC50+SM19712 9.1±0.2, pEC50-SM19712 9.2±0.1; HMA Emax+SM19712 72±7%, Emax–SM19712 59±7%; pEC50+SM19712 8.5±0.4, pEC50-SM19712 8.1±0.8), as well as between the second CRCs to CGRP in the absence or presence of SM-19712 (HCA Emax+SM19712 110±13%, Emax–SM19712 78±22%; pEC50+SM19712 7.5±0.5, pEC50-SM19712 7.9±0.01; HMA Emax+SM19712 38±13%, Emax–SM19712 44±1%; pEC50+SM19712 8.6±0.5, pEC50-SM19712 7.8±0.9). Furthermore, contractions to big endothelin were not different in the absence or presence of SM-19712 in either HCA (Emax+SM19712 118±14%, Emax-SM19712 115±32%; pEC50+SM19712 6.0±0.5, pEC50-SM19712 6.9±0.2) or HMA (Emax+SM19712 121±1%, Emax–SM19712 147±19%; pEC50–SM19712 7.4±0.4, pEC50+SM19712 7.0±0.8). Our results indicate that ECE-1 does not regulate the resensitization of CGRP responses in HCA and HMA.

Sumatriptan and dihydroergotamine in proximal and distal human isolated coronary arteries

Sumatriptan and dihydroergotamine (DHE) are both 5-HT receptor agonists and two of the most widely used drugs for the acute treatment of migraine. These drugs are contra-indicated in people with cardiovascular disease because of their vasoconstricting properties, as has previously been assessed in proximal coronary arteries. The effect of DHE in distal coronary arteries, however, has never been reported, although smaller coronary arteries might also account for angina-like symptoms, especially in women. The aim of this study was to compare the contractile effects of sumatriptan and DHE in proximal and distal human coronary arteries, and to relate our findings to the plasma concentrations obtained in clinical practice. Segments of proximal (O 3-5 mm) and distal (O 0.5–1 mm) human isolated coronary arteries were mounted in organ baths and concentration response curves for sumatriptan and DHE were constructed. In proximal coronary artery segments, maximal contractions to sumatriptan (16+/-18% of contraction to 100 mM KCl) and DHE (5+/-4%) were not significantly different. In contrast, in distal coronary arteries, the contractile responses to sumatriptan (18+/-11%) were significantly larger than those to DHE (4+/-2%). At clinically relevant concentrations (Cmax after different formulations), contractions to both sumatriptan and DHE in proximal as well as distal coronary arteries were below 6%. Thus, our results indicate that coronary artery contractions to DHE in distal coronary artery are smaller than those to sumatriptan, although in the clinical situation both drugs are likely to induce only a slight contraction.