Hypofunctionality of Gi proteins as aetiopathogenic mechanism for migraine and cluster headache

Migraine signaling pathways: purine metabolites that regulate migraine and predispose migraineurs to headache

Migraine is a debilitating disorder that afflicts over 1 billion people worldwide, involving attacks that result in a throbbing and pulsating headache. Migraine is thought to be a neurovascular event associated with vasoconstriction, vasodilation, and neuronal activation. Understanding signaling in migraine pathology is central to the development of therapeutics for migraine prophylaxis and for mitigation of migraine in the prodrome phase before pain sets in. The fact that both vasoactivity and neural sensitization are involved in migraine indicates that agonists which promote these phenomena may very well be involved in migraine pathology. One such group of agonists is the purines, in particular, adenosine phosphates and their metabolites. This manuscript explores what is known about the relationship between these metabolites and migraine pathology and explores the potential for such relationships through their known signaling pathways. Reported receptor involvement in vasoaction and nociception.

Honokiol-Rich Magnolia officinalis Bark Extract Attenuates Trauma-Induced Neuropathic Pain

Neuropathic pain (NP) affects about 8% of the general population. Current analgesic therapies have limited efficacy, making NP one of the most difficult to treat pain conditions. Evidence indicates that excessive oxidative stress can contribute to the onset of chronic NP and several natural antioxidant compounds have shown promising efficacy in NP models. Thus, this study aimed to investigate the pain-relieving activity of honokiol (HNK)-rich standardized extract of Magnolia officinalis Rehder & E. Wilson bark (MOE), well known for its antioxidant and anti-inflammatory properties, in the spared nerve injury (SNI) model. The molecular mechanisms and efficacy toward neuroinflammation were investigated in spinal cord samples from SNI mice and LPS-stimulated BV2 microglia cells. MOE and HNK showed antioxidant activity. MOE (30 mg/kg p.o.) produced an antiallodynic effect in SNI mice in the absence of locomotor impairment, reduced spinal p-p38, p-JNK1, iNOS, p-p65, IL-1ß, and Nrf2 overexpression, increased IL-10 and MBP levels and attenuated the Notch signaling pathway by reducing Jagged1 and NEXT. These effects were prevented by the CB1 antagonist AM251. HNK reduced the proinflammatory response of LPS-stimulated BV2 and reduced Jagged1 overexpression. MOE and HNK, by modulating oxidative and proinflammatory responses, might represent interesting candidates for NP management.

A Differential Hypofunctionality of Gαi Proteins Occurs in Adolescent Idiopathic Scoliosis and Correlates with the Risk of Disease Progression

Adolescent idiopathic scoliosis is the most prevalent spine deformity and the molecular mechanisms underlying its pathophysiology remain poorly understood. We have previously found a differential impairment of melatonin receptor signaling in AIS osteoblasts allowing the classification of patients into three biological endophenotypes or functional groups (FG1, FG2 and FG3). Here, we provide evidence that the defect characterizing each endophenotype lies at the level of Gαi proteins leading to a systemic and generalized differential impairment of Gi-coupled receptor signaling. The three Gαi isoforms exhibited a selective serine phosphorylation patterns for each AIS endophenotype resulting in a differential reduction in Gαi protein activity as determined by cellular dielectric spectroscopy and small interfering RNA methods. We found that one endophenotype (FG2) with phosphorylated Gαi₁ and Gαi₂ was consistently associated with a significantly high risk of spinal deformity progression when compared to the other two endophenotypes (FG1 and FG3). We further demonstrated that each endophenotype is conserved among affected family members. This study expands our understanding of the mechanism underlying the Gi-coupled receptor signaling dysfunction occurring in AIS and provides the first evidence for its hereditary nature. Collectively, our findings offers a new perspective on Gαi hypofunctionality in a human disease by revealing specific serine phosphorylation signatures of Gαi isoforms that may facilitate the identification of AIS patients at risk of spinal deformity progression.

GNAS1 T393C Polymorphism is Associated With Migraine

Migraineurs have an interictal sympathetic nervous system (SNS) hypofunctionality and hypersensitivity to adrenergic amines. The GNAS1 T393C polymorphism has been associated with a distinct SNS sensitivity in healthy subjects. We tested GNAS1 T393C variant in two independent sets of subjects. In the case-control subset, 365 migraine patients [194 with aura (MA)] vs. 347 healthy controls were studied. A significant excess of the CC genotype was found in migraneurs (31.2%) as opposed to controls (20.2%; P = 0.003). Using a logistic regression model corrected for sex, the CC genotype conferred a general risk for migraine twice [odds ratio (OR) 1.79, 95% confidence interval (CI) 1.27-2.53; P = 0.001] higher than CT/TT genotypes. Using parents from 117 migraine families, a marginally significant trend for association could be observed ( P = 0.025), but the transmission disequilibrium test for alleles maternally transmitted failed to demonstrate familial association. In this subgroup, CC genotype conferred a risk for migraine over twice (OR 2.20; 95% CI 1.14-4.40; P = 0.019) higher than TT/TC genotypes. In conclusion, the GNAS1 T393C variant is associated with migraine, which suggests a genetic basis for its higher SNS sensitivity.

Molecular analysis of cluster headache

OBJECTIVES

Cluster headache (CH) is characterized by severe, recurrent, unilateral attacks of extreme intensity and brief duration. Variants in a myriad of genes were studied in sporadic CH patients, often with conflicting results.

METHODS

We studied gene mutations in some candidate genes, hypocretin receptor 2, Clock, and alcohol dehydrogenase 4 (ADH4), in 54 unrelated sporadic CH patients and in 200 controls in 8 kindreds/families that included more affected and nonaffected cases. Furthermore, we performed the whole-genome scanning by comparative genomic hybridization, searching for rearrangements associated with DNA gain or loss in a subset of sporadic and familial CH and control participants.

RESULTS

The analysis of candidate genes revealed that only allele and genotype frequency of the 2 ADH4 mutations resulted significantly between sporadic CH and controls; the same mutations were homozygous in CH patients from 2 families. The comparative genomic hybridization analysis revealed 2 novel rearrangements that involved the intron regions of thyrotropin-releasing hormone-degrading enzyme and neurexin 3 (NRXN3) genes, respectively. The first arrangement was present either in CH or in controls, whereas the second one was specifically found in some sporadic and familial CH cases.

CONCLUSIONS

Our data (although obtained on a small number of cases) confirm the genetic heterogeneity of CH, suggesting that mutations in the ADH4 gene and a novel rearrangement involving NRXN3 gene might be related to CH in a subset of cases.

Indomethacin/prochlorperazine/caffeine: a review of its use in the acute treatment of migraine and in the treatment of episodic tension-type headache

The indomethacin/prochlorperazine/caffeine fixed combination (Difmetré®) combines the NSAID indomethacin with the phenothiazine antiemetic prochlorperazine and caffeine. It is currently available as two oral (effervescent tablet and coated tablet) and two rectal (suppository and low-dose suppository) formulations. Oral and rectal formulations of indomethacin/prochlorperazine/caffeine were effective and generally well tolerated in the treatment of migraine and episodic tension-type headache (TTH) in adult patients participating in randomized, multicentre, active-comparator controlled studies. For the most part, the efficacy of oral indomethacin/prochlorperazine/caffeine did not significantly differ from that of oral sumatriptan in patients with migraine and oral nimesulide in patients with episodic TTH. With rectal administration, indomethacin/prochlorperazine/caffeine was, in general, significantly more effective than sumatriptan in patients with migraine. Thus, oral and rectal formulations of indomethacin/prochlorperazine/caffeine provide a further option in the acute treatment of migraine and in the treatment of episodic TTH in adult patients.

Genetics of cluster headache

Cluster headache (CH) is a rare, excruciating primary headache disorder. A genetic basis has been suggested by family and twin studies, but the mode of transmission seems to vary and the amount of heritability is unclear. The number of genetic association studies investigating variants implicated in the pathophysiology of CH is limited. The HCRTR2 1246G > A and the ADH4 925A > G polymorphisms have been associated with CH. The former has been confirmed and may affect the hypothalamic hypocretin system. However, it only appears to account for a part of the genetic susceptibility for CH, and additional genetic and environmental factors are likely implicated. Pharmacogenetic studies have suggested that the GNB3 825C > T polymorphism may modify treatment response to triptans among CH patients by altering the signal transduction cascade via G protein-coupled receptors. Genetic studies in CH are notoriously difficult due to the complex nature of the disorder and the low prevalence of CH.

The central analgesia induced by antimigraine drugs is independent from Gi proteins: superiority of a fixed combination of indomethacin, prochlorperazine and caffeine, compared to sumatriptan, in an in vivo model

A hypofunctionality of Gi proteins has been found in migraine patients. The fixed combination of indomethacin, prochlorperazine and caffeine (Indoprocaf) is a drug of well-established use in the acute treatment of migraine and tension-type headache. The aim of this study was to investigate if Indoprocaf was able to exert its central antinociceptive action when Gi proteins activity is abolished by pertussis toxin (PTX), compared to its single active ingredients and to sumatriptan. The mice model of abdominal constriction test induced by an i.p. injection of a 0.6% solution of acetic acid was used. The study showed that Indoprocaf (a fixed combination of indomethacin 1 mg/kg, prochlorperazine 1 mg/kg and caffeine 3 mg/kg, s.c.) and sumatriptan (20 mg/kg, s.c.) exert their central antinociceptive action independently from the Gi proteins. In addition, the antinociceptive efficacy of Indoprocaf in this study was statistically superior to that of sumatriptan. This study also showed that the single active ingredients of Indoprocaf, indomethacin (1 mg/kg, s.c.), prochlorperazine (1 mg/kg, s.c.) and caffeine (3 mg/kg, s.c.), were able to exert their central antinociceptive action independently from the Gi proteins. However, Indoprocaf at analgesic doses was able to abolish almost completely the abdominal constrictions, with a statistically higher efficacy compared to the single active ingredients, showing an important synergic effect of Indoprocaf. This synergic effect was evident not only when Gi proteins activity was abolished by PTX, but also under control condition, when Gi proteins were active. This study suggests that the central antinociceptive action induced by antimigraine drugs is independent from Gi proteins.

[35S]GTP gamma S binding studies of amphiphilic drugs-activated Gi proteins: a caveat

This paper documents a serious problem met during the testing of Gi protein-activating properties of a new series of synthetic compounds by measuring the induced binding of [(35)S]GTPgammaS to different subtypes of Gi protein. The problem arose from the strong affinity between [(35)S]GTPgammaS and the tested compounds, that are characterized by several (2-4) positive charges and high lipophilicity. Apparently, such affinity yields insoluble, labelled complexes that, also in the absence of Gi protein, are retained on the filters and give rise to false positive results.

Receptor-independent modulation of reconstituted Galpha(i) protein mediated by liposomes

A cationic amphiphile, BC5 (N-pentadecylpiperidin-4-amine), was recently designed and tested for its ability to directly stimulate the activity of recombinant Galpha inhibitory subunits. However, amphiphilic drugs can self-associate and bind to plasma membranes, causing undesired side effects. In this contribution, we report on the incorporation of BC5 in 1,2-dipalmytoyl-sn-glycerophosphocoline (DPPC) liposomes and on the characterization of the mixed DPPC/BC5 systems at various lipid/drug mole ratios by means of dynamic light scattering, differential scanning calorimetry and fluorescence spectroscopy. The myristoylated Galpha(i) subunit (Galpha-mir) was reconstituted in 1,2-dimiristoyl-sn-glycerophosphocoline (DMPC) bilayers, as a mimic of the drug target. We compare several reconstitution procedures in liposomes and present for the first time a complete characterization of a Galpha subunit reconstitution in model membranes in terms of protein activity as a function of the reconstitution protocol. The incorporation of the drug in DPPC bilayers resulted in enhanced Gi-modulating efficiency (evaluated in terms of binding to GTPgammaS (guanosine-5'-(gamma-thio)-triphosphate)). A correlation of the physico-chemical features and binding activity of protein-containing membrane model is proposed.

In vivo evaluation of alpha(2)-adrenoceptors in cats with idiopathic cystitis

OBJECTIVE

To evaluate the in vivo response of alpha(2)-adrenoceptors to medetomidine administration in cats with feline idiopathic cystitis (FIC) during periods of stress and after environmental enrichment.

ANIMALS

13 cats with FIC and 12 healthy cats. Procedures-Cats were subjected to an acute-onset moderate stressor for 8 days. After stress, 20 microg of medetomidine/kg was administered IM on days 1, 3, and 8. Heart rate, blood pressure, pupil diameter, respiratory rate, and level of sedation were evaluated before and after administration of the drug. After day 8, cats were moved to an enriched environment, and tests were repeated on day 35.

RESULTS

Heart rate decreased and pupil diameter increased significantly after medetomidine administration in healthy cats, compared with cats with FIC. Cats with FIC had significantly lower respiratory rates. No significant differences in blood pressure or sedation level were found.

CONCLUSIONS AND CLINICAL RELEVANCE

Increased plasma catecholamine concentrations during the enrichment phase, which have been reported elsewhere, may have contributed to the differences in alpha(2)-adrenoceptor responses detected in cats with FIC.

G Protein β3 Polymorphism and Triptan Response in Cluster Headache

Only about 70% of migraine and cluster headache (CH) patients report significant treatment responses to triptans, which are agonists at 5-HT(1B/D) receptors belonging to the family of G protein-coupled receptors. We analyzed whether a common polymorphism in the gene for the G protein beta3 subunit (GNB3 C825T) modulates responder rates to triptans among a cohort of 231 unrelated Caucasian CH patients. A total of 180 CH patients used triptans, of whom 71.1% reported treatment success. The adjusted odds ratio for treatment response to triptans for heterozygous carriers of the GNB3 825T allele was 2.96 (95% confidence interval 1.34-6.56; P=0.0074) vs carriers of the 825CC genotype. The GNB3 genotype status did not affect responses to other acute and preventive therapeutic regimes including oxygen, verapamil, and corticosteroids, i.e., drugs not directly affecting G proteins. We conclude that pain relief by triptans is significantly modulated by a common genetic GNB3 variant.

A recombinant transductor–effector system: In vitro study of G inhibitory protein (G-alpha-i1) direct activators

Mutations and altered functionality of the inhibitory subfamily of G proteins (Gi) are involved in pathological states. Compounds able to activate Gi in a receptor-independent manner would be useful to treat these pathological conditions. Aimed to study Gi direct activation we have reconstituted a recombinant transductor-effector complex cloning both the mammalian Galpha(i1) subunit and adenylate cyclase (AC). The myristoylation of Galpha, fundamental for interaction with AC, was obtained in the procaryotic expression host Escherichia coli transformed with a single plasmid containing both the coding sequences for human Galpha(i1) and Saccharomyces cerevisiae myristoyl transferase. AC-V isoform was obtained by the expression of its cytosolic domains. A recent synthesized molecule, named BC5, was tested to evaluate its pharmacological profile in a Gi/AC cell-free complex model. In this functional transductor-effector system BC5 was able to activate Gi signalling, moreover providing a new tool to give a better insight into G-protein receptor-independent modulation.

beta-Receptor response to noradrenaline in cluster headache. A study of adipose tissue lipolysis

We have previously shown decreased lipolysis in both phases of cluster headache (CH), as an indication of a sympathetic dysregulation. Reduced lipolysis could be a result of diminished beta-receptor sensitivity in adipose tissue. The aim of this study was to measure the lipolytic response to noradrenaline in 10 CH patients in remission and in 10 healthy subjects, to estimate beta-receptor function. Microdialysis technique was used to measure the increase of glycerol, the end-product of lipolysis, during infusion of noradrenaline into the adipose tissue. Noradrenaline infusion resulted in a distinct elevation of glycerol. The average glycerol increase was significantly higher in CH patients (121% +/- 48) than in healthy subjects (77% +/- 41) (P < 0.05), which indicates increased beta-receptor response to noradrenaline in CH patients in remission. This may be due to up-regulated beta-receptor sensitivity, secondary to reduced sympathetic outflow and a primary autonomic disturbance in CH.

Gi/o proteins: Expression for direct activation enquiry

G protein-mediated pathways are fundamental mechanisms of cell signaling. In this paper, the expression and the characterization of the alphai1, alphai3, alphao1, beta1, and gamma2 subunits of the human G protein are described. This approach was developed to evaluate the G protein activation profile of new compounds. pCR-TOPO T7 vectors, engineered to contain the target sequences, were used to transform Escherichia coli competent cells. Subunits were over-expressed in a preparative scale as fusion proteins with a six-histidine tag, and subsequently purified by metal chelate chromatography. Afterward, the His-tag was removed by enterokinase digestion, and the secondary structures of the recombinant subunits were analyzed by circular dichroism. To assess the functionality of the subunits, the rate of GTP hydrolysis and GTPgammaS binding were evaluated both in the absence and in the presence of two modulators: the peptidic activator Mastoparan and the non-peptidic activator N-dodecyl-lysinamide (ML250). Tests were conducted on isolated alpha-subunit and on heterotrimeric alphabetagamma complex, alone or reconstituted in phospholipidic vesicles. Our results show that recombinant subunits are stable, properly folded and, fully active, which makes them suitable candidates for functional studies.

Design, synthesis, and preliminary pharmacological evaluation of a set of small molecules that directly activate gi proteins

Heterotrimeric G proteins play a pivotal role in the communication of cells with the environment. G proteins are stimulated by cell surface receptors (GPCR) that catalyze the exchange of GDP, bound to Galpha subunit, with GTP and can per se be the target of drugs. Based on the structure of two nonpeptidic modulators of Gi proteins, a series of new molecules characterized by a long hydrophobic chain and at least two nitrogen atoms protonated at physiological pH was designed. The compounds were tested for their ability to stimulate binding of GTPgammaS to recombinant Gi proteins. Gi activation properties were also evaluated by inhibition of adenylyl cyclase activity in intact lymphocytes. Most compounds were able to stimulate GTPgammaS binding and to inhibit cAMP production at micromolar doses. Among the active compounds, 34 showed good efficacy and was the most potent compound studied, particularly on alpha(o) subtype; its regioisomer, 36, was the most efficacious one. Compound 7 showed also an interesting profile as it showed selectivity toward the alpha(o) subtype, in both efficacy and potency. Some of the compounds synthesized and found to be active may be useful leads to develop more potent and selective Gi protein modulators.

Brain Hyperexcitability: The Basis for Antiepileptic Drugs in Migraine Prevention

Abnormal brain excitability may provide the susceptibility for triggering migraine attacks. Antiepileptic drugs may diminish neuronal excitability and consequently reduce the frequency of migraine. Because migraine aura is predominantly visual, hyperexcitability of the occipital cortex has been the focus of investigations. Functional magnetic resonance imaging of the brain and magnetoencephalography provide the most consistent evidence for the role of brain hyperexcitability in migraine and confirm that triggering an abnormal electric and metabolic event consistent with the cortical spreading depression (CSD) of Leao is anatomically and functionally linked with migraine aura symptoms. Future drug discovery should focus on the interface between the excitable cell and the earliest events of CSD.

Molecular Mechanisms of Migraine

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

Etiology and pathogenesis of cluster headache

This last decade has seen remarkable progress made toward unraveling the mystery of primary headache disorders like migraine and cluster. The vascular theory has been superseded by recognition that neurovascular phenomena seem to be the permissive and triggering factors in migraine and cluster headache. This understanding has been achieved through new imaging modalities such as positron emission tomography and functional magnetic resonance imaging. Prior to these imaging techniques it was impossible to study the primary headache disorders because these had no structural basis. There is now an increasing body of evidence that the brain is involved primarily in cluster and migraine and that vessel dilatation is an epiphenomenon.