Sumatriptan scavenges superoxide, hydroxyl, and nitric oxide radicals: in vitro electron spin resonance study

Additive Anticonvulsive Effects of Sumatriptan and Morphine on Pentylenetetrazole-Induced Clonic Seizures in Mice

Background and Purpose

Sumatriptan protects the brain from damage and enhance the anti-seizure effect of morphine. There is evidence that nitric oxide (NO) may mediate these effects of both drugs. In the present study, we investigated the effects of sumatriptan (0.1-20 mg/kg, intraperitoneal [i.p.]) and morphine (0.1-20 mg/kg, i.p.) alone or in combination on seizure thresholds in an in vivo model of seizure in mice. Using various NO synthase inhibitors as well as the NO precursor, we assessed possible involvement of NO signaling in these effects.

Methods

Clonic seizures were induced in male Naval Medical Research Institute mice by intravenous administration of pentylenetetrazol (PTZ).

Results

Acute sumatriptan administration exerted anti-convulsive effects at 0.5 (p<0.01) and 1 mg/kg (p<0.05), but pro-convulsive effects at 20 mg/kg (p<0.05). Morphine had anti-convulsive effects at 0.5 (p<0.05) and 1 mg/kg (p<0.001), but exerted pro-convulsive effect at 20 mg/kg (p<0.05). Combination treatment with sub-effective doses of sumatriptan (0.1 mg/kg) and morphine (0.1 mg/kg) significantly (p<0.05) exerted an anti-convulsive effect. Co-administration of the NO precursor L-arginine (60 mg/kg) with sub-effective doses of sumatriptan and morphine significantly (p<0.05) increased seizure threshold compared with sumatriptan alone, but not sumatriptan+morphine group. While concomitant administration of either the non-selective NO synthase (NOS) inhibitor L-NG-nitroarginine methyl ester (5 mg/kg) or the selective inducible NOS inhibitor aminoguanidine (50 mg/kg) with combined sub-effective doses of morphine and sumatriptan produced significant anticonvulsive effects, concomitant administration with the selective neuronal NOS inhibitor 7-nitroindazole (30 mg/kg) inhibited this effect.

Conclusions

Our data suggest a possible role for the NO signaling in the anticonvulsive effects of combined sumatriptan and morphine on the PTZ-induced clonic seizures in mice.

Development of an innovative turn-on fluorescent probe for targeted in-vivo detection of nitric oxide in rat brain extracts as a biomarker for migraine disease

Nitric oxide (NO) is one of the reactive nitrogen species (RNS) that has been proposed to be a key signaling molecule in migraine. Migraine is a neurological disorder that is linked to irregular NO levels, which necessitates precise NO quantification for effective diagnosis and treatment. This work introduces a novel fluorescent probe, 2,3-diaminonaphthelene-1,4-dione (DAND), which was designed and synthesized to selectively detect NO in-vitro and in-vivo as a migraine biomarker. DAND boasts high aqueous solubility, biocompatibility, and facile synthesis, which enable highly selective and sensitive detection of NO under physiological conditions. NO reacts with diamine moieties (recognition sites) of DAND, results in the formation of a highly fluorescent product (DAND-NO) known as 1H-naphtho[2,3-d][1,2,3]triazole-4,9-dione at λem 450 nm. The fluorescence turn-on sensing mechanism operates through an intramolecular charge transfer (ICT) mechanism. To maximize fluorescence signal intensity, parameters including DAND concentration, reaction temperature, reaction time and pH were systematically optimized for sensitive and precise NO determination. The enhanced detection capability (LOD = 0.08 μmol L-1) and high selectivity of the probe make it a promising tool for NO detection in brain tissue homogenates. This demonstrates the potential diagnostic value of the probe for individuals suffering from migraine. Furthermore, this study sheds light on the potential role of zolmitriptan (ZOLM), an antimigraine medication, in modulating NO levels in the brain of rats with nitroglycerin-induced migraine, emphasizing its significant impact on reducing NO levels. The obtained results could have significant implications for understanding how ZOLM affects NO levels and may aid in the development of more targeted and effective migraine treatment strategies.

Sedation Therapy in Intensive Care Units: Harnessing the Power of Antioxidants to Combat Oxidative Stress

In critically ill patients requiring intensive care, increased oxidative stress plays an important role in pathogenesis. Sedatives are widely used for sedation in many of these patients. Some sedatives are known antioxidants. However, no studies have evaluated the direct scavenging activity of various sedative agents on different free radicals. This study aimed to determine whether common sedatives (propofol, thiopental, and dexmedetomidine (DEX)) have direct free radical scavenging activity against various free radicals using in vitro electron spin resonance. Superoxide, hydroxyl radical, singlet oxygen, and nitric oxide (NO) direct scavenging activities were measured. All sedatives scavenged different types of free radicals. DEX, a new sedative, also scavenged hydroxyl radicals. Thiopental scavenged all types of free radicals, including NO, whereas propofol did not scavenge superoxide radicals. In this retrospective analysis, we observed changes in oxidative antioxidant markers following the administration of thiopental in patients with severe head trauma. We identified the direct radical-scavenging activity of various sedatives used in clinical settings. Furthermore, we reported a representative case of traumatic brain injury wherein thiopental administration dramatically affected oxidative-stress-related biomarkers. This study suggests that, in the future, sedatives containing thiopental may be redeveloped as an antioxidant therapy through further clinical research.

Harnessing Intranasal Delivery Systems of Sumatriptan for the Treatment of Migraine

Sumatriptan (ST) is a commonly prescribed drug for treating migraine. The efficiency of several routes of ST administration has been investigated. Recently, the intranasal route with different delivery systems has gained interest owing to its fast-acting and effectiveness. The present study is aimed at reviewing the available studies on novel delivery systems for intranasal ST administration. The oral route of ST administration is common but complicated with some problems. Gastroparesis in patients with migraine may reduce the absorption and effectiveness of ST upon oral use. Furthermore, the gastrointestinal (GI) system and hepatic metabolism can alter the pharmacokinetics and clinical effects of ST. The bioavailability of conventional nasal liquids is low due to the deposition of a large fraction of the delivered dose of a drug in the nasal cavity. Several delivery systems have been utilized in a wide range of preclinical and clinical studies to enhance the bioavailability of ST. The beneficial effects of the dry nasal powder of ST (AVP-825) have been proven in clinical studies. Moreover, other delivery systems based on microemulsions, microspheres, and nanoparticles have been introduced, and their higher bioavailability and efficacy were demonstrated in preclinical studies. Based on the extant findings, harnessing novel delivery systems can improve the bioavailability of ST and enhance its effectiveness against migraine attacks. However, further clinical studies are needed to approve the safety and efficacy of employing such systems in humans.

Neuroprotective effect of sumatriptan in pentylenetetrazole-induced seizure is mediated through N-methyl-D-aspartate/nitric oxide and cAMP response element-binding protein signaling pathway

Seizure occurs as a result of uncontrolled electrical disturbances within the brain. Various biomolecules such as N-methyl-D-aspartate (NMDA), nitric oxide (NO), and cAMP response element-binding protein (CREB) have been implicated in the pathophysiology of seizure. Sumatriptan is a specific 5-Hydroxytryptamine 1B/1D receptor agonist and has neuroprotective effects in various neuropsychiatric disorders. In the current study, we tried to investigate the possible interaction of sumatriptan with NMDA/NO and CREB signaling pathway in PTZ induced seizure. For this purpose, various agonist and antagonist of NMDA such as MK-801 and Ketamine, NO precursor L-ARG, and NOS inhibitors L-NAME and 7-NI were co-administered with sumatriptan in PTZ induced seizure model. The level of nitrite in mice hippocampus was determined by Griess reaction. The gene expression of NR1, NR2A, NR2B, and CREB were quantified by quantitative real time-polymerase chain reaction (qRT-PCR). Furthermore, the involved neuronal nitric oxide synthase (nNOS) protein expression was examined via western blot analysis. Effective dose of sumatriptan (1.2 mg/kg) alone and subeffective dose of sumatriptan (0.3 mg/kg) in combination with NMDA and/or NO antagonist showed significant (P < 0.001) anticonvulsant activity in mice. Furthermore, sumatriptan significantly inhibited the PTZ-induced mRNA expression of NR2A (P < 0.0001), NR2B (P < 0.05), and CREB (P < 0.01). Also, the expression of nNOS protein in PTZ treated group was reversed by sumatriptan (P < 0.01). Hence, current findings suggest that the anticonvulsant effect of sumatriptan was due to down regulation of NMDA/NO and CREB signaling pathway.

The efficacy of alpha-lipoic acid in improving oxidative, inflammatory, and mood status in women with episodic migraine in a randomised, double-blind, placebo-controlled clinical trial

AIM

Migraine is a common neurovascular disorder, which is associated with severe to moderate disabling headaches. Oxidative stress and inflammation might play a role in migraine pathogenesis and the mood disorders. Considering the antioxidant and anti-inflammatory properties of alpha-lipoic acid (ALA), this study was designed to investigate its effect on oxidative, inflammatory, and mood conditions in women with episodic migraine.

METHODS

In total, 92 women with episodic migraine participated in the study. The patients were randomly divided into two groups, receiving a 300-mg capsule of ALA or placebo twice daily for 3 months. To assess the oxidative and inflammatory status, the serum levels of total antioxidant capacity (TAC), total oxidant status (TOS), glutathione (GSH), malondialdehyde (MDA), oxidative stress index (OSI), and C-reactive protein (CRP) were determined at the beginning and at the end of the intervention. A depression, anxiety, stress scale (DASS-21-items) questionnaire was used to evaluate mood status.

RESULTS

Finally, 79 patients reached the final analysis stage. At the end of the intervention, a significant decrease in the serum levels of MDA (means difference [MD]: -0.83, 95% confidence intervals (CI): -1.04, -0.62 nmol/mL vs MD: -0.32, CI: -0.48, -0.15 nmol/mL; P < .001) and CRP (MD: -0.78, CI: -1.17, -0.39 mg/L vs MD: -0.63, CI: -1.80, 0.52 mg/L; P < .001) was observed in the ALA as compared with the placebo group, but changes in serum GSH (P = .086), TAC (P = .068), TOS (P = .225), and OSI (P = .404) were not statistically significant. In addition, depression, anxiety, and stress (with P < .001, in all cases) had significantly decreased in the intervention as compared with the control group.

CONCLUSION

The results of this study suggest that ALA supplementation for 3 months has beneficial effects on improving the oxidative, inflammatory, and mood conditions of patients suffering from episodic migraine.

Sumatriptan improves the locomotor activity and neuropathic pain by modulating neuroinflammation in rat model of spinal cord injury

OBJECTIVES

To investigate the therapeutic effects of sumatriptan in a rat model of spinal cord injury (SCI) and possible anti-inflammatory and analgesic mechanisms underlying this effect.

METHODS

Using an aneurysm mini-clip model of contusive SCI, T9-10 laminectomies were performed for 60 male rats. Animals were divided into six experimental groups (n = 10 per group) as follows: a minocycline administered positive control group, a saline-vehicle negative control group, a sham-operated group, and three experimental groups which received separate doses of sumatriptan (0.1, 0.3 and 1 mg/kg). Behavioural assessments were used to evaluate locomotor activity and neuropathic pain for 28 days. At the end of the study, spinal cord tissues were collected from sacrificed animals for histopathological analysis. Levels of calcitonin gene-related peptide (CGRP) and two pro-inflammatory cytokines (tumor necrosis factor [TNF]-α and interleukin [IL]-1β) were assessed by the enzyme-linked immunosorbent assay (ELISA).

RESULTS

Sumatriptan significantly (P < 0.001) improved the locomotor activity in SCI group. Sumatriptan was also more effective than the positive control, i.e. minocycline (0.3 mg/kg). Additionally, sumatriptan and minocycline similarly attenuated the mechanical and thermal allodynia in SCI (P < 0.001). TNF-α, IL-1β and CGRP levels in sumatriptan- and minocycline-treated groups significantly (P < 0.001) decreased compared to controls. Histopathological analysis also revealed a markedly improvement in hemorrhage followed by inflammatory cell invasion, neuronal vacuolation, and cyst formation in both sumatriptan- and minocycline-treated groups compared to control animals.

CONCLUSIONS

Sumatriptan improves functional recovery from SCI through its anti-inflammatory effects and reducing pro-inflammatory and pain mediators.

Sumatriptan reduces severity of status epilepticus induced by lithium-pilocarpine through nitrergic transmission and 5-HT1B/D receptors in rats: A pharmacological-based evidence

Status epilepticus (SE) is a life-threatening neurologic disorder that can be as both cause and consequence of neuroinflammation. In addition to previous reports on anti-inflammatory property of the anti-migraine medication sumatriptan, we have recently shown its anticonvulsive effects on pentylenetetrazole-induced seizure in mice. In the present study, we investigated further (i) the effects of sumatriptan in the lithium-pilocarpine SE model in rats, and (ii) the possible involvement of nitric oxide (NO), 5-hydroxytryptamin 1B/1D (5-HT_1B/1D ) receptor, and inflammatory pathways in such effects of sumatriptan. Status epilepticus was induced by lithium chloride (127 mg/kg, i.p) and pilocarpine (60 mg/kg, i.p.) in Wistar rats. While SE induction increased SE scores and mortality rate, sumatriptan (0.001-1 mg/kg, i.p.) improved it (P < 0.001). Administration of the selective 5-HT_1B/1D antagonist GR-127935 (0.01 mg/kg, i.p.) reversed the anticonvulsive effects of sumatriptan (0.01 mg/kg, i.p.). Although both tumor necrosis factor-α (TNF-α) and NO levels were markedly elevated in the rats' brain tissues post-SE induction, pre-treatment with sumatriptan significantly reduced both TNF-α (P < 0.05) and NO (P < 0.001) levels. Combined GR-127935 and sumatriptan treatment inhibited these anti-inflammatory effects of sumatriptan, whereas combined non-specific NOS (L-NAME) or selective neuronal NOS (7-nitroindazole) inhibitors and sumatriptan further reduced NO levels. In conclusion, sumatriptan exerted a protective effect against the clinical manifestations and mortality rate of SE in rats which is possibly through targeting 5-HT_1B/1D receptors, neuroinflammation, and nitrergic transmission.

Involvement of 5-HT1B/1D receptors in the inflammatory response and oxidative stress in intestinal ischemia/reperfusion in rats

Acute mesenteric ischemia (AMI) is caused by an abrupt cessation of blood flow to the small intestine. Reperfusion is the return of blood flow to the ischemic bowel. Intestinal ischemia/reperfusion (I/R) leads to the formation of reactive oxygen species, local inflammatory response, and may lead to the patient's death. Pre-treatment of the intestinal may reduce the high mortality associated with AMI. 5-Hydroxytryptamine 1B (5-HT1B) and 5-HT1D receptors have anti-inflammatory and neuroprotective effects in different experimental studies. We aimed to investigate the potential involvement of these receptors in intestinal I/R injury. Firstly, we assessed the expression and localization of 5-HT1B and 5-HT1D receptors in the enteric nervous system using an immunofluorescence-based method. Intestinal I/R in rats was induced by 30 min occlusion of superior mesenteric artery and reperfusion for 2 h. Rats were randomly divided in different control and I/R groups (n = 6) receiving either vehicle, sumatriptan (5-HT1B/1D receptors agonist; 0.1 mg/kg), GR127,935 (5-HT1B/1D receptors antagonist; 0.1 mg/kg) and combination of sumatriptan (0.1 mg/kg) + GR127,935 (0.1 mg/kg) before determination of biochemical and histological parameters. In the enteric nervous system, 5-HT1B and 5-HT1D receptors were expressed 17% and 11.5%, respectively. Pre-treatment with sumatriptan decreased 5-hydroxytryptamine (5HT) level by 53%, and significantly decreased calcitonin gene-related peptide (CGRP) levels, lipid pereoxidation, neutrophil infiltration, and level of pro-inflammatory markers in the serum. Histopathologic studies also showed a remarkable decrease in intestinal tissue injury. These findings suggest that sumatriptan may inhibit intestinal injury induced by I/R through modulating the inflammatory response by activation of 5-HT1B/1D receptors.

A Pre-Existing Myogenic Temporomandibular Disorder Increases Trigeminal Calcitonin Gene-Related Peptide and Enhances Nitroglycerin-Induced Hypersensitivity in Mice

Migraine is commonly reported among patients with temporomandibular disorders (TMDs), especially myogenic TMD. The pathophysiologic mechanisms related to the comorbidity of the two conditions remain elusive. In the present study, we combined masseter muscle tendon ligation (MMTL)-produced myogenic TMD with systemic injection of nitroglycerin (NTG)-induced migraine-like hypersensitivity in mice. Facial mechanical allodynia, functional allodynia, and light-aversive behavior were evaluated. Sumatriptan, an FDA-approved medication for migraine, was used to validate migraine-like hypersensitivity. Additionally, we examined the protein level of calcitonin gene-related peptide (CGRP) in the spinal trigeminal nucleus caudalis using immunohistochemistry. We observed that mice with MMTL pretreatment have a prolonged NTG-induced migraine-like hypersensitivity, and MMTL also enabled a non-sensitizing dose of NTG to trigger migraine-like hypersensitivity. Systemic injection of sumatriptan inhibited the MMTL-enhanced migraine-like hypersensitivity. MMTL pretreatment significantly upregulated the protein level of CGRP in the spinal trigeminal nucleus caudalis after NTG injection. Our results indicate that a pre-existing myogenic TMD can upregulate NTG-induced trigeminal CGRP and enhance migraine-like hypersensitivity.

Sumatriptan Increases Skin Flap Survival through Activation of 5-Hydroxytryptamine 1b/1d Receptors in Rats: The Mediating Role of the Nitric Oxide Pathway

BACKGROUND

Random pattern skin flaps are applicable for reconstructing any defect in plastic surgery. However, they are difficult to apply because of necrosis. Sumatriptan, a selective 5-hydroxytryptamine 1b/1d agonist, is routinely used to offset acute migraine attacks. Recent studies have suggested that sumatriptan may induce vasodilation at lower concentrations. The authors' aim is to investigate the effect of sumatriptan on skin flap survival and the role of nitric oxide in this phenomenon.

METHODS

Seventy-two male Sprague-Dawley rats were divided into eight groups. Increasing doses of sumatriptan (0.1, 0.3, and 1 mg/kg) were given intraperitoneally to three different groups after dorsal random pattern skin flaps were performed. To assess the exact role of 5-hydroxytryptamine 1b/1d receptors, GR-127935 was administered solely and with sumatriptan. N-ω-nitro-L-arginine methyl ester (L-NAME, a nonselective nitric oxide synthase inhibitor) was used to evaluate any possible involvement of nitric oxide in this study. All rats were examined 7 days later.

RESULTS

The authors' results demonstrated that flap survival was increased by lower doses of sumatriptan compared to a control group for both 0.3 mg/kg (p = 0.03, mean difference = 32, SE = 8) and 0.1 mg/kg (p = 0.02, mean difference = 26, SE = 8). This protective effect was eliminated by coadministration of GR-127935 or N-ω-nitro-L-arginine methyl ester with sumatriptan. Histopathologic studies revealed a significant increase in capillary count and collagen deposition and a decreased amount of edema, inflammation, and degeneration.

CONCLUSIONS

Sumatriptan in lower concentration increases skin flap survival by means of activation of 5-hydroxytryptamine 1b/1d receptors. This effect is mediated through the nitric oxide synthase pathway.

A study of oxidative stress in migraine with special reference to prophylactic therapy

OBJECTIVE

The role of oxidative stress markers in migraine and effect of treatment on these has been reported.

SUBJECTS AND METHODS

One hundred and fifty patients having > four attacks of migraine headache/month were included. Headache severity, Migraine Index (MI) and frequency of headache were noted. 120 patients received repetitive transcranial magnetic stimulation (rTMS) therapy and 30 patients received Amitriptyline (AMT). Recovery was defined by 50% improvement in frequency, severity or reduction in MI. Oxidative stress and antioxidant markers have been estimated in patients before and after treatment and correlate the clinical and outcome parameters.

RESULTS

Glutathione (GSH) (P < 0.001), glutathione-S-transferase (GST) (P = 0.049) and total antioxidant activity (TAC) (P < 0.001) level were significantly reduced in migraine patients. GSH (P = 0.02), GST (P = 0.05) and TAC (P < 0.001) were reduced in ictal migraineurs compared to controls. GSH (P < 0.001) and TAC (P = 0.003) levels increased after treatment compared to the base line. There is an increase in GSH levels in the patients who had improved following rTMS (P = 0.003); placebo (P = 0.001) and AMT (P = 0.013). TAC levels were also increased following rTMS (P = 0.009) and AMT (P = 0.020).

CONCLUSION

There is evidence of oxidative stress in migraine pathophysiology. Following treatment, oxidative stress declined following both pharmacological and rTMS.

Protective Roles of N-acetyl Cysteine and/or Taurine against Sumatriptan-Induced Hepatotoxicity

Purpose: Triptans are the drug category mostly prescribed for abortive treatment of migraine. Most recent cases of liver toxicity induced by triptans have been described, but the mechanisms of liver toxicity of these medications have not been clear. Methods: In the present study, we obtained LC₅₀ using dose-response curve and investigated cell viability, free radical generation, lipid peroxide production, mitochondrial injury, lysosomal membrane damage and the cellular glutathione level as toxicity markers as well as the beneficial effects of taurine and/or N-acetyl cysteine in the sumatriptan-treated rat parenchymal hepatocytes using accelerated method of cytotoxicity mechanism screening. Results: It was revealed that liver toxicity induced by sumatriptan in in freshly isolated parenchymal hepatocytes is dose-dependent. Sumatriptan caused significant free radical generation followed by lipid peroxide formation, mitochondrial injury as well as lysosomal damage. Moreover, sumatriptan reduced cellular glutathione content. Taurine and N-acetyl cysteine were able to protect hepatocytes against sumatriptan-induced harmful effects. Conclusion: It is concluded that sumatriptan causes oxidative stress in hepatocytes and the decreased hepatocytes glutathione has a key role in the sumatriptan-induced harmful effects. Also, N-acetyl cysteine and/or taurine could be used as treatments in sumatriptan-induced side effects.

Engineered silver nanoparticles are sensed at the plasma membrane and dramatically modify the physiology of Arabidopsis thaliana plants

Silver nanoparticles (Ag NPs) are the world's most important nanomaterial and nanotoxicant. The aim of this study was to determine the early stages of interactions between Ag NPs and plant cells, and to investigate their physiological roles. We have shown that the addition of Ag NPs to cultivation medium, at levels above 300 mg L(-1) , inhibited Arabidopsis thaliana root elongation and leaf expansion. This also resulted in decreased photosynthetic efficiency and the extreme accumulation of Ag in tissues. Acute application of Ag NPs induced a transient elevation of [Ca(2+) ]cyt and the accumulation of reactive oxygen species (ROS; partially generated by NADPH oxidase). Whole-cell patch-clamp measurements on root cell protoplasts demonstrated that Ag NPs slightly inhibited plasma membrane K(+) efflux and Ca(2+) influx currents, or caused membrane breakdown; however, in excised outside-out patches, Ag NPs activated Gd(3+) -sensitive Ca(2+) influx channels with unitary conductance of approximately 56 pS. Bulk particles did not modify the plasma membrane currents. Tests with electron paramagnetic resonance spectroscopy showed that Ag NPs were not able to catalyse hydroxyl radical generation, but that they directly oxidized the major plant antioxidant, l-ascorbic acid. Overall, the data presented shed light on mechanisms of the impact of nanosilver on plant cells, and show that these include the induction of classical stress signalling reactions (mediated by [Ca(2+) ]cyt and ROS) and a specific effect on the plasma membrane conductance and the reduced ascorbate.

Migraine Triggers and Oxidative Stress: A Narrative Review and Synthesis

BACKGROUND

Blau theorized that migraine triggers are exposures that in higher amounts would damage the brain. The recent discovery that the TRPA1 ion channel transduces oxidative stress and triggers neurogenic inflammation suggests that oxidative stress may be the common denominator underlying migraine triggers.

OBJECTIVE

The aim of this review is to present and discuss the available literature on the capacity of common migraine triggers to generate oxidative stress in the brain.

METHODS

A Medline search was conducted crossing the terms "oxidative stress" and "brain" with "alcohol," "dehydration," "water deprivation," "monosodium glutamate," "aspartame," "tyramine," "phenylethylamine," "dietary nitrates," "nitrosamines," "noise," "weather," "air pollutants," "hypoglycemia," "hypoxia," "infection," "estrogen," "circadian," "sleep deprivation," "information processing," "psychosocial stress," or "nitroglycerin and tolerance." "Flavonoids" was crossed with "prooxidant." The reference lists of the resulting articles were examined for further relevant studies. The focus was on empirical studies, in vitro and of animals, of individual triggers, indicating whether and/or by what mechanism they can generate oxidative stress.

RESULTS

In all cases except pericranial pain, common migraine triggers are capable of generating oxidative stress. Depending on the trigger, mechanisms include a high rate of energy production by the mitochondria, toxicity or altered membrane properties of the mitochondria, calcium overload and excitotoxicity, neuroinflammation and activation of microglia, and activation of neuronal nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. For some triggers, oxidants also arise as a byproduct of monoamine oxidase or cytochrome P450 processing, or from uncoupling of nitric oxide synthase.

CONCLUSIONS

Oxidative stress is a plausible unifying principle behind the types of migraine triggers encountered in clinical practice. The possible implications for prevention and for understanding the nature of the migraine attack are discussed.

Mechanisms of glyceryl trinitrate provoked mast cell degranulation

BACKGROUND

Migraine patients develop attacks several hours after intravenous infusion of glyceryl trinitrate. Due to the short half-life of nitric oxide, this delayed migraine cannot be caused by a direct action of nitric oxide derived from glyceryl trinitrate. The involvement of meningeal inflammation and dural mast cell degranulation is supported by the effectiveness of prednisolone on glyceryl trinitrate-induced delayed headache.

METHODS

Using a newly developed rat model mimicking the human glyceryl trinitrate headache model, we have investigated the occurrence of dural mast cell degranulation after a clinically relevant dose of glyceryl trinitrate.

RESULTS

A 6-fold increase in degranulation was observed starting at 2 hours after glyceryl trinitrate infusion. Interestingly, pre-treatment with the effective anti-migraine substances L-nitro-arginine methyl ester and sumatriptan prevented glyceryl trinitrate-induced mast cell degranulation whereas the calcitonin gene-related peptide-receptor antagonist olcegepant and the substance P receptor antagonist L-733,060 did not affect mast cell degranulation. However, topical application of two different nitric oxide donors did not cause mast cell degranulation ex vivo.

CONCLUSIONS

Direct application of an exogenous nitric oxide donor on dural mast cells does not cause mast cell degranulation ex vivo. In vivo application of the nitric oxide donor glyceryl trinitrate leads to a prominent level of degranulation via a yet unknown mechanism. This effect can be completely blocked by inhibition of the endogenous nitric oxide production and by 5-HT1B/1D receptor agonists but is unaffected by calcitonin gene-related peptide and substance P receptor antagonists.

Migraine: possible role of shear-induced platelet aggregation with serotonin release

BACKGROUND

Migraine patients are at an increased risk for stroke, as well as other thromboembolic events. This warrants further study of the role of platelets in a proportion of migraine patients.

OBJECTIVE

To extend the "platelet hypothesis" using literature data and observations made in a rat model of shear stress-induced platelet aggregation. Such aggregation causes release of serotonin, leading to vasoconstriction during sufficiently strong aggregation and to long-lasting vasodilation when aggregation diminishes. This vasodilation also depends on nitric oxide and prostaglandin formation.

RESULTS

A role for platelet aggregation in a number of migraineurs is indicated by reports of an increased platelet activity during attacks and favorable effects of antiplatelet medication. We hypothesize that in those patients, a migraine attack with or without aura may both be caused by a rise in platelet-released plasma serotonin, albeit at different concentration. At high concentrations, serotonin may cause vasoconstriction and, consequently, the neuronal signs of aura, whereas at low concentrations, it may already stimulate perivascular pain fibers and cause vasodilation via local formation of nitric oxide, prostaglandins, and neuropeptides. Platelet aggregation may be unilaterally evoked by elevated shear stress in a stenotic cervico-cranial artery, by reversible vasoconstriction or by other cardiovascular abnormality, eg, a symptomatic patent foramen ovale. This most likely occurs when a migraine trigger has further enhanced platelet aggregability; literature shows that many triggers either stimulate platelets directly or reduce endogenous platelet antagonists like prostacyclin.

CONCLUSION

New strategies for migraine medication and risk reduction of stroke are suggested.

Arabidopsis root K+-efflux conductance activated by hydroxyl radicals: single-channel properties, genetic basis and involvement in stress-induced cell death

Reactive oxygen species (ROS) are central to plant stress response, signalling, development and a multitude of other processes. In this study, the plasma-membrane hydroxyl radical (HR)-activated K(+) channel responsible for K(+) efflux from root cells during stress accompanied by ROS generation is characterised. The channel showed 16-pS unitary conductance and was sensitive to Ca(2+), tetraethylammonium, Ba(2+), Cs(+) and free-radical scavengers. The channel was not found in the gork1-1 mutant, which lacks a major plasma-membrane outwardly rectifying K(+) channel. In intact Arabidopsis roots, both HRs and stress induced a dramatic K(+) efflux that was much smaller in gork1-1 plants. Tests with electron paramagnetic resonance spectroscopy showed that NaCl can stimulate HR generation in roots and this might lead to K(+)-channel activation. In animals, activation of K(+)-efflux channels by HRs can trigger programmed cell death (PCD). PCD symptoms in Arabidopsis roots developed much more slowly in gork1-1 and wild-type plants treated with K(+)-channel blockers or HR scavengers. Therefore, similar to animal counterparts, plant HR-activated K(+) channels are also involved in PCD. Overall, this study provides new insight into the regulation of plant cation transport by ROS and demonstrates possible physiological properties of plant HR-activated K(+) channels.

Nitric oxide-related drug targets in headache

SUMMARY

Nitric oxide (NO) is a very important molecule in the regulation of cerebral and extra cerebral cranial blood flow and arterial diameters. It is also involved in nociceptive processing. Glyceryl trinitrate (GTN), a pro-drug for NO, causes headache in normal volunteers and a so-called delayed headache that fulfils criteria for migraine without aura in migraine sufferers. Blockade of nitric oxide synthases (NOS) by L-nitromonomethylarginine effectively treats attacks of migraine without aura. Similar results have been obtained for chronic the tension-type headache and cluster headache. Inhibition of the breakdown of cyclic guanylate phosphate (cGMP) also provokes migraine in sufferers, indicating that cGMP is the effector of NO-induced migraine. Similar evidence suggests an important role of NO in the tension-type headache and cluster headache. These very strong data from human experimentation make it highly likely that antagonizing NO effects will be effective in the treatment of primary headaches. Nonselective NOS inhibitors are likely to have side effects whereas selective compounds are now in early clinical trials. Antagonizing the rate limiting cofactor tetrahydrobiopterin seems another very likely new treatment. It is more unlikely that antagonism of cGMP or its formation will be feasible, but augmenting its breakdown via phosphodiesterase activation is a possibility, as well as other ways of inhibiting the NO-cGMP pathway.

Emerging concepts in acute mountain sickness and high-altitude cerebral edema: from the molecular to the morphological

Acute mountain sickness (AMS) is a neurological disorder that typically affects mountaineers who ascend to high altitude. The symptoms have traditionally been ascribed to intracranial hypertension caused by extracellular vasogenic edematous brain swelling subsequent to mechanical disruption of the blood-brain barrier in hypoxia. However, recent diffusion-weighted magnetic resonance imaging studies have identified mild astrocytic swelling caused by a net redistribution of fluid from the "hypoxia-primed" extracellular space to the intracellular space without any evidence for further barrier disruption or additional increment in brain edema, swelling or pressure. These findings and the observation of minor vasogenic edema present in individuals with and without AMS suggest that the symptoms are not explained by cerebral edema. This has led to a re-evaluation of the relevant pathogenic events with a specific focus on free radicals and their interaction with the trigeminovascular system.