Endothelin and subarachnoid hemorrhage: an overview

Serotonin 3 receptor antagonism reduces angiotensin II-induced abdominal aortic aneurysms: Contribution of periaortic fat-derived serotonin

Serotonin (5-HT) has been implicated in cerebral aneurysm rupture, but it is unclear whether 5-HT plays a role in aortic aneurysm development and rupture, despite well known contractile effects of 5-HT through aortic 5-HT receptors. Abdominal aortic aneurysms (AAAs) induced by angiotensin II (AngII) infusion to mice exhibit periaortic inflammation and are prone to rupture. Periaortic fat (PAF), a potential source of 5-HT through tryptophan hydroxylase 1 (Tph1), has been implicated in AAA development. We quantified mRNA abundance of 5-HT receptors (Htr1b, Htr2a, Htr2b, Htr3a, and Htr7) and Tph1 in thoracic and abdominal aortas and surrounding PAF. Compared with other 5-HT receptors, we detected high levels of serotonin 3 receptor type a (Htr3a) mRNA in the abdominal aortas and abdominal PAF. Tph1 mRNA and 5-HT immunostaining were detected in aortas and PAF, with 5-HT levels higher in abdominal than thoracic PAF, and higher in epididymal white than interscapular brown fat. AngII infusion facilitated evoked [3H]5-HT release from thoracic PAF and modestly reduced 5-HT levels in thoracic PAF and brown fat. Based on a high level of Htr3a mRNA in abdominal aortas and PAF, we investigated the development of AngII-induced AAAs when serotonin 3 receptors were pharmacologically antagonized with tropisetron. Tropisetron abrogated abdominal aortic lumen diameters, aneurysm (distal thoracic aneurysm and AAA) incidence, maximal AAA diameters, and aortic weights of AngII-infused male mice. These findings indicate a novel role for serotonin 3 receptor in AAA development, with a potential clinically relevant contribution for PAF as a local source of 5-HT. SIGNIFICANCE STATEMENT: Aortic aneurysms are life-threatening vascular disorders with no effective therapeutics. This study identified antagonism of the serotonin 3 receptor as a potential therapeutic target to reduce the formation and severity of experimentally-induced aneurysms in the thoracic and abdominal aorta. Additionally, periaortic fat was identified as a potential site for serotonin production in the development of aortic aneurysms.

Risk identification for the development of large-artery vasospasm after aneurysmatic subarachnoid hemorrhage - a multivariate, risk-, and location-adjusted prediction model

BACKGROUND

Vasospasm of the large cerebral arteries (CVS) after aneurysmatic subarachnoid hemorrhage (aSAH) reduces cerebral perfusion and causes delayed cerebral ischemia. Although endovascular spasmolysis shows convincing angiographic results, patients often do not improve in outcome. Delayed recognition of CVS contributes substantially to this effect. Therefore, this study aimed to confirm established and to identify unknown risk factors for CVS, which can be used for risk stratification.

METHODS

In this monocentric, retrospective cohort study of 853 patients with aSAH, we compared demographics, clinical, and radiographic parameters at the time of aneurysm occlusion between patients who developed CVS and those who did not. Significant cohort differences were included as predictors in a multivariate analysis to address confounding. Logistic regression models were used to determine odds ratios (ORs) for the presence of CVS for each predictor.

RESULTS

Of the 853 patients treated with aSAH, 304 (32%) developed CVS. In the univariable analysis, CVS was significantly associated with young age, female sex, aneurysm location, modified Fisher score, Barrow Neurological Institute (BNI) score, and surgical interventions. In the multivariable regression analysis, we identified BNI score (OR 1.33, 95% CI 1.11 to 1.58, p=0.002), decompressive craniectomy (OR 1.93, 95% CI 1.22 to 3.04, p=0.005), and aneurysm clipping (OR 2.22, 95% CI 1.50 to 3.29, p<0.001), as independent risk factors.

CONCLUSIONS

Young female patients with high BNI scores who undergo surgical interventions are more likely to develop CVS and should therefore be monitored most intensively after aneurysm occlusion.

Cerebral Vasospasm After Burr Hole Evacuation of Chronic Subdural Hematoma

Cerebral vasospasm is a frequent complication of subarachnoid hemorrhage. We report a case of chronic subdural hematoma complicated by cerebral vasospasm after burr hole evacuation. A 74-year-old woman underwent burr hole evacuation of a chronic subdural hematoma. She developed left hemiparesis and disturbance of consciousness on postoperative day 3. Magnetic resonance imaging showed a right parietal infarct and decreased cerebral blood flow signal in the right middle cerebral artery territory. Digital subtraction angiography showed multiple segmental narrowings of the right middle cerebral artery. Her neurological symptoms recovered with conservative treatment. Follow-up angiography showed improvement in the arterial narrowing, which finally led to a diagnosis of cerebral vasospasm. Cerebral vasospasm can occur after burr hole evacuation of chronic subdural hematoma. Magnetic resonance angiography is useful for determining the cause of postoperative neurological worsening in chronic subdural hematoma patients.

Effects of hyperoxemia on aneurysmal subarachnoid hemorrhage outcomes: a systematic review and meta-analysis

OBJECTIVE

In recent years, hyperoxemia in the intensive care unit has received attention as potentially contributing to negative outcomes in the setting of cardiac arrest, ischemic stroke, and traumatic brain injury. The authors sought to evaluate whether hyperoxemia contributes to worse outcomes in the setting of aneurysmal subarachnoid hemorrhage (aSAH) and to summarize suggested pathophysiological mechanisms.

METHODS

A systematic literature review was conducted without date restrictions on the PubMed and Web of Science databases on September 15, 2021. All studies that assessed the relationship between patients treated for aSAH and hyperoxemia were eligible independent of the criteria used to define hyperoxemia. All nonclinical studies and studies that did not report outcome data specific to patients with aSAH were excluded. A total of 102 records were found and screened, resulting in assessment of 10 full-text studies, of which 7 met eligibility criteria. Risk of bias was assessed using the Downs and Black checklist. A meta-analysis on the pooled 2602 patients was performed, and forest plots were constructed. Additionally, a review of the literature was performed to summarize available data regarding the pathophysiology of hyperoxemia.

RESULTS

The included studies demonstrated an association between hyperoxemia and increased morbidity and mortality following aSAH. The criteria used to determine hyperoxemia varied among studies. Pooling of univariate data showed hyperoxemia to be associated with poor neurological outcome (OR 2.26, 95% CI 1.66-3.07; p < 0.001), delayed cerebral ischemia (DCI) (OR 1.91, 95% CI 1.31-2.78; p < 0.001), and increased incidence of poor neurological outcome or mortality as a combined endpoint (OR 2.36, 95% CI 1.87-2.97; p < 0.001). Pooling of multivariable effect sizes showed the same relationship for poor neurological outcome (OR 1.28, 95% CI 1.07-1.55; p = 0.01) and poor neurological outcome and mortality as a combined endpoint (OR 1.17, 95% CI 1.11-1.23; p < 0.001). Additionally, review of preclinical studies underlined the contribution of oxidative stress due to hyperoxemia to acute secondary brain injury and DCI.

CONCLUSIONS

Reported outcomes from the available studies have indicated that hyperoxemia is associated with worse neurological outcome, mortality, and DCI. These findings provide a general guideline toward avoiding hyperoxemia in the acute setting of aSAH. Further studies are needed to determine the optimal ventilation and oxygenation parameters for acute management of this patient population.

Endothelin-1 axes in the framework of predictive, preventive and personalised (3P) medicine

Endothelin-1 (ET-1) is involved in the regulation of a myriad of processes highly relevant for physical and mental well-being; female and male health; in the modulation of senses, pain, stress reactions and drug sensitivity as well as healing processes, amongst others. Shifted ET-1 homeostasis may influence and predict the development and progression of suboptimal health conditions, metabolic impairments with cascading complications, ageing and related pathologies, cardiovascular diseases, neurodegenerative pathologies, aggressive malignancies, modulating, therefore, individual outcomes of both non-communicable and infectious diseases such as COVID-19. This article provides an in-depth analysis of the involvement of ET-1 and related regulatory pathways in physiological and pathophysiological processes and estimates its capacity as a predictor of ageing and related pathologies,a sensor of lifestyle quality and progression of suboptimal health conditions to diseases for their targeted preventionand as a potent target for cost-effective treatments tailored to the person.

Hyperoxemia and Cerebral Vasospasm in Aneurysmal Subarachnoid Hemorrhage

BACKGROUND

Cerebral vasospasm is a major contributor to disability and mortality after aneurysmal subarachnoid hemorrhage. Oxidation of cell-free hemoglobin plays an integral role in neuroinflammation and is a suggested source of tissue injury after aneurysm rupture. This study sought to determine whether patients with subarachnoid hemorrhage and cerebral vasospasm were more likely to have been exposed to early hyperoxemia than those without vasospasm.

METHODS

This single-center retrospective cohort study included adult patients presenting with aneurysmal subarachnoid hemorrhage to Vanderbilt University Medical Center between January 2007 and December 2017. Patients with an ICD-9/10 diagnosis of aneurysmal subarachnoid hemorrhage were initially identified (N = 441) and subsequently excluded if they did not have intracranial imaging, arterial PaO2 values or died within 96 h post-rupture (N = 96). The final cohort was 345 subjects. The degree of hyperoxemia was defined by the highest PaO2 measured within 72 h after aneurysmal rupture. The primary outcome was development of cerebral vasospasm, which included asymptomatic vasospasm and delayed cerebral ischemia (DCI). Secondary outcomes were mortality and modified Rankin Scale.

RESULTS

Three hundred and forty five patients met inclusion criteria; 218 patients (63%) developed vasospasm. Of those that developed vasospasm, 85 were diagnosed with delayed cerebral ischemia (DCI, 39%). The average patient age of the cohort was 55 ± 13 years, and 68% were female. Ninety percent presented with Fisher grade 3 or 4 hemorrhage (N = 310), while 42% presented as Hunt-Hess grade 4 or 5 (N = 146). In univariable analysis, patients exposed to higher levels of PaO2 by quintile of exposure had a higher mortality rate and were more likely to develop vasospasm in a dose-dependent fashion (P = 0.015 and P = 0.019, respectively). There were no statistically significant predictors that differentiated asymptomatic vasospasm from DCI and no significant difference in maximum PaO2 between these two groups. In multivariable analysis, early hyperoxemia was independently associated with vasospasm (OR = 1.15 per 50 mmHg increase in PaO2 [1.03, 1.28]; P = 0.013), but not mortality (OR = 1.10 [0.97, 1.25]; P = 0.147) following subarachnoid hemorrhage.

CONCLUSIONS

Hyperoxemia within 72 h post-aneurysmal rupture is an independent predictor of cerebral vasospasm, but not mortality in subarachnoid hemorrhage. Hyperoxemia is a variable that can be readily controlled by adjusting the delivered FiO2 and may represent a modifiable risk factor for vasospasm.

Vasorelaxing cell permeant phosphopeptide mimetics for subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) due to rupture of an intracranial aneurysm leads to vasospasm resulting in delayed cerebral ischemia. Therapeutic options are currently limited to hemodynamic optimization and nimodipine, which have marginal clinical efficacy. Nitric oxide (NO) modulates cerebral blood flow through activation of the cGMP-Protein Kinase G (PKG) pathway. Our hypothesis is that SAH results in downregulation of signaling components in the NO-PKG pathway which could explain why treatments for vasospasm targeting this pathway lack efficacy and that treatment with a cell permeant phosphopeptide mimetic of downstream effector prevents delayed vasospasm after SAH. Using a rat endovascular perforation model, reduced levels of NO-PKG pathway molecules were confirmed. Additionally, it was determined that expression and phosphorylation of a PKG substrate: Vasodilator-stimulated phosphoprotein (VASP) was downregulated. A family of cell permeant phosphomimetic of VASP (VP) was wasdesigned and shown to have vasorelaxing property that is synergistic with nimodipine in intact vascular tissuesex vivo. Hence, treatment targeting the downstream effector of the NO signaling pathway, VASP, may bypass receptors and signaling elements leading to vasorelaxation and that treatment with VP can be explored as a therapeutic strategy for SAH induced vasospasm and ameliorate neurological deficits.

Comparative transcriptome and methylome analysis of the hindbrain in olive flounder (Paralichthys olivaceus) considering individual behavior-type and oxygen metabolism

In previous studies we employed multiple behavior assays, including propensity to feed, simulated trawl capture and escape response, to prove the presence of bold and shy personality (BP,SP) in olive flounder (Paralichthys olivaceus). However, the molecular mechanism of the different personality has not been elucidated. In this study, firstly, we found that the SP flounder had lower red blood cell count (RBC) and haemoglobin concentration (HBG) than BP flounder. Secondly, the transcriptomic profiles of the hindbrain in flounder with distinct personality were compared. A total of 144 differently expressed genes (DEGs) were identified, including 70 up-regulated and 74 down-regulated genes in SP flounder compared with BP flounder. Genes involved in hypoxia stress were detected in SP flounder, accompanied with down-regulation of ribosomal RNA synthesis. In addition, genes related with calcium signaling pathway, including endothelin, b-Fos, c-Fos and c-Jun were up-regulated in SP flounder. Furthermore, personality-related genes including UI, CCK, c-Fos showed significantly higher level in SP flounder than in BP flounder. GO enrichment analysis indicated that the GO categories "the tight junction pathway" and "lipid transport or localization pathway" were enriched in SP flounder, suggesting that the central nervous system homeostasis would be compromised. Thirdly, using a simple and scalable DNA methylation profiling method (MethylRAD), which allows for methylation analysis for DEGs in RNA-seq, we found that only part of gene expression was negatively associated with promoter methylation. Altogether, our study will not only lay a foundation for further studies on animal personality but also facilitate the selective breeding of olive flounder in aquaculture.

Anesthetic and subanesthetic doses of isoflurane conditioning provides strong protection against delayed cerebral ischemia in a mouse model of subarachnoid hemorrhage

Delayed cerebral ischemia (DCI) is identified as one of the significant contributors to poor patient outcome after aneurysmal subarachnoid hemorrhage (SAH). We previously reported that a supratherapeutic dose of isoflurane conditioning (2%) provided robust protection against SAH-induced DCI. The aim of our current study is to compare the efficacy of the supratherapeutic dose of isoflurane to that typically used to establish general anesthesia or sedation. After IRB approval for animal studies, ten to fourteen-week-old wild-type male mice (C57BL/6) were divided into five groups - sham, SAH alone, or SAH with isoflurane conditioning (0.5%, 1%, and 2%). Conditioning was performed with one-hour of isoflurane initiated one-hour after induction of SAH via endovascular perforation technique. Vasospasm measurement in the middle cerebral artery was assessed 72 h after SAH. Neurological assessment was performed at baseline and for next three days after SAH. It was identified that all tested doses of isoflurane conditioning (0.5%, 1%, and 2%) significantly attenuated large artery vasospasm and markedly improved neurological deficits following SAH. No significant differences in neurovascular outcome were noted between the three doses of isoflurane conditioning. Our data show that isoflurane dosing typically used for general anesthesia (1%) or sedation (0.5%) provide similar levels of DCI protection in SAH as that provided by a supratherapeutic dose (2%). This result has important implications for future translational studies. Additional studies examining the therapeutic potential of anesthetic conditioning for SAH are therefore warranted.

Unruptured aneurysmal clipping complicated by delayed and refractory vasospasm: case report

Background

Delayed symptomatic vasospasm is a rare complication following clipping of an unruptured intracranial saccular aneurysm. There have been ten reported cases of delayed symptomatic vasospasm and only two of these occurred after 2 weeks from initial intervention. Our case is the first to document the refractory nature of such vasospasm despite aggressive first line therapy.

Case presentation

Here, we present a 67-year-old female who had surgical clipping of a 10x7mm right middle cerebral artery (MCA) bifurcation aneurysm. Her surgery and initial postoperative course were uncomplicated, but she presented with acute left hemiparesis, dysarthria, headache and vomiting on post-op day 29 secondary to vasospasm of M2. She was initially stabilized with intra-arterial verapamil then managed with volume expansion, permissive hypertension, and nimodipine. She developed recurrent vasospasm of M2 the following day and was again treated with intra-arterial verapamil. Magnetic resonance imaging (MRI) brain showed an infarction involving the right basal ganglia, frontal lobe, and parietal lobe and her hospital course was complicated by super-refractory status epilepticus. At her follow up appointment she displayed continued left lower extremity weakness, left visual field defect, and left-sided neglect.

Conclusions

Overall, cerebral vasospasms associated with unruptured aneurysms remain rare complications and are not often monitored for after initial recovery. Reviewing the documented cases highlights the unpredictability of when these events occur with our current knowledge. Current hypotheses for the mechanisms responsible for delayed and refractory vasospasms include: blood-derived breakdown products, mechanically induced vasospastic responses, and delayed reactions from the trigemino-cerebrovascular system (TCVS). The uncertainly of these events warrants further research and supports a strong argument for monitoring patients with initial surgical clipping up to a month out from their initial procedure.

Posterior reversible encephalopathy syndrome and reversible cerebral vasoconstriction syndrome associated spinal subdural hematoma: A case report

RATIONALE

Posterior reversible encephalopathy syndrome (PRES) and reversible cerebral vasoconstriction syndrome (RCVS) are separate clinical entities with distinct pathophysiological features. But in some special conditions PRES and RCVS can occur simultaneously.

PATIENT CONCERNS

We report the unique case of a 40-year-old female presented with crescendo headache, blurred vision, and recurrent generalized tonic-clonic seizure. She had a minor neck injury 1 week before but attracted no more attention. Neurological tests on admission yielded a Glasgow Coma Scale score of 13. No obvious focal neurological deficit apart from positive signs of meningeal irritation was presented.

DIAGNOSES

Xanthochromia and hemorrhagic cerebrospinal fluid with pleocytosis was found on lumbar puncture. Cranial computed tomography was negative but magnetic resonance imaging demonstrated bilateral areas of vasogenic edema in the parieto-occipital lobes and cerebellum consistent with PRES. An incidental subacute spinal subdural hematoma extending from the level of C6 to T1 was depicted by spinal magnetic resonance imaging, presumably as a complication of negligible neck trauma. Spinal digital subtraction angiography showed no evidence of spinal aneurysm, arteriovenous malformation, or dural arteriovenous fistula. Cerebral digital subtraction angiography showed segmental narrowing and dilatation of vessels, a potential feature of RCVS, involving the circle of Willis and their branches.

INTERVENTIONS

The patient was treated with nimodipine for vasodilation and other symptomatic therapies. The spinal subdural hematoma was not warranted for surgical intervention and managed with simple analgesics.

OUTCOMES

The patient experienced a dramatic improvement in neurological symptoms and was discharged without sequelae. Follow-up imaging showed complete resolution of all radiological changes.

LESSONS

Clinician should be aware of spinal subdural hematoma as the potential trigger in development of PRES and RCVS. We speculate that endothelial dysfunction and vascular tone dysregulation may be implicated to play the major pathophysiologic role.

Endothelin Receptor Antagonists: Status Quo and Future Perspectives for Targeted Therapy

The endothelin axis, recognized for its vasoconstrictive action, plays a central role in the pathology of pulmonary arterial hypertension (PAH). Treatment with approved endothelin receptor antagonists (ERAs), such as bosentan, ambrisentan, or macitentan, slow down PAH progression and relieves symptoms. Several findings have indicated that endothelin is further involved in the pathogenesis of certain other diseases, making ERAs potentially beneficial in the treatment of various conditions. In addition to PAH, this review summarizes the use and perspectives of ERAs in cancer, renal disease, fibrotic disorders, systemic scleroderma, vasospasm, and pain management. Bosentan has proven to be effective in systemic sclerosis PAH and in decreasing the development of vasospasm-related digital ulcers. The selective ERA clazosentan has been shown to be effective in preventing cerebral vasospasm and delaying ischemic neurological deficits and new infarcts. Furthermore, in the SONAR (Study Of Diabetic Nephropathy With Atrasentan) trial, the selective ERA atrasentan reduced the risk of renal events in patients with diabetes and chronic kidney disease. These data suggest atrasentan as a new therapy in the treatment of diabetic nephropathy and possibly other renal diseases. Preclinical studies regarding heart failure, cancer, and fibrotic diseases have demonstrated promising effects, but clinical trials have not yet produced measurable results. Nevertheless, the potential benefits of ERAs may not be fully realized.

The Role of Sartans in the Treatment of Stroke and Subarachnoid Hemorrhage: A Narrative Review of Preclinical and Clinical Studies

Background: Delayed cerebral vasospasm (DCVS) due to aneurysmal subarachnoid hemorrhage (aSAH) and its sequela, delayed cerebral ischemia (DCI), are associated with poor functional outcome. Endothelin-1 (ET-1) is known to play a major role in mediating cerebral vasoconstriction. Angiotensin-II-type-1-receptor antagonists such as Sartans may have a beneficial effect after aSAH by reducing DCVS due to crosstalk with the endothelin system. In this review, we discuss the role of Sartans in the treatment of stroke and their potential impact in aSAH. Methods: We conducted a literature research of the MEDLINE PubMed database in accordance with PRISMA criteria on articles published between 1980 to 2019 reviewing: "Sartans AND ischemic stroke". Of 227 studies, 64 preclinical and 19 clinical trials fulfilled the eligibility criteria. Results: There was a positive effect of Sartans on ischemic stroke in both preclinical and clinical settings (attenuating ischemic brain damage, reducing cerebral inflammation and infarct size, increasing cerebral blood flow). In addition, Sartans reduced DCVS after aSAH in animal models by diminishing the effect of ET-1 mediated vasoconstriction (including cerebral inflammation and cerebral epileptogenic activity reduction, cerebral blood flow autoregulation restoration as well as pressure-dependent cerebral vasoconstriction). Conclusion: Thus, Sartans might play a key role in the treatment of patients with aSAH.

Vascular pathology of large cerebral arteries in experimental subarachnoid hemorrhage: Vasoconstriction, functional CGRP depletion and maintained CGRP sensitivity

Subarachnoid hemorrhage (SAH) is associated with increased cerebral artery sensitivity to vasoconstrictors and release of the perivascular sensory vasodilator CGRP. In the current study the constrictive phenotype and the vasodilatory effects of exogenous and endogenous perivascular CGRP were characterized in detail applying myograph technology to cerebral artery segments isolated from experimental SAH and sham-operated rats. Following experimental SAH, cerebral arteries exhibited increased vasoconstriction to endothelin-1, 5-hydroxytryptamine and U46419. In addition, depolarization-induced vasoconstriction (60 mM potassium) was significantly increased, supporting a general SAH-associated vasoconstrictive phenotype. Using exogenous CGRP, we demonstrated that sensitivity of the arteries to CGRP-induced vasodilation was unchanged after SAH. However, vasodilation in response to capsaicin (100 nM), a sensory nerve activator used to release perivascular CGRP, was significantly reduced by SAH (P = 0.0079). Because CGRP-mediated dilation is an important counterbalance to increased arterial contractility, a reduction in CGRP release after SAH would exacerbate the vasospasms that occur after SAH. A similar finding was obtained with artery culture (24 h), an in vitro model of SAH-induced vascular dysfunction. The arterial segments maintained sensitivity to exogenous CGRP but showed reduced capsaicin-induced vasodilation. To test whether a metabolically stable CGRP analogue could be used to supplement the loss of perivascular CGRP release in SAH, SAX was systemically administered in our in vivo SAH model. SAX treatment, however, induced CGRP-desensitization and did not prevent the development of vasoconstriction in cerebral arteries after SAH.

Therapeutically Targeting Platelet-Derived Growth Factor-Mediated Signaling Underlying the Pathogenesis of Subarachnoid Hemorrhage-Related Vasospasm

INTRODUCTION

Vasospasm accounts for a large fraction of the morbidity and mortality burden in patients sustaining subarachnoid hemorrhage (SAH). Platelet-derived growth factor (PDGF)-β levels rise following SAH and correlate with incidence and severity of vasospasm.

METHODS

The literature was reviewed for studies investigating the role of PDGF in the pathogenesis of SAH-related vasospasm and efficacy of pharmacological interventions targeting the PDGF pathway in ameliorating the same and improving clinical outcomes.

RESULTS

Release of blood under high pressure into the subarachnoid space activates the complement cascade, which results in release of PDGF. Abluminal contact of blood with cerebral vessels increases their contractile response to PDGF-β and thrombin, with the latter upregulating PDGF-β receptors and augmenting effects of PDGF-β. PDGF-β figures prominently in the early and late phases of post-SAH vasospasm. PDGF-β binding to the PDGF receptor-β results in receptor tyrosine kinase domain activation and consequent stimulation of intracellular signaling pathways, including p38 mitogen-activated protein kinase, phosphatidylinositol-3-kinase, Rho-associated protein kinase, and extracellular regulated kinase 1 and 2. Consequent increases in intracellular calcium and increased expression of genes mediating cellular growth and proliferation mediate PDGF-induced augmentation of vascular smooth muscle cell contractility, hypertrophy, and proliferation.

CONCLUSION

Treatments with statins, serine protease inhibitors, and small molecular pathway inhibitors have demonstrated varying degrees of efficacy in prevention of cerebral vasospasm, which is improved with earlier institution.

TRPC Channels and Stroke

TRPC channels play important roles in neuronal death/survival in ischemic stroke, vasospasm in hemorrhagic stroke, thrombin-induced astrocyte pathological changes, and also in the initiation of stroke by affecting blood pressure and atherogenesis. TRPCs' unique channel characters and downstream pathways make them possible new targets for stroke therapy. TRPC proteins have different functions in different cell types. Considering TRPCs' extensive distribution in various tissues and cell types, drugs targeting them could induce more complicated effects. More specific agonists/antagonists and antibodies are required for future study of TRPCs as potential targets for stroke therapy.

Endothelin-1 Immunoreactivity and its Association with Intramedullary Hemorrhage and Myelomalacia in Naturally Occurring Disk Extrusion in Dogs

Background

The pathophysiology of ascending/descending myelomalacia (ADMM) after canine intervertebral disk (IVD) extrusion remains poorly understood. Vasoactive molecules might contribute.

Hypothesis/Objectives

To investigate the immunoreactivity of endothelin‐1 (ET‐1) in the uninjured and injured spinal cord of dogs and its potential association with intramedullary hemorrhage and extension of myelomalacia.

Animals

Eleven normal control and 34 dogs with thoracolumbar IVD extrusion.

Methods

Spinal cord tissue of dogs retrospectively selected from our histopathologic database was examined histologically at the level of the extrusion (center) and in segments remote from the center. Endothelin‐1 immunoreactivity was examined immunohistochemically and by in situ hybridization. Associations between the immunoreactivity for ET‐1 and the severity of intramedullary hemorrhage or the extension of myelomalacia were examined.

Results

Endothelin‐1 was expressed by astrocytes, macrophages, and neurons and only rarely by endothelial cells in all dogs. At the center, ET‐1 immunoreactivity was significantly higher in astrocytes (median score 4.02) and lower in neurons (3.21) than in control dogs (3.0 and 4.54) (P < .001; P = .004) irrespective of the grade of hemorrhage or myelomalacia. In both astrocytes and neurons, there was a higher ET‐1 immunoreactivity in spinal cord regions remote from the center (4.58 and 4.15) than in the center itself (P = .013; P = .001). ET‐1 mRNA was present in nearly all neurons with variable intensity, but not in astrocytes.

Conclusion and Clinical Importance

Enhanced ET‐1 immunoreactivity over multiple spinal cord segments after IVD extrusion might play a role in the pathogenesis of ADMM. More effective quantitative techniques are required.

Evaluation of endothelin-1 and MMPs-2, -9, -14 in cerebrospinal fluid as indirect indicators of blood-brain barrier dysfunction in chronic canine hypothyroidism

Chronic canine hypothyroidism is associated with blood-brain barrier (BBB) disruption. We hypothesized that this change is mediated by endothelin-1(ET-1) and matrix metalloproteinases (MMP) -2, -9, and -14, as evidenced by increased concentrations of these proteins in cerebrospinal fluid (CSF) compared to controls. CSF from 18 dogs, 9 controls and 9 with experimentally induced hypothyroidism was collected before and 6, 12, and 18 months after induction of hypothyroidism. Concentrations of ET-1 using an ELISA kit, and for MMP-2, -9, and -14 using gelatinase zymography were measured in CSF. ET-1 was undetectable in CSF of control and hypothyroid dogs at all time-points. Constitutively expressed MMP-2 was detectable in CSF samples in all dogs at all time-points. No other MMPs were detectable in CSF. No differences in CSF concentrations of ET-1 and MMP-2, 9, and 14 were found between hypothyroid and euthyroid dogs. Therefore, ET-1 and MMP-2, 9, and 14 are unlikely to be primary mediators of BBB damage in chronically hypothyroid dogs.

Inducible nitric oxide synthase (NOS-2) in subarachnoid hemorrhage: Regulatory mechanisms and therapeutic implications

Aneurysmal subarachnoid hemorrhage (SAH) typically carries a poor prognosis. Growing evidence indicates that overabundant production of nitric oxide (NO) may be responsible for a large part of the secondary injury that follows SAH. Although SAH modulates the activity of all three isoforms of nitric oxide synthase (NOS), the inducible isoform, NOS-2, accounts for a majority of NO-mediated secondary injuries after SAH. Here, we review the indispensable physiological roles of NO that must be preserved, even while attempting to downmodulate the pathophysiologic effects of NO that are induced by SAH. We examine the effects of SAH on the function of the various NOS isoforms, with a particular focus on the pathological effects of NOS-2 and on the mechanisms responsible for its transcriptional upregulation. Finally, we review interventions to block NOS-2 upregulation or to counteract its effects, with an emphasis on the potential therapeutic strategies to improve outcomes in patients afflicted with SAH. There is still much to be learned regarding the apparently maladaptive response of NOS-2 and its harmful product NO in SAH. However, the available evidence points to crucial effects that, on balance, are adverse, making the NOS-2/NO/peroxynitrite axis an attractive therapeutic target in SAH.

Evidence for proangiogenic cellular and humoral systemic response in patients with acute onset of spinal cord injury

CONTEXT/OBJECTIVE

Traumatic spinal cord injury (SCI) leads to disruption of local vasculature inducing secondary damage of neural tissue. Circulating endothelial progenitor cells (EPCs) play an important role in post-injury regeneration of vasculature, whereas endothelial cells (ECs) reflect endothelial damage.

METHODS

Twenty patients with SCI were assessed during the first 24 hours, at day 3, and day 7 post-injury and compared to 25 healthy subjects. We herein investigated EPC and EC counts by flow cytometry as well as the levels of soluble factors (SDF-1, HGF, VEGF, Ang2, EGF, endoglin, PLGF, FGF-2, ET-1, BDNF, IGF-1) regulating their migration and proangiogenic function. To better characterize peripheral blood (PB) cells, global gene expression profiles of PB-derived cells were determined using genome-wide RNA microarray technology.

RESULTS

We found significantly higher EPC (CD34(+)/CD133(+)/VEGFR2(+)) as well as EC (VEGFR2(+)) count in PB of patients with SCI within 7 days post-injury and the increased HGF, ET-1, Ang2, EGF, and PLGF plasma levels. Global gene expression analysis revealed considerably lower expression of genes associated with both innate and adaptive immune response in PB cells in patients.

CONCLUSION

Collectively, our findings demonstrate that SCI triggers bone marrow-derived EPC mobilization accompanied by increased circulating EC numbers. Significant changes in both chemoattractive and proangiogenic cytokines plasma levels occurring rapidly after SCI suggest their role in SCI-related regenerative responses to injury. Broadened knowledge concerning the mechanisms governing of human organism response to the SCI might be helpful in developing effective therapeutic strategies.

Endothelin systems in the brain: involvement in pathophysiological responses of damaged nerve tissues

In addition to their potent vasoconstriction effects, endothelins (ETs) show multiple actions in various tissues including the brain. The brain contains high levels of ETs, and their production is stimulated in many brain disorders. Accumulating evidence indicates that activation of brain ET receptors is involved in several pathophysiological responses in damaged brains. In this article, the roles of brain ET systems in relation to brain disorders are reviewed. In the acute phase of stroke, prolonged vasospasm of cerebral arteries and brain edema occur, both of which aggravate brain damage. Studies using ET antagonists show that activation of ETA receptors in the brain vascular smooth muscle induces vasospasm after stroke. Brain edema is induced by increased activity of vascular permeability factors, such as vascular endothelial growth factor and matrix metalloproteinases. Activation of ETB receptors stimulates astrocytic production of these permeability factors. Increases in reactive astrocytes are observed in neurodegenerative diseases and in the chronic phase of stroke, where they facilitate the repair of damaged nerve tissues by releasing neurotrophic factors. ETs promote the induction of reactive astrocytes through ETB receptors. ETs also stimulate the production of astrocytic neurotrophic factors. Recent studies have shown high expression of ETB receptors in neural progenitors. Activation of ETB receptors in neural progenitors promotes their proliferation and migration, suggesting roles for ETB receptors in neurogenesis. Much effort has been invested in the pursuit of novel drugs to induce protection or repair of damaged nerve tissues. From these studies, the pharmacological significance of brain ET systems as a possible target of neuroprotective drugs is anticipated.

CaMKII inhibition with KN93 attenuates endothelin and serotonin receptor-mediated vasoconstriction and prevents subarachnoid hemorrhage-induced deficits in sensorimotor function

Background

It has been suggested that transcriptional upregulation of cerebral artery contractile endothelin (ET_B) and 5-hydroxytryptamine (5-HT_1B) receptors play an important role in the development of late cerebral ischemia and increased vasoconstriction after subarachnoid hemorrhage (SAH). We tested the hypothesis that inhibition of calcium calmodulin-dependent protein kinase II (CaMKII) may reduce cerebral vasoconstriction mediated by endothelin and serotonin receptors and improve neurological outcome after experimental SAH.

Methods

SAH was induced in adult rats by injection of 250 μL autologous blood into the basal cisterns. The CaMKII activity in cerebral vessels was studied by Western blot and immunohistochemistry. The vasomotor responses of middle cerebral and basilar arteries were measured in a sensitive myograph system. The functional outcome was examined by the rotating pole test 2 and 3 days after SAH.

Results

SAH induced a rapid early increase in phosphorylated CaMKII protein at 1 h that was attenuated by cisternal administration of the CaMKII inhibitor KN93 (0.501 μg/kg) 45 min prior and immediately after SAH as evaluated by Western blot. Application of KN93 at 1 h and every 12 h post-SAH significantly reduced vascular CaMKII immunoreactivity at 72 h. In addition, contractile responses of cerebral arteries to endothelin-1 (ET-1) and 5-hydroxycarboxamide (5-CT) were increased at this time-point. KN93 treatment significantly attenuated the contraction induced by ET-1 and 5-CT. Importantly, treatment with the CaMKII inhibitor prevented SAH-induced deficits in neurological function, as evaluated by the rotating pole test, and similar sensorimotor scores were seen in sham-operated animals.

Conclusions

The present study has shown that SAH is associated with increased contractile responses to ET-1 and 5-CT in cerebral arteries and enhanced early activation of CaMKII. Treatment with the CaMKII inhibitor KN93 attenuated the contractile responses and prevented impaired sensorimotor function after SAH.

Correlation between plasma total nitric oxide levels and cerebral vasospasm and clinical outcome in patients with aneurysmal subarachnoid hemorrhage in Indian population

CONTEXT

Cerebral vasospasm remains a major cause of morbidity and mortality in patients with aneurysmal subarachnoid hemorrhage (aSAH). Reduced bioavailability of nitric oxide has been associated with the development of cerebral vasospasm after aSAH. Such data is not available in Indian population.

AIMS

The objective of the study was to measure the plasma total nitric oxide (nitrite and nitrate-NO x ) level in aSAH patients and healthy controls treated at a tertiary hospital in India and to investigate a possible association between plasma total nitric oxide level and cerebral vasospasm and clinical outcome following treatment in patients with aSAH.

SETTINGS AND DESIGN

A case-control study of aSAH patients was conducted. Plasma total NO x levels were estimated in aSAH patients with and without vasospasm and compared the results with NO x levels in healthy individuals.

MATERIALS AND METHODS

aSAH in patients was diagnosed on the basis of clinical and neuro-imaging findings. Plasma total NO x levels in different subject groups were determined by Griess assay.

RESULTS

Plasma total NO x level was found to be significantly decreased in patients with aSAH when compared to controls. Plasma total NO x level in the poor-grade SAH group was lower than that in the good-grade SAH group. Plasma total NO x level further reduced in patients with angiographic (P < 0.05) and clinical vasospasm.

CONCLUSIONS

Reduced plasma NO x level is seen in aSAH patients as compared to normal individuals. In aSAH patients reduced levels are associated with increased incidence of cerebral vasospasm and poor outcome. Plasma total NO x level could be used as a candidate biomarker for predicting vasospasm and outcome for this pathology.

The role of the microcirculation in delayed cerebral ischemia and chronic degenerative changes after subarachnoid hemorrhage

The mortality after aneurysmal subarachnoid hemorrhage (SAH) is 50%, and most survivors suffer severe functional and cognitive deficits. Half of SAH patients deteriorate 5 to 14 days after the initial bleeding, so-called delayed cerebral ischemia (DCI). Although often attributed to vasospasms, DCI may develop in the absence of angiographic vasospasms, and therapeutic reversal of angiographic vasospasms fails to improve patient outcome. The etiology of chronic neurodegenerative changes after SAH remains poorly understood. Brain oxygenation depends on both cerebral blood flow (CBF) and its microscopic distribution, the so-called capillary transit time heterogeneity (CTH). In theory, increased CTH can therefore lead to tissue hypoxia in the absence of severe CBF reductions, whereas reductions in CBF, paradoxically, improve brain oxygenation if CTH is critically elevated. We review potential sources of elevated CTH after SAH. Pericyte constrictions in relation to the initial ischemic episode and subsequent oxidative stress, nitric oxide depletion during the pericapillary clearance of oxyhemoglobin, vasogenic edema, leukocytosis, and astrocytic endfeet swelling are identified as potential sources of elevated CTH, and hence of metabolic derangement, after SAH. Irreversible changes in capillary morphology and function are predicted to contribute to long-term relative tissue hypoxia, inflammation, and neurodegeneration. We discuss diagnostic and therapeutic implications of these predictions.

Smooth muscle phenotype switching in blast traumatic brain injury-induced cerebral vasospasm

Due to increased survival rates among soldiers exposed to explosive blasts, blast-induced traumatic brain injury (bTBI) has become much more prevalent in recent years. Cerebral vasospasm (CVS) is a common manifestation of brain injury whose incidence is significantly increased in bTBI. CVS is characterized by initial vascular smooth muscle cell (VSMC) hypercontractility, followed by prolonged vessel remodeling and lumen occlusion, and is traditionally associated with subarachnoid hemorrhage (SAH), but recent results suggest that mechanical injury during bTBI can cause mechanotransduced VSMC hypercontractility and phenotype switching necessary for CVS development, even in the absence of SAH. Here, we review the mechanisms by which mechanical stimulation and SAH can synergistically drive CVS progression, complicating treatment options in bTBI patients.

Targeted over-expression of endothelin-1 in astrocytes leads to more severe brain damage and vasospasm after subarachnoid hemorrhage

Background

Endothelin-1 (ET-1) is a potent vasoconstrictor, and astrocytic ET-1 is reported to play a role in the pathogenesis of cerebral ischemic injury and cytotoxic edema. However, it is still unknown whether astrocytic ET-1 also contributes to vasogenic edema and vasospasm during subarachnoid hemorrhage (SAH). In the present study, transgenic mice with astrocytic endothelin-1 over-expression (GET-1 mice) were used to investigate the pathophysiological role of ET-1 in SAH pathogenesis.

Results

The GET-1 mice experienced a higher mortality rate and significantly more severe neurological deficits, blood–brain barrier breakdown and vasogenic edema compared to the non-transgenic (Ntg) mice following SAH. Oral administration of vasopressin V_1a receptor antagonist, SR 49059, significantly reduced the cerebral water content in the GET-1 mice. Furthermore, the GET-1 mice showed significantly more pronounced middle cerebral arterial (MCA) constriction after SAH. Immunocytochemical analysis showed that the calcium-activated potassium channels and the phospho-eNOS were significantly downregulated, whereas PKC-α expression was significantly upregulated in the MCA of the GET-1 mice when compared to Ntg mice after SAH. Administration of ABT-627 (ET_A receptor antagonist) significantly down-regulated PKC-α expression in the MCA of the GET-1 mice following SAH.

Conclusions

The present study suggests that astrocytic ET-1 involves in SAH-induced cerebral injury, edema and vasospasm, through ET_A receptor and PKC-mediated potassium channel dysfunction. Administration of ABT-627 (ET_A receptor antagonist) and SR 49059 (vasopressin V_1a receptor antagonist) resulted in amelioration of edema and vasospasm in mice following SAH. These data provide a strong rationale to investigate SR 49059 and ABT-627 as therapeutic drugs for the treatment of SAH patients.

Spatial alterations in endothelin receptor expression are temporally associated with the altered microcirculation after brain trauma

OBJECTIVES

To study the cellular distribution of endothelin receptors A and B (ETrA and ETrB) in the post-traumatic sensorimotor cortex and hippocampus.

MATERIALS AND METHODS

We inflicted closed head trauma to male Sprague-Dawley rats and visualized ETrA and ETrB immunoreactivity with 3,3'-diaminobenzidine.

RESULTS

ETrA immunolabeling was the most prominent in pyramidal neurons 24 and 48 hours post-trauma, while it reached its peak in the microvasculature at hour 4. ETrB immunolabeling was observed in endothelial cells, perivascular neurons, smooth muscle cells (SM) and pericytes, the expression being the most pronounced 24 hours post-trauma.

DISCUSSION

The results suggest that the vasoconstrictor effect of endothelin-1 (ET-1) is mediated primarily by ETrA. The dual effects of ETrB are reflected in its vasoconstrictor role at the vascular bed and conversely, in the attenuation of ET-1 availability and synthesis. We conclude that both receptors play a role in the disturbed microvascular autoregulation and in the sustained reduction of blood flow following trauma to the brain.

Genetics of cerebral vasospasm

Cerebral vasospasm (CV) is a major source of morbidity and mortality in aneurysmal subarachnoid hemorrhage (aSAH). It is thought that an inflammatory cascade initiated by extravasated blood products precipitates CV, disrupting vascular smooth muscle cell function of major cerebral arteries, leading to vasoconstriction. Mechanisms of CV and modes of therapy are an active area of research. Understanding the genetic basis of CV holds promise for the recognition and treatment for this devastating neurovascular event. In our review, we summarize the most recent research involving key areas within the genetics and vasospasm discussion: (1) Prognostic role of genetics—risk stratification based on gene sequencing, biomarkers, and polymorphisms; (2) Signaling pathways—pinpointing key inflammatory molecules responsible for downstream cellular signaling and altering these mediators to provide therapeutic benefit; and (3) Gene therapy and gene delivery—using viral vectors or novel protein delivery methods to overexpress protective genes in the vasospasm cascade.

MAPK signaling pathway regulates cerebrovascular receptor expression in human cerebral arteries

BACKGROUND

Cerebral ischemia results in enhanced expression of contractile cerebrovascular receptors, such as endothelin type B (ET(B)), 5-hydroxytryptamine type 1B (5-HT(1B)), angiotensin II type 1 (AT(1)) and thromboxane (TP) receptors in the cerebral arteries within the ischemic area. The receptor upregulation occurs via activation of the mitogen-activated protein kinases (MAPK) pathway. Previous studies have shown that inhibitors of the MAPK pathway diminished the ischemic area and contractile cerebrovascular receptors after experimental cerebral ischemia. The aim of this study was to examine if the upregulation of contractile cerebrovascular receptors after 48 h of organ culture of human cerebral arteries involves MAPK pathways and if it can be prevented by a MEK1/2 inhibitor. Human cerebral arteries were obtained from patients undergoing intracranial tumor surgery. The vessels were divided into ring segments and incubated for 48 h in the presence or absence of the specific MEK1/2 inhibitor U0126. The vessels were then examined by using in vitro pharmacological methods and protein immunohistochemistry.

RESULTS

After organ culture of the cerebral arteries the contractile responses to endothelin (ET)-1, angiotensin (Ang) II and thromboxane (TP) were enhanced in comparison with fresh human arteries. However, 5-carboxamidotryptamine (5-CT) induced decreased contractile responses after organ culture as compared to fresh arteries. Incubation with U0126 diminished the maximum contraction elicited by application of ET-1, Ang II and U46619 in human cerebral arteries. In addition, the MEK1/2 inhibitor decreased the contractile response to 5-CT. Immunohistochemistry revealed that organ culture resulted in increased expression of endothelin ET(A), endothelin ET(B) angiotensin AT(2), 5-hydroxytryptamine 5-HT(1B) and thromboxane A2 receptors, and elevated levels of activated pERK1/2, all localized to the smooth muscle cells of the cerebral arteries. Co-incubation with U0126 normalized these proteins.

CONCLUSION

The study demonstrated that there is a clear association between human cerebrovascular receptor upregulation via transcription involving activation of the MAPK pathway after organ culture. Inhibition of the MAPK pathways attenuated the vasoconstriction mediated by ET, AT and TP receptors in human cerebral arteries and the enhanced expression of their receptors. The results indicate that MAPK inhibition might be a novel target for treatment of cerebrovascular disorders.

The role of endothelin and endothelin antagonists in traumatic brain injury: a review of the literature

OBJECTIVES

To date, there is increasing evidence for the role of endothelins in the pathophysiological development of cerebral vasospasms associated with a variety of neurological diseases, e.g., stroke and subarachnoid hemorrhage. In contrast, only little is known regarding the role of endothelins in impaired cerebral hemodynamics after traumatic brain injury. Therapeutic work in blocking the endothelin system has led to the discovery of a number of antagonists potentially useful in restoring cerebral blood flow after traumatic brain injury, potentially reducing the detrimental effects of secondary brain injury. Therefore, the present work provides an overview of background topics such as structures and biosynthesis of endothelins, different types as well as potential mechanisms and sites of action. In addition, the role of age for the effects of endothelins on cerebral hemodynamics after traumatic brain injury is discussed.

RESULTS

Description of data supporting the role of the endothelins play in a host of neurological deficits.

CONCLUSIONS

Endothelin antagonists may be effective as novel treatments for various neuropathologies.

Inhibition of cerebrovascular raf activation attenuates cerebral blood flow and prevents upregulation of contractile receptors after subarachnoid hemorrhage

BACKGROUND

Late cerebral ischemia carries high morbidity and mortality after subarachnoid hemorrhage (SAH) due to reduced cerebral blood flow (CBF) and the subsequent cerebral ischemia which is associated with upregulation of contractile receptors in the vascular smooth muscle cells (SMC) via activation of mitogen-activated protein kinase (MAPK) of the extracellular signal-regulated kinase (ERK)1/2 signal pathway. We hypothesize that SAH initiates cerebrovascular ERK1/2 activation, resulting in receptor upregulation. The raf inhibitor will inhibit the molecular events upstream ERK1/2 and may provide a therapeutic window for treatment of cerebral ischemia after SAH.

RESULTS

Here we demonstrate that SAH increases the phosphorylation level of ERK1/2 in cerebral vessels and reduces the neurology score in rats in additional with the CBF measured by an autoradiographic method. The intracisternal administration of SB-386023-b, a specific inhibitor of raf, given 6 h after SAH, aborts the receptor changes and protects the brain from the development of late cerebral ischemia at 48 h. This is accompanied by reduced phosphorylation of ERK1/2 in cerebrovascular SMC. SAH per se enhances contractile responses to endothelin-1 (ET-1), 5-carboxamidotryptamine (5-CT) and angiotensin II (Ang II), upregulates ETB, 5-HT1B and AT1 receptor mRNA and protein levels. Treatment with SB-386023-b given as late as at 6 h but not at 12 h after the SAH significantly decreased the receptor upregulation, the reduction in CBF and the neurology score.

CONCLUSION

These results provide evidence for a role of the ERK1/2 pathway in regulation of expression of cerebrovascular SMC receptors. It is suggested that raf inhibition may reduce late cerebral ischemia after SAH and provides a realistic time window for therapy.

Pituitary dysfunction following traumatic brain injury or subarachnoid haemorrhage - in "Endocrine Management in the Intensive Care Unit"

Traumatic brain injury and subarachnoid haemorrhage are important causes of morbidity and mortality in the developed world. There is a large body of evidence that demonstrates that both conditions may adversely affect pituitary function in both the acute and chronic phases of recovery. Diagnosis of hypopituitarism and accurate treatment of pituitary disorders offers the opportunity to improve mortality and outcome in both traumatic brain injury and subarachnoid haemorrhage. In this article, we will review the history and pathophysiology of pituitary function in the acute phase following traumatic brain injury and subarachnoid haemorrhage, and we will discuss in detail three key aspects of pituitary dysfunction which occur in the early course of TBI; acute cortisol deficiency, diabetes insipidus and SIAD.

Pharmacological treatment of delayed cerebral ischemia and vasospasm in subarachnoid hemorrhage

Subarachnoid hemorrhage after the rupture of a cerebral aneurysm is the cause of 6% to 8% of all cerebrovascular accidents involving 10 of 100,000 people each year. Despite effective treatment of the aneurysm, delayed cerebral ischemia (DCI) is observed in 30% of patients, with a peak on the tenth day, resulting in significant infirmity and mortality. Cerebral vasospasm occurs in more than half of all patients and is recognized as the main cause of delayed cerebral ischemia after subarachnoid hemorrhage. Its treatment comprises hemodynamic management and endovascular procedures. To date, the only drug shown to be efficacious on both the incidence of vasospasm and poor outcome is nimodipine. Given its modest effects, new pharmacological treatments are being developed to prevent and treat DCI. We review the different drugs currently being tested.

Unfractionated heparin: multitargeted therapy for delayed neurological deficits induced by subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is associated with numerous "delayed neurological deficits" (DNDs) that have been attributed to multiple pathophysiological mechanisms, including ischemia, microthrombosis, free radical damage, inflammation, and vascular remodeling. To date, effective prophylactic therapy for SAH-induced DNDs has been elusive, due perhaps to the multiplicity of mechanisms involved that render typical, single-agent therapy seemingly futile. We hypothesized that heparin, which has multiple underappreciated salutary effects, might be useful as a multitargeted prophylactic agent against SAH-induced DNDs. We performed a comprehensive review of the literature to evaluate the potential utility of heparin in targeting the multiple pathophysiological mechanisms that have been identified as contributing to SAH-induced DNDs. Our literature review revealed that unfractionated heparin can potentially antagonize essentially all of the pathophysiological mechanisms known to be activated following SAH. Heparin binds >100 proteins, including plasma proteins, proteins released from platelets, cytokines, and chemokines. Also, heparin complexes with oxyhemoglobin, blocks the activity of free radicals including reactive oxygen species, antagonizes endothelin-mediated vasoconstriction, smooth muscle depolarization, and inflammatory, growth and fibrogenic responses. Our review suggests that the use of prophylactic heparin following SAH may warrant formal study.

Endothelin related pathophysiology in cerebral vasospasm: what happens to the cerebral vessels?

The central role of Endothelin (ET) in the development of cerebral vasospasm (CVS) after subarachnoid hemorrhage (SAH) is supported by several investigations. These investigations provided, furthermore, that changes of the ET-receptor expression and function in the wall of the cerebral arteries are a considerable factor for the development of CVS. The biological activity of ET-1 is mediated by two receptor subtypes, named ET(A) and ET(B). Under physiological conditions the dominant vasocontractile effect of ET-1 is mediated by ET(A)-receptors on smooth muscle cells (SMC), which is attenuated by an ET(B)-receptor dependent release of nitric oxide (NO) from endothelial cells (EC). In the physiological cerebrovasculature ECs express exclusively ET(B)- and SMCs only ET(A)-receptors. In case of CVS an increased expression of the ET(B)-receptor could be detected in cerebral vessels. However, the loss of the vasodilative and the missing of a vasocontractile ET(B)-receptor mediated effect was demonstrated. Therefore, any ET(B)-receptor mediated vasoactivity seems to be lost in case of CVS and the biological impact of the increased expression remains unclear so far. The ET(A)-receptor expression seems to be not increased during the development of CVS. Therefore, the proven increase of the ET-dependent vasocontractility seems to be rather by the loss of the ET(B)-receptor mediated effect than by an increased ET(A)-receptor activity. In spite of the more significant changes of the ET(B)-receptor expression the pathophysiological effect of ET, namely the vasoconstriction, seems to be exclusively mediated by the ET(A)-receptor. Therefore, tailored approaches for the treatment of CVS remain to be ET(A)-receptor selective antagonists.

Endothelin-1(1-31) induces spreading depolarization in rats

BACKGROUND

The vasoconstrictor endothelin-1(1-21) (ET-1) seems to induce cerebral vasospasm after aneurismal subarachnoid hemorrhage (aSAH). Moreover, ET-1 causes spreading depolarization (SD) via vasoconstriction/ischemia. ET-1(1-31) is an alternate metabolic intermediate in the generation of ET-1. Our aim was to investigate whether endothelin-1(1-31) causes SD in a similar fashion to ET-1.

METHOD

Increasing concentrations of either ET-1, ET-1(1-31) or vehicle were brain topically applied in 29 rats. Each concentration was superfused for one hour while regional cerebral blood flow (rCBF) and direct current electrocorticogram (DC-ECoG) were recorded.

FINDINGS

In response to the highest concentration of 10(-6) M, all animals of both ET groups developed typical SD. At concentrations below 10(-6) M only ET-1 induced SD (n=14 of 19 rats). Thus, the efficacy of ET-1(1-31) to induce SD was significantly lower (P<0.001, two-tailed Fisher's Exact Test).

CONCLUSIONS

Our findings suggest that ET-1(1-31) less potently induces SD compared to ET-1 which implicates that it is a less potent vasoconstrictor. Speculatively, it could be interesting to shift the metabolic pathway towards the alternate intermediate ET-1(1-31) after aSAH as an alternative strategy to ETA receptor inhibition. This could decrease ET-induced vasoconstriction and SD generation while a potentially beneficial basal ETA receptor activation is maintained.

Opposing actions of endothelin-1 on glutamatergic transmission onto vasopressin and oxytocin neurons in the supraoptic nucleus

Endothelin (ET-1) given centrally has many reported actions on hormonal and autonomic outputs from the CNS. However, it is unclear whether these effects are due to local ischemia via its vasoconstrictor properties or to a direct neuromodulatory action. ET-1 stimulates the release of oxytocin (OT) and vasopressin (VP) from supraoptic magnocellular (MNCs) neurons in vivo; therefore, we asked whether ET-1 modulates the excitatory inputs onto MNCs that are critical in sculpting the activity of these neurons. To investigate whether ET-1 modulates excitatory synaptic transmission, we obtained whole-cell recordings and analyzed quantal glutamate release onto MNCs in the supraoptic nucleus (SON). Neurons identified as VP-containing neurosecretory cells displayed a decrease in quantal frequency in response to ET-1 (10-100 pm). This decrease was mediated by ET(A) receptor activation and production of a retrograde messenger that targets presynaptic cannabinoid-1 receptors. In contrast, neurons identified as OT-containing MNCs displayed a transient increase in quantal glutamate release in response to ET-1 application via ET(B) receptor activation. Application of TTX to block action potential-dependent glutamate release inhibited the excitatory action of ET-1 in OT neurons. There were no changes in quantal amplitude in either MNC type, suggesting that the effects of ET-1 were via presynaptic mechanisms. A gliotransmitter does not appear to be involved as ET-1 failed to elevate astrocytic calcium in the SON. Our results demonstrate that ET-1 differentially modulates glutamate release onto VP- versus OT-containing MNCs, thus implicating it in the selective regulation of neuroendocrine output from the SON.

Advances in experimental subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) remains to be a devastating disease with high mortality and morbidity. Two major areas are becoming the focus of the research interest of SAH: these are cerebral vasospasm (CVS) and early brain injury (EBI). This mini review will provide a broad summary of the major advances in experimental SAH during the last 3 years. Treatments interfering with nitric oxide (NO)- or endothelin-pathways continue to show antispasmotic effects in experimental SAH. HIF 1 may play both a detrimental and beneficial role in the setting of SAH, depending on its activation stage. Inflammation and oxidative stress contribute to the pathophysiology of both CVS and EBI. Apoptosis, a major component of EBI after SAH, also underlie the etiology of CVS. Since we recognize now that CVS and EBI are the two major contributors to the significant mortality and morbidity associated with SAH, ongoing research will continue to elucidate the underlying pathophysiological pathways and treatment strategies targeting both CVS and EBI may be more successful and improve outcome of patients with SAH.

Metamorphosis of subarachnoid hemorrhage research: from delayed vasospasm to early brain injury

Delayed vasospasm that develops 3–7 days after aneurysmal subarachnoid hemorrhage (SAH) has traditionally been considered the most important determinant of delayed ischemic injury and poor outcome. Consequently, most therapies against delayed ischemic injury are directed towards reducing the incidence of vasospasm. The clinical trials based on this strategy, however, have so far claimed limited success; the incidence of vasospasm is reduced without reduction in delayed ischemic injury or improvement in the long-term outcome. This fact has shifted research interest to the early brain injury (first 72 h) evoked by SAH. In recent years, several pathological mechanisms that activate within minutes after the initial bleed and lead to early brain injury are identified. In addition, it is found that many of these mechanisms evolve with time and participate in the pathogenesis of delayed ischemic injury and poor outcome. Therefore, a therapy or therapies focused on these early mechanisms may not only prevent the early brain injury but may also help reduce the intensity of later developing neurological complications. This manuscript reviews the pathological mechanisms of early brain injury after SAH and summarizes the status of current therapies.