Endothelin in cerebrospinal fluid and plasma of patients in the early stage of ischemic stroke

Sovateltide (ILR-1620) Improves Motor Function and Reduces Hyperalgesia in a Rat Model of Spinal Cord Injury

BACKGROUND

Spinal cord injury (SCI) presents a major global health challenge, with rising incidence rates and substantial disability. Although progress has been made in understanding SCI's pathophysiology and early management, there is still a lack of effective treatments to mitigate long-term consequences. This study investigates the potential of sovateltide, a selective endothelin B receptor agonist, in improving clinical outcomes in an acute SCI rat model.

METHODS

Thirty male Sprague-Dawley rats underwent sham surgery (group A) or SCI and treated with vehicle (group B) or sovateltide (group C). Clinical tests, including Basso, Beattie, and Bresnahan scoring, inclined plane, and allodynia testing with von Frey hair, were performed at various time points. Statistical analyses assessed treatment effects.

RESULTS

Sovateltide administration significantly improved motor function, reducing neurological deficits and enhancing locomotor recovery compared with vehicle-treated rats, starting from day 7 post injury. Additionally, the allodynic threshold improved, suggesting antinociceptive properties. Notably, the sovateltide group demonstrated sustained recovery, and even reached preinjury performance levels, whereas the vehicle group plateaued.

CONCLUSIONS

This study suggests that sovateltide may offer neuroprotective effects, enhancing neurogenesis and angiogenesis. Furthermore, it may possess anti-inflammatory and antinociceptive properties. Future clinical trials are needed to validate these findings, but sovateltide shows promise as a potential therapeutic strategy to improve functional outcomes in SCI. Sovateltide, an endothelin B receptor agonist, exhibits neuroprotective properties, enhancing motor recovery and ameliorating hyperalgesia in a rat SCI model. These findings could pave the way for innovative pharmacological interventions for SCI in clinical settings.

Astrocytic endothelin-1 overexpression impairs learning and memory ability in ischemic stroke via altered hippocampal neurogenesis and lipid metabolism

Vascular etiology is the second most prevalent cause of cognitive impairment globally. Endothelin-1, which is produced and secreted by endothelial cells and astrocytes, is implicated in the pathogenesis of stroke. However, the way in which changes in astrocytic endothelin-1 lead to poststroke cognitive deficits following transient middle cerebral artery occlusion is not well understood. Here, using mice in which astrocytic endothelin-1 was overexpressed, we found that the selective overexpression of endothelin-1 by astrocytic cells led to ischemic stroke-related dementia (1 hour of ischemia; 7 days, 28 days, or 3 months of reperfusion). We also revealed that astrocytic endothelin-1 overexpression contributed to the role of neural stem cell proliferation but impaired neurogenesis in the dentate gyrus of the hippocampus after middle cerebral artery occlusion. Comprehensive proteome profiles and western blot analysis confirmed that levels of glial fibrillary acidic protein and peroxiredoxin 6, which were differentially expressed in the brain, were significantly increased in mice with astrocytic endothelin-1 overexpression in comparison with wild-type mice 28 days after ischemic stroke. Moreover, the levels of the enriched differentially expressed proteins were closely related to lipid metabolism, as indicated by Kyoto Encyclopedia of Genes and Genomes pathway analysis. Liquid chromatography-mass spectrometry nontargeted metabolite profiling of brain tissues showed that astrocytic endothelin-1 overexpression altered lipid metabolism products such as glycerol phosphatidylcholine, sphingomyelin, and phosphatidic acid. Overall, this study demonstrates that astrocytic endothelin-1 overexpression can impair hippocampal neurogenesis and that it is correlated with lipid metabolism in poststroke cognitive dysfunction.

Orai, RyR, and IP3R channels cooperatively regulate calcium signaling in brain mid-capillary pericytes

Pericytes are multifunctional cells of the vasculature that are vital to brain homeostasis, yet many of their fundamental physiological properties, such as Ca²⁺ signaling pathways, remain unexplored. We performed pharmacological and ion substitution experiments to investigate the mechanisms underlying pericyte Ca²⁺ signaling in acute cortical brain slices of PDGFRβ-Cre::GCaMP6f mice. We report that mid-capillary pericyte Ca²⁺ signalling differs from ensheathing type pericytes in that it is largely independent of L- and T-type voltage-gated calcium channels. Instead, Ca²⁺ signals in mid-capillary pericytes were inhibited by multiple Orai channel blockers, which also inhibited Ca²⁺ entry triggered by endoplasmic reticulum (ER) store depletion. An investigation into store release pathways indicated that Ca²⁺ transients in mid-capillary pericytes occur through a combination of IP₃R and RyR activation, and that Orai store-operated calcium entry (SOCE) is required to sustain and amplify intracellular Ca²⁺ increases evoked by the GqGPCR agonist endothelin-1. These results suggest that Ca²⁺ influx via Orai channels reciprocally regulates IP₃R and RyR release pathways in the ER, which together generate spontaneous Ca²⁺ transients and amplify Gq-coupled Ca²⁺ elevations in mid-capillary pericytes. Thus, SOCE is a major regulator of pericyte Ca²⁺ and a target for manipulating their function in health and disease.

The pharmacology of the TMEM16A channel: therapeutic opportunities

The TMEM16A Ca²⁺-gated Cl^- channel is involved in a variety of vital physiological functions and may be targeted pharmacologically for therapeutic benefit in diseases such as hypertension, stroke, and cystic fibrosis (CF). The determination of the TMEM16A structure and high-throughput screening efforts, alongside ex vivo and in vivo animal studies and clinical investigations, are hastening our understanding of the physiology and pharmacology of this channel. Here, we offer a critical analysis of recent developments in TMEM16A pharmacology and reflect on the therapeutic opportunities provided by this target.

The Ca2+-gated channel TMEM16A amplifies capillary pericyte contraction and reduces cerebral blood flow after ischemia

Pericyte-mediated capillary constriction decreases cerebral blood flow in stroke after an occluded artery is unblocked. The determinants of pericyte tone are poorly understood. We show that a small rise in cytoplasmic Ca2+ concentration ([Ca2+]i) in pericytes activated chloride efflux through the Ca2+-gated anion channel TMEM16A, thus depolarizing the cell and opening voltage-gated calcium channels. This mechanism strongly amplified the pericyte [Ca2+]i rise and capillary constriction evoked by contractile agonists and ischemia. In a rodent stroke model, TMEM16A inhibition slowed the ischemia-evoked pericyte [Ca2+]i rise, capillary constriction, and pericyte death; reduced neutrophil stalling; and improved cerebrovascular reperfusion. Genetic analysis implicated altered TMEM16A expression in poor patient recovery from ischemic stroke. Thus, pericyte TMEM16A is a crucial regulator of cerebral capillary function and a potential therapeutic target for stroke and possibly other disorders of impaired microvascular flow, such as Alzheimer's disease and vascular dementia.

Sovateltide Mediated Endothelin B Receptors Agonism and Curbing Neurological Disorders

Neurological/neurovascular disorders constitute the leading cause of disability and the second leading cause of death globally. Major neurological/neurovascular disorders or diseases include cerebral stroke, Alzheimer’s disease, spinal cord injury, neonatal hypoxic-ischemic encephalopathy, and others. Their pathophysiology is considered highly complex and is the main obstacle in developing any drugs for these diseases. In this review, we have described the endothelin system, its involvement in neurovascular disorders, the importance of endothelin B receptors (ETBRs) as a novel potential drug target, and its agonism by IRL-1620 (INN—sovateltide), which we are developing as a drug candidate for treating the above-mentioned neurological disorders/diseases. In addition, we have highlighted the results of our preclinical and clinical studies related to these diseases. The phase I safety and tolerability study of sovateltide has shown it as a safe and tolerable compound at therapeutic dosages. Furthermore, preclinical and clinical phase II studies have demonstrated the efficacy of sovateltide in treating acute ischemic stroke. It is under development as a first-in-class drug. In addition, efficacy studies in Alzheimer’s disease (AD), acute spinal cord injury, and neonatal hypoxic-ischemic encephalopathy (HIE) are ongoing. Successful completion of these studies will validate that ETBRs signaling can be an important target in developing drugs to treat neurological/neurovascular diseases.

Endothelin ETB Receptor-Mediated Astrocytic Activation: Pathological Roles in Brain Disorders

In brain disorders, reactive astrocytes, which are characterized by hypertrophy of the cell body and proliferative properties, are commonly observed. As reactive astrocytes are involved in the pathogenesis of several brain disorders, the control of astrocytic function has been proposed as a therapeutic strategy, and target molecules to effectively control astrocytic functions have been investigated. The production of brain endothelin-1 (ET-1), which increases in brain disorders, is involved in the pathophysiological response of the nervous system. Endothelin B (ET_B) receptors are highly expressed in reactive astrocytes and are upregulated by brain injury. Activation of astrocyte ET_B receptors promotes the induction of reactive astrocytes. In addition, the production of various astrocyte-derived factors, including neurotrophic factors and vascular permeability regulators, is regulated by ET_B receptors. In animal models of Alzheimer’s disease, brain ischemia, neuropathic pain, and traumatic brain injury, ET_B-receptor-mediated regulation of astrocytic activation has been reported to improve brain disorders. Therefore, the astrocytic ET_B receptor is expected to be a promising drug target to improve several brain disorders. This article reviews the roles of ET_B receptors in astrocytic activation and discusses its possible applications in the treatment of brain disorders.

Safety and Efficacy of Sovateltide (IRL-1620) in a Multicenter Randomized Controlled Clinical Trial in Patients with Acute Cerebral Ischemic Stroke

BACKGROUND

Sovateltide (IRL-1620, PMZ-1620), an endothelin-B receptor agonist, has been previously shown to increase cerebral blood flow, have anti-apoptotic activity and produce neurovascular remodeling when administered intravenously following acute cerebral ischemic stroke in rats. Its safety and tolerability were confirmed in healthy human volunteers (CTRI/2016/11/007509).

OBJECTIVE

Our objective was to determine the safety, tolerability and efficacy of sovateltide as an addition to standard of care (SOC) in patients with acute cerebral ischemic stroke.

METHODS

A prospective, multicentric, randomized, double-blind, placebo-controlled study was conducted to compare the safety (primary objective) and efficacy (secondary objective) of sovateltide in patients with acute cerebral ischemic stroke. Adult males or females aged 18-70 years who had experienced a radiologically confirmed ischemic stroke within the last 24 h were included in the study. Patients with intracranial hemorrhage and those receiving endovascular therapy were excluded. Patients randomized to the sovateltide group received three doses of sovateltide (each dose 0.3 µg/kg) administered as an intravenous bolus over 1 min at an interval of 3 ± 1 h on day 1, day 3 and day 6 (total dose of 0.9 µg/kg/day). Patients randomized to the placebo group received an equal volume of saline. Every patient in both groups received SOC for stroke. Efficacy was evaluated using neurological outcomes based on National Institute of Health Stroke Scale (NIHSS), modified Rankin Scale (mRS) and Barthel Index (BI) scores from day 1 through day 90. Quality of life was measured using the EuroQoL-5 Dimensions (EQ-5D) and Stroke-Specific Quality of Life (SSQoL) at 60 and 90 days of follow-up.

RESULTS

A total of 40 patients with acute cerebral ischemic stroke were enrolled in this study, of whom 36 completed the 90-day follow-up. Patients received saline (n = 18; 11 male and 7 female) or sovateltide (n = 18; 15 male and 3 female) within 24 h of onset of stroke. The number of patients receiving investigational drug within 20 h of onset of stroke was 14/18 in the saline group and 10/18 in the sovateltide group. The baseline characteristics and SOC in both cohorts was similar. Sovateltide was well-tolerated, and all patients received complete treatment with no incidence of drug-related adverse events. Hemodynamic, biochemical or hematological parameters were not affected by sovateltide. Sovateltide treatment resulted in improved mRS and BI scores on day 6 compared with day 1 (p < 0.0001), an effect not seen in the saline group. Sovateltide increased the frequency of favorable outcomes at 3 months. An improvement of ≥ 2 points on the mRS was observed in 60 and 40% of patients in the sovateltide and saline groups, respectively (p = 0.0519; odds ratio [OR] 5.25). An improvement on the BI of ≥ 40 points was seen in 64 and 36% of the sovateltide and saline groups, respectively (p = 0.0112; OR 12.44). An improvement of ≥6 points on the NIHSS was seen in 56% of patients in the sovateltide group versus 43% in the saline group (p = 0.2714; OR 2.275). The number of patients with complete recovery (defined as an NIHSS score of 0 and a BI of 100) was significantly greater (p < 0.05) in the sovateltide group than in the saline group. An assessment of complete recovery using an mRS score of 0 did not show a statistically significant difference between the treatment groups. Sovateltide treatment resulted in improved quality of life as measured by the EQ-5D and SSQoL on day 90.

CONCLUSION

Sovateltide was safe and well-tolerated and resulted in improved neurological outcomes in patients with acute cerebral ischemic stroke 90 days post-treatment.

TRIAL REGISTRATION

The study is registered at CTRI/2017/11/010654 and NCT04046484.

Association between Lys198Asn polymorphism of endothelin-1 gene and ischemic stroke: A meta-analysis

BACKGROUND

Endothelin (ET)-1 is a potent vasoconstrictor peptide produced by endothelial cells and associated with vascular dysfunction and cardiovascular disease. Lys198Asn is a single-nucleotide polymorphism (SNP) of gene encoding ET-1 (EDN1). It is hypothesized that it might have a role in altering ET-1 and ultimately leading to vascular dysfunction and ischemic stroke. We therefore conducted a meta-analysis to investigate the association between Lys198Asn polymorphism of EDN1 gene and susceptibility of ischemic stroke.

METHODS

This meta-analysis was conducted according to the guidance of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. We searched PubMed, Google Scholar, Embase, Web of Science, J-STAGE, and China National Knowledge Infrastructure (CNKI) for relevant studies. The association between Lys198Asn polymorphism and ischemic stroke susceptibility was evaluated by calculating the pooled ORs and 95% CIs.

RESULTS

Our analysis included 1,291 cases and 2,513 controls. Meta-analysis established a significant association between Lys198Asn SNP of EDN1 gene and ischemic stroke when assuming either recessive model (OR: 1.30; 95% CI: 1.02-1.65; p = .03; I2  = 41%) or dominant model (OR: 1.48; 95% CI: 1.24-1.76; p < .001; I2  = 61%). There was no evidence of publication bias in either of the recessive model (Egger test: p = .23; Begg test: p = .85) or dominant model (Egger test: p = .79; Begg test: p = .85). A subgroup analysis based on subtypes of ischemic stroke showed that Lys198Asn SNP was only associated with large vessel infarction but not with lacunar infarction caused by small vessel disease. A subgroup analysis based on ethnicity revealed that the Lys198Asn polymorphism of the EDN1 gene was associated with ischemic stroke only in Caucasians.

CONCLUSIONS

The present meta-analysis suggests that Lys198Asn polymorphism of EDN1 gene is associated with an increased risk for ischemic stroke.

Exposure to Blast Overpressure Impairs Cerebral Microvascular Responses and Alters Vascular and Astrocytic Structure

Exposure to blast overpressure may result in cerebrovascular impairment, including cerebral vasospasm. The mechanisms contributing to this vascular response are unclear. The aim of this study was to evaluate the relationship between blast and functional alterations of the cerebral microcirculation and to investigate potential underlying changes in vascular microstructure. Cerebrovascular responses were assessed in sham- and blast-exposed male rats at multiple time points from 2 h through 28 days after a single 130-kPa (18.9-psi) exposure. Pial microcirculation was assessed through a cranial window created in the parietal bone of anesthetized rats. Pial arteriolar reactivity was evaluated in vivo using hypercapnia, barium chloride, and serotonin. We found that exposure to blast leads to impairment of arteriolar reactivity >24 h after blast exposure, suggesting delayed injury mechanisms that are not simply attributed to direct mechanical deformation. Observed vascular impairment included a reduction in hypercapnia-induced vasodilation, increase in barium-induced constriction, and reversal of the serotonin effect from constriction to dilation. A reduction in vascular smooth muscle contractile proteins consistent with vascular wall proliferation was observed, as well as delayed reduction in nitric oxide synthase and increase in endothelin-1 B receptors, mainly in astrocytes. Collectively, the data show that exposure to blast results in delayed and prolonged alterations in cerebrovascular reactivity that are associated with changes in the microarchitecture of the vessel wall and astrocytes. These changes may contribute to long-term pathologies involving dysfunction of the neurovascular unit, including cerebral vasospasm.

Rodent Models of Developmental Ischemic Stroke for Translational Research: Strengths and Weaknesses

Cerebral ischemia can occur at any stage in life, but clinical consequences greatly differ depending on the developmental stage of the affected brain structures. Timing of the lesion occurrence seems to be critical, as it strongly interferes with neuronal circuit development and determines the way spontaneous plasticity takes place. Translational stroke research requires the use of animal models as they represent a reliable tool to understand the pathogenic mechanisms underlying the generation, progression, and pathological consequences of a stroke. Moreover, in vivo experiments are instrumental to investigate new therapeutic strategies and the best temporal window of intervention. Differently from adults, very few models of the human developmental stroke have been characterized, and most of them have been established in rodents. The models currently used provide a better understanding of the molecular factors involved in the effects of ischemia; however, they still hold many limitations due to matching developmental stages across different species and the complexity of the human disorder that hardly can be described by segregated variables. In this review, we summarize the key factors contributing to neonatal brain vulnerability to ischemic strokes and we provide an overview of the advantages and limitations of the currently available models to recapitulate different aspects of the human developmental stroke.

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.

Monitoring biomarkers of cellular injury and death in acute brain injury

BACKGROUND

Molecular biomarkers have revolutionalized diagnosis and treatment of many diseases, such as troponin use in myocardial infarction. Urgent need for high-fidelity biomarkers in neurocritical care has resulted in numerous studies reporting potential candidate biomarkers.

METHODS

We performed an electronic literature search and systematic review of English language articles on cellular/molecular biomarkers associated with outcome and with disease-specific secondary complications in adult patients with acute ischemic stroke (AIS), intracerebral hemorrhage (ICH), subarachnoid hemorrhage (SAH), traumatic brain injury (TBI), and post-cardiac arrest hypoxic ischemic encephalopathic injuries (HIE).

RESULTS

A total of 135 articles were included. Though a wide variety of potential biomarkers have been identified, only neuron-specific enolase has been validated in large cohorts and shows 100% specificity for poor outcome prediction in HIE patients not treated with therapeutic hypothermia. There are many promising candidate blood and CSF biomarkers in SAH, AIS, ICH, and TBI, but none yet meets criteria for routine clinical use.

CONCLUSION

Current studies vary significantly in patient selection, biosample collection/processing, and biomarker measurement protocols, thereby limiting the generalizability of overall results. Future large prospective studies with standardized treatment, biosample collection, and biomarker measurement and validation protocols are necessary to identify high-fidelity biomarkers in neurocritical care.

Regulatory mechanism of endothelin receptor B in the cerebral arteries after focal cerebral ischemia

BACKGROUND AND PURPOSE

Increased expression of endothelin receptor type B (ETBR), a vasoactive receptor, has recently been implied in the reduced cerebral blood flow and exacerbated neuronal damage after ischemia-reperfusion (I/R). The study explores the regulatory mechanisms of ETBR to identify drug targets to restore normal cerebral artery contractile function as part of successful neuroprotective therapy.

METHODS

We have employed in vitro methods on human and rat cerebral arteries to study the regulatory mechanisms and the efficacy of target selective inhibitor, Mithramycin A (MitA), to block the ETBR mediated contractile properties. Later, middle cerebral artery occluded (MCAO) rats were used to substantiate the observations. Quantative PCR, immunohistochemistry, western blot and wire myograph methods were employed to study the expression and contractile properties of cerebral arteries.

RESULTS

Increased expression of specificity protein (Sp1) was observed in human and rat cerebral arteries after organ culture, strongly correlating with the ETBR upregulation. Similar observations were made in MCAO rats. Treatment with MitA, a Sp1 specific inhibitor, significantly downregulated the ETBR mRNA and protein levels. It also significantly reduced the ETBR mediated cerebrovascular contractility. Detailed analysis indicated that ERK1/2 mediated phosphorylation of Sp1 might be essential for ETBR transcription.

CONCLUSION

Transcription factor Sp1 regulates the ETBR mediated vasoconstriction in focal cerebral ischemia via MEK-ERK signaling, which is also conserved in humans. The results show that MitA can effectively be used to block ETBR mediated vasoconstriction as a supplement to an existing ischemic stroke therapy.

Targeting endothelin receptors A and B attenuates the inflammatory response and improves locomotor function following spinal cord injury in mice

After spinal cord injury (SCI), the disruption of blood-spinal cord barrier by activation of the endothelin (ET) system is a critical event leading to leukocyte infiltration, inflammatory response and oxidative stress, contributing to neurological disability. In the present study, we showed that blockade of ET receptor A (ETAR) and/or ET receptor B (ETBR) prevented early inflammatory responses directly via the inhibition of neutrophil and monocyte diapedesis and inflammatory mediator production following traumatic SCI in mice. Long-term neurological improvement, based on a series of tests of locomotor performance, occurred only in the spinal cord‑injured mice following blockade of ETAR and ETBR. We also examined the post‑traumatic changes of the micro-environment within the injured spinal cord of mice following blockade of ET receptors. Oxidative stress reflects an imbalance between malondialdehyde and superoxide dismutase in spinal cord‑injured mice treated with vehicle, whereas blockade of ETAR and ETBR reversed the oxidation state imbalance. In addition, hemeoxygenase-1, a protective protease involved in early SCI, was increased in spinal cord‑injured mice following the blockade of ETAR and ETBR, or only ETBR. Matrix metalloproteinase-9, a tissue-destructive protease involved in early damage, was decreased in the injured spinal cord of mice following blockade of ETAR, ETBR or a combination thereof. The findings of the present study therefore suggested an association between ETAR and ETBR in regulating early pathogenesis of SCI and determining the outcomes of long‑term neurological recovery.

Pathophysiology of white matter perfusion in Alzheimer's disease and vascular dementia

The pathophysiology of white matter hypoperfusion is poorly understood. Barker et al. quantify ante-mortem hypoperfusion by measuring myelin proteins differentially susceptible to ischaemia, and assess the extent to which vasoregulatory factors protect from or contribute to ischaemic white matter injury in Alzheimer’s disease and vascular dementia.

Little is known about the contributors and physiological responses to white matter hypoperfusion in the human brain. We previously showed the ratio of myelin-associated glycoprotein to proteolipid protein 1 in post-mortem human brain tissue correlates with the degree of ante-mortem ischaemia. In age-matched post-mortem cohorts of Alzheimer’s disease (n = 49), vascular dementia (n = 17) and control brains (n = 33) from the South West Dementia Brain Bank (Bristol), we have now examined the relationship between the ratio of myelin-associated glycoprotein to proteolipid protein 1 and several other proteins involved in regulating white matter vascularity and blood flow. Across the three cohorts, white matter perfusion, indicated by the ratio of myelin-associated glycoprotein to proteolipid protein 1, correlated positively with the concentration of the vasoconstrictor, endothelin 1 (P = 0.0005), and negatively with the concentration of the pro-angiogenic protein, vascular endothelial growth factor (P = 0.0015). The activity of angiotensin-converting enzyme, which catalyses production of the vasoconstrictor angiotensin II was not altered. In samples of frontal white matter from an independent (Oxford, UK) cohort of post-mortem brains (n = 74), we confirmed the significant correlations between the ratio of myelin-associated glycoprotein to proteolipid protein 1 and both endothelin 1 and vascular endothelial growth factor. We also assessed microvessel density in the Bristol (UK) samples, by measurement of factor VIII-related antigen, which we showed to correlate with immunohistochemical measurements of vessel density, and found factor VIII-related antigen levels to correlate with the level of vascular endothelial growth factor (P = 0.0487), suggesting that upregulation of vascular endothelial growth factor tends to increase vessel density in the white matter. We propose that downregulation of endothelin 1 and upregulation of vascular endothelial growth factor in the context of reduced ratio of myelin-associated glycoprotein to proteolipid protein 1 are likely to be protective physiological responses to reduced white matter perfusion. Further analysis of the Bristol cohort showed that endothelin 1 was reduced in the white matter in Alzheimer’s disease (P < 0.05) compared with control subjects, but not in vascular dementia, in which endothelin 1 tended to be elevated, perhaps reflecting abnormal regulation of white matter perfusion in vascular dementia. Our findings demonstrate the potential of post-mortem measurement of myelin proteins and mediators of vascular function, to assess physiological and pathological processes involved in the regulation of cerebral perfusion in Alzheimer’s disease and vascular dementia.

Smooth muscle cell phenotypic switching in stroke

Disruption of cerebral blood flow after stroke induces cerebral tissue injury through multiple mechanisms that are not yet fully understood. Smooth muscle cells (SMCs) in blood vessel walls play a key role in cerebral blood flow control. Cerebral ischemia triggers these cells to switch to a phenotype that will be either detrimental or beneficial to brain repair. Moreover, SMC can be primarily affected genetically or by toxic metabolic molecules. After stroke, this pathological phenotype has an impact on the incidence, pattern, severity, and outcome of the cerebral ischemic disease. Although little research has been conducted on the pathological role and molecular mechanisms of SMC in cerebrovascular ischemic diseases, some therapeutic targets have already been identified and could be considered for further pharmacological development. We examine these different aspects in this review.

Status epilepticus induces vasogenic edema via tumor necrosis factor-α/ endothelin-1-mediated two different pathways

Status epilepticus (SE) induces vasogenic edema in the piriform cortex with disruptions of the blood-brain barrier (BBB). However, the mechanisms of vasogenic edema formation following SE are still unknown. Here we investigated the endothelin B (ET_B) receptor-mediated pathway of SE-induced vasogenic edema. Following SE, the release of tumor necrosis factor-α (TNF-α) stimulated endothelin-1 (ET-1) release and expression in neurons and endothelial cells. In addition, TNF-α-induced ET-1 increased BBB permeability via ET_B receptor-mediated endothelial nitric oxide synthase (eNOS) activation in endothelial cells. ET_B receptor activation also increased intracellular reactive oxygen species by NADPH oxidase production in astrocytes. These findings suggest that SE results in BBB dysfunctions via endothelial-astroglial interactions through the TNF-α-ET-1-eNOS/NADPH oxidase pathway, and that these ET_B receptor-mediated interactions may be an effective therapeutic strategy for vasogenic edema in various neurological diseases.

Electrophysiological effects of bosentan in rats with induced cerebral ischemia-reperfusion

We examined the effect of bosentan, an ETA and ETB receptor antagonist, on EEG, an indicator of neuronal activity, in rats with experimentally induced cerebral ischemia-reperfusion. The rats were divided into three groups with seven rats in each group. Before the procedures, the EEGs of all rats were recorded for ten minutes. 30 mg/kg bosentan in 2 cc physiological serum was administered to the first group, and the second and third groups were injected with 2 cc physiological serum intraperitoneally. After the administration, the right and the left common carotid arteries of the animals in Groups 1 and 2 were clipped for 10 minutes using aneurysm clippings. The rats in the third group received only a subcutaneous incision. Ten minutes after the clips were removed in the first and second groups and after the incision in the third group, EEG recordings were repeated for 10 minutes. All the rats were decapitated and MDA values in the brain tissue were measured for evaluation of the efficiency of induced cerebral ischemia. Induced cerebral ischemia was performed effectively because the MDA levels in Groups 1 and 2 were elevated, compared to the levels in Group 3 (p<0.05). After the application of the Cerebral Ischemia-Reperfusion Technique, the EEG showed minimal slowing in the rats in Group 1, and generalized diffuse slowing in the rats in Group 2 compared to pre-ischemic findings. Bosentan may reduce the damage induced by ischemia on neuronal electrophysiology, likely through its vasodilation effect on cerebral vessels.

Permanent distal occlusion of middle cerebral artery in rat causes local increased ETB, 5-HT₁B and AT₁ receptor-mediated contractility downstream of occlusion

BACKGROUND/AIMS

In response to experimental stroke, a characteristic functional and expressional upregulation of contractile G-protein-coupled receptors has been uncovered in the affected cerebral vasculature; however, the mechanism initiating this phenomenon remains unknown.

METHODS

Using a model of permanent distal occlusion of rat middle cerebral arteries, we investigated whether there was a regional difference in receptor-mediated contractility of segments located upstream and downstream of the occlusion site. The contractile response to endothelin, angiotensin and 5-hydroxytryptamine receptor stimulation was studied by sensitive wire myograph.

RESULTS

Only downstream segments exhibited an augmented contractile response to stimulation with each of the three ligands, with the response towards sarafotoxin 6c being especially augmented compared to sham, upstream and contralateral controls. This functional increase did not seem to relate to ischemic tissue damage, inflammatory cell infiltration or the element of reperfusion. Interestingly, immunohistochemistry did not show any difference in the level of immunoreactivity towards endothelin B (ETB) receptors between groups.

CONCLUSION

Single artery occlusion without significant visible infarct resulted in locally increased ETB, angiotensin type 1 and 5-hydroxytryptamine 1B receptor-mediated contractile responses only in segments located downstream of the occlusion site. This suggests lack of wall stress as an initiating trigger leading to regulation of contractile response after cerebral stroke.

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.

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.

Increased circulating endothelial progenitor cells in patients with haemorrhagic and ischaemic stroke: the role of endothelin-1

Ischaemic stroke induces endothelial progenitor cell (EPC) mobilisation from bone marrow into peripheral blood. Circulating EPCs play an important role in post-injury regeneration of vasculature, whereas endothelial cells (ECs) have been shown to reflect endothelial damage and may be responsible for increased Endothelin-1 (ET-1) expression. We investigated herein the association between numbers of circulating ECs and EPCs, the levels of soluble factors regulating their migration and function, and the clinical outcome in patients with haemorrhagic (HS) or ischaemic stroke (IS). Sixteen patients with HS and eighteen with IS were assessed during the first 24h, day 3, and day 7 after stroke and compared them with twenty-three control subjects. We found elevated EPC and EC concentrations using flow cytometry and increase in VEGF, SDF-1, HGF, and ET-1 plasma levels by ELISA in the HS patients, while ET-1 mRNA expression in peripheral blood cells was elevated in the IS patients. Significant correlations were observed between EPCs or ECs and Big ET-1 protein or mRNA levels in HS but not in the IS patients. We suggest that ET-1 may play a role in pathophysiology of stroke and subsequent EPC mobilisation; however, further studies aimed at the precise elucidation of this issue are required.

The CSF concentration of ADMA, but not of ET-1, is correlated with the occurrence and severity of cerebral vasospasm after subarachnoid hemorrhage

Under physiological conditions, vasoconstrictors and vasodilators are counterbalanced. After aneurysmal subarachnoid hemorrhage (SAH) disturbance of this equilibrium may evoke delayed cerebral vasospasm (CVS) leading to delayed cerebral ischemia (DCI). Most studies examined either the vasoconstrictor endothelin-1 (ET-1) or the vasodilative pathway of nitric oxide (NO) and did not include investigations regarding the relationship between vasospasm and ischemia. Asymmetric dimethyl-L-arginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), decreases the concentration of NO. Studies have correlated increasing concentrations of ADMA with the course and degree of CVS after SAH. We sought to determine, if ADMA and endothelin-1 (ET-1) are associated with CVS and/or DCI after SAH. CSF concentrations of ADMA and ET-1 were retrospectively determined in 30 patients after SAH and in controls. CVS was detected clinically and by arteriogaphy. DCI was monitored by follow-up CT scans. 17 patients developed arteriographic CVS and 4 patients developed DCI. ADMA but not ET-1 concentrations were correlated with occurrence and degree of CVS. However, ET-1 concentrations were correlated with WFNS grade on admission. Neither ADMA nor ET-1 correlated with DCI in this cohort. ET-1 concentrations seem to be associated with the impact of the SAH bleed. ADMA may be directly involved in the development and resolution of CVS after SAH via inhibition of NOS disturbing the balance of vasodilative and -constrictive components.

Cytokines and growth factors modify the upregulation of contractile endothelin ET(A) and ET(B) receptors in rat cerebral arteries after organ culture

AIM

Experimental cerebral ischaemia and organ culture of cerebral arteries induce an increased endothelin ET(B) receptor-mediated contraction. The aim of this study was to examine whether cytokines and growth factors, known to be activated in ischaemia, can influence the expression and function of endothelin receptors after organ culture.

METHODS

Rat middle cerebral arteries were cultured for 24 h at 37 °C in humidified 5% CO(2) and air in culture medium alone, or with tumour necrosis factor-α (TNF-α), interleukin-1β (IL-1β), platelet-derived growth factor (PDGF), epidermal growth factor (EGF) or basic fibroblast growth factor (bFGF). Concentration-response curves were obtained for sarafotoxin 6c (ET(B) receptor agonist) and endothelin-1 (here ET(A) receptor agonist, because of ET(B) receptor desensitization). The receptor mRNA expression was examined by real-time PCR and the protein expression by immunohistochemistry and Western blot.

RESULTS

Tumour necrosis factor-α (100 ng mL(-1) ) and EGF (20 ng mL(-1) ) potentiated the ET(B) receptor-mediated contraction (increase in pEC(50) without change in E(max) ). bFGF (10 ng mL(-1) ) and IL-1β (10 ng mL(-1) ) induced an enhanced ET(A) receptor-mediated contraction. bFGF (10 ng mL(-1) ) significantly increased the ET(B) mRNA level, and EGF (20 ng mL(-1) ) increased the ET(A) receptor protein. Increased ET(B) receptor mRNA and protein level also were observed after treatment with IL-1β (10 ng mL(-1) ).

CONCLUSION

This study shows that TNF-α, IL-1β, EGF and bFGF can modify the expression and function of endothelin receptors during organ culture. Because there is similar receptor upregulation in experimental stroke, the effect of cytokines and growth factors on endothelin receptor upregulation is an interesting aspect to study in vivo.

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.

The effect of endothelin receptor A antagonism on basilar artery endothelium-dependent relaxation after ischemic stroke

AIMS

Endothelin (ET) receptor A antagonism decreases neuronal damage in experimental models of stroke. Since large arteries like basilar artery contribute significantly to total cerebrovascular resistance and are major determinants of microvascular pressure, dysregulation of basilar artery function may worsen stroke injury. ET-1 is involved in the regulation of basilar constriction. However, whether stroke influences vasoreactivity of basilar artery and to what extent ET-1 contributes to basilar vascular dysfunction after stroke remained unknown. The goal of this study was to test the hypothesis that ET-1 impairs basilar artery vasorelaxation after ischemia/reperfusion (I/R) injury via activation of ET(A) receptor.

MAIN METHODS

Male Wistar rats were subjected to 3h middle cerebral artery occlusion (MCAO) and 21 h reperfusion. One group received ET(A) receptor antagonist atrasentan (5 mg/kg, i.p.) at reperfusion. At 24h, basilar arteries were isolated from control non-stroked, stroked and stroked+atrasentan-treated animals for vascular reactivity measurements using pressurized arteriograph.

KEY FINDINGS

Acetylcholine (Ach)-induced maximum relaxation (R(max)) was decreased in stroked animals as compared to non-stroked group and ET(A) antagonism partially restored it. There was also a trend for decreased EC(50) value for the antagonist treatment group indicating improved Ach sensitivity.

SIGNIFICANCE

These findings suggest that I/R not only affects vessels distal to the occlusion but also impairs relaxation of proximal large vessels. ET-1-mediated basilar artery dysfunction may contribute to neurovascular damage after stroke and early restoration of vascular function by ET receptor antagonism after I/R injury may offer a therapeutic strategy.

Brain endothelial barrier passage by monocytes is controlled by the endothelin system

Homeostasis of the brain is dependent on the blood-brain barrier (BBB). This barrier tightly regulates the exchange of essential nutrients and limits the free flow of immune cells into the CNS. Perturbations of BBB function and the loss of its immune quiescence are hallmarks of a variety of brain diseases, including multiple sclerosis (MS), vascular dementia, and stroke. In particular, diapedesis of monocytes and subsequent trafficking of monocyte-derived macrophages into the brain are key mediators of demyelination and axonal damage in MS. Endothelin-1 (ET-1) is considered as a potent pro-inflammatory peptide and has been implicated in the development of cardiovascular diseases. Here, we studied the role of different components of the endothelin system, i.e., ET-1, its type B receptor (ET(B)) and endothelin-converting enzyme-1 (ECE-1) in monocyte diapedesis of a human brain endothelial cell barrier. Our pharmacological inhibitory and specific gene knockdown studies point to a regulatory function of these proteins in transendothelial passage of monocytes. Results from this study suggest that the endothelin system is a putative target within the brain for anti-inflammatory treatment in neurological diseases.

Vascular plasticity in cerebrovascular disorders

Cerebral ischemia remains a major cause of morbidity and mortality with little advancement in subacute treatment options. This review aims to cover and discuss novel insight obtained during the last decade into plastic changes in the vasoconstrictor receptor profiles of cerebral arteries and microvessels that takes place after different types of stroke. Receptors like the endothelin type B, angiotensin type 1, and 5-hydroxytryptamine type 1B/1D receptors are upregulated in the smooth muscle layer of cerebral arteries after different types of ischemic stroke as well as after subarachnoid hemorrhage, yielding rather dramatic changes in the contractility of the vessels. Some of the signal transduction processes mediating this receptor upregulation have been elucidated. In particular the extracellular regulated kinase 1/2 pathway, which is activated early in the process, has proven to be a promising therapeutic target for prevention of vasoconstrictor receptor upregulation after stroke. Together, those findings provide new perspectives on the pathophysiology of ischemic stroke and point toward a novel way of reducing vasoconstriction, neuronal cell death, and thus neurologic deficits after stroke.

Association between homocysteine and endothelial dysfunction markers in stroke disease

BACKGROUND

Evidence shows that there is an increase in concentrations of markers of endothelial dysfunction immediately following acute ischaemic stroke. Several studies suggest that endothelial dysfunction may be partly caused by oxidation related to the effects of raised total plasma homocysteine.

OBJECTIVE

The aim of this study was to measure changes in total plasma homocysteine and markers of endothelial dysfunction in stroke disease within a known period of time post infarct.

SUBJECTS AND METHODS

We studied 40 acute ischaemic stroke patients (mean age +/- SD, 50.2 +/- 9.5 years) and 42 hospitalised non-stroke patients (mean age, 44.3 +/- 14.9 years). Fasting venous blood was obtained within 24 h, 3 days and 7 days after the stroke onset and hospitalisation for non-stroke patients for measurements of total plasma homocysteine, markers of endothelial dysfunction including intracellular adhesion molecule (i-CAM), vascular cell adhesion molecule-1 (v-CAM) and leukocyte adhesion molecule-1 (E-selectin) and C-reactive proteins (CRPs).

RESULTS

We found no significant differences in baseline total plasma homocysteine, E-selectin, v-CAM, vitamin B(12), and folate concentrations between ischaemic stroke patients and non-stroke controls. i-CAM concentrations were significantly higher and CRPs non-significantly lower at baseline in stroke patients compared with controls. Although all endothelial dysfunction markers increased significantly during the study period, the rise in E-selectin levels was less than that seen in i-CAM, and v-CAM. Total plasma homocysteine concentrations showed positive correlations with creatinine (r = 0.537; P < 0.02), and inverse correlations with both vitamin B(12) (r = -0.560; P < 0.001) and folate (r = -0.469; P < 0.002); however, there were no significant correlations between total plasma homocysteine or B-vitamins and markers of endothelial dysfunction in ischaemic stroke patients or controls.

CONCLUSIONS

We found evidence of an increase in markers of endothelial dysfunction following acute ischaemic stroke but this had no relationship with total plasma homocysteine concentrations.

Involvement of calcium-calmodulin-dependent protein kinase II in endothelin receptor expression in rat cerebral arteries

Experimental cerebral ischemia and organ culture of cerebral arteries result in the enhanced expression of endothelin ET(B) receptors in smooth muscle cells via increased transcription. The present study was designed to evaluate the involvement of calcium-calmodulin-dependent protein kinase (CAMK) in the transcriptional expression of endothelin receptors after organ culture. Rat basilar arteries were incubated for 24 h with or without the CAMK inhibitor KN93 or ERK1/2 inhibitor U0126. The contractile responses to endothelin-1 (ET-1; ET(A) and ET(B) receptor agonist) and sarafotoxin 6c (S6c; ET(B) receptor agonist) were studied using a sensitive myograph. The mRNA levels of the ET(A) and ET(B) receptors and CAMKII were determined by real-time PCR, and their protein levels were evaluated by immunohistochemistry and Western blot. The mRNA levels of CAMKII and the ET(B) receptor increased during organ culture, but there was no change in the expression of the ET(A) receptor. This effect was abolished by coincubation with KN93 or U0126. In functional studies, both inhibitors attenuated the S6c-induced contraction. Incubating the arteries with KN93, but not U0126, decreased the amount of phosphorylated CAMKII. The inhibitors had no effect on the levels of myosin light chain during organ culture, as measured by Western blot. CAMKII is involved in the upregulation of the endothelin ET(B) receptor and interacts with the ERK1/2 pathway to enhance receptor expression. CAMKII has no effect on the contractile apparatus in rat cerebral arteries.

Relation of candidate genes that encode for endothelial function to migraine and stroke: the Stroke Prevention in Young Women study

BACKGROUND AND PURPOSE

Migraine with aura is a risk factor for ischemic stroke, but the mechanism by which these disorders are associated remains unclear. Both disorders exhibit familial clustering, which may imply a genetic influence on migraine and stroke risk. Genes encoding for endothelial function are promising candidate genes for migraine and stroke susceptibility because of the importance of endothelial function in regulating vascular tone and cerebral blood flow.

METHODS

Using data from the Stroke Prevention in Young Women study, a population-based case-control study including 297 women aged 15 to 49 years with ischemic stroke and 422 women without stroke, we evaluated whether polymorphisms in genes regulating endothelial function, including endothelin-1 (EDN), endothelin receptor type B (EDNRB), and nitric oxide synthase-3 (NOS3), confer susceptibility to migraine and stroke.

RESULTS

EDN SNP rs1800542 and rs10478723 were associated with increased stroke susceptibility in whites (OR, 2.1; 95% CI, 1.1-4.2 and OR, 2.2; 95% CI, 1.1-4.4; P=0.02 and 0.02, respectively), as were EDNRB SNP rs4885493 and rs10507875, (OR, 1.7; 95% CI, 1.1-2.7 and OR, 2.4; 95% CI, 1.4-4.3; P=0.01 and 0.002, respectively). Only 1 of the tested SNP (NOS3 rs3918166) was associated with both migraine and stroke.

CONCLUSIONS

In our study population, variants in EDN and EDNRB were associated with stroke susceptibility in white but not in black women. We found no evidence that these genes mediate the association between migraine and stroke.

Endothelial endothelin-1 over-expression using receptor tyrosine kinase tie-1 promoter leads to more severe vascular permeability and blood brain barrier breakdown after transient middle cerebral artery occlusion

Endothelin-1 (ET-1) is up-regulated in the endothelial cells and astrocytes under ischemia. Transgenic mice with astrocytic ET-1 over-expression (GET-1) showed more severe neurological deficit and larger infarct after transient middle cerebral artery occlusion (MCAO). Here, the significance of endothelial ET-1 in ischemic brain injury was investigated using transgenic mice with the endothelial ET-1 over-expression (TET-1). Increased ET-1 level was observed in the TET-1 brain infarct core after transient MCAO. ET(A) receptor expression was induced in the penumbra and ET(A) antagonist (A-147627) partially normalized the infarct volume and neurological deficit. In the infarct core of TET-1 brain, superoxide, nitrotyrosine, and gp91(phox) levels were increased. TET-1 brain displayed increased matrix metalloproteinase-2 expression, water content, immunoglobulin leakage and decreased occludin level in the ipsilateral hemisphere indicative of BBB breakdown and hemispheric edema. Interestingly, AQP-4 expression was increased in the penumbra of TET-1 brain following transient MCAO leading to the water accumulation. Taken together, endothelial ET-1 over-expression and ETA receptor activation contributes to the increased oxidative stress, water accumulation and BBB breakdown after transient MCAO leading to more severe neurological deficit and increased infarct.

Endothelin 1 protects HN33 cells from serum deprivation-induced neuronal apoptosis through Ca(2+)-PKCalpha-ERK pathway

Endothelins (ETs), which were originally found to be potent vasoactive transmitters, were known to be implicated in nervous system, but the mode of mechanism remains unclear. ETs (ET-1, ET-2, and ET-3) were added to HN33 (mouse hippocampal neuron chi neuroblastoma) cells. Among the three types of ET, only ET-1 increased the intracellular calcium levels in a PLC dependent manner with the induction of ERK 1/2 activation. As the result of ET-1 exposure, the survival rate of HN33 cells and the PKCalpha translocation into the plasma membrane were increased. We suggest that ET-1 participated in the neuroprotective effect involving the calcium-PKCalpha-ERK1/2 pathway.

Antagonism of endothelin action normalizes altered levels of VEGF and its signaling in the brain of stroke-prone spontaneously hypertensive rat

Stroke-prone spontaneously hypertensive rats (SHRSP) often suffer from spontaneous stroke, in part, due to abnormalities in the cerebrovasculature. Here, we investigate the profile of key angiogenic factors and their basic signaling molecules in the brain of SHRSP during the age-dependent stages of hypertension. The profile of VEGF and its receptor, Flk-1, was dependent on age and stage of hypertension (i.e., down regulated at pre-hypertensive and malignant hypertensive stages, but up regulated at typical hypertensive stage), while that of its downstream components, pAkt and eNOS, were down regulated in a time-dependent manner in the frontal cortex of SHRSP compared to age-matched genetic control, normotensive WKY rats. On the other hand, the expression of endothelin-1 and its type A receptor (endothelin ETA receptor) were up regulated, depending on age and stage of hypertension. In contrast, levels of endothelin type B receptor were down regulated. The regional cerebral blood flow decreased during the development of malignant hypertension. Thus, subsequent experiments were designed to investigate whether endothelin-1 receptor antagonism, using endothelin-A/-B dual receptor antagonist SB209670, could normalize the molecular profile of these factors in SHRSP brain. Interestingly, blockage of endothelin-1 receptor restored to normal, levels of cerebral endothelin-1, endothelin ETA receptor and endothelin ETB receptor; VEGF and Flk-1; endothelial nitric oxide synthase (eNOS) and pAkt, in SHRSP, compared to age-matched WKY. Endothelin receptor blocker might be important to prevent the progression in the defect in VEGF and its angiogenic signaling cascade in the pathogenesis of hypertension-induced vascular remodeling in frontal cortex of SHRSP rats.

Biphasic elevation in cerebrospinal fluid and plasma concentrations of endothelin 1 after traumatic brain injury in human patients

Severe traumatic brain injury (TBI) is characterized by a high mortality and poor outcome. The pathomechanisms involved are cytokine-mediated proinflammatory and anti-inflammatory reactions and significant cerebral microcirculatory disorders. The role of endothelin 1 (ET-1), a very potent vasoconstrictive peptide, in the deterioration of cerebral perfusion after trauma is still unclear. The presented study investigated the changes in ET-1 in the cerebrospinal fluid (CSF) and plasma after TBI in humans, with special regard to the presence of subarachnoid hemorrhage (SAH) and clinical outcome. Twenty patients with TBI were consecutively enrolled into the study, 10 patients without SAH (TBI group) and 10 patients with SAH (TBI-H group). Paired samples of plasma and CSF were collected for 10 days after trauma. Analysis of the ET-1 concentrations showed that TBI is associated with initially increased ET-1 values in plasma (TBI, day 1; TBI-H, days 2-3) and significantly increased (P < 0.05, vs. control) CSF concentrations (TBI, days 1-2; TBI-H, days 1-3) in the first days after trauma. In the further time course, ET-1 values declined in both groups, reaching reference values in plasma. The CSF values remained significantly (P < 0.05 vs. control) elevated. Both groups showed a second peak on the beginning of the second week after trauma in plasma and CSF. Whereas plasma concentrations failed to reach significance, CSF values showed a significant peak on day 7 in both groups. The TBI-H patients had significantly (P < 0.05) higher values in the secondary peak compared with patients of the TBI group. The kinetics of traumatic SAH-dependent ET-1 needs to be assessed in further investigations.

Calponin phosphorylation in cerebral cortex microvessels mediates sustained vasoconstriction after brain trauma

OBJECTIVES

The purpose of this study was to determine the molecular and biochemical changes in the contractile protein, calponin (Cp), which temporally coincide with a previously reported state of sustained contractility following traumatic brain injury (TBI).

METHODS

Double immunofluorescence, western analysis and two-dimensional non-equilibrium pH gradient gel electrophoresis (NEPHGE)/SDS-PAGE techniques were utilized to determine both the location and extent of Cp within smooth muscle cells (SM) and the phosphorylation state of Cp following TBI, as induced using a weight drop acceleration impact model.

RESULTS

Double immunofluorescence for Cp and SM indicate that following injury, Cp migrates from the cytosol to a location subjacent to the SM membrane. Western analysis revealed a significant increase in Cp protein expression following injury that was maintained up to 48 hours post-injury. Combined Western analysis and NEPHGE indicated that Cp is phosphorylated following TBI.

DISCUSSION

Cp migration and phosphorylation may underlie the mechanism for increased vasoreactivity leading to hypoperfusion following TBI.

Effect of chronic ethanol consumption on endothelin-1 generation and conversion of exogenous big-endothelin-1 by the rat carotid artery

The purpose of the present work was to investigate whether conversion of exogenous applied big-endothelin-1 (Big-ET-1) as well as the basal release and mRNA levels of endothelin-1 (ET-1) is altered by ethanol consumption in the rat carotid. The measurement of the contraction induced by Big-ET-1 served as an indicative of functional endothelin (ET)-converting enzyme (ECE) activity. Cumulative application of exogenous Big-ET-1 elicited a concentration-related contraction with the concentration-response curve shifted to the right when compared to ET-1. In endothelium-intact rings, phosphoramidon (1 mmol/l), a nonselective ECE/neutral endopeptidase (NEP) inhibitor, produced a rightward displacement of the concentration-response curves and reduced the maximal contractile response to Big-ET-1. However, in endothelium-denuded rings phosphoramidon reduced the maximum contraction for Big-ET-1 but did not alter the potency when compared to the curves obtained in the absence of the inhibitor. Ethanol consumption for 2, 6, or 10 weeks reduced the contractile effect elicited by Big-ET-1 in carotid rings with intact endothelium when compared to control or isocaloric rings. However, no differences on Big-ET-1-induced contraction were observed after endothelial denudation. On the other hand, ethanol consumption increased ET-1-induced contraction. Finally, chronic ethanol consumption did not alter either the mRNA levels for pre-pro-ET-1 nor the basal release of ET-1. The present findings show that chronic ethanol consumption does not alter the mRNA levels for ET-1 or its basal release in the rat carotid. Moreover, ethanol intake reduces the contraction induced by exogenously applied Big-ET-1 in carotid rings with intact endothelium, a fact that might be the result of a reduced conversion of this peptide by ECE on its mature active peptide ET-1.

MEK1/2 inhibition attenuates vascular ETA and ETB receptor alterations after cerebral ischaemia

Cerebral ischaemia is associated with elevated levels of endothelin B (ETB) receptors in the ipsilateral middle cerebral artery (MCA). This up-regulation of ET receptors occurs via de novo transcription involving mitogen-activated protein kinases (MAPK). The aim of this study was to examine the effect of inhibition of the MAP kinase/ERK kinase (MEK)1/2 on ET receptor alteration, brain damage, and neurology in experimental cerebral ischaemia. Transient middle cerebral artery occlusion (MCAO) was induced in male Wistar rats by the intraluminal filament technique. The animals received 100 mg/kg intraperitoneally of the MEK1/2 inhibitor U0126 or vehicle in conjunction with the occlusion. After 24 h, the rats were decapitated and the brains removed. The middle cerebral arteries were dissected out and examined with myographs or immunohistochemistry. The ischaemic areas of the brains were compared. After the MCAO, the contractile responses of the ETA and ETB receptors were augmented in the ipsilateral MCA. U0126 decreased this alteration in ET receptor response. Furthermore, treatment with U0126 significantly decreased the brain damage and improved neurological scores. Immunohistochemistry showed that there were lower protein levels of phosphorylated extracellular signal-regulated kinases (ERK)1/2 and phosphorylated transcription factor Elk-1 in the U0126-treated rats compared to control. The results show that treatment with the MEK1/2 inhibitor U0126 in ischaemic stroke decreases brain damage, neurological symptoms, and ET receptor alteration. The vascular effects of U0126 provide new perspective on possible mechanisms of actions of MAPK inhibition in cerebral ischaemia.

Involvement of protein kinases on the upregulation of endothelin receptors in rat basilar and mesenteric arteries

Endothelin(B) (ET(B)) receptors are upregulated in experimental stroke or after 24 hrs of organ culture. This upregulation is manifested both as stronger contraction and as an increase in ET(B) receptor messenger RNA (mRNA) levels. The present study was designed to evaluate the importance of protein kinases (c-Jun N-terminal kinase [JNK], protein kinase C [PKC], and extracellular signal-regulated kinase [ERK1/2]) in ET(B) receptor upregulation after organ culture. Rat basilar and mesenteric arteries were incubated for 24 hrs in Dulbecco's modified Eagle's medium (DMEM) with or without the PKC inhibitor, RO-31-7549; the ERK1/2 inhibitor, SB386023; or the JNK inhibitor, SP600125, added 3, 6, or 12 hrs after initiation of incubation. Subsequently, vessel segments were mounted in myographs and the contractile responses to ET-1 and sarafotoxin 6c were studied. The ET(B) and ET(A) receptor mRNA levels were determined with a real-time polymerase chain reaction (PCR). The cellular localization and protein level of ET(B) receptors were evaluated by immunohistochemistry. The PKC and ERK1/2 inhibitors attenuated the contraction induced by S6c in the basilar arteries more than in the mesenteric arteries. The efficiency of the inhibitors was proportional to the incubation time. Real-time PCR showed a decrease in the ET(B) receptor mRNA levels in arteries treated with PKC or ERK inhibitors. The JNK inhibitor had a significant inhibitory effect on ET(B) receptor upregulation in the basilar arteries. Immunohistochemistry revealed that the ET(B) receptor upregulation occured in the smooth-muscle cells and that it had the same pattern as in the quantitative PCR. Our results show that the PKC, ERK1/2, and JNK are more important for the upregulation of contractile ET(B) receptors in cerebral arteries compared with mesenteric arteries. ERK1/2 seems to be more important for the ET(B) receptor upregulation, as compared with PKC and JNK. The evaluation of the time dependency suggests that the phenomenon can be reversed even after its initiation.

Obstructive sleep apnea: Plasma endothelin-1 precursor but not endothelin-1 levels are elevated and decline with nasal continuous positive airway pressure

Assessment of plasma endothelin-1 (ET-1) reveals conflicting results in cerebral and noncerebral conditions. Obstructive sleep apnea (OSA) syndrome has been used as a definite challenge for the investigation of endothelin measurements. Despite marked sleep-related breathing disturbances in untreated patients peripherally measurable ET-1 concentrations remained within the normal range and did not change after an appropriate therapy with continuous positive airway pressure (CPAP). In contrast, its precursor, big ET-1, was considerably elevated in untreated patients and dropped to normal values after long-term CPAP depending on compliance. Relatively stable big ET-1 elevations in untreated patients, during sleep and wakefulness, suggest that a general endothelial alteration beyond that explained by a direct impact of nocturnal breathing disturbances on the vascular system occurs. CPAP-therapy effectively lowered plasma big ET-1 in compliant patients and thus possibly their related risk for vascular diseases. Big ET-1 has been demonstrated to be a more appropriate marker of endothelial alteration than ET-1 because of its longer half-life. Simultaneous measurements are to be recommended.

Expression of endothelin-1 in the brain and lung of rats exposed to permanent hypobaric hypoxia

High-altitude hypoxia causes pulmonary hypertension in humans and animals. Endothelin-1 (ET-1) is a novel and long-lasting vasoconstrictor. However, no study has dealt with the effects of a hypobaric hypoxic environment (HHE) on ET-1 activity in the brain. We examined 134 male rats permanently exposed to the equivalent of 5500 m altitude for 1 to 8 weeks. In these HHE rats, the mean pulmonary arterial pressure was significantly raised. The level of ET-1 protein, measured by enzyme immunoassay, increased rapidly in the lungs on exposure to HHE, but decreased in the brain. The level of ET-1 mRNA, measured by semiquantitative RT-PCR, was raised at 1, 4, and 6 weeks' exposure in the lungs and at 4 or more weeks' exposure in 3 of 8 brain regions. By in situ hybridization and immunohistochemistry of brain sections, ET-1 mRNA and protein were detected in the endothelial cells, neurons, and astrocyte-like cells in control rats. In HHE rats, the immunoreactive intensity for ET-1 protein decreased rapidly with time in these cells within the brain, although a few weakly ET-1 protein-positive cells were detected until 8 weeks' exposure to HHE. Only a few weakly ET-1 mRNA-positive endothelial cells were detected in any HHE rats. Although the reactivity for ET-1 mRNA had decreased significantly in neurons and astrocyte-like cells at 1 and 2 weeks' exposure to HHE, it was again strong in both types of cells at 4 weeks' exposure to HHE. These results raise the possibility that during exposure to HHE, ET-1 production in the lung may play a role in the development of pulmonary hypertension, while a decrease in ET-1 production within the brain may help to protect neurons by preventing or limiting the constriction of cerebral microvessels during the hypoxia induced by HHE.

Endothelin-mediated induction of heme oxygenase-1 in the spinal cord is attenuated in transgenic mice overexpressing superoxide dismutase

Spinal cord blood flow and the induction of heme oxygenase-1 (HO-1), an indicator of oxidative stress, were studied in the spinal cords of adult wild-type and transgenic mice overexpressing the antioxidant copper, zinc superoxide dismutase (CuZn SOD) after intrathecal administration of the potent vasoactive peptide endothelin-1 (ET-1). Gelfoam, saturated with ET-1 (40, 80, or 400 micromol/L), was positioned in the intrathecal space at the midthoracic level in anesthetized animals. Blood flow was continuously monitored by laser Doppler for 10 min after the intrathecal application of ET-1. There was a significant reduction in spinal cord blood flow to approximately 40% of control values by 10 min after the intrathecal application of the peptide in both wild-type and transgenic mice. Moreover, SB209670, a nonselective endothelin receptor antagonist, blocked this reduction in flow. Each animal was euthanized 24 h after the intrathecal administration of ET-1, and the spinal cord was prepared for quantitative immunocytochemistry. HO-1 was primarily induced in astrocytes near the dorsal surface of the spinal cord in wild-type mice. This induction was attenuated in both wild-type, treated with SB209670, and untreated transgenic mice. Together, these findings suggest that ET-1 mediates oxidative stress in the spinal cord through the modulation of spinal cord blood flow.