Does endothelin-1 play a role in the pathogenesis of cerebral vasospasm?

Successful Fluid Management in Respiratory Failure due to Clazosentan Following a Cerebral Aneurysm Clipping: A Case Report

Clazosentan, a potent selective endothelin receptor subtype A antagonist, has been demonstrated to be effective in preventing cerebral vasospasms after subarachnoid hemorrhage. We report the successful management of respiratory failure due to pulmonary edema associated with clazosentan, with a hemodynamic monitoring system. A 49-year-old Japanese man underwent emergency clipping for a right internal carotid-posterior communicating artery aneurysm. The surgery and general anesthesia for the rupture proceeded with no complications. Clazosentan was administered from postoperative day 1 to prevent cerebral vasospasm. He presented with respiratory failure six days post surgery and chest X-ray imaging showed pulmonary edema. In our intensive care unit, the patient's N-terminal pro-brain natriuretic peptide was 476 pg/mL although trans-thoracic echography indicated a normal left ventricular ejection fraction (>60%) and normal diastolic function. The hemodynamic monitoring system showed 11 L/minute cardiac output and a cardiac index of 5.6 L/minute/m2. We thus diagnosed the cause of the patient's respiratory failure as due to excessive volume, as an adverse event of clazosentan. We changed the cerebral vasospasm-preventive drug to fasudil hydrochloride hydrate and forced urination. His body weight dropped approximately 9 kg as of day 9 in the ICU and he was weaned off the ventilator 23 days post surgery. This case indicates the importance of optimal infusion in patients with clazosentan. Optimal fluid management using a hemodynamic monitoring system could be useful for clazosentan-induced respiratory failure.

Initial real-world experience of clazosentan for subarachnoid hemorrhage in Japan

BACKGROUND

Cerebral vasospasm (CVS) is one of the most critical factors associated with clinical outcomes of patients with subarachnoid hemorrhage (SAH). Clazosentan has been investigated worldwide as a prophylactic agent to prevent CVS. We evaluated a new CVS management protocol which included clazosentan.

METHODS

Consecutive 138 patients with SAH, hospitalized in our institution between January 2017 and December 2022, were included in this study. Baseline characteristics, clinical findings, and operative records were analyzed retrospectively. From May 2022, 10 mg/h clazosentan was co-administered with fasudil to all patients according to the indication in the Japanese label. Patients admitted before this date received the conventional combined protocol using the fasudil hydrochloride, nicardipine, and ozagrel.

RESULTS

Eighteen (13.0%) patients received the new protocol during the CVS period (defined as day 1 up to day 14 after SAH onset). There were 54 (39.1%) elderly patients aged 75 years or older. Seventy-two (52.2%) patients underwent neurosurgical clipping, whereas 55 (39.9%) patients received endovascular coiling. Among the patients with new protocol, only one patient (5.6%) had symptomatic CVS, compared with 18 patients (15.0%) in those with conventional protocol. More patients who received the new protocol had fluid retention compared with control group (38.9% [7/18] vs. 8.3% [10/120]). Other results did not differ between the two groups.

CONCLUSIONS

Clinical outcomes of the new protocol were comparable to those of conventional protocol. Clazosentan may simplify anti-vasospasm treatment. Fluid retention was a specific side-effect of clazosentan, which requires attention especially in the first half of the CVS period.

A machine learning-derived gene signature for assessing rupture risk and circulatory immunopathologic landscape in patients with intracranial aneurysms

Background

Intracranial aneurysm (IA) is an uncommon but severe subtype of cerebrovascular disease, with high mortality after aneurysm rupture. Current risk assessments are mainly based on clinical and imaging data. This study aimed to develop a molecular assay tool for optimizing the IA risk monitoring system.

Methods

Peripheral blood gene expression datasets obtained from the Gene Expression Omnibus were integrated into a discovery cohort. Weighted gene co-expression network analysis (WGCNA) and machine learning integrative approaches were utilized to construct a risk signature. QRT-PCR assay was performed to validate the model in an in-house cohort. Immunopathological features were estimated using bioinformatics methods.

Results

A four-gene machine learning-derived gene signature (MLDGS) was constructed for identifying patients with IA rupture. The AUC of MLDGS was 1.00 and 0.88 in discovery and validation cohorts, respectively. Calibration curve and decision curve analysis also confirmed the good performance of the MLDGS model. MLDGS was remarkably correlated with the circulating immunopathologic landscape. Higher MLDGS scores may represent higher abundance of innate immune cells, lower abundance of adaptive immune cells, and worse vascular stability.

Conclusions

The MLDGS provides a promising molecular assay panel for identifying patients with adverse immunopathological features and high risk of aneurysm rupture, contributing to advances in IA precision medicine.

Melatonin as a Potential Neuroprotectant: Mechanisms in Subarachnoid Hemorrhage-Induced Early Brain Injury

Subarachnoid hemorrhage (SAH) is a common cerebrovascular disease with high mortality and disability rates. Despite progressive advances in drugs and surgical techniques, neurological dysfunction in surviving SAH patients have not improved significantly. Traditionally, vasospasm has been considered the main cause of death and disability following SAH, but anti-vasospasm therapy has not benefited clinical prognosis. Many studies have proposed that early brain injury (EBI) may be the primary factor influencing the prognosis of SAH. Melatonin is an indole hormone and is the main hormone secreted by the pineal gland, with low daytime secretion levels and high nighttime secretion levels. Melatonin produces a wide range of biological effects through the neuroimmune endocrine network, and participates in various physiological activities in the central nervous system, reproductive system, immune system, and digestive system. Numerous studies have reported that melatonin has extensive physiological and pharmacological effects such as anti-oxidative stress, anti-inflammation, maintaining circadian rhythm, and regulating cellular and humoral immunity. In recent years, more and more studies have been conducted to explore the molecular mechanism underlying melatonin-induced neuroprotection. The studies suggest beneficial effects in the recovery of intracerebral hemorrhage, cerebral ischemia-reperfusion injury, spinal cord injury, Alzheimer’s disease, Parkinson’s disease and meningitis through anti-inflammatory, antioxidant and anti-apoptotic mechanisms. This review summarizes the recent studies on the application and mechanism of melatonin in SAH.

[Pharmacological Profile and Clinical Study Results of endothelin receptor antagonist, Clazosentan Sodium (PIVLAZ® I.V. Infusion liquid 150 mg)]

Cerebral vasospasm occurs within 4 to 14 days from the onset of aneurysmal subarachnoid hemorrhage (aSAH) in 40 to 70% of patients. Of patients with cerebral vasospasm, 17 to 40% experience delayed ischemic neurological deficits and about half of them develop cerebral infarction. Although the mechanism of the onset of cerebral vasospasm has not been fully elucidated, one of mechanisms is considered that after the onset of aSAH, the level of endothelin, a potent and sustained vasoconstriction substance, increases by production induced by oxyhemoglobin and release from erythrocytes and thus cerebral vasospasm develops via endothelin (ET)_A receptor. PIVLAZ I.V. Infusion liquid 150 mg (clazosentan sodium) is an endothelin receptor antagonist with a binding affinity for ET_A receptor approximately 1,000 times higher than that for ET_B receptor. In the clinical study, the incidence of cerebral vasospasm-related morbidity and all-cause mortality was significantly decreased by clazosentan compared with the placebo. The marketing approval was obtained for the indication of "Prevention of cerebral vasospasm, and vasospasm-related cerebral infarction and cerebral ischemic symptoms after aSAH securing" in January 2022. It is expected to contribute to reducing the risk of sequela and improving quality of life in patients with aSAH.

Preventive Effect of Clazosentan against Cerebral Vasospasm after Clipping Surgery for Aneurysmal Subarachnoid Hemorrhage in Japanese and Korean Patients

BACKGROUND

Clazosentan has been explored worldwide for the prophylaxis of cerebral vasospasm after aneurysmal subarachnoid hemorrhage (aSAH). In a dose-finding trial (CONSCIOUS-1) conducted in Israel, Europe, and North America, clazosentan (1, 5, and 15 mg/h) significantly reduced the incidence of cerebral vasospasm, but its efficacy in Japanese and Korean patients was unknown. We conducted a double-blind comparative study to evaluate the occurrence of cerebral vasospasm in Japanese and Korean patients with aSAH.

METHODS

The aim of this multicenter, double-blind, randomized, placebo-controlled, dose-finding phase 2 clinical trial, was to evaluate the efficacy, pharmacokinetics, and safety of clazosentan (5 and 10 mg/h) against cerebral vasospasm after clipping surgery in Japanese and Korean patients with aSAH. Patients aged between 20 and 75 years were administered the study drug within 56 h after the aneurysm rupture and up to day 14 post-aSAH. The incidence of vasospasm, defined as an inner artery diameter reduction of major intracranial arteries ≥34% based on catheter angiography, was compared between each treatment group. Cerebral infarction due to vasospasm at 6 weeks and patients' outcome at 3 months was also compared.

RESULTS

Among 181 enrolled patients, 158 completed the study and were analyzed. The incidence of vasospasm up to day 14 after aSAH onset was 80.0% in the placebo group (95% CI 67.0-89.6), 38.5% in the 5 mg/h clazosentan group (95% CI 25.3-53.0), and 35.3% in the 10 mg/h clazosentan group (95% CI 22.4-49.9), indicating that the incidence of vasospasm was significantly reduced by clazosentan treatment (placebo vs. 5 mg/h clazosentan, p < 0.0001; placebo vs. 10 mg/h clazosentan, p < 0.0001). The occurrence of cerebral infarction due to vasospasm was 20.8% in the placebo group (95% CI 10.8-34.1), 3.8% in the 5 mg/h clazosentan group (95% CI 0.5-13.2), and 4.2% in the 10 mg/h clazosentan group (95% CI 0.5-14.3), indicating that clazosentan significantly reduced the occurrence of cerebral infarctions caused by vasospasm (placebo vs. 5 mg/h clazosentan, p = 0.0151; placebo vs. 10 mg/h clazosentan, p = 0.0165). The overall incidence of all-cause death and/or vasospasm-related morbidity/mortality was significantly reduced in the 10 mg/h clazosentan group compared with the placebo group (p = 0.0003).

CONCLUSION

These results suggest that clazosentan prevents cerebral vasospasm and subsequent cerebral infarction, and could thereby improve outcomes after performing a clipping surgery for aSAH in Japanese and Korean patients.

Blast-induced phenotypic switching in cerebral vasospasm

Vasospasm of the cerebrovasculature is a common manifestation of blast-induced traumatic brain injury (bTBI) reported among combat casualties in the conflicts in Afghanistan and Iraq. Cerebral vasospasm occurs more frequently, and with earlier onset, in bTBI patients than in patients with other TBI injury modes, such as blunt force trauma. Though vasospasm is usually associated with the presence of subarachnoid hemorrhage (SAH), SAH is not required for vasospasm in bTBI, which suggests that the unique mechanics of blast injury could potentiate vasospasm onset, accounting for the increased incidence. Here, using theoretical and in vitro models, we show that a single rapid mechanical insult can induce vascular hypercontractility and remodeling, indicative of vasospasm initiation. We employed high-velocity stretching of engineered arterial lamellae to simulate the mechanical forces of a blast pulse on the vasculature. An hour after a simulated blast, injured tissues displayed altered intracellular calcium dynamics leading to hypersensitivity to contractile stimulus with endothelin-1. One day after simulated blast, tissues exhibited blast force dependent prolonged hypercontraction and vascular smooth muscle phenotype switching, indicative of remodeling. These results suggest that an acute, blast-like injury is sufficient to induce a hypercontraction-induced genetic switch that potentiates vascular remodeling, and cerebral vasospasm, in bTBI patients.

Dantrolene mediates vasorelaxation in cerebral vasoconstriction: a case series

INTRODUCTION

Cerebral vasoconstriction syndromes such as vasospasm after subarachnoid hemorrhage (SAH) and trauma, or Call-Fleming syndrome are difficult to treat, and can lead to substantial disability and death. Dantrolene, a ryanodine receptor antagonist, inhibits intracellular calcium release from the sarco-endoplasmic reticulum. We examined the effect of dantrolene on middle cerebral artery (MCA) blood flow velocities as measured by transcranial Doppler (TCD).

METHODS

Three consecutive patients with elevated MCA TCD velocities receiving dantrolene (2.5 mg/kg i.v. q6h) were retrospectively reviewed. Average MCA peak systolic, mean flow velocities, and the pulsatility index (PI) before and after the dantrolene infusion were compared within patients. Systemic physiological parameters (blood pressure, heart rate, central venous pressure, intracranial pressure, body temperature, and cooling water temperature) were retrospectively collected 6 h before and after the dantrolene infusion.

RESULTS

MCA peak systolic velocities (mean +/- SE) for the three patients were 297 +/- 3, 248 +/- 8, and 268 +/- 19 cm/s before dantrolene and 159 +/- 9, 169 +/- 8, and 216 +/- 12 cm/s after dantrolene. Average mean flow velocities showed the same trend. Interestingly, the PI increased slightly from 0.6, 0.52, and 0.67 before dantrolene, to 1.17, 0.71, and 0.77 after dantrolene. Systemic physiological parameters remained stable in all three patients.

CONCLUSION

Dantrolene attenuated cerebral vasoconstriction as measured by TCD without altering systemic physiological parameters. This suggests that intracellular calcium release from ryanodine channels in smooth muscle might play a role in vasospasm. A prospective study is underway to test this hypothesis.

Genetic modification of cerebral arterial wall: implications for prevention and treatment of cerebral vasospasm

Genetic modification of cerebral vessels represents a promising and novel approach for prevention and/or treatment of various cerebral vascular disorders, including cerebral vasospasm. In this review, we focus on the current understanding of the use of gene transfer to the cerebral arteries for prevention and/or treatment of cerebral vasospasm following subarachnoid hemorrhage (SAH). We also discuss the recent developments in vascular therapeutics, involving the autologous use of progenitor cells for repair of damaged vessels, as well as a cell-based gene delivery approach for the prevention and treatment of cerebral vasospasm.

Single or Multiple Small Subarachnoid Hemorrhages by Puncturing a Small Branch of the Rat Basilar Artery Causes Chronic Cerebral Vasospasm

OBJECTIVE

This study looked at the effects of single and multiple small subarachnoid hemorrhage (SAH) caused by puncturing a small branch of the basilar artery in rats.

METHODS

Rats were subjected to single SAH (n = 21), multiple SAH (n = 21), sham operation (n = 21), or no procedures (control group, n = 7). SAH was induced in rats by transclival puncture of a small branch of the basilar artery. In the multiple-SAH hemorrhage groups, three small hemorrhages were produced in the same artery at three different times (initial and 24 and 48 h). In the single-SAH groups, one small hemorrhage was produced. Measurements of local cerebral blood flow (LCBF) were made at the initial SAH procedure and at three different time points. Seven animals from each general grouping were killed on Days 4, 10, and 14 (after LCBF was measured). Three different levels of the basilar artery were examined in each animal. Luminal area and arterial wall thickness were measured, and the findings were compared with control and corresponding sham group findings.

RESULTS

LCBF dropped dramatically (by 40%) immediately after SAH and reached levels near baseline within 15 minutes (n = 42) (P < 0.001). LCBF continued to drop after initial SAH and reached the lowest level on Day 10 (P < 0.001) or Day 14 (P < 0.05). Significant luminal narrowing (P < 0.01) and thickening of the arterial wall (P < 0.01) were observed in both groups.

CONCLUSION

Single or multiple small SAHs produced by puncturing the basilar artery in the rat cause similar acute and chronic cerebral vasospasm.

Mechanosensation and endothelin in astrocytes--hypothetical roles in CNS pathophysiology

Endothelin (ET) is a potent autocrine mitogen produced by reactive and neoplastic astrocytes. ET has been implicated in the induction of astrocyte proliferation and other transformations engendered by brain pathology, and in promoting the malignant behavior of astrocytomas. Reactive astrocytes containing ET are found in the periphery/penumbra of a wide array of CNS pathologies. Virtually all brain pathology deforms the surrounding parenchyma, either by direct mass effect or edema. Mechanical stress is a well established stimulus for ET production and release by other cell types, but has not been well studied in the brain. However, numerous studies have illustrated that astrocytes can sense mechanical stress and translate it into chemical messages. Furthermore, the ubiquitous reticular meshwork formed by interconnected astrocytes provides an ideal morphology for sensing and responding to mechanical disturbances. We have recently demonstrated stretch-induced ET production by astrocytes in vitro. Inspired by this finding, the purpose of this article is to review the literature on (1) astrocyte mechanosensation, and (2) the endothelin system in astrocytes, and to consider the hypothesis that mechanical induction of the ET system may influence astrocyte functioning in CNS pathophysiology. We conclude by discussing evidence supporting future investigations to determine whether specific inhibition of stretch-activated ion channels may represent a novel strategy for treating or preventing CNS disturbances, as well as the relevance to astrocyte-derived tumors.

Ischemic and hemorrhagic disturbances in cerebral circulation alter contractile responses of the rat middle cerebral artery

In our study, we examined middle cerebral artery (MCA) contractile responses in two animal models. After hemorrhagic disturbances in rats of Krushinsky-Molodkina strain (KMRs) a decrease in contractile responses to serotonin (5-HT) was observed. During incomplete global cerebral ischemia, MCAs had increased responsiveness to endothelin-1 (ET-1), but reduced responsiveness to serotonin. These findings suggest that cerebral circulation disorders alter cerebrovascular function possibly leading to secondary disturbances in brain circulation.

Comparison of three rat models of cerebral vasospasm

A substantial number of rat models have been used to research subarachnoid hemorrhage-induced cerebral vasospasm; however, controversy exists regarding which method of selection is appropriate for this species. This study was designed to provide extensive information about the three most popular subarachnoid hemorrhage rat models: the endovascular puncture model, the single-hemorrhage model, and the double-hemorrhage model. In this study, the basilar artery and posterior communicating artery were chosen for histopathological examination and morphometric analysis. Both the endovascular puncture model and single-hemorrhage model developed significant degrees of vasospasm, which were less severe when compared with the double-hemorrhage model. The endovascular puncture model and double-hemorrhage model both developed more vasospasms in the posterior communicating artery than in the basilar artery. The endovascular puncture model has a markedly high mortality rate and high variability in bleeding volume. Overall, the present study showed that the double-hemorrhage model in rats is a more suitable tool with which to investigate mechanism and therapeutic approaches because it accurately correlates with the time courses for vasospasm in humans.

L-type voltage-dependent Ca2+ channels in cerebral microvascular endothelial cells and ET-1 biosynthesis

We investigated the role of intracellular calcium concentration ([Ca2+]i) in endothelin-1 (ET-1) production, the effects of potential vasospastic agents on [Ca2+]i, and the presence of L-type voltage-dependent Ca2+ channels in cerebral microvascular endothelial cells. Primary cultures of endothelial cells isolated from piglet cerebral microvessels were used. Confluent cells were exposed to either the thromboxane receptor agonist U-46619 (1 microM), 5-hydroxytryptamine (5-HT; 0.1 mM), or lysophosphatidic acid (LPA; 1 microM) alone or after pretreatment with the Ca2+-chelating agent EDTA (100 mM), the L-type Ca2+ channel blocker verapamil (10 microM), or the antagonist of receptor-operated Ca2+ channel SKF-96365 HCl (10 microM) for 15 min. ET-1 production increased from 1.2 (control) to 8.2 (U-46619), 4.9 (5-HT), or 3.9 (LPA) fmol/microg protein, respectively. Such elevated ET-1 biosynthesis was attenuated by verapamil, EDTA, or SKF-96365 HCl. To investigate the presence of L-type voltage-dependent Ca2+ channels in endothelial cells, the [Ca2+]i signal was determined fluorometrically by using fura 2-AM. Superfusion of confluent endothelial cells with U-46619, 5-HT, or LPA significantly increased [Ca2+]i. Pretreatment of endothelial cells with high K+ (60 mM) or nifedipine (4 microM) diminished increases in [Ca2+]i induced by the vasoactive agents. These results indicate that 1) elevated [Ca2+]i signals are involved in ET-1 biosynthesis induced by specific spasmogenic agents, 2) the increases in [Ca2+]i induced by the vasoactive agents tested involve receptor as well as L-type voltage-dependent Ca2+ channels, and 3) primary cultures of cerebral microvascular endothelial cells express L-type voltage-dependent Ca2+ channels.

Effects of chronic administration of L-arginine on vasoactive responses induced by endothelin-1 and its plasma level in streptozotocin-induced diabetic rats

To investigate the mechanism underlying increased endothelin-1 (ET-1) release in diabetic rats, we administered L-arginine chronically to streptozotocin (STZ)-induced diabetic rats. The plasma concentrations of glucose, ET-1 and NOx (NO2- + NO3-) were all significantly raised at 10 weeks after the STZ injection. Chronic administration of L-arginine resulted in a significantly higher plasma NOx concentration and a significantly lower plasma ET-1 level at 10 weeks compared with the untreated diabetic group. ET-1 induced a biphasic vasodilator/vasoconstrictor response in the perfused isolated mesenteric arterial beds from all groups. The vasodilatation was significantly greater in diabetic rats than in age-matched controls. Chronic oral L-arginine administration had no significant effect on the enhanced ET-1-induced vasodilatation seen in the untreated diabetic rats. The vasoconstrictions induced by ET-1 and methoxamine were significantly attenuated in STZ-diabetic rats. The attenuated vasoconstrictor response to ET-1, but not that to methoxamine, was further attenuated by chronic treatment with L-arginine. We conclude that since chronic L-arginine administration not only reduced the increase in plasma ET-1 levels but also further attenuated the ET-1-induced vasoconstriction without affecting the change in vasodilatation, chronic L-arginine administration could be valuable for the treatment of the symptoms of diabetic mellitus related to ET-1.

Abnormalities of endothelial function in the pathogenesis of stroke: the importance of endothelin

Endothelial cells play a key role in the local regulation of the vascular smooth muscle tone by producing and releasing relaxing and contracting factors. Endothelin (ET)-1, one of the most potent endogenous vasoconstrictor substances known, is produced by endothelial cells. In the cerebral vasculature ET-1 is thought to be involved in several pathological conditions, including vasospasm following subarachnoid hemorrhage and stroke. This review contains evidence suggesting that endothelial dysfunction may contribute to the development of ischemic stroke and discusses the current knowledge concerning the role of ET-1 in the pathogenesis of stroke in animal models and in humans.

Hemoglobin increases endothelin-1 in endothelial cells by decreasing nitric oxide

We determined whether ferrous hemoglobin increases endothelin-1 (ET-1) secretion from bovine cerebral artery endothelial cells and the mechanisms involved. Exposure of endothelial cells to hemoglobin caused dose-dependent increases in pre-proET-1 mRNA and peptide. The increase in ET-1 peptide was inhibited by cycloheximide or actinomycin D whereas only cycloheximide decreased basal ET-1 release. N(G)-nitro-l-arginine significantly increased ET-1 concentration and reduced hemoglobin stimulation of ET-1 release. 8-Bromo-cGMP did not alter basal ET-1 concentration but suppressed hemoglobin-induced ET-1 production. Methemoglobin and S-nitrosylated methemoglobin were less potent inducers of ET-1 release. In summary, hemoglobin increases ET-1 in cerebral endothelial cells by mechanisms that involve transcription and translation. Nitric oxide production inhibits ET-1 production. Ferrous hemoglobin increases ET-1 by binding nitric oxide and abolishing this inhibitory pathway although other mechanisms are involved since N(G)-nitro-l-arginine reduces hemoglobin-induced ET-1 release.

Evaluation of big endothelin-1 concentrations in serum and ventricular cerebrospinal fluid after early surgical compared with nonsurgical management of ruptured intracranial aneurysms

OBJECT

Whereas the removal of subarachnoid blood is possible during early-stage aneurysm surgery, this cannot be achieved in aneurysms treated by endovascular means. The levels of potential spasmogens in the cerebrospinal fluid (CSF) in patients receiving endovascular treatment might therefore be higher, with the potential for more severe post-subarachnoid hemorrhage (SAH) vasospasm.

METHODS

Serum and CSF concentrations of big endothelin (ET)-1 were serially measured in patients with SAH receiving one of the following treatments: 1) early (within 72 hours of SAH) aneurysm surgical treatment (15 patients), 2) early endovascular treatment (17 patients), or 3) no intervention in the acute phase (12 patients). In patients suffering delayed infarctions higher levels of big ET-1 CSF were demonstrated than in those without infarctions (p = 0.01). In patients in whom surgery was performed in the acute phase lower big ET-1 CSF concentrations were demonstrated than in those who received embolization treatment or no treatment (p = 0.02). Subgroup analysis demonstrated that in patients receiving early endovascular treatment, higher big ET-1 CSF concentrations were revealed than in those undergoing early aneurysm surgery; this was true for patients with (microsurgerytreated, 1.84 +/- 0.83 pg/ml; and embolization-treated 2.19 +/- 0.54 pg/ml) and without (microsurgery-treated 1.76 +/- 0.61 pg/ml; and embolization-treated 2.01 +/- 0.48 pg/ml) delayed infarctions.

CONCLUSIONS

Among patients with SAH who received treatment during the acute phase, those undergoing early aneurysm surgery were shown to have lower big ET-1 CSF levels than those receiving embolization and no treatment (that is, the nonsurgical treatment groups). The clinical significance of this finding remains to be established in future clinical trials, because in the present study the trend toward lower levels of big ET-1 CSF in the microsurgically treated group was not paralleled by a lower delayed stroke rate or an improvement in neurological outcome.

Molecular keys to the problems of cerebral vasospasm

The mechanisms responsible for subarachnoid hemorrhage (SAH)-induced vasospasm are under intense investigation but remain incompletely understood. A consequence of SAH-induced vasospasm, cerebral infarction, produces a nonrecoverable ischemic tissue core surrounded by a potentially amenable penumbra. However, successful treatment has been inconsistent. In this review, we summarize the basic molecular biology of cerebrovascular regulation, describe recent developments in molecular biology to elucidate the mechanisms of SAH-induced vasospasm, and discuss the potential contribution of cerebral microcirculation regulation to the control of ischemia. Our understanding of the pathogenesis of SAH-induced vasospasm remains a major scientific challenge; however, molecular biological techniques are beginning to uncover the intracellular mechanisms involved in vascular regulation and its failure. Recent findings of microvascular regulatory mechanisms and their failure after SAH suggest a role in the development and size of the ischemia. Progress is being made in identifying the various components in the blood that cause SAH-induced vasospasm. Thus, our evolving understanding of the underlying molecular mechanism may provide the basis for improved treatment after SAH-induced vasospasm, especially at the level of the microcirculation.

Plasma endothelin concentrations after aneurysmal subarachnoid hemorrhage

OBJECT

The pathogenesis of cerebral vasospasm and delayed ischemia after subarachnoid hemorrhage (SAH) seems to be complex. An important mediator of chronic vasospasm may be endothelin (ET), with its powerful and long-lasting vasoconstricting activity. In this study the author investigated the correlation between serial plasma concentrations of ET and ischemic symptoms, angiographically demonstrated evidence of vasospasm, and computerized tomography (CT) findings after aneurysmal SAH.

METHODS

Endothelin-1 immunoreactivity in plasma was studied in 70 patients with aneurysmal SAH and in 25 healthy volunteers by using a double-antibody sandwich-enzyme immunoassay (immunometric) technique. On the whole, mean plasma ET concentrations in patients with SAH (mean +/- standard error of mean, 2.1 +/- 0.1 pg/ml) did not differ from those of healthy volunteers (1.9 +/- 0.2 pg/ml). Endothelin concentrations were significantly higher (p < 0.05) in patients who experienced delayed cerebral ischemia with fixed neurological deficits compared with those in other patients (post-SAH Days 0-5, 3.1 +/- 0.8 pg/ml compared with 2.1 +/- 0.2 pg/ml; post-SAH Days 6-14, 2.5 +/- 0.4 pg/ml compared with 1.9 +/- 0.2 pg/ml). Patients with angiographic evidence of severe vasospasm also had significantly (p < 0.05) elevated ET concentrations (post-SAH Days 0-5, 3.2 +/- 0.8 pg/ml; post-SAH Days 6-14, 2.7 +/- 0.5 pg/ml) as did those with a cerebral infarction larger than a lacuna on the follow-up CT scan (post-SAH Days 0-5, 3.1 +/- 0.8 pg/ml; post-SAH Days 6-14, 2.5 +/- 0.4 pg/ml) compared with other patients. Patients in whom angiography revealed diffuse moderate-to-severe vasospasm had significantly (p < 0.05) higher ET levels than other patients within 24 hours before or after angiography (2.6 +/- 0.3 compared with 1.9 +/- 0.2 pg/ml). In addition, patients with a history of hypertension or cigarette smoking experienced cerebral infarctions significantly more often than other patients, although angiography did not demonstrate severe or diffuse vasospasm more often in these patients than in others.

CONCLUSIONS

Endothelin concentrations seem to correlate with delayed cerebral ischemia and vasospasm after SAH. The highest levels of ET are predictive of the symptoms of cerebral ischemia and vasospasm, and ET may also worsen ischemia in patients with a history of hypertension. Thus, ET may be an important causal or contributing factor to vasospasm, but its significance in the pathogenesis of vasospasm remains unknown.

Critically attained threshold of cerebral hypoperfusion: the CATCH hypothesis of Alzheimer's pathogenesis

This review discusses the experimental and clinical data which indicate that chronic cerebral hypoperfusion can affect metabolic, anatomic, and cognitive function adversely. In aged but not young animals, chronic brain hypoperfusion results in regional pre- and post-synaptic changes, protein synthesis abnormalities, energy metabolic dysregulation, reduced glucose utilization, cholinergic receptor loss, and visuo-spatial memory deficits. Additionally, aging animals that are kept for prolonged periods of time after chronic brain hypoperfusion, also develop brain capillary degeneration in CA1 hippocampus and neuronal damage extending from the hippocampal region to the temporo-parietal cortex where neurodegenerative tissue atrophy eventually forms. All these pathologic events occur in rodents in the absence of senile plaques and neurofibrillary tangles. Alzheimer brains reveal similar biochemical and structural changes as those experimentally induced in aging animals. Moreover, regional cerebral hypoperfusion is one of the earlier (if not the earliest) clinical manifestations in both the sporadic and familial forms of Alzheimer's disease. In addition, therapy that improves or increases cerebral perfusion is generally of some benefit to Alzheimer patients. Conversely, a variety of disorders with different etiologies that impair or diminish cerebral perfusion are reported to be risk factors for this dementia. These findings have prompted us to propose the concept that advanced aging in the presence of a vascular risk factor can converge to create a critically attained threshold of cerebral hypoperfusion (CATCH) that triggers regional brain microcirculatory disturbances and impairs optimal delivery of energy substrates needed for normal brain cell function. The outcome of this defect generates a chain of events leading to the progressive evolution of brain metabolic, cognitive and tissue pathology that characterize Alzheimer's disease. The possible role of CATCH in familial and early onset Alzheimer's disease is briefly discussed from a theoretical vantagepoint. The growing and most recent evidence in support of the CATCH concept is the focus of this review.

Endothelin antagonists: substituted mesitylcarboxamides with high potency and selectivity for ET(A) receptors

We have previously disclosed the discovery of 2,4-disubstituted anilinothiophenesulfonamides with potent ET(A)-selective endothelin receptor antagonism and the subsequent identification of sitaxsentan (TBC11251, 1) as a clinical development compound (Wu et al. J. Med. Chem. 1997, 40, 1682 and 1690). The orally active 1 has demonstrated efficacy in a phase II clinical trial of congestive heart failure (Givertz et al. Circulation 1998, 98, Abstr. #3044) and was active in rat models of myocardial infarction (Podesser et al. Circulation 1998, 98, Abstr. #2896) and acute hypoxia-induced pulmonary hypertension (Chen et al. FASEB J. 1996, 10 (3), A104). We now report that an additional substituent at the 6-position of the anilino ring further increases the potency of this series of compounds. It was also found that a wide range of functionalities at the 3-position of the 2,4,6-trisubstituted ring increased ET(A) selectivity by approximately 10-fold while maintaining in vitro potency, therefore rendering the compounds amenable to fine-tuning of pharmacological and toxicological profiles with enhanced selectivity. The optimal compound in this series was found to be TBC2576 (7u), which has approximately 10-fold higher ET(A) binding affinity than 1, high ET(A)/ET(B) selectivity, and a serum half-life of 7.3 h in rats, as well as in vivo activity.

Endothelin-1 contributes to normocapnic hyperoxic pial artery vasoconstriction

The present study was designed to determine if hyperoxia elicits pial artery vasoconstriction and to characterize the contribution of endothelin-1 (ET-1) to that vascular response in newborn pigs equipped with a closed cranial window. Hyperoxic conditions were established by ventilating the piglets with 100% O(2) during normocapnia and concomitantly topically applying artificial CSF that had been bubbled with 100% O(2). Hyperoxia elevated CSF ET-1 from 23+/-1 to 45+/-4 pg/ml. Hyperoxia also elicited pial artery vasoconstriction that was attenuated by BQ123 (10(-6) M), an ET-1 antagonist (-15+/-1 vs. -5+/-1%). These data indicate that ET-1 contributes to hyperoxic pial artery vasoconstriction.

Adventitial expression of recombinant endothelial nitric oxide synthase gene reverses vasoconstrictor effect of endothelin-1

The present study was designed to determine the effect of recombinant endothelial nitric oxide synthase (eNOS) gene expression on reactivity of canine basilar arteries to endothelin-1 (ET-1). Experiments were performed ex vivo. The arteries were exposed (30 minutes at 37 degrees C) to adenoviral vectors encoding eNOS gene (AdCMVeNOS) or beta-galactosidase reporter gene (AdCMVbeta-Gal). Twenty-four hours after transduction, transgene expression was evident mainly in the vascular adventitia. Rings of control (nontransduced), AdCMVbeta-Gal- and AdCMVeNOS-transduced arteries with and without endothelium were suspended for isometric tension recording. Levels of guanosine 3',5'-cyclic monophosphate (cGMP) were measured by radioimmunoassay. During contractions to uridine 5'-triphosphate, ET-1 (10(-10) to 3x10(-9) mol/L) caused further increase in tension in control and AdCMVbeta-Gal-transduced arteries. In contrast, ET-1 caused concentration-dependent relaxations of AdCMVeNOS-transduced arteries. The relaxations to ET-1 in AdCMVeNOS-transduced arteries were endothelium-independent. They were abolished by N(G)-nitro-L-arginine methyl ester or by chemical treatment of adventitia with paraformaldehyde before gene transfer. ET-1 (10(-9) mol/L) significantly increased intracellular cGMP levels in AdCMVeNOS-transduced arteries without endothelium. In arteries transduced with AdCMVeNOS, higher concentrations (10(-9) to 3x10(-8) mol/L) of ET-2 also caused relaxations, whereas ET-3 and sarafotoxin, a selective ET(B) receptor agonist, did not produce any relaxations. The relaxations to ET-1 in AdCMVeNOS-transduced arteries were strongly reduced by BQ-123 (10(-7) mol/L), an ET(A) receptor antagonist, but were not affected by BQ-788 (3x10(-7) mol/L), an ET(B) receptor antagonist. These results suggest that genetically modified adventitia can produce nitric oxide and cause relaxations in response to ET-1 via activation of ET(A) receptors. Our findings support a novel concept that successful transfer and expression of recombinant eNOS gene can lead to a qualitative change in responsiveness to vasoconstrictor substances.

Prolonged blockade of endothelin ET(A) receptors decreases vascular reactivity in the aorta of spontaneously hypertensive rats in vitro

We investigated the effect of prolonged endothelin-1 type A (ET(A)) receptors blockade on the constrictor response to phenylephrine and the dilator response to acetylcholine (ACh) in isolated aortic rings from normotensive [Wistar-Kyoto (WKY)] rats and spontaneously hypertensive rats (SHRs). Animals were treated for 2 weeks with the ET(A)-receptor blocker LU135252 (50 mg/kg/day; n = 8). LU135252 treatment did not affect blood pressure in both strains. In isolated aortic segments, dilation to ACh and contractions to phenylephrine were decreased only in SHRs. Nitric oxide (NO) synthesis blockade (L-NAME, 0.1 mM) inhibited 90+/-11% (WKY rats) and 76+/-8% (SHRs) of ACh-induced dilation. Cyclooxygenases blockade (indomethacin, 10 microM) had no effect in both strains. Endothelium-derived hyperpolarizing factor(s) (EDHF) blockade (KCl, 20 mM) suppressed the remaining ACh-induced dilation in both strains. Treatment with LU135252 significantly decreased NO-dependent dilation, as compared with controls [70+/-8% vs. 90+/-11% (WKY rats) and 54+/-6% vs. 76+/-8% (SHRs) of total dilation; p<0.05]. On the other hand, EDHF-dependent dilation was significantly higher in the LU135252 groups [29+/-5% vs. 10+/-3% (WKY rats) and 44+/-7% vs. 19+/-4% (SHRs) of total dilation; p<0.05]. Thus prolonged ET(A)-receptor blockade decreased the responsiveness to phenylephrine and ACh in SHR aortas and changed the proportion of dilator agents in ACh-induced dilation.

Antisense preproendothelin-oligoDNA therapy for vasospasm in a canine model of subarachnoid hemorrhage

OBJECT

The purpose of this study is twofold: 1) to test antisense genetic techniques used in the prevention of cerebral vasospasm in a canine model of subarachnoid hemorrhage (SAH), targeting the endothelin-1 (ET-1) gene; and 2) to determine if fibrinolysis of subarachnoid clot with recombinant tissue plasminogen activator (rtPA) could enhance the effect of antisense treatment.

METHODS

A total of 39 dogs were studied in this experiment. Placebo (six animals), rtPA (six animals), antisense preproET-1 oligodeoxynucleotide (ASOD; five animals), or rtPA plus ASOD (combined treatment; six animals) was injected into the cisterna magna 30 minutes after a second SAH was induced on the 2nd day of the experiment. The animals were observed until Day 7, when they underwent follow-up angiography and then were killed; their basilar arteries were removed for analysis. Control animals included in this study (two animals in each group) received placebo, rtPA, ASOD, or rtPA plus ASOD without induction of SAH, or rtPA with mismatched (nonsense) preproET-1 oligodeoxynucleotide following SAH. Six additional dogs were analyzed earlier following SAH. Dogs that received placebo developed severe vasospasm (51+/-8% of baseline caliber). Administration of ASOD alone resulted in a mild reduction in vasospasm (64+/-13% of baseline caliber) and rtPA alone resulted in a moderate reduction in vasospasm (81+/-5% of baseline caliber); however, the combined therapy of rtPA plus ASOD almost completely prevented vasospasm (95+/-6%, of baseline caliber), which was significantly different from all other groups (p < 0.05). Morphological analysis of the basilar arteries yielded results similar to angiography with respect to vasospasm severity. The ASOD treatment combined with rtPA resulted in reduced ET-1 expression, as demonstrated by immunohistochemical staining of the arteries, and reduced preproET-1 levels on Day 4, as measured by reverse transcription-polymerase chain reaction. Nonsense DNA sequences had no effect on the vessels.

CONCLUSIONS

Antisense preproET-1 oligodeoxynucleotide treatment, when combined with clot lysis caused by rtPA, reduced vasospasm in the canine model of SAH, and this effect appeared to be related to reduced ET-1 synthesis. The results of this experiment support a causative role for ET-1 early in the course of vasospasm development in dogs. The apparent additive therapeutic effects of antisense and fibrinolytic treatments could be due to clot lysis, which allows better delivery of oligodeoxynucleotides to arteries within the subarachnoid space.

cGMP and cAMP cause pulmonary vasoconstriction in the presence of hemolysate

We recently reported that addition of a small amount of hemolysate to the salt solution that perfused isolated rat lungs hypersensitized the vasculature to subsequent additions of ANG II or exposure to hypoxia, and addition of NO gas (. NO) to the perfusate that contained hemolysate caused a strong vasoconstrictor rather than a vasodilator response. In the present study, we demonstrate that CO and the secondary messengers cGMP and cAMP (usually associated with vasodilation) exert similar effects in hemolysate-perfused lungs. Analogs of the cyclic nucleotides cGMP or cAMP (8-bromo-cGMP and dibutyryl-cAMP, respectively) caused profound vasoconstriction in the isolated rat lung perfused with a salt solution that contained hemolysate. The cGMP- or cAMP-analog-induced vasoconstriction was inhibited by chemically dissimilar Ca2+ antagonists, by the protein phosphatase inhibitor okadaic acid, and, to a lesser degree, by protein kinase inhibitor H-7. Antiphosphothreonine immunoblotting demonstrated that lungs perfused with hemolysate exhibit increased phosphorylation of several proteins. These data indicate that, in the presence of hemolysate, pulmonary vasculature responds to nominally vasodilatory stimuli, including analogs of cGMP and cAMP, with vasoconstriction rather than vasodilation. The importance of our finding is the paradoxical nature of the response to (analogs of) cyclic nucleotides because, to our knowledge, cyclic nucleotide-induced vasoconstriction has not been previously reported.

Differential regulation of intracellular Ca2+ signalling induced by high K+ and endothelin-1 in single smooth muscle cells of intact canine basilar artery: detection by means of confocal laser microscopy

Changes in intracellular calcium concentration ([Ca2+]i) in smooth muscle cells play the key role in regulation of vascular smooth muscle tone and pathogenesis of cerebral vasospasm. In this study, we adopted the confocal laser microscopy to detect the fluorescence signals arising from the individual smooth muscle cells of canine basilar artery. Ring preparations were made, loaded with fluo-3 and changes in fluorescence induced by high K+ and endothelin-1 (ET-1) were measured by confocal laser microscopy. In some unstimulated smooth muscle cells Ca2+ waves arising from discrete region of the cell propagated to the whole cell with a velocity of approximately 10 microm/s. High K+ (80 mmol/L) induced a rapid rise in [Ca2+]i, the peak level being consistently reached approximately 10 s after stimulation. In contrast, the time to peak level of [Ca2+]i induced by ET-1 (0.3 micromol/L) varied widely between 13 and 26 s among individual cells, an indication that the extent of nonuniform coordination of increases in [Ca2+]i in individual cells may be partly responsible for the different time courses of tension development of vascular smooth muscle in response to the vasoactive stimulants. The increase in [Ca2+]i induced by ET-1 was transient but a pronounced and sustained contraction developed further in response to ET-1. Thus ET-1 has a biological property as a potential candidate to elicit cerebral vasospasm. Confocal laser microscopy could be a useful tool to measure the changes in [Ca2+]i in individual smooth muscle cells of cerebral artery.

Involvement of the endothelin receptor subtype A in neuronal pathogenesis after traumatic brain injury

Endothelin-1 (ET-1) is a 21 amino acid peptide that has been closely linked to cerebral vasospasm and more recently to oxidative stress after traumatic brain injury. In this study, we have examined the effects of the endothelin receptor subtype A antagonist, Ro 61-1790, on acute cortical neuronal injury and delayed neuronal death in the cerebellum after mild traumatic brain injury. Rats were administered Ro 61-1790 or vehicle for 24 h after injury and euthanized at 1 day, 3 days, or 7 days. Heat shock protein70 (HSP70), a marker of neuronal stress/injury, was immunolocalized in the cortex. Induction of heme oxygenase-1 (HO-1) and enhanced immunoexpression of the complement C3bi receptor, both of which are indicators of cerebellar glial reactivity, and Purkinje cell loss were evaluated in the cerebellum. There was maximal induction of HSP70 in cortical neurons at 24 h postinjury in all animals. Drug treated animals showed significantly fewer HSP70 labeled cortical neurons at this time point. There were fewer reactive glia in the cerebellum of drug treated animals as compared to vehicle controls at 3 days postinjury. However, at 7 days postinjury glial reactivity and Purkinje cell loss were similar in both groups. These findings demonstrate that Ro 61-1790, when administered for the first 24 h postinjury, limits acute neuronal injury in the cortex, transiently influences glial reactivity in the cerebellum, and does not attenuate delayed Purkinje cell death. The latter finding may reflect the duration of infusion of the drug.

Chronic endothelin-1-induced changes in vascular reactivity in rat resistance arteries and aorta

The role of endothelin-1 in vascular homeostasis is not yet clearly established. We investigated the responses to phenylephrine and acetylcholine in rat mesenteric resistance artery and aorta mounted in vitro in myographs after a 2-week treatment with endothelin-1 (5 pmol kg(-1) min(-1), n = 8). Systolic arterial blood pressure increased in endothelin-1-treated rats (171 +/- 7 mmHg vs. 196 +/- 6 mmHg, P < 0.05). In the aorta, chronic endothelin-1 significantly increased the dilator response to acetylcholine (maximal dilatation: 76 +/- 3 vs. 86 +/- 3% in control, P < 0.05). Acetylcholine-induced dilatation was decreased by nitric oxide (NO) synthase inhibition with NG-nitro-L-arginine methyl ester (L-NAME 100 micromol/l) and partly restored by cyclooxygenases inhibition (indomethacin, 10 micromol/l). In endothelin-1-treated rats, L-NAME-sensitive acetylcholine dilatation was lower than in the control, but dilator cyclooxygenase product(s) were found instead of constrictor cyclooxygenase product(s). In mesenteric resistance arteries chronic endothelin-1 increased the participation of cyclooxygenase products in acetylcholine-induced dilatation from 10 +/- 2 to 19 +/- 3%. In both types of arteries, phenylephrine-induced contraction was not affected by chronic endothelin-1. Thus chronic endothelin-1 increased the participation of dilator cyclooxygenase product(s) in acetylcholine-induced dilatation in the aorta and the mesenteric resistance arteries.

Endothelin receptor antagonists: synthesis and structure-activity relationships of substituted benzothiazine-1,1-dioxides

The development of benzothiazine-1,1-dioxide derivatives as a new structural class of potent endothelin receptor antagonists is described. Structure-activity relationships (SAR) revealed that PD164800 (1) is a potent antagonist of the ETA receptor subtype.

Profiles of an intravenously available endothelin A-receptor antagonist, S-0139, for preventing cerebral vasospasm in a canine two-hemorrhage model

We examined the prophylactic effect of a novel nonpeptide endothelin (ET) A-receptor selective antagonist, S-0139, using a canine two-hemorrhage model and an ET-1-induced cerebral vasospasm model. The agent markedly prevented cerebral vasospasm in the canine two-hemorrhage model when given intracisternally or intravenously by continuous daily dosing. An efficacious intravenous method was to apply a relatively high initial dose followed by daily sustaining administration at a much lower dose, which alone would have been ineffective. The need for sustaining dosing may imply daily successive attacks of ETs in the cerebral vessel compartment after the introduction of autologous blood into the subarachnoid space. A small amount of S-0139 was detected from the cerebrospinal fluid (CSF) with an apparent lag time after its disappearance from the plasma following intravenous dosing of 0.83 mg/kg/min for 12 min, however, cerebral vasoconstriction induced by ET-1 dosing from the adventitial side was clearly inhibited during such a lag period. Moreover, its movement into the CSF was greatly enhanced after the application of autologous blood to the animals. From these results, we conclude that ET-1 play a major role in producing delayed cerebral vasospasm in this canine two-hemorrhage model, and S-0139 effectively antagonizes the action of ET-1 even by intravenous treatment because it moves easily into the cerebral vessel compartment from plasma.

Role of tyrosine kinase in erythrocyte lysate-induced contraction in rabbit cerebral arteries

OBJECT

This study was undertaken to explore whether erythrocyte lysate, a proposed cause of vasospasm, produces vasoconstriction by activation of tyrosine kinase in rabbit cerebral arteries.

METHODS

Isometric tension was used to monitor contractions in rabbit basilar arteries induced by erythrocyte lysate, 5-hydroxytryptamine (5-HT), or KCl in the absence or presence of tyrosine kinase inhibitors. Erythrocyte lysate, 5-HT, or KCl produced concentration-dependent contractions in rabbit basilar arteries. Preincubation with the tyrosine kinase inhibitors tyrphostin A23 and genistein (30 and 100 microM), but not diadzein, an inactive analog of genistein, attenuated significantly the contraction induced by erythrocyte lysate (p < 0.05). Tyrphostin A23, genistein, and diadzein (30 microM) failed to reduce the contraction caused by 5-HT. Genistein, but not tyrphostin A23 or diadzein (30 microM), attenuated significantly the contraction induced by KCl (p < 0.05). In another series, arterial rings were initially contracted with erythrocyte lysate, 5-HT, or KCl and the relaxant effect of genistein was then tested. Genistein relaxed rabbit basilar arteries that had been contracted by exposure to erythrocyte lysate, 5-HT, or KCl (30-100 microM; p < 0.05).

CONCLUSIONS

These data indicate that tyrosine kinase may play a role in the regulation of cerebral arterial contraction and tyrosine kinase inhibitors may be useful in the management of cerebral vasospasm.

P2 purinoceptors in cultured bovine middle cerebral artery endothelial cells

Extracellular adenosine triphosphate (ATP) plays an important role in the regulation of endothelial function. However, its receptors and their signal-transduction pathways in major cerebral arterial endothelial cells are largely unknown. This study was undertaken functionally to classify the P2 purinoceptors in cultured bovine middle cerebral artery endothelial cells by using [Ca2+]i microfluorimetry. The rank order of potency to increase [Ca2+]i was 2-methylthio-ATP approximately ATP approximately uridine triphosphate (UTP) > adenosine diphosphate (ADP) >> adenosine monophosphate (AMP) > alpha,beta-methylene-ATP > adenosine, suggesting that the effect was mediated by both P2y and P2u receptors. ATP, 2-methylthio-ATP, and UTP mobilized Ca2+ from intracellular stores and triggered Ca2+ entry. The effects of ATP, 2-methylthio-ATP, and UTP were reduced by phospholipase C inhibitor 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (NCDC), but only the effects of ATP and UTP were attenuated by pertussis toxin, indicating that P2y and P2u receptors may activate the same effector mechanisms by coupling to different G proteins. The [Ca2+]i entry caused by UTP was significantly reduced by the receptor-regulated Ca2+ channel blocker SK&F 96365, by P-450 inhibitor econazole and by inorganic Ca2+ entry blocker lanthanum. P2-receptor antagonists suramin, pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), and reactive blue 2 reduced the effects of ATP and 2-methylthio-ATP, but not those of UTP, in a concentration-dependent manner. These studies suggest a coexistence of P2y and P2u receptors in cultured bovine middle cerebral artery endothelial cells.

Structure-activity relationships of N2-aryl-3-(isoxazolylsulfamoyl)-2-thiophenecarboxamides as selective endothelin receptor-A antagonists

We report here that N2-aryl-3-(isoxazolylsulfamoyl)-2-thiophenecarboxamides are potent and selective small molecule ETA receptor antagonists. The aryl group was subjected to extensive structural modification. With monosubstitution, the para position was most useful in increasing potency, with methyl being preferred. With disubstitution, 2,4-disubstitution further enhanced activity with methyl or cyano groups being preferred at the 2-position. In this series, a benzo-[d][1,3]dioxole group is equivalent to a 4-methyl group in in vitro activity and afforded the compounds with both in vivo activity and moderate half-lives.

Effects of intraluminal or extraluminal endothelin on perfused rabbit basilar arteries

The authors investigated selective intra- and extraluminal effects of endothelin (ET) on perfused basilar and extracranial arteries and also studied the interaction between ET and extraluminal oxyhemoglobin (oxyHb). The basilar, mesenteric, and femoral arteries were isolated from 23 Japanese White rabbits. After isolation of the intra- and extraluminal sides of the preparation, 3 x 10(-10) to 3 x 10(-8) mol/L of ET was administered intra- or extraluminally. After extraluminal pretreatment with 10(-5) mol/L oxyHb, 10(-5) mol/L N(G)-monomethyl-L-arginine (L-NMMA), or 10(-6) mol/L indomethacin, 10(-10) to 10(-8) mol/L of ET was administered intra- or extraluminally. Arterial contraction was evaluated by measuring the increase in the perfusion pressure gradient with a differential pressure gauge. Both intra- and extraluminal ET (10(-9) to 3 x 10(-8) mol/L) showed potent and dose-dependent vasoconstricting effects on basilar arteries (p < 0.01). The effect of ET on the basilar arteries was significantly greater than on the femoral or mesenteric arteries (both p < 0.01). The effect of intraluminal ET was enhanced by extraluminal oxyHb (p < 0.05) and L-NMMA (p < 0.01), but not by extraluminal indomethacin. Extraluminal oxyHb did not potentiate the contraction induced by extraluminal ET. These results indicate that the sensitivity of the basilar artery to intraluminal ET is greater than that of the femoral or mesenteric artery. Endothelin may act as a potent vasoconstrictor intra- as well as extraluminally under conditions such as subarachnoid hemorrhage in which oxyHb is present in the extraluminal space and endothelium-derived relaxing factors are inhibited.

Structure-activity relationships in a series of orally active gamma-hydroxy butenolide endothelin antagonists

The design of potent and selective non-peptide antagonists of endothelin-1 (ET-1) and its related isopeptides are important tools defining the role of ET in human diseases. In this report we will describe the detailed structure-activity relationship (SAR) studies that led to the discovery of a potent series of butenolide ETA selective antagonists. Starting from a micromolar screening hit, PD012527, use of Topliss decision tree analysis led to the discovery of the nanomolar ET(A) selective antagonist PD155080. Further structural modifications around the butenolide ring led directly to the subnanomolar ETA selective antagonist PD156707, IC50's = 0.3 (ET(A)) and 780 nM (ET(B)). This series of compounds exhibited functional activity exemplified by PD156707. This derivative inhibited the ETA receptor mediated release of arachidonic acid from rabbit renal artery vascular smooth muscle cells with an IC50 = 1.1 nM and also inhibited the ET-1 induced contraction of rabbit femoral artery rings (ETA mediated) with a pA2 = 7.6. PD156707 also displayed in vivo functional activity inhibiting the hemodynamic responses due to exogenous administration of ET-1 in rats in a dose dependent fashion. Evidence for the pH dependence of the open and closed tautomerization forms of PD156707 was demonstrated by an NMR study. X-ray crystallographic analysis of the closed butenolide form of PD156707 shows the benzylic group located on the same side of the butenolide ring as the gamma-hydroxyl and the remaining two phenyl groups on the butenolide ring essentially orthogonal to the butenolide ring. Pharmacokinetic parameters for PD156707 in dogs are also presented.

New non-peptide endothelin-A receptor antagonists: synthesis, biological properties, and structure-activity relationships of 5-(dimethylamino)-N-pyridyl-,-N-pyrimidinyl-,-N-pyridazinyl-, and -N-pyrazinyl-1-naphthalenesulfonamides

Use of automated synthesis led to the discovery of several 6-membered nitrogen heterocycles as replacements for the N-isoxazolyl substituent present in the 1-naphthalenesulfonamides endothelin-A (ETA) antagonist 5-(dimethylamino)-N-(3,4-dimethyl-5-isoxazolyl)-1-naphthalenesu lfo namides (BMS 182874). In each of these heterocycles, a small substituent such as halogen para to the position of attachment to the sulfonamide nitrogen atom was found to be advantageous for ETA receptor affinity. Of these heterocycles, 2-pyrazines offered the greatest scope for improving receptor affinity. Optimization of the substituents at the 3- and 5-positions in the pyrazine ring led to potent, ETA-selective compounds such as 5-(dimethylamino)-N-(5-chloro-3-methoxy-2-pyrazinyl)-1- naphthalenesulfonamides (7m, ETA pIC50 8.1). When dosed orally at 10 mg/kg to conscious, normotensive rats infused with big ET-1, compounds such as 7m showed significant inhibition of the pressor response with a duration of effect lasting for the 5-h course of the experiment.

Effect of an endothelin-1 antagonist, BQ-485, on cerebral oxygen metabolism after complete global cerebral ischemia in dogs

Endothelin-1 (ET-1) plays an important role in the physiologic or pathophysiologic regulation of cerebral circulation. To evaluate the effects of the newly synthesized ETA receptor-selective antagonist, BQ-485 (N-perhydroazepin-l-ylcarbonyl-Leu-D-Trp-D-Trp-OH), on the cerebral metabolism of oxygen during the delayed cerebral hypoperfusion that follows global cerebral ischemia, we occluded the ascending aorta and caval veins of 10 beagle dogs for 12.5 min. The animals were randomized into two groups. BQ-485 was given directly into the carotid artery at 0.03 mg/kg per min for 30 min, starting 15 min after reperfusion in the treatment group (n = 5). Isotonic saline was infused in the control group (n = 5). A fiberoptic catheter was inserted into the superior sagittal sinus to monitor its oxygen saturation (SssO2) continuously. Arterial O2 content (CaO2), and sagittal sinus O2 content (CssO2) were monitored before and at 0.5, 1, 2, 4, 6 and 8 h after the ischemic insult. BQ-485 significantly prevented the expected decrease in SssO2 and increase in the cerebral O2 utilization coefficient at 4, 6 and 8 h after the ischemic insult (P < 0.05). Thus, BQ-485 ameliorated the mismatch between O2 supply and demand in the delayed hypoperfusion phase. We conclude that ET may be involved in the pathogenesis of delayed cerebral hypoperfusion after cardiac arrest.

Role of endothelin in pial artery vasoconstriction and altered responses to vasopressin after brain injury

Pial artery constriction following fluid-percussion injury to the brain is associated with elevated cerebrospinal fluid (CSF) vasopressin concentration in newborn pigs. It has also been observed that fluid-percussion injury reverses the function of vasopressin from that of a dilator to a constrictor. Endothelin-1 (ET-1), a purported mediator of cerebral vasospasm, can be released by several stimuli, including vasopressin. The present study was designed to investigate the role of ET-1 in pial artery constriction and in the reversal of vasopressin from a dilator to a constrictor, which is observed after fluid-percussion injury. Brain injury of moderate severity (1.9-2.3 atm) was produced in anesthetized newborn pigs that had been equipped with a closed cranial window. Endothelin-1 elicited pial dilation at low concentrations and vasoconstriction at higher concentrations. Fluid-percussion injury reversed the process of dilation to that of constriction at the low ET-1 concentration and potentiated this constriction at high ET-1 concentrations (10% +/- 1%, -8% +/- 1%, and -15% +/- 1% vs. -6% +/- 1%, -17% +/- 1%, and -26% +/- 2% for 10(-12), 10(10),10(-8) M ET-1 before and after fluid-percussion injury, respectively). Vasopressin modestly increased CSF ET-1 concentration before fluid-percussion injury. Fluid-percussion injury markedly increased CSF ET-1 concentration and the ability of vasopressin to release ET-1 (20 +/- 2, 26 +/- 3, and 40 +/- 4 pg/ml vs. 93 +/- 6, 141 +/- 9, and 247 +/- 31 pg/ml for control, 40 pg/ml vasopressin, and 400 pg/ml vasopressin before and after fluid-percussion injury, respectively). An ET-1 antagonist, BQ 123 (10(-6) M) blunted pial artery constriction following fluid-percussion injury (146 +/- 5 microns -127 +/- 6 microns vs.144 +/- 5 microns-136 +/- 4 microns). The BQ 123 also blocked the reversal of vasopressin's function from that of a dilator to a constrictor after fluid-percussion injury (8% +/- 1%, 21% +/- 3%, and -5% +/- 1%, -14% +/- 2% vs. 8% +/- 1%, 21% +/- 2% and 4% +/- 1%, 2% +/- 1% for 40 and 4000 pg/ml vasopressin before and after fluid-percussion injury in the absence and presence of BQ 123, respectively). The BQ 123 blocked the constrictor component to ET-1, whereas it had no effect on the dilator component. These data show that ET-1 contributes to pial constriction after fluid-percussion injury. These data also indicate that vasopressin-induced release of ET-1 contributes to the reversal of vasopressin from a dilator to a constrictor following fluid-percussion injury. Furthermore, these data indicate that elevated CSF vasopressin and ET-1 interact in a positive feedback manner to promote pial artery constriction following fluid-percussion injury.

Endothelin peptides in brain diseases

Recently, scientists interested in diseases of the human brain have paid much attention to the endothelin group of peptides. Under normal conditions they are found in some types of neurons and in endothelial cells of microvessels but not in glial cells. This review focuses on the endothelin peptides and their involvement in various brain diseases. Particular attention is paid to their expression in reactive astrocytes seen in many pathological conditions of the human brain. Endothelin-1 is a very potent vasoconstrictor which may be involved in the vasospasm occurring in subarachnoid haemorrhage. Intracerebral injection or application to cerebral arteries in animals will cause a focal necrosis, apparently due to severe vasoconstriction. Reactive astrocytes occurring in cases with infarcts, lacunae, Alzheimer's disease, progressive multifocal leukoencephalopathy (PML) and subacute sclerosing panencephalitis (SSPE) express endothelin-like immunoreactivity. Astrocytes in vitro may produce, store and release endothelins. To some extent astrocytes grown in vitro mimic reactive astrocytes in vivo since in cultures astrocytes are removed from their natural environment which may trigger reactive responses. Therefore, in vivo reactive astrocytes may produce, store and release endothelins just as in vitro. If endothelins are released from reactive astrocytes they may act as mitogens and may influence microcirculation by inducing vasoconstriction of intracerebral arterioles. In such ways endothelins may contribute to the final lesions seen in cases with infarcts, lacunae, traumatic conditions, Alzheimer's disease and inflammatory diseases of the brain.