Dysfunction of nitric oxide synthases as a cause and therapeutic target in delayed cerebral vasospasm after SAH

Inhaled Nitric Oxide Treatment for Aneurysmal SAH Patients With Delayed Cerebral Ischemia

Background

We demonstrated experimentally that inhaled nitric oxide (iNO) dilates hypoperfused arterioles, increases tissue perfusion, and improves neurological outcome following subarachnoid hemorrhage (SAH) in mice. We performed a prospective pilot study to evaluate iNO in patients with delayed cerebral ischemia after SAH.

Methods

SAH patients with delayed cerebral ischemia and hypoperfusion despite conservative treatment were included. iNO was administered at a maximum dose of 40 ppm. The response to iNO was considered positive if: cerebral artery diameter increased by 10% in digital subtraction angiography (DSA), or tissue oxygen partial pressure (PtiO₂) increased by > 5 mmHg, or transcranial doppler (TCD) values decreased more than 30 cm/sec, or mean transit time (MTT) decreased below 6.5 secs in CT perfusion (CTP). Patient outcome was assessed at 6 months with the modified Rankin Scale (mRS).

Results

Seven patients were enrolled between February 2013 and September 2016. Median duration of iNO administration was 23 h. The primary endpoint was reached in all patients (five out of 17 DSA examinations, 19 out of 29 PtiO₂ time points, nine out of 26 TCD examinations, three out of five CTP examinations). No adverse events necessitating the cessation of iNO were observed. At 6 months, three patients presented with a mRS score of 0, one patient each with an mRS score of 2 and 3, and two patients had died.

Conclusion

Administration of iNO in SAH patients is safe. These results call for a larger prospective evaluation.

Inflammation and Oxidative Stress: Potential Targets for Improving Prognosis After Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) has a high mortality rate and causes long-term disability in many patients, often associated with cognitive impairment. However, the pathogenesis of delayed brain dysfunction after SAH is not fully understood. A growing body of evidence suggests that neuroinflammation and oxidative stress play a negative role in neurofunctional deficits. Red blood cells and hemoglobin, immune cells, proinflammatory cytokines, and peroxidases are directly or indirectly involved in the regulation of neuroinflammation and oxidative stress in the central nervous system after SAH. This review explores the role of various cellular and acellular components in secondary inflammation and oxidative stress after SAH, and aims to provide new ideas for clinical treatment to improve the prognosis of SAH.

Role of endothelial nitric oxide synthase for early brain injury after subarachnoid hemorrhage in mice

The first few hours and days after subarachnoid hemorrhage (SAH) are characterized by cerebral ischemia, spasms of pial arterioles, and a significant reduction of cerebral microperfusion, however, the mechanisms of this early microcirculatory dysfunction are still unknown. Endothelial nitric oxide production is reduced after SAH and exogenous application of NO reduces post-hemorrhagic microvasospasm. Therefore, we hypothesize that the endothelial NO-synthase (eNOS) may be involved in the formation of microvasospasms, microcirculatory dysfunction, and unfavorable outcome after SAH. SAH was induced in male eNOS deficient (eNOS^-/-) mice by endovascular MCA perforation. Three hours later, the cerebral microcirculation was visualized using in vivo 2-photon-microscopy. eNOS^-/- mice had more severe SAHs, more severe ischemia, three time more rebleedings, and a massively increased mortality (50 vs. 0%) as compared to wild type (WT) littermate controls. Three hours after SAH eNOS^-/- mice had fewer perfused microvessels and 40% more microvasospasms than WT mice. The current study indicates that a proper function of eNOS plays a key role for a favorable outcome after SAH and helps to explain why patients suffering from hypertension or other conditions associated with impaired eNOS function, have a higher risk of unfavorable outcome after SAH.

Blood-Related Toxicity after Traumatic Brain Injury: Potential Targets for Neuroprotection

Emergency visits, hospitalizations, and deaths due to traumatic brain injury (TBI) have increased significantly over the past few decades. While the primary early brain trauma is highly deleterious to the brain, the secondary injury post-TBI is postulated to significantly impact mortality. The presence of blood, particularly hemoglobin, and its breakdown products and key binding proteins and receptors modulating their clearance may contribute significantly to toxicity. Heme, hemin, and iron, for example, cause membrane lipid peroxidation, generate reactive oxygen species, and sensitize cells to noxious stimuli resulting in edema, cell death, and increased morbidity and mortality. A wide range of other mechanisms such as the immune system play pivotal roles in mediating secondary injury. Effective scavenging of all of these pro-oxidant and pro-inflammatory metabolites as well as controlling maladaptive immune responses is essential for limiting toxicity and secondary injury. Hemoglobin metabolism is mediated by key molecules such as haptoglobin, heme oxygenase, hemopexin, and ferritin. Genetic variability and dysfunction affecting these pathways (e.g., haptoglobin and heme oxygenase expression) have been implicated in the difference in susceptibility of individual patients to toxicity and may be target pathways for potential therapeutic interventions in TBI. Ongoing collaborative efforts are required to decipher the complexities of blood-related toxicity in TBI with an overarching goal of providing effective treatment options to all patients with TBI.

Unique Contribution of Haptoglobin and Haptoglobin Genotype in Aneurysmal Subarachnoid Hemorrhage

Survivors of cerebral aneurysm rupture are at risk for significant morbidity and neurological deficits. Much of this is related to the effects of blood in the subarachnoid space which induces an inflammatory cascade with numerous downstream consequences. Recent clinical trials have not been able to reduce the toxic effects of free hemoglobin or improve clinical outcome. One reason for this may be the inability to identify patients at high risk for neurologic decline. Recently, haptoglobin genotype has been identified as a pertinent factor in diabetes, sickle cell, and cardiovascular disease, with the Hp 2-2 genotype contributing to increased complications. Haptoglobin is a protein synthesized by the liver that binds free hemoglobin following red blood cell lysis, and in doing so, prevents hemoglobin induced toxicity and facilitates clearance. Clinical studies in patients with subarachnoid hemorrhage indicate that Hp 2-2 patients may be a high-risk group for hemorrhage related complications and poor outcome. We review the relevance of haptoglobin in subarachnoid hemorrhage and discuss the effects of genotype and expression levels on the known mechanisms of early brain injury (EBI) and cerebral ischemia after aneurysm rupture. A better understanding of haptoglobin and its role in preventing hemoglobin related toxicity should lead to novel therapeutic avenues.

Microvasospasms After Experimental Subarachnoid Hemorrhage Do Not Depend on Endothelin A Receptors

Background and Purpose—

Perturbations in cerebral microcirculation (eg, microvasospasms) and reduced neurovascular communication determine outcome after subarachnoid hemorrhage (SAH). ET-1 (endothelin-1) and its receptors have been implicated in the pathophysiology of large artery spasms after SAH; however, their role in the development of microvascular dysfunction is currently unknown. Here, we investigated whether inhibiting ET A (endothelin A) receptors can reduce microvasospasms after experimentally induced SAH.

Methods—

SAH was induced in male C57BL/6 mice by filament perforation of the middle cerebral artery. Three hours after SAH, a cranial window was prepared and the pial and parenchymal cerebral microcirculation was measured in vivo using two-photon microscopy before, during, and after administration of the ET A receptor inhibitor clazosentan. In separate experiments, the effect of clazosentan treatment on neurological outcome was measured 3 days after SAH.

Results—

Clazosentan treatment had no effect on the number or severity of SAH-induced cerebral microvasospasms nor did it affect neurological outcome.

Conclusions—

Our results indicate that ET A receptors, which mediate large artery spasms after SAH, do not seem to play a role in the development of microarterial spasms, suggesting that posthemorrhagic spasms are mediated by distinct mechanisms in large and small cerebral vessels. Given that cerebral microvessel dysfunction is a key factor for outcome after SAH, further research into the mechanisms that underlie posthemorrhagic microvasospasms is urgently needed.

The role of nitric oxide in stroke

Stroke is considered to be an acute cerebrovascular disease, including ischemic stroke and hemorrhagic stroke. The high incidence and poor prognosis of stroke suggest that it is a highly disabling and highly lethal disease which can pose a serious threat to human health. Nitric oxide (NO), a common gas in nature, which is often thought as a toxic gas, because of its intimate relationship with the pathological processes of many diseases, especially in the regulation of blood flow and cell inflammation. However, recent years have witnessed an increased interest that NO plays a significant and positive role in stroke as an essential gas signal molecule. In view of the fact that the neuroprotective effect of NO is closely related to its concentration, cell type and time, only in the appropriate circumstances can NO play a protective effect. The purpose of this review is to summarize the roles of NO in ischemic stroke and hemorrhagic stroke.

Ischemic Preconditioning in the Intensive Care Unit

OPINION STATEMENT

Preconditioning is the premise that controlled preemptive exposure to sub-lethal doses of a stressor and can condition an organism or organ to later withstand a lethal dose. This process relies on marshaling endogenous survival resources that have evolved as part of an organism's evolutionary struggle to overcome at times harsh environmental conditions. This preconditioning response occurs through activation of myriad complex mechanisms that run the gamut from alterations in gene expression to the de novo synthesis and post-translational modification of proteins, and it may occur across exposure to a wide variety of stressors (i.e., ischemia, hypoxia, hypothermia, drugs). This review will focus on preconditioning in relation to an ischemic stressor (ischemic preconditioning) and how this process may be harnessed as a protective method to ameliorate targeted acute neurologic diseases especially. There has been considerable eagerness to translate ischemic preconditioning to the bedside, and to that end there have been recent trials examining its efficacy in various clinical settings. However, some of these trials have reached diverging conclusions with a protective effect seen in studies targeting acute kidney injury solely while no benefit was seen in larger trials targeting combined endpoints including cardio-, neuro-, and renoprotection in a cohort of patients undergoing cardiac surgery. While an extensive body of pre-clinical research offers ischemic preconditioning as a robust and highly faithful protective phenomenon, its clinical utility remains unproven. This current state may be due to persisting gaps in our understanding of how best to harness its power. This review will provide an overview of the biological mechanisms proposed to underlie ischemic preconditioning, explore initial disease targets, examine the challenges we must overcome to optimally engage this system, and report findings of recent clinical trials.

Cerebral vasospasm and delayed ischaemic deficit following elective aneurysm clipping

Although common after subarachnoid haemorrhage, cerebral vasospasm (CVS) and delayed ischaemic neurological deficit (DIND) rarely occur following elective clipping of unruptured aneurysms. The onset of this complication is variable and its pathophysiology is poorly understood. We report two patients with CVS associated with DIND following unruptured aneurysmal clipping. The literature is reviewed and the potential mechanisms in the context of patient presentations are discussed. A woman aged 53 and a man aged 70 were treated with elective clipping of unruptured middle cerebral artery aneurysms, the older patient also having an anterior communicating artery aneurysm clipped. The operations were uncomplicated with no intra-operative bleeding, no retraction, no contusion, no middle cerebral artery (MCA) temporary clipping, and no intra-operative rupture. Routine post-operative CT scan and CT angiogram showed that in both patients the aneurysms were excluded from the circulation and there was no perioperative subarachnoid blood. Both patients had no neurological deficit post-operatively, but on day 2 developed DIND and vasospasm of the MCA. Both patients had angiographic improvement with intra-arterial verapamil treatment. In one patient, this was done promptly and the patient made a complete recovery, but in the other, the diagnosis was delayed for more than 24hours and the patient had residual hemiparesis and dysphasia due to MCA territory infarction. CVS and DIND following treatment of unruptured aneurysms is a very rare event. However, clinicians should be vigilant as prompt diagnosis and management is required to minimise the risk of cerebral infarction and poor outcome.

Nitric oxide synthases: three pieces to the puzzle?

Subarachnoid hemorrhage remains to be a devastating diagnosis in this day and age, with very few effective interventions. Rising evidence is now pointing towards the marked importance of secondary complications after the hemorrhage, and its active role in morbidity and mortality of this stroke. This review will focus on the role of Nitric Oxide Synthases (NOSes) the role they play in the pathogenesis of SAH.

Estrogen induces nitric oxide production via nitric oxide synthase activation in endothelial cells

INTRODUCTION

17β-estradiol (E2) has been found to induce vasodilation in the cardiovascular system and at physiological levels, resulting in prevention of cerebral vasospasm following subarachnoid hemorrhage (SAH) in animal models. The goal of this study was to analyze the cellular mechanism of nitric oxide (NO) production and its relation to E2, in vitro in brain and peripheral endothelial cells.

METHODS

Human umbilical endothelial cells (HUVEC) and brain endothelial cells (bEnd.3) were treated with estradiol (E2, 0.1, 10, 100, and 1,000 nM), and supernatant was collected at 0, 5, 15, 30, 60, and 120 min for nitric oxide metabolome (nitrite, NO₂) measurements. Cells were also treated with E2 in the presence of 1400W, a potent eNOS inhibitor, and ICI, an antagonist of estradiol receptors (ERs). Effects of E2 on eNOS protein expression were assessed with Western blot analysis.

RESULTS

E2 significantly increased NO2 levels irrespective of its concentration in both cell lines by 35 % and 42 % (p < 0.05). The addition of an E2 antagonist, ICI (10 μM), prevented the E2-induced increases in NO2 levels (11 % p > 0.05). The combination of E2 (10 nM) and a NOS inhibitor (1400W, 5 μM) inhibited NO2 increases in addition (4 %, p > 0.05). E2 induced increases in eNOS protein levels and phosphorylated eNOS (eNOS(p)).

CONCLUSIONS

This study indicates that E2 induces NO level increases in cerebral and peripheral endothelial cells in vitro via eNOS activation and through E2 receptor-mediated mechanisms. Further in vivo studies are warranted to evaluate the therapeutic value of estrogen for the treatment of SAH-induced vasospasm.

CT perfusion-derived mean transit time of cortical brain has a negative correlation with the plasma level of Nitric Oxide after subarachnoid hemorrhage

BACKGROUND

Vasospasm of both large and small parenchymal arteries may contribute to the occurrence of delayed ischemic neurological deficits, and nitric oxide(NO) is an important mediators in the development of cerebral vasospasm after subarachnoid hemorrhage (SAH). We used a rabbit two-hemorrhage model to investigate changes in plasma NO after SAH, and the relationship between NO and brain microcirculation.

METHODS

SAH was induced in rabbits and a control group was sham operated. There were 32 rabbits in each group that survived the second operation, and they were randomly assigned to four groups of eight rabbits each for follow-up assessments on Days 1, 4, 7, or 14, respectively. Cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) were calculated at six regions of interest (ROIs): symmetrical areas of the frontal, parietal-occipital, and temporal lobes. Before the contrast CT scan, blood was drawn from the central artery of the ear for measurement of plasma NO.

RESULTS

In the control group, there was no difference in CBV, CBF, and MTT in the six ROIs, and plasma NO was unchanged. Compared to controls, in the SAH group, CBV decreased slightly in the six ROIs (P > 0.05), frontal lobe CBF decreased, MTT increased (P < 0.05, for both), and NO plasma levels were significantly lower (P < 0.01).

CONCLUSIONS

There was a significant correlation between the increase in MTT and the decrease in plasma NO (P < 0.05), We hypothesized that normalization of NO might have a positive influence on brain microcirculation following SAH.

A hypothesis: hydrogen sulfide might be neuroprotective against subarachnoid hemorrhage induced brain injury

Gases such as nitric oxide (NO) and carbon monoxide (CO) play important roles both in normal physiology and in disease. Recent studies have shown that hydrogen sulfide (H₂S) protects neurons against oxidative stress and ischemia-reperfusion injury and attenuates lipopolysaccharides (LPS) induced neuroinflammation in microglia, exhibiting anti-inflammatory and antiapoptotic activities. The gas H₂S is emerging as a novel regulator of important physiologic functions such as arterial diameter, blood flow, and leukocyte adhesion. It has been known that multiple factors, including oxidative stress, free radicals, and neuronal nitric oxide synthesis as well as abnormal inflammatory responses, are involved in the mechanism underlying the brain injury after subarachnoid hemorrhage (SAH). Based on the multiple physiologic functions of H₂S, we speculate that it might be a promising, effective, and specific therapy for brain injury after SAH.

Preconditioning the human brain: practical considerations for proving cerebral protection

Ischemic preconditioning has evolved as one of the most powerful strategies for cerebral protection in laboratory models of ischemia. Translating the success of laboratory studies to human cerebral protection will necessitate an approximation of laboratory conditions. This would require a practical, easily implemented method of preconditioning and clinical settings in which cerebral ischemia is anticipated, thereby allowing cerebral preconditioning prior to ischemia onset. Remote limb ischemic preconditioning is readily instituted and used in several ongoing cardiac studies for ischemic myocardial protection. It is a potentially promising intervention for brain protection as well. Suitable clinical settings, in which a preliminary study of ischemic preconditioning in neurological disorders appears feasible, include carotid endarterectomy or stenting, cardiac surgery, and subarachnoid hemorrhage with the accompanying risk of vasospasm. These are settings, in which there is substantial risk of brain ischemia, which occurs over a short and predictable period, allowing for preconditioning to be implemented prior to ischemia onset.

Nitric oxide (NO) and asymmetric dimethylarginine (ADMA): their pathophysiological role and involvement in intracerebral hemorrhage

OBJECTIVE

Nitric oxide (NO) has a variety of functions in physiological systems, particularly in the vasculature and the central nervous system. Currently, the imbalance of the pathway involving nitric oxide, nitric oxide synthase, and asymmetric dimethylarginine (NO-NOS-ADMA) is increasingly discussed in connection with endothelial dysfunction. Knowledge about the role of this pathway in intracerebral hemorrhage (ICH), which represents the most devastating stroke subtype, is increasing but still sparse. This article aims to review the current knowledge about the role and metabolism of NO and ADMA. It will also address the role of the NO-NOS-ADMA pathway in ICH and delineate some questions that should be addressed by future studies.

METHODS

A literature search regarding the data about NO, NOS, and ADMA and its role in ICH was conducted in PubMed.

RESULTS

Experimental data from cell culture and animal models indicate that, after the occurrence of ICH, neuronal and inducible nitric oxide synthases (nNOS and iNOS) are both overexpressed and uncoupled through the induction of blood compound metabolites, including thrombin and inflammatory mediators. ADMA, the most potent endogenous inhibitor of NOS, is also overproduced following dysregulation of its metabolizing enzymes. Dysfunction of the NO-NOS-ADMA pathway results in cell death, blood-brain barrier (BBB) disruption, and brain edema via different pathological mechanisms. However, the available data from clinical studies are still rare and partially contradictory.

CONCLUSION

Experimental data suggest an important role for the NO-NOS-ADMA pathway for secondary injury after ICH. Since the literature shows contradictory results, further studies are needed to address current confusion.

Involvement of endothelial-derived relaxing factors in the regulation of cerebral blood flow

Despite numerous researches and advances in the present times, delayed cerebral vasospasm remains a severe complication leading to a high mortality and morbidity in patients with subarachnoid hemorrhage (SAH). Since the discovery of endothelium-derived relaxing factor (EDRF) in 1980, its role in delayed cerebral vasospasm after SAH has been widely investigated as well as in regulation of basic cerebral blood flow, pathophysiology of vasoconstriction and application on prevention and treatment of cerebral vasospasm. Among all the EDRFs, nitric oxide has caught the most attention, and the other substances which display similar properties with characteristics of EDRF such as carbon monoxide (CO), hydrogen sulfide (H(2)S), hydrogen peroxide (H(2)O(2)), potassium ion (K(+)) and methane (CH(4)) have also evoked great interest in the research field. This review provides an overview of recent advances in investigations on the involvement of EDRFs in the regulation of cerebral blood flow, especially in cerebral vasospasm after SAH. Possible therapeutic measures and potential clinical implications for cerebral vasospasm are also summarized.

Impaired vascular responses of insulin-resistant rats after mild subarachnoid hemorrhage

Insulin resistance (IR) impairs cerebrovascular responses to several stimuli in Zucker obese (ZO) rats. However, cerebral artery responses after subarachnoid hemorrhage (SAH) have not been described in IR. We hypothesized that IR worsens vascular reactions after a mild SAH. Hemolyzed blood (300 μl) or saline was infused (10 μl/min) into the cisterna magna of 11-13-wk-old ZO (n = 25) and Zucker lean (ZL) rats (n = 25). One day later, dilator responses of the basilar artery (BA) and its side branch (BA-Br) to acetylcholine (ACh, 10(-6) M), cromakalim (10(-7) M, 10(-6) M), and sodium nitroprusside (10(-7) M) were recorded with intravital videomicroscopy. The baseline diameter of the BA was increased both in the ZO and ZL rats 24 h after the hemolysate injection. Saline-injected ZO animals showed reduced dilation to ACh (BA = 9 ± 3 vs. 22 ± 4%; and BA-Br = 23 ± 5 vs. 37 ± 7%) compared with ZL rats. Hemolysate injection blunted the response to ACh in both the ZO (BA = 4 ± 2%; and BA-Br = 12 ± 3%) and ZL (BA = 7 ± 2%; and BA-Br = 11 ± 3%) rats. Cromakalim (10(-6) M)-induced dilation was significantly reduced in the hemolysate-injected ZO animals compared with the saline control (BA = 13 ± 3 vs. 26 ± 5%; and BA-Br = 28 ± 8 vs. 44 ± 9%) and in the hemolysate-injected ZL rats compared with their saline control (BA = 24 ± 4 vs. 32 ± 4%; but not BA-Br = 39 ± 6 vs. 59 ± 9%). No significant difference in sodium nitroprusside reactivity was observed. Western blot analysis of the BA showed a lower baseline level of neuronal nitric oxide synthase expression and an enhanced cyclooxygenase-2 level in the hemolysate-injected ZO animals. In summary, cerebrovascular reactivity to both endothelium-dependent and -independent stimuli is severely compromised by SAH in IR animals.

Nitric oxide related pathophysiological changes following subarachnoid haemorrhage

Subarachnoid hemorrhage (SAH) comprises only about 7% of all strokes worldwide but is associated with severe mortality and morbidity. SAH is associated with a number of secondary pathologies, such as: transient cerebral vasospasm, delayed ischemic neuronal deficit (DIND), cortical spreading depression, microcirculatory modifications, microthrombosis and ischemic complications. Available data demonstrate that there are complex interactions among these secondary complications, and NO plays an important role among the interactions. NO has been implicated to be a crucial molecule in eliminating vasospasm, facilitating neuroprotection, anti-microthrombosis, cerebral ischemic tolerance and promoting endothelial cell function. Therefore, therapeutic agent targeting a key component in the pathopyhysiology of SAH such as NO and its related enzymes would be favorable for future development of SAH drugs. Alternatively, because of the complex nature of the secondary complications after SAH, agents with multiple efficacies on these complications, or the combination of several agents such as NO donors, oxide radical scavengers and neuroprotectants might be more desirable.

Simvastatin re-couples dysfunctional endothelial nitric oxide synthase in experimental subarachnoid hemorrhage

Reduced endothelial nitric oxide synthase (eNOS) function has been linked to secondary complications of subarachnoid hemorrhage (SAH). We previously found that there is increased eNOS function after SAH but that it is uncoupled, leading to secondary complications such as vasospasm, microthromboembolism and neuronal apoptosis. Here we test the hypothesis that recoupling eNOS with simvastatin can prevent these complications. SAH was created in mice that were treated with vehicle or simvastatin starting 2 weeks before or 30 minutes after SAH. SAH increased phosphorylated eNOS which was prevented by pre- or post-treatment with simvastatin. Simvastatin pre-treatment also prevented the increase in eNOS monomer formation that was associated with SAH, decreased superoxide anion radical production and increased NO. These changes were associated with decreased vasospasm, microthromboemboli and neuronal injury. The data suggest that simvastatin re-couples eNOS after SAH, leading to decreased secondary complications such as vasospasm, microthromboemboli and neuronal injury.

The role of nitric oxide donors in treating cerebral vasospasm after subarachnoid hemorrhage

Reduced intra- and perivascular availability of nitric oxide (NO) significantly contributes to the multifactorial pathophysiology of cerebral vasospasm after aneurysmal subarachnoid hemorrhage (SAH). The short half-life of NO demands its therapeutic substitution via NO donors. Classic NO donors such as sodium nitroprusside and nitroglycerin cannot be used as routine therapeutics because of serious side effects. Thus, a new generation of NO donors has been the subject of experimental investigations to avoid the drawbacks of the classic drugs. The purpose of this paper is to review the characteristics of different NO donors with regard to their promise and potential consequences in treating cerebral vasospasm. Additional novel concepts to increase NO concentrations, such as the activation of endothelial nitric oxide synthase (eNOS), are discussed.

Uncoupling of endothelial nitric oxide synthase after experimental subarachnoid hemorrhage

We studied whether endothelial nitric oxide synthase (eNOS) is upregulated and uncoupled in large cerebral arteries after subarachnoid hemorrhage (SAH) and also whether this causes cerebral vasospasm in a mouse model of anterior circulation SAH. Control animals underwent injection of saline instead of blood (n=16 SAH and n=16 controls). There was significant vasospasm of the middle cerebral artery 2 days after SAH (lumen radius/wall thickness ratio 4.3 ± 1.3 for SAH, 23.2 ± 2.1 for saline, P<0.001). Subarachnoid hemorrhage was associated with terminal deoxynucleotidyl transferase dUTP nick-end labeling, cleaved caspase-3, and Fluoro-Jade-positive neurons in the cortex and with CA1 and dentate regions in the hippocampus. There were multiple fibrinogen-positive microthromboemboli in the cortex and hippocampus after SAH. Transgenic mice expressing lacZ under control of the eNOS promoter had increased X-gal staining in large arteries after SAH, and this was confirmed by the increased eNOS protein on western blotting. Evidence that eNOS was uncoupled was found in that nitric oxide availability was decreased, and superoxide and peroxynitrite concentrations were increased in the brains of mice with SAH. This study suggests that artery constriction by SAH upregulates eNOS but that it is uncoupled and produces peroxynitrite that may generate microemboli that travel distally and contribute to brain injury.

Modification of endothelial nitric oxide synthase through AMPK after experimental subarachnoid hemorrhage

Severe subarachnoid hemorrhage (SAH) induces dysfunction of endothelial nitric oxide synthase (eNOS), resulting in severe vasospasm. Clinically, however, some portions of cerebral arteries may show only mild vasospasm. Although severe vasospastic arteries after SAH have been intensively studied, activity of eNOS associated with the mild form of the disease has received less attention. The purpose of the present study was to clarify molecular mechanisms underlying the regulation of eNOS activity in mild vasospastic arteries after SAH. In a rat single-hemorrhage model, basilar arteries were obtained up to 7 days after SAH. Western blot analysis was used to study the temporal profiles of eNOS, phosphorylated (p)-eNOS at Ser(1177) or Thr(495), inducible NOS (iNOS), AMP-activated protein kinase alpha (AMPK alpha, p-AMPK alpha at Thr(172)Akt, p-Akt at Ser(473), cyclic AMP-dependent protein kinase (PKA), and p-PKA at Thr(197) in basilar arteries. Immunohistochemical studies were performed to examine the spatial expression patterns of p-eNOS at Ser(1177) and p-AMPK alpha at Thr(172). Western blot analysis showed eNOS to be significantly phosphorylated at Ser(1177) from 1 to 2 days after SAH, accompanied by upregulation of iNOS and AMPK, while activation states of Akt and PKA did not show significant change. Immunohistochemistry revealed phosphorylation of eNOS and AMPK alpha in endothelial cells of the basilar artery. SAH might thus induce temporary activation of AMPK alpha, which phosphorylates eNOS at Ser(1177) in endothelial cells of mild vasospastic basilar arteries. This signal transduction may play an important role in controlling cerebral blood flow after SAH.

Inflammation and cerebral vasospasm after subarachnoid hemorrhage

Morbidity and mortality of patients with aneurysmal subarachnoid hemorrhage (aSAH) is significantly related to the development of chronic cerebral vasospasm. Despite extensive clinical and experimental research, the pathophysiology of the events that result in delayed arterial spasm is not fully understood. A review of the published literature on cerebral vasospasm that included but was not limited to all PubMed citations from 1951 to the present was performed. The findings suggest that leukocyte-endothelial cell interactions play a significant role in the pathophysiology of cerebral vasospasm and explain the clinical variability and time course of the disease. Experimental therapeutic targeting of the inflammatory response when timed correctly can prevent vasospasm, and supplementation of endothelial relaxation by nitric oxide-related therapies and other approaches could result in reversal of the arterial narrowing and improved outcomes in patients with aSAH.

Impairment of intracerebral arteriole dilation responses after subarachnoid hemorrhage. Laboratory investigation

OBJECT

Cerebrovascular dysfunction after subarachnoid hemorrhage (SAH) may contribute to ischemia, but little is known about the contribution of intracerebral arterioles. In this study, the authors tested the hypothesis that SAH inhibits the vascular reactivity of intracerebral arterioles and documented the time course of this dysfunction.

METHODS

Subarachnoid hemorrhage was induced using an endovascular filament model in halothane-anesthetized male Sprague-Dawley rats. Penetrating intracerebral arterioles were harvested 2, 4, 7, or 14 days postinsult, cannulated using a micropipette system that allowed luminal perfusion and control of luminal pressure, and evaluated for reactivity to vasodilator agents.

RESULTS

Spontaneous tone developed in all pressurized (60 mm Hg) intracerebral arterioles harvested in this study (from 66 rats), with similar results in the sham and SAH groups. Subarachnoid hemorrhage did not affect dilation responses to acidic pH (6.8) but led to a persistent impairment of endothelium-dependent dilation responses to adenosine triphosphate (p < 0.01), as well as a transient attenuation (p < 0.05) of vascular smooth muscle-dependent dilation responses to adenosine, sodium nitroprusside, and 8-Br-cyclic guanosine monophosphate (cGMP). Impairment of NO-mediated dilation was more sustained than adenosine- and 8-Br-cGMP-induced responses (up to 7 days postinsult compared with 2 days). All smooth muscle-dependent responses returned to sham levels by 14 days after SAH.

CONCLUSIONS

Subarachnoid hemorrhage led to a persistent impairment of endothelium-dependent dilation and a transient attenuation of vascular smooth muscle-dependent dilation responses to adenosine. Impairment of NO-mediated dilation occurred when the response to cGMP was intact, suggesting a change in cGMP levels rather than an alteration in intracellular mechanisms downstream from cGMP.

Role of inflammation (leukocyte-endothelial cell interactions) in vasospasm after subarachnoid hemorrhage

BACKGROUND

Delayed vasospasm is the leading cause of morbidity and mortality after aneurysmal subarachnoid hemorrhage (aSAH). This phenomenon was first described more than 50 years ago, but only recently has the role of inflammation in this condition become better understood.

METHODS

The literature was reviewed for studies on delayed vasospasm and inflammation.

RESULTS

There is increasing evidence that inflammation and, more specifically, leukocyte-endothelial cell interactions play a critical role in the pathogenesis of vasospasm after aSAH, as well as in other conditions including meningitis and traumatic brain injury. Although earlier clinical observations and indirect experimental evidence suggested an association between inflammation and chronic vasospasm, recently direct molecular evidence demonstrates the central role of leukocyte-endothelial cell interactions in the development of chronic vasospasm. This evidence shows in both clinical and experimental studies that cell adhesion molecules (CAMs) are up-regulated in the perivasospasm period. Moreover, the use of monoclonal antibodies against these CAMs, as well as drugs that decrease the expression of CAMs, decreases vasospasm in experimental studies. It also appears that certain individuals are genetically predisposed to a severe inflammatory response after aSAH based on their haptoglobin genotype, which in turn predisposes them to develop clinically symptomatic vasospasm.

CONCLUSION

Based on this evidence, leukocyte-endothelial cell interactions appear to be the root cause of chronic vasospasm. This hypothesis predicts many surprising features of vasospasm and explains apparently unrelated phenomena observed in aSAH patients. Therapies aimed at preventing inflammation may prevent and/or reverse arterial narrowing in patients with aSAH and result in improved outcomes.

Endothelial nitric oxide synthase tagging single nucleotide polymorphisms and recovery from aneurysmal subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is a hemorrhagic stroke subtype with a poor recovery profile. Cerebral vasospasm (CV), a narrowing of the cerebral vasculature, significantly contributes to the poor recovery profile. Variation in the endothelial nitric oxide (NO) synthase (eNOS) gene has been implicated in CV and outcome after SAH. The purpose of this project was to explore the potential association between three eNOS tagging single nucleotide polymorphisms (SNPs) and recovery from SAH. We included 195 participants with a diagnosis of SAH and DNA and 6-month outcome data available but without preexisting neurologic disease/deficit. Genotyping was performed using an ABI Prism 7000 Sequence Detection System and TaqMan assays. CV was verified by cerebral angiogram independently read by a neurosurgeon on 118 participants. Modified Rankin Scores (MRS) and Glasgow Outcome Scale (GOS) scores were collected 6 months posthemorrhage. Data were analyzed using descriptive statistics, analysis of variance (ANOVA) and chi-square analysis as appropriate. The sample was primarily female (n=147; 75.4%) and White (n=178; 91.3%) with a mean age of 54.6 years. Of the participants with CV data, 56 (47.5%) developed CV within 14 days of SAH. None of the SNPs individually were associated with CV presence; however, a combination of the three variant SNPs was significantly associated with CV (p=.017). Only one SNP (rs1799983, variant allele) was associated with worse 6-month GOS scores (p<.001) and MRS (p<.001). These data indicate that the eNOS gene plays a role in the response to SAH, which may be explained by an influence on CV.

Medical management of cerebral vasospasm: present and future

Cerebral vasospasm is one of the major complications of subarachnoid hemorrhage. The delayed occurrence of this complication allows for preventive management and early therapeutic interventions. Yet, accurate and timely diagnosis remains challenging and therapeutic options are rather limited. This review discusses new developments in the diagnosis and medical management of cerebral vasospasm made possible by technological advances and growing understanding of the complex pathophysiology of this disorder. CT protocols including CT perfusion and MRI with diffusion and perfusion sequences are increasingly employed in the evaluation of patients with suspected vasospasm. These radiological studies can add important information to that provided by transcranial Doppler and conventional angiography. Nimodipine for the prevention of delayed functional sequelae and hemodynamic augmentation therapy for the treatment of symptomatic vasospasm remains the mainstay of medical management. Novel strategies under investigation include the use of endothelin receptor antagonists, magnesium sulphate and statins. The value of albumin is being formally studied in an ongoing trial. Interventions to enhance nitric oxide may prove viable in the near future.

Cerebral hemorrhage and vasospasm in a child with congenital heart disease

INTRODUCTION

Intracerebral hemorrhages are relatively rare events in children and cerebral vasospasm after such hemorrhages is even more unusual. Children with structural congenital heart disease are particularly at risk for both thrombotic and embolic events but not to isolated hemorrhages.

DISCUSSION

We report a case of cerebral vasospasm in a child with structural congenital heart disease after a cerebral hemorrhage.

CONCLUSION

This case illustrates that this rare occurrence must be swiftly recognized and treated in order to maximize clinical outcome.

Determination of cerebrospinal fluid concentrations of arginine and dimethylarginines in patients with subarachnoid haemorrhage

Elevated cerebrospinal fluid (CSF) concentrations of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), are assumed to be related to delayed vasospasm after subarachnoid haemorrhage (SAH). However, data on CSF concentrations of L-arginine, ADMA and its structural isomer symmetric dimethylarginine (SDMA) are very sparse in humans. We here present a new hydrophilic interaction chromatography-tandem mass spectrometry (HILIC-MS-MS) method for the precise determination of these substances in CSF. The method requires only minimal sample preparation and features isotope labeled internal standards. First data of patients with SAH showed that on the day of admission CSF concentration values of L-arginine and ADMA were not significantly different from controls, but increased markedly during the course of the hospital stay. The decrease of the L-arginine to ADMA ratio points to a progressive impairment of the NO production rate in the brain after SAH which is confirmed by a simultaneous decrease in nitrate and nitrite concentrations in CSF.