Endothelial nitric oxide synthase mediates endogenous protection against subarachnoid hemorrhage-induced cerebral vasospasm

Alterations of caveolin-1 expression in a mouse model of delayed cerebral vasospasm following subarachnoid hemorrhage

The aim of the present study was to evaluate the expression levels of caveolin-1 in the basilar artery following delayed cerebral vasospasm (DCVS) in a rat model of subarachnoid hemorrhage (SAH), in order to investigate the association between caveolin-1 and DCVS, and its potential as a treatment for DCVS of SAH. A total of 150 Sprague Dawley rats were randomly allocated into blank, saline and SAH groups. The SAH and saline groups were subdivided into days 3, 5, 7 and 14 following the establishment of the model. The murine model of SAH was established by double injection of autologous arterial blood into the cisterna magana and DCVS was detected using Bederson neurological severity scores. Hematoxylin and eosin (HE) staining was used to observe the inner perimeter of the basilar artery pipe and variations in the thickness of the basilar artery wall. Alterations in the levels of caveolin-1 protein in the basilar artery were measured using immunofluorescence and western blot analysis; whereas alterations in the mRNA expression levels of caveolin-1 were detected by reverse transcription-quantitative polymerase chain reaction. In the present study, 15 mice succumbed to SAH-induced DCVS in the day 3 (n=3), 5 (n=5) and 7 (n=2) groups. No mortality was observed in the blank control and saline groups during the process of observation in the SAH group, All mice in the SAH groups exhibited Bederson neurological severity scores ≥1; whereas no neurological impairment was detected in the blank and normal saline groups, demonstrating the success of the model. HE staining was used to assess vasospasm and the results demonstrated that the inner perimeter of the basal artery pipe decreased at day 3 in the SAH group; whereas values peaked in the day 7 group. The thickness of the basal artery wall significantly increased (P<0.05), as compared with the blank and saline groups, in which no significant alterations in the wall thickness and the inner perimeter of the basal artery pipe were detected. As detected by immunofluorescence and western blot analysis, the expression levels of caveolin-1 protein significantly decreased in the day 7 of SAH group, as compared with the blank and saline groups (P<0.01), in which no significant alterations were detected. Caveolin-1 mRNA expression levels significantly increased at the day 7 in the SAH group, as compared with the blank and the saline groups (P<0.01), as detected by RT-qPCR. Furthermore, significant differences were detected at day 14 in the SAH group, as compared with the blank and the saline groups (P>0.05), in which no significant alterations were detected. Therefore, the results of the present study demonstrated that caveolin-1 protein was downregulated in the basilar artery of a rat modeling SAH, which may be associated with DCVS. This suggested that caveolin-1 may be a potential target for the treatment of DCVS.

Isoflurane postconditioning with cardiac support promotes recovery from early brain injury in mice after severe subarachnoid hemorrhage

AIMS

Neurocardiac dysfunction is a life-threatening systemic consequence of subarachnoid hemorrhage (SAH) that contributes to triggering delayed cerebral ischemia (DCI). This study aimed to determine the impact of dobutamine cardiac support during isoflurane postconditioning on post-SAH DCI.

MAIN METHODS

Male C57BL/6 mice were subjected to SAH, SAH plus isoflurane postconditioning, or SAH plus isoflurane postconditioning with dobutamine. Severity of SAH was graded from 1 to 4 (mild, 1-2; severe, 3-4) based on T2*-weighted magnetic resonance imaging (MRI). Cardiac output (CO) measured by transthoracic pulsed wave Doppler-echocardiography was titrated at a supra-normal level with intravenous dobutamine infusion. Neurological function was examined daily by neurological score and Rotarod tests. DCI was analyzed 3days later by determining new infarction on diffusion-weighted MRI. In a separate experiment, mice were pretreated with hypoxia-inducible factor (HIF) inhibitor 2-methoxyestradiol (2ME2).

KEY FINDINGS

Clinically relevant CO depression was notable in severe SAH grade mice, in which dobutamine CO management combined with isoflurane postconditioning showed earlier and improved functional recovery than postconditioning with single isoflurane inhalation. Incidence of infarction and volumes on day 3 reduced significantly in this subgroup. All of the effects during preconditioning were attenuated by 2ME2 pretreatment.

SIGNIFICANCE

Isoflurane postconditioning under dobutamine cardiac support improves recovery from SAH-induced early brain injury, leading to reduced DCI resultant from severe experimental SAH. These results indicate the importance of neuro-cardiac protection, in which HIF may be acting as a critical mediator, as a promising therapeutic approach to SAH.

Endothelial nitric oxide synthase: a potential therapeutic target for cerebrovascular diseases

Endothelial nitric oxide (NO) is a significant signaling molecule that regulates cerebral blood flow (CBF), playing a pivotal role in the prevention and treatment of cerebrovascular diseases. However, achieving the expected therapeutic efficacy is difficult using direct administration of NO donors. Therefore, endothelial nitric oxide synthase (eNOS) becomes a potential therapeutic target for cerebrovascular diseases. This review summarizes the current evidence supporting the importance of CBF to cerebrovascular function, and the roles of NO and eNOS in CBF regulation.

Hemoglobin induced NO/cGMP suppression Deteriorate Microcirculation via Pericyte Phenotype Transformation after Subarachnoid Hemorrhage in Rats

Subarachnoid hemorrhage (SAH) usually results from ruptured aneurysm, but how leaked hemoglobin regulates the microcirculation in the pathophysiology of early brain injury after SAH is still unclear. In the present study, we sought to investigate the role and possible mechanism of hemoglobin induced pericyte phenotype transformation in the regulation of microcirculation after SAH. Endovascular perforation SAH rat model, brain slices and cultured pericytes were used, and intervened with endothelial nitric oxide synthase (eNOS) antagonist L-NNA and its agonist scutellarin, hemoglobin, DETA/NO (nitric oxide(NO) donor), PITO (NO scavenger), 8-Br-cGMP (cGMP analog). We found modulating eNOS regulated pericyte α-SMA phenotype transformation, microcirculation, and neurological function in SAH rats. Modulating eNOS also affected eNOS expression, eNOS activity and NO availability after SAH. In addition, we showed hemoglobins penetrated into brain parenchyma after SAH. And hemoglobins significantly reduced the microvessel diameters at pericyte sites, due to the effects of hemoglobin inducing α-SMA expressions in cultured pericytes and brain slices via inhibiting NO/cGMP pathway. In conclusion, pericyte α-SMA phenotype mediates acute microvessel constriction after SAH possibly by hemoglobin suppressing NO/cGMP signaling pathway. Therefore, by targeting the eNOS and pericyte α-SMA phenotype, our present data may shed new light on the management of SAH patients.

Molecular, Cellular and Clinical Aspects of Intracerebral Hemorrhage: Are the Enemies Within?

Hemorrhagic stroke is a disease with high incidence and mortality rates. In addition to the mass lesions that result from hemorrhagic stroke, substances such as the blood-derived products (BDP) (hemoglobin (Hb), heme and iron) induce a potent inflammatory response and exert direct toxic effects on neurons, astrocytes, and microglia. In the present review, we discuss the mechanisms of brain injury secondary to hemorrhagic stroke, focusing on the involvement of BDP as major players of cellular redox imbalance, inflammation, and glutamate excitotoxicity. Potential natural mechanisms of protection against free Hb and heme such as haptoglobin and hemopexin, respectively, are highlighted. We finally discuss the experimental and clinical trials targeting free iron and heme scavenging as well as inflammation, as potential new therapies to minimize the devastating effects of hemorrhagic stroke on brain structure and function.

A Phase I proof-of-concept and safety trial of sildenafil to treat cerebral vasospasm following subarachnoid hemorrhage

OBJECTIVE

Studies show that phosphodiesterase-V (PDE-V) inhibition reduces cerebral vasospasm (CVS) and improves outcomes after experimental subarachnoid hemorrhage (SAH). This study was performed to investigate the safety and effect of sildenafil (an FDA-approved PDE-V inhibitor) on angiographic CVS in SAH patients.

METHODS

A2-phase, prospective, nonrandomized, human trial was implemented. Subarachnoid hemorrhage patients underwent angiography on Day 7 to assess for CVS. Those with CVS were given 10 mg of intravenous sildenafil in the first phase of the study and 30 mg in the second phase. In both, angiography was repeated 30 minutes after infusion. Safety was assessed by monitoring neurological examination findings and vital signs and for the development of adverse reactions. For angiographic assessment, in a blinded fashion, pre- and post-sildenafil images were graded as "improvement" or "no improvement" in CVS. Unblinded measurements were made between pre- and post-sildenafil angiograms.

RESULTS

Twelve patients received sildenafil; 5 patients received 10 mg and 7 received 30 mg. There were no adverse reactions. There was no adverse effect on heart rate or intracranial pressure. Sildenafil resulted in a transient decline in mean arterial pressure, an average of 17% with a return to baseline in an average of 18 minutes. Eight patients (67%) were found to have a positive angiographic response to sildenafil, 3 (60%) in the low-dose group and 5 (71%) in the high-dose group. The largest degree of vessel dilation was an average of 0.8 mm (range 0-2.1 mm). This corresponded to an average percentage increase in vessel diameter of 62% (range 0%-200%).

CONCLUSIONS

The results from this Phase I safety and proof-of-concept trial assessing the use of intravenous sildenafil in patients with CVS show that sildenafil is safe and well tolerated in the setting of SAH. Furthermore, the angiographic data suggest that sildenafil has a positive impact on human CVS.

Cerebral Ischemic Preconditioning: the Road So Far…

Cerebral preconditioning constitutes the brain's adaptation to lethal ischemia when first exposed to mild doses of a subtoxic stressor. The phenomenon of preconditioning has been largely studied in the heart, and data from in vivo and in vitro models from past 2-3 decades have provided sufficient evidence that similar machinery exists in the brain as well. Since preconditioning results in a transient protective phenotype labeled as ischemic tolerance, it can open many doors in the medical warfare against stroke, a debilitating cerebrovascular disorder that kills or cripples thousands of people worldwide every year. Preconditioning can be induced by a variety of stimuli from hypoxia to pharmacological anesthetics, and each, in turn, induces tolerance by activating a multitude of proteins, enzymes, receptors, transcription factors, and other biomolecules eventually leading to genomic reprogramming. The intracellular signaling pathways and molecular cascades behind preconditioning are extensively being investigated, and several first-rate papers have come out in the last few years centered on the topic of cerebral ischemic tolerance. However, translating the experimental knowledge into the clinical scaffold still evades practicality and faces several challenges. Of the various preconditioning strategies, remote ischemic preconditioning and pharmacological preconditioning appears to be more clinically relevant for the management of ischemic stroke. In this review, we discuss current developments in the field of cerebral preconditioning and then examine the potential of various preconditioning agents to confer neuroprotection in the brain.

Glycyrrhizin Attenuates Proinflammatory Cytokines through a Peroxisome Proliferator-Activated Receptor-γ-Dependent Mechanism and Experimental Vasospasm in a Rat Model

The peroxisome proliferator-activated receptor (PPAR) is downregulated in the cortex of experimental subarachnoid hemorrhage (SAH) animals. This study is to examine the effect of glycyrrhizin on the alternation of PPARs and proinflammatory cytokines in a rodent SAH model. CSF cytokines were evaluated by RT-PCR. Basilar arteries (BAs) were harvested to examine PPARs (RT-PCR and Western blot), and a morphological examination was conducted. Deformed endothelium and tortuous elastic lamina were observed in the BAs of the SAH groups, but they were absent in the glycyrrhizin groups or the healthy controls. The PPAR-γ and -δ protein levels were reduced in the SAH groups (p < 0.01). Glycyrrhizin significantly increased the expressed PPAR-γ protein and mRNA (preconditioning) and PPAR-δ mRNA (both treatment and preconditioning), which corresponded to the reduced IL-1β and TNF-α levels. The administration of a PPAR-γ inhibitor, BADGE, halted the reduction of IL-1β and TNF-α in the glycyrrhizin groups. Conclusively, glycyrrhizin exerts anti-inflammatory effects on SAH-induced vasospasm and attenuates the expression of PPARs, especially PPAR-γ, which corresponds to the severity of SAH-related inflammation. These findings also offer credit to the antivasospastic effect of glycyrrhizin and its vasculoprotective effect in animals subjected to SAH.

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.

HIF-1α Mediates Isoflurane-Induced Vascular Protection in Subarachnoid Hemorrhage

Objective

Outcome after aneurysmal subarachnoid hemorrhage (SAH) depends critically on delayed cerebral ischemia (DCI) – a process driven primarily by vascular events including cerebral vasospasm, microvessel thrombosis, and microvascular dysfunction. This study sought to determine the impact of postconditioning – the phenomenon whereby endogenous protection against severe injury is enhanced by subsequent exposure to a mild stressor – on SAH-induced DCI.

Methods

Adult male C57BL/6 mice were subjected to sham, SAH, or SAH plus isoflurane postconditioning. Neurological outcome was assessed daily via sensorimotor scoring. Contributors to DCI including cerebral vasospasm, microvessel thrombosis, and microvascular dysfunction were measured 3 days later. Isoflurane-induced changes in hypoxia-inducible factor 1alpha (HIF-1α)-dependent genes were assessed via quantitative polymerase chain reaction. HIF-1α was inhibited pharmacologically via 2-methoxyestradiol (2ME2) or genetically via endothelial cell HIF-1α-null mice (EC-HIF-1α-null). All experiments were performed in a randomized and blinded fashion.

Results

Isoflurane postconditioning initiated at clinically relevant time points after SAH significantly reduced cerebral vasospasm, microvessel thrombosis, microvascular dysfunction, and neurological deficits in wild-type (WT) mice. Isoflurane modulated HIF-1α-dependent genes – changes that were abolished in 2ME2-treated WT mice and EC-HIF-1α-null mice. Isoflurane-induced DCI protection was attenuated in 2ME2-treated WT mice and EC-HIF-1α-null mice.

Interpretation

Isoflurane postconditioning provides strong HIF-1α-mediated macro- and microvascular protection in SAH, leading to improved neurological outcome. These results implicate cerebral vessels as a key target for the brain protection afforded by isoflurane postconditioning, and HIF-1α as a critical mediator of this vascular protection. They also identify isoflurane postconditioning as a promising novel therapeutic for SAH.

Preconditioning effect on cerebral vasospasm in patients with aneurysmal subarachnoid hemorrhage

BACKGROUND

Recent experimental evidence indicates that endogenous mechanisms against cerebral vasospasm can be induced via preconditioning.

OBJECTIVE

To determine whether these vascular protective mechanisms are also present in vivo in humans with aneurysmal subarachnoid hemorrhage.

METHODS

A multicenter retrospective cohort of patients with aneurysmal subarachnoid hemorrhage was examined for ischemic preconditioning stimulus: preexisting steno-occlusive cerebrovascular disease (CVD) and/or previous cerebral infarct. Generalized estimating equation models were performed to determine the effect of the preconditioning stimulus on the primary end points of radiographic vasospasm, symptomatic vasospasm, and vasospasm-related delayed cerebral infarction and the secondary end point of discharge modified Rankin Scale score.

RESULTS

Of 1043 patients, 321 (31%) had preexisting CVD and 437 (42%) had radiographic vasospasm. Patients with preexisting CVD were less likely to develop radiographic vasospasm (odds ratio = 0.67; 95% confidence interval = 0.489-0.930; P = .02) but had no differences in other end points. In terms of the secondary end point, patients with preexisting CVD did not differ significantly from patients without preexisting CVD in mortality or unfavorable outcome in multivariate analyses, although patients with preexisting CVD were marginally more likely to die (P = .06).

CONCLUSION

This retrospective case-control study suggests that endogenous protective mechanisms against cerebral vasospasm-a preconditioning effect-may exist in humans, although these results could be the effect of atherosclerosis or some combination of preconditioning and atherosclerosis. Additional studies investigating the potential of preconditioning in aneurysmal subarachnoid hemorrhage are warranted.

The role of the nitric oxide pathway in brain injury and its treatment--from bench to bedside

Nitric oxide (NO) is a key signalling molecule in the regulation of cerebral blood flow. This review summarises current evidence regarding the role of NO in the regulation of cerebral blood flow at rest, under physiological conditions, and after brain injury, focusing on subarachnoid haemorrhage, traumatic brain injury, and ischaemic stroke and following cardiac arrest. We also review the role of NO in the response to hypoxic insult in the developing brain. NO depletion in ischaemic brain tissue plays a pivotal role in the development of subsequent morbidity and mortality through microcirculatory disturbance and disordered blood flow regulation. NO derived from endothelial nitric oxide synthase (eNOS) appears to have neuroprotective properties. However NO derived from inducible nitric oxide synthase (iNOS) may have neurotoxic effects. Cerebral NO donor agents, for example sodium nitrite, appear to replicate the effects of eNOS derived NO, and therefore have neuroprotective properties. This is true in both the adult and immature brain. We conclude that these agents should be further investigated as targeted pharmacotherapy to protect against secondary brain injury.

Endovascular perforation subarachnoid hemorrhage fails to cause Morris water maze deficits in the mouse

Cognitive dysfunction is the primary driver of poor long-term outcome in aneurysmal subarachnoid hemorrhage (SAH) survivors; modeling such deficits preclinically is thus key for mechanistic and translational investigation. Although rat SAH causes long-term deficits in learning and memory, it remains unknown whether similar deficits are seen in the mouse, a species particularly amenable to powerful, targeted genetic manipulation. We thus subjected mice to endovascular perforation SAH and assessed long-term cognitive outcome via the Morris water maze (MWM), the most commonly used metric for rodent neurocognition. No significant differences in MWM performance (by either of two protocols) were seen in SAH versus sham mice. Moreover, SAH caused negligible hippocampal CA1 injury. These results undercut the potential of commonly used methods (of SAH induction and assessment of long-term neurocognitive outcome) for use in targeted molecular studies of SAH-induced cognitive deficits in the mouse.

Should the STAIR criteria be modified for preconditioning studies?

Diverse preconditioning (PC) stimuli protect against a wide variety of neuronal insults in animal models, engendering enthusiasm that PC could be used to protect the brain clinically. Candidate clinical applications include cardiac and vascular surgery, after subarachnoid hemorrhage, and prior to conditions in which acute neuronal injury is anticipated. However, disappointments in clinical validation of multiple neuroprotectants suggest potential problems translating animal data into successful human therapies. Thus, despite strong promise of preclinical PC studies, caution should be maintained in translating these findings into clinical applications. The Stroke Therapy Academic Industry Roundtable (STAIR) working group and the National institute of Neurological Diseases and Stroke (NINDS) proposed working guidelines to improve the utility of preclinical studies that form the foundation of therapies for neurological disease. Here, we review the applicability of these consensus criteria to preconditioning studies and discuss additional considerations for PC studies. We propose that special attention should be paid to several areas, including 1) safety and dosage of PC treatments; 2) meticulously matching preclinical modeling to the human condition to be tested; and 3) timing of both the initiation and discontinuation of the PC stimulus relative to injury ictus.

Glycyrrhizin attenuates Toll like receptor-2, -4 and experimental vasospasm in a rat model

Upregulated TLRs are observed in the serum of animals following experimental subarachnoid hemorrhage. This study was to examine glycyrrhizin's effect on proinflammatory cytokines and TLRs in SAH rats. Administration with glycyrrhizin was initiated 24 hr before and 1 hr later using osmotic minipump. Basilar arteries were harvested to examine TLRs mRNA and protein (rt-PCR and western blot) and CSF cytokines (rt-PCR). Morphologically, deformed endothelium, tortuous elastic lamina, and smooth muscle necrosis were observed in the SAH rats, but were absent in the glycyrrhizin pretreatment group. The TLR-3 protein level was not increased in SAH animals, compared with the controls, while that of TLR-2 and -4 in the SAH only and SAH plus vehicle groups was significantly elevated (P < 0.01). Pretreatment and treatment with glycyrrhizin reduced TLR-2 and -4 by 28 ± 8% and 33.4 ± 9.2%, respectively. Likewise, glycyrrhizin was able to reduce the IL-1β and MCP-1 mRNA levels. This study shows glycyrrhizin exerts anti-inflammatory effects on SAH induced vasospasm and attenuates the ultrashort time expression of TLRs, like TLR-2 and -4. It corresponds to SAH induced early brain injury. These findings offer credit to the antivasospastic effect of glycyrrhizin and its effect on SAH induced early brain injury.

Magnesium lithospermate B, an active extract of Salvia miltiorrhiza, mediates sGC/cGMP/PKG translocation in experimental vasospasm

Background. Soluble guanylyl cyclases (sGCs) and Ras homolog gene family, member A (rhoA)/Ras homolog gene family kinase(rho-kinase) plays a role in vascular smooth muscle relaxation in subarachnoid hemorrhage (SAH). It is of interest to examine the effect of MLB on rhoA/ROCK and sGC/cGMP/PKG expression. Methods. A rodent SAH model was employed. Tissue samples were for sGCα1, sGCβ1, PKG, rhoA, ROCK (Western blot), and cGMP (ELISA) measurement. Results. MLB morphologically improved convolution of the internal elastic lamina, distortion of endothelial wall, and necrosis of the smooth muscle in the SAH rats. Expressed cGMP, sGCα1, sGCβ1, and PKG in the SAH groups were reduced (P < 0.01), and MLB precondition significantly induced cGMP, sGCα1, sGCβ1, and PKG. L-NAME reversed the vasodilation effect of MLB, reduced the bioexpression of PKG and cGMP (P < 0.01), and tends to reduce sGCα1 level and induce rhoA, ROCK level in MLB precondition + SAH groups. Conclusion. These results demonstrate that sGC/cGMP/PKG and NO/ET pathways play pivotal roles in SAH-induced vasospasm. Through activating sGC/cGMP/PKG pathway and partially by inactivating rho-kinase in a NO-dependent mechanism, MLB shows promise to be an effective strategy for the treatment of this disease entity.

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.

Inflammation, cerebral vasospasm, and evolving theories of delayed cerebral ischemia

Cerebral vasospasm (CVS) is a potentially lethal complication of aneurysmal subarachnoid hemorrhage (aSAH). Recently, the symptomatic presentation of CVS has been termed delayed cerebral ischemia (DCI), occurring as early as 3-4 days after the sentinel bleed. For the past 5-6 decades, scientific research has promulgated the theory that cerebral vasospasm plays a primary role in the pathology of DCI and subsequently delayed ischemic neurological decline (DIND). Approximately 70% of patients develop CVS after aSAH with 50% long-term morbidity rates. The exact etiology of CVS is unknown; however, a well-described theory involves an antecedent inflammatory cascade with alterations of intracellular calcium dynamics and nitric oxide fluxes, though the intricacies of this inflammatory theory are currently unknown. Consequently, there have been few advances in the clinical treatment of this patient cohort, and morbidity remains high. Identification of intermediaries in the inflammatory cascade can provide insight into newer clinical interventions in the prevention and management of cerebral vasospasm and will hopefully prevent neurological decline. In this review, we discuss current theories implicating the inflammatory cascade in the development of CVS and potential treatment targets.

Nitric oxide in cerebral vasospasm: theories, measurement, and treatment

In recent decades, a large body of research has focused on the role of nitric oxide (NO) in the development of cerebral vasospasm (CV) following subarachnoid hemorrhage (SAH). Literature searches were therefore conducted regarding the role of NO in cerebral vasospasm, specifically focusing on NO donors, reactive nitrogen species, and peroxynitrite in manifestation of vasospasm. Based off the assessment of available evidence, two competing theories are reviewed regarding the role of NO in vasospasm. One school of thought describes a deficiency in NO due to scavenging by hemoglobin in the cisternal space, leading to an NO signaling deficit and vasospastic collapse. A second hypothesis focuses on the dysfunction of nitric oxide synthase, an enzyme that synthesizes NO, and subsequent generation of reactive nitrogen species. Both theories have strong experimental evidence behind them and hold promise for translation into clinical practice. Furthermore, NO donors show definitive promise for preventing vasospasm at the angiographic and clinical level. However, NO augmentation may also cause systemic hypotension and worsen vasospasm due to oxidative distress. Recent evidence indicates that targeting NOS dysfunction, for example, through erythropoietin or statin administration, also shows promise at preventing vasospasm and neurotoxicity. Ultimately, the role of NO in neurovascular disease is complex. Neither of these theories is mutually exclusive, and both should be considered for future research directions and treatment strategies.

Genetics of cerebral vasospasm

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

Suppression of the Rho/Rho-kinase pathway and prevention of cerebral vasospasm by combination treatment with statin and fasudil after subarachnoid hemorrhage in rabbit

The Rho/Rho-kinase pathway is considered important in the pathogenesis of sustained smooth muscle cell contraction during cerebral vasospasm after aneurysmal subarachnoid hemorrhage (SAH). The aims of this study were to investigate whether combination treatment, with pitavastatin as an inhibitor of RhoA and fasudil as an inhibitor of Rho-kinase, prevents the cerebral vasospasm. SAH was simulated using the double-hemorrhage rabbit model, and pitavastatin, or fasudil, or both (combination treatment) were administrated. The basilar artery (BA) cross-sectional area only in the combination treatment group was statistically larger than in the SAH group (p < 0.05). BA Rho-kinase, as measured by ELISA, was statistically reduced only in the combination treatment group compared with the SAH group (p < 0.05). In the other two treatment groups, pitavastatin or fasudil treatment group showed larger BA cross-sectional areas and lower value for BA Rho-kinase, but there were no statistically significant differences compared with the SAH group. The expression of endothelial nitric oxide synthase (eNOS), evaluated by immunohistochemistry in the pitavastatin group and the combination group, was higher than in the SAH group. Results indicate that combination treatment could extensively prevent cerebral vasospasm due to the synergic effect of combining pitavastatin and fasudil on the Rho/Rho-kinase pathway and on eNOS.

Phosphodiesterase 5 inhibition attenuates cerebral vasospasm and improves functional recovery after experimental subarachnoid hemorrhage

BACKGROUND

Cerebral vasospasm is an independent predictor of poor outcome after subarachnoid hemorrhage (SAH). The nitric oxide-cyclic guanosine monophosphate (NO-cGMP) vasodilatory pathway is strongly implicated in its pathophysiology. Preliminary studies suggest that phosphodiesterase 5 (PDE5), an enzyme that degrades cGMP, may play a role because the PDE5 inhibitor sildenafil was found to reduce vasospasm after SAH. However, several questions that are critical when considering translational studies remain unanswered.

OBJECTIVE

To elucidate the mechanism of action of sildenafil against vasospasm and to assess whether sildenafil attenuates SAH-induced neuronal cell death, improves functional outcome after SAH, or causes significant physiological side effects when administered at therapeutically relevant doses.

METHODS

SAH was induced via endovascular perforation in male C57BL6 mice. Beginning 2 hours later, mice received sildenafil citrate (0.7, 2 or 5 mg/kg orally twice daily) or vehicle. Neurological outcome was assessed daily. Vasospasm was determined on post-SAH day 3. Brain PDE5 expression and activity, cGMP content, neuronal cell death, arterial blood pressure, and intracranial pressure were examined.

RESULTS

We found that PDE5 activity (but not expression) is increased after SAH, leading to decreased cGMP levels. Sildenafil attenuates this increase in PDE5 activity and restores cGMP levels after SAH. Post-SAH initiation of sildenafil was found to decrease vasospasm and neuronal cell death and markedly improve neurological outcome without causing significant physiological side effects.

CONCLUSION

Sildenafil, a US Food and Drug Administration-approved drug with a proven track record of safety in humans, is a promising new therapy for vasospasm and neurological deficits after SAH.

Magnesium lithospermate B alleviates the production of endothelin-1 through an NO-dependent mechanism and reduces experimental vasospasm in rats

OBJECTIVE

Magnesium lithospermate B (MLB), a working extract from Salvia miltiorrhiza, was effective against coronary artery disease, ischemic stroke, and chronic renal disease. This study examined the effect of MLB on endothelin-1/endothelial nitric oxide synthase (eNOS) in a subarachnoid hemorrhage (SAH) animal model.

METHODS

A rodent double-hemorrhage model was employed. Animals were randomly assigned to five groups (sham, SAH only, vehicle, 10 mg/kg/day MLB treatment, and pretreatment groups). A radiolabeled NOS Assay Kit was used to detect eNOS. Serum and cerebrospinal fluid sampling for ET-1 (ELISA) was measured. The basilar arteries (BAs) were garnered and sliced, and their cross-sectional areas were determined. In addition, NOS inhibitor nitro-arginine methyl ester (L-NAME) was employed in the SAH+ MLB treatment groups.

RESULTS

Significant vasoconstriction was perceived in the SAH group (lumen patency: 44.6%, p < 0.01), but not in the MLB group (lumen patency: 89.3%). The ET-1 level was reduced in the MLP plus SAH group (34%, p < 0.01) when compared with the SAH groups (SAH only and vehicle). MLB dose-dependently increased the level of eNOS when compared with the vehicle plus SAH group. However, the administration of L-NAME reversed the expression of eNOS and vasoconstriction (lumen patency: 56.2%) in the MLB group.

CONCLUSION

The enhanced expression of eNOS and decreased ET-1 levels in the MLB groups may reflect its anti-spastic effect. In the study of NOS, L-NAME reversed MLB's anti-vasospastic effect. This finding lends credence to the hypothesis that MLB modulates ET-1 levels through a NOS-dependent mechanism in the pathogenesis of cerebral vasospasm following SAH.

Reversal of cerebral vasospasm via intravenous sodium nitrite after subarachnoid hemorrhage in primates

OBJECT

Subarachnoid hemorrhage (SAH)-induced vasospasm is a significant underlying cause of aneurysm rupture-related morbidity and death. While long-term intravenous infusion of sodium nitrite (NaNO(2)) can prevent cerebral vasospasm after SAH, it is not known if the intravenous administration of this compound can reverse established SAH-induced vasospasm. To determine if the intravenous infusion of NaNO(2) can reverse established vasospasm, the authors infused primates with the compound after SAH-induced vasospasm was established.

METHODS

Subarachnoid hemorrhage-induced vasospasm was created in 14 cynomolgus macaques via subarachnoid implantation of a 5-ml blood clot. On Day 7 after clot implantation, animals were randomized to either control (saline infusion, 5 monkeys) or treatment groups (intravenous NaNO(2) infusion at 300 μg/kg/hr for 3 hours [7 monkeys] or 8 hours [2 monkeys]). Arteriographic vessel diameter was blindly analyzed to determine the degree of vasospasm before, during, and after treatment. Nitric oxide metabolites (nitrite, nitrate, and S-nitrosothiols) were measured in whole blood and CSF.

RESULTS

Moderate-to-severe vasospasm was present in all animals before treatment (control, 36.2% ± 8.8% [mean ± SD]; treatment, 45.5% ± 12.5%; p = 0.9). While saline infusion did not reduce vasospasm, NaNO(2) infusion significantly reduced the degree of vasospasm (26.9% ± 7.6%; p = 0.008). Reversal of the vasospasm lasted more than 2 hours after cessation of the infusion and could be maintained with a prolonged infusion. Nitrite (peak value, 3.7 ± 2.1 μmol/L), nitrate (18.2 ± 5.3 μmol/L), and S-nitrosothiols (33.4 ± 11.4 nmol/L) increased significantly in whole blood, and nitrite increased significantly in CSF.

CONCLUSIONS

These findings indicate that the intravenous infusion of NaNO(2) can reverse SAH-induced vasospasm in primates. Further, these findings indicate that a similar treatment paradigm could be useful in reversing cerebral vasospasm after aneurysmal SAH.

Neurovascular protection by ischaemic tolerance: role of nitric oxide

Nitric oxide (NO) has emerged as a key mediator in the mechanisms of ischaemic tolerance induced by a wide variety of preconditioning stimuli. NO is involved in the brain protection that develops either early (minutes-hours) or late (days-weeks) after the preconditioning stimulus. However, the sources of NO and the mechanisms underlying the protective effects differ substantially. While in early preconditioning NO is produced by the endothelial and neuronal isoform of NO synthase, in delayed preconditioning NO is synthesized by the inducible or 'immunological' isoform of NO synthase. Furthermore, in early preconditioning, NO acts through the canonical cGMP pathway, possibly through protein kinase G and opening of mitochondrial K(ATP) channels. In late preconditioning, the protection is mediated by peroxynitrite formed by the reaction of NO with superoxide derived from the enzyme NADPH oxidase. The mechanisms by which peroxynitrite exerts its protective effect may include improvement of post-ischaemic cerebrovascular function, leading to enhancement of blood flow to the ischaemic territory, and expression of prosurvival genes resulting in cytoprotection. The evidence suggests that NO can engage highly effective and multifunctional prosurvival pathways, which could be exploited for the prevention and treatment of cerebrovascular pathologies.

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.