Association of an endogenous inhibitor of nitric oxide synthase with cerebral vasospasm in patients with aneurysmal subarachnoid hemorrhage

Metabolomic Analysis in Neurocritical Care Patients

Metabolomics is the analytical study of metabolites in biological matrices using high-throughput profiling. Traditionally, the metabolome has been studied to identify various biomarkers for the diagnosis and pathophysiology of disease. Over the last decade, metabolomic research has grown to include the identification of prognostic markers, the development of novel treatment strategies, and the prediction of disease severity. In this review, we summarized the available evidence on the use of metabolome profiling in neurocritical care populations. Specifically, we focused on aneurysmal subarachnoid hemorrhage, traumatic brain injury, and intracranial hemorrhage to identify the gaps in the current literature and to provide direction for future studies. A primary literature search of the Medline and EMBASE databases was conducted. Upon removing duplicate studies, abstract screening and full-text screening were performed. We screened 648 studies and extracted data from 17 studies. Based on the current evidence, the utility of metabolomic profiling has been limited due to inconsistencies amongst studies and a lack of reproducible data. Studies identified various biomarkers for diagnosis, prognosis, and treatment modification. However, studies evaluated and identified different metabolites, resulting in an inability to compare the study results. Future research towards addressing the gaps in the current literature, including reproducing data on the use of specific metabolite panels, is needed.

The role of L-arginine metabolism in neurocritical care patients

Nitric oxide is an important mediator of vascular autoregulation and is involved in pathophysiological changes after acute neurological disorders. Nitric oxide is generated by nitric oxide synthases from the amino acid L-arginine. L-arginine can also serve as a substrate for arginases or lead to the generation of dimethylarginines, asymmetric dimethylarginine, and symmetric dimethylarginine, by methylation. Asymmetric dimethylarginine is an endogenous inhibitor of nitric oxide synthase and can lead to endothelial dysfunction. This review discusses the role of L-arginine metabolism in patients suffering from acute and critical neurological disorders often requiring neuro-intensive care treatment. Conditions addressed in this review include intracerebral hemorrhage, aneurysmal subarachnoid hemorrhage, and traumatic brain injury. Recent therapeutic advances in the field are described including current randomized controlled trials for traumatic brain injuries and hemorrhagic stroke.

Beneficial Effect of Sodium Nitrite on EEG Ischaemic Markers in Patients with Subarachnoid Haemorrhage

Subarachnoid haemorrhage (SAH) is associated with long-term disability, serious reduction in quality of life and significant mortality. Early brain injury (EBI) refers to the pathological changes in cerebral metabolism and blood flow that happen in the first few days after ictus and may lead on to delayed cerebral ischaemia (DCI). A disruption of the nitric oxide (NO) pathway is hypothesised as a key mechanism underlying EBI. A decrease in the alpha-delta power ratio (ADR) of the electroencephalogram has been related to cerebral ischaemia. In an experimental medicine study, we tested the hypothesis that intravenous sodium nitrite, an NO donor, would lead to increases in ADR. We studied 33 patients with acute aneurysmal SAH in the EBI phase. Participants were randomised to either sodium nitrite or saline infusion for 1 h. EEG measurements were taken before the start of and during the infusion. Twenty-eight patients did not develop DCI and five patients developed DCI. In the patients who did not develop DCI, we found an increase in ADR during sodium nitrite versus saline infusion. In the five patients who developed DCI, we did not observe a consistent pattern of ADR changes. We suggest that ADR power changes in response to nitrite infusion reflect a NO-mediated reduction in cerebral ischaemia and increase in perfusion, adding further evidence to the role of the NO pathway in EBI after SAH. Our findings provide the basis for future clinical trials employing NO donors after SAH.

Pathophysiology of Delayed Cerebral Ischemia After Subarachnoid Hemorrhage: A Review

Delayed cerebral ischemia is a major predictor of poor outcomes in patients who suffer subarachnoid hemorrhage. Treatment options are limited and often ineffective despite many years of investigation and clinical trials. Modern advances in basic science have produced a much more complex, multifactorial framework in which delayed cerebral ischemia is better understood and novel treatments can be developed. Leveraging this knowledge to improve outcomes, however, depends on a holistic understanding of the disease process. We conducted a review of the literature to analyze the current state of investigation into delayed cerebral ischemia with emphasis on the major themes that have emerged over the past decades. Specifically, we discuss microcirculatory dysfunction, glymphatic impairment, inflammation, and neuroelectric disruption as pathological factors in addition to the canonical focus on cerebral vasospasm. This review intends to give clinicians and researchers a summary of the foundations of delayed cerebral ischemia pathophysiology while also underscoring the interactions and interdependencies between pathological factors. Through this overview, we also highlight the advances in translational studies and potential future therapeutic opportunities.

Machine Learning-Driven Metabolomic Evaluation of Cerebrospinal Fluid: Insights Into Poor Outcomes After Aneurysmal Subarachnoid Hemorrhage

BACKGROUND

Aneurysmal subarachnoid hemorrhage (aSAH) is associated with a high mortality and poor neurologic outcomes. The biologic underpinnings of the morbidity and mortality associated with aSAH remain poorly understood.

OBJECTIVE

To ascertain potential insights into pathological mechanisms of injury after aSAH using an approach of metabolomics coupled with machine learning methods.

METHODS

Using cerebrospinal fluid (CSF) samples from 81 aSAH enrolled in a retrospective cohort biorepository, samples collected during the peak of delayed cerebral ischemia were analyzed using liquid chromatography-tandem mass spectrometry. A total of 138 metabolites were measured and quantified in each sample. Data were analyzed using elastic net (EN) machine learning and orthogonal partial least squares-discriminant analysis (OPLS-DA) to identify the leading CSF metabolites associated with poor outcome, as determined by the modified Rankin Scale (mRS) at discharge and at 90 d. Repeated measures analysis determined the effect size for each metabolite on poor outcome.

RESULTS

EN machine learning and OPLS-DA analysis identified 8 and 10 metabolites, respectively, that predicted poor mRS (mRS 3-6) at discharge and at 90 d. Of these candidates, symmetric dimethylarginine (SDMA), dimethylguanidine valeric acid (DMGV), and ornithine were consistent markers, with an association with poor mRS at discharge (P = .0005, .002, and .0001, respectively) and at 90 d (P = .0036, .0001, and .004, respectively). SDMA also demonstrated a significantly elevated CSF concentration compared with nonaneurysmal subarachnoid hemorrhage controls (P = .0087).

CONCLUSION

SDMA, DMGV, and ornithine are vasoactive molecules linked to the nitric oxide pathway that predicts poor outcome after severe aSAH. Further study of dimethylarginine metabolites in brain injury after aSAH is warranted.

Cerebral nitric oxide and mitochondrial function in patients suffering aneurysmal subarachnoid hemorrhage-a translational approach

Background

Cerebral ischemia and neuroinflammation following aneurysmal subarachnoid hemorrhage (SAH) are major contributors to poor neurological outcome. Our study set out to investigate in an exploratory approach the interaction between NO and energy metabolism following SAH as both hypoxia and inflammation are known to affect nitric oxide (NO) metabolism and NO in turn affects mitochondria.

Methods

In seven patients under continuous multimodality neuromonitoring suffering poor-grade aneurysmal SAH, cerebral metabolism and NO levels (determined as a sum of nitrite plus nitrate) were determined in cerebral microdialysate for 14 days following SAH. In additional ex vivo experiments, rat cortex homogenate was subjected to the NO concentrations determined in SAH patients to test whether these NO concentrations impair mitochondrial function (determined by means of high-resolution respirometry).

Results

NO levels showed biphasic kinetics with drastically increased levels during the first 7 days (74.5 ± 29.9 μM) and significantly lower levels thereafter (47.5 ± 18.7 μM; p = 0.02). Only during the first 7 days, NO levels showed a strong negative correlation with brain tissue oxygen tension (r = − 0.78; p < 0.001) and a positive correlation with cerebral lactate (r = 0.79; p < 0.001), pyruvate (r = 0.68; p < 0.001), glutamate (r = 0.65; p < 0.001), as well as the lactate-pyruvate ratio (r = 0.48; p = 0.01), suggesting mitochondrial dysfunction. Ex vivo experiments confirmed that the increase in NO levels determined in patients during the acute phase is sufficient to impair mitochondrial function (p < 0.001). Mitochondrial respiration was inhibited irrespectively of whether glutamate (substrate of complex I) or succinate (substrate of complex II) was used as mitochondrial substrate suggesting the inhibition of mitochondrial complex IV. The latter was confirmed by direct determination of complex IV activity.

Conclusions

Exploratory analysis of our data suggests that during the acute phase of SAH, NO plays a key role in the neuronal damage impairing mitochondrial function and facilitating accumulation of mitochondrial substrate; further studies are required to understand mechanisms underlying this observation.

Sequence Variation in the DDAH1 Gene Predisposes for Delayed Cerebral Ischemia in Subarachnoidal Hemorrhage

Delayed cerebral ischemia (DCI) often causes poor long-term neurological outcome after subarachnoidal hemorrhage (SAH). Asymmetric dimethylarginine (ADMA) inhibits nitric oxide synthase (NOS) and is associated with DCI after SAH. We studied single nucleotide polymorphisms (SNPs) in the NOS3, DDAH1, DDAH2, PRMT1, and AGXT2 genes that are part of the L-arginine–ADMA–NO pathway, and their association with DCI. We measured L-arginine, ADMA and symmetric dimethylarginine (SDMA) in plasma and cerebrospinal fluid (CSF) of 51 SAH patients at admission; follow-up was until 30 days post-discharge. The primary outcome was the incidence of DCI, defined as new infarctions on cranial computed tomography, which occurred in 18 of 51 patients. Clinical scores did not significantly differ in patients with or without DCI. However, DCI patients had higher plasma ADMA and SDMA levels and higher CSF SDMA levels at admission. DDAH1 SNPs were associated with plasma ADMA, whilst AGXT2 SNPs were associated with plasma SDMA. Carriers of the minor allele of DDAH1 rs233112 had a significantly increased relative risk of DCI (Relative Risk = 2.61 (1.25–5.43), p = 0.002). We conclude that the DDAH1 gene is associated with ADMA concentration and the incidence of DCI in SAH patients, suggesting a pathophysiological link between gene, biomarker, and clinical outcome in patients with SAH.

Phase dynamics of cerebral blood flow in subarachnoid haemorrhage in response to sodium nitrite infusion

Aneurysmal subarachnoid haemorrhage (SAH) is a devastating subset of stroke. One of the major determinates of morbidity is the development of delayed cerebral ischemia (DCI). Disruption of the nitric oxide (NO) pathway and consequently the control of cerebral blood flow (CBF), known as cerebral autoregulation, is believed to play a role in its pathophysiology. Through the pharmacological manipulation of in vivo NO levels using an exogenous NO donor we sought to explore this relationship. Phase synchronisation index (PSI), an expression of the interdependence between CBF and arterial blood pressure (ABP) and thus cerebral autoregulation, was calculated before and during sodium nitrite administration in 10 high-grade SAH patients acutely post-rupture. In patients that did not develop DCI, there was a significant increase in PSI around 0.1 Hz during the administration of sodium nitrite (33%; p-value 0.006). In patients that developed DCI, PSI did not change significantly. Synchronisation between ABP and CBF at 0.1 Hz has been proposed as a mechanism by which organ perfusion is maintained, during periods of physiological stress. These findings suggest that functional NO depletion plays a role in impaired cerebral autoregulation following SAH, but the development of DCI may have a distinct pathophysiological aetiology.

Asymmetric dimethylarginine exacerbates cognitive dysfunction associated with cerebrovascular pathology

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor and uncoupler of nitric oxide synthase, has gained attention as a risk factor for cardiac disease, metabolic syndrome, and cerebrovascular disease. In this study, we investigated the role of systemic ADMA overburden in cerebromicrovascular pathology associated with cognitive dysfunction using APPSwDI transgenic mice expressing human β-amyloid precursor protein Swedish (Tg-SwDI), a model of cerebrovascular β-amyloidosis. To induce systemic overburden of ADMA, Tg-SwDI mice were treated with a daily dose of exogenous ADMA. ADMA treatment resulted in elevated ADMA levels in the blood and brain of Tg-SwDI mice. ADMA treatment induced the brain nitrosative stress and inflammation as well as enhanced the brain Aβ deposition and cognitive impairment in Tg-SwDI mice. However, ADMA treatment had no such effects on wild type mice. ADMA treatment also exacerbated brain microvascular pathology in Tg-SwDI mice as observed by increased blood-brain barrier dysfunction, loss of tight junction proteins, increased endothelial stress fibers, and decreased microvessel density in the brain. In addition, similar observations were made in cultured human brain microvessel endothelial cells, where ADMA in the presence of VEGF-induced endothelial cell signaling for F-actin stress fiber inducing endothelial barrier dysfunction. Overall, these data document the potential role of ADMA in the cognitive pathology under conditions of cerebrovascular β-amyloidosis.

Cerebrospinal fluid untargeted metabolomic profiling of aneurysmal subarachnoid hemorrhage: an exploratory study

INTRODUCTION

Despite advancements in medical and surgical therapies, clinical outcomes of aneurysmal subarachnoid hemorrhage (aSAH) continue to be poor. Currently, aSAH pathophysiology remains poorly understood. No aSAH biomarkers are commonly used in the clinical setting. This exploratory study used metabolomics profiling to identify global metabolic changes and metabolite predictors of long-term outcome using cerebrospinal fluid (CSF) samples of aSAH patients.

METHODS AND METHODS

Gas chromatography time-of-flight mass spectrometry was applied to CSF samples collected from 15 consecutive high-grade aSAH patients (modified Fisher grade 3 or 4). Collected CSF samples were analyzed at two time points (admission and the anticipated vasospasm timeframe). Metabolite levels at both time points were compared and correlated with vasospasm status and Glasgow Outcome Scale (GOS) of patients at 1 year post-aSAH. Significance level was defined as p < 0.05 with false discovery rate correction for multiple comparisons.

RESULTS

Of 97 metabolites identified, 16 metabolites, primarily free amino acids, significantly changed between the two time points. These changes were magnified in modified Fisher grade 4 compared with grade 3. Six metabolites (2-hydroxyglutarate, tryptophan, glycine, proline, isoleucine, and alanine) correlated with GOS at 1 year post-aSAH independent of vasospasm status. When predicting patients who had low disability (GOS 5 vs. GOS ≤4), 2-hydroxyglutarate had a sensitivity and specificity of 0.89 and 0.83 respectively.

CONCLUSIONS

Our preliminary study suggests that specific metabolite changes occur in the brain during the course of aSAH and that quantification of specific CSF metabolites may be used to predict long-term outcome in patients with aSAH. This is the first study to implicate 2-hydroxyglutarate, a known marker of tissue hypoxia, in aSAH pathogenesis.

Vascular diseases and bleedings

Diseases of the central nervous system that are caused by an underlying vascular pathology typically result in either hemorrhage or ischemia. Most prominent entities include spontaneous subarachnoid hemorrhage, spontaneous intracerebral hemorrhage, and ischemic stroke. For anatomic reasons, cerebrospinal fluid (CSF) qualifies as body fluid for the exploration of biomarkers in these disorders. Even though in subarachnoid hemorrhage a few CSF parameters have been established for routine diagnostic purposes, there is still an unmet need and broad interest in the identification of molecules that would allow further insight into disease mechanisms and supplement patients' medical care. This chapter provides an overview on what is presently known about CSF biomarkers in spontaneous subarachnoid hemorrhage, spontaneous intracerebral hemorrhage, and ischemic stroke. We recapitulate current evidence on established diagnostic tests, discuss the role of various CSF molecules in the pathophysiology of these diseases, and illuminate their potential use in future clinical practice. Furthermore, we address methodologic aspects as well as shortcomings of research in this field.

Dimethylarginines in patients with intracerebral hemorrhage: association with outcome, hematoma enlargement, and edema

BACKGROUND

Asymmetric dimethylarginine (ADMA)--the most potent endogenous NO-synthase inhibitor, has been regarded as mediator of endothelial dysfunction and oxidative stress. Considering experimental data, levels of ADMA and its structural isomer symmetric dimethylarginine (SDMA) might be elevated after intracerebral hemorrhage (ICH) and associated with clinical outcome and secondary brain injury.

METHODS

Blood samples from 20 patients with acute ICH were taken at ≤ 24 h and 3 and 7 days after the event. Nine patients had favorable (modified Rankin Scale (mRS) at 90 days 0-2) outcome, and 11 patients unfavorable outcome (mRS 3-6). Patients' serum ADMA, SDMA, and L-arginine levels were determined by high-performance liquid chromatography-tandem mass spectrometry. Levels were compared to those of 30 control subjects without ICH. For further analysis, patients were grouped according to outcome, hematoma and perihematomal edema volumes, occurrence of hematoma enlargement, and cytotoxic edema as measured by computed tomography and serial magnetic resonance imaging.

RESULTS

Levels of ADMA--but not SDMA and L-arginine--were elevated in ICH patients compared to controls (binary logistic regression analysis: ADMA ≤ 24 h, p = 0.003; 3 days p = 0.005; 7 days p = 0.004). If patients were grouped according to outcome, dimethylarginines were increased in patients with unfavorable outcome. The binary logistic regression analysis confirmed an association of SDMA levels ≤ 24 h (p = 0.048) and at 3 days (p = 0.028) with unfavorable outcome. ADMA ≤ 24 h was increased in patients with hematoma enlargement (p = 0.003), while SDMA ≤ 24 h was increased in patients with large hematoma (p = 0.029) and perihematomal edema volume (p = 0.023).

CONCLUSIONS

Our data demonstrate an association between dimethylarginines and outcome of ICH. However, further studies are needed to confirm this relationship and elucidate the mechanisms behind.

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

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

Cerebral Vasospasm: A Review

Cerebral vasospasm is a prolonged but reversible narrowing of cerebral arteries beginning days after subarachnoid hemorrhage. Progression to cerebral ischemia is tied mostly to vasospasm severity, and its pathogenesis lies in artery encasement by blood clot, although the complex interactions between hematoma and surrounding structures are not fully understood. The delayed onset of vasospasm provides a potential opportunity for its prevention. It is disappointing that recent randomized, controlled trials did not demonstrate that the endothelin antagonist clazosentan, the cholesterol-lowering agent simvastatin, and the vasodilator magnesium sulfate improve patient outcome. Minimizing ischemia by avoiding inadequate blood volume and pressure, administering the calcium antagonist nimodipine, and intervention with balloon angioplasty, when necessary, constitutes current best management. Over the past two decades, our ability to manage vasospasm has led to a significant decline in patient morbidity and mortality from vasospasm, yet it still remains an important determinant of outcome after aneurysm rupture.

Early events after aneurysmal subarachnoid hemorrhage

The first 72 h after aneurysmal subarachnoid hemorrhage (SAH) is a critical period for the patient. Most of the deaths in the SAH patient population occur during this time, and a number of key events activate and trigger mechanisms that not only contribute to early brain injury but evolve over time and participate in the delayed complications. This review highlights the contribution of key events to the early brain injury and to overall outcome after SAH.

The pathophysiology and treatment of delayed cerebral ischaemia following subarachnoid haemorrhage

Cerebral vasospasm has traditionally been regarded as an important cause of delayed cerebral ischaemia (DCI) which occurs after aneurysmal subarachnoid haemorrhage, and often leads to cerebral infarction and poor neurological outcome. However, data from recent studies argue against a pure focus on vasospasm as the cause of delayed ischaemic complications. Findings that marked reduction in the incidence of vasospasm does not translate to a reduction in DCI, or better outcomes has intensified research into other possible mechanisms which may promote ischaemic complications. Early brain injury and cell death, blood-brain barrier disruption and initiation of an inflammatory cascade, microvascular spasm, microthrombosis, cortical spreading depolarisations and failure of cerebral autoregulation, have all been implicated in the pathophysiology of DCI. This review summarises the current knowledge about the mechanisms underlying the development of DCI. Furthermore, it aims to describe and categorise the known pharmacological treatment options with respect to the presumed mechanism of action and its role in DCI.

Endogenous nitric-oxide synthase inhibitor ADMA after acute brain injury

Previous results on nitric oxide (NO) metabolism after traumatic brain injury (TBI) show variations in NO availability and controversial effects of exogenous nitric oxide synthase (NOS)-inhibitors. Furthermore, elevated levels of the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA) were reported in cerebro-spinal fluid (CSF) after traumatic subarachnoid hemorrhage (SAH). Therefore, we examined whether ADMA and the enzymes involved in NO- and ADMA-metabolism are expressed in brain tissue after TBI and if time-dependent changes occur. TBI was induced by controlled cortical impact injury (CCII) and neurological performance was monitored. Expression of NOS, ADMA, dimethylarginine dimethylaminohydrolases (DDAH) and protein-arginine methyltransferase 1 (PRMT1) was determined by immunostaining in different brain regions and at various time-points after CCII. ADMA and PRMT1 expression decreased in all animals after TBI compared to the control group, while DDAH1 and DDAH2 expression increased in comparison to controls. Furthermore, perilesionally ADMA is positively correlated with neuroscore performance, while DDAH1 and DDAH2 are negatively correlated. ADMA and its metabolizing enzymes show significant temporal changes after TBI and may be new targets in TBI treatment.

Potential serum biomarkers in the pathophysiological processes of stroke

Stroke is a leading cause of death and serious long-term disability. Ischemic stroke is the major subtype of stroke. Currently, its diagnosis is mainly dependent upon clinical symptoms and neuroimaging techniques. Despite these clinical and imaging modalities, often strokes are not recognized after initial onset. As early intervention of medical or surgical therapy is often associated with improved outcomes, there is an urgent need to improve the speed and accuracy of stroke diagnosis. Stroke is a complex pathophysiological process involving; energy failure, imbalance of ion homeostasis, acidosis, intracellular calcium overload, neuronal excitotoxicity, free radical-mediated lipid oxidation, inflammatory cell infiltration, and glial cell activation. These events ultimately lead to neuronal apoptotic cell death or necrosis. In this review, we have summarized the serum biomarkers according to the pathophysiological processes of stroke, which have been intensively studied in clinical trials of stroke over the past five years, and also used Medline's 'related article' option to identify further articles. We focused on the potential biomarkers pertaining to vascular injury, metabolic changes, oxidative injury, and inflammation, and newly studied biomarkers, and discussed how these biomarkers could be used for the diagnosis or determining the prognosis of stroke.

Dietary nitrate facilitates an acetazolamide-induced increase in cerebral blood flow during visual stimulation

The carbonic anhydrase (CA) inhibitor acetazolamide (AZ) is used routinely to estimate cerebrovascular reserve capacity in patients, as it reliably increases cerebral blood flow (CBF). However, the mechanism by which AZ accomplishes this CBF increase is not entirely understood. We recently discovered that CA can produce nitric oxide (NO) from nitrite, and that AZ enhances this NO production in vitro. In fact, this interaction between AZ and CA accounted for a large part of AZ's vasodilatory action, which fits well with the known vasodilatory potency of NO. The present study aimed to assess whether AZ acts similarly in vivo in the human cerebrovascular system. Hence, we increased or minimized the dietary intake of nitrate in 20 healthy male participants, showed them a full-field flickering dartboard, and measured their CBF response to this visual stimulus with arterial spin labeling. Doing so, we found a significant positive interaction between the dietary intake of nitrate and the CBF modulation afforded by AZ during visual stimulation. In addition, but contrary to studies conducted in elderly participants, we report no effect of nitrate intake on resting CBF in healthy human participants. The present study provides in vivo support for an enhancing effect of AZ on the NO production from nitrite catalyzed by CA in the cerebrovascular system. Furthermore, our results, in combination with the results of other groups, indicate that nitrate may have significant importance to vascular function when the cerebrovascular system is challenged by age or disease.

Effect of cervical sympathetic block on cerebral vasospasm after subarachnoid hemorrhage in rabbits

PURPOSE

Cerebral vasospasm (CVS) is a major complication after subarachnoid hemorrhage (SAH) induced by the rupture of intracranial aneurysms. The aim of the present study was to investigate the effect and mechanism of cervical sympathetic block on cerebral vasospasm of the rabbits after SAH.

METHODS

After successful modeling of cervical sympathetic block, 18 healthy male white rabbits were randomly divided into three groups (n=6), ie, sham operation group (Group A), SAH group (Group B) and SAH with cervical sympathetic block group (Group C). Models of delayed CVS were established by puncturing cisterna magna twice with an injection of autologous arterial blood in Groups B and C. A sham injection of blood through cisterna magna was made in Group A. 0.5 ml saline was injected each time through a catheter for cervical sympathetic block after the first injection of blood three times a day for 3 d in Group B (bilateral alternating). 0.5 ml of 0.25% bupivacaine was injected each time through a catheter for cervical sympathetic block after the first injection of blood three times a day for 7 d in Group B. 2 ml venous blood and cerebrospinal fluid were obtained before (T1), 30 min (T2) and 7 d (T3) after the first injection of blood, respectively, and conserved in a low temperature refrigerator. Basilar artery value at T1, T2 and T3 was measured via cerebral angiography. The degree of damage to nervous system at T1 and T3 was recorded.

RESULTS

There was no significant difference in diameter of basilar artery at T1 among three groups. The diameters of basilar artery at T2 and T3 of Groups B and C were all smaller than that in Group A, which was smaller than Group C, with a significant difference. There was no significant difference in NO and NOS in plasma and cerebrospinal fluid among three groups. The NO and NOS contents at T2 and T3 of Groups B and C were all lower than Group A; Group C was higher than Group B, with a significant difference. The nerve function at T3 of Groups B and C were all lower than Group A and that of Group C higher than Group B, with a significant difference.

CONCLUSION

Cervical sympathetic block can relieve cerebral vasospasm after subarachnoid hemorrhage and increase NO content and NOS activity in plasma and cerebrospinal fluid to promote neural functional recovery.

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.

Hypothermia decreases cerebrospinal fluid asymmetric dimethylarginine levels in children with traumatic brain injury

OBJECTIVES

Pathological increases in asymmetric dimethylarginine, an endogenous nitric oxide synthase inhibitor, have been implicated in endothelial dysfunction and vascular diseases. Reduced nitric oxide early after traumatic brain injury may contribute to hypoperfusion. Currently, methods to quantify asymmetric dimethylarginine in the cerebrospinal fluid have not been fully explored. We aimed to develop and validate a method to determine asymmetric dimethylarginine in the cerebrospinal fluid of a pediatric traumatic brain injury population and to use this method to assess the effects of 1) traumatic brain injury and 2) therapeutic hypothermia on this mediator.

DESIGN, SETTING, AND PATIENTS

An ancillary study to a prospective, phase II randomized clinical trial of early hypothermia in a tertiary care pediatric intensive care unit for children with Traumatic brain injury admitted to Children's Hospital of Pittsburgh.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A UPLC-MS/MS method was developed and validated to quantitate asymmetric dimethylarginine. A total of 56 samples collected over 3 days with injury onset were analyzed from the cerebrospinal fluid of consented therapeutic hypothermia (n = 9) and normothermia (n = 10) children. Children undergoing diagnostic lumbar puncture (n = 5) were enrolled as controls. Asymmetric dimethylarginine was present at a quantifiable level in all samples. Mean asymmetric dimethylarginine levels were significantly increased in normothermic Traumatic brain injury children compared with that in control (0.19 ± 0.08 µmol/L and 0.11 ± 0.02 µmol/L, respectively, p = 0.01), and hypothermic children had significantly reduced mean asymmetric dimethylarginine levels (0.11 ± 0.05 µmol/L) vs. normothermic (p = 0.03) measured on day 3. Patient demographics including age, gender, and nitric oxide levels (measured as nitrite and nitrate using liquid chromatography coupled with Griess reaction) did not significantly differ between normothermia and hypothermia groups. Also, nitric oxide levels did not correlate with asymmetric dimethylarginine concentrations.

CONCLUSIONS

Asymmetric dimethylarginine levels were significantly increased in the cerebrospinal fluid of traumatic brain injury children. Early hypothermia attenuated this increase. The implications of attenuated asymmetric dimethylarginine on nitric oxide synthases activity and regional cerebral blood flow after traumatic brain injury by therapeutic hypothermia deserve future study.

Low Plasma Arginine:Asymmetric Dimethyl Arginine Ratios Predict Mortality After Intracranial Aneurysm Rupture

Background—

Asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthases, predicts mortality in cardiovascular disease and has been linked to cerebral vasospasm after aneurysmal subarachnoid hemorrhage (SAH). In this prospective study, we assessed whether circulating ADMA, arginine:ADMA ratio, and nitrite/nitrate levels were associated with survival and cerebral vasospasm in SAH patients.

Methods—

One hundred and eleven patients were observed day 1 to 15 after SAH, with serial measurements of transcranial Doppler flow velocities (V MCA ) and plasma biomarkers. Clinical status was assessed by the World Federation of Neurosurgical Societies grading scale.

Results—

Overall 30-day mortality was 18%, but differed between patients grouped by low, midrange, and high arginine:ADMA ratio in the first week after SAH. Mortality rates were 14/37, 1/37, and 5/37 in the 3 groups, respectively ( P -logrank=0.0003). Cox regression showed that low versus midrange or high arginine:ADMA was associated with a hazard ratio of 4.1 independent of World Federation of Neurosurgical Societies grade (95% confidence interval, 1.5–10.9; P =0.006). ADMA or arginine:ADMA had no association to V MCA , but there was an inverse relationship between V MCA and nitrite/nitrate levels ( P <0.0001). The NOS3 894G/G genotype was associated with 15% lower V MCA ( P =0.01). ATbG- NOS3 haplotype homozygosity was associated with up to 64% higher nitrite/nitrate levels ( P =0.003).

Conclusions—

This study suggests that plasma arginine:ADMA ratios predict mortality after SAH. Both clinical and physiological measures of changes in cerebral hemodynamics are coupled to the nitric oxide system.

CSF and Serum Biomarkers Focusing on Cerebral Vasospasm and Ischemia after Subarachnoid Hemorrhage

Delayed cerebral vasospasm (CVS) and delayed cerebral ischemia (DCI) remain severe complications after subarachnoid hemorrhage (SAH). Although focal changes in cerebral metabolism indicating ischemia are detectable by microdialysis, routinely used biomarkers are missing. We therefore sought to evaluate a panel of possible global markers in serum and cerebrospinal fluid (CSF) of patients after SAH. CSF and serum of SAH patients were analyzed retrospectively. In CSF, levels of inhibitory, excitatory, and structural amino acids were detected by high-performance liquid chromatography (HPLC). In serum, neuron-specific enolase (NSE) and S100B level were measured and examined in conjunction with CVS and DCI. CVS was detected by arteriography, and ischemic lesions were assessed by computed tomography (CT) scans. All CSF amino acids were altered after SAH. CSF glutamate, glutamine, glycine, and histidine were significantly correlated with arteriographic CVS. CSF glutamate and serum S100B were significantly correlated with ischemic events after SAH; however, NSE did not correlate neither with ischemia nor with vasospasm. Glutamate, glutamine, glycine, and histidine might be used in CSF as markers for CVS. Glutamate also indicates ischemia. Serum S100B, but not NSE, is a suitable marker for ischemia. These results need to be validated in larger prospective cohorts.

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

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

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.

The importance of early brain injury after subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is a medical emergency that accounts for 5% of all stroke cases. Individuals affected are typically in the prime of their lives (mean age 50 years). Approximately 12% of patients die before receiving medical attention, 33% within 48 h and 50% within 30 days of aSAH. Of the survivors 50% suffer from permanent disability with an estimated lifetime cost more than double that of an ischemic stroke. Traditionally, spasm that develops in large cerebral arteries 3-7 days after aneurysm rupture is considered the most important determinant of brain injury and outcome after aSAH. However, recent studies show that prevention of delayed vasospasm does not improve outcome in aSAH patients. This finding has finally brought in focus the influence of early brain injury on outcome of aSAH. A substantial amount of evidence indicates that brain injury begins at the aneurysm rupture, evolves with time and plays an important role in patients' outcome. In this manuscript we review early brain injury after aSAH. Due to the early nature, most of the information on this injury comes from animals and few only from autopsy of patients who died within days after aSAH. Consequently, we began with a review of animal models of early brain injury, next we review the mechanisms of brain injury according to the sequence of their temporal appearance and finally we discuss the failure of clinical translation of therapies successful in animal models of aSAH.

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.

New regulatory, signaling pathways, and sources of nitric oxide

Discovered in 1980 by the late Robert F. Furchgott, endothelium-derived relaxing factor, nitric oxide (NO), has been in the forefront of vascular research for several decades. What was originally a narrow approach, has been significantly widened due to major advances in understanding the chemical and biological properties of NO as well as its signaling pathways and discovering new sources of this notorious free radical gas. In this review, recent discoveries regarding NO and their implications on therapy for delayed cerebral vasospasm are presented.

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.

Nitric oxide synthase inhibitors and cerebral vasospasm

L-arginine is a source of nitric oxide (NO) that is cleaved from the terminal guanidino nitrogen atom by nitric oxide synthase (NOS). NO evokes, because of its free radical properties and affinity to heme, ferrous iron and cysteine, a wide spectrum of physiological and pathophysiological effects. For many years, different exogenous NOS inhibitors were used to elucidate the role of NOS and NO in health and disease. Later, endogenous NOS inhibitors, as asymmetric dimethylarginine (ADMA) were discovered. Endogenous inhibitors as ADMA are produced by post-translational methylation of L-arginine which is catalyzed by a family of protein N-methyltransferases (PRMT), using S-adenosylmethionine as a methyl group donor. ADMA is eliminated by dimethylarginine dimethylaminohydrolases (DDAH I or II). ADMA hydrolysis increases NOS activity and NO production. Furthermore, L-citrulline, a by-product of ADMA hydrolysis as well as of NO production by NOS, can in turn inhibit DDAH. Therefore, endogenous inhibition of NOS can be modified via different ways (1) changing the availability of L-arginine and/or of L-citrulline; (2) stimulating or inhibiting DDAH activity; (3) modifying methylation via regulating availability of adenosylmethionine; or (4) modifying PRMT activity. Research elucidating the role of NOS inhibitors in respect of delayed cerebral vasospasm after subarachnoid hemorrhage is summarized.

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.

Proteomic biomarker discovery in cerebrospinal fluid for cerebral vasospasm following subarachnoid hemorrhage

Currently, there are no established biomarkers for diagnosing preclinical vasospasm or monitoring its progression. Two areas of extensive biomarker research are neuroimaging and biochemical markers in body fluids, such as cerebrospinal fluid (CSF). We performed a review of studies conducted over the past 2 decades summarizing the science to date and the evolution of CSF biomarkers in subarachnoid hemorrhage (SAH). A Medline search performed using the search terms "subarachnoid hemorrhage marker AND cerebrospinal fluid," limited to the period January 1, 1990 to June 1, 2009, returned 62 references. Abstracts that did not deal primarily with SAH and potential markers in the CSF of humans were excluded, resulting in 27 abstracts. Only articles providing sufficient information for a substantiated analysis were selected. In addition, articles identified in reference lists of individual articles were selected if considered appropriate. Evidence was classified as class I-IV and recommendations were classified as category A-C according to European Federation of Neurological Societies guidelines. We evaluated CSF markers in SAH patients and divided them into 3 categories: A, markers with auspicious value; B, candidate markers; and C, noncandidate markers. Category A markers included tumor necrosis factor (TNF)-α, soluble tumor necrosis factor receptor I (sTNFR-I), and interleukin (IL)-1 receptor antagonist (IL-1ra), as well as the neurofilament proteins NFL and NfH. Category B markers included apolipoprotein E (ApoE), F2-isoprostane (F2-IsoP), NOx, and the indicators for thrombin activity membrane-bound tissue factor (mTF) and thrombin-antithrombin III complex (TAT) for neurologic outcome prediction, as well as E-selectin, lactate, alpha-II spectrin breakdown products (SBDPs), asymmetric dimethyl-L-arginine (ADMA), and monocyte chemoattractant protein-1 (MCP-1) for vasospasm prognostication. Category C markers included S100B, platelet-derived growth factor (PDGF), YKL-40, chitotriosidase, intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and IL-8. Cytokines and their receptors, as well as neuronal intracellular proteins, seem to be potential markers for outcome determination in patients after SAH.

Controlled delivery of nitric oxide inhibits leukocyte migration and prevents vasospasm in haptoglobin 2-2 mice after subarachnoid hemorrhage

OBJECTIVE

Cerebral vasospasm is the leading cause of morbidity and mortality after aneurysmal subarachnoid hemorrhage (SAH) occurs. The haptoglobin 2-2 genotype likely increases the risk for developing posthemorrhagic vasospasm, but potential treatments for vasospasm have never been tested in an animal model of this genotype. We used the nitric oxide (NO) donor diethylenetriamine (DETA)/NO incorporated into ethylene/vinyl acetate (EVAc) polymers to evaluate the efficacy of controlled NO repletion in a haptoglobin 2-2 mouse basilar artery SAH model.

METHODS

Mice were randomized to 3 groups: autologous blood injection and empty polymer implantation into the subarachnoid space (n = 16); blood injection and 30% DETA/NO-EVAc implantation (n = 20); and sham operation (n = 19). At 24 hours after surgery, activity level was assessed on a 3-point scale, and basilar arteries were processed for morphometric measurements. Leukocyte extravasation was assessed by immunohistochemistry (n = 12).

RESULTS

Treatment with controlled release of NO from DETA/NO-EVAc polymers after SAH resulted in a significant increase in basilar artery lumen patency (73.3% +/- 4.3% versus 96.5% +/- 4.3%, mean +/- standard error of the mean; P = 0.01), a significant improvement in activity after experimental SAH (2.14 +/- 0.14 versus 2.56 +/- 0.10 points; P = 0.025), and a significant decrease in extravasated leukocytes (21 +/- 4.55 versus 6.75 +/- 3.77 leukocytes per high-power field, untreated versus treated mice; P = 0.001).

CONCLUSION

Treatment with controlled release of NO prevented posthemorrhagic vasospasm in haptoglobin 2-2 mice, and mitigated neurological deficits, suggesting that DETA/NO-EVAc would be an effective therapy in patients with a genotype that confers higher risk for vasospasm after SAH. In addition to smooth muscle relaxation, inhibition of leukocyte migration may contribute to the therapeutic mechanism of NO.

Nitric oxide suppresses cerebral vasomotion by sGC-independent effects on ryanodine receptors and voltage-gated calcium channels

BACKGROUND/AIMS

In cerebral arteries, nitric oxide (NO) release plays a key role in suppressing vasomotion. Our aim was to establish the pathways affected by NO in rat middle cerebral arteries.

METHODS

In isolated segments of artery, isometric tension and simultaneous measurements of either smooth muscle membrane potential or intracellular [Ca(2+)] ([Ca(2+)](SMC)) changes were recorded.

RESULTS

In the absence of L-NAME, asynchronous propagating Ca(2+) waves were recorded that were sensitive to block with ryanodine, but not nifedipine. L-NAME stimulated pronounced vasomotion and synchronous Ca(2+) oscillations with close temporal coupling between membrane potential, tone and [Ca(2+)](SMC). If nifedipine was applied together with L-NAME, [Ca(2+)](SMC) decreased and synchronous Ca(2+) oscillations were lost, but asynchronous propagating Ca(2+) waves persisted. Vasomotion was similarly evoked by either iberiotoxin, or by ryanodine, and to a lesser extent by ODQ. Exogenous application of NONOate stimulated endothelium-independent hyperpolarization and relaxation of either L-NAME-induced or spontaneous arterial tone. NO-evoked hyperpolarization involved activation of BK(Ca) channels via ryanodine receptors (RYRs), with little involvement of sGC. Further, in whole cell mode, NO inhibited current through L-type voltage-gated Ca(2+) channels (VGCC), which was independent of both voltage and sGC.

CONCLUSION

NO exerts sGC-independent actions at RYRs and at VGCC, both of which normally suppress cerebral artery myogenic tone.

Asymmetric dimethylarginine: a novel marker of risk and a potential target for therapy in chronic kidney disease

PURPOSE OF REVIEW

Asymmetric dimethylarginine (ADMA) is a naturally occurring amino acid that reduces the bioavailability of nitric oxide. ADMA opposes important antiatherosclerotic effects of nitric oxide. ADMA not only correlates with traditional and nontraditional risk factors but is also considered a common pathway mediating the adverse vascular effects of traditional and nontraditional risk factors. Over the past 15 years, ADMA has generated increasing interest from both clinical scientist and basic researchers. The present study summarizes the latest developments in the field.

RECENT FINDINGS

Modulating (increasing) activity of dimethylamine dimethylaminohydrolase, the main enzyme metabolizing ADMA, emerges as a possible therapeutic option to lower ADMA and favorably influence organ dysfunction. These preclinical findings are thought to be of major importance as ADMA predicts cardiovascular events and mortality in the general population and in patients with chronic kidney disease. Also, ADMA uniformly predicts the progression of moderate and severe chronic kidney disease. Symmetrical dimethylarginine, the structural isomer of ADMA, which was mistakenly thought to be without biological relevance, indicates the degree of renal impairment.

SUMMARY

ADMA also beautifully explains many facets of the pathophysiology of chronic kidney disease. Future preclinical and especially clinical studies are required to prove the importance of ADMA in renal and cardiovascular disease.