Increased cerebral blood flow but no reversal or prevention of vasospasm in response to L-arginine infusion after subarachnoid hemorrhage

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

Background

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

Methods

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

Results

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

Conclusion

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

Arginase-1 Released into CSF After Aneurysmal Subarachnoid Hemorrhage Decreases Arginine/Ornithine Ratio: a Novel Prognostic Biomarker

We hypothesized that the enzyme arginase-1 is released into the cerebrospinal fluid (CSF) during red blood cell lysis and contributes to dysregulated metabolism of the nitric oxide (NO) precursor L-arginine during aneurysmal subarachnoid hemorrhage (SAH). This prospective case-control study included 43 patients with aneurysmal SAH and ventricular drainage for clinical reasons. Longitudinal CSF samples (99) were obtained in the course of SAH. Patients were dichotomized regarding the occurrence of cerebral vasospasm syndrome (CVS) (N = 19). Arginase-1 and the amino acids L-arginine and L-ornithine were quantified in CSF. Outcome assessments included delayed cerebral ischemia (DCI) and functional status after 3 months using the modified Rankin Scale (mRS). Arginase-1 was released into the CSF of SAH patients whereas this enzyme was undetectable in controls. Compared to patients without CVS, arginase-1 levels were higher in CVS patients until day 14 after clinical event. The well-known surrogate parameter for arginase acitivity, the L-arginine to L-ornithine ratio (Arg/Orn), correlated with CSF arginase-1 levels. Arg/Orn was reduced in patients with CVS from disease onset (days 1-3, p = 0.0009) until day 14. Logistic regression analysis of early Arg/Orn was predictive for CVS (p = 0.008) and DCI (p = 0.035), independent of age, Hunt and Hess grade, and intraventricular blood. Arg/Orn < 2.71 at disease onset predicted CVS with a sensitivity of 86.7% and specificity of 72.2%. Arg/Orn ≥ 2.71 predicted excellent functional outcome. We propose a novel mechanism contributing to NO deprivation during SAH: arginase-1 is released from erythrocytes into the CSF, leading to L-arginine consumption and reduced NO bioavailability. Furthermore, Arg/Orn is a robust predictor for occurrence of CVS, DCI, and functional outcome 3 months after aneurysmal SAH. Our data provide a novel prognostic biomarker and may contribute to the development of novel therapeutic strategies in SAH. Clinical Trial Registration-URL: http://www.drks.de . Unique identifier: DRKS00015293, date of registration: 13.09.2018.

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

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

Correlation between plasma total nitric oxide levels and cerebral vasospasm and clinical outcome in patients with aneurysmal subarachnoid hemorrhage in Indian population

CONTEXT

Cerebral vasospasm remains a major cause of morbidity and mortality in patients with aneurysmal subarachnoid hemorrhage (aSAH). Reduced bioavailability of nitric oxide has been associated with the development of cerebral vasospasm after aSAH. Such data is not available in Indian population.

AIMS

The objective of the study was to measure the plasma total nitric oxide (nitrite and nitrate-NO x ) level in aSAH patients and healthy controls treated at a tertiary hospital in India and to investigate a possible association between plasma total nitric oxide level and cerebral vasospasm and clinical outcome following treatment in patients with aSAH.

SETTINGS AND DESIGN

A case-control study of aSAH patients was conducted. Plasma total NO x levels were estimated in aSAH patients with and without vasospasm and compared the results with NO x levels in healthy individuals.

MATERIALS AND METHODS

aSAH in patients was diagnosed on the basis of clinical and neuro-imaging findings. Plasma total NO x levels in different subject groups were determined by Griess assay.

RESULTS

Plasma total NO x level was found to be significantly decreased in patients with aSAH when compared to controls. Plasma total NO x level in the poor-grade SAH group was lower than that in the good-grade SAH group. Plasma total NO x level further reduced in patients with angiographic (P < 0.05) and clinical vasospasm.

CONCLUSIONS

Reduced plasma NO x level is seen in aSAH patients as compared to normal individuals. In aSAH patients reduced levels are associated with increased incidence of cerebral vasospasm and poor outcome. Plasma total NO x level could be used as a candidate biomarker for predicting vasospasm and outcome for this pathology.

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.

Continuous selective intra-arterial application of nimodipine in refractory cerebral vasospasm due to aneurysmal subarachnoid hemorrhage

Background. Cerebral vasospasm is one of the leading courses for disability in aneurysmal subarachnoid hemorrhage. Effective treatment of vasospasm is therefore one of the main priorities for these patients. We report about a case series of continuous intra-arterial infusion of the calcium channel antagonist nimodipine for 1–5 days on the intensive care unit. Methods. In thirty patients with aneurysmal subarachnoid hemorrhage and refractory vasospasm continuous infusion of nimodipine was started on the neurosurgical intensive care unit. The effect of nimodipine on brain perfusion, cerebral blood flow, brain tissue oxygenation, and blood flow velocity in cerebral arteries was monitored. Results. Based on Hunt & Hess grades on admission, 83% survived in a good clinical condition and 23% recovered without an apparent neurological deficit. Persistent ischemic areas were seen in 100% of patients with GOS 1–3 and in 69% of GOS 4-5 patients. Regional cerebral blood flow and computed tomography perfusion scanning showed adequate correlation with nimodipine application and angiographic vasospasm. Transcranial Doppler turned out to be unreliable with interexaminer variance and failure of detecting vasospasm or missing the improvement. Conclusion. Local continuous intra-arterial nimodipine treatment for refractory cerebral vasospasm after aSAH can be recommended as a low-risk treatment in addition to established endovascular therapies.

Brain ischemia in patients with intracranial hemorrhage: pathophysiological reasoning for aggressive diagnostic management

Patients with intracranial hemorrhage have to be managed aggressively to avoid or minimize secondary brain damage due to ischemia, which contributes to high morbidity and mortality. The risk of brain ischemia, however, is not the same in every patient. The risk of complications associated with an aggressive prophylactic therapy in patients with a low risk of brain ischemia can outweigh the benefits of therapy. Accurate and timely identification of patients at highest risk is a diagnostic challenge. Despite the availability of many diagnostic tools, stroke is common in this population, mostly because the pathogenesis of stroke is frequently multifactorial whereas diagnosticians tend to focus on one or two risk factors. The pathophysiological mechanisms of brain ischemia in patients with intracranial hemorrhage are not yet fully elucidated and there are several important areas of ongoing research. Therefore, this review describes physiological and pathophysiological aspects associated with the development of brain ischemia such as the mechanism of oxygen and carbon dioxide effects on the cerebrovascular system, neurovascular coupling and respiratory and cardiovascular factors influencing cerebral hemodynamics. Consequently, we review investigations of cerebral blood flow disturbances relevant to various hemodynamic states associated with high intracranial pressure, cerebral embolism, and cerebral vasospasm along with current treatment options.

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.

Inhalation of nitric oxide prevents ischemic brain damage in experimental stroke by selective dilatation of collateral arterioles

RATIONALE

Stroke is the third most common cause of death in industrialized countries. The main therapeutic target is the ischemic penumbra, potentially salvageable brain tissue that dies within the first few hours after blood flow cessation. Hence, strategies to keep the penumbra alive until reperfusion occurs are needed.

OBJECTIVE

To study the effect of inhaled nitric oxide on cerebral vessels and cerebral perfusion under physiological conditions and in different models of cerebral ischemia.

METHODS AND RESULTS

This experimental study demonstrates that inhaled nitric oxide (applied in 30% oxygen/70% air mixture) leads to the formation of nitric oxide carriers in blood that distribute throughout the body. This was ascertained by in vivo microscopy in adult mice. Although under normal conditions inhaled nitric oxide does not affect cerebral blood flow, after experimental cerebral ischemia induced by transient middle cerebral artery occlusion it selectively dilates arterioles in the ischemic penumbra, thereby increasing collateral blood flow and significantly reducing ischemic brain damage. This translates into significantly improved neurological outcome. These findings were validated in independent laboratories using two different mouse models of cerebral ischemia and in a clinically relevant large animal model of stroke.

CONCLUSIONS

Inhaled nitric oxide thus may provide a completely novel strategy to improve penumbral blood flow and neuronal survival in stroke or other ischemic conditions.

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.

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.

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.

Management of post-subarachnoid hemorrhage vasospasm

Permanent neurologic injury and death remain common outcomes following aneurysmal subarachnoid hemorrhage. Although many sophisticated techniques are evolving for securing intracranial aneurysms to prevent rebleeding, progress is lagging in the management of posthemorrhagic complications, particularly cerebral vasospasm. Vasospasm can be defined either angiographically, by visible reduction in arterial lumen diameters, or clinically, with signs of focal or regional cerebral ischemia. The relationship between angiographic and clinical vasospasm is not straightforward. The most important known risk factors for developing posthemorrhagic vasospasm include volume and distribution of subarachnoid blood, and no preventive measures have proven effective. Established treatment strategies for vasospasm include hyperdynamic therapy, angioplasty, and selective intra-arterial injection of vasodilators. The vasodilatory approach has been called into question by recent data suggesting that reduction of arterial luminal diameters may be due largely to a proliferative arteriopathy. Novel treatment strategies have focused on protecting the cerebrum, targeting components of the inflammatory cascade, and identifying genetic factors predisposing toward vasospasm, all of which may soon yield new treatment modalities.

Continuous selective intraarterial infusion of nimodipine for therapy of refractory cerebral vasospasm

BACKGROUND

For endovascular treatment of vasospasm after aneurysmal subarachnoid hemorrhage (aSAH), an intraarterial treatment course with the calcium channel antagonist nimodipine infused for 30 min is proposed. As some patients still show ongoing vasospasm thereafter, we report on our experience with an extended time period of selective intraarterial nimodipine administration.

METHODS

In nine patients with aSAH and refractory cerebral vasospasm, we left the catheter in place within the internal carotid artery after angiography. On the neurosurgical ICU, a continuous infusion of intraarterial nimodipine was commenced, combined with intraarterial heparin anticoagulation. Therapy was controlled with extended neuromonitoring techniques.

RESULTS

Three patients died from refractory vasospasm and a fourth suffered lethal sepsis. Three patients survived in a good clinical condition, two of them without apparent neurologic deficit. The efficacy of intraarterial nimodipine was best verified with regional CBF monitoring. TCD failed to detect vasospasm in two patients and missed improvement in four. Brain tissue oxygenation increased in all patients, but was not indicative of vasospasm in one. CT perfusion reflected the treatment course adequately in the qualitative scans.

CONCLUSION

Selective continuous intraarterial nimodipine treatment for refractory cerebral vasospasm after aSAH seems feasible and may add to the endovascular therapeutic options. Appropriate monitoring technology is essential for further investigation of this novel technique.

Medical management of cerebral vasospasm: present and future

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

Intra-arterial nicardipine infusion improves CT perfusion-measured cerebral blood flow in patients with subarachnoid hemorrhage-induced vasospasm

BACKGROUND AND PURPOSE

Our aim was to determine the effects of intra-arterial (IA) nicardipine infusion on the cerebral hemodynamics of patients with aneurysmal subarachnoid hemorrhage (aSAH)-induced vasospasm by using first-pass quantitative cine CT perfusion (CTP).

MATERIALS AND METHODS

Six patients post-aSAH with clinical and transcranial Doppler findings suggestive of vasospasm were evaluated by CT angiography and CTP immediately before angiography for possible vasospasm treatment. CTP was repeated immediately following IA nicardipine infusion. Maps of mean transit time (MTT), cerebral blood volume (CBV), and cerebral blood flow (CBF) were constructed and analyzed in a blinded manner. Corresponding regions of interest on these maps from the bilateral middle cerebral artery territories and, when appropriate, the bilateral anterior or posterior cerebral artery territories, were selected from the pre- and posttreatment scans. Normalized values were compared by repeated measures analysis of variance.

RESULTS

Angiographic vasospasm was confirmed in all patients. In 5 of the 6 patients, both CBF and MTT improved significantly in affected regions in response to nicardipine therapy (mean increase in CBF, 41 +/- 43%; range, -9%-162%, P = .0004; mean decrease in MTT, 26 +/- 24%; range, 0%-70%, P = .0002). In 1 patient, we were unable to quantify improvement in flow parameters due to section-selection differences between the pre- and posttreatment examinations.

CONCLUSIONS

IA nicardipine improves CBF and MTT in ischemic regions in patients with aSAH-induced vasospasm. Our data provide a tissue-level complement to the favorable effects of IA nicardipine reported on prior angiographic studies. CTP may provide a surrogate marker for monitoring the success of treatment strategies in patients with aSAH-induced vasospasm.

Endothelial nitric oxide synthase gene single-nucleotide polymorphism predicts cerebral vasospasm after aneurysmal subarachnoid hemorrhage

Vasospasm is a major cause of morbidity and mortality after aneurysmal subarachnoid hemorrhage (aSAH). Studies have shown a link between single-nucleotide polymorphisms (SNPs) in the endothelial nitric oxide synthase (eNOS) gene and the incidence of coronary spasm and aneurysms. Alterations in the eNOS T-786 SNP may lead to an increased risk of post-aSAH cerebral vasospasm. In this prospective clinical study, 77 aSAH patients provided genetic material and were followed for the occurrence of vasospasm. In multivariate logistic regression analysis, genotype was the only factor predictive of vasospasm. The odds ratio (OR) for symptomatic vasospasm in patients with one T allele was 3.3 (95% confidence interval (CI): 1.1 to 10.0, P=0.034) and 10.9 for TT. Patients with angiographic spasm were 3.6 times more likely to have a T allele (95% CI: 1.3 to 9.6, P=0.013; for TT: OR 12.6). Patients with severe vasospasm requiring endovascular therapy were more likely to have a T allele (OR 3.5, 95% CI: 1.3 to 9.5, P=0.016; for TT: OR 12.0). Patients with the T allele of the eNOS gene are more likely to have severe vasospasm. Presence of this genotype may allow the identification of individuals at high risk for post-aSAH vasospasm and lead to early treatment and improved outcome.

Vasospasm as the sole cause of cerebral ischemia: how strong is the evidence?

✓ The authors review literature that challenges the view that vasospasm involving large arteries is the exclusive cause of delayed ischemic neurological deficits (DINDs) following subarachnoid hemorrhage. They discuss alternative mechanisms and review the evidence supporting a potential role for thromboembolism. They conclude that vasospasm and thromboembolism play interrelated and additive roles in the development of DINDs, and that this interaction provides opportunities for novel therapeutic approaches.

Nitric oxide in subarachnoid haemorrhage and its therapeutics implications

BACKGROUND

After the discovery that nitric oxide (NO) plays a major role in the regulation of vascular tone, this substance moved into the focus of interest with regard to vasospasm after subarachnoid haemorrhage (SAH). A multitude of interactions were discovered and some concepts of therapeutic intervention were developed.

METHOD

The present review is based on a Medline search with the terms "nitric oxide" and "subarachnoid haemorrhage".

FINDINGS

SAH and particularly liberated oxyhaemoglobin sequestrate the physiologically produced NO. Reactivity to NO appears to be principally preserved. As other types of injury, SAH leads to induction of inducible NO synthase (iNOS). The NO produced by this pathway cannot compensate for the lack of the physiological NO and may even lead to tissue damage by oxidative stress. Experimental therapeutic attempts use stimulation of NO production and delivery of NO donors. NO donors were also used in some small clinical trials. A final assessment of efficacy and safety is not yet possible.

CONCLUSION

NO physiology and pathophysiology are important in the genesis of vasospasm after subarachnoid haemorrhage. NO directed therapeutic strategies enlarge the spectrum of available instruments, but complete elimination of the problem of vasospasm cannot be expected.

Association between cerebrospinal fluid levels of asymmetric dimethyl-L-arginine, an endogenous inhibitor of endothelial nitric oxide synthase, and cerebral vasospasm in a primate model of subarachnoid hemorrhage

Object. Decreased availability of nitric oxide (NO) has been proposed to evoke delayed cerebral vasospasm after subarachnoid hemorrhage (SAH). Asymmetric dimethyl-l-arginine (ADMA) inhibits endothelial NO synthase (eNOS) and, therefore, may be responsible for decreased NO availability in cases of cerebral vasospasm. The goal of this study was to determine whether ADMA levels are associated with cerebral vasospasm in a primate model of SAH.

Methods. Twenty-two cynomolgus monkeys (six control animals and 16 with SAH) were used in this study. The levels of ADMA, l-arginine, l-citrulline, nitrites, and nitrates in cerebrospinal fluid (CSF) and serum were determined on Days 0, 7, 14, and 21 following onset of SAH. Cerebral arteriography was performed to assess the degree of vasospasm. Western blot analyses of the right and left middle cerebral arteries (MCAs) were performed to assess the expression of eNOS, type I protein—arginine methyl transferase (PRMT1) and dimethylarginine dimethylaminohydrolase (DDAH2).

Cerebrospinal fluid levels of ADMA remained unchanged in the control group (six animals) and in animals with SAH that did not have vasospasm (five animals; p = 0.17), but the levels increased in animals with vasospasm (11 animals) on Day 7 post-SAH (p < 0.01) and decreased on Days 14 through 21 (p < 0.05). Cerebrospinal fluid levels of ADMA correlated directly with the degree of vasospasm (correlation coefficient = 0.7, p = 0.0001; 95% confidence interval: 0.43–0.83). Levels of nitrite and nitrate as well as those of l-citrulline in CSF were decreased in animals with vasospasm. Furthermore, DDAH2 expression was attenuated in the right spastic MCA on Day 7 post-SAH, whereas eNOS and PRMT1 expression remained unchanged.

Conclusions. Changes in the CSF levels of ADMA are associated with the development and resolution of vasospasm found on arteriograms after SAH. The results indicate that endogenous inhibition of eNOS by ADMA may be involved in the development of delayed cerebral vasospasm. Inhibition of ADMA production may provide a new therapeutic approach for cerebral vasospasm after SAH.

Role of nitric oxide in the CBF autoregulation during acute stage after subarachnoid haemorrhage in rat pial artery

The present study was aimed to identify whether endogenously produced nitric oxide (NO) plays a role in preservation of cerebral blood flow (CBF) autoregulation in rat pial artery during the acute stage after subarachnoid haemorrhage (SAH). During the acute stage after SAH, the lower limit of CBF autoregulation significantly shifted to the higher arterial blood pressure in association with suppressed vasodilatation in response to acute hypotension, which was accompanied by significantly increased expression of endothelial nitric oxide synthase mRNA and increased production of superoxide anion in cerebral vessels. SAH-induced increase in superoxide production was further enhanced under pretreatment with N-nitro-L-arginine methyl ester in the cerebral vessels. Following additional administration of L-arginine (100 mg/kg, i.p.), the haemodynamic alterations were significantly restored in association with significantly reduced superoxide level in the cerebral vessels. In line with these findings, rats that received polyethylene glycol superoxide dismutase and catalase or Mn(III) tetrakis (4-benzoic acid) porphyrin chloride showed recovery of impaired autoregulatory vasodilation in response to acute hypotension. Thus, it is suggested that NO endogenously produced is importantly implicated in the preservation of CBF autoregulation during the acute stage after SAH via its capability to scavenge superoxide anion.

Endothelial dysfunction in a primate model of cerebral vasospasm

OBJECT

Although abnormalities in the control of endothelial vasomotility have been reported in both experimental and clinical studies, the mechanism of the endothelial dysfunction that occurs following subarachnoid hemorrhage (SAH) remains unclear. Because of the absence of previous in vivo studies of endothelial function in cerebral vessels in response to SAH or cerebral vasospasm, the authors investigated endothelium-dependent responses in an established primate model of vasospasm after SAH. Endothelial function was assessed by examining vascular responses to intracarotid injections of various drugs known to act via the endothelium. Drugs that have a rapid total body clearance were selected so that their pharmacological effects would be limited to the cerebral circulation after an intracarotid infusion.

METHODS

Seventeen adult male cynomolgus monkeys were used. Cerebrovascular endothelium-dependent responses were examined in control animals and in animals with SAH 7, 14, and 21 days after placement of a subarachnoid clot around the right middle cerebral artery. Cortical cerebral blood flow (CBF) and cerebrovascular resistance (CVR) were recorded continuously during 5-minute intracarotid infusions of 5% dextrose vehicle, acetylcholine, histamine, bradykinin, or Calcimycin. In control animals the intracarotid infusion of acetylcholine produced a significant (7.8 +/- 9.5%) increase in CBF and a 9.3 +/- 8.7% reduction in CVR in comparison with a control infusion of dextrose vehicle. The responses to acetylcholine disappeared in animals 7 days post-SAH, specifically in the subset of animals in which arteriography confirmed the presence of vasospasm. Infusion of Calcimycin produced no significant changes in CBF or CVR in control animals, but resulted in a significant reduction in CBF and increase in CVR in animals 7 days after SAH and in animals with vasospasm. An infusion of histamine or bradykinin had no significant effect on CBF or CVR.

CONCLUSIONS

An intracarotid infusion of acetylcholine, but not one of histamine, bradykinin, or Calcimycin, produced a measurable physiological response in the normal primate cerebrovasculature. Cerebral vasospasm that occurred after SAH produced a pathophysiological effect similar to the endothelial denudation shown in the in vitro experiments of Furchgott and Zawadzki, in which acetylcholine constricted the vessels via activation of receptors on smooth-muscle cells. Changes in vascular responses to acetylcholine and Calcimycin in animals with vasospasm, compared with control animals, provide evidence that endothelial dysfunction plays a key role in the development and/or sustenance of vasospasm after SAH.

Oxidation of bilirubin produces compounds that cause prolonged vasospasm of rat cerebral vessels: a contributor to subarachnoid hemorrhage-induced vasospasm

The authors have previously shown that bilirubin-oxidation products (BOXes) are present in CSF of subarachnoid hemorrhage patients with vasospasm, and that BOXes cause vasoconstriction in vitro. This study determined whether BOXes cause vasospasm in vivo. Identical volumes of either lysed blood or standardized amounts of BOXes were injected into the cisterna magna of adult rats. BOX injections caused 6 of 10 rats to die within 10 minutes, whereas 12 of 12 rats survived for 24 hours after blood injections. The mechanism for this significant (P < or = 0.01) increase in mortality was unclear. To directly test whether BOXes produced vasospasm, a cranial window technique was used. Application of 20 microL of 10-micromol/L bilirubin had little effect on the vessels. However, application of BOXes produced marked, dose-dependent small artery and arteriole vasospasm that approached a 90% decrease in diameter by 40 minutes after application in some vessels, and persisted for at least 24 hours. To determine if BOX-mediated vasospasm led to cortical injury, histology and immunocytochemistry were performed on animals that survived for 24 hours. There was a BOX-related stress protein response for HSP25 and HSP32 (HO-1) without evidence of infarction. The finding that the BOXes produce vasospasm of cerebral vessels in vivo, in conjunction with BOXes being found in CSF of vasospasm patients, supports our hypothesis that BOXes contribute to or cause cerebral vasospasm after subarachnoid hemorrhage.

Cerebrovascular inflammation following subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage frequently results in complications including intracranial hypertension, rebleeding and vasospasm. The extravasated blood is responsible for a cascade of reactions involving release of various vasoactive and pro-inflammatory factors (several of which are purported to induce vasospasm) from blood and vascular components in the subarachnoid space. The authors review the available evidence linking these factors to the development of inflammatory lesions of the cerebral vasculature, emphasizing: 1) neurogenic inflammation due to massive release of sensory nerve neuropeptides; 2) hemoglobin from lysed erythrocytes, which creates functional lesions of endothelial and smooth muscle cells; 3) activity, expression and metabolites of lipoxygenases cyclooxygenases and nitric oxide synthases; 4) the possible role of endothelin-1 as a pro-inflammatory agent; 5) serotonin, histamine and bradykinin which are especially involved in blood-brain barrier disruption; 6) the prothrombotic and pro-inflammatory action of complement and thrombin towards endothelium; 7) the multiple actions of activated platelets, including platelet-derived growth factor production; 8) the presence of perivascular and intramural macrophages and granulocytes and their interaction with adhesion molecules; 9) the evolution, origins, and effects of pro-inflammatory cytokines, especially IL-1, TNF-alpha and IL-6. Human and animal studies on the use of anti-inflammatory agents in subarachnoid hemorrhage include superoxide and other radical scavengers, lipid peroxidation inhibitors, iron chelators, NSAIDs, glucocorticoids, and serine protease inhibitors. Many animal studies claim reduced vasospasm, but these effects are not always confirmed in human trials, where symptomatic vasospasm and outcome are the major endpoints. Despite recent work on penetrating vessel constriction, there is a paucity of studies on inflammatory markers in the microcirculation.

Review of medical prevention of vasospasm after aneurysmal subarachnoid hemorrhage: a problem of neurointensive care

Cerebral vasospasm remains a devastating medical complication of aneurysmal subarachnoid hemorrhage (SAH). It is associated with high morbidity and mortality rates, even after the aneurysm has been secured surgically or radiologically. A great deal of experimental and clinical research has been conducted in an effort to find ways to prevent this complication. The literature includes extensive coverage of in vivo animal model studies of SAH and vasospasm. These experimental studies have contributed to tremendous advances in the understanding of the mechanisms leading to cerebral vasospasm. Most of the experimental settings, however, have demonstrated varying levels of ability to predict accurately what occurs in human SAH. Therefore, although animal models have been developed to test new therapies, most of the treatment effects have been shown to be less compelling when trials have been conducted in clinical settings. The interpretation of current literature is complicated further by the imprecise estimation of the incidence of cerebral vasospasm, which is due to various degrees of clinical expression, ranging from the absence of symptoms in the presence of increased blood flow velocities at transcranial Doppler or vessel diameter reduction at angiography to neurological manifestations of severe ischemic deficits. In addition, a change over time in the incidence pattern of human SAH and vasospasm, possibly related to improved surgical techniques and overall patient management, may have occurred. This topic review collects the relevant literature on clinical trials investigating prophylactic therapies for cerebral vasospasm in patients with aneurysmal SAH and emphasizes the need for large clinical trials to confirm the results derived from clinical experience. In addition, it points out some experimental therapies that may hold promise in future clinical trials to prevent the occurrence of vasospasm.

Endothelial nitric oxide synthase-dependent cerebral blood flow augmentation by L-arginine after chronic statin treatment

Nitric oxide, a product of nitric oxide synthase activity, relaxes vascular smooth muscle and elevates brain blood flow. We evaluated the importance of eNOS to cerebral blood flow augmentation after L-arginine infusion and increases in flow after eNOS upregulation in SV-129 mice. Blood flow was measured by laser-Doppler flowmetry before and after L-arginine infusion (450 mg/kg during a 15-minute period) or measured by 14C-iodoamphetamine indicator fractionation or 14C-iodoantipyrine tissue equilibration techniques. rCBF increased by 26% (laser Doppler flowmetry) after L-arginine infusion but did not change in mutant mice deficient in eNOS expression. After eNOS upregulation by chronic simvastatin treatment (2 mg/kg subcutaneously, daily for 14 days), L-arginine amplified and sustained the hyperemia (38%) and increased absolute brain blood flow from 86 +/- 7 to 119 +/- 10 mL/100 g per minute. Furthermore, pretreatment with simvastatin enhanced blood flow within ischemic brain tissue after middle cerebral artery occlusion. Together, these findings suggest that eNOS activity is critical for blood flow augmentation during acute L-arginine infusion, and chronic eNOS upregulation combined with L-arginine administration provides a novel strategy to elevate cerebral blood flow in the normal and ischemic brain.