Controlled release of a nitric oxide donor for the prevention of delayed cerebral vasospasm following experimental subarachnoid hemorrhage in nonhuman primates

Delayed Cerebral Ischemia After Subarachnoid Hemorrhage: Is There a Relevant Experimental Model? A Systematic Review of Preclinical Literature

Delayed cerebral ischemia (DCI) is one of the main prognosis factors for disability after aneurysmal subarachnoid hemorrhage (SAH). The lack of a consensual definition for DCI had limited investigation and care in human until 2010, when a multidisciplinary research expert group proposed to define DCI as the occurrence of cerebral infarction (identified on imaging or histology) associated with clinical deterioration. We performed a systematic review to assess whether preclinical models of SAH meet this definition, focusing on the combination of noninvasive imaging and neurological deficits. To this aim, we searched in PUBMED database and included all rodent SAH models that considered cerebral ischemia and/or neurological outcome and/or vasospasm. Seventy-eight publications were included. Eight different methods were performed to induce SAH, with blood injection in the cisterna magna being the most widely used (n = 39, 50%). Vasospasm was the most investigated SAH-related complication (n = 52, 67%) compared to cerebral ischemia (n = 30, 38%), which was never investigated with imaging. Neurological deficits were also explored (n = 19, 24%). This systematic review shows that no preclinical SAH model meets the 2010 clinical definition of DCI, highlighting the inconsistencies between preclinical and clinical standards. In order to enhance research and favor translation to humans, pertinent SAH animal models reproducing DCI are urgently needed.

The effect of pentoxifylline on cerebral vasospasm following experimental subarachnoid hemorrhage

OBJECTS

Cerebral vasospasm is an important event that occurs following subarachnoid hemorage which has significant mortality and morbidity. The goal in this study was to investigate the effect of pentoxifylline on vasospasm in an experimental subarachnoid hemorrhage model.

METHODS

In this study, 20 male New Zeland White rabbits weighing 3000-3500 g were assigned randomly to four groups. Animals in group 1 served as controls. Animals in group two received only intravenous pentoxifylline injection 3 times in 12 h intervals. In group 3, SAH was induced and no injection was given. Animals in group 4 received intravenous pentoxifylline (6 mg/kg) injections 3 times at 12^th, 24^th and 36^th hours after subarachnoid hemorrhage induction. All animals were sacrificed and basilar arteries were removed at 48th hour. Basilar artery vessel diameters, wall thicknesses and luminal section areas were measured with Spot for Windows version 4.1. Statistical analysis was performed using ANOVA and Kruskall-Wallis tests.

RESULTS

Mean basilar artery luminal section areas and luminal diameters in group 4 were significantly higher compared to group 3 (p < 0.05). Basilar artery wall thicknesses and were found to be higher in group 3 than in other groups and this was also statistically significant (p < 0.05).

CONCLUSION

Our study demonstrated that intravenous administration of pentoxifylline significantly decreases vasospasm after subarachnoid hemorrhage.

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.

The comparative effects of recombinant human erythropoietin and darbepoetin-alpha on cerebral vasospasm following experimental subarachnoid hemorrhage in the rabbit

BACKGROUND

Darbepoetin alpha is a hypersialylated analogue of erythropoietin effective for activating erythropoietin-receptors. This study investigated the vasodilator and neuroprotective effects of darbepoetin alpha on an experimental subarachnoid hemorrhage model and compared it with erythropoietin.

METHODS

Forty adult male New Zealand white rabbits were randomly divided into four groups of ten rabbits each: group 1 (control), group 2 (subarachnoid hemorrhage), group 3 (erythropoietin), and group 4 (darbepoetin alpha). Recombinant human erythropoietin was administered at a dose of 1,000 U/kg intraperitoneally after the induction of subarachnoid hemorrhage and continued every 8 h up to 72 h. Darbepoetin alpha was administered at a single intraperitoneal dose of 30 μg/kg. Animals were killed 72 h after subarachnoid hemorrhage. Basilar artery cross-sectional areas, arterial wall thicknesses, hippocampal degeneration scores and biochemical analyses were measured in all groups.

RESULTS

Both erythropoietin and darbepoetin alpha treatments were found to attenuate cerebral vasospasm and provide neuroprotection after subarachnoid hemorrhage in rabbits. Darbepoetin alpha revealed better morphometric and histopathological results than erythropoietin among experimental subarachnoid hemorrhage-induced vasospasm.

CONCLUSIONS

Our findings, for the first time, showed that darbepoetin alpha can prevent vasospasm and provides neuroprotection following experimental subarachnoid hemorrhage. Moreover, darbepoetin alpha showed better results when compared with erythropoietin.

Cerebral vasospasm pharmacological treatment: an update

Aneurysmal subarachnoid hemorrhage- (aSAH-) associated vasospasm constitutes a clinicopathological entity, in which reversible vasculopathy, impaired autoregulatory function, and hypovolemia take place, and lead to the reduction of cerebral perfusion and finally ischemia. Cerebral vasospasm begins most often on the third day after the ictal event and reaches the maximum on the 5th-7th postictal days. Several therapeutic modalities have been employed for preventing or reversing cerebral vasospasm. Triple "H" therapy, balloon and chemical angioplasty with superselective intra-arterial injection of vasodilators, administration of substances like magnesium sulfate, statins, fasudil hydrochloride, erythropoietin, endothelin-1 antagonists, nitric oxide progenitors, and sildenafil, are some of the therapeutic protocols, which are currently employed for managing patients with aSAH. Intense pathophysiological mechanism research has led to the identification of various mediators of cerebral vasospasm, such as endothelium-derived, vascular smooth muscle-derived, proinflammatory mediators, cytokines and adhesion molecules, stress-induced gene activation, and platelet-derived growth factors. Oral, intravenous, or intra-arterial administration of antagonists of these mediators has been suggested for treating patients suffering a-SAH vasospam. In our current study, we attempt to summate all the available pharmacological treatment modalities for managing vasospasm.

Release of NO from a nitrosyl ruthenium complex through oxidation of mitochondrial NADH and effects on mitochondria

Nitrosyl ruthenium complexes are promising NO donor agents with numerous advantages for the biologic applications of NO. We have characterized the NO release from the nitrosyl ruthenium complex [Ru(NO(2))(bpy)(2)(4-pic)](+) (I) and the reactive oxygen/nitrogen species (ROS/RNS)-mediated NO actions on isolated rat liver mitochondria. The results indicated that oxidation of mitochondrial NADH promotes NO release from (I) in a manner mediated by NO(2) formation (at neutral pH) as in mammalian cells, followed by an oxygen atom transfer mechanism (OAT). The NO released from (I) uncoupled mitochondria at low concentrations/incubation times and inhibited the respiratory chain at high concentrations/incubation times. In the presence of ROS generated by mitochondria NO gave rise to peroxynitrite, which, in turn, inhibited the respiratory chain and oxidized membrane protein-thiols to elicit a Ca(2+)-independent mitochondrial permeability transition; this process was only partially inhibited by cyclosporine-A, almost fully inhibited by the thiol reagent N-ethylmaleimide (NEM) and fully inhibited by the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO). These actions correlated with the release of cytochrome c from isolated mitochondria as detected by Western blotting analysis. These events, typically involved in cell necrosis and/or apoptosis denote a potential specific action of (I) and analogs against tumor cells via mitochondria-mediated processes.

Polymer-Based Nitric Oxide Therapies: Recent Insights for Biomedical Applications

Since the discovery of nitric oxide (NO) in the 1980s, this cellular messenger has been shown to participate in diverse biological processes such as cardiovascular homeostasis, immune response, wound healing, bone metabolism, and neurotransmission. Its beneficial effects have prompted increased research in the past two decades, with a focus on the development of materials that can locally release NO. However, significant limitations arise when applying these materials to biomedical applications. This Feature Article focuses on the development of NO-releasing and NO-generating polymeric materials (2006-2011) with emphasis on recent in vivo applications. Results are compared and discussed in terms of NO dose, release kinetics, and biological effects, in order to provide a foundation to design and evaluate new NO therapies.

Effect of N-acetylcysteine on vasospasm in subarachnoid hemorrhage

Vasospasm remains an extremely serious complication that affects patients presenting with subarachnoid hemorrhage (SAH) due to ruptured intracranial aneurysms. The current therapeutic armamentarium is still insufficient in many cases, and the search for new therapies is necessary. In this study, we evaluated the effect of N-acetylcysteine (NAC) on cerebral arterial vasospasm using an experimental model. Twenty-four wistar rats were divided into 4 groups: [1] Control, [2] SAH, [3] SAH+NAC and [4] SAH+Placebo. The experimental model employed double subarachnoid injections of autologous blood. The proposed dose of NAC was 250 mg/kg intraperitoneally per day. We analyzed the inner area of the basilar artery to assess the action of NAC. The experimental model proved to be very adequate, with a mortality rate of 4%. The inner area of the basilar artery in the SAH group showed significant difference to the control group (p=0.009). The use of NAC significantly reduced vasospasm as compared to the untreated group (p=0.048) and established no significant difference to the control group (p=0.098). There was no significant improvement with the administration of placebo (p=0.97). The model of the dual hemorrhage proved to be very useful for vasospasm simulation, with overall low mortality. The administration of NAC significantly reduced vasospasm resulting from SAH, and may represent a new therapeutic alternative.

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

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

Pharmacologically augmented S-nitrosylated hemoglobin improves recovery from murine subarachnoid hemorrhage

BACKGROUND AND PURPOSE

S-nitrosylated hemoglobin (S-nitrosohemoglobin) has been implicated in the delivery of O(2) to tissues through the regulation of microvascular blood flow. This study tested the hypothesis that enhancement of S-nitrosylated hemoglobin by ethyl nitrite inhalation improves outcome after experimental subarachnoid hemorrhage (SAH).

METHODS

A preliminary dosing study identified 20 ppm ethyl nitrite as a concentration that produced a 4-fold increase in S-nitrosylated hemoglobin concentration with no increase in methemoglobin. Mice were subjected to endovascular perforation of the right anterior cerebral artery and were treated with 20 ppm ethyl nitrite in air, or air alone for 72 hours, after which neurologic function, cerebral vessel diameter, brain water content, cortical tissue Po(2), and parenchymal red blood cell flow velocity were measured.

RESULTS

At 72 hours after hemorrhage, air- and ethyl nitrite-exposed mice had similarly sized blood clots. Ethyl nitrite improved neurologic score and rotarod performance; abated SAH-induced constrictions in the ipsilateral anterior, middle cerebral, and internal carotid arteries; and prevented an increase in ipsilateral brain water content. Ethyl nitrite inhalation increased red blood cell flow velocity and cortical tissue Po(2) in the ipsilateral cortex with no effect on systemic blood pressure.

CONCLUSIONS

Targeted S-nitrosylation of hemoglobin improved outcome parameters, including vessel diameter, tissue blood flow, cortical tissue Po(2), and neurologic function in a murine SAH model. Augmenting endogenous Po(2)-dependent delivery of NO bioactivity to selectively dilate the compromised cerebral vasculature has significant clinical potential in the treatment of 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.

Cerebral vasospasm following subarachnoid hemorrhage: time for a new world of thought

OBJECTIVE

Delayed cerebral vasospasm has long been recognized as an important cause of poor outcome after an otherwise successful treatment of a ruptured intracranial aneurysm, but it remains a pathophysiological enigma despite intensive research for more than half a century.

METHOD

Summarized in this review are highlights of research from North America, Europe and Asia reflecting recent advances in the understanding of delayed ischemic deficit.

RESULT

It will focus on current accepted mechanisms and on new frontiers in vasospasm research.

CONCLUSION

A key issue is the recognition of events other than arterial narrowing such as early brain injury and cortical spreading depression and of their contribution to overall mortality and morbidity.

Treatment of cerebral vasospasm with biocompatible controlled-release systems for intracranial drug delivery

OBJECTIVE

The pharmacological treatment of cerebral vasospasm (CVS) now includes the experimental use of controlled-release biocompatible compounds that deliver a desired drug locally into the subarachnoid space. A controlled-release system consists of an active material that is incorporated into a carrier, usually in the form of a pellet or a gel. With such systems, the desired agent is delivered slowly and continuously, for long periods of time, directly to the desired site. This technology makes it possible to achieve high local concentrations of therapeutic agents while minimizing systemic toxicity and circumventing the need to cross the blood-brain barrier. This review describes controlled-release systems developed to date for local drug delivery in the treatment of CVS in both animal models and humans.

METHODS

A MEDLINE PubMed database search was performed for articles published from 1975 to 2007 with the following search topics: "controlled-release system/polymer," "controlled-release implants," "cerebral vasospasm," "subarachnoid hemorrhage," "subarachnoid space," and "intracranial drug delivery."

RESULTS

Over the past several decades, several controlled-release systems (lactic/ glycolic acid pellets, ethylene vinyl acetate copolymer, liposomes, silicone elastomers) have been developed to deliver various pharmacological agents (papaverine, nicardipine, ibuprofen, nitric oxide donor, calcitonin gene-related peptide, fasudil, recombinant tissue plasminogen activator) intracranially to treat subarachnoid hemorrhage in animal models (rats, rabbits, dogs, and primates). Animal studies have shown promising results, and the few human studies that have been published using controlled-release systems with papaverine or nicardipine report similarly encouraging outcomes.

CONCLUSION

Controlled-release systems have evolved over the past few years and have been shown experimentally to be an effective strategy for the local delivery of drugs to treat CVS.

PERSISTENCE OF THE NITRIC OXIDE-DEPENDENT VASODILATORPATHWAY OF CEREBRAL VESSELS AFTEREXPERIMENTAL SUBARACHNOID HEMORRHAGE

OBJECTIVE

Efficiency of the treatment of cerebral vasospasm (CVS) after subarachnoid hemorrhage (SAH) by interfering with the nitric oxide-cyclic guanosine monophospate (cGMP) pathway seems to be inconsistent. So far, it remains unclear whether or not insufficient access to the drugs or impaired reactivity of the vessels is responsible for this inconsistency. Therefore, the aim of the present investigation was to characterize this pathway on cerebral arteries during CVS.

METHODS

CVS was induced using the rat double hemorrhage model and was determined by magnetic resonance perfusion weighted imaging. Rats were sacrificed on Day 3 and Day 5 after SAH. Immunohistochemical staining of the basilar artery for endothelial nitric oxide synthases and the alpha- and beta-subunits of the soluble guanylate cyclase was performed. Basilar artery ring segments on Day 5 were used for measurement of isometric force. Concentration effect curves for acetylcholine, sodium nitroprusside, and 8-bromo-cGMP were constructed and compared by maximum effect and pD2.

RESULTS

The immunohistochemical expression of endothelial nitric oxide synthase was comparable in all groups. The soluble guanylate cyclase alpha- and beta-subunits were significantly diminished on Day 3, but recovered by Day 5. The relaxation attributable to acetylcholine and 8-bromo-cGMP was virtually identical in controls and during CVS. Relaxation attributable to sodium nitroprusside, however, was significantly enhanced after SAH (maximum effect, control: 88 +/- 12%; Day 5: 117 +/- 26%).

CONCLUSION

The present investigations suggest the persistence of endothelium-, nitric oxide-, and cGMP-dependent relaxation during CVS. Therefore, the treatment of CVS interfering with this pathway seems not to be limited by alterations inside the vessel wall.

Systemic administration of phosphodiesterase V inhibitor, sildenafil citrate, for attenuation of cerebral vasospasm after experimental subarachnoid hemorrhage

OBJECTIVE

One of the phosphodiesterase isoenzymes, Type V (PDE V), specifically hydrolyzes cyclic guanosine monophosphate to cause vasoconstriction. This study analyses the effect of PDE V inhibition with sildenafil citrate (SC) on cerebral vasospasm and its effect on apoptotic changes of the vascular endothelium.

METHODS

Twenty-four rabbits were divided into four groups. The first group was composed of sham-surgery animals. The second group was the subarachnoid hemorrhage (SAH) group, in which cerebral vasospasm was induced. In the third group, sham-surgery rabbits were treated with SC. In the fourth group, animals were treated with SC after SAH. SC was administered for 48 hours, 0.7 mg/kg, three times per day in Groups 3 and 4. Basilar artery lumen circumferences were measured in all groups by computerized image analysis. The terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL) method was used to evaluate the rate of apoptosis between SAH and SC-treated SAH groups. Results were compared by analysis of variance and paired t tests, and P values less than 0.05 were considered significant.

RESULTS

Basilar artery circumferences between groups were significantly different (P < 0.001). SC (0.7 mg/kg, three times per d) significantly dilated the basilar arteries in both the sham-surgery group (2370 +/- 233 microm; P = 0.039) and the SAH group (2142 +/- 195 microm; P = 0.006) after 48 hours of treatment. The TUNEL method for apoptosis revealed that actual numbers of the apoptotic endothelial cells per cross section after SAH in the control (no treatment) (73 +/- 2) and SC-treated (0.7 mg/kg) groups(76 +/- 3) were not significantly different (P > 0.05).

CONCLUSION

The vasodilatory effect of SC was observed to be significant on normal cerebral vessels and after SAH-induced vasospasm. SC did not prevent apoptosis of the endothelium in our study, which suggests that prevention of apoptosis is not necessary in the treatment of cerebral vasospasm.

Intracranial delivery of the nitric oxide donor diethylenetriamine/nitric oxide from a controlled-release polymer: toxicity in cynomolgus monkeys

OBJECTIVE

Diethylenetriamine/nitric oxide (DETA/NO) has been shown to be an effective treatment for delayed posthemorrhagic vasospasm when released abluminally from ethylene-vinyl acetate copolymer (EVAc). However, the observed mortality associated with this drug warrants further investigation. To establish a maximum tolerable dose, this study evaluated the toxicity of DETA/NO released from EVAc in a dose-escalation series in cynomolgus monkeys (Macaca fascicularis).

METHODS

DETA/NO was incorporated into EVAc at a 20:80 dry weight ratio (DETA/NO:EVAc). A total of 13 animals underwent a right frontotemporal craniotomy for placement of a single polymer delivering no drug (n = 3), 0.5 +/- 0.1 mg/kg (n = 3), 0.9 +/- 0.1 mg/kg (n = 3), 1.9 +/- 0.2 mg/kg (n = 3), or a 3.2 mg/kg dose (n = 1) into the subarachnoid space.

RESULTS

The animal receiving the highest dose of DETA/NO (3.2 mg/kg) died 46 hours after surgery. The remaining animals survived for the planned duration of the study. One animal in the group receiving the 1.9 mg/kg dose experienced a seizure 25 hours after surgery and remained lethargic for 2 days before making a complete recovery. The remaining animals exhibited no adverse behavioral effects. Histopathological examination of brain tissue revealed hemorrhagic and ischemic changes at doses above 0.9 mg/kg. No evidence of vascular wall pathology or infection was observed in any animal.

CONCLUSION

The greatest amount of DETA/NO safely delivered from EVAc copolymer to the subarachnoid space of the cynomolgus monkey is approximately 1.0 mg/kg. These findings show that continuous intracisternal delivery of DETA/NO is a safe and potentially effective strategy for prophylactic treatment of delayed cerebral vasospasm.

Safe and efficient drug delivery system with liposomes for intrathecal application of an antivasospastic drug, fasudil

Pharmacological treatment for cerebral ischemia and cerebral vasospasm following subarachnoid hemorrhage (SAH) cannot attain sufficiently high concentrations of the drugs in the cerebrospinal fluid (CSF) without precipitating systemic side effects. We recently developed a liposomal drug delivery system for intrathecal application that can maintain effective concentrations of cerebral vasodilator, fasudil, in the CSF. A single intrathecal injection of liposomal fasudil could maintain a therapeutic drug concentration in the CSF over a period time due to their sustained-release property, significantly decreasing infarct size in a rat model of acute ischemia and reducing vasoconstriction of the rat and dog basilar artery in a model of SAH. In this review, we are introducing our new less-invasive intrathecal drug delivery system that provides an alternative and safe method to deliver therapeutic agents.