Normobaric hyperoxia-based neuroprotective therapies in ischemic stroke

Gas Therapy: Generating, Delivery, and Biomedical Applications

Oxygen (O2), nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H2S), and hydrogen (H2) with direct effects, and carbon dioxide (CO2) with complementary effects on the condition of various diseases are known as therapeutic gases. The targeted delivery and in situ generation of these therapeutic gases with controllable release at the site of disease has attracted attention to avoid the risk of gas poisoning and improve their performance in treating various diseases such as cancer therapy, cardiovascular therapy, bone tissue engineering, and wound healing. Stimuli-responsive gas-generating sources and delivery systems based on biomaterials that enable on-demand and controllable release are promising approaches for precise gas therapy. This work highlights current advances in the design and development of new approaches and systems to generate and deliver therapeutic gases at the site of disease with on-demand release behavior. The performance of the delivered gases in various biomedical applications is then discussed.

Normobaric Hyperoxia Combined With Endovascular Treatment Based on Temporal Gradient: A Dose-Escalation Study

BACKGROUND

Normobaric hyperoxia (NBO) has neuroprotective effects in acute ischemic stroke. Thus, we aimed to identify the optimal NBO treatment duration combined with endovascular treatment.

METHODS

This is a single-center, randomized controlled, open-label, blinded-end point dose-escalation clinical trial. Patients with acute ischemic stroke who had an indication for endovascular treatment at Tianjin Huanhu Hospital were randomly assigned to 4 groups (1:1 ratio) based on NBO therapy duration: (1) control group (1 L/min oxygen for 4 hours); (2) NBO-2h group (10 L/min for 2 hours); (3) NBO-4h group (10 L/min for 4 hours); and (4) NBO-6h group (10 L/min for 6 hours). The primary outcome was cerebral infarction volume at 72 hours after randomization using an intention-to-treat analysis model. The primary safety outcome was the 90-day mortality rate.

RESULTS

Between June 2022 and September 2023, 100 patients were randomly assigned to the following groups: control group (n=25), NBO-2h group (n=25), NBO-4h group (n=25), and NBO-6h group (n=25). The 72-hour cerebral infarct volumes were 39.4±34.3 mL, 30.6±30.1 mL, 19.7±15.4 mL, and 22.6±22.4 mL, respectively (P=0.013). The NBO-4h and NBO-6h groups both showed statistically significant differences (adjusted P values: 0.011 and 0.027, respectively) compared with the control group. Compared with the control group, both the NBO-4h and NBO-6h groups showed significant differences (P<0.05) in the National Institutes of Health Stroke Scale scores at 24 hours, 72 hours, and 7 days, as well as in the change of the National Institutes of Health Stroke Scale scores from baseline to 24 hours. Additionally, there were no significant differences among the 4 groups in terms of 90-day mortality rate, symptomatic intracranial hemorrhage, early neurological deterioration, or severe adverse events.

CONCLUSIONS

The effectiveness of NBO therapy was associated with oxygen administration duration. Among patients with acute ischemic stroke who underwent endovascular treatment, NBO therapy for 4 and 6 hours was found to be more effective. Larger-scale multicenter studies are needed to validate these findings.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT05404373.

Pyruvate Dehydrogenase Complex in Neonatal Hypoxic-Ischemic Brain Injury

The disruption of cerebral energy metabolism in relation to brain damage has been the subject of extensive research. However, the pyruvate dehydrogenase complex (PDHC), which is primarily characterized by poor cerebral energy metabolism following brain trauma, has received relatively little study in comparison to newborn hypoxic-ischemic brain injury. Mitochondrial PDHC, a multienzyme complex that functions as a crucial hub in energy metabolism and acts as a central metabolic node to mediate pyruvate oxidation after glycolysis and fuel the Krebs cycle to meet energy demands, has been reported to be one cause of energy metabolism dysfunction according to recent studies. Here we assess the potential mechanisms of neonatal hypoxic-ischemic brain injury-related brain dysfunction mediated by PDHC and further discuss the neuroprotective effects of therapeutic medicines that target PDHC activation. We also provide a summary of recent research on medicines that target PDHC in neonates with hypoxic-ischemic brain damage. Through an understanding of the mechanisms by which it is modulated and an investigation of the neuroprotective techniques available to activate brain PDHC and improve neonatal hypoxic-ischemic impairment, our review emphasizes the significance of PDHC impairment in neonatal hypoxic-ischemic brain injury.

Exploiting moderate hypoxia to benefit patients with brain disease: Molecular mechanisms and translational research in progress

Hypoxia is increasingly recognized as an important physiological driving force. A specific transcriptional program, induced by a decrease in oxygen (O2) availability, for example, inspiratory hypoxia at high altitude, allows cells to adapt to lower O2 and limited energy metabolism. This transcriptional program is partly controlled by and partly independent of hypoxia-inducible factors. Remarkably, this same transcriptional program is stimulated in the brain by extensive motor-cognitive exercise, leading to a relative decrease in O2 supply, compared to the acutely augmented O2 requirement. We have coined the term "functional hypoxia" for this important demand-responsive, relative reduction in O2 availability. Functional hypoxia seems to be critical for enduring adaptation to higher physiological challenge that includes substantial "brain hardware upgrade," underlying advanced performance. Hypoxia-induced erythropoietin expression in the brain likely plays a decisive role in these processes, which can be imitated by recombinant human erythropoietin treatment. This article review presents hints of how inspiratory O2 manipulations can potentially contribute to enhanced brain function. It thereby provides the ground for exploiting moderate inspiratory plus functional hypoxia to treat individuals with brain disease. Finally, it sketches a planned multistep pilot study in healthy volunteers and first patients, about to start, aiming at improved performance upon motor-cognitive training under inspiratory hypoxia.

Normobaric Hyperoxia Combined With Endovascular Treatment for Patients With Acute Ischemic Stroke: A Randomized Controlled Clinical Trial

BACKGROUND AND OBJECTIVES

To investigate the safety and efficacy of normobaric hyperoxia (NBO) combined with endovascular treatment (EVT) in patients with acute ischemic stroke (AIS).

METHODS

In this single-center, proof-of-concept, assessor-blinded, randomized, controlled pilot study, patients with AIS in the acute anterior circulation with large vessel occlusion who had an indication for EVT were randomly assigned to the EVT group or the NBO + EVT group. The NBO + EVT group was given 100% oxygen through a face mask initiated before vascular recanalization (10L/min for 4 hours), while the EVT group was given room air. The primary endpoint was infarct volume measured by MRI within 24-48 hours after randomization.

RESULTS

A total of 231 patients were screened, and 86 patients were randomized into a ratio of 1:1 (EVT group, n = 43; NBO + EVT group, n = 43). The median infarction volume of the NBO + EVT group at 24-48 hours after randomization was significantly smaller than that of the EVT group (median 20.1 vs 37.7 mL, p < 0.01). The median mRS score at 90 days was 2 for the NBO + EVT group when compared with 3 for the EVT group (adjusted value 1.8, 95% CI 1.3-4.2; p = 0.038). Compared with the EVT group, the NBO + EVT group had a lower incidence of symptomatic intracranial hemorrhagic (7% vs 12%), mortality (9% vs 16%), and adverse events (33% vs 42%); however, such a difference was not statistically significant.

DISCUSSION

NBO in combination with EVT seems to be a safe and feasible treatment strategy that could significantly reduce infarct volume, improve short-term neurobehavioral test score, and enhance clinical outcomes at 90 days when compared with EVT alone in patients with AIS. These observations need to be further confirmed by a large, multicenter, randomized clinical trial.

CLINICAL TRIALS REGISTRATION

NCT03620370.

CLASSIFICATION OF EVIDENCE

This pilot study provides Class I evidence that NBO combined with standard EVT decreases infarction volume in patients with acute anterior circulation stroke.

Normobaric hyperoxia plays a neuroprotective role after cerebral ischemia by maintaining the redox homeostasis and the level of connexin43 in astrocytes

Introduction

Acute cerebral ischemia is caused by an insufficient blood supply to brain tissue. Oxygen therapy, which is able to aid diffusion to reach the ischemic region, has been regarded as a possible treatment for cerebral ischemia. Recent animal and pilot clinical studies have reported that normobaric hyperoxia (NBO) showed neuroprotective effects if started soon after the onset of stroke. However, little is known about the role and mechanism of NBO treatment in astrocytes. Connexin43, one of the main gap junction proteins in astrocytes, is extremely sensitive to hypoxia and oxidative stress after cerebral ischemia.

Aims

In the present study, we used sutures to develop an ischemia/reperfusion model in rats to mimic clinical recanalization and investigated the role of connexin43 in NBO‐treated stroke rats, as well as the underlying mechanism of NBO therapy.

Results

Normobaric hyperoxia treatment maintained the homeostasis of oxidoreductases: glutathione peroxidase 4 (GPX4) and NADPH oxidase 4 (two important oxidoreductases) and rescued the ischemia/reperfusion‐induced downregulation of connexin43 protein in astrocytes. Furthermore, NBO treatment attenuated cerebral ischemia‐induced cytochrome c release from mitochondria and was involved in neuroprotective effects by regulating the GPX4 and connexin43 pathway, using Ferrostatin‐1 (an activator of GPX4) or Gap27 (an inhibitor of connexin43).

Conclusions

This study showed the neuroprotective effects of NBO treatment by reducing oxidative stress and maintaining the level of connexin43 in astrocytes, which could be used for the clinical treatment of ischemic stroke.

Normobaric Oxygen (NBO) Therapy Reduces Cerebral Ischemia/Reperfusion Injury through Inhibition of Early Autophagy

Objectives

Normobaric oxygen (NBO) therapy has great clinical potential in the treatment of ischemic stroke, but its underlying mechanism is unknown. Our study aimed to investigate the role of autophagy during the application of NBO on cerebral ischemia/reperfusion injury.

Methods

Male Sprague Dawley rats received 2 hours of middle cerebral artery occlusion (MCAO), followed by 2, 6, or 24 hours of reperfusion. At the beginning of reperfusion, rats were randomly given NBO (95% O₂) or room air (21% O₂) for 2 hours. In some animals, 3-methyladenine (3-MA, autophagy inhibitor) was administered 10 minutes before reperfusion. The severity of the ischemic injury was determined by infarct volume, neurological deficit, and apoptotic cell death. Western blotting was used to determine the protein expression of autophagy and apoptosis, while mRNA expression of apoptotic molecules was detected by real-time PCR.

Results

NBO treatment after ischemia/reperfusion significantly decreased infarct volume and neurobehavioral defects. The increased expression of the autophagy markers, including microtubule-associated protein 1A light chain 3 (LC3) and Beclin 1, after ischemia/reperfusion was reversed by NBO, while promoting Sequestosome 1 (p62/SQSTM1) expression. In addition, NBO reduced cerebral apoptosis in association with alleviated BAX expression and increased BCL-2 expression. 3-MA reduced autophagy and apoptotic death but did not further improve NBO-attenuated ischemic damage.

Conclusion

NBO induced remarkable neuroprotection from ischemic injury, which was correlated with blocked autophagy activity.

The Association Between Arterial Oxygen Level and Outcome in Neurocritically Ill Patients is not Affected by Blood Pressure

Background

In neurocritically ill patients, one early mechanism behind secondary brain injury is low systemic blood pressure resulting in inadequate cerebral perfusion and consequent hypoxia. Intuitively, higher partial pressures of arterial oxygen (PaO₂) could be protective in case of inadequate cerebral circulation related to hemodynamic instability.

Study purpose

We examined whether the association between PaO₂ and mortality is different in patients with low compared to normal and high mean arterial pressure (MAP) in patients after various types of brain injury.

Methods

We screened the Finnish Intensive Care Consortium database for mechanically ventilated adult (≥ 18) brain injury patients treated in several tertiary intensive care units (ICUs) between 2003 and 2013. Admission diagnoses included traumatic brain injury, cardiac arrest, subarachnoid and intracranial hemorrhage, and acute ischemic stroke. The primary exposures of interest were PaO₂ (recorded in connection with the lowest measured PaO₂/fraction of inspired oxygen ratio) and the lowest MAP, recorded during the first 24 h in the ICU. PaO₂ was grouped as follows: hypoxemia (< 8.2 kPa, the lowest 10th percentile), normoxemia (8.2–18.3 kPa), and hyperoxemia (> 18.3 kPa, the highest 10th percentile), and MAP was divided into equally sized tertiles (< 60, 60–68, and > 68 mmHg). The primary outcome was 1-year mortality. We tested the association between hyperoxemia, MAP, and mortality with a multivariable logistic regression model, including the PaO₂, MAP, and interaction of PaO₂*MAP, adjusting for age, admission diagnosis, premorbid physical performance, vasoactive use, intracranial pressure monitoring use, and disease severity. The relationship between predicted 1-year mortality and PaO₂ was visualized with locally weighted scatterplot smoothing curves (Loess) for different MAP levels.

Results

From a total of 8290 patients, 3912 (47%) were dead at 1 year. PaO₂ was not an independent predictor of mortality: the odds ratio (OR) for hyperoxemia was 1.16 (95% CI 0.85–1.59) and for hypoxemia 1.24 (95% CI 0.96–1.61) compared to normoxemia. Higher MAP predicted lower mortality: OR for MAP 60–68 mmHg was 0.73 (95% CI 0.64–0.84) and for MAP > 68 mmHg 0.80 (95% CI 0.69–0.92) compared to MAP < 60 mmHg. The interaction term PaO₂*MAP was nonsignificant. In Loess visualization, the relationship between PaO₂ and predicted mortality appeared similar in all MAP tertiles.

Conclusions

During the first 24 h of ICU treatment in mechanically ventilated brain injured patients, the association between PaO₂ and mortality was not different in patients with low compared to normal MAP.

Supplementary Information

The online version of this article (10.1007/s12028-020-01178-w) contains supplementary material, which is available to authorized users.

Normobaric oxygen therapy attenuates hyperglycolysis in ischemic stroke

Normobaric oxygen therapy has gained attention as a simple and convenient means of achieving neuroprotection against the pathogenic cascade initiated by acute ischemic stroke. The mechanisms underlying the neuroprotective efficacy of normobaric oxygen therapy, however, have not been fully elucidated. It is hypothesized that cerebral hyperglycolysis is involved in the neuroprotection of normobaric oxygen therapy against ischemic stroke. In this study, Sprague-Dawley rats were subjected to either 2-hour middle cerebral artery occlusion followed by 3- or 24-hour reperfusion or to a permanent middle cerebral artery occlusion event. At 2 hours after the onset of ischemia, all rats received either 95% oxygen normobaric oxygen therapy for 3 hours or room air. Compared with room air, normobaric oxygen therapy significantly reduced the infarct volume, neurological deficits, and reactive oxygen species and increased the production of adenosine triphosphate in ischemic rats. These changes were associated with reduced transcriptional and translational levels of the hyperglycolytic enzymes glucose transporter 1 and 3, phosphofructokinase 1, and lactate dehydrogenase. In addition, normobaric oxygen therapy significantly reduced adenosine monophosphate-activated protein kinase mRNA expression and phosphorylated adenosine monophosphate-activated protein kinase protein expression. These findings suggest that normobaric oxygen therapy can reduce hyperglycolysis through modulating the adenosine monophosphate-activated protein kinase signaling pathway and alleviating oxidative injury, thereby exhibiting neuroprotective effects in ischemic stroke. This study was approved by the Institutional Animal Investigation Committee of Capital Medical University (approval No. AEEI-2018-033) on August 13, 2018.

Prehospital supplemental oxygen for acute stroke - A retrospective analysis

OBJECTIVE

Brief early administration of supplemental oxygen (sO₂) to create hyperoxia may increase oxygenation to penumbral tissue and improve stroke outcomes. Hyperoxia may also result in respiratory compromise and vasoconstriction leading to worse outcomes. This study examines the effects of prehospital sO₂ in stroke.

METHODS

This is a retrospective analysis of adult acute stroke patients (aged ≥18 years) presenting via EMS to an academic Comprehensive Stroke Center between January 1, 2013 and December 31, 2017. Demographic and clinical characteristics obtained from Get with the Guidelines-Stroke registry and subjects' medical records were compared across three groups based on prehospital oxygen saturation and sO₂ administration. Chi-square, ANOVA, and multivariate logistic regression were used to determine if sO₂ status was associated with neurological outcomes or respiratory complications.

RESULTS

1352 eligible patients were identified. 62.7% (n = 848) did not receive sO₂ ("controls"), 10.7% (n = 144) received sO₂ due to hypoxia ("hypoxia"), and 26.6% (n = 360) received sO₂ despite normoxia ("hyperoxia"). The groups represented a continuum from more severe deficits (hypoxia) to less severe deficits (controls): mean prehospital GCS (hypoxia -12, hyperoxia - 2, controls - 14 p ≤ 0.001), mean initial NIHSS (hypoxia - 15, hyperoxia - 13, controls - 8 p < 0.001). After controlling for potential confounders, all groups had similar rates of respiratory complications and favorable neurological outcomes.

CONCLUSIONS

Hyperoxic subjects had no significant increase in respiratory complications, nor did they differ in neurologic outcomes at discharge when controlling for confounders. While limited by the retrospective nature, this suggests brief, early sO₂ for stroke may be safe to evaluate prospectively.

Mimicking oxygen delivery and waste removal functions of blood

In addition to immunological and wound healing cell and platelet delivery, ion stasis and nutrient supply, blood delivers oxygen to cells and tissues and removes metabolic wastes. For decades researchers have been trying to develop approaches that mimic these two immediately vital functions of blood. Oxygen is crucial for the long-term survival of tissues and cells in vertebrates. Hypoxia (oxygen deficiency) and even at times anoxia (absence of oxygen) can occur during organ preservation, organ and cell transplantation, wound healing, in tumors and engineering of tissues. Different approaches have been developed to deliver oxygen to tissues and cells, including hyperbaric oxygen therapy (HBOT), normobaric hyperoxia therapy (NBOT), using biochemical reactions and electrolysis, employing liquids with high oxygen solubility, administering hemoglobin, myoglobin and red blood cells (RBCs), introducing oxygen-generating agents, using oxygen-carrying microparticles, persufflation, and peritoneal oxygenation. Metabolic waste accumulation is another issue in biological systems when blood flow is insufficient. Metabolic wastes change the microenvironment of cells and tissues, influence the metabolic activities of cells, and ultimately cause cell death. This review examines advances in blood mimicking systems in the field of biomedical engineering in terms of oxygen delivery and metabolic waste removal.

Oxygen or cooling, to make a decision after acute ischemia stroke

The presence of a salvageable penumbra, a region of ischemic brain tissue with sufficient energy for short-term survival, has been widely agreed as the premise for thrombolytic therapy with tissue plasminogen activator (tPA), which remains the only United States Food and Drug Administration (FDA) approved treatment for acute ischemia stroke. However, the use of tPA has been profoundly constrained due to its narrow therapeutic time window and the increased risk of potentially deadly hemorrhagic transformation (HT). Blood brain barrier (BBB) damage within the thrombolytic time window is an indicator for tPA-induced HT and both normobaric hyperoxia (NBO) and hypothermia have been shown to protect the BBB from ischemia/reperfusion injury. Therefore, providing the O₂ as soon as possible (NBO treatment), freezing the brain (hypothermia treatment) to slow down ischemia-induced BBB damage or their combined use may extend the time window for the treatment of tPA. In this review, we summarize the protective effects of NBO, hypothermia or their use combined with tPA on ischemia stroke, based on which, the combination of NBO and hypothermia may be an ideal early stroke treatment to preserve the ischemic penumbra. Given this, there is an urge for large randomized controlled trials to address the effect.

Pyruvate dehydrogenase complex in cerebral ischemia-reperfusion injury

Pyruvate dehydrogenase (PDH) complex is a mitochondrial matrix enzyme that serves a critical role in the conversion of anaerobic to aerobic cerebral energy. The regulatory complexity of PDH, coupled with its significant influence in brain metabolism, underscores its susceptibility to, and significance in, ischemia-reperfusion injury. Here, we evaluate proposed mechanisms of PDH-mediated neurodysfunction in stroke, including oxidative stress, altered regulatory enzymatic control, and loss of PDH activity. We also describe the neuroprotective influence of antioxidants, dichloroacetate, acetyl-L-carnitine, and combined therapy with ethanol and normobaric oxygen, explained in relation to PDH modulation. Our review highlights the significance of PDH impairment in stroke injury through an understanding of the mechanisms by which it is modulated, as well as an exploration of neuroprotective strategies available to limit its impairment.

Cocktail treatment, a promising strategy to treat acute cerebral ischemic stroke?

Up to now, over 1,000 experimental treatments found in cells and rodents have been difficult to translate to human ischemic stroke. Since ischemia and reperfusion, two separate stages of ischemic stroke, have different pathophysiological mechanisms leading to brain injury, a combination of protective agents targeting ischemia and reperfusion respectively may obtain substantially better results than a single agent. Normobaric hyperoxia (NBO) has been shown to exhibit neuro- and vaso-protective effects by improving tissue oxygenation when it is given during ischemia, however the effect of NBO would diminish when the duration of ischemia and reperfusion was extended. Therefore, during reperfusion drug treatment targeting inflammation, oxidative stress and free radical scavenger would be a useful adjuvant to extend the therapeutic window of tissue plasminogen activator, the only United States Food and Drug Administration (FDA) approved treatment for acute ischemic stroke. In this review, we discussed the neuro- and vaso-protective effects of NBO and recent finding of combining NBO with other drugs.

ZNT-1 Expression Reduction Enhances Free Zinc Accumulation in Astrocytes After Ischemic Stroke

Excess intracellular zinc has been implicated in ischemic brain cell death. We previously reported that extracellular zinc increases intracellular free zinc level only in hypoxic astrocytes but not in normoxia astrocytes. However, the underlying mechanisms remain to be elucidated. Zinc transporters ZnTs and ZIPs mediate intracellular zinc efflux and extracellular zinc influx. In the present study, we determined the effect of hypoxia/reoxygenation on ZnT-1 and ZIP-1. Hypoxia/reoxygenation did not change the ZIP-1 level in astrocytes. Remarkably, hypoxia/reoxygenation dramatically decreased ZnT-1 expression, which can be difficult to reverse by the addition of extracellular zinc, although extracellular zinc treatment significantly increased ZnT-1 level at normoxia. These results suggest that hypoxia/reoxygenation blocked zinc efflux, whereas zinc influx may be at a similar level to that in normoxia, providing a novel mechanism for intracellular free zinc accumulation after ischemic stroke.

Hyperoxia in intensive care, emergency, and peri-operative medicine: Dr. Jekyll or Mr. Hyde? A 2015 update

This review summarizes the (patho)-physiological effects of ventilation with high FiO₂ (0.8–1.0), with a special focus on the most recent clinical evidence on its use for the management of circulatory shock and during medical emergencies. Hyperoxia is a cornerstone of the acute management of circulatory shock, a concept which is based on compelling experimental evidence that compensating the imbalance between O₂ supply and requirements (i.e., the oxygen dept) is crucial for survival, at least after trauma. On the other hand, “oxygen toxicity” due to the increased formation of reactive oxygen species limits its use, because it may cause serious deleterious side effects, especially in conditions of ischemia/reperfusion. While these effects are particularly pronounced during long-term administration, i.e., beyond 12–24 h, several retrospective studies suggest that even hyperoxemia of shorter duration is also associated with increased mortality and morbidity. In fact, albeit the clinical evidence from prospective studies is surprisingly scarce, a recent meta-analysis suggests that hyperoxia is associated with increased mortality at least in patients after cardiac arrest, stroke, and traumatic brain injury. Most of these data, however, originate from heterogenous, observational studies with inconsistent results, and therefore, there is a need for the results from the large scale, randomized, controlled clinical trials on the use of hyperoxia, which can be anticipated within the next 2–3 years. Consequently, until then, “conservative” O₂ therapy, i.e., targeting an arterial hemoglobin O₂ saturation of 88–95 % as suggested by the guidelines of the ARDS Network and the Surviving Sepsis Campaign, represents the treatment of choice to avoid exposure to both hypoxemia and excess hyperoxemia.

Does normobaric hyperoxia increase oxidative stress in acute ischemic stroke? A critical review of the literature

Stroke, one of the most debilitating cerebrovascular and nuerological diseases, is a serious life-threatening condition and a leading cause of long-term adult disability and brain damage, either directly or by secondary complications. Most effective treatments for stroke are time dependent such as the only FDA-approved therapy, reperfusion with tissue-type plasminogen activator; thus, improving tissue oxygenation with normobaric hyperoxia (NBO) has been considered a logical and potential important therapy. NBO is considered a good approach because of its potential clinical advantages, and many studies suggest that NBO is neuroprotective, reducing ischemic brain injury and infarct volume in addition to improving pathologic and neurobehavorial outcomes. However, increased reactive oxygen species (ROS) generation may occur when tissue oxygen level is too high or too low. Therefore, a major concern with NBO therapy in acute ischemic stroke is the potential increase of ROS, which could exacerbate brain injury. The purpose of this review is to critically review the current literature reports on the effect of NBO treatment on ROS and oxidative stress with respect to acute ischemic stroke. Considering the available data from relevant animal models, NBO does not increase ROS or oxidative stress if applied for a short duration; therefore, the potential that NBO is a viable neuroprotective strategy for acute ischemic stroke is compelling. The benefits of NBO may significantly outweigh the risks of potential increase in ROS generation for the treatment of acute ischemic stroke.

Normobaric hyperoxia slows blood-brain barrier damage and expands the therapeutic time window for tissue-type plasminogen activator treatment in cerebral ischemia

BACKGROUND AND PURPOSE

Prolonged ischemia causes blood-brain barrier (BBB) damage and increases the incidence of neurovasculature complications secondary to reperfusion. Therefore, targeting ischemic BBB damage pathogenesis is critical to reducing neurovasculature complications and expanding the therapeutic time window of tissue-type plasminogen activator (tPA) thrombolysis. This study investigates whether increasing cerebral tissue PO2 through normobaric hyperoxia (NBO) treatment will slow the progression of BBB damage and, thus, improve the outcome of delayed tPA treatment after cerebral ischemia.

METHODS

Rats were exposed to NBO (100% O2) or normoxia (21% O2) during 3-, 5-, or, 7-hour middle cerebral artery occlusion. Fifteen minutes before reperfusion, tPA was continuously infused to rats for 30 minutes. Neurological score, mortality rate, and BBB permeability were determined. Matrix metalloproteinase-9 was measured by gelatin zymography and tight junction proteins (occludin and cluadin-5) by Western blot in the isolated cerebral microvessels.

RESULTS

NBO slowed the progression of ischemic BBB damage pathogenesis, evidenced by reduced Evan blue leakage, smaller edema, and hemorrhagic volume in NBO-treated rats. NBO treatment reduced matrix metalloproteinase-9 induction and the loss of tight junction proteins in ischemic cerebral microvessels. NBO-afforded BBB protection was maintained during tPA reperfusion, resulting in improved neurological functions, significant reductions in brain edema, hemorrhagic volume, and mortality rate, even when tPA was given after prolonged ischemia (7 hours).

CONCLUSIONS

Early NBO treatment slows ischemic BBB damage pathogenesis and significantly improves the outcome of delayed tPA treatment, providing new evidence supporting NBO as an effective adjunctive therapy to extend the time window of tPA thrombolysis for ischemic stroke.

Supplemental oxygen delivery to suspected stroke patients in pre hospital and emergency department settings

BACKGROUND

Recent data suggests that high-flow oxygen started promptly after stroke symptom onset salvages ischemic brain tissue. We investigated the consistency of oxygen delivery to suspected stroke patients in the pre-hospital (PH) and Emergency Department (ED) settings, and associated adverse events (AEs).

METHODS

We retrospectively reviewed pre-hospital call reports of suspected stroke patients transported by our institution's paramedics. We extracted data on oxygen delivery in the PH and ED settings, demographics, Glasgow Coma Scale score (GCS), final diagnosis, and selected AEs (mortality, seizures, worsening neurological status, new infarction, and post-ischemic hemorrhage). Patients were grouped according to ED oxygen delivery: none, low-flow (2-4 L/min), and high-flow (10-15 L/min).

RESULTS

Oxygen delivery was documented in 84% of 366 stroke transports, with 98% receiving 10-15 L/min. Our hospital received 164 patients. Oxygen delivery in the ED was documented in 150 patients, with 38% receiving none, 47% low-flow, and 15% high-flow oxygen. There were no instances of oxygen refusal, premature termination, or technical difficulties. Advanced age and low GCS predicted the use of higher flow rates. High-flow oxygen was more frequently administered to patients with symptom onset < 3 hours, and those with intracerebral hemorrhage (ICH), hypoxic-ischemic encephalopathy (HIE) or seizures (p < 0.001). More patients receiving high-flow oxygen were documented to have an AE (p = 0.02), however the low- and no-oxygen groups more frequently had multiple AEs (p = 0.01). The occurrence of AEs was predicted by the diagnosis of ICH/HIE/seizures (p = 0.013) and acute ischemic stroke (AIS)/transient ischemic attack (TIA) (p = 0.009), but not by the amount of oxygen.

CONCLUSIONS

Suspected stroke patients routinely receive 10-15 L/min oxygen in the ambulance however in the ED there is wide variability due to factors such as clinical severity. Oxygen delivery appears safe in the PH and ED settings.

Extended normobaric hyperoxia therapy yields greater neuroprotection for focal transient ischemia-reperfusion in rats

Background

Normobaric hyperoxia (NBO) therapy is neuroprotective in acute ischemic stroke. However, how long the NBO should last to obtain optimal outcome is still unclear. Reports show that ischemic penumbra blood supply may remain compromised for a long period after ischemia-reperfusion, which would impair tissue oxygenation in ischemic penumbra. Therefore, we hypothesized that longer-lasting NBO may yield greater neuroprotection.

Methods

The relationship between treatment outcome and NBO duration was examined in this study. Rats were subjected to 90 min middle cerebral artery occlusion followed by reperfusion for 22.5 hours. NBO started at 30 min post ischemia and lasted for 2, 4 or 8 h. Treatment efficacy was evaluated by measuring infarction volume, oxidative stress and apoptosis.

Results

Among 2 h, 4 h and 8 h NBO, 8 h NBO offered the greatest efficacy in reducing 24-hour infarction volume, attenuating oxidative stress that was indicated by decreased production of 8-hydroxydeoxyguanosine and NADPH oxidase catalytic subunit gp91^phox, and alleviating apoptosis that was associated with reduced production of DNA fragment and caspase-3 activity in cortex penumbra.

Conclusions

Under our experimental conditions, longer duration of NBO treatment produced greater benefits in focal transient cerebral ischemia-reperfusion rats.