Normobaric hyperoxia delays and attenuates early nitric oxide production in focal cerebral ischemic rats

Salvia miltiorrhiza Alleviates Memory Deficit Induced by Ischemic Brain Injury in a Transient MCAO Mouse Model by Inhibiting Ferroptosis

Salvia miltiorrhiza (SM) has been used in oriental medicine for its neuroprotective effects against cardiovascular diseases and ischemic stroke. In this study, we investigated the therapeutic mechanism underlying the effects of SM on stroke using a transient middle cerebral artery occlusion (tMCAO) mouse model. Our results showed that SM administration significantly attenuated acute brain injury, including brain infarction and neurological deficits, 3 days after tMCAO. This was confirmed by our magnetic resonance imaging (MRI) study, which revealed a reduction in brain infarction with SM administration, as well as our magnetic resonance spectroscopy (MRS) study, which demonstrated the restoration of brain metabolites, including taurine, total creatine, and glutamate. The neuroprotective effects of SM were associated with the reduction in gliosis and upregulation of inflammatory cytokines, such as interleukin-6 (IL-6) and Tumor necrosis factor-α (TNF-α), along with the upregulation of phosphorylated STAT3 in post-ischemic brains. SM also reduced the levels of 4-Hydroxynonenal (4-HNE) and malondialdehyde (MDA), which are markers of lipid peroxidation, induced by oxidative stress upregulation in the penumbra of the tMCAO mouse brain. SM administration attenuated ischemic neuronal injury by inhibiting ferroptosis. Additionally, post-ischemic brain synaptic loss and neuronal loss were alleviated by SM administration, as demonstrated by Western blot and Nissl staining. Moreover, daily administration of SM for 28 days after tMCAO significantly reduced neurological deficits and improved survival rates in tMCAO mice. SM administration also resulted in improvement in post-stroke cognitive impairment, as measured by the novel object recognition and passive avoidance tests in tMCAO mice. Our findings suggest that SM provides neuroprotection against ischemic stroke and has potential as a therapeutic agent.

Nitric oxide promotes cerebral ischemia/reperfusion injury through upregulating hypoxia-inducible factor1-α-associated inflammation and apoptosis in rats

Nitric oxide (NO) was one of the key factors to sustain hypoxia-inducible factor-1- α (HIF-1α) activation during hypoxia. However, the mechanism by which NO production promotes upregulation of HIF-1α to cause cerebral ischemia/reperfusion (I/R) injury remains unclear. The present study investigated whether eliminating NO would decrease HIF-1α level, and then reduce the subsequent inflammatory actions as well as neuronal apoptotic death in middle cerebral artery occlusion (MCAO) rats. Our results revealed that HIF-1α was correlated with 3-NT, a marker for nitrosative/oxidative stress, in the brain of MCAO rats. Treatment with NOS inhibitor L-NAME suppressed HIF-1α/3-NT double-positive cells, suggesting that HIF-1α was correlated with NO overproduction during cerebral I/R. Furthermore, pro-inflammatory cytokines TNF-α, IL-1β and NF-κB p65 were significantly increased and colocalized with HIF-1α in the brain of MCAO rats, all of which could be attenuated by NO inhibition, suggesting that eliminating NO reduced MCAO-induced HIF-1α upregulation, which in turn exerted anti-inflammatory actions. Accordingly, cleaved caspase-3, as well as HIF-1α and TUNEL double-positive cells in ischemic brain were also decreased by L-NAME treatment. These results suggest that NO accumulation after cerebral ischemia leads to HIF-1α upregulation, which may activate pro-inflammatory cytokines, resulting in neuronal apoptotic death. These findings demonstrate a novel mechanism of NO-induced cerebral I/R injury.

Safety and efficacy of normobaric oxygenation on rescuing acute intracerebral hemorrhage-mediated brain damage-a protocol of randomized controlled trial

Background

All of the existing medication and surgical therapies currently cannot completely inhibit intracerebral hemorrhage (ICH)-mediated brain damage, resulting in disability in different degrees in the involved patients. Normobaric oxygenation (NBO) was reported attenuating ischemic brain injury. Herein, we aimed to explore the safety and efficacy of NBO on rescuing the damaged brain tissues secondary to acute ICH, especially those in the perihematoma area being threatened by ischemia and hypoxia.

Methods

A total of 150 patients confirmed as acute spontaneous ICH by computed tomography (CT) within 6 h after symptoms onset, will enroll in this study after signing the informed consent, and enter into the NBO group or control group randomly according to a random number. In the NBO group, patients will inhale high-flow oxygen (8 L/min, 1 h each time for 6 cycles daily) and intake low-flow oxygen (2 L/min) in intermittent periods by mask for a total of 7 days. While in the control group, patients will breathe in only low-flow oxygen (2 L/min) by mask for 7 consecutive days. Computed tomography and perfusion (CT/CTP) will be used to evaluate cerebral perfusion status and brain edema. CT and CTP maps in the two groups at baseline and day 7 and 14 after NBO or low-flow oxygen control will be compared. The primary endpoint is mRS at both Day14 post-ICH and the end of the 3rd month follow-up. The secondary endpoints include NIHSS and plasma biomarkers at baseline and Day-1, 7, and 14 after treatment, as well as the NIHSS at the end of the 3rd month post-ICH and the incidence of bleeding recurrence and the mortalities within 3 months post-ICH.

Discussion

This study will provide preliminary clinical evidence about the safety and efficacy of NBO on correcting acute ICH and explore some mechanisms accordingly, to offer reference for larger clinical trials in the future.

Trial registration

ClinicalTrials.gov NCT04144868. Retrospectively registered on October 29, 2019.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-021-05048-4.

Chrysophanol attenuates nitrosative/oxidative stress injury in a mouse model of focal cerebral ischemia/reperfusion

Nitrosative/oxidative stress plays an important role in neuronal death following cerebral ischemia/reperfusion (I/R). Chrysophanol (CHR) has been shown to afford significant neuroprotection on ischemic stroke, however, whether its mechanism is related to attenuating nitrosative/oxidative stress is not clear. In the present study, we investigated the effect of CHR on neuronal injury related to nitric oxide (NO) production by using mouse middle cerebral artery occlusion (MCAO) model. Our results revealed that nitrite plus nitrate (NO_x^-) and 3-nitrotyrosine (3-NT) levels increased in ischemic brain 14 days after reperfusion, and were subsequently attenuated by CHR treatment. Moreover, 3-NT is colocalized with NeuN and TUNEL, suggesting that neuronal apoptosis following I/R is associated with 3-NT and CHR suppresses NO-associated neuronal cell death. Accordingly, cleaved caspase-3 expression in ischemic brain was decreased by CHR treatment. I/R also decreased the activity of total superoxide dismutase (SOD) and manganese-dependent SOD (MnSOD), whilst increased reactive oxygen species (ROS) production significantly. Interestingly, CHR reversed this decrease in total SOD, and MnSOD activity, and inhibited ROS generation in the ischemic brain. Taken together, our results provide direct evidence suggesting that CHR attenuates nitrosative/oxidative stress injury induced by I/R, providing a novel therapeutic target in the treatment of acute ischemic stroke.

The effect of normobaric oxygen in patients with acute stroke: a systematic review and meta-analysis

Background Normobaric oxygen (NBO) has received considerable attention due to controversial data in brain protection in patients with acute stroke. This study aims to analyze current data of NBO on brain protection as used in the clinic. Methods We searched for and reviewed relevant articles and references from Pubmed, Medline, Embase, Cochrane, and Clincialtrials.gov that were published prior to October 2017. Data from prospective studies were processed using RevMan5.0 software, provided by Cochrane collaboration and transformed using relevant formulas. Results A total of 11 prospective RCT studies including 6366 patients with acute stroke (NBO group, 3207; control group, 3159) were enrolled in this analysis. △NIHSS represented the values of NIHSS at 4, 24 h, or 7 days post-stroke minus baseline NIHSS. Compared to controls, there was a minor trend toward NBO benefits in short-term prognostic indices, as indicated by decreased ΔNIHSS at our defined time points. By contrast, NBO decreased Barthel Index scores between 3 and 7 months, and increased death rates at 3, 6 months, and 1 year, whereas, modified Rankin Scale scores between 3 and 6 months were unchanged. Conclusions The existing trends toward benefits revealed in this meta-analysis help us appreciate the promising value of NBO, although current evidence of NBO on improving clinical outcomes of stroke is insufficient. Well-designed multi-center clinical trials are encouraged and urgently needed to further explore the efficacy of NBO on brain protection.

Highs and lows of hyperoxia: physiological, performance, and clinical aspects

Molecular oxygen (O₂) is a vital element in human survival and plays a major role in a diverse range of biological and physiological processes. Although normobaric hyperoxia can increase arterial oxygen content ([Formula: see text]), it also causes vasoconstriction and hence reduces O₂ delivery in various vascular beds, including the heart, skeletal muscle, and brain. Thus, a seemingly paradoxical situation exists in which the administration of oxygen may place tissues at increased risk of hypoxic stress. Nevertheless, with various degrees of effectiveness, and not without consequences, supplemental oxygen is used clinically in an attempt to correct tissue hypoxia (e.g., brain ischemia, traumatic brain injury, carbon monoxide poisoning, etc.) and chronic hypoxemia (e.g., severe COPD, etc.) and to help with wound healing, necrosis, or reperfusion injuries (e.g., compromised grafts). Hyperoxia has also been used liberally by athletes in a belief that it offers performance-enhancing benefits; such benefits also extend to hypoxemic patients both at rest and during rehabilitation. This review aims to provide a comprehensive overview of the effects of hyperoxia in humans from the "bench to bedside." The first section will focus on the basic physiological principles of partial pressure of arterial O₂, [Formula: see text], and barometric pressure and how these changes lead to variation in regional O₂ delivery. This review provides an overview of the evidence for and against the use of hyperoxia as an aid to enhance physical performance. The final section addresses pathophysiological concepts, clinical studies, and implications for therapy. The potential of O₂ toxicity and future research directions are also considered.

Molecular Bases of Brain Preconditioning

Preconditioning of the brain induces tolerance to the damaging effects of ischemia and prevents cell death in ischemic penumbra. The development of this phenomenon is mediated by mitochondrial adenosine triphosphate-sensitive potassium (KATP+) channels and nitric oxide signaling (NO). The aim of this study was to investigate the dynamics of molecular changes in mitochondria after ischemic preconditioning (IP) and the effect of pharmacological preconditioning (PhP) with the KATP+-channels opener diazoxide on NO levels after ischemic stroke in rats. Immunofluorescence-histochemistry and laser-confocal microscopy were applied to evaluate the cortical expression of electron transport chain enzymes, mitochondrial KATP+-channels, neuronal and inducible NO-synthases, as well as the dynamics of nitrosylation and nitration of proteins in rats during the early and delayed phases of IP. NO cerebral content was studied with electron paramagnetic resonance (EPR) spectroscopy using spin trapping. We found that 24 h after IP in rats, there is a two-fold decrease in expression of mitochondrial KATP+-channels (p = 0.012) in nervous tissue, a comparable increase in expression of cytochrome c oxidase (p = 0.008), and a decrease in intensity of protein S-nitrosylation and nitration (p = 0.0004 and p = 0.001, respectively). PhP led to a 56% reduction of free NO concentration 72 h after ischemic stroke simulation (p = 0.002). We attribute this result to the restructuring of tissue energy metabolism, namely the provision of increased catalytic sites to mitochondria and the increased elimination of NO, which prevents a decrease in cell sensitivity to oxygen during subsequent periods of severe ischemia.

Methylene blue and normobaric hyperoxia combination therapy in experimental ischemic stroke

INTRODUCTION

Ischemic stroke is a global burden that contributes to the disability and mortality of millions of patients. This study aimed to evaluate the efficacy of combined MB (methylene blue) and NBO (normobaric hyperoxia) therapy in experimental ischemic stroke.

METHODS

Rats with transient (60 min) MCAO (middle cerebral artery occlusion) were treated with: (1) air + vehicle (N = 8), (2) air + MB (N = 8), (3) NBO + vehicle (N = 7), and (4) NBO + MB (N = 9). MB (1 mg/kg) was administered at 30 min, again on days 2, 7, and 14 after stroke. NBO was given during MRI (30-150 min) on day 0, and again 1 h each during MRI on subsequent days. Serial diffusion, perfusion and T2 MRI were performed to evaluate lesion volumes. Foot-fault and cylinder tests were performed to evaluate sensorimotor function.

RESULTS

The major findings were: (1) NBO + MB therapy showed a greater decrease in infarct volume compared to NBO alone, but similar infarct volume compared to MB alone, (2) NBO + MB therapy accelerated sensorimotor functional recovery compared to NBO or MB alone, (3) Infarct volumes on day 2 did not change significantly from those on day 28 for all four groups, but behavioral function continued to show improved recovery in the NBO + MB group.

CONCLUSIONS

These findings support the hypothesis that combined NBO + MB further improves functional outcome and reduces infarct volume compared to either treatment alone and these improvements extended up to 28 days.

Effects of stroke severity and treatment duration in normobaric hyperoxia treatment of ischemic stroke

In order to improve clinical trial design and translation of normobaric oxygen (NBO) treatment of ischemic stroke, NBO treatment parameters need to be better understood. This study investigated NBO treatment efficacy at two different stroke severities and two NBO treatment durations in rats. For the 60-min middle cerebral artery occlusion (MCAO), NBO treatment for 25 min and 150 min were studied. For the 90-min MCAO, NBO treatment for 55 min and 150 min were studied. Cerebral blood flow (CBF), apparent diffusion coefficients (ADC) and T2 MRI were acquired during occlusion prior to treatment, after reperfusion, and 48h after MCAO. The effects of NBO treatment on lesion volumes, and CBF, ADC and T2 of ischemic core, perfusion-diffusion mismatch and normal tissue were analyzed longitudinally. The major findings were: i) NBO treatment was effective in both groups of stroke severities, salvaging similar percentage of initial abnormal ADC tissue, and ii) NBO treatments continued after reperfusion were more beneficial than NBO treatment during occlusion alone for both MCAO groups. These findings underscore the importance of the effects of NBO duration and stroke severity on treatment outcomes.

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.

The effect of concentration and duration of normobaric oxygen in reducing caspase-3 and -9 expression in a rat-model of focal cerebral ischaemia

The aim of this study was to determine the effect of different concentrations of normobaric oxygen (NBO) on neurological function and the expression of caspase-3 and -9 in a rat model of acute cerebral ischaemia. Sprague-Dawley rats (n=120) were randomly divided into four groups (n=30 per group), including 3 groups given NBO at concentrations of 33%, 45% or 61% and one control group given air (21% oxygen). After 2h of ischaemic occlusion, each group was further subdivided into six subgroups (n=5) during reperfusion according to the duration (3, 6, 12, 24, 48 or 72h) and concentration of NBO (33%, 45% or 61%) or air treatment. The Fluorescence Quantitative polymerase chain reaction (PCR) and immunohistochemistry were used to detect caspase-3 and -9 mRNA and protein relative expression respectively. The Neurologic Impairment Score (NIS) was significantly lower in rats given 61% NBO ≥3h after reperfusion when compared to the control group (P<0.05, Mann-Whitney U). NBO significantly reduced caspase-3 and -9 mRNA and protein expression when compared to the control group at all NBO concentrations and time points (P<0.05, ANOVA). The expression of caspase-3 and -9 was lower in the group given 61% NBO compared any other group, and this difference was statistically significant when compared to the group given 33% NBO for ≥48h and the control group (both P<0.05, ANOVA). These findings indicate that NBO may inhibit the apoptotic pathway by reducing caspase-3 and -9 expression, thereby promoting neurological functional recovery after stroke.

Endothelial dysfunction abrogates the efficacy of normobaric hyperoxia in stroke

Hyperoxia has been uniformly efficacious in experimental focal cerebral ischemia. However, pilot clinical trials have showed mixed results slowing its translation in patient care. To explain the discordance between experimental and clinical outcomes, we tested the impact of endothelial dysfunction, exceedingly common in stroke patients but under-represented in experimental studies, on the neuroprotective efficacy of normobaric hyperoxia. We used hyperlipidemic apolipoprotein E knock-out and endothelial nitric oxide synthase knock-out mice as models of endothelial dysfunction, and examined the effects of normobaric hyperoxia on tissue perfusion and oxygenation using high-resolution combined laser speckle and multispectral reflectance imaging during distal middle cerebral artery occlusion. In normal wild-type mice, normobaric hyperoxia rapidly and significantly improved tissue perfusion and oxygenation, suppressed peri-infarct depolarizations, reduced infarct volumes, and improved neurological function. In contrast, normobaric hyperoxia worsened perfusion in ischemic brain and failed to reduce infarct volumes or improve neurological function in mice with endothelial dysfunction. These data suggest that the beneficial effects of hyperoxia on ischemic tissue oxygenation, perfusion, and outcome are critically dependent on endothelial nitric oxide synthase function. Therefore, vascular risk factors associated with endothelial dysfunction may predict normobaric hyperoxia nonresponders in ischemic stroke. These data may have implications for myocardial and systemic circulation as well.

In vivo quantification of cerebral r2*-response to graded hyperoxia at 3 tesla

Objectives:

This study aims to quantify the response of the transverse relaxation rate of the magnetic resonance (MR) signal of the cerebral tissue in healthy volunteers to the administration of air with step-wise increasing percentage of oxygen.

Materials and Methods:

The transverse relaxation rate (R2*) of the MR signal was quantified in seven volunteers under respiratory intake of normobaric gas mixtures containing 21, 50, 75, and 100% oxygen, respectively. End-tidal breath composition, arterial blood saturation (SaO₂), and heart pulse rate were monitored during the challenge. R2* maps were computed from multi-echo, gradient-echo magnetic resonance imaging (MRI) data, acquired at 3.0T. The average values in the segmented white matter (WM) and gray matter (GM) were tested by the analysis of variance (ANOVA), with Bonferroni post-hoc correction. The GM R2*-reactivity to hyperoxia was modeled using the Hill's equation.

Results:

Graded hyperoxia resulted in a progressive and significant (P < 0.05) decrease of the R2* in GM. Under normoxia the GM-R2* was 17.2 ± 1.1 s^-1. At 75% O₂ supply, the R2* had reached a saturation level, with 16.4 ± 0.7 s^-1 (P = 0.02), without a significant further decrease for 100% O₂. The R2*-response of GM correlated positively with CO₂ partial pressure (R = 0.69 ± 0.19) and negatively with SaO₂ (R = -0.74 ± 0.17). The WM showed a similar progressive, but non-significant, decrease in the relaxation rates, with an increase in oxygen intake (P = 0.055). The Hill's model predicted a maximum R2* response of the GM, of 3.5%, with half the maximum at 68% oxygen concentration.

Conclusions:

The GM-R2* responds to hyperoxia in a concentration-dependent manner, suggesting that monitoring and modeling of the R2*-response may provide new oxygenation biomarkers for tumor therapy or assessment of cerebrovascular reactivity in patients.

Non-pharmaceutical therapies for stroke: mechanisms and clinical implications

Stroke is deemed a worldwide leading cause of neurological disability and death, however, there is currently no promising pharmacotherapy for acute ischemic stroke aside from intravenous or intra-arterial thrombolysis. Yet because of the narrow therapeutic time window involved, thrombolytic application is very restricted in clinical settings. Accumulating data suggest that non-pharmaceutical therapies for stroke might provide new opportunities for stroke treatment. Here we review recent research progress in the mechanisms and clinical implications of non-pharmaceutical therapies, mainly including neuroprotective approaches such as hypothermia, ischemic/hypoxic conditioning, acupuncture, medical gases and transcranial laser therapy. In addition, we briefly summarize mechanical endovascular recanalization devices and recovery devices for the treatment of the chronic phase of stroke and discuss the relative merits of these devices.

Effect of normobaric hyperoxia on gentamicin-induced nephrotoxicity in rats

OBJECTIVES

Gentamicin sulphate (GS) nephrotoxicity seems to be related to the generation of reactive oxygen species. There is evidence that oxygen preconditioning increases the activity of antioxidant enzymes.

MATERIALS AND METHODS

Forty eight female rats were divided into 6 groups (n=8) as follows: group 1 was the control, group 2 received daily GS, groups 3,4 and 5 received oxygen 2 hr/day for 2 days, 4 hr/day for 2 days, 4 hr/day for 4 days, recpectively and then received daily GS, group 6 received oxygen 2 hr/day for 2 days and then received 2 hr oxygen before daily GS injection. Oxygen (with 90% purity) used at the flow rate of 4 l/min. GS administred for 8 days (100 mg/kg, IP). Tissue sections prepared from the left kidney, stained with PAS method and then studied hisopathologically and stereologically. The right kidneys were homogenized and the supernatants were prepared. Serum MDA, creatinine and urea, renal MDA, gluthatione and catalase activity were measured. The data were analyzed by Mann-Whitney U test at the significant level of P<0.05.

RESULTS

Oxygen therapy significantly improves serum creatinine and urea, preserve tubular volume density, reduce tubular necrosis in groups 4 and 6 compared to group 2. Oxygen therapy significantly increases renal catalase in groups 4 and 6 compared to group 2.

CONCLUSION

Pretreatment with normobaric hyperoxia and daily oxygen therapy improved gentamicin nephrotoxicity possibly via inhibition of lipid peroxidation and increasing the renal catalase activity but could not restore any parameter at the same levels as control group.

Method parameters' impact on mortality and variability in rat stroke experiments: a meta-analysis

Background

Even though more than 600 stroke treatments have been shown effective in preclinical studies, clinically proven treatment alternatives for cerebral infarction remain scarce. Amongst the reasons for the discrepancy may be methodological shortcomings, such as high mortality and outcome variability, in the preclinical studies. A common approach in animal stroke experiments is that A) focal cerebral ischemia is inflicted, B) some type of treatment is administered and C) the infarct sizes are assessed. However, within this paradigm, the researcher has to make numerous methodological decisions, including choosing rat strain and type of surgical procedure. Even though a few studies have attempted to address the questions experimentally, a lack of consensus regarding the optimal methodology remains.

Methods

We therefore meta-analyzed data from 502 control groups described in 346 articles to find out how rat strain, procedure for causing focal cerebral ischemia and the type of filament coating affected mortality and infarct size variability.

Results

The Wistar strain and intraluminal filament procedure using a silicone coated filament was found optimal in lowering infarct size variability. The direct and endothelin methods rendered lower mortality rate, whereas the embolus method increased it compared to the filament method.

Conclusions

The current article provides means for researchers to adjust their middle cerebral artery occlusion (MCAo) protocols to minimize infarct size variability and mortality.

Normobaric hyperoxia-based neuroprotective therapies in ischemic stroke

Stroke is a leading cause of death and disability due to disturbance of blood supply to the brain. As brain is highly sensitive to hypoxia, insufficient oxygen supply is a critical event contributing to ischemic brain injury. Normobaric hyperoxia (NBO) that aims to enhance oxygen delivery to hypoxic tissues has long been considered as a logical neuroprotective therapy for ischemic stroke. To date, many possible mechanisms have been reported to elucidate NBO’s neuroprotection, such as improving tissue oxygenation, increasing cerebral blood flow, reducing oxidative stress and protecting the blood brain barrier. As ischemic stroke triggers a battery of damaging events, combining NBO with other agents or treatments that target multiple mechanisms of injury may achieve better outcome than individual treatment alone. More importantly, time loss is brain loss in acute cerebral ischemia. NBO can be a rapid therapy to attenuate or slow down the evolution of ischemic tissues towards necrosis and therefore “buy time” for reperfusion therapies. This article summarizes the current literatures on NBO as a simple, widely accessible, and potentially cost-effective therapeutic strategy for treatment of acute ischemic stroke.

Hyperbaric oxygen and hyperbaric air treatment result in comparable neuronal death reduction and improved behavioral outcome after transient forebrain ischemia in the gerbil

Anoxic brain injury resulting from cardiac arrest is responsible for approximately two-thirds of deaths. Recent evidence suggests that increased oxygen delivered to the brain after cardiac arrest may be an important factor in preventing neuronal damage, resulting in an interest in hyperbaric oxygen (HBO) therapy. Interestingly, increased oxygen supply may be also reached by application of normobaric oxygen (NBO) or hyperbaric air (HBA). However, previous research also showed that the beneficial effect of hyperbaric treatment may not directly result from increased oxygen supply, leading to the conclusion that the mechanism of hyperbaric prevention of brain damage is not well understood. The aim of our study was to compare the effects of HBO, HBA and NBO treatment on gerbil brain condition after transient forebrain ischemia, serving as a model of cardiac arrest. Thereby, we investigated the effects of repetitive HBO, HBA and NBO treatment on hippocampal CA1 neuronal survival, brain temperature and gerbils behavior (the nest building), depending on the time of initiation of the therapy (1, 3 and 6 h after ischemia). HBO and HBA applied 1, 3 and 6 h after ischemia significantly increased neuronal survival and behavioral performance and abolished the ischemia-evoked brain temperature increase. NBO treatment was most effective when applied 1 h after ischemia; later application had a weak or no protective effect. The results show that HBO and HBA applied between 1 and 6 h after ischemia prevent ischemia-evoked neuronal damage, which may be due to the inhibition of brain temperature increase, as a result of the applied rise in ambient pressure, and just not due to the oxygen per se. This perspective is supported by the finding that NBO treatment was less effective than HBO or HBA therapy. The results presented in this paper may pave the way for future experimental studies dealing with pressure and temperature regulation.

Protecting the future: neuroprotective strategies in the pediatric intensive care unit

PURPOSE OF REVIEW

Brain injury is the leading cause of death in pediatric intensive care units, and improvements in therapy and in understanding the pathogenesis are urgently needed. This review presents recent advances in the understanding of neuroprotective therapy and brain-specific monitoring for critically ill pediatric patients.

RECENT FINDINGS

Two neuroprotective strategies are becoming increasingly accepted as they are applied to different mechanisms of brain injury. The rapid application of hypothermia and avoidance of hyperoxia after cardiac arrest and other brain injuries are each being more commonly used as both human and animal data advocating for these approaches accumulate. In addition, more advanced and noninvasive technologies are emerging that are designed to serve as surrogates for brain function and may be used to help predict outcome. Near-infrared spectroscopy is one such commonly used technique that has prompted many studies to understand how to incorporate it into practice.

SUMMARY

Protection of the pediatric brain from both a primary insult and the common subsequent secondary injury is essential for improving long-term neurologic outcomes. Whereas monitoring technology is being constantly modified, it must be proven efficacious in order to understand the utility of new and presumed neuroprotective therapies like hypothermia and avoidance of hyperoxia.