Therapeutic effects of hyperbaric oxygen in a rat model of endothelin-1-induced focal cerebral ischemia

The Mechanisms of Action of Hyperbaric Oxygen in Restoring Host Homeostasis during Sepsis

The perception of sepsis has shifted over time; however, it remains a leading cause of death worldwide. Sepsis is now recognized as an imbalance in host cellular functions triggered by the invading pathogens, both related to immune cells, endothelial function, glucose and oxygen metabolism, tissue repair and restoration. Many of these key mechanisms in sepsis are also targets of hyperbaric oxygen (HBO2) treatment. HBO2 treatment has been shown to improve survival in clinical studies on patients with necrotizing soft tissue infections as well as experimental sepsis models. High tissue oxygen tension during HBO2 treatment may affect oxidative phosphorylation in mitochondria. Oxygen is converted to energy, and, as a natural byproduct, reactive oxygen species are produced. Reactive oxygen species can act as mediators, and both these and the HBO2-mediated increase in oxygen supply have the potential to influence the cellular processes involved in sepsis. The pathophysiology of sepsis can be explained comprehensively through resistance and tolerance to infection. We argue that HBO2 treatment may protect the host from collateral tissue damage during resistance by reducing neutrophil extracellular traps, inhibiting neutrophil adhesion to vascular endothelium, reducing proinflammatory cytokines, and halting the Warburg effect, while also assisting the host in tolerance to infection by reducing iron-mediated injury and upregulating anti-inflammatory measures. Finally, we show how inflammation and oxygen-sensing pathways are connected on the cellular level in a self-reinforcing and detrimental manner in inflammatory conditions, and with support from a substantial body of studies from the literature, we conclude by demonstrating that HBO2 treatment can intervene to maintain homeostasis.

Survey of Molecular Mechanisms of Hyperbaric Oxygen in Tissue Repair

For more than six decades, hyperbaric oxygen (HBO) has been used for a variety of indications involving tissue repair. These indications comprise a wide range of diseases ranging from intoxications to ischemia-reperfusion injury, crush syndrome, central nervous injury, radiation-induced tissue damage, burn injury and chronic wounds. In a systematic review, the molecular mechanisms triggered by HBO described within the last two decades were compiled. They cover a wide range of pathways, including transcription, cell-to-cell contacts, structure, adhesion and transmigration, vascular signaling and response to oxidative stress, apoptosis, autophagy and cell death, as well as inflammatory processes. By analyzing 71 predominantly experimental publications, we established an overview of the current concepts regarding the molecular mechanisms underlying the effects of HBO. We considered both the abovementioned pathways and their role in various applications and indications.

Hydrogen inhibits microglial activation and regulates microglial phenotype in a mouse middle cerebral artery occlusion model

Microglia participate in bi-directional control of brain repair after stroke. Previous studies have demonstrated that hydrogen protects brain after ischemia/reperfusion (I/R) by inhibiting inflammation, but the specific mechanism of anti-inflammatory effect of hydrogen is poorly understood. The goal of our study is to investigate whether inhalation of high concentration hydrogen (HCH) is able to attenuate I/R-induced microglia activation. Eighty C57B/L male mice were divided into four groups: sham, I/R, I/R + HCH and I/R + N₂/O₂ groups. Assessment of animals happened in “blind” matter. I/R was induced by occlusion of middle cerebral artery for one hour). After one hour, filament was withdrawn, which induced reperfusion. Hydrogen treated I/R animals inhaled mix of 66.7% H₂ balanced with O₂ for 90 minutes, starting immediately after initiation of reperfusion. Control animals (N₂/O₂) inhaled mix in which hydrogen was replaced with N₂ for the same time (90 minutes). The brain injury, such as brain infarction and development of brain edema, as well as neurobehavioral deficits were determined 23 hours after reperfusion. Effect of HCH on microglia activation in the ischemic penumbra was investigated by immunostaining also 23 hours after reperfusion. mRNA expression of inflammation related genes was detected by PCR. Our results showed that HCH attenuated brain injury and consequently reduced neurological dysfunction after I/R. Furthermore, we demonstrated that HCH directed microglia polarization towards anti-inflammatory M2 polarization. This study indicates hydrogen may exert neuroprotective effects by inhibiting the microglial activation and regulating microglial polarization. This study was conducted in agreement with the Animal Care and Use Committee (IACUC) and Institutional Animal Care guidelines regulation (Shanghai Jiao Tong University, China (approval No. A2015-011) in November 2015.

The Effect of Hyperbaric Oxygen Therapy on Functional Impairments Caused by Ischemic Stroke

Background

While research suggests a benefit of hyperbaric oxygen therapy (HBOT) for neurologic injury, controlled clinical trials have not been able to clearly define the benefits.

Objective

To investigate the effects of HBOT on physical and cognitive impairments resulting from an ischemic stroke.

Methods

Using a within-subject design a baseline for current functional abilities was established over a 3-month period for all subjects (n=7). Each subject then received two 4-week periods of HBOT for a total of 40 90-minute treatments over a 12-week period. Subjects completed a battery of assessments and had blood drawn six times over the 9-month total duration of the study.

Results

We found improvements in cognition and executive function as well as physical abilities, specifically, improved gait. Participants reported improved sleep and quality of life following HBOT treatment. We also saw changes in serum levels of biomarkers for inflammation and neural recovery. In the functional domains where improvement was observed following HBOT treatment, the improvements were maintained up to 3 months following the last treatment. However, the physiological biomarkers showed a pattern of more transient changes following HBOT treatment.

Conclusions

Findings from this study support the idea of HBOT as a potential intervention following stroke.

Hydrogen inhalation improves mouse neurological outcomes after cerebral ischemia/reperfusion independent of anti-necroptosis

This study aimed to investigate the role of necroptosis in the neuroprotection of hydrogen in a mouse model of cerebral ischemia/reperfusion (I/R) injury. C57BL mice were randomly divided into sham group, I/R group, hydrogen/oxygen group (HO), nitrogen/oxygen group (NO). Middle cerebral artery occlusion (MCAO) for 1 hour followed by reperfusion was introduced to animals which were allowed to inhale 66.7% hydrogen/33.3% oxygen for 90 minutes since the beginning of reperfusion. Mice in NO group inhaled 66.7% nitrogen/33.3% oxygen. 24 hours after MCAO, brain infarction, brain water content and neurological function were evaluated. The protein expression of mixed lineage kinase domain like protein (MLKL) was detected at 3, 6, 12, 24 and 72 hours after reperfusion in HO group and the protein and mRNA expression of MLKL at 24 hours after MCAO in four groups. Hydrogen inhalation significantly reduced infarct volume, attenuated brain edema and improved neurobehavioral deficit in MCAO mice. The MLKL expression increased after MCAO and peaked at 6-24 hours after reperfusion. However, hydrogen inhalation had no significant effect on the MLKL expression at transcriptional and translational levels after MCAO. This study indicates high concentration hydrogen improves mouse neurological outcome after cerebral I/R injury independent of anti-necroptosis.

The efficacy of hyperbaric oxygen in hemorrhagic stroke: experimental and clinical implications

Hemorrhagic stroke, accounting for 10-30% of stroke cases, carries high rates of morbidity and mortality. This review presents the current knowledge on the efficacy of hyperbaric oxygen (HBO)-based modalities in the preclinical research on hemorrhagic stroke. Both preconditioning and post-treatment with HBO are considered as prospective therapeutic options. High efficacy of HBO therapy (HBOT) for brain hemorrhage has been noted. We found that moderate hyperbaric pressures appear optimal for therapeutic effect, while the therapeutic window of opportunity is short. HBO preconditioning offers more modest neuroprotective benefit as compared to HBO post-treatment for experimental intracerebral hemorrhage. We advocate for mandatory calculations of percent changes in the experimentally investigated indexes of HBO effectiveness and stress the need to design new clinical trials on HBO for hemorrhagic stroke.

Hyperbaric oxygen therapy and preconditioning for ischemic and hemorrhagic stroke

To date, the therapeutic methods for ischemic and hemorrhagic stroke are still limited. The lack of oxygen supply is critical for brain injury following stroke. Hyperbaric oxygen (HBO), an approach through a process in which patients breathe in 100% pure oxygen at over 101 kPa, has been shown to facilitate oxygen delivery and increase oxygen supply. Hence, HBO possesses the potentials to produce beneficial effects on stroke. Actually, accumulated basic and clinical evidences have demonstrated that HBO therapy and preconditioning could induce neuroprotective functions via different mechanisms. Nevertheless, the lack of clinical translational study limits the application of HBO. More translational studies and clinical trials are needed in the future to develop effective HBO protocols.

Inhalation of water electrolysis-derived hydrogen ameliorates cerebral ischemia-reperfusion injury in rats - A possible new hydrogen resource for clinical use

Hydrogen is a kind of noble gas with the character to selectively neutralize reactive oxygen species. Former researches proved that low-concentration of hydrogen can be used to ameliorating cerebral ischemia/reperfusion injury. Hydrogen electrolyzed from water has a hydrogen concentration of 66.7%, which is much higher than that used in previous studies. And water electrolysis is a potential new hydrogen resource for regular clinical use. This study was designed and carried out for the determination of safety and neuroprotective effects of water electrolysis-derived hydrogen. Sprague-Dawley rats were used as experimental animals, and middle cerebral artery occlusion was used to make cerebral ischemia/reperfusion model. Pathologically, tissues from rats in hydrogen inhalation group showed no significant difference compared with the control group in HE staining pictures. The blood biochemical findings matched the HE staining result. TTC, Nissl, and TUNEL staining showed the significant improvement of infarction volume, neuron morphology, and neuron apoptosis in rat with hydrogen treatment. Biochemically, hydrogen inhalation decreased brain caspase-3, 3-nitrotyrosine and 8-hydroxy-2-deoxyguanosine-positive cells and inflammation factors concentration. Water electrolysis-derived hydrogen inhalation had neuroprotective effects on cerebral ischemia/reperfusion injury in rats with the effect of suppressing oxidative stress and inflammation, and it is a possible new hydrogen resource to electrolyze water at the bedside clinically.

Hyperbaric oxygen modalities are differentially effective in distinct brain ischemia models

The effectiveness and efficacy of hyperbaric oxygen (HBO) preconditioning and post-treatment modalities have been demonstrated in experimental models of ischemic cerebrovascular diseases, including global brain ischemia, transient focal and permanent focal cerebral ischemia, and experimental neonatal hypoxia-ischemia encephalopathy. In general, early and repetitive post-treatment of HBO appears to create enhanced protection against brain ischemia whereas delayed HBO treatment after transient focal ischemia may even aggravate brain injury. This review advocates the level of injury reduction upon HBO as an important component for translational evaluation of HBO based treatment modalities. The combined preconditioning and HBO post-treatment that would provide synergistic effects is also worth considering.

The Efficacy of Hyperbaric Oxygen Therapy on Middle Cerebral Artery Occlusion in Animal Studies: A Meta-Analysis

Background

Inconsistent results have been reported for hyperbaric oxygen therapy (HBO) for acute stroke. We conducted a systematic review and meta-analysis to evaluate the benefit of HBO in animal studies of middle cerebral artery occlusion (MCAO).

Methods

A systematic search of the literature published prior to September 2015 was performed using Embase, Medline (OvidSP), Web of Science and PubMed. Keywords included “hyperoxia” OR “hyperbaric oxygen” OR “HBO” AND “isch(a)emia” OR “focal cerebral ischemia” OR “stroke” OR “infarct” OR “middle cerebral artery occlusion (MCAO).” The primary endpoints were the infarct size and/or neurological outcome score evaluated after HBO treatment in MCAO. Heterogeneity was analyzed using Cochrane Library’s RevMan 5.3.5.

Results

Fifty-one studies that met the inclusion criteria were identified among the 1198 studies examined. When compared with control group data, HBO therapy resulted in infarct size reduction or improved neurological function (32% decrease in infarct size; 95% confidence interval (CI), range 28%–37%; p < 0.00001). Mortality was 18.4% in the HBO group and 26.7% in the control group (RR 0.72, 95% CI, 0.54–0.98; p = 0.03). Subgroup analysis showed that a maximal neuro-protective effect was reached when HBO was administered immediately after MCAO with an absolute atmospheric pressure (ATA) of 2.0 (50% decrease; 95% CI, 43% -57% decrease; p < 0.0001) and more than 6 hours HBO treatment (53% decrease; 95% CI, 41% -64% decrease; p = 0.0005).

Conclusions

HBO had a neuro-protective effect and improved survival in animal models of MCAO, especially in animals given more than 6 hours of HBO and when given immediately after MCAO with 2.0 ATA.

Delayed hyperbaric oxygen therapy promotes neurogenesis through reactive oxygen species/hypoxia-inducible factor-1α/β-catenin pathway in middle cerebral artery occlusion rats

BACKGROUND AND PURPOSE

Hyperbaric oxygen (HBO) has been reported to be neuroprotective and to improve neurofunctional outcomes in acute stroke. However, it is not clear whether delayed HBO enhances endogenous neurogenesis and promotes neurofunctional recovery. The aim of this study is to evaluate the effects of delayed HBO therapy on neurogenesis and its potential mechanisms.

METHODS

One hundred eleven male Sprague-Dawley rats that survived for 7 days from 2 hours of middle cerebral artery occlusion and reperfusion were used. Delayed and multiple HBO were administrated beginning at 7 days after middle cerebral artery occlusion and lasting for 42 days with 3 HBO-free intervals (5 days each). Motor sensory deficits were measured by foot-fault test, and learning and memory abilities were evaluated by Morris water maze. Neurogenesis was examined by double immunostaining of bromodeoxyuridine and doublecortin, bromodeoxyuridine and neuronal nuclei at day 42. For mechanism studies, inhibitors for reactive oxygen species (ROS), hypoxia-inducible factor (HIF)-1α, and β-catenin were administrated, and the levels of ROS, HIF-1α, β-catenin, lymphoid enhancer-binding factor-1, T-cell factor-1, neurogenin-1, doublecortin, and synapsin-1 were assessed by ELISA or Western blot at day 14.

RESULTS

Delayed HBO treatment promoted neurogenesis and improved neurofunctional recovery at day 42, and the improvements were reversed by inhibition of ROS and HIF-1α. Delayed HBO significantly increased ROS and HIF-1α, and upregulated the expression of neurogenin-1, doublecortin, and synapsin-1. Inhibition of ROS and HIF-1α removed the effects of delayed HBO.

CONCLUSIONS

Delayed HBO enhanced endogenous neurogenesis and improved neurofunctional recovery in the late-chronic phase of stroke possibly mediated by ROS/HIF-1α/β-catenin pathway. Delayed HBO may serve as an alternative treatment to improve long-term recovery of stroke survivors.

Hyperbaric oxygen for cerebral vasospasm and brain injury following subarachnoid hemorrhage

The impact of acute brain injury and delayed neurological deficits due to cerebral vasospasm (CVS) are major determinants of outcomes after subarachnoid hemorrhage (SAH). Although hyperbaric oxygen (HBO) had been used to treat patients with SAH, the supporting evidence and underlying mechanisms have not been systematically reviewed. In the present paper, the overview of studies of HBO for cerebral vasospasm is followed by a discussion of HBO molecular mechanisms involved in the protection against SAH-induced brain injury and even, as hypothesized, in attenuating vascular spasm alone. Faced with the paucity of information as to what degree HBO is capable of antagonizing vasospasm after SAH, the authors postulate that the major beneficial effects of HBO in SAH include a reduction of acute brain injury and combating brain damage caused by CVS. Consequently, authors reviewed the effects of HBO on SAH-induced hypoxic signaling and other mechanisms of neurovascular injury. Moreover, authors hypothesize that HBO administered after SAH may "precondition" the brain against the detrimental sequelae of vasospasm. In conclusion, the existing evidence speaks in favor of administering HBO in both acute and delayed phase after SAH; however, further studies are needed to understand the underlying mechanisms and to establish the optimal regimen of treatment.

The medical use of oxygen: a time for critical reappraisal

Oxygen treatment has been a cornerstone of acute medical care for numerous pathological states. Initially, this was supported by the assumed need to avoid hypoxaemia and tissue hypoxia. Most acute treatment algorithms, therefore, recommended the liberal use of a high fraction of inspired oxygen, often without first confirming the presence of a hypoxic insult. However, recent physiological research has underlined the vasoconstrictor effects of hyperoxia on normal vasculature and, consequently, the risk of significant blood flow reduction to the at-risk tissue. Positive effects may be claimed simply by relief of an assumed local tissue hypoxia, such as in acute cardiovascular disease, brain ischaemia due to, for example, stroke or shock or carbon monoxide intoxication. However, in most situations, a generalized hypoxia is not the problem and a risk of negative hyperoxaemia-induced local vasoconstriction effects may instead be the reality. In preclinical studies, many important positive anti-inflammatory effects of both normobaric and hyperbaric oxygen have been repeatedly shown, often as surrogate end-points such as increases in gluthatione levels, reduced lipid peroxidation and neutrophil activation thus modifying ischaemia-reperfusion injury and also causing anti-apoptotic effects. However, in parallel, toxic effects of oxygen are also well known, including induced mucosal inflammation, pneumonitis and retrolental fibroplasia. Examining the available 'strong' clinical evidence, such as usually claimed for randomized controlled trials, few positive studies stand up to scrutiny and a number of trials have shown no effect or even been terminated early due to worse outcomes in the oxygen treatment arm. Recently, this has led to less aggressive approaches, even to not providing any supplemental oxygen, in several acute care settings, such as resuscitation of asphyxiated newborns, during acute myocardial infarction or after stroke or cardiac arrest. The safety of more advanced attempts to deliver increased oxygen levels to hypoxic or ischaemic tissues, such as with hyperbaric oxygen therapy, is therefore also being questioned. Here, we provide an overview of the present knowledge of the physiological effects of oxygen in relation to its therapeutic potential for different medical conditions, as well as considering the potential for harm. We conclude that the medical use of oxygen needs to be further examined in search of solid evidence of benefit in many of the current clinical settings in which it is routinely used.

Lactulose ameliorates cerebral ischemia-reperfusion injury in rats by inducing hydrogen by activating Nrf2 expression

Molecular hydrogen has been proven effective in ameliorating cerebral ischemia/reperfusion (I/R) injury by selectively neutralizing reactive oxygen species. Lactulose can produce a considerable amount of hydrogen through fermentation by the bacteria in the gastrointestinal tract. To determine the neuroprotective effects of lactulose against cerebral I/R injury in rats and explore the probable mechanisms, we carried out this study. The stroke model was produced in Sprague-Dawley rats through middle cerebral artery occlusion. Intragastric administration of lactulose substantially increased breath hydrogen concentration. Behavioral and histopathological verifications matched biochemical findings. Behaviorally, rats in the lactulose administration group won higher neurological scores and showed shorter escape latency time in the Morris test. Morphologically, 2,3,5-triphenyltetrazolium chloride showed smaller infarction volume; Nissl staining manifested relatively clear and intact neurons and TUNEL staining showed fewer apoptotic neurons. Biochemically, lactulose decreased brain malondialdehyde content, caspase-3 activity, and 3-nitrotyrosine and 8-hydroxy-2-deoxyguanosine concentration and increased superoxide dismutase activity. The effects of lactulose were superior to those of edaravone. Lactulose orally administered activated the expression of NF-E2-related factor 2 (Nrf2) in the brain as verified by RT-PCR and Western blot. The antibiotics suppressed the neuroprotective effects of lactulose by reducing hydrogen production. Our study for the first time demonstrates a novel therapeutic effect of lactulose on cerebral ischemia/reperfusion injury and the probable underlying mechanisms. Lactulose intragastrically administered possessed neuroprotective effects on cerebral I/R injury in rats, which could be attributed to hydrogen production by the fermentation of lactulose through intestinal bacteria and Nrf2 activation.

Hyperbaric oxygen treatment suppresses MAPK signaling and mitochondrial apoptotic pathway in degenerated human intervertebral disc cells

Nucleus pulposus cells (NPCs) from degenerating discs produce catabolic and inflammatory factors, including interleukin (IL)-1 and nitric oxide (NO). Enhanced production of NO has been implicated in the apoptosis of degenerating disc cells. This study evaluates the effects of hyperbaric oxygen (HBO) on degenerated human NPCs. All hyperoxic cells were exposed to 100% O(2) at 2.5 atmospheres absolute (ATA). Phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK) in NPCs was detected using the phosphor-kinase array kit. RNA was isolated for real-time polymerase chain reaction (PCR) analysis of aggrecan and type II collagen gene expression. The levels of IL- 1β and NO were quantified by enzyme-linked immunosorbent assay (ELISA). To identify the HBO-induced anti-apoptotic pathways, expression of Bcl-2 and Bax proteins as well as activation of cysteine-containing aspartate-specific proteases (caspases) 3, 8, and 9 was evaluated using Western blotting after HBO treatment. Our data showed that HBO treatment decreased the expression of IL-1β, suppressed phosphorylation of ERK1/2, JNK, and p38 MAPK, decreased synthesis of NO, and increased the gene expression of aggrecan and type II collagen in NPCs as compared with the atmospheric treatment. HBO up-regulated the ratio of Bcl-2 to Bax expression and reduced the activity of caspases 9 and 3 but not of caspase 8, indicating a selective effect over the mitochondrial apoptosis pathway in degenerated NPCs. These results support our hypothesis that HBO treatment suppresses MAPK signaling and mitochondrial apoptotic pathway in degenerated human intervertebral disc cells.

AQP4 knockout aggravates ischemia/reperfusion injury in mice

BACKGROUND AND PURPOSE

The glial water channel aquaporin-4 (AQP4) has been shown to be involved in a wide range of brain disorders. Although its important role in stroke has already been documented, the underlying mechanism was not clarified yet. Therefore, this study was designed to investigate the impacts of AQP4 deletion in ischemia/reperfusion (I/R).

METHODS AND RESULTS

Herein we found a higher mortality and more severe neurological deficits in AQP4 knockout (AQP4(-/-)) mice after transient middle cerebral artery occlusion while no difference was observed in water content variation during I/R between two genotypes except a higher basal water content developed in AQP4(-/-) mouse brain, implying the same increment of water content over a higher basal level may provoke an even more elevated intracranial pressure, which might be an important cause of increased mortality in AQP4(-/-) mice. Moreover, AQP4 knockout aggravated I/R injury with enlarged infarct size and a more serious loss of CA1 neurons accompanied by a striking hypertrophy of astrocytes, suggesting an involvement of AQP4 in astrocytic dysfunction.

CONCLUSIONS

Our findings provide direct evidence that AQP4 plays a crucial role in the pathogenesis of I/R injury, which may confer a new option for stroke treatment.

Characterizing the role of the neuropeptide substance P in experimental subarachnoid hemorrhage

BACKGROUND

Raised intracranial pressure (ICP) following SAH predicts poor outcome and is due to hemorrhage volume and possibly, brain edema, hydrocephalus and increased volume of circulating intracranial blood. Interventions that reduce edema may therefore reduce ICP and improve outcome. The neuropeptide substance P (SP) mediates vasogenic edema formation in animal models of ischemic stroke, intracerebral hemorrhage and brain trauma, and may contribute to development of increased ICP. SP (NK1 tachykinin receptor) blockade using n-acetyl-l-tryptophan (NAT) reduces edema and improves outcome in these models. This study therefore assessed whether SP mediates edema formation in experimental SAH.

METHODS

SAH was induced in rats by either injection of autologous blood into the prechiasmatic cistern (injection SAH) or by arterial puncture of the Circle of Willis (filament SAH). NAT was injected (i.v.) 30min after SAH induction. Subgroups were assessed for brain water content, SP and albumin immunoreactivity, and functional outcome at 5, 24 and 48h or ICP over 5h.

RESULTS

A secondary ICP increase occurred within 2h of SAH. Brain edema followed filament SAH (p<0.001) and correlated with functional deficits (r=0.8, p<0.01). Increased albumin immunoreactivity (p<0.001) indicated vasogenic edema. However, NAT treatment did not improve ICP, edema or outcome.

CONCLUSIONS

Experimental SAH produced secondary ICP elevation, vasogenic brain edema and functional deficits, although it is unclear if edema contributed to ICP. Blockade of SP did not improve any outcome parameters, suggesting that neurogenic inflammation may be less critical than other factors in these models.

Use of normobaric and hyperbaric oxygen in acute focal cerebral ischemia - a preclinical and clinical review

High socioeconomic burden is attributed to acute ischemic stroke, but treatment strategies are still limited. Normobaric (NBO) and hyperbaric oxygen therapy (HBO) were frequently investigated in preclinical studies following acute focal cerebral ischemia with predominantly beneficial effects in different outcome measurements. Best results were achieved in transient cerebral ischemia, starting HBO early after artery occlusion, and by using relatively high pressures. On molecular level, oxygen application leads to blood-brain barrier stabilization, reduction of excitotoxic metabolites, and inhibition of inflammatory processes. Therefore, NBO and HBO appear excessively hopeful in salvaging impaired brain cells during ischemic stroke. However, harmful effects have been noted contributing to damaging properties, for example, vasoconstriction and free oxygen radicals. In the clinical setting, NBO provided positive results in a single clinical trial, but HBO failed to show efficacy in three randomized trials. To date, the translation of numerous evidentiary experimental results into clinical implementation remains open. Recently, oxygen became interesting as an additional therapy to neuroprotective or recanalization drugs to combine positive effects. Further preclinical research is needed exploring interactions between NBO, HBO, and key factors with multiphasic roles in acute damaging and delayed inflammatory processes after cerebral ischemia, for example, matrix-metalloproteinases and hypoxia-inducible factor-1α.

Vascular Dysfunction in Brain Hemorrhage: Translational Pathways to Developing New Treatments from Old Targets

Hemorrhagic stroke which is a form of stroke that affects 20% of all stroke patients is a devastating condition for which new treatments must be developed. Current treatment methods are quite insufficient to reduce long term morbidity and high mortality rate, up to 50%, associated with bleeding into critical brain structures, into ventricular spaces and within the subarachnoid space. During the last 10-15 years, significant advances in the understanding of important mechanisms that contribute to cell death and clinical deficits have been made. The most important observations revolve around a key set of basic mechanisms that are altered in brain bleeding models, including activation of membrane metalloproteinases, oxidative stress and both inflammatory and coagulation pathways. Moreover, it is now becoming apparent that brain hemorrhage can activate the ischemic stroke cascade in neurons, glial cells and the vascular compartment. The activation of multiple pathways allows comes the opportunity to intervene pharmacologically using monotherapy or combination therapy. Ultimately, combination therapy or pleiotropic compounds with multi-target activities should prove to be more efficacious than any single therapy alone. This article provides a comprehensive look at possible targets for small molecule intervention as well as some new approaches that result in metabolic down-regulation or inhibition of multiple pathways simultaneously.

Protection against focal ischemic injury to the brain by trans-sodium crocetinate. Laboratory investigation

OBJECT

Ischemic injury is a potential complication in a variety of surgical procedures and is a particular impediment to the success of surgeries involving highly vulnerable neural tissue. One approach to limiting this form of injury is to enhance metabolic supply to the affected tissue. Trans-sodium crocetinate (TSC) is a carotenoid compound that has been shown to increase tissue oxygenation by facilitating the diffusivity of small molecules, such as oxygen and glucose. The present study examined the ability of TSC to modify oxygenation in ischemic neural tissue and tested the potential neuroprotective effects of TSC in permanent and temporary models of focal cerebral ischemia.

METHODS

Adult male rats (330–370 g) were subjected to either permanent or temporary focal ischemia by simultaneous occlusion of both common carotid arteries and the left middle cerebral artery (3-vessel occlusion [3-VO]). Using the permanent ischemia paradigm, TSC was administered intravenously beginning 10 minutes after the onset of ischemia at 1 of 8 dosages, ranging from 0.023 to 4.580 mg/kg. Cerebral infarct volume was measured 24 hours after the onset of ischemia. The effect of TSC on infarct volume was also tested after temporary (2-hour) ischemia using a dosage of 0.092 mg/kg. In other animals undergoing temporary ischemia, tissue oxygenation was monitored in the ischemic penumbra using a Licox probe.

RESULTS

Administration of TSC reduced infarct volume in a dose-dependent manner in the permanent ischemia model, achieving statistical significance at dosages ranging from 0.046 to 0.229 mg/kg. The most effective dosage of TSC in the permanent ischemia experiment (0.092 mg/kg) was further tested using a temporary (2-hour) ischemia paradigm. Infarct volume was reduced significantly by TSC in this ischemia-reperfusion model as well. Recordings of oxygen levels in the ischemic penumbra of the temporary ischemia model showed that TSC increased tissue oxygenation during vascular occlusion, but reduced the oxygen overshoot (hyperoxygenation) that occurs upon reperfusion.

CONCLUSIONS

The novel carotenoid compound TSC exerts a neuroprotective influence against permanent and temporary ischemic injury when administered soon after the onset of ischemia. The protective mechanism of TSC remains to be confirmed; however, the permissive effect of TSC on the diffusivity of small molecules is a plausible mechanism based on the observed increase in tissue oxygenation in the ischemic penumbra. This represents a form of protection based on “metabolic reflow” that can occur under conditions of partial vascular perfusion. It is particularly noteworthy that TSC could conceivably limit the progression of a wide variety of cellular injury mechanisms by blunting the ischemic challenge to the brain.

Hyperbaric oxygen therapy and cerebral ischemia: neuroprotective mechanisms

INTRODUCTION

Numerous studies have demonstrated a protective effect of hyperbaric oxygen therapy in experimental ischemic brain injury, and many physiological and molecular mechanisms of hyperbaric oxygen therapy-related neuroprotection have been identified.

METHODS

Review of articles pertaining to hyperbaric oxygen therapy and cerebral ischemia in the National Library of Medicine and National Institutes of Health database, emphasizing mechanisms of hyperbaric oxygen therapy-related neuroprotection.

RESULTS

Hyperbaric oxygen therapy has been shown to ameliorate brain injury in a variety of animal models including focal cerebral ischemia, global cerebral ischemia, neonatal hypoxia-ischemia and subarachnoid hemorrhage. Small human trials of hyperbaric oxygen therapy in focal ischemia have not shown benefit, although one trial of hyperbaric oxygen therapy before cardiopulmonary bypass demonstrated improved neuropsychological and inflammatory outcomes with hyperbaric oxygen therapy. Hyperbaric oxygen therapy is associated with improved cerebral oxygenation, reduced blood-brain barrier breakdown, decreased inflammation, reduced cerebral edema, decreased intracranial pressure, reduced oxidative burden, reduced metabolic derangement, decreased apoptotic cell death and increased neural regeneration.

CONCLUSION

On a molecular level, hyperbaric oxygen therapy leads to activation of ion channels, inhibition of hypoxia inducible factor-1alpha, up-regulation of Bcl-2, inhibition of MMP-9, decreased cyclooxygenase-2 activity, decreased myeloperoxidase activity, up-regulation of superoxide dismutase and inhibition of Nogo-A (an endogenous growth-inhibitory factor). Ongoing research will continue to describe the mechanisms of hyperbaric oxygen therapy-related neuroprotection, and possibly expand hyperbaric oxygen therapy use clinically.

Transcription factor early growth response-1 induction mediates inflammatory gene expression and brain damage following transient focal ischemia

Early growth response-1 (Egr1) is a sequence-specific transcription factor (TF) which is induced under hypoxic conditions. We presently report that transient middle cerebral artery occlusion (MCAO) leads to increased expression of Egr1 in the brains of adult mice and rats between 2 h and 5 days of reperfusion with a peak increase of 8-12-fold at 1 day. When subjected to transient MCAO and 3 days of reperfusion, Egr1-/- mice showed significantly smaller infarcts (by 44.9 +/- 8.4%, p < 0.05) and improved neurological function than Egr1+/+ littermates. Following transient MCAO, brains of Egr1-/- mice showed less water accumulation and decreased neutrophil infiltration (by 42 +/- 8%, p < 0.05) compared to Egr1+/+ mice. The number of activated microglia/macrophages were also significantly lower (OX42+ cells by 53 +/- 9%, p < 0.05 and ED1+ cells by 59 +/- 11%) in the post-ischemic cortex of Egr1-/- mice compared to Egr1+/+ mice. In addition, post-ischemic inflammatory gene expression was less pronounced in the brains of Egr1-/- mice compared to Egr1+/+ mice. Preventing cerebral Egr1 protein induction with small interference RNAs that target Egr1 decreased inflammatory gene expression and led to smaller infarcts (by 40.2 +/- 6.9%, p < 0.05) and reduced neurological deficits in rats subjected to transient MCAO. Conversely, transient MCAO following adenoviral-mediated Egr1 over-expression exacerbated the infarct volume (by 29 +/- 5.3%, p < 0.05) and worsened the neurological deficits in rats. These studies indicate Egr1 as a significant contributor of inflammation and neuronal damage after stroke.