Prolonged and intermittent normobaric hyperoxia induce different degrees of ischemic tolerance in rat brain tissue

Normobaric hyperoxia therapy in acute ischemic stroke: A literature review

Background

Ischemic stroke is one of the most severe cerebrovascular diseases that leads to disability and death and seriously endangers health and quality of life. Insufficient oxygen supply is a critical factor leading to ischemic brain injury. However, effective therapies for ischemic stroke are lacking. Oxygen therapy has been shown to increase oxygen supply to ischemic tissues and improve prognosis after cerebral ischemia/reperfusion. Normobaric hyperoxia (NBHO) has been shown to have neuroprotective effects during ischemic stroke and is considered an appropriate neuroprotective therapy for ischemic stroke. Evidence indicates that NBHO plays a neuroprotective role through different mechanisms in acute ischemic stroke. Recent studies have also reported that combinations with other drug therapies can enhance the efficacy of NBHO in ischemic stroke. Here, we aimed to provide a summary of the potential mechanisms underlying the use of NBHO in ischemic stroke and an overview of the benefits of NBHO in ischemic stroke.

Methods

We screened 83 articles on PubMed and other websites. A quick review was conducted, including clinical trials, animal trials, and reviews of studies in the field of NBHO treatment published before July 1, 2023. The results were described and synthesized, and the bias risk and evidence quality of all included studies were assessed.

Results

The results were divided into four categories: the mechanism of NBHO, animal and clinical trials of NBHO, the clinical application and prospects of NBHO, and adverse reactions of NBHO.

Conclusion

NBHO is a simple, non-invasive therapy that may be delivered early after stroke onset, with promising potential for the treatment of acute ischemic stroke. However, the optimal therapeutic regimen remains uncertain. Further studies are needed to confirm its efficacy and safety.

Characterization of withanolides and bacoside A-loaded proniosomes: effect on oxidative stress and survival under hypergravity in rodent model

OBJECTIVE

This work provides characterization of withanolides and bacoside A proniosomes, and evaluating their potency in rat model for combating oxidative stress-induced blood-brain barrier (BBB) damage and their survival under hypergravity.

SIGNIFICANCE

The delivery system was aimed for sustained drug release in plasma and brain, which could improve their efficiency and provide a therapeutic approach to combat oxidative damage and restore BBB integrity.

METHODS

Proniosomes were prepared using withanolides extracted from the roots of W. somnifera and bacoside A derived from the leaf extract of B. monnieri by thin film hydration technique. In vitro release of withanolides and bacoside A from the proniosomes was studied. In vivo experiments were conducted in Wistar Albino rat model to evaluate the efficacy of drug-loaded proniosomes in improving the antioxidant activity in plasma and brain, restoring BBB integrity and combating hypergravity conditions.

RESULTS

The withanolides and bacoside A-loaded proniosomes showed slow and sustained release of just 62.0 ± 2.87 and 62.9 ± 3.41%, respectively, in 9 h period against the release of 98-99% for the extracts that served as control. Trials conducted in vivo revealed a significant (p < .05) increase in the activity of antioxidant enzymes in both plasma and brain. Also, minimal extravasation of Evans blue dye into the brain (15 ± 0.03 and 16 ± 0.03 ng/g in treated groups against 110 ± 0.01 ng/g in control) of the rats fed with drug-loaded proniosomes was indicative of minimal damage to BBB. Rats fed with drug-loaded proniosomes survived to the extent of 75-83.3% against simulated hypergravity as compared to the control group in which only 50% survived.

CONCLUSION

Proniosomes provided sustained release of drugs, which helped to protect BBB integrity, thereby combating hypergravity.

Effect of Sertoli Cell Transplant and Rapamycin Pretreatment on Middle Cerebral Artery Occlusion-Induced Brain Ischemia in a Rat Model

OBJECTIVES

Stroke exacts a heavy toll on death and disability worldwide. In animal studies, cell transplant has shown a positive effect by inducing neurogenesis, angiogenesis, and modulating inflammation. Cell transplant therapy could provide researchers with new strategies for treating stroke. The mechanistic target of rapamycin is a central signaling pathway for coordination and control; the administration of rapamycin, a key modulator of this pathway, could be a new therapeutic approach in neurological disorders.

MATERIALS AND METHODS

Adult rats were grouped into 5 main groups: control, sham, rapamycin receiving, Sertoli cell receiving, and rapamycin plus Sertoli cell receiving groups. Sertoli cells were taken from another rat tissue and injected into the right striatum region. After 5 days, ischemic induction was performed, and rapamycin injection (300 mg/kg) was performed 1 hour before surgery. After 24 hours, some regions of the brain, including the cortex, striatum, and piriform cortex-amygdala, were isolated for evaluation.

RESULTS

Our results showed that infarct volume, brain edema, and blood-brain barrier permeability assessments were significantly reduced in some areas of the brain in rats that received rapamycin plus Sertoli cells compared with results shown in the control group.

CONCLUSIONS

Pretreatment with Sertoli cell transplant plus rapamycin injection may enhance neural survival during ischemia through increased glial cell-derived neurotrophic factor and vascular endothelial growth factor, inhibiting the mechanistic target of rapamycin pathway and increasing autophagy performance.

Neuroprotective Effects of Normobaric Hyperoxia and Transplantation of Encapsulated Choroid Plexus Epithelial Cells on The Focal Brain Ischemia

Objective

Choroid plexus epithelial cells (CPECs) have the epithelial characteristic, produce cerebrospinal fluid, contribute to the detoxification process in the central nervous system (CNS), and are responsible for the synthesis and release of many nerve growth factors. On the other hand, studies suggest that normobaric hyperoxia (HO) by induction of ischemic tolerance (IT) can protect against brain damage and neurological diseases. We examined the effect of combination therapy of encapsulated CPECs and HO to protect against ischemic brain injury.

Materials and Methods

In this experimental study, six groups of adult male Wistar rats were randomly organized: sham, room air (RA)+middle cerebral artery occlusion (MCAO), HO+MCAO, RA+MCAO+encapsulated CPECs, HO+MCAO+encapsulated CPECs, RA+MCAO+empty capsules. RA/HO were pretreatment. The CPECs were isolated from the brain of neonatal Wistar rats, cultured, and encapsulated. Then microencapsulated CPECs were transplanted in the neck of the animal immediately after the onset of reperfusion in adult rats that had been exposed to 60 minutes MCAO. After 23 hours of reperfusion, the neurologic deficit score (NDS) was assessed. Next, rats were killed, and brains were isolated for measuring brain infarction volume, blood-brain barrier (BBB) permeability, edema, the activity of superoxide dismutase (SOD), and catalase (CAT) and also, the level of malondialdehyde (MDA).

Results

Our results showed that NDS decreased equally in HO+MCAO, RA+MCAO+encapsulated CPECs, and HO+MCAO+encapsulated CPECs groups. Brain infarction volume decreased up 79%, BBB stability increased, edema decreased, SOD and CAT activities increased, and MDA decreased in the combination group of HO and transplantation of encapsulated CPECs in the ischemic brain as compared with when HO or transplantation of encapsulated CPECs was applied alone.

Conclusion

The combination of HO and transplantation of encapsulated CPECs for stroke in rats was more effective than the other treatments, and it can be taken into account as a promising treatment for ischemic stroke.

The Effect of Allograft Transplantation of Sertoli Cell on Expression of NF-кB, Bax Proteins, and Ischemic Tolerance in Rats with Focal Cerebral Ischemia

One of the newest methods to reduce cerebral ischemia damages is cell therapy. The aim of this study is to evaluate the effect of Sertoli cell transplantation on ischemia-induced injuries in animal models of stroke. Rats were divided into four groups: transplant+ischemia, ischemia, sham, and control. Sertoli cells were separated from the other testis of rats and cultured. Unilateral Sertoli cell transplantation was performed in the right striatum by using stereotaxic surgery. For induction of brain ischemia, middle cerebral artery occlusion surgery was used 14 days after transplantation. By using western blotting method, expression of nuclear factor kappa (NF-кB) and Bax were evaluated. In this study, a remarkable decrease in neurological deficits, infection, blood-brain barrier permeability, and brain edema was observed in the cell transplant recipient group in comparison with the ischemia group. Probably, a reduction in inflammation (NF-кB factor) and apoptosis (Bax) following injection of Sertoli cells result in amelioration of ischemic damages induced by MCAO surgery.

Evaluating the effect of transplanting umbilical cord matrix stem cells on ischemic tolerance in an animal model of stroke

OBJECTIVE

Stroke, a cerebrovascular disease, has been introduced as the second cause of death and physical disability in the world. Recently, cell-based therapy has been considered by the scientific community as a promising strategy for reducing ischemic damages. The stem cells of the umbilical cord release growth and neurotrophic factors. The remarkable properties of these cells are the reason why they were selected as a potential candidate in the present research.

METHODS

In this study, the impact of transplanting umbilical cord stem cells on injuries resulting from ischemia was investigated. The male rats were categorized into three major. Using stereotaxic surgery, stem cells were injected to the right striatum of the brain. One week after transplantation, cerebral ischemic induction surgery was performed. The rats in the transplantation + ischemia group were separately divided into distinct sub-groups to explore the score of the neurological deficits, infarction volume, integrity of the blood-brain barrier, and brain edema.

RESULTS

In this study, a significant decrease was observed in the neurological deficits of the transplantation + ischemia group compared with those of the control group. Similarly, the volume of infarction, the permeability of the blood-brain barrier, and edema were significantly reduced in the transplantation + ischemia group in comparison with those of the control group.

CONCLUSION

The pretreatment of the transplanted umbilical cord stem cells in the striatum of ischemic rats possibly leads to restorative events, exerting a decreasing effect on cell death. Subsequently, these events may improve the motor ability and reduce ischemic injuries.

Mangiferin ameliorates collateral neuropathy in tBHP induced apoptotic nephropathy by inflammation mediated kidney to brain crosstalk

The kidneys and brain share similarities in anatomy and vaso-regulation and exhibit clinical interactions in various diseases. To investigate the probable mechanism of kidney to brain crosstalk, we developed an in vivo model of renal injury in mice through intoxication with the oxidative stress inducer, tBHP. Proteinuria, abnormalities in the renal tubules and KIM1 activation were found in tBHP intoxicated animals. Due to this renal pathophysiology, various pro-inflammatory molecules (TNF-α, IL-1β, IL-6, ICAM-1, VCAM-1) especially TNF-α, entered into the brain from kidneys, triggering cerebral inflammatory cascades leading to behavioral anomalies in association with membrane lipid peroxidation, BBB disruption and brain morphological alterations. Moreover, increased levels of reactive oxygen species, decreased antioxidant enzyme activity and an altered GSH/GSSG ratio were found in both these organs. Here, we introduced mangiferin as a protective molecule because of its anti-inflammatory and antioxidant properties. Mangiferin via inhibition of apoptosis and activation of the PI3K/Akt pathway protected the kidneys. It restored the deleterious phenomena in the damaged brain by downregulating the JNK and p38MAPK mediated pro-apoptotic cascade and activating the intracellular antioxidant thioredoxin, thereby protecting against tBHP induced nephropathy mediated neuropathophysiology.

Effect of intravenous injection of antagomiR-1 on brain ischemia

Stroke is one of the leading causes of death in the world, but the underlying molecular mechanism of this disease remains elusive, thus it will be great challenges to finding appropriate protection. MicroRNAs are short, single-stranded, non-coding RNAs and recent studies have shown that they are aberrantly expressed in ischemic condition. Due to the fact that miR-1 has harmful effects on neural damages during brain ischemia, limited miR-1 has been proven to be protective in middle cerebral artery occlusion (MCAO). Here, the possible positive effect of intravenous injection of antagomiR-1 as a post-ischemic treatment on neurological deficits, infarct volume, brain edema and blood-brain barrier (BBB) permeability was evaluated. The rats were divided randomly into three experimental groups, each with 21 animals. MCAO surgery was performed on all groups and one hour later, 0.1 ml normal saline, 0.1 ml rapamycin and 300 pmol/g miR-1 antagomir (soluble in 0.1 ml normal saline), were injected intravenously into control, positive control and treatment group, respectively. After 24 h, neurologic deficits score, infarct volume, brain edema and BBB permeability were measured. The results indicated that post-treatment with miR-1 antagomir significantly improved neurological deficits and reduced infarction volume, brain edema, and BBB permeability. These data proved that there is a positive effects of antagomiR-1 on ischemic neuronal injury and neurological impairment. Due to the fact that microRNAs are able to protect the brain, it would be a promising therapeutic approach to stroke treatment.

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.

Intra-cerebral cannabidiol infusion-induced neuroprotection is partly associated with the TNF-α/TNFR1/NF-кB pathway in transient focal cerebral ischaemia

BACKGROUND

Stroke is a neurological disease, which, in addition to high mortality, imposes many financial and mental burdens on families and the society. The main objective of this study was to investigate the effect of cannabidiol (CBD) on one of the major inflammatory pathways in cerebral ischaemia.

METHOD

Using stereotaxic surgery, the cannula was implanted into the right lateral ventricle of rats. CBD (50, 100, and 200 ng/rat; i.c.v.) was administrated for five consecutive days. After pretreatment, the rats were subjected to 60 min of right middle cerebral artery occlusion (MCAO). After 24 h, neurological deficits score, infarct volume, brain oedema, and blood-brain barrier (BBB) permeability in total, core, and penumbra areas were assessed. The expression of tumour necrosis factor alfa (TNF-α), tumour necrosis factor receptor 1 (TNFR1), and nuclear factor-kappa B (NF-кB) in the mentioned regions was also studied.

RESULTS

Administration of CBD (100 and 200 ng/rat) caused a significant reduction in infarction, brain oedema, and BBB permeability compared with the vehicle-received group. Down-regulation of TNF-α, TNFR1, and NF-кB expression was also observed by CBD.

CONCLUSION

The results achieved in this study support the idea that CBD has a cerebroprotective effect (partly through suppression of TNF-α, TNFR1, and NF-кB) on ischaemic injury.

ABBREVIATIONS

CBD, cannabidiol; ANOVA, analysis of variance; PVDF, polyvinylidene difluoride; SDS-PAGE, sodium dodecyl sulphate polyacrylamide gel electrophoresis; SEM, standard error of mean.

Twenty-Four-Hour Real-Time Continuous Monitoring of Cerebral Edema in Rabbits Based on a Noninvasive and Noncontact System of Magnetic Induction

Cerebral edema is a common disease, secondary to craniocerebral injury, and real-time continuous monitoring of cerebral edema is crucial for treating patients after traumatic brain injury. This work established a noninvasive and noncontact system by monitoring the magnetic induction phase shift (MIPS) which is associated with brain tissue conductivity. Sixteen rabbits (experimental group n = 10, control group, n = 6) were used to perform a 24 h MIPS and intracranial pressure (ICP) simultaneously monitored experimental study. For the experimental group, after the establishment of epidural freeze-induced cerebral edema models, the MIPS presented a downward trend within 24 h, with a change magnitude of −13.1121 ± 2.3953°; the ICP presented an upward trend within 24 h, with a change magnitude of 12–41 mmHg. The ICP was negatively correlated with the MIPS. In the control group, the MIPS change amplitude was −0.87795 ± 1.5146 without obvious changes; the ICP fluctuated only slightly at the initial value of 12 mmHg. MIPS had a more sensitive performance than ICP in the early stage of cerebral edema. These results showed that this system is basically capable of monitoring gradual increases in the cerebral edema solution volume. To some extent, the MIPS has the potential to reflect the ICP changes.

Cellular Preoxygenation Partially Attenuates the Antitumoral Effect of Cisplatin despite Highly Protective Effects on Renal Epithelial Cells

Our previous in vitro studies demonstrated that oxygen pretreatment significantly protects human embryonic renal tubular cell against acute cisplatin- (CP-) induced cytotoxicity. The present study was designed to investigate whether this protective effect is associated with decreasing therapeutic effects of cisplatin on malignant cells. For this purpose, cultured human embryonic kidney epithelial-like (AD293), cervical carcinoma epithelial-like (Hela), and ovarian adenocarcinoma epithelial-like (OVCAR-3) cells were subjected to either 2-hour pretreatment with oxygen (≥90%) or normal air and then to a previously determined 50% lethal dose of cisplatin for 24 hours. Cellular viability was evaluated via MTT and Neutral Red assays. Also, activated caspase-3 and Bax/Bcl-2 ratio, as the biochemical markers of cell apoptosis, were determined using immunoblotting. The hyperoxic preexposure protocol significantly protects renal AD293 cells against cisplatin-induced toxicity. Oxygen pretreatment also partially attenuated the cisplatin-induced cytotoxic effects on Hela and OVCAR-3 cells. However, it did not completely protect these cells against the therapeutic cytotoxic effects of cisplatin. In summary, the protective methods for reducing cisplatin nephrotoxic side effects like oxygen pretreatment might be associated with concurrent reduction of the therapeutic cytotoxic effects of cisplatin on malignant cells like cervical carcinoma (Hela) and ovarian adenocarcinoma (OVCAR-3) cells.

Normobaric oxygen treatment in acute ischemic stroke: a clinical perspective

Acute ischemic stroke is a common and serious neurological disease. Oxygen therapy has been shown to increase oxygen supply to ischemic tissues and improve outcomes after cerebral ischemia/reperfusion. Normobaric hyperoxia (NBO), an easily applicable and non-invasive method, shows protective effects on acute ischemic stroke animals and patients in pilot studies. However, many critical scientific questions are still unclear, such as the therapeutic time window of NBO, the long-term effects and the benefits of NBO in large clinic trials. In this article, we review the current literatures on NBO treatment of acute ischemic stroke in preclinical and clinical studies and try to analyze and identify the key gaps or unknowns in our understanding about NBO. Based on these analyses, we provide suggestions for future studies.

Hyperbaric oxygen and hyperbaric air preconditioning induces ischemic tolerance to transient forebrain ischemia in the gerbil

Ischemic preconditioning with sublethal stress triggers defensive mechanisms against ischemic brain damage; however, such manipulations are potentially dangerous and, therefore, safe stimuli have been sought. Hyperoxia preconditioning by administration of hyperbaric (HBO) or normobaric oxygen (NBO) may have neuroprotective potential. The aim of this study was to determine whether preconditioning with HBO and air (HBA) applied at 2.5 absolute pressure (ATA) or NBO preconditioning induces ischemic tolerance in the brain of gerbils subjected to 3min transient cerebral ischemia. Neuronal cell survival, changes in brain temperature, the generation of factors involved in neurodegeneration and basic behavior in nest building were all tested. Hyperoxic preconditioning prevented ischemia-induced neuronal cell loss, reduced the number of TUNEL positive cells in the CA1 region of the hippocampus and improved the nest building process compared to untreated ischemic animals. Preconditioning also suppressed the production of reactive oxygen species and increased Bax expression normally observed after an ischemic episode. Only HBO preconditioning inhibited ischemia-evoked increases in brain temperature. Our results show that hyperoxic preconditioning results in induction of ischemic tolerance and prevents ischemia-induced neuronal damage in the gerbil brain. Pressurized air preconditioning was as effective as HBO or NBO preconditioning in providing neuroprotection. The observed neuroprotection probably results from mild oxidative stress evoked by increased brain tissue oxidation and activation of antioxidant and antiapoptotic defenses.

Hyperoxia-induced preconditioning against renal ischemic injury is mediated by reactive oxygen species but not related to heat shock proteins 70 and 32

OBJECTIVE

Pre-exposure of rats to normobaric hyperoxia (O2 ≥ 95%) may induce late preconditioning against renal ischemia-reperfusion (IR) injury. In this study we investigated probable mechanisms of IR injury such as the role of reactive oxygen species (ROS), renal antioxidant agents, and heat shock proteins (HSP) 32 and 70 during delayed hyperoxia-preconditioning (HO).

METHODS

Fifty-two rats were divided into 7 groups: (A) IR, (B) HO + IR, (C) mercaptopropionyl glycine (MPG) + HO + IR, (D) MPG + IR, (E) HO + sham, (F) MPG + sham, and (G) sham. Rats in the following study groups (group B, C and E) were kept in a normobaric hyperoxic environment for 4 h/day for 6 consecutive days, after which they were subjected to 40 minutes of ischemia; animals in the control group (group A, D, F, and G) were kept in a normoxic cage. At the end of the preconditioning period, 24 hours of reperfusion was performed. Renal function was assessed by measuring serum creatinine (Cr), blood urea nitrogen (BUN), and creatinine clearance (CLCr). Induction of the antioxidant system was evaluated by measuring renal catalase (CAT) and superoxide dismutase (SOD) activities and glutathione (GSH) and malondialdehyde (MDA) content. The role of ROS was investigated by use of MPG (a ROS scavenger). HSP32 & 70 mRNA and protein also were determined.

RESULTS

The hyperoxia-preconditioned IR group (B) had a lower plasma Cr and BUN and greater CLCr compared with the IR group (A) (P ≤ .016). Administration of MPG led to an increase in plasma Cr and BUN and a decrease in CLCr in group C compared with the hyperoxia-preconditioned group B (P ≤ .004). The hyperoxia-preconditioned IR group had a greater CAT activity and GSH level compared with the IR group A (P ≤ .007), whereas the administration of MPG did not change the GSH level but led to a decrease in CAT activity in group D compared with group B (P < .001). SOD activity did not change in hyperoxia-preconditioned ischemic rats compared with ischemic rats. Hyperoxia preconditioning and MPG administration in ischemic animals did not result in any considerable change in MDA level compared with the IR group A. Also, there were no clinically relevant differences in HSP32 & 70 mRNA and protein between all groups.

CONCLUSION

The present study demonstrates that repeated pre-exposure to hyperoxia can decrease subsequent renal IR damage in this rat model of renal ischemia. Free radical production after hyperoxia appears to play a pivotal role in the hyperoxia-induced renal protection independent of HSP level. Antioxidant enzyme activities and especially catalase seem to be implicated in this renal protective mechanism.

Arjunolic acid, a pentacyclic triterpenoidal saponin of Terminalia arjuna bark protects neurons from oxidative stress associated damage in focal cerebral ischemia and reperfusion

BACKGROUND

Arjunolic acid (AA), a pentacyclic triterpenoidal saponin of Terminalia arjuna is well recognized for its antioxidant properties. We proposed to evaluate its antioxidant potential against focal cerebral ischemia reperfusion (I/R) injury in rats subjected to middle cerebral artery occlusion (MCAO).

METHODS

In the present study, rats were randomly divided into a sham, MCAO, AA (10 and 20mg/kg) treated groups. Rats received their respective treatment orally by gavage for 7 days prior to MCAO. Rats were anaesthetized with ketamine (100mg/kg), xylazine (10mg/kg) and subjected to 2h occlusion and 22h reperfusion. Neurological deficit, brain water content and oxidative stress markers were measured after 22h of reperfusion.

RESULTS

Rats pretreated with AA showed significantly reduced neurological deficit score, infarct size. AA prevented neuronal damage induced by I/R by regulating the levels of malondialdehyde (MDA), reduced glutathione (GSH), nitric oxide (NO), protein carbonyl content and mitochondria generated reactive oxygen species. In addition, it also controlled the enzyme activities of Na(+)-K(+) ATPase, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione reductase (GR).

CONCLUSIONS

Pre-treatment with AA effectively prevented the cerebral I/R induced oxidative damage by virtue of its antioxidant potential. These results indicate that supplementation of AA may be beneficial in stroke prone population.

Inhibition of brain swelling after ischemia-reperfusion by β-adrenergic antagonists: correlation with increased K+ and decreased Ca2+ concentrations in extracellular fluid

Infarct size and brain edema following ischemia/reperfusion are reduced by inhibitors of the Na⁺, K⁺, 2Cl⁻, and water cotransporter NKCC1 and by β₁-adrenoceptor antagonists. NKCC1 is a secondary active transporter, mainly localized in astrocytes, driven by transmembrane Na⁺/K⁺ gradients generated by the Na⁺,K⁺-ATPase. The astrocytic Na⁺,K⁺-ATPase is stimulated by small increases in extracellular K⁺ concentration and by the β-adrenergic agonist isoproterenol. Larger K⁺ increases, as occurring during ischemia, also stimulate NKCC1, creating cell swelling. This study showed no edema after 3 hr medial cerebral artery occlusion but pronounced edema after 8 hr reperfusion. The edema was abolished by inhibitors of specifically β₁-adrenergic pathways, indicating failure of K⁺-mediated, but not β₁-adrenoceptor-mediated, stimulation of Na⁺,K⁺-ATPase/NKCC1 transport during reoxygenation. Ninety percent reduction of extracellular Ca²⁺ concentration occurs in ischemia. Ca²⁺ omission abolished K⁺ uptake in normoxic cultures of astrocytes after addition of 5 mM KCl. A large decrease in ouabain potency on K⁺ uptake in cultured astrocytes was also demonstrated in Ca²⁺-depleted media, and endogenous ouabains are needed for astrocytic K⁺ uptake. Thus, among the ionic changes induced by ischemia, the decrease in extracellular Ca²⁺ causes failure of the high-K⁺-stimulated Na⁺,K⁺-ATPase/NKCC1 ion/water uptake, making β₁-adrenergic activation the only stimulus and its inhibition effective against edema.

Neuroprotective effect of pretreatment with Lavandula officinalis ethanolic extract on blood-brain barrier permeability in a rat stroke model

OBJECTIVE

To evaluate the protective effect of Lavandula officinalis (L. officinalis) extract against blood-brain barrier (BBB) permeability and its possible mechanisms in an experimental model of stroke.

METHODS

Focal cerebral ischemia was induced by the transient occlusion of the middle cerebral artery for 1 h in rats. Lavender extract (100, 200 mg/kg i.p.) was injected for 20 consecutive days. BBB permeability and oxidative stress biomarkers were evaluated using standard methods.

RESULTS

The results of this study showed that L. officinalis ethanolic extract significantly reduced the BBB permeability in experimental groups when compared with ischemia group. The lavender extract significantly reduced malondialdehyde levels of plasma and brain tissue in intact group when compared with control group.

CONCLUSIONS

L. officinalis extract reduced blood brain barrier permeability and alleviated neurological function in rats, and the mechanism may be related to augmentation in endogenous antioxidant defense and inhibition of oxidative stress in the rat brain.

Neuroprotective effect of punicalagin against cerebral ischemia reperfusion-induced oxidative brain injury in rats

BACKGROUND

Punicalagin (PG) is a hydrolyzable polyphenol in Punica granatum. It has been previously reported that it has a protective effect against hypoxia-induced ischemia brain injury. It is a potent antioxidant. The present study is aimed to evaluate the antioxidant potential of PG against focal cerebral ischemia-reperfusion injury in rats subjected to middle cerebral artery occlusion (MCAO).

METHODS

Rats were randomly divided into sham, MCAO, PG-treated groups. PG (15 and 30 mg/kg) vehicle was administered orally for 7 days before MCAO. Rats were anesthetized with ketamine (100 mg/kg), xylazine (10 mg/kg), and subjected to 2 hours occlusion, and 22 hours reperfusion. Neurologic deficit, brain water content (BWC), histopathology changes, and oxidative stress markers were evaluated after 22 hours of reperfusion. In comparison with MCAO model group, treatment with PG significantly reduced the neurologic deficit scores and BWC.

RESULTS

PG-attenuated neuronal damage occurred by downregulating the levels of malondialdehyde, sodium-potassium adenosine triphosphatase activity, nitric oxide, protein carbonyl content, and mitochondria-generated reactive oxygen species and upregulating the superoxide dismutase, catalase, glutathione peroxidase, reduced glutathione, glutathione reductase activities.

CONCLUSIONS

Taken together, these results suggested that supplementation of PG treatment effectively ameliorates the cerebral ischemia/reperfusion induced oxidative damage by virtue of its antioxidant potential.

Normobaric oxygen for cerebral ischemic injury

Oxygen inhalation has been shown to increase oxygen supply to tissues after cerebral ischemia/ reperfusion injury, protecting injured neural cells. However, hyperbaric oxygen may aggravate oxidative stress. By contrast, normobaric oxygen has the rapid and non-invasive characteristics and may have therapeutic effects on ischemic/hypoxic disease. Rats inhaled normobaric oxygen (95% O2) for 6 consecutive days, and then a rat model of focal cerebral ischemia was established. Nissl and 2,3,5-triphenyltetrazolium chloride (TTC) staining revealed that normobaric oxygen pretreatment improved neurological deficits and reduced infarct volume. Immunohistochemical staining and western blot assay revealed that the expression of hypoxia-inducible factor-1α, Notch-1, vascular endothelial growth factor and erythropoietin were increased. Behavioral studies also verified that neurological deficit scores increased. The hypoxia-inducible factor inhibitor 2-methoxyestradiol treatment at 1 hour before administration of normobaric oxygen could suppress the protective effect of normobaric oxygen. Given these observations, normobaric oxygen pretreatment may alleviate cerebral ischemic injury via the hypoxia-inducible factor signal pathway.

Effects of pretreatment with single-dose or intermittent oxygen on Cisplatin-induced nephrotoxicity in rats

Background:

Renal injury is the main side effect of cisplatin (CP), an anticancer drug. It has been shown that pretreatment with single-dose oxygen (0.5 to six hours) could reduce CP-induced renal toxicity in rats.

Objectives:

The present study aimed to compare the effects of pretreatment with single-dose and intermittent O₂ on CP-induced nephrotoxicity.

Materials and Methods:

Adult male rats were allocated to seven groups (eight rats in each group). The rats were kept in normal air or hyperoxic environment (O₂, 80%) for either a single six-hour period or intermittent six hours per day for seven days and then were subjected to intraperitoneal injection of saline or CP (5 mg/kg) at 48 hours, 72 hours, or seven days after exposure to O₂. Three days after CP (or Saline) injection, renal function tests, renal tissue injury scores, and cleaved Caspase-3 and Bax/Bcl-2 genes expression (as markers of renal cell apoptosis) were assessed.

Results:

Treatment with the 6-hour single-dose O₂ reduced renal injury significantly when CP was administrated 48 hours after O₂ pretreatment. Pretreatment with intermittent seven days of six hours per day had no protective effects and even relatively worsened renal injury when CP was injected 48 hours or 72 hours after the last session of O₂ pretreatment. The beneficial effects of pretreatment with O₂ on renal structure and function were seen if CP was administrates seven days after pretreatment with intermittent O₂.

Conclusions:

The pattern of pretreatment with O₂ could change this potential and highly protective strategy against CP-induced nephropathy to an ineffective or even mildly deteriorating one. Therefore, O₂ administration before CP injection to patients with cancer, for therapeutic purposes or as a preconditioning approach, should be performed and investigated with caution until exact effects of different protocols has been determined in human.

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.

Xiao-Xu-Ming Decoction Protects against Blood-Brain Barrier Disruption and Neurological Injury Induced by Cerebral Ischemia and Reperfusion in Rats

Xiao-Xu-Ming decoction (XXMD) is an effective prescription in the treatment of ischemic stroke, but the mechanisms involved are not well known. In the present study, 120 male Sprague-Dawley rats were randomly divided into 5 groups: sham control (sham), ischemia and reperfusion (IR), and IR plus 15, 30, and 60 g/kg/day XXMD. The stroke model was induced by 90 min of middle cerebral artery occlusion followed by reperfusion. The brain lesion areas were evaluated by 2,3,5-triphenyltetrazolium chloride staining, and neurological deficits were observed at different time points after reperfusion. Blood-brain barrier (BBB) disruption was evaluated by assessing brain water content and Evans blue content. Pathological changes in BBB ultrastructure were observed with transmission electron microscopy. MMP-9, -2, and VEGF expression levels were quantitatively determined by western blotting and immunohistochemistry. We found that XXMD (60 g/kg/day) treatment reduced cerebral infarct area, improved behavioral function, and attenuated ultrastructure damage and permeability of BBB following ischemia and reperfusion. Moreover, XXMD downregulated the expression levels of MMP-9, -2, and VEGF. These findings indicate that XXMD alleviates BBB disruption and cerebral ischemic injury, which may be achieved by inhibiting the expression of MMP-9, -2, and VEGF.

Enriched environment preconditioning induced brain ischemic tolerance without reducing infarct volume and edema: the possible role of enrichment-related physical activity increase

External stimuli, including environmental enrichment (EE) and physical activity, have been shown to significantly facilitate recovery from brain injury. However, whether EE can be used as a preconditioning method to induce cerebral ischemic tolerance has never been investigated. Furthermore, whether, and to what extent, such environmental stimuli regulate physical activity to promote neuroprotection is largely unclear. To examine the neuroprotective effects of pre-ischemic EE (PIEE) and to investigate the relationship between these effects and EE-induced physical activity, we tested neurobehavioral and morphological recovery of rats following transient focal cerebral ischemia. Our study showed that PIEE improved the recovery of motor function, spatial learning and memory without reduction in brain edema or infarct volume. We also found that PIEE robustly increased the level of physical activity of rats that positively correlated with the extent of neurobehavioral recovery. Our results suggest that PIEE may induce brain ischemic tolerance through, at least partially, increasing physical activity.

Effects of hyperoxia exposure on metabolic markers and gene expression in 3T3-L1 adipocytes

Adipose tissue often becomes poorly oxygenated in obese subjects. This feature may provide cellular mechanisms involving chronic inflammation processes such as the release of pro-inflammatory cytokines and macrophage infiltration. In this context, the purpose of the present study was to determine whether a hyperoxia exposure on mature adipocytes may influence the expression of some adipokines and involve favorable changes in specific metabolic variables. Thus, 3T3-L1 adipocytes (14 days differentiated) were treated with 95 % oxygen for 24 h. Cell viability, intra and extracellular reactive oxygen species (ROS) content, glucose uptake, as well as lactate and glycerol concentrations were measured in the culture media. Also, mRNA levels of hypoxia-inducible factor (HIF)-1α, leptin, interleukin (IL)-6, monocyte chemotactic protein (MCP)-1, peroxisome proliferator-activated receptor (PPAR)-γ, adiponectin, and angiopoietin-related protein (ANGPTL)4 were analyzed. Hyperoxia treatment increased intra and extracellular ROS content, reduced glucose uptake and lactate release and increased glycerol release. Additionally, a higher oxygen tension led to an upregulation of the expression of IL-6, MCP-1, and PPAR-γ, while ANGPTL4 was downregulated in the hyperoxia group with respect to control. The present data shows that hyperoxia treatment seems to produce an inflammatory response due to the release of ROS and the upregulation of pro-inflammatory adipokines, such as IL-6 and MCP-1. On the other hand, hyperoxia may have an indirect effect on insulin sensitivity due to the upregulation of PPAR-γ signaling as well as a possible modulation of both glucose and lipid metabolic markers. To our knowledge, this is the first study analyzing the effect of hyperoxia in 3T3-L1 adipocytes.

Time course of neuroprotection induced by normobaric hyperoxia in focal cerebral ischemia

BACKGROUND

The purpose of this study was to determine if normobaric hyperoxia (HO) preconditioning offers durable neuroprotection against cerebral ischemia and the role of reactive oxygen species in the ischemic tolerance mechanism.

MATERIALS AND METHODS

Rats were divided into four experimental main groups. First main group which was comprised four subgroups, were exposed to 90% HO for 6 days, 4 hours per day and subjected to 60 minutes of right middle cerebral artery occlusion (MCAO) after 2, 5, 10, and 15 days. Second group acted as control, was exposed to 21% oxygen (RA; room air) in the same chamber, and subjected to 60 minutes of right MCAO. Third main group comprised two subgroups, were exposed to 90% HO for 6 days, 4 hours per day, received normal saline (NS; 2HO+NS) and dimethylthiourea (DT) just before inhaling 90% HO (2HO+DT). Forth main group was exposed to 21% oxygen (2RA) in the same chamber and received normal saline (2RA+NS) and DT just before inhaling 21% oxygen (2RA+DT). Last two main groups were subjected to 60 minutes of right MCAO after 2 days. After 24-hour reperfusion, neurological deficit score (NDS), infarct volume, brain water content, and Evans blue extravasations were assessed in all animals.

RESULTS

First main group compared with the RA group, NDS, infarct volume, Brain water content, and Evans blue extravasations were reduced in 2, 5, and 10 days significantly, whereas there was no difference among groups 2HO+DT, 2RA+DT, and 2RA+NS.

CONCLUSIONS

In the model of transient focal cerebral ischemia, hyperoxia preconditioning induced effective but transient neuroprotective effects.

Ischemic tolerance in the brain: endogenous adaptive machinery against ischemic stress

Although more than 100 drugs have been examined clinically, tissue plasminogen activator remains the only drug approved for the treatment of acute ischemic stroke. Since the discovery of ischemic tolerance, it has been widely recognized that the brain possesses an endogenous protective machinery to protect against ischemic stress. Recent studies have clarified that both the upregulation of neuroprotective signaling and the downregulation of inflammatory or apoptotic pathways are involved equally in the acquisition of ischemic tolerance. The triggering stimuli for ischemic stresses are divided into hypoxic, oxidant/inflammatory, and glutamate stress. Glutamate stress, particularly the synaptic stimulation of the N-methyl-D-aspartate receptor, leads to activation of the cAMP response element-binding protein, which could subsequently induce gene expression of several neuroprotective molecules. Gene reprogramming and metabolic downregulation are intimately involved in ischemic tolerance as well as in hibernation and hypothermia. Micro-RNAs may be a key player for tuning the level of gene expression in ischemic tolerance. Future research should be performed to investigate the most effective combination for brain protection, enhancement of cell survival signaling, and inhibition of the inflammatory or apoptotic pathways.

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.

The neuroprotective effect of olive leaf extract is related to improved blood-brain barrier permeability and brain edema in rat with experimental focal cerebral ischemia

Recent studies suggest that olive extracts suppress inflammation and reduce stress oxidative injury. We sought to extend these observations in an in vivo study of rat cerebral ischemia-reperfusion injury. Four groups, each of 18 Wister rats, were studied. One (control) group received distilled water, while three treatment groups received oral olive leaf extract (50, 75 and 100mg/kg/day respectively). After 30 days, blood lipid profiles were determined, before a 60 min period of middle cerebral artery occlusion (MCAO). After 24h reperfusion, neurological deficit scores, infarct volume, brain edema, and blood-brain barrier permeability were each assessed in subgroups of six animals drawn from each main group. Olive leaf extract reduced the LDL/HDL ratio in doses 50, 75, and 100mg/kg/day in comparison to the control group (P<0.001), and offered cerebroprotection from ischemia-reperfusion. For controls vs. doses of 50mg/kg/day vs. 75 mg/kg/day vs. 100mg/kg/day, attenuated corrected infarct volumes were 209.79 ± 33.05 mm(3) vs. 164.36 ± 13.44 mm(3) vs. 123.06 ± 28.83 mm(3) vs. 94.71 ± 33.03 mm(3); brain water content of the infarcted hemisphere 82.33 ± 0.33% vs. 81.33 ± 0.66% vs. 80.75 ± 0.6% vs. 80.16 ± 0.47%, and blood-brain barrier permeability of the infarcted hemisphere 11.22 ± 2.19 μg/g vs. 9.56 ± 1.74 μg/g vs. 6.99 ± 1.48 μg/g vs. 5.94 ± 1.73 μg/g tissue (P<0.05 and P<0.01 for measures in doses 75 and 100mg/kg/day vs. controls respectively). Oral administration of olive leaf extract reduces infarct volume, brain edema, blood-brain barrier permeability, and improves neurologic deficit scores after transient middle cerebral artery occlusion in rats.

Exercise preconditioning and brain ischemic tolerance

It is well established that physical exercise can exert neuroprotection both in clinical settings and animal experiments. A series of studies have demonstrated that physical exercise may be a promising preconditioning method to induce brain ischemic tolerance through the promotion of angiogenesis, mediation of the inflammatory response, inhibition of glutamate over-activation, protection of the blood brain barrier (BBB) and inhibition of apoptosis. Through these mechanisms, exercise preconditioning may reduce the neural deficits associated with ischemia and the development of brain infarction and thus provide brain ischemic tolerance. An awareness of the benefits of exercise preconditioning may lead more patients to accept exercise therapy in cases of ischemic stroke.

Hyperoxia may be beneficial

The current practice of mechanical ventilation comprises the use of the least inspiratory O2 fraction associated with an arterial O2 tension of 55 to 80 mm Hg or an arterial hemoglobin O2 saturation of 88% to 95%. Early goal-directed therapy for septic shock, however, attempts to balance O2 delivery and demand by optimizing cardiac function and hemoglobin concentration, without making use of hyperoxia. Clearly, it has been well-established for more than a century that long-term exposure to pure O2 results in pulmonary and, under hyperbaric conditions, central nervous O2 toxicity. Nevertheless, several arguments support the use of ventilation with 100% O2 as a supportive measure during the first 12 to 24 hrs of septic shock. In contrast to patients without lung disease undergoing anesthesia, ventilation with 100% O2 does not worsen intrapulmonary shunt under conditions of hyperinflammation, particularly when low tidal volume-high positive end-expiratory pressure ventilation is used. In healthy volunteers and experimental animals, exposure to hyperoxia may cause pulmonary inflammation, enhanced oxidative stress, and tissue apoptosis. This, however, requires long-term exposure or injurious tidal volumes. In contrast, within the timeframe of a perioperative administration, direct O2 toxicity only plays a negligible role. Pure O2 ventilation induces peripheral vasoconstriction and thus may counteract shock-induced hypotension and reduce vasopressor requirements. Furthermore, in experimental animals, a redistribution of cardiac output toward the kidney and the hepato-splanchnic organs was observed. Hyperoxia not only reverses the anesthesia-related impairment of the host defense but also is an antibiotic. In fact, perioperative hyperoxia significantly reduced wound infections, and this effect was directly related to the tissue O2 tension. Therefore, we advocate mechanical ventilation with 100% O2 during the first 12 to 24 hrs of septic shock. However, controlled clinical trials are mandatory to test the safety and efficacy of this approach.

Pre-ischemic treadmill training induces tolerance to brain ischemia: involvement of glutamate and ERK1/2

Physical exercise has been shown to be beneficial in stroke patients and animal stroke models. However, the exact mechanisms underlying this effect are not yet very clear. The present study investigated whether pre-ischemic treadmill training could induce brain ischemic tolerance (BIT) by inhibiting the excessive glutamate release and event-related kinase 1/2 (ERK1/2) activation observed in rats exposed to middle cerebral artery occlusion (MCAO). Sprague–Dawley rats were divided into three groups (n = 12/group): sham surgery without prior exercise, MCAO without prior exercise and MCAO following three weeks of exercise. Pre-MCAO exercise significantly reduced brain infarct size (103.1 ± 6.7 mm³) relative to MCAO without prior exercise (175.9 ± 13.5 mm³). Similarly, pre-MCAO exercise significantly reduced neurological defects (1.83 ± 0.75) relative to MCAO without exercise (3.00 ± 0.63). As expected, MCAO increased levels of phospho-ERK1/2 (69 ± 5%) relative to sham surgery (40 ± 5%), and phospho-ERK1/2 levels were normalized in rats exposed to pre-ischemic treadmill training (52 ± 6%) relative to MCAO without exercise (69% ± 5%). Parallel effects were observed on striatal glutamate overflow. This study suggests that pre-ischemic treadmill training might induce neuroprotection by inhibiting the phospho-ERK1/2 over-activation and reducing excessive glutamate release

Pretreatment with hyperoxia reduces in vivo infarct size and cell death by apoptosis with an early and delayed phase of protection

OBJECTIVE

Exposure to normobaric hyperoxia protects the heart against ischemia-reperfusion injury ex vivo. In the present study, we investigated the effect of the early and late phase of hyperoxia on in vivo myocardial infarction and apoptosis.

METHODS

Rats were exposed to room air preoxygenation (O(2)≥ 95%) followed by regional ischemia (30 min) and 0, 90, 180, and 360 min of reperfusion. Hyperoxic exposure was performed for 120 min either immediately or 24h before coronary occlusion followed by 360-min reperfusion. Infarct size was evaluated by Evans blue/triphenyltetrazolium chloride staining. Apoptosis in the infarcted area was evaluated by terminal deoxy-nucleotidyl transferase-mediated deoxy uridine triphosphate (dUTP) nick end-labeling (TUNEL). Caspase 3 activity was measured by fluorometric enzyme assay, Bcl-2 and Bax protein expression assessed by western blotting and DNA laddering assessed with DNA gel electrophoresis.

RESULTS

The infarct size did not increase with increasing duration of reperfusion. However, apoptosis as evaluated by Bcl-2/Bax ratio, caspase 3 activity, and TUNEL-positive cells increased with increasing time of reperfusion. Both early and delayed pretreatment with hyperoxia reduced infarct size (p = 0.0013, p = 0.046), ameliorated ischemic arrhythmias and increased Bcl-2/Bax ratio (p = 0.015, p = 0.0159). Only hyperoxia immediately before coronary occlusion decreased caspase 3 activity (p = 0.026) and decreased TUNEL-positive staining (p = 0.046) with no visible DNA laddering.

CONCLUSIONS

Detection of myocardial apoptosis increased with prolongation of reperfusion time, as opposed to infarct detection where reperfusion was essential to detect infarction, but the infarct size did not increase with time. Pretreatment with hyperoxia significantly decreased infarct size and apoptotic cell death. Pretreatment, immediately before coronary occlusion, was most cardioprotective.

Normobaric hyperoxia therapy for traumatic brain injury and stroke: a review

Traumatic brain injury (TBI) and acute ischaemic stroke are major causes of mortality and morbidity and there is an urgent demand for new neuroprotective strategies following the translational failure of neuroprotective drug trials. Oxygen therapy--especially normobaric, may offer a simple and effective therapeutic strategy which we review in this paper. Firstly we review mechanisms underlying the therapeutic effects of hyperoxia (both normobaric and hyperbaric) including mitochondrial rescue, stabilisation of intracranial pressure, attenuation of cortical spreading depression and inducing favourable endothelial-leukocyte interactions, all effects of which are postulated to decrease secondary injury. Next we survey studies using hyperbaric oxygen therapy for TBI and stroke, which formed the basis for early studies on normobaric hyperoxia. Thirdly, we present clinical studies of the efficacy of normobaric hyperoxia on TBI and stroke, emphasising their safety, efficacy and practicality. Finally we consider safety concerns and side effects, particularly pulmonary pathology, respiratory failure and theoretical risks in paediatric patients. A neuroprotective role of normobaric hyperoxia is extremely promising and further studies are warranted.

Preconditioning-induced ischemic tolerance: a window into endogenous gearing for cerebroprotection

Ischemic tolerance defines transient resistance to lethal ischemia gained by a prior sublethal noxious stimulus (i.e., preconditioning). This adaptive response is thought to be an evolutionarily conserved defense mechanism, observed in a wide variety of species. Preconditioning confers ischemic tolerance if not in all, in most organ systems, including the heart, kidney, liver, and small intestine. Since the first landmark experimental demonstration of ischemic tolerance in the gerbil brain in early 1990's, basic scientific knowledge on the mechanisms of cerebral ischemic tolerance increased substantially. Various noxious stimuli can precondition the brain, presumably through a common mechanism, genomic reprogramming. Ischemic tolerance occurs in two temporally distinct windows. Early tolerance can be achieved within minutes, but wanes also rapidly, within hours. Delayed tolerance develops in hours and lasts for days. The main mechanism involved in early tolerance is adaptation of membrane receptors, whereas gene activation with subsequent de novo protein synthesis dominates delayed tolerance. Ischemic preconditioning is associated with robust cerebroprotection in animals. In humans, transient ischemic attacks may be the clinical correlate of preconditioning leading to ischemic tolerance. Mimicking the mechanisms of this unique endogenous protection process is therefore a potential strategy for stroke prevention. Perhaps new remedies for stroke are very close, right in our cells.

Hyperoxia-induced protection against rat's renal ischemic damage: relation to oxygen exposure time

BACKGROUND

Pre-exposure to hyperoxic gas (>or= 95%) has been shown to protect the heart and central nervous system from ischemia-reperfusion injury. In the present study, we investigated whether oxygen pretreatment induces delayed renal protection in rats. The possible role of some renal antioxidant agents was also investigated.

MATERIALS AND METHODS

Adult male Wistar rats were kept in a hyperoxic (HO) (>or= 95% O(2)) environment for 0.5 h, 1 h, 2 h, 3 h, 6 h, and 2 h/day for three consecutive days and 4 h/day for six consecutive days, and control group (IR) animals were kept in the cage with no HO, one day before subjecting their kidney to 40 minutes of ischemia and 24h of reperfusion. Renal function was assessed by comparing plasma creatinine (Cr), blood urea nitrogen (BUN), creatinine clearance (CLCr), and fractional excretion of sodium (FENa%). Histopathological injury score was also determined according to the Jablonski method. To examine the antioxidant system induction by hyperoxia, we measured renal catalase and superoxide dismutase activity, and renal glutathione and malondialdehyde content.

RESULTS

Our data demonstrated that only in 4 h/day HO for six consecutive days, the renal function tests (Cr, CLCr, BUN, and FENa%) and Jablonski histological injury were better than control group (p < 0.05). The beneficial effect of oxygen pretreatment in this group was associated with increased renal catalase activity compared with those obtained from control group (p < 0.05).

CONCLUSION

The present study demonstrates that repeated exposure to hyperoxic (>or= 95% O(2)) environment can reduce subsequent rat's renal ischemia-reperfusion damage. Induction of endogenous antioxidant system may partially explain this beneficial effect of hyperoxic preconditioning.