The hyperbaric oxygen preconditioning-induced brain protection is mediated by a reduction of early apoptosis after transient global cerebral ischemia

The effect of preconditioning agents on cardiotoxicity and neurotoxicity of carbon monoxide poisoning in animal studies: a systematic review

BACKGROUND

Carbon monoxide (CO) poisoning is a common intoxication and many people die yearly due to CO poisoning and preconditioning agents attenuate brain and cardiac injury caused by intoxication. It is critical to fully understand the efficacy of new methods to directly target the toxic effect of CO, such as conditioning agents, which are currently under development. This study aims to systematically investigate current evidence from animal experiments and the effects of administration preconditions in acute and late phases after CO poisoning on cardiotoxicity and neurotoxicity.

METHODS

Four databases (PubMed, Embase, Scopus, and Web of Science) were systematically searched without language restrictions, and hand searching was conducted until November 2021. We included studies that compare preconditioning agents with the control group after CO poisoning in animals. The SYRCLE RoB tool was used for risk of bias assessments.

RESULTS

Thirty-seven studies were included in the study. Erythropoietin, granulocyte colony-stimulating factor (GCSF), hydrogen-rich saline, and N-butylphthalide (NBP) were found to have positive effects on reducing neurotoxicity and cardiotoxicity. As other preconditions have fewer studies, no valuable results can be deduced. Most of the studies were unclear for sources of bias.

DISCUSSION

Administration of the examined preconditioning agents including NBP, hydrogen-rich saline, and GCSF in acute and late phases could attenuate neurotoxicity and cardiotoxicity of CO poisoned animals. For a better understanding of mechanisms and activities, and finding new and effective preconditioning agents, further preclinical and clinical studies should be performed to analyze the effects of preconditioning agents.

An overview of hyperbaric oxygen preconditioning against ischemic stroke

Ischemic stroke (IS) has become the second leading cause of morbidity and mortality worldwide, and the prevention of IS should be given high priority. Recent studies have indicated that hyperbaric oxygen preconditioning (HBO-PC) may be a protective nonpharmacological method, but its underlying mechanisms remain poorly defined. This study comprehensively reviewed the pathophysiology of IS and revealed the underlying mechanism of HBO-PC in protection against IS. The preventive effects of HBO-PC against IS may include inducing antioxidant, anti-inflammation, and anti-apoptosis capacity; activating autophagy and immune responses; upregulating heat shock proteins, hypoxia-inducible factor-1, and erythropoietin; and exerting protective effects upon the blood-brain barrier. In addition, HBO-PC may be considered a safe and effective method to prevent IS in combination with stem cell therapy. Although the benefits of HBO-PC on IS have been widely observed in recent research, the implementation of this technique is still controversial due to regimen differences. Transferring the results to clinical application needs to be taken carefully, and screening for the optimal regimen would be a daunting task. In addition, whether we should prescribe an individualized preconditioning regimen to each stroke patient needs further exploration.

Proteasome and Neuroprotective Effect of Hyperbaric Oxygen Preconditioning in Experimental Global Cerebral Ischemia in Rats

Objectives

We investigated the involvement of the proteasome in the mechanism of preconditioning with hyperbaric oxygen (HBO-PC).

Methods

The experiments were performed on male Wistar rats subjected to a transient global cerebral ischemia of 5 min duration (2-vessel occlusion model) and preconditioned or not with HBO for 5 preceding days (1 h HBO at 2.5 atmosphere absolute [ATA] daily). In subgroups of preconditioned rats, the proteasome inhibitor MG132 was administered 30 min prior to each preconditioning session. Twenty-four hours and 7 days post-ischemia, after neurobehavioral assessment, the brains were collected and evaluated for morphological changes and quantitative immunohistochemistry of cell markers and apoptosis-related proteins.

Results

We observed reduced damage of CA1 pyramidal cells in the HBO preconditioned group only at 7 days post-ischemia. However, both at early (24 h) and later (7 days) time points, HBO-PC enhanced the tissue expression of 20S core particle of the proteasome and of the nestin, diminished astroglial reactivity, and reduced p53, rabbit anti-p53 upregulated modulator of apoptosis (PUMA), and rabbit anti-B cell lymphoma-2 interacting mediator of cell death (Bim) expressions in the hippocampus and cerebral cortex. HBO-PC also improved T-maze performance at 7 days. Proteasome inhibitor abolished the beneficial effects of HBO-PC on post-ischemic neuronal injury and functional impairment and reduced the ischemic alterations in the expression of investigated proteins.

Significance

Preconditioning with hyperbaric oxygen-induced brain protection against severe ischemic brain insult appears to involve the proteasome, which can be linked to a depletion of apoptotic proteins and improved regenerative potential.

Review Cerebral Ischemic Tolerance and Preconditioning: Methods, Mechanisms, Clinical Applications, and Challenges

Stroke is one of the leading causes of morbidity and mortality worldwide, and it is increasing in prevalence. The limited therapeutic window and potential severe side effects prevent the widespread clinical application of the venous injection of thrombolytic tissue plasminogen activator and thrombectomy, which are regarded as the only approved treatments for acute ischemic stroke. Triggered by various types of mild stressors or stimuli, ischemic preconditioning (IPreC) induces adaptive endogenous tolerance to ischemia/reperfusion (I/R) injury by activating a multitude cascade of biomolecules, for example, proteins, enzymes, receptors, transcription factors, and others, which eventually lead to transcriptional regulation and epigenetic and genomic reprogramming. During the past 30 years, IPreC has been widely studied to confirm its neuroprotection against subsequent I/R injury, mainly including local ischemic preconditioning (LIPreC), remote ischemic preconditioning (RIPreC), and cross preconditioning. Although LIPreC has a strong neuroprotective effect, the clinical application of IPreC for subsequent cerebral ischemia is difficult. There are two main reasons for the above result: Cerebral ischemia is unpredictable, and LIPreC is also capable of inducing unexpected injury with only minor differences to durations or intensity. RIPreC and pharmacological preconditioning, an easy-to-use and non-invasive therapy, can be performed in a variety of clinical settings and appear to be more suitable for the clinical management of ischemic stroke. Hoping to advance our understanding of IPreC, this review mainly focuses on recent advances in IPreC in stroke management, its challenges, and the potential study directions.

An Extra Breath of Fresh Air: Hyperbaric Oxygenation as a Stroke Therapeutic

Stroke serves as a life-threatening disease and continues to face many challenges in the development of safe and effective therapeutic options. The use of hyperbaric oxygen therapy (HBOT) demonstrates pre-clinical effectiveness for the treatment of acute ischemic stroke and reports reductions in oxidative stress, inflammation, and neural apoptosis. These pathophysiological benefits contribute to improved functional recovery. Current pre-clinical and clinical studies are testing the applications of HBOT for stroke neuroprotection, including its use as a preconditioning regimen. Mild oxidative stress may be able to prime the brain to tolerate full extensive oxidative stress that occurs during a stroke, and HBOT preconditioning has displayed efficacy in establishing such ischemic tolerance. In this review, evidence on the use of HBOT following an ischemic stroke is examined, and the potential for HBOT preconditioning as a neuroprotective strategy. Additionally, HBOT as a stem cell preconditioning is also discussed as a promising strategy, thus maximizing the use of HBOT for ischemic stroke.

Hyperbaric oxygen alleviated cognitive impairments in mice induced by repeated cerebral ischemia-reperfusion injury via inhibition of autophagy

AIMS

In this study, we investigate the effect and underlying mechanism of hyperbaric oxygen (HBO) treatment on a model of repeated cerebral ischemia-reperfusion injury (IR).

MAIN METHODS

Eighty rats were randomly separated into sham, vehicle, hyperbaric air (HBA; 0.25 MPa, 60 min), and HBO (0.25 MPa, 60 min) groups. Repeated cerebral IR was induced by ligating the right and left bilateral common carotid arteries for 10 min and then allowing reperfusion for 10 min. This pattern was repeated three times. The neuroprotective effects of HBO were assessed by animal behavior, neuron morphology, inflammatory markers, intracellular calcium ion content, and autophagy-related protein and gene expression.

KEY FINDINGS

Our result showed that HBO improved learning and memory in the navigation trail and probe trail of the Morris water maze, and these findings were supported by the observation data from 2,3,5-Triphenyltet-razolium chloride staining, Nissl staining, and electron microscopic. Importantly, we found that HBO reduced excessive autophagy in the prefrontal cortex, which was evidenced by activating of the mammalian target of the rapamycin (mTOR) and 4E-BP1, as well as suppression of LC3II and ATG5. Moreover, HBO significantly inhibited the cerebral IR-induced inflammatory reaction. Furthermore, HBO treatment modulated autophagy pathway-related factors, including producing a decrease in the intracellular calcium ion concentration and p53 level; meanwhile, the levels of BDNF and p-Akt were increased.

SIGNIFICANCE

Our results indicated that HBO protected against IR-induced neuron injury by attenuating autophagy, inflammation, and calcium overload. These results provide a new mechanism and laboratory evidence for clinical treatment of VD.

Hyperbaric oxygen therapy: A new look on treating stroke and traumatic brain injury

Although hyperbaric oxygen therapy (HBOT) is common as a treatment for injuries, this study aimed to research the ability of HBOT in preconditioning to diminish any potential damage. The hypothesis stated that HBOT preconditioning alleviated the death of cells in primary rat neuronal cells (PRNCs) by transferring mitochondria from astrocytes. In this experiment, PRNCs were given an HBOT treatment before a tumor necrosis factor-alpha or lipopolysaccharide injury which resembled cell death associated with stroke and traumatic brain injury (TBI). After being examined, the study found more cell viability in the PRNCs that had received HBOT precondition and a mitochondrial transfer. The mitochondrial transfer was visualized by a series of images showing the transfer after the HBOT treatment. This study demonstrated the ability of HBOT preconditioning as a treatment for inflammation in stroke and TBI, with the transfer of mitochondria from astrocytes to PRNCs reducing cell death. Along with discussion of the study, this review also focuses on different stroke treatments in comparison with HBOT.

Prophylactic treatment of hyperbaric oxygen treatment mitigates inflammatory response via mitochondria transfer

Aims

Hyperbaric oxygen therapy (HBOT) has been widely used as postinjury treatment; however, we investigate its ability to mitigate potential damage as a preconditioning option. Here, we tested the hypothesis that HBOT preconditioning mitigates cell death in primary rat neuronal cells (PRNCs) through the transfer of mitochondria from astrocytes.

Methods

Primary rat neuronal cells were subjected to a 90‐minute HBOT treatment at 2.5 absolute atmospheres prior to either tumor necrosis factor‐alpha (TNF‐alpha) or lipopolysaccharide (LPS) injury to simulate the inflammation‐plagued secondary cell death associated with stroke and traumatic brain injury (TBI). After incubation with TNF‐alpha or LPS, the cell viability of each group was examined.

Results

There was a significant increase of cell viability accompanied by mitochondrial transfer in the injury groups that received HBOT preconditioning compared to the injury alone groups (44 ± 5.2 vs 68 ± 4.48, n = 20, P < 0.05). The transfer of mitochondria directly after HBOT treatment was visualized by capturing images in 5‐minute intervals, which revealed that the robust transfer of mitochondria begins soon after HBOT and persisted throughout the treatment.

Conclusion

This study shows that HBOT preconditioning stands as a robust prophylactic treatment for sequestration of inflammation inherent in stroke and TBI, possibly facilitating the transfer of resilient mitochondria from astrocytes to inflammation‐susceptible neuronal cells in mitigating cell death.

Models and methods for conditioning the ischemic brain

BACKGROUND

In the last decades the need to find new neuroprotective targets has addressed the researchers to investigate the endogenous molecular mechanisms that brain activates when exposed to a conditioning stimulus. Indeed, conditioning is an adaptive biological process activated by those interventions able to confer resistance to a deleterious brain event through the exposure to a sub-threshold insult. Specifically, preconditioning and postconditioning are realized when the conditioning stimulus is applied before or after, respectively, the harmul ischemia.

AIMS AND RESULTS

The present review will describe the most common methods to induce brain conditioning, with particular regards to surgical, physical exercise, temperature-induced and pharmacological approaches. It has been well recognized that when the subliminal stimulus is delivered after the ischemic insult, the achieved neuroprotection is comparable to that observed in models of ischemic preconditioning. In addition, subjecting the brain to both preconditioning as well as postconditioning did not cause greater protection than each treatment alone.

CONCLUSIONS

The last decades have provided fascinating insights into the mechanisms and potential application of strategies to induce brain conditioning. Since the identification of intrinsic cell-survival pathways should provide more direct opportunities for translational neuroprotection trials, an accurate examination of the different models of preconditioning and postconditioning is mandatory before starting any new project.

A Dual Role for Hyperbaric Oxygen in Stroke Neuroprotection: Preconditioning of the Brain and Stem Cells

Stroke continues to be an extremely prevalent disease and poses a great challenge in developing safe and effective therapeutic options. Hyperbaric oxygen therapy (HBOT) has demonstrated significant pre-clinical effectiveness for the treatment of acute ischemic stroke, and limited potential in treating chronic neurological deficits. Reported benefits include reductions in oxidative stress, inflammation, neural apoptosis, and improved physiological metrics such as edema and oxygen perfusion, all of which contribute to improved functional recovery. This pre-clinical evidence has failed to translate into an effective evidence-based therapy, however, due in large part to significant inconsistencies in treatment protocols and design of clinical studies. While the medical community works to standardize clinical protocols in an effort to advance HBOT for acute stroke, pre-clinical investigations continue to probe novel applications of HBOT in an effort to optimize stroke neuroprotection. One such promising strategy is HBOT preconditioning. Based upon the premise of mild oxidative stress priming the brain for tolerating the full-blown oxidative stress inherent in stroke, HBOT preconditioning has displayed extensive efficacy. Here, we first review the pre-clinical and clinical evidence supporting HBOT delivery following ischemic stroke and then discuss the scientific basis for HBOT preconditioning as a neuroprotective strategy. Finally, we propose the innovative concept of stem cell preconditioning, in tandem with brain preconditioning, as a promising regenerative pathway for maximizing the application of HBOT for ischemic stroke treatment.

Neuroprotective effects of hyperbaric oxygen (HBO) therapy on neuronal death induced by sciatic nerve transection in rat

Background

Recent studies shows that hyperbaric oxygen (HBO) therapy exerts some protective effects against neural injuries. The purpose of this study was to determine the neuroprotective effects of HBO following sciatic nerve transection (SNT).

Methods

Rats were randomly divided into five groups (n = 14 per group): Sham-operated (SH) group, SH + HBO group, SNT group, and SNT + pre- and SNT + post-HBO groups (100% oxygen at 2.0 atm absolute, 60 min/day for five consecutive days beginning on 1 day before and immediately after nerve transaction, respectively). Spinal cord segments of the sciatic nerve and related dorsal root ganglions (DRGs) were removed 4 weeks after nerve transection for biochemical assessment of malodialdehyde (MDA) levels in spinal cord, biochemical assessment of superoxide dismutase (SOD) and catalse (CAT) activities in spinal cord, immunohistochemistry of caspase-3, cyclooxigenase-2 (COX-2), S100beta (S100ß), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) in spinal cord and DRG.

Results

The results revealed that MDA levels were significantly decreased in the SNT + pre-HBO group, while SOD and CAT activities were significantly increased in SNT + pre- and SNT + post-HBO treated rats. Attenuated caspase-3 and COX-2 expression, and TUNEL reaction could be significantly detected in the HBO-treated rats after nerve transection. Also, HBO significantly increased S100ß expression.

Conclusions

Based on these results, we can conclude that pre- and post-HBO therapy had neuroprotective effects against sciatic nerve transection-induced degeneration.

Hyperbaric Environment: Oxygen and Cellular Damage versus Protection

The elevation of tissue pO2 induced by hyperbaric oxygen (HBO) is a physiological stimulus that elicits a variety of cellular responses. These effects are largely mediated by, or in response to, an increase in the production of reactive oxygen and nitrogen species (RONS). The major consequences of elevated RONS include increased oxidative stress and enhanced antioxidant capacity, and modulation of redox-sensitive cell signaling pathways. Interestingly, these phenomena underlie both the therapeutic and potentially toxic effects of HBO. Emerging evidence indicates that supporting mitochondrial health is a potential method of enhancing the therapeutic efficacy of, and preventing oxygen toxicity during, HBO. This review will focus on the cellular consequences of HBO, and explore how these processes mediate a delicate balance of cellular protection versus damage. © 2017 American Physiological Society. Compr Physiol 7:213-234, 2017.

Hyperbaric oxygen preconditioning ameliorates blood-brain barrier damage induced by hypoxia through modulation of tight junction proteins in an in vitro model

Aim

To explore the effects of hyperbaric oxygen preconditioning (HBOP) on the permeability of blood-brain barrier (BBB) and expression of tight junction proteins under hypoxic conditions in vitro.

Methods

A BBB in vitro model was constructed using the hCMEC/D3 cell line and used when its trans-endothelial electrical resistance (TEER) reached 80-120 Ω · cm² (tested by Millicell-Electrical Resistance System). The cells were randomly divided into the control group cultured under normal conditions, the group cultured under hypoxic conditions (2%O₂) for 24 h (hypoxia group), and the group first subjected to HBOP for 2 h and then to hypoxia (HBOP group). Occludin and ZO-1 expression were analyzed by immunofluorescence assay.

Results

Normal hCMEC/D3 was spindle-shaped and tightly integrated. TEER was significantly reduced in the hypoxia (P = 0.001) and HBOP group (P = 0.014) compared to control group, with a greater decrease in the hypoxia group. Occludin membranous expression was significantly decreased in the hypoxia group (P = 0.001) compared to the control group, but there was no change in the HBOP group. ZO-1 membranous expression was significantly decreased (P = 0.002) and cytoplasmic expression was significantly increased (P = 0.001) in the hypoxia group compared to the control group, although overall expression levels did not change. In the HBOP group, there was no significant change in ZO-1 expression compared to the control group.

Conclusion

Hyperbaric oxygen preconditioning protected the integrity of BBB in an in vitro model through modulation of occludin and ZO-1 expression under hypoxic conditions.

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.

Hyperbaric oxygen preconditioning: a reliable option for neuroprotection

Brain injury is the leading cause of death and disability worldwide and clinically there is no effective therapy for neuroprotection. Hyperbaric oxygen preconditioning (HBO-PC) has been experimentally demonstrated to be neuroprotective in several models and has shown efficiency in patients undergoing on-pump coronary artery bypass graft (CABG) surgery. Compared with other preconditioning stimuli, HBO is benign and has clinically translational potential. In this review, we will summarize the results in experimental brain injury and clinical studies, elaborate the mechanisms of HBO-PC, and discuss regimes and opinions for future interventions in acute brain injury.

Hyperbaric oxygen therapy as a potential treatment for post-traumatic stress disorder associated with traumatic brain injury

Traumatic brain injury (TBI) describes the presence of physical damage to the brain as a consequence of an insult and frequently possesses psychological and neurological symptoms depending on the severity of the injury. The recent increased military presence of US troops in Iraq and Afghanistan has coincided with greater use of improvised exploding devices, resulting in many returning soldiers suffering from some degree of TBI. A biphasic response is observed which is first directly injury-related, and second due to hypoxia, increased oxidative stress, and inflammation. A proportion of the returning soldiers also suffer from post-traumatic stress disorder (PTSD), and in some cases, this may be a consequence of TBI. Effective treatments are still being identified, and a possible therapeutic candidate is hyperbaric oxygen therapy (HBOT). Some clinical trials have been performed which suggest benefits with regard to survival and disease severity of TBI and/or PTSD, while several other studies do not see any improvement compared to a possibly poorly controlled sham. HBOT has been shown to reduce apoptosis, upregulate growth factors, promote antioxidant levels, and inhibit inflammatory cytokines in animal models, and hence, it is likely that HBOT could be advantageous in treating at least the secondary phase of TBI and PTSD. There is some evidence of a putative prophylactic or preconditioning benefit of HBOT exposure in animal models of brain injury, and the optimal time frame for treatment is yet to be determined. HBOT has potential side effects such as acute cerebral toxicity and more reactive oxygen species with long-term use, and therefore, optimizing exposure duration to maximize the reward and decrease the detrimental effects of HBOT is necessary. This review provides a summary of the current understanding of HBOT as well as suggests future directions including prophylactic use and chronic treatment.

Hyperbaric oxygen preconditioning inhibits skin flap apoptosis in a rat ischemia-reperfusion model

BACKGROUND

Hyperbaric oxygen (HBO) improves skin flap function and inhibits partial necrosis induced by ischemia-reperfusion (I/R) injury. Our study aimed to evaluate the mechanism underlying HBO regulation of the antiapoptosis factors associated with I/R injury of skin flaps.

METHODS

The rats were divided into sham surgery, I/R, and HBO groups. Rats from the HBO group received HBO preconditioning followed by I/R surgery. Blood perfusion of the skin flaps was measured with laser Doppler flowmeters. Tissue morphology and apoptosis were subsequently assessed based on hematoxylin-eosinhe and terminal deoxynucleotidyl transferase dUTP nick-end labeling staining. Protein expression of phosphorylated apoptosis signal-regulating kinase 1 (pASK-1), phosphorylated c-Jun N-terminal kinase (pJNK), B-cell lymphoma-2 (Bcl-2), and Bcl2-associated X protein (Bax) was examined by immunodetection, and Bcl-2 messenger RNA expression was detected by quantitative polymerase chain reaction. In addition, caspase-3 activity was also measured.

RESULTS

The result of microcirculation analysis showed that the survival and blood perfusion rates significantly increased in the skin flap after HBO exposure. Terminal deoxynucleotidyl transferase dUTP nick-end labeling staining revealed that cell apoptosis was significantly attenuated in the HBO group. Furthermore, HBO preconditioning increased the expression of Bcl-2 and inhibited pASK-1, pJNK, and Bax expression as determined by both immunohistochemistry and Western blot. Caspase-3 activity and the Bax/Bcl-2 ratio declined in the HBO group.

CONCLUSIONS

HBO preconditioning effectively ameliorates I/R injury by regulating the apoptosis signal-regulating kinase 1 and/or c-Jun N-terminal kinase pathway and anti- and proapoptosis factors.

Cerebral Ischemic Preconditioning: the Road So Far…

Cerebral preconditioning constitutes the brain's adaptation to lethal ischemia when first exposed to mild doses of a subtoxic stressor. The phenomenon of preconditioning has been largely studied in the heart, and data from in vivo and in vitro models from past 2-3 decades have provided sufficient evidence that similar machinery exists in the brain as well. Since preconditioning results in a transient protective phenotype labeled as ischemic tolerance, it can open many doors in the medical warfare against stroke, a debilitating cerebrovascular disorder that kills or cripples thousands of people worldwide every year. Preconditioning can be induced by a variety of stimuli from hypoxia to pharmacological anesthetics, and each, in turn, induces tolerance by activating a multitude of proteins, enzymes, receptors, transcription factors, and other biomolecules eventually leading to genomic reprogramming. The intracellular signaling pathways and molecular cascades behind preconditioning are extensively being investigated, and several first-rate papers have come out in the last few years centered on the topic of cerebral ischemic tolerance. However, translating the experimental knowledge into the clinical scaffold still evades practicality and faces several challenges. Of the various preconditioning strategies, remote ischemic preconditioning and pharmacological preconditioning appears to be more clinically relevant for the management of ischemic stroke. In this review, we discuss current developments in the field of cerebral preconditioning and then examine the potential of various preconditioning agents to confer neuroprotection in the brain.

Effect of hyperbaric oxygen preconditioning on peri-hemorrhagic focal edema and aquaporin-4 expression

The aim of the present study was to investigate the effect of hyperbaric oxygen preconditioning (HBO-PC) on peri-hemorrhagic focal edema and aquaporin-4 (AQP-4) expression in an experimental intracerebral hemorrhage (ICH) rat model. Sixty-six Sprague Dawley® rats were divided into three groups: The sham-surgery group (SHG; n=6); the control group (A-ICH; n=30), in which the rats were injected with autologous blood; and the experimental HBO-PC group (P-HBO; n=30). The rats underwent brain edema and AQP-4 detection at 5 postoperative time-points (24, 48 and 72 h and 5 and 7 days). The water content in the brain tissues of the A-ICH animals was higher than that in the brain tissues of the SHG rats at each time-point (P<0.05), and the edema in the P-HBO was significantly more severe 24 and 48 h postoperatively than that at 7 days postoperatively (P<0.05). The difference between the P-HBO and A-ICH was significant at 48 and 72 h postoperatively (P<0.05). AQP-4 was expressed in the post-hemorrhagic rat brains of all groups; the SHG animals exhibited low expression, while the A-ICH animals exhibited an increased expression 24 h postoperatively. In the A-ICH, expression peaked at 48 h postoperatively and began to decrease gradually after 72 h. At the 7-day time-point, the expression level in the A-ICH was closer to but still higher than that of the SHG animals (P<0.05). The differences between the P-HBO and A-ICH animals at the postoperative 24-h, 48-h and 7-day time-points were statistically significant (P<0.05). In conclusion, HBO-PC may downregulate AQP-4 expression to reduce the intracerebral edema, thus strengthening tolerance to ICH and protecting the nerves.

High-altitude pulmonary edema can be prevented by heat shock protein 70-mediated hyperbaric oxygen preconditioning

BACKGROUND

The primary goal of this study was to test whether high-altitude exposure (HAE of 9.7% O2 at 0.47 absolute atmosphere [ATA] for 3 days) was capable of increasing lung edema, neutrophil, and hemorrhage scores as well as decreasing lung levels of both aquaporin 1 (AQP1) and AQP5 proteins and messenger RNA (mRNA) expression in rats, with a secondary goal to test whether a preinduction of heat shock protein 70 (HSP70) by hyperbaric oxygen preconditioning (HBO2P of 100% O2 at 2.0 ATA for 1 hour per day for 5 consecutive days) attenuated the HAE-induced increased lung injury scores and decreased lung AQP1 and AQP5 protein and mRNA expressions.

METHODS

Rats were assigned to (1) non-HBO2P (21% O2 at 1.0 ATA) + non-HAE (21% O2 at 1.0 ATA) group; (2) non-HBO2P + HAE group; (3) HBO2P + HAE group; and HBO2P + HSP70 antibodies (Ab) + HAE group. For the HSP70 Ab group, a neutralizing HSP70 Ab was injected intravenously at 24 hours before HAE. All the physiologic and biochemical parameters were obtained at the end of HAE or the equivalent period of non-HAE. The cardiovascular and blood gas parameters were monitored for all experiments. Bronchoalveolar lavage (BAL) was performed to determine proinflammatory cytokines (interleukin 6, interleukin 1β, and tumor necrosis factor α). Parts of the lung were excised for myeloperoxidase activity measurement, whereas the rest was collected for lung damage score assessments. AQP1 and AQP5 protein and mRAN expressions were also determined in the lung tissues.

RESULTS

In the non-HBO2P + HAE group, the animals displayed higher values of lung myeloperoxidase activity, BAL proinflammatory cytokines, lung water weight, and acute lung injury scores compared with those of the non-HBO2P + non-HAE controls. In contrast, the non-HBO2P + HAE group rats had lower values of lung AQP1 and AQP5 protein and mRNA expressions, mean arterial pressure, heart rate, SO2, Paco2, HCO3, and pH compared with those of non-HBO2P + non-HAE group rats. The increased acute lung edema, neutrophil, and hemorrhage scores; increased BAL levels of proinflammatory cytokines; decreased lung AQP1 and AQP5 protein and mRNA expressions; and hypotension, bradycardia, hypoxia, and acidosis caused by HAE were all significantly attenuated by HBO2P.

CONCLUSION

Our data indicate that HBO2P may attenuate high-altitude acute lung injury by a preinduction of lung HSP70 in rats.

Early hyperoxemia may not increase mortality after cardiac arrest: a pilot study

Objective

International Liaison Committee on Resuscitation guidelines advocate an arterial saturation of 94% to 96% after return of spontaneous circulation (ROSC). However, a few clinical trials have investigated the impact of postresuscitative O₂ therapy after cardiac arrest. We studied whether early hyperoxemia is associated with a poor post-ROSC outcome after in-hospital cardiac arrest.

Methods

We retrospectively reviewed patients who experienced an in-hospital cardiac arrest from January 2005 to January 2011. Based on the results of the first arterial blood gas analysis (ABGA) within 10 minutes and a second ABGA from 60 to 120 minutes after ROSC, patients were classified into three groups: hyperoxemia (PaO₂ ≥ 300 mmHg), normoxemia (300 mmHg > PaO₂ ≥ 60 mmHg), and hypoxemia (PaO₂ < 60 mmHg or ratio of PaO₂ to fraction of inspired oxygen < 300). We examined whether early hyperoxemia was associated with survival and neurological outcome.

Results

There were 792 patients who met the inclusion criteria: 638 (80.6%) in the hypoxemia group, 62 (7.8%) in the normoxemia group, and 92 (11.6%) in the hyperoxemia group. Multiple logistic regression analysis showed that hyperoxemia was not associated with survival (odds ratio [OR], 1.07; 95% confidence interval [CI], 0.30 to 3.84) or neurological outcome (OR, 1.03; 95% CI, 0.31 to 3.40).

Conclusion

Postresuscitation hyperoxemia was not associated with survival or neurological outcome in patients with ROSC after in-hospital cardiac arrest.

Angiogenesis contributes to the neuroprotection induced by hyperbaric oxygen preconditioning against focal cerebral ischemia in rats

Ischemic stroke is one of the leading causes of mortality and disability worldwide. Previous studies have indicated that hyperbaric oxygen preconditioning (HBO-PC) can induce neuroprotection against focal cerebral ischemia. However, the underlying mechanisms are still not fully understood, and the optimal regimen for preconditioning must be confirmed. In the present study, we designed eight preconditioning regimens and compared their neuroprotective effects. Hyperbaric oxygen preconditioning every other day for there sessions exhibited the best neuroprotective effect; the infarct volume was reduced by almost 50% at 48 h after middle cerebral artery occlusion. We also found that HBO-PC significantly increased the microvessel density and the CD31-positive cells in the penumbra at 72 h after stroke. These results indicate that angiogenesis is involved in the neuroprotection induced by HBO-PC. Moreover, we explored the roles of HIF-1α and angiogenic factors in the angiogenesis process induced by HBO-PC. The results from western blotting demonstrated that protein expression of Ang-2 in the HBO-PC group was significantly increased. In conclusion, HBO-PC reduced brain injury and improved neurological function after focal cerebral ischemia, as partly mediated by the increased microvessel density in the penumbra, and this effect may result from the upregulation of Ang-2.

Preconditioning provides neuroprotection in models of CNS disease: paradigms and clinical significance

Preconditioning is a phenomenon in which brief episodes of a sublethal insult induce robust protection against subsequent lethal injuries. Preconditioning has been observed in multiple organisms and can occur in the brain as well as other tissues. Extensive animal studies suggest that the brain can be preconditioned to resist acute injuries, such as ischemic stroke, neonatal hypoxia/ischemia, surgical brain injury, trauma, and agents that are used in models of neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease. Effective preconditioning stimuli are numerous and diverse, ranging from transient ischemia, hypoxia, hyperbaric oxygen, hypothermia and hyperthermia, to exposure to neurotoxins and pharmacological agents. The phenomenon of "cross-tolerance," in which a sublethal stress protects against a different type of injury, suggests that different preconditioning stimuli may confer protection against a wide range of injuries. Research conducted over the past few decades indicates that brain preconditioning is complex, involving multiple effectors such as metabolic inhibition, activation of extra- and intracellular defense mechanisms, a shift in the neuronal excitatory/inhibitory balance, and reduction in inflammatory sequelae. An improved understanding of brain preconditioning should help us identify innovative therapeutic strategies that prevent or at least reduce neuronal damage in susceptible patients. In this review, we focus on the experimental evidence of preconditioning in the brain and systematically survey the models used to develop paradigms for neuroprotection, and then discuss the clinical potential of brain preconditioning.

Hypoxic preconditioning-induced mitochondrial protection is not disrupted in a cell model of mtDNA T8993G mutation-induced F1F0-ATP synthase defect: the role of mitochondrial permeability transition

Transient opening of the mitochondrial permeability transition pore plays a crucial role in hypoxic preconditioning-induced protection. Recently, the cyclophilin-D component of the mitochondrial permeability transition pore has been shown to interact with and regulate the F1F0-ATP synthase. However, the precise role of the F1F0-ATP synthase and the interaction between cyclophilin-D and F1F0-ATP synthase in the mitochondrial permeability transition pore and hypoxic preconditioning remain uncertain. Here we found that a 1-h hypoxic preconditioning delayed apoptosis and improved cell survival after stimulation with various apoptotic inducers including H2O2, ionomycin, and arachidonic acid in mitochondrial DNA T8993G mutation (NARP) osteosarcoma 143B cybrids, an F1F0-ATP synthase defect cell model. This hypoxic preconditioning protected NARP cybrid cells against focal laser irradiation-induced oxidative stress by suppressing reactive oxygen species formation and preventing the depletion of cardiolipin. Furthermore, the protective functions of transient opening of the mitochondrial permeability transition pore in both NARP cybrids and wild-type 143B cells can be augmented by hypoxic preconditioning. Disruption of the interaction between cyclophilin-D and F1F0-ATP synthase by cyclosporin A attenuated the mitochondrial protection induced by hypoxic preconditioning in both NARP cybrids and wild-type 143B cells. Our results demonstrate that the interaction between cyclophilin-D and F1F0-ATP synthase is important in the hypoxic preconditioning-induced cell protection. This finding improves our understanding of the mechanism of mitochondrial permeability transition pore opening in cells in response to hypoxic preconditioning, and will be helpful in further developing new pharmacological agents targeting hypoxia-reoxygenation injury and mitochondria-mediated cell death.

The Akt pathway is involved in rapid ischemic tolerance in focal ischemia in Rats

Although the protective mechanisms of delayed ischemic preconditioning have received extensive studies, few have addressed the mechanisms associated with rapid ischemic postconditioning. We investigated whether ischemic tolerance induced by rapid preconditioning is regulated by the Akt survival signaling pathway. Stroke was generated by permanent occlusion of the left distal middle cerebral artery (MCA) plus 30 min or 1 h occlusion of the bilateral common carotid artery (CCA) in male rats. Rapid preconditioning performed 1h before stroke onset reduced infarct size by 69% in rats with 30 min CCA occlusion, but by only 19% with 1 h occlusion. After control ischemia with 30 min CCA occlusion, Western Blot showed that P-Akt was transiently increased while Akt kinase assay showed that Akt activity was decreased. Although preconditioning did not change P-Akt levels at 1h and 5h compared with control ischemia, it attenuated reduction in Akt activity at 5h in the penumbra. However, preconditioning did not change the levels of P-PDK1, P-PTEN, and P-GSK3β in the Akt pathway, all of which were decreased after stroke. At last, the PI3K kinase inhibitor, LY294002, completely reversed the protection from ischemic preconditioning. In conclusion, Akt contributes to the protection of rapid preconditionin against stroke.

Heat-shock protein 70 is involved in hyperbaric oxygen preconditioning on decompression sickness in rats

Decompression sickness (DCS) is a major concern in diving and space walk. Hyperbaric oxygen (HBO) preconditioning has been proved to enhance tolerance to DCS via nitric oxide. Heat-shock protein (HSP) 70 was also found to have protective effects against DCS. We hypothesized that the beneficial effects of HBO preconditioning on DCS was related to levels of elevated HSP70. HSPs (70, 27 and 90) expressed in tissues of spinal cord and lung in rats was detected at different time points following HBO exposure by Western blot. HSP27 and HSP90 showed a slight but not significant increase after HBO. HSP70 increased and reached highest at 18 h following exposure before decreasing. Then rats were exposed to HBO and subjected to simulated air dive and rapid decompression to induce DCS 18 h after HBO. The severity of DCS, along with levels of HSP70 expression, as well as the extent of oxidative and apoptotic parameters in the lung and spinal cord were compared among different groups of rats pretreated with HBO, HBO plus NG-nitro-l-arginine-methyl ester (l-NAME), HBO plus quercetin or normobaric air. HBO preconditioning significantly reduced the morbidity of DCS (from 66.7% to 36.7%), reduced levels of oxidation (malondialdehyde, 8-hydroxyguanine and hydrogen peroxide) and apoptosis (caspase-3 and -9 activities and the number of apoptotic cells). l-NAME or quercetin eliminated most of the beneficial effects of HBO on DCS, and counteracted the stimulation of HSP70 by HBO. Bubbles in pulmonary artery were detected using ultrasound imaging to observe the possible effect of HBO preconditioning on DCS bubble formation. The amounts of bubbles in rats pretreated with HBO or air showed no difference. These results suggest that HSP70 was involved in the beneficial effects of HBO on DCS in rats, suspected be by the antioxidation and antiapoptosis effects.

Hyperbaric oxygen preconditioning attenuates hyperglycemia-enhanced hemorrhagic transformation by inhibiting matrix metalloproteinases in focal cerebral ischemia in rats

Hyperglycemia dramatically aggravates brain infarct and hemorrhagic transformation (HT) after ischemic stroke. Oxidative stress and matrix metalloproteinases (MMPs) play an important role in the pathophysiology of HT. Hyperbaric oxygen preconditioning (HBO-PC) has been proved to decrease oxidative stress and has been demonstrated to be neuroprotective in experimental stroke models. The present study determined whether HBO-PC would ameliorate HT by a pre-ischemic increase of reactive oxygen species (ROS) generation, and a suppression of MMP-2 and MMP-9 in hyperglycemic middle cerebral artery occlusion (MCAO) rats. Rats were pretreated with HBO (100% O₂, 2.5 atmosphere absolutes) 1 h daily for 5 days before MCAO. Acute hyperglycemia was induced by an injection of 50% dextrose. Neurological deficits, infarction volume and hemorrhagic volume were assessed 24 h and 7 days after ischemia. ROS scavenger n-acetyl cysteine (NAC), hypoxia-inducible factor-1α (HIF-1α), inhibitor 2-methoxyestradiol (2ME2) and activator cobalt chloride (CoCl₂), and MMP inhibitor SB-3CT were administrated for mechanism study. The activity of MMP-2 and MMP-9, and the expression HIF-1α were measured. HBO-PC improved neurological deficits, and reduced hemorrhagic volume; the expression of HIF-1α was significantly decreased, and the activity of MMP-2 and MMP-9 was reduced by HBO-PC compared with vehicle group. Our results suggested that HBO-PC attenuated HT via decreasing HIF-1α and its downstream MMP-2 and MMP-9 in hyperglycemic MCAO rats.

Serum leptin levels decrease after permanent MCAo in the rat and remain unaffected by delayed hyperbaric oxygen therapy

Hyperbaric oxygen therapy (HBOT), referring to the medical use of oxygen at a level higher than atmospheric pressure, exerts neuroprotective effects after ischemic stroke via various mechanisms. It has been demonstrated that HBOT modulates the synthesis and degradation of hormones. Leptin, an adipose derived hormone, has been found to confer neuroprotection following experimental stroke. However, it is not known whether HBOT alters leptin concentrations after permanent middle cerebral artery occlusion (pMCAo) in the rat. In this present study, we aimed to investigate the effect of HBOT on the serum concentration of leptin in rats subjected to pMCAo. HBOT was initiated 48 hrs after experimental pMCAo, at 2.5 atmospheres absolutes with 100% oxygen, 1 hr a day for 10 consecutive days. Body weight, neurobehavioral deficits and infarct size were evaluated. Blood was collected on day 1 and day 16 following HBOT. Serum leptin concentrations were measured with ELISA. Delayed HBOT reduced infarct size and improved neurobehavioral scores. Decreased serum levels of leptin were found in treated and untreated pMCAo animals, compared to the sham group on day 1 (P > 0.05) and day 16 (P < 0.05). However, no statistical significance was found between HBOT and the air group. We concluded that the neuroprotective effects of delayed HBOT in pMCAo rats were unlikely to be exerted through changes in the serum concentration of leptin.

Phosphorylation of p38 MAPK mediates hypoxic preconditioning-induced neuroprotection against cerebral ischemic injury via mitochondria translocation of Bcl-xL in mice

Hypoxic preconditioning (HPC) initiates intracellular signaling pathway to provide protection, but the role of p38 mitogen-activated protein kinase (p38 MAPK) in HPC-induced neuroprotection against cerebral ischemic injuries is a matter of debate. In this study, we found that HPC could reduce 6h middle cerebral artery occlusion (MCAO)-induced infarct volume, edema ratio and cell apoptosis, as well as enhancing the up-regulated p38 MAPK phosphorylation (P-p38 MAPK) levels in the peri-infarct region of mice after 6h MCAO. However, intracerebroventricular injection of p38 MAPK inhibitor SB203580 abolished this HPC-induced neuroprotection. HPC significantly increased the translocation of anti-apoptotic Bcl-2-related protein Bcl-xL from the cytosol to the mitochondria in the peri-infarct region of MCAO mice. Interestingly, the results of reciprocal immunoprecipitation showed that Bcl-xL and P-p38 MAPK were coimmunoprecipitated reciprocally only in the peri-infarct region of HPC and MCAO treated mice, while Bcl-xL and total p38 (T-p38 MAPK), not P-p38 MAPK, could be coimmunoprecipited by each other in the brain of normal control mice. In addition, we found SB203580 significantly decreased P-p38 MAPK levels, and inhibited HPC-induced mitochondria translocation of Bcl-xL in the brain of HPC and MCAO treated mice. Taken together, our findings suggested that P-p38 MAPK mediates HPC-induced neuroprotection against cerebral ischemic injury via mitochondria translocation of Bcl-xL, which might be a key anti-cell apoptotic mechanism of HPC.

Effect of hyperbaric oxygenation on intervertebral disc degeneration: an in vivo study with sprague-dawley rats

STUDY DESIGN

An in vivo study was conducted to test the effect of hyperbaric oxygenation (HBO) on intervertebral disc degeneration in Sprague-Dawley rats.

OBJECTIVE

To observe the changes in intervertebral disc height and levels of glycosaminoglycan, collagen, interleukin-1β (IL-1β), prostaglandin E2 (PGE2), and inducible nitric oxide synthase (iNOS) in degenerated intervertebral discs after HBO therapy.

SUMMARY OF BACKGROUND DATA

Although the involvement of IL-1β, PGE-2, NO, and low O2 concentration has been demonstrated in intervertebral disc degeneration, the actual mechanism is not clear. It has been reported that HBO influences changes in IL-1β, PGE-2, NO, and O2 concentration. Previously, a study demonstrated an in vitro positive effect of HBO on the human nucleus pulposus. Thus, an in vivo study in animals was necessary.

METHODS

Twelve Sprague-Dawley rats were each injected with chondroitinase ABC in 2 proximal intervertebral discs of the tail. After treating with 100% oxygen at 2.5 atmospheres 2 hours per days for 10 days, the change in disc height was determined by radiography. The amounts of PGE-2, iNOS, glycosaminoglycan, and total collagen in the intervertebral disc were quantified by enzyme-linked immunosorbent assay. Tissue morphology and the distribution of glycosaminoglycan, IL-1β, and iNOS in the intervertebral disc were assessed by histology and immunohistochemistry. The area of IL-1β in the intervertebral discs was quantified using image analysis software.

RESULTS

HBO therapy stopped the decrease in intervertebral disc height, caused an increase in the amount of glycosaminoglycan, and inhibited IL-1β, PGE-2, and iNOS production.

CONCLUSION

HBO provides a potential treatment modality for intervertebral disc degeneration.

Attenuating systemic inflammatory markers in simulated high-altitude exposure by heat shock protein 70-mediated hypobaric hypoxia preconditioning in rats

BACKGROUND/PURPOSE

The primary goal of this study was to test whether high-altitude exposure (HAE: 0.9% O(2) at 0.47 ATA for 24 hours) was capable of increasing the systemic inflammatory markers as well as the toxic organ injury indicators in rats, with a secondary goal to test whether preinduction of heat shock protein (HSP) 70 by hypobaric hypoxia preconditioning (HHP: 18.3% O(2) at 0.66 ATA for 5 h/day on 5 days consecutively for 2 weeks) attenuated the proposed increased serum levels of both the systemic inflammatory markers and the toxic organ injury indicators.

METHODS

Rats were assigned to: (1) non-HHP (21% O(2) at 1.0 ATA)+non-HAE (21% O(2) at 1.0 ATA) group; (2) non-HHP+HAE group; (3) HHP+non-HAE group; (4) HHP+HAE group; and (5) HHP+HSP70 antibodies (Ab)+HAE group. For the HSP70Ab group, a neutralizing HSP70Ab was injected intravenously at 24 hours prior to HAE. All the physiological and biochemical parameters were obtained at the end of HAE or the equivalent time period of non-HAE. Blood samples were obtained for determination of both the systemic inflammatory markers (e.g., serum tumor necrosis factor-α, interleukin-1β, E-selectin, intercellular adhesion molecule-1, and liver myeloperoxidase activity) and the toxic organ injury indicators (e.g., nitric oxide metabolites, 2,3-dihydroxybenzoic acid, and lactate dehydrogenase).

RESULTS

HHP, in addition to inducing overexpression of tissue HSP70, significantly attenuated the HAE-induced hypotension, bradycardia, hypoxia, acidosis, and increased tissue levels of both the systemic inflammatory markers and the toxic organ injury indicators. The beneficial effects of HHP in inducing tissue overexpression of HSP70 as well as in preventing the HAE-induced increased levels of the systemic inflammatory markers and the toxic organ injury indicators could be significantly reduced by HSP70Ab preconditioning.

CONCLUSION

These results suggest that HHP may downgrade both the systemic inflammatory markers and the toxic organ injury indicators in HAE by upregulating tissue HSP70.

The neuroprotective roles of BDNF in hypoxic ischemic brain injury

Hypoxia-ischemia (H/I) brain injury results in various degrees of damage to the body, and the immature brain is particularly fragile to oxygen deprivation. Hypothermia and erythropoietin (EPO) have long been known to be neuroprotective in ischemic brain injury. Brain-derived neurotrophic factor (BDNF) has recently been recognized as a potent modulator capable of regulating a wide repertoire of neuronal functions. This review was based on studies concerning the involvement of BDNF in the protection of H/I brain injury following a search in PubMed between 1995 and December, 2011. We initially examined the background of BDNF, and then focused on its neuroprotective mechanisms against ischemic brain injury, including its involvement in promoting neural regeneration/cognition/memory rehabilitation, angiogenesis within ischemic penumbra and the inhibition of the inflammatory process, neurotoxicity, epilepsy and apoptosis. We also provided a literature overview of experimental studies, discussing the safety and the potential clinical application of BDNF as a neuroprotective agent in the ischemic brain injury.

Hyperoxia: a review of the risks and benefits in adult cardiac surgery

Perioperative hyperoxia has been claimed to have a number of therapeutic advantages. However, in the setting of cardiac surgery and cardiopulmonary bypass (CPB), enthusiasm for its use has been tempered by concerns regarding the effect of high partial pressures of oxygen on cardiac, vascular, and respiratory function and the potential for exacerbation of ischemia-reperfusion injury. There is encouraging evidence from animal studies that hyperoxia is effective in myocardial preconditioning, at least in nondiseased hearts. There is also evidence that hyperoxia reduces gas microemboli production and longevity during CPB, although it is unclear whether this translates into a clinical benefit in terms of a reduction in postoperative neurological morbidity. Hyperoxia leads to changes in cardiovascular function. However, the effects of these changes remain unclear. At a tissue level, there is evidence that hyperoxia does not lead to improvement in partial pressure of oxygen. Indeed, the opposite may be the case with reductions in capillary density leading to areas of reduced tissue oxygenation. The risks of hyperoxia in association with CPB include lung injury, increased systemic reactive oxygen species generation, and exacerbation of reactive oxygen species-mediated myocardial injury at the time of reperfusion. Again, it is difficult to know whether the changes demonstrated are temporary or if they translate into a worsening of clinical outcomes. In conclusion, perhaps the key to the use of hyperoxia is in the timing. In the period pre-CPB, hyperoxia may precondition the myocardium and, paradoxically, confer a degree of protection against reactive oxygen species-induced injury at the time of reperfusion. Hyperoxia during CPB is probably harmful and should be avoided unless the risk from gas microemboli is thought to be significant, in which case the risks and benefits to the individual patient must be weighed.

Delayed hyperbaric oxygen therapy induces cell proliferation through stabilization of cAMP responsive element binding protein in the rat model of MCAo-induced ischemic brain injury

Treatments that could extend the therapeutic window of opportunity for stroke patients are urgently needed. Early administration of hyperbaric oxygen therapy (HBOT) has been proven neuroprotective in the middle cerebral artery occlusion (MCAo) in rodents. Our aim was to determine: 1) whether delayed HBOT after permanent MCAo (pMCAo) can still convey neuroprotection and restorative cell proliferation, and 2) whether these beneficial effects rely on HBO-induced activation of protein phosphatase-1γ (PP1-γ) leading to a decreased phosphorylation and ubiquitination of CREB and hence its stabilization. The experiments were performed in one hundred thirty-two male Sprague-Dawley rats with the body weight ranging from 240 to 270 g. Permanent MCAo was induced with the intraluminal filament occluding the right middle cerebral artery (MCA). In the first experiment, HBOT (2.5 ATA, 1h daily for 10 days) was started 48 h after pMCAo. Neurobehavioral deficits and infarct size as well as cyclic AMP response element-binding protein (CREB) expression and BrdU-DAB staining in the hippocampus and the peri-infarct region were evaluated on day 14 and day 28 post-MCAo. In the second experiment, HBOT (2.5 ATA, 1h) was started 3h after pMCAo. The effects of CREB siRNA or PP1-γ siRNA on HBO-induced infarct size alterations and target protein expression were studied. HBOT started with 48 h delay reduced infarct size, ameliorated neurobehavioral deficits and increased protein expression of CREB, resulting in increased cell proliferations in the hippocampus and peri-infarct region, on day 14 and day 28 post-MCAo. In the acute experiment pMCAo resulted in cerebral infarction and functional deterioration and reduced brain expression of PP1-γ, which led to increased phosphorylation and ubiquitination of CREB 24h after MCAo. However HBOT administered 3h after ischemia reversed these molecular events and resulted in CREB stabilization, infarct size reduction and neurobehavioral improvement. Gene silencing with CREB siRNA or PP1-γ siRNA reduced acute beneficial effects of HBO. In conclusion, delayed daily HBOT presented as potent neuroprotectant in pMCAo rats, increased CREB expression and signaling activity, and bolstered regenerative type cell proliferation in the injured brain. As shown in the acute experiment these effects of HBO were likely to be mediated by reducing ubiquitin-dependent CREB degradation owing to HBO-induced activation of PP1γ.

Effect of hyperbaric oxygen therapy on the intestinal ischemia reperfusion injury

PURPOSE

Adequate tissue oxygenation is essential for healing. Hyperbaric oxygen therapy (HBOT) has potential clinical applications to treat ischemic pathologies, however the exact nature of any protective effects are unclear at present. We therefore investigated the potential role of HBOT in modulating the ischemia/reperfusion (I/R) injury response in intestinal model of I/R injury.

METHODS

Male Wistar rats were subjected to surgery for the induction of intestinal ischemia followed by reperfusion. HBOT was provided before and/or after intestinal ischemia. Cell viability in the intestinal tissue was assessed using the MTT assay and by measuring serum malondealdehyde (MDA). Microvascular density and apoptosis were evaluated by immunohistochemistry.

RESULTS

The results indicate that HBOT treatment pre- and post-ischemia reduces lesion size to the intestinal tissue. This treatment increases cell viability and reduces the activation of caspase-3, which is associated with increased number of tissue CD34 cells and enhanced VEGF expression.

CONCLUSION

The hyperbaric oxygen therapy can limit tissue damage due to ischemia/reperfusion injury, by inducing reparative signaling pathways.

Ras family small GTPase-mediated neuroprotective signaling in stroke

Selective neuronal cell death is one of the major causes of neuronal damage following stroke, and cerebral cells naturally mobilize diverse survival signaling pathways to protect against ischemia. Importantly, therapeutic strategies designed to improve endogenous anti-apoptotic signaling appear to hold great promise in stroke treatment. While a variety of complex mechanisms have been implicated in the pathogenesis of stroke, the overall mechanisms governing the balance between cell survival and death are not well-defined. Ras family small GTPases are activated following ischemic insults, and in turn, serve as intrinsic switches to regulate neuronal survival and regeneration. Their ability to integrate diverse intracellular signal transduction pathways makes them critical regulators and potential therapeutic targets for neuronal recovery after stroke. This article highlights the contribution of Ras family GTPases to neuroprotective signaling cascades, including mitogen-activated protein kinase (MAPK) family protein kinase- and AKT/PKB-dependent signaling pathways as well as the regulation of cAMP response element binding (CREB), Forkhead box O (FoxO) and hypoxiainducible factor 1(HIF1) transcription factors, in stroke.

Reducing pulmonary injury by hyperbaric oxygen preconditioning during simulated high altitude exposure in rats

BACKGROUND

Hyperbaric oxygen preconditioning (HBO₂P + HAE) has been found to be beneficial in preventing the occurrence of ischemic damage to brain, spinal cord, heart, and liver in several disease models. In addition, pulmonary inflammation and edema are associated with a marked reduction in the expression levels of both aquaporin (AQP) 1 and AQP5 in the lung. Here, the aims of this study are first to ascertain whether acute lung injury can be induced by simulated high altitude in rats and second to assess whether HBO2P + HAE is able to prevent the occurrence of the proposed high altitude-induced ALI.

METHODS

Rats were randomly divided into the following three groups: the normobaric air (NBA; 21% O₂ at 1 ATA) group, the HBO₂P + high altitude exposure (HAE) group, and the NBA + HAE group. In HBO₂P + HAE group, animals received 100% O₂ at 2.0 ATA for 1 hour per day, for five consecutive days. In HAE groups, animals were exposed to a simulated HAE of 6,000 m in a hypobaric chamber for 24 hours. Right after being taken out to the ambient, animals were anesthetized generally and killed and thoroughly exsanguinated before their lungs were excised en bloc. The lungs were used for both histologic and molecular evaluation and analysis.

RESULTS

In NBA + HAE group, the animals displayed higher scores of alveolar edema, neutrophil infiltration, and hemorrhage compared with those of NBA controls. In contrast, the levels of both AQP1 and AQP5 proteins and mRNA expression in the lung in the NBA + HAE group were significantly lower than those of NBA controls. However, the increased lung injury scores and the decreased levels of both AQP1 and AQP5 proteins and mRNA expression in the lung caused by HAE was significantly reduced by HBO₂P + HAE.

CONCLUSIONS

Our results suggest that high altitude pulmonary injury may be prevented by HBO2P + HAE in rats.

Effect of hyperbaric oxygenation on intervertebral disc degeneration: an in vitro study with human lumbar nucleus pulposus

STUDY DESIGN

An in vitro study with degenerated human lumbar intervertebral disc specimens cultured under hyperbaric oxygenation (HBO).

OBJECTIVE

To observe the changes in interleukin (IL)-1β, prostaglandin (PG)-E2, nitric oxide (NO), cell growth, and apoptosis of the human nucleus pulposus cell (NPC) after HBO.

SUMMARY OF BACKGROUND DATA

Intervertebral disc degeneration has been demonstrated as related to IL-1β, PG-E2, NO, and O2 concentration but the actual mechanism is not clear. HBO also has also been reported in the literature to influence changes in IL-1β, prostaglandin E2, NO, and O2 concentration. However, the direct effect of HBO on the disc cells has not been previously reported.

METHODS

We collected 12 human lumbar degenerated disc specimens and evaluated the effects of HBO on the cultured NPCs. The amounts of IL-1β, PG-E2, and NO in the conditioned medium were quantified by enzyme-linked immunosorbent assay and high performance liquid chromatography. Cell growth was measured by increase in cell number. Cell viability and proteoglycan content were evaluated by histologic study using safranin O staining. In situ analysis of apoptosis was performed using Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining.

RESULTS

Our data indicated that HBO treatment inhibited IL-1β, PG-E2, and NO production but increased cell number and matrix synthesis of cultured NPCs. TUNEL staining showed that HBO treatment suppressed the apoptosis of cultured NPCs.

CONCLUSION

HBO provides a potential treatment modality for disc degeneration.

Hyperbaric oxygen therapy reduces the toll-like receptor signaling pathway in multiple organ failures

PURPOSE

Zymosan-induced generalized inflammation is the only experimental model that reproduces characteristics of human multiple organ dysfunction syndrome (MODS). Toll-like receptors (TLRs) are key components in innate immune responses and their signaling pathway is known to activate target genes such as nuclear factor-κB (NF-κB) and cytokines that are involved in inflammation and immune responses. We previously reported that hyperbaric oxygen (HBO) therapy is effective in the treatment of severe zymosan-induced inflammation in MODS. The aim of this study was to investigate the effect of HBO exposure on TLR2 and TLR4 signal transduction and organ dysfunction during MODS induced by zymosan in the rat.

METHODS

Male Wistar rats were randomized into four groups and treated as follows: (1) saline solution (control); (2) zymosan; (3) HBO 4 and 11 h after zymosan injection; (4) HBO 4 and 11 h after saline solution injection. Zymosan-induced damage of the lungs, liver, and small intestine was evaluated using histology and biochemistry. The activation of the TLR signaling pathway was measured with Western blot, reverse transcriptase polymerase chain reaction analysis (RT-PCR), and immunohistochemistry.

RESULTS

Zymosan induced a severe inflammatory response characterized by the activation of the TLR signaling pathway and by an organ dysfunction. HBO exposure significantly reduced the development of lung, liver, and intestine injury in our experimental model. It also significantly reduced the zymosan-induced expression of TLR2 and TLR4, NF-κB activation, and cytokine production.

CONCLUSIONS

Taken together, these results suggest that, by interfering with the TLR pathway, HBO treatment may exert a protective effect against tissue injury caused by zymosan-induced generalized inflammation.

Application of medical gases in the field of neurobiology

Medical gases are pharmaceutical molecules which offer solutions to a wide array of medical needs. This can range from use in burn and stroke victims to hypoxia therapy in children. More specifically however, gases such as oxygen, helium, xenon, and hydrogen have recently come under increased exploration for their potential theraputic use with various brain disease states including hypoxia-ischemia, cerebral hemorrhages, and traumatic brain injuries. As a result, this article will review the various advances in medical gas research and discuss the potential therapeutic applications and mechanisms with regards to the field of neurobiology.

Cyclooxygenase-2 mediates hyperbaric oxygen preconditioning in the rat model of transient global cerebral ischemia

BACKGROUND AND PURPOSE

Hyperbaric oxygen (HBO) preconditioning (PC) allows brain protection against transient global ischemia. In the present study, we hypothesize that the mechanism of HBO-PC involves the induction of cyclooxygenase-2 (COX-2) in cerebral tissues before ischemia, which leads to a suppression of COX-2 and its downstream targets after global ischemic insult.

METHODS

One hundred twenty-nine male Sprague Dawley rats (body weight 280-300 grams) were allocated to the naive control group and the sham operation group, and 3 groups of animals were subjected to 15-minute 4-vessel occlusion: untreated, preconditioned with HBO 2.5 atmospheres absolutes for 1 hour daily for 5 days, preconditioned as mentioned and administered with COX-2 inhibitor NS-398 (1 mg/kg body weight intraperitoneal) before each preconditioning session, and normal rats preconditioned with HBO without ischemia. The mortality, the incidence of seizures, and T-maze scores were recorded. The quantitative cell count in Nissl stain and TUNEL was conducted on day 7 after ischemia. The brain expression of COX-2 was analyzed with Western blotting and immunofluorescence staining.

RESULTS

HBO-PC increased the number of surviving neurons in the Cornu Ammonis area 1, which was associated with the reduced COX-2 expression in the hippocampus and in the cerebral cortex at 1 and 3 days after ischemia. HBO-PC improved functional performance and tended to decrease mortality and the frequency of seizures. These beneficial effects of HBO-PC were abolished by the COX-2 selective inhibitor NS-398.

CONCLUSIONS

HBO-PC reduced COX-2 expression and provided brain protection after global ischemia. Administration of COX-2 inhibitor with HBO before ischemia abolished preconditioning effect, thereby implicating COX-2 as a mediator of HBO-PC in the ischemic brain.

Hyperbaric oxygen preconditioning ameliorates anxiety-like behavior and cognitive impairments via upregulation of thioredoxin reductases in stressed rats

The present study examined the protective effect of hyperbaric oxygen preconditioning (HBO-PC) and the role of thioredoxin reductase (TrxR) in a post-traumatic stress disorder (PTSD)-induced rat model by using single prolonged stress (SPS). Rats were randomly divided into Sham, HBO, SPS and HBO+SPS groups. HBO-PC was conducted by exposing rats to 100% oxygen at 2.5atm absolute for 1h each day for 5 consecutive days. SPS was performed 24h after the last HBO-PC conditioning event. At 1h, 6h, 12h, 24h and 72h after SPS, TrxR mRNA expression was analyzed in the hippocampus; Nissl and TUNEL staining were performed at 72h after SPS. The results indicated that HBO-PC was able to significantly preserve viable neurons in the CA1 subfield of hippocampus following SPS exposure, as evidenced by reduced amounts of CA1 neuronal apoptosis. Furthermore, HBO-PC upregulate the expression of TrxR-1 and TrxR-2 mRNA in the hippocampus at 6h and 12h after SPS exposure and ameliorated anxiety-like behavior and cognitive impairments normally induced by SPS. Taken together, these findings suggest that HBO-PC is beneficial for the improvement of anxiety-like behavior and cognitive impairments induced by SPS exposure, and this effect might be associated with inhibition of neuronal apoptosis via upregulation of TrxR in stressed rats.

Hyperbaric oxygen preconditioning promotes survival of retinal ganglion cells in a rat model of optic nerve crush

In this study we tested the hypothesis that hyperbaric oxygen preconditioning (HBO-PC) reduces retinal neuronal death due to optic nerve crush (ONC). Adult male Sprague-Dawley rats were subjected to ONC accompanied by a contralateral sham operation. HBO-PC was conducted four times by giving 100% oxygen at 2.5 atmospheres absolute (ATA) for 1 h every 12 h for 2 days prior to ONC. The rats were euthanized at 1 or 2 weeks after ONC. Retinal ganglion cell (RGC) density was counted by hematoxylin and eosin (H&E) staining of the retina and retrograde labeling with FluoroGold application to the superior colliculus. Visual function was assessed by flash visual evoked potentials (FVEP). TUNEL straining and caspase-3 and caspase-9 activity in the retinas were assessed. The RGC density in the retinas of ONC HBO-PC-treated rats was significantly higher than that of the corresponding ONC-only rats (the survival rate was 67.2% versus 49.7% by H&E staining, and 60.3% versus 28.9% by retrograde labeling with FluoroGold, respectively; p < 0.01) at 2 weeks after ONC. FVEP measurements indicated a significantly better preserved latency and amplitude of the P1 wave in the ONC HBO-PC-treated rats than the ONC-only rats (92 +/- 7 msec, 21 +/- 3 microv in the sham-operated group, 117 +/- 12 msec, 14 +/- 2 microv in the HBO-PC-treated group, and 169 +/- 15 msec, 7 +/- 1 microv in the corresponding ONC group; p < 0.01). TUNEL assays showed fewer apoptotic cells in the HBO-PC-treated group, accompanied by the suppression of caspase-3 and caspase-9 activity. These results demonstrate that HBO-PC appears to be neuroprotective against ONC insult via inhibition of neuronal apoptosis pathways.