Hyperbaric oxygen treatment: the influence on the hippocampal superoxide dismutase and Na+,K+-ATPase activities in global cerebral ischemia-exposed rats

AMPK and its Activator Berberine in the Treatment of Neurodegenerative Diseases

Neurodegenerative disorders are heterogeneous diseases associated with either acute or progressive neurodegeneration, causing the loss of neurons and axons in the central nervous system (CNS), showing high morbidity and mortality, and there are only a few effective therapies. Here, we summarized that the energy sensor adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK), and its agonist berberine can combat the common underlying pathological events of neurodegeneration, including oxidative stress, neuroinflammation, mitochondrial disorder, glutamate excitotoxicity, apoptosis, autophagy disorder, and disruption of neurovascular units. The abovementioned effects of berberine may primarily depend on activating AMPK and its downstream targets, such as the mammalian target of rapamycin (mTOR), sirtuin1 (SIRT1), nuclear factor erythroid-2 related factor-2 (Nrf2), nuclear factor-κB (NF-κB), phosphoinositide 3-kinase/protein kinase B (PI3K/Akt), nicotinamide adenine dinucleotide (NAD+), and p38 mitogen-activated protein kinase (p38 MAPK). It is hoped that this review will provide a strong basis for further scientific exploration and development of berberine's therapeutic potential against neurodegeneration.

A review on the neuroprotective effects of hyperbaric oxygen therapy

Hyperbaric oxygen therapy, intermittent breathing of 100% oxygen at a pressure upper than sea level, has been shown to be some of the neuroprotective effects and used therapeutically in a wide range of neurological disorders. This review summarizes current knowledge about the neuroprotective effects of hyperbaric oxygen therapy with their molecular mechanisms in different models of neurological disorders.

Hyperbaric oxygen therapy for people with autism spectrum disorder (ASD)

BACKGROUND

The rising prevalence of autism spectrum disorder (ASD) has increased the need for evidence-based treatments to lessen the impact of symptoms. Presently, no therapies are available to effectively treat individuals with all of the symptoms of this disorder. It has been suggested that hyperbaric oxygen therapy may alleviate the biochemical dysfunction and clinical symptoms of ASD.

OBJECTIVES

To determine whether treatment with hyperbaric oxygen:1. improves core symptoms of ASD, including social communication problems and stereotypical and repetitive behaviors;2. improves noncore symptoms of ASD, such as challenging behaviors;3. improves comorbid states, such as depression and anxiety; and4. causes adverse effects.

SEARCH METHODS

On 10 December 2015, we searched CENTRAL, Ovid MEDLINE, Embase, and 15 other databases, four of which were Chinese language databases. We also searched multiple trial and research registers.

SELECTION CRITERIA

We selected randomized controlled trials (RCTs) and quasi-RCTs of any dose, duration, and frequency for hyperbaric oxygen therapy compared with no treatment or sham treatment for children and adults with ASD.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by The Cochrane Collaboration, in that three review authors independently selected studies, assessed them for risk of bias, and extracted relevant data. We also assessed the quality of the evidence by using the GRADE approach.

MAIN RESULTS

We included one trial with a total of 60 children with a diagnosis of ASD who randomly received hyperbaric oxygen therapy or a sham treatment. Using GRADE criteria, we rated the quality of the evidence as low because of the small sample size and wide confidence intervals (CIs). Other problems included selection bias and short duration or follow-up.Overall, study authors reported no improvement in social interaction and communication, behavioral problems, communication and linguistic abilities, or cognitive function. With regard to the safety of hyperbaric oxygen therapy (adverse events), they reported minor-grade ear barotrauma events. Investigators found significant differences between groups in total number of side effect events (Peto odds ratio (OR) 3.87, 95% CI 1.53 to 9.82) and in the number of children who experienced side effects (Peto OR 4.40, 95% CI 1.33 to 14.48).

AUTHORS' CONCLUSIONS

To date, there is no evidence that hyperbaric oxygen therapy improves core symptoms and associated symptoms of ASD. It is important to note that adverse effects (minor-grade ear barotrauma events) can occur. Given the absence of evidence of effectiveness and the limited biological plausibility and possible adverse effects, the need for future RCTs of hyperbaric oxygen therapy must be carefully considered.

Exposure to Hyperbaric Oxygen Intensified Vancomycin-Induced Nephrotoxicity in Rats

It has been suggested that oxidative stress is a potential mechanism for vancomycin-induced nephrotoxicity and hyperbaric oxygen therapy (HBO) has been shown to be effective in treating renal toxicity that has been pharmacologically induced in animal models. The aim of this study was to investigate the effect of HBO therapy on vancomycin-induced nephrotoxicity in rats. The study group comprised 36 Sprague Dawley male rats. We treated 30 with 500 mg/kg of intraperitoneal vancomycin once a day for 7 days. Half of these rats received a daily 1-hour treatment with HBO at 2 Atmospheres (ATM) on the same 7 days and formed the HBO+ group. The other 15 subjects received no HBO treatment (HBO- group). The remaining six rats served as the control group, three received HBO treatments alone and no treatment was administered to the other three rats. Laboratory results were obtained on day 8 and the intervention and control groups were compared. Rats in the HBO+ group gained less weight than the HBO- group (11.6 grams vs 22.6 grams; P = 0,008) and had significantly higher serum blood urea nitrogen (99.6 vs 52.6 mg/dL; P<0.001), serum creatinine (0.42 vs 0.16 mg/dL; P = 0.001) and magnesium (3.6 vs 3.1 mg/dL; P = 0.014). The vancomycin blood levels were also higher in the HBO+ group (27.8 vs 6.7 μg/mL; P = 0.078). There were no pathological kidney changes in the control group. All the kidneys from the treated groups (vancomycin +HBO and vancomycin HBO-) showed moderate to severe histopathological changes with no statistical significance between them. This study demonstrated that exposure to hyperbaric oxygen intensified vancomycin-induced nephrotoxicity in rats.

Kolaviron, a Garcinia kola biflavonoid complex, protects against ischemia/reperfusion injury: pertinent mechanistic insights from biochemical and physical evaluations in rat brain

The pathophysiology of stroke is characterized by biochemical and physical alterations in the brain. Modulation of such aberrations by therapeutic agents affords insights into their mechanism of action. Incontrovertible evidences that oxidative stress is involved in the pathophysiology of neurologic disorders have brought antioxidative compounds, especially plant phytochemicals, under increasing focus as potential remedies for the prevention and management of neurodegenerative diseases. Kolaviron, a biflavonoid complex isolated from Garcinia kola Heckel (Guttiferae) was evaluated for neuroprotectivity in brains of male Wistar rats submitted to bilateral common carotid artery occlusion-induced global ischemia/reperfusion injury (I/R). Animals were divided into six groups: sham treated, vehicle (I/R), 50 mg/kg kolaviron + I/R, 100 mg/kg kolaviron + I/R, 200 mg/kg kolaviron + I/R and quercetin (20 mg/kg i.p.) + I/R. The common carotid arteries were occluded for 30 min followed by 2 h of reperfusion. Relative brain weight and brain water content were determined and oxidative stress and neurochemical markers were also evaluated. I/R caused significant decreases in glutathione level and the activities of enzymic antioxidants, the sodium pump and acetylcholinesterase while significant increases were recorded in relative brain weight, brain water content, lipid peroxidation and the activities of glutamine synthetase and myeloperoxidase. There was a remarkable ablation of I/R induced oxidative stress, neurochemical aberrations and brain edema in animals pretreated with kolaviron. The results suggested that the protection afforded by kolaviron probably involved regulation of redox and electrolyte homeostasis as well as anti-inflammatory and antiexcitotoxic mechanisms.

Synaptic activity and bioenergy homeostasis: implications in brain trauma and neurodegenerative diseases

Powered by glucose metabolism, the brain is the most energy-demanding organ in our body. Adequate ATP production and regulation of the metabolic processes are essential for the maintenance of synaptic transmission and neuronal function. Glutamatergic synaptic activity utilizes the largest portion of bioenergy for synaptic events including neurotransmitter synthesis, vesicle recycling, and most importantly, the postsynaptic activities leading to channel activation and rebalancing of ionic gradients. Bioenergy homeostasis is coupled with synaptic function via activities of the sodium pumps, glutamate transporters, glucose transport, and mitochondria translocation. Energy insufficiency is sensed by the AMP-activated protein kinase (AMPK), a master metabolic regulator that stimulates the catalytic process to enhance energy production. A decline in energy supply and a disruption in bioenergy homeostasis play a critical role in multiple neuropathological conditions including ischemia, stroke, and neurodegenerative diseases including Alzheimer’s disease and traumatic brain injuries.

The potential role of ozone in ameliorating the age-related biochemical changes in male rat cerebral cortex

Controlled ozone (O(3)) administration is known to promote oxidative preconditioning and, thus, may reverse chronic oxidative stress that accompanies aging. Therefore, the present work was undertaken to study the potential role of O(3) in ameliorating certain age-related biochemical changes represented by impaired activities of inner mitochondrial membrane enzymes, compromised energy production and increased oxidative burden in male rat cerebral cortex. Prophylactic administration of O(3)-O(2) mixture to 3 month-old rats, at an intrarectal dose of 0.6 mg O(3) kg(-1) body weight twice/week for 3 months then once/week until the age of 15 months, normalized reduced glutathione content, adenosine triphosphate/adenosine diphosphate ratio, mitochondrial superoxide dismutase (SOD) and complex IV (cytochrome-c oxidase) activities, improved glutathione redox index (GSHRI), complex I (NADH-ubiquinone oxidoreductase) and mitochondrial nitric oxide synthase (mtNOS) activities, and attenuated the rise in malondialdehyde (MDA) and mitochondrial protein carbonyl levels. On the other hand, therapeutic administration of the same dose of O(3)-O(2) mixture to 14 month-old rats three times/week for 1 month, reduced mitochondrial protein carbonyl level only. Other favorable effects, including normalization of Na,K-adenosine triphosphatase (Na,K-ATPase) activity and reduction in lipofuscin level in the prophylactic group, as well as improvement in mitochondrial SOD and complex I activities with a decrease in total MDA level in the therapeutic group, were comparable to the effects observed in the corresponding O(2)-treated control groups. In conclusion, the present study revealed that prophylactic administration of O(3)-O(2) mixture provided better amelioration of age-related cerebrocortical alterations by combining the advantages of both O(3) and O(2) therapies.

Temporal and regional changes of superoxide dismutase and glutathione peroxidase activities in rats exposed to focal cerebral ischemia

Reactive oxygen species are important cause of tissue injury during cerebral ischemia and reperfusion (I/R). Superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) are intracellular enzymes responsible for endogenous antioxidant defense of tissues affected by I/R. The aim of this study was to examine temporal and regional changes of SOD and GSH-Px activities in animals exposed to transient focal cerebral ischemia. Male Wistar Hannover rats were subjected to the right middle cerebral artery occlusion for 2 h. The animals were sacrificed immediately, 0·5, 1, 2, 3, 6, 24, 48, 72 or 168 h after ischemic procedure. SOD and GSH-Px activities were determined spectrophotometrically in the hippocampus and parietal cortex, both unilaterally and contralaterally to the occlusion. Sham-operated animals were used as the control group. Our results indicated that transient focal cerebral ischemia causes significant changes in SOD activities in the hippocampus and parietal cortex such as in GSH-Px activities in the parietal cortex, unilaterally and contralaterally to the lesion in rats during different reperfusion periods. Statistically significant activation of GSH-Px was registered neither in the right nor in the left hippocampus of ischemic animals.

Effects of hyperbaric oxygen on the expression of claudins after cerebral ischemia-reperfusion in rats

The malfunction of tight junctions (TJs) between endothelial cells in the blood brain barrier (BBB) is the pathophysiological basis for cerebral ischemia-reperfusion (IR) injury. Claudins, major molecular elements of the TJs, play a key role in the paracellular permeability of the BBB. Although several studies have demonstrated the impact of hyperbaric oxygenation (HBO) on boosting oxygen supply and reducing infarct size, its effect and underlying mechanism on the integrity of the BBB is unknown. To study the function of HBO on claudins and the permeability of the BBB, we replicated the animal model of local cerebral IR. Using Evans blue dye, permeability of the BBB was examined. Transmission electron microscopy (TEM), immunohistochemistry, western blot, and gelatin zymography were used to detect the integrity of the BBB, the expression of claudin-1 and claudin-5, and the activity of matrix metalloproteinases (MMPs) in brain microvessel endothelium. Our data indicate that compared with the sham-operated group, IR increased permeability of the BBB to Evans blue dye (P < 0.01), peaking at 4 h. The BBB ultrastructure was disrupted and the expression of claudin-5 and claudin-1 decreased (P < 0.01) in the 4 and 72 h IR group, respectively. Increased claudin-5 and claudin-1 expression and decreased permeability of the BBB were observed in the HBO + IR group (P < 0.01) via the suppression of MMP-2 and MMP-9, respectively. Our study provides direct evidence that HBO decreases the permeability of the BBB by reducing the enzymatic activity of MMPs and augmenting the expression of claudins at different stages in cerebral IR injury.

Neuroprotective effect of hyperbaric oxygen therapy on anterior ischemic optic neuropathy

The study investigated the therapeutic effect of hyperbaric oxygen (HBO) on anterior ischemic optic neuropathy in a rodent model (rAION). rAION was laser-induced in one eye of 63 mice. The fellow (uninjured) eye served as an internal control. Thirty-three mice underwent two 90-min sessions of 100% oxygen (2 atm) treatment immediately following injury and one session daily thereafter for up to 14 days. The remaining mice were untreated. Retinas were harvested at different time points, and mRNA levels of various genes were analyzed by real-time polymerase chain reaction and histologic study. Untreated mice: day 1 post-rAION – SOD-1 (oxidative-stress-related) decreased to 82% of control (uninjured eye) levels (P < 0.05), Caspase-3 (proapoptotic) decreased to 89%, Bcl-xL mildly increased (117%; all NS); day 3 – HO-1 and endothelial nitric oxide synthase (eNOS; ischaemia-related) decreased to 74%, and Bcl-2-associated X protein, Caspase-3, and B-cell lymphoma 2 (Bcl-2; apoptotic) increased by 170, 120, and 111%, respectively (all NS); day21 – HO-1 increased to 222% (NS) and eNOS decreased to 48% (P < 0.05). Treated mice: day 1 – SOD-1 and Caspase-3 remained unchanged, Bcl-2 and Bcl-xL mildly increased (112 and 126% respectively); day 3 – HO-1 and eNOS increased, apoptosis-related gene decreased; day 21 – SOD-1 decreased whereas eNOS increased (P < 0.05), and HO-1 increased to a lesser degree than without treatment. None of the oxygen-treated animals had retinal ganglion cell loss or a decrease in Thy-1 expression. In conclusion, HBO treatment after rAION induction influences the expression of apoptosis-related genes as well as oxidative-stress-induced and ischaemia-related genes and may exert a neuroprotective effect.

Hyperbaric oxygenation alleviates MCAO-induced brain injury and reduces hydroxyl radical formation and glutamate release

The present study examined the effect of hyperbaric oxygen (HBO) on the formation of 2,3-dihydroxybenzoic acid (2,3-DHBA) and 2,5-dihydroxybenzoic acid (2,5-DHBA), the products of salicylate trapping of hydroxyl free radicals, and glutamate release in the striatum during acute ischemia and reperfusion. Non-HBO rats (n = 8) were subjected to 1-h ischemia. Study rats (n = 8) were treated with HBO at 2.8 ATA for 1 h during ischemia. Artificial CSF solution containing 5 mM sodium salicylate was perfused at 1 microl/min. Samples were continuously collected at 15 min intervals and the levels of 2,3-DHBA, 2,5-DHBA, and glutamate were analyzed. The lesion volume was determined by TTC stain. Occlusion of the middle cerebral artery induced a significant increase in the levels of 2,3-DHBA and 2,5-DHBA. A peak of approximately two and fourfold of baseline levels was reached at 45 min and was maintained at elevated levels during reperfusion. The level of glutamate increased approximately two times at 30 min during ischemia, continued to increase, and reached approximately three times baseline level during reperfusion. HBO significantly alleviated brain injury associated with decreased levels of 2,3-DHBA, 2,5-DHBA and glutamate. This study suggests that the decreased glutamate release and the reduced formation of hydroxyl free radicals might contribute to the neuroprotective effect of HBO.

Na,K-ATPase activity regulates AMPA receptor turnover through proteasome-mediated proteolysis

Neuronal activity largely depends on two key components on the membrane: the Na,K-ATPase (NKA) that maintains the ion gradients and sets the foundation of excitability, and the ionotropic glutamatergic AMPA receptors (AMPARs) through which sodium influx forms the driving force for excitation. Because the frequent sodium transients from glutamate receptor activity need to be efficiently extruded, a functional coupling between NKA and AMPARs should be a necessary cellular device for synapse physiology. We show that NKA is enriched at synapses and associates with AMPARs. NKA dysfunction induces a rapid reduction in AMPAR cell-surface expression as well as total protein abundance, leading to a long-lasting depression in synaptic transmission. AMPAR proteolysis requires sodium influx, proteasomal activity and receptor internalization. These data elucidate a novel mechanism by which NKA regulates AMPAR turnover and thereby synaptic strength and brain function.

Hyperbaric oxygen therapy and cerebral ischemia: neuroprotective mechanisms

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSION

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

Adenosine preconditions against ouabain but not against glutamate on CA1-evoked potentials in rat hippocampal slices

Hypoxic and ischaemic brain damage are believed to involve excessive release of glutamate, and recent work shows that glutamate-induced damage in brain slices can be reduced by preconditioning with hypoxia or glutamate itself. Because adenosine is a powerful preconditioning agent, we have investigated whether adenosine could precondition against glutamate in vitro. In rat hippocampal slices, glutamate depolarization reduced the amplitudes of antidromic- and orthodromic-evoked potentials, with only partial recovery. Applying adenosine before these insults failed to increase that recovery. Ouabain also produced depolarization with partial reversibility, but adenosine pretreatment increased the extent of recovery. The preconditioning effect of adenosine on ouabain responses was prevented by blocking receptors for N-methyl-D-aspartate (NMDA), but not receptors for kainate or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and was blocked by inhibiting nitric oxide synthase. Preconditioning was also abolished by the ATP-dependent potassium channel blockers, glibenclamide (cytoplasmic) or 5-hydroxydecanoate (mitochondrial). We conclude that adenosine does not precondition against glutamate in hippocampal slices, but that it does precondition against ouabain with a pharmacology similar to studies in vivo. Ischaemic neuronal damage is a complex of many factors, and because adenosine can precondition against ischaemic neuronal damage, its failure to protect against glutamate highlights limitations of using glutamate alone as a model for ischaemia. Because damage following ischaemia, trauma or excitotoxicity also involves reduced Na(+),K(+)-ATPase activity, and adenosine can precondition against ouabain, we propose that ouabain-induced damage represents an additional or alternative model for the contribution to cell damage of Na(+),K(+)-ATPase loss, this being more relevant to the mechanisms of preconditioning.

Hyperbaric oxygen treatment improves GFR in rats with ischaemia/reperfusion renal injury: a possible role for the antioxidant/oxidant balance in the ischaemic kidney

BACKGROUND

Ischaemic kidney injury continues to play a dominant role in the pathogenesis of acute renal failure (ARF) in many surgical and medical settings. A major event in the induction of renal injury is related to the generation of oxygen-free radicals. Hyperbaric oxygen therapy (HBO) is indicated for treatment of many ischaemic events but not for ARF. Therefore, the present study examined the effects of HBO on kidney function and renal haemodynamics in rats with ischaemic ARF.

METHODS

Renal ischaemia was induced by unilateral renal artery clamping (45 min) in rats. Within 24 h following ischaemia, rats were treated twice with HBO of 100% O(2) at 2.5 absolute atmospheres for 90 min each (+HBO). Untreated rats (-HBO) served as a control. Forty-eight hours later, GFR, RBF and endothelial-dependent vasorelaxation were measured. In addition, the immunoreactive staining of 4-hydroxy-2-noneal (4-HNE), a major product of endogenous lipid peroxidation, and superoxide dismutase (SOD) were assessed.

RESULTS

In the -HBO group, GFR was reduced by 94% compared with the untouched normal kidney (ischaemic: 0.06 +/- 0.03 ml/min, normal: 1.02 +/- 0.13 ml). In contrast, in the +HBO group, GFR of the ischaemic kidney (0.36 +/- 0.07 ml/min) was reduced only by 68% compared with the contralateral normal kidney (1.12 +/- 0.12 ml/min). In line with these findings, HBO improved the vasodilatory response to ACh as expressed in enhancement of both total and regional renal blood flow. In addition, HBO reduced the formation of 4-HNE by 33% and 76% and increased SOD by 30% and 70% in the cortex and outer stripe region of the medulla of the ischaemic kidney, respectively.

CONCLUSION

HBO attenuates the decline in GFR following renal ischaemia, and improves endothelial-dependent vasorelaxation, suggesting that treatment with HBO may be beneficial in the setting of ischaemic ARF.

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

It has been established that hyperbaric oxygen (HBO) treatment reduces brain edema, decreases infarct volume, contributes to neurological functional recovery and suppresses apoptosis in suture-induced focal cerebral ischemic animal models. In the present study, we evaluated the therapeutic effect of HBO in an endothelin-1-induced focal cerebral ischemia in rats and explored the associated mechanisms of HBO-induced brain protection. One hundred twenty male Sprague-Dawley rats (280 to 320 g) were randomly assigned to sham, focal cerebral ischemia and focal cerebral ischemia treated with HBO groups. Brain water content, neurological function, morphology and molecular biological markers were assessed. HBO (100% O2, 2.5 atmosphere absolute for 2 h) was initiated at 1 h after focal cerebral ischemia. Rats were killed at 24 h to harvest tissues for Western blot or for histology. In HBO-treated animals, an enhanced ratio of Bcl-2 and Bax and a reduced expression of hypoxia-inducible factor-1alpha (HIF-1alpha) in the hippocampus after focal cerebral ischemia were observed. These results indicate that HBO provides brain protection that is probably associated with the inhibition of HIF-1alpha and the elevation of Bcl-2.

Hyperbaric oxygen treatment attenuated the decrease in regional glucose metabolism of rats subjected to focal cerebral ischemia: A high resolution positron emission tomography study

Cerebral hypoxia may be the main component of cell damage caused by ischemia. Previous studies demonstrated a neuroprotective effect of early hyperbaric oxygen (HBO) treatment in various animal models of focal cerebral ischemia. Neuropathologic study showed that exposure of HBO may prevent cell death in ischemic cortex. In the present study, we aimed to assess cellular function of ischemic rat brain after HBO treatment by means of a high-resolution positron emission tomography scanner (microPET) used specifically for small animal imaging. The male Sprague-Dawley rats were subjected to permanent middle cerebral artery occlusion (MCAO), with the regional cerebral blood flow monitored in vivo by laser Doppler flowmetry. One hour after ischemia, HBO therapy (3 atm absolute, 1 h) was initiated. Local cerebral glucose utilization in the ischemic area was measured before, 1 h and 3 h after ischemia, with 2-[(18)F]-fluoro-2-deoxy-d-glucose (FDG) as a tracer. Neurological deficits and infarct volumes were assessed at 24 h after ischemia. Our study showed that early HBO therapy significantly reduced infarct volume of brain 24 h after ischemia. Moreover, glucose utilization in the ischemic area underwent a severe decrease during 1-3 h after MCAO, while the early HBO treatment significantly attenuated the decrease in cerebral metabolic rate of glucose in the ischemic core of the cortex compared with controls. We report for the first time the application of microPET to quantify the rates of glucose metabolism in the ischemic core of rats exposed to HBO. Our results suggest that the early exposure of HBO can partially reverse the downward trend for glucose utilization in the ischemic core, which might contribute to the reported beneficial effects of early HBO therapy on permanent cerebral ischemia.

Neuroprotective effect of hyperbaric oxygen in a rat model of subarachnoid hemorrhage

Acute brain ischemia after subarachnoid hemorrhage (SAH) induces oxidative stress in brain tissues. Up-regulated NADPH oxidase (NOX), a major enzymatic source of superoxide anion in the brain, may contribute to early brain injury after SAH. We evaluated the effects of hyperbaric oxygen (HBO) on protein expression of gp91(phox) catalytic subunit of NOX, lipid peroxidation as a marker of oxidative stress, and on neurological and neuropathological outcomes after SAH. Twenty-nine male Sprague-Dawley rats (300 to 350 g) were randomly allocated to control (sham operation), SAH (endovascular perforation), and SAH treated with HBO groups (2.8 ATA for 2 hours, at 1 hour after SAH). Cerebral blood flow was measured using laser Doppler flowmetry. Rats were sacrificed after 24 hours and brain tissues collected for histology (Nissl staining and gp91 (phox) immunohistochemistry) and biochemistry. Mortality and neurological scores were evaluated. Neuronal injury associated with enhanced gp91 (phox) immunostaining was observed in the cerebral cortex after SAH. The lipid peroxidation product, malondialdehyde, accumulated in the ipsilateral cerebral cortex. HBO treatment reduced expression of NOX, diminished lipid peroxidation, and reduced neuronal damage. HBO caused a drop in mortality and ameliorated functional deficits. HBO-induced neuroprotection after SAH may involve down-regulation of NOX and a subsequent reduction in oxidative stress.

Effects of hyperbaric oxygen exposure on experimental hepatic ischemia reperfusion injury: relationship between its timing and neutrophil sequestration

Recent studies have shown that hyperbaric oxygen therapy (HBOT) reduces neutrophil endothelial adherence in venules and also blocks the progressive arteriolar vasoconstriction associated with ischemia-reperfusion (I-R) injury in the extremities and the brain. In order to elucidate the effects of HBOT after I-R in digestive organs, particularly in the liver, we evaluated the following: 1) the relationship between timing of HBOT and tissue damage; and 2) HBOT's effects on neutrophil sequestration. Using a hepatic I-R (45 minute) model in male rats, survival rate, liver tissue damage, and neutrophil accumulation within the sinusoids in the HBOT-treated group (Group H) were compared to those in the nontreated group (Group C). For the HBOT-treated group, HBOT was administered as 100% oxygen, at 2.5 atm absolute, for 60 minutes. When HBOT was given 30 minute after I-R, the survival rate was much better in Group H than in Group C. HBOT performed within 3 hours of I-R markedly suppressed increases in the malondialdehyde level in tissues of the liver and lessened the congestion in the sinusoids. In addition, HBOT just after I-R caused decreased number of cells stained by the naphthol AS-D chloroacetate esterase infiltrating into the sinusoids. HBOT 3 hours after reperfusion, however, showed no clear effects upon neutrophil sequestration compared to Group C. These results indicate that HBOT performed within 3 hours of I-R alleviates hepatic dysfunction and improves the survival rate after I-R. Herein, we propose 1 possible mechanism for these beneficial effects: early HBOT given before neutrophil-mediated injury phase may suppress the accumulation of neutrophils after I-R. In conclusion, we believe that the present study should lead to an improved understanding of HBOT's potential role in hepatic surgery.

Mechanisms of hyperbaric oxygen and neuroprotection in stroke

Cerebral vascular diseases, such as neonatal encephalopathy and focal or global cerebral ischemia, all result in reduction of blood flow to the affected regions, and cause hypoxia-ischemia, disorder of energy metabolism, activation of pathogenic cascades, and eventual cell death. Due to a narrow therapeutic window for neuroprotection, few effective therapies are available, and prognosis for patients with these neurological injuries remains poor. Hyperbaric oxygen (HBO) has been used as a primary or adjunctive therapy over the last 50 years with controversial results, both in experimental and clinical studies. In addition, the mechanisms of HBO on neuroprotection remain elusive. Early applications of HBO within a therapeutic window of 3-6h or delayed but repeated administration of HBO can either salvage injured neuronal tissues or promote neurobehavioral functional recovery. This review explores the discrepancies between experimental and clinical observations of HBO, focusing on its therapeutic window in brain injuries, and discusses the potential mechanisms of HBO neuroprotection.

Hyperbaric and normobaric reoxygenation of hypoxic rat brain slices--impact on purine nucleotides and cell viability

Hyperbaric oxygen treatment has been suggested as able to reduce hypoxia induced neuronal damage. The aim of the study was to compare the impact of different reoxygenation strategies on early metabolical (purine nucleotide content determined by HPLC) and morphological changes (index of cell injury after celestine blue/acid fuchsin staining) of hypoxically damaged rat neocortical brain slices. For this purpose slices (300 microm and 900 microm) were subjected to either 5 or 30 min of hypoxia by gassing the incubation medium with nitrogen. During the following reoxygenation period treatment groups were administered either 100% oxygen (O) or room air (A) at normobaric (1 atm absolute, NB-O; NB-A) or hyperbaric (2.5 atm absolute, HB-O; HB-A) conditions. After 5 min of hypoxia, both HB-O and NB-O led to a complete nucleotide status restoration (ATP/ADP; GTP/GDP) in 300 microm slices. However, reoxygenation after 30 min of hypoxia was less effective, irrespective of the oxygen pressure. Furthermore, administering hyperbaric room air resulted in no significant posthypoxic nucleotide recovery. In 900 microm slices, both control incubation as well as 30 min of hypoxia resulted in significantly lower trinucleotide and higher dinucleotide levels compared to 300 microm slices. While there was no significant difference between HB-O and NB-O on the nucleotide status, morphological evaluation revealed a better recovery of the index of cell injury (profoundly injured/intact cell-ratio) in the HB-O group. Conclusively, the posthypoxic recovery of metabolical characteristics was dependent on the duration of hypoxia and slice thickness, but not on the reoxygenation pressure. A clear restorative effect on purine nucleotides was found only in early-administered HB-O as well as NB-O in contrast to room air treated slices. However, these pressure independent metabolic changes were morphologically accompanied by a significantly improved index of cell injury, indicating a possible neuroprotective role of HB-O in early posthypoxic reoxygenation.