The effects of hyperbaric air and hyperbaric oxygen on blood-brain barrier integrity in rats

Reaction of the Hippocampal Microglia to Hyperbaric Oxygen

We studied the reaction of rat hippocampal microgliocytes to hyperbaric oxygen at a pressure of 5 ata (absolute atmosphere). Immunohistochemical analysis with selective macrophage marker CD68 (ED1) and microglial marker Iba-1 allowed separate analysis of these two cell populations. It was shown that macrophages do not significantly contribute to reactive changes in the total pool of Iba-1⁺ hippocampal cells induced by hyperbaric oxygen.

Diving and attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) is a psychiatric condition that affects attention, concentration, impulse control and awareness. Not only these symptoms, but also the medications used to treat ADHD (psychostimulants) pose a risk to both the diver and his or her buddy. This article presents guidelines for recreational diving in combination with ADHD and psychostimulants. These guidelines are based solely on 'expert' opinion and were adopted at a meeting of the Dutch Association for Diving Medicine in 2017.

Diving and antidepressants

Psychoactive drugs pose a risk to both the diver and his or her buddy. Little is known about the safety of diving with antidepressants. Amongst the potential interactions with the diving environment are: somnolence; convulsions; a bleeding tendency (potentially worsening decompression illness, DCI), alterations to glucose metabolism and psychiatric side effects. Fluoxetine may potentially reduce the inflammatory process associated with DCI. This article presents guidelines for recreational diving in combination with antidepressants. These guidelines were endorsed at a meeting of the Dutch Association for Diving Medicine in 2015 and are solely based on 'expert' opinion.

Hyperbaric Oxygen Reduces Infarction Volume and Hemorrhagic Transformation Through ATP/NAD+/Sirt1 Pathway in Hyperglycemic Middle Cerebral Artery Occlusion Rats

BACKGROUND AND PURPOSE

Energy depletion is a critical factor leading to cell death and brain dysfunction after ischemic stroke. In this study, we investigated whether energy depletion is involved in hyperglycemia-induced hemorrhagic transformation after ischemic stroke and determined the pathway underlying the beneficial effects of hyperbaric oxygen (HBO).

METHODS

After 2-hour middle cerebral artery occlusion, hyperglycemia was induced by injecting 50% dextrose (6 mL/kg) intraperitoneally at the onset of reperfusion. Immediately after it, rats were exposed to HBO at 2 atmospheres absolutes for 1 hour. ATP synthase inhibitor oligomycin A, nicotinamide phosphoribosyl transferase inhibitor FK866, or silent mating type information regulation 2 homolog 1 siRNA was administrated for interventions. Infarct volume, hemorrhagic volume, and neurobehavioral deficits were recorded; the level of blood glucose, ATP, and nicotinamide adenine dinucleotide and the activity of nicotinamide phosphoribosyl transferase were monitored; the expression of silent mating type information regulation 2 homolog 1, acetylated p53, acetylated nuclear factor-κB, and cleaved caspase 3 were detected by Western blots; and the activity of matrix metalloproteinase-9 was assayed by zymography.

RESULTS

Hyperglycemia deteriorated energy metabolism and reduced the level of ATP and nicotinamide adenine dinucleotide and exaggerated hemorrhagic transformation, blood-brain barrier disruption, and neurological deficits after middle cerebral artery occlusion. HBO treatment increased the levels of the ATP and nicotinamide adenine dinucleotide and consequently increased silent mating type information regulation 2 homolog 1, resulting in attenuation of hemorrhagic transformation, brain infarction, as well as improvement of neurological function in hyperglycemic middle cerebral artery occlusion rats.

CONCLUSIONS

HBO induced activation of ATP/nicotinamide adenine dinucleotide/silent mating type information regulation 2 homolog 1 pathway and protected blood-brain barrier in hyperglycemic middle cerebral artery occlusion rats. HBO might be promising approach for treatment of acute ischemic stroke patients, especially patients with diabetes mellitus or treated with r-tPA (recombinant tissue-type plasminogen activator).

Strategies for transporting nanoparticles across the blood-brain barrier

The existence of blood-brain barrier (BBB) hampers the effective treatment of central nervous system (CNS) diseases. Almost all macromolecular drugs and more than 98% of small molecule drugs cannot pass the BBB. Therefore, the BBB remains a big challenge for delivery of therapeutics to the central nervous system. With the structural and mechanistic elucidation of the BBB under both physiological and pathological conditions, it is now possible to design delivery systems that could cross the BBB effectively. Because of their advantageous properties, nanoparticles have been widely deployed for brain-targeted delivery. This review paper presents the current understanding of the BBB under physiological and pathological conditions, and summarizes strategies and systems for BBB crossing with a focus on nanoparticle-based drug delivery systems. In summary, with wider applications and broader prospection the treatment of brain targeted therapy, nano-medicines have proved to be more potent, more specific and less toxic than traditional drug therapy.

Focal cerebral ischemic tolerance and change in blood-brain barrier permeability after repetitive pure oxygen exposure preconditioning in a rodent model

OBJECTIVE

The goal of this study was to demonstrate that repetitive pure oxygen exposure preconditioning (O2PC) for 8 hours per day for 3 or 7 days, a practicable preconditioning for clinical use, is able to induce cerebral ischemic tolerance (IT) and further clarify the accompanying changes in the blood-brain barrier (BBB) that may be involved.

METHODS

A total of 68 adult male Sprague-Dawley rats and eight 1-day-old rat pups were used in this study. The adult rats were exposed to pure O2 (38 rats) 8 hours a day for 3 or 7 days or to room air (in an identical setup) for 8 hours a day for 7 days as controls (30 rats). Arterial O2 tension (PaO2) was measured in 6 rats exposed to O2 and 3 controls. Focal cerebral ischemia was elicited by middle cerebral artery occlusion (MCAO) in 37 rats, of which 21 had been exposed to pure O2 for 3 or 7 days and 16 to room air for 7 days as controls. Neurological behavior was scored with the Garcia score in 15 MCAO rats, of which 10 had been exposed to pure O2 for 3 or 7 days and 5 to room air for 7 days as controls, and cerebral infarct volumes were assessed with TTC (2,3,5-triphenyltetrazolium chloride) staining in 10 rats (5 from each group) after 7 days of exposure. Formamide-extraction method was used to detect leakage of Evans blue (EB) dye in 7 rats exposed to pure O2 for 7 days and 7 exposed to room air for 7 days. Fluorescence microscopy was used to analyze the leaked EB in the nonischemic areas of 4 rats exposed to pure O2 for 7 days and 4 exposed to room air for 7 days before MCAO and the brain of the rats that had not been subjected to MCAO. Astrocyte changes associated with O2PC were evaluated by means of fluorescence microscopy and electron microscopy in 14 rats that were exposed to the same O2 or control conditions as the MCAO rats but without MCAO. Astrocytes were also obtained from 8 rat pups and cultured; levels of AQP4 and VEGF were detected by Western blot and ELISA in cells with and without O2 treatment.

RESULTS

A significant increase in PaO2 was seen after O2PC. The neurological score was significantly increased in the O2PC groups (10.6 ± 0.6 in the 3-day O2PC group, p < 0.05; 12 ± 0.84 in the 7-day O2PC group, p < 0.05) compared with the control group (7 ± 0.55). The ratio of cerebral infarct volume to contralateral cerebral hemisphere volume was significantly lower in the O2PC group than in the control group (0.204 ± 0.03 vs 0.48 ± 0.05, p < 0.05). The amount of leaked EB in the ischemic cerebral hemisphere was also lower in the O2-treated rats than in controls (7.53 ± 1.4 vs 11.79 ± 3.3 μg EB/g brain weight, p < 0.05). However, fluorescence microscopy showed significantly greater BBB permeability in the nonischemic areas in the O2PC group than in controls (p < 0.05). More red fluorescence could be observed in the nonischemic areas in both the ipsilateral and contralateral sides of the ischemic brain in the O2PC animals than in the nonischemic areas in the corresponding sides of the controls. Further investigation of the effect of the O2PC itself on the BBB of rats that were not subjected to MCAO showed that there was no EB leakage in the brain parenchyma in the rats exposed to room air, but some red fluorescence patches were noticed in the normal brain from the rats in the O2PC group. Astrocytes, including those from areas around the BBB, were activated in the O2PC group. Levels of both aquaporin 4 (AQP4) and vascular endothelial growth factor (VEGF) were significantly increased in cultured astrocytes after O2PC.

CONCLUSIONS

These findings suggest that O2PC is able to induce IT, which makes it a strong candidate for clinical use. Moreover, O2PC can also promote BBB opening, which may contribute to the induction of IT as well as representing a possible strategy for promoting drug transportation into the CNS. Activated astrocytes are likely to be involved in these processes through astrocyte-derived factors, such as AQP4 and VEGF.

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 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.

Corilagin Attenuates Radiation-Induced Brain Injury in Mice

Cranial irradiation-induced inflammation plays a critical role in the initiation and progression of radiation-induced brain injury (RIBI). Anti-inflammation treatment may provide therapeutic benefits. Corilagin (beta-1-O-galloyl-3, 6-(R)-hexahydroxydiphenoyl-D-glucose, C₂₇H₂₂O₁₈) was a novel member of the tannin family with anti-inflammatory properties and is isolated from some medicinal plants, such as Phyllanthus amarus and Caesalpinia coriaria. In this study, the effect of Corilagin on RIBI was investigated and the underlying mechanisms were explored. Spatial learning and memory ability of mice were investigated by the Morris water maze test. Evans blue leakage and electron microscopy were used to assess the integrity of blood-brain barrier (BBB). The mRNA and protein expressions of inflammatory cytokines, TNF-α and IL-1β, were measured by using real-time PCR and Western blotting. The activation of microglial cells and expression of TNF-α were examined by immunofluorescence staining. Phosphorylated signal transducers and activators of transcription 3 (p-STAT3) and IκBα, and the translocation of p65 from cytoplasm to nucleus were detected by using Western blotting. Morris water maze test showed that Corilagin ameliorated the neurocognitive deficits in RIBI mice. Evans blue leakage and electron microscopy exhibited that Corilagin partially protected the BBB integrity from cranial irradiation-caused damage; immunofluorescence staining showed that Corilagin could inhibit microglial activation and TNF-α expression. Real-time PCR and Western blotting revealed that Corilagin downregulated the expression of TNF-α and IL-1β and inhibited the irradiation-induced activation of NF-κB pathways by upregulating p-STAT3 expression. In conclusion, Corilagin could attenuate RIBI through inhibiting microglial activation and the expressions of inflammatory cytokines. Corilagin might inhibit the activation of NF-κB pathway in a STAT3-associated manner, thereby downregulating the inflammatory cytokine expressions.

Shenqi fuzheng injection attenuates irradiation-induced brain injury in mice via inhibition of the NF-κB signaling pathway and microglial activation

AIM

Radiation-induced brain injury (RIBI) is the most common and severe adverse effect induced by cranial radiation therapy (CRT). In the present study, we examined the effects of the traditional Chinese medicine Shenqi Fuzheng Injection (SFI) on RIBI in mice, and explored the underlying mechanisms.

METHODS

C57BL/6J mice were subjected to a single dose of 20-Gy CRT. The mice were treated with SFI (20 mL·kg(-1)·d(-1), ip) for 4 weeks. Morris water maze test was used to assess the cognitive changes. Evans blue leakage and a horseradish peroxidase (HRP) assay were used to evaluate the integrity of the blood-brain barrier (BBB). The expression of inflammatory factors and microglial activation in brain tissues were detected using RT-PCR, Western blotting and immunofluorescence staining.

RESULTS

CRT caused marked reductions in the body weight and life span of the mice, and significantly impaired their spatial learning. Furthermore, CRT significantly increased the BBB permeability, number of activated microglia, expression levels of TNF-α and IL-1β, and the levels of phosphorylated p65 and PIDD-CC (the twice-cleaved fragment of p53-induced protein with a death domain) in the brain tissues. Four-week SFI treatment (administered for 2 weeks before and 2 weeks after CRT) not only significantly improved the physical status, survival, and spatial learning in CRT-treated mice, but also attenuated all the CRT-induced changes in the brain tissues. Four-week SFI pretreatment (administered for 4 weeks before CRT) was less effective.

CONCLUSION

Administration of SFI effectively attenuates irradiation-induced brain injury via inhibition of the NF-κB signaling pathway and microglial activation.

Markers for blood-brain barrier integrity: how appropriate is Evans blue in the twenty-first century and what are the alternatives?

In recent years there has been a resurgence of interest in brain barriers and various roles their intrinsic mechanisms may play in neurological disorders. Such studies require suitable models and markers to demonstrate integrity and functional changes at the interfaces between blood, brain, and cerebrospinal fluid. Studies of brain barrier mechanisms and measurements of plasma volume using dyes have a long-standing history, dating back to the late nineteenth-century. Their use in blood-brain barrier studies continues in spite of their known serious limitations in in vivo applications. These were well known when first introduced, but seem to have been forgotten since. Understanding these limitations is important because Evans blue is still the most commonly used marker of brain barrier integrity and those using it seem oblivious to problems arising from its in vivo application. The introduction of HRP in the mid twentieth-century was an important advance because its reaction product can be visualized at the electron microscopical level, but it also has limitations. Advantages and disadvantages of these markers will be discussed together with a critical evaluation of alternative approaches. There is no single marker suitable for all purposes. A combination of different sized, visualizable dextrans and radiolabeled molecules currently seems to be the most appropriate approach for qualitative and quantitative assessment of barrier integrity.

Characteristics of a rat model of an open craniocerebral injury at simulated high altitude

To establish a rat model of an open craniocerebral injury at simulated high altitude and to examine the characteristics of this model. Rats were divided randomly into a normobaric group and a high-altitude group and their corresponding control groups. A rat model of an open craniocerebral injury was established with a nail gun shot. Simulated high-altitude conditions were established with a hypobaric chamber at 0.6 ATA to mimic pressure at an altitude of 4000 m. Mortality, brain water content (BWC), Evans blue content, pathology, regional cerebral blood flow (rCBF), partial pressure of brain tissue oxygen (PbtO₂), and brainstem auditory-evoked potential were observed after injury. The mortality of the high-altitude group was significantly greater than that of the normobaric group within 72 h after injury (P<0.05). BWC and Evans blue content increased by 48 h after injury (P<0.05); pathological changes in damaged brains were more serious. In contrast, rCBF and PbtO₂ had decreased markedly by 72 h (P<0.01); brainstem auditory-evoked potential values were significantly prolonged (P<0.05). Moreover, an inverse correlation between rCBF and BWC and a positive correlation between rCBF and PbtO₂ were found. The rat model of an open craniocerebral injury at simulated high altitude can be established successfully using a nail gun shot and a hypobaric chamber. The injury characteristics at high altitude were more serious, rapid, and prolonged than those in the normobaric group.