Hydrogen saline offers neuroprotection by reducing oxidative stress in a focal cerebral ischemia-reperfusion rat model
© Liu et al; licensee BioMed Central Ltd. 2011
Received: 5 March 2011
Accepted: 5 July 2011
Published: 5 July 2011
Hydrogen gas is neuroprotective in cerebral ischemia animal models. In this study, we tested the neuroprotective effects of hydrogen saline, which is safe and easy to use clinically, in a rat model of middle cerebral artery occlusion (MCAO). Sprague-Dawley male rats weighting 250-280 g were divided into sham, MCAO plus hydrogen saline and MCAO groups, and subjected to 90-min ischemia followed by 24 h of reperfusion. Hydrogen saline was injected intraperitoneally at 1 ml/100 g body weight. Infarct volume and brain water content were evaluated at different time points after reperfusion. Oxidative stress, inflammation, and apoptotic cell death markers were measured. Hydrogen saline significantly reduced the infarct volume and edema and improved the neurological function, when it was administered at 0, 3 and 6 h after reperfusion. Hydrogen saline decreased 8-hydroxyl-2'-deoxyguanosine (8-OHdG), reduced malondidehyde, interleukin-1β, tumor necrosis factor-α, and suppressed caspase 3 activity in the ischemic brain. These findings demonstrated hydrogen saline is neuroprotective when administered within 6 h after ischemia. Because hydrogen saline is safe and easy to use, it has clinical potentials to reduce neurological injuries.
Stroke is the second most frequent cause of death worldwide and the most frequent cause of permanent disability [1, 2]. Advances in intravascular techniques and thrombolytic agents have reduced functional deficits within an optimal time window in stroke patients. However, reperfusion itself generates an over-production of reactive oxygen species (ROS), leading to reperfusion injury . The burst of ROS is involved in the direct cytotoxic effects, including protein and lipid peroxidation, oxidative DNA damage, and post-ischemic inflammatory injury, through redox-mediated signaling pathways [4, 5]. Therefore it is important to scavenge the free radicals and suppress the inflammation.
Hydrogen gas has been used in medical applications to prevent decompression sickness (DCS) in deep divers for safety profiles . In 2007, Ohsawa et al found that molecular hydrogen can selectively reduce hydroxyl radical (OH) and peroxynitrite (ONOO-) in cell-free systems and exert a therapeutic antioxidant activity in rat middle cerebral artery occlusion (MCAO) model . Some other observations showed that hydrogen also had the protective effect on ischemia-reperfusion injury in the intestine, liver and heart through the inhibition of oxidant stress [8–10].
Hydrogen gas would be much cheaper than other antioxidants if it could be clinically applied. However, hydrogen inhalation is not convenient and may be dangerous because it is inflammable and explosive if the concentration of hydrogen in the air is greater than 4%. On the other hand, after saturated in the physiological saline, molecule hydrogen in the saline is more easy to apply and safer than hydrogen inhalation. Considering the safety and the convenience, hydrogen saline has been prepared in our department and our previous experiments have demonstrated the neuroprotective effects of intraperitoneal hydrogen saline in a neonatal hypoxia-ischemia rat model . Additionally, significantly improved post-ischemic functional recovery of rat hearts has also proved after hydrogen saline treatment . The present study aimed to investigate the neuroprotective effect of hydrogen saline in the rat MCAO model.
Materials and methods
All experimental procedures and protocols used in this study were reviewed and approved by the Animal Care and Use Committee of the Second Military Medical University. Furthermore, all were in accordance with the Guide for the Care and Use of Laboratory Animals. A total of 228 male Sprague-Dawley rats weighing 250-280 g were used in the present study. The rats were housed at 22-24°C under a 12-h-light/12-h-dark cycle, with food and water available ad libitumthroughout the studies. Rats were randomly distributed into three groups, sham group (n = 52), MCAO group (n = 72) and MCAO plus hydrogen group (n = 104). Rats in the sham group only received intraperitoneal administration of normal saline and those in the MCAO group underwent MCAO followed by administration of normal saline at different time points (0, 3 or 6 h) after reperfusion onset. However, rats in the MCAO plus hydrogen group received MCAO and intraperitoneal treatment with hydrogen saline (1 ml/100 g body weight) at designed time points (0, 3 or 6 h after reperfusion onset). MCAO was produced by the filament model initially reported by Zea-Longa et al  with some modifications. After 90 min of right middle cerebral artery occlusion, the reperfusion of the MCA was initiated by removing the MCA occlusive filament. Rats were sacrificed at 12, 24, 72 h, and 7 days after reperfusion, and immunihistochemistry and detections of malondidehyd (MDA), anti-superoxide anion, interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) were performed.
Neurological function was assessed using a standard scoring system : 0 = no apparent deficits, 1 = contralateral forelimb flexion, 2 = decreased grip of contralateral forelimb, 3 = contralateral circling if pulled by tail, 4 = spontaneous contralateral circling.
Evaluation of Infarct Volume
Infarct volume was determined by staining with 2, 3, 5-triphenyltetrazolium chloride (TTC, Sigma) as previously described . The infarct and total hemispheric areas of each section, at intervals of 2-mm in thickness, were traced and analyzed using image analysis system (Image J software). The infarct ratio was calculated by dividing the infarct volume by the total volume of the sections.
Brain Water Content
The brains were obtained and right hemisphere was quickly separated. Brain samples were weighted with a precise electronic balance and dried in an oven at 100 °C for 48 h . Then, the samples were re-weighed and the water content was determined according to the following formula: [(wet weight - dry weight)/wet weight] × 100%.
For Nissl staining, the 4-μm sections were hydrated in 1% toluidine blue at 50 °C for 20 min. After rinsing with double distilled water, they were dehydrated and mounted with permount. The cortex from each animal was captured and Imaging-Pro-Plus (LEIKA DMLB) was used to perform quantitative analysis of cell numbers.
Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) was performed on paraffin-embedded sections by using the in situcell death detection kit (Roche). According to standard protocols, the sections were de-paraffinized and rehydrated by heating the slides at 60 °C. Then these sections were incubated in a 20 μg/ml proteinase K working solution for 15 min at room temperature. The slides were rinsed three times with phosphate buffer solution (PBS) before they were incubated in TUNEL reaction mixture for 1 h at 37 °C. Dried area around sample and added Converter-AP on samples for 1 h at 37 °C. After rinsing with PBS (5 min, 3 times), color development was performed in dark with nitroblue tetrazolium (NBT) and 5-bromo-4-chloro-3-indolylphosphate (BCIP).
Immunohistochemistry was performed on 20 μm-thick free-floating coronal sections, which were prepared as previously described . After incubation in 3% hydrogen peroxide (H2O2) in PBS, the sections were incubated overnight at 4 °C with primary antibodies against 8-hydroxyl-2'-deoxyguanosine (8-OHdG, 100:1; America Alpha Diagnostic international, a marker for DNA damage), Nitrotyrosine (40:1; America upstate, a marker for nitration), bax (100:1; America Abcam) and bcl-2 (600:1; Americ Millipore). Sections were then treated with secondary antibodies (1:2000, Vectastain, Vector Laboratories). Immunoreactivity was visualized subsequently by the avidin-biotin complex method (Vectastain, Vector Laboratories) as described previously .
In each section, 6 visual fields (0.6 mm2) of cerebral cortex were randomly photographed. The number of staining cells in each field was counted at higher magnification (×200). Data were expressed as the number of cells per high-power field.
Detection of MDA
Lipid peroxidation levels were measured with the thiobarbituric acid (TBA) reaction. This method was used to obtain a spectrophotometric measurement of the color produced during the reaction of TBA with MDA at 535 nm. For this purpose, 2.5 ml of 100 g/l trichloroacetic acid solution was added to 0.5 ml of homogenate in centrifuge tube followed by heating in boiling water for 15 min. The mixture was allowed to cool to room temperature and centrifuged (Eppendorf, 5810R) at 1000 × g for 10 min. Then, 2 ml of supernatant was added to 1 ml of 6.7 g/l TBA solution in a test tube, followed by heating in boiling water for 15 min. The solution was then cooled and the absorbance was measured with a spectrophotometer (UV-WFZ75, Shanghai, China). TBARS levels were expressed as nmol/mg protein in the brain.
Caspase-3 activity assay
Brain samples from the cortex and hippocampus were taken from the impaired hemispheres of rats 24 h after hydrogen saline administration. The activity of caspase-3 was measured with caspase-3/CPP32 Fluorometric Assay Kit (BIOVISION Research Products 980, USA). Briefly, brain samples were homogenized in ice-cold lysis buffer and kept at 4 °C for 1 h. Brain homogenate was centrifuged at 12,000 g for 15 min at 4 °C. The supernatant was collected and stored at -80 °C for use. Protein concentration was measured using the Enhanced BCA Protein Assay Kit. A total of 50 μg of cell lysates were incubated in a 96-well plate with 2 × Reaction Buffer (50 μl). The reaction was started by adding 1 mM DEVD-APC substrate (5 μl). After incubation in dark at 37°C, the plate was read with a fluorometer equipped with a 400-nm excitation filter and 505-nm emission filter.
Determination of IL-1β and TNF-α Levels
The levels of IL-1β and TNFα of brain tissues were determined with solid phase sandwich ELISA kit (Invitrogen, USA) under a microplate reader (Stat Fax 3200) at 450 nm.
Infarct volume was reduced and brain edema was improved after treatment with hydrogen saline
Body weight loss was decreased accompanied by improved neurological score after hydrogen saline treatment
Nissl staining showed more viable cells after treatment with hydrogen saline
DNA oxidation was declined demonstrated by 8-OHdG staining after hydrogen saline treatment
Number of apoptotic cells was decreased in TUNEL staining by hydrogen saline treatment
After hydrogen saline treatment, expressed of Bcl-2 was increased accompanied by decreased Bax expression and Capase-3 activity
Lipid peroxidation was improved by hydrogen saline treatment
Levels of IL-1β and TNF-α were decreased by hydrogen saline treatment
In the present study, we evaluated the neuroprotective effects of hydrogen saline against cerebral ischemia-reperfusion injury. The major findings were that hydrogen saline could reduce cerebral infarction and improve neurological function in the MCAO rat model, which were mediated by the reduction of oxidative stress (8-OHdG, nitrotyrosine and MDA) and inflammatory factors, and subsequent decrease of neuronal apoptosis (TUENL positive cells, expression of Bcl-2 and Bax, and caspase-3 activity). The therapeutic window of hydrogen saline was similar to other prominent neuroprotectants. The protective effects were more pronounced if they were applied immediately after reperfusion, but the protective effects could be achieved to a certain extent when they were applied at 6 h after reperfusion. Our findings were consistent with previous studies in which protective effects of hydrogen gas through scavenging ROS have been confirmed in a cardiac ischemia-reperfusion injury model .
Increasing evidence has demonstrated ROS contribute to ischemia/reperfusion induced brain damage in a 2-phase pattern, an immediately occurring direct cytotoxic damage and a post-ischemia/reperfusion inflammatory injury . ROS is massively produced in the brain after ischemia/reperfusion, and oxidative damage to brain tissues has been regarded as a fundamental mechanism of brain damage after transient or permanent cerebral ischemic injury [19, 20]. All of these species interact with nearby cellular components, such as proteins, lipids, and DNA [4, 5]. Some components in the reactive oxygen species such as superoxide anion and H2O2can be detoxified by antioxidant defense enzymes, while there is no enzyme to detoxify OH and ONOO-, extremely reactive free radicals in cells, until a recent study reported that hydrogen gas could selectively reduce these two harmful free radicals . Hydrogen molecule is electronically neutral and has the ability to penetrate the membranes of cell, nucleus and mitochondria. 8-OHdG is a product of direct oxidation of DNA by hydroxyl radicals and has been used as a marker for oxidative stress . Our results showed reduced number of 8-OHdG positive cells after MCAO by hydrogen saline. Our findings were consistent with a recent study on hydrogen inhalation in which hydrogen inhalation also reduced the oxidative stress following ischemia/reperfusion .
Oxidative stress can also lead to inflammatory response after ischemic stroke, which is characterized by enhanced cytokines production . Among the known cytokines, IL-1β and TNF-α are produced by macrophages, endothelial cells, astrocytes and neurons, and play crucial roles in the ischemic brain injury . Reduction of oxidative stress by hydrogen saline may result in the suppressed production of TNF-α and IL-1β as demonstrated by our study. A possible direct anti-inflammatory effect of hydrogen saline in cerebral ischemia warrants further investigation.
Oxidative stress and inflammation contribute to the activation of program cell death following cerebral ischemia . Oxidative stress can cause changes in the mitochondrial permeability resulting in the release of cytochrome c which then activates caspase-3 executing cell death signals. By reducing oxidative stress and inflammation, hydrogen saline suppressed caspase-3 activity in the ischemic cortex, which might be related to the decreased release of cytochrome c. Two other important mitochondrial apoptotic factors Bcl-2 and Bax were examined in the present study . Consistently, hydrogen saline treatment also up-regulated the Bcl-2 expression and down-regulated the Bax expression.
Of note, although the protective effects were also observed in our previous study, the therapeutic effects of hydrogen saline were more profound than those of hydrogen inhalation. In addition, the effects of intravenous administration of hydrogen were inferior to those of intraperitoneal treatment, which may be explained by rapid elimination of hydrogen through pulmonary gas exchange. But the exact mechanism should be further investigated. Although the intravenous application was more clinical than intraperitoneal administration, intraperitoneal injection was frequently performed in animals. Therefore, in the present study, intraperitoneal administration of hydrogen saline was conducted to observe the neuroprotective effects. Furthermore, in our pilot study on animals and humans, some parameters did not show evident side effects even with several large doses of hydrogen saline were applied.
Taking together, hydrogen has been shown anti-oxidative stress and is beneficial on lipid and glucose metabolism in humans . Hydrogen water also decreased superoxide formation caused by ischemia-reperfusion in the brain slices of mice . For the safety and the convenience of hydrogen administration, hydrogen saline was prepared and protective effects of hydrogen saline confirmed in rat cardiac ischemia/reperfusion and neonatal hypoxia-ischemia models [11, 12]. In the present study, we further demonstrated that intraperitoneal administration of hydrogen saline yielded similar neuroprotective effects comparable to hydrogen inhalation [7, 22]. Therefore, our study for the first time showed hydrogen saline had potentials as an alternative pharmacological strategy in ischemic stroke.
This work was supported by grants 30971199 from the National Natural Science Foundation of China to Dr Xue-Jun Sun, and 08G066 from Research Project of Science and Technology of China to Dr Wei Zhang.
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