Hyperbaric Oxygen Pretreatment Research Articles

Hyperbaric oxygen therapy aggravates liver reperfusion injury in rats

To evaluate the effects of hyperbaric oxygen (HO) therapy in the protection against liver ischemia/reperfusion injury. Thirty-two male Wistar rats were divided into four groups of eight animals each: group A - laparotomy and liver manipulation, group B - liver ischemia and reperfusion, group C - HO pretreatment for 60 min followed by liver ischemia and reperfusion, and group D - pretreatment with ambient air at 2.5 absolute atmospheres for 60 min followed by liver ischemia and reperfusion. Plasma was assayed for aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH). Intra-arterial blood pressure was monitored continuously. Myeloperoxidase activity in the liver and lung was assessed 30 min after reperfusion. Plasma AST, ALT and LDH increased after reperfusion in all animals. Plasma ALT values and myeloperoxidase activity in the liver parenchyma were higher in HO-pretreated animals than in groups A, B and D. HO had a negative hemodynamic effect during liver reperfusion. Liver preconditioning with hyperbaric oxygen therapy aggravated liver ischemia/reperfusion injury in rats as demonstrated by plasma ALT and liver myeloperoxidase activity.

Beneficial Effects of Hyperbaric Oxygen Pretreatment on Massive Hepatectomy Model in Rats

The purpose of this study was to investigate the impact of hyperbaric oxygen (HBO) pretreatment in massive hepatectomy model, a surrogate model of small-for-size graft, using rats. (Experiment I) Rats were divided into the following four groups: HBO (-), HBO-1D (day), HBO-3D, and HBO-5D. Samples were taken after the completion of HBO pretreatment, and the following parameters were evaluated: reverse transcription polymerase chain reaction and immunohistochemical staining for HSP 70 and HO-1; biochemical parameters; and liver weight to body weight ratio (Lw/Bw ratio). (Experiment II) Rats were divided into four groups as follows; 70% hepatectomy (Hx), 70% Hx-HBO, 90% Hx, and 90% Hx-HBO group. Samples were taken 12, 24, 48, and 72 hr after hepatectomy and the following parameters were investigated: biochemical analysis; Lw/Bw ratio; PCNA labeling index; and survival. (Experiment I) The expression of HSP70 mRNA was significantly increased in the HBO-3D group compared with the HBO (-) group (P<0.05). HSP70- and HO-1-positive hepatocytes were significantly increased in the HBO-3D group compared with the HBO (-) group (P<0.05). (Experiment II) Transaminases were significantly decreased in both 70% and 90% Hx-HBO groups compared with Hx alone group (P<0.05). The Lw/Bw ratio and PCNA labeling index of the 90% Hx-HBO group were significantly increased compared with the 90% Hx group, 24, 48 and 72 hr after hepatectomy (P<0.05). The survival rate in the 90% Hx-HBO group was significantly higher than that in the 90% Hx group (P=0.01). HBO pretreatment had beneficial effects in a massive hepatectomy model in rats via the induction of HSP70 and HO-1.

Hyperbaric oxygen pretreatment reduces the incidence of decompression sickness in rats

We have previously hypothesised that the number of bubbles evolving during decompression from a dive, and therefore the incidence of decompression sickness (DCS), might be reduced by pretreatment with hyperbaric oxygen (HBO). The inert gas in the gas micronuclei would be replaced by oxygen, which would subsequently be consumed by the mitochondria. This has been demonstrated in the transparent prawn. To investigate whether our hypothesis holds for mammals, we pretreated rats with HBO at 304, 405, or 507 kPa for 20 min, after which they were exposed to air at 1,013 kPa for 33 min and decompressed at 202 kPa/min. Twenty control rats were exposed to air at 1,013 kPa for 32 min, without HBO pretreatment. On reaching the surface, the rat was immediately placed in a rotating cage for 30 min. The animal's behaviour enabled us to make an early diagnosis of DCS according to accepted symptoms. Rats were examined again after 2 and 24 h. After 2 h, 65% of the control rats had suffered DCS (45% were dead), whereas 35% had no DCS. HBO pretreatment at 304, 405 and 507 kPa significantly reduced the incidence of DCS at 2 h to 40, 40 and 35%, respectively. Compared with the 45% mortality rate in the control group after 24 h, in all of the pretreated groups this was 15%. HBO pretreatment is equally effective at 304, 405 or 507 kPa, bringing about a significant reduction in the incidence of DCS in rats decompressed from 1,013 kPa.

Preconditioning with hyperbaric oxygen induces tolerance against oxidative injury via increased expression of heme oxygenase-1 in primary cultured spinal cord neurons

Hyperbaric oxygen (HBO) preconditioning can induce ischemic tolerance in the spinal cord. The effect can be attenuated by the administration of an oxygen free radical scavenger or by inhibition of antioxidant enzymes. However, the mechanism underlying HBO preconditioning of neurons against ischemic injury remains enigmatic. Therefore, in the present study primary cultured spinal cord neurons were treated with HBO and then subjected to a hydrogen peroxide (H 2O 2) insult. The results show that H 2O 2 stimulation of the cultured spinal neurons caused severe DNA damage and decreased cell viability, and that these neurons were well protected against damage after a single exposure to HBO preconditioning (0.35 MPa, 98% O 2, 37 °C, 2 h). The protective effect started 4 h after pretreatment and lasted for at least 24 h. The cultured neurons after HBO treatment also exhibited increased heme oxygenase-1 (HO-1) expression at both the protein and mRNA levels, which paralleled the protective effect of HBO. Treatment with tin-mesoporphyrin IX (SnMP), a specific HO-1 inhibitor, before HBO pretreatment abolished the HBO-induced adaptive protection noted in the cultured spinal neurons. In conclusion, HBO preconditioning can protect primary cultured spinal cord neurons against oxidative stress, and the upregulation of HO-1 expression plays an essential role in HBO induced preconditioning effect.

Hyperbaric Oxygenation Attenuates Renal Ischemia–Reperfusion Injury in Rats

Background Oxygen-derived free radicals play an important role in ischemia–reperfusion injury (IR). Hyperbaric oxygenation (HO) decreases free radical production. The aim of this study was to determine the effect of HO treatment on renal ischemia–reperfusion injury in rats. Methods Rats were divided into four groups. All groups underwent right nephrectomy. Group I served as the control group; group II had left renal ischemia–reperfusion; group III was pretreated with HO; and group IV, ischemia–reperfusion and HO pretreatment. Tissue malondialdehyde (MDA) and glutathione (GSH) levels were measured, and histopathologic damage scored. Results HO pretreatment significantly decreased tissue MDA levels and histopathologic scores among rats with IR. There was an increased GSH in HO-pretreated rats with IR; however, the difference was not significant. Conclusion HO prior to ischemia displayed a beneficial effect on renal IR by reducing oxygen radical peroxidation of lipid membranes.

HO-1 Mediates the Effects of HBO Pretreatment Against Sepsis

We have recently shown that attenuation of sepsis-induced lung injury by hyperbaric oxygen (HBO) pretreatment involves expression regulation of inducible nitric oxide synthase (iNOS) and heme oxygenase (HO)-1. This study was performed to determine the effects of HBO pretreatment on acute kidney and liver injuries in septic rats and the roles of iNOS and HO-1. One group of adult male rats (n = 48) were pretreated with HBO. The other group of rats (n = 48) breathed air at normal atmospheric pressure instead. Rats in each group were randomly allocated to receive injection of lipopolysaccharide (LPS), normal saline (N/S), LPS plus hemin (a HO-1 inducer), hemin, LPS plus SnPP (a HO-1 inhibitor), SnPP, LPS plus hemin plus SnPP, or hemin plus SnPP. Hemin and SnPP were injected at 1 h before HBO or air pretreatment. Rats were maintained for 6 h before sacrifice. LPS caused prominent kidney and liver injuries as well as iNOS and HO-1 expression in stimulated rats. HBO pretreatment significantly attenuated LPS-induced kidney but not liver injury. However, in conjunction with hemin (a HO-1 inducer), HBO pretreatment did attenuate LPS-induced liver injury. In addition, the inhibition of iNOS expression by HBO pretreatment was associated with "super-induction" (i.e., further enhancement) of LPS-induced HO-1 expression. Furthermore, the therapeutic effect of HBO could be counteracted by SnPP (a HO-1 inhibitor). HBO pretreatment significantly attenuates LPS-induced acute organ injuries in septic rats. The beneficial effect of HBO pretreatment against sepsis is mediated, at least in part, by "super-induction" of HO-1.

Pre-treatment with hyperbaric oxygenation reduces bubble formation and platelet activation

Bubble formation and platelet activation are major factors contributing to decompression sickness. We hypothesized that pretreatment with hyperbaric oxygen immediately before a dive may reduce bubble formation and platelet activation in humans. Five healthy volunteer subjects (1 female and 4 males; age, 33.6±2.9 years; height, 170±3 cm; weight, 71±8 kg, body mass index, 24.5±22.0 kg/m2) participated in this study with a 4-day protocol. On day 1, a multiplace hyperbaric chamber was used to compress all subjects with air to 4 atmosphere absolute (ATA) for 25 minutes; they were then decompressed to surface pressure at a rate of 10 m/min. Once surface pressure was reached, they were monitored with precordial ultrasonic Doppler at 20 min, 50 min and 80 min. Venous blood samples were obtained immediately before and after pressure exposure. On day 2, all subjects were compressed at 1.6 ATA for 45 min with 100% oxygen; they were then decompressed to surface pressure at a rate of 10 m/min. As soon as they reached surface pressure, they were immediately exposed to the same compression-decompression protocol as day 1; blood samples were taken after the second pressure exposure. Platelet activation was examined before and after exposure. On days 3 and 4, we inverted the protocol to minimize the influence of the first immersion on bubble formation. In comparison to the standard compression protocol, compression after hyperbaric oxygenation led to significantly reduced bubble numbers and platelet activation (11.4%±0.7% vs. 5.4%±0.5%, p<0.05). This study shows that hyperbaric oxygenation pretreatment significantly reduces decompression-induced bubble formation and platelet activation. Hyperbaric oxygenation pretreatment may reduce the risk of decompression sickness in at-risk activities.

Hyperbaric oxygen attenuation of lipopolysaccharide‐induced acute lung injury involves heme oxygenase‐1

Hyperbaric oxygen (HBO) attenuates lipopolysaccharide (LPS)-induced acute lung injury. This beneficial effect of HBO involves inhibition of inducible nitric oxide synthase (iNOS) expression and subsequent nitric oxide (NO) biosynthesis. We sought to investigate the role of heme oxygenase-1 (HO-1) on this HBO inhibition of iNOS induction and acute lung injury in septic rat lungs. Before the experiment, 72 rats were randomly allocated to receive HBO or air treatment. With or without HBO pre-treatment, the rats were further divided into the following subgroups (n = 6): (i) LPS injection, (ii) normal saline (N/S) injection, (iii) hemin (a HO-1 inducer) plus LPS, (iv) hemin alone, (v) tin protoporphyrin (SnPP; a HO-1 inhibitor) plus LPS, and (vi) SnPP alone. All rats were maintained for 6 h and then sacrificed with a high-dose pentobarbital injection. Lung injuries and relevant enzymes expression were thus assayed. Histological analysis, PMNs/alveoli ratio, and wet/dry weight ratio measurements demonstrated that LPS caused significant lung injury and HBO and/or hemin significantly attenuated this LPS-induced lung injury. Increased pulmonary iNOS expression and NO production were associated with lung injury. Induction of HO-1, by HBO and/or hemin, significantly attenuated this LPS-induced iNOS expression and acute lung injury. SnPP, on the contrary, offset the effects of HBO and worsened the LPS-induced lung injury. HBO may act through inhibiting pulmonary iNOS expression to attenuate LPS-induced acute lung injury in septic rats. Furthermore, this HBO attenuation of iNOS expression involves HO-1 induction.

Effect of hyperbaric oxygenation on the regeneration of the liver after partial hepatectomy in rats.

The aim of the present study was to assess the influence of hyperbaric oxygenation (HBO) on rat liver regeneration before and after partial hepatectomy. Rats were sacrificed 54 h after 15% hepatectomy, liver and body weights were measured, and serum alanine transaminase (ALT) and aspartate transaminase (AST) activity and albumin levels were determined. The lipid peroxide level, as indicated by malondialdehyde production in the remnant liver was measured, and liver sections were analyzed by light microscopy. Five groups of 10 rats in each group were studied. The preHBO and pre-hyperbaric pressure (preHB) groups were treated before partial hepatectomy with 100% O2 and 21% O2, respectively, at 202,650 pascals, daily for 3 days (45 min/day). The control group was not treated before partial hepatectomy and recovered under normal ambient conditions after the procedure. Groups postHBO and postHB were treated after partial hepatectomy with HBO and HB, respectively, three times (45 min/day). The preHBO group presented a significant increase in the initiation of the regeneration process of the liver 54 h postoperatively. The liver/body weight ratio was 0.0618 +/- 0.0084 in the preHBO compared to 0.0517 +/- 0016 g/g in the control animals (P = 0.016). In addition, the preHBO group showed significant better liver function (evaluated by the lowest serum ALT and AST activities, P = 0.002 and P = 0.008, respectively) and showed a significant decrease in serum albumin levels compared to control (P < 0.001). Liver lipid peroxide concentration was lowest in the preHBO group (P < 0.001 vs control and postHBO group) and light microscopy revealed that the composition of liver lobules in the preHBO group was the closest to normal histological features. These results suggest that HBO pretreatment was beneficial for rat liver regeneration after partial hepatectomy.

Genotoxic and protective effects of hyperbaric oxygen in A549 lung cells.

The human lung cell line A549 is frequently used as an in vitro model for studying lung toxicity and genotoxicity of environmental mutagens and carcinogens. Hyperbaric oxygen (HBO) treatment has been shown to be an excellent model for investigating the genetic consequences of oxidative stress in vitro and in vivo. We have now studied the genotoxic effects of and adaptive protection by HBO in A549 cells. Using the alkaline Comet assay, our results show that HBO exposure directly induces DNA damage but reduces the DNA-damaging effect of a second HBO treatment of the cells 24 h later. HBO pretreatment also reduces potassium chromate-induced genotoxicity in A549 cells. Heme oxygenase-1 (HO-1) protein level is increased 24 h after HBO exposure and inhibition of HO-1 activity by tin-mesoporphyrin increased HBO genotoxicity. These results are in accordance with previous findings suggesting an involvement of HO-1 in the adaptive protection. Our study indicates that A549 cells are an appropriate cell culture system for the evaluation of genetic effects induced by HBO in lung cells.

Neuroprotective effects of hyperbaric oxygen treatment in experimental focal cerebral ischemia are associated with reduced brain leukocyte myeloperoxidase activity

Objective: Hyperbaric oxygen (HBO) reduces cerebral infarct size after middle cerebral artery occlusion (MCAO) in rats through an unknown mechanism. In other forms of injury, cellular protection with HBO is associated with diminished infiltration of polymorphonuclear neutrophils (PMN). We hypothesized that HBO given prior to or after MCAO reduces PMN infiltration into the brain, and that decreased PMN infiltration is associated with improved functional and anatomic outcome. Methods: Forty rats underwent MCAO and were randomized to pretreatment with HBO (3 ATA) immediately prior to ( n=13), or posttreatment immediately after surgery ( n=12), or to control (air 1 ATA) ( n=15). Five rats underwent sham surgery. Neurologic outcome was measured at 24 h in all animals. Brain myeloperoxidase (MPO) activity ( n=22) and infarct volume ( n=23) were determined. Results: MPO activity was significantly higher in controls (mean 0.28, 95% C.I. 0.17–0.38) than in the HBO pretreatment group (0.12, 0.08–0.16), HBO posttreatment group (0.16, 0.13–0.19), and the sham group (0.02, −0.02 to 0.05). HBO treated animals also had better neurologic outcomes (pretreatment 1.5, 0.9–2.1, posttreatment 2.6, 2.0–3.2) and smaller infarcts (pretreatment 27%, 18–37%, posttreatment 28%, 19–37%) than controls (neurologic outcome 3.7, 3.1–4.4, infarct volume 39%, 30–48%). Neurologic outcomes correlate better with MPO activity ( R 2=0.75) than with infarct volume ( R 2=0.25). Conclusion: These data confirm the neuroprotective effects of HBO in cerebral ischemia and suggest that the mechanism of this action may involve inhibition of PMN infiltration in the injured brain.

Preconditioning with hyperbaric oxygen and hyperoxia induces tolerance against spinal cord ischemia in rabbits.

The aim of this study was to determine if the ischemic tolerance could be induced in the spinal cord by pretreatment with hyperbaric oxygen (HBO) and what components of HBO (hyperoxia, hyperbaricity, and combination of these two) were critical in the induction of tolerance against ischemic injury. In experiment 1, 21 rabbits were randomly assigned to one of three groups (n = 7 each): animals in the control group received no HBO before spinal cord ischemia; animals in the HBO-1 and HBO-2 groups received HBO (2.5 atmosphere absolute [ATA], 100% O2) pretreatment 1 h/day for 3 and 5 days before ischemia, respectively. In experiment 2, 48 rabbits were randomly assigned to one of four groups (n = 12 each): the control group received no HBO (21% O2, 1 ATA, 1 h/day, 5 days) before spinal cord ischemia; the HB group received 1-h treatment in 21% O2 at 2.5 ATA each day for 5 days; the HO group received 1-h treatment in 100% oxygen at 1 ATA each day for 5 days; and the HBO group received HBO (2.5 ATA, 100% O2) treatment 1 h/day for 5 days. Twenty-four hours after the last treatment, spinal cord ischemia was induced by an infrarenal aorta clamping for 20 min. Forty-eight hours after reperfusion, hind-limb motor function and histopathology of the spinal cord were examined in a blinded fashion. In experiment 1, the neurologic outcome in the HBO-2 group was better than that of the control group (P = 0.004). The number of normal neurons in the anterior spinal cord in the HBO-2 group was more than that of the control group (P = 0.021). In experiment 2, the neurologic and histopathologic outcomes in the HBO group were better than that of the control group (P < 0.01). The histopathologic outcome in the HO group was better than that in the control group (P < 0.05). Serial exposure to high oxygen tension induced ischemic tolerance in spinal cord of rabbits. Simple hyperbaricity (2.5 ATA, 21% O2) did not induce ischemic tolerance.

Hyperbaric oxygenation pretreatment induces catalase and reduces infarct size in ischemic rat myocardium.

Ischemia-reperfusion injury is a major complication occurring in heart stroke, cardiopulmonary bypass surgeries, and heart transplantation. Reactive oxygen species generated during the reperfusion phase overwhelm the scavenging capacities of antioxidant enzymes, and result in oxidative damage to the myocardium. We examined whether hyperbaric oxygenation (HBO) pretreatment induces antioxidant enzymes and protects the heart from subsequent ischemia-reperfusion injury. Rats were intermittently exposed to 100% O2 at 3 ATA (where ATA is absolute atmosphere) for 1 h daily and then sacrificed after 24 h of recovery in room air. Isolated hearts were subjected to 40 min of ischemia and 90 min of reperfusion. HBO pretreatment was found to condition the heart and enhance enzymatic activity and gene expression of catalase, thereby significantly reducing infarct size after reperfusion. A catalase inhibitor, 3-amino-1,2,4-triazole, completely abolished the infarct-limiting effect of HBO pretreatment, which suggests that HBO-induced tolerance against ischemia-reperfusion injury is due to catalase induction. Our results imply that HBO preconditioning may be developed as a new preventive measure for reperfusion injury in the heart.

Preferential conditions for and possible mechanisms of induction of ischemic tolerance by repeated hyperbaric oxygenation in gerbil hippocampus.

We reported previously that repeated hyperbaric oxygenation (HBO) as pretreatment induced ischemic tolerance in the gerbil hippocampus. This study was conducted to determine the preferential conditions for induction of ischemic tolerance by HBO and the mechanism of this induction through immunohistochemical analysis of Bcl-2, Bax, and manganese superoxide dismutase expression. Five-minute forebrain ischemia was produced in gerbils after pretreatment with 2 atmospheres absolute (ATA) HBO once every other day for one, three, or five sessions, 2 ATA hyperbaric air once every other day for five sessions, or 3 ATA HBO once daily for 10 sessions. Histological examinations were then performed. Two days after pretreatment with 2 ATA HBO once every other day for five sessions or with 3 ATA HBO once daily for 10 sessions, sections were analyzed immunohistochemically. Pretreatment with 2 ATA HBO once every other day for three or five sessions induced ischemic tolerance; however, pretreatment with 2 ATA HBO for one session, 2 ATA hyperbaric air once every other day for five sessions, or 3 ATA HBO once daily for 10 sessions did not. Pretreatment with 2 ATA HBO once every other day for five sessions, but not with 3 ATA HBO once daily for 10 sessions, significantly increased Bcl-2 and manganese superoxide dismutase immunoreactivity in the CA1 sector. These results suggest that protection against mitochondrial alterations after ischemia through manganese superoxide dismutase and/or Bcl-2 expression may be related to induction of ischemic tolerance by repeated HBO pretreatment.

Hyperbaric oxygen pretreatment attenuates hepatic reperfusion injury.

Microcirculatory derangement, energy depletion and lipid peroxidation have been related to development of ischemia-reperfusion injury in the liver. This study investigates the effects of hyperbaric oxygen (HBO) on hepatic ischemia-reperfusion injury. Adult, male Sprague-Dawley rats were used. Three groups were evaluated: 1) sham-operated control (laparotomy only, no ischemia, no HBO), n=8; 2) ischemia control (1-h ischemia, 2-h reperfusion, no HBO), n=8; and 3) HBO pretreatment (100%, oxygen, 2.5 atm absolute, 90 min) plus ischemia (1-h ischemia, 2-h reperfusion), n=8. An in vivo microscope was used to investigate hepatic microcirculation. Tissue malondialdehyde (MDA) and adenosine triphosphate (ATP) were determined. In comparison with the ischemia control group, HBO significantly improved harmful insults following ischemia-reperfusion. HBO lessened adherent leukocyte count (6.00+/-1.31 cells/200 microm vs 11.38+/-2.88 cells/200 microm), and improved flow velocity (1.72+/-0.26 mm/s vs 0.83+/-0.19 mm/s) in post-sinusoidal venules. HBO also reduced MDA (1.04+/-0.24 nmol/mg protein vs 2.24+/-0.49 micromol/g protein), and increased ATP (2.03+/-0.17 micromol/g wet wt vs 0.73+/-0.11 micromol/g wet wt) levels. This study demonstrates that HBO before ischemia may ameliorate the ischemia-reperfusion injury of the liver in the rat model.

MODULATION OF THE RESPONSE OF A RODENT FIBROSARCOMA TO PHOTODYNAMIC THERAPY BY HYPERBARIC-OXYGEN TREATMENT

The ability of hyperbaric oxygen (HBO) treatment to modulate the response of a rodent fibrosarcoma to interstitial photodynamic therapy (PDT) using 630 nm light and intravenous polyhaematoporphyrin (PHP) was examined. Application of HBO for 30 min immediately prior to PDT resulted in a light dose-dependent increase in tumour growth retardation, maximum effect (+227%) being observed with 100J light, and no enhancement being seen at or above 400J. Application of HBO during or immediately after PDT had no effect on response. Reducing the interval between giving PHP and administering light from the usual 48 h to just 1 h increased the efficacy of PDT even in the absence of HBO pre-treatment. Under these circumstances, application of HBO did not realise any further increase in tumour response at any light dose. Our findings suggest that manipulation of tumour oxygenation may be able to improve the outcome of PDT under some circumstances, but that careful consideration of other treatment variables, such as light dose and drug-to-light interval, may provide similar, more easily achievable, improvements in efficacy.