Preconditioned hyperbaric oxygenation protects the liver against ischemia-reperfusion injury in rats

An overview of hyperbaric oxygen preconditioning against ischemic stroke

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

Effects of Hyperbaric Oxygen Preconditioning on Doxorubicin Cardiorespiratory Toxicity

Cardiorespiratory dysfunction resulting from doxorubicin (DOX) chemotherapy treatment is a debilitating condition affecting cancer patient outcomes and quality of life. DOX treatment promotes cardiac and respiratory muscle pathology due to enhanced reactive oxygen species (ROS) production, mitochondrial dysfunction and impaired muscle contractility. In contrast, hyperbaric oxygen (HBO) therapy is considered a controlled oxidative stress that can evoke a substantial and sustained increase in muscle antioxidant expression. This HBO-induced increase in antioxidant capacity has the potential to improve cardiac and respiratory (i.e., diaphragm) muscle redox balance, preserving mitochondrial function and preventing muscle dysfunction. Therefore, we determined whether HBO therapy prior to DOX treatment is sufficient to enhance muscle antioxidant expression and preserve muscle redox balance and cardiorespiratory muscle function. To test this, adult female Sprague Dawley rats received HBO therapy (2 or 3 atmospheres absolute (ATA), 100% O₂, 1 h/day) for 5 consecutive days prior to acute DOX treatment (20 mg/kg i.p.). Our data demonstrate that 3 ATA HBO elicits a greater antioxidant response compared to 2 ATA HBO. However, these effects did not correspond with beneficial adaptations to cardiac systolic and diastolic function or diaphragm muscle force production in DOX treated rats. These findings suggest that modulating muscle antioxidant expression with HBO therapy is not sufficient to prevent DOX-induced cardiorespiratory dysfunction.

Can hyperbaric oxygen safely serve as an anti-inflammatory treatment for COVID-19?

INTRODUCTION

SARS-CoV-2 affects part of the innate immune response and activates an inflammatory cascade stimulating the release of cytokines and chemokines, particularly within the lung. Indeed, the inflammatory response during COVID-19 is likely the cause for the development of acute respiratory distress syndrome (ARDS). Patients with mild symptoms also show significant changes on pulmonary CT-scan suggestive of severe inflammatory involvement.

HYPOTHESIS

The overall hypothesis is that HBO2 is safe and reduces the inflammatory response in COVID-19 pneumonitis by attenuation of the innate immune system, increase hypoxia tolerance and thereby prevent organ failure and reduce mortality.

EVALUATION OF THE HYPOTHESIS

HBO2 is used in clinical practice to treat inflammatory conditions but has not been scientifically evaluated for COVID-19. Experimental and empirical data suggests that HBO2 may reduce inflammatory response in COVID-19. However, there are concerns regarding pulmonary safety in patients with pre-existing viral pneumonitis.

EMPIRICAL DATA

Anecdotes from "compassionate use" and two published case reports show promising results.

CONSEQUENCES OF THE HYPOTHESIS AND DISCUSSION

Small prospective clinical trials are on the way and we are conducting a randomized clinical trial.

Hyperbaric Oxygen Preconditioning Can Reduce Postabdominoplasty Complications: A Retrospective Cohort Study

Supplemental Digital Content is available in the text.

Hyperbaric oxygen therapy (HBOT) can improve wound healing and has been found to have positive preconditioning effects in animal models. Among esthetic surgical procedures, abdominoplasty poses the highest rate of postoperative complications. The aim of this study was to evaluate the effect of preoperative HBOT as a preconditioning treatment for expected postsurgical complications.

Early hyperbaric oxygen therapy improves survival in a model of severe sepsis

Sepsis is a major clinical challenge, with therapy limited to supportive interventions. Therefore, the search for novel remedial approaches is of great importance. We addressed whether hyperbaric oxygen therapy (HBOT) could improve the outcome of sepsis using an acute experimental mouse model. Sepsis was induced in male CD-1 mice by cecal ligation and puncture (CLP) tailored to result in 80-90% mortality within 72 h of the insult. After CLP, mice were randomized into two groups receiving HBOT or not at different times after the initial insult or subjected to multiple HBOT treatments. HBOT conditions were 98% oxygen pressurized to 2.4 atmospheres for 1 h. HBOT within 1 h after CLP resulted in 52% survival in comparison with mice that did not receive the treatment (13% survival). Multiple HBOT at 1 and 6 h or 1, 6, and 21 h displayed an increase in survival of >50%, but they were not significantly different from a single treatment after 1 h of CLP. Treatments at 6 or 21 h after CLP, excluding the 1 h of treatment, did not show any protective effect. Early HBO treatment did not modify bacterial counts after CLP, but it was associated with decreased expression of TNF-α, IL-6, and IL-10 expression in the liver within 3 h after CLP. The decrease of cytokine expression was reproduced in cultured macrophages after exposure to HBOT. Early HBOT could be of benefit in the treatment of sepsis, and the protective mechanism may be related to a reduction in the systemic inflammatory response.

Heat Shock Protein 70 (HSP70) Reduces Hepatic Inflammatory and Oxidative Damage in a Rat Model of Liver Ischemia/Reperfusion Injury with Hyperbaric Oxygen Preconditioning

Background

Several clinical conditions can cause hepatic ischemia/reperfusion (I/R) injury. This study aimed to determine the mechanism of the protective effect of hyperbaric oxygen preconditioning (HBO₂P) on hepatic ischemia/reperfusion (I/R) injury in a rat model, and to investigate the effects on HBO₂P and I/R injury of blocking HSP70 using antibody (Ab) pretreatment.

Material/Methods

Male Sprague-Dawley rats underwent HBO₂P for 60 min at 2.0 atmosphere absolute (ATA) pressure for five consecutive days before surgical hepatic I/R injury, performed by clamping the portal vein and hepatic lobe. Four groups studied included: the non-HBO₂P+ non-I/R group, which underwent sham surgery (N=10); the non-HBO₂P + I/R group (N=10); the HBO₂P + I/R group (N=10); and the HBO₂P + HSP70-Ab + I/R group (N=10) received one dose of HSP70 antibody one day before hepatic I/R injury. Serum lactate dehydrogenase (LDH), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and pro-inflammatory cytokines, tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), and hepatic malondialdehyde (MDA) and myeloperoxidase (MPO) were measured biochemically. Rat liver tissues were examined histologically.

Results

In rats with hepatic I/R injury without HSP70 antibody pre-treatment, HBO₂P significantly reduced hepatic injury and levels of LDH, AST, ALT, TNF-α, IL-6, MDA, and MPO levels; in comparison, the group pre-treated with an antibody to inhibit HSP70 (the HBO₂P + HSP70-Ab + I/R group) showed significant reversal of the beneficial effects of HBO₂P on hepatic I/R injury (p<0.05).

Conclusions

In a rat model of hepatic I/R injury with HBO₂P, HSP70 reduced hepatic inflammatory and oxidative damage.

Strategies to Restore Adenosine Triphosphate (ATP) Level After More than 20 Hours of Cold Ischemia Time in Human Marginal Kidney Grafts

Background

The persisting organ shortage in the field of transplantation recommends the use of marginal kidneys which poorly tolerate ischemic damage. Adenosine triphosphate (ATP) depletion during cold ischemia time (CIT) is considered crucial for graft function. We tested different strategies of kidney perfusion before transplantation in the attempt to improve the technique.

Material/Methods

Twenty human discarded kidneys from donors after brain death and with at least 20 hours of CIT were randomized to the following experimental groups (treatment time three-hours at 4°C): a) static cold storage (CS); b) static cold hyperbaric oxygenation (Hyp); c) hypothermic perfusion (PE); d) hypothermic perfusion in hyperbaric oxygenation (PE-Hyp); and e) hypothermic oxygenated perfusion (PE-O₂).

Results

Histological results showed that perfusion with or without oxygen did not produce any endothelial damage. A depletion of ATP content following the preservation procedure was observed in CS, PE, and Hyp, while PE-Hyp and PE-O₂ were associated with a net increase of ATP content with respect to baseline level. In addition, PE-Hyp was associated with a significant downregulation of endothelial isoform of nitric oxide synthase (eNOS) gene expression and of hypoxia inducible factor-1α (HIF-1α).

Conclusions

Hyperbaric or normobaric oxygenation with perfusion improves organ metabolic preservation compared to other methods. This approach may prevent the onset of delayed graft function, but clinical trials are needed to confirm this.

Hyperbaric Oxygen Therapy in Liver Diseases

Hyperbaric oxygen therapy (HBOT) is an efficient therapeutic option to improve progress of lots of diseases especially hypoxia-related injuries, and has been clinically established as a wide-used therapy for patients with carbon monoxide poisoning, decompression sickness, arterial gas embolism, problematic wound, and so on. In the liver, most studies positively evaluated HBOT as a potential therapeutic option for liver transplantation, acute liver injury, nonalcoholic steatohepatitis, fibrosis and cancer, especially for hepatic artery thrombosis. This might mainly attribute to the anti-oxidation and anti-inflammation of HBOT. However, some controversies are existed, possibly due to hyperbaric oxygen toxicity. This review summarizes the current understandings of the role of HBOT in liver diseases and hepatic regeneration. Future understanding of HBOT in clinical trials and its in-depth mechanisms may contribute to the development of this novel adjuvant strategy for clinical therapy of liver diseases.

Pre-conditions for eliminating mitochondrial dysfunction and maintaining liver function after hepatic ischaemia reperfusion

The liver, the largest organ with multiple synthesis and secretion functions in mammals, consists of hepatocytes and Kupffer, stem, endothelial, stellate and other parenchymal cells. Because of early and extensive contact with the external environment, hepatic ischaemia reperfusion (IR) may result in mitochondrial dysfunction, autophagy and apoptosis of cells and tissues under various pathological conditions. Because the liver requires a high oxygen supply to maintain normal detoxification and synthesis functions, it is extremely susceptible to ischaemia and subsequent reperfusion with blood. Consequently, hepatic IR leads to acute or chronic liver failure and significantly increases the total rate of morbidity and mortality through multiple regulatory mechanisms. An increasing number of studies indicate that mitochondrial structure and function are impaired after hepatic IR, but that the health of liver tissues or liver grafts can be effectively rescued by attenuation of mitochondrial dysfunction. In this review, we mainly focus on the subsequent therapeutic interventions related to the conservation of mitochondrial function involved in mitigating hepatic IR injury and the potential mechanisms of protection. Because mitochondria are abundant in liver tissue, clarification of the regulatory mechanisms between mitochondrial dysfunction and hepatic IR should shed light on clinical therapies for alleviating hepatic IR‐induced injury.

Cellular Preoxygenation Partially Attenuates the Antitumoral Effect of Cisplatin despite Highly Protective Effects on Renal Epithelial Cells

Our previous in vitro studies demonstrated that oxygen pretreatment significantly protects human embryonic renal tubular cell against acute cisplatin- (CP-) induced cytotoxicity. The present study was designed to investigate whether this protective effect is associated with decreasing therapeutic effects of cisplatin on malignant cells. For this purpose, cultured human embryonic kidney epithelial-like (AD293), cervical carcinoma epithelial-like (Hela), and ovarian adenocarcinoma epithelial-like (OVCAR-3) cells were subjected to either 2-hour pretreatment with oxygen (≥90%) or normal air and then to a previously determined 50% lethal dose of cisplatin for 24 hours. Cellular viability was evaluated via MTT and Neutral Red assays. Also, activated caspase-3 and Bax/Bcl-2 ratio, as the biochemical markers of cell apoptosis, were determined using immunoblotting. The hyperoxic preexposure protocol significantly protects renal AD293 cells against cisplatin-induced toxicity. Oxygen pretreatment also partially attenuated the cisplatin-induced cytotoxic effects on Hela and OVCAR-3 cells. However, it did not completely protect these cells against the therapeutic cytotoxic effects of cisplatin. In summary, the protective methods for reducing cisplatin nephrotoxic side effects like oxygen pretreatment might be associated with concurrent reduction of the therapeutic cytotoxic effects of cisplatin on malignant cells like cervical carcinoma (Hela) and ovarian adenocarcinoma (OVCAR-3) cells.

Hyperbaric oxygen preconditioning: a reliable option for neuroprotection

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

Effect of hyperbaric hepatic hyperoxia on the liver of rats submitted to intermittent ischemia/reperfusion injury

PURPOSE

To determine the effect of hyperbaric hyperoxia as hepatic preconditioning on hepatocellular integrity in rats submitted to intermittent hepatic ischemia/reperfusion injury.

METHODS

Twenty male Wistar rats were divided into 4 groups (SHAM, I/R, HBO-I/R and CONTROL). The surgical technique consisted of total clamping of the hepatic pedicle for 15 min, followed by reperfusion for 5 min, performed twice. The application of hyperbaric oxygen (HBO) was carried out in a collective chamber (simultaneous exposure of 4 rats) pressurized directly with oxygen at 2 ATA for 60 min. Tissue malondialdehyde (MDA) levels were determined and blood samples were collected for the determination of serum AST and ALT levels. Data were analyzed statistically by the Mann-Whitney test, with the level of significance set at p < 0.05.

RESULTS

A statistically significant difference in MDA (p< 0.05) was observed between control and HBO-I/R, but not between control and I/R. Regarding AST, there was a difference between control and I/R and HBO-I/R. Analysis of ALT revealed a significant difference between control and I/R (p<0.05) and between I/R and HBO-I/R, with no difference between control and HBO-IR.

CONCLUSION

Hyperoxic preconditioning proved to be favorable regarding alanine transaminase, but not aspartate aminotranserase or malondialdehyde levels.

Hyperoxia-induced preconditioning against renal ischemic injury is mediated by reactive oxygen species but not related to heat shock proteins 70 and 32

OBJECTIVE

Pre-exposure of rats to normobaric hyperoxia (O2 ≥ 95%) may induce late preconditioning against renal ischemia-reperfusion (IR) injury. In this study we investigated probable mechanisms of IR injury such as the role of reactive oxygen species (ROS), renal antioxidant agents, and heat shock proteins (HSP) 32 and 70 during delayed hyperoxia-preconditioning (HO).

METHODS

Fifty-two rats were divided into 7 groups: (A) IR, (B) HO + IR, (C) mercaptopropionyl glycine (MPG) + HO + IR, (D) MPG + IR, (E) HO + sham, (F) MPG + sham, and (G) sham. Rats in the following study groups (group B, C and E) were kept in a normobaric hyperoxic environment for 4 h/day for 6 consecutive days, after which they were subjected to 40 minutes of ischemia; animals in the control group (group A, D, F, and G) were kept in a normoxic cage. At the end of the preconditioning period, 24 hours of reperfusion was performed. Renal function was assessed by measuring serum creatinine (Cr), blood urea nitrogen (BUN), and creatinine clearance (CLCr). Induction of the antioxidant system was evaluated by measuring renal catalase (CAT) and superoxide dismutase (SOD) activities and glutathione (GSH) and malondialdehyde (MDA) content. The role of ROS was investigated by use of MPG (a ROS scavenger). HSP32 & 70 mRNA and protein also were determined.

RESULTS

The hyperoxia-preconditioned IR group (B) had a lower plasma Cr and BUN and greater CLCr compared with the IR group (A) (P ≤ .016). Administration of MPG led to an increase in plasma Cr and BUN and a decrease in CLCr in group C compared with the hyperoxia-preconditioned group B (P ≤ .004). The hyperoxia-preconditioned IR group had a greater CAT activity and GSH level compared with the IR group A (P ≤ .007), whereas the administration of MPG did not change the GSH level but led to a decrease in CAT activity in group D compared with group B (P < .001). SOD activity did not change in hyperoxia-preconditioned ischemic rats compared with ischemic rats. Hyperoxia preconditioning and MPG administration in ischemic animals did not result in any considerable change in MDA level compared with the IR group A. Also, there were no clinically relevant differences in HSP32 & 70 mRNA and protein between all groups.

CONCLUSION

The present study demonstrates that repeated pre-exposure to hyperoxia can decrease subsequent renal IR damage in this rat model of renal ischemia. Free radical production after hyperoxia appears to play a pivotal role in the hyperoxia-induced renal protection independent of HSP level. Antioxidant enzyme activities and especially catalase seem to be implicated in this renal protective mechanism.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

A combined iron and thyroid hormone protocol suppresses ischemia–reperfusion injury in rat livers

Liver preconditioning (PC) against ischemia–reperfusion (IR) injury is attained by iron (Fe) or thyroid hormone (T₃) administration.

Effects of pretreatment with single-dose or intermittent oxygen on Cisplatin-induced nephrotoxicity in rats

Background:

Renal injury is the main side effect of cisplatin (CP), an anticancer drug. It has been shown that pretreatment with single-dose oxygen (0.5 to six hours) could reduce CP-induced renal toxicity in rats.

Objectives:

The present study aimed to compare the effects of pretreatment with single-dose and intermittent O₂ on CP-induced nephrotoxicity.

Materials and Methods:

Adult male rats were allocated to seven groups (eight rats in each group). The rats were kept in normal air or hyperoxic environment (O₂, 80%) for either a single six-hour period or intermittent six hours per day for seven days and then were subjected to intraperitoneal injection of saline or CP (5 mg/kg) at 48 hours, 72 hours, or seven days after exposure to O₂. Three days after CP (or Saline) injection, renal function tests, renal tissue injury scores, and cleaved Caspase-3 and Bax/Bcl-2 genes expression (as markers of renal cell apoptosis) were assessed.

Results:

Treatment with the 6-hour single-dose O₂ reduced renal injury significantly when CP was administrated 48 hours after O₂ pretreatment. Pretreatment with intermittent seven days of six hours per day had no protective effects and even relatively worsened renal injury when CP was injected 48 hours or 72 hours after the last session of O₂ pretreatment. The beneficial effects of pretreatment with O₂ on renal structure and function were seen if CP was administrates seven days after pretreatment with intermittent O₂.

Conclusions:

The pattern of pretreatment with O₂ could change this potential and highly protective strategy against CP-induced nephropathy to an ineffective or even mildly deteriorating one. Therefore, O₂ administration before CP injection to patients with cancer, for therapeutic purposes or as a preconditioning approach, should be performed and investigated with caution until exact effects of different protocols has been determined in human.

Preconditioned hyperbaric oxygenation protects skin flap grafts in rats against ischemia/reperfusion injury

Hyperbaric oxygen (HBO) therapy is an effective therapy for ischemia/reperfusion (I/R) injury of the brain, small intestine, testes and liver. However, the detailed molecular mechanisms underlying the effect of HBO therapy remain undetermined. In the current study, the hypothesis that preconditioning rats with HBO protects grafted skin flaps against subsequent I/R injury was investigated. In addition, the molecular mechanisms underlying HBO therapy were characterized by analyzing the roles of the following important inflammatory factors: High mobility group protein 1 (HMGB1) and nuclear factor-κ B (NF-κB). A total of 40 rats were randomly divided into the following five groups: (i) Sham surgery (SH); (ii) ischemia followed by reperfusion 3 days following surgery (I/R3d); (iii) ischemia followed by reperfusion 5 days following surgery (I/R5d); (iv) HBO preconditioning (HBO-PC) and ischemia followed by reperfusion 3 days following surgery (HBO-PC+3d); and (v) HBO-PC and ischemia followed by reperfusion 5 days following surgery (HBO-PC+5d). For the surgical procedure, all pedicled skin flaps were first measured and elevated (9×6 cm). The feeding vessels of the skin flaps were subsequently clamped for 3 h and released to restore blood flow. The rats in the HBO-PC+3d and HBO-PC+5d groups received 1 h HBO for 3 and 5 consecutive days, respectively, prior to surgery. Following surgery, the rats were euthanized, and grafted tissues were collected for western blotting and immunohistochemistry. HBO-PC increased blood perfusion in epigastric skin flaps and attenuated I/R injury following skin flap graft. Additionally, the elevated expression of HMGB1 and NF-κB proteins during I/R injury was attenuated by HBO-PC treatment. HBO-PC may therefore be applied to reduce I/R injury and improve the survival rate of grafted skin flaps. The molecular mechanisms underlying the effect of HBO therapy are associated with the attenuation of inflammatory responses.

The effects of lycopene on hepatic ischemia/reperfusion injury in rats

There is a very little information about the protective effect of lycopene (LYC) against hepatic ischemia–reperfusion injury. The present study was designed to examine the possible protective effect of the strong antioxidant and anti-inflammatory agent, LYC, on hepatic ischemia/reperfusion injury. For this purpose, rats were subjected to 45 min of hepatic ischemia followed by 60 min of reperfusion period. LYC at the doses of 2.5 and 5 mg/kg body weight (bw) were injected intraperitoneally, 60 min prior to ischemia. Upon sacrification, hepatic tissue samples were used for the measurement of catalase (CAT) activity and malondialdehyde (MDA) levels. Also, aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) were assayed in serum samples. As a result of the use of LYC at the doses of 2.5 and 5 mg/kg bw; while improvements of the ALT, AST, LDH and MDA values were partial and dose-dependent, the improvement of CAT activity was total and dose-independent (p < 0.05). Our findings suggest that LYC has a protective effect against ischemia/reperfusion injury on the liver.

Preconditioning with triiodothyronine improves the clinical signs and acute tubular necrosis induced by ischemia/reperfusion in rats

Background

Renal ischemia/reperfusion (I/R) injury is manifested by acute renal failure (ARF) and acute tubular necrosis (ATN). The aim of this study was to evaluate the effectiveness of preconditioning with 3, 3, 5 triiodothyronine (T₃) to prevent I/R renal injury.

Methodology/Principal Findings

The rats were divided into four groups: sham-operated, placebo-treated (SO-P), sham-operated T_3- treated (SO- T₃), I/R-injured placebo-treated (IR-P), and I/R-injured T₃-treated (IR- T₃) groups. At 24 h before ischemia, the animals received a single dose of T₃ (100 μg/kg). Renal function and plasma, urinary, and tissue variables were studied at 4, 24, and 48 h of reperfusion, including biochemical, oxidative stress, and inflammation variables, PARP-1 immunohistochemical expression, and ATN morphology. In comparison to the SO groups, the IR-P groups had higher plasma urea and creatinine levels and greater proteinuria (at all reperfusion times) and also showed: increased oxidative stress-related plasma, urinary, and tissue variables; higher plasma levels of IL6 (proinflammatory cytokine); increased glomerular and tubular nuclear PARP-1 expression; and a greater degree of ATN. The IR-T₃ group showed a marked reduction in all of these variables, especially at 48 h of reperfusion. No significant differences were observed between SO-P and SO-T₃ groups.

Conclusions

This study demonstrates that preconditioning rats with a single dose of T₃ improves the clinical signs and ATN of renal I/R injury. These beneficial effects are accompanied by reductions in oxidative stress, inflammation, and renal PARP-1 expression, indicating that this sequence of factors plays an important role in the ATN induced by I/R injury.

Recent advances in liver preconditioning: Thyroid hormone, n-3 long-chain polyunsaturated fatty acids and iron

Liver preconditioning (PC), defined as an enhanced tolerance to injuring stimuli induced by previous specific maneuvers triggering beneficial functional and molecular changes, is of crucial importance in human liver transplantation and major hepatic resection. For these reasons, numerous PC strategies have been evaluated in experimental models of ischemia-reperfusion liver injury, which have not been transferred to clinical application due to side effects, toxicity and difficulties in implementation, with the exception of the controversial ischemic PC. In recent years, our group has undertaken the assessment of alternate experimental liver PC protocols that might have application in the clinical setting. These include thyroid hormone (T(3)), n-3 long-chain polyunsaturated fatty acids (n-3 LCPUFA), or iron, which suppressed liver damage due to the 1 h ischemia-20 h reperfusion protocol. T(3), n-3 LCPUFA and iron are hormetic agents that trigger biologically beneficial effects in the low-dose range, whose multifactorial mechanisms of action are discussed in the work.

An innovative hyperbaric hypothermic machine perfusion protects the liver from experimental preservation injury

Purpose. Hypothermic machine perfusion systems seem more effective than the current static storage to prevent cold ischemic liver injury. Thus, we test an innovative hyperbaric hypothermic machine perfusion (HHMP), which combines hyperbaric oxygenation of the preservation solution and continuous perfusion of the graft. Methods. Rat livers were preserved with Celsior solution according to 4 different modalities: normobaric static preservation; hyperbaric static preservation at 2 atmosphere absolute (ATA); normobaric dynamic preservation, with continuous perfusion; hyperbaric dynamic preservation, with continuous perfusion at 2 ATA. After 24 h cold preservation, we assessed different parameters. Results. Compared to baseline, livers preserved with the current static storage showed severe ultrastructural damage, glycogen depletion and an increased oxidative stress. Normobaric perfused livers showed improved hepatocyte ultrastructure and ameliorated glycogen stores, but they still suffered a significant oxidative damage. The addition of hyperbaric oxygen produces an extra benefit by improving oxidative injury and by inducing endothelial NO synthase (eNOS) gene expression. Conclusions. Preservation by means of the present innovative HHMP reduced the liver injury occurring after the current static cold storage by lowering glycogen depletion and oxidative damage. Interestingly, only the use of hyperbaric oxygen was associated to a blunted oxidative stress and an increased eNOS gene expression.

Hyperbaric oxygen preconditioning attenuates hyperglycemia enhanced hemorrhagic transformation after transient MCAO in rats

BACKGROUND

Hemorrhagic transformation (HT) can be a devastating complication of ischemic stroke. Hyperbaric oxygen preconditioning (HBO-PC) has been shown to improve blood-brain barrier (BBB) permeability in stroke models. The purpose of this study is to examine whether HBO-PC attenuates HT after focal cerebral ischemia, and to investigate whether the mechanism of HBO-PC against HT includes up-regulation of antioxidants in hyperglycemic rats.

METHODS

Male Sprague-Dawley rats (280-320 g) were divided into the following groups: sham, middle cerebral artery occlusion (MCAO) for 2 h, and MCAO treated with HBO-PC. HBO-PC was conducted giving 100% oxygen at 2.5 atm absolute (ATA), for 1 h at every 24 h interval for 5 days. At 24 h after the last session of HBO-PC, rats received an injection of 50% glucose (6 ml/kg intraperitoneally) and were subjected to MCAO 15 min later. At 24 h after MCAO, neurological behavior tests, infarct volume, blood-brain barrier permeability, and hemoglobin content were measured to evaluate the effect of HBO-PC. Western blot analysis of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) was evaluated at multiple time-points before and after MCAO.

RESULTS

HBO-PC improved neurological behavior test, and reduced infarction volume, HT and Evans blue extravasation in the ipsilateral hemisphere at 24 h after MCAO. Western blot analysis failed to demonstrate up-regulation of Nrf2 in HBO-PC group before and after MCAO. Paradoxically, HBO-PC decreased HO-1 expression at 24 h after MCAO, as compared with htMCAO group.

CONCLUSIONS

HBO-PC improved neurological deficits, infarction volume, BBB disruption, and HT after focal cerebral ischemia. However, its mechanism against focal cerebral ischemia and HT may not include activation of Nrf2 and subsequent HO-1 expression.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The role of oxidative stress response revealed in preconditioning heat stimulation in skeletal muscle of rats

BACKGROUND

Our previous study showed that preconditioned local somatothermal stimulation (LSTS) protected subsequent ischemia-reperfusion injury of the skeletal muscle. The exact mechanisms of LSTS preconditioning remain unknown. The aim of this study was to test the hypothesis stating that heat stimulation induces free radical production, increases enzymatic scavenging activity, and subsequently enhances the expression of heat shock protein 70 (HSP-70) in skeletal muscles.

MATERIALS AND METHODS

After LSTS was applied onto the left quarter ventral abdomen muscle of male Sprague-Dawley rats, the underling muscles were collected at the intervals of baseline, 5-, 15-, 30-, and 60-min after LSTS. The time-dependent profiles of free radical production and enzymatic scavenging activity were measured. The influence of nitric oxide (NO) on HSP-70 expression was evaluated by pretreatment of an NO synthase inhibitor.

RESULTS

The concentrations of reactive oxygen species, NO metabolites, and malondialdehyde increased significantly 5 min after LSTS, whereas the scavenging activity reduced to the lowest level 5 min (dismutase) and 15 min (catalase and glutathione) after LSTS. Expression of HSP-70 was significantly lower in the LSTS with NO synthase inhibitor group than in the LSTS group.

CONCLUSIONS

LSTS induces oxidative stress and the scavenging response in the underlying skeletal muscle, which might explain the possible mechanisms of LSTS preconditioning-induced muscle plasticity.

Ischemic tolerance protects the rat retina from glaucomatous damage

Glaucoma is a leading cause of acquired blindness which may involve an ischemic-like insult to retinal ganglion cells and optic nerve head. We investigated the effect of a weekly application of brief ischemia pulses (ischemic conditioning) on the rat retinal damage induced by experimental glaucoma. Glaucoma was induced by weekly injections of chondroitin sulfate (CS) in the rat eye anterior chamber. Retinal ischemia was induced by increasing intraocular pressure to 120 mmHg for 5 min; this maneuver started after 6 weekly injections of vehicle or CS and was weekly repeated in one eye, while the contralateral eye was submitted to a sham procedure. Glaucoma was evaluated in terms of: i) intraocular pressure (IOP), ii) retinal function (electroretinogram (ERG)), iii) visual pathway function (visual evoked potentials, (VEPs)) iv) histology of the retina and optic nerve head. Retinal thiobarbituric acid substances levels were assessed as an index of lipid peroxidation. Ischemic conditioning significantly preserved ERG, VEPs, as well as retinal and optic nerve head structure from glaucomatous damage, without changes in IOP. Moreover, ischemia pulses abrogated the increase in lipid peroxidation induced by experimental glaucoma. These results indicate that induction of ischemic tolerance could constitute a fertile avenue for the development of new therapeutic strategies in glaucoma treatment.

Liver preconditioning induced by iron in a rat model of ischemia/reperfusion

AIMS

Liver preconditioning against ischemia-reperfusion (IR) injury is a major area of experimental research, in which regulation of gene expression with cytoprotective responses due to transient oxidative stress development has been reported. Considering that significant cytoprotection occurs after exposure to low levels of iron (Fe), we tested the hypothesis that sub-chronic administration of Fe to rats underlying transient oxidative stress preconditions the liver against IR injury.

MAIN METHODS

Animals received six doses (50 mg Fe-dextran/kg ip) every second day during 10 days, before partial IR (vascular clamping) or sham laparotomy (control). Transient oxidative stress was defined by liver glutathione and protein carbonyl contents (24, 48, and 72 h after Fe treatment). Plasma and liver Fe status and ferritin content (western blot) were assessed in animals not subjected to IR. Liver injury and inflammatory response were evaluated by serum transaminases, liver morphology and serum TNF-α. Fe preconditioning against IR injury was correlated with liver glutathione content and the redox-sensitive NF-κB signaling pathway (EMSA) and western blot analysis of haptoglobin.

KEY FINDINGS

Significant hepatoprotection against IR injury, underlying transient oxidative stress and enhancement in the total and labile Fe pools, was achieved by Fe administration. Abrogation of IR injury is related to reduced TNF-α response (91%), abolishment of the IR-induced liver glutathione depletion and recovery of the NF-κB signaling pathway (75%), lost during IR.

SIGNIFICANCE

Sub-chronic Fe administration protects the liver against IR injury through antioxidant and anti-inflammatory responses, with recovery of NF-κB activation and related acute-phase response signaling.

Ischemia/reperfusion injury in liver resection: a review of preconditioning methods

Ischemic preconditioning is one of the therapeutic interventions aiming at preventing ischemia/reperfusion-related injury. Numerous experimental studies and a few clinical series have shown that during liver resections, ischemic preconditioning is a promising strategy for optimizing the postoperative outcome. Moreover, various types of pharmacological intervention as well as different types of preconditioning, such as remote preconditioning, the use of heat shock, and hyperbaric oxygen, have been developed to attenuate the functional impairment accompanying ischemia/reperfusion injury. This review summarizes the various forms of preconditioning, thus suggesting that close cooperation between surgeons and anesthesiologists paves the way to apply novel strategies to improve the outcome of liver resection.

Short-time intermittent preexposure of living human donors to hyperoxia improves renal function in early posttransplant period: a double-blind randomized clinical trial

The purpose of this human study was to investigate the effect of oxygen pretreatment in living kidney donors on early renal function of transplanted kidney. Sixty living kidney donor individuals were assigned to receive either 8-10 L/min oxygen (Group I) by a non-rebreather mask with reservoir bag intermittently for one hour at four times (20, 16, 12, and 1 hours before transplantation) or air (Group II). After kidney transplantation, urine output, blood urea nitrogen (BUN), serum creatinine, need to additional diuretics (NTADs) in the first 24 hours after transplantation, delayed graft function (DGF), the creatinine clearance (CrCL) on 10th day, and duration of hospital stay from the first posttransplant day till normalization of renal function was recorded and compared in two groups. Mean CrCL in posttransplant day 10, NTAD after 24 hours of transplantation, and urine output during 6 hours after operation were significantly better in Group I compared with Group II (P < .05). Also, DGF during the first week after operation and duration of hospital stay was less in Group I compared with Group II. Intermittent exposure of human living kidney donor to hyperoxic environment may improve renal function following kidney transplantation.

Hyperbaric oxygen: its mechanisms and efficacy

BACKGROUND

This article outlines therapeutic mechanisms of hyperbaric oxygen therapy and reviews data on its efficacy for clinical problems seen by plastic and reconstructive surgeons.

METHODS

The information in this review was obtained from the peer-reviewed medical literature.

RESULTS

Principal mechanisms of hyperbaric oxygen are based on intracellular generation of reactive species of oxygen and nitrogen. Reactive species are recognized to play a central role in cell signal transduction cascades, and the discussion will focus on these pathways. Systematic reviews and randomized clinical trials support clinical use of hyperbaric oxygen for refractory diabetic wound-healing and radiation injuries; treatment of compromised flaps and grafts and ischemia-reperfusion disorders is supported by animal studies and a small number of clinical trials, but further studies are warranted.

CONCLUSIONS

Clinical and mechanistic data support use of hyperbaric oxygen for a variety of disorders. Further work is needed to clarify clinical utility for some disorders and to hone patient selection criteria to improve cost efficacy.

Effect of preconditioned hyperbaric oxygen and ozone on ischemia-reperfusion induced tourniquet in skeletal bone of rats

BACKGROUND

The aim of the study was to investigate effect of I/R injury on bone tissue and protective role of hyperbaric oxygen precondition (HBO-PC) and ozone precondition (O(3)-PC) on I/R injury by using biochemical analysis.

MATERIALS AND METHODS

Thirty-two rats were included in study. The animals were divided into four equal groups: sham operation, I/R, I/R+HBO and I/R+O(3). One session of 60 min, 3 ATA, 3-4 L/min, 100% oxygenation was defined as one dose of HBO. First dose of HBO was administrated 72 h before ischemia. Subsequent, one-dose of HBO administrated per 12 hours until ischemia time (total seven doses); 0.7 mg/kg ozone/oxygen mixture intraperitoneally was defined as one dose of ozone. First dose of O(3) was administered 72 h before ischemia (total four doses). I/R model was induced in anesthetized rats by unilateral (right) femoral artery clipping for 2 h followed by 22 h of reperfusion. The right tibia and were harvested. Tissue was assayed for levels of malondialdehyde (MDA) and protein carbonyl (PCO), activities of superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px).

RESULTS

MDA and PCO levels were increased in I/R group. SOD activity was increased; GSH-Px activity was decreased in I/R group. MDA and PCO levels were decreased, SOD and GSH-Px activities were increased in both HBO+I/R and O(3)+I/R groups.

CONCLUSION

It has been shown that levels of MDA and PCO in bone were increased followed by 2 h of ischemia and 22 h of reperfusion period. Ozone-PC and HBO-PC has protective effect against skeletal bone I/R injury by decreasing levels of MDA and PCO, increasing activities of SOD and GSH-Px in rats.

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

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

Hyperbaric oxygen therapy protects the liver from apoptosis caused by ischemia-reperfusion injury in rats

PURPOSE

: The present paper aimed to investigate the role of hyperbaric oxygen treatment (HBO) and the apoptosis in rat liver ischemia-reperfusion injury (IRI).

METHODS

: Thirty-seven male Wistar rats were subjected to 30 minutes of hepatic ischemia and 30 minutes of reperfusion and randomly distributed into six groups: G-I/R (n = 8), control without HBO; G-HBO/I (n = 8), HBO only during the ischemia period; G-HBO/R (n = 8), HBO only during the reperfusion period; G-HBO-I/R (n = 8), HBO during both the ischemia and reperfusion periods; G-Sh (n = 3), HBO without ischemia or reperfusion as sham group; G-C (n = 2) for control of current apoptosis expression on the normal liver tissue. HBO was carried out using a transparent, cylindrical acrylic chamber with a pressure of 2.0 ATA. Hepatic samples were stained for caspase-3 cleavage.

RESULTS

: Apoptotic cells were identified in all groups. In the hepatic specimens of animals HBO-treated during ischemia (GHBO-I), there was a significant decrease (P < 0.001) in the number of cells undergoing apoptosis (1.62 +/- 0.91). The apoptotic index showed no significant difference in the animals HBO-treated during ischemia/reperfusion (5.75 +/- 1.28) compared with the G-I/R (3.5 +/- 0.75), which had no HBO treatment. The apoptosis index (11.25 +/- 1.90) was significantly higher (P < 0.01) in HBO-treated animals during the reperfusion period when compared with any of the other groups.

CONCLUSION

: A favorable effect was obtained when hyperbaric oxygen was administered early during ischemia. The hyperbaric oxygen in later periods of reperfusion was associated with a more severe apoptosis index. (c) 2009 Wiley-Liss, Inc. Microsurgery 2009.

Hyperoxia-induced protection against rat's renal ischemic damage: relation to oxygen exposure time

BACKGROUND

Pre-exposure to hyperoxic gas (>or= 95%) has been shown to protect the heart and central nervous system from ischemia-reperfusion injury. In the present study, we investigated whether oxygen pretreatment induces delayed renal protection in rats. The possible role of some renal antioxidant agents was also investigated.

MATERIALS AND METHODS

Adult male Wistar rats were kept in a hyperoxic (HO) (>or= 95% O(2)) environment for 0.5 h, 1 h, 2 h, 3 h, 6 h, and 2 h/day for three consecutive days and 4 h/day for six consecutive days, and control group (IR) animals were kept in the cage with no HO, one day before subjecting their kidney to 40 minutes of ischemia and 24h of reperfusion. Renal function was assessed by comparing plasma creatinine (Cr), blood urea nitrogen (BUN), creatinine clearance (CLCr), and fractional excretion of sodium (FENa%). Histopathological injury score was also determined according to the Jablonski method. To examine the antioxidant system induction by hyperoxia, we measured renal catalase and superoxide dismutase activity, and renal glutathione and malondialdehyde content.

RESULTS

Our data demonstrated that only in 4 h/day HO for six consecutive days, the renal function tests (Cr, CLCr, BUN, and FENa%) and Jablonski histological injury were better than control group (p < 0.05). The beneficial effect of oxygen pretreatment in this group was associated with increased renal catalase activity compared with those obtained from control group (p < 0.05).

CONCLUSION

The present study demonstrates that repeated exposure to hyperoxic (>or= 95% O(2)) environment can reduce subsequent rat's renal ischemia-reperfusion damage. Induction of endogenous antioxidant system may partially explain this beneficial effect of hyperoxic preconditioning.

The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-alpha, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.

Hyperbaric oxygen therapy aggravates liver reperfusion injury in rats

PURPOSE

To evaluate the effects of hyperbaric oxygen (HO) therapy in the protection against liver ischemia/reperfusion injury.

METHODS

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.

RESULTS

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.

CONCLUSION

Liver preconditioning with hyperbaric oxygen therapy aggravated liver ischemia/reperfusion injury in rats as demonstrated by plasma ALT and liver myeloperoxidase activity.

Hyperbaric oxygen preconditioning protects against traumatic brain injury at high altitude

BACKGROUND

Recent studies have shown that preconditioning with hyperbaric oxygen (HBO) can reduce ischemic and hemorrhagic brain injury. We investigated effects of HBO preconditioning on traumatic brain injury (TBI) at high altitude and examined the role of matrix metalloproteinase-9 (MMP-9) in such protection.

METHODS

Rats were randomly divided into 3 groups: HBO preconditioning group (HBOP; n = 13), high-altitude group (HA; n = 13), and high-altitude sham operation group (HASO; n = 13). All groups were subjected to head trauma by weight-drop device, except for HASO group. HBOP rats received 5 sessions of HBO preconditioning (2.5 ATA, 100% oxygen, 1 h daily) and then were kept in hypobaric chamber at 0.6 ATA (to simulate pressure at 4000m altitude) for 3 days before operation. HA rats received control pretreatment (1 ATA, room air, 1 h daily), then followed the same procedures as HBOP group. HASO rats were subjected to skull opening only without brain injury. Twenty-four hours after TBI, 7 rats from each group were examined for neurological function and brain water content; 6 rats from each group were killed for analysis by H&E staining and immunohistochemistry.

RESULTS

Neurological outcome in HBOP group (0.71 +/- 0.49) was better than HA group (1.57 +/- 0.53; p < 0.05). Preconditioning with HBO significantly reduced percentage of brain water content (86.24 +/- 0.52 vs. 84.60 +/- 0.37; p < 0.01). Brain morphology and structure seen by light microscopy was diminished in HA group, while fewer pathological injuries occurred in HBOP group. Compared to HA group, pretreatment with HBO significantly reduced the number of MMP-9-positive cells (92.25 +/- 8.85 vs. 74.42 +/- 6.27; p < 0.01).

CONCLUSIONS

HBO preconditioning attenuates TBI in rats at high altitude. Decline in MMP-9 expression may contribute to HBO preconditioning-induced protection of brain tissue against TBI.

Effect of different periods of hyperbaric oxygen on ischemia-reperfusion injury of rat small bowel

PURPOSE

To determine whether hyperbaric oxygen (HBO) could effectively protect the small intestine mucosa against an ischemic insult, according to different periods of application.

METHODS

The gut of 32 male rats was subjected to 60-min ischemia (clamping the mesenteric artery and vein); After they were further reperfused upon clamp opening during 60 min. Animal groups were as follows. GII = placed on HBO during the ischemia period; GIII = placed on HBO during reperfusion; GIV = treated with HBO throughout the ischemia-reperfusion period. Some animals (GI) did not receive HBO treatment at all and served as reference of ischemia-reperfusion injury (IR). HBO was carried out in a cylindrical acrylic chamber (2.0 ATA). Samples of small bowel were prepared for H.E staining for histological evaluations.

RESULTS

The histological injury of mucosa was significantly less when HBO was administered during the ischemia period (17.6 +/- 0.6) as compared with the IR (21.3 +/- 1.8). HBO was not effective when applied during reperfusion (23.1 +/- 2.1) or during the ischemia plus reperfusion period (18.7 +/- 1.9). The thickness of the mucosa was preserved by HBO in ischemia (327.50 +/- 30.23 microm) in comparison with the IR (172.79 +/- 5.95 microm). In the periods of reperfusion (162.50 +/- 6.05 microm) and ischemia plus reperfusion (296.49 +/- 20.01 microm) the mucosa revealed a structural injury.

CONCLUSION

Hyperbaric oxygen affects the ischemic insult of small bowel, being the favorable effect obtained when hyperbaric oxygen was administered early in the ischemic period.

Delayed cardioprotective effects of hyperoxia preconditioning prolonged by intermittent exposure

BACKGROUND

In our previous study, it was indicated that pre-exposing rats to normobaric hyperoxia could induce a late preconditioning against infarction and arrhythmia. In this study, attempts were made to know whether the intermittent pre-exposure to the same environment could prolong the late phase of hyperoxia preconditioning.

METHODS

In the first series of experiments, rats were divided into five groups; group 1 was pre-exposed to normal air (NOR) and the other groups to hyperoxic air (O(2)>95%, 120 min once a d) 12, 24, 48, and 72 h (H12, H24, H48, and H72 groups) before 30 min ischemia. In the second series of experiments, rats were pre-exposed to intermittent hyperoxic air (1, 2, or 3 consecutive d) at different times before being subjected to ischemia (H48, H2-48, H2-72, H3-72, and H3-96 groups). The infarct size was measured by triphenyltetrazolium chloride staining, and lead II of electrocardiogram recorded to monitor ischemic-induced arrhythmia.

RESULTS

Compared with NOR group, the infarct size and incidence of arrhythmia were reduced significantly in H24 and H48 groups. When the exposure periods were enhanced to 2 d, the infarct size did not decrease significantly, but the incidence of arrhythmia reduced. When the pre-exposure times were enhanced to 3 d, both the infarct size and incidence of arrhythmia decreased significantly in H3-72 group, but not in H3-96 group.

CONCLUSION

These results show that the late phase of hyperoxia preconditioning may last for more than 48 h and prolong by intermittent per-exposure to the same environment.

DNA damage after long-term repetitive hyperbaric oxygen exposure

A single exposure to hyperbaric oxygen (HBO), i.e., pure oxygen breathing at supra-atmospheric pressures, causes oxidative DNA damage in humans in vivo as well as in isolated lymphocytes of human volunteers. These DNA lesions, however, are rapidly repaired, and an adaptive protection is triggered against further oxidative stress caused by HBO exposure. Therefore, we tested the hypothesis that long-term repetitive exposure to HBO would modify the degree of DNA damage. Combat swimmers and underwater demolition team divers were investigated because their diving practice comprises repetitive long-term exposure to HBO over years. Nondiving volunteers with and without endurance training served as controls. In addition to the measurement of DNA damage in peripheral blood (comet assay), blood antioxidant enzyme activities, and the ratio of oxidized and reduced glutathione content, we assessed the DNA damage and superoxide anion radical (O2•−) production induced by a single ex vivo HBO exposure of isolated lymphocytes. All parameters of oxidative stress and antioxidative capacity in vivo were comparable in the four different groups. Exposure to HBO increased both the level of DNA damage and O2•− production in lymphocytes, and this response was significantly more pronounced in the cells obtained from the combat swimmers than in all the other groups. However, in all groups, DNA damage was completely removed within 1 h. We conclude that, at least in healthy volunteers with endurance training, long-term repetitive exposure to HBO does not modify the basal blood antioxidant capacity or the basal level of DNA strand breaks. The increased ex vivo HBO-related DNA damage in isolated lymphocytes from these subjects, however, may reflect enhanced susceptibility to oxidative DNA damage.

Wound healing from a cellular stress response perspective

This meeting review highlights areas of mutual interest to investigators in the cellular stress response field and to those carrying out wound-healing research. Inflammation, perhaps the major unifying theme of this meeting, is an essential component of the adult wound response and understanding the control of inflammation is a common interest shared with researchers of the cellular stress response. The particular interest of the authors of this review is in chronic non-healing wounds that frequently occur in patients with major illnesses such as diabetes and diseases of the blood vessels. This orientation has undoubtedly influenced the selection of topics. It is fair to say that the authors were often surprised and certainly impressed with the overlapping interests and possibilities for collaboration among investigators of these two research areas.