Hyperbaric oxygen therapy prevents vascular derangement during zymosan-induced multiple-organ-failure syndrome

Oxygen therapy for sepsis and prevention of complications

Patients with sepsis have a wide range of respiratory disorders that can be treated with oxygen therapy. Experimental data in animal sepsis models show that oxygen therapy significantly increases survival, while clinical data on the use of different oxygen therapy protocols are ambiguous. Oxygen therapy, especially hyperbaric oxygenation, in patients with sepsis can aggravate existing oxidative stress and contribute to the development of disseminated intravascular coagulation. The purpose of this article is to compare experimental and clinical data on oxygen therapy in animals and humans, to discuss factors that can influence the results of oxygen therapy for sepsis treatment in humans, and to provide some recommendations for reducing oxidative stress and preventing disseminated intravascular coagulation during oxygen therapy.

Treatment with 24 h-delayed normo- and hyperbaric oxygenation in severe sepsis induced by cecal ligation and puncture in rats

Background

Septic shock remains a leading cause of death worldwide. Hyperbaric oxygen treatment (HBO₂) has been shown to alter the inflammatory response during sepsis and to reduce mortality. A therapeutic window of HBO₂ treatment has been demonstrated experimentally, but optimal timing remains uncertain. We investigated the effects of 24 h delayed normobaric oxygen (NBO₂) and HBO₂ treatment on the endogenous production of the inflammatory markers interleukin (IL)-6, tumor necrosis factor (TNF)-α and IL-10, and on mortality in rats with cecal ligation and puncture (CLP) induced sepsis.

Method

Fifty-five male Sprague-Dawley rats underwent CLP and were randomized to the following groups: 1) HBO₂ 2.5 bar absolute pressure (p_abs); 2) NBO₂ 1.0 bar p_abs; 3) Control (no-treatment), and they were individually monitored for 72 h with intermittent blood sampling.

Results

IL-6, TNF-α, and IL-10 were increased 24 h after the procedure, and IL-6 was significantly higher in non-survivors than in survivors. The level of IL-10 was significantly higher at hour 48 in the HBO₂ group compared to control (p = 0.01), but this was not the case at other time points. No other significant differences in cytokine levels were found for any group comparisons. Delayed NBO₂ and HBO₂ treatment failed to change the mortality in the animals.

Conclusion

High levels of IL-6 in non-surviving animals with sepsis suggest that IL-6 is a potential biomarker. We found a significantly higher concentration of IL-10 in the HBO₂ group at hour 48 vs. control animals. However, 24 h–delayed treatment with HBO₂ did not change the levels of pro-inflammatory cytokines and survival, suggesting that earlier intervention may be required to obtain an anti-inflammatory effect.

Sepsis and septic shock: Pathogenesis and treatment perspectives

The majority of bacteremias do not develop to sepsis: bacteria are cleared from the bloodstream. Oxygen released from erythrocytes and humoral immunity kill bacteria in the bloodstream. Sepsis develops if bacteria are resistant to oxidation and proliferate in erythrocytes. Bacteria provoke oxygen release from erythrocytes to arterial blood. Abundant release of oxygen to the plasma triggers a cascade of events that cause: 1. oxygen delivery failure to cells; 2. oxidation of plasma components that impairs humoral regulation and inactivates immune complexes; 3. disseminated intravascular coagulation and multiple organs' failure. Bacterial reservoir inside erythrocytes provides the long-term survival of bacteria and is the cause of ineffectiveness of antibiotics and host immune reactions. Treatment perspectives that include different aspects of sepsis development are discussed.

Mechanisms of action of hyperbaric oxygenation in stroke: a review

This article outlines the therapeutic mechanisms of hyperbaric oxygenation in acute stroke, based on information obtained from peer-reviewed medical literature. Hyperbaric oxygen is an approved treatment modality for ischemia-reperfusion injury in several conditions. It maintains the viability of the marginal tissue, reduces the mitochondrial dysfunction, metabolic penumbra, and blocks inflammatory cascades observed in acute stroke. Basic and clinical data suggest that hyperbaric oxygen could be a safe and effective treatment option in the management of acute stroke. Further work is needed to clarify its clinical utility when applied within the treatment window of "gold standard" treatments (<3-5 hours).

Hyperbaric oxygen for cerebral vasospasm and brain injury following subarachnoid hemorrhage

The impact of acute brain injury and delayed neurological deficits due to cerebral vasospasm (CVS) are major determinants of outcomes after subarachnoid hemorrhage (SAH). Although hyperbaric oxygen (HBO) had been used to treat patients with SAH, the supporting evidence and underlying mechanisms have not been systematically reviewed. In the present paper, the overview of studies of HBO for cerebral vasospasm is followed by a discussion of HBO molecular mechanisms involved in the protection against SAH-induced brain injury and even, as hypothesized, in attenuating vascular spasm alone. Faced with the paucity of information as to what degree HBO is capable of antagonizing vasospasm after SAH, the authors postulate that the major beneficial effects of HBO in SAH include a reduction of acute brain injury and combating brain damage caused by CVS. Consequently, authors reviewed the effects of HBO on SAH-induced hypoxic signaling and other mechanisms of neurovascular injury. Moreover, authors hypothesize that HBO administered after SAH may "precondition" the brain against the detrimental sequelae of vasospasm. In conclusion, the existing evidence speaks in favor of administering HBO in both acute and delayed phase after SAH; however, further studies are needed to understand the underlying mechanisms and to establish the optimal regimen of treatment.

Effect of hyperbaric oxygen therapy on the intestinal ischemia reperfusion injury

PURPOSE

Adequate tissue oxygenation is essential for healing. Hyperbaric oxygen therapy (HBOT) has potential clinical applications to treat ischemic pathologies, however the exact nature of any protective effects are unclear at present. We therefore investigated the potential role of HBOT in modulating the ischemia/reperfusion (I/R) injury response in intestinal model of I/R injury.

METHODS

Male Wistar rats were subjected to surgery for the induction of intestinal ischemia followed by reperfusion. HBOT was provided before and/or after intestinal ischemia. Cell viability in the intestinal tissue was assessed using the MTT assay and by measuring serum malondealdehyde (MDA). Microvascular density and apoptosis were evaluated by immunohistochemistry.

RESULTS

The results indicate that HBOT treatment pre- and post-ischemia reduces lesion size to the intestinal tissue. This treatment increases cell viability and reduces the activation of caspase-3, which is associated with increased number of tissue CD34 cells and enhanced VEGF expression.

CONCLUSION

The hyperbaric oxygen therapy can limit tissue damage due to ischemia/reperfusion injury, by inducing reparative signaling pathways.

Dose-related effects of hyperoxia on the lung inflammatory response in septic rats

We evaluated the effects of hyperoxia on pulmonary inflammatory changes in sepsis induced by cecal ligation and puncture (CLP) in rats. Seven groups were studied: sham-operated rats breathing air for 20 or 48 h; CLP breathing air for 20 or 48 h; and CLP + 100% oxygen for 20 h, or 70% oxygen for 48 h, or 100% oxygen intermittently (6 h/d) for 48 h. Video microscopy was used to monitor lung macromolecular leak, microvascular flow velocity, and shear rates, and lung morphometry was used for leukocyte infiltration and solid tissue area. Cell counts, tumor necrosis factor α, and nitrites were determined in peripheral blood and lung lavage fluid. Expression of adhesion molecules in blood leukocytes was evaluated by flow cytometry. Cecal ligation and puncture induced inflammation manifested in leukopenia, left shift, thrombocytopenia, increased expression of L selectin and CD11, increased serum and lavage fluid tumor necrosis factor α and leukocytes, and increased lung tissue area, macromolecular leak, and sequestration of leukocytes. Inhalation of 100% oxygen for 20 h increased nitrites (P < 0.01) and decreased leukocyte count in lavage fluid (P < 0.05) and attenuated lung macromolecular leak and changes in solid tissue area (P < 0.01). Inhalation of 70% oxygen (48 h) attenuated expression of adhesion molecules (P < 0.001) but failed to attenuate markers of lung inflammation. In contrast, intermittent 100% oxygen exerted favorable effects on markers of inflammation, attenuated leukocyte expression of L selectin and CD11 (P < 0.01), decreased pulmonary sequestration of leukocytes (P < 0.001), and ameliorated changes in macromolecular leak (P < 0.01) and lung solid tissue area (P < 0.05). Our data support the beneficial effects of safe subtoxic regimens of normobaric hyperoxia on the systemic and pulmonary inflammatory response following CLP.

The orphan nuclear receptor SHP acts as a negative regulator in inflammatory signaling triggered by Toll-like receptors

The orphan nuclear receptor SHP (small heterodimer partner) is a transcriptional corepressor that regulates hepatic metabolic pathways. Here we identified a role for SHP as an intrinsic negative regulator of Toll-like receptor (TLR)-triggered inflammatory responses. SHP-deficient mice were more susceptible to endotoxin-induced sepsis. SHP had dual regulatory functions in a canonical transcription factor NF-κB signaling pathway, acting as both a repressor of transactivation of the NF-κB subunit p65 and an inhibitor of polyubiquitination of the adaptor TRAF6. SHP-mediated inhibition of signaling via the TLR was mimicked by macrophage-stimulating protein (MSP), a strong inducer of SHP expression, via an AMP-activated protein kinase-dependent signaling pathway. Our data identify a previously unrecognized role for SHP in the regulation of TLR signaling.

Hyperbaric oxygen therapy reduces the toll-like receptor signaling pathway in multiple organ failures

PURPOSE

Zymosan-induced generalized inflammation is the only experimental model that reproduces characteristics of human multiple organ dysfunction syndrome (MODS). Toll-like receptors (TLRs) are key components in innate immune responses and their signaling pathway is known to activate target genes such as nuclear factor-κB (NF-κB) and cytokines that are involved in inflammation and immune responses. We previously reported that hyperbaric oxygen (HBO) therapy is effective in the treatment of severe zymosan-induced inflammation in MODS. The aim of this study was to investigate the effect of HBO exposure on TLR2 and TLR4 signal transduction and organ dysfunction during MODS induced by zymosan in the rat.

METHODS

Male Wistar rats were randomized into four groups and treated as follows: (1) saline solution (control); (2) zymosan; (3) HBO 4 and 11 h after zymosan injection; (4) HBO 4 and 11 h after saline solution injection. Zymosan-induced damage of the lungs, liver, and small intestine was evaluated using histology and biochemistry. The activation of the TLR signaling pathway was measured with Western blot, reverse transcriptase polymerase chain reaction analysis (RT-PCR), and immunohistochemistry.

RESULTS

Zymosan induced a severe inflammatory response characterized by the activation of the TLR signaling pathway and by an organ dysfunction. HBO exposure significantly reduced the development of lung, liver, and intestine injury in our experimental model. It also significantly reduced the zymosan-induced expression of TLR2 and TLR4, NF-κB activation, and cytokine production.

CONCLUSIONS

Taken together, these results suggest that, by interfering with the TLR pathway, HBO treatment may exert a protective effect against tissue injury caused by zymosan-induced generalized inflammation.

Ozone therapy and hyperbaric oxygen treatment in lung injury in septic rats

Various therapeutic protocols were used for the management of sepsis including hyperbaric oxygen (HBO) therapy. It has been shown that ozone therapy (OT) reduced inflammation in several entities and exhibits some similarity with HBO in regard to mechanisms of action. We designed a study to evaluate the efficacy of OT in an experimental rat model of sepsis to compare with HBO. Male Wistar rats were divided into sham, sepsis+cefepime, sepsis+cefepime+HBO, and sepsis+cefepime+OT groups. Sepsis was induced by an intraperitoneal injection of Escherichia coli; HBO was administered twice daily; OT was set as intraperitoneal injections once a day. The treatments were continued for 5 days after the induction of sepsis. At the end of experiment, the lung tissues and blood samples were harvested for biochemical and histological analysis. Myeloperoxidase activities and oxidative stress parameters, and serum proinflammatory cytokine levels, IL-1β and TNF-α, were found to be ameliorated by the adjuvant use of HBO and OT in the lung tissue when compared with the antibiotherapy only group. Histologic evaluation of the lung tissue samples confirmed the biochemical outcome. Our data presented that both HBO and OT reduced inflammation and injury in the septic rats' lungs; a greater benefit was obtained for OT. The current study demonstrated that the administration of OT as well as HBO as adjuvant therapy may support antibiotherapy in protecting the lung against septic injury. HBO and OT reduced tissue oxidative stress, regulated the systemic inflammatory response, and abated cellular infiltration to the lung demonstrated by findings of MPO activity and histopathologic examination. These findings indicated that OT tended to be more effective than HBO, in particular regarding serum IL-1β, lung GSH-Px and histologic outcome.

eNOS-beta-actin interaction contributes to increased peroxynitrite formation during hyperoxia in pulmonary artery endothelial cells and mouse lungs

Oxygen toxicity is the most severe side effect of oxygen therapy in neonates and adults. Pulmonary damage of oxygen toxicity is related to the overproduction of reactive oxygen species (ROS). In the present study, we investigated the effect of hyperoxia on the production of peroxynitrite in pulmonary artery endothelial cells (PAEC) and mouse lungs. Incubation of PAEC under hyperoxia (95% O(2)) for 24 h resulted in an increase in peroxynitrite formation. Uric acid, a peroxynitrite scavenger, prevented hyperoxia-induced increase in peroxynitrite. The increase in peroxynitrite formation is accompanied by increases in nitric oxide (NO) release and endothelial NO synthase (eNOS) activity. We have previously reported that association of eNOS with β-actin increases eNOS activity and NO production in lung endothelial cells. To study whether eNOS-β-actin association contributes to increased peroxynitrite production, eNOS-β-actin interaction were inhibited by reducing β-actin availability or by using a synthetic peptide (P326TAT) containing a sequence corresponding to the actin binding site on eNOS. We found that disruption of eNOS-β-actin interaction prevented hyperoxia-induced increases in eNOS-β-actin association, eNOS activity, NO and peroxynitrite production, and protein tyrosine nitration. Hyperoxia failed to induce the increases in eNOS activity, NO and peroxynitrite formation in COS-7 cells transfected with plasmids containing eNOS mutant cDNA in which amino acids leucine and tryptophan were replaced with alanine in the actin binding site on eNOS. Exposure of mice to hyperoxia resulted in significant increases in eNOS-β-actin association, eNOS activity, and protein tyrosine nitration in the lungs. Our data indicate that increased association of eNOS with β-actin in PAEC contributes to hyperoxia-induced increase in the production of peroxynitrite which may cause nitrosative stress in pulmonary vasculature.

Bench-to-bedside review: oxygen as a drug

Oxygen is one of the most commonly used therapeutic agents. Injudicious use of oxygen at high partial pressures (hyperoxia) for unproven indications, its known toxic potential, and the acknowledged roles of reactive oxygen species in tissue injury led to skepticism regarding its use. A large body of data indicates that hyperoxia exerts an extensive profile of physiologic and pharmacologic effects that improve tissue oxygenation, exert anti-inflammatory and antibacterial effects, and augment tissue repair mechanisms. These data set the rationale for the use of hyperoxia in a list of clinical conditions characterized by tissue hypoxia, infection, and consequential impaired tissue repair. Data on regional hemodynamic effects of hyperoxia and recent compelling evidence on its anti-inflammatory actions incited a surge of interest in the potential therapeutic effects of hyperoxia in myocardial revascularization and protection, in traumatic and nontraumatic ischemicanoxic brain insults, and in prevention of surgical site infections and in alleviation of septic and nonseptic local and systemic inflammatory responses. Although the margin of safety between effective and potentially toxic doses of oxygen is relatively narrow, the ability to carefully control its dose, meticulous adherence to currently accepted therapeutic protocols, and individually tailored treatment regimens make it a cost-effective safe drug.

Hyperbaric oxygenation reduces overexpression of c-Fos and oxidative stress in the brain stem of experimental endotoxemic rats

OBJECTIVE

Septic encephalopathy is associated with an increased mortality rate in septic patients. We have previously shown that a peripheral lipopolysaccharide (LPS) injection induces neuronal activation in the brain-stem nuclei of rats. Nitric oxide (NO) and superoxide are involved in LPS-induced brain damage. Hyperbaric oxygenation (HBO) provides protective effects against systemic oxidative stress and mortality in animals with septic shock. We examined the effects of HBO on neuronal activation and oxidative stress in the brain-stem nuclei of LPS-treated rats.

DESIGN AND INTERVENTIONS

Wistar rats were randomly distributed into six groups for the following treatments:(a) normal saline injection (NS); (b) HBO; (c) LPS; (d) LPS-HBO; (e) LPS-aminoguanidine (AG, an inhibitor of inducible nitric oxide synthase); or (f) hydralazine (HYD, a direct vasodilator). The HYD induces prolonged hypotension and was used as a comparison for LPS stimulation. The AG was used as a comparison for HBO treatment. Two HBO sessions were administered, 1 and 4[Symbol: see text]h after LPS.

RESULTS

HBO and AG significantly reversed the overproduction of c-Fos induced by LPS in the brain stems of rats, with greater reversal in the nucleus tractus solitarii (NTS) by HBO. Although AG did not reduce the superoxide level, HBO significantly abolished superoxide production and NADPH diaphorase expression in the brain stems of LPS-treated rats. The HYD induced much lower c-Fos expression in the brain-stem nuclei than that in LPS-treated animals and caused no significant increase in NADPH diaphorase expression or superoxide formation.

CONCLUSION

HBO protects against endotoxin-related neuronal activation and oxidative stress in the brain-stem nuclei of rats.

Effects of hyperbaric oxygen on glucose, lactate, glycerol and anti-oxidant enzymes in the skeletal muscle of rats during ischaemia and reperfusion

1. Hyperbaric (HBO(2)) and topical oxygen represent two accepted options to oxygenate tissues. The aim of the present study was to investigate the effect of HBO(2) on energy metabolism and anti-oxidant enzymes in a rat model of ischaemia-reperfusion (IR) skeletal muscle injury. 2. In the first study, 16 rats were randomized to a HBO(2)-treated group (Group 1; n = 8) and an untreated group (Group 2; n = 8). Under general anaesthesia, right hind limb ischaemia was produced by application of a rubber-band tourniquet for 3 h. After 2 h ischaemia, Group 1 rats received HBO(2) during the last hour of ischaemia. The HBO(2) consisted of 100% oxygen delivered at 282.8 kPa absolute pressure. Group 2 rats were not treated. Following the ischaemic period, the tourniquet was released for 1 h. A microdialysis probe was used to sample lactate, glucose and glycerol concentrations in the muscle extracellular tissue every 15 min throughout each experiment. 3. In the second study, 24 rats were randomized into four groups (n = 6 each). The first two groups were subjected to the IR injury protocol outlined above and either treated (Group 1) or untreated (Group 2) with HBO(2). Group 3 rats were anaesthetized, did not undergo IR injury, but underwent HBO(2) treatment. Group 4 rats were anaesthetized but did not undergo either IR injury or HBO(2) treatment. At end of each experiment, the biceps femoris muscle was removed and assayed for superoxide dismutase (SOD) and catalase (CAT) activity. Malondialdehyde (MDA) was measured to estimate the extent of membrane lipid peroxidation. 4. Three hours of skeletal muscle ischaemia resulted in a gradual decrease in the glucose concentration and a gradual increase in the lactate concentration within the extracellular fluid of the affected skeletal muscle tissue. Treatment with HBO(2) had no effect on the glucose concentration; however, HBO(2) significantly attenuated the ischaemia-induced increase in lactate and glycerol. In both groups, glucose concentration increased rapidly during reperfusion; glucose concentration returned to pre-ischaemic levels 15 min after reperfusion both with and without HBO(2). 5. Catalase activity and MDA increased significantly after 1 h of reperfusion. The HBO(2) attenuated the reperfusion-induced increase in CAT activity and MDA. 6. The results of the study suggest that HBO(2) may have some beneficial effect by decreasing lactate and glycerol levels and modulating anti-oxidant enzyme activity in postischaemic skeletal muscle in our rat model of tourniquet-induced IR skeletal muscle injury.

Can hyperbaric oxygen be used as adjunctive heart failure therapy through the induction of endogenous heat shock proteins?

Heart failure (HF) is a chronic condition that is expected to increase in incidence along with increased life expectancy and an aging population. As the incidence of HF increases, the cost to national healthcare budgets is expected to run into the billions. The costs of lost productivity and increased social reliance on state support must also be considered. Recently, acute myocardial infarction (AMI) has come to be seen as the major contributing factor to HF. Although thrombolysis may restore coronary perfusion after an AMI, it may also introduce ischemic reperfusion injury (IRI). In an attempt to ameliorate sustained protein damage caused by IRI, endogenous chaperone proteins known as heat shock proteins (HSPs) are induced as a consequence of the stress of IRI. Recently, hyperbaric oxygen has been shown to induce the production of HSPs in noncardiac tissue, with a resultant protective effect. This current opinion review article suggests a possible role for hyperbaric oxygen, as a technologically modern drug, in augmenting the induction of endogenous HSPs to repair and improve the function of failing hearts that have been damaged by AMI and IRI. In addition, this simple, safe, noninvasive drug may prove useful in easing the economic burden of HF on already overextended health resources.

Hyperbaric oxygen therapy prevents coagulation disorders in an experimental model of multiple organ failure syndrome

OBJECTIVE

To evaluate the effects of hyperbaric oxygen (HBO) therapy on the coagulation cascade using an experimental model of multiple organ failure syndrome (MOFS).

DESIGN

MOFS was induced by zymosan (500mg/kg i.p.) in rats. HBO therapy (2ATA) was administered in a cylindrical steel chamber 4 and 11h after zymosan administration. In a separate set of experiments animals were monitored for 72h, and systemic toxicity was scored.

INTERVENTION

Eighteen hours after zymosan administration, rats were killed and blood samples were used for analysis of hemocoagulative parameters, hemodynamics, and arterial blood gas.

MAIN RESULTS

Zymosan administration caused MOFS by affecting the coagulation cascade, as shown by a significant increase in plasma levels of fibrinogen, tissue plasminogen activator, inhibitor of tissue plasminogen activator of type 1, and plasma levels of fibrin degradation products vs. control rats. Zymosan-induced MOFS was also characterized by a significant increase in von Willebrand antigen plasma levels vs. controls. Moreover, zymosan administration induced a significant fall in mean arterial blood pressure and alteration in blood gas values. HBO therapy significantly reduced the derangements of coagulation cascade, the fall in mean blood pressure and alteration in blood gas induced by zymosan administration.

CONCLUSIONS

The hypercoagulability induced by zymosan could be responsible for organ failure and death. Our data demonstrate that HBO therapy significantly prevents the alteration in the coagulation cascade and arterial blood gas in an experimental model of MOFS.

Potential effects of hyperbaric oxygen therapy in acute pancreatitis

BACKGROUND

To extract from the biomedical published reports, the effects of hyperbaric oxygen (HBO) on inflammatory disease, in particular acute pancreatitis.

METHODS

This review will explain these effects and evaluate potential mechanisms of action of HBO in acute pancreatitis. A Medline/PubMed search (January 1966 to July 2004) with manual cross-referencing was conducted, including all relevant articles investigating the molecular and systemic effects of HBO on inflammatory diseases, particularly focusing on the studies of acute pancreatitis. All publication types, languages and subsets were searched.

RESULTS

Original and review articles and short communications were extracted. The selected original articles covered the molecular and systemic effects of HBO and the effects in inflammatory disease states. The major findings are that HBO can act as an anti-inflammatory agent and as an antimicrobial agent. Many of the effects of HBO would be beneficial in the treatment of acute severe pancreatitis. Work carried out to date in animal models of acute pancreatitis shows promising improvements in severity but studies are limited to date.

CONCLUSION

Acute pancreatitis impairs the pancreatic and systemic microcirculation and causes acute inflammation. These processes are potentially improved by HBO therapy.

Effects of hyperbaric oxygen treatment on liver functions, oxidative status and histology in septic rats

OBJECTIVE

The liver is thought to be responsible for multiple organ failure during sepsis. Increase in tissue oxygen consumption is a major component of the septic response. Hyperbaric oxygen (HBO) therapy provides more oxygenation in the whole body. This study examined the effect of HBO alone or in combination with cefepime (CEF) on the liver in septic rats.

DESIGN AND INTERVENTIONS

We divided 90 male rats into six groups; control, HBO, sepsis (SEP), SEP+HBO, SEP+CEF, and SEP+CEF+HBO. Sepsis was induced with an intraperitoneal injection of Escherichia coli (2.1 x 10(9) cfu). A total of six HBO sessions were performed at 2 atm absolute for 90 min at 6-h intervals. CEF was administered intraperitoneally at a dose of 50 mg/kg twice daily. Animals were killed 48 h after sepsis induction. Their liver and blood were removed for biochemical and histopathological analysis.

MEASUREMENTS AND RESULTS

Liver thiobarbituric acid reactive substances as well as serum alanine transaminase, aspartate transaminase and alkaline phosphatase levels increased while the activity of the antioxidant enzymes superoxide dismutase and catalase decreased significantly in septic rats. These parameters returned to nearly control levels in the SEP+CEF+HBO group. Histological observations supported these findings: Hepatocellular degeneration was observed and intensive polymorphonuclear cell infiltration appeared in all fields of septic animal livers. HBO alone could not sufficiently reverse these histopathological changes, but most liver sections presented normal histology when it was combined with CEF.

CONCLUSIONS

HBO may be a useful adjuvant therapy modality to improve the efficacy of sepsis treatment.

NITRIC OXIDE FROM INDUCIBLE NITRIC OXIDE SYNTHASE SENSITIZES THE INFLAMED AORTA TO HYPOXIC DAMAGE VIA RESPIRATORY INHIBITION

We tested whether nitric oxide (NO) could synergize with hypoxia to induce damage to the aorta isolated from rat. We found that 4 h of mild hypoxia (5% O2) caused substantial necrosis of isolated rat aortae (measured as lactate dehydrogenase release) if inducible NO synthase (iNOS) had previously been induced by endotoxin plus interferon-gamma. Mild hypoxia caused no significant necrosis in the absence of this inflammatory activation, and inflammatory activation caused little damage at a higher oxygen levels (21% oxygen). An iNOS inhibitor (1400W) prevented the necrosis induced by inflammation plus mild hypoxia, whereas the NO donor diethylenetriamine (DETA)/NO adduct, 0.5 mM) greatly sensitized the noninflammed aorta to necrosis induced by mild hypoxia. NO inhibited aortic respiration to a greater degree at lower oxygen concentrations, consistent with NO inhibition of cytochrome oxidase in competition with oxygen. A specific inhibitor of mitochondrial respiration, myxothiazol, caused necrosis of aortae over a similar time course to NO. DETA/NO plus mild hypoxia-induced cell death was substantially reduced by a glycolytic intermediate 3-phosphoglycerate, suggesting that necrosis resulted from energy depletion secondary to respiratory inhibition. This NO-induced sensitization of aorta to mild hypoxia may be important in sepsis and other pathologies where iNOS is expressed.