Variable tissue expression of transferrin receptors: relevance to acute respiratory distress syndrome.

Acute respiratory distress syndrome (ARDS) is associated with altered plasma and lung iron chemistry. Iron can promote microbial virulence and catalyse pro-oxidant reactions, thereby contributing to the oxidative stress that characterises the syndrome. Therefore, the expression of ferritin and transferrin receptors (TfR) were sought in the lungs and hearts of rodents treated with lipopolysaccharide (LPS), and measurements of TfR and ferritin protein expression were taken from lung biopsy specimens from patients with ARDS and appropriate controls. TfR messenger ribonucleic acid (mRNA) was significantly upregulated in the lungs and significantly downregulated in the hearts of rats 4 h after LPS. Ferritin mRNA levels (light and heavy chains) remained unaltered. Protein TfR levels were significantly upregulated in lungs and downregulated in hearts 4 h post-LPS. Ferritin protein levels were significantly downregulated in lungs compared to baseline values but were unaltered in hearts. Nonhaem iron levels were increased in lungs and decreased in hearts, and iron-regulatory-protein activity increased in hearts but not lungs. TfR protein levels were significantly increased in lung biopsies from patients with ARDS compared to controls. Transferrin receptors are upregulated in rodent lungs during inflammation but are downregulated in the heart. Transferrin receptor protein levels were significantly increased in the lungs in clinical acute respiratory distress syndrome. These findings have implications for the pathogenesis of acute respiratory distress syndrome, especially in relation to the role of iron as a mediator of oxidative stress.

Iron and the redox status of the lungs.

Iron is an element essential for the survival of most aerobic organisms. However, when its availability is not adequately controlled, iron, can catalyze the formation of a range of aggressive and damaging reactive oxygen species, and act as a microbial growth promoter. Depending on the concentrations formed such species can cause molecular damage or influence redox signaling mechanisms. This review describes recent knowledge concerning iron metabolism in the lung, during both health and disease. In the lower part of the lung a small redox active pool of iron is required for reasons that are at present unclear, but may be related to antimicrobial functions. When the concentration of iron is increased in the lung (usually because of environmental exposure), iron is deleterious and contributes to a range of chronic and acute respiratory diseases. Moreover, aberrant regulation of iron metabolism, and/or deficient antioxidant protection, is also associated with acute lung diseases, such as the acute respiratory distress syndrome (ARDS). Iron, with the consequent production of reactive oxygen species (ROS), microbial growth promotion, and adverse signaling is strongly implicated as a major contributor to the pathogenesis of numerous disease processes involving the lung. Heme oxgenase, an enzyme that produces reactive iron from heme catabolism, is also briefly discussed in relation to lung disease.

Risk of iron overload is decreased in beating heart coronary artery surgery compared to conventional bypass.

Conventional cardiopulmonary bypass surgery (CCPB) increases the iron loading of plasma transferrin often to a state of plasma iron overload, with the presence of low molecular mass iron. Such iron is a potential risk factor for oxidative stress and microbial virulence. Here we assess 'off-pump' coronary artery surgery on the beating heart for changes in plasma iron chemistry. Seventeen patients undergoing cardiac surgery using the 'Octopus' myocardial wall stabilisation device were monitored at five time points for changes in plasma iron chemistry. This group was further divided into those (n=9) who had one- or two- (n=8) vessel grafts, and compared with eight patients undergoing conventional coronary artery surgery. Patients undergoing beating heart surgery had significantly lower levels of total plasma non-haem iron, and a decreased percentage saturation of their transferrin at all time points compared to conventional bypass patients. Plasma iron overload occurred in only one patient undergoing CCPB. Beating heart surgery appears to decrease red blood cell haemolysis, and tissue damage during the operative procedures and thereby significantly decreases the risk of plasma iron overload associated with conventional bypass.

Thiols in cellular redox signalling and control.

Reactive oxygen (ROS) and reactive nitrogen species (RNS) produced in vivo at levels that cannot be dealt with adequately by endogenous antioxidant systems can lead to the damage of lipids, proteins, carbohydrates and nucleic acids. Oxidative modification of these molecules by toxic levels of ROS and RNS represents an extreme event that can lead to deleterious consequences such as loss of function. More recently, however, interest has focused on the formation of these species at sub-toxic levels and their potential to act as biological signal molecules. Subtoxic ROS and RNS production can lead to alterations in cellular and extracellular redox state, and it is such alterations that have been shown to signal changes in cell functions. By the use of a variety of cell types it has been shown that numerous cellular processes including gene expression can be regulated by subtle changes in redox balance Examples of this include the activation of certain nuclear transcription factors, and the determination of cellular fate by apoptosis or necrosis. Cellular redox balance is, under normal circumstances, probably under genetic control and maintained by an array of enzymatic systems that ensure that overall reducing conditions prevail. Thiols, by virtue of their ability to be reversibly oxidised, are recognised as key components involved in the maintenance of redox balance. Additionally, increasing evidence suggests that thiol groups located on various molecules act as redox sensitive switches thereby providing a common trigger for a variety of ROS and RNS mediated signalling events. In this review we discuss a number of cellular processes in which ROS and RNS have been implicated in redox signalling mechanisms. Particular attention has been paid to the importance of thiols and thiol-containing molecules in these processes.

The iron paradox of heart and lungs and its implications for acute lung injury.

Iron is an essential requirement for the growth, development, and long term survival of most aerobic organisms. When control over safe iron sequestration is lost or compromised, leading to the release of low molecular mass forms of iron, the heart appears to be particularly sensitive to iron toxicity with cardiomyopathies often developing as a consequence. Iron toxicity, leading to iron-overload, is often treated in humans with the iron chelator desferrioxamine mesylate. Such treatment regimens designed to protect the heart can, however, often lead to lung injury and, in fact, several compounds with known iron chelating properties can induce severe lung dysfunction and injury. Based on these clinical observations and our recent laboratory data, we propose that the lungs actively accumulate reactive forms of iron for use in cellular growth and proliferation, and for the oxidative destruction of microbes, whereas the heart responds in the opposite way by actively removing iron which it finds extremely toxic.

Iron signalling regulated directly and through oxygen: implications for sepsis and the acute respiratory distress syndrome.

Reactive oxygen species produced at toxic levels are damaging species. When produced at sub-toxic levels, however, they are involved as second messengers in numerous signal transduction pathways. In addition to these findings, we can add the concept that iron (often viewed as the "villain" in free radical biology) can also be considered as a signalling species. Iron is intimately involved in the regulation of its own storage, compartmentalization and turnover. During adult respiratory distress syndrome (ARDS) and sepsis, such regulation may be aberrant or altered in some predisposed way. Such changes may have profound implications for tissue damage, and for the modulation of the inflammatory response in these patients. The search for a genetic predisposition in patients that leads to the development of ARDS associated with abnormalities in iron turnover and signalling would seem to be an important and logical progression for studies into the disease. These may lead eventually to the design of effective treatment regimens that involve the control of iron.

Antioxidant binding of caeruloplasmin to myeloperoxidase: myeloperoxidase is inhibited, but oxidase, peroxidase and immunoreactive properties of caeruloplasmin remain intact.

The neutrophil enzyme myeloperoxidase (MPO) purposefully makes hypochlorous acid (HOCl) as part of the cells defence against microbial infections. During cell lysis, however, MPO will be released into the extracellular environment where production of HOCl, a powerful oxidant, will lead to molecular damage. Extracellular MPO binds to the copper-containing protein caeruloplasmin (Cp) and prevents MPO making HOCl. Cp has several important antioxidant functions in extracellular fluids associated with its ability to catalyse oxidation of ferrous ions and to remove peroxides. The binding of MPO to Cp did not inhibit these important extracellular antioxidant activities of Cp, but in so doing it provided additional antioxidant protection against formation of HOCl.

Acute respiratory distress syndrome secondary to cardiopulmonary bypass: do compromised plasma iron-binding anti-oxidant protection and thiol levels influence outcome?

OBJECTIVES: Cardiopulmonary bypass (CPB) surgery is often associated with mild lung injury and in some patients leads to acute lung injury and acute respiratory distress syndrome (ARDS). Aberrant plasma iron chemistry (increased iron loading of transferrin and/or the presence of redox-active low molecular mass iron) and increased plasma thiol levels are features of this type of surgery and represent a potential pro-oxidant risk for oxidative damage. Oxidative damage is a feature of ARDS, and we hypothesized that pro-oxidant forces may contribute to the onset and progression of ARDS. DESIGN: Prospective, single center, observational study. SETTING: University-affiliated tertiary referral cardiothoracic center. PATIENTS: A total of 19 patients with ARDS secondary to CPB surgery and 64 patients with ARDS secondary to a variety of other predisposing causes. INTERVENTIONS: Supportive techniques appropriate to the treatment of ARDS. MEASUREMENTS AND MAIN RESULTS: Blood samples were collected into lithium heparin tubes for all patient groups on the first day of the admission of patients to the intensive care unit immediately after the diagnosis of ARDS. Plasma was immediately assayed for thiol content and total protein and albumin levels. Plasma from patients with ARDS secondary to CPB surgery was also assayed for changes in iron chemistry. Nonsurviving patients with ARDS secondary to CPB surgery displayed significantly greater levels of aberrant iron chemistry (elevated levels of iron saturation of transferrin) with decreased iron-binding antioxidant protection and elevated plasma thiol levels than did survivors. Plasma thiol levels in patients with ARDS secondary to other predisposing causes were (with the exception of lung-surgery patients) significantly elevated in survivors compared with those in nonsurvivors of the syndrome. CONCLUSIONS: Increased levels of plasma thiol appear to be associated with mortality in patients with ARDS secondary to CPB surgery.

Free radicals and antioxidants in the year 2000. A historical look to the future.

In the late 1950's free radicals and antioxidants were almost unheard of in the clinical and biological sciences but chemists had known about them for years in the context of radiation, polymer and combustion technology. Daniel Gilbert, Rebeca Gerschman and their colleagues related the toxic effects of elevated oxygen levels on aerobes to those of ionizing radiation, and proposed that oxygen toxicity is due to free radical formation, in a pioneering paper in 1956. Biochemistry owes much of its early expansion to the development and application of chromatographic and electrophoretic techniques, especially as applied to the study of proteins. Thus, superoxide dismutase (SOD) enzymes (MnSOD, CuZnSOD, FeSOD) were quickly identified. By the 1980's Molecular Biology had evolved from within biochemistry and microbiology to become a dominant new discipline, with DNA sequencing, recombinant DNA technology, cloning, and the development of PCR representing milestones in its advance. As a biological tool to explore reaction mechanisms, SOD was a unique and valuable asset. Its ability to inhibit radical reactions leading to oxidative damage in vitro often turned out to be due to its ability to prevent reduction of iron ions by superoxide. Nitric oxide (NO.) provided the next clue as to how SOD might be playing a critical biological role. Although NO. is sluggish in its reactions with most biomolecules it is astoundingly reactive with free radicals, including superoxide. Overall, this high reactivity of NO. with radicals may be beneficial in vivo, e.g. by scavenging peroxyl radicals and inhibiting lipid peroxidation. If reactive oxygen species are intimately involved with the redox regulation of cell functions, as seems likely from current evidence, it may be easier to understand why attempts to change antioxidant balance in aging experiments have failed. The cell will adapt to maintain its redox balance. Indeed, transgenic animals over-expressing antioxidants show some abnormalities of function. There must therefore be a highly complex interrelationship between dietary, constitutive, and inducible antioxidants with the body, under genetic control. The challenge for the new century is to be able to understand these relationships, and how to manipulate them to our advantage to prevent and treat disease.

Iron overload in paediatrics undergoing cardiopulmonary bypass.

Pathological changes in iron status are known to occur during bypass and will be superimposed upon physiological abnormalities in iron distribution, characteristic of the neonatal period. We have sought to define the severity of iron overload in these patients. Plasma samples from 65 paediatric patients undergoing cardiopulmonary bypass (CPB) were analysed for non-haem iron, total iron binding capacity, transferrin and bleomycin-detectable iron. Patients were divided into four age groups for analysis. Within each age group, patients who were in iron overload at any time point were statistically compared to those who were not. The most significant changes in iron chemistry were seen in the plasma of neonates, with 25% in a state of plasma iron overload. 18.5% of infants and 14.3% of children at 1-5 years were also in iron overload at some time point during CPB. No children over 5 years, however, went into iron overload. Increased iron saturation of transferrin eliminates its ability to bind reactive forms of iron and to act as an antioxidant. When transferrin is fully saturated with iron, reactive forms of iron are present in the plasma which can stimulate iron-driven oxidative reactions. Our data suggest that paediatric patients are at greater risk of iron overload during CPB, and that some form of iron chelation therapy may be advantageous to decrease oxidative stress.

Does redox regulation of cell function explain why antioxidants perform so poorly as therapeutic agents?

In normal health, there is a balance between the formation of oxidising chemical species and their effective removal by protective antioxidants. Antioxidants are a diverse group of molecules with diverse functions. For example, they range from large highly specific proteinaceous molecules with catalytic properties to small lipid- and water-soluble molecules with non-specific scavenging or metal chelating properties. Antioxidants control the prevailing relationship between reducing or oxidising (redox) conditions in biological systems. Such control offers two major advantages: (i) the ability to remove toxic levels of oxidants before they damage critical biological molecules; and (ii) the ability to manipulate changes, at the subtoxic level, of molecules that can function as signal, trigger or messenger carriers. If cellular functions are signalled through redox control mechanisms, it would explain why we see such a poor response to antioxidants as therapeutic agents in human medicine.

Haem oxygenase shows pro-oxidant activity in microsomal and cellular systems: implications for the release of low-molecular-mass iron.

Haem oxygenase-1 (HO-1) is a highly inducible stress protein that removes haem from cells with the release of biliverdin, carbon monoxide and low-molecular-mass iron (LMrFe). Several antioxidant functions have been ascribed to HO; its induction is considered to be a protective event. However, LMrFe produced during haem catabolism might elicit a pro-oxidant response, with deleterious consequences. We therefore investigated the delicate balance between pro-oxidant and antioxidant events with the use of a microsomal lipid peroxidation (LPO) system. By using microsomal-bound HO in an NADPH-dependent LPO system, we assessed the pro-oxidant nature of the released LMrFe and the antioxidant effect of the released bilirubin. Hb, a biologically relevant substrate for HO, was included with the microsomes to supplement the source of haem iron and to promote LPO. We found significant increases in microsomal LPO, by using the thiobarbituric acid (TBA) test, after incubation with Hb. This Hb-stimulated peroxidation was inhibited by HO inhibitors and by iron chelators, suggesting a HO-driven, iron-dependent mechanism. GLC-MS was employed to measure the specific LPO product 4-hydroxy-2-nonenal and to confirm our TBA test results. A HO inhibitor attenuated an increase in intracellular LMrFe that occurred after treatment of rat pulmonary artery smooth-muscle cells with Hb. Additionally, exogenously added bilirubin at an equimolar concentration to the LMrFe present in both microsomal and liposomal systems was unable to prevent the pro-oxidant effect of the iron. Under certain circumstances HO can act as a pro-oxidant and seems to have a role in stimulating microsomal LPO.

Oxidative damage to proteins of bronchoalveolar lavage fluid in patients with acute respiratory distress syndrome: evidence for neutrophil-mediated hydroxylation, nitration, and chlorination.

OBJECTIVE: To assess the degree, source, and patterns of oxidative damage to bronchoalveolar lavage proteins as a modification of amino acid residues in patients with acute respiratory distress syndrome (ARDS). DESIGN: Prospective, controlled study. SETTING: Adult intensive care unit of a postgraduate teaching hospital. PATIENTS: Twenty-eight patients with established ARDS were studied and compared with six ventilated patients without ARDS and 11 normal healthy controls. INTERVENTIONS: Supportive techniques appropriate to ARDS. MEASUREMENTS AND MAIN RESULTS: Evidence of oxidative modification of bronchoalveolar lavage fluid protein, indicative of the production of specific reactive oxidizing species, was sought using a high-performance liquid chromatography technique. Bronchoalveolar lavage fluid samples from patients with ARDS, ventilated intensive care controls, and normal healthy controls were analyzed. Concentrations of orthotyrosine were significantly higher in the ARDS group than in either control group (7.98 + 3.78 nmol/mg for ARDS, 0.67 + 0.67 for ventilated controls, and 0.71 + 0.22 for healthy controls; p < .05). Chlorotyrosine concentrations were also significantly increased in the ARDS group over either control group (4.82 + 1.07 nmol/mg for ARDS, 1.55 + 1.34 for ventilated controls, and 0.33 + 0.12 for healthy controls; p < .05). Nitrotyrosine concentrations were similarly significantly increased in the ARDS groups compared with each control group (2.21 + 0.65 nmol/mg for ARDS, 0.29 + 0.29 for ventilated controls, and 0.06 + 0.03 for healthy controls; p < .05). Chlorotyrosine and nitrotyrosine concentrations showed significant correlations with myeloperoxidase concentrations in bronchoalveolar lavage fluid, measured using an enzyme-linked immunosorbent assay in patients with ARDS. These findings suggest a possible relationship between inflammatory cell activation, oxidant formation, and damage to proteins in the lungs of these patients CONCLUSIONS: Overall, our data strongly suggest heightened concentrations of oxidative stress in the lungs of patients with ARDS that lead to significantly increased oxidative protein damage.

Acute right ventricular restrictive physiology after repair of tetralogy of Fallot: association with myocardial injury and oxidative stress.

BACKGROUND: Acute right ventricular (RV) restrictive physiology after tetralogy of Fallot repair results in low cardiac output and a prolonged stay in the intensive care unit (ICU). However, its mechanism remains uncertain. METHODS AND RESULTS: In the first 24 hours after tetralogy of Fallot repair (n=11 patients), serial prospective measurements were performed of cardiac troponin T, indexes of NO production (NO(2)(-) and NO(3)(-) combined as NOx), and iron metabolism and antioxidants. RV diastolic function was assessed by transthoracic Doppler echocardiography. Patients who had a long stay in the ICU were characterized by restrictive RV physiology (nonrestrictive group [n=7]: 3.0+/-0.6 days [mean+/-SD]; restrictive group [n=4]: 10.7+/-3.1 days). Troponin T peak concentration and the area under its concentration-time curve (AUC) were higher in the restrictive RV group (peak: restrictive group 17. 0+/-2.8 microg/L, nonrestrictive group 10.4+/-4.6 microg/L, P<0.03; AUC: restrictive group 268.8+/-73.6 microg. h(-1). L(-1), nonrestrictive group 136.2+/-48.3 microg. h(-1). L(-1), P<0.03). Plasma NOx/creatinine concentrations were higher in the restrictive group than the nonrestrictive group at 2 hours after bypass (restrictive group 1.3+/-0.4, nonrestrictive group 0.8+/-0.2; P=0. 04) but were similar by 24 hours. Iron loading peaked 2 to 10 hours after bypass and was more severe in the restrictive group (peak transferrin saturation: restrictive group 83.9+/-13.0%, nonrestrictive group 58.3+/-16.2%, P=0.05; minimum total iron-binding capacity: restrictive group 0.59+/-0.21%, nonrestrictive group 0.76+/-0.06%, P=0.04; minimum iron-binding antioxidant activity to oxyorganic radicals: restrictive group 9. 5+/-22.4%, nonrestrictive group 50.6+/-11.4%, P=0.01). CONCLUSIONS: After tetralogy of Fallot repair, acute restrictive RV physiology is associated with greater intraoperative myocardial injury and postoperative oxidative stress with severe iron loading of transferrin.

Antioxidant protection against iron toxicity: plasma changes during cardiopulmonary bypass in neonates, infants, and children.

Cardiopulmonary bypass surgery is associated with the release of low molecular mass iron, which increases the saturation of plasma transferrin to over 50% in all adult patients treated. In a significant minority, however plasma transferrin becomes 100% iron saturated and non-transferrin bound iron can be detected in the plasma. An iron-saturated transferrin is also a common physiological finding in normal term and pre-term infants at a time when their plasma antioxidants, which protect against iron toxicity and radical scavenging, are profoundly different from those seen in adults. This study was conducted to assess the extent to which antioxidants, which protect against iron toxicity, are altered in neonates, infants, and children undergoing cardiopulmonary bypass surgery.

Glutathione peroxidase-like activity of caeruloplasmin as an important lung antioxidant.

The copper-containing plasma protein caeruloplasmin (Cp) has been shown to possess several oxidase activities, but with the exception of its ferrous ion oxidising (ferroxidase) activity which so far appear to be of minor biological relevance. Recently, Kim and colleagues (Kim et al. (1998) FEBS Lett. 431, pp. 473-475) observed that Cp can catalytically remove hydrogen peroxide in the presence of thiols. Here, we show that Cp can remove both hydrogen peroxide and lipid hydroperoxides at physiologically relevant concentrations of reduced glutathione known to be present in lung and lung lining fluid. The glutathione peroxidase-like activity of Cp together with its ferroxidase activity would completely remove the primary reactants required for both Fenton chemistry and lipid peroxidation.

Nitration of proteins in bronchoalveolar lavage fluid from patients with acute respiratory distress syndrome receiving inhaled nitric oxide.

Inhaled nitric oxide (.NO) is used to improve gas exchange and reduce pulmonary vascular resistance (PVR) in patients with the acute respiratory distress syndrome (ARDS). Although controlled studies have shown no survival benefit, some investigators have suggested that inhaled.NO may have antiinflammatory properties under these circumstances. In contrast, others have speculated that.NO given by inhalation could be cytotoxic, as it combines with superoxide at near diffusion-limited rates to produce the highly reactive oxidant peroxynitrite (ONOO(-)). We therefore quantified levels of 3-nitrotyrosine, a marker for ONOO(-) formation, in bronchoalveolar lavage fluid (BAL) from patients with ARDS receiving inhaled.NO, and from patients with comparable lung injury who were not so treated. We also measured levels of 3-chlorotyrosine as an index of neutrophil activation to assess indirectly the effects of inhaled.NO on lung inflammation. Patients receiving .NO had increased levels of 3-nitrotyrosine (6.76 +/- 2.79 versus 0.4 +/- 0.15 nmol/mg of protein, p < 0.05) and 3-chlorotyrosine (7.97 +/- 2.74 versus 1. 53 +/- 1.09 nmol/mg of protein, p < 0.05) in BAL protein compared with controls. In patients with ARDS, inhaled.NO increases the formation of 3-nitrotyrosine and is accompanied by an increase in levels of 3-chlorotyrosine (a marker of neutrophil activation). The possible long-term consequences of these observations remain to be evaluated.

Plasma hypoxanthine levels during crystalloid and blood cardioplegias: warm blood cardioplegia increases hypoxanthine levels with a greater risk of oxidative stress.

BACKGROUND: PATIENTS undergoing cardiopulmonary bypass (CPB) are subjected to severe oxidative stress, and frequently show evidence of acute lung injury post surgery. Associations between acute lung injury, oxidative stress, and aberrant ATP catabolism have been made and prompted us to consider whether the purine metabolites xanthine and hypoxanthine alter significantly during CPB when different types of cardioplegia are used. EXPERIMENTAL DESIGN: retrospective follow up study on stored plasma samples from patients randomly selected to receive either warm blood, cold blood, or crystalloid cardioplegia. SETTING: adult intensive care unit of post graduate teaching hospital. PATIENTS: thirty-eight patients undergoing aortic valve replacement, with or without artery grafting. Operation was carried out by a single surgeon. INTERVENTIONS: all patients received either a homograft aortic valve or a stentless porcine valve. RESULTS: No significant differences in xanthine levels at any time points during CPB, or between the different cardioplegic groups. Hypoxanthine levels were, however, significantly higher in patients receiving warm blood cardioplegia (74.84+/-16.715 microM, p=0.0151), and was most marked at time point 3 when the aortic cross clamp was released. PATIENTS receiving crystalloid cardioplegia showed higher levels of hypoxanthine (44.56+/-10.16 microM) than those receiving cold blood cardioplegia (21.57+/-7.106 microM). CONCLUSIONS: Considering these data together, it suggests that aberrant ATP catabolism, characteristic of ischaemia/reperfusion, is further disturbed during warm blood cardioplegia leading to a marked increase in plasma hypoxanthine levels. This has the potential to further increase oxidative stress during CPB.

Iron overload upregulates haem oxygenase 1 in the lung more rapidly than in other tissues.

Haem oxygenase-1 is upregulated by numerous insults, including oxidative stress, and under such circumstances it is considered to be a protective stratagem. We have measured the haem oxygenase-1 expression in heart, lung and liver tissues of control and iron-overloaded rats. Lung tissue from iron-overloaded rats displayed a significant increase in the haem oxygenase-1 protein but no changes in haem oxygenase-1 mRNA. Conversely, heart tissue showed a significant increase in haem oxygenase-1 mRNA but no changes in haem oxygenase-1 protein. We conclude that during oxidative stress caused by iron overload, lung tissue responds with a rapid upregulation of haem oxygenase-1 levels.

Hydrogen peroxide and catalase are inversely related in adult patients undergoing cardiopulmonary bypass: implications for antioxidant protection.

Adult patients undergoing cardiopulmonary bypass (CPB) surgery are subjected to increased oxidative stress and show a spectrum of lung injury. Increased levels of hydrogen peroxide (H2O2) are often seen during episodes of oxidative stress, such as the use of high FiO2s, and this molecule plays a key role in the formation of highly damaging oxidants such as the hydroxyl radical. Oxidative damage to plasma proteins was assessed by measuring free thiol groups, and antioxidant protection against H2O2 by measuring catalase activity. CPB patients (n = 39) receiving either 100% or 50% oxygen at the end of bypass were studied by measuring levels of H2O2 in breath condensate and levels of catalase in their plasma, and comparing these to pre-bypass levels. Post-bypass, all CPB patients exhaled significantly lower levels of H2O2 (P < 0.0001) at a time when they had significantly increased activity (0.809 +/- 0.11 versus 1.688 +/- 0.18 U/mg protein) of catalase in their plasma. There were no significant differences in these parameters between the 100% and 50% oxygen groups. At a time when oxidative stress is greatest, there appears to be a corresponding plasma increase in the antioxidant catalase. Whether this change is fortuitous or a response to oxidative stress is at present under consideration.