Evidence that hydrogen peroxide generated by 365-nm UVA radiation is not important in mammalian cell killing

We compared measurements of cell survival and DNA single-strand breaks (SSBs) caused by hydrogen peroxide (H2O2) and UVA radiation (365-nm) in both a parental and a H2O2-resistant variant of the Chinese hamster ovary HA1 line derived by culturing cells in progressively higher concentrations of H2O2. Both RNA slot blot analysis and enzyme analysis confirmed that the variant possesses high levels of both catalase activity and mRNA. The variant was completely resistant to the lethal effects of H2O2 over the concentration range tested (up to 480 microM), whereas the parental strain showed less than 1% survival at this concentration. Similarly, the H2O2-resistant strain exhibited far fewer SSBs after exposure to H2O2 than the parental strain. Addition of o-phenanthroline to the parental cells during H2O2 exposure almost completely inhibited SSB induction, evidence that these SSBs are produced via the Fenton pathway of Haber-Weiss reactions. Very little difference was found between the variant and the parent after exposure to 365-nm radiation: only a minor difference in survival kinetics and no difference is SSB induction were observed between the two cell lines. These results are consistent with a hypothesis that most lethal events caused in cells by UVA occur by pathways that do not involve the H2O2 that is produced by sensitized reactions within the cells.     

Exogenous application of glycinebetaine increases chilling tolerance in tomato plants

Tomato (Lycopersicon esculentum Mill. cv. Moneymaker) plants are chilling sensitive, and do not naturally accumulate glycinebetaine (GB), a metabolite that functions as a stress protectant. We reported previously that exogenous GB application enhanced chilling tolerance in tomato. To understand its protective role better, we have further evaluated various parameters associated with improved tolerance. Although its effect was most pronounced in younger plants, this benefit was diminished 1 week after GB application. When administered by foliar spray, GB was readily taken up and translocated to various organs, with the highest levels being measured in meristematic tissues, including the shoot apices and flower buds. In leaves, the majority of endogenous GB was found in the cytosol; only 0.6-22.0% of the total leaf GB was localized in chloroplasts. Immediately after GB application, levels of H(2)O(2), catalase activity and expression of the catalase gene (CAT1) were all higher in GB-treated than in control plants. One day after exposure to chilling stress, the treated plants had significantly greater catalase activity and CAT1 expression, although their H(2)O(2) levels remained unchanged. During the following 2 d of this chilling treatment, GB-treated plants maintained lower H(2)O(2) levels but had higher catalase activity than the controls. These results suggest that, in addition to protecting macromolecules and membranes directly, GB-enhanced chilling tolerance may involve the induction of H(2)O(2)-mediated antioxidant mechanisms, e.g. enhanced catalase expression and catalase activity.     

Role of glutathione in the adaptive tolerance to H2O2

Endogenous antioxidant defense systems are enhanced by various physiological stimuli including sublethal oxidative challenges, which induce tolerance to subsequent lethal oxidative injuries. We sought to evaluate the contributions of catalase and the glutathione system to the adaptive tolerance to H2O2. For this purpose, H9c2 cells were stimulated with 100 microM H2O2, which was the maximal dose at which no significant acute cell damage was observed. Twenty-four hours after stimulation, control and pretreated cells were challenged with a lethal concentration of H2O2 (300 microM). Compared with the control cells, pretreated cells were significantly tolerant of H2O2, with reduced cell lysis and improved survival rate. In pretreated cells, glutathione content increased to 48.20 +/- 6.38 nmol/mg protein versus 27.59 +/- 2.55 nmol/mg protein in control cells, and catalase activity also increased to 30.82 +/- 2.64 versus 15.46 +/- 1.29 units/mg protein in control cells, whereas glutathione peroxidase activity was not affected. Increased glutathione content was attributed to increased gamma-glutamylcysteine synthetase activity, which is known as the rate-limiting enzyme of glutathione synthesis. To elucidate the relative contribution of the glutathione system and catalase to tolerance of H2O2, control and pretreated cells were incubated with specific inhibitors of gamma-glutamyl cysteine synthetase (L-buthionine sulfoximine) or catalase (3-amino-1,2,4-triazole), and challenged with H2O2. Cytoprotection by the low-dose H2O2 pretreatment was almost completely abolished by L-buthionine sulfoximine, while it was preserved after 3-amino-1,2,4-triazole treatment. From these results, it is concluded that both the glutathione system and catalase can be enhanced by H2O2 stimulation, but increased glutathione content rather than catalase activity was operative in the tolerance of lethal oxidative stress.     

Variations of hydrogen peroxide and catalase expression in Bombyx eggs during diapause initiation and termination

For diapause eggs of the silkworm, Bombyx mori, diapause initiation is prevented with hydrochloric acid (HCl) at around 20 h post-oviposition while diapause status is terminated with chilling around 5°C. To investigate whether hydrogen peroxide (H(2)O(2)) and catalase expression are involved in diapause initiation and termination, the concentration of H(2)O(2), relatively higher levels of catalase mRNA and activity of catalase were compared between (1) 20-h-old diapause eggs and the HCl-treated diapause eggs, and (2) 10-day-old diapause eggs and the 5°C-chilled diapause eggs. Compared to diapause eggs, the HCl-treated eggs had significantly higher H(2)O(2) concentrations (up from approximately 1-3 μmol/g fresh mass to 5-8 μmol/g fresh mass), higher relative level of catalase mRNA (up from 0 to 35.2%) and higher catalase activity (up from 2.51 units/mg protein to 4.97 units/mg protein) at 96 h post-treatment. On the other hand, the 5°C chilling resulted in significant increases of H(2)O(2) concentration (up from 0.79 μmol/g fresh mass to 5.57 μmol/g fresh mass), relative level of catalase mRNA (up from 0 to 71.4%) and catalase activity (up from 0.88 units/mg protein to 3.42 units/mg protein) within 120 days. The results obtained in this work suggest that variations of H(2)O(2) and catalase expression in Bombyx eggs are involved in diapause initiation and termination.     

Two alternative substrate paths for compound I formation and reduction in catalase-peroxidase KatG from Burkholderia pseudomallei

Five residues in the multifunctional catalase-peroxidase KatG of Burkholderia pesudomallei are essential for catalase, but not peroxidase, activity. Asp141 is the only one of these catalase-specific residues not related with the covalent adduct found in KatGs that when replaced with a nonacidic residue reduces catalase activity to 5% of native levels. Replacing the nearby catalytic residue Arg108 causes a reduction in catalase activity to 35% of native levels, whereas a variant with both Asp141 and Arg108 replaced exhibits near normal catalase activity (82% of native), suggesting a synergism in the roles of the two residues in support of catalase activity in the enzyme. Among the Asp141 variants, D141E is unique in retaining normal catalase activity but with modified kinetics, suggesting more favorable compound I formation and less favorable compound I reduction. The crystal structure of the D141E variant has been determined at 1.8-A resolution, revealing that the carboxylate of Glu141 is moved only slightly compared with Asp141, but retains its hydrogen bond interaction with the main chain nitrogen of Ile237. In contrast, the low temperature ferric Electron Paramagnetic Resonance spectra of the D141A, R108A, and R108A/D141A variants are consistent with modifications of the water matrix and/or the relative positioning of the distal residue side chains. Such changes explain the reduction in catalase activity in all but the double variant R108A/D141A. Two pathways of hydrogen bonded solvent lead from the entrance channel into the heme active site, one running between Asp141 and Arg108 and the second between Asp141 and the main chain atoms of residues 237-239. It is proposed that binding of substrate H(2)O(2) to Asp141 and Arg108 controls H(2)O(2) access to the heme active site, thereby modulating the catalase reaction.     

Genetic engineering of glycinebetaine synthesis in tomato protects seeds, plants, and flowers from chilling damage

Tomato (Lycopersicon esculentum Mill.) plants, which normally do not accumulate glycinebetaine (GB), are susceptible to chilling stress. Exposure to temperatures below 10 degrees C causes various injuries and greatly decreases fruit set in most cultivars. We have transformed tomato (cv. Moneymaker) with a chloroplast-targeted codA gene of Arthrobacter globiformis, which encodes choline oxidase to catalyze the conversion of choline to GB. These transgenic plants express codA and synthesize choline oxidase, while accumulating GB in their leaves and reproductive organs up to 0.3 and 1.2 micromol g(-1) fresh weight (FW), respectively. Their chloroplasts contain up to 86% of total leaf GB. Over various developmental phases, from seed germination to fruit production, these GB-accumulating plants are more tolerant of chilling stress than their wild-type counterparts. During reproduction, they yield, on average, 10-30% more fruit following chilling stress. Endogenous GB contents as low as 0.1 micromol g(-1) FW are apparently sufficient to confer high levels of tolerance in tomato plants, as achieved via transformation with the codA gene. Exogenous application of either GB or H2O2 improves both chilling and oxidative tolerance concomitant with enhanced catalase activity. These moderately increased levels of H2O2 in codA transgenic plants, as a byproduct of choline oxidase-catalyzed GB synthesis, might activate the H2O2-inducible protective mechanism, resulting in improved chilling and oxidative tolerances in GB-accumulating codA transgenic plants. Thus, introducing the biosynthetic pathway of GB into tomato through metabolic engineering is an effective strategy for improving chilling tolerance.     

Catalase activity and hydrogen peroxide levels are inversely correlated in maize scutella during seed germination

Temporal patterns of hydrogen peroxide (H2O2) levels and total catalase activity are presented for post-imbibition scutella from six maize inbred lines expressing variable catalase activity. In all lines examined, H2O2 levels were highest during the initial days post-imbibition (1-2 dpi) and decreased thereafter, while total catalase activity was lowest during early dpi (1-2 dpi) and reached maximal activity at 4-6 dpi. In three of the six lines tested, a simple inverse correlation between catalase activity and H2O2 level was significant by Spearman's rank (P < 0.01). In addition to the general decline in H2O2 level throughout the dpi period, a reproducible increase in H2O2 level was observed at 4-5 dpi in five of six lines examined. Mutant lines lacking CAT-3 activity demonstrated a temporal shift in the occurrence of this increase. The role of total catalase (and individual isozymes) in controlling H2O2 levels during germination and the role of H2O2 as a potential regulator of catalase expression during germination are discussed.     

Catalase regulates cell growth in HL60 human promyelocytic cells: evidence for growth regulation by H(2)O(2)

Reactive oxygen species (ROS) including hydrogen peroxide (H(2)O(2)) are generated constitutively in mammalian cells. Because of its relatively long life and high permeability across membranes, H(2)O(2) is thought to be an important second messenger. Generation of H(2)O(2) is increased in response to external insults, including radiation. Catalase is located at the peroxisome and scavenges H(2)O(2). In this study, we investigated the role of catalase in cell growth using the H(2)O(2)-resistant variant HP100-1 of human promyelocytic HL60 cells. HP100-1 cells had an almost 10-fold higher activity of catalase than HL60 cells without differences in levels of glutathione peroxidase, manganese superoxide dismutase (MnSOD), and copper-zinc SOD (CuZnSOD). HP100-1 cells had higher proliferative activity than HL60 cells. Treatment with catalase or the introduction of catalase cDNA into HL60 cells stimulated cell growth. Exposure of HP100-1 cells to a catalase inhibitor resulted in suppression of cell growth with concomitant increased levels of intracellular H(2)O(2). Moreover, exogenously added H(2)O(2) or depletion of glutathione suppressed cell growth in HL60 cells. Extracellular signal regulated kinase 1/2 (ERK1/2) was constitutively phosphorylated in HP100-1 cells but not in HL60 cells. Inhibition of the ERK1/2 pathway suppressed the growth of HP100-1 cells, but inhibition of p38 mitogen-activated protein kinase (p38MAPK) did not affect growth. Moreover, inhibition of catalase blocked the phosphorylation of ERK1/2 but not of p38MAPK in HP100-1 cells. Thus our results suggest that catalase activates the growth of HL60 cells through dismutation of H(2)O(2), leading to activation of the ERK1/2 pathway; H(2)O(2) is an important regulator of growth in HL60 cells.     

Maintenance of higher H(2)O(2) levels, and its mechanism of action to induce growth in breast cancer cells: Important roles of bioactive catalase and PP2A

We assessed the catalase bioactivity and hydrogen peroxide (H(2)O(2)) production rate in human breast cancer (HBC) cell lines and compared these with normal human breast epithelial (HBE) cells. We observed that the bioactivity of catalase was decreased in HBC cells when compared with HBE cells. This was also accompanied by an increase in H(2)O(2) steady-state levels in HBC cells. Silencing the catalase gene led to a further increase in the steady-state level of H(2)O(2) which was also accompanied by an increase in growth rate of HBC cells. Catalase activity was up regulated on treatment with superoxide (O(2)(-)) scavengers such as pegylated SOD (PEG-SOD, indicating inhibition of catalase by the increased O(2)(-) produced by HBC cells. Transfection of either catalase or glutathione peroxidase to HBC cells decreased intracellular H(2)O(2) levels and led to apoptosis of these cells. The H(2)O(2) produced by HBC cells inhibited PP2A activity accompanied by increased phosphorylation of Akt and ERK1/2. The importance of catalase bioactivity in breast cancer was further confirmed as its bioactivity was also decreased in human breast cancer tissues when compared to normal breast tissues. We conclude that inhibition of catalase bioactivity by O(2)(-) leads to an increase in steady-state levels of H(2)O(2) in HBC cells, which in turn inhibits PP2A activity, leading to phosphorylation of ERK 1/2 and Akt and resulting in HBC cell proliferation.     

Resistance of Penicillium piceum F-648 to hydrogen peroxide under short term and prolonged oxidative stress

Resistance of Penicillium piceum F-648 to hydrogen peroxide under short-term and prolonged oxidative stress was studied. An increase in the activity of intracellular catalase in fungal cells after short-term exposure to hydrogen peroxide was shown. Activation of fungal cells induced by H2O2 depends on H2O2 concentration, time of exposure, and the growth phase of the fungus. Variants of P. piceum F-648 that produced two forms of extracellular catalase with different catalytic properties were obtained due to prolonged adaptation to H2O2. Catalase with low affinity for substrate was produced predominantly by the parent culture and variant 3; however, a high substrate affinity of catalase was observed in variant 5. Variant 5 of P. peniceum F-648 displayed a high catalytic activity and operational stability of catalase in the presence of phosphate ions and the concentration of substrate less than 30 mM at pH more than 7.     

UV-resistant Acinetobacter sp. isolates from Andean wetlands display high catalase activity

Andean wetlands are characterized by their extreme environmental conditions such as high UV radiation, elevated heavy metal content and salinity. We present here the first study on UV tolerance and antioxidant defense of four Acinetobacter strains: Ver3, Ver5 and Ver7, isolated from Lake Verde, and N40 from Lake Negra, both lakes located 4400 m above sea level. All four isolates displayed higher UV resistance compared with collection strains, with Ver3 and Ver7 being the most tolerant strains not only to UV radiation but also to hydrogen peroxide (H(2)O(2)) and methyl viologen (MV) challenges. A single superoxide dismutase band with similar activity was detected in all studied strains, whereas different electrophoretic pattern and activity levels were observed for catalase. Ver3 and Ver7 displayed 5-15 times higher catalase activity levels than the control strains. Analysis of the response of antioxidant enzymes to UV and oxidative challenges revealed a significant increase in Ver7 catalase activity after H(2)O(2) and MV exposure. Incubation of Ver7 cultures with a catalase inhibitor resulted in a significant decrease of tolerance against UV radiation. We conclude that the high catalase activity displayed by Ver7 isolate could play an important role in UV tolerance.     

Heat injury and repair in Campylobacter jejuni

A procedure for detecting and quantitating heat injury in Campylobacter jejuni was developed. Washed cells of C. jejuni A7455 were heated in potassium phosphate buffer (0.1 M, pH 7.3) at 46 degrees C. Samples were plated on brucella agar supplemented with Na2S2O3, FeSO4 X 7H2O, and sodium pyruvate and on a medium containing brilliant green, bile, Na2S2O3, FeSO4 X 7H2O, and sodium pyruvate. Colonies were counted after 5 days of incubation at 37 degrees C in an atmosphere containing 5% O2, 10% CO2, and 85% N2. After 45 min at 46 degrees C, there was virtually no killing and ca. two log cycles of injury. Cells grown at 42 degrees C were more susceptible to injury than cells grown at 37 degrees C. The addition to brucella agar supplemented with Na2S2O3, FeSO4 X 7H2O, and sodium pyruvate of three different antibiotic mixtures used in the isolation of C. jejuni from foods or clinical specimens did not prevent recovery of heat-injured C. jejuni. Cells lost 260 nm of absorbing materials during heat injury. The addition of 5% NaCl or 40% sucrose to the heating buffer prevented leakage but did not prevent injury. Of the additional salts, sugars, and amino acids tested for protection, only NH4Cl, KCl, and LiCl2 prevented injury. Heat-injured C. jejuni repaired (regained dye and bile tolerance) in brucella broth supplemented with Na2S2O3, FeSO4 X 7H2O, and sodium pyruvate within 4 h. Increasing the NaCl in this medium to 1.25% inhibited repair, and increasing it to 2% was lethal. Heat-injured C. jejuni will repair at 42 degrees C but not at 5 degrees C.     

Heat injury and repair in Campylobacter jejuni.

A procedure for detecting and quantitating heat injury in Campylobacter jejuni was developed. Washed cells of C. jejuni A7455 were heated in potassium phosphate buffer (0.1 M, pH 7.3) at 46 degrees C. Samples were plated on brucella agar supplemented with Na2S2O3, FeSO4 X 7H2O, and sodium pyruvate and on a medium containing brilliant green, bile, Na2S2O3, FeSO4 X 7H2O, and sodium pyruvate. Colonies were counted after 5 days of incubation at 37 degrees C in an atmosphere containing 5% O2, 10% CO2, and 85% N2. After 45 min at 46 degrees C, there was virtually no killing and ca. two log cycles of injury. Cells grown at 42 degrees C were more susceptible to injury than cells grown at 37 degrees C. The addition to brucella agar supplemented with Na2S2O3, FeSO4 X 7H2O, and sodium pyruvate of three different antibiotic mixtures used in the isolation of C. jejuni from foods or clinical specimens did not prevent recovery of heat-injured C. jejuni. Cells lost 260 nm of absorbing materials during heat injury. The addition of 5% NaCl or 40% sucrose to the heating buffer prevented leakage but did not prevent injury. Of the additional salts, sugars, and amino acids tested for protection, only NH4Cl, KCl, and LiCl2 prevented injury. Heat-injured C. jejuni repaired (regained dye and bile tolerance) in brucella broth supplemented with Na2S2O3, FeSO4 X 7H2O, and sodium pyruvate within 4 h. Increasing the NaCl in this medium to 1.25% inhibited repair, and increasing it to 2% was lethal. Heat-injured C. jejuni will repair at 42 degrees C but not at 5 degrees C.     

Oxidative stress response in eukaryotes: effect of glutathione, superoxide dismutase and catalase on adaptation to peroxide and menadione stresses in Saccharomyces cerevisiae

Aiming to clarify the mechanisms by which eukaryotes acquire tolerance to oxidative stress, adaptive and cross-protection responses to oxidants were investigated in Saccharomyces cerevisiae. Cells treated with sub-lethal concentrations of menadione (a source of superoxide anions) exhibited cross-protection against lethal doses of peroxide; however, cells treated with H2O2 did not acquire tolerance to a menadione stress, indicating that menadione response encompasses H2O2 adaptation. Although, deficiency in cytoplasmic superoxide dismutase (Sod1) had not interfered with response to superoxide, cells deficient in glutathione (GSH) synthesis were not able to acquire tolerance to H2O2 when pretreated with menadione. These results suggest that GSH is an inducible part of the superoxide adaptive stress response, which correlates with a decrease in the levels of intracellular oxidation. On the other hand, neither the deficiency of Sod1 nor in GSH impaired the process of acquisition of tolerance to H2O2 achieved by a mild pretreatment with peroxide. Using a strain deficient in the cytosolic catalase, we were able to conclude that the reduction in lipid peroxidation levels produced by the adaptive treatment with H2O2 was dependent on this enzyme. Corroborating these results, the pretreatment with low concentrations of H2O2 promoted an increase in catalase activity.     

Analysis of growth phase regulated KatA and CatE and their physiological roles in determining hydrogen peroxide resistance in Agrobacterium tumefaciens

Agrobacterium tumefaciens possesses two catalases, a bifunctional catalase-peroxidase, KatA and a homologue of a growth phase regulated monofunctional catalase, CatE. In stationary phase cultures and in cultures entering stationary phase, total catalase activity increased 2-fold while peroxidase activity declined. katA and catE were found to be independently regulated in a growth phase dependent manner. KatA levels were highest during exponential phase and declined as cells entered stationary phase, while CatE was detectable at early exponential phase and increased during stationary phase. Only small increases in H2O2 resistance levels were detected as cells entering stationary phase. The katA mutant was more sensitive to H2O2 than the parental strain during both exponential and stationary phase. Inactivation of catE alone did not significantly change the level of H2O2 resistance. However, the katA catE double mutant was more sensitive to H2O2 during both exponential and stationary phase than either of the single catalase mutants. The data indicated that KatA plays the primary role and CatE acts synergistically in protecting A. tumefaciens from H2O2 toxicity during all phases of growth. Catalase-peroxidase activity (KatA) was required for full H2O2 resistance. The expression patterns of the two catalases in A. tumefaciens reflect their physiological roles in the protection against H2O2 toxicity, which are different from other bacteria.     

Survival and antioxidant defence of the yeast Saccharomyces cerevisiae during starvation and oxidative stress

The role of catalase in response of the yeast Saccharomyces cerevisiae to oxidative stress induced by hydrogen peroxide under starvation was investigated. It was shown that under conditions used in this study 0.5 mM H2O2 did not change the number of viable cells in the wild strain YPH250, but this parameter was decreased by 15% in the acatalsaemic strain YWT1. Cells treatment with 0.5 mM H2O2 for 30 min did not modify the levels of carbonyl proteins in the parental strain, but caused its 1.4-fold increase in the defective strain. The observed 1.5-fold activation of catalase in the wild strain cells in response to H2O2-stress suggests that under starvation conditions catalase can be involved in the yeast cell protection, particularly they can prevent oxidative modification of some antioxidant and associated enzymes.     

Prevention of H2O2 generation by monoamine oxidase protects against CNS O2 toxicity.

Toxicity to the central nervous system (CNS) by hyperbaric oxygen (HBO) presumably relates to increased production of reactive oxygen species. The sites of generation of reactive oxygen species during HBO, however, have not been fully characterized in the brain. We investigated the relationship between regional generation of hydrogen peroxide (H2O2) in the brain in the presence of an irreversible inhibitor of catalase, aminotriazole (ATZ), and protection from CNS O2 toxicity by a monoamine oxidase (MAO) inhibitor, pargyline. At 6 ATA of oxygen, pargyline significantly protected rats from CNS O2 toxicity whereas ATZ enhanced O2 toxicity. In animals pretreated with ATZ, HBO inactivated 21-40% more catalase than air exposure in the six brain regions studied. Because ATZ-mediated inactivation of catalase was H2O2 dependent, the decrease in catalase activity during hyperoxia was proportional to the intracellular production of H2O2. Pargyline, administered 30 min before HBO, inhibited MAO by greater than 90%, prevented ATZ inhibition of catalase activity during HBO, and reversed the augmentation of CNS O2 toxicity by ATZ. These findings indicate that H2O2 generated by MAO during hyperoxia is important to the pathogenesis of CNS O2 toxicity in rats.     

Mechanisms of cellular resistance to hydrogen peroxide, hyperoxia, and 4-hydroxy-2-nonenal toxicity: the significance of increased catalase activity in H2O2-resistant fibroblasts.

An H2O2-resistant variant (OC14) of the HA1 Chinese hamster fibroblast cell line which demonstrates a 20-fold increase in catalase activity was utilized in the study of mechanisms responsible for cellular resistance to hydrogen peroxide, oxygen, and 4-hydroxy-2-nonenal toxicity. HA1 and OC14 cells were treated with 9 mM aminotriazole which resulted in a 60 to 80% reduction in catalase activity. Pretreatment with aminotriazole resulted in significant sensitization to the toxicity of 1-h exposures to exogenously applied H2O2, which was proportional to the reduction in catalase activity. Treatment with aminotriazole produced significant sensitization to the toxicity of 95% O2 after 45 h of O2 exposure but no sensitization to the toxicity of a 1-h exposure to 50 microM 4-hydroxy-2-nonenal. Inhibition of catalase activity by aminotriazole had no effect on the metabolism of 4-hydroxy-2-nonenal by either cell line tested. These results support the conclusion that in H2O2-resistant cells, catalase activity is a major determinant of cellular resistance to H2O2 toxicity, whereas catalase activity has a limited role in cellular resistance to an acute exposure to 95% O2 and is unrelated to cellular resistance to 4-hydroxy-2-nonenal.     

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.