Hymenolepis diminuta: Activity of anti-oxidant enzymes in different parts of rat gastrointestinal tract

The aim of this study was to assess the intensity of oxidative stress by measuring levels of lipid peroxidation products in the duodenum, jejunum and colon of rats infected with Hymenolepis diminuta and evaluate the effectiveness of protection against oxidative stress by measuring the glutathione levels and activity of anti-oxidant enzymes: superoxide dismutase, catalase, glutathione reductase and glutathione peroxidase.In exposed rats we observed a significant increase of lipid peroxidation products in the duodenum and jejunum. A significant decrease in superoxide dismutase activity in all the examined parts of the digestive tract was observed. Additionally, rats from 16 to 40 days post H. diminuta infection (dpi) had a decreased catalase activity in the colon, while at 60 dpi it increased. The glutathione peroxidase activity increased significantly in the colon at 60 dpi. The increase in glutathione reductase activity was observed in the colon in rats 60 dpi. There was a lack of changes in the levels of glutathione in the duodenum and a significant increase in its concentration in the jejunum and colon from 40 to 60 dpi and from 16 to 40 dpi, respectively. In this study we observed altered activity of anti-oxidant enzymes and glutathione level in experimental hymenolepidosis, as a consequence of oxidative stress. It may indicate a decrease in the efficiency of intestinal protection against oxidative stress induced by the presence of the parasite. The imbalance between oxidant and anti-oxidant processes may play a major role in pathology associated with hymenolepidosis.     

Cr(VI) Induces Lipid Peroxidation, Protein Oxidation and Alters the Activities of Antioxidant Enzymes in Human Erythrocytes

The effect of potassium dichromate (K(2)Cr(2)O(7)), a hexavalent chromium compound, on human erythrocytes was studied under in vitro conditions. Incubation of erythrocytes with different concentrations of K(2)Cr(2)O(7) resulted in marked hemolysis in a concentration-dependent manner. K(2)Cr(2)O(7) treatment also caused significant increase in protein oxidation, lipid peroxidation and decrease in total sulfhydryl content, indicating that it causes oxidative stress in human erythrocytes. However, there was no concomitant nitrosative stress as the nitric oxide levels in hemolysates from K(2)Cr(2)O(7)-treated erythrocytes were lower than in control. Exposure of erythrocytes to K(2)Cr(2)O(7) decreased the activities of catalase, glutathione peroxidase, thioredoxin reductase, glucose-6-phosphate dehydrogenase, and glutathione reductase, whereas the activities of Cu-Zn superoxide dismutase and glutathione S-transferase were increased. These results show that K(2)Cr(2)O(7) induces oxidative stress and alters the antioxidant defense mechanism of human erythrocytes.     

Mechanical ventilation promotes redox status alterations in the diaphragm.

Oxidative stress is an important mediator of diaphragm muscle atrophy and contractile dysfunction during prolonged periods of controlled mechanical ventilation (MV). To date, specific details related to the impact of MV on diaphragmatic redox status remain unknown. To fill this void, we tested the hypothesis that MV-induced diaphragmatic oxidative stress is the consequence of both an elevation in intracellular oxidant production in conjunction with a decrease in the antioxidant buffering capacity. Adult rats were assigned to one of two experimental groups: 1) control or 2) 12 h of MV. Compared with controls, diaphragms from MV animals demonstrated increased oxidant production, diminished total antioxidant capacity, and decreased glutathione levels. Heme oxygenase-1 (HO-1) mRNA and protein levels increased (23.0- and 5.1-fold, respectively) following MV. Thioredoxin reductase-1 and manganese superoxide dismutase mRNA levels were also increased in the diaphragm following MV (2.4- and 1.6-fold, respectively), although no change was detected in the levels of either protein. Furthermore, copper-zinc superoxide dismutase and glutathione peroxidase mRNA were not altered following MV, although protein content decreased -1.3- and -1.7-fold, respectively. We conclude that MV promotes increased oxidant production and impairment of key antioxidant defenses in the diaphragm; collectively, these changes contribute to the MV-induced oxidative stress in this key inspiratory muscle.     

Lipoamide protects retinal pigment epithelial cells from oxidative stress and mitochondrial dysfunction

alpha-Lipoic acid (LA) has been widely studied as an agent for preventing and treating various diseases associated with oxidative disruption of mitochondrial functions. To investigate a related mitochondrial antioxidant, we compared the effects of lipoamide (LM), the neutral amide of LA, with LA for measures of oxidative damage and mitochondrial dysfunction in a human retinal pigment epithelial (RPE) cell line. Acrolein, a major component of cigarette smoke and a product of lipid peroxidation, was used to induce oxidative mitochondrial damage in RPE cells. Overall, using comparable concentrations, LM was more effective than LA at preventing acrolein-induced mitochondrial dysfunction and oxidative stress. Relative to LA, LM improved ATP levels, membrane potentials, and activities of mitochondrial complexes I, II, and V and dehydrogenases that had been decreased by acrolein exposure. LM reduced acrolein-induced oxidant generation, calcium levels, protein oxidation, and DNA damage to a greater degree than LA. And, total antioxidant capacity, glutathione content, glutathione S-transferase, and superoxide dismutase activities and expression of nuclear factor-E2-related factor 2 were increased by LM relative to LA. These results suggest that LM is a more potent mitochondrial-protective agent and antioxidant than LA in protecting RPE from oxidative damage.     

Oxidative stress and antioxidant deficiencies in asthma: potential modification by diet

The lungs of asthmatic patients are exposed to oxidative stress due to the generation of reactive oxygen and nitrogen species as a consequence of chronic airway inflammation. Increased concentrations of NO*, H2O2 and 8-isoprostane have been measured in exhaled breath and induced sputum of asthmatic patients. O2*-, NO*, and halides interact to form highly reactive species such as peroxynitrite and HOBr, which in turn cause nitration and bromination of protein tyrosine residues. Oxidative stress may also reduce glutathione levels and cause inactivation of antioxidant enzymes such as superoxide dismutase, with a consequent increase in apoptosis, shedding of airway epithelial cells and airway remodelling. The oxidant/antioxidant equilibrium in asthmatic patients may be further perturbed by low dietary intakes of the antioxidant vitamins C and E, selenium and flavonoids, with a consequent lowering of the concentrations of these and other non-dietary antioxidants such as bilirubin and albumin in plasma and airway epithelial lining fluid. Although supplementation with vitamins C and E appears to offer protection against the adverse effects of ozone, recent randomised, placebo-controlled trials of vitamin C or E supplements for patients with mild asthma have not shown significant benefits over standard therapy. However, genetic variation in glutathione S-transferase may influence the susceptibility of asthmatic individuals to oxidative stress and the extent to which they are likely to benefit from antioxidant supplementation. Long-term prospective trials are required to determine whether modification of dietary intake will benefit asthma patients and reduce the socio-economic burden of asthma in the community.     

Tamarix gallica ameliorates thioacetamide-induced hepatic oxidative stress and hyperproliferative response in Wistar rats

Tamarix gallica, a hepatic stimulant and tonic, was examined for its ability to inhibit thioacetamide (TAA)-induced hepatic oxidative stress, toxicity and early tumor promotion response in male Wistar rats. TAA (6.6 mmol/kg body wt. i.p) enhanced lipid peroxidation, hydrogen peroxide content, glutathione S-transferase and xanthine oxidase with reduction in the activities of hepatic antioxidant enzymes viz., glutathione peroxidase, superoxide dismutase and caused depletion in the level of hepatic glutathione content. A marked increase in liver damage markers was also observed. TAA treatment also enhanced tumor promotion markers, ornithine decarboxylase (ODC) activity and [3H] thymidine incorporation into hepatic DNA. Pretreatment of rats orally with Tamarix gallica extract (25 and 50 mg/kg body weight) prevented TAA-promoted oxidative stress and toxicity. Prophylaxis with Tamarix gallica significantly reduced the susceptibility of the hepatic microsomal membrane for iron-ascorbate induced lipid peroxidation, H2O2 content, glutathione S-transferase and xanthine oxidase activities. There was also reversal of the elevated levels of liver marker parameters and tumor promotion markers. Our data suggests that Tamarix gallica is a potent chemopreventive agent and may suppress TAA-mediated hepatic oxidative stress, toxicity, and tumor promotion response in rats.     

Antioxidant defense and apoptotic effectors in ascorbic acid and β-glycerophosphate-induced osteoblastic differentiation

MC3T3-E1 cells grown in the presence of ascorbic acid and β-glycerophosphate (AA/β-GP) express alkaline phosphatase and produce an extensive collagenous extracellular matrix. Differentiated MC3T3-E1 cells are more sensitive to hydrogen peroxide-induced oxidative stress than undifferentiated cells. In this study, we compared the profile of antioxidant enzymes and molecular markers of apoptosis in undifferentiated and differentiated MC3T3-E1 cells (cell differentiation was induced by treatment with AA/β-GP). Differentiated osteoblasts showed lower expression and activity of catalase, glutathione S-transferase and glutathione peroxidase. The total superoxide dismutase activity and the expression of Cu/Zn superoxide dismutase were also lower, while the expression of Mn superoxide dismutase was higher in differentiated osteoblasts. The level of malondialdehyde, a widely used marker for oxidative stress, was lower in the AA/β-GP group compared with control cells, but this difference was not significant. Western blotting showed that treatment with AA/β-GP increased the Bax/Bcl-2 ratio used as an index of cellular vulnerability to apoptosis. In addition, the activities of caspases 3, 8 and 9 and cleaved poly (ADP) ribose polymerase were significantly higher in differentiated cells. These findings provide new insights into how changes in the activities of major antioxidant enzymes and in the signaling pathways associated with apoptosis may influence the susceptibility of bone cells to oxidative stress.     

Erythrocyte antioxidants in aging and dementia

Age of patients and oxidative stress in brain cells may contribute to pathogenesis of Alzheimer’s disease (AD). Erythrocytes (red blood cells, RBC) are considered as passive “reporter cells” for the oxidative status of the whole body and remain poorly investigated in AD. The aim of this study was to assess whether the antioxidant status of RBC changes in aging and AD. Blood was taken from AD and non-Alzheimer’s dementia patients, aged-matched and younger controls. The antioxidant status of RBC was evaluated in each person participated in the study by measuring levels of H₂O₂, organic hydroperoxides, glutathione (GSH) and glutathione disulfide (GSSG), activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glutathione S-transferase, and glucose-6-phosphate dehydrogenase. In both aging and dementia, oxidative stress in RBC was shown to increase as evidenced by elevated concentrations of H₂O₂, organic hydroperoxides, decreased GSH/GSSG ratio, and decreased glutathione S-transferase activity. Decreased glutathione peroxidase activity in RBC may be considered as a new peripheral marker for Alzheimer’s disease while changes of other parameters of oxidative stress reflect age-related events.     

Induction of Heat-Shock Protein 70 Expression by Geranylgeranylacetone Shows Cytoprotective Effects in Cardiomyocytes of Mice under Humid Heat Stress

Background

Increasing evidence has revealed that humid heat stress (HHS) causes considerable damage to human health. The cardiovascular system has been suggested to be the primary target of heat stress, which results in serious cardiovascular diseases. However, there is still a lack of effective approaches for the prevention and treatment of cardiovascular diseases induced by HHS.

Objective

Heat-shock proteins (Hsps), especially Hsp70, are reported to provide effective cytoprotection under various stress stimuli. In the present study, we evaluated the cytoprotective effect of geranylgeranylacetone (GGA), which was previously been reported to induce Hsp70 expression in cardiomyocytes under HHS.

Methods and Principal Findings

Using a mouse model of HHS, we showed that the pretreatment of GGA enhanced Hsp70 expression under HHS, as examined by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot. We then examined the effect of GGA pretreatment on the cardiomyocyte apoptosis induced by HHS using terminal-deoxynucleoitidyl transferase mediated nick end labeling (TUNEL) staining, and found that GGA pretreatment inhibited mitochondria-mediated apoptosis. GGA pretreatment could reverse the effect of HHS on cell apoptosis by increasing expression of Bcl-2, decreasing cytochrome c in cytosol, and increasing cytochrome c in mitochondria. However, GGA pretreatment had no effect on the oxidative stress induced by HHS as determined by levels of superoxide dismutase (SOD), malondialdehyde (MDA), and glutathione (GSH).

Conclusion

We have demonstrated that GGA pretreatment suppressed HHS-induced apoptosis of cardiomyocytes through the induction of Hsp70 overexpression.     

Differential accumulation of antioxidant mRNAs in Arabidopsis thaliana exposed to ozone.

Antioxidant isoenzymes function to eliminate free radicals and are localized to several different subcellular compartments within the plant cell. In Arabidopsis thaliana exposed to ozone (O3), we have monitored the accumulation of mRNAs encoding both cytosolic and chloroplastic antioxidant isoenzymes. Two different O3 exposure protocols yielded similar results. Upon O3 exposure, the steady-state levels of three mRNAs encoding cytosolic antioxidant isoenzymes (ascorbate peroxidase, copper/zinc superoxide dismutase, and glutathione S-transferase) increase. The glutathione S-transferase mRNA responds very quickly to the oxidative stress (2-fold increase in 30 min) and is elevated to very high levels, especially in plants grown with a 16-h photoperiod. In contrast, O3 exposure causes a decline in the levels of two chloroplastic antioxidant mRNAs (iron superoxide dismutase and glutathione reductase) and two photosynthetic protein mRNAs (chlorophyll a/b-binding protein and ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit). We show that this decline does not include all mRNAs encoding chloroplast-targeted proteins, since O3 causes an elevation of mRNA encoding the chloroplast-localized tryptophan biosynthetic enzyme phosphoribosylanthranilate transferase. Two alternative hypotheses that could explain this differential mRNA accumulation in response to O3 are discussed.     

Wood smoke extract induces oxidative stress-mediated caspase-independent apoptosis in human lung endothelial cells: role of AIF and EndoG

Although a link between toxic smoke and oxidant lung vascular injury has been indicated, the cellular mechanisms of smoke-induced injury to lung endothelial cells are unknown. We investigated oxidative stress and apoptosis induced by wood smoke extract (SE) in human pulmonary artery endothelial cells (HPAECs) and delineated their relationship. We found that SE increased intracellular reactive oxygen species (ROS), depleted intracellular glutathione, and upregulated Cu/Zn superoxide dismutase and heme oxygenase-1 (2 antioxidant enzymes), but it failed to alter the expression of catalase and glutathione peroxidase. In addition, SE promoted apoptosis as indicated by the external exposure of membrane phosphatidylserine, the loss of mitochondrial membrane potential, an increase in the level of Bax (a proapoptotic protein), and enhanced DNA fragmentation. This apoptosis was associated with mitochondrial-to-nuclear translocation of apoptosis-inducing factor (AIF) and endonuclease G (EndoG) (2 apoptogenic proteins) but was independent of caspase cascade activation. Whereas N-acetylcysteine (an antioxidant) effectively reversed the SE-induced increase in ROS and depletion of glutathione, it also suppressed SE-induced nuclear translocation of either AIF or EndoG and prevented the enhanced DNA fragmentation that would have resulted from this. We conclude that 1) although SE upregulates Cu/Zn superoxide dismutase and heme oxygenase-1, it nevertheless increases intracellular oxidative stress in HPAECs, and 2) SE promotes oxidative stress-mediated caspase-independent HPAEC apoptosis that involves mitochondrial-to-nuclear translocation of AIF and EndoG. Thus modulations of the expression of antioxidant enzymes and the caspase-independent apoptotic pathway are possible target choices for potential therapeutic regimes to treat smoke-induced lung injury.     

Heme oxygenase induction by menadione bisulfite adduct-generated oxidative stress in rat liver

The in vivo effect of menadione bisulfite adduct on both hepatic oxidative stress and heme oxygenase induction was studied. A marked increase in lipid peroxidation was observed 1 h after menadione bisulfite adduct administration. To evaluate liver antioxidant enzymatic defenses, superoxide dismutase, catalase and glutathione peroxidase activities were determined. Antioxidant enzymes significantly decreased 3 h after menadione bisulfite adduct injection. Heme oxygenase activity appeared 6 h after treatment, peaking 9 h after menadione bisulfite adduct administration. Such induction was preceded by a decrease in the intrahepatic GSH pool and an increase in hydrogen peroxide steady-state concentration, both effects taking place some hours before induction of heme oxygenase. Iron ferritin levels and ferritin content began to increase 6 h after heme oxygenase induction, and these increases were significantly higher 15 h after treatment and remained high for at least 24 h after menadione bisulfite adduct injection. Administration of bilirubin entirely prevented heme oxygenase induction as well as the decrease in hepatic GSH and the increase in lipid peroxidation when administered 2 h before menadione bisulfite adduct treatment. These results indicate that the induction of heme oxygenase by menadione bisulfite adduct may be a general response to oxidant stress, by increasing bilirubin and ferritin levels and could therefore provide a major cellular defense mechanism against oxidative damage.     

Induction of hepatic antioxidants in freshwater catfish (Channa punctatus Bloch) is a biomarker of paper mill effluent exposure

Enzymatic and non-enzymatic antioxidants serve as an important biological defense against environmental oxidative stress. Information on antioxidant defense in fish is meager despite that fish are constantly exposed to a myriad of environmental stress including the oxidants. This study, therefore, assesses the activities of antioxidant enzymes viz., glutathione peroxidase, catalase and glutathione S-transferase and the non-enzymatic antioxidants viz., glutathione and metallothionein in various tissues of freshwater fish Channa punctatus (Bloch), in response to short-term and long-term exposures to paper mill effluent. The fish were exposed to the effluent at a concentration of 1.0% (v/v) for 15, 30, 60 and 90 days. The exposure caused a time-dependent increase in glutathione level (P < 0.001), activities of glutathione peroxidase (P < 0.05 to P < 0.001), glutathione S-transferase (P < 0.001) and a marginal initial decrease in catalase activity in the liver (P < 0.01 to P < 0.001). Metallothionein was induced in liver after 60 days of exposure. Two isoforms of metallothionein were detected. Catalase activity also increased 60 days afterwards. Antioxidant pattern was different in gill and kidney showing that liver was more resistant to oxidative damage as compared to gills and kidney. Our results demonstrate a pollutant-induced adaptive response in fish. In addition, levels of enzymatic and non-enzymatic tissue antioxidants may serve as surrogate markers of exposure to oxidant pollutants in fish.     

Evaluation of oxidative stress biomarkers in patients with chronic renal failure: a case control study

Background

Oxidative stress is related to several diseases, including chronic renal insufficiency. The disequilibrium in the oxidant-antioxidant balance is the result of several metabolic changes. The majority of studies to-date have evaluated the grade of oxidative stress with a single biomarker, or a very limited number of them.

Findings

The present study used several important biomarkers to establish a score relating to oxidative stress status (glutathione S-transferase, superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, reduced and oxidized glutathione, thiobarbituric acid reactive substances and hemolysis test). The score of oxidative stress (SOS) was then applied to a group of patients with renal insufficiency not on hemodialysis, and compared to healthy control individuals.The score for patients with chronic renal insufficiency was significantly different from that of the healthy control group (0.62 ± 1.41 vs. -0.05 ± 0.94; p < 0.001). The comparison between patients with chronic renal insufficiency and control individuals showed significant differences with respect to changes in the enzymatic antioxidant systems (glutathione S-transferase, glutathione reductase), non-enzymatic antioxidant system (oxidized glutathione) and oxidizability (hemolysis test) indicating significant oxidative stress associated with chronic renal insufficiency.

Conclusions

Patients with chronic renal insufficiency not on hemodialysis are susceptible to oxidative stress. The mechanisms that underlie this status are the consequence of changes in glutathione and related enzymes. The SOS scoring system is a useful biochemical parameter to evaluate the influence of oxidative stress on the clinical status of these patients.

     

Total antioxidant capacity and nuclear DNA damage in keratinocytes after exposure to H2O2

Studies of oxidative stress have classically been performed by analyzing specific, single antioxidants. In this study, susceptibility to oxidative stress in the human keratinocyte cell line NCTC2544 exposed to hydrogen peroxide (H2O2) was measured by the TOSC (total oxyradical scavenging capacity) assay, which discriminates between the antioxidant capacity toward peroxyl radicals and hydroxyl radical. The generation of H2O2-induced DNA damage, total antioxidant capacity and levels of antioxidant enzymes (catalase, superoxide dismutase, glutathione reductase, glutathione S-transferase, glutathione peroxidase) were studied. Exposure to H2O2-induced DNA damage that was gradually restored while a significant reduction in cellular TOSC values was obtained independently of stressor concentrations and the degree of DNA repair. Whereas TOSC values and cell resistance to H2O2 showed a good relationship, the extent of DNA damage is independent from cellular total antioxidant capacity. Indeed, maximum DNA damage and cell mortality were observed in the first 4 h, whereas TOSC remained persistently low until 48 h. Catalase levels were significantly lower in exposed cells after 24 and 48 h. Keratinocytes exposed after 48 h to a second H2O2 treatment exhibited massive cell death. A possible linkage was observed between TOSC values and NCTC2544 resistance to H2O2 challenge. The TOSC assay appears to be a useful tool for evaluating cellular resistance to oxidative stress.     

Oxidative stress and antioxidant deficiencies in asthma: potential modification by diet

Abstract

The lungs of asthmatic patients are exposed to oxidative stress due to the generation of reactive oxygen and nitrogen species as a consequence of chronic airway inflammation. Increased concentrations of NO^?, H₂O₂ and 8-isoprostane have been measured in exhaled breath and induced sputum of asthmatic patients. O₂^??, NO^?, and halides interact to form highly reactive species such as peroxynitrite and HOBr, which in turn cause nitration and bromination of protein tyrosine residues. Oxidative stress may also reduce glutathione levels and cause inactivation of antioxidant enzymes such as superoxide dismutase, with a consequent increase in apoptosis, shedding of airway epithelial cells and airway remodelling. The oxidant/antioxidant equilibrium in asthmatic patients may be further perturbed by low dietary intakes of the antioxidant vitamins C and E, selenium and flavonoids, with a consequent lowering of the concentrations of these and other non-dietary antioxidants such as bilirubin and albumin in plasma and airway epithelial lining fluid. Although supplementation with vitamins C and E appears to offer protection against the adverse effects of ozone, recent randomised, placebo-controlled trials of vitamin C or E supplements for patients with mild asthma have not shown significant benefits over standard therapy. However, genetic variation in glutathione S-transferase may influence the susceptibility of asthmatic individuals to oxidative stress and the extent to which they are likely to benefit from antioxidant supplementation. Long-term prospective trials are required to determine whether modification of dietary intake will benefit asthma patients and reduce the socio-economic burden of asthma in the community.     

Hindlimb unloading increases oxidative stress and disrupts antioxidant capacity in skeletal muscle

Skeletal muscle disuse with space-flight and ground-based models (e.g., hindlimb unloading) results in dramatic skeletal muscle atrophy and weakness. Pathological conditions that cause muscle wasting (i.e., heart failure, muscular dystrophy, sepsis, COPD, cancer) are characterized by elevated "oxidative stress," where antioxidant defenses are overwhelmed by oxidant production. However, the existence, cellular mechanisms, and ramifications of oxidative stress in skeletal muscle subjected to hindlimb unloading are poorly understood. Thus we examined the effects of hindlimb unloading on hindlimb muscle antioxidant enzymes (e.g., superoxide dismutase, catalase, glutathione peroxidase), nonenzymatic antioxidant scavenging capacity (ASC), total hydroperoxides, and dichlorohydrofluorescein diacetate (DCFH-DA) oxidation, a direct indicator of oxidative stress. Twelve 6 month old Sprague Dawley rats were divided into two groups: 28 d of hindlimb unloading (n = 6) and controls (n = 6). Hindlimb unloading resulted in a small decrease in Mn-superoxide dismutase activity (10.1%) in the soleus muscle, while Cu,Zn-superoxide dismutase increased 71.2%. In contrast, catalase and glutathione peroxidase, antioxidant enzymes that remove hydroperoxides, were significantly reduced in the soleus with hindlimb unloading by 54.5 and 16.1%, respectively. Hindlimb unloading also significantly reduced ASC. Hindlimb unloading increased soleus lipid hydroperoxide levels by 21.6% and hindlimb muscle DCFH-DA oxidation by 162.1%. These results indicate that hindlimb unloading results in a disruption of antioxidant status, elevation of hydroperoxides, and an increase in oxidative stress.     

Enhancement of cytotoxicity of hydrogen peroxide by hyperthermia in chinese hamster ovary cells: role of antioxidant defenses

Regional hyperthermia has potential for human cancer treatment, particularly in combination with systemic chemotherapy or radiotherapy. The mechanisms involved in heat-induced cell killing are currently unknown. Hyperthermia may increase oxidative stress in cells, and thus, oxidative stress could have a role in the mechanism of cell death. We use hydrogen peroxide as a model oxidant to improve understanding of interactions between heat and oxidative stress. Heat increased cytotoxicity of hydrogen peroxide in Chinese hamster ovary cells. Altered levels of cellular antioxidants should create an imbalance between prooxidant and antioxidant systems, thus modifying cytotoxic responses to heat and to oxidants. We determine the involvement of the two cellular antioxidant defenses against peroxides, catalase and the glutathione redox cycle, in cellular sensitivity to heat, to hydrogen peroxide, and to heat combined with the oxidant. Defense systems were either inhibited or increased. For inhibition studies, intracellular glutathione was diminished to less than 15% of its initial level by treatment with L-buthionine sulfoximine (1 mM, 24 h). Inhibition of catalase was achieved with 3-amino-1,2,4-triazole (20 mM, 2 h), which caused a 80% decrease in endogenous enzyme activity. To increase antioxidants, cells were pretreated with the thiol-containing reducing agents, N-acetyl-L-cysteine, 2-oxo-4-thiazolidine carboxylate, and 2-mercaptoethane sulfonate. These compounds increased intracellular glutathione levels by 30%. Catalase activity was increased by addition of exogenous enzyme to cells. We show that levels of glutathione and catalase affect cellular cytotoxic responses to heat and hydrogen peroxide, either used separately or in combination. These findings are relevant to mechanisms of cell killing at elevated temperatures and suggest the involvement of oxidative stress.