Rate Of Hydrogen Peroxide Generation Research Articles

Two-Dimensional Covalent Organic Frameworks with Carbazole-Embedded Frameworks Facilitate Photocatalytic and Electrocatalytic Processes.

Catalytic technologies are pivotal in enhancing energy efficiency, promoting clean energy production, and reducing energy consumption in the chemical industry. The pursuit of novel catalysts for renewable energy is a long-term goal for researchers. In this work, we synthesized three two-dimensional covalent organic frameworks (COFs) featuring electron-rich carbazole-based architectures and evaluated their catalytic performance in photocatalytic organic reactions and electrocatalytic oxygen reduction reactions (ORRs). Pyrene-functionalized COF, termed as FCTD-TAPy, demonstrated excellent photocatalytic performance for amino oxidation coupling and showed a remarkable preference for substrates with electron-withdrawing groups (up to >99% Conv. and >99% Sel). Furthermore, FCTD-TAPy favored a four-electron transfer pathway during the ORR and exhibited favorable reaction kinetics (51.07 mV/dec) and a high turnover frequency (0.011 s-1). In contrast, the ORR of benzothiadiazole-based FCTD-TABT favored a two-electron transfer pathway, which exhibited a maximum double-layer capacitance of 14.26 mF cm-2, a Tafel slope of 53.01 mV/dec, and a hydrogen peroxide generation rate of 70.3 mmol g-1 h-1. This work underscores the potential of carbazole-based COFs as advanced catalytic materials and offers new insights into the design of metal-free COFs for enhanced catalytic performance.

Characterization and H2O2 production mechanisms study on self-oxidized graphite during the two-electron water oxidation electrochemical process

The 2e− water oxidation process is an eco-friendly way to produce H2O2 using water as the raw material. It avoids the low solubility of oxygen in water, unlike traditional oxygen reduction methods. However, electrocatalysts always suffer from self-oxidation during the oxidation reaction, leading to decreased activity. We solved this by using non-metal graphite electrocatalysts that undergo an evolution process to oxidized carboxylated graphite, which is even more active. A defect forms on the graphite surface that facilitates HCO3− adsorption. The –COOH group easily forms a –COOOH intermediate, which is advantageous for hydrogen peroxide generation. The hydrogen peroxide generation rate is 4.55 times higher than that of initial graphite. Graphite is an environmentally friendly catalyst that avoids the release of metal ions, making it more suitable for large-scale applications.

Influence of Magnetic Fields with Induction of 7 T on Physical and Chemical Properties of Aqueous NaCl Solutions

The physicochemical properties of NaCl aqueous solutions in a wide range of concentrations were studied. We determined that constant magnetic fields with an induction of up to 7 T had a significant effect on the physicochemical properties of these solutions. First, we detected a decrease in pH that was dependent on the magnetic field strength both in water and in NaCl solutions. This effect was not associated with the presence of sodium cations or chlorine anions in water. Secondly, with an increase in magnetic field induction the redox potential of aqueous solutions also increased. Magnetic fields did not cause any changes in the concentration of dissolved molecular oxygen in deionized water. In this case, in aqueous solutions of NaCl under the action of a magnetic field, a concentration-dependent tendency to a decrease in the concentration of dissolved molecular oxygen is observed. Third, it was shown that under the action of a magnetic field on a NaCl solution, the rate of hydrogen peroxide generation increased with increasing NaCl concentration. Fourth, the essential role of the primary state of aqueous solutions in relation to the gas composition and gas equilibrium under magnetic influence was established. The work also evaluated the contribution of flow-mixing during sample preparation on the physicochemical properties of the solutions.

Influence of Mechanical Effects on the Hydrogen Peroxide Concentration in Aqueous Solutions

An experiment has been performed, where water enriched in hydrogen peroxide was subjected to multiply dilution under mechanical action. It is established that, when the number of dilutions reaches a certain level, the correlation between the hydrogen peroxide concentration and the number of dilutions is lost; i.e., the concentration ceases to depend on the number of dilutions. Moreover, it is even somewhat increases because of the mechanical action accompanying the dilution. The hydrogen peroxide generation rate amounts to 10−9 (mol l−1)min−1 for impact times of few minutes.

Mitochondrial free radical overproduction due to respiratory chain impairment in the brain of a mouse model of Rett syndrome: protective effect of CNF1

Rett syndrome (RTT) is a pervasive neurodevelopmental disorder mainly caused by mutations in the X-linked MECP2 gene associated with severe intellectual disability, movement disorders, and autistic-like behaviors. Its pathogenesis remains mostly not understood and no effective therapy is available. High circulating levels of oxidative stress markers in patients and the occurrence of oxidative brain damage in MeCP2-deficient mouse models suggest the involvement of oxidative stress in RTT pathogenesis. However, the molecular mechanism and the origin of the oxidative stress have not been elucidated. Here we demonstrate that a redox imbalance arises from aberrant mitochondrial functionality in the brain of MeCP2-308 heterozygous female mice, a condition that more closely recapitulates that of RTT patients. The marked increase in the rate of hydrogen peroxide generation in the brain of RTT mice seems mainly produced by the dysfunctional complex II of the mitochondrial respiratory chain. In addition, both membrane potential generation and mitochondrial ATP synthesis are decreased in RTT mouse brains when succinate, the complex II respiratory substrate, is used as an energy source. Respiratory chain impairment is brain area specific, owing to a decrease in either cAMP-dependent phosphorylation or protein levels of specific complex subunits. Further, we investigated whether the treatment of RTT mice with the bacterial protein CNF1, previously reported to ameliorate the neurobehavioral phenotype and brain bioenergetic markers in an RTT mouse model, exerts specific effects on brain mitochondrial function and consequently on hydrogen peroxide production. In RTT brains treated with CNF1, we observed the reactivation of respiratory chain complexes, the rescue of mitochondrial functionality, and the prevention of brain hydrogen peroxide overproduction. These results provide definitive evidence of mitochondrial reactive oxygen species overproduction in RTT mouse brain and highlight CNF1 efficacy in counteracting RTT-related mitochondrial defects.

Protection of rat skeletal muscle fibers by either L-carnitine or coenzyme Q10 against statins toxicity mediated by mitochondrial reactive oxygen generation

Mitochondrial redox imbalance has been implicated in mechanisms of aging, various degenerative diseases and drug-induced toxicity. Statins are safe and well-tolerated therapeutic drugs that occasionally induce myotoxicity such as myopathy and rhabdomyolysis. Previous studies indicate that myotoxicity caused by statins may be linked to impairment of mitochondrial functions. Here, we report that 1-h incubation of permeabilized rat soleus muscle fiber biopsies with increasing concentrations of simvastatin (1–40 μM) slowed the rates of ADP-or FCCP-stimulated respiration supported by glutamate/malate in a dose-dependent manner, but caused no changes in resting respiration rates. Simvastatin (1 μM) also inhibited the ADP-stimulated mitochondrial respiration supported by succinate by 24% but not by TMPD/ascorbate. Compatible with inhibition of respiration, 1 μM simvastatin stimulated lactate release from soleus muscle samples by 26%. Co-incubation of muscle samples with 1 mM L-carnitine, 100 μM mevalonate or 10 μM coenzyme Q10 (Co-Q10) abolished simvastatin effects on both mitochondrial glutamate/malate-supported respiration and lactate release. Simvastatin (1 μM) also caused a 2-fold increase in the rate of hydrogen peroxide generation and a decrease in Co-Q10 content by 44%. Mevalonate, Co-Q10 or L-carnitine protected against stimulation of hydrogen peroxide generation but only mevalonate prevented the decrease in Co-Q10 content. Thus, independently of Co-Q10 levels, L-carnitine prevented the toxic effects of simvastatin. This suggests that mitochondrial respiratory dysfunction induced by simvastatin, is associated with increased generation of superoxide, at the levels of complexes-I and II of the respiratory chain. In all cases the damage to these complexes, presumably at the level of 4Fe-4S clusters, is prevented by L-carnitine.

In situ generation of hydrogen peroxide in catalytic membrane reactors

Commercial ceramic hollow fibres have been used as a starting material for the preparation of catalytic membrane reactors (CMRs). The original nominal pore sizes of the membranes were 4, 20, 100, 500 and 1400nm. The CMRs have been produced by palladium precursor impregnation followed by calcinations and reduction in hydrogen flow at 350°C. The direct generation of hydrogen peroxide from hydrogen and oxygen has been studied at ambient conditions. The efficiency of hydrogen peroxide generation, with respect to hydrogen supply, as well as the rate of H2O2 production and the maximum H2O2 concentration as a function of the original membrane pore size have been determined. The μ-XRD and SEM analyses have revealed that the Pd is uniformly distributed throughout the entire membranes. The rate of hydrogen peroxide generation has been shown to depend inversely on the membrane pore size. It has been demonstrated that the upper hydrogen peroxide concentration level is set by the catalyst deactivation and therefore not caused by reverse reactions or hydrogen peroxide reduction by the activated hydrogen. This finding has been confirmed by the XPS analysis.The in situ oxidation of phenol by a subsequent heterogeneous Fenton process in phenol-containing water has been assessed using the CMRs prepared. In these cases no significant activity has been detected. Addition of Fe(II) to the reaction solution has resulted in CMRs with considerable activity for phenol oxidation.In another series of ceramic hollow fibre membranes, the Pd impregnation was preceded by the incorporation of a second active phase (Fe2O3, CuAl2O4, TiO2 or CeO2). The rates of hydrogen peroxide generation as well as the maximum H2O2 concentration for these bi-functional CMRs have been determined following the same procedure developed for the first series of CMRs. All of them have shown activity in producing H2O2. The initial tests for phenol oxidation by the in situ generated H2O2 have demonstrated the viability of the proposed reaction system for waste water treatment.

Analysis of defence enzymes induced by antagonistic bacteriumBacillus subtilis strain AR12 towardsRalstonia solanacearum in tomato

Bacterial wilt, caused byRalstonia solanacearum (Smith) Yabuuchiet al., is an economically important disease on tomato in many provinces of China. Antagonistic bacteriumBacillus subtilis strain AR12 was used to control bacteria wilt of tomato (Lycopersicon esculentum Miller) in the greenhouse. The biocontrol efficiency was as high as 90.18%. Superoxide anion and hydrogen peroxide generation rates and changes in phenylalanine ammonia lyase (PAL), polyphenoloxidase (PPO), peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) activities were studied in tomato plants. Antagonist AR12 advanced and increased significantly activities of PAL, PPO, POD and SOD. As comparison, the activities of these four enzymes increased less and later in tomato only treated withR. solanacearum TM15 (control 2), and kept lowest level with few change in tomato with sterilised water (control 1). The maximum activities of these four enzymes in tomato treated with AR12 occurred in different stages: activity of PAL, PPO, POD, and SOD increased to the top level at 48, 48, 12 and 12 h, respectively, after pathogen inoculation and kept high level for some time. H2O2 is associated with hypersensitive response (HR) during systemic acquired resistance. H2O2 content increased significantly in tomato treated with AR12, but HR response was not seen. CAT and APX are the key H2O2 detoxifying enzymes. Activities of APX in tomato treated with AR12 were increased significantly, while CAT was degraded until 80 h after pathogen inoculation. This work support the view that increased antioxidant enzyme activities could be involved at least in part, in the beneficial effects of plant growth-promoting rhizobacteria strains on the performance of vegetable grown under the pathogen infection conditions.

Electrochemical generation of hydrogen peroxide using surface area-enhanced Ti-mesh electrodes

Ti-mesh electrodes coated with Ti were obtained by using an electrophoretic deposition (EPD) method. The Ti coating was porous and showed a good adherence to the Ti-mesh surface, due to sintering of Ti particles during thermal treatment at 900 °C. The Ti-coated mesh electrode has a BET surface area of 3.5 m 2/g, about four times larger than that of the bare electrode. The surface area-enhanced Ti-mesh electrode was applied in electrical generation of hydrogen peroxide. It was shown that the rate of hydrogen peroxide generation increased drastically compared to the fresh electrode, since the larger electrode surface area enhanced not only current density, but also the oxygen mass transfer rate.

Oxidation of herbicides by in situ synthesized hydrogen peroxide and fenton’s reagent in an electrochemical flow reactor: study of the degradation of 2,4-dichlorophenoxyacetic acid

This paper reports an investigation of H2O2 electrogeneration in a flow electrochemical reactor with RVC cathode, and the optimization of the O2 reduction rate relative to cell potential. A study of the simultaneous oxidation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) by the in situ electrogenerated H2O2 is also reported. Experiments were performed in 0.3 M K2SO4 at pH 10 and 2.5. Maximum hydrogen peroxide generation rate was reached at −1.6 V versus Pt for both acidic and alkaline solutions. Then, 100 mg L−1 of 2,4-D was added to the solution. 2,4-D, its aromatic intermediates such as chlorophenols, chlororesorcinol and chlorinated quinone, as well as TOC were removed at different rates depending on pH, the use of UV radiation and addition of Fe(II). The acidic medium favored the hydroxylation reaction, and first order apparent rate constants for TOC removal ranged from 10−5 to 10−4 s−1. In the presence of UV and iron, more than 90% of TOC was removed. This value indicates that some of the intermediates derived from 2,4-D decomposition remained in solution, mainly as more biodegradable light aliphatic compounds.

Hearts in adult offspring of copper-deficient dams exhibit decreased cytochrome c oxidase activity, increased mitochondrial hydrogen peroxide generation and enhanced formation of intracellular residual bodies

The long-term effects of low dietary copper (Cu) intake during pregnancy and lactation on cardiac mitochondria in first-generation adult rats was examined. Rat dams were fed diets containing either low (1 mg/kg Cu) or adequate (6 mg/kg Cu) levels of dietary Cu beginning 3 weeks before conception and ending 3 weeks after birth. Cytochrome c oxidase (CCO) activity was 51% lower in isolated cardiac mitochondria from 21-day-old offspring of Cu-deficient dams than in the offspring of Cu-adequate dams. CCO activities in the cardiac mitochondria of 63- and 290-day-old offspring were 22% lower and 14% lower, respectively, in the offspring of Cu-deficient dams after they had been repleted with adequate dietary Cu from the time they were 21 days old. Electron micrographs showed that the size of residual bodies and the cellular volume they occupied in cardiomyocytes rose significantly between 63 and 290 days in the Cu-repleted offspring of Cu-deficient dams, but not in the offspring of Cu-adequate dams. The rate of hydrogen peroxide generation by cardiac mitochondria also was 24% higher in the 290-day-old repleted offspring of Cu-deficient dams than in the offspring of Cu-adequate dams. The increase in hydrogen peroxide production by cardiac mitochondria and in the relative volume and size of dense deposits in cardiomyocytes is consistent with increased oxidative stress and damage resulting from prolonged reduction of CCO activity in the offspring of Cu-deficient dams.

Oxidation of pesticides by in situ electrogenerated hydrogen peroxide: Study for the degradation of 2,4-dichlorophenoxyacetic acid

This paper reports an investigation on the performance of the H 2O 2 electrogeneration process on a rotating RVC cylinder cathode, and the optimization of the O 2 reduction rate relative to cell potential. A study for the simultaneous oxidation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) by the in situ electrogenerated H 2O 2 is also reported. Experiments were performed in 0.3 M of K 2SO 4, pH of 10 and 3.5. Oxygen concentration in solution was kept in 25 mg L −1. Maximum hydrogen peroxide generation rate was reached at −1.6 V versus SCE for both, acidic and alkaline solutions. Then, 100 mg L −1 of 2,4-D was added to the solution. First order apparent rate constants for 2,4-D degradation ranged from 0.9 to 6.3 × 10 −5 m s −1, depending on the catalyst used (UV or UV + Fe(II)). TOC reduction was favored in acidic medium where a decreasing of 69% of the initial concentration was observed in the process catalyzed by UV + Fe(II). This figure was an indication that some of the intermediates derived from 2,4-D decomposition remained in solution, mainly as lighter aliphatic compounds.

Cardiac mitochondrial function is altered in the adult offspring of copper‐deficient dams

Prolonged reduction in cardiac cytochrome c oxidase (CCO) activity in neonates caused by maternal copper (Cu) deficiency during fetal and postnatal heart development may have pathophysiological consequences in the adult heart. Dams were fed AIN93G diets containing either 1 mg Cu/kg (CuD dams) or 6 mg Cu/kg (CuA dams) beginning 3 weeks before conception and ending 3 weeks after birth. CCO measured in isolated cardiac mitochondria was 51% lower in the 21-day-old pups of CuD dams compared to pups of CuA dams. Cardiac CCO activity in the offspring of CuD dams was 22% lower after 6 weeks of Cu repletion and 14% lower after 9 months of Cu repletion compared to the offspring of CuA dams. Electron micrographs showed that size of the dense deposits and the cellular volume occupied by the deposits in cardiomyocytes were 105% greater and 75% greater, respectively, in the offspring of CuD dams repleted with Cu for 9 months compared to the offspring repleted for 6 weeks. The comparable rise in the size of the dense deposits in the offspring of CuA dams was 40% but their relative volume was unchanged. After 9 months of Cu repletion, the rate of hydrogen peroxide generation by cardiac mitochondria using glutamate/malate as substrate was 24% greater in the offspring of CuD dams compared to the offspring of CuA dams. Increased hydrogen peroxide production by cardiac mitochondria and the increase in the relative volume and size of dense deposits in cardiomyocytes are consistent with increased oxidative stress and damage resulting from the partial reduction of CCO activity in the adult Cu-repleted offspring of CuD dams.

Mitochondrial Bound Hexokinase Activity as a Preventive Antioxidant Defense: STEADY-STATE ADP FORMATION AS A REGULATORY MECHANISM OF MEMBRANE POTENTIAL AND REACTIVE OXYGEN SPECIES GENERATION IN MITOCHONDRIA

Brain hexokinase is associated with the outer membrane of mitochondria, and its activity has been implicated in the regulation of ATP synthesis and apoptosis. Reactive oxygen species (ROS) are by-products of the electron transport chain in mitochondria. Here we show that the ADP produced by hexokinase activity in rat brain mitochondria (mt-hexokinase) controls both membrane potential (Deltapsi(m)) and ROS generation. Exposing control mitochondria to glucose increased the rate of oxygen consumption and reduced the rate of hydrogen peroxide generation. Mitochondrial associated hexokinase activity also regulated Deltapsi(m), because glucose stabilized low Deltapsi(m) values in state 3. Interestingly, the addition of glucose 6-phosphate significantly reduced the time of state 3 persistence, leading to an increase in the Deltapsi(m) and in H(2)O(2) generation. The glucose analogue 2-deoxyglucose completely impaired H(2)O(2) formation in state 3-state 4 transition. In sharp contrast, the mt-hexokinase-depleted mitochondria were, in all the above mentioned experiments, insensitive to glucose addition, indicating that the mt-hexokinase activity is pivotal in the homeostasis of the physiological functions of mitochondria. When mt-hexokinase-depleted mitochondria were incubated with exogenous yeast hexokinase, which is not able to bind to mitochondria, the rate of H(2)O(2) generation reached levels similar to those exhibited by control mitochondria only when an excess of 10-fold more enzyme activity was supplemented. Hyperglycemia induced in embryonic rat brain cortical neurons increased ROS production due to a rise in the intracellular glucose 6-phosphate levels, which were decreased by the inclusion of 2-deoxyglucose, N-acetyl cysteine, or carbonyl cyanide p-trifluoromethoxyphenylhydrazone. Taken together, the results presented here indicate for the first time that mt-hexokinase activity performed a key role as a preventive antioxidant against oxidative stress, reducing mitochondrial ROS generation through an ADP-recycling mechanism.

Effect of insulin on the rate of hydrogen peroxide generation in mitochondria.

We studied the effect of insulin on H2O2 generation by mitochondria in rat liver and heart. Insulin markedly increased the rate of H2O2 generation, which was realized via short-term activation of mitochondrial succinate dehydrogenase. In terms of the Michaelis-Menten equation describing the dependence of H2O2 generation by mitochondria on succinate concentration (succinate dehydrogenase substrate), insulin decreased the Michaelis-Menten constant and increased the maximum rate of H2O2 generation compared to the control.

O‐Hydroxyethylorutin‐Mediated Enhancement of Tomato Resistance to Botrytis cinerea depends on a Burst of Reactive Oxygen Species

Abstract o‐Hydroxyethylorutin, when applied exogenously to tomato plants was effective in enhancing resistance to Botrytis cinerea infection. Two tomato cultivars, high and low in susceptibility to B. cinerea, were analysed for superoxide anion, hydroxyl radical, hydrogen peroxide generation rates, for changes in lipid peroxidation and activities in superoxide dismutase, peroxidase and catalase. The reactions observed in uninfected tomato plants, in plants infected with B. cinerea, and in those treated with o‐hydroxyethylorutin and infected with the pathogen were compared. The most significant increase in superoxide anion and hydrogen peroxide generation was observed in plants pretreated with o‐hydroxyethylorutin and then infected with the pathogen. It was greater and generally occurred earlier in pretreated, less susceptible plants as compared to more susceptible ones. Some decrease in ascorbate peroxidase activity resulting from inoculation with B. cinerea plants pretreated with o‐hydroxyethylorutin was observed in studied plants. The results indicate that o‐hydroxyethylorutin‐induced tomato resistance to B. cinerea infection depends on its stimulation of reactive oxygen species generation and they confirm the important role of enhanced production of ROS in induced plant resistance reactions.

Effects of coenzyme Q 10 administration on its tissue concentrations, mitochondrial oxidant generation, and oxidative stress in the rat

Coenzyme Q (CoQ 10) is a component of the mitochondrial electron transport chain and also a constituent of various cellular membranes. It acts as an important in vivo antioxidant, but is also a primary source of O 2 −•/H 2O 2 generation in cells. CoQ has been widely advocated to be a beneficial dietary adjuvant. However, it remains controversial whether oral administration of CoQ can significantly enhance its tissue levels and/or can modulate the level of oxidative stress in vivo. The objective of this study was to determine the effect of dietary CoQ supplementation on its content in various tissues and their mitochondria, and the resultant effect on the in vivo level of oxidative stress. Rats were administered CoQ 10 (150 mg/kg/d) in their diets for 4 and 13 weeks; thereafter, the amounts of CoQ 10 and CoQ 9 were determined by HPLC in the plasma, homogenates of the liver, kidney, heart, skeletal muscle, brain, and mitochondria of these tissues. Administration of CoQ 10 increased plasma and mitochondria levels of CoQ 10 as well as its predominant homologue CoQ 9. Generally, the magnitude of the increases was greater after 13 weeks than 4 weeks. The level of antioxidative defense enzymes in liver and skeletal muscle homogenates and the rate of hydrogen peroxide generation in heart, brain, and skeletal muscle mitochondria were not affected by CoQ supplementation. However, a reductive shift in plasma aminothiol status and a decrease in skeletal muscle mitochondrial protein carbonyls were apparent after 13 weeks of supplementation. Thus, CoQ supplementation resulted in an elevation of CoQ homologues in tissues and their mitochondria, a selective decrease in protein oxidative damage, and an increase in antioxidative potential in the rat.

The oxidants and antioxidant enzymes in tomato leaves treated with o-hydroxyethylorutin and infected with Botrytis cinerea

Application of o-hydroxyethylorutin restricted the development of Botrytis cinerea in tomato leaves. Superoxide anion and hydrogen peroxide generation rates and changes in superoxide dismutase, peroxidase and catalase activities were studied in uninfected tomato plants, in plants infected with B. cinerea, and in plants treated with o-hydroxyethylorutin and infected with pathogen. About two times higher hydrogen peroxide concentration were found in plants treated with o-hydroxyethylorutin and infected with the pathogen at the early infection stages compared with untreated infected plants. In vitro tests showed that germination of B. cinerea conidia was significantly inhibited by H2O2. Higher H2O2 concentrations were needed to inhibit mycelial growth. The results indicate that o-hydroxyethylorutin triggers hydrogen peroxide production in tomato plants and suggest that enhanced levels of H2O2 are involved in restricted B. cinerea infection development.

Cytotoxicity, pro-oxidant effects and antioxidant depletion in rat lung alveolar macrophages exposed to ultrafine titanium dioxide.

In order to understand the pulmonary toxicity of ultrafine titanium dioxide (UF-TiO2) particles, various biochemical and chemical parameters were assayed in rat alveolar macrophages (AMs) and cell-free lavage fluid. Single intratracheal exposure of UF-TiO2 (2 mg per rat) caused cytotoxicity to pulmonary AMs. An increase in the population of AMs could be observed, followed by increased activities of lactate dehydrogenase and acid phosphatase in cell-free lavage fluid. In addition, AMs showed an adaptive response because the activities of glutathione peroxidase, glutathione reductase, glucose-6-phosphate dehydrogenase and glutathione S-transferase were increased in these cells. However, this enhancement of antioxidant enzymes could not diminish the enhanced lipid peroxidation and increased rate of hydrogen peroxide generation. The level of glutathione remained decreased in UF-TiO2-exposed rat AMs. The data suggest that the induction of antioxidant enzymes by these cells for self-protection is not sufficient to cope against the toxic action of UF-TiO2, which may lead to oxidative stress.

A senstive spectrophotometry-based mehtod for the determination of the rate of hydrogen peroxide generation in biological systems

A new sensitive spectrophotometric method for the determination of the rate of hydrogen perodoxide generation in biological systems has been developed. This method is based on the measurement of the oxidation rate of reduced cytochrome c H 2O 2 in the presence of a mediator and permits the detection of H 2O 2 generation rates as low as 50 nM min −1. The solution of the differential equations of the kinetic process permitted the calculation of the kinetic rate constants and assessemtn of the conditions required to measure the hydrogen peroxide generation rate.