Reactive Oxygen Species Generation System Research Articles

Wavelength engineerable porous organic polymer photosensitizers with protonation triggered ROS generation

Engineering excitation wavelength of photosensitizers (PSs) for enhanced reactive oxygen species (ROS) generation has inspired new windows for opportunities, enabling investigation of previously impracticable biomedical and photocatalytic applications. However, controlling the wavelength corresponding to operating conditions remains challenging while maintaining high ROS generation. To address this challenge, we implement a wavelength-engineerable imidazolium-based porous organic photocatalytic ROS generation system (KUP system) via a cost-effective one-pot reaction. Remarkably, the optimal wavelength for maximum performance can be tuned by modifying the linker, generating ROS despite the absence of metal ions and covalently attached heavy atoms. We demonstrate that protonated polymerization exclusively enables photosensitization and closely interacts with oxygen related to the efficiency of photosensitizing. Furthermore, superior tumor eradication and biocompatibility of the KUP system were confirmed through bioassays. Overall, the results document an unprecedented polymerization method capable of engineering wavelength, providing a potential basis for designing nanoscale photosensitizers in various ROS-utilizing applications.

Remote Manipulation of ROS-Sensitive Calcium Channel Using Near-Infrared-Responsive Conjugated Oligomer Nanoparticles for Enhanced Tumor Therapy In Vivo.

The regulation of reactive oxygen species (ROS)-sensitive calcium (Ca2+) channels is of great significance in the treatment of tumors. Here, a simple ROS generation system is developed to activate ROS-sensitive ion channels for enhancing calcium-cascade-mediated tumor cell death under near-infrared (NIR) light irradiation. Upon irradiation with an 808 nm laser, a low-lethality amount of ROS facilitates plasmid transient potential receptor melastatin-2 (pTRPM2) gene release via cleavage of the Se-Se bonds, which contributed to enhancing the expression of TRPM2 in tumor cells. Meanwhile, ROS could potently activate TRPM2 for Ca2+ influx to inhibit early autophagy and to further induce intracellular ROS production, which ultimately led to cell death in TRPM2 expressing tumor cells. Both in vitro and in vivo data show that nanoparticles have an excellent therapeutic effect on cancer upon NIR light. This work presents a simple modality based on NIR light to remotely control the ROS-sensitive ion channel for cancer therapy.

Sunlight-Activatable ROS Generator for Cell Death Using TiO2/c-Si Microwires.

Solar-driven reactive oxygen species (ROS) generation is an attractive disinfection technique for cell death and water purification. However, most photocatalysts require high stability in the water environment and the production of ROS with a sufficient amount and diffusion length to damage pathogens. Here, a ROS generation system was developed consisting of tapered crystalline silicon microwires coated with anatase titanium dioxide for a conformal junction. The system effectively absorbed >95% of sunlight over 300-1100 nm, resulting in effective ROS generation. The system was designed to produce various ROS species, but a logistic regression analysis with cellular survival data revealed that the diffusion length of the ROS is ∼9 μm, implying that the most dominant species causing cell damage is H2O2. Surprisingly, a quantitative analysis showed that only 15 min of light irradiation on the system would catalyze a local bactericidal effect comparable to the conventional germicidal level of H2O2 (∼3 mM).

Reactivity of redox sensitive paramagnetic nitroxyl contrast agents with reactive oxygen species.

The reactivity of nitroxyl free radicals, 4-hydroxyl-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPOL) and 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-N-oxyl (CmP), with reactive oxygen species (ROS) were compared as typical 6-membered and 5-membered ring nitroxyl compounds, respectively. The reactivity of the hydroxylamine forms of both these nitroxyl radicals (TEMPOL-H and CmP-H) was also assessed. Two free radical species of ROS, hydroxyl radical (•OH) and superoxide (O2•−), were subjected to a competing reaction. •OH was generated by UV irradiation from an aqueous H2O2 solution (H2O2-UV system), and O2•− was generated by a reaction between hypoxanthine and xanthine oxidase (HX-XO system). •OH and O2•− generated by the H2O2-UV and HX-XO systems, respectively, were measured by electron paramagnetic resonance (EPR) spin-trapping, and the amount of spin adducts generated by each system was adjusted to be equal. The time courses of the one-electron oxidation of TEMPOL, CmP, TEMPOL-H, and CmP-H in each ROS generation system were compared. A greater amount of TEMPOL was oxidized in the HX-XO system compared with the H2O2-UV system, whereas the reverse was observed for CmP. Although the hydroxylamine forms of the tested nitroxyl radicals were oxidized evenly in the H2O2-UV and HX-XO systems, the amount of oxidized CmP-H was approximately 3 times greater compared with TEMPOL-H.

Co-occurrence of tetraspanin and ROS generators

The nematode exoskeleton, commonly called the cuticle, is a highly structured extracellular matrix mainly composed of collagen. Secreted collagen molecules from the underlying epidermal cells are cross-linked via their tyrosyl residues. Reactive oxygen species (ROS) are required for the cross-linking reaction to produce tyrosyl radicals. The conserved ROS generator enzyme in C. elegans, BLI-3/CeDUOX1, a homolog of dual oxidases (DUOXs), is responsible for production of hydrogen peroxide. The ROS generation system must be properly controlled since ROS are highly reactive molecules that irreversibly inhibit the functions of cellular components such as nucleic acids and proteins. We recently reported that the ROS generation system directed by BLI-3 requires the tetraspanin protein, TSP-15. Herein we outline the process of cuticle development with a focus on the molecular roles of TSP-15 in the BLI-3 system. We also propose the co-occurrence of tetraspanin and ROS generators by convergent evolution.

Transitional Reactive Oxygen Species (ROS) Production in Fertilized Egg Embryos of Devil Stinger (Inimicus japonicus), a Marine Fish Species

A time-course analysis of reactive oxygen species (ROS) generation in fertilized eggs of the devil stinger (Inimicus japonicus) from 0 h post-fertilization (hpf) to the early larval stage indicated that the ROS level was highest in the 22 hpf embryo, and declined thereafter. Phorbol myristate acetate (PMA) had no effect on ROS generation by the 22 hpf embryo, whereas PMA significantly increased larval ROS generation, suggesting that the ROS generation mechanisms of the 22 hpf embryo and larva are different at least in terms of PMA-responsiveness. Our results suggest the presence of a specific ROS generation system in devil stinger embryo which can be transitionally activated during embryogenesis.

Synergistic Activities of a Silver(I) Glutamic Acid Complex and Reactive Oxygen Species (ROS): A Novel Antimicrobial and Chemotherapeutic Agent

The antimicrobial and chemotherapeutic activities of a silver(I) glutamic acid complex with the synergistic concomitant generation of reactive oxygen species (ROS) were investigated here. The ROS generation system employed was via Fenton chemistry. The antimicrobial and chemotherapeutic activities were investigated on Staphylococcus aureus ATCC 43300 and Escherichia coli bacteria, and Vero and MCF-7 tumor cell lines, respectively. Antimicrobial activities were conducted by determining minimum inhibitory concentration (MIC), while chemotherapeutic efficacies were done by serial dilution using standard techniques to determine the half maximal inhibitory concentration (IC50). The antimicrobial and chemotherapeutic results obtained were compared with positive control drugs gentamicin, oxacillin, penicillin, streptomycin and cisplatin, a ubiquitously used platinum-based antitumor drug, and with the silver(I) glutamic acid complex and hydrogen peroxide separately. Based on MIC and IC50 values, it was determined that this synergistic approach was very effective at extremely low concentrations, especially when compared with the other drugs evaluated here. This finding might be of great significance regarding metronomic dosing when this synergistic approach is clinically implemented. Since silver at low concentrations exhibits no toxic, mutagenic and carcinogenic activities, this might offer an alternative approach for the development of safer silver-based antimicrobial and chemotherapeutic drugs, thereby reducing or even eliminating the toxicity associated with current drugs. Accordingly, the present approach might be integrated into the systemic clinical treatment of infectious diseases and cancer.

Participation of reactive oxygen species in regulation of Са2+ - activated К + channels of erythrocytes

In this study, we investigated the effects of preincubation with the reactive oxygen species-generating system xanthine oxidase/xanthine on Ca2+-dependent potassium permeability of erythrocyte membrane. The increase of intracellular calcium concentration in presence of calcium ionophore A23187 led to erythrocyte membrane hyperpolarization due to opening of Ca2+-activated potassium channels. Erythrocyte membrane potential was recorded via measurement of pH of the incubation medium in presence of prothonophore. Incubation of erythrocytes with xanthine (100 µmol)/ xanthine oxidase (10 mU/ml) mixture resulted in significant loss of amplitude and rate of hyperpolarization response and also loss the rate of membrane potential restoration. These effects can be caused by hydrogen peroxide, one of products of reaction of xanthine oxidase/xanthine.

Reactive oxygen species generation through NADH oxidation by pterin derivatives

Pterin is an electron transfer compound in biological systems. Among the analogs, 6-formylpterin (6FP) has been demonstrated to have many marked physiological and pharmacological activities. In previous study, we have elucidated that 6FP derivatives in which the 3-position is modified possess reactive oxygen species (ROS), which are involved in the modulation of a variety of cell functions, generation activities through the oxidation of NADH to NAD(+) in the dark at neutral pH. In the present study, we have demonstrated that the ROS generation activity by 6FP derivative is enhanced in the presence of 3-methyl-1-phenyl-2-pyrazolin-5-one. In this reaction, 3-methyl-1-phenyl-2-pyrazolin-5-one is reacted with the formyl group on the 6-position of 6FP derivative to give the activated product. The present results would be helpful for designing pharmaceutical ROS generation system in vivo.

Comparison of the responses of peritoneal macrophages from Japanese flounder ( Paralichthys olivaceus) against high virulent and low virulent strains of Edwardsiella tarda

In vivo infection studies in Japanese flounder ( Paralichthys olivaceus) demonstrated that the number of viable cells of the virulent strain (NUF251) of Edwardsiella tarda increased gradually in kidney and hepato-pancreas after intraperitoneal injection, but the low virulent strain (NUF194) did not. To gain insight into the virulence factors of E. tarda, in vitro responses of Japanese flounder ( P. olivaceus) peritoneal macrophages to these strains were compared in terms of phagocytosis, bactericidal activity, and reactive oxygen species (ROS) generation as measured by chemiluminescence (CL) responses. Microscopic observation revealed that these two strains of E. tarda were phagocytosed by the peritoneal macrophages, and there was no significant difference in the mean numbers of ingested bacteria per macrophage between these strains. A gradual increase in the number of viable cells of the highly virulent strain within macrophages was observed during 9 h post-phagocytosis, whereas no significant replication of the low virulent strain within macrophages was detected. These results suggest that the virulent strain of E. tarda has an ability to survive and replicate within macrophages, while the low virulent strain has no such ability. When the peritoneal macrophages were exposed to the opsonized low virulent E. tarda strain, a rapid increase in CL response was induced. However, the highly virulent strain caused only background level of CL response. By the subsequent stimulation with phorbol myristate acetate, the macrophages exposed to the virulent E. tarda strain showed extremely higher CL response than that of the one exposed to the low virulent E. tarda strain. These results suggest that the virulent E. tarda prevents the activation of ROS generation system during phagocytosis, though the system is still capable of responding to other stimulation. The virulent strain significantly reduced the CL response induced by xanthine/xanthine oxidase system, while the low virulent strain had almost no effect. Furthermore, the virulent strain showed greater resistance to H 2O 2 than the low virulent strain. Our results suggest that the virulent strain of E. tarda is highly resistant to ROS, and such ability might allow the organism to survive and multiply within phagocytes, and may serve to disseminate E. tarda throughout the host during in vivo infection.

Production of reactive oxygen species (ROS) by devil stinger ( Inimicus japonicus) during embryogenesis

In aquacultural industry, the seed production of devil stinger, a valuable fish in Japan, has not succeeded yet due to the cryptogenic mass mortality. We found that survival rate of the larvae of devil stinger increased by the addition of green tea extract rich in catechin into rearing tank. Generation of reactive oxygen species (ROS) was detected in the embryo of devil stinger by chemiluminescence analysis under the normal growth conditions without addition of specific stimulants. Even in the unfertilized egg, certain level of ROS was detected. ROS were continuously detected during the development from fertilized egg to larva and tended to increase gradually. Observation of embryos and post-hatching larvae with hypersensitive photon-counting microscopy indicated that ROS were produced on the surface of embryo and the head region of larva especially peripheries of eyes. When the embryo proteins were analyzed by immunoblotting using antibody against the human neutrophil cytochrome b558 large subunit (gp91 phox), a main band of approximately 91 kDa was detected, suggesting the presence of NADPH oxidase-like ROS generating system in the embryo of devil stinger. After treatment with streptomycin and penicillin G for 1 day, the level of ROS production in larvae decreased with increase in the survival rate of larvae. Our results suggest that devil stinger has ROS generation system that is already activated at fairly early stage of development before the maturation of usual immune system.

Effects of reactive oxygen and nitrogen species on cyclooxygenase-1 and -2 activities

The effects of reactive oxygen species (superoxide anion radical—O2−, hydrogen peroxide—H2O2 and hydroxyl radical—OH; the reaction products of xanthine plus xanthine oxidase system) and reactive nitrogen species [nitric oxide—NO; from 1-hydroxyl-2-oxo-3-(N-methyl-3-aminopropyl)-3-methyl-1-triazene—NOC7 and peroxynitrite—ONOO−] on the activities of purified cyclooxygenase (COX)-1 and -2 were studied. Xanthine plus xanthine oxidase suppressed the COX-1 and -2 activities in a xanthine oxidase concentration-dependent fashion. This effect was reversed by addition of catalase to the reactive oxygen species-generating system but not by superoxide dismutase or mannitol, indicating that H2O2 is the responsible metabolite. NOC7 activated the COX-1 activity but inhibited the COX-2 activity at concentrations ranging from 1 to 50μM. Experiments utilizing a NO antidote, carboxy-2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide revealed that the observed effects of NOC7 are caused by NO. ONOO−, a product of NO and O2−, both activated and inhibited the COX-1 and -2 activities, depending on ONOO− concentration. At a low concentration of ONOO− (5μM) there was enhancement of the COX-1 and -2 activities, but with higher concentrations there was suppression of these two enzyme activities (COX-1, at 200μM; COX-2, >50μM). These results suggest that H2O2, NO and ONOO− can have different modulatory effects on the COX-1 and -2 activities.

Peripheral parameters of oxidative stress in patients with infiltrative Graves’ ophthalmopathy treated with corticosteroids

Infiltrative ophthalmopathy, which may develop in patients with Graves’ disease, is considered an inflammatory disorder of autoimmune background. There is growing evidence that changed reactive oxygen species (ROS) metabolism plays an important role in pathogenesis of autoimmune diseases. Corticotherapy is a principal method of ophthalmopathy treatment, and its therapeutic effect is partially connected with influence on ROS generation systems. This study was undertaken to investigate corticosteroids treatment influence on blood extracellular indices of ROS metabolism in Graves’ ophthalmopathy patients. Plasma indices of free radical generation and scavenging were determined in 22 euthyroid patients with active infiltrative Graves’ ophthalmopathy initially, after intensive corticotherapy and after completing of steroid treatment. Age- and sex-matched 24 healthy volunteers and 25 euthyroid Graves’ patients without overt ophthalmopathy served as controls. In the ophthalmopathy patients hydrogen peroxide (H 2O 2), lipid hydroperoxides (ROOH), thiobarbituric acid-reacting substances (TBARS) and ceruloplasmin (CP) levels and superoxide dismutase (SOD) and catalase (CAT) activities were increased, whereas glutathione peroxidase (GPx) and glutathione reductase (GR) activities were reduced. Intensive corticotherapy resulted in normalization (partial for ROOH) of ROS metabolism peripheral markers. After the withdrawal of corticosteroids a reduction of ophthalmopathy clinical activity was present, yet a marked restoration of increased oxidative stress indices was observed, along with activation of antioxidant defence systems (not significant for CAT activity). These data demonstrate that corticosteroids are effective in reduction of peripheral oxidative stress present in infiltrative Graves’ ophthalmopathy, but this effect tends to be transient.

Antioxidants and free radical scavenging activity of Phellinus baumii ( Phellinus of Hymenochaetaceae) extracts

This study was carried out to expand the utilization (for the pharmaceutical and food industries) of extracts of Phellinus baumii. Fractions rich in phenolics were extracted from P. baumii using various solvents. Antioxidant and free radical scavenging activity were studied using a β-carotene-linoleate model system and reactive oxygen species generation system. Total phenolic compounds in methanol and hot water extracts were 33.3 and 20.7 mg/100 ml, respectively; these values are higher than other solvent extracts. Therefore, methanol and hot water extracts exhibited good inhibition rates, of about 80–90%, by hydroxyl radical scavenging activity, hydrogen peroxide scavenging activity, effect of reducing power on metallic compound formation and antioxidant activity.

Possible role of hydroxyl radicals in the oxidation of dichloroacetonitrile by Fenton-like reaction

Dichloroacetonitrile (DCAN), is a member of haloacetonitrile group and detected in drinking water supplies as a by-product of chlorination process. The mechanism of DCAN-induced carcinogenesis is believed to be mediated by oxidative bioactivation of DCAN molecules. The present study was designed to investigate if reactive oxygen species (ROS), similar to that generated in biological systems, are capable of oxidative activation of DCAN. A model ROS generation system (Fenton-like reaction; Fe 2+ and H 2O 2) that predominantly produces hydroxyl radical (OH ·) was used. DCAN oxidation was monitored by the extent of cyanide (CN −) release. The results indicate that DCAN was markedly oxidized by this system, and the rate of oxidation was dependent on DCAN concentration. Four-fold increase in H 2O 2 concentration (50–200 mM) resulted in a 35-fold increase in CN − release. The rates of DACN oxidation in presence of various transition metals were in the following order; iron>copper>titanium. DCAN oxidation was enhanced significantly by the addition of vitamin C and sulfhydryl compounds such as glutathione, N-acetyl- l- cysteine, and dithiothreitol (10 mM) to 140, 130, 145 and 136% of control, respectively. Addition of H 2O 2 scavenger; catalase or iron chelator; desferrioxamine (DFO) resulted in a significant decrease in CN − release 47 and 41% of control, respectively. Addition of various concentrations of the free radical scavengers, DMSO, or mannitol, to the incubation mixtures caused a significant decrease in DCAN oxidation, 32 and 50% of control, respectively. Michaelis–Menten kinetic analysis of the rates of this reaction, with or without inhibitors, indicated that ROS mediated oxidation of DCAN was inhibited by catalase ( K i=0.01 mM)>DFO (0.02 mM)>mannitol (0.09 mM)>DMSO (0.12 mM). In conclusion, our results indicate that DCAN is oxidized by a ROS-mediated mechanism. This mechanism may have an important role in DCAN bioactivation and DCAN-induced genotoxicity at target organs where multiple forms of ROS generating systems are abundant.

Cytochrome c Is Released from Mitochondria in a Reactive Oxygen Species (ROS)-dependent Fashion and Can Operate as a ROS Scavenger and as a Respiratory Substrate in Cerebellar Neurons Undergoing Excitotoxic Death

In rat cerebellar granule cells both reactive oxygen species production and release of cytochrome c take place during glutamate toxicity. This investigation was aimed (i) to ascertain whether and how these two processes are related and (ii) to gain insight into the role played by the released cytochrome c in the onset of neurotoxicity. Cytochrome c release takes place owing to the generation of reactive oxygen species both in glutamate-treated cerebellar granule cells and in sister control cultures incubated in the presence of the reactive oxygen species-generating system consisting of xanthine plus xanthine oxidase. In the early phase of neurotoxicity (30-min glutamate exposure) about 40% of the maximum (as measured at 3 h of glutamate exposure) cytochrome c release was found to occur in cerebellar granule cells from mitochondria that were essentially coupled and intact and that had a negligible production of oxygen free radicals. Contrarily, mitochondria from cells treated with glutamate for 3 h were mostly uncoupled and produced reactive oxygen species at a high rate. The cytosolic fraction containing the released cytochrome c was able to transfer electrons from superoxide anion to molecular oxygen via the respiratory chain and was found to partially prevent glutamate toxicity when added externally to cerebellar neurons undergoing necrosis. In the light of these findings, we propose that in the early phase of neurotoxicity, cytochrome c release can be part of a cellular and mitochondrial defense mechanism against oxidative stress.

Superoxide-induced changes in endothelin (ET) receptors in hepatic stellate cells

Background/Aims: Reactive oxygen species are mediators of various pathophysiologic events, including postischemic reperfusion injury and inflammation. Generation of reactive oxygen species and consequent organ injury are associated with increased levels of a powerful vasoconstrictor peptide endothelin-1. Current evidence suggests that actions of endothelin-1 on the contractile and fibrogenic transdifferentiated stellate cells may play a critical role in hepatic pathophysiology. the aim of this investigation was to determine whether reactive oxygen species modulate the synthesis of endothelin-1 and its receptors in stellate cells. Methods: Primary cultures of transdifferentiated stellate cells were exposed to reactive oxygen species-generating system, hypoxanthine/xanthine oxidase, before determination of endothelin-1 and its receptors. Results: The treatment caused an initial decrease in ET-1 receptor density (about 30% at 30 min), followed by a significant increase over the basal level at 6 h. The increase in the receptors, which occurred specifically in the ET B subtype, progressed thereafter up to 24 h and was accompanied by an augmented functional response, as indicated by an enhanced endothelin-1-induced release of [ 3H]arachidonic acid from the prelabeled cells. Furthermore, treatment of cells for 24 h but not 30 min caused increased expression of ET B mRNA as determined by semi-quantitative polymerase chain reaction. The release of endothelin-1 in the culture medium was also enhanced by hypoxanthine/xanthine oxidase treatment. These effects of hypoxanthine/xanthine oxidase were inhibited by superoxide dismutase and dimethyl sulfoxide. ET-1-induced [ 3H]arachidonic acid release was also inhibited by the ET B receptor antagonist BQ788, but not by the ET A receptor antagonist BQ123. Conclusions: These findings indicate that interactions between ET-1 and stellate cells during episodes of the generation of reactive oxygen species can be an important mechanism in the pathophysiology of hepatic disorders.

Differential regulation of antioxidant enzymes in response to oxidants.

We have demonstrated the selective induction of manganese superoxide dismutase (MnSOD) or catalase mRNA after exposure of tracheobronchial epithelial cells in vitro to different oxidant stresses. Addition of H2O2 caused a dose-dependent increase in catalase mRNA in both exponentially growing and confluent cells. A 3-fold induction of catalase mRNA was seen at a nontoxic dose of 250 microM H2O2. Increase in the steady-state mRNA levels of glutathione peroxidase (GPX) and MnSOD were less striking. Expression of catalase, MnSOD, and GPX mRNA was highest in confluent cells. In contrast, constitutive expression of copper and zinc SOD (CuZnSOD) mRNA was greatest in dividing cells and was unaffected by H2O2 in both exponentially growing and confluent cells. MnSOD mRNA was selectively induced in confluent epithelial cells exposed to the reactive oxygen species-generating system, xanthine/xanthine oxidase, while steady-state levels of GPX, catalase, and CuZnSOD mRNA remained unchanged. The 3-fold induction of MnSOD mRNA was dose-dependent, reaching a peak at 0.2 unit/ml xanthine oxidase. MnSOD mRNA increases were seen as early as 2 h and reached maximal induction at 24 h. Immunoreactive MnSOD protein was produced in a corresponding dose- and time-dependent manner. Induction of MnSOD gene expression was prevented by addition of actinomycin D and cycloheximide. These data indicate that epithelial cells of the respiratory tract respond to different oxidant insults by selective induction of certain antioxidant enzymes. Hence, gene expression of antioxidant enzymes does not appear to be coordinately regulated in these cell types.

Role for iron in reactive oxygen species-mediated cytotoxicity to cultured rat gastric mucosal cells

The gastric epithelium is exposed to oxygen species that are generated within the lumen. Reactive oxygen species, enzymatically generated, cause injury to cultured rat gastric mucosal cells. Much interest has been focused on the role of iron in producing oxidant-mediated injury to the gastric mucosa, because iron is a catalyst that promotes the production of .OH possibly from O2-. and H2O2 (Haber-Weiss reaction) or from H2O2 alone (Fenton reaction). With the use of an iron chelator and an iron binding protein, we examined the role of iron in producing oxidant-mediated injury to cultured gastric mucosal cells. Reactive oxygen species and H2O2 were generated by hypoxanthine-xanthine oxidase and glucose-glucose oxidase, respectively, in buffer without iron. Pretreatment with deferoxamine diminished hypoxanthine-xanthine oxidase-induced 51Cr release from prelabeled cells, dose dependently. Furthermore, addition of deferoxamine to the reactive oxygen species-generating system also protected against the injury. However, apotransferrin (which binds extracellular iron) failed to protect cells. Pretreatment with .OH scavengers was partially protective. Depletion of glutathione with diethyl maleate enhanced reactive oxygen species-mediated cytolysis; such cytolysis was inhibited by deferoxamine. Deferoxamine also decreased 51Cr release induced by glucose-glucose oxidase. We conclude that intracellular iron plays a crucial role in mediating oxygen radical damage to gastric mucosal cells. The .OH, produced from H2O2 by the iron-catalyzed Fenton reaction, seems to be the main mediator of oxidant-induced cytotoxicity to gastric mucosal cells in vitro.

The effect of tranilast of the generation of reactive oxygen species.

The relative in vitro antioxidant efficacy of tranilast, a new orally active anti-allergic agent, was examined by studying its effects on the generation of reactive oxygen species (ROS) using zymosan-stimulated polymorphonuclear leukocytes and the cell-free, xanthine-xanthine oxidase system. The species investigated were superoxide radical anion (O2-), hydrogen peroxide (H2O2) and hydroxyl radical (OH.). At concentrations comparable to therapeutic blood levels, tranilast reduced both H2O2 and OH. levels. The inhibitory effect of tranilast was dose-dependent and all ROS levels examined were significantly decreased at the concentration of 100 micrograms/ml. This antioxidant effect of tranilast appeared to stem from its capability to scavenge ROS because the suppression of ROS was observed in both ROS generation systems at higher concentrations, even though the possibility existed that tranilast directly inhibited nicotineamide adenine dinucleotide phosphate oxidase and/or xanthine oxidase activity. This unique anti-inflammatory pharmacological activity of tranilast suggests its potential clinical application for allergic diseases complicated with inflammation.