Comparison of the inactivation of Bacillus subtilis transforming DNA by the potassium superoxide and xanthine-xanthine oxidase systems for generating superoxide

Effects of Chloride Ions on Dissolution, ROS Generation, and Toxicity of Silver Nanoparticles under UV Irradiation

This work investigates the effect of chloride ion (Cl^-) on dissolution, reactive oxygen species (ROS) generation, and toxicity of citrate-coated silver nanoparticles (AgNPs) under UV irradiation. The dissolution rate was decreased by 0.01 M Cl^- due to AgCl passivation on the AgNP surface. By contrast, high concentrations of Cl^- (0.1 or 0.5 M) promoted dissolution due to the formation of soluble Ag-Cl complexes (AgCl _x^{1- x}). The generation of O₂^•- in the AgNPs/Cl^-/UV system was promoted by 0.01 M Cl^-, whereas it was retarded by 0.1 or 0.5 M Cl^-, which was probably because the aggregation of AgNPs at high ionic strength reduced the nanoparticles' surface areas for radical formation. Additionally, Cl^- contributed to •OH generation in the AgNPs/Cl^-/UV system, in which the produced •OH concentrations increased with increasing Cl^- concentrations. The reduction reaction between silver ions and O₂^•- resulted in lower dissolution rates of AgNPs/Cl^- mixtures under UV irradiation than those in the dark. The phototoxicity of AgNPs toward E. coli with different concentrations of Cl^- followed the order of 0.5 M > 0 M > 0.1 M > 0.01 M. Both ROS and dissolved Ag played significant role in the phototoxicity of AgNPs. This work demonstrates the potential importance of anions in the fate and biological impact of AgNPs.

High-throughput superoxide anion radical scavenging capacity assay

A high-throughput superoxide anion radical (O2(•-)) scavenging capacity assay based on the xanthine oxidase/xanthine reaction system was developed and validated in the present study. The reaction conditions including detection wavelength, concentrations of reactant components, reaction temperature, reaction time, pH, terminator reagent, and sample dissolving solvents were optimized. The accuracy and reliability of the assay were assessed by evaluation of linearity (r(2) = 0 .9513-0.9957), precision (intraday RSD 1.13-4.05% and interday RSD 2.13-5.62%), accuracy (95.64-97.42% recovery), and stability (RSD 2.62-6.19%), as well as comparison with the conventional colorimetric method. The EC50 values obtained by the current method and the conventional assay were highly correlated (r > 0.99). This high-throughput O2(•-) scavenging assay may be used for screening and estimating potential superoxide anion radical (O2(•-)) scavengers, especially food extracts and natural products with a very small amount of test material.

Oxidative stress enhances the production and actions of adenosine in the kidney

The purpose of this study was to determine whether superoxide anions (O.) activate 5'-nucleotidase (5'-ND), thereby increasing the production of renal adenosine and regulating renal function. Using HPLC analysis, we found that incubation of renal tissue homogenate with the O. donor KO(2) doubled adenosine production and increased the maximal reaction velocity of 5'-ND from 141 to 192 nmol. min(-1). mg protein(-1). The O.-generating system, xanthine/xanthine oxidase increased the maximal reaction velocity of 5'-ND from 122 to 204 nmol. min(-1). mg protein(-1). Superoxide dismutase (SOD) with catalase produced a concentration-dependent reduction of 5'-ND activity in renal tissue homogenate, while the SOD inhibitor diethyldithiocarbamic acid significantly increased 5'-ND activity. Inhibition of disulfide bond formation by thioredoxin or thioredoxin reductase significantly decreased xanthine/xanthine oxidase-induced activation of renal 5'-ND. In in vivo experiments, inhibition of SOD by diethyldithiocarbamic acid (0.5 mg. kg(-1). min(-1) iv) enhanced renal vasoconstriction induced by endogenously produced adenosine and increased renal tissue adenosine concentrations under control condition and in ischemia and reperfusion. We conclude that oxidative stress activates 5'-ND and increases adenosine production in the kidney and that this redox regulatory mechanism of adenosine production is important in the control of renal vascular tone and glomerular perfusion.

Effect of superoxide and superoxide-generating systems on the prooxidant effect of iron in oil emulsion and raw turkey homogenates

Mechanisms of superoxide.O2--generating systems on the pro-oxidant effect of iron from various sources were studied. Reaction mixtures were prepared with distilled water, oil emulsion, or meat homogenates. Free ionic iron (ferrous and ferric), ferritin and hemoglobin (Hb) were used as iron sources, and KO2 and xanthine oxidase (XOD) systems were used to produce .O2-. Thiobarbituric acid reactive substances (TBARS) values and iron contents of the reaction mixtures were determined. Ferric iron and ferritin, in the presence or absence of superoxide-generating systems, had no catalytic effect on the oxidation of oil emulsion but became pro-oxidants when reducing agent (ascorbate) was present. Ferrous iron and Hb had strong catalytic effects on the oxidation of oil emulsion as shown by TBARS values. Superoxide and H2O2, generated from superoxide-generating systems, oxidized ferrous iron and ascorbate, and lowered the pro-oxidant effect of ferrous iron in oil emulsion. Addition of ferric or ferrous iron increased but Hb did not have any effect on the TBARS values of raw meat homogenates. The reaction mechanisms of superoxide and the superoxide-generating systems on the prooxidant effect of various iron sources indicated that .O2- was a strong oxidizer rather than a reducing agent, and the antioxidant effect of XOD system in oil was caused by the oxidation of ferrous iron to the ferric form by .O2- and/or H2O2.

Relationship of hepatocarcinogenicity and hepatocellular proliferation induced by mutagenic noncarcinogens vs carcinogens. II. 1- vs 2-nitropropane

2-Nitropropane (2-NP) is mutagenic in a number of short-term mutagenicity assays in vitro and in vivo, and is a potent hepatocarcinogen in rats. A structural isomer, 1-nitropropane (1-NP), is mutagenic in V79 cells and can induce unscheduled DNA synthesis in rat hepatocytes, yet did not induce tumors in rats following chronic exposure. We examined the correlation of cell proliferation and hepatocarcinogenesis induced by this mutagenic noncarcinogen-carcinogen pair in a rat liver proliferation model. Rats were exposed to gavage doses of 0.5, 1, or 2 mmol/kg of 1-NP or 2-NP daily for 10 days; the highest two dose groups were similar to the doses used in the carcinogenesis bioassay. Cell proliferation was quantitated by incorporation of bromodeoxyuridine, detected immunohistochemically, into newly synthesized DNA. Animals exposed to the vehicle exhibited a labeling index (LI) of approximately 1.9% and animals exposed to CCL4 had a LI of approximately 30%. Rats exposed to the hepatocarcinogen 2-NP exhibited a dose-related increase in LI to 6.3 and 11% at the 1 and 2 mmol/kg doses, respectively, and no increase above control at the 0.5 mmol/kg exposure level. Animals exposed to the noncarcinogenic isomer 1-NP showed no statistically significant increase in LI above controls at any dose level tested. Serum chemistries were consistent with mild to moderate decreases in hepatocellular function, cholestasis, and necrosis following 2-NP exposure, but only minimal effects were observed, probably due to slight dehydration resulting from 1-NP exposure. These data indicate a positive association between increased cell proliferation and hepatocarcinogenesis induced by these two nitropropane isomers.

The role of hydroxyl radical in chromosomal and plasmid damage in Neisseria gonorrhoeae in vivo

Viable Neisseria gonorrhoeae exposed to streptonigrin generate intracellular hydroxyl radical detected by spin-trapping with 5,5-dimethyl-l-pyrroline-N-oxide; gonococci exposed to paraquat generate primarily superoxide (J. Biol. Chem., 262: 13404-143048, 1987). The use of streptonigrin and paraquat provide a model with which to examine the action and site(s) of hydroxyl radical-mediated damage. N. gonorrhoeae exposed to streptonigrin, but not paraquat, developed extensive chromosomal, plasmid, and RNA damage. Addition of excess Fe+3 to the reaction mixture enhanced intracellular hydroxyl radical formation by paraquat, detectable as DNA damage. Desferal and dimethyl sulfoxide allowed approximately 25% of protection of plasmid DNA damage as judged by linear scanning densitometry. These results demonstrate DNA and RNA damage in viable organisms exposed to intracellular redox stress and confirm the critical role of hydroxyl radical in this process.

Single-strand DNA breaks in rodent and human cells produced by superoxide anion or its reduction products

Chinese hamster ovary cells and human P3 teratocarcinoma cells were exposed to superoxide anion (O2-) generated by the addition of potassium superoxide (KO2). DNA from the cells was examined by alkaline elution techniques for the production of single-strand breaks, as well as for the production of double-strand breaks and DNA-protein cross-links. It was demonstrated that KO2 produced only single-strand breaks in DNA in both cell lines, in a dose-dependent manner. The number of breaks was reduced by the prior addition of a metal chelator, indicating that some of the breaks may have been caused by the metal-catalyzed (Fenton reaction) reduction products, hydrogen peroxide or hydroxyl radical Catalase almost completely inhibited break induction by O2-, evidence for a role of hydrogen peroxide. The results of this study indicate that O2- and its reduction products can damage intracellular mammalian DNA.