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PubMed1994

Susceptibility of glutathione peroxidase and glutathione reductase to oxidative damage and the protective effect of spin trapping agents.

Susceptibility of two key protective enzymes, glutathione peroxidase (GPX) and glutathione reductase (GR), to oxidative damage and the possible protective action of spin traps have been studied. Several oxidizing protocols including: (a) Fe(II) or Fe(III)/ascorbate, (b) a singlet oxygen producing system (methylene blue and visible light), (c) ozone, and (d) a hydroxyl radical-generating system (hydrogen peroxide/uv light) have been employed. Our results show that both enzymes are susceptible to oxidative modification and damage as indicated by the loss of activity and formation of carbonyl groups (in the case of GR). Treatment of GR with any of the mentioned oxidants resulted in formation of carbonyl groups and inactivation except when treated with iron, where the observed carbonyl formation was not accompanied with significant activity loss. GPX was inactivated to varying degrees when treated with the mentioned oxidants, but no carbonyls were detected. Ultraviolet exposure per se resulted in inactivation of both enzymes. Presence of the spin traps N-tert-butyl-alpha-phenylnitrone or 5,5'-dimethyl-1-pyroline-N-oxide was effective in protecting the enzymes against oxidation by uv, hydrogen peroxide/uv, and ozone as determined by the preservation of activity and decreased carbonyl content. The degree of protection, however, was found to be specific for each enzyme and for the employed oxidizing system.

Animals↗
PubMed1995

Doxorubicin reduces the iron(III) complexes of the hydrolysis products of the antioxidant cardioprotective agent dexrazoxane (ICRF-187) and produces hydroxyl radicals.

Dexrazoxane (ICRF-187) is very effective in protecting against doxorubicin-induced cardiotoxicity. Dexrazoxane likely acts though its metal ion binding hydrolysis product ADR-925 by reducing doxorubicin-promoted iron-based oxygen-free radical damage. In this study we show that doxorubicin and epirubicin (but not daunorubicin, idarubicin, or mitoxantrone) are able to reduce iron(III)-ADR-925 and under aerobic conditions are able to produce hydroxyl radicals that are detectable by EPR spin trapping. The ability of iron(III)-ADR-925 to produce hydroxyl radicals in the presence of anthraquinones is compared with that of other ferric chelates, including those of the one-ring open hydrolysis intermediates of dexrazoxane, the tetraacid derivative of ADR-925, EDTA, DTPA, and deferoxamine. The anthraquinones that lacked an alpha-ketol side chain (daunorubicin, idarubicin, and mitoxantrone) produced much less hydroxyl radical than those that did (doxorubicin and epirubicin). The model alpha-ketol, dihydroxyacetone, was also able to promote the formation of hydroxyl radicals in the presence of iron(III) chelates. Since dexrazoxane and doxorubicin are administered together, the possibility must be considered that anthracyclines with alpha-ketol side chains may be oxidized by iron(III)-ADR-925, thus changing their antitumor activity.

Aerobiosis↗
PubMed1998

Antioxidant activities of isoflavones and their biological metabolites in a liposomal system.

Genistein and daidzein, the two major soy isoflavones, principally occur in nature as their glycosylated or methoxylated derivatives, which are cleaved in the large intestine to yield the free aglycones and further metabolites. The objective of this study was to compare the antioxidant activities of genistein and daidzein with their glycosylated and methoxylated derivatives and also those of their human metabolites. The abilities of these compounds to inhibit lipid peroxidation in a liposomal system were evaluated using fluorescence spectroscopy, and structural criteria that enhance antioxidant activity were established. The peroxidation initiators employed in the study were Fe(II) and Fe(III) metal ions and aqueous-phase, azo-derived peroxyl radicals. Both the parent isoflavonoids and their metabolites were more effective at suppressing metal-ion-induced peroxidations than the peroxyl-radical-induced peroxidation. Antioxidant activities for the isoflavone metabolites were comparable to or superior to those for the parent compounds. Equol and its 4-hydroxy and 5-hydroxy derivatives were the most potent antioxidants in the study, suggesting that absence of the 2, 3-double bond and the 4-oxo group on the isoflavone nucleus enhances antioxidant activity. Additionally, the number and position of hydroxyl groups were determining factors for isoflavonoid antioxidant activity, with hydroxyl substitution being of utmost importance at the C-4' position, of moderate importance at the C-5 position, and of little significance at the C-7 position.

Amidines↗
PubMed2001

Formation of compound I and compound II ferryl species in the reaction of hemoglobin I from Lucina pectinata with hydrogen peroxide.

The formation of ferryl heme (Fe(IV) = O) species, i.e., compound I and compound II, has been identified as the main intermediates in heme protein peroxidative reactions. We report stopped-flow kinetic measurements which illustrate that the reaction of hemoglobin I (HbI) from Lucina pectinata with hydrogen peroxide produce ferryl intermediates compound I and compound II. Compound I appears relatively stable displaying an absorption at 648 nm. The rate constant value (k'(2)) for the conversion of compound I to compound II is 3.0 x 10(-2) s(-1), more than 100 times smaller than that reported for myoglobin. The rate constant value for the oxidation of the ferric heme (k'(12) + k'(13)) is 2.0 x 10(2) M(-1) s(-1). These values suggest an alternate route for the formation of compound II (by k'(13)) avoiding the step from compound I to compound II (k'(2)). In HbI from L. pectinata the stabilization of compound I is attribute to the unusual collection of amino acids residues (Q64, F29, F43, F68) in the heme pocket active site of the protein.

Amino Acids↗
PubMed1994

Superoxide reduction of a disulfide: a model of intracellular redox modulation?

Superoxide dismutase (SOD), which breaks down superoxide to oxygen and hydrogen peroxide, is generally considered an antioxidant enzyme. However, superoxide is a potent reducing agent and as such could affect cellular function by reducing disulfides in important proteins, such as, ionic channels and pumps. In support of this concept, we show that superoxide, generated by two different sources, is able to reduce disulfide bonds in an in vitro model. Depending on the source of superoxide this reduction is accelerated by an unsaturated fatty acid or ferric iron and is inhibited by SOD.

Arachidonic Acid↗
PubMed1995

Effects of taurine and hypotaurine on lipid peroxidation.

It has been suggested that hypotaurine might inhibit lipid peroxidation in vivo by scavenging the initiator OH. The results presented demonstrate that hypotaurine affects other reactions relevant to the initiation, propagation and termination phases of lipid peroxidation. Hypotaurine a) decreases Fe2+ autoxidation, either spontaneous or catalyzed by Fe3+, that may generate perferryl iron; b) decreases Fe2+ oxidation, by cumene hydroperoxide, that forms the alkoxy radical; c) inhibits the lipid hydroperoxide dependent lipid peroxidation, favoring the onset of the termination phase. Hypotaurine does not affect the autoxidation of Fe2+ bound to phosphatidic acid containing liposomes. Taurine is ineffective in all the experimental systems tested.

Dimyristoylphosphatidylcholine↗
PubMed1999

EPR detection of protein-derived radicals in the reaction of H(2)O(2) with Fe bound in mitochondrial F(1)ATPase.

A severe inactivation is obtained upon the addition of H(2)O(2) to bovine heart F(1)ATPase samples containing Fe(III) in the nucleotide-independent site, and Fe(II) in the ATP-dependent site. EPR spectra at 4.9 K of these samples indicate that H(2)O(2) produces the complete oxidation of Fe(II) to Fe(III) and the concomitant appearance of two protein-derived radical species. The two signals (g = 2.036 and g = 2.007) display a different temperature dependence and saturation behavior. The relaxation properties of the radical at g = 2.036 suggest magnetic interaction with one of the two iron centers. Such events are not observed when H(2)O(2) is added either to native F(1)ATPase containing a high amount of Fe(II) and low amount of Fe(III) or to F(1)ATPase deprived of endogenous Fe and subsequently loaded with only Fe(III) in both sites. It is hypothesized that in F(1)ATPase samples containing both Fe(III) and Fe(II), intramolecular long-range electron transfer may occur from Fe(II) to a high oxidation state species of Fe formed in the nucleotide-independent site upon oxidation of Fe(III) by H(2)O(2).

Animals↗
PubMed2000

Lipid peroxidation in small and large phospholipid unilamellar vesicles induced by water-soluble free radical sources.

The susceptibility of small and large egg yolk phosphatidylcholine unilamellar vesicles to Fe(2+)/histidine-Fe(3+)- and Fenton reagent (Fe(2+)-H(2)O(2))-induced lipid peroxidation was evaluated by measuring the formation of thiobarbituric acid reactive substances (TBARS). It has been found that surface curvature or phospholipid packing exerts significant effect on the oxidative susceptibility of the unsaturated lipid bilayers and the highly curved and loosely packed small unilamellar vesicles (SUVs) exhibit much less resistance to the oxidative stress induced by the water-soluble free radical sources. The presence of lipid hydroperoxides in sonicated vesicles was excluded as the cause for higher level of lipid peroxidation in the phospholipid SUVs. Instead, the experimental results can be explained by the difference in ability of the water-soluble oxidants to penetrate the two types of lipid membranes. This hypothesis is supported by data obtained from fluorescence lifetime and quenching studies.

Animals↗
PubMed2000

Preparation and initial characterization of the compound I, II, and III states of iron methylchlorin-reconstituted horseradish peroxidase and myoglobin: models for key intermediates in iron chlorin enzymes.

To better understand the spectral properties of high valent and oxyferrous states in naturally occurring iron chlorin-containing proteins, we have prepared the oxoferryl compound I derivative of iron methylchlorin-reconstituted horseradish peroxidase (MeChl-HRP) and the compound II and oxyferrous compound III states of iron MeChl-reconstituted myoglobin. Initial spectral characterization has been carried out with UV-visible absorption and magnetic circular dichroism. In addition, the peroxidase activity of iron MeChl-HRP in pyrogallol oxidation has been found to be 40% of the rate for native HRP. Previous studies of oxoferryl chlorins have employed tetraphenylchlorins in organic solvents at low temperatures; stable oxyferrous chlorins have not been previously examined. The present study describes the compound I, II, and III states of histidine-ligated iron chlorins in a protein environment for the first time.

Animals↗
PubMed1997

Microbial toxicity of Cd and Hg in different soils related to total and water-soluble contents.

Microbial toxicity tests with Cd and Hg and up to 18 soil samples were combined with sorption and solubility measurements. The data ought to indicate to what extent toxic effects of the metals are influenced by sorption and the other factors that may alter their biocidal action. The microbial reduction of Fe(III) oxides to Fe2+ ions was used as a parameter of microbial activity to calculate the total amounts of Cd and Hg that cause 10, 50, and 90% inhibition [effective doses (ED)10, ED50, ED90]. The corresponding solution concentrations [effective concentrations: (EC)10, EC50, EC90] were derived from Freundlich adsorption isotherms. The very large variability in ED values in different soils (ED10: Cd, 5-95 mg/kg; Hg, 0.125-125 mg/kg) can be related to the sorption and solubility behavior of the metals. Nevertheless, the EC values of both metals also indicate a considerable variation (EC10: Cd, 0.01-1.13 mg/liter; Hg, < 0.001-0.041 mg/liter). The influence of soluble soilborne substances on metal speciation is the main reason for their varying toxic potential in different soil solutions. The strong and complex influence of soil properties on the toxicity of heavy metals in soils indicates that both chemical and biological methods of soil analysis are needed to assess the risks of soil contamination adequately.

Bacteria↗
PubMed1996

Changes in antioxidative activities induced by Fe (II) and Fe (III) in cultured Vero cells.

The toxicity of iron (II) and iron (III) chlorides was studied at different biochemical and cellular levels, including antioxidative and metabolic enzymes and two general indicators of cytotoxicity in Vero monkey kidney cells after 24-h exposure. Iron (II) was fourfold more toxic than Fe (III) in cell proliferation, with EC50 of 5.5 and 22 mM, respectively. Metabolic markers were far more sensitive than cytotoxicity assays at these concentrations. At the highest concentrations of toxicant tested [10 mM Fe(II) and 50 mM Fe(III)], both species produced nearly total inhibition of the relative uptake of neutral red (RNRU) and phosphofructokinase activity (PFK), and stimulated intracellular specific lactate dehydrogenase activity (LDH). Succinate dehydrogenase (SDH) and hexosaminidase (HEX) activities were reduced in dose-dependent manner, as was the antioxidative enzyme glucose-6-phosphate dehydrogenase (G-6-PDH) with both forms of iron. Glutathione reductase (GOR) and glutathione-S-transferase (GST) activities were stimulated by Fe (II) but were inhibited by the higher Fe (III) concentrations. In conclusion, the experimental model may be useful for the study of different metabolic effects induced by the two oxidation states of iron.

Animals↗
PubMed1983

Possible contribution of oxyhemoglobin to the iron-induced hemolysis simultaneous effect of iron and hemoglobin on lipid peroxidation.

The mechanism of iron toxicity in iron overloaded patients is not well established. A hypothesis was put forward that free radical processes are involved. Our earlier study indicates that iron-induced hemolysis is preceded by peroxidation of the membrane lipids. In the present work the simultaneous effect of iron and hemoglobin on lipid peroxidation was studied. It was found that in hemoglobin-containing liposome suspensions Fe2+ in concentrations above 10(-5) M inhibits the peroxidation, while Fe3+ drastically potentiates it, with concomitant transformation of oxyhemoglobin to methemoglobin. The experiments with scavengers of activated oxygen indicate superoxide anion radical (O-.2), hydroxyl radical (OH.) and singlet oxygen (1O2) participation. The possible mechanism of the phenomenon is discussed. A conclusion is drawn that the toxic effect of Fe3+ may be associated not only with iron--membrane interaction, but also with increased methemoglobin formation and O-.2 release.

Animals↗
PubMed1995

The iron component of sodium nitroprusside blocks NMDA-induced glutamate accumulation and intracellular Ca2+ elevation.

These studies were designed to compare the effects of nitric oxide (NO) generating compounds with those of several iron containing compounds which do not generate NO on glutamate receptor function. Stimulation of primary cultures of cerebellar granule cells with N-methyl-D-aspartate (NMDA) or kainate results in the elevation of intracellular calcium ([Ca2+]i) and cGMP and the release of glutamate. The iron containing compounds, sodium nitroprusside (SNP), potassium ferrocyanide (K4Fe(CN)6) and potassium ferricyanide (K3Fe(CN)6) decrease the NMDA-induced release of glutamate. SNP is the only compound of the above 3 agents which generates NO. A non-iron, NO generating compound, S-nitroso-N-acetylpenicillamin (SNAP), has no effect on the NMDA-induced glutamate release. Potassium ferrocyanide (Fe II), but not potassium ferricyanide (Fe III), blocks NMDA-induced cGMP elevations after 3 min exposure times. This contrasts with the NO generating compounds (both SNP and SNAP) which elevate cGMP levels. Furthermore, both potassium ferrocyanide (Fe II) and SNP (Fe II) suppress the elevation of [Ca2+]i induced by NMDA but neither potassium ferricyanide (Fe III) nor SNAP are effective in this regard. These effects are also independent of cyanide as another Fe II compound, ferrous sulfate (FeSO4) is also able to suppress NMDA-induced elevations of [Ca2+]i. SNP was unable to suppress kainate receptor functions. Collectively, these results indicate that Fe II, independently of NO, has effects on NMDA receptor function.

Animals↗