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W Bors

Publications and source records attributed to W Bors.

At least 19 recordsLinked to original sources
PubMed1995

Interaction of flavonoids with ascorbate and determination of their univalent redox potentials: a pulse radiolysis study.

Concurrent pulse-radiolytic generation of flavonoid aroxyl radicals and ascorbyl radicals causes a complex kinetic interplay of competing and parallel reactions. Evaluation by "kinetic modelling," that is, taking into account all possible reactions by a set of differential equations, allowed us to determine equilibria constants for the univalent steps by a novel method. From these kinetic data we were able to calculate the redox potentials for dihydroquercetin, quercetin, rutin (a quercetin 3-glycoside), kaempferol, fisetin, and luteolin. Despite the limited number of substances, two structural criteria became apparent: all substances containing the B-ring catechol group and the 2,3-double bond have a higher redox potential than ascorbate and are consequently able to oxidize it to the ascorbyl radical. With fisetin and kaempferol having values very similar to ascorbate, only the flavanone dihydro-quercetin was capable of reducing the ascorbyl radical, thus fulfilling the so-called "ascorbate-protective" function, originally proposed by Szent-Györgyi. While flavonoids are effective radical scavengers, these rather high redox potentials for most flavonols may explain their occasional prooxidative behavior.

Ascorbic Acid↗
PubMed1994

Signalling by O2-. and NO.: how far can either radical, or any specific reaction product, transmit a message under in vivo conditions?

With regard to the stability of the NO. radical as a chemical entity, it is without doubt able to serve as an intra- as well as an intercellular messenger. The radical O2-., in contrast, does not seem to be suited to far-range signalling in the vascular system. Its short chemical half-life, which is limited by the presence of various reactive blood constituents to below 50 ms, results in a free diffusion path length of less than 40 microns, i.e. only the distance between just a few cells. While accelerated 'downstream' transport by arterial blood may help to extend the action sphere, there is no possibility for O2-. to serve as a signal in an upstream direction. The estimates presented, however, do not invalidate arguments for a possible role of superoxide anions in intra- or pericellular signalling phenomena. Cross-talk between NO.- and O2-.-dependent signal routes, e.g. by peroxynitrite formation, is unlikely to be a relevant process under the conditions which prevail in the vascular system.

Blood Circulation↗
PubMed1993

Lack of an association between serum vitamin E and myocardial infarction in a population with high vitamin E levels.

The antioxidant effects of vitamin E may protect low density lipoproteins from peroxidation and thus inhibit the development of arteriosclerosis. Inverse associations between vitamin E levels and coronary heart disease have been reported from cross-sectional and ecologic studies. In the population-based MONICA Augsburg cohort (2023 men, 1999 women, age 25-64 years at baseline in 1984, 93% of whom were reexamined in 1987/88) we investigated the relationship between serum vitamin E concentrations and the risk of subsequent myocardial infarction (MI). Between 1984 and 1991, 46 cases of fatal and non-fatal myocardial infarction from this cohort were recruited for a nested case-control study. Four controls were sampled from the cohort for each case of MI with matching for age, sex, and total cholesterol. There were no marked differences between cases and their matched controls in the means of vitamin E concentrations (33.9 mumol/l vs. 32.8 mumol/l, P = 0.37) or in the mean vitamin E/total cholesterol ratios (4.89 mumol/mmol vs. 4.82 mumol/mmol, P = 0.75). The covariate adjusted relative risk (RR) for fatal plus non-fatal MI in the lowest tertile of vitamin E relative to the upper two tertiles was 0.72 (90% confidence interval: 0.33-1.57). Likewise, for the lowest tertile of the ratio (vitamin E/total cholesterol) the RR was 0.81 (0.42-1.56). The association was not modified by history of previous coronary heart disease, fatality of MI, temporal distance of MI onset from vitamin E determinations, or season.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

On the cytotoxicity of irradiated media. To what extent are stable products of radial chain reactions in physiological saline responsible for cell death?

In a previous publication (Czapski et al. 1992) we reported that HOCl accounts for the toxicity of irradiated phosphate-buffered saline towards Escherichia coli bacterial cells. We have now investigated the respective toxicities towards lambda phage and mammalian cells. For phage, as with bacteria, cytotoxicity of the irradiated media seems to derive from HOCl without detectable contribution of H2O2. Mammalian cells (V79 CHO), in contrast, are more sensitive to H2O2 than to HOCl. Both agents, however, are not able to account quantitatively for the toxicity of irradiated solutions towards V79 cells; a hitherto unidentified chlorine/oxygen derivative--being formed in the sub-micromolar concentration range--is suggested to be responsible for toxicity in the case of eukaryotes.

Animals↗
PubMed1991

Direct and indirect measurements of oxygen radicals.

Instead of covering the available detection methods in detail it is attempted to highlight the ambiguities inherent in oxygen radical detection under in vivo conditions. Due to physicochemical properties of the oxygen molecule, all organic matter is bound to autoxidize. From this it follows that a certain 'background' level of oxygen radical production will always be present and that it may be difficult to differentiate between inherent and induced oxygen radical production. Radicals by their very nature react 'unspecifically'. This infers that it is difficult to identify them unequivocally. The most common methods for oxygen radical detection are briefly mentioned.

Animals↗
PubMed1991

An expanded function for superoxide dismutase.

alpha-Hydroxyalkylperoxyl radicals were generated from the primary and secondary alcohols methanol, ethanol and 2-propanol in N2O/O2-saturated aqueous solutions by pulse radiolysis. These radicals reduced a ferric iron porphyrin complex, tetrakis-(4-N-methylpyridyl)porphine, with diffusion-controlled rate constants. The extreme sensitivity of the shift of the Soret absorption band in this reaction was used to determine, by competition kinetics, the reactivity of the peroxyl radicals with different proteins. Only native Cu,Zn-superoxide dismutase and metallothionein showed competitive behavior, with SOD exhibiting rate constants close to the dismutation rate for O2-. Metallothionein was slower by a factor of 30 with hydroxymethylperoxyl radicals. We propose, that SOD has unique properties of the protein surface in addition to the prosthetic copper site, having possibly evolved as a 'general-purpose radical-scavenging protein'.

Alcohols↗
PubMed1990

Radical reactions in vivo--an overview.

Generation of radicals in vivo depends on metabolic activities. The reactions are usually influenced by (i) the presence and concentration of oxygen; (ii) the availability of transition metals (effects of binding and compartimentalization); (iii) the level of reductants and antioxidants (e.g. nutritional effects). The effects of radicals are thought to be due to (i) membrane damage (affecting passive or active transport through altered fluidity/function interrelationships, intercellular messenging through modifications in the synthesis of prostaglandins and leukotrienes); (ii) protein damage (e.g. affecting membrane transporters, channel proteins, receptor or regulatory proteins, immunomodulators); (iii) damage to DNA. Defense mechanisms consist of (i) prevention of the 'spreading' of primary damage by low molecular weight antioxidants (e.g. vitamin E, GSH, vitamin C, beta-carotene, uric acid); (ii) prevention or limitation of 'secondary' damage by enzymes (e.g. GSH-peroxidase, catalase, superoxide dismutase, DT-diaphorase) and/or chelators; (iii) repair processes, e.g. lipid degradation/membrane repair enzymes (phospholipases, peroxidases, some transferases and reductases), protein disposal or repair enzymes (proteases, GSSG-reductase), DNA degradation repair enzymes (exonuclease III, endonucleases III and IV, glycosylases, polymerases). Recent hypotheses on a messenging function of the superoxide anion O2- are discussed and possible implications of cross-reactions between O2- and nitric oxide (endothelium-derived relaxing factor EDRF) are shortly mentioned.

Antioxidants↗
PubMed1990

Calcium in lipid peroxidation: does calcium interact with superoxide?

Using a pulse radiolysis approach to generate and observe superoxide anions (O2-.) in the absence and presence of calcium, we have attempted to verify the recent hypothesis of Babizhayev (Arch. Biochem. Biophys. 266, 446-451, 1988) of a Ca2(+)-O2-. interaction during lipid peroxidation. We could not observe rapid scavenging of O2-. or complex formation with Ca2+ to account for an inhibitory effect of this cation on lipid peroxidation. Neither could we agree that the stimulatory effect is due to liberation of catalytic ferrous iron from weak complexes by Ca2+. Drawing on reports in the literature, we propose an alternate explanation for the apparent stimulation of lipid peroxidation by low Ca2+ concentrations. In our view, this is not a direct effect, but reflects independently initiated processes of lipid peroxidation and Ca2+ translocation, which interact subsequently in a synergistic manner. The reported inhibition at high Ca2+ concentrations is considered an artifact as it was observed at levels far in excess of those relevant to animal systems (but not necessarily in some plant compartments).

Acetates↗
PubMed1990

Reaction of NO with O2-. implications for the action of endothelium-derived relaxing factor (EDRF).

Under physiological pH conditions (pH 7.2-7.4) the rate constant of the reaction NO + O2- yielding peroxonitrite (ONOO-) was determined as k = (3.7 +/- 1.1) x 10(7) M-1 s-1. The decay of peroxonitrite at this pH follows first order kinetics with a rate constant of 1.4 s 1. At alkaline pH peroxonitrite is practically stable. Possible consequences of these reactions for the biological lifetime of EDRF will be discussed.

Hydrogen-Ion Concentration↗
PubMed1990

Characterization of Cat-2t, a radiation-induced dominant cataract mutation in mice.

A dominant cataract mutation was detected recently among the offspring of x-ray-irradiated male mice. The mutation, which causes total lens opacity, has provisionally been designated by the gene symbol Cat-2t. In the lenses of heterozygous and homozygous Cat-2t mutants, the epithelial and fiber cells were swollen and the lens capsule was ruptured. The histologic analysis demonstrated a complete destruction of the cellular organization of the lens, which might be caused by its altered developmental processes. The data derived from biochemical investigations indicate that biochemistry of the cataractous Cat-2t lenses is affected: the osmotic state as indicated by the increased water content and increased Na(+)-K(+)-adenosinetriphosphatase (ATPase) activity; the energy state as indicated by the decreased adenosine triphosphate (ATP) concentration; and the redox state as indicated by the enhanced content of oxidized glutathione. Additionally, the lenticular protein composition is altered because of the presence of vimentin in the water-soluble fraction. This cannot be explained by the enhanced crosslinking activity of transglutaminase. The changes of the osmotic, energy, and redox states are considered to be secondary in relation to the altered lenticular development. In contrast, the variations concerning vimentin and transglutaminase might be a biochemical indication of the changed development. Possible similarities to other dominantly expressed murine cataract mutants are discussed.

Adenosine Triphosphate↗
PubMed1989

Biochemical analysis of young rats homozygous for the cataract mutation cat.

Cataractogenesis was studied in young rats homozygous for the radiation-induced recessive cataract mutation cat. Homozygous cat/cat rats have reduced body weight (about two-thirds of the wild type) when 3 weeks old. The litter size is also diminished to about two-thirds of the wild type. For lens-specific parameters, as compared with homozygous wild type, the wet weight of the cataractous lenses is reduced, although the concentration of water-soluble lens proteins per wet weight is the same. No major alterations could be detected in the pattern of the water-soluble lens proteins separated by isoelectric focusing or gel electrophoresis run with or without mercaptoethanol. Additionally, no statistically significant alterations could be detected in the biochemical parameters of the lens used as indicators for osmotic stress (water content of the lens and the Na+-K+-dependent ATPase), for the energy state (ATP) and for the redox state (oxidized glutathione and superoxide dismutase). In contrast, the activity of transglutaminase is significantly enhanced in lenses as well as in the liver of young cat-rats, which might be understood as a biochemical marker for alterations in the developmental program. Cataractogenesis in the cat-rat is, therefore, suggested to be part of a syndrome including dwarfism and reduced litter size.

Adenosine Triphosphatases↗
PubMed1989

Oxidative stress and inherited cataracts in mice.

To determine whether an unbalanced redox state might accompany the development of particular inherited mouse cataracts, the lenticular content of oxidized glutathione (GSSG) and the activity of superoxide dismutase (SOD) were chosen as markers. For wild-type lenses, an enhanced GSSG content could be observed in females as compared to males. Such a sex effect could not be detected for the SOD activity. In the mutants, GSSG content in cataractous lenses was found to be enhanced in 2 of 7 cases; the increases in other mutants were not significant. Changes of the SOD activity were even less consistent and only a random correlation of GSSG content and SOD activity with cataractogenesis could be deduced.

Animals↗
PubMed1989

The mechanism of cytochrome C reduction by alkyl radicals. Evidence for multiple reaction pathways.

The reactions of the hydroxyalkyl radicals .CH2OH and (CH3)2.COH with oxidized cytochrome c are for more complex than previously reported. Analysis of the pulse-radiolytic data by kinetic modelling revealed that only about 40% of the alkyl radicals reduce the ferric iron chromophore. Altogether, four different reactions have to be considered for the disappearance of the alkyl radicals, only two of which affect the metal site. The data show that these radicals, similar to the much more reactive hydrated electrons and hydrogen atoms, are capable to react with biological macromolecules in diverse ways.

Cytochrome c Group↗
PubMed1989

Oxygen radicals acting as chemical messengers: a hypothesis.

Based on a critical reappraisal of the reactions of radicals in a biological milieu, a hypothesis is proposed according to which superoxide anion radicals act as biological messengers rather than as mediators or precursors of cellular damage under oxidative stress conditions.

Animals↗
PubMed1988

A critical reevaluation of some assay methods for superoxide dismutase activity.

We have compared the direct method of pulse radiolysis to the indirect methods of cytochrome c and nitroblue tetrazolium for assaying the superoxide dismutase activity of a compound. We have shown that with pulse radiolysis, where high concentrations of O2- are generated, the "turnover" rate constant, kcat, can be determined directly, while with the indirect methods, where relatively low steady state concentrations of O2- are formed, the value of kcat determined by these methods, can be orders of magnitude lower than that determined directly. The main reason for the lower values obtained with the indirect methods is due to the fast reoxidation of the reduced compound by molecular oxygen. Additional problems which arise with the use of indirect methods for determining superoxide dismutase catalytic activity are discussed.

Copper↗