Myricetin affords protection against peroxynitrite-mediated DNA damage and hydroxyl radical formation

2011 ◽  
Vol 49 (9) ◽  
pp. 2439-2444 ◽  
Author(s):  
Wei Chen ◽  
Yudong Li ◽  
Jianrong Li ◽  
Qiang Han ◽  
Libin Ye ◽  
...  
Keyword(s):  
Dna Damage ◽  
Hydroxyl Radical ◽  
Radical Formation

scholarly journals Intracellular Copper Does Not Catalyze the Formation of Oxidative DNA Damage in Escherichia coli

2006 ◽  
Vol 189 (5) ◽  
pp. 1616-1626 ◽  
Author(s):  
Lee Macomber ◽  
Christopher Rensing ◽  
James A. Imlay
Keyword(s):  
Escherichia Coli ◽  
Dna Damage ◽  
Hydroxyl Radical ◽  
Oxidative Dna Damage ◽  
Copper Toxicity ◽  
Radical Formation ◽  
Pcr Analysis ◽  
Intracellular Copper

ABSTRACT Because copper catalyzes the conversion of H2O2 to hydroxyl radicals in vitro, it has been proposed that oxidative DNA damage may be an important component of copper toxicity. Elimination of the copper export genes, copA, cueO, and cusCFBA, rendered Escherichia coli sensitive to growth inhibition by copper and provided forcing circumstances in which this hypothesis could be tested. When the cells were grown in medium supplemented with copper, the intracellular copper content increased 20-fold. However, the copper-loaded mutants were actually less sensitive to killing by H2O2 than cells grown without copper supplementation. The kinetics of cell death showed that excessive intracellular copper eliminated iron-mediated oxidative killing without contributing a copper-mediated component. Measurements of mutagenesis and quantitative PCR analysis confirmed that copper decreased the rate at which H2O2 damaged DNA. Electron paramagnetic resonance (EPR) spin trapping showed that the copper-dependent H2O2 resistance was not caused by inhibition of the Fenton reaction, for copper-supplemented cells exhibited substantial hydroxyl radical formation. However, copper EPR spectroscopy suggested that the majority of H2O2-oxidizable copper is located in the periplasm; therefore, most of the copper-mediated hydroxyl radical formation occurs in this compartment and away from the DNA. Indeed, while E. coli responds to H2O2 stress by inducing iron sequestration proteins, H2O2-stressed cells do not induce proteins that control copper levels. These observations do not explain how copper suppresses iron-mediated damage. However, it is clear that copper does not catalyze significant oxidative DNA damage in vivo; therefore, copper toxicity must occur by a different mechanism.

scholarly journals 1,10-Phenanthroline stimulates internucleosomal DNA fragmentation in isolated rat-liver nuclei by promoting the redox activity of endogenous copper ions

1996 ◽  
Vol 313 (1) ◽  
pp. 163-169 ◽  
Author(s):  
Mark J. BURKITT ◽  
Lesley MILNE ◽  
Pierluigi NICOTERA ◽  
Sten ORRENIUS
Keyword(s):  
Hydrogen Peroxide ◽  
Dna Damage ◽  
Hydroxyl Radical ◽  
Dna Fragmentation ◽  
Rat Liver ◽  
Radical Formation ◽  
Complexing Agents ◽  
Isolated Rat Liver ◽  
Liver Nuclei ◽  
Isolated Rat

Isolated rat-liver nuclei were incubated with a series of membrane-permeable metal-ion-complexing agents and examined for DNA damage. Of the reagents tested, only 1,10-phenanthroline (OP) and neocuproine (NC) were found to induce DNA fragmentation. Agarose-gel electrophoresis of the DNA fragments generated in the presence of OP revealed internucleosomal cleavage, which is widely considered to be a hallmark for the enzymic DNA digestion that occurs during apoptosis. Ascorbate, particularly in the presence of hydrogen peroxide, increased the levels of fragmentation induced by OP. As well as undergoing fragmentation, the DNA from nuclei was also found to contain 8-hydroxydeoxyguanosine, which indicates attack (oxidation) by the hydroxyl radical. Complementary experiments in vitro involving ESR determinations of hydroxyl radical formation and measurements of DNA oxidation under biomimetic conditions demonstrated that Cu2+, but not Fe3+, forms a complex with either OP or NC (but not the other complexing agents tested) that stimulates hydroxyl radical formation and DNA damage in the presence of hydrogen peroxide and ascorbate. It is therefore proposed that OP in the nuclei incubations binds to Cu2+, which exists naturally in chromosomes, forming a complex that promotes hydroxyl-radical-dependent DNA fragmentation. These findings demonstrate the promotion of hydroxyl-radical-mediated DNA damage by endogenous Cu2+ and, perhaps more significantly, demonstrate that the internucleosomal DNA ‘laddering’ that is often used as an indicator of apoptosis may also result from DNA fragmentation by non-enzymic processes.

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