Journal article
Semiquinone radicals from oxygenated polychlorinated biphenyls: electron paramagnetic resonance studies
Chemical research in toxicology, Vol.21(7), pp.1359-1367
07/2008
DOI: 10.1021/tx8000175
PMCID: PMC2740386
PMID: 18549251
Abstract
Polychlorinated biphenyls (PCBs) can be oxygenated to form very reactive hydroquinone and quinone products. A guiding hypothesis in the PCB research community is that some of the detrimental health effects of some PCBs are a consequence of these oxygenated forms undergoing one-electron oxidation or reduction, generating semiquinone radicals (SQ (*-)). These radicals can enter into a futile redox cycle resulting in the formation of reactive oxygen species, that is, superoxide and hydrogen peroxide. Here, we examine some of the properties and chemistry of these semiquinone free radicals. Using electron paramagnetic resonance (EPR) to detect SQ (*-) formation, we observed that (i) xanthine oxidase can reduce quinone PCBs to the corresponding SQ (*-); (ii) the heme-containing peroxidases (horseradish and lactoperoxidase) can oxidize hydroquinone PCBs to the corresponding SQ (*-); (iii) tyrosinase acting on PCB ortho-hydroquinones leads to the formation of SQ (*-); (iv) mixtures of PCB quinone and hydroquinone form SQ (*-) via a comproportionation reaction; (v) SQ (*-) are formed when hydroquinone-PCBs undergo autoxidation in high pH buffer (approximately >pH 8); and, surprisingly, (vi) quinone-PCBs in high pH buffer can also form SQ (*-); (vii) these observations along with EPR suggest that hydroxide anion can add to the quinone ring; (viii) H 2 O 2 in basic solution reacts rapidly with PCB-quinones; and (ix) at near-neutral pH SOD can catalyze the oxidization of PCB-hydroquinone to quinone, yielding H 2 O 2. However, using 5,5-dimethylpyrroline-1-oxide (DMPO) as a spin-trapping agent, we did not trap superoxide, indicating that generation of superoxide from SQ (*-) is not kinetically favorable. These observations demonstrate multiple routes for the formation of SQ (*-) from PCB-quinones and hydroquinones. Our data also point to futile redox cycling as being one mechanism by which oxygenated PCBs can lead to the formation of reactive oxygen species, but this is most efficient in the presence of SOD.
Details
- Title: Subtitle
- Semiquinone radicals from oxygenated polychlorinated biphenyls: electron paramagnetic resonance studies
- Creators
- Yang Song - Department of Occupational and Environmental Health, The University of Iowa, Iowa City, Iowa 52242-1101, USABrett A WagnerHans-Joachim LehmlerGarry R Buettner
- Resource Type
- Journal article
- Publication Details
- Chemical research in toxicology, Vol.21(7), pp.1359-1367
- DOI
- 10.1021/tx8000175
- PMID
- 18549251
- PMCID
- PMC2740386
- NLM abbreviation
- Chem Res Toxicol
- ISSN
- 0893-228X
- eISSN
- 1520-5010
- Publisher
- United States
- Grant note
- P30 ES005605 / NIEHS NIH HHS R01 GM073929 / NIGMS NIH HHS K25ES012475 / NIEHS NIH HHS P42 ES013661 / NIEHS NIH HHS R01GM073929 / NIGMS NIH HHS P42ES013661 / NIEHS NIH HHS K25 ES012475 / NIEHS NIH HHS P30ES05605 / NIEHS NIH HHS
- Language
- English
- Date published
- 07/2008
- Academic Unit
- Occupational and Environmental Health; Iowa Neuroscience Institute; Radiation Oncology; Iowa Superfund Research Program
- Record Identifier
- 9984001096302771
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