Voprosy meditsinskoi khimii (ISSN 0042-8809)

Weak acid properties of hydroxylated naphthazarins and their reaction with superoxide anion-radical

   
Lebedev A.V., Ivanova M.V., Krasnovid N.I., Koltzova E. A.
PubMed Id: 10378300
Year: 1999 vol: 45  issue:2  pages: 123-130
Abstract: Weak acid properties, autoxidation and interaction of natural polyhydroxy1,4-naphthoquinones (PHNQ) with superoxide anion-radical (O2-· ) were studied by methods of potentiometric titration, polarography, and UV- and visible spectrophotometry. Sea urchin pigments 3-acetyl-2,6,7-trihydroxynaphthazarin (spinochrome C), 2,3,6,7-trihydroxynaphthazarin (spinochrome D), 2,3,6,7-trihydroxynaphthazarin (spinochrome E), 6-ethyl-2,3,7-trihydroxynaphthazarin (echinochrome A), synthetic 2,3-dihydroxy-6,7-dimethylnaphthazarin and 6-ethyl-2,3,7-trimethoxynaphthazarin (trimethoxyechinochrome A) were tested. Determined dissociation constants (pKi) were in the range of pH 5,3 - 8,5 (40% ethanol solvent). PHNQ autoxidation observrd in basic pH were inhibited by superoxide dismutase. Xanthine and xanthine oxidase was applied for O2-· generation. Interaction with O2-· led to sufficient time-dependent changing in spectra of echinochrome A , spinochromes D and E. There was weak O2-· influence on spinochrome C spectrum and no changing in trimethoxyechinochrome A spectrum. The spectra, that were transforming during time of reaction, contained pronounced isobestic point. It means formation the single reaction product. We proposed formation of 1,2,3,4-tetraketones from 2,3,5,8-tetrahydroxy-1,4-naphthoquinones (echinochrome A , spinochromes D and E) due to O2-· -induced oxidation of their OH-groups in 2 and 3 positions. Reaction constants were determined by competition method using nitro blue tetrazolium (NBT). The reaction constants were about 104 – 105 M-1s-1. They were decreased in the order: echinochrome A > spinochrome D > spinochrome C > NBT > trimethoxyechinochrome A. Thus, we concluded that some of the natural PGNQ, containing hydroxyl groups in 2nd and 3rd positions, could operate as powerful superoxide anion-radical scavengers. Recent studies have shown that the phenomenon of ethanol preference by animals and of alcohol consumption by humans may be related to the intensity of its metabolism in the body and depend on the activities of the ethanol and aldehyde metabolizing systems which are potential regulators of the acetaldehyde level in the cell. The special features of adaptative reactions of this system (alcohol dehydrogenase, microsomal ethanol oxidizing system, catalase, aldehyde dehydrogenase) were examined in rats, differing by the preference to water or ethanol (5%, 10%, 15%) under condition of a long contact with alcohol.
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Reference: Lebedev A.V., Ivanova M.V., Krasnovid N.I., Koltzova E. A., Weak acid properties of hydroxylated naphthazarins and their reaction with superoxide anion-radical, Voprosy meditsinskoi khimii, 1999, vol: 45(2), 123-130.
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