Quantitative structure–activity relationships in prooxidant cytotoxicity of polyphenols: Role of potential of phenoxyl radical/phenol redox couple
Section snippets
Enzyme kinetic studies
All the compounds and enzymes were obtained from Sigma, and used without further purification. The concentration of horseradish peroxidase (HRP) and myeloperoxidase (MPO) was determined spectrophotometrically according to ε402 = 102 mM−1 cm−1, and ε430 = 91 mM−1 cm−1[45], respectively. The kinetic measurements were carried out spectrophotometrically, using a Hitachi-557 spectrophotometer, in 0.1 M K-phosphate buffer (pH 7.0) containing 1 mM EDTA at 25 °C. The rates of MPO-catalyzed oxidation of
Results
The concentrations of polyhydroxybenzenes and flavonoids causing 50% death of FLK and HL-60 cells (cL50) determined in the present study or partly taken from our previous work [24], their single-electron oxidation potentials, determined by pulse radiolysis at pH 7.0 , and their calculated octanol/water distribution coefficients at pH 7.0 (log D) are given in Table 1. In reversible oxidation of hydroquinones and catechols to quinones, refers to semiquinone/hydroquinone redox couple. For
Discussion
The data of our study demonstrate that polyphenols exert the prooxidant character of cytotoxicity in FLK and HL-60 cells (Fig. 3A), which is at least partly attributed to the autooxidation of polyphenols in cell growth media, i.e., the formation of extracellular H2O2[25], [26] (Figs. 3A and B). However, the cytotoxicity of polyphenols is also affected by their intracellular activation, as it is indicated by the effects of the inhibitors of cytochromes P-450 and COMT (Figs. 4A–D). Thus, their
Acknowledgments
This work was supported in part by the Lithuanian Science and Studies Foundation (program FUINMAKOSA). We thank Dr. Florence Lederer (CNRS, Gif-sur-Yvette, France) for the access to a stopped-flow spectrophotometer, and Drs. Jonas Šarlauskas and Žilvinas Anusevičius (Institute of Biochemistry), and Mr. Vladimir Koršunov (Institute of Immunology) for the excellent technical assistance.
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