As2O3 oxidation by vitamin C: cell culture studies |
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Authors: | Andreja Zelenik Pevec Zdenka ?lejkovec Johannes T van Elteren Ingrid Falnoga |
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Institution: | (1) Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia;(2) National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia; |
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Abstract: | The ability of As2O3 to induce apoptosis in various malignant cell lines has made it a potential treatment agent for several malignancies. In
this study the chemical stability of As2O3 (As(III)) in cell-free growth media with various compositions was studied (MEM with different amount of amino acids and DMEM).
Special attention was given to evaluate the influence of serum (FBS; fetal bovine serum) absence and vitamin C addition on
the oxidation of As(III) to As(V) in cell-free growth media. FBS is an important source of antioxidants and vitamin C (ascorbic
acid) is acting as a prooxidant in millimolar concentrations. Media were incubated with As(III) (0.6, 2 and 7 μmol l−1) up to 72 h. Experiments were performed at 37°C in light or/and in the dark, with or without added serum (10%) or vitamin
C (1.4, 0.14 mM). Metabolites were followed with high-performance liquid chromatography directly coupled to a hydride generation-atomic
fluorescence spectrometry system. After 72 h up to 30% of As(III) was transformed into As(V) in MEMs and up to 35% in DMEM
when exposed in dark. Light had no influence on transformations in MEMs, but changed the situation dramatically in DMEM where
almost all As(III) was oxidized to As(V) after 72 h when exposed to light. Except for some faster oxidation rate the absence
of FBS had little effect on the transformation rate in all media. The most visible impact on As(III) oxidation was observed
by addition of vitamin C. Addition of vitamin C (1.4 mM) transformed almost all As(III) to As(V) within 72 h. In lower concentrations
(0.14 mM) a pro-oxidative effect was still observed reaching approximately 60% oxidation of As(III) during 72 h. All oxidation
processes could be explained by pseudo first order reaction kinetics, yielding reaction rates increasing with initial As(III)
concentration and vitamin C concentration whereas the FBS content additionally increased the As(III) oxidation rate in the
DMEM (light). The temporal oxidation of As(III) to As(V) in various cell-free growth media necessitates routine checking of
the valence state of arsenic during cell culture experiments and the results of biological effects attributed to As(III) should
be interpreted with caution. Special attention is needed particularly in cases with vitamin C which was acting pro-oxidatively
in all conditions examined. |
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