Scope: The cytotoxic and genotoxic potential of phase II metabolites of resveratrol (RSV) was investigated in human colon cells with special emphasis on human topoisomerase (TOP) II.
Methods and results: Cell-free screening of topoisomerase II (TOPII) inhibition by the decatenation assay showed inhibitory potential for RSV (≥200 μM) and for the first time for the three human phase II metabolites RSV-3-sulfate (≥200 μM), RSV-3-glucuronide (≥100 μM) and RSV-disulfate (≥100 μM). Conjugation at the C4'-position (RSV-4'-sulfate and RSV-4'-glucuronide) resulted in loss of the inhibitory potential in this assay. Cell-based experiments with RSV and the most abundant metabolite in humans, RSV-3-Sulf, revealed no TOP poisoning in HT29 and Caco-2 cells up to 250 μM. Further, the phase II metabolite exhibited only minor effects in the comet assay and showed negligible cytotoxic effects and apoptotic potential after 1 and 24 h incubation. Fluorescence microscopy and HPLC-DAD analysis identified cellular uptake of RSV and of RSV-3-Sulf although to a lesser extent when compared to RSV. Furthermore, within the cells fractional deconjugation of RSV-3-Sulf to the parent compound was observed.
Conclusion: Sulfate- and glucuronide-phase II metabolites might contribute to the genotoxic potential of RSV by inhibition of TOPII activity. By deconjugation at the target site RSV-3-Sulf might serve as a pool of the parent compound.
Keywords: Colon cancer cells; DNA damage; Resveratrol; Resveratrol metabolites; Topoisomerase.
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