Cell cycle disturbance in relation to micronucleus formation induced by the carcinogenic estrogen diethylstilbestrol

Micronuclei as a biological endpoint for genotoxicity: A minireview

The in vitro micronucleus assay has now been applied in many laboratories. This endpoint is useful in biomonitoring or ecotoxicology, as a sensitivity measure of human cells in cancer treatment and also to replace or supplement other in vitro genotoxicity assays. Learning more about the mechanisms of micronucleus formation allows conclusions about its biological significance. It has been demonstrated that disturbance of the mitotic apparatus (spindle, kinetochores) as well as impaired function of topoisomerase II can be involved in micronucleus formation. In addition, the roles of changes in DNA-conformation that are induced by alterations in the status of cytosine-methylation and of the cellular DNA repair capacity have been shown. The fate of micronucleus-containing cells is not known: the cells may theoretically be cytostatic and micronucleus-formation may therefore be a way of the organism to eliminate genetic damage or the cells may survive the loss of that chromosomal material and develop into transformed cells. Published data and ideas of selected areas within this field are reviewed.

Hormonal and genotoxic activity of resveratrol

Resveratrol (RES) is a natural polyphenol present in red wines and various human food items. The estrogenic activity of RES was demonstrated in two in vitro assay systems, i.e. binding to human estrogen receptor alpha and stimulation of MCF-7 cell proliferation. To investigate the inhibition of cell proliferation observed at high concentrations of RES, we analyzed the compound for genotoxic potential. RES induced cellular toxicity, micronuclei, and metaphase chromosome displacement in L5178Y mouse lymphoma cells. Likewise, the induction of micronuclei was observed in Chinese hamster V79 cells. Determination of kinetochore signals in micronuclei and cell cycle analysis suggested that RES did not cause a direct disturbance of mitosis. In support of this notion, cell-free tubulin polymerization studies indicated no direct effect of RES on microtubule assembly. According to an estimation of daily intake and bioavailability, concentrations that were found genotoxic in vitro might be reached in human exposure. On the other side, the estrogenic acitivity might be beneficial. Therefore, further investigations of mechanisms, possibly including animal models, would be desirable to clarifiy a potential risk for humans.

Micronucleus induction by neocarzinostatin and methyl methanesulfonate in ionizing radiation--sensitive Chinese hamster V79 cell mutants

Two mutant V79 Chinese hamster cell lines (V-E5, XR-V15B) which show hypersensitivities to DNA damage and their two parental cell lines (V79-LE, V79-B) were used for micronucleus studies. The characteristics of V-E5 strongly resemble those of cells derived from patients suffering from the genomic instability syndrome ataxia telangiectasia, whereas XR-V15B has a decreased ability to rejoin double-strand breaks. The two cell lines V-E5 and XR-V15B showed increased spontaneous micronucleus frequencies and higher sensitivity for micronucleus induction by methyl methanesulfonate (MMS) and neocarzinostatin (NCS) both with and without the use of cytochalasin B in the micronucleus assay. Thus, defects in cellular responses to DNA damage are modulating factors in micronucleus formation.