Recommendations and quality criteria for micronucleus studies with humans.

Micronucleus (MN) analyses in peripheral blood lymphocytes and exfoliated cells from different organs (mouth, nose, bladder and cervix) are at present the most widely used approaches to detect damage of genetic material in humans. MN are extranuclear DNA-containing bodies, which can be identified microscopically. They reflect structural and numerical chromosomal aberrations and are formed as a consequence of exposure to occupational, environmental and lifestyle genotoxins. They are also induced as a consequence of inadequate intake of certain trace elements and vitamins. High MN rates are associated with increased risk of cancer and a range of non-cancer diseases in humans. Furthermore, evidence is accumulating that measurements of MN could be a useful tool for the diagnosis and prognosis of different forms of cancer and other diseases (inflammation, infections, metabolic disorders) and for the assessment of the therapeutic success of medical treatments. Recent reviews of the current state of knowledge suggest that many clinical studies have methodological shortcomings. This could lead to controversial findings and limits their usefulness in defining the impact of exposure concentrations of hazardous chemicals, for the judgment of remediation strategies, for the diagnosis of diseases and for the identification of protective or harmful dietary constituents. This article describes important quality criteria for human MN studies and contains recommendations for acceptable study designs. Important parameters that need more attention include sufficiently large group sizes, adequate duration of intervention studies, the exclusion of confounding factors which may affect the results (sex, age, body mass index, nutrition, etc.), the evaluation of appropriate cell numbers per sample according to established scoring criteria as well as the use of proper stains and adequate statistical analyses.

Impact of infections, preneoplasia and cancer on micronucleus formation in urothelial and cervical cells: A systematic review.

Approximately 165,000 and 311,000 individuals die annually from urothelial (UC) and cervical (CC) cancer. The therapeutic success of these cancers depends strongly on their early detection and could be improved by use of additional diagnostic tools. We evaluated the current knowledge of the use of micronucleus (MN) assays (which detect structural and numerical chromosomal aberrations) with urine- (UDC) and cervix-derived (CDC) cells for the identification of humans with increased risks and for the diagnosis of UC and CC. Several findings indicate that MN rates in UDC are higher in individuals with inflammation and schistosomiasis that are associated with increased prevalence of UC; furthermore, higher MN rates were also found in CDC in women with HPV, Candidiasis and Trichomonas infections which increase the risks for CC. Only few studies were published on MN rates in UDS in patients with UC, two concern the detection of recurrent bladder tumors. Strong correlations were found in individuals with abnormal CC cells that are scored in Pap tests and histopathological abnormalities. In total, 16 studies were published which concerned these topics. MN rates increased in the order: inflammation < ASC-US/ASC-H < LSIL < HSIL < CC. It is evident that MNi numbers increase with the risk to develop CC and with the degree of malignant transformation. Overall, the evaluation of the literature indicates that MNi are useful additional biomarkers for the prognosis and detection of CC and possibly also for UC. In regard to the diagnosis/surveillance of UC, further investigations are needed to draw firm conclusions, but the currently available data are promising. In general, further standardization of the assays is needed (i.e. definition of optimal cell numbers and of suitable stains as well as elucidation of the usefulness of parameters reflecting cytotoxicity and mitotic activity) before MN trials can be implemented in routine screening.

Micronucleus formation kinetics in buccal mucosa cells of head and neck cancer patients undergoing radiotherapy.

In head and neck cancer, radiotherapy is one of the main treatment modalities besides surgery and chemotherapy either in a primary or an adjuvant setting. Radiation kills tumor cells by damaging the DNA within these cells. One of the methods to assess the degree of genomic damage is the micronucleus (MN) test. The effect of radiation therapy on the MN frequency in buccal mucosa cells has only been investigated in small studies looking at single time points or including a limited number of patients. In the present study, normal tissue buccal mucosa cells from 17 patients were analyzed for genomic damage at four different time points during radiation therapy. A clear increase was observed for every time point. Additionally, buccal mucosa cells of a cohort of 16 patients were analyzed after the end of the therapy and compared to samples from 25 patients sampled before the therapy. 10 healthy controls were included, of which 5 were sampled once, and 5 were sampled four times similar to the patients. Also, the influence of additional chemotherapy was investigated. No difference was observed between radiation-only patients and patients receiving additional chemotherapy. Age, gender, and tumor stage did not have an influence on the MN formation kinetics.

Terahertz radiation induces spindle disturbances in human-hamster hybrid cells.

The aim of this study was to investigate and quantify the production of spindle disturbances in A(L) cells, a human-hamster hybrid cell line, by 0.106 THz radiation (continuous wave). Monolayer cultures in petri dishes were exposed for 0.5 h to 0.106 THz radiation with power densities ranging from 0.043 mW/cm(2) to 4.3 mW/cm(2) or were kept under sham conditions (negative control) for the same period. As a positive control, 100 µg/ml of the insecticide trichlorfon, which is an aneuploidy-inducing agent, was used for an exposure period of 6 h. During exposure, the sample containers were kept at defined environmental conditions in a modified incubator as required by the cells. Based on a total of 6,365 analyzed mitotic cells, the results of two replicate experiments suggest that 0.106 THz radiation is a spindle-acting agent as predominately indicated by the appearance of spindle disturbances at the anaphase and telophase (especially lagging and non-disjunction of single chromosomes) of cell divisions. The findings in the present study do not necessarily imply disease or injury but may be important for evaluating possible underlying mechanisms.

Aldosterone causes DNA strand breaks and chromosomal damage in renal cells, which are prevented by mineralocorticoid receptor antagonists.

Epidemiological studies exploring the connection between hypertension and cancer incidence find a higher cancer mortality in hypertensive patients, particularly elevated in hypertension associated with a stimulation of the renin-angiotensin-aldosterone system. Primary aldosteronism, with plasma aldosterone levels between 0.5 and 1 nM (18-36 ng/dL) and local aldosterone levels up to 500 nM (18,000 ng/dL), is now recognised as a more common cause for hypertension. We recently found angiotensin II to be genotoxic due to its induction of oxidative stress. Since aldosterone in higher concentrations also has oxidative effects, its potential genotoxic action in pig LLC-PK1 cells with properties of proximal tubules was analysed. DNA damage was evaluated by two test systems: the comet assay, and the micronucleus frequency test. The results showed that aldosterone concentrations starting from 10 nM (360 ng/dL) caused a significant increase of DNA damage monitored with the comet assay in LLC-PK1, while there was no change in cell vitality and proliferation. The micronucleus frequency test revealed that 10 nM aldosterone also leads to the formation of micronuclei. Furthermore, the formation of superoxide radicals in the cells by this aldosterone concentration could be detected with the superoxide-specific stain dihydroethidium. Further evidence for oxidative stress-induced DNA damage was its reversibility by the antioxidants tempol and catalase. Addition of the steroidal mineralocorticoid receptor antagonist spironolactone or the novel selective nonsteroidal antagonist (R)-BR-4628 reduced the DNA damage and the amount of superoxide radicals indicating a receptor-dependent process.

Brief review of available evidence concerning the potential induction of genomic damage by methylphenidate.

Children affected by attention deficit/hyperactivity disorder are often treated with methylphenidate (MPH). Two years ago, an increase in genomic damage after 3 months of MPH treatment was reported by researchers from Texas, U.S.A., raising concern about potential carcinogenic effects. In a similar investigation conducted in Wuerzburg, Germany, we did not find a comparable elevation of genomic damage. MPH is not genotoxic in standard test systems, but yielded one positive result in a rodent carcinogenicity study at the highest test dose only (60-fold above therapeutic doses). In conclusion, changes in treatment strategies do not seem justified currently. Larger studies are under way and will hopefully eliminate any remaining doubt about potential genotoxic or carcinogenic consequences of MPH treatment.

Homocysteine exerts genotoxic and antioxidative effects in vitro.

INTRODUCTION: Patients with end-stage renal disease suffer from increased genomic damage and cancer incidence. One possible reason is the accumulation of uremic toxins such as homocysteine (Hcy). Elevated Hcy levels--usually indicative of cardiovascular events--correlated with the genomic damage in cross-sectional studies. Therefore we investigated the genotoxic effects of Hcy in vitro. METHODS: To analyse the genomic damage, micronucleus tests and the comet-assay were performed in L5178Y and HL60 cells. Additionally, the influence of Hcy on cell cycle progression, DNA-cytosine-methylation, oxidative stress levels and on the cellular glutathione content were determined. RESULTS: Low millimolar concentrations of Hcy-induced micronuclei in both cell lines but did not enhance the DNA damage observed with the comet-assay. Cell cycle progression was inhibited in S-phase, while DNA-cytosine-methylation remained unchanged. Furthermore, Hcy protected cells challenged with H(2)O(2) from oxidative stress. This was accompanied by an increased cellular glutathione level. CONCLUSION: Since the genotoxic effect was limited to high Hcy concentrations, a contribution of Hcy to the enhanced genomic damage in end-stage renal disease patients would only be conceivable upon local Hcy accumulation. Whether the detected antioxidant capacity of Hcy is relevant for any situation in patients remains to be elucidated.

Genotoxicity of phytoestrogens.

Plant extracts containing phytohormones are very popular as 'alternative' medicine for many kinds of diseases. They are especially favored by women who enter menopause and are concerned about the side effects of hormone replacement therapy. However, adverse health effects of phytoestrogens have often been ignored. This review examines the literature on genotoxicity and apoptotic effects of phytohormones. Genistein, coumestrol, quercetin, zearalenone, and resveratrol exerted genotoxic effects in in vitro test systems. Other phytoestrogens such as lignans, the isoflavones daidzein and glycetein, anthocyanidins, and the flavonol fisetin exhibited only weak or no effects in vitro. However, some metabolites of daidzein showed a genotoxic activity in vitro. Practically all of the phytoestrogens exhibit pro-apoptotic effects in some cell systems. Further investigations regarding dose-response-relationships and other aspects relevant for extrapolation to human exposure seem necessary. Until then, care may be advised in taking concentrated phytohormones. Nevertheless, the intake of substantial amounts of plant-food in a normal diet constitutes an important, individual contribution to cancer prevention.

Pilot study for comparison of reticulocyte-micronulei with lymphocyte-micronuclei in human biomonitoring.

Biomonitoring tries to determine the consequences for humans of exposures to environmental or pharmaceutical agents. Different end points have been employed to assess the burden of genomic damage. This is the first report comparing a recently introduced new end point, the reticulocyte-micronuclei analyzed by flow cytometry with the widely used lymphocyte-micronucleus assay, applied to two exposure scenarios leading to enhanced genomic damage. Radioiodine therapy was chosen to represent a short time exposure and hemodialysis treatment in end-stage renal failure was chosen to represent a chronic exposure. The results show that iodine radiation induced measurable genomic damage in the lymphocyte-micronucleus assay as well as in the reticulocyte-micronucleus test. Of two groups of patients under hemodialysis treatment, a reduced genomic damage was found with the lymphocyte-micronucleus test, but not with the reticulocyte-micronucleus test in the group undergoing daily hemodialysis, which removes uremic toxins more efficiently as compared to conventional hemodialysis, the treatment applied in the other group. The limited life-span of reticulocytes may make them less suitable for accumulation of chronic low level damage than lymphocytes. In conclusion, the lymphocyte-micronucleus test may be applicable to more exposure situations (including low chronic exposure), but the reticulocyte-micronucleus assay may be easier to perform in a clinical setting. The latter reflects a more rapid reduction of genomic damage after an acute exposure.

Anti-genotoxicity of coffee against N-methyl-N-nitro-N-nitrosoguanidine in mouse lymphoma cells.

The main aim of this work was to test the hypothesis that instant coffee, a commonly consumed polyphenolic beverage with antioxidant activity, can protect mammalian cells against genotoxic effects in vitro. For this purpose, the L5178Y mouse lymphoma cell line was selected to assess modulatory effects of coffee on the genotoxicity of N-methyl-N-nitro-N-nitrosoguanidine (MNNG). We initiated the work with a set of preliminary experiments in which the cytokinesis-block micronucleus test was performed. Results obtained from these experiments demonstrated a dose-related decrease in genotoxicity following co-treatment of mouse lymphoma cells with three doses of caffeinated instant coffee. Both pre-treatment and co-treatment showed significant antigenotoxic effects against MNNG. Caffeinated and decaffeinated instant coffee samples inhibited genotoxicity. There was no significant change in the antigenotoxic effect of caffeinated instant coffee after filtration using a 0.2 microm filter. Similar in vitro experiments demonstrated antigenotoxic effects against MNNG when boiled coffee was used instead of instant coffee. On the basis of the findings from the above preliminary experiments, further work was carried out to evaluate the possible protective effects of caffeinated instant coffee against MNNG-induced DNA damage, mutation and chromosomal damage. Results from three or five independent experiments demonstrated significant protective effects of caffeinated instant coffee against MNNG-induced DNA damage in the comet assay, mutation at the Tk locus and chromosomal damage in the cytokinesis-block micronucleus test.

Coffee-mediated protective effects against directly acting genotoxins and gamma-radiation in mouse lymphoma cells.

The cytokinesis-block micronucleus test was performed using L5178Y mouse lymphoma cells to ascertain whether or not standard (caffeinated) instant coffee, the commonly consumed polyphenolic beverage with antioxidant activity can protect against chromosomal damage induced by the directly acting agents N-methyl-N-nitro-N-nitrosoguanidine (MNNG), mitomycin C (MMC), methyl methanesulfonate (MMS) and gamma radiation. Our results demonstrated significant reductions in the in vitro genotoxic effects of MNNG, MMC, and MMS following co-treatment of mouse lymphoma cells with standard instant coffee. Subsequently, the comet assay was carried out to assess the effect of coffee co-treatment on the level of DNA damage induced by MMS in mouse lymphoma cells. The results demonstrated a significant reduction in MMS-induced DNA damage following co-treatment with standard instant coffee. Protective effects were observed in mouse lymphoma cells which were treated with coffee immediately after exposure to gamma radiation (1 and 2 Gy). Another experiment showed protection when the mammalian cells were irradiated (0.5 and 1 Gy) midway (at 2 h) during a 4 h coffee treatment. However, the protective effect against the lower dose (0.5 Gy) was not significant. In addition we assessed the modulatory effect of coffee on MNNG-induced apoptotic frequency by flow cytometry. The results revealed only a minor influence of coffee on the frequency of apoptotic cells induced by the test compounds, rendering an increase in sensitivity for apoptosis as a reason for the reduced genomic damage an unlikely or at least incomplete explanation.

Genotoxic activity of newly synthesized derivatives of cyano-pyridone in murine cells in vivo and in vitro.

Possible genotoxic activity of two newly synthesized cyanopyridone compounds [4-(N-methyl-phalimidyl-3)-3-cyano-4-methyl-pyridone-2 (MPhCMP) and 1-(4-hydroxyphenyl)-3-cyano-4-methyl-pyridone-2 (HCMP)] with in vitro antitumor activity was studied both in in vitro and in vivo murine test systems. In L5178Y mouse lymphoma cells, HCMP did not induce micronuclei (MN) at the highest available (because of toxicity) concentration (100 microg/ml), while MPhCMP at dose of 50 microg/ml induced 2.6-fold, and at dose of 100 microg/ml 3.95-fold increase of number of the cells with MN. The concentration of 100 microg/ml is a threshold of toxicity of MPhCMP. In experiments on possible DNA damaging activity (the comet assay) of both substances using the same doses as in in vitro mutagenesis assay, we did not reveal any evidence of DNA damage. The acute toxicity of compounds was studied on male Swiss albino mice. LD50 values of MPhCMP and HCMP were 177.5 and 288 mg/kg, respectively. MPhCMP was more potent MN inductor than HCMP (2.5-fold at doses equivalent to 1/2 of LD50). Both substances possessing in vitro antitumor activity along with weak genotoxicity have a good chance for successful in vivo antitumor studies in rodents.

Genotoxic activity of four newly synthesized pyrrolin-2-one derivatives.

PURPOSE: To study the genotoxic activity of 4 newly synthesized derivatives of pyrrolin-2-one by means of the micronucleus (MN) assay both in vivo and in vitro, and the DNA-damaging activity of these substances by means of the comet assay on murine cells in vitro. MATERIALS AND METHODS: The following compounds were studied: [3-(imidazolyl-1)-propylamide-4,5,5-trimethyl- pyrrolin-2-one] (IPA-TP); [3-cyclohexylamide-4,5,5 -trimethyl- pyrrolin-2-one](CH-TP); [3-piperonylamide-4,5,5- trimethyl-pyrrolin-2-one] (PA-TP); and [3-phenethylamide- 4,5,5-trimethyl-pyrrolin-2-one] (PHA-TP). L5178Y mouse lymphoma cells were used to study the activity of the compounds by the MN and the comet assays. The acute toxicity and MN-inducing activity of the 4 compounds was assessed on Swiss albino mice. RESULTS: IPA-TP, PA-TP, and PHA-TP were very weak MN inducers in mouse lymphoma cells, which induced MN only at toxic for lymphoma cells concentrations. No doseeffect relationship was registered. CH-TP was tested at low concentration because of bad solubility and was not MNinducer. IPA-TP and CH-TP were not active in the comet assay, while both PA-TP and PHA-TP were active. The study of acute toxicity showed the following results: LD(50) of IPATP, CH-TP, PA-TP and PHA-TP were 460 mg/kg, 650 mg/kg, 370 mg/kg, and 350 mg/kg, respectively. The substances were studied using the MN assay on mouse bone marrow polychromatic erythrocytes (PCEs), and all of them were active only at doses equal to 1/2 of LD(50). The increase of bone marrow cells with MN was 2.5-5.8-fold compared with the background MN level. Lower doses (1/5 of LD(50)) of all substances were not effective. CONCLUSION: A good agreement between in vivo and in vitro genotoxicity was obtained. IPA-TP, PA-TP, PHA-TP with potential antitumor activity, comparatively low acute toxicity and genotoxicity are good candidates for in vivo studies of antitumor activity.

[Incidence and spectrum of malignant disease among dialysis patients in North Bavaria]. / Inzidenz und Spektrum maligner Erkrankungen bei Dialysepatienten in Nordbayern.

BACKGROUND AND OBJECTIVE: In end-stage renal failure the incidence of cancer is increased. With regard to frequency and pattern of distribution of the tumors, there are substantial regional differences. Since this topic has to date received only minimal attention in Germany, we undertook a multi-centric analysis (8 dialysis centres) in North Bavaria in order to address the occurrence of malignant diseases in end-stage renal failure. PATIENTS AND METHODS: Of a total of 2228 patients, who underwent hemodialysis in the period from 1990 - 99 as a consequence of end-stage renal failure, the medical records of 1727 persons were analysed. Only those patients were considered, whose malignancy was diagnosed in the course of the dialysis. The Saarland cancer register served as a comparative age- and sex-matched population, with which we calculated the expected frequency of the various cancers as well as the standard incidence ratio (SIR) for the dialysis patients. RESULTS: In total 125 malignant diseases were documented. The cancer incidence was highest in the first year of treatment and was clearly lower in the subsequent periods. Of great importance was the age of the patients. The highest SIR scores were found for patients of middle age (35 - 50 years). An enhanced risk for cancer of the kidney, bladder, prostate, liver, oral cavity and the pharynx and larynx, as well as of the lymphatic and hemopoetic systems was found, while there was no or only a slight increase in the frequency of carcinoma of the mammary gland, stomach, colon-sigma-rectum and bronchial systems. CONCLUSION: The high incidence of cancer in end-stage renal failure should be given greater attention. Particularly in the high-risk group of younger dialysis patients, a regular screening - especially for tumors of the kidney, bladder and liver - appears justified.

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.

In vitro radiosensitivity measured in lymphocytes and fibroblasts by colony formation and comet assay: comparison with clinical acute reactions to radiotherapy in breast cancer patients.

PURPOSE: To compare colony-forming and comet assays on fibroblasts and lymphocytes of 32 breast cancer patients irradiated after breast-conserving operations and to correlate the results with acute clinical radiation reactions in the skin. MATERIAL AND METHODS: Skin fibroblasts were isolated and cultivated before radiotherapy and lymphocytes were drawn prior to the first and directly after the final external irradiation. The colony-forming assay was performed with fibroblasts and the comet assay with lymphocytes and fibroblasts of breast cancer patients according to standard protocols. The clinical radiation reactions of the patients were graded according to the RTOG system. RESULTS: No significant correlation (p =0.09) was detected between clinical acute skin reactions and the in vitro clonogenic data in fibroblasts. Results of the comet assay in lymphocytes, however, showed a significant correlation (p <0.05) with the clinical data when patients were divided into two groups with average and elevated acute reactions. Apart from initial damage, fibroblasts did not show significant differences between the two patient groups. Repeated comet assays in lymphocytes of the same patient drawn before treatment and before and after external radiotherapy demonstrated good reproducibility of the test and no significant impact of preceding radiation treatment. There was a good correlation (r =0.65) between the comet assay results in fibroblasts and lymphocytes of the same individual. CONCLUSIONS: In this cohort of patients, a significant correlation between the in vitro results of the comet assay in lymphocytes and clinical acute reactions was detected. The results of the comet assay and of fibroblast colony formation did not correlate with in vitro radiosensitivity.

Assaying the estrogenicity of phytoestrogens in cells of different estrogen sensitive tissues.

There is currently much concern that a wide range of both synthetic and naturally occurring environmental chemicals may act as endocrine disruptors (ED), and may adversely affect humans and wildlife. We examined the estrogenic effects of the phytoestrogens daidzein (DAI), equol (EQU) and O-desmethylangolensin (O-DMA), two metabolites of DAI, in three different assays. Binding affinity to the estrogen receptor alpha was 1000-10,000-fold lower compared with the endogenous estrogen estradiol. In the receptor positive cell line MCF-7 the phytoestrogens induced the expression of a reporter gene. The E-SCREEN is based on the estrogen-receptor binding induced proliferation of the human breast cancer cell line MCF-7. We also adapted the E-SCREEN for the estrogen-receptor positive human ovarian cancer cell line BG-1. The tested phytoestrogens induced cell proliferation in both cell lines, but not in the receptor negative human breast cancer cell line MDA-MB-231. The phytoestrogen-induced cell proliferation could be blocked by addition of the receptor antagonist 4-hydroxytamoxifen (OHT). Combination treatments with the endogenous estrogen estradiol showed competitive effects in MCF-7 cells. These studies demonstrated that the tested phytoestrogens exerted estrogenic responses in cells derived from two different tissues, breast and ovary. Furthermore, we demonstrated that BG-1 cells are a suitable additional cell system to investigate estrogenicity of test compounds.

Comet-assay analysis identifies genomic damage in lymphocytes of uremic patients.

This study investigates genomic damage in peripheral lymphocytes from patients with moderate to severe chronic renal insufficiency and those on long-term maintenance hemodialysis (MHD) and hemodiafiltration therapy. As a measure for genomic damage, the comet assay (single-cell gel electrophoresis) was applied. This test detects single- and double-strand breaks and alkali labile sites through electrophoretic mobility of the resulting fragments. The average damage (percentage of DNA in the tail region of the comet) observed in cells of the control group of 21 healthy subjects was 10.5% +/- 0.8%. There was a significant increase to 14.7% +/- 3.5% in cells of 23 patients with chronic renal failure, and a further increase to 17.1% +/- 3.5% in the subgroup of 12 patients with serum creatinine values greater than 6 mg/dL. Damage was 16.7% +/- 4.2% in cells of the MHD group (26 patients) and 20.1% +/- 3.0% in the subgroup with MHD therapy longer than 10 years (8 patients). Cellular DNA damage in the group of 15 maintenance hemodiafiltration patients was 15.6% +/- 2.1%, ranging between predialysis and MHD patients, and did not seem to increase with treatment time. These results, together with previously observed elevated frequencies of micronuclei, decreased DNA repair, and increased cancer incidence described for these patient groups, emphasize the need to further optimize the current therapy for reducing the degree of genomic damage.

Increased formation of micronuclei after hormonal stimulation of cell proliferation in human breast cancer cells.

The carcinogenicity of sex hormones is considered to be the result of a combination of genotoxic and epigenetic modes of action. For estrogens, genotoxic activities include DNA damage by reactive metabolites and indirect genotoxicity by redox cycling and production of reactive oxygen species. Here, we present data on the induction of micronuclei in estrogen receptor-positive (MCF-7) and -negative (MDA) human breast cancer cell lines treated with estradiol to support an additional mechanism of chromosomal damage. MCF-7 cells, but not MDA cells, treated with estradiol in the picomolar concentration range showed an increase in micronucleus formation which correlated with the estradiol-induced cell proliferation. Addition of the specific estradiol-receptor antagonist hydroxytamoxifen suppressed the estradiol-induced formation of micronuclei in MCF-7 cells. Increased frequencies were also seen after normalization of the data to the number of cell divisions by additional treatment of the cells with cytochalasin B. Thus, formation of micronuclei was not due to the chromosomal damaging activity of estradiol. The induced genomic damage may be explained by a hormone-specific forcing of responsive cells through the cell cycle, thereby overriding checkpoints operating under homeostatic control of the cell cycle.