A comprehensive review about micronuclei: mechanisms of formation and practical aspects in genotoxicity testing

HN1 interacts with γ-tubulin to regulate centrosomes in advanced prostate cancer cells

Prostate cancer is one of the most common cancer for men worldwide with advanced forms showing supernumerary or clustered centrosomes. Hematological and neurological expressed 1 (HN1) also known as Jupiter Microtubule Associated Homolog 1 (JPT1) belongs to a small poorly understood family of genes that are evolutionarily conserved across vertebrate species. The co-expression network of HN1 from the TCGA PRAD dataset indicates the putative role of HN1 in centrosome-related processes in the context of prostate cancer. HN1 expression is low in normal RWPE-1 cells as compared to cancerous androgen-responsive LNCaP and androgen insensitive PC-3 cells. HN1 overexpression resulted in differential response for cell proliferation and cell cycle changes in RWPE-1, LNCaP, and PC-3 cells. Since HN1 overexpression increased the proliferation rate in PC-3 cells, these cells were used for functional characterization of HN1 in advanced prostate carcinogenesis. Furthermore, alterations in HN expression led to an increase in abnormal to normal nuclei ratio and increased chromosomal aberrations in PC-3 cells. We observed the co-localization of HN1 with γ-tubulin foci in prostate cancer cells, further validated by immunoprecipitation. HN1 was observed as physically associated with γ-tubulin and its depletion led to increased γ-tubulin foci and disruption in microtubule spindle assembly. Higher HN1 expression was correlated with prostate cancer as compared to normal tissues. The restoration of HN1 expression after silencing suggested that it has a role in centrosome clustering, implicating a potential role of HN1 in cell division as well as in prostate carcinogenesis warranting further studies.

A Systematic Review of the Genotoxicity and Antigenotoxicity of Biologically Synthesized Metallic Nanomaterials: Are Green Nanoparticles Safe Enough for Clinical Marketing?

Background and objectives: Although studies have elucidated the significant biomedical potential of biogenic metallic nanoparticles (MNPs), it is very important to explore the hazards associated with the use of biogenic MNPs. Evidence indicates that genetic toxicity causes mutation, carcinogenesis, and cell death. Materials and Methods: Therefore, we systematically review original studies that investigated the genotoxic effect of biologically synthesized MNPs via in vitro and in vivo models. Articles were systematically collected by screening the literature published online in the following databases; Cochrane, Web of Science, PubMed, Scopus, Science Direct, ProQuest, and EBSCO. Results: Most of the studies were carried out on the MCF-7 cancer cell line and phytosynthesis was the general approach to MNP preparation in all studies. Fungi were the second most predominant resource applied for MNP synthesis. A total of 80.57% of the studies synthesized biogenic MNPs with sizes below 50 nm. The genotoxicity of Ag, Au, ZnO, TiO₂, Se, Cu, Pt, Zn, Ag-Au, CdS, Fe₃O₄, Tb₂O₃, and Si-Ag NPs was evaluated. AgNPs, prepared in 68.79% of studies, and AuNPs, prepared in 12.76%, were the two most predominant biogenic MNPs synthesized and evaluated in the included articles. Conclusions: Although several studies reported the antigenotoxic influence of biogenic MNPs, most of them reported biogenic MNP genotoxicity at specific concentrations and with a dose or time dependence. To the best of our knowledge, this is the first study to systematically evaluate the genotoxicity of biologically synthesized MNPs and provide a valuable summary of genotoxicity data. In conclusion, our study implied that the genotoxicity of biologically synthesized MNPs varies case-by-case and highly dependent on the synthesis parameters, biological source, applied assay, etc. The gathered data are required for the translation of these nanoproducts from research laboratories to the clinical market.

Doramectin induced cytotoxic and genotoxic effects on bovine peripheral lymphocytes and cumulus cells in vitro

The effect of doramectin (DOR) was tested on two experimental somatic bovine cells in vitro: peripheral lymphocytes (PL) and cumulus cells (CC). The cytotoxicity and genotoxicity of DOR were assessed using 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, single cell gel electrophoresis assay (SCGE) and cytokinesis-block micronucleus cytome (CBMN Cyt) assay. Both cells were treated with three concentrations of DOR (20, 40, 60 ng mL^-1) for 24 h. The results obtained from PL demonstrated that DOR was able to induce cytotoxic effect and DNA damage with all concentrations tested. Additionally, DOR increased micronuclei (MNi) frequency and nuclear buds (NBuds) with 20, 40, 60 ng mL^-1, and nucleoplasmic bridges (NPBs) only with 40 ng mL^-1. On the other hand, the three concentrations of DOR were not able to induce cytotoxic effect and DNA damage using SCGE in the bovine CC. Nevertheless, the two higher concentrations of DOR (20, 40 µg mL^-1) significantly increased the frequency of micronucleus formation in bovine CC. These results represent the first experimental evidence of genotoxic and cytotoxic effects exerted by DOR on bovine PL and CC.

Micronuclei Frequency in Tumors Is a Predictive Biomarker for Genetic Instability and Sensitivity to the DNA Repair Inhibitor AsiDNA

Therapeutic strategies targeting DNA repair pathway defects have been widely explored, but often only benefit small numbers of patients. Here we characterized potential predictive biomarkers for treatment with AsiDNA, a novel first-in-class DNA repair inhibitor. We evaluated genetic instability and DNA repair defects by direct and indirect assays in 12 breast cancer cell lines to estimate the spontaneous occurrence of single-strand and double-strand breaks (DSB). For each cell line, we monitored constitutive PARP activation, spontaneous DNA damage by alkaline comet assay, basal micronuclei levels, the number of large-scale chromosomal rearrangements (LST), and the status of several DNA repair pathways by transcriptome and genome analysis. Sensitivity to AsiDNA was associated with a high spontaneous frequency of cells with micronuclei and LST and specific alterations in DNA repair pathways that essentially monitor DSB repair defects. A high basal level of micronuclei as a predictive biomarker for AsiDNA treatment was validated in 43 tumor cell lines from various tissues and 15 models of cell- and patient-derived xenografts. Micronuclei quantification was also possible in patient biopsies. Overall, this study identified genetic instability as a predictive biomarker for sensitivity to AsiDNA treatment. That micronuclei frequency can be measured in biopsies and does not reveal the same genetic instability as conventional genome assays opens new perspectives for refining the classification of tumors with genetic instability. Cancer Res; 77(16); 4207-16. ©2017 AACR.

Evaluation of drinking water treatment combined filter backwash water recycling technology based on comet and micronucleus assay

Based on the fact that recycling of combined filter backwash water (CFBW) directly to drinking water treatment plants (WTP) is considered to be a feasible method to enhance pollutant removal efficiency, we were motivated to evaluate the genotoxicity of water samples from two pilot-scale drinking water treatment systems, one with recycling of combined backwash water, the other one with a conventional process. An integrated approach of the comet and micronucleus (MN) assays was used with zebrafish (Danio rerio) to investigate the water genotoxicity in this study. The total organic carbon (TOC), dissolved organic carbon (DOC), and trihalomethane formation potential (THMFP), of the recycling process were lower than that of the conventional process. All the results showed that there was no statistically significant difference (P>0.05) between the conventional and recycling processes, and indicated that the genotoxicity of water samples from the recycling process did not accumulate in 15 day continuous recycling trial. It was worth noting that there was correlation between the concentrations of TOC, DOC, UV254, and THMFPs in water and the DNA damage score, with corresponding R(2) values of 0.68, 0.63, 0.28, and 0.64. Nevertheless, both DNA strand breaks and MN frequency of all water samples after disinfection were higher than that of water samples from the two treatment units, which meant that the disinfection by-products (DBPs) formed by disinfection could increase the DNA damage. Both the comet and MN tests suggest that the recycling process did not increase the genotoxicity risk, compared to the traditional process.

Cytotoxic and genotoxic effects of two hair dyes used in the formulation of black color

According to the International Agency for Research on Cancer (IARC), some hair dyes are considered mutagenic and carcinogenic in in vitro assays and exposed human populations. Epidemiological studies indicate that hairdressers occupationally exposed to hair dyes have a higher risk of developing bladder cancer. In Brazil, 26% of the adults use hair dye. In this study, we investigated the toxic effects of two hair dyes, Basic Red 51 (BR51) and Basic Brown 17 (BB17), which are temporary dyes of the azo group (R-N=N-R'), used in the composition of the black hair dye. To this end, MTT and trypan blue assays (cytotoxicity), comet and micronucleus assay (genotoxicity) were applied, with HepG2 cells. For cytotoxic assessment, dyes were tested in serial dilutions, being the highest concentrations those used in the commercial formula for hair dyes. For genotoxic assessment concentrations were selected according to cell viability. Results showed that both dyes induced significant cytotoxic and genotoxic effects in the cells, in concentrations much lower than those used in the commercial formula. Genotoxic effects could be related to the azo structure present in the composition of the dyes, which is known as mutagenic and carcinogenic. These results point to the hazard of the hair dye exposure to human health.

Evaluation of removal efficiency for acute toxicity and genotoxicity on zebrafish in anoxic-oxic process from selected municipal wastewater treatment plants

The anoxic-oxic (A/O) process has been extensively applied for simultaneous removal of organic contaminants and nitrogen in wastewater treatment. However, very little is known about its ability to remove toxic materials. Municipal wastewater contains various kinds of pollutants, some of which have recalcitrant genotoxicity and may cause potential threat to environment, and even can lead to extinction of many species. In this study, we have selected three municipal wastewater treatment plants (WWTPs) employing anoxic-oxic (A/O) process to evaluate their ability to remove acute toxicity and genotoxicity of wastewater. Mortality rate of zebrafish (Danio rerio) was used to evaluate acute toxicity, while micronucleus (MN) and comet assays were used to detect genotoxicity. Results showed that in this process the acute toxicity was completely removed as the treatment proceeded along with decrease in chemical oxygen demand (COD) (<50 mgL(-1)) in the effluent. However, in these treatment processes the genotoxicity was not significantly reduced, but an increase in genotoxicity was observed. Both MN and comet assays showed similar results. The eliminated effluent may pose genotoxic threaten although its COD level has met the Chinese Sewage Discharge Standard. This study suggests that further treatment of the wastewater is required after the A/O process to remove the genotoxicity and minimize the ecotoxicological risk.