Chromosomal DNA damage in APOE ɛ4 carriers and noncarriers does not appear to be different

DNA damage may play a key role in promoting disease‐onset and accelerated disease progression in Alzheimer's disease (AD) by increasing the rates of neuronal cell death. The ?4 allele of the APOE gene is the best characterised genetic risk factor for AD, however, it is unknown if APOE ?4 carriers exhibit increased levels of DNA damage which may contribute to increased AD risk. 175 healthy participants (aged 34–67 years old) from South Australia were recruited into the study and provided a single blood sample for the isolation of peripheral blood lymphocytes, APOE genotyping and lymphocyte chromosomal DNA damage analysis using the Cytokinesis‐Block micronucleus cytome (CBMN‐Cyt) assay with the micronucleus index being the primary outcome measure. When compared to non‐APOE ?4 carriers, APOE ?4 carriers did not exhibit altered rates of i) cell division, represented by the nuclear division index (NDI, P = 0.372), ii) cell death as represented by apoptotic (P = 0.457) and necrotic (P = 0.393) frequencies and iii) chromosomal DNA damage as indicated by the number of micronuclei (MNi, P = 0.795), nucleoplasmic bridges (NPBs, P = 0.221) or nuclear buds (NBUDs, P = 0.293) scored in binucleated cells. In conclusion, although we and others have previously shown that rates of chromosomal DNA damage measured using the CBMN‐Cyt assay are elevated in individuals with cognitive impairment, in this South Australian cohort the frequency of genome instability is not substantially influenced by the presence of the APOE ?4 allele. Environ. Mol. Mutagen. 56:694–708, 2015. © 2015 Wiley Periodicals, Inc.     

Genotoxicity of synthetic amorphous silica nanoparticles in rats following short‐term exposure. Part 1: Oral route

Synthetic amorphous silica (SAS) in its nanosized form is now used in food applications although the potential risks for human health have not been evaluated. In this study, genotoxicity and oxidative DNA damage of two pyrogenic (NM‐202 and 203) and two precipitated (NM‐200 and ‐201) nanosized SAS were investigated in vivo in rats following oral exposure. Male Sprague Dawley rats were exposed to 5, 10, or 20 mg/kg b.w./day for three days by gavage. DNA strand breaks and oxidative DNA damage were investigated in seven tissues (blood, bone marrow from femur, liver, spleen, kidney, duodenum, and colon) with the alkaline and the (Fpg)‐modified comet assays, respectively. Concomitantly, chromosomal damage was investigated in bone marrow and in colon with the micronucleus assay. Additionally, malondialdehyde (MDA), a lipid peroxidation marker, was measured in plasma. When required, a histopathological examination was also conducted. The results showed neither obvious DNA strand breaks nor oxidative damage with the comet assay, irrespective of the dose and the organ investigated. Similarly, no increases in chromosome damage in bone marrow or lipid peroxidation in plasma were detected. However, although the response was not dose‐dependent, a weak increase in the percentage of micronucleated cells was observed in the colon of rats treated with the two pyrogenic SAS at the lowest dose (5 mg/kg b.w./day). Additional data are required to confirm this result, considering in particular, the role of agglomeration/aggregation of SAS NMs in their uptake by intestinal cells. Environ. Mol. Mutagen. 56:218–227, 2015. © 2014 Wiley Periodicals, Inc.     

SiO2 Nanoparticule-induced size-dependent genotoxicity – an in vitro study using sister chromatid exchange,micronucleus and comet assay

Fine particles with a characteristic size smaller than 100?nm (i.e. nanoparticlesspread out in nowadays life. Silicon or Si, is one of the most abundant chemical elements found on the Earth. Its oxide forms, such as silicate (SiO₄) and silicon dioxide, also known as silica (SiO₂), are the main constituents of sand and quartz contributing to 90% of the Earth's crust. In this work, three genotoxicity systems “sister chromatid exchange, cytokinesis block micronucleus test and single cell gel electrophoresis (comet) assay” were employed to provide further insight into the cytotoxic and mutagenic/genotoxic potential of SiO₂ nanoparticules (particle size 6?nm, 20?nm, 50?nm) in cultured peripheral blood lymphocytes as in vitro. It was observed that there is a significant decrease in Mitotic index (MI), Cytokinesis block proliferation index (CBPI), proliferation index (PRI) values expressed as Cell Kinetic parameters compared with negative control (p?2 (6?nm, 20?nm, 50?nm) (p?p?p?2 nanoparticles at different size (6, 20, 50?nm) progressively increased the SCE frequency and DNA damage on the basis the AU values compared with negative control (p?2 nanoparticules is dependent to particule size.     

Chromosomal DNA damage measured using the cytokinesis‐block micronucleus cytome assay is significantly associated with cognitive impairment in South Australians

Loss of genome integrity may be associated with increased risk for neurodegenerative disease. The aim of this study was to investigate whether mild cognitive impairment (MCI) or Alzheimer's disease (AD) individuals have increased DNA damage relative to age‐ and gender‐ matched controls using the cytokinesis‐block micronucleus cytome (CBMN‐Cyt) assay. DNA damage was measured as micronuclei (MN), nucleoplasmic bridges (NPB), and nuclear buds (NBUD) in binucleated cells. The assay was performed on blood samples from 80 participants consisting of (i) MCI cases (N = 20) and age‐ and gender‐ matched controls (N = 20), and (ii) AD cases (N = 20) and age‐ and gender‐ matched controls (N = 20). There was a significant increase in MCI NBUD frequency (P = 0.006) relative to controls, which was also observed in male (P = 0.03) and female (P = 0.04) subgroups. For AD cases, there were no significant differences in assay biomarkers relative to controls. There was a significant negative correlation between Mini Mental State Examination (MMSE) and (i) MN in all controls, (R = ?0.3, P = 0.04), and AD cases (R = ?0.4, P = 0.03), (ii) NPB in all controls, (R = ?0.4, P = 0.006) and AD cases (R = ?0.5, P = 0.01), and (iii) NBUD in MCI cases (R = ?0.5, P = 0.007) and AD cases (R = ?0.7, P = 0.0002). The results suggest that an increase in lymphocyte CBMN‐Cyt DNA damage biomarkers may be associated with cognitive decline. Environ. Mol. Mutagen. 56:32–40, 2015. © 2014 Wiley Periodicals, Inc.     

In vivo kinetics of the genotoxic and cytotoxic activities of cladribine and clofarabine

The aim of the present in vivo study was to determine the kinetics of the genotoxic and cytotoxic activities of cladribine and clofarabine in mouse normoblasts using flow cytometry. Mice in groups of five were treated with cladribine or clofarabine. Blood samples were obtained from the mouse tails before treatment and every 8 hr posttreatment for 72 hr. These samples were cytometrically scored for micronucleated reticulocytes (RETs), and the percentage of RETs was determined. The results showed that clofarabine and cladribine have early cytotoxic effects that are related to the genotoxic effects reported in previous studies; the drugs have both complex long-lasting genotoxic and cytotoxic kinetic activity, with similar profiles that suggest a relationship between the genotoxic and cytotoxic parameters. The initial genotoxkinetics timing of clofarabine is equivalent to those of difluorodeoxycytidine, likely because both agents inhibit DNA polymerase. Clofarabine shows a higher genotoxic and cytotoxic efficiency than cladribine, in agreement with previous results.     

Genetic toxicity assessment using liver cell models: past,present, and future

ABSTRACT

Genotoxic compounds may be detoxified to non-genotoxic metabolites while many pro-carcinogens require metabolic activation to exert their genotoxicity in vivo. Standard genotoxicity assays were developed and utilized for risk assessment for over 40 years. Most of these assays are conducted in metabolically incompetent rodent or human cell lines. Deficient in normal metabolism and relying on exogenous metabolic activation systems, the current in vitro genotoxicity assays often have yielded high false positive rates, which trigger unnecessary and costly in vivo studies. Metabolically active cells such as hepatocytes have been recognized as a promising cell model in predicting genotoxicity of carcinogens in vivo. In recent years, significant advances in tissue culture and biological technologies provided new opportunities for using hepatocytes in genetic toxicology. This review encompasses published studies (both in vitro and in vivo) using hepatocytes for genotoxicity assessment. Findings from both standard and newly developed genotoxicity assays are summarized. Various liver cell models used for genotoxicity assessment are described, including the potential application of advanced liver cell models such as 3D spheroids, organoids, and engineered hepatocytes. An integrated strategy, that includes the use of human-based cells with enhanced biological relevance and throughput, and applying the quantitative analysis of data, may provide an approach for future genotoxicity risk assessment.     

In vitro genotoxic and cytotoxic effects of doxepin and escitalopram on human peripheral lymphocytes

Antidepressants are drugs used for the treatment of many psychiatric conditions including depression. There are findings suggesting that these drugs might have genotoxic, carcinogenic, and/or mutagenic effects. Therefore, the present in vitro study is intended to investigate potential genotoxic and cytotoxic effects of the antidepressants escitalopram (selective serotonin reuptake inhibitor) and doxepin (Tricyclic antidepressant) on human peripheral lymphocytes cytokinesis-block micronucleus (CBMN), sister chromatid exchange (SCE), and single cell gel electrophoresis (alkaline comet assay) were used for the purpose of the study. In the study, four different concentrations of both drugs (1, 2.5, 5, and 10?µg/mL) were administered to human peripheral lymphocytes for 24?h. The tested concentrations of both drugs were found to exhibit no cytotoxic and mitotic inhibitory effects. SCE increase caused by 5 and 10?µg/mL of escitalopram was found statistically significant, while no statistically significant increase was observed in DNA damage and micronucleus (MN) formation. Moreover, the increase caused by doxepin in MN formation was not found statistically significant. Besides, 10?µg/mL of doxepin was demonstrated to significantly increase arbitrary unit and SCE formation. These findings suggest that the investigated concentrations of escitalopram and doxepin were non-cytotoxic but potentially genotoxic at higher concentrations.     

Combinations of genotoxic tests for the evaluation of group 1 IARC carcinogens

Many of the known human carcinogens are potent genotoxins that are efficiently detected as carcinogens in human populations but certain types of compounds such as immunosuppressants, sex hormones, etc. act via non‐genotoxic mechanism. The absence of genotoxicity and the diversity of modes of action of non‐genotoxic carcinogens make predicting their carcinogenic potential extremely challenging. There is evidence that combinations of different short‐term tests provide a better and efficient prediction of human genotoxic and non‐genotoxic carcinogens. The purpose of this study is to summarize the in vivo and in vitro comet assay (CMT) results of group 1 carcinogens selected from the International Agency for Research on Cancer and to discuss the utility of the comet assay along with other genotoxic assays such as Ames, in vivo micronucleus (MN), and in vivo chromosomal aberration (CA) test. Of the 62 agents for which valid genotoxic data were available, 38 of 61 (62.3%) were Ames test positive, 42 of 60 (70%) were in vivo MN test positive and 36 of 45 (80%) were positive for the in vivo CA test. Higher sensitivity was seen in in vivo CMT (90%) and in vitro CMT (86.9%) assay. Combination of two tests has greater sensitivity than individual tests: in vivo MN + in vivo CA (88.6%); in vivo MN + in vivo CMT (92.5%); and in vivo MN + in vitro CMT (95.6%). Combinations of in vivo or in vitro CMT with other tests provided better sensitivity. In vivo CMT in combination with in vivo CA provided the highest sensitivity (96.7%).     

网吧环境和槟榔致口腔颊黏膜细胞DNA损伤研究

目的 研究网吧环境和槟榔对口腔颊黏膜细胞DNA的损伤。方法 通过系统抽样抽取长沙市岳麓区5家网吧,在网吧内及网吧所在社区通过单纯随机抽样的方法选取无吸烟、饮酒等习惯的18~40岁健康男性,分别作为对照组(n=50)、网吧上网组(n=41)、咀嚼槟榔组(n=47)、网吧上网且咀嚼槟榔组(n=58)。收集受试者口腔颊黏膜细胞标本,采用单细胞凝胶电泳(single cell gel electrophoresis, SCGE)及颊细胞微核试验(buccal micronucleus cytome, BMCyt)检测DNA损伤情况。结果 网吧上网组和咀嚼槟榔组较对照组SCGE尾部DNA百分含量(%Tail DNA)及BMCyt微核频率(‰MN)显著增高(P＜0.05)。网吧上网且咀嚼槟榔组较网吧上网组和咀嚼槟榔组%Tail DNA及‰MN均显著增高(P＜0.05)。DNA损伤程度与网吧上网累积时间和槟榔咀嚼量呈剂量效应关系。结论 网吧环境和槟榔可分别导致口腔颊黏膜细胞DNA损伤,两者同时暴露会进一步增加DNA损伤程度。     

Micronucleus formation in human cancer cells is biased by chromosome size

Chromosomal instability is one of the hallmarks of cancer and caused by chromosome missegregation during mitosis, a process frequently associated with micronucleus formation. Micronuclei are formed when chromosomes fail to join a daughter nucleus during cell division and are surrounded by their own nuclear membrane. Although it has been commonly assumed that the gain or loss of specific chromosomes is random during compromised cell division, recent data suggest that the size of chromosomes can impact on chromosome segregation fidelity. To test whether chromosome missegregation rates scale with chromosome size in primary human cancer cells, we assessed chromosome sequestration into micronuclei in patient‐derived primary NCH149 glioblastoma cells, which display high‐level numerical chromosome instability (CIN), pronounced spontaneous micronucleus formation but virtually no structural CIN. The cells were analyzed by interphase fluorescence in situ hybridization using chromosome‐specific painting probes for all chromosomes. Overall, 33% of early passage NCH149 cells harbored micronuclei. Entrapment within a micronucleus clearly correlated with chromosome size with larger chromosomes being significantly more frequently missegregated into micronuclei than smaller chromosomes in primary glioblastoma cells. These findings extend the concept that chromosome size determines segregation fidelity by implying that size‐specific micronucleus entrapment occurs in primary human cancer cells as well.