The in vivo or ex vivo origin of micronuclei measured in human biomonitoring studies

Assessment of Micronuclei Frequency in the Peripheral Blood of Adult and Pediatric Patients Receiving Fractionated Total Body Irradiation

The cytokinesis-block micronucleus (CBMN) assay is an established method for assessing chromosome damage in human peripheral blood lymphocytes resulting from exposure to genotoxic agents such as ionizing radiation. The objective of this study was to measure cytogenetic DNA damage and hematology parameters in vivo based on MN frequency in peripheral blood lymphocytes (PBLs) from adult and pediatric leukemia patients undergoing hematopoietic stem cell transplantation preceded by total body irradiation (TBI) as part of the conditioning regimen. CBMN assay cultures were prepared from fresh blood samples collected before and at 4 and 24 h after the start of TBI, corresponding to doses of 1.25 Gy and 3.75 Gy, respectively. For both age groups, there was a significant increase in MN yields with increasing dose (p < 0.05) and dose-dependent decrease in the nuclear division index (NDI; p < 0.0001). In the pre-radiotherapy samples, there was a significantly higher NDI measured in the pediatric cohort compared to the adult due to an increase in the percentage of tri- and quadri-nucleated cells scored. Complete blood counts with differential recorded before and after TBI at the 24-h time point showed a rapid increase in neutrophil (p = 0.0001) and decrease in lymphocyte (p = 0.0006) counts, resulting in a highly elevated neutrophil-to-lymphocyte ratio (NLR) of 14.45 ± 1.85 after 3.75 Gy TBI (pre-exposure = 4.62 ± 0.49), indicating a strong systemic inflammatory response. Correlation of the hematological cell subset counts with cytogenetic damage, indicated that only the lymphocyte subset survival fraction (after TBI compared with before TBI) showed a negative correlation with increasing MN frequency from 0 to 1.25 Gy (r = -0.931; p = 0.007). Further, the data presented here indicate that the combination of CBMN assay endpoints (MN frequency and NDI values) and hematology parameters could be used to assess cytogenetic damage and early hematopoietic injury in the peripheral blood of leukemia patients, 24 h after TBI exposure.

Micronucleated erythrocytes in peripheral blood from neonate rats fed by nursing mothers exposed to X-rays

Most women with breast cancer can become pregnant and give birth while undergoing radiation therapy and breastfeeding is generally not contraindicated. The induction of long-lived reactive species in proteins, such as casein by X-ray radiation and DNA damage to unexposed organisms, has been shown when ingesting irradiated cheese. To determine whether exposing lactating rats to X-rays increases the number of micronucleated erythrocytes (MNEs) in peripheral blood of their unexposed or breastfeeding rat pups, 15 female Wistar rats were divided into three groups: Negative control; Experimental group exposed to X-rays, and group exposed to X-rays plus vitamin C. The mothers of groups 2 and 3 were irradiated for three consecutive days after giving birth, returning them to their respective cages each time to continue lactation. A blood sample was taken from the mothers and pups at 0, 24, and 48 hr. Blood smears were stained with acridine orange to analyze MNEs. In mother rats, the frequency of micronucleated polychromatic erythrocytes (MNPCEs) increased significantly at 24 and 48 hr in both study groups exposed to radiation. Likewise, in rat pups the MNPCE and MNE frequencies increased in both groups with radiation and radiation plus vitamin C at 24 and 48 hr, and a protection from vitamin C was observed. In conclusion, the genotoxic damage produced in rat pups that were lactated by mothers irradiated with X-rays is possibly due to the effect of long-lived reactive species that were formed in the breast milk of female Wistar rats during the irradiation process.

Genotoxicity and pharmacokinetic characterization of Cereus jamacaru ethanolic extract in rats

The effect of Cereus jamacaru ethanolic extract in rats was analyzed using genotoxicity assays and liver ABCB1 and CYP2D4 gene expression. The lyophilized extract of C. jamacaru cladodes was analyzed with LC-MS/MS. Male Wistar rats (n=36) were equally distributed into six groups that did (+) or did not (-) receive cyclophosphamide treatments: Control (-); Control (+); EXP 1 (-), and EXP 1 (+), both treated with 210 mg/kg of ethanolic extract; and EXP 2 (-) and EXP 2 (+), both treated with 420 mg/kg of ethanolic extract. After 30 d of treatment, body weight and food and water intake were monitored. Right femur of the rats and spinal canal fluid were harvested and used for genotoxicity assays, and the liver samples were used for gene expression studies. The phytochemical analysis identified novel compounds. Animals treated with C. jamacaru showed lower body weight and food ingestion compared to controls (P<0.05). The genotoxicity assay showed an absence of ethanolic extract cytotoxicity. CYP2D4 expression was higher in EXP 2 groups compared with EXP 1 (-) group (P<0.05). ABCB1A expression was higher in negative groups compared with the positive groups. These results indicated a new phytochemical characterization of C. jamacaru and its effect on food ingestion and body weight gain. Moreover, the genotoxicity assay suggested that C. jamacaru ethanolic extract treatment presents significant intrinsic genotoxic potential and the enhanced expression of ABCB1 and CYP2D4 on C. jamacaru extract treatment suggests a role of the efflux transporter and microsomal enzyme, respectively, in C. jamacaru pharmacokinetics.

Persistent Increased Frequency of Genomic Instability in Women Diagnosed with Breast Cancer: Before, during, and after Treatments

This study aimed to evaluate DNA damage in patients with breast cancer before treatment (background) and after chemotherapy (QT) and radiotherapy (RT) treatment using the Comet assay in peripheral blood and the micronucleus test in buccal cells. We also evaluated repair of DNA damage after the end of RT, as well as the response of patient's cells before treatment with an oxidizing agent (H2O2; challenge assay). Fifty women with a mammographic diagnosis negative for cancer (control group) and 100 women with a diagnosis of breast cancer (followed up during the treatment) were involved in this study. The significant DNA damage was observed by increasing in the index and frequency of damage along with the increasing of the frequency of micronuclei in peripheral blood and cells of the buccal mucosa, respectively. Despite the variability of the responses of breast cancer patients, the individuals presented lesions on the DNA, detected by the Comet assay and micronucleus Test, from the diagnosis until the end of the oncological treatment and were more susceptible to oxidative stress. We can conclude that the damages were due to clastogenic and/or aneugenic effects related to the neoplasia itself and that they increased, especially after RT.

Polyphenolic contents of Teucrium polium L. and Teucrium scordium L. associated with their protective effects against MMC-induced chromosomal damage in cultured human peripheral blood lymphocytes

Teucrium species have been used in traditional medicine for treatment of different diseases. The aim of this study was to investigate polyphenolic contents by high-performance liquid chromatography (HPLC), and the genotoxic effect of methanolic extracts of Teucrium polium and Teucrium scordium using the cytokinesis-block micronucleus (CBMN) assay on human peripheral blood lymphocytes (PBLs) from healthy donors. The HPLC  analysis  showed that extracts consist of phenolic acid (gallic, vanillic, caefic, chlorogenic, p-coumaric, sinapic) and flavonoids (catechin, rutin, myricetin, luteolin, quercetin and apigenin). Cultures were treated with extracts of both plants separately and in combinations with mitomycin C (MMC). In separate treatments, both herbal extracts significantly induced micronucleus (MN) frequency only at the highest concentrations. All concentrations of T. scordium , except the lowest, and all concentrations of T. polium extracts in combined treatment with MMC significantly reduced the frequency of MN. The extract of T. polium did not significantly aefct the nuclear division index (NDI), whereas T. scordium in higher concentrations, separately and in combined treatment with MMC, significantly decreased the NDI value. Our results suggest that both herbal extracts in combination with MMC have antimutagenic (T. polium) and proapoptotic effects (T. scordium), which indicates their protective effects in PBLs.

Toxic effects of mercury on the cell nucleus of Dictyostelium discoideum

Governmental agencies (www.epa.gov/mercury) and the scientific community have reported on the high toxicity due to mercury. Indeed, exposure to mercury can cause severe injury to the central nervous system and kidney in humans. Beyond its recognized toxicity, little is known regarding the molecular mechanisms involved in the actions of this heavy metal. Mercury has been also observed to form insoluble fibrous protein aggregates in the cell nucleus. We used D. discoideum to evaluate micronuclei formation and, since mercury is able to induce oxidative stress that could bring to protein aggregation, we assessed nuclear protein carbonylation by Western Blot. We observed a significant increase in micronuclei formation and 14 carbonylated proteins were identified. Moreover, we used isotope-coded protein label (ICPL) and mass spectrometry analysis of proteins obtained by lysis of purified nuclei, before of tryptic digestion to quantify nuclear proteins affected by mercury. In particular, we examined the effects of mercury that associate a classical genotoxic assay to proteomic effects into the nucleus. The data present direct evidences for mercury genotoxicity, nuclear protein carbonylation, quantitative change in core histones, and the involvement of pseudouridine synthase in mercury toxicity. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 417-425, 2017.

In vitro cytotoxic and genotoxic evaluation of peptides used in nuclear medicine (DOTATATE and Ubiquicidin29-41) in CHO-K1 cells

Micronucleus (MN) assay constitutes a valuable surrogate to the chromosome aberration technique for in vitro testing of the genotoxicity of substances. As test substances, two peptidic compounds (DOTATATE and Ubiquicidin_29-41) used in nuclear medicine, were tested for in vitro cytotoxicity and genotoxicity in CHO-K1 cells. None of the compounds showed detectable cytotoxicity (0.5-7.3 ng/mL for DOTATATE and 0.3-4.5 ng/mL for UBI_29-41), genotoxicity (0.72, 7.2 and 72.0 ng/ml for DOTATATE and 0.45, 4.5 and 45.0 ng/mL for UBI_29-41) or cell cycle changes as compared to untreated controls at the concentrations tested. Statistical analysis showed good concordance between two independent analysts. The results corroborate the notion of the safety of the compounds and present improvements of the in vitro MN assay when performed in a pre-clinical trial context that increase the throughput of small-to-medium testing facilities as an alternative to high content screening systems.

Comparative analysis of individual chromosome involvement in micronuclei induced by mitomycin C and bleomycin in human leukocytes

Background

Micronucleus (MN) assay is a well standardized approach for evaluation of clastogenic/aneugenic effects of mutagens. Fluorescence in situ hybridization (FISH) is successfully used to characterize the chromosomal content of MN. However, the relationships between nuclear positioning, length, and gene density of individual chromosomes and their involvement in MN induced by different mutagens have not been clearly defined.

Results

Chromosomal content of MN was characterized in human leukocytes treated with mitomycin C (MMC) and bleomycin (BLM) by FISH using centromeric (cep) and whole-chromosome painting (wcp) probes. Involvement of chromosomes 8, 15 and 20 in MMC-induced and chromosomes 1, 9 and 16 in BLM-induced MN was studied, and correlated with chromosome size, gene density and interphase position. The results obtained were analyzed together with previous own data on the frequencies of inclusion of chromosomes 3, 4, 6, 7, 9, 16, 17, 18, and X in MMC-induced MN. It could be shown that MMC- and BLM-induced MN could contain material derived from all chromosomes investigated. Involvement of whole chromosomes 8, 15 and 20 in MMC-induced MN negatively correlated with gene density; however, analysis together with earlier studied chromosomes did not confirm this correlation. Inclusion of chromosomes 8, 15 and 20 in MMC-induced MN does not depend on their size and interphase position; the same result was found for the twelve overall analyzed chromosomes. In BLM-treated cells significant correlation between frequencies of involvement of chromosomes 1, 9 and 16 in MN and their size was found.

Conclusions

Our results clearly revealed that BLM differs from MMC with respect to the distribution of induced chromosome damage and MN formation. Thus, DNA-damaging agents with diverse mechanism of action induce qualitatively different MN with regard to their chromosomal composition. Also this study demonstrates the utility of combined sequential application of cep and wcp probes for efficient detection of MN chromosomal content in terms of centric and acentric fragments.

Long-term exposure to cypermethrin and piperonyl butoxide cause liver and kidney inflammation and induce genotoxicity in New Zealand white male rabbits

Cypermethrin (CY) is a frequently used class II pyrethroid pesticide, while piperonyl butoxide (PBO) plays a major role in the pesticide formulation of synthetic pyrethroids. Synthetic pyrethroids are metabolized in mammals via oxidation and ester hydrolysis. PBO can prevent the metabolism of CY and enhances its pesticide effect. While this potentiation effect reduces the amount of pesticide required to eliminate insects, it is not clear how this mixture affects mammals. In our in vivo experiment, New Zealand white male rabbits were exposed to low and high doses of CY, PBO, and their combinations, for 4 months. Genotoxicity and cytotoxicity were monitored by measuring binucleated cells with micronuclei (BNMN), micronuclei (MN) and the cytokinesis block proliferation index (CBPI) in lymphocytes. After two months of exposure, a statistically significant increase in the frequency of BNMN was observed for all exposed animals (p < 0.001) in a dose-dependent way. MN were significantly elevated compared to controls (p < 0.001), with high dose groups reaching a 442% increase when co-exposed. BNMN and MN continued to increase after four months. Histopathological examination of lesions showed damage involving inflammation, attaining lymphoplasmatocytic infiltration in the high dose groups. Both CY and PBO cause liver and kidney inflammation and induce genotoxicity.

Automation of the cytokinesis-block micronucleus cytome assay by laser scanning cytometry and its potential application in radiation biodosimetry

Here we describe the adaptation of laser scanning cytometry (LSC) to measure micronuclei (MN) automatically in lymphocytes. MN frequencies were determined in irradiated human lymphocytes using the cytokinesis-block technique, and the results from LSC were compared with visual scoring results obtained from slides of cells stained using Fast Green and 4',6-diamidino-2-phenylindole (DAPI). This fluorescent approach allowed clear identification of binucleated cells and detection of MN. The dose responses measured visually and by LSC showed similar trends and correlated positively (r = 0.9689; P < 0.0001). High-content analysis was developed to further automatically score MN within mono-, tri- and tetra-nucleated cells and to determine the nuclear division index and nuclear circularity values. The high-throughput nature of LSC can provide unique advantages in future DNA damage diagnostics in experimental and epidemiological studies. Importantly, it allows for co-detection of other biomarkers of interest within a single lymphocyte, and further development of this capability is anticipated.

Micronuclei in genotoxicity assessment: from genetics to epigenetics and beyond

Micronuclei (MN) are extra-nuclear bodies that contain damaged chromosome fragments and/or whole chromosomes that were not incorporated into the nucleus after cell division. MN can be induced by defects in the cell repair machinery and accumulation of DNA damages and chromosomal aberrations. A variety of genotoxic agents may induce MN formation leading to cell death, genomic instability, or cancer development. In this review, the genetic and epigenetic mechanisms of MN formation after various clastogenic and aneugenic effects on cell division and cell cycle are described. The knowledge accumulated in literature on cytotoxicity of various genotoxins is precisely reflected and individual sensitivity to MN formation due to single gene polymorphisms is discussed. The importance of rapid MN scoring with respect to the cytokinesis-block micronucleus assay is also evaluated.

Evaluation of (anti)genotoxic activities of Phyllanthus niruri L. in rat bone marrow using the micronucleus test

Phyllanthus niruri L. (Euphorbiaceae), known as "quebra-pedra" (Portuguese for "stonebreaker"), is an herb used for kidney disorders. In light of its frequent use by the population, the present study aimed to investigate the genotoxic, antigenotoxic and cytotoxic activities of a standardized P. niruri extract in bone marrow rats. Three groups of 12 animals were treated daily by gavage over a period of 30 days, with 50, 150 or 250 mg/kg of P. niruri extract aqueous solution. The control group (n = 12) received tap water. At the end of treatment (day 31), groups were divided into two minor subgroups (n=6/group) and received cyclophosphamide (50 mg/kg, i.p.) or saline 0.9% (i.p.). After 24 hours, we evaluated the frequency of micronucleated polychromatic erythrocytes for each animal (MNPCE) at 1000 PCE. Cytotoxicity was evaluated with the PCE/NCE ratio (NEC = normochromatic erythrocytes). General toxicity was assessed during treatment using the parameters of body weight gain, ration and water consumption. The dry extract did not provoke changes in body weight, weight gain, ration and water intake or changes in the frequency of MNPCE or cytotoxicity in bone marrow. We propose that the P. niruri extract used here showed no genotoxic, antigenotoxic and cytotoxic activities under the experimental conditions.

Cytogenetic status of healthy children assessed with the alkaline comet assay and the cytokinesis-block micronucleus cytome assay

In the present study the alkaline comet assay and the cytokinesis-block micronucleus cytome (CBMN Cyt) assay were used to evaluate the baseline frequency of cytogenetic damage in peripheral blood lymphocytes (PBLs) of 50 healthy children from the general population in Croatia (age, 11.62±1.81 years). Mean values of tail length, tail intensity and tail moment, as comet assay parameters, were 12.92±0.10, 0.73±0.06 and 0.08±0.01, respectively. The mean frequency of micronuclei (MN) for all subjects was 2.32±0.28 per 1000 bi-nucleated cells, while the mean frequency of nucleoplasmic bridges (NPBs) was 1.72±0.24 and of nuclear buds (NBUDs) 1.44±0.19. The mean nuclear division index (NDI) was 1.70±0.05. When comet-assay parameters were considered, higher mean values for all three were found for the female population. According to the Mann-Whitney U test applied on the results of the comet assay, the only statistically significant difference between the male and female populations was found for tail length. Similar to the results obtained by the comet assay, girls showed higher mean values of all three measured parameters of the CBMN Cyt assay. This difference was statistically significant for total number of NPBs only. In the case of the NDI, a higher mean value was also obtained in girls, but this difference was not statistically significant. The results obtained present background data that could be considered as normal values for healthy children living in urban areas, and can later on serve as baseline values for further toxicological monitoring. Additionally, the usefulness of both techniques in measuring cytogenetic damage during bio-monitoring of children is confirmed.

Re-evaluation of a reported increased micronucleus frequency in lymphocytes of workers occupationally exposed to formaldehyde

A replicate evaluation of increased micronucleus (MN) frequencies in peripheral lymphocytes of workers occupationally exposed to formaldehyde (FA) was undertaken to verify the observed effect and to determine scoring variability. May-Grünwald-Giemsa-stained slides were obtained from a previously performed cytokinesis-block micronucleus test (CBMNT) with 56 workers in anatomy and pathology laboratories and 85 controls. The first evaluation by one scorer (scorer 1) had led to a highly significant difference between workers and controls (3.96 vs 0.81 MN per 1000 cells). The slides were coded before re-evaluation and the code was broken after the complete re-evaluation of the study. A total of 1000 binucleated cells (BNC) were analysed per subject and the frequency of MN (in ‰) was determined. Slides were distributed equally and randomly between two scorers, so that the scorers had no knowledge of the exposure status. Scorer 2 (32 exposed, 36 controls) measured increased MN frequencies in exposed workers (9.88 vs 6.81). Statistical analysis with the two-sample Wilcoxon test indicated that this difference was not significant (p=0.17). Scorer 3 (20 exposed, 46 controls) obtained a similar result, but slightly higher values for the comparison of exposed and controls (19.0 vs 12.89; p=0.089). Combining the results of the two scorers (13.38 vs 10.22), a significant difference between exposed and controls (p=0.028) was obtained when the stratified Wilcoxon test with the scorers as strata was applied. Interestingly, the re-evaluation of the slides led to clearly higher MN frequencies for exposed and controls compared with the first evaluation. Bland-Altman plots indicated that the agreement between the measurements of the different scorers was very poor, as shown by mean differences of 5.9 between scorer 1 and scorer 2 and 13.0 between scorer 1 and scorer 3. Calculation of the intra-class correlation coefficient (ICC) revealed that all scorer comparisons in this study were far from acceptable for the reliability of this assay. Possible implications for the use of the CBMNT in human biomonitoring studies are discussed.

UKEMS/Dutch EMS-sponsored workshop on biomarkers of exposure and oxidative DNA damage & 7th GUM-32P-postlabelling workshop, University of Münster, Münster, Germany, 28-29 March 2011

Environmental exposures are a major concern for human cancer. However, the precise contribution of specific risk factors and their interactions, both with each other and with genotype, continue to be difficult to elucidate. The exposome is the comprehensive characterisation of an individual's lifetime exposure history (Wild, C. P. (2009) Environmental exposure measurement in cancer epidemiology. Mutagenesis, 24, 117-125). Unravelling complex environmental and genetic aetiologies in order to plan effective public health interventions demands that both environmental exposures and genetic variations are reliably measured. The development, validation and application of biomarkers of exposure are manifestly critical to the future of cancer epidemiology. The aim of this workshop at the University of Münster was to discuss the current status of exposure biomarkers in cancer molecular epidemiology as well as new findings achieved by applying the methods to studies of mechanisms of human cancer. Day 1 focused on biomarkers of exposure (i.e. carcinogen DNA adducts), effect and susceptibility to gain greater understanding of environmental cancer risks and their modulation. Day 2 focused on the role of oxidative stress and DNA damage in human carcinogenesis including methodologies used for the measurement of oxidatively induced DNA lesions in human cells or tissues and the possible use of these lesions as cancer biomarkers.

Assessment of genotoxic effects and changes in gene expression in humans exposed to formaldehyde by inhalation under controlled conditions

Forty-one volunteers (male non-smokers) were exposed to formaldehyde (FA) vapours for 4 h/day over a period of five working days under strictly controlled conditions. For each exposure day, different exposure concentrations were used in a random order ranging from 0 up to 0.7 p.p.m. At concentrations of 0.3 and 0.4 p.p.m., four peaks of 0.6 or 0.8 p.p.m. for 15 min each were applied. During exposure, subjects had to perform bicycle exercises (∼80 W) four times for 15 min. Blood samples, exfoliated nasal mucosa cells and nasal biopsies were taken before the first and after the last exposure. Nasal epithelial cells were additionally sampled 1, 2 and 3 weeks after the end of the exposure period. The alkaline comet assay, the sister chromatid exchange test and the cytokinesis-block micronucleus test were performed with blood samples. The micronucleus test was also performed with exfoliated nasal mucosa cells. The expression (mRNA level) of the glutathione (GSH)-dependent formaldehyde dehydrogenase (FDH, identical to alcohol dehydrogenase 5; ADH5; EC 1.2.1.46) was measured in blood samples by quantitative real-time reverse transcription-polymerase chain reaction with TaqMan probes. DNA microarray analyses using a full-genome human microarray were performed on blood samples and nasal biopsies of selected subgroups with the highest FA exposure at different days. Under the experimental conditions of this study, inhalation of FA did not lead to genotoxic effects in peripheral blood cells and nasal mucosa and had no effect on the expression of the FDH gene. Inhalation of FA did also not cause alterations in the expression of genes in a microarray analysis with nasal biopsies and peripheral blood cells.