A simplified chromatin dispersion (nuclear halo) assay for detecting DNA breakage induced by ionizing radiation and chemical agents

DNA Damage in Bat Blood Leukocytes Using a Chromatin Dispersion Test (CDT): Biomarker of Environmental Genotoxicity

Environmental pollutants produce adverse effects on organisms and ecosystems. Biomonitoring and biomarkers offer a reasonable approach to make these assessments. Induced genetic changes can be using as a biomarker in organisms that react to a given compound in the ecosystem. Monitoring environmental genotoxicity necessitates the choice of model animals known as "sentinels or biological monitors" and the suitability of validated tests for DNA damage evaluation. We aimed to estimate the DNA damage produced by thermal stress in the leukocytes of the Mexican free-tailed bat (Tadarida brasiliensis). The DNA damage in bat leukocytes exposed to different temperatures (35 °C, 45 °C, and 55 °C) was evaluated by the adapted chromatin dispersion test (CDT) and the results were confirmed by the alkaline comet test. The CDT permitted a clear representation of leukocytes with fragmented DNA and of nonfragmented DNA. In addition, we detected nuclear anomalies in relation to cell death cellular swelling, nuclear fragmentation, and chromatin lysis. The alkaline comet assay revealed that the halos of diffuse chromatin include fragmented DNA. The assay of the method employing the CDT is well established, precise, and cost-effective for the routine quantitative analysis of DNA damage on the effect of the leukocytes of bats exposed to thermal stress. This could also apply as a sensitive screening tool for the evaluation of genotoxicity in environmental protection programs.

Chromatin Dispersion Test to Asses DNA Damage in Cervical Epithelial Cells

The chromatin dispersion test (CDT) is based on the removal of nuclear proteins under the assumption that cells with fragmented DNA produce a typical halo of circular DNA loops, which is absent in cells with non-fragmented DNA. This method represents a simple, rapid, accurate, highly reproducible, and inexpensive technique to assess nuclear DNA damage in somatic cells. The visualization of DNA damage and the capacity of the test to provide a threshold value to discriminate between high and low levels of cervical lesions would aid in determining the malignant transformation. All of these advantages associated with the CDT protocol could promote this technique as a tool for the quick and reliable diagnosis of cervical epithelial disorders, even at primary-care centers.

Evaluation of DNA fragmentation in dog sperm using the sperm chromatin dispersion test

The study's objective was to adapt the Sperm Chromatin Dispersion (SCD) protocol to evaluate sperm DNA fragmentation and implement a fragmentation control in dogs. Correlation between DNA status and routine sperm parameters was also analysed. To adapt the SCD, two different mercaptoethanol (ME) concentrations were assayed (2.5 and 5%) in fourteen ejaculates from seven dogs and semen incubation with 0.3 M NaOH for 15 min at room temperature was assayed as a control for sperm DNA fragmentation. Data were analysed using a Mann-Whitney test and either Pearson's or Spearman's correlation. The selected ME concentration to use in the SCD test was 5%, as it produced the largest DNA dispersion halo while preserving the core nucleus structure. Four DNA halo patterns were identified: large dispersion halos, medium halos, small halos and nuclei without halos. Semen incubated with NaOH showed 100% sperm without halos (damaged DNA). A significant positive correlation was observed between sperm with fragmented DNA and sperm with coiled tails. Thus, it was possible to adapt the SCD protocol to evaluate dog sperm DNA fragmentation in raw semen without using a commercial kit and establish incubation with NaOH as a DNA fragmentation control. Only coiled tails showed correlation with DNA fragmentation.

Evaluation of the genotoxic effect of heavy metals in pigeons from urban and rural habitat in Monterrey, Mexico, using the chromatin dispersion assay

PURPOSE

Evaluate genotoxic effect of heavy metals on Pigeon Erythrocytes (PE) from urban and rural habitat (outside of the city) in Monterrey, Mexico, using the chromatin dispersion assay.

MATERIALS AND METHODS

We quantified metals concentrations (Cd, Hg, Cu and Pb) in tail feathers of 22 pigeons from an urban and a rural site in northeastern Mexico. DNA damage in peripheral blood erythrocytes was measured by chromatin dispersion assay in 13 pigeon living in urban habitat and in nine living in rural habitat as the control. MicroNucleus (MN) test was used to confirm levels of DNA damage.

RESULTS

Birds in urban habitat had highest concentrations in feathers for all the metallic elements analysed with respect to birds in rural habitat. Concentrations of Cu and Hg showed a significant increase (p < 0.05). Our results showed a significant increase of DNA damage in urban-habitat pigeons compared with that of pigeons in rural area. These results were confirmed by a MN test.

CONCLUSIONS

Our preliminary findings demonstrate that PE examination via chromatin dispersion assay is a reliable, precise and inexpensive morphological bioassay for evaluating environmental genotoxicity associated with heavy metals. Further studies for evaluating the individual participation of contaminants in DNA damage are needed.

Zinc and selenium combination treatment protected diabetes-induced testicular and epididymal damage in rat

Diabetes increases the possibility of germ cell damage, hypogonadism, and male infertility. Diabetic condition negatively impacts zinc (Zn) and selenium (Se) levels in the body. Zn and Se are among the most important trace elements involved in the regulation of redox reaction, antioxidants enzymes activities, and DNA expression in a germ cell. The present study aimed to elucidate the combined effects of Zn and Se treatment on diabetes-induced germ cell damage in male Sprague Dawley rats. Type 1 diabetes was induced by the single intraperitoneal (i.p.) injection of streptozotocin (55 mg/kg). Zn (3 mg/kg, i.p.) and Se (0.5 mg/kg, i.p.) were administered daily for 8 consecutive weeks. All the animals were provided with normal feed and water throughout the study. The effects on germ cell damage were evaluated by body weight, feed-water intake, organ weight, sperm count, motility, sperm head morphology, biochemical analysis, histology, immunohistochemistry, halo assay, germ cell comet assay, testes terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end-labeling (TUNEL) assay, sperm TUNEL assay, serum protein pattern analysis, and subcellular analysis using transmission electron microscopy. Further, the expressions of nuclear erythroid-derived related factor 2, catalase, glutathione peroxidase 4, and glutathione peroxidase 5 were carried out to ascertain the mechanism of protection. The present results demonstrated that 8 weeks combined treatment of Zn (3 mg/kg, i.p.) and Se (0.5 mg/kg, i.p.) reduced diabetes-induced germ cell damage. This study further highlighted that Zn and Se combination treatment might be a better strategy for the germ cell protection in diabetes and deserve further investigation.

Detection of DNA damage in pigeon erythrocytes using a chromatin dispersion assay

The monitoring of environmental genotoxicity requires the selection of model organisms as 'sentinels' as well as the development of sensitive and reliable tests for the assessment of DNA damage. The aims of this study were to quantify genomic DNA strand breakage in the erythrocytes of Columba livia induced by thermal stress using the modified chromatin dispersion test and to validate the results by alkaline comet assay and DNA breakage detection-fluorescence in situ hybridization (DBD-FISH). The chromatin dispersion test allowed for clear visualization of erythrocyte cells with DNA damage and of cells with no DNA damage. DNA damage increased significantly with increase in temperature. Additionally, we observed nuclear abnormalities associated with apoptosis, such as karyorrhexis (nuclear disintegration) and karyolysis (nuclear dissolution). These results were validated by alkaline comet assay and DBD-FISH. In conclusion, this procedure is a reliable, precise, and inexpensive morphological bioassay for routine quantitative analysis of DNA breakage in pigeon erythrocytes induced by thermal stress. This method could also be useful as a practical screening tool for genotoxicity testing in environmental care.

Evaluation of oxidative DNA damage in pigeon erythrocytes using DNA breakage detection-fluorescence in situ hybridization (DBD-FISH)

DNA breakage detection-fluorescence in situ hybridization (DBD-FISH) enables detection and quantification of DNA breakage in the entire genome or within specific DNA sequences in single cells. We used this method to visualize and evaluate DNA damage in pigeon erythrocytes that were induced by elevated temperature and hydrogen peroxide. We also examined morphological changes in the cell nuclei. DBD-FISH demonstrated a significant increase of DNA damage in a temperature dependent manner, which resulted in nuclear abnormalities associated with apoptotic cells. These cells gave strong nuclear fluorescent signals that indicated cell death.

The Fast-Halo Assay for the Detection of DNA Damage

The need for express screening of the DNA damaging potential of chemicals has progressively increased over the past 20 years due to the wide number of new synthetic molecules to be evaluated, as well as the adoption of more stringent chemical regulations such as the EU REACH and risk reduction politics. In this regard, DNA diffusion assays such as the microelectrophoretic comet assay paved the way for rapid genotoxicity testing. A more significant simplification and speeding up of the experimental processes was achieved with the fast halo assay (FHA) described in the present chapter. FHA operates at the single cell level and relies on radial dispersion of the fragments of damaged DNA from intact nuclear DNA. The fragmented DNA is separated by diffusion in an alkaline solvent and is stained, visualized, and finally quantified using computer-assisted image analysis programs. This permits the rapid assessment of the extent of DNA breakage caused by different types of DNA lesions. FHA has proven to be sensitive, reliable, and flexible. This is currently one of the simplest, cheapest, and quickest assays for studying DNA damage and repair in living cells. It does not need expensive reagents or electrophoretic equipment and requires only 40 min to prepare samples for computer-based quantification. This technique can be particularly useful in rapid genotoxicity assessments and in high-throughput genotoxicity screenings.

MiR-101 induces senescence and prevents apoptosis in the background of DNA damage in MCF7 cells

Moderately increased DNA damage due to the exogenous miR-101 (4 fold) over-expression in MCF7 cells was substantiated by an increase in the number of γ-H2AX foci, correlating with a simple-to-do Halo-assay. miR-101 induced mild/moderate DNA damage favoured senescence rather than apoptosis. An experimental support emanated from the induced mild/moderate DNA damage with 1 µM/5 µM etoposide in MCF7 cells, which resulted in an endogenous miR-101 over-expression (10/4 fold, respectively), followed by senescence. On the other hand, the severe DNA damage induced with 10 µM etoposide, resulted in a low (<1 fold) endogenous expression of miR-101 and an elevated percentage of apoptotic cells. Using bioinformatics tools along with in-vitro and in-vivo validations, miR-101 was found to target and downregulate the mRNA expression of UBE2N and SMARCA4, involved in DNA damage repair (DDR) pathways. Recovery of the expression of the two novel targets in anti-miR-101 transfection validated the results. We conclude that a threshold range of over-expressed miR-101, capable of inducing mild/moderate DNA damage, is sensed by cells to become senescent. The observation derives further support from in-silico protein-protein network analysis where the two novel targets showed their involvement in senescence pathway.

HaloJ: an ImageJ program for semiautomatic quantification of DNA damage at single-cell level

Although Halo assay is a fast and more economic technique, it is not popular compared to comet assay for the measurement of DNA damage. One of the reasons behind this was nonavailability of suitable user-friendly program. Currently, most of the researchers were analyzing halo images manually using image analysis software (Scion Image or ImageJ). To address this problem, I have developed a semiautomatic halo analysis ImageJ program, HaloJ, and applied in the assessment of DNA damage at the single-cell level. In this article, we have shown that data obtained from the HaloJ program have a very good correlation with the data obtained using comet assay analysis program such as Comet Assay Software Project. To the best of our knowledge, this will be the first program to quantify DNA damage of halo images. This program will be of great use for researchers working on the DNA damage and repair, radiation biology, toxicology, cancer biology, and so on.

Alkaline nuclear dispersion assays for the determination of DNA damage at the single cell level

Over the past three decades the development of methods for visualizing at the cell level the extent of DNA breakage significantly contributed to genotoxicity testing: their availability greatly improved the knowledge in the field of genetic toxicology. These procedures are based on the separation and visualization of DNA fragments resulting from cleavage of nuclear DNA. The separation process can be obtained either electrically (comet assay, linear migration of DNA fragments) or chemically (alkaline dispersion assays, radial diffusion of DNA fragments). Once separated and stained, intact and fragmented DNA can be observed with fluorescence or light microscope. Appropriate computer-assisted image analysis allows quantitative determination of the extent of DNA breakage. These procedures have been proven to be sensitive, flexible, and reliable, and, as compared to former methods, they are simpler, are less time and money consuming, and have the unique capability of detecting DNA damage at the single cell level. This last feature has the additional advantage of allowing the identification of cellular subpopulations characterized by different sensitivity to the damaging agent. The fast halo assay (FHA) is currently the simplest and quickest nuclear dispersion assay; recent modifications of FHA have further improved the assay and pave the way to a full exploitation of its analytical potential. In this chapter the development, procedures, applications, and limits of these dispersion assays, with a particular focus on FHA, will be illustrated.