Ret, Abl1 (cAbl) and Trp53 gene fragmentations in comet-FISH assay act as in vivo biomarkers of radiation exposure in C57BL/6 and CBA/J mice

Exercise and Oxidative Damage in Nucleoid DNA Quantified Using Single Cell Gel Electrophoresis: Present and Future Application

High intensity exercise can enhance the production of reactive oxygen and nitrogen free radical species, which may cause a number of perturbations to cellular integrity, including deoxyribonucleic acid (DNA) modification. In the absence of adequate DNA repair, it is theoretically possible that several biological disorders may ensue, in addition to premature aging. This striking hypothesis and supposition can only be realized in the presence of sound methodology for the quantification of DNA damage and repair. The alkaline single-cell gel electrophoresis or "comet assay" is a simple and reliable method for measuring the components of DNA stability in eukaryotic cells. The assay is commonly used in research associated with genotoxicology and in human bio-monitoring studies concerned with gene-environment interactions; but is currently less appreciated and under-utilized in the domain of exercise science. No exercise related study for example, has incorporated the comet assay combined with fluorescent in situ hybridization methodology to detect and investigate whole genome, telomeric DNA, or gene region-specific DNA damage and repair in cells. Our laboratory and others have used the comet assay in conjunction with lesion-specific endonucleases to measure DNA strand breaks and oxidized bases to confirm that high intensity exercise can damage and destabilize DNA. Thus, the primary function of this review is to highlight recent advances and innovation with the comet assay, in order to enhance our future understanding of the complex interrelationship between exercise and DNA modification in eukaryotic cells. A brief synopsis of the current literature addressing DNA stability as a function of continuous aerobic exercise is also included.

Exposure to ionizing radiation reveals global dose- and time-dependent changes in the urinary metabolome of rat

The potential for exposures to ionizing radiation has increased in recent years. Although advances have been made, understanding the global metabolic response as a function of both dose and exposure time is challenging considering the complexity of the responses. Herein we report our findings on the dose- and time-dependency of the urinary response to ionizing radiation in the male rat using radiation metabolomics. Urine samples were collected from adult male rats, exposed to 0.5 to 10 Gy γ-radiation, both before from 6 to 72 h following exposures. Samples were analyzed by liquid chromatography coupled with time-of-flight mass spectrometry, and deconvoluted mass chromatographic data were initially analyzed by principal component analysis. However, the breadth and complexity of the data necessitated the development of a novel approach to summarizing biofluid constituents after exposure, called Visual Analysis of Metabolomics Package (VAMP). VAMP revealed clear urine metabolite profile differences to as little as 0.5 Gy after 6 h exposure. Via VAMP, it was discovered that the response to radiation exposure found in rat urine is characterized by an overall net down-regulation of ion excretion with only a modest number of ions excreted in excess over pre-exposure levels. Our results show both similarities and differences with the published mouse urine response and a dose- and time-dependent net decrease in urine ion excretion associated with radiation exposure. These findings mark an important step in the development of minimally invasive radiation biodosimetry. VAMP should have general applicability in metabolomics to visualize overall differences and trends in many sample sets.

Fluorescence in situ hybridization on electrophoresed cells to detect sequence specific DNA damage

Fluorescence in situ hybridization (FISH) to label fragments of DNA with probes which can specifically locate a genomic region of interest, combined with the single cell electrophoresis (Comet) assay, also termed Comet-FISH, allows the quantification of DNA damage and repair at a specific genomic locus. While the Comet assay alone quantifies only the overall DNA damage of an individual cell, subsequent FISH on the electrophoresed single cell genome enables the coincidental localization of fluorescently labelled sequences (i.e., probes) to the respective damaged or undamaged genes or specific genomic regions of interest. In that way sequence specific DNA damage, global genomic and transcription coupled repair or the three dimensional ultrastructure of cells from any tissue can be comparatively investigated. This protocol provides a detailed description of the principles and basic methodology of a standard Comet-FISH experiment to study interphase cells of any tissue. Also important variations of the protocol (e.g., neutral conditions to detect double strand breaks) as well as the production of fluorochrome-labelled DNA probes via random priming are described.

Genetic background and lymphocyte populations after total-body exposure to iron ion radiation

PURPOSE

Particle radiations could significantly impact astronaut health during space missions. This study quantified the effects of iron ion radiation on lymphocytes in two strains of mice differing in susceptibility to radiation-induced acute myeloid leukemia (AML) and thymic lymphoma (TL): C57BL/6 (AML resistant, TL sensitive) and CBA/Ca (AML sensitive, TL resistant).

MATERIALS AND METHODS

The animals (n = 60/strain) were irradiated with ⁵⁶Fe(26+) (1 GeV) to total doses of 0, 0.5, 2 and 3 Gray (Gy) at an average dose rate of 1 Gy/min and euthanised on days 4 and 30 thereafter; blood, spleen, and bone marrow were collected for flow cytometry analyses. Cells expressing the following molecules were quantified: Cluster of differentiation (CD) 4, CD8, CD25, CD34, CD71, B220 (isoform of CD45 on B cells), NK1.1 (marker on natural killer or NK cells, C57B mice), panNK (marker on NK cells, CBA mice), and Sca1 (stem cell antigen 1).

RESULTS

Exposure to radiation resulted in different distribution patterns in lymphocyte populations and leukocytes expressing activation and progenitor markers in the two mouse strains. Significant main effects were dependent upon strain, as well as radiation dose, body compartment, and time of assessment. Especially striking differences were noted on day 4 after 3 Gy irradiation, including in the CD4:CD8 ratio [blood, C57 (2.83 ± 0.25) vs. CBA (6.19 ± 0.24); spleen, C57 (2.29 ± 0.12) vs. CBA (4.98 ± 0.22)], %CD25(+) mononuclear cells in bone marrow [C57 (5.62 ± 1.19) vs. CBA (12.45 ± 0.93)] and %CD34(+)Sca1(+) cells in bone marrow [CD45¹° gate, C57 (2.72 ± 0.74) vs. CBA (21.44 ± 0.73)].

CONCLUSION

The results show that genetic background, as well as radiation dose and time post-exposure, had a profound impact on lymphocyte populations, as well as other leukocytes, after exposure to iron ion radiation.

Fluorescence in situ hybridization in combination with the comet assay and micronucleus test in genetic toxicology

Comet assay and micronucleus (MN) test are widely applied in genotoxicity testing and biomonitoring. While comet assay permits to measure direct DNA-strand breaking capacity of a tested agent MN test allows estimating the induced amount of chromosome and/or genome mutations. The potential of these two methods can be enhanced by the combination with fluorescence in situ hybridization (FISH) techniques. FISH plus comet assay allows the recognition of targets of DNA damage and repairing directly. FISH combined with MN test is able to characterize the occurrence of different chromosomes in MN and to identify potential chromosomal targets of mutagenic substances. Thus, combination of FISH with the comet assay or MN test proved to be promising techniques for evaluation of the distribution of DNA and chromosome damage in the entire genome of individual cells. FISH technique also permits to study comet and MN formation, necessary for correct application of these methods. This paper reviews the relevant literature on advantages and limitations of Comet-FISH and MN-FISH assays application in genetic toxicology.

The Comet-FISH assay for the analysis of DNA damage and repair

In this chapter, I describe the alkaline single-cell gel electrophoresis (Comet assay) combined with fluorescence in situ hybridization (FISH) technology, used in our laboratory, to study the incidence and repair of lesions induced in human cells by ultraviolet light. The Comet-FISH method permits the simultaneous and comparative analysis of DNA damage and its repair throughout the genome and in defined chromosomal regions. This very sensitive approach can be applied to any lesion, such as those induced by chemical carcinogens and products of cellular metabolism that can be converted to DNA single- or double-strand breaks. The unique advantages and limitations of the method for particular applications are discussed.

Enhanced sensitivity of the RET proto-oncogene to ionizing radiation in vitro

Exposure to ionizing radiation is a well-known risk factor for a number of human cancers, including leukemia and thyroid cancer. It has been known for a long time that exposure of cells to radiation results in extensive DNA damage; however, a small number of studies have tried to explain the mechanisms of radiation-induced carcinogenesis. The high prevalence of RET/PTC rearrangements in patients who have received external radiation, and the evidence of in vitro induction of RET rearrangements in human cells, suggest an enhanced sensitivity of the RET genomic region to damage by ionizing radiation. To assess whether RET is indeed more sensitive to radiations than other genomic regions, we used a COMET assay coupled with fluorescence in situ hybridization, which allows the measurement of DNA fragmentation in defined genomic regions of single cells. We compared the initial DNA damage of the genomic regions of RET, CXCL12/SDF1, ABL, MYC, PLA2G2A, p53, and JAK2 induced by ionizing radiation in both a lymphoblastoid and a fetal thyroid cell line. In both cell lines, RET fragmentation was significantly higher than in other genomic regions. Moreover, a differential distribution of signals within the COMET was associated with a higher percentage of RET fragments in the tail. RET was more susceptible to fragmentation in the thyroid-derived cells than in lymphoblasts. This enhanced susceptibility of RET to ionizing radiation suggests the possibility of using it as a radiation exposure marker.

FISH glossary: an overview of the fluorescence in situ hybridization technique

The introduction of FISH (fluorescence in situ hybridization) marked the beginning of a new era for the study of chromosome structure and function. As a combined molecular and cytological approach, the major advantage of this visually appealing technique resides in its unique ability to provide an intermediate degree of resolution between DNA analysis and chromosomal investigations while retaining information at the single-cell level. Used to support large-scale mapping and sequencing efforts related to the human genome project, FISH accuracy and versatility were subsequently capitalized on in biological and medical research, providing a wealth of diverse applications and FISH-based diagnostic assays. The diversification of the original FISH protocol into the impressive number of procedures available these days has been promoted throughout the years by a number of interconnected factors: the improvement in sensitivity, specificity and resolution, together with the advances in the fields of fluorescence microscopy and digital imaging, and the growing availability of genomic and bioinformatic resources. By assembling in a glossary format many of the "acronymed" FISH applications published so far, this review intends to celebrate the ability of FISH to re-invent itself and thus remain at the forefront of biomedical research.