Assessment of DNA damage in canine peripheral blood and bone marrow after total body irradiation using the single-cell gel electrophoresis technique

The comet assay in animal models: From bugs to whales - (Part 2 Vertebrates)

The comet assay has become one of the methods of choice for the evaluation and measurement of DNA damage. It is sensitive, quick to perform and relatively affordable for the evaluation of DNA damage and repair at the level of individual cells. The comet assay can be applied to virtually any cell type derived from different organs and tissues. Even though the comet assay is predominantly used on human cells, the application of the assay for the evaluation of DNA damage in yeast, plant and animal cells is also quite high, especially in terms of biomonitoring. The present extensive overview on the usage of the comet assay in animal models will cover both terrestrial and water environments. The first part of the review was focused on studies describing the comet assay applied in invertebrates. The second part of the review, (Part 2) will discuss the application of the comet assay in vertebrates covering cyclostomata, fishes, amphibians, reptiles, birds and mammals, in addition to chordates that are regarded as a transitional form towards vertebrates. Besides numerous vertebrate species, the assay is also performed on a range of cells, which includes blood, liver, kidney, brain, gill, bone marrow and sperm cells. These cells are readily used for the evaluation of a wide spectrum of genotoxic agents both in vitro and in vivo. Moreover, the use of vertebrate models and their role in environmental biomonitoring will also be discussed as well as the comparison of the use of the comet assay in vertebrate and human models in line with ethical principles. Although the comet assay in vertebrates is most commonly used in laboratory animals such as mice, rats and lately zebrafish, this paper will only briefly review its use regarding laboratory animal models and rather give special emphasis to the increasing usage of the assay in domestic and wildlife animals as well as in various ecotoxicological studies.

Single-cell gel electrophoresis (SCG)-A review and discussion

Single-cell gel electrophoresis (SCG) is a simple, sensitive and effective technique. Being able to reflect quantitatively the genotoxicity of many hazardous agents, it is promising for application in environmental genotoxic monitoring and the study of carcinogenesis. In clinics, it can be used to evaluate the DNA repair ability and monitor DNA breaks during cancer therapy. As a biomarker, it has its own merits and limitations, being different from other biomarkers such as sister chromatid exchange (SCE) test and micronuclei (MN) assay. In many studies, it is more sensitive than SCE or MN. Combination studies with other biomarkers like SCE, MN, chromosomal aberration, bcl-2 and genetic polymorphisms have begun to demonstrate its great importance for the understanding of carcinogenesis and the genotoxicities of environmental factors.

Hemopoietic progenitor cells in the blood as indicators of the functional status of the bone marrow after total-body and partial-body irradiation: experiences from studies in dogs

The granulocyte-macrophage colony-forming cells (GM-CFC) were studied in the blood of dogs to evaluate their relationship to the bone marrow GM-CFC under normal conditions and their involvement in hemopoietic regeneration after different types of exposure to ionizing radiation. The GM-CFC could be defined as regular blood elements showing characteristic levels of their concentration in individual dogs in the range from 20 to 300 cells per ml. In relative terms, the GM-CFC numbers present in the whole blood of normal dogs were found to be on the order of 0.1% of the GM-CFC numbers present in the bone marrow. A small fraction of the GM-CFC population in the bone marrow, i.e., about 1%, can be mobilized into the peripheral blood within three h by intravenous injection of dextran sulfate (DS). These cells are characterized by a small size and a low S-phase fraction similar to the GM-CFC that are normally present in the blood. Total-body irradiation with single doses of 0.8 Gy and more caused a characteristic pattern of sequential changes in the blood GM-CFC concentration that were related to the recovery of the bone marrow GM-CFC population. The blood GM-CFC concentration showed an extreme depression within the first 15 days, a transient increase from day 17 to day 35 and remained at subnormal values for several weeks and months. The regeneration of the GM-CFC population in the bone marrow that could be mobilized into the blood by DS was similarly delayed as the recovery of the blood GM-CFC values. In dogs which were kept under continuous radiation exposure (0.019 Gy/day) causing permanent damage to the hemopoietic system, the GM-CFC numbers in the blood remained permanently depressed. Partial-body irradiation of dogs with a myeloablative dose (11.7 Gy) given to the anterior part of their body was followed by sequential changes in the blood GM-CFC concentration specific for this type of exposure. The pattern of changes was determined by direct radiation effects, the compensatory responses in the protected bone marrow and the regeneration events in the irradiated bone marrow. On the other hand, it could be shown that the repopulation and the restoration of the hemopoietic tissue is initiated by the seeding of hemopoietic cells (including GM-CFC) from the protected marrow.

Evaluation of DNA damage in workers occupationally exposed to pesticides using single-cell gel electrophoresis (SCGE) assay. Pesticide genotoxicity revealed by comet assay

The comet assay, also called the single-cell gel electrophoresis (SCGE) assay, is a rapid and sensitive method for the detection of DNA damage (strand breaks and alkali-labile sites) in individual cells. The assay is based on the embedding of cells in agarose, their lysis in alkaline buffer and finally subjection to an electric current. In the present study, alkaline SCGE was used to evaluate the extent of primary DNA damage and DNA repair in peripheral blood lymphocytes of workers employed in pesticide production. After the period of high pesticide exposure, lymphocytes of the occupationally exposed workers manifested increased tail length and tail moment compared to the control group. After the workers spent 6 months out of the pesticide exposure zone, both endpoints were still above that of the control but significantly decreased as compared to the results of the first analysis.

Single cell gel electrophoresis assay: methodology and applications

The single cell gel electrophoresis or Comet assay is a sensitive, reliable, and rapid method for DNA double- and single-strand breaks, alkali-labile sites and delayed repair site detection, in eukaryotic individual cells. Given its overall characteristics, this method has been widely used over the past few years in several different areas. In this paper we review the studies published to date about the principles, the basic methodology with currently used variations. We also explore the applications of this assay in: genotoxicology, clinical area, DNA repair studies, environmental biomonitoring and human monitoring.