Evaluation of DNA damage in Eurasian marsh frogs (Pelophylax ridibundus) by comet assay for determination of possible pollution in the different lakes in central Anatolia, Turkey

Nuclear abnormalities and DNA damage indicate different genotoxic stress responses of marsh frogs (Pelophylax ridibundus, Pallas 1771) to industrial and agricultural water pollution in South Bulgaria

Amphibians are continuously exposed to pollutants and anthropogenic stressors in their natural habitats, representing a significant challenge to their survival. This study aimed to quantify the extent of DNA damage caused by chronic industrial and agrochemical surface water pollution in wild populations of the marsh frog (Pelophylax ridibundus). The observed genotoxic effects on the marsh frog DNA, manifesting as abnormalities in erythrocyte nuclei, micronuclei, and DNA strand breaks, demonstrate a clear cause-and-effect relationship with surface water parameters, heavy metals, metalloids, and pesticides. The most prevalent nuclear abnormalities observed were notched and blebbed nuclei and nuclear buds, indicative of chromosomal instability. The significant correlation between cadmium, lead, and copper contamination and the increased frequency of DNA breakage in the marsh frogs from the industrial site indicates that heavy metal contamination has a higher genotoxic potential than pesticide contamination. These findings underscore the vulnerability of amphibians inhabiting heavy metal-contaminated wetlands to genotoxic stress due to their lower tolerance to environmental genotoxins. Therefore, using in situ assays to detect erythrocyte nuclear abnormalities and DNA damage in P. ridibundus could serve as a reliable indicator of environmental quality and provide early detection of anthropogenic pollution.

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.

Response of digestive organs of Hypsiboas albopunctatus (Anura: Hylidae) to benzo[α]pyrene

Anurans are exposed to several pollutants. One of these is benzo[α]pyrene (BaP). This compound is produced by incomplete combustion and is toxic to the liver and intestine, where it is metabolized. Here, we tested how different concentrations of BaP affect the thickness of small intestine and liver melanomacrophages (MMCs) ofHypsiboas albopunctatusduring short- and long-term exposures. We conducted an experiment with a 3 × 2 factorial design to answer these two questions. Male specimens were separated into groups injected with either 3 or 7 mg/kg of BaP and euthanized after either 72 or 168 h. Then, we measured the thickness of the intestinal epithelium and the area occupied by MMCs. The thickness of intestinal epithelium decreased in both high and low concentration for short-term exposure compared to control, and increased in the long-term group in both low and high concentrations. The short-term decrease in thickness is due to the damage caused by BaP on the absorptive capacity of the epithelium, whereas the epithelium increased its thickness and recovered normal activity in the long-term. High BaP concentration decreased the area of MMCs in the short-term group. The increase in MMCs is associated with the detoxifying role of these cells, while the decrease was triggered by cellular stress due to high BaP concentration. The concentrations of BaP we used are close to those found in polluted environments. Therefore, water contaminated with BaP can potentially affect the morphology of internal organs of anurans.

The Comet Assay and its applications in the field of ecotoxicology: a mature tool that continues to expand its perspectives

Since Singh and colleagues, in 1988, launched to the scientific community the alkaline Single Cell Gel Electrophoresis (SCGE) protocol, or Comet Assay, its uses and applications has been increasing. The thematic areas of its current employment in the evaluation of genetic toxicity are vast, either in vitro or in vivo, both in the laboratory and in the environment, terrestrial or aquatic. It has been applied to a wide range of experimental models: bacteria, fungi, cells culture, arthropods, fishes, amphibians, reptiles, mammals, and humans. This document is intended to be a comprehensive review of what has been published to date on the field of ecotoxicology, aiming at the following main aspects: (i) to show the most relevant experimental models used as bioindicators both in the laboratory and in the field. Fishes are clearly the most adopted group, reflecting their popularity as bioindicator models, as well as a primary concern over the aquatic environment health. Amphibians are among the most sensitive organisms to environmental changes, mainly due to an early aquatic-dependent development stage and a highly permeable skin. Moreover, in the terrestrial approach, earthworms, plants or mammalians are excellent organisms to be used as experimental models for genotoxic evaluation of pollutants, complex mix of pollutants and chemicals, in both laboratory and natural environment. (ii) To review the development and modifications of the protocols used and the cell types (or tissues) used. The most recent developments concern the adoption of the enzyme linked assay (digestion with lesion-specific repair endonucleases) and prediction of the ability to repair of oxidative DNA damage, which is becoming a widespread approach, albeit challenging. For practical/technical reasons, blood is the most common choice but tissues/cells like gills, sperm cells, early larval stages, coelomocytes, liver or kidney have been also used. (iii) To highlight correlations with other biomarkers. (iv) To build a constructive criticism and summarize the needs for protocol improvements for future test applications within the field of ecotoxicology. The Comet Assay is still developing and its potential is yet underexploited in experimental models, mesocosmos or natural ecosystems.

Analysis of fish DNA biomarkers as a molecular-level approach for ecological health assessments in an urban stream

This study was performed to determine the ecosystem health of an urban stream using DNA damage biomarkers of sentinel fish species along with chemical analyses of water and sediments in the impacted and reference zones. The results based on single-cell gel electrophoresis showed that the extent of DNA damage was significantly elevated in the polluted zone. The severity of DNA damage in the impacted zone was largely attributed to high levels of heavy metals, such as As, Zn, Pb, and Ni. The DNA damage biomarker in benthic fish was sensitive to habitat change, which suggested that this fish species and biomarker are excellent tools for risk assessment. The acute toxicity tests demonstrated that SCGE was sufficient to reflect the different genotypes and pollution statuses and to propose the possibility of zebrafish erythrocytes as competitive materials.