Characterization of different DNA repair pathways in hepatic cells of Zebrafish (Danio rerio)

Indigo dyes: Toxicity, teratogenicity, and genotoxicity studies in zebrafish embryos

Wastewater released by textile dyeing industries is a major source of pollution. Untreated wastewater released from indigo dyeing operations affects aquatic ecosystems and threatens their biodiversity. We have assessed the toxicity of natural and synthetic indigo dye in zebrafish embryos, using the endpoints of teratogenicity, genotoxicity, and histopathology. The zebrafish embryo toxicity test (ZFET) was conducted, exposing embryos to ten concentrations of natural and synthetic indigo dyes; the 96-hour LC50 values were approximately 350 and 300 mg/L, respectively. Both dyes were teratogenic, causing egg coagulation, tail detachment, yolk sac edema, pericardial edema, and tail bend, with no significant difference in effects between the natural and synthetic dyes. Both dyes were genotoxic (using comet assay for DNA damage). Real-time RT-PCR studies showed upregulation of the DNA-repair genes FEN1 and ERCC1. Severe histological changes were seen in zebrafish larvae following exposure to the dyes. Our results show that indigo dyes may be teratogenic and genotoxic to aquatic organisms, underscoring the need for development of sustainable practices and policies for mitigating the environmental impacts of textile dyeing.

Alkaline Comet Assay to Assess Genotoxicity in Zebrafish Larvae

The zebrafish (Danio rerio) is a model organism widely used in several research fields due to its characteristics and numerous advantages, such as optical embryo transparency, fully sequenced genome, orthologous genes to humans, small size, high reproductive rate, easy gene editing and relatively low costs. Thus, a number of protocols have been developed that allow the use of this vertebrate model for toxic effect evaluation at various biological levels, including genotoxicity, using the comet assay technique.The comet assay or single-cell gel electrophoresis is a popular and sensitive method to study DNA damage in cells, which is described in this chapter. Briefly, cells suspended in agarose on a microscope slide are lysed, denatured, electrophoresed, neutralized, and stained to study the migration of DNA strand breaks. As a result, cells with increased DNA damage present a high fluorescence intensity and an increase of comet tail length. For the visual score, comets are classified according to the head integrity, tail intensity, and tail length into five classes, namely, class 0 until class 4 (comets with high damage and with almost all the DNA in the tail). These data are used to calculate the Genetic Damage Index (GDI) expressed as Arbitrary Units (AU).

2,4-Dichlorophenoxyacetic acid (2,4-D) affects DNA integrity and retina structure in zebrafish larvae

Monitoring the potential risk of herbicides in non-target organisms is a crucial issue for environmental safety. 2,4-D is an herbicide of high environmental relevance that has been shown to exert toxic effects to soil and aquatic biota. In the present study, we investigated the possible genotoxic and retinal development effects of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide in early life stages zebrafish (Danio rerio). Genotoxicity was evaluated by measuring DNA damage using the comet assay and also by the mRNA expression of genes implicated in apoptosis and/or DNA repair. Retinal development toxicity was evaluated with histological approach. The results obtained revealed that 2,4-D alters DNA integrity of zebrafish larvae. Moreover, transcriptomic data showed a significant induction of p-53 and casp-3 genes and a significant decrease of lig-4 in larvae exposed to the highest tested concentration of 2,4-D (0.8 mg/L). This suggested that p-53 gene regulates the process of DNA repair and apoptosis with increased levels of 2,4-D. The histopathological analysis revealed that early exposure to 2,4-D damaged the structure of larvae retina. Overall, this study is the first to report the DNA damage, casp-3, lig-4 and p-53 regulation, as well as the ocular developmental toxicity in zebrafish larvae at environmentally relevant concentrations of 2,4-D herbicide.

Assessment of diphenhydramine toxicity - Is its mode of action conserved between human and zebrafish?

The main aim of the study is to evaluate the effects of the pharmaceutical diphenhydramine (DPH) on embryo-larvae Danio rerio across distinct levels of organization - individual and subcellular - and correlate those effects with the DPH mode of action (MoA) assessed by in silico analysis. An embryos heartbeat rate reduction was observed at 10 mg/L DPH, but 0.001 to 10 mg/L did not significantly affect the zebrafish survival, hatching and morphology. Larvae swimming distance decreased (hypoactivity) at 1 and 10 mg/L DPH. Moreover, the straightforward movements decrease and the increase in the zigzag movements or movements with direction changes, shown an erratic swimming behavior. Energy budgets decreased for lipid (0.01 mg/L DPH) and carbohydrate (10 mg/L DPH) contents. Cholinesterase (neural function) and glutathione S-transferase (Phase II biotransformation/antioxidant processes) increased their activities at 10 mg/L DPH, where a decrease in the total glutathione content (antioxidant system) was observed. DNA damage was found at 0.01 and 10 mg/L DPH. However, a DNA repair occurred after subsequent 72 h in clean media. The in silico study revealed a relevant conservation between human and zebrafish DPH target molecules. These data provide a valuable ecotoxicological information about the DPH effects and MoA to non-target organisms.

Effect of benzophenone-3 on the blood cells of zebrafish (Danio rerio)

Benzophenone-3 (BP-3) is a common component of organic sunscreen widely used that can affect especially aquatic ecosystems health, including fish. To verify the biological effects of low concentrations of BP-3 on blood cells, one hundred and forty zebrafish (D. rerio) were used and then randomly divided into five groups: control group (water), solvent group (alcoholic water), and BP-3 group (BP-3 at 7 µg L^-1, BP-3 at 70 µg L^-1, and BP-3 at 700 µg L^-1). The blood slices were stained with Panoptic stain and with Giemsa solution for the hematological analysis. During the exposure to BP-3, no behavioral changes were observed. Although no significant difference in total leukocytes occurred, an increase in neutrophils and a reduction of lymphocytes at the highest concentration on both 7th and 14th days were detected. The total and cytoplasmic area of erythrocytes on the 7th day at the highest concentration were reduced. In addition, alterations on the erythrocyte nuclear morphology in fish exposed to BP-3 were usually visualized, mainly when considered the occurrence of blebbed nucleus and micronucleus, indicating that BP-3 exhibits cytotoxic and mutagenic effects. The results indicate that BP-3 can interfere with the morphophysiology of aquatic organisms.

Zebrafish (Danio rerio) using as model for genotoxicity and DNA repair assessments: Historical review, current status and trends

Genotoxic pollutants lead to both DNA damage and changes in cell repair mechanisms. Selecting suitable biomonitors is a fundamental step in genotoxicity studies. Thus, zebrafish have become a popular model used to assess the genotoxicity of different pollutants in recent years. They have orthologous genes with humans and hold almost all genes involved in different repair pathways. Therefore, the aim of the current study is to summarize the existing literature on zebrafish using as model system to assess the genotoxicity of different pollutants. Revised data have shown that comet assay is the main technique adopted in these studies. However, it is necessary standardizing the technique applied to zebrafish in order to enable better result interpretation and comparisons. Overall, pollutants lead to single-strand breaks (SSB), double-strand breaks (DSB), adduct formation, as well as to changes in the expression of genes involved in repair mechanisms. Although analyzing repair mechanisms is essential to better understand the genotoxic effects caused by pollutants, few studies have analyzed repair capacity. The current review reinforces the need of conducting further studies on the role played by repair pathways in zebrafish subjected to DNA damage. Revised data have shown that zebrafish are a suitable model to assess pollutant-induced genotoxicity.

The sine qua non of the fish invitrome today and tomorrow in environmental radiobiology

Fish cell lines, collectively referred to as the fish invitrome, are useful diagnostic tools to study radiation impacts on aquatic health and elucidate radiation mechanisms in fish. This paper will highlight the advantages, discuss the challenges, and propose possible future directions for uses of the fish invitrome in the field of environmental radiobiology. The fish invitrome contains at least 714 fish cell lines. However, only a few of these cell lines have been used to study radiation biology in fish and they represent only 10 fish species. The fish invitrome is clearly not yet explored for its full potential in radiation biology. Evidence suggests that they are useful and, in some cases, irreplaceable in making underlying theories and fundamental concepts in radiation responses in fish. The debate of whether environmental radiation is harmful, presents risks, has no effect on health, or is beneficial is on-going and is one that fish cell lines can help address in a time-effective fashion. Any information obtained with fish cell lines is useful in the framework of environment radiation risk assessments. Radiation threats to aquatic health will continue due to the very likely rise of nuclear energy and medicine in the future. The fish invitrome, in theory, lives forever and can meet new challenges at any given time to provide diagnostic risk analyses pertaining to aquatic health and environmental radiation protection.

Combining Different In Vitro Bioassays to Evaluate Genotoxicity of Water-Accommodated Fractions from Petroleum Products

Genotoxicity assessment is of high relevance for crude and refined petroleum products, since oil compounds are known to cause DNA damage with severe consequences for aquatic biota as demonstrated in long-term monitoring studies. This study aimed at the optimization and evaluation of small-scale higher-throughput assays (Ames fluctuation, micronucleus, Nrf2-CALUX^®) covering different mechanistic endpoints as first screening tools for genotoxicity assessment of oils. Cells were exposed to native and chemically dispersed water-accommodated fractions (WAFs) of three oil types varying in their processing degree. Independent of an exogenous metabolic activation system, WAF compounds induced neither base exchange nor frame shift mutations in bacterial strains. However, significantly increased chromosomal aberrations in zebrafish liver (ZF-L) cells were observed. Oxidative stress was indicated for some treatments and was not correlated with observed DNA damage. Application of a chemical dispersant increased the genotoxic potential rather by the increased bioavailability of dissolved and particulate oil compounds. Nonetheless, the dispersant induced a clear oxidative stress response, indicating a relevance for general toxic stress. Results showed that the combination of different in vitro assays is important for a reliable genotoxicity assessment. Especially, the ZF-L capable of active metabolism and DNA repair seems to be a promising model for WAF testing.