Evaluation of genotoxicity using the micronucleus assay and nuclear abnormalities in the tropical sea fish Bathygobius soporator (Valenciennes, 1837) (Teleostei, Gobiidae)

Micronucleus test and nuclear abnormality assay in zebrafish (Danio rerio): Past, present, and future trends

Nuclear abnormality (NA) assay in fish has been widely applied for toxicity risk assessment under field and laboratory conditions. The zebrafish (Danio rerio) has become a suitable model system for assessing the NA induced by pollutants. Thus, the current study aimed to summarize and discuss the literature concerning micronucleus (MN) and other NA in zebrafish and its applications in toxicity screening and environmental risk assessment. The data concerning the publication year, pollutant type, experimental design, and type of NA induced by pollutants were summarized. Also, molecular mechanisms that cause NA in zebrafish were discussed. Revised data showed that the MN test in zebrafish has been applied since 1996. The MN was the most frequently NA, but 15 other nuclear alterations were reported in zebrafish, such as notched nuclei, blebbed nuclei, binucleated cell, buds, lobed nuclei, bridges, and kidney-shaped. Several pollutants can induce NA in zebrafish, mainly effluents (mixture of pollutants), agrochemicals, and microplastics. The pollutant-induced NA in zebrafish depends on experimental design (i.e., exposure time, concentration, and exposure condition), developmental stages, cell/tissue type, and the type of pollutant. Besides, research gaps and recommendations for future studies are indicated. Overall, the current study showed that zebrafish is a suitable model to assess pollutant-induced mutagenicity.

Micronuclei in Fish Erythrocytes as Genotoxic Biomarkers of Water Pollution: An Overview

Freshwater and marine water bodies receive chemical contaminants from industrial, agricultural, urban, and domestic wastes. Eco-genotoxicity assays are useful tools to assess the cumulative genotoxicity of these pollutants. Fish are suitable indicators for biomonitoring of mutagenic and carcinogenic pollution.In this review, we present a complete overview of the studies performed so far using the micronucleus test in peripheral erythrocytes of fish exposed to polluted water. We have listed all the species of fish used and the geographical distribution of the investigations. We have analyzed and discussed all technical aspects of using this test in fish, as well as the advantages and disadvantages of the different experimental protocols. We have reported the results of all studies. This assay has become, for years, one of the simplest, fastest, and most cost-effective for assessing genotoxic risk in aquatic environments. However, there are still several factors influencing the variability of the results. Therefore, we have given indications and suggestions to achieve a standardization of experimental procedures and ensure uniformity of future investigations.

Common snook juveniles, Centropomus undecimalis, as biomonitor organisms to evaluate cytogenotoxicity effects of surface estuarine water from Southern Brazil

Centropomus undecimalis fish inhabit the highly contaminated Santos-São Vicente Estuarine System (SESS) and could be a good biomonitor of contaminants. This study aimed to investigate the cytogenotoxic potential of superficial water from SESS using C. undecimalis as a biomonitoring model and to validate the use of farmed fish as controls. Using biochemical (DNA damage and Lipid Peroxidation - LPO), cellular (erythrocyte nuclear abnormality - ENA) and tissue (8-OHdG immunoexpression) biomarkers, our results showed fish from SEES had higher LPO concentration in gills and higher frequency of reniform, lobed and total ENA in erythrocytes when compared with control farmed fish. Thus, SESS surface water are cytogenotoxic for blood and gills cells of fishes. C. undecimalis has shown to be a good biomonitor model and farmed fish can be used as control only if livers were not the target organs of study since the dietary food from farmed fish causes steatosis.

Genomic damage in Mugil curema (Actinopterygii: Mugilidae) reveals the effects of intense urbanization on estuaries in northeastern Brazil

The largest metropolitan centers in northeastern region of Brazil are all located near the coast, and industrial, tourist, and agro-industrial activities are the principal causes of water contamination due to discharges of untreated sewage. Adverse environmental conditions can often be detected by analyzing the genetic material of organisms exposed to pollutants, and furnish an overview of environmental quality. We evaluated possible damage to the DNA of one of the fish resources most widely consumed and commercialized by coastal communities in northeastern Brazil, Mugil curema ("tainha"). Erythrocytes from M. curema were analyzed by the presence of micronuclei and by comet assay (single cell gel electrophoresis, SCGE). Statistical comparisons to both tests revealed considerably greater genomic damage in polluted estuaries than in the control site (p < 0.05), suggesting strong genotoxic impacts on the specimens evaluated, principally among those taken near localities with dense demographic and industrial development.

Zn2+ induced molecular responses associated with oxidative stress, DNA damage and histopathological lesions in liver and kidney of the fish, Channa punctatus (Bloch, 1793)

Zn²⁺ is essential for normal physiological functioning of all organisms in small quantities, but when its concentration enhances in surrounding environment it acts as a toxicant to organisms. Common sources of Zn²⁺ pollution are electroplating, alloying, mining, and allied industrial operations. The present study aims to assess the biochemical, histopathological and genotoxicological implications under Zn²⁺ intoxication along with its accumulation patterns in prime biotransformation sites-liver and kidney, of a bottom feeder fish, Channa punctatus. Fish were chronically exposed to two different concentrations of Zn²⁺i.e., 5mg/L (permissible limit, T1) and 10mg/L (twice the permissible limit, T2). Simultaneous control was maintained. A significant (p<0.05) increment in Zn²⁺ bioaccumulation, antioxidant enzymes activities of SOD, CAT and GR and induction in micronuclei frequencies along with the significant (p<0.05) decrement in total protein and GSH were observed in all the exposed groups after 28 d. Altered biochemical parameters coupled with enhanced induction in micronuclei and accumulation of Zn²⁺ in liver and kidney of fish can be regarded as sensitive biomarkers of Zn²⁺ induced toxicological manifestations and thus, they may be effectively utilized for reliable ecotoxicological biomonitoring of aquatic regimes polluted with Zn²⁺.

Water quality parameters, biomarkers and metal bioaccumulation in native fish captured in the Ilha River, southern Brazil

The Ilha River is one of the main tributaries of the Sinos River, southern Brazil, and it is located in an area characterized by low population density and presence of agricultural activities. Thus, this study aimed to assess the water quality of two sites of the Ilha River (source and mouth, S1 and S2 respectively) in five sampling periods using water physicochemical and microbiological analyses, biomarkers, such as condition factor, micronucleus test, gill histopathological analysis, and metal bioaccumulation in the native fish Bryconamericus iheringii. Mean values of BOD₅, thermotolerant coliforms, aluminum, iron and lead exceeded the limits established by the Brazilian legislation for surface waters at both sampling sites. Significant higher micronucleus, nuclear abnormalities and mucous cells frequencies were found at S2 in, at least, one sampling period, whereas fish from S1 presented significant lower condition factor, higher frequencies of lamellar alterations and higher concentrations of chromium and nickel in muscle. Additionally, concentrations of cadmium, chromium and lead in fish muscle exceeded the limits considered safe for human consumption at both sites in at least one sampling period. Data from our study evidenced the mouth of the Ilha River suffers from point genotoxic effects, whereas the source is also contaminated by metals, despite being located in an area under minor anthropic activities.

Erythrocytes as a biological model for screening of xenobiotics toxicity

Erythrocytes are the main cells in circulation. They are devoid of internal membrane structures and easy to be isolated and handled providing a good model for different assays. Red blood cells (RBCs) plasma membrane is a multi-component structure that keeps the cell morphology, elasticity, flexibility and deformability. Alteration of membrane structure upon exposure to xenobiotics could induce various cellular abnormalities and releasing of intracellular components. Therefore the morphological changes and extracellular release of haemoglobin [hemolysis] and increased content of extracellular adenosine triphosphate (ATP) [as signs of membrane stability] could be used to evaluate the cytotoxic effects of various molecules. The nucleated RBCs from birds, fish and amphibians can be used to evaluate genotoxicity of different xenobiotics using comet, DNA fragmentation and micronucleus assays. The RBCs could undergo programmed cell death (eryptosis) in response to injury providing a useful model to analyze some mechanisms of toxicity that could be implicated in apoptosis of nucleated cells. Erythrocytes are vulnerable to peroxidation making it a good biological membrane model for analyzing the oxidative stress and lipid peroxidation of various xenobiotics. The RBCs contain a large number of enzymatic and non-enzymatic antioxidants. The changes of the RBCs antioxidant capacity could reflect the capability of xenobiotics to generate reactive oxygen species (ROS) resulting in oxidative damage of tissue. These criteria make RBCs a valuable in vitro model to evaluate the cytotoxicity of different natural or synthetic and organic or inorganic molecules by cellular damage measures.

The use of biomarkers as integrative tools for transitional water bodies monitoring in the Water Framework Directive context - A holistic approach in Minho river transitional waters

The Water Framework Directive (WFD) provides an important legislative opportunity to promote and implement an integrated approach for the protection of inland surface waters, transitional waters, coastal waters and groundwaters. The transitional waters constitute a central piece as they are usually under high environmental pressure and by their inherent characteristics present monitoring challenges. Integrating water quality monitoring with biological monitoring can increase the cost-effectiveness of monitoring efforts. One way of doing this is with biomarkers, which effectively integrate physical-chemical status and biological quality elements, dealing holistically with adverse consequences on the health of water bodies. The new Marine Strategy Framework Directive (MSFD) already incorporates the biomarker approach. Given the recent activities of OSPAR and HELCOM to harmonize existing monitoring guidelines between MSFD and WFD the use of similar methodologies should be fostered. To illustrate the potential of the biomarker approach, juveniles of flounder (Platichthys flesus) were used to evaluate the quality of the Minho river-estuary water bodies. The use of juveniles instead of adults eliminates several confounding factors such changes on the biological responses associated with reproduction. Here, a panel of well-established biomarkers, EROD, AChE, SOD, CAT, GST, LPO, ENA and FACs (1-Hydroxyrene) were selected and measured along with a gradient of different physical conditions, and integrated with trace elements characterization on both biota and sediments. In general, a clear profile along the water bodies was found, with low seasonal and spatial variation, consistent with a low impacted area. Overall, the results support the use of both the battery of biomarkers and the use of juvenile flounders in the monitoring of the water quality status within the WFD.

Arsenic-induced genotoxicity in Nile tilapia (Orechromis niloticus); the role of Spirulina platensis extract

Arsenic (As) is one of the most relevant environmental global single substance toxicants that have long been regarded as a carcinogenic and genotoxic potential. In this respect, we evaluated the cytogenetic effect of arsenic exposure in Nile tilapia (Oreochromis niloticus), in terms of erythrocyte alteration, apoptosis, and induction of micronuclei. Spirulina platensis (SP) is a filamentous cyanobacterium microalgae with potent dietary phytoantioxidant, anti-inflammatory, and anti-cancerous properties supplementation. The protective role of Spirulina as supplementary feeds was studied in Nile tilapia (O. niloticus) against arsenic-induced cytogenotoxicity. Four groups were assigned as control group (no SP or As), As group (exposed to water-born As in the form of NaAsO2 at 7 ppm), SP1 (SP at 7.5% + As at the same level of exposure), and SP2 (SP at 10% + As at the same level of exposure). As-treated group had a significant increase in all cytogenetic analyses including erythrocyte alteration, apoptosis, and induction of micronuclei after 2 weeks with continuous increase in response after 3 weeks. The combined treatment of Spirulina at two different concentrations of 7.5 and 10% had significantly declined the induction of erythrocyte alteration, apoptosis, and micronuclei formation induced by arsenic intoxication.

Induction of micronucleus of Oreochromis niloticus exposed to waters from the Cubatão do Sul River, southern Brazil

In an effort to characterize the pollution of surface waters by potentially genotoxic agents, this study aimed at assessing the frequency of micronucleated (MN) erythrocytes of the fish species, Oreochromis niloticus, from the Cubatão do Sul River. This river is the source of drinking water for the region of Florianópolis, capital of Santa Catarina State, Brazil. Negative control fish showed low frequency of MN, ranging between 0.49‰ and 0.90‰. Positive control (potassium dichromate 2.5 mg/L) organisms showed high MN frequency (16.82-17.25‰). The MN frequency increased along the river (Site 1--1.24‰ winter 2011; Site 4--9.76‰ summer 2011). Based on the observation of elevated MN erythrocytes frequency in O. niloticus exposed to water samples from along the river course, we conclude that the complex environmental mixtures of water from the Cubatão do Sul River have genotoxic potential. This genotoxicity most likely originated from agricultural runoff and domestic effluents released without treatment, based on the evidence from literature data and a survey in the region. This study provides a scientific basis for future studies regarding the genotoxicity of complex environmental mixtures in natural environments.