Cell-based assays seem not to accurately predict fish short-term toxicity of pesticides

A novel "Turn-Off-On" fluorescent probe for specific sequential detection of Cu2+ and glyphosate and its application in biological imaging

As common pollutants, Cu2+ and glyphosate pose a serious threat to human health and the ecosystem. Herein, a fluorescent probe (E)-7-(diethylamino)-N'(4-(diethylamino)-2-hydroxybenzyl)-2-oxo-2H chromophore-3-carbazide (DDHC) was designed and synthesised for the sequential recognition of Cu2+ and glyphosate. DDHC has the advantages of a short synthesis path, easy-to-obtain raw materials, good anti-interference ability, and strong stability. The interaction of the DDHC-Cu2+ complexes with glyphosate allows the amino and carboxyl groups in glyphosate molecules to coordinate with Cu2+ strongly, competing for the Cu2+ in the DDHC-Cu2+ complexes and releasing the DDHC, leading to the recovery of fluorescence. The recognition was further validated through Job's plot, HRMS, and DFT calculations. In addition, the successful recovery of Cu2+ and glyphosate in different environmental water samples fully demonstrates the practical application potential of DDHC. Especially, DDHC has low cytotoxicity and can enter zebrafish and HeLa cells, rapidly reacting with Cu2+ and glyphosate in the body, generating visible fluorescence quenching and recovery phenomena, achieving real-time visual monitoring of exogenous Cu2+ and glyphosate in zebrafish and HeLa cells. The targeting and dual selectivity of DDHC greatly enhance its potential application value in the field of detection, providing important theoretical support for studying the fate of multiple pollutants in the environment.

The H9c2(2-1) cell-based sulforhodamine B assay is a non-animal alternative to evaluate municipal wastewater quality over time

The present study validates the potential of the in vitro H9c2(2-1) cell-based sulforhodamine B (SRB) assay to evaluate the temporal variability of wastewater quality. The impact of effluent disposal on water quality and the efficiency of the wastewater treatment process were also assessed. To correlate standard analytical method results with in vitro results, a total of 16 physicochemical parameters, such as nutrients, pH, chemical oxygen demand, total suspended solids and metals, were determined in both raw and treated wastewater samples. Results revealed that the H9c2(2-1) cell-based SRB assay has an enormous potential to evaluate municipal wastewater quality over time and to discriminate influent and effluent toxic characteristics, as well as for water quality monitoring and surveillance of the efficacy of treatment processes. Finally, the gathered results alerted to the impact of phosphates in a biological system, leading us to recommend the selection of this parameter as a potential environmental health indicator.

Evaluation of in vitro toxicity information for zebrafish as a promising alternative for chemical hazard and risk assessment

In vitro assays are widely proposed as a test alternative to traditional in vivo standard acute and chronic toxicity tests. However, whether toxicity information derived from in vitro assays instead of in vivo tests could provide sufficient protection (e.g., 95 % of protection) for chemical risks remain evaluated. To investigate the feasibility of zebrafish (Danio rerio) cell-based in vitro test method as a test alternative, we comprehensively compared sensitivity differences among endpoints, among test methods (in vitro, FET and in vivo), and between zebrafish and rat (Rattus norvegicus), respectively using chemical toxicity distribution (CTD) approach. For each test method involved, sublethal endpoints were more sensitive than lethal endpoints for both zebrafish and rat, respectively. Biochemistry (zebrafish in vitro), development (zebrafish in vivo and FET), physiology (rat in vitro) and development (rat in vivo) were the most sensitive endpoints for each test method. Nonetheless, zebrafish FET test was the least sensitive one compared to its in vivo and in vitro tests for either lethal or sublethal responses. Comparatively, rat in vitro tests considering cell viability and physiology endpoints were more sensitive than rat in vivo test. Zebrafish was found to be more sensitive than rat regardless of in vivo or in vitro tests for each pairwise endpoint of concern. Those findings indicate that zebrafish in vitro test is a feasible test alternative to zebrafish in vivo and FET test and traditional mammalian test. It is suggesting that zebrafish in vitro test can be optimized by choosing more sensitive endpoints, such as biochemistry to provide sufficient protection for zebrafish in vivo test and to establish applications of zebrafish in vitro test in future risk assessment. Our findings are vital for evaluating and further application of in vitro toxicity toxicity information as an alternative for chemical hazard and risk assessment.

Hematological changes, redox imbalance, and changes in Na+/K+-ATPase activity caused by bisphenol-A and the integrated biomarker responses in Labeo rohita (Hamilton, 1822)

Bisphenol-A (BPA) is a plasticizer commonly used in the plastics industry to manufacture plastic materials. It is abundant in aquatic ecosystems, resulting in increased contamination and lower concentrations that may represent a significant threat to the aquatic system. Hence in the present study, an Indian major carp, Labeo rohita, was exposed to two different BPA concentrations (1 and 10 μg/L) for 30 days. Compared to control, the chronic effects resulted in significant alterations in red blood cell (RBC) and white blood cells (WBC) count. The exposure to BPA caused significant changes in antioxidant activity in gill, liver, and kidney tissues (inferred by catalase, glutathione peroxidase, and glutathione S-transferase activity) in L. rohita. Regarding lipid peroxidation (LPO), we observed an increase in liver and kidney alteration, while LPO was noted in gill tissue compared to the control. Furthermore, increased Na⁺/K⁺-ATPase activity was observed in gills at the end of the 10th day and a gradual decrease at the end of the 30th day. These results indicated that exposure to BPA alters the RBC and WBC levels, antioxidant enzyme activity (gills, liver, and kidney), and Na⁺/K⁺-ATPase activity in the gill of L. rohita exposed to BPA (at 1 and 10 μg/L). Therefore, our findings will help us gain better insight into the toxicity of BPA in freshwater ichthyofauna.

High-throughput screening paradigms in ecotoxicity testing: Emerging prospects and ongoing challenges

The rapidly increasing number of new production chemicals coupled with stringent implementation of global chemical management programs necessities a paradigm shift towards boarder uses of low-cost and high-throughput ecotoxicity testing strategies as well as deeper understanding of cellular and sub-cellular mechanisms of ecotoxicity that can be used in effective risk assessment. The latter will require automated acquisition of biological data, new capabilities for big data analysis as well as computational simulations capable of translating new data into in vivo relevance. However, very few efforts have been so far devoted into the development of automated bioanalytical systems in ecotoxicology. This is in stark contrast to standardized and high-throughput chemical screening and prioritization routines found in modern drug discovery pipelines. As a result, the high-throughput and high-content data acquisition in ecotoxicology is still in its infancy with limited examples focused on cell-free and cell-based assays. In this work we outline recent developments and emerging prospects of high-throughput bioanalytical approaches in ecotoxicology that reach beyond in vitro biotests. We discuss future importance of automated quantitative data acquisition for cell-free, cell-based as well as developments in phytotoxicity and in vivo biotests utilizing small aquatic model organisms. We also discuss recent innovations such as organs-on-a-chip technologies and existing challenges for emerging high-throughput ecotoxicity testing strategies. Lastly, we provide seminal examples of the small number of successful high-throughput implementations that have been employed in prioritization of chemicals and accelerated environmental risk assessment.

Integration of Bioinspired Fibrous Strands with 3D Spheroids for Environmental Hazard Monitoring

Numerous methods have been introduced to produce 3D cell cultures that can reduce the need for animal experimentation. This study presents a unique 3D culture platform that features bioinspired strands of electrospun nanofibers (BSeNs) and aquatic cell lines to compensate for shortcomings in the current cell spheroid generation techniques. The use of BSeNs in 3D zebrafish liver cell cultures is found to improve liver and reproductive functions through spheroid-based in vitro assays such as whole transcriptome sequencing and reproductive toxicity testing, with optimized properties exhibiting results similar to those obtained for fish embryo acute toxicity (FET, OECD TG 236) following exposure to environmental endocrine-disrupting chemicals (17β-Estradiol (E2), 4-hydroxytamoxifen (4-HT), and bisphenol compounds (bisphenol A (BPA) and 9,9-Bis(4-hydroxyphenyl)fluorene (BPFL)). These findings indicate that the beneficial effects of bioinspired materials that closely mimic ECM environments can yield efficient zebrafish cells with intrinsic functions and xenobiotic metabolism similar to those of zebrafish embryos. As a closer analog for the in vivo conditions that are associated with exposure to potentially hazardous chemicals, the straightforward culture model introduced in this study shows promise as an alternative tool that can be used to further eco-environmental assessment.

An array-based nanosensor for detecting cellular responses in macrophages induced by femtomolar levels of pesticides

Environmental agents can induce cellular responses at concentrations far below the limits of detection for current viability and biomarker-based cell sensing platforms. Hypothesis-free cell sensor platforms can be engineered to maximize sensitivity to phenotypic changes, providing a tool for lowering the threshold for detecting cellular changes. Pesticides are one of the most prevalent sources of chemical exposure due to their use in food and agriculture fields. We report here a FRET-based nanosensor array engineered to maximize responses to changes at cell surfaces after pesticide exposure. This sensor array robustly detected macrophage responses to femtomolar concentrations of common pesticides-orders of magnitude lower concentrations than traditional toxicological and biomarker-based strategies. Significantly, this platform was able to classify these responses by pesticide class, demonstrating the ability to distinguish between changes induced by these different agents. Taken together, hypothesis-free cell surface sensing is a promising tool for detecting the effects of ultra-trace environmental chemicals on human health, as well as detecting threshold responses for use in drug discovery and diagnostics.

Combined lethal toxicity, biochemical responses, and gene expression variations induced by tebuconazole, bifenthrin and their mixture in zebrafish (Danio rerio)

Pesticides commonly occur as mixtures in an aqueous environment, causing deleterious effects on human health and the environment. However, the mechanism underlying the combined effects on aqueous organisms remains largely unknown, especially at low concentrations. In the current study, we inspected the interactive toxicity of tebuconazole (TEB), a triazole fungicide, and bifenthrin (BIF), a pyrethroid insecticide, to zebrafish (Danio rerio) using various toxicological assays. Our data revealed that the 96 h-LC50 (lethal concentration 50) values of BIF to fish at different life periods (embryonic, larval, juvenile, and adult periods) ranged from 0.013 (0.011-0.016) to 0.41 (0.35-0.48) mg a.i. L-1, which were lower than that of TEB ranging from 1.1 (0.88-1.3) to 4.8 (4.1-5.7) mg a.i. L-1. Combination of TEB and BIF induced synergetic acute toxicity to embryonic fish. Activities of T-SOD, POD, and GST were distinctly altered in most individual and joint administrations. Expressions of 16 genes associated with oxidative stress, cellular apoptosis, immune system, and endocrine system at the mRNA level were evaluated, and the information revealed that embryonic zebrafish were impacted by both individual compounds and their combinations. Six genes (cas9, P53, gr, TRα, IL-8, and cxcl-clc) exhibited greater changes when exposed to pesticide mixtures. Therefore, the joint effects induced by the pesticides at low concentrations should be considered in the risk assessment of mixtures and regulated as priorities for mixture risk management in the aqueous ecosystem. More research is needed to identify the threshold concentrations of the realistic pesticide mixtures above which synergistic interactions occur.

H9c2(2-1)-based sulforhodamine B assay as a possible alternative in vitro platform to investigate effluent and metals toxicity on fish

To overcome restrictions on the use of fish in toxicity testing, the present study proposes to compare the 50% growth inhibition potential (EC₅₀) of four types of effluents on the rat cardiomyoblast H9c2(2-1) cell line by using the sulforhodamine B (SRB) cell mass colorimetric assay, with the corresponding fish lethal test results. Our objective was to evaluate if H9c2(2-1) cells shows comparable sensitivities, in both relative and absolute terms, to those provided by fish. In parallel, this study also compared the results of the chemical characterization with the legislation in force for environmental protection against effluent release into the receiving environment. Moreover, we tested the H9c2(2-1)-based SRB assays with the metals of concern found in the effluent samples. Both fish and cell assays showed the same toxicity rank for effluents: Metal > Oil > Municipal > Paper, and it should be stressed that the complementarity of using chemical and biological data represents a step forward to guarantee both environmental and human safety, since the chemical characterization showed a different toxicity rank: Metal > Municipal > Oil > Paper. Regarding metal elements, the short-term fish results showed a toxicity rank non-comparable with the rank obtained for cells. Nevertheless, the gathered results reveal the potentiality of the in vitro H9c2(2-1) platform as an alternative for fish lethal testing to assess, in absolute terms, the toxicity of effluents, particularly municipal effluents, and metals.

Stem cells of aquatic invertebrates as an advanced tool for assessing ecotoxicological impacts

Environmental stressors are assessed through methods that quantify their impacts on a wide range of metrics including species density, growth rates, reproduction, behaviour and physiology, as on host-pathogen interactions and immunocompetence. Environmental stress may induce additional sublethal effects, like mutations and epigenetic signatures affecting offspring via germline mediated transgenerational inheritance, shaping phenotypic plasticity, increasing disease susceptibility, tissue pathologies, changes in social behaviour and biological invasions. The growing diversity of pollutants released into aquatic environments requires the development of a reliable, standardised and 3R (replacement, reduction and refinement of animals in research) compliant in vitro toolbox. The tools have to be in line with REACH regulation 1907/2006/EC, aiming to improve strategies for potential ecotoxicological risks assessment and monitoring of chemicals threatening human health and aquatic environments. Aquatic invertebrates' adult stem cells (ASCs) are numerous and can be pluripotent, as illustrated by high regeneration ability documented in many of these taxa. This is of further importance as in many aquatic invertebrate taxa, ASCs are able to differentiate into germ cells. Here we propose that ASCs from key aquatic invertebrates may be harnessed for applicable and standardised new tests in ecotoxicology. As part of this approach, a battery of modern techniques and endpoints are proposed to be tested for their ability to correctly identify environmental stresses posed by emerging contaminants in aquatic environments. Consequently, we briefly describe the current status of the available toxicity testing and biota-based monitoring strategies in aquatic environmental ecotoxicology and highlight some of the associated open issues such as replicability, consistency and reliability in the outcomes, for understanding and assessing the impacts of various chemicals on organisms and on the entire aquatic environment. Following this, we describe the benefits of aquatic invertebrate ASC-based tools for better addressing ecotoxicological questions, along with the current obstacles and possible overhaul approaches.

Modeling Bioavailable Concentrations in Zebrafish Cell Lines and Embryos Increases the Correlation of Toxicity Potencies across Test Systems

Linking cellular toxicity to low-tier animal toxicity and beyond is crucial within the adverse outcome pathway concept and the 3R framework. This study aimed to determine and compare the bioavailable effect concentrations in zebrafish cell lines and embryos. Acute, short-term toxicity (48 h) of eight veterinary pharmaceuticals was measured in two zebrafish cell lines (hepatocytes, fibroblasts) and zebrafish embryos. Seven endpoints of cytotoxicity were recorded. The fish embryo acute toxicity test was modified by adding sublethal endpoints. Chemical distribution modeling (mass balance) was applied to compute the bioavailable compound concentrations in cells (Cfree) and embryos (Cint;aq) based on nominal effect concentrations (Cnom). Effect concentration ratios were calculated (cell effects/embryo effects). A low correlation was observed between cytotoxicity and embryo toxicity when nominal concentrations were used. Modeled bioavailable effect concentrations strongly increased correlations and placed regression lines close to the line of unity and axis origin. Cytotoxicity endpoints showed differences in sensitivity and predictability. The hepatocyte cell line depicted closer proximity to the embryo data. Conclusively, the high positive correlation between the cell- and embryo-based test systems emphasizes the appropriate modulation of toxicity when linked to bioavailable concentrations. Furthermore, it highlights the potential of fish cell lines to be utilized in integrated testing strategies.

Rat cardiomyocyte H9c2(2-1)-based sulforhodamine B assay as a promising in vitro method to assess the biological component of effluent toxicity

The treatment of wastewaters is crucial to maintain the ecological status of receiving waters, and thereby guarantee the protection of aquatic life and human health. Wastewater quality evaluation is conventionally based on physicochemical parameters, but increasing attention has been paid to integrate physicochemical and biological data. Nevertheless, the regulatory use of fish in biological testing methods has been subject to various ethical and cost concerns, and in vitro cell-based assays have thus become an important topic of interest. Hence, the present study intends: (a) to evaluate the efficiency of two different sample pre-concentration techniques (lyophilisation and solid phase extraction) to assess the toxicity of municipal effluents on rat cardiomyoblast H9c2(2-1) cells, and (b) maximizing the use of the effluent sample collected, to estimate the environmental condition of the receiving environment. The gathered results demonstrate that the H9c2(2-1) sulforhodamine B-based assay is an appropriate in vitro method to assess biological effluent toxicity, and the best results were attained by lyophilising the sample as pre-treatment. Due to its response, the H9c2(2-1) cell line might be a possible alternative in vitro model for fish lethal testing to assess the toxicity of municipal effluents. The physicochemical status of the sample suggests a high potential for eutrophication, and iron exceeded the permissible level for wastewater discharge, possibly due to the addition of ferric chloride for wastewater treatment. In general, the levels of carbamazepine and sulfamethoxazole are higher than those reported for other countries, and both surpassed the aquatic protective values for long-term exposure.

Screening-level evaluation of marine benthic dinoflagellates toxicity using mammalian cell lines

Complementary studies at different levels of the biological organization are fundamental to fully link environmental exposure to marine benthic dinoflagellate toxins and their effects. In order to contribute to this transdisciplinary evaluation, and for the first time, the present study aims to study the effects of Gambierdiscus excentricus, Ostreopsis cf. ovata, Prorocentrum hoffmannianum and Prorocentrum lima extracts on seven functionally different mammalian cell lines: HEK 293, HepG2, HNDF, H9c2(2-1), MC3T3-E1, Raw 264.7 and SH-SY5Y. All the cell lines presented cell mass decrease in a concentration-dependence of dinoflagellate extracts, exhibiting marked differences in cell toxicity. Gambierdiscus excentricus presented the highest effect, at very low concentrations with EC_50,24h (i.e., the concentration that gives half-maximal response after a 24-h exposure) between 1.3 and 13 cells mL^-1, followed by O. cf. ovata (EC_50,24h between 3.3 and 40 cells mL^-1), and Prorocentrum species (P. lima: EC_50,24h between 191 and 1027 cells mL^-1 and P. hoffmannianum: EC_50,24h between 152 and 783 cells mL^-1). Cellular specificities were also detected and rat cardiomyoblast H9c2(2-1) cells were in general the most sensitive to dinoflagellate toxic compounds, suggesting that this cell line is an animal-free potential model for dinoflagellate toxin testing. Finally, the sensitivity of cells expressing distinct phenotypes to each dinoflagellate extract exhibited low relation to human poisoning symptoms.

High sensitivity of rat cardiomyoblast H9c2(2-1) cells to Gambierdiscus toxic compounds

Ciguatera fish poisoning is a frequently reported non-bacterial food-borne illness related to the consumption of seafood contaminated with ciguatoxins, and possibly maitotoxins. These toxins are synthesized by marine dinoflagellate species of Gambierdiscus and Fukuyoa genera, and their abundance is a matter of great concern due to their adverse effects to aquatic life and human health. The present study aims to assess the sensitivity of rat cardiomyoblast H9c2(2-1) cells to Gambierdiscus toxic compounds using concentration- and time-dependent sulforhodamine B (SRB) colorimetric assays. Low concentrations of Gambierdiscus extracts (corresponding to 1.3-2.3 cells mL^-1) induced a concentration-dependent response. Specificity in time-dependent response of H9c2(2-1) cells was demonstrated for G. excentricus after a 180 min exposure compared to both G. cf. belizeanus and G. silvae species, with EC_50s obtained after 720 and 360 min, respectively. The sensitivity of H9c2(2-1) cells to dinoflagellate toxic compounds was also tested with other genera from benthic (Coolia malayensis, Ostreopsis cf. ovata, Prorocentrum hoffmannianum and P. lima) and planktonic (Amphidinium carterae and Lingulodinium polyedrum) habitats. Amphidinium, Coolia and Lingulodinium data did not present any concentration-response relationships, and EC₅₀ values could only be obtained after 720 and 1440 min of exposure to both Prorocentrum species and O. cf. ovata, respectively. This study demonstrated that the H9c2(2-1) SRB assay represents a promising and sensitive tool for the detection of Gambierdiscus toxic compounds present in water samples, particularly of G. excentricus at very low cell abundances.

Cell-based assays as an alternative for the study of aquatic toxicity of pharmaceuticals

An increasing number and amount of pharmaceuticals for human and veterinary use currently reach the aquatic environment, and the determination of their effects on aquatic organisms becomes of major importance. The 96-h fish lethal test is one of the conventional assays required for environmental hazardous assessment, but it is extremely time-consuming and costly, and it raises ethical concerns. In a broad study, we compared the ability of cell-based assays to detect, in absolute terms, lethal toxicity in fish due to pharmaceuticals in order to select sensitive cell lines to be posteriorly used as an alternative to fish testing. This study also explored the sensitivity of the rat cardiomyoblast H9c2(2-1) cell line and the suitability of the sulforhodamine B colorimetric assay regarding 15 pharmaceuticals belonging to 9 different therapeutic classes. The relation between in vivo and in vitro data was expressed as LC_50,96h/EC₅₀ ratios, and 66% of concordant data were attained. Accordingly, it was possible to conclude that cell-based assays could be considered a suitable alternative to fish lethal testing for pharmaceuticals, which, after validation, may dramatically reduce the number of fish required for environmental hazardous assessment. Several cell lines were selected as promising alternatives, but H9c2(2-1), HepG2, PLHC-1, and RTG-2 could be considered suitable starting cell types for further studies, as relevant results were obtained with low exposure times.