Applications of the RTgill-W1 Cell Line for Acute Whole-Effluent Toxicity Testing: In Vitro-In Vivo Correlation and Optimization of Exposure Conditions

Adaption and application of cell-based bioassays to whole-water samples

The increasing presence of contaminants of emerging concern in wastewater and their potential environmental risks require improved monitoring and analysis methods. Direct toxicity assessment (DTA) using bioassays can complement chemical analysis of wastewater discharge, but traditional in vivo tests have ethical considerations and are expensive, low-throughput, and limited to apical endpoints (mortality, reproduction, development, and growth). In vitro bioassays offer an alternative approach that is cheaper, faster, and more ethical, and can provide higher sensitivity for some environmentally relevant endpoints. This study explores the potential benefits of using whole water samples of wastewater and environmental surface water instead of traditional solid phase extraction (SPE) methods for in vitro bioassays testing. Whole water samples produced a stronger response in most bioassays, likely due to the loss or alteration of contaminants during SPE sample extraction. In addition, there was no notable difference in results for most bioassays after freezing whole water samples, which allows for increased flexibility in testing timelines and cost savings. These findings highlight the potential advantages of using whole water samples in DTA and provide a framework for future research in this area.

Gill epithelial cell line ASG-10 from Atlantic salmon as a new research tool for solving water quality challenges in aquaculture

Here we evaluated the gill epithelial cell line ASG-10 from Atlantic salmon, as an in vitro model for research on known water quality challenges in aquaculture. Ammonia/ammonium (NH3/NH4+), a recognized challenge in water-intensive recirculating aquaculture systems (RAS), induced lysosomal vacuolization, reduced protein degradation and cell migration of the ASG-10 cells. Aluminium (Aln+), another challenge in freshwater aquaculture facilities had only minor effects. Next, we investigated the tolerance for direct water exposure of ASG-10. The cells tolerated water with osmolarity between 169 and 419 mOsmol/kg for 24 h. However, cells exposed for 3 h to water at 863 mOsmol/kg changed cellular morphology and induced gene expression related to stress (gpx1, casp3, hsp70), and after 24 h exposure cellular viability was severely reduced. Nevertheless, when the cells were grown in transwell inserts, they tolerated 863 mOsmol/kg for 3 h and induction of stress response associated genes was considerably reduced. Lastly, the ASG-10 cells were exposed to water samples, with no known quality issues, from different aquaculture facilities. The cells showed no differences in viability or morphology compared to their representative control. In conclusion, the ASG-10 cell line is a promising in vitro model to study water quality challenges and whole water samples.

Cytotoxicity of 19 Pesticides in Rainbow Trout Gill, Liver, and Intestinal Cell Lines

The rainbow trout gill cell line (RTgill-W1), via test guideline 249 of the Organisation for Economic Co-operation and Development, has been established as a promising New Approach Methodology, although to advance confidence in the method more case studies are needed that: 1) expand our understanding of applicability domains (chemicals with diverse properties); 2) increase methodological throughput (96-well format); and 3) demonstrate biological relevance (in vitro to in vivo comparisons; gill vs. other cells). Accordingly, the objective of our study was to characterize the cytotoxicity of 19 pesticides against RTgill-W1 cells, and also liver (RTL-W1) and gut epithelial (RTgutGC) cell lines, and then to compare the in vitro and in vivo data. Of the 19 pesticides tested, 11, 9, and 8 were cytotoxic to the RTgill-W1, RTL-W1, and RTgutGC cells, respectively. Six pesticides (carbaryl, chlorothalonil, chlorpyrifos, dimethenamid-P, metolachlor, and S-metolachlor) were cytotoxic to all three cell lines. Aminomethylphosphonic acid, chlorantraniliprole, dicamba, diquat, imazethapyr, and permethrin exhibited cell-line-specific toxicity. No cytotoxic responses were observed for three herbicides (atrazine, glyphosate, and metribuzin) and four insecticides (clothianidin, diazinon, imidacloprid, and thiamethoxam). When cytotoxicity was measured, there was a strong correlation (rs  = 0.9, p < 0.0001) between in vitro median effect concentration (EC50) values (based on predicted concentrations using the In Vitro Mass Balance Model Equilibrium Partitioning (IV-MBM EQP) Ver. 2.1) derived from RTgill-W1 and RTL-W1 cells with in vivo median lethal concentration (LC50) values from 96-h acute toxicity studies with trout. In all 28 cases, the in vitro EC50 was within 18-fold of the in vivo LC50. These data help increase our understanding of the ecotoxicological domains of applicability for in vitro studies using cultured rainbow trout cells, while also demonstrating that these assays performed well in a 96-well format and have promise to yield data of biological relevance. Environ Toxicol Chem 2024;00:1-13. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Alternatives to Fish Acute Whole Effluent Toxicity (WET) Testing: Predictability of RTgill-W1 Cells and Fathead Minnow Embryos with Actual Wastewater Samples

Toxicity assays using fish cells and embryos continue to gain momentum as a more ethical and informative alternative to fish acute toxicity testing. The goal of our study was to test the accuracy of RTgill-W1 cells and the fathead minnow (Pimephales promelas) embryos to predict actual whole effluent toxicity (WET) in the fathead minnow larvae. The three models were compared concurrently using samples of various origins and treatment types. Additionally, the toxicity of reference toxicants (Cd, Cu, NH3-N, 3,4-dichloraniline, and benzalkonium chloride) spiked into a nontoxic wastewater was compared. The toxicity of reference toxicants was tested in isosmotic and hypoosmotic exposure media in RTgill-W1 cells. Of the 28 wastewater samples, 14 induced a toxic response in fish larvae. Embryos predicted 11 of the 14 wastewater samples toxic to the larvae, whereas RTgill-W1 cells predicted the toxicity of all 14 toxic samples to the larvae. In addition, embryos and RTgill-W1 cells predicted toxicity in two and six additional samples, respectively, that were nontoxic to larvae. Exposures in hypoosmotic medium significantly increased sensitivity of RTgill-W1 cells to all reference toxicants, excluding benzalkonium chloride, compared to exposures in isosmotic medium and showed toxicity levels similar to that in larvae. Thus, hypoosmotic exposure medium should be considered for aquatic toxicity testing applications. Overall, both gill cell and embryo models predicted toxicity in the majority of wastewater samples toxic to larvae and demonstrated their applicability for regulatory WET testing.

TiO2-MWCNT nanohybrid: Cytotoxicity, protein corona formation and cellular internalisation in RTG-2 fish cell line

Titanium dioxide nanoparticles-multiwalled carbon nanotubes (TiO_2-MWCNT) nanohydrid has an enhanced photocatalytic activity across the visible light with promising applications in environmental remediation, solar energy devices and antimicrobial technologies. However, it is necessary to evaluate the toxicological effects of TiO_2-MWCNT towards safe and sustainable development of nanohybrids. In this work, we studied the cytotoxicity, protein corona formation and cellular internalisation of TiO_2-MWCNT on fibroblasts derived from gonadal rainbow trout tissue (RTG-2) for the first time. This nanohydrid did not show any toxicity effect on RTG-2 cells up to 100 mg L^-1 after 24 h of exposure as monitored by alamar blue, neutral red and trypan blue assays (in presence or absence of foetal bovine serum, FBS). Futhermore, cryo-transmission electron microscopy analysis demonstrated that TiO₂ particles is attached on nanotube surface after FBS-protein corona formation in cell culture medium. Raman spectroscopy imaging showed that TiO_2-MWCNT can be internalised by RTG-2 cells. This work is a novel contribution towards better understanding the nanobiointeractions of nanohydrids linked to their in vitro effects on fish cells in aquatic nanoecotoxicology.

Fluid shear stress affects the metabolic and toxicological response of the rainbow trout gill cell line RTgill-W1

The Rainbow trout gill cell-line (RTgill-W1) has been accepted by the Organisation for Economic Co-operation and Development (OECD TG249) as a replacement for fish in acute toxicity tests. In these tests cells are exposed under static conditions. In contrast, in vivo, water moves over fish gills generating fluid shear stress (FSS) that alters cell physiology and response to toxicants. The current study uses a specialised 3D printed chamber designed to house inserts and allows for the flow (0.2 dynes cm²) of water over the cells. This system was used to assess RTgill-W1 cell responses to FSS in the absence and presence of copper (Cu) over 24 h. FSS caused increased gene expression of mechanosensitive channel peizo1 and the Cu-transporter atp7a, elevated reactive oxygen species generation and increased expression of superoxidase dismutase. Cell metabolism was unaffected by Cu (0.163 μM to 2.6 μM Cu) under static conditions but significantly reduced by FSS + Cu above 1.3 μM. Differential expression of metallothionein (mt) a and b was observed with increased expression of mta under static conditions and mtb under FSS on exposure to Cu. These findings highlight toxicologically relevant mechanosensory responses by RTgill-W1 to FSS that may influence toxicological responses.

Review of ecologically relevant in vitro bioassays to supplement current in vivo tests for whole effluent toxicity testing - Part 1: Apical endpoints

Whole effluent toxicity (WET) testing is commonly used to ensure that wastewater discharges do not pose an unacceptable risk to receiving environments. Traditional WET testing involves exposing animals to (waste)water samples to assess four major ecologically relevant apical endpoints: mortality, growth, development, and reproduction. Recently, with the widespread implementation of the 3Rs to replace, reduce and refine the use of animals in research and testing, there has been a global shift away from in vivo testing towards in vitro alternatives. However, prior to the inclusion of in vitro bioassays in regulatory frameworks, it is critical to establish their ecological relevance and technical suitability. This is part 1 of a two-part review that aims to identify in vitro bioassays that can be used in WET testing and relate them to ecologically relevant endpoints through toxicity pathways, providing the reader with a high-level overview of current capabilities. Part 1 of this review focuses on four apical endpoints currently included in WET testing: mortality, growth, development, and reproduction. For each endpoint, the link between responses at the molecular or cellular level, that can be measured in vitro, and the adverse outcome at the organism level were established through simplified toxicity pathways. Additionally, literature from 2015 to 2020 on the use of in vitro bioassays for water quality assessments was reviewed to identify a list of suitable bioassays for each endpoint. This review will enable the prioritization of relevant endpoints and bioassays for incorporation into WET testing.

Cosmetic Preservatives: Hazardous Micropollutants in Need of Greater Attention?

In recent years, personal care products (PCPs) have surfaced as a novel class of pollutants due to their release into wastewater treatment plants (WWTPs) and receiving environments by sewage effluent and biosolid-augmentation soil, which poses potential risks to non-target organisms. Among PCPs, there are preservatives that are added to cosmetics for protection against microbial spoilage. This paper presents a review of the occurrence in different environmental matrices, toxicological effects, and mechanisms of microbial degradation of four selected preservatives (triclocarban, chloroxylenol, methylisothiazolinone, and benzalkonium chloride). Due to the insufficient removal from WWTPs, cosmetic preservatives have been widely detected in aquatic environments and sewage sludge at concentrations mainly below tens of µg L^-1. These compounds are toxic to aquatic organisms, such as fish, algae, daphnids, and rotifers, as well as terrestrial organisms. A summary of the mechanisms of preservative biodegradation by micro-organisms and analysis of emerging intermediates is also provided. Formed metabolites are often characterized by lower toxicity compared to the parent compounds. Further studies are needed for an evaluation of environmental concentrations of preservatives in diverse matrices and toxicity to more species of aquatic and terrestrial organisms, and for an understanding of the mechanisms of microbial degradation. The research should focus on chloroxylenol and methylisothiazolinone because these compounds are the least understood.

Fish Embryo Acute Toxicity Testing and the RTgill-W1 Cell Line as In Vitro Models for Whole-Effluent Toxicity (WET) Testing: An In Vitro/In Vivo Comparison of Chemicals Relevant for WET Testing

The fathead minnow (Pimephales promelas) fish embryo acute toxicity (FET) test was compared to the fish gill cells (RTgill-W1) in vitro assay and to the fish larvae acute toxicity test to evaluate their sensitivity for whole-effluent toxicity (WET) testing. The toxicity of 12 chemicals relevant for WET testing was compared as proof of principle. The concentrations lethal to 50% of a population (LC50) of embryos were compared to those in fish larvae and to the 50% effect concentration (EC50) in RTgill-W1 cells from previous literature. Along with traditional FET endpoints (coagulation, somite development, tail detachment, and heartbeat), cardiotoxicity was evaluated for WET applicability. Heart rate was measured at LC20 and LC50 values of six subselected chemicals (Cd, Cu, Ni, ammonia, 3,4-dichloraniline, and benzalkonium chloride). In addition, the toxicity of Cd and Ni was evaluated in RTgill-W1 cells exposed in a hypoosmotic medium to evaluate the effect that osmolarity may have on metal toxicity. A significant correlation was found between the FET and larvae LC50 values but not between the RTgill-W1 EC50 and FET LC50 values. Although sensitivity to Ni and Cd was found to increase with hypoosmotic conditions for FET and RTgill-W1 cells, a correlation was only found with removal of Ni from the analysis. Hypoosmotic conditions increased sensitivity with a significant correlation between RTgill-W1 cells and larvae. Cardiotoxicity was shown in three of the five subselected chemicals (Cd, Cu, and 3,4-dichloroaniline). Overall, both in vitro alternative models have shown good predictability of toxicity in fish in vivo for WET chemicals of interest. Environ Toxicol Chem 2022;41:2721-2731. © 2022 SETAC.

Toxicological characterization of produced water from the Permian Basin

Produced water (PW) is a hypersaline waste stream generated from the shale oil and gas industry, consisting of numerous anthropogenic and geogenic compounds. Despite prior geochemical characterization, the comprehensive toxicity assessment is lacking for evaluating treatment technologies and the beneficial use of PW. In this study, a suite of in vitro toxicity assays using various aquatic organisms (luminescent bacterium Vibrio fischeri, fish gill cell line RTgill-W1, and microalgae Scenedesmus obliquus) were developed to investigate the toxicological characterizations of PW from the Permian Basin. The exposure to PW, PW inorganic fraction (PW-IF), and PW salt control (PW-SC) at 30-50% dilutions caused significant toxicological effects in all model species, revealing the high salinity was the foremost toxicological driver in PW. In addition, the toxicity level of PW was usually higher than that of PW-IF, suggesting that organic contaminants might also play a critical role in PW toxicity. When comparing the observed toxicity with associated chemical characterizations in different PW samples, strong correlations were found between them since higher concentrations of contaminants could generally result in higher toxicity towards exposed organisms. Furthermore, the toxicity results from the pretreated PW indicated that those in vitro toxicity assays had different sensitives to the chemical components present in PW. As expected, the combination of multiple pretreatments could lead to a more significant decrease in toxicity compared to the single pretreatment since the mixture of contaminants in PW might exhibit synergistic toxicity. Overall, the current work is expected to enhance our understanding of the potential toxicological impacts of PW to aquatic ecosystems and the relationships between the chemical profiles and observed toxicity in PW, which might be conducive to the establishment of monitoring, remediation, treatment, and reuse protocols for PW.

Inflammation of Gill Epithelia in Fish Causes Increased Permeation of Petrogenic Polar Organic Chemicals via Disruption of Tight Junctions

The epithelial cell layer that lines the gills of fish controls paracellular permeation of chemicals through tight junctions. The integrity of tight junctions can be affected by inflammation, which likely affects the bioavailability of chemicals. Here, the inflammation of the rainbow trout gill cell line RTgill-W1 was induced via exposure to bacterial lipopolysaccharides (LPS). Cells were then coexposed to extracts of oil sands process-affected water (OSPW), which contain complex mixtures of chemicals. After 24 h of exposure, cells exposed to LPS showed a reduction in transepithelial electrical resistance, an indicator of tight junction integrity. Quantitative reverse-transcription polymerase chain reaction (RT-PCR) analysis determined that abundances of transcripts of genes coding for tight junction proteins were significantly less in cells exposed to 20, 50, or 100 mg L^-1 LPS. Chemical analysis revealed increased permeation of constituents of OSPW across epithelia at all studied LPS concentrations. These in vitro findings were confirmed in vivo in rainbow trout exposed to LPS and OSPW for 48 h, which resulted in greater accumulation of chemicals relative to that for fish exposed to OSPW alone. Our results demonstrated that inflammation and disruption of tight junctions could lead to greater uptake of potentially harmful chemicals from the environment, which has implications for mixture risk assessment.

Role and relevance of fish cell lines in advanced in vitro research

Introduction

Cell line derived from fish has been established as a promising tool for studying many key issues of aquaculture covering fish growth, disease, reproduction, genetics, and biotechnology. In addition, fish cell lines are very useful in vitro models for toxicological, pathological, and immunological studies. The easier maintenance of fish cell lines in flexible temperature regimes and hypoxic conditions make them preferable in vitro tools over mammalian cell lines. Great excitement has been observed in establishing and characterizing new fish cell lines representing diverse fish species and tissue types. The well-characterized and authenticated cell lines are of utmost essential as these represent cellular functions very similar to in vivo state of an organism otherwise it would affect the reproducibility of scientific research.

Conclusion

The fish cell lines have exhibited encouraging results in several key aspects of in vitro research in aquaculture including virology, nutrition and metabolism, production of vaccines, and transgenic fish production. The review paper reports the cell lines developed from fish, their characterization, and biobanking along with their potential applications and challenges in in vitro research.