Xenobiotic metabolism in the fish hepatic cell lines Hepa-E1 and RTH-149, and the gill cell lines RTgill-W1 and G1B: Biomarkers of CYP450 activity and oxidative stress

Functional and molecular characterization of the Atlantic salmon gill epithelium cell line ASG-10; a tool for in vitro gill research

Fish gills are not only the respiratory organ, but also essential for ion-regulation, acid-base control, detoxification, waste excretion and host defense. Multifactorial gill diseases are common in farmed Atlantic salmon, and still poorly understood. Understanding gill pathophysiology is of paramount importance, but the sacrifice of large numbers of experimental animals for this purpose should be avoided. Therefore, in vitro models, such as cell lines, are urgently required to replace fish trials. An Atlantic salmon gill epithelial cell line, ASG-10, was established at the Norwegian Veterinary institute in 2018. This cell line forms a monolayer expressing cytokeratin, e-cadherin and desmosomes, hallmarks of a functional epithelial barrier. To determine the value of ASG-10 for comparative studies of gill functions, the characterization of ASG-10 was taken one step further by performing functional assays and comparing the cell proteome and transcriptome with those of gills from juvenile freshwater Atlantic salmon. The ASG-10 cell line appear to be a homogenous cell line consisting of epithelial cells, which express tight junction proteins. We demonstrated that ASG-10 forms a barrier, both alone and in co-culture with the Atlantic salmon gill fibroblast cell line ASG-13. ASG-10 cells can phagocytose and express several ATP-binding cassette transport proteins. Additionally, ASG-10 expresses genes involved in biotransformation of xenobiotics and immune responses. Taken together, this study provides an overview of functions that can be studied using ASG-10, which will be an important contribution to in vitro gill epithelial research of Atlantic salmon.

Atlantic Salmon Gill Epithelial Cell Line (ASG-10) as a Suitable Model for Xenobiotic Biotransformation

Fish are exposed to xenobiotics in the water. Uptake occurs mainly through the gills, which function as an exchange point with the environment. The gills' ability to detoxify harmful compounds by biotransformation is an essential protection mechanism. The enormous numbers of waterborne xenobiotics requiring ecotoxicological assessment makes it necessary to replace in vivo fish studies with predictive in vitro models. Here, we have characterized the metabolic capacity of the ASG-10 gill epithelial cell line from Atlantic salmon. Inducible CYP1A expression was confirmed by enzymatic assays and immunoblotting. The activities of important cytochrome P450 (CYP) and uridine 5'-diphospho-glucuronosyltransferase (UGT) enzymes were established using specific substrates and metabolite analysis by liquid chromatography (LC) triple quadrupole mass spectrometry (TQMS). Metabolism of the fish anesthetic benzocaine (BZ) in ASG-10 confirmed esterase and acetyl transferase activities through the production of N-acetylbenzocaine (AcBZ), p-aminobenzoic acid (PABA) and p-acetaminobenzoic acid (AcPABA). Moreover, we were able to determine hydroxylamine benzocaine (BZOH), benzocaine glucuronide (BZGlcA) and hydroxylamine benzocaine glucuronide (BZ(O)GlcA) by LC high-resolution tandem mass spectrometry (HRMS/MS) fragment pattern analysis for the first time. Comparison to metabolite profiles in hepatic fractions, and in plasma of BZ-euthanized salmon, confirmed the suitability of the ASG-10 cell line for investigating biotransformation in gills.

Interaction of Polycyclic Aromatic Hydrocarbon compounds in fish primary hepatocytes: From molecular mechanisms to genotoxic effects

Polycyclic Aromatic Hydrocarbons (PAHs) are persistent pollutants normally found in the environment as complex mixtures. Although several individual PAHs are classified as mutagenic and carcinogenic pollutants, the interaction effects between compounds in a mixture may trigger different toxicological mechanisms and, consequently, yield different effects to organisms which are not accounted for in risk assessment guidelines. Given the ubiquity of PAHs, understanding the mechanistic features of their mixtures is a pressing research need. Therefore, the present work aimed to disclose the interaction effects of three PAHs with different carcinogenic potential and chemical structure, in primary hepatocyte cells of gilt-headed seabreams (Sparus aurata). Hepatocytes were exposed to Phenanthrene (Phe), Benzo[a]pyrene (B[a]P) and Benzo[b]fluoranthene (B[b]F) and their mixtures at different proportions and several cellular responses were analyzed: cellular viability, CYP1A1 activity (EROD assay) and protein expression level (Western blot); transcript (mRNA) levels of CYP1A1, EPXH1 and GST-3 (qRT-PCR); genotoxic effects (DNA strand breakage) by the Comet assay. Results show that B[a]P induced CYP1A1 gene and protein expression increasing its activity and, therefore, increasing the production of metabolites that trigger genotoxic DNA damage (%). Most importantly, mixtures containing Phe and B[a]P increased even further CYP1A1 mRNA levels and DNA damage (up to 70 %) which suggests that, although Phe is considered a non-carcinogenic PAH, it potentiates CYP1A1 synthesis induced by B[a]P, increasing its genotoxicity. These findings indicate that the upregulation of CYP1A1 by carcinogenic PAHs will not weaken even when in mixtures with non-carcinogenic PAHs. On contrary, non-carcinogenic PAHs may potentiate the genotoxic effect of carcinogenic PAH and therefore mixture composition should be taken in account when assessing PAH toxicity. In fact, our results point to the need of redefining Environmental Risk Assessment protocols for mixtures of carcinogenic pollutants.

Toxicological assessment of functional polymer with single-walled carbon nanotubes in zebrafish embryos and its gill cell line

Carbon nanotubes (CNTs) have been widely used in developing polymer hybrid coatings for anticorrosive application. In the present study, poly [(3,5-dimethyl-lH-pyrazole-1-yl) methyl methacrylate-co-glycidyl methacrylate] (PyM) was prepared by solution polymerization. Single-wall carbon nanotubes (SWCNT) were incorporated in the PyM by solution blending technique at different proportions. The PyM and its SWCNT (PyM-SWCNT) nanocomposites were characterized by FT-IR spectroscopy, X-Ray Diffraction, FE-SEM and HR-TEM. Different concentrations of PyM or PyM-SWCNT prepared in the present study were assessed separately for their toxicity by in vivo and in vitro assays using zebrafish embryos and gill cell line of zebrafish (DrG), respectively. The nanocomposites at the concentration of 400 μg ml^-1 of PyM in 1.0% of SWCNT was found to be non-toxic and recommended for anticorrosive application whereas the nanocomposites with above 1% of SWCNT was found to be toxic. The nanocomposites with 1.5% of SWCNT delayed the hatching rate of eggs, decreased survival rate and heart beat in zebrafish embryos, and induced the morphological changes in DrG cells. Gene expression studies revealed that PyM-SWCNT with high concentration of SWCNT induced oxidative stress by activating ROS generations in zebrafish embryos and DrG cells. The immersion study of uncoated and coated with recommended concentration of PyM-SWCNT on mild steel (MS) in sea water was studied using FE-SEM and EDS, and the results showed effective corrosion protection without leaching behaviour. The nanocomposites with novel polymer in the present study may be used in the industry for anticorrosive purpose.

Effects of perfluoroalkyl substances (PFASs) and benzo[a]pyrene (BaP) co-exposure on phase I biotransformation in rainbow trout (Oncorhynchus mykiss)

The presence of perfluoroalkyl substances (PFASs) in the environment, especially in aquatic ecosystems, continues to be a significant concern for human and environmental health. Previous studies have suggested that several PFASs do not undergo biotransformation due to their chemical stability, yet perfluorooctanesulfonic acid (PFOS)- and perfluorooctanoic acid (PFOA)-exposed organisms have presented altered activity of important biotransformation pathways. Given the fundamental role of biotransformation in biological organisms and the significant distribution of PFAS in aquatic environments, the present study investigated the influence of PFOA and PFOS on phase I biotransformation enzymes in vitro using the rainbow trout liver RTL-W1 cell line and in vivo using juvenile rainbow trout. Cells and fish were exposed and co-exposed to environmentally relevant concentrations of PFOA, PFOS, and benzo[a]pyrene (BaP), for 72 h and 10 days, respectively, prior to measurements of cytotoxicity and biotransformation ability through measurements of CYP1A1-, CYP1A2-, and CYP3A4-like activities. Our results indicate that exposure to PFAS-BaP binary mixtures altered CYP1A-like activity in vivo; however, those alterations were not observed in vitro. Similarly, while BaP did not significantly induce CYP3A4 in vivo, exposure to the PFAS led to significantly lower enzymatic activity relative to basal levels. These observations may have implications for organisms simultaneously exposed to PFASs and other environmental pollutants for which biotransformation is necessary, especially in detoxification mechanisms. Furthermore, the interference with biotransformation pathways could potentially predispose exposed organisms to a compromised physiology, which may increase their vulnerability to other stressors and erode their survival fitness.

Selenium Nanoparticles Biosynthesized by Pantoea agglomerans and Their Effects on Cellular and Physiological Parameters in the Rainbow Trout Oncorhynchus mykiss

Simple Summary

Nanoparticles (Nps), new biotechnological tools, possess unique physical and chemical properties and are increasingly being used in several fields, such as manufacture, medicine and veterinary medicine. In this work, we evaluated the effects of selenium (Se) nanoparticles stabilized with L-Cysteine (Se⁰Nps/L-Cys) as a nutritional supplement, to modulate immunological, oxidative status, and productive parameters in O. mykiss. The results demonstrated that Se⁰Nps/L-Cys showed less toxicity and higher antioxidant activity than Se⁰Nps and Na₂SeO₃. The Se⁰Nps/L-Cys, as a dietary supplement, had a significantly better effect on both immunological and physiological parameters, causing improvements at the productive level of O. mykiss when compared with Se⁰Nps and Na₂SeO₃. We concluded that Se⁰Nps sythetised by P. agglomerans, used as dietary supplement, is an environmentally friendly and promising alternative for nutritional supplementation for O. mykiss.

Abstract

The applications of nanoparticles (Nps) as food additives, health enhancers, and antimicrobials in animal production are increasing. The aim of this study was to evaluate the effect of selenium (Se) nanoparticles (Se⁰Nps) stabilized with L-cysteine (Se⁰Nps/L-Cys), as a nutritional supplement, on immunological, oxidative status, and productive parameters in O. mykiss. TEM and SEM-EDS showed the accumulation of spherical Se⁰Nps entirely composed by elemental selenium (Se⁰) as intracellular and extracellular deposits in Pantoea agglomerans UC-32 strain. The in vitro antioxidant capacity of Se⁰Nps/L-Cys was significant more efficient ROS scavengers than Se⁰Nps and Na₂SeO₃. We also evaluate the effect of Se⁰Nps/L-Cys on cell viability and oxidative stress in RTgill-W1, RTS-11, or T-PHKM Oncorhynchus mykiss cell lines. Se⁰Nps/L-Cys showed less toxic and high antioxidant activity than Se⁰Nps and Na₂SeO₃. Finally, the dietary Se⁰Nps/L-Cys had a significant better effect on both plasma lysozyme and respiratory burst activity (innate immune response), on tissular Gpx activity (oxidative status), and on well-being (productive parameter) of O. mykiss when it is compared to Se⁰Nps and Na₂SeO₃. Se⁰Nps/L-Cys is a promising alternative for nutritional supplement for O. mykiss with better performance than Na₂SeO₃ and Se⁰Nps, ease to implementation, and reduced environmental impact.

Impacts of di-(2-ethylhexyl) phthalate on Folsomia candida (Collembola) assessed with a multi-biomarker approach

Di-(2-ethylhexyl) phthalate (DEHP) is extensively used as an additive to produce plastics, but it may damage non-target organisms in soil. In this study, the effects of DEHP on Folsomia candida in terms of survival, reproduction, enzyme activities, and DNA damage were investigated in spiked artificial soil using a multi-biomarker strategy. The 7-day LC₅₀ (median lethal concentration) and 28-day EC₅₀ (median effect concentration) values of DEHP were 1256.25 and 19.72 mg a.i. (active ingredient) kg^-1 dry soil, respectively. Biomarkers involved in antioxidant defense including catalase (CAT-catalase), glutathione S-transferases (GST), detoxifying enzymes including acetylcholinesterase (AChE), Cytochrome P450 (CYP450), and peroxidative damage (LPO-lipid peroxide) were also measured (EC₁₀, EC₂₀, and EC₅₀) after exposure for 2, 4, 7, and 14 days. The Comet assay was also applied to assess the level of genetic damage. The activity of CAT and LPO was drastically enhanced by the highest dose (EC₅₀) of DEHP on day two. The activities of GST and AChE in DEHP treatment groups were found to be blocked. In contrast, the activity of CYP450 was significantly enhanced compared to the respective control groups during the first four days of incubation. The Comet assay in F.candida demonstrated that DEHP (EC₅₀) could induce DNA damage. The obtained multi-biomarker data were analyzed using an integrated biomarker response (IBR) index, indicating that limited-time exposure triggered higher stress than long-term exposure at low concentrations of DEHP. These results demonstrate that DEHP may cause biochemical and genetic toxicity to F. candida, which illustrated the potential risks of DEHP in the soil environment and might affect soil ecosystem processes. Further studies are necessary to elucidate the toxic mechanisms of DEHP on other non-target organisms in soil.

Multi-approach assessment for the evaluation of spatio-temporal estrogenicity in fish from effluent-dominated surface waters under low instream flow

Current practices employed by most wastewater treatment plants (WWTP) are unable to completely remove endocrine disrupting compounds (EDCs) from reclaimed waters, and consistently discharge these substances to receiving systems. Effluent-dominated and dependent surface waters, especially during low instream flows, can increase exposure and risks to aquatic organisms due to adverse biological effects associated with EDCs. Given the ecological implications that may arise from exposure to such compounds, the present a multi-approach study examined spatio-temporal estrogenic potential of wastewater effluent to fish in East Canyon Creek (ECC), Utah, USA, a unique urban river with instream flows seasonally influenced by snowmelt. Juvenile rainbow trout (Oncorhynchus mykiss) were caged at different upstream and downstream sites from an effluent discharge during the summer and fall seasons. In the summer, where approximately 50% of the streamflow was dominated by effluent, fish from the upstream and a downstream site, located 13 miles away from the effluent discharge, presented significantly elevated concentrations of plasma vitellogenin (VTG). Similarly, significantly high 17β-estradiol to 11-ketotestosterone ratios were measured in the summer across all sites and time points, compared to the fall. In the laboratory, juvenile fish and primary hepatocytes were exposed to concentrated effluent and surface water samples. Quantification of VTG, although in significantly lower levels, resembled response patterns observed in fish from the field study. Furthermore, analytical quantification of common EDCs in wastewater revealed the presence of estriol and estrone, though these did not appear to be related to the observed biological responses, as these were more significant in sites were no EDCs were detected. These combined observations suggest potential estrogenicity for fish in ECC under continuous exposures and highlight the advantages of following weight-of-evidence (WoE) approaches for environmental monitoring, as targeted analytically-based assessments may or may not support the identification of causative contaminants for adverse biological effects.

In vitro metabolism of pesticides and industrial chemicals in fish

Metabolism is one of the most important factors in controlling the toxicity and bioaccumulation of pesticides in fish. In vitro systems using subcellular fractions, cell lines, hepatocytes and tissues of a specific organ, each of which is characterized by usability, enzyme activity and chemical transport via membrane, have been applied to investigate the metabolic profiles of pesticides. Not only species and organs but also the fishkeeping conditions are known to greatly affect the in vitro metabolism of pesticides. A comparison of the metabolic profiles of pesticides and industrial chemicals taken under similar conditions has shown that in vitro systems using a subcellular S9 fraction and hepatocytes qualitatively reproduce many in vivo metabolic reactions. More investigation of these in vitro systems for pesticides is necessary to verify their applicability to the estimation of pesticide metabolism in fish.

The evaluation of the potential ecotoxicity of pyroligneous acid obtained from fast pyrolysis

Pyroligneous acid (PA) is a by-product of bio-oil, which is obtained by pyrolysis of the wood. This product has been tested for use in several areas, such as agriculture, as a promising green herbicide; however, there are few scientific data regarding its environmental impacts. For this study, an ecotoxicity testing battery, composed of Daphnia magna acute toxicity test, Allium cepa test and in vitro Comet assay with the rainbow trout gonad-2 cell fish line (RTG-2) were used to evaluate the acute toxicity and genotoxicity of PA obtained from fast pyrolysis of eucalyptus wood fines. The PA presented acute toxicity to D. magna (microcrustacea) with EC₅₀ of 26.12 mg/L, and inhibited the seed germination (EC₅₀ 5.556 g/L) and root development (EC₅₀ 3.436 g/L) of A. cepa (higher plant). No signs of genotoxicity (chromosomal aberrations and micronuclei in A. cepa and primary DNA lesions in RTG-2 cells) were detected to this product. The acute toxicity and absence of genotoxicity may relate to the molecules found in the PA, being the phenolic fraction the key chemical candidate responsible for the toxicity observed. In addition, daphnids seem to be more sensitivity to the toxicity of PA than higher plants based on their EC₅₀ values. This first ecotoxicological evaluation of PA from fast pyrolysis pointed out the need of determining environmental exposure limits to promote the safer agriculture use of this product, avoiding impacts to living organisms.

Induction of oxidative stress, apoptosis and DNA damage by koumine in Tetrahymena thermophila

Koumine is a component of the Chinese medicinal herb Gelsemium elegans and is toxic to vertebrates. We used the ciliate Tetrahymena thermophila as a model to evaluate the toxic effects of this indole alkaloid in eukaryotic microorganisms. Koumine inhibited T. thermophila growth and viability in a dose-dependent manner. Moreover, this drug produced oxidative stress in T. thermophila cells and expressions of antioxidant enzymes were significantly elevated at high koumine levels (p < 0.05). Koumine also caused significant levels of apoptosis (p < 0.05) and induced DNA damage in a dose-dependent manner. Mitophagic vacuoles were present in cells indicating induction of autophagy by this drug. Expression of ATG7, MTT2/4, CYP1 and HSP70 as well as the MAP kinase pathway gene MPK1 and MPK3 were significantly altered after exposed to koumine. This study represents a preliminary toxicological evaluation of koumine in the single celled eukaryote T. thermophila.