Application of fish cell lines for evaluating the chromium induced cytotoxicity, genotoxicity and oxidative stress

Transfer of chromium from environment to fish in East Kolkata wetlands - evaluation by structural equation modeling

Chromium (Cr) is a significant pollutant in the effluents from leather industries and domestic city sewage. Cr was determined in water, sediment, and different tissues (gill, muscle, intestine, liver, and kidney) of Nile tilapia, Oreochromis niloticus harvested from wastewater-fed aquaculture (WFA) situated at Bamonghata, Bantala, Chowbaga and Chingrighata of East Kolkata Wetlands (EKW), a Ramsar site in West Bengal, India. The results showed that Cr concentration in surface water ranged between 0.05 to 0.15 mg/L, while Cr was detected at high concentration (100-300 mg/kg) in the sediment soil of the first three WFAs and in moderate concentration (50-110 mg/kg) in Chingrighata WFA. Average Cr concentrations in the tissues were ranked in the following sequence: kidney>liver>intestine>gill>muscle. However, the extent of accumulation of Cr in different tissues varied between the WFAs. We used Structural Equation Modeling (SEM) to determine the route of Cr transfer. The fitness of the model was evaluated by the performance measures. Cr accumulation pathways varied between the sites depending upon the level of Cr in water or sediment. Except for Bamonghata WFA, sediment was found as the principal source of accumulation of Cr in different tissues of O. niloticus. Cr refluxed from sediment into overlying water and accumulated in fish either through the food chain or through direct accumulation from water. In Bamonghata WFA, the role of sediment in the transfer of Cr could not be established due to the high water depth or biological non-availability of Cr in the sediment. It is concluded from this study that fish reared in the WFAs of EKW are still not hazardous in respect to Cr but require proper management to avoid the influx of Cr-containing effluents into the WFAs.

Symbiotic hemolymph bacteria reduce hexavalent chromium to protect the host from chromium toxicity in Procambarus clarkii

Hexavalent chromium (Cr(VI)) is a cytotoxic heavy metal pollutant that adversely affects all life forms. Interestingly, the crustacean Procambarus clarkii exhibits a relatively high tolerance to heavy metals. The underlying mechanisms remain unclear. In this study, we investigated the role of symbiotic bacteria in P. clarkii in alleviating Cr(VI)-induced damage and explored their potential mechanisms of action. Through transcriptomic analysis, we observed that Cr(VI) activated P. clarkii's antimicrobial immune responses and altered the bacterial composition in the hemolymph. After antibiotic treatment to reduce bacterial populations, Cr(VI)-induced intestinal and liver damage worsened, and crayfish exhibited lower levels of GSH/CAT/SOD activity. The Exiguobacterium, the symbiotic bacteria in the hemolymph of P. clarkii, were proved to be primary contributor to Cr(VI) tolerance. Further investigation suggested that it resists Cr(VI) through the activation of the ABC transporter system and the reduction of Cr(VI) via the reductase gene nfsA. To validate the role of Exiguobacterium in Cr(VI) tolerance, crayfish treated with antibiotics then supplemented with Exiguobacterium H6 and recombinant E. coli (with the nfsA gene), reduced Cr(VI)-induced ovarian damage. Overall, this study revealed that the symbiotic bacteria Exiguobacterium can absorb and reduce hexavalent chromium, mitigating Cr(VI)-induced damage in P. clarkii. These findings provide new insights into hexavalent chromium tolerance mechanisms in crustaceans.

Establishment and application of four long-term culture cell lines of the olive flounder Paralichthys olivaceus blastocysts

Four new embryonic cell lines derived from blastocysts of the olive flounder Paralichthys olivaceus, an important commercial marine fish, were established and characterized. They were designated as PoEFCI, PoEFCII, PoEFCIII, and PoEFCIV and were all fibroblastic cells. The cells were cultured in DMEM/F-12 medium supplemented with antibiotics, FBS, and growth factors at temperature of 25 °C and subcultured for >100 passages over 18 months. The origin of the cell lines was confirmed by examining the partial sequences of the cytochrome oxidase c subunit I (COI) gene of the flounder mitochondrial DNA (mtDNA). The four cell lines showed different growth curve patterns. According to the results of gene and protein expression and enzyme activity, the cell lines PoEFCI, PoEFCII, and PoEFC III could be pluripotent. The cells of all four cell lines were also successfully transfected with the green fluorescent protein (GFP) reporter gene, suggesting that they could be used to study gene function in the flounder or other fish. More importantly, PoEFCI-III were sensitive to chromium (Cr) and red sea bream Pagrus major iridovirus (RSIV), so they could be used as a powerful tool for the study of the toxicological investigation of heavy metals and RSIV in fish. Therefore, these cell lines would be useful for biotechnological and toxicological research on marine fish as an in vitro biological system.

Alkylphenols cause cytotoxicity and genotoxicity induced by oxidative stress in RTG-2 cell line

Alkylphenols ethoxylates are industrial surfactants, and the release in the environmental matrices produces degraded products, of which nonylphenol (NP) and octylphenol (OP) were the most common. They can be classified as endocrine disruptors since the estrogenic potential is widely recognized, but some others toxic aspects are in discussion. This study aimed to evaluate the toxicity of NP, OP, and mixtures of both through cellular, biochemical and genetic biomarkers in fish gonadal cell line RTG-2 exposed to nominal concentrations of 0.05; 0.5; 5; 50, and 100 μg mL^-1 of each chemical and their mixtures of 0.05, 0.5; 5 μg mL^-1 concentrations. After 24 h, the cells were collected for cytotoxic (neutral red - NR; crystal violet - CV, resazurin assay - RA and lactate-dehydrogenase - LDH), antioxidant system (glutathione-s-transferase - GST; superoxide-dismutase - SOD; glutathione-peroxidase - GPx and malondialdehyde - MDA) and genotoxic assays (alkaline comet assay and Fpg-modified alkaline comet assay). The chemicals and their mixtures were cytotoxic at 50 and 100 μg mL^-1, in general aspect, but LDH showed cytotoxicity since 0.05 μg mL^-1. The GST and SOD showed an activity increase trend in most tested groups, while GPx decreased at 5 μg mL^-1 of the mixture. The MDA increase in all groups resulted in lipid peroxidation. The reactive oxygen species caused DNA damage for all groups. The tested chemicals and concentrations have been found in the freshwater systems. They can induce cell toxicity in several parameters that could impair the gonadal tissues considering the RTG-2 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.

Pelagic and coastal green turtles (Chelonia mydas) experience differences in chemical exposure and effect

Green turtles foraging in coastal areas are exposed to land-based chemical pollutants that accumulate in the habitats to which they show high site fidelity. However, prior to coastal recruitment, they may be exposed to a different range of chemical threats. The recent development of species-specific in vitro bioassays for marine turtles allows for an effect-based assessment of toxicological endpoints. Blood was collected from green turtles of two life-stages, 'recent recruits' and 'coastal residents', in Hervey Bay and Moreton Bay. Organic contaminants were extracted from blood using the QuEChERS method, and cytotoxicity of the extracts measured in green turtle skin cells. Although not statistically significant, extracts from 'coastal residents' exhibited greater mean toxicity compared to 'recent recruits', possibly indicative of increased chemical accumulation from coastal habitat exposure. The bioassay results also indicated that turtles foraging in Hervey Bay are at greater risk of chemical exposure than those foraging in Moreton Bay.

Concentration- and time-dependence toxicity of graphene oxide (GO) and reduced graphene oxide (rGO) nanosheets upon zebrafish liver cell line

Graphene oxide (GO) and reduced graphene oxide (rGO) are carbon-based nanomaterials that have a wide range of applicability. Therefore, it is expected that their residual traces reach the aquatic environment, accumulate, and interact with its different compartments and the biota living in them. The concentration- and time-dependency response to GO and rGO in aquatic organisms are still poorly known. In the present study, the effects of GO and rGO on zebrafish hepatocytes were investigated using in vitro assays performed with established liver cell lines from zebrafish (ZFL). GO and rGO nanosheets were applied on ZFL cells at a concentration range of 1-100 µg mL^-1 for 24 and 72 h. The internalization of GO and rGO nanosheets, reactive oxygen species (ROS) production, cell viability, and cell death were evaluated. The internalization of GO increased as the concentrations of GO increased. The rGO nanosheets were smaller than GO nanosheets, and their hydrophobic characteristic favors their interaction with the cell membrane. However, the rGO nanosheets were not observed in the uptake assay. Exposure for 72 h was found to cause harmful effects in ZFL cells, causing higher ROS production in cells exposed to rGO and stopping cell replication. Nevertheless, GO did not stop cell replication, but exposed cells had higher levels of apoptosis and necrosis. After 72 h, both GO and rGO were toxic, but with different mechanisms of toxicity.

Development and characterization of a new gill cell line from the striped catfish, Pangasianodon hypophthalmus (Sauvage, 1878)

Cell lines as an in vitro model developed from different target organs of fish find their use in virus susceptibility, cytotoxicity, gene expression studies. The striped catfish, Pangasianodon hypophthalmus, is one of the main species in aquaculture, especially in Southeast Asian countries like Thailand, Indonesia, China, India, Bangladesh, and Vietnam. The present study reports the development of a new permanent cell line from the gills of P. hypophthalmus designated as PHG and its application in toxicological research. Leibovitz's L-15 cell culture medium supplemented with 15% fetal bovine serum (FBS) was used to maintain cell line PHG. The morphology of the PHG cell line was observed fibroblastic-like. PHG cells grew well at varying temperatures ranging from 24 to 30 °C with an optimum temperature of 28 °C. The PHG cell line was characterized using a sequence of mitochondrial cytochrome C oxidase subunit I, which authenticated the species of origin of the cell line. The cell line was transfected with a pEGFP-C1 plasmid, and the transfection reporter gene was successfully expressed 48 h post-transfection with 9% transfection efficiency. The toxicity assessment of two organophosphate pesticides, chlorpyrifos, and malathion using the PHG cell line revealed that the two organophosphate pesticides were cytotoxic to the cell line at varying concentrations.

Environmentally Relevant Hexavalent Chromium Disrupts Elemental Homeostasis and Induces Apoptosis in Zebrafish Liver

Although hexavalent chromium Cr [VI] is known as a toxicant in the aquatic environment, its effect in low, environmentally relevant concentration (ERC; 2 mg L^-1) is less characterized. Against this backdrop, the effects of Cr [VI] in ERC on zebrafish liver has been investigated in this study. Fluorescence microscopy and gel electrophoresis detected excess DNA damage and cell death via apoptosis in 2 mg L^-1 Cr [VI]-treated fish when compared with that of control. Besides, there were transcriptional activations of p53, Bax, Caspase 9 and Caspase 3 genes but downregulation of Bcl2 gene in the treated group, confirming the apoptotic pathway. Energy dispersive X-ray fluorescence (EDXRF) data showed significant (p < 0.05) increase in hepatic content of Cr, selenium, iron, manganese, calcium, sulfur and magnesium but depletion of zinc, copper and cobalt in the treated group. Collectively, the study shows that even a low, ERC of Cr [VI] is toxic to the zebrafish as it elicited marked apoptosis in the hepatocytes and altered the liver elemental profile.

Differences in marine megafauna in vitro sensitivity highlights the need for species-specific chemical risk assessments

Sea turtles, dolphins and dugongs can be exposed to large mixtures of contaminants due to the proximity of foraging locations to anthropogenic inputs. Differences in accumulation and effect result in differences of chemical risk to these species. However, little is known about the effect of contaminants in marine wildlife. Cell-based, or in vitro, exposure experiments offer an ethical alternative to investigate the effect of contaminants in wildlife. Data from in vitro studies can then be placed in an environmental context, by using screening risk assessments, comparing effect data with accumulation data from the literature, to identify risk to populations of marine wildlife. Cytotoxicity of Cr⁶⁺, Cd²⁺, Hg²⁺, 4,4'-DDE, and PFNA were investigated in primary skin fibroblasts of green turtles, loggerhead turtles, hawksbill turtles, dugongs, Burrunan dolphins, and common bottlenose dolphins. The general order of toxicity for all species was Hg²⁺> Cr⁶⁺ > Cd²⁺> 4,4'-DDE > PFNA, and significant differences in cytotoxicity were found between species for Cr⁶⁺, Cd²⁺ and PFNA. For Cd²⁺, in particular, cells from turtle species were less sensitive than mammalian species, and dugong cells were by far the most sensitive. The results from the cytotoxicity assay were then used in combination with published data on tissue contaminant concentrations to calculate risk quotients for identifying populations of each species most at risk from these chemicals. Cr, Cd and Hg were identified as posing risk in all six species. Dugongs were particularly at risk from Cd accumulation and dolphin species were particularly at risk from Hg accumulation. These results demonstrate the importance of using species-specific effect and accumulation data for developing chemical risk assessments and can be used to inform managers of priority contaminants, species, or populations. Development of additional in vitro endpoints, and improving links between in vitro and in vivo effects, would further improve this approach to understanding chemical risk in marine megafauna.

Inhibition of Metamorphosis, Thyroid Gland, and Skeletal Ossification Induced by Hexavalent Chromium in Bufo gargarizans Larvae

Hexavalent chromium (Cr [VI]) is one of the major detrimental heavy metal pollutants. In the present study, Bufo gargarizans were exposed to 0, 52, 104, 208, and 416 μg/L Cr (VI) from Gosner stage 2 until metamorphosis; and growth, development, and histological characteristics of the thyroid gland and skeletal ossification were examined. The results demonstrated that the survival rate of larvae exposed to Cr (VI) was not different from that measured in animals from the control group. However, high levels of Cr (VI) (104, 208, and 416 μg/L) were associated with significantly delayed growth and development. The suppression of skeletal ossification was observed at high Cr (VI) levels. Besides, histological alterations of the thyroid gland, such as follicular cell hyperplasia, colloid depletion, and peripheral colloid vacuolation, were found in 52 to 416 μg/L Cr (VI) treatments. The results of the present study highlight reductions in growth and development as well as percent metamorphosis and skeletal ossification due to histological alteration of the thyroid gland during exposure to Cr (VI) in B. gargarizans larvae. The present investigation could provide a basis for understanding the detrimental effects of Cr (VI) in amphibian larvae. Environ Toxicol Chem 2021;40:2474-2483. © 2021 SETAC.

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.

Perspectives of Genetic Damage and Epigenetic Alterations by Hexavalent Chromium: Time Evolution Based on a Bibliometric Analysis

Compounds containing hexavalent chromium [Cr(VI)] have been classified as Group I human carcinogens in 1990 by the International Agency for Research on Cancer, known to induce human lung cancers. To determine the nature of Cr(VI) carcinogenesis, much has been learned about genetic damage and epigenetic alterations. On the basis of bibliometric analysis of the available literature found between 1966 and 2020, the present study investigated the evolution of author keywords; provided a summary of relevant studies focused on populations, animals/plants, or cells; and depicted the co-operation among countries or institutions and research group development. Additionally, multiomics technology and bioinformatics analysis can be a valuable tool for figuring out new biomarkers from different molecular levels like gene, RNA, protein, and metabolite and ascertaining the mechanism pathways of Cr(VI) genotoxicity and carcinogenesis.

Synergistic Effect of Biosynthesized Silver Nanoparticles and Natural Phenolic Compounds against Drug-Resistant Fish Pathogens and Their Cytotoxicity: An In Vitro Study

Fish pathogens causing disease outbreaks represent a major threat to aquaculture industry and food security. The aim of the presented study is to develop safe and effective bioactive agents against two bacterial isolates: Aeromonas hydrophila and Pseudomonas fluorescens. We employed a broth microdilution method to investigate the antibacterial effect of biosynthesized silver nanoparticles (AgNPs); rutin, a natural flavonoid extracted from Ruta graveneoles; and heliomycin, a secondary metabolite produced by marine actinomycetes AB5, as monotherapeutic agents. Moreover, AgNPs in combination with rutin (AgNP + R) and heliomycin (AgNPs + H) were examined for their synergistic effect. The cytotoxic effect of individual bioactive compounds and in combination with AgNPs was investigated on epithelioma papulosum cyprini (EPC) fish cell lines. Individual treatment of AgNPs, rutin, and heliomycin exhibited a dose-dependent antimicrobial activity against A. hydrophila and P. fluorescens. Rutin minimum inhibitory concentration (MIC) showed the lowest cytotoxicity when tested on EPC cell lines, while heliomycin MIC was highly cytotoxic. Combined subtherapeutic doses of AgNPs + R and AgNPs + H displayed additive and synergistic effects against A. hydrophila and P. fluorescens, respectively, with improved results and relative safety profile. The study findings demonstrate that a combination of AgNPs and natural bioactive compounds may represent novel therapeutics fighting fish pathogens potentially affecting the fish farming industry.

Genotoxicity induced by hexavalent chromium leading to eryptosis in Ctenopharyngodon idellus

The initiation of eryptosis as a result of genotoxic action of Cr(VI), seen through micronucleus and comet assay in the peripheral erythrocytes of Ctenopharyngodon idellus was evaluated through RT-qPCR. For this, fish was exposed to sublethal concentration of hexavalent chromium (5.30 and 10.63 mg/L), and the blood was sampled on different endpoints (15, 30 and 45 days). Accumulation of chromium in the erythrocytes was also studied, which depicted a significant increase in toxicant concentration and time dependent manner. Both concentrations of hexavalent chromium induced DNA damage, visible in the form of comet tails. The presence of micronuclei in the erythrocytes was accompanied with occurrence of nuclear bud (NBu), lobed nucleus (Lb), notched nucleus (Nt), vacuolated nucleus (Vn), binucleated cell (Bn) as nuclear abnormalities; and acanthocytes (Ac), echinocytes (Ec), notched cells (Nc), microcytes (Mc) and vacuolated cytoplasm (Vc) as cytoplasmic abnormalities. The expression of genes related to intrinsic apoptotic pathway induced by Cr(VI) presented significant (p < 0.05) upregulation in the expression of p53, Bax, Apaf-1, caspase9 and caspase3, and downregulation of Bcl2; inferring the initiation of apoptotic pathway. The ration of Bax and Bcl2 also appended the apoptotic state of the erythrocytes. From the present investigation, it can be concluded that genotoxicity induced by hexavalent chromium lead to eryptosis in C. idellus.

Probing the effects of hexavalent chromium exposure on histology and fatty acid metabolism in liver of Bufo gargarizans tadpoles

Hexavalent chromium is one of the major detrimental heavy metal pollutants. B. gargarizans tadpoles were treated with different concentrations of Cr⁶⁺ (0, 13, 52, 104, 208, and 416 μg Cr⁶⁺ L^-1) from Gs 2 to Gs 42. The effect of Cr⁶⁺ on histopathological alterations and transcript levels of fatty acid metabolism-related genes as well as fatty acids composition and content in liver were examined. Histopathological changes were observed in liver at 52, 104, 208, and 416 μg Cr⁶⁺ L^-1. Moreover, RT-qPCR analyses showed the downregulated mRNA levels of the genes related to fatty acid synthesis (SCD, MECR, TECR and ELOVL1) and fatty acid β-oxidation (ACOT1, PPT1, HADH and ACAA2) at 416 μg Cr⁶⁺ L^-1. However, the mRNA expression of fatty acid β-oxidation-related genes (ECHS1, HADHA and ACAA1) were significantly upregulated at 13, 52, 104, 208 and 416 μg Cr⁶⁺ L^-1. In situ hybridization revealed BSEP was expressed in hepatocyte nucleus and plasma membrane, and HSD17B12 was abundantly expressed in the plasma membrane. The HSD17B12 mRNA levels were significantly upregulated in tadpoles exposed to all Cr⁶⁺ treatment groups, while the BSEP mRNA levels were downregulated at 104, 208 and 416 μg Cr⁶⁺ L^-1 groups compared to control. In addition, an increase in polyunsaturated fatty acids and a decrease in monounsaturated fatty acids were found in 52, 104 and 416 μg Cr⁶⁺ L^-1 groups. Overall, chronic exposure to Cr⁶⁺ may suppress fatty acid synthesis, disturb fatty acid β-oxidation, aggravate disorders of hepatic function and induce hepatic impairment in B. gargarizans tadpoles.

Chromium-Induced Reactive Oxygen Species Accumulation by Altering the Enzymatic Antioxidant System and Associated Cytotoxic, Genotoxic, Ultrastructural, and Photosynthetic Changes in Plants

Chromium (Cr) is one of the top seven toxic heavy metals, being ranked 21st among the abundantly found metals in the earth’s crust. A huge amount of Cr releases from various industries and Cr mines, which is accumulating in the agricultural land, is significantly reducing the crop development, growth, and yield. Chromium mediates phytotoxicity either by direct interaction with different plant parts and metabolic pathways or it generates internal stress by inducing the accumulation of reactive oxygen species (ROS). Thus, the role of Cr-induced ROS in the phytotoxicity is very important. In the current study, we reviewed the most recent publications regarding Cr-induced ROS, Cr-induced alteration in the enzymatic antioxidant system, Cr-induced lipid peroxidation and cell membrane damage, Cr-induced DNA damage and genotoxicity, Cr-induced ultrastructural changes in cell and subcellular level, and Cr-induced alterations in photosynthesis and photosynthetic apparatus. Taken together, we conclude that Cr-induced ROS and the suppression of the enzymatic antioxidant system actually mediate Cr-induced cytotoxic, genotoxic, ultrastructural, and photosynthetic changes in plants.

Distinctive fingerprints of genotoxicity induced by As, Cr, Cd, and Ni in a freshwater fish

Genotoxicity of three toxic elements (chromium, cadmium, nickel) and a metalloid (arsenic) has been studied in a freshwater fish, Channa punctatus using micronuclei (MN) test, comet assay, and erythrocyte nuclear alterations (ENAs) as fingerprints of genotoxicity. These tests yielded different results suggesting involvement of different mechanisms for their genotoxicity. While highest frequency of blebbed nuclei was observed in chromium-treated fish (6.5 ± 0.76), lowest was observed in cadmium-treated fish (4.0 ± 1.0). Maximum number of notched nuclei was recorded in arsenic-treated fish (5.5 ± 1.15) whereas highest numbers of lobed nuclei were found in cadmium-treated fish (4.5 ± 0.13). These differences might be attributed to selective bioaccumulation and chemodynamics of each element. Other parameters used to determine genotoxicity viz.: lipid peroxidation and DNA damage also suggested different mechanisms of their genotoxicity. It is suggested that an integrative approach, using a battery of tests for determining genotoxicity, should be made while making environmental health risk assessment and ecotoxicological studies of these toxic elements.

Applicability of in vitro methods in evaluating the biotransformation of polycyclic aromatic hydrocarbons (PAHs) in fish: Advances and challenges

The biotransformation of polycyclic aromatic hydrocarbons (PAHs) and the biochemical mechanisms involved in such process continue to be intensively studied in the fields of environmental science and toxicology. The investigation of PAH biotransformation in fish is fundamental to understand how piscine species cope with PAH exposure, as these compounds are ubiquitous in aquatic ecosystems and impact different levels of biological organization. New approaches are continuously developed in the field of ecotoxicology, allowing live animal testing to be combined with and, in some cases, replaced with novel in vitro systems. Many in vitro techniques have been developed and effectively applied in the investigation of the biochemical pathways driving the biotransformation of PAH in fish. In vitro experimentation has been fundamental in the advancement of not only understanding PAH-mediated toxicity, but also in highlighting suitable cell-based models for such investigations. Therefore, the present review highlights the value and applicability of in vitro systems for PAH biotransformation studies, and provides up-to-date information on the use of in vitro fish models in the evaluation of PAH biotransformation, common biomarkers, and challenges encountered when developing and applying such systems.

Cytotoxicity of organic and inorganic compounds to primary cell cultures established from internal tissues of Chelonia mydas

Chemical contaminants have been found in the tissues of sea turtles from all over the world; however, very little is known about the effects. Recently, in vitro alternatives to live animal testing have been applied to sea turtles due to their ethical and practical benefits. While primary skin fibroblasts have been established for several species of sea turtle, cells from internal organs are lacking, though they may be more relevant due to the well documented accumulation of contaminants within internal tissues. This study established primary cell cultures from the small intestine, heart, liver, ovary and skin of green turtles (Chelonia mydas). Cells were exposed to ten contaminants typically found in sea turtles to examine potential variations in sensitivity among cells established from different organs. Differences between cells established from different animals were also examined, including a comparison of cells established from a turtle with fibropapillomatosis (FP) and healthy turtles. Loggerhead (Caretta caretta) primary skin cells were also included for species comparisons. Significant differences were found between the organ types, with liver and heart being the least sensitive, and skin being the most sensitive. Overall, variation between the organ types was low. Primary skin fibroblasts may be a suitable and representative cell type for in vitro turtle toxicology research, as it is relatively easy to obtain from healthy live animals. Skin cultures provide a more sensitive indication of effect, and could be used as an early warning of the potential effects of chemical contamination. Some species differences were found but no differences were found between cell cultures from an FP turtle and healthy turtles. When EC₅₀ values were compared to accumulation values from the literature, inorganic contaminants, such as Zn, Cd, Cr, Hg, and Cu were identified as posing a potential risk to sea turtle populations around the world.

Effects of hexavalent chromium on intestinal histology and microbiota in Bufo gargarizans tadpoles

Chromium is detrimental heavy metal pollutants and can enter and affect aquatic organisms. In our experiment, B. gargarizans embryos were chronically exposed in different concentrations of Cr (VI) (0, 13, 104, and 416 μg Cr⁶⁺ L^-1) until reached Gosner stage 38. We measured morphological parameters of the body and intestine of B. gargarizans tadpoles, and examined alteration of intestinal tissue. Furthermore, we analyzed the intestinal microbial community of B. gargarizans tadpoles using 16S rRNA gene amplicon sequencing. Our research demonstrated that Cr (VI) exposure caused alteration of intestinal tissue structure in 416 μg Cr⁶⁺ L^-1 treatment groups. Total body length, body wet weight, intestinal length and wet weight of B. gargarizans tadpoles were significantly declined at 416 μg Cr⁶⁺ L^-1. In addition, 16S rRNA gene sequencing revealed that Cr (VI) exposure significantly altered the intestinal microbiota diversity and composition, and perturbed the community structure of the microbiota. As for the intestinal microbiota, at the phylum level, Fusobacteria significantly changed in all Cr (VI) treated groups. Saccharibacteria and TM6_Dependentiae were detected only in the high dose exposure groups. At the genus level, Aeromonas was significantly decreased in Cr (VI) treated groups. According to the results of functional prediction, Cr (VI) exposure affected metabolism and increased risk of disease by inducing the alterations of intestinal microbiota structure. Taken together, the present study provide a new framework elucidating the toxic effects Cr (VI) exposure on B. gargarizans tadpoles associated with intestinal histology and microbiota.

Primary green turtle (Chelonia mydas) skin fibroblasts as an in vitro model for assessing genotoxicity and oxidative stress

Little is known about the effects of contaminants that accumulate in sea turtles. When in vivo exposure studies have ethical and logistical barriers, as is the case with sea turtles, in vitro tools can provide important information on the effects of contaminants. Several in vitro studies have assessed cytotoxicity of contaminants to sea turtles cells, however to gain a more refined mechanistic understanding of the effects of contaminants, sub-lethal effects also require investigation. Considering the complex mixture of contaminants that sea turtles are potentially exposed to, high throughput testing methods are necessary so that a large number of contaminants (and mixtures) can be rapidly tested. This study examined oxidative stress (reactive oxygen species production) and genotoxicity (micronucleus formation) in primary green turtle skin fibroblasts in response to 16 organic and inorganic contaminants found in coastal environments. Significant induction of oxidative stress was found with Cu, Co, Cr, and Hg. Significant effects on genotoxicity were found with Cu, Co, Cr, Hg, Pb and metolachlor. Effect concentrations from the bioassays were used in a simple risk assessment of turtles worldwide using accumulation values from the literature to identify populations at risk. Cu, Co, Cr and Hg were identified as posing the biggest threat to sea turtles. This study demonstrated the validity of using primary turtle cell cultures in the assessment of risk associated with a large number of contaminants using a high-throughput toxicity testing format.

Endocrine disruption, oxidative stress and lipometabolic disturbance of Bufo gargarizans embryos exposed to hexavalent chromium

The aim of the current study was to determine the potential developmental and metabolic abnormalities caused by Cr (VI) exposure on Bufo gargarizans (B. gargarizans) embryos. B. gargarizans embryos were treated with different concentrations of Cr (VI) (13, 52, 104, 208, and 416 μg Cr⁶⁺ L^-1) for 6 days. Morphological abnormalities, total length, weight and developmental stage were monitored. Malformations of embryos were also examined using scanning electron microscopy (SEM). In addition, the transcript levels of several genes associated with lipid metabolism, oxidative stress, and thyroid hormones signaling pathways were also determined. Our results showed a time-dependent inhibitory effect of Cr (VI) on the growth and development of B. gargarizans embryos. On day 4, total length, weight, and developmental stage were significantly lower at 416 μg Cr⁶⁺ L^-1 relative to control embryos. On day 6, significant reductions in total length, weight, and developmental stage were observed at 104, 208, and 416 μg Cr⁶⁺ L^-1. Malformed embryos were found in all Cr (VI) treatments, which were characterized by axial flexures, yolk sac edema and rupture, surface tissue hyperplasia, stunted growth, wavy fin and fin flexure. RT-qPCR results showed that exposure to Cr (VI) down-regulated TRβ and Dio2 mRNA expression and up-regulated Dio3 mRNA level at 416 μg Cr⁶⁺ L^-1. The transcript levels of SOD and GPx were upregulated at 52, 208, and 416 μg Cr⁶⁺ L^-1, while the transcript level of HSP90 was downregulated at 52, 208, and 416 μg Cr⁶⁺ L^-1. Also, mRNA expression of lipid synthesis-related genes (FAE and ACC) were significantly downregulated in embryos treated with 208 and 416 μg Cr⁶⁺ L^-1, but mRNA expression of fatty acid β-oxidation-related genes (ACOX, CPT, and SCP) was significantly upregulated at 416 μg Cr⁶⁺ L^-1. Therefore, our results suggested that Cr (VI) could disrupt thyroid endocrine pathways and lipid synthesis, leading to the inhibition of growth and development in B. gargarizans embryos. Furthermore, the decreased ability of scavenging ROS induced by Cr (VI) might be responsible for the teratogenic effects of Cr (VI).

Pro- and antioxidant activity of chromium(III), iron(III), molybdenum(III) or nickel(II) and their mixtures

The aim of this study was to examine the effect of chromium(III), iron(III), molybdenum(III) and nickel(II) and their combinations on pro- and antioxidant activity in mouse embryo fibroblasts and liver cancer cells. The present study shows that chromium(III), iron(III), nickel(II) and molybdenum(III) induce oxidative stress. In the case of chromium(III), nickel(II) and molybdenum(III) the intracellular ROS were dominant. However, in the case of iron(III) MDA was dominant - the end product of lipid peroxidation. Antioxidant activity of superoxide dismutase and catalase increased in low concentration of chromium(III); however, they decreased in higher concentrations. The same enzymes decreased after iron(III), nickel(II) and molybdenum(III) treatment in dose dependent manner. The activity of glutathione peroxidise decreased in dose dependent manner in all used microelements. Additions of Cr(III) at 200 μM plus Fe(III) at 1000 μM showed synergistic effect in ROS production and in lowering antioxidant activity. The same type of interaction in pairs Cr(III) at 1000 μM plus Fe(III) or Ni(II) or Mo(III) at concentration of 200 μM was observed. The protective effects of Cr(III) in antioxidant activity and in lowering intracellular ROS production in pairs of Cr(III) at 200 μM and Ni(II) or Mo(III) at concentration of 1000 μM were observed.

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

The use of fish cell cultures has proven to be an effective tool in the study of environmental and aquatic toxicology. Valuable information can be obtained from comparisons between cell lines from different species and organs. In the present study, specific chemicals were used and biomarkers (e.g. 7-Ethoxyresorufin-O-deethylase (EROD) activity and reactive oxygen species (ROS)) were measured to assess the metabolic capabilities and cytotoxicity of the fish hepatic cell lines Hepa-E1 and RTH-149, and the fish gill cell lines RTgill-W1 and G1B. These cell lines were exposed to β-naphthoflavone (BNF) and benzo[a]pyrene (BaP), the pharmaceutical tamoxifen (TMX), and the organic peroxide tert-butylhydroperoxide (tBHP). Cytotoxicity in gill cell lines was significantly higher than in hepatic cells, with BNF and TMX being the most toxic compounds. CYP1-like associated activity, measured through EROD activity, was only detected in hepatic cells; Hepa-E1 cells showed the highest activity after exposure to both BNF and BaP. Significantly higher levels of CYP3A-like activity were also observed in Hepa-E1 cells exposed to TMX, while gill cell lines presented the lowest levels. Measurements of ROS and antioxidant enzymes indicated that peroxide levels were higher in gill cell lines in general. However, levels of superoxide were significantly higher in RTH-149 cells, where no distinctive increase of superoxide-related antioxidants was observed. The present study demonstrates the importance of selecting adequate cell lines in measuring specific metabolic parameters and provides strong evidence for the fish hepatocarcinoma Hepa-E1 cells to be an excellent alternative in assessing metabolism of xenobiotics, and in expanding the applicability of fish cell lines for in vitro studies.

A review of the applications of organo-functionalized magnetic graphene oxide nanocomposites for heavy metal adsorption

Graphene-based adsorbents have attracted wide interests as effective adsorbents for heavy metals removal from the environment. Due to their excellent electrical, mechanical, optical and transport properties, graphene and its derivatives such as graphene oxide (GO) have found various applications. However, in many applications, surface modification is necessary as pristine graphene/GO may be ineffective in some specific applications such as adsorption of heavy metal ions. Consequently, the modification of graphene/GO using various metals and non-metals is an ongoing research effort in the carbon-material realm. The use of organic materials represents an economical and environmentally friendly approach in modifying GO for environmental applications such as heavy metal adsorption. This review discusses the applications of organo-functionalized GO composites for the adsorption of heavy metals. The aspects reviewed include the commonly used organic materials for modifying GO, the performance of the modified composites in heavy metals adsorption, effects of operational parameters, adsorption mechanisms and kinetic, as well as the stability of the adsorbents. Despite the significant research efforts on GO modification, many aspects such as the interaction between the functional groups and the heavy metal ions, and the quantitative effect of the functional groups are yet to be fully understood. The review, therefore, offers some perspectives on the future research needs.