Cytological and biochemical response of R1 cells and isolated hepatocytes from rainbow trout (Oncorhynchus mykiss) to subacute in vitro exposure to disulfoton

Cytotoxicity Assays with Fish Cells as an Alternative to the Acute Lethality Test with Fish

In ecotoxicology, in vitro assays with fish cells are currently applied for mechanistic studies, bioanalytical purposes and toxicity screening. This paper discusses the potential of cytotoxicity assays with fish cells to reduce, refine or replace acute lethality tests using fish. Basal cytotoxicity data obtained with fish cell lines or fish primary cell cultures show a reasonable to good correlation with lethality data from acute toxicity tests, with the exception of compounds that exert a specific mode of toxic action. Basal cytotoxicity data from fish cell lines also correlate well with cytotoxicity data from mammalian cell lines. However, both the piscine and mammalian in vitro assays are clearly less sensitive than the fish test. Therefore, in vivo LC50 values (concentrations of the test compounds that are lethal to 50% of the fish in the experiment within 96 hours) currently cannot be predicted from in vitro values. This in vitro-in vivo difference in sensitivity appears to be true for both fish cell lines and mammalian cell lines. Given the good in vitro-in vivo correlation in toxicity ranking, together with the clear-cut difference in sensitivity, the role of cytotoxicity assays in a tiered alternative testing strategy could be in priority setting in relation to toxic hazard and in the toxicity classification of chemicals and environmental samples.

Cytotoxicity of silver and copper nanoparticles on rainbow trout (Oncorhynchus mykiss) hepatocytes

Nanoparticles are commonly used in the industry and are present in consumer goods; therefore, evaluation of their potential toxicity is necessary. The aim of the present study was to assess the cytotoxic effects of the nanoparticles of silver (AgNPs) at the concentration of 1.5 mg L^-1 and copper (CuNPs) at 0.15 mg L^-1 on rainbow trout (Oncorhynchus mykiss) hepatocytes after 28 days of exposure. Histological analysis revealed dilated sinusoids, shrunken hepatocytes, nuclear necrosis, and increased number of Kupffer cells in the liver of fish exposed to nanoparticles. The lowest hepatocyte proliferation index was observed in fish treated with AgNPs. Ultrastructural studies revealed mitochondrial edema and cristolysis, dilated and loosened endoplasmic reticulum, cytoplasm vacuolation, accumulation of lipid droplets, glycogen depletion, and formation of myelin-like bodies. The results also revealed that the liver of fish exposed to copper nanoparticles showed higher regenerative potential indicated by higher proliferation index, more abundant glycogen, and more numerous Kupffer cells compared to the fish treated with silver nanoparticles.

Cytological and biochemical effects of a mixture of 20 pollutants on isolated rainbow trout (Oncorhynchus mykiss) hepatocytes

Isolated hepatocytes of rainbow trout (Oncorhynchus mykiss) were exposed to different concentrations (1x, 10x, 50x) of a complex mixture of 20 environmentally relevant contaminants (PAHs, PCBs, pesticides) typical of the chemical burden of surface waters and sediments of small rivers in southwest Germany to investigate sublethal cytological and biochemical alterations. Results document that all concentrations clearly induced biochemical and morphological changes. The activities of enzymes such as lactate dehydrogenase and catalase as well as the rate of lipid peroxidation were significantly increased, whereas acid phosphatase activity decreased. Cytopathological effects included deformation of cellular shape, deformation and dilation of the nuclear envelope, increase in heterochromatin, nuclear inclusions, heterogeneity of mitochondria, vesiculation of RER cisternae, as well as increases in myelinated bodies, lysosomes, and peroxisomes. If compared with cytological alterations induced in isolated rainbow trout hepatocytes after exposure to sediment extracts from rivers of corresponding contamination, cytological effects of exposure to the complex chemical mixture displayed numerous similarities.

Nonylphenol provokes a vesiculation of the Golgi apparatus in three fish epidermis cultures

The aim of this work was to study the effects of nonylphenol and waste water on the cell ultrastructure of fish skin. Therefore, besides a recently established primary cell culture and a cell line, an epidermal tissue culture of fish was developed and tested. In all three systems a prominent vesiculation of the Golgi apparatus was observed after exposure to nonylphenol, which has not been described before and therefore strongly suggests an effect that might indicate exposure to nonylphenol and/or related substances. The Epithelial papulosum cyprini cell line was the most sensitive to nonylphenol, followed by the primary cell culture of epidermis cells and then the explant tissue culture. The vesiculation of the Golgi apparatus was accompanied by degenerative changes in the two cell cultures only. The lack of degenerative changes in the cells of the tissue culture was discussed with respect to the presence of differentiated cells that might better be able to protect themselves by mucous or by an activated xenobiotic metabolism. In a second type experiment, a waste water sample containing small concentrations of nonylphenol was applied to the cultures. It did not lead to a vesiculation of the Golgi apparatus, probably because the nonylphenol concentrations in the waste water were too low to induce the vesiculation. The cultures exposed to waste water revealed unspecific degenerative cellular changes. Additionally, explant cultures were prepared from fish that had survived a 6-month exposure to polluted river water. In these cultures a higher number of mitochondria containing myelin bodies were observed when compared to control cultures. Consequently, exposure to polluted water containing a mixture of substances in vitro and in vivo was found to lead to degenerative alterations in the ultrastructure of the cells.

Isolated hepatocytes of rainbow trout (Oncorhynchus mykiss) as a tool to discriminate between differently contaminated small river systems

Isolated hepatocytes of rainbow trout (Oncorhynchus mykiss) were exposed to native waters and acetone sediment extracts of Krähenbach and Körsch, two small rivers in south-west Germany with different levels of chemical contamination, and were investigated by means of electron microscopic and enzyme biochemical techniques to evaluate sublethal cytotoxic effects. Between both rivers as well as between free water phase and sediment, significant differences in the toxic burden could be detected. Results document that dilutions of Krähenbach and Körsch surface water and sediment extracts induce time- and dose-dependent morphological and biochemical changes. Especially in water and sediments of the river Körsch, strong contamination could be observed. After exposure to samples from the Körsch, both morphological and biochemical responses of isolated hepatocytes were more prominent than following exposure to samples of Krähenbach, thus reflecting the different chemical burden of the two river systems. Cytopathological effects also included deformation of nuclear envelopes and increase of heterochromatin, heterogeneity of mitochondria, vesiculation of cisternae of the rough endoplasmic reticulum, as well as proliferation of the smooth endoplasmic reticulum. Moreover, peroxisomal and lysosomal proliferation could be correlated to a stimulation of the corresponding marker enzymes, catalase and acid phosphatase. In both rivers, activities of lactate dehydrogenase and alanine aminotransferase as markers of cytosolic glycolysis and protein metabolism were increased indicating a general stimulation of cellular metabolism. Cytological changes in isolated hepatocytes thus not only serve to discriminate between different levels of contamination of water, but may also help to differentiate between pollution levels of sediments.

Fish cell lines as a tool in aquatic toxicology

In aquatic toxicology, cytotoxicity tests using continuous fish cell lines have been suggested as a tool for (1) screening or toxicity ranking of anthropogenic chemicals, compound mixtures and environmental samples, (2) establishment of structure-activity relationships, and (3) replacement or supplementation of in vivo animal tests. Due to the small sample volumes necessary for cytotoxicity tests, they appear to be particularly suited for use in chemical fractionation studies. The present contribution reviews the existing literature on cytotoxicity studies with fish cells and considers the influence of cell line and cytotoxicity endpoint selection on the test results. Furthermore, in vitro/in vivo correlations between fish cell lines and intact fish are discussed. During recent years, fish cell lines have been increasingly used for purposes beyond their meanwhile established role for cytotoxicity measurements. They have been successfully introduced for detection of genotoxic effects, and cell lines are now applied for investigations on toxic mechanisms and on biomarkers such as cytochrome P4501A. The development of recombinant fish cell lines may further support their role as a bioanalytical tool in environmental diagnostics.

Viability and differential function of rainbow trout liver cells in primary culture: coculture with two permanent fish cells

The study investigates the influence of different culture conditions on attachment, viability and functional status of rainbow trout (Oncorhynchus mykiss) liver cells in primary culture. Cells were isolated by a two-step collagenase perfusion and incubated in serum-free, chemically defined minimal essential medium (MEM), (a) as a monolayer on uncoated PRIMARIA dishes, (b) as a monolayer on culture dishes coated with calf collagen type 1, and (c) in coculture with the established fish cell lines RTH-149 or RTG-2. Cell attachment was assessed from DNA and protein concentrations per dish, viability was estimated from cellular lactate dehydrogenase release, and the metabolic status was investigated by measuring activities of the phosphoenolpyruvate carboxykinase and biotransformation enzymes as well as the total cytochrome P450 contents. Seeding of hepatocytes on collagen-coated dishes did not alter cell attachment or detachment from the (culture substrate, but had a small, but not significant effect on cell viability and metabolic parameters. Coculture of liver cells and RTG-2 cells reduced hepatocyte detachment from the culture substrate, and it was associated with a significant elevation of 7-ethoxyresorufin-O-deethylase activities in the hepatic cells. Cytochrome P450 contents, however, were not altered. The coculture effect on liver cell physiology clearly depended on the type of cell line, because coculture with RTH-149 cells led to similar, but much weaker effects than obtained in cocultures with RTG-2 cells. Electron microscopical observations revealed the existence of gap junctions and possible exocytosis-like transport between cell lines and hepatocytes. The results point to the potential of coculture systems to improve physiological parameters of trout liver cells in primary culture.

Light and scanning electron microscopic cytopathology of 3, 5-dichlorophenol in the permanent fish cell line RTG-2

The permanent fibrocyte-like fish cell line RTG-2 from rainbow trout (Oncorhynchus mykiss) gonads was investigated by means of light and scanning electron microscopy with respect to alterations as a consequence of sublethal exposure to 0, 1, 10, 16, 25, and 50 mg/liter 3,5-dichlorophenol (3,5-DCP) for 24 h. Control RTG-2 cells were spindle-like in shape and almost three times longer than wide. In subconfluent cultures, they displayed widely spread, flat leading lamellae and formed small groups. Along the edges of the cell protrusions, numerous retraction fibrils could be identified. Except for shallow ridges and small folds, the surface of untreated cells was completely smooth. Following exposure to 3,5-DCP, distinct dose-dependent alterations in cell shape, the appearance of surface blebs and invaginations, as well as progressive retraction of cell extensions could be observed from the lowest test concentration. Morphological changes could be correlated to suppression of lactate dehydrogenase and reduced neutral red retention capacity.

Liver of the brown trout, Salmo trutta (Teleostei, Salmonidae): a stereological study at light and electron microscopic levels

BACKGROUND

A quantitative study was undertaken for the first time on the normal liver of male and female 2-year-old brown trout, Salmo trutta.

METHODS

Liver was fixed by controlled perfusion. Organ-level morphometry provided weight and volume. A two-stage stereological approach was performed at light and electron microscopy levels. Systematic sampling and point-counting morphometry were used for estimating the relative volumes of the structural compartments. Total absolute volumes of these components were obtained by multiplying each volume density by the volume of its reference space.

RESULTS

Liver volume was 3,423.6 mm3 for males and 3,657.4 mm3 for females. Parenchyma accounted for 95% of hepatic volume. Veins and bile ducts occupied, respectively, 76% and 17% of the stroma, whereas arteries, connective tissue, and melanomacrophages together composed only 6%. Hepatocytes occupied 88% of the parenchyma. Nonhepatocytic cells (endothelium, biliary epithelial cells, Ito cells, and macrophages) composed 4% of the parenchyma, the capillary lumen 6%, and other spaces (Disse space, canaliculi, and lumina of preductules and ductules) composed 2%. Significant sexual differences were found: (1) Females showed a greater parenchymal volume density (0.85% vs. 0.35%) and absolute volume (29.5 mm2 vs. 11.7 mm3) of Ito cells; (2) macrophages of females also presented a greater parenchymal volume density (0.94% vs. 0.46%), but not absolute volume.

CONCLUSIONS

The need to analyze both relative and absolute stereological data was stressed. Similarities and differences were detected between brown trout and other species (fishes and mammals); the findings suggest that, despite architectural differences, some quantitative parameters of liver microanatomy were retained during phylogeny. Factors mediating sexual differences in Ito cells and macrophages were discussed and the need for further studies was highlighted.