Acetaminophen toxicity in cultured trout liver cells. II. Maintenance of cytochrome P450 1A1

In vitro estrogenicity of polybrominated flame retardants

Estrogenicity of five brominated flame retardants (BFRs), namely BDE-47, BDE-99, BDE-205, PBB-153 and technical Firemaster BP-6, were assessed by in vitro assays developed to detect chemicals with estrogenic properties. Recombinant yeast cells containing a human estrogen receptor gene failed to give any response to the chemicals tested. However, the positive control compound, estradiol-17beta, showed that the yeast cell assays had worked properly. The freshly separated fish hepatocyte assay based on the synthesis and secretion of vitellogenin from the isolated liver cells produced a clear dose-response curve in the presence of all tested flame retardants except Firemaster BP-6. The toxicity of the BFRs was detected by determining the cell ethoxyresorufin-O-deethylase activity (EROD). The BFRs tested induced hepatic EROD activity at low test concentrations, but started to inhibit activity at higher concentrations. The decreased detoxification capacity of the hepatocytes resulted in a decrease in the vitellogenin production of the cells. The capability of in vitro assays to detect estrogenic properties of chemicals seems to vary. Thus, further work is needed to understand the mechanisms responsible for these reactions.

Metabolic activity in primary cultures of fish hepatocytes

In aquatic toxicology, isolated liver cells from fish can be used as a tool to generate initial information on the hepatic metabolism of xenobiotics, and on the mechanisms of xenobiotic activation or deactivation. This isolation of teleost liver cells is achieved by enzymic dissociation, and monolayer cultures of fish hepatocytes in serum-free medium maintain good viability for 3-8 days. During in vitro culture, fish liver cells express stable levels of phase I and phase II enzymes, such as cytochrome P4501A or glutathione S-transferase, and the cells show an induction of biotransformation enzymes after exposure to xenobiotics. The xenobiotic metabolite pattern produced by fish hepatocytes in vitro is generally similar to that observed in vivo. Limitations to more-intensive application of cultured fish hepatocytes as a screen in aquatic hazard assessment are partly due to the rather limited scope of existing studies, i.e. the focus on one particular species (rainbow trout), and on one particular biotransformation enzyme (cytochrome P4501A), as well as a lack of comparative in vitro/in vivo studies.

Induction of CYP1A in primary cultures of rainbow trout (Oncorhynchus mykiss) liver cells: concentration-response relationships of four model substances

The study aims to evaluate short-term teleost hepatocyte cultures to establish dose-response curves for CYP1A induction and to rank the relative potencies of xenobiotics. Hepatocytes isolated from rainbow trout (Oncorhynchus mykiss) were incubated in vitro in coculture with RTG-2 cells in serum-free, chemically defined medium. Concentration-dependent induction of cytochrome P4501A was observed after treatment of the hepatocytes for 48 h with one of the four polyaromatic hydrocarbons: 3-methylcholanthrene, benzo[a]pyrene, benz[a]anthracene, and beta-naphthoflavone. The induction response was assessed by measuring 7-ethoxyresorufin-O-deethylase (EROD) and 7-ethoxycoumarin-O-deethylase (ECOD). From the data, EC50 and maximal induction response values were calculated. The rank order of EC50 values differed among the four model compounds, depending on the endpoint parameter. EC50 values for EROD and ECOD also differed in comparison to published affinity data for mammalian arylhydrocarbon receptor. The results of this study indicate the potential of primary teleostean hepatocyte cultures for studies on induction potency and regulation of piscine cytochrome P4501A. A drawback, however, appears to be the pronounced interindividual variation of the quantitative response of the cells.

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.

Dioxinlike properties of a trichloroethylene combustion-generated aerosol

Conventional chemical analyses of incineration by-products identify compounds of known toxicity but often fail to indicate the presence of other chemicals that may pose health risks. In a previous report, extracts from soot aerosols formed during incomplete combustion of trichloroethylene (TCE) and pyrolysis of plastics exhibited a dioxinlike response when subjected to a keratinocyte assay. To verify this dioxinlike effect, the complete extract, its polar and nonpolar fractions, some containing primarily halogenated aromatic hydrocarbons, were evaluated for toxicity using an embryo assay, for antiestrogenicity using primary liver cell cultures, and for the ability to transform the aryl hydrocarbon receptor into its DNA binding form using liver cytosol in a gel retardation assay. Each of these assays detect dioxinlike effects. Medaka (Oryzias latipes) embryos and primary liver cell cultures of rainbow trout (Oncorhynchus mykiss) were exposed to concentrations of extract ranging from 0.05 to 45 micrograms/l. Cardiotoxicity with pericardial, yolk sac, and adjacent peritoneal edema occurred after exposure of embryos to concentrations of 7 micrograms/l or greater. These same exposure levels were associated with abnormal embryo development and, at the higher concentrations, death. Some of the fractions were toxic but none was as toxic as the whole extract. In liver cells, total cellular protein and cellular lactate dehydrogenase activity were not altered by in vitro exposure to whole extract (0.05-25 micrograms/l). However, induction of cytochrome P4501A1 protein and ethoxyresorufin O-deethylase activity occurred. In the presence of whole extract, estradiol-dependent vitellogenin synthesis was reduced. Of the fractions, only fraction 1 (nonpolar) showed a similar trend, although vitellogenin synthesis inhibition was not significant. The soot extract and fractions bound to the Ah receptor and showed a significantly positive result in the gel retardation/DNA binding test. Chemical analyses using GC-MS with detection limits for 2,3,7,8-tetrachlorodibenzo-p-dioxin and dibenzofuran in the picomole range did not show presence of these compounds. Our results indicate that other chemicals associated with TCE combustion and not originally targeted for analysis may also pose health risks through dioxinlike mechanisms.

Long-term primary culture of epithelial cells from rainbow trout Oncorhynchus mykiss) liver

Long-term primary cultures of epithelial cells from rainbow trout (Oncorhynchus mykiss) liver have been established. Nearly homogenous (> 97%) populations of hepatocytes were placed into primary culture and remained viable and proliferative for at least 70 d. In addition to hepatocytes, proliferative biliary cells persisted in the cultures for at least 30 d. Finally, a third type of epithelial cell, which we have termed a "spindle cell," consistently appeared and proliferated to confluence in these cultures. The confluent cultures of spindle cells were successfully subcultured and passaged. The initial behavior, growth, and optimization of serum and media requirements for these cells is described. All three cell types proliferated as measured by thymidine incorporation, autoradiography, proliferating cellular nuclear antigen analysis, and propidium iodine staining. Further efforts to characterize the cells included western blotting and immunohistochemical staining with antibodies to cytokeratins previously reported in fish liver. From these data, it appears that all three cell populations are epithelial in nature. Furthermore, significant changes in actin organization, often indicative of transformation or pluripotent cells, were observed with increased time in primary culture.