Optimization of a precision-cut trout liver tissue slice assay as a screen for vitellogenin induction: comparison of slice incubation techniques.

An in vitro male rainbow trout liver slice assay has been developed for long-term incubation of precision-cut slices for the detection of vitellogenin (VTG) protein induction in response to xenobiotic chemicals. The assay was optimized to allow 72 h of incubation of slices to maximize detection of VTG, while maintaining slice viability. Two methods of incubation frequently used with rat liver slices were compared: (1) slices were submerged in media (11 degrees C) and cultured in 12-well plates (PL) with continuous shaking; or (2) slices were floated onto titanium screens, placed into glass vials, and held under dynamic organ culture (DOC) conditions (11 degrees C). Slices (200 µm) in modified L-15 media were exposed to 1.0 µM 17beta-estradiol (E2) or diethylstilbestrol (DES). Protein from media and slice was sampled for Western blot analysis, using a polyclonal antibody to detect appearance of VTG protein. Maximum VTG was seen at 72 h, with detectable protein at 24 and 48 h in slices and media following PL incubation. In contrast, slices incubated in DOC showed little detectable VTG above background levels after 72 h. This difference was not attributable to protein loss to vial or plate surfaces. Standard viability assays did not reveal any differences between slices incubated in PL or DOC. However, histopathological examination revealed earlier and more severe vacuolization in slices incubated in DOC. Significantly more E2 uptake and conversion to water-soluble metabolites was noted in PL, compared with DOC, as well as more production of VTG in response to DES and E2, correlated with less histologic change. The in vitro assay described allows tissue-level assessment of estrogenicity in aquatic organisms, and will be useful for assessing not only comparative species receptor binding and transactivation, but also the role of tissue-specific activation factors in the estrogenic response of fish.