Abstract :
A previously described neutral red uptake inhibition assay on cultured fathead minnow (FHM) fish cells revealed a good correlation with fish toxicity data (Brandao et al., 1992) for a series of 50 test compounds, belonging to completely different chemical classes. The major drawback was the lower sensitivity of the cytotoxicity assay. Aiming at a higher sensitivity the assay was adapted by reducing the cell number, by a longer treatment period, and by simultaneous treatment with sodium dodecyl sulfate and buthionine sulfoximine (BSO). The fluorimetrically measured protein content was chosen as the endpoint. The endogenous glutathione (GSH) content was reduced by 54% of the test chemicals, confirming the importance of GSH in detoxification processes. Higher sensitivity was, at least partly, obtained by treating the FHM cells with BSO, reducing the GSH content to 22% of that in control cells. The cytotoxicity of the 50 chemicals was measured using the modified more sensitive assay. Although some exceptions were observed, this new assay is at least one order of magnitude more sensitive. Toxicity values comparable with fish toxicity data were obtained, making the assay sensitive enough to measure the toxicity of environmental water samples.
