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.
Michael Gülden and Hasso Seibert
The use of fish cell line cytotoxicity tests as alternatives to acute lethality tests with fish is hampered by the clearly lower sensitivity of the fish cell line tests. Recently, it has been shown that this is not a unique feature of fish cells. In fact, the sensitivity of mammalian and human cell lines toward the cytotoxic actions of chemicals, in general, is comparable to that of fish cell lines. Reviewing some of our recent investigations, the objective of this paper is to show that the sensitivity of in vitro cytotoxicity testing and the correspondence between in vitro cytotoxic and acute fish toxic concentrations (LC50) can be increased, if: a) inhibition of cell growth instead of cell death is used as the endpoint; and b) the bioavailable free cytotoxic concentration (ECu50) of chemicals in vitro, instead of the nominal cytotoxic concentration (EC50), is used as the measure of cytotoxic potency. Based on these results, a pragmatic in vitro testing strategy for estimating the minimal aquatic toxic potency of chemicals is proposed.