Extending the Concept of Predicting Fish Acute Toxicity In Vitro to the Intestinal Cell Line RTgutGC

Testing chemicals for fish acute toxicity is a legal requirement in many countries as part of environmental risk assessment. To reduce the number of fish used, substantial efforts have been focused on alternative approaches. Prominently, the cell viability assay with the rainbow trout (Oncorhynchus mykiss) gill cell line, RTgill-W1, has proven to be highly predictive and robust. Like the gills, the intestine is considered a major site of chemical uptake and biotransformation, but, in contrast to the gills, it is expected to be exposed to more hydrophobic chemicals, which enter the fish via food. In the present study, we therefore aimed to extend the cell bioassay to the rainbow trout epithelial cell line from intestine, RTgutGC. Using 16 hydrophobic and volatile chemicals from the fragrance palette, we show that also the RTgutGC cell line can be used to predict fish acute toxicity of chemicals and yields intra-laboratory variability in line with other bioassays. By comparing the RTgutGC toxicity to a study employing the RTgill-W1 assay on the same group of chemicals, a fragrance-specific relationship was established that reflects an almost perfect 1:1 relationship between in vitro and in vivo toxicity results. Thus, both cell lines can be used to predict fish acute toxicity, either by extrapolating based on the in vivo-in vitro relationship or by taking the in vitro results at face value. We moreover demonstrate the derivation of non-toxic concentrations for downstream applications that rely on a healthy cell state, such as the assessment of biotransformation or chemical transfer.