Cryopreserved carp and trout hepatocytes for in vitro biotransformation assays

An international group of researchers from Canada, Switzerland and Germany lead by Fraunhofer IMB in Schmallenberg compared biotransformation rates from rainbow-trout (Oncorhynchus mykiss), a cold-water fish species, and common-carp (Cyprio carpio), a warm water fish species frequently used for bioconcentration-factor (BCF) testing in Asian countries. As model test compounds served benzo[a]pyrene (BaP) and methoxychlor (MXC). According to OECD test guideline 319A, hepatocytes were isolated and cryopreserved from fish that were maintained under controlled housing conditions. 

The results of this study suggest that the standard protocols for the substrate depletion assay and the cryopreservation techniques as established for trout hepatocytes (OECD319A) can be transferred to carp hepatocytes without the need for substantial modifications. First, depletion rates were comparable between fresh isolated and cryopreserved hepatocytes for both species. Next, the experimentally determined BCF values between both species were significantly different: For MXC, the rainbow trout showed much higher BCF values than common carp, whereas in the case of BAP trout displayed significantly lower BCF values than carp. 

The in vitro data were used to predict in vivo biotransformation constants and BCFs. Predicted biotransformation constants and BCFs were then compared to biotransformation constants and BCFs measured in vivo. Predicted BCF values were significantly higher in trout than in carp. However, the measured BCF values were not significantly different between both species. 

This suggests, that species-specific extrapolation models may have to be developed for reliable #in-vitro-in-vivo predictions. 

Further reading: Bischof I, Arnot JA, Jürling H, Knipschild G, Schlechtriem C, Schauerte A and Segner H (2022), In vitro biotransformation assays using fish liver cells: Comparing rainbow trout and carp hepatocytes. Front. Toxicol. 4:1021880. DOI 10.3389/ftox.2022.1021880