Searching for refiNed in vitro Approaches to Predict bioconcentration in FISH – SNAPFISH
01.09.2019 - 31.03.2022
Dr. Kilian Smith (now Hochschule Magdeburg-Stendal)
Description of the Project:
Chemical regulations require information as to whether a chemical is bioaccumulative. Steady-state bioconcentration factors (BCFs) in fish reflect the net result of the various chemical uptake versus loss processes, and can be determined directly (e.g., using OECD TG 305 for water-only exposure). However, this requires large numbers of animals and is also costly and labour-intensive. In the context of the Replace, Reduce and Refine targets (3Rs) for the use of animals in scientific research, alternative approaches to derive BCFs based on in vitro and/or in silico approaches are thus required.
One approach is the application of assays based on hepatocytes (HEP) or liver S9 fractions (S9) isolated from fish. The metabolic rates are then applied to estimate whole fish biotransformation losses as input to mass balance models describing fish bioaccumulation to predict steady-state BCFs (Nichols et al., 2013). This in vitro – in vivo extrapolation (IVIVE) has to account for the different amounts of metabolically active components (hepatocytes, microsomal protein or S9 material) in vitro and in vivo, along with differences in sorption in both cases. The equation that is commonly used in the context of BCF estimation originates from Obach (1996), and has first been used by Nichols et al. (2006). The applied BCF estimation scheme uses information on the actual hepatic metabolism kinetics in an organism as well as information about up-take kinetics and on other elimination kinetics such as excretion via the gills, urine or faeces.
However, the equation still requires further refinement to address existing experimental and IVIVE uncertainties and to provide more reliable BCF estimates especially for hydrophobic organic compounds (HOC), and avoid these BCF estimates to incorrectly exceed the associated regulatory thresholds.
This project has three main focus areas:
1) Further improve the reliability of measured HEP and S9 in vitro metabolic rates for HOC.
2) Determine how enzymatic turnover is impacted by differences in chemical availability between the media used in in vitro assays and liver blood.
3) Incorporate the above experimental information to improve existing IVIVE and other BCF prediction models.
Activities in 2019/2020:
The project has started in 09.2019 and the experimental work has started with the implementation of first liver S9 assays and the adaptation to passive dosing and passive sampling techniques.
The project was funded by the European Chemical Industry Council (CEFIC) within the long-research initiative (LRI) program.