Whole-animal models are still the gold standard for toxicity predictions and are required by regulatory agencies, yet for many biological pathways and mechanisms they do not provide a good extrapolation to humans.
In vitro surrogate assays provide more representative methods to rule out adverse effects early in the screening process. Presentations at the recent “ETS-2012: 10th International Conference on Early Toxicity Screening” focused on emerging trends.
Dedifferentiated HepG2 cells, originally derived from the liver, do not have liver-like transporter function or metabolism. However, this cell line offers a cheap methodology to answer qualitative questions, and to quantitatively compare the potency and efficacy of a broad spectrum of chemicals early in the process.
Life Technologies’ cryopreserved HepaRG™ cells are a new alternative. Terminally differentiated hepatic cells derived from a single human donor, liver progenitor cell line, HepaRG cells model an analogous biology that appears to be comparable to primary human hepatocytes.
These cells retain many primary human hepatocyte characteristics, such as morphology and expression of key metabolic enzymes, drug transporters, nuclear receptors including support of the CAR pathway, in addition to primary hepatocyte-like P450 activities.
“We believe this is the first hepatic cell line that supports ‘mature’ hepatic phenotypes analogous to cultured primary human hepatocytes, a clear step above HepG2 cells and other reported hepatic cell lines,” explained Stephen Ferguson, Ph.D., associate director R&D, Life Technologies.
“It may be possible to further improve predictivity with various in vitro hepatic models by incorporation of human primary Kupffer cells to model diseased/inflamed liver phenotypes in vitro. This model may be more reflective of a patient sub-population that has compromised liver function with diminished ability to metabolize and clear drugs.”
Early-stage research studies performed on primary hepatocytes and primary hepatocyte/Kupffer cell co-cultures suggest that Kupffer cells modulate metabolic activity, leading to altered toxicity profiling.
Also phagocytic, Kupffer cells potentially could be used as therapeutic targets, as well as to study cytokine signaling, chemical effects, and the interactions between these cells and hepatocytes.
“A comprehensive predictive in vitro hepatic model system does not exist right now. However, we can validate models that answer specific questions. As the use of in vitro hepatotoxicity screening increases, consensus will grow around the model systems,” concluded Dr. Ferguson.