Measurement of Cytochrome P450 Enzyme Induction and Inhibition in Human Hepatoma Cells

Cytochrome P450 enzymes are a diverse group of catalytic enzymes in
the liver that are mainly responsible for the biotransformation of organic
substances. Cytochrome P450 activity as well as both its induction
and inhibition are key factors in drug biotransformation and can be
involved in deactivation, activation, detoxification, and toxification
processes. Thus, the modulation of cytochrome P450 activity is an
important parameter when evaluating the potential toxicity of chemical
compounds using an in vitro system. The cytochrome P450 3A subfamily
proteins are among the most important drug-metabolizing enzymes in
human liver and are responsible for about half of all cytochrome P450-
dependent drug oxidations. In vitro, these enzymes are active not only
in primary human hepatocyte cultures, but also in differentiated human
hepatoma HepaRG cells. The present protocol describes the culture of
cryopreserved differentiated HepaRG cells and the evaluation of its
cytochrome P450 activity upon exposure to a chemical compound using
a commercially available luminogenic cytochrome P450 assay. This in
vitro model can be used to monitor the induction and inhibition of
cytochrome P450 3A following exposure to a particular test compound.