This table provides a quick reference for the potential use of cryopreserved hepatocytes from different species.

The table below summarizes our recommended conditions to measure CYP1A2 and CYP3A4 in microsomes prepared from cultured human hepatocytes. Other prototypical inducers are referenced in "Effects of prototypical microsomal enzyme inducers on cytochrome P450 expression in cultured human hepatocytes" Madan et al, Drug Metab Dispos, 31: 421-431, 2003.

Although enzyme induction can be assessed by adding marker substrates directly to cultured hepatocytes (in situ assay), there are several advantages to preparing microsomes from the cultured hepatocytes:

• The test article is washed out of the sample before analysis (the test article is more likely to cause interference when CYP activity is measured in the hepatocytes (in situ).

• CYP activities in microsomes prepared from cultured hepatocytes can be compared with CYP activities in microsomes prepared directly from liver to ensure the cultured hepatocytes were well differentiated.

• Microsomes from cultured hepatocytes can be stored, which allows additional assays to be performed at a later date.

• Microsomes can be used to measure CYP induction by western immunoblotting.

XenoTech performs both in vitro and ex vivo induction studies.  In vitro studies are conducted with cultured human hepatocytes (fresh, cryopreserved and immortalized), although they are occasionally performed with monkey, dog and rat hepatocytes depending on the client’s needs.  A study with cultured human hepatocytes is the in vitro method of choice to assess whether a drug candidate will cause clinically significant enzyme induction in the clinic.  Such studies are recommended by the FDA.