Frequently Asked Questions
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Contract Services
Can cryopreserved hepatocytes be used for metabolism and induction studies?
This table provides a quick reference for the potential use of cryopreserved hepatocytes from different species.
Species |
Recommended Application |
Metabolism Studies
(short-term incubations) |
Induction Studies
(long-term incubations) |
Human |
Yes |
Sometimes * |
Monkey |
Yes |
Not recommended * |
Dog |
Yes |
Not recommended * |
Rat |
Yes |
Yes |
* Most cryopreserved human, monkey and dog hepatocytes do not attach in culture; therefore, they may not be suitable for enzyme induction studies. Please
contact us for availability of inducible human hepatocytes.
What are prototypical inducers?
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.
Enzyme |
Prototypical Inducer (concentration) § |
Marker Substrate (concentration) § |
Optimized Incubation Time §§ |
CYP1A2 |
Omeprazole (100 µM) |
Phenacetin (80 µM) |
30 minutes |
CYP3A4 |
Rifampin (10 µM) |
Testosterone (250 µM) |
10 minutes |
§ Concentration refers to the final concentration in the incubation.
§§ Optimized incubation times are based on experiments performed at XenoTech to ensure that metabolite formation is measured while it is proportional with reaction time and when the fold induction is maximized (under the specified conditions).
What contract services are available through XenoTech?
We routinely perform the following types of contract services:
- Enzyme Inhibition
- Enzyme Induction (in vitro and ex vivo)
- Reaction Phenotyping (enzyme mapping)
- Metabolite Identification and/or characterization
- Drug Transporter studies
- Species Comparison
- Drug metabolism studies in hepatic and extrahepatic subcellular fractions
- Drug metabolism studies in hepatocytes
- Custom services involving other drug-metabolizing enzymes (e.g., UDP-glucuronosyltransferase)
- Covalent binding
- Hepatotoxicity
- Consultation services and courses in drug metabolism
What types of enzyme induction studies does XenoTech perform?
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.
Ex vivo
in vitro analysis of microsomal enzyme levels in livers from laboratory animals treated with the drug candidate
in vivo. Such studies are often incorporated as a part of a 14-day toxicity study.
Enzyme induction in laboratory animals may explain such findings as pharmacokinetic tolerance, liver enlargement and possibly liver and thyroid tumor formation.
Both types of induction study involve measuring changes in the expression of certain CYP and other drug-metabolizing enzymes based on changes in enzyme activity, enzyme levels (immunoreactive protein levels) and/or mRNA levels.