Human hepatocytes have become the gold standard for predicting human CYP450 induction in vitro due to inter-species differences (2-6). When freshly isolated human hepatocytes are overlaid with an extracellular matrix component, such as Geltrex™ Reduced Growth Factor Basement Membrane Matrix or Collagen I, Rat Tail, the cells retain the ability to respond to prototypical CYP450 inducers, which reflects what would be observed in vivo in regards to enzyme specificity and potency of enzyme induction (7, 8). In addition, primary cultures of human hepatocytes have the distinct advantage of exhibiting species-specific induction of CYP450 isoforms.
Master regulators of CYP450 induction such as the aryl hydrocarbon receptor (AhR), and the nuclear receptors pregnane X receptor (PXR) and constitutive androstane receptor (CAR), have been recognized as key mediators of drug-induced changes in the expression of CYP1A, CYP3A, CYP2B and the CYP2C enzymes, as well as of phase II enzymes and transporters (2, 8, 9). Therefore, in vitro induction study designs using selective positive control inducers provide a useful tool to characterize both the induction of CYP450s and the potential receptor pathways that may be involved.
This in situ induction protocol outlines the recommended approaches for using cultures of primary human hepatocytes derived from cryopreserved preparations to assess the potential of test compounds to induce pharmacologically important pathways.
- Review this protocol, as well as the protocol, Thawing and Use of Plateable and Suspension Cryopreserved Hepatocytes, to ensure you have all the necessary reagents and equipment prior to starting the procedure. Once thawed, cryopreserved hepatocytes must be used immediately and will not maintain viability if refrozen.
- Induction studies typically assess each inducer, test compound and negative control in triplicate. We suggest using 24-well collagen-coated plates and mapping out your wells in advance for the proper amount of cryopreserved hepatocytes and reagents.
- Consult Tech Support (contact info below) if you are adapting this protocol for use with animal hepatocytes.
- Use universal safety precautions and appropriate biosafety cabinet when handing primary hepatocytes.
Critical materials and reagents
- Cryopreserved plateable hepatocytes prequalified for induction, such as Life Technologies Cat. No. HMCPIS or HMCPIL, enough for ~10 x 106 cells per plate.
- The reagents in the plating protocol, including Geltrex™ Reduced Growth Factor Basement Membrane Matrix, which is required for this assay.
- Williams’ Medium E, 500 mL, Life Technologies Cat. No. CM6000
- Hepatocyte Maintenance Supplement Pack (Serum-free), 1 kit, Life Technologies Cat. No. CM4000
- Hank’s Balanced Salt Solution (HBSS)
- Lysis Buffer for RNA isolations
- 50-mL conical tubes
- RNAse-free microcentrifuge tubes
- CYP substrates, such as phenacetin, bupropion and testosterone
Compound stocks: test articles (TA), vehicle control (e.g. DMSO) and positive controls (PC). Suitable positive controls may include:
- 3-methylcholanthrene (3-MC, a prototypical CYP1A enzyme inducer)
- phenobarbital (PB, a prototypical CYP2B inducer)
- rifampicin (RIF, a prototypical CYP3A enzyme inducer)
Note: Omeprazole may be used as a less selective inducer of CYP1A and CITCO may be used as a selective inducer of CYP2B6
- 37°C water bath
- 37°C / 5% CO2 humidified incubator
- Orbital shaker placed inside incubator
- Plates/deep-well blocks for in situ activity harvest
Prepare plated hepatocytes with a Geltrex™ matrix overlay following these protocols:
- Protocol for thawing and use of plateable and suspension cryopreserved hepatocyte
Protocol for counting primary hepatocytes using trypan blue exclusion analysis
- The induction protocol can be started 2 hr after overlay completion, or up to 24 hr later
- Prepare incubation medium by combining Hepatocyte Maintenance Supplement Pack (Serum-free) with Williams Medium E per kit instructions, and warm to 37°C in a water bath (usually 15–20 min).
Prepare working concentrations of the inducers as follows:
- 2 mM 3-methylcholanthrene (3-MC) in DMSO
- 200 mM phenobarbital (PB) in DH2O
10 mM rifampicin (RIF) in DMSO
- Prepare the test article (TA) in solvent, such as methanol or DMSO, in multiple concentrations to allow production of a dose-response curve if desired, but minimally 3 concentrations of test article should be assessed spanning the in vivo or predicted Cmax exposure levels, such as 0.1X, 1X, and 10X Cmax.
Prepare working concentrations of the probe substrates as follows:
- 100 mM phenacetin in DMSO
- 500 mM bupropion in methanol
- 200 mM testosterone in methanol
In separate conical tubes, dissolve specified amount of inducers into 20 mL, 37°C prepared Incubation Medium (final concentrations are bolded):
- 20 μL of 2 mM 3-methylcholanthrene (3-MC) 2 μM
- 100 μL of 200 mM phenobarbital (PB) 1000 μM
- 20 μL of 10 mM rifampicin (RIF) 10 μM
Add 20 µL DMSO to the 1,000 µM PB conical tube so that the percentage of DMSO is equivalent among the treatment groups
- Prepare a negative control by adding 20 µL DMSO into 20 mL warm incubation medium.
In separate conical tubes, dissolve the test articles in warm incubation medium to yield final inducing concentrations 1,000-fold lower than the respective working concentrations. For example, 20 µL of a 10 mM test article into 20 mL of incubation medium yields a final concentration of 10 µM.
Note: If test articles are dissolved in a solvent other than DMSO, a negative control with an equivalent organic percentage must be included in the study design for fair comparison.
Remove the hepatocyte plate(s) from the incubator and replace the medium in the appropriate wells with 0.5 mL of the negative control, inducers, or test article solutions, preferably each in triplicate.
Important: Because hepatocytes are susceptible to drying out, aspirate each treatment group separately and replace with the experimental medium before dosing the next set.
- Return plate(s) to the incubator for 24 hr.
After 24 hr, replace the medium with freshly prepared inducing solutions, repeating steps 5 through 8. Fresh solutions should be prepared daily and applied every 24 hr during the duration of the experiment, which is typically 48 - 72 hours prior to harvest.
Day of Harvest
- On the day of harvest, warm the incubation medium to 37°C, as usual.
- Remove the induction plate(s) from the incubator.
- Aspirate the dosing medium from each well, wash and replace with warm incubation medium. Take precautions to avoid the hepatocytes drying out, as previously mentioned.
- In separate conical tubes, dissolve 20 µL probe substrates in 20 mL warm incubation medium to yield final incubation concentrations 1,000-fold lower than working concentrations.
- Remove the wash medium from the hepatocytes and replace with 0.5 mL of the probe substrate solutions prepared in the previous step. Incubations should be conducted in triplicate with the respective CYP450 treatment group.
- Incubate on an orbital shaker in the incubator for the time specified in Table 1. A speed of 120–150 rpm is recommended for a 24-well plate.
- Stop the incubations at the appropriate time points by collecting and freezing the sample medium, or by removing the sample medium and replacing it with an organic stop solution. Samples can be stored at -70°C before analysis.
If collecting samples for mRNA analysis, see steps 25–27.
Table 1: Assay conditions for the determination of enzyme activities in plated cryopreserved human hepatocytes
Enzyme Prototypical inducer Substrate Concentration Incubation time Marker metabolite CYP1A2 3-methylcholanthrene phenacetin 100 µM 15 min acetaminophen CYP2B6 phenobarbital bupropion 500 µM 20 min hydroxybupropion CYP3A4/5 rifampicin testosterone 200 µM 14 min 6β-hydroxytestosterone
Catalytic Activity Determination
- Extract and analyze samples by method of choice, typically HPLC or LC-MS/MS by monitoring the formation of metabolite.
- CYP activity can be expressed as pmol/min/million cells where pmol is defined as the amount of metabolite formed during the reaction. The number of hepatocytes per well (N) is related to the seeding density as defined in Table 2.
If optional RNA isolations are not performed, cell plates can be sealed and frozen directly for subsequent analyses.
Note: if performing protein determinations to normalize data across wells, keep in mind that the protein is not solely from hepatocytes, due to the presence of detectable protein in the extracellular matrix used to overlay the hepatocyte monolayers.
The fold-induction enzyme activity is determined by the ratio:
CYP activity(induced) / CYP activity(vehicle)
The percent adjusted positive control is determined by:
([CYP activity(induced) -- CYP activity(vehicle)] / [CYP activity(positive control) -- CYP activity(vehicle]) x 100
- If mRNA analyses are desired; upon removal of the probe substrates, wash hepatocytes twice with Hank’s Balanced Salt Solution (HBSS).
- Remove the HBSS from the wells and replace with an appropriate volume of lysis buffer. For most commercial methodologies, this is 300 µL per well for a 24-well plate.
- Collect the cell lysates in RNAse-free microcentrifuge tubes, or seal and freeze the entire plate at -70°C for subsequent isolations within 4 weeks.
Table 2: Parameters for human hepatocytes used in catalytic rate calculations. The assumption for N is that all hepatocytes adhered to the well with respect to seeding density.
Hepatocytes per well,
N (106 cells)
Sample Collection for mRNA Analysis
For questions related to this protocol, contact us at:
Phone: +1 919 237 4500 (Toll)
Phone: +1 866 952 3559 (U.S. Toll-free)
- US FDA (2006) Draft Guidance for Industry: Drug Interaction Studies—Study Design, Data Analysis, and Implications for Dosing and Labeling. US Food and Drug Administration Publication.
- Xu L, Li AP, Kaminski DL, Ruh MF (2000) 2,3,7,8 Tetrachlorodibenzo-p-dioxin induction of cytochrome P4501A in cultured rat and human hepatocytes. Chem Biol Interact 124:173–189.
- LeCluyse E (2001) Pregnane X receptor: Molecular basis for species differences in CYP3A induction by xenobiotics. Chem Biol Interact 134:283–289.
- LeCluyse EL, Alexandre E, Hamilton GA, Viollon-Abadie C et al. (2004) Isolation and culture of primary human hepatocytes. Methods Mol Bio 290:207–230.
- LeCluyse EL, Madan A, Hamilton G et al. (2000) Expression and regulation of cytochrome P450 enzymes in primary cultures of human hepatocytes. J Biochem Mol Toxicol 14:177–188.
- Madan A, Graham RA, Carroll KM et al. (2003) Effects of prototypical microsomal enzyme inducers on cytochrome P450 expression in cultured human hepatocytes. Drug Metab Dispos 31:421–431.
- Hamilton GA, Jolley SL, Gilbert D, et al. (2001) Regulation of cell morphology and cytochrome P450 expression in human hepatocytes by extracellular matrix and cell-cell interactions. Cell Tissue Res 306:85–99.
- LeCluyse EL (2001) Human hepatocyte culture systems for the in vitro evaluation of cytochrome P450 expression and regulation. Eur J Pharm Sci 13:343–368.
- Wang H, LeCluyse E (2003) Role of orphan nuclear receptors in the regulation of drug metabolizing enzymes. Clin Pharmacokinet 42:1331–1357.
- Bjornsson TD, Callaghan JT, Einolf HJ et al. (2003) Perspective: the conduct of in vitro and in vivo drug-drug interaction studies: a Pharmaceutical Research and Manufacturers of America (PhRMA) perspective. Drug Metab Dispos 31:815–832.