Expression of drug metabolizing enzymes in hepatocyte-like cells derived from human embryonic stem cells.

Human embryonic stem cells (hESC) offer a potential unlimited source for functional human hepatocytes, since they can differentiate into hepatocyte-like cells displaying a characteristic hepatic morphology and expressing several hepatic markers. Such cells could be used for, e.g. studies of drug metabolism and hepatotoxicity, which however would require a significant expression of drug metabolising enzymes. Thus, we have investigated the expression of cytochrome P450s (CYPs), UDP-glucuronosyltransferases (UGTs), drug transporters, transcription factors and other liver specific genes in hepatocyte-like cells derived from hESC using a simple direct differentiation protocol. The mRNA and protein expression of several important CYPs were determined using low density arrays, real time PCR and Western blotting. Significant CYP expression on the mRNA level was detected in hepatocyte-like cells derived from one out of two different hESC lines tested, which was much higher than in undifferentiated hESC and generally higher than in HepG2 cells. CYP1A2, CYP3A4/7 and low levels of CYP1A1 and CYP2C8/9/19 protein were detected in both lines. The mRNAs for a variety of CYPs and liver specific factors were shown to be inducible in both cell lines, and this was reflected in induced levels of CYP1A2 and CYP3A4/7 protein. This first report on expression of all major CYPs in hepatocyte-like cells derived from hESC represents an important step towards functional hepatocytes, but efforts to further differentiate the cells using optimized protocols are needed before they exhibit similar levels of drug metabolizing enzymes as primary human hepatocytes and liver.