Discussion

Human induced pluripotent stem (hiPS) cell-derived hepatocytes have the potential to serve as predictive human in vitro model systems for drug discovery,drug metabolism research, and hepatotoxicity studies provided that they possess relevant hepatic function. Until recently, however, the functionality of hiPS cell-derived hepatocytes has been insufficient for applications that demand high expression of multiple drug metabolizing enzymes. We have recently developed a novel, robust differentiation system to generate hepatocytes from human induced pluripotent stem cells. These resulting hiPS cell-derived hepatocytes have substantial CYP1A, 2C9, 2C19, 2D6, and 3A4 enzyme activities and important adult hepatic features, such as low expression of fetal genes (e.g., CYP3A7 and alphafetoprotein)and high expression of adult genes (e.g., CYP2C9, 2C19, and 3A4).
In this study, we illustrate the system’s differentiation protocol that begins with culturing any hiPS cell line, continues with directed differentiation into definitive
endoderm (DE) cells, and ends with further differentiation into hepatocytes,thereby mimicking normal embryonic development. Morphological images and immunostaining data demonstrate the robustness and reproducibility of the system to generate hepatocytes from several different cell lines. Of 28 different hPSCs tested, all 28 lines were efficiently differentiated into hepatocytes that exhibit substantial CYP1A, 2C9, 2C19, 2D6, and 3A4 enzyme activity and important adult hepatic features, such as low expression of fetal genes and high expression of adult genes. More importantly, these hepatocytes generated from multiple hiPSC lines show diverse CYP activity profiles, indicative of the inter-individual variation present in the human population. hiPS cell-derived hepatocytes are potentially suitable for toxicity assays: they correctly identify known hepatotoxins and respond similarly to human primary hepatocytes when exposed to test compounds. The new Cellartis® iPS Cell to Hepatocyte Differentiation System can reliably generate
an almost inexhaustible source of human hepatocytes from different genetic backgrounds for use in in vitro drug discovery, drug metabolism research, and toxicology-related studies.