CYP3A4 inducible model for in vitro analysis of human drug metabolism using a bioartificial liver

CYP3A is responsible for approximately 50% of the therapeutic drug-metabolizing activity in the liver. The present study was undertaken to establish the CYP3A4 inducible model for analysis of human drug metabolism using a bioartificial liver composed of the functional hepatocellular carcinoma cell (HCC) fine FLC-5. A radial-flow bioreactor (RFB), which is a carrier-filled type bioreactor, was used for 3-dimensional perfusion culture of FLC-5 cells. The CYP3A4 messenger RNA (mRNA) expression level 48 hours after rifampicin treatment in the RBF was approximately 100 times higher than that in a monolayer culture. Western blot analysis also demonstrated an increase in expression of the CYP3A protein. When testosterone, a substrate for CYP3A4, was added to the rifampicin-treated cell culture, 6beta-hydroxy testosterone as a metabolite was formed. Electrophoretic mobility shift assay (EMSA) with a CYP3A4 ER6 probe demonstrated that relatively high molecular weight complex containing pregnane X receptor (PXR)/retinoid X receptoralpha(RXRalpha), compared with that in the monolayer culture, is possibly generated in the RFB culture of FLC-5 treated with rifampicin. Similarly, the assay with a probe of HNF-4alpha-binding motif indicated the formation of a large protein complex in the RFB culture. Because it is known that PXR transactivates CYP3A4 gene via its response element and expression of PXR is regulated by HNF-4alpha, the large complexes binding to response elements of PXR or HNF-4a in the RFB culture may contribute to up-regulation of CYP3A4 mRNA. In conclusion, the bioartificial liver composed of human functional HCC cell line was useful in studying drug interactions during induction of human CYP3A4.