| Research Abstract |
Human fetal liver (HFL) cell culture was initiated from a pool of six normal human liver tissues. The proliferation and viability of HFL cells were evaluated using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide assay, and the cells increased by more than 100-fold by culture for 15 days. The levels of expression of albumin (ALB), hepatocyte growth factor 4 α, hepatocyte growth factor, CYP3A4, CYP3A5, and CYP3A7 mRNAs in HFL cells increased with culture period, while that of α-fetoprotein (AFP) mRNA decreased gradually. In HepG2 cells, however, the expression levels of ALB and AFP mRNAs were not changed, and the levels of expression of CYP3A4, CYP3A5, and CYP3A7 mRNAs decreased gradually. The mRNA expression of major CYP isoforms including CYP3As, i.e., CYP1A2, CYP2A6, CYP2B6, CYP2C (2C9 and 2C19), CYP2D6, and CYP2E1, could be detected in HepG2 cells. With the exception of CYP1A2, all of the CYP mRNAs expressed in HepG2 cells were detected in HFL cells. In HFL cells, CYP3A
… More
4 and CYP3A7 mRNA expression levels were markedly up-regulated by dexamethasone (DEX), but not by rifampicin (RIF). CYP3A5 mRNA level was not increased significantly by DEX, RIF, or phenobarbital (PB). On the other hand, CYP3A4, CYP3A5, and CYP3A7 mRNA expression levels in HepG2 cells were increased from 2- to 3-fold by treatment with DEX, PB, and RIF. Pregnane X receptor mRNA was expressed in HepG2 cells, but not HFL cells. Testosterone 6β -hydroxylase activity was induced to about 2-fold of control by DEX. However, concomitant treatment with RIF did not alter DEX-mediated induction of CYP3A mRNA expression and testosterone 6β-hydroxylase activity. DEX-mediated induction of CYP3A mRNA was suppressed in a dose-dependent manner by RU486, a glucocorticoid receptor (GR) antagonist. At 5 μM RU486, DEX-mediated induction of CYP3A4, CYP3A5, and CYP3A7 mRNA expression was inhibited almost completely. These results suggest that, in human fetal hepatocytes, PXR is not involved in DEX-mediated induction of CYP3A4 and CYP3A7, and that the induction is mediated directly by GR. Less
|
