Down-regulation of CYP1A2, CYP2B6, and CYP3A4 in human hepatocytes by prolyl hydroxylase domain 2 inhibitors via hypoxia-inducible factor-α stabilization.

Hypoxia inducible factor (HIF) is associated with the expression of cytochrome P450 (CYP), but the underlying mechanism remains uncertain. In this study, we investigated the effect of HIF-α stabilization caused by novel prolyl hydroxylase domain (PHD) 2 inhibitors, which are HIF-α stabilizers that mimic hypoxia, on the expressions of CYP1A2, CYP2B6, and CYP3A4 in human hepatocytes. An mRNA expression analysis of human hepatocytes treated with PHD2 inhibitors for 72 h showed the down-regulation of genes encoding CYP1A2, CYP2B6, and CYP3A4. The mRNA repressions were accompanied with an increase in erythropoietin (EPO) protein, a marker of HIF-α stabilization, indicating that HIF-α stabilization was involved in the down-regulation of the CYP isoforms. To understand the underlying mechanisms, we assessed the relationship between the expressions of the CYP isoforms and those of their regulating transcription factors (aryl hydrocarbon receptor [AhR], AhR nuclear translocator [ARNT], constitutive androstane receptor [CAR], pregnane X receptor [PXR], and retinoid X receptor [RXR]) in human hepatocytes treated with the HIF-α stabilizers. As a result, the mRNA level of AhR did not decrease, though ARNT expression was repressed. On the other hand, the mRNA expression levels of CAR, PXR, and RXR were repressed and closely associated with those of CYP2B6 and CYP3A4. Although the underlying mechanism of the down-regulation for CYP1A2 remain unclear, the presently reported results suggest that the down-regulation of CYP2B6 and CYP3A4 via HIF-α stabilization is caused by a decrease in the expressions of CAR, PXR, and RXR. Significance Statement We showed that HIF-α stabilization down-regulates CYP1A2, CYP2B6, and CYP3A4 using PHD2 inhibitors, which are HIF-α stabilizers, as a new tool to mimic hypoxia in human hepatocytes. To understand the underlying mechanisms, we assessed the relationship between the expressions of the CYP isoforms and those of their regulating transcription factors. Our findings would contribute to a better understanding of the hypoxia-triggered regulatory mechanism of drug metabolizing enzymes in human hepatocytes.