LPS-induced Down-regulation Of Nuclear Receptor Pregnane X Receptor And Its Target Gene CYP3A Ing Mouse Liver

The cytochrome P450 3A (CYP3A) is a member of the cytochrome P-450 monooxygenase superfamily, which is responsible for the oxidative metabolism of numerous clinically used drugs. Pregnane X receptor (PXR), a member of the nuclear receptor superfamily, regulates CYP3A gene transcription in a ligand-dependent manner. In present study, we investigated the in vivo effects of lipopolysaccharide (LPS) on PXR and CYP3A expressions in mouse liver. We also explored the role of Kupffer cells and reactive oxygen species (ROS) in LPS-induced down-regulation of PXR and its target gene CYP3A in mouse liver.1. LPS down-regulates nuclear receptor Pregnane X receptor and its target gene CYP3A in mouse liverThe in vivo effects of LPS on PXR and its target gene CYP3A expressions in mouse liver were investigated in this study. Mice were injected intraperitoneally with different doses of LPS (0.1-5.0 mg/kg). PXR and CYP3A11 mRNA levels were measured using RT-PCR. Results indicated that LPS significantly inhibited the expressions of PXR mRNA in a dose-dependent manner, followed by suppression of CYP3A11 mRNA in mouse liver. LPS also repressed the up-regulation of CYP3A11 mRNA levels and erythromycin TV-demethylase (ERND) catalytic activities in mice pre-treated with PXR ligand dexamethasone (DEX), rifampicin (RIF), mifepristone (RU486) and Phenobarbital (PB). These results indicated that LPS down-regulatednuclear receptor pregnane X receptor and its target gene CYP3A in mouse liver.2. Kupffer cells partially mediate LPS-induced down-regulation of PXR and its target gene CYP3A in mouse liverTo investigate whether Kupffer cells mediate LPS-induced down-regulation of PXR and CYP3A in mouse liver, mice were treated with GdCl3, a selective Kupffer cell toxicant, to inactivate Kupffer cells. Mice were then injected intraperitoneally with 1.0 mg/kg LPS. PXR and CYP3A11 mRNA levels were measured using RT-PCR. ERND was used as an indicator of CYP3A catalytic activity. Results showed that LPS-induced down-regulation of PXR and CYP3A11 mRNA in liver was significantly attenuated in mice pretreated with GdCl3. A single dose of GdCl3 (10 mg/kg) pretreatment also significantly attenuated LPS-induced down-regulation on DEX, RIF, RU486 and PB-inducible CYP3A11 mRNA expressions and ERND activities in mouse liver. These results indicated that Kupffer cells contribute to LPS-induced down-regulation of PXR and CYP3A in mouse liver.3. The role of ROS and NO in LPS-induced down-regulation of nuclear receptor pregnane X receptor and its target gene CYP3A in mouse liverIn the present study, we investigated the in vivo role of reactive oxygen species ( ROS ) and nitric oxide (NO ) in LPS-induced down-regulation on CYP3A expressions. Mice were treated with allopurinol, an inhibitor of xanthine oxidase, to inhibite xanthine oxidase in mice. LPS-induced down-regulation of PXR and CYP3A11 mRNA in liver was significantly attenuated in mice pretreated with allopurinol. Allopurinol pretreatment also significantly attenuated LPS-induced down-regulation on DEX, RIF, RU486 and PB-inducible CYP3A11 mRNA expressions and ERND activities in mouse liver. Furthermore, LPS-induced down-regulation of PXR and CYP3A11 mRNA was significantly attenuated in mice pretreated withdiphenyleneiodonium chloride (DPI), an inhibitor of NADPH oxidase. DPI pretreatments also attenuated the repressive effects of LPS on DEX, RIF, RU486 and PB-inducible CYP3A11 mRNA expressions and ERND catalytic activities in mouse liver. However, aminoguanidine, a selective inhibitor of inducible nitric oxide synthase (iNOS), has no effect on LPS-induced down-regulation of PXR and CYP3A11 mRNA. Finally, LPS-induced down-regulation of PXR and CYP3A11 mRNA was prevented in mice pretreated with either N-acetylcysteine (NAC) or ascorbic acid. These antioxidants also prevented the repressive effects of LPS on DEX, RIF, RU486 and PB-inducible CYP3A11 mRNA expressions and ERND catalytic activities in mouse liver. These results indicated that ROS, possibly produced b...