Lipopolysaccharide treatment downregulates the expression of the pregnane X receptor, cyp3a11 and mdr1a genes in mouse placenta
Introduction
The cytochrome P450 3A (CYP3A) is a member of the cytochrome P450 monooxygenase superfamily. In human, CYP3A4 and CYP3A5 gene products account for 30–40% of the total cytochrome P450 in the adult liver, which is responsible for the oxidative metabolism of numerous clinically used drugs and toxicants (Thummel et al., 1998). Although CYP3A4 and CYP3A5 in fetal liver are not detectable, fetal hepatocytes express CYP3A7 as early as 50–60 days gestation with continued significant levels of expression through the perinatal period (Stevens et al., 2003). Expression of CYP3A, an enzyme that catalyzes drugs and xenobiotics, can be detected in human placenta as early as the first trimester of pregnancy (Hakkola et al., 1996a, Hakkola et al., 1996b). In mice, cyp3a11 and cyp3a13 are major members of cyp3a subfamily in the adult liver. In the developing mouse embryo, the amount of cyp3a11 and cyp3a13 expressions gradually increases with the advancement of embryonic development (Choudhary et al., 2003). Multidrug resistance 1 (MDR1) gene belongs to the ATP-binding cassette (ABC) family. MDR1 encodes P-glycoprotein (P-gp), which functions as a transmembrane efflux pump that translocates its substrates from its intracellular domain to its extracellular domain (Fromm, 2004). P-glycoprotein is expressed constitutively in small intestine and liver. Pregnane X receptor (PXR) is a member of the nuclear receptor superfamily, which regulates CYP3A and MDR1 gene transcription in a ligand-dependent manner (Kliewer et al., 1998, Lehmann et al., 1998, Bertilsson et al., 1998, Teng and Piquette-Miller, 2005).
Lipopolysaccharide (LPS) is a toxic component of cell walls of Gram-negative bacteria and is widely present in the digestive tracts of humans and animals. Humans are constantly exposed to low levels of LPS through infection. Gastrointestinal distress and alcohol drinking often increase permeability of LPS from gastrointestinal tract into blood (Mathurin et al., 2000). On the other hand, numerous studies indicated that inflammation and infection reduce hepatic CYP levels in various species including human, rat and mouse (Morgan, 1997, Morgan, 2001). The effect of LPS on P450 expression is very well documented in a variety of systems and tissues (Renton and Nicholson, 2000, Li-Masters and Morgan, 2001, Morgan et al., 2002, Pan et al., 2003, Kalitsky-Szirtes et al., 2004). LPS-induced downregulation of cyp3a in liver has also been demonstrated in mouse model (Sewer et al., 1998). Moreover, LPS-induced downregulation of hepatic CYP3A is associated with a marked reduction in PXR mRNA and protein levels (Beigneux et al., 2002, Sachdeva et al., 2003). Our earlier studies showed that reactive oxygen species (ROS) mediate LPS-induced downregulation of PXR and its target gene cyp3a in mouse liver (Xu et al., 2004, Xu et al., 2005).
On the other hand, PXR, CYP3A and MDR1 were also expressed in placenta of human and rodent animals (Masuyama et al., 2001, Leazer and Klaassen, 2003, Novotna et al., 2004). Together with xenobiotic-metabolizing enzymes, MDR1 encoded P-gp in placenta is a drug efflux transporter that limits the entry of various potentially toxic drugs and xenobiotics into the fetus and is thus considered a placental protective mechanism (Lankas et al., 1998). Several studies have demonstrated that placental P-gp deficiency enhances susceptibility to chemically induced birth defects in mice (Lankas et al., 1998, Smit et al., 1999). However, it is not clear whether LPS represses the expression of PXR, CYP3A and MDR1 in placenta.
In present study, we investigated the effects of LPS on PXR, cyp3a11 and mdr1a gene expressions in mouse placenta. Our results found that LPS downregulates placental PXR, cyp3a11 and mdr1a gene expressions. ROS may be involved in LPS-induced downregulation of PXR, cyp3a11 and mdr1a in mouse placenta.
Section snippets
Chemicals
Lipopolysaccharide (Escherichia coli LPS, serotype 0127:B8), alpha-phenyl-N-t-butylnitrone (PBN) and N-acetylcysteine (NAC) were purchased from Sigma Chemical Co. (St. Louis, MO). All other reagents were from Sigma or as indicated in the specified methods.
Animals and treatments
The ICR mice (8–10-week-old; male mice: 28–30 g; female mice: 24–26 g) were purchased from Beijing Vital River whose foundation colonies were all introduced from Charles River Laboratories Inc. The animals were allowed free access to food and
Results and discussion
Cytochrome P450 3A is a member of the cytochrome P450 monooxygenase superfamily, which is responsible for the oxidative metabolism of numerous clinically used drugs. LPS-induced downregulation of CYP3A in liver has been demonstrated in a series of reports (Morgan et al., 2002). Several studies found that CYP3A is detectable in human and mouse placenta as early as the first trimester of pregnancy, which play a key role in the detoxification of drug or other xenobiotics (Hakkola et al., 1996a,
Acknowledgement
The Project (30371667) was supported by National Natural Science Foundation of China.
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