Tumor necrosis factor alpha partially contributes to lipopolysaccharide-induced downregulation of CYP3A in fetal liver: Its repression by a low dose LPS pretreatment

Abstract

With embryonic development, fetal hepatocytes gradually express various types of cytochromes P450 (CYPs) that play a key role in the detoxification of xenobiotics. In the present study, we showed that maternal lipopolysaccharide (LPS) exposure downregulated cyp3a11 mRNA and CYP3A protein in fetal liver. The increased level of TNF-α protein in fetal liver, transferred from either the maternal circulation or amniotic fluid, seems to be associated with LPS-induced downregulation of cyp3a11 mRNA and CYP3A protein in fetal liver. Interestingly, a low dose LPS (10 μg/kg) pretreatment attenuated LPS-induced downregulation of cyp3a11 mRNA and CYP3A protein in fetal liver. Correspondingly, a low dose LPS pretreatment attenuated LPS-induced downregulation of pregnane X receptor (pxr) in fetal liver. Additional experiment showed that a low dose LPS pretreatment decreased the level of TNF-α in maternal serum and amniotic fluid and counteracted LPS-induced expression of TNF-α mRNA in maternal liver and placenta. Although a low dose LPS pretreatment alleviated LPS-induced increase in TNF-α in fetal liver, it had little effect on TNF-α mRNA in fetal liver. These results suggest that a low dose LPS pretreatment protects fetuses against LPS-induced downregulation of hepatic cyp3a11 and pxr expression through the repression of maternally sourced TNF-α production.

Introduction

The liver is the major organ of amino acid and lipid metabolism, gluconeogenesis, synthesis of serum proteins, and xenobiotic detoxification. The fetal liver functions as the major hematopoietic organ in the mid- to late fetal stage (Dzierzak and Medvinsky, 1995, Hardy and Hayakawa, 2001). With embryonic development, fetal hepatocytes gradually express various types of cytochromes P450 (CYPs) that play a key role in the detoxification of drug or other xenobiotics (Hulla and Juchau, 1989, Krauer and Dayer, 1991, Rich and Boobis, 1997, de Wildt et al., 1999, Hines and McCarver, 2002). CYP3A is a member of the cytochrome P-450 monooxygenase superfamily. In human, CYP3A4 and CYP3A5 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 (Goodwin et al., 2002). Although CYP3A4 and CYP3A5 are not detectable in fetal liver, fetal hepatocytes express CYP3A7 as early as gestational day 50–60 (Stevens et al., 2003). In mice, cyp3a11 and cyp3a13 are major members of cyp3a subfamily in the adult liver (Stevens et al., 2003, Anakk et al., 2003). In the developing mouse embryo, the amount of cyp3a11 and cyp3a13 expression gradually increases with the advancement of embryonic development (Choudhary et al., 2003).

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 (Zhou et al., 2003). Numerous studies have demonstrated that LPS decreases the levels of CYP3A in livers of rats and mice (Morgan et al., 2002, Aitken et al., 2006). On the other hand, maternal LPS exposure results in intra-uterine fetal death and intra-uterine growth retardation in animals (Xu et al., 2005a, Xu et al., 2006, Xu et al., 2007, Chen et al., 2006). Recently, we found that the expression of hepatic cyp3a11 mRNA was significantly decreased in fetuses from dams that were exposed to LPS during pregnancy (Xu et al., 2005b). In the present study, we investigated the role of TNF-α in LPS-induced downregulation of CYP3A in fetal liver. Our results indicate that the increased level of TNF-α in fetal liver, possibly sourced from maternal circulation and perhaps from amniotic fluid, contributes, at least partially, to LPS-induced downregulation of CYP3A in fetal liver. A low dose LPS pretreatment protects fetuses against LPS-induced downregulation of CYP3A through inhibiting the release of maternally sourced TNF-α.