LIPOPOLYSACCHARIDE-MEDIATED REGULATION OF HEPATIC TRANSPORTER mRNA LEVELS IN RATS

Abstract

ABSTRACT:The function of hepatic transporters is to move organic substances across sinusoidal and canalicular membranes. During extrahepatic cholestasis, transporters involved in the movement of substances from blood to bile, such as sodium/taurocholate-cotransporting polypeptide (Ntcp) and multidrug resistance protein 2 (Mrp2), are down-regulated, whereas others that transport chemicals from liver to blood, such as Mrp3, are up-regulated. Unlike extrahepatic cholestasis, where transporter expression responds to the stress of accumulating bile constituents, lipopolysaccharide (LPS)-induced intrahepatic cholestasis may be directly caused by alterations in transporter expression. The aim of this study was to quantitatively determine the effect of LPS on transporter expression and study the mechanism(s) by which LPS alters mRNA levels of major hepatic transporters in Sprague-Dawley rats. Hepatic mRNA levels of Mrp2, Mrp6, multiple drug resistance protein 1a (Mdr1a), organic anion-transporting polypeptide 1 (Oatp1), Oatp2, Oatp4, Ntcp, bile salt export pump, organic cation transporter 1 (Oct1), and organic anion transporter 3 (Oat3) were dramatically decreased, beginning approximately 6 h after LPS administration, whereas Mrp5 and Oat2 levels were unchanged. In contrast, LPS increased mRNA levels of Mrp1, Mrp3, and Mdr1b concurrently with the down-regulated transporters. Pretreatment with dexamethasone, which decreases the release of cytokines, reversed the reduction of Mdr1a, Oatp1, Oatp2, Oct1, and Ntcp mRNA following LPS administration. Furthermore, dexamethasone pretreatment also prevented the LPS-mediated increase in Mrp1, Mrp3, and Mdr1b, whereas pretreatment with aminoguanidine or gadolinium chloride, an inhibitor of inducible nitric oxide synthetase and a Kupffer cell toxicant, respectively, had no effect on the LPSinduced changes. The concurrent repression and induction of various transporters, as well as dexamethasone abatement of both LPS-mediated repression and induction, indicates that these responses may be mediated through similar pathways.

Differential Regulation of Hepatic Transporters in the Absence of Tumor Necrosis Factor-α, Interleukin-1β, Interleukin-6, and Nuclear Factor-κB in Two Models of Cholestasis

“…The present data confirm previous reports that demonstrated the ability of LPS to down-regulate mRNA levels of the sinusoidal uptake transporters Oatp1, Oatp2, Ntcp, and Oatp4 in mouse and rat liver (Trauner et al, 1998;Geier et al, 2003;Cherrington et al, 2004;Siewert et al, 2004). Furthermore, the present study illustrates the fact that Oat2 mRNA levels in liver tend to decrease after LPS administration, which is similar to the observation in rats (Cherrington et al, 2004). Our data also demonstrated that LPS decreased mRNA levels of Bsep and Mrp2 in mouse liver.…”

“…These include Ntcp, Bsep, Oatp1, Oatp11, Mrp1, and Mrp9. The ability of LPS to down-regulate Ntcp, Oatp1, and Bsep mRNA expression has been demonstrated previously in vivo in rats and mice (Trauner et al, 1998;Hartmann et al, 2002;Geier et al, 2003;Cherrington et al, 2004;Siewert et al, 2004;Geier et al, 2005). The current results in IL-6(Ϫ/Ϫ) mice also confirm a previous report in which LPS administration resulted in transcriptional down-regulation of Ntcp, Bsep, and Oatp1 that was equally robust in WT and IL-6(Ϫ/Ϫ) mice (Siewert et al, 2004).…”

“…However, these data are not consistent with earlier studies that demonstrated the lack of changes in Mrp1 and down-regulation of Mrp3 in mice (Hartmann et al, 2002;Siewert et al, 2004). In rats, however, up-regulation of Mrp1, Mrp3, and Mrp5 has likewise been reported (Vos et al, 1998;Donner and Keppler, 2001;Cherrington et al, 2004). Importantly, the Mrp transporters that were induced by LPS function to export organic anions back into the blood from the hepatocyte.…”

“…In contrast, BDL induced up-regulation of Mrp3 and Mrp5 in livers of WT mice. Mrp5 up-regulation is a new finding among mice and rats (Soroka et al, 2001;Bohan et al, 2003;Cherrington et al, 2004;Denk et al, 2004). The lack of alteration in liver Mrp2 mRNA expression has been a common observation in rats although decreased expression has also been reported (Ogawa et al, 2000;Paulusma et al, 2000;Hyogo et al, 2001).…”

“…Second, recombinant TNF-␣ produces a downregulation of Ntcp and Mrp2 mRNA levels (Green et al, 1996;Kim et al, 2000). Third, administration of dexamethasone, an anti-inflammatory steroid, blocks release of cytokines and prevents down-regulation of transporters by LPS (Roelofsen et al, 1995;Kubitz et al, 1999;Cherrington et al, 2004).…”