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

Hepatic transporters are responsible for uptake and efflux of bile acids and xenobiotics as an essential aspect of liver function. When normal vectorial transport of bile acids by the apical uptake and canalicular excretion transporters is disrupted, cholestasis ensues, leading to accumulation of toxic bile constituents and considerable hepatocellular damage. The purpose of this study was to assess the role of cytokines and nuclear factorB (NFB) in the transcriptional regulation of transporters in two models of cholestasis, lipopolysaccharide (LPS) administration and bile duct ligation (BDL). In wild-type (WT) and knockout mouse strains lacking tumor necrosis factor (TNF) receptor-1, interleukin (IL)-1 receptor I, IL-6, or inhibitor of B (I B) kinase , transporter mRNA levels in liver were determined using branched DNA signal amplification 16 h after LPS administration or 3 days after BDL. In WT mice, LPS administration tended to decrease mRNA levels of organic aniontransporting polypeptide (Oatp) 2, Na -taurocholate cotransporting polypeptide (Ntcp), Oatp1, Oatp4, bile salt excretory protein (Bsep), multidrug resistance-associated protein (Mrp) 2, and Mrp6 compared with saline treatment, whereas it increased Mrp1, 3, and 5 levels. Similar changes were observed in each knockout strain after LPS administration. Conversely, BDL decreased only Oatp1 expression in WT mice, meanwhile increasing expression of Mrp1, 3, and 5 and Oatp2 expression in both WT and knockout strains. Because the transcriptional effects of BDLand LPS-induced cholestasis reflect dissimilarity in hepatic transporter regulation, we conclude that these disparities are not due to the individual activity of TNF, IL-1, IL-6, or NFB but to the differences in the mechanism of cholestasis. Cholestasis is generally defined as a condition in which bile flow is impaired. Consequent accumulation of bile constituents in hepatocytes produces oxidative stress, plasma membrane disruption, severe hepatocellular injury, and necrotic and/or apoptotic cell death, probably due to the detergent-like properties of bile salts (Kasahara et al., 2002). Accordingly, maintaining bile flow and enterohepatic circulation of bile acids are among the most important functions of hepatocyte membrane transport systems. At the sinusoidal membrane, Na taurocholate cotransporting polypeptide (Ntcp) is a secondary active transporter that is predominantly responsible for the uptake of bile salts from portal blood into hepatocytes. At the canalicular membrane, the ATP-dependent transporters bile salt excretory protein (Bsep) and multidrug resistance-associated protein2 (Mrp2) mediate secretion of bile salts and glutathione. Bsep and Mrp2 are thereby responsible for the generation of bile salt-dependent and bile salt-independent bile