Differential effects of microsomal enzyme–inducing chemicals on the hepatic expression of rat organic anion transporters, OATP1 and OATP2

Abstract

The organic anion transporting polypeptides, Oatp1 (Slc21a1) and Oatp2 (Slc21a5), mediate hepatic uptake of cardiac glycosides. Previously, we demonstrated that chemicals that increase cytochrome P450s differentially affect hepatic uptake of cardiac glycosides. We postulated that increased uptake of cardiac glycosides observed after pretreatment of animals with phenobarbital (PB) and pregnenolone-16␣-carbonitrile ( Hepatic clearance and biliary excretion of drugs and their metabolites can occur through passive transport or through active transport (carrier-mediated) systems. Previous studies from this laboratory described a phenomenon in which pretreatment of animals with chemicals known to differentially increase specific microsomal cytochrome P450 enzymes also enhanced both hepatic plasma clearance and biliary excretion of a number of choleophiles, including cardiac glycosides. [1][2][3][4] Specifically, pretreatment of rats with two compounds known classically to activate CYP2B and CYP3A transcription, the barbiturate phenobarbital (PB) and the synthetic steroid pregenenolone-16␣-carbonitrile (PCN), respectively, resulted in the decreased plasma half-life, increased hepatic clearance, and decreased toxicity of cardiac glycosides. In contrast, pretreatment of rats with chemicals known to act through the aryl hydrocarbon receptor resulted in a slight suppression of cardiac glycoside plasma clearance by the liver. 2 Further studies demonstrated that PCN increased the maximal velocity and affinity of ouabain uptake into hepatocytes, 3 suggesting that this chemical altered the hepatocellular capacity and affinity for choleophilic substrates. In subsequent studies, an energydependent, Na ϩ -independent carrier-mediated transport system for ouabain was identified. This Na ϩ -independent transport system was sensitive to inhibition by neutral (e.g., digoxin), acidic (e.g., taurocholate), and basic (e.g., quinine) compounds. 4 Together, these findings suggested that a multispecific, Na ϩ -independent hepatic transport system existed, which could be positively modulated by microsomal enzymeinducing chemicals, specifically PB and PCN.Since these earlier reports, 1-4 specific mediators of this hepatic Na ϩ -independent transport system have been cloned and characterized, and consist of several members of the rat organic anion transporting polypeptide (Oatp) family. The primary forms expressed in rat liver include, Oatp1 (gene symbol: Slc21a1), Oatp2 (Slc21a5), and liver-specific transporter 1 (rlst-1) or Oatp4 (Slc21a10). In rat liver, the organic anion transporting polypeptides, Oatp1, 5 Oatp2, 6,7 and rlst-1/ Oatp4, 8-10 transport a number of conjugated and unconjugated xenobiotics and endobiotics in a charge-independent manner. The substrates for this family of transporters include: the cardiac glycosides, the statin class of lipid-lowering drugs, human immunodeficiency virus-protease inhibitors, bile acids, eicosanoids, thyroid hormone and thyroid hormone conjugates, steroid hormone conjugates, and numerous peptidede...

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“…2, 3). This agrees with the results of Rausch-Derra et al and Staudinger et al [12][13][14] In addition, we have demonstrated that mrp2 mRNA expression is induced by PCN and 3-MC in mouse liver (Fig. 4).…”

“…Some studies using human and rodent models have demonstrated that ABC transporter family transporter proteins, such as Pgp, Oatp2, and mrp2, are upregulated by microsomal enzyme inducers. [10][11][12][13][14][15][16][17][18] In this study, we examined the effects of microsomal enzyme inducers on the mRNA expression of bcrp, which is also responsible for drug resistance and may have a pharmacological role. Bcrp mRNA expression was analyzed by two separate methods, and it was found that neither PCN nor 3-MC affected bcrp mRNA expression in the liver, duodenum, jejunum and ileum in BALB/c mice (Table 1).…”

“…PCN produces a marked elevation of Oatp2 mRNA and protein but, surprisingly, Oatp2 expression is suppressed in response to 3-MC. [12][13][14][15] It also has been demonstrated that treatment of human, rat and mouse primary hepatocytes with PB and PCN results in an increased expression of mrp2 mRNA. 16) In addition, the recent studies have been demonstrated that PCN and PB increase mrp2 protein in rat liver in a time-dependent manner, although they have no effect on the expression of mrp2 mRNA.…”

Postnatal Expression and Induction by Pregnenolone-16α-Carbonitrile of the Organic Anion-Transporting Polypeptide 2 in Rat Liver

“…Bicinchoninic acid protein assay kit was obtained from Pierce Chemical (Rockford, IL). Primary polyclonal antibody for rat oatp2 was developed in our laboratory against a synthetic peptide designed from a unique region of rat oatp2 protein (Rausch-Derra et al, 2001). Horseradish peroxidase-conjugated secondary antibody, protein molecular weight marker, and chemiluminescence reagents for Western blot analysis were from Amersham Biosciences, Inc. (Piscataway, NJ).…”

“…All probes were synthesized by Operon Technologies (Palo Alto, CA). The compete list of rat oatp2 oligonucleotide probes has been previously published (Rausch-Derra et al, 2001).…”