title: Effect of dexamethasone treatment on the expression and function of transport proteins in sandwich-cultured rat hepatocytes.
abstract: Dexamethasone (DEX) is a well established inducer of CYP3A. These studies examined the influence of DEX treatment on transport protein expression and function in sandwich-cultured (SC) rat hepatocytes. Freshly isolated hepatocytes were cultured between two layers of gelled collagen and maintained in Dulbecco's modified Eagle's medium supplemented with DEX (0.1 microM, 0-48 h and 0.1-100 microM, 48-96 h). The expression of sinusoidal [(organic anion transporting polypeptide 1a1 (Oatp1a1), Oatp1a4, multidrug resistance-associated protein 3 (Mrp3), and Na(+)-dependent taurocholate cotransporting polypeptide (Ntcp)] and canalicular [bile salt export pump (Bsep), multidrug resistance protein 1a/b (Mdr1a/b), and Mrp2] transport proteins was determined by Western blot analysis. The accumulation and biliary excretion index (BEI; percentage of accumulated substrate in canalicular networks) of the probe substrates taurocholate (TC; 1 microM, 10 min), rhodamine 123 (Rh123; 10 microM, 30 min), and carboxy-2',7'-dichlorofluorescein (CDF; 10 microM, 10 min) were employed as measures of canalicular transport protein function in SC rat hepatocytes. DEX treatment increased CYP3A1/2, Oatp1a4, and Mrp2 expression, decreased the expression of Ntcp, and did not seem to alter the expression of Oatp1a1, Mrp3, Mdr1a/b, or Bsep. The BEI of CDF, an Mrp2 substrate, increased from 18 to 37% after DEX treatment (100 microM). The accumulation of TC, an Ntcp substrate, was reduced (<50% of control), whereas the BEI of TC, also a Bsep substrate, was unchanged. Treatment of SC rat hepatocytes with DEX resulted in alterations in the expression of CYP3A1/2 and some hepatic transport proteins. Modest alterations in hepatic transport protein function were consistent with changes in protein expression.
authors.affiliation: Division of Drug Delivery and Disposition, School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7360, USA.
authors.forename: Ryan Z
authors.initials: RZ
authors.lastname: Turncliff
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Meier
authors.forename: Kim L R
authors.initials: KL
authors.lastname: Brouwer
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D026901:Membrane Transport Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D026901:Membrane Transport Proteins; D003907:Dexamethasone