Browsing by Subject "active transport"

The liver is the major site of drug metabolism and excretion. Within the liver endogenous and exogenous compounds are eliminated through many metabolizing enzymes. Drug removal is not only dependent on metabolic enzymes, but also on transporters. Before cellular metabolism can occur, a drug must first enter the hepatocyte. Very lipophilic drugs enter the cell membrane through passive diffusion, but polar or ionized organic compounds can enter the cell membrane only by transporters. Transporters in the basolateral membrane of the hepatocyte facilitate drug entry and access to drug metabolizing enzymes. Transporters in the canalicular domain (apical) of the hepatocyte faclitate removal of drugs or metabolites from the cell interior. Recent studies have shown that transporters can mediate drug-drug interactions, and transporter genes are subject to genetic polymorphism which may affect pharmacokinetic parameters of a drug, such as absorption, distribution, and excretion. This Master's thesis consists of two parts, a literature review and an experimental section. In the literature review two transporters, OATP1B1 and MRP2, are discussed in detail. OATP1B1 is expressed on the basolateral and MRP2 on the apical membrane of the hepatocyte. These transporters are responsible for the vectorial transcellular hepatobiliary transport of various organic anions in humans. The experimental section aims at modelling vectorial hepatobiliary transport of three compounds in a double-transfected (OATP1B1/MRP2) MDCKII cell line. All three compounds studied, rosuvastatin, estrone sulphate, and estradiol glucuronide, are substrates of both transporters. Wild type (WT) MDCKII cells were used as a control. Tight junctions form a barrier between cells. This barrier regulates the paracellular passage of, for example, water, ions, large molecules, and drugs. In the experimental section the tight junctions were reversibely opened to distinguish between trans- and paracelluar routs of transport of the three compounds studied. Permeation of rosuvastatin and estradiol glucuronide in the basolateral to apical direction was faster in the double-transfected cell line compared to the MDCKII-WT cell line. Permeation of estrone sulphate, however, behaved unexpectedly in the double-transfected cell line. The permeation of this compound was almost equal in the apical to basolateral and basolateral to apical direction. The reason for this unexpected finding remains unclear. By opening the tight junctions the permeation of all compounds in both cell lines was increased, indicating that the compounds studied preferred the paracellular route and the importance of transporters were reduced. The double-transfected MDCKII cell line is a useful in vitro model of hepatic vectorial transport of organic anions in humans.