rifampin and oltipraz

Sinusoidal and canalicular hepatic drug transporters constitute key factors involved in drug elimination from liver. Regulation of their expression via activation of xenosensors, such as aryl hydrocarbon receptor (AhR), constitutive androstane receptor (CAR), pregnane X receptor (PXR), and nuclear factor E2-related factor 2 (Nrf2), remains incompletely characterized. The present study was therefore designed to carefully analyze expression of major drug transporters in primary human hepatocytes exposed to dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin, TCDD) (an AhR activator), rifampicin (RIF) (a PXR activator), phenobarbital (PB) (a CAR activator), and oltipraz (OPZ) (a Nrf2 activator), using mainly reverse transcription-real time polymerase chain reaction assays. With a threshold corresponding to a 1.5-fold factor change in mRNA levels, observed in at least three of seven independent human hepatocyte cultures, efflux transporters such as MDR1, MRP2 and BCRP were up-regulated by PB, RIF, and OPZ, whereas MRP3 was induced by OPZ and RIF. MDR1 and BCRP expression was also increased by TCDD- and RIF-augmented mRNA levels of the influx transporter OATP-C. Bile acid transporters, i.e., bile salt export pump and Na(+)-taurocholate cotransporting polypeptide, and the sinusoidal transporter, OAT2, were down-regulated by all the tested chemicals. Influx transporters such as OCT1, OATP-B, and OATP8 were repressed by PB and TCDD. PB also decreased MRP6 expression, whereas mRNA levels of OCT1 and OATP8 were down-regulated by RIF and OPZ, respectively. Taken together, these data establish a complex pattern of transporter regulation by xenobiotics in human hepatocytes, in addition to interindividual variability in responsiveness. This may deserve further attention with respect to drug-drug interactions and adverse effects of hepatic drugs.

Topics: Adult; ATP Binding Cassette Transporter, Subfamily B, Member 1; ATP Binding Cassette Transporter, Subfamily G, Member 2; ATP-Binding Cassette Transporters; Constitutive Androstane Receptor; Gene Expression Regulation; Hepatocytes; Humans; Membrane Transport Proteins; Multidrug Resistance-Associated Protein 2; Multidrug Resistance-Associated Proteins; Neoplasm Proteins; NF-E2-Related Factor 2; Phenobarbital; Polychlorinated Dibenzodioxins; Pregnane X Receptor; Pyrazines; Receptors, Aryl Hydrocarbon; Receptors, Cytoplasmic and Nuclear; Receptors, Drug; Receptors, Steroid; Reverse Transcriptase Polymerase Chain Reaction; Rifampin; RNA, Messenger; Symporters; Thiones; Thiophenes; Transcription Factors; Xenobiotics

Dithiolethiones are thought to act as potent chemoprotective agents against aflatoxin B1 (AFB1)-induced hepatocarcinogenesis in the rat by inducing glutathione S-transferases (GSTs). To determine whether these antioxidants can be similarly effective in human beings, we have investigated metabolism of AFB1, in primary human hepatocytes with or without pretreatment by oltipraz (OPZ), a synthetic derivative of the natural 1,2-dithiole-3-thione. Aflatoxin M1 (AFM1), glutathione conjugates of AFB1 oxides (AFBSGs), and unchanged AFB1 were quantitated in cultures derived from eight human liver donors. Parenchymal cells obtained from the three GST M1-positive livers metabolized AFB1 to AFM1 and to AFBSGs derived from the isomeric exo-and endo-8,9-oxides, whereas no AFBSGs were formed in the GST M1-null cells. Pretreatment of the cells with 3-methylcholanthrene or rifampicin, inducers of CYP1A2 and CYP3A4, respectively, caused a significant increase in AFB1 metabolism. Although OPZ induced GST A2, and to a lesser extent GST A1 and GST M1, it decreased formation of AFM1 and AFBSG, which involves CYP1A2 and CYP3A4. Inhibition by OPZ of AFB1 metabolism by reducing CYP1A2 and CYP3A4 was also demonstrated by decreased activity of their monooxygenase activities toward ethoxyresorufin and nifedipine, respectively. The significant inhibition by OPZ of human recombinant yeast CYP1A2 and CYP3A4 was also shown. These results demonstrate that AFBSG can be formed by GST M1-positive human hepatocytes only, and suggest that chemoprotection with OPZ is due to an inhibition of activation of AFB1, in addition to a GST-dependent inactivation of the carcinogenic exo-epoxide.

Topics: Aflatoxin B1; Aged; Anticarcinogenic Agents; Cells, Cultured; Cytochrome P-450 CYP1A2; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme Inhibitors; Female; Glutathione Transferase; Humans; Infant; Liver; Male; Methylcholanthrene; Middle Aged; Mixed Function Oxygenases; Oxidoreductases; Pyrazines; Rifampin; Thiones; Thiophenes; Time Factors