Comparison of inducibility of multidrug resistance (MDR)1, multidrug resistance-associated protein (MRP)1, and MRP2 mRNAs by prototypical microsomal enzyme inducers in primary cultures of human and cynomolgus monkey hepatocytes.

This study investigated the changes in the mRNA levels of the ATP binding cassette (ABC) transporters multidrug resistance 1 (MDR1), multidrug resistance-associated protein 1 (MRP1), and multidrug resistance-associated protein 2 (MRP2) following exposure to the prototypical microsomal enzyme inducers rifampicin (Rif), dexamethasone (Dex), and omeprazole (Ome) in primary cultures of cryopreserved human and cynomolgus monkey hepatocytes. Analysis was performed by real-time reverse transcription-polymerase chain reaction using primers and TaqMan probes. First, the time course of the mRNA expression of these transporters in primary cultures of human and cynomolgus monkey hepatocytes was examined in detail. The ratio of MDR1 and MRP2 mRNA to beta-actin mRNA in both human and cynomolgus monkey hepatocytes remained constant from 48 to 72 h and from 24 to 72 h of culture, respectively. Second, the hepatocytes were exposed to the inducers and the changes in the levels of the transporter mRNAs were examined. Rif increased MDR1 and MRP1 mRNA levels in both human and cynomolgus monkey hepatocytes, while Ome slightly increased MDR1 and MRP1 mRNA levels in cynomolgus monkey hepatocytes. Rif and Ome increased MRP2 mRNA levels in both human and cynomolgus monkey hepatocytes. In contrast, Dex tended to decrease the mRNA levels of MDR1, MRP1, and MRP2 in both human and cynomolgus monkey hepatocytes. Cynomolgus monkey hepatocytes appeared to be more responsive than human hepatocytes to the inducers. These results indicate that primary cultures of cynomolgus monkey hepatocytes are as useful as primary cultures of human hepatocytes for evaluating the induction of MDR1, MRP1, and MRP2 mRNAs in preclinical studies.