INDUCIBILITY OF ETHOXYRESORUFIN DEETHYLASE AND UDP-GLUCURONOSYLTRANSFERASE ACTIVITIES IN 2 HUMAN HEPATOCARCINOMA CELL-LINES KYN-2 AND MZ-HEP-1

Two human hepatoma cell. lines, KYN-2 and Mz-Hep-1 were characterized in terms of glucuronidation capacity and inducibility of cytochrome P4 501A1/1A2 and several UDP-glucuronosyl-transferases (UGTs). Cytochrome P4501A1/1A2 activity was measured using 7-ethoxyresorufin and that of UGTs with 16 different substrates. The effects of dimethyl sulfoxide (DMSO), beta-naphthoflavone, alpha-naphthoflavone, and rifampicin on t hese drug-metabolizing enzyme activities were studied. DMSO treatment increased in a dose-dependent manner the ethoxyresorufin O-deethylase (EROD) activity in KYN-2 cells, while an opposite effect was observed in Mz-Hep-1 cells. In KYN-2 cells, EROD was more responsive toward bet a-naphthoflavone treatment in combination with DMSO. This activity was enhanced in Mz-Hep-1 cells more than 83 times by beta-naphthoflavone. The enhancement of EROD activity by DMSO and beta-naphthoflavone trea tments of KYN-2 cells was abolished by alpha-naphthoflavone treatment. In Mz-Hep-1, only the inducing effect of beta-naphthoflavone was abol ished by alpha-naphthoflavone treatment. Rifampicin treatment of KYN-2 cells reversed both the DMSO and beta-naphthoflavone effects on the E ROD activity. Glucuronidation of steroids, bile acids, fatty acids and drugs was effective in KYN-2 and Mz-Hep-1 cells. Both 1-naphthol gluc uronidation and the level of UGT16 protein detected by immunoblot and supporting this activity were lowered by DMSO treatment and increased by beta-naphthoflavone treatment in KYN-2 cells. In Mz-Hep-1 cells, D MSO and beta-naphthoflavone had no effect on 1-naphthol glucuronidatio n activity. DMSO, beta-naphthoflavone and rifampicin also affected the glucuronidation of various substrates supported by different UGT isof orms. These results indicate that KYN-2 and Mz-Hep-1 cells can be used as new in vitro models for the studies of drug metabolism and the reg ulation of the corresponding enzymes.