The effects of benzimidazole anthelmintics on P4501A in rat hepatocytes and HepG2 cells q V. Baliharov a a, * , L. Sk alov a a , R.F.M. Maas b , G. De Vrieze b , S. Bull b , J. Fink-Gremmels b a Faculty of Pharmacy, Charles University, Heyrovsk eho 1203, CZ-50005 Hradec Kr  alov e, Czech Republic b Faculty of Veterinary Medicine, Utrecht University, Yalelaan 16, 3508 TD Utrecht, The Netherlands Accepted 11 February 2003 Abstract Benzimidazole anthelmintics including albendazole, fenbendazole, and mebendazole are widely used in veterinary medicine. The effects of these benzimidazoles on cytochrome P4501A were investigated in primary cultures of rat hepatocytes and in the HepG2 cell line. After incubation of rat hepatocytes and HepG2 for 24-, 48-, and 72-h cells with drugs at various concentrations (0.1– 50 lM), the enzyme activities associated with P4501A1/2 (7-ethoxyresorufin O-deethylation and 7-methoxyresorufin O-demethy- lation) were measured. The P4501A1/2 protein levels in both model systems were determined by Western blotting. Although all benzimidazoles provoked a significant increase of P4501A1/2 protein levels and P4501A activities, large differences in the induction response were found which was dependent on drug structure, concentration, and model system used. Based on the results, rela- tionships between induction potency and structure of drug were demonstrated, as well as differences between the in vitro systems used. Therefore, pharmacological and toxicological consequences of cytochrome P4501A induction by benzimidazole drugs should be taken into account in veterinary therapy. Ó 2003 Elsevier Science Ltd. All rights reserved. Keywords: Benzimidazole anthelmintics; Cytochromes P4501A; Rat hepatocytes; HepG2 cells; Enzyme induction The cytochromes P450 play an essential role in the biotransformation of drugs and other xenobiotics. The inductionoftheseenzymes,anincreaseintheexpression of the gene encoding the enzyme as a response to the presenceofaxenobiotic,representsoneoftheimportant consequences of administration of pharmaceuticals. In- ducingeffectsofdrugsmayessentiallyalterphysiological processes and may have an impact on pharmacological or toxicological properties of medication and exposure to environmental contaminants (Boobis et al., 1990; Parke et al., 1990). Several benzimidazole drugs have been described to induce cytochromes P450 in humans and rodents (Gle- izes-Escala et al., 1996; Rolin et al., 1989). The anthel- mintics albendazole (ABZ), fenbendazole (FBZ), and mebendazole (MBZ) represent drugs with a benzimid- azole structure (see Fig. 1), which are widely used in veterinary medicine. ABZ administration led to an in- crease of the catalytic activity and protein content of P4501A in rats (Asteinza et al., 2000; Souhaili-El Amri et al., 1988). In addition, induction of P4501A, mea- sured by using 7-ethoxyresorufin as a specific substrate, was also observed in human microsomes and human HepG2 cell cultures (Rolin et al., 1989). The inductive effect of FBZ and its main sulphoxide metabolite, ox- fendazole (OFZ) on cytochrome P4501A1/2 was proved in rabbits in vivo, and in primary cultures of rabbit hepatocytes with the use of specific substrates and im- munoblotting (Gleizes-Escala et al., 1991, 1996). The effectofthecommonlyusedbenzimidazoleanthelmintic, MBZ, on P4501A has yet to be explored. Research in Veterinary Science 75 (2003) 61–69 www.elsevier.com/locate/rvsc q Abbreviations: ABZ, albendazole; FBZ, fenbendazole; MBZ, mebendazole; EROD, 7-ethoxyresorufin O-deethylase; MROD, 7- methoxyresorufin O-demethylase; MTT, dimethylthiazol diphenyl tetrazolium bromide; BCA, bicinchoninic acid; BSA, bovine serum albumin; DMSO, dimethylsulfoxide; DMEM, DulbeccoÕs modified EagleÕs medium; FCS, foetal calf serum. * Corresponding author. Fax: +420-49-551-2665. E-mail address: 95bav3361@faf.cuni.cz (V. Baliharov a). 0034-5288/03/$ - see front matter Ó 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0034-5288(03)00033-X