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Fenbendazole (FEN) and flubendazole (FLU) are benzimidazole anthelmintics often used in pig management for the control of nematodoses. The in vivo study presented here was designed to test the influence of FLU and FEN on cytochrome P4501A and other cytochrome P450 (CYP) isoforms, UDP-glucuronosyl transferase and several carbonyl reducing enzymes. The results indicated that FEN (in a single therapeutic dose as well as in repeated therapeutic doses) caused significant induction of pig CYP1A, while FLU did not show an inductive effect towards this isoform. Some of the other hepatic and intestinal biotransformation enzymes that were assayed were moderately influenced by FEN or FLU. Strong CYP1A induction following FEN therapy in pigs may negatively affect the efficacy and pharmacokinetics of FEN itself or other simultaneously or consecutively administered drugs. From the perspective of biotransformation enzyme modulation, FLU would appear to be a more convenient anthelmintic therapy of pigs than FEN.

Many benzimidazoles are known inducers of cytochromes P4501A (CYP1A) in laboratory animals and cell lines. As flubendazole and mebendazole are benzimidazole anthelmintics often used in a pheasant, in the present study an effect of these drugs in primary cultures of pheasant ( Phasianus colchicus ) hepatocytes was investigated. After 48 h incubation of the hepatocytes with the benzimidazoles (0.2–5 μM), CYP1A activities – ethoxyresorufin O -deethylation (EROD) and methoxyresorufin O -demethylation (MROD) activities were measured and the CYP1A protein levels were determined by Western blotting. None of the tested benzimidazoles influenced the CYP1A protein content. No pharmacologically significant enhancement of CYP1A after exposure of the hepatocytes to flubendazole and mebendazole was found. Inhibition of the EROD/MROD activities caused by both tested substances was observed only at the highest concentration (5 μM). From a point of view of CYP1A induction or inhibition, the treatment of pheasants by both anthelmintics tested seems to be safe. Our study demonstrates the inter-species differences in CYP1A inducibility and the importance of induction/inhibition studies on target animals.

Flubendazole (FLU) is a widely administered benzimidazole anthelmintic indicated for the control of parasitic diseases in farm animals including pigs and pheasants. This study was designed to test the biotransformation of FLU in control animals and animals treated with FLU in recommended therapeutic doses. The activities of several pheasant and porcine hepatic and intestinal carbonyl reducing enzymes and their modulation by FLU were also studied. Twelve adult pheasant hens, approximately 1 year old, were divided into two groups and treated for 7 days with placebo or 6 mg of FLU/kg of body weight. Eight male hog weaners, approximately 3 month old, were divided into two groups and treated for 5 days with placebo or 1.57 mg of FLU/kg of body weight. Subcellular fractions, prepared from livers and small intestines of control and FLU treated animals, were incubated with FLU. In vitro formation of two main FLU metabolites, reduced FLU, and hydrolyzed FLU were analyzed using HPLC. While FLU was reduced significantly more intensively in FLU-treated pheasants than in control animals, no differences were observed in pigs. These results were confirmed by measuring the enzyme activities: carbonyl reducing enzyme activities were increased in pheasants treated by FLU, whereas FLU did not affect these enzymes in pigs.

Adult mouflon ewes (Ovis musimon) were treated repeatedly with therapeutic doses of albendazole (ABZ, p.o. 7.5 mg/kg of body weight/day, for five consecutive days). Animals (treated or control) were sacrificed 24 h after the fifth dose of ABZ and liver and small intestine were collected to prepare microsomes. The activities of several biotransformation enzymes were measured in both hepatic and intestinal microsomes. A significant increase in the activity and amount of cytochromes P4501A (CYP1A) was observed in both tissues of ABZ treated mouflons compared to control animals. No other biotransformation enzymes tested were affected by five ABZ doses. The in vitro biotransformation of ABZ was studied in hepatic and intestinal microsomes from ABZ treated and control mouflons. Concentrations of two main ABZ metabolites - pharmacologically active ABZ sulfoxide and pharmacologically inactive ABZ sulfone were analysed using HPLC. A significant increase in rate of formation of ABZ sulfone (which is catalysed by CYP1A) was observed in hepatic as well as in intestinal microsomes from ABZ treated animals. The enhancement of ABZ deactivation by its repeated administration may affect the anthelmintic efficacy of this drug and may contribute to the development of parasite resistance.

Fenbendazole (FBZ), flubendazole (FLBZ) and mebendazole (MBZ) are benzimidazole anthelmintics widely used in veterinary medicine. The effects of these drugs on cytochromes P450 (CYP) were investigated in primary cultures of swine (Sus scrofa f. domestica) hepatocytes. After 48-h incubation of hepatocytes with benzimidazoles (0.1-2.5 microm), ethoxyresorufin O-deethylation (EROD), benzoxyresorufin O-dearylation (BROD), testosterone hydroxylase (6beta-TOH) and testosterone oxidase (17-TO) activities were measured and the CYP1A and 3A protein levels were determined by Western blotting. FBZ produced a significant, concentration-dependent increase of CYP1A activity (EROD) and protein level. No enhancement of CYP1A was observed after exposure to FLBZ and MBZ. All benzimidazoles tested did not cause any induction of CYP3A (BROD, 6beta-TOH, 17-TO activities and protein content). On the other hand, MBZ produced a significant, concentration-dependent decrease of CYP3A (BROD, 6beta-TOH and 17-TO) activities. Pharmacological and toxicological consequences of CYP1A induction and CYP3A inhibition should be taken into account in treatment of pigs with FBZ and MBZ.

Benfluron (B, [5-(2- N -oxo-2- N ′, N ″-dimethylaminoethoxy)-7-oxo-7 H -benzo[ c ]fluorene]) is a potential benzo[ c ]fluorene antineoplastic agent with high activity against a broad spectrum of experimental tumors in vitro and in vivo . The structure of B has been modified to repress its rapid deactivation through carbonyl reduction on C7. 3,9-Dimethoxybenfluron (D, [3,9-dimethoxy-5-(2- N -oxo-2- N ′, N ″-dimethylaminoethoxy)-7-oxo-7 H -benzo[ c ]fluorene]) is one of the B derivatives developed. The present paper was designed to compare the C7 carbonyl reduction of B and D in microsomes, cytosol and hepatocytes from human liver. Two purified human enzymes, microsomal 11β-hydroxysteroid dehydrogenase 1 (11β-HSD 1) and cytosolic carbonyl reductase, were tested if they are responsible for B and D carbonyl reduction in the respective fractions. Indeed, carbonyl reduction of D in comparison to that of B was 4 and 6–10 times less extensive in human liver microsomes and cytosol, respectively. Moreover, about 10–20 times higher amounts of dihydro B than dihydro D were detected in primary culture of human hepatocytes. 11β-HSD 1 was shown to be able to reduce B and D. For this enzyme, about 10 times higher rates of carbonyl reduction were observed for B than for D. Likewise, CR participates in B and D carbonyl reduction, although smaller amounts of both reduced metabolites were detected. In summary, carbonyl reduction of D was significantly less extensive than that of B in all in vitro experiments. This lower rate of D inactivation was especially pronounced in hepatocytes which represent a close to in vivo situation. Our results clearly demonstrate that dimethoxy substitution protects the carbonyl group of the benzo[ c ]fluorene moiety against the deactivation by microsomal and cytosolic reductases. Detailed knowledge on the participating enzymes may serve as a basis for the co-application of specific inhibitors in chemotherapy to further improve the pharmacokinetics of benzo[ c ]fluorene derivatives.

Contact handling with wild or semi-domesticated animals requires limiting animal stress to minimum. In this respect, single administration of drug should be preferred in contact therapy of mouflon ( Ovis musimon) infected by lancet fluke ( Dicrocoelium dendriticum). We tested single administration of albendazole (ABZ) (30 mg/kg of body weight) in a form of oral suspension and investigated to reach anthelmintic effects and to modu - late biotransformation enzymes in liver and small intestine. Two weeks after ABZ administration coprology and necropsy findings document the adulticide effect in liver. The activities of eight biotransformation enzymes and ABZ biotransformation were tested in hepatic and intestinal subcellular fractions from control and ABZ treated animals. The highest inductive effect of ABZ was detected on cytochromes P4501A (CYP1A) activities. Increased amount of CYP1A proteins was confirmed using western blotting. In hepatic and intestinal microsomes, velocity of albendazole sulfoxide (ABZSO) formation was unaffected, but a shift in ratio of individual ABZSO enantiomers was observed. The second step of ABZ biotransformation corresponding to the formation of the pharmacologically inactive albendazole sulfone, was significantly accelerated both in liver and intestine of ABZ treated animals. The increase of ABZ deactivation could facilitate the development of anthelmintic resistance in parasites. Although single ABZ dose is therapeutically effective, its potential to induce CYP1A should be taken in account for control - ing helmithoses.