Comparative hepatic metabolism of the anthelmintic flubendazole in rat, swine and sheep.

VIRKEL, G; MATÉ, L; LIFSCHITZ, A; CEBALLOS, L; ALVAREZ, L; LANUSSE, C

Congreso; 12th International Congress of the European Association for Veterinary Pharmacology and Toxicology; 2012

INTRODUCTION Flubendazole (FLBZ) is a broad-spectrum benzimidazole anthelmintic widely used in pigs and poultry. This drug has shown good efficacy to control gastrointestinal nematodes in sheep and macrofilaria in lymphatic filariasis and onchocerciasis in man (Mackenzie & Geary, 2011). Flubendazole contains a ketone group at position -5 of the benzimidazole ring which has implications on its metabolic pattern. For instance, carbonyl-reducing enzymes catalyze the NADPH-dependent conversion of FLBZ into its reduced metabolite (red-FLBZ) in sheep liver (Maté et al., 2008; Bártíková et al., 2010).The aim of the current work was to assess the comparative FLBZ metabolism pattern in rat, swine and sheep liver cytosolic and microsomal fractions. MATERIALS AND METHODS Liver microsomal and cytosolic fractions were obtained from male (n=3) and female (n=3) Wistar rats, male Texel lambs (n=6) and male Landrace piglets (n=4). Flubendazole keto-reduction was assessed by the rate of red-FLBZ formation in the presence of NADPH. Incubations with red-FLBZ as substrate were also carried out in the presence of NADP+. Substrates were incubated at 100 µM (15 min at 37ºC) and samples were analyzed by HPLC. Statistical comparisons among species were performed using non-parametric ANOVA. RESULTS Both liver cytosolic and microsomal fractions from each animal species were able to metabolize FLBZ into red-FLBZ. The cytosolic production of the red-FLBZ was higher (p<0.05) in sheep (1.86 ± 0.61 nmol/min.mg) compared to rats (0.13 ± 0.12 nmol/min.mg) and pigs (0.02 ± 0.00 nmol/min.mg). Male rat liver microsomes metabolized FLBZ into red-FLBZ to a greater extent (p<0.05) than female (0.87 ± 0.25 vs. 0.10 ± 0.06 nmol/min.mg). The production of red-FLBZ in liver microsomes was higher in sheep (1.62 ± 0.28 nmol/min.mg) compared to pigs (0.04 ± 0.02 nmol/min.mg, p<0.001) and female rats (0.10 ± 0.06 nmol/min.mg, p<0.05). A hydrolyzed metabolite (h-FLBZ) was only formed by both subcellular fractions from pig liver. The formation rate of h-FLBZ in swine hepatic microsomes was 7-fold higher (p<0.05) compared to that observed for red-FLBZ. Only sheep liver cytosolic and microsomal fractions were able to produce the NADP+-dependent oxidation of red-FLBZ into FLBZ parent drug at 0.68 ± 0.07 and 0.64 ± 0.12 nmol/min.mg, respectively. DISCUSSION phase I enzymes catalyzing the reduction of xenobiotics containing a carbonyl group include short-chain dehydrogenases/reductases (SDR) (Cox Rosemond & Walsh, 2004). A wide array of xenobiotic substrates was found to be metabolized by cytosolic carbonyl reductases and the membrane-bound 11β-hydroxysteroid dehydrogenase, the most relevant enzymes within the SDR superfamily. The findings reported here demonstrate that FLBZ metabolic pattern may greatly differ among animal species. Considering the potential advantages that FLBZ may offer to be used as an anthelmintic drug in both veterinary and human medicine, further work is required to understand the role of these carbonyl reducing enzymes on its metabolic fate across species.