Assessment of the inhibitory potency of benzydamine on albendazole hepatic metabolism in sheep

VIRKEL G.; MATÉ L.; LIFSCHITZ A.; SALLOVITZ J.; FARIAS C.; LANUSSE C.

Amsterdam

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

Organizing Committee of the 12th International Congress of the European Association for Veterinary Pharmacology and Toxicology

INTRODUCTION The benzimidazole methylcarbamate anthelmintic albendazole (ABZ) is still widely used to control helminth infections in livestock. The hepatic ABZ S-oxidation, by both flavin-monooxygenase (FMO) and cytochrome P450 systems (Virkel et al., 2004; Souhaili El Amri et al., 1988), results in a considerable reduction of its pharmacologic activity. Therefore, interference with the oxidative metabolism may enhance the systemic exposure of active drug/metabolites and, consequently, improve the anthelmintic efficacy. With the aim of searching for new potential pharmacologic strategies to inhibit ABZ metabolism, the current research evaluated the effects of the FMO substrate benzydamine (BZ) on the hepatic S-oxidation of this anthelmintic drug in sheep. The effects of BZ were compared to those produced by methimazole (MTZ), a well known FMO inhibitor of ABZ metabolism. MATERIALS AND METHODS Liver microsomes were obtained from healthy adult Corriedale rams (n=4). MTZ S-oxidation was the selected FMO-dependent specific activity (Dixit & Roche, 1984) using 0.125-5 mM substrate concentrations in the absence or in the presence of BZ (750 μM). ABZ S-oxidation was assessed by the amount of ABZ-sulphoxide (ABZSO) formed in the presence of NADPH. The substrate (100 µM) was incubated (15 min at 37ºC) either in the absence (control assays) or in the presence of variable concentrations (12.5 to 1000 μM) of BZ or MTZ. Samples were analyzed by HPLC. The statistical comparison of data was performed using the Student t-test. RESULTS In pooled sheep liver microsomes, the Clint of the FMO-dependent enzyme activity (MTZ S-oxidation) was lower in the presence of BZ (53 vs. 95 µL/min.mg). ABZ was metabolized to its (-) and (+) ABZ-sulphoxide (ABZSO) enantiomers. Both BZ and MTZ inhibited ABZ S-oxidation; the estimated IC50?s for both metabolic inhibitors are shown in Table 1. Table 1: Albendazole enantioselective S-oxidation by sheep liver microsomes. Mean (SD) IC50?s of the metabolic inhibitors benzydamine (BZ) and methimazole (MTZ). IC50 (µM)(1) BZ MTZ P value (*) (total) ABZSO 48  5 18  4 0.0004 (+)ABZSO 39  2 16  2 0.0006 (-)ABZSO 290 141(a) 357  86(a) 0.4776 (1) The concentration of BZ or MTZ causing a 50 % inhibition of the production of (total) ABZSO and both enantiomers. (*) Statistical comparisons between metabolic inhibitors. (a): Statistically different (p