Assessment of the main metabolism pathways for the flukicidal compound triclabendazole in sheep

Abstract

Triclabendazole (TCBZ) is an halogenated benzimidazole (BZD) compound worldwide used to control immature and adult stages of the liver fluke Fasciola hepatica. The purpose of this investigation was to characterize in vitro the patterns of hepatic and ruminal biotransformation of TCBZ and its metabolites in sheep. TCBZ parent drug was metabolized into its sulphoxide (TCBZSO), sulphone (TCBZSO2) and hydroxy derivatives by sheep liver microsomes. The same microsomal fraction was also able to oxidize TCBZSO into TCBZSO2 and hydroxy-TCBZSO (HO-TCBZSO). TCBZ sulphoxidation was significantly (P < 0.001) inhibited after inactivation of the flavin-monooxygenase (FMO) system (77% inhibition) as well as in the presence of the FMO substrate methimazole (MTZ) (71% inhibition). TCBZ sulphoxidative metabolism was also reduced (24% inhibition, P < 0.05) by the cytochrome P450 inhibitor piperonyl butoxide (PB). The rate of TCBZSO conversion into TCBZSO2 was also significantly inhibited by PB (55% inhibition), MTZ (52% inhibition) and also following FMO inactivation (58% inhibition). The data reported here indicate that the FMO is the main enzymatic pathway involved in TCBZ sulphoxidation (ratio FMO/P450 = 3.83 +/- 1.63), although both enzymatic systems participate in a similar proportion in the sulphonation of TCBZSO to form the sulphone metabolite (ratio FMO/P450 = 1.31 +/- 0.23). Additionally, ketoconazole (KTZ) did not affect TCBZ sulphoxidation but decreased (66% inhibition, P < 0.05) the formation of TCBZSO2. Similarly, inhibition of TCBZSO2 production was observed after incubation of TCBZSO in the presence of KTZ and erythromycin (ETM). Conversely, thiabendazole (TBZ) and fenbendazole (FBZ) did not affect the oxidative metabolism of both incubated substrates. The sheep ruminal microflora was able to reduce the sulphoxide (TCBZSO) into the parent thioether (TCBZ). The ruminal sulphoreduction of the HO-TCBZSO derivative into HO-TCBZ was also demonstrated. The rate of sulphoreduction of HO-TCBZSO was significantly (P < 0.05) higher than that observed for TCBZSO. The metabolic approach tested here contributes to the identification of the different pathways involved in drug biotransformation in ruminant species. These findings on the pattern of hepatic and ruminal biotransformation of TCBZ and its main metabolites are a further contribution to the understanding of the pharmacological properties of widely used anthelmintics in ruminants. Comprehension of TCBZ metabolism is critical to optimize its flukicidal activity.

Determination of Triclabendazole in Cattle Plasma as Its Sulphoxide and Sulphone Metabolites by Rotating Disk Sorptive Extraction Combined With High-Performance Liquid Chromatography and Its Application to Pharmacokinetic Studies

“…The disk has a cavity (0.44 cm 3 ) on one of its surfaces in which 50 mg of Oasis™ HLB sorbent was loaded. The cavity was covered with a fiberglass filter (1.4 cm diameter, mean pore size 3 µm) and sealed with a Teflon ring.…”

“…Despite its activity, TCB is practically absent in plasma, however, after distribution, its active metabolite TCB-SO is the responsible of the fasciolicide activity; meanwhile TCB-SO2 is an inactive metabolite that accounts for the drug elimination stage. 2,3 The antiparasitic activity of the TCB is time dependent. Its therapeutic effects occur when the administered product maintains effective concentrations of TCB and TCB-SO at the location of Fasciola hepatica.…”

Potentiation of triclabendazole sulphoxide-induced tegumental disruption by methimazole in a triclabendazole-resistant isolate of Fasciola hepatica

“…The most important enzyme systems involved in drug metabolism are the Phase 1 mixed function oxidases. These systems are highly versatile and can adapt to metabolise a range of substrates; they are also important in determining the persistence of therapeutically used drugs in target species (Virkel et al 2006). Triclabendazole (TCBZ) is an example of an antiparasitic xenobiotic.…”

Erratum to: Inhibition of triclabendazole metabolism in vitro by ketoconazole increases disruption to the tegument of a triclabendazole-resistant isolate of Fasciola hepatica

“…A stock solution of ketoconazole was initially prepared at a concentration of 1× 10 −1 M in methanol. The concentration of KTZ used was chosen to be similar to those used in previous in vitro studies (Bourrie et al 1996;Zhang et al 2002;Dupuy et al 2003;Virkel et al 2006). The concentrations of TCBZ and TCBZ.…”