Abstract
The enantioselective sulfoxidation of the prochiral anthelmintic compounds albendazole (ABZ) and fenbendazole (FBZ) was investigated in liver, lung and small intestinal microsomes obtained from healthy sheep and cattle. The microsomal fractions were incubated with a 40 μM concentration of either ABZ or FBZ. Inhibition of the flavin-containing monooxygenase (FMO) system was carried out by preincubation with 100 μM methimazole (MTZ) either with or without heat pretreatment (2 min at 50°C). ABZ and FBZ were metabolized to the (+) and (-) enantiomers of their sulfoxide metabolites, named albendazole sulfoxide (ABZSO) and oxfendazole (OFZ), respectively. ABZ sulfoxidation rates were higher (p < 0.001) than those observed for FBZ. The FMO-mediated liver sulfoxidation of ABZ was enantioselective (100%) toward the (+) ABZSO production in both species. Liver sulfoxidation of FBZ by FMO was also enantioselective toward (+) OFZ (sheep = 65%; cattle = 79%). Cytochrome P450 was found to be mainly involved in the production of (-) ABZSO in the liver. MTZ did not affect the sulfoxidation of ABZ by lung microsomes, which may indicate that FMO is not involved in the production of ABZSO in this tissue. A significant (p < 0.05) inhibition of (-) ABZSO production by liver microsomes was observed after ABZ incubation in the presence of erythromycin (cattle = 21%) and ketoconazole (sheep = 36%). Both CYP3A substrates induced a reduction in the production of (-) ABZSO (sheep = 67–78%, cattle = 50–78%) by lung microsomes. Overall, the results reported here contribute to the identification of the metabolic pathways involved in the biotransformation of benzimidazole anthelmintics extensively used for parasite control in ruminants.
Footnotes
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↵1 Abbreviations used are: BZD, benzimidazole; P450, cytochrome P450; ABZ, albendazole (methyl-[(5-propylthio)-1H-benzimidazol-2-yl]carbamate); ABZSO, albendazole sulfoxide; ABZSO2, albendazole sulfone; FBZ, fenbendazole (methyl-[(5-phenylthio)-1H-benzimidazol-2-yl]carbamate); OFZ, oxfendazole; FBZSO2, fenbendazole sulfone; MTZ, methimazole; ETM, erythromycin; KTZ, ketoconazole; DAK, N-deacetyl ketoconazole; HPLC, high-performance liquid chromatography; FMO, flavin-containing monooxygenase; GI, gastrointestinal.
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Research at the Laboratorio de Farmacología is supported by Consejo Nacional de Investigaciones Cientificas y Técnicas (Argentina), Universidad Nacional del Centro and Agencia Nacional de Promoción Científica y Tecnológica (PICT 08-07277) (all from Argentina).
- Received October 14, 2003.
- Accepted January 29, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
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