Comparative Hepatic and Extrahepatic Enantioselective Sulfoxidation of Albendazole and Fenbendazole in Sheep and Cattle

Abstract

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 M concentration of either ABZ or FBZ. Inhibition of the flavin-containing monooxygenase (FMO) system was carried out by preincubation with 100 M 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.Livestock animals are exposed to a variety of xenobiotic agents (i.e., veterinary drugs, feed-additives, pesticides, pollutants, etc.) during their production cycles. These compounds are likely to be metabolized by different enzymatic systems from both hepatic and extrahepatic tissues. The metabolic activity of the flavin-containing monooxygenase (FMO) and cytochrome P450 (P450) systems plays a major role in determining the persistence of therapeutically used drugs in target species, which may additionally impose a risk to the consumer as a consequence of the permanence of drug residue levels in edible tissues. Metabolic interactions with either the FMO or P450 enzymatic systems may drastically affect the disposition kinetics of different drugs used in animal production, which will have a relevant impact on the pattern of drug/metabolite residues in edible tissues, a major concern for public health and consumer safety.Benzimidazole (BZD 1 ) and pro-BZD anthelmintics are extensively metabolized in domestic animals and humans. Their metabolic pattern and the resultant pharmacokinetic behavior are relevant in the attainment of high and sustained concentrations of pharmacologically active drug/metabolites at the target parasite . Albendazole (ABZ; methyl-[(5-propylthio)-1H-benzimidazol-2-yl] carba...

Pharmacokinetics, Metabolism, and Excretion of the Antiviral Drug Arbidol in Humans

“…It was reported that the major monooxygenases that catalyze the formation of aliphatic sulfoxides are the P450s and FMOs (16)(17)(18)(19)(20)(21). Identification of the human P450 and FMO enzymes Remaining activity % is metabolic activity in the presence of inhibitor divided by metabolic activity in microsomes.…”

Mammalian flavin-containing monooxygenases: structure/function, genetic polymorphisms and role in drug metabolism

“…Unfortunately, antibodies directed toward FMOs typically inhibit catalytic activity weakly, if at all, and the only chemical inhibitors are competitive substrates. The most commonly used alternative substrate to inhibit FMO in vitro (Mani et al, 1993;Narimatsu et al, 1999;Rawden et al, 2000;Pike et al, 2001;Attar et al, 2003;Wynalda et al, 2003;Virkel et al, 2004) and in vivo (Ruse & Waring, 1991;Nace et al, 1997;Wang et al, 2000) has been methimazole (see next section for further discussion of methimazole). FMO activity is unaffected by non-ionic detergent or carbon monoxide, but most FMOs are readily inhibited by short incubations at temperatures of 45-50 °C.…”

“…FMO readily S-oxygenates simple sulfides such as methyl-, ethyl-, ethyl methyl, 4-chlorophenyl methyl, and diphenyl sulfides Nnane & Damani, 2003a. Sulfide-containing drugs, for which FMO is active in S-oxygenation to sulfoxides, include cimetidine, rantidine, thioridazine, 7-(1,3-thiazolidin-2-methyl) theophylline, (+)-cis-3,5-dimethyl-2-(3-pyridyl)-thiazolidin-4-one, sulindac sulfide, clindamycin, albendazole, and fenbendazole (Eriksson & Bostrom, 1988;Grosa et al, 1992;Cashman et al, 1993b;Lanusse et al, 1993;Moroni et al, 1995a;Nunoya et al, 1995;Hamman et al, 2000;Rawden et al, 2000;Nnane & Damani, 2003aWynalda et al, 2003;Virkel et al, 2004). Although not employed as a therapeutic drug, the cyclic sulfide tetrahydrothiophene is the best substrate to date, as evidenced by submicromolar K m values, found by us with FMO.…”

CYP2J2 and CYP2C19 Are the Major Enzymes Responsible for Metabolism of Albendazole and Fenbendazole in Human Liver Microsomes and Recombinant P450 Assay Systems

“…Their metabolic patterns and the resultant pharmacokinetic behaviors are relevant in the attainment of high and sustained concentrations of pharmacologically active drugs/metabolites at the target parasite (8). Evidence from microsomal investigations in a number of species suggests that CYP3A4 and flavin-containing monooxygenase (FMO) are major enzymes responsible for the formation of sulfoxide metabolites from albendazole (4,9,10) and fenbendazole (4,5) (Fig. 1).…”

“…Benzimidazole anthelmintics are extensively metabolized in domestic animals and humans. Animal and microsomal incubation studies have demonstrated rapid conversion of albendazole and fenbendazole to a sulfoxide metabolite and subsequently a sulfone metabolite (2)(3)(4)(5)(6). Sulfoxide metabolites are responsible for the systemic biological activity of benzimidazole drugs (7).…”