Biotransformation of Dimetridazole by Primary Cultures of Pig Hepatocytes

Abstract

Monolayer cultures of pig hepatocytes were used to investigate the role of the liver in the biotransformation of the veterinary drug dimetridazole (1,2-dimethyl-5-nitroimidazole). 14C-Labeled dimetridazole (DMZ) was primarily hydroxylated to 1-methyl-2-hydroxymethyl-5-nitroimidazole (up to 90%) and to a minor extent N-demethylated to 2-methyl-(4,5)-nitroimidazole (6−10%). Prolonged incubation with the parent drug but also the 2-hydroxymethyl metabolite resulted in the formation of two other minor metabolites. The major one of these was identified as the glucuronide of the 2-hydroxymethyl metabolite, based on its molecular mass and the succesful hydrolysis with β-glucuronidase. The second showed a molecular mass of 144 and is hypothesized to be 2-hydroxymethyl-5-nitroimidazole. No evidence was obtained for the formation of a cysteine or glutathione conjugate involved in the detoxification of reactive intermediates. In addition to free metabolites, there was a time-related formation of protein-bound metabolites up to a maximum of 30 pmol/mg of protein after exposure to 50 μM DMZ for 48 h. In general, these metabolites accounted for 0.06−0.15% of the metabolized DMZ. Unextractable metabolites were also observed after incubation of cells with the 2-hydroxymethyl and 1-desmethyl metabolites. It is concluded that the 1-desmethyl and, in particular, the 2-hydroxymethyl metabolite are the major metabolites formed by pig hepatocytes. These compounds are thus far the only metabolites identified in vivo, but together with the parent compound, they accounted for only a small part (<5%) of the excreted drug. Therefore, the site of formation of the majority of the unknown in vivo metabolites may be extrahepatic, and complimentary models are needed to investigate this hypothesis. Keywords: Pig hepatocytes; dimetridazole; nitroimidazoles; bound residues

Identification of metabolites of the anabolic steroid methandienone formed by bovine hepatocytes in vitro†

“…The aim of this work was to investigate the in vitro metabolism using isolated calf hepatocytes to predict the types of metabolite possibly excreted in the urine of calves. The beneficial use of isolated hepatocytes from food producing animals for studying the biotransformation of veterinary drugs and growth-promoting agents has been demonstrated by Hoogenboom et al [9][10][11] To achieve this goal, the in vitro biotransformation was carried out over a period of 24 h. Throughout the time interval samples were taken and analysed by GC-MS with two different ionisation techniques, i.e. electron impact and chemical ionisation.…”

Quantitative structure activity relationships for the electron transfer reactions ofAnabaenaPCC 7119 ferredoxin‐NADP+oxidoreductase with nitrobenzene and nitrobenzimidazolone derivatives: mechanistic implications

“…In addition to these compounds, nitroaromatics can undergo a single electron reduction by ferredoxin‐NADP + oxidoreductase [14,18]. Nitroaromatic compounds are widely used as industrial intermediate reagents in the production of dyes, rubbers, explosives and pharmaceuticals or are used as agrochemicals such as pesticides or veterinary drugs [19–21]. Attempts to correlate and quantitatively understand the role of ferredoxin‐NADP + oxidoreductase in the reduction and bioactivation of nitroaromatics were hampered by the relatively low reactivity of the mononitroaromatic substrates studied so far.…”

Quantitative structure activity relationships for the conversion of nitrobenzimidazolones and nitrobenzimidazoles by DT‐diaphorase: implications for the kinetic mechanism

“…In addition to quinones, nitroaromatics can be reduced by DT‐diaphorase. Nitroaromatic compounds are widely used as industrial intermediate reagents in the production of dyes, rubbers and pharmaceuticals or are used as agrochemicals such as pesticides or veterinary drugs [9–11]. Although nitroaromatics can be reduced by DT‐diaphorase, the activity of the enzyme with nitroaromatics is considerably lower than that with quinones [2, 12–14].…”