The metabolic fate of [¹⁴C]-fenclozic acid in the hepatic reductase null (HRN) mouse

Abstract

1. The distribution, metabolism, excretion and hepatic effects of fenclozic acid were investigated following a single oral dose of 10 mg/kg to hepatic reductase null (HRN) mice. 2. The majority of the [(14)C]-fenclozic acid was eliminated via the urine/aqueous cage wash, (55%) with a smaller portion excreted in the faeces, (5%). The total recovery of radioactivity in the excreta over the 72 h period studied was ca. 60%. 3. Metabolism of fenclozic acid in the HRN mice was entirely to the carboxylic acid function and was dominated by amino acid conjugation to glycine and taurine, with lesser amounts of an acyl glucuronide. 4. Whole body autoradiography of mice showed general distribution into all tissues except the brain. Radioactivity was still detectable in the kidney and liver of the HRN mice at 72 h post-dose. Covalent binding studies showed evidence of binding to kidney, liver and plasma proteins however, the degree of binding was less than 50 pmol equiv/mg protein for all tissues. 5. The HRN mouse appears to be a useful in vivo model for the study of the Phase II conjugation metabolism of fenclozic acid in the absence of hepatic cytochrome P450-related oxidative metabolism.

Acute liver effects, disposition and metabolic fate of [14C]-fenclozic acid following oral administration to normal and bile-cannulated male C57BL/6J mice

“…The degree of inflammatory cell infiltration was minimal and related to the regions of centrilobular necrosis alone. Interestingly, in a previous study when fenclozic acid was administered to HRN mice at 10 mg/kg (as described in Pickup et al 2014), where hepatic cytochrome P450s are non-functional, and there was no evidence of centrilobular necrosis, or indeed any other effect on the liver (see Fig. 1).…”

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Fig. 1Photomicrographs of representative samples of the livers from wild type (WT) and hepatic cytochrome P450 reductase null (HRN) mice treated with a single 10 mg/kg oral dose of [ 14 C] fenclozic acid (see Pickup et al 2014). a , b  HRN mice dosed with vehicle control, c , d  HRN mice dosed with [ 14 C]-fenclozic acid, and e , g  WT mice dosed with [ 14 C]-fenclozic acid.

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“…18, 40 and 10 pg/mg protein detected for liver, kidney and plasma, respectively (Table 2), which was slightly higher than that observed for these tissues in HRN mice given an equivalent dose in our previous study (ca. 13, 26 and 3 pg/mg protein for liver, kidney and plasma, respectively) (Pickup et al 2014). Interestingly, these quantities of CVB were approximately an order of magnitude greater than those observed for the idiosyncratic liver toxin diclofenac (see Boelsterli 2003) dosed at 10 mg/kg to C57BLl/6J mice where the extent of covalent binding (at 24 h) were ca.…”

“…UHPLC analysis with radioactivity and mass spectrometric detection revealed the presence of a number of drug-related peaks corresponding to fenclozic acid itself, the acyl glucuronide, glycine and taurine conjugates ( M10, M14 and M13, respectively) and an ether glucuronide ( M20 ) (Supplementary data Figure S1A). The mass spectra for the acyl conjugates were previously described following studies in HRN mice and the rat (Pickup et al 2014; Martin et al 2014). Whilst urine represented the major route for the elimination of [ 14 C]-labelled fenclozic acid-related material ca.…”

“…Indeed, although potentially reactive acyl glucuronides are also formed during the metabolism of fenclozic acid in vitro covalent binding in microsomal systems supplemented with UDPGA was lower than systems optimised for oxidative metabolism. Further studies in the HRN™ (hepatic reductase null) mouse, where hepatic CYP450s are inactive and the drug is essentially subject to biotransformation via acyl conjugation to glucuronic acid and amino acid conjugates, showed only low levels of hepatic covalent binding (Pickup et al 2014). More recently, studies in bile duct-cannulated rats showed the presence of metabolites that were clearly derived from reactive metabolites detoxified via reaction with glutathione (Martin et al 2014).…”