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ABSTRACT:Accurate prediction of pharmacokinetics (PK) parameters in humans from animal data is difficult for various reasons, including species differences. However, chimeric mice with humanized liver (PXB mice; urokinase-type plasminogen activator/severe combined immunodeficiency mice repopulated with approximately 80% human hepatocytes) have been developed. The expression levels and metabolic activities of cytochrome P450 (P450) and non-P450 enzymes in the livers of PXB mice are similar to those in humans. In this study, we examined the predictability for human PK parameters from data obtained in PXB mice. Elimination of selected drugs involves multiple metabolic pathways mediated not only by P450 but also by non-P450 enzymes, such as UDP-glucuronosyltransferase, sulfotransferase, and aldehyde oxidase in liver. ). Elimination half-life (t 1/2 ) after intravenous administration also showed a good correlation (r 2 ‫؍‬ 0.886, p ‫؍‬ 1.506 ؋ 10 ؊4) between humans and PXB mice. The rank order of CL and t 1/2 in human could be predicted at least, although it may not be possible to predict absolute values due to rather large prediction errors. Our results indicate that in vitro and in vivo experiments with PXB mice should be useful at least for semiquantitative prediction of the PK characteristics of candidate drugs in humans.

ABSTRACT:Aldehyde oxidase-mediated oxidation of N 1 -methylnicotinamide to N 1 -methyl-2-pyridine-5-carboxamide (2-PY) and N 1 -methyl-4-pyridone-5-carboxamide (4-PY) in chimeric mice constructed by transplanting human hepatocytes into urokinase-type plasminogen activator-transgenic severe combined immunodeficient mice was examined in vivo and in vitro. The activity in liver cytosol of chimeric mice with a high replacement index was approximately 4-fold higher than that in control mice. Furthermore, the oxidation products in control mice were 2-PY and 4-PY, whereas, in chimeric mice, the major product was 2-PY, as in humans. The aldehyde oxidase in chimeric mouse liver was confirmed to be of human type by immunoblotting analysis. The ratio of pyridones (2-PY/4-PY) excreted in the urine of chimeric mice was closer to that of humans than to that of control mice. Thus, the aldehyde oxidase in chimeric mice has human-type functional characteristics. Tateno et al. (2004) established chimeric mice in which the liver was almost completely repopulated with human hepatocytes. Such mice should be an excellent in vivo model for predicting drug metabolism, drug-drug interactions, drug induction, and inhibition of drug-metabolizing enzymes in humans. Katoh et al. (2004Katoh et al. ( , 2005b reported that the patterns of cytochrome P450 isoforms and phase II enzymes, such as UDP-glucuronosyltransferase, sulfotransferase, N-acetyltransferase, and glutathione S-transferase, in chimeric mice having a nearly 90% replacement rate with human hepatocytes were almost identical with those in human liver, and they used these mice to estimate the in vivo induction of cytochrome P450 enzymes in humans (Katoh et al., 2005a). Nishimura et al. (2005) reported that hepatocytes from chimeric mice with nearly completely humanized liver are useful for predictive screening of the induction potency of new drugs on drug-metabolizing enzymes in humans. We were interested in knowing whether drug metabolism by a cytosolic drugmetabolizing enzyme, aldehyde oxidase, in these mice is also similar to that in humans.Aldehyde oxidase (EC 1.2.3.1) contains flavin adenine dinucleotide, molybdenum, and iron-sulfur centers. It has been suggested to be relevant to the pathophysiology of a number of clinical disorders (Berger et al., 1995;Wright et al., 1995;Moriwaki et al., 1997). The enzyme in liver of various species catalyzes the oxidation of various aldehydes and nitrogenous heterocyclic xenobiotics, such as methotrexate and cyclophosphamide (Beedham, 1985;Kitamura et al., 2006), and also catalyzes the metabolism of physiological compounds, such as retinaldehyde (Huang and Ichikawa, 1994). However, there are marked species differences and strain differences of the enzyme activities for oxidative reaction in rats and mice (Beedham, 1985;Schofield et al., 2000;Kitamura et al., 2006;Sugihara et al., 2006). This has presented problems in preclinical studies. Many aldehyde oxidase substrates, such as methotrexate and phthalazine, show similar metabolic profiles ...

ABSTRACT:Prediction of human drug metabolism is important for drug development. Recently, the number of new drug candidates metabolized by not only cytochrome P450 (P450) but also non-P450 has been increasing. It is necessary to consider species differences in drug metabolism between humans and experimental animals. We examined species differences of drug metabolism, especially between humans and rats, for ibuprofen and (S)-naproxen as nonsteroidal anti-inflammatory drugs, which are metabolized by P450 and UDP-glucuronosyltransferase, sulfotransferase, and amino acid N-acyltransferase for taurine conjugation in liver, using human chimeric mice (h-PXB mice) repopulated with human hepatocytes and rat chimeric mice (r-PXB mice) transplanted with rat hepatocytes. We performed the direct comparison of excretory metabolites in urine between h-PXB mice and reported data for humans as well as between r-PXB mice and rats after administration of ibuprofen and (S)-naproxen. Good agreement for urinary metabolites (percentage of dose) was observed not only between humans and h-PXB mice but also between rats and r-PXB mice. Therefore, the metabolic profiles in humans and rats reflected those in h-PXB mice and r-PXB mice. Our results indicated that h-PXB mice should be helpful for predicting the quantitative metabolic profiles of drugs mediated by P450 and non-P450 in liver, and r-PXB mice should be helpful for evaluation of species differences in these metabolic enzymes.