Human plasma and liver concentrations of styrene estimated by combining a simple physiologically based pharmacokinetic model with rodent data.

Long-term exposure to certain volatile organic compounds is a significant public health concern. A variety of food containers and drinking cups prepared from polystyrene or polystyrene-related plastics could contain styrene monomer. In the current study, the concentrations of styrene in plasma and liver were surveyed and determined after oral doses of 25 mg/kg to rats and 200 mg/kg to control and humanized-liver mice. Plasma concentrations of styrene in rats were still detected 2 hr after 10-25 mg/kg oral doses. In contrast, after an order of magnitude higher oral dose of styrene (200 mg/kg) to mice, styrene in mouse plasma was rapidly cleared within 15 min to the limit-of-detection level. However, unmetabolized styrene was detected in mouse liver 24 hr after oral treatment. A simple physiologically based pharmacokinetic (PBPK) model capable of estimating blood and liver concentrations of styrene was established for rats. A human PBPK model was then set up for styrene by using the same intrinsic hepatic clearances in rats and humans and by applying allometric scaling to rat parameters obtained from the plasma concentrations of styrene in rats. By reverse dosimetry analysis (from concentrations to doses), we found that the 95th percentile values of styrene concentrations (0.132 ng/mL) reported in United States biomonitoring data of more than 1000 human blood samples may imply exposure to repeated oral doses of styrene of 2.89 µg/kg/day. These results suggest that styrene biomonitoring data in human blood samples imply exposures roughly similar to or lower than the established tolerable daily intake level of 7.7 µg/kg/day.

Association of pharmacokinetic profiles of lenalidomide in human plasma simulated using pharmacokinetic data in humanized-liver mice with liver toxicity detected by human serum albumin RNA.

Lenalidomide has been shown to be potentially teratogenic in thalidomide-sensitive animal species. Screening for thalidomide analogs devoid of teratogenicity/toxicity-attributable to drug metabolism and disposition, but having immunomodulatory properties-is a strategic pathway towards development of new anticancer drugs. Plasma concentrations of lenalidomide were investigated in immunodeficient control and humanized-liver mice following oral administration of lenalidomide (50 mg/kg). Plasma concentrations of lenalidomide (1-2 hr after administration) were slightly but significantly higher in humanized-liver mice than in control mice (p < 0.05). Human albumin mRNA, a liver-specific toxicity marker, was found in the blood of humanized-liver mice 24 hr after lenalidomide administration. Simulations of human plasma concentrations of lenalidomide were achieved with simplified physiologically-based pharmacokinetic models in control and humanized-liver mice or by the direct fitting analysis of reported human data, in accordance with reported lenalidomide concentrations after low dose administration in humans. The results indicate that pharmacokinetic profiles of lenalidomide, a compound resulting from introducing one aromatic amino group into thalidomide and removing one keto group, resulted in less species variation in in vivo pharmacokinetics in control and humanized-liver mice and that immunodeficient humanized-liver mice can serve as experimental model animals for human liver injury in drug development at high doses, with human albumin RNA analysis in plasma.

Human plasma concentrations of trimethylamine N-oxide extrapolated using pharmacokinetic modeling based on metabolic profiles of deuterium-labeled trimethylamine in humanized-liver mice.

Medicinal carnitine-derived and dietary-derived malodorous trimethylamine and its non-malodorous metabolite trimethylamine N-oxide were historically regarded as nontoxic. Clinical and toxicological interest has recently arisen because of their potential association with atherosclerosis. We previously reported a human physiologically based pharmacokinetic (PBPK) model for trimethylamine and its primary metabolite, trimethylamine N-oxide, based on reported rat trimethylamine pharmacokinetics. However, rats are poor metabolizers with respect to trimethylamine N-oxygenation, and this species difference was investigated in vitro using substrate depletion rates in rat and human liver microsomes. The current study investigated the pharmacokinetics of deuterium-labeled trimethylamine orally administered to immunodeficient humanized-liver mice transplanted with commercially available human hepatocytes. Trimethylamine N-oxide was extensively formed in vivo in humanized-liver mice, but not in control mice. The experimental pharmacokinetic data of deuterium-labeled trimethylamine and its N-oxide in humanized-liver mice were scaled up for application to a human PBPK model. The human plasma concentration curves generated by the resulting simple PBPK model were consistent with concentrations in humans reported in the literature. The model can also simulate human plasma levels of trimethylamine and trimethylamine N-oxide during treatment with the prescription medicine L-carnitine and in trimethylamine loading tests. The predicted plasma levels were in the ranges that occur under the consumption of daily dietary foodstuff; such levels are associated with few toxicological impacts. The present PBPK model for trimethylamine and trimethylamine N-oxide could estimate daily doses by both forward and reverse dosimetry and could facilitate risk assessment in humans.

In vivo and in vitro diclofenac 5-hydroxylation mediated primarily by cytochrome P450 3A enzymes in common marmoset livers genotyped for P450 2C19 variants.

Common marmosets (Callithrix jacchus) are potentially useful nonhuman primate models for preclinical studies. An anti-inflammatory drug, diclofenac is reportedly metabolized mainly by human cytochrome P450 (P450) 2C9 to 4'-hydroxydiclofenac and minorly by P450 3A4 to 5-hydroxydiclofenac that leads to reactive intermediates. In this study, in vivo pharmacokinetics in six marmosets and in vitro metabolism in nine marmoset liver microsomes were analyzed using diclofenac to evaluate marmosets as preclinical drug metabolism models. In wild-type marmosets genotyped for P450 2C19 p.[(Phe7Leu; Ser254Leu; Ile469Thr)], plasma levels of 5-hydroxydiclofenac and 4'-hydroxydiclofenac were roughly similar, but the homozygotes showed approximately three-times higher plasma levels of 5-hydroxydiclofenac than those of 4'-hydroxydiclofenac after oral administrations of diclofenac (50 mg/kg). Nine marmoset liver microsomes catalyzed mainly diclofenac 5-hydroxylation with no significant effects of the the P450 2C19 genotype, and partly diclofenac 4'-hydroxylation that depended on the P450 2C19 genotype, at substrate concentrations of 10 µM and 100 µM. Both Michaels-Menten constant Km values for diclofenac 4'-hydroxylation in human and marmoset liver microsomes were ∼30 µM and those for diclofenac 5-hydroxylation were ∼120 µM. Ketoconazole significantly suppressed only diclofenac 5-hydroxylation in marmoset or human liver microsomes at 0.030 µM, indicating main contribution of P450 3A enzymes, which were found to be P450 3A5/90 using recombinant marmoset P450 3A enzymes. These results suggest that marmosets would be a functional animal model for in vivo and in vitro metabolites likely generated via arene oxide intermediates of diclofenac by P450 3A enzymes in humans, primarily because marmosets lack the ortholog of human P450 2C9.

R-warfarin clearances from plasma associated with polymorphic cytochrome P450 2C19 and simulated by individual physiologically based pharmacokinetic models for 11 cynomolgus monkeys.

1. Cynomolgus monkey cytochrome P450 2C19 (formerly known as P450 2C75), homologous to human P450 2C19, has been identified as R-warfarin 7-hydroxylase. In this study, simulations of R-warfarin clearance in individual cynomolgus monkeys genotyped for P450 2C19 p.[(Phe100Asn; Ala103Val; Ile112Leu)] were performed using individual simplified physiologically based pharmacokinetic (PBPK) modeling. 2. Pharmacokinetic parameters and absorption rate constants, volumes of the systemic circulation, and hepatic intrinsic clearances for individual PBPK models were estimated for eleven cynomolgus monkeys. 3. One-way ANOVA revealed significant effects of the genotype (p < 0.01) on the observed elimination half-lives and areas under the curves of R-warfarin among the homozygous mutant, heterozygous mutant, and wild-type groups. R-Warfarin clearances in individual cynomolgus monkeys genotyped for P450 2C19 were simulated by simplified PBPK modeling. The modeled hepatic intrinsic clearances were significantly associated with the P450 2C19 genotypes. The liver microsomal elimination rates of R-warfarin for individual animals after in vivo administration showed significant reductions associated with the genotype (p < 0.01). 4. This study provides important information to help simulate clearances of R-warfarin and related medicines associated with polymorphic P450 2C19 in individual cynomolgus monkeys, thereby facilitating calculation of the fraction of hepatic clearance.

Effects of aging and rifampicin pretreatment on the pharmacokinetics of human cytochrome P450 probes caffeine, warfarin, omeprazole, metoprolol and midazolam in common marmosets genotyped for cytochrome P450 2C19.

1. The pharmacokinetics were investigated for human cytochrome P450 probes after single intravenous and oral administrations of 0.20 and 1.0 mg/kg, respectively, of caffeine, warfarin, omeprazole, metoprolol and midazolam to aged (10-14 years old, n = 4) or rifampicin-treated/young (3 years old, n = 3) male common marmosets all genotyped as heterozygous for a cytochrome P450 2C19 variant. 2. Slopes of the plasma concentration-time curves after intravenous administration of warfarin and midazolam were slightly, but significantly (two-way analysis of variance), decreased in aged marmosets compared with young marmosets. The mean hepatic clearances determined by in silico fitting for individual pharmacokinetic models of warfarin and midazolam in the aged group were, respectively, 23% and 56% smaller than those for the young group. 3. Significantly enhanced plasma clearances of caffeine, warfarin, omeprazole and midazolam were evident in young marmosets pretreated with rifampicin (25 mg/kg daily for 4 days). Two- to three-fold increases in hepatic intrinsic clearance values were observed in the individual pharmacokinetic models. 4. The in vivo dispositions of multiple simultaneously administered drugs in old, young and P450-enzyme-induced marmosets were elucidated. The results suggest that common marmosets could be experimental models for aged, induced or polymorphic P450 enzymes in P450-dependent drug metabolism studies.

Association with polymorphic marmoset cytochrome P450 2C19 of in vivo hepatic clearances of chirally separated R-omeprazole and S-warfarin using individual marmoset physiologically based pharmacokinetic models.

1. Simulated clearances of R-warfarin and efavirenz were recently reported for individual cynomolgus monkeys genotyped for cytochrome P450 2C19 and 2C9, respectively. To expand and verify this modeling procedure, simulations of R/S-omeprazole and R/S-warfarin clearances after oral administrations in individual marmosets were performed using individual simplified physiologically based pharmacokinetic (PBPK) modeling consisting of gut, liver and central compartments. 2. Pharmacokinetics of R/S-omeprazole were chirally determined using the previously reported plasma microsamples in this study. The areas under the plasma concentration/time curves (AUC) of R-omeprazole and S-warfarin, but not S-omeprazole and R-warfarin, after oral administrations in the P450 2C19 homozygous mutant group were significantly higher than those in the wild-type group. These modeled hepatic intrinsic clearances were also significantly associated with the marmoset P450 2C19 genotypes. Other parameter values, e.g. absorption rate constants or systemic circulation volumes, were not likely determining factors. 3. The reported individual AUC values measured in 4-6 marmosets after oral R-omeprazole and S-warfarin administrations were significantly correlated with the AUC values predicted using the PBPK models after virtual administrations. 4. This study indicates that clearances of R-omeprazole, S-warfarin and related medicines associated with polymorphic P450 2C19 in individual marmosets can be simulated using simplified individual PBPK models.

Efavirenz clearances in vitro and in vivo in six cynomolgus monkeys associated with polymorphic cytochrome P450 2C9 and simulated by individual physiologically based pharmacokinetic models.

Cynomolgus monkey cytochrome P450 2C9 (formerly known as P450 2C43) variation was reportedly associated with metabolic clearance of the antiretroviral drug efavirenz in vivo (in three wild-type, one heterozygote and two homozygote animals), being unlikely in the case of human P450 2B6-dependent efavirenz clearance. In this study, the liver microsomal elimination rates of efavirenz for the same individual animals previously treated with intravenous/oral administrations of efavirenz showed significant reductions associated with the P450 2C9 p.[(I112L)] genotype (p < 0.05). Simulations of efavirenz clearance after oral administrations in individual cynomolgus monkeys were performed using individual simplified physiologically based pharmacokinetic (PBPK) modeling consisting of gut, liver and central compartments. The modeled hepatic intrinsic clearances were also significantly associated with the P450 2C9 genotypes, however, absorption rate constants or volumes of the systemic circulation were not likely determining factors for the individual efavirenz clearance variations in the six cynomolgus monkeys. This study provides important information to help simulate the clearances of efavirenz and related medicines associated with polymorphic P450 2C9 in individual cynomolgus monkeys, thereby facilitating the calculation of the fraction of liver microsomal clearance for estimating in vivo drug clearance with simplified PBPK modeling.