Small minipigs (Bland name, Micromini Pig; registered as a novel variety of pig in the Japanese Ministry of Agriculture, Forestry and Fisheries) were developed with the aim of non-clinical pharmacological/toxicological use. They were principally mated with<10 kg body weight at 7 months-old resulting in good handling. Cytochrome P450 (P450)-and flavin-containing monooxygenases (FMO)-dependent drug oxidation activity of liver microsomes prepared from male Microminipigs (8 months-old) was compared with that for pooled dogs, monkeys, and humans. High P450 2D-dependent bufuralol 1'-hydroxylation and FMO-dependent benzydamine N-oxygenation activity was observed in liver microsomes from Microminipigs. Typical P450 1A, 2B, 2C, 2E, and 3A-dependent drug oxidation activity was also seen in Microminipigs. However, occasional differences might give undetected low P450 2A-dependent coumarin 7-hydroxylation in Microminipigs at 8-months-old, in contrast to liver microsomes from one 10-days-old Microminipis and commercially available pooled minipigs which had low but detectable coumarin 7-hydroxylation activity. The present results suggest that there is some overlap in Microminipig and human P450 substrate specificity. These findings should provide important information for greater understanding of drug metabolism in Microminipigs, as an experimental animal model for non-clinical use.
The present study defined a simplified physiologically based pharmacokinetic (PBPK) model for nicotine and its primary metabolite cotinine in humans, based on metabolic parameters determined in vitro using relevant liver microsomes, coefficients derived in silico, physiological parameters derived from the literature, and an established rat PBPK model. The model consists of an absorption compartment, a metabolizing compartment, and a central compartment for nicotine and three equivalent compartments for cotinine. Evaluation of a rat model was performed by making comparisons with predicted concentrations in blood and in vivo experimental pharmacokinetic values obtained from rats after oral treatment with nicotine (1.0 mg/kg, a no-observed-adverseeffect level) for 14 days. Elimination rates of nicotine in vitro were established from data from rat liver microsomes and from human pooled liver microsomes. Human biomonitoring data (17 ng nicotine and 150 ng cotinine per mL plasma 1 h after smoking) from pooled five male Japanese smokers (daily intake of 43 mg nicotine by smoking) revealed that these blood concentrations could be calculated using a human PBPK model. These results indicate that a simplified PBPK model for nicotine/cotinine is useful for a forward dosimetry approach in humans and for estimating blood concentrations of other related compounds resulting from exposure to low chemical doses.
The present study defined a simplified physiologically based pharmacokinetic (PBPK) model for dichlorodiphenyltrichloroethane [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane, DDT] in humans based on metabolic parameters determined in vitro using relevant liver microsomes, coefficients derived in silico, physiological parameters derived from the literature, and an established rat PBPK model. The model consists of an absorption compartment, a metabolizing liver compartment, and a central compartment for DDT. Evaluation of the rat model was performed by making comparisons between predicted concentrations in blood and in vivo experimental pharmacokinetic values obtained from rats after daily oral treatment with DDT (10 mg/kg, a no-observed-adverse-effect level) for 14 days. Elimination rates of DDT in vitro were established from data from rat liver microsomes and from pooled human liver microsomes. The ratio of intrinsic clearance values of DDT based on rat in vivo and rat in vitro experiments was used as the scaling factor for estimating in vivo hepatic intrinsic clearance in humans in the final human PBPK model. These results indicate that a simplified PBPK model for DDT is useful for a forward dosimetry approach in rats and/or humans and for estimating blood concentrations of other related compounds resulting from exposure to low chemical doses.
The present study defined a simplified physiologically based pharmacokinetic (PBPK) model for 1,4-dioxane in humans based on in vitro metabolic parameters determined using relevant liver microsomes, coefficients derived in silico, physiological parameters derived from the literature, and a developed PBPK model in rats. The model consists of a chemical absorption compartment, a metabolizing compartment, and a central compartment for 1,4-dioxane. Evaluation of the rat model was performed by comparisons with experimental pharmacokinetic values from blood and urine obtained from rats in vivo after daily oral treatment with 1,4-dioxane (500 mg/kg, a noobserved-adverse-effect level) for 14 days. Elimination rates of 1,4-dioxane in vitro were established using data from rat liver microsomes and from pooled human liver microsomes. 1,4-Dioxane was expected to be absorbed and cleared rapidly from the body in silico, as was the case for rats confirmed experimentally in vivo with repeated low-dose treatments. These results indicate that the simplified PBPK model for 1,4-dioxane is useful for a forward dosimetry approach in humans. This model may also be useful for simulating blood concentrations of other related compounds resulting from exposure to low chemical doses.
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