In vitro human tissue models in risk assessment: report of a consensus-building workshop.

Advances in the technology of human cell and tissue culture and the increasing availability of human tissue for laboratory studies have led to the increased use of in vitro human tissue models in toxicology and pharmacodynamics studies and in quantitative modeling of metabolism, pharmacokinetic behavior, and transport. In recognition of the potential importance of such models in toxicological risk assessment, the Society of Toxicology sponsored a workshop to evaluate the current status of human cell and tissue models and to develop consensus recommendations on the use of such models to improve the scientific basis of risk assessment. This report summarizes the evaluation by invited experts and workshop attendees of the current status of such models for prediction of human metabolism and identification of drug-drug interactions, prediction of human toxicities, and quantitative modeling of pharmacokinetic and pharmaco-toxicodynamic behavior. Consensus recommendations for the application and improvement of current models are presented.     

A physiologically based pharmacokinetic model of vitamin D

Despite the plethora of studies discussing the benefits of vitamin D on physiological functioning, few mathematical models of vitamin D predict the response of the body on low‐concentration supplementation of vitamin D under sunlight‐restricted conditions. This study developed a physiologically based pharmacokinetic (PBPK) model utilizing published human data on the metabolic cascade of orally derived, low‐concentration (placebo, 5 μg and 10 μg) supplementation of vitamin D over the course of 28 days in the absence of sunlight. Vitamin D and its metabolites are highly lipophilic and binding assays of these compounds in serum may not account for binding by lipids and additional proteins. To compensate for the additional bound amounts, this study allowed the effective adipose–plasma partition coefficient to vary dynamically with the concentration of each compound in serum utilizing the Hill equation for binding. Through incorporating the optimized parameters with the adipose partition coefficient adaptation to the PBPK model, this study was able to fit serum concentration data for circulating vitamin D at all three supplementation concentrations within confidence intervals of the data. Copyright © 2017 John Wiley & Sons, Ltd.     

The Irrelevance of In Vitro Dissolution in Setting Product Specifications for Drugs Like Dextromethorphan That are Subject to Lysosomal Trapping

The purpose of the present study was to develop a physiologically based pharmacokinetic model for dextromethorphan (DEX) and its metabolites in extensive and poor metabolizers. The model was used to study the influence of dissolution rates on the sensitivity of maximum plasma concentration and area under the concentration-time curve for immediate release formulations. Simulation of in vitro cellular transwell permeability was used to confirm lysosomal trapping. GastroPlus? was used to build a mechanistic absorption and physiologically based pharmacokinetic model of DEX. The model simulations were conducted with and without lysosomal trapping. The simulated results matched well with observed data only when lysosomal trapping was included. The model shows that DEX is rapidly absorbed into the enterocytes, but DEX and its metabolites only appear slowly in the portal vein and plasma, presumably due to lysosomal trapping. For this class of drug, the rate of in vitro and in vivo dissolution is not a sensitive factor in determining bioequivalence. This study shows that dissolution and the rate of absorption into the enterocytes are clinically irrelevant for the performance of DEX immediate release product. An understanding of the entire underlying mechanistic processes of drug disposition is needed to define clinically relevant product specifications for DEX.     

消炎汤调节肠道微生态改善大鼠慢性盆腔炎的研究

目的探讨消炎汤通过调节肠道微生态的变化对慢性盆腔炎大鼠的治疗作用。方法采用子宫内注射苯酚胶浆建立大鼠慢性盆腔炎模型,造模2周后ig消炎汤5、10、20 g/kg,连续14 d,观察大鼠子宫内膜形态,qPCR检测子宫组织中细胞间黏附分子(ICAM-1mRNA)表达情况,并采用16SrRNA高通道测序观察慢性盆腔炎大鼠肠道菌群的构成和比例。结果各给药组中充血水肿现象少见,且炎症浸润程度好于妇科千金片组。与模型组相比,消炎汤各剂量组子宫组织中ICAM-1mRNA的表达均有下调,尤以消炎汤20 g/kg组为甚(P0.01)。与模型组相比,消炎汤20 g/kg组Simpson指数显著上升(P0.05)。给予消炎汤治疗后肠道菌群多样性、丰度均得到一定程度改善,但未见统计学差异。与模型组相比,消炎汤10、20g/kg组乳杆菌、梭状芽孢杆菌OUT比例有不同程度升高。治疗后,消炎汤20、10g/kg组OUT比例较模型组明显下降。结论消炎汤能够明显改善慢性盆腔炎大鼠子宫的炎症程度,有效减少黏连的发生,作用机制与其调节肠道微生态影响雌激素代谢有关。     

A physiologically based pharmacokinetic model for methyl tert-butyl ether in humans: implementing sensitivity and variability analyses.

Methyl tert-butyl ether (MTBE) is added to gasoline to reduce carbon monoxide and ozone precursors from automobile emissions. The objectives of this study were to verify the ability of a physiologically based pharmacokinetic (PBPK) model to predict MTBE blood levels in humans and to investigate the effect of variability in the metabolism of MTBE and its influence on the predicted MTBE blood levels. The model structure for MTBE was flow-limited and had six essential compartments: lung, liver, rapidly perfused tissues, slowly perfused tissues, fat, and kidney. In this model, two pathways of metabolism are described to occur in the liver by Michaelis-Menten kinetics. Metabolic rate constants were measured in vitro using human liver microsomes and extrapolated to in vivo whole-body metabolism. Model predictions were compared with data on blood levels of MTBE taken from humans during and after a 1-h inhalation exposure to 1.7 ppm MTBE and after 4-h inhalation exposures to 4 or 40 ppm MTBE. The PBPK model accurately predicted MTBE pharmacokinetics at the high and low MTBE exposure concentrations for all time points. At the intermediate MTBE exposure concentration, however, the model underpredicted early time points while adequately predicting later time points. Results of the sensitivity analysis indicated that the influence of metabolic parameters on model output was dependent on MTBE exposure concentration. Subsequent variability analysis indicated that there was more variability in the actual measured MTBE blood levels than in the blood levels predicted by the PBPK model when using the range of metabolic parameters measured in vitro in human liver samples. By incorporating an understanding of the metabolic processes, this PBPK model can be used to predict blood levels of MTBE, which is important in determining target tissue dose estimates for risk assessment.     

Development of a human physiologically based pharmacokinetic (PBPK) model for inorganic arsenic and its mono- and di-methylated metabolites

A physiologically-based pharmacokinetic (PBPK) model was developed to estimate levels of arsenic and its metabolites in human tissues and urine after oral exposure to arsenate (As(V)), arsenite (As(III)) or organoarsenical pesticides. The model consists of interconnected individual PBPK models for inorganic arsenic (As(V) and As(III)), monomethylarsenic acid (MMA(V)), and, dimethylarsenic acid (DMA(V)). Reduction of MMA(V) and DMA(V) to their respective trivalent forms also occurs in the lung, liver, and kidney including excretion in urine. Each submodel was constructed using flow limited compartments describing the mass balance of the chemicals in GI tract (lumen and tissue), lung, liver, kidney, muscle, skin, heart, and brain. The choice of tissues was based on physiochemical properties of the arsenicals (solubility), exposure routes, target tissues, and sites for metabolism. Metabolism of inorganic arsenic in liver was described as a series of reduction and oxidative methylation steps incorporating the inhibitory influence of metabolites on methylation. The inhibitory effects of As(III) on the methylation of MMA(III) to DMA, and MMA(III) on the methylation of As(III) to MMA were modeled as noncompetitive. To avoid the uncertainty inherent in estimation of many parameters from limited human data, a priori independent parameter estimates were derived using data from diverse experimental systems with priority given to data derived using human cells and tissues. This allowed the limited data for human excretion of arsenicals in urine to be used to estimate only parameters that were most sensitive to this type of data. Recently published urinary excretion data, not previously used in model development, are also used to evaluate model predictions.     

Predicting fetal perchlorate dose and inhibition of iodide kinetics during gestation: a physiologically-based pharmacokinetic analysis of perchlorate and iodide kinetics in the rat.

Perchlorate (ClO4-) disrupts endocrine homeostasis by competitively inhibiting the transport of iodide (I-) into the thyroid. The potential for health effects from human exposure to ClO4- in drinking water is not known, but experimental animal studies are suggestive of developmental effects from ClO4- induced iodide deficiency during gestation. Normal hormone-dependent development relies, in part, on synthesis of hormones in the fetal thyroid from maternally supplied iodide. Although ClO4- crosses the placenta, the extent of inhibition in the fetal thyroid is unknown. A physiologically-based pharmacokinetic (PBPK) model was developed to simulate ClO4- exposure and the resulting effect on iodide kinetics in rat gestation. Similar to concurrent model development for the adult male rat, this model includes compartments for thyroid, stomach, skin, kidney, liver, and plasma in both mother and fetus, with additional compartments for the maternal mammary gland, fat, and placenta. Tissues with active uptake are described with multiple compartments and Michaelis-Menten (M-M) kinetics. Physiological and kinetic parameters were obtained from literature and experiment. Systemic clearance, placental-fetal transport, and M-M uptake parameters were estimated by fitting model simulations to experimental data. The PBPK model is able to reproduce maternal and fetal iodide data over five orders of magnitude (0.36 to 33,000 ng/kg 131I-), ClO4- distribution over three orders of magnitude (0.01 to 10 mg/kg-day ClO4-) and inhibition of maternal thyroid and total fetal I- uptake. The model suggests a significant fetal ClO4- dose in late gestation (up to 82% of maternal dose). A comparison of model-predicted internal dosimetrics in the adult male, pregnant, and fetal rat indicates that the fetal thyroid is more sensitive to inhibition than that of the adult.