Ethanol induced modification of m-xylene toxicokinetics in humans

Reconstruction of Exposure to m-Xylene from Human Biomonitoring Data Using PBPK Modelling, Bayesian Inference, and Markov Chain Monte Carlo Simulation

There are numerous biomonitoring programs, both recent and ongoing, to evaluate environmental exposure of humans to chemicals. Due to the lack of exposure and kinetic data, the correlation of biomarker levels with exposure concentrations leads to difficulty in utilizing biomonitoring data for biological guidance values. Exposure reconstruction or reverse dosimetry is the retrospective interpretation of external exposure consistent with biomonitoring data. We investigated the integration of physiologically based pharmacokinetic modelling, global sensitivity analysis, Bayesian inference, and Markov chain Monte Carlo simulation to obtain a population estimate of inhalation exposure to m-xylene. We used exhaled breath and venous blood m-xylene and urinary 3-methylhippuric acid measurements from a controlled human volunteer study in order to evaluate the ability of our computational framework to predict known inhalation exposures. We also investigated the importance of model structure and dimensionality with respect to its ability to reconstruct exposure.

Ethanol-Induced Increase in the Metabolic Clearance of 1,1,1-Trichloroethane in Human Volunteers

This study evaluated the effect of moderate doses of ethanol over a short period of time on the toxicokinetics of an organic solvent, 1,1,1-trichloroethane. A group of 10 moderate drinkers were recruited and exposed via inhalation for 2 h to a low concentration of 1,1,1-trichloroethane (175 ppm) on two separate occasions. Subjects were administered ethanol (0.35 g/kg body weight) on each of the 7 days preceding one of the exposures. Blood and urine samples were collected during and following each exposure, with blood analyzed for 1,1,1-trichloroethane and urine analyzed for the metabolites of 1,1,1-trichloroethane: trichloroethanol and trichloroacetic acid. Prior ethanol consumption resulted in a significant increase in apparent metabolic clearance of 1,1,1-trichloroethane (mean increase = 25.4%). The results of this study demonstrate that ethanol consumption over time can affect the rate at which an organic solvent is cleared through metabolism in humans. For chemicals with toxic metabolic products, this inductive effect of ethanol consumption on the rate of biotransformation could be potentially harmful to exposed individuals. Metabolic clearance of compounds with high hepatic extraction may not be affected by enzyme induction as it is likely that these compounds are essentially completely metabolized while passing through the liver.

The effects of alcohol and diallyl sulphide on CYP2E1 activity in humans: a phenotyping study using chlorzoxazone

The effects of acute administration of dietary levels of ethanol and the garlic oil extract, diallyl sulphide (DAS), on cytochrome P450 2E1 (CYP2E1) activity in volunteers were studied using the selective probe substrate, chlorzoxazone (CZX). The ratio of the CZX metabolite 6- hydroxychlorzoxazone (6-OHCZX) to CZX was taken to indicate CYP2E1 activity. The mean differences between the baseline and DAS-treated (0.2 mg/kg) CYP2E1 activities were significantly different (two-tailed p value = 0.0242, n = 8). Likewise, the mean differences between the baseline and ethanol-treated (0.8 g/kg) CYP2E1 activities were also significantly different (two-tailed p value = 0.0005, n = 7). The reduction in in vivo CYP2E1 activity by DAS is consistent with reported inhibition observed in vitro. The marked reduction in CYP2E1 activity following acute ingestion of ethanol is consistent with a competitive inhibition mechanism of CZX metabolism. The inhibitory effect of DAS maybe additive with daily consumption of Allium vegetables in particular. This may explain the lower 6-OHCZX/CZX metabolic ratios measured in various European and Mexican cohorts and is consistent with the lower incidence of stomach, liver and colon cancers observed in southern Europeans.

Toxicokinetics of organic solvents: a review of modifying factors

This article reviews, with an emphasis on human experimental data, factors known or suspected to cause changes in the toxicokinetics of organic solvents. Such changes in the toxicokinetic pattern alters the relation between external exposure and target dose and thus may explain some of the observed individual variability in susceptibility to toxic effects. Factors shown to modify the uptake, distribution, biotransformation, or excretion of solvent include physical activity (work load), body composition, age, sex, genetic polymorphism of the biotransformation, ethnicity, diet, smoking, drug treatment, and coexposure to ethanol and other solvents. A better understanding of modifying factors is needed for several reasons. First, it may help in identifying important potential confounders and eliminating negligible ones. Second, the risk assessment process may be improved if different sources of variability between external exposures and target doses can be quantitatively assessed. Third, biological exposure monitoring may be also improved for the same reason.