Difference between revisions of "Human PBPK model for dioxin"
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Contents
Scope
Human PBPK model for dioxin is a tool for calculating dioxin concentrations in human tissues after a given exposure pattern.
Definition
Basic info
| Last modification: | 04/07/2007 | Model version : | |
| Software status : | Free software | OS : | Linux |
| Supplier : | INERIS | Installation : | See source |
| Possible developments : | yes | Source : | TOXI/INERIS web site [1] |
| Supplier address: | INERIS Verneuil en Halatte, France | Referent(s)* : | S. MICALLEF (INERIS)
Sandrine.micallef@ineris.fr |
Discipline : keywords: toxicokinetic model, 2,3,7,8-tétra-chloro-p-dioxin (TCDD), PBPK
SCOPE OF THE MODEL
Physiologically Based Toxicokinetic (PBTK) model for Dioxine. The presented PBTK model allows to simulate ingestion exposures to 2,3,7,8-tétra-chloro-p-dioxin (TCDD) for a woman over her whole life. TCDD is a persistent chemical found in trace amounts all over the globe. It accumulates in animal fat all along the trophic chain. Human exposure to TCDD is therefore almost unavoidable, even if in trace amounts. TCDD has multiple effects on health.
MODEL DESCRIPTION
The proposed model is based on a previous one proposed by van der Molen and colleagues in 1996[2]. The model computes various measures of internal dose as a function of time. The superposition of a peak exposure to a time-varying background intake can be described. All ingested TCDD is supposed to be absorbed. TCDD is supposed to distribute between blood, fat, muscles and skin, and viscera. The model equations are solved dynamically (by numerical integration) with the MCSim simulation package to give a good precision both on short-term and long-term scales. The body mass and the volume of the various body tissues change with the age of the simulated individual.
Figure 1 : Toxicokinetic model used to describe TCDD toxicokinetic in the human body[2]. compartments are characterized with volume V and partition coefficient P. Exchanges between are governed by blood flows, F. Elimination is assumed proportional to the elimination constant, ke. The set value of each parameter is given in Table 1. The ingested quantity by unit of time ki (in ng/min), is determined by the exposure scenario.
Table 1 : Numerical values of the parameters of the toxicokinetic model for TCDD in the woman.
| Parameter(a) | Symbol | Numerical Value |
| Ventilation rate | Fp | 8,0 |
| Blood over air ventilation rate | R | 1,14 |
| Blood flow rates | ||
| Fat | Ff | 0,09 |
| Liver | Fl | 0,24 |
| Muscles and skin | fm | 0,18 |
| Viscera | fv | – (b) |
| Volumes | ||
| Total body volume | Vt | – (c) |
| Fat | Vf | – (c) |
| Liver | Vl | – (c) |
| Muscles and skin | Vm | – (c) |
| Viscera | Vv | – (c) |
| Partition Coefficient | ||
| Fat | Pf | 300 |
| Liver | Pl | 25 |
| Muscles and skin | Pm | 4 |
| Viscera | Pv | 10 |
| Elimination constant | ke | 8,4510-8 (d) |
(a) Units : volumes (L), blood flow (L/min), et elimination constant (min-1). (b) Blood flow rate to viscera is calculated by difference between 1 and the sum of blood flow rates toward the other compartments. (c) Volumes evolve with time. (d) Corresponds to a half-life of 15,6 years.
Figure 1 gives a graphical representation of the model used. Only ingestion exposure is described in this model (the totality of the exposure dose is assumed to be absorbed). The TCDD is supposed to be distributed into different compartments of the body : blood, fat, muscles and skin. The original formulation of van der Molen and coll.[2] regards all these compartments as being with balance in an instantaneous way. This assumption is acceptable only if slow evolutions of absorption are the limiting factor of the kinetics of the product. Since the simulation of a short peak of exposure interests us, we developed a traditional dynamic formulation[3], specifies at the same time on short scales of time and the long-term.
Model equations Equations defining the proposed model are the following : For quantites of TCDD in fat, viscera, muscle and skin, and liver : (1) (2) (3) (4) La concentration artérielle est calculée par : (5)
The cardiac output, Ft, is proportinal to the ventilation rate, Fp : (1) The body volume evolve as a function of age : (6) The volume of fat, viscera, liver also evolve as a function of age[2]: (7) (8) (9) Volume of "muscles and skin" compartment is calculated as the difference between 90% of the total body volume (because bones are not included) and the other compartments : (10) Units used are : quantities of TCDD are expressed in ng, TCDD concentrations in ng/L, age in years volumes in liter, flows in L/min, the elimination constant in min-1, the ingested quantity by unit of time in ng/min. The body density is assumed equal to 1.
Figure 2 presents the temporal evolution of these parameters for a woman (the evolution is overall similar for a man). The reference averaged values used for the parameters not evolving with time are given in Table 1. The equations of the model were coded using the MCSim software[4].
Figure 2 : Temporal evolution of volumes for the woman[2].
VALIDATION
To be done
APPLICATIONS EXAMPLES
Example of the use of this model can be found in the paper by Bois[5]
See also
- Van der Molen GW, Kooijman BALM, Wittsiepe J, et al. Estimation of dioxin and furan elimination rates with a pharmacokinetic model
JOURNAL OF EXPOSURE ANALYSIS AND ENVIRONMENTAL EPIDEMIOLOGY 10 (6): 579-585 Part 1 NOV-DEC 2000.
- Van der Molen GW, Kooijman SALM, Michalek JE, et al. The estimation of elimination rates of persistent compounds: A re-analysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin levels in Vietnam veterans CHEMOSPHERE 37 (9-12): 1833-1844 OCT-NOV 1998.
Model template
| Dioxin PBPK model |
|---|
| The results are total amounts (ng) of dioxin, except blood concentration (ng/l). |
The input data used for this variable:
|
REFERENCES
- ↑ http://toxi.ineris.fr/activites/toxicologie_quantitative/toxicocinetique/modeles/dioxine/sub_dioxine.php
- ↑ 2.0 2.1 2.2 2.3 2.4 Van der Molen, G. W., S. A. L. M. Kooijman and W. Slob (1996). "A generic toxicokinetic model for persistent lipophilic compounds in humans: an application to TCDD." Fundamental and Applied Toxicology 31: 83-94.
- ↑ Gerlowski, L. E. and R. K. Jain (1983). "Physiologically based pharmacokinetic modeling: principles and applications." Journal of Pharmaceutical Sciences 72: 1103-1127.
- ↑ Bois, F. Y. and D. Maszle (1997). "MCSim: a simulation program." Journal of Statistical Software 2(9): [1].
- ↑ Bois, F. Y. (2003). "Modélisation toxicocinétique de la concentration sanguine de 2,3,7,8-tetrachloro-p-dioxine après ingestion chez la femme." Environnement, Risques et Santé 2(1). [Toxicokinetic modelling of 2,3,7,8-tétrachloro-p-dioxin blood concentration after ingestion by women. Environnement, Risque et Santé, (2003) 2:45-53. ]
