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A pharmacodynamic analysis of TCDD-induced cytochrome P450 gene expression in multiple tissues: dose- and
M J Santostefano1, X Wang, V M Richardson
1Curriculum in Toxicology, University of North Carolina, Chapel Hill, North Carolina 27599-7270, USA. santostefano.michael@epamail.epa.gov
Abstract:
The ability of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) to alter gene expression and the demonstration that the induction of CYP1A2 is responsible for hepatic TCDD sequestration suggest that both pharmacokinetic and pharmacodynamic events must be incorporated for a quantitative description of TCDD disposition. In this paper, a biologically based pharmacodynamic (BBPD) model for TCDD-induced biochemical responses in multiple tissues was developed. The parameters responsible for tissue response were estimated simultaneously with a refined physiologically based pharmacokinetic (PBPK) model developed by Wang et al. (1997a), by using the time-dependent effects of TCDD on induced CYP1A1/CYP1A2 gene expression in multiple target tissues (liver, lungs, kidneys, and skin) of female Sprague-Dawley rats treated with 10 microgram TCDD/kg for 30 min, 1, 3, 8, or 24 h, or 7, 14, or 35 days. This refined BBPD model developed based on the time-course of TCDD-induced CYP1A1/CYP1A2 protein expression, and associated enzymatic activities well described the dose-dependent effects of TCDD on cytochrome P450 protein expression and associated enzyme activities in the multiple tissues of female Sprague-Dawley rats at 3 days following a single exposure to TCDD (0.01-30.0 micromgram TCDD/kg). This is the first BBPD model to quantitatively describe the time- and dose-dependent effects of TCDD on induced CYP1A1/CYP1A2 protein expression and associated enzyme activities in multiple target tissues for TCDD-induced biochemical responses.
Insights
A new model integrates pharmacokinetics and pharmacodynamics to quantify 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) effects. This biologically based pharmacodynamic (BBPD) model accurately predicts TCDD
Area of Science:
- Environmental Toxicology
- Pharmacology
- Biochemistry
Background:
- 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) alters gene expression, with CYP1A2 induction mediating its hepatic sequestration.
- Quantitative descriptions of TCDD disposition require integrating pharmacokinetic and pharmacodynamic events.
Purpose of the Study:
- To develop a biologically based pharmacodynamic (BBPD) model for TCDD-induced biochemical responses in multiple tissues.
- To quantitatively describe the time- and dose-dependent effects of TCDD on CYP1A1/CYP1A2 protein expression and enzyme activities.
Main Methods:
- A BBPD model was developed and integrated with a refined physiologically based pharmacokinetic (PBPK) model.
- Parameters were estimated using time-dependent TCDD effects on CYP1A1/CYP1A2 gene expression in rat liver, lungs, kidneys, and skin.
- Data from Sprague-Dawley rats treated with varying doses and durations of TCDD exposure were utilized.
Main Results:
- The refined BBPD model accurately described dose-dependent TCDD effects on cytochrome P450 protein expression and enzyme activities.
- The model successfully predicted TCDD's impact across multiple tissues following single exposures.
- This represents the first BBPD model to quantitatively capture time- and dose-dependent TCDD effects on CYP1A1/CYP1A2 induction.
Conclusions:
- The developed BBPD model provides a robust framework for understanding TCDD's complex toxicokinetics and toxicodynamics.
- This model enables quantitative predictions of TCDD's biochemical effects in various tissues over time and dose.
- Further application of this model can aid in risk assessment and management of dioxin exposure.