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    Modeling of Ah-receptor dependent P450 induction I. Cellular model definition and its incorporation in a PBPK model of 2,3,7,8-TCDD

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    Authors
    Zeilmaker MJ
    van Eijkeren JCH
    Type
    Report
    Language
    en
    
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    Title
    Modeling of Ah-receptor dependent P450 induction I. Cellular model definition and its incorporation in a PBPK model of 2,3,7,8-TCDD
    Translated Title
    Modellering van Ah-receptor afhankelijke P450 inductie. Model definitie van P-450 inductie in de cel en zijn opname in een PBPK model van 2,3,7 ,8-TCDD
    Publiekssamenvatting
    De extrapolatie van de toxiciteit van chemische stoffen van proefdieren naar de mens vindt traditioneel plaats op basis van de dagelijks toegediende hoeveelheid van een stof. Echter, voor stoffen met sterk accumulerende eigenschappen zoals 2,3,7,8-TetraChloroDibenzo-p-Dioxine (TCDD) ligt een extrapolatie op basis van de hoeveelheid van de stof die zich in het lichaam opgehoopt heeft meer voor de hand. Het uitvoeren van een dergelijke extrapolatie vereist het kwantificeren van de ophoping van TCDD in het lichaam. Om het accumulatiemechanisme in de risicoschatting van TCDD op te nemen is een algemeen geldend model voor de interacties van liganden (dioxinen, maar ook polycyclische aromatische koolwaterstoffen) met de Ah-receptor in de cel ontwikkeld. Het model bevat de binding van de ligand aan de Ah-receptor, de binding van het ligand-Ah-receptor complex aan specifieke DNA bindingssequenties ('Xenobiotic Responsive Elements'), Ah-receptor afhankelijke de novo P450 synthese en de binding van de ligand aan de geinduceerde P450 eiwitten, inclusief het metabolisme van de ligand. Dit Ah-receptor P450 inductiemodel werd opgenomen in een fysiologisch georienteerd farmacokinetisch model ('PBPK model') voor de rat. Dit ratten-PBPK-model is voor TCDD gekalibreerd en gevalideerd en zal naar de mens geschaald worden. Vervolgens zal het humane PBPK model gebruikt worden om het voor de mens veilig geachte blootstellingsniveau van TCDD te berekenen. Dit blootstellingsniveau zal vergeleken worden met de, middels vergelijkbare methoden, door de WHO en, meer recent, de Gezondheidsraad berekende 'Tolerable Daily Intake' voor TCDD.<br>
    The interspecies extrapolation of chemical toxicity is traditionally based on the daily administered dose of the chemical. However, in the case of compounds with strong bioaccumulating properties, such as 2,3,7,8-TetraChloroDibenzo-p-Dioxin (TCDD), chronic toxicity is expected to scale better with the amount of TCDD in the body than with the daily administered dose. In order to use the amount of TCDD in the body as the starting point for the extrapolation of TCDD toxicity quantification is needed of the accumulation of TCDD in the body. In order to incorporate the disposition mechanism into the safety evaluation of TCDD we developed a generic model for the interactions of ligands (dioxins, polyaromatic hydrocarbons) with the Ah-receptor in the cell. This cellular model contains the binding of the ligand to the Ah-receptor, the binding of the ligand-Ah-receptor complex to specific DNA binding domains (Xenobiotic Responsive Elements (XRE)), Ah-receptor dependent de novo P450 synthesis and the binding of the ligand to induced P450 proteins together with their metabolism. The Ah-receptor/P450 induction model was incorporated in a Physiologically Based PharmacoKinetic (PBPK) model of the rat. This rat PBPK model was calibrated and validated for TCDD. The PBPK model presented here will be scaled from the rat to man. The human PBPK model will be used to calculate a safe human exposure level to TCDD. This exposure level, which is presented in a separate report, will be compared with the Tolerable Daily Intake of TCDD as calculated with similar modeling techniques by WHO and, more recently, the Health Council of the Netherlands.<br>
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    Rijksinstituut voor Volksgezondheid en Milieu RIVM
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      Modeling of Ah-receptor dependent P450 induction I. Cellular model definition and its incorporation in a PBPK model of 2,3,7,8-TCDD

      Zeilmaker MJ; Eijkeren JCH van; LBO (Rijksinstituut voor Volksgezondheid en Milieu RIVM, 1997-10-30)
      The interspecies extrapolation of chemical toxicity is traditionally based on the daily administered dose of the chemical. However, in the case of compounds with strong bioaccumulating properties, such as 2,3,7,8-TetraChloroDibenzo-p-Dioxin (TCDD), chronic toxicity is expected to scale better with the amount of TCDD in the body than with the daily administered dose. In order to use the amount of TCDD in the body as the starting point for the extrapolation of TCDD toxicity quantification is needed of the accumulation of TCDD in the body. In order to incorporate the disposition mechanism into the safety evaluation of TCDD we developed a generic model for the interactions of ligands (dioxins, polyaromatic hydrocarbons) with the Ah-receptor in the cell. This cellular model contains the binding of the ligand to the Ah-receptor, the binding of the ligand-Ah-receptor complex to specific DNA binding domains (Xenobiotic Responsive Elements (XRE)), Ah-receptor dependent de novo P450 synthesis and the binding of the ligand to induced P450 proteins together with their metabolism. The Ah-receptor/P450 induction model was incorporated in a Physiologically Based PharmacoKinetic (PBPK) model of the rat. This rat PBPK model was calibrated and validated for TCDD. The PBPK model presented here will be scaled from the rat to man. The human PBPK model will be used to calculate a safe human exposure level to TCDD. This exposure level, which is presented in a separate report, will be compared with the Tolerable Daily Intake of TCDD as calculated with similar modeling techniques by WHO and, more recently, the Health Council of the Netherlands.

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