A physiologically based pharmacokinetic model for inhaled carbon tetrachloride

Area of Science:

• Toxicology
• Pharmacokinetics
• Environmental Health

Background:

• Carbon tetrachloride (CCl4) is a toxic industrial solvent with known health risks.
• Understanding CCl4's absorption, distribution, metabolism, and excretion (ADME) is crucial for risk assessment.
• Previous studies provided limited time-course data on CCl4 and its metabolites in rats.

Purpose of the Study:

• To develop and validate a physiologically based pharmacokinetic (PB-PK) model for inhaled CCl4 in rats.
• To describe the time course of CCl4 and its metabolites (exhaled 14CO2, fecal, and urinary radioactivity).
• To scale the validated rat model for predicting CCl4 pharmacokinetics in non-human primates and humans.

Main Methods:

• Inhaled, radiolabeled CCl4 (14CCl4) exposure studies in male Sprague-Dawley rats.
• Development of a PB-PK model incorporating partition coefficients, physiological parameters, and metabolic constants (Vmax, Km).
• Gas uptake studies to determine CCl4 metabolic pathways and rates.

Main Results:

• The PB-PK model accurately predicted exhaled 14CCl4, 14CO2, and urinary/fecal radioactivity elimination.
• CCl4 metabolism was described by a single saturable pathway, with 84% forming fecal metabolites, 9.5% urinary, and 6.5% CO2.
• Model scaling successfully predicted CCl4 behavior in monkeys and humans, aligning with existing data.

Conclusions:

• The developed PB-PK model provides a robust framework for understanding CCl4 pharmacokinetics and toxicity.
• At 100 ppm, inhaled CCl4 in rats leads to metabolism exceeding enzyme saturation levels.
• The model supports risk assessment and extrapolation of CCl4 toxicity data across species.