Bayesian estimation of pharmacokinetic and pharmacodynamic parameters in a mode-of-action-based cancer risk assessment for chloroform.
Chloroform is a carcinogen in rodents and its carcinogenicity is secondary to events associated with cytotoxicity and regenerative cell proliferation. In this study, a physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) model that links the processes of chloroform metabolism, reparable cell damage, cell death, and regenerative cellular proliferation was developed to support a new cancer dose-response assessment for chloroform. Model parameters were estimated using Markov Chain Monte Carlo (MCMC) analysis in a two-step approach: (1) metabolism parameters for male and female mice and rats were estimated against available closed chamber gas uptake data; and (2) PD parameters for each of the four rodent groups were estimated from hepatic and renal labeling index data following inhalation exposures. Subsequently, the resulting rodent PD parameters together with literature values for human age-dependent physiological and metabolism parameters were used to scale up the rodent model to a human model. The human model was used to predict exposure conditions under which chloroform-mediated cytolethality is expected to occur in liver and kidney of adults and children. Using the human model, inhalation Reference Concentrations (RfCs) and oral Reference Doses (RfDs) were derived using an uncertainty factor of 10. Based on liver and kidney dose metrics, the respective RfCs were 0.9 and 0.09 ppm; and the respective RfDs were 0.4 and 3 mg/kg/day.
Liao
Kai H
KH
Center for Human Health Assessment, The Hamner Institutes for Health Sciences, Research Triangle Park, NC 27709, USA.
Tan
Yu-Mei
YM
Conolly
Rory B
RB
Borghoff
Susan J
SJ
Gargas
Michael L
ML
Andersen
Melvin E
ME
Clewell
Harvey J
HJ
D000818:Animals; D001499:Bayes Theorem; D001693:Biological Transport, Active; D002273:Carcinogens / Q000493:pharmacokinetics / Q000494:pharmacology / Q000633:toxicity*; D002725:Chloroform / Q000493:pharmacokinetics* / Q000494:pharmacology / Q000633:toxicity*; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D007668:Kidney / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D008390:Markov Chains; D051379:Mice; D008954:Models, Biological; D009010:Monte Carlo Method; D009369:Neoplasms / Q000139:chemically induced; D009374:Neoplasms, Experimental / Q000139:chemically induced* / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D018570:Risk Assessment
D002273:Carcinogens; D002725:Chloroform