title: Computational model of steroidogenesis in human H295R cells to predict biochemical response to endocrine-active chemicals: model development for metyrapone.
abstract: BACKGROUND
  An in vitro steroidogenesis assay using the human adrenocortical carcinoma cell line H295R is being evaluated as a possible screening assay to detect and assess the impact of endocrine-active chemicals (EACs) capable of altering steroid biosynthesis. Data interpretation and their quantitative use in human and ecological risk assessments can be enhanced with mechanistic computational models to help define mechanisms of action and improve understanding of intracellular concentration-response behavior.
  
  
  OBJECTIVE
  The goal of this study was to develop a mechanistic computational model of the metabolic network of adrenal steroidogenesis to estimate the synthesis and secretion of adrenal steroids in human H295R cells and their biochemical response to steroidogenesis-disrupting EAC.
  
  
  METHODS
  We developed a deterministic model that describes the biosynthetic pathways for the conversion of cholesterol to adrenal steroids and the kinetics for enzyme inhibition by metryrapone (MET), a model EAC. Using a nonlinear parameter estimation method, the model was fitted to the measurements from an in vitro steroidogenesis assay using H295R cells.
  
  
  RESULTS
  Model-predicted steroid concentrations in cells and culture medium corresponded well to the time-course measurements from control and MET-exposed cells. A sensitivity analysis indicated the parameter uncertainties and identified transport and metabolic processes that most influenced the concentrations of primary adrenal steroids, aldosterone and cortisol.
  
  
  CONCLUSIONS
  Our study demonstrates the feasibility of using a computational model of steroidogenesis to estimate steroid concentrations in vitro. This capability could be useful to help define mechanisms of action for poorly characterized chemicals and mixtures in support of predictive hazard and risk assessments with EACs.
authors.affiliation: National Exposure Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711, USA. breen.michael@epa.gov
authors.forename: Michael S
authors.initials: MS
authors.lastname: Breen
authors.forename: Miyuki
authors.initials: M
authors.lastname: Breen
authors.forename: Natsuko
authors.initials: N
authors.lastname: Terasaki
authors.forename: Makoto
authors.initials: M
authors.lastname: Yamazaki
authors.forename: Rory B
authors.initials: RB
authors.lastname: Conolly
mesh_terms: D000311:Adrenal Glands / Q000187:drug effects* / Q000378:metabolism; D045744:Cell Line, Tumor; D019295:Computational Biology / Q000379:methods; D052244:Endocrine Disruptors / Q000494:pharmacology*; D006801:Humans; D008797:Metyrapone / Q000494:pharmacology*; D008962:Models, Theoretical; D013256:Steroids / Q000378:metabolism*
chemical_list: D052244:Endocrine Disruptors; D013256:Steroids; D008797:Metyrapone