title: Glutathione metabolism modeling: a mechanism for liver drug-robustness and a new biomarker strategy.
abstract: BACKGROUND
  Glutathione metabolism can determine an individual's ability to detoxify drugs. To increase understanding of the dynamics of cellular glutathione homeostasis, we have developed an experiment-based mathematical model of the kinetics of the glutathione network. This model was used to simulate perturbations observed when human liver derived THLE cells, transfected with human cytochrome P452E1 (THLE-2E1 cells), were exposed to paracetamol (acetaminophen).
  
  
  METHODS
  Human liver derived cells containing extra human cytochrome P4502E1 were treated with paracetamol at various levels of methionine and in the presence and absence of an inhibitor of glutamyl-cysteine synthetase (GCS). GCS activity was also measured in extracts. Intracellular and extracellular concentrations of substances involved in glutathione metabolism were measured as was damage to mitochondria and proteins. A bottom up mathematical model was made of the metabolic pathways around and including glutathione.
  
  
  RESULTS
  Our initial model described some, but not all the metabolite-concentration and flux data obtained when THLE-2E1 cells were exposed to paracetamol at concentrations high enough to affect glutathione metabolism. We hypothesized that the lack of correspondence could be due to upregulation of expression of glutamyl cysteine synthetase, one of the enzymes controlling glutathione synthesis, and confirmed this experimentally. A modified model which incorporated this adaptive response adequately described the observed changes in the glutathione pathway. Use of the adaptive model to analyze the functioning of the glutathione network revealed that a threshold input concentration of methionine may be required for effective detoxification of reactive metabolites by glutathione conjugation. The analysis also provided evidence that 5-oxoproline and ophthalmic acid are more useful biomarkers of glutathione status when analyzed together than when analyzed in isolation, especially in a new, model-assisted integrated biomarker strategy.
  
  
  CONCLUSIONS
  A robust mathematical model of the dynamics of cellular changes in glutathione homeostasis in cells has been developed and tested in vitro.
  
  
  CONCLUSIONS
  Mathematical models of the glutathione pathway that help examine mechanisms of cellular protection against xenobiotic toxicity and the monitoring thereof, can now be made.
authors: University of Manchester, Manchester M1 7DN, UK.
authors: Suzanne
authors: S
authors: Geenen
authors: Franco B
authors: FB
authors: du Preez
authors: Jacky L
authors: JL
authors: Snoep
authors: Alison J
authors: AJ
authors: Foster
authors: Sunil
authors: S
authors: Sarda
authors: J Gerry
authors: JG
authors: Kenna
authors: Ian D
authors: ID
authors: Wilson
authors: Hans V
authors: HV
authors: Westerhoff
mesh_terms: D000082:Acetaminophen / Q000633:toxicity; D015415:Biomarkers / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003470:Culture Media; D005978:Glutathione / Q000378:metabolism*; D006801:Humans; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008954:Models, Biological; D053719:Tandem Mass Spectrometry
chemical_list: D015415:Biomarkers; D003470:Culture Media; D000082:Acetaminophen; D005978:Glutathione
keywords: Acetaminophen toxicity; Adaptation; Biomarker; Gene expression-metabolism hybrid model; Glutathione metabolism