1. Translational models ofdrug-induced liver injury Dominic Williams MRC Centre for Drug Safety Science The University of Liverpool dom@liv.ac.uk
2. Centre Strategy for Investigating ADRs Investigation of the chemical Investigation of the patient
3. Integrated Mechanistic Drug Safety: Patient SAR SMR STR DrugClass Animal Chemistry Outcomes Biomarkers Bioanalysis Man Clinical Problem Research Question Mechanism In vitro Clinical Samples
4. Integrated Mechanistic Drug Safety: Chemical SAR SMR STR In vitro Bioanalysis Drug / Compound Biological Validation Chemical Validation Chemical Studies Man Animal Clinical Validation & Application
6. Mechanistic Classification of Adverse Drug Reactions TYPE A (augmented) predictable exaggeration of pharmacological effect dose dependent TYPE B (idiosyncratic) unpredictable apparently dose-independent less common more severe TYPE C (chemical) predictable from chemical structure eg. Paracetamol Park et al., 1998
22. The Hepatocyte: Defence Against Chemical Stress 1st line defence DRUG METABOLISM 2nd line defence ANTIOXIDANT RESPONSE 3rd line defence APOPTOSIS Basal expression of genes co-ordinating cell defence: Phase II enzymes, antioxidant proteins Induction of genes co-ordinating cell defence: Phase II enzymes, antioxidant proteins Stress Suicide of the cell: apoptosis Chemical / metabolite NECROSIS Reactive oxygen species Transcription factor: Nrf2 GSH Increasing levels of chemical stress
23. Mechanism of Nrf2-regulated Gene Induction Chemical (metabolite) Nrf2 Chemical Nrf2 GSH repletion Nrf2 Target genes ARE GSH depletion Adduct formation Protein oxidation Cell defence proteins: Glutamate CysteineLigase Glutathione transferases NAD(P)H quinoneoxidoreductase Haemoxygenase Glucuronyltransferase Catalase Nrf2 Keap1 Proteasomal proteolysis Restore cellular redox status ADAPTATION Goldring et al., 2004; Williams et al., 2004; Randle et al., 2008; Copple et al., 2008; Reismanet al., 2009
40. CCl3 In vivo Induction of Nrf2 by Model Hepatotoxins Covalent Binding GSH Depletion Nrf2 Induction O O C H C H H N 3 3 N Required Yes O H O B r B r B r O Required Yes O O Yes May occur CCl4 C l C l May occur Yes H N O S H N O S 2 2 2 2 O O N N C O H H Randle et al., 2008 C O H H O 2 2
82. Protein-reactive metabolite(s)Both animal models and in vitro systems are limited when assessing the hazard to susceptible patients: Biology of individual Occurrence, Frequency & Severity of Drug Hepatotoxicity f1 f2 + = Chemistry of drug
Editor's Notes
Major consequence of bioactivation is in fact bioinactivation
Most common consequence of bioactivation is in fact bioinactivation
This slide shows the STRESSED situation, where the system is subject to excessive electrophilic or oxidative stress e.g. Exposure to NAPQIElectrophilic and oxidative stress are detected directly by Keap1 through its cysteine ‘sensors’This stimulates enhanced Nrf2 activation
This slide shows the STRESSED situation, where the system is subject to excessive electrophilic or oxidative stress e.g. Exposure to NAPQIElectrophilic and oxidative stress are detected directly by Keap1 through its cysteine ‘sensors’This stimulates enhanced Nrf2 activation
....This is reinforced by signals from the plant through depletion of GSH (depressed GSH/GSSG ratio)Resulting in further Nrf2 activation – e.g. Through phosphorylation and also by directly enhancing the activity of antioxidant enzymes, e.g. By dimerisation
In saddition other signalling pathways may be recruited to strenghten the defence response, e.g. AP1 and NfkB, which can act either directly or indirectly to enhance ARE-mediated signalsThere is increasing evidence of cross-talk between such pathways e.g. Nrf2 and NfkBFurther supporting the value of a full SYTEMS APPROACH