SNSF | P3 Research Database

Carnitine; liver injury; fatty liver; bile duct ligation; bile acids

English title	Drug-drug interactions and toxicity of thienopyridine drugs
Applicant	Krähenbühl Stephan
Number	112483
Funding scheme	Project funding (Div. I-III)
Research institution	Abteilung Klinische Pharmakologie Kantonsspital Basel
Institution of higher education	University of Basel - BS
Main discipline	Clinical Pharmacology
Start/End	01.04.2006 - 30.09.2010
Approved amount	296'000.00

Lead

Lay summary
Clopidogrel and ticlopidine are thienopyridine prodrugs needing enzymatic activation by cytochrome P450 (CYP) 3A and 2B6 in order to exert their anti-platelet effects. Activation of these drugs is associated with the generation of a free mercapto group, which may be responsible not only for the therapeutic effect, but also for their toxicity. The most important toxic effects include myelotoxicity (neutropenia and agranulocytosis) and liver injury. In part A of my grant proposal, I plan first to set up an in vitro system consisting of human hepatic microsomes (or “supersomes”, containing on specific cytochrome P450 isozyme) to study activation of the thienopyridines. In a second step, this system will be used to study potential drug-drug interactions in vitro, namely by adding CYP inhibitors to this system. The system will then be developed further by the addition of thrombocytes to the incubations, in order to investigate also the dynamics of the thienopyridines. In additional investigations, such interactions (e.g. the possible interaction between amiodarone andclopidogrel) will then be studied in vivo in a clinical study. Finally, the clinical consequence of such interactions will be estimated by conducting a pharmacoepidemiological study using a large British database. In part B of my grant proposal, hepatic and myelotoxicity of the thienopyridines will be investigated. Since active metabolites are produced in the liver, I plan first to focus on hepatotoxicity. This will be studied using HepG2 cells, either in the presence of human hepatic microsomes or with cells overexpressing human CYP3A4. If toxicity can be demonstrated, I plan to study hepatic toxicity of the thienopyridines in the heterozygote Sod2-/+ mouse, which is sensitive for ROS-associated liver damage. Reactive metabolites can also lead to the formation of neo-antigens, triggering an immune response against the liver. This possibility will be assessed using an animal model for T cell-associated hepatotoxicity. Finally, myelotoxicity of the thienopyridines will be investigated using the well characterized colony-forming unit granulocyte/macrophage (CFU-GM) assay. If toxicity can be observed, its mechanism will be investigated using the HL-60 promyelocytic leukemia cell line. Activation of the thienopyridines will be achieved using coincubation with human hepatic microsomes or by using HL-60 cells overexpressing CYP3A4. The studies will shed light on the possible drug-drug interactions with the thienopyridines, which may be associated with a loss of activation and efficacy. In addition, they will help us to understand the mechanism for their toxicity, which is important for other drugs with a similar structure.