Mitochondria are important targets for drug-associated organ toxicity. Clinically, mitochondrial toxicity most often represents as so called idiosyncratic toxicity, meaning that this type of toxicity is rare (usually not detected during drug development) and that the precise mechanisms are not known. The current concept assumes the presence of genetic and/or other risk factors rendering patients with idiosyncratic toxicity more sensitive to specific drugs.

Considering the importance of mitochondria as a target for idiosyncratic toxicity, we propose A. to establish a framework allowing efficient screening of drugs for mitochondrial toxicity and B. to test the hypothesis that underlying mitochondrial diseases predispose for mitochondrial toxicity of drugs in animal models. Regarding project A, cultured cells (human cell lines, isolated human cells or cells derived from human stem cells) are used to assess cellular toxicity (by monitoring of oxygen consumption, lactate production, cellular ATP levels and cytotoxicity). If mitochondrial toxicity is detected; mitochondria are isolated from these cells and used for specific functional and biochemical assessments. In parallel, a proteomics approach is performed, involving protein separation and isolation with FPLC and gel electrophoresis and, finally, protein identification and quantification using Maldi-TOF. Most of these techniques are available in our laboratory or in laboratories at the university of Basel.

Using these approaches, we plan to study first the effects of well known mitochondrial toxins (benzbromarone, hydroxy-cobalamin[c-lactam] and valproate) on mitochondria in human cell lines (HepG2 cells and HUH-7 cells). After its establishment, this technique will be suitable for the assessment of potential mitochondrial toxicity for any other compound. In project B, we propose to test two known mitochondrial toxicants, valproate and simvastatin, in animal models with known mitochondrial dysfunction, namely jvs+/- mice (mice with decreased tissue carnitine stores due to a mutation in the renal carnitine carrier OCTN2) and LCAD-/- (mice with a knock out of long-chain acyl-CoA dehydrogenase, an enzyme involved in the β-oxidation of fatty acids). Doses of the toxicants known to be sub- or only slightly toxic for wild type mice will be administered and signs of toxicity compared between wild-type and experimental mice treated with such doses of the respective toxicant.

The proposed projects will enlarge our understanding about the mechanisms involved in mitochondrial toxicity of drugs, in particular the interaction with mitochondrial proteins. We will be able to assess the consequences of toxicant exposure on the mitochondrial proteome, genome and/or metabolome, possibly leading to the identification of specific drug targets. This will lead to the detection of possible biomarkers, the construction of “intelligent” cellular systems suitable for screening for mitochondrial toxicity and to the identification of patients at risk for developing idiosyncratic toxicity.