Linking energy metabolism to dysfunctions in mitochondrial respiration--a metabolomics in vitro approach.

The study presented here describes the application of metabolite profiling of highly polar, intracellular metabolites after incubation of a mammalian fibroblast cell line with inhibitors of mitochondrial function. A metabolomics approach was used to assess the complex response of the cellular energy metabolism. Metabolic profiles of phosphorylated and carboxylated intracellular metabolites were assessed by UPLC-MS/MS and used to predict the mode of mitochondrial toxicity. Based on distinct metabolic patterns, multivariate data analysis allowed for the discrimination of two groups of toxins: inhibitors of the electron transport in mitochondrial membranes (complex IV inhibitors) and uncouplers of oxidative phosphorylation. Beyond these known interferences, metabolic profiling was able to reveal additional inhibitory effects on the cellular energy metabolism. Most prominently, for three of the toxins, metabolic patterns also disclosed an enhanced activity of the glycerol phosphate shuttle inferring the inhibition of NADH dehydrogenase at complex I. Secondly, inhibition of the electron transport was accompanied by a limiting availability of citric acid cycle intermediates and aspartate. Concomitantly, specific perturbations of the purine nucleotide cycle were observed. We have shown here that metabolomic approaches may assist to predict complex modes of action of toxic compounds on cellular level as well as to unravel specific dysfunctions in the energy metabolism.