The type II NADH dehydrogenase inhibitor HDQ leads to {Delta}{Psi}m collapse and ATP depletion in Toxoplasma

Eukaryot Cell. 2009 Mar 13. [Epub ahead of print]

The type II NADH dehydrogenase inhibitor HDQ leads to {Delta}{Psi}m collapse and ATP depletion in Toxoplasma gondii

Lin SS, Gross U, Bohne W.

Institute of Medical Microbiology, University of Göttingen, Kreuzbergring 57, Göttingen D-37075; GERMANY.

The apicomplexan parasite Toxoplasma gondii expresses type II NADH dehydrogenases (NDH2s) instead of a canconial complex I at the inner mitochondrial membrane. These non-proton pumping enzymes are considered as promising drug targets, due to their absence in mammalian cells. We recently showed by inhibition kinetics that TgNDH2-I is a target of the quinolone-like compound HDQ, which inhibits T. gondii replication in the nanomolar range. In this study, the cationic fluorescent probes Mitotracker and DiOC6(3) were used to monitor the influence of HDQ on DeltaPsim in T. gondii. Real-time imaging revealed that nanomolar HDQ concentrations led to a DeltaPsim collapse within minutes, which is followed by a severe ATP depletion of 30% after 1 h and 70% after 24 h. The DeltaPsim depolarization was attenuated when substrates for other dehydrogenases which can donate electrons to ubiquinone were added to digitonin-permeabilized cells, or when infected cultures were treated with the F0-ATPase inhibitor oligomycin. A prolonged treatment with sublethal concentrations of HDQ induced differentiation into bradyzoites. This dormant stage is likely to be less dependent on DeltaPsim, since DeltaPsim-positive parasites were found at a significant lower frequency in alkaline pH induced bradyzoites than in tachyzoites. Together, our studies reveal that oxidative phosphorylation is essential for maintaining the ATP level in the fast growing tachyzoite stage and that HDQ interferes with this pathway by inhibiting the electron transport chain at the level of ubiquinone reduction.

PMID: 19286986 [PubMed - as supplied by publisher]