Type II NADH dehydrogenase inhibitor 1-hydroxy-2-dodecyl-4(1H)quinolone leads to collapse of mitochondrial inner-membrane potential and ATP depletion in Toxoplasma gondii.
The apicomplexan parasite Toxoplasma gondii expresses type II NADH dehydrogenases (NDH2s) instead of canonical complex I at the inner mitochondrial membrane. These non-proton-pumping enzymes are considered to be promising drug targets due to their absence in mammalian cells. We recently showed by inhibition kinetics that T. gondii NDH2-I is a target of the quinolone-like compound 1-hydroxy-2-dodecyl-4(1H)quinolone (HDQ), which inhibits T. gondii replication in the nanomolar range. In this study, the cationic fluorescent probes Mitotracker and DiOC(6)(3) (3,3'-dihexyloxacarbocyanine iodine) were used to monitor the influence of HDQ on the mitochondrial inner membrane potential (Delta Psi m) in T. gondii. Real-time imaging revealed that nanomolar HDQ concentrations led to a Delta Psi m collapse within minutes, which is followed by severe ATP depletions of 30% after 1 h and 70% after 24 h. Delta Psi m depolarization was attenuated when substrates for other dehydrogenases that can donate electrons to ubiquinone were added to digitonin-permeabilized cells or when infected cultures were treated with the F(o)-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 the Delta Psi m, since Delta Psi m-positive parasites were found at a significantly 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.
Lin
San San
SS
Institute of Medical Microbiology, University of Göttingen, Kreuzbergring 57, D-37075 Göttingen, Germany.
Gross
Uwe
U
Bohne
Wolfgang
W
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects*; D051336:Mitochondrial Membranes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D009245:NADH Dehydrogenase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015800:Protozoan Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015363:Quinolones / Q000494:pharmacology*; D014122:Toxoplasma / Q000187:drug effects* / Q000378:metabolism
C521526:1-hydroxy-2-dodecyl-4(1H)quinolone; D004791:Enzyme Inhibitors; D015800:Protozoan Proteins; D015363:Quinolones; D000255:Adenosine Triphosphate; C088908:NADH dehydrogenase II; D009245:NADH Dehydrogenase