title: Rapid kill of malaria parasites by artemisinin and semi-synthetic endoperoxides involves ROS-dependent depolarization of the membrane potential.
abstract: OBJECTIVE
  Artemisinin and artemisinin semi-synthetic derivatives (collectively known as endoperoxides) are first-line antimalarials for the treatment of uncomplicated and severe malaria. Endoperoxides display very fast killing rates and are generally recalcitrant to parasite resistance development. These key pharmacodynamic features are a result of a complex mechanism of action, the details of which lack consensus. Here, we report on the primary physiological events leading to parasite death.
  
  
  METHODS
  Parasite mitochondrial (ΔΨm) and plasma membrane (ΔΨp) electrochemical potentials were measured using real-time single-cell imaging following exposure to pharmacologically relevant concentrations of endoperoxides (artemisinin, dihydroartemisinin, artesunate and the synthetic tetraoxane RKA182). In addition, mitochondrial electron transport chain components NADH:quinone oxidoreductase (alternative complex I), bc1 (complex III) and cytochrome oxidase (complex IV) were investigated to determine their functional sensitivity to the various endoperoxides.
  
  
  RESULTS
  Parasite exposure to endoperoxides resulted in rapid depolarization of parasite ΔΨm and ΔΨp. The rate of depolarization was decreased in the presence of a reactive oxygen species (ROS) scavenger and Fe(3+) chelators. Depolarization of ΔΨm by endoperoxides is not believed to be through the inhibition of mitochondrial electron transport chain components, owing to the lack of significant inhibition when assayed directly.
  
  
  CONCLUSIONS
  The depolarization of ΔΨm and ΔΨp is shown to be mediated via the generation of ROS that are initiated by iron bioactivation of endoperoxides and/or catalysed by iron-dependent oxidative stress. These data are discussed in the context of current hypotheses concerning the mode of action of endoperoxides.
authors: Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, UK.
authors: Thomas
authors: T
authors: Antoine
authors: Nicholas
authors: N
authors: Fisher
authors: Richard
authors: R
authors: Amewu
authors: Paul M
authors: PM
authors: O'Neill
authors: Stephen A
authors: SA
authors: Ward
authors: Giancarlo A
authors: GA
authors: Biagini
mesh_terms: D037621:Artemisinins / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002470:Cell Survival / Q000187:drug effects; D004579:Electron Transport / Q000187:drug effects; D007501:Iron / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects*; D051336:Mitochondrial Membranes / Q000187:drug effects / Q000502:physiology; D018384:Oxidative Stress; D010544:Peroxidases / Q000494:pharmacology*; D010963:Plasmodium falciparum / Q000187:drug effects* / Q000502:physiology*; D017382:Reactive Oxygen Species / Q000378:metabolism*
chemical_list: D037621:Artemisinins; D017382:Reactive Oxygen Species; C031327:artemisinin; D007501:Iron; D010544:Peroxidases
keywords: Plasmodium; free radicals; haem; iron; lipid peroxidation; mitochondria; oxidative damage