title: Relationships between the mitochondrial permeability transition and oxidative stress during ara-C toxicity.
abstract: The mitochondrial permeability transition and oxidative stress seem to be critical alterations in cellular physiology that take place during programmed cell death. Failure to undergo apoptosis is associated with drug resistance in acute myeloid leukemia and other cancers. Therefore, it is important to establish causal relationships between the physiological changes that take place in apoptosis, because these are potential targets for novel treatment strategies to overcome this form of drug resistance. We describe the use of multilaser flow cytometry methods to make correlated measurements of mitochondrial membrane potential (MMP), the generation of reactive oxygen intermediates, the cellular content of reduced glutathione (GSH), intracellular calcium, and exposure of phosphatidylserine on the cell surface. Using these combined methods, we have mapped a "death sequence" that occurs after treatment of leukemic blasts with clinically relevant concentrations of 1-beta-D-arabinofuranosylcytosine (ara-C). Dual labeling of MMP and cellular glutathione content showed that loss of MMP, indicative of the permeability transition, took place in cells that were depleted of glutathione. The loss of MMP coincided with phosphatidylserine exposure and preceded a state of high reactive oxygen generation. Finally, there was an increase in intracellular calcium. These results demonstrate that the mitochondrial permeability transition takes place during ara-C toxicity but suggest that this occurs downstream of the loss of GSH. Thus, oxidative stress after ara-C-induced toxicity seems to be a biphasic phenomenon, with the permeability transition occurring after a depletion of GSH and preceding a state of high reactive oxygen generation.
authors.affiliation: Department of Pathology, Ontario Cancer Institute/Princess Margaret Hospital, Toronto, Canada.
authors.forename: K L
authors.initials: KL
authors.lastname: Backway
authors.forename: E A
authors.initials: EA
authors.lastname: McCulloch
authors.forename: S
authors.initials: S
authors.lastname: Chow
authors.forename: D W
authors.initials: DW
authors.lastname: Hedley
mesh_terms: D002118:Calcium / Q000378:metabolism; D003561:Cytarabine / Q000494:pharmacology*; D005434:Flow Cytometry; D006801:Humans; D007425:Intracellular Membranes / Q000502:physiology; D015470:Leukemia, Myeloid, Acute; D008564:Membrane Potentials; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology*; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D010539:Permeability; D010718:Phosphatidylserines / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013997:Time Factors; D014407:Tumor Cells, Cultured
chemical_list: D010718:Phosphatidylserines; D017382:Reactive Oxygen Species; D003561:Cytarabine; D002118:Calcium