title: Mitochondrial ascorbic acid prevents mitochondrial O₂·⁻ formation, an event critical for U937 cell apoptosis induced by arsenite through both autophagic-dependent and independent mechanisms.
abstract: A 16 h exposure of U937 cells to 2.5 µM arsenite promotes superoxide (O2(·-)) formation and inhibition of the activity of aconitase, a O2(·-) sensitive enzyme. Both responses were abolished by the complex I inhibitor rotenone, or by the respiration-deficient phenotype. Interestingly, a similar suppressive effect was mediated by a short term pre-exposure to a low concentration of L-ascorbic acid (AA), previously shown to be actively taken up by the cells and by their mitochondria. The mitochondrial origin of O2(·-) was confirmed by fluorescence microscopy studies, whereas different approaches failed to detect a contribution of NADPH oxidase. Under similar conditions, arsenite induced autophagy as well as a decline in mitochondrial membrane potential resulting in delayed (48 h) apoptosis. Importantly, all these events turned out to be sensitive to treatments associated with prevention of O2(·-) formation, including AA, and were only partially blunted by inhibitors of autophagy. As a final note, the toxic effects mediated by O2(·-)were entirely dependent on its conversion to H2O2. AA-sensitive mitochondrial O2(·-) formation is therefore involved in autophagy and apoptosis induced by arsenite in U937 cells, although part of the lethal response appears mediated by an autophagy-independent mechanism.
authors.affiliation: Dipartimento Di Scienze Biomolecolari, Università Degli Studi Di Urbino "Carlo Bo,", Urbino, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Guidarelli
authors.affiliation: Dipartimento Di Scienze Biomolecolari, Università Degli Studi Di Urbino "Carlo Bo,", Urbino, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Carloni
authors.affiliation: Dipartimento Di Scienze Biomolecolari, Università Degli Studi Di Urbino "Carlo Bo,", Urbino, Italy.
authors.forename: Walter
authors.initials: W
authors.lastname: Balduini
authors.affiliation: Dipartimento Di Scienze Biomolecolari, Università Degli Studi Di Urbino "Carlo Bo,", Urbino, Italy.
authors.forename: Mara
authors.initials: M
authors.lastname: Fiorani
authors.affiliation: Dipartimento Di Scienze Biomolecolari, Università Degli Studi Di Urbino "Carlo Bo,", Urbino, Italy.
authors.forename: Orazio
authors.initials: O
authors.lastname: Cantoni
mesh_terms: D000154:Aconitate Hydratase / Q000037:antagonists & inhibitors / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D018053:Arsenites / Q000633:toxicity; D001205:Ascorbic Acid / Q000008:administration & dosage* / Q000378:metabolism; D001343:Autophagy / Q000187:drug effects*; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism / Q000633:toxicity; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008928:Mitochondria / Q000378:metabolism* / Q000473:pathology; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors / Q000378:metabolism; D012402:Rotenone / Q000008:administration & dosage; D013481:Superoxides / Q000378:metabolism* / Q000633:toxicity; D020298:U937 Cells
chemical_list: D018053:Arsenites; D012402:Rotenone; D013481:Superoxides; D006861:Hydrogen Peroxide; D019255:NADPH Oxidases; D000154:Aconitate Hydratase; D001205:Ascorbic Acid
keywords: apoptosis; arsenite; autophagy; mitochondria; superoxide; vitamin C