title: A mitochondria-targeted triphenylphosphonium-conjugated nitroxide functions as a radioprotector/mitigator.
abstract: Removal of excessive mitochondrial reactive oxygen species by electron scavengers and antioxidants is a promising therapeutic strategy to reduce the detrimental effects of radiation exposure. Here we exploited triphenylphosphonium (TPP) cation as a means to target nitroxide radicals to mitochondria. We synthesized a library of TPP-conjugated nitroxides and tested their radioprotective effects in gamma-irradiated mouse embryo cells and human epithelial BEAS-2B cells. Cells were incubated with conjugates either before or after irradiation. We found that [2-(1-oxyl-2,2,6,6-tetramethyl-piperidin-4-ylimino)-ethyl]-triphenyl-phosphonium (TPEY-Tempo) significantly blocked radiation-induced apoptosis as revealed by externalization of phosphatidylserine on the cell surface and inhibition of cytochrome c release from mitochondria. Using electron paramagnetic resonance, we showed that TPEY-Tempo was integrated into cells and mitochondria, where it underwent one-electron reduction to hydroxylamine. TPEY-Tempo acted as an electron scavenger that prevented superoxide generation and cardiolipin oxidation in mitochondria. Finally, TPEY-Tempo increased the clonogenic survival rate of irradiated cells. The cellular integration efficiencies of nonradioprotective TPP conjugates, including Mito-Tempo (Alexis, San Diego, CA), were markedly lower, although these homologues were integrated into isolated succinate-energized mitochondria to a similar extent as TPEY-Tempo. We conclude that mitochondrial targeting of TPP-conjugated nitroxides represents a promising approach for the development of novel radioprotectors.
authors.affiliation: Center for Free Radical and Antioxidant Health, Department of Environmental and Occupational Health, University of Pittsburgh, 100 Technology Drive, Pittsburgh, PA 15219, USA.
authors.forename: Jianfei
authors.initials: J
authors.lastname: Jiang
authors.forename: Detcho A
authors.initials: DA
authors.lastname: Stoyanovsky
authors.forename: Natalia A
authors.initials: NA
authors.lastname: Belikova
authors.forename: Yulia Y
authors.initials: YY
authors.lastname: Tyurina
authors.forename: Qing
authors.initials: Q
authors.lastname: Zhao
authors.forename: Muhammad A
authors.initials: MA
authors.lastname: Tungekar
authors.forename: Valentyna
authors.initials: V
authors.lastname: Kapralova
authors.forename: Zhentai
authors.initials: Z
authors.lastname: Huang
authors.forename: Arlan H
authors.initials: AH
authors.lastname: Mintz
authors.forename: Joel S
authors.initials: JS
authors.lastname: Greenberger
authors.forename: Valerian E
authors.initials: VE
authors.lastname: Kagan
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D002853:Chromatography, Liquid; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D009589:Nitrogen Oxides / Q000737:chemistry*; D016566:Organoselenium Compounds / Q000737:chemistry*; D011837:Radiation-Protective Agents / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D009589:Nitrogen Oxides; D016566:Organoselenium Compounds; D011837:Radiation-Protective Agents; C092819:triphenylselenonium chloride