title: Pro-oxidative synergic bactericidal effect of NO: kinetics and inhibition by nitroxides.
abstract: NO plays diverse roles in physiological and pathological processes, occasionally resulting in opposing effects, particularly in cells subjected to oxidative stress. NO mostly protects eukaryotes against oxidative injury, but was demonstrated to kill prokaryotes synergistically with H2O2. This could be a promising therapeutic avenue. However, recent conflicting findings were reported describing dramatic protective activity of NO. The previous studies of NO effects on prokaryotes applied a transient oxidative stress while arbitrarily checking the residual bacterial viability after 30 or 60min and ignoring the process kinetics. If NO-induced synergy and the oxidative stress are time-dependent, the elucidation of the cell killing kinetics is essential, particularly for survival curves exhibiting a "shoulder" sometimes reflecting sublethal damage as in the linear-quadratic survival models. We studied the kinetics of NO synergic effects on H2O2-induced killing of microbial pathogens. A synergic pro-oxidative activity toward gram-negative and gram-positive cells is demonstrated even at sub-μM/min flux of NO. For certain strains, the synergic effect progressively increased with the duration of cell exposure, and the linear-quadratic survival model best fit the observed survival data. In contrast to the failure of SOD to affect the bactericidal process, nitroxide SOD mimics abrogated the pro-oxidative synergy of NO/H2O2. These cell-permeative antioxidants, which hardly react with diamagnetic species and react neither with NO nor with H2O2, can detoxify redox-active transition metals and catalytically remove intracellular superoxide and nitrogen-derived reactive species such as (•)NO2 or peroxynitrite. The possible mechanism underlying the bactericidal NO synergy under oxidative stress and the potential therapeutic gain are discussed.
authors.affiliation: Department of Chemistry and Biochemistry, Queens College, City University of New York, Flushing, NY 11367, USA.
authors.forename: Reeta
authors.initials: R
authors.lastname: Yadav
authors.affiliation: Department of Oral and Maxillofacial Surgery, Barzilai Medical Center, Ashkelon, Israel; School of Medicine, Barwon Health, Deakin University, Geelong, VIC 3220, Australia.
authors.forename: Yuval
authors.initials: Y
authors.lastname: Samuni
authors.affiliation: Department of Oral and Maxillofacial Surgery, Barzilai Medical Center, Ashkelon, Israel.
authors.forename: Alex
authors.initials: A
authors.lastname: Abramson
authors.affiliation: Department of Oral and Maxillofacial Surgery, Hebrew University-Hadassah Medical Center, Jerusalem 91120, Israel.
authors.forename: Rephael
authors.initials: R
authors.lastname: Zeltser
authors.affiliation: Department of Oral and Maxillofacial Surgery, Hebrew University-Hadassah Medical Center, Jerusalem 91120, Israel.
authors.forename: Nardi
authors.initials: N
authors.lastname: Casap
authors.affiliation: Department of Chemistry and Biochemistry, Queens College, City University of New York, Flushing, NY 11367, USA.
authors.forename: Tonmoy K
authors.initials: TK
authors.lastname: Kabiraj
authors.affiliation: Department of Chemistry and Biochemistry, Queens College, City University of New York, Flushing, NY 11367, USA.
authors.forename: Maureen
authors.initials: M
authors.lastname: L Banach
authors.affiliation: Department of Chemistry and Biochemistry, Queens College, City University of New York, Flushing, NY 11367, USA. Electronic address: uri.samuni@qc.cuny.edu.
authors.forename: Uri
authors.initials: U
authors.lastname: Samuni
mesh_terms: D016924:Actinomyces viscosus / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D016976:Aggregatibacter actinomycetemcomitans / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003497:Cyclic N-Oxides / Q000494:pharmacology; D004357:Drug Synergism; D004926:Escherichia coli / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D050296:Microbial Viability / Q000187:drug effects; D015233:Models, Statistical; D009569:Nitric Oxide / Q000494:pharmacology*; D009599:Nitroprusside / Q000494:pharmacology; D016877:Oxidants / Q000494:pharmacology*; D013291:Streptococcus / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D013482:Superoxide Dismutase / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D003497:Cyclic N-Oxides; D016877:Oxidants; D009599:Nitroprusside; D009569:Nitric Oxide; D006861:Hydrogen Peroxide; D013482:Superoxide Dismutase
keywords: Free radicals; Hydrogen peroxide; Microbial pathogens; Nitric oxide; Oxidative stress; Synergy