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Paradoxical potentiation of methylene blue-mediated antimicrobial photodynamic inactivation by sodium azide: role of ambient oxygen and azide radicals.
- Source :
-
Free radical biology & medicine [Free Radic Biol Med] 2012 Dec 01; Vol. 53 (11), pp. 2062-71. Date of Electronic Publication: 2012 Oct 06. - Publication Year :
- 2012
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Abstract
- Sodium azide (NaN(3)) is widely employed to quench singlet oxygen during photodynamic therapy (PDT), especially when PDT is used to kill bacteria in suspension. We observed that addition of NaN(3) (100 μM or 10 mM) to gram-positive Staphylococcus aureus and gram-negative Escherichia coli incubated with methylene blue (MB) and illuminated with red light gave significantly increased bacterial killing (1-3 logs), rather than the expected protection from killing. A different antibacterial photosensitizer, the conjugate between polyethylenimine and chlorin(e6) (PEI-ce6), showed reduced PDT killing (1-2 logs) after addition of 10mM NaN(3). Azide (0.5mM) potentiated bacterial killing by Fenton reagent (hydrogen peroxide and ferrous sulfate) by up to 3 logs, but protected against killing mediated by sodium hypochlorite and hydrogen peroxide (considered to be a chemical source of singlet oxygen). The intermediacy of N(3)() was confirmed by spin-trapping and electron spin resonance studies in both MB-photosensitized reactions and Fenton reagent with addition of NaN(3). We found that N(3)() was formed and bacteria were killed even in the absence of oxygen, suggesting the direct one-electron oxidation of azide anion by photoexcited MB. This observation suggests a possible mechanism to carry out oxygen-independent PDT.<br /> (Copyright © 2012 Elsevier Inc. All rights reserved.)
- Subjects :
- Anti-Bacterial Agents chemistry
Anti-Bacterial Agents radiation effects
Drug Synergism
Escherichia coli drug effects
Free Radicals chemistry
Free Radicals pharmacology
Hydrogen Peroxide pharmacology
Iron pharmacology
Methylene Blue chemistry
Methylene Blue radiation effects
Microbial Viability drug effects
Oxidation-Reduction
Photochemotherapy
Reactive Oxygen Species chemistry
Sodium Hypochlorite pharmacology
Staphylococcus aureus drug effects
Anti-Bacterial Agents pharmacology
Methylene Blue pharmacology
Photosensitizing Agents pharmacology
Reactive Oxygen Species metabolism
Sodium Azide pharmacology
Subjects
Details
- Language :
- English
- ISSN :
- 1873-4596
- Volume :
- 53
- Issue :
- 11
- Database :
- MEDLINE
- Journal :
- Free radical biology & medicine
- Publication Type :
- Academic Journal
- Accession number :
- 23044264
- Full Text :
- https://doi.org/10.1016/j.freeradbiomed.2012.09.006