title: Thiocyanate potentiates antimicrobial photodynamic therapy: in situ generation of the sulfur trioxide radical anion by singlet oxygen.
abstract: Antimicrobial photodynamic therapy (PDT) is used for the eradication of pathogenic microbial cells and involves the light excitation of dyes in the presence of O2, yielding reactive oxygen species including the hydroxyl radical (OH) and singlet oxygen ((1)O2). In order to chemically enhance PDT by the formation of longer-lived radical species, we asked whether thiocyanate (SCN(-)) could potentiate the methylene blue (MB) and light-mediated killing of the gram-positive Staphylococcus aureus and the gram-negative Escherichia coli. SCN(-) enhanced PDT (10 µM MB, 5 J/cm(2) 660 nm hv) killing in a concentration-dependent manner of S. aureus by 2.5 log10 to a maximum of 4.2 log10 at 10mM (P<0.001) and increased killing of E. coli by 3.6 log10 to a maximum of 5.0 log10 at 10mM (P<0.01). We determined that SCN(-) rapidly depleted O2 from an irradiated MB system, reacting exclusively with (1)O2, without quenching the MB excited triplet state. SCN(-) reacted with (1)O2, producing a sulfur trioxide radical anion (a sulfur-centered radical demonstrated by EPR spin trapping). We found that MB-PDT of SCN(-) in solution produced both sulfite and cyanide anions, and that addition of each of these salts separately enhanced MB-PDT killing of bacteria. We were unable to detect EPR signals of OH, which, together with kinetic data, strongly suggests that MB, known to produce OH and (1)O2, may, under the conditions used, preferentially form (1)O2.
authors: Department of Chemistry, Columbia University, New York, NY, USA; The Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA.
authors: Tyler G
authors: TG
authors: St Denis
authors: The Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA; Department of Dermatology, Dermatooncology and Venerology, Semmelweis University School of Medicine, Budapest, Hungary.
authors: Daniela
authors: D
authors: Vecchio
authors: Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, Krakow, Poland.
authors: Andrzej
authors: A
authors: Zadlo
authors: The Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA; School of Chemistry, University of Wollongong, NSW2522, Australia.
authors: Ardeshir
authors: A
authors: Rineh
authors: The Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA.
authors: Magesh
authors: M
authors: Sadasivam
authors: The Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA; Department of Dermatology, Dermatooncology and Venerology, Semmelweis University School of Medicine, Budapest, Hungary; Department of Dermatology, Semmelweis University School of Medicine, 1085 Budapest, Hungary.
authors: Pinar
authors: P
authors: Avci
authors: The Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA; Department of Dermatology, Dermatooncology and Venerology, Semmelweis University School of Medicine, Budapest, Hungary; Department of Infectious Disease, First Affiliated College & Hospital, Guangxi Medical University, Nanning, China.
authors: Liyi
authors: L
authors: Huang
authors: Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, Krakow, Poland; Faculty of Physics, Astronomy, and Applied Computer Science, Jagiellonian University, Krakow, Poland.
authors: Anna
authors: A
authors: Kozinska
authors: The Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA.
authors: Rakkiyappan
authors: R
authors: Chandran
authors: Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, Krakow, Poland.
authors: Tadeusz
authors: T
authors: Sarna
authors: The Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA; Department of Dermatology, Dermatooncology and Venerology, Semmelweis University School of Medicine, Budapest, Hungary; Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA, USA. Electronic address: hamblin@helix.mgh.harvard.edu.
authors: Michael R
authors: MR
authors: Hamblin
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology*; D004926:Escherichia coli / Q000187:drug effects; D008751:Methylene Blue / Q000737:chemistry / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D010084:Oxidation-Reduction; D010778:Photochemotherapy; D026082:Singlet Oxygen / Q000737:chemistry; D013211:Staphylococcus aureus / Q000187:drug effects; D013461:Sulfur Oxides / Q000737:chemistry*; D013861:Thiocyanates / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D013461:Sulfur Oxides; D013861:Thiocyanates; D026082:Singlet Oxygen; C011118:sulfur trioxide; C031760:thiocyanate; D008751:Methylene Blue
keywords: 4-protio-3-carbamoyl-2,2,5,5-tetraperdeuteromethyl-3-pyrrolin-1-yloxy; 5,5-dimethyl-1-pyrroline-N-oxide; Antimicrobial photodynamic inactivation; Cyanide; DMPO; ESR spin trapping; Gram-negative bacteria; Gram-positive bacteria; MB; PB; PBS; PDT; PS; Prussian Blue; Sulfite; Thiocyanate; mHCTPO; methylene blue; phosphate-buffered saline; photodynamic therapy; photosensitizer
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