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J Photochem Photobiol B. 2018 Jan;178:277-286. doi: 10.1016/j.jphotobiol.2017.10.036. Epub 2017 Oct 31.

Potentiation by potassium iodide reveals that the anionic porphyrin TPPS4 is a surprisingly effective photosensitizer for antimicrobial photodynamic inactivation.

Author information

1
Department of Infectious Diseases, First Affiliated Hospital, Guangxi Medical University, Nanning, China; Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA; Department of Dermatology, Harvard Medical School, Boston, MA, USA.
2
Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA; The National Institute of Laser Enhanced Science, Cairo University, Egypt.
3
Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA; Department of Otorhinolaryngology, Head and Neck Surgery, First Clinical Medical College and Hospital, Guangxi University of Chinese Medicine, Nanning, China.
4
Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, USA; Department of Dermatology, Harvard Medical School, Boston, MA, USA; Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA, USA. Electronic address: hamblin@helix.mgh.harvard.edu.

Abstract

We recently reported that addition of the non-toxic salt, potassium iodide can potentiate antimicrobial photodynamic inactivation of a broad-spectrum of microorganisms, producing many extra logs of killing. If the photosensitizer (PS) can bind to the microbial cells, then delivering light in the presence of KI produces short-lived reactive iodine species, while if the cells are added after light the killing is caused by molecular iodine produced as a result of singlet oxygen-mediated oxidation of iodide. In an attempt to show the importance of PS-bacterial binding, we compared two charged porphyrins, TPPS4 (thought to be anionic and not able to bind to Gram-negative bacteria) and TMPyP4 (considered cationic and well able to bind to bacteria). As expected TPPS4+light did not kill Gram-negative Escherichia coli, but surprisingly when 100mM KI was added, it was highly effective (eradication at 200nM+10J/cm2 of 415nm light). TPPS4 was more effective than TMPyP4 in eradicating the Gram-positive bacteria, methicillin-resistant Staphylococcus aureus and the fungal yeast Candida albicans (regardless of KI). TPPS4 was also highly active against E. coli after a centrifugation step when KI was added, suggesting that the supposedly anionic porphyrin bound to bacteria and Candida. This was confirmed by uptake experiments. We compared the phthalocyanine tetrasulfonate derivative (ClAlPCS4), which did not bind to bacteria or allow KI-mediated killing of E. coli after a spin, suggesting it was truly anionic. We conclude that TPPS4 behaves as if it has some cationic character in the presence of bacteria, which may be related to its delivery from suppliers in the form of a dihydrochloride salt.

KEYWORDS:

Anionic porphyrin; Antimicrobial photodynamic inactivation; Cationic porphyrin; ClAlPCS4; Potassium iodide; TMPyP4; TPPS4

PMID:
29172135
PMCID:
PMC5771845
DOI:
10.1016/j.jphotobiol.2017.10.036
[Indexed for MEDLINE]
Free PMC Article

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