Antimicrobial photodynamic activity and cytocompatibility of [Au.sub.25][.sub.18] clusters photoexcited by blue LED light irradiation

• Published in: International journal of nanomedicine 2017-01, Vol.12, p.2703
• Main Authors: Miyata, Saori, Miyaji, Hirofumi, Kawasaki, Hideya, Yamamoto, Masaki, Nishida, Erika, Takita, Hiroko, Akasaka, Tsukasa, Ushijima, Natsumi, Iwanaga, Toshihiko, Sugaya, Tsutomu
• Format: Article
• Language: English
• Subjects: Anti-infective agents; Nanoparticles; Photochemotherapy; Physiological aspects; Properties
• ISSN: 1178-2013
• DOI: 10.2147/IJN.S131602

Antimicrobial photodynamic therapy (aPDT) has beneficial effects in dental treatment. We applied captopril-protected gold ([Au.sub.25][(Capt).sub.18])) clusters as a novel photosensitizer for aPDT. Photoexcited Au clusters under light irradiation generated singlet oxygen ([.sup.1][O.sub.2]). Accordingly, the antimicrobial and cytotoxic effects of [Au.sub.25][(Capt).sub.18] clusters under dental blue light-emitting diode (LED) irradiation were evaluated. [.sup.1][O.sub.2] generation of [Au.sub.25][(Capt).sub.18] clusters under blue LED irradiation (420-460 nm) was detected by a methotrexate (MTX) probe. The antimicrobial effects of photoexcited Au clusters (0, 5, 50, and 500 [micro]g/mL) on oral bacterial cells, such as Streptococcus mutans, Aggregatibacter actinomycetemcomitans, and Porphyromonas gingivalis, were assessed by morphological observations and bacterial growth experiments. Cytotoxicity testing of Au clusters and blue LED irradiation was then performed against NIH3T3 and MC3T3-E1 cells. In addition, the biological performance of Au clusters (500 [micro]g/mL) was compared to an organic dye photosensitizer, methylene blue (MB; 10 and 100 [micro]g/mL). We confirmed the ([.sup.1][O.sub.2]) generation ability of [Au.sub.25][(Capt).sub.18] clusters through the fluorescence spectra of oxidized MTX. Successful application of photoexcited Au clusters to aPDT was demonstrated by dose-dependent decreases in the turbidity of oral bacterial cells. Morphological observation revealed that application of Au clusters stimulated destruction of bacterial cell walls and inhibited biofilm formation. Aggregation of Au clusters around bacterial cells was fluorescently observed. However, photoexcited Au clusters did not negatively affect the adhesion, spreading, and proliferation of mammalian cells, particularly at lower doses. In addition, application of Au clusters demonstrated significantly better cytocompatibility compared to MB. We found that a combination of [Au.sub.25][(Capt).sub.18] clusters and blue LED irradiation exhibited good antimicrobial effects through [.sup.1][O.sub.2] generation and biosafe characteristics, which is desirable for aPDT in dentistry. Keywords: Aggregatibacter actinomycetemcomitans, antimicrobial photodynamic therapy, photosensitizer, Porphyromonas gingivalis, singlet oxygen, Streptococcus mutans