Parietin: an efficient photo-screening pigment in vivo with good photosensitizing and photodynamic antibacterial effects in vitro

• Published in: Photochemical & photobiological sciences 2017-02, Vol.16 (2), p.201-210
• Main Authors: Comini, Laura R., Morán Vieyra, F. Eduardo, Mignone, Ricardo A., Páez, Paulina L., Laura Mugas, M., Konigheim, Brenda S., Cabrera, José L., Núñez Montoya, Susana C., Borsarelli, Claudio D.
• Format: Article
• Language: English
• Subjects: Animals; Anti-Bacterial Agents - chemistry; Anti-Bacterial Agents - pharmacology; Biochemistry; Biomaterials; Cell Survival - drug effects; Cercopithecus aethiops; Chemistry; Emodin - analogs & derivatives; Emodin - chemistry; Emodin - isolation & purification; Emodin - pharmacology; Gram-Negative Bacteria - drug effects; Gram-Negative Bacteria - radiation effects; Gram-Positive Bacteria - drug effects; Gram-Positive Bacteria - radiation effects; Humans; Leukocytes - drug effects; Leukocytes - metabolism; Leukocytes - radiation effects; Lichens - chemistry; Lichens - metabolism; Light; Microbial Sensitivity Tests; Photosensitizing Agents - chemistry; Photosensitizing Agents - isolation & purification; Photosensitizing Agents - pharmacology; Physical Chemistry; Plant Sciences; Singlet Oxygen - chemistry; Singlet Oxygen - metabolism; Spectrophotometry, Ultraviolet; Superoxides - chemistry; Superoxides - metabolism; Teloschistes flavicans; Ultraviolet Rays; Vero Cells
• ISSN: 1474-905X; 1474-9092
• DOI: 10.1039/c6pp00334f

The photophysical, photoinduced pro-oxidant and antibacterial properties in vitro of the natural occurring parietin (PTN; 1,8-dihydroxy-3-methoxy-6-methyl-9,10-anthraquinone) were evaluated. PTN was extracted from the lichen identified as Teloschistes flavicans (Sw.) Norm. (Telochistaceae). Results indicate that in chloroform solution, PTN presents spectroscopic features corresponding to an excited-state intramolecular proton-transfer (ESIPT) state with partial keto–enol tautomerization. In argon-saturated solutions, the singlet excited state is poorly fluorescent ( F F = 0.03), decaying by efficient intersystem crossing to an excited triplet state 3 PTN*, as detected by laser-flash photolysis experiments. In the presence of triplet molecular oxygen, the 3 PTN* was fully quenched producing singlet molecular oxygen ( 1 O 2 ) with a quantum yield of 0.69. In addition, in buffer solutions, PTN has the ability to also generate a superoxide radical anion (O 2 ? - ) in a human leukocyte model and its production was enhanced under UVA-Vis irradiation. Finally, the in vitro antibacterial capability of PTN in the dark and under UVA-Vis illumination was compared in microbial cultures of both Gram positive and negative bacteria. As a result, PTN showed promising photo-induced antibacterial activity through the efficient photosensitized generation of both 1 O 2 and O 2 ? - species. Thus, we have demonstrated that PTN, an efficient photo-screening pigment in lichens, is also a good photosensitizer in solution with promising applications in antibacterial photodynamic therapy.