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

MORÁN VIEYRA, F. EDUARDO; COMINI, LAURA R.; LAURA MUGAS, M.; PÁEZ, PAULINA L.; NÚÑEZ MONTOYA, SUSANA C.; CABRERA, JOSÉ L.; MIGNONE, RICARDO A.; KONIGHEIM, BRENDA S.; BORSARELLI, CLAUDIO D.

Photochemical and Photobiological Sciences

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2017 vol. 16 p. 201 - 217

1474-905X

The photophysical, photoinduced pro-oxidant and antibacterial properties in vitro of the natural occurringparietin (PTN; 1,8-dihydroxy-3-methoxy-6-methyl-9,10-anthraquinone) were evaluated. PTN wasextracted from the lichen identified as Teloschistes flavicans (Sw.) Norm. (Telochistaceae). Results indicatethat in chloroform solution, PTN presents spectroscopic features corresponding to an excited-state intramolecularproton-transfer (ESIPT) state with partial keto?enol tautomerization. In argon-saturated solutions,the singlet excited state is poorly fluorescent (ΦF = 0.03), decaying by efficient intersystem crossingto an excited triplet state 3PTN*, as detected by laser-flash photolysis experiments. In the presence oftriplet molecular oxygen, the 3PTN* was fully quenched producing singlet molecular oxygen (1O2) with aquantum yield of 0.69. In addition, in buffer solutions, PTN has the ability to also generate a superoxideradical anion (O2?−) in a human leukocyte model and its production was enhanced under UVA-Visirradiation. Finally, the in vitro antibacterial capability of PTN in the dark and under UVA-Vis illuminationwas compared in microbial cultures of both Gram positive and negative bacteria. As a result, PTN showedpromising photo-induced antibacterial activity through the efficient photosensitized generation of both1O2 and O2?− species. Thus, we have demonstrated that PTN, an efficient photo-screening pigment inlichens, is also a good photosensitizer in solution with promising applications in antibacterial photodynamictherapy.