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

Abstract

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 (Φ = 0.03), decaying by efficient intersystem crossing to an excited triplet state PTN*, as detected by laser-flash photolysis experiments. In the presence of triplet molecular oxygen, thePTN* was fully quenched producing singlet molecular oxygen (O) with a quantum yield of 0.69. In addition, in buffer solutions, PTN has the ability to also generate a superoxide radical anion (O˙) 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 O and O˙ 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.

The Dark Side: Photosensitizer Prodrugs

“…One of the main advantages of PDT is the possibility to combine this treatment with other complementary techniques [1]. For instance, combinations with photothermal therapy (PTT), chemotherapy, or immunotherapy have been reported [2][3][4][5][6][7][8].…”

“…These optically silent PS prodrugs are photodynamically inactive until they encounter the proper chemical or biological trigger, inducing a conformation change and becoming photodynamically active. Such chemical or physiological triggers include (1) pH, (2) redox potential, (3) enzymatic activities, (4) DNA, or (5) temperature. This review is dedicated to the development and testing of such photosensitizer prodrugs.…”

Change is permanent: thoughts on the fading of cochineal-based watercolor pigments

“…Bleaching reactions are promoted in proton-donating solvents. Recent studies have shown that a number of deactivation pathways can occur in anthraquinones, including emission from tautomeric states following excited state internal electron transfer and from population of a dark, non-radiative state that irreversibly leads to a colorless molecule [34,35].…”

Antibacterial Compounds from Mushrooms: A Lead to Fight ESKAPEE Pathogenic Bacteria?

“…•- [20,21]. In another study, the antibiofilm activity of parietin has been demonstrated against S. aureus and E. faecalis [22], which is particularly interesting as biofilms are implicated in 80 % of human microbial infections.…”