Fungal Anthraquinone Photoantimicrobials Challenge the Dogma of Cationic Photosensitizers.

The photoantimicrobial potential of four mushroom species (i.e., Cortinarius cinnabarinus, C. holoxanthus, C. malicorius, and C. sanguineus) was explored by studying the minimal inhibitory concentrations (MIC) via a light-modified broth microdilution assay based on the recommended protocols of the European Committee on Antimicrobial Susceptibility Testing (EUCAST). The extracts were tested against Candida albicans, Escherichia coli, and Staphylococcus aureus under blue (λ = 428 and 478 nm, H = 30 J/cm2) and green light (λ = 528 nm, H = 30 J/cm2) irradiation. Three extracts showed significant photoantimicrobial effects at concentrations below 25 µg/mL. Targeted isolation of the major pigments from C. sanguineus led to the identification of two new potent photoantimicrobials, one of them (i.e., dermocybin) being active against S. aureus and C. albicans under green light irradiation [PhotoMIC530 = 39.5 µM (12.5 µg/mL) and 2.4 µM (0.75 µg/mL), respectively] and the other one (i.e., emodin) being in addition active against E. coli in a low micromolar range [PhotoMIC428 = 11.1 µM (3 µg/mL)]. Intriguingly, dermocybin was not (photo)cytotoxic against the three tested cell lines, adding an additional level of selectivity. Since both photoantimicrobials are not charged, this discovery shifts the paradigm of cationic photosensitizers.

A convenient separation strategy for fungal anthraquinones by centrifugal partition chromatography.

As recently shown, some fungal pigments exhibit significant photoactivity turning them into promising agents for the photodynamic treatment of microbial infections or malignant diseases. In the present study, a separation strategy for fungal anthraquinones was developed based on centrifugal partition chromatography. A suitable method was explored employing a methanolic extract of the fruiting bodies of Cortinarius sanguineus (Agaricales, Basidiomycota). An excellent fractionation was achieved using a biphasic solvent system comprising chloroform/ethyl acetate/methanol/water/acetic acid (3:1:3:2:1, v/v/v/v/v) operating in ascending mode. Experiments on an analytical scale with extracts of closely related Cortinarius species exhibited broad applicability of the devised system. Up to six pigments could be purified directly from the crude extract. Preparative-scale fractionation of the methanol extracts of C. malicorius and C. sanguineus demonstrated that up-scaling was possible without compromising selectivity.