Photoinactivation of Candida albicans mediated by a tetracationic phthalocyanine

M. ALBANA DI PALMA, A. LAURA OCHOA, M. ELISA MILANESIO, M. GABRIELA ALVAREZ, EDGARDO N. DURANTINI

Córdoba

Congreso; 16th International Congress on Photobiology; 2014

The incidence of superficial and deep-seated fungal infections has increased markedly over the last 20 years. Candida albicans represents a critical problem to health and is one of the main causes of fungal diseases worldwide. Further increasing problem is the emergence of resistant yeast strains due to extensive and prolonged use of antifungal agents. Consequently, the search for new effective antifungal treatments is awfully necessary. Photodynamic inactivation (PDI) of microorganisms has been proposed a new alternative to controlling C. albicans infections. In this work, the photodynamic action induced by zinc(II) 2,9,16,23-tetrakis[4 (N-methylpyridyloxy)]phthalocyanine (ZnPPc4+) was investigated in AOT reverse micelles and C. albicans. ZnPPc4+ produced singlet molecular oxygen, 1O2, with a quantum yield ofΔ=0.56 in AOT system. Also, this phthalocyanine photodecomposed nitro blue tetrazolium (NBT) efficiently in presence of NADH. In vitro investigations showed that ZnPPc4+ was rapidly bound to C. albicans cells (<5 min). A high amount of phthalocyanine was retained in the cells after two washing steps, indicating a strong interaction between the photosensitizer and C. albicans. After 30 min irradiation, a decrease of 5 log in the cell viability was obtained for C. albicans ZnPPc4+. The generation of 1O2 in the yeast cell was evaluated using 9,10-dimethylanthracene (DMA). Thus, cells were incubated with DMA in dark, washed once and treated with ZnPPc4+. Photooxidation of DMA was determined by fluorescence, indicating a rapid disappearance of the substrate bound to the cells. Similar result was found washing the cells after incubation with ZnPPc4+. Also, the photogeneration of superoxide anion radical by ZnPPc4+ was not detected using NBT method in cell suspensions. However, decomposition of NBT was observed when NADH was added to the cell suspensions. The results indicate that ZnPPc4+ is an interesting phthalocyanine for photodynamic inactivation of yeasts in liquid suspensions. The killing of  C. albicans cells by this cationic phthalocyanine and visible light irradiation seem to be mediated mainly by 1O2. Although in a minor contribution, the participation of other active oxygen species should not be completely ruled out.