Effects of photodynamic therapy using bisdemethoxycurcumin combined with melatonin or acetyl-melatonin on C. Albicans

The current study aims to explore the efficacy of antifungal photodynamic therapy (PDT) on C. albicans biofilms by combining photosensitizers, bisdemethoxycurcumin (BDMC), and melatonin (MLT) or acetyl-melatonin (AcO-MLT). Additionally, the relationship between different types of reactive oxygen species and PDT's antifungal efficacy was investigated. BDMC, MLT and AcO-MLT were applied, alone and in combination, to 48-hour C. albicans biofilm cultures (n = 6/group). Blue and red LED light (250 mW/cm² with 37.5 J/cm² for single or 75 J/cm² for dual photosensitizer groups) were used to irradiate BDMC groups and MLT/AcO-MLT groups, respectively. For combination groups, blue LEDs and subsequently red LEDs were used. Drop plate assays were performed at 0, 1 and 6 h post-treatment. Colony forming units (CFUs) were then counted after 48 h. Hydroxyl radicals and singlet oxygen were measured using fluorescence spectroscopy and electron spin resonance (ESR) spectroscopy. Additionally, cell cytotoxicity was tested on human oral keratinocytes. Significant CFU reductions were observed with combinations 20 µM BDMC + 20 µM AcO-MLT and 60 µM BDMC + 20 µM MLT at 0 and 1 h post-treatment, respectively. Singlet oxygen production increased with the addition of MLT/AcO-MLT and had moderate-substantial correlations with inhibition at all times. Hydroxyl radical production was not significantly different from the control. Additionally, BDMC exhibited subtle cytotoxicity on human oral keratinocytes. PDT using BDMC + MLT or AcO-MLT, with blue and red LED light, effectively inhibits C. albicans biofilm through singlet oxygen generation. Melatonin acts as a photosensitizer in PDT to inhibit fungal infection.