Influence of porphyrin cationic charges on photoinactivation of Candida albicans morphotypes

Abstract

The increasing resistance of Candida albicans to conventional antifungal therapies highlights the need for alternative treatment strategies. In this study, photodynamic inactivation (PDI) was evaluated using four cationic porphyrins (AB3+, A2B22+, A3B3+, and A44+), differing in symmetry and number of positive charges. These compounds were tested against C. albicans in its planktonic, pseudohyphal, and biofilm forms. Upon incubation with 1.0 µM porphyrin, rapid cellular uptake was observed, with A3B3+ and A44+, showing the highest accumulation (0.65 and 0.50 nmol/10⁶ cells, respectively). The amount of porphyrin bound to cells remained stable over time, with no significant changes beyond 5 min of incubation. PDI was performed using different porphyrin concentrations (0.5?5.0 µM) and light exposure times (5?30 min). A3B3+ and A44+ exhibited potent photoinactivation, reducing cell viability by over 5 log (>99.999%) after 5 min of irradiation using 2.5 µM porphyrin. Reactive oxygen species quenching experiments indicated that singlet molecular oxygen was the primary cytotoxic agent. Additionally, A3B3+ and A44+ effectively eradicated C. albicans cells on agar surfaces. These porphyrins also inactivated pseudohyphal suspensions of C. albicans, achieving a reduction greater than 5 log, when incubated with 5 µM porphyrin and 5 min of irradiation. Using this concentration, C. albicans biofilms were completely photoinactivated after 60 min of light exposure. These findings demonstrate that highly charged cationic porphyrins are promising photosensitizers for the targeted elimination of C. albicans across its major morphological states.