The SPFH Protein Superfamily in Fungi: Impact on Mitochondrial Function and Implications in Virulence

Gallic acid triphenylphosphonium derivatives TPP+-C10 and TPP+-C12 inhibit mitochondrial function in Candida albicans exerting antifungal and antibiofilm effects

AIMS

To evaluate the antifungal and antibiofilm activity of gallic acid derivatives TPP+-C10 and TPP+-C12 and their effects on mitochondrial function on two Candida albicans reference strains (ATCC 90029 and ATCC 10231).

METHODS AND RESULTS

First, we determined minimal inhibitory concentration (MIC) using a microdilution assay. Both compounds exerted antifungal effects, and their MICs ranged from 3.9 to 13 µM, with no statistically significant differences between them (P > 0.05, t-test). These concentrations served as references for following assays. Subsequently, we measured oxygen consumption with a Clark electrode. Our observations revealed that both drugs inhibited oxygen consumption in both strains with TPP+-C12 exerting a more pronounced inhibitory effect. We then employed flow cytometry with TMRE as a probe to assess mitochondrial membrane potential. For each strain assayed, the compounds induced a decay in transmembrane potential by 75%-90% compared to the control condition (P < 0.05, ANOVA). Then, we measured ATP levels using a commercial kit. TPP+-C12 showed a 50% decrease of ATP content (P < 0.05 ANOVA), while TPP+-C10 exhibited a less pronounced effect. Finally, we assessed the antibiofilm effect using the MTT reduction assay. Both compounds were effective, but TPP+-C12 displayed a greater potency, requiring a lower concentration to inhibit 50% of biofilms viability (P < 0.05, t-test).

CONCLUSIONS

Derivatives of gallic acid linked to a TPP+ group exert antifungal and antibiofilm activity through impairment of mitochondrial function in C. albicans.

Triazine-Based Small Molecules: A Potential New Class of Compounds in the Antifungal Toolbox

Invasive fungal infections caused by Candida species remain a significant public health problem worldwide. The increasing prevalence of drug-resistant infections and a limited arsenal of antifungal drugs underscore the need for novel interventions. Here, we screened several classes of pharmacologically active compounds against mammalian diseases for antifungal activity. We found that the synthetic triazine-based compound melanogenin (Mel) 56 is fungicidal in Candida albicans laboratory and clinical strains with minimal inhibitory concentrations of 8−16 µg/mL. Furthermore, Mel56 has general antifungal activity in several non-albicans Candida species and the non-pathogenic yeast Saccharomyces cerevisiae. Surprisingly, Mel56 inhibited the yeast-to-hyphae transition at sublethal concentrations, revealing a new role for triazine-based compounds in fungi. In human cancer cell lines, Mel56 targets the inner mitochondrial integral membrane prohibitin proteins, PHB1 and PHB2. However, Mel56 treatment did not impact C. albicans mitochondrial activity, and antifungal activity was similar in prohibitin single, double, and triple homozygous mutant strains compared to the wild-type parental strain. These results suggests that Mel56 has a novel mechanism-of-action in C. albicans. Therefore, Mel56 is a promising antifungal candidate warranting further analyses.