Anti-virulence strategy of diaryl chalcogenide compounds against Candida albicans infection

Abstract

Candida albicans is an important opportunistic pathogenic fungus that frequently causes serious systemic infection in humans. Due to the vital roles of biofilm formation and the yeast-to-hypha transition in the infection process, we have selected a series of diaryl chalcogenides and tested their efficacy against C. albicans SC5314 pathogenicity by the inhibition of biofilm formation and the yeast-to-hypha transition. The compounds 5-sulfenylindole and 5-selenylindole were found to have excellent abilities to inhibit both biofilm formation and hyphal formation in C. albicans SC5314. Intriguingly, the two leading compounds also markedly attenuated C. albicans SC5314 virulence in human cell lines and mouse infection models at micromolar levels. Furthermore, our results showed that the presence of the compounds at 100 µM resulted in a marked decrease in the expression of genes involved in the cAMP-PKA and MAPK pathways in C. albicans SC5314. Intriguingly, the compounds 5-sulfenylindole and 5-selenylindole not only attenuated the cytotoxicity of Candida species strains but also showed excellent synergistic effects with antifungal agents against the clinical drug-resistant C. albicans strain HCH12. The compound 5-sulfenylindole showed an obvious advantage over fluconazole as it could also restore the composition and richness of the intestinal microbiota in mice infected by C. albicans. Together, these results suggest that diaryl chalcogenides can potentially be designed as novel clinical therapeutic agents against C. albicans infection. The diaryl chalcogenides of 5-sulfenylindole and 5-selenylindole discovered in this study can provide new direction for developing antifungal agents against C. albicans infection.

Keywords: Candida albicans; diaryl chalcogenide; gut microbiota; hyphal morphogenesis; virulence.

Figure 1.

Influences of diaryl chalcogenides on C. albicans SC5314 hyphal formation, biofilm formation and virulence. Effects of diaryl chalcogenides on the hyphal formation (a) and biofilm formation (b) of C. albicans SC5314 at 100 µM. (c) analysis of the effect of compounds and fluconazole (1 µg/mL) on the cytotoxicity of C. albicans SC5314 to A549 cells. Cell cytotoxicity was detected and measured as LDH release. The LDH released by A549 cells in (c) after inoculation with C. albicans in the absence of compounds was defined as 100% and used to normalize the LDH release ratios of other treatments. The compounds were dissolved in DMSO, and the equivalent amount of DMSO was added as a control. Each experiment was performed at least three times in triplicate. Data represent the means ± standard deviation of three independent experiments. *, P < 0.05; **, P < 0.01; ***, P < 0.001 (unpaired t-test).

Figure 2.

Different concentrations (6.25–100 µM) of compounds 3 and 8 and fluconazole (1 µg/mL) on C. albicans SC5314 hyphal formation (a), biofilm formation (b) and cytotoxicity (c). Data are means ± standard deviations from three independent experiments. ***P < 0.001 vs DMSO (unpaired t-test).

Figure 3.

Efficacy of diaryl chalcogenide compound 3 (100 µM) and compound 8 (100 µM) against C. albicans SC5314 in the mouse infection model. (a) survival rate of mice after infection with C. albicans SC5314 without treatment with (●) and by treated with fluconazole (10 µg/mL, ○), compound 3 (▲) and compound 8 (▽). (b) the in vivo pathogen cell numbers of C. albicans SC5314 in the mouse tongue after infection without treatment with and by treated with compound 3 and compound 8 (100 µM). (c) pathological sections were evaluated to determine the effects of compounds 3 and 8 (100 µM) on C. albicans SC5314 infection. The red arrows showed the C. albicans SC5314 infection sites in the mouse tongues. Data are the mean ± standard deviation of three independent experiments. ***, P < 0.001 (unpaired t-test). CA: C. albicans.

Figure 4.

Analysis of biofilm formation (a), cytotoxicity (b) and hyphal formation (c) of different Candida spp. and N. glabrata clinical isolates in the absence or presence of compound 3 and compound 8 (100 µM). Data represent the means ± standard deviation of three independent experiments. **, P < 0.01; ***, P < 0.001 (unpaired t-test).

Figure 5.

Effects of compounds (100 µM) and their synergistic activities with fluconazole on the biofilm formation (a) and virulence (b) of the clinical drug-resistant C. albicans strain. Data are means ± standard deviations from three independent experiments. **, P < 0.01; ***, P < 0.001 (unpaired t-test).