Insights into the candidacidal mechanism of Ctn[15-34] - a carboxyl-terminal, crotalicidin-derived peptide related to cathelicidins.

PURPOSE: Ctn[15-34], a carboxyl-terminal fragment of crotalicidin (a cathelicidin from the venom gland of a South American rattlesnake), has shown antifungal activity against clinical and standard strains of Candida species. The aim of the present work was to investigate the underlying mechanisms of the candidicidal activity of Ctn[15-34]. METHODOLOGY: The time-kill profile and drug synergism were evaluated by means of a microdilution assay and multi-parametric flow cytometry. The presumptive interaction of Ctn[15-34] with lipid membranes was estimated in vitro with a lipid-mimic compound, the chromogenic substance 4-nitro-3-(octanoyloxy)benzoic acid (4N3OBA).Results/Key findings. The absorbance increment (at 425 nm) indicated a concentration- and time-dependent in-solution association between Ctn[15-34] and 4N3OBA. The interaction of Ctn[15-34] with Candida cells was confirmed by flow cytometric measurements with the 5(6)-carboxyfluorescein-labelled peptide (CF-Ctn[15-34]). Analysis of the killing time of Candida exposed to Ctn[15-34] and amphotericin B (AMB) showed that both the peptide and polyene drug reduce the number of c.f.u. but in mechanistically different ways. The Ctn[15-34] peptide alone caused yeast cell membrane disruption, which was confirmed by lactate dehydrogenase leakage and biomarkers of cell death mediated by necrosis. CONCLUSION: Overall, Ctn[15-34] displays a synergistic antifungal activity with AMB, an effect that can be further developed into a multi-target therapeutic option with other antimycotics currently in use.