Different anti-Candida activities of two human lactoferrin-derived peptides, Lfpep and kaliocin-1

Abstract

The synthetic peptides Lfpep and kaliocin-1 include the sequences from positions 18 to 40 and 153 to 183 of human lactoferrin, respectively. Lfpep is a cationic peptide with bactericidal and giardicidal effects, whereas kaliocin-1 is a novel bactericidal peptide that corresponds to a highly homologous sequence present in the transferrin family of proteins. Both peptides presented fungicidal activity against Candida spp., including fluconazole- and amphotericin B-resistant clinical isolates. Lfpep exhibited higher antifungal activity (8- to 30-fold) and salt resistance than kaliocin-1. The killing activity of Lfpep was mediated by its permeabilizing activity on Candida albicans cells, whereas kaliocin-1 was unable to disrupt the cytoplasmic membrane, as indicated by its inability to allow permeation of propidium iodide and the small amount of K+ released. The amino acid sequence of kaliocin-1 includes the "multidimensional antimicrobial signature" conserved in disulfide-containing antimicrobial peptides and a striking similarity to brevinin-1Sa, an antimicrobial peptide from frog skin secretions, exhibiting a "Rana box"-like sequence. These features may be of interest in the design of new antifungals.

FIG. 1.

Candidacidal activities of kaliocin-1 and Lfpep. (A and B) Dose- and time-dependent reductions in the number of viable C. albicans cells (10⁵ cells/ml) incubated with kaliocin-1 (A) or Lfpep (B) in 10 mM Tris-HCl (pH 7.4) at 37°C. (C) Effect of NaCl on the candidacidal activities of 150 μM kaliocin-1 and 50 μM Lfpep tested for 1 h in 10 mM Tris-HCl (pH 7.4) containing different concentrations of NaCl. The percentage of viable cells was determined relative to that for cells incubated without peptides. The results are the means ± standard deviations of at least three separate experiments.

FIG. 2.

Effects of kaliocin-1 and Lfpep on the cytoplasmic membrane of C. albicans cells. The fluorescence profiles of C. albicans cells (10⁵ cells/ml) treated for 30 min with 50 μM Lfpep, 150 μM kaliocin-1 (Kal-1), or 16 μg/ml amphotericin B (AmB) or untreated cells (C; control) stained with propidium iodide to determine membrane permeabilization (A) or DiOC₅(3) to measure the membrane potential (B) are shown. The fluorescence distribution was analyzed by flow cytometry.