Candidacidal activities of human lactoferrin peptides derived from the N terminus

In light of the need for new antifungal agents, the candidacidal activities of human lactoferrin (hLF) and synthetic peptides representing the first, hLF(1-11), and second, hLF(21-31), cationic domains of its N terminus were compared. The results revealed that hLF(1-11) was more effective in killing fluconazole-resistant Candida albicans than hLF(21-31) and much more effec tive than lactoferrin, as determined microbiologically and by propidium iod ide (PI) staining. By using hLF(1-11) and various derivatives, it,vas found that the second and third residues of the N terminus of hLP(1-11) were cri tical for its candidacidal activity. Detailed investigation to elucidate th e mechanism of action of hLF(1-11) revealed a dose-dependent release of ATP by Candida upon exposure to hLF(1-11). Our observations that sodium azide reduced the PI uptake and candidacidal activity of hLF(1-11) and that, upon exposure to hLF(1-11), the fluorescent dye rhodamine 123 first accumulated inside the mitochondria and later was released into the cytoplasm indicate that the peptide triggers the energized mitochondrion. Furthermore, oxidiz ed ATP, which interferes with the interaction of ATP with its extracellular receptors, blocked the candidacidal action of hLF(1-11), as measured micro biologically and by PI staining. Addition of ATP (or analogues) aas not a s ufficient stimulus to kill C. albicans or to act synergistically with subop timal concentrations of the peptide. The main conclusions are that the firs t two arginines at the N terminus of hLF are critical in the candidacidal a ctivity of hLF(1-11) and that extracellular ATP is essential but not suffic ient for the peptide to exert its candidacidal activity.