Modulation of the in vitro candidacidal activity of human neutrophil defensins by target cell metabolism and divalent cations.

Abstract

We tested the in vitro susceptibility of Candida albicans to three defensins from human neutrophilic granulocytes (HNP-1, 2, and 3), a homologous defensin from rabbit leukocytes (NP-1), and four unrelated cationic peptides. Although the primary amino acid sequences of HNP-1, 2, and 3 are identical except for a single amino-terminal amino acid alteration, HNP-1 and HNP-2 killed C. albicans but HNP-3 did not. C. albicans blastoconidia were protected from HNP-I when incubations were performed in the absence of oxygen or in the presence of inhibitors that blocked both of its mitochondrial respiratory pathways. Neither anaerobiosis nor mitochondrial inhibitors substantially protected C. albicans exposed to NP-1, poly-L-arginine, poly-L-lysine, or mellitin. Human neutrophilic granulocyte defensin-mediated candidacidal activity was inhibited by both Mg2+ and Can, and was unaffected by Fe2". In contrast, Fe2" inhibited the candidacidal activity of NP-i and all of the model cationic peptides, whereas Mg2+ inhibited none of them. These data demonstrate that susceptibility of C. albicans to human defensins depends both on the ionic environment and on the metabolic state of the target cell. The latter finding suggests that leukocyte-mediated microbicidal mechanisms may manifest oxygen dependence for reasons unrelated to the production of reactive oxygen intermediates by the leukocyte.

Large-scale synthesis and functional elements for the antimicrobial activity of defensins

“…The Candida albicans strains were insensitive to HNP3, which has a negatively charged Asp residue at this position. The results are consistent with the previously reported candidacidal activity of human defensins [28], although the C. albicans strains and the assay procedures used were different.…”

“…There are variations in the sequences at the N-and C-termini and in the middle portion of these peptides. These differences have been found to be reflected in their antimicrobial spectrum and specificity of organisms for which they are cidal [14,28]. This functional diversity observed for similarly structured molecules raises interest in identifying the crucial residues responsible for their specificity and antimicrobial potency.…”

“…For instance, human neutrophil defensins HNP1 (human neutrophil peptide 1) and HNP2 have been reported to be potent candidacidal agents. However, HNP3, which differs only in one amino acid at the N-terminus, has been found to be least active against C. albicans [28]. HNP1 and HNP2 have been found to be equipotent in their ability to kill Capnocytophaga species, and their activity has been reported to be significantly greater than that of HNP3 [29].…”

The human salivary peptide histatin 5 exerts its antifungal activity through the formation of reactive oxygen species

“…For example, studies on human defensins (HNP1, -2, and -3)-mediated cytotoxicity showed the requirement for peptide internalization and for target cell metabolic processes (27). Other examples are the candidacidal activity of HNP-1, which is negatively affected in the presence of respiratory inhibitors (28), and the activity of killer toxin from Pichia kluyveri against Saccharomyces cerevisiae cells that is highly dependent on the physiological state of cells (29) in a very similar fashion as that described for histatin 5. It is therefore feasible that the present discovery that ROS formation is a quintessential step in the killing process provoked by histatin 5 is not restricted to histatin 5 activity, but may represent a common mechanism of target-cell killing afforded by agents that are dependent on active cell metabolism.…”

Host Defense Peptides in Wound Healing

“…As immune modulators, HNP-1, -2, and -3 upregulate TNF-α and interleukin (IL)-1 in human monocytes that have been activated by bacteria (61,62). Furthermore, HNP-1 and -2 have the ability to directly kill gram-negative and -positive bacteria (48), Candida albicans (63), and enveloped viruses such as members of the herpes family (64,65). HNP-5 has concentrationdependent microbicidal activity against Escherichia coli, Listeria monocytogenes, Salmonella typhimurium, and C. albicans (66).…”