Synthetic Histidine-Rich Peptides Inhibit Candida Species and Other Fungi In Vitro: Role of Endocytosis and Treatment Implications

Abstract

A family of histidine-rich peptides, histatins, is secreted by the parotid gland in mammals and exhibits marked inhibitory activity against a number of Candida species. We were particularly interested in the mechanism by which histidine-rich peptides inhibit fungal growth, because our laboratory has synthesized a variety of such peptides for drug and nucleic acid delivery. In contrast to naturally occurring peptides that are linear, peptides made on synthesizers can be varied with respect to their degrees of branching. Using this technology, we explored whether histidine-lysine (HK) polymers of different complexities and degrees of branching affect the growth of several species of Candida. Polymers with higher degrees of branching were progressively more effective against Candida albicans, with the four-branched polymer, H2K4b, most effective. Furthermore, H2K4b accumulated efficiently in C. albicans, which may indicate its ability to transport other antifungal agents intracellularly. Although H2K4b had greater antifungal activity than histatin 5, their mechanisms were similar. Toxicity in C. albicans induced by histatin 5 or branched HK peptides was markedly reduced by 4,4-diisothiocyanato-stilbene-2,2-disulfonate, an inhibitor of anion channels. We also determined that bafilomycin A1, an inhibitor of endosomal acidification, significantly decreased the antifungal activity of H2K4b. This suggests that the pH-buffering and subsequent endosomal-disrupting properties of histidine-rich peptides have a role in their antifungal activity. Moreover, the ability of the histidine component of these peptides to disrupt endosomes, which allows their escape from the lysosomal pathway, may explain why these peptides are both effective antifungal agents and nucleic acid delivery carriers.

BAR Domain Proteins Rvs161 and Rvs167 Contribute to Candida albicans Endocytosis, Morphogenesis, and Virulence

“…Both rvs161⌬ and rvs167⌬ cells were more resistant to Hst 5, an antimicrobial peptide that acts in the oropharyngeal environment, which is consistent with a proposed role for endocytosis in its uptake (17,23,51). Both rvs161⌬ and rvs167⌬ were more sensitive to H 2 O 2 , which likely makes them more sensitive to attack by the immune system.…”

The P-113 Fragment of Histatin 5 Requires a Specific Peptide Sequence for Intracellular Translocation inCandida albicans, Which Is Independent of Cell Wall Binding

“…Alternatively, Hst 5 could be taken up by Ssa2-mediated endocytosis and then released into the cytosol by retrograde transport, as has been described for yeast killer toxins in S. cerevisiae (5,14). Evidence for the involvement of endocytotic processes has also been reported for branched Hst 5 analogues (40). However, the time required for endocytotic trafficking does not seem to coincide with the rapid (Ͻ5 min) appearance of Hst 5 in the cytosol, nor does Hst 5 possess a classical HDEL endoplasmic retention signal essential for retrograde transport in S. cerevisiae.…”

Peptide-Based Polymer Therapeutics

“…Later on, Kallenbach et al [161,222,223] developed more simple dendrimeric peptides based on four copies of a dipeptide RW (RW) 4D which also demonstrated efficient activity against Escherichia coli and Staphylococcus aureus, but diminishing the haemolytic activity when compared the linear chains RW (n = 3-5). Zhu et al [162] has recently tested the antimicrobial activity of a set of branched His-Lys dendrimers on Candida species and other fungi, finding that the four-branched dendrimer H2K4b was the most active among all. There are many other dendrimers that have been tested to be effective against a variety of bacterial strains, including multidrug-resistant strains [157,[224][225][226][227].…”