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Purpose: To determine the efficacy of Histatin-5 (Hst5) peptide treatment in ameliorating dry eye disease (DED) phenotype in an in-vivo mouse model of scopolamine and desiccating stress (SDS) dry eye., Methods: SDS was induced in female C57BL/6 mice by subcutaneous injections of scopolamine hydrobromide and exposure to low relative humidity and forced air draft for five days. Mouse eyes were topically treated with synthetic Hst5 peptide or balanced salt solution (BSS) twice a day for four days. Control mice were not exposed to SDS induction and did not receive any treatments. Oregon green dextran (OGD) staining was used to evaluate corneal permeability. Histologically, staining with periodic acid schiff (PAS), immunohistochemistry (IHC) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), were used to quantify the number of goblet cells (GC), CD45 + immune cells and apoptotic cells respectively in formalin fixed paraffin embedded (FFPE) mouse whole eye sections., Results: Compared to treatment with BSS, Hst5 treatment significantly lowered corneal epithelial permeability, prevented conjunctival epithelial GC loss, decreased conjunctival CD45 + immune cell infiltration and reduced conjunctival epithelial cell apoptosis., Conclusions: Hst5 peptide topical treatment significantly improves the clinical parameters observed in SDS experimental model of DED. This is the first report of the efficacy of Hst5 treatment of dry eye phenotype, and potential novel treatment for DED in the clinic. Hst5 represents a new class of efficacious therapeutic agents, demonstrating pro-epithelial and anti-inflammatory activities at the ocular surface., Competing Interests: Declaration of competing interest V.K.A. is the co-inventor or inventor on multiple provisional and pending patents related to histatin peptides, owned by the Board of Trustees of the University of Illinois. The remaining authors declare no competing interests. VKA is an equity owner of ViSo Therapeutics Inc., (Copyright © 2022. Published by Elsevier Inc.)

Antimicrobial peptides (AMPs) have potential antifungal activities; however, their intracellular protein targets are poorly reported. Proteome microarray is an effective tool with high-throughput and rapid platform that systematically identifies the protein targets. In this study, we have used yeast proteome microarrays for systematical identification of the yeast protein targets of Lactoferricin B (Lfcin B) and Histatin-5. A total of 140 and 137 protein targets were identified from the triplicate yeast proteome microarray assays for Lfcin B and Histatin-5, respectively. The Gene Ontology (GO) enrichment analysis showed that Lfcin B targeted more enrichment categories than Histatin-5 did in all GO biological processes, molecular functions, and cellular components. This might be one of the reasons that Lfcin B has a lower minimum inhibitory concentration (MIC) than Histatin-5. Moreover, pairwise essential proteins that have lethal effects on yeast were analyzed through synthetic lethality. A total of 11 synthetic lethal pairs were identified within the protein targets of Lfcin B. However, only three synthetic lethal pairs were identified within the protein targets of Histatin-5. The higher number of synthetic lethal pairs identified within the protein targets of Lfcin B might also be the reason for Lfcin B to have lower MIC than Histatin-5. Furthermore, two synthetic lethal pairs were identified between the unique protein targets of Lfcin B and Histatin-5. Both the identified synthetic lethal pairs proteins are part of the Spt-Ada-Gcn5 acetyltransferase (SAGA) protein complex that regulates gene expression via histone modification. Identification of synthetic lethal pairs between Lfcin B and Histatin-5 and their involvement in the same protein complex indicated synergistic combination between Lfcin B and Histatin-5. This hypothesis was experimentally confirmed by growth inhibition assay.

Background: Candidiasis is a major opportunistic fungal infection in humans. The low number of antifungal drugs available to treat Candida infections and the increasing incidence of multidrug resistant (MDR) strains point to an urgent need of identifying new therapeutic options. The role of salivary components can provide insights for the development of new methodologies of control., Objective: The aim of this study was to evaluate the ability of histatin-5, a constitutive immunological peptide present in saliva, in reversing fungal MDR phenotype, using a resistant Saccharomyces cerevisiae strain as model of study., Results: A total of 2.5μg and 5μg of histatin-5 revealed to be able to chemosensitize (to revert antifungal resistance) a MDR strain to fluconazole impairing its intrinsic resistance. The presence of histatin-5 decreased the strain growth when associated to fluconazole, and also assisted in the retention of rhodamine 6G within cell cytoplasm. The ATPase activity of Pdr5p, an ABC efflux transporter, was significantly reduced up to 65% within physiological concentration of the peptide., Conclusion: Results revealed that histatin-5 is able to revert MDR phenotype and may be considered a potential alternative MDR inhibitor. Since Pdr5p is homologous to Candida albicans CaCdr1p and CaCdr2p, data obtained might be extrapolated to these transporters, inferring that associating fluconazole and histatin-5 may be a useful tool to circumvent failure treatments of infections caused by Candida MDR strains., (Copyright © 2017 Elsevier Masson SAS. All rights reserved.)

Candida albicans is an opportunistic fungal pathogen and a commensal organism that commonly colonizes mucosal surfaces, including those inside the human mouth. To help control C. albicans, human saliva contains the antifungal peptide histatin 5 (Hst-5), which has strong antifungal activity against C. albicans. However, the pathogen produces secreted aspartic proteases (Saps) that cleave Hst-5 at lysine residues and eliminate its antifungal properties. We designed variants of Hst-5 with its lysine residues substituted with arginine or leucine to evaluate the effect on proteolysis by Saps. We found site-, residue-, and Sap-dependent effects from single amino acid substitutions. The K17R and K17L modifications led to dramatic results, with over 77% and 100% intact peptide remaining after incubation with Sap9 and Sap2, respectively, compared to 47% and 61% of Hst-5. This decrease in proteolysis was accompanied by a reduction in cleavage on the C-terminal side of K17, suggesting the Saps prefer lysine at K17 for cleavage. Incubation with C. albicans cells and culture supernatant corroborated the results with purified Saps and highlighted their biological relevance. The modifications to Hst-5 do not diminish the antifungal activity of Hst-5, and, in fact, the K17R, K17L, and K11R peptides retained significantly more antifungal activity after treatment with Saps than Hst-5. Our results indicate that single amino acid modifications drastically impact both proteolysis at the modification sites and the overall level of proteolysis of the peptide, demonstrating the potential of designing peptides for resistance to proteolysis as a means for improving therapeutic efficacy., (© 2017 Federation of European Biochemical Societies.)

Histatin5 (Hst-5) is a member of the histatin family of antimicrobial peptides secreted by human parotid and submandibular glands. With the natural antibacterial activity, it plays an important role in the first-line barrier of oral cave against pathogens, especially for the fungal intrusion. In this study, we explored the utility of Hst-5 in the treatment of vulvovaginal candidiasis, a common condition of women of the childbearing age. We used a synthesized Hst-5 over five consecutive days as the topical treatment in a murine model of vulvovaginal candidiasis. According to the fungal colony counts, fungal burden in the vagina lavage dropped remarkably after treatment with Hst-5. Furthermore, cytological analysis of the lavage fluid indicated that the number of cast-off cells including cornified epithelial cells and inflammatory cells also decreased; histological evaluation of the vagina tissue revealed less fungi adhering to the vaginal wall in treated animals than in controls. Combined, these results suggested for the first time the potential utility of Hst-5 as a topical treatment for vulvovaginal candidiasis, uncovering the possibility of exploiting the natural antibiotic peptides in other aspects., (© FEMS 2017. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: Histatins are histidine rich polypeptides produced in the parotid and submandibular gland and secreted into the saliva. Histatin-3 and -5 are the most important polycationic histatins. They possess antimicrobial activity against fungi such as Candida albicans. Histatin-5 has a higher antifungal activity than histatin-3 while histatin-3 is mostly involved in wound healing in the oral cavity. We found that these histatins, like other polycationic peptides and proteins, such as LL-37, lysozyme and histones, interact with extracellular actin., Results: Histatin-3 and -5 polymerize globular actin (G-actin) to filamentous actin (F-actin) and bundle F-actin filaments. Both actin polymerization and bundling by histatins is pH sensitive due to the high histidine content of histatins. In spite of the equal number of net positive charges and histidine residues in histatin-3 and -5, less histatin-3 is needed than histatin-5 for polymerization and bundling of actin. The efficiency of actin polymerization and bundling by histatins greatly increases with decreasing pH. Histatin-3 and -5 induced actin bundles are dissociated by 100 and 50 mM NaCl, respectively. The relatively low NaCl concentration required to dissociate histatin-induced bundles implies that the actin-histatin filaments bind to each other mainly by electrostatic forces. The binding of histatin-3 to F-actin is stronger than that of histatin-5 showing that hydrophobic forces have also some role in histatin-3- actin interaction. Histatins affect the fluorescence of probes attached to the D-loop of G-actin indicating histatin induced changes in actin structure. Transglutaminase cross-links histatins to actin. Competition and limited proteolysis experiments indicate that the main histatin cross-linking site on actin is glutamine-49 on the D-loop of actin., Conclusions: Both histatin-3 and -5 interacts with actin, however, histatin 3 binds stronger to actin and affects actin structure at lower concentration than histatin-5 due to the extra 8 amino acid sequence at the C-terminus of histatin-3. Extracellular actin might regulate histatin activity in the oral cavity, which should be the subject of further investigation.

Histatin-5 (Hst-5, DSHAKRHHGYKRKFHEKHHSHRGY) is a member of a histidine-rich peptide family secreted by major salivary glands, exhibiting high fungicidal activity against Candida albicans. In the present work, we demonstrate the 3D structure of the head-to-tail cyclic variant of Hst-5 in TFE solution determined using NMR spectroscopy and molecular dynamics simulations. The cyclic histatin-5 reveals a helix-loop-helix motif with α-helices at positions Ala(4)-His(7) and Lys(11)-Ser(20). Both helical segments are arranged relative to each other at an angle of ca. 142°. The head-to-tail cyclization increases amphipathicity of the peptide, this, however, does not affect its antimicrobial potency., (Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.)

Candida albicans is an opportunistic fungal pathogen and a commensal organism that commonly colonizes mucosal surfaces, including those inside the human mouth. To help control C. albicans, human saliva contains the antifungal peptide histatin 5 (Hst‐5), which has strong antifungal activity against C. albicans. However, the pathogen produces secreted aspartic proteases (Saps) that cleave Hst‐5 at lysine residues and eliminate its antifungal properties. We designed variants of Hst‐5 with its lysine residues substituted with arginine or leucine to evaluate the effect on proteolysis by Saps. We found site‐, residue‐, and Sap‐dependent effects from single amino acid substitutions. The K17R and K17L modifications led to dramatic results, with over 77% and 100% intact peptide remaining after incubation with Sap9 and Sap2, respectively, compared to 47% and 61% of Hst‐5. This decrease in proteolysis was accompanied by a reduction in cleavage on the C‐terminal side of K17, suggesting the Saps prefer lysine at K17 for cleavage. Incubation with C. albicans cells and culture supernatant corroborated the results with purified Saps and highlighted their biological relevance. The modifications to Hst‐5 do not diminish the antifungal activity of Hst‐5, and, in fact, the K17R, K17L, and K11R peptides retained significantly more antifungal activity after treatment with Saps than Hst‐5. Our results indicate that single amino acid modifications drastically impact both proteolysis at the modification sites and the overall level of proteolysis of the peptide, demonstrating the potential of designing peptides for resistance to proteolysis as a means for improving therapeutic efficacy. [ABSTRACT FROM AUTHOR]

Histatin5 (Hst-5) is a member of the histatin family of antimicrobial peptides secreted by human parotid and submandibular glands. With the natural antibacterial activity, it plays an important role in the first-line barrier of oral cave against pathogens, especially for the fungal intrusion. In this study, we explored the utility of Hst-5 in the treatment of vulvovaginal candidiasis, a common condition of women of the childbearing age. We used a synthesized Hst-5 over five consecutive days as the topical treatment in a murine model of vulvovaginal candidiasis. According to the fungal colony counts, fungal burden in the vagina lavage dropped remarkably after treatment with Hst-5. Furthermore, cytological analysis of the lavage fluid indicated that the number of cast-off cells including cornified epithelial cells and inflammatory cells also decreased; histological evaluation of the vagina tissue revealed less fungi adhering to the vaginal wall in treated animals than in controls. Combined, these results suggested for the first time the potential utility of Hst-5 as a topical treatment for vulvovaginal candidiasis, uncovering the possibility of exploiting the natural antibiotic peptides in other aspects. [ABSTRACT FROM AUTHOR]

Highlights: [•] Recombinant protegrin-1 dimer and LL-37/histatin-5 peptides were expressed in E. coli. [•] Biotin carboxyl carrier protein mediated acidic amino acid was utilized as fusion tag. [•] High positive charge of antimicrobial peptides could be neutralized by fusion partner. [•] Expressed protein could be purified through either histidine tag or biotin–avidin system. [•] Novel hybrid peptide and dimer exhibited antimicrobial activity against bacteria. [ABSTRACT FROM AUTHOR]