Histatins: salivary peptides with copper(II)- and zinc(II)-binding motifs

Impact of metal coordination and pH on the antimicrobial activity of histatin 5 and the products of its hydrolysis

This work focuses on the relationship between the coordination chemistry and antimicrobial activity of Zn(II) and Cu(II) complexes of histatin 5 and the products of its hydrolysis: its N-terminal fragment (histatin 5-8) and C-terminal fragment (histatin 8). Cu(II) coordinates in an albumin-like binding mode and Zn(II) binds to up to 3 His imidazoles. The antimicrobial activity of histatins and their metal complexes (i) strongly depends on pH - they are more active at pH 5.4 than at 7.4; (ii) the complexes and ligands alone are more effective in eradicating Gram-positive bacteria than the Gram-negative ones, and (iii) Zn(II) coordination is able to change the structure of the N-terminal region of histatin 5 (histatin 5-8) and moderately increase all of the studied histatins' antimicrobial potency.

Structure modification of anoplin for fighting resistant bacteria

The emergence of bacterial resistance has posed a significant challenge to clinical antimicrobial treatment, rendering commonly used antibiotics ineffective. The development of novel antimicrobial agents and strategies is imperative for the treatment of resistant bacterial infections. Antimicrobial peptides (AMPs) are considered a promising class of antimicrobial agents due to their low propensity for resistance and broad-spectrum activity. Anoplin is a small linear α-helical natural antimicrobial peptide that was isolated from the venom of the solitary wasp Anplius samariensis. It exhibits rich biological activity, particularly broad-spectrum antimicrobial activity and low hemolytic activity. Over the past three decades, more than 40 research publications on anoplin have been made available online. This review focuses on the advancements of anoplin in antimicrobial research, encompassing its sources, characterization, antimicrobial activity, influencing factors and structural modifications. The aim is to provide assistances for the development of new antimicrobial agents that can combat bacterial resistance.

Salivary elemental signature of dental caries: a systematic review and meta-analysis of ionomics studies

Trace- and macro-chemical elements are crucial for cellular physiological functioning, and their alterations in biological fluids might be associated with an underlying pathological state. Hence, this study aimed to examine and summarize the published literature concerning the application of salivary ionomics for caries diagnosis. An extensive search of studies was conducted using PubMed, EMBASE, Web of Science, and Scopus, without any language and year restriction for answering the following PECO question: "In subjects (i.e., children, adolescents, or adults) with good systematic health, are there any variations in the salivary concentrations of trace- or macro-elements between caries-free (CF) individuals and caries-active (CA) subjects?" A modified version of the QUADOMICS tool was used to assess the quality of the included studies. The Review Manager Version 5.4.1. was used for data analyses. The analysis of salivary chemical elements that significantly differed between CF and CA subjects was also performed. Thirty-four studies were included, involving 2299 CA and 1669 CF subjects, having an age range from 3 to 64 years in over 16 countries. The meta-analysis revealed a statistically significant difference (p < 0.05) in the salivary levels of calcium, phosphorus, chloride, magnesium, potassium, sodium, and zinc between CA and CF subjects, suggesting higher levels of calcium, phosphorus, potassium, and sodium in CF subjects while higher levels of chloride, magnesium, and zinc in CA patients. Half of the included studies (17/34) were considered high quality, while the remaining half were considered medium quality. Only zinc and chloride ions were found to be higher significantly and consistent in CF and CA subjects, respectively. Conflicting outcomes were observed for all other salivary chemical elements including aluminum, bromine, calcium, copper, fluoride, iron, potassium, magnesium, manganese, sodium, ammonia, nitrite, nitrate, phosphorus, lead, selenium, and sulfate ions.

In Silico-Based Design of a Hybrid Peptide with Antimicrobial Activity against Multidrug-Resistant Pseudomonas aeruginosa Using a Spider Toxin Peptide

The escalating prevalence of antibiotic-resistant bacteria poses an immediate and grave threat to public health. Antimicrobial peptides (AMPs) have gained significant attention as a promising alternative to conventional antibiotics. Animal venom comprises a diverse array of bioactive compounds, which can be a rich source for identifying new functional peptides. In this study, we identified a toxin peptide, Lycotoxin-Pa1a (Lytx-Pa1a), from the transcriptome of the Pardosa astrigera spider venom gland. To enhance its functional properties, we employed an in silico approach to design a novel hybrid peptide, KFH-Pa1a, by predicting antibacterial and cytotoxic functionalities and incorporating the amino-terminal Cu(II)- and Ni(II) (ATCUN)-binding motif. KFH-Pa1a demonstrated markedly superior antimicrobial efficacy against pathogens, including multidrug-resistant (MDR) Pseudomonas aeruginosa, compared to Lytx-Pa1a. Notably, KFH-Pa1a exerted several distinct mechanisms, including the disruption of the bacterial cytoplasmic membrane, the generation of intracellular ROS, and the cleavage and inhibition of bacterial DNA. Additionally, the hybrid peptide showed synergistic activity when combined with conventional antibiotics. Our research not only identified a novel toxin peptide from spider venom but demonstrated in silico-based design of hybrid AMP with strong antimicrobial activity that can contribute to combating MDR pathogens, broadening the utilization of biological resources by incorporating computational approaches.

The salivary peptide histatin-1 enhances bone repair in vivo

The salivary peptide histatin-1 was recently described as a novel osteogenic factor that stimulates cell adhesion, migration, and differentiation in bone-lineage cells. Since these cell responses collectively contribute to bone regeneration, we hypothesized that histatin-1 harbors the capacity to enhance bone tissue repair at the preclinical level. By using a model of monocortical bone defect, we explored the effects of histatin-1 in tibial mineralization and organic matrix formation in vivo. To this end, different amounts of histatin-1 were embedded in one-mm3 collagen sponges and then applied to tibial monocortical defects in C57bl/6 mice. After seven days, mice were euthanized, and samples were processed for subsequent analysis. Micro-computed tomography screening showed that histatin-1 increased intraosseous mineralization, and this phenomenon was accompanied by augmented collagen matrix deposition and closure of cortical defect edges, as determined by Hematoxylin-Eosin and Masson's Trichrome staining. Moreover, immunohistochemical analyses showed that histatin-1 increased the expression of the osteogenic marker alkaline phosphatase, which was accompanied by augmented blood vessel formation. Collectively, our findings show that histatin-1 itself promotes bone regeneration in an orthotopic model, proposing this molecule as a therapeutic candidate for use in bone regenerative medicine.

The effect of metalation on antimicrobial piscidins imbedded in normal and oxidized lipid bilayers

Metalation of the N-terminal Amino Terminal Cu(ii)- and Ni(ii)-binding (ATCUN) motif may enhance the antimicrobial properties of piscidins. Molecular dynamics simulations of free and nickelated piscidins 1 and 3 (P1 and P3) were performed in 3 : 1 POPC/POPG and 2.6 : 1 : 0.4 POPC/POPG/aldo-PC bilayers (POPC, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine: POPG, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol; aldo-PC, 1-palmitoyl-2-(9'-oxo-nonanoyl)-sn-glycero-3-phosphocholine) bilayer models. Nickel(ii) binding decreases the conformation dynamics of the ATCUN motif and lowers the charge of the N-terminus to allow it to embed deeper in the bilayer without significantly changing the overall depth due to interactions of the charged half-helix of the peptide with the headgroups. Phe1⋯Ni2+ cation-π and Phe2-Phe1 CH-π interactions contribute to a small fraction of structures within the nickelated P1 simulations and may partially protect a bound metal from metal-centered chemical activity. The substitution of Phe2 for Ile2 in P3 sterically blocks conformations with cation-π interactions offering less protection to the metal. This difference between metalated P1 and P3 may indicate a mechanism by which peptide sequence can influence antimicrobial properties. Any loss of bilayer integrity due to chain reversal of the oxidized phospholipid chains of aldo-PC may be enhanced in the presence of metalated piscidins.

Metal coordinating-induced self-assembly of cyclic lipopeptides into high-performance antimicrobial supramolecules

This study designed a green hydrothermally-chelating approach to generate robust antimicrobial complexes via metal-coordinated supramolecular self-assembly of cyclic lipopeptides (CLs). The metal ion (Ca²⁺ and Zn²⁺)-coordinated CL (Ca/CL or Zn/CL complex; 1 mg/mL) demonstrated potent antibacterial activity against fungi (A. niger) and bacteria (E. coli and S. aureus) respectively, and in particular, completely suppressed the microbial resistance. Further physicochemical and spectal analysis showed that this coordination approach led to CL with enhanced hydrophobic and intermolecular electrostatic interactions, forming β-sheet-rich secondary structures allowing the complexes easily contact with and destroy the membrane of microorganisms. Practical application experiments validated that the Ca/CL and Zn/CL complexes strongly avoided table grape and fresh tomato from the contamination of pathogen. The findings of this study laid foundation for the utilization of metal ions to improve the biological activity of natural antimicrobial peptides.

The Synergy between Zinc and Antimicrobial Peptides: An Insight into Unique Bioinorganic Interactions

Antimicrobial peptides (AMPs) are essential components of innate immunity across all species. AMPs have become the focus of attention in recent years, as scientists are addressing antibiotic resistance, a public health crisis that has reached epidemic proportions. This family of peptides represents a promising alternative to current antibiotics due to their broad-spectrum antimicrobial activity and tendency to avoid resistance development. A subfamily of AMPs interacts with metal ions to potentiate antimicrobial effectiveness, and, as such, they have been termed metalloAMPs. In this work, we review the scientific literature on metalloAMPs that enhance their antimicrobial efficacy when combined with the essential metal ion zinc(II). Beyond the role played by Zn(II) as a cofactor in different systems, it is well-known that this metal ion plays an important role in innate immunity. Here, we classify the different types of synergistic interactions between AMPs and Zn(II) into three distinct classes. By better understanding how each class of metalloAMPs uses Zn(II) to potentiate its activity, researchers can begin to exploit these interactions in the development of new antimicrobial agents and accelerate their use as therapeutics.

Modulation of ocular surface desiccation in a murine model by histatin-5 application

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.

Serum copper concentration reflect inflammatory activation in the complex coronary artery disease - A pilot study

INTRODUCTION

Coronary artery disease possess inflammatory background related to enzymatic processes with trace elements involvements as co-factors. The aim of the study was to compare serum, urine and salivary copper, magnesium, calcium and zinc levels with inflammatory indices obtained from the whole blood count in patients with complex coronary artery disease.

MATERIAL AND METHOD

Fifty-two (42(81 %) males, 10 (19 %) females) consecutive patients (mean (SD) age 68 (9) years with symptomatic complex coronary artery disease were enrolled into prospective single center study in 2021. Serum, saliva and urine samples were collected at the day of admission for trace elements concentration (copper, zinc, magnesium, calcium) and compared with inflammatory indexes obtained from preoperative and perioperative period.

RESULTS

Multivariable regression analysis revealed relation between the copper serum concentration and neutrophil to lymphocyte ratio (NLR) and systemic inflammatory index (SII).

CONCLUSION

Serum copper concentration interplay with preoperative inflammatory activation in complex coronary disease measured by NLR and SII. The copper serum concentration possesses the strongest relation to preoperative inflammatory activation in patients reffered for off-pump coronary artery bypass grafting.

Activity and Synergy of Cu-ATCUN Antimicrobial Peptides

Antibiotic resistance demands innovative strategies and therapies. The pairs of antimicrobial peptides tested in this work show broad-spectrum synergy and are capable of interacting with diverse bacterial membranes. In most cases, the ATCUN motif enhanced the activity of peptides tested in combination. Our studies also show CP10A to be a multifaceted peptide, displaying both cell membrane and intracellular activity and acting as a chameleon, improving the activity of other peptides as needed. The results of the synergy experiments demonstrate the importance of varied modes of action and how these changes can affect the ability to combat pathogens, while also illustrating the value of the metal-binding domain in enhancing the activity of antimicrobial peptides in combination.

An injectable multifunctional thermo-sensitive chitosan-based hydrogel for periodontitis therapy

Bacteria are recognized as the driving factors of periodontitis. However, excessive reactive oxygen species (ROS) can harm periodontal tissue while also causing an uncontrolled inflammatory response. Hence, eliminating excessive ROS and blocking ROS-induced abnormal inflammatory response by antioxidants are achieving remarkable results in periodontitis therapy. Moreover, influenced by the deep and irregular periodontal pockets, injectable thermo-sensitive chitosan-based hydrogels have attracted a lot of attention. This study aimed to formulate an antibacterial and antioxidant therapeutic regimen by incorporating antimicrobial peptides (Nal-P-113) and/or antioxidants (polydopamine nanoparticles, PDNPs) into chitosan-based hydrogels. The hydrogel was characterized in vitro and finally examined in rats using the experimental periodontitis model. The release kinetics showed that the hydrogel could stably release Nal-P-113 and PDNPs for up to 13 days. The scavenging activity of the hydrogel against DPPH was about 80 % and the antibacterial ratio against Streptococcus gordonii (S. gordonii), Fusobacterium nucleatum (F. nucleatum) and Porphyromonas gingivalis (P. gingivalis) was about 99 %. Importantly, it was examined that the hydrogel had the ability to prevent periodontal tissue damage. Thus, chitosan-based hydrogels may provide a basis for designing multifunctional local drug delivery biomaterials for the treatment of periodontitis.

Aging envisage imbalance of the periodontium: A keystone in oral disease and systemic health

Aging is a gradual and progressive deterioration of integrity across multiple organ systems that negatively affects gingival wound healing. The cellular responses associated with wound healing, such as collagen synthesis, cell migration, proliferation, and collagen contraction, have been shown to be lower in gingival fibroblasts (the most abundant cells from the connective gingival tissue) in aged donors than young donors. Cellular senescence is one of the hallmarks of aging, which is characterized by the acquisition of a senescence-associated secretory phenotype that is characterized by the release of pro-inflammatory cytokines, chemokines, growth factors, and proteases which have been implicated in the recruitment of immune cells such as neutrophils, T cells and monocytes. Moreover, during aging, macrophages show altered acquisition of functional phenotypes in response to the tissue microenvironment. Thus, inflammatory and resolution macrophage-mediated processes are impaired, impacting the progression of periodontal disease. Interestingly, salivary antimicrobial peptides, such as histatins, which are involved in various functions, such as antifungal, bactericidal, enamel-protecting, angiogenesis, and re-epithelization, have been shown to fluctuate with aging. Several studies have associated the presence of Porphyromonas gingivalis, a key pathogen related to periodontitis and apical periodontitis, with the progression of Alzheimer's disease, as well as gut, esophageal, and gastric cancers. Moreover, herpes simplex virus types 1 and 2 have been associated with the severity of periodontal disease, cardiovascular complications, and nervous system-related pathologies. This review encompasses the effects of aging on periodontal tissues, how P. gingivalis and HSV infections could favor periodontitis and their relationship with other pathologies.

Expansion of nickel binding- and histidine-rich proteins during gastric adaptation of Helicobacter species

Acquisition and homeostasis of essential metals during host colonization by bacterial pathogens rely on metal uptake, trafficking and storage proteins. How these factors have evolved within bacterial pathogens is poorly defined. Urease, a nickel enzyme, is essential for Helicobacter pylori to colonize the acidic stomach. Our previous data suggest that acquisition of nickel transporters and a Histidine-rich protein (HRP) involved in nickel storage in H. pylori and gastric Helicobacter spp. have been essential evolutionary events for gastric colonization. Using bioinformatics, proteomics and phylogenetics, we extended this analysis to determine how evolution has framed the repertoire of HRPs among 39 Epsilonproteobacteria; 18 gastric and 11 non-gastric enterohepatic (EH) Helicobacter spp., as well as 10 other Epsilonproteobacteria. We identified a total of 213 HRPs distributed in 22 protein families named orthologous groups (OG) with His-rich domains, including 15 newly described OGs. Gastric Helicobacter spp. are enriched in HRPs (7.7 ± 1.9 HRPs/strain) as compared to EH Helicobacter spp. (1.9 ± 1.0 HRPs/strain) with a particular prevalence of HRPs with C-terminal Histidine-rich domains in gastric species. The expression and nickel-binding capacity of several HRPs was validated in five gastric Helicobacter spp. We established the evolutionary history of new HRP families, such as the periplasmic HP0721-like proteins and the HugZ-type heme-oxygenases. The expansion of Histidine-rich extensions in gastric Helicobacter spp. proteins is intriguing but can tentatively be associated with the presence of the urease nickel-enzyme. We conclude that this HRP expansion is associated with unique properties of organisms that rely on large intracellular nickel amounts for their survival.

Chemical Barrier Proteins in Human Body Fluids

Chemical barriers are composed of those sites of the human body where potential pathogens can contact the host cells. A chemical barrier is made up by different proteins that are part of the antimicrobial and immunomodulatory protein/peptide (AMP) family. Proteins of the AMP family exert antibacterial, antiviral, and/or antifungal activity and can modulate the immune system. Besides these proteins, a wide range of proteases and protease inhibitors can also be found in the chemical barriers maintaining a proteolytic balance in the host and/or the pathogens. In this review, we aimed to identify the chemical barrier components in nine human body fluids. The interaction networks of the chemical barrier proteins in each examined body fluid were generated as well.

Tackling antimicrobial stewardship through synergy and antimicrobial peptides

The unrestricted use of antibiotics has led to rapid development of antibiotic resistance (AR) and renewed calls to address this serious problem. This review summarizes the most common mechanisms of antibiotic action, and in turn antibiotic resistance, as well as pathways to mitigate the harm. Focus is then turned to emerging antibiotic strategies, including antimicrobial peptides (AMPs), with a discussion of their modes of action, biochemical features, and potential challenges for their use as antibiotics. The role of synergy in antimicrobials is also examined, with a focus on the synergy of AMPs and other emerging interactions with synergistic potential.

Identification of VEGFR2 as the Histatin-1 receptor in endothelial cells

Histatin-1 is a salivary peptide with antimicrobial and wound healing promoting activities, which was previously shown to stimulate angiogenesis in vitro and in vivo via inducing endothelial cell migration. The mechanisms underlying the proangiogenic effects of Histatin-1 remain poorly understood and specifically, the endothelial receptor for this peptide, is unknown. Based on the similarities between Histatin-1-dependent responses and those induced by the prototypical angiogenic receptor, vascular endothelial growth factor receptor 2 (VEGFR2), we hypothesized that VEGFR2 is the Histatin-1 receptor in endothelial cells. First, we observed that VEGFR2 is necessary for Histatin-1-induced endothelial cell migration, as shown by both pharmacological inhibition studies and siRNA-mediated ablation of VEGFR2. Moreover, Histatin-1 co-immunoprecipitated and co-localized with VEGFR2, associating spatial proximity between these proteins with receptor activation. Indeed, pulldown assays with pure, tagged and non-tagged proteins showed that Histatin-1 and VEGFR2 directly interact in vitro. Optical tweezers experiments permitted estimating kinetic parameters and rupture forces, indicating that the Histatin-1-VEGFR2 interaction is transient, but specific and direct. Sequence alignment and molecular modeling identified residues Phe26, Tyr30 and Tyr34 within the C-terminal domain of Histatin-1 as relevant for VEGFR2 binding and activation. This was corroborated by mutation and molecular dynamics analyses, as well as in direct binding assays. Importantly, these residues were required for Histatin-1 to induce endothelial cell migration and angiogenesis in vitro. Taken together, our findings reveal that VEGFR2 is the endothelial cell receptor of Histatin-1 and provide insights to the mechanism by which this peptide promotes endothelial cell migration and angiogenesis.

HPLC method with post-column derivatization for the analysis of endogenous histidine in human saliva validated using the total-error concept

Histidine (His) is an essential amino acid that plays an important biological role and associated with various pathological conditions. A simple and reliable method for the determination of endogenous histidine in human saliva was optimized and validated. The analyte was separated from the saliva matrix by cation exchange chromatography and detected fluorimetrically (λ_ex/λ_em = 360/440 nm) after online, specific post-column derivatization (PCD) reaction with o-phthalaldehyde. The chemical and instrumental variables of the post-column reaction were optimized using Box-Behnken experimental design to achieve maximum sensitivity. Method validation was carried out employing the total-error concept. Histidine could be analyzed reliably in the range of 0.5-5.0 μΜ, with an LOD (S/N = 3) of 50 nM. Monte Carlo simulations and capability analysis were used to investigate the ruggedness of the PCD reaction. The sampling strategy, sample preparation and stability were also investigated. Seventeen saliva samples were successfully analyzed with histidine levels being in the range of 2.7-19.5 μΜ.

Macro and trace elements signature of periodontitis in saliva: A systematic review with quality assessment of ionomics studies

Objectives

The present systematic review examined the available evidence on distinctive salivary ion profile in periodontitis compared to periodontal health and provided a qualitative assessment of the literature.

Background

Macro and trace elements are essential for cellular physiology, and their changes in biological fluids can be revelatory of an underlying pathological status.

Methods

Data from relevant studies identified from PubMed, Embase, and Scopus databases were retrieved to answer the following PECO question: “In systemically healthy individuals, are there any differences in any salivary macro or trace element concentration between periodontally healthy subjects (H) and patients with periodontitis (P)?” Quality of included studies was rated using a modified version of the QUADOMICS tool. A consistency analysis was performed to identify significantly discriminant chemical elements.

Results

After the screening of 873 titles, 13 studies were included reporting data on 22 different elements. Among them, levels of sodium and potassium were consistently and significantly higher in P compared to H. Conflicting results were found for all the other elements, despite concentration of calcium, copper, and manganese mostly increased in saliva of P. Levels of magnesium were found higher in P than in H in 2 studies but lower in 3. Zinc resulted significantly increased in saliva from H compared to P individuals in 2 studies, but one study reported opposite results. Four studies were considered as high quality, while reporting of operative protocols and statistical analysis was a major limitation for the others. Due to high methodologic heterogeneity, meta‐analysis was not performed.

Conclusions

Levels of macro or trace elements were differentially identified in saliva across diverse periodontal conditions, having a major potential for investigation of oral homeostasis and for high‐resolution periodontal diagnosis. Products of inflammatory physiologic cellular impairment, such as sodium and potassium, were the most consistently associated with periodontitis (PROSPERO CRD42021235744).

Histatin 5 Metallopeptides and Their Potential against Candida albicans Pathogenicity and Drug Resistance

Usually caused by Candida albicans, buccal candidiasis begins with the morphological transition between yeast and hyphal cells. Over time and without the correct treatment, it can be disseminated through the bloodstream becoming a systemic infection with high mortality rates. C. albicans already shows resistance against antifungals commonly used in treatments. Therefore, the search for new drugs capable of overcoming antifungal resistance is essential. Histatin 5 (Hst5) is an antimicrobial peptide of the Histatin family, that can be found naturally in human saliva. This peptide presents high antifungal activity against C. albicans. However, Hst5 action can be decreased for interaction with enzymes and metal ions present in the oral cavity. The current work aims to bring a brief review of relevant aspects of the pathogenesis and resistance mechanisms already reported for C. albicans. In addition, are also reported here the main immune responses of the human body and the most common antifungal drugs. Finally, the most important aspects regarding Histatin 5 and the benefits of its interaction with metals are highlighted. The intention of this review is to show the promising use of Hst5 metallopeptides in the development of effective drugs.

Phosphorylation Impacts Cu(II) Binding by ATCUN Motifs

ATCUN (amino terminal Cu(II) and Ni(II) binding) motifs chelate Cu(II) ions strongly. However, the impact of the phosphorylation of neighboring residues on such complexation has not been elucidated. The copper(II) dissociation constants of original and phosphorylated peptides from human histatin-1 and human serum albumin were compared using spectroscopic methods. Phosphorylation markedly weakened Cu(II) binding. Thus, these results indicate that phosphorylation may be a vital mechanism governing metal ion binding.

The phosphorylation of serine residues within or nearby an ATCUN motif markedly weakens Cu(II) binding. It indicates that phosphorylation may be a vital mechanism of metal ion binding regulation.

Metal Binding Antimicrobial Peptides in Nanoparticle Bio-functionalization: New Heights in Drug Delivery and Therapy

Peptides are considered very important due to the diversity expressed through their amino acid sequence, structure variation, large spectrum, and their essential role in biological systems. Antimicrobial peptides (AMPs) emerged as a potent tool in therapy owing to their antimicrobial properties but also their ability to trespass the membranes, specificity, and low toxicity. They comprise a variety of peptides from which specific amino acid-rich peptides are of interest to the current review due to their features in metal interaction and cell penetration. Histidine-rich peptides such as Histatins belong to the metal binding salivary residing peptides with efficient antibacterial, antifungal, and wound-healing activities. Furthermore, their ability to activate in acidic environment attracted the attention to their potential in therapy. The current review covers the current knowledge about AMPs and critically assess the potential of associating with metal ions both structurally and functionally. This review provides interesting hints for the advantages provided by AMPs and metal ions in biomedicine, making use of their direct properties in brain diseases therapy or in the creation of new bio-functionalized nanoparticles for cancer diagnosis and treatment.

Top-Down Proteomics of Human Saliva Highlights Anti-inflammatory, Antioxidant, and Antimicrobial Defense Responses in Alzheimer Disease

Alzheimer disease (AD) is the most prevalent neurodegenerative disease in the elderly, characterized by accumulation in the brain of misfolded proteins, inflammation, and oxidative damage leading to neuronal cell death. By considering the viewpoint that AD onset and worsening may be influenced by environmental factors causing infection, oxidative stress, and inflammatory reaction, we investigated the changes of the salivary proteome in a population of patients with respect to that in healthy controls (HCs). Indeed, the possible use of saliva as a diagnostic tool has been explored in several oral and systemic diseases. Moreover, the oral cavity continuously established adaptative and protective processes toward exogenous stimuli. In the present study, qualitative/quantitative variations of 56 salivary proteoforms, including post-translationally modified derivatives, have been analyzed by RP-HPLC-ESI-IT-MS and MS/MS analyses, and immunological methods were applied to validate MS results. The salivary protein profile of AD patients was characterized by significantly higher levels of some multifaceted proteins and peptides that were either specific to the oral cavity or also expressed in other body districts: (i) peptides involved in the homeostasis of the oral cavity; (ii) proteins acting as ROS/RNS scavengers and with a neuroprotective role, such as S100A8, S100A9, and their glutathionylated and nitrosylated proteoforms; cystatin B and glutathionylated and dimeric derivatives; (iii) proteins with antimicrobial activity, such as α-defensins, cystatins A and B, histatin 1, statherin, and thymosin β4, this last with a neuroprotective role at the level of microglia. These results suggested that, in response to injured conditions, Alzheimer patients established defensive mechanisms detectable at the oral level. Data are available via ProteomeXchange with identifier PXD021538.

Coordination of Redox Ions within a Membrane-Binding Peptide: A Tale of Aromatic Rings

The amino-terminal-copper-and-nickel-binding (ATCUN) motif, a tripeptide sequence ending with a histidine, confers important functions to proteins and peptides. Few high-resolution studies have been performed on the ATCUN motifs of membrane-associated proteins and peptides, limiting our understanding of how they stabilize Cu²⁺/Ni²⁺ in membranes. Here, we leverage solid-state NMR to investigate metal-binding to piscidin-1 (P1), a host-defense peptide featuring F1F2H3 as its ATCUN motif. Bound to redox ions, P1 chemically and physically damages pathogenic cell membranes. We design ¹³C/¹⁵N correlation experiments to detect and assign the deprotonated nitrogens produced and/or shifted by Ni²⁺-binding. Occupying multiple chemical states in P1-apo, H3 and the neighboring H4 respond to metalation by populating only the τ-tautomer. H3, as a proximal histidine, directly coordinates the metal, compared to the distal H4. Density functional theory calculations reflect this noncanonical arrangement and point toward cation-π interactions between the F1/F2/H4 aromatic rings and metal. These structural findings, which are relevant to other ATCUN-containing membrane peptides, could help design new therapeutics and materials for use in the areas of drug-resistant bacteria, neurological disorders, and biomedical imaging.

Enhanced Synergism and Mechanism of Action Studies of Synthetic Antimicrobial Metallopeptides

Antimicrobial peptides (AMPs) are found throughout most kingdoms of life, are an important part of host immunity, and have been shown to act synergistically in various organisms to ameliorate bacterial infections. Herein, we report the synergistic behavior observed between two AMPs, Sub5 and CP10A, against E. coli. In addition, enhanced synergistic activity against E. coli and MRSA 43300 for two derivatives of Sub5, extended with the amino-terminal copper and nickel (ATCUN) binding motif, is observed when dosed together with CP10A, while displaying little cytotoxicity towards human dermal fibroblasts. All three combinations of peptides co-localized within bacterial cells as evidenced by fluorescence confocal microscopy. Investigations into the mechanism of synergy shows that all peptides indirectly damage DNA within cells, while only the ATCUN derivatives can oxidize phospholipids. Combinations of peptides were also shown to upregulate the concentration of reactive oxygen species within both E. coli and MRSA 43300. These results suggest that the production of reactive oxygen species is an important aspect mechanistically and further highlights the potential of these metallopeptides to aid in the treatment of antibiotic-resistant infections.

Cellular responses of histatin-derived peptides immobilized titanium surface using a tresyl chloride-activated method

Effects of histatin-derived peptides immobilization by tresyl chloride-activation technique for MC3T3-E1 cellular responses on titanium (Ti) were evaluated. MC3T3-E1 were cultured on sandblasted and acid-etched Ti disks immobilized with histatin-derived peptides, including histatin-1, JH8194, and mixed histatin-1 with JH8194. Surface topography and cellular morphology were examined using a scanning electron microscope. Elemental composition and conformational peptides on Ti surface were examined using energy dispersive X-ray and fourier transform infrared spectroscopy, respectively. Cellular adhesion, proliferation, osteogenesis-related genes, and alkaline phosphatase activity were evaluated. The results showed that peptides were successfully immobilized on Ti surface. Cell attachments on histatin-1 and mixed peptides coated groups are higher than control. Histatin-1 achieved the significantly highest cellular proliferation. Histatin-derived peptides improved the osteogenesis related-gene expression and alkaline phosphatase activity (p<0.05). This study suggested that histatin-1 immobilization by tresyl chloride-activation technique enhanced cellular responses and might be able to promote cellular activities around the dental implants.

Characterization of pepcan-23 as pro-peptide of RVD-hemopressin (pepcan-12) and stability of hemopressins in mice

Hemopressins ((x)-PVNFKLLSH) or peptide endocannabinoids (pepcans) can bind to cannabinoid receptors. RVD-hemopressin (pepcan-12) was shown to act as endogenous allosteric modulator of cannabinoid receptors, with opposite effects on CB1 and CB2, respectively. Moreover, the N-terminally elongated pepcan-23 was detected in different tissues and was postulated to be the pro-peptide of RVD-hemopressin. Currently, data about the pharmacokinetics, tissue distribution and stability of hemopressin-type peptides are lacking. Here we investigated the secondary structure and physiological role of pepcan-23 as precursor of RVD-hemopressin. We assessed the metabolic stability of these peptides, including hemopressin. Using LC-ESI-MS/MS, pepcan-23 was measured in mouse tissues and human whole blood (~50 pmol/mL) and in plasma was the most stable endogenous peptide containing the hemopressin sequence. Using peptide spiked human whole blood, mouse adrenal gland and liver homogenates demonstrate that pepcan-23 acts as endogenous pro-peptide of RVD-hemopressin. Furthermore, administered pepcan-23 converted to RVD-hemopressin in mice. In circular dichroism spectroscopy, pepcan-23 showed a helix-unordered-helix structure and efficiently formed complexes with divalent metal ions, in particular Cu(II) and Ni(II). Hemopressin and RVD-hemopressin were not bioavailable to the brain and showed poor stability in plasma, in agreement with their overall poor biodistribution. Acute hemopressin administration (100 mg/kg) did not modulate endogenous RVD-hemopressin/pepcan-23 levels or influence the endocannabinoid lipidome but increased 1-stearoyl-2-arachidonoyl-sn-glycerol. Overall, we show that pepcan-23 is a biological pro-peptide of RVD-hemopressin and divalent metal ions may regulate this process. Given the lack of metabolic stability of hemopressins, administration of pepcan-23 as pro-peptide may be suitable in pharmacological experiments as it is converted to RVD-hemopressin in vivo.

Histatin-1 is a novel osteogenic factor that promotes bone cell adhesion, migration, and differentiation

Histatin-1 is a salivary antimicrobial peptide involved in the maintenance of enamel and oral mucosal homeostasis. Moreover, Histatin-1 has been shown to promote re-epithelialization in soft tissues, by stimulating cell adhesion and migration in oral and dermal keratinocytes, gingival and skin fibroblasts, endothelial cells and corneal epithelial cells. The broad-spectrum activity of Histatin-1 suggests that it behaves as a universal wound healing promoter, although this is far from being clear yet. Here, we report that Histatin-1 is a novel osteogenic factor that promotes bone cell adhesion, migration, and differentiation. Specifically, Histatin-1 promoted cell adhesion, spreading, and migration of SAOS-2 cells and MC3T3-E1 preosteoblasts in vitro, when placed on a fibronectin matrix. Besides, Histatin-1 induced the expression of osteogenic genes, including osteocalcin, osteopontin, and Runx2, and increased both activity and protein levels of alkaline phosphatase. Furthermore, Histatin-1 promoted mineralization in vitro, as it augmented the formation of calcium deposits in both SAOS-2 and MC3T3-E1 cells. Mechanistically, although Histatin-1 failed to activate ERK1/2, FAK, and Akt, which are signaling proteins associated with osteogenic differentiation or cell migration, it triggered nuclear relocalization of β-catenin. Strikingly, the effects of Histatin-1 were recapitulated in cells that are nonosteogenically committed, since it promoted surface adhesion, migration, and the acquisition of osteogenic markers in primary mesenchymal cells derived from the apical papilla and dental pulp. Collectively, these observations indicate that Histatin-1 is a novel osteogenic factor that promotes bone cell differentiation, surface adhesion and migration, as crucial events required for bone tissue regeneration.

Effects and mechanisms of histatins as novel skin wound-healing agents

Wound healing is a complex and important physiological process that maintains the integrity of skin after various injuries. Abnormal wound healing, especially of chronic wounds, impairs normal physical function. Therefore, the search for effective and safe healing agents is one of the main concerns. Histatins are histidine-rich low molecular weight peptides that are expressed in the saliva of both humans and higher primates. Histatins have two main biological effects, cell stimulation and bacteria killing, with the former playing an important role in wound healing by promoting epithelial cell and fibroblast migration and angiogenesis and enhancing the re-epithelialization of the wounded area. Because of these biological effects, histatins have been shown to be promising agents of improved wound healing. Histatins are categorized into many subtypes, of which histatin 1 and its hydrolysates are the most effective in promoting wound healing. This review addresses the bioactivity of histatins in wound healing, such as their stimulatory effects on epithelial cells and fibroblasts, and elucidates the possible mechanisms by which histatin subtypes induce their biological effects.

Structure-Function Insights of Jaburetox and Soyuretox: Novel Intrinsically Disordered Polypeptides Derived from Plant Ureases

Intrinsically disordered proteins (IDPs) and intrinsically disordered regions (IDRs) do not have a stable 3D structure but still have important biological activities. Jaburetox is a recombinant peptide derived from the jack bean (Canavalia ensiformis) urease and presents entomotoxic and antimicrobial actions. The structure of Jaburetox was elucidated using nuclear magnetic resonance which reveals it is an IDP with small amounts of secondary structure. Different approaches have demonstrated that Jaburetox acquires certain folding upon interaction with lipid membranes, a characteristic commonly found in other IDPs and usually important for their biological functions. Soyuretox, a recombinant peptide derived from the soybean (Glycine max) ubiquitous urease and homologous to Jaburetox, was also characterized for its biological activities and structural properties. Soyuretox is also an IDP, presenting more secondary structure in comparison with Jaburetox and similar entomotoxic and fungitoxic effects. Moreover, Soyuretox was found to be nontoxic to zebra fish, while Jaburetox was innocuous to mice and rats. This profile of toxicity affecting detrimental species without damaging mammals or the environment qualified them to be used in biotechnological applications. Both peptides were employed to develop transgenic crops and these plants were active against insects and nematodes, unveiling their immense potentiality for field applications.

A secreted fungal histidine- and alanine-rich protein regulates metal ion homeostasis and oxidative stress

Like pathogens, beneficial endophytic fungi secrete effector proteins to promote plant colonization, for example, through perturbation of host immunity. The genome of the root endophyte Serendipita indica encodes a novel family of highly similar, small alanine- and histidine-rich proteins, whose functions remain unknown. Members of this protein family carry an N-terminal signal peptide and a conserved C-terminal DELD motif. Here we report on the functional characterization of the plant-responsive DELD family protein Dld1 using a combination of structural, biochemical, biophysical and cytological analyses. The crystal structure of Dld1 shows an unusual, monomeric histidine zipper consisting of two antiparallel coiled-coil helices. Similar to other histidine-rich proteins, Dld1 displays varying affinity to different transition metal ions and undergoes metal ion- and pH-dependent unfolding. Transient expression of mCherry-tagged Dld1 in barley leaf and root tissue suggests that Dld1 localizes to the plant cell wall and accumulates at cell wall appositions during fungal penetration. Moreover, recombinant Dld1 enhances barley root colonization by S. indica, and inhibits H₂ O₂ -mediated radical polymerization of 3,3'-diaminobenzidine. Our data suggest that Dld1 has the potential to enhance micronutrient accessibility for the fungus and to interfere with oxidative stress and reactive oxygen species homeostasis to facilitate host colonization.

Bio- and Nanotechnology as the Key for Clinical Application of Salivary Peptide Histatin: A Necessary Advance

Candida albicans is a common microorganism of human’s microbiota and can be easily found in both respiratory and gastrointestinal tracts as well as in the genitourinary tract. Approximately 30% of people will be infected by C. albicans during their lifetime. Due to its easy adaptation, this microorganism started to present high resistance to antifungal agents which is associated with their indiscriminate use. There are several reports of adaptive mechanisms that this species can present. Some of them are intrinsic alteration in drug targets, secretion of extracellular enzymes to promote host protein degradation and efflux receptors that lead to a diminished action of common antifungal and host’s innate immune response. The current review aims to bring promising alternatives for the treatment of candidiasis caused mainly by C. albicans. One of these alternatives is the use of antifungal peptides (AFPs) from the Histatin family, like histatin-5. Besides that, our focus is to show how nanotechnology can allow the application of these peptides for treatment of this microorganism. In addition, our intention is to show the importance of nanoparticles (NPs) for this purpose, which may be essential in the near future.

Antimicrobial Susceptibility Testing of Antimicrobial Peptides to Better Predict Efficacy

During the development of antimicrobial peptides (AMP) as potential therapeutics, antimicrobial susceptibility testing (AST) stands as an essential part of the process in identification and optimisation of candidate AMP. Standard methods for AST, developed almost 60 years ago for testing conventional antibiotics, are not necessarily fit for purpose when it comes to determining the susceptibility of microorganisms to AMP. Without careful consideration of the parameters comprising AST there is a risk of failing to identify novel antimicrobials at a time when antimicrobial resistance (AMR) is leading the planet toward a post-antibiotic era. More physiologically/clinically relevant AST will allow better determination of the preclinical activity of drug candidates and allow the identification of lead compounds. An important consideration is the efficacy of AMP in biological matrices replicating sites of infection, e.g., blood/plasma/serum, lung bronchiolar lavage fluid/sputum, urine, biofilms, etc., as this will likely be more predictive of clinical efficacy. Additionally, specific AST for different target microorganisms may help to better predict efficacy of AMP in specific infections. In this manuscript, we describe what we believe are the key considerations for AST of AMP and hope that this information can better guide the preclinical development of AMP toward becoming a new generation of urgently needed antimicrobials.

Artificial Metalloenzymes: Recent Developments and Innovations in Bioinorganic Catalysis

Cellular life is orchestrated by the biochemical components of cells that include nucleic acids, lipids, carbohydrates, proteins, and cofactors such as metabolites and metals, all of which coalesce and function synchronously within the cell. Metalloenzymes allow for such complex chemical processes, as they catalyze a myriad of biochemical reactions both efficiently and selectively, where the metal cofactor provides additional functionality to promote reactivity not readily achieved in their absence. While the past 60 years have yielded considerable insight on how enzymes catalyze these reactions, a need to engineer and develop artificial metalloenzymes has been driven not only by industrial and therapeutic needs, but also by innate human curiosity. The design of miniature enzymes, both rationally and through serendipity, using both organic and inorganic building blocks has been explored by many scientists over the years and significant progress has been made. Herein, recent developments over the past 5 years in areas that have not been recently reviewed are summarized, and prospects for future research in these areas are addressed.

A Systematic Review of Emerging Therapeutic Strategies in the Management of Chemical Injuries of the Ocular Surface

OBJECTIVES

To evaluate recent in vivo studies on emerging therapies for managing corneal epithelial injuries.

METHODS

The search was conducted on PubMed for articles published between January 2015 and September 2019 and in English language.

RESULTS

Thirty studies were identified for evaluation, including those on mesenchymal stem cells, amniotic membrane-derived therapies, endogenous peptides and their inhibitors, as well as hydrogel therapies. Intermediate to strong levels of evidence are presented regarding the use of these strategies on chemically injured cornea, including their effects on healing of corneal epithelial defect, anti-inflammatory properties, prevention of corneal neovascularization, as well as restoration of anatomy and functions of the anterior eye, although clinical trials are needed to determine the safety and efficacy of these strategies on humans.

CONCLUSION

Recent advances and understanding in various novel therapeutic methods for corneal epithelial chemical injuries should provide potential alternatives to current standard treatment regimens and help reduce risks of complications, hence improve patient outcomes.

Histidine in Health and Disease: Metabolism, Physiological Importance, and Use as a Supplement

L-histidine (HIS) is an essential amino acid with unique roles in proton buffering, metal ion chelation, scavenging of reactive oxygen and nitrogen species, erythropoiesis, and the histaminergic system. Several HIS-rich proteins (e.g., haemoproteins, HIS-rich glycoproteins, histatins, HIS-rich calcium-binding protein, and filaggrin), HIS-containing dipeptides (particularly carnosine), and methyl- and sulphur-containing derivatives of HIS (3-methylhistidine, 1-methylhistidine, and ergothioneine) have specific functions. The unique chemical properties and physiological functions are the basis of the theoretical rationale to suggest HIS supplementation in a wide range of conditions. Several decades of experience have confirmed the effectiveness of HIS as a component of solutions used for organ preservation and myocardial protection in cardiac surgery. Further studies are needed to elucidate the effects of HIS supplementation on neurological disorders, atopic dermatitis, metabolic syndrome, diabetes, uraemic anaemia, ulcers, inflammatory bowel diseases, malignancies, and muscle performance during strenuous exercise. Signs of toxicity, mutagenic activity, and allergic reactions or peptic ulcers have not been reported, although HIS is a histamine precursor. Of concern should be findings of hepatic enlargement and increases in ammonia and glutamine and of decrease in branched-chain amino acids (valine, leucine, and isoleucine) in blood plasma indicating that HIS supplementation is inappropriate in patients with liver disease.

Anionic food color tartrazine enhances antibacterial efficacy of histatin-derived peptide DHVAR4 by fine-tuning its membrane activity

Here it is demonstrated how some anionic food additives commonly used in our diet, such as tartrazine (TZ), bind to DHVAR4, an antimicrobial peptide (AMP) derived from oral host defense peptides, resulting in significantly fostered toxic activity against both Gram-positive and Gram-negative bacteria, but not against mammalian cells. Biophysical studies on the DHVAR4-TZ interaction indicate that initially large, positively charged aggregates are formed, but in the presence of lipid bilayers, they rather associate with the membrane surface. In contrast to synergistic effects observed for mixed antibacterial compounds, this is a principally different mechanism, where TZ directly acts on the membrane-associated AMP promoting its biologically active helical conformation. Model vesicle studies show that compared to dye-free DHVAR4, peptide-TZ complexes are more prone to form H-bonds with the phosphate ester moiety of the bilayer head-group region resulting in more controlled bilayer fusion mechanism and concerted severe cell damage. AMPs are considered as promising compounds to combat formidable antibiotic-resistant bacterial infections; however, we know very little on their in vivo actions, especially on how they interact with other chemical agents. The current example illustrates how food dyes can modulate AMP activity, which is hoped to inspire improved therapies against microbial infections in the alimentary tract. Results also imply that the structure and function of natural AMPs could be manipulated by small compounds, which may also offer a new strategic concept for the future design of peptide-based antimicrobials.

Specific metallo-protein interactions and antimicrobial activity in Histatin-5, an intrinsically disordered salivary peptide

Histatin-5 (Hst-5) is an antimicrobial, salivary protein that is involved in the host defense system. Hst-5 has been proposed to bind functionally relevant zinc and copper but presents challenges in structural studies due to its disordered conformation in aqueous solution. Here, we used circular dichroism (CD) and UV resonance Raman (UVRR) spectroscopy to define metallo-Hst-5 interactions in aqueous solution. A zinc-containing Hst-5 sample exhibits shifted Raman bands, relative to bands observed in the absence of zinc. Based on comparison to model compounds and to a family of designed, zinc-binding beta hairpins, the alterations in the Hst-5 UVRR spectrum are attributed to zinc coordination by imidazole side chains. Zinc addition also shifted a tyrosine aromatic ring UVRR band through an electrostatic interaction. Copper addition did not have these effects. A sequence variant, H18A/H19A, was employed; this mutant has less potent antifungal activity, when compared to Hst-5. Zinc addition had only a small effect on the thermal stability of this mutant. Interestingly, both zinc and copper addition shifted histidine UVRR bands in a manner diagnostic for metal coordination. Results obtained with a K13E/R22G mutant were similar to those obtained with wildtype. These experiments show that H18 and H19 contribute to a zinc binding site. In the H18A/H19A mutant the specificity of the copper/zinc binding sites is lost. The experiments implicate specific zinc binding to be important in the antimicrobial activity of Hst-5.

Presence of Histatin-1 in Human Tears and Association with Aqueous Deficient Dry Eye Diagnosis: A Preliminary Study

The aims of this study were to determine if histatin-1 (H1) is present in normal human tears and whether tear levels of H1 varied between normal patients and those with aqueous deficient dry eye disease (ADDE). Patient samples were obtained from 11 normal patients and 11 severe ADDE patients. Relevant patient characteristics, including age, sex, and dry eye disease (DED) diagnostic parameters were collected. Multiple qualitative and quantitative methods were used to compare the concentration of H1 between patient groups. Mixed linear modeling was used to compare H1 levels between groups, and diagnostic performance was assessed using the receiver-operator-characteristic (ROC). ADDE patients had significantly lower H1 concentrations (85.9 ± 63.7 ng/ml) than the normal group (891.6 ± 196.5 ng/ml) (p < 0.001), while controlling for age and sex. ROC analysis indicated that H1 concentration is potentially a biomarker for ADDE (area under curve = 0.96). Reclassification of patients by DED parameters including, Ocular Surface Disease Index (OSDI) (≤13, >13) and Schirmer I (without anesthesia) (<10 mm, ≥10 mm) showed significant differences in H1 level (OSDI, p = 0.004) and Schirmer I ((p = 0.010). In conclusion, this is the first preliminary report of the presence of H1 in human tears. H1 concentrations are lower in ADDE patients and H1 may have diagnostic potential in evaluation ADDE patients.

Potential Therapeutic Effects of Gut Hormones, Ghrelin and Obestatin in Oral Mucositis

Chemotherapy and/or head and neck radiotherapy are frequently associated with oral mucositis. Oral pain, odynophagia and dysphagia, opioid use, weight loss, dehydration, systemic infection, hospitalization and introduction of a feeding tube should be mentioned as the main determinated effect of oral mucositis. Oral mucositis leads to a decreased quality of life and an increase in treatment costs. Moreover, oral mucositis is a life-threatening disease. In addition to its own direct life-threatening consequences, it can also lead to a reduced survival due to the discontinuation or dose reduction of anti-neoplasm therapy. There are numerous strategies for the prevention or treatment of oral mucositis; however, their effectiveness is limited and does not correspond to expectations. This review is focused on the ghrelin and obestatin as potentially useful candidates for the prevention and treatment of chemo- or/and radiotherapy-induced oral mucositis.

Cu-ATCUN Derivatives of Sub5 Exhibit Enhanced Antimicrobial Activity via Multiple Modes of Action

Antimicrobial peptides (AMPs) are short, amphipathic peptides that are typically cationic in sequence and display broad-spectrum activity against bacteria, fungi, and protists. Herein, we report the effect of appending the amino terminal copper and nickel binding motif (ATCUN) to Sub5. The Cu-ATCUN derivatives show a two- to three-fold increase in antimicrobial activity for a variety of microbes, relative to Sub5, with MICs as low as 0.3 ± 0.1 μM toward Enterococcus faecium. Sub5 and the ATCUN derivatives bind both plasmid DNA and 16s A-site rRNA with low micromolar affinity. Native Sub5 and the metallopeptide derivatives were shown to promote damage against DNA to similar extents in cellular studies against both Escherichia coli and Staphylococcus epidermidis, with an almost threefold higher activity against the latter organism. Liposome experiments show that the metallopeptides have a greater affinity for model membranes of E. coli and S. aureus relative to Sub5, which correlates with their enhanced antimicrobial activity. Sub5 and the metalloderivatives also display no cytotoxicity toward adult human dermal fibroblasts. Addition of the ATCUN motif conferred the ability to promote lipid oxidation toward E. coli and S. epidermidis and enhanced membrane permeability, as evidenced by the extent of ATP leaked from cellular membranes relative to Sub5 alone. These data suggest that Cu-ATCUN derivatives inhibit microbes through multiple modes of action, resulting in an enhancement in their overall potency.

Metal-ion Binding to Host Defense Peptide Piscidin 3 Observed in Phospholipid Bilayers by Magic Angle Spinning Solid-state NMR

Cationic antimicrobial peptides (AMPs) are essential components of the innate immune system. They have attracted interest as novel compounds with the potential to treat infections associated with multi-drug resistant bacteria. In this study, we investigate piscidin 3 (P3), an AMP that was first discovered in the mast cells of hybrid striped bass. Prior studies showed that P3 is less active than its homolog piscidin 1 (P1) against planktonic bacteria. However, P3 has the advantage of being less toxic to mammalian cells and more active on biofilms and persister cells. Both P1 and P3 cross bacterial membranes and co-localize with intracellular DNA but P3 is more condensing to DNA while P1 is more membrane active. Recently, we showed that both peptides coordinate Cu2+ through an amino-terminal copper and nickel (ATCUN) motif. We also demonstrated that the bactericidal effects of P3 are linked to its ability to form radicals that nick DNA in the presence of Cu2+ . Since metal binding and membrane crossing by P3 is biologically important, we apply in this study solid-state NMR spectroscopy to uniformly 13 C-15 N-labeled peptide samples to structurally characterize the ATCUN motif of P3 bound to bilayers and coordinated to Ni2+ and Cu2+ . These experiments are supplemented with density functional theory calculations. Taken together, these studies refine the arrangement of not only the backbone but also side chain atoms of an AMP simultaneously bound to metal ions and phospholipid bilayers.