Immunocytochemical Localization of Histatins in Human Salivary Glands

Long-Term Post-COVID-19 Associated Oral Inflammatory Sequelae

The oral cavity remains an underappreciated site for SARS-CoV-2 infection despite the myriad oral conditions observed in COVID-19 patients. Recently, replicating SARS-CoV-2 was found inside salivary epithelial cells resulting in inflammation and atrophy of salivary glands. Saliva possesses healing properties crucial for maintaining the health of the oral mucosa. Specifically, salivary antimicrobial peptides, most notable, histatin-5 exclusively produced in salivary glands, plays a vital role in innate immunity against colonizing microbial species. The demonstration of SARS-CoV-2 destruction of gland tissue where histatin-5 is produced strongly indicate that histatin-5 production is compromised due to COVID-19. Here we present a case of a patient presenting with unexplained chronic oral dysesthesia and dysgeusia post-recovery from COVID-19. To explore potential physiological mechanisms behind the symptoms, we comparatively analyzed saliva samples from the patient and matched healthy subject for histatin-5 and key cytokines. Findings demonstrated significantly reduced histatin-5 levels in patient's saliva and activation of the Th17 inflammatory pathway. As histatin-5 exhibits potent activity against the opportunistic oral pathogen Candida albicans, we evaluated saliva potency against C. albicans ex vivo. Compared to control, patient saliva exhibited significantly reduced anti-candidal efficacy. Although speculative, based on history and salivary analysis we hypothesize that salivary histatin-5 production may be compromised due to SARS-CoV-2 mediated salivary gland destruction. With the current lack of emphasis on implications of COVID-19 on oral health, this report may provide lacking mechanistic insights that may lead to reassessment of risks for oral opportunistic infections and mucosal inflammatory processes in acutely-ill and recovered COVID-19 patients.

Salivary Histatin 5 Level in Women with Vaginal Candidiasis

Histatins (Hsts) are considered a prominent member of antimicrobial peptides rich in histidine, bearing antifungal activity against Candida species. Hst5 is the most effective among them. Although Hst5 is not found in the cervicovaginal fluid, it has been detected in the human serum. Saliva acts as a mirror, reflecting the cause and effect relationship between several diseases. We aimed to show the salivary Hst5 levels with vaginal candidiasis. Women in the reproductive age group (18-50 years) were enrolled in the study. Patients and controls were classified based on the presence or absence of vaginal discharge suggestive of candidiasis, respectively. Vaginal and salivary samples were collected from all the women. Vaginal samples were cultured for the growth of Candida species. Salivary samples were tested by protein electrophoresis to detect Hst5 levels, and the results were compared between the two groups. A total of 80 women were included in this study. The mean age of women in vaginal candidiasis and control groups was 34.25 ± 8.06 and 36.83 ± 7.29 years, respectively. Candida species were isolated from the vaginal samples of the patient group (34 C. albicans, 6 non-Candida albicans) but not from the control group. Hst5 levels in the patient and control group were found to be 0.0571 ± 0.003 ng/mL and 0.0641 ± 0,0031 ng/mL, respectively. Hst5 levels were found to be significantly lower in the vaginal candidiasis group (p=0.001). We conclude that decreased salivary Hst5 levels in women are associated with vaginal candidiasis. Candida infection is a cause or result of lower salivary Hst5 levels, and it may be an important finding for the etiopathogenesis, diagnosis, and treatment of the disease, but further analysis is needed.

Injectable supramolecular gelatin hydrogel loading of resveratrol and histatin-1 for burn wound therapy

Prolonged inflammatory response and insufficient vascularization cause delayed and poor wound healing. In this study, we fabricated a supramolecular host-guest gelatin (HGM) hydrogel loaded with resveratrol (Res) and histatin-1 (His-1) to suppress inflammation and promote vascularization at skin burn wound sites. The HGM hydrogel showed good properties of shear-thinning and injectability, thereby allowing easy in situ injection and fast adaption to irregular wounds. Res and His-1 were demonstrated to enhance angiogenesis in vitro using cell migration and tube formation assays based on human umbilical vein endothelial cells (HUVECs). In an established rat burn wound model, HGM/Res/His-1 hydrogel treatment promoted wound healing by inhibiting expression of the pro-inflammatory factors of interleukin 6 (IL-6), interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) and increasing the expression of transforming growth factor β1 (TGF-β1) and platelet endothelial cell adhesion molecule-1 (CD31). HGM/Res/His-1 hydrogel treatment showed comparable efficacy with that of the commercial dressing, Tegaderm™, and therefore shows promising potential for clinical translation.

Biotic and abiotic factors of bactericidal properties variability of ruminant saliva

The microflora of the oral cavity of domestic ruminants, presented by transitive gram-negative species of bacteria (cocci and sticks) in cows, transient and obligate gram-positive (usually cocci) bacteria in sheep was studied. The lowest contamination of the sheep mouth mucosa was observed in autumn, and the largest in summer. Seasonal features of bactericidal activity of saliva and its main components (lysozyme, properdin and complement system) are shown. Differences of the above indicators in cows and sheep are considered. Low activity is typical for saliva complement system in ruminants in general and sheep in particular. Lysozyme activity and properdin content are maximum in cows and sheep in summer, with elongation towards autumn (exception – lysozyme activity in sheep extends in spring).

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.

A Control Alternative for the Hidden Enemy in the Wine Cellar

Brettanomyces bruxellensis has been described as the principal spoilage yeast in the winemaking industry. To avoid its growth, wine is supplemented with SO2, which has been questioned due to its potential harm to health. For this reason, studies are being focused on searching for, ideally, natural new antifungals. On the other hand, it is known that in wine production there are a variety of microorganisms, such as yeasts and bacteria, that are possible biological controls. Thus, it has been described that some microorganisms produce antimicrobial peptides, which might control yeast and bacteria populations. Our laboratory has described the Candida intermedia LAMAP1790 strain as a natural producer of antimicrobial compounds against food spoilage microorganisms, as is B. bruxellensis, without affecting the growth of S. cerevisiae. We have demonstrated the proteinaceous nature of the antimicrobial compound and its low molecular mass (under 10 kDa). This is the first step to the possible use of C. intermedia as a selective bio-controller of the contaminant yeast in the winemaking industry.

Distinguishing Molecular Features of Allergic Fungal Rhinosinusitis

Objective

Allergic fungal rhinosinusitis (AFRS) is a clinical subtype of chronic rhinosinusitis with nasal polyps (CRSwNP), characterized by eosinophilic mucin, evidence of fungal elements within the mucin, fungal-specific type I hypersensitivity, and characteristic computed tomography findings. It remains controversial whether AFRS represents a disease with a unique pathophysiology from chronic rhinosinusitis or is merely a severe form of CRSwNP. The goal of this study was to identify molecular features unique to AFRS.

Study Design

Cross-sectional case-control.

Setting

Single academic tertiary referral institution.

Subjects and Methods

Subjects included 86 patients undergoing endoscopic sinus surgery: CRSwNP (n = 34), AFRS (n = 37), and healthy controls (n = 15). Pathway and correlation analyses were performed with whole-genome microarray data for study patients undergoing surgery for recalcitrant chronic rhinosinusitis. Our findings were confirmed with quantitative polymerase chain reaction and immunohistochemical studies.

Results

AFRS was uniquely characterized by a pronounced association with adaptive T helper 2–associated immune gene expression. AFRS exhibited altered expression of proteins associated with secretory salivary peptides—namely, histatin, a peptide with known antifungal activity in the oral cavity. Furthermore, the expression of histatins correlated negatively with that of type 2 inflammatory mediators. We confirm the decreased expression of histatins in AFRS when compared with CRSwNP by quantitative polymerase chain reaction and localized its expression to a submucosal cell population.

Conclusion

There exist clear molecular profiles that distinguish AFRS from CRSwNP. This divergence translates into an altered ability to control fungal growth and may in part explain some of the phenotypical differences between CRSwNP and AFRS.

Histatins, wound healing, and cell migration

Wounds in the oral mucosa heal faster and more efficiently than those in the skin, although the mechanisms underlying these differences are not completely clear. In the last 10 years, a group of salivary peptides, the histatins, has gained attention on behalf of their ability to improve several phases of the wound-healing process. In addition to their roles as anti-microbial agents and in enamel maintenance, histatins elicit other biological effects, namely by promoting the migration of different cell types contained in the oral mucosa and in non-oral tissues. Histatins, and specifically histatin-1, promote cell adhesion and migration in oral keratinocytes, gingival and dermal fibroblasts, non-oral epithelial cells, and endothelial cells. This is particularly relevant, as histatin-1 promotes the re-epithelialization phase and the angiogenic responses by increasing epithelial and endothelial cell migration. Although the molecular mechanisms associated with histatin-dependent cell migration remain poorly understood, recent studies have pointed to the control of signaling endosomes and the balance of small GTPases. This review aimed to update the literature on the effects of histatins in cell migration, with a focus on wound healing. We will also discuss the consequences that this increasing field will have in disease and therapy design.

The salivary peptide histatin-1 promotes endothelial cell adhesion, migration, and angiogenesis

Saliva is a key factor that contributes to the high efficiency of wound healing in the oral mucosa. This is not only attributed to physical cues but also to the presence of specific peptides in the saliva, such as histatins. Histatin-1 is a 38 aa antimicrobial peptide, highly enriched in human saliva, which has been previously reported to promote the migration of oral keratinocytes and fibroblasts in vitro However, the participation of histatin-1 in other crucial events required for wound healing, such as angiogenesis, is unknown. Here we demonstrate that histatin-1 promotes angiogenesis, as shown in vivo, using the chick chorioallantoic membrane model, and by an in vitro tube formation assay, using both human primary cultured endothelial cells (HUVECs) and the EA.hy926 cell line. Specifically, histatin-1 promoted endothelial cell adhesion and spreading onto fibronectin, as well as endothelial cell migration in the wound closure and Boyden chamber assays. These actions required the activation of the Ras and Rab interactor 2 (RIN2)/Rab5/Rac1 signaling axis, as histatin-1 increased the recruitment of RIN2, a Rab5-guanine nucleotide exchange factor (GEF) to early endosomes, leading to sequential Rab5/Rac1 activation. Accordingly, interfering with either Rab5 or Rac1 activities prevented histatin-1-dependent endothelial cell migration. Finally, by immunodepletion assays, we showed that salivary histatin-1 is required for the promigratory effects of saliva on endothelial cells. In conclusion, we report that salivary histatin-1 is a novel proangiogenic factor that may contribute to oral wound healing.-Torres, P., Díaz, J., Arce, M., Silva, P., Mendoza, P., Lois, P., Molina-Berríos, A., Owen, G. I., Palma, V., Torres, V. A. The salivary peptide histatin-1 promotes endothelial cell adhesion, migration, and angiogenesis.

Silver Enhancement for Transmission Electron Microscopy Imaging of Antibody Fragment-Gold Nanoparticles Conjugates Immobilized on Ordered Mesoporous Silica

Ordered mesoporous silica (OMS) materials are receiving great attention as possible carriers for valuable but unstable drugs as, for example, therapeutic proteins. A key issue is to prove that the therapeutic protein is effectively able to penetrate the pores of OMS during the adsorption step. Here, we immobilized an antibody fragment [F(ab')GAMIgG] conjugated with ultrasmall gold nanoparticles (GNPs) onto amino-functionalized SBA-15 (SBA-NH2) mesoporous silica. The aim of this work is the visualization of the location of the conjugates adsorbed onto SBA-NH2 with transmission electron microscopy (TEM). Because of the ultrasmall size of GNPs (<1 nm), we use the silver enhancement procedure to amplify their size. In this procedure, ultrathin sections of conjugate-loaded SBA-NH2 particles are prepared by a ultramicrotome sectioning technique. The ultrasmall GNPs located on the top side of the 70-90 nm thick slices act as microcrystallization nucleation sites for the deposition of reduced metallic silver. Consequently, the ultrasmall GNPs increase their size. This allows for the direct imaging of the conjugates adsorbed. We clearly localize the F(ab')GAMIgG-GNPs conjugates either on the external surface of the particles or inside the mesopores of SBA-NH2 through TEM.

Impaired Histatin-5 Levels and Salivary Antimicrobial Activity against C. albicans in HIV Infected Individuals

HIV-infected individuals constitute a population highly susceptible to opportunistic infections, particularly oral candidiasis caused by the most pathogenic human fungal species Candida albicans. Host-produced salivary antimicrobial peptides are considered to be an important part of the host innate immune system involved in protection of the oral cavity against colonization and infection by microbial species. Histatin-5 (Hst-5) specifically has exhibited potent anti-candidal properties in vitro. However, its importance in protecting the oral mucosa against candidal colonization and importantly, its contribution to the observed enhanced susceptibility of HIV-infected individuals to candidiasis has not been previously investigated. To that end, a novel immunoassay was used to demonstrate significant decrease in salivary Hst-5 levels in HIV+ individuals concomitant with enhanced candidal prevalence. Further, saliva's anti-candidal potency was found to be proportional to Hst-5 concentration and significantly compromised in HIV+ subjects compared to controls. The key role for Hst-5 was further confirmed upon exposure to the Hst-5-specific antibody where saliva's initial killing activity was substantially compromised. Combined, these findings identify Hst-5 as a key anti-candidal salivary component and demonstrate its decreased levels in HIV infection providing new insights into oral Innate immune defense mechanisms and the enhanced susceptibility of HIV+ individuals to oral candidiasis.

Structural characterization and antimicrobial activity of the Zn(II) complex with P113 (demegen), a derivative of histatin 5

Zinc binding to P113 (or demegen), a 12 amino acid (AKRHHGYKRKFH-NH(2)) fragment of histatin 5, was investigated by means of NMR and CD techniques, yielding delineation of the metal binding site and the 3D structure of the complex in water and in DMSO as well. The three His imidazole and the N-terminus nitrogens were found to act as the zinc coordinating atoms. A comparison with the previously reported Cu(II)-P113 complex disclosed that the two structures were rather diverse, in spite of an identical donor set. The two complexes were also tested for their antimicrobial activity in vitro against seven bacteria and two yeast strains: a minor activity of both complexes vs that of free ligand was given evidence, suggesting both metal ions may possibly play a negative role in vivo.

Peptide-based Antifungal Therapies against Emerging Infections

Acquired drug resistance to mycotic infections is rapidly emerging as a major medical problem. Opportunistic fungal infections create therapeutic challenges, particularly in high risk immunocompromised patients with AIDS, cancer, and those undergoing transplantation. Higher mortality and/or morbidity rates due to invasive mycosis have been increasing over the last 20 years, and in light of growing resistance to commonly used antibiotics, novel antifungal drugs and approaches are required. Currently there is considerable interest in antifungal peptides that are ubiquitous in plant and animal kingdoms. These small cationic peptides may have specific targets or may be multifunctional in their mechanism of action. On the basis of recent advances in protein engineering and solid phase syntheses, the utility and potential of selected peptides as efficient antifungal drugs with acceptable toxicity profiles are being realized. This review will discuss recent advances in peptide therapy for opportunistic fungal infections.

Transcriptional regulation of the salivary histatin gene: finding of a strong positive regulatory element and its binding protein

Histatins are salivary proteins found and expressed in human salivary glands. They play a role in the non-immune system of antimicrobial defense, for instance, against Candida albicans. The transcriptional regulatory sequences of the histatin gene, HIS1, have remained obscure for a long time. Here, we cloned the putative promoter from human genomic DNA and tested it in a luciferase reporter system. This promoter is much more active in salivary gland cells than in other cell types. Analysis of deletion mutants revealed that the region encompassing -2254 to -1748 is a strong positive transcriptional element, and its functional core sequence (termed HTN27 box) works in correct and reverse orientations in synergy with downstream sequences, the region spanning -680 to +28 and a proximal promoter. The plus single-stranded HTN27 box is specifically bound by a 100 kDa protein that is present in HSG cells, but not in HeLa cells. These findings indicate that the regulation of the histatin gene expression may be intricate, and it seems to have a cell-type preference in the salivary gland cells.

Facts and artifacts in proteomics of body fluids. What proteomics of saliva is telling us?

This review briefly depicts several salient points of the current status of knowledge on salivary peptidoma. It outlines the intrinsic difficulties in its characterization connected to different factors of variability, such as: i) the high genetic polymorphisms, complicated by individual insertions/deletions and alternative splicing; ii) complex post-translational maturations comprehending different proteolytic cleavages, glycosylation, phosphorylation and sulfation processes; iii) physiological variations and different contributions to the whole. Moreover, several technological and analytical problems and pitfalls that had to be surmounted during our studies focussed on the extensive qualitative and quantitative characterization of salivary peptidoma and mainly based on LC-MS analyses of intact naturally occurring peptides are here described. The hope is that the information provided might be helpful to other groups engaged on the analysis of saliva or other body fluids for clinical applications.

Electron microscopic detection of statherin in secretory granules of human major salivary glands

In order to increase current knowledge regarding statherin secretion into the oral cavity, ultrastructural localization of this peptide was investigated in human salivary glands by using a post-embedding immunogold staining technique. Statherin reactivity was found inside the granules of serous cells of parotid and submandibular glands. In parotid granules immunostaining was preferentially present in the less electron-dense region, whereas in submandibular serous granules the reactivity was uniform and the dense core always stained. By contrast, none or weak reactivity was observed in serous cells of major sublingual glands. These findings reveal for the first time the subcellular localization of statherin by electron transmission microscopy and confirm that of the three major types of salivary glands, the parotid and submandibular glands are the greatest source of salivary statherin. Moreover, they suggest that more than one packaging mechanism may be involved in the storage of statherin within serous granules of salivary glands.

The P-113 fragment of histatin 5 requires a specific peptide sequence for intracellular translocation in Candida albicans, which is independent of cell wall binding

The activity of histatin 5 (Hst 5) against Candida albicans is initiated through cell wall binding, followed by translocation and intracellular targeting. The C. albicans cell wall protein Ssa2 is involved in the transport of Hst 5 into cells as part of cell killing. P-113 (a 12-amino-acid candidacidal active fragment of Hst 5) and P-113Q2.10 (which is inactivated by a glutamine substitution of the Lys residues at positions 2 and 10) were compared for their levels of cell wall binding and intracellular translocation in Candida wild-type (wt) and ssa2Delta strains. Both P-113 and P-113Q2.10 bound to the walls of C. albicans wt and ssa2Delta cells, although the quantity of P-113Q2.10 in cell wall extracts was higher than that of P-113 in both strains. Increasing the extracellular NaCl concentration to 100 mM completely inhibited the cell wall association of both peptides, suggesting that these interactions are primarily ionic. The accumulation of P-113 in the cytosol of wt cells reached maximal levels within 15 min (0.26 microg/10(7) cells), while ssa2Delta mutant cells had maximal cytosolic levels of less than 0.2 microg/10(7) cells even after 30 min of incubation. Furthermore, P-113 but not P-113Q2.10 showed specific binding with a peptide array of C. albicans Ssa2p. P-113Q2.10 was not transported into the cytosol of either C. albicans wt or ssa2Delta cells, despite the high levels of cell wall binding, showing that the two cationic lysine residues at positions 2 and 10 in the P-113 peptide are important for transport into the cytosol and that binding and transport are independent functional events.

Evaluation of bactericidal activity of human biological fluids by flow cytofluorimetry

The ability of biological fluids to kill microbes is an important feature of the human immune system. Following incubation of fluorescein isothiocyanate-labeled Staphylococcus aureus with biological specimens and subsequent staining with propidium iodide, the proportions of killed bacteria were estimated by flow cytometry. FACScan is a simple, quick and reliable method to evaluate bactericidal activity of biological fluids. The results of the cytometric method correlated well with the results of the classic microbiological method. The proposed method is highly informative for evaluating bactericidal activity of sera in immunocompromised patients.

Oral fluid proteolytic effects on histatin 5 structure and function

Histatins are human salivary antifungal proteins that are prone to extensive enzymatic degradation upon their release into the oral cavity. Histatin proteolysis, leading to the disappearance of the intact protein can be expected to have functional consequences. Histatin 5, comprising 24 residues, is the smallest of the major salivary histatins and the most active in terms of its antifungal properties. The rate and mode of histatin 5 degradation were determined by incubating the protein in whole saliva supernatant for various time intervals. Fragmentation products were collected by reversed-phase high performance liquid chromatography (RP-HPLC), characterised structurally by matrix-assisted laser desorption/ionisation-time of flight (MALDI-TOF) mass spectrometry and functionally in a fungal growth inhibition assay. Of the 19 fragments identified, 16 were derived from single proteolytic cleavage events in histatin 5. A remarkable finding was the inter-subject consistency in the histatin 5 degradation pattern. Added histatin 5 disappeared from whole saliva supernatant at an average rate of 105+/-22 microg/ml/h, which in part could explain the virtual absence of histatin 5 in whole saliva. Despite the rapid proteolysis of histatin 5, the early degradation mixture was as active in antifungal assays as intact histatin 5. These data demonstrate that the oral-fluid mediated proteolysis of histatin 5 represents an intrinsic biological property of whole saliva. The data also reveal that the early proteolysis phase of histatin 5 does not abolish the antifungal properties associated with this protein.

Salivary histatins in human deep posterior lingual glands (of von Ebner)

OBJECTIVE

Human saliva contains a family of low molecular weight histidine-rich proteins, named histatins, characterised by bactericidal and fungicidal activities in vitro against several microbial pathogens, such as Streptococcus mutans and Candida albicans. They represent a major component of an innate host non-immune defense system. In an earlier study we described the distribution of histatins in the glandular parenchyma of human major salivary glands, confirming that all human major salivary glands are involved in the secretion of histatins into saliva. In the present study we determined the expression and localisation of histatins in human posterior deep lingual glands (von Ebner's glands) by means of immunoelectron microscopy.

DESIGN

Thin sections of normal human salivary glands, embedded in Epon resin, were incubated with rabbit polyclonal antibodies specific for human histatins and successively with a gold conjugated goat anti-rabbit IgG used as secondary antibody. Sections incubated with medium devoid of primary antibody or containing non-immune serum were used as controls.

RESULTS

The serous secreting cells represented the main source of histatins in the glandular parenchyma of von Ebner's glands. At the electron microscopic level, labeling was associated with rough endoplasmic reticulum, Golgi complex and secretory granules that represented the main cytoplasmic site of histatin localisation. However, variability in the intensity of labeling was observed among adjacent cells.

CONCLUSIONS

The present results show for the first time that human von Ebner's glands produce and represent a significant source of histatins, supporting the hypothesis of their important role in preventing microbial assaults on the tissues in the posterior region of the tongue and in the circumvallate papillae.

Human antimicrobial peptides: defensins, cathelicidins and histatins

Antimicrobial peptides, which have been isolated from many bacteria, fungi, plants, invertebrates and vertebrates, are an important component of the natural defenses of most living organisms. The isolated peptides are very heterogeneous in length, sequence and structure, but most of them are small, cationic and amphipathic. These peptides exhibit broad-spectrum activity against Gram-positive and Gram-negative bacteria, yeasts, fungi and enveloped viruses. A wide variety of human proteins and peptides also have antimicrobial activity and play important roles in innate immunity. In this review we discuss three important groups of human antimicrobial peptides. The defensins are cationic non-glycosylated peptides containing six cysteine residues that form three intramolecular disulfide bridges, resulting in a triple-stranded beta-sheet structure. In humans, two classes of defensins can be found: alpha-defensins and beta-defensins. The defensin-related HE2 isoforms will also be discussed. The second group is the family of histatins, which are small, cationic, histidine-rich peptides present in human saliva. Histatins adopt a random coil conformation in aqueous solvents and form alpha-helices in non-aqueous solvents. The third group comprises only one antimicrobial peptide, the cathelicidin LL-37. This peptide is derived proteolytically from the C-terminal end of the human CAP18 protein. Just like the histatins, it adopts a largely random coil conformation in a hydrophilic environment, and forms an alpha-helical structure in a hydrophobic environment.