Mass spectrometric identification of key proteolytic cleavage sites in statherin affecting mineral homeostasis and bacterial binding domains

Saliva identification in forensic samples by automated microextraction and intact mass analysis of statherin

The enzyme α-amylase has long been a commonly targeted protein in serological tests for saliva. While being especially abundant in saliva, α-amylase is detectable in vaginal secretions, sweat, fecal matter, breast milk and other matrices. As a result, assays for α-amylase only provide a presumptive indication of saliva. The availability of mass spectrometry-based tools for the detection of less abundant, but more specific, protein targets (e.g., human statherin) has enabled the development of high confidence assays for human saliva. Sample throughput, however, has traditionally been low due to multi-step workflows for protein extraction, quantitation, enzymatic digestion, solid phase cleanup, and nano-/capillary-based chromatography. Here, we present two novel "direct" single-stage extraction strategies for sample preparation. These feature immunoaffinity purification and reversed-phase solid-phase microextraction in conjunction with intact mass analysis of human statherin for saliva identification. Mass analysis was performed on the Thermo Scientific Q-Exactive™ Orbitrap mass spectrometer with a 10-min analytical run time. Data analysis was performed using Byos® from Protein Metrics. Two sample sets were analyzed with a population of 20 individuals to evaluate detection reliability. A series of casework-type samples were then assayed to evaluate performance in an authentic forensic context. Statherin was confidently identified in 92% and 71% of samples extracted using the immunoaffinity purification and solid phase microextraction approaches, respectively. Overall, immunoaffinity purification outperformed the solid phase microextraction, especially with complex mixtures. In toto, robotic extraction and intact mass spectrometry enable the reliable identification of trace human saliva in a variety of sample types.

Protein-based bioactive coatings: from nanoarchitectonics to applications

Protein-based bioactive coatings have emerged as a versatile and promising strategy for enhancing the performance and biocompatibility of diverse biomedical materials and devices. Through surface modification, these coatings confer novel biofunctional attributes, rendering the material highly bioactive. Their widespread adoption across various domains in recent years underscores their importance. This review systematically elucidates the behavior of protein-based bioactive coatings in organisms and expounds on their underlying mechanisms. Furthermore, it highlights notable advancements in artificial synthesis methodologies and their functional applications in vitro. A focal point is the delineation of assembly strategies employed in crafting protein-based bioactive coatings, which provides a guide for their expansion and sustained implementation. Finally, the current trends, challenges, and future directions of protein-based bioactive coatings are discussed.

Promoting mineralization at biological interfaces Ex vivo with novel amelotin-based bio-nano complexes

Conclusion

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AMTN/AMTN-Col functionalized HANP are potent mineral-promoting bio-nano complexes.

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AMTN/AMTN-Col coated HANP promote collagen mineralization.

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AMTN/AMTN-Col coated HANP enhance resin-dentin bond strength.

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AMTN/AMTN-Col coated HANP are potential candidates for clinical application.

Robust and sensitive peptidomics workflow for plasma based on specific extraction, lipid removal, capillary LC setup and multinozzle ESI emitter

We present a new workflow for the LC-MS determination of native peptides in plasma at picomolar levels. Collected whole blood was quickly diluted with an ice-cold solution in order to stop protease activity. Diluted plasma samples were extracted by protein denaturation followed by solid-phase-extraction with a polymeric stationary phase that removed most proteins and lipids. Using a specific LC-MS setup with 3 pumps, 240 μL of extracts were injected without drying-reconstitution, a step known to cause peptide losses. After an 18-fold dilution on-line, peptides were trapped on a 1 × 10 mm C8 column, back-flushed and resolved on a 0.3 × 100 mm C18 column. Extract reproducibility, robustness (column clogging), extraction yields, matrix effects, calibration curves and limits of detection were evaluated with plasma extracts and spiked-in standards. The sensitivity and applicability of 3 electrospray sources were evaluated at capillary flow rates (10 μL/min). We show that ionization sources must have a spray angle with the MS orifice when "real" extracts are injected and that a multinozzle emitter can improve very significantly peptide detection. Finally, using our workflow, we have performed a peptidomics study on dried-blood-spots collected over 65 h in a healthy volunteer and discovered 5 fragments (2.9-3.8 KDa) of the protein statherin showing circadian oscillations. This is the first time that statherin is observed in blood where its role clearly deserves further investigations. Our peptidomic protocol shows low picomolar limits of detection and can be readily applied with or without minor modifications for most peptide determinations in various biomatrices.

Functional Specialization of Human Salivary Glands and Origins of Proteins Intrinsic to Human Saliva

Salivary proteins are essential for maintaining health in the oral cavity and proximal digestive tract, and they serve as potential diagnostic markers for monitoring human health and disease. However, their precise organ origins remain unclear. Through transcriptomic analysis of major adult and fetal salivary glands and integration with the saliva proteome, the blood plasma proteome, and transcriptomes of 28+ organs, we link human saliva proteins to their source, identify salivary-gland-specific genes, and uncover fetal- and adult-specific gene repertoires. Our results also provide insights into the degree of gene retention during gland maturation and suggest that functional diversity among adult gland types is driven by specific dosage combinations of hundreds of transcriptional regulators rather than by a few gland-specific factors. Finally, we demonstrate the heterogeneity of the human acinar cell lineage. Our results pave the way for future investigations into glandular biology and pathology, as well as saliva's use as a diagnostic fluid.

Endogenous salivary citrate is associated with enhanced rheological properties following oral capsaicin stimulation

NEW FINDINGS

What is the central question of this study? What are the relationships between physical properties of saliva, protein composition and metabolite composition? What is the main finding and its importance? Salivary citrate, one of the major endogenous metabolites in saliva, increased upon capsaicin stimulation and was associated with improved physical properties measured by extensional rheology. This suggests salivary gland citrate transporters might be a valuable area of future study.

ABSTRACT

Saliva displays viscoelastic properties which enable coating, lubrication and protection of the oral mucosa and hard tissues. Individuals lacking saliva or perceiving oral dryness can manage their symptoms using artificial saliva preparations, but these often fail to mimic the sensation and functionality of natural saliva. It is widely acknowledged that mucins (MUC7 and MUC5B) confer saliva's rheological properties, but artificial saliva containing purified mucins is still often an inadequate substitute. This work aimed to explore salivary components that influence salivary extensional rheology to better understand how natural saliva could be replicated. Saliva was stimulated via control and capsaicin solutions in healthy volunteers. Extensional rheology was analysed using a CaBER-1 (capillary breakup) extensional rheometer. Protein composition, including mucins, was measured by gel-electrophoresis band densitometry and metabolites were measured by 1 H nuclear magnetic resonance spectroscopy. Capsaicin stimulation significantly increased capillary breakup time, extensional viscosity and the abundance of most major salivary proteins. Stimulation also increased salivary citrate and choline concentrations. Significant correlations were found between capillary breakup time and amylase (r = 0.67, P < 0.05), statherin (ρ = 0.66, P < 0.05) and citrate (ρ = 0.81, P < 0.01). The relationship between citrate and salivary rheology was subsequently investigated in vitro. These results suggest that citrate and non-mucin proteins are stronger predictors of salivary rheology than the more often studied mucin glycoproteins. Potential mechanisms are discussed and future work in this area could help formulate more effective saliva substitutes, more closely resembling natural saliva.

Anatomical stability of human fungiform papillae and relationship with oral perception measured by salivary response and intensity rating

Fungiform papillae house taste buds on the anterior dorsal tongue. Literature is inconclusive as to whether taste perception correlates with fungiform papillae density (FPD). Gustatory reflexes modulate the amount and composition of saliva subsequently produced, and thus may be a more physiologically objective measure of tastant-receptor interactions. Taste perception fluctuates with time but the stability of individual fungiform papillae is unclear. This study followed ten healthy volunteers longitudinally at baseline, one and six months. FPD, diameter and position were measured and participants rated intensity perception of sucrose, caffeine, menthol and capsaicin solutions. Salivary flow rate, protein concentration and relative changes in protein composition were measured following each tastant. FPD, diameter and position were unchanged at six months. FPD did not correlate with intensity rating for any taste. FPD did correlate with changes in salivary protein output following sucrose (ρ = 0.72, p = 0.02) and changes in levels of proline-rich protein and mucin 7 following capsaicin (ρ = 0.71, p = 0.02, ρ = 0.68, p = 0.04, respectively). These results suggest that over six months fungiform papillae are anatomically stable, playing a greater role in mediating the physiological salivary response to stimuli rather than determining the perceived intensity of taste.

Protein Profile of the Acquired Enamel Pellicle after Rinsing with Whole Milk, Fat-Free Milk, and Water: An in vivo Study

This study detected changes in the protein profile of the acquired enamel pellicle (AEP) formed in vivo after rinsing with whole milk, fat-free milk, or water. Nine subjects in good oral condition took part in the study. The acquired pellicle was formed in the morning, for 120 min, after prophylaxis with pumice. Following this, the volunteers rinsed with 10 mL of whole milk, fat-free milk, or deionized water for 30 s, following a blinded crossover protocol. After 60 min, the pellicle was collected with filter paper soaked in 3% citric acid and processed for analysis by liquid chromatography-electrospray ionization tandem mass spectrometry. The obtained tandem mass spectrometry spectra were searched against a human protein database (Swiss-Prot). The proteomic data related to protein quantification were analysed using the PLGS software. A total of 260 proteins were successfully identified in the AEP samples collected from all groups. Forty-nine were common to all 3 groups, while 72, 62, and 49 were specific to the groups rinsing with whole milk, fat-free milk, and water, respectively. Some were typical components of the AEP, such as cystatin-B, cystatin-SN, isoforms of α-amylase, IgA and IgG, lysozyme C, protein S100 A78, histatin-1, proline-rich protein 27, statherin, and lactotransferrin. Other proteins are not commonly described as part of the AEP but could act in defence of the organism against pathogens. Distinct proteomic profiles were found in the AEP after rinsing with whole or fat-free milk, which could have an impact on bacterial adhesion and tooth dissolution. The use of fat-free milk could favourably modulate the adhesion of bacteria to the AEP as well as biofilm formation when compared with whole milk.

Molecular Interaction Between Salivary Proteins and Food Tannins

Polyphenols interaction with salivary proteins (SP) has been related with organoleptic features such as astringency. The aim of this work was to study the interaction between some human SP and tannins through two spectroscopic techniques, fluorescence quenching, and saturation transfer difference-nuclear magnetic resonance (STD-NMR). Generally, the results showed a significant interaction between SP and both condensed tannins and ellagitannins. Herein, STD-NMR proved to be a useful tool to map tannins' epitopes of binding, while fluorescence quenching allowed one to discriminate binding affinities. Ellagitannins showed the greatest binding constants values (K_SV from 20.1 to 94.1 mM^-1; K_A from 0.7 to 8.3 mM^-1) in comparison with procyanidins (K_SV from 5.4 to 40.0 mM^-1; K_A from 1.1 to 2.7 mM^-1). In fact, punicalagin was the tannin that demonstrated the highest affinity for all three SP. Regarding SP, P-B peptide was the one with higher affinity for ellagitannins. On the other hand, cystatins showed in general the lower K_SV and K_A values. In the case of condensed tannins, statherin was the SP with the highest affinity, contrasting with the other two SP. Altogether, these results are evidence that the distinct SP present in the oral cavity have different abilities to interact with food tannins class.

A rapid differential display analysis of nasal swab fingerprints to distinguish allergic from non-allergic rhinitis subjects by mesoporous silica particles and MALDI-TOF mass spectrometry

Discriminating different rhinitis cases can sometimes be difficult as the diagnostic criteria used to identify the various subgroups are not always unambiguous. The nasal fluid (NF) highly reflects the pathophysiology of these inflammatory diseases. However, its collection, as nasal lavage fluid, may cause discomfort. Due to the non-invasiveness and rapidity of collection, nasal swab might represent an alternative to overcome these problems and also an ideal source of biomarkers. In this study, we demonstrate that the combined use of mesoporous silica (MPS) with MALDI-TOF MS allows the rapid detection of differential nasal peptide profiles from nasal swabs of healthy (H), allergic rhinitis (AR) and non-allergic rhinitis (NAR) subjects. NF peptides from nasal swabs were captured by the mean of MPS then profiled by MALDI-TOF MS. As a proof-of-principle, we also explored the ability of our platform to discriminate between nasal swabs of patients with AR and NAR, and between these groups and H controls. Four peaks resulted differentially expressed between NAR and AR, two peaks discriminated AR from H while one peak segregated NAR from H group. Therefore, peptides selected and enriched by our platform could form a part of a diagnostic ''rhinomic'' profile of the allergic and non-allergic patients.

Anti-tumoral activity of human salivary peptides

Chemotherapy continues to be the standard treatment for advanced or metastasized cancer. However, commonly used chemotherapeutic agents may induce damage in healthy cells and tissues. Thus, in recent years, there has been an increased focus on the development of new, efficient anticancer drugs exhibiting low toxicity and that are not affected by mechanisms of chemoresistance. In the present work, we tested synthetic and naturally obtained human salivary peptides against breast, prostate, colon, osteosarcoma and bladder cancer cell lines (T47-D, PC-3, HT-29, MG63, T-24, respectively). Results have showed that there is a reduced cell population increase that is peptide-, cell- and possibly pathway-specific, with the most potent effect observed in observed in T-47D breast cancer cells. Protein expression and microscopy results further indicate that, in this cell line, the peptide with the sequence GPPPQGGRPQG (GG peptide) interferes with the ability of cell adhesion proteins to stabilize adherens junctions, such as E-cadherin, leading to apoptosis. These promising results encourage future works aimed at disclosing the vast potential of salivary peptides as new therapeutic agents.

Hydroxyapatite Growth Inhibition Effect of Pellicle Statherin Peptides

In our recent studies, we have shown that in vivo–acquired enamel pellicle is a sophisticated biological structure containing a significant portion of naturally occurring salivary peptides. From a functional aspect, the identification of peptides in the acquired enamel pellicle is of interest because many salivary proteins exhibit functional domains that maintain the activities of the native protein. Among the in vivo–acquired enamel pellicle peptides that have been newly identified, 5 peptides are derived from statherin. Here, we assessed the ability of these statherin pellicle peptides to inhibit hydroxyapatite crystal growth. In addition, atomistic molecular dynamics (MD) simulations were performed to better understand the underlying physical mechanisms of hydroxyapatite growth inhibition. A microplate colorimetric assay was used to quantify hydroxyapatite growth. Statherin protein, 5 statherin-derived peptides, and a peptide lacking phosphate at residues 2 and 3 were analyzed. Statherin peptide phosphorylated on residues 2 and 3 indicated a significant inhibitory effect when compared with the 5 other peptides ( P < 0.05). MD simulations showed a strong affinity and fast adsorption to hydroxyapatite for phosphopeptides, whereas unphosphorylated peptides interacted weakly with the hydroxyapatite. Our data suggest that the presence of a covalently linked phosphate group (at residues 2 and 3) in statherin peptides modulates the effect of hydroxyapatite growth inhibition. This study provides a mechanism to account for the composition and function of acquired enamel pellicle statherin peptides that will contribute as a base for the development of biologically stable and functional synthetic peptides for therapeutic use against dental caries and/or periodontal disease.

The enamel protein amelotin is a promoter of hydroxyapatite mineralization

Amelotin (AMTN) is a recently discovered protein that is specifically expressed during the maturation stage of dental enamel formation. It is localized at the interface between the enamel surface and the apical surface of ameloblasts. AMTN knock-out mice have hypomineralized enamel, whereas transgenic mice overexpressing AMTN have a compact but disorganized enamel hydroxyapatite (HA) microstructure, indicating a possible involvement of AMTN in regulating HA mineralization directly. In this study, we demonstrated that recombinant human (rh) AMTN dissolved in a metastable buffer system, based on light scattering measurements, promotes HA precipitation. The mineral precipitates were characterized by scanning and transmission electron microscopy and electron diffraction. Colloidal gold immunolabeling of AMTN in the mineral deposits showed that protein molecules were associated with HA crystals. The binding affinity of rh-AMTN to HA was found to be comparable to that of amelogenin, the major protein of the forming enamel matrix. Overexpression of AMTN in mouse calvaria cells also increased the formation of calcium deposits in the culture medium. Overexpression of AMTN during the secretory stage of enamel formation in vivo resulted in rapid and uncontrolled enamel mineralization. Site-specific mutagenesis of the potential serine phosphorylation motif SSEEL reduced the in vitro mineral precipitation to less than 25%, revealing that this motif is important for the HA mineralizing function of the protein. A synthetic short peptide containing the SSEEL motif was only able to facilitate mineralization in its phosphorylated form ((P)S(P) SEEL), indicating that this motif is necessary but not sufficient for the mineralizing properties of AMTN. These findings demonstrate that AMTN has a direct influence on biomineralization by promoting HA mineralization and suggest a critical role for AMTN in the formation of the compact aprismatic enamel surface layer during the maturation stage of amelogenesis.

Antimicrobial peptides: an alternative for innovative medicines?

Antimicrobial peptides are small molecules with activity against bacteria, yeasts, fungi, viruses, bacteria, and even tumor cells that make these molecules attractive as therapeutic agents. Due to the alarming increase of antimicrobial resistance, interest in alternative antimicrobial agents has led to the exploitation of antimicrobial peptides, both synthetic and from natural sources. Thus, many peptide-based drugs are currently commercially available for the treatment of numerous ailments, such as hepatitis C, myeloma, skin infections, and diabetes. Initial barriers are being increasingly overcome with the development of cost-effective, more stable peptides. Herein, we review the available strategies for their synthesis, bioinformatics tools for the rational design of antimicrobial peptides with enhanced therapeutic indices, hurdles and shortcomings limiting the large-scale production of AMPs, as well as the challenges that the pharmaceutical industry faces on their use as therapeutic agents.

Top-down analytical platforms for the characterization of the human salivary proteome

Comprehensive analysis and characterization of the human salivary proteome is an important step towards the possible use of saliva for diagnostic and prognostic purposes. The contribution of the different sources to whole saliva, and the evaluation of individual variability and physiological modifications have been investigated by top-down proteomic approaches, disclosing the faceted and complex profile of the human salivary proteome. All this information is essential to develop saliva protein biomarkers. In this Review the major results obtained in the field by top-down platforms, and the improvements required to allow a more complete picture, will be discussed.

Dynamic changes in saliva after acute mental stress

Stress-related variations of fluoride concentration in supernatant saliva and salivary sediment, salivary cortisol, total protein and pH after acute mental stress were assessed. The hypothesis was that stress reactions have no influence on these parameters. Thirty-four male students were distributed into two groups: first received the stress exposure followed by the same protocol two weeks later but without stress exposure, second underwent the protocol without stress exposure followed by the stress exposure two weeks later. The stressor was a public speech followed by tooth brushing. Saliva was collected before, immediately after stress induction and immediately, at 10, 30 and 120 min. after tooth brushing. Cortisol concentrations, total protein, intraoral pH, and fluoride content in saliva were measured. The data were analyzed statistically. Salivary sediment was ca 4.33% by weight of whole unstimulated saliva. Fluoride bioavailability was higher in salivary sediment than in supernatant saliva. The weight and fluoride concentration was not altered during 2 hours after stress exposure. After a public speech, the salivary cortisol concentration significantly increased after 20 minutes compared to the baseline. The salivary protein concentration and pH also increased. Public speaking influences protein concentration and salivary pH but does not alter the fluoride concentration of saliva.

Rapid antemortem detection of CWD prions in deer saliva

Chronic wasting disease (CWD) is an efficiently transmitted prion disease of cervids, now identified in 22 United States, 2 Canadian provinces and Korea. One hallmark of CWD is the shedding of infectious prions in saliva, as demonstrated by bioassay in deer. It is also clear that the concentration of prions in saliva, blood, urine and feces is much lower than in the nervous system or lymphoid tissues. Rapid in vitro detection of CWD (and other) prions in body fluids and excreta has been problematic due to the sensitivity limits of direct assays (western blotting, ELISA) and the presence of inhibitors in these complex biological materials that hamper detection. Here we use real-time quaking induced conversion (RT-QuIC) to demonstrate CWD prions in both diluted and prion-enriched saliva samples from asymptomatic and symptomatic white-tailed deer. CWD prions were detected in 14 of 24 (58.3%) diluted saliva samples from CWD-exposed white-tailed deer, including 9 of 14 asymptomatic animals (64.2%). In addition, a phosphotungstic acid enrichment enhanced the RT-QuIC assay sensitivity, enabling detection in 19 of 24 (79.1%) of the above saliva samples. Bioassay in Tg[CerPrP] mice confirmed the presence of infectious prions in 2 of 2 RT-QuIC-positive saliva samples so examined. The modified RT-QuIC analysis described represents a non-invasive, rapid ante-mortem detection of prions in complex biologic fluids, excreta, or environmental samples as well as a tool for exploring prion trafficking, peripheralization, and dissemination.

Proteomic evaluation of acquired enamel pellicle during in vivo formation

Acquired enamel pellicle (AEP) is a protein film that forms on the enamel surface of teeth by selective adsorption of proteins and peptides present in the mouth. This protein film forms the interface between enamel and the damage oral biofilm, which modulates the attachment of bacteria found in oral biofilm. The overall goal of this study was to gain insight into the biological formation of the human in vivo AEP. This study hypothesized that AEP is created by the formation of successive protein layers, which consist of initial binding to enamel and subsequent protein-protein interactions. This hypothesis was examined by observing quantitative and qualitative changes in pellicle composition during the first two hours of AEP formation in the oral cavity. Quantitative mass spectrometry approaches were used to generate an AEP protein profile for each time-point studied. Relative proteomic quantification was carried out for the 50 proteins observed in all four time-points. Notably, the abundance of important salivary proteins, such as histatin 1, decrease with increasing of the AEP formation, while other essential proteins such as statherin showed constant relative abundance in all time-points. In summary, this is the first study that investigates the dynamic process to the AEP formation by using proteomic approaches. Our data demonstrated that there are significant qualitative and quantitative proteome changes during the AEP formation, which in turn will likely impact the development of oral biofilms.

An evolutionary perspective of mammal salivary peptide families: cystatins, histatins, statherin and PRPs

Saliva's role in the oral cavity, such as lubrication, protection of tissues and antimicrobial action is a reflex of its composition, among which are several peptide families like statherin, histatins, proline rich proteins (PRPs) and some members of the cystatin family. These peptides present different evolutionary pathways being in the case of histatin, statherin and PRP families restricted to few millions and comprising few species when compared with cystatins, where duplication occurred at more than 650 mya. Though the recognized relevance of phylogenetic approaches to disclose relationships among different species, information on the salivary proteins that allow the association between peptide families-related structure and function in the oral cavity is scarce. In the present study, the four major salivary peptides classes are reviewed considering the few known phylogenetic studies focusing on their evolution among mammals. New perspectives and challenges for future and multidisciplinary experimental works are drawn.

Human infant saliva peptidome is modified with age and diet transition

In order to describe developmental changes in human salivary peptidome, whole saliva was obtained from 98 infants followed longitudinally at 3 and 6months of age. Data on teeth eruption and diet at the age of 6months were also recorded. Salivary peptide extracts were characterised by label-free MALDI-MS. Peptides differentially expressed between the two ages, and those significantly affected by teeth eruption or introduction of solid foods were identified by MALDI TOF-TOF and LC ESI MS-MS. Out of 81 peaks retained for statistical analysis, 26 were overexpressed at the age of 6months. Exposure to solid foods had a more pronounced effect on profiles (overexpression of nine peaks) than teeth eruption (overexpression of one peak). Differential peaks corresponded to fragments of acidic and basic PRPs, statherin and histatin. Comparison with existing knowledge on adult saliva peptidome revealed that proteolytic processing of salivary proteins is qualitatively quite comparable in infants and in adults. However, age and diet are modulators of salivary peptidome in human infants.

Whole-saliva proteolysis and its impact on salivary diagnostics

There is growing interest in the use of human whole saliva for diagnostics and disease monitoring as an alternative to blood samples. In contrast to blood, whole saliva is a non-sterile body fluid. Proper hand-ling and storage are required to preserve the integrity of potential biomarkers. We investigated salivary autoproteolytic degradation using a variety of approaches. We determined inhibition of protease activities by monitoring the endogenous proteome. In addition, the stability of highly protease-susceptible proteins-histatin 5, statherin, and PRP1-was assessed. Experimental variables included (a) protease inhibitors, (b) salivary pH, (c) incubation temperatures, and (d) sample heating. A cocktail containing AEBSF, aprotinin, pancreatic trypsin inhibitor, leupeptin, antipain, and EDTA could not prevent histatin 5, statherin, or PRP1 degradation in whole saliva. Among the other treatments evaluated, short-term storage of freshly collected samples on ice was effective without interfering with the chemistry of the proteome. In conclusion, whole saliva contains a unique mixture of enzymes as evidenced from their resilience to protease inhibition. Analytical evidence on protein stability is needed to ensure the validity of salivary biomarker study outcomes. Analysis of the data presented will provide help and guidance for the use of saliva samples for diagnostic purposes.