The proteomes of human parotid and submandibular/sublingual gland salivas collected as the ductal secretions

Systems analysis of salivary gland development and disease

Branching morphogenesis is a crucial developmental process in which vertebrate organs generate extensive epithelial surface area while retaining a compact size. In the vertebrate submandibular salivary gland, branching morphogenesis is crucial for the generation of the large surface area necessary to produce sufficient saliva. However, in many salivary gland diseases, saliva-producing acinar cells are destroyed, resulting in dry mouth and secondary health conditions. Systems-based approaches can provide insights into understanding salivary gland development, function, and disease. The traditional approach to understanding these processes is the identification of molecular signals using reductionist approaches; we review current progress with such methods in understanding salivary gland development. Taking a more global approach, multiple groups are currently profiling the transcriptome, the proteome, and other 'omes' in both developing mouse tissues and in human patient samples. Computational methods have been successful in deciphering large data sets, and mathematical models are starting to make predictions regarding the contribution of molecules to the physical processes of morphogenesis and cellular function. A challenge for the future will be to establish comprehensive, publicly accessible salivary gland databases spanning the full range of genes and proteins; plans are underway to provide these resources to researchers in centralized repositories. The greatest challenge for the future will be to develop realistic models that integrate multiple types of data to both describe and predict embryonic development and disease pathogenesis.

Human common salivary protein 1 (CSP-1) promotes binding of Streptococcus mutans to experimental salivary pellicle and glucans formed on hydroxyapatite surface

The saliva proteome includes host defense factors and specific bacterial-binding proteins that modulate microbial growth and colonization of the tooth surface in the oral cavity. A multidimensional mass spectrometry approach identified the major host-derived salivary proteins that interacted with Streptococcus mutans (strain UA159), the primary microorganism associated with the pathogenesis of dental caries. Two abundant host proteins were found to tightly bind to S. mutans cells, common salivary protein-1 (CSP-1) and deleted in malignant brain tumor 1 (DMBT1, also known as salivary agglutinin or gp340). In contrast to gp340, limited functional information is available on CSP-1. The sequence of CSP-1 shares 38.1% similarity with rat CSP-1. Recombinant CSP-1 (rCSP-1) protein did not cause aggregation of S. mutans cells and was devoid of any significant biocidal activity (2.5 to 10 μg/mL). However, S. mutans cells exposed to rCSP-1 (10 μg/mL) in saliva displayed enhanced adherence to experimental salivary pellicle and to glucans in the pellicle formed on hydroxyapatite surfaces. Thus, our data demonstrate that the host salivary protein CSP-1 binds to S. mutans cells and may influence the initial colonization of this pathogenic bacterium onto the tooth surface.

Mass spectrometry in high-throughput proteomics: ready for the big time

Mass spectrometry has evolved and matured to a level where it is able to assess the complexity of the human proteome. We discuss some of the expected challenges ahead and promising strategies for success.

Identification of tetranectin as a potential biomarker for metastatic oral cancer

Lymph node involvement is the most important predictor of survival rates in patients with oral squamous cell carcinoma (OSCC). A biomarker that can indicate lymph node metastasis would be valuable to classify patients with OSCC for optimal treatment. In this study, we have performed a serum proteomic analysis of OSCC using 2-D gel electrophoresis and liquid chromatography/tandem mass spectrometry. One of the down-regulated proteins in OSCC was identified as tetranectin, which is a protein encoded by the CLEC3B gene (C-type lectin domain family 3, member B). We further tested the protein level in serum and saliva from patients with lymph-node metastatic and primary OSCC. Tetranectin was found significantly under-expressed in both serum and saliva of metastatic OSCC compared to primary OSCC. Our results suggest that serum or saliva tetranectin may serve as a potential biomarker for metastatic OSCC. Other candidate serum biomarkers for OSCC included superoxide dismutase, ficolin 2, CD-5 antigen-like protein, RalA binding protein 1, plasma retinol-binding protein and transthyretin. Their clinical utility for OSCC detection remains to be further tested in cancer patients.

Comparative human salivary and plasma proteomes

The protein compositions, or the proteomes, found in human salivary and plasma fluids are compared. From recent experimental work by many laboratories, a catalogue of 2290 proteins found in whole saliva has been compiled. This list of salivary proteins is compared with the 2698 proteins found in plasma. Approximately 27% of the whole-saliva proteins are found in plasma. However, despite this apparent low degree of overlap, the distribution found across Gene Ontological categories, such as molecular function, biological processes, and cellular components, shows significant similarities. Moreover, nearly 40% of the proteins that have been suggested to be candidate markers for diseases such as cancer, cardiovascular disease, and stroke can be found in whole saliva. These comparisons and correlations should encourage researchers to consider the use of saliva to discover new protein markers of disease and as a diagnostic non-proximal fluid to detect early signs of disease throughout the body.

Distinct regulation by lipopolysaccharides of the expression of interleukin-1β by murine macrophages and salivary glands

The regulation of interleukin (IL)-1 expression and secretion by salivary glands and macrophages in response to lipopolysaccharides (LPS) was compared. In wild-type mice, injection of LPS significantly decreased the volume of saliva stimulated by pilocarpine and increased its protein and amylase concentration. It did not modify the salivary concentration of IL-1β. The cytokine was expressed by submandibular acini and ducts. Macrophages also expressed IL-1β but at lower concentration than salivary glands. The pre-incubation of macrophages with LPS increased the phosphorylation of IκB and the expression of IL-1β. Adenosine triphosphate also promoted the secretion of the cytokine by these cells. These responses were absent in submandibular gland cells. These glands expressed CD14, TLR4 and MyD88. P2X(7)-KO mice secreted a lower volume of saliva which contained less proteins and amylase. In conclusion, IL-1β is constitutively expressed by submandibular glands and its secretion is not regulated by a P2X(7) agonist. In these cells, LPS do not activate the nuclear factor-κB-pro-IL-1β axis in spite of the expression of the proteins involved in their recognition.

Large-scale phosphoproteome of human whole saliva using disulfide-thiol interchange covalent chromatography and mass spectrometry

To date, only a handful of phosphoproteins with important biological functions have been identified and characterized in oral fluids, and these include some of the abundant protein constituents of saliva. Whole saliva (WS) samples were trypsin digested, followed by chemical derivatization using dithiothreitol (DTT) of the phospho-serine/threonine-containing peptides. The DTT-phosphopeptides were enriched by covalent disulfide-thiol interchange chromatography and analysis by nanoflow liquid chromatography and electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The specificity of DTT chemical derivatization was evaluated separately under different base-catalyzed conditions with NaOH and Ba(OH)(2), blocking cysteine residues by iodoacetamide and enzymatic O-deglycosylation prior to DTT reaction. Further analysis of WS samples that were subjected to either of these conditions provided supporting evidence for phosphoprotein identifications. The combined chemical strategies and mass spectrometric analyses identified 65 phosphoproteins in WS; of these, 28 were based on two or more peptide identification criteria with high confidence and 37 were based on a single phosphopeptide identification. Most of the identified proteins (∼80%) were previously unknown phosphoprotein components. This study represents the first large-scale documentation of phosphoproteins of WS. The origins and identity of WS phosphoproteome suggest significant implications for both basic science and the development of novel biomarkers/diagnostic tools for systemic and oral disease states.

Surface Integrity Governs the Proteome of Hypomineralized Enamel

Growing interest in the treatment and prevention of Molar/Incisor Hypomineralization (MIH) warrants investigation into the protein composition of hypomineralized enamel. Hypothesizing abnormality akin to amelogenesis imperfecta, we profiled proteins in hypomineralized enamel from human permanent first molars using a biochemical approach. Hypomineralized enamel was found to have from 3- to 15-fold higher protein content than normal, but a near-normal level of residual amelogenins. This distinguished MIH from hypomaturation defects with high residual amelogenins (amelogenesis imperfecta, fluorosis) and so typified it as a hypocalcification defect. Second, hypomineralized enamel was found to have accumulated various proteins from oral fluid and blood, with differential incorporation depending on integrity of the enamel surface. Pathogenically, these results point to a pre-eruptive disturbance of mineralization involving albumin and, in cases with post-eruptive breakdown, subsequent protein adsorption on the exposed hydroxyapatite matrix. These insights into the pathogenesis and properties of hypomineralized enamel hold significance for prevention and treatment of MIH.

Options and considerations when selecting a quantitative proteomics strategy

The vast majority of proteomic studies to date have relied on mass spectrometric techniques to identify, and in some cases quantify, peptides that have been generated by proteolysis. Current approaches differ in the types of instrument used, their performance profiles, the manner in which they interface with biological research strategies, and their reliance on and use of prior information. Here, we consider the three main mass spectrometry (MS)-based proteomic approaches used today: shotgun (or discovery), directed and targeted strategies. We discuss the principles of each technique, their strengths and weaknesses and the dependence of their performance profiles on the composition of the biological sample. Our goal is to provide a rational framework for selecting strategies optimally suited to address the specific research issue under consideration.

Current development of saliva/oral fluid-based diagnostics

Saliva can be easily obtained in medical and non-medical settings, and contains numerous bio-molecules, including those typically found in serum for disease detection and monitoring. In the past two decades, the achievements of high-throughput approaches afforded by biotechnology and nanotechnology allow for disease-specific salivary biomarker discovery and establishment of rapid, multiplex, and miniaturized analytical assays. These developments have dramatically advanced saliva-based diagnostics. In this review, we discuss the current consensus on development of saliva/oral fluid-based diagnostics and provide a summary of recent research advancements of the Texas-Kentucky Saliva Diagnostics Consortium. In the foreseeable future, current research on saliva based diagnostic methods could revolutionize health care.

Confident assignment of intact mass tags to human salivary cystatins using top-down Fourier-transform ion cyclotron resonance mass spectrometry

A hybrid linear ion-trap Fourier-transform ion cyclotron resonance mass spectrometer was used for top-down characterization of the abundant human salivary cystatins, including S, S1, S2, SA, SN, C, and D, using collisionally activated dissociation (CAD) after chromatographic purification of the native, disulfide intact proteins. Post-translational modifications and protein sequence polymorphisms arising from single nucleotide polymorphisms (SNPs) were assigned from precursor and product ion masses at a tolerance of 10 ppm, allowing confident identification of individual intact mass tags. Cystatins S, S1, S2, SA, and SN were cleaved of a N-terminal 20 amino acid signal peptide and cystatin C a 26-residue peptide, to yield a generally conserved N-terminus. In contrast, cystatin D isoforms with 24 and 28 amino acid residue N-terminal truncations were found such that their N-termini were not conserved. Cystatin S1 was phosphorylated at Ser3, while S2 was phosphorylated at Ser1 and Ser3, in agreement with previous work. Both cystatin D isoforms carried the polymorphism C46R (SNP: rs1799841). The 14,328 Da isoform of cystatin SN previously assigned with polymorphism P31L due to a SNP (rs2070856) was found only in whole saliva. Parotid secretions contained no detectable cystatins while whole saliva largely mirrored the contents of submandibular/sublingual (SMSL) secretions. With fully characterized cystatin intact mass tags it will now be possible to examine the correlation between the abundance of these molecules and human health and disease.

Alterations in the salivary proteome associated with periodontitis

AIM

To identify changes in the salivary proteome associated with active periodontitis.

MATERIALS AND METHODS

Quantitative proteomics (two-dimensional sodium dodecyl sulphate polyacrylamide gel electrophoresis) was used to investigate whole saliva from individuals with severe periodontitis and their proteomic profiles before and after periodontal treatment were compared.

RESULTS

A comparison of 128 proteins across all saliva samples identified 15 protein spots with altered abundance. The predominant alteration observed was an increase in the abundance of the S100 proteins S100A8/A9/A6. Of the remaining proteins with altered abundance, haptoglobin, prolactin inducible protein and parotid secretory protein have previously been associated with host defence.

CONCLUSION

These results highlight the predominant involvement of S100 proteins in the host response during periodontitis, identify host defence components that have not been linked previously to this disease and suggest new potential biomarkers for monitoring disease activity in periodontitis.

Immunohistochemical localization of Clara cell secretory proteins (CC10-CC26) and Annexin-1 protein in rat major salivary glands

The oral cavity is continuously bathed by saliva secreted by the major and minor salivary glands. Saliva is the first biological medium to confront external materials that are taken into the body as part of food or drink or inhaled volatile substances, and it contributes to the first line of oral defence. In humans, it has been shown that sputum and a variety of biological fluids contain Clara cell secretory proteins (CC10-CC26). Various studies of the respiratory apparatus have suggested their protective effect against inflammatory response and oxidative stress. Recently, CC10 deficiency has been related to the protein Annexin-1 (ANXA1), which has immunomodulatory and anti-inflammatory properties. Considering the defensive role of both Clara cell secretory proteins and ANXA1 in the respiratory apparatus, and the importance of salivary gland secretion in the first line of oral defence, we decided to evaluate the expression of CC10, CC26 and ANXA1 proteins in rat major salivary glands using immunohistochemistry. CC10 expression was found only in the ductal component of the sublingual gland. Parotid and submandibular glands consistently lacked CC10 immunoreactivity. In the parotid gland, both acinar and ductal cells were always CC26-negative, whereas in the submandibular gland, immunostaining was localized in the ductal component and in the periodic acid Schiff (PAS)-positive area. In the sublingual gland, ductal cells were always positive. Acinar cells were not immunostained at all. ANXA1 was expressed in ductal cells in all three major glands. In parotid and sublingual glands, acinar cells were negative. In submandibular glands, immunostaining was present in the mucous PAS-positive portion, whereas serous acinar cells were consistently negative. The existence of some CC10-CC26-ANXA1-positive cells in rat salivary glandular tissue is an interesting preliminary finding which could support the hypothesis, suggested for airway tissue, that these proteins have a defensive and protective role. Protein expression heterogeneity in the different portions of the glands could be an important clue in further investigations of their role.

Salivary transcriptomic biomarkers for detection of resectable pancreatic cancer

BACKGROUND & AIMS

Lack of detection technology for early pancreatic cancer invariably leads to a typical clinical presentation of incurable disease at initial diagnosis. New strategies and biomarkers for early detection are sorely needed. In this study, we have conducted a prospective sample collection and retrospective blinded validation to evaluate the performance and translational utilities of salivary transcriptomic biomarkers for the noninvasive detection of resectable pancreatic cancer.

METHODS

The Affymetrix HG U133 Plus 2.0 Array (Affymetrix, Santa Clara, CA) was used to profile transcriptomes and discover altered gene expression in saliva supernatant. Biomarkers discovered from the microarray study were subjected to clinical validation using an independent sample set of 30 pancreatic cancer patients, 30 chronic pancreatitis patients, and 30 healthy controls.

RESULTS

Twelve messenger RNA biomarkers were discovered and validated. The logistic regression model with the combination of 4 messenger RNA biomarkers (KRAS, MBD3L2, ACRV1, and DPM1) could differentiate pancreatic cancer patients from noncancer subjects (chronic pancreatitis and healthy control), yielding a receiver operating characteristic plot, area under the curve value of 0.971 with 90.0% sensitivity and 95.0% specificity.

CONCLUSIONS

The salivary biomarkers possess discriminatory power for the detection of resectable pancreatic cancer, with high specificity and sensitivity. This report provides the proof of concept of salivary biomarkers for the noninvasive detection of a systemic cancer and paves the way for prediction model validation study followed by pivotal clinical validation.

Current developments in salivary diagnostics

Salivary diagnostics is an emerging field that has progressed through several important developments in the past decade, including the publication of the human salivary proteome and the infusion of federal funds to integrate nanotechnologies and microfluidic engineering concepts into developing compact point-of-care devices for rapid analysis of this secretion. In this article, we discuss some of these developments and their relevance to the prognosis, diagnosis and management of periodontitis, as an oral target, and cardiovascular disease, as a systemic example for the potential of these biodiagnostics. Our findings suggest that several biomarkers are associated with distinct biological stages of these diseases and demonstrate promise as practical biomarkers in identifying and managing periodontal disease, and acute myocardial infarction. The majority of these studies have progressed through biomarker discovery, with the identified molecules requiring more robust clinical studies to enable substantive validation for disease diagnosis. It is predicted that with continued advances in this field the use of a combination of biomarkers in multiplex panels is likely to yield accurate screening tools for these diagnoses in the near future.

Collection, storage, and processing of saliva samples for downstream molecular applications

Saliva is an ideal translational research tool and diagnostic medium and is being used in novel ways to provide molecular biomarkers for a variety of oral and systemic diseases and conditions. The ability to analyze saliva to monitor health and disease is a highly desirable goal for oral health promotion and research. Saliva has been used to detect caries risk, periodontitis, oral cancer, breast cancer, salivary gland diseases, and systemic disorders such as hepatitis, HIV and HCV. Technology advancement has allowed high-throughput studies to be performed at a scale unrealized previously and is serving to advance the discovery and validation of salivary disease biomarkers. Of course, successful measurement of salivary analytes requires optimal collection, processing, and storage procedures and conditions. This chapter describes protocols for saliva collection, processing, and storage for the molecular analysis of salivary diagnostic constituents.

Proteomic analysis of saliva: 2D gel electrophoresis, LC-MS/MS, and Western blotting

Saliva harbors a wide spectrum of proteins that may reflect the health/disease status in the human body. Profiling of the proteins in saliva from a disease population can potentially yield valuable clinical parameters to be used for diagnosis and prognosis of the disease. Advances in proteomic technologies have enabled comprehensive profiling of protein expression in cells, tissue, and body fluids. When applied to readily accessible saliva samples from disease patients for biomarker study, such a global approach allows attaining the most discriminatory protein biomarkers that can best predict the disease status. In this chapter, we describe the protocols for proteomic analysis of saliva using 2D gel electrophoresis, Western blotting, and LC-MS/MS.

A dynamic range compression and three-dimensional peptide fractionation analysis platform expands proteome coverage and the diagnostic potential of whole saliva

Comprehensive identification of proteins in whole human saliva is critical for appreciating its full diagnostic potential. However, this is challenged by the large dynamic range of protein abundance within the fluid. To address this problem, we used an analysis platform that coupled hexapeptide libraries for dynamic range compression (DRC) with three-dimensional (3D) peptide fractionation. Our approach identified 2340 proteins in whole saliva and represents the largest saliva proteomic dataset generated using a single analysis platform. Three-dimensional peptide fractionation involving sequential steps of preparative isoelectric focusing (IEF), strong cation exchange, and capillary reversed-phase liquid chromatography was essential for maximizing gains from DRC. Compared to saliva not treated with hexapeptide libraries, DRC substantially increased identified proteins across physicochemical and functional categories. Approximately 20% of total salivary proteins are also seen in plasma, and proteins in both fluids show comparable functional diversity and disease-linkage. However, for a subset of diseases, saliva has higher apparent diagnostic potential. These results expand the potential for whole saliva in health monitoring/diagnostics and provide a general platform for improving proteomic coverage of complex biological samples.

Resemblance of salivary protein profiles between children with early childhood caries and caries-free controls

Although prolonged bottle feeding with a carbohydrate-rich content is commonly agreed to be the main etiologic factor for early childhood caries (ECC), in recent years additional endogenous factors, including the composition of saliva, have been suspected as predisposing factors in children for the development of this aggressive form of dental caries. As a basis for investigating the putative involvement of salivary proteins in the etiology of ECC, a qualitative comparison of major salivary protein profiles between children with ECC and caries-free controls was performed. Saliva was collected from 30 children with ECC and, after separation by sodium dodecyl sulphate-polyacrylamide gel electrophoresis, was compared with saliva from 20 caries-free controls for the general composition of proteins by means of silver staining, glycoprotein staining, and lectin blotting. Gels and blots were analysed using densitometry, and the protein-banding patterns resulting from the individuals' samples were compared by image analysis for the presence or absence of protein bands. Dendrograms obtained after comparison of all samples showed a high degree of similarity for the experimental groups. In summary, the results attest a uniform expression of the major protein components in children's saliva, regardless of the clinical manifestation of ECC, and thus pave the way for further detailed investigations of more subtle differences in the salivary proteome.

Quantitative analysis of age specific variation in the abundance of human female parotid salivary proteins

Human saliva is a protein-rich, easily accessible source of potential local and systemic biomarkers to monitor changes that occur under pathological conditions; however, little is known about the changes in abundance associated with normal aging. In this study, we performed a comprehensive proteomic profiling of pooled saliva collected from the parotid glands of healthy female subjects, divided into two age groups 1 and 2 (20-30 and 55-65 years old, respectively). Hydrophobic charge interaction chromatography was used to separate high- from low-abundance proteins prior to characterization of the parotid saliva using multidimensional protein identification technology (MudPIT). Collectively, 532 proteins were identified in the two age groups. Of these proteins, 266 were identified exclusively in one age group, while 266 proteins were common to both groups. The majority of the proteins identified in the two age groups belonged to the defense and immune response category. Of note, several defense related proteins (e.g., lysozyme, lactoferrin and histatin-1) were significantly more abundant in group 2 as determined by G-test. Selected representative mass spectrometric findings were validated by Western blot analysis. Our study reports the first quantitative analysis of differentially regulated proteins in ductal saliva collected from young and older female subjects. This study supports the use of high-throughput proteomics as a robust discovery tool. Such results provide a foundation for future studies to identify specific salivary proteins which may be linked to age-related diseases specific to women.

Salivary diagnostics

The ability to monitor health status, disease onset and progression, and treatment outcome through non-invasive means is a most desirable goal in the health care promotion and delivery. There are three prerequisites to materialize this goal: specific biomarkers associated with a health or disease state; a non-invasive approach to detect and monitor the biomarkers; and the technologies to discriminate the biomarkers. A national initiative catalyzed by the National Institute of Dental & Craniofacial Research (NIDCR) has created a roadmap to achieve these goals through the use of oral fluids as the diagnostic medium to scrutinize the health and/or disease status of individuals. Progress has shown this is an ideal opportunity to bridge state of the art saliva-based biosensors, optimized to disease discriminatory salivary biomarkers, for diagnostic applications. Oral fluid being the 'mirror of body' is a perfect medium to be explored for health and disease surveillance. The translational applications and opportunities are enormous.

Salivary biomarkers for the detection of malignant tumors that are remote from the oral cavity

Proteomic analyses by mass spectrometry are propelling the field of medical diagnostics forward at unprecedented rates because of its ability reliably to identify proteins that are at the femtomole level in concentration. These advancements have also benefited biomarker research to the point where saliva is now recognized as an excellent diagnostic medium for the detection of malignant tumors that are remote from the oral cavity. Saliva is easy to collect and may provide diagnostic information about a variety of cancers. In particular, proof-of-principle has been demonstrated for salivary biomarker research. This article reviews the literature, discusses the theories associated with saliva-based tumor diagnostics, and presents the current research focused on the use of saliva as a diagnostic medium for the detection of cancer.

Saliva: an emerging biofluid for early detection of diseases

The capability to assess physiological states, detect morbidity initiation and progression, and monitor posttreatment therapeutic outcomes through a noninvasive approach is one of the most desirable goals for healthcare research and delivery. Saliva, a multi-constituent oral fluid, has high potential for the surveillance of general health and disease. To reach the above goal through saliva-based diagnostics, two prerequisites must be fulfilled: (1) discovering biomarker(s) for different diseases among the complicated components of saliva, and (2) advancing sensitivity and specificity of biomarker(s) through persistent development of technologies. Under the support and research blueprint initiated by the National Institute of Dental and Craniofacial Research (NIDCR), salivary diagnostics has not only steadily progressed with respect to accuracy and availability, but has also bridged up-to-date nanotechnology to expand the areas of application. With collective efforts over several years, saliva has been demonstrated to be a promising bodily fluid for early detection of diseases, and salivary diagnostics has exhibited tremendous potential in clinical applications. This review presents an overview of the value of saliva as a credible diagnostic tool, the discovery of salivary biomarkers, and the development of salivary diagnostics now and in the future.

Sheep and goat saliva proteome analysis: a useful tool for ingestive behavior research?

Sheep and goats differ in diet selection, which may reflect different abilities to deal with the ingestion of plant secondary metabolites. Although saliva provides a basis for immediate oral information via sensory cues and also a mechanism for detoxification, our understanding of the role of saliva in the pre-gastric control of the intake of herbivores is rudimentary. Salivary proteins have important biological functions, but despite their significance, their expression patterns in sheep and goats have been little studied. Protein separation techniques coupled to mass spectrometry based techniques have been used to obtain an extensive comprehension of human saliva protein composition but far fewer studies have been undertaken on animals' saliva. We used two-dimensional electrophoresis gel analysis to compare sheep and goats parotid saliva proteome. Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) and liquid chromatography tandem mass spectrometry (LC-MS/MS) were used to identify proteins. From a total of 260 sheep and 205 goat saliva protein spots, 117 and 106 were identified, respectively. A high proportion of serum proteins were found in both salivary protein profiles. Major differences between the two species were detected for proteins within the range of 25-35 kDa. This study presents the parotid saliva proteome of sheep and goat and highlights the potential of proteomics for investigation relating to intake behavior research.

Influences of protein films on antibacterial or bacteria-repellent surface coatings in a model system using silicon wafers

Immobilization of defined chemical functionalities to biomaterial surfaces is employed to optimize them not only for tissue compatibility but also for prevention of bacterial infection. Grafting surfaces with chains of poly(ethylene glycol) (PEG) results in bacterial repellence whereas modification with cationic groups conveys them with bactericidal properties. Since biomaterials in situ will become exposed to a protein-rich environment, it is necessary to investigate the influence of prior protein adsorption on the antibacterial activity of this type of chemical surface modification. In the present study, we immobilized short-chain PEG and two pyridinium group-containing methacrylate monomers, 12-methacryloyloxydodecylpyridinium bromide (MDPB) and 6-methacryloyloxyhexylpyridinium chloride (MHPC), to silicon wafer model surfaces to investigate the influence of prior protein adsorption on the bactericidal activity of the surface coating towards subsequently attached bacteria. Adsorbed amounts of human serum albumin and salivary proteins were found to be two times higher on cationic compared to PEG-modified surfaces. An analogous tendency was found for attachment of Streptococcus gordonii and Streptococcus mutans to the same surfaces without prior protein exposure. However, most bacteria attached to cationic surfaces were found to be dead. Prior exposure of cationic surfaces to protein solutions drastically altered bacterial attachment dependent on the type of protein solution and bacterial species employed. Significantly, the original bactericidal activity of pyridinium-coated surfaces was found greatly reduced upon adsorption of a protein film. As a conclusion we propose that future approaches should combine the protein- and bacteria-repellent properties of PEG-coatings with the bactericidal function of charged cationic groups.

Direct quantitation of peptide mixtures without standards using clusters formed by electrospray ionization mass spectrometry

In electrospray ionization mass spectrometry, ion abundances depend on a number of different factors, including analyte surface activity, competition between analytes for charge, analyte concentration, as well as instrumental factors, including mass-dependent ion transmission and detection. Here, a novel method for obtaining quantitative information about solution-phase concentrations of peptide mixtures is described and demonstrated for five different peptide mixtures with relative concentrations ranging from 0.05% to 50%. In this method, the abundances of large clusters containing anywhere from 0 to 13 impurity molecules are measured and directly related to the relative solution-phase concentration of the peptides. For clusters containing approximately 15 or more peptides, the composition of the clusters approaches the statistical value indicating that these clusters are formed nonspecifically and that any differences in ion detection or ionization efficiency are negligible at these large cluster sizes. This method is accurate to within approximately 20% or better, even when the relative ion intensities of the protonated monomers can differ by over an order of magnitude compared to their solution-phase concentrations. Although less accurate than other quantitation methods that employ internal standards, this method does have the key advantages of speed, simplicity, and the ability to quantitate components in solution even when the identities of the components are unknown.

Activity-based mass spectrometric characterization of proteases and inhibitors in human saliva

Proteases present in oral fluid effectively modulate the structure and function of some salivary proteins and have been implicated in tissue destruction in oral disease. To identify the proteases operating in the oral environment, proteins in pooled whole saliva supernatant were separated by anion-exchange chromatography and individual fractions were analyzed for proteolytic activity by zymography using salivary histatins as the enzyme substrates. Protein bands displaying proteolytic activity were particularly prominent in the 50-75 kDa region. Individual bands were excised, in-gel trypsinized and subjected to LC/ESI-MS/MS. The data obtained were searched against human, oral microbial and protease databases. A total of 13 proteases were identified all of which were of mammalian origin. Proteases detected in multiple fractions with cleavage specificities toward arginine and lysine residues, were lactotransferrin, kallikrein-1, and human airway trypsin-like protease. Unexpectedly, ten protease inhibitors were co-identified suggesting they were associated with the proteases in the same fractions. The inhibitors found most frequently were alpha-2-macroglobulin-like protein 1, alpha-1-antitrypsin, and leukocyte elastase inhibitor. Regulation of oral fluid proteolysis is highly important given that an inbalance in such activities has been correlated to a variety of pathological conditions including oral cancer.

The proteome of the human parotid gland secretion in elderly with and without root caries

OBJECTIVE

Saliva is important for oral health, including the prevention of dental decay. The purpose of the present work was to indicate whether the parotid gland has altered function in the elderly, particularly in terms of proteins secreted, and whether its functional status could be associated with the presence of root caries.

MATERIAL AND METHODS

Ductal parotid gland secretion was obtained from 51 individuals: 21 elderly with carious roots (Patients), 20 elderly (Controls), and 10 adults (Young) without root caries. Pooled aliquots were analyzed by liquid chromatography/tandem mass spectrometry to yield lists of major proteins present in the three groups.

RESULTS

Approximately 200 unique proteins were detected, of which 73 were identified repeatedly with high confidence and therefore included in the comparison. Some of the differences observed, when comparing Patients with respectively elderly Controls and the Young, resembled changes found in patients with Sjogren's syndrome, a condition associated with dental decay. Other changes involved proteins that are likely to impact on the oral microbiota, such as the absence of dermcidin and the presence of collagen in Patients. Cystatin S, a putative indicator of caries, was present at a higher level in Patients.

CONCLUSIONS

Parotid function tends to change upon aging, with possible consequences as to caries activity. However, analyses of individual samples revealed considerable variations in protein patterns.

Use of saliva-based nano-biochip tests for acute myocardial infarction at the point of care: a feasibility study

BACKGROUND

For adults with chest pain, the electrocardiogram (ECG) and measures of serum biomarkers are used to screen and diagnose myocardial necrosis. These measurements require time that can delay therapy and affect prognosis. Our objective was to investigate the feasibility and utility of saliva as an alternative diagnostic fluid for identifying biomarkers of acute myocardial infarction (AMI).

METHODS

We used Luminex and lab-on-a-chip methods to assay 21 proteins in serum and unstimulated whole saliva procured from 41 AMI patients within 48 h of chest pain onset and from 43 apparently healthy controls. Data were analyzed by use of logistic regression and area under curve (AUC) for ROC analysis to evaluate the diagnostic utility of each biomarker, or combinations of biomarkers, in screening for AMI.

RESULTS

Both established and novel cardiac biomarkers demonstrated significant differences in concentrations between patients with AMI and controls without AMI. The saliva-based biomarker panel of C-reactive protein, myoglobin, and myeloperoxidase exhibited significant diagnostic capability (AUC = 0.85, P < 0.0001) and in conjunction with ECG yielded strong screening capacity for AMI (AUC = 0.96) comparable to that of the panel (brain natriuretic peptide, troponin-I, creatine kinase-MB, myoglobin; AUC = 0.98) and far exceeded the screening capacity of ECG alone (AUC approximately 0.6). En route to translating these findings to clinical practice, we adapted these unstimulated whole saliva tests to a novel lab-on-a-chip platform for proof-of-principle screens for AMI.

CONCLUSIONS

Complementary to ECG, saliva-based tests within lab-on-a-chip systems may provide a convenient and rapid screening method for cardiac events in prehospital stages for AMI patients.

Systemic disease-induced salivary biomarker profiles in mouse models of melanoma and non-small cell lung cancer

Background

Saliva (oral fluids) is an emerging biofluid poised for detection of clinical diseases. Although the rationale for oral diseases applications (e.g. oral cancer) is intuitive, the rationale and relationship between systemic diseases and saliva biomarkers are unclear.

Methodology/Principal Findings

In this study, we used mouse models of melanoma and non-small cell lung cancer and compared the transcriptome biomarker profiles of tumor-bearing mice to those of control mice. Microarray analysis showed that salivary transcriptomes were significantly altered in tumor-bearing mice vs. controls. Significant overlapping among transcriptomes of mouse tumors, serum, salivary glands and saliva suggests that salivary biomarkers have multiple origins. Furthermore, we identified that the expression of two groups of significantly altered transcription factors (TFs) Runx1, Mlxipl, Trim30 and Egr1, Tbx1, Nr1d1 in salivary gland tissue of melanoma-bearing mice can potentially be responsible for 82.6% of the up-regulated gene expression and 62.5% of the down-regulated gene expression, respectively, in the saliva of melanoma-bearing mice. We also showed that the ectopic production of nerve growth factor (NGF) in the melanoma tumor tissue as a tumor-released mediator can induce expression of the TF Egr-1 in the salivary gland.

Conclusions

Taken together, our data support the conclusion that upon systemic disease development, significant changes can occur in the salivary biomarker profile. Although the origins of the disease-induced salivary biomarkers may be both systemic and local, stimulation of salivary gland by mediators released from remote tumors plays an important role in regulating the salivary surrogate biomarker profiles.

Identification of pro- and mature brain-derived neurotrophic factor in human saliva

OBJECTIVE

Growth factors, including brain-derived neurotrophic factor (BDNF), are polypeptides that are involved in the maintenance, survival, and death of central and peripheral cells. Numerous growth factors have been identified in saliva and are thought to promote wound healing and maintenance of the oral epithelium. The aim of this study was to determine if BDNF is also found in human saliva.

METHODS

Whole, unstimulated saliva samples (n = 30) were analyzed by SDS-PAGE and Western blot using an anti-human BDNF antibody. Proteolytic cleavage products were similarly assessed following the incubation of pooled saliva with N-glycanase F and plasmin. Subjects were also genotyped for the BDNF Val66Met single nucleotide polymorphism (SNP).

RESULTS

These experiments revealed the presence of immunoreactive bands at 14, 32 and 34 kDa, corresponding to mature (mBDNF) and proBDNF, as well as a truncated pro-form at 24 kDa. Not every sample contained all forms of BDNF. Treatment with N-glycanase and plasmin reduced the size of the higher molecular weight bands, confirming the glycosylated pro-form of BDNF. mBDNF was detected significantly less often in subjects with the Val66Met SNP, compared to those without the polymorphism (chi(2) = 4.05; P < 0.05).

CONCLUSIONS

While the function of salivary BDNF still requires elucidation, these findings suggest that it may be possible to use saliva in lieu of blood in future studies of BDNF and the Val66Met polymorphism.

The minor salivary gland proteome in Sjögren's syndrome

OBJECTIVE

To identify the global protein expression (the proteome) in the minor salivary glands from primary Sjögren's syndrome (pSS) patients and non-SS controls.

MATERIALS AND METHODS

Minor labial salivary glands were obtained from six pSS patients and from six age-matched non-SS controls, lysed in SDS buffer and pooled into two groups, respectively. The lysates were analysed by liquid chromatography electrospray ionization combined with tandem mass spectrometry. Also, the proteins were separated by two-dimensional polyacrylamide gel electrophoresis and protein spots were subjected to mass spectrometry.

RESULTS

Heat shock proteins, mucins, carbonic anhydrases, enolase, vimentin and cyclophilin B were among the proteins identified. The differences in the proteomes of minor salivary glands from pSS patients and non-SS controls were mainly related to ribosomal proteins, immunity and stress. Alpha-defensin-1 and calmodulin were among six proteins exclusively identified in pSS patients.

CONCLUSION

We have identified several minor salivary gland proteins that may have implications for clarifying the SS pathophysiology. This experiment adds to the knowledge of proteins produced in salivary glands in health and disease, and may form the basis of further studies on biomarkers of prognostic and diagnostic value.

Dysregulated molecular networks in head and neck carcinogenesis

Multiple genetic and epigenetic events, including the aberrant expression and function of molecules regulating cell signaling, growth, survival, motility, angiogenesis, and cell cycle control, underlie the progressive acquisition of a malignant phenotype in squamous carcinomas of the head and neck (HNSCC). In this regard, there has been a recent explosion in our understanding on how extracellular components, cell surface molecules, and a myriad of intracellular proteins and second messenger systems interact with each other, and are organized in pathways and networks to control cellular and tissue functions and cell fate decisions. This emerging ability to understand the basic mechanism controlling inter- and intra-cellular communication has provided an unprecedented opportunity to understand how their dysregulation contributes to the growth and dissemination of human cancers. Here, we will discuss the emerging information on how the use of modern technologies, including gene array and proteomic studies, combined with the molecular dissection of aberrant signaling networks, including the EGFR, ras, NFkappaB, Stat, Wnt/beta-catenin, TGF-beta, and PI3K-AKT-mTOR signaling pathways, can help elucidate the molecular mechanisms underlying HNSCC progression. Ultimately, we can envision that this knowledge may provide tremendous opportunities for the diagnosis of premalignant squamous lesions, and for the development of novel molecular-targeted strategies for the prevention and treatment of HNSCC.

Proteomic analysis of human parotid gland exosomes by multidimensional protein identification technology (MudPIT)

Human ductal saliva contributes over a thousand unique proteins to whole oral fluids. The mechanism by which most of these proteins are secreted by salivary glands remains to be determined. The present study used a mass spectrometry-based, shotgun proteomics approach to explore the possibility that a subset of the proteins found in saliva are derived from exosomes, membrane-bound vesicles of endosomal origin within multivesicular endosomes. Using MudPIT (multidimensional protein identification technology) mass spectrometry, we catalogued 491 proteins in the exosome fraction of human parotid saliva. Many of these proteins were previously observed in ductal saliva from parotid glands (265 proteins). Furthermore, 72 of the proteins in parotid exosomes overlap with those previously identified as urinary exosome proteins, proteins which are also frequently associated with exosomes from other tissues and cell types. Gene Ontology (GO) and KEGG pathway analyses found that cytosolic proteins comprise the largest category of proteins in parotid exosomes (43%), involved in such processes as phosphatidylinositol signaling system, calcium signaling pathway, inositol metabolism, protein export, and signal transduction, among others; whereas the integral plasma membrane proteins and associated/peripheral plasma membrane proteins (26%) were associated with extracellular matrix-receptor interaction, epithelial cell signaling, T-cell and B-cell receptor signaling, cytokine receptor interaction, and antigen processing and presentation, among other biological functions. In addition, these putative saliva exosomal proteins were linked to specific diseases (e.g., neurodegenerative disorders, prion disease, cancers, type I and II diabetes). Consequently, parotid glands secrete exosomes that reflect the metabolic and functional status of the gland and may also carry informative protein markers useful in the diagnosis and treatment of systemic diseases.

Proteomic identification of salivary biomarkers of type-2 diabetes

The identification of biomarkers to noninvasively detect prediabetes/diabetes will facilitate interventions designed to prevent or delay progression to frank diabetes and its attendant complications. The purpose of this study was to characterize the human salivary proteome in type-2 diabetes to identify potential biomarkers of diabetes. Whole saliva from control and type-2 diabetic individuals was characterized by multidimensional liquid chromatography/tandem mass spectrometry (2D-LC-MS/MS). Label-free quantification was used to identify differentially abundant protein biomarkers. Selected potential biomarkers were then independently validated in saliva from control, diabetic, and prediabetic subjects by Western immunoblotting and ELISA. Characterization of the salivary proteome identified a total of 487 unique proteins. Approximately 33% of these have not been previously reported in human saliva. Of these, 65 demonstrated a greater than 2-fold difference in abundance between control and type-2 diabetes samples. A majority of the differentially abundant proteins belong to pathways regulating metabolism and immune response. Independent validation of a subset of potential biomarkers utilizing immunodetection confirmed their differential expression in type-2 diabetes, and analysis of prediabetic samples demonstrated a trend of relative increase in their abundance with progression from the prediabetic to the diabetic state. This comprehensive proteomic analysis of the human salivary proteome in type-2 diabetes provides the first global view of potential mechanisms perturbed in diabetic saliva and their utility in detection and monitoring of diabetes. Further characterization of these markers in a larger cohort of subjects may provide the basis for new, noninvasive tests for diabetes screening, detection, and monitoring.

Diagnostic model of saliva protein finger print analysis of patients with gastric cancer

AIM: To explore the method for early diagnosis of gastric cancer by screening the expression spectrum of saliva protein in gastric cancer patients using mass spectrometry for proteomics.

METHODS: Proportional peptide mass fingerprints were obtained by analysis based on proteomics matrix-assisted laser desorption ionization time-of-flight/mass spectrometry. A diagnosis model was established using weak cation exchange magnetic beads to test saliva specimens from gastric cancer patients and healthy subjects.

RESULTS: Significant differences were observed in the mass to charge ratio (m/z) peaks of four proteins (1472.78 Da, 2936.49 Da, 6556.81 Da and 7081.17 Da) between gastric cancer patients and healthy subjects.

CONCLUSION: The finger print mass spectrum of saliva protein in patients with gastric cancer can be established using gastric cancer proteomics. A diagnostic model for distinguishing protein expression mass spectra of gastric cancer from non-gastric-cancer saliva can be established according to the different expression of proteins 1472.78 Da, 2936.49 Da, 6556.81 Da and 7081.17 Da. The method for early diagnosis of gastric cancer is of certain value for screening special biological markers.