Hypo-phosphorylation of salivary peptidome as a clue to the molecular pathogenesis of autism spectrum disorders

RP-HPLC-ESI-MS profile of naturally occurring salivary peptides of subjects with autistic spectrum disorder [ASD; N = 27:12 with diagnosis of autism, 1 with diagnosis of Asperger, 14 with diagnosis of pervasive developmental disorders not otherwise specified (PDD-NOS)] was compared to that of age-matched controls with the goal of identifying differences that could turn out to become hallmarks of at least a subgroup of ASD individuals. Phosphorylation level of four specific salivary phospho-peptides, namely statherin, histatin 1 (both, p < 0.0001) and acidic proline-rich proteins (both entire and truncated isoforms) (p < 0.005) was found significantly lower in autistic patients, with hypo-phosphorylation of at least one peptide observed in 18 ASD subjects (66%). Developmental scale assessment (Griffith or WISC-R) carried out on 14 ASD subjects highlighted a normal to borderline cognitive development in 10 of them, all included in the hypo-phosphorylated group. Phosphorylation of salivary peptides involves a Golgi casein kinase common to many organs and tissues, CNS included, whose expression seems to be synchronized during fetal development. Hypo-phosphorylation of salivary peptides suggests potential asynchronies in the phosphorylation of other secretory proteins, which could be relevant in CNS development either during embryonic development or in early infancy. These results suggest that analysis of salivary phospho-peptides might help to discriminate a considerable subgroup of ASD patients.

HPLC-ESI-MS analysis of oral human fluids reveals that gingival crevicular fluid is the main source of oral thymosins beta(4) and beta(10)

Thymosin beta(4) (Tbeta(4)), its sulfoxide, and thymosin beta(10 )(Tbeta(10)) were detected in human saliva and identified by different strategies based on RP HPLC coupled to electrospray multidimensional IT MS. Tbeta(4 )was almost always detected in whole saliva, its sulfoxide sporadically, Tbeta(10) rarely. Tbeta(4) was undetectable in parotid saliva and less concentrated in submandibular/sublingual saliva than in whole saliva. Analysis of gingival crevicular fluid revealed high relative amounts of Tbeta(4), Tbeta(4) sulfoxide, and Tbeta(10) in all the samples. Tbeta(4) mean concentration was 200 times higher in crevicular fluid (20 micromol/L, N = 9) than in whole saliva (0.1 micromol/L, N = 9). Crevicular fluid concentration of Tbeta(4 )(ca. 5% represented by its sulfoxide) and beta(10 )significantly correlated (r = 0.856; N = 9), and their ratio was about 5. A significant correlation was also observed between Tbeta(4 )concentrations in whole saliva and gingival crevicular fluid (r = 0.738; N = 9). Immunohistochemical analysis of the major salivary glands showed that immunoreactivity for Tbeta(4) is restricted to ductal cells, with minor degree of focal positivity in some acinar cells. On the whole, results indicate that gingival sulcus is a main, although not the sole, source for oral Tbeta(4 )and Tbeta(10).

α-Defensin Levels in Whole Saliva of Totally Edentulous Subjects

Salivary levels of α-defensins 1–4 and histatins 1, 3 and 5 were determined in 11 totally edentulous patients, 11 younger healthy adults with normal gingival mucosa (Control group I) and 8 subjects, age-matched with edentulous patients, having a minimum of 25 teeth (Control group II). Whole saliva was treated with trifluoroacetic acid and the acidic soluble fraction analyzed by High Performance Liquid Chromatography-Mass Spectrometry. The area of the extracted ion current peaks was used for peptide quantification. Levels of α-defensinsl-4, but not of histatins, were significantly lower in totally edentulous patients with respect to both Control group I and Control group II. The two control groups did not show significant differences. The reduced level of oral α-defensins, which are mainly of crevicular origin, is most likely due to the absence of the gingival sulcus in the edentulous subjects. The near absence of α-defensins might be in part responsible for the higher vulnerability of the oral cavity to oral pathogen infections observed in totally edentulous patients.

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.

Structural and functional characterization of the porcine proline–rich antifungal peptide SP-B isolated from salivary gland granules

A 1905-Da cationic proline-rich peptide, named SP-B, was recently isolated by our group as the main component of salivary gland granules, and its primary sequence fully characterized by means of automated Edman sequencing and LC-MS/MS tools. In the present study SP-B is shown to possess antifungal activity when challenged with strains of Cryptococcus neoformans, Candida albicans and Aspergillus fumigatus, while only negligible antibacterial activity was detected. Furthermore, SP-B was found to be non-cytotoxic when tested on fibroblast cell lines. To obtain information regarding its structure affinity, capillary electrophoresis (CE), circular dichroism (CD) and attenuated total reflection (ATR)-FT/IR experiments were performed. CE revealed a pH dependence of the hydrodynamic radial dimensions both in aqueous and 2,2,2-trifluoroethanol solutions. CD and ATR-FT/IR measurements confirmed the structure-pH relationship, revealing a secondary structure composed of mixed proportions of polyproline-II, unordered and turn motifs, the last being more evident in the zwitterionic form of the peptide. From these findings SP-B peptide could be classified as a new member of the proline-rich antimicrobial peptide family.

Proteomic study of salivary peptides and proteins in patients with Sjögren's syndrome before and after pilocarpine treatment

OBJECTIVE

To investigate the effect of pilocarpine on the salivary peptide and protein profile in patients with primary Sjögren's syndrome (SS) and to study the differences between patients with primary SS, patients with SS associated with other rheumatic diseases, and healthy control subjects.

METHODS

Saliva specimens were obtained from 9 primary SS patients, 9 secondary SS patients, and 10 healthy controls. Samples were analyzed for levels of 62 different salivary proteins using high-performance liquid chromatography coupled with mass spectrometry using a spectrometer equipped with an electrospray ionization source. In 6 of the primary SS patients, saliva was collected at 30 minutes, 60 minutes, and 24 hours after taking 5 mg of pilocarpine.

RESULTS

Before pilocarpine, approximately 60% of salivary proteins in samples from primary SS patients were not identifiable or showed lower levels than those in healthy controls. After 30-60 minutes following pilocarpine treatment, approximately one-third of the less represented proteins was found in a similar percentage of primary SS patients and controls. Almost all of the proteins that were detectable at lower levels in primary SS patients compared with controls reached levels similar to those in controls at 30-60 minutes after pilocarpine. The parotid gland proteins had the best response to pilocarpine. Primary SS patients were characterized by higher alpha-defensin 1 levels and by the presence of beta-defensin 2. Secondary SS patients showed an intermediate protein profile between that of the primary SS patients and the controls.

CONCLUSION

Pilocarpine partially restored the levels and numbers of identifiable proteins in saliva from patients with primary SS. Higher levels of alpha-defensin 1 and the presence of beta-defensin 2 in the saliva of patients with primary SS could be markers of oral inflammation in this patient group.

Pro-oxidant activity of histatin 5 related Cu(II)-model peptide probed by mass spectrometry

Histatin 5 is a cationic salivary peptide with strong candidacidal and bactericidal activity at physiological concentration. In this paper we demonstrate by optical spectroscopy and ESI-IT-MS experiments that a synthetic peptide related to the N-terminus of histatin 5 specifically binds copper ions in vitro and that the complex metal-peptide generates reactive oxygen species at physiological concentration of ascorbate, leading to significant auto-oxidation of the peptide within short reaction time. The oxidative activity of this peptide is associated to the presence of a specific metal binding site present at its N-terminus. The motif is constituted by the amino acid sequence NH(2)-Asp-Ser-His, representing a copper and nickel amino terminal binding site, known as "ATCUN motif". The results of the study suggest that the production of reactive oxygen species can be an intrinsic property of histatin 5 connected to its ability to bind metals.

Tyrosine Polysulfation of Human Salivary Histatin 1. A Post-Translational Modification Specific of the Submandibular Gland

Histatin 1 (His-1) derivatives showing serial mass increases of 80.0 +/- 0.1 Da were detected in human saliva by HPLC-ESI-MS. The same derivatives were also found in granules of submandibular glands and secretions of submandibular/sublingual glands, but not in granules and secretions of parotid glands. Only one phosphate group was present in His-1 and its derivatives, since treatment with alkaline phosphatase provided an 80.0 Da mass decrease. His-1 derivatives were almost completely transformed into His-1 by treatment with 1 M HCl at 100 degrees C, suggesting the presence of O-sulfotyrosine, which is more labile than phospho-Tyr to acidic hydrolysis. CE-MS analysis of pronase extensive digestion of derivatives confirmed the presence of sulfotyrosine. Derivatives were digested by trypsin, proteinase K, and protease V-8 and analyzed by different MS strategies. The results allowed locating sulfation on the last four tyrosines (Tyr 27, 30, 34, and 36). This study is the first report of the gland-specific sulfation of a salivary phosphopeptide in vivo.

Rapid determination of short chain carnitines in human plasma by electrospray ionisation-ion trap mass spectrometry using capillary electrophoresis instrument as sampler

A capillary electrophoresis apparatus was used as sampler for flow injection analysis (FIA) in tandem mass spectrometry of L-carnitine and its acetyl- and propionyl-metabolites in human plasma. The capillary electrophoresis instrument was coupled to the ion trap mass spectrometer by an electrospray ionization coaxial sheath liquid interface. The electrophoresis capillary introduced the sample directly into the source by applying a prolonged sample injection. The use of the capillary electrophoresis apparatus miniaturised the FIA procedure, substantially reducing the quantities of solvents and samples used, and allowed rapid automated sequential analyses. The method was optimised and validated using a dialyzed human plasma matrix. The plasma samples were analysed after a simple, rapid deproteinisation procedure with acetonitrile and diluted 70 times before direct injection into the mass spectrometer for product ion scan MS/MS analysis in positive ionisation. The total analysis time was 5 min, including capillary preconditioning and acquisition time (3 min). The method was sensitive, allowing the determination of L-, L-acetyl- and L-propionyl-carnitines at 140, 14 and 3.6 nM concentrations (injected values) corresponding to lower limit of quantitation values in plasma of 10, 1 and 0.25 microM, respectively. The method was processed for full validation and applied to the analysis of L-carnitine and its short chain derivatives in human plasma samples.

Proteomic Analysis of Salivary Acidic Proline-Rich Proteins in Human Preterm and At-Term Newborns

A 1 year follow-up investigation of salivary acidic proline-rich proteins (aPRPs) in preterm and at-term newborns using HPLC-ESI-IT-MS showed that (i) this class of proteins is constitutive rather than inducible, as it is still found in the oral cavity of preterm newborns from 180 days of postconception age (PCA); (ii) the expression of PRH-2 locus anticipates that of PRH-1, since Db isoforms are expressed some months after the PRP-1 and PRP-2 isoforms. The evaluation of the relative abundances of the different aPRPs isoforms and derivatives (differently phosphorylated and cleaved) as a function of PCA showed that (iii) the proteolytic enzymes generating truncated isoforms are also constitutive because they are fully active since 180 days of PCA; (iv) the kinase involved in aPRP phosphorylation is not fully mature in preterm newborns, but its activity increases with PCA, synchronizing with that of at-term newborns and reaching the adult levels at about 500-600 days of PCA, in concomitance with the beginning of deciduous dentition.

Detection in human saliva of different statherin and P-B fragments and derivatives

Statherin is a multifunctional polypeptide specific of human saliva involved in oral calcium homeostasis, phosphate buffering and formation of protein networks. Salivary P-B peptide is usually included into the basic proline-rich protein family but it shows some similarities with statherin and its specific biological role is still undefined. In this study, various fragments and derivatives of statherin and P-B peptide were consistently detected by RP-HPLC ESI-IT MS in 23 samples of human saliva. They were: statherin mono- and non-phosphorylated, statherin Des-Phe(43) (statherin SV1), statherin Des-Thr(42),Phe(43), statherin Des-Asp(1), statherin Des(6-15) (statherin SV2), statherin Des(1-9), statherin Des(1-10), statherin Des(1-13) and P-B Des(1-5). Statherin SV3 (statherin Des(6-15), Phe(43)) was detected only in one sample. Identity of the fragments was confirmed either by MS/MS experiments or by enzymatic digestion or by Edman sequencing. Detection of the fragments suggests that statherin and P-B peptide are submitted to post-translational proteolytic cleavages that are common to other classes of salivary proteins.

HPLC–MS characterization of cyclo-statherin Q-37, a specific cyclization product of human salivary statherin generated by transglutaminase 2

In the present study the analytical potential of HPLC-MS/MS was utilized for the structural characterization of a post-translational modification of statherin. Human salivary statherin (M(av)5380.0 +/- 0.3 Da) is transformed by the action of transglutaminase 2 into a cyclic derivative with an average molecular mass of 5363.0 +/- 0.3 Da. The intra-molecular bridge is generated by the loss of an ammonia molecule between the unique Ione-pair donating nucleophile Lys-6 and one acceptor among the seven glutamine residues of statherin. Digestion of the cyclic derivative with chymotrypsin, proteinase K, and carboxypeptidase Y, monitored by HPLC-electrospray ionization-ion trap-mass spectrometric analysis, demonstrated that cyclization involved almost specifically Gln-37 (> 95%), with the percentage of Gln-39 implicated in the cross-linkiing being less than 5%. The main derivative was named cyclostatherin Q37. Guineapig transglutaminase 2 showed high affinity for statherin in vitro (Km = 0.65 +/- 0.06 microM). Cyclo-statherin was detected in vivo by HPLC-electrospray ionization ion trap-mass spectrometry analysis of whole human saliva and it accounted for about 1% of total statherin. Detection of cyclo-statherin in whole saliva is suggestive of a putative role of this molecule in the formation of the "oral protein pellicle".

Peptides of human gingival crevicular fluid determined by HPLC-ESI-MS

The acidic-soluble protein content of human gingival crevicular fluid was analyzed by reverse-phase high-performance liquid chromatography (RP-HPLC), and the eluent deriving from the chromatography separation was directly introduced into an ion-trap mass spectrometer through electrospray ionization (ESI-IT MS). By this technique the molecular weight of peptides/proteins was determined with a precision of approximately 1/10,000 amu. On the basis of the chromatographic behavior and the knowledge of the molecular mass value, some peptides and proteins soluble in acidic solution were unambiguously recognized. Besides high quantities of human serum albumin, alpha-defensins 1-4 and minor amounts of cystatin A, statherin, basic PB salivary peptide and other unidentified components were detected. The presence of alpha-defensins in gingival crevicular fluid is in agreement with their relevant contribution to protein composition deriving from granulocyte secretions. Other peptides and proteins abundant in human saliva, such as proline-rich proteins (PRPs) and histatins, were not detected in gingival crevicular fluid. Further investigations will be necessary to establish the origin of statherin and PB salivary peptide in gingival crevicular fluid.

Two proline-rich peptides from pig (Sus scrofa) salivary glands generated by pre-secretory pathway underlying the action of a proteinase cleaving ProAla bonds

The primary structures of two salivary proline-rich peptides (PRP-SP-A, M 6156.0 amu and PRP-SP-B, M 1905.0 amu), from pig (Sus scrofa) were determined. The PRP-SP-B peptide, 21 residues long, overlaps with a sequence repeated 43 times in three deposited cDNAs coding for PRP proteins cloned from porcine parotid glands (Swiss-Prot codes: Q95JC9, Q95JD1, Q95JD0). PRP-SP-A peptide, 56 amino acid residues long, overlaps with the N-terminus repeats of Q95JC9 and Q95JD1 and it is phosphorylated at Ser 12 and 14. The two peptides were found both in whole saliva and in granules from pig parotid glands. The biosynthesis of the two peptides implies the action of a proteinase responsible for Pro downward arrow Ala cleavage in the pre-secretory process.

Determination of the post-translational modifications of salivary acidic proline-rich proteins

Human salivary acidic proline-rich proteins were analyzed by electrospray-ion trap mass spectrometry and by matrix-assisted laser desorption/ionization-time of flight mass spectrometry. All acidic-PRP isoforms share a common N-terminal region, which contains a pyroglutamic acid residue at the N-terminus, and two phosphorylation sites on Ser 8 and 22. At the same time, HPLC-MS spectra revealed isoforms of PRP-1 and PRP-3 having a different number of phosphoserine residues, namely, a mono-phosphorylated form of PRP-1 and PRP-3 and a tri-phosphorylated form of PRP-1. The analysis of the masses of tryptic digests suggested that the third phosphate residue should be located on Ser 17. Another protein with a mass of 30,923 amu was detected along the HPLC pattern and MS data of its tryptic digest suggested that it corresponds to the dimer of Pa, the isoform of PRP-1 with a substitution Arg-Cys at 103 position. Finally, structural identification is pending for another post-translational modification of acidic-PRP that provides an increase of 111-114 amu.

The coupling of RP-HPLC and ESI-MS in the study of small peptides and proteins secreted in vitro by human salivary glands that are soluble in acidic solution

The aim of this study was the development of a method based on the coupling of RP-HPLC and ESI-MS for identifying and quantifying proteins and peptides secreted by human salivary glands in vitro. Salivary gland specimens, obtained from informed patients undergoing surgical resection, were incubated in an optimized medium. Incubation media of glandular specimens, selected on the basis of cytomorphological and ultrastructural analysis, were investigated by HPLC-MS. Several salivary peptides/proteins, previously recognized in human whole saliva, were searched for along the chromatogram by the selected ion monitoring (SIM) strategy. Analysis of the incubation media of parotid glands revealed the presence of basic PRPs PC, PD, PH, IB-1, II-2, and acidic PRP-1 and PRP-3 in all of the investigated samples. Basic PRPs PB and PA, acidic PRPs, and cystatins SN and S1 were detected in all of the incubation media of submandibular glands, whereas histatin 1 was detected in only one sample. Moreover, the method allowed detection of some post-translational derivatives of known salivary proteins, as well as of several previously unidentified small peptides. The present method represents a sensitive and powerful instrument to detect peptides and proteins secreted by human salivary glands in vitro.

Statherin levels in saliva of patients with precancerous and cancerous lesions of the oral cavity: a preliminary report

OBJECTIVE

The aim of this study was to measure concentration of human salivary statherin in patients with oral cavity pathologies and salivary gland diseases.

SUBJECTS AND METHODS

Levels of statherin were analysed with High Performance Liquid Chromatography (HPLC) in following groups of subjects: group A: 24 patients with neoplastic diseases of salivary glands, group B: 13 patients with inflammatory lesions of salivary glands, group C: 13 patients with precancerous and cancerous lesions of the oral cavity excluding salivary gland tumors, group D: 20 healthy volunteers (control group).

RESULTS

Our preliminary data indicated a sensible reduction of the statherin level in the saliva of patients with precancerous and cancerous lesions of the oral cavity (group C) compared with the healthy subjects (group D). The statherin levels are not significantly reduced either in the inflammatory (group B) or in the salivary glands tumours (group A), compared with the healthy subjects (group D).

CONCLUSION

Statherin could play a protective effect in oral cavity in association with its other functions.

Different isoforms and post-translational modifications of human salivary acidic proline-rich proteins

The human salivary acidic proline-rich proteins (aPRPs) complex was investigated by different chromatographic and mass spectrometric approaches and the main aPRPs, namely PRP-1, PRP-2 and PIF-s (15,515 amu), Db-s (17,632 amu) and Pa (15,462 amu) proteins, were detected. All these isoforms are phosphorylated at Ser-8 and Ser-22 and have a pyroglutamic moiety at the N-terminus. Apart from Pa, all the other aPRPs undergo a proteolytic cleavage at Arg-106 residue (Arg-127 in Db-s protein), that generates the small PC peptide (4371 amu) and PRP-3, PRP-4, PIF-f (11,162 amu) and Db-f (13,280 amu) proteins, all of which were detected. With regard to the Pa protein, the main form detected was the dimeric derivative (Pa 2-mer, 30,922 amu) originated by a disulfide bond involving Cys-103 residue. Besides these known isoforms, several previously undetected aPRP derivatives were found (in minor amounts): (i) the triphosphorylated derivatives of PRP-1/PRP-2/PIF-s and Db-s, showing the additional phosphate group at Ser-17; (ii) the mono-phosphorylated forms at either Ser-22 or Ser-8 of PRP-1/PRP-2/PIF-s, PRP-3/PRP-4/PIF-f, Db-s and Db-f; (iii) a nonphosphorylated form of PRP-3/PRP-4/PIF-f; (iv) the triphosphorylated and diphosphorylated forms of Pa 2-mer. Moreover, minor quantities of PRP-3/PRP-4/PIF-f lacking the C-terminal Arg (11,006 amu), and of Pa 2-mer lacking the C-terminal Gln (30,793 amu) were found. By this approach the different phenotypes of PRH1 locus in 59 different subjects were characterized.

Characterization of the human salivary basic proline-rich protein complex by a proteomic approach

Thirteen samples of human normal whole saliva were analyzed by RP-HPLC-ESI-MS and MALDI-TOF-MS to investigate the basic proline-rich protein complex. Between known basic-PRPs the P-B, P-C (or IB-8b), P-D (or IB-5), P-E (or IB-9), P-F (or IB-8c), P-H (or IB-4), IB-6, II-2, IB-1, and IB-8a glucosylated were identified, whereas the II-1, IB-7, PA, and D1-A peptides were not detected. Some detected masses not attributable to known basic-PRPs were putatively ascribed to II-2 and IB-1 nonphosphorylated, II-2 and IB-1 missing the C-terminal arginine residue, and the 1-62 fragment of IB-6, named P-J peptide. A correlation matrix analysis revealed a cluster of correlation among all the basic PRPs (apart from the P-B peptide) which is in agreement with their common parotid origin.

Different binding thermodynamics of Ni2+, Cu2+, and Zn2+ to bacitracin A1 determined by capillary electrophoresis

Thermodynamics of the binding of Ni(2+), Cu(2+) and Zn(2+) to bacitracin A(1) was studied by capillary electrophoresis measuring the peptide effective mobility at different pH in the presence of increasing concentration of the three ligands. The affinity follows the order Ni(2+) > Cu(2+) > Zn(2+), with association constant values of (2.3 +/- 0.1)x10(4), (4.9 +/- 0.2)x10(3), and (1.5 +/- 0.1)x10(3) M(-1), respectively. The only model able to rationalize mobility data implies that metal ion binds to the P(0) peptide form. Moreover, mobility values indicated a change of bacitracin A(1) acidic properties on Ni(2+) and Cu(2+) binding, with a shift of the pK(a) of N-terminal Ile-1 from 7.6 to about 5 and of the pK(a) of the delta-amino group of D-Orn-7 from 9.7 to about 7. Even though on Zn(2+) binding a shift of the N-terminal Ile-1 pK(a) was observed, restrictions in the pH range suitable for investigation, due to precipitation phenomena, did not allow establish if the shift of D-Orn-7 lateral chain pK(a) also occurred. Nonetheless, if present, the shift should be limited to the 7.8-9.7 range. Mobility data indicated that the Stokes radius of the complexes is ca. 3 A lower than that of the free peptide. The present results indicate that metal-ion binding to bacitracin A(1) is more complex than previously assumed.