In vitro hydroxyapatite adsorbed salivary proteins

Mass spectrometry-based proteomic approaches for salivary protein biomarkers discovery and dental caries diagnosis: A critical review

Dental caries is a multifactorial chronic disease resulting from the intricate interplay among acid-generating bacteria, fermentable carbohydrates, and several host factors such as saliva. Saliva comprises several proteins which could be utilized as biomarkers for caries prevention, diagnosis, and prognosis. Mass spectrometry-based salivary proteomics approaches, owing to their sensitivity, provide the opportunity to investigate and unveil crucial cariogenic pathogen activity and host indicators and may demonstrate clinically relevant biomarkers to improve caries diagnosis and management. The present review outlines the published literature of human clinical proteomics investigations on caries and extensively elucidates frequently reported salivary proteins as biomarkers. This review also discusses important aspects while designing an experimental proteomics workflow. The protein-protein interactions and the clinical relevance of salivary proteins as biomarkers for caries, together with uninvestigated domains of the discipline are also discussed critically.

Proteome analysis of high affinity mouse saliva proteins to hydroxyapatite

Caries sensitivity varies between the two strains of inbred mice, BALB/cA has high sensitivity and C3H/HeN has low sensitivity. One potential reason seems to be a difference in pellicle-forming saliva protein composition. Here, we performed a proteomic analysis in order to identify differences of hydroxyapatite (HAP) adsorbed saliva proteins between these two mouse strains. HAP column chromatography revealed twice the quantity of high-affinity saliva proteins in C3H/HeN compared to BALB/cA. One- and two-dimensional electrophoresis showed 2 bands/spots with deviating migration. They were identified as murine carbonic anhydrase VI (CAVI) by peptide mass fingerprinting and confirmed with western blotting using a specific polyclonal antibody. Total RNA from the salivary glands of both mouse strains, PCR amplification of cDNA with a CAVI specific primer, and sequence analysis revealed one different base in codon 96, resulting in one different amino acid. Glyco-chains of CAVI deviate in one N-glycan, confirmed by mass analysis. CAVI activity was estimated from distinct circular dichroism spectra of the molecules and found higher in C3H/HeN mice. In summary, the CAVI composition of BALB/cA and C3H/HeN differs in one amino acid and a glyco-chain modification. Further, saliva from caries resistant C3H/HeN mice displayed higher CAVI activity and also overall hydroxyapatite adsorption, suggesting a relationship with caries susceptibility.

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CAVI was the salivary protein with high affinity for hydroxyapatite in two mice strains with different caries susceptibility.

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CAVI of the two strains showed differences in molecular weight, amino acids and genes, glyco-chain modification and enzyme activity.

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Differences in CAVI activity might contribute to caries susceptibility.

Effects of fetuin-A with diverse functions and multiple mechanisms on human health

Fetuin-A (Alfa 2-Heremans-Schmid) is a glycoprotein that is mainly synthesized by hepatocytes and then released into the bloodstream. While fetuin-A, a multifunctional protein, has inhibitory effects on health in the processes of calcification, mineralization, coronary artery calcification (CAC), and kidney stone formation by various mechanisms, it has such stimulatory effects as obesity, diabetes, and tumor progression processes. Fetuin-A produces these effects on the organism mainly by playing a role in the secretion levels of some inflammatory cytokines and exosomes, preventing unwanted calcification, inhibiting the autophosphorylation of tyrosine kinase, suppressing the release of adiponectin and peroxisome proliferator-activated receptor-γ (PPARγ), activating the toll-like receptor 4 (TLR-4), triggering the phosphatidylinositol 3 (PI3) kinase/Akt signaling pathway and cell proliferation, and mimicking the transforming growth factor-beta (TGF-β) receptor. In the present review, fetuin-A was examined in a wide perspective from the structure and release of fetuin-A to its effects on health.

Carbonic Anhydrase 6 Gene Variation influences Oral Microbiota Composition and Caries Risk in Swedish adolescents

Carbonic anhydrase VI (CA6) catalyses the reversible hydration of carbon dioxide in saliva with possible pH regulation, taste perception, and tooth formation effects. This study assessed effects of variation in the CA6 gene on oral microbiota and specifically the acidophilic and caries-associated Streptococcus mutans in 17-year old Swedish adolescents (n = 154). Associations with caries status and secreted CA6 protein were also evaluated. Single Nucleotide Polymorphisms (27 SNPs in 5 haploblocks) and saliva and tooth biofilm microbiota from Illumina MiSeq 16S rDNA (V3-V4) sequencing and culturing were analysed. Haploblock 4 (rs10864376, rs3737665, rs12138897) CCC associated with low prevalence of S. mutans (OR (95% CI): 0.5 (0.3, 0.8)), and caries (OR 0.6 (0.3, 0.9)), whereas haploblock 4 TTG associated with high prevalence of S. mutans (OR: 2.7 (1.2, 5.9)) and caries (OR: 2.3 (1.2, 4.4)). The TTG-haploblock 4 (represented by rs12138897(G)) was characterized by S. mutans, Scardovia wiggsiae, Treponema sp. HOT268, Tannerella sp. HOT286, Veillonella gp.1 compared with the CCC-haploblock 4 (represented by rs12138897(C)). Secreted CA6 in saliva was weakly linked to CA6 gene variation. In conclusion, the results indicate that CA6 gene polymorphisms influence S. mutans colonization, tooth biofilm microbiota composition and risk of dental caries in Swedish adolescents.

Proteomic Analysis of the Initial Oral Pellicle in Caries-Active and Caries-Free Individuals

PURPOSE

To 1) elucidate individual proteomic profiles of the 3-min biofilm of caries-active and caries-free individuals and 2) compare these proteomic profiles against the background of caries.

EXPERIMENTAL DESIGN

The initial oral pellicle of 12 caries-active and 12 caries-free individuals is generated in situ on ceramics specimens. The individual, host-specific proteomic profiles of this basic pellicle layer are analyzed by a chemical elution protocol combined with an elaborate mass spectrometry and evaluated bioinformatically.

RESULTS

A total of 1188 different proteins are identified. Additionally, 68 proteins are present in the profiles of all individuals, suggesting them as ubiquitously occurring base-proteins of the initial human pellicle. Thereof, the single profiles exhibit high inter-individual differences independent of their group affiliation, stating the initial pellicle to represent a rather "individual fingerprint". Quantitative analyses imply slight indication for 23 proteins potentially capable of counting for caries-specific biomarkers.

CONCLUSIONS AND CLINICAL RELEVANCE

The introduced protocol enables the individual analysis of minimal protein amounts and allows for highly precise characterizations and comparisons of individual proteomic profiles. The results contain a considerable higher extent of protein identifications and might serve as a base for future large scale analyzes to identify discrimination factors for the development of caries susceptibility tests.

Bioinspired heptapeptides as functionalized mineralization inducers with enhanced hydroxyapatite affinity

The regeneration of mineral crystals under physiological conditions is an efficient way to repair defects in hard tissues. To achieve robust mineralization on surfaces such as the tooth enamel, an inducer requires strong affinity with the substrates and should be able to induce mineralization. Thus far, most studies used a single molecule containing two components to realize the above functions separately, which might be troublesome to synthesize and purify. In this work, inspired by the statherin in the salivary acquired pellicle, we designed a simple peptide sequence, Asp-Asp-Asp-Glu-Glu-Lys-Cys (peptide-7), to accomplish the dual tasks of adsorption and mineralization on enamel surfaces. We speculate the calcium binding ability of the negatively charged carboxylic acid groups in the peptide itself contributes to the dual functions of peptide-7. In vitro and in vivo experiments demonstrated its excellent repair effect on enamel as compared to fluoride. More importantly, due to the strong affinity between peptides and hydroxyapatite, a compact mineralized crystal layer and a strong adhesion between the regenerated minerals and the bottom substrates were observed, similar to the effect induced by fluoride. This work sheds light on the interaction mechanism between peptide-7 and minerals. In addition, since it is safer than fluoride, peptide-7 may have potential applications in the repair of other hard tissues and the functionalization of biomaterials.

The relationship between serum and urinary Fetuin-A levels and kidney stone formation among kidney stone patients

Introduction

Mineralization inhibitors are required to prevent the precipitation of minerals and inhibit the formation of kidney stones and other ectopic calcifications. In laboratory studies, Fetuin-A as a glycoprotein has inhibited hydroxyapatite precipitation in calcium and phosphate supersaturated solutions; however, information about patients with kidney stones is limited. The aim of this study was to investigate the association of serum and urinary Fetuin-A levels with calcium oxalate kidney stones.

Material and methods

In this case-control study, 30 patients with kidney stones and 30 healthy individuals without any history of urolithiasis who were referred to the urology ward of Sina Hospital of Tehran, Iran, in 2015 were entered into the study. All patients underwent computerized tomography scans. After collecting demographic information, serum and urine levels of Fetuin-A and some other calcification inhibitors and promoters, were measured and compared using T-test, Mann-Whitney and logistic regression between the two study groups.

Results

Patients with kidney stones, on average, had lower levels of Serum Fetuin-A (1522.27 ±755.39 vs. 1914.64 ±733.76 μg/ml; P = 0.046) as well as lower levels of Urine Fetuin-A (944.62 ±188.5 vs. 1409.68 ±295.26 μg/ml; P <0.001). Multivariate logistic analysis showed that urinary calcium and serum creatinine are the risk factors and Fetuin-A is a urinary protective factor for kidney stones.

Conclusions

PFC Our study showed that patients with kidney stones had lower serum and urinary levels of Fetuin-A. In the logistic regression model, urinary Fetuin-A was reported as a protective factor for kidney stones.

The Interactions of CPP-ACP with Saliva

The repair of early dental caries lesions has been demonstrated by the application of the remineralisation technology based on casein phosphopeptide-stabilised amorphous calcium phosphate complexes (CPP-ACP). These complexes consist of an amorphous calcium phosphate mineral phase stabilised and encapsulated by the self-assembly of milk-derived phosphopeptides. During topical application of CPP-ACP complexes in the oral cavity, the CPP encounters the enamel pellicle consisting of salivary proteins and peptides. However the interactions of the CPP with the enamel salivary pellicle are not known. The studies presented here reveal that the predominant peptides of CPP-ACP complexes do interact with specific salivary proteins and peptides of the enamel pellicle, and provide a mechanism by which the CPP-ACP complexes are localised at the tooth surface to promote remineralisation.

Molecular docking characterization of a four-domain segment of human fibronectin encompassing the RGD loop with hydroxyapatite

Fibronectin adsorption on biomaterial surfaces plays a key role in the biocompatibility of biomedical implants. In the current study, the adsorption behavior of the 7–10th type III modules of fibronectin (FN-III_7–10) in the presence of hydroxyapatite (HAP) was systematically investigated by using molecular docking approach. It was revealed that the FN-III₁₀ is the most important module among FN-III_7–10 in promoting fibronectin binding to HAP by optimizing the interaction energy; the arginine residues were observed to directly interact with the hydroxyl group of HAP through electrostatic forces and hydrogen bonding. Moreover, it was found that the HAP-binding sites on FN-III₁₀ are mainly located at the RGD loop region, which does not affect the interaction between the fibronectin protein and its cognate receptors on the cell surface.

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.

Histatin 1 Resists Proteolytic Degradation when Adsorbed to Hydroxyapatite

Histatins are salivary proteins that exhibit a high affinity for hydroxyapatite and contribute to the acquired enamel pellicle. Previous studies have observed that, despite the high proteolytic activity in saliva, significant numbers of histatin molecules in acquired enamel pellicle are intact. Our working hypothesis was that histatins are less susceptible to proteinases present in saliva when adsorbed on the hydroxyapatite. To test this premise, we incubated histatin 1 with hydroxyapatite and human whole saliva. Proteolytic products of this incubation were then characterized by PAGE, HPLC, and mass spectrometry. This study shows for the first time that binding to hydroxyapatite confers intact histatin 1 with resistance to proteolytic degradation.

Hydroxyapatite nanoparticles as a controlled-release carrier of BMP-2: absorption and release kinetics in vitro

Recently, nanoparticles have been extensively developed as controlled-release carriers; however, there has been little research on hydroxyapatite nanoparticles (HANPs) and their potential applications. In this study, HANPs were investigated as a controlled-release carrier of bone morphogenetic protein-2 (BMP-2), the absorption and release kinetics of which were analyzed in vitro. Different concentrations of BMP-2 solution were used to evaluate the adsorptive properties of HANPs. It was observed that the amount of BMP-2 adsorbed onto HANPs could be as high as 70 mug/mg and that adsorption rate was highly correlated with the concentration of BMP-2 solution used. After absorption, the suspension of HANPs absorbed BMP-2 (HANPs/BMP-2) was incubated at 37 degrees C for 15 days and the release kinetics of BMP-2 from HANPs/BMP-2 was determined daily. The release profile showed sustained release of BMP-2 over the period of the investigation. Collectively, these results suggest that HANPs has the potential to function as a carrier for drug delivery systems and as a scaffold material in bone tissue engineering.

The influence of liposomal formulation factors on the interactions between liposomes and hydroxyapatite

Liposomes may have potentials as a drug delivery system in the oral cavity; hence, the adsorption to, oral tissues may be of importance. The aim of this study was to find an optimal liposomal formulation with appropriate in vitro stability and which liposomal formulation parameters may be of importance for the interaction to tooth enamel surfaces. Charged liposomes were adsorbed in vitro onto hydroxyapatite (HA), used as a model substance for human dental enamel. For a systematic approach of lipid selection, statistical experimental design and multivariate analysis were conducted to interpret the data. The factors investigated were the type of charge (positive, negative), type of main phospholipid (egg-PC, DPPC, DMPC), type of charged lipid (diacyl-TAP, -ethylPC, -PA, -PG, -PS), the amount of charged component (2.5, 10mol%) and the inclusion of cholesterol in the lipid bilayer. The results indicated that positively charged liposomes expressed significantly higher adsorption levels than the negatively charged ones. The effect of incorporating cholesterol did not turn out to be significant. Both positive egg-PC and DPPC liposomes exhibited high adsorption levels; however egg-PC liposomes were unstable during storage. For positively charged liposomes, the factor "type of main lipid" was found to be of significance for the adsorption, whereas, for negatively charged liposomes, no such important factors were found. Based on the adsorption profile to HA and the in vitro stability in phosphate buffer, the most promising liposomal formulation to target for human enamel in this study was the positively charged DPPC liposomes with 10mol% charged lipid included. However, more experiments are needed to determine the optimum mol% of positively charged lipid for the adsorption onto HA.

Anisotropic demineralization and oriented assembly of hydroxyapatite crystals in enamel: smart structures of biominerals

It is interesting to note that the demineralization of natural enamel does not happen as readily as that of the synthesized hydroxyapatite (HAP), although they share a similar chemical composition. We suggest that the hierarchical structure of enamel is an important factor in the preservation of the natural material against dissolution. The anisotropic demineralization of HAP is revealed experimentally, and this phenomenon is understood by the different interfacial structures of HAP-water at the atomic level. It is found that HAP {001} facets can be more resistant against dissolution than {100} under acidic conditions. Although {100} is the largest surface of the typical HAP crystal, it is {001}, the smallest habit face, that is chosen by the living organisms to build the outer surface of enamel by an oriented assembly of the rodlike crystals. We reveal that such a biological construction can confer on enamel protections against erosion, since {001} is relatively dissolution-insensitive. Thus, the spontaneous dissolution of enamel surface can be retarded in biological milieu by such a smart construction. The current study demonstrates the importance of hierarchical structures in the functional biomaterials.

On-plate digestion using a commercial microfraction collector for nano-HPLC matrix-assisted laser desorption/ionization tandem time-of-flight protein analysis

A new method for on-plate protein digestion and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry analysis is proposed involving an automated one-step sample separation using nanoflow HPLC followed by nanoliter fraction collection and on-plate digestion with trypsin. This procedure uses a commercial automatic nanoliter fraction collection system for on-line spotting of the eluent onto a MALDI target. After protein digestion, the reaction is stopped by the addition of acidified matrix using the same automated system. Collected spots are subsequently analyzed using a MALDI tandem time-of-flight (TOF/TOF) mass spectrometer for protein sequencing and identification.

Peptide profile of human acquired enamel pellicle using MALDI tandem MS

The present study proposes a strategy for human in vivo acquired enamel pellicle (AEP) peptidome characterisation based on sequential extraction with guanidine and TFA followed by MALDI-TOF/TOF identification. Three different nanoscale analytical approaches were used: samples were subjected to tryptic digestion followed by nano-HPLC and mass spectrometry (MS and MS/MS) analysis. Undigested samples were analysed by LC-MS (both linear and reflector modes) and LC-MS/MS analysis, and samples were subjected to nano-HPLC followed by on-plate digestion and mass spectrometry (MS and MS/MS) analysis. The majority of the identifications corresponded to peptide/protein fragments of salivary protein, belonging to the classes: acidic PRPs, basic PRPs, statherin, cystatins S and SN and histatin 1 (all also identified in intact form). Overall, more than 90 peptides/proteins were identified. Results clearly show that peptides with acidic groups are enriched in the TFA fraction while peptides with no acidic or phosphate groups are prevalent on the guanidine extract. Also, phosphorylated peptides were observed mainly on the TFA fraction. Fragments present in the AEP show a predominance of cleavage points located at Arg, Tyr and Lys residues. Obtained data suggest that proteolytic activity could influence AEP formation and composition.

Production from dairy cows of semi-industrial quantities of milk-protein concentrate (MPC) containing efficacious anti-Candida albicans IgA antibodies

Bovine milk antibodies directed against human pathogenic organisms have potential as prophylactic or therapeutic treatments of disorders affecting mucosal surfaces. The cow, however, does not naturally secrete high levels of IgA in milk, the predominant immunoglobulin of the mucosal immune system. We have patented an immunisation protocol that results in increased production of IgA in ruminant milk and in this study established that our protocol can be used on a scale sufficient to produce semi-industrial quantities of milk for processing. Cows were immunised with a common pathogenic yeast, Candida albicans and responded with high levels of antigen-specific IgA antibodies in their milk. The spray-dried milk-protein concentrate (85% protein) powder was shown to reduce adherence of Cand. albicans cells in in vitro adherence assays, demonstrating an ability to retain efficacy through the processing. These results suggest that this milk product may be of therapeutic value if the reduction in Cand. albicans adhesion observed in vitro translates to reduced colonisation in vivo.

Peptidomic analysis of human acquired enamel pellicle

Human acquired enamel pellicle is the result of a selective interaction of salivary proteins and peptides with the tooth surface. In the present work, the characterization of the peptides as well as the type of interactions established with the enamel surface was performed. Peptides from in vivo bovine enamel implants in the human oral cavity were sequentially extracted using guanidine and trifluoroacetic acid solutions and the fractions obtained were analysed by LC-MS and LC-MS/MS. Based on the LC-MS data, six phosphorylated peptides were identified in an intact form, strongly adsorbed to the enamel surface. Data from the LC-MS/MS analyses allowed us to identified 30 fragment peptides non-covalently bonded to enamel [basic proline-rich proteins, histatins (1 and 3) and acidic proline-rich protein classes]. The tandem mass spectrometry experiments showed the existence of a pattern of amide bond cleavage for the different identified peptide classes suggesting a selective proteolytic activity. For histatins, a predominance of cleavage at Arg, Lys and His residues was observed, while for basic proline-rich proteins, cleavage at Arg and Pro residues prevailed. In the case of acidic proline-rich proteins, a clearly predominance of cleavage of the Gln-Gly amide bond was evident.

Proteomic analysis of human whole and parotid salivas following stimulation by different tastes

Whole and parotid salivas, collected after stimulation with tastants, were analyzed by 2D electrophoresis and mass spectrometry. In whole saliva, the number of proteins affected by taste stimulation increased in the order sweet < umami < bitter < acid. Annexin A1 and calgranulin A, involved in inflammation, were over-represented after umami, bitter, and sour stimulations. Their low abundance or absence in parotid saliva after bitter stimulation suggested that they originated from other oral glands or tissues.

Candida albicans binds to saliva proteins selectively adsorbed to silicone

Explanted voice prostheses obtained from 5 patients at the time of prosthesis replacement were consistently colonized by yeast, in particular Candida albicans. A simple, reproducible, in vitro model of C. albicans adherence to saliva-coated voice prosthesis silicone was developed. Whole saliva promoted adherence of C. albicans to silicone in a dose-dependent manner. Saliva rinses from voice prosthesis patients also promoted binding of C. albicans to silicone in vitro (mean adherence 14.9% +/- 2.8% of input C. albicans cells). This was significantly higher than C. albicans adherence to silicone in the absence of saliva (P < .001) or adherence promoted by saliva rinses from healthy volunteers (P < .005). Polyacrylamide gel electrophoresis analysis and a blot overlay adherence assay revealed that certain salivary proteins were selectively adsorbed to silicone and that C. albicans yeast cells adhered specifically to the adsorbed salivary proteins.

Two-dimensional electrophoresis study of in vitro pellicle formation and dental caries susceptibility

In the present study, a proteomic approach was applied to evaluate the influence of salivary protein composition on in vitro dental pellicle formation and its possible correlation with dental caries. Whole saliva, collected from caries-free and caries-susceptible subjects, was analyzed by two-dimensional electrophoresis, and protein spots were identified by mass spectrometry. Data analysis of salivary protein composition showed a statistically significant correlation between the quantity of acidic proline-rich proteins (PRPs), lipocalin, cystatin SN and cystatin S, and samples from the caries-free group of subjects [decayed, missing or filled teeth (DMFT) = 0]. Samples from subjects with a high DMFT index appear to be correlated with high levels of amylase, immunoglobulin A, and lactoferrin. In vitro pellicle-composition experiments showed the same correlations found for whole saliva. As cystatins are known physiological inhibitors of cathepsins, the higher quantities of lipocalin, and cystatins S and SN found in the samples from the caries-free subjects suggest that inhibition of proteolytic events on other salivary proteins may indirectly provide tooth protection. The correlation between higher levels of the phosphorylated acidic PRPs 1/2 with samples from the caries-free group also suggests a protective role for these proteins.

The Effect of Hydroxyapatite on the Remineralization of Dental Fissure Sealant

The purpose of this study is to investigate the remineralization of enamel in the human tooth by fissure sealant containing various amount of hydroxyapatite. Prior to remineralization experiments, the necessary requirements of the dental fissure sealant, the curing depth and the curing time, were measured with the content of the hydroxyapatite according to the standard of ISO 6874. Various amount of hydroxyapatite was mixed uniformly using sonicator up to 20 wt% to the fissure sealant. In spite both the curing time and the curing depth were decreased with increasing the content of hydroxyapatite, all samples were satisfied the ISO requirements. Remineralization experimental samples were produced by bonding fissure sealant containing various amount of hydroxyapatite to human tooth enamel using manufacturer’s information. After exposure to the simulated body fluid at 36.5oC for 4 weeks, the bonding strength and the surface morphology were examined using Instron and scanning electronic microscope, respectively. The bonding strength between the fissure sealant and the human teeth was drastically enhanced with the amount of hydroxyapatite. The remineralization zone could be observed along with the boundary of hydroxyapatite and fissure sealant using a scanning electronic microscope.