Salivary mucin: a factor in the lower prevalence of gastroesophageal reflux disease in African-Americans?

MUC5B induces in vitro neutrophil extracellular trap formation: Implication in otitis media

BACKGROUND

Chronic otitis media (COM) is characterized by middle ear fluid predominantly containing cytokines, Nontypeable haemophilus influenzae (NTHi), the mucin MUC5B, and neutrophil extracellular traps (NETs). NETs consist of extracellular DNA coated with antibacterial proteins such as myeloperoxidase (MPO) and citrullinated histone 3 (CitH3). NETs can damage tissues and sustain inflammation. Our study aimed to develop an in vitro model of NETosis, testing COM inductors.

METHODS

NETosis was evaluated in fresh blood human neutrophils attached to collagen-coated plates and in suspension exposed to phorbol myristate acetate (PMA) as a control, and COM relevant mediators. Confocal microscopy, DNA fluorescence assay and flow cytometry were used to quantify NETosis.

RESULTS

PMA exposure induced DNA, MPO, and CitH3 by immunofluorescence (IF) most significantly at 3 hours (3.8-fold for DAPI, 7.6-fold for MPO, and 6.9-fold for CitH3, all P < .05). IL-8 and TNF-α cytokines showed milder increases of DAPI, MPO, and CitH3 positive cells. NTHi had no effect on these NETs markers. Purified salivary MUC5B (10 to 40 μg/mL) produced potent increases, comparable to PMA. A composite NET score summing the fold-increases for DAPI, MPO, and CitH3 demonstrated PMA at 13.6 to 19 relative to control set at 1; and MUC5B at 8.6 to 16.3 (all P < .05). IL-8 and TNF-α showed scores of 5.4 and 3, respectively, but these were not statistically significant.

CONCLUSION

We developed a reliable in vitro assay for NETosis which demonstrated that salivary MUC5B is a potent inductor of NETs whereas IL-8, TNF-α, live and lyzed NTHi demonstrated minimal to no NETosis.

LEVEL OF EVIDENCE

NA.

Relationship between salivary mucin or amylase and the periodontal status

OBJECTIVE

Here we determine the relationship between salivary levels of mucin and amylase and the clinical parameters of periodontal disease before and after periodontal treatment.

SUBJECTS

Ninety two subjects were clinically examined and distributed into four groups namely clinically healthy, mild, moderate and severe periodontitis, according to the periodontal status, classified according the values of clinical attachment level (CAL) and probing pocket depth (PPD). Unstimulated saliva was collected for 5 min. Salivary proteins, amylase and mucin were determined by colorimetric methods.

RESULTS

A significant positive correlation (P < 0.0001) was observed between salivary mucin, amylase or protein and PPD or CAL before periodontal treatment while flow rate showed a negative correlation. Mucin and amylase output also showed a positive correlation with PPD or CAL. After treatment, the improvement of clinical parameters was accompanied by a diminution of salivary mucin, amylase or protein concentration and output in moderate and severe group.

CONCLUSIONS

The increment of mucin and amylase output in relation to periodontal status indicates that salivary glands respond to the disease by increasing the protective potential of saliva when necessary and return to the normal rate of secretion after the resolution of the inflammatory process.

The role of mucin in GERD and its complications

Acid, pepsin and other noxious material reach the esophageal mucosa and interact with the luminal aspect of the squamous epithelium. The first protective barrier to these potentially injurious substances is the mucus buffer layer that covers the mucosa. In healthy people, the esophagus has a protective surface adherent mucus gel barrier. Levels of mucin glycoprotein are considerably increased in response to acid and pepsin. A wide spectrum of mucin genes are expressed in normal esophageal mucosa, squamous cell carcinoma of the esophagus, Barrett epithelium and esophageal adenocarcinoma. The mucins MUC5AC and MUC6 are expressed to a similar degree in Barrett metaplasia and gastric mucosa, as is MUC2 in Barrett intestinal metaplasia and small bowel mucosa. Increased expression of MUC1 is associated with progression from dysplasia to adenocarcinoma of the esophagus. Thus, mucins have an important role in the defense of esophageal mucosa against the acid, pepsin and bile that are present in the refluxate. Changes in the expression of mucins occur in patients with GERD, and might lead to the development of new drugs.

Interfacial instabilities affect microfluidic extraction of small molecules from non-Newtonian fluids

As part of a project to develop an integrated microfluidic biosensor for the detection of small molecules in saliva, practical issues of extraction of analytes from non-Newtonian samples using an H-filter were explored. The H-filter can be used to rapidly and efficiently extract small molecules from a complex sample into a simpler buffer. The location of the interface between the sample and buffer streams is a critical parameter in the function of the H-filter, so fluorescence microscopy was employed to monitor the interface position; this revealed apparently anomalous fluorophore diffusion from the samples into the buffer solutions. Using confocal microscopy to understand the three-dimensional distribution of the fluorophore, it was found that the interface between the non-Newtonian sample and Newtonian buffer was both curved and unstable. The core of the non-Newtonian sample extended into the Newtonian buffer and its position was unstable, producing a fluorescence intensity profile that gave rise to the apparently anomalously fast fluorophore transport. These instabilities resulted from the pairing of rheologically dissimilar fluid streams and were flowrate dependent. We conclude that use of non-Newtonian fluids, such as saliva, in the H-filter necessitates pretreatment to reduce viscoelasticity. The interfacial variation in position, stability and shape caused by the non-Newtonian samples has substantial implications for the use of biological samples for quantitative analysis and analyte extraction in concurrent flow extraction devices.

Salivary proteome and its genetic polymorphisms

Salivary diagnostics for oral as well as systemic diseases is dependent on the identification of biomolecules reflecting a characteristic change in presence, absence, composition, or structure of saliva components found under healthy conditions. Most of the biomarkers suitable for diagnostics comprise proteins and peptides. The usefulness of salivary proteins for diagnostics requires the recognition of typical features, which make saliva as a body fluid unique. Salivary secretions reflect a degree of redundancy displayed by extensive polymorphisms forming families for each of the major salivary proteins. The structural differences among these polymorphic isoforms range from distinct to subtle, which may in some cases not even affect the mass of different family members. To facilitate the use of modern state-of-the-art proteomics and the development of nanotechnology-based analytical approaches in the field of diagnostics, the salient features of the major salivary protein families are reviewed at the molecular level. Knowledge of the structure and function of salivary gland-derived proteins/peptides has a critical impact on the rapid and correct identification of biomarkers, whether they originate from exocrine or non-exocrine sources.

Health benefits of saliva: a review

OBJECTIVE

The aim is to present a review of the literature on human saliva composition, flow rates and some of the health benefits of saliva, with emphasis on studies from our laboratory that have looked at effects of age and age-related diseases on saliva output and composition.

DATA

Saliva influences oral health both through its non-specific physico-chemical properties, as well as through more specific effects. The proline-rich proteins, statherin and the histatins are salivary proteins that influence calcium phosphate chemistry, initial plaque formation and candida infection. Increases or decreases in mastication may affect saliva output. Our cross-sectional studies of saliva in a large population-based study cohort (N=1130) indicate that there is an age-related decline in saliva output for unstimulated whole, stimulated parotid, unstimulated submandibular/sublingual and stimulated submandibular/sublingual saliva, as well as some compositional alterations in anti-microbial and other proteins. Some of these alterations also appear to be specific for certain age-related medical conditions, such as diabetes mellitus.

CONCLUSIONS

These studies and data presented confirm the importance of saliva in maintaining a healthy oral environment; the practitioner is encouraged to consider saliva output and medical conditions that may compromise it as part of routine dental treatment planning.

Non-erosive reflux disease (NERD)--acid reflux and symptom patterns

BACKGROUND

Recent reports suggest that patients with non-erosive reflux disease (NERD) treated with anti-reflux medications show lower symptom improvement rates than patients with erosive oesophagitis treated with the same medications.

AIM

To determine the acid reflux and symptom patterns of patients with NERD in comparison with those with erosive oesophagitis and Barrett's oesophagus, and to identify different NERD subgroups.

METHODS

One hundred and forty-nine consecutive patients seen for classic heartburn symptoms were evaluated for the study. Oesophageal mucosal injury was assessed by upper endoscopy and classified by Hetzel-Dent criteria. Patients with Hetzel-Dent grades 0-1 were considered to have NERD. The extent of oesophageal acid exposure was determined by ambulatory 24-h oesophageal pH monitoring.

RESULTS

Seventy-one patients were found to have NERD, 36 erosive oesophagitis and 42 Barrett's oesophagus. Compared with patients with erosive oesophagitis (75%) and Barrett's oesophagus (93%), those with NERD (45%) were significantly less likely to have an abnormal pH test (P = 0.0001). Patients with Barrett's oesophagus had the highest mean number of acid reflux events (210 +/- 17.7), compared with those with erosive oesophagitis (139.7 +/- 15.2) and NERD (95.3 +/- 9.4) (P = 0.0001); however, the rate of perceived acid reflux events was similar and very low in all groups (NERD, 3.6%; erosive oesophagitis, 2.9%; Barrett's oesophagus, 2.17%). NERD-positive patients (abnormal pH test) had a similar extent of oesophageal acid exposure to those with erosive oesophagitis. NERD-positive patients were more likely to demonstrate a symptom index greater than 75% than NERD-negative patients (normal pH test) (61.9% vs. 10.5%; P = 0.0001). In the NERD-negative group, those with a negative symptom index reported having heartburn at pH < 4 only 12.7% of the time, compared with 70.7% of the time in those with a positive symptom index, despite a similar mean number of heartburn episodes.

CONCLUSIONS

Patients with NERD commonly demonstrate a negative pH test. Acid reflux characteristics and symptom patterns suggest a heterogeneous group of patients.

Patterns of secretion of mucins and non-mucin glycoproteins in human submandibular/sublingual secretion

The present investigation has characterised the influence of gustatory stimulation and duration of stimulation on the secretion pattern of salivary mucins MG1 and MG2 and non-mucin glycoproteins in submandibular/sublingual secretion (SMSL). Resting SMSL was collected for three 2 min intervals and stimulated SMSL was collected for ten 1 min intervals from six healthy subjects. Flow rates and total protein were significantly different under the two conditions. The secretion patterns of these proteins under resting and stimulated conditions was examined on periodic acid-Schiff reagent (PAS)-stained polyacrylamide gels using a Kodak Digital-Science Image Station. Image analyses revealed that the level of MG1 increased and the level of MG2 remained nearly the same after stimulation. Six other major glycoproteins (designated Band 1-6) were identified on the basis of their electrophoretic mobilities and immuno-reactivity on Western blots. After stimulation the intensity of Band 1 (lactoferrin and peroxidase) and Band 2 (amylase) decreased whereas the intensity of Band 3 (carbonic anhydrase), Band 4 (proline-rich glycoprotein) and Bands 5 and 6 (basic glycosylated proline-rich proteins) increased. These patterns probably reflect secretion from preformed vesicles since de novo synthesis would be unexpected within the time frame of these experiments. The variable patterns observed suggest that mucins and non-mucin glycoproteins in SMSL derive from different subsets of secretory vesicles, some of which may originate in mucous and others in serous acini, as well as in ductal cells. Quantification of mucins was performed by image analysis technology using purified MG1 and MG2 standards. Finally, the present investigation has shown that the secretory patterns of mucins and non-mucin glycoproteins from submandibular/sublingual glands are complex and represent an important aspect of salivary gland physiology.

Electron microscopic immunogold localization of salivary mucins MG1 and MG2 in human submandibular and sublingual glands

The human salivary mucins MG1 and MG2 are well characterized biochemically and functionally. However, there is disagreement regarding their cellular and glandular sources. The aim of this study was to define the localization and distribution of these two mucins in human salivary glands using a postembedding immunogold labeling method. Normal salivary glands obtained at surgery were fixed in 3% paraformaldehyde-0.1% glutaraldehyde and embedded in Lowicryl K4M or LR Gold resin. Thin sections were labeled with rabbit antibodies to MG1 or to an N-terminal synthetic peptide of MG2, followed by gold-labeled goat anti-rabbit IgG. The granules of all mucous cells of the submandibular and sublingual glands were intensely reactive with anti-MG1. No reaction was detected in serous cells. With anti-MG2, the granules of both mucous and serous cells showed reactivity. The labeling was variable in both cell types, with mucous cells exhibiting a stronger reaction in some glands and serous cells in others. In serous granules, the electron-lucent regions were more reactive than the dense cores. Intercalated duct cells near the acini displayed both MG1 and MG2 reactivity in their apical granules. In addition, the basal and lateral membranes of intercalated duct cells were labeled with anti-MG2. These results confirm those of earlier studies on MG1 localization in mucous cells and suggest that MG2 is produced by both mucous and serous cells. They also indicate differences in protein expression patterns among salivary serous cells.

The effects of duration and intensity of stimulation on total protein and mucin concentrations in resting and stimulated whole saliva

The present investigation has characterized the influence of the duration and intensity of stimulation on the secretion pattern of total protein and salivary mucins MG1 and MG2 in whole saliva. Resting and stimulated whole saliva was collected from six healthy subjects on 2 consecutive days. Whole saliva was collected for 2 five-minute intervals under resting conditions followed by collection under masticatory stimulation induced by the chewing of parafilm (1 g) at 10 or 60 strokes/min for 15 min. Flow rates were different under the 2 levels of stimulation. The concentration of total protein was different in resting and stimulated whole saliva but was not affected by the duration or intensity of stimulation. Analysis of mucin concentrations determined by capture ELISAs revealed that the pattern of MG1 secretion was similar to that of total protein. The pattern of MG2 secretion was unique in that no differences were observed in the concentration of this mucin under resting and stimulated conditions. This study shows that the pattern of protein secretion in whole saliva does not reflect the combined pattern observed for protein secretion in parotid and submandibular/sublingual glands, and that the secretion patterns of MG1 and MG2 in whole saliva are quite different from one another.