Organic secretory products, adaptive responses and innervation in the parotid gland of ferret: A histochemical study

Proteomic analysis of sialoliths from calcified, lipid and mixed groups as a source of potential biomarkers of deposit formation in the salivary glands

Salivary stones, also known as sialoliths, are formed in a pathological situation in the salivary glands. So far, neither the mechanism of their formation nor the factors predisposing to their formation are known despite several hypotheses. While they do not directly threaten human life, they significantly deteriorate the patient's quality of life. Although this is not a typical research material, attempts are made to apply various analytical tools to characterise sialoliths and search for the biomarkers in their proteomes. In this work, we used mass spectrometry and SWATH-MS qualitative and quantitative analysis to investigate the composition and select proteins that may contribute to solid deposits in the salivary glands. Twenty sialoliths, previously characterized spectroscopically and divided into the following groups: calcified (CAL), lipid (LIP) and mixed (MIX), were used for the study. Proteins unique for each of the groups were found, including: for the CAL group among them, e.g. proteins from the S100 group (S100 A8/A12 and P), mucin 7 (MUC7), keratins (KRT1/2/4/5/13), elastase (ELANE) or stomatin (STOM); proteins for the LIP group-transthyretin (TTR), lactotransferrin (LTF), matrix Gla protein (MPG), submandibular gland androgen-regulated protein 3 (SMR3A); mixed stones had the fewest unique proteins. Bacterial proteins present in sialoliths have also been identified. The analysis of the results indicates the possible role of bacterial infections, disturbances in calcium metabolism and neutrophil extracellular traps (NETs) in the formation of sialoliths.

Neutrophil Extracellular Traps Promote the Development and Growth of Human Salivary Stones

Salivary gland stones, or sialoliths, are the most common cause of the obstruction of salivary glands. The mechanism behind the formation of sialoliths has been elusive. Symptomatic sialolithiasis has a prevalence of 0.45% in the general population, is characterized by recurrent painful periprandial swelling of the affected gland, and often results in sialadenitis with the need for surgical intervention. Here, we show by the use of immunohistochemistry, immunofluorescence, computed tomography (CT) scans and reconstructions, special dye techniques, bacterial genotyping, and enzyme activity analyses that neutrophil extracellular traps (NETs) initiate the formation and growth of sialoliths in humans. The deposition of neutrophil granulocyte extracellular DNA around small crystals results in the dense aggregation of the latter, and the subsequent mineralization creates alternating layers of dense mineral, which are predominantly calcium salt deposits and DNA. The further agglomeration and appositional growth of these structures promotes the development of macroscopic sialoliths that finally occlude the efferent ducts of the salivary glands, causing clinical symptoms and salivary gland dysfunction. These findings provide an entirely novel insight into the mechanism of sialolithogenesis, in which an immune system-mediated response essentially participates in the physicochemical process of concrement formation and growth.

Organic secretion in ductal cells of the sublingual salivary gland of ferret: Histochemical observations

The presence of organic secretion in ductal cells of the sublingual salivary gland of ferret has been questioned, which prompted the present investigation. Paraffin or cryostat sections from aldehyde fixed or quenched sublingual glands of this species were tested for some amino acid residues, mucosubstances, oxidative and hydrolytic enzymes, and lectins. The glands showed inconspicuous ducts of simple appearances on routine histology. The histochemical procedures, however, revealed a granulated substance in the apical (periluminal) region of ductal cells, which contained tryptophan, disulphides, neutral mucosubstances, αFuc and GalNAc, and showed chloroacetate esterase activity. Occurrence of the substance varied between different ducts of the same gland and/or cells of the same duct. The ductal cells also showed diffuse peroxidase and acid phosphatase, and Golgi-like thiamine pyrophosphatase activities. Acetylcholinesterase-positive nerve fibres embraced the ducts. The results support a particular localisation of protein-bound amino acid residues and enzymatic catalytic activities indicative of organic secretion, possibly tissue kallikrein, in sublingual ductal cells of ferret.

A perspective of comparative salivary and breast pathology. Part I: microstructural aspects, adaptations and cellular events

This is the first part of a review comparing the pathology of salivary and mammary glands. Here, less obvious similarities and differences in functional histology and their influences on pathology are examined with emphasis on myoepithelial cells, stromal components, analogues of mucosa-associated lymphoid tissue, steroid receptors, and intraparenchymal cells of monocytic lineage. Particular cell phenotypes (oncocytic, apocrine, neuroendocrine and clear) are critically evaluated and responses to atrophy, infarction and fine-needle aspiration biopsy procedures are highlighted together with aspects of metaplasia, regeneration, ageing and microcalcification. Areas of controversy or uncertainty which may benefit from further investigations are also discussed.

Microliths in the parotid of ferret investigated by electron microscopy and microanalysis

The present investigation is an attempt to determine the occurrence, elemental composition and formation of microliths in the parotid of ferret. Parotids from four normal ferrets were examined by electron microscopy and X-ray microanalysis. Crystalline microliths were found in phagosomes of acinar cells, which occasionally contained secretory material, and in phagosomes situated between mitochondria of striated ductal cells. Crystalline microliths and microliths that consisted of granular material either without crystals or mixed with a component of crystals were found in lumina, where they were often associated with cellular debris. The crystals contained calcium and phosphorus. Phagy and stagnation related to pockets of inefficient secretory activity have been previously found to be features of the parotid of ferret. Thus, possibly persistent degradation of redundant cellular material, particularly secretory granules, in phagosomes results in accumulation of calcium and leads to calcified microliths, whereas consolidation of stagnant debris extracellularly does not involve such accumulation and leads to non-calcified or mixed microliths.

Microenvironmental adaptations in the parotid of ferret investigated by electron microscopy

Previous histochemical investigations suggested that the microenvironment in the parotid of ferret would foster microlithiasis because of a combination of pockets of inefficient secretion, brisk phagy and secretory material rich in calcium. We have undertaken the present ultrastructural investigation in an attempt to provide corroborative evidence. Parotids from four normal ferrets were examined by electron microscopy. Phagosomes in which there was cellular debris and occasionally secretory granules were present in acinar cells, which indicates crinophagy, and residual bodies were present in ductal cells. Atrophic parenchymal cells, degenerate parenchymal cells and apoptotic bodies were present. Cellular debris and secretory material were present in lumina, which indicates stagnation. The results indicate that removal of redundant secretory material and cells and low flow of saliva are features of the parotid of ferret and support the concept of pockets of inefficient secretory activity.

Mast Cells in the Salivary Glands and Tongue of the Ferret: Demonstration and Some Histochemical Observations

Previous investigations failed to demonstrate mast cells in the alimentary tract and extraparietal glands of the ferret. It was decided therefore to test this and assess factors that may be of influence. Major salivary glands and tongues of mature ferrets, which had been fixed in formalin-calcium, were examined by means of light microscopical histochemistry. Staining of paraffin sections with techniques depending on basic dyes or esterolytic activity was carried out for conventional times with and without previous oxidation, hot acid hydrolysis, and trypsin and beta-glucuronidase digestion. Aldehyde fuchsin and high iron diamine consistently revealed the presence of few mast cells in interstitial stroma of salivary glands and lingual musculature, and in the lamina propria of lingual mucosa. Alcian blue at 0.5 M MgCl2 and safranin produced less consistent results, and even fewer metachromatic mast cells were detected. No staining of mast cells was obtained with the technique for naphthol AS-D chloroacetate esterase. Pretreatment did not increase the numbers and/or staining reactions of mast cells. The results refute the previous misconception and suggest that ferret is a species with a low incidence of mast cells largely expressing a connective-tissue phenotype.

Histological and histochemical observations on salivary microliths in ferret

The fortuitous observation of salivary microliths in ferret was pursued in the present investigation. Major salivary glands obtained post-mortem from mature ferrets of either sex were examined with the use of histology and light microscopical histochemistry for calcium, protein, amino acids, mucosubstances and hydrolytic enzymes. Microliths were detected in most parotids, but were absent from submandibular and sublingual glands. The microliths were usually seen in lumens, and occasionally in parenchyma and interstices. They were variably stained for calcium, tryptophan, and neutral and acidic mucosubstances, similarly to acinar or ductal secretory granules. Unlike secretory granules, microliths showed autofluorescence, high levels of tyrosine and a low concentration of -SS- groups. Acid phosphatase and beta-glucuronidase reaction surrounded non-luminal microliths. The present data establish ferret as a new model for the investigation of salivary microliths and do not support the notion of microliths being almost absent from the parotid. Probably there is secretory inactivity in ferret parotid and this fosters the formation and accumulation of microliths containing calcium and disintegrated secretory material.