Lipid composition of the matrix of human submandibular salivary gland stones

Microarchitecture and Crystalline Composition: A Comprehensive Exploration of Salivary Gland Stones

OBJECTIVE

To investigate the microarchitecture and crystalline composition of sialoliths and to explore their formation mechanisms.

METHODS

Sixty-six sialolith samples (51 from the submandibular glands and 15 from the parotid glands) were retrospectively collected. Their diameter and quality were measured. Micro-computed tomography, scanning electron microscopy, and polycrystalline X-ray diffractometer (XRD) were utilized to determine their microstructure and crystalline composition.

RESULTS

Stone diameter and weight averaged at 9.6 mm and 0.31 g, respectively. Submandibular stones showed larger size and weight than parotid stones. Microstructurally, the main stones were concentric (n = 51) or mixed (n = 15). Most concentric stones occurred at submandibular glands, while 80% of the mixed stones were parotid stones. Stone surface exhibited three microscopic structures: lamellar, grape-like, and porous, indicating their differences in mineralization process and composition. XRD revealed that all stones contained hydroxyapatite, with 57 containing whitlockite. Concentration of hydroxyapatite in concentric stones was significantly higher than that in mixed stones (p = 0.036) and correlated positively with stone diameter (p = 0.001). The microstructure and crystalline composition of multiple and recurrent stones were similar to that of single stones.

CONCLUSION

Sialoliths display pronounced diversity in microarchitecture and crystalline composition, reflecting the differences in mineralization process and local microenvironments among stones.

The Translational Role of MUC8 in Salivary Glands: A Potential Biomarker for Salivary Stone Disease?

Mucin (MUC) 8 has been shown to play an important role in respiratory disease and inflammatory responses. In the present study, we investigated the question of whether MUC8 is also produced and secreted by salivary glands and whether it may also play a role in the oral cavity in the context of inflammatory processes or in the context of salivary stone formation. Tissue samples from parotid and submandibular glands of body donors (n = 6, age range 63–88 years), as well as surgically removed salivary stones from patients (n = 38, age range 48–72 years) with parotid and submandibular stone disease were immunohistochemically analyzed targeting MUC8 and TNFα. The presence of MUC8 in salivary stones was additionally analyzed by dot blot analyses. Moreover, saliva samples from patients (n = 10, age range 51–72 years), who had a salivary stone of the submandibular gland on one side were compared with saliva samples from the other “healthy” side, which did not have a salivary stone, by ELISA. Positive MUC8 was detectable in the inter- and intralobular excretory ducts of both glands (parotid and submandibular). The glandular acini showed no reactivity. TNFα revealed comparable reactivity to MUC8 in the glandular excretory ducts and also did not react in glandular acini. Salivary stones demonstrated a characteristic distribution pattern of MUC8 that differed between parotid and submandibular salivary stones. The mean MUC8 concentration was 71.06 ng/mL in female and 33.21 ng/mL in male subjects (p = 0.156). Saliva from the side with salivary calculi contained significantly (15-fold) higher MUC8 concentration levels than saliva from the healthy side (p = 0.0005). MUC8 concentration in salivary stones varied from 4.59 ng/mL to 202.83 ng/mL. In females, the MUC8 concentration in salivary stones was significantly (2.3-fold) higher, with an average of 82.84 ng/mL compared to 25.27 ng/mL in male patients (p = 0.034). MUC8 is secreted in the excretory duct system of salivary glands and released into saliva. Importantly, MUC8 salivary concentrations vary greatly between individuals. In addition, the MUC8 concentration is gender-dependent (♀ > ♂). In the context of salivary stone diseases, MUC8 is highly secreted in saliva. The findings support a role for MUC8 in the context of inflammatory events and salivary stone formation. The findings allow conclusions on a gender-dependent component of MUC8.

Classification of submandibular salivary stones based on ultrastructural studies

INTRODUCTION

Sialolithiasis remains a clinical problem with unclear etiopathogenesis, lack of prevention methods, and only surgical treatment.

MATERIALS AND METHODS

An ultrastructure examination of submandibular sialoliths obtained from patients with chronic sialolithiasis was conducted using a scanning electron microscope and X-ray photoelectron spectroscopy.

RESULTS

Based on the results, we divided sialoliths into three types: calcified (CAL), organic/lipid (LIP), and mixed (MIX). The core structure of the CAL and MIX is very similar. The core of the LIP has a prevalence of organic components. The intermediate layers' structure of the CAL is different from LIP and MIX. In LIP and MIX, the organic component begins to increase in intermediate layers rapidly. The structure of the superficial layers for all types of sialoliths is similar.

CONCLUSIONS

We introduced a new classification of the submandibular salivary gland stones. Based on the results, it can be said that sialoliths type CAL and LIP have their separate path of origin and development, while MIX is formed as CAL stone, and the further pathway of their growth passes as LIP stones. Organic components were much more than inorganic in all layers of salivary gland stones, which highly prevents their dissolution in the patient's salivary gland duct.

Intraductal Lithotripsy in Sialolithiasis Using the Calculase III™ Ho:YAG Laser: First Experiences

BACKGROUND AND OBJECTIVES

To report the first experiences with a newly available Ho:YAG laser system for the treatment of salivary stones.

STUDY DESIGN/MATERIALS AND METHODS

A retrospective study in a tertiary referral center was conducted. Patients diagnosed with sialolithiasis were treated in Erlangen using the Calculase III™ Ho:YAG laser (Karl Storz, Tuttlingen, Germany). Preset parameters had a frequency of 4 Hz and energy of 0.8-1.2 J, resulting in 3.2-4.8 W. Following total fragmentation, one to two serial sialendoscopies were performed to achieve complete fragment clearance.

RESULTS

A total of 55 stones in 49 patients were treated; 17 stones in 15 submandibular glands and 38 in 34 parotids. In total, 61 laser lithotripsies (range 1-3 per stone) were performed using various modes (long, short, and burst) and with preset parameters of 4 Hz and energy of 0.8-1.2 J, resulting in effective power of 3.2-4.8 W. Complete fragmentation was achieved in all the accessible stones. Sialendoscopes, fibers, or the mode used had no significant influence on success rates. A multimodal therapy concept was employed to treat stones in 12.24% of the cases; 95.92% of the patients were ultimately stone-free, and all became symptom-free. All glands were preserved.

CONCLUSIONS

The new Calculase III™ Ho:YAG laser was effective in the treatment of sialolithiasis with no increased risk of complications in the patients or damage to the sialendoscopes. Clinical factors such as the type of gland involved, or the location and size of stones had a greater impact on success rates than the technical or preset parameters. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

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.

Association between cholelithiasis and sialolithiasis: Two longitudinal follow-up studies

This study aimed to evaluate the association between cholelithiasis and sialolithiasis using a national sample cohort in Korea.The Korean National Health Insurance Service-National Sample Cohort (patients ≥20 years old) was collected from 2002 to 2013. In study I, we extracted cholelithiasis patients (n = 21,170) and 1:4 matched control I subjects (n = 84,680) and analyzed the occurrence of sialolithiasis. In study II, we extracted sialolithiasis patients (n = 761) and 1:4 matched control II subjects (n = 3044) and analyzed the occurrence of cholelithiasis. Hazard ratios (HRs) were determined using the stratified Cox proportional hazard model.The HR for sialolithiasis was 1.49 (95% CI = 0.88-2.52) in the cholelithiasis group (P = .14), and the HR for cholelithiasis was 1.18 (95% CI = 0.53-2.59) in the sialolithiasis group (P = .69).We did not find an association between cholelithiasis and sialolithiasis.

Mineralization of Sialoliths Investigated by Ex Vivo and In Vivo X-ray Computed Tomography

The fraction of organic matter present affects the fragmentation behavior of sialoliths; thus, pretherapeutic information on the degree of mineralization is relevant for a correct selection of lithotripsy procedures. This work proposes a methodology for in vivo characterization of salivary calculi in the pretherapeutic context. Sialoliths were characterized in detail by X-ray computed microtomography (μCT) in combination with atomic emission spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Correlative analysis of the same specimens was performed by in vivo and ex vivo helical computed tomography (HCT) and ex vivo μCT. The mineral matter in the sialoliths consisted essentially of apatite (89 vol%) and whitlockite (11 vol%) with average density of 1.8 g/cm3. In hydrated conditions, the mineral mass prevailed with 53 ± 13 wt%, whereas the organic matter, with a density of 1.2 g/cm3, occupied 65 ± 10% of the sialoliths' volume. A quantitative relation between sialoliths mineral density and X-ray attenuation is proposed for both HCT and μCT.

Local Response of Sialoliths to Lithotripsy: Cues on Fragmentation Outcome

Lithotripsy methods show relatively low efficiency in the fragmentation of sialoliths compared with the success rates achieved in the destruction of renal calculi. However, the information available on the mechanical behavior of sialoliths is limited and their apparently tougher response is not fully understood. This work evaluates the hardness and Young's modulus of sialoliths at different scales and analyzes specific damage patterns induced in these calcified structures by ultrasonic vibrations, pneumoballistic impacts, shock waves, and laser ablation. A clear correlation between local mechanical properties and ultrastructure/chemistry has been established: sialoliths are composite materials consisting of hard and soft components of mineralized and organic nature, respectively. Ultrasonic and pneumoballistic reverberations damage preferentially highly mineralized regions, leaving relatively unaffected the surrounding organic matter. In contrast, shock waves leach the organic component and lead to erosion of the overall structure. Laser ablation destroys homogeneously the irradiated zones regardless of the mineralized/organic nature of the underlying ultrastructure; however, damage is less extensive than with mechanical methods. Overall, the present results show that composition and internal structure are key features behind sialoliths' comminution behavior and that the organic matter contributes to reduce the therapeutic efficiency of lithotripsy methods.

Characterization of a submandibular gland sialolith: micromorphology, crystalline structure, and chemical compositions

OBJECTIVE

The aim of this study was to understand the mechanism of mineralization and growth of a sialolith by analyzing its micromorphology, crystalline structure, and chemical compositions.

STUDY DESIGN

A sialolith was removed along with submandibular salivary gland from a patient. After cross-cutting and polishing the sialolith, its morphology, chemical compositions, crystalline structure, and chemical states were analyzed by using optical camera, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffractometer, Fourier transform infrared spectrophotometer, and transmittance electron microscopy.

RESULTS

The sialolith had a core composed of organic material, such as lipid compounds, and the surrounding mineralized shell structure mostly consisted of hydroxyapatite. In the transition zone between the organic core and mineralized shell layers, inorganic layers were arranged alternately with organic layers. Congregated globular structures were calcified with hydroxyapatite and whitlockite crystallites. Analysis of crystalline structures and chemical compositions suggested that calcium phosphate minerals containing magnesium, such as whitlockite, were developed in the initial stage and gradually transformed into crystallites composed of hydroxyapatite during the growth of crystallites.

CONCLUSIONS

Sialolith with an organic core grew as inorganic materials were deposited and calcified in alternate layers. The mineralization process might include the initial whitlockite development and successive transformation into more stable hydroxyapatite.

Lithogenesis: induction of renal calcifications by nanobacteria

Nanobacteria have been isolated from kidney stones and it has been suggested that they may act as a nucleus for the initiation of the renal stones. In the present study, we examine their role in biocrystallization and their in vivo effects on kidney pathology. Calcium oxalate monohydrate (COM) assay was carried out in the presence of nanobacteria to study biocrystallization. Wistar rats were given an intravenous injection of nanobacteria and the kidneys were examined for pathological changes. The COM assay showed accelerated biocrystallization of (14)C-oxalate in the presence of nanobacteria, indicating them to be efficient candidates for biomineralization. Histopathological studies revealed bacteria induced renal tubular calcifications and various manifestations of infection. Our studies confirm that nanobacteria may be involved in the pathogenesis of renal tubular calcification.

Presence of lipids in urine, crystals and stones: implications for the formation of kidney stones

BACKGROUND

Cell membranes and their lipids play critical roles in calcification. Specific membrane phospholipids promote the formation of calcium phosphate and become a part of the organic matrix of growing calcification. We propose that membrane lipids also promote the formation of calcium oxalate (CaOx) and calcium phosphate (CaP) containing kidney stones, and become a part of their stone matrix.

METHODS

Human urine, crystals of CaOx and CaP produced in the urine of healthy individuals, and urinary stones containing struvite, uric acid, CaOx and CaP crystals for the presence of membrane lipids were analyzed. Crystallization of CaOx monohydrate at Langmuir monolayers of dipalmitoylphosphatidylglycerol (DPPG), dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylserine (DPPS), dioleoylphosphatidylglycerol (DOPG), palmitoyloleoylphosphatidylglycerol (POPG) and dimyristoylphosphatidylglycerol (DMPG) was investigated to directly demonstrate that phospholipid assemblies can catalyze CaOx nucleation.

RESULTS

Urine as well as CaOx and CaP crystals made in the urine and various types of urinary stones investigated contained some lipids. Urine of both CaOx and uric acid stone formers contained significantly more cholesterol, cholesterol ester and triglycerides than urine of healthy subjects. However, urine of CaOx stone formers contained more acidic phospholipids. The organic matrix of calcific stones contained significantly more acidic and complexed phospholipids than uric acid and struvite stones. For each Langmuir monolayer precipitation was heterogeneous and selective with respect to the orientation and morphology of the CaOx crystals. Crystals were predominantly monohydrate, and most often grew singly with the calcium rich (10-1) face toward the monolayer. The number of crystals/mm2 decreased in the order DPPG> DPPC and was inversely proportional to surface pressure and mean molecular area/molecule.

CONCLUSIONS

Stone forming conditions in the kidneys greatly impact their epithelial cells producing significant differences in the urinary lipids between healthy and stone forming individuals. Altered membrane lipids promote face selective nucleation and retention of calcium oxalate crystals, and in the process become a part of the growing crystals and stones.

Analytical ultrastructural investigation of microliths in salivary glands of cat

Microliths in Araldite-embedded pieces of submandibular and sublingual glands of cat were stained in semithin sections by Methylene Blue and Azure II followed by Basic Fuchsin, and were examined in ultrathin sections by electron-microscopical X-ray microanalysis. Calcium and phosphorus were detected in substantial aggregates of crystals that were stained by Basic Fuchsin and appeared to be hydroxyapatite, but were not detected in granular material that was stained by Methylene Blue and Azure II and appeared to be organic. The polychromatic stain thus appears to be a useful indicator of calcified material. The majority of microliths in acini contained substantial aggregates of crystals, whereas the majority of those in ducts did not. This corresponds to the distribution of the glandular calcium, and suggests that microliths are variously enriched with calcium according to its local level.

The presence of microcalculi in normal human submandibular and parotid salivary glands

A search for microcalculi in 10 submandibular and 10 parotid glands obtained from autopsies revealed them in 8 submandibular glands in all decades from the third to the seventh, and in one parotid gland in the fourth decade. They were found in serous acinar cells, striated ductal cells, lumina and interstitium. They may form in autophagosomes in parenchymal cells and usually pass into lumina to be expelled in the saliva.

Presence of lipids in urinary stones: results of preliminary studies

The presence of lipids in urinary stones was determined by histochemical and biochemical methods. When crystals of calcium oxalate, made by mixing calcium chloride and potassium oxalate solutions and sections of human calcium oxalate urinary stones, were exposed to osmium vapors, there was no staining of the pure crystals whereas the stone sections were stained. De-paraffinized sections of demineralized calcium oxalate stones showed positive sudanophilia on staining with Sudan black B. Both these experiments indicate the presence of lipids in calcium oxalate stones. Lipids were extracted from uric acid, struvite, and calcium oxalate stones using standard techniques. Phospholipids were separated by one-dimensional thin layer chromatography. All the stones studied contained lipids. In calcium oxalate stones they accounted for 10.15% of the matrix. Calcium oxalate and struvite stones contained more phospholipids than uric acid stones. Cardiolipin, sphingomyelin, phosphatidyl choline, phosphatidyl inositol, phosphatidyl ethanolamine, phosphatidyl serine, and phosphatidyl glycerol were identified in lipid extracts. Demineralization by ethylenediaminetetra-acetate (EDTA) treatment increased lipid output from calcium oxalate stones by 15.5%.

Ultrastructural and histochemical observations on microcalculi in chronic submandibular sialadenitis

A search for microcalculi was made in 14 cases of chronic submandibular sialadenitis. Microcalculi were found in all cases. They were within serous acinar cells and ductal cells, within lumina, and interstitially. They were stained variably by periodic-acid/Schiff and Alcian Blue at pH 2.5. Ultrastructural analytical examination showed them to consist of crystals containing calcium and phosphorus. The observations support the possibility that microcalculi form in autophagosomes, enter lumina and occasionally become impacted to produce sialolithiasis and sialadenitis.

Ultrastructural and histochemical observations on intracellular and luminal microcalculi in the feline sublingual salivary gland

As the genesis of salivary calculi in man has not been established, the fortuitous observation of microcalculi in sublingual glands of cats prompted this study. Microcalculi were seen occasionally within acinar cells and lumina and macrophages, and rarely interstitially. Microcalculi were stained with the periodic-acid/Schiff technique, and acid-phosphatase activity was associated with intracellular microcalculi. Intracellular microcalculi were seen ultrastructurally in acinar cells in membrane-bound vacuoles that also contained debris and sometimes what appeared to be secretory material. X-ray microanalysis showed the microcalculi to consist of crystals containing calcium and phosphorus. The observations suggest that the microcalculi form within autophagosomes in acinar cells by a precipitation of calcium and phosphorus present in degenerate material, and that the microcalculi eventually enter lumina, where they may be discharged in the saliva or retained and enlarge.

Lipids of developing dental plaque in caries-resistant and caries-susceptible adult people

Dental plaque maturation in both caries-resistant (CR) and caries-susceptible (CS) subjects was accompanied by a decrease in total lipid content but was more pronounced with CR subjects; their plaque after 72 h contained 44.6 per cent less lipids than that of CS. At each stage of maturation, differences were also found in the proportion of lipid classes. In 24 h-plaque, the lipids of CR-group, although containing amounts of glycolipids and phospholipids similar to those of CS, contained 1.6 times less neutral lipids. The 48 h-plaque of CS subjects showed 2.5 times more neutral lipids, 1.2 times more phospholipids and 1.4 times less glycolipids. The 72 h-CR plaque contained 1.9 times less neutral lipids, 1.6 times more glycolipids and 1.3 times more phospholipids than CS-plaque. Among the neutral lipids in both groups, the changes with maturation were associated with decrease in free fatty acids and increase in triglycerides, cholesterol and cholesteryl esters. Phospholipids of CR-plaque contained less phosphatidylcholine and more phosphatidylethanolamine than CS-plaque. With plaque maturation both groups showed decreases in the glycolipids characteristic of saliva and an increase in the content of bacterial type of glycolipids. Plaque maturation is evidently accompanied by dynamic changes in lipids reflecting a shift from salivary to bacterial contribution.

Lipids of supragingival calculus

The matrix of supragingival calculus constitutes 15.7% of the calculus dry weight and contains 54.9% protein and 10.2% lipids. Of the total lipids, 61.8% are represented by neutral lipids, 28% by glycolipids, and 10.2% by phospholipids. The neutral lipids exhibit a high content of free fatty acids (63.9%) and triglycerides (15.8%). The glycolipids are comprised of simple glycosphingolipids (17.2%), mainly lactosyl- and glucosylceramides, and of neutral and sulfated glyceroglucolipids (82.8%). The phospholipids contain large quantities of phosphatidylethanolamine (34.2%) and diphosphatidylglycerol (25.5%). Comparison with salivary and submandibular stone lipids indicates that both saliva and bacteria contribute to the lipid content of supragingival calculus.

Lipid composition of human parotid salivary gland stones

The parotid gland stone matrix constitutes 20.2% of the stone dry weight and contains 8.5% of lipids. Of the total lipids, 74% are represented by neutral lipids, 17% by glycolipids, and 9% by phospholipids. The neutral lipids exhibit a high content of free fatty acids (52.7%) and cholesteryl esters (31.1%). The glycolipids are composed of simple glycosphingolipids (7.1%), and of neutral and sulfated glyceroglucolipids (92.9%). Phosphatidylethanolamine and diphosphatidylglycerol are the principal constituents of the phospholipid fraction.