Lipids in human salivary secretions and salivary calculus

Inhibition of platelet-activating factor (PAF)-induced platelet aggregation by fatty acids from human saliva

Experiments were undertaken to identify the nature of a previously identified inhibitor of PAF-induced platelet aggregation (PA) in human saliva. Human saliva fractionated by preparative thin layer chromatography (TLC) yielded a fraction that co-migrated with fatty acids (FAs) and inhibited PAF-induced aggregation of platelets. Synthetic FAs tested for their capacities to inhibit 0.1 nM PAF-induced PA showed that only the cis-unsaturated compounds were inhibitory with activities of some of the polyunsaturated FAs (PUFA) reaching almost 100% at 20 μM. Eicosapentanoic acid (EPA) and 8,11,14-eicosatrienoic acid also deaggregated the PAF-induced aggregates. With the exception of oleic acid (OLA), cis-monounsaturated FAs, and elaidic acid, the trans isomer of OLA, were poor inhibitors. In a direct comparison with other platelet agonists, ADP, thrombin, and ionophore A23187, the active saliva fraction and selected individual (FA) inhibited, to greater or lesser extent, PA induced by each of the agonists. EPA, OLA, linoleic acid (LNA), and the active saliva fraction were potent inhibitors of ADP-induced PA, EPA completely inhibited thrombin-induced PA and the saliva fraction showed only weak - moderate inhibitory activity to both thrombin- and ionophore A23187-induced PA. Other reports of endogenous PAF inhibitors in mammalian tissues are compared to the present results. PAF can trigger and amplify inflammatory cascades suggesting a possible modulation role for cis-unsaturated FAs in some diseases.

Quantitative and qualitative analyses of human salivary NEFA with gas-chromatography and mass spectrometry

Salivary non-esterified fatty acids (NEFA) are proposed to play a role in oral health, oral fat detection, and they may hold diagnostic and prognostic potential. Yet, little is known about the array and concentrations of NEFA in saliva. The aim of the study was to conduct qualitative and quantitative analyses of salivary NEFA in healthy humans and to present a new, efficient protocol to perform such analyses. Resting saliva samples from fifteen participants were collected. The salivary lipids were extracted using a modified Folch extraction. The NEFA in the extracted lipids were selectively subjected to pentafluorobenzyl bromide (PFB) derivatization and qualitatively and quantitatively analyzed using gas chromatography-mass spectrometry (GC-MS). A total of 16 NEFA were identified in resting saliva. The four major NEFA were palmitic, linoleic, oleic, and stearic acids. Their concentrations ranged from 2 to 9 μM. This is the first study to characterize individual human salivary NEFA and their respective concentrations. The method used in the study is sensitive, precise, and accurate. It is specific to fatty acids in non-esterified form and hence enables analysis of NEFA without their separation from other lipid classes. Thus, it saves time, reagents and prevents loss of sample. These properties make it suitable for large scale analysis of salivary NEFA.

Serous cells in the parotid glands of two species of tamarins: polarized secretory granules

The parotid glands of two species of tamarins were examined by electron microscopy. Endpiece cells are typical in appearance, with an extensive rough endoplasmic reticulum, prominent Golgi apparatuses, and numerous serous granules. In the saddleback tamarin, the secretory granules contain a dense spherule pressed against the inner aspect of the limiting membrane, leading to a surface bulge. During the course of merocrine secretion (a form of exocytosis), such morphologically polarized granules approach the luminal plasma membranes with the bulge in the vanguard. It is these protuberances that fuse with the plasmalemma. In contrast, although serous granules in the cotton top tamarin contain a spherule, they lack surface bulges and their docking on luminal membranes seems to be a random event with respect to their surface morphology. Moreover, certain other types of cells in a taxonomically wide spectrum of species have granules with a less obvious structural polarity, as well as cells whose granules lack morphological polarity but have a functional polarity that comes into play during exocytosis of such secretory granules.

Phospholipid Profiles in the Salivary Glands of Rats of Different Ages

It has been reported that diabetes and Sjögren's syndrome patients exhibit variations in the amount of salivation and in the lipid components in saliva and salivary glands. We examined whether lipid compositions, especially phospholipid ones in the salivary glands of rats varied with aging. We analyzed phospholipid and fatty acid compositions in the salivary glands of young (5 to 6 weeks), adult (20 weeks), and old (50 weeks) rats and biochemical components in their blood. The aging (adult and old) rats had higher triacylglycerol, total lipid, total cholesterol and glucose contents in the plasma than the young one. The aging ones also had higher total lipid contents in the major salivary glands (parotid, submandibular and sublingual glands). They had higher wet weights of the major salivary glands and epididymal fat pads than the young ones, but had lower ratios of the major salivary glands to body weight. All of them had high phospholipid contents in the parotid and submandibular glands as compared to sublingual gland, but the aging ones had lower percentage of phospholipid contents of all salivary glands. Phosphatidylcholine and phosphatidylethanolamine were predominant among the phospholipids in the major salivary glands, and little difference was observed in phospholipid composition among the three groups. Palmitic and stearic acids (saturated acids), and linoleic, oleic and arachidonic acids (unsaturated acids) were major components of fatty acids of phospholipids in the major salivary glands. The aging ones had higher linoleic and lower arachidonic acid contents in the glands than the young one. In summary, the aging rats had higher total lipid contents than the young ones and had lower phospholipid contents of the major salivary glands. The n-6 fatty acid contents differed between aging and young ones. The results suggest that phospholipids in the major salivary glands change with the development of rat.

Fatty acid profile of human saliva: a possible indicator of dietary fat intake

OBJECTIVE

Since conventional food questionnaires are not precise in assessing the dietary fatty acids, the purpose of this study was to determine the relationship between the salivary fatty acid profile and the alimentary habits of two different groups in an attempt to develop a more reliable way to determine the lipidic intake.

DESIGN

Twenty adults of both sexes, with mixed (M) or vegetarian (V) diets were studied. Data about the fat intake were obtained by means of a Food Frequency Questionnaire (FFQ) and the presence of the main salivary fatty acids was determined by gas chromatography.

RESULTS

A greater salivary concentration of alpha-linolenic acid (18:3 n-3) (2.82) was found in V than in M subjects (1.65) (p = 0.001), whilst arachidonic acid (20:4 n-6) was lower in V (3.93) than in M (4.52) (p = 0.045). The same difference regarding arachidonic acid was observed in the dietary fatty acid intake, also showing a significant correlation between its dietary and salivary levels in vegetarian subjects.

CONCLUSIONS

These results show that salivary arachidonic acid, relevant for their eicosanoid production related to the tumourigenesis process and cardiovascular diseases, is influenced by dietary fats.

Supragingival calculus: formation and control

Dental calculus is composed of inorganic components and organic matrix. Brushite, dicalcium phosphate dihydrate, octacalcium phosphate, hydroxyapatite, and whitlockite form the mineral part of dental calculus. Salivary proteins selectively adsorb on the tooth surface to form an acquired pellicle. It is followed by the adherence of various oral micro-organisms. Fimbriae, flagella, and some other surface proteins are essential for microbial adherence. Microbial co-aggregation and co-adhesion enable some micro-organisms, which are incapable of adhering, to adhere to the pellicle-coated tooth surface. Once organisms attach to the tooth surface, new genes could be expressed so that mature dental plaque can form and biofilm bacteria assume increased resistance to antimicrobial agents. Supersaturation of saliva and plaque fluid with respect to calcium phosphates is the driving force for plaque mineralization. Both salivary flow rate and plaque pH appear to influence the saturation degree of calcium phosphates. Acidic phospholipids and specific proteolipids present in cell membranes play a key role in microbial mineralization. The roles of crystal growth inhibitors, promoters, and organic acids in calculus formation are discussed. Application of biofilm culture systems in plaque mineralization is concisely reviewed. Anti-calculus agents used--centering on triclosan plus polyvinyl methyl ether/maleic acid copolymer, pyrophosphate plus polyvinyl methyl ether/maleic acid copolymer, and zinc ion-in commercial dentifrices are also discussed in this paper.

The effect of essential fatty acid deficiency on the fatty acid composition of different salivary glands and saliva in rats

The main purpose was to compare the changes in fatty acid composition of lipids induced by essential fatty acid (EFA) deficiency in the rat submandibular, parotid and sublingual glands. Three groups of rats were fed for 28 weeks (1 week gestation, 3 weeks lactation and 24 weeks thereafter) diets containing 7% hydrogenated coconut oil (HCO) (EFA-deficient in both n-6 and n-3), 7% soybean oil (SBO) (control) and 7% safflower oil (SFO) (deficient in n-3). Rats were killed and salivary glands were dissected out. Lipids were extracted and the fatty acid composition of total lipids and phospholipids was determined by gas chromatography-mass spectrometry. The fatty-acid compositional changes indicative of an EFA deficiency, such as decreases in the levels of 18:2 n-6, along with an accumulation of 20:3 n-9, were generally observed in all the salivary glands of rats fed 7% HCO diet. In the submandibular glands, the proportions of 16:1, 18:1 n-9 and 18:1 n-7 were also higher in the HCO-fed group than in the other two groups. There were some differences in the fatty acid composition of the three glands. Total lipids of parotid gland had higher levels of 12:0 and 18:1 n-9 as compared to the other two glands. The levels of 18:0, 20:3 n-9, 20:3 n-6 and 20:4 n-6 were, however, lower in the parotid gland as compared with the other glands. In total phospholipids of rats fed SBO- and SFO-containing diets, the sublingual gland had lower levels of 18:2 n-6 and higher levels of 20:4 n-6 than the parotid or the submandibular. These differences in fatty acid composition may be related to possible differences in chain elongation/desaturation. The changes in fatty acid composition were also reflected in total lipids of plasma, liver and whole saliva of rats fed the various diets. A number of fatty acids were identified in saliva by gas chromatography-mass spectrometry.

Lipids in human saliva

A simple and reproducible method of determining the quality and quantity of neutral lipids in human saliva was tested. Parotid, submandibular and whole stimulated saliva were collected from 10 healthy adults. The lipids were extracted by the Folch method. A special method for extraction of glycolipids was also tested but gave no additional recovery. Thin-layer chromatography was used for separating the different lipid classes. The concentrations of total lipids in parotid, submandibular and whole stimulated saliva were 0.2, 0.9 and 1.3 mg/dl, respectively. Cholesteryl esters, cholesterol, triglycerides, diglycerides, monoglycerides and free fatty acids accounted for 96-99 percent of the total salivary lipids. Thus, polar lipids such as phospholipids contributed only a minor fraction, indicating that the lipids are not primarily of membrane origin. Ultracentrifugation of saliva samples at d = 1.21 g ml(-1) showed that the salivary lipids did not float like blood plasma lipoproteins. Therefore, they must be in a different state of aggregation from lipids in blood or lymph. No significant lipase activity of the type that acts on plasma lipoproteins was found in parotid or submandibular saliva. The content of free fatty acids and partial glycerides was high.

Sialochemistry in Sjögren's syndrome: a review

Sjögren's syndrome (SS) is an autoimmune exocrinopathy. The salivary glands are the site of activated T- and B-lymphocytes, along with gradual parenchymal destruction, diminished flow and altered composition of the secretory product. At present, sialochemistry has achieved no significance for the evaluation of SS patient. However, the number of sialochemical publications is steadily growing. This study review current sialochemical findings in patients with SS and relate the observations to the present concept of diagnosis, pathogenesis and prognosis of SS. An ideal combination of the collection of low-stimulated pure secretion, measurements of absolute flow-rates, and biopsy from the same glands seem to be unobtainable in SS patients. But two procedures may be appropriate: stimulated parotid secretion combined with parotid biopsies, or absorbance of low-stimulated labila saliva combined with labial gland biopsy. Sufficient data on disease-specific alterations in salivary composition in SS are still lacking. However, detection of specific changes in protein synthesis or in glycosylation as well as the detection of inflammatory cell products should be possible with the use of sensitive biochemical assays.

Structural studies of human saliva

Samples of mixed saliva and of parotid and sublingual/submandibular saliva fractions from four donors were subjected to instantaneous solidification in liquid nitrogen followed by sectioning in a microtome/cryostat. The sections were stained with hematoxylin-eosin, periodic acid-Schiff, Alcian blue, Oil-red-O, or Sudan Black B and then examined at the light-microscopic level. In all the sectioned samples several previously never described features were observed, the most pronounced of which were a loose overall network structure and collections of lipoid droplets often in a loose arrangement. In the mixed saliva sample sections many of the microorganism-like structures were observed in large bunches associated with epithelial cells and densely staining saliva components. The present method was tested in a series of experiments for possible errors.

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.

An enzyme histochemical study of human salivary duct calculi

An investigation was undertaken to study the distribution of enzymes associated with submandibular gland salivary calculi. Ten calculi were freeze-sectioned and incubated for acid and alkaline phosphatases and for lactate, succinate and maleate dehydrogenases. All calculi were partly covered by a 50-210 micrometers wide zone of organic material consisting of connective tissue and metaplastic squamous epithelium facing the mineralized calculus, or of a structureless substance attached to the mineralized calculus. The epithelium showed an intense staining reaction for acid phosphatase and lactate dehydrogenase and a moderate reaction for succinate dehydrogenase throughout all levels of the epithelium. The structureless peripheral zone exhibited a moderate activity of acid phosphatase and succinate dehydrogenase located to an area close to the mineralized matrix. Also alkaline phosphatase and lactate dehydrogenase were found in a special pattern in the structureless zone. Sodium fluoride and sodium vanadate added to the incubation medium inhibited acid phosphatase activity whereas cupric chloride only lowered the staining reaction. Enzyme activity was found only within the peripheral zone of organic material with one exception. The results suggest that the calcification process of salivary calculi is not a passive calcification of necrotic material or mucin but rather an active process promoted by enzymes in the surrounding organic substances.

Association of lipids with proteins and glycoproteins in human saliva

The distribution of lipids in the fractions of parotid and submandibular saliva following Bio-Gel A-50 column chromatography was measured. Over 50% of the total lipids of submandibular saliva was found in the fraction which contained mainly the high-molecular-weight glycoprotein. This fraction also contained most of the glycolipids, free fatty acids, phospholipids, and cholesterol. In the parotid saliva, the fraction containing the basic glycoprotein (the major glycoprotein fraction of parotid saliva) contained 35% of the total saliva lipids and was enriched in phospholipids ana cholesterol esters.

Lipid composition of human labial salivary gland secretions

Extraction of the dialysed and lyophilized labial saliva with chloroform/methanol yielded 423.8 +/- 73.0 micrograms of lipids/ml of saliva, a level 4-5 times higher than in the major salivary glands. Of the total lipids, 32.4 per cent were represented by neutral lipids, 44.6 per cent by glycolipids and 23.0 per cent by phospholipids. Neutral lipids had a high content of free fatty acids (43.8 per cent), cholesteryl esters (26.9 per cent) and triglycerides (15.4 per cent). The glycolipids consisted mainly of neutral (74.6 per cent) and sulphated (25.4 per cent) glyceroglucolipids, whereas phosphatidylethanolamine, phosphatidylcholine, sphingomyelin and phosphatidylserine accounted for 54.7 per cent of the total phospholipids.

Lipid composition of submandibular saliva from normal and cystic fibrosis individuals

The submandibular saliva of patients with cystic fibrosis was found to contain about 66% more lipids/100 ml of saliva than that of normal individuals and exhibited elevated levels of neutral lipids, phospholipids, and glycolipids. No significant differences were noted in the proportions of individual neutral lipid and phospholipid components present in both types of samples. The glycolipids of normal saliva consisted entirely of glyceroglucolipids, whereas those of cystic fibrosis saliva, in addition to glyceroglucolipids, also contained small amounts of glycosphingolipids. These quantitative and qualitative differences may affect the physicochemical properties of the secretion.

Lipid composition of the matrix of human submandibular salivary gland stones

The lyophilized stone matrix, prepared by exhaustive dialysis of pulverized stones against 10 per cent EDTA and water, yielded 9.6 +/- 0.9 mg per cent of lipids. Following fractionation of the lipid extract on silicic acid columns, 57 per cent of lipids were found in the neutral lipid fraction, 40 per cent in the glycolipid fraction and 3 per cent in the phospholipid fraction. Of the total neutral lipids, 77.3 per cent were represented by free fatty acids, 14.7 per cent by cholesterol, 4.1 per cent by triglycerides and 3.2 per cent by cholesterol esters. The glycolipid fraction was comprised of simple glycosphingolipids (11.3 per cent), mainly lactosyl- and glucosylceramides, and of neutral and sulphated glyceroglucolipids (88.7 per cent). The sulphated glyceroglucolipids consisted of tri- and tetraglucosyl glyceroglucolipids, whereas hexa- and octaglucosyl glyceroglucolipids were the predominant constituents of the neutral glyceroglucolipid fraction. The phospholipids exhibited a high content of sphingomyelin (22.3 per cent), phosphatidylcholine (12.1 per cent), phosphatidylethanolamine (11.4 per cent), phosphatidylserine (10.5 per cent) and lysophosphatidylcholine (13.3 per cent). The major fatty acids of the neutral lipid fraction were hexadecanoate, octadecanoate and octadecenoate. The glycolipids contained large quantities of hexadecanoate and tetracosanoate, while the hexadecanoate, octadecanoate and tetracosanoate were the principal fatty acids of the phospholipid fraction.

Ultrastructure of salivary calculi

Twenty-one submandibular salivary calculi from 19 patients were examined with the light and electron microscope. Adjacent to the peripheral parts of the calculi metaplastic squamous epithelium or connective tissue was seen in close contact to the mineralized matrix. Disintegrated cellular substances from these tissue components were in some cases found to condense in a peripherally located zone of the salivary calculi. The morphology of the examined salivary calculi varied extensively not only within each calculus but also from one calculus to another. High and low incidence of crystals gave rise to the lamellated pattern. In some cases the crystals were so abundant as to five a dense homogeneous appearance. In the central parts of the calculi spheroid bodies of very low electron density with a size ranging from 1 to 100micrometer were found in an amorphous matrix. The origin of these structures is discussed. In the peripheral parts of some calculi osmiophilic spherical bodies with an electron microscopical appearance similar to lipid granules as well as bacteria of cocci or coliform type were found. Degenerated bacteria might in some cases contribute in forming part of the peripheral organic matrix.

The relation of lipids to the mineral components in salivary calculi

Using lipid histochemical and microradiographic methods, the distribution of lipids and the inorganic component in different areas of salivary calculi was investigated. Two main groups of lipids were found, i.e. hydrophilic phospholipids and hydrophobic lipids. The hydrophilic phospholipids were shown to be composed mainly of phosphosphingosides and of the hydrophobic lipids cholesterol was demonstrated. Phosphosphingosides were localized in more or less lamellar zones as also in large homogeneous areas. In some cases the calculi were surrounded by a structureless non-mineralized zone exhibiting a strongly positive reaction for phosphosphingosides. Cholesterol was found in isolated band-formed areas. Phosphosphingosides and cholesterol were especially prevalent in areas showing a low or slight degree of mineralization. In areas showing a high degree of mineralization the corresponding lipids gave a weak or absent histochemical reaction. After EDTA-decalcification, however, an increase in the concentration of lipid was noticed in high mineralized areas, indicating a masking process. The influence of various factors on the presence and distribution of different lipids was discussed.

Fusion of the envelope of mucous droplets with the luminal plasma membrane in acinar cells of the cat submandibular gland

The release of mucus from acinar cells of the cat submandibular gland was examined by electron microscopy. The limiting membrane of mucous droplets fuses with the luminal plasma membrane to form a five-layered contact. This is converted to a three-layered membrane (unit membrane) by avulsion of the plasmalemma. Attenuation and rupture of this membranous barrier permits the contents of the mucous droplets to flow into the lumen.

Some chemical characteristics of human minor salivary gland secretions

The minor salivary glands contribute to the composition of whole saliva, but little information has been available about their chemical constituents. Pilocarpine-stimulated labial and palatine secretion from 4 human subjects was investigated by paper and disc electrophoresis, immunochemical analysis, and for content of carbohydrates, amino acids, lipids, hexuronic acids and sulphate. No significant differences were noted between the labial and palatine secretions by any of the methods employed. The minor gland secretions appeared to consist mainly of mucosubstances, possibly with blood group specificity. In addition, three water-soluble components with the characteristics of albumin, alpha-amylase and secretory IgA were seen. The minor gland secretions had an amino acid profile different from those of the major salivary glands and contained higher proportions of carbohydrate. Only one lipid component, with the characteristics of a polar lipid, was seen. Hexuronic acids were not detected in either secretion, whereas both contained sulphate. It would appear that the minor mucous glands contribute to the content of mucosubstances in whole saliva, whereas their content of water-soluble material is negligible in this respect.

Lipid and calculus matrix calcification in vitro

Lipid is necessary for calcification of a calculus matrix. Matrix was prepared by decalcification of dental calculus. The matrix calcified when it was exposed to a metastable calcium phosphate solution. After extraction with chloroform-methanol, the matrix lost the capacity to calcify. The lipid extract was calcifiable.