Biological rhythm of saliva ghrelin in humans

Background: We previously reported that ghrelin in saliva, orexigenic hormone that induces NPY release, was produced and released by salivary glands in humans. The purpose of this study was to investigate a possible circadian rhythm in saliva ghrelin concentration in human subjects as a function of time and meal. Saliva samples were collected at three-hour intervals throughout a 24-h period in 12 healthy volunteer males and ten healthy volunteer females who were provided with meals on a fixed schedule, and saliva collections were made within 15 minutes after each meal. Saliva ghrelin levels were measured by using a commercial radioimmunoassay (RIA) kit that uses ¹²⁵I-labeled bioactive ghrelin as a tracer and a rabbit polyclonal antibody raised against full-length octanoylated human ghrelin. Immunohistochemical analysis of salivary glands was also performed. The results of this investigation indicated the following. (1) The saliva ghrelin level was slightly higher in female subjects in comparison with male subjects. (2) Saliva ghrelin levels were elevated before each meal and fell to trough levels after eating. (3) Saliva ghrelin levels showed a circadian rhythm that rose throughout the day to a zenith at 0300, then dropped at 0600 - 0900. (4) Saliva ghrelin also weakly correlated with BMI. (5) Immunohistochemical analysis showed that ghrelin was localized in the striated and excretory ducts of salivary glands of human. The present work is the first report of the circadian rhythm of saliva ghrelin level in human subjects as a function of time and meal. Meal plays an important role in lowering saliva ghrelin concentration in humans. However, present data did not exclude whether the circadian changes in saliva ghrelin expression were regulated by the biological clock or by food intake.     

Nesfatin-1 and ghrelin levels in serum and saliva of epileptic patients: hormonal changes can have a major effect on seizure disorders

Nesfatin-1 and ghrelin are the two recently discovered peptide hormones involved in the control of appetite. Besides its main appetite-control function, ghrelin also has anticonvulsant effects, while nesfatin-1 causes depolarization in the paraventricular nucleus (PVN). The aims of this study, therefore, were to investigate: (i) whether there are differences in the concentrations of nesfatin-1 and ghrelin in saliva and serum samples between eplilepsy patients and normal controls and (ii) whether salivary glands produce nesfatin-1. The study included a total of 73 subjects: 8 patients who were newly diagnosed with primary generalized seizures and had recently started antiepileptic drug therapy; 21 who had primary generalized seizures and were continuing with established antiepileptic drug therapy; 24 who had partial seizures (simple: n = 12 or complex: n = 12) and were continuing with established antiepileptic drug therapy; and 20 controls. Salivary gland tissue samples were analyzed for nesfatin-1 expression by immunochemistry and ELISA. Saliva and serum ghrelin levels were measured by ELISA and RIA, and nesfatin-1 levels by ELISA. Nesfatin-1 immunoreactivity was detected in the striated and interlobular parts of the salivary glands and the ducts. The nesfatin-1 level in the brain was around 12 times higher than in the salivary gland. Before antiepileptic treatment, both saliva and serum nesfatin-1 levels were around 160-fold higher in patients who are newly diagnosed with primary generalized epilepsy (PGE) than in controls; these levels decreased with treatment but remained about 10 times higher than the control values. Saliva and serum nesfatin-1 levels from patients with PGE and partial epilepsies who were continuing antiepileptic drugs were also 10-fold higher than control values. Serum and saliva ghrelin levels were significantly (twofold) lower in epileptic patients before treatment than in controls; they recovered somewhat with treatment but remained below the control values. These results suggest that the low ghrelin and especially the dramatically elevated nesfatin-1 levels might contribute to the pathophyisology of epilepsy. Therefore, serum and saliva ghrelin and especially the remarkably increased nesfatin-1 might be candidate biomarkers for the diagnosis of epilepsy and for monitoring the response to anti-epileptic treatment.     

A comparison of leptin and ghrelin levels in plasma and saliva of young healthy subjects

In the last 10 years, saliva has been increasingly used as a diagnostic fluid and in predictions of disease progression. Leptin and ghrelin are synthesized in several tissues including the salivary glands. The action of ghrelin is antagonistic to that of leptin. This study was undertaken to measure and compare the saliva ghrelin-leptin and plasma ghrelin-leptin levels in healthy young subjects. In 30 healthy subjects, after an overnight fast, saliva and plasma leptin levels were measured using the ELISA method while saliva and plasma immunoreactive ghrelin levels were measured using a commercial radioimmunoassay (RIA). The latter uses 125I-labeled bioactive ghrelin as a tracer and a rabbit polyclonal antibody raised against full-length octanoylated human ghrelin (Phoenix, Europe, Karlsruhe, Germany). The results of this investigation revealed that saliva leptin levels (6.19+/-2.10 microg/l) were lower than plasma levels (7.39+/-3.23 microg/l) while saliva ghrelin levels (188.5+/-84.7 pg/ml) were higher than plasma levels (126.4+/-38.5 pg/ml), when male and female subjects were considered together. Saliva leptin levels (5.93+/-1.94 microg/l) were lower than plasma levels (6.22+/-2.92 pg/ml) while saliva ghrelin levels (190.3+/-80.2 pg/ml) were higher than plasma levels (120.4+/-35.7 pg/ml) in young males. Saliva leptin levels (6.47+/-2.29 microg/l) were lower than plasma levels (8.73+/-3.14 microg/l) while saliva ghrelin levels (183.2+/-90.2 pg/ml) were higher than plasma levels (129.3+/-42.8 pg/ml) in young females, and both saliva and plasma leptin levels were slightly lower in male subjects in comparison with female subjects. Also, Immunohistochemistry study indicated that ghrelin positivity was found in ductus epithelium of salivary gland. We have demonstrated for the first time that saliva ghrelin levels were higher than in plasma while saliva leptin levels were almost the same as in plasma. Measurements of ghrelin and leptin in saliva is non-invasive, simple, and generally much preferred by patients and thus may be an acceptable alternative to plasma sampling.     

A comparison of ghrelin, glucose, alpha-amylase and protein levels in saliva from diabetics

During the past decade, many salivary parameters have been used to characterize disease states. Ghrelin (GAH) is recently-discovered peptide hormone secreted mainly from the stomach but also produced in a number of other tissues including salivary glands. The aim of this work was to examine the relationship between active (aGAH) and inactive (dGAH) ghrelin in the saliva and other salivary parameters in type II diabetic patients and healthy controls. Salivary parameters were assessed in a single measurement of unstimulated whole saliva from 20 obese and 20 non-obese type II diabetes patients, and in 22 healthy controls. Total protein and alpha-amylase were determined by colorimetric methods, and glucose by the glucose-oxidase method. Saliva aGAH and dGAH levels were measured using a commercial radioimmunoassay (RIA) kit. Salivary concentrations of aGAH and dGAH ghrelin were more markedly decreased in obese diabetic subjects than in the two other groups. Glucose and alpha-amylase levels were higher in diabetic subjects than in controls. Furthermore, there were correlations between GAH levels and BMI, and between GAH and blood pressure. However, there was no marked variability in saliva flow rates among the groups. These results indicate that measurement of salivary GAH and its relationship to other salivary parameters might help to provide insight into the role of ghrelin in diabetes.     

The evaluation of basic fibroblast growth factor and fibroblastic growth factor receptor 1 levels in saliva and serum of patients with salivary gland tumor

Basic fibroblast growth factor (FGF2) is a well-known endothelial mitogen that regulates endothelial cell proliferation, migration, differentiation, and survival. In the present study, we investigated the levels of FGF2 and fibroblastic growth factor receptor 1 (FGFR1) in saliva and serum of patients with salivary gland tumors. Saliva and serum samples were collected from 43 patients with salivary gland tumors and 40 healthy volunteers. The FGF2 and FGFR1 concentrations in saliva and serum samples were measured by enzyme-linked immunosorbent assay. We found that the levels of FGF2 and FGFR1 in saliva and serum from patients with salivary gland tumors were significantly higher than those from healthy control subjects. These results suggest that salivary FGF2 and FGFR1 can be used as potential biomarkers in the diagnosis of salivary gland tumors.     

Expression of obestatin and ghrelin in papillary thyroid carcinoma

Ghrelin and obestatin are two peptide hormones with opposing roles in the control of appetite: orexigenic and anorexigenic, respectively. Loss of appetite is a common, serious complication of many forms of malignancy. The goals of this study were to investigate: (i) whether there are differences in ghrelin and obestatin peptide expression in thyroid tissues from a series of papillary carcinoma cases and normal controls, and (ii) whether there are correlations between tissue ghrelin and obestatin levels in series of papillary carcinoma cases and normal controls. Immunohistochemical analysis showed that in sections of benign human thyroid tissue, anti-ghrelin antibody reacted with intense staining in colloid-filled follicles. In benign thyroid tissues, colloids displayed plentiful dispersion in comparison with papillary microcarcinomas, whereas colloids in malignant thyroid tissues were uncommon. We found markedly lower tissue ghrelin levels in thyroid tissue of patients with papillary carcinomas, compared with normal thyroid tissues (P = 0.001). Immunohistochemical analysis also showed that obestatin in papillary carcinoma stained positively to various degrees. Obestatin tissue levels in papillary carcinomas tended to be slightly higher than those in normal thyroid tissue, but this was not statistically significant (P = 0.29). We also report that thyroid tissue of patients with Hashimoto’s thyroiditis produced ghrelin and obestatin at similar levels as in normal thyroid tissue, even though colloid in Hashimoto’s disease is scarce. We conclude that depressed expression of ghrelin, but not obestatin, is specific to papillary carcinoma, and this difference might constitute a diagnostic tool to differentiate papillary carcinoma from normal thyroid tissue. We currently do not know how these peptides are regulated and what factors are involved in papillary carcinoma, which inhibit the expression of ghrelin but not obestatin. This issue warrants further studies.     

Members of the salivary gland surface protein (SGS) family are major immunogenic components of mosquito saliva

Mosquitoes transmit Plasmodium and certain arboviruses during blood feeding, when they are injected along with saliva. Mosquito saliva interferes with the host's hemostasis and inflammation response and influences the transmission success of some pathogens. One family of mosquito salivary gland proteins, named SGS, is composed of large bacterial-type proteins that in Aedes aegypti were implicated as receptors for Plasmodium on the basal salivary gland surface. Here, we characterize the biology of two SGSs in the malaria mosquito, Anopheles gambiae, and demonstrate their involvement in blood feeding. Western blots and RT-PCR showed that Sgs4 and Sgs5 are produced exclusively in female salivary glands, that expression increases with age and after blood feeding, and that protein levels fluctuate in a circadian manner. Immunohistochemistry showed that SGSs are present in the acinar cells of the distal lateral lobes and in the salivary ducts of the proximal lobes. SDS-PAGE, Western blots, bite blots, and immunization via mosquito bites showed that SGSs are highly immunogenic and form major components of mosquito saliva. Last, Western and bioinformatic analyses suggest that SGSs are secreted via a non-classical pathway that involves cleavage into a 300-kDa soluble fragment and a smaller membrane-bound fragment. Combined, these data strongly suggest that SGSs play an important role in blood feeding. Together with their role in malaria transmission, we propose that SGSs could be used as markers of human exposure to mosquito bites and in the development of disease control strategies.     

Identification of aquaporin-5 and lipid rafts in human resting saliva and their release into cevimeline-stimulated saliva

BACKGROUND: It is unknown whether AQP5 and lipid rafts are released into human unstimulated (resting) saliva and saliva in response to secretagogues. METHODS: In order to quantitate the salivary concentration of AQP5, we produced a polyclonal antibody for human AQP5 and developed an enzyme-like immunosorbent assay (ELISA). RESULTS: AQP5 and lipid rafts were identified in human resting saliva. The amount of AQP5 in resting saliva showed a diurnal variation with high levels during waking hours, and an age-related decrease in AQP5 was coincident with the volume of resting saliva. Cevimeline, a muscarinic acetylcholine receptor (mAChR) agonist, induced the release of AQP5 with lipid rafts, amylase, mucin, and lysozyme. Changes in saliva AQP5 levels after cevimeline administration occurred simultaneously with changes in saliva flow rates. Confocal microscopy revealed that AQP5 was located in the apical plasma membrane and showed a diffuse pattern in parotid glands under resting conditions. Following cevimeline administration, AQP5 was predominantly associated with the APM and was localized in the lumen. GENERAL SIGNIFICANCE: AQP5 and lipid rafts were released with salivary proteins from human salivary glands by the stimulation of M3 mAChRs, and that changes in saliva AQP5 levels can be used as an indicator of salivary flow rate and also as a useful index of M3 mAChR agonist's action on human salivary glands.     

Different responses of circulating ghrelin, obestatin levels to fasting, re-feeding and different food compositions, and their local expressions in rats

Obestatin, a sibling of ghrelin derived from preproghrelin, opposes several physiological actions of ghrelin. Our previous study has demonstrated that both plasma ghrelin and obestatin levels were decreased significantly 2h after food intake in human. To further expand current knowledge, we investigated the temporal profiles of their levels in ad libitum fed rats, 48h fasted rats and 48h fasted rats refed 2h with a standard chow, crude fiber, 50% glucose or water, and their expressions in stomach, liver and pancreatic islets immunohistochemically. Plasma ghrelin and obestatin levels were measured by EIA. Plasma leptin, insulin and glucose levels were also evaluated. Both plasma ghrelin and obestatin levels increased significantly in fasted rats compared with ad libitum fed rats. The ingestion of standard chow produced a profound and sustained suppression of ghrelin levels, whereas plasma obestatin levels decreased significantly but recovered quickly. Intake of crude fiber or 50% glucose, however, produced a more profound and sustained suppression of obestatin levels, though they had relatively less impact on ghrelin levels. Plasma glucose was the only independent predictor of ghrelin levels, obestatin levels, and ghrelin to obestatin ratios. Obestatin immunoreactivity was detected in the fundus of stomach, liver and pancreatic islets, with roughly similar patterns of distribution to ghrelin. These data show quantitative and qualitative differences in circulating ghrelin and obestatin responses to the short-term feeding status and nutrient composition, and may support a role for obestatin in regulating metabolism and energy homeostasis.     

Effect of the Aedes fluviatilis saliva on the development of Plasmodium gallinaceum infection in Gallus (gallus) domesticus

Effect of Aedes fluviatilis saliva on the development of Plasmodium gallinaceum experimental infection in Gallus (gallus) domesticus was studied in distinct aspects. Chickens subcutaneously infected with sporozoites in the presence of the mosquito salivary gland homogenates (SGH) showed higher levels of parasitaemia when compared to those ones that received only the sporozoites. However, the parasitaemia levels were lower among chickens previously immunized by SGH or non-infected mosquito bites compared to the controls, which did not receive saliva. High levels of anti-saliva antibodies were observed in those immunized chickens. Moreover, 53 and 102 kDa saliva proteins were recognized by sera from immunized chickens. After the sporozoite challenge, the chickens also showed significant levels of anti-sporozoite antibodies. However, the ability to generate anti-sporozoites antibodies was not correlated to the saliva immunization. Our results suggest that mosquito saliva components enhance P. gallinaceum parasite development in naive chickens. However, the prior exposure of chickens to salivary components controls the parasitemia levels in infected individuals.     

Detection of Hsp60 in saliva and serum from type 2 diabetic and non-diabetic control subjects

There is increasing evidence that mitochondrial dysfunction and oxidative stress may be integral to the pathogenesis of type 2 diabetes mellitus. Heat shock protein (Hsp60) is a mitochondrial stress protein known to be induced under conditions of mitochondrial impairment. Although this intracellular protein is normally found in the mitochondrion, several studies have shown that this protein is also present in systemic circulation. In this study, we report the presence of elevated levels of Hsp60 in both saliva and serum of type 2 diabetic patients compared to non-diabetic controls. Hsp60 was detectable in the saliva of 10% of control and 93% of type 2 diabetic patients. Levels detected were in the range of 3–7 ng/ml in control and 3–75 ng/ml in type 2 diabetic patients. Serum Hsp60 levels in the range of 3–88 ng/ml were detected in 33% of control subjects, and levels in the range of 28–1,043 ng/ml were detected in 100% of type 2 diabetic patients. This is the first reporting of the presence of mitochondrial stress protein in salivary secretions. The serum Hsp60 levels were 16-fold higher compared to those in saliva, and there was a good positive correlation between salivary and serum Hsp60 levels (r = 0.55). While the exact mechanisms responsible for the secretion of Hsp60 into biological fluids such as saliva and blood are not yet known. The presence of this molecular marker of mitochondrial stress in saliva offers a non-invasive route to further investigate the biological functions of extracellular Hsp60 in type 2 diabetes mellitus and other conditions.     

Distribution of obestatin and ghrelin in human tissues: immunoreactive cells in the gastrointestinal tract, pancreas, and mammary glands.

Obestatin and ghrelin are two peptides derived from the same prohormone. It is well established that ghrelin is produced by endocrine cells in the gastric mucosa. However, the distribution of human obestatin immunoreactive cells is not thoroughly characterized. A polyclonal antibody that specifically recognizes human obestatin was produced. Using this antibody and a commercial antibody vs ghrelin, the distribution of obestatin and ghrelin immunoreactive cells was determined in a panel of human tissues using immunohistochemistry. The two peptides were detected in the mucosa of the gastrointestinal tract, from cardia to ileum, and in the pancreatic islets. Interestingly, epithelial cells in the ducts of mammary glands showed distinct immunoreactivity for both ghrelin and obestatin. By double immunofluorescence microscopy, it was shown that all detected cells were immunoreactive for both peptides. Furthermore, the subcellular localization of obestatin and ghrelin was essentially identical, indicating that obestatin and ghrelin are stored in the same secretory vesicles.     

Low parotid saliva calmodulin in patients with taste and smell dysfunction

Parotid saliva calmodulin was found both in 32 normal volunteers and in 60 patients with taste and smell dysfunction; salivary calmodulin concentration was significantly lower in the patients than in the volunteers. There were no differences in salivary calmodulin concentration with respect to age, sex, or salivary flow rate in either normal volunteers or patients. When patients were categorized by diagnosis, calmodulin concentration was found to be decreased in all patient groups. The concentration of calmodulin in saliva was about 10 times that found in serum, suggesting that the parotid gland is a major source of this protein.     

Total reactive antioxidant potential in human saliva of smokers and non-smokers.

Uric acid is the most important non-enzymatic antioxidant present in human saliva. There is a great variability among individuals, both in salivary uric acid content and saliva total reactive antioxidant potential (TRAP). The uric acid present in saliva correlates with plasma uric acid, suggesting that the former is imported from plasma. There are not statistical differences between uric acid or TRAP values in saliva of smokers and non-smokers. Also, smoking a cigarette does not modify the levels of antioxidants present in saliva.     

Identification and characterization of tyrosylprotein sulfotransferase from human saliva

Tyrosylprotein sulfotransferase (TPST), the enzyme responsible for the sulfation of tyrosine residues, has been identified and characterized in submandibular salivary glands previously (William et al. Arch Biochem Biophys 338: 90-96). Tyrosylprotein sulfotransferase catalyses the sulfation of a variety of secretory and membrane proteins and is believed to be present only in the cell. In the present study, this enzyme was identified for the first time in human saliva. Analysis of human saliva and parotid saliva for the presence of tyrosylprotein sulfotransferase revealed tyrosine sulfating activity displayed by both whole saliva and parotid saliva at pH optimum of 6.8. In contrast to tyrosylprotein sulfotransferase isolated from submandibular salivary glands, salivary enzyme does not require the presence of Triton X-100, NaF and 5'AMP for maximal activity. Similar to the submandibular TPST, the enzyme from saliva also required MnCl2 for its activity. Maximum TPST activity was observed at 20 mM MnCl2. The enzyme from saliva was immunoprecipitated and purified by immunoaffinity column using anti-TPST antibody. Affinity purified salivary TPST showed a single band of 50-54 kDa. This study is the first report characterizing a tyrosylprotein sulfotransferase in a secretory fluid.     

Plasma obestatin levels in men with chronic atrophic gastritis

Obestatin is a recently discovered active peptide isolated from the stomach. The purpose of the present study was to investigate the modification of plasma obestatin levels in men with chronic atrophic gastritis. Men older than 65 years undergoing upper gastrointestinal endoscopy were included. All patients with chronic atrophic gastritis underwent multiple biopsies. Fasting plasma obestatin and ghrelin levels were examined in 50 men with chronic atrophic gastritis and 50 healthy men. Plasma obestatin levels were significantly lower in patients with chronic atrophic gastritis than in healthy subjects. Plasma ghrelin levels and ghrelin to obestatin ratio was decreased in men with chronic atrophic gastritis. There was a significant relationship between atrophy and decreased obestatin. A negative correlation was found between circulating obestatin levels and body mass index (BMI) in healthy subjects, but not in patients with chronic atrophic gastritis. The data indicated that chronic atrophic gastritis influenced plasma obestatin levels as well as ghrelin to obestatin ratio in elderly men.     

The scientific exploration of saliva in the post-proteomic era: from database back to basic function

The proteome of human saliva can be considered as being essentially completed. Diagnostic markers for a number of diseases have been identified among salivary proteins and peptides, taking advantage of saliva as an easy-to-obtain biological fluid. Yet, the majority of disease markers identified so far are serum components and not intrinsic proteins produced by the salivary glands. Furthermore, despite the fact that saliva is essential for protecting the oral integuments and dentition, little progress has been made in finding risk predictors in the salivary proteome for dental caries or periodontal disease. Since salivary proteins, and in particular the attached glycans, play an important role in interactions with the microbial world, the salivary glycoproteome and other post-translational modifications of salivary proteins need to be studied. Risk markers for microbial diseases, including dental caries, are likely to be discovered among the highly glycosylated major protein species in saliva. This review will attempt to raise new ideas and also point to under-researched areas that may hold promise for future applicability in oral diagnostics and prediction of oral disease.     

Obestatin induction of early-response gene expression in gastrointestinal and adipose tissues and the mediatory role of G protein-coupled receptor, GPR39

Obestatin was identified as a brain/gut peptide hormone encoded by the ghrelin gene and found to interact with the G protein-coupled receptor, GPR39. We investigated target cells for obestatin based on induction of an early-response gene c-fos in different tissues. After ip injection of obestatin, c-fos staining was found in the nuclei of gastric mucosa, intestinal villi, white adipose tissues, hepatic cords, and kidney tubules. Immunohistochemical analyses using GPR39 antibodies further revealed cytoplasmic staining in these tissues. In cultured 3T3-L1 cells, treatment with obestatin, but not motilin, induced c-fos expression. In these preadipocytes, treatment with obestatin also stimulated ERK1/2 phosphorylation. Because phenotypes of GPR39 null mice are partially consistent with a role of GPR39 in mediating obestatin actions, we hypothesized that inconsistencies on the binding of iodinated obestatin to GPR39 are due to variations in the bioactivity of iodinated obestatin. We obtained monoiodoobestatin after HPLC purification and demonstrated its binding to jejunum, stomach, ileum, pituitary, and white adipose tissue. Furthermore, human embryonic kidney 293T cells transfected with plasmids encoding human or mouse GPR39 or a human GPR39 isoform, but not the ghrelin receptor, exhibited high-affinity binding to monoiodoobestatin. Binding studies using jejunum homogenates and recombinant GPR39 revealed obestatin-specific displacement curves. Furthermore, treatment with obestatin induced c-fos expression in gastric mucosa of wild-type, but not GPR39 null, mice, underscoring a mediating role of this receptor in obestatin actions. The present findings indicate that obestatin is a metabolic hormone capable of binding to GPR39 to regulate the functions of diverse gastrointestinal and adipose tissues.     

Comparative profiling of human saliva by intact protein LC/ESI-TOF mass spectrometry

Human saliva is finding increasing interest for proteomic and biomarker-discovery studies, due to the ease of collection and potential for simpler processing workflows compared to serum or plasma. However, it is known that salivary protein composition can vary with physiological and environmental factors. In this work, we have examined intra- and inter-person variability of saliva protein composition using an LC/MS methodology to profile low molecular weight human salivary proteins. Whole saliva was analyzed from four individuals over three consecutive days. Additional samples were used to determine baseline analytical and sample processing variation and to identify phosphoproteins. Individuals were observed to have a similar salivary protein pattern over multiple days, although the expression levels of particular proteins were variable. Significant differences in protein profiles were observed between subjects, allowing for delineation of individuals based on their protein profile. Comparison with alkaline phosphatase treated saliva revealed that several identified proteins were singly, doubly, or triply phosphorylated.