Inactivation of human salivary glutathione transferase P1-1 by hypothiocyanite: a post-translational control system in search of a role

Glutathione transferases (GSTs) are a superfamily of detoxifying enzymes over-expressed in tumor tissues and tentatively proposed as biomarkers for localizing and monitoring injury of specific tissues. Only scarce and contradictory reports exist about the presence and the level of these enzymes in human saliva. This study shows that GSTP1-1 is the most abundant salivary GST isoenzyme, mainly coming from salivary glands. Surprisingly, its activity is completely obscured by the presence of a strong oxidizing agent in saliva that causes a fast and complete, but reversible, inactivation. Although salivary α-defensins are also able to inhibit the enzyme causing a peculiar half-site inactivation, a number of approaches (mass spectrometry, site directed mutagenesis, chromatographic and spectrophotometric data) indicated that hypothiocyanite is the main salivary inhibitor of GSTP1-1. Cys47 and Cys101, the most reactive sulfhydryls of GSTP1-1, are mainly involved in a redox interaction which leads to the formation of an intra-chain disulfide bridge. A reactivation procedure has been optimized and used to quantify GSTP1-1 in saliva of 30 healthy subjects with results of 42±4 mU/mg-protein. The present study represents a first indication that salivary GSTP1-1 may have a different and hitherto unknown function. In addition it fulfills the basis for future investigations finalized to check the salivary GSTP1-1 as a diagnostic biomarker for diseases.

Role of lipid oxidation, chelating agents, and antioxidants in metallic flavor development in the oral cavity

This study investigated the production of metallic flavor, which is a combination of taste and retronasal odor. Chemical reactions in the oral cavity and saliva of healthy subjects were investigated after ingesting iron and copper solutions above and near threshold levels. Significant increase in lipid oxidation (p < 0.001) occurred after metal ingestion, detected as TBARS values. Ferrous ion caused the greatest flavor sensation and lipid oxidation, followed by cupric and cuprous ions. Ferric ion did not cause metallic sensation. Occurrence of oxidation was supported by damage to salivary proteins, detected as protein-carbonyls, and by a significant increase of odorous lipid oxidation related aldehydes. Sensory evaluation demonstrated that antioxidants (vitamins E and C) minimally reduced metallic flavor but that chelating agents (EDTA and lactoferrin) removed the metallic flavor. The role of lipid oxidation is essential for the production of a metallic flavor from ingestion of ferrous, cupric, and cuprous ions.

Endometrial cysteine-rich secretory protein 3 is inhibited by human chorionic gonadotrophin, and is increased in the decidua of tubal ectopic pregnancy

Ectopic pregnancy (EP) remains a considerable cause of morbidity and occasional mortality. Currently, there is no reliable test to differentiate ectopic from intrauterine gestation. We have previously used array technology to demonstrate that differences in gene expression in decidualized endometrium from women with ectopic and intrauterine gestations could be used to identify candidate diagnostic biomarkers for EP. The aim of this study was to further investigate the decidual gene with the highest fold increase in EP, cysteine-rich secretory protein-3 (CRISP-3). Decidualized endometrium from gestation-matched women undergoing surgical termination of pregnancy (n = 8), evacuation of uterus for miscarriage (n = 6) and surgery for EP (n = 11) was subjected to quantitative RT-PCR, morphological assessment, immunohistochemistry and western blot analysis. Sera were analysed for progesterone and human chorionic gonadotrophin (hCG) levels. Immortalized endometrial epithelial cells were cultured with physiological concentrations of hCG. CRISP-3 mRNA and protein expression were greater in endometrium from ectopic when compared with intrauterine pregnancies (P < 0.05). CRISP-3 protein was localized to epithelium and granulocytes of endometrium. CRISP-3 serum concentrations were not different in women with ectopic compared with intrauterine pregnancies. CRISP-3 expression in endometrium was not related to the degree of decidualization or to serum progesterone levels. Endometrial CRISP-3 expression was inversely proportional to serum hCG concentrations (P < 0.001). Stimulation of endometrial epithelial cells with hCG in vitro caused a reduction in CRISP-3 expression (P < 0.01). The measurement of CRISP-3 in endometrium could provide an additional tool in the diagnosis of failing early pregnancy of unknown location. The absence of a local reduction in expression of CRISP-3 in decidualized endometrium of women with EP may be due to reduced exposure to hCG due to the ectopic location of the trophoblast.

A peptide domain of bovine milk lactoferrin inhibits the interaction between streptococcal surface protein antigen and a salivary agglutinin peptide domain

The peptide domain of salivary agglutinin responsible for its interaction with cell surface protein antigen (PAc) of Streptococcus mutans or bovine lactoferrin was found in the same peptide, scavenger receptor cysteine-rich domain peptide 2 (SRCRP2). Inhibition studies suggest that PAc and lactoferrin, of which residues 480 to 492 seem important, competitively bind to the SRCRP2 domain of salivary agglutinin.

Calcium blocks fungicidal activity of human salivary histatin 5 through disruption of binding with Candida albicans

Salivary histatin 5 (Hst 5) kills the fungal pathogen C. albicans via a mechanism that involves binding and subsequent efflux of cellular ATP. Our aims were to identify inorganic ions found in saliva that influence Hst 5 fungicidal activity. Increasing ionic strength with relevant salivary anions (Cl(-) and CO(3)(-)) did not reduce Hst 5 binding or uptake by yeast cells, but reduced the Hst-induced efflux of ATP. Extracellular MgCl(2) (25 mM) maximally inhibited 30-40% of Hst 5 killing with 40% reduction in ATP efflux, while pre-treatment of cells with only 2 mM CaCl(2) inhibited 80-90% of killing, and prevented ATP efflux. Loss of fungicidal activity by the addition of CaCl(2) or MgCl(2) was a result of inhibition of binding of Hst 5 to C. albicans cells. Calcium is a potent inhibitor of Hst 5 candidacidal activity at physiological concentrations and may be the primary salivary ion responsible for the masking effect of saliva.

A sulfated proteoglycan is necessary for storage of exocrine secretory proteins in the rat parotid gland

Sulfated proteoglycans have been proposed to play a role in the sorting and storage of secretory proteins in exocrine secretory granules. Rat parotid acinar cells expressed a 40- to 60-kDa proteoglycan that was stored in secretory granules. Treatment of the tissue with the proteoglycan synthesis inhibitor paranitrophenyl xyloside resulted in the complete abrogation of the sulfated proteoglycan. Pulse-chase experiments in the presence of the xyloside analog showed a significant reduction in the stimulated secretion and granule storage of the newly synthesized regulated secretory proteins amylase and parotid secretory protein. Inhibition of proteoglycan sulfation by chlorate did not affect the sorting of these proteins. The effect of proteoglycan synthesis inhibition on protein sorting was completely reversed upon treatment with a weak acid. These results suggest that the sulfated proteoglycan is necessary for sorting and storage of regulated secretory proteins in the exocrine parotid gland. Preliminary evidence suggests that the mechanism involves the modulation of granule pH by the proteoglycan rather than a direct interaction with other granule components.

Characterization and cDNA cloning of halyxin, a heterogeneous three-chain anticoagulant protein from the venom of Agkistrodon halys brevicaudus

We report upon the isolation, characterization, and cDNA cloning of an anticoagulant protein, halyxin from Agkistrodon halys brevicaudus venom. The protein exists as a 29kDa protein, and is separated into three chains on SDS-PAGE under reducing conditions. However, we cloned only two cDNAs encoding halyxin from the cDNA library of the snake venom gland, on the basis of the determined amino acid sequences. The complete amino acid sequences were deduced from their nucleotide sequences and named halyxin A (129 amino acid residues) and B chain (123 amino acid residues). The deduced amino acid sequence of halyxin A chain corresponds to the two smaller chains. Thus, it is considered that halyxin A chain could be synthesized as a single-chain protein that is subsequently cleaved to yield the mature two-chain protein. The amino acid sequence of halyxin is similar to that of other snake venom proteins of the C-type lectin superfamily, and prolongs plasma-clotting time. In the presence of Ca(2+) ions, halyxin binds to coagulation factors IX, X, IXa, and Xa, but not to other vitamin K-dependent coagulation factors. It also inhibits factor Xa in a non-competitive manner but does not affect other activated coagulation factors.

Saliva flow rate, amylase activity, and protein and electrolyte concentrations in saliva after acute alcohol consumption

OBJECTIVE

The aim of our study was to evaluate the effects of acute alcohol consumption on saliva secretion rate and selected salivary parameters in healthy nonalcoholic volunteers.

STUDY DESIGN

Twenty-four volunteers (37.7 +/- 9.6 years, mean +/- SD) consumed 0.6 g or 0.7 g alcohol/kg of body weight (for women and men, respectively) in a soft drink. Saliva samples were collected, first (S0) before any alcohol was consumed, 45 minutes after consumption (S1) and, finally, 60 minutes after S1 (S2). Flow rates of both resting whole saliva and paraffin-stimulated (SWS) whole saliva were assessed. SWS was assessed for amylase, total protein, inorganic phosphate (PO4(3-)), sodium (Na+), potassium (K+), and calcium (Ca2+) content.

RESULTS

SWS, but not resting whole saliva (in milliliters/minute), decreased significantly after consumption of alcohol. Amylase activity (P =.010) and the concentrations of Na+ (P =.000) and Ca2+ (P =.002) decreased significantly between S0 and S1. When SWS was analyzed for output, the total protein concentration (S0 to S1, P =.000; S0 to S2, P =.033) and amylase activity (S0 to S1, P =.000) decreased significantly. Further, the output of all the studied electrolytes decreased significantly as blood alcohol concentration increased.

CONCLUSIONS

We conclude that acute alcohol consumption causes a decrease in SWS flow rate. The decrease in flow rate also results in impaired output of total protein and amylase, as well as in a decrease in the output of electrolytes.

The effects of MMP inhibitors on human salivary MMP activity and caries progression in rats

Previous studies suggest that salivary and pulp-derived host enzymes, matrix metalloproteinases (MMPs), may be involved in dentin caries pathogenesis. To study the inhibition of acid-activated human salivary MMPs by non-antimicrobial chemically modified tetracyclines (CMTs), we used a functional activity assay with 125I-labeled gelatin as a substrate. To address the role of MMPs in the progression of fissure caries in vivo, we administered the MMP inhibitors CMT-3 and zoledronate to young rats per os for 7 weeks, 5 days a week. Caries lesions were visualized by Schiff reagent in sagittally sectioned mandibular molars. Marked reduction in gelatinolytic activity of human salivary MMPs was observed with CMT-3. CMT-3 and zoledronate, both alone and in combination, also reduced dentin caries progression in the rats. These results suggest that MMPs have an important role in dentin caries pathogenesis, and that MMP inhibitors may prove to be useful in the prevention of caries progression.

Inhibition of salivary amylase by black and green teas and their effects on the intraoral hydrolysis of starch

Tea decoctions prepared from a number of black and green teas inhibited amylase in human saliva. Black teas gave higher levels of inhibition than green teas, and removal of tea tannins with gelatin led to the loss of inhibitory activity from all decoctions. Streptococcal amylase was similarly inhibited by tea decoctions. Fluoride was without effect on amylase. Since salivary amylase hydrolyzes food starch to low molecular weight fermentable carbohydrates, experiments were carried out to determine whether tea decoctions would interfere with the release of maltose in food particles that became entrapped on the dentition. Subjects consumed salted crackers and rinsed subsequently for 30 s with black or green tea decoctions, or water. Maltose release was reduced by up to about 70% after rinsing with the teas. Black tea decoction was significantly more effective than green tea, in agreement with the in vitro data. The observations supported the hypothesis that tea consumption can be effective in reducing the cariogenic potential of starch-containing foods such as crackers and cakes. Tea may reduce the tendency for these foods to serve as slow-release sources of fermentable carbohydrate.

Blockade of isoprenaline-induced fluid and protein secretion by the mandibular glands of the red kangaroo, Macropus rufus, with selective antagonists

Selective and non-selective beta-adrenoceptor antagonists were used to block the increases in fluid and protein secretion caused by sympathomimetic stimulation of the mandibular gland of red kangaroos during intracarotid infusion of isoprenaline. Atenolol or ICI118551 at antagonist:agonist ratios up to 300:1 caused increasing but incomplete blockade of fluid secretion and protein release. Both selective antagonists had equal potency and both antagonists were more effective at blocking protein release than at blocking fluid secretion. Consequently, the mechanisms underpinning fluid secretion are more sensitive to beta-sympathomimetic stimulation than those causing protein release. Propranolol at antagonist:agonist ratios of 300:1 was more potent than the selective antagonists, almost totally blocking the increases in fluid secretion and protein release. The data are consistent with the acini of the kangaroo mandibular gland having both beta(1)- and beta(2)-adrenoceptors and with the increased fluid secretion and protein release by isoprenaline being mediated by both receptor subtypes.

The influence of different fluoride salts on fluoride-mediated inhibition of peroxidase activity in human saliva

Fluoride-mediated inhibition of peroxidase potential activity in human saliva was investigated using NaF, NH4F, CaF2, Na2PO3F (MFP), SnF2 and TiF4. At pH 5.5 and for a 20 mM F concentration, the inhibition percentages increased from 2% for MFP and 5% for CaF2 to 61% for NaF and 65% for NH4F, while a 100% inhibition was observed at 10 mM for TiF4 and at 5 mM for SnF2. The inhibition was enhanced at acid pH and removed at pH 7. The inhibition could be attributed to ionized F-, except for SnF2 and TiF4, in which part of the inhibition could be imputed to the cations.

Effects of delmopinol on antimicrobial peroxidase systems and lysozyme in vitro and in human whole saliva

Delmopinol is a new surface-active agent which can reduce plaque formation and gingivitis. This study was aimed to analyze whether delmopinol (0.0032-0.65 mM) interferes with the activity of two surface-active oral antimicrobial enzymes, salivary peroxidase and lysozyme. In addition to human whole saliva (pH 5.0 and 6.0), the experiments were done in 0.1 M phosphate buffer (pH 6.0) with purified lactoperoxidase (LPO) and myeloperoxidase (MPO). LPO and MPO were significantly inhibited in buffer by delmopinol concentrations > 6.5 mM and > or = 3.2 mM, respectively. No such inhibition was found for total peroxidase activity in mixed saliva. In vitro, delmopinol was found to desorb surface-bound peroxidases in an active form to the liquid phase. In further analyses, the possible effect of delmopinol on peroxidase-generated hypothiocyanite (HOSCN/OSCN-) was studied in saliva and buffer. No effect was found in buffer, but salivary HOSCN/OSCN- declined significantly with 6.5 mM delmopinol. This was obviously due to an enhanced decay of hypothiocyanite, rather than its reduced rate of formation. No delmopinol-related inhibition of lysozyme occurred in saliva or buffer. The results suggest that high concentration (6.4 mM -0.2%) of delmopinol may lower the concentrations of antimicrobial HOSCN/OSCN- in saliva but has no effect on human lysozyme.

A salivary nitrophorin (nitric-oxide-carrying hemoprotein) in the bedbug Cimex lectularius

Salivary gland homogenate of the bedbug Cimex lectularius caused vasodilation of the preconstricted rabbit aortic ring in the absence of endothelium. Vasodilation was augmented in the presence of superoxide dismutase and inhibited in the presence of Methylene Blue. Utilization of the Griess reaction indicated the presence of reactive nitrogen equivalents of the order of 337 +/- 57 pg equivalent NO2- per pair of salivary glands (mean +/- S.E.M.; N = 3). Salivary gland homogenates have a nitrosyl-hemoprotein that releases nitric oxide in a pH-dependent manner. The fraction containing the NO-carrying hemoprotein, when separated by HPLC, caused vasodilation of the preconstricted rabbit aortic strip. Furthermore, the presence of a nitrosyl-hemoprotein in Cimex lectularius salivary gland was verified by electron paramagnetic resonance spectroscopy. It is proposed that, as in the case of Rhodnius prolixus (Triatominae), Cimex lectularius salivary glands contain a hemoprotein (nitrophorin) that carries NO from the glands to the host tissues. However, because Cimex lectularius and Rhodnius prolixus belong to different hemipteran families (Cimicidae and Reduvidae) and evolved independently to blood feeding, Cimex lectularius and Rhodnius prolixus nitrophorin may be a case of convergent evolution.

Fluoride inhibits the antimicrobial peroxidase systems in human whole saliva

Fluoride (F-) ions at concentrations present in vivo at the plaque/enamel interface (0.05-10 mM) inhibited the activities of lactoperoxidase (LP), myeloperoxidase (MP) and total salivary peroxidase (TSP) in a pH- and dose-dependent way. The inhibition was observed only at pH < or = 6.5 and with F- concentrations > or = 0.1 mM. At pH 5.5 LP activity was inhibited by 85% and MP by 34% with 10 mM F-. TSP activity was also inhibited only at low pH (5.5) by approximately 25%. Furthermore, the generation of the actual antimicrobial agent in vivo, hypothiocyanite (HOSCN/OSCN-), of the oral peroxidase systems was inhibited by F-, again at low pH (5.0-5.5) both in buffer (by 45%) and in saliva (by 15%). This inhibition was observed only with the highest F- concentrations studied (5-10 mM). Fluoridated toothpaste (with 0.10 or 0.14% F) mixed with saliva did not inhibit TSP or HOSCN/OSCN- generation. This may have been due to the 'buffering' effect of toothpaste which did not allow salivary pH to drop below 5.9. We conclude that the F- ions in acidic fluoride products, e.g. in gels or varnishes (but not in toothpastes), may have the potential to locally inhibit the generation of a nonimmune host defense factor, HOSCN/OSCN/SCN-, produced by oral peroxidase systems. The possible clinical significance of this finding remains to be shown.

Inhibition of synthesis of rat parotid secretory proteoglycan in a gland slice system

The chondroitin sulphate contained within the secretory granules of the rat parotid gland and its saliva was shown to be in the form of a proteoglycan by using inhibitors of proteoglycan synthesis in a gland slice system. Gland slices were incubated in either p-nitrophenyl-beta-D-xyloside or chlorate in the presence of both [3H]-leucine and [35S]-sulphate. The slices were next homogenized and either the 250 g supernatant fraction (for initial experiments) or secretory granule-containing fractions were isolated. Protein and proteoglycans of these fractions were precipitated in 10% trichloracetic acid (TCA), and glycosaminoglycans in cetylpyridinium chloride. [3H]-leucine and [35S]-sulphate were quantitated in each type of precipitate by scintillation counting. The results showed that 1 mM xyloside had no effect on protein or glycosaminoglycan synthesis but blocked incorporation of radiosulphate into TCA-precipitable material. Sixteen mM chlorate almost totally inhibited incorporation of radiosulphate into glycosaminoglycan and TCA-precipitable material. These findings demonstrate that the rat parotid secretory chondroitin sulphate is indeed a proteoglycan because its synthesis is blocked by the protein-core analogue acceptor, p-nitrophenyl-beta-D-xyloside. This system offers opportunities for exploring the functional role of chondroitin sulphate proteoglycan in this salivary gland.

Inhibition of adhesion-promoting activity of a human salivary protein which promotes adhesion of Streptococcus mutans JBP to hydroxyapatite

The adhesion-promoting proteins (APP) (molecular mass approx. 300 kDa), which promote adhesion of Streptococcus mutans JBP (serotype c) to hydroxyapatite, were isolated from human submandibular-sublingual (SMSL) saliva by gel filtration on a Trisacryl GP2000 M column. The effects of hexoses, pentoses, methyl-pentoses, hexosamines, N-acetylhexosamines, a basic amino acid, polyamines and ammonium chloride on the bacterial adhesion-promoting activity of the APP were examined. Galactosamine, mannosamine, L-lysine, spermine, putrescine, and ammonium chloride inhibited the adhesion-promoting activities of the APP. The other sugars, including the N-acetylhexosamines, were without effect. Thus, compounds containing a primary amino-group appear to have a specific inhibitory effect on adhesion of S. mutans JBP to APP adsorbed onto hydroxyapatite, an activity which is lost if the amino-group is acetylated.

Effects of a beta-blocking agent, timolol maleate, on saliva in healthy volunteers

The effects of timolol maleate on the secretion and composition of human saliva were studied in vivo. Eight healthy volunteers received orally 10 mg timolol maleate. Stimulated parotid saliva samples, resting whole saliva samples, and blood samples were collected immediately before and four times after the drug intake at intervals of 1 h. The levels of total protein, lysozyme, IgA, IgG and IgM, salivary peroxidase, myeloperoxidase, lactoferrin, amylase, thiocyanate (SCN-), and hypothiocyanite (OSCN-) were analyzed from saliva samples. Drug levels were measured both from parotid saliva and blood samples. Results were compared to the analyses of the samples collected in a similar way but without administration of any drugs. Decreased levels of total protein, lactoferrin, amylase, and salivary peroxidase were observed in parotid saliva after a single oral dose of timolol maleate. No such decrease was found in lysozyme, myeloperoxidase, SCN-, OSCN-, or immunoglobulins. Salivary flow rate was not significantly changed after drug intake. The results suggest that the beta-blocking drug may cause qualitative changes in the composition of saliva by inhibiting the synthesis and/or release of acinar proteins.

Chlorpromazine inhibition of muscarinic-cholinergic responses in the rat parotid gland

The ability of chlorpromazine (CPZ) to inhibit muscarinic-cholinergic secretory events was studied in vitro in rat parotid acinar cells. CPZ inhibited carbachol-induced amylase release in a dose-dependent fashion but had no effect on that elicited by isoproterenol. The inhibition of parotid protein synthesis induced by carbachol, but not that induced by A23187, was blocked by CPZ. CPZ exhibited a dose-dependent inhibition of [3H] quinuclidinyl benzilate (QNB) binding to muscarinic receptors, and altered the KD of the receptor for the ligand. These results are consistent with an ability of CPZ to inhibit muscarinic-cholinergic-induced salivary secretion by complex interference with receptor binding. In addition, CPZ may block parotid-muscarinic responses by impeding a post-receptor signaling step which is proximal to Ca2+ mobilization.