Composition and function of saliva

1. Composition and function of saliva

2. Major salivary components Histatins Statherins Lysozyme Proline-rich proteins Carbonic anhydrases Amylases Peroxidases Lactoferrin Mucin 2 (MG2) sIgA Mucin 1 (MG1) 1 10 100 1000 10000 Size (kDa)

3. Amylases, Cystatins, Histatins, Mucins, Peroxidases Carbonic anhydrases, Histatins Multifunctionality Anti- Bacterial Buffering Amylases, Mucins, Lipase Cystatins, Mucins Anti- Viral Digestion Salivary Families Mineral- ization Anti- Fungal Cystatins, Histatins, Proline- rich proteins, Statherins Histatins Lubricat- ion &Visco- elasticity Tissue Coating Amylases, Cystatins, Mucins, Proline-rich proteins, Statherins Mucins, Statherins adapted from M.J. Levine, 1993

4. Mucin Functions • Tissue Coating • Protective coating about hard and soft tissues • Primary role in formation of acquired pellicle • Concentrates anti-microbial molecules at mucosal interface • Lubrication • Align themselves with direction of flow (characteristic of asymmetric molecules) • Increases lubricating qualities (film strength) • Film strength determines how effectively opposed moving surfaces are kept apart

5. Mucin Functions (cont’d) • Aggregation of bacterial cells • Bacterial adhere to mucins may result in surface attachment, or • Mucin-coated bacteria may be unable to attach to surface • Bacterial adhesion • Mucin oligosaccharides mimic those on mucosal cell surface • React with bacterial adhesins, thereby blocking them

6. Amylases • Hydrolyzes (1-4) bonds of starches such as amylose and amylopectin • Maltose is the major end-product (20% is glucose) • Why is it also present in tears, serum, bronchial, and male and female urogenital secretions? • A role in modulating bacterial adherence?

7. Lingual Lipase • Secreted by von Ebner’s glands of tongue • Involved in first phase of fat digestion • Hydrolyzes medium- to long-chain triglycerides • Important in digestion of milk fat in new-born • Unlike other mammalian lipases, it is highly hydrophobic and readily enters fat globules

8. Statherins • Calcium phosphate salts of dental enamel are soluble • Supersaturation of calcium phosphates maintain enamel integrity • Statherins prevent precipitation or crystallization of supersaturated calcium phosphate in ductal saliva and oral fluid

9. Proline-rich Proteins (PRPs) • Inhibit calcium phosphate crystal growth • Present in the initially formed enamel pellicle and in “mature” pellicles

10. Enamel pellicle formation • 0.1-1.0 µm thick layer of macromolecular material on the mineral surface of teeth • Selective adsorption of hydroxyapatite-reactive salivary proteins, serum proteins and microbial products • Diffusion barrier • Protects against bacterial acids • Slows loss of dissolved calcium and phosphate ions

11. Remineralization of enamel • Early (incipient) caries are repaired despite presence of mineralization inhibitors in saliva • Sound surface layer of early carious lesion forms impermeable barrier to diffusion of high mol.wt. inhibitors. • Still permeable to calcium and phosphate ions • Inhibitors may encourage mineralization by preventing crystal growth on the surface of lesion by keeping pores open

12. Calculus formation • Calculus forms in plaque despite inhibitory action of statherin and PRPs in saliva • May be due to failure to diffuse into calcifying plaque • Proteolytic enzymes of oral bacteria or lysed leukocytes may destroy inhibitory proteins • Plaque bacteria may produce their own inhibitors

13. Anti-microbial activities of saliva

14. Lactoferrin • Nutritional immunity (iron starvation) • Some microorganisms (e.g., E. coli) have adapted to this mechanism by producing enterochelins. • bind iron more effectively than lactoferrin • iron-rich enterochelins are then reabsorbed by bacteria • Lactoferrin, with or without iron, can be degraded by some bacterial proteases. • In unbound state, a direct bactericidal effect

15. Lysozyme • Present in numerous organs and most body fluids • Oral LZ is derived from at least four sources • major and minor salivary glands, phagocytic cells and gingival crevicular fluid (GCF) • Biological function • Classic concept of anti-microbial activity of LZ is based on its muramidase activity (hydrolysis of (1-4) bond between N-acetylmuramic acid and N-acetylglucosamine in the peptidoglycan layer. • Gram negative bacteria generally more resistant than gram positive because of outer LPS layer

16. Other anti-microbial activities of LZ • Muramidase activity (lysis of peptidoglycan layer) • Cationic-dependent activation of bacterial autolysins • strongly cationic protein (pI 10.5-11) • disrupts membranes • Aggregation of bacteria • Inhibition of bacterial adhesion to tooth surfaces • Inhibition of glucose uptake and acid production • De-chaining of streptococci

17. Histatins • A group of small histidine-rich proteins • Potent inhibitors of Candida albicans growth

18. Cystatins • Are inhibitors of cysteine-proteases • Are ubiquitous in many body fluids • Considered to be protective against unwanted proteolysis • bacterial proteases • lysed leukocytes • May play inhibit proteases in periodontal tissues • Also have an effect on calcium phosphate precipitation

19. Salivary peroxidase systems • Sialoperoxidase (SP, salivary peroxidase) • Produced in acinar cells of parotid glands • Also present in submandibular saliva • Readily adsorbed to various surfaces of mouth • enamel, salivary sediment, bacteria, dental plaque • Myeloperoxidase (MP) • From leukocytes entering via gingival crevice • 15-20% of total peroxidase in whole saliva

20. Components of the peroxidase anti-microbial system • Peroxidase enzymes (SP or MP) • Hydrogen peroxide (H2O2) • oral bacteria (facultative aerobes/catalase negative) produce large amounts of peroxide • S. sanguis, S. mitis, S. mutans • Thiocyanate ion (SCN-) which is converted to hypothiocyanite ion (OSCN-) by peroxidase • salivary concentration is related to diet and smoking habits

21. SP and/or MP H2O2 + SCN- OSCN- +H2O Thiocyanate reactions • The pK for HOSCN/OSCN- is 5.3 • More acid favors HOSCN • Due to uncharged nature, HOSCN penetrates bacterial cell envelope better Acid/Base Equilib. HOSCN OSCN- + H+ Hypothiocyanite ion Hypothiocianous acid

22. HOSCN/OSCN--mediated cell damage • can oxidize sulfhydryl groups of enzymes • block glucose uptake • inhibit amino acid transport • damage inner membrane, leading to leakage of cell • disrupt electrochemical gradients

23. Unstimulated bacteria Inhibited bacteria Active bacteria Regulation of oral microorganisms by SP/MP Food Ingestion Recovery carbohydrates Stimulation thiols spontaneous O2 Autoinhibition H+ OSCN-/HOSCN SCN- + H2O2 Metabolism Inhibition +SP Salivary Glands