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. Multifunctionality Amylases, Cystatins, Carbonic anhydrases,
Histatins, Mucins,
Peroxidases
Carbonic anhydrases,
Histatins
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 Lubrication
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
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 )
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. Thiocyanate reactions
H2O2 + SCN-
OSCN- +H2O
SP and/or MP
Acid/Base Equilib.
HOSCN
OSCN- + H+
Hypothiocianous acid
Hypothiocyanite ion
The pK for HOSCN/OSCN- is 5.3
More acid favors HOSCN
Due to uncharged nature, HOSCN penetrates bacterial cell envelope better

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