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Composition and function of saliva
Slide no. 1
Dennis E. Lopatin, Ph.D.
Major salivary components
Histatins
Statherins
Lysozyme
Proline-rich proteins
Carbonic anhydrases
Amylases
Peroxidases
Lactoferrin
Mucin 2 (MG2)
sIgA
Mucin 1 (MG1)
1
Slide no. 2
10
100
Size (kDa)
1000
10000
Dennis E. Lopatin, Ph.D.
Multifunctionality
Amylases, Cystatins,
Carbonic anhydrases,
Histatins, Mucins,
Histatins
AntiPeroxidases
Buffering
Bacterial
Amylases,
Cystatins,
Mucins, Lipase
AntiMucins
Digestion
Viral
Salivary
Families
MineralAntiization
Fungal
Cystatins,
Histatins
Histatins, ProlineLubricatrich proteins,
Tissue ion &ViscoStatherins
Coating elasticity
Amylases,
Cystatins, Mucins,
Mucins, Statherins
Proline-rich proteins, Statherins
Slide no. 3
adapted from M.J. Levine, 1993
Dennis E. Lopatin, Ph.D.
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
Slide no. 4
Dennis E. Lopatin, Ph.D.
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
Slide no. 5
Dennis E. Lopatin, Ph.D.
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?
Slide no. 6
Dennis E. Lopatin, Ph.D.
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

Slide no. 7
Dennis E. Lopatin, Ph.D.
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

Slide no. 8
Dennis E. Lopatin, Ph.D.
Proline-rich Proteins (PRPs)
 Inhibit calcium phosphate crystal growth
 Present in the initially formed enamel pellicle and in
“mature” pellicles
Slide no. 9
Dennis E. Lopatin, Ph.D.
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
Slide no. 10
Dennis E. Lopatin, Ph.D.
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

Slide no. 11
Dennis E. Lopatin, Ph.D.
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

Slide no. 12
Dennis E. Lopatin, Ph.D.
Anti-microbial activities of saliva
Slide no. 13
Dennis E. Lopatin, Ph.D.
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

Slide no. 14
Dennis E. Lopatin, Ph.D.
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 Nacetylmuramic acid and N-acetylglucosamine in the peptidoglycan layer.
– Gram negative bacteria generally more resistant than gram positive
because of outer LPS layer
Slide no. 15
Dennis E. Lopatin, Ph.D.
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

Slide no. 16
Dennis E. Lopatin, Ph.D.
Histatins
A group of small histidine-rich proteins
 Potent inhibitors of Candida albicans growth

Slide no. 17
Dennis E. Lopatin, Ph.D.
Cystatins



Are inhibitors of cysteine-proteases
Are ubiquitous in many body fluids
Considered to be protective against unwanted proteolysis
– bacterial proteases
– lysed leukocytes


Slide no. 18
May play inhibit proteases in periodontal tissues
Also have an effect on calcium phosphate precipitation
Dennis E. Lopatin, Ph.D.
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
Slide no. 19
Dennis E. Lopatin, Ph.D.
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
Slide no. 20
Dennis E. Lopatin, Ph.D.
Thiocyanate reactions
H2O2 + SCN-
SP and/or MP
OSCN- +H2O
Acid/Base Equilib.
HOSCN
Hypothiocianous acid
OSCN- + H+
Hypothiocyanite ion
The pK for HOSCN/OSCN- is 5.3
 More acid favors HOSCN
 Due to uncharged nature, HOSCN
penetrates bacterial cell envelope better

Slide no. 21
Dennis E. Lopatin, Ph.D.
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

Slide no. 22
Dennis E. Lopatin, Ph.D.
Regulation of oral microorganisms by SP/MP
Recovery
Food Ingestion
Unstimulated
bacteria
carbohydrates
Stimulation
thiols
spontaneous
Inhibited
bacteria
Autoinhibition
OSCN-/HOSCN
Inhibition
Slide no. 23
O2
Active
bacteria
H+
SCN- + H2O2
+SP
Salivary Glands
Metabolism
Dennis E. Lopatin, Ph.D.