Saliva biochemistry

SALIVA BIOCHEMISTRY

Germain INTWALI UR-CMHS

School of DentistryDental therapy dpt.

Intended learning outcomes

Biochemistry of saliva and teeth

14.1. Describe the biochemical composition of saliva

14.2. Describe the biochemical composition of teeth

14.3. Explain the pH changes of saliva

14.4. Describe the functions of saliva

THE BIOCHEMISTRY OF SALIVA

Saliva is produced in and secreted from acinar cells in salivary glands

Secretion volume per day: 1.0-1.5 liters from major s. glands (Parotid, sub mandibular and sublingual)

This include resting flow and stimulated during eating

pH of saliva: 7-8


Composition of saliva: Water 94-99.5% Solid substance range from 0.5% to 6% in unstimulated

and stimulated saliva

Solid substances are: Inorganic constituents: Ca, Mg, F, Na, HCO3, K, Na, Cl and

NH4 ions Organic contituents: Ure, Uric acid, free glucose, free

amino acids, lactate and fatty acids, Organic micromolecules: Proteins, amylase, peroxidase,

thiocyanate, lysozymes, lipids, IgA, IgM, and IgG Elements from oral cavity: Desquamated epithelial cells,

PMNL, and bacteria

Gases: O2, Co2, and N2.


Composition in groups:

Aqueous: water, salivary amylase, lingual lipase, IgA, Kallikrein, Muramidase and Lactoferrin

Electrolytes: Ca, PH, F, K, Na, Cl

Mucus secretion proteins: Mucin, Statherins, Proline rich proteins, antimicrobial proteins such as; Lactoferrin, Histatins, Lysozymes, Cystatins, Peroxidases, Secretory immunoglobins


Saliva is hypotonic to plasma

Na+, Cl- low in saliva than plasma

K+, HCO3- higher in saliva than plasm

pH changes from acidic (6-7) at rest to basic (pH 8) at ultimate stimulation due to Higher HCO3- in the saliva


Functions:

Moistening food

Beggining of digestion

Adjust salt appetite

Contains factors that inhibit adhesion and destroy bacteria (Anti-bacteria)

Antifungal (Histatins)

Antiviral (Cystatins, Mucins)

Buffering


Functions:

Lubrication and visco-elasticity

Mineralizations

Buffering oral environment

HYDROGEN IONS

1. PROTONS (H+)

Concentration dictates pH of the oral environment

pH of saliva varies according to flow rate (young infants also have slightly more alkaline saliva)

Why is pH important in the mouth?

Typical salivary pH (adult) is around 6 – 7.4

-a- Maintaining ionic product for hydroxyapatite (see later)-b- Isoelectric point for salivary protein precipitation on to tooth surfaces-c- Optimal pH for salivary enzymes

EFFECT OF CARBOHYDRATE CONSUMPTION ON PLAQUE pH

Time (min)

pH

4

5

6

7

8

0 40 80

CHO CHO

The Stephan Curve: Stephan, RM, J Am Dent Ass. 27: 718-723, 1940

Mineral dissolves

EFFECT OF SUCROSE ON PLAQUE pH

4

5

6

7

pH

Sucrose0.025%

Sucrose1.25%

Sucrose2.5%

Sucrose5%

Sucrose10%

3% UREA 3% UREA

Time (min)0 113

Chew wax3 min

Chew wax3 min

Chew wax3 min

Chew wax3 min

Chew wax3 min

Chew wax3 min

Telemetric data from: Imfeldt, 1977

pH of SALIVA (cont)

The pH of saliva varies with flow rate

Higher flow rates increase salivary buffering

Flow rate pH

In general:

=

EFFECT OF FLOW RATE ON pH OF SALIVA

0.25 mL/min

0.5 mL/min

1 mL/minstimulation begun

unstimulated

0 5 10 15 20 25

5.8

6.2

6.6

7.0

7.4

pH

Time (min)

2. BICARBONATE IONSImportant BUFFER at high flow rates

Concentration in saliva varies with salivary flow as bicarbonate content of saliva increases with metabolic activity of the salivary glands

Range: < 1 mM (unstimulated) to 60 mM (highest flow rates)

Concentration in mechanically stimulated saliva typically around 15 mM

Produced by the striated epithelium of the salivary gland ducts

EFFECT OF FLOW RATE ON BICARBONATE CONCENTRATION IN

SALIVA

0

8

16

24

32

HC

O3 (

mM

)

stimulation begun

unstimulated

1 mL/min

0.5 mL/min

0.25 mL/min

Time (min)

5 10 15 20 25

0

BUFFERING OF PROTONS BY BICARBONATE

H+ + HCO3 H2CO3 H2O + CO2-

pKa = 6.1

Carbonic anhydrase

Carbonic anhydrase is present in salivary glands (and also in saliva)

BICARBONATE PRODUCTION IN SALIVA

HCO3

H2CO3 H2O + CO2H+

LUNGS

CATABOLISM IN GLAND

HCO3

H2CO3 H2O + CO2H+

Excess in saliva

PLASMA

SALIVARY GLAND

-

-

3. POTASSIUM AND SODIUM IONSBoth present as counter ions to preserve electrical neutrality

Concentration range: Sodium: 6 – 26 mM

Potassium: 14 – 32 mM

Sodium is the counter ion for bicarbonate

Potassium is the counter ion for phosphate

Flow rate Na+

In general:

= but K+

EFFECT OF FLOW RATE ON SODIUM AND POTASSIUM CONCENTRATIONS IN

SALIVA

Rate of secretion mL / 6 min

Con

cen

trati

onm

eq

/ L

20

40

60

1 2 3

Na

K

4. CALCIUM AND MAGNESIUM IONS

Mg++Present in saliva but role and origin unclear.

Possible origins: Cellular degradation (host / bacterial); Early carious attack

(Mg++ rich mineral is first to be removed during acid attack)

Concentration range in saliva: 0.2 – 0.5 mM

Flow rate Mg++

In general:

=

4. CALCIUM AND MAGNESIUM IONS (cont)

Ca++

Actively secreted by major salivary glands

Forms complexes with calcium-binding salivary proteins

Concentration range in saliva: 1 – 2 mM

Flow rate Ca++

In general:

=

Behaviour with flow rate variable due to protein binding

Important role in maintenance of ionic product for hydroxyapatite (see later)

(& protein)

EFFECT OF FLOW RATE ON Ca++ AND Mg++ CONCENTRATIONS IN SALIVA

Ca (

mM

)

0

40

80

120

Mg

(µM

)

stimulation begun

unstimulated

0 5 10 15 20 25

0.9

1.1

1.3

0.04 mL/min

1.00 mL/min

Time (min)

1.5

Ca++

Mg++

EFFECT OF FLOW RATE ON CONCENTRATION OF PROTEIN IN

SALIVA

Time (min)

1 mL/min

0.5 mL/min

0.25 mL/minunstimulated

stimulation begun

Pro

tein

(m

g%

)

110

190

270

350

5 10 15 20 25

5. PHOSPHATE IONS

Flow rate H2PO4- / HPO4

=

In general:

=

Concentration range in saliva: 2 -23 mM

Acts as a buffer, especially in unstimulated saliva

Important in maintenance of ionic product for hydroxyapatite

EFFECT OF FLOW RATE ON INORGANIC ORTHOPHOSPHATE CONCENTRATION IN

SALIVA

Time (min)

4

8

12

Inorg

an

ic p

hosp

hate

(m

M)

unstimulated

stimulation begun

0.25 mL/min0.5 mL/min

1 mL/min

5 10 15 20 250

HYDROXYAPATITEThe mineral component of the mammalian skeletal tissues is a calcium phosphate salt:

HYDROXYAPATITE (HAP; HA, OHA)

Ca10(PO4)6(OH)2

Ionic product for HAP:

Pi = [Ca]10 x [PO4]6 x [OH]2

ROLE OF CALCIUM AND PHOSPHATE IN MAINTAINING TOOTH MINERAL INTEGRITY

AND REMINERALISATION

Saliva is supersaturated with respect to hydroxyapatite

This is essential for:

Maintenance of ionic product

Remineralisation

BUT

Without the presence of inhibitors in saliva, spontaneous precipitation would occur



The mineral component of enamel and dentine is a substituted hydroxyapatite; HAP. Ca10(PO4)6(OH)2

HAP dissolution (and precipitation) therefore depends upon the concentration of Ca++, PO4

3- (and OH-) in saliva.

Protonation of the phosphate group is pH dependent

PO43- HPO4

2- H2PO4- H3PO4

+H+ +H+ +H+

-H+ -H+ -H+

pKa = 12.7 pKa = 7.2 pKa = 2.12



When pH falls, increasing protonation of the phosphate groups results in the formation of salts of greater solubility and vice versa

Ca10(PO4)6(OH)2HAPHydroxyapatite

Brushite / Dicalcium phosphate

CaHPO4 / CaHPO4.2H2ODCPD

Octacalcium phosphate OCP Ca8(PO4)4(HPO4)2.5H2O

Tricalcium phosphate TCP Ca3(PO4)2

Monocalcium phosphateMCP Ca(H2PO4)2

6. CHLORIDE IONS

Preserves electrical neutrality

Activates salivary amylase

Concentration range in saliva: 17 – 29 mM

Flow rate Cl-

In general:

=

6. FLUORIDE ION

Fluoride ion is normally present at very low concentrations in whole saliva (range = 0.001 – 0.005 mM)

Fluoride replaces (OH) in the HAP lattice structure, increasing its stability and inhibiting acid dissolution

Fluoride facilitates HAP precipitation and therefore promotes remineralisation.

Fluoride accumulates in porous enamel (and dentine), including caries lesions

Fluoride concentrations in plaque are higher than those in saliva

Salivary fluoride in patients living in areas of water fluoridation is approx. 2x that of patients living in non-fluoridated regions.

This is a small absolute difference but the benefits in caries reduction are highly significant.

Special thanksTo Dr. Mumena Chrispinus:

A senior lecture and vice Dean of the school of Dentistry at the College of Medicine and Health Sciences- UNIVERSITY OF Rwanda.

Addition: Dean of the OPHTALMOGY DEPT. at UR- CMHS

Saliva biochemistry

Health & Medicine

Transcript of Saliva biochemistry