Transcript Document
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.