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Collagen and collagen disorders


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Collagen is most abundant protein in mammals, the main fibrous component of skin, bone, tendon and cartilage.
Collagen comprises one- third of the total protein, accounts for three-quarters of the dry weight of skin, and is the most prevalent component of the extracellular matrix.
The collagen family consists of 28 members and these are classified by Roman numbers on the basis of their chronology of discovery.

Published in: Education, Technology

Collagen and collagen disorders

  1. 1. Dr. Achi joshi Dept Of Periodontics SAIMS 1
  2. 2.  Introduction  Structure  Biosynthesis of collagen  Types and functions of collagen  Degradation and remodelling of collagen  Biomedical applications  Collagen in periodontal tissue  Collagen disorders  Conclusion 2
  3. 3.  Collagen is most abundant protein in mammals and accounts for 25-30% of their protein content.  Collagen is the main fibrous component of skin, bone, tendon and cartilage.  Collagen comprises one- third of the total protein, accounts for three-quarters of the dry weight of skin, and is the most prevalent component of the extracellular matrix. 3
  4. 4.  The word collagen comes from the Greek word, “kola,” meaning, “Glue producing”  French word, collagene designates glue-producing constraints because collagenous tissue were used as source of glue and gelatin. 4
  5. 5.  When it is heated in water, it gradually breaks down to produce soluble derived protein i.e. gelatin or animal glue.  Miller and Matukas discovered collagen in 1969, since then 26 new collagen types have been found. 5
  6. 6.  The collagen molecule is a rigid rod like structure that resists stretching.  Therefore this protein is an important structural component in tissues such as the periodontal ligament, muscles and tendons in which the mechanical forces need to be transmitted.  Collagen can also influence cell shape, differentiation and many other cellular activities. Thus, forming an important group of multifunctional connective tissue protein that participates in many biological functions. 6
  7. 7.  All collagens are composed of 3 polypeptide alpha chains coiled around each other to form the tripe helix configuration.  The α chains are left handed helices that wrap around each other into a right handed rope like triple helical rod.  Each such helix is around 1.4 nanometers in diameter and 300 nanometers in length  The triple helix may be of a continuous stretch or it may be interrupted by non collagenous elements. 7
  8. 8.  There are around 3 amino acids per turn.  The triple-helical sequences are comprised of Gly-X-Y repeats, X and Y being frequently proline and 4-hydroxy- proline, respectively.  Glycine occupies every third position in the repeating amino acid sequence, it is essential for the triple helical conformation because larger amino acids will not fit in the center of the triple helix. 8
  9. 9.  In the α chain of type I collagen there are 338 Gly – X – Y triplets repeated in a sequence and additional 32 amino acids flank the long triplet sequence at each end. They are known as telopeptides. There is both an amino terminal ( -NH2 ) and a carboxy terminal (-COOH ) telopeptide.  Proline and hydroxyproline in the α chains are imino acids with a rigid cyclical structure. 9
  10. 10.  Stabilization of the triple helix is by-  the presence of glycine as every third residue,  a high content of proline and hydroxyproline, inter-chain hydrogen bonds, and electrostatic interactions involving lysine and aspartate. 10
  11. 11.  Collagen biosynthesis, starting with transcription of genes within nucleus to aggregation of collagen heterotrimers into large fibrils is a complex multistep process.  The entire process of collagen biosynthesis- Gene expression Translational and post translational events or intracellular steps in collagen synthesis Extracellular collagen biosynthetic events Regulation of synthesis 11
  12. 12.  There are more than 40 genes described for collagen types I to XXVIII.  Collagen is a structural protein and its synthesis is similar to synthesis of any other protein molecule and involves process of transcription and translation of genes.  From collagen genes mRNA for each collagen type is transcribed, it undergoes many processing steps to produce a final code for that specific collagen type. This step is called mRNA processing.  The initial RNA transcript is processed to mRNA and it gives rise to the primary 12
  13. 13.  The polypeptide chain formed initially is a helical molecule with two non-helical extensions one at the NH2 and the other at the –COOH terminal end (telopeptide)  The –NH2 terminal extension has a leader or signal sequence that directs the entry of the molecule into the rough endoplasmic reticulum. 13
  14. 14.  The pre- pro-collagen molecule is converted to pro collagen molecule by removal of signal peptide by signal peptidase and undergoes multiple steps of post- translational modifications. 14
  15. 15.  Hydroxyproline and hydroxylysine are formed in the RER by the hydroxylation of prolyl and lysyl residues. This is an essential step in biosynthesis of collagen for it stabilises the molecules.  Requirements for hydroxylation are: Specific enzymes-  prolyl hydroxylase and lysyl hydroxylase  α-ketoglutarate  Ferrous ions  Molecular oxygen  Ascorbic acid (Vitamin C) 15
  16. 16.  The enzyme galactosyl transferase catalyzes the addition of galactose to a hydroxylysyl residue .  Glucosyl transferase catalyzes the further addition of glucose. 16
  17. 17. Formation of procollagen  Following hydroxylation and glycosylation, three polypeptide chains form a triple helix . Secretion of procollagen  Procollagen passes into the Golgi complex before its secretion into the interstitial spaces. 17
  18. 18.  In the interstitial spaces, Procollagen collagen.  Procollagen amino-peptidase and procollagen carboxylase catalyze the removal of the two peptide chains that form the extension of the procollagen molecule. 18
  19. 19.  Cross-linkage of fibrils to form fibres  There is oxidative deamination of specific lysyl or hydroxylysyl residues to form aldehydes; the reaction is catalyzed by lysyl oxidase. 19
  20. 20. 20
  21. 21. 21
  22. 22.  The collagen family consists of 28 members and these are classified by Roman numbers on the basis of their chronology of discovery.  Variations are brought by  Differences in the assembly of basic polypeptide chains  Different lengths of the helix  Various interruptions in the helix and  Differences in the terminations of the helical domains. 22
  23. 23. 23 Type Function I Provides tensile strength to connective tissue II Provides tensile strength to connective tissue III Forms structural framework of spleen, liver, lymph nodes, smooth muscle, adipose tissue. Provides tensile strength to connective tissue IV Forms meshwork of the lamina densa of the basal lamina to provide support and filtration V Provides tensile strength, associated with type I collagen, also with placental ground substance.
  24. 24. 24 VI Bridging between cells and matrix (has binding properties for cells, proteoglycan, a type I collagen) VII Forms anchoring fibrils that fasten lamina densa to underlying lamina reticularis VIII Tissue support, porous meshwork, provide compressive strength IX Associates with type II collagen fibers
  25. 25. 25 X Calcium binding XI Provides tensile strength, controlling lateral growth of type II fibrils XII Associated with type I collagen fibers XIII Cell matrix and cell adhesion XIV Modulates fibril interactions XV Proteolytic release of antiangiogenic factor
  26. 26. 26 XVI Unknown XVII Cell to matrix attachment XVIII Proteolytic release of antiangiogenic factor XIX formation of hippocampal synapses XXIV Regulation of type I fibrillogenesis, marker of osteoblast differentiation and bone formation XXVII cartilage calcification, Association with type II fibrils (?)
  27. 27.  Extracellular matrix remodeling requires the degradation of its components. In general, four types of proteolytic enzymes, capable of ECM degradation, exist:  Matrix metalloproteinases (MMPs)  Serine proteinases (e.g. plasmin)  Cysteine proteinases (e.g. cathepsin K) and  Aspartic proteinases. 27
  28. 28.  The MMPs are considered to be essential for the degradation .  The collagenases are responsible for the first degradation step of collagen, in which the fibers are cleaved into the characteristic 1/4 and 3/4 fragments.  Gelatinases and cysteine proteases further degrade the collagen fragments. 28
  29. 29.  Collagen degradation is an essential component of tissue development during growth and of tissue maintenance in the adult.  Collagenases are widely distributed in the tissues and they bring about collagen turnover, which is under physiological control, and can bring about pathological destruction of connective tissue or provoke excessive new collagen deposition and fibrosis. 29
  30. 30. Collagen degradation The Collagenase Independent Intracellular Route The Collagenase Mediated Extracellular Route 30
  31. 31.  Imbalance between activated MMPs and their endogenous inhibitors leads to pathologic breakdown of extracellular matrix during periodontitis. 31
  32. 32.  Collagen is regarded as one of the most useful biomaterials.  The excellent biocompatibility and safety due to its biological characteristics, such as  biodegradability  biocompatibility  weak antigenicity. 32
  33. 33.  To repair tissues such as bone, tendon, ligament, skin, vascular and connective tissues.  Drug delivery applications: to develop scaffolds for delivery of genes, cell, growth factors, anesthetics, analgesics, antibiotics etc.  For LDD in periodontal pockets  Tissue augmentation: For use in plastic surgery  To enhance blood coagulation and platelet activation  To enhance durability of allograft tissues.  In guided tissue regeneration. 33
  34. 34.  Can be used for the generation of bone substitutes, wound dressings, nerve regeneration.  Artificial skin.  For use as a research tool to study diseases such as diabetes, aging and to evaluate drugs. 34
  35. 35.  Available in abundance and easily purified from living organisms (constitutes more than 30% of vertebrate tissues)  Non-antigenic.  Biodegradable and bio-reabsorbable.  Non-toxic and biocompatible.  Biological plastic due to high tensile strength and minimal expressibility.  Hemostatic — promotes blood coagulation. 35
  36. 36.  Formulated in a number of different forms.  Biodegradability can be regulated by cross-linking.  Easily modifiable to produce materials as desired by utilizing its functional groups.  Compatible with synthetic polymers. 36
  37. 37.  High cost of pure type I collagen.  Variability of isolated collagen (e.g. crosslink density, fiber size, trace impurities, etc.)  Hydrophilicity which leads to swelling and more rapid release.  Variability in enzymatic degradation rate as compared with hydrolytic degradation.  Complex handling properties.  Side effects, such as bovine spongeform encephalopathy (BSF) and mineralization. 37
  38. 38.  The collagen of periodontium is largely Type I , with lesser amounts of type III , IV , VI and XII.  Collagen fibers of the periodontium ( particularly Type I ) provide the structural requirements to withstand intrusive forces of mastication ( tooth support ) and also to accommodate growing tooth in mammals. 38
  39. 39. 39
  40. 40. 40  Out of 22 to 25% of organic component 94 to 98% is mainly collagen type I.  It contains type I collagen predominantly with the molecular configuration of [α1 (I) α2 (I)].  During its formation in the osteoblast the large procollagen precursor undergoes important post translational modifications. Suitably located proline and lysine residues are hydroxylated to hydroxyproline and hydroxylysine respectively.
  41. 41.  Predominant collagen present in cementum is type I collagen (forms 90% of the organic matrix).  Other collagens associated with cementum include type III, a less cross-linked collagen found in high concentrations during development, repair, and regeneration of mineralized tissues and type XII that binds to type I collagen and to non-collagenous matrix proteins.  Collagens found in trace amount in cementum are types V, VI and XIV. 41
  42. 42.  Collagens are the most abundant biochemical constituents of gingival connective tissue.  The collagen matrix of gingival CT is well organized into fiber bundles, which constitute the gingival supra alveolar fiber apparatus. 42
  43. 43. 43  Based on their preferential orientation, architectural arrangement and sites of insertion they are classified as- 1.Dentogingival 2.Dentoperiosteal 3.Alveologingival 4.Periosteogingiva 5.Circular and semicircular 6.Transgingival 7.Transseptal 8.Interpapillary 9.Intercircular 10.Intergingival
  44. 44.  Periodontal ligament is composed of collagen fibers bundles connecting cementum and alveolar bone proper.  The vast majority of collagen fibrils in the periodontal ligament are arranged in definite and distinct fiber bundles and these are termed as principal fibers.  It contains type I and type III collagen, relative proportion of type III to type I varies from 10-25% 44 APICAL OBLIQUE INTER RADICULAR HORIZONTAL TRANSEPATAL ALVEOLAR CREST
  45. 45.  Type III collagen fibers are smaller in diameter and appear to withstand deformation better than type I. It also helps reduce fibril diameter with type I.  Type IV is found in the basement membranes and type V with cell surfaces(0.1-0.2%).  Major crosslink is of di-hydroxy-lysine while hydroxyl-lysine is a minor component  The presence of covalent cross-links between collagen molecules stabilizes the ligament fibres and increases the tensile strength 45
  46. 46.  Majority of PDL collagen fibers are arranged in to Horizontal & Oblique directed groups to adapt to axial forces.  The complex 3D arrangement of fibers means that some bundles would always be placed in Tension, irrespective of the direction of an applied force. This enables local areas of the PDL to resist compressive forces 46
  47. 47.  Tooth support system is a multiphasic system comprising of fibres , ground substances, blood vessels, fluids acting together to resist mechanical forces.  Internal Orientation of collagen fibers influences the mechanical properties of the tissue . Collagen fibers best resist axially directed force as majority of PDL collagen fibers are arranged in to Horizontal & Oblique direction. 47
  48. 48.  OVERLAPPING ARRANGEMENT of fibers as visible in Electron Microscope looks like the spokes of a cycle wheel.  This is very crucial in withstanding Rotational & Intrusive Forces.  This overlapping arrangement helps in spreading the load uniformly and reduce the strain on PDL. 48
  49. 49.  The terminal ends of the collagenous principal fibers are inserted in to bones to form Sharpey’s Fibers.  These are enclosed within a sheath of collagen Type III and it not only confers elasticity on the fibers but it also maintains the elasticity of the fibers when they are inserted in to the bone by preventing their mineralization. 49
  50. 50.  Collagenous tissues exhibit a quantifiable periodicity of structure of variable scale, the waveform that describes this periodicity has been referred to as crimp.  In the polarizing microscope crimping can be seen by regular banding of dark lines across the bundles.  Causes-  Sharp Zig-Zag arrangement of collagen fibers with quantifiable periodicity angular deflection from axis  Microanatomical organization of collagenous sheets and bundles in sinusoidal wave forms. 50
  51. 51.  Significance-  It is an early ,easily extensible , non linear region that causes the straightening out of the crimp, this enables the ligament to absorb impact tensile loads without extending collagen fibrils and without producing heat.  Fibroblast processes in the developing collagenous tissues play a role in fabricating the crimped arrangement and consequently that crimping may be an important feature in tooth eruption.  It also has been proposed that crimp some times can generate contractile forces in collagen molecules. 51
  52. 52. Gingivitis  Collagenolytic activity is increased in inflamed gingival tissue by the enzyme collagenase. Following changes are seen in three different stages of gingivitis:  In initial lesion – perivascular loss of collagen can be seen.  In early lesion - increase in the amount of collagen destruction is seen, 70% of collagen is destroyed around the cellular infiltrate.  This is necessary so that tissues can be pushed apart to accommodate the infiltrating cells and it is considered to be a space creating process.  The main fiber groups affected appear to be circular and dentogingival fiber assemblies. 52
  53. 53.  In established lesion – collagen fibers are destroyed around the infiltrate of intact and disrupted plasma cells, neutrophils, lymphocytes, monocytes and mast cells.  Collagen loss continues in both lateral and apical directions as the inflammatory cell infiltrate expands resulting in collagen depleted spaces extending deeper into the tissues which are then available for leukocyte infiltration. 53
  54. 54. In periodontal pockets  Apical to the junctional epithelium, collagen fibers are destroyed and the area becomes occupied by inflammatory cells and edema.  As the consequence of the loss of collagen,the apical cells of the junctional epithelium proliferate along the root, extending finger like projections two or three cells in thickness. 54
  55. 55. 1. Drug delivery- For LDD in periodontal pockets  The key benefit of localised drug delivery over systemic therapy is that high concentrations of drug can be maintained at the target site, while avoiding risk of systemic toxicity and associated side-effects.  The drugs can be loaded into collagen membranes by hydrogen bonding, covalent bonding or simple entrapment. 55
  56. 56. 56 PPAB is collagen fibril based formulation containing tetracycline hydrochloride (2 mg of tetracycline) in 25 mg of collagen fibrils. Periocol®- TC Sterile collagen Fibres with Tetracycline Hydrochloride for periodontal infections.
  57. 57. 2. Tissue augmentation- recession coverage  Collagen membranes are used as an alternative to connective tissue grafts in mucogingival surgeries.  It shows similar histologic and clinical outcomes, achieving complete root coverage when compared with connective tissue grafts.  It gets completely incorporated in the adjacent host connective tissues without any signs of inflammation. 57
  58. 58. 58
  59. 59. 3. Bone substitute- as bone grafts in intra-bony defects  Collagen has been used as implantable carriers for bone inducing proteins  Collagen itself is used as bone substitutes due to its osteo-inductive activity.  Demineralized bone collagen is used as a bone graft material for the treatment of acquired and congenital bone defects either by itself or in combination with hydroxyapatite crystals. 59
  60. 60. 60 Osseograft/DMBM is one such de-mineralized bone derived Type-I collagen for bone void filling applications. Dembone is Demineralized Freeze-dried Cortical Bone Powder, prepared from cortical bone harvested from carefully screened human donors, demineralized in HCl acid, freeze dried and triple sterilized before vacuum packing.
  61. 61. 61 SyboGraf™ Sterile Synthetic Nanocrystalline Hydroxyapatite Bone Graft. particle size ranging from 200-300 and 600-700 microns.
  62. 62. 4. In guided tissue regeneration- GTR membranes  Guided tissue regeneration (GTR) is a procedure that attempts to reconstitute the lost tissues and is based on the concept of selective repopulation.  The first report of a human tooth treated by guided tissue regeneration was by Nyman et al in 1982, with the term GTR coined by Gottlow et al in 1986.  To exclude the fast-growing cells of the gingival epithelium from migrating to the wound, GTR procedures use barrier devices that are placed between the periodontal flap and the osseous defect to maintain a space for repopulation of the defect with cells having regenerative potential. 62
  63. 63. 63 Healiguide thin sheet made of high purity Type-I collagen derived from selected animal tissues. Periocol® / Helisorb®-GTR Type 1 collagen membrane of fish origin for GTR applications Cologuide
  64. 64. 5. Hemostat During the healthy process of blood clotting, platelets become activated by thrombin and aggregate at the site of injury. Stimulated by the protein fibrinogen, the platelets then clump by binding to the collagen that becomes exposed following rupture of the endothelial lining of blood vessels. Collagen is therefore a natural haemostat and a wide variety of collagen-based products are used in surgery and dentistry to control excessive bleeding or haemorrhage. 64
  65. 65. 65 Absorbable sterile fibrillar collagen wound filler, constituted using high purity type-1 reconstituted collagen •Hemostatic agent •Control bleeding and stabilizes blood clots •Protects wound bed GelSpon® Sterile Absorbable Haemostatic Gelatin Sponges
  66. 66.  Collagen diseases may be genetic, auto-immune or miscellaneous like defects due to nutritional deficiencies, drug induced defects etc. An inborn error of metabolism involving abnormal structure or metabolism of collagen results in collagen disorders. All these affect the biosynthesis, assembly, post-translational modification, secretion, or other processes involved in normal collagen production. 66
  67. 67.  Heritable collagen disorders are caused by mutations in the genes coding for collagen α chain.  The mutations affect the extracellular matrix by decreasing the amount of secreted collagen, impairing molecular and supra-molecular assembly through the secretion of a mutant collagen, or by inducing endoplasmic reticulum stress and the unfolded protein response. 67
  68. 68.  The disease is characterized by-  extremely fragile bones  reduced bone mass  blue sclera,  hearing loss and  scoliosis. 68
  69. 69.  This is due to mutations in one of the two genes, COL1A1 and COL1A2, which encode the two chains of type I collagen, the major protein of bone.  The most common mutations of this disease is due to substitution of glycine with a bigger amino acid. 69
  70. 70. 70 Heterogeneous group of heritable disorders of connective tissue characterized by –  articular hypermobility  skin hyperextensibility, and  tissue fragility affecting skin, ligaments, joints, blood vessels, and internal organs. Cause- mutations in the COL5A1 and COL5A2 genes encoding the α1 and α2 chains of type V are defined.
  71. 71.  Gorlin sign  Early onset generalized periodontitis resulting in the premature loss of deciduous and permanent teeth.  The gingiva is fragile and hemorrhage may be difficult to control during surgical procedures.  Absence of the inferior labial and lingual frenula has been reported in EDS II, EDS III and suggested to be a highly specific and sensitive marker for these disorders. 71
  72. 72.  Alport syndrome is a progressive hereditary nephritis with Extra- renal complications, like sensory-neural hearing loss and ocular abnormalities.  Caused by deletion mutations in COL4A5 and COL4A6 genes or COL4A3 and COL4A4 genes encoding the α3 (IV) and α4 (IV) chains.  X-linked  This syndrome affects some of the basal membranes and is characterized by renal failure, loss of hearing and lens abnormalities. 72
  73. 73. 73  Epidermolysis bullosa (EB) is a clinically and genetically heterogeneous group of inherited disorders that are characterized by blistering of the skin and certain other tissues.  Caused by  mutations in COL7A1, affecting the structure of type VII collagen. Type VII collagen forms delicate fibrils that anchor the basal lamina to collagen fibrils in the dermis. These anchoring fibrils are reduced in this form of the disease, causing friction and blistering.
  74. 74. 74
  75. 75.  A rare, inherited disorders of skeletal development and linear growth.  Involve disturbances of the cartilage components of the growing skeleton, it is Mutations of the gene for type II collagen, COL2A1, produce a broad spectrum of clinical phenotypes that fall under the general designation, spondyloepiphyseal dysplasia (SED). 75
  76. 76.  Knobloch syndrome is an autosomal recessive disorder characterized by high myopia, vitreo-retinal degeneration, occipital bone damage, and congenital encephalocele.  pathological mutations in the COL18A1 gene at 21q22.3 have been identified.  These mutations cause the loss of one or all collagen COL18A1 isoforms or endostatin. 76
  77. 77.  Bethlem myopathy is an autosomal dominant inherited relatively mild disease that is characterized by muscle weakness and distal joint contractures.  Type VII collagen plays a role in connecting cells and extracellular matrix and that mutations in genes encoding collagen VII result in Bethlem myopathy. 77
  78. 78.  It is a unique autosomal dominant syndrome of premature osteoarthritis, retinal degeneration, hearing loss and orofacial abnormalities  caused by mutations in the COL2A1, COL11A1 and COL11A2 procollagen genes of type 2 and 1 collagen. 78
  79. 79.  This autosomal dominant disorder usually presents after the age of 2–3 years with mild short stature, bowing of the lower extremities, and a waddling gait. 79
  80. 80. Osteolathyrism is a collagen cross-linking deficiency caused by dietary over-reliance on the seeds of Lathyrus sativus (kesari dal) in some parts of India. Osteolathyrogenic compounds like Beta-aminopropionitrile (BAPN) and Beta-oxalyl aminoalanine [BOAA] found in Kesari dhal inhibit enzyme lysyl oxidase required for the formation of cross links in the triple helices EFFECT weakness and fragility of skin, bones, and blood vessels Paralysis of the lower extremities associated with neurolathyrism 80
  81. 81.  Collagen diseases share similarities with autoimmune diseases, because autoantibodies specific to each collagen disease are produced.  Multiple organs may be affected. 81
  82. 82.  Lupus erythematosus is a multifactorial autoimmune collagen vascular or connective tissue disease, which may affect the oral mucosa in either its cutaneous and systemic forms with varied prevalence  Oral lesions include ulceration, pain, erythema and hyperkeratosis. Other oral complaints are xerostomia, stomatodynia, candidiasis, periodontal disease and dysgeusia. 82
  83. 83.  This disease is considered to be a consequence of disturbances in the homeostatic equilibrium between synthesis and degradation of extracellular matrix, wherein collagen forms a major component, thus can be recognized as a collagen-metabolic disorder.  It is characterized by a juxta epithelial inflammatory reaction followed by fibroelastic change in the lamina propria and associated epithelial atrophy. 83
  84. 84. 84
  85. 85.  Key function of ascorbic acid is its involvement in the synthesis of collagen fibers from proline via hydroxyproline.  Other metabolic reactions for which vitamin C is required are the hydroxylation of lysine into hydroxylysine in collagen.  In individuals who suffer from a deficiency of this vitamin, the α-chains of the tropocollagen molecules are unable to form stable helices and the tropocollagen molecules are incapable of aggregating into fibrils. 85
  86. 86.  Avitaminosis C is associated with the failure of wound healing or the rupture of capillaries due to intrinsic intercellular weakness with lack of connective tissue support of the capillary walls.  Oral manifestations –  Fetid odor and loosened teeth,  gingivae are boggy, ulcerated and bleed easily  interdental and marginal gingiva become bright red, smooth, swollen and shiny. 86
  87. 87.  In the hyperglycemic state, numerous proteins and matrix molecules undergo a non-enzymatic glycosylation, resulting in accumulated glycation end products (AGEs).  Collagen is cross-linked by AGE formation, making it less soluble and less likely to be normally repaired or replaced.  As a result, collagen in the tissues of patients with poorly controlled diabetes is aged and more susceptible to breakdown i.e., less resistant to destruction by periodontal infections. 87
  88. 88. 1. Hereditary gingival fibromatosis  both dominant autosomal inheritance and recessive autosomal inheritance  It is a gradually progressive benign enlargement that affects the marginal, attached, and interdental gingiva.  Histopathologically, it implies an increase in both extracellular matrix and cell numbers. 88
  89. 89. 2. drug induced enlargement  A. phenytoin  Fibroblasts become sensitive to phenytoin, and this results in subsequent increased production of collagen.  The enzyme collagenase secreted by phenytoin-sensitive fibroblasts is relatively inactive to degrade collagen.  An imbalance in production and degradation results in the over accumulation of collagen and hence in an increase in the bulk of connective tissue. 89
  90. 90.  B. Calcium channel blockers  After an interaction between nifedipine and gingival fibroblasts, overproduction of collagen and extracellular ground substance occurs and leads to an increase in the size of the gingiva.  C. Cyclosporin induced  It was found that CsA could react with a phenotypically distinct subpopulation of gingival fibroblasts to enhance protein synthesis. 90
  91. 91.  Collagens have ubiquitous distribution throughout the animal kingdom. Collagens serve important mechanical functions within the body, particularly in connective tissues and also exert important functions in the cellular microenvironment.  It is an important constituent of periodontium therefore knowledge of the structure, biosynthesis and interactions of collagen with other components, its regulation and degradation mechanisms and changes it undergoes with age and diseased state is essential, for the understanding of the functioning of the periodontium. 91