Biochemistry of connective tissue Pathochemistry of inflammation

Transcription

1 Biochemistry of connective tissue Pathochemistry of inflammation Outline: 1. Biochemistry of connective tissue 2. Healing of wounds 3. Pathochemistry of wound healing 4. Sources 1. Connective tissue Tissue that supports, connects, separates other tissues and organs in the body Consists primarily of fibroblasts ECM + collagen synthesis Extracellular matrix materials production structure of organs in body help fulfilling functions of these organs and tissues Included in these materials: collagen and elastin (structural proteins), fibronectin (adhesive proteins), heparan sulfate and chondroitin sulfate (glycosaminoglycans) Absence of these components pathological clinical consequences Figure Healing of wounds Process of tissue repair with the help of local wound factors and systematic mediators after skin injury Regeneration // replacement new and functional tissue Phases: Figure 2

2 1) Hemostasis (min-h) Ensures that blood loss is minimized after an injury and that thrombocytes react to the same injury Activation of thrombocytes and endothelial cells contraction of injured vessel and soft clot formation to stop bleeding Action of thrombin (present in blood as inactive proenzyme) formation of thrombus of fibrin Activation of protein factors, phospholipids and calcium ions of hemocoagulation cascade Vasoconstriction thrombocytes activity hemocoagulation fibrinolysis 1) Redirection of leakage Contraction of smooth muscles by adrenalin, pain reflexes Serotonin + thromboxane A2 by thrombocytes Adhesion + aggregation + secretion 2) Collagen exposure causes thrombocytes to accumulate Binding to collagen and to vwb factor activation Activation leads to secretion of content granules Coagulation of blood common pathway triggered by injury to blood vessel (in vitro coagulation cascade) 1) Tissue thromboplastin (factor III) membrane protein on the vessel wall activates coagulation factor VII 2) Factor VIIa generates factor IXa 3) With the help of factor VIIIa, phospholipids and calcium Xa is generated 4) This leads to activation of prothrombin active thrombin is released 5) Thrombin (factor IIa) catalyzes the conversion of fibrinogen (plasma protein) into fibrin 6) Fibrin (converted with the help of thrombin) is responsible for creation of a fibrous network in the primary thrombus (weak fibrin clot) 7) Tranglutaminase (XIII) finally stabilizes the thrombus (strong fibrin Figure 3

3 clot) - transamidation reaction between Gln and K side chains on adjacent fibrin monomers 8) Fibrin clot physically traps the infectious microorganisms and tries to prevent their invasion into the bloodstream Several anticoagulant factors, present in the blood, try to avoid excessive blood cloting, e.g. by binding the serine proteases in the pathway to inhibit their activity Coagulation factors Vitamin K Calcium Von Willebrand factor Anticoagulation factors Protein C Antithrombin III Plaminogen NO ad PGI2 Heparin Walfarin Hirudin Aspirin Fibrinolysis When bleeding stops, which means, the fibrin thrombus is formed Fibrin clot (thrombus) breakdown dissolution by plasmin (serine protease) Plasminogen (precursor) is activated by Plasminogen activator (urokinase) and by Tissue plasminogen activator (from endothelial cells) antiplasmin and macroglobulin both inhibit fibrinolysis by binding to the active plasmin Goal: prevent any problems with excessive clotting Figure 4 g/fibrinolysis-chart.jpg 2) Inflammation: 1) Vasoconstriction achieved by smooth muscles around larger blood vessels to redirect the flow 2) Vasodilation (histamine, prostaglandins, complement C3/C5) 3) Leucocytes produce selectins, which bind selectin receptors on the inner wall of the venule leukocyte travels on the inner wall 4) Activation of adhesion molecules on the endothelial cells these adhesion molecules are bound by integrins (molecules on leukocyte surface)

4 5) Diapedesis = integrins facilitate squeezing of leucocytes between endothelial cells 6) Due to final blood clotting cascade bleeding in the surrounding small blood vessels stops and entrance of (further) microbes into the bloodstream is thus inhibited 7) 2 systems involved in immune response (innate + acquired immune system), by trying to recognize and destroy any microorganism, that might have entered the body through the wound 8) Innate immune system: seeks to distinguish btw. Bacteria and viruses or foreign proteins/antigens phagocytes digest and so destroy the threat Complement system supports non-specific defence with the help of complement factors (serine proteases present in blood), is activated by the presence of any pathogen or by simulation by Acute-phase proteins. An enzyme cascade composed of three parts (Classical, Lecithin and Alternative pathways) is triggered. Activation of factor C1 due to contact with IgM or IgG, when these bind to the surface of microbes, leads to the activation of factors C4 and C2. Factors C2a and C4B together form C3 convertase, which catalyses the step in the cascade leading to the three working ways of the system. First complement factors (factors C1-C4 from the classical pathway, factors B/D from the alternative pathway) try to attract immune cells that are capable of phagocytosing threats like pathogens (=Chemotaxis). Then, opsonins (responsible for Opsonization) bind covalently to molecules on the pathogens surface, for them to be recognized by macrophages, and so, eliminated. Factors C5 and C9 are responsible for the last stage of this system, the Membrane attack. Ion-permeable-pores are created on the pathogens surface, making it unstable and finally leading to lysis. Acquired immune system: ability of the (B/T) lymphocytes to create a memory based on the antigens they meet. Each lymphocyte in the body carries a different receptor for a different antigen. This provides the ability of a more specific response to some pathogens. 9) Activation cellular and humoral immune responses needed for successful pathogen elimination. Antigen presenting cells (B lymphocytes, macrophages, dendritic cells) are responsible for taking up the pathogens and proteolytically degrading them. If T cells have Figure 5 Figure 6 Innate_Humoral_And_Cell_Mediated_Immunity_files/image030.jpg

5 a receptor that binds to the antigen, binding will lead to proliferation (stimulated by interleukins), in order to quantitatively degrade the pathogen. B cells are recognized by T-helper cells, which later leads to maturation into plasma cells along with antibody secretion. All types of healing processes undergo this phase Assists immune cells in reaching the site of infection Immunological prevention of infection (protective function) Localization of infection place + inhibition of spreading + returning to physiological state Manifestation: Rubor, calor, tumor, dolor, function laesa Purifying of wound neutrophils, mastocytes, macrophages 3) Proliferation (1-2d) aim: diminish lesioned tissue are by contraction + fibroplasia establish epithelial barrier to activate keratinocytes closure of lesion angiogenesis, fibroplasia, reepithelization begin: within first 48h up to the 14 th day after onset of lesion vascular remodeling (angiogenesis) blood flow changes newly modeled microvascular plexus makes it possible to transport oxygen, fluid, nutrients and immuno-competent to stroma granulation tissue begins to form app. 4 days after lesion fibroblastic proliferation, collagenous and elastic biosynthesis creates a 3D extra cellular network of connective tissue repair process modulated by keratinocytes at border of lesion + cytokines and growth factors (cell differentiation and proliferation) fibroblasts proliferate and deposit collagen (main component of connective tissue scar) formation of intact basal membrane between epidermis and dermis epithelial cells proliferate and migrate from borders of wound (reepithelization) epidermal cells of hair follicles remove coagulation and damaged stroma 4) Remodelling aim: reorganization + resynthesis of ECM ensure maximal stressability Figure 7

6 begins 2-3 weeks after onset, can last for >1 year attempt to recover normal tissue structure formation of less vascular and cellular scar tissue with inc. conc. of collagen fibres as soon as surface of lesion covered by keratinocytes epidermal migration ceases and new stratified epidermis with basal lamina re-establishes from wound borders During maturation + remodelling processes majority of vessels, fibroblasts and inflam. Cells disappear from wound are (emigration, apoptosis etc.) systemic disorders (diabetes), immunosuppression, smoking etc. can hinder early closure of the wound 3. Pathobiochemistry of inflammation Eicosanoids Cell signalling molecules (G-protein, camp) Precursor: arachidonic acid Arachidonic acid can then follow 2 pathways: - cyclo oxygenase prostaglandins and tromboxanes - lipoxygenase leukotrienes Function in various physiological states and in pathological events, such as inflammatory response intensity and persistence of pain, fever Figure 8 Prostaglandins vasodilators, inhibitors of aggregation of blood platelets Thromboxanes blood clotting Cyclo oxygenase inhibitory effect if enzyme (also known as: prostaglandin synthase) is active, prostaglandins are produced Elevated levels of the enzyme are found during inflammation 2 isoenzymes: COX-1 stomach, kidneys COX-2 inflammation Nonsteroidal anti-inflammatory drugs reduce pain, fever, inflammation, prevent blood clots work by inhibiting activity of COX-2 Selective inhibitors Non-selective ihnibitors Therapeutic effect (COX-1, COX-2) Therapeutic effect (COX-2) Ex.: Aspirin, Voltaren, Brufen ex.: Aclexa, Cerebrex

7 Monotoring of inflammation Acute phase reactants Proteins present in plasma concentration in plasma dependant on inflammation Roles in: - inflammative protection - hemocoagulation and fibrinolysis - protease inhibitors - ROS protection Positive APR APP (Ig, Ceruloplasmin, Fibrinogen) CRP SAA Negative APR Albumin Prealbumin Transferin Erythrocyte sedimentation rate (ESR) Non-specific measure of inflammation in body Blood placed into a tube (Westergren) with anticoagulation agents (natrium citrate) Measurement of ability of red blood cells to sedimentate, and so accumulate at the bottom of the container, within an hour measurement in milimeters of plasma upon sedimentation (women- 3-8mm/h, men- 2-5mm/h) Values increase with age Sedimentation speed directly dependent on erythrocyte aggregate production Influenced by fibrinogen, Ig and APF Causes of high values: Inflammation Anaemia Infection Tumour/autoimmune diseases (aging, pregnancy)

8 Sources: - Seminar presentation: Biochemistry of connective tissue. Pathobiochemistry of inflammation - Lecture presentations: Biochemistry of Extracellular matrix, Immune system, Blood cells and coagulation - Marks Basic medical biochemistry - Color atlas of biochemistry -