Cell Injury and Adaptation Lecture Notes PDF

CELL INJURY, CELL DEATH & ADAPTATIONS MIAME ROSE Y. LIMA, MD  An Overview Overview of Cellular Response to Stress and Noxious Stimuli Causes of Cell Injury Overview of Cell Injury and Cell Death Necrosis Apoptosis An Overview….. contd Cellular Adaptations Intracellula...

CELL INJURY, CELL DEATH & ADAPTATIONS MIAME ROSE Y. LIMA, MD  An Overview Overview of Cellular Response to Stress and Noxious Stimuli Causes of Cell Injury Overview of Cell Injury and Cell Death Necrosis Apoptosis An Overview….. contd Cellular Adaptations Intracellular Accumulations Pathologic Calcification OVERVIEW OF CELLULAR RESPONSES TO STRESS AND NOXIOUS STIMULI 🠶Adaptations are reversible functional and structural responses to changes in physiologic states (e.g., pregnancy) and some pathologic stimuli, during which new but altered steady states are achieved, allowing the cell to survive and continue to function. CAUSES OF CELL INJURY 🠶 Oxygen Deprivation 🠶 Physical Agents 🠶 Chemical Agents and Drugs 🠶Infectious Agents 🠶 Immunologic Reactions 🠶Genetic Abnormalities 🠶Nutritional Imbalances  CAUSES OF CELL INJURY 1. Oxygen Deprivation (Hypoxia) (i) Ischemia: Loss of blood supply to a tissue (ii) Anaemia: Decreased haemoglobin, which in turns leads to decreased oxygenation 2. Physical Agents (I )Mechanical trauma. (ii) Extremes of temperature (burns and deep cold) (iii) Radiation and Electric shock 3. Chemical Agents and Drugs (i) Poisons such as Arsenic and Cyanide (ii) Glucose or salts in hypertonic concentrations (iii) Environmental or Air Pollutants (iv) Alcohol and Narcotic Drugs (v) Insecticides and herbicides  CAUSES OF CELL INJURY 4. Infectious Agents Like Viruses, Bacteria, Fungi, Parasites 5. Immunologic Reactions: Immune system serves as defense against biologic agents; Immune reactions may in fact, cause cell injury , for example: (i) Autoimmune Diseases (ii) Anaphylactic Reactions 6. Genetic Derangements: Genetic defects may result in pathologic changes as conspicuous and obvious as the congenital malformations associated with down syndrome or a subtle as the single amino acid substitution in haemoglobin S of Sickle Cell Anaemia  CAUSES OF CELL INJURY 7. Nutritional Imbalances (i) Protein Calorie Deficiencies (ii) Vitamin Deficiency (iii) Lipids excess predispose to Atherosclerosis 8. Aging Cellular senescence leads to alterations in replication and repair abilities of individual cells and tissues. All of these changes result in a diminished ability to respond to damage and, eventually , the death of cells and of the organism Overview of Cell Injury & Cell Death  Point of No Return Two phenomena consistently characterize irreversibility : (1) The inability to reverse mitochondrial dysfunction (lack of oxidative phosphorylation and ATP generation) even after resolution of original injury (2) Profound disturbances in membrane function Reversible Cell Injury: Morphologic Changes The two main morphologic correlates of reversible cell injury are: (i) Cellular Swelling: It is the result of failure of energy dependent ion pumps in the plasma membrane, leading to an inability to maintain ionic and fluid homeostasis. (ii) Fatty Change: It occurs in hypoxic injury and various forms of toxic or metabolic injury. It is manifested by the appearance of small or large lipid vacuoles in the cytoplasm. It occurs mainly in cells involved in and dependent on fat metabolism, such as hepatocytes and myocardial cells Reversible Cell Injury: Morphologic Changes (i) Cellular Swelling It is the first manifestation of almost all forms of injury to cells. It is difficult to appreciate with light microscope; it may be more apparent at the level of whole organ. Gross Examination: When it effects many cells in an organ, it causes some pallor, increased turgor, and increase in weight of the organ. Microscopic Examination: May reveal small, clear vacuoles, within the cytoplasm ; these represent distended and pinchedoff segments of the endoplasmic reticulum. This pattern of non- lethal injury is sometimes called hydropic change or vacuolar degeneration. Reversible Cell Injury: Morphologic Changes (ii) Fatty Change It is manifested by the appearance of lipid vacuoles in the cytoplasm. Injured cells may also show increased eosinophilic staining. This eosinophilic staining becomes more pronounced with progression to necrosis Ultra structural changes of Reversible Cell Injury (1)Blebbing of plasma membrane (2)Blunting or distortion of microvilli (3)Loosening of intercellular attachments (4) Swelling and appearance of phospholipid – rich amorphous densities in mitochondria (5) Dilation of endoplasmic reticulum (6) Detachment of ribosomes (7) Nuclear alterations with clumping of chromatin Morphologic changes in reversible and irreversible cell injury (necrosis) Normal kidney tubules with viable epithelial cells Morphologic changes in reversible and irreversible cell injury (necrosis) Early (reversible) ischemic injury showing surface blebs, Increased eosinophilia of cytoplasm ,and swelling of occasional cells. Morphologic changes in reversible and irreversible cell injury (necrosis) Necrotic (irreversible) cell injury of epithelial cells with loss of nuclei and fragmentation of cells and leakage of contents A normal cell and changes in reversible and irreversible cell injury (Necrosis) CELL DEATH 🠶 There are two principal types of cell death, necrosis and apoptosis, which differ in their mechanisms, morphology, and roles in physiology and disease. 1. Necrosis 2. Apoptosis NECROSIS “Sum of the morphologic changes that follow cell death in a living tissue or organism’’. Two mechanisms are involved in necrosis: 1. Enzymatic digestion of cells by catalytic enzymes (i) Autolysis: Catalytic enzymes derived from the lysosomes of dead cells. (ii) Heterolysis: Catalytic enzyme derived from lysosomes of immigrant leucocytes. 2. Denaturation of Proteins Morphologic Changes in Necrosis A. Changes in Cytoplasm Increased Eosinophilia: It is due to: a) Loss of normal basophilia imparted by RNA in the cytoplasm b) Increased binding of Eosin to denatured intracytoplasmic proteins Cell will assume a glassy homogenous appearance. It is due to loss of glycogen particles Due to digestion of cytoplasmic organelles by enzymes, the cytoplasm will appear vacuolated and appear moth-eaten Calcification of dead cell may occur Morphologic Changes in Necrosis B. Changes in Nucleus Pyknosis: Shrinkage of nucleus Karyolysis: Dissolution of nucleus Karyorrhexis: Fragmentation of nucleus  TYPES OF NECROSIS Several distinct types of necrosis are recognized: 1. Coagulative Necrosis 2. Liquefactive Necrosis 3. Caseous Necrosis 4. Gangrenous Necrosis 5. Fibrinoid Necrosis 6. Fat Necrosis  I. COAGULATIVE NECROSIS Coagulative Necrosis is the most common type of necrosis. The process of coagulative necrosis, with preservation of the general tissue architecture is characteristic of hypoxic death of cells (due to lack of blood supply) in all tissues except brain The pathogenesis of coagulative necrosis is denaturation of proteins. Myocardial Infarction is an important example of coagulative necrosis. It is also seen in infarcts of heart, kidney and spleen. Part of kidney deprived of its blood supply by an arterial embolus. This is an example of caogulative necrosis Cellular and nuclear detail has been Lost. The ghost outline of a glomerulus can be seen in the centre, with remnants of tubule elsewhere  Fig A Fig B Fig A: Normal Myocardium Fig B: Myocardium with coagulation necrosis (upper two thirds of figure), showing strongly eosinophilic anucleate myocardial fibers. Leucocytes in the interstetium are an early reaction to necrotic muscle. Compare with A and with normal fibers in the lower part of figure COAGULATIVE NECROSIS – MYOCARDIAL INFARCTION When there is marked cell injury, there is cell death. This microscopic appearance of myocardium is a mess because so many cells have died that the tissue is not recognizable. Many nuclei have become Pyknotic (shrunken and dark) and have then undergone Karorrhexis (fragmentation) and Karyoloysis (dissolution). The cytoplasm and cell borders are not recognizable  II. LIQUEFACTIVE NECROSIS Liquefactive Necrosis is characteristically seen in: (i) Hypoxic death of cells within the central nervous system (ii) Bacterial or occasionally fungal infections. Liquefaction completely digests the dead cells. The end result is transformation of the tissue into a liquid viscous mass. If the process had been initiated by acute inflammation, the material is frequently creamy yellow because of the presence of dead white cells and is called pus. A focus of liquefactive necrosis in the kidney caused by fungal seeding. The focus is filled with white cells and cellular debris, crating a renal abscess that obliterates the normal architecture  LIQUEFACTIVE NECROSIS BRAIN Grossly, the cerebral infarction at the upper left here demonstrates liquefactive necrosis. Eventually, the removal of dead tissue leaves behind a cavity.  III. CASEOUS NECROSIS A distinctive form of coagulative necrosis. It is encountered most often in foci of Tuberculosis Infection.The term caseous is derived from gross appearance of tissue (white and cheesy). Microscopic Appearance: The necrotic focus appears as amorphous granular debris composed of fragmented, coagulated cells and amorphous granular debris enclosed within a distinctive inflammatory border known a “ Granulomatous Reaction”  Gross Appearance of Caseous necrosis: Foci of caseous necrosis in Tuberculosis of Lung Microscopic Appearance of Caseation Necrosis: Characteristic Tubercle showing central necrosis, along with epithelioid cells, multinucleated Giant cells and lymphocytes EXTENSIVE CASEOUS NECROSIS LUNG IN TUBERCULOSIS Extensive caseous necrosis lung in Tuberculosis, with confluent cheesy granulomas in the upper portion.  IV. GANGRENOUS NECROSIS Gangrene is massive necrosis (Caused by acute ischemia or severe bacterial infection) followed by putrefaction Gangrene is a special type of necrosis, in which bacterial infection is superimposed on coagulative necrosis and coagulative necrosis is modified by the liquefactive action of the bacteria The bacteria proliferate in and digest the dead tissue often with the production of foul smelling gases. The tissue becomes green or black because of the production of iron sulphide from degraded haemoglobin (PUTREFACTION) There are two main types of gangrene: (i) primary ; (ii) Secondary  IV. GANGRENOUS NECROSIS There are two main types of gangrene: (i) primary ; (ii) Secondary (I) Primary (Gas Gangrene): It is due to infection of deep contaminated wounds in which there is considerable muscle damage, by bacteria of the CLOSTRIDIA group- anaerobic spore forming gram positive bacilli which produce saccharolytic and proteolytic enzymes resulting in digestion of muscle tissue with gas formation. The infection rapidly spreads and there is associated severe toxaemia (spread of poisons in the blood) (ii) Secondary Gangrene: This is due to invasion of necrotic tissue usually by a mixed bacterial flora including putrefactive organisms and occurs in two forms: a) Wet gangrene: It occurs due to Arterial and venous occlusion. The tissues are moist at the start of the process either due to oedema or venous congestion. Examples are in strangulation of viscera and occlusion of leg arteries in obese diabetic patients b) Dry Gangrene: It occurs due to Arterial occlusion. Occurs especially in the toes and feet of elderly suffering from gradual arterial occlusions; the putrefactive process is very slow and only small numbers of putrefactive organisms are present. In Dry gangrene distal to arterial occlusion, tissue fluid formation will stop, but since veins are patent, the already present tissue fluid will be drained into the veins as normal DRY GANGRENE WET GANGRENE Due to Arterial occlusion Due to Arterial and Venous occlusion Occurs n limbs in cases of Occurs in limbs in - Senile gangrene - Crush injuries - Berger's gangrene - Tight tourniquets - Raynaud’s disease - Bed sores - Sometimes in diabetic gangrene - Diabetic gangrene Does not occurs in internal organs Occurs in internal organs (intestine) Very slow Putrefaction Rapid Putrefaction decomposition of dead tissue by bacteria leading to formation of iron sulphide, which in turns impart greenish – black colour to tissue) Mild Toxemia Severe Toxemia Gangrenous part is dry and mummified Gangrenous part is swollen Prominent line of demarcation(Dead Poor line of demarcation gangrenous part separates from the living part very distinctively)  DRY GANGRENE TOES This is Gangrene, or necrosis of toes. The toes were involved in a frost bite injury. This is an example of ‘dry gangrene’ in which there is mainly coagulative necrosis due to anoxic injury.  WET GANGRENE LEG This is Gangrene of the lower extremity. In this case the term ‘wet gangrene’ is more applicable because of the liquefactive component from superimposed infection in addition to the coagulative necrosis from loss of blood supply. This patient had Diabetes Mellitus.  V: FAT NECROSIS Fat Necrosis may be due to: (i) Direct Trauma to adipose tissue and extracellular liberation of fat. The result may be a palpable mass, particularly at a superficial site such as the breast (ii) Enzymatic lysis of fat due to release of Lipases. In Acute Pancreatitis there is release of pancreatic lipase. As a result, fat cells have their stored fat split into fatty acids, which then combine with calcium to precipitate out as white soaps.  FAT NECROSIS PANCREAS Cellular injury to the pancreatic acini leads to release of powerful enzymes which damage fat by the production of soaps (combination of calcium salts with fat; fat saponification)), and these appear grossly as the soft Chalky white areas seen in this cut surface Fat Necrosis in acute pancreatitis: The areas of chalky white deposits represents foci of fat necrosis with calcium soap formation (Saponification) at sites of lipid breakdown in the mesentery  VI. FIBRINOID NECROSIS Fibrinoid Necrosis is a type of Connective Tissue Necrosis It is seen particularly in conditions where there is Deposition of Antigen – Antibody Complexes. The important examples are Autoimmune Disorders like Systemic Lupus Erythematosus, Rheumatic Fever and Polyartirtis Nodosa. In these conditions the media and smooth muscle of blood vessels are especially involved.  VI. FIBRINOID NECROSIS Fibrinoid Necrosis is characterized by loss of normal structure and replacement by a homogenous, bright pink-staining necrotic material that resembles fibrin microscopically. Note, however, that “fibrinoid” is not the same as occurs in inflammation and blood coagulation. Areas of fibrinoid necrosis contains various amounts of Immunoglobulins, complement, albumin, break down products of collagen and fibrin Fibrinioid Necrosis in an artery in a patient with polyarteritis nodosa. The wall of the artery shows a circumferential bright pink area of necrosis with protein deposition and inflammation ( dark nuclei of neutrophils)  Differences Between Different Types of Necrosis CAGULATIVE LIQUEFACT- CASEOUS FAT FIBRINOID NECROSIS IVE NECROSIS NECROSIS NECROSIS NECROSIS Occurs due to Occurs due to Occurs due to Occurs due to Due to ischemia ischemia granuloma- trauma or vascular tous disease enzymatic fat inflammation injury In various In Brain In any tissue In Pancreas Around Blood tissues and Breast Vessels Tissue Architecture Cheesy Architecture Architecture architecture destroyed material; distorted not much preserved Architecture affected disturbed Involves Denaturation Caseation Rupture of Fat Accumulation denaturation of Proteins & cells of Fibrinoid of protein & Autolysis material lysosomal enzymes  Biochemical Markers of Necrosis Enzymes Tissue Creatinine Kinase(MB isoenzyme) Heart Certainties Kinase(BB isoenzyme) Brain Creatinine Kinase(MM isoenzyme) Skeletal Muscle Lactic Dehydrogenase(Isoenzyme 1) Heart, Erythrocytes, Skeletal Muscle Lactic Dehydrogenase (Isoenzyme 5) Liver, Skeletal Muscle Aspartate Aminotransferase(AST) Heart, Liver, Skeletal Muscle (Glutamic Oxaloacetate Transferase ; SGOT) Alanine Aminotransferase (ALT) Liver, Skeletal Muscle (Glutamic Oxaloacetic Transferase ; SGPT) Amylase Pancreas, Salivary Gland APOPTOSIS  APOPTOSIS “Programmed Cell Death” It is a form of cell death designed to eliminate unwanted host cells through activation of coordinated, internally programmed series of events effected by a dedicated set of gene products. Apoptosis occurs when a cell dies through activation of an internally controlled suicide program. It is a subtly orchestrated disassembly of cellular components designed to eliminate unwanted cells, during embryogenesis and in various physiologic processes. Doomed cells are removed with minimum disruption to the surrounding tissue. It also occurs, however, under pathologic conditions, in which it is sometimes accompanied by necrosis  Apoptosis refers to a mechanism of cell death affecting usually single cells or a group of cells scattered in a population of healthy cells. It differs from necrosis and represents most of the times a physiological or at times a pathological response by which defective cells and abnormal cells die and are eliminated. The process is rapid and (completed in few hours), and is considered in 2 stages: Stage 1 (Dying Process): a) Active metabolic changes in the cell cause cytoplasmic and nuclear condensation and nuclear membrane is intact. b) Cell disintegrates into multiple Apoptotic Bodies, each surrounded by a part of plasma membrane. Stage 2 (Elimination Process): Phagocytosis of Apoptotic Bodies by surrounding cells, e.g., liver cells, tumour cells. This is followed by rapid digestion. The surrounding cells move together to fill the vacant space leaving virtually no evidence of the process.  PATHOGENESIS OF APOPTOSIS Apoptosis results from the action of intacellular cysteine protease called CASPASES which are activated following cleavage and lead to endonuclease digestion of DNA and disintegration of the cell skeleton. There are two major pathways by which caspases are activated: (i) Activation through Death Factor (Fas Ligand): The is by signaling through membrane proteins such as Fas or TNF receptor intracellular death domain. An example of this mechanism is shown by activated cytotoxic T cells expressing Fas ligand. (ii) Release of Cytochrome – C from the Mitochondria: The second pathway is via the release of Cytochrome – C from mitochondria. Cytochrome – C binds to Apaf – 1 which then activates caspases. DNA damage induced by irradiation or chemotherapy may act through this pathway. Mechanisms of Apoptosis: the two pathways of apoptosis differ in their induction and regulation, and both culminate in the activation of caspases. In the mitochondrial pathway, proteins of Bcl-2 family, which regulate mitochondrial permeability become imbalanced and leakage of various substances from mitochondria leads to caspase activation. In the death receptor pathway , signals form plasma membrane receptors lead to assembly of adaptor protiens into a “death – inducing signaling complex” ,which activates caspases and the end result is the same  APOPTOSIS SPECIFIC GENE Gene that stimulates Apoptosis e.g., bax – gene APOPTOSIS INHIBITING GENE Gene that blocks apoptosis e.g., bcl - gene  PHYSIOLOGIC CONDIITONS HAVING EVIDENT APOPTOSIS 1. The programmed destruction of cells during embryogenesis. 2. Hormone dependent involution in the adults, such as endometrial breakdown during menstrual cycle and regression of lactating breast after weaning 3. Cell depletion in proliferating cell population, such as intestinal crypt epithelia, in order to maintain a constant number 4. Elimination of cells that have served their useful purpose, such as neutrophils in an acute inflammatory response and lymphocytes at the end of an immune situations 5. Elimination of potentially harmful self-reactive lymphocytes either before or after they have completed their maturation, in order to prevent reactions against the body’s owns tissues  PATHOLOGIC CONDIITONS HAVING EVIDENT APOPTOSIS 6. 6. Cell death induced by cytotoxic T lymphocytes, a defense mechanism against viruses and tumours that serves to kill virus-infected and neoplastic cells. 7. DNA damage: Radiation, cytotoxic anticancer drugs, extremes of temperatures and even hypoxia can damage DNA, either directly or through production of free radicals. 8. Accumulation of misfolded proteins :Importantly folded proteins may arise because of mutations in the genes encoding these proteins or because of extrinsic factors , such as damage caused by free radicals. Excessive accumulation of these proteins in the ER leads to a condition called Endoplasmic Reticulum Stress (ER Stress), which culminates in a apoptotic death of cells  PATHOLOGIC CONDITIONS HAVING EVIDENT APOPTOSIS 9. Cell injury in certain infections, particularly viral infections, in which loss of infected cells is largely due to apoptotic death may be induced by the virus ( as in adenovirus and HIV infections) 10. Pathologic atrophy in parenchymal organs after duct obstruction, such as occurs in the pancreas, parotid gland and kidney MORPHOLOGIC CHANGES IN APOPTOSIS Cell Shrinkage: Cell is smaller in size; Cytoplasm is dense; organelles are tightly packed. Chromatin Condensation: Chromatin aggregates peripherally, under the nuclear membrane; nucleus may break in fragments Formation of cytoplasmic blebs and apoptotic bodies. Phagocytosis of apoptotic bodies by adjacent healthy cells MORPHOLOGIC CHANGES IN APOPTOSIS ON HISTOLOGIC SECTIONS: Apoptosis involves single cell or small clusters of cells. The apoptotic cell appears as a round or oval mass of intensely eosinophilic cytoplasm with dense nuclear chromatin The sequential ultra structural changes seen in coagulation necrosis (left) & Apoptosis (right). In apoptosis, the initial changes consist of nuclear chromatin condensation and fragmentation, followed by cytoplasmic budding and phagocytosis of the extruded apoptotic bodies. Signs of coagulation necrosis include chromatin clumping, organellar swelling, and eventual membrane damage. Apoptosis of a liver cell in viral hepatitis. The cell is reduced in size and contains brightly eosinophilic cytoplasm and a condensed nucleus  DYSREGULATED APOPTOSIS (“too little or too much’) Disorders associated with reduced apoptosis: An inappropriately low rate of apoptosis may prolong survival of abnormal cells. These accumulated cells then give rise to: a) Cancers, especially those carcinomas with p53 mutations b) Autoimmune disorders, which could arise, if autoreacitve lymphocytes are not removed after immune response. Disorders associated with increased apoptosis. These disorders are characterized by a marked loss of normal or protective cells and include: a) Neurodegenerative diseases b) Virus – induced lymphocyte depletion c) Aplastic Anaemia  COMPARISON OF CELL DEATH BY APOPTOSIS & NECROSIS FEATURE APOPTOSIS NECROSIS Cell Suicide Cell Homicide Induction May be induced by Invariably due to pathological physiological or pathological injury stimuli Extent Single cells Cell groups Biochemical events (I) Energy- dependent (i) Impairment or cessation of fragmentation of DNA by ion homeostasis endogenous endonucleases (ii) Lysosomes leak lytic (ii) Lysosomes intact enzymes Cell membrane Maintained Lost integrity Morphology Cell fragmentation to form Cell swelling and lysis apoptotic bodies Inflammatory None Usual response Fate of dead cells Ingested by neighbouring Ingested by neutrophils and cells macrophages (i)