Necrosis and apoptosis (Foundation Block, pathology) Lecturer name: Dr. Maha Arafah Lecture Date: 17-9-2012 Cell injury L2

Objectives List causes of cell injury List mechanisms of cell injury Understand the changes in reversible and irreversible cell injury Define necrosis and apoptosis List the different conditions associated with apoptosis, its morphology and its mechanism List the different types of necrosis, examples of each and its features Know the difference between apoptosis and necrosis

DEFICIENCY OF OXYGEN Ischemia vs. Hypoxia PHYSICAL AGENTS Etiologic agents DEFICIENCY OF OXYGEN Ischemia vs. Hypoxia PHYSICAL AGENTS CHEMICAL AGENTS INFECTION IMUNOLOGICAL REACTIONS GENETIC DERANGEMENTS NUTRITIONAL IMBALANCE AGING

Brain – massive haemorrhagic focus (ischemia) in the cortex This is a lesion caused by DEFICIENCY OF OXYGEN

Abscess of the brain (bacterial) This is a lesion caused by infectious agent

Hepatic necrosis (patient poisoned by carbon tetrachloride) This is a lesion caused by chemical agent

Pulmonary caseous necrosis (coccidioidomycosis) This is a lesion caused by infectious agent

Gangrenous necrosis of fingers secondary to freezing This is a lesion caused by physical agent

The “boutonnière” (buttonhole) deformity This is a lesion caused by intrinsic factors (autoimmune disease)

Liver: macronudular cirrhosis (HBV) This is a lesion caused by infectious agent: Viral hepatitis (chemical:alcohol, genetic:a1-AT deficiency)

morphology of cells in reversible and irreversible injury

myocadial cells: loss of function after 1-2 min of ischemia However do not die until 20 to 30 min of ischemia EM: 2-3 hours, LM 6-12 hours

Morphologic changes in Reversible Injury Early changes: (1) Cloudy swelling or hydropic changes: Cytoplasmic swelling and vacuolar degeneration due to intracellular accumulation of water and electrolytes secondary to failure of energy- dependent sodium pump. (2) Mitochondrial and endoplasmic reticulum swelling due to loss of osmotic regulation. (3) Clumping of nuclear chromatin.

Vacuolar (hydropic) change in cells lining the proximal tubules of the kidney Reversible changes

Morphologic changes in irreversible injury: 1. Severe vacuolization of the mitochondria, with accumulation of calcium-rich densities. 2. Extensive damage to plasma membranes. 3. Massive calcium influx activate phospholipase, proteases, ATPase and endonucleases with break down of cell component. 4. Leak of proteins, ribonucleic acid and metabolite. 5. Breakdown of lysosomes with autolysis. 6. Nuclear changes: Pyknosis, karyolysis, karyorrhexis.

IRREVERSIBLE CELL INJURY- NECROSIS

Morphologic changes in irreversible injury - Dead cell are either collapsed and form a whorled phospholipid masses or degraded into fatty acid with calcification. - Cellular enzymes are released into circula- tion. This provides important clinical parameter of cell death e.g. increased level of creatinin kinase in blood after myocardial infarction

Myocardial infarct This is a lesion caused by oxygen deprivation Cell Pathology This is a lesion caused by oxygen deprivation Myocardial infarct

Mechanisms of cell injury Depletion of ATP Damage to Mitochondria Influx of Calcium Free radicals production Disruption of cell membrane and chromatin

Mechanisms of cell injury

Cell Death Death of cells occurs in two ways: Necrosis--changes produced by enzymatic digestion ofcells after irreversible injury Apoptosis--vital process that helps eliminate unwanted cells--an internally programmed series of events effected by dedicated gene products Autolysis Autolysis is the death of individual cells and tissues after the death of the whole organism. The cells are degraded by the post-mortem release of digestive enzymes from the cytoplasmic lysosomes. Autophagy: Self eating in starvation

Necrosis Necrosis is defined as the morphological changes that result from cell death within living tissues. In necrosis, death of a large number of cells in one area occurs. These changes occur because of digestion and denaturation of cellular proteins.

Patterns of Necrosis: In Tissues or Organs As a result of cell death the tissues or organs display one of these six macroscopic changes: Coagulative necrosis Liquifactive necrosis Caseous necrosis Fat necrosis Gangrenous necrosis Fibrinoid necrosis

Patterns of Necrosis In Tissues or Organs Coagulative necrosis: Denaturation of intracellular protein leads to the pale firm nature of the tissues affected. The cells show the microscopic features of cell death but the general architecture of the tissue and cell ghosts remain discernible for a short time. The outline of the dead cells are maintained and the tissue is somewhat firm. Example: kidney and heart injury caused by ischaemia.

Removal of the dead tissue leaves behind a scar Coagulative necrosis Kidney: ischemia and infarction (loss of blood supply and resultant tissue anoxia). Removal of the dead tissue leaves behind a scar

Acute renal tubular necrosis (ischemia) : increased eosinophilia and pyknosis in necrotic cells Normal Necrotic

Coagulative necrosis: Remember: True coagulation necrosis involves groups of cells, and is almost always accompanied, by acute inflammation (infiltrate)

Patterns of Necrosis In Tissues or Organs 2. Liquefactive necrosis: The dead cells undergo disintegration and affected tissue is liquefied. This results from release of hydrolytic lysosomal enzymes and leads to an accumulation of semi- fluid tissue. Example: cerebral infarction. Abscess

Liquefactive necrosis in brain leads to resolution with cystic spaces.

Liquefactive necrosis of the brain: macrophages cleaning up the necrotic cellular debris Removal of the dead tissue leaves behind a cavity

Removal of the dead tissue leaves behind a cavity or scar Liquefactive necrosis: two lung abscesses Removal of the dead tissue leaves behind a cavity or scar

Removal of the dead tissue leaves behind a scar Localized liquefactive necrosis liver abscess Removal of the dead tissue leaves behind a scar

Patterns of Necrosis In Tissues or Organs 3. Caseous necrosis: A form of coagulative necrosis but appear cheese-like. The creamy white appearance of the dead tissue is probably a result of the accumulation of partly digested waxy lipid cell wall components of the TB organisms. The tissue architecture is completely destroyed. Example: tuberculosis lesions fungal infections Coccidioidomycosis blastomycosis histoplasmosis

Caseous necrosis in a hilar pulmonary lymp node infected with tuberculosis.

Pulmonary tuberculosis:tubercle contains amorphous finely granular, caseous ('cheesy') material typical of caseous necrosis. Removal of the dead tissue leaves behind a scar

Caseous necrosis is characterized by acellular pink areas of necrosis, surrounded by a granulomatous inflammatory process. N

Patterns of Necrosis In Tissues or Organs 4. Fat necrosis: This can result from direct trauma or enzyme released from the diseased pancreas. Example: Necrosis of fat by pancreatic enzymes. Traumatic fat necrosis in breast Adipocytes rupture and the released fat undergoes lipolysis catalyzed by lipases. Macrophages ingest the oily material and a giant cell inflammatory reaction may follow. Another consequence is the combination of calcium with the released fatty acids.

Fat necrosis secondary to acute pancreatitis

Fat Necrosis  Specific to adipose tissue with triglycerides. With enzymatic destruction(lipases) of cells, fatty  acids are precipitated as calcium soaps. Grossly- chalky white deposits in the tissue. Microscopically – amorphous, basohilic /purple deposits at the periphery of necrotic adipocytes. 

Patterns of Necrosis In Tissues or Organs 5. Gangrenous necrosis: This life-threatening condition occurs when coagulative necrosis of tissue is associated with superadded infection by putrefactive bacteria. These are usually anaerobic gram-positive Clostridia spp. Derived from the gut or soil which thrive in conditions of low oxygen tension.

Patterns of Necrosis In Tissues or Organs 5. Gangrenous necrosis: Gangrenous tissue is foul smelling and black. The bacteria produce toxins which destroy collagen and enable the infection to spread rapidly. If fermentation occurs, gas gangrene ensues. Infection can become systemic (i.e. reach the bloodstream, septicaemia). The commonest clinical situation is gangrene of the lower limb caused by poor blood supply and superimposed bacterial infection. This is a life-threatening emergency and the limb should be amputated.

Example: necrosis of distal limbs, usually foot and toes in diabetes. “Wet" gangrene “ of the lower extremity in patient with diabetes mellitus: liquefactive component from superimposed infection coagulative necrosis from loss of blood supply.

Patterns of Necrosis In Tissues or Organs 6. Fibrinoid necrosis: typically seen in vasculitis and glomerular autoimmune diseases

Fibrinoid necrosis: afferent arteriole and part of the glomerulus are infiltrated with fibrin, (bright red amorphous material)

Outcome of necrosis Depending on circumstances: necrotic tissue may be walled off by scar tissue, totally converted to scar tissue, get destroyed (producing a cavity or cyst), get infected (producing an abscess or "wet gangrene"), or calcify. If the supporting tissue framework does not die, and the dead cells are of a type capable of regeneration, you may have complete healing.

Apoptosis Vital process. Programmed cell death. Can occurs in physiological or pathological conditions.

Physiologic process to die Apoptosis Physiologic process to die This process helps to eliminate unwanted cells by an internally programmed series of events effected by dedicated gene products. It serves several vital functions and is seen under various settings. Remember: apoptosis require energy to die

Apoptosis A. Physiologic SEEN IN THE FOLLOWING CONDITIONS: A. Physiologic During development for removal of excess cells during embryogenesis To maintain cell population in tissues with high turnover of cells, such as skin, bowels. To eliminate immune cells after cytokine depletion, and autoreactive T-cells in developing thymus. Hormone-dependent involution - Endometrium, ovary, breasts etc.

Apoptosis B. Pathologic To remove damaged cells by virus Atrophy (virtually never accompanied by necrosis). To eliminate cells after DNA damage by radiation, cytotoxic agents etc. Cell death in tumors.

Morphology of Apoptosis Shrinkage of cells Condensation of nuclear chromatin peripherally under nuclear membrane Formation of apoptotic bodies by fragmentation of the cells and nuclei. The fragments remain membrane- bound and contain cell organelles with or without nuclear fragments. Phagocytosis of apoptotic  bodies by adjacent healthy cells or phagocytes. Unlike necrosis, apoptosis is not accompanied by inflammatory reaction

Liver biopsy - viral hepatitis: acidophilic body (councilman body) (apoptosis, i.e., induced, or programmed, individual cell death). Vacuolar change is reversible.

Skin, apoptotic Keratinocyte

MECHANISMS OF APOPTOSIS 1. Chromatin condensation is mediated by calcium-sensitive endonuclease leading to internucleosomal DNA fragmentation. 2. Alteration in cell volume (shrinkage) due to action of transglutaminase. 3. Phagocytosis of apoptotic bodies is mediated by receptors on the macrophages. 4. Apoptosis is dependent on gene activation and new protein synthesis, e.g. bcl-2, c-myc oncogene and p53.

Apoptosis summary

Apoptosis regulating genes

Genes that regulate apoptosis: Oncogene Bcl-2 Bcl-2 overexpression prevents apoptosis Antagonized by cell death genes Bcl-2 overexpression is found in follicular lymphoma. Tumor suppressor gene p-53 Will cause cells with DNA damage to go apoptosis Reversed by overexpression of bcl-2

Objectives Define necrosis and apoptosis List the different conditions associated with apoptosis, its morphology and its mechanism List the different types of necrosis, examples of each and its features Know the difference between apoptosis and necrosis

Difference between apoptosis and necrosis Coagulation Necrosis Apoptosis Stimuli Hypoxia, Toxins Physiologic and pathologic conditions Histologic appearance Cell swelling, coagulation necrosis disruption of organelles Single cell, chromatin condensation, apoptotic bodies DNA breakdown Random and diffuse internucleosomal Mechanism ATP depletion membrane injury Gene activation, endonucleases, proteases Tissue reaction Inflammation No inflammation, phagocytosis of apoptotic bodies Energy Not needed Needed