Cellular Pathology 2: Cell Injury PDF

Cellular Pathology 2: Cell Injury Michael M. Yakubovskyy, MD, PhD 1 Content and Learning Objectives Content Definitions Learning Objectives LO1. Compare and contrast the reversible and irreversible cell injury, cell death, and necrosis. Causes and LO2. Correlate between the causes and pathophys...

Cellular Pathology 2: Cell Injury Michael M. Yakubovskyy, MD, PhD 1 Content and Learning Objectives Content Definitions Learning Objectives LO1. Compare and contrast the reversible and irreversible cell injury, cell death, and necrosis. Causes and LO2. Correlate between the causes and pathophysiological mechanisms mechanisms of cell of cell injury and provide clinical examples. Explain relationship injury between ischemia and reperfusion injury. LO3. Compare and contrast the light microscopic and ultrastructural Morphology of cell features of reversible and irreversible cell injury in association with injury underlying biochemical mechanisms. 2 Definitions •LO1. Define reversible and irreversible cell injury, cell death, and necrosis. Definition and Classification • • Cell injury (damage): a sequence of pathologic events that occur, when the limits of adaptive capability are exceeded, or no adaptive response is possible Cell death: death of single cells and groups of cells in a living organism 4 Reversible Injury —> Point of No Return —> Irreversible Injury —> Death: Diagram PNR 5 PNR: Point of No Return Causes and Mechanisms of Cell Injury •LO2. Explain the causes and pathophysiologic mechanisms of cell injury and provide clinical examples. Explain relationship between ischemia and reperfusion injury. Causes and Mechanisms of Cell Injury (and) Necrosis Causes Mechanisms 1 Hypoxia and ischemia 1 ATP depletion 2 Microorganisms 3 Chemical agents and drugs 2 Generation of free radicals 4 Physical agents (heat, cold, radiation, mechanical trauma) 3 Calcium influx 4 Reperfusion injury 5 Immunologic reactions 5 Membrane damage 6 Genetic derangements 6 Mitochondrial damage 7 Nutritional imbalances 7 DNA damage 7 Hypoxia vs. Ischemia • • Hypoxia: a reduction in amount of oxygen available to tissues Causes of hypoxia o o o o Ischemia: a reduction in blood supply to tissues (Refer to the next slide.) Anemia: reduced oxygen-carrying capacity of the blood Ventilation defects e.g., neonatal respiratory distress syndrome Perfusion defects e.g., interstitial lung fibrosis 8 Ischemia • Common clinical conditions associated with ischemia - • Occlusion by an atherosclerotic plaque, e.g., coronary/cerebral/mesenteric artery Torsion of a vessel e.g., mesenteric or testicular artery Compression from outside e.g., by a tourniquet Low cardiac output due to left-sided heart failure, shock, or severe collapse —> generalized ischemia Major pathophysiologic mechanism: ischemia —> hypoxia —> reduction in oxidative phosphorylation —> ATP depletion 9 ATP Depletion, Major Adverse Effects • • • + Na + Na Insufficiency of ATP-dependent pump —> gain of and water —> swelling of mitochondria, ER, and the cell in toto Detachment of ribosomes from rER and dissociation of polysomes into monosomes —> reduction in protein synthesis Activation of anaerobic glycolysis —> depletion of glycogen stores and accumulation of lactic acid —> acidosis (—> pH 6.0) —> clumping of nuclear chromatin 10 Free Radicals and Reactive Oxygen Species: Definitions • • • Free radicals: chemical species with a single unpaired electron in an outer orbital Reactive oxygen species (ROS): oxygen-derived free radicals Physiologic function: contribute to aerobic respiration and inflammation https://commons.wikimedia.org/wiki/File:ROSDw001.png Dw001, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons 11 Sources of Free Radicals • Physiology o o • Redox reactions in mitochondria —> O2· (superoxide radical or superoxide) · and OH · Reactions with transition metals (iron and copper) —> generation of OH Pathology o Inflammatory response: generation of • o o · NO —> NO· + O2· = ONOO¯ (peroxynitrite, a potent oxidant) · OH · H Radiation-induced water radiolysis: generation of + Enzymatic metabolism of drugs and chemicals e.g., acetaminophen and CCl4 12 Mechanisms of ROS-Induced Injury • Lipid peroxidation of membranes o • • ROS break double-bonds in polyunsaturated fatty acids —> peroxide production —> autocatalytic chain reaction (propagation) Protein cross-linking and oxidation —> unfolding and/or misfolding with following accumulation DNA damage o Single- and double-strand DNA brakes, and cross-linking 13 Calcium Influx • • Causes of calcium influx: ischemia/hypoxia, toxins, and reperfusion Sources for intracytoplasmic calcium increase: mitochondria, sER, and interstitium 14 https://commons.wikimedia.org/wiki/File:Animal_mitoch ondrion_diagram_en_(edit).svg LadyofHats, Public domain, via Wikimedia Commons Adverse Effects of • Influx Activation of lytic enzymes o o Phospholipases —> damage of organelle and cell membranes —> leakage of lysosomal enzymes in the cytosol, and cytosol components in the interstitium Proteases —> damage of cytoskeleton (actin cortex below the cytomembrane) —> loss of microvilli and formation of cytomembrane blebs • • 2+ Ca Non-lysosomal neutral proteases: calpains Opening of mitochondrial permeability transition pores (MPTP) in the inner mitochondrial membrane —> leakage of (toxic) matrix components 15 Summary Diagram of IschemiaInduced Cell Injury Reperfusion Injury • • • Beneficial effects of reperfusion: restoration of blood supply in the ischemic area —> restoration of ATP production Adverse effects of reperfusion: exacerbation of cell injury (reperfusion injury) Mechanisms of reperfusion injury o o o 2+ Ca —> Additional influx of see above Influx of O2 —> generation of additional ROS —> see above Influx of leukocytes —> activation of inflammatory response to necrotic tissue 17 Morphology of Cell Injury •LO3. Compare and contrast the light microscopic and ultrastructural features of reversible and irreversible cell injury in association with underlying biochemical mechanisms. Structural Changes: Principal Steps 1. Reversible injury: injury of membranes with increased permeability (both cyto- and organellar membranes) 2. Somewhere here: point of no return (PNR) 3. Irreversible injury: rupture of membranes o o o Mitochondrial membrane rupture —> inability to restore generation of ATP Lysosomal membrane rupture —> autolysis Cytomembrane rupture —> leakage of intracellular proteins into the interstitium and blood —> specific markers of organ injury 4. Cell death (postmortem cellular changes) 20 Reversible Injury: Structural Changes Structure EM Swelling/rarefaction of matrix Mitochondria Accumulation of small amorphous densities rER Cytomembrane Lipid droplets Dilation LM Cytoplasmic vacuoles (cellular swelling) Detachment of ribosomes Blebbing and blunting Loss of microvilli Increased in size and amount Empty spaces in H+E stained slides 21 Mitochondria in Cell Injury: Matrix Swelling, Loss of Cristae, Small Amorphous Densities, EM Control https://commons.wikimedia.org/wiki/File:Mitochondria,_mammalian_lung_-_TEM_(2).jpg Louisa Howard, Public domain, via Wikimedia Commons 22 1) Sesso A, Belizário JE, Marques MM, Higuchi ML, Schumacher RI, Colquhoun A, Ito E, Kawakami J - Anatomical record (Hoboken, N.J. : 2007) (2012) Cellular Swelling (A&B) and Lipid Droplets (B), Histo A Kidney, Tubular Epithelium B Hepatocytes 23 •Two o Irreversible Injury: Morphology o types of changes Membrane rupture: cytomembrane and mitochondrial membrane Accumulation of large amorphous densities in mitochondria (calcium and/or phospholipids) 24 Cell Membrane Rupture, EM 25 1)https://openi.nlm.nih.gov/imgs/512/273/4372376/PMC4372376_pone.0121674.g004.png?keywords=fragmentation,swelling,lysis,condensations,bleb,transmission,absence The End 26