Cell injury Dr. Maha Arafah Assistant Professor Department of Pathology King Khalid University Hospital and King Saud University Email: marafah@ksu.edu.sa marafah @hotmail.com Saturday, Oct 9, 2010 9:00 to 10:00 am

CONCEPT OF INJURY AND CELLULAR RESPONSE TO INJURY Overview of Cell Injury and Cell Death L2: Necrosis and Apoptosis L3: Cellular accumulation and Calcification L4: Adaptation to environmental stress

Overview of Cell Injury and Cell Death Definition Causes Reversible cell injury ( nonlethal hit) Irreversible injury and cell death ( lethal hit) Mechanisms of Cell Injury Free radical injury Morphology of cells in injury

Objectives Upon completion of this lecture, the student should: Understand the concepts of reversible and irreversible (lethal) cell injury. Know the causes of cell injury. Be aware of the mechanisms of cell injury which include the actions of: Bacterial toxins. Free radicals. Hypoxia. Chemical injury Effects of viruses. Radiation. Be aware of the morphology of cells in reversible and irreversible injury

CELLULAR RESPONSE TO INJURY CONCEPT OF INJURY AND CELLULAR RESPONSE TO INJURY Cells are constantly exposed to a variety of stresses. When too severe, INJURY results. Injury alters the preceding normal steady state of the cell.

ALL CELLS

ALL ORGANISMS

Living in the World

Must cope with…

Stress!!!

Etiologic agents

MECHANISMS OF CELL INJURY General principles: The cellular response to injurious stimuli depends on 1. type of injury 2. Its duration 3. Severity The consequences depend on the type, status, adaptability, and genetic makeup of the injured cell. The structural and biochemical components of a cell are so integrally connected that multiple secondary effects rapidly occur Cellular function is lost far before cell death occurs

Objectives Know the causes of cell injury. Upon completion of this lecture, the student should: Understand the concepts of reversible and irreversible (lethal) cell injury. Know the causes of cell injury. Be aware of the mechanisms of cell injury which include the actions of: Bacterial toxins. Free radicals. Hypoxia. Chemical injury Effects of viruses. Radiation. Be aware of the morphology of cells in reversible and irreversible injury

Causes of cell injury EXCESS or DEFICIENCY OF OXYGEN 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)

(chemical:alcohol, genetic:a1AT deficiency) This is a lesion caused by HBV infectious agent (chemical:alcohol, genetic:a1AT deficiency) Liver: cirrhosis

Objectives Upon completion of this lecture, the student should: Understand the concepts of reversible and irreversible (lethal) cell injury. Know the causes of cell injury. Be aware of the mechanisms of cell injury which include the actions of: Bacterial toxins. Free radicals. Hypoxia. Chemical injury. Effects of viruses. Radiation. Be aware of the morphology of cells in reversible and irreversible injury

Mechanisms of cell injury Cell membrane damage Complement-mediated cell membrane lysis via the membrane attack complex (MAC) Bacterial toxins Free radicals   Mitochondrial damage leading to inadequate aerobic respiration Hypoxia (lack of oxygen) Cyanide poisoning Ribosomal damage leading to altered protein synthesis Alcohol in liver cells Antibiotics in bacteria Nuclear change Viruses Radiation

MECHANISMS OF CELL INJURY Integrity of Cell Membranes Mechanisms of membrane damage in cell injury: Decreased O2 and increased cytosolic Ca2+ are typically seen in ischemia but may accompany other forms of cell injury. Production of reactive oxygen species Lysis of enzymes Activation of complement system Lysis by viruses

MECHANISMS OF CELL INJURY Effect of plasma membrane damage Loss of structural integrity Loss of function

MECHANISMS OF CELL INJURY DEPLETION OF ATP ATP depletion and decreased ATP synthesis are frequently associated with both hypoxic and chemical (toxic) injury Depletion of ATP to <5% to 10% of normal levels has widespread effects on many critical cellular systems: Plasma membrane energy-dependent sodium pump is reduced, resulting in cell swelling increased rate of anaerobic glycolysis, glycogen stores are rapidly depleted. Glycolysis results in the accumulation of lactic acid. This reduces the intracellular pH, resulting in decreased activity of many cellular enzymes. Failure of the Ca2+ pump leads to influx of Ca2+ In cells deprived of oxygen or glucose, unfolded protein formed, that may lead to cell injury and even death.

MECHANISMS OF CELL INJURY Heat shock proteins: Definition: They are proteins which stabilize other cellular proteins. Function: Guide the newly synthesized protein and the misfolded proteins to degradation. Protect proteins from cellular stresses.

Chaperones

Repair of Protein Damage

MECHANISMS OF CELL INJURY MITOCHONDRIAL DAMAGE Mitochondria are important targets for virtually all types of injurious stimuli, including hypoxia and toxins. Cell injury is frequently accompanied by morphologic changes in mitochondria.

GENERAL MECHANISMS OF INJURY Result in apoptosis

INFLUX OF INTRACELLULAR CALCIUM AND LOSS OF CALCIUM HOMEOSTASIS Calcium ions are important mediators of cell injury. Cytosolic free calcium is maintained at extremely low concentrations (<0.1 μmol) compared with extracellular levels of 1.3 mmol (most intracellular calcium is sequestered in mitochondria and endoplasmic reticulum) Such gradients are modulated by membrane-associated, energy-dependent Ca2+, Mg2+-ATPases. Ischemia and certain toxins cause an early increase in cytosolic calcium concentration, owing to the net influx of Ca2+ across the plasma membrane and the release of Ca2+ from mitochondria and endoplasmic reticulum

Failure of intracellular calcium homeostasis

MECHANISMS OF CELL INJURY the integrity of the genetic apparatus of the cell Caused by: Ionizing radiation Viruses Mutagenic chemicals

MECHANISMS OF CELL INJURY (4) the integrity of the genetic apparatus of the cell Effect of DNA abnormalities: 1. Failure of synthesis of proteins and enzyme 2. Failure of mitosis 3. Progression to cancer

Free radicals and cell membrane damage

MECHANISMS OF INJURY BY FREE RADICALS Free radicals are highly reactive atoms which have an unpaired electron in an outer orbital. This state is unstable and react with organic and inorganic chemical. The most important free radicals are derived from oxygen   Superoxide Hydrogen peroxide Hydroxy radical 

Injury by free radical Free radical can be produced in cells in response to a variety of processes, including radiation, normal metabolic oxidation reactions and drug metabolism processes.

MECHANISMS OF INJURY BY FREE RADICALS What happen when the cell is injured by free radicals? Lipid peroxidation Protein damage DNA damage 

A. Superoxide dismutase. 2O2- + 2H ---> H2O2 + O2 Normal mechanism to protect against free radical injury 1. Enzyme A. Superoxide dismutase. 2O2- + 2H ---> H2O2 + O2 B. Glutathione peroxidase. H2O2 + 2 GSH ---> 2H2O + GSSG C. Catalase. 2H2O2 ----> O2 + 2 H2O 2. Antioxidant: vit E, vit C Sulfhydryl containing compounds e.g. cysteine Proteins e.g., transferrin and albumin

ISCHEMIC AND HYPOXIC INJURY

ISCHEMIC AND HYPOXIC INJURY Oxygen is required for oxidative phosphorylation. Hypoxia and ischemia occur in: a] Hypoglycaemia. b] Hypoxia due to : 1. Respiratory obstruction or disease. 2. Ischemia. 3. Anaemia. 4. Alteration of hemoglobin. c] Enzyme inhibition by cyanide. d] Uncoupling of oxidative phosphorylation.

ISCHEMIC AND HYPOXIC INJURY The result is defective ATP production First cells affected are those with highest demand of oxygen.

How Ionizing Radiation Kills Cells  Proliferating Cells - by DNA damage. Leads to apoptosis.  Nonproliferating cells- by lipid peroxidation.

How Viruses Kill Cells Directly Cytopathic Viruses – e.g. Poliovirus Indirectly cytopathic Viruses -  e.g. hepatitis B

How Viruses Kill Cells Direct cytopathic viruses insert their proteins into the plasma membranes, disrupting the cells permeability (membrane damage) Indirect cytopathic viruses also in insert their proteins into the plasma membrane, but to create an antigenic target for cytotoxic T lymphocytes. 

How Chemicals Kill Cells : Group I : interact directly with cellular contents to cause damage (mercury, lead and iron (toxic heavy metals)  Group II: whose metabolite is toxic e.g. hepatotoxins: (Carbon tetrachloride(CCl4), acetominophen, bromobenzene) Group III: bind cytochrome P450 (the mixed function oxygenase involved in drug metabolism)     

Reversible and irreversible cell injury : time and exposure factors Chemical injury Reversible and irreversible cell injury : time and exposure factors

Sequelae of cell injury Depend on: A. cell features Specialization. Cells that are enzyme rich, nucleated or have specialized organelles within the cytoplasm may be more vulnerable. Cell state. Cells that have an inadequate supply of oxygen are more prone to injury. Regenerative ability. The potential of a cell population to divide is important in the response of tissues to injury.

Sequelae of cell injury Depend on: B. Injury features: Type of injury. The injury may be ischaemic, toxic, chemical, etc. Exposure time. The length of time of exposure to a toxin or reduced oxygen concentration will affect the change of a cell surviving the insult. Severity. The ability to survive an injury will also depend upon its severity, e.g. is the lack of oxygen partial (hypoxia) or complete (anoxia).

Objectives Upon completion of this lecture, the student should: Understand the concepts of reversible and irreversible (lethal) cell injury. Know the causes of cell injury. Be aware of the mechanisms of cell injury which include the actions of: Bacterial toxins. Free radicals. Hypoxia. Chemical injury Effects of viruses. Radiation. Be aware of the morphology of cells in reversible and irreversible injury

morphology of cells in reversible and irreversible injury

Morphologic changes in Reversible Injury Early changes: (1) Cloudy swelling or hydropic changes: Cytoplasmic swelling and vacuolation due to intracellular accumulation of water and electrolytes secodary 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

Hydropic vacuoles in the endoplasmic reticulum of hepatocyte Reversible changes

Nucleus Hydropic vacuoles in the endoplasmic reticulum of hepatocyte

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

Following ischemic heart injury, the following sequence is observed: rapid biochemical and ultrastructural responses light microscopic evidence of reversible injury after several minutes ultrastructural evidence of irreversible injury in 20-60 minutes unequivocal light microscopic evidence of cell death after 11-12 hours

MECHANISMS OF INJURY: Ischemia

TAKE HOME MESSAGES:   Cellular injury is caused by various elements include bacterial toxins,, hypoxia, alcohol, viruses and radiation. Depletion of ATP, free radicals production, disruption of cell membrane and chromatin are important mechanism in cell injury Cellular injury could be reversible (sublethal) or irreversible (lethal).