Cellular Injury (year 2010 )

1. Cellular Injury (year 2010 ) Dr. Huda M.Zahawi, FRC.Path.

2. Topic Outline • Causes of cell injury • Types of Injury • Priciples & Mechanisms of cell injury • Outcome : ?Reversible ? Irreversible • Morphology • Adaptation to Injury • Patterns & types of Cell Death • Process of Aging

3. Cellular Injury & Adaptation • Normal cell is in a steady dynamic state “Homeostasis” : • The ability or tendency of an organism or cell to maintain internal equilibrium by adjusting its physiological processes.

4. Cells are constantly exposed to stresses. • Normal physiologic stress • Severe stresses: injury results, and alters the normal steady state of the cell, consequently, • It can survive in a damaged state and adapt to the injury (reversible injury or adaptation) • It can die (irreversible injury or cell death).

5. STRESS INJURY NORMALCELL Adaptation Reversible injury Irreversible injury Cellular swelling Vacuolar change Fatty change Atrophy Hypertophy Hyperplasia Metaplasia Necrosis Apoptosiss

6. Causes of Cell Injury • Hypoxia and ischemia • Free radicals • Chemical agents • Physical agents • Infections • Immunological reactions • Genetic defects • Nutritional defects • Aging

7. TYPES OF INJURY

8. 1- Hypoxia & Ischemia • Causes of Hypoxia • low levels of oxygen in the air • poor or absent Hemoglobin function • decreased erythropoiesis • respiratory or cardiovascular diseases, or ischemia (reduced supply of blood)

9. Ischemia & Hypoxia induce mitochondrial damage. • This results in decreased ATP which in turn reduces energy for all cell functions ! • If persistent  CELL DEATH

11. Hypoxia is a common cause of cell injury Result : Cell resorts to anaerobic glycolysis Ischemia is the commonest cause of hypoxia, & injures the cells faster than pure hypoxia Why ?? Restoration of blood may lead to recovery OR Ischemia/ Reperfusion injury  Progressive cell damage Examples : Myocardial & Cerebral infarction

12. Ischemia/Reperfusion Injury • Restoration of blood flow influx of high levels of calcium • Reperfusion increases recruitment of inflammatory cells  free radical injury • Damaged mitochondria induce free radical production & compromise antioxidant defense mechanisms • Dead tissue becomes antigenicAB  activation of complement immune response

13. Recommendation : • In some cases , high oxygen therapy to improve hypoxia is NOT given because it generates oxygen derived FREE RADICALS ( Reactive Oxygen Species ROS)

14. 2- Free Radicals • Free radicals are chemical species with a single unpaired electron in an outer orbital, they are chemically unstable and therefore readily react with other molecules, resulting in chemical damage. • To gain stability, the radical gives up or steals an electron. • Radicals can bind to proteins, carbohydrates lipids, producing damage.

15. Chemical injury Physical injury Inflammation Oxygen toxicity Reperfusion injury Malignant transformation Aging Sources of Free Radicals in pathology

16. Formation of Free Radicals : • Endogenous from normal metabolism • Reduction Oxidation reaction (REDOX) in mitochondria • Transition metals (Copper, Iron) catalyze Free Radicals formation by donating or accepting free electrons (Fenton reaction) Ferric iron Ferrous iron superoxide

17. Exogenous formation : • Ionizing radiation • Drug metabolism

18. Free Radicals (Examples) • Reactive Oxygen Species (ROS) generated by mitochondrial respiration : • OxygenSuperoxide • H2O2 (Hydrogen peroxide) • OH (hydroxyl group) • Inflammation : • Accumulation of leucocytes • NO (Nitric oxide) reactive nitrite

19. Mechanism of injury by Free Radicals • 1-Lipid peroxidation (oxidative degradation of lipids): • Destruction of unsaturated fatty acids by binding to methylene groups (CH2) that posses reactive hydrogen molecules

20. 2-Protein destruction: By cross linking proteins forming disulfide bonds (S-S) → inactivate enzymes, & polypeptide degradation • 3- DNA alteration: By producing single strand breaks in DNA • Induce mutation that interfere with cell growth

21. Inactivation Free Radicals • Spontaneous decay • Enzymes • Superoxide dismutase, • glutathione peroxidase, and catalase • Antioxidants • Block synthesis or inactivate free radicals • Include Vitamin E, Vitamin C, albumin, ceruloplasmin, and transferrin

22. 3- Chemical Agents • Chemical agents can cause cellular injury by: • direct contact of the chemical with molecular components of the cell. • Indirect injury • formation of free radicals, or lipid peroxidation.

23. Examples of injurious chemicals • Cyanide disrupts cytochrome oxidase. • Mercuric chloride binds to cell membrane in cell resulting in increased permeability. • Chemotherapeutic agents & antibiotics may act in the same way. • Carbon Monoxide (CO) • Ethanol • Lead

24. Action of Carbon Monoxide : • Has a very high affinity to hemoglobin (carboxyhemoglobin: COHb) • The effect of large quantities of COHb is death (carbon monoxide poisoning). • Smaller quantities of COHb leads to tiredness,dizziness & unconsciousness.

25. Action of Ethanol : • The conversion of ethanol to acetaldehyde leads to formation of free radical. • Acetaldehyde initiates changes in liver • Fatty change • Liver enlargement • Liver cell necrosis.

26. liver enlargement with deposition of fat

27. Action of Lead : • Mimics other metals (calcium, iron and zinc) which act as cofactors in many catalyzing enzymatic reactions. • Acts on the CNS by interfering with neurotransmitters, blocking glutamate receptor. (May cause wrist, finger,&foot paralysis). • Affects hemoglobin synthesis

28. Indirect injury of some chemicals : • Activation in the liver by the P- 450mixed function oxidases in SER . • CCL4 CCL3 (FR)  membrane phospholipid peroxidation & ER destruction: • ↓ protein ↓ lipid  No apoproteins for lipid transport  Fatty liver • Mitochondrial injury  ↓ATP  Failure of cell function  increased cytosolic Ca+  cell death • Acetaminophen may act similarly

29. 4- Physical agents • Mechanical injury resulting in tearing, or crushing of tissues. e.g.: blunt injuries , car accidents…. • Ionizing Radiation • Water and DNA are the most vulnerable target

30. Physical agents (cont……) • Extreme temperatures • Hypothermia • Hyperthermia • Atmospheric Pressure • Blast injuries • Water pressure – increased or decreased

31. 5-Infectious Agents • Bacteria: produce toxins • Endotoxin • Exotoxin • Viruses : • Decrease the ability to synthesize proteins • Change host cell’s antigenic properties

32. 5-Immunological reactions • Cell membranes are injured by contact with immune components such as lymphocytes, macrophages….etc • Exposure to these agents causes changes in membrane permeability

33. 6- Genetic Diseases • Genetics play a substantial role in cellular structure and function. • A genetic disorder can cause a dramatic change in the cell’s shape, structure, receptors, or transport mechanisms.eg : • Enzyme deficiencies • Sickle Cell Anemia

34. 7- Nutritional Imbalances • Adequate amounts of proteins, lipids, carbohydrates are required. • Low levels of plasma proteins, like albumin, encourages movement of water into the tissues, thereby causing edema. • Hyperglycemia, hypoglycemia, • Vitamin deficiencies (vitamins E, D, K, A, and folic acid) • Excess food intake is also classified as a nutritional imbalance

35. Mechanism of cell injury & sites of damage

36. General Considerations: • Function is lost before morphological changes occur • EM changes • Microscopic changes • Gross changes

38. Result of injury depends on : • Injury : Type Duration Severity • Type of cell: • Specialization • Adequacy of blood supply, hormones, nutrients • Regenerative ability or adaptability • Genetic make up

39. Steps & Cellular targets in Injury :

40. 1- Mitochondria: Interruption of oxidative metabolism • Loss of energy due to formation of mitochondrial permeability transition pore (MPT)  loss of membrane potential  prevents ATP generation (ATP depletion) • Cytochrome c released into cytosol  activates apoptosis. • O2 depletion ROS

41. 2- Cell Membranes • Important sites of damage : • Mitochondrial membrane ATP • Plasma membrane failure of Na pump leads to cellular amounts of water • Lysosomal membrane  enzyme release, activation & digestion of cell components

42. 3- Influx of Calcium: • Ca stability is maintained by ATP • Loss of Ca homeostasis  cytosolic Ca+  activation of: • phospholipases • proteases • ATPases • Endonucleases

44. 4-Protein synthesis: High fluid levels cause ribosomes to separate from the swollen endoplasmic reticulum  protein synthesis, glycolysis Metabolic acidosis 5- Genetic apparatus DNA defects & mutations

45. Injury at one locus leads to wide ranging secondary effects • Cascading effect

46. Subcellular response to injury

47. 1- Hypertrophy of Smooth Endoplasmic Reticulum in liver induced by some drugs e.g. barbiturates , alcohol…. etc. 2-Mitochondrial alterations in size & number e.g. in atrophy, hypertrophy, alcoholic liver 3-Cytoskeletal abnormalities e.g. microtubule abnormality involved in cell mobility

48. 4- Lysosomal Catabolism: Enzymatic digestion of foreign material (Heterophagy / pinocytosis &phagocytosis) orintracellular material (Autophagy). Persistent debris → residual body (Undigestible lipid peroxidation products → Lipofuscin pigment.

49. Morphology of reversible cell injury: Ultrastructurally : • Generalized swelling of the cell and its organelles • Blebbing of the plasma membrane • Detachment of ribosomes from the endoplasmic reticulum • Clumping of nuclear chromatin.

50. Transition to irreversible cell injury : • Increasing swelling of the cell • Swelling and disruption of lysosomes • Severe swelling & dysfunction of mitochondria with presence of large calcium rich densities in swollen mitochondria • Disruption membranes→ phospholipase • Irreversible nuclear changes