Cell Injury 1&2

Cell Injury, Death, and Adaptation

The Cell and the Environment ●

Adaptive Responses – Atrophy – Hypertrophy – Hyperplasia – Metaplasia

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Cell Injury – Reversible (degeneration) – Irreversible ( Cell death):

Necrosis Apoptosis

Causes of Cell Injury ● ● ● ● ● ● ●

Hypoxia Physical Agents Chemicals and Drugs Microbiologic Agents Immunologic Reactions Genetic Defects Nutritional Imbalances

Mechanisms of Cell Injury ● ●

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ISCHEMIC AND HYPOXIC INJURY FREE RADICAL MEDIATION OF CELL INJURY – Radiation – Inflammation – Oxygen toxicity – Chemicals – Reperfusion injury

CHEMICAL INJURY

Ischemic and Hypoxic Injury ●

Reversible Injury may show the followings: 1- Decreased oxidative phosphorylation * reduced ATP • increased cytosolic free calcium * reduced activity of “sodium pump” • accumulation of sodium by cell • isosmotic gain of water (swelling) • diffusion of potassium from cell

2- Increased Cytosolic Calcium – Sources * mitochondria * endoplasmic reticulum * external to the cell – Consequences (activates enzymes) * ATPase • decreased ATP * phospholipase • decreased phospholipids * endonuclease • nuclear chromatin damage

3- Increased anaerobic glycolysis * glycogen depletion * lactic acid accumulation * accumulation of inorganic phosphates * reduced intracellular pH

4- Detachment of ribosomes * reduced protein synthesis 5- Worsening mitochondrial function 6- Increasing membrane permeability 7- Cytoskeleton dispersion * loss of microvilli * formation of cell surface blebs 8- Swelling of mitochondria, endoplasmic reticulum, and entire cells

8- Mitochondrial changes * severe vacuolization * amorphous calcium-rich densities – Extensive plasma membrane damage – Prominent swelling of lysosomes – Massive influx of calcium (on reperfusion) – Continued loss of cell proteins, coenzymes, ribonucleic acids and other metabolites – Leakage of enzymes measured in serum

– Injury to lysosomal membranes * leakage of degradative enzymes • activation of acid hydrolases due to

reduced intracellular pH with degradation of cell components – Prominent leakage of cellular enzymes – Influx of macromolecules from interstitium – “Myelin figures”-whorled phospholipid masses

Mechanisms of Irreversible Injury – 1- Phenomena characterizing irreversibility

A- inability to reverse mitochondrial dysfunction B- profound disturbances in membrane function is a central factor – 2- Potential causes of membrane damage A- progressive loss of membrane phospholipids • activation of phospholipase • reduced synthesis of phospholipids

B- cytoskeletal abnormalities • activation of proteases • cell swelling C- toxic oxygen radicals • after restoration of blood flow (mainly from polys) D- lipid breakdown products • from phospholipid degradation • detergent effect on membranes – 3- Ultimately a massive influx of calcium

Mechanisms of Cell Injury FREE RADICAL MEDIATION OF CELL INJURY

Free Radical Mediation of Cell Injury ●

Free Radical Injury Contributes To: – Chemical and radiation injury – Oxygen and other gaseous toxicity – Cellular aging – Microbial killing by phagocytic cells – Inflammatory damage – Tumor destruction by macrophages – Others

Free Radical Mediation of Cell Injury ●

Definition Of Free Radicals – Extremely unstable, highly reactive chemical

species with a single unpaired electron in an outer orbital ●

Examples Of Free Radicals .

.

.2

– OH , H , O

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Source of Free Radicals – Hydrolysis of water into OH. and H. by ionizing

radiation – Redox reactions in normal physiology * respiration * intracellular oxidase action * transition metal reactions – Metabolism of exogenous chemicals

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Free Radical Injury Mechanisms – Lipid peroxidation of membranes * double bonds in polyunsaturated lipids – Lesions in DNA * reactions with thymine with single-strand

breaks – Cross-linking of proteins * sulfhydryl-mediated protein cross-linking

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Free Radical Degradation – Unstable with spontaneous decay – Decay accelerated by * superoxide dismutase * glutathione * catalase – Antioxidants (vitamin E, ceruloplasmin) * block formation or scavenge

Mechanisms of Cell Injury CHEMICAL INJURY

Chemical Injury ●

Mechanisms of Chemical Injury – Direct combination with cell component * mercury binding to sulfhydryl groups – Conversion to reactive toxic metabolite * principally involves liver * usually by P-450 mixed function oxidases * involves free radical formation .

* CCl4 conversion to CCl3

Forms and Morphology of Cell Injury INTRACELLULAR ACCUMULATIONS

Intracellular Accumulations ●

General Principles – Transient or permanent – Harmless or injurious – Cytoplasm (lysosomes) or nucleus – Synthesized by the affected cell or produced

elsewhere

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General Principles – Endogenous * normal substance produced at normal or

increased rate/rate of metabolism inadequate for removal (fatty liver) * normal or abnormal substance cannot be metabolized (storage diseases) – Exogenous • cell cannot degrade substance (carbon)

Intracellular Accumulations 1- Fatty Change (Steatosis) – Causes * alcohol abuse, other toxins, anoxia,

obesity, protein malnutrition – Pathogenesis * various steps involved * regress of hepatic triglycerides requires complex with apoproteins to form lipoproteins

Intracellular Accumulations ●

Fatty Change (Steatosis) – Liver * increased weight, yellow color * fat vacuoles within cytoplasm of

hepatocytes

Intracellular Accumulations ●

Fatty Change (Steatosis) – Heart * focal fat deposits in myocardium (anemia) * diffuse fat deposits in myocardium

(profound hypoxia, diphtheric myocarditis)

Intracellular Accumulations ●

Cholesterol and Cholesterol Esters – Atherosclerosis * macrophages and smooth muscle cells

filled with vacuoles – Xanthomas * macrophage accumulation/hereditary and acquired hyperlipidemias

Intracellular Accumulations 2- Proteins – Renal tubular epithelium in proteinuria – Plasma cells may accumulate

immunoglobulins (Russel bodies)

Intracellular Accumulations 3- Glycogen – Diabetes mellitus * glycogen accumulation in renal tubular

epithelium, hepatocytes, cardiac myocytes, pancreatic beta cells. – Glycogen storage diseases (glycogenoses) • enzymatic defects in synthesis or breakdown of glycogen

Intracellular Accumulations 4- Pigments: A- Exogenous Pigments – 1- Carbon (Anthracosis) * Carbon is phagocytosed by alveolar

macrophages and transported by lymphatic to lymph nodes * Mild accumulations usually are of no consequence--heavy accumulations may induce a fibroblastic response

Intracellular Accumulations – 2- Tattoos * dyes phagocytosed

by macrophages

Intracellular Accumulations B- Endogenous Pigments 1- Lipofuscin (“wear and tear pigment) * brownish yellow especially in heart, liver, and brain--function of age or atrophy (“brown atrophy”) * represents complexes of lipid/protein * derived from free radical peroxidation of subcellular membranes

2- Melanin * brown-black pigment derived from tyrosine in melanocytes * may also accumulate in basal keratinocytes and dermal macrophages

3- Hemosiderin * hemoglobin derived iron containing golden-yellow pigment * represents large aggregates of ferritin micelles * small amounts normal in phagocytic cells of reticuloendothelial system. * local excesses in focal hemorrhage * systemic iron overload (hemosiderosis) • in macrophages and parenchyma mainly in liver, pancreas, heart, and endocrine organs

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Endogenous Pigments – Hemosiderin * systemic iron overload (hemosiderosis) • increased absorption or impaired utilization of

iron; hemolytic anemias; transfusions • extensive accumulation--- hemochromatosis & organ fibrosis

Forms and Morphology of Cell Injury PATHOLOGIC CALCIFICATION

Pathologic Calcification

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Dystrophic Calcification – Normal serum calcium – Areas of necrosis or injury – Intracellular or extracellular

Pathologic Calcification ●

Metastatic Calcification – Occurs in normal tissue – Occurs with hypercalcemia * hyperparathyroidism; bone catabolism with

tumors involving bone; vitamin D intoxication; sarcoidosis; renal failure – Primarily affects vessels, kidneys, lungs, and gastric mucosa

Amyloidosis ●

Nature Of Amyloid – Abnormal proteinaceous substance – Deposited between cells – Not a single chemical entity – Appears as a pink translucent material on

H&E stain

Amyloidosis ●

Chemical Nature Of Amyloid – AL (amyloid light chain) * associated with B-cell dyscrasias * produced by immunoglobulin-secreting cells. – AA (amyloid associated) * non-immunoglobulin * derived from SAA (serum amyloid-associated

precursor protein) * associated with chronic inflammatory diseases

Amyloidosis ●

Chemical Nature Of Amyloid – Transthyretin (a normal serum protein) * mutant form deposited in familial amyloid

polyneuropathies – Beta-2-microglobulin (normal serum protein) * deposits in long-term hemodialysis – Beta-2-amyloid protein (derived from amyloid precursor protein -APP) * deposits in brain in Alzheimer’s disease

Types 1- Immunocyte Dyscrasias With Amyloidosis ●

Characteristics – Complete immunoglobulin light chains (AL) produced

by aberrant monoclonal B-cells, such as in multiple myeloma – Serum M (myeloma) spike – Bence Jones protein (either lambda or kappa light chains)

2- Reactive Systemic Amyloidosis Characteristics – AA protein deposits – Occurs in setting of chronic inflammation

3- Heredofamilial Amyloidosis – Familial Mediterranean fever * AA protein-may be due to recurrent bouts of

inflammation of joints and serosal surfaces – Familial amyloid polyneuropathies * mutant transthyretins deposited

4- Localized Amyloidosis – Heterogeneous chemical composition and clinical

presentation – Often associated with local infiltration of plasma cells (AL type amyloid) – Medullary carcinoma of thyroid (amyloid chemically related to calcitonin - a hormone secreted by the tumor cells.

5- Amyloidosis Of Aging – Senile cardiac amyloidosis * transthyretin – Senile cerebral amyloidosis (in Alzheimer’s disease) * beta-2 amyloid protein

Pathogenesis Of Amyloidosis ●

Reactive Systemic Amyloidosis – Elevated SAA (synthesized by liver in

response to IL-6 & IL-1) – Abnormal breakdown of SAA. ●

Immunocyte Dyscrasias – AL synthesized by B-cells – Abnormal degradation.

Morphology Of Amyloidosis ●

Generalizations – Reactive systemic amyloidosis typically

affects kidneys, liver, spleen, lymph nodes, adrenals, thyroid, and other tissues. – Immunocyte-associated amyloidosis more often involves heart, GI & respiratory tracts, peripheral nerves, skin, and tongue. * deposits may also occur in organs listed for reactive systemic amyloidosis

Morphology Of Amyloidosis ●

Histologic Appearance – Pink staining intercellular substance with

H&E stain – Red-orange staining with Congo red * green under polarized light – Often causes parenchymal cell atrophy or drop out

Amyloidosis Of The Kidney ●

Gross – Unchanged or large and pale

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Microscopic – Deposits mainly in glomeruli – Also present in peritubular interstitium and

walls of blood vessels

Amyloidosis Of Other Organs ●

Spleen – “Sago spleen”-splenic follicles – “Lardaceous spleen”-splenic sinuses & pulp

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Liver, Heart, Endocrine glands – Enlarged – Interstitial deposits of amyloid – Pressure atrophy

Gaucher Disease ●

Characteristics – Glucocerebrosidase deficiency – Accumulation of glucocerebrosides – Involves phagocytic cells – Predominantly affects liver, spleen and bone

marrow and maybe CNS at the end stage. – Phagocytes enlarged with a fibrillar “wrinkled tissue paper” cytoplasm

Gaucher Disease ●

Types – Type 1 (99%) hepatosplenomegaly and

absence of CNS involvement-longevity somewhat shortened – Type 2 severe CNS involvement; secondary involvement of spleen/liver--highly lethal – Type 3 involves brain and viscera with a course intermediate to types 1 and 2

Cell Death (Necrosis)

Individual Cell Death ●

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Common event in some regenerating tissues: such as skin and gut epithelium and during embryogenesis Not a typical event in developed tissues such as brain becomes a serious occurrence when many cells are involved in such organs as the liver Programmed cell death: Apoptosis

What are the important factors on the outcome of injury on cells? Severity of injury and duration have a major effect on the outcome of injury

Etiology of Tissue Necrosis 1) Hypoxia 2) Physical injury a) Trauma b) Radiation ‑ U.V., Cosmic, X‑ray 3) Chemicals ‑ variable 4) Biological toxins ‑ endotoxins 5) Immunological reactions 6) Inborn genetic disorders 7) Nutritional

Mechanisms of Necrosis Basic mechanisms: 1) Impaired oxidative phosphorylation 2) Membrane dissolution 3) Osmotic regulation

Major Signs of Necrosis Similar to Apoptosis 1) Nuclear degeneration ‑ Chromatin clumping ‑ Karyopyknosis (shrinking) ‑ Karyolysis (dissolution of chromatin) ‑ Karyorrhexis (fragmentation of chromatin) 2) Cytoplasmic changes

Types of Necrosis ●

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Liquefactive necrosis: Necrosis in brain, abscesses Coagulative necrosis: Necrosis of kidney, liver, or heart muscle Caseous necrosis: Infection with Mycobacterium tuberculosis Gangrene: Necrosis of an appendage, usually limbs Fat necrosis

Coagulative necrosis ●

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Caused by ischemia. Ischemia results in decreased ATP, increased cytosolic Ca++, and free radical formation, which each eventually cause membrane damage. Example: Infarct: localized area of ischemic necrosis as in myocardial infarct.

Liquefactive Necrosis ●

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Usually caused by focal bacterial infections, because they can attract polymorphonuclear leukocytes. The enzymes in the polys are released to fight the bacteria, but also dissolve the tissues nearby, causing an accumulation of pus, effectively liquefying the tissue (hence, the term liquefactive). Example: Abscess

Caseation Necrosis ●

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Caseous: A distinct form of coagulative necrosis seen in mycobacterial infections (e.g., tuberculosis), or in tumor necrosis, in which the coagulated tissue no longer resembles the cells, but is in chunks of unrecognizable debris. Usually there is a giant cell and granulomatous reaction, sometimes with polys, making the appearance distinctive. Example: Tuberculosis.

Fat necrosis ●

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Fat Necrosis: A term for necrosis in fat, caused either by release of pancreatic enzymes from pancreas or gut (Enzymatic fat necrosis) or by trauma to fat, either by a physical blow or by surgery (Traumatic fat necrosis). The effect of the enzymes (lipases) is to release free fatty acids, which then can combine with calcium to produce detergents (soapy deposits in the tissues). Histologically, one sees shadowy outlines of fat cells (like coagulative necrosis), but with Ca++ deposits, foam cells, and a surrounding inflammatory reaction.

Consequences of Necrosis ● ●

Healing vs. permanent damage Local vs. systemic effects. 1) Type of tissue

2) Size of lesion 3) Location of lesion

AUTOLYSIS ●

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Lysis of tissues by their own enzymes, following the death of the organism. Therefore, the key difference is that there is no vital reaction (i.e., no inflammation). Autolysis is essentially rotting of the tissue. Early autolysis is indistinguishable from early coagulative necrosis due to ischemia, unless the latter is focal.