CELL INJURY, 1 & 2. Cell Injury, Definitions When the cell is exposed to an injurious agent or stress, a sequence of events follows that is loosely termed.

CELL INJURY,1 & 2

Cell Injury, Definitions

When the cell is exposed to an injurious agent or stress, a sequence of events follows that is loosely termed cell injury.

Cell injury is reversible up to a certain point If the stimulus persists or is severe enough from the

beginning, the cell reaches a point of no return and suffers irreversible cell injury and ultimately cell death.

Cell death, is the ultimate result of cell injury

Patterns Of Cell Death

There are two principal patterns of cell death:

1- Necrosis and

2- Apoptosis.

Necrosis

Necrosis is the type of cell death that occurs after ischemia and chemical injury

Necrosis is always pathologic.

Apoptosis

Apoptosis occurs when a cell dies through activation of an internally controlled suicide program.

Apoptosis is designed to eliminate unwanted cells during embryogenesis and in various physiologic processes and certain pathologic conditions.

Causes of Cell Injury

1) Oxygen Deprivation (Hypoxia). It is a common cause of cell injury and cell death.

-Hypoxia can be due to :A- inadequate oxygenation of the blood due to

Cardiorespiratory failureB- loss of the oxygen-carrying capacity of the blood, as

in anemia or carbon monoxide poisoning. Depending on the severity of the hypoxic state, cells

may adapt, undergo injury, or die.

Causes of Cell Injury cont.

2) Physical Agents :

- Mechanical trauma,

- Burns,

- Deep cold

- Sudden changes in atmospheric pressure,

- radiation, and electric shock


3) Chemical Agents and Drugs - oxygen, in high concentrations- poisons, such as arsenic, cyanide, or mercuric

salts- environmental and air pollutants- insecticides, herbicides, industrial and

occupational hazards- alcohol and narcotic drugs and therapeutic

drugs


4) Infectious Agents e.g. bacteria, fungi, viruses and parasites.

5) Immunologic Reactions.

6) Genetic Derangements.

7) Nutritional Imbalances

MECHANISM OF CELL INJURY

1. DEPLETION OF ATP:

. ATP depletion and decreased ATP synthesis are associated with both hypoxic and chemical (toxic) injury.

. ATP is required for many synthetic and degradative processes within the cell.

MECHANISM OF CELL INJURY cont.

ATP is produced in two ways.

A- The major pathway is oxidative phosphorylation of adenosine diphosphate.

B-The second is the glycolytic pathway, which generate ATP in absence of oxygen using glucose derived from body fluids or from glycogen


Effects of depleted ATP

a) The activity of the plasma membrane energy-dependent sodium pump is reduced. It causes sodium to accumulate intracellularly and potassium to diffuse out of the cell causing cell swelling, and dilation of the endoplasmic reticulum.


b) If oxygen supply to cells is reduced, as in ischemia, oxidative phosphorylation ceases and cells rely on glycolysis for energy production (anaerobic metabolism) resulting in depletion of glycogen stores. Glycolysis results in the accumulation of lactic acid which reduces the intracellular pH, resulting in decreased activity of many cellular enzymes.


c) Failure of the Ca2+ pump leads to influx of Ca2+, with damaging effects on numerous cellular components

d) Ribosomes detach from the RER and polysomes breakdown into monosomes, leading to reduction in protein synthesis. Ultimately, irreversible damage to mitochondrial and lysosomal membranes occurs, and cell undergoes necrosis


e) In cells deprived of oxygen or glucose, proteins may become misfolded, and trigger the unfolded protein response leading to cell injury and even death.


2- Mitochondrial Damage:

. Mitochondria are important targets for all types of injury, including hypoxia and toxins.


Mitochondria can be damaged by :

A- Increases of cytosolic Ca2+

B- Oxidative stress

C- Breakdown of phospholipids, and by

D- Lipid breakdown products.


. Mitochondrial damage results in the formation of a high-conductance channel, called mitochondrial permeability transition, present in the inner mitochondrial membrane. In the initial phase it is reversible but once mitochondrial permeability transition is irreversble it becomes a deathblow to the cell.

Mitochondrial damage can also be associated with leakage of cytochrome c into the cytosol.

MECHANISM OF CELL INJURY cont.3.INFLUX OF INTRACELLULAR CALCIUM &

LOSS OF CALCIUM HOMEOSTASIS. . Ischemia causes an increase in cytosolic calcium

concentration. Increased Ca2+ in turn activates a number of enzymes, e.g.

- ATPases (thereby hastening ATP depletion), -Phospholipases (which cause membrane damage), - Proteases (which break down both membrane and

cytoskeletal proteins), and -Endonucleases (which are responsible for DNA and

chromatin fragmentation).


4. ACCUMULATION OF OXYGEN-DERIVED FREE RADICALS (OXIDATIVE STRESS)

- Small amounts of partially reduced reactive oxygen forms are produced as a byproduct of mitochondrial respiration.

- Some of these free radicals can damage lipids, proteins, and nucleic acids.

- They are referred to as reactive oxygen species.


- Cells have defense systems to prevent injury caused by these products.

- An imbalance between free radical-generating and radical-scavenging systems results in oxidative stress causing cell injury.


Free radical-mediated damage are seen in - chemical and radiation injury- ischemia-reperfusion injury- cellular aging, and- microbial killing by phagocytes.


- Free radicals are chemical species that have single unpaired electron in an outer orbit.

- They are initiated within cells in several ways:

a) Absorption of radiant energy (e.g., ultraviolet light, x-rays).

b) Enzymatic metabolism of exogenous chemicals or drugs .


c) The reduction-oxidation reactions that occur during normal metabolic processes. During normal respiration, small amounts of toxic intermediates are produced; these include superoxide anion radical (O2-), hydrogen peroxide (H2O2), and hydroxyl ions (OH).

d) Transition metals such as iron and copper e) Nitric Oxide (NO), an important chemical mediator

generated by various cells, can act as a free radical.


-The main effects of these reactive species are Lipid peroxidation of membranes: result in extensive

membrane, organellar, and cellular damage. Oxidative modification of proteins. resulting in protein

fragmentation. Lesions in DNA. This DNA damage has been

implicated in cell aging and malignant transformation of cells


-Cells have developed multiple mechanisms to remove free radicals and thereby minimize injury.

1- Antioxidants. Examples vitamins E and A and ascorbic acid.

2- Enzymes which break down hydrogen peroxide and superoxide anion e.g. Catalase, Superoxide dismutases,and Glutathione peroxidase.


5. Defects In Membrane Permeability:

- In ischemic cells, membrane damage may be the result of ATP depletion and calcium-modulated activation of phospholipases.

- It can also be damaged directly by certain bacterial toxins, viral proteins etc.


The biochemical mechanisms which contribute to membrane damage are:

Mitochondrial dysfunction Cytoskeletal abnormalities Reactive oxygen species Lipid breakdown products

Figure 1-10 Cellular and biochemical sites of damage in cell injury.

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Figure 1-11 Functional and morphologic consequences of decreased intracellular ATP during cell injury.


© 2005 Elsevier

Reversible & Irreversible Cell Injury

Earliest changes associated with cell injury are : decreased generation of ATP, loss of cell membrane integrity, defects in protein synthesis, cytoskeletal

damage, and DNA damage.

Reversible and Irreversible Cell Injury

Within limits, the cell can compensate for these derangements and,

If the injurious stimulus is removed the damage can be reversed.

Persistent or excessive injury, however, causes cells to pass the threshold into irreversible injury.


Irreversble injury is marked by :

- severe mitochondrial vacuolization,

- extensive damage to plasma membranes,

- swelling of lysosomes and

- the appearance large, amorphous densities in mitochondria..


Two phenomena consistently characterize irreversibility.

1) The inability to reverse mitochondrial dysfunction (lack of oxidative phosphorylation and ATP generation) even after removal of the original injury.

2) Profound loss in membrane function

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Ischaemic cell injury

As the oxygen tension within the cell decreases, there is loss of oxidative phosphorylation and decreased generation of ATP followed by sodium pump failure, with loss of potassium, influx of sodium and water, and cell swelling.

There is progressive loss of glycogen, decreased protein synthesis and reduced intracellular Ph.

Ischaemic cell injury cont.

If hypoxia continues, worsening ATP depletion causes further morphologic deterioration e.g. loss of ultrastructural features such as microvilli and the formation of "blebs" at the cell surface. "Myelin figures," may be seen within the cytoplasm or extracellularly.

If oxygen is restored, all of these disturbances are reversible.

Ischaemic cell injury cont

If ischemia persists, irreversible injury and necrosis ensue.

Irreversible injury is associated morphologically with severe swelling of mitochondria, extensive damage to plasma membranes, and swelling of lysosomes.

Large, flocculent, amorphous densities develop in the mitochondrial matrix.

The dead cell are phagocytosed by other cells.

ISCHEMIA-REPERFUSION INJURY

Restoration of blood flow to ischemic tissues can result in recovery of cells if they are reversibly injured.

Ischemia-reperfusion injury is a clinically important process in such conditions as myocardial infarction and stroke.


New damaging processes are set in motion during reperfusion, causing the death of cells that might have recovered otherwise New damage may be initiated during reoxygenation by increased generation of oxygen free radicals from parenchymal and endothelial cells and from infiltrating leukocytes

Reactive oxygen species can further promote the mitochondrial permeability transition,


Ischemic injury is associated with inflammation as a result of the production of cytokines and increased expression of adhesion molecules by hypoxic parenchymal and endothelial cells.

These agents recruit circulating polymorphonuclear leukocytes to reperfused tissue; the ensuing inflammation causes additional injury.

Activation of the complement pathway may contribute to ischemia-reperfusion injury.

NECROSIS

Necrosis refers to a spectrum of morphologic changes that follow cell death in living tissue, due to degradative action of enzymes on the injured cell.

It occurs in irreversible injury. This may elicit inflammation in the

surrounding tissue.

NECROSIS

There is denaturation of intracellular proteins and enzymatic digestion of the cell.

The enzymes are derived either from the lysosomes of the dead cells themselves, in which case the enzymatic digestion is referred to as autolysis, or from the lysosomes of immigrant leukocytes, during inflammatory reactions.

Morphology of necrosis.

Necrotic cells show increased eosinophilia with a glassy

homogeneous appearance. The cytoplasm becomes vacuolated and

appears moth-eaten. Finally, calcification of the dead cells may

occur.

Morphology of necrosis cont.

Nuclear changes show one of three patterns, all due to nonspecific breakdown of DNA

1- karyolysis : basophilia of the chromatin may fade 2- Pyknosis, (also seen in apoptotic cell death) is characterized

by nuclear shrinkage and increased basophilia. Here the DNA apparently condenses into a solid, shrunken basophilic mass.

3- Karyorrhexis: fragmentation of the nucleus.

With the passage of time (a day or two), the nucleus in the necrotic cell totally disappears

Morphology of necrosis

By electron microscopy, necrotic cells are characterized by :

overt discontinuities in plasma membrane, marked dilation of mitochondria with the

appearance of large amorphous densities, intracytoplasmic myelin figures, amorphous osmiophilic debris, and aggregates of fluffy material probably

representing denatured protein

Types of necrosis

There are different types of necrosis :

- Coagulative necrosis, - Liquefactive necrosis,

- Caseous necrosis and

- Fat necrosis

Coagulative necrosis:

There is preservation of the basic outline of the coagulated cell for a span of some days.

The affected tissues has a firm texture e.g. myocardial infarct Ultimately, the necrotic myocardial cells are removed by fragmentation and phagocytosis of the cellular debris by scavenger leukocytes and by the action of proteolytic lysosomal enzymes brought in by the immigrant white cells.

Coagulative necrosis:

Coagulative necrosis, with preservation of the general tissue architecture, is characteristic of hypoxic death of cells in all tissues except the brain.

Liquefactive necrosis

Is characteristic of focal bacterial or, occasionally, fungal infections.

It is also seen in hypoxic death of cells within the central nervous system.

Liquefaction completely digests the dead cells.

The end result is transformation of the tissue into a liquid viscous mass..

Liquefactive necrosis

If the process was initiated by acute inflammation, the material is frequently creamy yellow because of the presence of dead white cells and is called pus

Gangrenous necrosis

Is a term used by surgeons. It is usually applied to a limb, generally the

lower leg, that has lost its blood supply and has undergone coagulation necrosis.

When bacterial infection is superimposed, coagulative necrosis is modified by the liquefactive action of the bacteria and the attracted leukocytes (so-called wet gangrene).

Caseous necrosis

Is a type of coagulative necrosis, seen in tuberculous infection.

The term caseous is derived from the cheesy white gross appearance of the area of necrosis.

On microscopic examination, the necrotic area appears as amorphous pink granular debris surrounded by granuloma.

Fat necrosis

Is focal areas of fat destruction, due to release of activated pancreatic lipases into the substance of the pancreas and the peritoneal cavity.

This occurs in acute pancreatitis. The released fatty acids combine with

calcium to produce grossly visible chalky white areas (fat saponification)..

Fat necrosis

On histologic examination:

The necrosis takes the form of foci of shadowy outlines of necrotic fat cells, with basophilic calcium deposits, surrounded by an inflammatory reaction

APOPTOSIS

Apoptosis is programmed cell death. It is a pathway of cell death that is induced by a

tightly regulated intracellular program in which cells destined to die activate their own enzymes to degrade their own nuclear DNA, nuclear proteins and cytoplasmic proteins.

The cell's plasma membrane remains intact, but its structure is altered in such a way that the apoptotic cell sends signal to macrophages to phagocytose it.

APOPTOSIS cont.

The dead cell is rapidly phagocytosed and cleared, before its contents have leaked out, and therefore cell death by this pathway does not elicit an inflammatory reaction in the host.

Thus, apoptosis is fundamentally different from necrosis, which is characterized by loss of membrane integrity, enzymatic digestion of cells, and frequently a host reaction.

Apoptosis and necrosis sometimes coexist.

CAUSES OF APOPTOSIS

Apoptosis means "falling off." It occurs normally in many situations, and serves to

eliminate unwanted or potentially harmful cells and cells that have outlived their usefulness.

It is also a pathologic event when cells are damaged beyond repair, especially when the damage affects the cell's DNA; in these situations, the irreparably damaged cell is eliminated.

Apoptosis can be physiologic, adaptive, and pathologic.

Apoptosis in Physiologic Situations

The programmed destruction of cells during embryogenesis.

Hormone-dependent involution in the adult, such as endometrial cell breakdown during the menstrual cycle, the regression of the lactating breast after weaning, and prostatic atrophy after castration.

Cell deletion in proliferating cell populations,eg. intestinal epithelia.

Apoptosis in Physiologic Situations

Death of host cells that have served their useful purpose, such as neutrophils in an acute inflammatory response, and lymphocytes at the end of an immune response.

Elimination of potentially harmful self-reactive lymphocytes..

Cell death induced by cytotoxic T cells, a defense mechanism against viruses and tumors that serves to eliminate virus-infected and neoplastic cells

Apoptosis in Pathologic Conditions

Cell death produced by a variety of injurious stimuli eg. radiation and cytotoxic anticancer drugs damage DNA.

Cell injury in certain viral diseases, such as viral hepatitis.

Pathologic atrophy in parenchymal organs after duct obstruction, such as occurs in the pancreas, parotid gland, and kidney.

Cell death in tumors.

Morphology of Apoptosis

Cell shrinkage. Chromatin condensation. This is the most

characteristic feature of apoptosis. The chromatin aggregates peripherally, under the nuclear membrane.

The nucleus itself may break up into fragments.


Formation of cytoplasmic blebs and apoptotic bodies. The apoptotic cell first shows extensive surface blebbing, then undergoes fragmentation into membrane-bound apoptotic bodies composed of cytoplasm and tightly packed organelles, with or without nuclear fragments.

Phagocytosis of apoptotic cells or cell bodies, usually by macrophages.


On histologic examination, in tissues stained with hematoxylin and eosin, apoptosis involves single cells or small clusters of cells.

The apoptotic cell appears as a round or oval mass of intensely eosinophilic cytoplasm with dense nuclear chromatin fragments.

There is no inflammation.

Figure 1-9 The sequential ultrastructural changes seen in necrosis (left) and apoptosis (right). In apoptosis, the initial changes consist of nuclear chromatin condensation and fragmentation, followed by cytoplasmic budding and phagocytosis of the extruded apoptotic bodies. Signs of cytoplasmic blebs, and digestion and leakage of cellular

components. (Adapted from Walker NI, et al: Patterns of cell death. Methods Archiv Exp Pathol 13:18-32, 1988. Reproduced with permission of S. Karger AG, Basel.)


© 2005 Elsevier

Feature Necrosis Apoptosis

Cell size Enlarged (swelling) Reduced (shrinkage)

Nucleus Pyknosis → karyorrhexis → karyolysis

Fragmentation into nucleosome size fragments

Plasma membrane

Disrupted Intact; altered structure, especially orientation of lipids

Cellular contents

Enzymatic digestion; may leak out of cell

Intact; may be released in apoptotic bodies

Adjacent inflammation

Frequent No

Physiologic or pathologic role

Invariably pathologic (culmination of irreversible cell injury)

Often physiologic, means of eliminating unwanted cells; may be pathologic after some forms of cell injury, especially DNA damage

Cell Injury ,3 & 4

Intracellular Accumulations

Intracellular accumulation of abnormal amounts of various substances.

(1) a normal cellular constituent accumulated in excess, such as water, lipids, proteins, and carbohydrates

(2) an abnormal substance, either exogenous, such as a mineral or products of infectious agents, or endogenous, such as a product of abnormal synthesis or metabolism

(3) a pigment.

Intracellular Accumulations

-The substance may be either the cytoplasm or the nucleus.

- In some instances, the cell may be producing the abnormal substance, and

- In others it may be merely storing products of pathologic processes occurring elsewhere in the body

COMMON CAUSES OF INTRACELLULAR ACCUMULATION

1- A normal endogenous substance is produced at a normal or increased rate, but the rate of metabolism is inadequate to remove it. Eg.fatty change in the liver.

2- A normal or abnormal endogenous substance accumulates because of genetic or acquired defects in the metabolism, packaging, transport, or secretion of these substances. Eg. lysosomal storage diseases.

COMMON CAUSES OF INTRACELLULAR ACCUMULATION

3- An abnormal exogenous substance is deposited and accumulates because the cell has neither the enzymatic machinery to degrade the substance nor the ability to transport it to other sites. Eg.accumulations of carbon particles.

LIPIDS

All major classes of lipids can accumulate in cells:

triglycerides, cholesterol/cholesterol esters, and phospholipids. In addition, abnormal complexes of lipids and

carbohydrates accumulate in the lysosomal storage diseases.

Steatosis (Fatty Change)

The terms steatosis and fatty change is abnormal accumulations of triglycerides within parenchymal cells.

Often seen in liver, but it also in heart, muscle, and kidney.


The causes of steatosis include :- toxins, - protein malnutrition, - diabetes mellitus, - obesity,- anoxia and - alcohol abuse


Free fatty acids from adipose tissue or ingested food are normally transported into hepatocytes. In the liver, they are esterified to triglycerides, converted into cholesterol or phospholipids, or oxidized to ketone bodies.

Release of triglycerides from the hepatocytes requires apoproteins to form lipoproteins.

Excess accumulation of triglycerides within the liver may result from defects in any one of the events in the sequence from fatty acid entry to lipoprotein exit.

Morphology of Steatosis

Clear vacuoles within parenchymal cells. The sections may then be stained with Sudan IV or Oil Red-O, both of which impart an orange-red color to the contained lipids.

Liver. In mild fatty change gross appearance is normal. With progressive accumulation, the organ enlarges and becomes increasingly yellow and greasy.

Morphology of Steatosis

Light microscopy: vacuoles in the cytoplasm displacing the nucleus to the periphery of the cell

Occasionally, contiguous cells rupture, and the enclosed fat globules coalesce, producing so-called fatty cysts

Cholesterol and Cholesterol Esters

- Cells use cholesterol for the synthesis of cell membranes.

-Accumulations in the form of intracellular vacuoles, are seen in several pathologic processes eg. Atherosclerosis


Atherosclerosis. In atherosclerotic plaques, smooth muscle cells and macrophages within the intimal layer of arteries are filled with lipid vacuoles, most of which are made up of cholesterol and cholesterol esters.

Some of these fat-laden cells rupture, releasing lipids into the extracellular space.

The extracellular cholesterol esters may crystallize in the shape of long needles, producing clefts in tissue sections.


Xanthomas. Intracellular accumulation of cholesterol within macrophages is also characteristic of acquired and hereditary hyperlipidemic states seen in connective tissue of the skin and in tendons.

Inflammation and necrosis. Foamy macrophages are frequently found at sites of cell injury and inflammation, owing to phagocytosis of cholesterol from the membranes of injured cells.


Cholesterolosis. Accumulations of cholesterol-laden macrophages in the lamina propria of the gallbladder.

Niemann-Pick disease, type C. In this lysosomal storage disease, an enzyme involved in cholesterol trafficking is mutated, and hence cholesterol accumulates in multiple organs.

GLYCOGEN

Glycogen is a readily available energy store that is present in the cytoplasm.

Excessive intracellular deposits of glycogen are seen in patients with an abnormality in either glucose or glycogen metabolism.

They appear as clear vacuoles within the cytoplasm. Staining with mucicarmine or the periodic acid schiff

(PAS) reaction imparts a rose-to-violet color to the glycogen.

GLYCOGEN cont.

Diabetes mellitus is the prime example of a disorder of glucose metabolism. In this disease, glycogen is found in the epithelial cells of the distal portions of the proximal convoluted tubules, as well as within liver cells, β cells of the islets of Langerhans, and heart muscle cells

GLYCOGEN cont.

Glycogen also accumulates within the cells in a group of closely related disorders, all genetic, collectively referred to as the glycogen storage diseases, or glycogenoses. In these diseases, enzymatic defects in the synthesis or breakdown of glycogen result in massive accumulation, and cell death.

PIGMENTS

Pigments are colored substances, some of which are normal constituents of cells (e.g., melanin), whereas others are abnormal and collect in cells only under special circumstances.

Pigments can be exogenous, coming from outside the body, or endogenous, synthesized within the body itself

Exogenous Pigments

.The most common exogenous pigment is carbon or coal dust, which is an air pollutant.

. When inhaled, it is picked up by macrophages within the alveoli and is then transported through lymphatic channels to the regional lymph nodes.

. Accumulations of this pigment blacken the tissues of the lungs (anthracosis) and the involved lymph nodes.

. In coal miners, the aggregates of carbon dust may induce a fibroblastic reaction or even emphysema and thus cause a serious lung disease known as coal worker's pneumoconiosis .

Exogenous Pigments

Tattooing is a form of localized, exogenous pigmentation of the skin. The pigments inoculated are phagocytosed by dermal macrophages.

Endogenous Pigments

Lipofuscin is an insoluble pigment, also known as wear-and-tear or aging pigment.

Lipofuscin is not injurious to the cell or its functions. Its importance lies in its being the telltale sign of free

radical injury and lipid peroxidation. In tissue sections, it appears as a yellow-brown,

finely granular intracytoplasmic, often perinuclear pigment It is prominent in the liver and heart of aging patients or patients with severe malnutrition and cancer cachexia.

Figure 1-40 Lipofuscin granules in a cardiac myocyte as shown by A, light microscopy (deposits indicated by arrows), and B, electron microscopy (note the perinuclear, intralysosomal location).


© 2005 Elsevier

Endogenous Pigments cont.

Melanin, is an endogenous, non-hemoglobin-derived, brown-black pigment formed when the enzyme tyrosinase catalyzes the oxidation of tyrosine to dihydroxyphenylalanine in melanocytes.

The other black pigment in this category is homogentisic acid, a black pigment that occurs in patients with alkaptonuria, a rare metabolic disease. Here the pigment is deposited in the skin, connective tissue, and cartilage, and the pigmentation is known as ochronosis


Hemosiderin is a hemoglobin-derived, golden yellow-to-brown, iron containing pigment in cells. Iron is normally stored in the form of ferritin micelles. When there is a local or systemic excess of iron, ferritin forms hemosiderin granules, which are easily seen with the light microscope. Excesses of iron cause hemosiderin to accumulate within cells, either as a localized process or as a systemic derangement.


Local excesses of iron and hemosiderin result from hemorrhages or vascular congestion, eg hemosiderosis is the common bruise.

With lysis of the erythrocytes, the hemoglobin eventually undergoes transformation to hemosiderin.


Systemic overload of iron, hemosiderin is deposited in many organs and tissues, a condition called hemosiderosis.

It is seen with: (1) increased absorption of dietary iron, (2) impaired use of iron, (3) hemolytic anemias, and (4) transfusions because the transfused red cells constitute an exogenous load of iron


Morphology. Iron pigment appears as a coarse, golden, granular pigment lying within the cell's cytoplasm usually in the macrophages.In severe systemic hemosiderosis the pigment may accumulate in the parenchymal cells throughout the body (liver, pancreas, heart, and endocrine organs).

Iron can be visualized in tissues by the Prussian blue histochemical reaction, in which it appears blue-black.

Endogenous Pigments cont

In most cases of systemic hemosiderosis, the pigment does not damage the parenchymal cells or impair organ function.

The more severe cases eg. a disease called hemochromatosis, it resulting in liver fibrosis, heart failure, and diabetes mellitus

Pathologic Calcification

Pathologic calcification is the abnormal tissue deposition of calcium salts.

There are two forms of pathologic calcification. When the deposition occurs locally in dying tissues, it is known as dystrophic calcification; it occurs despite normal serum levels of calcium and in the absence of derangements in calcium metabolism.

Pathologic Calcification cont.

In contrast, the deposition of calcium salts in otherwise normal tissues is known as metastatic calcification, and it almost always results from hypercalcemia secondary to some disturbance in calcium metabolism.

Dystrophic calcification

Seen in areas of necrosis and/or damage eg.in the atheromas of advanced atherosclerosis or in aging or damaged heart valves. Whatever the site of deposition, the calcium salts appear macroscopically as fine, white granules or clumps, often felt as gritty deposits. Sometimes a tuberculous lymph node is virtually converted to stone

Morphology.

Histologically, calcium salts are basophilic, amorphous granular. They can be intracellular, extracellular, or both. In the course of time, heterotopic bone may be formed in the focus of calcification.

Progressive deposition on outer layers may create lamellated configurations, called psammoma bodies (papillary cancers).

Metastatic calcification

Occur in normal tissues whenever there is hypercalcemia. There are four principal causes of hypercalcemia:

1)increased secretion of parathyroid hormone (PTH) with subsequent bone resorption, as in hyperparathyroidism

Metastatic calcification cont.

2) destruction of bone tissue: Bone tumors (e.g., multiple myeloma, leukemia) or metastatic bone cancers, or immobilization;

3) vitamin D-related disorders, including vitamin D intoxication.

4) renal failure, which causes retention of phosphate, leading to secondary hyperparathyroidism.

Amyloidosis

AMYLOIDOSIS

Amyloid is a pathologic proteinaceous substance, deposited between cells in various tissues and organs of the body in a wide variety of clinical settings.

Light microscope: amyloid appears as amorphous, eosinophilic, hyaline, extracellular substance that gradually encroaches on and produces pressure atrophy of adjacent cells.

AMYLOIDOSIS cont.

On congo red stain: amyloid gives a pink or red color under ordinary light and an apple green birefringence under polarizing light.

There are three major and several minor biochemical forms of amyloid.

Amyloidosis is not a single disease; rather it is a group of diseases having in common the deposition of similar-appearing proteins.

Physical Nature of Amyloid

By electron microscopy, amyloid is seen to be made up largely of nonbranching fibrils of indefinite length This structure is identical in all types of amyloidosis.

The fibers have characteristic cross-β-pleated sheets and are responsible for the distinctive staining and birefringence of Congo red-stained amyloid

Figure 6-53 Structure of an amyloid fibril, depicting the β-pleated sheet structure and binding sites for the Congo red dye, which is used for diagnosis of amyloidosis. (Modified from Glenner GG: Amyloid deposit and amyloidosis. The β-fibrilloses. N Engl J Med 52:148, 1980. By permission of The New England

Journal of Medicine.)


© 2005 Elsevier

Chemical Nature of Amyloid

- Approximately 95% of the amyloid material consists of fibril proteins, the remaining

- 5% is P component and other glycoproteins. - 15 biochemically distinct forms of amyloid

proteins that have been identified.

Amyloidosis,Most common Forms:

(1) AL (amyloid light chain) is derived from plasma cells and contains immunoglobulin light chains

(2) AA (amyloid-associated) is a unique nonimmunoglobulin protein synthesized by the liver

(3) Aβ amyloid is found in the cerebral lesion of Alzheimer disease and is discussed in greater detail in

Other biochemical forms of Amyloid

Transthyretin (TTR): is deposited familial amyloid polyneuropathies and in the heart of aged individuals (senile systemic amyloidosis).

β2-microglobulin: seen in amyloidosis that occurs in patients on long-term hemodialysis.

β-amyloid protein (Aβ), found in Alzheimer disease.The Aβ protein is derived from a glycoprotein, called amyloid precursor protein.

Classification of Amyloidosis.

Amyloid may be classified based on its constituent chemical fibrils into categories such as AL, AA, and ATTR.

Amyloid may be systemic (generalized), or localized.

The systemic, or generalized, pattern is subclassified into primary amyloidosis, when associated with B- cell dyscrasias, or secondary amyloidosis, when it occurs as a complication of an underlying chronic inflammatory or tissue destructive process. Hereditary or familial amyloidosis constitutes a separate group.

Clinicopathologic Category

Associated Diseases

Major Fibril Protei

n

Chemically Related

Precursor Protein

Systemic (Generalized)Amyloidosis

Immunocyte dyscrasias with amyloidosis (primary amyloidosis)

Multiple myeloma and other monoclonal B-cell proliferations

AL Immunoglobulin light chains, chiefly λ type

Reactive systemic amyloidosis (secondary amyloidosis)

Chronic inflammatory conditions

AA SAA

Hemodialysis-associated amyloidosisHereditary amyloidosis

Chronic renal failure

Aβ2 m β2-

microglobulin

Familial Mediterranean fever

- AA SAA

Familial amyloidotic neuropathies (several types)

- ATTR Transthyretin

Systemic senile amyloidosis

- ATTR Transthyretin

Localized Amyloidosis

Senile cerebral Alzheimer disease Aβ APP

Endocrine

Medullary carcinoma of thyroid

- A Cal Calcitonin

Islet of Langerhans Type II diabetes AIAPP Islet amyloid peptide

Isolated atrial amyloidosis

- AANF Atrial natriuretic factor

Prion diseases Various prion diseases of the CNS

Misfolded prion protein (PrPsc)

Normal prion protein PrP

Immunocyte Dyscrasias with Amyloidosis (Primary Amyloidosis).

Usually systemic and is of AL type. Is the most common form of amyloidosis. In most

cases, the patients have some form of plasma cell dyscrasia eg. multiple myeloma or a plasma-cell tumor.

The malignant B cells characteristically synthesize abnormal amounts of a single specific immunoglobulin (monoclonal gammopathy).

In addition the light chains (Bence Jones protein) may be elevated.

Reactive/ Secondary Systemic Amyloidosis.

The amyloid deposition is systemic and is composed of AA protein.

It is secondary to an associated inflammatory condition like rheumatoid arthritis, ankylosing spondylitis, and inflammatory bowel disease, particularly Crohn disease and ulcerative colitis. It may also occur in association with tumors, like renal cell carcinoma and Hodgkin disease.

Hemodialysis-Associated Amyloidosis

Patients on long-term hemodialysis for renal failure develop amyloidosis owing to deposition of β2-microglobulin in the synovium, joints, and tendon sheaths.

Heredofamilial Amyloidosis

Most of them are rare . The most common is familial Mediterranean fever.

This is a febrile disorder of unknown cause characterized by attacks of fever accompanied by inflammation of serosal surfaces, including peritoneum, pleura, and synovial membrane. The amyloid fibril proteins are made up of AA.

Familial amyloidotic polyneuropathies: a familial disorders characterized by deposition of amyloid in peripheral and autonomic.The fibrils are made up of mutant transthyretins (ATTR).

Localized Amyloidosis.

Sometimes, amyloid deposits are limited to a single organ or tissue without involvement of any other site in the body.

The deposits may produce grossly detectable nodular masses or be evident only on microscopic examination.

Nodular (tumor-forming) deposits of amyloid are most often encountered in the lung, larynx, skin, urinary bladder, tongue, and the region about the eye.

Endocrine Amyloid

Microscopic deposits of localized amyloid may be found in certain endocrine tumors, such as medullary carcinoma of the thyroid gland, islet tumors of the pancreas, pheochromocytomas, and undifferentiated carcinomas of the stomach, and in the islets of Langerhans in patients with type II diabetes mellitus.

Amyloid of Aging

Several well-documented forms of amyloid deposition occur with aging.

Senile systemic amyloidosis: systemic deposition of amyloid in elderly patients(heart) was previously called senile cardiac amyloidosis.

Those who are symptomatic present with a restrictive cardiomyopathy and arrhythmias.

The amyloid in this form is composed of the normal TTR molecule.

Pathogenesis

Amyloidosis results from abnormal folding of proteins, which are deposited as fibrils in extracellular tissues and disrupt normal function. Misfolded proteins are often unstable and self-associate, ultimately leading to the formation of fibrils that are deposited in tissues.

Pathogenesis cont.

The proteins that form amyloid fall into two general categories:

(1) normal proteins that have an inherent tendency to fold improperly and form fibrils, and do so when they are produced in increased amounts, and

(2) mutant proteins that are structurally unstable and prone to misfolding and then form fibrils.

Morphology

Primary amyloidosis cannot reliably be distinguished from the secondary amyloidosis but more often it involves the heart, kidney, gastrointestinal tract, peripheral nerves, skin, and tongue.

Secondary amyloidosis usually involves kidneys, liver, spleen, lymph nodes, adrenals, and thyroid as well as many other tissues

Morphology cont.

Macroscopically the affected organs are often enlarged and firm and have a waxy appearance. If the deposits are sufficiently large, painting the cut surface with iodine imparts a yellow color that is transformed to blue violet after application of sulfuric acid.

Morphology cont.

Histologic diagnosis of amyloid is based on its characteristic staining with dye Congo red, which under ordinary light imparts a pink or red color to amyloid deposits. Under polarized light, the Congo red-stained amyloid shows a green birefringence

Morphology in Kidney

Most common organ involved. Histologically the amyloid is deposited in the

1) Glomeruli: in the mesangial matrix, and basement membranes of the glomerular capillaries. With progression there is hyalinization of the glomeruli.

2) Peritubular region extending into interstitium.3) Blood vessels: hyaline thickening of the arteriolar

wall and narrowing of lumen, eventually causing ischemia with tubular atrophy and interstitial fibrosis.

Morphology in Spleen

May cause splenomegaly. There are two patterns of deposition.

1) Deposit is in the splenic follicles, producing tapioca-like granules on gross inspection, called sago spleen.

2) Deposit in splenic sinuses and connective tissue of the red pulp. Fusion of deposits gives rise to large, areas of amyloidosis, designated the lardaceous spleen.

Morphology in Liver

May cause hepatomegaly. The amyloid appears first in the space of Disse and

then progressively encroaches on adjacent hepatic parenchymal cells and sinusoids.

In time due to pressure atrophy, there disappearance of hepatocytes, causing replacement of large areas of liver by amyloid. Vascular involvement and deposits in Kupffer cell are frequent.

Morphology in Heart

May be enlarged and firm. Histologically the deposits are subendocardial and within the myocardium between the muscle fibers.

Expansion of these myocardial deposits eventually causes pressure atrophy of myocardial fibers.

When they are subendocardial, the conduction system may be damaged, causing electrocardiographic abnormalities.

Clinical Correlation

. Amyloidosis may be found incidently with no clinical manifestations, or it may cause death.

.The symptoms depend on the magnitude of the deposits and on the organs affected.

. At first nonspecific symptoms such as weakness, weight loss, light-headedness, or syncope. Specific findings appear later and most often relate to renal, cardiac, and gastrointestinal involvement.


1) Renal involvement: proteinuria, can cause of the nephrotic syndrome. Progressive obliteration of glomeruli in advanced cases leads to renal failure and uremia

2) Cardiac amyloidosis: insidious congestive heart failure. The most serious complications are conduction disturbances and arrhythmias, which may prove fatal.


3) Gastrointestinal amyloidosis: may be asymptomatic. Amyloidosis of the tongue may cause enlargement and hamper speech and swallowing. Depositions in the stomach and intestine may lead to malabsorption, diarrhea, and disturbances in digestion.

Diagnosis

The diagnosis of amyloidosis depends on demonstration of amyloid deposits in tissues.

The most common sites biopsied are the kidney or rectal or gingival tissues in patients suspected of having systemic amyloidosis.

In suspected cases of immunocyte-associated amyloidosis, serum and urine protein electrophoresis and immunoelectrophoresis should be performed. Bone marrow aspirates often show plasmacytosis.

Scintigraphy with radiolabeled serum amyloid P component is a rapid and specific test. It also gives a measure of the extent of amyloidosis, and can be used to follow patients undergoing treatment

Prognosis

The prognosis for patients with generalized amyloidosis is poor especially those with immunocyte-derived amyloidosis or with myeloma-associated amyloidosis.

Patients with reactive systemic amyloidosis have a better prognosis and it depends to some extent on the control of the underlying condition.

Resorption of amyloid after treatment of the associated condition is a rare.

New therapeutic strategies aimed at correcting protein misfolding and inhibiting fibrillogenesis are being developed.

CELL INJURY, 1 & 2. Cell Injury, Definitions When the cell is exposed to an injurious agent or stress, a sequence of events follows that is loosely termed.

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