CELL INJURY for Medical (lecture 2) Sufia Husain Assistant Prof & Consultant KKUH, Riyadh.

APOPTOSIS CELLULAR ACCUMULATION

APOPTOSIS Apoptosis is programmed cell death. Apoptosis means “falling off”. It is a type of cell suicide. Is results from activation of ‘death pathway genes’. It is a pathway of cell death in which cells destined to die activate their own enzymes to degrade their own nuclear DNA and proteins. It can be Physiological or adpative. Pathologic. NOTE: Apoptosis and necrosis sometimes coexist.

Apoptosis in Physiologic Situations The programmed destruction of cells during embryogenesis. Hormone-dependent: e.g. endometrial cell breakdown during the menstrual cycle, the regression of the lactating breast after weaning, and prostatic atrophy after castration (adaptive atrophy). Apoptosis in proliferating cells e.g. intestinal epithelial lining is always being replaced. Cells that after performing their function undergo apaotosis e.g neutrophils and lymphocytes in inflammation. Sometimes body produced harmful lymphocytes and they are also destroyed by apoptosis.

Apoptosis in Pathologic Conditions Cell death produced by injury e.g. radiation. In certain diseases e.g. viral hepatitis the infected hepatocytes undergo apoptosis (acidophilic bodies) or injury of skin cells (keratinocytes) leads to apoptosis of keratinocytes (Civatte bodies). Pathologic atrophy in organs e.g. pancreas, parotid gland, and kidney Corticosteroid induced atrophy of the neonatal thymus Cell death in tumors (usually accompanied by necrosis).

Mechanism of Apoptosis Activation by death pathway genes Cell shrinkage. Chromatin condensation in the nucleus: This is the most characteristic feature of apoptosis. The nucleus may break up into fragments. Formation of cytoplasmic blebs and apoptotic bodies: The apoptotic cell first shows surface blebbing, then fragments into membrane-bound apoptotic bodies. The apoptotic bodies contain cytoplasm and organelles, with or without nuclear material. The cell's plasma membrane remains intact. The plasma membrane of the apoptotic cell sends signal to macrophages to phagocytose it. Phagocytosis of apoptotic bodies, mainly by macrophages. There is no release of the cytoplasmic content and therefore there is no inflammation in the surrounding tissue.

Morphology of Apoptosis On histology 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 nucleus. There is no inflammation. apoptosis in liver cell apoptosis in epidermis.

Important enzymes of apoptosis Cysteine proteases named caspases Ca2+- and mg2+-dependent endonucleases Regulation of apoptosis It is mediated by a number of genes and their products e.g: bcl-2 gene inhibits apoptosis bax genes facilitates apoptosis p53 facilitates apoptosis by inhibiting bcl2 and promoting bax genes.

The changes seen in necrosis (left) and apoptosis (right) The changes seen in necrosis (left) and apoptosis (right). Apoptosis is different from necrosis. In necrosis there is loss of membrane integrity, enzymatic digestion of cells, and frequently an inflammatory reaction. Apoptosis and necrosis sometimes coexist.

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

Intracellular Accumulations Some substances can accumulate inside the cell in large amounts and cause problems in the cell and the organ. The substance may accumulate in either the cytoplasm or the nucleus. This is called as Intracellular accumulation. The substance can be: (1) a normally present in the cell which has accumulated in excess, such as water, lipids, proteins, and carbohydrates (2) an abnormal substance, either Exogenous e.g. a mineral or products of infectious agents Endogenous e.g. a product of abnormal synthesis or metabolism (3) a pigment.

1. Accumulation of LIPIDS All major classes of lipids can accumulate in cells: triglycerides, cholesterol/cholesterol esters, and phospholipids

1. Accumulation of LIPIDS Steatosis (Fatty Change) Fatty change is the abnormal accumulation of triglycerides inside cells. It is mainly seen in liver, but it is also seen in heart, muscle, and kidney. The causes of steatosis include: Toxins e.g alcohol abuse protein malnutrition, diabetes mellitus, obesity, Anoxia/starvation Pregnancy Severe anemia Excess accumulation of triglycerides within the hepatocytes occurs when there is an imbalance between the uptake, utilization, & secretion of fat by the affected cell. The terms steatosis and fatty change is abnormal Morphology of Steatosis in liver Gross: In mild cases liver looks normal. In severe cases liver is enlarged, yellow and greasy. Light microscopy: clear vacuoles in the cytoplasm displacing the nucleus to the periphery of the cell Occasionally, cells rupture, and the fat globules merge, producing a so-called fatty cysts. The lipid stains orange-red with Sudan IV or Oil Red-O stains.

1. Accumulation of LIPIDS

1. Accumulation of LIPIDS Cholesterol and Cholesterol Esters Accumulation of cholesterol in the form of intracellular vacuoles can be seen in atherosclerosis in which there is accumulation of cholesterol in the smooth muscle cells and macrophages in the wall of arteries.

2. ACCUMULATION OF 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. Glycogen stains pinkish/violet with mucicarmine stain or the periodic acid schiff (PAS) stain. Glycogen accumulation is seen in: Diabetes mellitus: is a disorder of glucose metabolism. In this disease, glycogen is found in the proximal convoluted tubules of kidney, in liver, the β cells of the islets of Langerhans, heart muscle cells etc. Glycogen storage diseases: it is a group of genetic diseases in which there is abnormal glycogen metabolism.

3. ACCUMULATION OF PIGMENTS Pigments are colored substances, some of which are normal constituents of cells (e.g. melanin), whereas others are abnormal. Pigments can be exogenous, coming from outside the body, or endogenous, synthesized within the body itself.

Endogenous Pigments A) Lipofuscin is also known as wear- and-tear or aging pigment. Lipofuscin is endogenous and causes no damage to cells. It indicates history of free radical injury and lipid peroxidation. It is yellow-brown, granular intra- cytoplasmic pigment It is prominent in the liver and heart of aging patients, in atrophic tissue, patients with severe malnutrition and cancer cachexia Top 2 figure are from heart and bottom from liver

Endogenous Pigments cont. B) Melanin: an endogenous, non-hemoglobin, brown- black pigment normally present in the cytoplasm of melanocytes in the skin’s epidermis. It is responsible for the color of our skin. It is derived from tyrosine and stored in melanosomes of the melanocytes. The function of melanin is to prevent the harmful effects of UV light. It accumulates in large amounts in benign and malignant melanocytic tumors. In inflammatory conditions of the skin it spreads from epidermis into the underlying dermis. This is called as post inflammatory hyperpigmentation of the skin. Masson-Fontana stain is used to identify melanin. Top 2 figures: normal skin with basal melanin. Bottom figure: post inflammatory hyperpigmentation

Endogenous Pigments cont. C) Hemosiderin: is a hemoglobin-derived golden brown iron containing pigment in cells. Hemosiderin exists normally in small amounts in tissue macrophages of the bone marrow, liver, & spleen. Hemosiderin accumulates in excess after rbc breakdown (hemolysis) or hemorrhage and leads to 2 main types of conditions: Hemosiderosis: accumulation of hemosiderin mainly in macrophages. The pigment does not cause tissue damage. It can be: localized hemosiderosis (e.g. common bruise: there is lysis of rbcs, release of hemoglobin and the iron is converted to hemosiderin) systemic hemosiderosis. Hemochromatosis; a more extensive accumulation of hemosiderin, often in parenchymal cells with tissue damage, scarring & organ dysfunction. Results in liver fibrosis, heart failure, diabetes mellitus and skin discoloration(bronzed diabetes).

Endogenous Pigments cont The causes of excess systemic iron are: increased absorption of dietary iron, impaired use of iron, hemolytic anemias, Exogenous iron from blood transfusions. Morphology: Iron pigment is golden and granular in cytoplasm of macrophages or in cells of the liver, pancreas, heart etc. It appears blue-black with Pearl Prussian blue stain

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 present in the alveoli and is also transported the neighbouring lymph nodes. Accumulation of this pigment blacken the tissues of the lungs (anthracosis) and the involved lymph nodes. There is too much carbon dust in the lung of coal miners, which leads to lung disease known as coal worker's pneumoconiosis. Other exogenous pigments that can be harmful when they accumulate in large amounts are silica, lead, iron dust and silver. Plumbism is lead poisoning and argyria is silver poisoning. In both cases there may be permanent grey discoloration of skin and conjunctivae. Tattooing is a form of localized, exogenous pigmentation of the skin. The pigments inoculated are phagocytosed by dermal macrophages.

Anthracosis lung

Amyloid Deposition Amyloidosis is an extracellular deposition of fibrillary amyloid protein in various organs (kidney, liver, blood vessels, heart etc.) leading to organ damage. It is associated with a number of inherited and inflammatory disorders. Amyloidosis is a disorder of protein misfolding. Amyloid is composed of nonbranching fibrils of β-pleated sheets. There are 2 main clinical forms of amyloidosis Primary amyloidosis: is associated with plasma cell abnormality e.g. multiple myeloma. AL type amyloid is deposited. Secondary amyloidosis: is associated with chronic inflammatory or autoimmune diseases( osteomyelitis, tuberculosis, rheumatoid arthritis etc). In it AA (amyloid associated protien) type amyloid is deposited. Light microscopy H&E stain Pathpedia.com

EM Morphology of amyloid Light microscopy: it is pink eosinophilic material. It appears bright orange with Congo red stain. And when the congo red stained tissue is exposed to polarized light it produces an apple-green birefringence. Electron microscopy: amyloid deposits are composed of nonbranching fibrils, 7.5 to 10 nanomicron in diameter. Diagnosis: can be made with biopsy of organs like the kidney, rectum, gingiva and skin. CONGO RED STAIN EM JOP. J Pancreas (Online) 2001; 2(4):124-139. POLARIZED LIGHT Briggs JH, Singleton WG, Burke MM, Hart LA, Parker RJ - Cases J (2009)