Amyloidosis Lecture Notes PDF

Nineveh university - College of medicine Immunopathology 2024-2025 Dr. Hadeel. T. Ali. AL-Obaidy College of medicine, Nineveh university M.B.Ch.B, MS...

Nineveh university - College of medicine Immunopathology 2024-2025 Dr. Hadeel. T. Ali. AL-Obaidy College of medicine, Nineveh university M.B.Ch.B, MSc., (Path.) C.A.B. (Path.) AMYLOIDOSIS: group of diseases having in common the deposition of amyloid. Amyloid : pathologic protein deposited in the extracellular space in various tissues and organs of the body in variety of clinical conditions.  Pathogenesis ❖Normal proteins if produced in abnormal amounts ❖or production of normal amounts of mutant proteins Physical and Chemical Nature of Amyloid All types of amyloid are composed of insoluble, linear, rigid and non-branching fibrils of indefinite length and a diameter of approximately 7.5 to 10 nm by the electron microscope. ❑ About 95% of the amyloid material consists of fibril proteins. ❑Remaining 5% are Non-fibrillar components consists of proteoglycans, glycosaminoglycans, serum P components , etc. I. FIBRIL PROTEINS It consists of two major distinct proteins and more than 20 minor forms. A. Major forms: These are AL, AA. 1. AL (amyloid light chain) protein: ❑ Consists of complete immunoglobulin (Ig) light chains or the amino-terminal fragments of light chains, or both. ❑ Produced by plasma cells. ❑Associated with monoclonal B cell proliferation (e.g. plasma cell tumors). ❑It is included in primary systemic amyloidosis. 2. AA (amyloid-associated) protein: ❑ Non-immunoglobulin. ❑Derived from a larger precursor in the serum called SAA (serum amyloid-associated) protein synthesized by the liver. ❑ Increased synthesis of SAA protein occurs under the influence of cytokines (e.g. IL-6 and IL-1) during inflammation. ❑Associated with chronic inflammation (called as secondary amyloidosis). B. Minor forms: 1. Transthyretin (TTR): ❑ It is a normal serum protein that transports thyroxine and retinol. ❑ Mutations in gene encoding TTR alter its structure , misfolds. ❑Found in a familial amyloid polyneuropathies. 2. Amyloid B 2-microglobulin: ❑B 2-microglobulin is a normal serum protein. ❑ B2-microglobulin is found in amyloidosis of patients on long-term hemodialysis. 3. Amyloid B-peptide (AB) ❑AB is distinct from AB2M and is deposited in cerebral amyloid angiopathy and neurofibrillary tangles in Alzheimer’s disease. ❑AB is derived from amyloid beta precursor protein (AbPP). 4. Endocrine amyloid from hormone precursor proteins e.g. amyloid derived from pro-calcitonin (ACal), islet amyloid polypeptide (AIAPP, amylin), pro-insulin (AIns), prolactin (APro) etc. 5. Amyloid of prion protein (APrP) ❑It is derived from precursor prion protein which is a plasma membrane glycoprotein. ❑Prion proteins are proteinaceous infectious particles lacking in RNA or DNA. II. NON-FIBRILLAR COMPONENTS Non-fibrillar components comprise about 5% of the amyloid material. These components include the following: 1. Amyloid P (AP)-component ❑synthesized in the liver and is present in all types of amyloid. ❑derived from circulating serum amyloid P-component, a glycoprotein resembling the normal serum α1-glycoprotein 2. Apolipoprotein-E (apoE) It is a regulator of lipoprotein metabolism and is found in all types of amyloid. 3. Sulfated glycosaminoglycans (GAGs) These are constituents of matrix proteins.  Classification of Amyloidosis A- According To the Distribution of Amyloid deposition into: ❑Generalized (Systemic); distant sites from the cells producing these abnormal proteins. ❑localized; close to cells producing it. B- According to the etiology: ❑Inherited (primary) ❑Acquired (secondary) C- According to the type of amyloid fibril protein  Systemic amyloidosis It is sub classified into: A) Primary Amyloidosis : Due to blood dyscrasia e.g. multiple myeloma ( a malignant tumor of plasma cells). The amyloid deposition is systemic and of AL type. Malignant plasma cells secrete excessive amount of immunoglobulin light chains called Bence Jones protein which is also present in serum and urine. B) Secondary amyloidosis: The amyloid deposition is systemic and of AA type. Secondary amyloidosis is due to: 1) Infections e.g. T.B. 2) Non infectious chronic inflammatory processes : as ❖Bronchiactasis ❖Chronic osteomylitis ❖Rheumatoid arthritis ❖Inflammatory bowel diseases It is possible that chronic inflammation causes activation of macrophages resulting in secretion of IL-1 and 6 which stimulate liver cells to form serum amyloid associated protein which form AA protein of amyloidosis. C) Senile systemic amyloidosis in elderly. characterized by the systemic deposition of amyloid in elderly patients usually between 70 to 80 years. The amyloid is composed of the normal TTR molecule. D) Hemodialysis-associated Amyloidosis Patients with chronic renal failure on long-term hemodialysis have high levels of B2 microglobulin in the serum because it cannot be filtered through dialysis membranes so deposited as amyloid.  Hereditary or Familial Amyloidosis It constitutes a heterogeneous group, are rare and occur in certain geographic areas. 1. Familial Mediterranean Fever Autosomal recessive disorder. Characterized by recurrent attacks of fever accompanied with inflammation of serosal surfaces (peritoneum, pleura, and synovial membrane). The gene encodes a protein called pyrin (for its relation to fever), regulate inflammatory reactions by producing high levels of pro-inflammatory cytokines IL-1. The amyloid fibril proteins are of AA type probably produced due to recurrent bouts of inflammation. 2. Familial Amyloidotic Neuropathies It is characterized by deposition of amyloid in peripheral and autonomic nerves and the fibrils are made up of mutant TTRs.  Localized amyloidosis Amyloid deposits are limited to a single organ or tissue without involvement of any other site producing localized nodular mass e.g. lung, larynx, skin, tongue.etc. amyloid deposit is of AL type, some of these localized lesions are due to endocrine tumors ( endocrine amyloid) like medullary carcinoma of thyroid and carcinoma of stomach. Clinical Features Clinical manifestations initially may be nonspecific (e.g. weakness, weight loss). Specific symptoms appear later and are related to renal, cardiac, and gastrointestinal involvement. ❖Renal involvement: It gives rise to proteinuria sometime massive enough to cause nephrotic syndrome. In advanced cases, the obliteration of glomeruli causes renal failure and uremia. ❖ Cardiac amyloidosis: It may present as congestive heart failure, conduction disturbances and arrhythmias. ❖ Gastrointestinal amyloidosis: It may be asymptomatic, or present as malabsorption, diarrhea, and digestive disturbances. Diagnosis ❑ Biopsy: histologic demonstration of amyloid deposits in tissues. The most common sites are the kidney, rectum or gingival tissues in systemic amyloidosis. ▪ The rectum is the best site for taking the biopsy. ▪ Examination of abdominal fat aspirates stained with Congo red is quite specific, but has low sensitivity. ▪ Bone marrow aspirates may show monoclonal plasmacytosis. ▪ Electron microscopy (Definite diagnosis )show nonbranching fibrils of indefinite length and a diameter of approximately 7.5 to 10 nm. ❑ In immunocyte-associated amyloidosis, serum and urine protein electrophoresis and immunoelectrophoresis should be done.  Special stains for amyloid Congo red: It is the most widely used specific stain for amyloid. Under light microscope, with Congo red stain, amyloid appears red but under polarized light, the Congo red stained amyloid shows apple-green birefringence. Thioflavin ‘T’ and ‘S’ give secondary immunofluorescence with ultraviolet light. Thioflavin T is more useful for demonstrating juxtaglomerular apparatus of the kidney. Metachromatic stains like crystal violet and methyl violet give rose pink appearance. Amyloid is PAS positive. Morphology Main Organs Involved: ❑ Primary amyloidosis: Heart, GI tract, respiratory tract, peripheral nerves, skin and tongue. ❑ Secondary amyloidosis: Kidneys, liver, spleen, lymph nodes, adrenals, and thyroid. Gross: o May or may not be apparent grossly. o If large amount accumulates affected organs are enlarged, firm and have a waxy appearance o Cut surface: If the amyloid deposits are large, painting the cut surface with iodine gives a yellow color, which is transformed to blue violet after application of sulfuric acid (which acidifies iodine). Microscopy: o Amyloid deposits are always extracellular. o Appears as an amorphous, eosinophilic, hyaline, glassy substance. o Many other substances (e.g. collagen, fibrin) also stain eosinophilic with hematoxylin and eosin. Hence, it is necessary to differentiate amyloid from these other hyaline deposits by using special stains.  In kidney: Amyloid is deposited an glomeruli (in basement membrane of capillary loops) and wall of blood vessels. In spleen: Amyloid causes marked enlargement of spleen and is deposited in splenic sinuses and splenic follicles. In the liver: Amyloid causes marked enlargement of liver and is deposited in the wall of blood vessels and sinusoids In the heart: Amyloid leads to cardiac enlargement in elderly and is deposited in between myocardial fibers Macroscopically the affected organ enlarged, firm & has waxy consistency hepatic amyloidosis Normal glomeruli In kidney: Amyloid is deposited in glomeruli (in basement membrane of capillary loops) and wall of blood vessels Amyloidosis of kidney-congo red stain Amyloidosis of kidney- polarized light, the Congo red stained amyloid shows apple-green birefringence.