Non-hematogenous endogenous pigments 0 This group contains the following : 1. Melanins. 2. Lipofuscins. 3. Chromaffin. 4. Pseudomelanosis. 5. Dubin-Johnson pigments. 6. Ceroid-type lipofuscins. 7. Hamazaki-Weisenberg bodies.
1. Melanins 0 Melanins are a group of pigments whose colour varies from light brown to black. 0 They are normally found in the skin, eye, substania nigra of the brain and hair follicles. 0 Under pathological conditions it is found in benign nevus cell tumours and malignant melanomas. 0 The melanins are bond to proteins, and these complexes are localized in the cytoplasm of cells within melanin granules.
0 Melanins are produced from tyrosine by the action of an enzyme tyrosinase, this enzyme act upon the tyrosine to produce the substance kown as dihydroxyphenylalanine (DOPA), which is subsequently rapidly acted upon by the same enzyme to produce an intrmedate pigment which then polymerizes to produce melanin.
Methods of demonstration 0 A number of methods can be used : 1. Reducing methods such as Masson-Fontana silver technique and Schmorl's ferric-ferricyanide reduction test. 2. Enzyme methods e.g. DOPA reaction. 3. Solubility and bleaching characteristics. 4. Fluorescent methods. 5. Immunocytochemistry.
Reducing methods 0 Melanin is a powerful reducing agent so its able to reduce ammonical silver solution to form metallic silver (Masson's method). 0 Melanin will reduce ferricyanide to ferrocyanide with the production of Prussian blue in the prescence of ferric salts (Schmorl's method). This type of reactio is also seen in other pigments such as lipofuscins, bile and neuroendocrine cell granules.
Enzyme methods 0 Cells that are capable of producing melinin can be demonstrated by the DOPA. The enzyme tyrosinase that is localized within these cells will oxidase DOPA to form an insoluble brown black pigments. 0 The best results are obtained when using post fixed cryostat sections.
2. Lipofuscins 0 These yellow brown to redish brown pigments occur widely throughout the body and are thought to be produced by an oxidation process of lipids and lipoproteins. 0 The oxidation process occurs slowly and progressively, and therefore the pigments exhibit variable staining reactions, different colours and variation in shape and size. 0 Lipofuscins can be found in the following sites:
0 Hepatocytes. 0 Cardiac muscles particularly around the nucleus. 0 Inner reticular layer of the normal adrenal cortex. 0 Testis. 0 Ovary. 0 Cytoplasmic inclusions in the neurons of the brain. 0 Some lipid storage disorders e.g. Batten's disease. 0 Other tissues such as bone marrow, involuntary muscles, cervix and kidney.
Methods of demonstration 0 The lipofuscins react with a variety of histochemical methods such as: 0 Periodic acid-schiff's method. 0 Schmorl's ferric-ferricynade reduction test. 0 Long Ziehl-Neelson method. 0 Sudan black B method. 0 Gomori's aldehyde fuchsin technique. 0 Masson-Fontana silver method. 0 Basophilia using methyl green.
3. Chromaffin 0 This pigments is normally found in the cells of the adrenal medulla as a dark brown materials. 0 It may occur in the tumours of the adrenal medulla (pheochromocytomas). 0 Fixation in formalin, alcohol is not recommended, dichromate containing fixatives is recommended. 0 Chromaffin can be demonstrated by Lillie's Nile blue A, Schmorl's reaction, PAS technique.
4. Pseudomelanosis 0 This pigments can be found in macrophages in the lamina propria of the large intestine and appendix. 0
5. Dubin-Johnson pigments 0 This pigments is found in the liver of patients with Dobin-Johnson syndrome and is due to defective canalicular transport of bilirubin. 0 Its brownish black granular intracellular pigments situated in the centrilobular hepatocytes. 0 Its simmilar to the lipofuscin, but ultra structurally are differ.
6. Hamazaki-Weisenberg bodies 0 These small yellow-brown spindle-shaped structures are found mainly in the sinuses of lymph nodes, either lying free or as cytoplasmic inclusions. 0 They associated with sacoidosis, melanosis coli. 0 Histochemically they are similar to lipofuscin, and at ultra structural level have an appearance that suggests that they are probably giant lysosomal residual bodies.
0 The end