Hemosiderin or haemosiderin is an iron-storage complex. The breakdown of heme gives rise to biliverdin and iron. The body then traps the released iron and stores it as hemosiderin in tissues. Hemosiderin is also generated from the abnormal metabolic pathway of ferritin. It is only found within cells and appears to be a complex of ferritin, denatured ferritin and other material. The iron within deposits of hemosiderin is very poorly available to supply iron when needed. Hemosiderin can be identified histologically with Perls' Prussian blue stain; iron in hemosiderin turns blue to black when exposed to potassium ferrocyanide. In normal animals, hemosiderin deposits are small and commonly inapparent without special stains. Excessive accumulation of hemosiderin is usually detected within cells of the mononuclear phagocyte system or occasionally within epithelial cells of liver and kidney. Several disease processes result in deposition of larger amounts of hemosiderin in tissues; although these deposits often cause no symptoms, they can lead to organ damage. Hemosiderin is most commonly found in macrophages and is especially abundant in situations following hemorrhage, suggesting that its formation may be related to phagocytosis of red blood cells and hemoglobin. Hemosiderin can accumulate in different organs in various diseases. Iron is required by many of the chemical reactions in the body but is toxic when not properly contained. Thus, many methods of iron storage have developed.
Pathophysiology
Hemosiderin often forms after bleeding. When blood leaves a ruptured blood vessel, the red blood celldies, and the hemoglobin of the cell is released into the extracellular space. Phagocytic cells called macrophages engulf the hemoglobin to degrade it, producing hemosiderin and biliverdin. Excessive systemic accumulations of hemosiderin may occur in macrophages in the liver, lungs, spleen, kidneys, lymph nodes, and bone marrow. These accumulations may be caused by excessive red blood cell destruction, excessive iron uptake/hyperferraemia, or decreased iron utilization uptake hypoferraemia.
