IRON DISTRIBUTION IN THALASSEMIC BONE BY ENERGY-LOSS SPECTROSCOPY ANDELECTRON SPECTROSCOPIC IMAGING

Iron overload occurs frequently in thalassemia as a consequence of reg ular blood transfusions, and iron has been found to accumulate in bone , but skeletal toxicity of iron is not clearly established. In this st udy, hone biopsies of thalassemic patients were investigated by light (n = 6) and electron microscopy (n = 8) in order to analyze iron distr ibution and possible iron-associated cellular lesions. Sections (5 mum thick) were used for histomorphometry and iron histochemistry. Ultrat hin sections were examined with an energy filtering transmission elect ron microscope. Iron was identified by electron energy loss spectrosco py (EELS), and iron distribution was visualized by electron spectrosco pic imaging (ESI) associated with computer-assisted treatment (two-win dow method). This study shows that EELS allows the detection of 4500-9 000 iron atoms, and that computer-assisted image processing is essenti al to eliminate background and to obtain the net distribution of an el ement by ESI. This study shows also that stainable iron was present al ong trabecular surfaces, mineralizing surfaces, and on cement lines in the biopsies of all patients. Moreover, iron was detected by EELS in small granules (diffusely distributed or condensed in large clusters), in osteoid tissue, and in the cytoplasm of bone cells, but not in the mineralized matrix. The shape and size (9-13 nm) of these granules we re similar to those reported for ferritin. As for iron toxicity, all p atients had osteoid volume and thickness and osteoblast surface in the normal range. Stainable iron surfaces did not correlate with osteobla st surfaces, plasma ferritin concentrations, or the duration of transf usion therapy. Numerous osteoblasts contained damaged mitochondria, an d impaired osteoblast activity can therefore not be excluded.