Effects of iron overload on bone remodeling in pigs

For study of the effects of an iron overload on bone remodeling, 5 control pigs were compared with 5 pigs given a total dose of 10.8 g of parenteral iron in 36 days. Treated pigs developed an iron tissue overload demonstrated by a marked increase in bone and liver iron. Except for a modest increase in SGOT, there was no biochemical or histologic sign of liver damage. Serum levels of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D were unchanged in the treated pigs. There was no accumulation of iron in the parathyroid glands and the serum immunoreactive parathyroid hormone level was unchanged in the treated animals. Bone histomorphometry after double tetracycline labeling showed that in the treated pigs osteoblast cell surfaces, double and total labeled surfaces, appositional rate, and formation at tissue level were significantly decreased, and reversal surfaces were increased. Mineralization was not impaired because the osteoid thickness was unchanged. From the morphometric measurements it was concluded that osteoblast recruitment and the collagen synthesis rate were decreased. Mean wall thickness, which indicates the amount of bone synthesized, was also lowered. In contrast, the osteoclastic resorption surfaces and the depth of lacunae resulting from osteoclast resorption were unchanged by treatment. Despite this imbalance between formation and resorption, trabecular bone mass estimated on trabecular bone volume and bone ash was unchanged after 36 days' treatment. Perls' stain revealed that iron deposits were present in osteoblast and osteoclast cells and also inside the bone matrix, because there was a linear deposit along the trabecular surfaces, cement line, and osteoid-mineralized bone interface. Therefore, because treatment induced no modification of the major humoral regulators of bone metabolism, it is suggested that iron, which was present in bone cells and matrix, could play a role in bone remodeling.