Abstract
We analyzed the effect of glucocorticoid on bone regeneration after bone marrow ablation in tibiae of 8โweekโold rats. Methylprednisolone sodium succinate (MPSS) was injected intramuscularly at a dose of 100 mg/kg/day for 3 days. Tibiae on days 1, 3, 5, 7, 10, 12, and 14 after ablation were subjected to tartrateโresistant acid phosphatase staining, immunohistochemistry, in situ hybridization, and transmission electron microscopy (TEM), and measurement of the volume of newlyโformed bone and the osteoclast number. MPSS significantly decreased the newlyโformed bone volume on day 7, and immature bone still remained on day 10 in the MPSSโtreated group. The volume of this bone was significantly higher than that in the control group. However, there were no differences between the groups in the osteoclast number, the expression of mRNAs for osteoblast differentiation markers, and alkaline phosphatase and cathepsin K judged by immunohistochemistry. TEM findings showed no difference in the form of osteoblasts, whereas osteoclasts in the MPSSโtreated group had less developed ruffled borders, compared to those in the control group. These results suggest that MPSS treatment affects neither the differentiation nor the shape of osteoblasts, and does not change the osteoclast number or the cathepsin K level. However, high dose MPSS inhibits both bone formation and resorption during bone regeneration after rat tibial bone marrow ablation, and inhibits ruffled border formation in osteoclasts. These data will be useful to develop bone regenerative therapies for bone diseases due to high dose steroid administration. Microsc. Res. Tech., 2006. ยฉ 2006 WileyโLiss, Inc.