Effect of recombinant human granulocyte colony-stimulating factor (rh G-CSF) on rat bone: inhibition of bone formation at the endosteal surface of vertebra and tibia.

The effect of recombinant human granulocyte colony-stimulating factor (rh G-CSF) on bone was evaluated by histomorphometry using Sprague-Dawley rats. rh G-CSF was injected at doses of 0, 50, 150, and 450 microg/kg for 6 weeks. In vivo double fluorochrome labeling was performed before sacrifice. No significant change in body weight was observed. Bone mineral density (BMD) of lumbar vertebrae and femora was significantly decreased in G-CSF-treated groups. In the lumbar vertebra, osteoid surface, osteoid thickness, trabecular thickness, and labeled surface in G-CSF-treated groups were also significantly lower. In addition, osteoclast number and osteoclast surface were significantly higher in the G-CSF-treated groups. The endocortical surface at the mid-tibia showed lower labeled surface and mineral apposition rate in G-CSF-treated groups, without significant changes at the periosteal surface. Furthermore, numerous granulocytes fully occupied the bone marrow area. We conclude that proliferating granulocytes in the bone marrow may inhibit bone-forming cells from contacting the bone surface, resulting in reduction of bone formation; and increased osteoclastic bone resorption induced by G-CSF treatment contributed to the reduction of BMD.