Abstract
Objective
Vascular endothelial growth factor (VEGF) is an angiogenic promoter that is rapidly induced as a response to local hypoxia. We investigated VEGF expression in rabbits in a controlled experiment to clarify the onset of ischemic events in corticosteroid-induced osteonecrosis (ON).
Methods
Ninety-nine mature Japanese white rabbits were divided into 6 treatment groups and an untreated control group. The treatment groups received a single intramuscular injection of 4 mg/kg methylprednisolone acetate; they were euthanized at different times, and tissue samples were obtained from their femora. We examined the development of ON and the expression of VEGF using histopathology, immunohistochemistry, Northern blot analysis, and Western blot analysis.
Results
On histopathological examination, the earliest indication of ON was 5 days after the corticosteroid treatment. The frequency of ON occurrence reached a plateau at or after Week 1. VEGF expression was accompanied by the development of ON. VEGF-positive cells detected by immunohistochemistry were found among bone marrow cells, frequently located in the area surrounding ON, suggesting that VEGF production was switched on as a result of the ischemic events that cause ON. The level of VEGF-mRNA expression indicated by Northern blot analysis peaked at 3 days after the corticosteroid treatment and decreased gradually to the levels present in the control group at 7 days after treatment. Western blot analysis revealed VEGF protein production at 3 days after the corticosteroid treatments. Levels of VEGF expression 2 weeks or more after the corticosteroid treatment were almost the same as in the control group.
Conclusion
We observed early expression of VEGF in the cells around the corticosteroid-induced ON lesions in rabbits. These results suggest that the ischemic events that cause ON begin soon after the initial corticosteroid treatment.
Key Indexing Terms:Footnotes
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T. Kabata, MD, PhD, Assistant Professor, Department of Orthopaedic Surgery, Kanazawa University School of Medicine; T. Matsumoto, MD, PhD, Professor, Department of Orthopaedic Surgery, Kanazawa Medical University; S. Yagishita, MD, PhD, Department of Orthopaedic Surgery, Kanazawa University School of Medicine; T. Wakayama, MD, PhD, Associate Professor; S. Iseki, MD, PhD, Associate Professor, Department of Anatomy (I), Kanazawa University School of Medicine; K. Tomita, MD, PhD, Professor, Department of Orthopaedic Surgery, Kanazawa University School of Medicine.
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Supported by the Japanese Investigation Committee for Osteonecrosis of Femoral Head, under the auspices of the Ministry of Health and Welfare of Japan.
- Accepted for publication July 10, 2008.
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