DNA oxidation injury in bone early after steroid administration is involved in the pathogenesis of steroid-induced osteonecrosis.

OBJECTIVE: Using a rabbit model, we investigated the DNA oxidation injury occurring in bone following steroid administration and focused on the relation between DNA oxidation injury and osteonecrosis.
METHODS: Japanese white rabbits weighing about 3.5 kg were injected with a single intramuscular dose of methylprednisolone 4 mg/kg and divided into groups consisting of 10 rabbits each, which were killed after 3, 5 and 14 days (groups A, B and C respectively). As a control, five untreated rabbits (group N) were also studied. An immunohistochemical study of the diaphysis of the proximal femur was conducted using the monoclonal antibody N45.1, which is a highly specific antibody against 8-hydroxy-2'-deoxyguanosine, an index of DNA oxidation injury. Also, using NIH Image freeware, the positive area (8-OHdG %PA) of each group was calculated and the four groups were compared.
RESULTS: Osteonecrosis was detected only in group C (70%). N45.1 positivity was noted in bone marrow haematopoietic cells and was particularly marked in groups B and C. 8-OHdG %PA was 1.6 +/- 0.2% in group N, 2.2 +/- 0.4% in group A, 4.8 +/- 0.4% in group B and 5.1 +/- 0.5% in group C, with significantly greater oxidation injury found in groups B and C (P < 0.001).
CONCLUSION: Oxidative injury was demonstrated soon after the administration of methylprednisolone in a rabbit model prior to the development of osteonecrosis. This finding may suggest new strategies to prevent steroid-induced osteonecrosis, such as the optimally timed (early) administration of antioxidant agents.