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.