Abstract
Summary Statement
The incidence of osteonecrosis was significantly lower in the anti-vasospasm agent group (32%) than that in the control group (75%). Vasospasm is one of the important factors involved in the pathogenesis of steroid-induced osteonecrosis.
Introduction
A number of studies have suggested that ischemia is the principal pathomechanism of osteonecrosis, however, the detailed mechanism responsible for ischemia remains unclear. It has recently been reported that the Rho/Rho-kinase mediated pathway (Rho-kinase pathway) is considered to be involved in the possible pathogenesis of various cardiovascular disorders as well as cerebral vasospasm. We examined the effects of fasudil (Rho-kinase inhibitor), an anti-vasospasm agent, on the development of steroid-induced osteonecrosis in rabbits.
Materials & Methods
One group of rabbits received 15 mg/kg of fasudil intravenously, which were then injected once intramuscularly with 20 mg/kg of methylprednisolone (n = 33, MF group), and one received methylprednisolone alone as a control (n = 28, M group). Eight rabbits from each group were sacrificed 24 hour after the methylprednisolone injection to analyze them by immunohistochemical staining, a Western blotting analysis. Two weeks after the steroid injection, the femora and humeri were examined histopathologically for the incidence of osteonecrosis.
Results
The incidence of osteonecrosis was significantly lower in the MF group (32%) than that in the M group (75%) (P < 0.01). Immunohistochemically, endothelinA-receptor (ETA Rc) expressions levels were decreased in the smooth muscle of the bone marrow in the MF group in comparison to that in the M group. In the M group, the average relative phospho-myosin light chain (p-MLC) expression level in the bone marrow tissue was significantly higher than that observed in the MF group (P < 0.01). In the MF group, the average relative total-eNOS expression level as well as the average relative phospho-eNOS (p-eNOS) expression level was almost 1.5 times higher than that observed in the M group (P < 0.05). The eNOS expressions levels in both serum and bone marrow in the MF group were significantly higher than those in the M group (P < 0.05).
Discussion/Conclusion
The potential mechanisms resulting in vasospasm include the increased release of vasoconstrictors or increased sensitivity to these vasoconstrictors. ET-1 has been demonstrated to cause vascular smooth muscle cell constriction via ETA Rc stimulation. The expression of ETA Rc in rabbits treated with methylprednisolone plus fasudil (MF group) decreased in comparison with that in rabbits treated with the methylprednisolone alone (M group). In this study, both the eNOS and p-eNOS expressions levels in the M group were decreased in comparison to those observed in the MF group. A previous study suggested that high-dose steroid administration causes the overproduction of reactive oxygen species, and thereby perturbs nitric oxide (NO) availability in the vascular endothelium, leading to vascular endothelial dysfunction in patients receiving high-dose steroid therapy. Considering the pathogenesis of the development of osteonecrosis, we speculate that endothelial dysfunction may thus be a preliminary condition leading to the vasospasm. In conclusion, this study indicates that vasospasm is one of the important factors involved in the pathogenesis of steroid-induced osteonecrosis and that the anti-vasospasm agents seem to decrease the incidence of steroid-induced osteonecrosis.
