Development of non-traumatic osteonecrosis of the femoral head requires toll-like receptor 7 and 9 stimulations and is boosted by repression on nuclear factor kappa B in rats

Okazaki, Shunichiro; Nagoya, Satoshi; Matsumoto, Hiroshi; Mizuo, Keisuke; Sasaki, Mikito; Watanabe, Satoshi; Yamashita, Toshihiko; Inoue, Hiromasa

It is well known that corticosteroids are mainly metabolized in the liver by a hepatic corticosteroid-metabolizing enzyme. 36, 37 Recently, we reported that differences in liver function were observed between patients with corticosteroidinduced ONFH and those without ONFH within 1 week after corticosteroid therapy. 38 Moreover, Ichiseki et al 39 reported that a disturbance in oxidative stress in the liver was observed within 24 h in an oxidative stress-induced ONFH rat model. These reports suggest that various changes in the liver in the early phase after treatment contribute to the development of ONFH. In the present study, we found that ONFH occurs within 3 days after MPSL treatment in rats, suggesting that detection of the early phase disease after MPSL treatment is important in clarifying the pathogenesis of ONFH. We also found that the activity of NF-kB in the liver at 1 day was significantly repressed by corticosteroid treatment after TLR7 ligand administration. Auphan et al 17 reported that glucocorticoids are the most potent anti-inflammatory and immunosuppressive agents. Repression of NF-kB activity via glucocorticoid receptors is one critical component of the inhibitory effect that glucocorticoids have on proinflammatory and immune responses. 18 Therefore, our results suggest that ONFH results from the activation of NF-kB and IRF7 via the MyD88-dependent pathway, followed by a subsequent repression in NF-kB activity by corticosteroid treatment, whereas IRF7 activity is not affected by corticosteroid treatment. Therefore, this result indicates that a repression in IRF7 activity using a specific inhibitor interferes with the development of ONFH in spite of the simultaneous repression in NF-kB activity resulting from MPSL treatment. BAY11-7082 was reported to be an Ikk a inhibitor and Ikk b inhibitor with potential to inhibit NF-kB and IRF7 activity. 21 In the present study, MPSL treatment significantly repressed the activity of NF-kB in Imiquimod þ MPSL compared with Imiquimod þ Saline rats (Figure 3) , and accordingly, the co-administration of BAY11-7082 and MPSL did not repress the activity of NF-kB in Imiquimod þ BAY11 þ MPSL compared with Imiquimod þ MPSL rats (Figure 4 ). In contrast, MPSL treatment did not alter the activity of IRF7 in Imiquimod þ MPSL compared with Imiquimod þ Saline rats (Figure 3 ), whereas the co-administration of BAY11-7082 and MPSL significantly repressed the activity of IRF7 in Imiquimod þ BAY11 þ MPSL compared with Imiquimod þ MPSL rats (Figure 4) . And co-administration of BAY11-7082 and MPSL significantly lowered the incidence of ONFH through a repression in IRF7 activity. These findings confirmed that the effect of corticosteroid treatment on the transcription factor activity in the liver triggered the development of ONFH, and the repression in NF-kB activity by corticosteroid treatment boosted the development of ONFH.