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

To elucidate the precise time of onset of ONFH in rats and evaluate the effects of MPSL on the ONFH development, the Imiquimod þ Saline (3 Â n ¼ 6 and n ¼ 10) was used as a control group, and it and the Imiquimod þ MPSL (4 Â n ¼ 10) group (which group significantly developed ONFH compared with the Saline þ MPSL group) were each divided into four equal subgroups. One subgroup from each treatment group was killd on Day 1, 3, 7, and 14, respectively, after the last treatment to detect changes that led to the development of ONFH. Table 2 shows the incidence of ONFH in each group. ONFH was observed in the Imiquimod þ Saline and Imiquimod þ MPSL rats killed on Day 3, 7, and Figure 2 shows the histopathological appearance of the femoral head after hematoxylin and eosin staining in the Imiquimod þ Saline rats with ONFH (A) and those without ONFH (B) at 3 days. Empty lacunae were observed within the necrotic bone trabeculae, and bone marrow cells showing fat cell necrosis were observed in the medullary space across most areas of the femoral head as observed in the Imiquimod þ MPSL and CpG-C þ MPSL rats (Figure 2a) . Normal trabeculae as well as hematopoietic and fat cells were observed in the femoral head as observed in the Saline þ MPSL rats (Figure 2b ). In the present study, we found that ONFH occurs within 3 days after MPSL treatment in rats. Figure 3 shows the activity of the transcription factors NF-kB and IRF7 in the liver. The activity of NF-kB was repressed significantly in rats treated with MPSL at 1 day after the administration of TLR ligands (Figure 3 ; Imiquimod þ Saline vs Imiquimod þ MPSL, 100±10.6 vs 69.3±4.9; Po0.01).