Background: Glucocorticoid (GC)-associated osteonecrosis of the femoral head (ONFH) is the most common in non-traumatic ONFH. Despite a strong relationship between GC and ONFH, the detailed mechanisms have remained elusive. Recent studies have shown that GC could directly injure the blood vessels and reduce blood supply in the femoral head. Endothelial progenitor cells (EPCs), which were inhibited quantitatively and functionally during ONFH, play an important role in maintaining the normal structure and function of vascular endothelium. Phosphatase and tensin homolog (PTEN) is a tumor suppressor gene that promotes cell apoptosis, and its expression was found to be elevated in GC-associated ONFH patients. However, whether direct inhibition of PTEN attenuates GC-associated apoptosis and dysfunction of the EPCs remains largely unknown. Methods: We investigated the effect of, VO-OHpic, a potent inhibitor of PTEN, in attenuating GC-associated apoptosis and dysfunction of EPCs and the molecular mechanism. SD rats were used to study the effect of VO-OHpic on angiogenesis and osteonecrosis in vivo. Results: The results revealed that methylprednisolone (MPS) obviously inhibit angiogenesis of EPCs by inducing apoptosis, destroying the normal mitochondrial structure, and disrupting function of mitochondria. VO-OHpic treatment is able to reverse the harmful effects by inhibiting the mitochondrial apoptosis pathway and activating the NF-E2-related factor 2 (Nrf2) signaling. Si-Nrf2 transfection significantly reduced the protective effects of VO-OHpic on EPCs. Our in vivo studies also showed that intraperitoneal injection of VO-OHpic obviously attenuates the osteonecrosis of the femoral head induced by MPS and potently increases the blood supply in the femoral head. Conclusion: Taken together, the data suggests that inhibition of PTEN with VO-OHpic attenuates apoptosis and promotes angiogenesis of EPCs in vitro via activating Nrf2 signaling pathway and inhibiting the mitochondrial apoptosis pathway. Moreover, VO-OHpic also mitigates GC-associated ONFH and potentiates angiogenesis in the femoral head.

Iguratimod is a novel disease-modifying antirheumatic drug which is widely used in China. Recent evidence showed that iguratimod attenuated Walker 256 rat mammary gland carcinoma cells induced bone destruction and osteoclasts formation in vivo. Thus, we presumed that iguratimod may suppress osteoclastogenesis and prevent osteoclast-related diseases including postmenopausal osteoporosis. In this study, ovariectomized (OVX) mice were used to detect the effects of iguratimod in vivo. Bone marrow mononuclear cells (BMMCs) were cultured to detect the effects of iguratimod on receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL)-induced osteoclastogenesis in vitro and the molecular mechanisms involved. The results demonstrated that iguratimod prevented ovariectomy-induced bone loss by suppressing osteoclast activity. Consistently, iguratimod suppressed RANKL-induced osteoclastgenesis and bone resorption. Furthermore, iguratimod inhibited RANKL-stimulated tumor necrosis factor receptor-associated factor 6 (TRAF6) - transforming growth factor β-activated kinase-1 (TAK1) complex formation, followed by suppressing the activation of downstream mitogen-activated protein kinase (MAPK), NF-κB and c-fos. Iguratimod subsequently decreased the expression of osteoclast-specific genes via targeting nuclear factor of activated T cells c1 (NFATc1). In conclusion, our results clearly show that iguratimod can inhibit OVX-induced bone loss and osteoclastogenesis through modulating RANKL signaling. Therefore, iguratimod may be used as a novel therapy to mitigate postmenopausal osteoporosis.