Background/Purpose: Osteoporosis is an ageing-associated diseases requiring better therapeutic modality. Eupatilin is a major flavonoid from Artemisia. We aimed to evaluate the effects of eupatilin on RANKL-induced osteoclast differentiation and its mechanism of action.

Methods:  ICR mice were divided into 4 groups:  saline-treated (Control), only LPS-treated, only eupatilin-treated, and LPS and eupatilin-treated groups. Eupatilin or PBS was administered orally 1 day before LPS injection. Eupatilin or PBS was administered orally every other day for 8 days. LPS was injected intraperitoneally on days 1 and 4. The mice were sacrificed after 8 days, and the left femurs were analyzed by high-resolution micro-computed tomography. To confirm the therapeutic effect of eupatilin on LPS-induced bone loss in vivo, ICR mice were divided into 6 groups : PBS-treated, LPS-treated, and LPS plus eupatilin-treated groups. Eupatilin or PBS was administered orally every day from 4, 6, or 8 days. LPS was injected intraperitoneally on days 1 and 4. Mice were sacrificed after 10 days, and the left femurs were analyzed by high-resolution micro-CT. We further assessed the effect of eupatilin on OVX-induced bone loss. Eight-week-old female C57BL/6 mice were either 6 sham-operated mice or 12 OVX mice. OVX mice were divided into two groups: OVX controland eupatilin groups. After, eupatilin was administrated orally for 4 weeks. Femur metaphysic regions were scanned using a high-resolution micro-CT.  

Results: Upon stimulation prior to RANKL treatment or poststimulation of BMCs in the presence of RANKL with eupatilin complete blockade of RANK-dependent osteoclastogenesis was accomplished. This blockade was accompanied by inhibition of rapid phosphorylation of Akt, GSK3b, ERK and IkB as well as downregulation of c-Fos and NFATc1 at protein levels, suggesting that transcriptional suppression is a key acting mechanism on the anti-osteoclastogenesis. Transient reporter assays or gain of function assays confirmed that eupatilin was, indeed, a potent transcriptional inhibitor in osteoclasts (OC). Surprisingly, when multinucleated osteoclasts (MNCs) were cultured on bone scaffolds in the presence of eupatilin bone resorption activity was also completely blocked by dismantling actin ring, suggesting that another major acting site of eupatilin is cytoskeletal rearrangement. The eupatilin-treated MNCs revealed a shrunk cytoplasm and accumulation of multi-nuclei, eventually becoming fibroblast-like cells. No apoptosis occurred. Inhibition of phosphorylation of cofilin by eupatilin suggests that actin may play an important role in the catastrophic morphological change of MNCs. Human OC were similarly responded to eupatilin.  When eupatilin was administered to LPS-induced osteoporotic mice after manifestation of osteoporosis, it was capable of preventing bone loss. The ovariectomized (OVX) mice remarkably exhibited bone protection effects.

Conclusion: Taken together, eupatilin is an effective versatile therapeutic intervention for osteoporosis as dual blockaders; 1) transcriptional suppression of c-Fos and NFATc1 of differentiating OC and 2) inhibition of actin rearrangement of pathogenic MNCs.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/massive-elimination-of-multinucleated-osteoclasts-by-eupatilin-is-due-to-dual-inhibition-of-transcription-and-cytoskeletal-rearrangement/