Sulforaphane inhibits multiple myeloma cell-induced osteoclast differentiation and macrophage proliferation by elevating ferroportin1.

Purpose: Osteolysis is a common complication in patients with multiple myeloma (MM). Our previous studies have demonstrated that MM cells can promote osteoclast differentiation of macrophages. In this study, we explored the effect of sulforaphane (SFN), a natural NRF2 activator found in broccoli, on MM cell-induced osteoclast differentiation.

Methods: Conditional medium (CM) derived from MM cells was used to induce osteoclast differentiation, and TRAP staining was performed to examine osteoclast. Gene expression was detected by western blotting or real-time PCR. Cell counting and EdU staining were performed to test macrophage proliferation.

Results: We showed that the CM of MM cells downregulated the expression of ferroportin1 (Fpn1), the only known iron exporter in vertebrate cells, thereby increasing cellular iron levels in murine macrophage cells RAW264.7. Deferoxamine (DFO), an iron chelator, effectively blocked MM cell CM-induced osteoclast differentiation and macrophage proliferation, suggesting that iron overload played a key role in these cellular events. Subsequent mechanistic investigations revealed that MM cell CM induced osteoclast differentiation and macrophage proliferation by activating the JNK/AP-1/NFATC1 pathway and PI3K/AKT pathway. SFN was found to increase Fpn1 expression, leading to decreased cellular iron levels in RAW264.7 cells activated by MM cell CM. Importantly, the osteoclast differentiation and macrophage proliferation induced by MM cell CM were significantly inhibited by SFN.

Conclusion: Altogether, our findings indicated that SFN inhibits MM cell-induced osteoclast differentiation and macrophage proliferation by elevating FPN1 levels. SFN could be a promising therapeutic strategy for MM-associated osteolysis.