Involvement of redox balance in in vitro osteoclast formation of RAW 264.7 macrophage cells in response to LPS

Here we report that LPS induces osteoclast (OC) formation in murine RAW 264.7 macrophage cells in RPMI-1640 medium but not in α-minimum essential medium (α-MEM) as the original culture medium. LPS-induced OC formation in both media was examined to clarify the differential response. Receptor activator of NF-κB ligand induced OC formation in either α-MEM or RPMI-1640 medium. However, LPS-induced OC formation in RAW 264.7 cells maintained in RPMI-1640 medium, but not α-MEM, which was also supported by mouse bone marrow-derived macrophages, although they were less sensitive to LPS than RAW 264.7 cells. LPS augmented the expression of nuclear factor of activated T-cells (NFATc1) as a key transcription factor of osteoclastogenesis in cells maintained in RPMI-1640 medium, but reduced it in cells maintained in α-MEM. A high concentration of LPS was cytotoxic against cells maintained in α-MEM. Glutathione exclusively present in RPMI-1640 medium prevented LPS-induced cell death in α-MEM and augmented LPS-induced NFATc1 expression, followed by enhanced LPS-induced OC formation. LPS induced higher generation of reactive oxygen species in α-MEM than RPMI-1640 medium. An antioxidant enhanced LPS-induced OC formation, whereas a pro-oxidant reduced it. Taken together, redox balance in the culture condition was suggested to regulate in vitro LPS-induced OC formation.