N-acetyl cysteine inhibits lipopolysaccharide-mediated induction of interleukin-6 synthesis in MC3T3-E1 cells through the NF-kB signaling pathway

Background Interleukin-6 (IL-6) is a potent stimulator of osteoclastic activity. Lipopolysaccharide (LPS) has been shown to regulate the expression of potent inflammatory factors, including TNF-alpha and IL-6. Currently, effective therapeutic treatments for bacteria-caused bone destruction are limited. N-acetyl cysteine (NAC) is an antioxidant small molecule that possibly modulates osteoblastic differentiation. However, whether NAC can affect the LPS-mediated reduction of IL-6 synthesis in MC3T3-E1 cells is still unknown. Aims: The aim of this study was to investigate the role of NAC in the LPS-mediated reduction of IL-6 synthesis by MC3T3-E1 cells and to explore the underlying molecular mechanisms. In addition, we aimed to determine the involvement of the NF-kB pathway in any changes in IL-6 expression observed in response to LPS and NAC. Methods: MC3T3-E1 cells (ATCC, CRL-2593) were cultured in alpha-minimum essential medium. Cells were stimulated using NAC or LPS at various concentrations. Cell proliferation was observed at multiple time points using a cell counting kit 8 (CCK-8). IL-6 mRNA expression and protein synthesis were determined using quantitative polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assay analyses. NF-kB mRNA expression and protein synthesis was determined using qPCR and Western blots analyses. Results: The results demonstrate that LPS induced IL-6 and NF-kB mRNA expression and protein synthesis in the cultured MC3T3-E1 cells. However, these effects were abolished following pre-treatment with NAC. Pretreatment with NAC (1 mmol/1) or BAY11-7082 (10 mu mol/1) both significantly inhibited the NF-kB activity induced by LPS. Conclusion: NAC inhibits the LPS-mediated induction of IL-6 synthesis in MC3T3-E1 cells through the NF-kB pathway.