N-Methyl Pyrrolidone Promotes Osteoblast Differentiation Impaired by Tumor Necrosis Factor-alpha

Skeletal changes accompanying aging or chronic inflammatory disorders, such as rheumatoid arthritis, osteoporosis, peri-implantitis and periodontitis, are associated with both increased risk of fractures and systemic bone loss. These changes occur through inflammatory cytokine-mediated stimulation of osteoclast resorption and inhibition of osteoblast function. Tumor necrosis factor-alpha (TNF-alpha), a pro-inflammatory cytokine with a profound role in many skeletal diseases, has been described as a mediator of bone loss in osteolysis and other inflammatory bone diseases. In addition to its known bone resorptive action, TNF-alpha reduces bone formation by inhibiting osteoblast differentiation (1). Recently, it was shown that N-methyl pyrrolidone (NMP) enhance bone formation and inhibit osteoclast differentiation and function (2, 3). Here, we investigated the effects of NMP on osteoblast differentiation using mouse C2C12 cells, a widely used model to examine the early stages of osteoblast differentiation, in the presence of TNF-alpha. The addition of TNF-alpha to C2C12 cells suppressed the Bone Morphogenetic Protein (BMP)-2-induced expression of key osteoblastic markers including Runx2 and alkaline phosphatase activity (ALP). NMP had no independent effects on Runx2 and alkaline phosphatase activity; however, it repressed the suppressive effects of TNF-alpha. Further results suggest that TNF-alpha inhibits BMP-2-induced osteoblast differentiation probably by modulating p38 phosphorylation. NMP reversed this effect by a mechanism involving p38 and ERK pathways. Moreover, NMP inhibited TNF-alpha stimulated TNF-alpha receptor 1 and 2 (TNFR1 and TNFR2) expression. All together, these results demonstrated that NMP promotes BMP -2-induced osteoblastic differentiation impaired by TNF-alpha, suggesting a possible role of NMP as a potent drug for bone regeneration or for the treatment of bone diseases associated with excessive bone resorption. Keywords: bone morphogenetic protein, N-methyl pyrrolidone, osteoinduction, tumor necrosis factor