Lipopolysaccharide stimulation improves the odontoblastic differentiation of human dental pulp cells

Lipopolysaccharide (LPS) is one of the causative agents of pulpitis and previous studies have demonstrated that the LPS stimulation of human aortic valve interstitial cells induces inflammatory mediators and the gene expression of osteogenic factors. Therefore, in the present study, it was hypothesized that LPS affects the odontoblastic differentiation of human dental pulp cells (hDPCs). In order to investigate this, an in vitro study using hDPCs was performed. Increased alkaline phosphatase (ALP) activity was observed in the hDPCs treated with LPS, which was more marked when the cells were costimulated with odontogenic induction medium (OM). LPS also appeared to increase the gene expression levels of dentin sialophosphoprotein and dentin matrix protein-1 and the protein expression level of dental sialoprotein in the hDPCs, particularly in combination with OM. In addition, the size and the number of nodules formed in the hDPCs exposed to OM and LPS were increased compared to those stimulated by OM alone. To determine the role of nuclear factor kappa B (NF-kappa B) during the LPS-induced odontoblastic differentiation of hDPCs, immunofluorescence was performed. The nuclear translocation of NF-kappa B, induced by LPS was confirmed, suggesting its involvement in the LPS-induced increase in odontoblastic differentiation of hDPCs. In conclusion, there may be an association between LPS stimulation, with or without OM, and odontoblastic differentiation.