Morinda citrifolia (Noni) Enhances Osteogenic Differentiation of Human Periodontal Ligamental Fibroblasts Under the LPS-induced Inflammatory Condition

Objectives: In chronic periodontitis condition, lipopolysaccharide (LPS) from gram negative bacteria contributes to secretion of inflammatory cytokines and eventually inhibits osteogenic differentiation and bone formation. To achieve successful periodontal treatment and regeneration, it will be necessary to overcome the inflammation-mediated inhibition of bone formation. Our previous study has shown that Morinda citrifolia (Noni) can promote osteogenic differentiation under physiologic condition. Therefore, the purpose of this study is to examine whether Noni can rescue the osteogenic differentiation of human periodontal ligament (hPDL) fibroblasts under LPS-induced inflammatory condition.
Methods: Inflammatory conditioned media were prepared by treating RAW264.7 murine monocyte cells with vehicle, LPS, or LPS+ Noni. hPDL cells were challenged with those conditioned media under induction of osteogenic differentiation. Osteogenic differentiation was confirmed by examining expression levels of osteogenic differentiation markers, alkaline phosphatase activity and matrix mineralization (Alizarin red S staining). Expression levels of Smurf1 and β-catenin were assessed by quantitative RT-PCR and immunoblotting. Ubiquitination assay was also performed.
Results: LPS-conditioned medium significantly attenuated osteogenic differentiation of hPDL cells. In contrast, conditioned medium from LPS+Noni treatment can significantly enhance osteogenic differentiation of hPDL cells, compared to LPS-conditioned medium. In defining the signaling pathways, Noni+LPS conditioned medium was able to enhance pAKT, pGSK3β and β-catenin, compared to LPS-conditioned medium. Interestingly, LPS-conditioned medium significantly increased expression levels of Smurf1 mRNA and protein and enhanced degradation of β-catenin protein, which were prevented by addition of Noni.
Conclusions: These results suggest that LPS inhibit osteogenic differentiation by increasing the levels of inflammatory mediators and Smurf1, contributing to attenuating new bone formation. Inhibition of inflammatory condition and downregulation of Smurf1 expression by Noni may help to improve bone regeneration and repair under chronic inflammatory conditions in periodontal disease.