Inhibition of osteoblastic cell differentiation by lipopolysaccharide extract from Porphyromonas gingivalis

Lipopolysaccharide from Porphyromonas gingivalis (P-LPS), an important path ogenic bacterium, is closely associated with inflammatory destruction of pe riodontal tissues. P-LPS induces the release of cytokines and local factors from inflammatory cells, stimulates osteoclastic-cell differentiation, and causes alveolar bone resorption. However, the effect of P-LPS on osteoblas tic-cell differentiation remains unclear. In this study, we investigated th e effect of P-LPS extract prepared by the hot-phenol-water method, on the d ifferentiation of primary fetal rat calvaria (RC) cells, which contain a su bpopulation of osteoprogenitor cells, into osteoblastic cells. P-LPS extrac t significantly inhibited bone nodule (BN) formation and the activity of al kaline phosphatase (ALPase), an osteoblastic marker, in a dose-dependent ma nner (0 to 100 ng of P-LPS extract per mi). P-LPS extract (100 ng/ml) signi ficantly decreased BN formation to 27% of the control value and inhibited A LPase activity to approximately 60% of the control level on days 10 to 21 b ut did not affect RC cell proliferation and viability. P-LPS extract time-d ependently suppressed the expression of ALPase mRNA, with an inhibitory pat tern similar to that of enzyme activity. The expression of mRNAs for osteoc alcin and osteopontin, matrix proteins related to bone metabolism, was mark edly suppressed by P-LPS extract. Furthermore, P-LPS extract increased the expression of mRNAs for CD14, LPS receptor, and interleukin-1 beta in RC ce lls. These results indicate that P-LPS inhibits osteoblastic-cell different iation and suggest that LPS-induced bone resorption in periodontal disease may be mediated by effects on osteoblastic as well as osteoclastic cells.