Effects of lipopolysaccharide extracted from Prevotella intermedia on bone formation and on the release of osteolytic mediators by fetal mouse osteoblasts in vitro

Prevotella intermedia, a Gram-negative obligate anaerobic black-pigmented oral bacterium, belongs to a small group of microorganisms that is closely associated with the initiation of periodontal diseases. Lipopolysaccharide (LPS), an outer membrane component, is one of the main virulence factors of this bacterium. The aim of this study was to examine the effects of Prev. intermedia lipopolysaccharide, extracted by the hot-phenol-water method, on differentiation (alkaline phosphatase activity) and mineralisation (calcium incorporation) of fetal mouse calvarial cells in vitro and to determine the release of the important osteolytic factors nitric oxide, interleukin-6 (IL-6) and matrix metalloproteinases by these cells after treatment with different concentrations of Prev. intermedia lipopolysaccharide (0.2–25 μg/ml). By gelatin zymography, we also characterized the matrix metalloproteinases released by these osteoblasts. Treatment with Prev. intermedia lipopolysaccharide dose-dependently inhibited bone formation by reducing alkaline phosphatase activity and calcium incorporation and induced the release of nitric oxide, IL-6 and the latent proforms of MMP-2 and MMP-9 by fetal mouse osteoblasts in organoid culture. These results indicate that the lipopolysaccharide from Prev. intermedia not only participates in periodontal tissue destruction and alveolar bone resorption, but also inhibits bone formation.