Abstract
Lipopolysaccharide (LPS) plays very important roles in periodontal disease and osteoclastic resorp-tion of alveolar bone. Although LPS stimulates osteoclastic bone resorption in vivo and in vitro, its mechanism is not clear. Recently we showed that long-term human umbilical cord blood and bone marrow cell cultures can adapted to form multinu-cleate cells (MNC's) that express an osteoclast phenotype (resorption lacunae on calcified matrices and cross-reactivity with mAb 23 C 6: CD -51, a monoclonal antibody that preferentially binds osteoclasts in bone biopsy specimens), and we also suggested that the CFU-GM (the granulocyte-macrophage progenitor cell) is the progenitor for the osteoclast. In the present experiments, we studied the biological effect of LPS, an extracel-lular product from Porphyromonas gingivalis (P. gingivalis) and Escherihia coli (E. coli), on the mechanism of osteoclast formation from CFU-GM-derived cells and on bone resorption. Addition of LPS (10-100 ng/ml) from either of these bacteria to these cultures significantly increased the forma-tion of 23 C 6-positive MNC's. Addition of anti-human IL-1 antibody to cultures treated with LPS totally inhibited the increase in MNC formation stimulated by either LPS. Both LPS's stimulated bone resorption, but the P. gingivalis LPS caused a 1.4 fold greater increase in the resorption area compared with the E. coli one. The effects of LPS on regulation of tyrosine phosphorylation were also studied in experiments utilizing osteoclast precur-sor cells. The phosphorylation was detectable in LPS-treated CFU-GM cells. When these cells were incubated with LPS from P. gingivalis, a 42-kD protein band containing phoshotyrosine was detected. Addition of 100 nM herbimycin A to cultures treated with either LPS totally inhibited the bone resorption stimulated by these LPS's. However, herbimycin A did not inhibit the MNC formation. These experiments suggest that LPS stimulates osteoclast formation through a primary action on osteoclast precursor cells, which cells are induced by the action of IL-1 produced by the LPS which in turn stimulates osteoclast formation, resulting in osteoclastic bone resorption. These findings also suggest that c-src kinase is involved in the regulation of bone-resorbing activity of osteoclasts by LPS.
