Quantitative analysis of osteoclast-specific gene markers stimulated by lipopolysaccharide.

Lipopolysaccharide (LPS) in the outer layers of Gram-negative bacteria plays an important role in initiating and sustaining periapical lesions. To understand the mechanisms of osteoclastic bone resorption in periapical lesions induced by LPS, we stimulated osteoclast precursors, RAW 264.7 cells with LPS. LPS stimulated osteoclastogenesis when osteoclast precursors were primed with activator for NF-kappaB ligand (RANKL) as little as 24 h. By employing real-time PCR analysis, we have confirmed that osteoclast-like cells stimulated by LPS express high level of osteoclast-specific gene markers such as TRAP, cathepsin K, and calcitonin receptor. These results suggest that bone-resportive action by LPS is partially independent of RANKL.