Osteoclast inhibition by factors from cells associated with regenerative tissue

Guided tissue regeneration (GTR) uses expanded polytetrafluoroethylene (ePTFE) membranes to favor the repopulation of the healing wound with cells with bone regenerative potential. As bone remodeling is a tightly coupled process, inhibition of osteoclast-mediated bone resorption may be critical to regeneration. Thus, this study was undertaken to determine whether cells associated with regenerative tissue can inhibit osteoclast differentiation and activity and to begin characterizing and identifying the factor(s) mediating the observed effects. Conditioned media were harvested from human periodontal cell lines established in culture: cells adherent to ePTFE membranes, recovered from patients after GTR; cells adherent to ePTFE augmentation membranes, recovered from edentulous ridge augmentation procedures; and periodontal ligament cells from periodontally healthy bicuspids. Conditioned medium from each of these regenerative cell lines reduced the number of tartrate-resistant acid phosphatase-positive osteoclast-like cells formed from hemopoietic precursors in mouse bone marrow cultures. Also, both the total resorbed surface area and number of resorption pits formed by these cells on calcium phosphate ceramic films were reduced. The factor in the conditioned medium which inhibited osteoclast differentiation was soluble, heat labile, and resided in the lower molecular weight (< 30 kDa) fraction, the same fraction which would contain cytokines. Western blot analysis of the conditioned medium detected a band at the molecular weight of interferon gamma (IFN-gamma), using a polyclonal rabbit anti-human IFN-gamma. Thus, the factor in the conditioned medium with inhibitory activity may have identity with IFN-gamma or one of the other anti-inflammatory cytokines.