Prostaglandin E2, interleukin 1α, and tumor necrosis factor-α increase human osteoclast formation and bone resorption in vitro

Prostaglandin E-2 (PGE(2)) and the cytokines interleukin (IL) 1 alpha and tumor necrosis factor (TNF)alpha increase bone resorption in vivo, but the effect of these agents on osteoclastic bone resorption has never been studied in an in vitro human system. Our recently described human bone marrow culture system, in which osteoclasts are generated (vitronectin and calcitonin receptor-positive cells which resorb bone), was used to study the effects of these agents. Addition of indomethacin to macrophage colony-stimulating factor (M-CSF)-treated cultures nearly abolished osteoclast parameters, indicating that prostaglandins are virtually essential for human osteoclast formation. Additionally, PGE(2) dose responsively increased osteoclast numbers and bone resorption. The effects of M-CSF and PGE(2) are independent, as demonstrated by unaltered PGE(2) concentrations in culture supernatants in spite of the dose-responsive increase in osteoclast parameters in response to M-CSF. The generation of osteoclasts in the presence of PGE(2) occurred in favor of CD 14-positive macrophage formation. IL 1 alpha and TNF alpha increased osteoclast parameters in a dose-responsive manner. Maximum stimulation yielded culture supernatant levels of PGE(2) approximately the same as those concentrations of exogenous PGE(2) that dramatically induced osteoclast formation. This osteoclast-inducing effect was inhibited both by indomethacin and by the specific inhibitor of inducible prostaglandin G/H synthase, NS-398 and this was reversed by addition of exogenous PGE(2). These results demonstrate unequivocally that IL 1 alpha and TNF alpha enhance human osteoclast formation and suggest that they mediate their effects through PGE(2).