Tumor necrosis factor-alpha (cachectin) stimulates bone resorption in mouse calvaria via a prostaglandin-mediated mechanism.

Recombinant human (h) and murine (m) tumor necrosis factor (TNF)-alpha stimulated bone resorption and the production of prostaglandin (PG) E2 in neonatal mouse calvaria in organ culture. In experiments of 72-h duration, the effect on bone resorption was of large magnitude (an average increase in medium calcium of 3.3 mg/dl above control values in 11 separate experiments) and occurred over a concentration range of 0.1-20 ng/ml mTNF and 0.5-50 ng/ml hTNF. Accompanying the TNF-enhanced release of bone calcium there was enhanced accumulation of PGE2 in the culture medium. The increases in medium calcium and PGE2 were both inhibited completely by nontoxic concentrations of 4 different PG cyclooxygenase inhibitors (indomethacin, piroxicam, ibuprofen, and acetylsalicylic acid) but not by the noncyclooxygenase inhibitor salicylic acid. The magnitude of the PGE2 response, but not the calcium release, was less for bones treated with TNF than for those treated with equipotent doses of epidermal growth factor or human transforming growth factors-alpha or -beta, suggesting that the local site of production of PGE2 in bone may be different for TNF than for the other factors. Repeated sc injections of hTNF to intact mice for a 48-h period produced a statistically significant elevation of the plasma calcium concentration. Because TNF is produced by cells of the monocyte/macrophage lineage in response to invasive stimuli such as the presence of tumor, our findings indicate that a host factor produced in response to malignant cells can cause enhanced bone resorption. Thus, the concept of the humoral hypercalcemias of malignancy must be expanded to include mediators not produced by the tumor cells themselves.