Gutta‐percha‐stimulated mouse macrophages release factors that activate the bone resorptive system of mouse calvarial bone

This study investigated the capacity of macrophages exposed to gutta-percha particles to produce factors affecting bone metabolism. Peritoneal mouse macrophages were isolated and incubated with and without gutta-percha particles, and the supernatants were assessed for bone resorbing activity by adding macrophage-conditioned media to cultures of neonatal mouse calvarial bones. Bone resorption was measured by mineral mobilization (45Ca release) and matrix degradation (3H from [3H]proline labelled bones). The results showed that supernatant from gutta-percha-stimulated macrophages enhanced bone resorption. This effect was related to the amount of gutta-percha, and the concentration and time of exposure to the conditioned media. Stimulated macrophages released enhanced amounts of prostaglandins E2 and I2; however, indomethacin, which inhibits the prostanoid response, had no effect on bone resorbing activity. The stimulatory effect on bone resorption was inhibited by calcitonin, interleukin-1 receptor antagonistic protein, and by antiserum neutralizing mouse interleukin-1alpha(IL-1alpha), but not by anti-IL-1beta. Filtration experiments revealed that the molecules involved in the resorption activity had an apparent molecular weight between 3000 and 30,000 Da. These experiments show that mouse peritoneal macrophages, when exposed to gutta-percha particles, release factors which have a bone resorbing activity that is primarily due to enhanced production of IL-1alpha.