Production of interleukin-6 by osteoblastic cells is independent of medium inorganic phosphate

A state of severe bone loss is often observed in patients and animals suffering from phosphate (Pi) depletion. Conversely, Pi surfeit may have an anabolic effect on bone and may antagonize bone resorption. To study whether Pi has a direct effect on the production of the bone-resorbing interleukin-6 (IL-6) by osteoblasts, we cultured MC3T3-E1, UMR-106, and isolated rat calvaria cells in media containing varying concentrations of Pi (0-3 mM) and measured the production of IL-6 released into the media. IL-6 production was steady with time and was stimulated by parathyroid hormone, 1,25-dihydroxyvitamin D3, and interleukin-1 alpha. However, IL-6 production did not change with varying Pi concentrations. We concluded that the IL-6 production by osteoblastic cells is independent of the medium Pi.