OSTEOBLAST-MEDIATED EFFECTS OF ZINC ON ISOLATED RAT OSTEOCLASTS - INHIBITION OF BONE-RESORPTION AND ENHANCEMENT OF OSTEOCLAST NUMBER

Zinc is an important element in biology yet little is understood of it s role in bone cell metabolism and function. This study examined the e ffects of zinc on osteoclast (OC) function in cultures derived from ne onatal rats and in cocultures of OC and UMR 106-01 osteoblast-like cel ls (UMR/OC cocultures), Treatment with zinc (10(-12)-10(-4) mol/L) had no effect on either bone resorption or the number of multinucleate ce lls positive for tartrate-resistant acid phosphatase (TRACP + ve MNC) in OC cultured for 24 h on bone slices, However, in UMR/OC cocultures, 10(-4) mol/L zinc (but not lower concentrations) decreased resorption pit formation by approximately 50% and increased TRACP + ve MNC numbe r by approximately 40%. When osteoblast-like cells were pretreated wit h zinc prior to, but not during, coculture with OC, effects on TRACP ve MNC and pit number persisted, although the effect was reduced. Zin c treatment also inhibited resorption and stimulated TRACP and calcito nin receptor (CTR) + ve MNC numbers in long-term (96-120 h) UMR/OC coc ultures. Our results indicate that zinc increases TRACP + ve CTR + ve MNC numbers yet inhibits bone-resorbing activity, and that these effec ts are dependent on the presence of osteoblastic cells. Zinc is abunda nt in bone and may act as a local regulator of bone cells.