In vitro effects of zinc on markers of bone formation

Zinc deficiency is associated with a reduced rate of bone formation that ca n be corrected by supplementation of the deficient diet with adequate amoun ts of zinc. This study was conducted to examine the effects of zinc on bone cell parameters associated with bone formation. Tibiae were removed from 19-d-old chicken embryos and incubated for 48 h in Dulbecco's modified Eagle's medium supplemented with antibiotics, bovine s erum albumin, and HEPES. The addition of zinc (25-200 mu g/dL) to tibial cu ltures resulted in a concentration-dependent increase in alkaline phosphata se activity, an increase in the incorporation of proline into bone protein and an increase in the posttranslational oxidation of proline to peptidyl h ydroxyproline. These effects of zinc were all diminished by the addition of 2,6-pyridine dicarboxylic acid, a chelator of zinc. The addition of either cyeloheximide (10(-5)M), dactinomycin (10(-8)M), or hydroxyurea (10(-3)M) to tibial cultures also attenuated the effects of zinc. The effect of zinc on bone cell DNA synthesis was measured by following the incorporation of H -3-thymidine into DNA and by fluorometric measurement of cellular DNA conte nt. These methods revealed that the addition of zinc to cultured tibiae res ulted in a concentration-dependent increase in tibial DNA content and synth esis rate. The magnitude of the zinc-induced DNA increase was similar to th e magnitude of the zinc-induced increases in alkaline phosphatase activity, proline incorporation, and hydroxyproline synthesis. Normalization of thes e latter responses to tibial DNA content yield data indicating that the eff ect of zinc on bone formation results from a zinc-induced increase in bone cell proliferation.