Effect of soluble zinc on differentiation of osteoprogenitor cells

Amorphous calcium phosphates (ACPs) are attractive fillers for osseous defects and are stabilized through the incorporation of transition metals such as zirconium and zinc. As ACP converts in solution to hydroxyapatite (HAP) in a manner marked by a transient release of calcium and phosphate ions, it is capable of stimulating osteoblastic differentiation. Zinc is known to retard ACP conversion to HAP, and--when incorporated into ceramic biomaterials--has been shown to stimulate osteoblastic differentiation. Because zinc deficiency in vivo is marked by skeletal defects, we postulated that zinc ions released from ACP and other minerals could stimulate proliferation and osteoblastic differentiation of progenitor cells. To test this hypothesis, rat bone marrow stromal cells were cultured in osteogenic medium containing basal (3 x 10(-6) M) or supplemented Zn(2+) concentrations (1 x 10(-5) and 4 x 10(-5) M) for up to 3 weeks. No significant effects of zinc concentration on cell number, alkaline phosphatase activity, total protein content, collagen synthesis, or matrix mineralization were found.