Zinc compounds inhibit osteoclast-like cell formation at the earlier stage of rat marrow culture but not osteoclast function

Abstract

The effect of zinc compounds on osteoclast-like cell formation in rat marrow culture in vitro was investigated. The bone marrow cells were cultured for 7 days in α-minimal essential medium containing a well-known bone resorbing hormone (1, 25-dihydroxyvitamin D₃ and parathyroid hormone [1–34]). Osteoclast-like cell formation was estimated by staining for tartrateresistant acid phosphatase (TRACP), a marker enzyme of osteoclasts. The presence of 1, 25-dihydroxyvitamin D₃ (10⁻⁸ M) or parathyroid hormone (PTH; 10⁻⁸ M) induced a remarkable increase in osteoclast-like multinucleated cells (MNC). These increases were clearly inhibited by the presence of zinc sulfate or zinc-chelating dipeptide (β-alanyl-L-histidinato zinc; AHZ) in the concentration range of 10⁻⁷ to 10⁻⁵ M. The inhibitory effect was seen at the earlier stage of osteoclast-like MNC formation. However, zinc compounds (10⁻⁶ M) did not have an effect on PTH (10⁻⁸ M)-induced osteoclast-like cell formation in the presence of EGTA (5 × 10⁻⁴ M), dibucaine (10⁻⁵ M) or staurosporine (10⁻⁹ M). Moreover, when osteoclasts isolated from rat femoraldiaphyseal tissues were cultured for 24 h in the presence of zinc compounds (10⁻⁷ to 10⁻⁵ M), the compounds did not have an effect on cell numbers or lysosomal enzymes activity (acid phosphatase and β-glucuronidase) in the cells. The present study clearly demonstrates that zinc compounds inhibit osteoclast-like cell formation at the earlier stage with differentiation of marrow cells.