EFFECT OF SKELETAL ALKALINE-PHOSPHATASE INHIBITORS ON BONE CELL-PROLIFERATION INVITRO

  • 1 January 1982
    • journal article
    • research article
    • Vol. 7  (6) , 316-323
Abstract
Chicken skeletal alkaline phosphatase is subject to competitive inhibitions by vanadate (Ki [inhibition constant] = 0.38 mM in carbonate, Ki = 0.08 mM in Tris, both at pH 7.4) and phenylphosphonate (Ki = 15 mM in carbonate, Ki 1.3 mM in Tris, both at pH 7.4), and uncompetitive inhibition by levamisole (Ki = 0.08 mM in carbonate, Ki = 0.10 mM in Tris, both at pH 7.4). Competitive inhibitors were more effective in Tris buffer because nonreactive ternary complexes were formed between alkaline phosphatase, the inhibitor and Tris. Effects of vanadate, phenylphosphonate and levamisole on the proliferation of embryonic chick calvarial cells in vitro were biphasic. Low doses of each agent stimulated 3H-thymidine incorporation into TCA[trichloroacetic acid]-insoluble material; higher doses were inhibitory. Neither effect could be attributed to inhibition of alkaline phosphatase activity (e.g., 20 .mu.M vanadate should inhibit alkaline phosphatase by 3% but stimulated cell proliferation by 187%; 50 .mu.M vanadate should inhibit alkaline phosphatase by 7% but inhibited 3H-thymidine incorporation by 90%). None of the alkaline phosphatase inhibitors tested affected the cellular concentration of the enzyme during the 24-h incubation. Alkaline phosphatase inhibitors can have nonspecific effects on bone cells in culture. For cells in the osteoblast cell line, an inhibition of alkaline phosphatase activity is not consistently related to a decrease in cell proliferation.