INORGANIC POLYPHOSPHATE IN HUMAN OSTEOBLAST-LIKE CELLS

Significant amounts of inorganic polyphosphates and of polyphosphate-d egrading exopolyphosphatase activity were detected in human mandibular -derived osteoblast-like cells. The amount of both soluble and insolub le long-chain polyphosphate in unstimulated osteoblast-like cells was higher than in human gingival cells, erythrocytes, peripheral blood mo nonuclear cells, and human blood plasma. The cellular content of polyp hosphate in osteoblast-like cells strongly decreased after a combined treatment of the cells with the stimulators of osteoblast proliferatio n and differentation, dexamethasone, beta-glycerophosphate, epidermal growth factor, and ascorbic acid. The amount of soluble long-chain pol yphosphate, but not the amount of insoluble long-chain polyphosphate, further decreased after an additional treatment with 1 alpha,25-dihydr oxyvitamin D-3 (1,25(OH)(2)D-3), The decrease in polyphosphate content during treatment with dexamethasone, beta-glycerophosphate, epidermal growth factor, and ascorbic acid was accompanied by a decrease in exo polyphosphatase, pyrophosphatase, and alkaline phosphatase activity. H owever, additional treatment with 1,25(OH)(2)D-3 resulted in an increa se in these enzyme activities. Osteoblast-like cell exopolyphosphatase activity and exopolyphosphatase activity in yeast, rat tissues, and h uman leukemia cell line HL60 were inhibited by the bisphosphonates eti dronate and, to a lesser extent, clodronate and pamidronate. From our results, we assume that inorganic polyphosphate may be involved in mod ulation of the mineralization process in bone tissue.