EFFECT OF IPRIFLAVONE ON EXPRESSION OF MARKERS CHARACTERISTIC OF THE OSTEOBLAST PHENOTYPE IN RAT BONE-MARROW STROMAL CELL-CULTURE

The effects of ipriflavone on cellular proliferation and differentiati on of osteoblasts were investigated using stromal cells isolated from the femoral bone marrow of young rats. To induce the formation of mine ralized bone-like tissue in vitro, the cells were cultured in the pres ence of beta-glycerophosphate and dexamethasone. Ipriflavone was added when subculturing was started. After 14 days of culturing with iprifl avone (10(-7)-10(-5) M), increases in both the alkaline phosphatase ac tivity and the hydroxyproline content per culture dish and a sight dec rease in the saturated cell density were observed. Furthermore, contin uous treatment with ipriflavone for 14-33 days resulted in an increase in the area of bone-like mineralized tissue accompanied by an increas e in the secretion of osteocalcin. When culture medium lacking dexamet hasone was used, rat bone marrow stromal cells neither differentiated into osteoblasts nor formed bone-like tissue, and under these conditio ns, ipriflavone had no effect on the proliferation or the phenotypic e xpression of the cells. These results suggest that ipriflavone directl y stimulates markers of the osteoblast phenotype at a certain stage in bone formation without affecting undifferentiated cells that have not been committed to the osteogenic lineage.