Effect of KCA-098 on the function of osteoblast-like cells and the formation of TRAP-positive multinucleated cells in a mouse bone marrow cell population

KCA-098 (3,9-bis(N,N-dimethylcarbamoyloxy)-5H-benzofuro[3,2-c]quinoline-6-one), an analogue of coumestrol (a naturally occurring weak phytoestrogen), dose-dependently increased alkaline phosphatase activity of osteoblastic ROS 17/2.8 cells and freshly isolated osteoblasts from neonatal mouse calvaria, and reduced cell proliferation, In addition, KCA-098 increased the synthesis of collagenese-digestible protein (CDP) of ROS 17/2.8 cells. On the other hand, KCA-098 had no effect on the basal synthesis of osteocalcin but reduced the 1 alpha,25-dihydroxyvitamin D-3 (1 alpha,25(OH)(2)D-3)-induced increase in osteocalcin synthesized by ROS 17/2.8 cells. Therefore, KCA-098 had a bidirectional effect on the differentiation of osteoblasts (i.e., stimulating both alkaline phosphatase activity and synthesis of CDP and inhibiting osteocalcin synthesis). However, as KCA-098 stimulated the mineralization of chick embryonic bone in organ culture and recovered the bone density reduced by ovariectomy of rats, it would serve overall to stimulate the differentiation of osteoblasts. On the other hand, KCA-098 inhibited the formation of tartrate-resistant, acid phosphate positive multinucleated cells (TRAP(+)MNC) induced by 1 alpha,25(OH)(2)D-3, parathyroid hormone (PTH), and prostaglandin E(2) (PGE(2)) in cultures of mouse bone marrow cells, showing that it inhibits the formation of osteoclastlike cells. Coumestrol and 17 beta-estradiol had no effect on the proliferation and alkaline phosphatase activity of ROS 17/2.8 cells. They did, however, dose dependently inhibit osteoclast-like cell formation as well as KCA-098 did, indicating that the main action of coumestrol and 17 beta-estradiol on bone tissue is the inhibition of bone resorption.