The role of nacreous factors in preventing osteoporotic bone loss through both osteoblast activation and osteoclast inactivation.

Excessive bone resorption by osteoclasts relative to bone formation by osteoblasts results in the development of osteoporosis. Anti-osteoporotic agents that are able both to inhibit bone resorption and to stimulate bone formation are not available. We now show that water-soluble nacreous factors prepared from the pearl oyster Pteria martensii prevent osteoporotic bone loss associated with estrogen deficiency in mice mainly through osteoclast inactivation. Nacreous factors stimulated osteoblast biomineralization in vitro in association with activation of signaling by c-Jun NH(2)-terminal kinase (JNK) and Fos-related antigen-1 (Fra-1). They also suppressed both osteoclast formation by blocking up-regulation of nuclear factor of activated T cells cytoplasmic 1 (NFATc1) as well as bone pit formation mediated by mature osteoclasts, likely by disrupting the actin ring of these cells. Our findings thus show that the components of a natural material have beneficial effects on bone remodeling that are mediated through regulation of both osteoblast and osteoclast function. They may thus provide a basis for the development of biomimetic bone material as well as anti-osteoporotic agents.