Bioactivity of nacre water-soluble organic matrix from the bivalve mollusk Pinctada maxima in three mammalian cell types: fibroblasts, bone marrow stromal cells and osteoblasts.

In vivo and in vitro studies provide strong evidence of the osteogenic activity of nacre obtained from Pinctada maxima. The in vitro studies indicate that diffusible factors from nacre are involved in cell stimulation. The water-soluble matrix (WSM) was extracted from nacre by a non-decalcifying process, and four fractions (SE(1)-SE(4)) were separated by SE-HPLC. Those fractions were tested in vitro on MRC5 fibroblasts. Alkaline phosphatase (ALP) activity was measured as a marker of osteoblastic differentiation. The anti-apoptotic protein Bcl-2 was also immunodetected in cultured osteoblasts from rat calvaria. WSM and fraction SE(4) increased ALP activity. BMP-2 had the same effect on the cells as WSM and SE(4). WSM greatly increased the amount of Bcl-2 in the cytoplasm and nucleus of osteoblasts. These in vitro studies support our initial hypothesis that nacre organic matrix (WSM) of a bivalve mollusk contains signal-molecules that can stimulate the osteogenic pathway in mammalian cells that are targets for bone induction.