PubMed2001
The nacre (mother of pearl) layer of the oyster Pinctada maxima shell can initiate bone formation by human osteoblasts in vivo and in vitro and is a new biomaterial that induces osteogenesis. This activity of nacre could be due to its water-soluble matrix. We examined the action of a water-soluble extract of nacre on the osteoblast phenotype of cells isolated from rat neonatal calvaria by measuring alkaline phosphatase (ALP) activity and by localization of the anti-apoptotic protein Bcl-2 by immunocytochemistry. ALP activity was increased 7% (p<0.001) by 100 microg proteins/ml extract and 20% (p<0.001) by 50 microg proteins/ml extract, but a low concentration of extract decreased the ALP activity by 8%. Cells treated with a high aspartic acid content fraction of the extract had increased ALP activity (23%, p<0.0001). Nacre extract and the fraction have no effect on the proliferation of mature osteoblasts. Immunoreactive Bcl-2 was overproduced in the cytoplasm and nuclei of osteoblasts at all stages of culture. Bcl-2 was found over the whole chromatin in quiescent and mitotic cells at the end of mitosis in the two nuclei in one cell, before cytodieresis. Bcl-2 was also found over chromosomes. Thus, nacre extract stimulates Bcl-2 production in osteoblasts, that is correlated with the cell cycle. Bcl-2 was also abundant in the nucleoli of extract-treated cells. Thus, the concentration and subcellular distribution of Bcl-2 in osteoblasts in primary cultures is influenced by nacre extract, and related to the cell cycle and the regulation of gene expression. Hence, knowledge of how water-soluble extracts of Pinctada maxima nacre act on osteoblasts in vitro may reveal the mechanisms involved in its action in vivo on bone cells and bone regeneration.