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Biochemical, Molecular, and Genetic Mechanisms

The Soybean Isoflavone Genistein Induces Differentiation of MG63 Human Osteosarcoma Osteoblasts¹

Christopher Morris^*, Julian Thorpe, Luigi Ambrosio^** and Matteo Santin^*,2

^* School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton BN2 4GJ, UK; The Sussex Centre for Advanced Microscopy, School of Life Sciences, University of Sussex, Falmer Campus, Brighton BN1 9QG, UK; and ^** Institute of Biomedical Composite Materials, CNR, 80130 Naples, Italy

² To whom correspondence should be addressed. E-mail: m.santin{at}brighton.ac.uk.

A soybean-rich diet was shown to reduce the incidence of osteoporosis in Eastern countries; its effect on bone metabolism was ascribed to the action of the soybean isoflavones such as genistein. Although many studies have shown isoflavone-induced osteoblast differentiation, its preventative action on bone mass loss has not been clarified. Here, the osteogenetic effects of genistein on human cell line MG63 osteoblasts were elucidated using a variety of approaches. In particular, phalloidin-rhodamine staining revealed that genistein-treated osteoblasts possessed a more organized cytoskeleton, and genistein's inhibitory effect upon cell proliferation was associated with exposure of phosphatidylserines on the external plasmalemma surface. Although this phosphatidylserine exposure is considered a typical apoptotic marker, scanning and transmission electron microscopy revealed that genistein-treated osteoblasts released matrix vesicles and showed no evidence of chromatin condensation. Assays, stainings, and scanning electron microscopy showed that genistein-treated osteoblasts synthesized relatively high levels of collagen and alkaline phosphatase and, even in a nonosteogenic growth medium, formed mineralized bone noduli. A clear pattern of genistein-induced osteoblast activation therefore emerges, in which all of the essential components required for the rapid production of mineralized bone extracellular matrix are stimulated by this soybean isoflavone.

KEY WORDS: • soybean isoflavones • genistein • osteoblast differentiation • bone formation • mineralization