The isoflavone genistein enhances osteoblastogenesis: signaling pathways involved.

Phytoestrogens have been proposed as a natural therapy for prevention of bone loss. In this work, we studied the mechanism of action of genistein on osteoblast differentiation. Primary cell cultures of calvarial osteoblasts isolated from female Wistar rats were in vitro exposed to genistein. Osteoblast differentiation markers were measured. Genistein stimulated osteoblast migration (71-257% above control). An earlier upregulation of estrogen receptor alpha gene expression and an enhancement of mRNA levels of the Runt-related transcription factor 2 were detected after 3 days of culture. The isoflavone significantly increased osteocalcin expression, extracellular collagen deposition, and alkaline phosphatase activity. The mechanism displayed by genistein involved estrogen receptor and nitric oxide pathway participation, since cell preincubation with the estrogen receptor antagonist ICI 182780, or the nitric oxide synthase inhibitor L-NAME, suppressed the phytoestrogen action. Evidence of MAPK and PI3K transduction systems participation on the stimulatory action of genistein on extracellular collagen deposition and alkaline phosphatase activity was also obtained. Genistein favored monocyte adhesion to osteoblasts (77% above control) in an ER; NOS; and MAPK kinase-dependent and PI3K-dependent manner. Co-cultured osteoblast-monocyte long term exposed (21 days) to genistein exhibited a high number of multinucleated and tartrate-resistant acid phosphatase-positive cells added to osteoblasts, suggesting that the phytoestrogen promotes osteoclast differentiation. In conclusion, genistein promoted osteoblastogenesis through the participation of ER and NOS pathways, and the contribution of ERK or PI3K signal transduction pathways, and also stimulates osteoclast differentiation from its mononuclear progenitor.

Beneficial role of the phytoestrogen genistein on vascular calcification.

Although soy phytoestrogen are proposed to prevent or improve postmenopausal vascular and bone diseases, the currently available data are controversial and unclear. In this study we evaluated the molecular and biochemical action of genistein on the cellular events involved in vascular calcification. Rat monocytes, aortic vascular cell and osteoblasts cultures in vitro exposed to Gen were employed. Gen down regulated the expression of cell adhesion molecules involved in stable leukocyte attachment. Using flow cytometry we found that the PE significantly diminished monocyte integrins CD11b, CD11c and CD18 expression either under basal and pro-inflammatory environment. At endothelial level, Gen also reduced Intercellular Adhesion Molecule 1 mRNA expression. On vascular muscle cells, the PE markedly reduced cell proliferation and migration. When vascular calcification was studied, muscle cells transdifferentiation into osteoblasts like cells was evaluated. Cells were cultured in osteogenic medium for 21 days. The expression of alkaline phosphatase and the presence of calcified nodules in the extracellular matrix were selected as features of muscle transdifferentiation. Calcified muscle cells exhibited higher levels of alkaline phosphatase activity and enhanced deposition of calcium nodules respect to native cells. Both osteoblastic markers were significantly reduced after Gen treatment. In contrast to this anti-osteogenic action, on bone cells Gen promoted osteoblasts growth, enhanced alkaline phosphatase activity and increased matrix mineralization. Its mitogenic action on osteoblasts directly depends on nitric oxide endothelial production stimulated by the PE. The data presented suppose a beneficial role of Gen on bone and vascular cells, with a cross link between both systems.