Divergent effects of orthosilicic acid and dimethylsilanediol on cell survival and adhesion in human osteoblast-like cells

Although dietary silicon (SI) is recognized to be an Important factor for the growth and development of bone and connective tissue, its biochemical role has yet to be identified. The predominant Si-containing species in blood and other biofluids is orthosilicic acid, Si(OH)(4). Dimethylsilanediol, (CH3)(2)Si(OH)(2), is an environmental contaminant that results from decomposition of silicone compounds used in personal hygiene, helath care and industrial products. We examined the in vitro effects of both Si species on the survival (colony forming efficiency). proliferation (DNA content), differentiation (alkaline phosphatase activity) and adhesion (realtive protein content) of the human osteoblast-like cell lines Saos-2 and hFOB 1.19. Orthosilicic acid yeilded a small, dose-dependent decrease in Saos-2 cell survivability up to its 1700 mu mol/L solubility limit, by which point survival was 20% less than that of untreated cells. This negative association, although small, correlated with a reduction in the proliferation and adhesion of Saos-2 cells as well as of hFOB 1.19 and osteoclast-like GCT cells. By contrast, dimethysilanediol treatment had no dicernable influence on Saos-2 survivability at concentrations up to 50 mu mol/L, and yet significantly enhanced cell survival at higher doses. Moreover, dimethysilanediol did not affect proliferation or adhesion of any cell line. The findings show that orthosilicic acid and dimethysilanediol affect osteoblast-like cells very differently, providing insight into the mechanism by which silicon influences bone health, although the specific site of Si activity remains unknown. There was no evidence to suggest that dimethysilanediol is cytotoxic at envirnonmental/physiological concentrations. (C) 2008 Elsevier GmbH. All rights reserved.