Effects of sub-toxic Cadmium concentrations on bone gene expression program: results of an in vitro study

Since occupational and environmental exposure to the heavy metal Cadmium (Cd) affects human health this study investigated the effects of exposure to a single, or multiple, sub-toxic Cd concentrations on sub-confluent and confluent human osteoblast growth and expression of specific bone differentiation markers. RT-PCR quantified gene expression of type I collagen, metalloprotease (MMP13), runt-related transcription factor-2 (RUNX2), osterix, osteocalcin, osteonectin, alkaline phosphatase, integrins and bone sialoprotein (BSP). Expression of fibroblast growth factors 1 and 2 (FGF1, FGF2), transforming growth factor-beta(3) (TGFbeta(3)) and bone morphogenetic protein-2 (BMP2) were also evaluated to determine whether Cd-related effects were mediated by an imbalance in expression. Depending on osteoblast concentration and maturation stages, Cd inhibited or stimulated cell growth, decreased type I collagen, increased MMP13, FGF1 and BMP2 gene expression and stimulated the mineralization process only in continuously exposed cultures. These results suggest that in vivo, acute or chronic exposure to sub-toxic Cd concentrations may affect bone formation differently and support the hypothesis that Cd-induced bone disorders may involve downstream changes in growth factor expression. The results are of interest in forensic and occupational medicine in establishing preventive measures to reduce professional exposure risks.