Cadmium Stimulates the Osteoclastic Differentiation of RAW264.7 Cells in Presence of Osteoblasts

Low level of cadmium exposure may have direct effects on bone. But the probable mechanism is far from clarified. Using a co-culture system, the present study investigated the effects of low level of cadmium exposure on osteoclast differentiation in the presence of osteoblasts. Primary osteoblasts were isolated from calvarial bone of newborn Sprague Dawley rats. Primary osteoblasts and RAW264.7 cells were exposed to cadmium (0-60 nmol/l) in a co-culture system. Then, osteoblast viability was observed by MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) assay. Osteoclast formation and tartrate-resistant acid phosphatase 5b levels were determined by tartrate-resistant acid phosphatase staining and enzyme-linked immunosorbent assay. Osteoprotegerin and receptor activator of NF-kB ligand mRNA expression in osteoblasts were studied via reverse transcription polymerase chain reaction. Viability of osteoblast was obviously decreased by Cd exposure (P < 0.05). Cadmium significantly stimulated the formation of osteoclasts in co-culture system (7.5-60 nmol/l) compared with the control. The levels of tartrate-resistant acid phosphatase 5b in RAW264.7 cells co-cultured with osteoblasts were significantly enhanced by cadmium exposure compared with that without cadmium. The mRNA expression of receptor activator of NF-kB ligand was upregulated by cadmium at 15 and 60 nmol/l. But cadmium had no obvious influence on osteoprotegerin mRNA expression. This data suggested that osteoblasts might be involved in the progress of cadmium effects on osteoclasts.