Bone-prognostic status after cessation of cadmium exposure for one month in male rats.

This study investigated bone status after decreased cadmium (Cd) exposure in male rats. Sprague-Dawley male rats were randomly divided into three groups. One group was injected subcutaneously with sodium chloride as control. The others were given CdCl2 by subcutaneous injection at doses of 0.5 mg Cd/kg body weight (bw) for 2 months (Cd+2m) and for 3 months (Cd+3m). For the Cd+2m group, the rats were shifted to cessation of Cd injection for 1 month after 2 months' exposure. At month 3, micro-computed tomography (micro-CT) analyses were performed on the proximal tibia and lumbar spine, and urine was collected from all rats. Rats were then killed and blood collected for metabolic-marker measurement and Cd assay. Bone tissues were also collected for bone-mass assay, biomechanical test, and bone-histology analysis. Cd burdens of rats in the Cd+2m and Cd+3m groups were both significantly greater than those in the control group. Cd burdens of rats were lower in the Cd+2m group compared with the Cd+3m group. Bone damage occurred in the Cd+2m and Cd+3m groups compared with the control group (p<0.05), but no significant improvement was found in the Cd+2m group compared with the Cd+3m group. Cd damage to bone could not be reversed over the short term. More attention should be paid to Cd's toxic effects on bone after decreased exposure.

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.

Effects of cadmium on bone microstructure and serum tartrate-resistant acid phosphatase 5b in male rats.

This study investigated the effects of cadmium on bone microstructure and serum tartrate-resistant acid phosphatase 5b (Tracp 5b) in male rats. Sprague-Dawley male rats were divided into three groups that were given CdCl(2) by subcutaneous injection at doses of 0, 0.1 and 0.5 mg/kg body weight (bw) for 12 weeks, respectively. Before killing at the 12th week, microcomputed tomography scanning was performed on the proximal tibia, and urine samples were collected from all of the rats. All rats were then killed, and their blood was collected for biomarkers assay. Bone tissues were dissected for mineral density determinations and histology. The concentration of cadmium in the blood, urine and bone of rats treated with cadmium were significantly higher than in the control group. The bone mineral density, bone mineral concentrations and bone microstructure index of rats treated with cadmium at 0.5 mg/kg bw were clearly lower than in the control rats. Histological investigation also revealed damage to the bone microstructure caused by cadmium. Tracp 5b concentrations in rats treated with cadmium were dose dependently higher than the control. The concentration of cadmium in blood, urine and bone was significantly correlated with Tracp 5b and bone microstructure parameters. Cadmium was shown to induce bone microstructure damage, especially to trabecular bone. The elevated concentrations of serum Tracp 5b suggest that bone resorption mediated via osteoclasts is an important mechanism for the toxic effects of cadmium on bone.

Cadmium induces differentiation of RAW264.7 cells into osteoclasts in the presence of RANKL.

The mechanism of cadmium effects on bone is not fully understood. In this study, we investigated the effects of cadmium on osteoclasts differentiation and the probable mechanism. RAW264.7 cells were exposed to cadmium (0-60 nmol/L) in the presence or absence of receptor-activated nuclear factor κ B ligand (RANKL) for 5 days. Then, the viability, tartrate-resistant acid phosphatase (TRAP) activity and the formation of TRAP positive multinucleated osteoclasts were observed. Receptor activator of nuclear factor κ B (RANK), tumor necrosis factor receptor associated factor 6 (TRAF6), c-src, c-fos, fos-related antigen 1 (Fra1) expression were determined by reverse transcription polymerase chain reaction. Cadmium increased TRAP activity (20-40%) and TRAP positive cell formation in the presence of RANKL, but had no obvious influence on them without RANKL. RANK, TRAF6, Fra1, c-src and c-fos (at 15-30 nmol/L) expression were enhanced (30-70%) by cadmium in the presence of RANKL, but cadmium had little influence on them in the absence of RANKL. This study demonstrated that cadmium could induce differentiation of osteoclasts precursor into osteoclasts in the presence of RANKL. Even though the changes of gene expression were small, RANKL/RANK and downstream genes may play an important role in cadmium effects on osteoclasts.