AB0107 Influence of cobalt (II) + and chromium (III)-ions on bone formation in human osteoblast-like cells in-vitro
Authors: S. Drynda, A. Drynda, J. Kekow, C.H. Lohmann, J. Bertrand
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Healthy bone is a result of the homeostasis between bone formation and resorption. The process of bone formation includes two major functions, which are the secretion of the organic matrix (mainly type I collagen) and the deposition of minerals into this matrix. This function of osteoblasts can be affected by numerous factors, as hormones, inflammation, mechanical load and other external stimuli. In patients with artificial joint replacements, the release of particles or ions or cobalt and chromium ions from arthroplasties may exert local effects on the periprosthetic tissue leading to prosthesis loosening. <h3>Objectives</h3> It was the aim of the study to analyse the effect of Co<sup>2+</sup> and Cr<sup>3+</sup> ions on the capability of osteoblast-like cells to form bone. <h3>Methods</h3> Two human osteoblast-like cell lines MG63 and SaOs-2 were used to study the influence of Co<sup>2+</sup> and Cr<sup>3+</sup> ions on matrix secretion and mineralization. Cells (3 × 10<sup>5</sup>) were seeded in 2 ml DMEM (10% FCS) onto 12 well plates and stimulated with CoCl<sub>2</sub> and CrCl<sub>3</sub> in concentrations between 50–250 µM for 24 hours. Total RNA was extracted and changes of expression levels of collagen1A1 were analysed by real-time PCR. Secretion of collagen1 was analysed by Sirius Red staining (0.1% in water-saturated picric acid). After extraction of dye with 0.1N NaOH the absorption was measured at 540 nm. For mineralization the cells were cultured for up to 4 weeks in DMEM (10% FCS) supplemented with 0.2 mM ascorbic acid, 10 nM dexamethasone and 10 mM glycerophosphate and different concentrations of Co<sup>2+</sup> and Cr<sup>3+</sup>. Calcium deposits were detected by 1% Alizarin Red S staining (pH 4.1), for quantification the dye was extracted using cetylpyridinium chloride, the absorption was determined at 562 nm. <h3>Results</h3> We observed that SaOs-2 cells, the more differentiated cells compared to MG63, exhibited a high potential for mineralization but secreted low amounts of collagen type 1. In contrast, MG63 cells produced high amounts of collagen1 and had a low potential for mineralization. When cultures were treated with Co<sup>2+</sup> and Cr<sup>3+</sup>, we found that bivalent cobalt ions and trivalent chromium ions had different effects on osteoblasts. While Co<sup>2+</sup> reduced the secretion of collagen type 1 in osteoblast-like cells, Cr<sup>3+</sup> did not impair the collagen type 1 production. The secretion of this protein was partially attributable to a reduced gene transcription. In contrast, the mineralization was not impaired by Co<sup>2+</sup>. However, Cr<sup>3+</sup> at a concentration of 250 µM resulted in a decrease of mineralisation by 89% compared to controls. Even at the concentration of 50 µM a reduced mineralization by 34% was observed. The increase of the phosphate source resulted in an increased mineralization, suggesting that the capture of phosphate by Cr<sup>3+</sup> (formation of CrPO<sub>4</sub>), which is required for the mineralization could explain the inhibitory effect of chromium. <h3>Conclusions</h3> Our data suggest that Co<sup>2+</sup> and Cr<sup>3+</sup> ions affect bone formation at various stages of differentiation. While Co<sup>2+</sup> ions impair the formation of the bone organic matrix, Cr<sup>3+</sup> ions affect the deposition of inorganic minerals. Whether the inhibitory effect of chromium ions on the mineralization is caused by soluble Cr<sup>3+</sup>-ions itself or by solid CrPO<sub>4</sub> needs to be clarified in further studies. <h3>Acknowledgements</h3> The study was supported by Stiftung Endoprothetik (S01/16). <h3>Disclosure of Interest</h3> None declared