Abstract: Abstract: Objective Research the cytotoxicity of chromium (Cr3+) and cobalt(Co2+) ions and the mechanism of osteolysis after artificial joint replacement by RANK express in rats monocyte/macrophages(RAW264.7) stimulated with Co2+ and Cr3+. Methods Culture monocyte-macrophage cells in vitro. Monocyte-macrophage cells exposed to Co2+ and Cr3+ ions, The cell viability was assured by MTT test. The cells were divided into 5 groups, Group A: monocyte /macrophages; Group B: monocyte /macrophages + 500ppm Cr3+ ;Group C: monocyte /macrophages +500ppm Cr3++ 20μM SP600125; Group D: monocyte /macrophages + 10ppm Co2+; Group E: monocyte /macrophages + 10ppm Co2+ + 20μM SP600125 ; Then,Semi-quantitative reverse transcription PCR method was used to detect the level of RANK mRNA after 24h and 48h. Results Compared to the control, MTT test demonstrated that Co2+and Cr3+ ions can both obviously decrease the cell viability of monocyte /macrophages. Cells exposed to Co2+ and Cr3+ ions，compared to the control（Group A），mRNA expression of RANK was both incresaed at 24h and 48h（P<0.05）,and SP600125 (JNK Inhibitor) could inhibite cells to express of RANK mRNA in cells stimulated with Co2+ and Cr3+（P<0.05）. Conclusion Co2+、Cr3+ ions have a cytotoxic effect on monocyte/macrophages and can stimulate the expression of RANK in monocyte /macrophages.In addition,metal ions could stimulate monocyte /macrophages to express RANK through JNK pathway.

Key words: artificial joint, cobalt ion, column ion, monocyte macrophages, RANK