Concentration-Dependent Effects of Cobalt and Chromium Ions on Osteoarthritic Chondrocytes.

OBJECTIVE: Cobalt and chromium (CoCr) ions from metal implants are released into the joint due to biotribocorrosion, inducing apoptosis and altering gene expression in various cell types. Here, we asked whether CoCr ions concentration-dependently changed viability, transcriptional activity, and inflammatory response in human articular chondrocytes. DESIGN: Human articular chondrocytes were exposed to Co (1.02-16.33 ppm) and Cr (0.42-6.66 ppm) ions and cell viability and early/late apoptosis (annexin V and 7-AAD) were assessed in 2-dimensional cell cultures using the XTT assay and flow cytometry, respectively. Changes in chondrocyte morphology were assessed using transmitted light microscopy. The effects of CoCr ions on transcriptional activity of chondrocytes were evaluated by quantitative polymerase chain reaction (qPCR). The inflammatory responses were determined by measuring the levels of released pro-inflammatory cytokines (interleukin-1ß [IL-1ß], IL-6, IL-8, and tumor necrosis factor-α [TNF-α]). RESULTS: CoCr ions concentration-dependently reduced metabolic activity and induced early and late apoptosis after 24 hours in culture. After 72 hours, the majority of chondrocytes (>90%) were apoptotic at the highest concentrations of CoCr ions (16.33/6/66 ppm). SOX9 expression was concentration-dependently enhanced, whereas expression of COL2A1 linearly decreased after 24 hours. IL-8 release was enhanced proportionally to CoCr ions levels, whereas IL-1ß, IL-6, and TNF-α levels were not affected by the treatments. CONCLUSIONS: CoCr ions showed concentration- and time-dependent effects on articular chondrocytes. Fractions of apoptotic articular chondrocytes were proportional to CoCr ion concentrations. In addition, metabolic activity and expression of chondrocyte-specific genes were decreased by CoCr ions. Furthermore, exposure to CoCr ions caused a release of pro-inflammatory cytokines.

Biotribological Testing and Analysis of Articular Cartilage Sliding against Metal for Implants.

Osteochondral defects in middle-aged patients might be treated with focal metallic implants. First developed for defects in the knee joint, implants are now available for the shoulder, hip, ankle and the first metatarsalphalangeal joint. While providing pain reduction and clinical improvement, progressive degenerative changes of the opposing cartilage are observed in many patients. The mechanisms leading to this damage are not fully understood. This protocol describes a tribological experiment to simulate a metal-on-cartilage pairing and comprehensive analysis of the articular cartilage. Metal implant material is tested against bovine osteochondral cylinders as a model for human articular cartilage. By applying different loads and sliding speeds, physiological loading conditions can be imitated. To provide a comprehensive analysis of the effects on the articular cartilage, histology, metabolic activity and gene expression analysis are described in this protocol. The main advantage of tribological testing is that loading parameters can be adjusted freely to simulate in vivo conditions. Furthermore, different testing solutions might be used to investigate the influence of lubrication or pro-inflammatory agents. By using gene expression analysis for cartilage-specific genes and catabolic genes, early changes in the metabolism of articular chondrocytes in response to mechanical loading might be detected.