Joint replacement failure is usually caused by the formation of wear debris resulting in aseptic loosening. Particulate metal and soluble metal ions from orthopaedic alloys (cobalt chromium or vanadium titanium aluminium) that are used in medical prostheses can accumulate in tissues and blood leading to increased chromosome aberrations in bone marrow and peripheral blood lymphocytes. This paper demonstrates that two of the metals used in orthopaedic prostheses, chromium and vanadium can produce delayed as well as immediate effects on the chromosomes of human fibroblasts in vitro. Fibroblasts were exposed to metal ions for only 24 hours and were then expanded over 30 population doublings involving ten passages. The initial increase of chromosomal aberrations, micronuclei formation and cell loss due to lethal mutations persisted over multiple population doublings, thereby demonstrating genomic instability. Differences were seen in the reactions of normal human fibroblasts and those infected with a retrovirus carrying the cDNA encoding hTERT that rendered the normal human fibroblasts telomerase-positive and replicatively immortal. This suggests that chromosomal instability caused by metal ions is influenced by telomere length or telomerase activity. Formerly this syndrome of genomic instability has been demonstrated in two forms following irradiation. One type is non-clonal and involves the appearance of lethal aberrations that cannot have been carried by the surviving cells. The other type is clonal and the aberrations are not lethal. These may arise as a result of complex rearrangements occurring at a high rate post-insult in surviving cells. The consequences of genomic instability are not yet known but it is possible that the increase of chromosomal aberrations that have been previously observed in human patients could be due to immediate and delayed expression of cellular damage after exposure to orthopaedic metals.

Wear debris from worn cobalt chrome joint replacements causes an increase in chromosomal translocations and aneuploidy. In this study the relationship between the amount of DNA damage and the changes in gene expression was investigated in human fibroblasts after exposure to artificial cobalt chrome particles. The comparison was made with different doses of particles, at different time intervals and in fibroblasts of different ages, those that had completed 10 population doublings (10 PD fibroblasts) and those that had completed 35 population doublings (35 PD fibroblasts). The genes (TGF-©¬2, p38 MAPK, Integrin ¥â1, SOD1, Caspase 10, PURA, FRA-1 and VNR) were chosen after a previous screen with cDNA microarrays. The percentage of senescent cells was evaluated using an immunohistochemical assay for ¥â-galactosidase activity. The 35 PD fibroblasts showed significantly more ¥â-galactosidase activity than the 10 PD fibroblasts. The level of DNA damage, as detected with the alkaline comet assay, was greater at higher doses, at longer exposures (up to 24 hours) and in 10 PD fibroblasts. The expression of all the genes listed above was generally lower after exposure to cobalt chrome particles using semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). The reduction in gene expression, like the increase in DNA damage was greater at higher doses and at longer exposure times. After 24hr exposure the reduction in gene expression was greater in 10 PD fibroblasts compared to 35 PD fibroblasts. After 6hr exposure this was only true at higher doses of particles and the opposite was seen after a lower dose of particles. These results show that levels of gene expression of TGF-©¬2, p38 MAPK, Integrin ¥â1, SOD1, Caspase10, PURA, FRA-1 and VNR may be correlated with the level of DNA damage and that this depends on the dose and length of exposure and the age of the cells. This highlights the potential importance of these genes in the mutagenicity of cobalt chrome particles in human fibroblasts.