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1.4 CHEMICAL SCIENCES
It has been established that cells surviving radiation may produce descendants many cell divisions post-exposure in which, there are high incidences of chromosomal aberrations arising de novo, gene mutation and lethal mutations/delayed cell death. These effects are collectively known as genomic instability and are induced at frequencies greater than that of spontaneous mutations. Formally this syndrome ‘genomic instability’ has only been definitively proven to occur following irradiation. This leads us to the consideration that heavy metals could also induce the genomic instability phenotype, and if so, it could have implications for those exposed through their occupation, through smoking or for patients with a metal prosthesis. Preliminary studies have revealed that lethal mutations are induced by heavy metals such as cadmium and nickel. In this study the progeny of cells treated with cadmium chloride, nickel chloride and titanium debris were examined for the genomic instability phenotype. The endpoints of interest in this study were chromosomal instability and lethal mutations/delayed cell death. The cells employed in this study were primary human lung fibroblast cells designated HF19. These cells have the advantage of having a normal karyotype for cytogenetical analysis. The cytogenetical analysis was performed on the progeny of HF19 cells treated with cadmium and nickel for 1 and 24 hours respectively. These results demonstrated the occurrence of ‘de novo’ chromosome aberrations which were persistent throughout the progeny of these cells for up to 50 population doublings post-exposure to these chemical carcinogens. Chromosomal instability was also shown to be induced by particulate titanium debris for up to 40 population doublings post-exposure. The results also demonstrated increased incidences of tetraploidy and endoreduplication for all agents tested. Although the incidences of multi-aberrational metaphases were low the results demonstrated a definite trend towards genomic instability. The clonogenic assay revealed that lethal mutations/delayed cell death was evident in the progeny of HF19 cells post exposure to cadmium and nickel for 1 and 24 hours. This delayed cell death was evident for up to 25 population doublings post-exposure to cadmium and nickel. The clonogenic analysis also revealed that concentrations of cadmium and nickel that produced no apparent cytotoxicity to the initially treated cells, allowed the survival of a population of cells which, are more prone to exhibit reproductive failure during subsequent cell divisions. The clonogenic assay revealed that particulate titanium debris also induced lethal mutations/delayed cell death for up to 30 population doublings post exposure, The induction of stress proteins by HF19 cells exposed to cadmium, nicked and titanium debris was investigated to establish a possible explanation as to why there was a low appearance of multi-aberrational cells observed from the cytogenetical analysis of these cells. These investigations revealed that all insults induced metallothionein and P-glyprotein in more than 60% of all cells examined by immunocytochemical analysis. Immunofluorescent staining for microtubules demonstrated that cadmium, nickel and titanium debris caused disruption to the spindle. These results suggest that the observed disruption to the spindle may be the mechanism by cadmium, nickel and titanium debris induce tetraploidy and endoreduplication. The morphology of HG19 cells treated with cadmium, nickel and titanium debris was also examined by electron microscopy. These results revealed that all three insults were capable of inducing cytological and structural damage to HG19 cells. This study demonstrates that chemical carcinogens and particulate debris can induce both chromosomal aberrations and delayed death in human cells in a manner similar to radiation.
Coen, Natasha. (2003). Genomic instability induced by two chemical carcinogens, Cadmium and Nickel and by particulate Titanium debris from an implant. Doctoral thesis. Technological University Dublin. doi:10.21427/D7R603