Bile acids are often refluxed into the lower oesophagus and are candidate carcinogens in the development of oesophageal adenocarcinoma. We show here that the secondary bile acid, deoxycholic acid (DCA), is the only one of the commonly refluxed bile acids tested here, to show genotoxicity, in terms of chromosome damage and mutation induction in the human p53 gene. This genotoxicity was apparent at both neutral and acidic pH, whilst there was a considerable increase in bile-induced toxicity at acidic pH. The higher levels of cell death and low cell survival rates at acidic pH may imply that acid bile exposure is toxic rather than carcinogenic, as dead cells do not seed cancer development. We also show that DCA (at neutral and acid pH) induced the release of reactive oxygen species (ROS) within the cytoplasm of exposed cells. We further demonstrate that the genotoxicity of DCA is ROS mediated, as micronucleus induction was significantly reduced when cells were treated with DCA + the anti-oxidant vitamin C. In conclusion, we show that DCA, is an effective genotoxin at both neutral and acidic pH. As bile acids like DCA can induce DNA damage at neutral pH, suppressing the acidity of the refluxate will not completely remove its carcinogenic potential. The genotoxicity of DCA is however, ROS dependent, hence anti-oxidant supplementation, in addition to acid suppression may block DCA driven carcinogenesis in Barrett's patients.

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The genetically engineered cell line SD1 was constructed by co-transfection of V79 Chinese hamster cells with two plasmids: one containing a full-length cDNA encoding rat CYP2B1 and the second incorporating a selective marker gene. This cell line has been used in gene mutation tests and in cytokinesis-block micronucleus assays to identify procarcinogens which are metabolized by CYP2B1 to reactive metabolites. An elevated frequency of spontaneous micronuclei was recorded in SD1 cells compared to parental V79 cultures. Karyotypic analysis revealed a chromosomal instability which was manifested by amplification of the p-arms of a chromosome designated 'n' (derived from chromosome 8). This chromosome was variable in length and sometimes exhibited a telomeric fusion which led to the formation of a dicentric chromosome. Fluorescence in situ hybridization with digoxigenin-labelled plasmid DNA showed the presence of pSV450 plasmid DNA coamplified with genomic DNA sequences located in the terminal region of chromosome 'n'.