Cytogenetic analysis of human bile for mutagenicity and co-mutagenicity

The mutagenic potential of duodenoesophageal reflux

SUMMARY BACKGROUND DATA

Duodenogastric-esophageal reflux disease is directly linked to Barrett's esophagus and to the development of esophageal adenocarcinoma. Despite this link, little is known about the mutagenic potential of refluxed material on the esophageal mucosa. We hypothesize that the reflux of gastric and duodenal content causes mutations in esophageal mucosa in vivo.

METHODS

Seven Sprague Dawley/Big Blue F1 lacI transgenic rats underwent esophagoduodenostomy (ED) to surgically create duodeno-gastric-esophageal reflux. Fourteen nonoperated rats served as negative (n = 7) and as positive (n = 7/methyl-N-amyl-nitrosamine [MNAN] intraperitoneally) controls. The animals were killed 16 weeks after operation or injection, the entire esophageal mucosa was harvested, and mutation frequency was determined through standard Big Blue Mutagenesis Assay.

RESULTS

Gross esophagitis was evident in all operated animals. The frequency of lacI mutations in esophageal mucosal cells of animals with ED was significantly higher, nearly 1.5-fold, than that of nonoperated animals. Nitrosamine administration resulted in a nearly 20-fold increase of lacI mutation frequency. Thirteen mutations were successfully sequenced, 46% occurred at CpG dinucleotide sites and 61% were either C to T or G to A transitions.

CONCLUSIONS

The data provide preliminary evidence of the mutagenic potential of bile reflux on esophageal epithelium. The specific mutations are markedly higher than would be expected by chance and are similar to that found in p53 mutations of human esophageal adenocarcinoma, providing a link to human esophageal cancer.

Co-mutagenicity of glyco- and tauro-deoxycholic acids in the Ames test

Mutagenicity and co-mutagenicity of glyco- and tauro-deoxycholic acids (GDCA and TDCA), which are abundant in human bile, were examined by the Ames test. The two chemicals were not mutagenic for themselves to Salmonella typhimurium TA98 and TA100, with and without S9 mix. They enhanced, however, the mutagenic activities of the pro-mutagens, 2-aminoanthracene (2AA) and benzo[a]pyrene (BaP), for both TA98 and TA100 with S9 mix. They were more co-mutagenic for the pro-mutagens on TA98 than on TA100. On TA98, the mutagenic activities of 2AA with GDCA (5 mumol/plate) and with TDCA (5 mumol/plate) were 9.7-fold and 11.8-fold as high as that of the corresponding control (2AA only), respectively. BaP with GDCA (2.5 mumol/plate) and with TDCA (2.5 mumol/plate) showed 2.8-fold and 3.0-fold increases over the corresponding control level (BaP only), respectively. It is hence concluded that GDCA and TDCA may enhance the activity of some mutagens existing in bile.

Mutagenicity of blue rayon extracts of human bile in the Ames test

The mutagenicity of human bile was examined in the Ames Salmonella/microsome assay. Bile samples were obtained from the gallbladders resected from patients with cholelithiasis, choledocholithiasis, gallbladder cancer, extrahepatic bile duct cancer and other diseases. For extraction of mutagenic components, the bile samples were treated with blue rayon and the adsorbed materials were assayed with Salmonella typhimurium TA98 in the presence of S9 mix. Twenty-four bile samples were tested and positive mutagenic activity was found in 14 samples. A 200-microliter bile equivalent material gave 6.3 times as many revertant colonies as the solvent control. With several samples that had undergone two cycles of blue rayon extraction, clear dose-response relationships in mutagenicity were demonstrated.