The DNA-damaging effect of bile acids and the protective effect of cellulose.

Colon cancer is the second most common type of cancer in the United States. Its incidence is linked epidemiologically to high levels of bile acids in the feces. Bile acids have been implicated as promotors and cocarcinogens in the etiology of colon cancer and as comutagens and mutagens in bacteria. These observations suggest the hypothesis that bile acids may interact directly with DNA. Using agarose gel electrophoresis we showed that bile acids convert covalently closed circular plasmid DNA to the open circular form, indicating strand breakage. We next treated the single stranded circular DNA of phage M13 with bile acids and found that the transfection efficiency of this DNA declined up to a thousand-fold. The concentrations of bile acids used were of the same magnitude as the fecal bile acid concentrations found in colorectal cancer patients. This inactivation was largely prevented when the bile acids were pretreated with cellulose fiber