Unconjugated secondary bile acids in the serum of patients with colorectal adenomas

Abstract

A positive association between deoxcholic acid (DCA) in the serum and colorectal adenomas, the precursors of colorectal cancer has recently been found, which supported the hypothesis of a pathogenic role of DCA in colonic carcinogenesis. This approach was based on the hypothesis that DCA formed in the colon is absorbed into the portal venous blood and exhibits a constant spillover to the systemic circulation. To further substantiate this hypothesis this study investigated whether in the serum of adenoma patients DCA was higher in the unconjugated fraction, which originates directly from the colon. DCA was found to be 2.8-fold higher in the unconjugated fraction of patients with colorectal adenomas than in controls (0.89 v 0.32 μmol/l, p<0.0025), 1.9-fold in the total DCA fraction (1.89 v 0.95 μmol/l, p<0.0001), and 1.4-fold in the conjugated fraction (0.67 v 0.47 μmol/l, p<0.05). It was further found that the bacterial isomerisation product 3β-DCA was twofold higher in the unconjugated fraction of adenoma patients than in controls (0.08 v 0.04 μmol/l, p=0.27), 1.8-fold in the total iso-DCA fraction (0.11 v 0.06 μmol/l, p<0.05), and 1.5-fold in the conjugated iso-DCA fraction (0.03 v 0.02 μmol/l, p=0.68). The data suggest that the positive association between the serum DCA concentration and colorectal adenoma as described previously results from the DCA fraction that is absorbed from the colon. This further supports a pathogenic role of DCA in the carcinogenesis of colorectal cancer.