Sulphation of lithocholic acid in the colon-carcinoma cell line CaCo-2

High levels of bile acids in the colon may correlate with an increased risk of colon cancer, but the underlying mechanisms are not known. Proteoglycan structures have been shown to change when human colon cells differentiate in vitro. The expression of [S-35]sulphated molecules was used as a phenoty pic marker to study the effects of bile acids on the human-colon-carcinoma cell line CaCo-2. [S-35]sulphated compounds were isolated from the medium o f cell fractions of cells metabolically labelled with [S-35]sulphate in the absence and presence of cholic acid, deoxycholic acid, chenodeoxycholic ac id and lithocholic acid (LA). Labelled molecules were analysed by gel chrom atography, HPLC and SDS/PAGE in combination with chemical and enzymic metho ds. The expression of S-35-labelled proteoglycans was not affected by any o f the bile acids tested. However, the level of sulphated metabolites increa sed 7-18-fold in different experiments during a 22 h labelling period in th e presence of an LA concentration of 10 mu g/ml (26.6 nmol/ml) compared wit h controls. Further analyses showed that this was due, at least in part, to the sulphation of LA itself. This sulphation of LA was a rapid process fol lowed by secretion back to the medium. Brefeldin A did not reduce the sulph ation of LA, indicating that this conversion takes place in the cytosol, ra ther than in the Golgi apparatus of the CaCo-2 cells. LA in colon may be su lphated efficiently by the colonocytes to reduce the toxic effects of this particular bile acid. Sulphation may possibly be an important protective me chanism in the colon.