Comparison of 5-aminosalicylic acid and N-acetylaminosalicylic acid uptake by the isolated human colonic epithelial cell.

Isolated human colonic epithelial cell suspensions were incubated with either 0.1 mM 5-aminosalicylic acid (5-ASA) or 0.1 mM acetylaminosalicylic acid (Ac-ASA) for up to two hours. Intra- and extracellular 5-ASA and Ac-ASA were measured by high performance liquid chromatography. Mean 5-ASA uptake in one hour was 160.5 nmol/g dry weight, compared with an Ac-ASA uptake of only 5.75 nmol/g dry weight. No unchanged 5-ASA was detected inside the cell. Repeated washing had no effect on the intracellular Ac-ASA concentration. This discrepancy in drug uptake may explain why Ac-ASA seems to be ineffective when given to patients with ulcerative colitis.