The effects of coffee on conjugation reactions in human colon carcinoma cells

We examined the effect of coffee on conjugation reactions in the human colon carcinoma cell line, Caco-2. After supplementing Caco-2 cultures with both 1-naphthol (200 μM) and various concentrations of coffee, the accumulation of 1-naphthyl sulfate and glucuronide in the growth medium was determined by analytical HPLC over a 24-h period. A strong reduction in sulfo-conjugation (<50% of the control value) was observed in cells treated with coffee (IC₅₀=4.3%), but no effect on glucuronic acid conjugation (glucuronidation) was observed. Coffee was also found to inhibit sulfotransferase (SULT) activity towards 1-naphthol in vitro to a similar extent (IC₅₀=5.1%) as in intact Caco-2 cells, but exhibited no effect upon UDP-glucuronosyl transferase (UGT) activity in vitro. PCR analyses showed no significant changes in the expression of either SULT genes (SULT1A1 and SULT1A3) or UGT genes (UGT1A1 and UGT1A6) following treatment with coffee solutions of up to 5% in concentration. These results suggest that the consumption of coffee can modify sulfo-conjugation reactions within intestinal epithelial cells, which may possibly affect the bioavailability of therapeutic drugs and the toxicity of environmental chemicals.