Purpose: The gut fermentation product of dietary fiber, butyrate, inhibits growth of HT29, an established tumor cell line. It also induces detoxifying enzymes belonging to the glutathione S-transferase family (GSTs), namely hGSTM2, hGSTP1, hGSTA4, but not of hGSTT1 . Here we investigated kinetics of effects in HT29 and compared sensitivities with preneoplastic LT97 colon adenoma cells, to assess mechanisms of colon cancer chemoprevention in two stages of cell transformation.
Methods: We determined cell growth after butyrate treatment by quantifying DNA, GST expression by Northern/Western Blotting or biochemical analysis and butyrate consumption by measuring the residual concentrations in the cell culture supernatants. Stability of GST-theta (hGSTT1) mRNA was assessed in HT29 cells after inhibition of transcription with actinomycin D.
Results: LT97 adenoma cells consumed twofold more butyrate and were more sensitive to growth inhibition than HT29 (EC(50)1.9 mM and 4.0 mM, respectively). Butyrate did not induce GSTs, but instead reduced hGSTT1 in LT97 and HT29.
Conclusions: Butyrate has suppressing-agent activities in human colon cells by inhibiting two survival factors, namely hGSTT1 and cell growth, with LT97 more sensitive than HT29. These findings indicate that butyrate formation in the gut lumen of humans could be protective by reducing survival of transformed colon cells.