Butyrate, one of the major products of gut fermentation, is known to inhibit proliferation, induce apoptosis and differentiation, and increase phase II
enzyme activities in
tumor cells, whereas little information is available on protective effects in less-transformed colon cells. The aim of this study was to investigate whether the chemoprotective mechanism of
glutathione S-transferase (GST) induction by
butyrate could also play a role in earlier stages of colon
carcinogenesis and whether chemoresistance of cells toward the endogenous genotoxic risk factor
4-hydroxy-2-nonenal (HNE) could be a consequence of
butyrate treatment. As cell models, we used the human tumor cell lines HT29 and HT29 clone 19A, a differentiated subclone with properties resembling primary colon cells. We determined the expression of GSTP1
protein (
enzyme-linked
immunosorbent assay), the major GST in HT29, GSTP1
mRNA (Northern blotting), GST activity, intracellular
glutathione, and total
protein. The genotoxic impact of HNE (100-200 microM) was compared in
butyrate-treated and nontreated cells using single-cell
microgel electrophoresis. Our results show that GSTP1
mRNA, GSTP1
protein, GST activity, and total
protein were increased (1.2- to 2.5-fold) and
glutathione levels were maintained after 24-72 h of incubation with 4 mM
butyrate. Moreover, a marked reduction of HNE-induced genotoxicity was caused by preincubation with
butyrate.
Butyrate also induced the phosphorylation of
extracellular signal-regulated kinases (ERK1/2, Western blotting) after 5-30 min, which indicates a regulation of GST expression by this signal pathway. Most effects were greater in HT29 parent cells than in clone cells. In conclusion,
butyrate enhances expression of GST and other
proteins in both cell lines, which leads to an enhanced chemoprotection, reducing the impact of HNE genotoxicity. Thus
butyrate could play a role in early and later stages of
cancer prevention by reducing exposure to relevant risk factors.