Effects of selected dietary polyphenols on mucin expression in epithelial cells

Abstract

Human epithelial tissues express more than 20 mucins. These glycoproteins serve as lubricants but may exhibit various other functions such as signalling or immune functions. They aretissue-specific and their expression in various tissues is tightly regulated. In the gut, their expression might be influenced by some nutrients and previously, this has been observed for some food bioactives such as milk peptides. In our study, we investigated how gene expression of four mucins is affected by the presence of three selected dietary plant polyphenols. These comprised of MUC 2, major secreted mucin, MUC 3 the most studied of adhering membrane mucin, and MUC 13 and MUC 17, the recently discovered mucins. For the study, epithelial Caco-2 and mucin-producing HT-29 cell culture seeded in 9:1 ratio were used. The cell lines were cultured in Dulbecco’s modified Eagles medium (DMEM) with 10% foetal bovine serum and supplements and incubated at 37°C in 5% CO2 until 80% confluence. Quercetin, epicatechin, chlorogenic acid (naturally occurring in apples, tea leaves and coffee) were added to the culture medium at concentration of 10 µM for 48 h. We analysed variation in mucin gene expression by Real-time RT PCR, related to polyphenols treatment. Our in vitro results indicate that the intake of these three polyphenols may play an important role in regulating mucin expression, which may also be related to cancer development. Several studies, in literature have demonstrated that MUC 2, MUC 13 and MUC 17 are frequently overexpressed in gastric cancer and intestinal metaplasia, instead MUC 3 is up-regulated during the same pathological condition. Level of MUC 2 expression remain more or less constant respect to control after treatments with quercetin and epicatechin, instead treatment with chlorogenic acid decrease MUC 2 expression. Concentrations were selected based on MTT assay results as nontoxic, although mild cytotoxic effect cannot be ruled out. In contrast, level of MUC 3, MUC 13 and MUC 17 expression increases significantly after epicatechin and chlorogenic acid treatments and although causal role has not been extablished, this is in line with evidence of anticancerogenic potential of polyphenols. For the first time, we have demonstrated that these polyphenols can modulate mucus expression and may contribute to the protection of intestinal cells against various stress factors. The ongoing reseach aims to investigate the effect of plant polyphenols on mucins in vivo