Potential Role of ROS in Butyrate- and Dietary Fiber-Mediated Growth Inhibition and Modulation of Cell Cycle-, Apoptosis- and Antioxidant-Relevant Proteins in LT97 Colon Adenoma and HT29 Colon Carcinoma Cells

SIMPLE SUMMARY: The aim of the present study was to elucidate the potential contribution of oxidative stress to chemopreventive effects of butyrate and fermentation supernatants (FS) of different fiber samples. LT97 and HT29 cells were treated with butyrate or FS with or without N-acetyl-cysteine (NAC) and the impact on proliferation and formation of reactive oxygen species (ROS) and expression of cell cycle-, apoptosis-, and antioxidant-relevant proteins was investigated. We were able to demonstrate that butyrate- and FS-mediated chemopreventive effects are modulated differentially in both cells lines by NAC. These results suggest a potential contribution of ROS to the observed chemopreventive effects of butyrate and fiber FS depending on the cell line used. This study provides important insights into the role of ROS in butyrate- and dietary fiber-mediated chemopreventive effects towards colon cancer cells from different transformation stages and it provides a basis for further mechanistic studies. ABSTRACT: The aim of the present study was to examine whether reactive oxygen species (ROS) contribute to chemopreventive effects of fermentation supernatants (FS) of different dietary fibers (Synergy1(®), oat-, barley-, yeast β-glucan, Curdlan) and butyrate as a fermentation metabolite. LT97 and HT29 cells were treated with butyrate and FS alone or with N-acetyl-cysteine (NAC) and their impact on ROS formation, cell growth, and protein expression (Cyclin D2, p21, PARP, Bid, GPx2) was investigated. Butyrate and FS significantly decreased cell growth. ROS levels were significantly increased, particularly in LT97 cells, while co-treatment with NAC decreased ROS formation and growth inhibitory effects in both cell lines. After treatment with butyrate and FS, Cyclin D2 expression was reduced in LT97 cells and p21 expression was increased in both cell lines. Levels of full-length PARP and Bid were decreased, while levels of cleaved PARP were enhanced. GPx2 expression was significantly reduced by fiber FS in HT29 cells. A notable effect of NAC on butyrate- and FS-modulated protein expression was observed exclusively for PARP and Bid in HT29 cells. From the present results, a contribution of ROS to growth inhibitory and apoptotic effects of butyrate and FS on LT97 and HT29 cells cannot be excluded.