High‐polyphenol sorghum bran extracts decrease glutathione peroxidase expression and activity in colon cancer celle

Abstract

Polyphenols are secondary plant metabolites found in many fruits, vegetables, and also grains. Sorghum bicoloris a cereal grain that contains varying amounts of polyphenols. Many polyphenols have been implicated in the regulation of colon cancer through modulating cellular antioxidant defense enzymes, which includes the glutathione peroxidases (GPX). These redox‐active enzymes protect cells from oxidative stress and are therefore involved in the regulation of tumorigenesis. Because cancer cells are thought to be undergoing oxidative stress, antioxidant defense enzymes, including but not limited to GPX, are often upregulated in those cells, contributing to their survival. The goal of our study is to investigate the impact of high‐polyphenol sorghum extracts on the expression and activity of these antioxidant enzymes. Our hypothesis is that glutathione peroxidase expression and catalytic activity will decrease in colon cancer cells treated with high‐polyphenol Sorghum extracts, thus potentially presenting a dietary chemoprevention strategy. The USDA ARS Kansas provided us with extracts from high‐polyphenol Sorghum bran, labeled ‘HP’ or ‘SC’. Human colon cancer cells (HCT116) were incubated with 1.25 mg extract per mL medium for 24hr hours. Total RNA was isolated with the Trizol method, and reverse transcribed to cDNA. mRNA expression was subsequently quantified using qPCR and normalized to the housekeeping gene GAPDH. Catalytic activity of GPX was determined with enzyme specific commercially‐available assays that measure the conversion of 1.0 µmol of NADPH to NADP+. Our preliminary results show that, compared to the solvent control, extract ‘HP’ slightly and extract ‘SC’ significantly (p<0.05) decreased mRNA expression of GPX 1 in HTC116 cells. However, GPX2 mRNA was modestly (p>0.05) increased in cells exposed to SC extract. Overall GPX activity, which measures catalytic activity of all present cellular GPXs, was significantly decreased by extracts ‘SC’ and ‘HP’. These results suggest that high polyphenol sorghum extracts may influence gene expression and catalytic activity of glutathione peroxidases involved in cellular antioxidant defense, and that GPX activity primarily reflects GPX1 as expected. Further investigation using other cell lines and antioxidant systems may help explain whether and how Sorghum extracts may modulate tumor prevention and promotion.