The Effects of Green Tea Catechins on Oxidative Stress and Red Wheat on Measures of Oxidative and Nitrosative Stress, Colon Cancer Risk, and Gut Microbiome Composition

Abstract

There have been very few long-term investigations of the in vivo antioxidant effects associated with consumption of green tea catechins, especially in healthy populations. In the first study, we evaluated the in vivo antioxidant effects of 12-month green tea catechin supplementation in healthy, postmenopausal women by measuring urinary excretion of secondary lipid peroxidation products. Green tea catechin supplementation reduced excretion of a nonpolar aldehyde that was identified as nonanal and/or decatrienal. Our results suggest that green tea catechins may exert modest antioxidant effects in healthy populations that do not have elevated oxidative stress.We previously reported that red wheat, the class of wheat used to make yeast bread products, reduced various colon cancer biomarkers. In the second study, we evaluated the chemopreventive effects of red wheat and the aleurone and testa layers by examining morphological markers of colon cancer risk (aberrant crypt foci; ACF), a cancer stem cell marker (doublecortin-like kinase 1; Dclk1), a marker of oxidative and nitrosative stress (3-nitrotyrosine; 3-NT), and gut microbiome composition. The number of medium ACF (3-5 aberrant crypts/ACF) was reduced by consumption of refined red wheat and the aleurone layer. Large ACF (≥ 6 aberrant crypts/ACF) were decreased by the whole and refined red wheat and refined white wheat. Refined red wheat and the aleurone and testa layers reduced 3-NT positivity in aberrant crypts. The microbiome composition differed between diet groups and was driven by altered abundances of Faecalitalea, Lactobacillus, Mucispirillum, and Phascolarctobacterium. Consumption of whole and refined red wheat resulted in enrichment of Faecalitalea and Lactobacillus and depletion of Mucispirillum. These results suggest that the aleurone and testa layers may be partially responsible for the chemoprevention by red wheat, which possibly involves reductions in oxidative/nitrosative stress and modulation of the gut microbiome. In summary, green tea catechins may exert modest antioxidant effects, even under physiological conditions of little oxidative stress. The aleurone and testa layers may play a role in chemoprevention by red wheat, which involves a reduction in oxidative/nitrosative stress and beneficial modulation of gut microbiome composition.