Dietary fiber and fiber-bound polyphenols of grape peel powder promote GSH recycling and prevent apoptosis in the colon of rats with TNBS-induced colitis

Ulcerative colitis (UC) is a chronic inflammatory bowel disease that reduces glutathione (GSH) levels. We aimed to investigate the effect of dietary supplementation with grape peel powder (GPP) on the GSH system in a rat model of colitis induced by 2,4,6-trinitrobenzenesulfonic acid (TNBS) and to identify the role of grape bioactive fractions, namely soluble phenolics (EP), fiber-bound polyphenols (NEP-F), and dietary fiber (F). Colitis reduced colonic GSH levels and glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione-S-transferase (GST) activities. NEP-F completely restored GR and GPx , while all diets restored GST activities. Colitis increased the mRNA expression of both subunits of glutamate-cysteine ligase and induced apoptosis in the colon. The reestablishment of GSH levels promoted by GPP was associated with the recycling of oxidized glutathione by increased GR activity instead of GSH synthesis. NEP-F and F fractions were responsible for the protective effect of GPP against apoptosis.