Egg Yolk Peptides Up-regulate Glutathione Synthesis and Antioxidant Enzyme Activities in a Porcine Model of Intestinal Oxidative Stress

Long-term oxidative stress in the gastrointestinal tract can lead to the development of chronic intestinal disorders. Many food-derived antioxidants are effective in vitro, but the variable reports of in vivo efficacy and the pro-oxidant nature of some antioxidants necessitate alternative strategies for the reduction of in vivo oxidative stress. Compounds that up-regulate the production of endogenous antioxidants such as glutathione (GSH) and antioxidant enzymes provide novel approaches for the restoration of redox homeostatis. Egg yolk peptides (EYP) prepared from Alcalase and protease N digestion of delipidated egg yolk proteins were found to exhibit antioxidative stress properties. The effect of EYP supplementation was examined in a hydrogen peroxide-induced human colon cell line and in an animal model of intestinal oxidative stress. EYP significantly reduced the pro-inflammatory cytokine, IL-8, in Caco-2 cells. In piglets given intraperitoneal infusions of hydrogen peroxide, EYP treatment increased GSH and gamma-glutamylcysteine synthetase mRNA expression and activity, significantly increased antioxidant enzyme activities, in particular catalase and glutathione S-transferase activities, and reduced protein and lipid oxidation in the duodenum, jejunum, ileum, and colon. Furthermore, EYP boosted the systemic antioxidant status in blood by increasing the GSH concentration in red blood cells. These results suggest that EYP supplementation is a novel strategy for the reduction of intestinal oxidative stress.