title: Tryptophan from human milk induces oxidative stress and upregulates the Nrf-2-mediated stress response in human intestinal cell lines.
abstract: Chemical screening of digested human milk protein using the oxygen radical absorbance capacity (ORAC(FL)) antioxidant assay confirmed the presence of a peptide fraction (PF23) with high antioxidant activity [5.53 mmol Trolox equivalents (TE)/g] that contained tryptophan as a main component. We evaluated the effects of both PF23 and tryptophan alone on the modulation of oxidative stress in cultured intestinal cells using a dichlorofluorescein diacetate probe. Despite the high ORAC(FL) value, PF23 enhanced (P < 0.05) 2, 2'-azobis (2-amidinopropane) dihydrochloride (peroxyl radical generator)-induced intracellular oxidation in the Caco-2 human adenocarcinoma cell line, suggesting prooxidant activity. Compared to selected peptide fractions with relatively lower ORAC(FL) values, PF23 induced oxidative stress more than all other peptide fractions tested (P < 0.05) and contained more tryptophan than the others (P < 0.05). Similar prooxidant activity was observed for tryptophan when it was added to culture medium for both the Caco-2 cells and FHs 74 Int primary fetal enterocytes, while also exhibiting a high ORAC(FL) value (9.69 mmol TE/g). The effect of tryptophan that involves activation of the Nrf-2 pathway and transcription of antioxidant enzymes was therefore investigated in FHs 74 Int cells. Exposure of infant intestinal cells to tryptophan resulted in Nrf-2 activation and an increase in the gene transcript level of glutathione peroxidase 2. We conclude that tryptophan-induced oxidative stress associated with tryptophan-containing milk peptides induces an adaptive response that involves the activation of the antioxidant responsive signaling pathway in intestinal cells.
authors.affiliation: Food, Nutrition and Health, Vancouver, BC, Canada.
authors.forename: Ingrid
authors.initials: I
authors.lastname: Elisia
authors.forename: Apollinaire
authors.initials: A
authors.lastname: Tsopmo
authors.forename: James K
authors.initials: JK
authors.lastname: Friel
authors.forename: William
authors.initials: W
authors.lastname: Diehl-Jones
authors.forename: David D
authors.initials: DD
authors.lastname: Kitts
mesh_terms: D018938:Caco-2 Cells; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000166:cytology / Q000187:drug effects*; D008895:Milk, Human / Q000737:chemistry*; D051267:NF-E2-Related Factor 2 / Q000502:physiology*; D018384:Oxidative Stress / Q000187:drug effects*; D014364:Tryptophan / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects*
chemical_list: D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D014364:Tryptophan