TY - JOUR
T1 - Tryptophan from human milk induces oxidative stress and upregulates the Nrf-2-mediated stress response in human intestinal cell lines
AU - Elisia, Ingrid
AU - Tsopmo, Apollinaire
AU - Friel, James K.
AU - Diehl-Jones, William
AU - Kitts, David D.
PY - 2011/8/1
Y1 - 2011/8/1
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=79961114358&partnerID=8YFLogxK
U2 - 10.3945/jn.111.139451
DO - 10.3945/jn.111.139451
M3 - Journal Article
C2 - 21677072
AN - SCOPUS:79961114358
SN - 0022-3166
VL - 141
SP - 1417
EP - 1423
JO - Journal of Nutrition
JF - Journal of Nutrition
IS - 8
ER -