Antioxidative stress effect of phosphoserine dimers is mediated via activation of the Nrf2 signaling pathway

Scope Phosphoserine‐containing peptides have been shown to exert antioxidative stress effects, by lowering lipid peroxidation, increasing intracellular glutathione, and increasing the expression of antioxidant enzymes in human intestinal epithelial cells. However, the role of phosphoserine residues in antioxidative stress activity, and their mechanism of action, remains unknown. Methods and results The antioxidative stress activity of phosphoserine and phosphoserine peptides was examined using an in vitro model of hydrogen peroxide (H 2 O 2 )‐induced oxidative stress in Caco‐2 cells. Phosphoserine dimers (2PS) reduced IL‐8 secretion in H 2 O 2 ‐treated Caco‐2 cells, and reduced H 2 O 2 ‐induced expression of genes involved in inflammation and generation of reactive oxygen species (ROS), including chemokine (C‐C motif) ligand 5 (CCL5), lactoperoxidase (LPO), myeloperoxidase (MPO), neutrophil cytosolic factor 1/2 (NCF1/2), and nitric oxide synthase 2A (NOS2), and upregulated metallothionein 3 (MT3), peroxiredoxin 3 (PRDX3), and surfactant, pulmonary‐associated protein D (SFTPD), which are involved in protection against oxidative stress and activation of the Nrf2 signaling pathway. At the protein level, 2PS reduced H 2 O 2 ‐induced phosphorylation of the ERK1/2 and JNK MAPKs, and increased Nrf2 expression. Moreover, the ability of 2PS to reduce H 2 O 2 ‐induced IL‐8 secretion, a marker of inflammation and oxidative stress, was abrogated in Nrf2 knockdown cells. Conclusion These results suggest that 2PS reduce H 2 O 2 ‐induced oxidative stress via the Nrf2 signaling pathway, and reveal a potential mechanism for the antioxidative stress activity of phosphoserine‐containing peptides.