In this study, the effect of peptides HL-7 and HL-10 was examined on human breast cancer cells (MCF-7 cell line) in the presence and absence of H2O2 and the results were compared with glutathione (GSH) served as a positive control. The results showed that the peptides showed dose-dependent cytotoxicity (P < 0.01). Additionally, enzyme activity measurements were performed to study the effect of the peptides on the activity of antioxidant enzymes in MCF-7 cell line. The results showed that in parallel to increase in the peptide concentration, the activity of antioxidant enzymes [catalase (CAT) and glutathione peroxidase (GPx)] was increased significantly in HL-7- and HL-10- treated cells after 24 h (P < 0.01). Also, to investigate the mechanism of action of the two peptides, the changes in the gene expression of CAT and GPx enzymes in the cells treated with different concentrations of peptide (25, 50, 75 and 100 μM) were evaluated using real-time PCR. The results showed that the mRNA levels of antioxidant enzymes were increased in a dose-dependent manner (P < 0.01). The increase in the activity and gene expression of the enzymes in response to HL-7 peptide was higher than HL-10 and GSH peptides. The two peptides, HL-7, and HL-10 seem to act as antioxidant agents by enhancing the gene expression and activity of antioxidant enzymes.

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