*2.4. HO-1/Nrf2 Pathway Activation by Cytoprotective Peptides*

HO-1 is one of the phase II detoxifying enzymes. In a ROS detoxifying mechanism, this enzyme must be induced by activation of a transcription factor such as Nrf2. This event is regarded as one of the most important cellular defense mechanisms [23]. As shown in Figure 4C,D, HO-1 expression slightly increased in the presence of H2O2 treatment alone, indicating spontaneous reaction for cytoprotection, and this finding is similar to a previous report [1]. However, the amount of HO-1 induction in the presence of H2O2 treatment alone is not enough to protect HUVECs, but we demonstrated that peptide treatment can increase the induction of HO-1, indicating the cytoprotective effect against exogenous stimuli. The induction of HO-1 is further confirmed by evidence of the translocation of Nrf2 into the nucleus, which regulates the expression of HO-1. As shown in Figure 4E, Nrf2 was detectable in the cytoplasm in the non-treated and H2O2 treated cells, whereas Nrf2 was slightly detectable in the nucleus in the H2O2 treated cells. Compared with the cells treated with H2O2 alone, treatment with FTVN and EPTF or their combination resulted in

upregulation of Nrf2 expression in both the cytoplasm and nucleus of HUVECs, indicating activation of Nrf2 followed by induction of HO-1.
