*2.4. Measurement of Intracellular ROS, GSH, Malondialdehyde, and NO Levels*

Endothelial cells were treated with 50 μM phenolic acid and 600 μM H2O2. Next, the cells were washed with PBS and stained with 25 μM diacetyldichlorofluorescein. The fluorescence intensity was analyzed. Glutathione and malondialdehyde levels were measured using the DTNB-GSSG reductase recycling and TBARS assays, respectively. Nitric oxide levels were measured using Griess reagent.

### *2.5. Western Blot Analysis*

The EA.hy 926 endothelial cells were cultured in a 6-well plate with or without sinapic acid at a density of 6 × 105 cells/mL. Total proteins and nuclear proteins were extracted using the Pro-PrepTM protein extraction solution (iNtRON Biotechnology, Seongnam, Korea) and NE-PER® nuclear and cytoplasmic extraction reagents (Thermo Fisher Scientific, Inc., Worcester, MA, USA), respectively. Membranes were incubated with primary and secondary antibodies (1:2000 dilution for β-actin; 1:1000 dilution for p-eNOS, eNOS, p-Akt, Akt, NQO-1, PCNA, HO-1, GCLC, anti-mouse, and anti-rabbit; 1:500 dilution for Nrf-2). The bands were visualized using X-ray film.
