3.5. Intracellular ROS level
To confirm the antioxidant efficacy of PN at a cellular level, endothelial cells were treated with PN prior to a brief exposure to H2O2. The result showed that, compared to H2O2-treated cells, the hydroethanolic extract (50–200 μg/mL) attenuated intracellular ROS more effectively than the water extract (200 μg/mL) (Fig. 4A), without affecting cell viability (Fig. 4B). It should be noted that the hydroethanolic extract of PN (50 μg/mL) was relatively equipotent to quercetin (10 μM or 3.38 μg/mL), a well-known antioxidant, ferulic acid (5 μM or 0.97 μg/mL), and vanillic acid (50 μM or 8.41 μg/mL). Ferulic and vanillic acids were among the chemical markers found in PN (Fig. 2). Noticeably, a reduction of intracellular ROS induced by PN at the concentrations of 500 μg/mL and 1000 μg/mL was due to the loss of cell viability (Fig. 4B).