HUVECs were seeded in 96-well plates (5 × 103/well) and treated with 5, 10, or 20 μg/ml of PF exosomes or the same concentrations of exosome-depleted PF for 24 hr in hypoxia (1% pO2). The medium was then replaced with a complete medium with supplemental BrdU (10 μM) for 24 hr. BrdU incorporation was measured using the BrdU ELISA assay kit (Roche). Caspase-3/7 activity was measured at 24 hr using a luminescent cell death detection kit according to the manufacturer’s instructions (Caspase-GLO assay; Promega).