Procyanidin B2 is a natural flavonoid, with anti-cancer, antioxidant activities. In Vitro: Procyanidin B2 shows antiproliferative activity to MCF-7 cells, with an IC₅₀ of 19.21 μM. However, Procyanidin B2 exhibits no effect on DNA-ladder formation^[1]. Procyanidin B2 (0.1, 1, 2 μM) inhibits the activation of pyrin domain containing 3 (NLRP3) inflammasome in human umbilical vein ECs (HUVECs), and the inhibition is via suppression of AP-1 activity, and such effect can be abolished by overexpression of c-Jun. Procyanidin B2 (2 μM for 12 h) also reduces ROS in HUVECs^[2]. In Vivo: Procyanidin B2 (40, 20, and 10 mg/kg, p.o.) protects against cerebral ischemia-induced infarct volume and brain edema in rats. Procyanidin B2 (40 mg/kg, p.o) also improves functional outcomes, regulates blood-brain barrier (BBB) permeability after cerebral ischemia. Moreover, Procyanidin B2 attenuates cerebral ischemia-induced tight junction degradation, mitochondrial depolarization and intracellular oxidative stress. Procyanidin B2 (40 mg/kg, p.o) increases Nrf2 activation and HO-1, GSTα, and NQO1 protein expression in normal brains in vivo^[3].