Geraniin is a tannin that has been found in P. urinaria and has diverse biological activities. It scavenges 2,2-diphenyl-1-picrylhydrazyl (DPPH; IC50s = 0.92 and 1.27 μM at pH 4.5 and 7.9, respectively), superoxide (IC50 = 2.65 μM), and hydroxyl radicals (IC50 = 1.44 μM) in cell-free assays. Geraniin inhibits herpes simplex virus 1 (HSV-1) and HSV-2 replication in plaque reduction assays (IC50s = 35 and 18.4 μM, respectively). It inhibits angiotensin-converting enzyme (ACE) in vitro (IC50 = 13.22 μM) and reduces both systolic and diastolic blood pressure in spontaneously hypertensive rats when administered at a dose of 5 mg/kg. Geraniin (5, 10, and 20 μM) induces apoptosis and halts the cell cycle at the S phase in A549 lung cancer cells. It reduces tumor growth in an A549 mouse xenograft model when administered at doses of 10 and 20 mg/kg.
