St. John's Wort (Hypericum perforatum) extracts and isolated phenolic compounds are effective antioxidants in several in vitro models of oxidative stress

The antioxidant potential of a total ethanolic extract of Hypericum perforatum (TE) was assessed, and correlated with the phenolic composition. TE was fully characterized by HPLC-DAD and HPLC-MSn, and phenolic compounds were isolated by semi-preparative HPLC. The free radical-scavenging properties of the TE were studied using DPPH center dot (EC50 = 49 mu g dwb/ml), AAPH (EC50 = 50 mu g dwb/ml) and the antioxidant potential was evaluated using lipid peroxidation induced by ascorbate/iron (EC50 = 28 mu g dwb/ml). Moreover, the TE was able to scavenge NO (by using sodium nitroprusside) and HOCl (by evaluating TNB reduction). Furthermore, the antioxidant potentials of the isolated compounds were evaluated and several compounds, namely flavonoids, were significantly less effective at DPPH center dot- and AAPH-scavenging, compared to their ability to prevent iron-mediated lipid peroxidation. Therefore, TE was able to scavenge several free radicals, indicating beneficial cellular protection against oxidative stress. (C) 2008 Elsevier Ltd. All rights reserved.