Antioxidant and free radical scavenging activities of Hypericum perforatum L. (st. John's wort).

Hypericum perforatum is used as a folk remedy for the treatment of various neurological disorders. In this study, antioxidant activity of flower-bearing branches of H. perforatum was investigated employing various in vitro assay systems. IC₅₀ for DPPH radical-scavenging activity was 96.0 ± 3.7 µg ml^-1. Extract showed potent nitric oxide scavenging activity between 6.25 and 100 µg ml^-1. Percentage of inhibition was increased with increasing concentrations of the extract. IC₅₀ was 21.1±1.8 µg ml^-1. Extract showed good reducing power that was comparable with vitamin C (p> 0.05). Extract showed very weak Fe²⁺ chelating ability. Percentage of inhibition was 41% at 200 µg ml^-1 in scavenging of H₂O₂. This plant was a good source of phenols and contains very high amount of total phenolics. Total phenol compounds, as determined by the Folin Ciocalteu method, was 505.7 ± 18 mg GAE and the total flavonoid content, by AlCl₃ method was 23.8 ± 1.6 mg QE. Antioxidant activity may be attributed, at least in part, to the presence of high amount of phenols and flavonoids in the extract. Potent nitric oxide scavenging activity may explain reported anti-inflammatory and CNS activities of this plant. These activities may be partially mediated by NO pathway. [ABSTRACT FROM AUTHOR]