Comparison of relative antioxidant activities of British medicinal plant species in vitro

We have determined the relative levels of endogenous antioxidant activity i n a range of British medicinal plant species (representative of a variety o f plant families, selected on the basis of their widespread use in traditio nal herbal medicine), via competitive scavenging of the ABTS(.+) or O-2(-.) radicals in vitro. A number of plant species with appreciable levels (i.e. greater than or comparable with the activity in corresponding extracts of Ginkgo biloba or Panax ginseng, as recognised phytological sources of antio xidant activity) of antioxidant activity against the ABTS(.+) radical were identified as potentially novel sources of free radical scavenging compound s; however none of these extracts showed measurable antioxidant activity wh en assayed against the O-2(-.) radical. It, therefore, follows that any com parative determination of antioxidant activity should clearly define the ra dical species and assay method employed. For those extracts showing activit y against the ABTS(.+) radical, in general, it was not possible to predict the potential antioxidant capacity of a given plant species (or the most ac tive part of the plant) on a taxonomical basis, or from its use in traditio nal or modern medicine. In the longer term further characterisation of the active compounds from plant species with appreciable antioxidant activity i dentified in the present investigation may prove of value for treatment of disorders such as Alzheimer's disease, in which free radical induced tissue damage has been implicated. (C) 2000 Elsevier Science Ireland Ltd. All rig hts reserved.