Antioxidant capacity of 55 medicinal herbs traditionally used to treat the urinary system: a comparison using a sequential three solvent extraction process

Background: The prevalence of chronic renal disease exceeds 10% in industrialized societies. Oxidative damage is thought to be one of the main mechanisms involved in nearly all chronic renal pathologies. Objective: We aimed to use the oxygen radical absorbance capacity (ORAC) method and a sequential multisolvent extraction process to compare the in vitro antioxidant capacity of 55 medicinal herbs and prioritize them for in vivo studies investigating the value of herbal therapies in the treatment of renal disorders. Methods: The herbs were chosen on the basis of their traditional use in kidney or urinary system disorders, or because they have attracted the attention of recent investigations into renal pathologies. The three solvents used for extraction were ethyl acetate, methanol, and 50% aqueous methanol. Silybum marianum (milk thistle) seed and Camellia sinensis (tea) leaf, both known to possess high antioxidant capacity, were included for comparison. Results: Twelve of the 55 herbs were comparable to or exceeded ORAC levels of milk thistle seed or tea leaf. The highest radical-scavenging activity was found in Olea europaea (olive leaf), Cimicifuga racemosa (black cohosh), Rheum palmatum (rhubarb), Glycyrrhiza glabra (licorice), and Scutellaria lateriflora (Virginia skullcap). Conclusions: The antioxidant capacity of many of the herbs studied may, at least in part, be responsible for their reputation as being protective of organs of the urinary system. Overall, the combined ORAC values for the methanol and aqueous methanol extracts comprised 84% of the total ORAC value. Sequential extraction with solvents of different polarities may be necessary to fully extract the antioxidant principles from medicinal plants.