Varieties of medicinal plants are well-known to possess powerful antioxidants and often considered for use as cancer preventing agents. Dietary supplements from plant extracts are made available for the purposes of scavenging free radicals. However, due to their strong reactive nature, herbal extracts may also produce free radicals which lead to other effects such as cell killing as observed in studies showing tumor cell death caused by herbal treatments. In this study, we examined a range of herbs commonly used in traditional medicine for their ability to generate radical intermediates in both aqueous and ethanolic extracts using Electron Paramagnetic Resonance (EPR) spectroscopy. Crude aqueous and ethanolic extracts of Phyllanthus emblica Linn, Phylanthus urinaria Linn, Houttuynia cordata Thumb, Acanthus ebracteatus Vahl, Rhinacanthus nasutus Kurz, Thunbergia laurifolia Linn, and Moringa oleifera Lam were tested for their ability to generate free radicals under different conditions. The results showed that all of the herbal extracts could act as prooxidants under extreme alkali condition (pH12); P. emblica, P. urinaria and A. ebracteatus extracts were able to produce free radical in phosphate buffer at near neutral pH (pH7.4). At near physiological conditions where H2O2 and peroxidase are available, H. cordata in addition to the three herbs mentioned prior was able to generate a free radical product. The HPTLC data also showed that gallic acid, chlorogenic acid and quercetin were present as constituents of these plants and thus could play a role in their free radical production. This study provides evidence that herbal extracts can produce free radicals and cause cellular toxicity rather than simply scavenging free radicals.
Key words: free radical, electron paramagnetic resonance, herbal extract, phenolic compound
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