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- Plant aqueous extracts: antioxidant capacity via haemolysis and bacteriophage P22 protectionPublication . Gião, Maria S.; Leitão, Isabel; Pereira, Ana; Borges, André B.; Guedes, Catarina J.; Fernandes, João C.; Belo, Luís; Santos-Silva, Alice; Hogg, Tim A.; Pintado, Manuela E.; Malcata, F. XavierThe bacteriophage P22/Salmonella Typhimurium system, as well as human erythrocytes have been used to assay for protection, against forced oxidation caused by hydrogen peroxide, brought about by several aqueous extracts of selected adventitious plants grown in Portugal. This study proved, for the first time, that the aforementioned bacteriophage-based system is a suitable method to assess the antioxidant activity of plant extracts; among the 12 plants tested, raspberry (Rubus idaeus), sage (Salvia sp.), savory (Satureja montana) and yarrow (Achillea millefolium) were found to effectively protect against oxidative damage caused by H2O2. Haemolysis was inhibited via pre-treatment with every plant extract tested, except heath at 0.1% (w/v). The two analytical methods produced different results – and for some plants, there was a dependence (either direct or inverse) of the quantitative protection effect on extract concentration, whereas for others no significant dependence was found at all. Savory yielded the most promising results, using either method. Therefore, the P22/Salmonella system can be used as a suitable in vivo assay, and human erythrocytes as a suitable in vitro assay to confirm (or not) the antioxidant capacity of plant extracts in biological matrices.
- Antioxidant activity of chitooligosaccharides upon two biological systems: erythrocytes and bacteriophagesPublication . Fernandes, João C.; Eaton, Peter; Nascimento, Henrique; Gião, Maria S.; Ramos, Oscar. L.; Belo, Luís; Santos-Silva, Alice; Pintado, Manuela E.; Malcata, F. XavierMost of the reports to date on the antioxidant capacity of chitosans and chitooligosaccharides (COS) are based on strictly chemical methods. When studying antioxidants with potential in vivo applications, the method used to evaluate the antioxidant activity should be representative of the conditions in which the antioxidant might have a protective effect. In this work we evaluate the antioxidant activity of two COS mixtures and a low MW chitosan (LMWC) upon two biological oxidizable substrates – erythrocytes and phages, subjected to accelerated oxidation conditions. Our results suggest that COS/LMWC can be used as antioxidants in biological systems. All the tested compounds reduced either the hemolytic and DNA damage, by inhibiting H2O2- and AAPH-radicals. However, the results obtained for these biological assays did not reveal a dose dependence, contrary to the chemical assay, suggesting that the protective concentrations should be established, in order to prevent enhancement of the oxidative damage – i.e. a prooxidant effect.