Antioxidant content activity and nitric oxide scavenging ability of Ilex guayusa compared with Camellia sinensis and Aspalathus linearis tea

Abstract

Guayusa tea, an extract of the Ilex guayusa plant, is ritualistically consumed by the Runa tribes of Ecuador. It is known for its healing abilities and for giving lucid dreams as well as being used by the Amaguajes Indians of South America to treat diabetes and has been shown to retard the development of steptozocin-induced diabetes in mice. Guayusa tea is now commercially available as Runa tea and in select areas of the USA as tea bags or iced tea. Guayusa tea has not been scientifically evaluated, or compared with more popular commercialised tea brands such as Camellia sinensis black tea (BT), green tea (GT) and Aspalathus linearis rooibos tea (RT), regarding possible health benefits. The aim of this study is to address this limitation in knowledge regarding the antioxidant and anti-inflammatory properties of this tea. Chemical evaluation was performed according to the International Organisation of Standardisation (ISO) approved methods. Methanol extracts of commercially available guyasa tea and crushed factory leaves of fermented and unfermented guaysua tea was compared to nine brands of black and green Camellia sinensis tea brands. Antioxidant reducing capacity was observed with the use of an ISO-approved Folin-Ciocalteu (F-C) method. To elaborate on findings antioxidant activity were further evaluated using the Trolox equivalent antioxidant capacity (TEAC), 1,1-diphenyl-2-picrylhyrazyl (DPPH) and oxygen radical antioxidant capacity (ORAC) assays. The methods that involve an electron transfer mode of action such as the F-C, TEAC and DPPH showed antioxidant activity of all samples of guayusa tea to be significantly lower than all Camellia sinensis brands evaluated. In contrast the results obtained from the ORAC assay, which involves a hydrogen atom transfer mode of action showed that guayusa tea had statistically similar antioxidant capacity to GT and BT Camellia sinensis brands. To assess the possible health benefits associated with guayusa tea, water extracts of commercial and crushed black and green factory guaysa tea leaves were analysed and compared to BT, GT (Camellia sinensis) and RT (Aspalathus linearis) of the same brand with the F-C and ORAC assays. The health benefits were further evaluated in cellular models. The dichloro-dihydro-fluorescein diacetate (DCFH-DA) assay was used to evaluate cellular antioxidant activity in the SC-1 and Caco-2 cell lines. LPS-stimulated RAW 267.9 cells were used to evaluate the nitric oxide (NO) scavenging properties of the tea extracts in a cellular environment. Cell viability was determined with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. With the F-C reducing and the ORAC assay, the antioxidant activity of all guayusa tea samples were significantly lower than BT and GT, but similar to RT. Similar results were obtained for he NO scavenging activity. With regards to the cell culture-based assays, in both SC-1 and Caco-2 cell lines the DCFH-DA assay showed that guayusa had similar cellular protective effects to BT and GT, and higher than RT. For the NO suppressing assay in the RAW 264.7 cell line, guayusa tea showed similar results to BT, GT and RT. In this study, Ilex guaysa extracts were shown to have antioxidant, cellular protective and anti-inflammatory properties. In some instances, such as with the ORAC assay conducted on alcohol extracts, guyausa tea showed antioxidant activity similar to that of BT and GT. Water extracts had antioxidant activity (F-C and ORAC assay) less than GT and BT but greater than RT. In contrast in cell model systems the antioxidant and anti-inflammatory properties of guayusa tea related to NO scavenging was similar to GT and BT. Overall, in a non-cellular setting, guayusa tea provides little antioxidant activity, especially when compared with Camellia sinensis tea, widely known for its antioxidant and health benefits. However, when exposed to a cellular environment, guayusa tea performs similarly to Camellia sinensis tea in terms of antioxidant acitivity which suggests that it may have health benefits in a biological system which can be more profoundly assessed and elaborated in future studies.