Polyphenols' Chemical Structure Affects Oxidative Protection

LITTLE ROCK, Ark.Researchers at the University of Arkansas conducted a study, co-authored by scientists from USDA, NIS Labs, AIBMR Life Sciences and SIPI, on isolated polyphenols from acai fruit (Euterpe oleracea Mart.) in which they found combining both chemical and cell-based assays provided a more comprehensive understanding of the antioxidant effects and potential biological relevance (Food Chem. 2010;122(3):610-617). Seven major flavonoids were isolated from freeze-dried acai pulp by various chromatographic methods. Their structures were elucidated as orientin (1), homoorientin (2), vitexin (3), luteolin (4), chrysoeriol (5), quercetin (6) and dihydrokaempferol (7) by NMR, MS and compared with the reported literature. Compounds 3 and 6 were reported from acai pulp for the first time. Antioxidant capacities of these flavonoids were evaluated by ORAC assay, cell-based antioxidant protection (CAP-e) assay and reactive oxygen species (ROS) formation in polymorphonuclear (PMN) cells (ROS PMN assay). ORAC values varied distinctly among the seven compounds based on numbers and positions of hydroxyl groups and/or other substitute groups. The ORAC values of aglycones are generally higher than that of glycosides. CAP-e results indicated only three compounds (4, 6 and 7) could enter the cytosol and contribute to the reduction of oxidative damage within the cell. The ROS PMN assay showed that five compounds (23 and 57) demonstrated exceptional effects by reducing ROS formation in PMN cells, which produced high amounts of ROS under oxidative stress.

Additionally, in 2008 NIS Labs conducted a study comparing ORAC, CAP-e and ROS PMN (JAgric Food Chem. 2008;56(18):8319-25). The methods were applied to four natural products, all containing antioxidants capable of entering and protecting cells in the CAP-e assay. The magnitude of this effect was not directly correlated to the ORAC value of each product. Furthermore, the products showed different effects in the ROS PMN assay. Acai provided strong inhibition of ROS formation, indicating anti-inflammatory properties. In contrast, Immunel and EpiCor mildly enhanced ROS formation, suggesting activation of the innate immune response. HA Joint Formula showed a complex nonlinear dose-response in the ROS PMN assay, illustrating complex natural products may have similar antioxidant properties but different effects on human cells. Cell-based antioxidant protection is addressed best in the CAP-e assay, since some natural products contain compounds that may provoke cellular signaling in other cell types. The PMN cell type is a useful model for assessment of overall anti-inflammatory versus immune supportive properties of a product. The sequential use of the three methods serves to bridge analytical and biological testing methods.

Based on this data, the CAP-e bioassay was shown to be a highly useful tool in helping provide a more comprehensive understanding of the biological properties of such polyphenol compounds.