The cellular antioxidant activity in red blood cells (CAA-RBC): A new approach to bioavailability and synergy of phytochemicals and botanical extracts

In the present work, human red blood cells (RBC) were used to determine cellular antioxidant activity (CAA-RBC) of pure phytochemicals and botanical extracts, with the aim to predict their bioavailability.Amongst the pure flavonoids, isorhamnetin, tamarixetin, myricetin, and kaempferol showed the highest activity in the CAA-RBC assay; whereas, with the “chemical” oxygen radical absorbance capacity (ORAC) assay, the compounds that showed the highest activity were isorhamnetin, resveratrol, apigenin and catechin. When the CAA-RBC assay was applied to herbal extracts, the Vitis vinifera showed the highest value, a position that this extract maintained also when the ORAC assay was used. Other extracts showed a different order of effectiveness with the two methods.We also employed the CAA-RBC to assess synergistic or antagonistic effects of combinations of herbal extracts and we again compared the results with the ORAC assay. Punica granatum + Malus domestica synergized in the CAA-RBC assay, but not in the ORAC assay; Aspalathus linearis extract interacted positively with Vaccinium myrtillus, both in the ORAC assay and in the CAA-RBC assay. We concluded that the CAA-RBC assay, coupled with the ORAC assay, was useful for evaluating intracellular bioactivity and synergy amongst phytochemicals or extracts.