Abstract:

Screening the voluminous literature describing the quantifications of antioxidant levels in patients with various clinical disorders and after the administration of supplements has revealed that nearly all the studies have exclusively involved measurements in plasma. Since the classic tests have mainly quantified levels of low-molecular- weight antioxidants and albumin in human plasma but not those associated with erythrocyte enzymes and hemoglobin, such studies have not taken into account the roles of circulating cells, all laden with catalase and additional enzymes. This finding raises serious doubt as to whether reports on antioxidant quantifications exclusively in plasma can be trusted to represent true oxidant-scavenging abilities. Using a new chemiluminescence assay and an assay involving the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) (which are adapted to quantify antioxidants in whole blood),1 we have shown that erythrocytes, platelets, and lymphocytes not only rapidly scavenge reactive oxygen species but also avidly bind to their surfaces a large variety of antioxidant polyphenols, which further enhance their oxidantscavenging abilities.2,3 Such complexes could further act synergistically with low-molecular-weight antioxidants in plasma and with albumin to decompose reactive oxygen species. The synergistic scavenging effect of reactive oxygen species can be induced by a combination of human erythrocytes, plasma, and the representative polyphenol, epicatechin (Fig. 1). The advantage of the luminescence assay over the other classic methods is that it can quantify antioxidants in whole blood and that only 2 to 3 mm3 are needed to rapidly assess its oxidantscavenging ability. As proposed by Richards et al.4 and by Minetti and Malorni,5 erythrocytes have potent antioxidant properties that can act as sinks and as protectors against reactive oxygen species but may also act as pro-oxidant cells. It has been suggested that the genuine oxidant-scavenging ability of blood is most probably a result of the synergistic effects exerted by the antioxidants associated with blood cells, mostly due to catalase, superoxide dismutase, glutathione peroxidase, oxidoreductase, and hemoglobin, cells that are coated in an accumulative manner by dietary polyphenols, free circulating polyphenols, and low-molecular-weight antioxidants and albumin in plasma.2,3 The ability of blood cells to bind antioxidant polyphenols may be an important phenomenon with far-reaching in vivo consequences. With all these factors taken together, it is paramount that antioxidants be measured in whole blood and not in plasma alone in clinical settings.