High-throughput fluorescence screening of antioxidative capacity in human serum

Diphenylhexatriene-labeled phosphatidylcholine and propionic acid have been established as selective fluorescence markers for the continuous determination of oxidation processes in the lipid and aqueous phases of unfractionated human serum. Oxidation of the respective fluorophores leads to a decrease in fluorescence intensity from which the time-dependent degradation of the marker molecule can be determined. The lag times preceding the propagation of oxidation are representative for the antioxidative capacity of the system, which may be influenced by exogenous factors, e.g., the antioxidants from the diet. Supplementation of human serum by quercetin, rutin, vitamin E, vitamin C, or total apple phenolics in vitro led to a decrease in oxidizability depending on the oxidation marker and the hydrophobicity of the antioxidant. Quercetin and vitamin E showed a higher in vitro capacity of protecting lipoproteins against oxidation. In contrast, rutin and vitamin C were more efficient as inhibitors in the aqueous phase. The same effect on serum was found after dietary consumption of apples. This result is in line with the known observation that intake of plant polyphenols leads to an increase in serum levels of hydrophilic antioxidants.