Radical scavenger activity of three flavonoid metabolites studied by inhibition of chemiluminescence in human PMNs

3,4-Dihydroxyphenylacetic acid (I), 3-hydroxyphenylacetic acid (II), and 3-(4-hydroxyphenyl)propionic acid (III), metabolites which arise from quercetin glycosides, resp., from flavones and probably from procyanidins by the human intestinal microflora, have been tested for their effects on oxygen radical prodn. by human PNMs stimulated with FMLP or opsonized zymosan. Oxygen radicals were detected by luminol-augmented chemiluminescence measurements. Furthermore free radical scavenging activity of these metabolites was investigated in a cell-free system in which oxygen radicals were generated by horseradish peroxidase with H2O2 as substrate. I reduced considerably chemiluminescence in PMNs in an amt. which was much more pronounced than those of the two metabolites. Concns. of 1 micro mol/l showed an inhibition by 84% with FMLP as stimulant and by 15% with opsonized zymosan, indicating that different signal transduction pathways are influenced in PMNs. Using the same conditions the unmetabolized quercetin showed an inhibition of chemiluminescence by 74% (FMLP), resp. 20% (opsonized zymosan). In the cell-free system I suppressed much more effectively chemiluminescence than II. In contrast, III led to an increase of chemiluminescence generated in the cell-free system (FMLP and zymosan), i.e. by 30% and by 25%, at the highest concn. of 4 micro mol/l. In conclusion, flavonoid metabolites differ in their effects on free radical prodn. of PMNs and their radical scavenging potencies