RADICAL SCAVENGER ACTIVITY OF 3 FLAVONOID METABOLITES STUDIED BY INHIBITION OF CHEMILUMINESCENCE IN HUMAN-PMNS

3,4-Dihydroxyphenylacetic acid, 3-hydroxyphenylacetic acid, and 3-(4-h ydroxyphenyl)-propionic acid, metabolites which arise from quercetin g lycosides, respectively, from flavones and probably from procyanidins by the human intestinal microflora, have been tested for their effects on oxygen radical production by human PMNs stimulated with FMLP or op sonized zymosan. Oxygen radicals were detected by luminol-augmented ch emiluminescence measurements. Furthermore free radical scavenging acti vity of these metabolites was investigated in a cell-free system in wh ich oxygen radicals were generated by horseradish peroxidase with H2O2 as substrate. 3,4-Dihydroxyphenylacetic acid reduced considerably che miluminescence in PMNs in an amount which was much more pronounced tha n those of the other two metabolites. Concentrations of 1 mu mol/l sho wed an inhibition by 84% with FMLP as stimulant and by 15% with opsoni zed zymosan, indicating that different signal transduction pathways ar e influenced in PMNs. Using the same conditions the unmetabolized quer cetin showed an inhibition of chemiluminescence by 74% (FMLP), resp. 2 0% (opsonized zymosan). In the cell free system 3,4-dihydroxyphenylace tic acid suppressed much more effectively chemiluminescence than 3-hyd roxyphenylacetic acid. In contrast, 3-(4-hydroxyphenyl)propionic acid led to an increase of chemiluminescence generated in the cell-free sys tem (FMLP and zymosan), i.e. by 30% and by 25%, at the highest concent ration of 4 mu mol/l. In conclusion, flavonoid metabolites differ in t heir effects on free radical production of PMNs and their radical scav enging potencies.