Abstract
3,4-Dihydroxyphenylacetic acid, 3-hydroxyphenylacetic acid, and 3-(4-hydroxyphenyl)-propionic
acid, metabolites which arise from quercetin glycosides, 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 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. 3,4-Dihydroxyphenylacetic acid reduced considerably chemiluminescence
in PMNs in an amount which was much more pronounced than those of the other two metabolites.
Concentrations of 1 µmol/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 3,4-dihydroxyphenylacetic acid suppressed much more effectively
chemiluminescence than 3-hydroxyphenylacetic acid. In contrast, 3-(4-hydroxyphenyl)-propionic
acid 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 concentration of 4 µmol/l. In
conclusion, flavonoid metabolites differ in their effects on free radical production
of PMNs and their radical scavenging potencies.
Key words
Flavonoid metabolites - radical scavenger activity - chemiluminescence - horseradish
peroxidase
1 Part of the thesis of J. Heilmann
