ABSTRACT
Flavonoids are low molecular weight compounds that are most concentrated in seeds, citrus fruits, olive oil, tea, and red wine, and that have potent antioxidant, cytoprotective, and anti-inflammatory activities. Flavonoids are composed of a three-ring structure (A, B, and C) with various substitutions; they can be subdivided according to the presence of an oxy group at position 4, a double bond between carbon atoms 2 and 3, or a hydroxyl group in position 3 of the C (middle) ring. Particular hydroxylation patterns of the B ring of the flavones permit them to inhibit histamine, tryptase, interleukin-6, and interleukin-8 release from human umbilical-cord-derived cultured mast cells, as well as from macrophages. The catechol (o-dihydroxy) group in the B ring, as in quercetin, confers potent inhibitory ability, while a pyrogallol (trihydroxy) group, as in myricetin, produces even higher activity. However, addition of one hydroxyl group on position 2′ of the B ring, as in the flavonol morin, renders this compound inactive. The C2-C3 double bond of the C ring appears to increase scavenger activity because it confers stability to the phenoxy-radicals produced, while the 4-oxo (keto double bond at position 4 of the C ring) increases free radical scavenger activity by delocalizing electrons from the B ring. The 3-OH group on the C ring appears to be critical for anti-inflammatory activity (Table 15.1). Inhibition of mast cell secretion was shown to be mediated by a 78-kD phosphoprotein which
Abstract .................................................................................................................. 215 Introduction ............................................................................................................ 216 Mast Cell Inhibitory Activity ................................................................................. 217 Discussion .............................................................................................................. 221 Acknowledgments ..................................................................................................223 References ..............................................................................................................223
