Effects of hypolaetin-8-glucoside and related flavonoids on soybean lipoxygenase and snake venom phospholipase A2.

Hypolaetin-8-glucoside, a novel flavonoid isolated from Sideritis mugronensis and possessing anti-inflammatory and gastroprotective properties in the rat, was compared with the structurally related flavonoids hypolaetin, isoscutellarein, rutin, quercetin and kaempferol for inhibitory effects on the enzymes soybean 15-lipoxygenase and snake venom phospholipase A2. The aglycone flavonoids dose-dependently inhibited snake venom phospholipase A2 but the glycosides hypolaetin-8-glucoside and rutin were inactive. All 6 flavonoids inhibited soybean 15-lipoxygenase with no differences between glycosides and aglycones, although flavonols appeared more active than flavones. The inhibition of these enzyme activities cannot explain the anti-inflammatory action of hypolaetin-8-glucoside, unless a significant proportion of the drug reaches the target tissue as the aglycone, hypolaetin.