In vitro anticomplementary activity of constituents from Morinda morindoides

In a screening program for complement classical pathway modulation, an 80% MeOH extract of the leaves of Morinda morindoides showed potent dose-dependent anticomplementary activity. Bioassay-guided chromatographic separation of the active constituents led to the isolation of ten flavonoids of which two were aglycones. The compounds were tested in vitro for their putative complement-inhibiting properties on the classical (CP) and the alternative (AP) pathways of the complement system. The results indicated that quercetin [1], quercetin 3-O-rhamnoside (quercitrin) [5], and quercetin 3-O-rutinoside (rutin) [7] showed similar anticomplementary activities (inhibition) on the CP of complement. A mixture of two kaempferol triglycosides isolated and denoted as M(015), also had a good inhibitory effect. The effects of these compounds were dose-dependent for this pathway. On the AP of complement, quercetin [1] and M(015) had, respectively, more pronounced inhibitory and activatory effects than the other tested flavonoids, but their effects were not dose-dependent for this pathway. The other isolated flavonoids showed weak effects or were inactive for both pathways.