A handful of bioactive compounds from plants have been reported to possess platelet-activating factor (PAF) antagonist activity. However, their mode of action is not well understood. Selected bioactive compounds that exhibit PAF antagonist activity and synthetic PAF antagonists were subjected to docking simulations using the MOE 2007.09 software package. The docking study of PAF antagonists was carried out on the PAF receptor (PAFR) protein which involves in various pathological responses mediated by PAF. The docking results revealed that amentoflavone (3) showed good interactions with the PAFR model where the flavone and phenolic moieties were mostly involved in these interactions. Knowledge on PAF antagonists' interactions with the PAFR model is a useful screening tool of potential PAF antagonists prior to performing PAF inhibitory assay.
Forty-nine methanol extracts of 37 species of Malaysian medicinal plants were investigated for their inhibitory effects on platelet-activating factor (PAF) binding to rabbit platelets, using 3H-PAF as a ligand. Among them, the extracts of six Zingiberaceae species (Alpinia galanga Swartz., Boesenbergia pandurata Roxb., Curcuma ochorrhiza Val., C. aeruginosa Roxb., Zingiber officinale Rosc. and Z. zerumbet Koenig.), two Cinnamomum species (C. altissimum Kosterm. and C. pubescens Kochummen.), Goniothalamus malayanus Hook. f. Momordica charantia Linn. and Piper aduncum L. are potential sources of new PAF antagonists, as they showed significant inhibitory effects with IC50 values ranging from 1.2 to 18.4 microg ml(-1).
Ten compounds isolated from Alpinia mutica Roxb., Curcuma xanthorrhiza Roxb. and Kaempferia rotunda Linn. (Family: Zingiberaceae) were investigated for their platelet-activating factor (PAF) antagonistic activities on rabbit platelets using 3H-PAF as a ligand. Among them, four compounds showed significant inhibitory effects. Alpinetin and 5,6-dehydrokawain isolated from A. mutica exhibited IC50 values of 41.6 and 59.3 microM, respectively. The IC50 values of 3-deacetylcrotepoxide and 2-hydroxy-4,4',6'-trimethoxychalcone from K. rotunda were 45.6 and 57.4 microM, respectively. 1-Methoxy-2-methyl-5-(1',5'-dimethylhex-4'-enyl)-benzene, synthesized by methylation of xanthorrhizol which was obtained from C. xanthorrhiza, showed an IC50 value of 40.9 microM. The results indicated that these compounds were relatively strong PAF receptor binding inhibitors.
The methanol extract of the leaves of Garcinia nervosa var. pubescens King, which showed strong inhibitory effects on platelet-activating factor (PAF) receptor binding, was subjected to bioassay-guided isolation to obtain a new biflavonoid, II-3,I-5, II-5,II-7,I-4',II-4'-hexahydroxy-(I-3,II-8)-flavonylflavanonol together with two known flavonoids, 6-methyl-4'-methoxyflavone and acacetin. The structures of the compounds were elucidated by spectroscopic methods. The compounds were evaluated for their ability to inhibit PAF receptor binding to rabbit platelets using ³H-PAF as a ligand. The biflavonoid and acacetin showed strong inhibition with IC₅₀ values of 28.0 and 20.4 µM, respectively. The results suggest that these compounds could be responsible for the strong PAF antagonistic activity of the plant.