Abstract
Acetylmelodorinol, chrysin and polycarpol, together with benzoic acid, benzoquinone and stigmasterol were isolated from the leaves of Mitrella kentii (Bl.) Miq. The compounds were evaluated for their ability to inhibit prostaglandin E2 (PGE2) and thromboxane B2 (TXB2) production in human whole blood using a radioimmunoassay technique. Their inhibitory effect on platelet activating factor (PAF) receptor binding to rabbit platelet was determined using 3H-PAF as a ligand. Among the compounds tested, chrysin showed a strong dose-dependent inhibitory activity on PGE2 production (IC50 value of 25.5 µM), which might be due to direct inhibition of cyclooxygenase-2 (COX-2) enzymatic activity. Polycarpol, acetylmelodorinol and stigmasterol exhibited significant and concentration-dependent inhibitory effects on TXB2 production with IC50 values of 15.6, 19.1 and 19.4 µM, respectively, suggesting that they strongly inhibited COX-1 activity. Polycarpol and acetylmelodorinol showed strong dose-dependent inhibitory effects on PAF receptor binding with IC50 values of 24.3 and 24.5 µM, respectively.
Highlights
The hydrolysis of the sn-2 position of membrane glycerophospholipids to liberate arachidonic acid (AA), a precursor of eicosanoids including prostaglandins (PGs) and leukotrienes (LTs), is catalyzed by phospholipase A2 (PLA2)
The compounds were identified as benzoic acid, acetylmelodorinol [18], chrysin [19], benzoquinone [20], stigmasterol [21] and polycarpol [18] by comparing their physicochemical and spectroscopic properties with literature values, in addition to their 2D NMR spectra and Electrospray ionization mass spectrometry (ESI-MS)
Among the compounds isolated from the leaves of Mitrella kentii, chrysin showed a potent dose-dependent inhibitory activity on Prostaglandin E2 (PGE2) production in human blood induced by LPS, indicating that it might directly inhibit COX-2 enzymatic activity
Summary
The hydrolysis of the sn-2 position of membrane glycerophospholipids to liberate arachidonic acid (AA), a precursor of eicosanoids including prostaglandins (PGs) and leukotrienes (LTs), is catalyzed by phospholipase A2 (PLA2). Prostaglandin E2 (PGE2), a metabolite of AA through the cyclooxygenase-2 (COX-2) pathway, has received great attention because of its role and contribution to inflammation. In our screening study to identify compounds from tropical plants as potential anti-inflammatory agents, we observed that the methanol extract of the leaves of M. kentii showed strong inhibitory effects on PGE2 and TXB2 production in human whole blood (>50.0% inhibition) and PAF receptor binding to rabbit platelets (>60% inhibition). We report on the isolation of acetylmelodorinol, chrysin and polycarpol, together with benzoic acid, benzoquinone and stigmasterol, from this plant and their ability to inhibit COX-1 and COX-2 activities through inhibition of the production of TXB2 and PGE2 in human whole blood and displacement of 3H-PAF-specific binding in washed rabbit platelets
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