In vitro anti-inflammatory and antioxidant activities of stilbenoids of Vanda coerulea (Orchidaceae)

In the framework of our investigations towards the isolation of biologically active constituents from Orchidaceae, we carried out biological screening of various Orchids. Among the metabolites isolated from Vanda coerulea, three stilbenoids corresponding to imbricatin, methoxycoelonin and gigantol, display protective antioxidant and anti-inflammatory properties via complementary mechanisms: free radical scavenging activity and inhibition of PGE-2 liberation on HaCAT irradiated cells with UV_B (60mJ/cm²). Imbricatin, the major stilbenoid in V. coerulea stem extract, displays an excellent hydroxyl radical scavenging activity (IC₅₀ 8.8µM) on HaCAT cells model in a concentration-dependant manner evaluated by dichlorodihydrofluoresceine (DCFH) assay [1]. It also inhibits significantly PGE-2 liberation, implied in skin inflammation, induction of various matrix metalloproteinases or inhibition of collagen synthesis in fibroblasts [2]. Besides, this stilbenoid shows the best scavenging activities on 2,2-diphenyl-1-picrylhydrazyl, DPPH (IC₅₀ 11.0µM) and hydroxyl radicals in tubo with an IC₅₀ of 0.11µM, twice as lower as reference molecule

quercetol.

	IC50 (µM)
	In tubo			In vitro (HaCaT)
compounds	DPPH	O2 ·-	HO·	HO·	PGE-2
Imbricatin	11.0±0.7	98.3±16.8	0.11±0.04	8.8±1.7	12.2±2.9
Methoxycoelonin	15.9±1.9	722.7±111.4	0.82±0.17	10.2±2.6	19.3±3.8
Gigantol	Nd	Nd	1.7±0.04	20.6±0.5	Nd
Standard Quercetol	2.9±0.4	6.2±2.3	0.29±0.01	13.8±2.2	Nd
Standard Resveratrol	Nd	Nd	Nd	Nd*	6.6±0.8
IC50: half maximal Inhibitory Concentration Nd: not determined Nd*: resveratrol shows pro-oxidant properties in DCFH assay

References: [1] LeBel, C.P. et al. (1992) Chem. Res. Toxicol. 5:227–231.

[2] Seo, J.Y. et al. (2003) Mech. Ageing Dev. 124:903–910.