Abstract
BackgroundIn our investigations towards the isolation of potentially biologically active constituents from Orchidaceae, we carried out phytochemical and biological analyses of Vanda species. A preliminary biological screening revealed that Vanda coerulea (Griff. ex. Lindl) crude hydro-alcoholic stem extract displayed the best DPPH /•OH radical scavenging activity and in vitro inhibition of type 2 prostaglandin (PGE-2) release from UVB (60 mJ/cm2) irradiated HaCaT keratinocytes.Principal FindingsBio-guided fractionation and phytochemical analysis led to the isolation of five stilbenoids: imbricatin (1) methoxycoelonin (2) gigantol (3) flavidin (4) and coelonin (5). Stilbenoids (1–3) were the most concentrated in crude hydro-alcoholic stem extract and were considered as Vanda coerulea stem biomarkers. Dihydro-phenanthropyran (1) and dihydro-phenanthrene (2) displayed the best DPPH/•OH radical scavenging activities as well as HaCaT intracellular antioxidant properties (using DCFH-DA probe: IC50 8.8 µM and 9.4 µM, respectively) compared to bibenzyle (3) (IC50 20.6 µM). In turn, the latter showed a constant inhibition of PGE-2 production, stronger than stilbenoids (1) and (2) (IC50 12.2 µM and 19.3 µM, respectively). Western blot analysis revealed that stilbenoids (1–3) inhibited COX-2 expression at 23 µM. Interestingly, stilbenoids (1) and (2) but not (3) were able to inhibit human recombinant COX-2 activity.ConclusionsMajor antioxidant stilbenoids (1–3) from Vanda coerulea stems displayed an inhibition of UVB-induced COX-2 expression. Imbricatin (1) and methoxycoelonin (2) were also able to inhibit COX-2 activity in a concentration-dependent manner thereby reducing PGE-2 production from irradiated HaCaT cells. Our studies suggest that stilbenoids (1–3) could be potentially used for skin protection against the damage caused by UVB exposure.
Highlights
Skin is continuously exposed to ultraviolet (UV) radiations from sunlight and to environmental pollution
Major antioxidant stilbenoids (1–3) from Vanda coerulea stems displayed an inhibition of UVB-induced cyclo-oxygenase 2 (COX-2) expression
Our studies suggest that stilbenoids (1–3) could be potentially used for skin protection against the damage caused by UVB exposure
Summary
Skin is continuously exposed to ultraviolet (UV) radiations from sunlight and to environmental pollution. UVB (290–320 nm) radiations trigger the production of reactive oxygen species (ROS), increasing oxidative stress in irradiated skin. In times of increased ROS production (caused by sunlight, smoke and pollution) protective controls may not be adequate anymore resulting in an oxidant-antioxidant imbalance, defined as oxidative stress. It can cause many adverse effect (ageing) and pathological conditions (inflammation, cancer) via the modulation of biochemical, genetic and signal transduction pathways [1,2,3]. In our investigations towards the isolation of potentially biologically active constituents from Orchidaceae, we carried out phytochemical and biological analyses of Vanda species. Lindl) crude hydro-alcoholic stem extract displayed the best DPPH /NOH radical scavenging activity and in vitro inhibition of type 2 prostaglandin (PGE-2) release from UVB (60 mJ/cm2) irradiated HaCaT keratinocytes
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