Antioxidant Biomarkers from Vanda coerulea Stems Reduce Irradiated HaCaT PGE-2 Production as a Result of COX-2 Inhibition

Background: In 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)-O-center dot radical scavenging activity and in vitro inhibition of type 2 prostaglandin (PGE-2) release from UVB (60 mJ/cm(2)) irradiated HaCaT keratinocytes. Principal Findings: Bio-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 hydroalcoholic stem extract and were considered as Vanda coerulea stem biomarkers. Dihydro-phenanthropyran (1) and dihydrophenanthrene (2) displayed the best DPPH/(OH)-O-center dot radical scavenging activities as well as HaCaT intracellular antioxidant properties (using DCFH-DA probe: IC50 8.8 mu M and 9.4 mu M, respectively) compared to bibenzyle (3) (IC50 20.6 mu M). In turn, the latter showed a constant inhibition of PGE-2 production, stronger than stilbenoids (1) and (2) (IC50 12.2 mu M and 19.3 mu M, respectively). Western blot analysis revealed that stilbenoids (1-3) inhibited COX-2 expression at 23 mu M. Interestingly, stilbenoids (1) and (2) but not (3) were able to inhibit human recombinant COX-2 activity. Conclusions: Major 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.