Antioxidant and photoprotective activity of a lipophilic extract containing neolignans from Krameria triandra roots.

The antioxidant/photoprotective potential of a standardized Krameria triandra (KT) root extract (15% neolignans) has been evaluated in different cell models, rat erythrocytes and human keratinocytes cell lines, exposed to chemical (cumene hydroperoxide, CuOOH) and physical (UVB radiation) free radical inducers. The extract was significantly more active (IC50 0.28 +/- 0.04 microg/ml) than the typical chain-breaking antioxidant alpha-tocopherol (IC50 = 6.37 +/- 0.41 microg/ml) in inhibiting the CuOOH-induced hemolysis in rat blood cells. The KT constituent 2-(2,4-dihydroxyphenyl)-5-(E)-propenylbenzofuran, was the most active (IC50 = 0.03 +/- 0.005 microg/ml), followed by eupomatenoid 6 (IC50 = 0.29 +/- 0.06 microg/ml) and conocarpan (IC50 = 0.77 +/- 0.08 microg/ml). The same order of potency was observed in red blood cells exposed to UVB irradiation in continuo, with IC50 values 0.78 +/- 0.08 microg/ml for KT extract, 0.18 +/- 0.02 microg/ml for 2-(2,4-dihydroxyphenyl)-5-(E)-propenylbenzofuran, 0.95 +/- 0.11 microg/ml for eupomatenoid 6, and 3.8 +/- 0.39 microg/ml for conocarpan. In cultured human keratinocytes exposed to UVB radiation (50 mJ/cm2), KT extract (2.5-20 microg/ml) significantly and dose-dependently restrained the loss in cell viability and the intracellular oxidative damage: glutathione (GSH) depletion and the rise in dichlorofluorescein (DCF), marker of peroxide accumulation, were suppressed by 20 microg/ml KT and in parallel cell morphology maintained. The cytoprotective effect of the extract was confirmed in a more severe model of cell damage: exposure of keratinocytes to higher UVB doses (300 mJ/cm2), which induce a 50% cell death. In keratinocyte cultures supplemented with 10 microg/ml, cell viability was almost completely preserved and more efficiently than with (-)-epigallocatechin 3-gallate and green tea. The results of this study indicate the potential use of Rhatany extracts, standardized in neolignans, as topical antioxidants/radical scavengers against skin photodamage.