Oak leaf extract as topical antioxidant: free radical scavenging and iron chelating activities and in vivo skin irritation potential.

The topical application of antioxidants may be beneficial for the protection of the skin against UV damage. An extract of Quercus robur leaves was prepared and evaluated considering its putative application as topical antioxidant. The solvent and extractive method selection was monitored by 1,1-diphenyl-2-picryl hydrazyl (DPPH) free radical scavenging activity and polyphenols extraction (measured by the Folin Ciocalteu assay). Iron chelating activity and the phenolic composition (HPLC/DAD) were assessed on the extract obtained under optimized conditions. Skin irritation potential was investigated by performing an in vivo patch test in 19 volunteers. The extraction solvent which resulted in the highest activity was ethanol:water (4:6) and thus it was selected for further preparation of this extract. The IC50s for the iron chelation and DPPH scavenging assays were 153.8 +/- 26.3 microg x mL-1 and 7.53 +/- 0.71 microg x mL-1 (mean +/- SD), respectively. The total phenolic content was found to be 346.3 +/- 6.7 mg gallic acid equivalents (GAE)/g extract (mean +/- SD). Three phenolic compounds were identified in the extract namely: ellagic acid, rutin and hyperoside. The major identified component was ellagic acid. The patch test carried out showed that the extract can be regarded as safe for topical application.