Topical application of solubilized Reseda luteola extract inhibits ultraviolet B-induced inflammation in human volunteers in vivo

The flavone luteolin displays numerous anti-inflammatory effects at micromolar concentrations which cannot be completely explained by its anti-oxidant capacities. In the present work we investigated a dry extract from Reseda luteola rich in flavones (40% w/w), especially luteolin, some of its glucosides, methylethers, and apigenin, obtained by a multistep extraction process using water and ethanol as solvents (drug to extract ratio 26–28:1). We investigated the skin tolerance and anti-inflammatory potential of a nanoparticular solubilisate of the Reseda extract (s-RE) in two independent studies in vivo. Reseda luteola extract was solubilized with polysorbate, resulting in product micelles with a diameter of 10 (±1.5) nm. Standardized inflammation was induced by irradiating test areas on the back of healthy volunteers with defined doses of ultraviolet B (UVB). In the first study different concentrations of s-RE were tested in 10 volunteers to evaluate dose-dependency of anti-inflammatory effects of s-RE. In the second randomized, double-blind, placebo-controlled study a defined concentration of s-RE (2.5% w/w) was tested in 40 volunteers in comparison to the vehicle (glycerol) and hydrocortisone (1% w/w). s-RE dose-dependently inhibited UVB-induced erythema when applied 30 minutes before irradiation. Topical application of s-RE after irradiation also prevented UVB-induced erythema. S-RE was as effective as hydrocortisone, whereas the vehicle had no effect. Occlusive application of s-RE on non irradiated test sites did not cause any skin irritation. Due to excellent skin tolerance combined with potent anti-inflammatory properties s-RE bears potential especially for the prevention but also for the treatment of inflammatory skin conditions such as UV-induced erythema.