Does willow bark extract have a sildenafil-like action? Effects of different fractions on the synthesis of cGMP and NO in human umbilical vein endothelial cells (HUVEC)

Objectives: In the past years several methods have been implemented for testing substances which may exhibit sildenafil like properties. Willow bark extract, used in therapy of painful musculoskeletal diseases, has been supposed also to exhibit effects on endothelial cells and thus induce NO and might then indirectly increase cGMP and act slidenafil-like. We therefore investigated different fractions with a HUVEC cell model.

Method: We measured intracellular concentrations of cGMP and the release of NO after treatment of HUVEC cells with 5 different fractions (A-E) of the standardized willow bark extract STW 33-I (extraction medium water, DER 16–23:1), covering the whole spectrum of components from lipophilic to hydrophilic compounds.

Results: Fraction E showed a significant cGMP enhancement in concentrations from 10–100µg/ml. In investigating the validity of the assay this effect was comparable to a positive control (NO donor and PDE5 inhibitor (TO156)). Fractions A and E increased NO release whereas fraction C led to inhibition of NO release.

Conclusions: Fractions of willow bark extract increasing NO release and cGMP level, such as fraction E, might be interesting candidates for natural aphrodisiac products with a sildenafil-like mode of action. Fractions exhibiting the property to reduce NO release like fraction C might be further tested for their anti-inflammatory response as previous research findings from the study of inflammatory diseases showed the importance of free radicals like NO in enhancing the disease outcome. Taken together, this study shows that willow bark extract has several exciting modes of action possibly interesting for further indications.