Planta Med 2011; 77 - PM179
DOI: 10.1055/s-0031-1282937

Antidepressant mechanisms of action of willow bark extract STW 33-I

O Kelber 1, SN Okpanyi 1, A Freischmidt 2, EU Heinrich 1, J Müller 1, J Heilmann 2, G Ulrich Merzenich 3, D Weiser 1
  • 1Scientific Department, Steigerwald Arzneimittelwerk GmbH, Darmstadt, Germany
  • 2Pharmazeutsche Biologie, Institut für Pharmazie, Universität Regensburg, Germany
  • 3Medizinische Klinik III, Universitätsklinikum, Rheinische Friedrich-Wilhelms-Universität Bonn, Germany

Therapies in chronic musculoskeletal pain can be supplemented by antidepressants (1). For willow bark extracts, known for their anti-inflammatory and analgesic properties (2), additional antidepressant effects have been suggested (3). To elucidate the underlying potential mechanisms of action, the willow bark extract STW 33-I (Proaktiv®) and four of its fractions separated by polarity (4) have been studied.

Male Sprague Dawley rats (n=6/group) were treated for two weeks once daily per os with different doses of the extract and with fractions produced by liquid/liquid partition, in comparison to a control and reference group (imipramine 20mg/kg b.w.). On day 15, a forced swim test according to Porsolt was performed and the locomotor activity was determined. Treatment was continued for further four days and neurotransmitter concentrations were determined in frontal cortex, hypothalamus, hippocampus and striatum.

A significant shortening of the cumulative period of immobility was seen after treatment with 15, 30, 60mg/kg b.w. of the extract, whereas the locomotor activity did not increase. Higher doses of STW 33-I were ineffective. Fractions were characterized analytically by HPLC and tested in doses resembling their yield in the extract, with best effects in doses equivalent to the lowest extract dose tested. 5-HT levels in the hippocampal tissue were increased significantly.

STW 33-I and its fractions showed an antidepressant like effect. The serotonergic system seems to be involved. This central effect of the willow bark extract STW 33-I may contribute to its clinical efficacy in musculoskeletal pain.

Keywords: Willow bark extract, pain, FST, analgesia, depression, hippocampus, serotonin, 5-HT

Acknowledgement: This contribution is dedicated in memoriam to Prof. Dr. Hilke Winterhoff, Institut für Pharmakologie und Toxikologie, Westfälische Wilhelms-Universität, Münster, Germany, and former Chair of the Permanent Committee on Biological and Pharmacological Activity of Natural Products of GA, who passed away on May 9, 2010

References: 1. Perrot S et al. (2008) Rheumatology doi: 10.1093/rheumatology/ken110; 2. Nahrstedt A et al. (2007) Wien Med Wochenschr 157:348–351; 3. Hegger S et al. (2005) Kongress Phytopharmaka Phytotherapie, Berlin 2005:S19, (4) Bonaterra GA et al. (2010) Phytomedicine 17: 1106–1113