Screen of receptor and uptake-site activity of hypericin component of St. John's wort reveals sigma receptor binding

The mechanism of the antidepressant action of St. John's wort (Hypericum perforatum) remains unknown. A central component similar to that of the other clinically-popular antidepressants (e.g., inhibitors of 5-HT or norepinephrine reuptake or MAO) is suspected to play a role, but other mechanisms distinct from the SSRIs, NSRIs or MAOIs are possible. The extract of St. John's wort that is used clinically consists of multiple compounds. Hypericin is believed to be one of the major components responsible for the antidepressant effect. In the present study, the affinity of hypericin was determined at thirty receptor or reuptake sites. At 1.0 microM, hypericin inhibited less than 40% of specific radioligand binding at all sites except mAChR and sigma receptors. The demonstration of sigma receptor binding of hypericin is a novel finding and it might contribute to a new understanding of the clinical attributes of St. John's Wort.