St. John's wort: New study may shed light on mechanism of antidepressant
action
Extracts of St. John's wort (Hypericum perforatum) are used
widely in Germany and the United States as antidepressant agents in
cases of mild-to-moderate depression. Yet the mechanism of action remains
unknown. Previous studies have pinpointed several weak effects, yet
none seem sufficient to explain the extract's activity. There are at
least ten potentially pharmacologically active components in the extract,
one of which is hypericin, the substance believed to have the greatest
degree of involvement in the extract's antidepressant effects. The present
study examined the affinity of hypericin at 30 receptor or uptake sites;
it inhibited less than 40% of specific radioligand binding at all sites
except mAChR and alpha receptors. The alpha receptor finding is novel
and is a potentially important clue to the mechanism of action of St.
John's wort, as these receptors have been found to have an association
with the antidepressant action of synthetic agents such as MAO inhibitors
and selective 5-HT reuptake inhibitors (SSRI). Though the efficacy of
St. John's wort as an antidepressant may be attributed to the concerted
activity of several mechanisms, the affinity of hypericin for alpha
receptors presents new possibilities for the cause of this extract's
clinical success.
Raffa R., "Screen of receptor
and uptake-site activity of hypericin component of St. John's wort
reveals alpha receptor binding." Life Sciences 1998; 62(16):PL
265-270. |
