Analysis of in vitro serotonergic activity of black cohosh (Cimicifuga racemosa) and identification of a potential active constituent, N-methylserotonin

Cimicifuga racemosa (L.) Nutt. (black cohosh), a well known medicinal plant, is used to provide relief of menopausal hot flashes, although various clinical trials have provided conflicting efficacy data. Although black cohosh is a common component of several dietary supplements, the active constituents remain unknown. Previously we reported that a 75% ethanol extract had serotonergic activity [1] and could have a similar mechanism of action as some anti-depressants known to relieve hot flashes. The serotonergic system, particularly the 5-HT7 receptor and the serotonin transporter, are intimately involved with temperature and mood regulation. All extracts and compounds were evaluated for serotonergic activity using competitive ligand binding assays for the 5-HT7 receptor, cAMP induction, and a selective serotonin reuptake inhibition (SSRI) assay. Studies found the crude extracts displaced the specific binding of [3H] lysergic acid diethylamide (LSD) to the 5-HT7 receptor and caused modest cAMP production. Bioassay guided fractionation of the MeOH extract led to isolation of the pure compounds, cimicifugic acids A, B, E, F, fukinolic acid, and N-methylserotonin. The triterpenes and phenolic acids weakly bound to the 5-HT7 receptor, yet failed to induce cAMP production, or have SSRI activity. In contrast, N-methylserotonin showed potent 5-HT7 receptor binding (IC50=21 nM), induced cAMP production (EC50=21.8 nM), and was able to block the serotonin transporter activity (IC50=493 nM). To our knowledge, this is the first report of N-methylserotonin in black cohosh which may account for the serotonergic activity.