The effects of St. John's Wort (Hypericum perforatum) on NK cell activity in vitro

St. John's Wort (Hypericum perforatum; H. perforatum) is a popular herbal s upplement used to treat mild to moderate depression. H, perforatum possesse s serotonergic properties such as inhibition of serotonin (5-hydroxytryptam ine; 5-HT) reuptake. Serotonergic pharmacotherapy is associated with amelio ration of depression as well as increases in natural killer (NK) cell activ ity (NKCA). Also, 5-HT and 5-HT analogs augment NKCA in vitro. Considering the serotonergic properties of H. perforatum, the effects of H. perforatum on NKCA were assessed in vitro. Mononuclear cells (MNCs) from normal donors were exposed in vitro to an extract of H. perforatum (LI160s) or establish ed 5-HT stimulators of NKCA. After an overnight incubation, cells were wash ed and a standard Cr-51-release cytotoxicity assay performed to assess NKCA . LI160s at all concentrations failed to augment NKCA. However, in corrobor ation of previous studies, 5-HT, the selective serotonin reuptake inhibitor s (SSRLs), paroxetine and norfluoxetine, and alpha-interferon augmented NKC A above control levels. Though an efficacious treatment for mild to moderat e depression, H. perforatum differs from commonly prescribed serotonergic a ntidepressants insofar as H. perforatum fails to enhance NKCA in vitro. The refore, the present results are consistent with pharmacologic studies indic ating that H. perforatum possesses, at best, weak serotonergic activity. (C ) 2000 Elsevier Science B.V. All rights reserved.