Objective: Tamoxifen, used for treatment and chemoprevention of breast cancer, is converted to 4-hydroxy-tamoxifen and other metabolites by cytochrome P450 (CYP) enzymes. It can often initiate or exacerbate vasomotor symptoms (VMS). Selective serotonin reuptake inhibitors (SSRIs) have been prescribed for VMS in such participants in which estrogens are contraindicated. However, SSRIs are strong CYP2D6 inhibitors and can reduce the efficacy of tamoxifen. A nonhormonal purified Swedish pollen extract (Relizen is also prescribed in other countries under different registered trade names: Sérélys, Femal, Femalen), has shown efficacy versus placebo in treating VMS in a randomized, double-blind controlled trial. The objective of this study was to evaluate the in vitro effects of purified Swedish pollen extract on the CYP2D6 enzyme.
Methods: PE-F/S, the powder form of purified Swedish pollen extract, contains 75% pollen/pistil extract P182 and 25% pollen extract GCFem. It was tested for its potential to inhibit the human CYP isoenzyme, CYP2D6, in pooled human liver microsomes. Quinidine, a known inhibitor of CYP2D6, was used as a reference. Concentrations of purified Swedish pollen extract ranged from 1.65 to 400 μg/mL, approximately five times the recommended daily dose for VMS.
Results: Inhibition of CYP2D6 with purified Swedish pollen extract was negligible at all concentrations and ranged from -6.53% to 10.67%. Inhibition of CYP2D6 enzyme with Quinidine increased in a linear dose-related fashion from -7.07% at 2.06 nM to 84.05% at 500 nM.
Conclusions: Purified Swedish pollen extract is a nonhormonal treatment of VMS that does not show inhibition of the CYP2D6 enzyme. This may have important clinical utility for women using tamoxifen for breast cancer treatment or chemoprevention who experience VMS.