Evaluation of Manuka Honey Estrogen Activity Using the MCF-7 Cell Proliferation Assay

Aims: To assess the estrogenic activity of Manuka honey using the MCF7 cell proliferation assay.

Study Design: In vitro cell based E-screen.

Place and Duration of Study: Ulster University, Coleraine, UK, September 2015 to September 2016.

Methodology: Manuka honey (UMF15+) was characterized for total phenolic content (TPC) using the Folin-Ciocalteu assay and antioxidant power, using the 2, 2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) assay. Estrogenic activity was assessed using MCF-7 cells cultured in DMEM-F2 phenol red-free media supplemented with 10% charcoal stripped FBS and evaluated using Sulforhodamine B (SRB) colorimetric assay. All experiments were conducted in triplicate (n-12-48) and genistein was the positive control. The effect of Manuka honey (UMF15+) treatment on intracellular reactive oxygen species (ROS) was measured using the 2'-7'-dichlorodihydrofluorescein diacetate (DCFH-DA) assay.

Results: Manuka honey (UMF15+) antioxidant power was related to total phenols content. MCF7 growth promotion occurred at very low concentrations of honey (5x10-6-5x10-3% v/v honey; or 2.75 x10-10M - 2.75 x10-7 M TPC) indicative of estrogenic activity whilst higher concentrations of honey (>0.5% v/v) were inhibitory. Similarly, the genistein positive control demonstrated estrogenic activity indicated by MCF-7 cell growth at low concentrations (5x10-9-5x10-8 M) and toxicity at high concentrations. Estrogenic characteristics were quantified in terms of the relative proliferative potency (RPP) and relative proliferative effect (RPE) for Manuka honey of 18% and 22.5-27.5%, respectively. For genistein RPP was 0.1% and RPE was 70% compared to values of 100% for estradiol. Intracellular ROS increased for MCF-7 cells treated with increasing honey concentrations.

Conclusion: Manuka honey (UMF15+) exhibits estrogenic activity monitored as growth promotion of MCF-7 breast cancer cells with estrogenic parameters being comparable to values reported for some purified flavonoids. Treatment of MCF-7 cells produced a dose-dependent rise in intracellular ROS.