Evaluation of Manuka Honey Estrogen Activity Using the MCF-7 Cell Proliferation Assay
Kathleen Henderson
Faculty of Life and Health Sciences, School of Biomedical Sciences, Ulster University, Cromore Road, Coleraine BT52 1SA, United Kingdom
Tahrir Aldhirgham
Faculty of Life and Health Sciences, School of Biomedical Sciences, Ulster University, Cromore Road, Coleraine BT52 1SA, United Kingdom
Poonam Singh Nigam
Faculty of Life and Health Sciences, School of Biomedical Sciences, Ulster University, Cromore Road, Coleraine BT52 1SA, United Kingdom
Richard Owusu-Apenten *
Faculty of Life and Health Sciences, School of Biomedical Sciences, Ulster University, Cromore Road, Coleraine BT52 1SA, United Kingdom
*Author to whom correspondence should be addressed.
Abstract
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.
Keywords: Manuka honey, estrogenic activity, breast cancer, antioxidant activity, E-SCREEN, MCF-7