• Determination of Iron (III) Reducing Antioxidant Capacity for Manuka Honey and Comparison with ABTS and Other Methods

      Yusof, Hasif I. M.; Owusu-Apenten, Richard K.; Nigam, Poonam S.; Universiti Kebangsaan Malaysia Medical Centre; Ulster University; University of Chester (SCIENCEDOMAIN International, 2018-06-11)
      Aims: Applying multiple assays with trolox as the sole reference compound is a recent AOAC proposal to improve the reliability of total antioxidant capacity determinations. The aim of this study was to evaluate, iron (III) reducing antioxidant capacity (iRAC) for Manuka honey samples and comparisons with ABTS and other well-known assays. Study Design: In-vitro, laboratory-based study. Place and Duration of Study: School of Biomedical Sciences, Faculty of Life and Health Sciences, Ulster University, Cromore Road, Coleraine, BT52 1SA, UK; September 2015-May 2016. Methodology: Manuka honey rated Unique Manuka Factor (UMF) 5+, 10+, 15+, 18+ and a nonrated (NR) sample were analysed using five assays for total antioxidant capacity namely, iRAC, ABTS, DPPH, FRAP, and Folin assays. Values for total antioxidant capacity were normalized as Trolox Equivalent Antioxidant capacity (TEAC) for comparison within and between assays. Results: The TAC were correlated for all methods (R2 = 0.83-0.99) and also correlated with the total phenols content. Actual TEAC value for a given honey ranged by 21-70-fold depending on the assay method with the following general order of increase; DPPH < FRAP (pH 3.6) < iRAC (pH 7.0) <ABTS (pH7) < Folin (pH ~11). The trends in TAC values are discussed alongside of TEAC values for 50 food items and some challenges for comparing different antioxidant methods are highlighted. Conclusion: Total antioxidant capacity of Manuka honey changes in a regular manner probably affected by assay pH. The findings are important for attempts to standardize antioxidant methods as currently applied to foods, beverages and dietary supplements. Further research is recommended to examine the effect of normalizing antioxidant methods for solvent composition and pH.
    • Effect of Methotrexate and Tea Polyphenols on the Viability and Oxidative Stress in MDA-MB-231 Breast Cancer Cells

      Owusu-Apenten, Richard K.; Kelly, Theresa; University of Ulster (SCIENCEDOMAIN International, 2015-03-24)
      Aim: To determine the effect of tea polyphenols and methotrexate on viability and reactive oxygen species (ROS) in a naturally resistant breast cancer cell line MDA-MB-231. Methodology: MDA-MB-231 cells were selected as a model for methotrexate resistant breast cancer. Drug tests were performed over 72 hours at concentrations 0-100 µM. Pre-treatments were with quercetin (QE) or epigallocatechin gallate (EGCG) for 5 hours followed by methotrexate. Cytotoxicity was measured using the MTT assay or resazurin fluorescence assay. ROS was determined using the 2’, 7’-dichlorofluorescein diacetate assay. Intracellular GSH was measured using the monochlorobimane assay. Results: Methotrexate was cytotoxic to MDA-MB-231 cells with IC50 of 35±4 µM. The IC50 value was 68±9.4 µM with QE and 83±16 µM for EGCG. The pre-treatment with QE and EGCG lowered the IC50 for methotrexate by 28% (P =0.009) and 16% (P=0.2027). Intracellular ROS concentrations increased after treatment with methotrexate, QE or EGCG singly and ROS decreased with combination treatment compared with the response for methotrexate only. There were no significant changes in intracellular GSH. Conclusion: Pretreatment with tea polyphenols partially sensitized breast cancer cells towards methotrexate and decreases intracellular ROS. More research is needed to optimize the sensitizing effect of tea phenols on the breast cancer cell response to methotrexate.