In vitro Antioxidant Activity and Polyphenolic Content of a Polyherbal Tea and Its Constituents

Abstract

Aims: Type 2 diabetes mellitus (T2DM) is associated with debilitating co-morbidities, mainly due to chronic hyperglycaemia-induced damage which is mediated by excess reactive oxygen species (ROS). Plant preparations have been shown to contain polyphenolic compounds that function as antioxidants. Various herbal teas have been sold as treatment of diabetes mellitus.  The aim of this study was to evaluate a commercial, polyherbal tea, Diabetea and its constituents: Achillea millefolium L., Agathosma betulina Bartl. & Weidl., Salvia officinalis. L., Taraxacum officinalis L., Thymus vulgaris. L., Trigonella foenum-graecum L. and Urtica urens L. to assess their antioxidant and polyphenolic content. Methodology: The polyphenol-linked cell-free and cell-based antioxidant activities of hot water (HW) and dichloromethane (DCM) extracts of Diabetea and its constituents were evaluated for ABTS●+ and DPPH● radical scavenging ability and for ROS scavenging activity using 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) in Ea.hy926 endothelial cells, respectively. The phenolic and flavonoid content was also assessed.  Results: All HW extracts were rich in polyphenols. T. vulgaris contained the highest amount of flavonoids (760.2±1.3 mg rutin equivalent (RE)/g) of all extracts, followed by S. officinalis (491.7±12.5 mg RE/g). The extracts of T. vulgaris were the most active against ABTS●+ (~600.0 mg trolox equivalents (TE)/g activity) and DPPH● (535.0 mg TE/g activity). The HW extracts of T. vulgaris, S. officinalis and U. urens significantly (p<0.05) mitigated cellular ROS, whereas none of the DCM extracts had this effect. The HW extracts of the Diabetea, A. betulina, T. officinalis and T. foenum-graecum and most DCM extracts (exception A. betulina) had a significant (p<0.05) intracellular pro-oxidant activity. The cell-free antioxidant activity of the HW extracts correlated significantly (r=0.98) with its polyphenolic content.  Conclusion: Diabetea exerted strong cell-free antioxidant activity. The HW extracts contained greater polyphenol-linked antioxidant activity than the DCM extracts. The HW extracts of T. vulgaris, S. officinalis and U. urens contain bioactive compounds that exert in vitro antidiabetic potential. Identification of the compounds responsible for this activity is warranted.