Anti-hyperglycaemic and insulin releasing effects of Camellia sinensis leaves and isolation and characterization of active compounds

Prawej Ansari, PR Flatt, P Harriott, Yasser Abdel-Wahab

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Abstract

Antidiabetic actions of Camellia sinensis leaves, used traditionally for type 2 diabetes (T2DM) treatment, have been determined. Insulin release, membrane potential and intracellular calcium ([Ca2+]i) were studied using the pancreatic beta-cell line, BRIN-BD11, and primary mouse pancreatic islets. Cellular glucose-uptake/insulin action by 3T3-L1 adipocytes, starch digestion, glucose diffusion, DPP-IV activity and glycation were determined together with in vivo studies assessing glucose homeostasis in high fat fed (HFF) rats. Active phytoconstituents with insulinotropic activity were isolated using RP-HPLC, LCMS and NMR. Hot water extract of Camellia sinensis, increased insulin secretion in concentration dependent manner. Insulinotropic effects were significantly reduced by diazoxide, verapamil and under calcium-free conditions, being associated with membrane depolarization and increased intracellular Ca2+. Insulin releasing effects were observed in presence of KCl, tolbutamide and IBMX, indicating actions beyond K+ and Ca2+channels. Extract also increased glucose uptake/insulin action in 3T3L1 adipocyte cells and inhibited protein glycation, DPP-IV enzyme activity, starch digestion and glucose diffusion. Oral administration of extract enhanced glucose tolerance and insulin release in HFF rats. Extended treatment (250mg/5ml/kg orally) for 9 days, led to improvements of body weight, energy intake, plasma and pancreatic insulin, and corrections of both islet size and β-cell mass. These effects were accompanied by lower glycaemia and significant reduction of plasma DPP-IV activity. Compounds isolated by HPLC/LCMS, isoquercitrin and rutin (464.2 Da & 610.3 Da), stimulated insulin release and improved glucose tolerance. These data indicate that Camellia sinensis leaves warrant further evaluation as an effective adjunctive therapy for T2DM and source of bioactive compounds.
Original languageEnglish
Pages (from-to)xx
JournalBritish Journal of Nutrition
Volumexx
Early online date17 Dec 2020
DOIs
Publication statusE-pub ahead of print - 17 Dec 2020

Keywords

  • Diabetes
  • insulin
  • glucose
  • DPP-IV
  • phytochemicals

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