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Article

The Traditional Plant Treatment, Sambucus nigra (elder), Exhibits Insulin-Like and Insulin-Releasing Actions In Vitro¹

School of Biomedical Sciences, University of Ulster, Coleraine, Northern Ireland, BT52 1SA, United Kingdom

²To whom correspondence should be addressed.

Sambucus nigra (elder) has been documented as a traditional treatment of diabetes. In the present study, an aqueous extract of elder (AEE, 1 g/L) significantly increased 2-deoxy-glucose transport, glucose oxidation and glycogenesis of mouse abdominal muscle in the absence of added insulin (2 x 2 factorial design). in acute 20-min tests, 0.25–1 g/L AEE evoked a stepwise stimulation of insulin secretion from clonal pancreatic ß-cells. The insulin releasing effect of AEE (0.5 g/L) was significantly potentiated by 16.7 mmol/L of glucose and significantly reduced by 0.5 mmol/L of diazoxide. AEE did not further enhance insulin secretion in cells stimulated by 10 mmol/L of L-alanine, 1 mmol/L of 3-isobutyl-1-methylxanthine or a depolarizing concentration of KCl (25 mmol/L). Prior exposure of clonal pancreatic beta-cells to AEE did not alter subsequent stimulation of insulin secretion induced by 10 mmol/L of L-alanine, thereby precluding a detrimental effect on cell viability. The insulinotropic action of AEE was partially dependent upon use of heat during extract preparation. Activity of AEE was heat-stable, acetone-insoluble and unaltered by prolonged exposure to acid/alkali (0.1 mol/L of HCl and NaOH). However, activity was significantly decreased 41% by dialysis to remove components with molecular mass <2000 Da. Sequential extraction with solvents revealed activity in both methanol and water fractions, indicating a cumulative effect of more than one extract constituent. Known constituents of elder, including lectin, rutin and the lipophilic triterpenoid (lupeol) and sterol (ß-sitosterol), did not stimulate insulin secretion. The results demonstrate the presence of insulin-releasing and insulin-like activity in the traditional antidiabetic plant, Sambucus nigra.

KEY WORDS: • elder (Sambucus nigra) • streptozotocin-diabetic mice • insulin • traditional plant treatments • diabetes