Tocotrienols Stimulate Insulin Secretion of Rat Pancreatic Isolated Islets in a Dynamic Culture

Background: Tocotrienols (T3) are the naturally occurring vitamin E derivatives that possess antioxidant properties and therapeutic potential in diabetic complications. The bioactivities of the derivatives are determined by the number and arrangement of methyl substitution on the structure. Objective: The objective of this study was to determine the effects of T3 derivatives, delta-T3, gamma-T3 and alpha-T3 on insulin secretion of rat pancreatic islets in a dynamic culture. Method: Pancreatic islets isolated from male Wistar rats were treated with T3 for 1 h at 37 degrees C in a microfluidic system with continuous operation that provided a stable cell culture environment. Glucose (2.8 mM and 16.7 mM, as basal and stimulant, respectively) and potassium chloride (KCl) (30 mM) were added to the treatment in calcium free medium. The supernatant was collected for insulin measurements. Results: Short-term exposure (1 h) of delta-T3 to beta cells in the stimulant glucose condition significantly potentiated insulin secretion in a dose-dependent manner. gamma-T3 and alpha-T3 also displayed dose-dependent effect but were less effective in the activation of insulin secretion. Essentially, KCl, a pancreatic beta cell membrane depolarizing agent, added into the treatment further enhanced the insulin secretion of delta-T3, gamma-T3 and alpha-T3 with ED50 values of 504, 511 and 588 mu M, respectively. Conclusion: The findings suggest the potential of delta-T3 in regulating glucose-stimulated insulin secretion (GSIS) in response to the intracellular calcium especially in the presence of KCl.