Theaflavins prevent the onset of diabetes through ameliorating glucose tolerance mediated by promoted incretin secretion in spontaneous diabetic Torii rats
Baorui Li, Lei Fu, Ruchia Kojima, Ayaka Yamamoto, Tomoya Ueno, Toshiro Matsui
Abstract
The in vivo anti-hyperglycemic effect of non-absorbable theaflavins, polyphenolic ingredients of black tea, was evaluated in spontaneously diabetic Torii (SDT) rats. A mixture of theaflavins (25 mg/kg/day) was administered to 8-week (wk)-old SDT rats for 20 weeks, showing to improve the impaired glucose tolerance of 22-wk old pre-diabetic SDT rats in both an oral glucose tolerance test and in a plasma insulin evaluation. At 28-wk diabetic SDT rats presented with increased fasting blood glucose levels (139 ± 23 mg/dL), and the intake of the theaflavins significantly (p < 0.05) reduced this effect (74 ± 11 mg/dL), demonstrating an anti-diabetic effect in vivo. The 20 week administration of theaflavins induced increased incretin secretion compared to that of the control, while there were no changes neither in dipeptidyl peptidase-IV activity nor glucose transporter expression. Collectively, these findings demonstrate that non-absorbable theaflavins exert anti-pre-diabetic and anti-diabetic effects by improving impaired insulin secretion.