Theaflavins prevent the onset of diabetes through ameliorating glucose tolerance mediated by promoted incretin secretion in spontaneous diabetic Torii rats

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.