Effect of Cinnamomum cassia Stem-Bark Extracts on the Synthesis and Secretion of Insulin in RIN-m5F Cells

Cinnamomum cassia (C. cassia) crude stem-bark extracts possess some hypoglycemic properties through inhibiting the uptake of glucose by the intestines and/or enhancing insulin sensitivity. To further investigate the mechanism through which the hypoglycemic effect is exerted, this research explored the influence of the extracts of the crude stem-bark of C. cassia, with various polarities, on particular aspects of glucose consumption as well as glucose-stimulated insulin synthesis and secretion by RIN-m5F cells. All C. cassia extracts did not enhance glucose consumption when compared to the untreated cells (p˂0.001). However, lower concentrations of the extracts significantly increased mRNA levels of Glucose Transporter 2 (GLUT2) and glucokinase genes. Furthermore, all C. cassia extracts significantly stimulated/increased total insulin synthesis (intracellular and secreted) when compared with the control cells, though the effect was not dose-dependent except for water extracts at higher concentration (p<0.001). The results of this investigation revealed that generally, the extracts upregulated the expression of Musculoaponeurotic fibrosarcoma homolog A (MafA), the transcription factor involved in insulin gene expression, while that of the Pancreatic Duodenal Homeobox-1 (PDX-1) gene was mostly suppressed. In concluding, the results of this study proposes that C. cassia stem-bark extracts may exert hypoglycemic effects through stimulating insulin synthesis and secretion in the RIN-m5F pancreatic beta cells.