Establishment of a simple method to search natural products that suppress α-glucosidase amount in intestinal epithelial cell

Diabetes is a chronic disease characterized by elevated blood glucose level. α-Glucosidase is an enzyme involved in digestion of carbohydrates. Inhibition of α-glucosidase suppresses rapid and large increase in post-prandial blood glucose level, which is effective for the treatment of diabetes patients. On the other hand, reduction of α-glucosidase amount may work in the same way to treat diabetic patients. However, not much study is taking this approach to treat diabetes patients. Therefore, we established a simple method to examine the amount of α-glucosidase expressed by the small intestinal epithelial cells, which is useful to search natural products that decrease α-glucosidase amount.

Caco-2 cell is frequently employed as a model of intestinal epithelial cell, and is known to express α-glucosidase when differentiated. a-Glucosidase amount expressed by Caco-2 cell can be measured indirectly through the enzyme reaction rate. Addition of fluorescent substrate to Caco-2 cell induced a time dependent increase in fluorescence which reflects the enzyme reaction rate. With this simple method, several plant materials were screened for an activity to reduce α-glucosidase amount. Among the screened plants, Perilla frutescens var. crispa, and Calluna vulgaris were found to show reduction of α-glucosidase reaction rate in a dose dependent manner.

To confirm whether reduction of enzyme reaction rate reflect the reduction of α-glucosidase amount, α-glucosidase mRNA expression and protein amount were quantitated by real-time PCR and Western blotting. The extracts of P.frutescens and C.vulgaris suppressed sucrase-isomaltase, one of the intestinal α-glucosidase complexes, at mRNA and protein level, demonstrating that this method is useful to search natural products that suppress α-glucosidase amount.