Anti-hyperglycemic activity of polyphenols isolated from barnyard millet (Echinochloa utilis L.) and their role inhibiting α-glucosidase

The extracts and chemical compounds isolated from barnyard millet (Echinochloa utilis) grains were investigated as part of a search for naturally derived anti-hyperglycemic medicinal plants. Among the five different solvent extracts, the ethyl acetate extract showed the lowest IC₅₀ value against Saccharomyces cerevisiae α-glucosidase (70.2 μg/mL). Chromatography yielded eight phenolic compounds that may have been responsible for this effect. Among them, N-p-coumaroyl serotonin (1, CS), feruloyl serotonin (2, FS), and luteolin (5) potently inhibited α-glucosidase with IC₅₀ values of 1.3–17.8 μM compared with those of deoxynojirimycin (DNJ, IC₅₀ = 2.5 ± 0.1 μM) and acarbose (IC₅₀ = 255.1 ± 15.6 μM). Additionally, for the first time, we found that CS and FS were significantly inhibited mammalian rat intestinal sucrase (IC₅₀ of 3.0 and 8.2 μM) and reduced glucose content (73 and 52 % at 0.1 mg/wells) in Caco-2 (human intestinal epithelial) cells. Furthermore, oral glucose tolerance test revealed improved glucose tolerance following treatment with the barnyard millet grains extract by retarding the postprandial rise in blood glucose in vivo. These results suggest that barnyard millet grain can be used as a natural functional medicine to prevent and alleviate type-2 diabetes.