Michio Aitani

Effects of Bay m 1099, an α-Glucosidase Inhibitor, on Starch Metabolism in Germinating Wheat Seeds

To examine the significance of α-glucosidase in starch metabolism in vivo, wheat seedlings and seeds were treated with Bay m 1099 (Miglitol, N-hydroxyethyl-1-deoxynojirimycin), an α-glucosidase inhibitor. Bay m 1099 did not affect germination, but it inhibited growth of seedlings at the high dosage (100 μg/ml medium). Treatment of normally grown seedlings with Bay m 1099 (10 and 100 μg/ml) decreased α-glucosidase activity with a dose response and caused accumulation of maltose in tissues with decreases in glucose. The decrease in glucose formation would inhibit plant growth, which was observed particularly at higher dosages of the inhibitor. When wheat seeds were treated with Bay m 1099 at 10 μg/ml for 4 days, under which the growth of the plants after germination was minimized, the induction of α-glucosidase, but not amylase, in kernels was considerably suppressed during germination and maltose metabolism to glucose was disturbed. In addition, the Bay m 1099 treatment decreased the initial rate of starch degradation by 48%, compared with the control. These results suggest that wheat α-glucosidase participates in maltose hydrolysis as well as in the onset of starch degradation with collaboration of amylase.

Purple Rice Extract Exhibits Preventive Activities on Experimental Diabetes Models and Human Subjects

Purple rice is colored rice containing anthocyanins and has mainly been consumed in Southeast Asian countries. Consumption of a large amount of rice would cause undesirable effects in patients with diabetes or high blood glucose. However, if the colored ingredients have antidiabetic effects, purple rice consumption may be an effective alternative dietary approach to prevent diabetes, instead of white rice. Thus, we evaluated the effect of Purple Rice Extract (PRE) on various diabetes models. PRE inhibited α-glucosidase, α-amylase and aldose reductase activities with IC50 values of 409, 135 and 26 μg/mL, respectively. In a diabetic retinopathy model using retinal microvascular endothelial cells, PRE (30 μg/mL) significantly suppressed cell damage induced by a high concentration of glucose. On the other hand, PRE significantly delayed starch and sucrose absorption at 3 and 1 g/kg, respectively, in rats. Moreover, single oral dosing of PRE (25 mg) to human subjects significantly suppressed postprandial blood sugar elevation after the ingestion of rice (200 g). These results suggest that PRE is effective for the control of blood sugar to prevent the progression of diabetic symptoms.

Effects of Bay m 1099, an α-Glucosidase Inhibitor, on Starch Degradation in Germinating Mung Beans

To examine the mechanism of starch degradation in legume cotyledons and the physiological role of α-glucosidase, mung bean seeds were germinated in the presence of Bay m 1099, an α-glucosidase inhibitor. Bay m 1099 (10 μg/ml medium), which minimized the growth deterioration of the mung bean seedlings, caused no changes in the overall rate of starch degradation and of soluble carbohydrate production in the cotyledons, although α-glucosidase activity had been completely suppressed. Total amylase and phosphorylase activities were not influenced by Bay m 1099. These results suggest that the mung bean α-glucosidase is less responsible for starch degradation, unlike wheat α-glucosidase [Konishi et al., Biosci. Biotech. Biochem., 58, 135-139 (1994)].