To clarify the suppression of postprandial blood glucose rise via a a-glucosidase (AGH) inhibitory action by natural compounds, propolis was examined in this study. A single oral administration of propolis extract (50% methanol fraction on XAD-2 column chromatography) in Sprague-Dawley rats demonstrated a potent antihyperglycemic effect with the significant AUC 0-120 min reduction of 38% at a dose of 20 mg/kg compared to that of controls. Among the active compounds isolated from the fraction, 3,4,5-tri-caffeoylquinic acid was found to be a prominent candidate that exerts the effect and shows a strong maltase-specific inhibition with an IC 50 value of 24 m mM. In addition, the noncompetitive inhibition power apparently increased with the number of caffeoyl groups bound to quinic acid.

In order to evaluate the anti-hyperglycemic effect of natural compounds via the inhibition of alpha-glucosidase (AGH), the potential inhibitory effect of anthocyanins, caffeic acid analogs, and caffeoylquinic acid analogs have been reviewed. A new AGH assay system to mimic the membrane-bound AGH at the small intestine was proposed and evaluated.

Some Sri Lanka plant stuffs were examined regarding in vitro and in vivo alpha-glucosidase (AGH) inhibitory actions. According to the results, water extracts and methanol extracts of dried fruits of Nelli (Phylanthus embelica), methanol extracts of dried flowers of Ranawara (Cassia auriculata), and water extracts of latex of Gammalu (Pterocarpus marsupium) were found to have a potential AGH inhibitory activity. In particular, Ranawara methanol extract showed the strongest AGH inhibitory activity in vitro preferably on maltase giving an IC(50) value of 0.023 mg/mL and inhibited the maltase activity competitively. As a result of single oral administration of Ranawara (C. auriculata) methanol extract in Sprague-Dawley rats, a significant and potent lowering of blood glycemic response toward maltose ingestion was observed at 30 min after dosing of 5 mg/kg, thus, concurrently suppressed insulin activity. The ED(50) of the extract (4.9 mg/kg) clearly indicated that the antihyperglycemic effect was as potent as that of therapeutic drug, acarbose (ED(50) 3.1 mg/kg).

No abstract

Noninsulin-dependent diabetes mellitus (NIDDM), which is a major adult disease, is caused by a secretary decrease of insulin from pancreatic Langerhans β cells, or a lowering of the insulin resistance. 1 One of the most direct and beneficial types of therapy for NIDDM is achieved by control of the blood glucose level after a meal by delaying glucose absorption. 2 Among the therapeutic drugs used to prevent a high blood glucose level, the inhibitors of α-glucosidase (AGH, EC 3.2.1.20), which is a membrane-bound enzyme at the epithelium of the small intestine that catalyzes the cleavage of glucose from disaccharide, are effective for delaying glucose absorption. 3,4 To date, certain synthetic inhibitors of AGH 5 have been developed and used for the therapeutic treatment of NIDDM. 6 In the field of food chemistry, much attention has been devoted to a search for food materials with AGH inhibitory activity from natural resources and that have a high demand for a rapid and continuous assay method of AGH inhibitory activity. A spectrophotometric method using a pseudo-substrate, pnitrophenyl-α-D-glucopyranoside, and free AGH from baker's yeast has been widely used for in vitro assays. 7,8 It was pointed out, however, that the evaluated inhibitory effects of pharmaceuticals did not match with those obtained by an in vivo experiment. 9 The reason for this discordance comes from the difference in the environment of AGH in the mammalian intestine. We previously reported on a pseudo-in vivo assay system using immobilized rat intestinal AGH on Sepharose, which mimics the environment of the mammalian small intestine. 10 Biosensors still offer great potential as the next revolution in analysis. The high sensitivity of enzymes coupled with the electrochemical signal transducer should ideally result in an enzyme electrode capable of measuring the concentration of the substrate in a medium containing a diverse mixture of other compounds. 11 So far, the development of biosensors has focused on the system for a single channel. The development of a system for multi-channel biosensors is very important to increase the frequency of the sample treatment. We have been devoted to the development of multi-channel flow-type biosensors. 12-16 A micro titer plate detection system with 96-wells is another type of multi-channel detection system using immobilized enzymes. For instance, Ukeda et al. developed a spectrophotometric system which used immobilized enzymes on the surface of the micro titer plate. [17][18][19] Recently, a multi-channel dissolved oxygen meter (DOX96) was developed with the intention of making simultaneous evaluations of drug resistance for microorganisms. 20 Arai et al. inoculated mixtures of a test drug and a culture medium containing microorganisms in the wells of the electrode plate (96-wells, MEC-96), and evaluated the drug resistance by monitoring the oxygen consumption accompanying the respiration of viable microorganisms. 21 These kinds of evaluations, however, were qualitative with respect to measurements of th...