Antidiabetic effect of an active fraction extracted from dragon's blood (Dracaena Cochinchinensis)

The active fraction extracted from dragon's blood displayed an inhibitory effect on alpha-glucosidase activity with an IC50 of 0.152 microg/mL, which is nearly half of the crude material. Its inhibition on alpha-glucosidase was noncompetitive. In addition, when this fraction was orally administered to mice dosed with Acarbose (20 mg/kg), the active fraction (100, 300, 500 mg/kg) significantly suppressed increase of blood glucose levels after sucrose loading in a dose-dependent manner. These results suggest that this extract from dragon's blood exerts an anti-diabetic effect by suppressing intestinal carbohydrate absorption and thereby reducing the postprandial increase of blood glucose.     

alpha-Glucosidase inhibitors from the seeds of Syagrus romanzoffiana

Bioassay-guided fractionation against alpha-glucosidase resulted in isolation and characterization of eight active compounds from the EtOH extract of the seeds of Syagrus romanzoffiana. Of these, seven are stilbenoids, and two of them, 13-hydroxykompasinol A (1) and scirpusin C (4), possess potent inhibitory activity against alpha-glucosidase type IV from Bacillus stearothermophilus with the IC50 value of 6.5 and 4.9 microM, respectively. The in vivo assay on normal Wistar rats using oral sucrose challenge also demonstrated that kompasinol A (2) and 3,3',4,5,5'-pentahydroxy-trans-stilbene (5) possess significant effect in reducing the postprandial blood glucose level (10.2% and 12.1% at 10mg/kg, respectively). These results suggest that stilbenoids might be explored for their therapeutic potential as hypoglycemic agents.     

Suppressive effect of a hot water extract of adzuki beans (Vigna angularis) on hyperglycemia after sucrose loading in mice and diabetic rats

A hot water extract obtained by boiling adzuki beans (Vigna angularis) to produce bean paste for Japanese cake showed inhibitory activity against alpha-glucosidase, alpha-amylase, maltase, sucrase, and isomaltase after HP-20 column chromatography. The IC(50) values for each hydrolylase were 0.78 mg/ml (alpha-amylase), 2.45 mg/ml (maltase), 5.37 mg/ml (sucrase), and 1.75 mg/ml (isomaltase). The active fraction showed potential hypoglycemic activity in both normal mice and streptozotocin (STZ)-induced diabetic rats after an oral administration of sucrose, but did not show any effect on the blood glucose concentration after glucose administration, suggesting that the active fraction suppressed the postprandial blood glucose level by inhibiting alpha-glucosidase and alpha-amylase, irrespective of the endogenous blood insulin level.     

α-Glucosidase Inhibitory Activity of a 70% Methanol Extract from Ezoishige (Pelvetia babingtonii de Toni) and Its Effect on the Elevation of Blood Glucose Level in Rats

The 70% methanol extract from ezoishige (Pelvetia babingtonii de Toni) inhibited the rat-intestinal α-glucosidase, sucrase and maltase activities, with IC₅₀ values of 2.24 and 2.84 mg/ml. Sucrose was orally administered with or without the extract to rats at 1000 mg/kg. The postprandial elevation in the blood glucose level at 15 and 30 min after the administration of sucrose with the extract was significantly suppressed when compared with the control. These results suggest that the extract from ezoishige has potent α-glucosidase inhibitors and would be effective for suppressing postprandial hyperglycemia.     

Hypoglycemic effect of 13-membered ring thiocyclitol, a novel alpha-glucosidase inhibitor from Kothala-himbutu (Salacia reticulata)

A novel 13-membered ring thiocyclitol, isolated from an aqueous extract of Kothala-himbutu (Salacia reticulata), inhibited alpha-glucosidase in vitro. The inhibitory activity was investigated by maltose- and sucrose-loading on Wistar rats. This study found significant lowering of postprandial glucose levels, and the potency of 13-membered ring thiocyclitol was confirmed in vivo.     

Inhibition of Alpha-glucosidase and Amylase by Luteolin,a Flavonoid

Twenty-one naturally occurring flavonoids were tested for inhibitory activities against alpha-glucosidase (EC 3.2.1.20) and alpha-amylase (EC 3.2.1.1). Luteolin, amentoflavone, luteolin 7-O-glucoside, and daidzein were the strongest inhibitors among the compounds tested. Luteolin inhibited alpha-glucosidase by 36% at the concentration of 0.5 mg/ml and was stronger than acarbose, the most widely prescribed drug, in inhibitory potency, suggesting that it has the possibility to effectively suppress postprandial hyperglycemia in patients with non-insulin dependent diabetes mellitus. Luteolin also inhibited alpha-amylase effectively although it was less potent than acarbose. The clinical value of luteolin needs to be further evaluated.     

In vitro alpha-glucosidase and alpha-amylase enzyme inhibitory effects of Andrographis paniculata extract and andrographolide

There has been an enormous interest in the development of alternative medicines for type 2 diabetes, specifically screening for phytochemicals with the ability to delay or prevent glucose absorption. The goal of the present study was to provide in vitro evidence for potential inhibition of alpha-glucosidase and alpha-amylase enzymes, followed by a confirmatory in vivo study on rats to generate a stronger biochemical rationale for further studies on the ethanolic extract of Andrographis paniculata and andrographolide. The extract showed appreciable alpha-glucosidase inhibitory effect in a concentration-dependent manner (IC(50)=17.2+/-0.15 mg/ml) and a weak alpha-amylase inhibitory activity (IC(50)=50.9+/-0.17 mg/ml). Andrographolide demonstrated a similar (IC(50)=11.0+/-0.28 mg/ml) alpha-glucosidase and alpha-amylase inhibitory activity (IC(50)=11.3+/-0.29 mg/ml). The positive in vitro enzyme inhibition tests paved way for confirmatory in vivo studies. The in vivo studies demonstrated that A. paniculata extract significantly (P<0.05) reduced peak blood glucose and area under curve in diabetic rats when challenged with oral administration of starch and sucrose. Further, andrographolide also caused a significant (P<0.05) reduction in peak blood glucose and area under the curve in diabetic rats. Hence alpha-glucosidase inhibition may possibly be one of the mechanisms for the A. paniculata extract to exert antidiabetic activity and indicates that AP extract can be considered as a potential candidate for the management of type 2 diabetes mellitus.     

Antidiabetic properties of polysaccharide- and polyphenolic-enriched fractions from the brown seaweed Ascophyllum nodosum

We screened seaweed species from Atlantic Canada for antidiabetic activity by testing extracts for alpha-glucosidase inhibitory effect and glucose uptake stimulatory activity. An aqueous ethanolic extract of Ascophyllum nodosum was found to be active in both assays, inhibiting rat intestinal alpha-glucosidase (IC50 = 77 microg/mL) and stimulating basal glucose uptake into 3T3-L1 adipocytes during a 20-minute incubation by about 3-fold (at 400 microg/mL extract). Bioassay-guided fractionation of the A. nodosum extract showed that alpha-glucosidase inhibition was associated with polyphenolic components in the extract. These polyphenolics, along with other constituents appeared to be responsible for the stimulatory activity on glucose uptake. However, attempts to further concentrate this activity through fractionation techniques were unsuccessful. A crude polyphenol extract (PPE), an enriched polyphenolic fraction (PPE-F1) and a polysaccharide extract (PSE) were prepared from commercial A. nodosum powder and administered to streptozotocin-diabetic mice for up to 4-weeks by daily gavage at 200 mg/kg body mass. PPE and PPE-F1 improved fasting serum glucose level in diabetic mice; however, the effect was only statistically significant at day 14. In addition, PPE-F1 was shown to blunt the rise in blood glucose after an oral sucrose tolerance test in diabetic mice. Mice treated with PPE and PPE-F1 had decreased blood total cholesterol and glycated serum protein levels compared with untreated diabetic mice, whereas PPE also normalized the reduction in liver glycogen level that occurred in diabetic animals. All 3 A. nodosum preparations improved blood antioxidant capacity.     

Suppression of postprandial hypertriglyceridemia in rats and mice by oolong tea polymerized polyphenols

Oolong tea-polymerized polyphenols (OTPP) are characterized polyphenols produced from semi-fermented tea (oolong tea). In the present study, we evaluated the suppressive effects of oolong tea extract and OTPP on postprandial hypertriglyceridemia in rats and mice. Lymphatic recovery of triglycerides in rats cannulated in the thoracic duct was delayed by the administration of oolong tea extract at 100 and 200 mg per head, and more effectively than with green tea extract. OTPP delayed lymphatic triglyceride absorption at 20 mg/head, though (-)-epigallocatechin gallate (EGCG) did not do so at the same dose. OTPP also suppressed postprandial hypertriglyceridemia after administration of olive oil in mice. The area under the curve (AUC) of plasma triglycerides was significantly decreased, by 53% and 76%, in the 500 and 1,000 mg/kg OTPP groups respectively, as compared with the control group. These results suggest that OTPP is responsible for the suppression of hypertriglyceridemia by ingestion of oolong tea.     

Dose-Dependent Suppression of Tea Catechins with a Galloyl Moiety on Postprandial Hypertriglyceridemia in Rats

Tea has long been believed to be a healthy beverage, and its beneficial effects are almost all attributed to catechins. The effect of catechins on postprandial hypertriglyceridemia in rats was investigated in this study. A lipid emulsion administered orally to rats with (?)-epigallocatechin gallate at a dose of 100 mg/kg resulted in the increase in plasma triacylglycerol being significantly inhibited after 1 and 2 h compared to the case without (?)-epigallocatechin gallate. The effect of (?)-epigallocatechin was weaker than that of (?)-epigallocatechin gallate. A tea extract (THEA-FLAN 90S), mainly composed of catechins with a galloyl moiety, dose-dependently suppressed postprandial triacylglycerol after the administration of a lipid emulsion at doses of 50–200 mg/kg. The administration of the tea extract alone at a dose of 200 mg/kg had no effect on the plasma triacylglycerol level. These results strongly suggest that catechins with a galloyl moiety would be promising agents for suppressing dietary fat absorption through the small intestine.     

Dose-dependent suppression of tea catechins with a galloyl moiety on postprandial hypertriglyceridemia in rats

Tea has long been believed to be a healthy beverage, and its beneficial effects are almost all attributed to catechins. The effect of catechins on postprandial hypertriglyceridemia in rats was investigated in this study. A lipid emulsion administered orally to rats with (-)-epigallocatechin gallate at a dose of 100 mg/kg resulted in the increase in plasma triacylglycerol being significantly inhibited after 1 and 2 h compared to the case without (-)-epigallocatechin gallate. The effect of (-)-epigallocatechin was weaker than that of (-)-epigallocatechin gallate. A tea extract (THEA-FLAN 90S), mainly composed of catechins with a galloyl moiety, dose-dependently suppressed postprandial triacylglycerol after the administration of a lipid emulsion at doses of 50-200 mg/kg. The administration of the tea extract alone at a dose of 200 mg/kg had no effect on the plasma triacylglycerol level. These results strongly suggest that catechins with a galloyl moiety would be promising agents for suppressing dietary fat absorption through the small intestine.     

Anti-hyperglycemic activity of an aqueous extract from flower buds of Cleistocalyx operculatus (Roxb.) Merr and Perry

A screening of 5 plants used for making drinks in Vietnam revealed a Cleistocalyx operculatus (Roxb.) Merr and Perry flower bud extract to have the highest inhibitory activity against the alpha-glucosidase enzyme. The anti-hyperglycemic effects of an aqueous extract from flower buds of Cleistocalyx operculatus (CO), a commonly used material for drink preparation in Vietnam, were therefore investigated in vitro and in vivo. In vitro, the CO extract inhibited the rat-intestinal maltase and sucrase activities, with IC50 values of 0.70 and 0.47 mg/ml, respectively. These values are lower than those for a guava leaf extract (GE; IC50 0.97 and 1.28 mg/ml, respectively). Postprandial blood glucose testing of normal mice and STZ-induced diabetic rats by maltose loading (2 g/kg body weight (bw)) showed that the blood glucose reduction with CO (500 mg/kg bw) was slightly less than that with acarbose (25 mg/kg bw) but was more potent than that with GE (500 mg/kg bw). In an 8-week experiment, the blood glucose level of STZ diabetic rats treated with 500 mg of CO/kg bw/day was markedly decreased in comparison with that of non-treated diabetic rats. Consequently, CO is considered to be a promising material for preventing and treating diabetes.     

Antihyperglycemic effect of polyphenols from Acerola (Malpighia emarginata DC.) fruit

A crude acerola polyphenol fraction (C-AP) was prepared by subjecting an acerola extract to a C18 cartridge column, and eluting the adsorbed fraction with ethanol containing 10% of acetic acid. C-AP appeared in a previous study to have an inhibitory effect on alpha-glucosidase and particularly on maltase activities. To elucidate the antihyperglycemic effect of C-AP further, we examined the regulation by C-AP of glucose uptake in Caco-2 cell; this resulted in the inhibition of glucose uptake. We next conducted single administration tests of glucose and maltose to ICR mice to investigate whether C-AP really controlled the intestinal glucose absorption in an animal body. The results showed that C-AP significantly suppressed the plasma glucose level after administering both glucose and maltose, suggesting that C-AP had a preventive effect on hyperglycemia in the postprandial state. The mechanism for this effect is considered to have been both suppression of the intestinal glucose transport and the inhibition of alpha-glucosidase. Despite such a preventive effect, the therapeutic effect of C-AP on hyperglycemia appeared to be low from the experiment with KKAy mice.     

Suppressive effect of peach leaf extract on glucose absorption from the small intestine of mice

The crude extract of peach leaves dose-dependently suppressed the postprandial elevation in the blood glucose level after an oral administration of soluble starch to mice. This study examines the mechanism for this suppressive effect in vivo. An oral carbohydrate-loading test on mice showed that the peach leaf extract suppressed the glucose-induced increase in the blood level of glucose, but without affecting the insulin level. An enteral soluble starch and glucose loading test on mice also showed that the crude extract (1,000 mg/kg) significantly suppressed the postprandial elevation of the blood glucose level and increased the amount of glucose that remained in the intestine to within the same range as that with phloridzin (500 mg/kg), a natural sodium-dependent glucose transporter (SGLT)-specific inhibitor. In contrast, the extract did not suppress the postprandial elevation of the blood triglyceride and cholesterol levels in mice, and did not affect the normal blood glucose level in a feeding test for 21 d. These results reveal that the extract of peach leaves suppressed the postprandial elevation of blood glucose level by inhibiting the absorption of glucose in the small intestine of mice.     

Hypoglycemic activity of the antioxidant saponarin, characterized as alpha-glucosidase inhibitor present in Tinospora cordifolia

Tinospora cordifolia, used in anti-diabetic herbal drug preparations, was reported [12] to contain an alpha-glucosidase inhibitor, characterized as saponarin (apigenin-6-C-glucosyl-7-O-glucoside). The leaf extract had appreciable antioxidant and hydroxyl radical scavenging activities and contained the flavonoid in the range of 32.1 +/- 1.5-45.5 +/- 3.5 mg/g of dry solid. Saponarin showed mixed competitive inhibition on activities of alpha-glucosidase and sucrase of different origins. IC(50), Ki and ki' values determined were 48 muM, 8 muM and 19.5 microM respectively for intestinal maltase and 35 microM, 6 microM and 13 microM respectively for intestinal sucrase. When given orally to maltose-fed rat, saponarin showed hypoglycemic activity in the range of 20-80 mg/kg compared to 100-200 mg/kg for acarbose as reported.     

Luteolin,a flavone,does not suppress postprandial glucose absorption through an inhibition of alpha-glucosidase action

In order to clarify the postprandial glucose suppression via alpha-glucosidase (AGH) inhibitory action by natural compounds, flavonoids were examined in this study. Among the flavonoids (luteolin, kaempferol, chrysin, and galangin), luteolin showed the potent maltase inhibitory activity with the IC50 of 2.3 mM, while less inhibitions were observed against sucrase. In addition, the effects of maltase inhibition by flavonoids were observed in the descending order of potency of luteolin > kaempferol > chrysin > galangin. Apparently, the AGH inhibition power greatly increased with the replacement of hydroxyl groups at 3' and 4'-position of the B-ring. However, the inhibitory power of luteolin was poorer than a therapeutic drug (acarbose: IC50; 430 nM). As a result of a single oral administration of maltose or sucrose (2 g/kg) in SD rats, no significant change in blood glucose level with the doses of 100 and 200 mg/kg of luteolin was observed. These findings strongly suggested that luteolin given at less than 200 mg/kg did not possess the ability to suppress the glucose production from carbohydrates through the inhibition of AGH action in the gut.     

Effect of physiological (in lamb) or drug-induced (in adult) immaturity of ram spermatozoa on seminal plasma alpha-glucosidase activity

We have been able to collect ejaculates from four pre-pubertal Finnish Landrace and Suffolk lambs. Respective seminal plasma alpha-glucosidase specific activity was low (less than 0.3 mU/mg) whatever the season of observation. At puberty, it reached a level higher than 1 mU/mg as observed in adult rams. Administration of alpha-chlorohydrin to 14 adult rams (25 mg/kg/day during 25 days) led to the appearance of immature sperm. Seminal plasma alpha-glucosidase activity dropped from 1.5 to 0.5 mU/mg in both breeds, while fructose was raised from 2 to 6 mg/ml. L-carnitine and blood plasma testosterone remained unchanged during treatment. Semen characteristics appeared normal one month after the end of treatment when fructose concentration decreased simultaneously and enzymatic activity increased during two months to normal levels. The present findings suggest that seminal plasma alpha-glucosidase may be considered as a useful epididymal marker in ram.     

A study of the influence of yeast cell debris on protein and alpha-glucosidase adsorption at various zones within the expanded bed using in-bed sampling

Expanded bed adsorption chromatography is used to capture products directly from unclarified feedstocks, thus combining solid-liquid separation, product concentration and preliminary purification into a single step. However, when non-specific ion-exchangers are used as the adsorbent in the expanded bed, there is the possibility that electrostatic interactions of cells or cell debris with the adsorbent may interfere with the adsorption of soluble products. These interactions depend on the particle size of the cell debris and its surface charge, which in turn depend on the extent of disruption used to release the intracellular products. The interactions occurring during expanded bed adsorption between the anionic ion-exchanger STREAMLINE DEAE and particulate yeast homogenates obtained by high pressure homogenisation at different intensities of disruption achieved by operating at different pressures were studied, while maintaining all other parameters constant. In-bed sampling from the expanded bed using ports fitted up the height of expanded bed was used to study the retention of yeast cells and cell debris within the bed and its influence on the adsorption of total soluble protein and alpha-glucosidase within various zones of the expanded bed. The retention of the biomass present in the homogenate obtained at a lower intensity of disruption was found to be high at the lower end of the column (17% from 13.8 MPa sample compared to 1% from 41.4 MPa sample). This interaction of the particulate material with the adsorbent was found to reduce the dynamic binding capacity of the adsorbent for total soluble protein from 3.6 mg/mL adsorbent for 41.4 MPa sample to 3.0 mg/mL adsorbent for 13.8 MPa sample. The adsorption of alpha-glucosidase was found to increase with an increase in the concentration of the enzyme in the feed, which increased with the intensity of disruption. Selective adsorption of 6,732 U alpha-glucosidase per mg of total protein bound, was noticed for the feedstock prepared at a higher disruption intensity at 41.4 MPa compared to adsorption of 1,262 U/mg of total protein bound for that prepared at 13.8 MPa. The selective adsorption of alpha-glucosidase due to its high concentration together with simultaneous high specific activity of the enzyme in the feed indicated the significance of selective release of enzymes during microbial cell disruption for efficient expanded bed adsorption processes.     

Effects of prolonged (6 months) alpha-glucosidase inhibition on blood glucose control and insulin requirements in patients with insulin-dependent diabetes mellitus

To examine prolonged alpha-glucosidase inhibition on blood glucose control, Acarbose, a potent alpha-glucosidase inhibitor, was administered for six months to insulin-dependent diabetic patients. Acarbose administration significantly diminished postprandial blood glucose increases by 20-30% and reduced insulin requirements by about 40% in these patients. Symptoms related to its use almost disappeared after the first month of treatment. These results suggest that prolonged alpha-glucosidase inhibition improves glucose tolerance in patients with insulin-dependent diabetes mellitus. Thus, an agent like acarbose might be a useful adjunct to insulin in the treatment of diabetic patients.     

Production and properties of alpha-glucosidase from Lactobacillus acidophilus.

Lactobacillus acidophilus IFO 3532 was found to produce only intracellular alpha-glucosidase (alpha-D-glucoside glucohydrolase; EC 3.2.1.20). Maximum enzyme production was obtained in a medium containing 2% maltose as inducer at 37 degrees C and at an initial pH of 6.5. The enzyme was formed in the cytoplasm and accumulated as a large pool during the logarithmic growth phase. Enzyme production was strongly inhibited by 4 microM CuSO4, 40 microM CoCl2, and beef extract; MnSO4 and the presence of proteose peptone and yeast extract in the medium greatly enhanced enzyme production. A 16.6-fold purification of alpha-glucosidase was achieved by (NH4)2SO4 fractionation and DEAE-cellulose column chromatography. The enzyme showed high specificity for maltose. The Km for alpha-p-nitrophenyl-beta-D-glucopyranoside was 11.5 mM, and the Vmax for alpha-p-nitrophenyl-beta-D-glucopyranoside hydrolysis was 12.99 mumol/min per mg of protein. The optimal pH and temperature for enzyme activity were 5.0 and 37 degrees C, respectively. The enzyme activity was inhibited by Hg2+, Cu2+, Ni2+, Zn2+, Ca2+, Co2+, urea, rose bengal, and 2-iodoacetamide, whereas Mn2+, Mg2+, L-cysteine, L-histidine, Tris, and EDTA stimulated enzyme activity. Transglucosylase activity was present in the partially purified enzyme, and isomaltose was the only glucosyltransferase product. Amylase activity in the purified preparation was relatively weak, and no isomaltase activity was detected.