Sugar beet α-glucosidase (SBG), a member of glycoside hydrolase family 31, shows exceptional long-chain specificity, exhibiting higher kcat/Kms for longer maltooligosaccharides. However, its amino acid sequence is similar to other short-chain-specific α-glucosidases. To gain structural insights into the long-chain-substrate recognition of SBG, a crystal structure complex with the pseudotetrasaccharide, acarbose, was determined at 1.7 Å resolution. The active site pocket of SBG was formed by a (β/α)8 barrel domain and a long loop (the N-loop) bulging from the N-terminal domain similar to other related enzymes. Two residues, Phe236 and Asn237 in the N-loop were important for the long-chain specificity. Kinetic analysis of an Asn237 mutant enzyme and a previous study of a Phe236 mutant enzyme demonstrated that these residues create subsites +2 and +3. The structure also indicated that Phe236 and Asn237 guided the reducing end of long substrates to subdomain b2, which is an additional element inserted into the (β/α)8 barrel domain. Subdomain b2 of SBG included Ser497, which was identified as the residue at subsite +4 by site-directed mutagenesis.

A truncated form of an α-amylase, GTA, from thermophilic Geobacillus thermoleovorans CCB_US3_UF5 was biochemically and structurally characterized. The recombinant GTA, which lacked both the N- and C-terminal transmembrane regions, functioned optimally at 70°C and pH 6.0. While enzyme activity was not enhanced by the addition of CaCl2, GTA's thermostability was significantly improved in the presence of CaCl2. The structure, in complex with an acarbose-derived pseudo-hexasaccharide, consists of the typical three domains and binds one Ca(2+) ion. This Ca(2+) ion was strongly bound and not chelated by EDTA. A predicted second Ca(2+)-binding site, however, was disordered. With limited subsites, two novel substrate-binding residues, Y147 and Y182, may help increase substrate affinity. No distinct starch-binding domain is present, although two regions rich in aromatic residues have been observed. GTA, with a smaller domain B and several shorter loops compared to other α-amylases, has one of the most compact α-amylase folds that may contribute greatly to its tight Ca(2+) binding and thermostability.

We here report a quantitative study on the binding kinetics of inhibition of the enzyme glucoamylase and how individual active site amino acid mutations influence kinetics. To address this challenge, we have developed a fast and efficient method for anchoring native acarbose to gold chip surfaces for surface plasmon resonance studies employing wild type glucoamylase and active site mutants, Y175F, E180Q, and R54L, as analytes. The key method was the chemoselective and protecting group-free oxime functionalization of the pseudo-tetrasaccharide-based inhibitor acarbose. By using this technique we have shown that at pH 7.0 the association and dissociation rate constants for the acarbose-glucoamylase interaction are 10(4)M(-1)s(-1) and 10(3)s(-1), respectively, and that the conformational change to a tight enzyme-inhibitor complex affects the dissociation rate constant by a factor of 10(2)s(-1). Additionally, the acarbose-presenting SPR surfaces could be used as a glucoamylase sensor that allowed rapid, label-free affinity screening of small carbohydrate-based inhibitors in solution, which is otherwise difficult with immobilized enzymes or other proteins.

Objective:

To evaluate the effect and safety of HbA1c and glycemic control of acarbose chewable tablets in patients with type 2 diabetic. Method: A multicentre, randomized, double-blinded, double-dummy, positive controlled clinical trial was conducted. Two hundred thirty-four Chinese patients with type 2 diabetic were enrolled in eight clinical centres, who were divided randomly into the acarbose chewable tablet group (experimental group, n = 116) and the acarbose treatment group (control group, n = 118).

Results:

Two hundred seven patients (88.5%) took part in the 12-week trial. At the beginning and end of the clinical trial, HbA1c and blood glucose as well as safety indexes were measured. After the treatment, the level of finger two-hour postprandial blood glucose (PPBG) was decreased 4.15 mmol/L (26.82%) and 3.54 mmol/L (22.77%), respectively, in the experiment group and the control group. The levels of venous two-hour PPBG in the experiment group and the control group were decreased 4.04 mmol/L (25.38%) and 2.75 mmol/L (17.26%), respectively, with the means of HbA1c lowering 11.67% and 12.44%, respectively. Fasting blood glucose (FBG) also was reduced significantly in both groups. Patients in both groups showed obvious weight reduction (P < 0.0001). There were no significant differences in the incidence of adverse events between the two groups.

Conclusion:

In summary, acarbose chewable tablets have a definite curative effect in treating type 2 diabetic patients as HbA1c and blood glucose levels decreased significantly after the 12-week treatment.

This study was designed to investigate whether daidzein inhibits α-glucosidase and α-amylase activities and alleviates postprandial hyperglycemia in streptozotocin-induced diabetic mice. Daidzein showed prominent inhibitory effects against α-glucosidase and α-amylase. The IC50 values of daidzein against α-glucosidase and α-amylase were 0.048 and 0.301mmol, respectively, which showed that daidzein was more effective than acarbose. The increase in postprandial blood glucose levels was more significantly suppressed in the daidzein-administered group than in the water group of both streptozotocin-induced diabetic and normal mice. Moreover, the area under the curve was significantly lowered following daidzein administration (2043 versus 2475mmolminl) in the streptozotocin-induced diabetic mice. These results indicated that daidzein may be a potent α-glucosidase inhibitor and suppress the postprandial hyperglycemia caused by starch.

  We are studying the medicinal synthetic chemistry of biomolecular component mimics such as carbohydrates, nucleosides, amino acids, and peptides. In this review, the synthesis and biological activities of iminosugars as carbohydrate mimics are discussed. Glycosidases and glycosyltransferases are involved in a wide range of anabolic and catabolic process, including digestion, the lysosomal catabolism of glycoconjugates, glycoprotein biosynthesis. Hence, modifying or blocking these processes in vivo using inhibitors is a topic of great interest from the therapeutic point of view. Iminosugars are sugars in which the endocyclic oxygen is replaced by a basic nitrogen atom. They are regarded as transition state mimics in certain types of enzyme reactions. This makes the field of iminosugars as carbohydrate mimics an exciting area of research. We synthesized all of the stereoisomers of polyhydroxypiperidines such as fagomine, 1-deoxynojirimycine, and isofagomine. In addition, their both enantiomers, as substrates for a variety of glycosidases were evaluated. Secondly, the asymmetric synthesis of α-1-C-alkyl-arabinoiminofuranoses was achieved by asymmetric allylic alkylation, RCM, and Negishi cross coupling as key reactions. Surprisingly, the L-forms showed a quite potent inhibitory activity toward rat intestinal maltase, while the activities of the D-forms were much weaker. Some of the prepared L-forms showed potent inhibitory activities towards intestinal maltase, with IC50 values comparable to those of commercial drugs such as acarbose, voglibose, and miglitol, which are used in the treatment of type 2 diabetes. Among them, the inhibitory activity towards intestinal sucrase of α-1-C-L-butylarabinoiminofuranose was quite strong towards intestinal sucrase compared to the above commercial drugs.

Treatment with the alpha-glucosidase inhibitor (AGI) acarbose is associated with a significant reduction the risk of cardiovascular events. However, the underlying mechanisms of this effect are unclear. AGIs were recently suggested to participate in stimulating glucagon-like peptide 1 (GLP-1) secretion. We therefore examined the effects of a 24-week treatment of acarbose on endogenous GLP-1, nitric oxide (NO) levels, nitric oxide synthase (NOS) activity, and carotid intima-media thickness (CIMT) in newly diagnosed patients with type 2 diabetes (T2D).Blood was drawn from 24 subjects (14 male, 10 female, age: 50.7 ± 7.36 years, BMI: 26.64 ± 3.38 kg/m2, GHbA1c: 7.00 ± 0.74%) with drug-naïve T2D at 0 and 120 min following a standard mixed meal for the measurements of active GLP-1, NO and NOS. The CIMT was measured prior to and following 24 weeks of acarbose monotherapy (mean dose: 268 mg daily).Following 24 weeks of acarbose treatment, both fasting and postprandial plasma GLP-1 levels were increased. In patients with increased postprandial GLP-1 levels, serum NO levels and NOS activities were also significantly increased and were positively related to GLP-1 levels. Although the CIMT was not significantly altered following treatment with acarbose, a decreased CIMT was negatively correlated with increased GLP-1 levels.Twenty-four weeks of acarbose monotherapy in newly diagnosed patients with T2D is associated with significantly increased levels of both fasting and postprandial GLP-1 as well as significantly increased NO levels and NOS activity for those patients in whom postprandial GLP-1 levels were increased. Therefore, the benefits of acarbose on cardiovascular risk may be related to its stimulation of GLP-1 secretion.

Abstract

Background:

Recent studies have identified postprandial glycemic excursions as risk factors for diabetes complications. This study aimed to compare the effects of nateglinide and acarbose treatments on postprandial glycemic excursions in Chinese subjects with type 2 diabetes. Subjects and

Methods:

This was a multicenter, open-label, randomized, active-controlled, parallel-group study. One hundred three antihyperglycemic agent-naive subjects with type 2 diabetes (hemoglobin A1c range, 6.5-9.0%) were prospectively recruited from four hospitals in China. The intervention was nateglinide (120 mg three times a day) or acarbose (50 mg three times a day) therapy for 2 weeks. A continuous glucose monitoring system was used to calculate the incremental area under the curve of postprandial blood glucose (AUCpp), the incremental glucose peak (IGP), mean amplitude of glycemic excursions, SD of blood glucose, the mean of daily differences, and 24-h mean blood glucose (MBG). Subjects' serum glycated albumin and the plasma insulin levels were also analyzed.

Results:

Both agents caused significant reductions on AUCpp and IGP. Similarly, both treatment groups showed significant improvements in the intra- and interday glycemic excursions, as well as the 24-h MBG and serum glycated albumin compared with baseline (P<0.001). However, neither of the agents produced a significantly better effect (P>0.05). Moreover, the nateglinide-treated group had significantly increased insulin levels at 30 min and at 120 min after a standard meal compared with baseline, whereas the acarbose-treated group decreased. No serious adverse events occurred in either group. The rates of hypoglycemic episodes were comparable in the two groups, and no severe hypoglycemic episode occurred in either group.

Conclusions:

Nateglinide and acarbose were comparably effective in reducing postprandial glycemic excursions in antihyperglycemic agent-naive Chinese patients with type 2 diabetes, possibly through different pathophysiological mechanisms.

The prevalence of type 2 diabetes is increasing dramatically in the Middle East and North Africa region. However, there are few trials that have determined the effect of antidiabetic treatment in an observational setting in these countries.This was a noninterventional study performed in Morocco in 2006-2007 and in the Middle East in 2005-2006 to observe the efficacy and safety of acarbose in patients with pretreated or untreated type 2 diabetes. Glycemic parameters (fasting blood glucose, one-hour postprandial blood glucose, and HbA1c) were recorded within a 3-month period. The observation period included an initial visit at the start of acarbose therapy and up to three follow-ups.Acarbose was effective in reducing glycemic parameters in patients from Morocco (n = 1082) and the Middle East (n = 1737). The mean one-hour postprandial blood glucose decreased by 35.5% to 165.4 ± 47.9 mg/dL in the Middle East and by 35.5% to 179.0 ± 49.9 mg/dL in Morocco. Mean fasting blood glucose decreased by 30.8% to 126.6 ± 34.2 mg/dL (Middle East) and by 34.5% to 150.6 ± 47.1 mg/dL (Morocco). The absolute reduction in HbA1c was 1.3% in the Middle East (final value 7.4%) and 1.0% in Morocco (final value 7.5%). Overall, 107 patients (Middle East) and 26 patients (Morocco) experienced minor drug-related adverse events, which were mainly gastrointestinal. The tolerability of acarbose was rated as very good/good by 80.8% in the Middle East and by 68.6% in Morocco.This study illustrates the efficacy and safety of acarbose in the treatment of type 2 diabetic patients in an observational setting.

The present study aimed to establish relationship between urease and alpha-amylase inhibitory activities on the one hand and on the other between anti-enzymatic activities and total phenolic contents of the methanolic extract of roots of Rumex acetosella and its fractions in various solvents. The methanolic extract and its fractions in chloroform, ethyl acetate, n-butanol and water showed remarkable inhibitory activities against both urease and alpha-amylase, there was a close correspondence between urease and alpha-amylase inhibitory activities of the plant samples. The n-butanol fraction which had the highest total phenolic content (252.19±2.32 µg of Gallic Acid Equivalents/mg of dry mass of the sample) showed prominent activity against both urease and alpha-amylase indicating a possible role of phenolics in inhibiting the activities of these enzymes. The samples displayed enzyme inhibitory activities in a dose dependent manner and their effectiveness was comparable with that of the standards, thiourea (for urease) and acarbose (for alpha-amylase). The samples were manifold more effective against urease than alpha-amylase; 2.8 mg/mL of MeOH extract produced about 81% inhibition in alpha-amylase activity, while only 10 µg/mL of the extract was required to create the same inhibition in urease activity. The IC50 values of methanolic, chloroform, ethyl acetate, n-butanolic, aqueous and standard solutions were 1.29, 1.31, 1.90, 1.38, 0.85 and 1.20 (mg/mL) respectively against alpha-amylase and 0.99, 3.89, 1.76, 0.91, 0.85 and 0.97 (μg/mL) respectively against urease. The total phenolic content in MeOH, hexane, chloroform, ethyl acetate, n-butanol and water fractions was 108.88±2.65, 43.70±1.90, 34.44±2.30, 230.71±1.78, 252.19±2.32 and 94.07±2.25 respectively.