Miglitol: a review of its therapeutic potential in type 2 diabetes mellitus

Development of a fast and efficient CE enzyme assay for the characterization and inhibition studies of α-glucosidase inhibitors

The inhibition of the α-glucosidase enzyme plays an important role in the treatment of diabetes mellitus. We have established a highly sensitive, fast, and convenient CE method for the characterization of the enzyme and inhibition studies of α-glucosidase inhibitors. The separation conditions were optimized; the pH value and concentration of the borate-based separation buffer were optimized in order to achieve baseline separation of p-nitrophenyl-α-d-glucopyranoside and p-nitrophenolate. The optimized method using 25 mM tetraborate buffer, pH 9.5, was evaluated in terms of repeatability, LOD, LOQ, and linearity. The LOD and LOQ were 0.32 and 1.32 μM for p-nitrophenyl-α-D-glucopyranoside and 0.83 and 3.42 μM for p-nitrophenolate, respectively. The value of the Michaelis-Menten constant (K(m)) determined for the enzyme is 0.61 mM, which is in good agreement with the reported data. The RSDs (n = 6) for the migration time was 0.67 and 1.83% for substrate and product, respectively. In the newly established CE method, the separation of the reaction analytes was completed in <4 min. The developed CE method is rapid and simple for measuring enzyme kinetics and for assaying inhibitors.

In Vitro Anti-diabetic Activity of Sclerocarya Birrea and Ziziphus Mucronata

Type 2 diabetes mellitus is on the increase worldwide. Current treatments possess undesirable side-effects and therefore investigations into alternative remedies, which may be cost-effective and devoid of such side-effects, are on-going. Aqueous and methanol extracts of the bark of Sclerocarya birrea (A. Rich.) Hochst. subsp. caffra (Sond.) Kokwaro (Anacardiaceae) and Ziziphus mucronata Willd. subsp. mucronata (Rhamnaceae) were subjected to testing in order to assess their in vitro anti-diabetic activity. Total polyphenolic content and antioxidant activity, as well as the effect on α-amylase, α-glucosidase and cytotoxicity, were measured. Furthermore, glucose uptake was evaluated in C2C12 myotubes, 3T3-L1 adipocytes and HepG2 hepatocarcinoma cells, and insulin secretion in RIN-m5F rat pancreatic β-cells. The extracts of both plants inhibited the activities of α-amylase and α-glucosidase in a concentration dependent manner, with results being comparable with the positive control, acarbose. All the extracts contained antioxidant activity, with the methanol extracts of S. birrea displaying the strongest free radical scavenging capacity (IC50 = 2.16 μg/mL). Most of the extracts were not cytotoxic to the cell lines with IC50 values > 100 μg/mL. Extracts of both plants significantly increased glucose uptake in C2C12, 3T3-L1 and HepG2 cells. However, insulin secretion from RIN-m5F cells was not altered. This study provides evidence that the plants possess in vitro anti-diabetic properties.

Concomitant use of miglitol and mitiglinide as initial combination therapy in type 2 diabetes mellitus

AIM

To evaluate the efficacy of miglitol and mitiglinide alone or in combination on the metabolic profile and incretin secretion in Japanese type 2 diabetes patients.

METHODS

Patients on diet and exercise with or without metformin, were randomized to receive either miglitol, mitiglinide, or a combination, three times daily for 12 weeks.

RESULTS

At 12 weeks, HbA1c decreased significantly (p<0.001) and 1,5-AG increased significantly (p<0.001) in all three groups, with the greatest change seen with combination therapy. Effective improvement of postprandial hyperglycemia was demonstrated by a meal-loading test in all three interventions but serum insulin concentration was not increased by miglitol. In a subset of patients without prior metformin administration, faster and better glycemic control was achieved with the initial combination. After meal loading, serum total GLP-1 significantly increased only with miglitol monotherapy (p<0.05) and serum total GIP significantly decreased (p<0.01) in the arms employing miglitol after 12 weeks.

CONCLUSION

Miglitol/mitiglinide combination is more potent than monotherapy in improving glycemic control through the reduction of postprandial glucose excursion and the simultaneous sparing of additional insulin secretion. A marked difference in the effects of miglitol and mitiglinide on incretin secretion was also demonstrated.

Miglitol improves postprandial endothelial dysfunction in patients with acute coronary syndrome and new-onset postprandial hyperglycemia

BACKGROUND

Hyperglycemia, a risk factor for development of cardiovascular disease, causes endothelial dysfunction. Alpha-glucosidase inhibitors (α-GIs) improve postprandial hyperglycemia (PPHG) and may have favorable effects on associated cardiovascular disease. Effects of α-GIs in patients with acute coronary syndrome (ACS) and PPHG remain unclear; thus, we assessed the effect of α-GI miglitol on endothelial function in such patients by digital reactive hyperemia peripheral arterial tonometry (RH-PAT).

METHODS

Fifty-four patients with ACS who underwent primary percutaneous coronary intervention were enrolled in the study: 36 with new-onset PPHG and 18 with normal glucose tolerance. Eighteen PPHG patients were given 50 mg of miglitol with each meal for 1 week. Endothelial function was assessed on the basis of the RH-PAT index (RHI) before and after the 1-week miglitol treatment. The other 18 PPHG patients and the 18 NGT patients were not given any anti-diabetic agent for 1 week, and endothelial function was assessed.

RESULTS

Postprandial RHI decreased significantly in patients with PPHG. Miglitol improved PPHG significantly; postprandial RHI also improved (p = 0.007). Significant inverse correlation was found between the postprandial change in RHI and postprandial fasting-to-60-minutes surge in glucose (r = -0.382, p = 0.009). Moreover, the improvement in endothelial function correlated with the reduced postprandial glucose surge achieved with miglitol (r = -0.462, p = 0.001).

CONCLUSIONS

Postprandial changes in glucose are related to endothelial dysfunction in ACS. Miglitol-based improvement in PPHG appears to improve endothelial function. The effect of miglitol on glucose-dependent endothelial function might improve outcomes of ACS.

C-branched iminosugars: α-glucosidase inhibition by enantiomers of isoDMDP, isoDGDP, and isoDAB-L-isoDMDP compared to miglitol and miglustat

The Ho crossed aldol condensation provides access to a series of carbon branched iminosugars as exemplified by the synthesis of enantiomeric pairs of isoDMDP, isoDGDP, and isoDAB, allowing comparison of their biological activities with three linear isomeric natural products DMDP, DGDP, and DAB and their enantiomers. L-IsoDMDP [(2S,3S,4R)-2,4-bis(hydroxymethyl)pyrrolidine-3,4-diol], prepared in 11 steps in an overall yield of 45% from d-lyxonolactone, is a potent specific competitive inhibitor of gut disaccharidases [K(i) 0.081 μM for rat intestinal maltase] and is more effective in the suppression of hyperglycaemia in a maltose loading test than miglitol, a drug presently used in the treatment of late onset diabetes. The partial rescue of the defective F508del-CFTR function in CF-KM4 cells by L-isoDMDP is compared with miglustat and isoLAB in an approach to the treatment of cystic fibrosis.

Spectroscopic studies (FTIR, FT-Raman and UV), potential energy surface scan, normal coordinate analysis and NBO analysis of (2R,3R,4R,5S)-1-(2-hydroxyethyl)-2-(hydroxymethyl) piperidine-3,4,5-triol by DFT methods

This work presents the characterization of (2R,3R,4R,5S)-1-(2-hydroxyethyl)-2-(hydroxymethyl)piperidine-3,4,5-triol (abbreviated as HEHMPT) by quantum chemical calculations and spectral techniques. The spectroscopic properties were investigated by FT-IR, FT-Raman and UV-Vis techniques. The FT-IR spectrum (4000-400 cm(-1)) and FT-Raman spectrum (4000-100 cm(-1)) in solid phase was recorded for HEHMPT. The UV-Vis absorption spectrum of the HEHMPT that dissolved in water was recorded in the range of 100-400 nm. The structural and spectroscopic data of the molecule were obtained from B3LYP and M06-2X with 6-31G(d,p) basis set calculations. The theoretical wavenumbers were scaled and compared with experimental FT-IR and FT-Raman spectra. The complete assignments were performed on the basis of the normal co-ordinate analysis (NCA), experimental results and potential energy distribution (PED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method, interpreted in terms of fundamental modes. The stable geometry of the compound has been determined from the potential energy surface scan. The stability of molecule has been analyzed by NBO analysis. The molecule orbital contributions were studied by using the total (TDOS), partial (PDOS), and overlap population (OPDOS) density of states. The electronic properties like UV spectral analysis and HOMO-LUMO energies were reported. The calculated HOMO and LUMO energies shows that charge transfer interactions taking place within the molecule. Mulliken population analysis on atomic charges is also calculated.

Tissue distribution and identification of radioactivity components at elimination phase after oral administration of [¹⁴C]CS-1036, an α-amylase inhibitor, to rats

(2R,3R,4R)-4-hydroxy-2-(hydroxymethyl)pyrrolidin-3-yl 4-O-(6-deoxy-β-D-glucopyranosyl)-α-D-glucopyranoside (CS-1036) is a potent inhibitor of pancreatic and salivary α-amylase. After oral administration of [¹⁴C]CS-1036 to rats, the radioactivity was still detectable up to 7-14 days after administration in various tissues, and its terminal phase in plasma could be explained neither by the exposure of CS-1036 nor its major metabolite M1. The slow elimination of radioactivity in various tissues was hypothesized to be caused by covalent binding to macromolecules or use for biogenic components. To assess the use for biogenic components, amino acid analysis of plasma proteins and lipid analysis of adipose tissue were conducted after repeated oral administration of [¹⁴C]CS-1036 by high-performance liquid chromatography and accelerated mass spectrometry and by thin layer chromatography and liquid chromatography/mass spectrometry, respectively. In amino acid analysis, glutamic acid, aspartic acid, alanine, and proline were identified as major radioactive amino acids, and radioactive nonessential amino acids occupied 76.0% of the radioactivity. In lipid analysis, a part of the radioactive lipids were identified as the fatty acids constituting the neutral lipids by lipase-hydrolysis. The radioactive fatty acids from neutral lipids were identified as palmitic acid, oleic acid, and 8,11,14-eicosatrienoic acid. Intestinal flora were involved in CS-1036 metabolism and are indicated to be involved in the production of small molecule metabolites, which are the sources for amino acids and fatty acids, from [¹⁴C]CS-1036. In conclusion, radioactivity derived from [¹⁴C]CS-1036 was incorporated as the constituents of amino acids of plasma proteins and fatty acids of neutral lipids.

Absorption, elimination, and metabolism of CS-1036, a novel α-amylase inhibitor in rats and monkeys, and the relationship between gastrointestinal distribution and suppression of glucose absorption

The absorption, metabolism, and excretion of (2R,3R,4R)-4-hydroxy-2-(hydroxymethyl)pyrrolidin-3-yl 4-O-(6-deoxy-β-d-glucopyranosyl)-α-d-glucopyranoside (CS-1036), a novel and potent pancreatic and salivary α-amylase inhibitor, were evaluated in F344/DuCrlCrlj rats and cynomolgus monkeys. The total body clearance and volume of distribution of CS-1036 were low (2.67-3.44 ml/min/kg and 0.218-0.237 l/kg for rats and 2.25-2.84 ml/min/kg and 0.217-0.271 l/kg for monkeys). After intravenous administration of [(14)C]CS-1036 to rats and monkeys, radioactivity was mainly excreted into urine (77.2% for rats and 81.1% for monkeys). After oral administration, most of the radioactivity was recovered from feces (80.28% for rats and 88.13% for monkeys) with a low oral bioavailability (1.73-2.44% for rats and 0.983-1.20% for monkeys). In rats, intestinal secretion is suggested to be involved in the fecal excretion as a minor component because fecal excretion after intravenous administration was observed (15.66%) and biliary excretion was almost negligible. Although intestinal flora was involved in CS-1036 metabolism, CS-1036 was the main component in feces (70.3% for rats and 48.7% for monkeys) and in the intestinal contents (33-68% for rats up to 2 hours after the dose) after oral administration. In Zucker diabetic fatty rats, CS-1036 showed a suppressive effect on plasma glucose elevation after starch loading with a 50% effective dose at 0.015 mg/kg. In summary, CS-1036 showed optimal pharmacokinetic profiles: low oral absorption and favorable stability in gastrointestinal lumen, resulting in suppression of postprandial hyperglycemia by α-amylase inhibition.

Pharmacokinetic considerations for the treatment of diabetes in patients with chronic kidney disease

INTRODUCTION

People with chronic kidney disease (CKD) of stages 3 - 5 (creatinine clearance < 60 ml/min) represent ≈ 25% of patients with type 2 diabetes mellitus (T2DM), but the problem is underrecognized or neglected in clinical practice. However, most oral antidiabetic agents have limitations in case of renal impairment (RI), either because they require a dose adjustment or because they are contraindicated for safety reasons.

AREAS COVERED

The author performed an extensive literature search to analyze the influence of RI on the pharmacokinetics (PK) of glucose-lowering agents and the potential consequences for clinical practice.

EXPERT OPINION

As a result of PK interferences and for safety reasons, the daily dose should be reduced according to glomerular filtration rate (GFR) or even the drug is contraindicated in presence of severe CKD. This is the case for metformin (risk of lactic acidosis) and for many sulfonylureas (risk of hypoglycemia). At present, however, the exact GFR cutoff for metformin use is controversial. New antidiabetic agents are better tolerated in case of CKD, although clinical experience remains quite limited for most of them. The dose of DPP-4 inhibitors should be reduced (except for linagliptin), whereas both the efficacy and safety of SGLT2 inhibitors are questionable in presence of CKD.

Lipid lowering and antioxidant effect of miglitol in triton treated hyperlipidemic and high fat diet induced obese rats

Miglitol, an anti-diabetic drug, has been shown to reduce plasma lipids and inhibit free radical generation. The anti-hyperlipidemic and antioxidant effects of miglitol were studied in triton-induced hyperlipidemic rats and high fat diet-fed obese rats. Plasma cholesterol and triglycerides levels were significantly lowered by miglitol at 100 mg/kg body weight doses. Miglitol inhibited generation of superoxide anion and hydroxyl free radicals by 14 and 31 % in enzymatic systems and 19 and 25 % in non-enzymatic systems, respectively. The in-vitro effect of the drug on adipogenesis using 3T3-L₁ preadipocytes at 2-, 5- and 10-μM concentrations showed significant inhibition of adipogenesis (34.2 %) at 10-μM concentration. High fat diet-fed rat model was used to investigate anti-hyperlipidemic, anti-obesity and antioxidant effect of miglitol. Miglitol increased the activities of lecithin-cholesterol-acyltransferase (19 %), post heparin lipolytic activity (26 %), lipoprotein lipase (26 %) and triglyceride lipase (31 %) which result in a decrease in plasma lipid levels. The antioxidant enzymes viz., catalase, superoxide dismutase, glutathione peroxidase, glutathione reductase and thioredoxin reductase were increased by the drug in the treated animals. The antihyperlipidemic and antioxidant effect of miglitol can be correlated to its effect on different enzymes and it can be used for inhibiting the development of cardiovascular diseases.

Dibenzocycloheptanoids from the leaves of Cinnamomum subavenium

Five dibenzocycloheptatrienes (1-3, 5, and 6) and one dibenzocycloheptadiene (8) together with 16 known compounds were isolated from the leaves of Cinnamomum subavenium. Application of HPLC-SPE-NMR to a selected fraction afforded two additional dibenzocycloheptatrienes (4, 7). The glycosides 2-7 comprise two diastereomers because of the chiral glycosyl moiety and the axial chirality of the biphenyl system. Their structures were elucidated via ECD and 2D NMR analyses and chemical degradation. Subavenosides D (5) and E (6) showed moderate inhibitory activity against α-glucosidase type IV from Bacillus stearothermophilus with IC₅₀ values of 50.7 and 19.0 μM, respectively.

Comparisons of the effects of 12-week administration of miglitol and voglibose on the responses of plasma incretins after a mixed meal in Japanese type 2 diabetic patients

To compare the effects of miglitol [an alpha-glucosidase inhibitor (AGI) absorbed in the intestine] and voglibose (an AGI not absorbed) on plasma glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP) levels, 26 and 24 Japanese type 2 diabetic patients were randomly assigned to receive miglitol or voglibose, respectively. After 12-week administration of both drugs, during 2-h meal tolerance test, plasma glucose, serum insulin and total GIP were significantly decreased and active GLP-1 was significantly increased. Miglitol group showed a significantly lower total GIP level than voglibose group. Miglitol, but not voglibose, significantly reduced body weight (BW). In all participants, the relative change in BW was positively correlated with that of insulin significantly and of GIP with a weak tendency, but not of GLP-1. In conclusion, both drugs can enhance postprandial GLP-1 responses and reduce GIP responses. The significant BW reduction by miglitol might be attributable to its strong GIP-reducing efficacy.

Effect of the α-glucosidase inhibitor miglitol on the glucose profile in Japanese type 2 diabetic patients receiving multiple daily insulin injections

Strict postprandial glycemic control may have a preventive effect on atherogenesis in patients with type 2 diabetes. The α-glucosidase inhibitor (α-GI) miglitol is useful for controlling the early postprandial increase of glucose, but the combined effect of miglitol and multiple daily insulin injections (MDI) on glucose excursion has not been evaluated. First, we retrospectively compared the daily glucose profile, evaluated by self-monitoring of blood glucose (SMBG) at nine times on the day before discharge from hospital, between type 2 diabetic patients receiving MDI (n=81) or MDI plus miglitol at 150 mg daily (n=24). Second, we prospectively examined the effect of adding miglitol to MDI on the daily glucose profile (SMBG) in 19 other type 2 diabetic patients. Although the daily insulin dosage and the glucose level before meals did not differ between the two groups, the 1-h postprandial glucose level after each meal, 2-h glucose level after lunch and dinner, mean and standard deviation of glucose, and amplitude of glucose excursion were significantly lower or smaller in the MDI plus miglitol group than in the MDI group. All of these glucose parameters were significantly improved by adding miglitol to MDI in the prospective cohort of 19 patients. In conclusion, adding miglitol to MDI reduces postprandial glucose levels and attenuates daily glucose fluctuation in type 2 diabetic patients. This trial was registered with UMIN (no. UMIN000005383).

Effect of 3-month repeated administration of miglitol on vascular endothelial function in patients with diabetes mellitus and coronary artery disease

Repeated postprandial hyperglycemia may play an important role in the development of atherosclerosis by suppressing vascular endothelial function. Although miglitol suppresses the elevation of blood glucose levels shortly after a meal more than other α-glucosidase inhibitors, the effect of 3-month repeated administration of miglitol on endothelial dysfunction is unknown. Fifty patients with type 2 diabetes and coronary artery disease were enrolled in the present study. The patients were randomly divided into 2 groups, the first treated with miglitol and the second with voglibose for 3 months. Blood chemistry (lipid and blood glucose profiles, glycosylated hemoglobin, 1,5-anhydroglucitol, serum insulin levels, and C-reactive protein) and flow-mediated dilatation were measured at the beginning and end of the trial period. Patient characteristics and blood chemistry of the 2 groups were similar at the beginning of the trial. At the end of the trial, glycosylated hemoglobin decreased in the 2 groups, but the improvements in 1,5-anhydroglucitol in the miglitol group were significantly higher than in the voglibose group. Insulin resistance index, C-reactive protein, and percentage flow-mediated dilatation were also improved in the miglitol group but not in the voglibose group. In conclusion, 3-month repeated administration of miglitol improved vascular endothelial dysfunction by strongly suppressing postprandial hyperglycemia. Miglitol may have antiatherogenic effects in patients with type 2 diabetes and coronary artery disease.

Synthesis and α-glucosidase inhibitory mechanisms of bis(2,3-dibromo-4,5-dihydroxybenzyl) ether, a potential marine bromophenol α-glucosidase inhibitor

Bis(2,3-dibromo-4,5-dihydroxybenzyl) ether (BDDE), derived from the marine algae, is a potential α-glucosidase inhibitor for type 2 diabetes treatment. In the present study, a synthetic route was established as a valid approach to obtain BDDE. Fluorescence spectra, circular dichroism spectra and molecular docking methods were employed to elucidate the inhibitory mechanisms of BDDE against α-glucosidase. The results showed that BDDE could be prepared effectively and efficiently with the established synthetic methods. Synthetic BDDE bound with α-glucosidase and induced minor conformational changes of the enzyme. The docking results indicated the interaction between BDDE and α-glucosidase was driven by both hydrophobic forces and hydrogen bonds. The docked BDDE molecule was completely buried in the α-glucosidase binding pocket with part of the molecule reaching the catalytic center and overlapping with the position of glucose, and the rest of the molecule extending towards protein surface. This study provides useful information for the understanding of the BDDE-α-glucosidase interaction and for the development of novel α-glucosidase inhibitors.

Iminosugars as therapeutic agents: recent advances and promising trends

For the purpose of this article, iminosugars are polyhydroxylated secondary and tertiary amines in which the molecules resemble monosaccharide sugars in which the ring oxygen is replaced by the nitrogen. The bicyclic structures may biologically resemble disaccharides. Very few iminosugars have been available up to now for evaluation of their pharmaceutical applications. The early compounds were discovered and selected for study due to glycosidase inhibition, which is now known to not be necessary for pharmacological activity and may cause off-target effects. Glyset® and Zavesca®, derived from the glucosidase-inhibiting natural product 1-deoxynojirimycin, are the first two examples of iminosugar drugs. Since the discovery of this first generation, many new natural products have been identified with a wide range of biological activities but few are widely available. Among the biological properties of these compounds are good oral bioavailability and very specific immune modulatory and chaperoning activity. Although the natural products from plants and microorganisms can have good specificity, modifications of the template natural products have been very successful recently in producing bioactive compounds with good profiles. The field of iminosugars continues to open up exciting new opportunities for therapeutic agent discovery and offers many new tools for precisely modifying carbohydrate structures and modulating glycosidase activity in vivo. Current efforts are directed towards a greater range of structures and a wider range of biochemical targets.

Advances in the treatment of type 2 diabetes mellitus

There is a rising worldwide prevalence of diabetes, especially type 2 diabetes mellitus (T2DM), which is one of the most challenging health problems in the 21st century. The associated complications of diabetes, such as cardiovascular disease, peripheral vascular disease, stroke, diabetic neuropathy, amputations, renal failure, and blindness result in increasing disability, reduced life expectancy, and enormous health costs. T2DM is a polygenic disease characterized by multiple defects in insulin action in tissues and defects in pancreatic insulin secretion, which eventually leads to loss of pancreatic insulin-secreting cells. The treatment goals for T2DM patients are effective control of blood glucose, blood pressure, and lipids (if elevated) and, ultimately, to avert the serious complications associated with sustained tissue exposure to excessively high glucose concentrations. Prevention and control of diabetes with diet, weight control, and physical activity has been difficult. Treatment of T2DM has centered on increasing insulin levels, either by direct insulin administration or oral agents that promote insulin secretion, improving sensitivity to insulin in tissues, or reducing the rate of carbohydrate absorption from the gastrointestinal tract. This review presents comprehensive and up-to-date information on the mechanism(s) of action, efficacy, pharmacokinetics, pleiotropic effects, drug interactions, and adverse effects of the newer antidiabetic drugs, including (1) peroxisome proliferator-activated-receptor-γ agonists (thiazolidinediones, pioglitazone, and rosiglitazone); (2) the incretin, glucagon-like peptide-) receptor agonists (incretin-mimetics, exenatide. and liraglutide), (3) inhibitors of dipeptidyl-peptidase-4 (incretin enhancers, sitagliptin, and vildagliptin), (4) short-acting, nonsulfonylurea secretagogue, meglitinides (repaglinide and nateglinide), (5) amylin anlog-pramlintide, (6) α-glucosidase inhibitors (miglitol and voglibose), and (7) colesevelam (a bile acid sequestrant). In addition, information is presented on drug candidates in clinical trials, experimental compounds, and some plants used in the traditional treatment of diabetes based on experimental evidence. In the opinion of this reviewer, therapy based on orally active incretins and incretin mimetics with long duration of action that will be efficacious, preserve the β-cell number/function, and block the progression of diabetes will be highly desirable. However, major changes in lifestyle factors such as diet and, especially, exercise will also be needed if the growing burden of diabetes is to be contained.

A novel competitive class of α-glucosidase inhibitors: (E)-1-phenyl-3-(4-styrylphenyl)urea derivatives

Competitive glycosidase inhibitors are generally sugar mimics that are costly and tedious to obtain because they require challenging and elongated chemical synthesis, which must be stereo- and regiocontrolled. Here, we show that readily accessible achiral (E)-1-phenyl-3-(4-strylphenyl)ureas are potent competitive α-glucosidase inhibitors. A systematic synthesis study shows that the 1-phenyl moiety on the urea is critical for ensuring competitive inhibition, and substituents on both terminal phenyl groups contribute to inhibition potency. The most potent inhibitor, compound 12 (IC(50)=8.4 μM, K(i)=3.2 μM), manifested a simple slow-binding inhibition profile for α-glucosidase with the kinetic parameters k(3)=0.005256 μM(-1) min(-1), k(4)=0.003024 min(-1), and K(i)(app) =0.5753 μM.

Isolation and identification of sea buckthorn (Hippophae rhamnoides) phenolics with antioxidant activity and α-glucosidase inhibitory effect

This study was performed to evaluate the antioxidant and α-glucosidase inhibitory effects from the extract, fractions, and isolated compounds of sea buckthorn leaves. Six compounds, kaempferol-3-O-β-D-(6''-O-coumaryl) glycoside, 1-feruloyl-β-D-glucopyranoside, isorhamnetin-3-O-glucoside, quercetin 3-O-β-D-glucopyranoside, quercetin 3-O-β-D-glucopyranosyl-7-O-α-L-rhamnopyranoside, and isorhamnetin-3-O-rutinoside, were isolated from sea buckthorn leaf extracts. The butanol fraction (EC(50) = 1.81 μg/mL) along with quercetin 3-O-β-D-glucopyranoside (EC(50) = 1.86 μg/mL) had a higher DPPH radical-scavenging activity and showed stronger reducing power (OD(700) = 1.83 and 1.78, respectively). The butanol fraction (477 mg GAE/g) contained the highest amount of phenolic compounds and also the most powerful α-glucosidase inhibitory effect (86%) at 5 μg/mL. The results indicate that sea buckthorn leaf extracts could potentially be used for food additives and the development of useful natural compounds.

Synthesis of polyhydroxy 7- and N-alkyl-azepanes as potent glycosidase inhibitors

An effective synthetic method for polyhydroxylated azepanes that contain an alkyl group (Me or Bu) at either the 7- or N-positions is developed. The synthetic routes are accomplished in eight to ten steps from d-(-)-quinic acid. Among the compounds synthesized, the polyhydroxy 7-butyl azepane (compound 3), which possessed the R-configuration at C-7 position, is shown to give potent inhibition against β-galactosidase (IC(50)= 3 microM). Preliminary biological data indicate that the length of alkyl groups along with the proper stereochemistry at the C-7 position is essential for acquiring extra binding affinity. Using similar synthetic routes, the polyhydroxy N-methyl and N-butyl azepanes are synthesized for the comparison of their biological activities.

α-Glucosidase inhibition and the in vivo hypoglycemic effect of butyl-isobutyl-phthalate derived from the Laminaria japonica rhizoid

The rhizoid of Laminaria japonica is widely used in Chinese medicine as a treatment for diabetes. Therefore, a bioactivity-tailored isolation and detailed chemical characterization was used to identify the antidiabetes compounds found in the L. japonica rhizoid. Liquid chromatography/mass spectrometry (LC/MS), proton NMR and carbon NMR spectra analyses demonstrated that the active compound was butyl-isobutyl-phthalate (BIP). BIP demonstrated a significant concentration-dependent, non-competitive inhibitory activity against α-glucosidase in vitro, with an IC(50) of 38 μm. In vivo, the ethyl acetate fraction (EAF) and purified BIP displayed a significant hypoglycemic effect in streptozocin-induced diabetic mice. The present study indicates BIP could be considered as an α-glucosidase inhibitor and developed as an important antidiabetes agent for type II diabetes therapy.

Towards a stable noeuromycin analog with a D-manno configuration: synthesis and glycosidase inhibition of D-manno-like tri- and tetrahydroxylated azepanes

Noeuromycin is a highly potent albeit unstable glycosidase inhibitor due to its hemiaminal function. While stable D-gluco-like analogs have been reported, no data are available for D-manno-like structures. A series of tri- and tetrahydroxylated seven-membered iminosugars displaying either a D-manno-or a L-gulo-like configuration, were synthesized from methyl α-D-mannopyranoside using a reductive amination-mediated ring expansion as the key step. Screening towards a range of commercial glycosidases demonstrated their potency as competitive glycosidase inhibitors while cellular assay showed selective albeit weak glycoprotein processing mannosidase inactivation.

Synthesis of N-, S-, and C-glycoside castanospermine analogues with selective neutral alpha-glucosidase inhibitory activity as antitumour agents

sp(2)-Iminosugar-type castanospermine analogues bearing an alpha-configured N-, S-, or C-linked pseudoanomeric group have been designed as selective inhibitors of the neutral alpha-glucosidases involved in N-glycoprotein processing; evaluation in breast cancer cell growth indicated a significant antiproliferative potential that was dependent on the nature of the pseudoanomeric group.

Single administration of alpha-glucosidase inhibitors on endothelial function and incretin secretion in diabetic patients with coronary artery disease - Juntendo University trial: effects of miglitol on endothelial vascular reactivity in type 2 diabetic patients with coronary heart disease (J-MACH) -

BACKGROUND

Post-prandial hyperglycemia, hyperlipidemia, and endothelial dysfunction play an important role in the pathogenesis of atherosclerosis. Improvement in post-prandial hyperglycemia on alpha-glucosidase inhibitors (alpha-GIs) is associated with a risk reduction of cardiovascular diseases, but the post-prandial effects of alpha-GIs on endothelial function and incretin secretion in type 2 diabetic patients with coronary artery disease (CAD) remain unclear.

METHODS AND RESULTS

The post-prandial effects of a single administration of miglitol and voglibose on endothelial function and changing levels of glucose, insulin, lipids, glucagon-like peptide (GLP)-1, and gastric inhibitory polypeptide (GIP) were compared after a standard meal loading in 11 diabetic patients with CAD, using a placebo-controlled cross-over design. The changing levels of glucose, insulin and triglycerides at 60 min were significantly lower in the miglitol group than in the voglibose and placebo groups (all P<0.01). GLP-1 levels were significantly higher at 120 min (P<0.05) and GIP levels were significantly lower at 30 min and 60 min (P<0.05) in the miglitol group compared to other treatments. The reactive hyperemia duration at 120 min was significantly maintained in the miglitol group compared to the other groups.

CONCLUSIONS

A single administration of miglitol significantly improved post-prandial glucose/lipid metabolism, incretin secretion, and endothelial dysfunction in diabetic patients with CAD, suggesting that miglitol may be a useful anti-atherogenic agent (UMIN000002264).