Antihyperglycemic effects of N-containing sugars from Xanthocercis zambesiaca, Morus bombycis, Aglaonema treubii, and Castanospermum australe in streptozotocin-diabetic mice

d-Fagomine lowers postprandial blood glucose and modulates bacterial adhesion

d-Fagomine is an iminosugar originally isolated from seeds of buckwheat (Fagopyrum sculentumMoench), present in the human diet and now available as a pure crystalline product. We testedd-fagomine for activities connected to a reduction in the risk of developing insulin resistance, becoming overweight and suffering from an excess of potentially pathogenic bacteria. The activities were: intestinal sucrase inhibitionin vitro(rat mucosa and everted intestine sleeves), modulation of postprandial blood glucose in rats, bacterial agglutination and bacterial adhesion to pig intestinal mucosa. When ingested together with sucrose or starch,d-fagomine lowered blood glucose in a dose-dependent manner without stimulating insulin secretion.d-Fagomine reduced the area under the curve (0–120 min) by 20 % (P < 0·01) and shifted the time to maximum blood glucose concentration (Tmax) by 15 min at doses of 1–2 mg/kg body weight when administered together with 1 g sucrose/kg body weight. Moreover,d-fagomine (0·14 mm) agglutinated 60 % of Enterobacteriaceae (Escherichia coli,Salmonella entericaserovar Typhimurium) populations (P < 0·01), while it did not show this effect onBifidobacteriumspp. orLactobacillusspp. At the same concentration,d-fagomine significantly (P < 0·001) inhibited the adhesion of Enterobacteriaceae (95–99 % cells in the supernatant) and promoted the adhesion ofLactobacillus acidophilus(56 % cells in the supernatant) to intestinal mucosa.d-Fagomine did not show any effect on bacterial cell viability. Based on all this evidence,d-fagomine may be used as a dietary ingredient or functional food component to reduce the health risks associated with an excessive intake of fast-digestible carbohydrates, or an excess of potentially pathogenic bacteria.

Anti-diabetic effect of standardized herbal formula PM021 consisting of Mori Folium and Aurantii Fructus on type II diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats

PM021, which consists of two herbal components, Mori Folium and Aurantii Fructus, is routinely used to treat diabetes in Korea. In this study, the anti-diabetic effect of PM021 on an animal model of developing type 2 diabetes of Otsuka Long-Evans Tokushima Fatty (OLETF) rats was investigated. Eight weeks of age male OLETF rats were treated daily with PM021 or vehicle for five months. Specifically, changes in body weight, blood glucose, urine volume, food intake and oral glucose tolerance were measured in rats for five months. The rats in this study were divided into four groups: a Long-Evans Tokushima Otsuka (LETO) rat group, which is a genetic control group for OLETF, that received no treatment; a PM021 treatment group of LETO rats; OLETF rats that received no treatment; and OLETF rats that received PM021 treatment. The results showed that PM021 significantly prevented increases in body weight, blood glucose, and urine and food intake that resulted from the induction of obesity and diabetes. PM021 also improved glucose tolerance in OLETO rats. However, PM021 had no effect on LETO rats, a control group of OLETF rats. Taken together, these findings indicate that PM021 has distinct anti-diabetic effects without any adverse effects or toxicities.

Silk fibroin has a protective effect against high glucose induced apoptosis in HIT-T15 cells

High glucose levels induce cell death in many cell types, including pancreatic β-cells. Although protective agents against glucotoxicity have been searched for extensively, so far none have been found. In this report, we tested silk fibroin (SF) as a candidate material for antiglucotoxicity in the pancreatic β-cell (HIT-T15 cell) line. Approximately 50% of cells were killed after treatment with 80 mg/mL glucose. This reduction of cell number was recovered by the addition of SF at 50 mg/mL. SF treatment also decreased cellular reactive oxygen species (ROS) and increased proliferating cellular nuclear antigen (PCNA) immunoreactivity. In addition, TUNEL assays demonstrated that SF protects against glucose-induced apoptosis of HIT-T15 cells, suggesting that SF might protect cells from cell death by lowering cellular ROS levels. SF also induced expression of the insulin-like growth factor-1 (IGF-1) gene, and IGF-1 expression may be the cause of SF-induced protection against glucose toxicity. Taken together, these results suggest that SF could serve as a potential therapeutic agent to treat the hyperglycemia-induced death of pancreatic β-cells.

Simple, selective, and rapid quantification of 1-deoxynojirimycin in mulberry leaf products by high-performance anion-exchange chromatography with pulsed amperometric detection

1-Deoxynojirimycin (DNJ) occurs in mulberry and other plants and is a highly potent glycosidase inhibitor reported to suppress blood glucose levels, thus preventing diabetes. Derivatization is required for quantification of DNJ upon use of spectral detection methods. Because of this difficulty, the DNJ contents of mulberry-based food products are rarely stated, even if DNJ is their active component. A simple, selective, and rapid method of high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) to quantify DNJ in mulberry-based food products was developed. Stability testing of DNJ under heat treatment was also performed. A water extract of mulberry tea sample was subjected to HPAEC-PAD in a CarboPac MA1 column with a sodium hydroxide gradient. DNJ was clearly separated at a retention time of 7.26 min without interference and was selectively detected in the water extract. The detection limit was 5 ng. Heat stability studies suggested that DNJ was heat stable. HPAEC-PAD was not subject to interference, was highly selective for DNJ, and was superior to other high-performance liquid chromatography (HPLC) techniques in terms of sample preparation, resolution, and sensitivity. The method allowed simple, selective, and rapid analysis of DNJ in food matrices and might be useful for development of mulberry-based food products. Heat treatment could be an option for sterilizing mulberry-based products.

Comparison of absorption of 1-deoxynojirimycin from mulberry water extract in rats

In this study, we compared the absorption and excretion of DNJ in mulberry leaf extract against that of the purified compound (DNJ) using GC-TOF-MS, a newly developed analytical method, when administered orally to rats. Moreover, we also compared absorption levels in small intestinal cells using the Caco-2 cell line. In the cell study, DNJ absorption from the mulberry extract seemed to be inhibited when compared to that of the purified DNJ compound. The concentration of DNJ in rat plasma was also significantly (p < 0.05) lower when the mulberry extract was administered versus the purified DNJ compound. The metabolic pattern of DNJ from the mulberry leaf extract indicated that most was excreted in the feces, whereas a lower amount was detected in the urine, which was similar to the purified DNJ compound. These findings indicate that the bioavailability of DNJ in mulberry leaf extract might be lower than that of highly purified DNJ.

Synthesis, computational study and glycosidase inhibitory activity of polyhydroxylated conidine alkaloids--a bicyclic iminosugar

New bicyclic conidine iminosugars 1d and 1e were synthesized from D-glucose. Thus, D-glucose was converted to sugar beta-amino acids 3a and 3b in good yields. Individual treatment of 3a/3b with the Mukaiyama reagent afforded sugar beta-lactams 4a/4b that on reduction with LiAlH(4)/AlCl(3) gave azetidines 5a/5b with a sugar appendage. Reductive aminocyclization of sugar azetidines 5a/5b afforded the corresponding conidine iminosugars 1d/1e. Based on the (1)H NMR and DFT calculation studies the conformation of 1d was assigned as half chair A2 and that of 1e as a boat B2. The glycosidase inhibitory activities of 1d and 1e such as alpha-mannosidase, alpha-glucosidase and alpha-galactosidase were studied. The alpha-amylase activity was compared with acarbose. Compound 1d was found to be a moderate inhibitor of glycosidases while 1e was noticed to be a good inhibitor of alpha-mannosidase and a moderate inhibitor of other glycosidases. These results were substantiated by molecular docking studies using WHAT IF software and the AUTODOCK 3.0 program.

Evaluation of different teas against starch digestibility by mammalian glycosidases

Current work investigated the ability of different tea (green, oolong and black teas) in inhibiting human salivary alpha-amylase (HSA) and mammalian alpha-glucosidase (AGH). The inhibitory profiles were correlated to their major polyphenol content (theaflavins and catechins). The fully fermented black tea was demonstrated to be most potent in inhibiting HSA and AGH (IC50 of 0.42 to 0.67 and 0.56 to 0.58 mg of tea leaves/mL respectively). Its capability in retarding the digestion of a real food system (rice noodle) was further elucidated with an in vitro digestion study. Results indicated that black tea was able to retard starch digestion moderately, thereby allowing a gradual reduction of sugar liberation. Polyphenolic profile analysis suggested that the oxidized catechins, theaflavins, may be responsible for its activity. We have found that refractive index (RI) measurement is a rapid, direct, and highly convenient method for quantifying the degree of enzymatic starch digestion and kinetics. The RI method has good linearity range, limit of detection (0.1596 mg/mL, maltose equivalent) and limit of quantitation (0.6312 mg/mL) and was successfully applied in our study.

Antiobesity effects and improvement of insulin sensitivity by 1-deoxynojirimycin in animal models

The alpha-glucosidase inhibitor 1-deoxynojirimycin (DNJ) is one of the simplest naturally occurring carbohydrate mimics, with promising biological activity in vivo. Although there is considerable interest in the pharmacological effects of DNJ, the antidiabetic effects of DNJ in type 2 diabetes mellitus have received little attention. In this work, DNJ was isolated from the silkworm (Bombyx mori), and its antidiabetic effects were evaluated in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an established animal model of human type 2 diabetes mellitus, and in control Long-Evans Tokushima Otsuka (LETO) rats. DNJ treatment showed significant antidiabetic effects in OLETF rats, with significant improvements in fasting blood glucose levels and glucose tolerance and, especially, increased insulin sensitivity. Furthermore, there was significant loss of body weight in both groups. DNJ also showed significant antihyperglycemic effects in streptozotocin- and high-fat-diet-induced hyperglycemic rats. Its efficacy and dose profiles were better than those of acarbose, a typical alpha-glucosidase inhibitor in clinical use. Furthermore, a substantial fraction of DNJ was absorbed into the bloodstream within a few minutes of oral administration. DNJ was also detected in the urine. These findings suggest that its postprandial hypoglycemic effect in the gastrointestinal tract is a possible but insufficient mechanism of action underlying the antidiabetic effects of DNJ. Its antiobesity effect and improvement of insulin sensitivity are other possible antidiabetic effects of DNJ.

Vinylogous Mukaiyama aldol reactions with 4-oxy-2-trimethylsilyloxypyrroles: relevance to castanospermine synthesis

Background

The diastereoselectivity of a vinylogous Mukaiyama aldol reaction of a series of N-substituted 4-oxy-2-trimethylsilyloxypyrroles with a tartrate-based aldehyde has been explored as a model reaction for castanospermine synthesis.

Results

The study has revealed that the reaction is sensitive to the nature of the combination of N- and 4-oxy substituents. With a N-PMB or N-Bn and 4-methoxy combination, the reaction generates an aldol adduct with the correct absolute configurations for C-8 and C-8a of the indolizidine alkaloid castanospermine. The adduct was transformed to an indolizidine, whose ketal could not be transformed appropriately for the target alkaloid.

Conclusion

The first successful diastereoselective Mukaiyama aldol strategy for the C-8 and C-8a stereogenic centres of castanospermine is presented using silyloxypyrrole chemistry. The results suggest that a full enantioselective synthesis can be realized provided that C-1 functionalisation is accomplished early in the synthesis, post-coupling.

Pharmacological inhibition of glucosylceramide synthase enhances insulin sensitivity

A growing body of evidence implicates ceramide and/or its glycosphingolipid metabolites in the pathogenesis of insulin resistance. We have developed a highly specific small molecule inhibitor of glucosylceramide synthase, an enzyme that catalyzes a necessary step in the conversion of ceramide to glycosphingolipids. In cultured 3T3-L1 adipocytes, the iminosugar derivative N-(5'-adamantane-1'-yl-methoxy)-pentyl-1-deoxynojirimycin (AMP-DNM) counteracted tumor necrosis factor-alpha-induced abnormalities in glycosphingolipid concentrations and concomitantly reversed abnormalities in insulin signal transduction. When administered to mice and rats, AMP-DNM significantly reduced glycosphingolipid but not ceramide concentrations in various tissues. Treatment of ob/ob mice with AMP-DNM normalized their elevated tissue glucosylceramide levels, markedly lowered circulating glucose levels, improved oral glucose tolerance, reduced A1C, and improved insulin sensitivity in muscle and liver. Similarly beneficial metabolic effects were seen in high fat-fed mice and ZDF rats. These findings provide further evidence that glycosphingolipid metabolites of ceramide may be involved in mediating the link between obesity and insulin resistance and that interference with glycosphingolipid biosynthesis might present a novel approach to the therapy of states of impaired insulin action such as type 2 diabetes.

Fructose-6-phosphate Aldolase in Organic Synthesis: Preparation ofd-Fagomine,N-Alkylated Derivatives, and Preliminary Biological Assays

[Structure: see text] D-fructose-6-phosphate aldolase (FSA) mediates a novel straightforward two-step chemo-enzymatic synthesis of D-fagomine and some of its N-alkylated derivatives in 51% isolated yield and 99% de. The key step is the FSA-catalyzed aldol addition of simple dihydroxyacetone (DHA) to N-Cbz-3-aminopropanal. The use of FSA greatly simplifies the enzymatic procedures that used dihydroxyacetonephosphate or DHA/esters. Some N-alkyl derivatives synthesized elicited antifungal and antibacterial activity as well as enhanced inhibitory activity, and selectivity against beta-galactosidase and alpha-glucosidase.

Synthesis of Pentahydroxy Indolizidine Alkaloids Using Ring Closing Metathesis: Attempts To Find the Correct Structure of Uniflorine A

Ring closing metathesis of d-glucose derived diene-substrate containing nitrogen functionality followed by asymmetric dihydroxylation afforded sugar substituted dihydroxylated pyrrolidines 8a-c which on 1,2-acetonide deprotection and reductive amination afforded putative uniflorine A 2a and its analogues 2b-c, respectively.

Intramolecular 5-endo-Trig Aminomercuration of β-Hydroxy-γ-alkenylamines: Efficient Route to a Pyrrolidine Ring and Its Application for the Synthesis of (+)-Castanospermine and Analogues

The intramolecular aminomercuration reaction of sugar-derived beta-hydroxy-gamma-alkenylamines 8a-c undergoes 5-endo-trig cyclization in high yield. The sugar-substituted pyrrolidines thus obtained were elaborated to the synthesis of polyhydroxylated indolizidine alkaloids, namely, castanospermine 1a, 1-epi-castanospermine 1b, and 8a-epi-castanospermine 1c, having promising glycosidase inhibitory activities.

Medical benefits of using natural compounds and their derivatives having multiple pharmacological actions

The multiple pharmacological actions of a unique compound are a prerequisite for classifying drugs as highly efficacious, because the multiple pharmacological actions offer the possibility of treating various symptoms of chronic diseases as described below. 1) Sustained hyperglycemia induces macrovascular and microvascular complications in type 2 diabetes mellitus. Antihyperglycemic medication and the control of postprandial hyperglycemia are essentially important for normalizing plasma glucose level. Gymnemic acid IV isolated from Gymnema sylvestre (Asclepiadaceae) leaves has antisweet, antihyperglycemic, glucose uptake inhibitory, and gut glycosidase inhibitory effects. Most of these pharmacological effects may synergistically contribute to alleviating type 2 diabetes-related symptoms. 2) Diabetic skeletal and vascular smooth muscles are hypersensitive to chemical transmitters, cytokines and autacoids. The sensitivity of neuromuscular synapses is enhanced in diabetes, which seems to be closely associated with neuropathy as one of the diabetic complications. beta-Eudesmol found in Atractylodes lancea rhizome has a desensitizing channel blocking action to nicotinic acetylcholine receptors, anti-angiogenic action in vascular endothelium, and neuronal differentiation actions. These multiple pharmacological actions are favorable for treating angiogenic diseases possibly including the complications of diabetes, namely, retinopathy and nephropathy, and cancer. 3) Nipradilol is clinically utilized as a topical antiglaucoma drug. The ocular hypotensive effects of this compound are brought about by its alpha1 and beta-adrenergic receptor blocking actions, and nitric oxide (NO) releasing action. NO directly activates cyclooxygenases. All these pharmacologic effects are beneficial for treating glaucoma. The selectivity and specificity of drug action are required for treating acute diseases, infections or for acting as useful reagents. The pleiotropic actions of natural compounds and their derivatives serve as important clues for developing new drugs for various chronic diseases.

Protein tyrosine phosphatase 1B inhibitors from Morus root bark

An organic layer prepared from the Chinese crude drug 'Sang-Bai-Pi' (Morus root bark) was studied in order to identify the inhibitory compounds for protein tyrosine phosphatase 1B (PTP1B). Bioassay-guided fractionation resulted in the isolation of sanggenon C (1), sanggenon G (2), mulberrofuran C (3) and kuwanon L (4) as PTP1B inhibitors, along with moracin O (5) and moracin P (6). Compounds 1-4 inhibited PTP1B with IC(50) values ranging from 1.6+/-0.3 microM to 16.9+/-1.1 microM.

Novel Synthesis of Castanospermine and 1-Epicastanospermine

[reaction: see text] Polyhydroxylated indolizidines have potential for treatment of HIV, hepatitis C and HSV infection, multiple sclerosis, angiogenesis, cancer, and diabetes. A new synthetic approach to the title compounds from a 5-C-methoxypyranosyl azide has been developed. The route incorporates the aldol reaction and a novel catalytic reductive amination cascade to generate the indolizidine ring.

General synthesis and biological evaluation of α-1-C-substituted derivatives of fagomine (2-deoxynojirimycin-α-C-glycosides)

A general synthesis of alpha-1-C-substituted derivatives of fagomine (2-deoxynojirimycin-alpha-C-glycosides) by ring-opening reactions of an aziridine with various heteroatomic nucleophiles, including thiol, amine, alcohol, carboxylate and phosphate, is described. The nine-step reaction sequence proceeded in an overall yield of 14-28% from tri-O-benzyl-D-glucal. Biological evaluation of alpha-1-C-substituted derivatives of fagomine, of the 2-deoxy analog of alpha-homonojirimycin 19 and its 1,N-anhydro derivative 22 as glycosidase inhibitors is reported. The glycosyl phosphate mimetic 15k was found to display no inhibitory activity towards glycogen phosphorylase b and phosphoglucomutase.

Hypoglycemic and antihyperglycemic effects of diethyl ether fraction isolated from the aqueous extract of the leaves of Cogniauxia podoleana Baillon in normal and alloxan-induced diabetic rats

Cogniauxia podoleana Baillon (Cucurbitaceae family) leaves are used in Congolese traditional medicine for the treatment of diabetes mellitus. Based on an increasing number of reports on blood glucose level reduction associated with some saponins and flavonoids isolated from medicinal plants, the hypoglycemic and antihyperglycemic effects of flavonoid and saponin fractions were investigated. Saponin fractions were obtained by the fractionation of aqueous extract of leaves using benzene and ethyl acetate. Flavonoid fraction was isolated from the aqueous phase obtained after the settling of benzene-aqueous extract mixture by means of diethyl ether. The diethyl ether fraction (100mg/kg) reduced the blood glucose levels in 40.0% 3h after oral administration to normal rats. In contrast, the oral administration of benzene and ethyl acetate fractions at a dose of 100mg/kg to normal rats did not decrease the blood glucose levels. The diethyl ether fraction at a dose of 50mg/kg was found to reduce the increase of blood glucose levels in 29.4 and 44.5%, respectively, 3 and 4h after oral administration to alloxan-induced diabetic rats, whereas at a dose of 100mg/kg, it decreased the levels of hyperglycemia in 41.4 and 70.4%, respectively, after 3 and 4h. These data confirm the antidiabetic activity of the leaves of Cogniauxia podoleana Baillon in Congolese traditional medicine for diabetes mellitus treatment. However, it was important to note that the antihyperglycemic action could not be attributed to the presence of flavonoids; contamination is detected (amino acids, carbohydrates and other compounds) in the diethyl ether fraction containing flavonoids.

Suppression of Glucose Absorption by Various Health Teas in Rats

The inhibitory effects on the intestinal digestion and absorption of sugar of health teas that claim beneficial dietary and diabetes-controlling effects were compared in rats using portal cannulae. The measured durations were the times during which the elevation of portal glucose levels resulting from continuous intragastric infusion of sucrose or maltose was suppressed by concentrated teas. The teas investigated included salacia oblonga, mulberry, guava, gymunema, taheebo, yacon, and banaba. The duration of the inhibitory effect on the sucrose load of salacia oblonga, mulberry, and guava were 110 min, 20 min, and 10 min, respectively. In contrast, gymunema, taheebo, yacon, and banaba had no significant effect on the continuous infusion of sucrose. These results suggest that there is considerable difference in the efficacy of commercial health teas in influencing glucose absorption.

Determination of 1-deoxynojirimycin in mulberry leaves using hydrophilic interaction chromatography with evaporative light scattering detection

A simple and rapid method for determining 1-deoxynojirimycin (DNJ), a potent glucosidase inihibitor present in mulberry leaves (Morus alba and Morus bombysis), by high-performance liquid chromatography coupled to an evaporative light scattering detector (ELSD) has been developed. DNJ was separated from an extract of mulberry leaves on a TSKgel Amide-80 column, which is a representative column for hydrophilic interaction chromatography. During postcolumn detection, DNJ was detected by ELSD and concurrently identified by mass spectrometry. The detection limit was 100 ng. This method is sufficiently sensitive for determining DNJ in mulberry leaves and other related products.

Simple and rapid determination of 1-deoxynojirimycin in mulberry leaves

A simple and rapid method for determining 1-deoxynojirimycin (DNJ), a potent glucosidase inhibitor present in mulberry leaves (Morus alba and Morus bombysis), by high performance liquid chromatography coupled to an evaporative light scattering detector (ELSD) has been developed. DNJ was separated from extract of mulberry leaves on TSK gel Amide-80 column, which is a representative column for hydrophilic interaction chromatography. During post column detection, DNJ was detected by ELSD and concurrently identified by mass spectrometry. The detection limit was 100 ng. This method is sufficiently sensitive for determining DNJ in mulberry leaves and other related products.

Asymmetric synthesis of the four possible fagomine isomers

The asymmetric synthesis of fagomine and its congeners 1-4 has been achieved by catalytic ring-closing metathesis (RCM). The synthesis involved the construction of the piperidene-type chiral building block 5 followed by dihydroxylation, starting from the d-serine-derived Garner aldehyde 6.