N-containing sugars from Morus alba and their glycosidase inhibitory activities

Concise synthesis of calystegines B2 and B3via intramolecular Nozaki-Hiyama-Kishi reaction

The key step in the concise syntheses of calystegine B2 and its C-2 epimer calystegine B3 was the construction of cycloheptanone 8via an intramolecular Nozaki-Hiyama-Kishi (NHK) reaction of 9, an aldehyde containing a Z-vinyl iodide. Vinyl iodide 9 was obtained by the Stork olefination of aldehyde 10, derived from carbohydrate starting materials. Calystegines B2 (3) and B3 (4) were synthesized from d-xylose and l-arabinose derivatives respectively in 11 steps in excellent overall yields (27% and 19%).

CuAAC click chemistry with N-propargyl 1,5-dideoxy-1,5-imino-D-gulitol and N-propargyl 1,6-dideoxy-1,6-imino-D-mannitol provides access to triazole-linked piperidine and azepane pseudo-disaccharide iminosugars displaying glycosidase inhibitory properties

Protecting group-free synthesis of 1,2:5,6-di-anhydro-D-mannitol, followed by ring opening with propargylamine and subsequent ring closure produced a separable mix of piperidine N-propargyl 1,5-dideoxy-1,5-imino-D-gulitol and azepane N-propargyl 1,6-dideoxy-1,6-imino-D-mannitol. In O-acetylated form, these two building blocks were subjected to CuAAC click chemistry with a panel of three differently azide-substituted glucose building blocks, producing iminosugar pseudo-disaccharides in good yield. The overall panel of eight compounds, plus 1-deoxynojirimycin (DNJ) as a benchmark, was evaluated as prospective inhibitors of almond β-glucosidase, yeast α-glucosidase and barley β-amylase. The iminosugar pseudo-disaccharides showed no inhibitory activity against almond β-glucosidase, while the parent N-propargyl 1,5-dideoxy-1,5-imino-D-gulitol and N-propargyl 1,6-dideoxy-1,6-imino-D-mannitol likewise proved to be inactive against yeast α-glucosidase. Inhibitory activity could be reinstated in the former series by appropriate substitution on nitrogen. The greater activity of the piperidine could be rationalized based on docking studies. Further, potent inhibition of β-amylase was observed with compounds from both the piperidine and azepane series.

Identification and Determination of the Polyhydroxylated Alkaloids Compounds with α-Glucosidase Inhibitor Activity in Mulberry Leaves of Different Origins

Mulberry leaves have commonly been utilized in China as a herbal medicine for the treatment of diabetes for thousands of years. To evaluate the quality, an ultra-high performance liquid chromatography coupled with quadrupole time of flight mass spectrometry (UPLC-Q-TOF/MS) method was developed for identification of polyhydroxylated alkaloids with α-glucosidase inhibitor activity in mulberry leaf. As a result, five alkaloid compounds were identified or tentatively characterized. Among them, the compound 1-deoxynojirimycin (DNJ) was selected as the most typical and active chemical marker and quantified using an improved high performance liquid chromatography (HPLC) normal phase coupled with evaporative light scattering detector (ELSD) method. The developed method was fully validated in terms of linearity, sensitivity, precision and repeatability, as well as recovery, and subsequently applied to evaluate twenty-nine batches of mulberry leaves from different collections. From the analytical data it was discovered that the average content of DNJ is 1.53 mg/g, while the total contents of DNJ in the 29 mulberry leaf sample ranged from 0.20 to 3.88 mg/g, which suggested remarkable differences, although it reached the highest levels in early August. These data may provide an important reference for the quality of mulberry leaves used as herbal medicine for the treatment of diabetes or as a material to obtain the DNJ of α-glucosidase inhibitor or as a functional food.

Aglycone mimics for tuning of glycosidase inhibition: design, synthesis and biological evaluation of bicyclic pyrrolidotriazole iminosugars

Various fuco-configured bicyclic pyrrolidotriazole aglycone mimics were synthesised using copper-catalysed coupling of allyl bromides with terminal alkynes and Sonogashira–Hagihara reaction followed by intramolecular azide-alkyne ‘click’ reaction.

Synthesis of novel flavone hydrazones: in-vitro evaluation of α-glucosidase inhibition, QSAR analysis and docking studies

Thirty derivatives of flavone hydrazone (5-34) had been synthesized through a five-step reaction and screened for their α-glucosidase inhibition activity. Chalcone 1 was synthesized through aldol condensation then subjected through oxidative cyclization, esterification, and condensation reaction to afford the final products. The result for baker's yeast α-glucosidase (EC 3.2.1.20) inhibition assay showed that all compounds are active with reference to the IC50 value of the acarbose (standard drug) except for compound 3. Increase in activity observed for compounds 2 to 34 clearly highlights the importance of flavone, hydrazide and hydrazone linkage in suppressing the activity of α-glucosidase. Additional functional group on N-benzylidene moiety further enhances the activity significantly. Compound 5 (15.4 ± 0.22 μM), a 2,4,6-trihydroxy substituted compound, is the most active compound in the series. Other compounds which were found to be active are those having chlorine, fluorine, and nitro substituents. Compounds with methoxy, pyridine, and methyl substituents are weakly active. Further studies showed that they are not active in inhibiting histone deacetylase activity and do not possess any cytotoxic properties. QSAR model was being developed to further identify the structural requirements contributing to the activity. Using Discovery Studio (DS) 2.5, various 2D descriptors were being used to develop the model. The QSAR model is able to predict the pIC50 and could be used as a prediction tool for compounds having the same skeletal framework. Molecular docking was done for all compounds using homology model of α-glucosidase to identify important binding modes responsible for inhibition activity.

Synthesis, in vitro biological activities and in silico study of dihydropyrimidines derivatives

We describe here the synthesis of dihydropyrimidines derivatives 3a-p, and evaluation of their α-glucosidase enzyme inhibition activities. Compounds 3b (IC50=62.4±1.5 μM), 3c (IC50=25.3±1.26 μM), 3d (IC50=12.4±0.15 μM), 3e (IC50=22.9±0.25 μM), 3g (IC50=23.8±0.17 μM), 3h (IC50=163.3±5.1 μM), 3i (IC50=30.6±0.6 μM), 3m (IC50=26.4±0.34 μM), and 3o (IC50=136.1±6.63 μM) were found to be potent α-glucosidase inhibitors in comparison to the standard drug acarbose (IC50=840±1.73 μM). The compounds were also evaluated for their in vitro cytotoxic activity against PC-3, HeLa, and MCF-3 cancer cell lines, and 3T3 mouse fibroblast cell line. All compounds were found to be non cytotoxic, except compounds 3f and 3m (IC50=17.79±0.66-20.44±0.30 μM), which showed a weak cytotoxic activity against the HeLa, and 3T3 cell lines. In molecular docking simulation study, all the compounds were docked into the active site of the predicted homology model of α-glucosidase enzyme. From the docking result, it was observed that most of the synthesized compounds showed interaction through carbonyl oxygen atom and polar phenyl ring with active site residues of the enzyme.

γ-Aminoalcohol rearrangement applied to pentahydroxylated azepanes provides pyrrolidines epimeric to homoDMDP

A series of pentahydroxylated pyrrolidines, displaying five contiguous stereogenic centres and epimeric to α-glucosidase inhibitor homoDMDP, have been synthesized. The key step involves a γ-aminoalcohol rearrangement applied to polyhydroxylated azepanes. These five-membered iminosugars demonstrate micromolar inhibition of glycosidases.

d-Fagomine attenuates metabolic alterations induced by a high-energy-dense diet in rats

d-Fagomine attenuates the negative effects of a high-energy-dense diet on plasma glucose, triglycerides and metabolic hormones, as well as on weight gain in rats.

Organocatalyzed solvent free an efficient novel synthesis of 2,4,5-trisubstituted imidazoles for α-glucosidase inhibition to treat diabetes

A new and efficient solvent free synthesis of 2,4,5-trisubstituted imidazoles (3a-3j) was achieved by N-acetyl glycine (NAG) catalyzed three components condensation of aldehydes, benzil and ammonium acetate. Our synthetic methodology accommodated a range of various substituted alkyl and aryl aldehydes. Evaluation of α-glucosidase inhibitory activity of these imidazole derivatives revealed that most of them presented good α-glucosidase inhibition at low micro-molar concentrations. Among the synthesized compounds, compound 3c, bearing the ortho-hydroxy phenyl substituent at position 2 displayed the highest inhibitory activity with an IC50 value 74.32±0.59 μM. In silico molecular docking for all compounds and computational studies of the most active compound 3c were also performed.

Volatile Glycosides from the Leaves of Morus alba with a Potential Contribution to the Complex Anti-diabetic Activity

The leaves and root bark of Morus alba, the white mulberry tree, are well-known traditional medicines for the treatment of type II diabetes. Several different types of constituents have been suggested to be responsible for the anti-diabetic activity of mulberry drugs, such as iminosugars, flavonoids and other phenolic compounds, glycopeptides and ecdysteroids. Our group recently suggested that a volatile-oil like fraction of the hot water extract of M. alba leaves, containing several phenyl-propane derivatives, can increase the glucose consumption of adipocytes. Here we report the isolation of three glycosylated volatile constituents from mulberry leaves, two megastigmane derivatives along with the β-D-glucoside of eugenol. Furthermore, a commercially available mixture of probiotic bacteria was assessed to study the effect of the intestinal flora on the megastigmane derivatives. Significant amounts of the aglycons of both compounds were liberated, suggesting that these compounds can be metabolized in the large intestines and absorbed without the sugar moiety after the consumption of a traditional mulberry tea. Based on literature data, both the glycosides and their aglycons have a potential contribution to the beneficial effects of mulberry leaves in type 2 diabetes.

Natural product and natural product derived drugs in clinical trials

The 25 Natural Product (NP)-derived drugs launched since 2008 and the 100 NP-derived compounds and 33 Antibody Drug Conjugates (ADCs) in clinical trials or in registration at the end of 2013 are reviewed.

Evaluation of general toxicity and genotoxicity of the silkworm extract powder

The silkworm extract powder contain 1-deoxynojirimycin (DNJ), a potent α-glycosidase inhibitor, has therapeutic potency against diabetes mellitus. Therefore, natural products containing DNJ from mulberry leaves and silkworm are consumed as health functional food. The present study was performed to evaluate the safety of the silkworm extract powder, a health food which containing the DNJ. The repeated toxicity studies and gentic toxicity studies of the silkworm extract powder were performed to obtain the data for new functional food approval in MFDS. The safety was evaluated by a single-dose oral toxicity study and a 90 day repeated-dose oral toxicity study in Sprague-Dawley rats. The silkworm extract powder was also evaluated for its mutagenic potential in a battery of genetic toxicity test: in vitro bacterial reverse mutation assay, in vitro chromosomal aberration test, and in vivo mouse bone marrow micronucleus assay. The results of the genetic toxicology assays were negative in all of the assays. The approximate lethal dose in single oral dose toxicity study was considered to be higher than 5000 mg/kg in rats. In the 90 day study, the dose levels were wet at 0, 500, 1000, 2000 mg/kg/day, and 10 animals/sex/dose were treated with oral gavage. The parameters that were monitored were clinical signs, body weights, food and water consumptions, ophthalmic examination, urinalysis, hematology, serum biochemistry, necropsy findings, organ weights, and histopathological examination. No adverse effects were observed after the 90 day administration of the silkworm extract powder. The No-Observed-Adverse-Effect-Level (NOAEL) of silkworm extract powder in the 90 day study was 2000 mg/kg/day in both sexes, and no target organ was identified.

Production and Characterization of a New α-Glucosidase Inhibitory Peptide from Aspergillus oryzae N159-1

An α-glucosidase inhibitor was developed from Aspergillus oryzae N159-1, which was screened from traditional fermented Korean foods. The intracellular concentration of the inhibitor reached its highest level when the fungus was cultured in tryptic soy broth medium at 27℃ for five days. The inhibitor was purified using a series of purification steps involving ultrafiltration, Sephadex G-25 gel permeation chromatography, strong cation exchange solid phase extraction, reverse-phase high performance liquid chromatography, and size exclusion chromatography. The final yield of the purification was 1.9%. Results of the liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis indicated that the purified α-glucosidase inhibitor was a tri-peptide, Pro-Phe-Pro, with the molecular weight of 360.1 Da. The IC50 value of the peptide against α-glucosidase activity was 3.1 mg/mL. Using Lineweaver-Burk plot analysis, the inhibition pattern indicated that the inhibitor acts as a mixed type inhibitor.

Silk fibroin hydrolysate exerts an anti-diabetic effect by increasing pancreatic β cell mass in C57BL/KsJ-db/db mice

Components of silk including silk fibroin have long been used as anti-diabetic remedies in oriental medicine. However, detailed mechanisms underlying these antidiabetic effects remain unclear. In this study, we examined the anti-diabetic activity of silk fibroin hydrolysate (SFH) in C57BL/KsJ db/db (db/db) mice, a well-known animal model of non-insulin dependent diabetes mellitus. When the db/db mice were administered SFH in drinking water for 6 weeks, hyperglycemia in the animals gradually disappeared and the level of glycosylated hemoglobin decreased, indicating that SFH plays important role in reducing the symptoms of diabetes. In addition, SFH-treated db/db mice exhibited improved glucose tolerance with increased plasma insulin levels. Immunohistochemical and morphological analyses showed that SFH up-regulated insulin production by increasing pancreatic β cell mass in the mice. In summary, our results suggest that SFH exerts anti-diabetic effects by increasing pancreatic β cell mass in a non-insulin dependent diabetes mellitus mouse model.

Convenient Synthesis of 1,4-Dideoxy-1,4-imino-D-ribitol from D-Ribose

This paper describes a convenient synthesis of 1,4-dideoxy-1,4-imino-D-ribitol (DRB) from D-ribose. L-Lyxonolactone, a key intermediate in this synthesis, was prepared by base-promoted hydrolysis of a 5-chlorinated D-ribonolactone derivative with inversion of configuration at the C-4 position. Cyclization of the generated dimesylated L-lyxitol with benzylamine proceeded with another configurational inversion at C-4 to afford the D-ribo-configured pyrrolidine system, which upon deprotection gave DRB.

Chlorogenic acid and rutin play a major role in the in vivo anti-diabetic activity of Morus alba leaf extract on type II diabetic rats

The leaves of the white mulberry tree (Morus alba L.) are used worldwide in traditional medicine as anti-diabetics. Various constituents of mulberry leaves, such as iminosugars (i.e. 1-deoxynojirimicin), flavonoids and related compounds, polysaccharides, glycopeptides and ecdysteroids, have been reported to exert anti-diabetic activity, but knowledge about their contribution to the overall activity is limited. The objective of the present work was to determine the in vivo anti-diabetic activity of an extract of mulberry leaves (MA), and to examine to what extent three major constituents, chlorogenic acid, rutin and isoquercitrin, might contribute to the observed activity. Quantities of the three constituents of interest in the extract were determined by using HPLC-DAD. Activity was determined by using a type II diabetic rat model. After 11 days of per os administration of 250 or 750 mg/kg of MA or the corresponding amounts of each individual compound, a dose dependent decrease of non-fasting blood glucose levels were found for MA, chlorogenic acid and rutin, but not for isoquercitrin. Based on our results, chlorogenic acid and rutin might account for as much as half the observed anti-diabetic activity of MA, hence they can be considered as excellent markers for the quality control of mulberry products.

Production of the α-glycosidase inhibitor 1-deoxynojirimycin from Bacillus species

1-Deoxynojirimycin (DNJ), a potent α-glycosidase inhibitor, has therapeutic applications in treatments of HIV, Gaucher's disease, and diabetes. DNJ has been extracted from natural sources (mulberry leaves) for therapeutic purposes; however, DNJ ingredients are in limited supply and are costly to obtain on a large scale. Since certain strains of Bacillus and Streptomyces species reportedly produce DNJ, they may serve as potential sources for high-yield DNJ production. In this study, we obtained evidence for a DNJ production in Bacillus subtilis DSM704 by hydrophilic interaction chromatography-tandem mass spectrometry. In addition, from a screen of 750 microorganisms, we identified additional Bacillus strains (Bacillus amyloliquefaciens AS385 and Bacillus subtilis B4) that produce DNJ in large quantities. Investigation of the effect of various culture conditions, using Bacillus subtilis DSM704 and the DNJ high-production Bacillus strains, provided evidence for the importance of sorbitol supplementation on the yield of the DNJ precursor, 2-amino-2-deoxy-D-mannitol, thereby increasing DNJ production. The role of sorbitol in increased DNJ production was supported by an observed increase in mRNA expression of the biosynthetic gene, gabT1. When Bacillus amyloliquefaciens AS385 was cultured in medium supplemented with sorbitol, extracellular DNJ concentration reached a maximum of 460 mg/l of medium (equivalent to 9.20mg/g of freeze-dried medium), indicating that this strain can serve as a source for food- and drug-grade products. These findings not only lead to a further understanding of the DNJ biosynthetic pathway, but also suggest a method for microbial mass production of DNJ for therapeutic applications.

Conformationally-locked N-glycosides with selective β-glucosidase inhibitory activity: identification of a new non-iminosugar-type pharmacological chaperone for Gaucher disease

A series of conformationally locked N-glycosides having a cis-1,2-fused pyranose-1,3-oxazoline-2-thione structure and bearing different substituents at the exocyclic sulfur has been prepared. The polyhydroxylated bicyclic system was built in only three steps by treatment of the corresponding readily available 1,2-anhydrosugar with KSCN using TiO(TFA)(2) as catalyst, followed by S-alkylation and acetyl deprotection. In vitro screening against several glycosidase enzymes showed highly specific inhibition of mammalian β-glucosidase with a marked dependence of the potency upon the nature of the exocyclic substituent. The most potent representative, bearing an S-(ω-hydroxyhexadecyl) substituent, was further assayed as inhibitor of the human lysosomal β-glucocerebrosidase and as pharmacological chaperone in Gaucher disease fibroblasts. Activity enhancements in N370S/N370S mutants analogous to those achieved with the reference compound ambroxol were attained with a more favorable chaperone/inhibitor balance.

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.

Efficacy of silkworm (Bombyx mori L.) chrysalis oil as a lipid source in adult Wistar rats

The effects of silkworm chrysalis oil, rich in n-3 α-linolenic acid (ALA), on lipid metabolism in Wistar rats were investigated. The rats were fed diets containing 7% soybean oil (control), silkworm chrysalis oil (SWO), or fish oil (FO) for 8weeks. Plasma triglyceride and glucose levels were significantly lower in the SWO group after 8weeks compared to the control and FO groups. The total cholesterol and blood urea nitrogen levels were higher in the control group than in the SWO and FO groups at 8weeks post-consumption. However, aspartate amino transferase and alanine amino transferase levels were not significantly different among all groups. A higher arachidonic acid (AA) content was detected in the control group, while lower AA levels were observed with the increase in EPA and DHA in the SWO and FO groups. These results suggest that n-3 α-linolenic acid-rich silkworm chrysalis oil can improve hyperlipidaemia and hyperglycaemia.

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.

Chemical genetics and cereal starch metabolism: structural basis of the non-covalent and covalent inhibition of barley β-amylase

There are major issues regarding the proposed pathway for starch degradation in germinating cereal grain. Given the commercial importance but genetic intractability of the problem, we have embarked on a program of chemical genetics studies to identify and dissect the pathway and regulation of starch degradation in germinating barley grains. As a precursor to in vivo studies, here we report systematic analysis of the reversible and irreversible inhibition of the major β-amylase of the grain endosperm (BMY1). The molecular basis of inhibitor action was defined through high resolution X-ray crystallography studies of unliganded barley β-amylase, as well as its complexes with glycone site binder disaccharide iminosugar G1M, irreversible inhibitors α-epoxypropyl and α-epoxybutyl glucosides, which target the enzyme's catalytic residues, and the aglycone site binders acarbose and α-cyclodextrin.

Accumulation of 1-deoxynojirimycin in silkworm, Bombyx mori L

1-deoxynojirimycin (1-DNJ) contents in the silkworm, Bombyx mori, at different developmental stages and tissues were investigated by using reverse-phase high-performance liquid chromatography. The 1-DNJ contents of silkworm larvae change significantly with their developmental stages. The male larvae showed higher accumulation efficiency of 1-DNJ than the females and also a significant variation was observed among the silkworm strains. The present results show that tissue distribution of 1-DNJ was significantly higher in blood, digestive juice, and alimentary canal, but no 1-DNJ was observed in the silkgland. Moreover, 1-DNJ was not found in silkworms fed with artificial diet that does not contain mulberry leaf powder. This proves that silkworms obtain 1-DNJ from mulberry leaves; they could not synthesize 1-DNJ by themselves. The accumulation and excretion of 1-DNJ change periodically during the larval stage. There was no 1-DNJ in the newly-hatched larvae and 1-DNJ was mainly accumulated during the early and middle stages of every instar, while excreted at later stages of larval development. Further, it is possible to extract 1-DNJ from the larval feces and it is optimal to develop the 1-DNJ related products for diabetic auxiliary therapy.

Combined effect of total alkaloids from Feculae Bombycis and natural flavonoids on diabetes

Both total alkaloids from Feculae Bombycis (TAFB) and natural flavonoids can inhibit α-glucosidase activity to depress the glucose level in blood. To investigate the cooperative effect of TAFB and flavonoids on blood glucose, we have studied their combined function compared with individual ingredients on enzymology, in-vitro and in-vivo. In the enzymological assay, the combination of TAFB and flavonoids showed more effective inhibition, compared with either TAFB or flavonoids alone, to α-glucosidase activity. In the everted intestine model in-vitro, the combined inhibition of starch hydrolysation and glucose transference to blood was much stronger than with separate components. In short-term studies with normal and experimentally-induced diabetic mice in-vivo, the combination of TAFB and flavonoids also had a stronger suppressive effect on the postprandial elevation in blood glucose after oral administration. In long-term treatment to diabetic mice in-vivo, the compound prescription could depress not only the fasting blood glucose, but also the fasting blood total cholesterol. These results demonstrated that TAFB and flavonoids could inhibit α-glucosidase activity cooperatively, which would successfully depress blood glucose level in the therapy of diabetes.

Protective effects of dietary chamomile tea on diabetic complications

Matricaria chamomilla L., known as "chamomile", has been used as an herbal tea or supplementary food all over the world. We investigated the effects of chamomile hot water extract and its major components on the prevention of hyperglycemia and the protection or improvement of diabetic complications in diabetes mellitus. Hot water extract, esculetin (3) and quercetin (7) have been found to show moderate inhibition of sucrase with IC50 values of 0.9 mg/mL and 72 and 71 microM, respectively. In a sucrose-loading test, the administration of esculetin (50 mg/kg body weight) fully suppressed hyperglycemia after 15 and 30 min, but the extract (500 mg/kg body weight) and quercetin (50 mg/kg body weight) were less effective. On the other hand, a long-term feed test (21 days) using a streptozotocin-induced rat diabetes model revealed that the same doses of extract and quercetin showed significant suppression of blood glucose levels. It was also found that these samples increased the liver glycogen levels. Moreover, chamomile extract showed potent inhibition against aldose reductase (ALR2), with an IC50 value of 16.9 microg/mL, and its components, umbelliferone (1), esculetin (3), luteolin (6), and quercetin (7), could significantly inhibit the accumulation of sorbitol in human erythrocytes. These results clearly suggested that daily consumption of chamomile tea with meals could contribute to the prevention of the progress of hyperglycemia and diabetic complications.