Study of the inhibition of four alpha amylases by acarbose and its 4IV-α-maltohexaosyl and 4IV-α-maltododecaosyl analogues

Investigating Taste Perception of Maltodextrins Using Lactisole and Acarbose

Previous research has demonstrated that complex carbohydrates (maltodextrins) can be perceived in the oral cavity. However, little research has been conducted to thoroughly investigate complex carbohydrate taste perception and contributing factors. This study explored the effects of the degree of polymerization and the concentration of complex carbohydrates on taste perception. Additionally, the impact of lactisole and acarbose on carbohydrate taste perception was investigated. Using a blinded, Latin Square design, participants (n = 40) received samples (control) or samples with acarbose (5 mM) or lactisole (1.4 mM). Per visit, participants received solutions: (1) short chain maltodextrin (average DP 6) (SCM), (2) long chain maltodextrin (average DP 24) (LCM), (3) maltose, and (4) glucose. Samples were evaluated in duplicate, both at low concentration and high concentration. Participants tasted the samples and rated sweetness, starchiness, and viscosity (mouthfeel) perceived on a 10 cm continuous line scale and perceived intensity on a Labelled Magnitude Scale. There was a significant effect of degree of polymerisation on sweetness (p = 0.001) and intensity (p = 0.001). For low concentration samples, no significant differences were found between LCM and acarbose LCM or SCM and acarbose SCM for sweetness, starchiness, or mouthfeel (all p > 0.05). Significant differences were observed between LCM and lactisole LCM for sweetness (1.1 ± 0.1 vs. 2.5 ± 0.3, p = 0.001), starchiness (1.4 ± 0.2 vs. 2.3 ± 0.3, p = 0.005), and mouthfeel (1.4 ± 0.2 vs. 2.3 ± 0.3, p = 0.013). In conclusion, the taste perception of maltodextrins is influenced by the degree of polymerisation. Furthermore, for this study, the sweet taste receptor was not involved in maltodextrin taste perception. While salivary α-amylase did not appear to influence taste perception with low concentration maltodextrins, further investigation is necessary.

Acarbose glycosylation by AcbE for the production of acarstatins with enhanced α-amylase inhibitory activity

Acarbose is a potent glycosidase inhibitor widely used in the clinical treatment of type 2 diabetes mellitus (T2DM). Various acarbose analogs have been identified while exploring compounds with improved pharmacological properties. In this study, we found that AcbE from Actinoplanes sp. SE50/110 catalyzes the production of acarbose analogs that exhibit significantly improved inhibitory activity towards α-amylase than acarbose. Recombinant AcbE mainly catalyzed the formation of two new compounds, namely acarstatins A and B, using acarbose as substrate. Using high-resolution mass spectrometry, nuclear magnetic resonance, and glycosidase hydrolysis, we elucidated their chemical structures as O-α-d-maltosyl-(1 → 4)-acarbose and O-α-d-maltotriosyl-(1 → 4)-acarbose, respectively. Acarstatins A and B exhibited 1584- and 1478-fold greater inhibitory activity towards human salivary α-amylase than acarbose. Furthermore, both acarstatins A and B exhibited complete resistance to microbiome-derived acarbose kinase 1-mediated phosphorylation and partial resistance to acarbose-preferred glucosidase-mediated hydrolysis. Therefore, acarstatins A and B have great potential as candidate therapeutic agents for T2DM.

Control of postprandial hyperglycemia by oral administration of the sea anemone mucus-derived α-amylase inhibitor (magnificamide)

Diabetes mellitus is a serious threat to human health in both developed and developing countries. Optimal disease control requires the use of a diet and a combination of several medications, including oral hypoglycemic agents such as α-glucosidase inhibitors. Currently, the arsenal of available drugs is insufficient, which determines the relevance of studying new potent α-amylase inhibitors. We implemented the recombinant production of sea anemone derived α-amylase inhibitor magnificamide in Escherichia coli. Peptide was isolated by a combination of liquid chromatography techniques. Its folding and molecular weight was proved by 1H NMR and mass spectrometry. The Ki value of magnificamide against human pancreatic α-amylase is 3.1 nM according to Morrison equation for tight binding inhibitors. Our study of the thermodynamic characteristics of binding of magnificamide to human salivary and pancreatic α-amylases by isothermal titration calorimetry showed the presence of different binding mechanisms with Kd equal to 0.11 µM and 0.1 nM, respectively. Experiments in mice with streptozotocin-induced diabetes mimicking diabetes mellitus type 1 were used to study the efficiency of magnificamide against postprandial hyperglycemia. It was found that at a dose of 0.005 mg kg-1, magnificamide effectively blocks starch breakdown and prevents the development of postprandial hyperglycemia in T1D mice. Our results demonstrated the therapeutic potential of magnificamide for the control of postprandial hyperglycemia.

Natural Inhibitors of Mammalian α-Amylases as Promising Drugs for the Treatment of Metabolic Diseases

α-Amylase is a generally acknowledged molecular target of a distinct class of antidiabetic drugs named α-glucosidase inhibitors. This class of medications is scarce and rather underutilized, and treatment with current commercial drugs is accompanied by unpleasant adverse effects. However, mammalian α-amylase inhibitors are abundant in nature and form an extensive pool of high-affinity ligands that are available for drug discovery. Individual compounds and natural extracts and preparations are promising therapeutic agents for conditions associated with impaired starch metabolism, e.g., diabetes mellitus, obesity, and other metabolic disorders. This review focuses on the structural diversity and action mechanisms of active natural products with inhibitory activity toward mammalian α-amylases, and emphasizes proteinaceous inhibitors as more effective compounds with significant potential for clinical use.

Acarbose May Function as a Competitive Exclusion Agent for the Producing Bacteria

Acarbose is a well-known microbial specialized metabolite used clinically to treat type 2 diabetes. This natural pseudo-oligosaccharide (PsOS) shows potent inhibitory activity toward various glycosyl hydrolases, including α-glucosidases and α-amylases. While acarbose and other PsOSs are produced by many different bacteria, their ecological or biological role in microbial communities is still an open question. Here, we show that several PsOS-producing actinobacteria, i.e., Actinoplanes sp. SE50/110 (acarbose producer), Streptomyces glaucescens GLA.O (acarbose producer), and Streptomyces dimorphogenes ATCC 31484 (trestatin producer), can grow in the presence of acarbose, while the growth of the non-PsOS-producing organism Streptomyces coelicolor M1152 was suppressed when starch is the main source of energy. Further investigations using recombinant α-amylases from S. coelicolor M1152 and the PsOS-producing actinobacteria revealed that the S. coelicolor α-amylase was inhibited by acarbose, whereas those from the PsOS-producing bacteria were not inhibited by acarbose. Bioinformatic and protein modeling studies suggested that a point mutation in the α-amylases of the PsOS-producing actinobacteria is responsible for the resistance of those enzymes toward acarbose. Converting the acarbose-resistant α-amylase AcbE to its A304H variant diminished its acarbose-resistance property. Taken together, the results suggest that acarbose is used by the producing bacteria as a competitive exclusion agent to suppress the growth of other microorganisms in their natural environment, while the producing organisms equip themselves with α-amylase variants that are resistant to acarbose.

The Inhibition of α-Glucosidase, α-Amylase and Protein Glycation by Phenolic Extracts of Cotoneaster bullatus, Cotoneaster zabelii, and Cotoneaster integerrimus Leaves and Fruits: Focus on Anti-Hyperglycemic Activity and Kinetic Parameters

Cotoneaster species have gained significant importance in traditional Asian medicine for their ability to prevent and treat hyperglycemia and diabetes. Therefore, in this study, some aspects of the beneficial health effects of hydromethanolic extracts of C. bullatus, C. zabelii, and C. integerrimus leaves and fruits were evaluated, including their influence on α-glucosidase, α-amylase, and nonenzymatic protein glycation. The activity was investigated in relation to the polyphenolic profile of the extracts determined by UV-spectrophotometric and HPLC-PDA-fingerprint methods. It was revealed that all leaf and fruit extracts are a promising source of biological components (caffeic acid pseudodepsides, proanthocyanidins, and flavonols), and the leaf extracts of C. bullatus and C. zabelii contain the highest levels of polyphenols (316.3 and 337.6 mg/g in total, respectively). The leaf extracts were also the most effective inhibitors of digestive enzymes and nonenzymatic protein glycation. IC50 values of 8.6, 41.8, and 32.6 µg/mL were obtained for the most active leaf extract of C. bullatus (MBL) in the α-glucosidase, α-amylase, and glycation inhibition tests, respectively. In the kinetic study, MBL was displayed as a mixed-type inhibitor of both enzymes. The correlations between the polyphenol profiles and activity parameters (|r| > 0.72, p < 0.05) indicate a significant contribution of proanthocyanidins to the tested activity. These results support the traditional use of Cotoneaster leaves and fruits in diabetes and suggest their hydrophilic extracts be promising in functional applications.

Loss of Sucrase-Isomaltase Function Increases Acetate Levels and Improves Metabolic Health in Greenlandic Cohorts

BACKGROUND & AIMS

The sucrase-isomaltase (SI) c.273_274delAG loss-of-function variant is common in Arctic populations and causes congenital sucrase-isomaltase deficiency, which is an inability to break down and absorb sucrose and isomaltose. Children with this condition experience gastrointestinal symptoms when dietary sucrose is introduced. We aimed to describe the health of adults with sucrase-isomaltase deficiency.

METHODS

The association between c.273_274delAG and phenotypes related to metabolic health was assessed in 2 cohorts of Greenlandic adults (n = 4922 and n = 1629). A sucrase-isomaltase knockout (Sis-KO) mouse model was used to further elucidate the findings.

RESULTS

Homozygous carriers of the variant had a markedly healthier metabolic profile than the remaining population, including lower body mass index (β [standard error], -2.0 [0.5] kg/m²; P = 3.1 × 10^-5), body weight (-4.8 [1.4] kg; P = 5.1 × 10^-4), fat percentage (-3.3% [1.0%]; P = 3.7 × 10^-4), fasting triglyceride (-0.27 [0.07] mmol/L; P = 2.3 × 10^-6), and remnant cholesterol (-0.11 [0.03] mmol/L; P = 4.2 × 10^-5). Further analyses suggested that this was likely mediated partly by higher circulating levels of acetate observed in homozygous carriers (β [standard error], 0.056 [0.002] mmol/L; P = 2.1 × 10^-26), and partly by reduced sucrose uptake, but not lower caloric intake. These findings were verified in Sis-KO mice, which, compared with wild-type mice, were leaner on a sucrose-containing diet, despite similar caloric intake, had significantly higher plasma acetate levels in response to a sucrose gavage, and had lower plasma glucose level in response to a sucrose-tolerance test.

CONCLUSIONS

These results suggest that sucrase-isomaltase constitutes a promising drug target for improvement of metabolic health, and that the health benefits are mediated by reduced dietary sucrose uptake and possibly also by higher levels of circulating acetate.

The human microbiome encodes resistance to the antidiabetic drug acarbose

The human microbiome encodes a large repertoire of biochemical enzymes and pathways, most of which remain uncharacterized. Here, using a metagenomics-based search strategy, we discovered that bacterial members of the human gut and oral microbiome encode enzymes that selectively phosphorylate a clinically used antidiabetic drug, acarbose^1,2, resulting in its inactivation. Acarbose is an inhibitor of both human and bacterial α-glucosidases³, limiting the ability of the target organism to metabolize complex carbohydrates. Using biochemical assays, X-ray crystallography and metagenomic analyses, we show that microbiome-derived acarbose kinases are specific for acarbose, provide their harbouring organism with a protective advantage against the activity of acarbose, and are widespread in the microbiomes of western and non-western human populations. These results provide an example of widespread microbiome resistance to a non-antibiotic drug, and suggest that acarbose resistance has disseminated in the human microbiome as a defensive strategy against a potential endogenous producer of a closely related molecule.

Insights into the Inhibition Mechanism of Human Pancreatic α-Amylase, a Type 2 Diabetes Target, by Dehydrodieugenol B Isolated from Ocimum tenuiflorum

Use of human pancreatic α-amylase (HPA) inhibitors is one of the effective antidiabetic strategies to lower postprandial hyperglycemia via reduction in the dietary starch hydrolysis rate. Many natural products from plants are being studied for their HPA inhibitory activity. The present study describes isolation of dehydrodieugenol B (DDEB) from Ocimum tenuiflorum leaves using sequential solvent extraction, structure determination by one-dimensional (1D) and two-dimensional (2D) NMR analyses, and characterization as an HPA inhibitor using kinetics, binding thermodynamics, and molecular docking. DDEB uncompetitively inhibited HPA with an IC50 value of 29.6 μM for starch and apparent K i ' of 2.49 and Ki of 47.6 μM for starch and maltopentaose as substrates, respectively. The circular dichroism (CD) study indicated structural changes in HPA on inhibitor binding. Isothermal titration calorimetry (ITC) revealed thermodynamically favorable binding (ΔG of -7.79 kcal mol-1) with a dissociation constant (K d) of 1.97 μM and calculated association constant (K a) of 0.507 μM. Molecular docking showed stable HPA-inhibitor binding involving H-bonds and Pi-alkyl, alkyl-alkyl, and van der Waals (vDW) interactions. The computational docking results support the noncompetitive nature of DDEB binding. The present study could be helpful for exploration of the molecule as a potential antidiabetic drug candidate to control postprandial hyperglycemia.

Inhibition of starch digestion: The role of hydrophobic domain of both α-amylase and substrates

The physicochemical mechanism of starch digestion is very complicated since it may be affected by the non-valence interactions of the amylase inhibitor with the substrate or the enzyme. The role of hydrophobic interaction in the process of starch digestion is not clear. In this study, pluronics (PLs) with different hydrophobicity were used as model amphiphilic compounds to study their inhibition on starch digestion using multi-spectroscopic methods. The results showed that the hydrophobic nature of PLs changed starch structure, but it had a greater effect on the structure of α-amylase by exposing more tryptophan residues and increasing α-helix and β-sheet contents. Further investigation by using different chain-length fatty acids confirmed the results. The finding in this study is informative to design and fabricate α-amylase inhibitors for controlling starch digestion at the molecular level.

A neutral polysaccharide from green tea: Structure, effect on α-amylase activity and hydrolysis property

A neutral tea polysaccharide (TPSN) was isolated from green tea. Gas chromatography analysis showed that TPSN was composed of d-glucose, l-arabinose and d-galactose residues at a molar ratio of 90.0: 9.1: 0.9. The weight-averaged molecular weight of TPSN was determined as about 2.0 × 10⁵ g mol^-1 using static light scattering analysis. The result of nuclear magnetic resonance (NMR) spectroscopy indicated that TPSN and water-soluble starch had similar structures. TPSN exhibited inhibitory activity towards α-amylase through the noncompetitive inhibition mechanism, but the tertiary structure of α-amylase related to enzymatic activity, analyzed using circular dichroism spectroscopy, was not affected by TPSN. Meanwhile, TPSN exhibited hydrolysis properties catalyzed by α-amylase. Molecular docking analysis revealed that the various behaviors of TPSN to α-amylase could be attributed to that the different chain segments of TPSN combined with different amino acid residues of α-amylase.

Magnificamide Is a New Effective Mammalian α-Amylase Inhibitor

Recombinant analogue of the sea anemone Heteractismagnifica peptide was obtained, and the kinetic parameters of its interaction with mammalian α-amylases were determined. Magnificamide inhibits α-amylases significantly stronger than the medical drug acarbose (Precose^TM or Glucobay^TM). Magnificamide is assumed to find application as a drug for prevention and treatment of metabolic disorders and type 2 diabetes mellitus.

The Sweet Taste of Acarbose and Maltotriose: Relative Detection and Underlying Mechanism

Although sweet-tasting saccharides possess similar molecular structures, their relative sweetness often varies to a considerable degree. Current understanding of saccharide structure/sweetness interrelationships is limited. Understanding how certain structural features of saccharides and/or saccharide analogs correlate to their relative sweetness can provide insight on the mechanisms underlying sweetness potency. Maltotriose is a short-chain glucose-based oligosaccharide, which we recently reported to elicit sweet taste. Acarbose, an α-glucosidase inhibitor, is a pseudo-saccharide that has an overall resemblance to a glucose-based oligosaccharide and thus may be viewed as a structural analog. During other studies, we recognized that acarbose can also elicit sweet taste. Here, we formally investigated the underlying taste detection mechanism of acarbose, while confirming our previous findings for maltotriose. We found that subjects could detect the sweet taste of acarbose and maltotriose in aqueous solutions but were not able to detect them in the presence of a sweet taste inhibitor lactisole. These findings support that both are ligands of the human sweet taste receptor, hT1R2/hT1R3. In a separate experiment, we measured the relative sweetness detection of acarbose, maltotriose, and other sweet-tasting mono- and disaccharides (glucose, fructose, maltose, and sucrose). Whereas maltotriose was found to have a similar discriminability profile to glucose and maltose, the discriminability of acarbose matched that of fructose at the concentrations tested (18, 32, and 56 mM). These findings are discussed in terms of how specific molecular features (e.g., degree of polymerization and monomer composition) may contribute to the relative sweetness of saccharides.

Magnificamide, a β-Defensin-Like Peptide from the Mucus of the Sea Anemone Heteractis magnifica, Is a Strong Inhibitor of Mammalian α-Amylases

Sea anemones’ venom is rich in peptides acting on different biological targets, mainly on cytoplasmic membranes and ion channels. These animals are also a source of pancreatic α-amylase inhibitors, which have the ability to control the glucose level in the blood and can be used for the treatment of prediabetes and type 2 diabetes mellitus. Recently we have isolated and characterized magnificamide (44 aa, 4770 Da), the major α-amylase inhibitor of the sea anemone Heteractis magnifica mucus, which shares 84% sequence identity with helianthamide from Stichodactyla helianthus. Herein, we report some features in the action of a recombinant analog of magnificamide. The recombinant peptide inhibits porcine pancreatic and human saliva α-amylases with Ki’s equal to 0.17 ± 0.06 nM and 7.7 ± 1.5 nM, respectively, and does not show antimicrobial or channel modulating activities. We have concluded that the main function of magnificamide is the inhibition of α-amylases; therefore, its functionally active recombinant analog is a promising agent for further studies as a potential drug candidate for the treatment of the type 2 diabetes mellitus.

A study towards drug discovery for the management of type 2 diabetes mellitus through inhibition of the carbohydrate-hydrolyzing enzymes α-amylase and α-glucosidase by chalcone derivatives

The inhibition of carbohydrate-hydrolyzing enzymes, α-amylase and α-glucosidase, is one of the major therapeutic strategies for the treatment of type 2 diabetes mellitus. Chalcones have been recognized for their multiple biological activities, including antidiabetic properties, through unclear mechanisms. In the present work, a panel of chalcones bearing hydroxy, methoxy, methyl, nitro, chloro, fluoro and bromo substituents were evaluated against α-amylase and α-glucosidase activities, most of them for the first time. The results showed that the substitution patterns and the type of substituents of chalcones influence their inhibitory activity. The presence of hydroxy groups at C-2'- and C-4' of the A ring and at C-3 and C-4 of the B ring favors the intended effect. Chalcones holding nitro groups and chloro substituents, together with a hydroxy group in the chalcone scaffold, showed strong inhibition of the α-glucosidase activity. The present study provides related scaffolds that may serve as the basis for the design and synthesis of new structures in order to obtain the ideal antidiabetic chalcone.

Evaluation of a flavonoids library for inhibition of pancreatic α-amylase towards a structure-activity relationship

α-Amylase has been considered an important therapeutic target for the management of type 2 diabetes mellitus (T2DM), decreasing postprandial hyperglycaemia (PPHG). In the present work, a panel of 40 structurally related flavonoids was tested, concerning their ability to inhibit α-amylase activity, using a microanalysis screening system, an inhibitory kinetic analysis and molecular docking calculations. From the obtained results, it was possible to observe that the flavone with a -Cl ion at 3-position of C-ring, an –OH group at 3′- and 4′- positions of B-ring and at 5- and 7- positions of A-ring and the C2 = C3 double bond, was the most active tested flavonoid, through competitive inhibition. In conclusion, some of the tested flavonoids have shown promising inhibition of α-amylase and may be considered as possible alternatives to the modulation of T2DM.

Acylated Aminooligosaccharides with Inhibitory Effects against α-Amylase from Streptomyces sp. HO1518

Five new acylated aminooligosaccharides (1–5), together with one known related analogue (6), were isolated from Streptomyces sp. HO1518. Their structure was identified by extensive spectroscopic analysis, including 1D and 2D NMR data and high resolution electrospray ionization mass spectrometry (HRESIMS), and by comparison with those reported in the literature. All of the new compounds showed more promising porcine pancreatic α-amylase (PPA) inhibitory activities than the clinical drug acarbose, indicating them as potential pharmaceutical drug leads toward type II diabetes.

Therapeutic potential of α-glucosidase inhibitors in type 2 diabetes mellitus: an evidence-based review

INTRODUCTION

Postprandial hyperglycemia (PPHG) contributes to micro- and macro-vascular complications more than fasting hyperglycemia in patients with type 2 diabetes mellitus. Due to the traditional carbohydrate-rich diet, Asians, particularly Indians and Chinese need agents to control the higher risk of uncontrolled PPHG. Targeting PPHG with α-glucosidase inhibitors (AGIs), either alone or in combination with other oral hypoglycemic agents and insulin, provide overall glycemic control with transient mild gastrointestinal disorders. Treatment with AGIs, especially acarbose, has also shown to provide beneficial effects on lipid levels, blood pressure, coagulation factors, carotid intima-media thickness and endothelial dysfunction. New insights of acarbose therapy obtained like increased activity of gut hormones and improved gut microbiota may explain the benefits on weight, whereas increased production of H2 may explains its cardiovascular benefits to some extent.

AREAS COVERED

A systematic search strategy was developed to identify randomized controlled trials in MEDLINE, PubMed, EMBASE and ongoing trials databases.

EXPERT OPINION

AGIs as a class and acarbose in particular, are most useful in combatting PPHG and glucose variability across the spectrum of diabetes therapy, particularly in Asian patients. Together with their effects on incretin hormones and gut-microbiota AGIs can be considered beyond glycemic control as 'cardio-protective agents.'

Microwave and micronization treatments affect dehulling characteristics and bioactive contents of dry beans (Phaseolus vulgaris L.)

BACKGROUND

Heat pretreatment is considered the first step in grain milling. This study therefore evaluated microwave and micronization heat treatments in improving the dehulling characteristics, phenolic composition and antioxidant and α-amylase activities of bean cultivars from three market classes.

RESULTS

Heat treatments improved dehulling characteristics (hull yield, rate coefficient and reduced abrasive hardness index) depending on bean cultivar, whereas treatment effects increased with dehulling time. Micronization increased minor phenolic components (tartaric esters, flavonols and anthocyanins) of all beans but had variable effects on total phenolic content depending on market class. Microwave treatment increased α-amylase inhibitor concentration, activity and potency, which were strongly correlated (r²  = 0.71, P < 0.0001) with the flavonol content of beans. Heat treatment had variable effects on the phenolic composition of bean hulls obtained by abrasive dehulling without significantly altering the antioxidant activity of black and pinto bean hulls. Principal component analysis on 22 constituents analyzed in this study demonstrated the differences in dehulling characteristics and phenolic components of beans and hulls as major factors in segregating the beneficial heat treatment effects.

CONCLUSION

Heat treatment may be useful in developing novel dietary fibers from beans with variable composition and bioactivity with a considerable range of applications as functional food ingredients.

Actinobacterial enzyme inhibitors--a review

Actinobacteria have potential as important new sources of enzyme inhibitors. Enzyme inhibitors have great demand in medicine, agriculture and biotechnology. In medicine, enzyme inhibitors can be used as therapeutic agents for bacterial, fungal, viral and parasitic diseases as well as treating cancer, neurodegenerative, immunological and cardiovascular diseases. Enzyme inhibitors are also valuable for the control of carbohydrate-dependent diseases such as diabetes, obesity and hyperlipidemia and melanogenesis in skin. They can be also involved in crop protection against plant pathogens, herbivorous pests and abiotic stresses such as drought. In this review, we discuss about several actinobacterial enzyme inhibitors with various industrial uses and biotechnological applications.

Two novel potent α-amylase inhibitors from the family of acarviostatins isolated from the culture of Streptomyces coelicoflavus ZG0656

Two novel aminooligosaccharides were separated from the culture filtrate of Streptomyces coelicoflavus ZG0656. Their chemical structures were determined by acidic hydrolysis, electrospray-ionization tandem mass spectrometry (ESI-MS/MS), and NMR spectroscopy. The compounds were named acarviostatins III0(-1) and III23 according to the nomenclature of this group of metabolites. The two novel acarviostatins were both mixed noncompetitive inhibitors of porcine pancreatic α-amylase (PPA). The inhibition constants (K(i)) for acarviostatins III0(-1) and III23 were 0.009 and 0.026 μM, respectively, 151 and 52 times more potent than acarbose.

Phytonutrients for controlling starch digestion: evaluation of grape skin extract

The objective of this work was to evaluate the structure-function relationship between grape skin extract and human α-amylase. The grape skin extract was characterised as resveratrol-3-O-glucoside by RP-HPLC-ESI-MS, which showed strong inhibition towards α-amylase and the IC50 value was 1.35 mg/ml. The kinetic results demonstrated grape skin extract obeyed the non-competitive mode against amylase. Fluorescence data revealed the ability of grape skin binding to amylase belonged to static quenching mechanism with a complex formation and there was only one binding site in α-amylase for grape skin extract. Docking study showed a best pose with total energy value of -118.3 kJ/mol and grape skin extract interacted with side chain of Asp300 with hydrogen bonds and Van der Waals forces. This preliminary observation provides the basis for further evaluation of the suitability of grape skin extract as natural inhibitor with potential health benefits.

Extracts of Maqui ( Aristotelia chilensis ) and Murta ( Ugni molinae Turcz.): sources of antioxidant compounds and α-Glucosidase/α-Amylase inhibitors

The objective of this work was to evaluate the antioxidant and antihemolytic activities of crude, aqueous, and organic-aqueous extracts of maqui ( Aristotelia chilensis ) and murta ( Ugni molinae Turcz.), together with their inhibiting effect on enzymes involved in the metabolism of carbohydrates. Radical scavenging activity, inhibition of linoleic acid oxidation in a micellar system, antihemolytic activity, and inhibition of α-amylases and α-glucosidases were analyzed. Crude extracts of maqui leaves and fruits were found to be important sources of polyphenolic compounds, showing 69.0 ± 0.9 and 45.7 ± 1.1 mg GAE/g dm, respectively. Polyphenols from maqui leaves were active as antioxidants and antihemolytic compounds (p < 0.05), showing a noncompetitive inhibiting effect on α-glucosidase. Flavan-3-ol polymers and glycosylated flavonols, such as quercetin glucoside and kaempferol glucoside, were tentatively identified in extracts. This preliminary observation provides the basis for further examination of the suitability of polyphenol-enriched extracts from maqui and murta as nutritional or medicinal supplements with potential human health benefits.

Taxonomy of the Streptomyces strain ZG0656 that produces acarviostatin alpha-amylase inhibitors and analysis of their effects on blood glucose levels in mammalian systems

AIMS

To clarify the taxonomic status of strain ZG0656 and analyse the effects of its acarviostatin products on blood glucose levels in mammalian systems.

METHODS AND RESULTS

Our program to screen for new alpha-amylase inhibitors led to the isolation of strain ZG0656. The polyphasic taxonomic study revealed that strain ZG0656 represents a novel variation of Streptomyces coelicoflavus, for which we propose the name S. coelicoflavus var. nankaiensis. Four chemically distinct alpha-amylase inhibitors, acarviostatins I03, II03, III03 and IV03, were isolated from strain ZG0656. Acarviostatins III03 and IV03 are both novel oligomers. All four acarviostatins are mixed noncompetitive porcine pancreas alpha-amylase inhibitors. Acarviostatin III03 is the most potent alpha-amylase inhibitor known to date. Moreover, in the in vitro and in vivo experiments, acarviostatins III03 showed significant inhibition of starch hydrolysis and glucose transfer to blood.

CONCLUSIONS

Strain ZG0656 is a novel variation of S. coelicoflavus, whose products are novel effective alpha-amylase inhibitors. Among the products, acarviostatins III03 could significantly depress blood glucose levels in mammalian systems and be developed towards a possible therapeutic agent for diabetes.

SIGNIFICANCE AND IMPACT OF THE STUDY

Acarviostatin III03 is the most potent alpha-amylase inhibitor known to date. The oligomer will benefit the research on the relationship between alpha-amylase and various inhibitors and will offer more choices in diabetes treatments.

Four acarviosin-containing oligosaccharides identified from Streptomyces coelicoflavus ZG0656 are potent inhibitors of alpha-amylase

Four aminooligosaccharides were isolated and purified from the culture filtrate of Streptomyces coelicoflavus ZG0656. Their chemical structures were determined by electrospray ionization tandem mass spectrometry (ESI-MS/MS) and two-dimensional nuclear magnetic resonance (NMR) spectroscopy. The names acarviostatins I03, II03, III03, and IV03 were given to the oligomers due to their acarviosin core structures. Acarviostatins III03 and IV03, which contain three and four acarviosin-glucose moieties, respectively, were identified as novel compounds. The four acarviostatins were all mixed noncompetitive inhibitors of porcine pancreatic alpha-amylase (PPA). The inhibition constants (K(i)) for acarviostatins III03 and IV03 were 0.008 and 0.033muM, respectively. Acarviostatin III03 is the most effective alpha-amylase inhibitor known to date, with a K(i) value 260 times more potent than acarbose.

Two novel aminooligosaccharides isolated from the culture of Streptomyces coelicoflavus ZG0656 as potent inhibitors of alpha-amylase

Two novel aminooligosaccharides were separated from the culture filtrate of Streptomyces coelicoflavus ZG0656. Their chemical structures were determined by electrospray ionization tandem mass spectrometry (ESI-MS/MS) and 2D nuclear magnetic resonance (NMR) spectroscopy. Because of their acarviosine core structures, the names acarviostatins II23 and II13 were given to the novel compounds. The two acarviostatins were both mixed noncompetitive inhibitors of porcine pancreatic alpha-amylase (PPA), with inhibition constants (K(i)) of 0.009 microM (acarviostatin II23) and 0.010 microM (acarviostatin II13). Therefore, acarviostatin II23 and acarviostatin II13 are, respectively, 231 and 208 times more potent than acarbose.

Amylomaltase of Pyrobaculum aerophilum IM2 produces thermoreversible starch gels

Amylomaltases are 4-alpha-glucanotransferases (EC 2.4.1.25) of glycoside hydrolase family 77 that transfer alpha-1,4-linked glucans to another acceptor, which can be the 4-OH group of an alpha-1,4-linked glucan or glucose. The amylomaltase-encoding gene (PAE1209) from the hyperthermophilic archaeon Pyrobaculum aerophilum IM2 was cloned and expressed in Escherichia coli, and the gene product (PyAMase) was characterized. PyAMase displays optimal activity at pH 6.7 and 95 degrees C and is the most thermostable amylomaltase described to date. The thermostability of PyAMase was reduced in the presence of 2 mM dithiothreitol, which agreed with the identification of two possible cysteine disulfide bridges in a three-dimensional model of PyAMase. The kinetics for the disproportionation of malto-oligosaccharides, inhibition by acarbose, and binding mode of the substrates in the active site were determined. Acting on gelatinized food-grade potato starch, PyAMase produced a thermoreversible starch product with gelatin-like properties. This thermoreversible gel has potential applications in the food industry. This is the first report on an archaeal amylomaltase.

In situ extension as an approach for identifying novel alpha-amylase inhibitors

A new approach for the discovery and subsequent structural elucidation of oligosaccharide-based inhibitors of alpha-amylases based upon autoglucosylation of known alpha-glucosidase inhibitors is presented. This concept, highly analogous to what is hypothesized to occur with acarbose, is demonstrated with the known alpha-glucosidase inhibitor, d-gluconohydroximino-1,5-lactam. This was transformed from an inhibitor of human pancreatic alpha-amylase with a K(i) value of 18 mm to a trisaccharide analogue with a K(i) value of 25 mum. The three-dimensional structure of this complex was determined by x-ray crystallography and represents the first such structure determined with this class of inhibitors in any alpha-glycosidase. This approach to the discovery and structural analysis of amylase inhibitors should be generally applicable to other endoglucosidases and readily adaptable to a high throughput format.