Structures of human pancreatic α-amylase in complex with acarviostatins: Implications for drug design against type II diabetes

An experimental and computational approach to evaluate the antidiabetic activity of Commiphora wightii gum extract

BACKGROUND

Plant formulations with antidiabetic and antioxidant properties have recently gained popularity due to their lower cost and lesser side effects. Guggul gum is one such formulation that is extensively being used to cure various ailments.

OBJECTIVE

The present study was designed to explore the antioxidant and antidiabetic properties of the aqua-ethanolic Guggul gum extract (GE) from Commiphora wightii using in silico studies and in vitro assays.

METHODS

Gas Chromatography Mass Spectroscopy (GCMS) identified compounds were docked to the Human pancreatic α-amylase (HPA, PDB ID: 1HNY) for in silico studies to predict the inhibition. Molecular dynamics simulations (MDS) were performed using GROMACS for 100 ns. The inhibition of the enzyme was further evaluated at in vitro level to show the compounds' hypoglycemic role.

RESULTS

The extract showed a good amount of phenolic (5.14 ± 0.011 mg), flavonoid (0.66 ± 0.023 mg) and terpenoid (1.08 ± 0.018 mg) content along with a promising free radical scavenging activity of 41.96 ± 4.02%. In the in silico studies, 3 out of 6 GCMS-identified bioactive compounds showed permissible values of bioavailability properties suggesting them as a potential candidate for antidiabetic drugs. Similarly, in molecular docking studies, 3 compounds showed more binding energy than the standard drug acarbose indicating better inhibition. MDS studies showed Compound 4 (Diisooctyl phthalate), was the most stable with the lowest root mean square deviation (RMSD) and root mean square fluctuation (RMSF) values, a consistent radius of gyration (Rg), and stable solvent accessible surface area (SASA). This was further confirmed by in vitro analysis where the pancreatic α-amylase inhibitory activity of the extract and the standard drug (acarbose) were comparable at an IC50 value of 4.17 ± 1.26 mg/mL and 3.69 ± 0.89 mg/mL respectively.

CONCLUSION

The results demonstrated GE as a potential alternative to commercial antidiabetic drugs. Out of the major 6 GCMS-identified compounds, Compound 4 showed the most stable conformation during MDS studies. However, the isolation of the identified compounds could be done in the future for in vivo studies.

Correlating enzymatic reactivity for different substrates using transferable data-driven collective variables

Machine learning (ML) is transforming the investigation of complex biological processes. In enzymatic catalysis, one significant challenge is identifying the reactive conformations (RC) of the enzyme:substrate complex where the substrate assumes a precise arrangement in the active site necessary to initiate a reaction. Traditional methods are hindered by the complexity of the multidimensional free energy landscape involved in the transition from nonreactive to reactive conformations. Here, we applied ML techniques to address this challenge, focusing on human pancreatic α-amylase, a crucial enzyme in type-II diabetes treatment. Using ML-based collective variables (CVs), we correlated the probability of being in a RC with the experimental catalytic activity of several malto-oligosaccharide substrates. Our findings demonstrate a remarkable transferability of these CVs across various compounds, significantly streamlining the modeling process and reducing both computational demand and manual intervention in setting up simulations for new substrates. This approach not only advances our understanding of enzymatic processes but also holds substantial potential for accelerating drug discovery by enabling rapid and accurate evaluation of drug efficacy across different generations of inhibitors.

Antidiabetic potential of thiazolidinedione derivatives with efficient design, molecular docking, structural activity relationship, and biological activity: an update review (2021-2023)

Thiazolidinedione has been used successfully by medicinal chemists all over the world in the development of potent antidiabetic derivatives. The few compounds with excellent antidiabetic potency that we have identified in this review could be used as a lead for further research into additional antidiabetic mechanisms. The information provided in this review regarding the design, biological activity, structure-activity relationships, and docking studies may be useful for scientists who wish to further explore this scaffold in order to fully utilize its biological potential and develop antidiabetic agents that would overcome the limitations of currently available medications for the treatment of diabetes. This review outlines the antidiabetic potential of Thiazolidinedione-based derivatives that have been published in the year 2021- till date.

Integrative bioinformatic and experimental analysis of benzoylbenzodioxol derivatives: hypoglycemic potential in diabetic mice

We investigated the hypoglycemic activity and pharmacokinetic study of two synthesized benzoyl benzodioxol derivatives, compound I (methyl 2-(6-(2-bromobenzoyl)benzo[d][1,3]dioxol-5-yl)acetate), and compound II, 2-(6-benzoylbenzo[d][1,3]dioxol-5-yl)acetic acid, which showed very strong α-amylase inhibiting activity in our previous study. Then, diabetes was induced by the injection of streptozotocin to mice. The molecular docking simulations and analyses of density functional theory analyses were conducted to study the binding interactions with human pancreatic alpha-amylase, and their pharmacokinetic properties were further evaluated by ADMET profiling. Compound I showed the most important hypoglycemic effect, decreasing the blood glucose by 32.4%, higher than that of compound II by 14.8% and even the positive control acarbose by 22.9%. Histopathological examination revealed that diabetic livers showed portal inflammation with some apoptotic hepatocytes due to streptozotocin treatment, whereas controls without any treatment maintained normal liver architecture. Molecular docking studies gave results for the best binding affinity of the compound I, through its strong water bridges and π-π interactions, and also through analysis with density functional theory, was more stable and reactive when compared to compound II. Further ADMET analysis showed that both compounds shared a promising pharmacokinetic profile, and compound I had the potential for CNS penetration. Thus, compound I was selected as the best candidate for developing new hypoglycemic agents with potent efficacy, good binding interactions, and excellent pharmacokinetic properties.

Kinetics and molecular modeling studies on the inhibition mechanism of GH13 α-glycosidases by small molecule ligands

Alpha-glucosidase inhibitors play an important role in Diabetes Mellitus (DM) treatment since they prevent postprandial hyperglycemia. The Glycoside Hydrolase family 13 (GH13) is the major family of enzymes acting on substrates containing α-glucoside linkages, such as maltose and amylose/amylopectin chains in starch. Previously, our group identified glycoconjugate 1H-1,2,3-triazoles (GCTs) inhibiting two GH13 α-glycosidases: yeast maltase (MAL12) and porcine pancreatic amylase (PPA). Here, we combined kinetic studies and computational methods on nine GCTs to characterize their inhibitory mechanism. They all behaved as reversible inhibitors, and kinetic models encompassed noncompetitive and various mechanisms of mixed-type inhibition for both enzymes. Most potent inhibitors displayed Ki values of 30 μM for MAL12 (GPESB16) and 37 μM for PPA (GPESB15). Molecular dynamics and docking simulations indicated that on MAL12, GPESB15 and GPESB16 bind in a cavity adjacent to the active site, while on the PPA, GPESB15 was predicted to bind at the entrance of the catalytic site. Notably, despite its putative location within the active site, the binding of GPESB15 does not obstruct the substrate's access to the cleavage site. Our study contributes to paving the way for developing novel therapeutic strategies for managing DM-2 through GH13 α-glycosidases inhibition.

Novel pyrazoline linked acyl thiourea pharmacophores as antimicrobial, urease, amylase and α-glucosidase inhibitors: design, synthesis, SAR and molecular docking studies

In the present work, a small library of novel pyrazolinyl-acyl thiourea (5a-j) was designed and synthesized through a multistep sequence and the synthesized compounds were screened for their antifungal, antibacterial and antioxidant activities as well as urease, amylase and α-glucosidase inhibitory activities. The synthesized series (5a-o) was characterized using a combination of spectroscopic techniques, including FT-IR, 1H NMR and 13C NMR. All compounds (5a-j) were found to have significant potency against urease, α-glucosidase, α-amylase, and DPPH. The synthesized compounds were also screened for potential antibacterial and anti-fungal inhibition activities. IC50 values for all the prepared compounds for urease, α-glucosidase, amylase, and DPPH inhibition were determined and derivatives 5b and 5g were found to be the most potent urease inhibitors with IC50 values of 54.2 ± 0.32 and 43.6 ± 0.25 μM, respectively. Whilst compound 5b (IC50 = 68.3 ± 0.11 μM) is a potent α-glucosidase inhibitor, compound 5f (90.3 ± 1.08 μM) is a potent amylase inhibitor and compound 5b (103.4 ± 1.15 μM) is a potent antioxidant. The different substitutions on the phenyl ring were the basis for structure-activity relationship (SAR) study. The molecular docking study was performed for the confirmation of binding interactions.

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.

Characterization and Investigation of Novel Benzodioxol Derivatives as Antidiabetic Agents: An In Vitro and In Vivo Study in an Animal Model

In this study, we synthesized benzodioxol carboxamide derivatives and investigated their antidiabetic potential. The synthesized compounds (Ia-Ic and IIa-IId) underwent characterization via HRMS, 1H-, 13CAPT-NMR, and MicroED. Their efficacy against α-amylase was assessed in vitro, while MTS assays were employed to gauge cytotoxicity across cancer and normal cell lines. Additionally, the antidiabetic impact of compound IIc was evaluated in vivo using a streptozotocin-induced diabetic mice model. Notably, IIa and IIc displayed potent α-amylase inhibition (IC50 values of 0.85 and 0.68 µM, respectively) while exhibiting a negligible effect on the Hek293t normal cell line (IC50 > 150 µM), suggesting their safety. Compound IId demonstrated significant activity against four cancer cell lines (26-65 µM). In vivo experiments revealed that five doses of IIc substantially reduced mice blood glucose levels from 252.2 mg/dL to 173.8 mg/dL in contrast to the control group. The compelling in vitro anticancer efficacy of IIc and its safety for normal cells underscores the need for further in vivo assessment of this promising compound. This research highlights the potential of benzodioxol derivatives as candidates for the future development of synthetic antidiabetic drugs.

Network pharmacology based anti-diabetic attributes of bioactive compounds from Ocimum gratissimum L. through computational approach

The present research was framed to determine the key compounds present in the plant Ocimum gratissimum L. targeting protein molecules of Diabetes Mellitus (DM) by employing In-silico approaches. Phytochemicals previously reported to be present in this herb were collated through literature survey and public phytochemical databases, and their probable targets were anticipated using BindingDB (p ≥ 0.7). STRING and KEGG pathway databases were employed for pathway enrichment analysis. Homology modelling was executed to elucidate the structures of therapeutic targets. Further, Phytocompounds from O. gratissimum were subjected for docking with four therapeutic targets of DM by using AutoDock vina through POAP pipeline implementation. 30 compounds were predicted to target 136 protein molecules including aldose reductase, DPP4, alpha-amylase, and alpha-glucosidase. Neuroactive ligand-receptor interaction, MAPK, PI3K-Akt, starch and insulin resistance were predicted to have potentially modulation by phytocompounds. Based on the phytocompound's binding score with the four targets of DM, Rutin scored the lowest binding energy (-11 kcal/mol) with Aldose reductase by forming 17 intermolecular interactions. In conclusion, based on the network and binding score, phytocompounds from O. gratissimum have a synergistic and considerable effect in the management of DM via multi-compound, multi-target, and multi-pathway mechanisms.

Dihydropyrazole Derivatives Act as Potent α-Amylase Inhibitors and Free Radical Scavengers: Synthesis, Bioactivity Evaluation, Structure-Activity Relationship, ADMET, and Molecular Docking Studies

Dihydropyrazole (1-22) derivatives were synthesized from already synthesized chalcones. The structures of all of the synthesized compounds were confirmed by elemental analysis and various spectroscopic techniques. Furthermore, the synthesized compounds were screened against α amylase as well as investigated for antioxidant activities. The synthesized compounds demonstrate good to excellent antioxidant activities with IC₅₀ values ranging between 30.03 and 913.58 μM. Among the 22 evaluated compounds, 11 compounds exhibit excellent activity relative to the standard ascorbic acid IC₅₀ = 287.30 μM. Interestingly, all of the evaluated compounds show good to excellent α amylase activity with IC₅₀ values lying in the range between 0.5509 and 810.73 μM as compared to the standard acarbose IC₅₀ = 73.12 μM. Among the investigated compounds, five compounds demonstrate better activity compared to the standard. In order to investigate the binding interactions of the evaluated compounds with amylase protein, molecular docking studies were conducted, which show an excellent docking score as compared to the standard. Furthermore, the physiochemical properties, drug likeness, and ADMET were investigated, and it was found that none of the compounds violate Lipiniski's rule of five, which shows that this class of compounds has enough potential to be used as a drug candidate in the near future.

Insights on the Hypoglycemic Potential of Crocus sativus Tepal Polyphenols: An In Vitro and In Silico Study

Post-prandial hyperglycemia typical of diabetes mellitus could be alleviated using plant-derived compounds such as polyphenols, which could influence the activities of enzymes involved in carbohydrate digestion and of intestinal glucose transporters. Here, we report on the potential anti-hyperglycemic effect of Crocus sativus tepals compared to stigmas, within the framework of valorizing these by-products of the saffron industry, since the anti-diabetic properties of saffron are well-known, but not those of its tepals. In vitro assays showed that tepal extracts (TE) had a greater inhibitory action than stigma extracts (SE) on α-amylase activity (IC50: TE = 0.60 ± 0.09 mg/mL; SE = 1.10 ± 0.08 mg/mL; acarbose = 0.051 ± 0.07) and on glucose absorption in Caco-2 differentiated cells (TE = 1.20 ± 0.02 mg/mL; SE = 2.30 ± 0.02 mg/mL; phlorizin = 0.23 ± 0.01). Virtual screening performed with principal compounds from stigma and tepals of C. sativus and human pancreatic α-amylase, glucose transporter 2 (GLUT2) and sodium glucose co-transporter-1 (SGLT1) were validated via molecular docking, e.g., for human pancreatic α-amylase, epicatechin 3-o-gallate and catechin-3-o-gallate were the best scored ligands from tepals (-9.5 kcal/mol and -9.4 kcal/mol, respectively), while sesamin and episesamin were the best scored ones from stigmas (-10.1 kcal/mol). Overall, the results point to the potential of C. sativus tepal extracts in the prevention/management of diabetes, likely due to the rich pool of phytocompounds characterized using high-resolution mass spectrometry, some of which are capable of binding and interacting with proteins involved in starch digestion and intestinal glucose transport.

Mangosteen Metabolites as Promising Alpha-Amylase Inhibitor Candidates: In Silico and In Vitro Evaluations

Diabetes is a chronic metabolic disorder characterized by raised glucose levels in the blood, resulting in grave damage over time to various body organs, including the nerves, heart, kidneys, eyes, and blood vessels. One of its therapeutic treatment approaches involves the inhibition of enzymes accountable for carbohydrate digestion and absorption. The present work is aimed at evaluating the potential of some reported metabolites from Garcinia mangostana (mangosteen, Guttiferae) as alpha-amylase inhibitors. Forty compounds were assessed for their capacity to inhibit alpha-amylase using in silico studies as well as in vitro assays. Molecular docking was carried out to analyze their binding capacities in the 3D structure of alpha-amylase (PDB ID: 4GQR). Among the tested compounds, 6-O-β-D-glucopyranosyl-2,4,6,3',4',6'-hexahydroxybenzophenone (8), aromadendrin-8-C-glucoside (5), epicatechin (6), rhodanthenone (4), and garcixanthone D (40) had a high XP G.score and a Glide G.score of -12.425, -11.855, -11.135, and -11.048 Kcal/mol, respectively. Compound 8 possessed the XP and Glide docking score of -12.425 Kcal/mol compared to the reference compounds myricetin and acarbose which had an XP and Glide docking score of -12.319 and 11.201 Kcal/mol, respectively. It interacted through hydrogen bond formations between its hydroxyl groups and the residues His 101, Asp 197, Glu 233, Asp 300, and His 305, in addition to water bridges and hydrophobic interactions. Molecular mechanics-generalized born surface area (MM-GBSA) was used to calculate the binding free energy and molecular dynamic studies that indicated the stability of the alpha-amylase-compound 8 complex during the 100 ns simulation in comparison with myricetin- and acarbose-alpha-amylase complexes. Additionally, the in vitro alpha-amylase inhibition assay findings validated the in silico study's findings. This could further validate the potential of G. mangostana as a candidate for diabetes management.

Adaptation to Endophytic Lifestyle Through Genome Reduction by Kitasatospora sp. SUK42

Endophytic actinobacteria offer great potential as a source of novel bioactive compounds. In order to investigate the potential for the production of secondary metabolites by endophytes, we recovered a filamentous microorgansism from the tree Antidesma neurocarpum Miq. After phenotypic analysis and whole genome sequencing we demonstrated that this organism, SUK42 was a member of the actinobacterial genus Kitasatospora. This strain has a small genome in comparison with other type strains of this genus and has lost metabolic pathways associated with Stress Response, Nitrogen Metabolism and Secondary Metabolism. Despite this SUK42 can grow well in a laboratory environment and encodes a core genome that is consistent with other members of the genus. Finally, in contrast to other members of Kitasatospora, SUK42 encodes saccharide secondary metabolite biosynthetic gene clusters, one of which with similarity to the acarviostatin cluster, the product of which displays α-amylase inhibitory activity. As extracts of the host plant demonstrate this inhibitory activity, it suggests that the potential medicinal properties of A. neurocarpum Miq might be provided by the endophytic partner and illustrate the potential for exploitation of endophytes for clinical or industrial uses.

Phytochemical Profiling in Conjunction with In Vitro and In Silico Studies to Identify Human α-Amylase Inhibitors in Leucaena leucocephala (Lam.) De Wit for the Treatment of Diabetes Mellitus

Bioactive constituents from natural sources are of great interest as alternatives to synthetic compounds for the treatment of various diseases, including diabetes mellitus. In the present study, phytochemicals present in Leucaena leucocephala (Lam.) De Wit leaves were identified by gas chromatography-mass spectrometry and further examined by qualitative and quantitative methods. α-Amylase enzyme activity assays were performed and revealed that L. leucocephala (Lam.) De Wit leaf extract inhibited enzyme activity in a dose-dependent manner, with efficacy similar to that of the standard α-amylase inhibitor acarbose. To determine which phytochemicals were involved in α-amylase enzyme inhibition, in silico virtual screening of the absorption, distribution, metabolism, excretion, and toxicity properties was performed and pharmacophore dynamics were assessed. We identified hexadecenoic acid and oleic acid ((Z)-octadec-9-enoic acid) as α-amylase inhibitors. The binding stability of α-amylase to those two fatty acids was confirmed in silico by molecular docking and a molecular dynamics simulation performed for 100 ns. Together, our findings indicate that L. leucocephala (Lam.) De Wit-derived hexadecanoic acid and oleic acid are natural product-based antidiabetic compounds that can potentially be used to manage diabetes mellitus.

Alpha-amylase as molecular target for treatment of diabetes mellitus: A comprehensive review

The alpha (α)-amylase is a calcium metalloenzyme that aids digestion by breaking down polysaccharide molecules into smaller ones such as glucose and maltose. In addition, the enzyme causes postprandial hyperglycaemia and blood glucose levels to rise. α-Amylase is a well-known therapeutic target for the treatment and maintenance of postprandial blood glucose elevations. Various enzymatic inhibitors, such as acarbose, miglitol and voglibose, have been found to be effective in targeting this enzyme, prompting researchers to express an interest in developing potent alpha-amylase inhibitor molecules. The review mainly focused on designing different derivatives of drug molecules such as benzofuran hydrazone, indole hydrazone, spiroindolone, benzotriazoles, 1,3-diaryl-3-(arylamino) propan-1-one, oxadiazole and flavonoids along with their target-receptor interactions, IC₅₀ values and other biological activities.

Microbial Oligosaccharides with Biomedical Applications

Microbial oligosaccharides have been regarded as one of the most appealing natural products attributable to their potent and selective bioactivities, such as antimicrobial activity, inhibition of α-glucosidases and lipase, interference of cellular recognition and signal transduction, and disruption of cell wall biosynthesis. Accordingly, a handful of bioactive oligosaccharides have been developed for the treatment of bacterial infections and type II diabetes mellitus. Given that naturally occurring oligosaccharides have increasingly gained recognition in recent years, a comprehensive review is needed. The current review highlights the chemical structures, biological activities and divergent biosynthetic origins of three subgroups of oligomers including the acarviosine-containing oligosaccharides, saccharomicins, and orthosomycins.

Potential anti-diabetic properties of Merlot grape pomace extract: An in vitro, in silico and in vivo study of α-amylase and α-glucosidase inhibition

A practical approach to control glycemia in diabetes is to use plant natural products that delay hydrolysis of complex sugars and promote the diminution of the release of glucosyl units into the blood plasma. Polyphenolics have been described as being effective in inhibiting amylases and α-glucosidases. Grape pomace is an important sub product of the wine industry, still rich in many compounds such as polyphenolics. In this context, the purpose of this study was to search for possible effects of a grape pomace extract on salivary and pancreatic α-amylases and α-glucosidase, as well as on intestinal glucose absorption. The Merlot grape pomace extract (MGPE) was prepared using a hydroalcoholic mixture (40% ethanol + 60% water). In vitro inhibition was quantified using potato starch (for amylases) and maltose (for α-glucosidase) as substrates. In vivo inhibition was evaluated by running starch and maltose tolerance tests in rats with or without administration of MGPE. Ranking of the extract compounds for its affinity to the α-amylases was accomplished by computer simulations using three different programs. Both α-amylases, pancreatic and salivary, were inhibited by the MGPE. No inhibition on α-glucosidase, however, was detected. The IC₅₀ values were 90 ± 10 μg/mL and 143 ± 15 μg/mL for salivary and pancreatic amylases, respectively. Kinetically this inhibition showed a complex pattern, with multiple binding of the extract constituents to the enzymes. Furthermore, the in silico docking simulations indicated that several phenolic substances, e.g., peonidin-3-O-acetylglucoside, quercetin-3-O-glucuronide and isorhamnetin-3-O-glucoside, besides catechin, were the most likely polyphenols responsible for the α-amylase inhibition caused by MGPE. The hyperglycemic burst, an usual phenomenon that follows starch administration, was substantially inhibited by the MGPE. Our results suggest that the MGPE can be adequate for maintaining normal blood levels after food ingestion.

Critical review on conventional spectroscopic α-amylase activity detection methods: merits, demerits, and future prospects

α-Amylase is an endoenzyme that catalyses the hydrolysis of internal α-l,4 glycosidic linkages in polysaccharides to produce maltose, maltotriose, and α-limit dextrins. It is widely used in the laboratorial and industrial workflow for several applications. There are several methods utilizing different techniques and substrates to assess α-amylase activity, among which the spectroscopic methods have found widespread applicability due to their ease of use and cost-effectiveness. Depending upon the reaction principle, these assays are classified into four groups: reducing sugar, enzymatic, chromogenic, and amyloclastic methods. Despite the presence of numerous methods, there is no general reliable method to assess α-amylase activity. Each method is shown to have its own merits and demerits. Many improvements have been made to make the available methods more accurate, reliable, and easy. This communication briefly discusses the basic reaction mechanisms and critically reviews the advantages and shortcomings associated with each method. Further recommendations are made for future development. © 2020 Society of Chemical Industry.

Inhibition of α-amylase by flavonoids: Structure activity relationship (SAR)

Flavonoids are recognized to regulate animals' food digestion processes trough interaction with digestive enzymes. The binding capacity of hesperetin (HES), luteolin (LUT), quercetin (QUE), catechin (CAT) and rutin (RUT) with pancreatic α-amylase were evaluated, using UV-Vis spectroscopy, fluorescence and molecular docking. Using p-nitrophenyl-α-d-maltopentoside (pNPG5) as substrate analog, LUT showed the best inhibitory capacity, even better than that of the positive control, acarbose (ACA). A mixed-type inhibition was observed for HES, LUT and QUE, a competitive-type for ACA, while no inhibition was observed with CAT and RUT. In agreement with kinetic results, α-amylase presented a higher affinity for LUT, when analyzed by fluorescence quenching. The binding of flavonoids to amylase followed a static mechanism, where the binding of one flavonoid per enzyme molecule was observed. Docking analysis showed that flavonoids bound near to enzyme active site, while ACA bound in another site behind the catalytic triad. Extrinsic fluorescence analysis, together with docking analysis pointed out that hydrophobic interactions regulated the flavonoid-α-amylase interactions. The present study provides evidence to understand the relationship of flavonoids structure with their inhibition mechanism.

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.

Synthesis of novel inhibitors of α-amylase based on the thiazolidine-4-one skeleton containing a pyrazole moiety and their configurational studies

Postprandial hyperglycemia can be controlled by delaying the absorption of glucose resulting from carbohydrate digestion. α-Amylase is the initiator of the hydrolysis of polysaccharides, and therefore developing α-amylase inhibitors can lead to development of new treatments for metabolic disorders like diabetes mellitus. In the present work, we set out to rationally develop α-amylase inhibitors based on the thiazolidine-4-one scaffold. The structures of all these newly synthesized hybrids were confirmed by spectroscopic analysis (IR, 1H-NMR, MS). The appearance of two sets of signals for some protons in 1H NMR revealed the existence of a mixture of 2E,5Z (37.1-42.0%) and 2Z,5Z isomers (58.4-62.8%), which was further supported by DFT studies. All the newly synthesized compounds have potential inhibitory properties as revealed through in vitro α-amylase inhibition activity. Compound 5a at 100 μg mL-1 concentration showed a remarkable inhibition of 90.04%. In vitro α-amylase inhibition was further supported by docking studies of compound 5a against the active site of human pancreatic α-amylase (PDB ID: ; 2QV4). The docking studies revealed that the bonding interactions found between 5a and human pancreatic α-amylase are similar to those responsible for α-amylase inhibition by acarbose.

Polyphenolic Compounds and Digestive Enzymes: In Vitro Non-Covalent Interactions

The digestive enzymes–polyphenolic compounds (PCs) interactions behind the inhibition of these enzymes have not been completely studied. The existing studies have mainly analyzed polyphenolic extracts and reported inhibition percentages of catalytic activities determined by UV-Vis spectroscopy techniques. Recently, pure PCs and new methods such as isothermal titration calorimetry and circular dichroism have been applied to describe these interactions. The present review focuses on PCs structural characteristics behind the inhibition of digestive enzymes, and progress of the used methods. Some characteristics such as molecular weight, number and position of substitution, and glycosylation of flavonoids seem to be related to the inhibitory effect of PCs; also, this effect seems to be different for carbohydrate-hydrolyzing enzymes and proteases. The digestive enzyme–PCs molecular interactions have shown that non-covalent binding, mostly by van der Waals forces, hydrogen binding, hydrophobic binding, and other electrostatic forces regulate them. These interactions were mainly associated to non-competitive type inhibitions of the enzymatic activities. The present review emphasizes on the digestive enzymes such as α-glycosidase (AG), α-amylase (PA), lipase (PL), pepsin (PE), trypsin (TP), and chymotrypsin (CT). Existing studies conducted in vitro allow one to elucidate the characteristics of the structure–function relationships, where differences between the structures of PCs might be the reason for different in vivo effects.

α-Amylase Modulation: Discovery of Inhibitors Using a Multi-Pharmacophore Approach for Virtual Screening

Better control of postprandial hyperglycemia can be achieved by delaying the absorption of glucose resulting from carbohydrate digestion. Because α-amylase initiates the hydrolysis of polysaccharides, the design of α-amylase inhibitors can lead to the development of new treatments for metabolic disorders such as type II diabetes and obesity. In this study, a rational computer-aided approach was developed to identify novel α-amylase inhibitors. Three-dimensional pharmacophores were developed based on the binding mode analysis of six different families of compounds that bind to this enzyme. In a stepwise virtual screening workflow, seven molecules were selected from a library of 1.4 million. Five out of seven biologically tested compounds showed α-amylase inhibition, and the two most potent compounds inhibited α-amylase with IC₅₀ values of 17 and 27 μm. The scaffold benzylideneacetohydrazide was shared by four of the discovered inhibitors, emerging as a novel drug-like non-carbohydrate fragment and constituting a promising lead scaffold for α-amylase inhibition.

Modeling of cooked starch digestion process using recombinant human pancreatic α-amylase and maltase-glucoamylase for in vitro evaluation of α-glucosidase inhibitors

In human, digestion of cooked starch mainly involves breaking down of α-amylase to α-limit dextrins and small linear malto-oligosaccharides, which are in turn hydrolyzed to glucose by the gut mucosal maltase-glucoamylase (MGAM). Human pancreatic α-amylase (HPA), amino- and carboxyl-terminal portions of MGAM (ntMGAM and ctMGAM) catalyze the hydrolysis of α-D-(1,4) glycosidic linkages in starch, playing a crucial role in the production of glucose in the human lumen. Accordingly, these enzymes are effective drug targets for the treatments of type 2 diabetes and obesity. In this study, a Plackett-Burman based statistical screening procedure was adopted to determine the most critical factors affecting cooked starch digestion by the combination of HPA, ctMGAM and ntMGAM. Six factors were tested and experimental results showed that pH and temperature were the major influencing factors, with optimal pH and temperature at 6.0 and 50 °C, respectively. Surprisingly, ntMGAM had no significant contribution to the glucose production from starch digestion compared to the HPA and ctMGAM. The optimal proportion of HPA and ctMGAM in a starch digestion system was further determined by response surface methodology. Results showed a maximum starch digestion (88.05%) within 0.5 h when used HPA:ctMGAM=1:9 (U). The inhibitory effects of various inhibitors on the cooked starch digestion by HPA1/ctMGAM9 were evaluated by determining their half maximal inhibitory concentration (IC50) values. Acarviostatin II03 showed the highest inhibitory activity, with 67 times higher potency than acarbose. Moreover, acarviostatin II03 could significantly depress postprandial blood glucose levels in mice, better than that by acarbose. These findings suggest that our in vitro enzymatic system can simulate in vivo starch digestion process, and thus can be used to screen and evaluate α-glucosidase inhibitors.

Isolation and characterization of a proteinaceous α-amylase inhibitor AAI-CC5 from Streptomyces sp. CC5, and its gene cloning and expression

An α-amylase inhibitor producing Streptomyces sp. strain CC5 was isolated from soil. A proteinaceous α-amylase inhibitor AAI-CC5 was purified from strain CC5. AAI-CC5 specifically inhibited mammalian α-amylases. The molecular weight of the inhibitor was determined to be 8,212 Da by MALDI-TOF Mass Spectrum. The N-terminal 15 amino acid residues of the purified AAI-CC5 were DTGSPAPECVEYFQS, which is dissimilar to other reported proteinaceous α-amylase inhibitors. AAI-CC5 is a pH insensitive and heat-stable protein, and cannot be hydrolysed by trypsin. AAI-CC5 was cloned and expressed in Escherichia coli BL21 (DE3) with a hexa-histidine tag on the C terminal. AAI-CC5 shared 82 % identity with Parvulustat. The recombinant α-amylase inhibitor was purified to homogeneity by one-step affinity chromatography using Ni(2+)-NTA resin with molecular mass of 9,404 Da. Steady state kinetics studies of α-amylase and the inhibitor revealed an irreversible, non-competitive inhibition mechanism with IC50 and Ki value of 6.43 ×1 10(-11) and 4.45 × 10(-11) M respectively. These results suggest this novel α-amylase inhibitor possessed powerful inhibitory activity for α-amylase, and it may be a candidate in research of diabetes therapy and obesity treatment.

Bioactive oligosaccharide natural products

Covering up to December 2013. Oligosaccharide natural products target a wide spectrum of biological processes including disruption of cell wall biosynthesis, interference of bacterial translation, and inhibition of human α-amylase. Correspondingly, oligosaccharides possess the potential for development as treatments of such diverse diseases as bacterial infections and type II diabetes. Despite their potent and selective activities and potential clinical relevance, isolated bioactive secondary metabolic oligosaccharides are less prevalent than other classes of natural products and their biosynthesis has received comparatively less attention. This review highlights the unique modes of action and biosynthesis of four classes of bioactive oligosaccharides: the orthosomycins, moenomycins, saccharomicins, and acarviostatins.

Molecular modeling of Ruellia tuberosa L compounds as a-amylase inhibitor: an in silico comparation between human and rat enzyme model

Inhibition of α-amylase is an important strategy to control post-prandial hyperglycemia. The present study on Ruellia tuberosa, known as traditional anti-diabetic agent, is being provided in silico study to identify compounds inhibiting α-amylase in rat and human. Compounds were explored from PubChem database. Molecular docking was studied using the autodock4. The interactions were further visualized and analyzed using the Accelrys Discovery Studio version 3.5. Binding energy of compounds to α-amylase was varying between -1.92 to -6.66 kcal/mol in rat pancreatic alpha amylase and -3.06 to -8.42kcal/mol in human pancreatic alpha amylase, and inhibition konstanta (ki) was varying between 13.12- 39460µM in rat and 0.67-5600µM in human. The docking results verify that betulin is the most potential inhibitor of all towards rat model alpha amylase and human alpha amylase. Further analysis reveals that betulin could be a potential inhibitor with non-competitive pattern like betulinic acid. In comparison, betulin has smaller Ki (0.67µM) than acarbose (2.6 µM), which suggesting that betulin is more potential as inhibitor than acarbose, but this assumption must be verified in vitro.

α-Amylase: an enzyme specificity found in various families of glycoside hydrolases

α-Amylase (EC 3.2.1.1) represents the best known amylolytic enzyme. It catalyzes the hydrolysis of α-1,4-glucosidic bonds in starch and related α-glucans. In general, the α-amylase is an enzyme with a broad substrate preference and product specificity. In the sequence-based classification system of all carbohydrate-active enzymes, it is one of the most frequently occurring glycoside hydrolases (GH). α-Amylase is the main representative of family GH13, but it is probably also present in the families GH57 and GH119, and possibly even in GH126. Family GH13, known generally as the main α-amylase family, forms clan GH-H together with families GH70 and GH77 that, however, contain no α-amylase. Within the family GH13, the α-amylase specificity is currently present in several subfamilies, such as GH13_1, 5, 6, 7, 15, 24, 27, 28, 36, 37, and, possibly in a few more that are not yet defined. The α-amylases classified in family GH13 employ a reaction mechanism giving retention of configuration, share 4-7 conserved sequence regions (CSRs) and catalytic machinery, and adopt the (β/α)8-barrel catalytic domain. Although the family GH57 α-amylases also employ the retaining reaction mechanism, they possess their own five CSRs and catalytic machinery, and adopt a (β/α)7-barrel fold. These family GH57 attributes are likely to be characteristic of α-amylases from the family GH119, too. With regard to family GH126, confirmation of the unambiguous presence of the α-amylase specificity may need more biochemical investigation because of an obvious, but unexpected, homology with inverting β-glucan-active hydrolases.

Reflection on design and testing of pancreatic alpha-amylase inhibitors: an in silico comparison between rat and rabbit enzyme models

Background

Inhibitors of pancreatic alpha-amylase are potential drugs to treat diabetes and obesity. In order to find compounds that would be effective amylase inhibitors, in vitro and in vivo models are usually used. The accuracy of models is limited, but these tools are nonetheless valuable. In vitro models could be used in large screenings involving thousands of chemicals that are tested to find potential lead compounds. In vivo models are still used as preliminary mean of testing compounds behavior in the whole organism. In the case of alpha-amylase inhibitors, both rats and rabbits could be chosen as in vivo models. The question was which animal could present more accuracy with regard to its pancreatic alpha-amylase.

Results

As there is no crystal structure of these enzymes, a molecular modeling study was done in order to compare the rabbit and rat enzymes with the human one. The overall result is that rabbit enzyme could probably be a better choice in this regard, but in the case of large ligands, which could make putative interactions with the −4 subsite of pancreatic alpha-amylase, interpretation of results should be made cautiously.

Conclusion

Molecular modeling tools could be used to choose the most suitable model enzyme that would help to identify new enzyme inhibitors. In the case of alpha-amylase, three-dimensional structures of animal enzymes show differences with the human one which should be taken into account when testing potential new drugs.

Kinetics studies on the inhibition mechanism of pancreatic α-amylase by glycoconjugated 1H-1,2,3-triazoles: a new class of inhibitors with hypoglycemiant activity

Glycoconjugated 1H-1,2,3-triazoles (GCTs) comprise a new class of glycosidase inhibitors that are under investigation as promising therapeutic agents for a variety of diseases, including type 2 diabetes mellitus. However, few kinetics studies have been performed to clarify the mode of inhibition of GCTs with their target glycosidases. Our group has previously shown that some methyl-β-D-ribofuranosyl-1H-1,2,3-triazoles that inhibit baker's yeast maltase were also able to reduce post-prandial glucose levels in normal rats. We hypothesized that this hypoglycemiant activity was attributable to inhibition of mammalian α-glucosidases involved in sugar metabolism, such as pancreatic α-amylase. Hence, the aim of this work was to test a series of 26 GCTs on porcine pancreatic α-amylase (PPA) and to characterize their inhibition mechanisms. Six GCTs, all ribofuranosyl-derived GCTs, significantly inhibited PPA, with IC(50) values in the middle to high micromolar range. Our results also demonstrated that ribofuranosyl-derived GCTs are reversible, noncompetitive inhibitors when using 2-chloro-4-nitrophenyl-α-D-maltotrioside as a substrate. E/ES affinity ratios (α) ranged from 0.3 to 1.1, with the majority of ribofuranosyl-derived GCTs preferentially forming stable ternary ESI complexes. Competition assays with acarbose showed that ribofuranosyl-derived GCTs bind to PPA in a mutually exclusive fashion. The data presented here show that pancreatic α-amylase is one of the possible molecular targets in the pharmacological activity of ribofuranosyl-derived GCTs. Our results also provide important mechanistic insight that can be of major help to develop this new class of synthetic small molecules into more potent compounds with anti-diabetic activity through rational drug design.

Developing inhibitors of glycan processing enzymes as tools for enabling glycobiology

Glycoconjugates are ubiquitous biomolecules found in all kingdoms of life. These diverse structures are metabolically responsive and occur in a cell line- and protein-specific manner, conferring tissue type-specific properties. Glycans have essential roles in diverse processes, including, for example, intercellular signaling, inflammation, protein quality control, glucohomeostasis and cellular adhesion as well as cell differentiation and proliferation. Many mysteries remain in the field, however, and uncovering the physiological roles of various glycans remains a key pursuit. Realizing this aim necessitates the ability to subtly and selectively manipulate the series of different glycoconjugates both in cells and in vivo. Selective small-molecule inhibitors of glycan processing enzymes hold great potential for such manipulation as well as for determining the function of 'orphan' carbohydrate-processing enzymes. In this review, we discuss recent advances and existing inhibitors, the prospects for small-molecule inhibitors and the challenges associated with generating high-quality chemical probes for these families of enzymes. The coordinated efforts of chemists, biochemists and biologists will be crucial for creating and characterizing inhibitors that are useful tools both for advancing a basic understanding of glycobiology in mammals as well as for validating new potential therapeutic targets within this burgeoning field.

Draft genome sequence of Streptomyces coelicoflavus ZG0656 reveals the putative biosynthetic gene cluster of acarviostatin family α-amylase inhibitors

AIMS

The aims of this study are to obtain the draft genome sequence of Streptomyces coelicoflavus ZG0656, which produces novel acarviostatin family α-amylase inhibitors, and then to reveal the putative acarviostatin-related gene cluster and the biosynthetic pathway.

METHODS AND RESULTS

The draft genome sequence of S. coelicoflavus ZG0656 was generated using a shotgun approach employing a combination of 454 and Solexa sequencing technologies. Genome analysis revealed a putative gene cluster for acarviostatin biosynthesis, termed sct-cluster. The cluster contains 13 acarviostatin synthetic genes, six transporter genes, four starch degrading or transglycosylation enzyme genes and two regulator genes. On the basis of bioinformatic analysis, we proposed a putative biosynthetic pathway of acarviostatins. The intracellular steps produce a structural core, acarviostatin I00-7-P, and the extracellular assemblies lead to diverse acarviostatin end products.

CONCLUSIONS

The draft genome sequence of S. coelicoflavus ZG0656 revealed the putative biosynthetic gene cluster of acarviostatins and a putative pathway of acarviostatin production.

SIGNIFICANCE AND IMPACT OF THE STUDY

To our knowledge, S. coelicoflavus ZG0656 is the first strain in this species for which a genome sequence has been reported. The analysis of sct-cluster provided important insights into the biosynthesis of acarviostatins. This work will be a platform for producing novel variants and yield improvement.

Structural insight into substrate specificity of human intestinal maltase-glucoamylase

Human maltase-glucoamylase (MGAM) hydrolyzes linear alpha-1,4-linked oligosaccharide substrates, playing a crucial role in the production of glucose in the human lumen and acting as an efficient drug target for type 2 diabetes and obesity. The amino- and carboxyl-terminal portions of MGAM (MGAM-N and MGAM-C) carry out the same catalytic reaction but have different substrate specificities. In this study, we report crystal structures of MGAM-C alone at a resolution of 3.1 Å, and in complex with its inhibitor acarbose at a resolution of 2.9 Å. Structural studies, combined with biochemical analysis, revealed that a segment of 21 amino acids in the active site of MGAM-C forms additional sugar subsites (+ 2 and + 3 subsites), accounting for the preference for longer substrates of MAGM-C compared with that of MGAM-N. Moreover, we discovered that a single mutation of Trp1251 to tyrosine in MGAM-C imparts a novel catalytic ability to digest branched alpha-1,6-linked oligosaccharides. These results provide important information for understanding the substrate specificity of alpha-glucosidases during the process of terminal starch digestion, and for designing more efficient drugs to control type 2 diabetes or obesity.