Inhibition study of red rice polyphenols on pancreatic α-amylase activity by kinetic analysis and molecular docking

Inhibition mechanism of different structural polyphenols against α-amylase studied by solid-state NMR and molecular docking

Polyphenol has the considerable effects for inhibition of digestive enzymes, however, inhibition mechanism of molecular size-dependent polyphenols on enzyme activity is still lacking. Herein, inhibition effect and binding interactions of three different structural polyphenols (catechol, quercetin and hesperidin) on α-amylase were studied. Inhibition assays proved that polyphenols significantly inhibited α-amylase and their effects were increased with their molecular sizes. Hesperidin showed the highest inhibition ability of α-amylase, which was determined as IC50 = 0.43 mg/mL. Fluorescence and FT-IR spectroscopy proved that inter-molecular interactions between polyphenols and α-amylase occurred through non-covalent bonds. Besides, the secondary structure of α-amylase was obviously changed after binding with polyphenols. Inter-molecular interactions were investigated using solid-state NMR and molecular docking. Findings proved that hydrogen bonds and π-π stacking interactions were the mainly inter-molecular interactions. We hope this contribution could provide a theoretical basis for developing some digestive enzyme inhibitors from natural polyphenols.

The inhibition mechanism of bound polyphenols extracted from mung bean coat dietary fiber on porcine pancreatic α-amylase: kinetic, spectroscopic, differential scanning calorimetric and molecular docking

The inhibitory mechanisms of purified bound polyphenols extracted from mung bean coat dietary fiber (pMBDF-BP) on porcine pancreatic α-amylase (PPA) were investigated through inhibition kinetics, fluorescence spectroscopy, circular dichroism, differential scanning calorimetry and molecular docking. It was shown that pMBDF-BP exerted significant reversible inhibition on PPA in a mixed-type inhibition manner (IC50 = 18.57 ± 0.30 μg/mL), and the combination of the three major components exhibited a synergistic inhibitory effect on PPA. Further, pMBDF-BP bound to the active site or form a polyphenol-enzyme complex at the inactive site through hydrogen bonding and hydrophobic forces, via enhancing the hydrophobicity of the microenvironment surrounding tryptophan and tyrosine residues and promoting the secondary structure of PPA towards a more stable conformation, eventually reducing the enzyme activity. This study provided theoretical evidences for the utilization of bound polyphenols extracted from mung bean coat dietary fiber as a functional component in natural inhibitors of α-amylase.

Chitosan and its oligosaccharide accelerate colonic motility and reverse serum metabolites in rats after excessive protein consumption

Excessive protein consumption (EPC) could increase the gastrointestinal burden and impair gut motility. The present study was designed to explore the improvement of chitosan (CTS) and chitosan oligosaccharide (COS) on colonic motility and serum metabolites in rats after EPC. The results of in vivo experiments fully proved that CTS and COS could improve gut motility and reverse the serum metabolites in rats as indicated by LC-MS/MS analysis, and the COS group even showed a better effect than the CTS group. Furthermore, short-chain fatty acids (SCFAs), which could promote gut motility, were also increased to alleviate EPC-induced constipation after supplementation with CTS or COS. In addition, CTS and COS could decrease the concentration of ammonia in serum and down-regulate the levels of H2S and indole. In summary, the present study revealed that CTS and COS could produce SCFAs, improve the colonic motility in rats, reverse the levels of valine, adenosine, cysteine, 1-methyladenosine, indole, and uracil, and enhance aminoacyl-tRNA biosynthesis and valine, leucine and isoleucine degradation. The present study provides novel insights into the potential roles of CTS and COS in alleviating the adverse effects of EPC.

Modulating the glycemic response of starch-based foods using organic nanomaterials: strategies and opportunities

Traditionally, diverse natural bioactive compounds (polyphenols, proteins, fatty acids, dietary fibers) are used as inhibitors of starch digestive enzymes for lowering glycemic index (GI) and preventing type 2 diabetes mellitus (T2DM). In recent years, organic nanomaterials (ONMs) have drawn a great attention because of their ability to overcome the stability and solubility issues of bioactive. This review aimed to elucidate the implications of ONMs in lowering GI and as encapsulating agents of enzymes inhibitors. The major ONMs are presented. The mechanisms underlying the inhibition of enzymes, the stability within the gastrointestinal tract (GIT) and safety of ONMs are also provided. As a result of encapsulation of bioactive in ONMs, a more pronounced inhibition of enzymes was observed compared to un-encapsulated bioactive. More importantly, the lower the size of ONMs, the higher their inhibitory effects due to facile binding with enzymes. Additionally, in vivo studies exhibited the potentiality of ONMs for protection and sustained release of insulin for GI management. Overall, regulating the GI using ONMs could be a safe, robust and viable alternative compared to synthetic drugs (acarbose and voglibose) and un-encapsulated bioactive. Future researches should prioritize ONMs in real food products and evaluate their safety on a case-by-case basis.

Insights into Recent Updates on Factors and Technologies That Modulate the Glycemic Index of Rice and Its Products

Rice is a staple food and energy source for half the world's population. Due to its quick digestion and absorption in the gastrointestinal tract, rice is typically regarded as having a high or medium-high glycemic index (GI); however, this can vary depending on the variety, nutrient compositions, processing, and accompanying factors. This report included a table of the glycemic index for rice and rice products in different countries, which could give an overview and fundamental information on the recent GI of different rice varieties. In addition, latest updates about the mechanism effects of rice nutritional profiles and processing techniques on GI were also provided and discussed. The influence of state-of-the-art GI regulation methods was also evaluated. Furthermore, the effectiveness and efficiency of applied technologies were also given. Furthermore, this review offered some aspects about the potential nutraceutical application of rice that food scientists, producers, or consumers might consider. Diverse types of rice are grown under various conditions that could affect the GI of the product. The instinct nutrients in rice could show different effects on the digestion rate of its product. It also revealed that the rice product's digestibility is process-dependent. The postprandial glucose response of the rice products could be changed by modifying processing techniques, which might produce the new less-digestive compound or the inhibition factor in the starch hydrolysis process. Because of the significant importance of rice, this paper also concluded the challenges, as well as some important aspects for future research.

Insoluble dietary fiber from wheat bran retards starch digestion by reducing the activity of alpha-amylase

This study investigated effects of insoluble dietary fiber (IDF) from wheat bran on starch digestion in vitro, analyzed the inhibition kinetics of IDF toward α-amylase and discussed the underlying mechanisms. Digestion results showed IDF significantly retarded starch digestion with reduced digestion rate and digestible starch content. Enzyme inhibition kinetics indicated IDF was a mixed-type inhibitor to α-amylase, because IDF could bind α-amylase, as evidenced by confocal laser scanning microscopy. Fluorescence quenching and UV-vis absorption experiments conformed this, found IDF led to static fluorescence quenching of α-amylase, mainly through van der Waals and/or hydrogen bonding forces. This interaction induced alternations in α-amylase secondary structure, showing more loosening and misfolding structures. This may prevent the active site of enzyme from capturing substrates, contributing to reduced α-amylase activity. These results would shed light on the utilization of IDF in functional foods for the management of postprandial blood glucose.

Mechanistic Understanding of Tyrosinase Inhibition by Polymeric Proanthocyanidins from Acacia confusa Stem Bark and Their Effect on the Browning Resistance of Fresh-Cut Asparagus Lettuce

Tyrosinase inhibitors are capable of preventing unfavorable enzymatic browning of fruits and vegetables. In this study, the capacity of Acacia confusa stem bark proanthocyanidins (ASBPs) to inhibit tyrosinase activity was evaluated. ASBPs were shown to be a high-potential inhibitor of tyrosinase with IC50 values of 92.49 ± 4.70 and 61.74 ± 8.93 μg/mL when using L-tyrosine and L-DOPA as the substrate, respectively. The structural elucidation performed with UV-vis, FT-IR spectroscopy, ESI-MS and thiolysis coupled to HPLC-ESI-MS suggested that ASBPs had structural heterogeneity in monomer units and interflavan linkages and consisted mainly of procyanidins dominant with B-type linkages. To gain insights into the inhibitory mechanisms of ASBPs against tyrosinase, different spectroscopic and molecular docking methods were further conducted. Results validated that ASBPs possessed the ability to chelate copper ions and could prevent the oxidation process of substrates by tyrosinase. The hydrogen bond formed with Lys-376 residue played a key role in the binding force of ASBPs with tyrosinase that induced a certain alteration in the microenvironment and secondary structure of tyrosinase, resulting in the enzymatic activity being ultimately restricted. It was also observed that ASBPs treatment effectively inhibited the activities of PPO and POD to retard the surface browning of fresh-cut asparagus lettuce and thus extended their shelf-life. The results provided preliminary evidence supporting the exploitation of ASBPs into potential antibrowning agents for the fresh-cut food industry.

Structural changes and molecular mechanism study on the inhibitory activity of epigallocatechin against α-glucosidase and α-amylase

In this study, the inhibition and mechanism of epigallocatechin (EGC) on two key glycoside hydrolases (α-glucosidase, α-amylase) were explored from the molecular structure level. The chemical structure of EGC was characterized by X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, and proton nuclear magnetic resonance spectroscopy. EGC's inhibition on these enzymes was colorimetrically determined. The effects of EGC on the chemical structure and spatial configuration of the enzymes were explored via FTIR spectroscopy, fluorescence spectroscopy, and molecular docking techniques. The results showed that EGC exhibited the inhibition of α-glucosidase and α-amylase in a non-competitive manner, showing a continuous upward trend as EGC's concentration increased. There was a fluorescence quenching effect of EGC on α-glucosidase and α-amylase. Molecular docking confirmed that EGC can bind to amino acid residues in the enzyme through intermolecular hydrogen bonds and hydrophobic interactions, resulting in the changed chemical structure and spatial conformation of the enzymes. This decreased enzyme activity. This result suggested that EGC has the potential to inhibit two key glycoside hydrolases, and it would be beneficial to incorporate EGC into functional foods for diabetics.

An on-line detection system for screening small molecule inhibitors of α-Amylase and α-Glucosidase in Prunus mume

High-throughput screening of inhibitors from natural products is an efficient approach to target key enzymes in diabetes progression. In this study, an on-line detection system was established for the first time to rapidly screen inhibitors of α-amylase and α-glucosidase from Prunus mume. Among 28 identified compounds, 26 and 21 compounds showed strong inhibitory effect against α-amylase and α-glucosidase, respectively. Their inhibitory effects were validated by in vitro enzyme assay and fluorescence quenching which demonstrated that these inhibitors effectively interfered enzyme active sites. The inhibition kinetics suggested that chemical structures are of great importance for interfering the enzyme structures and their microenvironment polarity. Among evaluated compounds, isorhamnetin-3-O-glucoside (19) showed the strongest binding activities to α-amylase and α-glucosidase (6.34×10⁶·nmol^-1 and 6.28×10⁶·nmol^-1, respectively) by the on-line detection system. Its IC₅₀ values were 0.16 ± 0.06 and 0.09 ± 0.01 µM against α-amylase and α-glucosidase, respectively. 19 gave a much higher K_i for α-amylase (0.1307 mM) than α-glucosidase (0.0063 mM), indicating its selectivity towards α-glucosidase. This reported method was rapid and reliable to identify prototype inhibitors against key enzymes in diabetes, and thus might serve as a general platform to screen enzyme inhibitors from natural products.

Longan seed polyphenols inhibit α-amylase activity and reduce postprandial glycemic response in mice

The effects of longan seed polyphenols (LSPs) on postprandial glycemic response in mice were investigated, enzyme inhibition kinetics of LSPs against α-amylase were studied using an inhibition assay in vitro, and the underlying mechanisms were discussed by analyzing the impacts of LSPs on the structure of α-amylase using multispectral approaches. The results showed LSPs significantly suppressed blood glucose response in a dose-dependent manner. Enzyme inhibition analysis demonstrated LSPs inhibited α-amylase activity in a mixed type (IC₅₀ 3.02 mg mL^-1). UV-vis absorption spectroscopy and fluorescence quenching spectroscopy suggest LSPs tend to bind with α-amylase through static interaction at one binding site, mainly through hydrogen bonding and van der Waals forces. The secondary structure of α-amylase was changed by LSPs as reviewed by circular dichroism, showing a more compact skeleton and more flexible loop of α-amylase. This hinders the substrate from reaching the binding site of the enzyme, resulting in reduced enzyme activity. These suggest the potential application of LSPs as a hypoglycemic agent in functional foods.

The mechanism of delaying starch digestion by luteolin

In this study, the mechanisms of the delay of starch digestion by luteolin were revealed by studying the luteolin-PPA (porcine pancreatic α-amylase) interaction and luteolin-starch interaction. The luteolin-PPA interaction was investigated by inhibitory kinetics analysis, fluorescence quenching, circular dichroism (CD), Fourier transform infrared (FT-IR) spectroscopy and molecular docking. The results of the inhibitory kinetics revealed that luteolin was a mixed-type inhibitor of PPA and that the inhibitory action was reversible. Fluorescence spectroscopy (including fluorescence quenching and thermodynamics) and molecular docking analyses indicated that hydrogen bonds and hydrophobic forces were the main forces between PPA and luteolin. CD and FT-IR spectroscopy analyses showed that the interaction between luteolin and PPA changed the secondary structure of PPA and induced a decline in its activity. In addition, the luteolin-starch interaction was also studied using UV-visible absorption and X-ray diffraction analyses. These indicated that luteolin could bind with PPA, and that hydrogen bonds and van der Waals forces may be present. Overall, luteolin delayed starch digestion not only by binding with PPA but also by binding with starch. Thus, luteolin has the potential to prevent and control diabetes by being added into starch-based food to delay starch digestion.

Bioflavonoid (Hesperidin) Restrains Protein Oxidation and Advanced Glycation End Product Formation by Targeting AGEs and Glycolytic Enzymes

Alpha-amylase (α-amylase) not long ago has acquire recognition as a possible drug target for the management of diabetes. Here, we have investigated the binding and enzyme activity of α-amylase by hesperidin; a naturally occurring flavanone having wide therapeutic potential. Hesperidin exerted an inhibitory influence on α-amylase activity with an IC₅₀ value of 16.6 µM. Hesperidin shows a significant binding toward α-amylase with a binding constant (K_a) of the order of 10⁴ M^-1. The evaluation of thermodynamic parameters (∆H and ∆S) suggested that van der Waals force and hydrogen bonding drive seemingly specific hesperidin-α-amylase complex formation. Glycation and oxidation studies were performed using human serum albumin (HSA) as ideal protein. Hesperidin inhibited fructosamine content ≈40% at 50 µM and inhibited advanced glycation end products (AGEs) formation by 71.2% at the same concentration. Moreover, significant recovery was evident in free -SH groups and carbonyl content of HSA. Additionally, molecular docking also entrenched in vitro observations and provided an insight into the important residues (Trp58, Gln63, His101, Glu233, Asp300, and His305) at the heart of hesperidin-α-amylase interaction. This study delineates mechanistic insight of hesperidin-α-amylase interaction and provides a platform for use of hesperidin to treat AGEs directed diseases.

Functionalization of whey protein isolate fortified with blackcurrant concentrate by spray-drying and freeze-drying strategies

A solution of whey protein isolate was combined with blackcurrant concentrate via spray-drying and freeze-drying techniques separately to develop novel protein ingredients, (SWB and FWB). Chemical compositions, colour profiles, total anthocyanin content and encapsulation efficacy of the protein ingredients were evaluated. An in vitro digestion process was employed to observe the changes in total phenolic content, antioxidant activity, and predictive in vitro glycaemic response of the protein ingredients. The half maximal inhibitory concentration (IC₅₀) towards α-Amylase, and a molecular docking study on the interactions of α-Amylase with anthocyanins, were both performed to investigate the potential mechanisms of hypoglycaemic properties of these protein ingredients. The protein contents of SWB and FWB were 67.94 ± 0.47% and 68.16 ± 0.77%, respectively. Blackcurrant concentrate significantly (p < 0.001) changed the colour profiles of whey protein isolate. SWB obtained a higher total phenol content (3711.28 ± 4.36 μg/g), total anthocyanin content (85390.80 ± 162.81 μg/100 g), and greater encapsulation efficacy (99.64 ± 0.16%) than those of FWB (3413.03 ± 20.60 μg/g, 64230.24 ± 441.08 μg/100 g, and 95.43 ± 0.14%, respectively). Total phenolic content and antioxidant activities of SWB and FWB decreased after the in vitro digestion. The reducing sugar released during the in vitro digestion from SWB and FWB decreased compared with their corresponding controls (SWC and FWC). FWB (IC₅₀ = 73.46 μg/mL) exhibited stronger α-Amylase inhibitory activity than SWB (IC₅₀ = 81.46 μg/mL). Different anthocyanins differed from binding affinities to bind with the active sites of α-Amylase via formation of hydrogen bonds. This study suggested whey protein encapsulated-blackcurrant concentrate might be an innovative food product with improved nutritional profiles. Both spray- and freeze-drying are potential options to this encapsulation.

Structural changes of rice starch and activity inhibition of starch digestive enzymes by anthocyanins retarded starch digestibility

The effects of anthocyanins on in vitro and in vivo digestibility of rice starch were evaluated in this study. Then, the effects of anthocyanins on physicochemical properties of rice starch and on starch digestive enzymes (α-amylase and α-glucosidase) were investigated to understand the mechanism of the effects of anthocyanins on starch digestibility. Characterization of physicochemical properties of rice starch indicates a structural change due to the presence of anthocyanins, hindering its access to starch digestive enzymes. Besides, anthocyanins inhibited the activities of starch digestive enzymes by binding to their active sites, competing with the substrates and changing the secondary structure of the enzymes. The above stated changes of rice starch and starch digestive enzymes due to the presence of anthocyanins both contributed to retarding the digestibility of rice starch. This study could offer some theoretical guidance to the development of new type rice-based food with low glycemic index.

Polyphenolic inhibition of enterocytic starch digestion enzymes and glucose transporters for managing type 2 diabetes may be reduced in food systems

With the current global surge in diabetes cases, there is a growing interest in slowing and managing diabetes and its effects. While there are medications that can be used, they have adverse side effects such as hypoglycemia and weight gain. To overcome these problems, bioactive compounds commonly found in fruits, vegetables and cereal grains are used to slow starch digestion and transport of simple sugars across the intestinal epithelia thereby reducing plasma blood glucose spike. These effects are achieved through inhibition of amylases, glucosidases and glucose transporters present in the gastrointestinal tract and brush boarder membrane. The extent of inhibition by polyphenols is dependent on molecular structure, doses and food matrix. Glycemic lowering effect of polyphenols have been demonstrated both in in vivo and in vitro studies. However, when these compounds are incorporated in food systems, they can interact with other polymers in the food matrix leading to lesser inhibition of digestion and/or glucose transporters compared to isolated or pure compounds as often witnessed in most in vitro studies.

Three flavanols delay starch digestion by inhibiting α-amylase and binding with starch

The study aimed to reveal the different mechanisms of delaying starch digestion by ECG, EGCG and Procyanidin based on the perspective of α-amylase-flavanol interaction and starch-flavanol interaction. The interaction characteristics of flavanols with α-amylase were studied from five aspects: enzyme inhibition, kinetics, fluorescence quenching, circular dichroism (CD) and computer simulation. The IC50 of flavanols (ECG, EGCG and Procyanidin) against α-amylase were 172.21 ± 0.22, 732.15 ± 0.13 and 504.45 ± 0.19 μg/mL according to the results of α-amylase inhibition experiment, respectively. ECG and Procyanidin showed mixed inhibition against α-amylase, while EGCG showed non-competition against α-amylase. However, thermodynamic parameters，computer-based docking and dynamic simulation proved that ECG and EGCG-α-amylase complexs were mainly driven by van der Waals and hydrogen bonds, while Procyanidin-α-amylase complexs was driven by hydrophobic interaction. In addition, it was indicated, by means of starch‑iodine complex spectroscopy, that flavanols inhibited the digestion of starch not only through bind with α-amylase but also through bind with starch. Thus, flavanols as a starch-based food additive have the potential to be employed as adjuvant therapy for diabetes.

Extraction assisted by far infrared radiation and hot air circulation with deep eutectic solvent for bioactive polysaccharides from Poria cocos (Schw.) wolf

In this study, a new ternary choline chloride-deep eutectic solvent was used to efficiently extract bioactive polysaccharides from poria cocos assisted by the new tool of the far infrared radiation (FIR) together with hot air circulation (HAC).

Mechanistic study on inhibition of porcine pancreatic α-amylase using the flavonoids from dandelion

This study was designed to investigate quantitatively the inhibition and molecular mechanism of pancreatic α-amylase exhibited by flavonoids from dandelion to reveal its potential use in relieving postprandial hyperglycemia. The results show that the flavonoids reversibly inhibited the α-amylase in a non-competitive manner with Michaelis-Menten constant (K_m) and half-inhibitory concentration (IC₅₀) value of 10.51 and 0.0067 mg/mL, respectively. The flavonoids present a strong ability to quench the intrinsic fluorescence of α-amylase through static quenching by forming a complex. The values of the binding site (n) at different temperatures were found to be approximately the unity, indicating the presence of a single class of molecular binding of the dandelion flavonoids on α-amylase. The positive values of enthalpy and entropy change reveal that the binding was predominately driven by hydrophobic interactions. This study suggests a benefit of incorporating the dandelion flavonoids in making functional foods in managing the diet of the diabetes.

Screening and identifying of α-amylase inhibitors from medicine food homology plants: Insights from computational analysis and experimental studies

There is a growing interest in screening α-amylase inhibitors from natural products for application in the development of new antidiabetic drugs or functional foods. In this study, a structure-based virtual screening was applied to rapidly identify the α-amylase inhibitors from medicine food homology (MFH) plants. Similarity search, docking & scoring were used for further filter small molecules. As a result, 21 corresponding potential α-amylase inhibitors from MFH plants were obtained. And, six polyphenol compounds (curcumin, procyanidins, epicatechin gallate (ECG), epigallocatechin gallate (EGCG), hesperidin, and puerarin) were highlighted for further verification after a thorough assessment of the classification of hit molecules as well as docking scores. The results of the enzyme inhibition test showed that ECG, EGCG, and procyanidins had the better binding ability of α-amylase among these six polyphenols. The Ki values of ECG, EGCG, and procyanidins on α-amylase were 0.70, 1.68, and 0.24, respectively. The CD spectra results indicated that the three polyphenols can cause conformational changes in α-amylase. PRACTICAL APPLICATIONS: A structure-based virtual screening method for rapid identifying α-amylase inhibitors from MFH plants was developed successfully in this study. These findings suggested that natural polyphenols such as ECG, EGCG, and procyanidins may be a potential inhibitor of α-amylase which could be used as a nutrient supplement for the prevention of diabetes mellitus or can be further used in the development of hypoglycemic drugs. At the same time, it can provide theoretical guidance for the better utilization and development of medicine food homology plants containing these potential α-amylase inhibitors. Moreover, this work may provide ideas and references for the screening of other target protein inhibitors.

Inhibition of starch digestion by flavonoids: Role of flavonoid-amylase binding kinetics

In this study, kinetics of binding between α-amylase and green tea flavonoids were investigated by fluorescence quenching (FQ). Their effect on α-amylase inhibition was evaluated. Whereas epicatechin (EC) and epigallocatechin (EGC) exhibited slow binding kinetics (in the order of minutes), epicatechin gallate (ECG) and epigallocatechin gallate (ECGC) exhibited very rapid binding (in the order of seconds) with Human Salivary α-amylase (HSA) and Porcine Pancreatic α-amylase (PPA). EGCG reached maximum inhibition of HSA and PPA with short incubation time whereas maximum inhibition of HSA and PPA by EC was reached only after 45 to 60 min of incubation. Similar results with ECG and EGC, but not in line with FQ kinetics, highlighted possible interferences of starch-flavonoid interaction in the binding and inhibition process. These results suggest that incubation times of enzymes and flavonoids shall be evaluated prior to enzyme inhibition testing in order to ensure consistent and reliable results.

Preparation, characterization and in vitro hypoglycemic activity of banana condensed tannin-inulin conjugate

To enhance the hypoglycemic effects of inulin, banana condensed tannins (BCT) were grafted onto inulin via a free radical method to synthesize the novel BCT grafted inulin (BCT-g-inulin) complex. Spectroscopic methods, XRD, TGA, 1H NMR, GPC and morphology analyses were utilized to characterize the structural properties of the BCT-g-inulin complex, and our results confirmed the conjugation of BCT and inulin. The conjugation possibly occurred between the hydroxyl group attached at the C6 position of inulin and the C6/C8 position of flavon-3-ol units of BCT. The grafting ratio and grafting efficiency of the BCT-g-inulin complex were 357.54 ± 2.98 g kg-1 complex and 74.57 ± 1.44%, respectively. The data of the antioxidant assays indicated that the BCT-g-inulin complex showed a significantly higher antioxidant activity than native inulin. Also, the grafting reaction remarkably improved the in vitro anti-diabetic activity of inulin. The glucose adsorption capacity and glucose dialysis retardation index of the BCT-g-inulin complex were remarkably higher than those of inulin, while the BCT-g-inulin complex showed much stronger inhibitory effects against α-amylase and α-glucosidase compared with inulin. Notably, the inhibition of both α-amylase and α-glucosidase by the BCT-g-inulin complex occurred through mixed-competitive mode. On the basis of fluorescence spectroscopy, the fluorescence of α-amylase and α-glucosidase could be quenched by the BCT-g-inulin complex through a static quenching mechanism. Hence, the BCT-g-inulin complex might have the potential to be developed as an effective anti-diabetic agent.

Chain conformation of an acidic polysaccharide from green tea and related mechanism of α-amylase inhibitory activity

An acidic tea polysaccharide (TPSA) isolated from green tea was fractionated using a precipitation-fractionation method into seven fractions with different molecular weights. TPSA was characterized as a hyperbranched polysaccharide with a globular homogeneous conformation by analysis of solution parameters of each fraction using static light scattering and viscosity analyses. Observation by transmission electron microscopy confirmed that TPSA occurred as globular homogeneous particles with size in the range of 20-40 nm. To simulate the branched chain segments of TPSA, four model molecules were designed based on chemical structure of TPSA. Molecular docking analysis indicated that the branched chain segments of TPSA similar to the TPSA-4 model molecule showed preferential binding to α-amylase to form the TPSA/α-amylase complex through hydrogen bonding interactions. Circular dichroism spectroscopy showed that the structure of α-amylase was not significantly affected by TPSA. The mechanism of α-amylase inhibitory activity of TPSA was simulated by molecular docking analysis. The branched chain segments of TPSA similar to the TPSA-4 model molecule likely act as a potential competitor to the starch substrate to inhibit the activity of α-amylase.

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.

In vitro inhibitory effects of Chinese bayberry (Myrica rubra Sieb. et Zucc.) leaves proanthocyanidins on pancreatic α-amylase and their interaction

Chinese bayberry leaves proanthocyanidins (BLPs) belongs to the prodelphinidin category with potent EGCG unit, whose inhibition effect on α-amylase and their interaction were investigated by in vitro digestion and enzyme kinetic analysis, multi fluorescence spectroscopies (fluorescence quenching, synchronous fluorescence, and three-dimensional fluorescence), circular dichroism spectra, Fourier transform infrared spectroscopy and in silico modelling. The results revealed that BLPs was a mixed inhibitor to α-amylase with the IC₅₀ value of 3.075 ± 0.073 μg/mL. BLPs could lead to a static fluorescence quenching of α-amylase, mainly by means of interacting with amino acids (mainly Try and Tyr residues) in one site on α-amylase molecule under the action of hydrogen bonding and/or Van der Waals force. This interaction further induced the change of secondary conformational structure, functional group structure and hydrophobicity of α-amylase, thus resulting in lowering activity. Molecular docking simulated that this binding occurred in a cavity on the surface of the α-amylase molecule, and BLPs trimer showed a relatively high binding energy. The present study provided a new insight of BLPs as an α-amylase inhibitor, which could be considered in anti-diabetic therapy.

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.

Inhibitory Effect of Condensed Tannins from Banana Pulp on Cholesterol Esterase and Mechanisms of Interaction

In the present study, the inhibitory effect of condensed tannins (CTs) on cholesterol esterase (CEase) was studied. The underlying mechanisms were evaluated by reaction kinetics, turbidity and particle size analyses, multispectroscopy methods, thermodynamics, and computer molecular simulations. CTs showed potent CEase inhibitory activity with an IC₅₀ value of 64.19 μg/mL, and the CEase activity decreased with increasing CT content in a mixed-competitive manner, which was verified by molecular docking simulations. Fluorescence and UV-vis measurements revealed that complexes were formed from CEase and CTs by noncovalent interaction. Isothermal titration calorimetry indicated that the interaction between CEase and CTs occurred through hydrogen bonding and hydrophobic interactions. Circular dichroism analysis suggested that CTs inhibited the activity of CEase by altering the secondary structure of CEase. The inhibition of CTs on CEase in the gastrointestinal tract might be one mechanism for its cholesterol-lowering effect.

Investigation on the Interaction Behavior Between Oenothein B and Pepsin by Isothermal Titration Calorimetry and Spectral Studies

Oenothein B (OeB) is a dimeric macrocyclic ellagitannin isolated from Herbs and fruits that have a variety of biological activities. In order to better understand the effect of OeB on the activity of the digestive enzyme pepsin, interactions between OeB and pepsin were investigated in vitro under simulated physiological conditions based on enzyme inhibition studies, fluorescence, isothermal titration calorimetry, CD, and molecular docking. It was found OeB is an effective inhibitor of pepsin, likely acting in a reversible manner through both competitive and noncompetitive inhibition. Fluorescence quenching of pepsin by OeB was a static quenching. CD spectra showed the addition of OeB causes the main chain of pepsin to loosen and expand and the partial β-sheet structure to be converted to a disordered structure. Isothermal titration calorimetry and docking studies revealed the main binding mechanism of OeB and pepsin was through noncovalent interactions, hydrophobic interactions with OeB and the internal hydrophobic group of pepsin, and then hydrogen bonding between OeB and the Val243 and Asp77 residues of pepsin. Noncovalent bonds between OeB and pepsin change the polarity and structure of enzymes, decreasing enzymatic activity. Compared with small molecular polyphenols, OeB has a weaker hydrophobic interaction with pepsin and less effect on the secondary structure of pepsin. These findings are the first direct elucidation of the interactions between the oligomer ellagitannin OeB and pepsin, further contributing to understanding binding between oligomer ellagitannins and digestive enzymes. PRACTICAL APPLICATION: The results of this study indicate that the interaction between OeB and pepsin has a certain inhibitory effect on pepsin. In order to reduce the impact of OeB on human digestion and its own activities, nano-encapsulation technology can be used in the future to protect oligomeric ellagitannin such as OeB.

In vitro and in silico elucidation of antidiabetic and anti-inflammatory activities of bioactive compounds from Momordica charantia L

Bitter melon (Momordica charantia) has been used to manage diabetes and related conditions in various parts of the world. In the present study, ten compounds were isolated from acetone and methanol extracts of bitter melon. The chemical structures of compounds were unambiguously elucidated by 1D, 2D NMR, and high-resolution mass spectra. Identified compounds 1-7 exhibited significant inhibition of α-amylase and moderate inhibition of α-glucosidase activities. Momordicoside G and gentisic acid 5-O-β-d-xyloside showed the highest inhibition of α-amylase (70.5%), and α-glucosidase (56.4%), respectively. Furthermore, molecular docking studies of isolated compounds 1-7 were able to bind to the active sites of both enzymes. Additionally, the isolated compounds 1-7 significantly attenuated lipopolysaccharide (LPS)-induced inflammation, downregulating the expression of pro-inflammatory markers NF-κB, INOS, IL-6, IL-1β, TNF-α, and Cox-2 in murine macrophage RAW 264.7 cells. One phenolic derivative, gentisic acid 5-O-β-d-xyloside, was isolated and identified for the first time from bitter melon, and significantly suppressed the expression of Cox-2 and IL-6 compared to the LPS-treated group. α-Amylase and α-glucosidase are targets of anti-diabetes drugs, our findings suggest that compounds purified from bitter melon may have potential to use as functional food ingredients for the prevention of type 2 diabetes and related inflammatory conditions.