Development of a fast and efficient CE enzyme assay for the characterization and inhibition studies of α-glucosidase inhibitors

In vitro antidiabetic activity of Treculia africana leaf extracts: identification of chlorogenic acid and α-mangostin

OBJECTIVE

This research studied two extracts from Treculia africana leaves for their potential against hyperglycaemia-related disorders.

METHODS

The influence of the extracts on α-glucosidase activity and albumin glycation was investigated, and cell viability was estimated in HT-29 human colorectal cells. Phenolic and flavonoid contents and antiradical activity were also detected. The extracts were examined using HPLC-DAD analysis.

KEY FINDINGS

The methanol and dichloromethane leaf extracts showed a significant concentration-dependent inhibition of α-glucosidase activity (IC50= 3.73 and 21.28 µg/ml, respectively). Both extracts also inhibited ribose-induced glycation of bovine serum albumin from 250 µg/ml. Phytochemical analysis revealed the presence of chlorogenic acid and α-mangostin in the extracts. The extracts did not change HT-29 cell viability up to 250 µg/ml, thus showing very low cytotoxicity.

CONCLUSIONS

The methanol leaf extract of T. africana inhibited α-glucosidase activity in a concentration-dependent manner, supporting the use of the leaves in traditional medicine to control hyperglycaemia. Chlorogenic acid and α-mangostin, the latter identified for the first time in this species, were found in the T. africana leaves. Further, in vivo studies and pilot clinical trials should be conducted using standardized T. africana leaf extracts to evaluate their potential effectiveness in diabetes mellitus.

Magnolol and Luteolin Inhibition of α-Glucosidase Activity: Kinetics and Type of Interaction Detected by In Vitro and In Silico Studies

Magnolol and luteolin are two natural compounds recognized in several medicinal plants widely used in traditional medicine, including type 2 diabetes mellitus. This research aimed to determine the inhibitory activity of magnolol and luteolin on α-glucosidase activity. Their biological profile was studied by multispectroscopic methods along with inhibitory kinetic analysis and computational experiments. Magnolol and luteolin decreased the enzymatic activity in a concentration-dependent manner. With 0.075 µM α-glucosidase, the IC₅₀ values were similar for both compounds (~ 32 µM) and significantly lower than for acarbose (815 μM). Magnolol showed a mixed-type antagonism, while luteolin showed a non-competitive inhibition mechanism. Thermodynamic parameters suggested that the binding of magnolol was predominantly sustained by hydrophobic interactions, while luteolin mainly exploited van der Waals contacts and hydrogen bonds. Synchronous fluorescence revealed that magnolol interacted with the target, influencing the microenvironment around tyrosine residues, and circular dichroism explained a rearrangement of the secondary structure of α-glucosidase from the initial α-helix to the final conformation enriched with β-sheet and random coil. Docking studies provided support for the experimental results. Altogether, the data propose magnolol, for the first time, as a potential α-glucosidase inhibitor and add further evidence to the inhibitory role of luteolin.

Anti-α-Glucosidase and Antiglycation Activities of α-Mangostin and New Xanthenone Derivatives: Enzymatic Kinetics and Mechanistic Insights through In Vitro Studies

Diabetes mellitus is characterized by chronic hyperglycemia that promotes ROS formation, causing severe oxidative stress. Furthermore, prolonged hyperglycemia leads to glycation reactions with formation of AGEs that contribute to a chronic inflammatory state. This research aims to evaluate the inhibitory activity of α-mangostin and four synthetic xanthenone derivatives against glycation and oxidative processes and on α-glucosidase, an intestinal hydrolase that catalyzes the cleavage of oligosaccharides into glucose molecules, promoting the postprandial glycemic peak. Antiglycation activity was evaluated using the BSA assay, while antioxidant capacity was detected with the ORAC assay. The inhibition of α-glucosidase activity was studied with multispectroscopic methods along with inhibitory kinetic analysis. α-Mangostin and synthetic compounds at 25 µM reduced the production of AGEs, whereas the α-glucosidase activity was inhibited only by the natural compound. α-Mangostin decreased enzymatic activity in a concentration-dependent manner in the micromolar range by a reversible mixed-type antagonism. Circular dichroism revealed a rearrangement of the secondary structure of α-glucosidase with an increase in the contents of α-helix and random coils and a decrease in β-sheet and β-turn components. The data highlighted the anti-α-glucosidase activity of α-mangostin together with its protective effects on protein glycation and oxidation damage.

α-Glucosidase and advanced glycation end products inhibition with Vernonia amygdalina root and leaf extracts: new data supporting the antidiabetic properties

OBJECTIVE

This study aims to investigate antidiabetic activity of several Vernonia amygdalina extracts to study their potential use in medicine.

METHODS

Aqueous and ethanol extracts were obtained by maceration and Soxhlet extraction from roots and leaves of V. amygdalina. The extracts were tested as inhibitors of α-glucosidase activity and of advanced glycation end products (AGEs) formation. Further, radical scavenging activity was examined detecting the oxygen radical absorbance capacity, while the potential cytotoxicity of extracts was estimated with MTT assay.

KEY FINDINGS

In aqueous and ethanol extracts, several polyphenolic compounds were identified; in detail, (-)-catechin and luteolin were found in leaf extracts, while caffeic acid, chlorogenic acid and the terpenoid vernodalol were recognized in root extracts. Regarding antidiabetic activity, the aqueous root extracts efficiently inhibited α-glucosidase activity in a concentration-dependent manner (IC50 = 5.6 µg/ml and 39.8 µg/ml, respectively of macerated and Soxhlet extracts), whereas those obtained from leaves exhibited lower potency. Furthermore, AGEs formation was reduced by all V. amygdalina extracts starting from 10 µg/ml.

CONCLUSIONS

The aqueous extracts of V. amygdalina roots obtained by maceration and Soxhlet extraction show remarkable anti-α-glucosidase activity, and all extracts have favourable antiglycation and antioxidant activities.

Research progress on the inhibition of enzymes by polyoxometalates

Polyoxometalates (POMs) are a kind of inorganic cluster metal complex with various biological activities, such as anti-Alzheimer's disease, antibacterial, anti-cancer, anti-diabetes, anti-virus and so on.

Clinical and pharmaceutical applications of affinity ligands in capillary electrophoresis: A review

Affinity capillary electrophoresis (ACE) is a separation technique that combines a biologically-related binding agent with the separating power and efficiency of capillary electrophoresis. This review will examine several classes of binding agents that have been used in ACE and applications that have been described for the resulting methods in clinical or pharmaceutical analysis. Binding agents that will be considered are antibodies, aptamers, lectins, serum proteins, carbohydrates, and enzymes. This review will also describe the various formats in which each type of binding agent has been used in CE, including both homogeneous and heterogeneous methods. Specific areas of applications that will be considered are CE-based immunoassays, glycoprotein/glycan separations, chiral separations, and biointeraction studies. The general principles and formats of ACE for each of these applications will be examined, along with the potential advantages or limitations of these methods.

Advances in enzyme substrate analysis with capillary electrophoresis

Capillary electrophoresis provides a rapid, cost-effective platform for enzyme and substrate characterization. The high resolution achievable by capillary electrophoresis enables the analysis of substrates and products that are indistinguishable by spectroscopic techniques alone, while the small volume requirement enables analysis of enzymes or substrates in limited supply. Furthermore, the compatibility of capillary electrophoresis with various detectors makes it suitable for KM determinations ranging from nanomolar to millimolar concentrations. Capillary electrophoresis fundamentals are discussed with an emphasis on the separation mechanisms relevant to evaluate sets of substrate and product that are charged, neutral, and even chiral. The basic principles of Michaelis-Menten determinations are reviewed and the process of translating capillary electrophoresis electropherograms into a Michaelis-Menten curve is outlined. The conditions that must be optimized in order to couple off-line and on-line enzyme reactions with capillary electrophoresis separations, such as incubation time, buffer pH and ionic strength, and temperature, are examined to provide insight into how the techniques can be best utilized. The application of capillary electrophoresis to quantify enzyme inhibition, in the form of KI or IC50 is detailed. The concept and implementation of the immobilized enzyme reactor is described as a means to increase enzyme stability and reusability, as well as a powerful tool for screening enzyme substrates and inhibitors. Emerging techniques focused on applying capillary electrophoresis as a rapid assay to obtain structural identification or sequence information about a substrate and in-line digestions of peptides and proteins coupled to mass spectrometry analyses are highlighted.

Recent advances in screening of enzymes inhibitors based on capillary electrophoresis

Capillary electrophoresis with many advantages plays an important role in pharmaceutical analysis and drug screening. This review gives an overview on the recent advances in the developments and applications of capillary electrophoresis in the field of enzyme inhibitor screening. The period covers 2013 to 2017. Both the pre-capillary enzyme assays and in-capillary enzyme assays which include electrophoretically mediated microanalysis (EMMA) and immobilized enzyme microreactor (IMER) are summarized in this article.

Sensitive fluorimetric assays for α-glucosidase activity and inhibitor screening based on β-cyclodextrin-coated quantum dots

A fluorescence method was established for a α-glucosidase activity assay and inhibitor screening based on β-cyclodextrin-coated quantum dots. p-Nitrophenol, the hydrolysis product of the α-glucosidase reaction, could quench the fluorescence of β-cyclodextrin-coated quantum dots via an electron transfer process, leading to fluorescence turn-off, whereas the fluorescence of the system turned on in the presence of α-glucosidase inhibitors. Taking advantage of the excellent properties of quantum dots, this method provided a very simple, rapid and sensitive screening method for α-glucosidase inhibitors. Two α-glucosidase inhibitors, 2,4,6-tribromophenol and acarbose, were used to evaluate the feasibility of this screening model, and IC50 values of 24 μM and 0.55 mM were obtained respectively, which were lower than those previously reported. The method may have potential application in screening α-glucosidase inhibitors.

An online immobilized α-glucosidase microreactor for enzyme kinetics and inhibition assays

A novel online α-glucosidase-immobilized microreactor was developed by immobilizing α-glucosidase on capillary inner wall. The microreactor combination with capillary electrophoresis was applied in studying enzyme kinetics and inhibition kinetics.