Inhibitory effect of voglibose and gymnemic acid on maltose absorption in vivo

Analyzing the potential of selected plant extracts and their structurally diverse secondary metabolites for α-glucosidase inhibitory activity: in vitro and in silico approach

Inhibiting α-glucosidase activity is a therapeutic method to regulate post-prandial hyperglycemia in humans. Here, in-vitro and in-silico studies were used to find α-glucosidase inhibitory plant secondary metabolites (PSM). Among 408 solvent extracts from 70 plants tested for α-glucosidase inhibition, 174 had IC50 ≤ 3 mg/ml. α-glucosidase inhibitory PSM is found in several plant species and solvent extracts, indicating their diversity. Further, ensemble molecular docking and structural activity relationship analysis supported this hypothesis where the top 100 PSM with the least binding energy (BE) among the 539 PSM belonged to sesquiterpenoids (34%), catechols (11%), flavonoids (9%) and steroidal lactones (8%). Shortlisted 11 PSM were subjected to molecular dynamic simulation. Withanolide J recorded the least BE of -66.424 ± 22.333 kJ/mol, followed by Withacoagulin I (-64.665 ± 24.030 kJ/mol). When different simulation frames were analyzed, PSM of withanolide groups was stabilized in the narrow entrance of the active pocket forming H-bond with LYS156, TYR158, PHE159, PHE303 PRO312, LEU313, ARG315 and PHE134. Similarly, Hydroxytuberosone and 1, 8-Dihydroxy-3-carboxy-9, 10-anthraquinone (DHCA) formed H-bond with ASP307 located on the loop at the entrance of the active pocket. In the case of Neoliquiritin and Kaempferol-3-o-alpha-L-rhamnoside (KALR), glucose moiety interacted with the GLU277 and ASP215 (catalytic amino acid residues) through H-bonds. In addition, these 11 PSM were found to fulfil the criteria of drug-likeness as per Lipinski's rule of five and pharmacokinetic profile. The present study strengthens the library of α-glucosidase inhibitory plants and PSM, providing valuable information for Type-II Diabetes mellitus management.Communicated by Ramaswamy H. Sarma.

Biological significance of carbohydrate active enzymes and searching their inhibitors for therapeutic applications

Glycans are the most abundant and diverse group of biomolecules with a crucial role in all the biological processes. Their structural and functional diversity is not genetically encoded, but depends on Carbohydrate Active Enzymes (CAZymes) which carry out all catalytic activities in terms of synthesis, modification, and degradation. CAZymes comprise large families of enzymes with specific functions and are widely used for various commercial applications ranging from biofuel production to textile and food industries with impact on biorefineries. To understand the structure and functional mechanism of these CAZymes for their modification for industrial use, together with knowledge of therapeutic aspects of their dysfunction associated with various diseases, CAZyme inhibitors can be used as a valuable tool. In search for new inhibitors, the screening of various secondary metabolites using high-throughput techniques and rational design techniques have been explored. The inhibitors can thus help tune CAZymes and are emerging as a potential research interest.

In Vitro Antidiabetic Effects of Isolated Triterpene Glycoside Fraction from Gymnema sylvestre

A triterpene glycoside (TG) fraction isolated and purified from ethanolic extract of Gymnema sylvestre (EEGS) was investigated for blood glucose control benefit using in vitro methods. The HPLC purified active fraction TG was characterized using FTIR, LC-MS, and NMR. The purified fraction (TG) exhibited effective inhibition of yeast α-glucosidase, sucrase, maltase, and pancreatic α-amylase with IC₅₀ values 3.16 ± 0.05 μg/mL, 74.07 ± 0.51, 5.69 ± 0.02, and 1.17 ± 0.24 μg/mL, respectively, compared to control. TG was characterized to be a mixture of triterpene glycosides: gymnemic acids I, IV, and VII and gymnemagenin. In vitro studies were performed using mouse pancreatic β-cell lines (MIN6). TG did not exhibit any toxic effects on β-cell viability and showed protection against H₂O₂ induced ROS generation. There was up to 1.34-fold increase in glucose stimulated insulin secretion (p<0.05) in a dose-dependent manner relative to standard antidiabetic drug glibenclamide. Also, there was further one-fold enhancement in the expression of GLUT2 compared to commercial standard DAG (deacylgymnemic acid). Thus, the present study highlights the effective isolation and therapeutic potential of TG, making it a functional food ingredient and a safe nutraceutical candidate for management of diabetes.

Characteristics of proanthocyanidins in leaves of Chamaecyparis obtusa var. formosana as strong α-glucosidase inhibitors

BACKGROUND

In recent decades, there has been a growing demand for natural products with a view to using them as α-glucosidase inhibitors for reducing postprandial hyperglycemia. In this study, the hot water extract (HWE) from Chamaecyparis obtusa var. formosana (Hayata) Rehder (Cupressaceae) leaves and its soluble fractions were screened for α-glucosidase inhibition properties. The n-butanol-soluble fraction of HWE was further fractionated into 14 subfractions (B1-B14) using a Sephadex LH-20 column. The α-glucosidase-inhibitory activities and proanthocyanidin contents of all subfractions were determined. The structural characteristics of proanthocyanidins in proanthocyanidin-rich fractions were also elucidated.

RESULTS

HWE produced a dose-dependent inhibition of α-glucosidase at low dose. Its IC₅₀ value was 1.4 µg mL^-1 , showing high inhibitory activity. Subfractions B7-B14 displayed powerful α-glucosidase-inhibitory activities with IC₅₀ values ranging between 1 and 0.015 µg mL^-1 and contained abundant proanthocyanidins exceeding 300 mg g^-1 . The proanthocyanidins with higher mean degree of polymerization (mDP), higher proportions of procyanidin dimer (A1 or A2) and (epi)afzelechin of extension units and a lower proportion of epicatechin of terminal units displayed high α-glucosidase-inhibitory activities.

CONCLUSION

Proanthocyanidins in HWE were viewed as potential natural α-glucosidase inhibitors for decreasing postprandial hyperglycemia. The results indicated that specific structural characteristics of proanthocyanidins would be required for α-glucosidase-inhibitory activity. © 2018 Society of Chemical Industry.

α-Glucosidase inhibition by luteolin: kinetics, interaction and molecular docking

α-Glucosidase is a critical associated enzyme with type 2 diabetes mellitus in humans. Inhibition of α-glucosidase is important due to the potential effect of down regulating glucose absorption in patients. In this study, the inhibitory activity of flavone luteolin on α-glucosidase and their interaction mechanism were investigated by multispectroscopic methods along with molecular docking technique. It was found that luteolin reversibly inhibited α-glucosidase in a noncompetitive manner with an IC50 value of (1.72 ± 0.05) × 10(-4) mol L(-1), and the inhibition followed a multi-phase kinetic process with a first-order reaction. Luteolin had a strong ability to quench the intrinsic fluorescence of α-glucosidase through a static quenching procedure. The positive values of enthalpy and entropy change suggested that the binding of luteolin to α-glucosidase was driven mainly by hydrophobic interactions, and the binding distance was estimated to be 4.56 nm. Analysis of synchronous fluorescence, circular dichroism, and Fourier transform infrared spectra demonstrated that the binding of luteolin to α-glucosidase induced rearrangement and conformational changes of the enzyme. Moreover, the results obtained from molecular docking indicated that luteolin had a high affinity close to the active site pocket of α-glucosidase and indirectly inhibited the catalytic activity of the enzyme.

α-glucosidase inhibitors from plants: A natural approach to treat diabetes

Diabetes is a common metabolic disease characterized by abnormally high plasma glucose levels, leading to major complications, such as diabetic neuropathy, retinopathy, and cardiovascular diseases. One of the effective managements of diabetes mellitus, in particular, non-insulin-dependent diabetes mellitus (NIDDM) to decrease postprandial hyperglycemia, is to retard the absorption of glucose by inhibition of carbohydrate hydrolyzing enzymes, such as α-glucosidase and α-amylase, in the digestive organs. α-Glucosidase is the key enzyme catalyzing the final step in the digestive process of carbohydrates. Hence, α-glucosidase inhibitors can retard the liberation of d-glucose from dietary complex carbohydrates and delay glucose absorption, resulting in reduced postprandial plasma glucose levels and suppression of postprandial hyperglycemia. In recent years, many efforts have been made to identify effective α-glucosidase inhibitors from natural sources in order to develop a physiologic functional food or lead compounds for use against diabetes. Many α-glucosidase inhibitors that are phytoconstituents, such as flavonoids, alkaloids, terpenoids,anthocyanins, glycosides, phenolic compounds, and so on, have been isolated from plants. In the present review, we focus on the constituents isolated from different plants having α-glucosidase inhibitory potency along with IC50 values.

Alpha-glucosidase inhibitory activity of bromophenol purified from the red alga Polyopes lancifolia

A bromophenol, bis(2,3-dibromo-4,5-dihydroxybenzyl) ether, was purified from the red alga Polyopes lancifolia. Its IC(50) values were 0.098 and 0.120 microM against Saccharomyces cerevisiae and Bacillus stearothermophilus alpha-glucosidases, respectively, and 1.00 and 1.20 mM against rat-intestinal sucrase and maltase. This bromophenol competitively inhibited S. cerevisiae alpha-glucosidase with a K(I) value of 0.068 microM and was very stable at pH 2 for 60 min at 37 degrees C. Therefore, this P. lancifolia bromophenol may have potential as natural nutraceutical for the management of type 2 diabetes.

Potent alpha-glucosidase inhibitors purified from the red alga Grateloupia elliptica

Diabetes mellitus is a most serious and chronic disease whose incidence rates are increasing with incidences of obesity and aging of the general population over the world. One therapeutic approach for decreasing postprandial hyperglycemia is to retard absorption of glucose by inhibition of alpha-glucosidase. Two bromophenols, 2,4,6-tribromophenol and 2,4-dibromophenol, were purified from the red alga Grateloupia elliptica. IC(50) values of 2,4,6-tribromophenol and 2,4-dibromophenol were 60.3 and 110.4 microM against Saccharomyces cerevisiae alpha-glucosidase, and 130.3 and 230.3 microM against Bacillus stearothermophilus alpha-glucosidase, respectively. In addition, both mildly inhibited rat-intestinal sucrase (IC(50) of 4.2 and 3.6mM) and rat-intestinal maltase (IC(50) of 5.0 and 4.8mM). Therefore, bromophenols of G. elliptica have potential as natural nutraceuticals to prevent diabetes mellitus because of their high alpha-glucosidase inhibitory activity.

[Magic of the physician's word]

OBJECTIVE

The aim of this work was to find obesity control method without rebound. In our previous studies, gymnemate extracted from Gymnema sylvestre, inhibited oleic acid absorption. The Otsuka Long-Evans Tokushima Fatty (OLETF) rat, a genetic multifactor syndrome model, exhibits progressive overweight, hyperlipidemia and hyperglycemia. The effect of gymnemate on obesity in OLETF was investigated.

METHODS

Three groups were divided (n=4-8): (1) OLETF-gymnemate, gymnema water extract (containing gymnemate) diet (62.5 g/kg) and water (2.5 g/kg) were supplied 2 weeks from 26-28 weeks, following it general diet and water were fed 3 weeks to observe if it rebound, (2) OLETF-control and (3) the counterpart Long-Evans Tokushima Otsuka rats as normal-control.

RESULTS

With gymnemate treatment, the food and water intake were decreased about 1/3 and 2/3, along with body weight reduced 57.2+/- 6.4 and 75.5+/- 6.3 g during 1 and 2 weeks respectively. In the end of experiment (3 weeks after gymnemate withdrawal), the body weight was decreased to no significant difference with normal-control. The total cholesterol was decreased about 1/3, moreover LDL+VLDL (low-density and very-low-density lipoprotein) cholesterol decreased about 1/2. The proportion of HDL (high-density lipoprotein) cholesterol to the total cholesterol was increased. The serum triglyceride was decreased to the 1/4 of OLETF control. The level of serum cholesterol and triglyceride was no significant difference in gymnemate group with normal group.

CONCLUSION

Supplementation with gymnemate promoted weight loss by its ability to reduce hyperlipidemia, which was no withdrawal rebound: an important discovery. Supplementation with gymnemate is a novel therapeutic tool for weight management, especially in multifactor syndrome.