Inhibitory mechanism of sinensetin on α-glucosidase and non-enzymatic glycation: Insights from spectroscopy and molecular docking analyses

Inhibition effects of xanthohumol on α-amylase and α-glucosidase: Kinetics, multi-spectral and molecular docking

α-Amylase and α-glucosidase, two therapeutic targets for diabetes management, play crucial roles in carbohydrate metabolism and glucose absorption. Xanthohumol, one chalcone derived from hops, has demonstrated potential as a natural healthy phytonutrient. But its inhibition effects against α-amylase and α-glucosidase were still unclear. This study employs a comprehensive analytical strategy, including kinetics, multi-spectral, and molecular docking methods, to dissect the inhibition effects of xanthohumol against α-amylase and α-glucosidase. Our findings indicated that xanthohumol exerted a reversible mixed-type inhibition on both enzymes, with IC50 values of 71.07 ± 5.82 μM for α-amylase and 32.58 ± 3.11 μM for α-glucosidase. Multi-spectral analyses (fluorescence quenching, synchronous fluorescence, 3D fluorescence, ANS-binding fluorescence, and CD) revealed that xanthohumol binding induced conformation changes and microenvironment alterations in the enzymes, thereby inhibiting their activities. Molecular docking and dynamics studies further substantiated the interaction forces between xanthohumol and the enzymes. This research provided insights into the effects of xanthohumol as an inhibitor of α-amylase and α-glucosidase, offering valuable data to support the development of xanthohumol as a natural therapeutic for diabetes management.

Ultrasonic degradation of mulberry twigs polysaccharides: Effect on in vitro hypoglycemic activity and prebiotic potential

This study aimed to enhance the in vitro hypoglycemic activity of mulberry twigs polysaccharides (MTP) through ultrasonic degradation and to elucidate its underlying mechanisms and prebiotic potential. The results demonstrated that ultrasonic degradation effectively increased its inhibitory activity against α-glucosidase. Structural characterization of MTP revealed that ultrasonic degradation significantly decreasing its molecular weight and monosaccharide composition. Mechanistic studies indicated that the inhibition of α-glucosidase by the degraded product MTP-240 was reversible and followed a single static quenching process. In vitro fermentation assays revealed that MTP-240 promoted the production of short-chain fatty acids (SCFAs), surpassing the inulin control, with pentanoic acid accumulating most substantially. Additionally, MTP-240 enhanced the growth of Bifidobacterium, a beneficial gut bacterium associated with improved glucose levels and antioxidant capacity. These findings suggested that ultrasonic degradation was an effective method for enhancing the glycosidase inhibitory activity of polysaccharides, and the degraded MTP possesses the potential to be developed as a food additive with dual functions of glycosidase inhibition and prebiotic activity. This research provides a theoretical basis for the further development of mulberry resources and related functional foods.

Dimethylallylated stilbenoids by chemo-selective prenyltransferases and their α-glucosidase inhibitory effects

Prenylated stilbenoids are known for their unique health benefits and have been found to exhibit strong α-glucosidase inhibitory activities. In this study, the dimethylallylation of eight stilbenoids was investigated, which was catalyzed by engineered enzymes of the fungal prenyltransferase AnaPT. These reactions of stilbenoids catalyzed by AnaPT_F265D and AnaPT_F265G are chemo-selective and 17 products are all C-dimethylallylated stilbenoids, including twelve mono- and five di-dimethylallylated stilbenoids, significantly expanding the structure diversity of naturally occurring dimethylallylated stilbenoids. 10 Compounds were reported for the first time in this study. The molecular docking of 1D1 with AnaPT was also conducted, which revealed that N115 was likely a key residue. Our results showed that the catalytic efficiencies of AnaPT_F265D_N115K and AnaPT_F265D_N115A were higher than the other mutants obtained. Eight compounds (1D1, 2D1, 3D2-3D4, 6D1, 6D4, and 8D1) exhibited inhibitory effects on α-glucosidase with IC50 values ranging from 5.43 ± 0.16 to 42.61 ± 0.17 μM. Among them, compound 8D1 with IC50 value of 5.43 ± 0.16 μM showed about 40 times stronger than the positive control, acarbose with an IC50 of 217.07 ± 1.92 μM in α-glucosidase inhibitory assays. These fundings not only enrich the structure diversity of dimethylallylated stilbenoids but also lay the foundation for the discovery of potential candidate compounds for the treatment of diabetes and anti-obesity drugs.

Enrichment, Antioxidant and Enzyme Inhibition Activities of Flavonoids from Artemisia Selengensis Turcz

Macroporous resin was used to enrich flavonoids in the ethyl acetate extract of Artemisia Selengensis Turcz. Based on a single factor experiment, the enrichment process was optimized using the response surface method. The optimal parameters of the enrichment process were a sample concentration of 0.3 mg/mL, a loading rate of 1 mL/min, an elution flow rate of 2 mL/min, and a total flavonoid content of 155.38±0.97 mg/g. The flavonoids enriched by AB-8 macroporous resin demonstrated significant scavenging activities against DPPH, ABTS+, and hydroxyl free radicals, and also exhibited certain inhibitory effects on α-amylase and α-glucosidase. Among them, the scavenging ability of the flavonoids enriched by AB-8 macroporous resin on hydroxyl free radical (IC50=30.31±1.92 μg/mL) was the closest to Vc, and the inhibitory effect on α-glucosidase (IC50=16.19±1.35 μg/mL) was the best. These findings confirmed the potential of Artemisia Selengensis Turcz. was a natural antioxidant and hypoglycemic drug.

Inhibitory mechanisms of galloylated forms of theaflavins on α-glucosidase

Theaflavins, oxidation product of tea polyphenols, have demonstrated significant inhibitory effects on α-glucosidase, which is beneficial in alleviating hyperglycemia. This study found that the inhibition of four monomers of theaflavins on α-glucosidase was related to the presence of the galloyl moiety (GM), with IC50 values ranging from TFDG (0.26 mg/mL) < TF3'G (0.33 mg/mL) < TF3G (0.39 mg/mL) ≪ TF (3.26 mg/mL). The multi-spectroscopic analyses revealed that theaflavin monomers changed the microenvironment around aromatic amino acid residues and conformation of α-glucosidase, with the hierarchy being TFDG > TF3'G > TF3G > TF. The binding of theaflavins with α-glucosidase was confirmed by differential scanning calorimetry (DSC), isothermal titration calorimetry (ITC), molecular docking and molecular dynamics simulations analysis. It was confirmed that theaflavins can form stable complexes with α-glucosidase, and that hydrogen bonding and van der Waals forces play important roles in the binding of theaflavins to α-glucosidase. The strongest binding affinity was observed between TFDG and the enzyme's active site, which corresponded with its enzyme activity inhibition ability. The study suggests that GM substitution plays a crucial role in enhancing the binding of theaflavins to α-glucosidase, thereby inducing greater conformational changes and leading to a stronger inhibitory effect on α-glucosidase.

Effect of Planting Systems on the Physicochemical Properties and Bioactivities of Strawberry Polysaccharides

Suitable planting systems are critical for the physicochemical and bioactivities of strawberry (Fragaria × ananassa Duch.) polysaccharides (SPs). In this study, SPs were prepared through hot water extraction, and the differences in physicochemical characteristics and bioactivities between SPs derived from elevated matrix soilless planting strawberries (EP-SP) and those from and conventional soil planting strawberries (GP-SP) were investigated. A higher extraction yield was observed for EP-SP (5.88%) than for GP-SP (4.67%), and slightly higher values were measured for the average molecular weight (632.10 kDa vs. 611.88 kDa) and total sugar content (39.38% vs. 34.92%) in EP-SP. In contrast, a higher protein content (2.12% vs. 1.65%) and a more ordered molecular arrangement were exhibited by GP-SP. Monosaccharide composition analysis revealed that EP-SP contained higher levels of rhamnose (12.33%) and glucose (49.29%), whereas GP-SP was richer in galactose (11.06%) and galacturonic acid (19.12%). Thermal analysis indicated only minor differences in decomposition temperatures (approximately 225-226 °C) and thermal stability between the samples. However, GP-SP showed a higher enthalpy change (ΔHg = 18.74 J/g) compared to EP-SP (13.93 J/g). Biological activity assays revealed that GP-SP generally exerted stronger non-enzymatic glycation inhibition at both early and final stages (IC50: 7.47 mg/mL vs. 7.82 mg/mL and 11.18 mg/mL vs. 11.87 mg/mL, respectively), whereas EP-SP was more effective against intermediate α-dicarbonyl compounds (maximum inhibition of 75.32%). Additionally, GP-SP exerted superior α-glucosidase inhibition (IC50 = 2.4583 mg/mL), in line with kinetic and fluorescence quenching analyses showing a higher enzyme-substrate complex binding affinity (Kis = 1.6682 mg/mL; Ka = 5.1352 × 105 M-1). Rheological measurements demonstrated that EP-SP solutions exhibited a pronounced increase in apparent viscosity at higher concentrations (reaching 3477.30 mPa·s at 0.1 s-1 and 70 mg/mL) and a stronger shear-thinning behavior, while GP-SP showed a comparatively lower viscosity and lower network order. These findings suggest that different planting systems significantly affect both the molecular structures and functionalities of SPs, with GP-SP demonstrating enhanced hypoglycemic and anti-glycation properties. It is therefore recommended that suitable planting systems be selected to optimize the functionality of plant-derived polysaccharides for potential applications in the food and pharmaceutical industries.

Investigating the Inhibition of Diindolylmethane Derivatives on SARS-CoV-2 Main Protease

The SARS-CoV-2 main protease (Mpro) is an essential enzyme that promotes viral transcription and replication. Mpro conserved nature in different variants and its nonoverlapping nature with human proteases make it an attractive target for therapeutic intervention against SARS-CoV-2. In this work, the interaction mechanism between Mpro and diindolylmethane derivatives was investigated by molecular docking, enzymatic inhibition assay, UV-vis, fluorescence spectroscopy, and circular dichroism spectroscopy. Results of IC50 values show that 1p (9.87 μM) was the strongest inhibitor for Mpro in this work, which significantly inhibited the activity of Mpro. The binding constant (4.07 × 105 Lmol-1), the quenching constant (5.41 × 105 Lmol-1), and thermodynamic parameters indicated that the quenching mode of 1p was static quenching, and the main driving forces between 1p and Mpro are hydrogen bond and van der Waals force. The influence of molecular structure on the binding is investigated. Chlorine atoms and methoxy groups are favorable for the diindolylmethane derivative inhibitors of Mpro. This work confirms the changes in the microenvironment of Mpro by 1p, and provides clues for the design of potential inhibitors.

Investigation on the anti-α-glucosidase mechanism of aspergillus triazolate A from Oxalis corniculate L

Diabetes mellitus characterized by abnormal glucose concentration is a metabolic disease. α-Glu inhibitors from natural sources are a good choice for searching for high-efficiency and low-toxicity hypoglycemic drugs. In this study, a naturally effective α-Glu inhibitor aspergillus triazolate A (ATA) with a peculiar structure was first found in Oxalis corniculate L., then its activity and mechanism were first elucidated through various methods. These mechanisms included enzyme kinetics, circular dichroism spectra, fluorescence spectra, synchronous fluorescence spectrum, 3D fluorescence spectrum, and molecular docking. Meanwhile, the ability to reduce postprandial blood glucose was further investigated in vivo. Research results revealed that ATA was a mixed type α-Glu inhibitor with an IC50 value of 66.87 ± 1.50 μM, which bound to the enzyme from a single site through hydrogen bonding and hydrophobic forces causing the looser secondary structure of α-Glu. It was also found that the binding site of α-Glu was closer to the Trp residue, and the endogenous fluorescence of α-Glu was quenched in a static quenching form. Moreover, the sucrose loading test in vivo revealed that the ATA of 20 mg/kg could effectively reduce the postprandial blood glucose level. Hence, ATA could be used as lead compound to develop novel α-Glu inhibitors.

Inhibition mechanism of buckwheat hulls polyphenols on α-amylase and α-glucosidase using kinetics, spectroscopics and molecular docking approaches

The work investigated the activity inhibition of phenolic compounds in buckwheat (Fagopyrum esculentum Moench) hulls (BH) on α-amylase and α-glucosidase, and clarified their possible mechanisms based on kinetics, spectroscopics and molecular docking analysis. The total polyphenols (BHP) from BH using an ultrasound-assisted alcohol extraction method was 210.50 mg GAE/g DW. The study identified a total of 33 polyphenolic compounds in the extracts of BH using UPLC-Q-Exactive Orbitrap/MS, revealing that sixteen of these were novel polyphenolic substances not previously documented in this plant. BHP demonstrated significant inhibitory effects on both α-amylase and α-glucosidase enzymes, with IC50 values recorded at 27.16 μg/mL and 7.00 μg/mL, respectively, suggesting noncompetitive and mixed-type inhibition mechanisms. The fluorescence intensity of the enzymes was effectively quenched by BHP through a combination of dynamic and static quenching mechanisms, driven predominantly by hydrophobic interactions. BHP's interaction with the enzymes resulted in conformational changes that reduced their enzymatic activities. Molecular docking further revealed that six polyphenolic components of BHP had a strong affinity for binding with the active sites nestled in the enzymes' hydrophobic cavities, inhibiting their activity and potentially contributing to a reduction in blood glucose levels. The results could provide perspective for using BHP in the functional components of sugar-controlling foods.

Inhibitory Mechanism of Camellianin A against α-Glucosidase: In Vitro and Molecular Simulation Studies

α-Glucosidase is an important target for type II diabetes treatment, and the search for natural α-glucosidase inhibitors is currently a hot topic in functional food research. Camellianin A is the main flavonoid in the leaves of Adinandra nitida, but research on its inhibition of α-glucosidase is rarely reported. In view of this, the present study systematically investigated the inhibitory impact of camellianin A on α-glucosidase, combining the fluorescence method and molecular docking to explore their interaction, aiming to reveal the relevant inhibitory mechanism. The results indicated that camellianin A possessed excellent α-glucosidase inhibitory activity (IC50, 27.57 ± 0.59 μg/mL), and van der Waals force and hydrogen bonding dominated the binding process between camellianin A and α-glucosidase, with a binding-site number of 1. A molecular docking experiment suggested that camellianin A formed hydrogen bonding with Glu771, Trp391, Trp710, Gly566, Asp568, and Phe444 of α-glucosidase, consistent with the thermodynamic result. Our result can provide a reference for the development of natural α-glucosidase inhibitors.

Comprehending the inhibition mechanism of indole-based bis-acylhydrazone compounds on α-glucosidase: Spectral and theoretical approaches

Indole-based bis-acylhydrazone compounds can inhibit the activity of α-glucosidase and control the concentration of blood glucose. In this paper, the characteristics of three indole-based bis-acylhydrazone compounds with different inhibitory activities of α-glucosidase as well as the interaction with α-glucosidase were studied by experiments and computational simulation techniques. Enzyme kinetic and spectral experiments showed that the indole-based bis-acylhydrazone compounds were able to inhibit enzyme activity through mixed inhibition dominated by competitive inhibition, and during the binding reaction, indole-based bis-acylhydrazone compounds can quench the intrinsic fluorescence of α-glucosidase through static quenching and an aggregation of the indole-based bis-acylhydrazone with α-glucosidase produces a stable complex with a molar ratio of 1:1, and the combination of indole-based bis-acylhydrazone compounds could lead to slight change in the conformation of α-glucosidase. The theoretical simulation demonstrated that the stability of the complex systems was positively correlated with the inhibitory activity of indole-based bis-acylhydrazone compounds, and the indole-based bis-acylhydrazone compounds occupied the active site in the multi-ligand system, resulting in a significant decrease in the binding ability of starch to active amino acids. These results suggested that indole-based bis-acylhydrazone compound was expected to be a new type of α-glucosidase inhibitor.

Flavonoids with lipase inhibitory activity from lemon squeezing waste: isolation, multispectroscopic and in silico studies

BACKGROUND

Obesity is recognized as a lifestyle-related disease and the main risk factor for a series of pathological conditions, including cardiovascular diseases, hypertension and type 2 diabetes. Citrus limon is an important medicinal plant, and its fruits are rich in flavonoids investigated for their potential in managing obesity. In the present work, a green extraction applied to lemon squeezing waste (LSW) was optimized to recover pancreatic lipase (PL) inhibitors.

RESULTS

The microwave-assisted procedure yielded an extract with higher lipase inhibitory activity than those obtained by maceration and ultrasound. The main compounds present in the extract were identified by high-performance liquid chromatographic-mass spectrometric analysis, and hesperidin, eriocitrin and 4'-methyllucenin II were isolated. The three compounds were evaluated for in vitro PL inhibitory activity, and 4'-methyllucenin II resulted in the most promising inhibitor (IC50 = 12.1 μmol L-1; Ki = 62.2 μmol L-1). Multispectroscopic approaches suggested the three flavonoids act as competitive inhibitors and the binding studies indicated a greater interaction between PL and 4'-methyllucenin II. Docking analysis indicated the significant interactions of the three flavonoids with the PL catalytic site.

CONCLUSION

The present work highlights flavonoid glycosides as promising PL inhibitors and proposes LSW as a safe ingredient for the preparation of food supplements for managing obesity. © 2024 Society of Chemical Industry.

Relationships between degree of polymerization and activities: A study on condensed tannins from the bark of Ficus altissima

Condensed tannins were isolated from the bark of Ficus altissima and fractionated into four subcomponents on a Sephadex LH-20 column with 60 %, 80 %, 100 % methanol, and 70 % acetone, separately. Their structures were characterized by MALDI-TOF MS coupled with HPLC-ESI-MS and confirmed to be polymers of B-type procyanidin glucosides, procyanidins, and prodelphinidin glucosides. The degree of polymerization (DP) of these polymers was as high as 21, and the mDPs of the four subcomponents were calculated as 2.4, 6.6, 10.5 and 13.4, respectively. They competitively or noncompetitively suppressed the activities of tyrosinase and α-glucosidase through hydrogen bonding and hydrophobic interaction. And they also showed a powerful antioxidative activity. Correlation analyses verified that the anti-tyrosinase capacity exhibited a significant positive correlation (R2monophenolase = 0.9167 and R2diphenolase = 0.9302) with mDP within the methanol-water system, and the anti-α-glucosidase activity also showed a significant positive correlation with the mDP (R2 = 0.9187). In contrast, the antioxidant capability showed a significant negative correlation with the mDP (R2DPPH = 0.9258, R2ABTS = 0.9372). This study confirmed that condensed tannins from the bark of F. altissima were desirable anti-tyrosinase, anti-α-glucosidase, and antioxidant agents, and elucidated the relationships of their mDP (molecular weight) and activities, which provided a scientific basis for the comprehensive utilization of these polymers in the food, cosmetics, medicine and other fields.

Hypoglycemic Effect of Polysaccharides from Physalis alkekengi L. in Type 2 Diabetes Mellitus Mice

Type 2 diabetes mellitus (T2DM) is a common metabolic disease that adversely impacts patient health. In this study, a T2DM model was established in ICR mice through the administration of a high-sugar and high-fat diet combined with the intraperitoneal injection of streptozotocin to explore the hypoglycemic effect of polysaccharides from Physalis alkekengi L. After six weeks of treatment, the mice in the high-dosage group (800 mg/kg bw) displayed significant improvements in terms of fasting blood glucose concentration, glucose tolerance, serum insulin level, insulin resistance, and weight loss (p < 0.05). The polysaccharides also significantly regulated blood lipid levels by reducing the serum contents of total triglycerides, total cholesterol, and low-density lipoproteins and increasing the serum content of high-density lipoproteins (p < 0.05). Furthermore, they significantly enhanced the hepatic and pancreatic antioxidant capacities, as determined by measuring the catalase and superoxide dismutase activities and the total antioxidant capacity (p < 0.05). The results of immunohistochemistry showed that the P. alkekengi polysaccharides can increase the expression of GPR43 in mice colon epithelial cells, thereby promoting the secretion of glucagon-like peptide-1. In summary, P. alkekengi polysaccharides can help to regulate blood glucose levels in T2DM mice and alleviate the decline in the antioxidant capacities of the liver and pancreas, thus protecting these organs from damage.

Screening of α-Glucosidase Inhibitors in Cichorium glandulosum Boiss. et Huet Extracts and Study of Interaction Mechanisms

Cichorium glandulosum Boiss. et Huet (CGB) extract has an α-glucosidase inhibitory effect (IC50 = 59.34 ± 0.07 μg/mL, positive control drug acarbose IC50 = 126.1 ± 0.02 μg/mL), but the precise enzyme inhibitors implicated in this process are not known. The screening of α-glucosidase inhibitors in CGB extracts was conducted by bioaffinity ultrafiltration, and six potential inhibitors (quercetin, lactucin, 3-O-methylquercetin, hyperoside, lactucopicrin, and isochlorogenic acid B) were screened as the precise inhibitors. The binding rate calculations and evaluation of enzyme inhibitory effects showed that lactucin and lactucopicrin exhibited the greatest inhibitory activities. Next, the inhibiting effects of the active components of CGB, lactucin and lactucopicrin, on α-glucosidase and their mechanisms were investigated through α-glucosidase activity assay, enzyme kinetics, multispectral analysis, and molecular docking simulation. The findings demonstrated that lactucin (IC50 = 52.76 ± 0.21 μM) and lactucopicrin (IC50 = 17.71 ± 0.64 μM) exhibited more inhibitory effects on α-glucosidase in comparison to acarbose (positive drug, IC50 = 195.2 ± 0.30 μM). Enzyme kinetic research revealed that lactucin inhibits α-glucosidase through a noncompetitive inhibition mechanism, while lactucopicrin inhibits it through a competitive inhibition mechanism. The fluorescence results suggested that lactucin and lactucopicrin effectively reduce the fluorescence of α-glucosidase by creating lactucin-α-glucosidase and lactucopicrin-α-glucosidase complexes through static quenching. Furthermore, the circular dichroism (CD) and Fourier transform infrared spectroscopy (FT-IR) analyses revealed that the interaction between lactucin or lactucopicrin and α-glucosidase resulted in a modification of the α-glucosidase's conformation. The findings from molecular docking and molecular dynamics simulations offer further confirmation that lactucopicrin has a robust binding affinity for certain residues located within the active cavity of α-glucosidase. Furthermore, it has a greater affinity for α-glucosidase compared to lactucin. The results validate the suppressive impact of lactucin and lactucopicrin on α-glucosidase and elucidate their underlying processes. Additionally, they serve as a foundation for the structural alteration of sesquiterpene derived from CGB, with the intention of using it for the management of diabetic mellitus.

Inhibition of α-amylase digestion by a Lonicera caerulea berry polyphenol starch complex revealed via multi-spectroscopic and molecular dynamics analyses

Polyphenol-starch complexes exhibit synergistic and beneficial effects on both polyphenols and resistant starches. This study evaluates the inhibitory effects and mechanisms of α-amylase on a Lonicera caerulea berry polyphenol-wheat starch (LPWS) complex following high hydrostatic pressure treatments of 400 MPa for 30 min and 600 MPa for 30 min. The IC50 values for α-amylase inhibition by the complex were 3.61 ± 0.10 mg/mL and 3.42 ± 0.08 mg/mL at a 10 % (w/w) polyphenol content. This interaction was further supported by Fourier-transform infrared spectroscopy and circular dichroism, which confirmed that the alpha helix component of the secondary structure of α-amylase was reduced due to the complex. Multifluorescence spectroscopy revealed that the complex induces changes in the microenvironment of fluorophores surrounding the α-amylase active site. Molecular dynamics simulations and molecular docking revealed that the active site of amylose within the complex becomes enveloped in polyphenol clusters. This wrapping effect reduced the hydrogen bonds between amylose and α-amylase, decreasing from 16 groups to just one group. In summary, the LPWS complex represents a low-digestible carbohydrate food source, thus laying the groundwork for the research and development of functional foods aimed at postprandial hypoglycemic effects.

Investigation of steric hindrance effect on the interactions between four alkaloids and HSA by isothermal titration calorimetry and molecular docking

The binding of four alkaloids with human serum albumin (HSA) was investigated by isothermal titration calorimetry (ITC), spectroscopy and molecular docking techniques. The findings demonstrated that theophylline or caffeine can bind to HAS, respectively. The number of binding sites and binding constants are obtained. The binding mode is a static quenching process. The effects of steric hindrance, temperature, salt concentration and buffer solution on the binding indicated that theophylline and HSA have higher binding affinity than caffeine. The fluorescence and ITC results showed that the interaction between HSA and theophylline or caffeine is an entropy-driven spontaneous exothermic process. The hydrophobic force was the primary driving factor. The experimental results were consistent with the molecular docking data. Based on the molecular structures of the four alkaloids, steric hindrance might be a major factor in the binding between HSA and these four alkaloids. This study elucidates the mechanism of interactions between four alkaloids and HSA.

Mechanistic study on the inhibition of α-amylase and α-glucosidase using the extract of ultrasound-treated coffee leaves

BACKGROUND

Our previous studies have shown that ultrasound-treated γ-aminobutyric acid (GABA)-rich coffee leaves have higher angiotensin-I-converting enzyme inhibitory activity than their untreated counterpart. However, whether they have antidiabetic activity remains unknown. In this study, we aimed to investigate the inhibitory activities of coffee leaf extracts (CLEs) prepared with ultrasound (CLE-U) or without ultrasound (CLE-NU) pretreatment on α-amylase and α-glucosidase. Subsequently, we evaluated the binding interaction between CLE-U and both enzymes using multi-spectroscopic and in silico analyses.

RESULTS

Ultrasound pretreatment increased the inhibitory activities of CLE-U against α-amylase and α-glucosidase by 21.78% and 25.13%, respectively. CLE-U reversibly inhibits both enzymes, with competitive inhibition observed for α-amylase and non-competitive inhibition for α-glucosidase. The static quenching of CLE-U against both enzymes was primarily driven by hydrogen bond and van der Waals interactions. The α-helices of α-amylase and α-glucosidase were increased by 1.8% and 21.3%, respectively. Molecular docking results showed that the key differential compounds, including mangiferin, 5-caffeoylquinic acid, rutin, trigonelline, GABA, caffeine, glutamate, and others, present in coffee leaves interacted with specific amino acid residues located at the active site of α-amylase (ASP197, GLU233, and ASP300). The binding of α-glucosidase and these bioactive components involved amino acid residues, such as PHE1289, PRO1329, and GLU1397, located outside the active site.

CONCLUSION

Ultrasound-treated coffee leaves are potential anti-diabetic substances, capable of preventing diabetes by inhibiting the activities of α-amylase and α-glucosidase, thus delaying starch digestion. Our study provides valuable information to elucidate the possible antidiabetic capacity of coffee leaves through the inhibition of α-amylase and α-glucosidase activities. © 2023 Society of Chemical Industry.

Inhibition mechanisms of four ellagitannins from terminalia chebula fruits on acetylcholinesterase by inhibition kinetics, spectroscopy and molecular docking analyses

Acetylcholinesterase (AChE) is an important therapeutic target for the treatment of Alzheimer's disease (AD), and the development of natural AChE inhibitors as candidates has played a significant role in drug discovery. In this study, the inhibition mechanisms of four ellagitannins, punicalagin, chebulinic acid, geraniin and corilagin, from Terminalia chebula fruits on AChE were investigated systematically by a combination of inhibition kinetics, multi-spectroscopic methods and molecular docking. The kinetic results showed that punicalagin, chebulinic acid and geraniin exhibited strong reversible inhibitory effects on AChE in an uncompetitive manner with the IC50 values of 0.43, 0.50, and 0.51 mM, respectively, while corilagin inhibited AChE activity in a mixed type with the IC50 value of 0.72 mM. The results of fluorescence and UV-vis spectra and fluorescence resonance energy transfer (FRET) revealed that four ellagitannins could significantly quenched the intrinsic fluorescence of AChE though a static quenching along with non-radiative energy transfer. Thermodynamic analyses showed that values of ΔG, ΔH and ΔS were negative, indicating that all binding processes were spontaneous, and the hydrogen bonding and Van der Waals forces might make a great contribution to the formation of inhibitor-AChE complexes. The synchronous fluorescence, three-dimensional (3D) fluorescence, UV-vis, and FT-IR spectra studies suggested that four ellagitannins could lead to alterations in the micro-environment and secondary structure of AChE, and thus the conformational change of AChE. Moreover, molecular docking demonstrated that four ellagitannins could interacted with main amino acid residues of AChE with affinity energies ranging from -9.9 to -8.7 kJ/mol, and further confirmed the above experimental results. This study provided valuable findings for the potential application of four ellagitannins as promising candidates in the exploration of natural AChE inhibitors for the treatment of AD.

Binding interactions of hydrophobically-modified flavonols with β-glucosidase: fluorescence spectroscopy and molecular modelling study

Natural flavonoids are capable of inhibiting glucosidase activity, so they can be used for treating diabetes mellitus and hypertension. However, molecular-level details of their interactions with glucosidase enzymes remain poorly understood. This paper describes the synthesis and spectral characterization of a series of fluorescent flavonols and their interaction with the β-glucosidase enzyme. To tune flavonol-enzyme interaction modes and affinity, we introduced different polar halogen-containing groups or bulky aromatic/alkyl substituents in the peripheral 2-aryl ring of a flavonol moiety. Using fluorescence spectroscopy methods in combination with molecular docking and molecular dynamics simulations, we examined the binding affinity and identified probe binding patterns, which are critical for steric blockage of the key catalytic residues of the enzyme. Using a fluorescent assay, we demonstrated that the binding of flavonol 2e to β-glucosidase decreased its enzymatic activity up to 3.5 times. In addition, our molecular docking and all-atom molecular dynamics simulations suggest that the probe binding is driven by hydrophobic interactions with aromatic Trp and Tyr residues within the catalytic glycone binding pockets of β-glucosidase. Our study provides a new insight into structure-property relations for flavonol-protein interactions, which govern their enzyme binding, and outlines a framework for a rational design of new flavonol-based potent inhibitors for β-glucosidases.

Computational approaches for innovative anti-viral drug discovery using Orthosiphon aristatus blume miq against dengue virus

Dengue virus has emerged as infectious mosquito borne disease involved in lowering platelets and white blood cells (WBC) count particularly. The genome structure is based on several structural and non-structural proteins essential for viral replication and progeny. One of the major proteins of replication is non-structural protein 3 (NS3) that transforms polyproteins into functional proteins with a cofactor non-structural protein (NS2B). Heat Shock Protein 70 (HSP70), is a human protein that assists in replication, viral entry and virion synthesis. Therefore, to inhibit the spread of dengue infection, there is a need of antivirals targeting replication proteins and other human proteins that help in dengue virus multiplication. By systemic approach based on molecular docking, ADMET (absorption, distribution, metabolism, excretion and toxicity) properties and molecular dynamic simulation (MD), potent inhibitors can be predicted. Inhibition of NS2B/NS3 dengue and HSP70 proteins involved in multiple steps in dengue virus progression can be prevented by using different phytochemicals. Molecular docking was performed using AutoDock Vina, PatchDock, and SwissDock. Interactions of obtained complex were observed in PyMOL and PLIP. Validation was checked by PROCHEK, simulation was performed using iMODS followed by preclinical testing by admetSAR. Ladanein, a flavonoid of Orthosiphon aristatus, was obtained as the lead compound to inhibit major replication protein of dengue virus with inhibitory potential against HSP70 protein. In summary, various in silico approaches were used to obtain the best phytochemical having anti-dengue potential.Communicated by Ramaswamy H. Sarma.

Exploring inhibitory effect and mechanism of hesperetin-Cu (II) complex against protein glycation

Inhibition of advanced glycation end products (AGEs) formed in protein glycosylation is crucial for minimizing diabetic complications. Herein, the anti-glycation potential of hesperetin-Cu (II) complex was investigated. Hesperetin-Cu (II) complex strongly inhibited three stages glycosylation products in bovine serum albumin (BSA)-fructose model, especially for the inhibition of AGEs (88.45%), which was stronger than hesperetin (51.76%) and aminoguanidine (22.89%). Meanwhile, hesperetin-Cu (II) complex decreased the levels of BSA carbonylation and oxidation products. 182.50 µg/mL of hesperetin-Cu (II) complex inhibited 66.71% β-crosslinking structures of BSA, and scavenged 59.80% superoxide anions and 79.76% hydroxyl radicals. Moreover, after incubating with methylglyoxal for 24 h, hesperetin-Cu (II) complex removed 85.70% methylglyoxal. The mechanisms of protein antiglycation by hesperetin-Cu (II) complex may be through protecting structure, trapping methylglyoxal, scavenging free radicals and interacting with BSA. This study may contribute to the development of hesperetin-Cu (II) complex as a functional food additive against protein glycation.

Inhibitory Efficacy of Cycloartenyl Ferulate against α-Glucosidase and α-Amylase and Its Increased Concentration in Gamma-Irradiated Rice (Germinated Rice)

Cycloartenyl ferulate is a derivative of γ-oryzanol with varied biological activity, including diabetes mellitus treatment. This research focused on improving the cycloartenyl ferulate accumulation in germinated rice by gamma irradiation under saline conditions. Moreover, the inhibitory potential of cycloartenyl ferulate against carbohydrate hydrolysis enzymes (α-glucosidase and α-amylase) was investigated through in vitro and in silico techniques. The results revealed that cycloartenyl ferulate increased in germinated rice under saline conditions upon gamma irradiation. A suitable condition for stimulating the highest cycloartenyl ferulate concentration (852.20±20.59 μg/g) in germinated rice was obtained from the gamma dose at 100 Gy and under 40 mM salt concentration. The inhibitory potential of cycloartenyl ferulate against α-glucosidase (31.31±1.43%) was higher than against α-amylase (12.72±1.11%). The inhibition mode of cycloartenyl ferulate against α-glucosidase was demonstrated as a mixed-type inhibition. A fluorescence study confirmed that the cycloartenyl ferulate interacted with the α-glucosidase's active site. A docking study revealed that cycloartenyl ferulate bound to seven amino acids of α-glucosidase with a binding energy of -8.8 kcal/mol and a higher binding potential than α-amylase (-8.2 kcal/mol). The results suggested that the gamma irradiation technique under saline conditions is suitable for stimulating γ-oryzanol, especially cycloartenyl ferulate. Furthermore, cycloartenyl ferulate demonstrated its potential as a candidate compound for blood glucose management in diabetes mellitus treatment.

Dietary sinensetin and polymethoxyflavonoids: Bioavailability and potential metabolic syndrome-related bioactivity

Sinensetin is among the most ubiquitous polyphenols in citrus fruit and recently has been extensively studied for its ability to prevent or treat diseases. The current literature on the bioavailability of sinensetin and its derivatives was reviewed and the potential ameliorative effects of metabolic syndrome in humans were evaluated. Sinensetin and its derivatives mainly aggregated in the large intestine and extensively metabolized through gut microbiota (GM) and the liver. So intestinal microorganisms had a significant influence on the absorption and metabolism of sinensetin. Interestingly, not only GM acted on sinensetin to metabolize them, but sinensetin also regulated the composition of GM. Thus, sinensetin was metabolized as methyl, glucuronide and sulfate metabolites in the blood and urine. Furthermore, sinensetin was reported to have the beneficial effect of ameliorating metabolic syndromes, including disorders of lipid metabolism (obesity, NAFLD, atherosclerosis), glucose metabolism disorder (insulin resistant) and inflammation, in terms of improving the composition of intestinal flora and modulating metabolic pathway factors in relevant tissues. The present work strongly elucidated the potential mechanism of sinensetin in improving metabolic disorders and supported the contribution of sinensetin to health benefits, thus offering a better perspective in understanding the role played by sinensetin in human health.

Exploration of the inhibitory mechanisms of trans-polydatin/resveratrol on α-glucosidase by multi-spectroscopic analysis, in silico docking and molecular dynamics simulation

Plant-derived phenolics as natural α-glucosidase (α-GLU) inhibitors have attached great attention in the treatment of type-II diabetes mellitus currently. In this study, trans-polydatin and its aglycone resveratrol were found to show a notable inhibitory activity on α-GLU in a mixed-type manner with IC₅₀ values of 18.07 and 16.73 μg/mL, respectively, which were further stronger than anti-diabetic drug acrabose (IC₅₀ = 179.86 μg/mL). Multi-spectroscopic analysis results indicated that polydatin/resveratrol bound to α-GLU with one affinity binding site which was mainly driven by hydrogen bonds and van der Waals forces, and this binding process resulted in conformational alteration of α-GLU. In silico docking study showed that polydatin/resveratrol can well interact with the surrounding amino acid residues in the active cavity of α-GLU. Molecular dynamics simulation further clarified the structure and characterization of α-GLU-polydatin/resveratrol complexes. This study might supply a theoretical basis for the designing of novel functional foods with polydatin/resveratrol.

Penta-O-galloyl-β-d-glucose inhibits the formation of advanced glycation end-products (AGEs): A mechanistic investigation

Penta-O-galloyl-β-d-glucose (PGG) was prepared from tannic acid methanolysis products based on HSCCC, and its protective effects and mechanism on the glucose-induced glycation were investigated for the first time. PGG was confirmed to exhibit strong anti-AGEs effects in bovine serum albumin (BSA)-glucose (Glu) and BSA-methylglyoxal (MGO) glycation systems. It was showed that PGG could inhibit the AGEs formation by blocking glycated intermediates (fructosamine and α-dicarbonyl compounds), eliminating radicals, and chelating metal-ions. In-depth mechanism analysis proved that PGG could prevent BSA from glycation by hindering the accumulation of amyloid fibrils, stabilizing the BSA secondary structures, and binding the partial glycation sites. Furthermore, PGG exhibited a prominent trapping capacities on the reactive intermediate MGO by generating PGG-mono-MGO adduct. This research indicated that PGG could be an effective agent to block Glu/MGO-triggered glycation and offered new insights into PGG as a functional ingredient in food materials for preventing diabetic syndrome.

Chromone-based benzohydrazide derivatives as potential α-glucosidase inhibitor: Synthesis, biological evaluation and molecular docking study

In order to find new α-glucosidase inhibitors with high efficiency and low toxicity, novel chromone-based benzohydrazide derivatives 6a-6s were synthesized and characterized through ¹H NMR, ¹³C NMR, and HRMS. All the new synthesized compounds were tested for inhibitory activities against α-glucosidase. Compounds 6a-6s with IC₅₀ values ranging from 4.51 ± 0.09 to 27.21 ± 0.83 μM, showed a potential α-glucosidase inhibitory activity as compared to the positive control (acarbose: IC₅₀ = 790.40 ± 0.91 μM). Compound 6i exhibited the highest α-glucosidase inhibitory activity with an IC₅₀ value of 4.51 ± 0.09 μM. Theinteractionbetween α-glucosidase and 6i was further confirmed by enzyme kinetic, fluorescence quenching, circular dichroism, and molecular docking study. In vivo experiment showed that 6i could suppress the rise of blood glucose levels after sucrose loading. The cytotoxicity result indicated that 6i exhibited low cytotoxicity in vitro.

Structure-activity relationships and the underlying mechanism of α-amylase inhibition by hyperoside and quercetin: Multi-spectroscopy and molecular docking analyses

Inhibiting the activity of α-amylase has been considered an effective strategy to manage hyperglycemia. Hyperoside and quercetin are the main natural flavonoids in various plants, and the inhibition mechanism on α-amylase remains unclear. In this study, the structure-activity relationships between hyperoside/quercetin and α-amylase were evaluated by enzyme kinetic analysis, multi-spectroscopic techniques, and molecular docking analysis. Results showed that hyperoside and quercetin exhibited significant α-amylase inhibitory activities with IC₅₀ values of 0.491 and 0.325 mg/mL, respectively. The α-amylase activity decreased in the presence of hyperoside and quercetin in a competitive and noncompetitive manner, respectively. UV-vis spectra suggested that the aromatic amino acid residues (Trp and Tyr) microenvironment of α-amylase changed in the presence of these two flavonoids. FTIR and CD spectra showed the vibrations of the amide bands and the secondary structure content changes. The fluorescence quenching mechanism of α-amylase by hyperoside and quercetin belonged to the static quenching type. Finally, molecular docking intuitively showed that hyperoside/quercetin formed hydrogen bonds with the key active site residues (Asp197, Glu233, and Asp300) in α-amylase. MD simulation indicated hyperoside/quercetin-α-amylase docked complexes had good stability. Taken together, this research provides new sights to developing potent drugs or functional foods with hyperoside and quercetin, offering new avenues for hyperglycemia treatment.

Antiglycoxidative properties of amantadine – a systematic review and comprehensive in vitro study

An important drug used in the treatment of Parkinson’s disease is amantadine. We are the first to perform a comprehensive study based on various glycation and oxidation factors, determining the impact of amantadine on protein glycoxidation. Sugars (glucose, fructose, galactose) and aldehydes (glyoxal, methylglyoxal) were used as glycation agents, and chloramine T was used as an oxidant. Glycoxidation biomarkers in albumin treated with amantadine were generally not different from the control group (glycation/oxidation factors), indicating that the drug did not affect oxidation and glycation processes. Molecular docking analysis did not reveal strong binding sites of amantadine on the bovine serum albumin structure. Although amantadine poorly scavenged hydroxyl radical and hydrogen peroxide, it had significantly lower antioxidant and antiglycation effect than all protein oxidation and glycation inhibitors. In some cases, amantadine even demonstrated glycoxidant, proglycation, and prooxidant properties. In summary, amantadine exhibited weak antioxidant properties and a lack of antiglycation activity.

Identification of the effective α-amylase inhibitors from Dalbergia odorifera: Virtual screening, spectroscopy, molecular docking, and molecular dynamic simulation

Inhibiting the activity of α-amylase has been considered as one efficient way to prevent and treat type 2 diabetes recently. Dalbergia odorifera, a kind of Leguminosae plant, has a positive therapeutic effect on type 2 diabetes, possibly contributing by some constituents that can inhibit the activity of α-amylase. In this study, we found that eriodictyol was one potential constituent through virtual screening. The interaction mode between eriodictyol and α-amylase was elucidated by molecular docking, multi-spectroscopic analysis, and molecular dynamic simulation. The results revealed that eriodictyol quenched the intrinsic fluorescence of α-amylase, and the quenching mode was static quenching. Eriodictyol could spontaneously interact with α-amylase, mostly stabilized and influenced by the hydrophobic interaction, while the binding sites (n) was 1.13 ± 0.07 and binding constant (K_b) was (1.43 ± 0.14) × 10⁵ at 310 K, respectively. In addition, FT-IR and CD had been applied to identify that eriodictyol can trigger the conformational change of α-amylase. Taken together, the results provided some experimental data for developing new α-amylase inhibitors from Dalbergia odorifera, which may further prevent and treat diabetes and diabetes complications.

Inhibitory effect of flavonoid glycosides on digestive enzymes: In silico, in vitro, and in vivo studies

Flavonoid glycosides (FGs) appear to be good candidates for controlling blood glucose levels, so regular consumption of vegetables/fruits rich in FGs may prevent the consequences of type 2 diabetes (DM). Inhibition of digestive enzymes using natural FGs is a suitable dietary tool to regulate the hydrolysis of polysaccharides and overcome hyperglycemia. The aim of the current research is to find FGs that can effectively inhibit the digestive enzymes α-glucosidase (α-Gl) and α-amylase (α-Am). Accordingly, twenty-three FGs were selected and filtered through docking-based virtual screening. Based on the molecular docking and molecular dynamics (MD) simulation, among the 23 selected FGs, nicotiflorin and swertisin significantly inhibited α-Gl and α-Am, respectively. In vitro analysis revealed the inhibitory capacity of nicotiflorin on α-Gl was equal to IC50 at 0.148 mg/ml and the inhibitory activity of swertisin on α-Am was equal to IC50 at 1.894 mg/ml. It was found that nicotiflorin and swertisin act much like as a competitive inhibitor on α-Gl and α-Am, respectively. Furthermore, the fluorescence intensity of both enzymes decreased after interaction with two FGs. FT-IR and scanning electron microscopy (SEM) measurements suggested that the interactions could alter the conformation and microenvironment of the enzymes. Moreover, in vivo evaluation showed that the administration of nicotiflorin and swertisin can alleviate the blood glucose level of rats compared to the starch group (p < 0.05). The findings highlight that nicotiflorin and swertisin can be considered as possible inhibitors in treating diabetes mellitus via digestive enzymes inhibition.

Sinensetin suppresses angiogenesis in liver cancer by targeting the VEGF/VEGFR2/AKT signaling pathway

Sinensetin (SIN) is a polymethoxy flavone primarily present in citrus fruits. This compound has demonstrated anticancer activity. However, the underlying mechanism of its action has not been fully understood. The present study investigated the impact of SIN on angiogenesis in a liver cancer model. In a murine xenograft tumor model, SIN inhibited the growth of HepG2/C3A human liver hepatoma cell-derived tumors and reduced the expression levels of platelet/endothelial cell adhesion molecule-1 and VEGF. In HepG2/C3A cells, SIN repressed VEGF expression by downregulating hypoxia-inducible factor expression. In cultured human umbilical vein endothelial cells, SIN increased apoptosis and repressed migration and tube formation. In addition, SIN decreased the phosphorylation of VEGFR2 and inhibited the AKT signaling pathway. Molecular docking demonstrated that the VEGFR2 core domain effectively combined with SIN at various important residues. Collectively, these data suggested that SIN inhibited liver cancer angiogenesis by regulating VEGF/VEGFR2/AKT signaling.

Interaction study of engeletin toward cytochrome P450 3A4 and 2D6 by multi-spectroscopy and molecular docking

The inhibitory effects of engeletin on the activities of human cytochrome P450 3A4 and 2D6 (CYP3A4 and CYP2D6) were investigated by enzyme kinetics, multi-spectroscopy and molecular docking. Engeletin was found to strongly inhibit CYP3A4 and CYP2D6, with the IC₅₀ of 1.32 μM and 2.87 μM, respectively. The inhibition modes of engeletin against CYP3A4 and CYP2D6 were a competitive type and a mixed type, respectively. The fluorescence of the two CYPs was quenched statically by engeletin, which was bound to CYP3A4 stronger than to CYP2D6 at the same temperature. Circular dichroism spectroscopy, three-dimensional fluorescence, ultraviolet-visible spectroscopy and synchronous fluorescence confirmed that the conformation and micro-environment of the two CYPs protein were changed after binding with engeletin. Molecular docking, ultraviolet-visible spectroscopy and the fluorescence data revealed that engeletin had strong binding affinity to the two CYPs through hydrogen and van der Waals forces. The findings here suggested that engeletin may cause the herb-drug interactions for its inhibition of CYP3A4 and CYP2D6 activities.

Potential mechanisms of methylglyoxal-induced human embryonic kidney cells damage: Regulation of oxidative stress, DNA damage, and apoptosis

Methylglyoxal (MGO) is a reactive carbonyl species that can cause cellular damage and is closely related to kidney disease, especially diabetic nephropathy. The toxic effect of MGO (0.5, 1, and 2 mM) on human embryonic kidney (HEK293) cells and its underlying mechanism were explored in this study. Cell viability, apoptosis and the signaling pathways were measured with MTT, fluorescent staining and western blot experiments, the results showed that MGO could induce oxidative stress and cell inflammation, the level of reactive oxygen species (ROS) increased, and p38MAPK, JNK and NF-κB signaling pathways were activated. Meanwhile, MGO also induced DNA damage. The expression of DNA oxidative damage marker 8-hydroxy-2'-deoxyguanosine (8-OHdG) increased, the expression of double-strand break marker γH2AX increased significantly, and ATM/Chk2/p53 DNA damage response signaling pathway was activated. Furthermore, the expression of the receptor for advanced glycation end products (RAGE) also increased. Finally, mitochondrial membrane potential (MMP) decreased, fluorescence intensity of Hoechst33258 increased, and the protein expression ratio of Bax/Bcl-2 increased significantly after the treatment of MGO. These results demonstrated that MGO might induce HEK293 cells damage by regulating oxidative stress, inflammation, DNA damage, and cell apoptosis, which revealed the specific mechanism of MGO-induced damage to HEK293 cells.

Bovine lactoferrin and Lentinus edodes mycelia polysaccharide complex: The formation and the activity to protect islet β cells

The formation of complexes may be used for the development of delivery systems in foods field. The aim of this study was to explore the interaction mechanism between Lentinus edodes mycelia polysaccharide (LMP) and bovine lactoferrin (BLF), and the activity of LMP-BLF complex to inhibit oxidative stress in islet β cells. The interaction mechanisms of LMP with BLF were investigated with multi-spectroscopic techniques. The multi-spectroscopic analysis result showed that LMP bound with BLF by van der Waals force and hydrogen bond. The quenching mechanism of BLF with LMP was static quenching. Cell viability, reactive oxygen species (ROS) level, apoptosis and the related signaling pathways were detected with thiazolyl blue tetrazolium bromide (MTT) assay, 2,7-Dichlorofluorescin diacetate (DCFH-DA) staining, Hoechst 33258 staining and Western blot methods respectively. The complex alleviated apoptosis induced by hydrogen peroxide (H₂O₂), and inhibited oxidative stress via MAPK pathways in MIN6 cells. In addition, the complex was able to promote glucose uptake in HepG2 cells. These results will broaden our understanding of LMP-BLF complexes and the applications of polysaccharide-protein complexes in the foods field.

Pomegranate peel-derived punicalagin: Ultrasonic-assisted extraction, purification, and its α-glucosidase inhibitory mechanism

The pomegranate peel is a by-product of pomegranate fruit rich in polyphenols. In this study, pomegranate peel polyphenols were explored using LC-MS/MS, and punicalagin was the most abundant compound. The highest yield (505.89 ± 1.73 mg/g DW) of punicalagin was obtained by ultrasonic-assisted extraction (UAE) with the ethanol concentration of 53%, sample-to-liquid ratio of 1:25 w/v, ultrasonic power of 757 W, and extraction time of 25 min. Punicalagin was further purified by the macroporous resin D101 and prep-HPLC, reaching the purity of 92.15%. The purified punicalagin had the IC₅₀ of 82 ± 0.02 µg/mL against α-glucosidase, similar to the punicalagin standard with IC₅₀ of 58 ± 0.014 µg/mL, both exhibiting a mixed inhibitory mechanism. Molecular docking further revealed that a steric hindrance with the intermolecular energy of -7.99 kcal/mol was formed between punicalagin and α-glucosidase. Overall, pomegranate peel is a promising source of punicalagin to develop anti-diabetic functional foods.

Multi-Mechanistic In Vitro Evaluation of Antihyperglycemic, Antioxidant and Antiglycation Activities of Three Phenolic-Rich Indian Red Rice Genotypes and In Silico Evaluation of Their Phenolic Metabolites

The study evaluated the antidiabetic potential of three traditional Indian red rice genotypes/RR (Kattuyanam/KA, Chennangi/CH & Karungkuruvai/KU) using a combination of in vitro, metabolomics (Quadrupole-Time of Flight-Liquid chromatography-Mass spectrometry/Q-TOF-LC-MS/MS), and in silico techniques. In terms of antihyperglycemic potential, KA exhibited the highest inhibitory activity against α-amylase; CH against α-glucosidase; and KU against DPPIV and PTP1B enzymes. KA exhibited the highest antioxidant activity (DPPH, FRAP, and ABTS) and greater inhibition of protein glycation compared to other RR indicating its potential to mitigate diabetic complications. The metabolomic analysis confirmed the presence of 99 phenolics in the sample extracts (KU-71, KA-70, CH-68). Molecular docking studies revealed seven metabolites to be good inhibitors of the four target enzymes and activators of insulin receptor substrate/IRS. The antihyperglycemic and oxidation-glycation reduction composite index revealed KA to have the highest overall antidiabetic potential. Hence, the RR could be utilized in functional foods with a multi-barrelled strategy for diabetes prevention/management.

Unlocking the secret of lignin-enzyme interactions: Recent advances in developing state-of-the-art analytical techniques

Bioconversion of renewable lignocellulosics to produce liquid fuels and chemicals is one of the most effective ways to solve the problem of fossil resource shortage, energy security, and environmental challenges. Among the many biorefinery pathways, hydrolysis of lignocellulosics to fermentable monosaccharides by cellulase is arguably the most critical step of lignocellulose bioconversion. In the process of enzymatic hydrolysis, the direct physical contact between enzymes and cellulose is an essential prerequisite for the hydrolysis to occur. However, lignin is considered one of the most recalcitrant factors hindering the accessibility of cellulose by binding to cellulase unproductively, which reduces the saccharification rate and yield of sugars. This results in high costs for the saccharification of carbohydrates. The various interactions between enzymes and lignin have been explored from different perspectives in literature, and a basic lignin inhibition mechanism has been proposed. However, the exact interaction between lignin and enzyme as well as the recently reported promotion of some types of lignin on enzymatic hydrolysis is still unclear at the molecular level. Multiple analytical techniques have been developed, and fully unlocking the secret of lignin-enzyme interactions would require a continuous improvement of the currently available analytical techniques. This review summarizes the current commonly used advanced research analytical techniques for investigating the interaction between lignin and enzyme, including quartz crystal microbalance with dissipation (QCM-D), surface plasmon resonance (SPR), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, atomic force microscopy (AFM), nuclear magnetic resonance (NMR) spectroscopy, fluorescence spectroscopy (FLS), and molecular dynamics (MD) simulations. Interdisciplinary integration of these analytical methods is pursued to provide new insight into the interactions between lignin and enzymes. This review will serve as a resource for future research seeking to develop new methodologies for a better understanding of the basic mechanism of lignin-enzyme binding during the critical hydrolysis process.