Inhibitory effect of corosolic acid on α-glucosidase: kinetics, interaction mechanism, and molecular simulation

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.

Role of polyphenols in the management of diabetic complications

BACKGROUND

Diabetes Mellitus is an endocrine disorder that will affect, about 693 million adults by 2045 worldwide, (>50% increase from 2017). The conventional treatment of the disease, include the oral hypoglycemic drugs which are given in combination with other drugs and are known to possess various adverse effects like gastrointestinal disturbance, nausea, water retention etc. PURPOSE: Due to the urgent need of combating this disorder without side effects, the alternative and complementary therapies should be explored due to their natural origins and comparable safety. Herbal sources serve as new leads, due to the presence of phytoconstituents with potential therapeutic properties, efficacy and safety. In this review, we tried to summarise the polyphenolic phytoconstituents effective in the treatment of diabetic complications.

METHODS

A systematic literature search was conducted using 4 databases (Google scholar, Pubmed, Scopus, Embase) for the identification of relevant data. Search was performed using various key words such as "diabetes", "polyphenols", "marine sources","anti-diabetic polyphenols". The in vitro studies involving the cell lines used in diabetes and animal models were also considered for inclusion. Additional research papers were identified by reviewing abstracts, scrutinizing reference lists, and reviewing previously published review articles.

RESULTS

Polyphenols, a group of phytoconstituents are known worldwide for their tremendous antioxidant potential. So, various research groups have explored their mechanism and therapeutic value in diabetic complications, to improve the insulin sensitivity and glucose metabolism, in controlling the glycemic conditions.

CONCLUSION

Polyphenols exhibit effective therapeutic potential in managing diabetic complications through their multifaceted mechanism of action. They exhibit antioxidative, anti-inflammatory, and anti-glycemic properties, which collectively contribute to their beneficial effects in mitigating diabetic complications. Thus, the inclusion of polyphenols into the diet, may be cosidered as an approach of managing diabetes on long term basis. In this review, we have tried to identify polyphenols effective in diabetes and summarize their mechanism of action along with their potential, for the treatment of diabetic complications.

Insight into the Inhibitory Mechanisms of Hesperidin on α-Glucosidase through Kinetics, Fluorescence Quenching, and Molecular Docking Studies

The α-glucosidase inhibitor is of interest to researchers due to its association with type-II diabetes treatment by suppressing postprandial hyperglycemia. Hesperidin is a major flavonoid in orange fruit with diverse biological properties. This paper evaluates the effects of hesperidin on α-glucosidase through inhibitory kinetics, fluorescence quenching, and molecular docking methods for the first time. The inhibition kinetic analysis shows that hesperidin reversibly inhibited the α-glucosidase activity with an IC50 value of 18.52 μM and the inhibition was performed in an uncompetitive type. The fluorescence quenching studies indicate that the intrinsic fluorescence of α-glucosidase was quenched via a static quenching process and only one binding site was present between the hesperidin and α-glucosidase. The interaction between them was spontaneous and mainly driven by hydrogen bonds, as well as hydrophobic forces. Furthermore, the molecular docking results suggest that hesperidin might bond to the entrance or outlet part of the active site of α-glucosidase through a network of five hydrogen bonds formed between hesperidin and the four amino acid residues (Trp709, Arg422, Asn424, and Arg467) of α-glucosidase and the hydrophobic effects. These results provide new insight into the inhibitory mechanisms of hesperidin on α-glucosidase, supporting the potential application of a hesperidin-rich orange product as a hypoglycemic functional food.

Therapeutic Potentials of Microalgae and Their Bioactive Compounds on Diabetes Mellitus

Diabetes mellitus is a metabolic disorder characterized by hyperglycemia due to impaired insulin secretion, insulin resistance, or both. Oxidative stress and chronic low-grade inflammation play crucial roles in the pathophysiology of diabetes mellitus. There has been a growing interest in applying natural products to improve metabolic derangements without the side effects of anti-diabetic drugs. Microalgae biomass or extract and their bioactive compounds have been applied as nutraceuticals or additives in food products and health supplements. Several studies have demonstrated the therapeutic effects of microalgae and their bioactive compounds in improving insulin sensitivity attributed to their antioxidant, anti-inflammatory, and pancreatic β-cell protective properties. However, a review summarizing the progression in this topic is lacking despite the increasing number of studies reporting their anti-diabetic potential. In this review, we gathered the findings from in vitro, in vivo, and human studies to discuss the effects of microalgae and their bioactive compounds on diabetes mellitus and the mechanisms involved. Additionally, we discuss the limitations and future perspectives of developing microalgae-based compounds as a health supplement for diabetes mellitus. In conclusion, microalgae-based supplementation has the potential to improve diabetes mellitus and be applied in more clinical studies in the future.

Inhibition mechanism of α-glucosidase inhibitors screened from Tartary buckwheat and synergistic effect with acarbose

Tartary buckwheat has been shown to provide a good antihyperglycemic effect. However, it is unclear which active compounds play a key role in attenuating postprandial hyperglycemia. Presently, acetone extract from the hull of Tartary buckwheat had the best effect for α-glucosidase inhibition (IC₅₀ = 0.02 mg/mL). Twelve potential α-glucosidase inhibitors from Tartary buckwheat were screened and identified by the combination of ultrafiltration and high-performance liquid chromatography coupled with mass spectrometry. Myricetin and quercetin exhibited the highest anti-α-glucosidase activity with IC₅₀ values of 0.02 and 0.06 mg/mL, respectively. These inhibitors manifested different types of inhibition manners against α-glucosidase via direct interaction with the amino acid residues. The results of structure-activity relationships indicated that an increase in the number of -OH on the B-ring greatly strengthened α-glucosidase inhibitory activity, but glucoside and rutinoside replacement on the C-ring obviously weakened this influence. Furthermore, a synergistic effect was observed between inhibitors with different inhibition manners.

Screening and Inhibition Mechanism of Xanthine Oxidase Inhibitors in Ethanolic Extracts of Chimonanthus salicifolius Hu Leaves

This study aimed to evaluate the inhibition of the ethanol elutions of Chimonanthus salicifolius Hu leaves (CsHL) against xanthine oxidase (XO). The results of XO inhibition assay and enzymatic superoxide free radical scavenging assay in vitro showed that 70 % ethanol eluate (EE) had the best inhibitory effect and followed by 40 % EE. High performance liquid chromatograph analysis showed that quercetin and kaempferol were the potential active components of XO inhibition. The inhibition mechanism of quercetin and kaempferol on XO was investigated by kinetic analysis and fluorescence quenching titration assay. The molecular simulation further revealed that quercetin and kaempferol bind to XO mainly by hydrogen bonding and van der Waals, blocking the entry of substrates and leading to the inhibition of XO. In conclusion, the CsHL have inhibitory effects on XO activity, which provides a theoretical basis for relieving or preventing hyperuricemia and gout as a natural food or medicinal plant in the future.

Control of eriocitrin release from pH-sensitive gelatin-based microgels to inhibit α-glucosidase: an experimental and computational study

α-Glucosidase is among the intestinal epithelial enzymes that produce absorbable glucose in the final stage of glycan catabolism. It leads to an increase in blood glucose levels as a result of high glucose uptake in diabetic patients. However, inhibition of this essential biochemical process can be a useful therapeutic approach to diabetes mellitus (DM). Eriocitrin (ER) is an abundant "flavanone glycoside" in citrus fruits with rich antioxidant properties whose effects on α-Glu inhibition in the small intestine remain to be determined. Herein, pH-sensitive microgels (MGs) were designed based on cross-linked methacrylate with acrylamide (AM) and acrylic acid (AAc) (molar ratio 70 : 30 of AAc : AM) as a controlled release system for sustained delivery of ER into the small intestine. The presence of amide and acrylate in MGs and the mechanical resistance were determined using FT-IR spectroscopy, rheology, and viscoelastometry. In vitro experiments showed that MGs could protect ER against diffusion in the gastric location and adjust its release in the intestinal milieu. The intestinal α-Glu activity was inhibited by ER (IC₅₀ value of 12.50 ± 0.73 μM) in an uncompetitive dose-dependent manner. The presence of ER altered the structure of α-Glu and reduced the hydrophobic pockets of the enzyme. Molecular docking analysis along with molecular dynamics simulation displayed that ER-α-Glu formation is directed by hydrogen binding with Asp69, Asp215, Glu411, Asp307, and Tyr347 residues. Moreover, in vivo assessment showed that rat blood glucose concentration decreased after ER administration compared with the control group. The results highlight that ER-loaded-MGs can be considered as a useful releasing strategy in treating DM via α-Glu inhibition.

Exploring the binding mechanism of ferulic acid and ovalbumin: insights from spectroscopy, molecular docking and dynamics simulation

BACKGROUND

Ferulic acid (FA), a phenolic acid widely occurring in nature, has attracted extensive attention because of its biological activity. Ovalbumin (OVA) is a commonly used carrier protein. The mechanism of FA binding with OVA was investigated by utilizing a variety of spectral analyses, accompanied by computer simulation.

RESULTS

It was discovered that the fluorescence quenching mechanism of OVA by FA was a static mode as a result of the formation of an FA-OVA complex, which was verified by the concentration distributions and pure spectrum of the constituents decomposed from the high overlap spectrum signals using multivariate curve resolution-alternate least squares algorithm. Hydrogen bonds and Van der Waals forces drove the formation of FA-OVA complex with a binding constant of 1.69 × 10⁴  L mol^-1 . The presence of FA induced the loose structure of OVA with an attenuation of α-helix content and improved the thermal stability of OVA. Computer docking indicated that FA interacted with the amino acid residues Arg84, Asn88, Leu101 and Ser103 of OVA through hydrogen bonds. Molecular dynamics simulation proved that the combination of FA with OVA boosted the conformational stability of OVA and hydrogen bonds brought a crucial part in stabilizing the structure of the complex.

CONCLUSIONS

The study may supply the theoretical basis for the design of FA transport system using OVA as carrier protein to improve the instability and low bioavailability of FA. © 2021 Society of Chemical Industry.

Exploring two types of prenylated bitter compounds from hop plant (Humulus lupulus L.) against α-glucosidase in vitro and in silico

Hops are abundant in natural bioactive compounds. In this work, nine prenylated bitter compounds from hop were evaluated for their inhibitory activity against α-glucosidase. As a result, four flavonoids and one phloroglucinol (lupulone, LP) outperformed acarbose in inhibiting α-glucosidase. Isoxanthohumol (IX) and LP with two types of structures were selected for inhibition mechanism studies by spectroscopic methods and molecular dynamics simulation (MD). Results showed that IX acted as noncompetitive inhibitor and bound to α-glucosidase in allosteric sites via hydrogen bonds, hydrophobic, van der Waals (vdW), and electrostatic force, whereas LP was uncompetitive inhibitor and bound to catalytic sites via hydrophobic and vdW interactions. Notably, the conformation around binding site of α-glucosidase formed stable α-helix and tightened after binding IX and LP, respectively, which helped to elucidate noncompetitive and uncompetitive inhibitory mechanisms. This work demonstrated that two types of prenylated bitter compounds are discrepant in their mechanisms of interaction with α-glucosidase.

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.

Corosolic acid and its structural analogs: A systematic review of their biological activities and underlying mechanism of action

BACKGROUND

The corosolic acid (CA), also known as plant insulin, is a pentacyclic triterpenoid extracted from plants such as Lagerstroemia speciosa. It has been shown to have anti-diabetic, anti-inflammatory and anti-tumor effects. Its structural analogs ursolic acid (UA), oleanolic acid (OA), maslinic acid (MA), asiatic acid (AA) and betulinic acid (BA) display similar individual pharmacological activities to those of CA. However, there is no systematic review documenting pharmacological activities of CA and its structural analogues. This study aims to fill this gap in literature.

PURPOSE

This systematic review aims to summarize the medical applications of CA and its analogues.

METHODS

A systematic review summarizes and compares the extraction techniques, pharmacokinetic parameters, and pharmacological effects of CA and its structural analogs. Hypoglycemic effect is one of the key inclusion criteria for searching Web of Science, PubMed, Embase and Cochrane databases up to October 2020 without language restrictions. 'corosolic acid', 'ursolic acid', 'oleanolic acid', 'maslinic acid', 'asiatic acid', 'betulinic acid', 'extraction', 'pharmacokinetic', 'pharmacological' were used to extract relevant literature. The PRISMA guidelines were followed.

RESULTS

At the end of the searching process, 140 articles were selected for the systematic review. Information of CA and five of its structural analogs including UA, OA, MA, AA and BA were included in this review. CA and its structural analogs are pentacyclic triterpenes extracted from plants and they have low solubilities in water due to their rigid scaffold and hydrophobic properties. The introduction of water-soluble groups such as sugar or amino groups could increase the solubility of CA and its structural analogs. Their biological activities and underlying mechanism of action are reviewed and compared.

CONCLUSION

CA and its structural analogs UA, OA, MA, AA and BA are demonstrated to show activities in lowering blood sugar, anti-inflammation and anti-tumor. Their oral absorption and bioavailability can be improved through structural modification and formulation design. CA and its structural analogs are promising natural product-based lead compounds for further development and mechanistic studies.

Discovery of uncompetitive inhibitors of SapM that compromise intracellular survival of Mycobacterium tuberculosis

SapM is a secreted virulence factor from Mycobacterium tuberculosis critical for pathogen survival and persistence inside the host. Its full potential as a target for tuberculosis treatment has not yet been exploited because of the lack of potent inhibitors available. By screening over 1500 small molecules, we have identified new potent and selective inhibitors of SapM with an uncompetitive mechanism of inhibition. The best inhibitors share a trihydroxy-benzene moiety essential for activity. Importantly, the inhibitors significantly reduce mycobacterial burden in infected human macrophages at 1 µM, and they are selective with respect to other mycobacterial and human phosphatases. The best inhibitor also reduces intracellular burden of Francisella tularensis, which secretes the virulence factor AcpA, a homologue of SapM, with the same mechanism of catalysis and inhibition. Our findings demonstrate that inhibition of SapM with small molecule inhibitors is efficient in reducing intracellular mycobacterial survival in host macrophages and confirm SapM as a potential therapeutic target. These initial compounds have favourable physico-chemical properties and provide a basis for exploration towards the development of new tuberculosis treatments. The efficacy of a SapM inhibitor in reducing Francisella tularensis intracellular burden suggests the potential for developing broad-spectrum antivirulence agents to treat microbial infections.

Preparative separation of structural isomeric pentacyclic triterpenes from Eriobotrya japonica (Thunb.) leaves by high speed countercurrent chromatography with hydroxypropyl-β-cyclodextrin as additive

Maslinic acid and corosolic acid with high purity were successfully separated from Eriobotrya japonica (Thunb.) leaves by two-step countercurrent chromatographic separation. Two biphasic solvent systems composed of petroleum ether-ethyl acetate-ethanol-water (6:4:5:5, v/v) and petroleum ether-ethyl acetate-ethanol-0.10 mol/L of hydroxypropyl-β-cyclodextrin with pH 7.0 (8:2:3.5:6.5, v/v) were selected according to the partition performance of the main structural isomeric pentacyclic triterpenes. The influences of pH value and concentration of hydroxypropyl-β-cyclodextrin in separation of two isomers were investigated. In first step countercurrent chromatographic separation, a mixture of two target structural isomers (14.12 mg of sample I) was separated from 40.00 mg of a partially purified sample. In second step countercurrent chromatographic separation, maslinic acid and corosolic acid were completely isolated from 12.00 mg of sample I with hydroxypropyl-β-cyclodextrin as aqueous phase additive. The recoveries of the two isomers were over 90%, yielding 5.18 mg of maslinic acid and 5.47 mg of corosolic acid, respectively.

An Overview of Molecular Dynamic Simulation for Corrosion Inhibition of Ferrous Metals

Molecular dynamics (MD) simulation is a powerful tool to study the molecular level working mechanism of corrosion inhibitors in mitigating corrosion. In the past decades, MD simulation has emerged as an instrument to investigate the interactions at the interface between the inhibitor molecule and the metal surface. Combined with experimental measurement, theoretical examination from MD simulation delivers useful information on the adsorption ability and orientation of the molecule on the surface. It relates the microscopic characteristics to the macroscopic properties which enables researchers to develop high performance inhibitors. Although there has been vast growth in the number of studies that use molecular dynamic evaluation, there is still lack of comprehensive review specifically for corrosion inhibition of organic inhibitors on ferrous metal in acidic solution. Much uncertainty still exists on the approaches and steps in performing MD simulation for corrosion system. This paper reviews the basic principle of MD simulation along with methods, selection of parameters, expected result such as adsorption energy, binding energy and inhibitor orientation, and recent publications in corrosion inhibition studies.

The effects of bioactive compounds from blueberry and blackcurrant powders on the inhibitory activities of oat bran pastes against α-amylase and α-glucosidase linked to type 2 diabetes

The α-amylase and α-glucosidase inhibitory activities by extracts of oat bran, blueberry and blackcurrant powders, as well as oat bran pastes supplemented 25% of blueberry and blackcurrant powder, were studied by measuring their half inhibitory (IC50) concentrations. Addition of blueberry or blackcurrant powder into oat bran paste increased α-amylase and α-glucosidase inhibitory activities with a decrease in IC50 values. The main anthocyanidin content was measured by pH differential method and the potential inhibitory mechanisms of these extracts were also investigated by detailed inhibition kinetics and docking simulations. The results showed that: (1) cyanidin and delphinidin were the main anthocyanidin profiles in extracts; (2) only blackcurrant powder was a competitive inhibitor, while other extracts were all mixed-type inhibitors against α-amylase; (3) both blueberry- and blackcurrant-enriched pastes were competitive inhibitors, while other extracts were all mixed-type inhibitors towards α-glucosidase; (4) the α-amylase and α-glucosidase inhibitory activities by extracts were potentially driven by hydrogen bonding, cyanidin-3-glucoside and delphinidin-3-glucoside had stronger binding affinity compared to malvidin-3-glucoside and cyanidin-3-rutinside. This study suggested supplementary of blueberry and blackcurrant with oat bran might be a potential source of bioactive products for antidiabetic activity.

α-Glucosidase inhibitors from Chinese bayberry (Morella rubra Sieb. et Zucc.) fruit: molecular docking and interaction mechanism of flavonols with different B-ring hydroxylations

Inhibition of α-glucosidase alleviates postprandial high glycemic levels in diabetic or prediabetic population.