Structure-related protein tyrosine phosphatase 1B inhibition by naringenin derivatives

Characterization of PKCα-rutin interactions and their application as a treatment strategy for pulmonary arterial hypertension by inhibiting ferroptosis

As a common plant-derived dietary flavonoid, rutin receives widespread attention because of its good antioxidant bioactivities. Protein kinase Cα (PKCα) is a serine/threonine kinase that is involved in uncountable cellular processes, among which ferroptosis, a novel form of cell death, is triggered by lipid peroxidation and has been reported to be associated with pulmonary arterial hypertension (PAH). But it is still not well appreciated how rutin inhibits ferroptosis in PAH and what function PKCα has in this process. In this study, we first observed whether rutin could prevent PAH by attenuating ferroptosis with a PAH animal model and pulmonary artery smooth muscle cells (PASMCs) under hypoxia. Mitochondrial metabolomics and network pharmacology were employed to clarify the metabolic alterations and screen target proteins, and the results showed that PKCα was a vital node in rutin regulating mitochondrial metabolism related to ferroptosis in PAH. Based on molecular docking and multispectral analysis, we found that rutin could directly interact with PKCα through hydrogen bonds, which could induce static quenching, and then influence the secondary structure of PKCα. In conclusion, these findings mainly point to a novel mechanism that rutin protects PAH rats by modifying the structure and altering the activity of PKCα, and thus suppressing ferroptosis. This work reveals that the interaction behaviors between small molecules and bio-macromolecules are a critical factor to develop natural biological active ingredients and gives an insight into the potential applications of flavonoids in health and disease.

A comparative study of the interaction of naringenin with lysozyme by multi-spectroscopic methods, activity comparisons, and molecular modeling procedures

The present study applied steady-state fluorescence, UV-Vis spectrophotometry, molecular docking studies, and circular dichroism (CD) to investigate the interaction of naringenin with lysozyme in an aqueous medium. The UV-Vis measurement indicated the changes in lysozyme secondary and tertiary structure change as a function of the concentration of naringenin. Naringenin could be used to turn the static quenching mechanism into the intrinsic fluorescence of lysozyme. The negative amount of Gibbs free energy (ΔG°) suggested that the binding operation was spontaneous. Fluorescence studies also demonstrated the changes occurring in the Trp microenvironment upon the concatenation into lysozyme. Analysis of thermodynamic parameters also revealed that hydrophobic forces played a fundamental role in determining the complex stability; this was consistent with the previous modeling studies. Circular dichroism also suggested that the alpha-helicity of lysozyme was enhanced as ligand was bound. Naringenin inhibited lysozyme enzymatic activity, displaying its affinity with the lysozyme active site. Further, molecular docking studies demonstrated that naringenin could bind to both residues essential for catalytic activity in the proximity of Trp 62 and Trp 63.

Compendium of naringenin: potential sources, analytical aspects, chemistry, nutraceutical potentials and pharmacological profile

Naringenin is flavorless, water insoluble active principle belonging to flavanone subclass. It exhibits a diverse pharmacological profile as well as divine nutraceutical values. Although several researchers have explored this phytoconstituent to evaluate its promising properties, still it has not gained recognition at therapeutic levels and more clinical investigations are still required. Also the neutraceutical potential has limited marketed formulations. This compilation includes the description of reported therapeutic potentials of naringenin in variety of pathological conditions alongwith the underlying mechanisms. Details of various analytical investigations carried on this molecule have been provided along with brief description of chemistry and structural activity relationship. In the end, various patents filed and clinical trial data has been provided. Naringenin has revealed promising pharmacological activities including cardiovascular diseases, neuroprotection, anti-diabetic, anticancer, antimicrobial, antiviral, antioxidant, anti-inflammatory and anti-platelet activity. It has been marketed in the form of nanoformulations, co-crystals, solid dispersions, tablets, capsules and inclusion complexes. It is also available in various herbal formulations as nutraceutical supplement. There are some pharmacokinetic issue with naringenin like poor absorption and low dissolution rate. Although these issues have been sorted out upto certain extent still further research to investigate the bioavailability of naringenin from herbal supplements and its clinical efficacy is essential.

Screening apo-SOD1 conformation stabilizers from natural flavanones using native ion mobility mass spectrometry and fluorescence spectroscopy methods

RATIONALE

A large number of studies have shown that the production of aberrant and deleterious copper zinc superoxide dismutase (SOD1) species is closely related to amyotrophic lateral sclerosis (ALS). Therefore, it is of great significance to screen effective inhibitors of misfolding and aggregation of SOD1 for treating ALS disease.

METHODS

The interaction between flavanone compounds with apo-SOD1was investigated using native electrospray ion mobility mass spectrometry (native ESI-IM-MS). Binding affinities of ligands were compared using native MS, ESI-MS/MS, collision-induced unfolding, and competitive experiments. The effect of ligands on apo-SOD1 aggregation was investigated using the fluorescence spectroscopy method.

RESULTS

The results of MS showed that the binding affinity of liquiritin apioside was the strongest, better than the corresponding monosaccharide and aglycone, indicating that the presence and the number of glycosyl group are beneficial to enhance ligand affinity to protein. The results of fluorescence spectroscopy for inhibiting protein aggregation in vitro were consistent with the binding affinity. In addition, the results of the collision-induced unfolding indicated that liquiritin apioside can slow down the unfolding of the protein. Meanwhile, the results of competition experiment suggested that liquiritin apiosides share different binding sites with naringin and 5-fluorouridine, which are significant for the structural stability of SOD1.

CONCLUSIONS

This study revealed that the binding of liquiritin apioside can stabilize apo-SOD1 dimer and inhibit the aggregation of apo-SOD1, and illustrated that native ESI-IM-MS is a powerful tool for providing insight into investigating the structure-activity relationship between small molecules and protein, and screening protein conformation stabilizers.

Identification of Flavonoid C-Glycosides as Promising Antidiabetics Targeting Protein Tyrosine Phosphatase 1B

Protein tyrosine phosphatase 1B (PTP1B), a negative regulator of the insulin signaling pathway, has gained attention as a validated druggable target in the management of type 2 diabetes mellitus (T2DM). The lack of clinically approved PTP1B inhibitors has continued to prompt research in plant-derived therapeutics possibly due to their relatively lesser toxicity profiles. Flavonoid C-glycosides are one of the plant-derived metabolites gaining increased relevance as antidiabetic agents, but their possible mechanism of action remains largely unknown. This study investigates the antidiabetic potential of flavonoid C-glycosides against PTP1B in silico and in vitro. Of the seven flavonoid C-glycosides docked against the enzyme, three compounds (apigenin, vitexin, and orientin) had the best affinity for the enzyme with a binding score of -7.3 kcal/mol each, relative to -7.4 kcal/mol for the reference standard, ursolic acid. A further probe (in terms of stability, flexibility, and compactness) of the complexes over a molecular dynamics time study of 100 ns for the three compounds suggested orientin as the most outstanding inhibitor of PTP1B owing to its overall -34.47 kcal/mol binding energy score compared to ursolic acid (-19.24 kcal/mol). This observation was in accordance with the in vitro evaluation result, where orientin had a half maximal inhibitory concentration (IC₅₀) of 0.18 mg/ml relative to 0.13 mg/ml for the reference standard. The kinetics of inhibition of PTP1B by orientin was mixed-type with V _max and K _m values of 0.004 μM/s and 0.515 μM. Put together, the results suggest orientin as a potential PTP1B inhibitor and could therefore be further explored in the management T2DM as a promising therapeutic agent.

Structural Bases for Hesperetin Derivatives: Inhibition of Protein Tyrosine Phosphatase 1B, Kinetics Mechanism and Molecular Docking Study

In the present study, we investigated the structure-activity relationship of naturally occurring hesperetin derivatives, as well as the effects of their glycosylation on the inhibition of diabetes-related enzyme systems, protein tyrosine phosphatase 1B (PTP1B) and α-glycosidase. Among the tested hesperetin derivatives, hesperetin 5-O-glucoside, a single-glucose-containing flavanone glycoside, significantly inhibited PTP1B with an IC₅₀ value of 37.14 ± 0.07 µM. Hesperetin, which lacks a sugar molecule, was the weakest inhibitor compared to the reference compound, ursolic acid (IC₅₀ = 9.65 ± 0.01 µM). The most active flavanone hesperetin 5-O-glucoside suggested that the position of a sugar moiety at the C-5-position influences the PTP1B inhibition. It was observed that the ability to inhibit PTP1B is dependent on the nature, position, and number of sugar moieties in the flavonoid structure, as well as conjugation. In the kinetic study of PTP1B enzyme inhibition, hesperetin 5-O-glucoside led to mixed-type inhibition. Molecular docking studies revealed that hesperetin 5-O-glucoside had a higher binding affinity with key amino residues, suggesting that this molecule best fits the PTP1B allosteric site cavity. The data reported here support hesperetin 5-O-glucoside as a hit for the design of more potent and selective inhibitors against PTP1B in the search for a new anti-diabetic treatment.

The effects of naringenin and naringin on the glucose uptake and AMPK phosphorylation in high glucose treated HepG2 cells

Background

Naringin and its aglycone naringenin are citrus-derived flavonoids with several pharmacological effects. On the other hand, the mechanism for the anti-diabetic effects of naringenin and naringin are controversial and remain to be clarified further.

Objective

This study examined the relationship between glucose uptake and AMP-activated protein kinase (AMPK) phosphorylation by naringenin and naringin in high glucose-treated HepG2 cells.

Methods

Glucose uptake was measured using the 2-NBDG fluorescent D-glucose analog. The phosphorylation levels of AMPK and GSK3β (Glycogen synthase kinase 3 beta) were observed by Western blotting. Molecular docking analysis was performed to evaluate the binding affinity of naringenin and naringin to the γ-subunit of AMPK.

Results

The treatment with naringenin and naringin stimulated glucose uptake regardless of insulin stimulation in high glucose-treated HepG2 cells. Both flavonoids increased glucose uptake by promoting the phosphorylation of AMPK at Thr172 and increased the phosphorylation of GSK3β. Molecular docking analysis showed that both naringenin and naringin bind to the γ-subunit of AMPK with high binding affinities. In particular, naringin showed higher binding affinity than the true modulator, AMP with all three CBS domains (CBS1, 3, and 4) in the γ-subunit of AMPK. Therefore, both naringenin and naringin could be positive modulators of AMPK activation, which enhance glucose uptake regardless of insulin stimulation in high glucose-treated HepG2 cells.

Conclusions

The increased phosphorylation of AMPK at Thr172 by naringenin and naringin might enhance glucose uptake regardless of insulin stimulation in high glucose treated HepG2 cells.

Plants Secondary Metabolites as Blood Glucose-Lowering Molecules

Recently, significant advances in modern medicine and therapeutic agents have been achieved. However, the search for effective antidiabetic drugs is continuous and challenging. Over the past decades, there has been an increasing body of literature related to the effects of secondary metabolites from botanical sources on diabetes. Plants-derived metabolites including alkaloids, phenols, anthocyanins, flavonoids, stilbenoids, saponins, tannins, polysaccharides, coumarins, and terpenes can target cellular and molecular mechanisms involved in carbohydrate metabolism. In addition, they can grant protection to pancreatic beta cells from damage, repairing abnormal insulin signaling, minimizing oxidative stress and inflammation, activating AMP-activated protein kinase (AMPK), and inhibiting carbohydrate digestion and absorption. Studies have highlighted many bioactive naturally occurring plants' secondary metabolites as candidates against diabetes. This review summarizes the current knowledge compiled from the latest studies published during the past decade on the mechanism-based action of plants-derived secondary metabolites that can target various metabolic pathways in humans against diabetes. It is worth mentioning that the compiled data in this review will provide a guide for researchers in the field, to develop candidates into environment-friendly effective, yet safe antidiabetics.

Naringenin Nano-Delivery Systems and Their Therapeutic Applications

Naringenin (NRG) is a polyphenolic phytochemical belonging to the class of flavanones and is widely distributed in citrus fruits and some other fruits such as bergamot, tomatoes, cocoa, and cherries. NRG presents several interesting pharmacological properties, such as anti-cancer, anti-oxidant, and anti-inflammatory activities. However, the therapeutic potential of NRG is hampered due to its hydrophobic nature, which leads to poor bioavailability. Here, we review a wide range of nanocarriers that have been used as delivery systems for NRG, including polymeric nanoparticles, micelles, liposomes, solid lipid nanoparticles (SLNs), nanostructured lipid carriers (NLCs), nanosuspensions, and nanoemulsions. These nanomedicine formulations of NRG have been applied as a potential treatment for several diseases, using a wide range of in vitro, ex vivo, and in vivo models and different routes of administration. From this review, it can be concluded that NRG is a potential therapeutic option for the treatment of various diseases such as cancer, neurological disorders, liver diseases, ocular disorders, inflammatory diseases, skin diseases, and diabetes when formulated in the appropriate nanocarriers.

A comprehensive review on the antidiabetic activity of flavonoids targeting PTP1B and DPP-4: a structure-activity relationship analysis

Type 2 diabetes (T2D) is an expanding global health problem, resulting from defects in insulin secretion and/or insulin resistance. In the past few years, both protein tyrosine phosphatase 1B (PTP1B) and dipeptidyl peptidase-4 (DPP-4), as well as their role in T2D, have attracted the attention of the scientific community. PTP1B plays an important role in insulin resistance and is currently one of the most promising targets for the treatment of T2D, since no available PTP1B inhibitors were still approved. DPP-4 inhibitors are among the most recent agents used in the treatment of T2D (although its use has been associated with possible cardiovascular adverse events). The antidiabetic properties of flavonoids are well-recognized, and include inhibitory effects on the above enzymes, although hitherto not therapeutically explored. In the present study, a comprehensive review of the literature of both synthetic and natural isolated flavonoids as inhibitors of PTP1B and DPP-4 activities is made, including their type of inhibition and experimental conditions, and structure-activity relationship, covering a total of 351 compounds. We intend to provide the most favorable chemical features of flavonoids for the inhibition of PTP1B and DPP-4, gathering information for the future development of compounds with improved potential as T2D therapeutic agents.

Synthesis of novel seven-membered carbasugars and evaluation of their glycosidase inhibition potentials

Here, we report the synthesis of five novel seven-membered carbasugar analogs. We adopted a chiral-pool strategy starting from the cheap and readily available d-mannitol to synthesize these ring-expanded carbasugars. Apart from several regioselective protecting group manipulations, these syntheses involved Wittig olefination and ring-closing metathesis as the key steps. We observed an unprecedented deoxygenation reaction of an allylic benzyl ether upon treatment with H₂/Pd during the synthesis. Preliminary biological evaluation of the carbasugars revealed that these ring expanded carbasugars act as inhibitors of various glycosidases. This study highlights the importance of the synthesis of novel ring expanded carbasugars and their biological exploration.

Here, we report the synthesis of five novel seven-membered carbasugar analogs.

Protein Tyrosine Phosphatase (PTP1B): A promising Drug Target Against Life-threatening Ailments

Background:

Protein tyrosine phosphatases are enzymes which help in the signal transduction in diabetes, obesity, cancer, liver diseases and neurodegenerative diseases. PTP1B is the main member of this enzyme from the protein extract of human placenta. In phosphate inhibitors development, significant progress has been made over the last 10 years. In early-stage clinical trials, few compounds have reached whereas in the later stage trials or registration, yet none have progressed. Many researchers investigate different ways to improve the pharmacological properties of PTP1B inhibitors.

Objective:

In the present review, authors have summarized various aspects related to the involvement of PTP1B in various types of signal transduction mechanisms and its prominent role in various diseases like cancer, liver diseases and diabetes mellitus.

Conclusion:

There are still certain challenges for the selection of PTP1B as a drug target. Therefore, continuous future efforts are required to explore this target for the development of PTP inhibitors to treat the prevailing diseases associated with it.

Phenolic content, antioxidant capacity, and α-amylase and α-glucosidase inhibitory activities of Dimocarpus longan Lour

The aim of this study was to compare the phenolic compound profiles and antioxidant capacities of eight varieties of longan (Dimocarpus longan Lour.) planted in the middle and upper Yangtze River area. The total polyphenols content (TPC) and total flavonoids content (TFC) of dried longan pulp ranged from 1.07 ± 0.05 to 1.22 ± 0.05 mg gallic acid equivalents/g and 0.25 ± 0.07 to 0.87 ± 0.14 mg rutin equivalents/g. UHPLC-QqQ-MS/MS analysis revealed 12 individual polyphenol compounds in longan. The Fuwan8, Dongliang and FD97 varieties showed the strongest DPPH scavenging activity (IC₅₀ of 1.03 g/mL). The highest ABTS⁺ scavenging activity was found in the Dongliang. In the enzyme assays, the Fuwan8 and Dongliang varieties demonstrated maximum α-amylase and α-glucosidase inhibition activities, with values of 97.56 and 88.58%, respectively. The principal component analysis indicated that the Rongyu8 and Songfengben cultivars have nearly analogous polyphenol compounds.

Comparative Study of Dietary Flavonoids with Different Structures as α-Glucosidase Inhibitors and Insulin Sensitizers

This work was designed to comparatively investigate 27 dietary flavonoids that act as α-glucosidase inhibitors and insulin sensitizers. On the basis of the results of an in vitro experiment of α-glucosidase inhibition, myricetin (IC₅₀ = 11.63 ± 0.36 μM) possessed the strongest inhibitory effect, followed by apigenin-7-O-glucoside (IC₅₀ = 22.80 ± 0.24 μM) and fisetin (IC₅₀ = 46.39 ± 0.34 μM). A three-dimensional quantitative structure-activity relationship model of α-glucosidase inhibitors with good predictive capability [comparative molecular field analysis, q² = 0.529, optimum number of components (ONC) = 10, R² = 0.996, F = 250.843, standard error of estimation (SEE) = 0.064, and two descriptors; comparative similarity index analysis, q² = 0.515, ONC = 10, R² = 0.997, F = 348.301, SEE = 0.054, and four descriptors] was established and indicated that meta positions of ring B favored bulky and minor, electron-withdrawing, and hydrogen bond donor groups. The presence of electron-donating and hydrogen bond acceptor groups at position 4' of ring B could improve α-glucosidase activity. Position 3 of ring C favored minor, electron-donating, and hydrogen bond donor groups, whereas position 7 of ring A favored bulky and hydrogen bond acceptor groups. Molecular docking screened five flavonoids (baicalein, isorhamnetin-3-O-rutinoside, apigenin-7-O-glucoside, kaempferol-7-O-β-glucoside, and cyanidin-3-O-glucoside) that can act as insulin sensitizers and form strong combinations with four key protein targets involved in the insulin signaling pathway. Apigenin-7-O-glucoside (60 μM) can effectively improve insulin resistance, and glucose uptake increased by approximately 73.06% relative to the model group of insulin-resistant HepG2 cells. Therefore, apigenin-7-O-glucoside might serve as the most effective α-glucosidase inhibitor and insulin sensitizer. This work may guide diabetes patients to improve their condition through dietary therapy.

Insight into the PTP1B Inhibitory Activity of Arylbenzofurans: An In Vitro and In Silico Study

Protein tyrosine phosphatase 1B (PTP1B) plays a specific role as a negative regulator of insulin signaling pathways and is a validated therapeutic target for Type 2 diabetes. Previously, arylbenzofurans were reported to have inhibitory activity against PTP1B. However, detailed investigation regarding their structure activity relationship (SAR) has not been elucidated. The main aim of this work was to investigate the PTP1B inhibitory activity of 2-arylbenzofuran analogs (sanggenofuran A (SA), mulberrofuran D2 (MD2), mulberrofuran D (MD), morusalfuran B (MB), mulberrofuran H (MH)) isolated from the root bark of Morus alba. All compounds demonstrated potent inhibitory activity with IC₅₀ values ranging from 3.11 to 53.47 µM. Among the tested compounds, MD2 showed the strongest activity (IC₅₀, 3.11 µM), followed by MD and MB, while SA and MH demonstrated the lowest activity. Lineweaver-Burk and Dixon plots were used for the determination of inhibition type whereas ligand and receptor interactions were investigated in modeled complexes via molecular docking. Our study clearly supports 2-arylbenzofuran analogs as a promising class of PTP1B inhibitors and illustrates the key positions responsible for the inhibitory activity, their correlation, the effect of prenyl/geranyl groups, and the influence of resorcinol scaffold, which can be further explored in-depth to develop therapeutic agents against T2DM.

Rubrofusarin as a Dual Protein Tyrosine Phosphate 1B and Human Monoamine Oxidase-A Inhibitor: An in Vitro and in Silico Study

A number of nature-derived biologically active compounds comprise glycosides. In some cases, the glycosidic residue is needed for bioactivity; however, in other cases, glycosylation just improves some pharmacokinetic/dynamic parameters. The patterns of protein tyrosine phosphatase 1B (PTP1B) and human monoamine oxidase A (hMAO-A) inhibition by rubrofusarin 6-O-β-d-glucopyranoside (1), rubrofusarin 6-O-β-d-gentiobioside (2), rubrofusarin triglucoside (3), and cassiaside B2 (4) were compared with the aglycone, rubrofusarin, isolated from Cassia obtusifolia seeds. Rubrofusarin showed potent inhibition against the PTP1B enzyme (IC₅₀; 16.95 ± 0.49 μM), and its glycosides reduced activity (IC₅₀; 87.36 ± 1.08 μM for 1 and >100 μM for 2-4) than did the reference drug, ursolic acid (IC₅₀; 2.29 ± 0.04 μM). Similarly, in hMAO-A inhibition, rubrofusarin displayed the most potent activity with an IC₅₀ value of 5.90 ± 0.99 μM, which was twice better than the reference drug, deprenyl HCl (IC₅₀; 10.23 ± 0.82 μM). An enzyme kinetic and molecular docking study revealed rubrofusarin to be a mixed-competitive inhibitor of both these enzymes. In a western blot analysis, rubrofusarin increased glucose uptake significantly and decreased the PTP1B expression in a dose-dependent manner in insulin-resistant HepG2 cells, increased the expression of phosphorylated protein kinase B (p-Akt) and phosphorylated insulin receptor substrate-1 (p-IRS1) (Tyr 895), and decreased the expression of glucose-6-phosphatase (G6Pase) and phosphoenol pyruvate carboxykinase (PEPCK), key enzymes of gluconeogenesis. Our overall results show that glycosylation retards activity; however, it reduces toxicity. Thus, Cassia seed as functional food and rubrofusarin as a base can be used for the development of therapeutic agents against comorbid diabetes and depression.

Design and Biological Evaluation of Novel Imidazolyl Flavonoids as Potent and Selective Protein Tyrosine Phosphatase Inhibitors

BACKGROUND

Protein tyrosine phosphatases 1B are considered to be a desirable validated target for therapeutic development of type II diabetes and obesity.

METHODS

A new series of imidazolyl flavonoids as potential protein tyrosine phosphatase inhibitors were synthesized and evaluated.

RESULTS

Bioactive results indicated that some synthesized compounds exhibited potent protein phosphatase 1B (PTP1B) inhibitory activities at the micromolar range. Especially, compound 8b showed the best inhibitory activity (IC50=1.0 µM) with 15-fold selectivity for PTP1B over the closely related T-cell protein tyrosine phosphatase (TCPTP). Cell viability assays indicated that 8b is cell permeable with lower cytotoxicity. Molecular modeling and dynamics studies revealed the reason for selectivity of PTP1B over TCPTP. Quantum chemical studies were carried out on these compounds to understand the structural features essential for activity.

CONCLUSION

Compound 8b should be a potential selective PTP1B inhibitor.

Identification of novel imidazole flavonoids as potent and selective inhibitors of protein tyrosine phosphatase

A series of imidazole flavonoids as new type of protein tyrosine phosphatase inhibitors were synthesized and characterized. Most of them gave potent protein phosphatase 1B (PTP1B) inhibitory activities. Especially, compound 11a could effectively inhibit PTP1B with an IC₅₀ value of 0.63 μM accompanied with high selectivity ratio (9.5-fold) over T-cell protein tyrosine phosphatase (TCPTP). This compound is cell permeable with relatively low cytotoxicity. The high binding affinity and selectivity was disclosed by molecular modeling and dynamics studies. The structural features essential for activity were confirmed by quantum chemical studies.

Honey extracts inhibit PTP1B, upregulate insulin receptor expression, and enhance glucose uptake in human HepG2 cells

Honey is a food known for its medical properties. In this work, we have studied the impact of different types of honey on insulin signalling pathway. We found that honey extracts inhibit the enzyme PTP1B, one of the main negative regulators of insulin receptor signalling. HPLC-MS analysis allowed us to confirm the presence of several natural PTP1B inhibitors in the honey extracts analysed. Statistical analysis methods show a correlation between specific ¹H-NMR resonance frequencies/HPLC peaks and the inhibitory power of the samples. This finding will allow the prediction of the biological properties of honey samples applying relative simple analytical methods. Finally, we demonstrated that the treatment of HepG2 cells with honey extracts enhances the expression of insulin receptor, and stimulates glucose uptake. For the first time, our results demonstrate that bioactive components of honey could improve glycaemic control by both inhibiting PTP1B and stimulating the expression of insulin receptor in liver cells.

Anti-Diabetic Activity of 2,3,6-Tribromo-4,5-Dihydroxybenzyl Derivatives from Symphyocladia latiuscula through PTP1B Downregulation and α-Glucosidase Inhibition

The marine alga, Symphyocladia latiuscula (Harvey) Yamada, is a good source of bromophenols with numerous biological activities. This study aims to characterize the anti-diabetic potential of 2,3,6-tribromo-4,5-dihydroxybenzyl derivatives isolated from S. latiuscula via their inhibition of tyrosine phosphatase 1B (PTP1B) and α-glucosidase. Additionally, this study uses in silico modeling and glucose uptake potential analysis in insulin-resistant (IR) HepG2 cells to reveal the mechanism of anti-diabetic activity. This bioassay-guided isolation led to the discovery of three potent bromophenols that act against PTP1B and α-glucosidase: 2,3,6-tribromo-4,5-dihydroxybenzyl alcohol (1), 2,3,6-tribromo-4,5-dihydroxybenzyl methyl ether (2), and bis-(2,3,6-tribromo-4,5-dihydroxybenzyl methyl ether) (3). All compounds inhibited the target enzymes by 50% at concentrations below 10 μM. The activity of 1 and 2 was comparable to ursolic acid (IC₅₀; 8.66 ± 0.82 μM); however, 3 was more potent (IC₅₀; 5.29 ± 0.08 μM) against PTP1B. Interestingly, the activity of 1–3 against α-glucosidase was 30–110 times higher than acarbose (IC₅₀; 212.66 ± 0.35 μM). Again, 3 was the most potent α-glucosidase inhibitor (IC₅₀; 1.92 ± 0.02 μM). Similarly, 1–3 showed concentration-dependent glucose uptake in insulin-resistant HepG2 cells and downregulated PTP1B expression. Enzyme kinetics revealed different modes of inhibition. In silico molecular docking simulations demonstrated the importance of the 7–OH group for H-bond formation and bromine/phenyl ring number for halogen-bond interactions. These results suggest that bromophenols from S. latiuscula, especially highly brominated 3, are inhibitors of PTP1B and α-glucosidase, enhance insulin sensitivity and glucose uptake, and may represent a novel class of anti-diabetic drugs.

Biochemical Characterization of the α-l-Rhamnosidase DtRha from Dictyoglomus thermophilum: Application to the Selective Derhamnosylation of Natural Flavonoids

α-l-Rhamnosidases are catalysts of industrial tremendous interest, but their uses are still somewhat limited by their poor thermal stabilities and selectivities. The thermophilic DtRha from Dictyoglomus thermophilum was cloned, and the recombinant protein was easily purified to homogeneity to afford 4.5 mg/L culture of biocatalyst. Michaelis-Menten parameters demonstrated it to be fully specific for α-l-rhamnose. Most significantly, DtRha demonstrated to have a stronger preference for α(1 → 2) linkage rather than α(1 → 6) linkage when removing rhamnosyl moiety from natural flavonoids. This selectivity was fully explained by the difference of binding of the corresponding substrates in the active site of the protein.

In vitro protein tyrosine phosphatase 1B inhibition and antioxidant property of different onion peel cultivars: A comparative study

The aim of the present study was a comparative investigation of water and 70% ethanol extracts derived from yellow and red onion (Allium cepa L.) peels against diabetes and diabetic complications. The total phenolic contents (TPCs) and total flavonoid contents (TFCs) of each cultivar, measured to assess phytochemical characteristics, showed a direct correlation with the in vitro antioxidant effects. Among the two captives, the yellow onion peel extract showed higher antioxidant activity than red one. However, all extracts exhibited significant protein tyrosine phosphatase 1B (PTP1B) inhibitory activity (IC50; 0.30-0.86 μg/ml), showing water extracts more potent (IC50; approximately 0.3 μg/mL), than the 70% ethanol extracts (IC50; approximately 0.8 μg/ml). Similarly, in insulin-resistant HepG2 cells, all extracts enhanced the glucose uptake and reduced the expression of PTP1B in a concentration-dependent manner, water extract displaying better activity. Our results overall suggest that in vitro antioxidant and antidiabetic potentials vary among red and yellow cultivars and extracting solvents, which could therefore be a promising strategy to prevent diabetes and associated complications.

Computational insights into β-site amyloid precursor protein enzyme 1 (BACE1) inhibition by tanshinones and salvianolic acids from Salvia miltiorrhiza via molecular docking simulations

The rhizome of Salvia miltiorrhiza has emerged as a rich source of natural therapeutic agents, and its several compounds are supposed to exhibit favorable effects on Alzheimer's disease (AD). The present work investigate the anti-AD potentials of 12 tanshinones, three salvianolic acids and three caffeic acid derivatives from S. miltiorrhiza via the inhibition of β-site amyloid precursor protein cleaving enzyme 1 (BACE1). Among the tested compounds, deoxyneocryptotanshinone (1), salvianolic acid A (13) and salvianolic acid C (15) displayed good inhibitory effect on BACE1 with IC₅₀ values of 11.53 ± 1.13, 13.01 ± 0.32 and 9.18 ± 0.03 μM, respectively. Besides this, enzyme kinetic analysis on BACE1 revealed 13, a competitive type inhibitor while 1 and 15 showed mixed-type inhibition. Furthermore, molecular docking simulation displayed negative binding energies (AutoDock 4.2.6 = -10.0 to -7.1 kcal/mol) of 1, 13, and 15 for BACE1, indicating these compounds bound tightly to the active site of the enzyme with low energy and high affinity. The results of the present study clearly demonstrate that S. miltiorrhiza and its constituents have potential anti-AD activity and can be used as a therapeutic agent for the treatment of AD.

Structure Related Inhibition of Enzyme Systems in Cholinesterases and BACE1 In Vitro by Naturally Occurring Naphthopyrone and Its Glycosides Isolated from Cassia obtusifolia

Cassia obtusifolia Linn. have been used to improve vision, inflammatory diseases, and as hepatoprotective agents and to promote urination from ancient times. In the present study, we investigated the influence of glycosylation of components of C. obtusifolia and structure-activity relationships (SARs) with respect to the inhibition of acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and β-site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1), which are related to Alzheimer’s disease (AD). All six C. obtusifolia-derived compounds, rubrofusarin (1), rubrofusarin 6-O-β-d-glucopyranoside (2), rubrofusarin 6-O-β-d-gentiobioside (3), nor-rubrofusarin 6-O-β-d-glucoside (4), isorubrofusarin 10-O-β-d-gentiobioside (5), and rubrofusarin 6-O-β-d-triglucoside (6) showed promising inhibitory activity against AChE/BACE1. Compounds 3 and 4 showed most significant inhibition against AChE and BACE1, respectively. The SARs results emphasized the importance of gentiobiosyl moiety in the rubrofusarin for AChE inhibition, whereas the presence of hydroxyl group at C-8 and the glucosyl moiety at the C-6 position in the nor-rubrofusarin appeared to largely determine BACE1 inhibition. Kinetics and docking studies showed the lowest binding energy and highest affinity for mixed-type inhibitors, 3 and 4. Hydrophobic bonds interactions and the number of hydrogen bonds determined the strength of the protein-inhibitor interaction. These results suggest that C. obtusifolia and its constituents have therapeutic potential, and that the SARs of its active components are further explored with a view towards developing a treatment for AD.

Inhibition of protein tyrosine phosphatase (PTP1B) and α-glucosidase by geranylated flavonoids from Paulownia tomentosa

Protein tyrosine phosphatase 1B (PTP1B) and α-glucosidase are important targets to treat obesity and diabetes, due to their deep correlation with insulin and leptin signalling, and glucose regulation. The methanol extract of Paulownia tomentosa fruits showed potent inhibition against both enzymes. Purification of this extract led to eight geranylated flavonoids (1-8) displaying dual inhibition of PTP1B and α-glucosidase. The isolated compounds were identified as flavanones (1-5) and dihydroflavonols (6-8). Inhibitory potencies of these compounds varied accordingly, but most of the compounds were highly effective against PTP1B (IC50 = 1.9-8.2 μM) than α-glucosidase (IC50 = 2.2-78.9 μM). Mimulone (1) was the most effective against PTP1B with IC50 = 1.9 μM, whereas 6-geranyl-3,3',5,5',7-pentahydroxy-4'-methoxyflavane (8) displayed potent inhibition against α-glucosidase (IC50 = 2.2 μM). All inhibitors showed mixed type Ι inhibition toward PTP1B, and were noncompetitive inhibitors of α-glucosidase. This mixed type behavior against PTP1B was fully demonstrated by showing a decrease in Vmax, an increase of Km, and Kik/Kiv ratio ranging between 2.66 and 3.69.