Magnetic Ligand Fishing as a Targeting Tool for HPLC-HRMS-SPE-NMR: α-Glucosidase Inhibitory Ligands and Alkylresorcinol Glycosides from Eugenia catharinae

Immobilized PAD4 enzyme on magnetic nanoparticles for screening natural inhibitors from traditional Chinese medicines

Dysregulation of peptidyl arginine deiminase 4 (PAD4) is involved in a variety of diseases including rheumatoid arthritis (RA) and Alzheimer's disease (AD), and it has emerged as potential and promising therapeutic target. However, no PAD4 inhibitor is ready for clinical use. Immobilized enzyme screening technology has gained increasing attention due to its low cost, reusability, easy separation from the reaction mixture, and resistance to changes in environmental conditions. In this study, PAD4 was immobilized on the magnetic nanoparticles (MNP) to prolong its activity stability, and a simple and rapid screening strategy of traditional Chinese medicine inhibitors based on immobilized PAD4 was established. The PAD4 enzyme was immobilized on magnetic nanoparticles (MNP) via Schiff base reaction using glutaraldehyde (GA) as crosslinking agent. Compared with free PAD4, the resulting MNP@GA@PAD4 exhibited an enhanced tolerance to temperature and storage stability, and its reusability was greatly improved with 66 % of initial enzyme activity after being recycled 10 times. The inhibitory activity of the immobilized PAD4 was assessed using two known PAD4 inhibitors GSK484 and BB-Cl-amidine. The semi-maximum inhibitory concentrations (IC50) of GSK484 and BB-Cl-amidine for MNP@GA@PAD4 were 1.00 and 0.97 μM, respectively, for free PAD4 were 0.64 and 0.85 μM, respectively. Finally, the MNP@GA@PAD4 was employed to rapid screen of natural PAD4 inhibitors from forty traditional Chinese medicines (TCMs). Under the same conditions, the controlled experiment was conducted with free PAD4. The screening results of TCMs inhibitors on MNP@GA@PAD4 and free PAD4 were similar, the alcohol extracts of Cinnamomi Cortex and Caryophylli Flos had significant inhibitory effects on PAD4 enzyme activity. The IC50 values of Cinnamomi Cortex extract for MNP@GA@PAD4 and free PAD4 were determined as 27 and 48 μg/mL, respectively. The IC50 values of Caryophylli Flos extracts for MNP@GA@PAD4 and free PAD4 were determined as 48 and 32 μg/mL, respectively. For the first time, this study proposed a method to immobilize PAD4 on magnetic materials, and developed a rapid, reusable and feasible strategy to screening natural PAD4 inhibitors from TCMs.

Fast screening of α-glucosidase inhibitors from Ginkgo biloba leaf by using α-glucosidase immobilized on magnetic metal-organic framework

In this study, a ligand fishing method for the screening of α-glucosidase inhibitors from Ginkgo biloba leaf was established for the first time using α-glucosidase immobilized on the magnetic metal-organic framework. The immobilized α-glucosidase exhibited enhanced resistance to temperature and pH, as well as good thermal stability and reusability. Two ligands, namely quercitrin and quercetin, were screened from Ginkgo biloba leaf and identified by ultra-high performance liquid chromatography-tandem mass spectrometry. The half-maximal inhibitory concentration values for quercitrin and quercetin were determined to be 105.69 ± 0.39 and 83.49 ± 0.79 µM, respectively. Molecular docking further confirmed the strong inhibitory effect of these two ligands. The proposed approach in this study demonstrates exceptional efficiency in the screening of α-glucosidase inhibitors from complex natural medicinal plants, thus exhibiting significant potential for the discovery of antidiabetic compounds.

New α-Glucosidase Inhibitors from the Whole Plant of Hypericum beanii Based on Ligand Fishing and Molecular Networking Analysis

In this work, a new rapid and targeted method for screening α-glucosidase inhibitors from Hypericum beanii was developed and verified. Ten new polycyclic polyprenylated acylphloroglucinols (PPAPs), hyperlagarol A-J (1-10), and nine known PPAPs (11-19) were obtained from H. beanii. Their structures were identified by using comprehensive analyses involving mass spectrometry, ultraviolet spectroscopy, infrared spectroscopy, nuclear magnetic resonance spectroscopy, and electron capture dissociation calculations. 1 and 2 are two new rare 2,3-seco-spirocyclic PPAPs, 3 and 4 are two novel 12,13-seco-spirocyclic PPAPs, 5 and 6 are two novel spirocyclic PPAPs, 7 and 8 are two new unusual spirocyclic PPAPs with complex bridged ring systems, and 9 and 10 are two novel nonspirocyclic PPAPs. α-GC inhibitory activities of all isolated compounds were tested. Most of them displayed inhibitory activities against α-glucosidase, with the IC50 values ranging from 6.85 ± 0.65 to 112.5 ± 9.03 μM. Moreover, the inhibitory type and mechanism of the active compounds were further analyzed using kinetic studies and molecular docking.

Methyl rosmarinate is an allosteric inhibitor of SARS-CoV-2 3 CL protease as a potential candidate against SARS-cov-2 infection

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been ongoing for more than three years and urgently needs to be addressed. Traditional Chinese medicine (TCM) prescriptions have played an important role in the clinical treatment of patients with COVID-19 in China. However, it is difficult to uncover the potential molecular mechanisms of the active ingredients in these TCM prescriptions. In this paper, we developed a new approach by integrating the experimental assay, virtual screening, and the experimental verification, exploring the rapid discovery of active ingredients from TCM prescriptions. To achieve this goal, 4 TCM prescriptions in clinical use for different indications were selected to find the antiviral active ingredients in TCMs. The 3-chymotrypsin-like protease (3CLpro), an important target for fighting COVID-19, was utilized to determine the inhibitory activity of the TCM prescriptions and single herb. It was found that 10 single herbs had better inhibitory activity than other herbs by using a fluorescence resonance energy transfer (FRET) - based enzymatic assay of SARS-CoV-2 3CLpro. The ingredients contained in 10 herbs were thus virtually screened and the predicted active ingredients were experimentally validated. Thus, such a research strategy firstly removed many single herbs with no inhibitory activity against SARS-CoV-2 3CLpro at the very beginning by FRET-based assay, making our subsequent virtual screening more effective. Finally, 4 active components were found to have stronger inhibitory effects on SARS-CoV-2 3CLpro, and their inhibitory mechanism was subsequently investigated. Among of them, methyl rosmarinate as an allosteric inhibitor of SARS-CoV-2 3CLpro was confirmed and its ability to inhibit viral replication was demonstrated by the SARS-CoV-2 replicon system. To validate the binding mode via docking, the mutation experiment, circular dichroism (CD), enzymatic inhibition and surface plasmon resonance (SPR) assay were performed, demonstrating that methyl rosmarinate bound to the allosteric site of SARS-CoV-2 3CLpro. In conclusion, this paper provides the new ideas for the rapid discovery of active ingredients in TCM prescriptions based on a specific target, and methyl rosmarinate has the potential to be developed as an antiviral therapeutic candidate against SARS-CoV-2 infection.

Deep eutectic solvent extraction combined with magnetic bead ligand fishing for identification of α-glucosidase inhibitors from Pueraria lobata

In this study, a deep eutectic solvent (DES) extraction combined with a magnetic bead ligand affinity analytical method was developed and used for α-glucosidase inhibitor identification from Pueraria lobata. Several critical parameters affecting the analysis performance, including the type of DES, molar ratio, water amount, pH, salt concentration, and volume of DES, were investigated. The selected analytical sample preparation conditions were as follows. The composition of DES is choline chloride-1,4-butanediol (1:3), the water content is 40%, pH is 7.0 and the volume of extraction solution is 2 mL. The obtained sample extraction solution was analyzed directly using α-glucosidase immobilized magnetic beads (GMBs). Three α-glucosidase inhibitors in Pueraria lobata, including puerarin, daidzin, and daidzein, were identified. Luteolin was used as a positive control to evaluate the method's selectivity. Results showed it could selectively bond to the GMBs in the DES. As the affinity analysis was performed directly in a DES, the solution-removing process could be avoided. The intra-day and inter-day precisions of the method are 5.21% and 6.38%, respectively. The solvent amount was 1/50-1/2000 of that used in traditional methods.

Enzyme immobilized on magnetic fluorescent bifunctional nanoparticles for α-glucosidase inhibitors virtual screening from Agrimonia pilosa Ledeb extracts accompanied with molecular modeling

Agrimonia pilosa Ledeb (APL) is a significant source of inhibitors for α-glucosidase, which is an essential target enzyme for the treatment of type 2 diabetes, cancer and acquired immune deficiency syndrome. Ligand fishing is a suitable approach for the highly selective screening of bioactive substances in complex mixtures. Yet it is unable to conduct biomedical imaging screening, which is crucial for real-time identification. In this case, a bioanalytical platform combining magnetic fluorescent ligand fishing and in-situ imaging technique was established for the screening and identification of α-glucosidase inhibitors (AGIs) from APL crude extract, utilizing α-glucosidase coated CuInS2/ZnS-Fe3O4@SiO2 (AG-CIZSFS) nanocomposites as extracting material and fluorescent tracer. The AG-CIZSFS nanocomposites prepared through solvothermal and crosslinking methods displayed fast magnetic separation, excellent fluorescence performance and high enzyme activity. The tolerance of immobilized enzyme to temperature and pH was stronger than that of free enzyme. Prior to proof-of-concept with APL crude extract, a number essential parameters (glutaraldehyde concentration, immobilized time, enzyme amount, reaction solution pH, incubation temperature, incubation time, percentage of methanol in eluen, elution times and eluent volume) were optimized using an artificial test mixture. The fished ligands were identified by UPLC-MS/MS and their biological activities were preliminarily evaluated by real-time cellular morphological imaging of human colon carcinoma (HCT-116) cells based on confocal laser scanning microscope (CLSM). Their α-glucosidase inhibitory activities were further verified and studied by classical pNPG method and molecular docking. The isolated compounds exhibited significant α-glucosidase inhibitory activities with a IC50 value of 11.57 µg·mL-1. Six potential AGIs including tribuloside, ivorengenin A, tormentic acid, 1β, 2β, 3β, 19α-Tetra hydroxyurs-12-en-28-oic acid, corosolic acid and pomolic acid were ultimately screened out and identified from APL crude extracts. The proposed approach, which combined highly specific screening with in-situ visual imaging, provided a powerful platform for discovering bioactive components from multi-component and multi-target traditional Chinese medicine (TCM).

Antimicrobial polyketides and sesquiterpene lactones from the deep-sea cold-seep-derived fungus Talaromyces minioluteus CS-113 triggered by the histone deacetylase inhibitor SAHA

Seven new highly oxygenated natural products with diverse chemical structural types, including three new glucosidic polyketides, talaminiosides A-C (1-3), a pair of racemic aromatic polyketides, (±)-talaminone A (4a and 4b), two new azaphilone polyketides, (+)-5-chloromitorubrinic acid (5) and 7-epi-purpurquinone C (7), and one new drimane sesquiterpene lactone, 11-hydroxyminioluteumide B (8), together with a pinazaphilone B sodium salt (6) and 10 known compounds (9-18), were isolated and identified from the culture extract of Talaromyces minioluteus CS-113, a fungus obtained from deep-sea cold-seep sediments collected from the South China Sea. LCMS results indicated that compounds 3 and 4 might be produced by the real activation of silent BGCs triggered by the histone deacetylase inhibitor SAHA, and some of the other compounds were enhanced minor components. Their structures were elucidated by the detailed interpretation of NMR spectroscopic and mass spectrometric data, X-ray crystallographic analysis, ECD and specific rotation (SR) calculations, and DP4+ probability analysis. Compound 7, an azaphilone derivative, exhibited potent activities against several agricultural pathogenic fungi with MIC values equivalent or comparable to amphotericin B. The structure-activity relationship of the isolated azaphilones is briefly discussed. This is the first report of the chemical diversity study of deep-sea cold-seep-derived fungi triggered by SAHA, providing a useful strategy for the activation of cryptic fungal metabolites from deep-sea-derived fungi.

Immobilized enzyme for screening and identification of anti-diabetic components from natural products by ligand fishing

Diabetes is a chronic metabolic disease caused by insufficient insulin secretion and insulin resistance. Natural product is one of the most important resources for anti-diabetic drug. However, due to the extremely complex composition, this research is facing great challenges. After the advent of ligand fishing technology based on enzyme immobilization, the efficiency of screening anti-diabetic components has been greatly improved. In order to provide critical knowledge for future research in this field, the application progress of immobilized enzyme in screening anti-diabetic components from complex natural extracts in recent years was reviewed comprehensively, including novel preparation technologies and strategies of immobilized enzyme and its outstanding application prospect in many aspects. The basic principles and preparation steps of immobilized enzyme were briefly described, including entrapment, physical adsorption, covalent binding, affinity immobilization, multienzyme system and carrier-free immobilization. New formatted immobilized enzymes with different carriers, hollow fibers, magnetic materials, microreactors, metal organic frameworks, etc., were widely used to screen anti-diabetic compositions from various natural products, such as Ginkgo biloba, Morus alba, lotus leaves, Pueraria lobata, Prunella vulgaris, and Magnolia cortex. Furthermore, the challenges and future prospects in this field were put forward in this review.

Identification of yeast α-glucosidase inhibitors from Pueraria lobata by ligand fishing based on magnetic mesoporous silicon combined with knock-out/knock-in technology

In this study, a ligand fishing technique based on magnetic mesoporous silicon was established and used to screen α-glucosidase inhibitors from Pueraria lobata. To clarify quantity-activity relationships in a holistic view, the knock-out/knock-in technology was used to analyse the interactions of several active constituents in P. lobata. Magnetic mesoporous silicon with a large specific surface area and better biocompatibility was synthesised. Subsequently, α-glucosidase was immobilised on -NH₂-modified magnetic mesoporous silicon, and the compounds in the crude extract of P. lobata were screened across enzyme binding. The structures of the ligands were elucidated using UPLC-Q-TOF-MS/MS, and their activities were verified by knock-out/knock-in experiments and molecular docking. Daidzein and puerarin showed α-glucosidase inhibitory activities with an IC₅₀ of 0.088 ± 0.003 mg mL^-1 and 0.414 ± 0.005 mg mL^-1, respectively. Among them, puerarin, which accounted for more than 40% of the total content, showed synergistic effects with other components and was the main contributor to the α-glucosidase inhibitory activity of P. lobata.

Biodiscoveries within the Australian plant genus Eremophila based on international and interdisciplinary collaboration: results and perspectives on outstanding ethical dilemmas

In a cross-continental research initiative, including researchers working in Australia and Denmark, and based on joint external funding by a 3-year grant from the Novo Nordisk Foundation, we have used DNA sequencing, extensive chemical profiling and molecular networking analyses across the entire Eremophila genus to provide new knowledge on the presence of natural products and their bioactivities using polypharmocological screens. Sesquiterpenoids, diterpenoids and dimers of branched-chain fatty acids with previously unknown chemical structures were identified. The collection of plant material from the Eremophila genus was carried out according to a 'bioprospecting agreement' with the Government of Western Australia. We recognize that several Eremophila species hold immense cultural significance to Australia's First Peoples. In spite of our best intentions to ensure that new knowledge gained about the genus Eremophila and any potential future benefits are shared in an equitable manner, in accordance with the Nagoya Protocol, we encounter serious dilemmas and potential conflicts in making benefit sharing with Australia's First Peoples a reality.

Chemical Characterization, α-Glucosidase, α-Amylase and Lipase Inhibitory Properties of the Australian Honey Bee Propolis

The use of functional foods and nutraceuticals as a complementary therapy for the prevention and management of type 2 diabetes and obesity has steadily increased over the past few decades. With the aim of exploring the therapeutic potentials of Australian propolis, this study reports the chemical and biological investigation of a propolis sample collected in the Queensland state of Australia which exhibited a potent activity in an in vitro α-glucosidase inhibitory screening. The chemical investigation of the propolis resulted in the identification of six known prenylated flavonoids including propolins C, D, F, G, H, and solophenol D. These compounds potently inhibited the α-glucosidase and two other enzymes associated with diabetes and obesity, α-amylase, and lipase on in vitro and in silico assays. These findings suggest that this propolis is a potential source for the development of a functional food to prevent type 2 diabetes and obesity. The chemical analysis revealed that this propolis possessed a chemical fingerprint relatively similar to the Pacific propolis found in Okinawa (South of Japan), Taiwan, and the Solomon Islands. This is the first time the Pacific propolis has been identified in Australia.

Drug discovery from natural products - Old problems and novel solutions for the treatment of neurodegenerative diseases

The use of natural products has been shown to be a fruitful approach in the discovery of novel pharmaceuticals. In fact, many currently approved drugs originated from compounds that were first identified in nature. Chemical diversity of natural compounds cannot be matched by man-made libraries of chemically synthesized molecules. Many natural compounds interact with and modulate regulatory protein targets and can be considered evolutionarily-optimized drug-like molecules. Despite this, many pharmaceutical companies have reduced or eliminated their natural product discovery programs in the last two decades. Screening natural products for pharmacologically active compounds is a challenging task that requires high resource commitment. Novel approaches at the early stage of the drug discovery pipeline are needed to allow for rapid screening and identification of the most promising molecules. Here, we review the possible evolutionary roots for drug-like characteristics of numerous natural compounds. Since many of these compounds target evolutionarily conserved cellular signaling pathways, we propose novel, early-stage drug discovery approaches to identify drug candidates that can be used for the potential prevention and treatment of neurodegenerative diseases. Invertebrate in vivo animal models of neurodegenerative diseases and innovative tools used within these models are proposed here as a screening funnel to identify new drug candidates and to shuttle these hits into further stages of the drug discovery pipeline.

Identification of TrkB Binders from Complex Matrices Using a Magnetic Drug Screening Nanoplatform

Brain-derived neurotrophic factor (BDNF) and its receptor tyrosine receptor kinase B (TrkB) have been shown to play an important role in numerous neurological disorders, such as Alzheimer's disease. The identification of biologically active compounds interacting with TrkB serves as a drug discovery strategy to identify drug leads for neurological disorders. Here, we report effective immobilization of functional TrkB on magnetic iron oxide nanoclusters, where TrkB receptors behave as "smart baits" to bind compounds from mixtures and magnetic nanoclusters enable rapid isolation through magnetic separation. The presence of the immobilized TrkB was confirmed by specific antibody labeling. Subsequently, the activity of the TrkB on iron oxide nanoclusters was evaluated with ATP/ADP conversion experiments using a known TrkB agonist. The immobilized TrkB receptors can effectively identify binders from mixtures containing known binders, synthetic small molecule mixtures, and Gotu Kola (Centella asiatica) plant extracts. The identified compounds were analyzed by an ultrahigh-performance liquid chromatography system coupled with a quadrupole time-of-flight mass spectrometer. Importantly, some of the identified TrkB binders from Gotu Kola plant extracts matched with compounds previously linked to neuroprotective effects observed for a Gotu Kola extract approved for use in a clinical trial. Our studies suggest that the possible therapeutic effects of the Gotu Kola plant extract in dementia treatment, at least partially, might be associated with compounds interacting with TrkB. The unique feature of this approach is its ability to fast screen potential drug leads using less explored transmembrane targets. This platform works as a drug-screening funnel at early stages of the drug discovery pipeline. Therefore, our approach will not only greatly benefit drug discovery processes using transmembrane proteins as targets but also allow for evaluation and validation of cellular pathways targeted by drug leads.

Magnetic particles for enzyme immobilization: A versatile support for ligand screening

Enzyme inhibitors represent a substantial fraction of all small molecules currently in clinical use. Therefore, the early stage of drug-discovery process and development efforts are focused on the identification of new enzyme inhibitors through screening assays. The use of immobilized enzymes on solid supports to probe ligand-enzyme interactions have been employed with success not only to identify and characterize but also to isolate new ligands from complex mixtures. Between the available solid supports, magnetic particles have emerged as a promising support for enzyme immobilization due to the high superficial area, easy separation from the reaction medium and versatility. Particularly, the ligand fishing assay has been employed as a very useful tool to rapidly isolate bioactive compounds from complex mixtures, and hence the use of magnetic particles for enzyme immobilization has been widespread. Thus, this review provides a critical overview of the screening assays using immobilized enzymes on magnetic particles between 2006 and 2021.

Phenolic constituents isolated from Senna tora sprouts and their neuroprotective effects against glutamate-induced oxidative stress in HT22 and R28 cells

The consumption of sprouts has been steadily increasing due to their being an excellent source of nutrition. It is known that the bioactive constituents of legumes can be increased after germination. In this study, the extract from Senna tora sprouts is shown to exhibit improved radical scavenging activities and better neuroprotective effects in HT22 hippocampal neuronal (HT22) and R28 retina precursor (R28) cells than those from seeds due to an increased content of phenolic constituents, especially compounds 1 and 3-6. A phytochemical investigation of S. tora sprouts resulted in the isolation of two new naphthopyrone glycosides (1-2) with 27 previously reported compounds. Their structures were determined via interpreting spectroscopic data. Compounds 1 and 3-6 were found to possess radical scavenging activities and neuroprotective effects against oxidative stress in both neuronal cells. Hence, Senna tora sprouts and their constituents may be developed as natural neuroprotective agents via antioxidative effects.

A new prenylated coumarin diglycoside with insulin-release promoting activity from Clausena dunniana

A new prenylated coumarin diglycoside, 6-prenylcoumarin-7-O-β-D-apiofuranosyl-(1→6)-β-D-glucopyranoside (1) and five known flavonoid glycosides (2-6) were isolated from the leaves and stems of Clausena dunniana. The structures of these isolates were elucidated based on comprehensive MS, UV, IR, and NMR spectroscopic data analysis and comparison with the data reported in literature. Compounds 2-6 are obtained from the title plant for the first time. All these isolates were evaluated for their insulin-release promoting effects, and compounds 1, 2, and 4 exhibited significant activities (2.0 to 3.3-fold higher in comparison with the control, p < 0.01) at 40 μM.[Formula: see text].

An Integrated Strategy for the Detection, Dereplication, and Identification of DNA-Binding Biomolecules from Complex Natural Product Mixtures

A fundamental factor in natural product drug discovery programs is the necessity to identify the active component(s) from complex chemical mixtures. Whereas this has traditionally been accomplished using bioassay-guided fractionation, we questioned whether alternative techniques could supplement and, in some cases, even supplant this approach. We speculated that a combination of ligand-fishing methods and modern analytical tools (e.g., LC-MS and online natural product databases) offered a route to enhance natural product drug discovery. Herein, a candidate solution referred to as the lickety-split ligand-affinity-based molecular angling system (LLAMAS) is described. This approach utilizes an ultrafiltration-based LC-PDA-MS/MS-guided DNA-binding assay in combination with the (i) Global Natural Products Social Molecular Networking, (ii) Dictionary of Natural Products, and (iii) SciFinder platforms to identify DNA binders in complex chemical mixtures. LLAMAS was initially vetted in tests using known small-molecule DNA binders and then optimized to a 96-well plate-based format. A set of 332 plant samples used in traditional Chinese medicine was screened for DNA-binding activity with LLAMAS, resulting in the identification of seven DNA-binding molecules, including berberine (12), palmatine (13), coptisine (14), fangchinoline (15), tetrandrine (16), daurisoline (17), and dauricine (18). These results demonstrate that LLAMAS is an effective natural product discovery platform for the efficient identification and dereplication of DNA-binding molecules from complex mixtures.

Magnetic ligand fishing using immobilized DPP-IV for identification of antidiabetic ligands in lingonberry extract

In this work, a new magnetic ligand fishing probe for discovery of DPP-IV inhibitory ligands was developed and it was tested as a proof of concept on the fruit extract of Vaccinium vitis-idaea (lingonberry). The ligands were shown to have appreciable dipeptidyl peptidase IV (DPP-IV) inhibitory activity (IC₅₀: 31.8 μg mL-1).) Inhibition of DPP-IV is a well-known therapeutic approach for management of type 2 diabetes (T2D). DPP-IV was successfully immobilized onto magnetic beads and was shown to retain its catalytic activity and selectivity over a model mixture. A total of four ligands were successfully fished out and identified as cyanidin-3-galactoside (2), cyanidin-3-arabinoside (3), proanthocynidin A (4), and 10-carboxyl-pyranopeonidin 3-O-(6″-O-p-coumaroyl)-glucoside (5) using HPLC/HRMS.

Rapid Screening α-Glucosidase Inhibitors from Natural Products by At-Line Nanofractionation with Parallel Mass Spectrometry and Bioactivity Assessment

In this study, a novel at-line nanofractionation screening platform was successfully developed for the rapid screening and identification of α-glucosidase inhibitors from natural products. A time-course bioassay based on high density well-plates was performed in parallel with high resolution mass spectrometry (MS), providing a straightforward and rapid procedure to simultaneously obtain chemical and biological information of active compounds. Through multiple nanofractionations into the same well-plate and comparisons of the orthogonal separation results of hydrophilic interaction liquid chromatography (HILIC) and reversed-phase liquid chromatography (RPLC), the α-glucosidase inhibitors can be accurately identified from co-eluates. The screening platform was comprehensively evaluated and validated, and was applied to the screenings of green tea polyphenols and Ginkgo folium flavonoids. After accurate peak shape and retention time matching between the bioactivity chromatograms and MS chromatograms, ten α-glucosidase inhibitors were successfully screened out and identified. The proposed screening method is rapid, effective and can avoid ignoring low abundant/active inhibitors.

Construction of Fe3O4@α-glucosidase magnetic nanoparticles for ligand fishing of α-glucosidase inhibitors from a natural tonic Epimedii Folium

Inhibition of α-glucosidase activity is an effective way for treatment of type 2 diabetes mellitus. Epimedii Folium is an important source of α-glucosidase inhibitors (AGIs), however bioactive compounds and pharmacological mechanisms remained unclear. In this study, a novel strategy was established, which harnessed α-glucosidase functionalized magnetic beads to fish out potential AGIs, followed by UPLC-MS/MS analysis for their identification. Furthermore, molecular docking was employed to predict binding patterns between the AGIs and the enzyme, and IC₅₀ values was estimated as well. After response surface methodology optimization, the highest activity of Fe₃O₄@α-glucosidase has been achieved when 1.17 mg/mL of α-glucosidase was immobilized in phosphate buffer (pH 6.81) for 4.22 h. Moreover, eight flavonoids were fished out from the extract of Epimedii Folium, and then identified to be epimedin A, epimedin B, epimedin C, icariin, sagittatoside A, sagittatoside B, 2"-O-rhamnosyl icariside II and baohuoside I. All of them were further confirmed to be AGIs through in vitro inhibitory assay and molecular docking. Among those, baohuoside I and sagittatoside B possessed stronger inhibitory activity than acarbose. The approach has a significant prospect in conveniently screening bioactive compounds that target various receptors, which provided an efficient platform for new drug development from natural products.

Recent advances in screening active components from natural products based on bioaffinity techniques

Natural products have provided numerous lead compounds for drug discovery. However, the traditional analytical methods cannot detect most of these active components, especially at their usual low concentrations, from complex natural products. Herein, we reviewed the recent technological advances (2015–2019) related to the separation and screening bioactive components from natural resources, especially the emerging screening methods based on the bioaffinity techniques, including biological chromatography, affinity electrophoresis, affinity mass spectroscopy, and the latest magnetic and optical methods. These screening methods are uniquely advanced compared to other traditional methods, and they can fish out the active components from complex natural products because of the affinity between target and components, without tedious separation works. Therefore, these new tools can reduce the time and cost of the drug discovery process and accelerate the development of more effective and better-targeted therapeutic agents.

Micro- and nano-sized amine-terminated magnetic beads in a ligand fishing assay

Functionalized micro- and nano-sized magnetic beads (MBs) have been widely used as versatile supports for proteins, enzymes, and drugs. Immobilized protein on MB surfaces has been successfully applied for ligand fishing assays allowing for direct identification of active ligands from complex mixtures, such as natural products and synthetic libraries. MBs with different properties such as different core compositions, sizes, coatings, and surface modifications are available commercially. Studies have been conducted to understand the role of these properties for ligand fishing assays. Here we evaluated, for the first time, the effect of MB size on the ligand fishing assay for acetylcholinesterase from Electrophorus electricus (AChE). For this purpose, four commercially available amine-terminated magnetic particles with diameters ranging from 4.5 nm to 106 μm were evaluated to fish out galantamine, a well-known AChE inhibitor, from an aqueous solution. All MBs were efficient at using glutaraldehyde to covalently immobilize AChE. The particles with diameters of about 1 μm (small microparticles) presented a higher protein mass capacity per milligram of particle than did those with diameters of about 4.5 nm (nanoparticles) and those with diameters of about 106 μm (large microparticles). The influence of these supports on the produced AChE-MBs with regards to hydrolysis turnover and ligand fishing was evaluated and is fully discussed.

Bioavailability and Bioactivity of Alkylresorcinols from Different Cereal Products

Cereal products are the most important dietary source for energy intake and several bioactive compounds with high concentrations in the bran and the germ. Different cereal products provide a rich source of bioactive phytochemicals, namely, phenolic acids, carotenoids, tocopherols, alkylresorcinols, benzoxazines, phytosterols, and lignans. The bioactive substance alkylresorcinols (ARs) present in the whole cereal can inhibit enzyme activity, prevent bacterial or fungal infection, reduce cholesterol absorption, prevent cancer, and resist oxidation. In this paper, we discussed the biological activity of ARs in whole cereal products. Understanding the effects of processing on cereal phytochemicals will help us to develop improved processes for processing cereal foods with higher retention rates of bioactive compounds.

Target protein-oriented isolation of Hes1 dimer inhibitors using protein based methods

Natural products isolation using protein based methods is an attractive for obtaining bioactive compounds. To discover neural stem cell (NSC) differentiation activators, we isolated eight inhibitors of Hes1 dimer formation from Psidium guajava using the Hes1-Hes1 interaction fluorescent plate assay and one inhibitor from Terminalia chebula using the Hes1-immobilized beads method. Of the isolated compounds, gallic acid (8) and 4-O-(4”-O-galloyl-α-L-rhamnopyranosyl)ellagic acid (11) showed potent Hes1 dimer formation inhibitory activity, with IC₅₀ values of 10.3 and 2.53 μM, respectively. Compound 11 accelerated the differentiation activity of C17.2 NSC cells dose dependently, increasing the number of neurons with a 125% increase (5 μM) compared to the control.

Ligand Fishing: An Approach for the Discovery of Inhibitors from Complex Biological Mixtures

Ligand fishing is a convenient bioanalytical screening method that is based on the affinity selection of a ligand from a complex biological sample by an immobilized receptor. It is a versatile affinity-based screening approach and it has found application in multiple interacting pairs such as enzyme-inhibitor/activator, antigen-antibody, receptor-ligand, and protein-protein. Important parameters that affect the successful operation of the method are the high specificity and strong binding affinity of the interacting pair (e.g., enzyme-ligand complex) and the elution of the bound ligand from the complex. This chapter provides protocols for the synthesis of affinity adsorbent and its application in off-line ligand-fishing procedure for a 6His-tagged glutathione transferase (GST).

Emerging strategies for the activity assay and inhibitor screening of alpha-glucosidase

The high incidence of diabetes mellitus has caused widespread concern around the world, and has quickly become one of the most prevalent and costly chronic diseases.

Current status and contemporary approaches to the discovery of antitumor agents from higher plants

Higher plant constituents have afforded clinically available anticancer drugs. These include both chemically unmodified small molecules and their synthetic derivatives currently used or those in clinical trials as antineoplastic agents, and an updated summary is provided. In addition, botanical dietary supplements, exemplified by mangosteen and noni constituents, are also covered as potential cancer chemotherapeutic agents. Approaches to metabolite purification, rapid dereplication, and biological evaluation including analytical hyphenated techniques, molecular networking, and advanced cellular and animal models are discussed. Further, enhanced and targeted drug delivery systems for phytochemicals, including micelles, nanoparticles and antibody drug conjugates (ADCs) are described herein.

Screening of the potentially active compounds from Polygonatum sibiricum using RAW264.7 cellular membranes coated magnetic beads fishing followed by HPLC analysis

Target biomolecule-immobilized magnetic beads could be used as a powerful tool for screening active compounds present in natural products. Low damage rates of the target proteins, associated with the availability of diverse automated online approaches for analysis, make it a valuable tool for affinity studies. RAW264.7 cells (a kind of murine macrophage cell line) were used in this study. These cellular membranes were immobilized onto the surface of MBs and were used for screening the active compounds of Polygonatum sibiricum. Combining this technique with HPLC led to the identification of an active compound and its biological activity was confirmed. This is the first report establishing the use of RAW264.7 cellular membrane-coated magnetic bead fishing followed by HPLC analysis for screening active compounds from natural products.

Solid-Supported Proteins in the Liquid Chromatography Domain to Probe Ligand-Target Interactions

Ligand-target interactions play a central role in drug discovery processes because these interactions are crucial in biological systems. Small molecules-proteins interactions can regulate and modulate protein function and activity through conformational changes. Therefore, bioanalytical tools to screen new ligands have focused mainly on probing ligand-target interactions. These interactions have been evaluated by using solid-supported proteins, which provide advantages like increased protein stability and easier protein extraction from the reaction medium, which enables protein reuse. In some specific approaches, precisely in the ligand fishing assay, the bioanalytical method allows the ligands to be directly isolated from complex mixtures, including combinatorial libraries and natural products extracts without prior purification or fractionation steps. Most of these screening assays are based on liquid chromatography separation, and the binding events can be monitored through on-line or off-line methods. In the on-line approaches, solid supports containing the immobilized biological target are used as chromatographic columns most of the time. Several terms have been used to refer to such approaches, such as weak affinity chromatography, high-performance affinity chromatography, on-flow activity assays, and high-performance liquid affinity chromatography. On the other hand, in the off-line approaches, the binding event occurs outside the liquid chromatography system and may encompass affinity and activity-based assays in which the biological target is immobilized on magnetic particles or monolithic silica, among others. After the incubation step, the supernatant or the eluate from the binding assay is analyzed by liquid chromatography coupled to various detectors. Regardless of the selected bioanalytical approach, the use of solid supported proteins has significantly contributed to the development of automated and reliable screening methods that enable ligands to be isolated and characterized in complex matrixes without purification, thereby reducing costs and avoiding time-laborious steps. This review provides a critical overview of recently developed assays.

Immobilized α-amylase magnetic beads for ligand fishing: Proof of concept and identification of α-amylase inhibitors in Ginkgo biloba

Diabetes mellitus is a widespread metabolic disorder that affects millions of people around the world. The disease is a major burden on both economic and social levels, and there is a need for improved drugs with fewer side effects in the management of the disease. Current methods for isolation of anti-diabetic lead compounds from complex mixtures suffer from low resolution and sensitivity, and there is a need for improved alternatives. In this work, magnetic ligand fishing combined with high-performance liquid chromatography - photodiode-array detection - high-resolution mass spectrometry - solid-phase extraction - nuclear magnetic resonance spectroscopy (HPLC-PDA-HRMS-SPE-NMR) was developed and validated, with the aim of accelerating discovery of natural products targeting α-amylase. The enzyme was successfully immobilized onto magnetic beads and retained its catalytic activity for a period of 75 days, and the specificity of this method was successfully validated by testing the N-terminus coupled α-amylase immobilized magnetic beads on an artificial mixture. A proof of concept experiment, using a crude ethyl acetate extract of Ginkgo biloba leaves, proved that it was possible to fish out four α-amylase ligands. HPLC-PDA-HRMS-SPE-NMR analysis confirmed the presence of bilobetin, isoginkgetin, ginkgetin and sciadopitysin in the solutions resulting from α-amylase ligand fishing with Ginkgo biloba. IC₅₀ curves revealed a reversed relationship between concentration of sciadopitysin and inhibition of α-amylase activity, suggesting that this compound activated the enzyme instead of inhibiting it.

Screening and analysis of cyclooxygenase-2 inhibitors from the complex matrix: A case study to illustrate the important effect of immobilized enzyme activity in magnetic ligand fishing

Magnetic ligand fishing is one of the most widely used methods to screen and separate potentially bioactive compounds from complex mixtures. However, it is poorly understood the ambiguous relations between immobilized enzyme activity and fishing results (accuracy and sensitivity). Therefore, to investigate the underlying relationship of them, we fabricated the immobilized enzyme with different activities by introducing a novel support material, nickel ions (Ni²⁺) functionalized magnetic mesoporous silica microspheres (MMSM@PDA-Ni²⁺). It possesses a higher activity than the previous report because of site-directed immobilization. Then, the immobilized COX-2 with different activities were prepared using different immobilization methods, including Ni²⁺ affinity-oriented immobilization, polydopamine (PDA) covalent immobilization, and conventional glutaraldehyde (GA) covalent immobilization. A standard mixture (COX-2 inhibitors and noninhibitors) and green tea extract were used to compare and evaluate the fishing results systematically. It displayed the fished inhibitors were dramatically reduced with the decreased activity of immobilized COX-2, indicating that immobilized enzyme activity played a critical role in a reliable magnetic ligand fishing analysis. This development questions some of the previous studies aimed at rapid screening bioactive compounds in natural products and opens new possibilities for accurate and sensitive magnetic ligand fishing analysis. Also, the introduced novel materials with mild immobilization strategy preserve enzyme activity and spatial conformational, therefore, provides a valuable tool in future applications.

Fabrication of paper-based enzyme immobilized microarray by 3D-printing technique for screening α-glucosidase inhibitors in mulberry leaves and lotus leaves

Background

The discovery of bioactive compounds in traditional Chinese medicine (TCM) has become an important field in TCM modernization. Ligand fishing is a suitable method for discovery of bioactive compounds in complex mixtures such as TCM with high selectivity. Because of unique advantage of low cost and convenience, paper-based microdevices can be good carriers for enzyme immobilized ligand fishing.

Methods

As an important enzyme for glucose metabolism, α-glucosidase was immobilized on polycaprolactone–chitosan-modified paper to prepare the microdevice with unique microfluid structure generated by 3D printing technology, which can be easily applied to screen active compounds in herbal extracts. The preparation conditions of the paper microarray were optimized. The activity of immobilized α-glucosidase was verified by colorimetric reactions which can be easily monitored by cellphone. The paper microarray with α-glucosidase immobilized was used to screen active compounds in the water extracts of mulberry leaves and lotus leaves.

Results

Several key parameters including Na₂CO₃ solution concentration, Na₂CO₃ solution volume, glutaraldehyde concentration, crosslinking time of glutaraldehyde and time of α-glucosidase immobilization were optimized. The proposed paper-based microarray was successfully applied in screening active compounds in two herbal extracts. Four compounds including chlorogenic acid, quercetin-3-O-glucuronide, isoquercetin, and quercetin were identified as α-glucosidase inhibitors. The compounds with significant non-specific adsorption caused by chitosan, such as isoquercitrin, astragalin, quercetin, were also found to be active compounds.

Conclusions

An enzyme immobilized paper microarray was designed and fabricated in this work. Polycaprolactone and chitosan were used to modify filter paper to prepare paper microarrays. Parameters of paper device preparation were optimized. Our findings suggested that 3D-printing paper-based microarrays can be a simple and low-cost approach for discovery of active compounds of TCM.

Electronic supplementary material

The online version of this article (10.1186/s13020-019-0236-y) contains supplementary material, which is available to authorized users.

Cell-membrane coated iron oxide nanoparticles for isolation and specific identification of drug leads from complex matrices

The lack of suitable tools for the identification of potential drug leads from complex matrices is a bottleneck in drug discovery. Here, we report a novel method to screen complex matrices for new drug leads targeting transmembrane receptors. Using α3β4 nicotinic receptors as a model system, we successfully demonstrated the ability of this new tool for the specific identification and effective extraction of binding compounds from complex mixtures. The formation of cell-membrane coated nanoparticles was confirmed by transmission electron microscopy. In particular, we have developed a direct tool to evaluate the presence of functional α3β4 nicotinic receptors on the cell membrane. The specific ligand binding to α3β4 nicotinic receptors was examined through ligand fishing experiments and confirmed by high-performance liquid chromatography coupled with diode-array detection and electrospray ionization mass spectrometry. This tool has a great potential to transform the drug discovery process focusing on identification of compounds targeting transmembrane proteins, as more than 50% of all modern pharmaceuticals use membrane proteins as prime targets.

Combined magnetic ligand fishing and high-resolution inhibition profiling for identification of α-glucosidase inhibitory ligands: A new screening approach based on complementary inhibition and affinity profiles

Plants are well-recognized sources of inhibitors for α-glucosidase - a key target enzyme for management of type 2 diabetes. Recently, two advanced bioactivity-profiling techniques, i.e., ligand fishing and high-resolution inhibition profiling, have shown great promises for accelerating identification of α-glucosidase inhibitors from complex plant extracts. Non-specific affinities and non-specific inhibitions are major sources of false positive hits from ligand fishing and high-resolution inhibition profiling, respectively. In an attempt to minimize such false positive hits, we describe a new screening approach based on ligand fishing and high-resolution inhibition profiling for detection of high-affinity ligands and assessment of inhibitory activity, respectively. The complementary nature of ligand fishing and high-resolution inhibition profiling was explored to identify α-glucosidase inhibitory ligands from a complex mixture, and proof-of-concept was demonstrated with crude ethyl acetate extract of Ginkgo biloba. In addition to magnetic beads with a 3-carbon aliphatic linker, α-glucosidase was immobilized on magnetic beads with a 21-carbon aliphatic linker; and the two different types of magnetic beads were compared for their hydrolytic activity and fishing efficiency.

Bioassay-guided isolation and identification of gametocytocidal compounds from Artemisia afra (Asteraceae)

BACKGROUND

Optimal adoption of the malaria transmission-blocking strategy is currently limited by lack of safe and efficacious drugs. This has sparked the exploration of different sources of drugs in search of transmission-blocking agents. While plant species have been extensively investigated in search of malaria chemotherapeutic agents, comparatively less effort has been channelled towards exploring them in search of transmission-blocking drugs. Artemisia afra (Asteraceae), a prominent feature of South African folk medicine, is used for the treatment of a number of diseases, including malaria. In search of transmission-blocking compounds aimed against Plasmodium parasites, the current study endeavoured to isolate and identify gametocytocidal compounds from A. afra.

METHODS

A bioassay-guided isolation approach was adopted wherein a combination of solvent-solvent partitioning and gravity column chromatography was used. Collected fractions were continuously screened in vitro for their ability to inhibit the viability of primarily late-stage gametocytes of Plasmodium falciparum (NF54 strain), using a parasite lactate dehydrogenase assay. Chemical structures of isolated compounds were elucidated using UPLC-MS/MS and NMR data analysis.

RESULTS

Two guaianolide sesquiterpene lactones, 1α,4α-dihydroxybishopsolicepolide and yomogiartemin, were isolated and shown to be active (IC50 < 10 μg/ml; ~ 10 μM) against both gametocytes and intra-erythrocytic asexual P. falciparum parasites. Interestingly, 1α,4α-dihydroxybishopsolicepolide was significantly more potent against late-stage gametocytes than to early-stage gametocytes and intra-erythrocytic asexual P. falciparum parasites. Additionally, both isolated compounds were not overly cytotoxic against HepG2 cells in vitro.

CONCLUSION

This study provides the first instance of isolated compounds from A. afra against P. falciparum gametocytes as a starting point for further investigations on more plant species in search of transmission-blocking compounds.

Ligand fishing with cellular membrane-coated cellulose filter paper: a new method for screening of potential active compounds from natural products

Ligand fishing is a widely used approach for screening active compounds from natural products. Recently, cell membrane (CM) as affinity ligand has been applied in ligand fishing, including cell membrane chromatography (CMC) and CM-coated magnetic bead. However, these methods possess many weaknesses, including complicated preparation processes and time-consuming operation. In this study, cheap and easily available cellulose filter paper (CFP) was selected as carrier of CM and used to fabricate a novel CM-coated CFP (CMCFP) for the first time. The type of CFP was optimized according to the amount of immobilized protein, and the immobilization of CM onto CFP by the insertion and self-fusion process was verified by confocal imaging. The CMCFP exhibited good selectivity and stability and was used for fishing potentially active compounds from extracts of Angelica dahurica. Three potentially active compounds, including bergapten, pabulenol, and imperatorin, were fished out and identified. The traditional Chinese medicine systems pharmacology database and analysis platform was used to build an active compound-target protein network, and accordingly, the gamma-aminobutyric acid receptor subunit alpha-1 (GABRA1) was deduced as potential target of CM for the active compounds of Angelica dahurica. Molecular docking was performed to evaluate the interaction between active compounds and GABRA1, and bergapten was speculated as a new potentially active compound. Compared with other methods, the fishing assay based on CMCFP was more effective, simpler, and cheaper.

Nanoenabled Bioseparations: Current Developments and Future Prospects

The use of nanomaterials in bioseparations has been recently introduced to overcome the drawbacks of the conventional methods. Different forms of nanomaterials, particularly magnetic nanoparticles (MNPs), carbon nanotubes (CNTs), casted nanoporous membranes, and electrospun nanofiber membranes were utilized in biological separation for the aim of production of different biomolecules such as proteins, amino acids, nucleic acids, and enzymes. This paper critically reviews the state-of-the-art efforts undertaken in this regard, with emphasis on the synthesis and performance evaluation of each nanoform. Challenges and future prospects in developing nanoenabled bioseparations are also discussed, for the purpose of highlighting potential advances in the synthesis and fabrication of novel nanomaterials as well as in the design of efficient nanoenabled processes for separating a wide spectrum of biomolecules.

Enzyme immobilized on polyamidoamine-coated magnetic microspheres for α-glucosidase inhibitors screening from Radix Paeoniae Rubra extracts accompanied with molecular modeling

In this study, a method for direct screening and identification of α-glucosidase inhibitors (AGIs) from extracts of natural products was established based on polyamidoamine (PAMAM) coated magnetic microspheres. A facile route to synthesize the magnetic PAMAM was employed and α-glucosidase was successfully covalently attached to its surface through cross linking of glutaraldehyde. Using the enzyme-loaded magnetic microspheres, potential inhibitors were fished out from crude extracts directly, followed by structure confirmation. The inhibitory activities of the screened components were further investigated by the enzyme-loaded magnetic microspheres. The Fe₃O₄ @PAMAM@α-Glu microspheres displayed favorable dispersibility, fast magnetic separation, large enzyme binding amount (42.9 μg•mg^-1) and high enzyme activity. Moreover, the α-glucosidase on the surface of PAMAM coating maintained high storage stability and remarkable reusability. Taking advantage of specific interaction of the α-glucosidase with AGIs, the materials could selectively capture a known AGI (+)-catechin under the interference of an inactive compound salicylic acid, with a binding capacity as high as 15.4%. Additionally, using the Fe₃O₄ @PAMAM@α-Glu microspheres in the inhibition assay, the enzymatic reaction could be stopped by magnetic separation instead of the traditional addition of Na₂CO₃ solution, which not only eliminated the disturbance of termination reagent to the results, but also reused the immobilized α-glucosidase. The screening and inhibitory activity verification of potential ligands in Radix Paeoniae Rubra ("Chi-shao" in Chinese) extracts were achieved by using Fe₃O₄ @PAMAM@α-Glu microspheres, demonstrating practical applicability of our method. Therefore, the magnetic PAMAM-based screening approach could be a feasible and alternative strategy for discovering enzyme inhibitors from natural product extracts.

Rapid screening and identification of bioactive compounds specifically binding to beta 2-adrenoceptor from San-ao decoction using affinity magnetic fine particles coupled with high-performance liquid chromatography-mass spectrometry

Background

San-ao decoction (SAD) has been widely used in Chinese medicine against respiratory diseases, such as asthma and rhinallergosis. The bioactive compounds for such pharmacological action remain unknown.

Methods

We developed a methodology to isolate the bioactive compounds of SAD. The assay involved the immobilization of beta 2-adrenoceptor (β ₂-AR) onto magnetic fine particles, the capture of target compounds by the immobilized receptor, the identification of the receptor bound compounds by reversed-phase high-performance liquid chromatography coupled with tandem mass spectrometry.

Results

Vicenin, shaftoside, isoshaftoside, liquiritin apioside and isoliquiritin apioside were identified as β ₂-AR ligands in SAD extract. The binding of these compounds to β ₂-AR occurred on serine¹⁶⁹, serine¹⁷⁰ and phenylalanine²⁵⁶ of the receptor.

Conclusions

The developed methodology has high stability and specificity for recognizing and isolating target compounds. It is an alternative method for rapidly screening bioactive compounds of immobilized receptor from Chinese prescriptions.

Minor Nortriterpenoids from the Twigs and Leaves of Rhododendron latoucheae

A hyphenated NMR technique (analytical HPLC with a DAD connected to MS, SPE, and NMR) has proven effective for the full structural analysis and identification of minor natural products in complex mixtures. Application of this hyphenated technique to the CH₂Cl₂-soluble fraction of Rhododendron latoucheae led to the identification of 15 new minor ursane-type 28-nortriterpenoids (1-15). Compounds 1 and 12 inhibited HSV-1 with IC₅₀ values of 6.4 and 0.4 μM, respectively.

High-Resolution PTP1B Inhibition Profiling Combined with HPLC-HRMS-SPE-NMR for Identification of PTP1B Inhibitors from Miconia albicans

Protein tyrosine phosphatase 1B (PTP1B) is an intracellular enzyme responsible for deactivation of the insulin receptor, and consequently acts as a negative regulator of insulin signal transduction. In recent years, PTP1B has become an important target for controlling insulin resistance and type 2 diabetes. In the present study, the ethyl acetate extract of leaves of Miconia albicans (IC₅₀ = 4.92 µg/mL) was assessed by high-resolution PTP1B inhibition profiling combined with HPLC-HRMS-SPE-NMR for identification of antidiabetic compounds. This disclosed eleven PTP1B inhibitors, including five polyphenolics: 1-O-(E)-caffeoyl-4,6-di-O-galloyl-β-d-glucopyranose (2), myricetin 3-O-α-l-rhamnopyranoside (3), quercetin 3-O-(2″-galloyl)-α-l-rhamnopyranoside (5), mearnsetin 3-O-α-l-rhamnopyranoside (6), and kaempferol 3-O-α-l-arabinopyranoside (8) as well as eight triterpenoids: maslinic acid (13), 3-epi-sumaresinolic acid (14), sumaresinolic acid (15), 3-O-cis-p-coumaroyl maslinic acid (16), 3-O-trans-p-coumaroyl maslinic acid (17), 3-O-trans-p-coumaroyl 2α-hydroxydulcioic acid (18), oleanolic acid (19), and ursolic acid (20). These results support the use of M. albicans as a traditional medicine with antidiabetic properties and its potential as a source of PTP1B inhibitors.

Magnetic beads-based neuraminidase enzyme microreactor as a drug discovery tool for screening inhibitors from compound libraries and fishing ligands from natural products

Neuraminidase (NA) is a glycoside hydrolase that has been proposed as a potential therapeutic target for influenza. Thus, the identification of compounds that modulate NA activity could be of great therapeutic importance. The aim of this study is to develop a drug discovery tool for the identification of novel modulators of NA from both compound libraries and natural plant extracts. NA was immobilized onto the surface of magnetic beads and the inherent catalytic activity of NA-functionalized magnetic beads was characterized. Based on the enzymatic activity (hydrolysis ratio), the inhibitory activities of 12 compounds from plant secondary metabolites were screened, and the desired anti-NA activities of flavonoids were certified. Ligand fishing with the immobilized enzyme was optimized using an artificial test mixture consisting of oseltamivir, lycorine and matrine prior to carrying out the proof-of-concept experiment with the crude extract of Flos Lonicerae. The combination of ligand fishing and HPLC-MS/MS identified luteolin-7-O-β-D-glucoside, luteolin, 3,5-di-O-caffeoylquinic acid and 3,4-di-O-caffeoylquinic acid as neuraminidase inhibitory ligands in Flos Lonicerae. This is the first report on the use of neuraminidase functionalized magnetic beads for the identification of active ligands from a botanical matrix, and it sets the basis for the de novo identification of NA modulators from complex biological mixtures.