Advances in mass spectrometry-based post-column bioaffinity profiling of mixtures

High-Efficiency Effect-Directed Analysis Leveraging Five High Level Advancements: A Critical Review

Organic contaminants are ubiquitous in the environment, with mounting evidence unequivocally connecting them to aquatic toxicity, illness, and increased mortality, underscoring their substantial impacts on ecological security and environmental health. The intricate composition of sample mixtures and uncertain physicochemical features of potential toxic substances pose challenges to identify key toxicants in environmental samples. Effect-directed analysis (EDA), establishing a connection between key toxicants found in environmental samples and associated hazards, enables the identification of toxicants that can streamline research efforts and inform management action. Nevertheless, the advancement of EDA is constrained by the following factors: inadequate extraction and fractionation of environmental samples, limited bioassay endpoints and unknown linkage to higher order impacts, limited coverage of chemical analysis (i.e., high-resolution mass spectrometry, HRMS), and lacking effective linkage between bioassays and chemical analysis. This review proposes five key advancements to enhance the efficiency of EDA in addressing these challenges: (1) multiple adsorbents for comprehensive coverage of chemical extraction, (2) high-resolution microfractionation and multidimensional fractionation for refined fractionation, (3) robust in vivo/vitro bioassays and omics, (4) high-performance configurations for HRMS analysis, and (5) chemical-, data-, and knowledge-driven approaches for streamlined toxicant identification and validation. We envision that future EDA will integrate big data and artificial intelligence based on the development of quantitative omics, cutting-edge multidimensional microfractionation, and ultraperformance MS to identify environmental hazard factors, serving for broader environmental governance.

Efficient lipidomic approach for the discovery of lipid ligands for immune receptors by combining LC-HRMS/MS analysis with fractionation and reporter cell assay

C-type lectin receptors (CLRs), which are pattern recognition receptors responsible for triggering innate immune responses, recognize damaged self-components and immunostimulatory lipids from pathogenic bacteria; however, several of their ligands remain unknown. Here, we propose a new analytical platform combining liquid chromatography-high-resolution tandem mass spectrometry with microfractionation capability (LC-FRC-HRMS/MS) and a reporter cell assay for sensitive activity measurements to develop an efficient methodology for searching for lipid ligands of CLR from microbial trace samples (crude cell extracts of approximately 5 mg dry cell/mL). We also developed an in-house lipidomic library containing accurate mass and fragmentation patterns of more than 10,000 lipid molecules predicted in silico for 90 lipid subclasses and 35 acyl side chain fatty acids. Using the developed LC-FRC-HRMS/MS system, the lipid extracts of Helicobacter pylori were separated and fractionated, and HRMS and HRMS/MS spectra were obtained simultaneously. The fractionated lipid extract samples in 96-well plates were thereafter subjected to reporter cell assays using nuclear factor of activated T cells (NFAT)-green fluorescent protein (GFP) reporter cells expressing mouse or human macrophage-inducible C-type lectin (Mincle). A total of 102 lipid molecules from all fractions were annotated using an in-house lipidomic library. Furthermore, a fraction that exhibited significant activity in the NFAT-GFP reporter cell assay contained α-cholesteryl glucoside, a type of glycolipid, which was successfully identified as a lipid ligand molecule for Mincle. Our analytical platform has the potential to be a useful tool for efficient discovery of lipid ligands for immunoreceptors.

Matrix solid-phase dispersion combined with micro-fractionation bioactivity evaluation screening polymethoxylated flavones from Citrus peels

Polymethoxyflavones were a unique class of natural and safe flavonoids containing two or more methoxy groups, which were also the most abundant edible part in Citrus peel. The optimum condition in the process of selective extraction of polymethoxylated flavones from Citrus peel by matrix solid-phase dispersion (MSPD) was as follows: SBA-15 as adsorbent, ethyl acetate as eluent, the mass ratio of adsorbent to sample 1:1, and the mixture of sample and adsorbent was ground for 3 min. Twelve antioxidants were successfully screened by micro-fractionation bioactivity evaluation assay, in which four of them were flavonoid glycosides, seven of them were polymethoxylated flavones, and one was phenylpropanoid. 1-sinapoly-β-D-glucopyranoside (1) was reported for the first time in Citrus peel. And antioxidant capacity of 1-sinapoly-β-D-glucopyranoside, 5, 7, 8, 3', 4', 5'-hexamethoxyflavone (6), hexamethoxyflavone (11), and 5, 6, 7, 4'-tetramethoxyflavone (7) were reported for the first time. Nobiletin (compound 8), 3, 5, 6, 7, 8, 3', 4'-heptamethoxyflavone (9) and tangeretin (10) were isolated and purified by countercurrent chromatography combined with preparative liquid chromatography. Antioxidant activity evaluation indicated that the three isolated polymethoxylated flavones owned similar antioxidant activity. This study indicated that MSPD combined with micro-fractionation bioactive evaluation was efficient in screening bioactive compounds for rapid extraction and effective pinpointing bioactive substances in natural products.

High-performance liquid chromatography micro-fraction bioactive evaluation combined with countercurrent chromatographic separation of antioxidants from Citrus peel and their tyrosinase inhibition activities

In the present study, high-performance liquid chromatography micro-fraction bioactive evaluation and high speed countercurrent chromatography were performed on screening, identification and isolation of antioxidants from Citrus peel. Three compounds were screened as antioxidants and tyrosinase inhibitors using 2,2'-azino-bis (3-ethyl-benzothiazoline-6-sulfonic acid) radical cation scavenging assay and tyrosinase activity test, then they were identified as eriocitrin, narirutin and hesperidin. Moreover, the solvent system ethyl acetate-n-butanol-water (6:4:10, v/v/v) was used for separation of ethyl acetate extract of Citrus peel by high speed countercurrent chromatography. In total, 0.45 mg of eriocitrin with 87.10% purity, 2.04 mg of narirutin with 95.19% purity and 1.35 mg of hesperidin with 95.19% purity were obtained from 20 mg of ethyl acetate extract of Citrus peel in a single run and then each component was subjected to 2,2'-azino-bis (3-ethyl-benzothiazoline-6-sulfonic acid) radical cation scavenging assay and tyrosinase inhibition assay. Eriocitrin showed great antioxidant activity (the half-maximum concentration: 3.65 µM) and tyrosinase inhibition activity (the half-maximum concentration: 115.67 µM), while narirutin and hesperidin exhibited moderate activity. Tyrosinase inhibition activity for eriocitrin in vitro was reported for the first time. Furthermore, molecular docking between eriocitrin and mushroom tyrosinase was also studied.

High-Resolution Bioassay Profiling with Complemented Sensitivity and Resolution for Pancreatic Lipase Inhibitor Screening

How to rapidly and accurately screen bioactive components from complex natural products remains a major challenge. In this study, a screening platform for pancreatic lipase (PL) inhibitors was established by combining magnetic beads-based ligand fishing and high-resolution bioassay profiling. This platform was well validated using a mixture of standard compounds, i.e., (-)- epigallocatechin gallate (EGCG), luteolin and schisandrin. The dose-effect relationship of high-resolution bioassay profiling was demonstrated by the standard mixture with different concentrations for each compound. The screening of PL inhibitors from green tea extract at the concentrations of 0.2, 0.5 and 1.0 mg/mL by independent high-resolution bioassay profiling was performed. After sample pre-treatment by ligand fishing, green tea extract at the concentration of 0.2 mg/mL was specifically enriched and simplified, and consequently screened through the high-resolution bioassay profiling. As a result, three PL inhibitors, i.e., EGCG, (-)-Gallocatechin gallate (GCG) and (-)-Epicatechin gallate (ECG), were rapidly identified from the complex matrix. The established platform proved to be capable of enriching affinity binders and eliminating nonbinders in sample pre-treatment by ligand fishing, which overcame the technical challenges of high-resolution bioassay profiling in the aspects of sensitivity and resolution. Meanwhile, the high-resolution bioassay profiling possesses the ability of direct bioactive assessment, parallel structural analysis and identification after separation. The established platform allowed more accurate and rapid screening of PL inhibitors, which greatly facilitated natural product-based drug screening.

A Comprehensive 2D-LC/MS Online Platform for Screening of Acetylcholinesterase Inhibitors

The continuous interest in discovering new bioactive molecules derived from natural products (NP) has stimulated the development of improved screening assays to help overcome challenges in NP-based drug discovery. Here, we describe a unique platform for the online screening of acetylcholinesterase inhibitors without the need for pre-treating the sample. In the current study, we have demonstrated the ability to combine reversed-phase separation with a capillary immobilized enzyme reactor (cIMER) in two-dimensional liquid chromatography system coupled with mass spectrometry detection. We systematically investigated the effects of method parameters that are of practical significance and are known to affect the enzyme assay and interfere in the analysis such as: bioreactor dimensions, loop sizes, amount of immobilized enzyme, second dimension flow rates, reaction time, substrate concentration, presence of organic modifier, limit of detection and signal suppression. The performance of this new platform was evaluated using a mixture containing three known AChE inhibitors (tacrine, galanthamine and donepezil) and an ethanolic extract obtained from the dry bulbs of Hippeastrum calyptratum (Amaryllidaceae) was investigated to provide a proof of concept of the applicability of the platform for the analysis of complex mixtures such as those derived from NPs.

UHPLC With On-Line Coupled Biochemical Detection for High Throughput Screening of Acetylcholinesterase Inhibitors in Coptidis Rhizoma and Cortex Phellodendri

We developed a new on-line method of ultra-performance liquid chromatography coupled with biochemical detection (UHPLC-BCD) to screen acetylcholinesterase (AChE) inhibitors in complex matrixes. Chromatography separation was performed using an Xtimate UHPLC C18 column (100 mm × 2.1 mm, 1.8 μm) and a gradient elution with methanol-0.1% formic acid at a flow rate of 0.08 mL/min. The BCD was based on a colorimetric method using Ellman's reagent, and the detection wavelength was at 405 nm. Galanthamine was used as a positive reference to validate the methodology. The detection and quantitation limits of the UHPLC-BCD method were 0.018 and 0.060 μg, respectively. A functional equation was generated in terms of the negative peak area (X) and galanthamine concentration (Y, μg/mL). The regression equation was Y = 0.0028X2 + 0.4574X + 50.7776, R2 = 0.9993. UHPLC-fourier-transform mass spectrometry detection results revealed that five alkaloids showed obvious AChE inhibitory activities including coptisin, epiberberine, jatrorrhizine, berberine and palmatine. The relative AChE inhibitory activities of jatrorrhizine, berberine and palmatine in the Coptidis Rhizoma sample were equal to that of 257.0, 2355 and 283.9 μg/mL of galanthamine, respectively. This work demonstrated that the UHPLC-BCD method was convenient and feasible, and could be widely used for the screening and activity evaluation of the bioactive components in the complex extracts.

LABEL-FREE BIO-AFFINITY MASS SPECTROMETRY FOR SCREENING AND LOCATING BIOACTIVE MOLECULES

Despite the recent increase in the development of bioactive molecules in the drug industry, the enormous chemical space and lack of productivity are still important issues. Additional alternative approaches to screen and locate bioactive molecules are urgently needed. Label-free bio-affinity mass spectrometry (BA-MS) provides opportunities for the discovery and development of innovative drugs. This review provides a comprehensive portrayal of BA-MS techniques and of their applications in screening and locating bioactive molecules. After introducing the basic principles, alongside some application notes, the current state-of-the-art of BA-MS-assisted drug discovery is discussed, including native MS, size-exclusion chromatography-MS, ultrafiltration-MS, solid-phase micro-extraction-MS, and cell membrane chromatography-MS. Finally, several challenges and limitations of the current methods are summarized, with a view to potential future directions for BA-MS-assisted drug discovery. © 2019 John Wiley & Sons Ltd. Mass Spec Rev.

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.

At-line LC-QTOF-MS micro-fractionation of Derris scandens (Roxb.) Benth, coupled to radioassay for the early identification of PDE5A1 inhibitors

INTRODUCTION

Chromatographic techniques coupled with bioassays are popularly used for the detection of bioactive compounds in natural products. In this study phytochemicals responsible for showing Phosphodiesterase type 5 (PDE5) inhibitory activity in Derris scandens were studied using at-line method.

OBJECTIVE

The objective of this study was to develop an at-line liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) micro-fractionation method for rapid separation and identification of PDE5A1 inhibitors in 95% ethanolic extract of D. scandens.

METHODOLOGY

Initially, the correlation between LC-MS and PDE5A1 inhibitory activity was studied using three concentrations of 1:1 mixture of sildenafil and derrisisoflavone A; PDE5A1 inhibitors. The mixture was separated by high-performance liquid chromatography (HPLC) column and the eluent was split into two flows in the ratio of 1:9. The major part was collected in a 96-well plate, in each well consecutively every 30 s. The minor part was fed into an electrospray ionisation (ESI)-QTOF-MS system. After subsequent solvent removal, the collected micro-fractions were subjected to radioassay to determine PDE5A1 inhibition.

RESULTS

The result showed, PDE5A1 inhibitory activities of the micro-fractions were observed in a dose response manner and found to be in agreement with an off-line study. Similarly, 95% ethanolic extract of D. scandens was subjected to the at-line LC-QTOF-MS micro-fractionation developed, resulting in separation and tentative identification of 25 compounds with PDE5A1 inhibitory activity. Most of the compounds contained prenylated isoflavone skeleton. Additionally, the active micro-fractions also showed selectivity on PDE5A1 over PDE6 and PDE1B.

CONCLUSION

Our results demonstrated that the at-line coupled LC-QTOF-MS micro-fractionation with PDE5A1 inhibitory assay is a valuable tool for identifying PDE5A1 inhibitors from complex extracts.

Bioactivity Profiling of Small-Volume Samples by Nano Liquid Chromatography Coupled to Microarray Bioassaying Using High-Resolution Fractionation

High-throughput screening platforms for the identification of bioactive compounds in mixtures have become important tools in the drug discovery process. Miniaturization of such screening systems may overcome problems associated with small sample volumes and enhance throughput and sensitivity. Here we present a new screening platform, coined picofractionation analytics, which encompasses microarray bioassays and mass spectrometry (MS) of components from minute amounts of samples after their nano liquid chromatographic (nanoLC) separation. Herein, nanoLC was coupled to a low-volume liquid dispenser equipped with pressure-fed solenoid valves, enabling 50-nL volumes of column effluent (300 nL/min) to be discretely deposited on a glass slide. The resulting fractions were dried and subsequently bioassayed by sequential printing of nL-volumes of reagents on top of the spots. Unwanted evaporation of bioassay liquids was circumvented by employing mineral oil droplets. A fluorescence microscope was used for assay readout in kinetic mode. Bioassay data were correlated to MS data obtained using the same nanoLC conditions in order to assign bioactives. The platform provides the possibility of freely choosing a wide diversity of bioassay formats, including those requiring long incubation times. The new method was compared to a standard bioassay approach, and its applicability was demonstrated by screening plasmin inhibitors and fibrinolytic bioactives from mixtures of standards and snake venoms, revealing active peptides and coagulopathic proteases.

Drug Discovery on Natural Products: From Ion Channels to nAChRs, from Nature to Libraries, from Analytics to Assays

Natural extracts are complex mixtures that may be rich in useful bioactive compounds and therefore are attractive sources for new leads in drug discovery. This review describes drug discovery from natural products and in explaining this process puts the focus on ion-channel drug discovery. In particular, the identification of bioactives from natural products targeting nicotinic acetylcholine receptors (nAChRs) and serotonin type 3 receptors (5-HT3Rs) is discussed. The review is divided into three parts: "Targets," "Sources," and "Approaches." The "Targets" part will discuss the importance of ion-channel drug targets in general, and the α7-nAChR and 5-HT3Rs in particular. The "Sources" part will discuss the relevance for drug discovery of finding bioactive compounds from various natural sources such as venoms and plant extracts. The "Approaches" part will give an overview of classical and new analytical approaches that are used for the identification of new bioactive compounds with the focus on targeting ion channels. In addition, a selected overview is given of traditional venom-based drug discovery approaches and of diverse hyphenated analytical systems used for screening complex bioactive mixtures including venoms.

Nanofractionation Platform with Parallel Mass Spectrometry for Identification of CYP1A2 Inhibitors in Metabolic Mixtures

With early assessment of inhibitory properties of drug candidates and their circulating metabolites toward cytochrome P450 enzymes, drug attrition, especially later in the drug development process, can be decreased. Here we describe the development and validation of an at-line nanofractionation platform, which was applied for screening of CYP1A2 inhibitors in Phase I metabolic mixtures. With this platform, a metabolic mixture is separated by liquid chromatography (LC), followed by parallel nanofractionation on a microtiter well plate and mass spectrometry (MS) analysis. After solvent evaporation, all metabolites present in the nanofractionated mixture are assayed utilizing a fluorescence CYP1A2 inhibition bioassay performed on the plate. Next, a bioactivity chromatogram is constructed from the bioassay results. By peak shape and retention time correlation of the bioactivity peaks with the obtained MS data, CYP1A2-bioactive inhibiting metabolites can be identified. The method correctly evaluated the potency of five CYP1A2 inhibitors. Mixtures comprising potent inhibitors of CYP1A2 or in vitro-generated metabolites of ellipticine were evaluated for their inhibitory bioactivities. In both cases, good LC separation of all compounds was achieved and bioactivity data could be accurately correlated with the parallel recorded MS data. Generation and evaluation of Phase II metabolites of hydroxylated ellipticine was also pursued.

A multiple biomarker assay for quality assessment of botanical drugs using a versatile microfluidic chip

Quality control is critical for ensuring the safety and effectiveness of drugs. Current quality control method for botanical drugs is mainly based on chemical testing. However, chemical testing alone may not be sufficient as it may not capture all constituents of botanical drugs. Therefore, it is necessary to establish a bioassay correlating with the drug's known mechanism of action to ensure its potency and activity. Herein we developed a multiple biomarker assay to assess the quality of botanicals using microfluidics, where enzyme inhibition was employed to indicate the drug's activity and thereby evaluate biological consistency. This approach was exemplified on QiShenYiQi Pills using thrombin and angiotensin converting enzyme as "quality biomarkers". Our results demonstrated that there existed variations in potency across different batches of the intermediates and preparations. Compared with chromatographic fingerprinting, the bioassay provided better discrimination ability for some abnormal samples. Moreover, the chip could function as "affinity chromatography" to identify bioactive phytochemicals bound to the enzymes. This work proposed a multiple-biomarker strategy for quality assessment of botanical drugs, while demonstrating for the first time the feasibility of microfluidics in this field.

Screening and evaluation of active compounds in polyphenol mixtures by HPLC coupled with chemical methodology and its application

An off-line high performance liquid chromatography (HPLC) coupled with chemical methods has been developed to evaluate antioxidant activity of 11 standard polyphenol compounds (SPCs) and vitamin C (Vc) in terms of radical scavenging abilities. The structure-activity relationships of each SPC were also discussed. SPCs showed different abilities in scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azinobis-3-ethyl-benzthiazoline-6-sulphonate (ABTS+) and hydroxyl (OH) free radicals. Among SPCs, quercetin and kaempferol, as typical flavonoids, displayed the greatest radical-scavenging activities and even exhibited higher activity in OH radical removal ability than that of Vc. Furthermore, the proposed method was also applied to screening polyphenolic antioxidant components from Cichorium endivia L. (C. endivia) seed extract. The results indicated that cynarin in the extract was a more active compound to scavenge DPPH and ABTS+ radicals than chlorogenic acid, while chlorogenic acid had stronger capacity in scavenging OH free radicals.

Statistical Correlations between HPLC Activity-Based Profiling Results and NMR/MS Microfraction Data to Deconvolute Bioactive Compounds in Mixtures

Recent approaches in natural product (NP) research are leading toward the discovery of bioactive chemical entities at the microgram level. In comparison to classical large scale bioassay-guided fractionation, the use of LC-MS metabolite profiling in combination with microfractionation for both bioactivity profiling and NMR analysis, allows the identification of bioactive compounds at a very early stage. In that context, this study aims to assess the potential of statistic correlation analysis to enable unambiguous identification of features related to bioactive compounds in mixtures, without the need for complete isolation. For that purpose, a mixture of NPs was microfractionated by rapid small-scale semi-preparative HPLC for proof-of-concept. UHPLC-ESI-TOFMS profiles, micro-flow CapNMR spectra and a cancer chemopreventive assay carried out on every microfraction were analysed by statistical correlations.

At-Line Cellular Screening Methodology for Bioactives in Mixtures Targeting the α7-Nicotinic Acetylcholine Receptor

The α7-nicotinic acetylcholine receptor (α7-nAChR) is a ligand-gated ion channel expressed in different regions of the central nervous system (CNS). The α7-nAChR has been associated with Alzheimer’s disease, epilepsy, and schizophrenia, and therefore is extensively studied as a drug target for the treatment of these diseases. Important sources for new compounds in drug discovery are natural extracts. Since natural extracts are complex mixtures, identification of the bioactives demands the use of analytical techniques to separate a bioactive from inactive compounds. This study describes screening methodology for identifying bioactive compounds in mixtures acting on the α7-nAChR. The methodology developed combines liquid chromatography (LC) coupled via a split with both an at-line calcium (Ca2+)-flux assay and high-resolution mass spectrometry (MS). This allows evaluation of α7-nAChR responses after LC separation, while parallel MS enables compound identification. The methodology was optimized for analysis of agonists and positive allosteric modulators, and was successfully applied to screening of the hallucinogen mushroom Psilocybe Mckennaii. The crude mushroom extract was analyzed using both reversed-phase and hydrophilic interaction liquid chromatography. Matching retention times and peak shapes of bioactives found with data from the parallel MS measurements allowed rapid pinpointing of accurate masses corresponding to the bioactives.

At-line coupling of LC-MS to bioaffinity and selectivity assessment for metabolic profiling of ligands towards chemokine receptors CXCR1 and CXCR2

This study describes an analytical method for bioaffinity and selectivity assessment of CXCR2 antagonists and their metabolites. The method is based on liquid chromatographic separation (LC) of metabolic mixtures followed by parallel mass spectrometry (MS) identification and bioaffinity determination. The bioaffinity is assessed using radioligand binding assays in 96-well plates after at-line nanofractionation. The described method was optimized for chemokines and low-molecular weight CXCR2 ligands. The limits of detection (LODs; injected amounts) for MK-7123, a high affinity binder to both CXCR1 and CXCR2 receptors belonging to the diaminocyclobutendione chemical class, were 40pmol in CXCR1 binding and 8pmol in CXCR2 binding. For CXCL8, the LOD was 5pmol in both binding assays. A control compound was always taken along with each bioassay plate as triplicate dose-response curve. For MK-7123, the calculated IC50 values were 314±59nM (CXCR1 binding) and 38±11nM (CXCR2 binding). For CXCL8, the IC50 values were 6.9±1.4nM (CXCR1 binding) and 2.7±1.3nM (CXCR2 binding). After optimization, the method was applied to the analysis of metabolic mixtures of eight LMW CXCR2 antagonists generated by incubation with pig liver microsomes. Moreover, metabolic profiling of the MK-7123 compound was described using the developed method. Three bioactive metabolites were found, two of which were (partially) identified. This method is suitable for bioaffinity and selectivity assessment of mixtures targeting the CXCR2. In contrary to conventional LC-MS based metabolic profiling studies done at the early lead discovery stage, additional qualitative bioactivity information of drug metabolites is obtained with the method described.

Microfluidic Chip–Based Online Screening Coupled to Mass Spectrometry

Thrombin and factor Xa (FXa) are critical enzymes of the blood coagulation cascade and are excellent targets of anticoagulant agents. Natural sources present an array of anticoagulants that can be developed as antithrombotic drugs. High-resolution, online screening techniques have been developed for the identification of drug leads from complex mixtures. In this study, we have developed and optimized a microfluidic online screening technique coupled to nano–liquid chromatography (LC) and in parallel with a mass spectrometer for the identification of thrombin and FXa inhibitors in mixtures. Inhibitors eluting from the nano-LC were split postcolumn in a 1:1 ratio; half was fed into a mass spectrometer (where its mass is detected), and the other half was fed into a microfluidic chip (which acts as a microreactor for the online assays). With our platform, thrombin and FXa inhibitors were detected in the assay in parallel with their mass identification. These methods are suitable for the identification of inhibitors from sample amounts as low as sub-microliter volumes.

Development of Plate Reader and On-Line Microfluidic Screening to Identify Ligands of the 5-Hydroxytryptamine Binding Protein in Venoms

The 5-HT3 receptor is a ligand-gated ion channel, which is expressed in the nervous system. Its antagonists are used clinically for treatment of postoperative- and radiotherapy-induced emesis and irritable bowel syndrome. In order to better understand the structure and function of the 5-HT3 receptor, and to allow for compound screening at this receptor, recently a serotonin binding protein (5HTBP) was engineered with the Acetylcholine Binding Protein as template. In this study, a fluorescence enhancement assay for 5HTBP ligands was developed in plate-reader format and subsequently used in an on-line microfluidic format. Both assay types were validated using an existing radioligand binding assay. The on-line microfluidic assay was coupled to HPLC via a post-column split which allowed parallel coupling to a mass spectrometer to collect MS data. This high-resolution screening (HRS) system is well suitable for compound mixture analysis. As a proof of principle, the venoms of Dendroapsis polylepis, Pseudonaja affinis and Pseudonaja inframacula snakes were screened and the accurate masses of the found bioactives were established. To demonstrate the subsequent workflow towards structural identification of bioactive proteins and peptides, the partial amino acid sequence of one of the bioactives from the Pseudonaja affinis venom was determined using a bottom-up proteomics approach.

Identification of photosynthesis inhibitors of pelagic marine algae using 96-well plate microfractionation for enhanced throughput in effect-directed analysis

Because of large-scale production and use of an increasing diversity of chemicals in modern society, estuarine and coastal waters may be contaminated with numerous substances. Some of these compounds have the potential to affect microalgae at the base of the pelagic food chain. Therefore, we identified the main chemical stressors that negatively affect the effective photosystem II efficiency (ϕPSII) in marine microalgae of the Dutch estuarine and coastal waters. An enhanced effect-directed analysis (EDA) was carried out by combining reversed-phase ultra performance liquid chromatography fractionation of extracts from passive samplers, followed by effect assessment using the pulse amplitude modulation fluorometry assay and chemical analysis of biologically active fractions using high-resolution mass spectrometry. This study focuses on a novel microfractionation technique using 96-well plates to enhance throughput in EDA, structure elucidation, and the analytical and effect confirmation of the compounds that are identified. Although there are numerous unknown compounds present in estuarine and coastal waters, our EDA study shows that atrazine, diuron, irgarol, isoproturon, terbutryn, and terbutylazine are the main contributors to the observed effect on the ϕPSII of marine microalgae.

High-resolution screening combined with HPLC-HRMS-SPE-NMR for identification of fungal plasma membrane H(+)-ATPase inhibitors from plants

Crude extracts of 33 plant species were assessed for fungal plasma membrane (PM) H(+)-ATPase inhibition. This led to identification of 18 extracts showing more than 95% inhibition at a concentration of 7.5 mg/mL and/or a concentration-dependent activity profile. These extracts were selected for semi-high-resolution fungal PM H(+)-ATPase inhibition screening, and, on the basis of these results, Haplocoelum foliolosum (Hiern) Bullock and Sauvagesia erecta L. were selected for investigation by high-resolution fungal PM H(+)-ATPase inhibition screening. Structural analysis performed by high-performance liquid chromatography-high-resolution mass spectrometry-solid-phase extraction-nuclear magnetic resonance spectroscopy (HPLC-HRMS-SPE-NMR) led to identification of chebulagic acid (1) and tellimagrandin II (2) from H. foliolosum. Preparative-scale isolation of the two metabolites allowed determination of IC50 values for PM H(+)-ATPase, and growth inhibition of Saccharomyces cerevisiae and Candida albicans. Chebulagic acid and tellimagrandin II are both potent inhibitors of the PM H(+)-ATPase with inhibitory effect on the growth of S. cerevisiae.

Miniaturized bioaffinity assessment coupled to mass spectrometry for guided purification of bioactives from toad and cone snail

A nano-flow high-resolution screening platform, featuring a parallel chip-based microfluidic bioassay and mass spectrometry coupled to nano-liquid chromatography, was applied to screen animal venoms for nicotinic acetylcholine receptor like (nAChR) affinity by using the acetylcholine binding protein, a mimic of the nAChR. The potential of this microfluidic platform is demonstrated by profiling the Conus textile venom proteome, consisting of over 1,000 peptides. Within one analysis (<90 min, 500 ng venom injected), ligands are detected and identified. To show applicability for non-peptides, small molecular ligands such as steroidal ligands were identified in skin secretions from two toad species (Bufo alvarius and Bufo marinus). Bioactives from the toad samples were subsequently isolated by MS-guided fractionation. The fractions analyzed by NMR and a radioligand binding assay with α7-nAChR confirmed the identity and bioactivity of several new ligands.

High-resolution screening combined with HPLC-HRMS-SPE-NMR for identification of potential health-promoting constituents in sea aster and searocket--new Nordic food ingredients

Sea aster (Aster tripolium L.) and searocket (Cakile maritima Scop.), potential ingredients in the New Nordic Diet, were analyzed by high-resolution radical scavenging and high-resolution α-glucosidase inhibition assays. Results from the two bioactivity profiles were used to guide subsequent structural analysis toward constituents with potential health-promoting effects. Structural analysis was performed by high-performance liquid chromatography-high-resolution mass spectrometry-solid-phase extraction and automated tube transfer nuclear magnetic resonance spectroscopy, that is, HPLC-HRMS-SPE-ttNMR. High-resolution mass spectrometry together with detailed analysis of one- and two-dimensional proton detected NMR experiments enabled unambiguous assignment of the targeted analytes. This revealed a series of caffeoyl esters (1, 2, 5), flavonoid glycosides (3, 4, 6, 11-15), flavonoids (7-9), sinapate esters (10, 16, 17), and sinapinic acid (18) associated with radical scavenging and/or α-glucosidase inhibition. In vitro assays implemented in this study showed that sea aster holds potential as a future functional food ingredient for lowering postprandial blood glucose level for diabetics, but further investigations are needed to prove the effect in vivo.

Tandem mass spectrometry study of p38α kinase inhibitors and related substances

The p38 mitogen-activated protein kinase α (p38α) is an important drug target widely investigated for therapy of chronic inflammatory diseases. Its inhibitors are rather lipophilic and as such not very favourable lead compounds in drug discovery. Therefore, we explored various approaches to access new chemical space, create diversity, and generate lead libraries with improved solubility and reduced lipophilicity, based on known p38α inhibitors, e.g., BIRB796 and TAK-715. Compound modification strategies include incubation with human liver microsomes and bacterial cytochrome P450 mutants from Bacillus megaterium and treatment by electrochemical oxidation, H2O2, and intense light irradiation. The MS/MS fragmentation pathways of p38α inhibitors and their conversion products have been studied in an ion-trap-time-of-flight MS(n) instrument. Interpretation of accurate mass MS(n) data for four sets of related compounds revealed unexpected and peculiar fragmentation pathways that are discussed in detail. Emphasis is put on the usefulness of HRMS(n)-based structure elucidation in a screening setting and on peculiarities of the fragmentation with regard to the analytes and the MS instrument. In one example, an intramolecular rearrangement reaction accompanied by the loss of a bulky group is observed. For BIRB796, the double-charge precursor ion is used in MS(2), providing a wider range of fragment ions in our instrument. For TAK-715, a number of related compounds could be produced in a large-scale incubation with a Bacillus megaterium mutant, thus enabling comparison of the structure elucidation by (1)H NMR and MS(n). A surprisingly large number of homolytic cleavages are observed. Competition between two fragmentation pathways involving either the loss of CH3(•) or OH(•) radicals was observed for SB203580 and its conversion products.

Development of On-line Liquid Chromatography-Biochemical Detection for Soluble Epoxide Hydrolase Inhibitors in Mixtures

In this study, an end-point-based fluorescence assay for soluble epoxide hydrolase (sEH) was transformed into an on-line continuous-flow format. The on-line biochemical detection system (BCD) was coupled on-line to liquid chromatography (LC) to allow mixture analysis. The on-line BCD was based on a flow system wherein sEH activity was detected by competition of analytes with the substrate hydrolysis. The reaction product was measured by fluorescence detection. In parallel to the BCD data, UV and MS data were obtained through post-column splitting of the LC effluent. The buffer system and reagent concentrations were optimized resulting in a stable on-line BCD with a good assay window and good sensitivity (S/N > 60). The potency of known sEH inhibitors (sEHis) obtained by LC-BCD correlates well with published values. The LC-BCD system was applied to test how oxidative microsomal metabolism affects the potency of three sEHis. After incubation with pig liver microsomes, several metabolites of sEHis were characterized by MS, while their individual potencies were measured by BCD. For all compounds tested, active metabolites were observed. The developed method allows for the first time the detection of sEHis in mixtures providing new opportunities in the development of drug candidates.

A unifying review of bioassay-guided fractionation, effect-directed analysis and related techniques

The success of modern methods in analytical chemistry sometimes obscures the problem that the ever increasing amount of analytical data does not necessarily give more insight of practical relevance. As alternative approaches, toxicity- and bioactivity-based assays can deliver valuable information about biological effects of complex materials in humans, other species or even ecosystems. However, the observed effects often cannot be clearly assigned to specific chemical compounds. In these cases, the establishment of an unambiguous cause-effect relationship is not possible. Effect-directed analysis tries to interconnect instrumental analytical techniques with a biological/biochemical entity, which identifies or isolates substances of biological relevance. Successful application has been demonstrated in many fields, either as proof-of-principle studies or even for complex samples. This review discusses the different approaches, advantages and limitations and finally shows some practical examples. The broad emergence of effect-directed analytical concepts might lead to a true paradigm shift in analytical chemistry, away from ever growing lists of chemical compounds. The connection of biological effects with the identification and quantification of molecular entities leads to relevant answers to many real life questions.

Development of on-line high performance liquid chromatography (HPLC)-biochemical detection methods as tools in the identification of bioactives

Biochemical detection (BCD) methods are commonly used to screen plant extracts for specific biological activities in batch assays. Traditionally, bioactives in the most active extracts were identified through time-consuming bio-assay guided fractionation until single active compounds could be isolated. Not only are isolation procedures often tedious, but they could also lead to artifact formation. On-line coupling of BCD assays to high performance liquid chromatography (HPLC) is gaining ground as a high resolution screening technique to overcome problems associated with pre-isolation by measuring the effects of compounds post-column directly after separation. To date, several on-line HPLC-BCD assays, applied to whole plant extracts and mixtures, have been published. In this review the focus will fall on enzyme-based, receptor-based and antioxidant assays.

Pharmaceutical and biomedical applications of affinity chromatography: recent trends and developments

Affinity chromatography is a separation technique that has become increasingly important in work with biological samples and pharmaceutical agents. This method is based on the use of a biologically related agent as a stationary phase to selectively retain analytes or to study biological interactions. This review discusses the basic principles behind affinity chromatography and examines recent developments that have occurred in the use of this method for biomedical and pharmaceutical analysis. Techniques based on traditional affinity supports are discussed, but an emphasis is placed on methods in which affinity columns are used as part of HPLC systems or in combination with other analytical methods. General formats for affinity chromatography that are considered include step elution schemes, weak affinity chromatography, affinity extraction and affinity depletion. Specific separation techniques that are examined include lectin affinity chromatography, boronate affinity chromatography, immunoaffinity chromatography, and immobilized metal ion affinity chromatography. Approaches for the study of biological interactions by affinity chromatography are also presented, such as the measurement of equilibrium constants, rate constants, or competition and displacement effects. In addition, related developments in the use of immobilized enzyme reactors, molecularly imprinted polymers, dye ligands and aptamers are briefly considered.

On-line electrochemistry-bioaffinity screening with parallel HR-LC-MS for the generation and characterization of modified p38α kinase inhibitors

In this study, an integrated approach is developed for the formation, identification and biological characterization of electrochemical conversion products of p38α mitogen-activated protein kinase inhibitors. This work demonstrates the hyphenation of an electrochemical reaction cell with a continuous-flow bioaffinity assay and parallel LC-HR-MS. Competition of the formed products with a tracer (SKF-86002) that shows fluorescence enhancement in the orthosteric binding site of the p38α kinase is the readout for bioaffinity. Parallel HR-MSⁿ experiments provided information on the identity of binders and non-binders. Finally, the data produced with this on-line system were compared to electrochemical conversion products generated off-line. The electrochemical conversion of 1-{6-chloro-5-[(2R,5S)-4-(4-fluorobenzyl)-2,5-dimethylpiperazine-1-carbonyl]-3aH-indol-3-yl}-2-morpholinoethane-1,2-dione resulted in eight products, three of which showed bioaffinity in the continuous-flow p38α bioaffinity assay used. Electrochemical conversion of BIRB796 resulted, amongst others, in the formation of the reactive quinoneimine structure and its corresponding hydroquinone. Both products were detected in the p38α bioaffinity assay, which indicates binding to the p38α kinase.

High-Resolution Bioactivity Profiling of Mixtures toward the Acetylcholine Binding Protein Using a Nanofractionation Spotter Technology

This study describes the evaluation, validation, and use of contactless postcolumn fractionation of bioactive mixtures with acetylcholine binding protein (AChBP) affinity analysis with help of a spotter technology. The high-resolution fractionation tailors the fractionation frequency to the chromatographic peaks. Postcolumn reagents for AChBP bioaffinity profiling are mixed prior to droplet ejection into 1536-well plates. After an incubation step, microplate reader analysis is used to determine bioactive compounds in a mixture. For ligands tested, a good correlation was found for IC50s determined in flow injection analysis mode when compared with traditional radioligand binding assays. After the evaluation and validation, bioaffinity profiling of actual mixtures was performed. The advantage of this “atline” technology using postcolumn bioaffinity analysis when compared to continuous flow online postcolumn bioaffinity profiling is the possibility to choose postcolumn incubation times freely without compromising resolution due to diffusion effects.

Functional proteomics: application of mass spectrometry to the study of enzymology in complex mixtures

This review covers recent developments in mass spectrometry-based applications dealing with functional proteomics with special emphasis on enzymology. The introduction of mass spectrometry into this research field has led to an enormous increase in knowledge in recent years. A major challenge is the identification of "biologically active substances" in complex mixtures. These biologically active substances are, on the one hand, potential regulators of enzymes. Elucidation of function and identity of those regulators may be accomplished by different strategies, which are discussed in this review. The most promising approach thereby seems to be the one-step procedure, because it enables identification of the functionality and identity of biologically active substances in parallel and thus avoids misinterpretation. On the other hand, besides the detection of regulators, the identification of endogenous substrates for known enzymes is an emerging research field, but in this case studies are quite rare. Moreover, the term biologically active substances may also encompass proteins with diverse biological functions. Elucidation of the functionality of those-so far unknown-proteins in complex mixtures is another branch of functional proteomics and those investigations will also be discussed in this review.