Preparation of an epitope-imprinted polymer with antibody-like selectivity for beta2-microglobulin and application in serum sample analysis with a facile method of on-line solid-phase extraction coupling with high performance liquid chromatography

Preparation of poly(caffeic acid)-coated epitope molecularly imprinted polymers and investigation of adsorption performance toward ovalbumin

Food allergy can lead to severe allergic reactions that are potentially fatal for human, hence the detection of food allergens such as ovalbumin (OVA) is important. In this study, a poly(caffeic acid)-coated epitope molecularly imprinted polymer (EMIP) was prepared by chelation and autoxidation of caffeic acid with hexamethylenediamine. EMIP has not only imprinted cavities highly matched with OVA in size and spatial structure, but also externally abundant hydrophilic groups, resulting in few non-specific binding and good hydrophilicity. With high specificity, significant paramagnetism, and great reusability, EMIP can distinguish OVA from other proteins and selectively enrich OVA in egg white samples, which opens up a promising route to the determination of allergens in food products.

Two-dimensional chromatography in screening of bioactive components from natural products

INTRODUCTION

Screening and analysis of bioactive components from natural products is a fundamental part of new drug development and innovation. Two-dimensional (2D) chromatography has been demonstrated to be an effective method for screening and preparation of specific bioactive components from complex natural products.

OBJECTIVE

To collect details of application of 2D chromatography in screening of natural product bioactive components and to outline the research progress of different separation mechanisms and strategies.

METHODOLOGY

Three screening strategies based on 2D chromatography are reviewed, including traditional separation-based screening, bioactivity-guided screening and affinity chromatography-based screening. Meanwhile, in order to cover these aspects, selections of different separation mechanisms and modes are also presented.

RESULTS

Compared with traditional one-dimensional (1D) chromatography, 2D chromatography has unique advantages in terms of peak capacity and resolution, and it is more effective for screening and identifying bioactive components of complex natural products.

CONCLUSION

Screening of natural bioactive components using 2D chromatography helps separation and analysis of complex samples with greater targeting and relevance, which is very important for development of innovative drug leads.

Lifting the Veil: Characteristics, Clinical Significance, and Application of β-2-Microglobulin as Biomarkers and Its Detection with Biosensors

Because β-2-microglobulin (β₂M) is a surface protein that is present on most nucleated cells, it plays a key role in the human immune system and the kidney glomeruli to regulate homeostasis. The primary clinical significance of β₂M is in dialysis-related amyloidosis, a complication of end-stage renal disease caused by a gradual accumulation of β₂M in the blood. Therefore, the function of β₂M in kidney-related diseases has been extensively studied to evaluate its glomerular and tubular functions. Because increased β₂M shedding due to rapid cell turnover may indicate other underlying medical conditions, the possibility to use β₂M as a versatile biomarker rose in prominence across multiple disciplines for various applications. Therefore, this work has reviewed the recent use of β₂M to detect various diseases and its progress as a biomarker. While the use of state-of-the-art β₂M detection requires sophisticated tools, high maintenance, and labor cost, this work also has reported the use of biosensor to quantify β₂M over the past decade. It is hoped that a portable and highly efficient β₂M biosensor device will soon be incorporated in point-of-care testing to provide safe, rapid, and reliable test results.

Controlled synthesis of open-mouthed epitope-imprinted polymer nanocapsules with a PEGylated nanocore and their application for fluorescence detection of target protein

Epitope imprinting is an effective way to create artificial receptors for protein recognition. Surface imprinting with immobilized templates and sacrificial supports can generate high-quality imprinted cavities of homogeneous orientation and good accessibility, but it is still challenging to fabricate nanoscale imprinted materials by this approach. Herein, we propose a method for the controlled synthesis of open-mouthed epitope-imprinted polymer nanocapsules (OM-MIP NCs) by limiting the imprinting polymerization on the template-bearing side of the Janus nanoparticles (JNPs). Concurrent bromoacetyl (Ac–Br) and 2-bromoisobutyryl (iB–Br) functionalization of the major portion of SiO₂ nanoparticles is achieved via the molten-wax-in-water Pickering emulsion approach. The cysteinyl-derived epitope templates are immobilized through the Ac–Br groups, and then surface imprinting is fulfilled via ATRP initiated by the iB–Br groups. The SiO₂ supports are partially etched and then PEGlated, affording OM-MIP NCs with a PEGylated nanocore. The inside nanocore can facilitate collection of the NCs by centrifugation, and its PEGylation can inhibit non-specific binding. The surface imprinting can be optimized through the ATRP time, and the etching can be tailored via the concentration of NH₄HF₂ employed. For proof-of-concept, with a C-terminus nonapeptide of bovine serum albumin (BSA) chosen as a model epitope and polymerizable carbon dots added to the pre-polymerization solution, fluorescent OM-MIP NCs were fabricated for BSA sensing. The as-synthesized NCs exhibited satisfactory detection performance, with an imprinting factor of 6.1, a limit of detection of 38.1 nM, a linear range of 0.25–6 μM, and recoveries of 98.0 to 104.0% in bovine serum samples.

Surface epitope imprinting over the one side of Janus SiO₂ NPs via ATRP affords open-mouthed epitope-imprinted nanocapsules with imprinted cavities of homogeneous orientation and good accessibility for fluorescence detection of target protein.

Epitope-imprinted polymers: applications in protein recognition and separation

Molecularly imprinted polymers (MIPs) have evolved as promising platforms for specific recognition of proteins. However, molecular imprinting of the whole protein molecule is complicated by its large size, conformational instability, and structural complexity. These inherent limitations can be overcome by using epitope imprinting. Significant breakthroughs in the synthesis and application of epitope-imprinted polymers (EIPs) have been achieved and reported. This review highlights recent advances in epitope imprinting, from the selection of epitope peptide sequences and functional monomers to the methods applied in polymerization and template removal. Technological innovations in detection and extraction of proteins by EIPs are also provided.

Facilitating serum determination of neuron specific enolase at clinically relevant levels by coupling on-line molecularly imprinted solid-phase extraction to LC-MS/MS

The identification and quantification of biomarkers is essential for the diagnosis, treatment, and long-term monitoring of many human diseases. In the present work, macromolecular synthetic receptors with pre-determined affinity and selectivity for the signature peptide of a prognostically significant small cell lung cancer (SCLC) biomarker - neuron-specific enolase (NSE) - were prepared in a porous polymer microsphere format using a template-directed synthesis strategy performed under precipitation polymerization conditions. The polymer microspheres were packed into short trap columns and then exploited as molecularly selective sorbents in a fully automated, on-line molecularly imprinted solid-phase extraction (MISPE) protocol. The on-line MISPE protocol was optimised with respect to the composition of the loading mobile phase, the flow rate, and the extraction time. The molecularly imprinted polymers (MIPs) showed high affinity and useful selectivity for the peptide target - the hexapeptide ELPLYR - compared to non-imprinted control polymers. The MIPs were able to retain the biomarker on-column for extraction times of up to 20 min, and the on-line MISPE method enabled complete recovery of the biomarker over the linear range 10-100 ng mL^-1 when the biomarker was present in spiked ammonium bicarbonate solution (R² = 0.994). For extractions of ELPLYR from very complex biological matrices, the recoveries of ELPLYR from reversed-phase SPE (RP-SPE)-treated and untreated digested human serum were 100.8 ± 6.2% and 61.6 ± 1.9%, respectively. Extractions of ELPLYR from spiked untreated digested serum were linear in the range of 7.5-375 ng mL^-1 (R² = 0.99). The limit of detection (LOD) and limit of quantification (LOQ) for the biomarker in digested serum were estimated to be 1.8 ng mL^-1 and 6.0 ng mL^-1, respectively, which is below the median reference level of NSE in humans (8.6 ng mL^-1). This work sets in place the basis for a new diagnostic tool for SCLC that is sensitive, robust, automated, and antibody-free, and which works very well with complex human plasma samples.

Cancer biomarker detection in human serum samples using nanoparticle decorated epitope-mediated hybrid MIP

The determination of disease-associated molecules at trace amounts is a key factor for early and efficient diagnosis from human body fluids. Herein, an ultrasensitive electrochemical sensor based on hybrid epitope imprinting and nanomaterial amplification was developed. The hybrid epitope imprinting was achieved by electropolymerization in the presence of two computationally selected and cysteine modified epitopes of neuron specific enolase (NSE), as-synthesized gold nanoparticles (AuNPs), and functional monomer. The AuNPs decorated epitope-mediated hybrid MIPs, as well as the standard hybrid MIPs, were utilized for the preparation of electrochemical sensors to demonstrate the impact of nanomaterial's modification in the polymer network for biomarker sensing. The fabrication process of both sensor types was investigated by employing cyclic voltammetry, square wave voltammetry, atomic force microscopy, and scanning electron microscopy. The biomarker assay using the standard hybrid MIPs resulted in 2.5-fold higher sensitivity compared to single epitope imprints, whereas the AuNP-hybrid MIPs enhanced the sensitivity level to a great extent and allowed the recognition of NSE in human serum in a concentration range of 25-4000 pg/mL. Comparative selectivity studies with non-imprinted polymer resulted in an imprinting factor of 4.2, confirming the high target selectivity of AuNP-MIP cavities. Cross-reaction of the sensor with four reference molecules (dopamine, bovine serum albumin, glucose and elongated peptide) was negligible. As compared to current strategies for epitope imprinting which rely on single epitopes for the formation of molecular cavities, the hybrid epitope-MIPs, particularly with the inclusion of AuNPs have provided more desirable sensing platforms with high sensitivity, affinity and specificity.

Application of molecularly imprinted polymers as artificial receptors for imaging

Medical diagnostics aims at specific localization of molecular targets as well as detection of abnormalities associated with numerous diseases. Molecularly imprinted polymers (MIPs) represent an approach of creating a synthetic material exhibiting selective recognition properties toward the desired template. The fabricated target-specific MIPs are usually well reproducible, economically efficient, and stable under critical conditions as compared to routinely used biorecognition elements such as fluorescent proteins, antibodies, enzymes, or aptamers and can even be created to those targets for which no antibodies are available. In this review, we summarize the methods of polymer fabrication. Further, we provide key for selection of the core material with imaging function depending on the imaging modality used. Finally, MIP-based imaging applications are highlighted and presented in a comprehensive form from different aspects. STATEMENT OF SIGNIFICANCE: In this review, we summarize the methods of polymer fabrication. Key applications of Molecularly imprinted polymers (MIPs) in imaging are highlighted and discussed with regard to the selection of the core material for imaging as well as commonly used imaging targets. MIPs represent an approach of creating a synthetic material exhibiting selective recognition properties toward the desired template. The fabricated target-specific MIPs are usually well reproducible, economically efficient, and stable under critical conditions as compared to routinely used biorecognition elements, e.g., antibodies, fluorescent proteins, enzymes, or aptamers, and can even be created to those targets for which no antibodies are available.

Advances in the development of molecularly imprinted polymers for the separation and analysis of proteins with liquid chromatography

This review documents recent advances in the design, synthesis, characterization, and application of molecularly imprinted polymers in the form of monoliths and particles/beads for the use in the separation and analysis of proteins with solid-phase extraction or liquid chromatography. The merits of three-dimensional molecular imprinting, whereby the molecular template is randomly embedded in the polymer, and two-dimensional imprinting, in which the template is confined to the surface, are described. Target protein binding can be achieved by either using the entire protein as a template or by using a protein substructure as template, that is, a peptide, as in the "epitope" approach. The intended approach and strategy then determine the choice of polymerization method. A synopsis has been provided on methods used for the physical, chemical, and functional characterizations and associated performance evaluations of molecularly imprinted and nonimprinted control polymers, involving a diverse range of analytical techniques commonly used for low and high molecular mass analytes. Examples of recent applications demonstrate that, due to the versatility of imprinting methods, molecularly imprinted monoliths or particles/beads can be adapted to protein extraction/depletion and separation procedures relevant to, for example, protein biomarker detection and quantification in biomedical diagnostics and targeted proteomics.

Simultaneous quantification of Cyt c interactions with HSP27 and Bcl-xL using molecularly imprinted polymers (MIPs) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based targeted proteomics

Cytochrome c (Cyt c) plays an important role in cell apoptosis. However, it could be functionally compromised by interaction with anti-apoptosis proteins, known as protein-protein interactions (PPIs). Among the proteins potentially interacting with Cyt c, both HSP27 and Bcl-xL serve as pivotal anti-apoptosis proteins. Because multiple PPIs, especially those involve the same protein, could affect each other, their simultaneous and quantitative detection is highly needed. In this study, a combined approach of molecularly imprinted polymers (MIPs) and LC-MS/MS-based targeted proteomics was developed for simultaneous quantification of Cyt c-HSP27 and Cyt c-Bcl-xL interactions. Surrogate peptides of Cyt c, HSP27 and Bcl-xL were first selected and used for the corresponding proteins quantification in targeted proteomics analysis. For MIPs, epitope approach was employed and a short peptide of Cyt c was selected as template for protein complexes recognition and enrichment. The characteristics of the synthesized MIPs including adsorption capacity, kinetics and efficiency were then evaluated. After validation, this combined assay was applied to quantitative analysis of total Cyt c including Cyt c in mitochondria and cytosol, total HSP27, total Bcl-xL and Cyt c-HSP27 and Cyt c-Bcl-xL protein complexes in breast cells. The result was also compared with that using Co-IP/Western Blotting. SIGNIFICANCE: Protein-protein interactions (PPIs) are essential for many cellular processes and the changes of PPIs are often associated with cellular dysfunction. More importantly, each protein typically has more than one interaction partner and multiple PPIs, especially those involve the same protein, could affect each other. The selectivity of these interactions determines the activities of proteins and further the developmental potential of the cell. Thus, simultaneous and quantitative detection of multiple PPIs is highly needed in biological research and related disciplines. However, it is still challenging to even qualitatively or semi-quantitatively analyze multiple PPIs because of the limitations of current experimental techniques for interaction detection. In this study, molecularly imprinted polymers (MIPs) epitope approach was combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) targeted proteomics for the simultaneous and quantitative detection of Cyt c-HSP27 and Cyt c-Bcl-xL interactions in breast cancer. Given high sensitivity, high selectivity and wide dynamic range of LC-MS/MS, MIPs approach was employed here to separate and enrich protein complexes prior to targeted proteomics analysis.