High performance affinity chromatography and related separation methods for the analysis of biological and pharmaceutical agents

Screening and analysis of the targeted compounds in Choerospondias axillaris extract by receptor chromatographic column with immobilized angiotensin II type 1 receptor

As a result of the lack of modern techniques, the study of Tibetan medicine has been hindered in identifying bioactive compounds. Herein, we established a chromatographic approach using an immobilized angiotensin II type 1 receptor (AT1R) via a one-step method triggered by haloalkane dehalogenase. The bioactive compounds from Choerospondias axillaris (Guangzao) were screened and identified using the immobilized AT1R followed by MS. Frontal analysis (FA) and adsorption energy distribution (AED) were used to evaluate the association constants. Molecular docking was used to investigate the binding configurations, and the surface efficiency index, binding efficiency index, and ligand-lipophilicity efficiency (LLE) were calculated to assess the drug-like properties. The results identified naringenin, pinocembrin, and chrysin as the compounds that specifically bind to AT1R in Guangzao. FA and AED confirmed that there is only one type of binding site between these compounds and AT1R. The association constants were (2.40 ± 0.02) × 104 M-1 for naringenin (5.22 ± 0.26) × 104 M-1 for pinocembrin, and (4.27 ± 0.14) × 104 M-1 for chrysin, respectively. These compounds can bind with AT1R through the orthosteric binding pocket. Naringenin exhibited better LLE than pinocembrin and chrysin. These results confirmed the feasibility of using the immobilized AT1R column for screening and analyzing bioactive compounds in Tibetan medicines.

A case study application of AQbD to the re-development and validation of an affinity chromatography analytical procedure for mAb titer quantitation

Protein A (ProA) high-performance liquid chromatography (HPLC) is a common analytical procedure for measuring monoclonal antibody (mAb) titers due to its high specificity and efficiency. Accurate and reliable results of this procedure are imperative, as the quantitation of the total mAb present for in-process samples directly impacts downstream purification steps related to the removal of process-related impurities. This study aimed to improve a platform ProA HPLC analytical procedure which was previously developed using traditional approaches and was not always reliable. By retrospectively applying Analytical Quality by Design (AQbD) principles and statistical assessments of performance, a bias in the calibration standard due to protein-adsorption to common sample vial materials was identified. The inclusion of Tween® 20 into the mobile phase used as sample diluent was optimized to ensure procedure performance and improve analytical range. The resulting procedure robustness was evaluated using Design of Experiment (DoE) approaches and performance was verified against Analytical Target Profile (ATP) criteria as recommended by regulatory agencies. The resulting linearity displayed R2 values of 1.00 with intercept biases of 1.2 % (analyst 1) and 0.8 % (analyst 2), accuracy across all levels was reported at 99.2 % recovery, and intermediate precision was reported as 3.0 % RSD. Application of this new platform procedure has since reduced development timelines for new mAb products by 50 % and allowed for accurate titer determination to support >5 early phase product-specific process decisions without requiring extensive analytical procedure development. This work demonstrates the utility and relative ease of adopting AQbD concepts, even for established procedures, and supporting them with a lifecycle approach to managing procedure performance.

Impact of proteins and protein fouling on virus retention during virus removal filtration

Virus filtration is a crucial step in ensuring the high levels of viral clearance required in the production of biotherapeutics produced in mammalian cells or derived from human plasma. Previous studies have reported that virus retention is often reduced in the presence of therapeutic proteins due to membrane fouling; however, the underlying mechanisms controlling this behavior are still not well understood. Experimental studies were performed with a single layer of the commercially available dual-layer PegasusTM SV4 virus removal filter to more easily interpret the experimental results. Bacteriophage ФX174 was used as a model parvovirus, and human immunoglobulin (hIgG) and Bovine Serum Albumin (BSA) were used as model proteins. Data obtained with 5 g/L solutions of hIgG showed more than a 100-fold reduction in virus retention compared to that in the protein-free solution. Similar effects were seen with membranes that were pre-fouled with hIgG and then challenged with ФX174. The experimental data were well-described using an internal polarization model that accounts for virus capture and accumulation within the virus filter, with the hIgG nearly eliminating the irreversible virus capture while also facilitating the release of previously captured virus. These results provide important insights into the performance and validation of virus removal filters in bioprocessing.

A review of aptamer-conjugated nanomaterials for analytical sample preparation: Classification according to the utilized nanomaterials

BACKGROUND

Sample extraction before detection is a critical step in analysis. Since targets of interest are often found in complex matrices, the sample can not be directly introduced to the analytical instrument. Nanomaterials with unique physical-chemical properties are excellent supports for use in sorbent-based extraction. However, they lack selectivity and thus need to be functionalized with target-capturing molecules. Antibodies and molecularly imprinted polymers (MIPs) can be used for this purpose, but they have some problems that limit their practical applications. Hence, functionalization of nanomaterials for selectivity remains a problem.

RESULTS

Nucleic acid aptamers are affinity reagents that can provide superiority to antibodies since they can be selected in vitro and at a lower cost. Moreover, aptamers can be chemically synthesized and easily modified with different functional groups. Hence, aptamers are good candidates to impart selectivity to the nanomaterials. Recent studies focus on the integration of aptamers with magnetic nanoparticles, carbon-based nanomaterials, metal-organic frameworks, gold nanoparticles, gold nanorods, silica nanomaterials, and nanofibers. The unique properties of nanomaterials and aptamers make the aptamer-conjugated nanomaterials attractive for use in sample preparation. Aptamer-functionalized nanomaterials have been successfully used for selective extraction of proteins, small molecules, and cells from different types of complex samples such as serum, urine, and milk. In particular, magnetic nanoparticles have a wider use due to the rapid extraction of the sample under magnetic field.

SIGNIFICANCE

In this review, we aim to emphasize how beneficial features of nanomaterials and aptamers could be combined for extraction or enrichment of the analytes from complex samples. We aim to highlight that the benefits are twofold in terms of selectivity and efficiency when employing nanomaterials and aptamers together as a single platform.

Review of Eukaryote Cellular Membrane Lipid Composition, with Special Attention to the Fatty Acids

Biological membranes, primarily composed of lipids, envelop each living cell. The intricate composition and organization of membrane lipids, including the variety of fatty acids they encompass, serve a dynamic role in sustaining cellular structural integrity and functionality. Typically, modifications in lipid composition coincide with consequential alterations in universally significant signaling pathways. Exploring the various fatty acids, which serve as the foundational building blocks of membrane lipids, provides crucial insights into the underlying mechanisms governing a myriad of cellular processes, such as membrane fluidity, protein trafficking, signal transduction, intercellular communication, and the etiology of certain metabolic disorders. Furthermore, comprehending how alterations in the lipid composition, especially concerning the fatty acid profile, either contribute to or prevent the onset of pathological conditions stands as a compelling area of research. Hence, this review aims to meticulously introduce the intricacies of membrane lipids and their constituent fatty acids in a healthy organism, thereby illuminating their remarkable diversity and profound influence on cellular function. Furthermore, this review aspires to highlight some potential therapeutic targets for various pathological conditions that may be ameliorated through dietary fatty acid supplements. The initial section of this review expounds on the eukaryotic biomembranes and their complex lipids. Subsequent sections provide insights into the synthesis, membrane incorporation, and distribution of fatty acids across various fractions of membrane lipids. The last section highlights the functional significance of membrane-associated fatty acids and their innate capacity to shape the various cellular physiological responses.

Enantioselective voltammetric sensor based on mesoporous graphitized carbon black Carbopack X and fulvene derivative

For medicine and pharmaceuticals, the problem of determining and recognizing the enantiomers of biologically active compounds is an actual issue because the enantiomers of the same substance can have different effects on living organisms. This paper describes the development of an enantioselective voltammetric sensor (EVS) based on a glassy carbon electrode (GCE) modified with mesoporous graphitized carbon black Carbopack X (CpX) and a fulvene derivative (1S,4R)-2-cyclopenta-2,4-dien-1-ylidene-1-isopropyl-4-methylcyclohexane (CpIPMC) for recognition and determination of tryptophan (Trp) enantiomers. Synthesized CpIPMC was characterized by 1 H and 13 C nuclear magnetic resonance (NMR), chromatography-mass spectrometry, and polarimetry. The proposed sensor platform was studied by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Using the square-wave voltammetry (SWV), it was established that the developed sensor is an effective chiral platform for the quantitative determination of Trp enantiomers, including in a mixture and in biological fluids like urine and blood plasma, with adequate precision and recovery ranged from 96% to 101%.

Evaluation of covalent coupling strategies for immobilizing ligands on silica colloidal crystal films by optical interferometry

Immobilizing ligands is a crucial part of preparing optical sensors and directly connected to the sensitivity, stability, and other characteristics of sensors. In this work, an ordered porous layer interferometry (OPLI) system that can monitor the covalent coupling process of ligands in real time was developed. Films of silica colloidal crystal (SCC), as optical interference substrates, were surface modified by three different reagents: chloroacetic acid, glutaric anhydride, and carboxymethyl dextran. Staphylococcus aureus protein A (SPA), the ligand, was immobilized on SCC films. The covalent coupling process of SPA and SCC films can be dynamically monitored by the OPLI system. In addition, the three different strategies were evaluated by comparing the efficiency of the sensors prepared by different methods for binding Immunoglobulin G (IgG). The glutaric anhydride-modified sensor offers apparent advantages in terms of bound IgG quantity and affinity. This system provides a simple and intuitive way to determine the efficiency of different covalent coupling strategies. Furthermore, the sensor covalently coupled with SPA also excels in the determination of IgG content in complex systems such as milk. At the same time, the covalent coupling gives the sensor the ability to be stored stably over time.

Measurement of Protein Kinetics Using a Liquid Phase-Based Biosensing Platform

Macromolecular association is crucial to many fields in biomedical sciences, including drug development, gene editing, and diagnostics. In particular, protein-protein association and dissociation rate constants are typically determined using surface plasmon resonance systems, which require costly instrumentation and cumbersome procedures (e.g., blocking, washing, and separation). Herein, we demonstrate that protein-binding constants can be readily determined using a real-time biosensing platform facilitated by graphene oxide-modified microwell plates and fluorophore-labeled proteins, where the fluorescent probes remain highly fluorescent during protein association, whereas fluorescent bioprobes that are not associated with their counterparts are quenched by graphene oxide. Binding data of three pairs of proteins were systematically determined employing this single-step platform and compared with those data reported by the suppliers or the literature, suggesting that this approach is comparable and consistent with the existing ones. Such pairs include (i) human immunoglobulin G (H-IgG)-fluorophore-labeled anti-H-IgG, (ii) prostate-specific antigen (PSA)-quantum dot-labeled anti-PSA, and (iii) anti-RBD-fluorophore-labeled SARS-CoV-2 spike receptor-binding domain recombinant protein. We also offer an open-source software that automatically determines the binding kinetics constants of proteins. This Technical Note introduces a simple, yet effective, platform to determine relevant information on protein kinetics, which can be performed using a microwell plate reader and economical materials like graphene oxide. We foresee a new generation of diagnostics based on our affordable protein kinetics analysis.

Plasmonic Nanosensors: Design, Fabrication, and Applications in Biomedicine

Current advances in the fabrication of smart nanomaterials and nanostructured surfaces find wide usage in the biomedical field. In this context, nanosensors based on localized surface plasmon resonance exhibit unprecedented optical features that can be exploited to reduce the costs, analytic times, and need for expensive lab equipment. Moreover, they are promising for the design of nanoplatforms with multiple functionalities (e.g., multiplexed detection) with large integration within microelectronics and microfluidics. In this review, we summarize the most recent design strategies, fabrication approaches, and bio-applications of plasmonic nanoparticles (NPs) arranged in colloids, nanoarrays, and nanocomposites. After a brief introduction on the physical principles behind plasmonic nanostructures both as inherent optical detection and as nanoantennas for external signal amplification, we classify the proposed examples in colloid-based devices when plasmonic NPs operate in solution, nanoarrays when they are assembled or fabricated on rigid substrates, and nanocomposites when they are assembled within flexible/polymeric substrates. We highlight the main biomedical applications of the proposed devices and offer a general overview of the main strengths and limitations of the currently available plasmonic nanodevices.

Towards continuous mAb purification: clearance of host cell proteins from CHO cell culture harvests via "flow-through affinity chromatography" using peptide-based adsorbents

The growth of advanced analytics in manufacturing monoclonal antibodies (mAb) has highlighted the challenges associated with the clearance of host cell proteins (HCPs). Of special concern is the removal of "persistent" HCPs, including immunogenic and mAb-degrading proteins, that co-elute from the Protein A resin and can escape the polishing steps. Responding to this challenge, we introduced an ensemble of peptide ligands that target the HCPs in Chinese hamster ovary (CHO) cell culture fluids and enable mAb purification via flow-through affinity chromatography. This work describes their integration into LigaGuardTM, an affinity adsorbent featuring an equilibrium binding capacity of ~30 mg of HCPs per mL of resin as well as dynamic capacities up to 16 and 22 mg/mL at 1- and 2-minute residence times, respectively. When evaluated against cell culture harvests with different mAb and HCP titers and properties, LigaGuardTM afforded high HCP clearance, with logarithmic removal values (LRVs) up to 1.5, and mAb yield above 90%. Proteomic analysis of the effluents confirmed the removal of high-risk HCPs, including cathepsins, histones, glutathione-S transferase, and lipoprotein lipases. Finally, combining LigaGuardTM for HCP removal with affinity adsorbents for product capture afforded a global mAb yield of 85%, and HCP and DNA LRVs > 4. This article is protected by copyright. All rights reserved.

Entrapment of Proteins Within Columns for High-Performance Affinity Chromatography

Entrapment is a noncovalent immobilization method that enables a large biological binding agent, such as a protein, to be put within a support without modifying the structure of the binding agent. This chapter describes an on-column entrapment method that can be used with proteins and HPLC-grade silica to prepare columns for high-performance liquid chromatography. In this method, a protein is trapped within a dihydrazide-activated silica support by using oxidized glycogen as a capping agent. This method allows the protein to be placed within the support in a soluble form and with little or no loss of activity. The approach and reagents needed for this method are described in this chapter, along with some applications reported for columns that have been made using on-column protein entrapment.

Two Original Experimental Setups for Staircase Frontal Affinity Chromatography at the Miniaturized Scale

Frontal affinity chromatography is a powerful, underappreciated technique for the qualitative (screening) and quantitative (K_d determination) evaluation of biological interactions. Its development has been previously hampered by its sample consumption, limited throughput, and lack of dedicated instrumentation especially at a miniaturized scale. This work describes two original experimental devices allowing nano-frontal affinity chromatography titrations (nano-FAC) to be automatically implemented in the time-saving staircase mode. The first nano-FAC system utilizes a capillary electrophoresis device (7100 CE Agilent system) in the pressurization mode with in situ UV detection. The second nano-FAC experimental setup implements a nano-LC device (Ultimate 3000 Thermo) modified with a 10-port valve equipped with two superloops (loop volume, 5 μL) operating alternatively and automatically in a single run. The benefits and drawbacks of each approach are exemplified using two model protein-ligand interactions (concanavalin A-mannose and concanavalin A-glucose). The two methods result in concordant dissociation constants (K_d) and number of active site (B_act) values, obtained in a fully automated manner, with low sample consumption and good throughput.

Targeting and Covalently Immobilizing the EGFR through SNAP-Tag Technology for Screening Drug Leads

Membrane protein immobilization is particularly significant in in vitro drug screening and determining drug-receptor interactions. However, there are still some problems in the immobilization of membrane proteins with controllable direction and high conformational stability, activity, and specificity. Cell membrane chromatography (CMC) retains the complete biological structure of membrane proteins. However, conventional CMC has the limitation of poor stability, which results in its limited life span and low reproducibility. To overcome this limitation, we propose a method for the specific covalent immobilization of membrane proteins in cell membranes. We used the SNAP-tag as an immobilization tag fused to the epidermal growth factor receptor (EGFR), and Cys145 located at the active site of the SNAP-tag reacted with the benzyl group of O⁶-benzylguanine (BG). The SNAP-tagged EGFR was expressed in HEK293 cells. We captured the SNAP-tagged EGFR from the cell membrane suspension onto a BG-derivative-modified silica gel. Our immobilization strategy improved the life span and specificity of CMC and minimized loss of activity and nonspecific attachment of proteins. Next, a SNAP-tagged EGFR/CMC online HPLC-IT-TOF-MS system was established to screen EGFR antagonists from Epimedii folium. Icariin, magnoflorine, epimedin B, and epimedin C were retained in this model, and pharmacological assays revealed that magnoflorine could inhibit cancer cell growth by targeting the EGFR. This EGFR immobilization method may open up possibilities for the immobilization of other membrane proteins and has the potential to serve as a useful platform for screening receptor-binding leads from natural medicinal herbs.

Affinity monolith chromatography: A review of general principles and recent developments

Affinity monolith chromatography (AMC) is a liquid chromatographic technique that utilizes a monolithic support with a biological ligand or related binding agent to isolate, enrich, or detect a target analyte in a complex matrix. The target-specific interaction exhibited by the binding agents makes AMC attractive for the separation or detection of a wide range of compounds. This article will review the basic principles of AMC and recent developments in this field. The supports used in AMC will be discussed, including organic, inorganic, hybrid, carbohydrate, and cryogel monoliths. Schemes for attaching binding agents to these monoliths will be examined as well, such as covalent immobilization, biospecific adsorption, entrapment, molecular imprinting, and coordination methods. An overview will then be given of binding agents that have recently been used in AMC, along with their applications. These applications will include bioaffinity chromatography, immunoaffinity chromatography, immobilized metal-ion affinity chromatography, and dye-ligand or biomimetic affinity chromatography. The use of AMC in chiral separations and biointeraction studies will also be discussed.

Investigation of lipase-ligand interactions in porcine pancreatic extracts by microscale thermophoresis

The evaluation of binding affinities between large biomolecules and small ligands is challenging and requires highly sensitive techniques. Microscale thermophoresis (MST) is an emerging biophysical technique used to overcome this limitation. This work describes the first MST binding method to evaluate binding affinities of small ligands to lipases from crude porcine pancreatic extracts. The conditions of the MST assay were thoroughly optimized to successfully evaluate the dissociation constant (K_d) between pancreatic lipases (PL) and triterpenoid compounds purified from oakwood. More precisely, the fluorescent labeling of PL (PL*) using RED-NHS dye was achieved via a buffer exchange procedure. The MST buffer was composed of 20 mM NaH₂PO₄ + 77 mM NaCl (pH 6.6) with 0.05% Triton-X added to efficiently prevent protein aggregation and adsorption, even when using only standard, uncoated MST capillaries. Storage at -20 °C ensured stability of PL* and its fluorescent signal. MST results showed that crude pancreatic extracts were suitable as a source of PL for the evaluation of binding affinities of small ligands. Quercotriterpenoside-I (QTT-I) demonstrated high PL* binding affinity (31 nM) followed by 3-O-galloylbarrinic acid (3-GBA) (500 nM) and bartogenic acid (BA) (1327 nM). To enrich the 50 kDa lipase responsible for the majority of hydrolysis activity in the crude pancreatic extracts, ammonium sulfate precipitation was attempted and its efficiency confirmed using capillary electrophoresis (CE)-based activity assays and HRMS. Moreover, to accurately explain enzyme modulation mechanism, it is imperative to complement binding assays with catalytic activity ones.

Rapid screening of bioactive compound in Sanzi Yangqin Decoction and investigating of binding mechanism by immobilized β2-adrenogic receptor chromatography coupled with molecular docking

Screening bioactive compounds from traditional Chinese medicines plays pivotal role in preventing and curing diseases. Sanzi Yangqin Decoction (SYD) is a commonly used prescription for the treatment of cough, asthma and some other respiratory diseases for hundreds of years in practice. This reminds us that there may exist some bioactive compounds strongly binding with the recognized receptors mediating these diseases like β₂-adrenegic receptor (β₂-AR). Therefore, this work intends to screen bioactive compounds from SYD and revealed the binding mechanism by immobilized β₂-AR chromatography and molecular docking. Taking advantages of a 3-high based enzymatic trans-methylation reaction (high speed, high specificity and high activity), the immobilization of β₂-AR was successfully achieved. Representative chromatographic peaks of SYD on the immobilized β₂-AR column was collected and recognized as rosmarinic acid and sinapine thiocyanate. Tension changes of the trachea ring showed that the two compounds were in a concentration-dependent manner when exerting their effects and the concentration ranges were 10^-9-10^-4 mol/L and 10^-12-10^-7 mol/L, respectively. Molecular docking revealed Ser203, Ser204, Ser207, Tyr316 and Asn312 were the main residues for the two compounds to bind with β₂-AR. We concluded that the proposed method is becoming an alternative in rapid recognizing bioactive compounds from complex matrix.

Affinity chromatography: A review of trends and developments over the past 50 years

The field of affinity chromatography, which employs a biologically-related agent as the stationary phase, has seen significant growth since the modern era of this method began in 1968. This review examines the major developments and trends that have occurred in this technique over the past five decades. The basic principles and history of this area are first discussed. This is followed by an overview of the various supports, immobilization strategies, and types of binding agents that have been used in this field. The general types of applications and fields of use that have appeared for affinity chromatography are also considered. A survey of the literature is used to identify major trends in these topics and important areas of use for affinity chromatography in the separation, analysis, or characterization of chemicals and biochemicals.

Encapsulation-Controlled Photoisomerization of a Styryl Derivative: Stereoselective Formation of the Anti Z-Isomer in the Cucurbit[7]uril Cavity

The photochemical isomerization of a styrylpyridinium dye (SP) bearing an unsymmetrically attached benzo-15-crown-5 ether has been studied in aqueous solution in the absence and presence of cucurbit[7]uril (CB[7]). The detailed analysis of the UV/Vis and NMR spectra showes that the isomeric composition of the photostationary mixtures of SP can be modulated by the host-guest complexation with CB[7]. It was found that steric hindrance caused by encapsulation of SP in the host cavity induces the exclusive formation of the anti conformer of Z-SP in contrast with the mixture of both anti and syn conformers obtained during photoisomerization of the dye without CB[7]. Remarkably, the displacement of anti Z-SP from CB[7] does not lead to the transformation of the anti Z-isomer into the syn Z-isomer pointing out the conformational memory of the system. The results provide an interesting example of the supramolecular stereorecognition by the achiral CB[7] host.

Towards Peptide and Protein Recognition by Antibody Mimicking Synthetic Polymers – Background, State of the Art, and Future Outlook

Antibody–peptide/protein interactions are instrumental for many processes in the pharmaceutical and biotechnology industries and as tools for biomedical and biochemical research. The recent development of molecularly imprinted polymer nanoparticles displaying antibody-like recognition of peptides and proteins offers the possibility for substituting antibodies with these robust materials for applications where the structural integrity and function of antibodies is compromised by temperature, pH, solvent, etc. The background to the development of this class of antibody-mimicking material and the state-of-the-art in their synthesis and application is presented in this review.

An alternative approach for the preparation of a core–shell bimetallic central metal–organic framework as a hydrophilic interaction liquid chromatography stationary phase

A new type of core–shell composite material was prepared and applied as a hydrophilic interaction liquid chromatography (HILIC) stationary phase.

Development of an on-line immunoextraction/entrapment system for protein capture and use in drug binding studies by high-performance affinity chromatography

An on-line purification and entrapment system was developed that could extract a protein from a sample such as serum and entrap this protein within a small column for use in high-performance affinity chromatography. Human serum albumin (HSA) was employed as a model protein for this work. Immunoextraction columns containing polyclonal anti-HSA antibodies were developed to capture and isolate HSA from applied samples. This was followed by the use of a strong cation-exchange column to recapture and focus HSA as it eluted from the immunoextraction columns. The recaptured HSA was entrapped within 1.0 cm × 2.1 mm I.D. columns containing hydrazide-activated silica and in the presence of oxidized glycogen as a capping agent. The binding and elution properties of HSA on the various components of this system were examined and optimized. The entrapped columns produced by this system were then evaluated for their use in binding studies with several sulfonylurea drugs. The HSA columns created by this approach typically contained 0.3-0.6 nmol HSA and were stable over several weeks and more than 50-60 sample injections. Drug binding constants could be determined with these columns in 8 min or less by zonal elution and gave good agreement with literature values. The same system could be used for the capture and entrapment of other proteins by utilizing antibodies against the given target for immunoextraction.

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.

Kinetic Analysis by Affinity Chromatography

Important information on chemical processes in living systems can be obtained by the rates at which these biological interactions occur. This review will discuss several techniques based on traditional and high-performance affinity chromatography that may be used to examine the kinetics of biological reactions. These methods include band-broadening measurements, techniques for peak fitting, split-peak analysis, peak decay studies, and ultrafast affinity extraction. The general principles and theory of each method, as applied to the determination of rate constants, will be discussed. The applications of each approach, along with its advantages and limitations, will also be considered.

Development of a microcolumn one-site immunometric assay for a protein biomarker: Analysis of alpha1-acid glycoprotein

A one-site immunometric assay based on affinity microcolumns was developed for the analysis of alpha₁-acid glycoprotein (AGP) as a model protein biomarker. In this assay, a sample containing AGP was incubated with an excess amount of a labeled binding agent, such as fluorescein-labeled anti-AGP antibodies or F_ab fragments. The excess binding agent was removed by passing this mixture through a microcolumn that contained an immobilized form of AGP, while the signal was measured for the binding agent-AGP complex in the non-retained fraction. Theoretical and practical factors were both considered in selecting the concentration of labeled binding agent, the incubation time of this agent with the sample, and the application conditions for this mixture onto the microcolumn. The effects of using various labeling methods and intact antibodies vs F_ab fragments were also considered. The final assay was performed with fluorescein-labeled anti-AGP antibodies and a 2.1 mm i.d. × 1.0 cm AGP microcolumn operated at 0.30 mL min^-1. This method required only 1 µL of serum or plasma, had a detection limit of 0.63 nM AGP, and gave a potential throughput of 2 min per sample. This assay was used to measure AGP in normal serum and plasma from patients with systemic lupus erythematosus, giving good agreement with the literature and a reference method. The same approach and guidelines can be used to create assays for other protein biomarkers by changing the labeled binding agent and immobilized protein within the microcolumn.

Development and evaluation of silica-based lectin microcolumns for glycoform analysis of alpha1-acid glycoprotein

Silica-based lectin microcolumns were developed and optimized for the separation and analysis of glycoform fractions in alpha₁-acid glycoprotein (AGP) based on both the degree of branching and level of fucosylation. Concanavalin A (Con A) and Aleuria Aurantia lectin (AAL) were immobilized onto HPLC-grade silica by reductive amination and packed into 2.1 mm i.d. × 5.0 cm microcolumns. Factors examined for these microcolumns include their protein content, binding capacity, binding strength and band-broadening under isocratic conditions (Con A) or step elution conditions (AAL) and in the presence of various flow rates or temperatures. These factors were examined by using experiments based on frontal analysis, zonal elution, peak profiling and peak decay analysis. Up to 200 μg AGP could be loaded onto a Con A microcolumn and provide linear elution conditions, and 100 μg AGP could be applied to an AAL microcolumn. The final conditions for separating retained and non-retained AGP glycoform fractions on a Con A microcolumn used a flow rate of 50 μL min^-1 and a temperature of 50 °C, which gave a separation of these fractions within 20 min or less. The final conditions for an AAL microcolumn included a flow rate of 0.75 mL min^-1, a temperature of 50 °C, and the use of 2.0 mM l-fucose as a competing agent for elution, giving a separation of non-retained and retained AGP glycoforms in 6 min or less. The inter-day precisions were ±0.7-4.0% or less for the retention times of the AGP glycoforms and ±2.2-3.0% or less for their peak areas.

Optimization of protein entrapment in affinity microcolumns using hydrazide-activated silica and glycogen as a capping agent

Several approaches were compared for the entrapment of proteins within hydrazide-activated silica for use in affinity microcolumns and high performance affinity chromatography. Human serum albumin (HSA) and concanavalin A (Con A) were used as model proteins for this work. Items considered in this study included the role played by the solution volume, amount of added protein, and use of slurry vs. on-column entrapment on the levels of solute retention and extent of protein immobilization that could be obtained by means of entrapment. The levels of retention and protein immobilization were evaluated by injecting warfarin or 4-methylumbellipheryl α-D-mannopyranoside as solutes with known binding properties for HSA or Con A. Altering both the solution volume and amount of added protein led to an increase of up to 17-fold in the extent of protein immobilization for HSA in slurry-based entrapment; on-column entrapment provided an additional 3.6-fold increase in protein content vs. the optimized slurry method. Similar general trends were seen for Con A. The protein contents obtained by entrapment for HSA or Con A (i.e., up to ~87 and 46 mg/g silica, respectively) were comparable to or higher than levels reported for the covalent immobilization of these proteins onto silica. The retention of warfarin on the entrapped HSA was at least 1.7-fold higher than has been obtained under comparable support and mobile phase conditions when using covalent immobilization. These results indicated that entrapment can be an attractive alternative to covalent immobilization for proteins such as HSA and Con A, with this approach serving as a potential means for obtaining good solute binding and retention in work with affinity microcolumns or related microscale devices.

Route and Type of Formulation Administered Influences the Absorption and Disposition of Vitamin B12 Levels in Serum

The administration of biological compounds that optimize health benefits is an ever-evolving therapeutic goal. Pharmaceutical and other adjunctive biological compounds have been administered via many different routes in order to produce a systemic pharmacological effect. The article summarizes the findings from an Australian comparative study in adults administered vitamin B₁₂ through different oral delivery platforms. A total of 16 subjects (9 males, 7 females) voluntarily partook in a comparative clinical study of five different vitamin B₁₂ formulations across a six-month period, completing 474 person-hours of cumulative contribution, that was equivalent to an n = 60 participation. A nanoparticle delivered vitamin B₁₂ through a NanoCelle platform was observed to be significantly (p < 0.05) better absorbed than all other dose equivalent platforms (i.e., tablets, emulsions, or liposomes) from baseline to 1, 3, and 6 h of the study period. The nanoparticle platform delivered vitamin B₁₂ demonstrated an enhanced and significant absorption profile as exemplified by rapid systemic detection (i.e., 1 h from baseline) when administered to the oro-buccal mucosa with no reports of any adverse events of toxicity. The nanoparticle formulation of methylcobalamin (1000 µg/dose in 0.3 mL volume) showed bioequivalence only with a chewable-dissolvable tablet that administered a five times higher dose of methylcobalamin (5000 µg) per tablet. This study has demonstrated that an active metabolite embedded in a functional biomaterial (NanoCelle) may constitute a drug delivery method that can better access the circulatory system.