Separation and detection techniques for peptides and proteins in stability research and bioanalysis

Particle Detection and Characterization for Biopharmaceutical Applications: Current Principles of Established and Alternative Techniques

Detection and characterization of particles in the visible and subvisible size range is critical in many fields of industrial research. Commercial particle analysis systems have proliferated over the last decade. Despite that growth, most systems continue to be based on well-established principles, and only a handful of new approaches have emerged. Identifying the right particle-analysis approach remains a challenge in research and development. The choice depends on each individual application, the sample, and the information the operator needs to obtain. In biopharmaceutical applications, particle analysis decisions must take product safety, product quality, and regulatory requirements into account. Biopharmaceutical process samples and formulations are dynamic, polydisperse, and very susceptible to chemical and physical degradation: improperly handled product can degrade, becoming inactive or in specific cases immunogenic. This article reviews current methods for detecting, analyzing, and characterizing particles in the biopharmaceutical context. The first part of our article represents an overview about current particle detection and characterization principles, which are in part the base of the emerging techniques. It is very important to understand the measuring principle, in order to be adequately able to judge the outcome of the used assay. Typical principles used in all application fields, including particle–light interactions, the Coulter principle, suspended microchannel resonators, sedimentation processes, and further separation principles, are summarized to illustrate their potentials and limitations considering the investigated samples. In the second part, we describe potential technical approaches for biopharmaceutical particle analysis as some promising techniques, such as nanoparticle tracking analysis (NTA), micro flow imaging (MFI), tunable resistive pulse sensing (TRPS), flow cytometry, and the space- and time-resolved extinction profile (STEP^®) technology.

Identification and Detection of Bioactive Peptides in Milk and Dairy Products: Remarks about Agro-Foods

Food-based components represent major sources of functional bioactive compounds. Milk is a rich source of multiple bioactive peptides that not only help to fulfill consumers 'nutritional requirements but also play a significant role in preventing several health disorders. Understanding the chemical composition of milk and its products is critical for producing consistent and high-quality dairy products and functional dairy ingredients. Over the last two decades, peptides have gained significant attention by scientific evidence for its beneficial health impacts besides their established nutrient value. Increasing awareness of essential milk proteins has facilitated the development of novel milk protein products that are progressively required for nutritional benefits. The need to better understand the beneficial effects of milk-protein derived peptides has, therefore, led to the development of analytical approaches for the isolation, separation and identification of bioactive peptides in complex dairy products. Continuous emphasis is on the biological function and nutritional characteristics of milk constituents using several powerful techniques, namely omics, model cell lines, gut microbiome analysis and imaging techniques. This review briefly describes the state-of-the-art approach of peptidomics and lipidomics profiling approaches for the identification and detection of milk-derived bioactive peptides while taking into account recent progress in their analysis and emphasizing the difficulty of analysis of these functional and endogenous peptides.

Modulating the 3' end-DNA and the fermentation process for enhanced production and biological activity of porcine interferon-gamma

Porcine gamma interferon is a cytokine produced by activated T cells and NK cells with broad-spectrum antiviral activity and immunomodulatory function. However, pIFN-γ is a secretory protein that has a short half-life in organisms and is easily inactivated, making it difficult to apply widely in clinics. Therefore, we tried to optimize the expression of pIFN-γ in Pichia pastoris to obtain a large amount of highly active, easily purified pIFN-γ protein in vitro. Through C-terminal sequence analysis, we found a signal sequence (EKREAEAE) that was easily enzymolysed by a signal peptide enzyme, resulting in degradation and inactivation of the pIFN-γ protein. In this study, we optimized the pIFN-γ gene recombination sequence and mutated the 3' end of the pIFN-γ gene, resulting in a higher expression level and stronger biological activity, as well as a significant upregulation in the expression of the interferon-stimulated genes Mx1 and OAS1 in IPEC-J2 jejunal epithelial cells. Our data also showed that the fermentation process could significantly improve productivity. A recombinant Pichia pastoris strain with the optimized pIFN-γ gene could obtain a high yield of pIFN-γ protein, up to 9536 mg/L, after staged incubation for 0–24 h at 28°C, pH 6.0, and 50% dissolved oxygen (DO), followed by incubation for 24–72 h at 25°C, pH 6.0 and 30% DO. These data demonstrated, for the first time, that the expression level of pIFN-γ in Pichia pastoris was improved significantly by gene optimization with 3' end mutation and a fermentation process that maintained good biological activity, which is beneficial to the application of pIFN-γ in animal husbandry.

Whole-grain oats (Avena sativa L.) as a carrier of lactic acid bacteria and a supplement rich in angiotensin I-converting enzyme inhibitory peptides through solid-state fermentation

This study explored a novel strategy to develop solid-state whole-grain oats as a novel carrier of lactic acid bacteria and a nutraceutical supplement rich in ACE inhibitory peptides. Oats were fermented by Lactobacillus plantarum B1-6, Rhizopus oryzae, or a combination of L. plantarum B1-6 and R. oryzae. L. plantarum showed a much better growth performance in oats when it was combined with R. oryzae than when it was cultured alone, as evidenced by an increase in viable cell count to 9.70 log cfu g-1 after 72 h of fermentation. The coinoculated fermented oats (CFO) and the R. oryzae-fermented oats (RFO) were then selected for investigations on protein hydrolysis and on the functional properties of the released bioactive peptides. The results showed that the soluble protein contents changed from 7.05 mg g-1 to 14.43 and 10.21 mg g-1 for CFO and RFO, respectively. However, the degree of hydrolysis and the content of peptides with molecular masses less than 10 000 Da indicated that the CFO proteins can be degraded to a greater degree. As analyzed by electrophoresis and reversed-phase high-performance liquid chromatography, the protein and peptide profiles of CFO and RFO demonstrated that the proteins from CFO were more obviously hydrolyzed and more small peptides were obtained. In addition, both CFO and RFO presented higher ACE inhibitory activities than unfermented oats, whereas the protein extracts from CFO exerted a lower IC50 value of 0.42 mg protein per mL compared with the protein extracts from the other samples. This research has broadened our knowledge on the development of whole-grain oat products as a probiotic carrier and on the difference between mixed solid-state fermentation (SSF) and fungi SSF in terms of protein degradation and the capacity to release ACE inhibitory peptides. Our approach could be used to obtain probiotic food products and probably to develop oats as a potential therapeutic ingredient targeting hypertension.

Structure-informed detection and quantification of peptides in food and biological fluids

Peptides with biological properties, that is, bioactive peptides, are a class of biomolecules whose health-promoting properties are increasingly being exploited in food and health products. However, research on targeted techniques for the detection and quantification of these peptides is still in its infancy. Such information is needed in order to enhance the biological and chemometric characterization of peptides and their subsequent application in the functional food and pharmaceutical industries. In this review, the role of classic techniques such as electrophoretic, chromatographic, and peptide mass spectrometry in the structure-informed detection and quantitation of bioactive peptides are discussed. Prospects for the use of aptamers in the characterization of bioactive peptides are also discussed. PRACTICAL APPLICATIONS: Although bioactive peptides have huge potential applications in the functional foods and health area, there are limited techniques in enhancing throughput detection, quantification, and characterization of these peptides. This review discusses state-of-the-art techniques relevant in complementing bioactive detection and profiling irrespective of the small number of amino acid units. Insights into challenges, possible remedies and prevailing areas requiring thorough research in the extant literature for food chemists and biotechnologists are also presented.

Application of capability indices and control charts in the analytical method control strategy

In this study, we assessed the usefulness of control charts in combination with the process capability indices, C_pm and C_pk , in the control strategy of an analytical method. The traditional X-chart and moving range chart were used to monitor the analytical method over a 2-year period. The results confirmed that the analytical method is in-control and stable. Different criteria were used to establish the specifications limits (i.e. analyst requirements) for fixed method performance (i.e. method requirements). If the specification limits and control limits are equal in breadth, the method can be considered "capable" (C_pm  = 1), but it does not satisfy the minimum method capability requirements proposed by Pearn and Shu (2003). Similar results were obtained using the C_pk index. The method capability was also assessed as a function of method performance for fixed analyst requirements. The results indicate that the method does not meet the requirements of the analytical target approach. A real-example data of a SEC with light-scattering detection method was used as a model whereas previously published data were used to illustrate the applicability of the proposed approach.

Separation of peptides on superficially porous particle based macrocyclic glycopeptide liquid chromatography stationary phases: consideration of fast separations

Macrocyclic glycopeptide based liquid chromatography stationary phases are known for their highly selective peptide separations. Fast and ultrafast (t _R < 1 min) high-efficiency separations were achieved with superficially porous particle (SPP)-based stationary phases. Separations of pharmaceutically important classes of peptides such as enkephalins and bradykinins have been achieved in less than 5 min in isocratic elution modes. Selectivity for peptides structurally similar to one another was increased with use of teicoplanin-based stationary phases compared with commercial C₁₈ stationary phases. Ultrafast isocratic separations of structurally related peptides were achieved with teicoplanin- and vancomycin-based short SPP columns. Acidic mobile phases produced better separations. Ammonium formate was the optimal mobile phase buffer additive. Use of an appropriate combination of a macrocyclic glycopeptide stationary phase and a mobile phase permits faster and more electrospray ionization mass spectrometry compatible isocratic separations than previous gradient approaches. The tryptic peptide separation characteristics of the teicoplanin stationary phase are demonstrated. Additionally, compared with commercial C₁₈ stationary phases, teicoplanin showed tryptic peptide separations with different selectivities. Graphical Abstract Ultrafast separation of enkephalin peptide epimers.

Pre-study and in-study validation of a size-exclusion chromatography method with different detection modes for the analysis of monoclonal antibody aggregates

Size exclusion chromatography (SEC) with different detection modes was assessed as a means to characterize the type of bevacizumab aggregate that forms under thermal stress, quantitatively monitoring the aggregation kinetics. The combination of SEC with light-scattering (SEC/LS) detection was validated using in-study validation process. This was performed by applying a strategy based on a control chart to monitor the process parameters and by inserting quality control samples in routine runs. The SEC coupled with a differential refractive-index detector (SEC/RI) was validated using a pre-study validation process in accordance with the ICH-Q2 (R1) guidelines and in-study monitoring in accordance with the Analytical Target Profile (ATP) criteria. The total error and β-expectation tolerance interval rules were used to assess method suitability and control the risk of incorrectly accepting unsuitable analytical methods. The aggregation kinetics data were interpreted using a modified Lumry-Eyring model. The true order of the reaction was determined using the initial-rate approach. All the kinetic data show a linear Arrhenius dependence within the studied temperature range. The Arrhenius approach over-predicted the aggregation rate for 5°C, but provides an idea of the aggregation process and amount of aggregate formed. In any case, real-time stability data are necessary to establish the product shelf-life.

Preventive and therapeutic potential of peptides from cereals against cancer

Epidemiological studies have shown that regular consumption of food based on whole-grain cereals and their products is associated with reduced risks of various types of degenerative chronic diseases. Food proteins are considered an important source of nutraceutical peptides and amino acids that can exert biological functions to promote health and prevent disease, including cancer. There have been several reports on peptides with anti-tumour activity in recent years. Plant-derived peptides, such as rapeseed, amaranth and soybean lunasin have received main attention. In this review, we extend this vision to analyse the evidence of current advances in peptides in cereals such as wheat, maize, rice, barley, rye and pseudocereals compared with soybean. We also show evidence of several mechanisms through which bioactive peptide exerts anti-tumour activity. Finally, we report the current status of major strategies for the fractionation, isolation and characterisation of bioactive peptides in cereals.

BIOLOGICAL SIGNIFICANCE

In recent reports, it has been shown that peptides are an interesting alternative in the search for new treatments for cancer. One of the most studied sources of these peptides is food proteins; however, a review that includes more recent findings for cereals as a potential source of bioactive peptides in the treatment of cancer, the techniques for their isolation and characterisation and the assays used to prove their bioactivity is not available. This review can be used as a tool in the search for new sources of anti-cancer peptides. The authors have no conflicts of interest, financial or otherwise.

Effect of high shear rate on stability of proteins: kinetic study

Size-exclusion chromatography (SEC) was used to monitor the time-course of protein degradation induced by high shear rates during the formulation and manufacture of controlled-release pharmaceutical dosage forms. SEC with multi-angle laser light-scattering (MALLS) detection was used to characterize the aggregation products, determining their absolute molecular weight. A stability-indicating method was developed and validated to obtain reliable drug degradation data. The results obtained according to the ICH guidelines confirm that the system and methods proposed are suitable for their intended use. The degradation kinetics are influenced by the type of protein and the effect of the shear rate on their stability. Reversible pseudo-first order degradation kinetics were observed for bovine beta-lactoglobulin, whereas for human (HSA) and bovine serum albumin (BSA), a monomer-dimer transition was observed, independently of the rate of shear. However, trimer formation was also observed for HSA, especially at high shear rates. The kinetic model may thus be described as a two-step process: a monomer-dimer, and dimer-trimer transition.

Characterization of antimalarial SPf66 peptide using MALDI-TOF MS, CD and SEC

SPf66 is the first chemically synthesized peptide to elicit a partial protective immune response against malaria. Size-exclusion chromatography (SEC) with multi-angle laser light-scattering (MALLS) detection and hydrogen/deuterium (H/D) exchange monitored by (matrix-assisted laser desorption/ionization) MALDI-TOF (time-of-flight) mass spectrometry (MS) were used to assess the conformation and stability in aqueous solution after storage at different temperatures. Moreover, the feasible conformational changes of this peptide were also measured by circular dichroism (CD)-spectroscopy. The absolute molecular weight of SPf66 monomer and dimer species were 4765 and 8960Da using SEC with MALLS detection, and 4643 and 9490Da by MALDI-TOF MS, the discrepancy being between both methods lower than 5.7%, a value quite close to those found in other proteins. The results from H/D exchange monitored by MALDI-TOF MS and CD-spectroscopy show that the SPf66 monomer lacks ordered structure, whereas the SPf66 dimer species presents segments of secondary structure as a determined by CD measurements.

Chromatographic characterization of synthetic peptides: SPf66 malaria vaccine

The development and validation of a quantitative size-exclusion chromatography (SEC) method for SPf66 malaria vaccine was achieved. The results show the reliability of the analytical method for the intended use. SPf66 malaria vaccine characterization was perforrmed using both relative techniques such as the conventional SEC and absolute techniques: mass spectrometry and multi-angle laser-light scattering detection. The relative and absolute molecular masses were in the 4600-18,000 Da range. The results clearly indicate the presence of the monomer and dimer species, whereas the third species could be the trimer or tetramer.

Recent advances in capillary electrophoresis of peptides

The article gives a comprehensive review on the recent developments in the applications of high-performance capillary electromigration methods, including zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography and electrochromatography, to analysis, preparation and physicochemical characterization of peptides. The article presents new approaches to the theoretical description and experimental verification of electromigration behavior of peptides, and covers the methodological aspects of capillary electroseparations of peptides, such as strategy and rules for the rational selection of separation mode and experimental conditions, sample treatment, suppression of peptide adsorption to the inner capillary wall, new developments in individual separation modes and new designs of detection systems. Several types of applications of capillary electromigration methods to peptide analysis are presented: conventional qualitative and quantitative analysis for determination of purity, determination in biomatrices, monitoring of physical and chemical changes and enzymatic conversions, amino acid and sequence analysis and peptide mapping of proteins. Some examples of micropreparative peptide separations are given and capabilities of capillary electromigration techniques to provide important physicochemical characteristics of peptides are demonstrated.