Flow field-flow fractionation: Recent applications for lipidomic and proteomic analysis

Exosomes, and the potential for exosome-based interventions against COVID-19

Since late 2019, the world has been devastated by the coronavirus disease 2019 (COVID-19) induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with more than 760 million people affected and ∼seven million deaths reported. Although effective treatments for COVID-19 are currently limited, there has been a strong focus on developing new therapeutic approaches to address the morbidity and mortality linked to this disease. An approach that is currently being investigated is the use of exosome-based therapies. Exosomes are small, extracellular vesicles that play a role in many clinical diseases, including viral infections, infected cells release exosomes that can transmit viral components, such as miRNAs and proteins, and can also include receptors for viruses that facilitate viral entry into recipient cells. SARS-CoV-2 has the ability to impact the formation, secretion, and release of exosomes, thereby potentially facilitating or intensifying the transmission of the virus among cells, tissues and individuals. Therefore, designing synthetic exosomes that carry immunomodulatory cargo and antiviral compounds are proposed to be a promising strategy for the treatment of COVID-19 and other viral diseases. Moreover, exosomes generated from mesenchymal stem cells (MSC) might be employed as cell-free therapeutic agents, as MSC-derived exosomes can diminish the cytokine storm and reverse the suppression of host anti-viral defences associated with COVID-19, and boost the repair of lung damage linked to mitochondrial activity. The present article discusses the significance and roles of exosomes in COVID-19, and explores potential future applications of exosomes in combating this disease. Despite the challenges posed by COVID-19, exosome-based therapies could represent a promising avenue for improving patient outcomes and reducing the impact of this disease.

Comparison of a thickness-tapered channel in flow field-flow fractionation with a conventional channel with flow rate programming

The thickness-tapered channel structure in flow field-flow fractionation (FlFFF), recently introduced by constructing a channel with a linear decrease in thickness along its length, demonstrated effectiveness in steric/hyperlayer separation of supramicron particles with improvements in separation speed, elution recovery, and an expanded dynamic size range of separation. In this study, we conducted a comparative analysis of the performance between the impact of field (or crossflow rate) programming or outflow rate programming for the separation of polystyrene latex standards (50 ∼ 800 nm) with a conventional channel having uniform thickness and a thickness-tapered channel without programming. Outlet flow rate and crossflow rate conditions were also varied. Although the particle size resolution of the tapered channel does not surpass that of field programming in uniform thickness channel, it achieves higher-speed separation without a significant loss of resolution and without the need for a complex flow controller system even at a low outflow rate condition. Furthermore, it yielded an improved resolution for particles close to the steric transition regime (400 ∼ 600 nm) in the normal mode of separation. Due to the continuous increase in mean flow velocity down the channel, the tapered channel exhibits flexibility in separating submicron-sized particles at high crossflow rate conditions or low outflow rate conditions, of which the latter can be advantageous when coupled with mass spectrometry in a miniaturized setup.

In situ characterization of silver nanoparticles sulfidation processes in aquatic solution by hollow fiber flow-field flow fractionation coupled with ICP-QQQ

The sulfidation is considered as one of the most important environmental transformation processes of silver nanoparticles (AgNPs), which affects their transport, uptake and toxicity. Herein, based on the hollow fiber flow-field flow fractionation coupled with triple quadrupole inductively coupled plasma mass spectrometry (HF5-ICP-QQQ), we developed an efficient approach to accurately characterize the sulfidation process of AgNPs in aquatic solutions. HF5 could efficiently remove interferential ions and separate nanoparticles with different sizes online, and ICP-QQQ could accurately detect S element through monitoring 32S16O+ in mass shift mode. By the proposed method, two kinds of AgNPs, citrate-coated AgNPs and PVP-coated AgNPs, were selected as models to trace their transfer behaviors during the sulfidation. The results showed once AgNPs were exposed to Na2S solution, the overlapping fractograms of 32S16O+ and 107Ag+ were rapidly detected by HF5-ICP-QQQ to indicate the co-presence of Ag and S, and thus confirming the production of Ag2S and AgNPs underwent a rapid sulfidation process. There were substantial differences in the influence of the two coated agents on the stability of the particles under the conditions examined. In the presence of sulfide, PVP-coated AgNPs could maintain initial size distribution with higher stability, while the size distribution of citrate-coated AgNPs changed considerably. The developed HF5-ICP-QQQ method provides a reliable tool to identify and characterize the transformation process of AgNPs in aquatic solution, which contributed to a deeper understanding of the environmental fate and behavior of AgNPs with different coating.

Size exclusion chromatography of biopharmaceutical products: From current practices for proteins to emerging trends for viral vectors, nucleic acids and lipid nanoparticles

The 21st century has been particularly productive for the biopharmaceutical industry, with the introduction of several classes of innovative therapeutics, such as monoclonal antibodies and related compounds, gene therapy products, and RNA-based modalities. All these new molecules are susceptible to aggregation and fragmentation, which necessitates a size variant analysis for their comprehensive characterization. Size exclusion chromatography (SEC) is one of the reference techniques that can be applied. The analytical techniques for mAbs are now well established and some of them are now emerging for the newer modalities. In this context, the objective of this review article is: i) to provide a short historical background on SEC, ii) to suggest some clear guidelines on the selection of packing material and mobile phase for successful method development in modern SEC; and iii) to highlight recent advances in SEC, such as the use of narrow-bore and micro-bore columns, ultra-wide pore columns, and low-adsorption column hardware. Some important innovations, such as recycling SEC, the coupling of SEC with mass spectrometry, and the use of alternative detectors such as charge detection mass spectrometry and mass photometry are also described. In addition, this review discusses the use of SEC in multidimensional setups and shows some of the most recent advances at the preparative scale. In the third part of the article, the possibility of SEC for the characterization of new modalities is also reviewed. The final objective of this review is to provide a clear summary of opportunities and limitations of SEC for the analysis of different biopharmaceutical products.

Changes in cargoes of platelet derived extracellular vesicles heterogeneous subpopulations induced by PM0.1--Undisclosed cardiovascular injury communication mechanism

Epidemiological evidence has indicated a closely link between PM0.1 exposure and the incidence rate of cardiovascular diseases. This study explores the underlying communication roles of platelet-derived extracellular vesicles (PEVs) heterogeneous subpopulations in cardiovascular injury. PEVs and PMEVs which were extracted from platelet-rich plasma (PRP) un-exposure or exposure to PM0.1 by TIM4 affinity beads. By optimizing separation conditions, replacing pipelines, and resetting injection procedures, Asymmetric flow field-flow fractionation (AF4) was employed to separate, purify, characterize, and enrich PEVs and PMEVs heterogeneous subpopulations (small PEVs, PEVs-S/PMEVs-S: <100 nm; medium PEVs, PEVs-M/PMEVs-M: 100-200 nm; and large PEVs, PEVs-L/PMEVs-L: >200 nm). The results showed that the cargoes of PMEVs heterogeneous subpopulations which were released by PRP stimulated by PM0.1 were changed obviously. Moreover, compared with PEVs, PMEVs can lead to a decrease in the survival rate of Human Umbilical Vein Endothelial Cells (HUVECs). In PMEVs-S subpopulations, the alterations of lipids associated with membrane fusion and cell signaling transport (such as PC, Cer), as well as miRNAs related to inflammation, angiogenesis, and migration (miR-223, miR-22, miR-126, and miR-150), are similar to those in PMEVs-M subpopulations but distinct from PMEVs-L subpopulations. This study revealed the diverse communication mechanisms underlying PM0.1-induced cardiovascular injury, thereby offering potential avenues for the development of new biomarkers and therapeutic targets.

Field-flow fractionation - an excellent tool for fractionation, isolation and/or purification of biomacromolecules

Field-flow fractionation (FFF) with its several variants, has developed into a mature methodology. The scope of the FFF investigations has expanded, covering both a wide range of basic studies and especially a wide range of analytical applications. Special attention of this review is given to the achievements of FFF with reference to recent applications in the fractionation, isolation, and purification of biomacromolecules, and from which especially those of (in alphabetical order) bacteria, cells, extracellular vesicles, liposomes, lipoproteins, nucleic acids, and viruses and virus-like particles. In evaluating the major approaches and trends demonstrated since 2012, the most significant biomacromolecule applications are compiled in tables. It is also evident that asymmetrical flow field-flow fractionation is by far the most dominant technique in the studies. The industry has also shown current interest in FFF and adopted it in some sophisticated fields. FFF, in combination with appropriate detectors, handles biomacromolecules in open channel in a gentle way due to the lack of shear forces and unwanted interactions caused by the stationary phase present in chromatography. In addition, in isolation and purification of biomacromolecules quite high yields can be achieved under optimal conditions.

Liposomes characterization for market approval as pharmaceutical products: Analytical methods, guidelines and standardized protocols

Liposomes are nano-sized lipid-based vesicles widely studied for their drug delivery capabilities. Compared to standard carries they exhibit better properties such as improved site-targeting and drug release, protection of drugs from degradation and clearance, and lower toxic side effects. At present, scientific literature is rich of studies regarding liposomes-based systems, while 14 types of liposomal products have been authorized to the market by EMA and FDA and many others have been approved by national agencies. Although the interest in nanodevices and nanomedicine has steadily increased in the last two decades the development of documentation regulating and standardizing all the phases of their development and quality control still suffers from major inadequacy due to the intrinsic complexity of nano-systems characterization. Many generic documents (Type 1) discussing guidelines for the study of nano-systems (lipidic and not) have been proposed while there is a lack of robust and standardized methods (Type 2 documents). As a result, a widespread of different techniques, approaches and methodologies are being used, generating results of variable quality and hard to compare with each other. Additionally, such documents are often subject to updates and rewriting further complicating the topic. Within this context the aim of this work is focused on bridging the gap in liposome characterization: the most recent standardized methodologies suitable for liposomes characterization are here reported (with the corresponding Type 2 documents) and revised in a short and pragmatical way focused on providing the reader with a practical background of the state of the art. In particular, this paper will put the accent on the methodologies developed to evaluate the main critical quality attributes (CQAs) necessary for liposomes market approval.

Realizing the AF4-UV-SAXS on-line coupling on protein and antibodies using high flux synchrotron radiation at the CoSAXS beamline, MAX IV

In this paper, we demonstrate the coupling of synchrotron small angle X-ray scattering (SAXS) to asymmetrical flow-field flow fractionation (AF4) for protein characterization. To the best of our knowledge, this is the first time AF4 is successfully coupled to a synchrotron for on-line measurements on proteins. This coupling has potentially high impact, as it opens the possibility to characterize individual constituents of sensitive and/or complex samples, not suited for separation using other techniques, and for low electron density samples where high X-ray flux is required, e.g., biomolecules and biologics. AF4 fractionates complex samples in native or close to native environment, with low shear forces and system surface area. Many orders of magnitude in size can be fractionated in one measurement, without having to reconfigure the experimental setup. We report AF4 fractionations with correlated UV and statistically adequate SAXS data of bovine serum albumin and a monoclonal antibody and evaluate SAXS data recorded for the two protein systems.

Optimization for size separation of graphene oxide sheets by flow/hyperlayer field-flow fractionation

Graphene oxide (GO)-a chemical derivative of graphene with numerous oxygen functional groups on its surface-has attracted considerable interest because of its intriguing properties in relation to those of pristine graphene. In addition to the inherent wide lateral size distribution of GO sheets arising from the typical oxidative exfoliation of graphite, control of the lateral size of GO is critical for desired GO-based applications. Herein, flow/hyperlayer field-flow fractionation (flow/hyperlayer FFF) is optimized to separate GO sheets by lateral dimensions. Optimized fractionation is achieved by investigating the influences of carrier solvent, channel thickness, and flow rate conditions on the steric/hyperlayer separation of GO sheets by flow FFF. Due to the strong hydrodynamic lift forces of extremely thin GO sheets, a thick flow FFF channel (w = 350 μm) and a very low field strength are required to retain the GO sheets within the channel. GO sheets with narrow size fractions are successfully collected from two different graphite sources during flow/hyperlayer FFF runs and are examined to verify the size evolution. Considering the average lateral diameter of the GO fraction calculated on the basis of the assumption of a circular disk shape, the retention of the GO sheets is 2.2-5.0 times faster than that of spherical particles of the same diameter. This study demonstrates that through flow/hyperlayer FFF, the size distribution of GO sheets can be determined and narrow size fractions can be collected (which is desirable for GO-based applications), which are commonly influenced by the GO lateral dimension.

Flow Field-Flow Fractionation with a Thickness-Tapered Channel

This study introduces the thickness-tapered channel design for flow field-flow fractionation (FlFFF) for the first time. In this design, the channel thickness linearly decreases along the channel axis such that the flow velocity increases down the channel. Channel thickness is an important variable for controlling retention time and resolution in field-flow fractionation. Especially, in the steric/hyperlayer mode of FlFFF, in which particles (>1 μm) migrate at elevated heights above the channel wall owing to hydrodynamic lift forces, the migration of long-retaining smaller-sized particles can be enhanced in a relatively thin channel or by increasing the migration flow rate; however, an upper size limit that can be resolved is simultaneously sacrificed. A thickness-tapered channel was constructed without a channel spacer by carving the surface of a channel block such that the channel inlet was deeper than the outlet (w = 400 → 200 μm). The performance of a thickness-tapered channel was evaluated using polystyrene standards and compared to that of a channel of uniform thickness (w = 300 μm) with a similar effective channel volume in terms of sample recovery, dynamic size range of separation, and steric transition under different flow rate conditions. The thickness-tapered channel can be an alternative to maintain the resolving power for particles with an upper large-diameter limit, faster separation of particles with a lower limit, and higher elution recovery without implementing the additional field-programming option.

Size Separation of Exosomes and Microvesicles Using Flow Field-Flow Fractionation/Multiangle Light Scattering and Lipidomic Comparison

Extracellular vesicles (EVs) are cell-derived membrane-bound particles, including exosomes and microvesicles that differ in cellular origin, content, and lipid composition. This study reports that exosomes and microvesicles can be simultaneously separated by size using flow field-flow fractionation (FlFFF) employed with field programming and that the detection of low-concentration EV species can be significantly improved using multiangle light scattering (MALS). The efficiency of ultracentrifugation (UC) and ultrafiltration (UF) in isolating EVs from the culture media of DU145 cells was compared, and the results showed that UF retrieves more EVs than UC. Two size fractions (small and large) of both exosomes and microvesicles were collected during the FlFFF runs and examined using Western blotting to confirm each EV, and transmission electron microscopy was performed for size analysis. Sizes were compared using the root-mean-square radius obtained from the MALS calculation. The collected fractions were further examined using nanoflow ultrahigh-performance liquid chromatography-electrospray ionization-tandem mass spectrometry for the size-dependent lipidomic profiles of exosomes and microvesicles, showing that lipids were more enriched in the fraction containing large exosomes than in that containing small exosomes; however, an opposite trend was observed with microvesicles. The present study demonstrated that UF followed by FlFFF-MALS can be utilized for the size separation of exosomes and microvesicles without sequential centrifugation, which is useful for monitoring the changes in the size distribution of EVs depending on the biological status along with generating size-dependent lipidomic profiles.

Subcellular Transcriptomics and Proteomics: A Comparative Methods Review

The internal environment of cells is molecularly crowded, which requires spatial organization via subcellular compartmentalization. These compartments harbor specific conditions for molecules to perform their biological functions, such as coordination of the cell cycle, cell survival, and growth. This compartmentalization is also not static, with molecules trafficking between these subcellular neighborhoods to carry out their functions. For example, some biomolecules are multifunctional, requiring an environment with differing conditions or interacting partners, and others traffic to export such molecules. Aberrant localization of proteins or RNA species has been linked to many pathological conditions, such as neurological, cancer, and pulmonary diseases. Differential expression studies in transcriptomics and proteomics are relatively common, but the majority have overlooked the importance of subcellular information. In addition, subcellular transcriptomics and proteomics data do not always colocate because of the biochemical processes that occur during and after translation, highlighting the complementary nature of these fields. In this review, we discuss and directly compare the current methods in spatial proteomics and transcriptomics, which include sequencing- and imaging-based strategies, to give the reader an overview of the current tools available. We also discuss current limitations of these strategies as well as future developments in the field of spatial -omics.

Label-Free Isolation of Exosomes Using Microfluidic Technologies

Exosomes are cell-derived structures packaged with lipids, proteins, and nucleic acids. They exist in diverse bodily fluids and are involved in physiological and pathological processes. Although their potential for clinical application as diagnostic and therapeutic tools has been revealed, a huge bottleneck impeding the development of applications in the rapidly burgeoning field of exosome research is an inability to efficiently isolate pure exosomes from other unwanted components present in bodily fluids. To date, several approaches have been proposed and investigated for exosome separation, with the leading candidate being microfluidic technology due to its relative simplicity, cost-effectiveness, precise and fast processing at the microscale, and amenability to automation. Notably, avoiding the need for exosome labeling represents a significant advance in terms of process simplicity, time, and cost as well as protecting the biological activities of exosomes. Despite the exciting progress in microfluidic strategies for exosome isolation and the countless benefits of label-free approaches for clinical applications, current microfluidic platforms for isolation of exosomes are still facing a series of problems and challenges that prevent their use for clinical sample processing. This review focuses on the recent microfluidic platforms developed for label-free isolation of exosomes including those based on sieving, deterministic lateral displacement, field flow, and pinched flow fractionation as well as viscoelastic, acoustic, inertial, electrical, and centrifugal forces. Further, we discuss advantages and disadvantages of these strategies with highlights of current challenges and outlook of label-free microfluidics toward the clinical utility of exosomes.

Characterization and purification of pentameric chimeric protein particles using asymmetric flow field-flow fractionation coupled with multiple detectors

Porcine circovirus causes the post-weaning multi-systemic wasting syndrome. Despite the existence of commercial vaccines, the development of more effective and cheaper vaccines is expected. The usage of chimeric antigens allows serological differentiation between naturally infected and vaccinated animals. In this work, recombinant pentameric vaccination protein particles spontaneously assembled from identical subunits-chimeric fusion proteins derived from circovirus capsid antigen Cap and a multimerizing subunit of mouse polyomavirus capsid protein VP1 were purified and characterized using asymmetric flow field-flow fractionation (AF4) coupled with UV and MALS/DLS (multi-angle light scattering/dynamic light scattering) detectors. Various elution profiles were tested, including constant cross-flow and decreasing cross-flow (linearly and exponentially). The optimal sample retention, separation efficiency, and resolution were assessed by the comparison of the hydrodynamic radius (R_h) measured by online DLS with the R_h values calculated from the simplified retention equation according to the AF4 theory. The results show that the use of the combined elution profiles (exponential and constant cross-flow rates) reduces the time of the separation, prevents undesirable sample-membrane interaction, and yields better resolution. Besides, the results show no self-associations of the individual pentameric particles into larger clusters and no sample degradation during the AF4 separation. The R_g/R_h ratios for different fractions are in good correlation with morphological analyses performed by transmission electron microscopy (TEM). Additionally to the online analysis, the individual fractions were subjected to offline analysis, including batch DLS, TEM, and SDS-PAGE, followed by Western blot.

High-Speed Screening of Lipoprotein Components Using Online Miniaturized Asymmetrical Flow Field-Flow Fractionation and Electrospray Ionization Tandem Mass Spectrometry: Application to Hepatocellular Carcinoma Plasma Samples

This study introduces a high-speed screening method for the quantitative analysis of lipoprotein components in human plasma samples using online miniaturized asymmetrical flow field-flow fractionation and electrospray ionization-tandem mass spectrometry (mAF4-ESI-MS/MS). Using an mAF4 channel, high-density lipoproteins and low-density lipoproteins can be fractionated by size at a high speed (<10 min) and directly fed to ESI-MS/MS for the simultaneous screening of targeted lipid species and apolipoprotein A1 (ApoA1). By employing the heated electrospray ionization probe as an ionization source, an mAF4 effluent flow rate of up to a few tens of microliters per minute can be used, which is adequate for direct feeding to MS without splitting the outflow, resulting in a consistent feed rate to MS for stable MS detection. mAF4-ESI-MS/MS was applied to hepatocellular carcinoma (HCC) plasma samples for targeted quantification of 25 lipid biomarker candidates and ApoA1 compared with healthy controls, the results of which were in statistical agreement with the quantified results obtained by nanoflow ultrahigh performance liquid chromatography-tandem mass spectrometry. Moreover, the present method provided the simultaneous detection of changes in lipoprotein size and the relative amount. This study demonstrated the potential of mAF4-ESI-MS/MS as an alternative high-speed screening platform for the top-down analysis of targeted lipoprotein components in patients with HCC, which is applicable to other diseases that involve the perturbation of lipoproteins.

Applications of asymmetrical flow field-flow fractionation for separation and characterization of polysaccharides: A review

Polysaccharides are the most abundant natural biopolymers on the earth and are widely used in food, medicine, materials, cosmetics, and other fields. The physicochemical properties of polysaccharides such as particle size and molecular weight often affect their practical applications. In recent years, asymmetrical flow field-flow fractionation (AF4) has been widely used in the separation and characterization of polysaccharides because it has no stationary phases or packing materials, which reduces the risk of shear degradation of polysaccharides. In this review, the principle of AF4 was introduced briefly. The operation conditions of AF4 for the analysis of polysaccharides were discussed. The applications of AF4 for the separation and characterization of polysaccharides from different sources (plants, animals, and microorganisms) over the last decade were critically reviewed.

Perturbations of Lipids and Oxidized Phospholipids in Lipoproteins of Patients with Postmenopausal Osteoporosis Evaluated by Asymmetrical Flow Field-Flow Fractionation and Nanoflow UHPLC-ESI-MS/MS

Osteoporosis, a degenerative bone disease characterized by reduced bone mass and high risk of fragility, is associated with the alteration of circulating lipids, especially oxidized phospholipids (Ox-PLs). This study evaluated the lipidomic changes in lipoproteins of patients with postmenopausal osteoporosis (PMOp) vs. postmenopausal healthy controls. High-density lipoproteins (HDL) and low-density lipoproteins (LDL) from plasma samples were size-sorted by asymmetrical flow field-flow fractionation (AF4). Lipids from each lipoprotein were analyzed by nanoflow ultrahigh performance liquid chromatography-electrospray ionization-tandem mass spectrometry (nUHPLC-ESI-MS/MS). A significant difference was observed in a subset of lipids, most of which were increased in patients with PMOp, when compared to control. Phosphatidylethanolamine plasmalogen, which plays an antioxidative role, was increased in both lipoproteins (P-16:0/20:4, P-18:0/20:4, and P-18:1/20:4) lysophosphatidic acid 16:0, and six phosphatidylcholines were largely increased in HDL, but triacylglycerols (50:4 and 54:6) and overall ceramide levels were significantly increased only in LDL of patients with PMOp. Further investigation of 33 Ox-PLs showed significant lipid oxidation in PLs with highly unsaturated acyl chains, which were decreased in LDL of patients with PMOp. The present study demonstrated that AF4 with nUHPLC-ESI-MS/MS can be utilized to systematically profile Ox-PLs in the LDL of patients with PMOp.