Cortical cell elution by sedimentation field-flow fractionation

Sedimentation Field-Flow Fractionation: A Diagnostic Tool for Rapid Antimicrobial Susceptibility Testing

Conventional antimicrobial susceptibility testing (AST) methods require 24-48 h to provide results, creating the need for a probabilistic antibiotic therapy that increases the risk of antibiotic resistance emergence. Consequently, the development of rapid AST methods has become a priority. Over the past decades, sedimentation field-flow fractionation (SdFFF) has demonstrated high sensitivity in early monitoring of induced biological events in eukaryotic cell populations. This proof-of-concept study aimed at investigating SdFFF for the rapid assessment of bacterial susceptibility to antibiotics. Three bacterial species were included (Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa) with two panels of antibiotics tailored to each bacterial species. The results demonstrate that SdFFF, when used in "Hyperlayer" elution mode, enables monitoring of antibiotic-induced morphological changes. The percentage variation of the retention factor (PΔR) was used to quantify the biological effect of antibiotics on bacteria with the establishment of a threshold value of 16.8% to differentiate susceptible and resistant strains. The results obtained with SdFFF were compared to that of the AST reference method, and a categorical agreement of 100% was observed. Overall, this study demonstrates the potential of SdFFF as a rapid method for the determination of antibiotic susceptibility or resistance since it is able to provide results within a shorter time frame than that needed for conventional methods (3-4 h vs 16-24 h, respectively), enabling earlier targeted antibiotic therapy. Further research and validation are necessary to establish the effectiveness and reliability of SdFFF in clinical settings.

Field-Flow Fractionation in Molecular Biology and Biotechnology

Field-flow fractionation (FFF) is a family of single-phase separative techniques exploited to gently separate and characterize nano- and microsystems in suspension. These techniques cover an extremely wide dynamic range and are able to separate analytes in an interval between a few nm to 100 µm size-wise (over 15 orders of magnitude mass-wise). They are flexible in terms of mobile phase and can separate the analytes in native conditions, preserving their original structures/properties as much as possible. Molecular biology is the branch of biology that studies the molecular basis of biological activity, while biotechnology deals with the technological applications of biology. The areas where biotechnologies are required include industrial, agri-food, environmental, and pharmaceutical. Many species of biological interest belong to the operational range of FFF techniques, and their application to the analysis of such samples has steadily grown in the last 30 years. This work aims to summarize the main features, milestones, and results provided by the application of FFF in the field of molecular biology and biotechnology, with a focus on the years from 2000 to 2022. After a theoretical background overview of FFF and its methodologies, the results are reported based on the nature of the samples analyzed.

Autophagy inhibition reinforces stemness together with exit from dormancy of polydisperse glioblastoma stem cells

Therapeutic resistance and infiltrative capacities justify the aggressiveness of glioblastoma. This is due to cellular heterogeneity, especially the presence of stemness-related cells, i.e. Cancer Stem Cells (CSC). Previous studies focused on autophagy and its role in CSCs maintenance; these studies gave conflicting results as they reported either sustaining or disruptive effects. In the present work, we silenced two autophagy related genes -either Beclin1 or ATG5- by shRNA and we explored the ensuing consequences on CSCs markers’ expression and functionalities. Our results showed that the down regulation of autophagy led to enhancement in expression of CSCs markers, while proliferation and clonogenicity were boosted. Temozolomide (TMZ) treatment failed to induce apoptotic death in shBeclin1-transfected cells, contrary to control. We optimized the cellular subset analysis with the use of Sedimentation Field Flow Fractionation, a biological event monitoring- and cell sorting-dedicated technique. Fractograms of both shBeclin1 and shATG5 cells exhibited a shift of elution peak as compared with control cells, showing cellular dispersion and intrinsic sub-fraction modifications. The classical stemness fraction (i.e. F3) highlighted data obtained with the overall cellular population, exhibiting enhancement of stemness markers and escape from dormancy. Our results contributed to illustrate CSCs polydispersity and to show how these cells develop capacity to bypass autophagy inhibition, thanks to their acute adaptability and plasticity.

A New Label-Free Approach to Glioblastoma Cancer Stem Cell Sorting and Detection

Cancer stem cells (CSCs) play critical roles in cancer, making them important targets for new diagnostic and therapeutic approaches. Since CSCs are heterogeneous and not abundant in tumors, and few specific markers for these cells currently exist, new methods to isolate and characterize them are required. To address this issue, we developed a new label-free methodology to isolate, enrich, and identify CSCs from an heterogeneous tumor cell subpopulation using a cell sorting method (sedimentation field flow fractionation, SdFFF) and a biosensor as a detector. Enrichment was optimized using an original protocol and U87-MG glioblastoma cells cultured in a normal (N) or defined (D) medium (± fetal bovine serum, FBS) under normoxic (N, p_O2 = 20%) or hypoxic (H, p_O2 < 2%) conditions to obtain four cell populations: NN, NH, DN, and DH. After elution of CSCs via SdFFF using the hyperlayer mode (inertial elution mode for micrometer-sized species), we isolated eight subpopulations with distinct CSC contents based on phenotypical and functional properties, ranging from NN F1 with a lower CSC content to DH F3 with a higher CSC content. Reflecting biological differences, the intrinsic intracellular dielectric permittivity increased from NN to DH conditions. The largest difference in electromagnetic signature was observed between NN F1 and DH F3, in which the CSC content was lowest and highest, respectively. The results demonstrate that microwave dielectric spectroscopy can be used to reliably and efficiently distinguish stem cell characteristics. This new instrumental and methodological approach is an important innovation that allows both enrichment and detection of CSCs, opening the door to novel diagnostic and therapeutic approaches.

Isolation of Astrocytes Displaying Myofibroblast Properties and Present in Multiple Sclerosis Lesions

A wide heterogeneity of lesions can affect the central nervous system (CNS). In all situations where neurons are damaged, including multiple sclerosis (MS), a common reactive astrocytosis is present. Sedimentation field-flow fractionation (SdFFF) was used to sort astrocyte subpopulations. After SdFFF elution, cells, prepared from rat newborn cortex, were cultured and analyzed by immunocytofluorescence for glial fibrillary acidic protein (GFAP) and α-smooth muscle (SM) actin (a specific marker for myofibroblasts) expression. Cell contractile capacity was studied. Samples from patients with MS were also analyzed. Three main fractions (F1, F2, and F3) were isolated and compared with the total eluted population (TP). TP, F1, F2, and F3, contained respectively 74, 96, 12, and 98% of GFAP expressing astrocytes. In F3, astrocytes only expressed GFAP while in F1, astrocytes expressed both GFAP and α-SM actin. In F2 and TP, α-SM actin expression was barely detected. F3-derived cells showed higher contractile capacities compared with F1-derived cells. In one specific case of MS known as Baló's concentric MS, astrocytes expressing both GFAP and α-SM actin were detected. Using SdFFF, a population of astrocytes presenting myofibroblast properties was isolated. This subpopulation of astrocytes was also observed in a MS sample suggesting that it could be involved in lesion formation and remodeling during CNS pathologies.

Neural Stem Cell Properties of an Astrocyte Subpopulation Sorted by Sedimentation Field-Flow Fractionation

Astrocytes encompass a heterogeneous cell population. Using sedimentation field-flow fractionation (SdFFF) method, different, almost pure, astrocyte subpopulations were isolated. Cells were collected from cortex of newborn rats and sorted by SdFFF to obtain different fractions, which were subjected to protein analysis and characterized by immunocytofluorescence. The behavior of the cells was analyzed in vitro, under culture conditions used for neural stem cells. These culture conditions were also applied to cells derived from an adult cortical tissue after traumatic brain injury (TBI). Finally, the astrocytic neural stem-like cells were transplanted in damaged sciatic nerve. Protein analysis indicated a high expression of glial fibrillary acidic protein (GFAP) and vimentin in fraction F3-derived cells. These cells formed neurospheres when cultured with epidermal growth factor and large colonies in a collagen-containing semi-solid matrix. Neurospheres expressed GFAP and nestin and were able in addition to generate neurons expressing MAP2 and oligodendrocytes expressing Olig2. When transplanted in a damaged nerve, cells of F3-derived neurospheres colonized the damaged area. Finally, after TBI in adult rats, cells able to form neurospheres containing a subpopulation of astrocytes expressing vimentin were obtained. Using the SdFFF method, an astrocyte subpopulation presenting stem cell properties was isolated from a newborn rat cortex and from an injured adult rat cortex. The specific activation of this astrocyte subpopulation may provide a potential therapeutic approach to restore lost neuronal function in injured or diseased brain.

Kinetics of chemically mediated neurodegeneration/neuroregeneration of mouse olfactory epithelium: monitoring by hyperlayer sedimentation field flow fractionation

The increase in the incidence of neurodegenerative diseases linked to aging or injury needs to be addressed in research into neuroprotective or neuroregenerative therapies, and requires the development of specific biological models. To achieve this goal we propose (1) the use of the mouse olfactory epithelium as a biological support which specifically exhibits a regenerative or a self-renewing capacity and during the lifetime necessitates the presence of neural stem cells, and (2) the use of an intraperitoneal injection of 2,6-dichlorobenzonitrile (diclobenil) as a chemical inducer of neurodegeneration in olfactory epithelium by selectively killing mature cells. We developed a biological model to follow the processes of neurodegeneration (chemically induced) and neuroregeneration (self-renewal of olfactory epithelium). The purpose of this study was to develop a method to monitor quickly neurodegeneration/neuroregeneration processes in order to further screen protective and regenerative therapies. For this purpose, we used the sedimentation field flow fractionation elution of olfactory epithelium. We obtained specific elution profiles and retention parameters allowing the monitoring of the induction and kinetics of biological processes. The use of insulin-like growth factor 1α as a neuroprotective agent in an innovative nebulization protocol showed sedimentation field flow fractionation to be a simple, fast and low-cost method to monitor such a biological event on the scale of an entire organism.

Investigating the relationship between cell cycle stage and diosgenin-induced megakaryocytic differentiation of HEL cells using sedimentation field-flow fractionation

Differentiation therapy could be one strategy for stopping cancer cell proliferation. A plant steroid, diosgenin, is known to induce megakaryocytic differentiation in human erythroleukemia (HEL) cells. In recent studies, the use of sedimentation field-flow fractionation (SdFFF) allowed the preparation of subpopulations that may differ in regard to sensitivity to differentiation induction. The specific goal of this study was to determine the relationship between cell cycle stage and sensitivity to megakaryocytic differentiation induction of HEL cells. After first confirming the capacity of diosgenin to specifically select targets, hyperlayer SdFFF cell sorting was used to prepare fractions according to cell cycle position from crude HEL cells. The sensitivities of these fractions to diosgenin-induced differentiation were then tested. The coupling of SdFFF cell separation to imaging flow cytometry showed that G1-phase cells were more sensitive to differentiation induction than S/G2M-phase cells, confirming the relationship between cell status at the start of induction, the extent of the biological event, and the potential of SdFFF in cancer research.

Determination of Viable Yeast Cells by Gravitational Field-Flow Fractionation with Fluorescence Detection

Vinification processing is largely related to yeast performance and depends on the initial cell viability. To optimize the quality of wine fermentation, control of the yeast quality is mandatory. The present paper describes a new method using gravitational field flow fractionation (GrFFF) with fluorescence detection for the determination of yeast cell viability before the fermentation process. A GrFFF calibration procedure was developed using commercial yeast to prepare standards of viable cells and propidium iodide (PI) as fluorescent probe for nonviable cells. The suitability of the new method was tested with several commercial yeast strains with a g/L content ranging from 1 to 3. The validation of the method was performed by comparing GrFFF viability values with those obtained using Coulter counter and flow cytometry techniques.

Sedimentation field flow fractionation to study human erythroleukemia cell megakaryocytic differentiation after short period diosgenin induction

Anti-cancer differentiation therapy could be one strategy to stop cancer cell proliferation. We propose a new sedimentation field flow fractionation (SdFFF) cell separation application in the field of cancer research. It concerns the study of megakaryocytic differentiation processes after a short exposure to an inducting agent (diosgenin). Washout process and early dual SdFFF separation--removing the influence of diosgenin and decreasing the influence of undifferentiated cells--resulted in the preparation of an enriched population to study the mechanism and kinetics of megakaryocytic differentiation. A short exposure to diosgenin was able to induce complete differentiation leading to maximal maturation which ended naturally after 192h incubation without the influence of a secondary effect of diosgenin. The study of isolated undifferentiated cells also showed that no resistance to diosgenin was observed. This result suggested different sensitivities to differentiation induction, and SdFFF cell separation would be of great interest to explore this phenomena.

Pre-apoptotic sub-population cell sorting from diosgenin apoptosis induced 1547 cells by Sedimentation Field-Flow Fractionation

Apoptosis is one of the most important phenomena in cell biology. Pre-apoptotic cells, defined as cells engaged in early stages of apoptosis, could be used as a cellular tool to study apoptosis pathways. The human 1547 osteosarcoma cell line and diosgenin (a plant steroid) association was selected as an in vitro cellular apoptosis model. In a previous study, using this model, we demonstrated that SdFFF monitored apoptosis induction as early as 6h after incubation. In this study, we investigated the capacity of Sedimentation Field-Flow Fractionation (SdFFF) to sort an enriched population of pre-apoptotic cells from 1547 cells incubated for 6 h with 40 microM diosgenin. In that way, two different separation devices which differed especially in channel thickness, 125 and 175 microm, were used and compared. Results showed, for the first time, that SdFFF is an effective method to obtain an enriched pre-apoptotic sub-population. These results suggest, as a new application, that SdFFF could be an included tool in the study of apoptotic mechanisms or the kinetic action of apoptotic drugs.

Megakaryocyte cell sorting from diosgenin-differentiated human erythroleukemia cells by sedimentation field-flow fractionation

Anticancer differentiation therapy could be one strategy to stop cancer cell proliferation. Human erythroleukemia (HEL) cell line, incubated with 10 microM diosgenin, underwent megakaryocytic differentiation. Thus, the association diosgenin/HEL could be used as a model of chemically induced cellular differentiation and anticancer treatment. The goal of this work was to determine the capacity of sedimentation field-flow fractionation (SdFFF) to sort megakaryocytic differentiated cells. SdFFF cell sorting was associated with cellular characterization methods to calibrate specific elution profiles. As demonstrated by cell size measurement methods, cellular morphology, ploidy, and phenotype, we obtained an enriched, sterile, viable, and functional fraction of megakaryocytic cells. Thus, SdFFF is proposed as a routine method to prepare differentiated cells that will be further used to better understand the megakaryocytic differentiation process.

Field-flow fractionation and biotechnology

The gentle separation mechanism has made field-flow fractionation particularly suited to samples of biotechnological interest, from proteins and nucleic acids to viruses, subcellular units and whole cells. Recent progress in field-flow fractionation technology, as well as the development of coupled techniques combining field-flow fractionation capabilities with the specificity and sensitivity of well-established analytical methods, opens up new biotechnological applications for field-flow fractionation. The most recent appealing applications include: sorting and fingerprinting of bacteria for whole-cell vaccine production; noninvasive and tagless sorting of immature and stem cells; separation of intact proteins and enzymes in top-down proteomics; and the development of flow-assisted, multianalyte immunoassays using nano- and micron-sized particles with immobilized biomolecules.

Biocompatible channels for field-flow fractionation of biological samples: correlation between surface composition and operating performance

Biocompatible methods capable of rapid purification and fractionation of analytes from complex natural matrices are increasingly in demand, particularly at the forefront of biotechnological applications. Field-flow fractionation is a separation technique suitable for nano-sized and micro-sized analytes among which bioanalytes are an important family. The objective of this preliminary study is to start a more general approach to field-flow fractionation for bio-samples by investigation of the correlation between channel surface composition and biosample adhesion. For the first time we report on the use of X-ray photoelectron spectroscopy (XPS) to study the surface properties of channels of known performance. By XPS, a polar hydrophobic environment was found on PVC material commonly used as accumulation wall in gravitational field-flow fractionation (GrFFF), which explains the low recovery obtained when GrFFF was used to fractionate a biological sample such as Staphylococcus aureus. An increase in separation performance was obtained first by conditioning the accumulation wall with bovine serum albumin and then by using the ion-beam sputtering technique to cover the GrFFF channel surface with a controlled inert film. XPS analysis was also employed to determine the composition of membranes used in hollow-fiber flow field-flow fractionation (HF FlFFF). The results obtained revealed homogeneous composition along the HF FlFFF channel both before and after its use for fractionation of an intact protein such as ferritin.

Diosgenin dose-dependent apoptosis and differentiation induction in human erythroleukemia cell line and sedimentation field-flow fractionation monitoring

To limit or stop cancer spreading, one of the most prevalent strategies is to induce cancer cell death. Differentiation therapy and apoptosis induction are two ways to achieve this goal. Sedimentation field-flow fractionation (SdFFF) has been described as an effective tool for cell separation, respecting integrity and viability. Because SdFFF takes advantage of intrinsic properties of eluted cells (size, density, shape), we studied the capacity of SdFFF to monitor specific biophysical modifications that occurred during cellular apoptosis or differentiation induction. Then, we used, as an in vitro cellular model of apoptosis and differentiation, diosgenin dose-dependent induction in the polyvalent human erythroleukemia cell line. Two other chemicals were used: phorbol myristate acetate (differentiation inducer) and staurosporine (apoptosis inducer). Our results demonstrated a correlation between SdFFF elution profile changes and induction of effective biological processes. Thus, after acquisition of a reference profile, SdFFF could be used alone to follow chemically induced biological events, suggesting many different applications such as testing series of molecules, evaluation of new cellular/biological models used in different life science fields, or sorting purified populations with the aim of better understanding mechanisms of induced cellular events.

Sedimentation field flow fractionation purification of immature neural cells from a human tumor neuroblastoma cell line

The use of stem cells for therapeutic applications is now an important objective for the future. Stem cell preparation is difficult and time-consuming depending on the origin of cells. Sedimentation field flow fractionation (SdFFF) is an effective tool for cell separation, respecting integrity and viability. We used the human neuroblastic SH-SY5Y clone of the SK-N-SH cell line as a source of immature neural cells. Our results demonstrated that by using SdFFF cell sorter under strictly defined conditions, and immunological cell characterization, we are now able to provide, in less than 15 min, a sterile, viable, usable and purified immature neural cell fraction without inducting cell differentiation.

Sonication effect on cellular material in sedimentation and gravitational field flow fractionation

Sonication procedures are generally used prior to field flow fractionation (FFF) separation in order to produce suspensions without aggregates. Yeast cells manufactured in active dry wine yeast (ADWY) were placed in an ultrasound water bath in order to disrupt possible clumps and to obtain a single-cell suspension to be used in optimal conditions during fermentation processes. In order to determine whether this sample preparation procedure meets absolute needs, different yeast samples before and after sonication were analysed by two field flow fractionation techniques. It is shown that 2 min of sonication in the sample preparation process is sufficient to obtain an optimal dispersion of the yeast cells, that is, without critical percentage of aggregates. To demonstrate this effect, photographs of the yeast cell suspensions were performed with non-sonicated and sonicated yeast sample dispersion. The resulting data are compared with the elution profiles obtained from the two different FFF techniques. It is demonstrated that fractogram profiles prove the effectiveness of sonication methodologies.