Human lymphocyte sorting by gravitational field-flow fractionation

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.

Human umbilical cord blood cells suffer major modification by fixatives and anticoagulants

Introduction: Developing techniques for the tagless isolation of homogeneous cell populations in physiological-like conditions is of great interest in medical research. A particular case is Gravitational Field-Flow Fractionation (GrFFF), which can be run avoiding cell fixation, and that was already used to separate viable cells. Cell dimensions have a key role in this process. However, their dimensions under physiological-like conditions are not easily known since the most diffused measurement techniques are performed on fixed cells, and the fixation used to preserve tissues can alter the cell size. This work aims to obtain and compare cell size data under physiological-like conditions and in the presence of a fixative.

Methods: We developed a new protocol that allows the analysis of blood cells in different conditions. Then, we applied it to obtain a dataset of human cord blood cell dimensions from 32 subjects, comparing two tubes with anticoagulants (EDTA and Citrate) and two tubes with different preservatives (CellRescue and CellSave). We analyzed a total of 2071 cells by using confocal microscopy via bio-imaging to assess dimensions (cellular and nuclear) and morphology.

Results: Cell diameter measured does not differ when using the different anticoagulants, except for the increase reported for monocyte in the presence of citrate. Instead, cell dimensions differ when comparing anticoagulants and cell preservative tubes, with a few exceptions. Cells characterized by high cytoplasm content show a reduction in their size, while morphology appears always preserved. In a subgroup of cells, 3D reconstruction was performed. Cell and nucleus volumes were estimated using different methods (specific 3D tool or reconstruction from 2D projection).

Discussion: We found that some cell types benefit from a complete 3D analysis because they contain non-spherical structures (mainly for cells characterized by poly-lobated nucleus). Overall, we showed the effect of the preservatives mixture on cell dimensions. Such an effect must be considered when dealing with problems highly dependent on cell size, such as GrFFF. Additionally, such information is crucial in computational models increasingly being employed to simulate biological events.

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.

A tag-less method for direct isolation of human umbilical vein endothelial cells by gravitational field-flow fractionation

The analysis of cellular and molecular profiles represents a powerful tool in many biomedical applications to identify the mechanisms underlying the pathological changes. The improvement of cellular starting material and the maintenance of the physiological status in the sample preparation are very useful. Human umbilical vein endothelial cells (HUVEC) are a model for prediction of endothelial dysfunction. HUVEC are enzymatically removed from the umbilical vein by collagenase. This method provides obtaining a good sample yield. However, the obtained cells are often contaminated with blood cells and fibroblasts. Methods based on negative selection by in vitro passages or on the use of defined marker are currently employed to isolate target cells. However, these approaches cannot reproduce physiological status and they require expensive instrumentation. Here we proposed a new method for an easy, tag-less and direct isolation of HUVEC from raw umbilical cord sample based on the gravitational field-flow fractionation (GrFFF). This is a low-cost, fully biocompatible method with low instrumental and training investments for flow-assisted cell fractionation. The method allows obtaining pure cells without cell culture procedures as starting material for further analysis; for example, a proper amount of RNA can be extracted. The approach can be easily integrated into clinical and biomedical procedures.

Analytical strategies for improving the robustness and reproducibility of bioluminescent microbial bioreporters

Whole-cell bioluminescent (BL) bioreporter technology is a useful analytical tool for developing biosensors for environmental toxicology and preclinical studies. However, when applied to real samples, several methodological problems prevent it from being widely used. Here, we propose a methodological approach for improving its analytical performance with complex matrix. We developed bioluminescent Escherichia coli and Saccharomyces cerevisiae bioreporters for copper ion detection. In the same cell, we introduced two firefly luciferases requiring the same luciferin substrate emitting at different wavelengths. The expression of one was copper ion specific. The other, constitutively expressed, was used as a cell viability internal control. Engineered BL cells were characterized using the noninvasive gravitational field-flow fractionation (GrFFF) technique. Homogeneous cell population was isolated. Cells were then immobilized in a polymeric matrix improving cell responsiveness. The bioassay was performed in 384-well black polystyrene microtiter plates directly on the sample. After 2 h of incubation at 37 °C and the addition of the luciferin, we measured the emitted light. These dual-color bioreporters showed more robustness and a wider dynamic range than bioassays based on the same strains with a single reporter gene and that uses a separate cell strain as BL control. The internal correction allowed to accurately evaluate the copper content even in simulated toxic samples, where reduced cell viability was observed. Homogenous cells isolated by GrFFF showed improvement in method reproducibility, particularly for yeast cells. The applicability of these bioreporters to real samples was demonstrated in tap water and wastewater treatment plant effluent samples spiked with copper and other metal ions.

Morphological evaluation of cell differentiation after the isolation of single cells by a femtosecond laser-induced impulsive force

When nerve growth factor (NGF) is interacted with PC12 cells derived from rat pheochromocytoma, they are partially differentiated into neuron-like cells with neurites. In this work, PC12 cells differentiated by NGF were selectively isolated using a localized impulsive force in a μm-scale area, which was generated by focusing an infrared femtosecond laser into a cell culture medium. In order to evaluate the ability of the isolation method, differentiated and undifferentiated cells were isolated and their morphological changes after the isolation were compared. In both cases, their neurites were once contracted and some of them gradually regenerated day by day. When differentiated cells were isolated, the percentage of differentiated cells with regenerated neurites, 6 h after the isolation, was about 3.3 times higher than that when undifferentiated ones were isolated. This result was compared with a control trypsin experiment. In the comparison, it was indicated that the same degree of cell function was maintained when the present isolation method was used.

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.