Analysis and Comparison of Electrical Pulse Parameters for Gene Electrotransfer of Two Different Cell Lines

Interplay between Electric Field Strength and Number of Short-Duration Pulses for Efficient Gene Electrotransfer

Electroporation is a method that shows great promise as a non-viral approach for delivering genes by using high-voltage electric pulses to introduce DNA into cells to induce transient gene expression. This research aimed to evaluate the interplay between electric pulse intensity and 100 µs-duration pulse numbers as an outcome of gene electrotransfer efficacy and cell viability. Our results indicated a close relationship between pulse number and electric field strength regarding gene electrotransfer efficacy; higher electric pulse intensity resulted in fewer pulses needed to achieve the same gene electrotransfer efficacy. Subsequently, an increase in pulse number had a more negative impact on overall gene electrotransfer by significantly reducing cell viability. Based on our data, the best pulse parameters to transfect CHO cells with the pMax-GFP plasmid were using 5 HV square wave pulses of 1000 V/cm and 2 HV of 1600 V/cm, correspondingly resulting in 55 and 71% of transfected cells and maintaining 79 and 54% proliferating cells. This shows ESOPE-like 100 µs-duration pulse protocols can be used simultaneously to deliver cytotoxic drugs as well as immune response regulating genetically encoded cytokines.

Effect of Experimental Electrical and Biological Parameters on Gene Transfer by Electroporation: A Systematic Review and Meta-Analysis

The exact mechanisms of nucleic acid (NA) delivery with gene electrotransfer (GET) are still unknown, which represents a limitation for its broader use. Further, not knowing the effects that different experimental electrical and biological parameters have on GET additionally hinders GET optimization, resulting in the majority of research being performed using a trial-and-error approach. To explore the current state of knowledge, we conducted a systematic literature review of GET papers in in vitro conditions and performed meta-analyses of the reported GET efficiency. For now, there is no universal GET strategy that would be appropriate for all experimental aims. Apart from the availability of the required electroporation device and electrodes, the choice of an optimal GET approach depends on parameters such as the electroporation medium; type and origin of cells; and the size, concentration, promoter, and type of the NA to be transfected. Equally important are appropriate controls and the measurement or evaluation of the output pulses to allow a fair and unbiased evaluation of the experimental results. Since many experimental electrical and biological parameters can affect GET, it is important that all used parameters are adequately reported to enable the comparison of results, as well as potentially faster and more efficient experiment planning and optimization.

Functional Requirements and Quality Assurance Necessary for Successful Incorporation of Electroporation-Based Therapies Into Clinical Practice

Electroporation-based therapies have a huge potential for implementation into clinical practice in socioeconomically disadvantaged populations. Currently, the price of electroporators and electrodes is relatively high, but custom low budget devices can be developed. In the paper, we describe three most established applications in medicine, with the focus on the basic mechanisms, which should be taken into account during the development process of a clinical electroporator. Also, typical pulse parameters used in each of the described applications are defined. In the second part of the paper, we describe technical functional requirements for a clinical electroporator and safety guidelines, with the focus on medical device standard. At the end of the paper, the focus moves to a more general problematic, such as quality assurance and the importance of measurement during the pulse delivery, which we firmly believe is necessary for successful electroporation.

Fundamental study on a gene transfection methodology for mammalian cells using water-in-oil droplet deformation in a DC electric field

We have developed a gene transfection method called water-in-oil droplet electroporation (EP) that uses a dielectric oil and a liquid droplet containing live cells and exogenous DNA. When a cell suspension droplet is placed between a pair of electrodes, an intense DC electric field can induce droplet deformation, resulting in an instantaneous short circuit caused by the droplet elongating and contacting the two electrodes simultaneously. Small transient pores are generated in the cell membrane during the short, allowing the introduction of exogenous DNA into the cells. The droplet EP was characterized by varying the following experimental parameters: applied voltage, number of short circuits, type of medium (electric conductivity), concentration of exogenous DNA, and size of the droplet. In addition, the formation of transient pores in the cell membrane during droplet EP and the transfection efficiency were evaluated.

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Characterization of water-in-oil droplet electroporation.

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The electric field strength is the most critical experimental parameter.

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The volume of the droplet affects viability and gene expression.

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Droplet deformation under a DC electric field is critical.

Post-pulse addition of trans-cyclohexane-1,2-diol improves electrotransfer mediated gene expression in mammalian cells

Electric field mediated gene transfer is facing a problem in expression yield due to the poor transfer across the nuclear envelope. Trans-cyclohexane-1,2-diol (TCHD) was shown to significantly increase chemically mediated transfection by collapsing the permeability barrier of the nuclear pore complex. We indeed observed a significant increase in expression by electrotransfer when cells are treated post pulse by a low non toxic concentration of TCHD. This was obtained for different pulsing conditions, cell strains and plasmid constructs. An interesting improvement in cell viability can be obtained. This can significantly enhance the non-viral gene electrical delivery.

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Trans-cyclohexane-1,2-diol (TCHD) collapses the permeability barrier of the nuclear pore complex.

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TCHD improves expression in gene electrotransfer.

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Post pulse TCHD addition is the most effective protocol.

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TCHD does not affect the cell viability when coupled to electrotransfer.

Irreversible electroporation enhances delivery of gemcitabine to pancreatic adenocarcinoma

INTRODUCTION

Irreversible electroporation (IRE) utilizes short, high-voltage pulses to irreversibly permeabilize the cell membrane, resulting in apoptotic cell death. In addition to the irreversible zone, IRE creates a reversible zone that could be utilized for enhanced drug delivery. The hypothesis of this study is that a zone of reversible electroporation exists and allows for increased chemotherapy delivery.

METHODS

Ten immunocompromised mice with orthotopic human pancreatic adenocarcinoma tumors (Panc1) were treated with either IRE between two doses of gemcitabine (15 mg/kg) (ECT) (N = 5) or gemcitabine alone (N = 5). Gemcitabine levels in the serum, liver, and pancreas were analyzed with liquid chromatography/mass spectrometry (LC/MS).

RESULTS

Concentration of gemcitabine within reversibly electroporated pancreatic tissue was higher in mice receiving ECT compared to those receiving gemcitabine alone (13,567 ng/ml vs.4,126 ng/ml; P = 0.0009). Pancreatic gemcitabine levels were 5.52 and 5.96 times higher than liver and serum levels, respectively, in the ECT group compared to 2.85 and 2.53 times higher (P = 0.117, P = 0.058), respectively, in mice receiving gemcitabine alone.

CONCLUSION

IRE can potentially reduce local recurrence by allowing increased drug delivery to the tissue in the reversible electroporation zone. This holds significant potential in augmenting efficacy of gemcitabine in treatment of locally advanced and borderline resectable pancreatic adenocarcinoma. J. Surg. Oncol. 2016;114:181-186. © 2016 Wiley Periodicals, Inc.

New insights into the mechanisms of gene electrotransfer--experimental and theoretical analysis

Gene electrotransfer is a promising non-viral method of gene delivery. In our in vitro study we addressed open questions about this multistep process: how electropermeabilization is related to electrotransfer efficiency; the role of DNA electrophoresis for contact and transfer across the membrane; visualization and theoretical analysis of DNA-membrane interaction and its relation to final transfection efficiency; and the differences between plated and suspended cells. Combinations of high-voltage and low-voltage pulses were used. We obtained that electrophoresis is required for the insertion of DNA into the permeabilized membrane. The inserted DNA is slowly transferred into the cytosol, and nuclear entry is a limiting factor for optimal transfection. The quantification and theoretical analysis of the crucial parameters reveals that DNA-membrane interaction (N_DNA) increases with higher DNA concentration or with the addition of electrophoretic LV pulses while transfection efficiency reaches saturation. We explain the differences between the transfection of cell suspensions and plated cells due to the more homogeneous size, shape and movement of suspended cells. Our results suggest that DNA is either translocated through the stable electropores or enters by electo-stimulated endocytosis, possibly dependent on pulse parameters. Understanding of the mechanisms enables the selection of optimal electric protocols for specific applications.

Cell type-specific response to high intracellular loading of polyacrylic acid-coated magnetic nanoparticles

Magnetic nanoparticles (NPs) are a special type of NP with a ferromagnetic, electron-dense core that enables several applications such as cell tracking, hyperthermia, and magnetic separation, as well as multimodality. So far, superparamagnetic iron oxide NPs (SPIONs) are the only clinically approved type of metal oxide NPs, but cobalt ferrite NPs have properties suitable for biomedical applications as well. In this study, we analyzed the cellular responses to magnetic cobalt ferrite NPs coated with polyacrylic acid (PAA) in three cell types: Chinese Hamster Ovary (CHO), mouse melanoma (B16) cell line, and primary human myoblasts (MYO). We compared the internalization pathway, intracellular trafficking, and intracellular fate of our NPs using fluorescence and transmission electron microscopy (TEM) as well as quantified NP uptake and analyzed uptake dynamics. We determined cell viability after 24 or 96 hours’ exposure to increasing concentrations of NPs, and quantified the generation of reactive oxygen species (ROS) upon 24 and 48 hours’ exposure. Our NPs have been shown to readily enter and accumulate in cells in high quantities using the same two endocytic pathways; mostly by macropinocytosis and partially by clathrin-mediated endocytosis. The cell types differed in their uptake rate, the dynamics of intracellular trafficking, and the uptake capacity, as well as in their response to higher concentrations of internalized NPs. The observed differences in cell responses stress the importance of evaluation of NP–cell interactions on several different cell types for better prediction of possible toxic effects on different cell and tissue types in vivo.

Comparison of flow cytometry, fluorescence microscopy and spectrofluorometry for analysis of gene electrotransfer efficiency

In this study, we compared three different methods used for quantification of gene electrotransfer efficiency: fluorescence microscopy, flow cytometry and spectrofluorometry. We used CHO and B16 cells in a suspension and plasmid coding for GFP. The aim of this study was to compare and analyse the results obtained by fluorescence microscopy, flow cytometry and spectrofluorometry and in addition to analyse the applicability of spectrofluorometry for quantifying gene electrotransfer on cells in a suspension. Our results show that all the three methods detected similar critical electric field strength, around 0.55 kV/cm for both cell lines. Moreover, results obtained on CHO cells showed that the total fluorescence intensity and percentage of transfection exhibit similar increase in response to increase electric field strength for all the three methods. For B16 cells, there was a good correlation at low electric field strengths, but at high field strengths, flow cytometer results deviated from results obtained by fluorescence microscope and spectrofluorometer. Our study showed that all the three methods detected similar critical electric field strengths and high correlations of results were obtained except for B16 cells at high electric field strengths. The results also demonstrated that flow cytometry measures higher values of percentage transfection compared to microscopy. Furthermore, we have demonstrated that spectrofluorometry can be used as a simple and consistent method to determine gene electrotransfer efficiency on cells in a suspension.

An experimental system for controlled exposure of biological samples to electrostatic discharges

Electrostatic discharges occur naturally as lightning strokes, and artificially in light sources and in materials processing. When an electrostatic discharge interacts with living matter, the basic physical effects can be accompanied by biophysical and biochemical phenomena, including cell excitation, electroporation, and electrofusion. To study these phenomena, we developed an experimental system that provides easy sample insertion and removal, protection from airborne particles, observability during the experiment, accurate discharge origin positioning, discharge delivery into the sample either through an electric arc with adjustable air gap width or through direct contact, and reliable electrical insulation where required. We tested the system by assessing irreversible electroporation of Escherichia coli bacteria (15 mm discharge arc, 100 A peak current, 0.1 μs zero-to-peak time, 0.2 μs peak-to-halving time), and gene electrotransfer into CHO cells (7 mm discharge arc, 14 A peak current, 0.5 μs zero-to-peak time, 1.0 μs peak-to-halving time). Exposures to natural lightning stroke can also be studied with this system, as due to radial current dissipation, the conditions achieved by a stroke at a particular distance from its entry are also achieved by an artificial discharge with electric current downscaled in magnitude, but similar in time course, correspondingly closer to its entry.

Design and implementation of a microelectrode assembly for use on noncontact in situ electroporation of adherent cells

In situ electroporation of adherent cells provides significant advantages with respect to electroporation systems for suspension cells, such as causing minimal stress to cultured cells and simplifying and saving several steps within the process. In this study, a new electrode assembly design is shown and applied to in situ electroporate adherent cell lines growing in standard multiwell plates. We designed an interdigitated array of electrodes patterned on copper with printed circuit board technology and covered with nickel/gold. Small interelectrode distances were used to achieve effective electroporation with low voltages. Epoxy-based microseparators were constructed to avoid direct contact with the cells and to create more uniform electric fields. The device was successful in the electropermeabilization of two different adherent cell lines, C2C12 and HEK 293, as assessed by the intracellular delivery of the fluorescent dextran FD20S. Additionally, as a collateral effect, we observed cell electrofusion in HEK 293 cells, thus making this device also useful for performing cell fusion. In summary, we show the effectiveness of this minimally invasive device for electroporation of adherent cells cultured in standard multiwell plates. The cheap technologies used in the fabrication process of the electrode assembly indicate potential use as a low-cost, disposable device.

Lucifer Yellow uptake by CHO cells exposed to magnetic and electric pulses

BACKGROUND

The cell membrane acts as a barrier that hinders free entrance of most hydrophilic molecules into the cell. Due to numerous applications in medicine, biology and biotechnology, the introduction of impermeant molecules into biological cells has drawn considerable attention in the past years. One of the most famous methods in this field is electroporation, in which electric pulses with high intensity and short duration are applied to the cells. The aim of our study was to investigate the effect of time-varying magnetic field with different parameters on transmembrane molecular transport.

MATERIALS AND METHODS

'Moreover, a comparison was made between the uptake results due to magnetic pulse exposure and electroporation mediated uptake.' at the end of Background part. The Chinese hamster ovary (CHO) cells were exposed to magnetic pulses of 2.2 T peak strength and 250 μs duration delivered by Magstim stimulator and double 70 mm coil. Three different frequencies of 0.25, 1 and 10 Hz pulses with 112, 56 and 28 number of pulses were applied (altogether nine experimental groups) and Lucifer Yellow uptake was measured in each group. Moreover, maximum uptake of Lucifer Yellow obtained by magnetic pulses was compared to the measured uptake due to electroporation with typical parameters of 8 pulses of 100 μs, repetition frequency of 1 Hz and electric field intensities of 200 to 600 V/cm.

RESULTS AND CONCLUSIONS

Our results show that time-varying magnetic field exposure increases transmembrane molecular transport and this uptake is greater for lower frequencies and larger number of pulses. Besides, the comparison shows that electroporation is more effective than pulsed magnetic field, but the observed uptake enhancement due to magnetic exposure is still considerable.

The role of electrically stimulated endocytosis in gene electrotransfer

Gene electrotransfer is an established method for transfer of genes into cells, however, the mechanism of transfer of DNA across the cell membrane is still not known. Some studies suggest that DNA is translocated through membrane pores while others propose that DNA enters the cell via electro-endocytosis, but no direct observation was performed. In this paper we investigated the second hypothesis. Cells were stained with membrane dye FM 1-43FX, which is used for observation of endocytosis, and then exposed to electric pulses. We analyzed if endocytosis was stimulated by applying electric pulses with intensities below and above the threshold value for gene electrotransfer. No increase in endocytosis from 20 min or even up to 2h after the pulse delivery was observed, regardless of the electric field strength. These observations do not correlate with electrotransfer efficiency, which increases with field strength and is observed only above the threshold value. Our results suggest that electro-endocytosis is not a crucial mechanism for gene electrotransfer and that the hypothesis of DNA entry by translocation through permeabilized membrane is more plausible. The presented results are important for better understanding of the mechanisms of gene electrotransfer and for its optimization for clinical applications.