Membrane perturbation by an external electric field: a mechanism to permit molecular uptake

Gene Electrotransfer Efficiency in 2D and 3D Cancer Cell Models Using Different Electroporation Protocols: A Comparative Study

Electroporation, a method relying on a pulsed electric field to induce transient cell membrane permeabilization, can be used as a non-viral method to transfer genes in vitro and in vivo. Such transfer holds great promise for cancer treatment, as it can induce or replace missing or non-functioning genes. Yet, while efficient in vitro, gene-electrotherapy remains challenging in tumors. To assess the differences of gene electrotransfer in respect to applied pulses in multi-dimensional (2D, 3D) cellular organizations, we herein compared pulsed electric field protocols applicable to electrochemotherapy and gene electrotherapy and different "High Voltage-Low Voltage" pulses. Our results show that all protocols can result in efficient permeabilization of 2D- and 3D-grown cells. However, their efficiency for gene delivery varies. The gene-electrotherapy protocol is the most efficient in cell suspensions, with a transfection rate of about 50%. Conversely, despite homogenous permeabilization of the entire 3D structure, none of the tested protocols allowed gene delivery beyond the rims of multicellular spheroids. Taken together, our findings highlight the importance of electric field intensity and the occurrence of cell permeabilization, and underline the significance of pulses' duration, impacting plasmids' electrophoretic drag. The latter is sterically hindered in 3D structures and prevents the delivery of genes into spheroids' core.

Cell Membrane Oscillations under Radiofrequency Electromagnetic Modulation

Cell responses to external radiofrequencies (RF) are a fundamental problem of much scientific research, clinical applications, and even daily lives surrounded by wireless communication hardware. In this work, we report an unexpected observation that the cell membrane can oscillate at the nanometer scale in phase with the external RF radiation from kHz to GHz. By analyzing the oscillation modes, we reveal the mechanism behind the membrane oscillation resonance, membrane blebbing, the resulting cell death, and the selectivity of plasma-based cancer treatment based on the difference in the membrane's natural frequencies among cell lines. Therefore, a selectivity of treatment can be achieved by aiming at the natural frequency of the target cell line to focus the membrane damage on the cancer cells and avoid normal tissues nearby. This gives a promising cancer therapy that is especially effective in the mixing lesion of the cancer cells and normal cells such as glioblastoma where surgical removal is not applicable. Along with these new phenomena, this work provides a general understanding of the cell coupling with RF radiation from the externally stimulated membrane behavior to the cell apoptosis and necrosis.

Single-cell electroporation with high-frequency nanosecond pulse bursts: Simulation considering the irreversible electroporation effect and experimental validation

To study the electroporation characteristics of cells under high-frequency nanosecond pulse bursts (HFnsPBs), the original electroporation mathematical model was improved. By setting a threshold value for irreversible electroporation (IRE) and considering the effect of an electric field on the surface tension of a cell membrane, a mathematical model of electroporation considering the effect of IRE is proposed for the first time. A typical two-dimensional cell system was discretized into nodes using MATLAB, and a mesh transport network method (MTNM) model was established for simulation. The dynamic processes of single-cell electroporation and molecular transport under the application of 50 unipolar HFnsPBs with field intensities of 9 kV cm^-1 and different frequencies (10 kHz, 100 kHz and 500 kHz) to the target system was simulated with a 300 s simulation time. The IRE characteristics and molecular transport were evaluated. In addition, a PI fluorescent dye assay was designed to verify the correctness of the model by providing time-domain and spatial results that were compared with the simulation results. The simulation achieved IRE and demonstrated the cumulative effects of multipulse bursts and intraburst frequency on irreversible pores. The model can also reflect the cumulative effect of multipulse bursts on reversible pores by introducing an assumption of stable reversible pores. The experimental results agreed qualitatively with the simulation results. A relative calibration of the fluorescence data gave time-domain molecular transport results that were quantitatively similar to the simulation results. This article reveals the cell electroporation characteristics under HFnsPBs from a mechanism perspective and has important guidance for fields involving the IRE of cells.

Model for deformation of cells from external electric fields at or near resonant frequencies

This paper presents a numerical model to investigate the deformation of biological cells by applying external electric fields operating at or near cell resonant frequencies. Cells are represented as pseudo solids with high viscosity suspended in liquid media. The electric field source is an atmospheric plasma jet developed inhouse, for which the emitted energy distribution has been measured. Viscoelastic response is resolved in the entire cell structure by solving a deformation matrix assuming an isotropic material with a prescribed modulus of elasticity. To investigate cell deformation at resonant frequencies, one mode of natural cell oscillation is considered in which the cell membrane is made to radially move about its eigenfrequency. An electromagnetic wave source interacts with the cell and induces oscillation and viscoelastic response. The source carries energy in the form of a distribution function which couples a range of oscillating frequencies with electric field amplitudes. Results show that cell response may be increased by the external electric field operating at or near resonance. In the elastic regime, response increases until a steady threshold value, and the structure moves as a damped oscillator. Generally, this response is a function of both frequency and magnitude of the source, with a maximum effect found at resonance. To understand the full effect of the source energy spectrum, the system is solved by considering five frequency-amplitude couplings. Results show that the total solution is a nonlinear combination of the individual solutions. Additionally, sources with different signal phases are simulated to determine the effect of initial conditions on the evolution of the system, and the result suggests that there may be multiple solutions within the same order of magnitude for elastic response and velocity. Cell rupture from electric stress may occur during application given a high energy source.

Cell engineering with microfluidic squeezing preserves functionality of primary immune cells in vivo

Ex vivo manipulation of primary cells is critical to the success of this emerging generation of cell-based therapies, such as chimeric antigen receptor T cells for the treatment of cancer and CRISPR for the correction of developmental diseases. However, the limitations of existing delivery approaches may dramatically restrict the impact of genetic engineering to study and treat disease. In this paper, we compared electroporation to a microfluidic membrane deformation technique termed “squeezing” and found that squeezed cells had dramatically fewer side effects than electroporation and gene expression profiles similar to those of unmanipulated cells. The significant differences in outcomes from the two techniques underscores the importance of understanding the impact of intracellular delivery methods on cell function for research and clinical applications.

The translational potential of cell-based therapies is often limited by complications related to effectively engineering and manufacturing functional cells. While the use of electroporation is widespread, the impact of electroporation on cell state and function has yet to be fully characterized. Here, we use a genome-wide approach to study optimized electroporation treatment and identify striking disruptions in the expression profiles of key functional transcripts of human T cells. These genetic disruptions result in concomitant perturbation of cytokine secretion including a 648-fold increase in IL-2 secretion (P < 0.01) and a 30-fold increase in IFN-γ secretion (P < 0.05). Ultimately, the effects at the transcript and protein level resulted in functional deficiencies in vivo, with electroporated T cells failing to demonstrate sustained antigen-specific effector responses when subjected to immunological challenge. In contrast, cells subjected to a mechanical membrane disruption-based delivery mechanism, cell squeezing, had minimal aberrant transcriptional responses [0% of filtered genes misregulated, false discovery rate (FDR) q < 0.1] relative to electroporation (17% of genes misregulated, FDR q < 0.1) and showed undiminished effector responses, homing capabilities, and therapeutic potential in vivo. In a direct comparison of functionality, T cells edited for PD-1 via electroporation failed to distinguish from untreated controls in a therapeutic tumor model, while T cells edited with similar efficiency via cell squeezing demonstrated the expected tumor-killing advantage. This work demonstrates that the delivery mechanism used to insert biomolecules affects functionality and warrants further study.

Investigation of Optimized Treatment Conditions for Acoustic-Transfection Technique for Intracellular Delivery of Macromolecules

Manipulation of cellular functions and structures by introduction of genetic materials inside cells has been one of the most prominent research areas in biomedicine. High-frequency ultrasound acoustic-transfection has recently been developed and confirmed by intracellular delivery of small molecules into HeLa cells at the single-cell level with high cell viability. After we proved the concept underlying the acoustic-transfection technique, treatment conditions for different human cancer cell lines have been intensively investigated to further develop acoustic-transfection as a versatile and adaptable transfection method by satisfying the requirements of high-delivery efficiency and cell membrane permeability with minimal membrane disruption. To determine optimal treatment conditions for different cell lines, we developed a quantitative intracellular delivery score based on delivery efficiency, cell membrane permeability and cell viability after 4 and 20 h of treatment. The intracellular delivery of macromolecules and the simultaneous intracellular delivery of two molecules under optimal treatment conditions were successfully achieved. We found that DNA plasmid was delivered by acoustic-transfection technique into epiblast stem cells, which expressed transient mCherry fluorescence.

Directed multistep biocatalysis using tailored permeabilized cells

: Recent developments in the field of biocatalysis using permeabilized cells are reviewed here, with a special emphasis on the newly emerging area of multistep biocatalysis using permeabilized cells. New methods of metabolic engineering using in silico network design and new methods of genetic engineering provide the opportunity to design more complex biocatalysts for the synthesis of complex biomolecules. Methods for the permeabilization of cells are thoroughly reviewed. We provide an extended review of useful available databases and bioinformatics tools, particularly for setting up genome-scale reconstructed networks. Examples described include phosphorylated carbohydrates, sugar nucleotides, and polyketides.

Modulation of cell function by electric field: a high-resolution analysis

Regulation of cell function by a non-thermal, physiological-level electromagnetic field has potential for vascular tissue healing therapies and advancing hybrid bioelectronic technology. We have recently demonstrated that a physiological electric field (EF) applied wirelessly can regulate intracellular signalling and cell function in a frequency-dependent manner. However, the mechanism for such regulation is not well understood. Here, we present a systematic numerical study of a cell-field interaction following cell exposure to the external EF. We use a realistic experimental environment that also recapitulates the absence of a direct electric contact between the field-sourcing electrodes and the cells or the culture medium. We identify characteristic regimes and present their classification with respect to frequency, location, and the electrical properties of the model components. The results show a striking difference in the frequency dependence of EF penetration and cell response between cells suspended in an electrolyte and cells attached to a substrate. The EF structure in the cell is strongly inhomogeneous and is sensitive to the physical properties of the cell and its environment. These findings provide insight into the mechanisms for frequency-dependent cell responses to EF that regulate cell function, which may have important implications for EF-based therapies and biotechnology development.

Membrane disorder and phospholipid scrambling in electropermeabilized and viable cells

Membrane electropermeabilization relies on the transient permeabilization of the plasma membrane of cells submitted to electric pulses. This method is widely used in cell biology and medicine due to its efficiency to transfer molecules while limiting loss of cell viability. However, very little is known about the consequences of membrane electropermeabilization at the molecular and cellular levels. Progress in the knowledge of the involved mechanisms is a biophysical challenge. As a transient loss of membrane cohesion is associated with membrane permeabilization, our main objective was to detect and visualize at the single-cell level the incidence of phospholipid scrambling and changes in membrane order. We performed studies using fluorescence microscopy with C6-NBD-PC and FM1-43 to monitor phospholipid scrambling and membrane order of mammalian cells. Millisecond permeabilizing pulses induced membrane disorganization by increasing the translocation of phosphatidylcholines according to an ATP-independent process. The pulses induced the formation of long-lived permeant structures that were present during membrane resealing, but were not associated with phosphatidylcholine internalization. These pulses resulted in a rapid phospholipid flip/flop within less than 1s and were exclusively restricted to the regions of the permeabilized membrane. Under such electrical conditions, phosphatidylserine externalization was not detected. Moreover, this electrically-mediated membrane disorganization was not correlated with loss of cell viability. Our results could support the existence of direct interactions between the movement of membrane zwitterionic phospholipids and the electric field.

Electrochemotherapy is effective in the treatment of rat bone metastases

Bone metastases impair general health status, quality of life and survival of patients. Electrochemotherapy (ECT), which combines electroporation (EP) and the administration of anticancer drugs, has been recently introduced into clinical practice for the local treatment of solid tumours. In the present study, the ability of EP with bleomycin (Bleo) to induce MRMT-1 rat breast cancer cell death was investigated in vitro. Then, an in vivo model for bone metastases was set up by the inoculation of MRMT-1 cells in rat proximal tibia. 7 days after tumour induction the animals were treated with Bleo, EP, Bleo followed by EP (ECT), or left untreated. ECT eliminated the tumour in 6 out of 8 (75 %) treated metastases. Radiological evaluation showed that the Honore score in ECT-treated animals was significantly lower when compared with the other groups (p < 0.0005) and not significantly different from healthy controls. Bone morphology in ECT-treated animals, evaluated by histological and microtomographical analyses, showed intact cortical and trabecular bone structure with new bone apposition. Histomorphometric evaluation showed that ECT-treated metastases had significantly higher bone volume, trabecular number, trabecular thickness and bone mineral density compared with those of untreated metastases (respectively p < 0.0005 for BV/TV, Tb.N and BMD; p < 0.05 for Tb.Th) or metastases treated with Bleo (p < 0.05 for BV/TV, Tb.N, p < 0.005 for BMD) or EP (p < 0.005 for BV/TV, Tb.N; p < 0.0005 for BMD). These findings suggest that early ECT treatment of bone metastases is minimally invasive, safe and effective, thus providing pre-clinical evidence for its use in the treatment of human bone metastases.

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 actin cytoskeleton has an active role in the electrotransfer of plasmid DNA in mammalian cells

Electrotransfer of molecules is a well established technique which finds extensive use for gene transfer and holds great promise for anticancer treatment. Despite its widespread application, the mechanisms governing the entry of DNA into the cell and its intracellular trafficking are not yet known. The aim of this study is to unravel the role of the actin cytoskeleton during gene electrotransfer in cells. We performed single-cell level approaches to observe the organization of the actin cytoskeleton in Chinese hamster ovary (CHO) cells. In addition, we performed experiments at the multiple-cell level to evaluate the efficiency of DNA transfer after alteration of the actin cytoskeleton using the drug latrunculin B. Actin patches colocalizing with the DNA at the plasma membrane were observed with additional characteristics similar to those of the DNA aggregates in terms of time, number, and size. The disruption of the microfilaments reduces the DNA accumulation at the plasma membrane and the gene expression. This is the first direct experimental evidence of the participation of the actin cytoskeleton in DNA electrotransfer.

Probing field-induced tissue polarization using transillumination fluorescent imaging

Despite major successes of biophysical theories in predicting the effects of electrical shocks within the heart, recent optical mapping studies have revealed two major discrepancies between theory and experiment: 1), the presence of negative bulk polarization recorded during strong shocks; and 2), the unexpectedly small surface polarization under shock electrodes. There is little consensus as to whether these differences result from deficiencies of experimental techniques, artifacts of tissue damage, or deficiencies of existing theories. Here, we take advantage of recently developed near-infrared voltage-sensitive dyes and transillumination optical imaging to perform, for the first time that we know of, noninvasive probing of field effects deep inside the intact ventricular wall. This technique removes some of the limitations encountered in previous experimental studies. We explicitly demonstrate that deep inside intact myocardial tissue preparations, strong electrical shocks do produce considerable negative bulk polarization previously inferred from surface recordings. We also demonstrate that near-threshold diastolic field stimulation produces activation of deep myocardial layers 2-6 mm away from the cathodal surface, contrary to theory. Using bidomain simulations we explore factors that may improve the agreement between theory and experiment. We show that the inclusion of negative asymmetric current can qualitatively explain negative bulk polarization in a discontinuous bidomain model.

Enhanced hexadecane degradation and low biomass production by Aspergillus niger exposed to an electric current in a model system

The effects of an electric current on growth and hexadecane (HXD) degradation by Aspergillus niger growth were determined. A 450-mL electrochemical cell with titanium ruthenium-oxide coated electrodes and packed with 15 g of perlite (inert biomass support) was inoculated with A. niger (2.0×10(7) spores (g of dry inert support)(-1)) and incubated for 12 days (30 °C; constant ventilation). 4.5 days after starting culture a current of 0.42 mA cm(-2) was applied for 24h. The current reduced (52±11%) growth of the culture as compared to that of a culture not exposed to current. However, HXD degradation was 96±1.4% after 8 days whereas it was 81±1.2% after 12 days in control cultures. Carbon balances of cultures not exposed to current suggested an assimilative metabolism, but a non-assimilative metabolism when the current was applied. This change can be related to an increase in total ATP content. The study contributes to the knowledge on the effects of current on the mycelial growth phase of A. niger, and suggests the possibility of manipulating the metabolism of this organism with electric current.

Electroporation-induced inward current in voltage-clamped guinea pig ventricular myocytes

Electroporation induced by high-strength electrical fields has long been used to investigate membrane properties and facilitate transmembrane delivery of molecules and genes for research and clinical purposes. In the heart, electric field-induced passage of ions through electropores is a factor in defibrillation and postshock dysfunction. Voltage-clamp pulses can also induce electroporation, as exemplified by findings in earlier studies on rabbit ventricular myocytes: Long hyperpolarizations to ≤-110 mV induced influx of marker ethidium and irregular inward currents that were as large with external NMDG(+) as Na(+). In the present study, guinea pig ventricular myocytes were bathed with NMDG(+), Na(+) or NMDG(+) + La(3+) solution (36°C) and treated with five channel blockers. Hyperpolarization of myocytes in NMDG(+) solution elicited an irregular inward current (I (ep)) that reversed at -21.5 ± 1.5 mV. In myocytes hyperpolarized with 200-ms steps every 30 s, I (ep) occurred in "episodes" that lasted for one to four steps. Boltzmann fits to data on the incidence of I (ep) per experiment indicate 50% incidence at -129.7 ± 1.4 mV (Na(+)) and -146.3 ± 1.6 mV (NMDG(+)) (slopes ≈-7.5 mV). I (ep) amplitude increased with negative voltage and was larger with Na(+) than NMDG(+) (e.g., -2.83 ± 0.34 vs. -1.40 ± 0.22 nA at -190 mV). La(3+) (0.2 mM) shortened episodes, shifted 50% incidence by -35 mV and decreased amplitude, suggesting that it inhibits opening/promotes closing of electropores. We compare our findings with earlier ones, especially in regard to electropore selectivity. In the Appendix, relative permeabilities and modified excluded-area theory are used to derive estimates of electropore diameters consistent with reversal potential -21.5 mV.

In vitro gene transfer by electrosonoporation

Among the nonviral methods for gene delivery in vitro, electroporation is simple, inexpensive and safe. To upregulate the expression level of transfected gene, we investigated the applicability of electrosonoporation. This approach consists of a combination of electric pulses and ultrasound assisted with gas microbubbles. Cells were first electroporated with plasmid DNA encoding-enhanced green fluorescent protein and then sonoporated in presence of contrast microbubbles. Twenty-four hours later, cells that received electrosonoporation demonstrated a four-fold increase in transfection level and a six-fold increase in transfection efficiency compared with cells having undergone electroporation alone. Although electroporation induced the formation of DNA aggregates into the cell membrane, sonoporation induced its direct propulsion into the cytoplasm. Sonoporation can improve the transfer of electro-induced DNA aggregates by allowing its free and rapid entrance into the cells. These results demonstrated that in vitro gene transfer by electrosonoporation could provide a new potent method for gene transfer.

Single-cell electroporation

Single-cell electroporation (SCEP) is a relatively new technique that has emerged in the last decade or so for single-cell studies. When a large enough electric field is applied to a single cell, transient nano-pores form in the cell membrane allowing molecules to be transported into and out of the cell. Unlike bulk electroporation, in which a homogenous electric field is applied to a suspension of cells, in SCEP an electric field is created locally near a single cell. Today, single-cell-level studies are at the frontier of biochemical research, and SCEP is a promising tool in such studies. In this review, we discuss pore formation based on theoretical and experimental approaches. Current SCEP techniques using microelectrodes, micropipettes, electrolyte-filled capillaries, and microfabricated devices are all thoroughly discussed for adherent and suspended cells. SCEP has been applied in in-vivo and in-vitro studies for delivery of cell-impermeant molecules such as drugs, DNA, and siRNA, and for morphological observations.

Gene electrotransfer: from biophysical mechanisms to in vivo applications : Part 1- Biophysical mechanisms

Electropulsation is one of the nonviral methods successfully used to deliver genes into living cells in vitro and in vivo. This approach shows promise in the field of gene and cellular therapies. The present review focuses on the processes supporting gene electrotransfer in vitro. In the first part, we will report the events occurring before, during, and after pulse application in the specific field of plasmid DNA electrotransfer at the cell level. A critical discussion of the present theoretical considerations about membrane electropermeabilization and the transient structures involved in the plasmid uptake follows in a second part.

Visualization of membrane loss during the shrinkage of giant vesicles under electropulsation

We study the effect of permeabilizing electric fields applied to two different types of giant unilamellar vesicles, the first formed from EggPC lipids and the second formed from DOPC lipids. Experiments on vesicles of both lipid types show a decrease in vesicle radius, which is interpreted as being due to lipid loss during the permeabilization process. We show that the decrease in size can be qualitatively explained as a loss of lipid area, which is proportional to the area of the vesicle that is permeabilized. Three possible modes of membrane loss were directly observed: pore formation, vesicle formation, and tubule formation.

What is (still not) known of the mechanism by which electroporation mediates gene transfer and expression in cells and tissues

Cell membranes can be transiently permeabilized under application of electric pulses. This treatment allows hydrophilic therapeutic molecules, such as anticancer drugs and DNA, to enter into cells and tissues. This process, called electropermeabilization or electroporation, has been rapidly developed over the last decade to deliver genes to tissues and organs, but there is a general agreement that very little is known about what is really occurring during membrane electropermeabilization. It is well accepted that the entry of small molecules, such as anticancer drugs, occurs mostly through simple diffusion after the pulse while the entry of macromolecules, such as DNA, occurs through a multistep mechanism involving the electrophoretically driven interaction of the DNA molecule with the destabilized membrane during the pulse and then its passage across the membrane. Therefore, successful DNA electrotransfer into cells depends not only on cell permeabilization but also on the way plasmid DNA interacts with the plasma membrane and, once into the cytoplasm, migrates towards the nucleus. The focus of this review is to describe the different aspects of what is known of the mechanism of membrane permeabilization and associated gene transfer and, by doing so, what are the actual limits of the DNA delivery into cells.