Does the shape of the electric pulse matter in electroporation?

Current Advances and Future Prospects of Bulk and Microfluidic-Enabled Electroporation Systems

Reversible electroporation (EP) is a pivotal biophysical technology that leverages pulsed electric fields to enhance the permeability of cell membranes, thereby facilitating the introduction of foreign material into cells. In this review, we provide an overview of bulk electroporators and microfluidic-enabled EP systems, focusing on their controversial points of mechanisms, architectures, and parameter settings. Bulk electroporators have been extensively commercialized with settled form including pulse generator and accessories (i.e., EP cuvette and plates). Researchers have made efforts to increase the throughput and simplify the operation of bulk EP systems. Additionally, microfluidics has emerged as a promising technology for optimizing EP parameters and enhancing the performance. Given the significant structural differences between these two types of EP systems, their operating conditions such as temperature, voltage, and pulse parameters are discussed. Research tend to operate single cells under more concentrated electric field induced by low voltage, enabling a quantitative exogenous materials delivery and numerical simulation. However, due to cost constraints and properties of materials utilized in laboratories, the commercialization of laboratory prototypes has been impeded. Furthermore, the technological limitations, current commercialization status, and development trends have been examined.

Induction of feline fetal fibroblasts into pluripotent stem cells using cat-derived reprogramming factors

There are few studies on the establishment of induced pluripotent stem cells (iPSCs) in cats. Although induction using heterologous reprogramming factors delivered via viral vectors has been reported, its safety and reprogramming efficiency still require improvement. In addition, the reprogramming mechanism needs further elucidation. In this study, we constructed a series of expression vectors for cat-derived reprogramming transcription factors based on the piggyBac transposon system and transfected various factor combinations into cat fetal fibroblasts (CFFs) under different electroporation conditions to generate cat iPSCs (ciPSCs). Additionally, the specific roles of these factors in reprogramming were investigated. The results showed that under the optimized electroporation conditions (DMEM/F12 buffer, 300 V, 10 ms pulse duration, 2 pulses, 25 μg plasmid DNA, and 4 mm cuvette), the survival rate and transfection efficiency of CFFs reached 64 % and 67.8 %, respectively. Based on this condition, a seven-factor combination (cOSKM + pNL + SV40 Large T) was confirmed as a better inducer for establishing ciPSCs. The obtained ciPSCs exhibit good pluripotency and passaging stability. They express stemness-related genes and proteins, and can form embryoid bodies (EBs) capable of differentiating into all three germ layers. OCT4 (O), SOX2 (S), KLF4 (K), and c-MYC (M) play important cooperative and synergistic roles in the mesenchymal-to-epithelial transition (MET) during the initial stages of reprogramming, while the supplement of NANOG (N) and LIN28 (L) can further promote MET and is important for successful reprogramming. It lays a foundation for the further breeding of cloned and genetically modified cats, and provides a tool for studying embryonic developmental diseases, screening drugs, and applying to tissue regeneration.

New effective and less painful high frequency electrochemotherapy protocols: From optimization on 3D models to pilot study on veterinary patients

Electroporation, a physical method that permeabilizes cell membranes, is increasingly used in cancer treatment. By enhancing the uptake of hydrophilic antitumor drugs, it boosts their cytotoxic effects and has proven effective in both human and veterinary medicine through electrochemotherapy. However, this treatment requires loco-regional or even general anesthesia, as electrical pulses cause muscle contractions and pain. Several clinical studies have demonstrated that application of high frequency pulses (above 5000 Hz) and short pulse duration (under 11 μs) causes much less discomfort to patients. In order to reduce the pain associated with contractions while maintaining the effectiveness of the treatment, we have developed new protocols using a high-frequency generator that delivers electric field pulses at a pulse repetition rate up to 2 MHz, associated to a multipolar electrode. In vitro tests on colorectal cancer cells were performed to assess the efficiency of cisplatin and bleomycin in inducing cell death. The efficiency obtained after one single treatment on both cell suspensions and on 3D multicellular spheroid models were similar to the ones obtained using ESOPE (European standard operating procedures for electrochemotherapy) protocol, which is currently used in clinics. In addition, as tumor cells die in an immunogenic cell death (ICD) mode and can release danger associated molecular patterns (DAMPs), major hallmarks of ICD were evaluated following the treatment by quantifying the apoptotic cell death, caspases 3/7 activation and key DAMPs. Subsequently, pilot studies on small number of conscious cats and horses under mild sedation confirmed that these protocols did not cause any noticeable muscle contractions and resulted in either partial or complete responses. New high-frequency electroporation protocols, described herein, show great promise in shifting electrochemotherapy into an effective and painless cancer treatment.

Electric Field-Induced Effects in Eukaryotic Cells: Current Progress and Limitations

Electric fields (EFs) offer a powerful tool for manipulating cells and modulating their behavior, holding significant promise for regenerative medicine and cell biology. We provide a comprehensive overview of the effects of different types of EF on eukaryotic cells with the special focus on physical mechanisms and signaling pathways involved. Direct current EF induces electrophoresis and electroosmosis, influencing cell migration, proliferation, and differentiation. Alternating current EF, through dielectric polarization and dielectrophoresis, enables cell manipulation, trapping, and sorting. Pulsed EF, particularly high-intensity, short-duration pulses, induces reversible and irreversible electroporation, facilitating drug and gene delivery. The review covers some technological aspects of EF generation, emphasizing the importance of experimental setups, and integration with microfluidic platforms for high-throughput analysis and precise manipulations. Furthermore, the synergistic potential of combining EFs with optical tweezers is highlighted, enabling fine-tuned control of cell positioning, intercellular interactions, and measurement of biophysical properties. Finally, the review addresses limitations of EF application, such as field heterogeneity and potential side effects, and outlines the directions for future studies, including developing the minimally invasive delivery methods.

Influences of pulsed electric field parameters on cell electroporation and electrofusion events: Comprehensive understanding by experiments and molecular dynamics simulations

Electroporation and electrofusion are efficient methods, which have been widely used in different areas of biotechnology and medicine. Pulse strength and width, as an external condition, play an important role in the process of these methods. However, comparatively little work has been done to explore the effects of pulsed electric field parameters on electroporation and electrofusion. Herein, influences of pulse strength and width on the electroporation and electrofusion of phospholipid bilayers were systematically investigated by using experiments combined with molecular dynamics simulations. Experimental results and machine learning-based regression analysis showed that the number of pores is mainly determined by pulse strength, while the sizes of pores were enlarged by increasing the pulse widths. In addition, the formation of large-size pores is the most crucial factor that affects the fusion rate of myeloma cells. The same trend has taken place on coarse-grained and all-atom MD simulations. The result suggested that electroporation events occur only in an electric field exceeding the strength of threshold, and the unbalanced degree of electric potential between two membranes leads to pores formation during the process of electroporation. Generally, this work provides a comprehensive understanding of how pulse strength and width govern the poration event of bilayer lipid membranes, as well as guidance on the experimental design of electrofusion.

Advances in Pharmaceutical Science in Electrochemotherapy: A Tribute to Prof. Jolanta Saczko

This Special Issue is dedicated to the memory of Professor Jolanta Saczko (1964-2023), a remarkable leader whose guidance and dedication were instrumental in advancing electroporation-based research in Poland [...].

Inactivation of bacteria using synergistic hydrogen peroxide with split-dose nanosecond pulsed electric field exposures

The use of pulsed electric fields (PEF) as a nonthermal technology for the decontamination of foods is of growing interest. This study aimed to enhance the inactivation of Escherichia coli, Listeria innocua, and Salmonella enterica in Gomori buffer using a combination of nsPEF and hydrogen peroxide (H2O2). Three sub-MIC concentrations (0.1, 0.3, and 0.5%) of H2O2 and various contact times ranging from 5-45 min were tested. PEF exposures as both single (1000 pulse) and split-dose (500+500 pulse) trains were delivered via square-wave, monopolar, 600 ns pulses at 21 kV/cm and 10 Hz. We demonstrate that >5 log CFU/mL reduction can be attained from combination PEF/H2O2 treatments with a 15 min contact time for E. coli (0.1%) and a 30 min contact time for L. innocua and S. enterica (0.5%), despite ineffective results from either individual treatment alone. A 5 log reduction in microbial population is generally the lowest acceptable level in consideration of food safety and represents inactivation of 99.999% of bacteria. Split-dose PEF exposures enhance lethality for several tested conditions, indicating greater susceptibility to PEF after oxidative damage has occurred.

Numerical assessments of geometry, proximity and multi-electrode effects on electroporation in mitochondria and the endoplasmic reticulum to nanosecond electric pulses

Most simulations of electric field driven bioeffects have considered spherical cellular geometries or probed symmetrical structures for simplicity. This work assesses cellular transmembrane potential build-up and electroporation in a Jurkat cell that includes the endoplasmic reticulum (ER) and mitochondria, both of which have complex shapes, in response to external nanosecond electric pulses. The simulations are based on a time-domain nodal analysis that incorporates membrane poration utilizing the Smoluchowski model with angular-dependent changes in membrane conductivity. Consistent with prior experimental reports, the simulations show that the ER requires the largest electric field for electroporation, while the inner mitochondrial membrane (IMM) is the easiest membrane to porate. Our results suggest that the experimentally observed increase in intracellular calcium could be due to a calcium induced calcium release (CICR) process that is initiated by outer cell membrane breakdown. Repeated pulsing and/or using multiple electrodes are shown to create a stronger poration. The role of mutual coupling, screening, and proximity effects in bringing about electric field modifications is also probed. Finally, while including greater geometric details might refine predictions, the qualitative trends are expected to remain.

Plasmid DNA Delivery into the Skin via Electroporation with a Depot-Type Electrode

Objectives: Non-viral mediated plasmid DNA transfection by electroporation (EP) is an established method for gene transfection. In this study, the usefulness of direct EP at an intradermal (i.d.) site (DEP) with implanted electrodes to achieve a high protein expression level was investigated. In addition, DEP application with various intervals with a low application voltage was also evaluated to confirm its effect on protein expression. Methods: Green fluorescent protein (GFP)- and luciferase-encoding DNA were administrated, and GFP and luciferase were evaluated. Results: A higher protein expression level was observed after green fluorescent protein (GFP)- and luciferase-encoding DNA were delivered by i.d. injection followed by DEP application. When luciferase expression was observed with an in vivo imaging system, continuous expression was confirmed over 21 days after i.d. injection followed by DEP at 100 V. This approach provided increased gene expression levels compared with conventional EP methods via the stratum corneum layer. In addition, the effect of application voltage on luciferase expression was investigated; two-time applications (repeated DEP) at 20 V with 5 min intervals showed similar luciferase expression level to single DEP application with 100 V. Histological observations showed the skin became thicker after a single DEP at 100 V, whereas no apparent thickness changes were confirmed after repeated DEP at 20 V with 5 min intervals. Conclusions: This study revealed that direct i.d. voltage application achieved high protein expression levels even at low voltages. Skin is a promising administration site for DNA vaccines, so this approach may be effective for DNA vaccine delivery into skin tissue.

Radiofrequency ablation with sine and square electrical waveforms to enhance ablation range

Radiofrequency ablation (RFA) is a local treatment modality for primary liver cancers. Although various input parameters of the RF generator have been adjusted to improve the ablation ranges, the limited ablation ranges remain an obstacle to RFA. This study aimed to compare the ablation ranges and efficacy of sine and square electrical waveforms in a mouse tumor model. An RF generator with an adjustable electrical waveform was developed, and its ablation range in the porcine liver was compared. For all RF parameters, the square electrical waveform ablation range was greater than that of the sine electrical waveform (all p < 0.001) in the porcine liver. The 45 BALB/c nude mice were used to evaluate the efficacy of the two electrical waveforms after the RFA. The mean tumor volume in the square group was significantly lower than that in the sine group (p < 0.001), indicating a higher survival rate (60%). The cellular coagulative necrosis, inflammatory cell infiltration, heat shock proteins, cellular necrosis, and tumor necrosis were significantly greater in square electrical waveform than in sine electrical waveform (all; p < 0.05). RFA with square electrical waveforms has therapeutic potential for tumor management with an enhanced ablation range.

Burst sine wave electroporation (B-SWE) for expansive blood-brain barrier disruption and controlled non-thermal tissue ablation for neurological disease

The blood-brain barrier (BBB) limits the efficacy of treatments for malignant brain tumors, necessitating innovative approaches to breach the barrier. This study introduces burst sine wave electroporation (B-SWE) as a strategic modality for controlled BBB disruption without extensive tissue ablation and compares it against conventional pulsed square wave electroporation-based technologies such as high-frequency irreversible electroporation (H-FIRE). Using an in vivo rodent model, B-SWE and H-FIRE effects on BBB disruption, tissue ablation, and neuromuscular contractions are compared. Equivalent waveforms were designed for direct comparison between the two pulsing schemes, revealing that B-SWE induces larger BBB disruption volumes while minimizing tissue ablation. While B-SWE exhibited heightened neuromuscular contractions when compared to equivalent H-FIRE waveforms, an additional low-dose B-SWE group demonstrated that a reduced potential can achieve similar levels of BBB disruption while minimizing neuromuscular contractions. Repair kinetics indicated faster closure post B-SWE-induced BBB disruption when compared to equivalent H-FIRE protocols, emphasizing B-SWE's transient and controllable nature. Additionally, finite element modeling illustrated the potential for extensive BBB disruption while reducing ablation using B-SWE. B-SWE presents a promising avenue for tailored BBB disruption with minimal tissue ablation, offering a nuanced approach for glioblastoma treatment and beyond.

Possibilities and efficiency of MSC co-transfection for gene therapy

Mesenchymal stem/stromal cells (MSCs) are not only capable of self-renewal, trans-differentiation, homing to damaged tissue sites and immunomodulation by secretion of trophic factors but are also easy to isolate and expand. Because of these characteristics, they are used in numerous clinical trials for cell therapy including immune and neurological disorders, diabetes, bone and cartilage diseases and myocardial infarction. However, not all trials have successful outcomes, due to unfavourable microenvironmental factors and the heterogenous nature of MSCs. Therefore, genetic manipulation of MSCs can increase their prospect. Currently, most studies focus on single transfection with one gene. Even though the introduction of more than one gene increases the complexity, it also increases the effectivity as different mechanism are triggered, leading to a synergistic effect. In this review we focus on the methodology and efficiency of co-transfection, as well as the opportunities and pitfalls of these genetically engineered cells for therapy.

Application of pulsed electric field technology to skin engineering

Tissue engineering encompasses a range of techniques that direct the growth of cells into a living tissue construct for regenerative medicine applications, disease models, drug discovery, and safety testing. These techniques have been implemented to alleviate the clinical burdens of impaired healing of skin, bone, and other tissues. Construct development requires the integration of tissue-specific cells and/or an extracellular matrix-mimicking biomaterial for structural support. Production of such constructs is generally expensive and environmentally costly, thus eco-sustainable approaches should be explored. Pulsed electric field (PEF) technology is a nonthermal physical processing method commonly used in food production and biomedical applications. In this review, the key principles of PEF and the application of PEF technology for skin engineering will be discussed, with an emphasis on how PEF can be applied to skin cells to modify their behaviour, and to biomaterials to assist in their isolation or sterilisation, or to modify their physical properties. The findings indicate that the success of PEF in tissue engineering will be reliant on systematic evaluation of key parameters, such as electric field strength, and their impact on different skin cell and biomaterial types. Linking tangible input parameters to biological responses critical to healing will assist with the development of PEF as a sustainable tool for skin repair and other tissue engineering applications.

Biological autoluminescence enables effective monitoring of yeast cell electroporation

The application of pulsed electric fields (PEFs) is becoming a promising tool for application in biotechnology, and the food industry. However, real-time monitoring of the efficiency of PEF treatment conditions is challenging, especially at the industrial scale and in continuous production conditions.  To overcome this challenge, we have developed a straightforward setup capable of real-time detection of yeast biological autoluminescence (BAL) during pulsing. Saccharomyces cerevisiae culture was exposed to 8 pulses of 100 µs width with electric field strength magnitude 2-7 kV cm-1. To assess the sensitivity of our method in detecting yeast electroporation, we conducted a comparison with established methods including impedance measurements, propidium iodide uptake, cell growth assay, and fluorescence microscopy. Our results demonstrate that yeast electroporation can be instantaneously monitored during pulsing, making it highly suitable for industrial applications. Furthermore, the simplicity of our setup facilitates its integration into continuous liquid flow systems. Additionally, we have established quantitative indicators based on a thorough statistical analysis of the data that can be implemented through a dedicated machine interface, providing efficiency indicators for analysis.

Ultra-Low Intensity Post-Pulse Affects Cellular Responses Caused by Nanosecond Pulsed Electric Fields

High-intensity nanosecond pulse electric fields (nsPEF) can preferentially induce various effects, most notably regulated cell death and tumor elimination. These effects have almost exclusively been shown to be associated with nsPEF waveforms defined by pulse duration, rise time, amplitude (electric field), and pulse number. Other factors, such as low-intensity post-pulse waveform, have been completely overlooked. In this study, we show that post-pulse waveforms can alter the cell responses produced by the primary pulse waveform and can even elicit unique cellular responses, despite the primary pulse waveform being nearly identical. We employed two commonly used pulse generator designs, namely the Blumlein line (BL) and the pulse forming line (PFL), both featuring nearly identical 100 ns pulse durations, to investigate various cellular effects. Although the primary pulse waveforms were nearly identical in electric field and frequency distribution, the post-pulses differed between the two designs. The BL's post-pulse was relatively long-lasting (~50 µs) and had an opposite polarity to the main pulse, whereas the PFL's post-pulse was much shorter (~2 µs) and had the same polarity as the main pulse. Both post-pulse amplitudes were less than 5% of the main pulse, but the different post-pulses caused distinctly different cellular responses. The thresholds for dissipation of the mitochondrial membrane potential, loss of viability, and increase in plasma membrane PI permeability all occurred at lower pulsing numbers for the PFL than the BL, while mitochondrial reactive oxygen species generation occurred at similar pulsing numbers for both pulser designs. The PFL decreased spare respiratory capacity (SRC), whereas the BL increased SRC. Only the PFL caused a biphasic effect on trans-plasma membrane electron transport (tPMET). These studies demonstrate, for the first time, that conditions resulting from low post-pulse intensity charging have a significant impact on cell responses and should be considered when comparing the results from similar pulse waveforms.

Calcium Electrochemotherapy for Tumor Eradication and the Potential of High-Frequency Nanosecond Protocols

Calcium electroporation (CaEP) is an innovative approach to treating cancer, involving the internalization of supraphysiological amounts of calcium through electroporation, which leads to cell death. CaEP enables the replacement of chemotherapeutics (e.g., bleomycin). Here, we present a standard microsecond (μsCaEP) and novel high-frequency nanosecond protocols for calcium electroporation (nsCaEP) for the elimination of carcinoma tumors in C57BL/6J mice. We show the efficacy of CaEP in eliminating tumors and increasing their survival rates in vivo. The antitumor immune response after the treatment was observed by investigating immune cell populations in tumors, spleens, lymph nodes, and blood, as well as assessing antitumor antibodies. CaEP treatment resulted in an increased percentage of CD4+ and CD8+ central memory T cells and decreased splenic myeloid-derived suppressor cells (MDSC). Moreover, increased levels of antitumor IgG antibodies after CaEP treatment were detected. The experimental results demonstrated that the administration of CaEP led to tumor growth delay, increased survival rates, and stimulated immune response, indicating a potential synergistic relationship between CaEP and immunotherapy.

Basic Principles of RNA Interference: Nucleic Acid Types and In Vitro Intracellular Delivery Methods

Since its discovery in 1989, RNA interference (RNAi) has become a widely used tool for the in vitro downregulation of specific gene expression in molecular biological research. This basically involves a complementary RNA that binds a target sequence to affect its transcription or translation process. Currently, various small RNAs, such as small interfering RNA (siRNA), micro RNA (miRNA), small hairpin RNA (shRNA), and PIWI interacting RNA (piRNA), are available for application on in vitro cell culture, to regulate the cells' gene expression by mimicking the endogenous RNAi-machinery. In addition, several biochemical, physical, and viral methods have been established to deliver these RNAs into the cell or nucleus. Since each RNA and each delivery method entail different off-target effects, limitations, and compatibilities, it is crucial to understand their basic mode of action. This review is intended to provide an overview of different nucleic acids and delivery methods for planning, interpreting, and troubleshooting of RNAi experiments.