The interplay of excitation and electroporation in nanosecond pulse stimulation

What is the best pulse shape for pacing purposes?

Introduction

Cell pacing is a fundamental procedure for generating action potentials (AP) in excitable tissues. Various pulse shapes have been proposed for this purpose, with the aim of either facilitating the achievement of the excitation threshold or minimizing energy delivery to the patient. This study seeks to identify the optimal pulse shape for each of these objectives.

Methods

To determine the most effective pulse forms, we employed a mathematical model simulating nonlinear tissue responses to a range of pulse shapes.

Results

Our results demonstrate that the rectangular pulse is optimal for reaching the excitation threshold, while the Gaussian pulse is superior in minimizing energy delivery. Other pulse shapes examined, including ramp-up, ramp-down, half-sine, and triangular (tent-like), fall between these two in terms of performance.

Discussion

From a clinical perspective, the appropriate pulse shape should be selected based on the specific goal. For minimizing the pulse amplitude required to cross the excitation threshold, the rectangular pulse is recommended. In contrast, if reducing energy delivery to the patient is paramount, the Gaussian pulse is the preferred choice. In other scenarios, a judicious selection can be made based on the outcomes of our model and the clinical requirements.

Anti-tumor effects of nanosecond pulsed electric fields in a murine model of pancreatic cancer

Nanosecond Pulsed Electric Fields (nsPEFs) treatment has demonstrated anti-tumor effects on various cancer cell lines. However, the use of this treatment in pancreatic cancer is limited. This study demonstrated that nsPEFs treatment effectively suppressed the proliferation and metastasis of pancreatic cancer cells, while also inducing DNA damage. Meanwhile, animal experiments have shown that nsPEFs effectively suppressed the growth of pancreatic cancer, even in cases where the tumor volume exceeded 500-600 mm3 at the initiation of treatment. Notably, a single treatment session was found to significantly inhibit tumor growth, while also showing no adverse effects on the main organs of the mice. RNA sequencing and bioinformatics revealed that seven key genes (CDK1, CENPA, UBE2C, CCNB2, PLK1, CCNA2, and CCNB14) were significantly correlated with the overall survival rate of patients with pancreatic cancer. Through the application of the competing endogenous RNA (ceRNA) hypothesis, two miRNAs (has-let-7b-5p and hsa-miR-193b-3p) and four lncRNAs (MIR4435-2HG, ZNF436-AS1, LINC01089, and MIR4435-2HG) were identified as significantly impacting the overall survival of pancreatic cancer patients. We have effectively developed an mRNA-miRNA-lncRNA network that has the potential to stimulate further investigation into the underlying mechanisms of nsPEFs on pancreatic cancer.

The performance of a new nanosecond pulsed-field ablation surgical clamp in the ablation of cardiac tissue: A chronic porcine model

OBJECTIVE

The purpose of this chronic porcine model is to demonstrate the safety and efficacy of a new nanosecond pulsed-field ablation (nsPFA) parallel clamp in ablating different cardiac tissue.

METHODS

The Pulse Biosciences nsPFA CellFX Clamp System was tested on 6 pigs. Ablations were performed in all 4 heart chambers by delivering a sequence of very short-duration, high-amplitude electrical pulses taking 1.25 seconds per application independent of tissue thickness or type. Testing for electrical exit block was performed at the time of surgery and at study termination. At 35 days, animals were killed humanely and anonymized histopathology was performed to assess lesion width, depth, and transmurality. Lesion pattern and general safety were compared with 6 animals in which a bipolar radiofrequency clamp was used (AtriCure Synergy Isolator System).

RESULTS

There were no device-related serious adverse events in the nsPFA group. There was 1 early device-related mortality at day 24 in the RFA group from perforation of 1 of the ventricular ablation sites. There were also 2 intracardiac thrombotic events with 1 systemic thromboembolic event in the radiofrequency group. Exit block was confirmed in all animals from both groups for the pulmonary veins and the posterior wall. Histologic findings were consistent and demonstrated mature scar formation in all nsPFA ablation specimens, whereas a 7.1% rate of incomplete histopathological scar maturation was present in the RFA group.

CONCLUSIONS

In this chronic porcine model, a single 1.25-second application independent of tissue thickness with the CellFX Parallel Clamp System demonstrated promising safety and efficacy profile. All lesions produced by this technology resulted in persistent exit block around pulmonary veins and the posterior atrial wall consistent with a reliable, contiguous and transmural ablation without injury to adjacent organs.

The Effects of Bipolar Cancellation Phenomenon on Nano-Electrochemotherapy of Melanoma Tumors: In Vitro and In Vivo Pilot

The phenomenon known as bipolar cancellation is observed when biphasic nanosecond electric field pulses are used, which results in reduced electroporation efficiency when compared to unipolar pulses of the same parameters. Basically, the negative phase of the bipolar pulse diminishes the effect of the positive phase. Our study aimed to investigate how bipolar cancellation affects Ca2+ electrochemotherapy and cellular response under varying electric field intensities and pulse durations (3-7 kV/cm, 100, 300, and 500 ns bipolar 1 MHz repetition frequency pulse bursts, n = 100). As a reference, standard microsecond range parametric protocols were used (100 µs × 8 pulses). We have shown that the cancellation effect is extremely strong when the pulses are closely spaced (1 MHz frequency), which results in a lack of cell membrane permeabilization and consequent failure of electrochemotherapy in vitro. To validate the observations, we have performed a pilot in vivo study where we compared the efficacy of monophasic (5 kV/cm × ↑500 ns × 100) and biphasic sequences (5 kV/cm × ↑500 ns + ↓500 ns × 100) delivered at 1 MHz frequency in the context of Ca2+ electrochemotherapy (B16-F10 cell line, C57BL/6 mice, n = 24). Mice treated with bipolar pulses did not exhibit prolonged survival when compared to the untreated control (tumor-bearing mice); therefore, the bipolar cancellation phenomenon was also occurrent in vivo, significantly impairing electrochemotherapy. At the same time, the efficacy of monophasic nanosecond pulses was comparable to 1.4 kV/cm × 100 µs × 8 pulses sequence, resulting in tumor reduction following the treatment and prolonged survival of the animals.

Modulating Ca2+ influx into adrenal chromaffin cells with short-duration nanosecond electric pulses

Isolated bovine adrenal chromaffin cells exposed to single 2-, 4-, or 5-ns pulses undergo a rapid, transient rise in intracellular Ca2+ mediated by Ca2+ entry via voltage-gated Ca2+ channels (VGCCs), mimicking the activation of these cells in vivo by acetylcholine. However, pulse durations 150 ns or longer elicit larger amplitude and longer-lived Ca2+ responses due to Ca2+ influx via both VGCCs and a yet to be identified plasma membrane pathway(s). To further our understanding of the differential effects of ultrashort versus longer pulse durations on Ca2+ influx, chromaffin cells were loaded with calcium green-1 and exposed to single 3-, 5-, 11-, 25-, or 50-ns pulses applied at their respective Ca2+ activation threshold electric fields. Increasing pulse duration from 3 or 5 ns to only 11 ns was sufficient to elicit increased amplitude and longer-lived Ca2+ responses in the majority of cells, a trend that continued as pulse duration increased to 50 ns. The amplification of Ca2+ responses was not the result of Ca2+ release from intracellular stores and was accompanied by a decreased effectiveness of VGCC inhibitors to block the responses and a reduced reliance on extracellular Na+ and membrane depolarization to evoke the responses. Inhibitors of pannexin channels, P2X receptors, or non-selective cation channels failed to attenuate 50-ns-elicited Ca2+ responses, ruling out these Ca2+-permeable channels as secondary Ca2+ entry pathways. Analytical calculations and numerical modeling suggest that the parameter that best determines the response of chromaffin cells to increasing pulse durations is the time the membrane charges to its peak voltage. These results highlight the pronounced sensitivity of a neuroendocrine cell to pulse durations differing by only tens of nanoseconds, which has important implications for the future development of nanosecond pulse technologies enabling electrostimulation applications for spatially focused and graded in vivo neuromodulation.

Central Causation of Autism/ASDs via Excessive [Ca2+]i Impacting Six Mechanisms Controlling Synaptogenesis during the Perinatal Period: The Role of Electromagnetic Fields and Chemicals and the NO/ONOO(-) Cycle, as Well as Specific Mutations

The roles of perinatal development, intracellular calcium [Ca2+]i, and synaptogenesis disruption are not novel in the autism/ASD literature. The focus on six mechanisms controlling synaptogenesis, each regulated by [Ca2+]i, and each aberrant in ASDs is novel. The model presented here predicts that autism epidemic causation involves central roles of both electromagnetic fields (EMFs) and chemicals. EMFs act via voltage-gated calcium channel (VGCC) activation and [Ca2+]i elevation. A total of 15 autism-implicated chemical classes each act to produce [Ca2+]i elevation, 12 acting via NMDA receptor activation, and three acting via other mechanisms. The chronic nature of ASDs is explained via NO/ONOO(-) vicious cycle elevation and MeCP2 epigenetic dysfunction. Genetic causation often also involves [Ca2+]i elevation or other impacts on synaptogenesis. The literature examining each of these steps is systematically examined and found to be consistent with predictions. Approaches that may be sed for ASD prevention or treatment are discussed in connection with this special issue: The current situation and prospects for children with ASDs. Such approaches include EMF, chemical avoidance, and using nutrients and other agents to raise the levels of Nrf2. An enriched environment, vitamin D, magnesium, and omega-3s in fish oil may also be helpful.

Therapeutic perspectives of high pulse repetition rate electroporation

Electroporation, a technique that uses electrical pulses to temporarily or permanently destabilize cell membranes, is increasingly used in cancer treatment, gene therapy, and cardiac tissue ablation. Although the technique is efficient, patients report discomfort and pain. Current strategies that aim to minimize pain and muscle contraction rely on the use of pharmacological agents. Nevertheless, technical improvements might be a valuable tool to minimize adverse events, which occur during the application of standard electroporation protocols. One recent technological strategy involves the use of high pulse repetition rate. The emerging technique, also referred as "high frequency" electroporation, employs short (micro to nanosecond) mono or bipolar pulses at repetition rate ranging from a few kHz to a few MHz. This review provides an overview of the historical background of electric field use and its development in therapies over time. With the aim to understand the rationale for novel electroporation protocols development, we briefly describe the physiological background of neuromuscular stimulation and pain caused by exposure to pulsed electric fields. Then, we summarize the current knowledge on electroporation protocols based on high pulse repetition rates. The advantages and limitations of these protocols are described from the perspective of their therapeutic application.

Development of 3D melanoma cultures on a hyaluronic acid-based scaffold with synthetic self-assembling peptides: Electroporation enhancement

Electrochemotherapy (ECT) with bleomycin is an effective antitumor treatment. Still, researchers are investigating new drugs and electroporation conditions to improve its efficacy. To this aim, in vivo assays are accurate but expensive and ethically questionable. Conversely, in vitro assays, although cheaper and straightforward, do not reflect the architecture of the biological tissue because they lack a tridimensional (3D) structure (as in the case of two-dimensional [2D] in vitro assays) or do not include all the extracellular matrix components (as in the case of 3D in vitro scaffolds). To address this issue, 3D in vitro models have been proposed, including spheroids and hydrogel-based cultures, which require a suitable low-conductive medium to allow cell membrane electroporation. In this study, a synthetic scaffold based on hyaluronic acid (HA) and self-assembling peptides (SAPs; EAbuK), condensed with a Laminin-derived adhesive sequence (IKVAV), is proposed as a reliable alternative. We compare SKMEL28 cells cultured in the HA-EAbuK-IKVAV scaffold to the control (HA only scaffold). Three days after seeding, the culture on the HA-EAbuK-IKVAV scaffold showed collagen production. SKMEL28 cells cultured on the HA-EAbuK-IKVAV scaffold started to be electroporated at 400 V/cm, whereas, at the same electric field intensity, those cultured on HA were not. As a reference, 2D experiments showed that electroporation of SKMEL28 cells starts at 600 V/cm using an electroporation buffer and at 800 V/cm in a culture medium, but with very low efficiency (<50 % of cells electroporated). 3D cultures on HA-EAbuK-IKVAV allowed the simulation of a more reliable microenvironment and may represent a valuable tool for studying electroporation conditions. Using Finite Element Analysis (FEA) to compute the transmembrane potential, we detected the influence of inhomogeneity of the extracellular matrix on electroporation effect. Our 3D cell culture electroporation simulations showed that the transmembrane potential increased when collagen surrounded the cells. Of note, in the collagen-enriched HA-EAbuK-IKVAV scaffold, EP was already improved at lower electric field intensities. This study shows the influence of the extracellular matrix on electric conductivity and electric field distribution on cell membrane electroporation and supports the adoption of more reliable 3D scaffolds in experimental electroporation studies.

Cellular excitability and ns-pulsed electric fields: Potential involvement of lipid oxidation in the action potential activation

Recent studies showed that nanosecond pulsed electric fields (nsPEFs) can activate voltage-gated ion channels (VGICs) and trigger action potentials (APs) in excitable cells. Under physiological conditions, VGICs' activation takes place on time scales of the order 10-100 µs. These time scales are considerably longer than the applied pulse duration, thus activation of VGICs by nsPEFs remains puzzling and there is no clear consensus on the mechanisms involved. Here we propose that changes in local electrical properties of the cell membrane due to lipid oxidation might be implicated in AP activation. We first use MD simulations of model lipid bilayers with increasing concentration of primary and secondary lipid oxidation products and demonstrate that oxidation not only increases the bilayer conductance, but also the bilayer capacitance. Equipped with MD-based characterization of electrical properties of oxidized bilayers, we then resort to AP modelling at the cell level with Hodgkin-Huxley-type models. We confirm that a local change in membrane properties, particularly the increase in membrane conductance, due to formation of oxidized membrane lesions can be high enough to trigger an AP, even when no external stimulus is applied. However, excessive accumulation of oxidized lesions (or other conductive defects) can lead to altered cell excitability.

Genetically engineered HEK cells as a valuable tool for studying electroporation in excitable cells

Electric pulses used in electroporation-based treatments have been shown to affect the excitability of muscle and neuronal cells. However, understanding the interplay between electroporation and electrophysiological response of excitable cells is complex, since both ion channel gating and electroporation depend on dynamic changes in the transmembrane voltage (TMV). In this study, a genetically engineered human embryonic kidney cells expressing NaV1.5 and Kir2.1, a minimal complementary channels required for excitability (named S-HEK), was characterized as a simple cell model used for studying the effects of electroporation in excitable cells. S-HEK cells and their non-excitable counterparts (NS-HEK) were exposed to 100 µs pulses of increasing electric field strength. Changes in TMV, plasma membrane permeability, and intracellular Ca2+ were monitored with fluorescence microscopy. We found that a very mild electroporation, undetectable with the classical propidium assay but associated with a transient increase in intracellular Ca2+, can already have a profound effect on excitability close to the electrostimulation threshold, as corroborated by multiscale computational modelling. These results are of great relevance for understanding the effects of pulse delivery on cell excitability observed in context of the rapidly developing cardiac pulsed field ablation as well as other electroporation-based treatments in excitable tissues.

The Effects of Interphase and Interpulse Delays and Pulse Widths on Induced Muscle Contractions, Pain and Therapeutic Efficacy in Electroporation-Based Therapies

Electroporation is used in medicine for drug and gene delivery, and as a nonthermal ablation method in tumor treatment and cardiac ablation. Electroporation involves delivering high-voltage electric pulses to target tissue; however, this can cause effects beyond the intended target tissue like nerve stimulation, muscle contractions and pain, requiring use of sedatives or anesthetics. It was previously shown that adjusting pulse parameters may mitigate some of these effects, but not how these adjustments would affect electroporation's efficacy. We investigated the effect of varying pulse parameters such as interphase and interpulse delay while keeping the duration and number of pulses constant on nerve stimulation, muscle contraction and assessing pain and electroporation efficacy, conducting experiments on human volunteers, tissue samples and cell lines in vitro. Our results show that using specific pulse parameters, particularly short high-frequency biphasic pulses with short interphase and long interpulse delays, reduces muscle contractions and pain sensations in healthy individuals. Higher stimulation thresholds were also observed in experiments on isolated swine phrenic nerves and human esophagus tissues. However, changes in the interphase and interpulse delays did not affect the cell permeability and survival, suggesting that modifying the pulse parameters could minimize adverse effects while preserving therapeutic goals in electroporation.

Next generation CANCAN focusing for remote stimulation by nanosecond electric pulses

Focusing electric pulse effects away from electrodes is a challenge because the electric field weakens with distance. Previously we introduced a remote focusing method based on bipolar cancellation, a phenomenon of low efficiency of bipolar nanosecond electric pulses (nsEP). Superpositioning two bipolar nsEP into a unipolar pulse canceled bipolar cancellation ("CANCAN" effect), enhancing bioeffects at a distance despite the electric field weakening. Here, we introduce the next generation (NG) CANCAN focusing with unipolar nsEP packets designed to produce bipolar waveforms near electrodes (suppressing electroporation) but not at the remote target. NG-CANCAN was tested in CHO cell monolayers using a quadrupole electrode array and labeling electroporated cells with YO-PRO-1 dye. We routinely achieved 1.5-2 times stronger electroporation in the center of the quadrupole than near electrodes, despite a 3-4-fold field attenuation. With the array lifted 1-2 mm above the monolayer (imitating a 3D treatment), the remote effect was enhanced up to 6-fold. We analyzed the role of nsEP number, amplitude, rotation, and inter-pulse delay, and showed how remote focusing is enhanced when re-created bipolar waveforms exhibit stronger cancellation. Advantages of NG-CANCAN include the exceptional versatility of designing pulse packets and easy remote focusing using an off-the-shelf 4-channel nsEP generator.

Surgical Ablation of Cardiac Tissue with Nanosecond Pulsed Electric Fields in Swine

BACKGROUND

Myocardial tissue can be ablated by the application nanosecond pulsed fields (nsPEFs). The applied electric fields irreversibly permeabilize cell membranes and thereby kill myocytes while leaving the extracellular matrix intact.

METHODS

In domestic pigs (n = 10), hearts were exposed via sternotomy and either ablated in vivo ([Formula: see text] = 5) or in excised, Langendorff-perfused hearts ([Formula: see text] = 5). The nsPEFs consisted of 6-36 pulses of 300 ns each, delivered at 3-6 Hz; the voltage applied varied from 10 to 12 kV. Atrial lesions were either created after inserting the bottom jaw of the bipolar clamp into the atrium via a purse string incision (2-3 lesions per atrium) or by clamping a double layer of tissue at the appendages (one lesion per atrium). Ventricular lesions were created after an incision at the apex. The transmurality of each lesion was determined at three points along the lesion using a triphenyl tetrazolium chloride (TTC) stain.

RESULTS

All 27 atrial lesions were transmural. This includes 13/13 purse string lesions (39/39 sections, tissue thickness 2.5-4.5 mm) and 14/14 appendage lesions (42/42 sections, tissue thickness 8-12 mm). All 3 right ventricular lesions were transmural (9/9 sections, 18 pulses per lesion). Left ventricular lesions were always transmural for 36 pulses (3/3 lesions, 9/9 sections). All lesions have highly consistent width across the wall. There were no pulse-induced arrhythmias or other complications during the procedure.

CONCLUSIONS

nsPEF ablation reliably created acute lesions in porcine atrial and ventricular myocardium. It has far better penetration and is faster than both radiofrequency ablation and cryoablation and it is free from thermal side effects.

How to alleviate cardiac injury from electric shocks at the cellular level

Electric shocks, the only effective therapy for ventricular fibrillation, also electroporate cardiac cells and contribute to the high-mortality post-cardiac arrest syndrome. Copolymers such as Poloxamer 188 (P188) are known to preserve the membrane integrity and viability of electroporated cells, but their utility against cardiac injury from cardiopulmonary resuscitation (CPR) remains to be established. We studied the time course of cell killing, mechanisms of cell death, and protection with P188 in AC16 human cardiomyocytes exposed to micro- or nanosecond pulsed electric field (μsPEF and nsPEF) shocks. A 3D printer was customized with an electrode holder to precisely position electrodes orthogonal to a cell monolayer in a nanofiber multiwell plate. Trains of nsPEF shocks (200, 300-ns pulses at 1.74 kV) or μsPEF shocks (20, 100-μs pulses at 300 V) produced a non-uniform electric field enabling efficient measurements of the lethal effect in a wide range of the electric field strength. Cell viability and caspase 3/7 expression were measured by fluorescent microscopy 2-24 h after the treatment. nsPEF shocks caused little or no caspase 3/7 activation; most of the lethally injured cells were permeable to propidium dye already at 2 h after the exposure. In contrast, μsPEF shocks caused strong activation of caspase 3/7 at 2 h and the number of dead cells grew up to 24 h, indicating the prevalence of the apoptotic death pathway. P188 at 0.2-1% reduced cell death, suggesting its potential utility in vivo to alleviate electric injury from defibrillation.

Sub-MHz bursts of nanosecond pulses excite neurons at paradoxically low electric field thresholds without membrane damage

Neuromodulation applications of nanosecond electric pulses (nsEP) are hindered by their low potency to elicit action potentials in neurons. Excitation by a single nsEP requires a strong electric field which injures neurons by electroporation. We bypassed the high electric field requirement by replacing single nsEP stimuli with high-frequency brief nsEP bursts. In hippocampal neurons, excitation thresholds progressively decreased at nsEP frequencies above 20-200 kHz, with up to 20-30-fold reduction at sub-MHz and MHz rates. For a fixed burst duration, thresholds were determined by the duty cycle, irrespective of the specific nsEP duration, rate, or number of pulses per burst. For 100-μs bursts of 100-, 400-, or 800-ns pulses, the threshold decreased as a power function when the duty cycle exceeded 3-5 %. nsEP bursts were compared with single "long" pulses whose duration and amplitude matched the duration and the time-average amplitude of the burst. Such pulses deliver the same electric charge as bursts, within the same time interval. High-frequency nsEP bursts excited neurons at the time-average electric field 2-3 times below the threshold for a single long pulse. For example, the excitation threshold of 139 ± 14 V/cm for a single 100-μs pulse decreased to 57 ± 8 V/cm for a 100-μs burst of 100-ns, 0.25-MHz pulses (p < 0.001). Applying nsEP in bursts reduced or prevented the loss of excitability in multiple stimulation attempts. Stimulation by high-frequency nsEP bursts is a powerful novel approach to excite neurons at paradoxically low electric charge while also avoiding the electroporative membrane damage.

Nanosecond electric pulses are equally effective in electrochemotherapy with cisplatin as microsecond pulses

BACKGROUND

Nanosecond electric pulses showed promising results in electrochemotherapy, but the underlying mechanisms of action are still unexplored. The aim of this work was to correlate cellular cisplatin amount with cell survival of cells electroporated with nanosecond or standardly used 8 × 100 μs pulses and to investigate the effects of electric pulses on cisplatin structure.

MATERIALS AND METHODS

Chinese hamster ovary CHO and mouse melanoma B16F1 cells were exposed to 1 × 200 ns pulse at 12.6 kV/cm or 25 × 400 ns pulses at 3.9 kV/cm, 10 Hz repetition rate or 8 × 100 μs pulses at 1.1 (CHO) or 0.9 (B16F1) kV/cm, 1 Hz repetition rate at three cisplatin concentrations. Cell survival was determined by the clonogenic assay, cellular platinum was measured by inductively coupled plasma mass spectrometry. Effects on the structure of cisplatin were investigated by nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry.

RESULTS

Nanosecond pulses equivalent to 8 × 100 μs pulses were established in vitro based on membrane permeabilization and cell survival. Equivalent nanosecond pulses were equally efficient in decreasing the cell survival and accumulating cisplatin intracellularly as 8 × 100 μs pulses after electrochemotherapy. The number of intracellular cisplatin molecules strongly correlates with cell survival for B16F1 cells, but less for CHO cells, implying the possible involvement of other mechanisms in electrochemotherapy. The high-voltage electric pulses did not alter the structure of cisplatin.

CONCLUSIONS

Equivalent nanosecond pulses are equally effective in electrochemotherapy as standardly used 8 × 100 μs pulses.

Identification of electroporation sites in the complex lipid organization of the plasma membrane

The plasma membrane of a biological cell is a complex assembly of lipids and membrane proteins, which tightly regulate transmembrane transport. When a cell is exposed to strong electric field, the membrane integrity becomes transiently disrupted by formation of transmembrane pores. This phenomenon termed electroporation is already utilized in many rapidly developing applications in medicine including gene therapy, cancer treatment, and treatment of cardiac arrhythmias. However, the molecular mechanisms of electroporation are not yet sufficiently well understood; in particular, it is unclear where exactly pores form in the complex organization of the plasma membrane. In this study, we combine coarse-grained molecular dynamics simulations, machine learning methods, and Bayesian survival analysis to identify how formation of pores depends on the local lipid organization. We show that pores do not form homogeneously across the membrane, but colocalize with domains that have specific features, the most important being high density of polyunsaturated lipids. We further show that knowing the lipid organization is sufficient to reliably predict poration sites with machine learning. Additionally, by analysing poration kinetics with Bayesian survival analysis we show that poration does not depend solely on local lipid arrangement, but also on membrane mechanical properties and the polarity of the electric field. Finally, we discuss how the combination of atomistic and coarse-grained molecular dynamics simulations, machine learning methods, and Bayesian survival analysis can guide the design of future experiments and help us to develop an accurate description of plasma membrane electroporation on the whole-cell level. Achieving this will allow us to shift the optimization of electroporation applications from blind trial-and-error approaches to mechanistic-driven design.

Electroporation and cell killing by milli- to nanosecond pulses and avoiding neuromuscular stimulation in cancer ablation

Ablation therapies aim at eradication of tumors with minimal impact on surrounding healthy tissues. Conventional pulsed electric field (PEF) treatments cause pain and muscle contractions far beyond the ablation area. The ongoing quest is to identify PEF parameters efficient at ablation but not at stimulation. We measured electroporation and cell killing thresholds for 150 ns–1 ms PEF, uni- and bipolar, delivered in 10- to 300-pulse trains at up to 1 MHz rates. Monolayers of murine colon carcinoma cells exposed to PEF were stained with YO-PRO-1 dye to detect electroporation. In 2–4 h, dead cells were labeled with propidium. Electroporation and cell death thresholds determined by matching the stained areas to the electric field intensity were compared to nerve excitation thresholds (Kim et al. in Int J Mol Sci 22(13):7051, 2021). The minimum fourfold ratio of cell killing and stimulation thresholds was achieved with bipolar nanosecond PEF (nsPEF), a sheer benefit over a 500-fold ratio for conventional 100-µs PEF. Increasing the bipolar nsPEF frequency up to 100 kHz within 10-pulse bursts increased ablation thresholds by < 20%. Restricting such bursts to the refractory period after nerve excitation will minimize the number of neuromuscular reactions while maintaining the ablation efficiency and avoiding heating.

Ca2+ dependence and kinetics of cell membrane repair after electropermeabilization

Electroporation, in particular with nanosecond pulses, is an efficient technique to generate nanometer-size membrane lesions without the use of toxins or other chemicals. The restoration of the membrane integrity takes minutes and is only partially dependent on [Ca²⁺]. We explored the impact of Ca²⁺ on the kinetics of membrane resealing by monitoring the entry of a YO-PRO-1 dye (YP) in BPAE and HEK cells. Ca²⁺ was promptly removed or added after the electric pulse (EP) by a fast-step perfusion. YP entry increased sharply after the EP and gradually slowed down following either a single- or a double-exponential function. In BPAE cells permeabilized by a single 300- or 600-ns EP at 14 kV/cm in a Ca²⁺-free medium, perfusion with 2 mM of external Ca²⁺ advanced the 90% resealing and reduced the dye uptake about twofold. Membrane restoration was accomplished by a combination of fast, Ca²⁺-independent resealing (τ = 13-15 s) and slow, Ca²⁺-dependent processes (τ ~70 s with Ca²⁺ and ~ 110 s or more without it). These time constants did not change when the membrane damage was doubled by increasing EP duration from 300 to 600 ns. However, injury by microsecond-range EP (300 and 600 μs) took longer to recover even when the membrane initially was less damaged, presumably because of the larger size of pores made in the membrane. Full membrane recovery was not prevented by blocking both extra- and intracellular Ca²⁺ (by loading cells with BAPTA or after Ca²⁺ depletion from the reticulum), suggesting the recruitment of unknown Ca²⁺-independent repair mechanisms.

High Frequency Bipolar Electroporator with Double-Crowbar Circuit for Load-Independent Forming of Nanosecond Pulses

In this work, a novel electroporation system (electroporator) is presented, which is capable of forming high frequency pulses in a broad range of parameters (65 ns–100 µs). The electroporator supports voltages up to 3 kV and currents up to 40 A and is based on H-bridge circuit topology. A synchronized double crowbar driving sequence is introduced to generate short nanosecond range pulses independently of the electroporator load. The resultant circuit generates pulses with repetition frequencies up to 5 MHz and supports unipolar, bipolar, and asymmetrical pulse sequences with arbitrary waveforms. The shortest pulse duration step is hardware limited to 33 ns. The electroporator was experimentally tested on the H69AR human lung cancer cell line using 20 kV/cm bipolar and unipolar 100 ns–1 μs pulses. Based on a YO-PRO-1 permeabilization assay, it was determined that the electroporator is suitable for applied research on electroporation. The system offers high flexibility in experimental design to trigger various electroporation-based phenomena.

Incorporation of electroendocytosis and nanosecond pulsed electric field in electrochemotherapy of breast cancer cells

The study aimed to evaluate the possibility to perform electrochemotherapy using nanosecond pulsed electric field (nsPEF) and low electric field (LEF) monopolar electrical impulses to alleviate the problems of conventional electroporation. Two types of pulses have been used to treat MCF-7 human breast carcinoma cell line: very low voltage (electric field strength) long trains of short unipolar electric pulses, and low frequencies of extremely intense (40kV/cm), ultra-short (10ns) electric pulses. The electropermeabilization efficiency of the formed endocytotic vesicles was measured using the cloning efficacy test. The cell viability was decreased significantly at a repetition frequency begins from 0.01 Hz by ~35% and reached complete cell loss at 1 Hz of nanosecond pulses for cells treated before with monopolar pulses at 20 V/cm in the presence of BLM with 4 µM concentration. The uptake of non-permeant drugs has been done without plasma membrane permeabilization (classical electroporation), but by endocytosis. Nanosecond electric pulses can disrupt the membrane of endocytotic vesicles and release the cytotoxic drug bleomycin.

Intrinsic properties of primary hippocampal neurons contribute to PIP2 depletion during nsEP-induced physiological response

High-energy, short-duration electric pulses (EPs) are known to be effective in neuromodulation, but the biological mechanisms underlying this effect remain unclear. Recently, we discovered that nanosecond electric pulses (nsEPs) could initiate the phosphatidylinositol_4,5-bisphosphate (PIP₂) depletion in non-excitable cells identical to agonist-induced activation of the G_q11 coupled receptors. PIP₂ is the precursor for multiple intracellular second messengers critically involved in the regulation of intracellular Ca²⁺ homeostasis and plasma membrane (PM) ion channels responsible for the control of neuronal excitability. In this paper we demonstrate a novel finding that five day in vitro (DIV5) primary hippocampal neurons (PHNs) undergo significantly higher PIP₂ depletion after 7.5 kV/cm 600 ns EP exposure than DIV1 PHNs and day 1-5 (D1-D5) non-excitable Chinese hamster ovarian cells with muscarinic receptor 1 (CHO-hM₁). Despite the age of development, the stronger 15 kV/cm 600 ns or longer 7.5 kV/cm 12 µs EP initiated profound PIP₂ depletion in all cells studied, outlining damage of the cellular PM and electroporation. Therefore, the intrinsic properties of PHNs in concert with nanoporation explain the stronger neuronal response to nsEP at lower intensity exposures. PIP₂ reduction in neurons could be a primary biological mechanism responsible for the stimulation or inhibition of neuronal tissues.

Effects of high-frequency nanosecond pulses on prostate cancer cells

Electroporation with pulsed electric fields show a potential to be applied as an experimental focal therapy of tumors. Sub-microsecond regime of electric pulses displays unique electrophysical features operative in cells and membranes. Recently, MHz compression of nanosecond pulses electric fields (nsPEFs) bursts proved to enhance the effectiveness of the therapy. High morbidity of prostate cancer (PCa) and risk of overtreatment associated with this malignancy call for new minimal-invasive treatment alternative. Herein we present the in vitro study for developing applications based on this new technology. In this study, we used flow cytometric analysis, cell viability assay, caspase activity analysis, wound healing assay, confocal microscopy study, and immunofluorescence to investigate the biological effect of high-frequency nsPEFs on PCa cells. Our results show that high-frequency nsPEFs induces the permeabilization and cell death of PCa cells. The cytotoxicity is significantly enhanced in MHz compression of pulses and with the presence of extracellular Ca²⁺. High-frequency nsPEFs trigger changes in PCa cells' cytoskeleton and their mobility. The presented data show a therapeutic potential of high-frequency nsPEFs in a PCa setting. The sub-microsecond regime of pulses can potentially be applied in nanosecond electroporation protocols for PCa treatment.

Safety factor for electrostimulation with nanosecond pulses

While electrical stimulation with pulses of milli- or microsecond duration is possible without electroporation, stimulation with nanosecond pulses typically entails electroporation, and nanosecond pulses can even cause electroporation without stimulation. A recently proposed explanation for this intriguing finding is that stimulation requires not only that a threshold membrane potential is reached, but also that it is sustained for a certain time t_min, while electroporation occurs almost immediately after a higher threshold potential is reached. Here we analytically derive stimulation and electroporation thresholds for membranes that satisfy these assumptions. We analyze the safety factor, i.e. the ratio between electroporation and stimulation threshold and its dependence on pulse duration, membrane charging time constant, and t_min. We find that the safety factor is sharply reduced if both the pulse duration and the membrane charging time constant are below t_min. We discuss different approaches to get models with varying t_min that could be used to experimentally test this theory and cardiac applications.

Peculiarities of Neurostimulation by Intense Nanosecond Pulsed Electric Fields: How to Avoid Firing in Peripheral Nerve Fibers

Intense pulsed electric fields (PEF) are a novel modality for the efficient and targeted ablation of tumors by electroporation. The major adverse side effects of PEF therapies are strong involuntary muscle contractions and pain. Nanosecond-range PEF (nsPEF) are less efficient at neurostimulation and can be employed to minimize such side effects. We quantified the impact of the electrode configuration, PEF strength (up to 20 kV/cm), repetition rate (up to 3 MHz), bi- and triphasic pulse shapes, and pulse duration (down to 10 ns) on eliciting compound action potentials (CAPs) in nerve fibers. The excitation thresholds for single unipolar but not bipolar stimuli followed the classic strength–duration dependence. The addition of the opposite polarity phase for nsPEF increased the excitation threshold, with symmetrical bipolar nsPEF being the least efficient. Stimulation by nsPEF bursts decreased the excitation threshold as a power function above a critical duty cycle of 0.1%. The threshold reduction was much weaker for symmetrical bipolar nsPEF. Supramaximal stimulation by high-rate nsPEF bursts elicited only a single CAP as long as the burst duration did not exceed the nerve refractory period. Such brief bursts of bipolar nsPEF could be the best choice to minimize neuromuscular stimulation in ablation therapies.

Interference targeting of bipolar nanosecond electric pulses for spatially focused electroporation, electrostimulation, and tissue ablation

Stimulation and electroporation by nanosecond electric pulses (nsEP) are distinguished by a phenomenon of bipolar cancellation, which stands for a reduced efficiency of bipolar pulses compared to unipolar ones. When two pairs of stimulating electrodes are arrayed in a quadrupole, bipolar cancellation inhibits nsEP effects near the electrodes, where the electric field is the strongest. Two properly shaped and synchronized bipolar nsEP overlay into a unipolar pulse towards the center of the electrode array, thus canceling the bipolar cancellation (a "CANCAN effect"). High efficiency of the re-created unipolar nsEP outweighs the weakening of the electric field with distance and focuses nsEP effects to the center. In monolayers of CHO, BPAE, and HEK cells, CANCAN effect achieved by the interference of two bipolar nsEP enhanced electroporation up to tenfold, with a peak at the quadrupole center. Introducing a time interval between bipolar nsEP prevented the formation of a unipolar pulse and eliminated the CANCAN effect. Strong electroporation by CANCAN stimuli killed cells over the entire area encompassed by the electrodes, whereas the time-separated pulses caused ablation only in the strongest electric field near the electrodes. The CANCAN approach is promising for uniform tumor ablation and stimulation targeting away from electrodes.

Nanosecond pulsed electric fields impair viability and mucin expression in mucinous colorectal carcinoma cell

Nanosecond pulsed electric fields (nsPEFs) are a non-thermal technology that can induce a myriad of biological responses and changes in cellular physiology. nsPEFs have gained significant attention as a novel cancer therapy. However, studies investigating the application of nsPEF in mucinous carcinomas are scarce. In this study, we explored several biological responses in two mucinous colorectal adenocarcinoma cell lines, LS 174T and HT-29, to nsPEF treatment. We determined the overall cell survival and viability rates following nsPEF treatment using CCK-8 and colony formation assays. We measured the intracellular effects of nsPEF treatment by analyzing cell cycle distribution, cell apoptosis and mitochondrial potential. We also analyzed mucin production at both mRNA and protein levels. Our results showed that nsPEF treatment significantly reduced mucinous cell viability in a dose-dependent manner. nsPEF treatment increased cell cycles arrest at G₀/G₁ while the proportion of G₂/M cells gradually decreased. Cell apoptosis increased following nsPEF treatment with a clear loss in mitochondrial membrane potential. Furthermore, the protein expression of functional mucin family members decreased after nsPEF treatment. In conclusion, nsPEF treatment reduced MCRC cell viability, cell proliferation, and mucin protein production while promoted apoptosis. Our work is a pilot study that projects some insights into the potential clinical applications of nsPEFs in treating mucinous colorectal carcinoma.

5 ns electric pulses induce Ca2+-dependent exocytotic release of catecholamine from adrenal chromaffin cells

Previously we reported that adrenal chromaffin cells exposed to a 5 ns, 5 MV/m pulse release the catecholamines norepinephrine (NE) and epinephrine (EPI) in a Ca²⁺-dependent manner. Here we determined that NE and EPI release increased with pulse number (one versus five and ten pulses at 1 Hz), established that release occurs by exocytosis, and characterized the exocytotic response in real-time. Evidence of an exocytotic mechanism was the appearance of dopamine-β-hydroxylase on the plasma membrane, and the demonstration by total internal reflection fluorescence microscopy studies that a train of five or ten pulses at 1 Hz triggered the release of the fluorescent dye acridine orange from secretory granules. Release events were Ca²⁺-dependent, longer-lived relative to those evoked by nicotinic receptor stimulation, and occurred with a delay of several seconds despite an immediate rise in Ca²⁺. In complementary studies, cells labeled with the plasma membrane fluorescent dye FM 1-43 and exposed to a train of ten pulses at 1 Hz underwent Ca²⁺-dependent increases in FM 1-43 fluorescence indicative of granule fusion with the plasma membrane due to exocytosis. These results demonstrate the effectiveness of ultrashort electric pulses for stimulating catecholamine release, signifying their promise as a novel electrostimulation modality for neurosecretion.