Dynamic effects of point source electroporation on the rat brain tissue

Alzheimer's disease and drug delivery across the blood-brain barrier: approaches and challenges

Alzheimer's disease (AD) is a diverse disease with a complex pathophysiology. The presence of extracellular β-amyloid deposition as neuritic plaques and intracellular accumulation of hyper-phosphorylated tau as neurofibrillary tangles remain the core neuropathologic criteria for diagnosing Alzheimer's disease. Nonetheless, several recent basic discoveries have revealed significant pathogenic roles for other essential cellular and molecular processes. Previously, there were not so many disease-modifying medications (DMT) available as drug distribution through the blood-brain barrier (BBB) is difficult due to its nature, especially drugs of polypeptides nature and proteins. Recently FDA has approved lecanemab as DMT for its proven efficacy. It is also complicated to deliver drugs for diseases like epilepsy or any brain tumor due to the limitations of the BBB. After the advancements in the drug delivery system, different techniques are used to transport the medication across the BBB. Other methods are used, like enhancement of brain blood vessel fluidity by liposomes, infusion of hyperosmotic solutions, and local intracerebral implants, but these are invasive approaches. Non-invasive approaches include the formulation of nanoparticles and their coating with polymers. This review article emphasizes all the above-mentioned techniques, procedures, and challenges to transporting medicines across the BBB. It summarizes the most recent literature dealing with drug delivery across the BBB.

Utilizing Human-Induced Pluripotent Stem Cells to Study Cardiac Electroporation Pulsed-Field Ablation

BACKGROUND

Electroporation is a promising nonthermal ablation method for cardiac arrhythmia treatment. Although initial clinical studies found electroporation pulsed-field ablation (PFA) both safe and efficacious, there are significant knowledge gaps concerning the mechanistic nature and electrophysiological consequences of cardiomyocyte electroporation, contributed by the paucity of suitable human in vitro models. Here, we aimed to establish and characterize a functional in vitro model based on human-induced pluripotent stem cells (hiPSCs)-derived cardiac tissue, and to study the fundamentals of cardiac PFA.

METHODS

hiPSC-derived cardiomyocytes were seeded as circular cell sheets and subjected to different PFA protocols. Detailed optical mapping, cellular, and molecular characterizations were performed to study PFA mechanisms and electrophysiological outcomes.

RESULTS

PFA generated electrically silenced lesions within the hiPSC-derived cardiac circular cell sheets, resulting in areas of conduction block. Both reversible and irreversible electroporation components were identified. Significant electroporation reversibility was documented within 5 to 15-minutes post-PFA. Irreversibly electroporated regions persisted at 24-hours post-PFA. Per single pulse, high-frequency PFA was less efficacious than standard (monophasic) PFA, whereas increasing pulse-number augmented lesion size and diminished reversible electroporation. PFA augmentation could also be achieved by increasing extracellular Ca2+ levels. Flow-cytometry experiments revealed that regulated cell death played an important role following PFA. Assessing for PFA antiarrhythmic properties, sustainable lines of conduction block could be generated using PFA, which could either terminate or isolate arrhythmic activity in the hiPSC-derived cardiac circular cell sheets.

CONCLUSIONS

Cardiac electroporation may be studied using hiPSC-derived cardiac tissue, providing novel insights into PFA temporal and electrophysiological characteristics, facilitating electroporation protocol optimization, screening for potential PFA-sensitizers, and investigating the mechanistic nature of PFA antiarrhythmic properties.

Cytoskeletal Remodeling and Gap Junction Translocation Mediates Blood-Brain Barrier Disruption by Non-invasive Low-Voltage Pulsed Electric Fields

High-voltage pulsed electric fields (HV-PEF) delivered with invasive needle electrodes for electroporation applications is known to induce off-target blood-brain barrier (BBB) disruption. In this study, we sought to determine the feasibility of minimally invasive PEF application to produce BBB disruption in rat brain and identify the putative mechanisms mediating the effect. We observed dose-dependent presence of Evans Blue (EB) dye in rat brain when PEF were delivered with a skull mounted electrode used for neurostimulation application. Maximum region of dye uptake was observed while using 1500 V, 100 pulses, 100 µs and 10 Hz. Results of computational models suggested that the region of BBB disruption was occurring at thresholds of 63 V/cm or higher; well below intensity levels for electroporation. In vitro experiments recapitulating this effect with human umbilical vein endothelial cells (HUVEC) demonstrated cellular alterations that underlie BBB manifests at low-voltage high-pulse conditions without affecting cell viability or proliferation. Morphological changes in HUVECs due to PEF were accompanied by disruption of actin cytoskeleton, loss of tight junction protein-ZO-1 and VE-Cadherin at cell junctions and partial translocation into the cytoplasm. Uptake of propidium iodide (PI) in PEF treated conditions is less than 1% and 2.5% of total number of cells in high voltage (HV) and low-voltage (LV) groups, respectively, implying that BBB disruption to be independent of electroporation under these conditions. 3-D microfabricated blood vessel permeability was found to increase significantly following PEF treatment and confirmed with correlative cytoskeletal changes and loss of tight junction proteins. Finally, we show that the rat brain model can be scaled to human brains with a similar effect on BBB disruption characterized by electric field strength (EFS) threshold and using a combination of two bilateral HD electrode configurations.

Breaking barriers: exploring mechanisms behind opening the blood-brain barrier

The blood-brain barrier (BBB) is a selectively permeable membrane that separates the bloodstream from the brain. While useful for protecting neural tissue from harmful substances, brain-related diseases are difficult to treat due to this barrier, as it also limits the efficacy of drug delivery. To address this, promising new approaches for enhancing drug delivery are based on disrupting the BBB using physical means, including optical/photothermal therapy, electrical stimulation, and acoustic/mechanical stimulation. These physical mechanisms can temporarily and locally open the BBB, allowing drugs and other substances to enter. Focused ultrasound is particularly promising, with the ability to focus energies to targeted, deep-brain regions. In this review, we examine recent advances in physical approaches for temporary BBB disruption, describing their underlying mechanisms as well as evaluating the utility of these physical approaches with regard to their potential risks and limitations. While these methods have demonstrated efficacy in disrupting the BBB, their safety, comparative efficacy, and practicality for clinical use remain an ongoing topic of research.

BBB opening by low pulsed electric fields, depicted by delayed-contrast MRI, enables efficient delivery of therapeutic doxorubicin doses into mice brains

BACKGROUND

Pharmacological treatment of CNS diseases is limited due to the presence of the blood-brain barrier (BBB). Recent years showed significant advancement in the field of CNS drug delivery enablers, with technologies such as MR-guided focused ultrasound reaching clinical trials. This have inspired researchers in the field to invent novel brain barriers opening (BBo) technologies that are required to be simple, fast, safe and efficient. One such technology, recently developed by us, is BDF (Barrier Disrupting Fields), based on low pulsed electric fields (L-PEFs) for opening the BBB in a controlled, safe, reversible and non-invasive manner. Here, we conducted an in vivo study to show that BDF is a feasible technology for delivering Doxorubicin (Doxo) into mice brain. Means for depicting BBBo levels were developed and applied for monitoring the treatment and predicting response. Overall, the goals of the presented study were to demonstrate the feasibility for delivering therapeutic Doxo doses into naïve and tumor-bearing mice brains and applying delayed-contrast MRI (DCM) for monitoring the levels of BBBo.

METHODS

L-PEFs were applied using plate electrodes placed on the intact skull of naïve mice. L-PEFs/Sham mice were scanned immediately after the procedure by DCM ("MRI experiment"), or injected with Doxo and Trypan blue followed by delayed (4 h) perfusion and brain extraction ("Doxo experiment"). Doxo concentrations were measured in brain samples using confocal microscopy and compared to IC50 of Doxo in glioma cell lines in vitro. In order to map BBBo extent throughout the brain, pixel by pixel MR image analysis was performed using the DCM data. Finally, the efficacy of L-PEFs in combination with Doxo was tested in nude mice bearing intracranial human glioma tumors.

RESULTS

Significant amount of Doxo was found in cortical regions of all L-PEFs-treated mice brains (0.50 ± 0.06 µg Doxo/gr brain) while in Sham brains, Doxo concentrations were below or on the verge of detection limit (0.03 ± 0.02 µg Doxo/gr brain). This concentration was x97 higher than IC50 of Doxo calculated in gl261 mouse glioma cells and x8 higher than IC50 of Doxo calculated in U87 human glioma cells. DCM analysis revealed significant BBBo levels in the cortical regions of L-PEFs-treated mice; the average volume of BBBo in the L-PEFs-treated mice was x29 higher than in the Sham group. The calculated BBBo levels dropped exponentially as a function of BBBo threshold, similarly to the electric fields distribution in the brain. Finally, combining non-invasive L-PEFs with Doxo significantly decreased brain tumors growth rates in nude mice.

CONCLUSIONS

Our results demonstrate significant BBBo levels induced by extra-cranial L-PEFs, enabling efficient delivery of therapeutic Doxo doses into the brain and reducing tumor growth. As BBBo was undetectable by standard contrast-enhanced MRI, DCM was applied to generate maps depicting the BBBo levels throughout the brain. These findings suggest that BDF is a promising technology for efficient drug delivery into the brain with important implications for future treatment of brain cancer and additional CNS diseases.

Passing of Nanocarriers across the Histohematic Barriers: Current Approaches for Tumor Theranostics

Over the past several decades, nanocarriers have demonstrated diagnostic and therapeutic (i.e., theranostic) potencies in translational oncology, and some agents have been further translated into clinical trials. However, the practical application of nanoparticle-based medicine in living organisms is limited by physiological barriers (blood-tissue barriers), which significantly hampers the transport of nanoparticles from the blood into the tumor tissue. This review focuses on several approaches that facilitate the translocation of nanoparticles across blood-tissue barriers (BTBs) to efficiently accumulate in the tumor. To overcome the challenge of BTBs, several methods have been proposed, including the functionalization of particle surfaces with cell-penetrating peptides (e.g., TAT, SynB1, penetratin, R8, RGD, angiopep-2), which increases the passing of particles across tissue barriers. Another promising strategy could be based either on the application of various chemical agents (e.g., efflux pump inhibitors, disruptors of tight junctions, etc.) or physical methods (e.g., magnetic field, electroporation, photoacoustic cavitation, etc.), which have been shown to further increase the permeability of barriers.

Advances of Electroporation-Related Therapies and the Synergy with Immunotherapy in Cancer Treatment

Electroporation is the process of instantaneously increasing the permeability of a cell membrane under a pulsed electric field. Depending on the parameters of the electric pulses and the target cell electrophysiological characteristics, electroporation can be either reversible or irreversible. Reversible electroporation facilitates the delivery of functional genetic materials or drugs to target cells, inducing cell death by apoptosis, mitotic catastrophe, or pseudoapoptosis; irreversible electroporation is an ablative technology which directly ablates a large amount of tissue without causing harmful thermal effects; electrotherapy using an electric field can induce cell apoptosis without any aggressive invasion. Reversible and irreversible electroporation can also activate systemic antitumor immune response and enhance the efficacy of immunotherapy. In this review, we discuss recent progress related to electroporation, and summarize its latest applications. Further, we discuss the synergistic effects of electroporation-related therapies and immunotherapy. We also propose perspectives for further investigating electroporation and immunotherapy in cancer treatment.

Opening the Blood Brain Barrier with an Electropermanent Magnet System

Opening the blood brain barrier (BBB) under imaging guidance may be useful for the treatment of many brain disorders. Rapidly applied magnetic fields have the potential to generate electric fields in brain tissue that, if properly timed, may enable safe and effective BBB opening. By tuning magnetic pulses generated by a novel electropermanent magnet (EPM) array, we demonstrate the opening of tight junctions in a BBB model culture in vitro, and show that induced monophasic electrical pulses are more effective than biphasic ones. We confirmed, with in vivo contrast-enhanced MRI, that the BBB can be opened with monophasic pulses. As electropermanent magnets have demonstrated efficacy at tuning B0 fields for magnetic resonance imaging studies, our results suggest the possibility of implementing an EPM-based hybrid theragnostic device that could both image the brain and enhance drug transport across the BBB in a single sitting.

Current Strategies to Enhance Delivery of Drugs across the Blood–Brain Barrier

The blood–brain barrier (BBB) has shown to be a significant obstacle to brain medication delivery. The BBB in a healthy brain is a diffusion barrier that prevents most substances from passing from the blood to the brain; only tiny molecules can pass across the BBB. The BBB is disturbed in specific pathological illnesses such as stroke, diabetes, seizures, multiple sclerosis, Parkinson’s disease, and Alzheimer’s disease. The goal of this study is to offer a general overview of current brain medication delivery techniques and associated topics from the last five years. It is anticipated that this review will stimulate readers to look into new ways to deliver medications to the brain. Following an introduction of the construction and function of the BBB in both healthy and pathological conditions, this review revisits certain contested questions, such as whether nanoparticles may cross the BBB on their own and if medications are selectively delivered to the brain by deliberately targeted nanoparticles. Current non-nanoparticle options are also discussed, including drug delivery via the permeable BBB under pathological circumstances and the use of non-invasive approaches to improve brain medication absorption.

Electroporation-Based Therapy for Brain Tumors: A Review

Electroporation-based therapy (EBT), as a high-voltage-pulse technology has been prevalent with favorable clinical outcomes in the treatment of various solid tumors. This review paper aims to promote the clinical translation of EBT for brain tumors. First, we briefly introduced the mechanism of pore formation in a cell membrane activated by external electric fields using a single cell model. Then, we summarized and discussed the current in vitro and in vivo preclinical studies, in terms of (1) the safety and effectiveness of EBT for brain tumors in animal models, and (2) the blood-brain barrier (BBB) disruption induced by EBT. Two therapeutic effects could be achieved in EBT for brain tumors simultaneously, i.e., the tumor ablation induced by irreversible electroporation (IRE) and transient BBB disruption induced by reversible electroporation (RE). The BBB disruption could potentially improve the uptake of antitumor drugs thereby enhancing brain tumor treatment. The challenges that hinder the application of EBT in the treatment of human brain tumors are discussed in the review paper as well.

Non-Invasive Low Pulsed Electrical Fields for Inducing BBB Disruption in Mice-Feasibility Demonstration

The blood–brain barrier (BBB) is a major hurdle for the treatment of central nervous system disorders, limiting passage of both small and large therapeutic agents from the blood stream into the brain. Thus, means for inducing BBB disruption (BBBd) are urgently needed. Here, we studied the application of low pulsed electrical fields (PEFs) for inducing BBBd in mice. Mice were treated by low PEFs using electrodes pressed against both sides of the skull (100–400 square 50 µs pulses at 4 Hz with different voltages). BBBd as a function of treatment parameters was evaluated using MRI-based treatment response assessment maps (TRAMs) and Evans blue extravasation. A 3D numerical model of the mouse brain and electrodes was constructed using finite element software, simulating the electric fields distribution in the brain and ensuring no significant temperature elevation. BBBd was demonstrated immediately after treatment and significant linear regressions were found between treatment parameters and the extent of BBBd. The maximal induced electric field in the mice brains, calculated by the numerical model, ranged between 62.4 and 187.2 V/cm for the minimal and maximal applied voltages. These results demonstrate the feasibility of inducing significant BBBd using non-invasive low PEFs, well below the threshold for electroporation.

Cytoskeletal Disruption after Electroporation and Its Significance to Pulsed Electric Field Therapies

Pulsed electric fields (PEFs) have become clinically important through the success of Irreversible Electroporation (IRE), Electrochemotherapy (ECT), and nanosecond PEFs (nsPEFs) for the treatment of tumors. PEFs increase the permeability of cell membranes, a phenomenon known as electroporation. In addition to well-known membrane effects, PEFs can cause profound cytoskeletal disruption. In this review, we summarize the current understanding of cytoskeletal disruption after PEFs. Compiling available studies, we describe PEF-induced cytoskeletal disruption and possible mechanisms of disruption. Additionally, we consider how cytoskeletal alterations contribute to cell-cell and cell-substrate disruption. We conclude with a discussion of cytoskeletal disruption-induced anti-vascular effects of PEFs and consider how a better understanding of cytoskeletal disruption after PEFs may lead to more effective therapies.

The application of point source electroporation and chemotherapy for the treatment of glioma: a randomized controlled rat study

The prognosis of Glioblastoma Multiforme patients is poor despite aggressive therapy. Reasons include poor chemotherapy penetration across the blood-brain barrier and tumor infiltration into surrounding tissues. Here we studied the effects of combined point-source electroporation (EP) and systemic chemotherapy in glioma-bearing rats. 128 rats were studied. Treatment groups were administered systemic Cisplatin/Methotrexate before EP (either 90 or 180 pulses). Control groups were treated by EP, chemotherapy, or no treatment. Tumor volumes were determined by MRI. Tumors growth rates of the EP + Methotrexate group (1.02 ± 0.77) were significantly lower (p < 0.01) than the control (5.2 ± 1.0) 1-week post treatment. No significant difference was found compared to Methotrexate (1.7 ± 0.5). Objective response rates (ORR) were 40% and 57% for the Methotrexate and EP + Methotrexate groups respectively. Tumor growth rates and ORR of the EP + Cisplatin groups (90 pulses 0.98 ± 0.2, 57%, 180 pulses 1.2 ± 0.1, 33%) were significantly smaller than the control (6.4 ± 1.0, p < 0.01, p < 0.02, 0%) and Cisplatin (3.9 ± 1.0, p < 0.04, p < 0.05, 13%) groups. No significant differences were found between the control groups. Increased survival was found in the EP + Cisplatin group, Χ² = 7.54, p < 0.006 (Log Rank). Point-source EP with systemic chemotherapy is a rapid, minimal-invasive treatment that was found to induce significant antineoplastic effects in a rat glioma model.

Temporal Characterization of Blood-Brain Barrier Disruption with High-Frequency Electroporation

Treatment of intracranial disorders suffers from the inability to accumulate therapeutic drug concentrations due to protection from the blood–brain barrier (BBB). Electroporation-based therapies have demonstrated the capability of permeating the BBB, but knowledge of the longevity of BBB disruption (BBBD) is limited. In this study, we quantify the temporal, high-frequency electroporation (HFE)-mediated BBBD in an in vivo healthy rat brain model. 40 male Fisher rats underwent HFE treatment; two blunt tipped monopolar electrodes were advanced into the brain and 200 bursts of HFE were delivered at a voltage-to-distance ratio of 600 V/cm. BBBD was verified with contrast enhanced T1W MRI (gadopentetate dimeglumine) and pathologically (Evans blue dye) at time points of 1, 24, 48, 72, and 96 h after HFE. Contrast enhanced T1W scans demonstrated BBBD for 1 to 72 h after HFE but intact BBB at 96 h. Histologically, tissue damage was restricted to electrode insertion tracks. BBBD was induced with minimal muscle contractions and minimal cell death attributed to HFE. Numerical modeling indicated that brief BBBD was induced with low magnitude electric fields, and BBBD duration increased with field strength. These data suggest the spatiotemporal characteristics of HFE-mediated BBBD may be modulated with the locally applied electric field.

Transient blood-brain barrier disruption is induced by low pulsed electrical fields in vitro: an analysis of permeability and trans-endothelial electric resistivity

The blood–brain barrier (BBB) is limiting transcellular and paracellular movement of molecules and cells, controls molecular traffic, and keeps out toxins. However, this protective function is the major hurdle for treating brain diseases such as brain tumors, Parkinson’s disease, Alzheimer’s disease, etc. It was previously demonstrated that high pulsed electrical fields (PEFs) can disrupt the BBB by inducing electroporation (EP) which increases the permeability of the transcellular route. Our goal was to study the effects of low PEFs, well below the threshold of EP on the integrity and function of the BBB. Ten low voltage pulses (5–100 V) were applied to a human in vitro BBB model. Changes in permeability to small molecules (NaF) were studied as well as changes in impedance spectrum and trans-endothelial electric resistivity. Viability and EP were evaluated by Presto-Blue and endogenous Lactate dehydrogenase release assays. The effect on tight junction and adherent junction protein was also studied. The results of low voltage experiments were compared to high voltage experiments (200–1400 V). A significant increase in permeability was found at voltages as low as 10 V despite EP only occurring from 100 V. The changes in permeability as a function of applied voltage were fitted to an inverse-exponential function, suggesting a plateau effect. Staining of VE-cadherin showed specific changes in protein expression. The results indicate that low PEFs can transiently disrupt the BBB by affecting the paracellular route, although the mechanism remains unclear.

A microfluidic model of the blood-brain barrier to study permeabilization by pulsed electric fields

Pulsed electric fields interact with the blood-brain barrier (BBB) and have been shown to increase the BBB permeability under some pulsing regimes. Pulsed electric fields may enhance drug delivery to the brain by disrupting the integrity of the BBB and allowing otherwise impermeable drugs to reach target areas. Microfluidic, in vitro models offer an alternative platform for exploring the impact of pulsed electric fields on the BBB because they create physiologically relevant microenvironments and eliminate the confounding variables of animal studies. We developed a microfluidic platform for real-time measurement of BBB permeability pre- and post-treatment with pulsed electric fields. Permeability is measured optically by the diffusion of fluorescent tracers across a monolayer of human cerebral microcapillary endothelial cells (hCMECs) cultured on a permeable membrane. We found that this device is able to capture real-time permeability of hCMEC monolayers for both reversible and irreversible electroporation pulsing regimes. Furthermore, preliminary testing of deep brain stimulation pulsing regimes reveals possible impacts on BBB integrity. This device will enable future studies of pulsed electric field regimes for improved understanding of BBB permeabilization.

Electroporation by concentric-type needle electrodes and arrays

The efficacy of genomic medicine depends on gene transfer efficiency. In this area, electroporation has been found to be a highly promising method for physical gene transfer. However, electroporation raises issues related to electrical safety, tissue damage, and the number of required wounds. Concentric-type needle electrodes seek to address these issues by using a lower bias (10V), a single wound, fewer processing steps, and a smaller working area (≈10mm³), thus offering greater accuracy and precision. Moreover, the needle can be arrayed to simultaneously treat several target regions. This paper proposes a novel method using concentric-type needle electrodes to improve the efficacy of genomic medicine in terms of electrical safety, human factor and usability engineering.

A statistical model describing combined irreversible electroporation and electroporation-induced blood-brain barrier disruption

Background

Electroporation-based therapies such as electrochemotherapy (ECT) and irreversible electroporation (IRE) are emerging as promising tools for treatment of tumors. When applied to the brain, electroporation can also induce transient blood-brain-barrier (BBB) disruption in volumes extending beyond IRE, thus enabling efficient drug penetration. The main objective of this study was to develop a statistical model predicting cell death and BBB disruption induced by electroporation. This model can be used for individual treatment planning.

Material and methods

Cell death and BBB disruption models were developed based on the Peleg-Fermi model in combination with numerical models of the electric field. The model calculates the electric field thresholds for cell kill and BBB disruption and describes the dependence on the number of treatment pulses. The model was validated using in vivo experimental data consisting of rats brains MRIs post electroporation treatments.

Results

Linear regression analysis confirmed that the model described the IRE and BBB disruption volumes as a function of treatment pulses number (r² = 0.79; p < 0.008, r² = 0.91; p < 0.001). The results presented a strong plateau effect as the pulse number increased. The ratio between complete cell death and no cell death thresholds was relatively narrow (between 0.88-0.91) even for small numbers of pulses and depended weakly on the number of pulses. For BBB disruption, the ratio increased with the number of pulses. BBB disruption radii were on average 67% ± 11% larger than IRE volumes.

Conclusions

The statistical model can be used to describe the dependence of treatment-effects on the number of pulses independent of the experimental setup.