The molecular basis of electroporation

Electroporation enhances cell death in 3D scaffold-based MDA-MB-231 cells treated with metformin

Triple-negative breast cancer (TNBC), the most aggressive subtype of breast cancer lacks estrogen, progesterone, and HER2 receptors and hence, is therapeutically challenging. Towards this, we studied an alternate therapy by repurposing metformin (FDA-approved type-2 diabetic drug with anticancer properties) in a 3D-scaffold culture, with electrical pulses. 3D cell culture was used to simulate the tumor microenvironment more closely and MDA-MB-231, human TNBC cells, treated with both 5 mM metformin (Met) and 8 electrical pulses at 2500 V/cm, 10 µs (EP1) and 800 V/cm, 100 µs (EP2) at 1 Hz were studied in 3D and 2D. They were characterized using cell viability, reactive oxygen species (ROS), glucose uptake, and lactate production assays at 24 h. Cell viability, as low as 20 % was obtained with EP1 + 5 mM Met. They exhibited 1.65-fold lower cell viability than 2D with EP1 + 5 mM Met. ROS levels indicated a 2-fold increase in oxidative stress for EP1 + 5 mM Met, while the glucose uptake was limited to only 9 %. No significant change in the lactate production indicated glycolytic arrest and a non-conducive environment for MDA-MB-231 growth. Our results indicate that 3D cell culture, with a more realistic tumor environment that enhances cell death using metformin and electrical pulses could be a promising approach for TNBC therapeutic intervention studies.

Evaluation of the efficiency of various methods to load fluoroquinolones into Escherichia coli outer membrane vesicles as a novel antibiotic delivery platform

The development of novel antibacterial agents that are effective against Gram-negative bacteria is limited primarily by transport issues. This class of bacteria maintains a complex cell envelope consisting of two membrane bilayers, preventing the passage of most antibiotics. These drugs must therefore pass through protein channels called porins; however, many antibiotics are too large to pass through porins, and a common mechanism of acquired resistance is down-regulation of porins. To overcome this transport limitation, we have proposed the use of outer membrane vesicles (OMVs), released by Gram-negative bacteria, which deliver cargo to other bacterial cells in a porin-independent manner. In this work, we systematically studied the ability to load fluoroquinolones into purified Escherichia coli OMVs using in vivo and in vitro passive loading methods, and active loading methods such as electroporation and sonication. We observed limited loading of all of the antibiotics using passive loading techniques; sonication and electroporation significantly increased the loading, with electroporation at low voltages (200 and 400V) resulting in the greatest encapsulation efficiencies. We also demonstrated that imipenem, a carbapenem antibiotic, can be readily loaded into OMVs, and its administration via OMVs increases the effectiveness of the drug against E. coli. Our results demonstrate that small molecule antibiotics can be readily incorporated into OMVs to create novel delivery vehicles to improve antibiotic activity.

Effect of cholesterol on nanoparticle translocation across a lipid bilayer

Nanoparticles (NPs) have attracted significant attention as carriers for the delivery of drugs, genes, and macromolecules for biomedical and therapeutic applications. These technologies require NPs to be delivered to the interior of the cell. However, this translocation is unlikely because of the presence of a cell membrane composed of phospholipids, cholesterol, proteins, and glycans. The cell membrane composition can influence its rigidity; thus, membrane composition is a crucial factor in determining the translocation of NPs across the cell membrane. Here, we focus on cholesterol, which is an essential component of biological cell membranes, and investigate NP translocation across membranes containing cholesterol under an applied electric field using a coarse-grained molecular dynamics simulation. We found that NPs could translocate directly across cholesterol-containing membranes without irreversible membrane disruption. This unique translocation was induced by two key phenomena. Before NP translocation, a phospholipid-rich/cholesterol-poor domain was formed at the NP-membrane contact interface. Second, a smaller transmembrane pore was formed in the cholesterol-containing membrane during membrane crossing of the NP. Our findings imply that the delivery of NPs to the cell interior across the cholesterol-containing membrane can be achieved by appropriately controlling the strength of the applied electric field, depending on the cholesterol content in the membrane.

Tissue Ablation: Applications and Perspectives

Tissue ablation techniques have emerged as a critical component of modern medical practice and biomedical research, offering versatile solutions for treating various diseases and disorders. Percutaneous ablation is minimally invasive and offers numerous advantages over traditional surgery, such as shorter recovery times, reduced hospital stays, and decreased healthcare costs. Intra-procedural imaging during ablation also allows precise visualization of the treated tissue while minimizing injury to the surrounding normal tissues, reducing the risk of complications. Here, the mechanisms of tissue ablation and innovative energy delivery systems are explored, highlighting recent advancements that have reshaped the landscape of clinical practice. Current clinical challenges related to tissue ablation are also discussed, underlining unmet clinical needs for more advanced material-based approaches to improve the delivery of energy and pharmacology-based therapeutics.

The comparison of the dynamics of Ca2+ and bleomycin intracellular delivery after cell sonoporation and electroporation in vitro

Ca2+, in combination with SP or EP, induces cell cytotoxicity much faster compared to BLM. The application of BLM in combination with, SP or EP, reaches the level of cell death, induced by similar combination with Ca2+, only after 72 h. The methods of SP and EP were calibrated according to the level of differential cytotoxicity, determined after 6 days (using cell clonogenic assay). The combination of Ca2+ SP induces cell death faster than Ca2+ EP - after Ca2+ SP it increases to a maximum level after 15 min and remains constant for up to 6 days, while the cytotoxic efficiency after Ca2+ EP increases to the level of Ca2+ SP only after 72 h. The combination of BLM SP shows a very similar dynamics to BLM EP - both reach maximal level of cytotoxicity after 48-72 h. Ca2+ and BLM in combination with SP have shown similar levels of cytotoxicity at higher acoustic pressures (≥250 kPa); therefore, Ca2+ SP can be used to induce immediate and maximal level of cytotoxic effect. The faster cytotoxic efficiency of Ca2+ in combination with SP than EP was determined to be due to the involvement of microbubble inertial cavitation.

The estimation of pore size distribution of electroporated MCF-7 cell membrane

The size of the pores created by external electrical pulses is important for molecule delivery into the cell. The size of pores and their distribution on the cell membrane determine the efficiency of molecule transport into the cell. There are very few studies visualizing the presence of electropores. In this study, we aimed to investigate the size distribution of electropores that were created by high intensity and short duration electrical pulses on MCF-7 cell membrane. Scanning Electron Microscopy (SEM) was used to visualize and characterize the membrane pores created by the external electric field. Structural changes on the surface of the electroporated cell membrane was observed by Atomic Force Microscopy (AFM). The size distribution of pore sizes was obtained by measuring the radius of 500 electropores. SEM imaging showed non-uniform patterning. The average radius of the electropores was 12 nm, 51.60% of pores were distributed within the range of 5 to 10 nm, and 81% of pores had radius below 15 nm. These results showed that microsecond (µs) high intensity electrical pulses cause the creation of heterogeneous nanopores on the cell membrane.

Calculating transmembrane voltage on the electric pulse-affected cancerous cell membrane: using molecular dynamics and finite element simulations

CONTEXT

Electroporation is a technique that creates electrically generated pores in the cell membrane by modifying transmembrane potential. In this work, the finite element method (FEM) was used to examine the induced transmembrane voltage (ITV) of a spherical-shaped MCF-7 cell, allowing researchers to determine the stationary ITV. A greater ITV than the critical value causes permeabilization of the membrane. Furthermore, the present study shows how a specific surface conductivity can act as a stand-in for the thin layer that constitutes a cell membrane as the barrier between extracellular and intracellular environments. Additionally, the distribution of ITV on the cell membrane and its maximum value were experimentally evaluated for a range of applied electric fields. Consequently, the entire cell surface area was electroporated 66% and 68% for molecular dynamics (MD) simulations and FEM, respectively, when the external electric field of 1500 V/cm was applied to the cell suspension using the previously indicated numerical methods. Furthermore, the lipid bilayers' molecular structure was changed, which led to the development of hydrophilic holes with a radius of 1.33 nm. Applying MD and FEM yielded threshold values for transmembrane voltage of 700 and 739 mV, respectively.

METHOD

Using MD simulations of palmitoyloleoyl-phosphatidylcholine (POPC), pores in cell membranes exposed to external electric fields were numerically investigated. The dependence on the electric field was estimated and developed, and the amount of the electroporated cell surface area matches the applied external electric field. To investigate more, a mathematical model based on an adaptive neuro-fuzzy inference system (ANFIS) is employed to predict the percent cell viability of cancerous cells after applying four pulses during electroporation. For MD simulations, ArgusLab, VMD, and GROMACS software packages were used. Moreover, for FEM analysis, COMSOL software package was used. Also, it is worth mentioning that for mathematical model, MATLAB software is used.

Molecular Simulations Reveal the Free Energy Landscape and Transition State of Membrane Electroporation

The formation of pores over lipid membranes by the application of electric fields, termed membrane electroporation, is widely used in biotechnology and medicine to deliver drugs, vaccines, or genes into living cells. Continuum models for describing the free energy landscape of membrane electroporation were proposed decades ago, but they have never been tested against spatially detailed atomistic models. Using molecular dynamics (MD) simulations with a recently proposed reaction coordinate, we computed potentials of mean force of pore nucleation and pore expansion in lipid membranes at various transmembrane potentials. Whereas the free energies of pore expansion are compatible with previous continuum models, the experimentally important free energy barrier of pore nucleation is at variance with established models. The discrepancy originates from different geometries of the transition state; previous continuum models assumed the presence of a membrane-spanning defect throughout the process, whereas, according to the MD simulations, the transition state of pore nucleation is typically passed before a transmembrane defect has formed. A modified continuum model is presented that qualitatively agrees with the MD simulations. Using kinetics of pore opening together with transition state theory, our free energies of pore nucleation are in excellent agreement with previous experimental data.

Effect of pulsed electric field (PEF) on NaCl diffusion in beef and consequence on meat quality

The impact of various field strength (2, 3, 4 kV/cm) and treatment time (60s and 90s) combinations on NaCl content and diffusion coefficient of beef were evaluated in the current study. Weight change, water content, water holding capacity, and texture of beef after brining were also explored. The results demonstrated pulsed electric field (PEF) pre-treatment significantly increased NaCl uptake when the brining time was 150 min (P < 0.05). The maximum NaCl content increased by 19.50% and the diffusion coefficient increased by 58.50%. Relatively mild PEF (60s) could improve beef qualities, but longer treatment time (90s) was detrimental to these qualities. Meanwhile, more complete myofibrillar structure and lower lipid oxidation extent were observed in the samples treated by PEF, contributing to the higher a* values. In conclusion, short processing time (60s) and high field strength (4 kV/cm) treatment is a potential strategy for meat brining acceleration and quality improvement in practical industrial production.

Designing Reaction Coordinate for Ion-Induced Pore-Assisted Mechanism of Halide Ions Permeation through Lipid Bilayer by Umbrella Sampling

Ion permeation mechanism through lipid membranes helps to understand cellular processes. We propose new reaction coordinates that allow ions to permeate according to their water affinity and interaction with the hydrophilic layer. Simulations were done for three different halides (F-, Cl-, and I-) in two different lipid bilayers, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dinervonoyl-sn-glycero-3-phosphocholine (DNPC). It is found that the involvement of the water molecules decreases the free energy barrier. The ions were found to follow different pathways for permeation. Formation of proper pores required a collaboration effort of the hydration shell water molecules and the hydrophilic lipid layer, which was favored in the case of Cl- ions. The optimum charge density and good water affinity of Cl- with respect to F- and I- ions helped to form the pore. The effect was prominently seen in the case of DNPC membrane because of its higher hydrophobic thickness. The umbrella sampling results were compared with other methods such as the Markov state model (MSM) and well-tempered metadynamics (WT-metaD).

Reduced Graphene Oxide-Coated Fabrics for Joule-Heating and Antibacterial Applications

Multifunctional textiles have emerged as a significant area of research due to their growing importance and diverse applications. The main requirement for these fabrics is electroconductivity, which is usually gained by incorporating conductive materials such as graphene into the textile structure. In this article, an electrochemical method was demonstrated to integrate different loadings of reduced graphene oxide (rGO) into fabrics for enhanced electrical conductivity. The process involves spray coating of graphene oxide (GO) onto the fabric, followed by in situ electrochemical reduction of GO, resulting in a coating layer of rGO nanosheets. The rGO-coated fabric exhibited exceptional Joule-heating capabilities, achieving 127 °C under a 9 V direct voltage with only 770 μg/cm2 of rGO loading. Moreover, the antibacterial properties of the rGO-coated fabric were demonstrated, showing a significant reduction rate of over 99.99% against both Bacillus subtilis and Escherichia coli. Joule-heating and antibacterial performances of the rGO-coated fabric were investigated over eight repeated cycles, demonstrating excellent repeatability. The simplicity of the fabrication method, along with the electrothermal and antibacterial effects of the rGO-coated fabric, makes it a promising material for various practical applications.

Effects of Nitro-Oxidative Stress on Biomolecules: Part 1-Non-Reactive Molecular Dynamics Simulations

Plasma medicine, or the biomedical application of cold atmospheric plasma (CAP), is an expanding field within plasma research. CAP has demonstrated remarkable versatility in diverse biological applications, including cancer treatment, wound healing, microorganism inactivation, and skin disease therapy. However, the precise mechanisms underlying the effects of CAP remain incompletely understood. The therapeutic effects of CAP are largely attributed to the generation of reactive oxygen and nitrogen species (RONS), which play a crucial role in the biological responses induced by CAP. Specifically, RONS produced during CAP treatment have the ability to chemically modify cell membranes and membrane proteins, causing nitro-oxidative stress, thereby leading to changes in membrane permeability and disruption of cellular processes. To gain atomic-level insights into these interactions, non-reactive molecular dynamics (MD) simulations have emerged as a valuable tool. These simulations facilitate the examination of larger-scale system dynamics, including protein-protein and protein-membrane interactions. In this comprehensive review, we focus on the applications of non-reactive MD simulations in studying the effects of CAP on cellular components and interactions at the atomic level, providing a detailed overview of the potential of CAP in medicine. We also review the results of other MD studies that are not related to plasma medicine but explore the effects of nitro-oxidative stress on cellular components and are therefore important for a broader understanding of the underlying processes.

Enhancing the antibacterial effect of iron oxide and silver nanoparticles by extremely low frequency electric fields (ELF-EF) against S. aureus

Staphylococcus aureus is the cause of many infectious and inflammatory diseases and a lot of studies aim to discover alternative ways for infection control and treatment rather than antibiotics. This work attempts to reduce bacterial activity and growth characteristics of Staphylococcus aureus using nanoparticles (iron oxide nanoparticles and silver nanoparticles) and extremely low frequency electric fields (ELF-EF). Bacterial suspensions of Staphylococcus aureus were used to prepare the samples, which were evenly divided into groups. Control group, 10 groups were exposed to ELF-EF in the frequency range (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1 Hz), iron oxide NPs treated group, iron oxide NPs exposed to 0.8 Hz treated group, silver NPs treated group and the last group was treated with silver NPs and 0.8 Hz. Antibiotic sensitivity testing, dielectric relaxation, and biofilm development for the living microbe were used to evaluate morphological and molecular alterations. Results showed that combination of nanoparticles with ELF-EF at 0.8 Hz enhanced the bacterial inhibition efficiency, which may be due to structural changes. These were supported by the dielectric measurement results which indicated the differences in the dielectric increment and electrical conductivity for the treated samples compared with control samples. This was also confirmed by biofilm formation measurements obtained. We may conclude that the exposure of Staphylococcus aureus bacteria to ELF-EF and NPs affected its cellular activity and structure. This technique is nondestructive, safe and fast and could be considered as a mean to reduce the use of antibiotics.

Phase-field model of bilipid membrane electroporation

This paper proposes a new model of membrane electropermeabilisation that combines the water content of the membrane and the transmembrane voltage. Interestingly, thanks to a well defined free-energy of the membrane, we somehow generalise the seminal approach of Chizmadzhev, Weaver and Krassowska, getting rid of the geometrical cylindrical assumption upon which most of the current electroporation models are based. Our approach is physically relevant and we recover a surface diffusion equation of the lipid phase proposed by Leguèbe et al. in a previous phenomenological model. We also perform a fine analysis of the involved nonlocal operators in two simple configurations (a spherical membrane and a flat periodic membrane) that enables us to compare the time constants of the phenomenon in spherical and flat membranes. An accurate splitting scheme combined with Fast Fourier Transforms is developed for efficient computations of the model. Our numerical results enable us to make a link between the molecular dynamics simulations of membrane permeabilisation and the experimental observations on vesicles and cells.

Studying the roles of salt ions in the pore initiation and closure stages in the biomembrane electroporation

Electroporation shows great potential in biology and biomedical applications. However, there is still a lack of reliable protocol for cell electroporation to achieve a high perforation efficiency due to the unclear influence mechanism of various factors, especially the salt ions in buffer solution. The tiny membrane structure of a cell and the electroporation scale make it difficult to monitor the electroporation process. In this study, we used both molecular dynamics (MD) simulation and experimental methods to explore the influence of salt ions on the electroporation process. Giant unilamellar vesicles (GUVs) were constructed as the model, and sodium chloride (NaCl) was selected as the representative salt ion in this study. The results show that the electroporation process follows lag-burst kinetics, where the lag period first appears after applying the electric field, followed by a rapid pore expansion. For the first time, we find that the salt ion plays opposite roles in different stages of the electroporation process. The accumulation of salt ions near the membrane surface provides an extra potential to promote the pore initiation, while the charge screening effect of the ions within the pore increases the line tension of the pore to induce the instability of the pore and lead to the closure. The GUV electroporation experiments obtain qualitatively consistent results with MD simulations. This work can provide guidance for the selection of parameters for cell electroporation process.

A molecular dynamics study of phospholipid membrane electroporation induced by bipolar pulses with different intervals

The mechanism of changes in cell electroporation (EP) during the intervals of bipolar pulses is still unclear, and few studies have investigated the effect of the intervals at the molecular level. In this study, EP induced by bipolar pulses (BP) with different intervals was investigated using all-atom molecular dynamics simulations. Firstly, EP was formed during the positive pulses of 2 ns and 0.5 V nm^-1, then the effects of various intervals of 0, 1, 5, and 10 ns on EP evolution were investigated, and the dynamic changes of different degrees of EP induced by the following negative pulses of 2 ns and 0.5 V nm^-1 were analyzed. The elimination effect of intervals was determined and it was related to the degrees of EP and the time of intervals. At the last moment of the intervals the phospholipid membrane was classified and quantitatively defined in three states according to the degrees of EP, namely, Resealing, Destabilizing and Retaining states. These states appeared due to the combined effect of both the positive pulse and the interval, and the states represent the degrees of EP which had different responses after applying the negative pulse. These results can improve our understanding of the fundamental mechanism of BP-induced EP.

Equivalence of Charge Imbalance and External Electric Fields during Free Energy Calculations of Membrane Electroporation

Electric fields across lipid membranes play important roles in physiology, medicine, and biotechnology, rationalizing the wide interest in modeling transmembrane potentials in molecular dynamics simulations. Transmembrane potentials have been implemented with external electric fields or by imposing charge imbalance between the two water compartments of a stacked double-membrane system. We compare the two methods in the context of membrane electroporation, which involves a large change of membrane structure and capacitance. We show that, given that Ewald electrostatics are defined with tinfoil boundary conditions, the two methods lead to (i) identical potentials of mean force (PMFs) of pore formation and expansion at various potentials, demonstrating that the two methods impose equivalent driving forces for large-scale transitions at membranes, and (ii) to identical polarization of water within thin water wires or open pores, suggesting that the two methods furthermore impose equivalent local electric fields. Without tinfoil boundary conditions, effects from external fields on pore formation are spuriously suppressed or even removed. Together, our study shows that both methods, external fields and charge imbalance, are well suitable for studying large-scale transitions of lipid membranes that involve changes of membrane capacitance. However, using charge imbalance is technically more challenging for maintaining a constant transmembrane potential since it requires updating of the charge imbalance as the membrane capacitance changes.

Advances in pulsed electric stimuli as a physical method for treating liquid foods

There is a need for alternative technologies that can deliver safe and nutritious foods at lower costs as compared to conventional processes. Pulsed electric field (PEF) technology has been utilised for a plethora of different applications in the life and physical sciences, such as gene/drug delivery in medicine and extraction of bioactive compounds in food science and technology. PEF technology for treating liquid foods involves engineering principles to develop the equipment, and quantitative biochemistry and microbiology techniques to validate the process. There are numerous challenges to address for its application in liquid foods such as the 5-log pathogen reduction target in food safety, maintaining the food quality, and scale up of this physical approach for industrial integration. Here, we present the engineering principles associated with pulsed electric fields, related inactivation models of microorganisms, electroporation and electropermeabilization theory, to increase the quality and safety of liquid foods; including water, milk, beer, wine, fruit juices, cider, and liquid eggs. Ultimately, we discuss the outlook of the field and emphasise research gaps.

Anticorrelated position fluctuation of lipids in forming membrane water pores: molecular dynamics simulations study with dengue virus capsid protein

The traffic of molecules into or out of cells is regulated by many membrane-associated mechanisms. Membrane pores are considered as one of the major passage mechanisms, although molecular-level understanding of pore formation is still vague. The opening of a membrane pore depends on many factors, including the influence of some proteins. The ability of the cell-penetrating peptides and supercharged proteins to form membrane pores has been reported. We studied pore formation through dipalmitoylphosphatidylcholine (DPPC) lipid bilayers by supercharged dengue virus capsid (C) protein. Atomistic molecular dynamics simulations confirmed the formation of membrane pores by a combined effect of the C protein and the membrane electric field. Analyses of simulated trajectories showed highly correlated vertical position fluctuations between the C_α atom of the membrane-anchored arginine residues and the phosphorus atoms of the surrounding DPPC lipids. Certain regions of the bilayer were negatively correlated while the others were positively correlated with respect to the fluctuations of the C_α atom of the anchored arginine residues. When positively correlated lipids in one leaflet vertically aligned with the negatively correlated lipids in the other leaflet, a local anticorrelated region was generated by weakening the bilayer. The membrane pore was always formed close to this anticorrelated region. Once formed, the C protein followed the hydrated pathway provided by the water-filled pores to cross the membrane.Communicated by Ramaswamy H. Sarma.

Non-equilibrium molecular dynamics study of human aquaporin-2 in the static external electric fields

In this paper, non-equilibrium MD simulations (NEMD) of human aquaporin-2 (AQP2) in the presence of an external static electric field have been performed along + z and - z directions of the pore axis. The impacts of the electric field direction on the gating mechanism corresponding to the selectivity filter (SF) region of AQP2 have been studied. Besides, the effects of applied external electric field on the PMF profile of water molecules translocation, water permeability, and molecules dipole orientation are investigated. Our results showed that when the external electric field is implemented along the + z direction of the channels, the selectivity filter region is kept in the wide conformation for the majority of the time. Therefore, a remarkable increase in the overall water permeability can be seen compared to the case without any external electric field. This is in contrast to the effects of - z-directed electric field on the conformations of the selectivity filter, which induces mostly narrow conformations in this constriction region. A substantial higher energy barrier emerged in the middle of the AQP2's pores under the effect of -z-directed electric field in comparison with the zero and + z-directed electric field strengths, which is mainly ascribed to the deviation from bipolar dipole orientation within the AQP2's pores.Communicated by Ramaswamy H. Sarma.

The Antimicrobial Peptide 1018-K6 Interacts Distinctly with Eukaryotic and Bacterial Membranes, the Basis of Its Specificity and Bactericidal Activity

Since penicillin was discovered, antibiotics have been critical in the fight against infections. However, antibiotic misuse has led to drug resistance, which now constitutes a serious health problem. In this context, antimicrobial peptides (AMPs) constitute a natural group of short proteins, varying in structure and length, that act against certain types of bacterial pathogens. The antimicrobial peptide 1018-K6 (VRLIVKVRIWRR- NH2) has significant bactericidal and antibiofilm activity against Listeria monocytogenes isolates, and against different strains and serotypes of Salmonella. Here, the mechanism of action of 1018-K6 was explored further to understand the peptide-membrane interactions relevant to its activity, and to define their determinants. We combined studies with model synthetic membranes (liposomes) and model biological membranes, assessing the absorption maximum and the quenching of 1018-K6 fluorescence in aqueous and lipid environments, the self-quenching of carboxyfluorescein, as well as performing lipid sedimentation assays. The data obtained reflect the differential interactions of the 1018-K6 peptide with eukaryotic and prokaryotic membranes, and the specific interactions and mechanisms of action in the three prokaryotic species studied: Salmonella Typhimurium^2GN, Escherichia coli^3GN, and Staphylococcus aureus^3GP. The AMP 1018-K6 is a candidate to prevent (food preservation) or treat (antibiotic use) infections caused by certain pathogenic bacteria, especially some that are resistant to current antibiotics.

Amphotericin B assembles into seven-molecule ion channels: An NMR and molecular dynamics study

Amphotericin B, an antifungal drug with a long history of use, forms fungicidal ion-permeable channels across cell membranes. Using solid-state nuclear magnetic resonance spectroscopy and molecular dynamics simulations, we experimentally elucidated the three-dimensional structure of the molecular assemblies formed by this drug in membranes in the presence of the fungal sterol ergosterol. A stable assembly consisting of seven drug molecules was observed to form an ion conductive channel. The structure is somewhat similar to the upper half of the barrel-stave model proposed in the 1970s but substantially different in the number of molecules and in their arrangement. The present structure explains many previous findings, including structure-activity relationships of the drug, which will be useful for improving drug efficacy and reducing adverse effects.

Minimally Invasive Interventional Procedures for Metastatic Bone Disease: A Comprehensive Review

Metastases are the main type of malignancy involving bone, which is the third most frequent site of metastatic carcinoma, after lung and liver. Skeletal-related events such as intractable pain, spinal cord compression, and pathologic fractures pose a serious burden on patients’ quality of life. For this reason, mini-invasive treatments for the management of bone metastases were developed with the goal of pain relief and functional status improvement. These techniques include embolization, thermal ablation, electrochemotherapy, cementoplasty, and MRI-guided high-intensity focused ultrasound. In order to achieve durable pain palliation and disease control, mini-invasive procedures are combined with chemotherapy, radiation therapy, surgery, or analgesics. The purpose of this review is to summarize the recently published literature regarding interventional radiology procedures in the treatment of cancer patients with bone metastases, focusing on the efficacy, complications, local disease control and recurrence rate.

Bacterial Membranes Are More Perturbed by the Asymmetric Versus Symmetric Loading of Amphiphilic Molecules

Characterizing the biophysical properties of bacterial membranes is critical for understanding the protective nature of the microbial envelope, interaction of biological membranes with exogenous materials, and designing new antibacterial agents. Presented here are molecular dynamics simulations for two cationic quaternary ammonium compounds, and the anionic and nonionic form of a fatty acid molecule interacting with a Staphylococcus aureus bacterial inner membrane. The effect of the tested materials on the properties of the model membranes are evaluated with respect to various structural properties such as the lateral pressure profile, lipid tail order parameter, and the bilayer’s electrostatic potential. Conducting asymmetric loading of molecules in only one leaflet, it was observed that anionic and cationic amphiphiles have a large impact on the Staphylococcus aureus membrane’s electrostatic potential and lateral pressure profile as compared to a symmetric distribution. Nonintuitively, we find that the cationic and anionic molecules induce a similar change in the electrostatic potential, which points to the complexity of membrane interfaces, and how asymmetry can induce biophysical consequences. Finally, we link changes in membrane structure to the rate of electroporation for the membranes, and again find a crucial impact of introducing asymmetry to the system. Understanding these physical mechanisms provides critical insights and viable pathways for the rational design of membrane-active molecules, where controlling the localization is key.

Theoretical model of the influence of irreversibly electroporated cells on post pulse drug delivery to reversibly electroporated cells

This study numerically investigates the drug uptake by a population that includes both reversibly and irreversibly electroporated cells. A theoretical continuum model is developed and simulations are conducted in conditions representing low porosity (cells in tissues) and high porosity (cells in suspension). This model considers only passive diffusion following the electroporation pulse and estimates the permeability increases of reversibly electroporated cells using empirically based predictions that relate the long-lived electropore density to the electric field magnitude. A parametric study investigates whether the permeability and resealing rate of irreversibly electroporated cells influence the delivery to the surviving reversibly electroporated cells. The results show that this influence is negligible when the cell number density is low (cells in dilute suspensions). For conditions of cells in tissue when both the fraction of the total cells that are irreversibly electroporated and the permeability of the irreversibly electroporated cells are high enough, the irreversibly electroporated cells rapidly take up the drug and deplete the extracellular space of the available drug. This lowered extracellular concentration can result in less drug delivery to reversibly electroporated cells.

Electric-driven membrane poration: A rationale for water role in the kinetics of pore formation

Electroporation is a well-established technique used to stimulate cells, enhancing membrane permeability by inducing reversible membrane pores. In the absence of experimental observation of the dynamics of pore creation, molecular dynamics studies provide the molecular-level evidence that the electric field promotes pore formation. Although single steps in the pore formation process are well assessed, a kinetic model representing the mathematical description of the electroporation process, is lacking. In the present work we studied the basis of the pore formation process, providing a rationale for the definition of a first-order kinetic scheme. Here, authors propose a three-state kinetic model for the process based on the assessed mechanism of water defects intruding at the water/lipid interface, when applying electric field intensities at the edge of the linear regime. The methodology proposed is based on the use of two robust biophysical quantities analyzed for the water molecules intruding at the water/lipid interface: (i) number of hydrogen bonds; (ii) number of contacts. The final model, sustained by a robust statistical sampling, provides kinetic constants for the transitions from the intact bilayer state to the hydrophobic pore state.

All-atom molecular dynamics simulations of the combined effects of different phospholipids and cholesterol content on electroporation

In this paper, we applied all-atom molecular dynamics (MD) simulations to study the effects of phospholipids and cholesterol content on bilayer membrane electroporation.

Cloning and Transformation with Plasmid Vectors

Plasmids occupy a place of honor in molecular cloning: They were used in the first recombinant DNA experiments and, 40 or more years later, they remain as the carriage horses of molecular cloning. After almost half a century of sequential improvement in design, today's plasmid vectors are available in huge variety, are often optimized for specific purposes, and bear only passing resemblance to their forebears. Here, various features of plasmid vectors and methods for transforming E. coli cells are introduced.

On the molecular mechanisms implicated in the bipolar cancellation of membrane electroporation

Bipolar cancellation is the phenomenon in which the permeability of cell membranes subjected to high intensity short pulsed electric field (ns-μs range) is reduced or eliminated when the system is subjected to bipolar instead of monopolar pulses. Although several studies have tried to explain bipolar cancellation, the underlying mechanisms remain unclear. Very few articles study bipolar cancellation by means of molecular dynamics (MD) simulation. In this paper, we investigated the molecular mechanisms underlying the difference in electroporation induced by bipolar and monopolar picosecond electric pulses (EPs) using MD simulation. The electric field gradients and electric forces on water molecules of the two pulses were analyzed in detail for the first time. For a certain pulse width, when the field intensity is relatively small, the direction of bipolar electric force on the interfacial water molecule reverses as the bipolar EPs reverse, while the electric force on interfacial water molecules of the cathode side remains in the same direction as that of applied monopolar EPs. The bipolar electric force reversal delays the water protrusion and increases the pore formation time. Therefore, this phenomenon could correspond to bipolar cancellation. When the field intensity is relatively large, although the bipolar electric force direction still reverses, half of the total time of the monopolar EPs has no electric fields. The electric forces of monopolar no-field half-cycles are much smaller than those of the bipolar EPs. Therefore, the pore formation time of bipolar EPs reduces, and this phenomenon is called bipolar enhancement. The occurrence of bipolar cancellation or bipolar enhancement depends on conditions such as the width and intensity of the pulse.

Genetic, cellular, and structural characterization of the membrane potential-dependent cell-penetrating peptide translocation pore

Cell-penetrating peptides (CPPs) allow intracellular delivery of bioactive cargo molecules. The mechanisms allowing CPPs to enter cells are ill-defined. Using a CRISPR/Cas9-based screening, we discovered that KCNQ5, KCNN4, and KCNK5 potassium channels positively modulate cationic CPP direct translocation into cells by decreasing the transmembrane potential (V_m). These findings provide the first unbiased genetic validation of the role of V_m in CPP translocation in cells. In silico modeling and live cell experiments indicate that CPPs, by bringing positive charges on the outer surface of the plasma membrane, decrease the V_m to very low values (–150 mV or less), a situation we have coined megapolarization that then triggers formation of water pores used by CPPs to enter cells. Megapolarization lowers the free energy barrier associated with CPP membrane translocation. Using dyes of varying dimensions in CPP co-entry experiments, the diameter of the water pores in living cells was estimated to be 2 (–5) nm, in accordance with the structural characteristics of the pores predicted by in silico modeling. Pharmacological manipulation to lower transmembrane potential boosted CPP cellular internalization in zebrafish and mouse models. Besides identifying the first proteins that regulate CPP translocation, this work characterized key mechanistic steps used by CPPs to cross cellular membranes. This opens the ground for strategies aimed at improving the ability of cells to capture CPP-linked cargos in vitro and in vivo.

Before a drug can have its desired effect, it must reach its target tissue or organ, and enter its cells. This is not easy because cells are surrounded by the plasma membrane, a fat-based barrier that separates the cell from its external environment. The plasma membrane contains proteins that act as channels, shuttling specific molecules in and out of the cell, and it also holds charge, with its inside surface being more negatively charged than its outside surface.

Cell-penetrating peptides are short sequences of amino acids (the building blocks that form proteins) that carry positive charges. These positive charges allow them to cross the membrane easily, but it is not well understood how.

To find out how cell-penetrating peptides cross the membrane, Trofimenko et al. attached them to dyes of different sizes. This revealed that the cell-penetrating peptides enter the cell through temporary holes called water pores, which measure about two nanometres across. The water pores form when the membrane becomes ‘megapolarized’, this is, when the difference in charge between the inside and the outside of the membrane becomes greater than normal. This can happen when the negative charge on the inside surface or the positive charge on the outer surface of the membrane increase. Megapolarization depends on potassium channels, which transport positive potassium ions outside the cell, making the outside of the membrane positive. When cell-penetrating peptides arrive at the outer surface of the cell near potassium channels, they make it even more positive. This increases the charge difference between the inside and the outside of the cell, allowing water pores to form. Once the peptides pass through the pores, the charge difference between the inside and the outside of the cell membrane dissipates, and the pores collapse.

Drug developers are experimenting with attaching cell-penetrating peptides to drugs to help them get inside their target cells. Currently there are several experimental medications of this kind in clinical trials. Understanding how these peptides gain entry, and what size of molecule they could carry with them, provides solid ground for further drug development.

Atorvastatin Modulates the Efficacy of Electroporation and Calcium Electrochemotherapy

Electroporation is influenced by the features of the targeted cell membranes, e.g., the cholesterol content and the surface tension of the membrane. The latter is eventually affected by the organization of actin fibers. Atorvastatin is a statin known to influence both the cholesterol content and the organization of actin. This work analyzes the effects of the latter on the efficacy of electroporation of cancer cells. In addition, herein, electroporation was combined with calcium chloride (CaEP) to assess as well the effects of the statin on the efficacy of electrochemotherapy. Cholesterol-rich cell lines MDA-MB231, DU 145, and A375 underwent (1) 48 h preincubation or (2) direct treatment with 50 nM atorvastatin. We studied the impact of the statin on cholesterol and actin fiber organization and analyzed the cells’ membrane permeability. The viability of cells subjected to PEF (pulsed electric field) treatments and CaEP with 5 mM CaCl₂ was examined. Finally, to assess the safety of the therapy, we analyzed the N-and E-cadherin localization using confocal laser microscopy. The results of our investigation revealed that depending on the cell line, atorvastatin preincubation decreases the total cholesterol in the steroidogenic cells and induces reorganization of actin nearby the cell membrane. Under low voltage PEFs, actin reorganization is responsible for the increase in the electroporation threshold. However, when subject to high voltage PEF, the lipid composition of the cell membrane becomes the regulatory factor. Namely, preincubation with atorvastatin reduces the cytotoxic effect of low voltage pulses and enhances the cytotoxicity and cellular changes induced by high voltage pulses. The study confirms that the surface tension regulates of membrane permeability under low voltage PEF treatment. Accordingly, to reduce the unfavorable effects of preincubation with atorvastatin, electroporation of steroidogenic cells should be performed at high voltage and combined with a calcium supply.

Direct translocation of a negatively charged nanoparticle across a negatively charged model cell membrane

Nanoparticles have attracted much attention as a carrier for drug, gene, and macromolecule delivery in next-generation biomedical and therapeutic technologies. In delivery applications, nanoparticles tend to have negative charge due to the negative charge of biomolecules used as delivery cargo, while biological cell membranes are also negatively charged. This means that negatively charged nanoparticles (NC-NPs) are required to translocate across these negatively charged cell membranes (NC-CMs). However, this translocation is unlikely to occur because of electrostatic interactions. Here, we investigated the translocation of a NC-NP across a NC-CM under a transmembrane electric potential through coarse-grained molecular dynamics simulations. To model the transmembrane potential, two approaches were adopted: externally applied electric field and ionic charge imbalance. We showed that a NC-NP can directly translocate across a NC-CM via a non-disruptive pathway under a weak external electric field with an ionic charge imbalance. It was also found that the ionic charge imbalance contributes to the membrane crossing of a NC-NP as well as the self-resealing of the cell membrane after a NC-NP translocation. Our findings imply that NC-NPs can be delivered into a cell by combining applied electric field with membrane hyperpolarization/depolarization induced by an external stimulus.

Advances in Atrial Fibrillation Ablation: Energy Sources Here to Stay

Energy sources used for catheter ablation of atrial fibrillation (AF) ablation have undergone an exceptional journey over the past 50 years. Traditional energy sources, such as radiofrequency and cryoablation, have been the mainstay of AF ablation. Novel investigations have led to inclusion of other techniques, such as laser, high-frequency ultrasound, and microwave energy, in the armamentarium of electrophysiologists. Despite these modalities, AF has remained one of the most challenging arrhythmias. Advances in the understanding of electroporation promise to overcome the shortcomings of conventional energy sources. A thorough understanding of the biophysics and practical implications of the existing energy sources is paramount.

Nanocapsule designs for antimicrobial resistance

The pressing need of new antimicrobial products is growing stronger, particularly because of widespread antimicrobial resistance, endangering our ability to treat common infections. The recent coronavirus pandemic has dramatically highlighted the necessity of effective antibacterial and antiviral protection. This work explores at the molecular level the mechanism of action of antibacterial nanocapsules assembled in virus-like particles, their stability and their interaction with mammal and antimicrobial model membranes. We use Molecular Dynamics with force-fields of different granularity and protein design strategies to study the stability, self-assembly and membrane poration properties of these nanocapsules.

Metal Binding Antimicrobial Peptides in Nanoparticle Bio-functionalization: New Heights in Drug Delivery and Therapy

Peptides are considered very important due to the diversity expressed through their amino acid sequence, structure variation, large spectrum, and their essential role in biological systems. Antimicrobial peptides (AMPs) emerged as a potent tool in therapy owing to their antimicrobial properties but also their ability to trespass the membranes, specificity, and low toxicity. They comprise a variety of peptides from which specific amino acid-rich peptides are of interest to the current review due to their features in metal interaction and cell penetration. Histidine-rich peptides such as Histatins belong to the metal binding salivary residing peptides with efficient antibacterial, antifungal, and wound-healing activities. Furthermore, their ability to activate in acidic environment attracted the attention to their potential in therapy. The current review covers the current knowledge about AMPs and critically assess the potential of associating with metal ions both structurally and functionally. This review provides interesting hints for the advantages provided by AMPs and metal ions in biomedicine, making use of their direct properties in brain diseases therapy or in the creation of new bio-functionalized nanoparticles for cancer diagnosis and treatment.

Microfluidic electrical cell lysis for high-throughput and continuous production of cell-free varicella-zoster virus

Varicella-zoster virus (VZV), the causative agent of varicella and herpes zoster, is highly cell-associated and spreads via cell-to-cell contact in tissue culture. The lack of cell-free VZV hampers studies on VZV biology as well as antiviral and vaccine development. In the present study, a poly(methylmethacrylate) microfluidic device integrated with arrays of microelectrode was fabricated to continuously electrolyse VZV-infected cells to produce cell-free viruses. By designing multiple constrictions and microelectrode arrays, a high electric field is focused on the constricted region of the microchannel to disrupt large numbers of virus-infected cells with high-throughput on a microfluidic platform. Plaque assay and scanning electron microscopy were conducted to quantify and characterize cell-free VZV produced using the microfluidic continuous-flow electrical cell lysis device. The process of microfluidic electrical cell lysis followed by subsequent filtration and virus concentration process yielded a 1.4-2.1 × 10⁴ plaque-forming units (PFUs) per mL of cell-free VZV from 7.0 × 10⁶ VZV-infected human foreskin fibroblasts (HFF) cells. The high electric field formed inside a microfluidic channel combined with the continuous-flow of virus-infected cells within the microchannel enabled the rapid and efficient production of high-titer cell-free virus in large quantities with relatively low input of the voltage.

Effects of osmotic pressure on the irreversible electroporation in giant lipid vesicles

Irreversible electroporation (IRE) is a nonthermal tumor/cell ablation technique in which a series of high-voltage short pulses are used. As a new approach, we aimed to investigate the rupture of giant unilamellar vesicles (GUVs) using the IRE technique under different osmotic pressures (Π), and estimated the membrane tension due to Π. Two categories of GUVs were used in this study. One was prepared with a mixture of dioleoylphosphatidylglycerol (DOPG), dioleoylphosphatidylcholine (DOPC) and cholesterol (chol) for obtaining more biological relevance while other with a mixture of DOPG and DOPC, with specific molar ratios. We determined the rate constant (kp) of rupture of DOPG/DOPC/chol (46/39/15)-GUVs and DOPG/DOPC (40/60)-GUVs induced by constant electric tension (σc) under different Π. The σc dependent kp values were fitted with a theoretical equation, and the corresponding membrane tension (σoseq) at swelling equilibrium under Π was estimated. The estimated membrane tension agreed well with the theoretical calculation within the experimental error. Interestingly, the values of σoseq were almost same for both types of synthesized GUVs under same osmotic pressure. We also examined the sucrose leakage, due to large osmotic pressure-induced pore formation, from the inside of DOPG/DOPC/chol(46/39/15)-GUVs. The estimated membrane tension due to large Π at which sucrose leaked out was very similar to the electric tension at which GUVs were ruptured without Π. We explained the σc and Π induced pore formation in the lipid membranes of GUVs.

Electromagnetically Stimuli-Responsive Nanoparticles-Based Systems for Biomedical Applications: Recent Advances and Future Perspectives

Nanoparticles (NPs) in the biomedical field are known for many decades as carriers for drugs that are used to overcome biological barriers and reduce drug doses to be administrated. Some types of NPs can interact with external stimuli, such as electromagnetic radiations, promoting interesting effects (e.g., hyperthermia) or even modifying the interactions between electromagnetic field and the biological system (e.g., electroporation). For these reasons, at present these nanomaterial applications are intensively studied, especially for drugs that manifest relevant side effects, for which it is necessary to find alternatives in order to reduce the effective dose. In this review, the main electromagnetic-induced effects are deeply analyzed, with a particular focus on the activation of hyperthermia and electroporation phenomena, showing the enhanced biological performance resulting from an engineered/tailored design of the nanoparticle characteristics. Moreover, the possibility of integrating these nanofillers in polymeric matrices (e.g., electrospun membranes) is described and discussed in light of promising applications resulting from new transdermal drug delivery systems with controllable morphology and release kinetics controlled by a suitable stimulation of the interacting systems (nanofiller and interacting cells).

Modifications of Plasma Membrane Organization in Cancer Cells for Targeted Therapy

Modifications of the composition or organization of the cancer cell membrane seem to be a promising targeted therapy. This approach can significantly enhance drug uptake or intensify the response of cancer cells to chemotherapeutics. There are several methods enabling lipid bilayer modifications, e.g., pharmacological, physical, and mechanical. It is crucial to keep in mind the significance of drug resistance phenomenon, ion channel and specific receptor impact, and lipid bilayer organization in planning the cell membrane-targeted treatment. In this review, strategies based on cell membrane modulation or reorganization are presented as an alternative tool for future therapeutic protocols.

Growth in a biofilm sensitizes Cutibacterium acnes to nanosecond pulsed electric fields

The Gram-positive anaerobic bacterium Cutibacterium acnes (C. acnes) is a commensal of the human skin, but also an opportunistic pathogen that contributes to the pathophysiology of the skin disease acne vulgaris. C. acnes can form biofilms; cells in biofilms are more resilient to antimicrobial stresses. Acne therapeutic options such as topical or systemic antimicrobial treatments often show incomplete responses. In this study we measured the efficacy of nanosecond pulsed electric fields (nsPEF), a new promising cell and tissue ablation technology, to inactivate C. acnes. Our results show that all tested nsPEF doses (250 to 2000 pulses, 280 ns pulses, 28 kV/cm, 5 Hz; 0.5 to 4 kJ/ml) failed to inactivate planktonic C. acnes and that pretreatment with lysozyme, a naturally occurring cell-wall-weakening enzyme, increased C. acnes vulnerability to nsPEF. Surprisingly, growth in a biofilm appears to sensitize C. acnes to nsPEF-induced stress, as C. acnes biofilm-derived cells showed increased cell death after nsPEF treatments that did not affect planktonic cells. Biofilm inactivation by nsPEF was confirmed by treating intact biofilms grown on glass coverslips with an indium oxide conductive layer. Altogether our results show that, contrary to other antimicrobial agents, nsPEF kill more efficiently bacteria in biofilms than planktonic cells.

Tuning the transdermal transport by application of external continuous electric field: a coarse-grained molecular dynamics study

The control of skin permeability to specific substances (e.g., medications, vitamins, and nutrients) through stratum corneum is a challenge. Iontophoresis is an option in spite of the lack of a detailed understanding of the underlying molecular mechanism. In the present work, the simulations concerning application of an external continuous electric field to stratum corneum, in a range of low intensity (0-24 mV nm^-1), were carried out using the coarse-grained molecular dynamics approach. Using a set of random seed replicas of the starting configuration, we observed that in the range of electric field intensity of 22-23 mV nm^-1, water-rich lipid vesicles were formed in 20% of cases. Pores appeared in the remaining 80%. We argue that lipids undergo fast re-orientations under electric field inducing mechanical instability, which originates the pores. We presented a simple electrostatic model to interpret the results where the mismatch between electrical permittivities of the membrane and external media and the gradient of the local electric field in the membrane surface, govern the time scales and electric fields for vesicle formation. Our results indicate that just 10% difference between electrical permittivities of the membrane and external media decreases 1/6 the minimal time required for vesicle formation. The minimal electric field required decreases 10 times. The control and tunning of formation of biologically compatible vesicles, capable of transporting substances under low-intensity electric fields, has a promising application in fields such as drug therapy and dermo-cosmetics allowing the use of hydrophilic substances in dermal applications.

Free energy of hydrophilic and hydrophobic pores in lipid bilayers by free energy perturbation of a restraint

The free energy of pore formation in lipid bilayers has been previously calculated using a variety of reaction coordinates. Here, we use free energy perturbation of a cylindrical lipid exclusion restraint to compute the free energy profile as a function of pore radius in dimyristoylphosphatidylcholine (DMPC) and dioleoylphosphatidylcholine (DOPC) bilayers. Additionally restraining the headgroups to lie on the membrane surface allows us to also calculate the free energy profile of hydrophobic pores, i.e., cylindrical pores lined by acyl chains. For certain pore radii, the free energy of wetting of hydrophobic pores is calculated using the density bias method. It is found that wetting of hydrophobic pores becomes thermodynamically favorable at 5.0 Å for DMPC and 6.5 Å for DOPC, although significant barriers prevent spontaneous wetting of the latter on a nanosecond time scale. The free energy of transformation of hydrophilic pores to hydrophobic ones is also calculated using free energy perturbation of headgroup restraints along the bilayer normal. This quantity, along with wetting and pore growth free energies, provides complete free energy profiles as a function of radius. Pore line tension values for the hydrophilic pores obtained from the slope of the free energy profiles are 37.6 pN for DMPC and 53.7 pN for DOPC. The free energy profiles for the hydrophobic pores are analyzed in terms of elementary interfacial tensions. It is found that a positive three-phase line tension is required to explain the results. The estimated value for this three-phase line tension (51.2 pN) lies within the expected range.

The application of PEF technology in food processing and human nutrition

During the last decades, many novel techniques of food processing have been developed in response to growing demand for safe and high quality food products. Nowadays, consumers have high expectations regarding the sensory quality, functionality and nutritional value of products. They also attach great importance to the use of environmentally-friendly technologies of food production. The aim of this review is to summarize the applications of PEF in food technology and, potentially, in production of functional food. The examples of process parameters and obtained effects for each application have been presented.

Modification of lipid membrane compressibility induced by an electric field

Changes in membrane deformation and compressibility, induced by an external electric field, are investigated using coarse-grained martini force field simulations in a salt-free environment. We observe changes in the area of the membrane above a critical electric field. Below this value, the membrane compressibility modulus is found to decrease monotonically. For higher electric fields, the membrane projected area remains constant while the net interfacial area increases, with the corresponding compressibility moduli, show the opposite behavior. We find that the mechanical parameters, surface tension and bending modulus, of a freely floating membrane in the absence of explicit ions, are unaffected by the presence of the electric field. We believe these results have a bearing on our understanding of the electroformation of uncharged lipids in a salt-free environment.

Influence of the dimensionality of the periodic boundary conditions on the transport of a drug-peptide complex across model cell membranes

Many research efforts are devoted to improving the efficiency of chemotherapy. One of the aspects is to facilitate the transport of drugs across the cell membranes by attaching the therapeutics to a carrier molecule. The current study focuses on computational investigation of such a system with doxorubicin as the model drug, which is covalently bound to a cell-penetrating peptide. The correct description of its membrane translocation at the molecular level requires proper choice of the model membrane and of the simulation parameters. For the purpose, two phospholipid bilayers are built, one containing solely DPPC and another with mixed lipid content mimicking the composition of a human erythrocyte membrane. Atomistic molecular dynamics simulations are carried out in two types of periodic boundary conditions (2D and 3D PBC), in order to assess the effect of the periodicity dimensionality on the intermolecular interactions. The evolution of some basic characteristics of the bilayers and of the drug-peptide complex is tracked: mass density profiles, electrostatic potentials, lateral diffusion coefficients and areas per lipid, lipid-complex radial distribution functions, secondary structure of the peptide and orientation of the drug relative to the membrane. Thus, the influence of the periodic boundary conditions is quantified and it shows that the mixed system in 3D PBC is the most suitable for analysis of the translocation of the transporting moiety across cell membranes.

High-throughput continuous-flow microfluidic electroporation of mRNA into primary human T cells for applications in cellular therapy manufacturing

Implementation of gene editing technologies such as CRISPR/Cas9 in the manufacture of novel cell-based therapeutics has the potential to enable highly-targeted, stable, and persistent genome modifications without the use of viral vectors. Electroporation has emerged as a preferred method for delivering gene-editing machinery to target cells, but a major challenge remaining is that most commercial electroporation machines are built for research and process development rather than for large-scale, automated cellular therapy manufacturing. Here we present a microfluidic continuous-flow electrotransfection device designed for precise, consistent, and high-throughput genetic modification of target cells in cellular therapy manufacturing applications. We optimized our device for delivery of mRNA into primary human T cells and demonstrated up to 95% transfection efficiency with minimum impact on cell viability and expansion potential. We additionally demonstrated processing of samples comprising up to 500 million T cells at a rate of 20 million cells/min. We anticipate that our device will help to streamline the production of autologous therapies requiring on the order of 10[Formula: see text]-10[Formula: see text] cells, and that it is well-suited to scale for production of trillions of cells to support emerging allogeneic therapies.

Dye Transport through Bilayers Agrees with Lipid Electropore Molecular Dynamics

Although transport of molecules into cells via electroporation is a common biomedical procedure, its protocols are often based on trial and error. Despite a long history of theoretical effort, the underlying mechanisms of cell membrane electroporation are not sufficiently elucidated, in part, because of the number of independent fitting parameters needed to link theory to experiment. Here, we ask if the electroporation behavior of a reduced cell membrane is consistent with time-resolved, atomistic, molecular dynamics (MD) simulations of phospholipid bilayers responding to electric fields. To avoid solvent and tension effects, giant unilamellar vesicles (GUVs) were used, and transport kinetics were measured by the entry of the impermeant fluorescent dye calcein. Because the timescale of electrical pulses needed to restructure bilayers into pores is much shorter than the time resolution of current techniques for membrane transport kinetics measurements, the lifetimes of lipid bilayer electropores were measured using systematic variation of the initial MD simulation conditions, whereas GUV transport kinetics were detected in response to a nanosecond timescale variation in the applied electric pulse lifetimes and interpulse intervals. Molecular transport after GUV permeabilization induced by multiple pulses is additive for interpulse intervals as short as 50 ns but not 5-ns intervals, consistent with the 10-50-ns lifetimes of electropores in MD simulations. Although the results were mostly consistent between GUV and MD simulations, the kinetics of ultrashort, electric-field-induced permeabilization of GUVs were significantly different from published results in cells exposed to ultrashort (6 and 2 ns) electric fields, suggesting that cellular electroporation involves additional structures and processes.