A study of dielectric membrane breakdown in the Fucus egg

Modelling of reversible tissue electroporation and its thermal effects in drug delivery

Electroporation is a very useful tool for drug delivery into various diseased tissues of the human body. This technique helps to improve the clinical treatment by transferring drugs into the targeted cells rapidly. In electroporation, drug particles enter easily into the intracellular compartment through the temporarily permeabilized cell membrane due to the applied electric field. In this work, a mathematical model of drug delivery focusing on reversible tissue electroporation is presented. In addition, the thermal effects on the tissue, which is an outcome of Joule heating, are also considered. This model introduces a time-dependent mass transfer coefficient, which is significant to drug transport. Multiple pulses with low voltage are applied to reach sufficient drugs into the targeted cells. Based on the physical circumstances, a set of differential equations are considered and solved. The changes in drug concentration with different parameters (e.g., diffusion coefficient, drug permeability, pulse length, and pulse number) are analyzed. The model optimizes the electroporation parameters to uptake sufficient drugs into the cells with no thermal damage. This model can be used in clinical experiments to predict drug uptake into the infected cells by controlling the model parameters according to the nature of infections.

Nonthermal irreversible electroporation for intracranial surgical applications

Object

Nonthermal irreversible electroporation (NTIRE) is a novel, minimally invasive technique to treat cancer, which is unique because of its nonthermal mechanism of tumor ablation. This paper evaluates the safety of an NTIRE procedure to lesion normal canine brain tissue.

Methods

The NTIRE procedure involved placing electrodes into a targeted area of brain in 3 dogs and delivering a series of short and intense electric pulses. The voltages of the pulses applied were varied between dogs. Another dog was used as a sham control. One additional dog was treated at an extreme voltage to determine the upper safety limits of the procedure. Ultrasonography was used at the time of the procedure to determine if the lesions could be visualized intraoperatively. The volumes of ablated tissue were then estimated on postprocedure MR imaging. Histological brain sections were then analyzed to evaluate the lesions produced.

Results

The animals tolerated the procedure with no apparent complications except for the animal that was treated at the upper voltage limit. The lesion volume appeared to decrease with decreasing voltage of applied pulses. Histological examination revealed cell death within the treated volume with a submillimeter transition zone between necrotic and normal brain.

Conclusions

The authors' results reveal that NTIRE at selected voltages can be safely administered in normal canine brain and that the volume of ablated tissue correlates with the voltage of the applied pulses. This preliminary study is the first step toward using NTIRE as a brain cancer treatment.

Mass Transfer Model for Drug Delivery in Tissue Cells with Reversible Electroporation

Reversible electroporation is the temporary permeabilization of the cell membrane through the formation of nano-scale pores that are transient defects in the membrane. These pores are caused by short electrical pulses, typically on the order of a few to several hundred microseconds that are delivered by electroporation electrodes inserted around the treated tissue. Reversible electroporation has become an important technique in molecular medicine. It is used to introduce macromolecules such as genes or anti-cancer drugs, to which the cell membrane is normally not permeable, into the cytosol. For optimal application of molecular medicine, it is important to be able to predict precisely the mass transfer in tissue during reversible electroporation. In this study, we introduce a first attempt at developing a macroscopic mathematical model for analyzing the mass transfer into cells during reversible electroporation of tissue. The model combines a macroscopic model of the electrical fields around electroporation electrodes with a new cells-scale model of electroporation-driven mass transfer and with a macroscopic mass transfer model in tissue. The model is illustrated for a situation typical to that in electrochemotherapy in which cancer is treated with reversible electroporation and a non-cell membrane permeant drug such as bleomycin.

In vivo results of a new focal tissue ablation technique: irreversible electroporation

This paper reports results of in vivo experiments that confirm the feasibility of a new minimally invasive method for tissue ablation, irreversible electroporation (IRE). Electroporation is the generation of a destabilizing electric potential across biological membranes that causes the formation of nanoscale defects in the lipid bilayer. In IRE, these defects are permanent and lead to cell death. This paper builds on our earlier theoretical work and demonstrates that IRE can become an effective method for nonthermal tissue ablation requiring no drugs. To test the capability of IRE pulses to ablate tissue in a controlled fashion, we subjected the livers of male Sprague-Dawley rats to a single 20-ms-long square pulse of 1000 V/cm, which calculations had predicted would cause nonthermal IRE. Three hours after the pulse, treated areas in perfusion-fixed livers exhibited microvascular occlusion, endothelial cell necrosis, and diapedeses, resulting in ischemic damage to parenchyma and massive pooling of erythrocytes in sinusoids. However, large blood vessel architecture was preserved. Hepatocytes displayed blurred cell borders, pale eosinophilic cytoplasm, variable pyknosis and vacuolar degeneration. Mathematical analysis indicates that this damage was primarily nonthermal in nature and that sharp borders between affected and unaffected regions corresponded to electric fields of 300-500 V/cm.

Membrane electroporation theories: a review

Electroporation, the transient increase in the permeability of cell membranes when exposed to a high electric field, is an established in vitro technique and is used to introduce DNA or other molecules into cells. When the trans-membrane voltage induced by an external electric field exceeds a certain threshold (normally 0.2-1 V), a rearrangement of the molecular structure of the membrane occurs, leading to pore formation in the membrane and a considerable increase in the cell membrane permeability to ions, molecules and even macromolecules. This phenomenon is, potentially, the basis for many in vivo applications such as electrochemotherapy and gene therapy, but still lacks a comprehensive theoretical basis. This article reviews the state of current electroporation theories and briefly considers current and potential applications in biology and medicine.

Tissue ablation with irreversible electroporation

This study introduces a new method for minimally invasive treatment of cancer-the ablation of undesirable tissue through the use of irreversible electroporation. Electroporation is the permeabilization of the cell membrane due to an applied electric field. As a function of the field amplitude and duration, the permeabilization can be reversible or irreversible. Over the last decade, reversible electroporation has been intensively pursued as a very promising technique for the treatment of cancer. It is used in combination with cytotoxic drugs, such as bleomycin, in a technique known as electrochemotherapy. However, irreversible electroporation was completely ignored in cancer therapy. We show through mathematical analysis that irreversible electroporation can ablate substantial volumes of tissue, comparable to those achieved with other ablation techniques, without causing any detrimental thermal effects and without the need of adjuvant drugs. This study suggests that irreversible electroporation may become an important and innovative tool in the armamentarium of surgeons treating cancer.

Formation and properties of aqueous leaks induced in human erythrocytes by electrical breakdown

Leaks were induced in human erythrocytes by brief (tau = 1-40 microseconds) discharges of high electric fields (3-20 kV/cm). Leak permeabilities were characterized by measuring (a) net and tracer fluxes of K+ and nonelectrolytes under protection of the cells against colloid-osmotic lysis, or (b) rates of colloid osmotic lysis in various salt solutions. The induced permeabilities are essentially stable for hours at 0-2 degrees C. Leak permeability P increases exponentially with the breakdown voltage ED according to a function of the general type P = bED. The basis b varies with the pulse length. A log-linear presentation reveals a biphasic linear relationship with a break at which the slope (= log b) decreases markedly. Elevated ionic strengths of the suspension medium during the electric discharge enhance leak formation. Leak permeability exhibits an apparent activation energy of 29 +/- 5 kJ/mol, indicative of diffusion through aqueous pathways. Somewhat differing equivalent pore radii emerge from measurements with different probes: 0.6-0.8 nm from tracer fluxes of polyols (Mr = 3600, ED = 4-7 kV/cm) and 0.8-1.9 nm from osmotic protection studies with polyethylene glycols (Mr = 200-3300, ED = 6-10 kV/cm). These numbers and the non-monoexponential increase of leak permeability with the field strength suggest a dual mechanism for the increase of leak permeability: an increase of the number of pores at low breakdown voltage and an additional increase of pore size at higher voltage. Estimated numbers of pores range from 1 to 10 per cell, which suggests dynamic fluctuating structural defects to be involved. The leaks discriminate small monovalent inorganic ions in the sequence of free solution mobility. Organic anions are discriminated according to size and charge. Common properties of these electrically induced defects and of chemically induced leaks (diamide, periodate, t-butylhydroperoxide) in the erythrocyte membrane suggest close similarities in the molecular organization.

Induction of calcium-dependent, localized cortical granule breakdown in sea-urchin eggs by voltage pulsation

A technique that employs a high-voltage pulses to produce pores in cell membranes (Kinosita and Tsong (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 1923) has been used to investigate the role of Ca2+ in the early events of activation of sea-urchin eggs. Exposure of eggs to a voltage pulse of 1 kV/cm for 100 microseconds resulted in localized exocytosis of the contents of cortical granules and development of a partial fertilization envelope. This effect was triggered by entrance of Ca2+ through the voltage-induced pores. In a medium containing 100 microM Ca2+ and 45Ca2+ tracer, the voltage-treated eggs admitted 3.6 +/- 0.3 fmol Ca2+/egg within a few seconds. Untreated eggs took up only 1.0 +/- 0.2 fmol/egg after minutes of incubation. Furthermore, depletion of Ca2+ or the presence of EGTA in the external medium prevented elevation of the fertilization envelope by the voltage pulsation. Delay in Ca2+ addition after the voltage pulsation reduced the fraction of eggs that developed partial fertilization envelope. Loss of essential cytoplasmic components during the delay period is judged unlikely, since these eggs were viable, could form partial fertilization envelopes if re-pulsed in the presence of Ca2+, and could develop to normal blastula stage embryos upon fertilization with sperm. Thus, we interpret this effect as due to a resealing of pores; the half-life of pores being 20 s. The elevation of partial fertilization envelopes occurred only at the loci facing the anode, and multiple pulses with mixing resulted in the formation of multiple fertilization envelopes. These envelopes were stable for up to several hours; further propagation (wave spreading) was not observed. The above results indicate that a primary reaction in the sequence of steps in fertilization envelope formation involves Ca2+ to trigger cortical granule breakdown and formation of the fertilization envelope.

High electric field effects on the cell membranes of Halicystis parvula : A charge pulse study

The electrical breakdown behavior of the giant algal cell Halicystis parvula was studied in order to predict the optimum conditions for electrically induced cell-to-cell fusion. Using the charge pulse technique, the membranes were charged at different pulse lengths to the maximum voltage Vc. Because of a reversible, high-conductance state of the membrane (electrical breakdown), it was not possible to exceed the critical membrane breakdown potential. The breakdown voltage exhibited a strong dependence on the charging time (pulse length) between 10 μs and 100 μs. Below 10 μs the breakdown voltage of the two membranes, tonoplast and plasmalemma, assumed a constant value of about 1.9 V, whereas above a pulse length of about 100 μs the breakdown voltage was nearly constant with a value of about 0.6 V. The extreme values for the breakdown voltage at very short and at very long charging times agree fairly well with results which have been obtained on cells of Valonia utricularis and planar lipid bilayer membranes. However, the pulse length dependence of the breakdown voltage was found to be quite different in H. parvula. In addition, the membrane conductance increase during breakdown in H. parvula cells is much more pronounced than in membranes of V. utricularis, but similar to lipid bilayer membranes. From this result it is suggested that the membrane structure of H. parvula is quite different from V. utricularis (larger lipid domains).

Inhibition and recovery of growth processes in roots of Pisum sativum L. exposed to 60-Hz electric fields

Roots of Pisum sativum L. were chronically exposed in aqueous inorganic nutrient medium to 60-Hz electric fields between 140 and 490 V/m (growth medium conductivity approximately 0.08 S/m). The growth rate, meristematic mitotic index, and growth rate recovery of the roots were determined. At 140 V/m there was no perturbation in growth rate or mitotic index. At 430 V/m the growth rate and the mitotic index were reduced. The mitotic index had a maximum depression (approximately 55% of control), which occurred at 4 h. The depression in growth rate was immediate and constant over time. When roots were exposed to an electric field at 430 V/m for 2 days, the growth rate was depressed by about 40%. When the field was terminated, the growth rate steadily increased and was almost normal after 5 days. At 490 V/m root growth rate was almost completely arrested. According to these results, there is a narrow range of induced membrane potentials that span the range from slightly altered to almost completely arrested growth rates.