The effect of high-frequency electric pulses on tumor blood flow in vivo

Abstract The aim of this study was to evaluate the effect of a 5-kHz repetition frequency of electroporating electric pulses in comparison to the standard 1-Hz frequency on blood flow of invasive ductal carcinoma tumors in Balb/C mice. Electroporation was performed by the delivery of eight electric pulses of 1,000 V cm-1 and 100 ls duration at a repetition frequency of 1 Hz or 5 kHz. Blood flow changes in tumors were measured by laser Doppler flowmetry. Monitoring was performed continuously for 10 min before application of the electric pulses as well as immediately after application of the electric pulses for 40 min. The delivery of electric pulses to tumors induced changes in tumor blood flow. The reduction in blood flow started after the stimulation and continued for the 40-min period of observation. There was a significant difference in blood flow changes 3 min after application of the electric pulses at 1-Hz or 5-kHz repetition frequency. However, after 3 min the difference became nonsignificant. The findings showed that the high pulse frequency (5 kHz) had an effect comparable to the 1-Hz frequency on tumor blood flow except at very short times after pulse delivery, when pulses at 5 kHz produced a more intense reduction of blood flo

2-NBDG, a Fluorescent Analogue of Glucose, as a Marker for Detecting Cell Electropermeabilization In Vitro

Abstract This study investigated whether molecules spontaneously transported inside cells, like glucose derivatives, can also be used as electropermeabilization markers. Uptake of a fluorescent deoxyglucose derivative (2-NBDG) by normal and electropermeabilized cells in culture was analyzed. 2-NBDG was added to DC-3F cell suspensions and cells, exposed or not to eight square-wave electric pulses of 100-ls duration and of appropriate field amplitude at a repetition frequency of 1 Hz or 5 kHz, were incubated at 37 C. 2-NBDG uptake was temperature-, concentration- and time-dependent in cells submitted or not to the electric pulses. In spite of significant uptake of 2-NBDG mediated by GLUT transporters into nonpermeabilized cells, the electric pulses significantly increased about ten to hundred times the 2-NBDG uptake into the cells. The increase in the field amplitude from 900 to 1,500 V/cm resulted in a progressive increase of 2-NDBG. Our results show that under the conditions of in vivo exposure duration to FDG and the physiological concentration of D-glucose, electric pulses increased 2-NBDG uptake into electropermeabilized cells. Under our experimental conditions, the percentage of permeabilized cells within the population of cells exposed to electric pulses remained at the same level regardless of the pulse frequency used, 1 Hz or 5 kHz. The findings showed that glucose derivatives can also be used to detect electropermeabilized cells exposed to electric pulses

Nanosecond electric pulses penetrate the nucleus and enhance speckle formation

Nanosecond electric pulses generate nanopores in the interior membranes of cells and modulate cellular functions. Here, we used confocal microscopy and flow cytometry to observe Smith antigen antibody (Y12) binding to nuclear speckles, known as small nuclear ribonucleoprotein particles (snRNPs) or intrachromatin granule clusters (IGCs), in Jurkat cells following one or five 10 ns, 150 kV/cm pulses. Using confocal microscopy and flow cytometry, we observed changes in nuclear speckle labeling that suggested a disruption of pre-messenger RNA splicing mechanisms. Pulse exposure increased the nuclear speckled substructures by 2.5-fold above basal levels while the propidium iodide (PI) uptake in pulsed cells was unchanged. The resulting nuclear speckle changes were also cell cycle dependent. These findings suggest that 10 ns pulses directly influenced nuclear processes, such as the changes in the nuclear RNA–protein complexes

Quantification of propidium iodide delivery with millisecond electric pulses: A model study

A model study of propidium iodide delivery with millisecond electric pulses is presented; this work is a companion of the experimental efforts by Sadik et al. [1]. Both membrane permeabilization and delivery are examined with respect to six extra-cellular conductivities. The transmembrane potential of the permeabilized regions exhibits a consistent value, which corresponds to a bifurcation point in the pore-radius-potential relation. Both the pore area density and membrane conductance increase with an increasing extra-cellular conductivity. On the other hand, the inverse correlation between propidium iodide delivery and extra-cellular conductivity as observed in the experiments is quantitatively captured by the model. This agreement confirms that this behavior is primarily mediated by electrophoretic transport during the pulse. The results suggest that electrophoresis is important even for the delivery of small molecules such as propidium iodide. The direct comparison between model prediction and experimental data presented in this work helps validate the former as a robust predictive tool for the study of electroporation

Modelling single cell electroporation with bipolar pulse parameters and dynamic pore radii

We develop a model of single spherical cell electroporation and simulate spatial and temporal aspects of the transmembrane potential and pore radii as an effect of any form of applied electric field. The extent of electroporation in response to sinusoidal electric pulses of two different frequencies in a range of extracellular conductivity for two different cell radii are compared. Results show that pore radii tend to be more normalized for AC fields. The relative difference in fractional pore area is reduced by the use of a 1 MHz sinusoidal applied electric field over a 100 kHz field

Radiosensitising effect of electrochemotherapy with bleomycin in LPB sarcoma cells and tumors in mice

BACKGROUND: Bleomycin is poorly permeant but potent cytotoxic and radiosensitizing drug. The aim of the study was to evaluate whether a physical drug delivery system – electroporation can increase radiosensitising effect of bleomycin in vitro and in vivo. METHODS: LPB sarcoma cells and tumors were treated either with bleomycin, electroporation or ionizing radiation, and combination of these treatments. In vitro, response to different treatments was determined by colony forming assay, while in vivo, treatment effectiveness was determined by local tumor control (TCD(50)). Time dependence of partial oxygen pressure in LPB tumors after application of electric pulses was measured by electron paramagnetic oxyimetry. RESULTS: Electroporation of cells in vitro increased radiosensitising effect of bleomycin for 1.5 times, in vivo radiation response of tumors was enhanced by 1.9 fold compared to response of tumors that were irradiated only. Neither treatment of tumors with bleomycin nor application of electric pulses only, affected radiation response of tumors. Application of electric pulses to the tumors induced profound but transient reduction of tumor oxygenation. Although tumor oxygenation after electroporation partially restored at the time of irradiation, it was still reduced at the level of radiobiologically relevant hypoxia. CONCLUSION: Our study shows that application of electric pulses to cells and tumors increases radiosensitising effect of bleomycin. Furthermore, our results demonstrate that the radiobiologically relevant hypoxia induced by electroporation of tumors did not counteract the pronounced radiosensitising effect of electrochemotherapy with bleomycin

Field-Induced Resistive Switching in Metal-Oxide Interfaces

We investigate the polarity-dependent field-induced resistive switching phenomenon driven by electric pulses in perovskite oxides. Our data show that the switching is a common occurrence restricted to an interfacial layer between a deposited metal electrode and the oxide. We determine through impedance spectroscopy that the interfacial layer is no thicker than 10 nm and that the switch is accompanied by a small capacitance increase associated with charge accumulation. Based on interfacial I-V characterization and measurement of the temperature dependence of the resistance, we propose that a field-created crystalline defect mechanism, which is controllable for devices, drives the switch.Comment: 4 pages, 3 figure