Effect of Low Frequency Electrical Current on the Biophysical and Molecular Properties of Cancer Cells

Abstract

Background: Different cells and tissues are known to exhibit varied electromagnetic, electrical and molecular properties. During the repair process, cancer cells as well as normal proliferating cells have higher transmembrane potential than healthy cells. Since the dielectric properties are frequency dependent, applying varying frequencies of current can alter the transmembrane ionic flux of any conductive cell. This, in turn, can generate heat via the joule effect. Thus, it might be possible to alter the tumor microenvironment using low frequency electric current. Methods: The present study was designed to analyze the effect of low frequency AC (Alternating Current) on molecular properties of cells and understand its effect on tissue bio-impedance. An in vitro and ex-vivo study was conducted in mouse model of mammary tumor and compared with a phantom model. Low frequency AC sinusoidal current of constant amplitude was generated by the sine wave oscillator (1-5 mA and frequency of 100 Hz) and the bio-impedance values were recorded with the help of two needle or sensing electrodes. Molecular changes were also documented from the samples subjected to low frequency current. Protein levels of Heat Shock Protein 90 (HSP90) and beta-actin were also analyzed to evaluate any thermal effects. Additional information about genome stability and chromatin de-condensation was assessed by levels of histone Post Translational Modifications (PTMs) γH2AX and H3K9Ac, respectively. Results: An increase in tissue bio-impedance (decrease in the capacitance or conductance) value was observed with an increase in the frequency of the applied current. The bio-impedance value for normal tissue was found to be in the range 17-27 Ωk at 100 Hz (applied for a period of 1 minute) and it increased to the range of 27-37 Ωk at 1 kHz. Additionally, lower impedance value of (range 16-22 Ωk) at 100 Hz and (range 24-33 Ωk) at 1 kHz was observed for cancer tissue. At the morphological level, some cell swelling in tissue samples and cell isolates was observed at low frequency current of 100 Hz, possibly contributed by heating. An increased cell swelling, shrinkage in the cell membrane can be achieved [24]. When an electromagnetic field (DC/low frequency AC current) is applied to the cell (circuit) or cellular resistive components, lattice heat will develop due to the loss of kinetic energy by the accelerated electrons due to collision with the atoms. This is nothing but the resistance (impedance) that corresponds to an increase in lattice heat, which is irretrievable. By Joule's law, we can see that the heat energy dissipated by current (I) flowing through a resi-stor of resistance R is H = I ^ 2 * R. This energy in the crystal lattice (tissue) induces thermal movement of electrons that will be in a random direction. This randomness can be defined as entropy. The change in entropy is denoted by dS = dQ/T, where dQ is the change in heat energy between two time intervals and T is the final temperature. Thus, by applying an external electromagnetic field (DC/Low frequency), we can further increase in the entropy of the system. Laws governing thermodynamics state that there exist two energy states and entropy between two closely inter-dependent systems. Entropy is a measure of randomness resulting from the increase in heat energy supplied to a system. Cancer initiating processes follows the second law of thermodynamics where energy/heat flows towards the disturbed area (cancer entropy) to supply much needed energy. This continues until the required demand is met through aerobic pyruvic acid metabolic pathway and subsequently by aerobic glycolysis (Warburg hypothesis), whereby a new threshold of steady state or a higher state of entropy is reached. Consequently, when the normal energy equilibrium aneuploidy and epigenetic modifications. The results obtained from such large well controlled in-vitro and in-vivo experiments under normal physiological conditions can then be exploited to develop label free cancer diagnostics & therapeutics.