Mitochondrial depolarization and ATP loss during high frequency nanosecond and microsecond electroporation.

It is predicted that ultra-short electric field pulses (nanosecond) can selectively permeabilize intracellular structures (e.g., mitochondria) without significant effects on the outer cell plasma membrane. Such a phenomenon would have high applicability in cancer treatment and could be employed to modulate cell death type or immunogenic response. Therefore, in this study, we compare the effects of 100 µs x 8 pulses (ESOPE - European Standard Operating Procedures on Electrochemotherapy) and bursts of 100 ns pulses for modulation of the mitochondria membrane potential. We characterize the efficacies of various protocols to trigger permeabilization, depolarize mitochondria (evaluated 1 h  after treatment), the extent of ATP depletion and generation of reactive oxygen species (ROS). Finally, we employ the most prominent protocols in the context of Ca electrochemotherapy in vitro. We provide experimental proof that 7.5-12.5 kV/cm x 100 ns pulses can be used to modulate mitochondrial potential, however, the permeabilization of the outer membrane is still a prerequisite for depolarization. Similar to 100 µs x 8 pulses, the higher the permeabilization rate, the higher the mitochondrial depolarization. Nevertheless, 100 ns pulses result in lesser ROS generation when compared to ESOPE, even when the energy input is several-fold higher than for the microsecond procedure. At the same time, it shows that even the short 100 ns pulses can be successfully used for Ca electrochemotherapy, ensuring excellent cytotoxic efficacy.

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