Delayed hypersensitivity to nanosecond pulsed electric field in electroporated cells

Abstract

We demonstrate that conditioning of mammalian cells by electroporation with nanosecond pulsed electric field (nsPEF) facilitates their response to the next nsPEF treatment. The experiments were designed to unambiguously separate the electroporation-induced sensitization and desensitization effects. Electroporation was achieved by bursts of 300-ns, 9 kV/cm pulses (50 Hz, n = 3–100) and quantified by propidium dye uptake within 11 min after the nsPEF exposure. We observed either sensitization to nsPEF or no change (when the conditioning was either too weak or too intense, or when the wait time after conditioning was too short). Within studied limits, conditioning never caused desensitization. With settings optimal for sensitization, the second nsPEF treatment became 2.5 times (25 °C) or even 6 times (37 °C) more effective than the same nsPEF treatment delivered without conditioning. The minimum wait time required for sensitization development was 30 s, with still longer delays increasing the effect. We show that the delayed hypersensitivity was not mediated by either cell swelling or oxidative effect of the conditioning treatment; biological mechanisms underlying the delayed electrosensitization remain to be elucidated. Optimizing nsPEF delivery protocols to induce sensitization can reduce the dose and adverse side effects of diverse medical treatments which require multiple pulse applications.

Electroporation and cell killing by milli- to nanosecond pulses and avoiding neuromuscular stimulation in cancer ablation

“…13 A). A small but significant reduction of the threshold was observed with the longest 100-s, 1-Hz treatments, which was most likely the result of electrosensitization 41 , 42 . Increasing the pulse frequency beyond 100 kHz also resulted in a modest reduction of the thresholds, which was far smaller than seen when all pulses were compressed into a single high-rate train 64 – 66 .…”

“…In fact, neuromuscular effects can be also markedly reduced with unipolar nsPEF delivered at a low frequency 39 . Applying nsPEF at low repetition rates or splitting pulse trains into short bursts with long intervals alleviates the concerns for concurrent thermal effects and may have an additional benefit of ablation with fewer pulses, by inducing electrosensitization 40 – 42 .…”

The second phase of bipolar, nanosecond-range electric pulses determines the electroporation efficiency

“…Alternatively, it could be bipolar nsEP which decrease the sensitivity to the next bipolar nsEP, whereas unipolar pulses have little impact. In either scenario, this behavior resembles the effect of electrosensitization[29–32], an electroporation-induced hypersensitivity to subsequent electroporation treatments, which develops within seconds or tens of seconds after the first nsEP delivery. Electrosensitization increases when pulses are delivered at longer intervals, i.e., when the pulse repetition rate is low enough[29,32].…”

Electropermeabilization of cells by closely spaced paired nanosecond-range pulses

“…Moreover, with long enough interpulse intervals (e.g., 10–30 s), cells become more sensitive to new pulses, a phenomenon known as electrosensitization [10–13]. A pre-exposure to electroporation pulses, or conditioning, can enhance the effect of the next electroporation treatment as much as 2.5 times (25 °C) or even 6 times (37 °C) [10]. Such hypersensitivity results from biological rather than just physical-chemical effects of electroporation, although its exact mechanism remains elusive.…”