Nanosecond pulsed electric fields activate AMP-activated protein kinase: implications for calcium-mediated activation of cellular signaling

Pulsed Electric Fields Induce STING Palmitoylation and Polymerization Independently of Plasmid DNA Electrotransfer

Gene therapy approaches may target skeletal muscle due to its high protein-expressing nature and vascularization. Intramuscular plasmid DNA (pDNA) delivery via pulsed electric fields (PEFs) can be termed electroporation or electrotransfer. Nonviral delivery of plasmids to cells and tissues activates DNA-sensing pathways. The central signaling complex in cytosolic DNA sensing is the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING). The effects of pDNA electrotransfer on the signaling of STING, a key adapter protein, remain incompletely characterized. STING undergoes several post-translational modifications which modulate its function, including palmitoylation. This study demonstrated that in mouse skeletal muscle, STING was constitutively palmitoylated at two sites, while an additional site was modified following electroporation independent of the presence of pDNA. This third palmitoylation site correlated with STING polymerization but not with STING activation. Expression of several palmitoyl acyltransferases, including zinc finger and DHHC motif containing 1 (zDHHC1), coincided with STING activation. Expression of several depalmitoylases, including palmitoyl protein thioesterase 2 (PPT2), was diminished in all PEF application groups. Therefore, STING may not be regulated by active modification by palmitate after electroporation but inversely by the downregulation of palmitate removal. These findings unveil intricate molecular changes induced by PEF application.

Changes in Gene Expression After Exposing Arabidopsis thaliana Plants to Nanosecond High Amplitude Electromagnetic Field Pulses

The biological effects of exposure to electromagnetic fields due to wireless technologies and connected devices are a subject of particular research interest. Ultrashort high-amplitude electromagnetic field pulses delivered to biological samples using immersed electrodes in a dedicated cuvette have widely demonstrated their effectiveness in triggering several cell responses including increased cytosolic calcium concentration and reactive oxygen species (ROS) production. In contrast, the effects of these pulses are poorly documented when electromagnetic pulses are delivered through an antenna. Here we exposed Arabidopsis thaliana plants to 30,000 pulses (237  kV m-1 , 280 ps rise-time, duration of 500 ps) emitted through a Koshelev antenna and monitored the consequences of electromagnetic fields exposure on the expression levels of several key genes involved in calcium metabolism, signal transduction, ROS, and energy status. We found that this treatment was mostly unable to trigger significant changes in the messenger RNA accumulation of calmodulin, Zinc-Finger protein ZAT12, NADPH oxidase/respiratory burst oxidase homolog (RBOH) isoforms D and F, Catalase (CAT2), glutamate-cystein ligase (GSH1), glutathione synthetase (GSH2), Sucrose non-fermenting-related Kinase 1 (SnRK1) and Target of rapamycin (TOR). In contrast, Ascorbate peroxidases APX-1 and APX-6 were significantly induced 3 h after the exposure. These results suggest that this treatment, although quite strong in amplitude, is mostly ineffective in inducing biological effects at the transcriptional level when delivered by an antenna. © 2023 The Authors. Bioelectromagnetics published by Wiley Periodicals LLC on behalf of Bioelectromagnetics Society.

Aligned Electroactive Electrospun Fibrous Scaffolds for Peripheral Nerve Regeneration

Effective repair and functional recovery of large peripheral nerve deficits are urgent clinical needs. A biofunctional electroactive scaffold typically acts as a "bridge" for the repair of large nerve defects. In this study, we constructed a biomimetic piezoelectric and conductive aligned polypyrrole (PPy)/polydopamine (PDA)/poly-l-lactic acid (PLLA) electrospun fibrous scaffold to improve the hydrophilicity and cellular compatibility of PLLA and restore the weakened piezoelectric effect of PDA, which is beneficial in promoting Schwann cell differentiation and dorsal root ganglion neuronal extension and alignment. The aligned PPy/PDA/PLLA fibrous scaffold bridged the sciatic nerve of Sprague-Dawley rats with a 10 mm deficit, prevented autotomy, and promoted nerve regeneration and functional recovery, thereby activating the calcium and AMP-activated protein kinase signaling pathways. Therefore, electroactive fibrous scaffolds exhibit great potential for neural tissue regeneration.

Electromagnetic fields ameliorate hepatic lipid accumulation and oxidative stress: potential role of CaMKKβ/AMPK/SREBP-1c and Nrf2 pathways

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide, and is related to disturbed lipid metabolism and redox homeostasis. However, a definitive drug treatment has not been approved for this disease. Studies have found that electromagnetic fields (EMF) can ameliorate hepatic steatosis and oxidative stress. Nevertheless, the mechanism remains unclear.

METHODS

NAFLD models were established by feeding mice a high-fat diet. Simultaneously, EMF exposure is performed. The effects of the EMF on hepatic lipid deposition and oxidative stress were investigated. Additionally, the AMPK and Nrf2 pathways were analysed to confirm whether they were activated by the EMF.

RESULTS

Exposure to EMF decreased the body weight, liver weight and serum triglyceride (TG) levels and restrained the excessive hepatic lipid accumulation caused by feeding the HFD. The EMF boosted CaMKKβ protein expression, activated AMPK phosphorylation and suppressed mature SREBP-1c protein expression. Meanwhile, the activity of GSH-Px was enhanced following an increase in nuclear Nrf2 protein expression by PEMF. However, no change was observed in the activities of SOD and CAT. Consequently, EMF reduced hepatic reactive oxygen species (ROS) and MDA levels, which means that EMF relieved liver damage caused by oxidative stress in HFD-fed mice.

CONCLUSIONS

EMF may activate the CaMKKβ/AMPK/SREBP-1c and Nrf2 pathways to control hepatic lipid deposition and oxidative stress. This investigation indicates that EMF may be a novel therapeutic method for NAFLD.

Chemotherapy and Physical Therapeutics Modulate Antigens on Cancer Cells

Cancer cells possess specific properties, such as multidrug resistance or unlimited proliferation potential, due to the presence of specific proteins on their cell membranes. The release of proliferation-related proteins from the membrane can evoke a loss of adaptive ability in cancer cells and thus enhance the effects of anticancer therapy. The upregulation of cancer-specific membrane antigens results in a better outcome of immunotherapy. Moreover, cytotoxic T-cells may also become more effective when stimulated ex-vivo toward the anticancer response. Therefore, the modulation of membrane proteins may serve as an interesting attempt in anticancer therapy. The presence of membrane antigens relies on various physical factors such as temperature, exposure to radiation, or drugs. Therefore, changing the tumor microenvironment conditions may lead to cancer cells becoming sensitized to subsequent therapy. This paper focuses on the therapeutic approaches modulating membrane antigens and enzymes in anticancer therapy. It aims to analyze the possible methods for modulating the antigens, such as pharmacological treatment, electric field treatment, photodynamic reaction, treatment with magnetic field or X-ray radiation. Besides, an overview of the effects of chemotherapy and immunotherapy on the immunophenotype of cancer cells is presented. Finally, the authors review the clinical trials that involved the modulation of cell immunophenotype in anticancer therapy.

10 ns PEFs induce a histological response linked to cell death and cytotoxic T-lymphocytes in an immunocompetent mouse model of peritoneal metastasis

PURPOSE

The application of nanosecond pulsed electric fields (nsPEFs) could be an effective therapeutic strategy for peritoneal metastasis (PM) from colorectal cancer (CRC). The aim of this study was to evaluate in vitro the sensitivity of CT-26 CRC cells to nsPEFs in combination with chemotherapeutic agents, and to observe the subsequent in vivo histologic response.

METHODS

In vitro cellular assays were performed to assess the effects of exposure to 1, 10, 100, 500 and 1000 10 ns pulses in a cuvette or bi-electrode system at 10 and 200 Hz. nsPEF treatment was applied alone or in combination with oxaliplatin and mitomycin. Cell death was detected by flow cytometry, and permeabilization and intracellular calcium levels by fluorescent confocal microscopy after treatment. A mouse model of PM was used to investigate the effects of in vivo exposure to pulses delivered using a bi-electrode system; morphological changes in mitochondria were assessed by electron microscopy. Fibrosis was measured by multiphoton microscopy, while the histological response (HR; hematoxylin-eosin-safran stain), proliferation (KI67, DAPI), and expression of immunological factors (CD3, CD4, CD8) were evaluated by classic histology.

RESULTS

10 ns PEFs exerted a dose-dependent effect on CT-26 cells in vitro and in vivo, by inducing cell death and altering mitochondrial morphology after plasma membrane permeabilization. In vivo results indicated a specific CD8+ T cell immune response, together with a strong HR according to the Peritoneal Regression Grading Score (PRGS).

CONCLUSIONS

The effects of nsPEFs on CT-26 were confirmed in a mouse model of CRC with PM.

Nanosecond pulsed electric fields induce extracellular release of chromosomal DNA and histone citrullination in neutrophil-differentiated HL-60 cells

Nanosecond pulsed electric fields (nsPEFs) have gained attention as a novel physical stimulus for life sciences. Although cancer therapy is currently their promising application, nsPEFs have further potential owing to their ability to elicit various cellular responses. This study aimed to explore stimulatory actions of nsPEFs, and we used HL-60 cells that were differentiated into neutrophils under cultured conditions. Exposure of neutrophil-differentiated HL-60 cells to nsPEFs led to the extracellular release of chromosomal DNA, which appears to be equivalent to neutrophil extracellular traps (NETs) that serve as a host defense mechanism against pathogens. Fluorometric measurement of extracellular DNA showed that DNA extrusion was rapidly induced after nsPEF exposure and increased over time. Western blot analysis demonstrated that nsPEFs induced histone citrullination that is the hydrolytic conversion of arginine to citrulline on histones and facilitates chromatin decondensation. DNA extrusion and histone citrullination by nsPEFs were cell type-specific and Ca²⁺-dependent events. Taken together, these observations suggest that nsPEFs drive the mechanism for neutrophil-specific immune response without infection, highlighting a novel aspect of nsPEFs as a physical stimulus.

Enhanced Antitumor Efficacy Achieved Through Combination of nsPEFs and Low-Dosage Paclitaxel

Looking for a safe and effective cancer therapy for patients is becoming an important and promising research direction. Nanosecond pulsed electric field (nsPEF) has been found to be a potential non-thermal therapeutic technique with few side effects in pre-clinical studies. On the other hand, paclitaxel (PTX), as a common chemotherapeutic agent, shows full anti-tumor activities and is used to treat a wide variety of cancers. However, the delivery of PTX is challenging due to its poor aqueous solubility. Hence, high dosages of PTX have been used to achieve effective treatment, which creates some side effects. In this study, nsPEF was combined with low-level PTX, in order to validate if this combined treatment could bring about enhanced efficacy and allow reduced doses of PTX in clinical application. Cell proliferation, apoptosis, and cell cycle distribution were examined using MTT and flow cytometry assay, respectively. Results showed that combination treatments of nsPEF and PTX exhibited significant synergistic effects in vitro. The underlying mechanism might be that these two agents acted at different targets and coordinately enhanced MDA-MB-231 cell death.

Dual-function of Baicalin in nsPEFs-treated Hepatocytes and Hepatocellular Carcinoma cells for Different Death Pathway and Mitochondrial Response

Nanosecond pulsed electric fields (nsPEFs) is emerged as a potential curative modality to ablate hepatocellular carcinoma (HCC). The application of local ablation is usually limited by insufficiency of liver function. While baicalin, a flavonoid isolated from Scutellaria baicalensis Georgi, has been proven to possess both anti-tumor and protective effects. Our study aimed to estimate different responses of hepatic cancer cells and hepatocytes to the combination of nsPEFs and baicalin. Cell viability, apoptosis and necrosis, mitochondrial transmembrane potential (MTP) and reactive oxygen species (ROS) were examined by CCK-8, FCM, JC-1 and fluorescent probe, respectively. After treatment by nsPEFs, most hepatocytes died by apoptosis, nevertheless, nearly all cancer cells were killed through necrosis. Low concentration of baicalin synergically enhanced nsPEFs-induced suppression and necrosis of HCC cells, nevertheless, the application of baicalin protected normal hepatocytes from the injury caused by nsPEFs, owing to elevating mitochondrial transmembrane potential and reducing ROS generation. Our work provided an advantageous therapy for HCC through the enhanced combination treatment of nsPEFs and baicalin, with which could improve the tumor-ablation effect and alleviate the injury of hepatic tissues simultaneously.

Effect of Low-Field High-Frequency nsPEFs on the Biological Behaviors of Human A375 Melanoma Cells

OBJECTIVE

To evaluate the effect of low-field high-frequency nanosecond pulsed electric fields (nsPEFs) on multiple biological behaviors of human A375 melanoma cells and to optimize suitable parameters for further study and clinical use.

METHODS

An nsPEF generator was developed to generate appropriate pulses. Cell apoptosis and the cell cycle were evaluated by flow cytometry. The CCK-8 assay was performed to explore the effect of nsPEFs on the viability of A375 melanoma cells. Cell migration was assessed using a Transwell Boyden Chamber. The proliferation of A375 melanoma cells was determined by the cloning efficacy test. Furthermore, the nude mouse tumorigenicity assay was used to detect the effectiveness of nsPEFs in vivo.

RESULTS

The nsPEFs with our tested parameters failed to induce apoptosis of A375 melanoma cells, though nsPEFs with high pulse duration (500 ns) induced necrosis. However, the viability and migration of A375 melanoma cells were significantly inhibited by nsPEFs. nsPEFs also suppressed the proliferation of A375 melanoma cells by restricting cells in G0/G1 phase. Moreover, animal experiments demonstrated that nsPEFs inhibited the growth of melanoma in vivo.

CONCLUSION

Low-field high-frequency nsPEFs failed to induce apoptosis but effectively inhibited the growth of melanoma via affecting other biological behaviors of melanoma cells, such as cell viability, proliferation, and migration.

SIGNIFICANCE

This study investigated the influence of low-field high-frequency nsPEFs on melanoma through evaluating their effects on multiple biological behaviors and is helpful in the treatment of melanoma and other tumors.

Calcium-dependent activation of transglutaminase 2 by nanosecond pulsed electric fields

Exposure of cultured human cells to nanosecond pulsed electric fields (nsPEFs) elicits various cellular events, including Ca²⁺ influx and cell death. Recently, nsPEFs have been regarded as a novel physical treatment useful for biology and medicine, but the underlying mechanism of action remains to be fully elucidated. In this study, we investigated the effect of nsPEFs on transglutaminases (TGs), enzymes that catalyze covalent protein modifications such as protein-protein crosslinking. Cellular TG activity was monitored by conjugation of cellular proteins with biotin-cadaverine, a cell-permeable pseudosubstrate for TGs. We applied nsPEFs to HeLa S3 cells and found that overall catalytic activity of cellular TGs was greatly increased in a Ca²⁺-dependent manner. The Ca²⁺ ionophore ionomycin significantly augmented nsPEF-induced TG activation, further supporting the importance of Ca²⁺. Among human TG family members, TG2 is known to be the most ubiquitously expressed, and its catalytic activity requires elevated intracellular Ca²⁺. Given the requirement of Ca²⁺ for TG activation by nsPEFs, we performed depletion of TG2 by RNA interference (RNAi). We observed that TG2 RNAi suppressed the nsPEF-induced TG activation and partially alleviated the cytotoxic effects of nsPEFs. These findings demonstrate that TG2 activation is a Ca²⁺-dependent event in nsPEF-exposed cells and exerts negative effects on cell physiology.

Electrosensitization Increases Antitumor Effectiveness of Nanosecond Pulsed Electric Fields In Vivo

Nanosecond pulsed electric fields are emerging as a new modality for tissue and tumor ablation. We previously reported that cells exposed to pulsed electric fields develop hypersensitivity to subsequent pulsed electric field applications. This phenomenon, named electrosensitization, is evoked by splitting the pulsed electric field treatment in fractions (split-dose treatments) and causes in vitro a 2- to 3-fold increase in cytotoxicity. The aim of this study was to show the benefit of split-dose treatments for in vivo tumor ablation by nanosecond pulsed electric field. KLN 205 squamous carcinoma cells were embedded in an agarose gel or grown subcutaneously as tumors in mice. Nanosecond pulsed electric field ablations were produced using a 2-needle probe with a 6.5-mm interelectrode distance. In agarose gel, splitting a pulsed electric field dose of 300, 300-ns pulses (20 Hz, 4.4-6.4 kV) in 2 equal fractions increased cell death up to 3-fold compared to single-train treatments. We then compared the antitumor effectiveness of these treatments in vivo. At 24 hours after treatment, sensitizing tumors by a split-dose pulsed electric field exposure (150 + 150, 300-ns pulses, 20 Hz, 6.4 kV) caused a 4- and 2-fold tumor volume reduction as compared to sham and single-train treatments, respectively. Tumor volume reduction that exceeds 75% was 43% for split-dose–treated animals compared to only 12% for single-dose treatments. The difference between the 2 experimental groups remained statistically significant for at least 1 week after the treatment. The results show that electrosensitization occurs in vivo and can be exploited to assist in vivo cancer ablation.

Raising the avermectins production in Streptomyces avermitilis by utilizing nanosecond pulsed electric fields (nsPEFs)

Avermectins, a group of anthelmintic and insecticidal agents produced from Streptomyces avermitilis, are widely used in agricultural, veterinary, and medical fields. This study presents the first report on the potential of using nanosecond pulsed electric fields (nsPEFs) to improve avermectin production in S. avermitilis. The results of colony forming units showed that 20 pulses of nsPEFs at 10 kV/cm and 20 kV/cm had a significant effect on proliferation, while 100 pulses of nsPEFs at 30 kV/cm exhibited an obvious effect on inhibition of agents. Ultraviolet spectrophotometry assay revealed that 20 pulses of nsPEFs at 15 kV/cm increased avermectin production by 42% and reduced the time for reaching a plateau in fermentation process from 7 days to 5 days. In addition, the decreased oxidation reduction potential (ORP) and increased temperature of nsPEFs-treated liquid were evidenced to be closely associated with the improved cell growth and fermentation efficiency of avermectins in S. avermitilis. More importantly, the real-time RT-PCR analysis showed that nsPEFs could remarkably enhance the expression of aveR and malE in S. avermitilis during fermentation, which are positive regulator for avermectin biosynthesis. Therefore, the nsPEFs technology presents an alternative strategy to be developed to increase avermectin output in fermentation industry.

Effects of high voltage nanosecond electric pulses on eukaryotic cells (in vitro): A systematic review

For this systematic review, 203 published reports on effects of electroporation using nanosecond high-voltage electric pulses (nsEP) on eukaryotic cells (human, animal, plant) in vitro were analyzed. A field synopsis summarizes current published data in the field with respect to publication year, cell types, exposure configuration, and pulse duration. Published data were analyzed for effects observed in eight main target areas (plasma membrane, intracellular, apoptosis, calcium level and distribution, survival, nucleus, mitochondria, stress) and an additional 107 detailed outcomes. We statistically analyzed effects of nsEP with respect to three pulse duration groups: A: 1-10ns, B: 11-100ns and C: 101-999ns. The analysis confirmed that the plasma membrane is more affected with longer pulses than with short pulses, seen best in uptake of dye molecules after applying single pulses. Additionally, we have reviewed measurements of nsEP and evaluations of the electric fields to which cells were exposed in these reports, and we provide recommendations for assessing nanosecond pulsed electric field effects in electroporation studies.

Enhanced breast cancer therapy with nsPEFs and low concentrations of gemcitabine

Background

Chemotherapy either before or after surgery is a common breast cancer treatment. Long-term, high dose treatments with chemotherapeutic drugs often result in undesirable side effects, frequent recurrences and resistances to therapy.

Methods

The anti-cancer drug, gemcitabine (GEM) was used in combination with pulse power technology with nanosecond pulsed electric fields (nsPEFs) for treatment of human breast cancer cells in vitro. Two strategies include sensitizing mammary tumor cells with GEM before nsPEF treatment or sensitizing cells with nsPEFs before GEM treatment. Breast cancer cell lines MCF-7 and MDA-MB-231 were treated with 250 65 ns-duration pulses and electric fields of 15, 20 or 25 kV/cm before or after treatment with 0.38 μM GEM.

Results

Both cell lines exhibited robust synergism for loss of cell viability 24 h and 48 h after treatment; treatment with GEM before nsPEFs was the preferred order. In clonogenic assays, only MDA-MB-231 cells showed synergism; again GEM before nsPEFs was the preferred order. In apoptosis/necrosis assays with Annexin-V-FITC/propidium iodide 2 h after treatment, both cell lines exhibited apoptosis as a major cell death mechanism, but only MDA-MB-231 cells exhibited modest synergism. However, unlike viability assays, nsPEF treatment before GEM was preferred. MDA-MB-231 cells exhibited much greater levels of necrosis then in MCF-7 cells, which were very low. Synergy was robust and greater when nsPEF treatment was before GEM.

Conclusions

Combination treatments with low GEM concentrations and modest nsPEFs provide enhanced cytotoxicity in two breast cancer cell lines. The treatment order is flexible, although long-term survival and short-term cell death analyses indicated different treatment order preferences. Based on synergism, apoptosis mechanisms for both agents were more similar in MCF-7 than in MDA-MB-231 cells. In contrast, necrosis mechanisms for the two agents were distinctly different in MDA-MB-231, but too low to reliably evaluate in MCF-7 cells. While disease mechanisms in the two cell lines are different based on the differential synergistic response to treatments, combination treatment with GEM and nsPEFs should provide an advantageous therapy for breast cancer ablation in vivo.

Calcium-mediated pore expansion and cell death following nanoelectroporation

Opening of long-lived pores in the cell membrane is the principal primary effect of intense, nanosecond pulsed electric field (nsPEF). Here we demonstrate that the evolution of pores, cell survival, the time and the mode of cell death (necrotic or apoptotic) are determined by the level of external Ca(2+) after nsPEF. We also introduce a novel, minimally disruptive technique for nsEP exposure of adherent cells on indium tin oxide (ITO)-coated glass coverslips, which does not require cell detachment and enables fast exchanges of bath media. Increasing the Ca(2+) level from the nominal 2-5μM to 2mM for the first 60-90min after permeabilization by 300-nsPEF increased the early (necrotic) death in U937, CHO, and BPAE cells. With nominal Ca(2+), the inhibition of osmotic swelling rescued cells from the early necrosis and increased caspase 3/7 activation later on. However, the inhibition of swelling had a modest or no protective effect with 2mM Ca(2+) in the medium. With the nominal Ca(2+), most cells displayed gradual increase in YO-PRO-1 and propidium (Pr) uptake. With 2mM Ca(2+), the initially lower Pr uptake was eventually replaced by a massive and abrupt Pr entry (necrotic death). It was accompanied by a transient acceleration of the growth of membrane blebs due to the increase of the intracellular osmotic pressure. We conclude that the high-Ca(2+)-dependent necrotic death in nsPEF-treated cells is effected by a delayed, sudden, and osmotically-independent pore expansion (or de novo formation of larger pores), but not by the membrane rupture.

Different involvement of extracellular calcium in two modes of cell death induced by nanosecond pulsed electric fields

Exposure of cultured cells to nanosecond pulsed electric fields (nsPEFs) induces various cellular responses, including the influx of extracellular Ca2+ and cell death. Recently, nsPEFs have been regarded as a novel means of cancer therapy, but their molecular mechanism of action remains to be fully elucidated. Here, we demonstrate the involvement of extracellular Ca2+ in nsPEF-induced cell death. Extracellular Ca2+ was essential for necrosis and consequent poly(ADP-ribose) (PAR) formation in HeLa S3 cells. Treatment with a Ca2+ ionophore enhanced necrosis as well as PAR formation in nsPEF-exposed HeLa S3 cells. In the absence of extracellular Ca2+, HeLa S3 cells were less susceptible to nsPEFs and exhibited apoptotic proteolysis of caspase 3 and PARP-1. HeLa S3 cells retained the ability to undergo apoptosis even after nsPEF exposure but instead underwent necrosis, suggesting that necrosis is the preferential mode of cell death. In K562 and HEK293 cells, exposure to nsPEFs resulted in the formation of necrosis-associated PAR, whereas Jurkat cells exclusively underwent apoptosis independently of extracellular Ca2+. These observations demonstrate that the mode of cell death induced by nsPEFs is cell-type dependent and that extracellular Ca2+ is a critical factor for nsPEF-induced necrosis.

Nanosecond pulsed electric fields induce poly(ADP-ribose) formation and non-apoptotic cell death in HeLa S3 cells

Nanosecond pulsed electric fields (nsPEFs) have recently gained attention as effective cancer therapy owing to their potency for cell death induction. Previous studies have shown that apoptosis is a predominant mode of nsPEF-induced cell death in several cell lines, such as Jurkat cells. In this study, we analyzed molecular mechanisms for cell death induced by nsPEFs. When nsPEFs were applied to Jurkat cells, apoptosis was readily induced. Next, we used HeLa S3 cells and analyzed apoptotic events. Contrary to our expectation, nsPEF-exposed HeLa S3 cells exhibited no molecular signs of apoptosis execution. Instead, nsPEFs induced the formation of poly(ADP-ribose) (PAR), a hallmark of necrosis. PAR formation occurred concurrently with a decrease in cell viability, supporting implications of nsPEF-induced PAR formation for cell death. Necrotic PAR formation is known to be catalyzed by poly(ADP-ribose) polymerase-1 (PARP-1), and PARP-1 in apoptotic cells is inactivated by caspase-mediated proteolysis. Consistently, we observed intact and cleaved forms of PARP-1 in nsPEF-exposed and UV-irradiated cells, respectively. Taken together, nsPEFs induce two distinct modes of cell death in a cell type-specific manner, and HeLa S3 cells show PAR-associated non-apoptotic cell death in response to nsPEFs.

Induction of Cell Death Mechanisms and Apoptosis by Nanosecond Pulsed Electric Fields (nsPEFs)

Pulse power technology using nanosecond pulsed electric fields (nsPEFs) offers a new stimulus to modulate cell functions or induce cell death for cancer cell ablation. New data and a literature review demonstrate fundamental and basic cellular mechanisms when nsPEFs interact with cellular targets. NsPEFs supra-electroporate cells creating large numbers of nanopores in all cell membranes. While nsPEFs have multiple cellular targets, these studies show that nsPEF-induced dissipation of ΔΨm closely parallels deterioration in cell viability. Increases in intracellular Ca2+ alone were not sufficient for cell death; however, cell death depended of the presence of Ca2+. When both events occur, cell death ensues. Further, direct evidence supports the hypothesis that pulse rise-fall times or high frequency components of nsPEFs are important for decreasing ΔΨm and cell viability. Evidence indicates in Jurkat cells that cytochrome c release from mitochondria is caspase-independent indicating an absence of extrinsic apoptosis and that cell death can be caspase-dependent and -independent. The Ca2+ dependence of nsPEF-induced dissipation of ΔΨm suggests that nanoporation of inner mitochondria membranes is less likely and effects on a Ca2+-dependent protein(s) or the membrane in which it is embedded are more likely a target for nsPEF-induced cell death. The mitochondria permeability transition pore (mPTP) complex is a likely candidate. Data demonstrate that nsPEFs can bypass cancer mutations that evade apoptosis through mechanisms at either the DISC or the apoptosome.