EPR-Spin Trapping and Flow Cytometric Studies of Free Radicals Generated Using Cold Atmospheric Argon Plasma and X-Ray Irradiation in Aqueous Solutions and Intracellular Milieu

Sialylation Shields Glycoproteins from Oxidative Stress: Mechanistic Insights into Sialic Acid Oxidation and Structural Stability

Sialylation, a crucial yet labile protein modification, is increasingly recognized for its role in modulating protein structure, function, and stability. While the impact of oxidative stress on protein integrity is well-established, the protective role of sialylation against such damage remains poorly understood. This study employs a microscale low-temperature plasma device to generate a controlled, deep radical oxidation environment mimicking cellular oxidative stress. By subjecting free sialic acids (Neu5Ac and Neu5Gc) to time-resolved deep radical exposure, high-resolution mass spectrometry, and high-fidelity density functional theory calculations, we establish an unprecedented oxidation pathway, revealing unique stepwise side chain oxidation prior to ring opening. Comprehensive radical oxidation maps comprising over 100 oxidative intermediates provide a molecular basis for the higher propensity of Neu5Gc over Neu5Ac in resisting radical oxidation. Further, using human transferrin as a model glycoprotein, we demonstrate the protective role of sialylation against oxidative unfolding. Through a combination of site mapping, enzymatic treatments, and all-ion unfolding ion mobility-mass spectrometry, we identify specific protein sialylation patterns and structural motifs that are crucial for maintaining structural stability under oxidative stress. Our findings provide unprecedented insights into the intricate interplay between sialylation and oxidative stress, highlighting the importance of sialylation in stabilizing protein conformations under various oxidative stresses.

Antitumor effects of plasma‑activated solution on a murine melanoma model in vivo and in vitro

Melanoma is a common malignant skin tumor with highly invasive features and a high metastasis rate that can be difficult to treat clinically. Large-scale resection of primary cutaneous melanoma is often used to avoid postoperative recurrence. For advanced patients, radiotherapy, targeted therapy and immunotherapy are often needed. Low-temperature plasma has been proved to have significant antitumor effects on a variety of cancer cell lines cultured in vitro. The main limitation of direct low-temperature plasma treatment is that it has weak penetration ability and can only treat superficial lesions. In recent years, research on low-temperature plasma-activated solution has revealed that it also have good antitumor effects and low-temperature plasma penetration depth problems can be solved by local injection. The present study revealed that low-temperature plasma-activated phosphate buffer solution exhibited good antitumor effects and biosafety against melanoma in vitro and in vivo. It demonstrated that low-temperature plasma-activated solution has antitumor effects due to its regulation of intracellular redox, destruction of mitochondrial function and DNA damage. In vivo experiments demonstrated that treatment with low-temperature plasma-activated solution not only exhibited antitumor effects but also caused no significant damage to hematopoietic function or liver and kidney functions in mice. All these results demonstrated that low-temperature plasma-activated solution represent a promising antitumor treatment strategy.

Positron Emission Tomography of Nitric Oxide by a Specific Radical-Generating Dihydropyridine Tracer

Nitric oxide (NO) plays a pivotal role as a biological signaling molecule, presenting challenges in its specific detection and differentiation from other reactive nitrogen and oxygen species within living organisms. Herein, a 18F-labeled (fluorine-18, t1/2 = 109.7 min) small-molecule tracer dimethyl 4-(4-(4-[18F]fluorobutoxy)benzyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate ([18F]BDHP) is developed based on the dihydropyridine scaffold for positron emission tomography (PET) imaging of NO in vivo. [18F]BDHP exhibits a highly sensitive and efficient C-C cleavage reaction specifically triggered by NO under physiological conditions, leading to the production of a 18F-labeled radical that is readily retained within the cells. High uptakes of [18F]BDHP are found within and around NO-generating cells, such as macrophages treated with lipopolysaccharide or benzo(a)pyrene. MicroPET/CT imaging of arthritic animal model mice reveals distinct tracer accumulation in the arthritic legs, showcasing a higher distribution of NO compared with the control legs. In summary, a specific radical-generating dihydropyridine tracer with a unique radical retention strategy has been established for the marking of NO in real-time in vivo.

Evaluation of cold atmospheric pressure plasma irradiation of water as a method of singlet oxygen generation

We used cold atmospheric pressure plasma jet to examine in detail 1O2 generation in water. ESR with 2,2,5,5-tetramethyl-3-pyrroline-3-carboxamide, a secondary amine probe, was used for the detection of 1O2. Nitroxide radical formation was detected after cold atmospheric pressure plasma jet irradiation of a 2,2,5,5-tetramethyl-3-pyrroline-3-carboxamide solution. An 1O2 scavenger/quencher inhibited the ESR signal intensity induced by cold atmospheric pressure plasma jet irradiation, but this inhibition was not 100%. As 2,2,5,5-tetramethyl-3-pyrroline-3-carboxamide reacts with oxidizing species other than 1O2, it was assumed that the signal intensity inhibited by NaN3 corresponds to only the nitroxide radical generated by 1O2. The concentration of 1O2 produced by cold atmospheric pressure plasma jet irradiation for 60 s was estimated at 8 μM. When this 1O2 generation was compared to methods of 1O2 generation like rose bengal photoirradiation and 4-methyl-1,4-etheno-2,3-benzodioxin-1(4H)-propanoic acid (endoperoxide) thermal decomposition, 1O2 generation was found to be, in decreasing order, rose bengal photoirradiation ≥ cold atmospheric pressure plasma jet > endoperoxide thermal decomposition. Cold atmospheric pressure plasma jet is presumed to not specifically generate 1O2, but can be used to mimic states of oxidative stress involving multiple ROS.

Degradation of Zearalenone by Dielectric Barrier Discharge Cold Plasma and Its Effect on Maize Quality

In this study, a dielectric barrier discharge (DBD) cold plasma was used to degrade zearalenone, and the degradation efficiency and the quality of maize were evaluated. The results showed that the zearalenone degradation rates increased with the increase in voltage and time. When it was treated at 50 KV for 120 s, the degradation percentage of the zearalenone in maize could reach 56.57%. The kinetics’ analysis showed that the degradation followed a first-order reaction. The crude fiber of the maize reduced after the cold plasma treatment. In addition, cold plasma treatment did not significantly change the crude protein content, but slightly changed the fatty acid and color. The changes in maize quality are generally acceptable. DBD cold plasma may be a promising approach to reducing zearalenone in maize.

Some Beneficial Effects of Inert Gases on Blood Oxidative Metabolism: In Vivo Study

The aim of the study was to assess the effect of external use of inert gases (helium and argon) on the state of free radical processes in vivo. The experiment was performed on 30 male Wistar stock rats (age-3 months, weight-200-220 g.), randomly distributed into 3 equal groups. The first group of animals was intact (n = 10). The animals of the second and third groups were treated with argon and helium streams, respectively. Our research has allowed us to establish that the studied inert gases have a modulating effect on the state of oxidative metabolism of rat blood, and the nature of this effect is directly determined by the type of gas. The results of this study allowed us to establish the potential antioxidant effect of the helium stream, mainly realized due to the activation of the catalytic properties of the enzymatic link of the antioxidant system of rat blood plasma. At the same time, the revealed features of shifts in oxidative metabolism during treatment with argon flow include not only stimulation of the antioxidant system but also the pronounced induction of free radical oxidation. Thus, the conducted studies made it possible to verify the specificity of the response of the oxidative metabolism of blood plasma to the use of inert gases, depending on their type.

Cold Atmospheric Plasma Targeting Hematological Malignancies: Potentials and Problems of Clinical Translation

Cold atmospheric plasma is an ionized gas produced near room temperature; it generates reactive oxygen species and nitrogen species and induces physical changes, including ultraviolet, radiation, thermal, and electromagnetic effects. Several studies showed that cold atmospheric plasma could effectively provoke death in a huge amount of cell types, including neoplastic cells, via the induction of apoptosis, necrosis, and autophagy. This technique seems able to destroy tumor cells by disturbing their more susceptible redox equilibrium with respect to normal cells, but it is also able to cause immunogenic cell death by enhancing the immune response, to decrease angiogenesis, and to provoke genetic and epigenetics mutations. Solutions activated by cold gas plasma represent a new modality for treatment of less easily reached tumors, or hematological malignancies. Our review reports on accepted knowledge of cold atmospheric plasma’s effect on hematological malignancies, such as acute and chronic myeloid leukemia and multiple myeloma. Although relevant progress was made toward understanding the underlying mechanisms concerning the efficacy of cold atmospheric plasma in hematological tumors, there is a need to determine both guidelines and safety limits that guarantee an absence of long-term side effects.

Cold Argon Athmospheric Plasma for Biomedicine: Biological Effects, Applications and Possibilities

Currently, plasma medicine is a synthetic direction that unites the efforts of specialists of various profiles. For the successful formation of plasma medicine, it is necessary to solve a large complex of problems, including creating equipment for generating cold plasma, revealing the biological effects of this effect, as well as identifying and justifying the most promising areas of its application. It is known that these biological effects include antibacterial and antiviral activity, the ability to stimulate hemocoagulation, pro-regenerative properties, etc. The possibility of using the factor in tissue engineering and implantology is also shown. Based on this, the purpose of this review was to form a unified understanding of the biological effects and biomedical applications of argon cold plasma. The review shows that cold plasma, like any other physical and chemical factors, has dose dependence, and the variable parameter in this case is the exposure of its application. One of the significant characteristics determining the specificity of the cold plasma effect is the carrier gas selection. This gas carrier is not just an ionized medium but modulates the response of biosystems to it. Finally, the perception of cold plasma by cellular structures can be carried out by activating a special molecular biosensor, the functioning of which significantly depends on the parameters of the medium (in the field of plasma generation and the cell itself). Further research in this area can open up new prospects for the effective use of cold plasma.

Simplifying quantitative measurement of free radical species using an X-band EPR spectrometer

The quantitative measurement of free radicals in liquid using an X-band electron paramagnetic resonance (EPR) was systematized. Quantification of free radicals by EPR requires a standard sample that contains a known spin amount/concentration. When satisfactory reproducibility of the sample material, volume, shape, and positioning in the cavity for EPR measurements can be guaranteed, a sample tested and a standard can be directly compared and the process of quantification can be simplified. The purpose of this study was to simplify manual quantitative EPR measurement. A suitable sample volume for achieving a stable EPR intensity was estimated. The effects of different solvents on the EPR sensitivity were compared. The stability and reproducibility of the EPR intensity of standard nitroxyl radical solutions were compared among different types of sample tubes. When the sample tubes, sample volumes, and/or solvents were the same, the EPR intensity was reproduced with an error of 2% or less for μM samples. The quantified sample and the standard sample in the same solvent and the same volume drawn into the same sample tube was able to be directly compared. The standard sample for quantification should be measured just before or after every daily experiment.

Non-thermal plasma-induced DMPO-OH yields hydrogen peroxide

Recent developments in electronics have enabled the medical applications of non-thermal plasma (NTP), which elicits reactive oxygen species (ROS) and reactive nitrogen species (RNS), such as hydroxyl radical (●OH), hydrogen peroxide (H2O2), singlet oxygen (1O2), superoxide (O2●-), ozone, and nitric oxide at near-physiological temperatures. In preclinical studies or human clinical trials, NTP promotes blood coagulation, eradication of bacterial, viral and biofilm-related infections, wound healing, and cancer cell death. To elucidate the solution-phase biological effects of NTP in the presence of biocompatible reducing agents, we employed electron paramagnetic resonance (EPR) spectroscopy to quantify ●OH using a spin-trapping probe, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO); 1O2 using a fluorescent probe; and O2●- and H2O2 using luminescent probes in the presence of thiols or tempol. NTP-induced ●OH was significantly scavenged by dithiothreitol (DTT), reduced glutathione (GSH), and oxidized glutathione (GSSG) in 2 or 5 mM DMPO. NTP-induced O2●- was significantly scavenged by 10 μM DTT and GSH, while 1O2 was not efficiently scavenged by these compounds. GSSG degraded H2O2 more effectively than GSH and DTT, suggesting that the disulfide bonds reacted with H2O2. In the presence of 1-50 mM DMPO, NTP-induced H2O2 quantities were unchanged. The inhibitory effect of tempol concentration (50 and 100 μM) on H2O2 production was observed in 1 and 10 mM DMPO, whereas it became ineffective in 50 mM DMPO. Furthermore, DMPO-OH did not interact with tempol. These results suggest that DMPO and tempol react competitively with O2●-. Further studies are warranted to elucidate the interaction between NTP-induced ROS and biomolecules.

Evaluation of photodynamic effect of Indocyanine green (ICG) on the colon and glioblastoma cancer cell lines pretreated by cold atmospheric plasma

BACKGROUND

Cold Atmospheric Plasma (CAP) has been proposed as a new approach based on its anticancer potential. However, its biological effects in combination with other physical modalities may also enhance efficiency and expand the applicability of the CAP method Photodynamic Therapy (PDT) may be improved by the use of indocyanine green (ICG) photosensitizer with absorption wavelength in the near infrared region to allow for deeper treatment depth.. In this study, the effectiveness of cold atmospheric helium plasma (He-CAP) as a pretreatment on the efficiency of ICG mediated PDT was investigated.

METHODS AND MATERIAL

First, toxicity of different concentrations of ICG on HT-29 and U-87MG cell lines was examined for 24 h. IC₁₀ and IC₃₀ of ICG were determined and then cells were treated with this ICG concentrations with different plasma radiation doses and light exposures for 48 h. Finally, MTT assay was performed for all treatment groups. The experiments were repeated at least 4 times at each group for two cell lines, separately. In order to compare the results, several indicators such as treatment efficiency, synergistic ratio, and the amount of optical exposure required for 50% cell death (ED₅₀) were also defined. Finally, SPSS 20 software is used for statistical analysis of data.

RESULTS

Pretreatment with CAP could significantly reduce cell survival in both cell lines (P<0.05). Also concentrations, irradiation time with CAP, and appropriate light exposure in both cell lines increased therapeutic efficiency compared to either treatment alone (P<0.05). While increasing the efficiency of photodynamic therapy varied between the two cell lines, the improvement in the PDT process was demonstrated by pretreatment with CAP.

CONCLUSION

Synergistic effect in the cell death with PDT were observed following He-CAP treatment and the results indicated that pretreatment with He-CAP improves the efficiency of photodynamic therapy.

Intracellular Responses Triggered by Cold Atmospheric Plasma and Plasma-Activated Media in Cancer Cells

Cold atmospheric plasma (CAP), an ionized gas operating at room temperature, has been increasingly studied with respect to its potential use in medicine, where its beneficial effects on tumor reduction in oncology have been demonstrated. This review discusses the cellular changes appearing in cell membranes, cytoplasm, various organelles, and DNA content upon cells’ direct or indirect exposure to CAP or CAP-activated media/solutions (PAM), respectively. In addition, the CAP/PAM impact on the main cellular processes of proliferation, migration, protein degradation and various forms of cell death is addressed, especially in light of CAP use in the oncology field of plasma medicine.

L-Dehydroascorbate efficiently degrades non-thermal plasma-induced hydrogen peroxide

Non-thermal plasma (NTP) devices generate reactive oxygen species (ROS) and reactive nitrogen species, such as singlet oxygen (¹O₂), superoxide (O₂^-), hydroxyl radical (^●OH), hydrogen peroxide (H₂O₂), ozone, and nitric oxide at near-physiological temperature. In preclinical studies, NTP promotes blood coagulation, wound healing with disinfection, and selective killing of cancer cells. Although these biological effects of NTP have been widely explored, the stoichiometric quantitation of ROS in the liquid phase has not been performed in the presence of biocompatible reducing agents, which may modify the final biological effects of NTP. Here, we utilized electron paramagnetic resonance spectroscopy to quantitate ^●OH, using a spin-trapping probe 5,5-dimethyl-1-pyrroline-N-oxide; ¹O₂, using a fluorescent probe; and O₂^- and H₂O₂, using luminescent probes, after NTP exposure in the presence of antioxidants. l-ascorbate (Asc) at 50 μM concentration (physiological concentration in serum) significantly scavenged ^●OH, whereas (-)-epigallocatechin gallate (EGCG) and α-tocopherol were also effective at performing scavenging activities at 250 μM concentrations. Asc significantly scavenged O₂^- and H₂O₂ at 100 μM. l-Dehydroascorbate (DHA), an oxidized form of Asc, degraded H₂O₂, whereas it did not quench ^●OH or O₂^-, which are sources of H₂O₂. Furthermore, EGCG efficiently scavenged NTP-induced ¹O₂, O₂^-, and H₂O₂ in Chelex-treated water. These results indicate that the redox cycling of Asc/DHA and metabolites of DHA are important to be considered when applying NTP to cells and tissues. Additionally, ROS-reducing compounds, such as EGCG, affect the outcome. Further studies are warranted to elucidate the interaction between ROS and biomolecules to promote the medical applications of NTP.

Plasma Treatment Limits Cutaneous Squamous Cell Carcinoma Development In Vitro and In Vivo

Cutaneous squamous cell carcinoma (SCC) is the most prevalent cancer worldwide, increasing the cost of healthcare services and with a high rate of morbidity. Its etiology is linked to chronic ultraviolet (UV) exposure that leads to malignant transformation of keratinocytes. Invasive growth and metastasis are severe consequences of this process. Therapy-resistant and highly aggressive SCC is frequently fatal, exemplifying the need for novel treatment strategies. Cold physical plasma is a partially ionized gas, expelling therapeutic doses of reactive oxygen and nitrogen species that were investigated for their anticancer capacity against SCC in vitro and SCC-like lesions in vivo. Using the kINPen argon plasma jet, a selective growth-reducing action of plasma treatment was identified in two SCC cell lines in 2D and 3D cultures. In vivo, plasma treatment limited the progression of UVB-induced SSC-like skin lesions and dermal degeneration without compromising lesional or non-lesional skin. In lesional tissue, this was associated with a decrease in cell proliferation and the antioxidant transcription factor Nrf2 following plasma treatment, while catalase expression was increased. Analysis of skin adjacent to the lesions and determination of global antioxidant parameters confirmed the local but not systemic action of the plasma anticancer therapy in vivo.

Direct EPR detection of atomic nitrogen in an atmospheric nitrogen plasma jet

In this study, an atmospheric nitrogen plasma jet generated by a custom-built micro-plasma device was analyzed at room temperature by continuous wave and pulse EPR spectroscopy in real time. Transiently formed nitrogen atoms were detected without the necessity to use spin-traps or other reagents for their stabilization. In contrast to results from optical emission spectroscopy, only signals from the ⁴S ground state of ¹⁴N and ¹⁵N could be detected. EPR data analysis revealed an isotropic g value of 1.9971 and isotropic hyperfine coupling constants of a(¹⁴N) = (10.47 ± 0.02) MHz and a(¹⁵N) = (14.69 ± 0.02) MHz. Moreover, lifetime and relaxation data could be determined; both are discussed in terms of spectral widths and actual concentrations of the transiently formed nitrogen species within the plasma jet. The data show that the lifetimes of atomic nitrogen and charged particles such as N⁺ must be different, and for the latter below the observation time window of EPR spectroscopy. We demonstrate that the real-time (pulsed) EPR technique is a fast and reliable alternative to detect atomic nitrogen in atmospheric pressure plasma jets. The method may be used for a continuous monitoring of the quality of plasma jets.

xCT (SLC7A11) expression confers intrinsic resistance to physical plasma treatment in tumor cells

Cold physical plasma is a partially ionized gas investigated as a new anticancer tool in selectively targeting cancer cells in monotherapy or in combination with therapeutic agents. Here, we investigated the intrinsic resistance mechanisms of tumor cells towards physical plasma treatment. When analyzing the dose-response relationship to cold plasma-derived oxidants in 11 human cancer cell lines, we identified four 'resistant' and seven 'sensitive' cell lines. We observed stable intracellular glutathione levels following plasma treatment only in the 'resistant' cell lines indicative of altered antioxidant mechanisms. Assessment of proteins involved in GSH metabolism revealed cystine-glutamate antiporter xCT (SLC7A11) to be significantly more abundant in the 'resistant' cell lines as compared to 'sensitive' cell lines. This decisive role of xCT was confirmed by pharmacological and genetic inhibition, followed by cold physical plasma treatment. Finally, microscopy analysis of ex vivo plasma-treated human melanoma punch biopsies suggested a correlation between apoptosis and basal xCT protein abundance. Taken together, our results demonstrate that xCT holds the potential as a biomarker predicting the sensitivity of tumor cells towards plasma treatment.

Non-thermal plasma and ultrasound-assisted open lactic acid fermentation of distillery stillage

Stillage is the main by-product of bioethanol production and the cost of its treatment significantly affects the economy of bioethanol production. A process of thermal sterilization before lactic acid fermentation (LAF) is energy demanding and is causing deterioration of valuable compounds in stillage. In this study, ultrasound (UT) and plasma (PT) treatments were used for microbial inactivation, and a significant reduction in the number of viable microorganisms in the stillage after PT and UT was observed. After application of treatment, LAF by Lactobacillus rhamnosus ATCC 7469 was initiated. The concentration of LA is used to quantify the efficiency of the stillage revalorization. The highest LA productivity of 1.21 g/Lh and yield of 0.82 g/g were obtained after PT, while UT of 10 min provided productivity of 1.02 g/Lh and LA yield of 0.69 g/g. The results were benchmarked against closed LAF. Around 20% better revalorization of stillage by PT was achieved when compared with conventional sterilization. In addition, an excellent L (+) LA stereoselectivity of 95.5% was attained after PT. From the aspect of energy efficiency, that of PT was three times lower than UT and almost ten times lower than thermal sterilization, but it is the most expensive due to the high consumption of gas which could reduce application of closed Ar atmosphere on larger scales. This way, a simpler and energy efficient process for LA production on stillage was accomplished by "open" fermentation.

Plasma-Derived Reactive Species Shape a Differentiation Profile in Human Monocytes

Background: Monocyte-derived macrophages are key regulators and producers of reactive oxygen and nitrogen species (ROS/RNS). Pre-clinical and clinical studies suggest that cold physical plasma may be beneficial in the treatment of inflammatory conditions via the release of ROS/RNS. However, it is unknown how plasma treatment affects monocytes and their differentiation profile. Methods: Naïve or phorbol-12-myristate-13-acetate (PMA)-pulsed THP-1 monocytes were exposed to cold physical plasma. The cells were analyzed regarding their metabolic activity as well as flow cytometry (analysis of viability, oxidation, surface marker expression and cytokine secretion) and high content imaging (quantitative analysis of morphology. Results: The plasma treatment affected THP-1 metabolisms, viability, and morphology. Furthermore, a significant modulation CD55, CD69, CD271 surface-expression and increase of inflammatory IL1β, IL6, IL8, and MCP1 secretion was observed upon plasma treatment. Distinct phenotypical changes in THP-1 cells arguing for a differentiation profile were validated in primary monocytes from donor blood. As a functional outcome, plasma-treated monocytes decreased the viability of co-cultured melanoma cells to a greater extent than their non-treated counterparts. Conclusions: Our results suggest plasma-derived ROS/RNS shaped a differentiation profile in human monocytes as evidenced by their increased inflammatory profile (surface marker and cytokines) as well as functional outcome (tumor toxicity).

Formation of reactive oxygen species by irradiation of cold atmospheric pressure plasma jet to water depends on the irradiation distance

Because application of cold atmospheric pressure plasma jet (CAPPJ) to biological samples have taken large attentions, it is important to examine the effects of various CAPPJ parameters on the generation of reactive species. Here, we investigated the generation of reactive species in water by CAPPJ irradiation by changing the following parameters: irradiation time, sample volume, and irradiation distance between the sample surface and plasma jet tip. We measured 1) change in the ESR signal intensity of 4-hydroxy-2,2,6,6-tetrametylpeperidine-1-oxyl (Tempol), 2) spin-trapping with 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 3) Fricke dosimeter reaction, and 4) hydrogen peroxide (H₂O₂) formation induced by CAPPJ irradiation. By the experiment of volume dependency, it is suggested that the reactive species detected in water are formed largely in the plasma gas phase. The reduction of ESR signal intensity of Tempol and the formation of DMPO-OH were strongly dependent on irradiation distance, but the relationship between H₂O₂ generation and distance was weak. The formation of species that oxidize Fe²⁺ to Fe³⁺ was shown by the Fricke dosimeter reaction, and reactions at irradiation distances longer than 3 cm were mainly attributable to H₂O₂. It may be possible to apply different reactive species to the samples by changing the CAPPJ irradiation distance.

Roles of intracellular and extracellular ROS formation in apoptosis induced by cold atmospheric helium plasma and X-irradiation in the presence of sulfasalazine

Sulfasalazine (SSZ) is a well-known anti-inflammatory drug and also an inhibitor of the cystine-glutamate antiporter that is known to reduce intracellular glutathione (GSH) level and increase cellular oxidative stress, indicating its anti-tumor potential. However, the combination of SSZ with other physical modalities remains unexplored. Here, the effects of SSZ on cold atmospheric helium plasma (He-CAP), which produces approximately 24 x higher concentration of hydroxyl radicals (. OH) compared to X-irradiation (IR) in aqueous solution, and on IR-induced apoptosis in human leukemia Molt-4 cells were studied to elucidate the mechanism of apoptosis enhancement. Both the Annexin V-FITC/PI and DNA fragmentation assay revealed that pre-treatment of cells with SSZ significantly enhanced He-CAP and IR-induced apoptosis. Similar enhancement was observed during the loss of mitochondrial membrane potential, intracellular Ca²⁺ ions, and mitochondria- and endoplasmic reticulum-related proteins. The concentration of intracellular reactive oxygen species (ROS) was much higher in He-CAP treated cells than in X-irradiated cells. On the other hand, strong enhancement of Fas expression and caspase-8 and -3 activities were only observed in X-irradiated cells. It might be possible that the higher concentration of intracellular and extracellular ROS suppressed caspase activities and Fas expression in He-CAP-treated cells. Notably, pretreating the cells with an antioxidant N-acetyl-L-cysteine (NAC) dramatically decreased apoptosis in cells treated by He-CAP, but not by IR. These results suggest that IR-induced apoptosis is due to specific and effective ROS distribution since intracellular ROS formation is marginal and the high production of ROS inside and outside of cells plays unique roles in He-CAP induced apoptosis. We conclude that our data provides efficacy and mechanistic insights for SSZ, which might be helpful for establishing SSZ as a future sensitizer in He-CAP or IR therapy for cancer.

Analysis of Short-Lived Reactive Species in Plasma-Air-Water Systems: The Dos and the Do Nots

This Feature addresses the analysis of the reactive species generated by nonthermal atmospheric pressure plasmas, which are widely employed in industrial and biomedical research, as well as first clinical applications. We summarize the progress in detection of plasma-generated short-lived reactive oxygen and nitrogen species in aqueous solutions, discuss the potential and limitations of various analytical methods in plasma-liquid systems, and provide an outlook on the possible future research goals in development of short-lived reactive species analysis methods for a general nonspecialist audience.

Cold atmospheric helium plasma causes synergistic enhancement in cell death with hyperthermia and an additive enhancement with radiation

Cold atmospheric plasmas (CAPs) have been proposed as a novel therapeutic method for its anti-cancer potential. However, its biological effects in combination with other physical modalities remain elusive. Therefore, this study examined the effects of cold atmospheric helium plasma (He-CAP) in combination with hyperthermia (HT) 42 °C or radiation 5 Gy. Synergistic enhancement in the cell death with HT and an additive enhancement with radiation were observed following He-CAP treatment. The synergistic effects were accompanied by increased intracellular reactive oxygen species (ROS) production. Hydrogen peroxide (H₂O₂) and superoxide (O₂^•–) generation was increased immediately after He-CAP treatment, but fails to initiate cell death process. Interestingly, at late hour’s He-CAP-induced O₂^•– generation subsides, however the combined treatment showed sustained increased intracellular O₂^•– level, and enhanced cell death than either treatment alone. He-CAP caused marked induction of ROS in the aqueous medium, but He-CAP-induced ROS seems insufficient or not completely incorporated intra-cellularly to activate cell death machinery. The observed synergistic effects were due to the HT effects on membrane fluidity which facilitate the incorporation of He-CAP-induced ROS into the cells, thus results in the enhanced cancer cell death following combined treatment. These findings would be helpful when establishing a therapeutic strategy for CAP in combination with HT or radiation.

Analysis of reactive oxygen and nitrogen species generated in three liquid media by low temperature helium plasma jet

In order to identify aqueous species formed in Plasma activated media (PAM), quantitative investigations of reactive oxygen and nitrogen species (ROS, RNS) were performed and compared to Milli-Q water and culture media without and with Fetal Calf Serum. Electron paramagnetic resonance, fluorometric and colorimetric analysis were used to identify and quantify free radicals generated by helium plasma jet in these liquids. Results clearly show the formation of ROS such as hydroxyl radical, superoxide anion radical and singlet oxygen in order of the micromolar range of concentrations. Nitric oxide, hydrogen peroxide and nitrite-nitrate anions (in range of several hundred micromolars) are the major species observed in PAM. The composition of the medium has a major impact on the pH of the solution during plasma treatment, on the stability of the different RONS that are produced and on their reactivity with biomolecules. To emphasize the interactions of plasma with a complex medium, amino acid degradation by means of mass spectrometry was also investigated using methionine, tyrosine, tryptophan and arginine. All of these components such as long lifetime RONS and oxidized biological compounds may contribute to the cytotoxic effect of PAM. This study provides mechanistic insights into the mechanisms involved in cell death after treatment with PAM.

Oxygen atoms are critical in rendering THP-1 leukaemia cells susceptible to cold physical plasma-induced apoptosis

Cold physical plasma has been suggested as a powerful new tool in oncology. However, some cancer cells such as THP-1 leukaemia cells have been shown to be resistant towards plasma-induced cell death, thereby serving as a good model for optimizing plasmas in order to foster pro-apoptotic anticancer effects. A helium/oxygen radio frequency driven atmospheric plasma profoundly induced apoptosis in THP-1 cells whereas helium, humidified helium, and humidified helium/oxygen plasmas were inefficient. Hydrogen peroxide – previously shown as central plasma-derived agent – did not participate in the killing reaction but our results suggest hypochlorous acid to be responsible for the effect observed. Proteomic analysis of THP-1 cells exposed to He/O₂ plasma emphasized a prominent growth retardation, cell stress, apoptosis, and a pro-immunogenic profile. Altogether, a plasma setting that inactivates previously unresponsive leukaemia cells is presented. Crucial reactive species in the plasma and liquid environment were identified and discussed, deciphering the complexity of plasma from the gas phase into the liquid down to the cellular response mechanism. These results may help tailoring plasmas for clinical applications such as oxidation-insensitive types of cancer.

An Atmospheric Pressure Plasma Setup to Investigate the Reactive Species Formation

Non-thermal atmospheric pressure ('cold') plasmas have received increased attention in recent years due to their significant biomedical potential. The reactions of cold plasma with the surrounding atmosphere yield a variety of reactive species, which can define its effectiveness. While efficient development of cold plasma therapy requires kinetic models, model benchmarking needs empirical data. Experimental studies of the source of reactive species detected in aqueous solutions exposed to plasma are still scarce. Biomedical plasma is often operated with He or Ar feed gas, and a specific interest lies in investigation of the reactive species generated by plasma with various gas admixtures (O₂, N₂, air, H₂O vapor, etc.) Such investigations are very complex due to difficulties in controlling the ambient atmosphere in contact with the plasma effluent. In this work, we addressed common issues of 'high' voltage kHz frequency driven plasma jet experimental studies. A reactor was developed allowing the exclusion of ambient atmosphere from the plasma-liquid system. The system thus comprised the feed gas with admixtures and the components of the liquid sample. This controlled atmosphere allowed the investigation of the source of the reactive oxygen species induced in aqueous solutions by He-water vapor plasma. The use of isotopically labelled water allowed distinguishing between the species originating in the gas phase and those formed in the liquid. The plasma equipment was contained inside a Faraday cage to eliminate possible influence of any external field. The setup is versatile and can aid in further understanding the cold plasma-liquid interactions chemistry.

Helium-based cold atmospheric plasma-induced reactive oxygen species-mediated apoptotic pathway attenuated by platinum nanoparticles

Plasma is generated by ionizing gas molecules. Helium (He)‐based cold atmospheric plasma (CAP) was generated using a high‐voltage power supply with low‐frequency excitation (60 Hz at 7 kV) and He flow at 2 l/min. Platinum nanoparticles (Pt‐NPs) are potent antioxidants due to their unique ability to scavenge superoxides and peroxides. These features make them useful for the protection against oxidative stress‐associated pathologies. Here, the effects of Pt‐NPs on He‐CAP‐induced apoptosis and the underlying mechanism were examined in human lymphoma U937 cells. Apoptosis was measured after cells were exposed to He‐CAP in the presence or absence of Pt‐NPs. The effects of combined treatment were determined by observing the changes in intracellular reactive oxygen species (ROS) and both mitochondrial and Fas dependent pathway. The results indicate that Pt‐NPs substantially scavenge He‐CAP‐induced superoxides and peroxides and inhibit all the pathways involved in apoptosis execution. This might be because of the SOD/catalase mimetic effects of Pt‐NPs. These results showed that the Pt‐NPs can induce He‐CAP desensitization in human lymphoma U937 cells.

Effects of nitrogen on the apoptosis of and changes in gene expression in human lymphoma U937 cells exposed to argon-based cold atmospheric pressure plasma

Cold atmospheric pressure plasma (CAP) is known as a source of biologically active agents, such as reactive oxygen species (ROS) and reactive nitrogen species (RNS). In the present study, we examined the effects of nitrogen (N2) on the apoptosis of and changes in gene expression in human lymphoma U937 cells exposed to argon (Ar)-CAP. Enormous amounts of hydroxyl (·OH) radicals in aqueous solution were produced using Ar‑CAP generated using a 20 kHz low frequency at 18 kV with a flow rate of 2 l/min. The increase in the levels of ·OH radicals was significantly attenuated by the addition of N2 to Ar gas. On the other hand, the level of total nitrate/nitrite in the supernatant was significantly elevated in the Ar + N2-CAP‑exposed U937 cells. When the cells were exposed to Ar‑CAP, a significant increase in apoptosis was observed, whereas apoptosis was markedly decreased in the cells exposed to Ar + N2-CAP. Microarray and pathway analyses revealed that a newly identified gene network containing a number of heat shock proteins (HSPs), anti-apoptotic genes, was mainly associated with the biological function of the prevention of apoptosis. Quantitative PCR revealed that the expression levels of HSPs were significantly elevated in the cells exposed to Ar + N2-CAP than those exposed to Ar‑CAP. These results indicate that N2 gas in Ar‑CAP modifies the ratio of ROS to RNS, and suppresses the apoptosis induced by Ar‑CAP. The modulation of gaseous conditions in CAP may thus prove to be useful for future clinical applications, such as for switching from a sterilizing mode to cytocidal effect for cancer cells.

Non-Thermal Plasma in Contact with Water: The Origin of Species

Non‐thermal atmospheric pressure plasma has attracted considerable attention in recent years due to its potential for biomedical applications. Determining the mechanism of the formation of reactive species in liquid treated with plasma is thus of paramount importance for both fundamental and applied research. In this work, the origin of reactive species in plasma‐treated aqueous solutions was investigated by using spin‐trapping, hydrogen and oxygen isotopic labelling and electron paramagnetic resonance (EPR) spectroscopy. The species originating from molecules in the liquid phase and those introduced with the feed gas were differentiated by EPR and ¹H NMR analysis of liquid samples. The effects of water vapour and oxygen admixtures in the feed gas were investigated. All the reactive species detected in the liquid samples were shown to be formed largely in the plasma gas phase. It is suggested that hydrogen peroxide (determined by UV/Vis analysis) is formed primarily in the plasma tube, whereas the radical species ⋅OOH, ⋅OH and ⋅H are proposed to originate from the region between the plasma nozzle and the liquid sample.