Nitric oxide decreases the stability of DMPO spin adducts

Influence of Inorganic Anions on the Chemical Stability of Molybdenum Disulfide Nanosheets in the Aqueous Environment

Chemical stability is closely associated with the transformations and bioavailabilities of engineered nanomaterials and is a key factor that governs broader and long-term application. With the growing utilization of molybdenum disulfide (MoS2) nanosheets in water treatment and purification processes, it is crucial to evaluate the stability of MoS2 nanosheets in aquatic environments. Nonetheless, the effects of anionic species on MoS2 remain largely unexplored. Herein, the stability of chemically exfoliated MoS2 nanosheets (ceMoS2) was assessed in the presence of inorganic anions. The results showed that the chemical stability of ceMoS2 was regulated by the nucleophilicities and the resultant charging effects of the anions in aquatic systems. The anions promote the dissolution of ceMoS2 by triggering a shift in the chemical potential of the ceMoS2 surface as a function of the anion nucleophilicity (i.e., charging effect). Fast charging with HCO3- and HPO42-/H2PO4- was validated by a phase transition from 1T to 2H and the emergence of MoV, and it promoted oxidative dissolution of the ceMoS2. Additionally, under sunlight, ceMoS2 dissolution was accelerated by NO3-. These findings provide insight into the ion-induced fate of ceMoS2 and the durability and risks of MoS2 nanosheets in environmental applications.

Efficient wastewater disinfection by raised 1O2 yield through enhanced electron transfer and intersystem crossing via photocatalysis of peroxymonosulfate with CuS quantum dots modified MIL-101(Fe)

Peroxymonosulfate (PMS)-based photocatalysis is a promising alternative approach for wastewater disinfection. Singlet oxygen (¹O₂) is sensitive and efficient for bacterial inactivation. This study developed a ¹O₂-predominated PMS disinfection technique under visible light with CuS quantum dots (QDs) modified MIL-101(Fe) (CSQDs@MF). CuS QDs modification greatly enhanced the ¹O₂ quantum yield by 80% than that of MIL-101(Fe). Photoelectricity and photoluminescence tests demonstrated that both the enhanced electron transfer and energy transfer were responsible for improved ¹O₂ generation in Vis/PMS/CSQDs@MF system. The system took 60 min to inactivate 7.5-log E. coli, and it could be applied in a broad pH and dissolve oxygen range. Bacterial inactivation mechanism suggested that ¹O₂ attacked cell membrane first, then induced oxidative stress, up-regulated intracellular ROS level, eventually broke DNA strand. The system showed good disinfection performance on Gram-positive B. subtilis and fecal coliforms in practical wastewater, implying it is a promising alternative disinfection technology for wastewater treatment.

Evaluating the influence of cold plasma bubbling on protein structure and allergenicity in sesame milk

BACKGROUND

Sesame is a traditional oilseed comprising essential amino acids. However, the presence of allergens in sesame is a significant problem in its consumption; thus, this study attempted to reduce these allergens in sesame oilseeds.

OBJECTIVE

The present study aimed to evaluate the effect of cold plasma processing on structural changes in proteins, and thereby the alteration of allergenicity in sesame milk. Method: Sesame milk (300 mL) was processed using atmospheric pressure plasma bubbling unit (dielectric barrier discharge, power: 200 V, and airflow rate: 16.6 mL/min) at different exposure times (10, 20, and 30 min).

RESULTS

The efficiency of plasma-bubbling unit as measured by electron paramagnetic resonance in terms of producing reactive hydroxyl (OH) radicals proved that generation of reactive species increased with exposure time. Further, the plasma-processed sesame milk subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and differential scanning calorimetery analysis revealed that plasma bubbling increased the oxidation of proteins with respect to bubbling time. The structural analysis by Fourier transform infrared spectroscopy and circular dichroism revealed that the secondary structure of proteins was altered after plasma application. This change in the protein structure helped in changing the immunoglobulin E (IgE)-binding epitopes of the protein, which in turn reduced the allergen-binding capacity by 23% at 20-min plasma bubbling as determined by the sandwich-type enzyme-linked immunosorbent assay. However, 30-min plasma bubbling intended to increase allergenicity, possibly because of increase in IgE binding due to the generation of neo epitopes.

CONCLUSION

These changes proved that plasma bubbling is a promising technology in oxidizing protein structure, and thereby reducing the allergenicity of sesame milk. However, increase in binding at 30-min bubbling is to be studied to facilitate further reduction of the binding capacity of IgE antibodies.

Non-Thermal Plasma as a Unique Delivery System of Short-Lived Reactive Oxygen and Nitrogen Species for Immunogenic Cell Death in Melanoma Cells

Breakthroughs in cancer immunotherapies have demonstrated considerable success, though not without limitations. Non-thermal plasma (NTP) for cancer therapy has been emerging as a potential adjuvant treatment via induction of immunogenic cell death (ICD). Cancer cells undergoing ICD stimulate a patient's immune system to mount an anticancer response. While promising, the underlying mechanisms of NTP-induced ICD must be closely examined. Here, the interaction between non-thermal plasma and cancerous cells is studied. The short-lived reactive oxygen and nitrogen species (e.g., hydroxyl radicals, atomic oxygen, nitric oxide) produced by plasma are the main effectors that elicit ICD in melanoma while, surprisingly, persistent species do not. This is demonstrated in vitro using a dielectric barrier discharge plasma system and is validated in a vaccination assay in vivo. Plasma generation of reactive species appears to be dictated by the total energy. Collectively, this work provides fundamental insight into plasma interactions with biological material. Furthermore, it lays the foundation for future development of NTP systems for clinical translation. The addition of plasma systems into the existing arsenal of cancer therapies opens the possibility for new combination strategies for safer and more robust control of cancer.

Photo-Reduction of CO₂ by VIS Light on Polythiophene-ZSM-5 Zeolite Hybrid Photo-Catalyst

A new hybrid photo-catalyst based on ZSM-5 zeolite suitable for reduction of carbon dioxide was synthesized. The photo-catalyst was prepared by oxidative polymerization of thiophene with FeCl₃ in the presence of ZSM-5 with participation of ultrasound. The synthesized photo-catalyst strongly absorbs light radiation up to approx. 650 nm, with the absorption edge in the NIR region. Reactive radicals were generated by VIS light irradiation in an aqueous suspension consisting of the photo-catalyst with CO₂. Formic acid and acetic acid were generated as the main products of the CO₂ reduction. EPR spin trapping technique was applied to identify the reactive radical intermediates. In this work, the mechanism of product formation is also discussed.

Nitric oxide reverses drug resistance by inhibiting ATPase activity of p-glycoprotein in human multi-drug resistant cancer cells

BACKGROUND

Development of resistance to chemotherapy drugs is a significant problem in treating human malignancies in the clinic. Overexpression of drug efflux proteins, including P-170 glycoprotein (P-gp), an ATP-dependent efflux protein, is one of the main mechanisms responsible for multi-drug resistance (MDR). Because our previous studies have shown that nitric oxide (˙NO) or its related species inhibit the ATPase activities of topoisomerase II, we hypothesized that ˙NO should also inhibit the ATPase activity of P-gp and increase drug accumulation in MDR cells, causing a reversal of drug resistance.

RESULTS

Cytotoxicity and cellular accumulation studies showed that ˙NO significantly inhibited the ATPase activity of P-gp in isolated membranes and in NCI/ADR-RES tumor cells, causing an increase in drug accumulation and reversals of adriamycin and taxol resistance in the MDR cells. While ˙NO had no effects on topoisomerase II-induced, adriamycin-dependent DNA cleavage complex formation, it significantly inhibited adriamycin-induced DNA double-strand breaks. Electron spin resonance studies showed an increase in adriamycin-dependent hydroxyl radical formation in the presence of an NO-donor.

CONCLUSIONS

The reversal of drug resistance is due to inhibition of the ATPase activity by ˙NO, resulting in enhancement of the drug accumulation in the MDR cells. Furthermore, DNA damage was not responsible for this reversal of adriamycin resistance. However, formation of adriamycin-dependent toxic free radical species and subsequent cellular damage may be responsible for the increased cytotoxicity of adriamycin by ˙NO in NCI/ADR-RES cells.

GENERAL SIGNIFICANCE

Appropriately designed NO donors would be ideal for the treatment of P-gp-overexpressing tumors in the clinic.

Graphite particles induce ROS formation in cell free systems and human cells

It is commonly accepted that the toxicity of carbonaceous particulate matter (PM) is due to the production of reactive oxygen species (ROS) which induce biological damage in the exposed cells. It is also known that PM produced during the combustion processes consists of a carbonaceous core "dressed" with other organic and/or inorganic materials. In spite of this knowledge, the role of these materials in the production of ROS has not yet been clear. This work aims at understanding whether "naked" carbonaceous particles are capable of forming ROS either in cell-free or in-cell systems. The problem has been treated based on the data collected from pure graphite samples of different sizes obtained by ball-milling pure graphite for various lengths of time. The experimental approach considered Raman, ESR (spin trapping), cell viability and fluorescence spectroscopy measurements. These techniques allowed us to carry out measurements both in cell and cell-free systems and the results consistently indicate that also pure naked carbonaceous particles can catalyze the electron transfer that produces superoxide ions. The process depends on the particle size and enlightens the role of the edges of the graphitic platelets. Evidence has been collected that even "naked" graphitic nanoparticles are capable of producing ROS and decreasing the cell viability thus representing a potential danger to human health.

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.

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

Electron paramagnetic resonance (EPR)-spin trapping and flow cytometry were used to identify free radicals generated using argon-cold atmospheric plasma (Ar-CAP) in aqueous solutions and intracellularly in comparison with those generated by X-irradiation. Ar-CAP was generated using a high-voltage power supply unit with low-frequency excitation. The characteristics of Ar-CAP were estimated by vacuum UV absorption and emission spectra measurements. Hydroxyl (·OH) radicals and hydrogen (H) atoms in aqueous solutions were identified with the spin traps 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M₄PO), and phenyl N-t-butylnitrone (PBN). The occurrence of Ar-CAP-induced pyrolysis was evaluated using the spin trap 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS) in aqueous solutions of DNA constituents, sodium acetate, and L-alanine. Human lymphoma U937 cells were used to study intracellular oxidative stress using five fluorescent probes with different affinities to a number of reactive species. The analysis and quantification of EPR spectra revealed the formation of enormous amounts of ·OH radicals using Ar-CAP compared with that by X-irradiation. Very small amounts of H atoms were detected whereas nitric oxide was not found. The formation of ·OH radicals depended on the type of rare gas used and the yield correlated inversely with ionization energy in the order of krypton > argon = neon > helium. No pyrolysis radicals were detected in aqueous solutions exposed to Ar-CAP. Intracellularly, ·OH, H₂O₂, which is the recombination product of ·OH, and OCl^- were the most likely formed reactive oxygen species after exposure to Ar-CAP. Intracellularly, there was no practical evidence for the formation of NO whereas very small amounts of superoxides were formed. Despite the superiority of Ar-CAP in forming ·OH radicals, the exposure to X-rays proved more lethal. The mechanism of free radical formation in aqueous solutions and an intracellular milieu is discussed.

Detection and identification of oxidants formed during •NO/O2•⁻ reaction: a multi-well plate CW-EPR spectroscopy combined with HPLC analyses

New techniques and probes are routinely emerging for detecting short-lived free radicals such as superoxide radical anion (O₂(•-)), nitric oxide ((•)NO), and transient oxidants derived from peroxynitrite (ONOO(-)/ONOOH). Recently, we reported the profiles of oxidation products (2-hydroxyethidium, ethidium, and various dimeric products) of the fluorogenic probe hydroethidine (HE) in the (•)NO/O₂(•-) system (Zielonka et al. 2012). In this study, we used HPLC analyses of HE oxidation products in combination with continuous wave electron paramagnetic resonance (CW-EPR) spin trapping with 5-tert-butoxycarbonyl-5-methyl-1-pyrroline N-oxide (BMPO) to define the identity of the oxidizing species formed in the (•)NO/O₂(•-) system. EPR spin-trapping technique is still considered as the gold standard for characterization of free radicals and their intermediates. We monitored formation of BMPO-superoxide (BMPO-(•)OOH) and BMPO-hydroxyl (BMPO-(•)OH) radical adducts. Simultaneous analyses of results from EPR spin-trapping and HPLC measurements are helpful in the interpretation of the mechanism of formation of products of HE oxidation.

Gd2@C79N: isolation, characterization, and monoadduct formation of a very stable heterofullerene with a magnetic spin state of S = 15/2

The dimetallic endohedral heterofullerene (EHF), Gd(2)@C(79)N, was prepared and isolated in a relatively high yield when compared with the earlier reported heterofullerene, Y(2)@C(79)N. Computational (DFT), chemical reactivity, Raman, and electrochemical studies all suggest that the purified Gd(2)@C(79)N, with the heterofullerene cage, (C(79)N)(5-) has comparable stability with other better known isoelectronic metallofullerene (C(80))(6-) cage species (e.g., Gd(3)N@C(80)). These results describe an exceptionally stable paramagnetic molecule with low chemical reactivity with the unpaired electron spin density localized on the internal diatomic gadolinium cluster and not on the heterofullerene cage. EPR studies confirm that the spin state of Gd(2)@C(79)N is characterized by a half-integer spin quantum number of S = 15/2. The spin (S = ½) on the N atom of the fullerene cage and two octet spins (S = 7/2) of two encapsulated gadoliniums are coupled with each other in a ferromagnetic manner with a small zero-field splitting parameter D. Because the central line of Gd(2)@C(79)N is due to the Kramer's doublet with a half-integer spin quantum number of S = 15/2, this relatively sharp line is prominent and the anisotropic nature of the line is weak. Interestingly, in contrast with most Gd(3+) ion environments, the central EPR line (g = 1.978) is observable even at room temperature in a toluene solution. Finally, we report the first EHF derivative, a diethyl bromomalonate monoadduct of Gd(2)@C(79)N, which was prepared and isolated via a modified Bingel-Hirsch reaction.

Nitration of lysozyme by ultrasonic waves; demonstration by immunochemistry and mass spectrometry

Solutions containing hen egg white lysozyme (HEWL) and nitrite were exposed to ultrasonic irradiation in order to study the possible sonochemical modifications. This is the first demonstration of the nitration of tyrosine residues in a protein (lysozyme) by the use of an ultrasonic field alone. Sonochemically nitrated lysozyme was detected using the immunochemical techniques dot blot immunodetection and enzyme-linked immunosorbent assay (ELISA). The sonically oxidised and nitrated protein solutions were analysed by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Hydroxylated species were found in the absence of nitrite, whereas nitration was the major modification in the presence of nitrating agent, implying a competing mechanism between hydroxyl radicals and nitrite. Circular dichroism (CD) indicated that the ultrasonic experimental conditions chosen in this study had little effect on the tertiary and secondary structures of HEWL. Whilst enzymatic assay showed that the presence of nitrite provided a protective effect on the inactivation of the protein under ultrasonic irradiation, nevertheless partially purified, sonically nitrated lysozyme showed a dramatic decrease in lytic activity.

Formation of nitric oxide from nitrite by the ferriheme b protein nitrophorin 7

Recently, the conversion of nitrite into NO by certain heme proteins, in particular hemoglobin, gained much interest as a physiologically important source of NO in human tissue. However, in an aqueous environment, nitrite reduction at an iron porphyrin occurs either through oxidation of ferroheme to ferriheme or with the assistance of a second substrate molecule. Here we report on the reduction of nitrite in the absence of a second substrate at the heme center of the ferriheme protein nitrophorin 7 (NP7) resulting in the formation of NO and restoration of the ferriheme center. The product was spectroscopically characterized, in particular by resonance Raman and FT-IR spectroscopy. Performing the reaction in the presence of the NO trap 2-(4-trimethylammonio)phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (TMA-PTIO) revealed that continuous NO production is possible, i.e., that NP7 is fully restored upon a single turnover. Thus, NP7 is the first case of a b-type heme that performs reduction of nitrite as a single substrate out of the iron(III) state.

Nitration of respiratory epithelial cells by myeloperoxidase depends on extracellular nitrite

To investigate peroxidase induced 3'-nitrotyrosine (3NT) formation, neutrophil derived myeloperoxidase (MPO) (0.025 microM) was directly administered to A549 epithelial cells with or without H(2)O(2) (150 microM). Little evidence of 3NT was found. In contrast, there was a dose dependent increase in intracellular NO (p<0.001, n=8) following MPO (0.025 microM) treatment, which was further enhanced (p<0.0003, n=8) by addition of H(2)O(2). Extracellular NO also increased after MPO (p<0.002, n=5) and with MPO and H(2)O(2) (p<0.004, n=5). Substantial 3NT formation was only detected following addition of nitrite (NO(2)(-), > or =100 microM), which induced a dose dependent increase in epithelial 3NT. In contrast, protein carbonyl formation and increased GSSG/GSH ratios were associated with MPO treatment even in the absence of NO(2)(-). Co-culture of A549 epithelial cells with polymorphonuclear leukocytes (PMN) (10(6)/ml) led to immunocytochemical detection of epithelial 3NT and induction of nitric oxide synthase (NOS2). However, in a Transwell system direct contact between PMN and A549 cells was necessary for immunodetection of 3NT but not of NOS2 consistent with a role for high local nitrite concentrations. These findings demonstrate dissociation between epithelial endogenous NO production and 3NT formation. Although MPO can influence cellular oxidative stress, particularly in the presence of H(2)O(2), 3NT formation requires the presence of high concentrations of NO(2)(-) in the milieu.

Enhanced hydroxyl radical production by dihydroxybenzene-driven Fenton reactions: implications for wood biodegradation

Brown rot fungi degrade wood, in initial stages, mainly through hydroxyl radicals (.OH) produced by Fenton reactions. These Fenton reactions can be promoted by dihydroxybenzenes (DHBs), which can chelate and reduce Fe(III), increasing the reactivity for different substrates. This mechanism allows the extensive degradation of carbohydrates and the oxidation of lignin during wood biodegradation by brown rot fungi. To understand the enhanced reactivity in these systems, kinetics experiments were carried out, measuring .OH formation by the spin-trapping technique of electron paramagnetic resonance spectroscopy. As models of the fungal DHBs, 1,2-dihydroxybenzene (catechol), 2,3-dihydroxybenzoic acid and 3,4-dihydroxybenzoic acid were utilized as well as 1,2-dihydroxy-3,5-benzenedisulfonate as a non-Fe(III)-reducing substance for comparison. Higher amounts and maintained concentrations of .OH were observed in the driven Fenton reactions versus the unmodified Fenton process. A linear correlation between the logarithms of complex stability constants and the .OH production was observed, suggesting participation of such complexes in the radical production.