Superoxide Radical Production Research Articles

Effects of radical scavengers for reactive oxygen species on vitamin K-induced phototoxicity under UVA irradiation

Vitamin K possesses efficacy as a topical dermatological agent. However, vitamin K is phototoxic and susceptible to photodegradation. Herein, we investigated the mechanisms underlying the phototoxicity of phylloquinone (PK, vitamin K1) and menaquinone-4 (MK-4, vitamin K2) under ultraviolet A (UVA) irradiation using various reactive oxygen species (ROS) scavengers. This resulted in the production of superoxide anion radicals via type I and singlet oxygen via type II photodynamic reactions, which were quenched by the ROS scavengers: superoxide dismutase and sodium azide (NaN3). In HaCaT cells, MK-4 and PK induced the production of intracellular ROS, particularly hydrogen peroxide, in response to UVA irradiation. Furthermore, the addition of catalase successfully decreased maximum ROS levels by approximately 30%. NaN3 and catalase decreased the maximum reduction in cell viability induced by UVA-irradiated PK and MK-4 in cell viability by approximately 2–7-fold. Additionally, ROS scavengers had no effect on the photodegradation of PK or MK-4 at 373 nm. Therefore, the phototoxicities of PK and MK-4 were attributed to the generation of singlet oxygen and hydrogen peroxide, underscoring the importance of photoshielding in circumventing phototoxicity.

Microwave‐assisted Fast Synthesis of a Donor‐Acceptor Covalent Organic Framework towards Photooxidative Amidation Catalysis

The synthesis of covalent organic frameworks (COFs) at bulk scale require robust, straightforward, and cost‐effective techniques. However, the traditional solvothermal synthetic methods of COFs suffer low scalability as well as requirement of sensitive reaction environment and multiday reaction time (2‐10 days) which greatly restricts their practical application. Here, we report microwave assisted rapid and optimized synthesis of a donor‐acceptor (D−A) based highly crystalline COF, TzPm‐COF in second (10 sec) to minute (10 min) time scale. With the increasing of the time from seconds to minutes crystallinity, porosity and morphological changes are also observed for TzPm‐COF. Owing to visible range light absorption, suitable band alignment, and low exciton binding energy (Eb=64.6 meV), TzPm‐COF can efficaciously produce superoxide radical anion (O2•−) after activating molecular oxygen (O2) which eventually drives aerobic photooxidative amidation reaction with high recyclability. This photocatalytic approach works well with a variety of substituted aromatic aldehydes having electron‐withdrawing or donating groups and cyclic, acyclic, primary or secondary amines with moderate to high yield. Furthermore, catalytic mechanism was established by monitoring the real‐time reaction progress through in‐situ diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) study.

Microwave-assisted Fast Synthesis of a Donor-Acceptor Covalent Organic Framework towards Photooxidative Amidation Catalysis.

The synthesis of covalent organic frameworks (COFs) at bulkscalerequire robust, straightforward, andcost-effective techniques. However, the traditional solvothermal synthetic methods of COFs suffer low scalability as well as requirement of sensitive reaction environment and multiday reaction time (2-10 days) which greatly restricts their practical application. Here, we report microwave assisted rapid and optimized synthesis of a donor-acceptor (D-A) based highly crystalline COF, TzPm-COF in second (10 sec) to minute (10 min) time scale. With the increasing of the time from seconds to minutes crystallinity, porosity and morphological changes are also observed for TzPm-COF. Owing to visible range light absorption, suitable band alignment, and low exciton binding energy (Eb=64.6meV),TzPm-COF canefficaciously produce superoxide radical anion (O2•-) after activating molecular oxygen (O2) which eventually drives aerobic photooxidative amidation reaction with high recyclability. This photocatalytic approach works well with a variety of substituted aromatic aldehydes having electron-withdrawing or donating groups and cyclic, acyclic, primary or secondary amines with moderate to high yield. Furthermore, catalytic mechanism was established by monitoring the real-time reaction progress through in-situ diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) study.

EFFECT OF AMMONIUM PYRROLIDINEDITHIOCARBAMATE ON THE DEVELOPMENT OF OXIDATIVE STRESS IN BICEPS FEMORIS MUSCLES OF RATS DURING MODELLED METABOLIC SYNDROME

Excessive consumption of high-calorie food, a sedentary lifestyle and increased psycho-emotional stress are risk factors for the development of metabolic syndrome. These factors are especially relevant for residents of countries with highly developed economies. Metabolic syndrome is accompanied not only by metabolic disorders, but also leads to the development of a systemic inflammatory response, which is associated with excessive production and circulation of cytokines in the blood. As a rule, the activation of the transcription factor NF-κB leads to an increase in the production of pro-inflammatory cytokines.
 The aim of this work is to determine the effect of the NF-κB transcription factor activation inhibitor on the activity of antioxidant enzymes, the production of superoxide anion radical, the content of oxidatively modified proteins, and the concentration of malondialdehyde in the biceps femoris muscle of rats who underwent experimental metabolic syndrome.
 The study included 24 sexually mature male Wistar rats weighing 200-260 g. The animals were divided into 4 groups of 6 animals each. The first group was the control group; the second group involved the rats exposed to metabolic syndrome simulated by adding a 20% fructose solution as the only source of drinking water to the standard vivarium diet for 60 days; the third group involved the animals received ammonium pyrrolidine dithiocarbamate in a dose of 76 mg/kg intraperitoneally 3 times a week for 60 days; the fourth group was exposed to the combined effect of the ammonium pyrrolidinedithiocarbamate administration during modeled metabolic syndrome. In this study we investigated a 10% homogenate of the biceps femoris muscle with the research focus on several parameters: superoxide anion radical production, superoxide dismutase and catalase activity, malondialdehyde concentration, and the presence of oxidatively modified proteins.
 Simulation of the metabolic syndrome led to the development of oxidative stress in the biceps muscle of rats that was accompanied by an increase in the production of the superoxide anion radical and a decrease in the activity of antioxidant enzymes. The administration of ammonium pyrrolidinedithiocarbamate during modeled metabolic syndrome caused a decrease in the basic production of superoxide anion radical, production of superoxide anion radical by the microsomal electron transport chain and production of superoxide anion radical by the mitochondrial electron transport chain by 30.28%, 26.21 %, and 27.00%, respectively, compared to the rats in metabolic syndrome group. Superoxide dismutase activity increased by 78.81% and catalase activity grew by 144.74% compared to the metabolic syndrome group. The concentration of free malondialdehyde under the administration of ammonium pyrrolidinedithiocarbamate during metabolic syndrome reduced by 51.80%, and the content of oxidatively modified proteins decreased by 31.74% compared to the metabolic syndrome group.
 The administration of ammonium pyrrolidinedithiocarbamate, an NF-κB transcription factor activation inhibitor, effectively prevents the development of oxidative stress in the biceps femoris muscle of rats with modeled metabolic syndrome.
 This study is a part of the initiative research project No. 0124U000092 "High- and low-intensity phenotypes of systemic inflammatory response: molecular mechanisms and new medical technologies for their prevention and correction".

THE INFLUENCE OF QUERCETIN ON THE PRODUCTION OF REACTIVE OXYGEN-NITROGEN FORMS IN THE STRUCTURE OF THE INTERSTITIAL SPACE OF RAT TESTICLES WITH LONG-TERM EFFECT OF TRIPTORELIN

Quercetin is a flavonoid commonly found in fruits, vegetables, and seeds. Flavonoids can help prevent cardiovascular diseases, reduce the risk of degenerative brain processes and cancer. Studies have shown that blocking the synthesis of luteinising hormone can lead to oxidative stress in the liver, heart, and salivary glands of rats. The purpose of this study was to assess alterations in the interstitial space of rat testes, identify sources of nitric oxide production, and measure the intensity of oxidative stress in the testes during long-term experimental central blocking of luteinising hormone synthesis by tryptorelin. The study was conducted on 15 sexually mature male white rats. The animals were divided into two groups. The first group (control) received a subcutaneous injection of 0.9% sodium chloride solution. The second group (experimental) received a subcutaneous injection of tryptorelin at a dose of 0.3 mg/kg of active ingredient for 365 days, with simultaneous addition of quercetin to the diet, which was administered orally through a gastric tube three times a day. Total nitric oxide production was assessed by measuring the activity of total NO synthase (gNOS). The activity of gNOS was determined by the increase in nitrite (NO2-) after incubation in Tris-buffered saline. The nitrite concentration was determined using the Gris-Ilosvay reagent at a wavelength of 540 nm. The activity of the inducible (iNOS) and constitutive (cNOS) isoforms was also determined using a selective iNOS inhibitor, aminoguanidine hydrochloride. The production of superoxide anion radical (O2--) was measured by the increase in the formation of diformazan resulting from the reaction of O2-- with nitroblue tetrazolium after incubation in a buffered solution containing sodium hydroxide. The administration of quercetin mitigates the adverse effects of tryptorelin on the structural and functional components of the connective tissue in the rat testes. This effect is observed on day 365 and is characterised by fibrosis and impaired nitric oxide production by constitutive isoforms of NO synthase.

Reactive oxygen species augment contractile responses of saphenous artery in 10-15-day-old but not adult rats: Substantial role of NADPH oxidases

Reactive oxygen species (ROS) produced by NADPH oxidases (NOX, a key source of ROS in vascular cells) are involved in the regulation of vascular tone, but this has been explored mainly for adult organisms. Importantly, the mechanisms of vascular tone regulation differ significantly in early postnatal ontogenesis and adulthood, while the vasomotor role of ROS in immature systemic arteries is poorly understood. We tested the hypothesis that the functional contribution of NADPH oxidase-derived ROS to the regulation of peripheral arterial tone is higher in the early postnatal period than in adulthood. We studied saphenous arteries from 10‐ to 15‐day‐old (“young”) and 3‐ to 4-month-old (“adult”) male rats using lucigenin-enhanced chemiluminescence, quantitative PCR, Western blotting, and isometric myography. We demonstrated that both basal and NADPH-stimulated superoxide anion radical (O2•−) production was significantly higher in the arteries from young in comparison to adult rats. Importantly, pan-inhibitor of NADPH oxidase VAS2870 (10 μM) reduced NADPH-induced O2•− production in arteries of young rats. Saphenous arteries of both young and adult rats demonstrated high levels of Nox2 and Nox4 mRNAs, while Nox1 and Nox3 mRNAs were not detected. The protein contents of NOX2 and NOX4 were significantly higher in arterial tissue of young compared to adult animals. Moreover, VAS2870 (10 μM) had no effect on methoxamine-induced contractile responses of adult arteries but decreased them significantly in young arteries; such effect of VAS2870 persisted after removal of the endothelium. Finally, NOX2 inhibitor GSK2795039 (10 μM), but not NOX1/4 inhibitor GKT137831 (10 μM) weakened methoxamine-induced contractile responses of arteries from young rats. Thus, ROS produced by NOX2 have a pronounced contractile influence in saphenous artery smooth muscle cells of young, but not adult rats, which is associated with the increased vascular content of NOX2 protein at this age.

Synthesis of Fe–N doped porous carbon/silicate composites regulated by minerals in coal gasification fine slag for synergistic electrocatalytic treatment of phenolic wastewater

Coal gasification fine slag (CGFS), as a difficult-to-dispose solid waste in the coal chemical industry, consists of minerals and residual carbon. Due to the aggregate structure of minerals blocking pores and encapsulating active substances, the high-value utilization of CGFS still remains a challenge. Based on the intrinsic characteristics of CGFS, this study synthesized Fe–N doped porous carbon/silicate composites (Fe-NC) by alkali activation and pyrolysis for electrocatalytic degradation of phenolic wastewater. Meanwhile, minerals were utilized to regulate the surface chemical and pore structure, turning their disadvantages into advantages, which caused a sharp increase in m-cresol mineralization. The positive effect of minerals on composite properties was investigated by characterization techniques, electrochemical analyses and density functional theory (DFT) calculations. It was found that the mesoporous structure of the mineral-regulated composites was further developed, with more carbon defects and reactive substances on its surface. Most importantly, silicate mediated iron conversion through strong interaction with H2O2, high work function gradient with electroactive iron, and excellent superoxide radical (•O2−) production capacity. It effectively improved the reversibility and kinetics of the entire electrocatalytic reaction. Within the Fe-NC311 electrocatalytic system, the m-cresol removal rate reached 99.55 ± 1.24%, surpassing most reported Fe–N-doped electrocatalysts. In addition, the adsorption and electrooxidation experiment confirmed that the synergistic effect of Fe–N doped porous carbon and silicate simultaneously promoted the capture of pollutants and the transformation of electroactive molecules, and hence effectively shortened the diffusion path of short-lived radicals, which was further supported by molecular dynamics simulation. Therefore, this research provides new insights into the problem of mineral limitations and opens an innovative approach for CGFS recycling and environmental remediation.

The Effects of Silver Nanoparticles (AgNPs) on Thermophilic Bacteria: Antibacterial, Morphological, Physiological and Biochemical Investigations.

Since thermophilic microorganisms are valuable sources of thermostable enzymes, it is essential to recognize the potential toxicity of silver nanoparticles used in diverse industrial sectors. Thermophilic bacteria Geobacillus vulcani 2Cx, Bacillus licheniformis 3CA, Paenibacillus macerans 3CA1, Anoxybacillus ayderensis FMB1, and Bacillus paralicheniformis FMB2-1 were selected, and their MIC and MBC values were assessed by treatment with AgNPs in a range of 62.5-1500 μg mL-1. The growth inhibition curves showed that the G. vulcani 2Cx, and B. paralicheniformis FMB2-1 strains were more sensitive to AgNPs, demonstrating a reduction in population by 71.1% and 31.7% at 62.5 μg mL-1 and by 82.9% and 72.8% at 250 μg mL-1, respectively. TEM and FT-IR analysis revealed that AgNPs caused structural damage, cytoplasmic leakage, and disruption of cellular integrity. Furthermore, cell viability showed a significant decrease alongside an increase in superoxide radical (SOR; O2-) production. β-galactosidase biosynthesis decreased to 28.8% level at 500 μg mL-1 AgNPs for G. vulcani 2Cx, 32.2% at 250 μg mL-1 for A. ayderensis FMB1, and 38.8% only at 62.5 μg mL-1, but it was completely inhibited at 500 μg mL-1 for B. licheniformis 3CA. Moreover, B. paralicheniformis FMB2-1 showed a significant decrease to 11.2% at 125 μg mL-1. This study is the first to reveal the toxic effects of AgNPs on thermophilic bacteria.

Photo-Induced Disproportionation-Mediated Photodynamic Therapy: Simultaneous Oxidation of Tetrahydrobiopterin and Generation of Superoxide Radicals.

We herein present an approach of photo-induced disproportionation for preparation of Type-I photodynamic agents. As a proof of concept, BODIPY-based photosensitizers were rationally designed and prepared. The photo-induced intermolecular electron transfer between homotypic chromophores leads to the disproportionation reaction, resulting in the formation of charged intermediates, cationic and anionic radicals. The cationic radicals efficiently oxidize the cellularimportant coenzyme, tetrahydrobiopterin (BH4 ), and the anionic radicals transfer electrons to oxygen to produce superoxide radicals (O2 - ⋅). One of our Type-I photodynamic agents not only self-assembles in water but also effectively targets the endoplasmic reticulum. It displayed excellent photocytotoxicity even in highly hypoxic environments (2 % O2 ), with a half-maximal inhibitory concentration (IC50 ) of 0.96 μM, and demonstrated outstanding antitumor efficacy in murine models bearing HeLa tumors.

Photo‐Induced Disproportionation‐Mediated Photodynamic Therapy: Simultaneous Oxidation of Tetrahydrobiopterin and Generation of Superoxide Radicals

AbstractWe herein present an approach of photo‐induced disproportionation for preparation of Type‐I photodynamic agents. As a proof of concept, BODIPY‐based photosensitizers were rationally designed and prepared. The photo‐induced intermolecular electron transfer between homotypic chromophores leads to the disproportionation reaction, resulting in the formation of charged intermediates, cationic and anionic radicals. The cationic radicals efficiently oxidize the cellularimportant coenzyme, tetrahydrobiopterin (BH4), and the anionic radicals transfer electrons to oxygen to produce superoxide radicals (O2−⋅). One of our Type‐I photodynamic agents not only self‐assembles in water but also effectively targets the endoplasmic reticulum. It displayed excellent photocytotoxicity even in highly hypoxic environments (2 % O2), with a half‐maximal inhibitory concentration (IC50) of 0.96 μM, and demonstrated outstanding antitumor efficacy in murine models bearing HeLa tumors.

Double-Solvent-Induced Derivatization of Bi-MOF to Vacancy-Rich Bi4O5Br2: Toward Efficient Photocatalytic Degradation of Ciprofloxacin in Water and HCHO Gas.

MOF-derived photocatalytic materials have potential in degrading ciprofloxacin (CIP) in water and HCHO gas pollutants. Novel derivatization means and defect regulation are effective techniques for improving the performance of MOF-derived photocatalysis. Vacancy-rich Bi4O5Br2 (MBO-x) were derived in one step from Bi-MOF (CAU-17) by a modified double-solvent method. MBO-50 produced more oxygen vacancies due to the combined effect of the CAU-17 precursor and double solvents. The photocatalytic performance of MBO was evaluated by degrading CIP and HCHO. Thanks to the favorable morphology and vacancy structure, MBO-50 demonstrated the best photocatalytic efficiency, with 97.0% removal of CIP (20 mg L-1) and 90.1% removal of HCHO (6.5 ppm) at 60 min of light irradiation. The EIS Nyquist measurement, transient photocurrent response, photoluminescence spectra, and the calculation of energy band information indicated that the vacancy sites can effectively capture photoexcited electrons during the charge transfer process, thus limiting the recombination of electrons and holes, improving the energy band structure, and making it easier to produce superoxide anion radical (·O2-) and to degrade CIP and HCHO. The improvement of photocatalytic performance of MBO-50 in HCHO degradation due to the bromine vacancy generation and filling mechanism was discussed in detail. This work provides a promising new idea for the modulation of MOF-derived photocatalytic materials.

Effect of Curcumin on Alloxan Induced Diabetes Mellitus in Mice

Effect of Curcumin on Alloxan Induced Diabetes Mellitus in Mice

Enhanced sunlight-driven photocatalysis owing to synergetic effect of gold nanoparticles-incorporated ZnO/rGO ternary heterostructures

The combination of gold nanoparticles (Au NPs) incorporated ZnO/rGO heterostructures is unique for sunlight-driven photocatalysis (SPC). Here, hydrothermally synthesized pristine ZnO nanostructures (NSs), ZnO/rGO binary nanocomposites (BNCs) and ZnO/rGO/Au ternary nanocomposites (TNCs) of bandgap (Eg) values 3.56 eV, 3.37 eV and 3.17 eV, respectively are reported. These NSs are analyzed optically, structurally and morphologically via UV–Vis absorption spectroscopy, X-ray diffraction and SEM techniques, respectively. The SPC of methylene blue (MB) organic dye was considered using all three samples. The slow charge transfer over grain boundaries of ZnO results in the prohibition of photogenerated electron-hole pairs, exhibiting low photodegradation efficiency (87%). However, in BNCs the creation of alternative pathway of the carriers due to low work function level of rGO as compared to ZnO enhances the charge separation with an increased photocatalytic efficiency (92%). In contrast, TNCs show rather fast photodegradation efficiency (96%) as the photoexcited electrons on Au NPs surface migrate to the CB of ZnO because of the SPR stimulation of Au. These electrons easily shift to the conductive rGO layers and react with oxygen species (O2) producing superoxide radicals (•O2–). Thus, TNCs sample has appeared to be auspicious candidate for the photodegradation of organic pollutants in untreated water.

Ex Vivo 13C-Metabolic Flux Analysis of Porcine Circulating Immune Cells Reveals Cell Type-Specific Metabolic Patterns and Sex Differences in the Pentose Phosphate Pathway.

In general, females present with stronger immune responses than males, but scarce data are available on sex-specific differences in immunometabolism. In this study, we characterized porcine peripheral blood mononuclear cell (PBMC) and granulocyte energy metabolism using a Bayesian 13C-metabolic flux analysis, which allowed precise determination of the glycolytic, pentose phosphate pathway (PPP), and tricarboxylic acid cycle (TCA) fluxes, together with an assessment of the superoxide anion radical (O2•-) production and mitochondrial O2 consumption. A principal component analysis allowed for identifying the cell type-specific patterns of metabolic plasticity. PBMCs displayed higher TCA cycle activity, especially glutamine-derived aspartate biosynthesis, which was directly related to mitochondrial respiratory activity and inversely related to O2•- production. In contrast, the granulocytes mainly utilized glucose via glycolysis, which was coupled to oxidative PPP utilization and O2•- production rates. The granulocytes of the males had higher oxidative PPP fluxes compared to the females, while the PBMCs of the females displayed higher non-oxidative PPP fluxes compared to the males associated with the T helper cell (CD3+CD4+) subpopulation of PBMCs. The observed sex-specific differences were not directly attributable to sex steroid plasma levels, but we detected an inverse correlation between testosterone and aldosterone plasma levels and showed that aldosterone levels were related with non-oxidative PPP fluxes of both cell types.

13C-Metabolic flux analysis detected a hyperoxemia-induced reduction of tricarboxylic acid cycle metabolism in granulocytes during two models of porcine acute subdural hematoma and hemorrhagic shock.

Supplementation with increased inspired oxygen fractions has been suggested to alleviate the harmful effects of tissue hypoxia during hemorrhagic shock (HS) and traumatic brain injury. However, the utility of therapeutic hyperoxia in critical care is disputed to this day as controversial evidence is available regarding its efficacy. Furthermore, in contrast to its hypoxic counterpart, the effect of hyperoxia on the metabolism of circulating immune cells remains ambiguous. Both stimulating and detrimental effects are possible; the former by providing necessary oxygen supply, the latter by generation of excessive amounts of reactive oxygen species (ROS). To uncover the potential impact of increased oxygen fractions on circulating immune cells during intensive care, we have performed a 13C-metabolic flux analysis (MFA) on PBMCs and granulocytes isolated from two long-term, resuscitated models of combined acute subdural hematoma (ASDH) and HS in pigs with and without cardiovascular comorbidity. Swine underwent resuscitation after 2 h of ASDH and HS up to a maximum of 48 h after HS. Animals received normoxemia (PaO2 = 80 - 120 mmHg) or targeted hyperoxemia (PaO2 = 200 - 250 mmHg for 24 h after treatment initiation, thereafter PaO2 as in the control group). Blood was drawn at time points T1 = after instrumentation, T2 = 24 h post ASDH and HS, and T3 = 48h post ASDH and HS. PBMCs and granulocytes were isolated from whole blood to perform electron spin resonance spectroscopy, high resolution respirometry and 13C-MFA. For the latter, we utilized a parallel tracer approach with 1,2-13C2 glucose, U-13C glucose, and U-13C glutamine, which covered essential pathways of glucose and glutamine metabolism and supplied redundant data for robust Bayesian estimation. Gas chromatography-mass spectrometry further provided multiple fragments of metabolites which yielded additional labeling information. We obtained precise estimations of the fluxes, their joint credibility intervals, and their relations, and characterized common metabolic patterns with principal component analysis (PCA). 13C-MFA indicated a hyperoxia-mediated reduction in tricarboxylic acid (TCA) cycle activity in circulating granulocytes which encompassed fluxes of glutamine uptake, TCA cycle, and oxaloacetate/aspartate supply for biosynthetic processes. We further detected elevated superoxide levels in the swine strain characterized by a hypercholesterolemic phenotype. PCA revealed cell type-specific behavioral patterns of metabolic adaptation in response to ASDH and HS that acted irrespective of swine strains or treatment group. In a model of resuscitated porcine ASDH and HS, we saw that ventilation with increased inspiratory O2 concentrations (PaO2 = 200 - 250 mmHg for 24 h after treatment initiation) did not impact mitochondrial respiration of PBMCs or granulocytes. However, Bayesian 13C-MFA results indicated a reduction in TCA cycle activity in granulocytes compared to cells exposed to normoxemia in the same time period. This change in metabolism did not seem to affect granulocytes' ability to perform phagocytosis or produce superoxide radicals.

Nitrogen-doped Bi2O2CO3 nanoplates embedded with surface oxygen vacancies for augmented photocatalytic degradation of levofloxacin

Herein, a series of two-dimensional nitrogen-doped Bi2O2CO3 nanoplates embedded with oxygen vacancies (OVs) are synthesized via a bottom-up self-assembly from one-step hydrolysis. They can serve as efficient photocatalysts that allow a degradation ratio of levofloxacin (LEV) up to 94.4 % in 50 min under simulated sunlight, which is 2.5 times over undoped Bi2O2CO3. Incorporation of N atoms into the Bi2O2CO3 lattice not only extends the light absorption range for more effective utilization of solar light, but also narrows the band gap and increases the OVs concentration. Therefore, the separation of photo-induced charge-carriers is promoted, and further, the production of active species, mainly holes (h+) and superoxide radicals (•O2−), is accelerated.

Superoxide, nitric oxide and peroxynitrite production by macrophages under different physiological oxygen tensions

Macrophages count on two O2-consuming enzymes to form reactive radical species: NAPDH oxidase 2 (Nox2) and nitric oxide synthase 2 (inducible isoform, iNOS) that produce superoxide radical (O2•−) and nitric oxide (•NO), respectively. If formed simultaneously, the diffusion-controlled reaction of O2•− and •NO yields peroxynitrite, a potent cytotoxic oxidant. In human tissues and cells, the oxygen partial pressure (pO2) normally ranges within 2–14 %, with a typical average pO2 value for most tissues ca. 5 %. Given that O2 is a substrate for both Nox2 and iNOS, its tissue and cellular concentration can affect O2•− and •NO production. Also, O2 is a modulator of the macrophage adaptative response and may influence iNOS expression in a hypoxia inducible factor 1-α (HIF1α-)-dependent manner. However, most of the reported experiments in cellula, analyzing the formation and effects of O2•− and •NO during macrophage activation and cytotoxicity towards pathogens, have been performed in cells exposed to atmospheric air supplemented with 5 % CO2; under these conditions, most cells are exposed to supraphysiologic oxygen tensions (ca. 20 % O2) which are far from the physiological pO2. Here, the role of O2 as substrate in the oxidative response of J774A.1 macrophages was explored upon exposure to different pO2 and O2•− and •NO formation rates were measured, obtaining a KM of 26 and 42 μM O2 for Nox2 and iNOS, respectively. Consequently, peroxynitrite formation was influenced by pO2, reaching a maximum at ≥ 10 % O2, but even at levels as low as 2 % O2, a substantial formation rate of this oxidant was detected. Indeed, the cytotoxic capacity of immunostimulated macrophages against the intracellular parasite T. cruzi was significant, even at low pO2 values, confirming the role of peroxynitrite as a potent oxidizing cytotoxin within a wide range of physiological oxygen tensions.

Alleviation of salt toxicity by melatonin supplementation in eggplant involves the up-regulation of ascorbate–glutathione and glyoxalase system

Eggplant is considered an important vegetable to evaluate the abiotic stress responses, especially salt stress, that compromise the growth as well as development of plants. Melatonin (MT) has recently surfaced as an emerging stress-alleviating molecule that can relief salinity-triggered toxicity in plants. Nonetheless, the probable mechanism involved in functioning of MT under saline stress has not yet been demonstrated to full extent in plants. Hence, we experimented to get insight into the crucial mechanisms involved in MT-triggered saline stress tolerance using eggplant. Biomass production and growth traits are substantially reduced under saline stress due to impairment of photosynthesis, hindering photosystem function, and accumulation of secondary metabolites. In contrast, application of MT remarkably enhanced the growth attributes, improved photosynthetic efficiency, maximum PSII efficacy (Fv/Fm), gas exchange parameters, elevated uptake of Potassium (K+) and reduced accumulation of Sodium (Na+) ion. Furthermore, MT efficiency recovered integrity of the cell [reduced malondialdehyde (MDA) and relative electrolyte leakage (REL)] through inducing the activities of antioxidant enzymes and regulating AsA-GSH pool, tightened the production of superoxide radical (O2•−) and hydrogen peroxide (H2O2). In particular, MT treatment increased Gly 1 enzyme activity and reduced MG enzyme activity in the leaves of eggplant seedling. In addition, proline, soluble sugar, and protein contents in eggplant leaves are enhanced as a result of MT treatment. We conclude that our research findings define the important role of MT in mitigating the toxicity triggered in eggplants due to salinity by improving photosynthesis, redox balance, and uptake of nutrients, secondary metabolism and hence increased biomass synthesis.

Nitrogen-rich penicillin residue biochar for activation of peroxymonosulfate for an efficient degradation of tetracycline and its dual-pathway mechanism

Advanced oxidation processes based on peroxymonosulfate (PMS) are effective methods for treatment of organic contaminants. Catalysts have a key role in these processes. In this study, we employed a novel penicillin residue-derived nitrogen-rich biochar to activate PMS for tetracycline (TC) degradation. Experimental results indicate that the removal rate reached its maximum (86.2%) within 20 min under the optimal conditions. In addition, after five cycles, the removal efficiency decreased only slightly. A combined analysis of the physical structure and chemical properties with chemical scavengers, electron paramagnetic resonance, and electrochemical tests confirmed that the catalyst had a dual role. Nitrogen doping and CO groups on the catalyst acted as active sites, which could produce superoxide radicals (O2•-) and singlet oxygen (1O2). The catalyst can also act as an electron transfer mediator to enhance the degradation process. Liquid chromatography–mass spectrometry (LCMS) was used to reveal the intermediates of TC degradation, potential degradation pathways are proposed, and the toxicity of the intermediates was analyzed. This research provides an effective strategy for the treatment of tetracycline and new approach to adequately remove antibiotic residues.

Rice resistance against Bipolaris oryzae infection is mediated by lower foliar potassium concentration

AbstractBrown spot, caused by Bipolaris oryzae, is a very important disease of rice. This study investigated the effect of potassium (K) on rice resistance to brown spot. The working hypothesis tested was that higher foliar K concentration could allow plants to respond more efficiently against fungal infection. Plants were grown in nutrient solution amended with three K rates (0.5, 1.0 and 2.5 mM) and noninoculated or inoculated with B. oryzae. The photosynthetic performance of plants, activities of defence and antioxidant enzymes and the concentrations of reactive oxygen species, phenolics and lignin were determined. Foliar K concentration was significantly higher by 38% and 91% for plants supplied with 1.0 and 2.5 mM K, respectively, compared to plants supplied with 0.5 mM K. Brown spot severity was significantly higher (≥20%) for plants supplied with 1.0 and 2.5 mM K than those supplied with 0.5 mM K (≤15%). Higher brown spot severity for plants supplied with 2.5 mM K resulted in changes in the photosynthetic apparatus, reduced chlorophyll a + b and carotenoids concentrations, and higher production of hydrogen peroxide and superoxide anion radical. In contrast, higher activities of defence and antioxidant enzymes and more production of phenolics for plants supplied with 0.5 mM K helped them to cope with B. oryzae infection more efficiently. In conclusion, rice resistance against brown spot was achieved by keeping a lower foliar K concentration linked to more active defence reactions, a robust antioxidative system and less damage to the photosynthetic apparatus.