Anammox process in anaerobic baffled biofilm reactors with columnar packings: Characteristics of flow field and microbial community

The enrichment of anammox bacteria is a key issue in the application of anammox processes. A new type of reactor － anaerobic baffle biofilm reactor (ABBR) developed from anaerobic baffle reactor (ABR) was filled with columnar packings and established for effective enrichment of anammox bacteria. The flow field analysis showed that, compared with ABR, ABBR narrowed the dead zone so as to improve the substrate transferring performances. Two ABBRs with different types of columnar packings (Packings 1 and Packings 2) were constructed to culture anammox biofilms. Packings 1 consisted of the single-form honeycomb carriers while Packings 2 was modular composite packings consisting of non-woven fabric and honeycomb carriers. The effects of different types of columnar packings on microbial community and nitrogen removal were studied. The ABBR filled with Packings 2 had a higher retention rate of biomass than the ABBR filled with Packings 1, making the anammox start-up period be shortened by 21.28%. The enrichment of anammox bacteria were achieved and the dominant anammox bacteria were Candidatus Brocadia in both R1 and R2. However, there were four genera of anammox bacteria in R2 and one genus of anammox bacteria in R1, and the cell density of anammox bacteria in R2 was 95% higher than that in R1. R2 has the advantage of maintaining excellent and stable nitrogen removal performance at high nitrogen loading rate. The results revealed that the packings composed of two types of carriers may have a better enrichment effect on anammox bacteria. This study is of great significance for the rapid enrichment of anammox bacteria and the technical promotion of anammox process.

Modern optical approaches in redox biology: Genetically encoded sensors and Raman spectroscopy

The objective of the current review is to summarize the current state of optical methods in redox biology. It consists of two parts, the first is dedicated to genetically encoded fluorescent indicators and the second to Raman spectroscopy. In the first part, we provide a detailed classification of the currently available redox biosensors based on their target analytes. We thoroughly discuss the main architecture types of these proteins, the underlying engineering strategies for their development, the biochemical properties of existing tools and their advantages and disadvantages from a practical point of view. Particular attention is paid to fluorescence lifetime imaging microscopy as a possible readout technique, since it is less prone to certain artifacts than traditional intensiometric measurements. In the second part, the characteristic Raman peaks of the most important redox intermediates are listed, and examples of how this knowledge can be implemented in biological studies are given. This part covers such fields as estimation of the redox states and concentrations of Fe-S clusters, cytochromes, other heme-containing proteins, oxidative derivatives of thiols, lipids, and nucleotides. Finally, we touch on the issue of multiparameter imaging, in which biosensors are combined with other visualization methods for simultaneous assessment of several cellular parameters.

Impaired metabolic flexibility to fasting is associated with increased ad libitum energy intake in healthy adults

OBJECTIVE

We investigated how changes in 24-h respiratory exchange ratio (RER) and substrate oxidation during fasting versus an energy balance condition influence subsequent ad libitum food intake.

METHODS

Forty-four healthy, weight-stable volunteers (30 male and 14 female; mean [SD], age 39.3 [11.0] years; BMI 31.7 [8.3] kg/m2) underwent 24-h energy expenditure measurements in a respiratory chamber during energy balance (50% carbohydrate, 30% fat, and 20% protein) and 24-h fasting. Immediately after each chamber stay, participants were allowed 24-h ad libitum food intake from computerized vending machines.

RESULTS

Twenty-four-hour RER decreased by 9.4% (95% CI: -10.4% to -8.5%; p < 0.0001) during fasting compared to energy balance, reflecting a decrease in carbohydrate oxidation (mean [SD], -2.6 [0.8] MJ/day; p < 0.0001) and an increase in lipid oxidation (2.3 [0.9] MJ/day; p < 0.0001). Changes in 24-h RER and carbohydrate oxidation in response to fasting were correlated with the subsequent energy intake such that smaller decreases in fasting 24-h RER and carbohydrate oxidation, but not lipid oxidation, were associated with greater energy intake after fasting (r = 0.31, p = 0.04; r = 0.40, p = 0.007; and r = -0.27, p = 0.07, respectively).

CONCLUSIONS

Impaired metabolic flexibility to fasting, reflected by an inability to transition away from carbohydrate oxidation, is linked with increased energy intake.

Low-molecular-weight thiol transferases in redox regulation and antioxidant defence

Low-molecular-weight (LMW) thiols are produced in all living cells in different forms and concentrations. Glutathione (GSH), coenzyme A (CoA), bacillithiol (BSH), mycothiol (MSH), ergothioneine (ET) and trypanothione T(SH)2 are the main LMW thiols in eukaryotes and prokaryotes. LMW thiols serve as electron donors for thiol-dependent enzymes in redox-mediated metabolic and signaling processes, protect cellular macromolecules from oxidative and xenobiotic stress, and participate in the reduction of oxidative modifications. The level and function of LMW thiols, their oxidized disulfides and mixed disulfide conjugates in cells and tissues is tightly controlled by dedicated oxidoreductases, such as peroxiredoxins, glutaredoxins, disulfide reductases and LMW thiol transferases. This review provides the first summary of the current knowledge of structural and functional diversity of transferases for LMW thiols, including GSH, BSH, MSH and T(SH)2. Their role in maintaining redox homeostasis in single-cell and multicellular organisms is discussed, focusing in particular on the conjugation of specific thiols to exogenous and endogenous electrophiles, or oxidized protein substrates. Advances in the development of new research tools, analytical methodologies, and genetic models for the analysis of known LMW thiol transferases will expand our knowledge and understanding of their function in cell growth and survival under oxidative stress, nutrient deprivation, and during the detoxification of xenobiotics and harmful metabolites. The antioxidant function of CoA has been recently discovered and the breakthrough in defining the identity and functional characteristics of CoA S-transferase(s) is soon expected.

The utilisation of agricultural by-products in processed meat products: Effects on physicochemical, nutritional and sensory quality - Invited Review

Several plant-based materials are discarded by the food industry due to oversupply, lack of transport, and inappropriate storage. These materials contain valuable essential micronutrients such as minerals, vitamins and bioactive components (e.g., polyphenol, tocopherols, ascorbic acid, carotenoids) with antioxidant, antimicrobial, and anti-inflammatory effects, among others. In the context of making our agriculture-food based economy more circular and sustainable, and to develop foods with clean labels and less E-numbers, fruits, vegetables, yams, cereal distillers, oilseeds and other plant by-products could be utilised and upcycled back into new food formulations. Meat products are a particularly suitable matrix for this purpose, due to their susceptibility to lipid and protein oxidation and microbial spoilage (which shorten their shelf life). This review brings together the latest (2020-23) reformulation efforts, preservative methods and other innovative pathways, including studies on by-products as plant-based additives and bio-actives. It will cover the use of plant-based by-products as natural additives into production of processed meat products such as burgers, fermented meats and sausages, produced from ruminant and monogastric animals (except poultry). The extraction methods, inclusion levels, processing methods used and the quality of the resulting meat products will be reported, including preservative effects (microbial growth, oxidative stability and shelf life) and effects on instrumental, nutritional and sensory quality. Furthermore, it will also critically discuss the gaps identified, recommendation of the most promising ingredients for quality enhancement, and provide directions for future research.

Neutral pH photoenzymatic activity of Au-doped g-C3N4 nanosheet for colorimetric detection of total antioxidant capacity in food samples

Total antioxidant capacity (TAC) is vital for food quality evaluation. The emergence of various nanozymes with TMB as substrate offered a new avenue for TAC detection due to simple operation and fast response, but a long-standing challenge is its low activity at physiological pH, which may account for the discrepancy between the measured TAC and the actual antioxidant capacity in vivo. Herein, Au doping was explored to break the pH limitation of g-C3N4 nanosheets (CNNS) photozyme. The catalytic activities of Au@CNNS at pH 4.0 and 7.4 were 14.9- and 6.2-fold higher than that of CNNS at pH 4. The neutral pH photozymatic activity (photosensitized oxidation of TMB, oxidase mimic) of Au@CNNS was explored for sensitivity TAC detection (LOD: 1.0 μM TE), which featured more convenient operations and higher sensitivity over the DPPH assay. The proposed Au@CNNS-based photozymatic colorimetric method was explored for accurate detection of TAC in drinks and juices.

A review on the transformation of birnessite in the environment: Implication for the stabilization of heavy metals

Birnessite is ubiquitous in the natural environment where heavy metals are retained and easily transformed. The surface properties and structure of birnessite change with the changes in external environmental conditions, which also affects the fate of heavy metals. Clarifying the effect and mechanism of the birnessite phase transition process on heavy metals is the key to taking effective measures to prevent and control heavy metal pollution. Therefore, the four transformation pathways of birnessite are summarized first in this review. Second, the relationship between transformation pathways and environmental conditions is proposed. These relevant environmental conditions include abiotic (e.g., co-existing ions, pH, oxygen pressure, temperature, electric field, light, aging, pressure) and biotic factors (e.g., microorganisms, biomolecules). The phase transformation is achieved by the key intermediate of Mn(III) through interlayer-condensation, folding, neutralization-disproportionation, and dissolution-recrystallization mechanisms. The AOS (average oxidation state) of Mn and interlayer spacing are closely correlated with the phase transformation of birnessite. Last but not least, the mechanisms of heavy metals immobilization in the transformation process of birnessite are summed up. They involve isomorphous substitution, redox, complexation, hydration/dehydration, etc. The transformation of birnessite and its implication on heavy metals will be helpful for understanding and predicting the behavior of heavy metals and the crucial phase of manganese oxides/hydroxides in natural and engineered environments.

Feasibility of low-intensity ultrasound treatment with hydroxylamine to accelerate the initiation of partial nitrification and allow operation under intermittent aeration

Partial nitrification is a key aspect of efficient nitrogen removal, although practically it suffers from long start-up cycles and unstable long-term operational performance. To address these drawbacks, this study investigated the effect of low intensity ultrasound treatment combined with hydroxylamine (NH2OH) on the performance of partial nitrification. Results show that compared with the control group, low-intensity ultrasound treatment (0.10 W/mL, 15 min) combined with NH2OH (5 mg/L) reduced the time required for partial nitrification initiation by 6 days, increasing the nitrite accumulation rate (NAR) and ammonia nitrogen removal rate (NRR) by 20.4% and 6.7%, respectively, achieving 96.48% NRR. Mechanistic analysis showed that NH2OH enhanced ammonia oxidation, inhibited nitrite-oxidizing bacteria (NOB) activity and shortened the time required for partial nitrification initiation. Furthermore, ultrasonication combined with NH2OH dosing stimulated EPS (extracellular polymeric substances) secretion, increased carbonyl, hydroxyl and amine functional group abundances and enhanced mass transfer. In addition, 16S rRNA gene sequencing results showed that ultrasonication-sensitive Nitrospira disappeared from the ultrasound + NH2OH system, while Nitrosomonas gradually became the dominant group. Collectively, the results of this study provide valuable insight into the enhancement of partial nitrification start-up during the process of wastewater nitrogen removal.

Characterization of ferredoxins involved in electron transfer pathways for nitrogen fixation implicates differences in electronic structure in tuning 2[4Fe4S] Fd activity

Ferredoxins (Fds) are small proteins which shuttle electrons to pathways like biological nitrogen fixation. Physical properties tune the reactivity of Fds with different pathways, but knowledge on how these properties can be manipulated to engineer new electron transfer pathways is lacking. Recently, we showed that an evolved strain of Rhodopseudomonas palustris uses a new electron transfer pathway for nitrogen fixation. This pathway involves a variant of the primary Fd of nitrogen fixation in R. palustris, Fer1, in which threonine at position 11 is substituted for isoleucine (Fer1T11I). To understand why this substitution in Fer1 enables more efficient electron transfer, we used in vivo and in vitro methods to characterize Fer1 and Fer1T11I. Electrochemical characterization revealed both Fer1 and Fer1T11I have similar redox transitions (-480 mV and - 550 mV), indicating the reduction potential was unaffected despite the proximity of T11 to an iron‑sulfur (FeS) cluster of Fer1. Additionally, disruption of hydrogen bonding around an FeS cluster in Fer1 by substituting threonine with alanine (T11A) or valine (T11V) did not increase nitrogenase activity, indicating that disruption of hydrogen bonding does not explain the difference in activity observed for Fer1T11I. Electron paramagnetic resonance spectroscopy studies revealed key differences in the electronic structure of Fer1 and Fer1T11I, which indicate changes to the high spin states and/or spin-spin coupling between the FeS clusters of Fer1. Our data implicates these electronic structure differences in facilitating electron flow and sets a foundation for further investigations to understand the connection between these properties and intermolecular electron transfer.

Substitution of both histidines in the active site of yeast alcohol dehydrogenase 1 exposes underlying pH dependencies

Histidine residues 44 and 48 in yeast alcohol dehydrogenase (ADH) bind to the coenzymes NAD(H) and contribute to catalysis. The individual H44R and H48Q substitutions alter the kinetics and pH dependencies, and now the roles of other ionizable groups in the enzyme were studied in the doubly substituted H44R/H48Q ADH. The substitutions make the enzyme more resistant to inactivation by diethyl pyrocarbonate, modestly improve affinity for coenzymes, and substantially decrease catalytic efficiencies for ethanol oxidation and acetaldehyde reduction. The pH dependencies for several kinetic parameters are shifted from pK values for wild-type ADH of 7.3-8.1 to values for H44R/H48Q ADH of 8.0-9.6, and are assigned to the water or alcohol bound to the catalytic zinc. It appears that the rate of binding of NAD+ is electrostatically favored with zinc-hydroxide whereas binding of NADH is faster with neutral zinc-water. The pH dependencies of catalytic efficiencies (V/EtKm) for ethanol oxidation and acetaldehyde reduction are similarly controlled by deprotonation and protonation, respectively. The substitutions make an enzyme that resembles the homologous horse liver H51Q ADH, which has Arg-47 and Gln-51 and exhibits similar pK values. In the wild-type ADHs, it appears that His-48 (or His-51) in the proton relay systems linked to the catalytic zinc ligands modulate catalytic efficiencies.

Why is HSO5- so effective against bacteria? Insights into the mechanisms of Escherichia coli disinfection by unactivated peroxymonosulfate

This study examined the antimicrobial efficacy of peroxymonosulfate (PMS) against bacteria, using Escherichia coli (E. coli) as a model organism. Our investigation delineates the complex mechanisms exerted by unactivated PMS. Thus, an initial redox reaction between PMS and the target biomolecules of bacteria generates SO4•- as the pivotal reactive species for bacterial inactivation; to a lesser extent, •OH, 1O2, or O2•- may also participate. Damage generated during oxidation was identified using an array of biochemical techniques. Specifically, redox processes are promoted by PMS and SO4•- targets and disrupt various components of bacterial cells, predominantly causing extracellular damage as well as intracellular lesions. Among these, external events are the key to cell death. Finally, by employing gene knockout mutants, we uncovered the role of specific gene responses in the intracellular damage induced by radical pathways. The findings of this study not only expand the understanding of PMS-mediated bacterial inactivation but also explain the ten-fold higher effectiveness of PMS than that reported for H2O2. Hence, we provide clear evidence that unactivated PMS solutions generate SO4•- in the presence of bacteria, and consequently, should be considered an effective disinfection method.

Assessment of the mode of action of perchloroethylene-induced mouse liver tumors

Perchloroethylene (PCE) is used as a solvent and chemical intermediate. Following chronic inhalation exposure, PCE selectively induced liver tumors in mice. Understanding the mode of action (MOA) for PCE carcinogenesis in mice is important in defining its possible human cancer risk. The proposed MOA is based on the extensive examination of the peer-reviewed studies that have assessed the mouse liver effects of PCE and its major oxidative metabolite trichloroacetic acid (TCA). Similar to PCE, TCA has also been demonstrated to liver tumors selectively in mice following chronic exposure. The Key Events (KE) of the proposed PCE MOA involve oxidative metabolism of PCE to TCA [KE 1]; activation of the peroxisome proliferator-activated receptor alpha (PPARα) [KE 2]; alteration in hepatic gene expression including cell growth pathways [KE 3]; increase in cell proliferation [KE 4]; selective clonal expansion of hepatic preneoplastic foci [KE 5]; and formation of hepatic neoplasms [KE 6]. The scientific evidence supporting the PPARα MOA for PCE is strong and satisfies the requirements for a MOA analysis. The PPARα liver tumor MOA in rodents has been demonstrated not to occur in humans; thus, human liver cancer risk to PCE is not likely.

Reevaluation of the protein requirement in Chinese elderly adults without sarcopenia with the indicator amino acid oxidation technique

It is now generally believed that elderly may have slightly higher dietary protein requirements than those of the young-middle-aged adults. We have previously conducted related studies by the indicator amino acid oxidation (IAAO) technique, but more research data are needed to revise the protein requirements of the elderly. The main objective was to reevaluate the dietary protein requirements of healthy Chinese adults (65-80 years) without sarcopenia by using the IAAO technique. Nine healthy adult men and seven healthy adult women participated in the study, with protein intakes ranging from 0·1 to 1·8 g/(kg·d). Diets that delivered energy at a 1·5 resting energy expenditure were isocaloric. The amounts of phenylalanine and tyrosine needed to remain constant for each protein dosage. By applying a nonlinear mixed-effects model analysis on the F13CO2 data, which revealed a breakpoint in F13CO2 in response to graded protein intakes, the mean protein requirement was calculated. The mean estimated average requirement (EAR) for healthy elderly Chinese adults without sarcopenia was determined to be 0·94 g/(kg·d). The protein recommended nutrient intake (RNI) determined using various derivation approaches ranged from 1·13 to 1·36 g/(kg·d). The EAR for Chinese adults without sarcopenia aged 65-80 years in this study is 6·8 % higher than the current recommended EAR (0·88 g/(kg·d)). The RNI derived using various derivation approaches are all greater than the current RNI (0·98 g/(kg·d)). This trial was registered with the Chinese clinical trial registry as ChiCTR2200061382.

Mitochondrial responses to constant and cyclic hypoxia depend on the oxidized fuel in a hypoxia-tolerant marine bivalve Crassostrea gigas

Sessile benthic organisms like oysters inhabit the intertidal zone, subject to alternating hypoxia and reoxygenation (H/R) episodes during tidal movements, impacting respiratory chain activities and metabolome compositions. We investigated the effects of constant severe hypoxia (90 min at ~ 0% O2 ) followed by 10 min reoxygenation, and cyclic hypoxia (5 cycles of 15 min at ~ 0% O2 and 10 min reoxygenation) on isolated mitochondria from the gill and the digestive gland of Crassostrea gigas respiring on pyruvate, palmitate, or succinate. Constant hypoxia suppressed oxidative phosphorylation (OXPHOS), particularly during Complex I-linked substrates oxidation. It had no effect on mitochondrial reactive oxygen species (ROS) efflux but increased fractional electron leak (FEL). In mitochondria oxidizing Complex I substrates, exposure to cyclic hypoxia prompted a significant drop after the first H/R cycle. In contrast, succinate-driven respiration only showed significant decline after the third to fifth H/R cycle. ROS efflux saw little change during cyclic hypoxia regardless of the oxidized substrate, but Complex I-driven FEL tended to increase with each subsequent H/R cycle. These observations suggest that succinate may serve as a beneficial stress fuel under H/R conditions, aiding in the post-hypoxic recovery of oysters by reducing oxidative stress and facilitating rapid ATP re-synthesis. The impacts of constant and cyclic hypoxia of similar duration on mitochondrial respiration and oxidative lesions in the proteins were comparable indicating that the mitochondrial damage is mostly determined by the lack of oxygen and mitochondrial depolarization. The ROS efflux in the mitochondria of oysters was minimally affected by oxygen fluctuations indicating that tight regulation of ROS production may contribute to robust mitochondrial phenotype of oysters and protect against H/R induced stress.

The effect of common paralytic agents used for fluorescence imaging on redox tone and ATP levels in Caenorhabditis elegans

One aspect of Caenorhabditis elegans that makes it a highly valuable model organism is the ease of use of in vivo genetic reporters, facilitated by its transparent cuticle and highly tractable genetics. Despite the rapid advancement of these technologies, worms must be paralyzed for most imaging applications, and few investigations have characterized the impacts of common chemical anesthetic methods on the parameters measured, in particular biochemical measurements such as cellular energetics and redox tone. Using two dynamic reporters, QUEEN-2m for relative ATP levels and reduction-oxidation sensitive GFP (roGFP) for redox tone, we assess the impact of commonly used chemical paralytics. We report that no chemical anesthetic is entirely effective at doses required for full paralysis without altering redox tone or ATP levels, and that anesthetic use alters the detected outcome of rotenone exposure on relative ATP levels and redox tone. We also assess the use of cold shock, commonly used in combination with physical restraint methods, and find that cold shock does not alter either ATP levels or redox tone. In addition to informing which paralytics are most appropriate for research in these topics, we highlight the need for tailoring the use of anesthetics to different endpoints and experimental questions. Further, we reinforce the need for developing less disruptive paralytic methods for optimal imaging of dynamic in vivo reporters.

Redox active plant phenolic, acetosyringone, for electrogenetic signaling

Redox is a unique, programmable modality capable of bridging communication between biology and electronics. Previous studies have shown that the E. coli redox-responsive OxyRS regulon can be re-wired to accept electrochemically generated hydrogen peroxide (H2O2) as an inducer of gene expression. Here we report that the redox-active phenolic plant signaling molecule acetosyringone (AS) can also induce gene expression from the OxyRS regulon. AS must be oxidized, however, as the reduced state present under normal conditions cannot induce gene expression. Thus, AS serves as a "pro-signaling molecule" that can be activated by its oxidation-in our case by application of oxidizing potential to an electrode. We show that the OxyRS regulon is not induced electrochemically if the imposed electrode potential is in the mid-physiological range. Electronically sliding the applied potential to either oxidative or reductive extremes induces this regulon but through different mechanisms: reduction of O2 to form H2O2 or oxidation of AS. Fundamentally, this work reinforces the emerging concept that redox signaling depends more on molecular activities than molecular structure. From an applications perspective, the creation of an electronically programmed "pro-signal" dramatically expands the toolbox for electronic control of biological responses in microbes, including in complex environments, cell-based materials, and biomanufacturing.

Structural Rearrangements of Pigeon Cryptochrome 4 Undergoing a Complete Redox Cycle

Cryptochrome is currently the major contender of a protein to underpin magnetoreception, the ability to sense the Earth's magnetic field. Among various types of cryptochromes, cryptochrome 4 has been identified as the likely magnetoreceptor in migratory birds. All-atom molecular dynamics (MD) studies have offered first insights into the structural dynamics of cryptochrome but are limited to a short time scale due to large computational demands. Here, we employ coarse-grained MD simulations to investigate the emergence of long-lived states and conformational changes in pigeon cryptochrome 4. Our coarse-grained simulations complete the picture by permitting observation on a significantly longer time scale. We observe conformational transitions in the phosphate-binding loop of pigeon cryptochrome 4 upon activation and identify prominent motions in residues 440-460, suggesting a possible role as a signaling state of the protein or as a gated interaction site for forming protein complexes that might facilitate downstream processes. The findings highlight the importance of considering longer time scales in studying cryptochrome dynamics and magnetoreception. Coarse-grained MD simulations offer a valuable tool to unravel the complex behavior of cryptochrome proteins and shed new light on the mechanisms underlying their role in magnetoreception. Further exploration of these conformational changes and their functional implications may contribute to a deeper understanding of the molecular mechanisms of magnetoreception in birds.

In Solution Identification of the Lysine-Cysteine Redox Switch with a NOS Bridge in Transaldolase by Sulfur K-Edge X-ray Absorption Spectroscopy

A novel covalent post-translational modification (lysine-NOS-cysteine) was discovered in proteins, initially in the enzyme transaldolase of Neisseria gonorrhoeae (NgTAL) [Nature 2021, 593, 460-464], acting as a redox switch. The identification of this novel linkage in solution was unprecedented until now. We present detection of the NOS redox switch in solution using sulfur K-edge X-ray absorption spectroscopy (XAS). The oxidized NgTAL spectrum shows a distinct shoulder on the low-energy side of the rising edge, corresponding to a dipole-allowed transition from the sulfur 1s core to the unoccupied σ* orbital of the S-O group in the NOS bridge. This feature is absent in the XAS spectrum of reduced NgTAL, where Lys-NOS-Cys is absent. Our experimental and calculated XAS data support the presence of a NOS bridge in solution, thus potentially facilitating future studies on enzyme activity regulation mediated by the NOS redox switches, drug discovery, biocatalytic applications, and protein design.

PEGylated mesoporous silica core-shell redox-responsive nanoparticles for delivering paclitaxel to breast cancer cells

Controlling the drug release and restricting its presence in healthy organs is extremely valuable. In this study, mesoporous silica nanoparticles (MSN) as the core, loaded with paclitaxel (PTX), were coated with a non-porous silica shell functionalized with disulfide bonds. The nanoparticles were further coated with polyethylene glycol (PEG) via disulfide linkages. We analyzed the physicochemical properties of nanoparticles, including hydrodynamic size via Dynamic Light Scattering (DLS), zeta potential, X-ray Diffraction (XRD) patterns, Fourier-Transform Infrared (FTIR) spectra, and imaging through Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). The drug release profile in two distinct glutathione (GSH) concentrations of 2 µM and 10 µM was measured. The cellular uptake of nanoparticles by MCF-7 cell line was determined using Confocal Laser Scanning Microscopy (CLSM) images and flow cytometry. Furthermore, the cell viability and the capability of nanoparticles to induce apoptosis in MCF-7 cell line were studied using the MTT assay and flow cytometry, respectively. Our investigations revealed that the release of PTX from the drug delivery system was redox-responsive. Also, results indicated an elevated level of cellular uptake and efficient induction of apoptosis, underscoring the promising potential of this redox-responsive drug delivery system for breast cancer therapy.

Oxidation pathways and kinetics of the 1,1,2,3-tetrafluoropropene (CF2CF-CH2F) reaction with Cl-atoms and subsequent aerial degradation of its product radicals in the presence of NO

To give a comprehensive account of the environmental acceptability of 1,1,2,3-tetrafluoropropene (CF2CF-CH2F) in the troposphere, we have examined the oxidation reaction pathways and kinetics of CF2CF-CH2F initiated by Cl-atoms using the second-order Møller-Plesset perturbation (MP2) theory along with the 6-31+G(d,p) basis set. We also performed single-point energy calculations to further refine the energies at the CCSD(T) level along with the basis sets 6-31+G(d,p) and 6-311++G(d,p). The estimation of the relative energies and thermodynamic parameters of the CF2CF-CH2F + Cl reaction clearly shows that Cl-atom addition reaction pathways are more dominant compared to H-abstraction reaction pathways. The value of the rate coefficient for each reaction channel is calculated using the conventional transition state theory (TST) over the temperature range of 200-1000 K at 1 atm. The estimated overall rate coefficients for the title reaction are found to be 1.10 × 10-12, 1.21 × 10-10, and 1.13 × 10-8 cm3 per molecule per s via the respective calculation methods viz. MP2/6-31+G(d,p), CCSD(T)//MP2/6-31+G(d,p), and CCSD(T)/6-311++G(d,p)//MP2/6-31+G(d,p), at 298.15 K. Moreover, the calculated rate coefficients and percentage branching ratio values suggest that the Cl-atom addition reaction at the β-carbon atom is more preferable to that of the α-carbon addition to CF2CF-CH2F. Based on the rate coefficient values calculated by the three different methods, the atmospheric lifetime for the title reaction at 298.15 K is estimated. The radiative efficiency (RE) and Global Warming Potential (GWP) results of the title molecule show that its GWP would be negligible. Further, we have explored the degradation of its product radicals in the presence of O2 and NO. From the degradation results, we have found that CF2(Cl)COF, FCOCH2F, FCFO and FCOCl are formed as stable end products along with various radicals such as ˙CF2Cl and ˙CH2F. Therefore, these findings of kinetic and mechanistic data can be applied to the development and implementation of a novel CFC replacement.

Emerging mechanisms in the redox regulation of mitochondrial cytochrome c oxidase assembly and function

In eukaryotic cells, mitochondria perform cellular respiration through a series of redox reactions ultimately reducing molecular oxygen to water. The system responsible for this process is the respiratory chain or electron transport system (ETS) composed of complexes I-IV. Due to its function, the ETS is the main source of reactive oxygen species (ROS), generating them on both sides of the mitochondrial inner membrane, i.e. the intermembrane space (IMS) and the matrix. A correct balance between ROS generation and scavenging is important for keeping the cellular redox homeostasis and other important aspects of cellular physiology. However, ROS generated in the mitochondria are important signaling molecules regulating mitochondrial biogenesis and function. The IMS contains a large number of redox sensing proteins, containing specific Cys-rich domains, that are involved in ETS complex biogenesis. The large majority of these proteins function as cytochrome c oxidase (COX) assembly factors, mainly for the handling of copper ions necessary for the formation of the redox reactive catalytic centers. A particular case of ROS-regulated COX assembly factor is COA8, whose intramitochondrial levels are increased by oxidative stress, promoting COX assembly and/or protecting the enzyme from oxidative damage. In this review, we will discuss the current knowledge concerning the role played by ROS in regulating mitochondrial activity and biogenesis, focusing on the COX enzyme and with a special emphasis on the functional role exerted by the redox sensitive Cys residues contained in the COX assembly factors.

Oxidative Defect Detection Within Free and Packed DNA Systems: A Quantum Mechanical/Molecular Mechanics (QM/ MM) Approach

Base excision repair enzymes (BERs) detect and repair oxidative DNA damage with efficacy despite the small size of the defects and their often only minor structural impact. A charge transfer (CT) model for rapid scanning of DNA stretches has been evoked to explain the high detection rate in the face of numerous, small lesions. The viability of CT DNA defect detection is explored via hybrid QM/MM computational studies that leverage the accuracy of quantum mechanics (QM) for a region of interest and the descriptive power of molecularmechanics (MM) for the remainder of the system. We find that the presence of an oxidative lesion lowers theredox free energy of oxidation by approximately 1.0 eV regardless of DNA compaction (free DNA versus packed DNA in nucleosome core particles) and damage location indicating the high feasibility of a CT-based process for defect detection in DNA.

Bioproduction of cerium-bearing magnetite and application to improve carbon-black supported platinum catalysts

BACKGROUND

Biogeochemical processing of metals including the fabrication of novel nanomaterials from metal contaminated waste streams by microbial cells is an area of intense interest in the environmental sciences.

RESULTS

Here we focus on the fate of Ce during the microbial reduction of a suite of Ce-bearing ferrihydrites with between 0.2 and 4.2 mol% Ce. Cerium K-edge X-ray absorption near edge structure (XANES) analyses showed that trivalent and tetravalent cerium co-existed, with a higher proportion of tetravalent cerium observed with increasing Ce-bearing of the ferrihydrite. The subsurface metal-reducing bacterium Geobacter sulfurreducens was used to bioreduce Ce-bearing ferrihydrite, and with 0.2 mol% and 0.5 mol% Ce, an Fe(II)-bearing mineral, magnetite (Fe(II)(III)2O4), formed alongside a small amount of goethite (FeOOH). At higher Ce-doping (1.4 mol% and 4.2 mol%) Fe(III) bioreduction was inhibited and goethite dominated the final products. During microbial Fe(III) reduction Ce was not released to solution, suggesting Ce remained associated with the Fe minerals during redox cycling, even at high Ce loadings. In addition, Fe L2,3 X-ray magnetic circular dichroism (XMCD) analyses suggested that Ce partially incorporated into the Fe(III) crystallographic sites in the magnetite. The use of Ce-bearing biomagnetite prepared in this study was tested for hydrogen fuel cell catalyst applications. Platinum/carbon black electrodes were fabricated, containing 10% biomagnetite with 0.2 mol% Ce in the catalyst. The addition of bioreduced Ce-magnetite improved the electrode durability when compared to a normal Pt/CB catalyst.

CONCLUSION

Different concentrations of Ce can inhibit the bioreduction of Fe(III) minerals, resulting in the formation of different bioreduction products. Bioprocessing of Fe-minerals to form Ce-containing magnetite (potentially from waste sources) offers a sustainable route to the production of fuel cell catalysts with improved performance.

Therapeutic exploitation of ferroptosis

Pathological breakdown of membrane lipids through excessive lipid peroxidation (LPO) was first described in the mid-20th century and is now recognized as a form of regulated cell death, dubbed ferroptosis. Accumulating evidence unveils how metabolic regulation restrains peroxidation of phospholipids within cellular membranes, thereby impeding ferroptosis execution. Unleashing these metabolic breaks is currently therapeutically explored to sensitize cancers to ferroptosis inducing anti-cancer therapies. Reversely, these natural ferroptotic defense mechanisms can fail resulting in pathological conditions or diseases such as ischemia-reperfusion injury, multi-organ dysfunction, stroke, infarction, or neurodegenerative diseases. This minireview outlines current ferroptosis-inducing anti-cancer strategies and highlights the detection as well as the therapeutic targeting of ferroptosis in preclinical experimental settings. Herein, we also briefly summarize observations related to LPO, iron and redox deregulation in patients that might hint towards ferroptosis as a contributing factor.

Metabolic coupling between soil aerobic methanotrophs and denitrifiers in rice paddy fields

Paddy fields are hotspots of microbial denitrification, which is typically linked to the oxidation of electron donors such as methane (CH4) under anoxic and hypoxic conditions. While several anaerobic methanotrophs can facilitate denitrification intracellularly, whether and how aerobic CH4 oxidation couples with denitrification in hypoxic paddy fields remains virtually unknown. Here we combine a ~3300 km field study across main rice-producing areas of China and 13CH4-DNA-stable isotope probing (SIP) experiments to investigate the role of soil aerobic CH4 oxidation in supporting denitrification. Our results reveal positive relationships between CH4 oxidation and denitrification activities and genes across various climatic regions. Microcosm experiments confirm that CH4 and methanotroph addition promote gene expression involved in denitrification and increase nitrous oxide emissions. Moreover, 13CH4-DNA-SIP analyses identify over 70 phylotypes harboring genes associated with denitrification and assimilating 13C, which are mostly belonged to Rubrivivax, Magnetospirillum, and Bradyrhizobium. Combined analyses of 13C-metagenome-assembled genomes and 13C-metabolomics highlight the importance of intermediates such as acetate, propionate and lactate, released during aerobic CH4 oxidation, for the coupling of CH4 oxidation with denitrification. Our work identifies key microbial taxa and pathways driving coupled aerobic CH4 oxidation and denitrification, with important implications for nitrogen management and greenhouse gas regulation in agroecosystems.

Molecular basis of an atypical dsDNA 5mC/6mA bifunctional dioxygenase CcTet from Coprinopsis cinerea in catalyzing dsDNA 5mC demethylation

The eukaryotic epigenetic modifications 5-methyldeoxycytosine (5mC) and N6-methyldeoxyadenine (6mA) have indispensable regulatory roles in gene expression and embryonic development. We recently identified an atypical bifunctional dioxygenase CcTet from Coprinopsis cinerea that works on both 5mC and 6mA demethylation. The nonconserved residues Gly331 and Asp337 of CcTet facilitate 6mA accommodation, while D337F unexpectedly abolishes 5mC oxidation activity without interfering 6mA demethylation, indicating a prominent distinct but unclear 5mC oxidation mechanism to the conventional Tet enzymes. Here, we assessed the molecular mechanism of CcTet in catalyzing 5mC oxidation by representing the crystal structure of CcTet-5mC-dsDNA complex. We identified the distinct mechanism by which CcTet recognizes 5mC-dsDNA compared to 6mA-dsDNA substrate. Moreover, Asp337 was found to have a central role in compensating for the loss of a critical 5mC-stablizing H-bond observed in conventional Tet enzymes, and stabilizes 5mC and subsequent intermediates through an H-bond with the N4 atom of the substrates. These findings improve our understanding of Tet enzyme functions in the dsDNA 5mC and 6mA demethylation pathways, and provide useful information for future discovery of small molecular probes targeting Tet enzymes in DNA active demethylation processes.

Type III intermediate filaments in redox interplay: key role of the conserved cysteine residue

Intermediate filaments (IFs) are cytoskeletal elements involved in mechanotransduction and in the integration of cellular responses. They are versatile structures and their assembly and organization are finely tuned by posttranslational modifications. Among them, type III IFs, mainly vimentin, have been identified as targets of multiple oxidative and electrophilic modifications. A characteristic of most type III IF proteins is the presence in their sequence of a single, conserved cysteine residue (C328 in vimentin), that is a hot spot for these modifications and appears to play a key role in the ability of the filament network to respond to oxidative stress. Current structural models and experimental evidence indicate that this cysteine residue may occupy a strategic position in the filaments in such a way that perturbations at this site, due to chemical modification or mutation, impact filament assembly or organization in a structure-dependent manner. Cysteine-dependent regulation of vimentin can be modulated by interaction with divalent cations, such as zinc, and by pH. Importantly, vimentin remodeling induced by C328 modification may affect its interaction with cellular organelles, as well as the cross-talk between cytoskeletal networks, as seems to be the case for the reorganization of actin filaments in response to oxidants and electrophiles. In summary, the evidence herein reviewed delineates a complex interplay in which type III IFs emerge both as targets and modulators of redox signaling.

Bioenergetics of iron snow fueling life on Europa

The main sources of redox gradients supporting high-productivity life in the Europan and other icy ocean world oceans were proposed to be photolytically derived oxidants, such as reactive oxygen species (ROS) from the icy shell, and reductants (Fe(II), S(-II), CH4, H2) from bottom waters reacting with a (ultra)mafic seafloor. Important roadblocks to maintaining life, however, are that the degree of ocean mixing to combine redox species is unknown, and ROS damage biomolecules. Here, we envisage a unique solution using an acid mine drainage (AMD)-filled pit lakes analog system for the Europan ocean, which previous models predicted to be acidic. We hypothesize that surface-generated ROS oxidize dissolved Fe(II) resulting in Fe(III) (hydr)oxide precipitates, that settle to the seafloor as "iron snow." The iron snow provides a respiratory substrate for anaerobic microorganisms ("breathing iron"), and limits harmful ROS exposure since they are now neutralized at the ice-water interface. Based on this scenario, we calculated Gibbs energies and maximal biomass productivities of various anaerobic metabolisms for a range of pH, temperatures, and H2 fluxes. Productivity by iron reducers was greater for most environmental conditions considered, whereas sulfate reducers and methanogens were more favored at high pH. Participation of Fe in the metabolic redox processes is largely neglected in most models of Europan biogeochemistry. Our model overcomes important conceptual roadblocks to life in icy ocean worlds and broadens the potential metabolic diversity, thus increasing total primary productivity, the diversity and volume of habitable environmental niches and, ultimately, the probability of biosignature detection.

Peripheral peroxisomal β-oxidation engages neuronal serotonin signaling to drive stress-induced aversive memory in C. elegans

Physiological dysfunction confers negative valence to coincidental sensory cues to induce the formation of aversive associative memory. How peripheral tissue stress engages neuromodulatory mechanisms to form aversive memory is poorly understood. Here, we show that in the nematode C. elegans, mitochondrial disruption induces aversive memory through peroxisomal β-oxidation genes in non-neural tissues, including pmp-4/very-long-chain fatty acid transporter, dhs-28/3-hydroxylacyl-CoA dehydrogenase, and daf-22/3-ketoacyl-CoA thiolase. Upregulation of peroxisomal β-oxidation genes under mitochondrial stress requires the nuclear hormone receptor NHR-49. Importantly, the memory-promoting function of peroxisomal β-oxidation is independent of its canonical role in pheromone production. Peripheral signals derived from the peroxisomes target NSM, a critical neuron for memory formation under stress, to upregulate serotonin synthesis and remodel evoked responses to sensory cues. Our genetic, transcriptomic, and metabolomic approaches establish peroxisomal lipid signaling as a crucial mechanism that connects peripheral mitochondrial stress to central serotonin neuromodulation in aversive memory formation.

Cr(VI) Reduction and Sequestration by FeS Nanoparticles Formed in situ as Aquifer Material Coating to Create a Regenerable Reactive Zone

Remediation of large and dilute plumes of groundwater contaminated by oxidized pollutants such as chromate is a common and difficult challenge. Herein, we show that in situ formation of FeS nanoparticles (using dissolved Fe(II), S(-II), and natural organic matter as a nucleating template) results in uniform coating of aquifer material to create a regenerable reactive zone that mitigates Cr(VI) migration. Flow-through columns packed with quartz sand are amended first with an Fe2+ solution and then with a HS- solution to form a nano-FeS coating on the sand, which does not hinder permeability. This nano-FeS coating effectively reduces and immobilizes Cr(VI), forming Fe(III)-Cr(III) coprecipitates with negligible detachment from the sand grains. Preconditioning the sand with humic or fulvic acid (used as model natural organic matter (NOM)) further enhances Cr(VI) sequestration, as NOM provides additional binding sites of Fe2+ and mediates both nucleation and growth of FeS nanoparticles, as verified with spectroscopic and microscopic evidence. Reactivity can be easily replenished by repeating the procedures used to form the reactive coating. These findings demonstrate that such enhancement of attenuation capacity can be an effective option to mitigate Cr(VI) plume migration and exposure, particularly when tackling contaminant rebound post source remediation.

Uncovering the roles of Mycobacterium tuberculosis melH in redox and bioenergetic homeostasis: implications for antitubercular therapy

Mycobacterium tuberculosis (Mtb), the pathogenic bacterium that causes tuberculosis, has evolved sophisticated defense mechanisms to counteract the cytotoxicity of reactive oxygen species (ROS) generated within host macrophages during infection. The melH gene in Mtb and Mycobacterium marinum (Mm) plays a crucial role in defense mechanisms against ROS generated during infection. We demonstrate that melH encodes an epoxide hydrolase and contributes to ROS detoxification. Deletion of melH in Mm resulted in a mutant with increased sensitivity to oxidative stress, increased accumulation of aldehyde species, and decreased production of mycothiol and ergothioneine. This heightened vulnerability is attributed to the increased expression of whiB3, a universal stress sensor. The absence of melH also resulted in reduced intracellular levels of NAD+, NADH, and ATP. Bacterial growth was impaired, even in the absence of external stressors, and the impairment was carbon source dependent. Initial MelH substrate specificity studies demonstrate a preference for epoxides with a single aromatic substituent. Taken together, these results highlight the role of melH in mycobacterial bioenergetic metabolism and provide new insights into the complex interplay between redox homeostasis and generation of reactive aldehyde species in mycobacteria.

IMPORTANCE

This study unveils the pivotal role played by the melH gene in Mycobacterium tuberculosis and in Mycobacterium marinum in combatting the detrimental impact of oxidative conditions during infection. This investigation revealed notable alterations in the level of cytokinin-associated aldehyde, para-hydroxybenzaldehyde, as well as the redox buffer ergothioneine, upon deletion of melH. Moreover, changes in crucial cofactors responsible for electron transfer highlighted melH's crucial function in maintaining a delicate equilibrium of redox and bioenergetic processes. MelH prefers epoxide small substrates with a phenyl substituted substrate. These findings collectively emphasize the potential of melH as an attractive target for the development of novel antitubercular therapies that sensitize mycobacteria to host stress, offering new avenues for combating tuberculosis.

Acidic Derivatization of Thiols Using Diethyl 2-Methylenemalonate: Thiol-Michael Addition Click Reaction for Simultaneous Analysis of Cysteine and Cystine in Culture Media Using LC-MS/MS

Cysteine (Cys) and its oxidized form, cystine (Cys2), play crucial roles in biological systems and have considerable applications in cell culture. However, Cys in cell culture media is easily oxidized to Cys2, leading to solubility issues. Traditional analytical methods struggle to maintain the oxidation states of Cys and Cys2 during analysis, posing a significant challenge to accurately measuring and controlling these compounds. To effectively control the Cys and Cys2 levels, a rapid and accurate analytical method is required. Here, we screened derivatizing reagents that can react with Cys even under acidic conditions to realize a novel analytical method for simultaneously determining Cys and Cys2 levels. Diethyl 2-methylenemalonate (EMM) was found to possess the desired traits. EMM, characterized by its dual electron-withdrawing attributes, allowed for a rapid reaction with Cys under acidic conditions, preserving intact information for understanding the functions of target compounds. Combined with LC-MS/MS and an internal standard, this method provided high analytical accuracy in a short analytical time of 9 min. Using the developed method, the rapid oxidation of Cys in cell culture media was observed with the headspace of the storage container considerably influencing Cys oxidation and Cys2 precipitation rates. The developed method enabled the direct and simplified analysis of Cys behavior in practical media samples and could be used in formulating new media compositions, ensuring quality assurance, and real-time analysis of Cys and Cys2 in cell culture supernatants. This novel approach holds the potential to further enhance the media performance by enabling the timely optimal addition of Cys.

Assessing the Chemical-Free Oxidation of Trace Organic Chemicals by VUV/UV as an Alternative to Conventional UV/H2O2

Low-pressure mercury lamps with high-purity quartz can emit both vacuum-UV (VUV, 185 nm) and UV (254 nm) and are commercially available and promising for eliminating recalcitrant organic pollutants. The feasibility of VUV/UV as a chemical-free oxidation process was verified and quantitatively assessed by the concept of H2O2 equivalence (EQH2O2), at which UV/H2O2 showed the same performance as VUV/UV for the degradation of trace organic contaminants (TOrCs). Although VUV showed superior H2O activation and oxidation performance, its performance highly varied as a function of light path length (Lp) in water, while that of UV/H2O2 proportionally decreased with decreasing H2O2 dose regardless of Lp. On increasing Lp from 1.0 to 3.0 cm, the EQH2O2 of VUV/UV decreased from 0.81 to 0.22 mM H2O2. Chloride and nitrate hardly influenced UV/H2O2, but they dramatically inhibited VUV/UV. The competitive absorbance of VUV by chloride and nitrate was verified as the main reason. The inhibitory effect was partially compensated by •OH formation from the propagation reactions of chloride or nitrate VUV photolysis, which was verified by kinetic modeling in Kintecus. In water with an Lp of 2.0 cm, the EQH2O2 of VUV/UV decreased from 0.43 to 0.17 mM (60.8% decrease) on increasing the chloride concentration from 0 to 15 mM and to 0.20 mM (53.5% decrease) at 4 mM nitrate. The results of this study provide a comprehensive understanding of VUV/UV oxidation in comparison to UV/H2O2, which underscores the suitability and efficiency of chemical-free oxidation with VUV/UV.

Selective Nitrate Electroreduction to Ammonia on CNT Electrodes with Controllable Interfacial Wettability

The development of electrocatalysts that can efficiently reduce nitrate (NO3-) to ammonia (NH3) has garnered increasing attention due to their potential to reduce carbon emissions and promote environmental protection. Intensive efforts have focused on catalyst development, but a thorough understanding of the effect of the microenvironment around the reactive sites of the catalyst is also crucial to maximize the performance of the electrocatalysts. This study explored an electrocatalytic system that utilized quaternary ammonium surfactants with a range of alkyl chain lengths to modify an electrode made of carbon nanotubes (CNT), with the goal of regulating interfacial wettability toward NO3- reduction. Trimethyltetradecylammonium bromide with a moderate alkyl chain length created a very hydrophobic interface, which led to a high selectivity in the production of NH3 (∼87%). Detailed mechanistic investigations that used operando Fourier-transform infrared (FTIR) spectroscopy and online differential electrochemical mass spectrometry (DEMS) revealed that the construction of a hydrophobic modified CNT played a synergistic role in suppressing a side reaction involving the generation of hydrogen, which would compete with the reduction of NO3-. This electrocatalytic system led to a favorable process for the reduction of NO3- to NH3 through a direct electron transfer pathway. Our findings underscore the significance of controlling the hydrophobic surface of electrocatalysts as an effective means to enhance electrochemical performance in aqueous media.

Construction of a dual-signal readout platform for effective glutathione S-transferase sensing based on polyethyleneimine-capped silver nanoclusters and cobalt-manganese oxide nanosheets with oxidase-mimicking activity

A novel dual-mode fluorometric and colorimetric sensing platform is reported for determining glutathione S-transferase (GST) by utilizing polyethyleneimine-capped silver nanoclusters (PEI-AgNCs) and cobalt-manganese oxide nanosheets (CoMn-ONSs) with oxidase-like activity. Abundant active oxygen species (O2•-) can be produced through the CoMn-ONSs interacting with dissolved oxygen. Afterward, the pink oxDPD was generated through the oxidation of colorless N,N-diethyl-p-phenylenediamine (DPD) by O2•-, and two absorption peaks at 510 and 551 nm could be observed. Simultaneously, oxDPD could quench the fluorescence of PEI-AgNCs at 504 nm via the inner filter effect (IFE). However, in the presence of glutathione (GSH), GSH prevents the oxidation of DPD due to the reducibility of GSH, leading to the absorbance decrease at 510 and 551 nm. Furthermore, the fluorescence at 504 nm was restored due to the quenching effect of oxDPD on decreased PEI-AgNCs. Under the catalysis of GST, GSH and1-chloro-2,4-dinitrobenzo (CDNB) conjugate to generate an adduct, initiating the occurrence of the oxidation of the chromogenic substrate DPD, thereby inducing a distinct colorimetric response again and the significant quenching of PEI-AgNCs. The detection limits for GST determination were 0.04 and 0.21 U/L for fluorometric and colorimetric modes, respectively. The sensing platform illustrated reliable applicability in detecting GST in real samples.

Platinum Nanoparticles Supported by Carbon Nanotubes: Improvement in electrochemical sensor performance for caffeine determination

Platinum nanoparticles supported by carbon nanotubes were obtained by a simple chemical route and used for preparation of electrochemical sensor towards caffeine determination. Carbon nanotubes were used before and after an acid treatment, yielding two different materials. Morphological and structural characterization of these materials showed platinum nanoparticles (size around 12 nm) distributed randomly along carbon nanotubes. Modified electrodes were directly prepared through a dispersion of these materials. Voltammetric studies in the presence of caffeine revealed an electrocatalytic effect of platinum oxides, electrochemically produced from the chemical oxidation of the platinum nanoparticles. This behavior was explored in the development a selective method for caffeine determination based on platinum oxide reduction at a lower potential value (+0.45 V vs. Ag/AgCl). Using the best set of experimental conditions, it was shown a linear relationship for the caffeine concentration ranging from 5.0 to 25 µmol L-1 with a sensitivity of 449 nA L µmol-1. Limits of detection and quantification of 0.54 and 1.80 µmol L-1 were calculated, respectively. Recovery values for real samples of caffeine pharmaceutical formulations between 98.6% and 101.0% (n = 3) were obtained using the proposed procedure. Statistical calculations showed good concordance (95% confidence level) between the added and recovery values.

Long-term intake of thermo-induced oxidized oil results in anxiety-like and depression-like behaviors: involvement of microglia and astrocytes

Frequent consumption of fried foods has been strongly associated with a higher risk of anxiety and depression, particularly among young individuals. The existing evidence has indicated that acrylamide produced from starchy foods at high temperatures can induce anxious behavior. However, there is limited research on the nerve damage caused by thermo-induced oxidized oil (TIOO). In this study, we conducted behavioral tests on mice and found that prolonged consumption of TIOO led to significant anxiety behavior and a tendency toward depression. TIOO primarily induced these two emotional disorders by affecting the differentiation of microglia, the level of inflammatory factors, the activation of astrocytes, and glutamate circulation in brain tissue. By promoting the over-differentiation of microglia into M1 microglia, TIOO disrupted their differentiation balance, resulting in an up-regulation of inflammatory factors (IL-1β, IL-6, TNF-α, NOS2) in M1 microglia and a down-regulation of neuroprotective factors IL-4/IL-10 in M2 microglia, leading to nerve damage. Moreover, TIOO activated astrocytes, accelerating their proliferation and causing GFAP precipitation, which damaged astrocytes. Meanwhile, TIOO stimulates the secretion of the BDNF and reduces the level of the glutamate receptor GLT-1 in astrocytes, leading to a disorder in the glutamate-glutamine cycle, further exacerbating nerve damage. In conclusion, this study suggests that long-term intake of thermo-induced oxidized oil can trigger symptoms of anxiety and depression.

Lipid Peroxidation-Related Redox Signaling in Osteosarcoma

Oxidative stress and lipid peroxidation play important roles in numerous physiological and pathological processes, while the bioactive products of lipid peroxidation, lipid hydroperoxides and reactive aldehydes, act as important mediators of redox signaling in normal and malignant cells. Many types of cancer, including osteosarcoma, express altered redox signaling pathways. Such redox signaling pathways protect cancer cells from the cytotoxic effects of oxidative stress, thus supporting malignant transformation, and eventually from cytotoxic anticancer therapies associated with oxidative stress. In this review, we aim to explore the status of lipid peroxidation in osteosarcoma and highlight the involvement of lipid peroxidation products in redox signaling pathways, including the involvement of lipid peroxidation in osteosarcoma therapies.

Iterative oxidation by TET1 is required for reprogramming of imprinting control regions and patterning of mouse sperm hypomethylated regions

Ten-eleven translocation (TET) enzymes iteratively oxidize 5-methylcytosine (5mC) to generate 5-hydroxymethylcytosine (5hmC), 5-formylcytosine, and 5-carboxylcytosine to facilitate active genome demethylation. Whether these bases are required to promote replication-coupled dilution or activate base excision repair during mammalian germline reprogramming remains unresolved due to the inability to decouple TET activities. Here, we generated two mouse lines expressing catalytically inactive TET1 (Tet1-HxD) and TET1 that stalls oxidation at 5hmC (Tet1-V). Tet1 knockout and catalytic mutant primordial germ cells (PGCs) fail to erase methylation at select imprinting control regions and promoters of meiosis-associated genes, validating the requirement for the iterative oxidation of 5mC for complete germline reprogramming. TET1V and TET1HxD rescue most hypermethylation of Tet1-/- sperm, suggesting the role of TET1 beyond its oxidative capability. We additionally identify a broader class of hypermethylated regions in Tet1 mutant mouse sperm that depend on TET oxidation for reprogramming. Our study demonstrates the link between TET1-mediated germline reprogramming and sperm methylome patterning.

Microorganisms uptake zero-valent sulfur via membrane lipid dissolution of octasulfur and intracellular solubilization as persulfide

Zero-valent sulfur, commonly utilized as a fertilizer or fungicide, is prevalent in various environmental contexts. Its most stable and predominant form, octasulfur (S8), plays a crucial role in microbial sulfur metabolism, either through oxidation or reduction. However, the mechanism underlying its cellular uptake remains elusive. We presented evidence that zero-valent sulfur was adsorbed to the cell surface and then dissolved into the membrane lipid layer as lipid-soluble S8 molecules, which reacted with cellular low-molecular thiols to form persulfide, e.g., glutathione persulfide (GSSH), in the cytoplasm. The process brought extracellular zero-valent sulfur into the cells. When persulfide dioxygenase is present in the cells, GSSH will be oxidized. Otherwise, GSSH will react with another glutathione (GSH) to produce glutathione disulfide (GSSG) and hydrogen sulfide (H2S). The mechanism is different from simple diffusion, as insoluble S8 becomes soluble GSSH after crossing the cytoplasmic membrane. The uptake process is limited by physical contact of insoluble zero-valent sulfur with microbial cells and the regeneration of cellular thiols. Our findings elucidate the cellular uptake mechanism of zero-valent sulfur, which provides critical information for its application in agricultural practices and the bioremediation of sulfur contaminants and heavy metals.

Increased stress vulnerability in the offspring of socially isolated rats: Behavioural, neurochemical and redox dysfunctions

Stressful events during pregnancy impact on the progeny neurodevelopment. However, little is known about preconceptional stress effects. The rat social isolation represents an animal model of chronic stress inducing a variety of dysfunctions. Moreover, social deprivation during adolescence interferes with key neurodevelopmental processes. Here, we investigated the development of behavioural, neurochemical and redox alterations in the male offspring of socially isolated female rats before pregnancy, reared in group (GRP) or in social isolation (ISO) from weaning until young-adulthood. To this aim, females were reared in GRP or in ISO conditions, from PND21 to PND70, when they were mated. Their male offspring was housed in GRP or ISO conditions through adolescence and until PND70, when passive avoidance-PA, novel object recognition-NOR and open field-OF tests were performed. Levels of noradrenaline (NA), serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), glutamate (GLU) and GABA were assessed in the prefrontal cortex (PFC). Moreover, cortical ROS levels were quantified, as well as NF-kB and the NADPH oxidase NOX2 expression, redox status (expressed as GSH:GSSG ratio) and SOD1 amount. A significant decrease of the latency time in the PA was observed in the offspring of ISO females. In the NOR test, while a significant increase in the exploratory activity towards the novel object was observed in the offspring of GRP females, no significant differences were found in the offspring of ISO females. No significant differences were found in the OF test among experimental groups. Theoffspring of ISO females showed increased NA and 5-HIAA levels, whereas in the offspring persistently housed in isolation condition from weaninguntil adulthood, we detected reduced 5-HT levels and ehnanced 5-HIAA amount. No significant changes in GLU concentrations were detected, while decreased GABA content was observed in the offspring of ISO females exposed to social isolation. Increased ROS levels as well as reduced NF-κB, NOX2 expression were detected in the offspring of ISO females. This was accompanied by reduced redox status and enhanced SOD1 levels. In conclusion, our results suggest that female exposure to chronic social stress before pregnancy might have a profound influence on the offspring neurodevelopment in terms of cognitive, neurochemical and redox-related alterations, identifying this specific time window for possible preventive and therapeutic strategies.

Uptake, accumulation and metabolism of UV-320 in vegetables and its impact on growth and quality

UV-320 is classified as a Substance of Very High Concern (SVHC) by the European Chemicals Agency and has attracted significant attention due to its presence in the environment. Understanding the uptake, translocation and metabolic patterns of UV-320 in vegetables is essential for assessing their ability to bioaccumulate and potential risks to human health. In this study, we investigated the uptake and translocation of UV-320 in lettuce and radish by hydroponic experiments. The results showed that the root concentration factors (Croot/Csolution, RCF) of lettuce and radish were in the range of 47.9 to 464 mL/g and 194 to 787 mL/g, respectively. The transfer factors (Cshoot/Croot, TF) were observed to be 0.001-0.012 for lettuce and 0.02-0.05 for radish. Additionally, non-targeted screening identified twelve phase I and one phase II metabolites of UV-320 in vegetables, which were confirmed based on their molecular formulas and structures. The metabolic pathways involving oxidation, ketonylation and deamination were proposed in vegetables. Also, we have observed that UV-320 inhibits the growth of vegetables. Meanwhile, we evaluated the health risk of UV-320 in lettuce and radish and found that the consumption of lettuce is relatively safe, while the consumption of radish has a risk of HQ >1 for both adults and children, which should be seriously considered. This study provides valuable insights into the behavior and ecological risks of UV-320 in the environment.

The redox-active defensive Selenoprotein T as a novel stress sensor protein playing a key role in the pathophysiology of heart failure

Maladaptive cardiac hypertrophy contributes to the development of heart failure (HF). The oxidoreductase Selenoprotein T (SELENOT) emerged as a key regulator during rat cardiogenesis and acute cardiac protection. However, its action in chronic settings of cardiac dysfunction is not understood. Here, we investigated the role of SELENOT in the pathophysiology of HF: (i) by designing a small peptide (PSELT), recapitulating SELENOT activity via the redox site, and assessed its beneficial action in a preclinical model of HF [aged spontaneously hypertensive heart failure (SHHF) rats] and against isoproterenol (ISO)-induced hypertrophy in rat ventricular H9c2 and adult human AC16 cardiomyocytes; (ii) by evaluating the SELENOT intra-cardiomyocyte production and secretion under hypertrophied stimulation. Results showed that PSELT attenuated systemic inflammation, lipopolysaccharide (LPS)-induced macrophage M1 polarization, myocardial injury, and the severe ultrastructural alterations, while counteracting key mediators of cardiac fibrosis, aging, and DNA damage and restoring desmin downregulation and SELENOT upregulation in the failing hearts. In the hemodynamic assessment, PSELT improved the contractile impairment at baseline and following ischemia/reperfusion injury, and reduced infarct size in normal and failing hearts. At cellular level, PSELT counteracted ISO-mediated hypertrophy and ultrastructural alterations through its redox motif, while mitigating ISO-triggered SELENOT intracellular production and secretion, a phenomenon that presumably reflects the extent of cell damage. Altogether, these results indicate that SELENOT could represent a novel sensor of hypertrophied cardiomyocytes and a potential PSELT-based new therapeutic approach in myocardial hypertrophy and HF.

Bioinformatics-Guided Reconstitution of Biosynthetic Machineries of Fungal Eremophilane Sesquiterpenes

Eremophilanes exhibit diverse biological activities and chemical structures. This study reports the bioinformatics-guided reconstitution of the biosynthetic machinery of fungal eremophilanes, eremofortin C and sporogen-AO1, to elucidate their biosynthetic pathways. Their biosyntheses include P450-catalyzed multistep oxidation and enzyme-catalyzed isomerization by the DUF3237 family protein. Successful characterization of six P450s enabled us to discuss the functions of eremophilane P450s in putative eremophilane biosynthetic gene clusters, providing opportunities to understand the oxidative modification pathways of fungal eremophilanes.

Solution structure and pressure response of thioredoxin-1 of Plasmodium falciparum

We present here the solution structures of the protein thioredoxin-1 from Plasmodium falciparum (PfTrx-1), in its reduced and oxidized forms. They were determined by high-resolution NMR spectroscopy at 293 K on uniformly 13C-, 15N-enriched, matched samples allowing to identification of even small structural differences. PfTrx-1 shows an α/β-fold with a mixed five-stranded β-sheet that is sandwiched between 4 helices in a β1 α1 β2 α2 β3 α3 β4 β5 α4 topology. The redox process of the CGPC motif leads to significant structural changes accompanied by larger chemical shift changes from residue Phe25 to Ile36, Thr70 to Thr74, and Leu88 to Asn91. By high-field high-pressure NMR spectroscopy, rare conformational states can be identified that potentially are functionally important and can be used for targeted drug development. We performed these experiments in the pressure range from 0.1 MPa to 200 MPa. The mean combined, random-coil corrected B1* values of reduced and oxidized thioredoxin are quite similar with -0.145 and -0.114 ppm GPa-1, respectively. The mean combined, random-coil corrected B2* values in the reduced and oxidized form are 0.179 and 0.119 ppm GPa-2, respectively. The mean ratios of the pressure coefficients B2/B1 are -0.484 and -0.831 GPa-1 in the reduced and oxidized form respectively. They differ at some points in the structure after the formation of the disulfide bond between C30 and C33. The thermodynamical description of the pressure dependence of chemical shifts requires the assumption of at least three coexisting conformational states of PfTrx-1. These three conformational states were identified in the reduced as well as in the oxidized form of the protein, therefore, they represent sub-states of the two main oxidation states of PfTrx-1.

Development of a sensor for disulfide bond formation in diverse bacteria

In bacteria, disulfide bonds contribute to the folding and stability of proteins important for processes in the cellular envelope. In Escherichia coli, disulfide bond formation is catalyzed by DsbA and DsbB enzymes. DsbA is a periplasmic protein that catalyzes disulfide bond formation in substrate proteins, while DsbB is an inner membrane protein that transfers electrons from DsbA to quinones, thereby regenerating the DsbA active state. Actinobacteria including mycobacteria use an alternative enzyme named VKOR, which performs the same function as DsbB. Disulfide bond formation enzymes, DsbA and DsbB/VKOR, represent novel drug targets because their inhibition could simultaneously affect the folding of several cell envelope proteins including virulence factors, proteins involved in outer membrane biogenesis, cell division, and antibiotic resistance. We have previously developed a cell-based and target-based assay to identify molecules that inhibit the DsbB and VKOR in pathogenic bacteria, using E. coli cells expressing a periplasmic β-Galactosidase sensor (β-Galdbs), which is only active when disulfide bond formation is inhibited. Here, we report the construction of plasmids that allows fine-tuning of the expression of the β-Galdbs sensor and can be mobilized into other gram-negative organisms. As an example, when expressed in Pseudomonas aeruginosa UCBPP-PA14, which harbors two DsbB homologs, β-Galdbs behaves similarly as in E. coli, and the biosensor responds to the inhibition of the two DsbB proteins. Thus, these β-Galdbs reporter plasmids provide a basis to identify novel inhibitors of DsbA and DsbB/VKOR in multidrug-resistant gram-negative pathogens and to further study oxidative protein folding in diverse gram-negative bacteria.

IMPORTANCE

Disulfide bonds contribute to the folding and stability of proteins in the bacterial cell envelope. Disulfide bond-forming enzymes represent new drug targets against multidrug-resistant bacteria because inactivation of this process would simultaneously affect several proteins in the cell envelope, including virulence factors, toxins, proteins involved in outer membrane biogenesis, cell division, and antibiotic resistance. Identifying the enzymes involved in disulfide bond formation in gram-negative pathogens as well as their inhibitors can contribute to the much-needed antibacterial innovation. In this work, we developed sensors of disulfide bond formation for gram-negative bacteria. These tools will enable the study of disulfide bond formation and the identification of inhibitors for this crucial process in diverse gram-negative pathogens.

The Catalysis Mechanism of E. coli Nitroreductase A, a Candidate for Gene-Directed Prodrug Therapy: Potentiometric and Substrate Specificity Studies

E. coli nitroreductase A (NfsA) is a candidate for gene-directed prodrug cancer therapy using bioreductively activated nitroaromatic compounds (ArNO2). In this work, we determined the standard redox potential of FMN of NfsA to be -215 ± 5 mV at pH 7.0. FMN semiquinone was not formed during 5-deazaflavin-sensitized NfsA photoreduction. This determines the two-electron character of the reduction of ArNO2 and quinones (Q). In parallel, we characterized the oxidant specificity of NfsA with an emphasis on its structure. Except for negative outliers nitracrine and SN-36506, the reactivity of ArNO2 increases with their electron affinity (single-electron reduction potential, E17) and is unaffected by their lipophilicity and Van der Waals volume up to 386 Å. The reactivity of quinoidal oxidants is not clearly dependent on E17, but 2-hydroxy-1,4-naphthoquinones were identified as positive outliers and a number of compounds with diverse structures as negative outliers. 2-Hydroxy-1,4-naphthoquinones are characterized by the most positive reaction activation entropy and the negative outlier tetramethyl-1,4-benzoquinone by the most negative. Computer modelling data showed that the formation of H bonds with Arg15, Arg133, and Ser40, plays a major role in the binding of oxidants to reduced NfsA, while the role of the π-π interaction of their aromatic structures is less significant. Typically, the calculated hydride-transfer distances during ArNO2 reduction are smallwer than for Q. This explains the lower reactivity of quinones. Another factor that slows down the reduction is the presence of positively charged aliphatic substituents.

Novel Alphaproteobacteria transcribe genes for nitric oxide transformation at high levels in a marine oxygen-deficient zone

Marine oxygen-deficient zones (ODZs) are portions of the ocean where intense nitrogen loss occurs primarily via denitrification and anammox. Despite many decades of study, the identity of the microbes that catalyze nitrogen loss in ODZs is still being elucidated. Intriguingly, high transcription of genes in the same family as the nitric oxide dismutase (nod) gene from Methylomirabilota has been reported in the anoxic core of ODZs. Here, we show that the most abundantly transcribed nod genes in the Eastern Tropical North Pacific ODZ belong to a new order (UBA11136) of Alphaproteobacteria, rather than Methylomirabilota as previously assumed. Gammaproteobacteria and Planctomycetia also transcribe nod, but at lower relative abundance than UBA11136 in the upper ODZ. The nod-transcribing Alphaproteobacteria likely use formaldehyde and formate as a source of electrons for aerobic respiration, with additional electrons possibly from sulfide oxidation. They also transcribe multiheme cytochrome (here named ptd) genes for a putative porin-cytochrome protein complex of unknown function, potentially involved in extracellular electron transfer. Molecular oxygen for aerobic respiration may originate from nitric oxide dismutation via cryptic oxygen cycling. Our results implicate Alphaproteobacteria order UBA11136 as a significant player in marine nitrogen loss and highlight their potential in one-carbon, nitrogen, and sulfur metabolism in ODZs.IMPORTANCEIn marine oxygen-deficient zones (ODZs), microbes transform bioavailable nitrogen to gaseous nitrogen, with nitric oxide as a key intermediate. The Eastern Tropical North Pacific contains the world's largest ODZ, but the identity of the microbes transforming nitric oxide remains unknown. Here, we show that highly transcribed nitric oxide dismutase (nod) genes belong to Alphaproteobacteria of the novel order UBA11136, which lacks cultivated isolates. These Alphaproteobacteria show evidence for aerobic respiration, using oxygen potentially sourced from nitric oxide dismutase, and possess a novel porin-cytochrome protein complex with unknown function. Gammaproteobacteria and Planctomycetia transcribe nod at lower levels. Our results pinpoint the microbes mediating a key step in marine nitrogen loss and reveal an unexpected predicted metabolism for marine Alphaproteobacteria.

MmcA is an electron conduit that facilitates both intracellular and extracellular electron transport in Methanosarcina acetivorans

Methanogens are a diverse group of Archaea that obligately couple energy conservation to the production of methane. Some methanogens encode alternate pathways for energy conservation, like anaerobic respiration, but the biochemical details of this process are unknown. We show that a multiheme c-type cytochrome called MmcA from Methanosarcina acetivorans is important for intracellular electron transport during methanogenesis and can also reduce extracellular electron acceptors like soluble Fe3+ and anthraquinone-2,6-disulfonate. Consistent with these observations, MmcA displays reversible redox features ranging from -100 to -450 mV versus SHE. Additionally, mutants lacking mmcA have significantly slower Fe3+ reduction rates. The mmcA locus is prevalent in members of the Order Methanosarcinales and is a part of a distinct clade of multiheme cytochromes that are closely related to octaheme tetrathionate reductases. Taken together, MmcA might act as an electron conduit that can potentially support a variety of energy conservation strategies that extend beyond methanogenesis.