Toxic DNA damage by hydrogen peroxide through the Fenton reaction in vivo and in vitro

The minimal meningococcal ProQ protein has an intrinsic capacity for structure-based global RNA recognition

FinO-domain proteins are a widespread family of bacterial RNA-binding proteins with regulatory functions. Their target spectrum ranges from a single RNA pair, in the case of plasmid-encoded FinO, to global RNA regulons, as with enterobacterial ProQ. To assess whether the FinO domain itself is intrinsically selective or promiscuous, we determine in vivo targets of Neisseria meningitidis, which consists of solely a FinO domain. UV-CLIP-seq identifies associations with 16 small non-coding sRNAs and 166 mRNAs. Meningococcal ProQ predominantly binds to highly structured regions and generally acts to stabilize its RNA targets. Loss of ProQ alters transcript levels of >250 genes, demonstrating that this minimal ProQ protein impacts gene expression globally. Phenotypic analyses indicate that ProQ promotes oxidative stress resistance and DNA damage repair. We conclude that FinO domain proteins recognize some abundant type of RNA shape and evolve RNA binding selectivity through acquisition of additional regions that constrain target recognition.

FinO-domain proteins are bacterial RNA-binding proteins with a wide range of target specificities. Here, the authors employ UV CLIP-seq and show that minimal ProQ protein of Neisseria meningitidis binds to various small non-coding RNAs and mRNAs involved in virulence.

Comparing the Efficacy of Formaldehyde with Hydrogen Peroxide Fumigation on Infectious Bronchitis Virus

BACKGROUND

The recent reclassification of formaldehyde as a presumed carcinogen prompted the investigation into the comparative efficacy of hydrogen peroxide as a fumigant in microbiological safety cabinets.

INTRODUCTION

The aim of the study was to quantify the biocidal efficacy of formaldehyde fumigation, including variables such as exposure time and concentration, and then to compare this to the biocidal efficacy achieved from a hydrogen peroxide vapor fumigation system. The study also investigated the ability of both fumigants to permeate the microbiological safety cabinet (MBSC), including the workspace, under the work tray, and after the HEPA filters. Furthermore, the effect of organic soiling on efficacy was also assessed. Infectious bronchitis virus (IBV) was used as the biological target to develop this study model.

METHODS

A model using IBV was developed to determine the efficacy of formaldehyde and hydrogen peroxide as fumigants. Virus was dried on stainless steel discs, and variables including concentration, time, protein soiling, and location within an MBSC were assessed.

RESULTS

It was demonstrated that formaldehyde fumigation could achieve a 6-log reduction in the titer of the virus throughout the cabinet, and high protein soiling in the presentation did not affect efficacy. Appropriate cycle parameters for the hydrogen peroxide system were developed, and when challenged with IBV, it was shown that vaporized hydrogen peroxide could achieve an equal 6-log titer reduction as formaldehyde within the cabinet workspace and overcome the presence of soiling.

CONCLUSION

Hydrogen peroxide was demonstrated to be a viable alternative to formaldehyde under most situations tested. However, the hydrogen peroxide system did not achieve an equal titer reduction above the cabinet's first HEPA filter using the cabinet workspace cycle, and further optimization of the hydrogen peroxide cycle parameters, including pulsing of the cabinet fans, may be required to achieve this.

Vitamin B and Vitamin C Affect DNA Methylation and Amino Acid Metabolism in Mycobacterium bovis BCG

Vitamins are essential nutrients and key cofactors of enzymes that regulate cellular metabolism, and also activate the immune system. Recent studies have shown that vitamin B1 (V_{B 1}) and vitamin C (Vc) can inhibit Mycobacterium tuberculosis growth, but the precise mechanism is still not well understood. In the present study, we have used RNA-sequencing (RNA-seq), liquid chromatography coupled to mass spectrometry (LC-MS) and single-molecule real-time (SMRT) sequencing to analyze the transcriptional, metabolic and methylation profiles of Mycobacterium bovis BCG when treated with V_{B 1} and Vc. Our results show that, after vitamin treatment, variant metabolites were mainly clustered in pathways related to amino acid metabolism. Treatment with both vitamins significantly up-regulated the gene encoding cysteine synthase A. Additionally, only BCG that was treated with V_C showed m4c modifications. Genes harboring this methylation were up-regulated, suggesting that m4c methylation can promote gene transcription to some extent. Overall, this study contributes to the understanding of the effects of V_{B 1} and V_C, and suggests that these vitamins constitute potential anti-tuberculosis drugs.

Tailoring H2O2 generation kinetics with magnesium alloys for efficient disinfection on titanium surface

A new antibacterial strategy for Ti has been developed without the use of any external antibacterial agents and surface treatments. By combining Mg alloys with Ti, H2O2, which is an oxidizing agent that kills bacteria, was spontaneously generated near the surface of Ti. Importantly, the H2O2 formation kinetics can be precisely controlled by tailoring the degradation rates of Mg alloys connected to Ti. Through microstructural and electrochemical modification of Mg with alloying elements (Ca, Zn), the degradation rates of Mg alloys were controlled, and the H2O2 release kinetics was accelerated when the degradation rate of Mg alloys increased. With the introduction of an in vivo assessment platform comprised of Escherichia coli (E. coli) and transgenic zebrafish embryos, we are able to design optimized antibacterial systems (Ti-Mg and Ti-Mg-3wt% Zn) that can selectively eradicate E. coli while not harming the survival rate, development, and biological functions of zebrafish embryos. We envision that our antibacterial strategy based on utilization of sacrificial Mg alloys could broaden the current palette of antibacterial platforms for metals.

Therapeutic Strategies and Biomarkers to Modulate PARP Activity for Targeted Cancer Therapy

Poly-(ADP-ribose) polymerase 1 (PARP1) is commonly known for its vital role in DNA damage response and repair. However, its enzymatic activity has been linked to a plethora of physiological and pathophysiological transactions ranging from cellular proliferation, survival and death. For instance, malignancies with BRCA1/2 mutations heavily rely on PARP activity for survival. Thus, the use of PARP inhibitors is a well-established intervention in these types of tumors. However, recent studies indicate that the therapeutic potential of attenuating PARP1 activity in recalcitrant tumors, especially where PARP1 is aberrantly overexpressed and hyperactivated, may extend its therapeutic utility in wider cancer types beyond BRCA-deficiency. Here, we discuss treatment strategies to expand the tumor-selective therapeutic application of PARP inhibitors and novel approaches with predictive biomarkers to perturb NAD⁺ levels and hyperPARylation that inactivate PARP in recalcitrant tumors. We also provide an overview of genetic alterations that transform non-BRCA mutant cancers to a state of "BRCAness" as potential biomarkers for synthetic lethality with PARP inhibitors. Finally, we discuss a paradigm shift for the use of novel PARP inhibitors outside of cancer treatment, where it has the potential to rescue normal cells from severe oxidative damage during ischemia-reperfusion injury induced by surgery and radiotherapy.

Organelle-specific analysis of labile Fe(ii) during ferroptosis by using a cocktail of various colour organelle-targeted fluorescent probes

Ferroptosis is an emerging type of cell death mode that is dependent on iron. Unfortunately, the detailed analysis of the function of organelle labile Fe(ii) in oxidative damage and lethality of the cells has not been demonstrated so far, mainly due to the lack of efficient methods to visualize labile Fe(ii) at the targeted organelles. We have recently reported a series of Fe(ii)-selective fluorescent probes, i.e., Ac-MtFluNox, Lyso-RhoNox, and ER-SiRhoNox, which can detect Fe(ii) specifically in the mitochondria, lysosomes, and endoplasmic reticulum (ER), respectively. These probes demonstrate similar reaction rates and off/on contrasts with various colours and intracellular distributions, enabling simultaneous multi-colour imaging that allows the monitoring of labile Fe(ii) levels at each targeted organelle. In this paper, by using a cocktail of these probes, we successfully visualised the aberrant elevation of labile Fe(ii) in the lysosomes and ER prior to HT1080 cell death induced by erastin, which is an inducer of ferroptosis.

L-lysine potentiates aminoglycosides against Acinetobacter baumannii via regulation of proton motive force and antibiotics uptake

Acinetobacter baumannii, a Gram-negative opportunistic pathogen, is a leading cause of hospital- and community-acquired infections. Acinetobacter baumannii can rapidly acquire diverse resistance mechanisms and undergo genetic modifications that confer resistance and persistence to all currently used clinical antibiotics. In this study, we found exogenous L-lysine sensitizes Acinetobacter baumannii, other Gram-negative bacteria (Escherichia coli and Klebsiella pneumoniae) and a Gram-positive bacterium (Mycobacterium smegmatis) to aminoglycosides. Importantly, the combination of L-lysine with aminoglycosides killed clinically isolated multidrug-resistant Acinetobacter baumannii and persister cells. The exogenous L-lysine can increase proton motive force via transmembrane chemical gradient, resulting in aminoglycoside acumination that further accounts for reactive oxygen species production. The combination of L-lysine and antibiotics highlights a promising strategy against bacterial infection.

Non-lethal exposure to H2O2 boosts bacterial survival and evolvability against oxidative stress

Unicellular organisms have the prevalent challenge to survive under oxidative stress of reactive oxygen species (ROS) such as hydrogen peroxide (H₂O₂). ROS are present as by-products of photosynthesis and aerobic respiration. These reactive species are even employed by multicellular organisms as potent weapons against microbes. Although bacterial defences against lethal and sub-lethal oxidative stress have been studied in model bacteria, the role of fluctuating H₂O₂ concentrations remains unexplored. It is known that sub-lethal exposure of Escherichia coli to H₂O₂ results in enhanced survival upon subsequent exposure. Here we investigate the priming response to H₂O₂ at physiological concentrations. The basis and the duration of the response (memory) were also determined by time-lapse quantitative proteomics. We found that a low level of H₂O₂ induced several scavenging enzymes showing a long half-life, subsequently protecting cells from future exposure. We then asked if the phenotypic resistance against H₂O₂ alters the evolution of resistance against oxygen stress. Experimental evolution of H₂O₂ resistance revealed faster evolution and higher levels of resistance in primed cells. Several mutations were found to be associated with resistance in evolved populations affecting different loci but, counterintuitively, none of them was directly associated with scavenging systems. Our results have important implications for host colonisation and infections where microbes often encounter reactive oxygen species in gradients.

Throughout evolution, bacteria were exposed to reactive oxygen species and evolved the ability to scavenge toxic oxygen radicals. Furthermore, multicellular organisms evolved the ability to produce such oxygen species directed against pathogens. Recent studies also suggest that ROS such as H₂O₂ play an important role during host gut colonisation by its microbiota. Traditionally, experiments with different antimicrobials have been carried out using fixed concentrations while in nature, including in intra-host environments, microbes are more likely to experience this type of stress in steps or gradients. Here we show that bacteria treated with sub-lethal concentrations of H₂O₂ (priming) survive far better than non-treated cells when they subsequently encounter a higher concentration. We also found that the 'priming' response has a protective role from lethal mutagenesis. This protection is provided by long-lived proteins that, upon priming, remain at a high level for several generations as determined by time-lapse LC-mass spectrometry. Bacteria that were primed evolved H₂O₂ resistance faster and to a higher level. Moreover, mutations that increase resistance to H₂O₂, as determined by whole-genome sequencing (WGS), do not occur in known scavenger encoding genes but in loci coding for other functions, at least in E. coli.

Antioxidant Activities of Streptomyces sp. strain MUSC 14 from Mangrove Forest Soil in Malaysia

The mangrove ecosystem of Malaysia remains yet to be fully explored for potential microbes that produce biologically active metabolites. In the present study, a mangrove-derived Streptomyces sp. strain MUSC 14 previously isolated from the state of Pahang, Malaysia Peninsula, was studied for its potential in producing antioxidant metabolites. The identity of Streptomyces sp. strain MUSC14 was consistent with the genotypic and phenotypic characteristics of the Streptomyces genus. The antioxidant potential of Streptomyces sp. strain MUSC 14 was determined through screening of its methanolic extract against sets of antioxidant assays. The results were indicative of Streptomyces sp. strain MUSC 14 displaying strong antioxidant activity against ABTS, DPPH free radicals and metal chelating activity of 62.71 ± 3.30%, 24.71 ± 2.22%, and 55.82 ± 2.35%, respectively. The result of ferric reducing activity measured in terms of dose was equivalent to 2.35–2.45 μg of positive control ascorbic acid. Furthermore, there was a high correlation between the total phenolic content and the antioxidant activities with r = 0.979, r = 0.858, and r = 0.983 representing ABTS, DPPH, and metal chelation, respectively. Overall, the present study suggests that Streptomyces sp. strain MUSC 14 from mangrove forest soil has potential to produce antioxidant metabolites that can be further exploited for therapeutic application.

Mycobacterium abscessus subsp. massiliense expressing bacterioferritin have improved resistance to stressful conditions

AIMS

The importance of bacterioferritin in the virulence and pathogenicity of the genus Mycobacterium is still unclear. The aim of this study was to analyse if the expression of a recombinant bacterioferritin from M. tuberculosis (Mtb) by Mycma could improve the capacity of this bacillus to resist the host defence mechanisms.

METHODS AND RESULTS

Recombinant Mycma, expressing bacterioferritin (Rv1876) from Mtb, was developed by transformation with pMIP12_Rv1876. To determine bacterioferritin influence on Mycma physiology and virulence, the mycobacteria growth was analysed in vitro and in vivo. It was observed that the expression of bacterioferritin improved the growth rate of recombinant Mycma_BfrA under iron excess and oxidative stress, as compared to the wild type. Furthermore, in the murine model of infection, it was observed that Mycma_BfrA-infected mice had higher bacillary load and a more pronounced lesion in the lungs when compared with the wild type.

CONCLUSION

This study showed that bacterioferritin confers additional resistance to stress conditions, resulting in increased pathogenicity of Mycma during mice infection.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides new insights about the importance of bacterioferritin in the virulence and pathogenicity of the Mycobacterium genus.

Oxygen embolism after hydrogen peroxide irrigation during hip arthroscopy: a case report

Background

Hydrogen peroxide has been widely used in Orthopaedics including Orthopaedic oncology, trauma and joint surgeries. However, we encountered an oxygen embolism and myoglobinuria after hydrogen peroxide was used to irrigate a septic hip arthroscopically.

Case presentation

A 61-year-old male patient with right hip septic arthritis underwent an arthroscopic hip washout and debridement. During the operation, the surgeon used 100 ml of 3% hydrogen peroxide to irrigate the joint cavity. Two minutes after irrigation, there was a transient decrease in oxygen saturation, heart rate and blood pressure, with significant subcutaneous emphysema around the wound. Concentrated urine was drained out 8 h after operation which resolved the following day. Post-operatively, the patient was managed in the intensive care unit for a pulmonary embolism and discharged without further complications.

Conclusion

Medical staff should be aware of the risk of oxygen embolism and be extremely careful when using hydrogen peroxide in patient care. Oxygen embolism following hydrogen peroxide use is rare, however, once encountered, it may bring serious consequences. Therefore, the use of hydrogen peroxide in closed spaces or arthroscopic procedures should be discontinued.

Transferrin Insufficiency and Iron Overload in Follicular Fluid Contribute to Oocyte Dysmaturity in Infertile Women With Advanced Endometriosis

Purpose: To screen out specific protein with different concentration in follicular fluid from advanced endometriosis and determine its direct effect on mouse oocytes matured in vitro. Methods: FF samples were obtained from 25 patients (EMS group, n = 15; control group, n = 10) to screen the differential proteins by using iTRAQ Labeling and 2D LC-MS. Transferrin (TRF) in was found significantly decreased in EMS group, which was verified using ELISA in enlarged FF samples (EMS group, n = 31; control group, n = 27). The contents of ferric ion in FFs were detected by ELISA and TRF saturations were calculated in two groups. Germinal vesicle (GV) oocytes of mouse were maturated in vitro interfered with the FFs in five groups, whose concentrations of TRF were modulated, and maturation in vitro rates were compared among groups. Results: The reduced concentration of TRF with three analogs and increased concentration of ferric ion were found in the FF of the EMS group (p < 0.05). The numerical values of TSAT was 54.8% in EMS group, indicating iron overload in the FF. The EMS-FF showed significantly decreased maturation in vitro rate (p < 0.05) of mouse oocytes, which was improved with the supplementation of TRF, compared with the control-FF. The effect was blocked by the TRF antibody (p < 0.05). Conclusions: Being aware of the relatively small sample size, our results possibly suggest that TRF insufficiency and iron overload in FF from advanced EMS contribute to oocytes dysmaturity, which may be a cause of EMS-related infertility.

Manuka honey chelates iron and impacts iron regulation in key bacterial pathogens

AIM

The aim of this study was to test the hypothesis that Manuka honey (MH) chelates iron and promotes an iron-limiting environment, which contributes to its antimicrobial activity.

METHODS AND RESULTS

Employing a ferrozine-based assay, we observed that MH is an iron chelator that depletes iron from solution. Siderophores are small molecules that bind ferric iron (III) with high affinity and their levels are upregulated by bacteria under iron-limiting conditions. We demonstrated by quantitating siderophore production that Escherichia coli and Pseudomonas aeruginosa treated with MH sub-minimum inhibitory concentrations (sub-MIC) experience an iron-limiting environment and increase siderophore production. In addition, supplementation with ferrous iron (II) significantly increased growth of E. coli, Staphylococcus aureus and P. aeruginosa cultured at their MH MIC above that observed in nonsupplemented controls. By contrast, supplementation with ferric iron (III) significantly increased growth for only E. coli and P. aeruginosa, above their nonsupplemented controls.

CONCLUSIONS

Manuka honey chelates iron, thereby generating an iron-limiting environment for E. coli and P. aeruginosa, and to a lesser extent S. aureus, which contributes to its antimicrobial properties.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our work demonstrates that MH-induced iron chelation is an antimicrobial mechanism that differentially impacts the bacterial species tested here. Iron chelation affects multiple diverse physiological processes in bacteria and would contribute to the lack of bacterial resistance to MH. Iron metabolism is tightly regulated; bacteria require this essential nutrient for survival, but in excess it is toxic. Additional exploration of MH's iron chelation mechanism will facilitate its future use in mainstream medicine.

The Cation Diffusion Facilitator Family Protein EmfA Confers Resistance to Manganese Toxicity in Brucella abortus 2308 and Is an Essential Virulence Determinant in Mice

The gene designated bab_rs23470 in the Brucella abortus 2308 genome encodes an ortholog of the cation diffusion facilitator family protein EmfA which has been linked to resistance to Mn toxicity in Rhizobium etli A B. abortus emfA null mutant derived from strain 2308 displays increased sensitivity to elevated levels of Mn in the growth medium compared to that of the parent strain but wild-type resistance to Fe, Mg, Zn, Cu, Co, and Ni. Inductively coupled plasma mass spectroscopy also indicates that the B. abortus emfA mutant retains significantly higher levels of cellular Mn after exposure to this metal than the parent strain, which is consistent with the proposed role of EmfA as a Mn exporter. Phenotypic analysis of mutants indicates that EmfA plays a much more important role in maintaining Mn homeostasis and preventing the toxicity of this metal in Brucella than does the Mn-responsive transcriptional regulator Mur. EmfA is also an essential virulence determinant for B. abortus 2308 in C57BL/6 and C57BL/6^Nramp1+/+ mice, which suggests that avoiding Mn toxicity plays a critical role in Brucella pathogenesis.IMPORTANCE Mn nutrition is essential for the basic physiology and virulence of Brucella strains. The results of the study presented here demonstrate that the cation diffusion facilitator (CDF)-type metal exporter EmfA plays critical roles in maintaining Mn homeostasis and preventing Mn toxicity in Brucella and is an essential virulence determinant for these bacteria. EmfA and other cellular components involved in Mn homeostasis represent attractive targets for the development of improved vaccines and chemotherapeutic strategies for preventing and treating brucellosis in humans and animals.

Manganese Is Required for the Rapid Recovery of DNA Synthesis following Oxidative Challenge in Escherichia coli

Divalent metals such as iron and manganese play an important role in the cellular response to oxidative challenges and are required as cofactors by many enzymes. However, how these metals affect replication after oxidative challenge is not known. Here, we show that replication in Escherichia coli is inhibited following a challenge with hydrogen peroxide and requires manganese for the rapid recovery of DNA synthesis. We show that the manganese-dependent recovery of DNA synthesis occurs independent of lesion repair, modestly improves cell survival, and is associated with elevated rates of mutagenesis. The Mn-dependent mutagenesis involves both replicative and translesion polymerases and requires prior disruption by H₂O₂ to occur. Taking these findings together, we propose that replication in E. coli is likely to utilize an iron-dependent enzyme(s) that becomes oxidized and inactivated during oxidative challenges. The data suggest that manganese remetallates these or alternative enzymes to allow genomic DNA replication to resume, although with reduced fidelity.IMPORTANCE Iron and manganese play important roles in how cell's cope with oxygen stress. However, how these metals affect the ability of cells to replicate after oxidative challenges is not known. Here, we show that replication in Escherichia coli is inhibited following a challenge with hydrogen peroxide and requires manganese for the rapid recovery of DNA synthesis. The manganese-dependent recovery of DNA synthesis occurs independently of lesion repair and modestly improves survival, but it also increases the mutation rate in cells. The results imply that replication in E. coli is likely to utilize an iron-dependent enzyme(s) that becomes oxidized and inactivated during oxidative challenges. We propose that manganese remetallates these or alternative enzymes to allow genomic DNA replication to resume, although with reduced fidelity.

Sucrose enhances colour formation in dry sausages by up-regulating gene expression of nitric oxide synthase in Staphylococcus vitulinus

The effects of glucose and sucrose on the gene expression of nitric oxide synthase (NOS) in Staphylococcus vitulinus and colour formation in dry sausages were investigated. The results showed that sucrose addition promoted nitric oxide (NO) production in media when compared with glucose. In addition, sucrose could up-regulate nos (encoding NOS) and katA (encoding catalase KatA) gene expression by enhancing oxidative stress levels. In the sausages inoculated with S. vitulinus, a*-values (indicating redness) of the sausages with added sucrose were higher than those of samples with added glucose (P < 0.05) but did not differ from those in the nitrite treatment group (P > 0.05). The UV-vis spectra results showed that nitrosylmyoglobin (NO-Mb) was formed in the sausages with either S. vitulinus or nitrite added. In the S. vitulinus-inoculated sausages, sucrose addition led to a higher NO-Mb content than that after glucose addition, which was attributed to up-regulation of the nos gene. This study provides a potential method to enhance NO yield in S. vitulinus and colour formation in dry sausages without nitrite addition.

The underlying mechanism of calcium peroxide pretreatment enhancing methane production from anaerobic digestion of waste activated sludge

Recent investigations verified that calcium peroxide (CaO₂) could be used to pretreat waste activated sludge to promote methane yield from anaerobic digestion. However, the underlying mechanism of how CaO₂ pretreatment promotes methane production is unclear. This work therefore aims to provide insights into such systems. Experimental results showed that with an increase of CaO₂ dosage from 0 to 0.14 g/g VSS (volatile suspended solids) the methane yield increased linearly from 146.3 to 215.9 mL/g VSS. Further increases of CaO₂ resulted in decreases in methane yield. CaO₂ pretreatment promoted the disintegration of sludge and the degradation of sludge recalcitrant organics (especially humus and lignocellulose), thereby providing more substrates for subsequent methane production. Ultraviolet absorption spectroscopy indicated that CaO₂ enhanced the cleavage of unsaturated conjugated bonds and reduced the aromaticity of humus and lignocellulose. Fourier transform infrared spectroscopy showed that CaO₂ changed the structures and functional groups of humus and lignocellulose, making them transform to be biodegradable. GC/MS analyses exhibited that the degradation products of humus and lignocellulose included several types of small molecular organics such as ester-like, acid-like, and alcohol-like substances. Further investigation demonstrated that substantial methane could be produced from these degradation products. It was also found that the presence of recalcitrant organics was detrimental to anaerobes relevant to anaerobic digestion, and the degradation of such recalcitrant organics mitigated their inhibitions to the anaerobes. Model-based analysis suggested that CaO₂ pretreatment increased the maximum methane yield and methane production rate, which were consistent with the analysis above.

Interaction between Streptococcus pneumoniae and Staphylococcus aureus Generates ·OH Radicals That Rapidly Kill Staphylococcus aureus Strains

Streptococcus pneumoniae rapidly kills Staphylococcus aureus by producing membrane-permeable hydrogen peroxide (H2O2). The mechanism by which S. pneumoniae-produced H2O2 mediates S. aureus killing was investigated. An in vitro model that mimicked S. pneumoniae-S. aureus contact during colonization of the nasopharynx demonstrated that S. aureus killing required outcompeting densities of S. pneumoniae Compared to the wild-type strain, isogenic S. pneumoniae ΔlctO and S. pneumoniae ΔspxB, both deficient in production of H2O2, required increased density to kill S. aureus While residual H2O2 activity produced by single mutants was sufficient to eradicate S. aureus, an S. pneumoniae ΔspxB ΔlctO double mutant was unable to kill S. aureus A collection of 20 diverse methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) strains showed linear sensitivity (R2 = 0.95) for S. pneumoniae killing, but the same strains had different susceptibilities when challenged with pure H2O2 (5 mM). There was no association between the S. aureus clonal complex and sensitivity to either S. pneumoniae or H2O2 To kill S. aureus, S. pneumoniae produced ∼180 μM H2O2 within 4 h of incubation, while the killing-defective S. pneumoniae ΔspxB and S. pneumoniae ΔspxB ΔlctO mutants produced undetectable levels. Remarkably, a sublethal dose (1 mM) of pure H2O2 incubated with S. pneumoniae ΔspxB eradicated diverse S. aureus strains, suggesting that S. pneumoniae bacteria may facilitate conversion of H2O2 to a hydroxyl radical (·OH). Accordingly, S. aureus killing was completely blocked by incubation with scavengers of ·OH radicals, dimethyl sulfoxide (Me2SO), thiourea, or sodium salicylate. The ·OH was detected in S. pneumoniae cells by spin trapping and electron paramagnetic resonance. Therefore, S. pneumoniae produces H2O2, which is rapidly converted to a more potent oxidant, hydroxyl radicals, to rapidly intoxicate S. aureus strains.IMPORTANCEStreptococcus pneumoniae strains produce hydrogen peroxide (H2O2) to kill bacteria in the upper airways, including pathogenic Staphylococcus aureus strains. The targets of S. pneumoniae-produced H2O2 have not been discovered, in part because of a lack of knowledge about the underlying molecular mechanism. We demonstrated that an increased density of S. pneumoniae kills S. aureus by means of H2O2 produced by two enzymes, SpxB and LctO. We discovered that SpxB/LctO-produced H2O2 is converted into a hydroxyl radical (·OH) that rapidly intoxicates and kills S. aureus We successfully inhibited the toxicity of ·OH with three different scavengers and detected ·OH in the supernatant. The target(s) of the hydroxyl radicals represents a new alternative for the development of antimicrobials against S. aureus infections.

Fenton reactions drive nucleotide and ATP syntheses in cancer

We present a computational study of tissue transcriptomic data of 14 cancer types to address: what may drive cancer cell division? Our analyses point to that persistent disruption of the intracellular pH by Fenton reactions may be at the root of cancer development. Specifically, we have statistically demonstrated that Fenton reactions take place in cancer cytosol and mitochondria across all the 14 cancer types, based on cancer tissue gene-expression data integrated via the Michaelis-Menten equation. In addition, we have shown that (i) Fenton reactions in cytosol of the disease cells will continuously increase their pH, to which the cells respond by generating net protons to keep the pH stable through a combination of synthesizing glycolytic ATPs and consuming them by nucleotide syntheses, which may drive cell division to rid of the continuously synthesized nucleotides; and (ii) Fenton reactions in mitochondria give rise to novel ways for ATP synthesis with electrons ultimately coming from H2O2, largely originated from immune cells. A model is developed to link these to cancer development, where some mutations may be selected to facilitate cell division at rates dictated by Fenton reactions.

How do cells cope with RNA damage and its consequences?

Similar to many other biological molecules, RNA is vulnerable to chemical insults from endogenous and exogenous sources. Noxious agents such as reactive oxygen species or alkylating chemicals have the potential to profoundly affect the chemical properties and hence the function of RNA molecules in the cell. Given the central role of RNA in many fundamental biological processes, including translation and splicing, changes to its chemical composition can have a detrimental impact on cellular fitness, with some evidence suggesting that RNA damage has roles in diseases such as neurodegenerative disorders. We are only just beginning to learn about how cells cope with RNA damage, with recent studies revealing the existence of quality-control processes that are capable of recognizing and degrading or repairing damaged RNA. Here, we begin by reviewing the most abundant types of chemical damage to RNA, including oxidation and alkylation. Focusing on mRNA damage, we then discuss how alterations to this species of RNA affect its function and how cells respond to these challenges to maintain proteostasis. Finally, we briefly discuss how chemical damage to noncoding RNAs such as rRNA, tRNA, small nuclear RNA, and small nucleolar RNA is likely to affect their function.

A Tumor-Microenvironment-Activated Nanozyme-Mediated Theranostic Nanoreactor for Imaging-Guided Combined Tumor Therapy

Activatable theranostic agents that can be activated by tumor microenvironment possess higher specificity and sensitivity. Here, activatable nanozyme-mediated 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) loaded ABTS@MIL-100/poly(vinylpyrrolidine) (AMP) nanoreactors (NRs) are developed for imaging-guided combined tumor therapy. The as-constructed AMP NRs can be specifically activated by the tumor microenvironment through a nanozyme-mediated "two-step rocket-launching-like" process to turn on its photoacoustic imaging signal and photothermal therapy (PTT) function. In addition, simultaneously producing hydroxyl radicals in response to the high H₂ O₂ level of the tumor microenvironment and disrupting intracellular glutathione (GSH) endows the AMP NRs with the ability of enhanced chemodynamic therapy (ECDT), thereby leading to more efficient therapeutic outcome in combination with tumor-triggered PTT. More importantly, the H₂ O₂ -activated and acid-enhanced properties enable the AMP NRs to be specific to tumors, leaving the normal tissues unharmed. These remarkable features of AMP NRs may open a new avenue to explore nanozyme-involved nanoreactors for intelligent, accurate, and noninvasive cancer theranostics.

Metabolism and Redox in Pulmonary Vascular Physiology and Pathophysiology

Significance: This review considers how some systems controlling pulmonary vascular function are potentially regulated by redox processes to examine how and why conditions such as prolonged hypoxia, pathological mediators, and other factors promoting vascular remodeling contribute to the development of pulmonary hypertension (PH). Recent Advances and Critical Issues: Aspects of vascular remodeling induction mechanisms described are associated with shifts in glucose metabolism through the pentose phosphate pathway and increased cytosolic NADPH generation by glucose-6-phosphate dehydrogenase, increased glycolysis generation of cytosolic NADH and lactate, mitochondrial dysfunction associated with superoxide dismutase-2 depletion, changes in reactive oxygen species and iron metabolism, and redox signaling. Future Directions: The regulation and impact of hypoxia-inducible factor and the function of cGMP-dependent and redox regulation of protein kinase G are considered for their potential roles as key sensors and coordinators of redox and metabolic processes controlling the progression of vascular pathophysiology in PH, and how modulating aspects of metabolic and redox regulatory systems potentially function in beneficial therapeutic approaches.

Characterization and Expression of Genes Encoding Superoxide Dismutase in the Oriental Armyworm, Mythimna separata (Lepidoptera: Noctuidae)

Superoxide dismutase (SOD) is an antioxidant metalloenzyme that catalyzes the dismutation of the superoxide anion O2- to O2 and H2O2. Many studies have focused on the role of SOD in response to abiotic stress, but its role during biotic stress, such as changes in organismal population density, has rarely been investigated. The oriental armyworm, Mythimna separata, is an economically important pest that exhibits phenotypic changes in response to population density. Solitary and gregarious phases occur at low and high population density, respectively. To examine the role of SODs in response to population density stress, we cloned two genes encoding SOD, MsCuZnSOD and MsMnSOD, and compared their expression in solitary and gregarious phases of M. separata. The MsCuZnSOD and MsMnSOD ORFs were 480 and 651 bp and encoded predicted protein products of 159 and 216 amino acids, respectively. The two SODs contained motifs that are typical of orthologous proteins. Real-time PCR indicated that the two SOD genes were expressed throughout developmental stages and were significantly upregulated in more mature stages of gregarious M. separata. Expression of the two SOD genes in various tissues of sixth-instar larvae was higher in gregarious versus solitary insects. Furthermore, expression of the SOD genes was significantly upregulated in response to crowding in solitary individuals, but suppressed in gregarious insects subjected to isolation. Collectively, these results suggest that population density may be key factor in the induction of SOD genes in M. separata.

Nano-and Micromotors Designed for Cancer Therapy

Research on nano- and micromotors has evolved into a frequently cited research area with innovative technology envisioned for one of current humanities' most deadly problems: cancer. The development of cancer targeting drug delivery strategies involving nano-and micromotors has been a vibrant field of study over the past few years. This review aims at categorizing recent significant results, classifying them according to the employed propulsion mechanisms starting from chemically driven micromotors, to field driven and biohybrid approaches. In concluding remarks of section 2, we give an insight into shape changing micromotors that are envisioned to have a significant contribution. Finally, we critically discuss which important aspects still have to be addressed and which challenges still lie ahead of us.

Oxidative Stress: Role and Response of Short Guanine Tracts at Genomic Locations

Over the decades, oxidative stress has emerged as a major concern to biological researchers. It is involved in the pathogenesis of various lifestyle-related diseases such as hypertension, diabetes, atherosclerosis, and neurodegenerative diseases. The connection between oxidative stress and telomere shortening via oxidative guanine lesion is well documented. Telomeres are confined to guanine rich ends of chromosomes. Owing to its self-association properties, it adopts G-quadruplex structures and hampers the overexpression of telomerase in the cancer cells. Guanine, being the most oxidation prone nucleobase, when structured in G-quadruplex entity, is found to respond peculiarly towards oxidative stress. Interestingly, this non-Watson-Crick structural feature exists abundantly in promoters of various oncogenes, exons and other genomic locations. The involvement of G-quadruplex architecture in oncogene promoters is well recognized in gene regulation processes. Development of small molecules aimed to target G-quadruplex structures, have found to alter the overexpression of oncogenes. The interaction may lead to the obstruction of diseased cell having elevated level of reactive oxygen species (ROS). Thus, presence of short guanine tracts (Gn) forming G-quadruplexes suggests its critical role in oxidative genome damage. Present review is a modest attempt to gain insight on the association of oxidative stress and G-quadruplexes, in various biological processes.

The roles of reactive oxygen species and antioxidants in cryopreservation

Cryopreservation has facilitated advancement of biological research by allowing the storage of cells over prolonged periods of time. While cryopreservation at extremely low temperatures would render cells metabolically inactive, cells suffer insults during the freezing and thawing process. Among such insults, the generation of supra-physiological levels of reactive oxygen species (ROS) could impair cellular functions and survival. Antioxidants are potential additives that were reported to partially or completely reverse freeze-thaw stress-associated impairments. This review aims to discuss the potential sources of cryopreservation-induced ROS and the effectiveness of antioxidant administration when used individually or in combination.

Nanosecond pulsed electric signals can affect electrostatic environment of proteins below the threshold of conformational effects: The case study of SOD1 with a molecular simulation study

Electric fields can be a powerful tool to interact with enzymes or proteins, with an intriguing perspective to allow protein manipulation. Recently, researchers have focused the interest on intracellular enzyme modifications triggered by the application of nanosecond pulsed electric fields. These findings were also supported by theoretical predictions from molecular dynamics simulations focussing on significant variations in protein secondary structures. In this work, a theoretical study utilizing molecular dynamics simulations is proposed to explore effects of electric fields of high intensity and very short nanosecond duration applied to the superoxide dismutase (Cu/Zn-SOD or SOD-1), an important enzyme involved in the cellular antioxidant defence mechanism. The effects of 100-nanosecond pulsed electric fields, with intensities ranging from 108 to 7x108 V/m, on a single SOD1 enzyme are presented. We demonstrated that the lowest intensity of 108 V/m, although not inducing structural changes, can produce electrostatic modifications on the reaction centre of the enzyme, as apparent from the dipolar response and the electric field distribution of the protein active site. Electric pulses above 5x108 V/m produced a fast transition between the folded and a partially denatured state, as inferred by the secondary structures analysis. Finally, for the highest field intensity used (7x108 V/m), a not reversible transition toward an unfolded state was observed.

The role of thiols in antioxidant systems

The sulfur biochemistry of the thiol group endows cysteines with a number of highly specialized and unique features that enable them to serve a variety of different functions in the cell. Typically highly conserved in proteins, cysteines are predominantly found in functionally or structurally crucial regions, where they act as stabilizing, catalytic, metal-binding and/or redox-regulatory entities. As highly abundant low molecular weight thiols, cysteine thiols and their oxidized disulfide counterparts are carefully balanced to maintain redox homeostasis in various cellular compartments, protect organisms from oxidative and xenobiotic stressors and partake actively in redox-regulatory and signaling processes. In this review, we will discuss the role of protein thiols as scavengers of hydrogen peroxide in antioxidant enzymes, use thiol peroxidases to exemplify how protein thiols contribute to redox signaling, provide an overview over the diverse set of low molecular weight thiol-based redox systems found in biology, and illustrate how thiol-based redox systems have evolved not only to protect against but to take full advantage of a world full of molecular oxygen.

A Minor Subpopulation of Mycobacteria Inherently Produces High Levels of Reactive Oxygen Species That Generate Antibiotic Resisters at High Frequency From Itself and Enhance Resister Generation From Its Major Kin Subpopulation

Antibiotic-exposed bacteria produce elevated levels of reactive oxygen species (ROS), to which either they succumb or get mutated genome-wide to generate antibiotic resisters. We recently showed that mycobacterial cultures contained two subpopulations, short-sized cells (SCs; ∼10%) and normal/long-sized cells (NCs; ∼90%). The SCs were significantly more antibiotic-susceptible than the NCs. It implied that the SCs might naturally be predisposed to generate significantly higher levels of ROS than the NCs. This in turn could make the SCs more susceptible to antibiotics or generate more resisters as compared to the NCs. Investigation into this possibility showed that the SCs in the actively growing mid-log phase culture naturally generated significantly high levels of superoxide, as compared to the equivalent NCs, due to the naturally high expression of a specific NADH oxidase in the SCs. This caused labile Fe²⁺ leaching from 4Fe-4S proteins and elevated H₂O₂ formation through superoxide dismutation. Thus, the SCs of both Mycobacterium smegmatis and Mycobacterium tuberculosis inherently contained significantly higher levels of H₂O₂ and labile Fe²⁺ than the NCs. This in turn produced significantly higher levels of hydroxyl radical through Fenton reaction, promoting enhanced antibiotic resister generation from the SCs than from the NCs. The SCs, when mixed back with the NCs, at their natural proportion in the actively growing mid-log phase culture, enhanced antibiotic resister generation from the NCs, to a level equivalent to that from the unfractionated whole culture. The enhanced antibiotic resister generation from the NCs in the reconstituted SCs-NCs natural mixture was found to be due to the high levels of H₂O₂ secreted by the SCs. Thus, the present work unveils and documents the metabolic designs of two mycobacterial subpopulations where one subpopulation produces high ROS levels, despite higher susceptibility, to generate significantly higher number of antibiotic resisters from itself and to enhance resister generation from its kin subpopulation. These findings show the existence of an inherent natural mechanism in both the non-pathogenic and pathogenic mycobacteria to generate antibiotic resisters. The presence of the SCs and the NCs in the pulmonary tuberculosis patients’ sputum, reported by us earlier, alludes to the clinical significance of the study.

Synergistic antibacterial activity of silver nanoparticles and hydrogen peroxide

The increasing challenge of antibiotic resistance requires not only the discovery of new antibiotics, but also the development of new alternative approaches. Herein, the synergistic antibacterial activity of silver nanoparticles and hydrogen peroxide combination is reported. Unlike the bacteriostatic or slightly bactericidal activity achieved by using each agent alone, using these two agents in combination, even at relatively low concentrations, resulted in complete eradication of both the Gram negative Escherichia coli and the Gram positive Staphylococcus aureus in short treatment times indicating a clear synergistic effect between them. Modifying the surface chemistry of silver nanoparticles and the accompanied change in their surface charge enabled a further enhancement of such synergistic effect implying the importance of this aspect. Mechanistically, a Fenton-like reaction between silver nanoparticles and hydrogen peroxide is discussed and hypothesized to be the basis of the observed synergy. Achieving such a significant antibacterial activity at low concentrations reduces the potential toxicity of these agents and hence enables their utilization as an alternative antibacterial approach in wider range of applications.

Vitamin D Treatment Reverses the Induced Oxidative Stress Damage to DNA

BACKGROUND AND OBJECTIVE

The aim of the current study was to investigate in detail the effect of the active metabolite of vitamin D3 [1, 25 (OH)2 D3] in ameliorating the induced oxidative damage to DNA.

MATERIALS AND METHODS

Primary cortical neuron cultures from one week old Wister rats were set up in sterile conditions. The neuron cultures were maintained for up to 72 h in culture in the presence of varying doses of vitamin D. Cells were exposed to (0.5 mM H2O2) for 2 h prior to collection of condition medium and cell pellet for Biochemical Assays. Control and H2O2 treated cultures were maintained without any treatment with vitamin D.

RESULTS

Pre-treatment with 0.25 μg mL-1 for 24 and 48 h significantly reduced the oxidative stress. 8-hydroxydeoxyguanosine a ubiquitous marker of oxidative stress had also shown to be significantly reduced. The DNA damage marker PolyUB of histones was observed in the neuron treated with H2O2 only.

CONCLUSION

This study revealed that oxidation of DNA by hydrogen peroxide caused extensive DNA damage, resulting in polyubiquitination of histones. The pre-treatment with vitamin D3 however completely reversed the DNA damage cascade induced by hydrogen peroxide and protected the DNA.

Rescue of DNA damage after constricted migration reveals a mechano-regulated threshold for cell cycle

Migration through 3D constrictions can cause nuclear rupture and mislocalization of nuclear proteins, but damage to DNA remains uncertain, as does any effect on cell cycle. Here, myosin II inhibition rescues rupture and partially rescues the DNA damage marker γH2AX, but an apparent block in cell cycle appears unaffected. Co-overexpression of multiple DNA repair factors or antioxidant inhibition of break formation also exert partial effects, independently of rupture. Combined treatments completely rescue cell cycle suppression by DNA damage, revealing a sigmoidal dependence of cell cycle on excess DNA damage. Migration through custom-etched pores yields the same damage threshold, with ∼4-µm pores causing intermediate levels of both damage and cell cycle suppression. High curvature imposed rapidly by pores or probes or else by small micronuclei consistently associates nuclear rupture with dilution of stiff lamin-B filaments, loss of repair factors, and entry from cytoplasm of chromatin-binding cGAS (cyclic GMP-AMP synthase). The cell cycle block caused by constricted migration is nonetheless reversible, with a potential for DNA misrepair and genome variation.

A Short Review of Iron Metabolism and Pathophysiology of Iron Disorders

Iron is a vital trace element for humans, as it plays a crucial role in oxygen transport, oxidative metabolism, cellular proliferation, and many catalytic reactions. To be beneficial, the amount of iron in the human body needs to be maintained within the ideal range. Iron metabolism is one of the most complex processes involving many organs and tissues, the interaction of which is critical for iron homeostasis. No active mechanism for iron excretion exists. Therefore, the amount of iron absorbed by the intestine is tightly controlled to balance the daily losses. The bone marrow is the prime iron consumer in the body, being the site for erythropoiesis, while the reticuloendothelial system is responsible for iron recycling through erythrocyte phagocytosis. The liver has important synthetic, storing, and regulatory functions in iron homeostasis. Among the numerous proteins involved in iron metabolism, hepcidin is a liver-derived peptide hormone, which is the master regulator of iron metabolism. This hormone acts in many target tissues and regulates systemic iron levels through a negative feedback mechanism. Hepcidin synthesis is controlled by several factors such as iron levels, anaemia, infection, inflammation, and erythropoietic activity. In addition to systemic control, iron balance mechanisms also exist at the cellular level and include the interaction between iron-regulatory proteins and iron-responsive elements. Genetic and acquired diseases of the tissues involved in iron metabolism cause a dysregulation of the iron cycle. Consequently, iron deficiency or excess can result, both of which have detrimental effects on the organism.

Endonucleases responsible for DNA repair of helix-distorting DNA lesions in the thermophilic crenarchaeon Sulfolobus acidocaldarius in vivo

The DNA repair mechanisms of hyperthermophiles can provide important insights for understanding how genetic information is maintained under extreme environments. Recent biochemical studies have identified a novel endonuclease in hyperthermophilic archaea, NucS/EndoMS, that acts on branched DNA substrates and mismatched bases. NucS/EndoMS is thought to participate in the DNA repair of helix-distorting DNA lesions, including UV-induced DNA damage and DNA adducts, and mismatched bases; however, the specific in vivo role of NucS/EndoMS in hyperthermophilic archaeal DNA repair has not been reported. To explore the role of this protein, we knocked out the nucS/endoMS gene of the thermophilic crenarchaeon Sulfolobus acidocaldarius and characterized the mutant phenotypes. While the nucS/endoMS-deleted strain exhibited sensitivity to DNA adducts, it did not have high mutation rates or any sensitivity to UV irradiation. It has been proposed that the XPF endonuclease is involved in homologous recombination-mediated stalled-fork DNA repair. The xpf-deficient strain exhibited sensitivity to helix-distorting DNA lesions, but the sensitivity of the nucS/endoMS and xpf double knockout strain did not increase compared to that of the single knockout strains. We conclude that the endonuclease NucS/EndoMS works with XPF in homologous recombination-mediated stalled-fork DNA repair for the removal of helix-distorting DNA lesions in S. acidocaldarius.

Thermal behaviors and harmful volatile constituents released from asphalt components at high temperature

Asphalt binder releases lots of heat and harmful volatiles at high temperature. To further understand thermal behaviors, dynamic release and toxic constituents of emitted volatiles during the combustion of asphalt binder, such fractions as saturates, aromatics, resins and asphaltenes (SARA) were first prepared. Thermal behaviors, volatile constituents and combustion residue microstructures of SARA fractions are discussed. Results indicate that polymerization degree of asphalt binder is high and the content of polycyclic aromatic compounds is large. Combustion processes of resins and asphaltenes only show single-stage exothermic reactions, but other two fractions present obvious multi-stage combustion reactions. As the heating rate is raised, the incomplete combustion of SARA fractions is increased, and more volatiles are released. Main volatiles released from SARA fractions are inflammable, toxic, corrosive or explosive compounds, and such common volatiles as acetaldehyde and propane are released from each SARA fraction. More toxic volatiles are released at combustion stage I, but macromolecular volatiles are mainly released at stage II. Volatile release behaviors of saturates and aromatics are more obviously affected by the heating rate. Combustion residues show more intact morphologies from saturates to asphaltenes, and mainly contain C, O and S elements. Asphalt binder is hazardous material at high temperature.

Long-Term Risks of Intravenous Iron in End-Stage Renal Disease Patients

Patients with end-stage renal disease on dialysis commonly receive intravenous iron to treat anemia along with erythropoiesis-stimulating agents. While studies of intravenous iron have demonstrated efficacy in raising hemoglobin, the quantity of administered intravenous iron has raised concerns about iron overload leading to long-term toxicities. The goal of this review is to understand recent trends in intravenous iron use, potential mechanisms of iron toxicity, and to evaluate the available evidence in the literature for potential long-term cardiovascular and infectious complications. We include findings from the recently published landmark clinical trial of intravenous iron for patients receiving hemodialysis to contextualize treatment recommendations.

Mitochondrial DNA, nuclear context, and the risk for carcinogenesis

The inheritance of mitochondrial DNA (mtDNA) from mother to child is complicated by differences in the stability of the mitochondrial genome. Although the germ line mtDNA is protected through the minimization of replication between generations, sequence variation can occur either through mutation or due to changes in the ratio between distinct genomes that are present in the mother (known as heteroplasmy). Thus, the unpredictability in transgenerational inheritance of mtDNA may cause the emergence of pathogenic mitochondrial and cellular phenotypes in offspring. Studies of the role of mitochondrial metabolism in cancer have a long and rich history, but recent evidence strongly suggests that changes in mitochondrial genotype and phenotype play a significant role in the initiation, progression and treatment of cancer. At the intersection of these two fields lies the potential for emerging mtDNA mutations to drive carcinogenesis in the offspring. In this review, we suggest that this facet of transgenerational carcinogenesis remains underexplored and is a potentially important contributor to cancer. Environ. Mol. Mutagen. 60:455-462, 2019. © 2018 Wiley Periodicals, Inc.

Hydrogen peroxide and cutaneous biology: Translational applications, benefits, and risks

Hydrogen peroxide (H₂O₂) is an endogenous reactive oxygen species that contributes to oxidative stress directly as a molecular oxidant and indirectly through free radical generation. Topically applied 1% to 45% H₂O₂ can be used for a range of clinical purposes, which will be reviewed here in addition to its safety. In concentrations from 1% to 6%, H₂O₂ has antimicrobial properties and can act as a debriding agent through its effervescence, making low-concentration H₂O₂ useful for wound care. H₂O₂ has also been shown to promote venous insufficiency ulcer healing, but studies in other wound types are needed. In 1% formulations, H₂O₂ is used outside the United States to treat acne and has shown efficacy similar to or greater than benzoyl peroxide, with reduced side effects. In a concentration of 40%, H₂O₂ is US Food and Drug Administration-approved to treat seborrheic keratoses and may cause fewer pigmentary changes than cryotherapy, although elimination often requires 2 to 4 treatments. However, H₂O₂ should be used with caution, as exposure can cause adverse effects through its oxidant capabilities. Low H₂O₂ concentrations cause only transient symptoms (blanching and blistering), but exposure to 9% to 45% H₂O₂ can cause more severe skin damage, including epidermal necrosis leading to erythema and bullae. Overall, H₂O₂ has numerous therapeutic uses, and novel indications, such as treating actinic keratoses and skin cancers, continue to be explored.

Apotransferrin in Combination with Ciprofloxacin Slows Bacterial Replication, Prevents Resistance Amplification, and Increases Antimicrobial Regimen Effect

There has been renewed interest in combining traditional small-molecule antimicrobial agents with nontraditional therapies to potentiate antimicrobial effects. Apotransferrin, which decreases iron availability to microbes, is one such approach. We conducted a 48-h one-compartment in vitro infection model to explore the impact of apotransferrin on the bactericidal activity of ciprofloxacin. The challenge panel included four Klebsiella pneumoniae isolates with ciprofloxacin MIC values ranging from 0.08 to 32 mg/liter. Each challenge isolate was subjected to an ineffective ciprofloxacin monotherapy exposure (free-drug area under the concentration-time curve over 24 h divided by the MIC [AUC/MIC ratio] ranging from 0.19 to 96.6) with and without apotransferrin. As expected, the no-treatment and apotransferrin control arms showed unaltered prototypical logarithmic bacterial growth. We identified relationships between exposure and change in bacterial density for ciprofloxacin alone (R2 = 0.64) and ciprofloxacin in combination with apotransferrin (R2 = 0.84). Addition of apotransferrin to ciprofloxacin enabled a remarkable reduction in bacterial density across a wide range of ciprofloxacin exposures. For instance, at a ciprofloxacin AUC/MIC ratio of 20, ciprofloxacin monotherapy resulted in nearly 2 log10 CFU increase in bacterial density, while the combination of apotransferrin and ciprofloxacin resulted in 2 log10 CFU reduction in bacterial density. Furthermore, addition of apotransferrin significantly reduced the emergence of ciprofloxacin-resistant subpopulations compared to monotherapy. These data demonstrate that decreasing the rate of bacterial replication with apotransferrin in combination with antimicrobial therapy represents an opportunity to increase the magnitude of the bactericidal effect and to suppress the growth rate of drug-resistant subpopulations.

Nanocatalysts-augmented Fenton chemical reaction for nanocatalytic tumor therapy

It is the challenging goal in cancer biomedicine to search novel cancer-therapeutic modality with concurrent high therapeutic efficiency on combating cancer and low side effects to normal cells/tissues. The recently developed nanocatalytic cancer therapy based on catalytic Fenton reaction represents one of the promising paradigms for potential clinical translation, which has got fast progress very recently. This progress report discusses the rational design and fabrication of Fenton reaction-based nanocatalysts for triggering the in-situ Fenton chemical reaction within tumor microenvironment to generate highly toxic hydroxyl radicals (•OH), which is highly efficient for killing the cancer cells and suppressing the tumor growth. Several strategies for optimizing the nanocatalytic cancer-therapeutic efficiency of Fenton reaction have been highlighted, including screening high-performance Fenton nanocatalysts, increasing peroxide-hydrogen amounts as the reactants, changing the Fenton-reaction conditions (e.g., temperature, acidity and photo-triggering), and Fenton reaction-based synergistic cancer therapy such as some sequential nanocatalytic reactions with improved therapeutic outcome. The facing challenges and future developments of Fenton reaction-based nanocatalytic cancer therapy are also discussed for further promoting the clinical translation of this emerging cancer-therapeutic modality to benefit the cancer patients.

Alarmone Ap4A is elevated by aminoglycoside antibiotics and enhances their bactericidal activity

This paper demonstrates that aminoglycoside antibiotics induce the production of the Ap4A in bacteria. Increased intracellular Ap4A, in turn, promotes bacterial cell killing by this class of antibiotics, which correlated well with elevated damage to the bacterial membrane upon aminoglycoside treatment. These findings reveal a striking connection between aminoglycoside killing and the Ap4A production particularly under conditions of oxidative stress. Importantly, the results of this study suggest that targeting Ap4A degradation or inducing its hypersynthesis during therapy with aminoglycosides might help solve the well-known toxicity issue associated with this class of antibiotics by reducing the level of drug needed for effective treatment.

Second messenger molecules play important roles in the responses to various stimuli that can determine a cell's fate under stress conditions. Here, we report that lethal concentrations of aminoglycoside antibiotics result in the production of a dinucleotide alarmone metabolite–diadenosine tetraphosphate (Ap4A), which promotes bacterial cell killing by this class of antibiotics. We show that the treatment of Escherichia coli with lethal concentrations of kanamycin (Kan) dramatically increases the production of Ap4A. This elevation of Ap4A is dependent on the production of a hydroxyl radical and involves the induction of the Ap4A synthetase lysyl-tRNA synthetase (LysU). Ectopic alteration of intracellular Ap4A concentration via the elimination of the Ap4A phosphatase diadenosine tetraphosphatase (ApaH) and the overexpression of LysU causes over a 5,000-fold increase in bacterial killing by aminoglycosides. This increased susceptibility to aminoglycosides correlates with bacterial membrane disruption. Our findings provide a role for the alarmone Ap4A and suggest that blocking Ap4A degradation or increasing its synthesis might constitute an approach to enhance aminoglycoside killing potency by broadening their therapeutic index and thereby allowing lower nontoxic dosages of these antibiotics to be used in the treatment of multidrug-resistant infections.

Redox Mechanisms in Neurodegeneration: From Disease Outcomes to Therapeutic Opportunities

SIGNIFICANCE

Once considered to be mere by-products of metabolism, reactive oxygen, nitrogen and sulfur species are now recognized to play important roles in diverse cellular processes such as response to pathogens and regulation of cellular differentiation. It is becoming increasingly evident that redox imbalance can impact several signaling pathways. For instance, disturbances of redox regulation in the brain mediate neurodegeneration and alter normal cytoprotective responses to stress. Very often small disturbances in redox signaling processes, which are reversible, precede damage in neurodegeneration. Recent Advances: The identification of redox-regulated processes, such as regulation of biochemical pathways involved in the maintenance of redox homeostasis in the brain has provided deeper insights into mechanisms of neuroprotection and neurodegeneration. Recent studies have also identified several post-translational modifications involving reactive cysteine residues, such as nitrosylation and sulfhydration, which fine-tune redox regulation. Thus, the study of mechanisms via which cell death occurs in several neurodegenerative disorders, reveal several similarities and dissimilarities. Here, we review redox regulated events that are disrupted in neurodegenerative disorders and whose modulation affords therapeutic opportunities.

CRITICAL ISSUES

Although accumulating evidence suggests that redox imbalance plays a significant role in progression of several neurodegenerative diseases, precise understanding of redox regulated events is lacking. Probes and methodologies that can precisely detect and quantify in vivo levels of reactive oxygen, nitrogen and sulfur species are not available.

FUTURE DIRECTIONS

Due to the importance of redox control in physiologic processes, organisms have evolved multiple pathways to counteract redox imbalance and maintain homeostasis. Cells and tissues address stress by harnessing an array of both endogenous and exogenous redox active substances. Targeting these pathways can help mitigate symptoms associated with neurodegeneration and may provide avenues for novel therapeutics. Antioxid. Redox Signal. 30, 1450-1499.