Redox Buffering Capacity Research Articles

Endurance Exercise-induced Anabolic Balance And Redox Buffering Capacity Is Associated With Mitochondrial Fusion

Endurance Exercise-induced Anabolic Balance And Redox Buffering Capacity Is Associated With Mitochondrial Fusion

Ablating the glutaredoxin-2 (Glrx2) gene protects male mice against non-alcoholic fatty liver disease (NAFLD) by limiting oxidative distress

In the present study, we investigated the consequences of deleting the glutaredoxin-2 gene (Glrx2−/−) on the development of non-alcoholic fatty liver disease (NAFLD) in male and female C57BL6N mice fed a control (CD) or high-fat diet (HFD). We report that the HFD induced a significant increase in body mass in the wild-type (Wt) and Glrx2−/− male, but not female, mice, which was associated with the hypertrophying of the abdominal fat. Interestingly, while the Wt male mice fed the HFD developed NAFLD, the deletion of the Glrx2 gene mitigated vesicle formation, intrahepatic lipid accumulation, and fibrosis in the males. The protective effect associated with ablating the Glrx2 gene in male mice was due to enhancement of mitochondrial redox buffering capacity. Specifically, liver mitochondria from male Glrx2−/− fed a CD or HFD produced significantly less hydrogen peroxide (mtH2O2), had lower malondialdehyde levels, greater activities for glutathione peroxidase and thioredoxin reductase, and less protein glutathione mixed disulfides (PSSG) when compared to the Wt male mice fed the HFD. These effects correlated with the S-glutathionylation of α-ketoglutarate dehydrogenase (KGDH), a potent mtH2O2 source and key redox sensor in hepatic mitochondria. In comparison to the male mice, both Wt and Glrx2−/− female mice displayed almost complete resistance to HFD-induced body mass increases and the development of NAFLD, which was attributed to the superior redox buffering capacity of the liver mitochondria. Together, our findings show that modulation of mitochondrial S-glutathionylation signaling through Glrx2 augments resistance of male mice towards the development of NAFLD through preservation of mitochondrial redox buffering capacity. Additionally, our findings demonstrate the sex dimorphisms associated with the manifestation of NAFLD is related to the superior redox buffering capacity and modulation of the S-glutathionylome in hepatic mitochondria from female mice.

A study of scarless wound healing through programmed inflammation, proliferation and maturation using a redox balancing nanogel.

In the study, we have shown the efficacy of an indigenously developed redox balancing chitosan gel with impregnated citrate capped Mn3O4 nanoparticles (nanogel). Application of the nanogel on a wound of preclinical mice model shows role of various signaling molecules and growth factors, and involvement of reactive oxygen species (ROS) at every stage, namely hemostasis, inflammation, and proliferation leading to complete maturation for the scarless wound healing. While in vitro characterization of nanogel using SEM, EDAX, and optical spectroscopy reveals pH regulated redox buffering capacity, in vivo preclinical studies on Swiss albino involving IL-12, IFN-γ, and α-SMA signaling molecules and detailed histopathological investigation and angiogenesis on every stage elucidate role of redox buffering for the complete wound healing process.

Chitosan functionalized Mn3O4 nanoparticles counteracts ulcerative colitis in mice through modulation of cellular redox state

Recent findings suggest a key role for reactive oxygen species (ROS) in the pathogenesis and progression of ulcerative colitis (UC). Several studies have also highlighted the efficacy of citrate functionalized Mn3O4 nanoparticles as redox medicine against a number of ROS-mediated disorders. Here we show that synthesized nanoparticles consisting of chitosan functionalized tri-manganese tetroxide (Mn3O4) can restore redox balance in a mouse model of UC induced by dextran sulfate sodium (DSS). Our in-vitro characterization of the developed nanoparticle confirms critical electronic transitions in the nanoparticle to be important for the redox buffering activity in the animal model. A careful administration of the developed nanoparticle not only reduces inflammatory markers in the animals, but also reduces the mortality rate from the induced disease. This study provides a proof of concept for the use of nanomaterial with synergistic anti-inflammatory and redox buffering capacity to prevent and treat ulcerative colitis.

Characterization of Manganese Oxide Modified Activated Carbon for Remediation of Redox-Sensitive Contaminants

Manganese oxide modified activated carbon (MOMAC) was synthesized as a novel in situ sediment and soil amendment for treatment of redox-sensitive contaminants, such as mercury (Hg), through buffering of reduction–oxidation (redox) potential and sorption. This study characterized MOMAC synthesis products at three different Mn concentrations on activated carbon (AC) surfaces and compared them with homogeneously precipitated Mn oxide (MnOx) and unmodified AC for properties influencing redox buffering and sorption capacity. Bulk spectroscopic analyses (XAS and XPS), XRD, and electron microscopy showed that homogeneous MnOx matched the local structure of vernadite (δ-Mn(IV)O2), while MOMAC formed aggregates on the AC surface composed mostly of vernadite with fractions of manganite (γ-Mn(III)OOH) (17–46%) and sorbed Mn(II) (11–21%). Higher bulk surface area and lower Mn average oxidation state were associated with MOMAC and are attributed to the reduction of Mn(IV) by Mn(II) adsorbed on AC or diffused into AC pores. Cation exchange reactions of Na+ and Ca2+ also contributed to Mn oxidation state changes by driving disproportionation of Mn(III) to Mn(II) and Mn(IV). In batch slurry experiments with and without Hg-contaminated sediment from Oak Ridge National Laboratory (TN, U.S.A.), addition of MOMAC and MnOx resulted in higher solution redox potential and lower pH compared to AC and no-amendment controls. MnOx poised solution redox at higher potential than MOMAC, but MOMAC was more effective at sorbing Hg released by the oxidation of sediment HgS(s), Hg0, and/or organic-associated Hg. By combining redox buffering with sorption, MOMAC is a promising in situ amendment that may efficiently target redox-sensitive contaminants in aquatic sediments.

Multi-Omics Approach Reveals Redox Homeostasis Reprogramming in Early-Stage Clear Cell Renal Cell Carcinoma.

Clear cell renal cell carcinoma (ccRCC) is a malignant tumor originating from proximal tubular epithelial cells, and despite extensive research efforts, its redox homeostasis characteristics and protein S-nitrosylation (or S-nitrosation) (SNO) modification remain largely undefined. This serves as a reminder that the aforementioned features demand a comprehensive inspection. We collected tumor samples and paracancerous normal samples from five patients with early-stage ccRCC (T1N0M0) for proteomic, SNO-proteome, and redox-targeted metabolic analyses. The localization and functional properties of SNO proteins in ccRCC tumors and paracancerous normal tissues were elucidated for the first time. Several highly useful ccRCC-associated SNO proteins were further identified. Metabolic reprogramming, redox homeostasis reprogramming, and tumorigenic alterations are the three major characteristics of early-stage ccRCC. Peroxidative damage caused by rapid proliferation coupled with an increased redox buffering capacity and the antioxidant pool is a major mode of redox homeostasis reprogramming. NADPH and NADP+, which were identified from redox species, are both effective biomarkers and promising therapeutic targets. According to our findings, SNO protein signatures and redox homeostasis reprogramming are valuable for understanding the pathogenesis of ccRCC and identifying novel topics that should be seriously considered for the diagnosis and precise therapy of ccRCC.

Geochemistry and palaeo-hydrogeology of the weathered zone in the Opalinus Clay

The effects of weathering and decompaction on the Opalinus Clay in northern Switzerland were studied on the basis of a 146 m long drillcore profile. Below 6 m of Quaternary sediments, the rock down to 16 m depth is affected by partial or complete dissolution of siderite, calcite, pyrite and organic matter, with goethite as the only identified product. The reduction level of Fe (Fe2+/Fetot) in the rock increases with depth from <20% to >80% in unweathered rock below 24 m. Porosity reaches 0.39 in the shallowest samples before dropping to normal values of around 0.13 below 30 m. Pore-water composition obtained by rock squeezing evolves with depth from fresh water of the Ca-SO4-HCO3 type to a 10–12 g/L Na-SO4-Cl type in unweathered rock below 40 m. Ground-water samples taken in the weathered zone indicate reducing conditions at present and therefore reflect a remaining redox buffering capacity even in the strongly oxidised rock. The interpretation of the rock properties, in conjunction with the chemical and isotopic signatures of ground and pore waters, suggests that substantial weathering occurred primarily during stages with a lower ground-water table in the Pleistocene, providing access to oxygen via gas diffusion across the partially unsaturated zone. Three evolutionary stages can be distinguished: 1) Long-term pyrite oxidation during Pleistocene surface exposure under dry climate and diffusive transport of SO42− into the formation. This explains the higher SO42− pore-water concentrations even in the unweathered rock at depth when compared to regional data from deep boreholes. 2) Build-up of the curved Cl− and water-isotope diffusion profiles since ∼50–60 ka with a depth penetration of 40–80 m. 3) Holocene rise of the water table, leading to self sealing of fractures and the establishment of a diffusive regime in the weathered zone. Under saturated conditions, the depth penetration of rock oxidation is quite limited, which illustrates the substantial buffering capacity of the Opalinus Clay against external geochemical disturbances.

Mycobacterium tuberculosis SufR responds to nitric oxide via its 4Fe–4S cluster and regulates Fe–S cluster biogenesis for persistence in mice

The persistence of Mycobacterium tuberculosis (Mtb) is a major problem in managing tuberculosis (TB). Host-generated nitric oxide (NO) is perceived as one of the signals by Mtb to reprogram metabolism and respiration for persistence. However, the mechanisms involved in NO sensing and reorganizing Mtb's physiology are not fully understood. Since NO damages iron-sulfur (Fe–S) clusters of essential enzymes, the mechanism(s) involved in regulating Fe–S cluster biogenesis could help Mtb persist in host tissues. Here, we show that a transcription factor SufR (Rv1460) senses NO via its 4Fe–4S cluster and promotes persistence of Mtb by mobilizing the Fe–S cluster biogenesis system; suf operon (Rv1460-Rv1466). Analysis of anaerobically purified SufR by UV–visible spectroscopy, circular dichroism, and iron-sulfide estimation confirms the presence of a 4Fe–4S cluster. Atmospheric O2 and H2O2 gradually degrade the 4Fe–4S cluster of SufR. Furthermore, electron paramagnetic resonance (EPR) analysis demonstrates that NO directly targets SufR 4Fe–4S cluster by forming a protein-bound dinitrosyl-iron-dithiol complex. DNase I footprinting, gel-shift, and in vitro transcription assays confirm that SufR directly regulates the expression of the suf operon in response to NO. Consistent with this, RNA-sequencing of MtbΔsufR demonstrates deregulation of the suf operon under NO stress. Strikingly, NO inflicted irreversible damage upon Fe–S clusters to exhaust respiratory and redox buffering capacity of MtbΔsufR. Lastly, MtbΔsufR failed to recover from a NO-induced non-growing state and displayed persistence defect inside immune-activated macrophages and murine lungs in a NO-dependent manner. Data suggest that SufR is a sensor of NO that supports persistence by reprogramming Fe–S cluster metabolism and bioenergetics.

Redox Buffering Capacity of Nanomaterials as an Index of ROS-Based Therapeutics and Toxicity: A Preclinical Animal Study.

Precise control of intracellular redox status, i.e., maintenance of the physiological level of reactive oxygen species (ROS) for mediating normal cellular functions (oxidative eustress) while evading the excess ROS stress (distress), is central to the concept of redox medicine. In this regard, engineered nanoparticles with unique ROS generation, transition, and depletion functions have the potential to be the choice of redox therapeutics. However, it is always challenging to estimate whether ROS-induced intracellular events are beneficial or deleterious to the cell. Here, we propose the concept of redox buffering capacity as a therapeutic index of engineered nanomaterials. As a steady redox state is maintained for normal functioning cells, we hypothesize that the ability of a nanomaterial to preserve this homeostatic condition will dictate its therapeutic efficacy. Additionally, the redox buffering capacity is expected to provide information about the nanoparticle toxicity. Here, using citrate-functionalized trimanganese tetroxide nanoparticles (C-Mn3O4 NPs) as a model nanosystem, we explored its redox buffering capacity in erythrocytes. Furthermore, we went on to study the chronic toxic effect (if any) of this nanomaterial in the animal model to co-relate with the experimentally estimated redox buffering capacity. This study could function as a framework for assessing the capability of a nanomaterial as redox medicine (whether maintains eustress or damages by creating distress), thus orienting its application and safety for clinical use.

Dysmetabolisms Can Affect Total Antioxidant Capacity (TAC) of Human Plasma: Determination of Reference Intervals of TAC by Way of CUPRAC-BCS Method.

The total antioxidant capacity (TAC) of human plasma is an index of the redox buffer capacity of this biological fluid and could be a biomarker for those disorders affecting redox status. Distinguishing physiological from pathological conditions needs a reference. Therefore, this work aims to define the reference intervals for TAC of human plasma of apparently healthy adult individuals. TAC was measured using the CUPRAC-BCS (CUPric reducing antioxidant capacity-bathocuproinedisulfonic acid) method previously optimized and tested in a clinical laboratory. A population of 500 blood donors was selected, plus an additional 222 pathological patients carrying specific defective metabolisms, namely, hyperuricemia, hyperbilirubinemia, and type 2 diabetic mellitus. The reference intervals of TAC were calculated according to international guidelines. Due to the response of a partitioning test, the reference intervals for healthy population were separately defined for male (258) and female (151) groups. The reference intervals (µmol L−1) resulted: 727–1248 for the male subgroup and 637–1048 for the female subgroup. The absence of an age effect on TAC values was verified. The reference intervals evaluated allow a discussion on some pathological conditions overloading the plasma with redox-active waste substances.

Conjugated redox polymer with poly(3,4-ethylenedioxythiophene) backbone and hydroquinone pendant groups as the solid contact in potassium-selective electrodes

We have used for the first time a conjugated redox polymer with hydroquinone (HQ) pendant groups covalently attached to the poly(3,4-ethylenedioxythiophene) (PEDOT) backbone as the solid contact (SC) in plasticized poly(vinyl chloride) (PVC) based K+-selective electrodes (K-SCISE). Redox couples are one of the simplest ways to precisely adjust the standard potential (E°) of the SCISEs, but usually the initially high E° reproducibility is lost quite quickly due to leaching out of non-covalently bound redox molecules from the SCISE. In PEDOT-HQ, the covalently attached HQ groups prevent the leaching and simultaneously allow additional charge storage in PEDOT-HQ that is ca. 25–30 times higher than for unsubstituted PEDOT. Before the ion-selective membrane (ISM) deposition, we controlled the potential of the SC with high reproducibility (±0.4 mV, n = 5) by pre-polarization in a mixture of acetonitrile containing potassium tetrakis(pentafluorophenyl)borate and perchloric acid as proton source. Pre-polarization of the SC close to the formal potential where the redox buffer capacity is highest gave the best potential reproducibility. However, after the ISM deposition, the K-SCISEs showed in the best case an E° reproducibility of ±2.8 mV (n = 5). Chronopotentiometric measurements reveal that only a minor fraction of the very high redox capacitance of PEDOT-HQ can be utilized for the ion-to-electron transduction beneath the ISM. The influence of this shortcoming on the E° reproducibility of the SCISEs has been underestimated for most SC materials. Modification of the commonly used PVC-ISM formulations to allow faster ion transfer at the SC/ISM interface could be one way of overcoming the disadvantage.

A rapid colorimetric method for determining glutathione based on the reaction between cobalt oxyhydroxide nanosheets and 3,3′,5,5′-Tetramethylbenzidine

As an antioxidant, glutathione (GSH) can react with reactive oxygen species (ROS) and heavy metals to help alleviate oxidative stress (OS) and damage in cells. Accurately measuring the GSH level is important to gauge the integrity of cell redox buffering capacity. In this work, a convenient method for qualitative and quantitative determination of GSH was developed based on the reaction between CoOOH nanosheets and 3,3′,5,5′-tetramethylbenzidine (TMB). Colorless TMB solution can be oxidized by CoOOH to oxidized TMB (oxTMB) which is blue in color. However, in the presence of GSH, CoOOH preferentially reacted with GSH, producing less oxTMB and lighting the blue color. The changes of the blue color of oxTMB can be directly observed by naked eyes and accurately measured by UV–vis absorbance at 652 nm. Based on that, GSH can be detected in a wide range from 0.1 to 300 µM with a low limit of detection of 0.08 μM which was performed with a quantitativehigh-throughput96-wellplate. In addition, GSH in human SH-SY5Y neuroblastoma cells was successfully determined using our method, and the results show excellent agreement with those measured by a commercial GSH detection kit based on the use of Ellman’s reagent.

Oxidative stress and antioxidant metabolites in wheat (Triticum aestivum L.) varieties during grain development under water deficit conditions

Two wheat (Triticum aestivum L.) varieties viz. WH 1105 and WH 1025 are subjected to drought stress. The non enzymatic antioxidant defense system which contains antioxidant metabolites such as ascorbic acid, glutathione and carotenoids contents were studied in drought sensitive and drought resistant varieties days after anthesis (DAA) in leaf and grain samples. As part of protective mechanism against drought, wheat plants produced more of ascorbic acid and glutathione with a concomitant decrease in carotenoid content. The increase in ascorbic acid and glutathione were more in WH 1025 than WH 1105. Carotenoids protect plants by minimizing ROS formation by quenching oxygen. The reduction in carotenoid content was observed in both wheat varieties days after anthesis (DAA) in leaf and grain samples but more reduction was observed in WH 1105 which is a drought sensitive variety of wheat. These antioxidant metabolites played a key role in protecting wheat plants against reactive oxygen species (ROS) mediated oxidative damage and their redox buffering capacity generates stress tolerance in drought tolerant wheat variety WH 1025.

Exercise-mediated downregulation of MALAT1 expression and implications in primary and secondary cancer prevention

Long non-coding RNAs (lncRNAs) play critical roles in various biological functions and disease processes including cancer. The metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) was initially identified as a lncRNA with elevated expression in primary human non-small cell lung tumors with high propensity to metastasize, and subsequently shown to be highly expressed in numerous other human cancers including breast, ovarian, prostate, cervical, endometrial, gastric, pancreatic, sarcoma, colorectal, bladder, brain, multiple myeloma, and lymphoma.MALAT1 is deeply involved in several physiological processes, including alternative splicing, epigenetic modification of gene expression, cellular senescence, healthy aging, and redox homeostasis.The aim of this work was to investigate the modulation exerted by a single bout of endurance exercise on the level of MALAT1 expression in peripheral blood mononuclear cells (PBMCs) from healthy male donors displaying different training status and redox homeostasis features. Our findings show that MALAT1 is downregulated after acute endurance exercise in subjects whose fitness level guarantee a high expression of SOD1 and SOD2 antioxidant genes and low levels of endogenous oxidative damage. In vitro protocols in Jurkat lymphoblastoid cells exposed to pro-oxidant environment confirmed the link between MALAT1 expression and antioxidant gene modulation, documenting p53 phosphorylation and its recruitment to MALAT1 promoter. Remarkably, analyses of Microarray-Based Gene Expression Profiling revealed high MALAT1 expression in leukemia patients in comparison to healthy control and a significant negative correlation between MALAT1 and SOD1 expression.Collectively our results highlight the beneficial effect of a physically active lifestyle in counteracting aberrant cancer-related gene expression programs by improving the redox buffering capacity.

Glucose, glycolysis, and neurodegenerative diseases.

Prolonged survival of a typical postmitotic neuron hinges on a balance between multiple processes, among these are a sustenance of ATP production and protection against reactive oxygen species. In neuropathological conditions, mitochondrial defects often lead to both a drop in ATP levels, as well as increase reactive oxygen species production from inefficient electron transport processes and NADPH-oxidases activities. The former often resulted in the phenomenon of compensatory aerobic glycolysis. The latter stretches the capacity of the cell's redox buffering capacity, and may lead to damages of key enzymes involved in energy metabolism. Several recent reports have indicated that enhancing glucose availability and uptake, as well as increasing glycolytic flux via pharmacological or genetic manipulation of glycolytic enzymes, could be protective in animal models of several major neurodegenerative diseases, including Parkinson's disease, Huntington's disease, and Amyotrophic lateral sclerosis. Activation of canonical Wnt signaling, which improves disease symptoms in mouse models of Alzheimer's disease also appears to work via an elevation of glycolytic enzymes and enhance glucose metabolism. Here, I discuss these findings and the possible underlying mechanisms of how an increase in glucose uptake and glycolysis could be neuroprotective. Increased glycolytic production of ATP would help alleviate energy deficiency, and ATP's hydrotropic effect may enhance solubility and clearance of toxic aggregates prevalent in many neurodegenerative diseases. Furthermore, channeling of glucose into the Pentose Phosphate Pathway would increase the redox buffering capacity of the cell.

Neuronal Activity and Its Role in Controlling Antioxidant Genes.

Forebrain neurons have relatively weak intrinsic antioxidant defenses compared to astrocytes, in part due to hypo-expression of Nrf2, an oxidative stress-induced master regulator of antioxidant and detoxification genes. Nevertheless, neurons do possess the capacity to auto-regulate their antioxidant defenses in response to electrical activity. Activity-dependent Ca2+ signals control the expression of several antioxidant genes, boosting redox buffering capacity, thus meeting the elevated antioxidant requirements associated with metabolically expensive electrical activity. These genes include examples which are reported Nrf2 target genes and yet are induced in a Nrf2-independent manner. Here we discuss the implications for Nrf2 hypofunction in neurons and the mechanisms underlying the Nrf2-independent induction of antioxidant genes by electrical activity. A significant proportion of Nrf2 target genes, defined as those genes controlled by Nrf2 in astrocytes, are regulated by activity-dependent Ca2+ signals in human stem cell-derived neurons. We propose that neurons interpret Ca2+ signals in a similar way to other cell types sense redox imbalance, to broadly induce antioxidant and detoxification genes.

Activity-Based Sensing of S-Depalmitoylases: Chemical Technologies and Biological Discovery.

While lipids were first appreciated as a critical hydrophobic barrier, our understanding of their roles at the cellular and organismal levels continues to grow. Not only are they important independent operators, providing a platform for both static and dynamic organization and communication within the cell, they also exert significant effects via the chemical modification of proteins. Addition of a lipid post-translational modification (PTM) alters protein hydrophobicity and behavior, with distinct consequences for subcellular trafficking, localization, intra- and intermolecular interactions, and stability. One of the most abundant and widespread protein lipidation events is S-acylation, installation of a long-chain lipid to the thiol of a cysteine side chain through a thioester linkage. S-Acylation is often referred to as S-palmitoylation, due to the prevalence of palmitate as the lipid modification. Unlike many lipid PTMs, S-acylation is enzymatically reversible, enabling the cell to tune proteome-wide properties through dynamic alterations in protein lipidation status. While much has been uncovered about the molecular effects of S-acylation and its implications for physiology, current biochemical and chemical methods only assess substrate lipidation levels or steady-state levels of enzyme activity. Yet, the writer protein acyl transferases (PATs) and eraser acyl protein thioesterases (APTs) are dynamically active, responsible for sometimes-rapid changes in S-palmitoylation status of target proteins. Thus, to understand the full scope, significance, and subtlety of S-deacylation and its regulation in the cell, it is necessary to observe the timing and cellular geography of regulatory enzyme activities. In this Account, we review the chemical tools developed by our group to selectively visualize and perturb the activity of APTs in live cells, highlighting the biological insights gained from their application. To visualize APT activity, we masked fluorogenic molecules with thioacylated, peptide-based APT substrate mimetics; APT activity and thus thiol deprotection releases a fluorescent product in the turn-on depalmitoylation probes (DPPs), while in ratiometric depalmitoylation probes (RDPs) the emission of the parent fluorophore is altered. Application of these probes in live cells reveals that APT activity is sensitive to cell signaling events and metabolic disturbances. Additionally, as indicated above, the location of regulatory enzymes is critical in lipid signaling, and one organelle of particular interest, due to its role in maintaining cellular homeostasis and its legion of lipidated proteins, is the mitochondria. Therefore, we developed a class of spatially constrained mitoDPPs to visualize mitochondrial APT activity as well as a selective inhibitor of mitochondrial deacylation activity, mitoFP. With these tools, we identify two mitochondrial S-depalmitoylases and connect mitochondrial S-depalmitoylation to redox buffering capacity. Moreover, some of the changes in activity observed are specific to the mitochondria, confirming spatial as well as temporal regulation of eraser protein activity. Overall, this chemical toolkit for S-depalmitoylase activity, imaging reagents and a targeted inhibitor, will continue to illuminate the regulatory mechanisms and roles of S-depalmitoylation within the complex homeostatic networks of the cell.

Solid-Contact Ion-Selective Electrodes Comprising Hydrophobic Redox Buffers

A calibration-free measurement with an ionophore-doped polymeric membrane ion-selective electrode requires that the phase boundary potential at the sample/sensing membrane interface is controlled by the activity of the target ion in the sample of interest, while all other phase boundary potentials in the electrochemical cell are constant and long term stable. Historically, the biggest difficulty lies in establishing a reproducible phase boundary potential at the interface of the sensing membrane and the underlying electron conductor. Efforts over several decades to use conducting polymers as an interlayer between the ion-selective membrane and an underlying electron conductor, such as a metal or carbon, have had limited success. While the performance of such devices has been much improved in terms of light sensitivity and hydrophobicity of the conducting polymer layer, devices that can be considered calibration-free are still elusive. To that end, hydrophobic redox buffers have been introduced as an alternative to conducting polymers. While hydrophilic redox buffers play central roles in all living organisms, control many geological and environmental processes, and are often utilized in the laboratory, buffering of redox potentials in hydrophobic media is a topic that has in the past been overlooked. This presentation will address principles for the use of hydrophobic redox buffers, and it will discuss recent examples of hydrophobic redox buffers suitable for the fabrication of ion-selective electrode membranes that are calibration-free. (1) Redox Buffer Capacity of Ion-Selective Electrode Solid Contacts Doped with Organometallic Complexes, Zhen, X. V.; Rousseau, C. R.; Buhlmann, P. Anal. Chem., 2018, 90, 11000-11007. (2) Paper-Based All-Solid-State Ion-Sensing Platform with a Solid Contact Comprising Colloid-Imprinted Mesoporous Carbon and a Redox Buffer, Hu, J.; Zhao, W.; Bühlmann, P.; Stein, A., ACS Appl. Nano Mat. 2018, 1, 293–301.

Impaired Redox Capacity, Muscle Injury, and Microtubule Alterations Conspire to Impact Skeletal Muscle Function

Previously, we linked increases in microtubule (MT) density, MT modification by detyrosination (i.e., deTyr-tub), and NADPH Oxidase 2 (Nox2) expression, to the excess in reactive oxygen species (ROS) and Ca2+ signals responsible for contraction injury in diseased muscle. In the present study, we hypothesized that a reduction in muscle redox buffering, as a result of chronic oxidative stress, is central to the MT changes that impair muscle function. Evidence suggest that oxidative stress is central to MT alterations in disease. Specifically, Nox2 expression precedes MT alterations (Khairallah et al, 2011), and its signaling regulates MT structure (Loehr et al, 2016) in dystrophic muscle. Furthermore, evidence shows oxidative regulation of the tubulin carboxypeptidase responsible for deTyr-tub (Nieuwenhuis et al, 2017). In order to test the contribution of altered redox capacity on MTs and muscle function, we treated adult C57BL/6J mice, with saline, butathione sulfoxamine (BSO; to deplete glutathione), taxol (MT polymerizer, promotes deTyr), or BSO+Taxol for 4 days. We show redox buffer capacity (GSH:GSSG) was significantly reduced with BSO and BSO+Taxol. However, only BSO+Taxol increased MT density and its level of deTyr-tub; a result consistent with BSO promoting Taxol's chemotherapeutic efficacy (Liebmann et al, 1993). With these MT alterations, we show that in vivo gastrocnemius function was unchanged with BSO or Taxol alone, while BSO+Taxol reduced muscle contractility and enhanced muscle contraction injury. Lastly, our examination of gastrocnemius muscle 1 day post contraction injury revealed that BSO treatment yielded a significant increase in MT density and deTyr-tub vs control despite injuring to the same extent. Taken together, we conclude that while decreased redox buffer capacity is insufficient to elicit MT alterations that impact function, it establishes a permissive environment for Taxol or injury to induce these changes.

Enhanced dissimilatory perchlorate reduction in the presence of humic acids or 2,6-anthraquinone disulfonate as quinone redox mediators

Humic acids (HA) and anthraquinone-2,6-Disulfonate (AQDS) are conceived as quinone-based redox mediators (QRM) in contaminant transformation processes, however, their effects on perchlorate (ClO4−) reduction remain unclear. This study explored the efficacy of quinone-mediated perchlorate reduction and the redox reactions occurred in QRM-amended systems. Relative to the average perchlorate reduction rate (k) in the control system, k was increased by 1.8, 1.9, and 2.3-fold in the presence of 100 mg/L commercial HA, extracted HA, and AQDS, respectively. Moreover, in AQDS-amended systems, k was further increased by 66.3% and 158.6%, respectively, with the addition of 0.003 g and 0.032 g hematite to the 200 mL culture. The critical redox reactions implying the electron transferring mechanism were explored and proven to be enzymatically driven. The presence of AQDS shortened the nitrate-induced lag of perchlorate reduction by stimulating nitrate exhaustion rate (2.83 mM NO3− h−1 compared to 1.26 mM NO3− h−1 in the control). Also, the inhibition of the 5-h aeration was alleviated (36.6% compared to 52.5% in the control) due to the higher redox-buffer capacity in AQDS-amended systems. Thaeura was predominant in all perchlorate-acclimated inocula, while the presence of QRM contributed to the enrichment of Desulfuromonas and Geobacter.