Breakdown Of H2O2 Research Articles

In situ oxygen-generating bio-heterojunctions for enhanced anti-bacterial treatment of anaerobe-induced periodontitis

Periodontitis, a chronic inflammatory condition associated with bacterial infection, is the leading cause of tooth loss in adults. Pathogenic bacteria that persist in deep periodontal pockets with hyperglycemic levels following traditional manual debridement can contribute to a persistent local inflammatory microenvironment, posing a significant challenge and highlighting the critical need for improved therapeutic approaches. In addition, the anaerobic environment during these treatments is beneficial to the colonization of anaerobes and may amplify inflammatory responses. Herein, we designed a glucose oxidase (GOx)-coating MXene-SnS2 bio-heterojunctions (MS@G bio-HJs) for multi-modal and effective treatment of anti-bacteria and anti-inflammatory. Upon the hyperglycemic nidus in periodontal pockets, GOx catalyzes the conversion of glucose into hydrogen peroxide (H2O2). Subsequently, the breakdown of H2O2 into hydroxyl radicals through Sn2+/Sn4+-involved Fenton-like reactions enables in situ liberation of oxygen (O2), contributing to relieve local hypoxia. The proposed bio-HJs presents a satisfactory bactericidal capability with anti-bacterial rates of more than 99 % upon near-infrared irradiation, in virtue of multi-modal therapies including photodynamic, photothermal and chemodynamic treatments. Furthermore, in vivo assays utilizing infectious rat models demonstrated that the proposed bio-HJs exhibits high biocompatibility and capacity to alleviate hypoxia and reduce pathogenic virulence factors, potentially contributing to periodontal tissue regeneration. These findings suggest that the versatile bio-HJs could be a promising therapeutic candidate for treating infectious periodontal diseases.

Dual fluorescence-colorimetric sensing platform based on the peroxidase-mimetic performance of the Fe2AlB2 MAX phase for the quantification of acetamiprid and imidacloprid pesticides

The extensive use of pesticides in modern agriculture has raised concerns about environmental contamination and adverse human health effects. Therefore, developing highly sensitive detection methods to identify pesticide residues is crucial for food safety and ecosystem protection. In this study, the Fe2AlB2 MAX phase was synthesized and characterized. After evaluating its peroxidase-mimetic performance using a colorimetric method, a new, sensitive, and simple dual fluorescence-colorimetric sensor was developed for the quantification of two common pesticides, acetamiprid (ACP) and imidacloprid (IMP), using fluorescein (FL). The developed method is based on the inhibitory impact of ACP and IMP on the enzymatic performance of the Fe2AlB2 MAX phase, specifically the inhibition of hydroxyl radical (OH) generation, which enhances the absorption and emission intensities of FL. The results confirmed that OH generated through the breakdown of H2O2 via the catalytic activity of the MAX phase can decrease the intrinsic absorption and emission intensities of FL. However, ACP and IMP inhibit the peroxidase-like activity of the MAX phase, leading to increased absorption and emission intensities of FL. The limit of detection values calculated for spectrophotometric and spectrofluorimetric quantifications were 2.8 μM and 0.051 μM for ACP and 1.72 μM and 0.013 μM for IMP, respectively. Furthermore, the proposed method was successfully utilized to accurately and reliably determine ACP and IMP in spiked real samples with satisfactory accuracy and precision. These developed methods offer several advantages, making them promising candidates for the direct, rapid screening of pesticide residues.

Selective Electrochemical Oxygen Reduction to Hydrogen Peroxide by Confinement of Cobalt Porphyrins in a Metal-Organic Framework.

Sustainable alternatives for the energy intensive synthesis of H2O2 are necessary. Molecular cobalt catalysts show potential but are typically restricted by undesired bimolecular pathways leading to the breakdown of both H2O2 and the catalyst. The confinement of cobalt porphyrins in the PCN-224 metal-organic framework leads to an enhanced selectivity towards H2O2 and stability of the catalyst. Consequently, oxygen can now be selectively reduced to hydrogen peroxide with a stable conversion for at least 5 h, illustrating the potential of catalysts confined in MOFs to increase the selectivity and stability of electrocatalytic conversions.

Photochemical Synthesis and Characterization of a Uranyl Peroxide Triethylamine N‐OxideDimer

A µ‐peroxido‐bis[di‐triethylamine N‐oxide‐dichloro‐dioxouranium] complex with the formula [(UO2)2O2(ON(CH2CH3)3)4Cl2] (complex 1) was synthesized photochemically from a reaction containing uranyl chloride, triethylamine, and H2O2. The photochemical breakdown of H2O2 yielded •OH radicals that reacted with triethylamine to form triethylamine N‐oxide (TEAO) in situ, which subsequently coordinated to UO22+ cations in a monodentate fashion via the N‐oxide functional groups. Structure determination using single crystal X‐ray diffraction revealed that TEAO ligands also formed intermolecular and intramolecular hydrogen bonds with UO22+ and peroxide moieties, and the intermolecular H‐bonding interactions displayed a temperature dependence with Oyl ‐ ‐ H – C and Oper ‐ ‐ H – C distances shortening at 100(2) K by ca. 0.1 Å. Raman spectroscopy data were collected on single crystals of 1 and peak fitting of these results allowed for assignments of peaks including C‐N stretches for TEAO ligands bound to UO22+ cations at 696.8 cm‐1, 717.8 cm‐1, and 776.5 cm‐1, which are redshifted by approximately 30 cm‐1 when compared to free triethylamine. UO22+ν1 and O22‐ν1 stretches, U‐Oper stretches, and notably, U‐Cl stretches were all identified as well, with U‐Cl modes at 198.9 cm‐1 and 212.1 cm‐1 substantially redshifted compared to the uranyl chloride starting material.

Rapid aqueous preparation of carbon quantum dots and their application as nanozyme for the detection of hydrogen peroxide and uric acid

A green and rapid method was developed to synthesize a series of carbon quantum dots (Fe,N/CQDs, Fe,S/CQDs, S,N/CQDs and Fe,S,N/CQDs) through thermal decomposition using persimmon frost as a carbon source. All the synthesized CQDs have peroxidase-like activity, and the comparision of their steady-state kinetic parameters inferred that the peroxidase-like activity of Fe,S,N/CQDs is superior to those of Fe,S/CQDs and Fe,N/CQDs. Furthermore, Fe,S,N/CQDs exhibited good affinity towards 3,3′,5,5′-Tetramethylbenzidine (TMB) and H2O2 compared to natural horseradish peroxidase (HRP) and other nanozymes. In theory, uric acid (UA) can produce H2O2 with the catalysis by uricase. Fe,S,N/CQDs could catalyze the breakdown of H2O2 to produce reactive oxygen species (ROS), which can oxidize TMB (colorless) to oxTMB (blue). Based on the nanozyme-catalyzed oxidation of TMB, a simple and sensitive colorimetric sensor was developed for the quantitative analysis of H2O2 and UA. Low limit of detection (0.73 μM), wide linear range (1–80 μM) and good repeatability were obtained. The sensor was also demonstrated for the determination of UA in biological samples and satisfactory results were obtained.

INTRODUCING ELECTROMAGNETIC ENERGY FROM HYDROCOLLOID WOUND DRESSING PASTE PENETRATING A GLASS BARRIER DISRUPTING HUMAN SKIN LIPID DROPLETS SIZE AND MEMBRANES: POSSIBLE IMPLICATIONS IN CANCER CELLS GENESIS AND/OR CURE

Prior publication demonstrated exogenous energy from a Hydrocolloid Wound Dressing strip had penetrated a 1 mm glass slide barrier slowing the evaporation of drops of water diluted Potassium Ferricyanide crystals of formula K3[Fe(CN6)]; and consequently, altering a human mini organ hair follicle metabolism. In that paper, a recommendation was made stating that “The introduction of exogenous non-biological material, namely a hydrocolloid wound dressing justified inclusion in future research protocols “In this manuscript, in vitro research is presented whereby harvested human skin lipid droplets were exposed also to a hydrocolloid wound dressing paste (HCWP) sandwiched between two glass slides (SDW). Results via microscopy images demonstrate the deleterious effect of the electromagnetic energy emitted by the HCWP, again documented penetrating a 1 mm glass on human skin lipid droplets membranes. Implications up to and including cancer genesis of this newly documented energy emission are unknown, although, it should be emphasized that the reprogramming of lipid metabolism is a hallmark of many cancers, including breast cancer. Additionally in 2016 electromagnetic energy emitted by the breakdown of H2O2 during cell respiration had been hypothesized to be a contributing factor in cancer genesis.

The role of peroxiredoxins PrxA and PrxB in the antioxidant response, carbon utilization and development in Aspergillus nidulans

In addition to their role in the breakdown of H2O2, some peroxiredoxins (Prxs) have chaperone and H2O2 sensing functions. Acting as an H2O2 sensor, Prx Gpx3 transfers the oxidant signal to the transcription factor Yap1, involved in the antioxidant response in Saccharomyces cerevisiae. We have shown that Aspergillus nidulans Yap1 ortholog NapA is necessary for the antioxidant response, the utilization of arabinose, fructose and ethanol, and for proper development. To address the Prx roles in these processes, we generated and characterized mutants lacking peroxiredoxins PrxA, PrxB, PrxC, or TpxC. Our results show that the elimination of peroxiredoxins PrxC or TpxC does not produce any distinguishable phenotype. In contrast, the elimination of atypical 2-cysteine peroxiredoxins PrxA and PrxB produce different mutant phenotypes. ΔprxA, ΔnapA and ΔprxA ΔnapA mutants are equally sensitive to H2O2 and menadione, while PrxB is dispensable for this. However, the sensitivity of ΔprxA and ΔprxA ΔnapA mutants is increased by the lack of PrxB. Moreover, PrxB is required for arabinose and ethanol utilization and fruiting body cell wall pigmentation. PrxA expression is partially independent of NapA, and the replacement of peroxidatic cysteine 61 by serine (C61S) is enough to cause oxidative stress sensitivity and prevent NapA nuclear accumulation in response to H2O2, indicating its critical role in H2O2 sensing. Our results show that despite their high similarity, PrxA and PrxB play differential roles in Aspergillus nidulans antioxidant response, carbon utilization and development.

Enhancement of activity and lifetime of nano-iron oxide catalyst for environmentally friendly catalytic phenol oxidation process

The amount and characteristics of wastewater produced are determined by the process configuration. Refineries produce contaminated effluent of phenol levels up to 300–600 mg/L. For wet oxidation of phenol, multiloading and multifunctional MnO2/Fe2O3 were utilized in the present study to develop a cost-effective nanocatalyst to clean refinery wastewater at a high rate of phenol removal and a long lifetime of catalyst activity. The catalysts were doped with two different loading of 2% and 5% of MnO2. For full oxidation of carcinogenic phenolic compounds into the unharmful CO2 and H2O, the catalytic breakdown of H2O2 as an oxidation agent produces oxygen bubbles and hydroxyl radicals. The prepared catalysts were evaluated in a batch reactor and the results showed that the loading of MnO2 over the Fe2O3 has a positive impact on the oxidation of phenol as increasing the MnO2 loading increased the rate of phenol oxidation and did not result in the deactivation of the available catalyst pores. The highest conversion of phenol achieved was 94 wt% at 80 min and 75 °C over the 5% MnO2/Fe2O3 catalyst. Also, it was observed that the prepared catalyst sustained the deactivation for several cycles of catalytic oxidation of phenol as the catalyst activity remained almost constant as time proceeds to 120 min.

Carbon Dots‐Decorated g‐C3N4 as Peroxidase Nanozyme for Colorimetric Detection of Cr(VI) in Aqueous Medium

AbstractCarbon dots (CD) generated from biomass were fabricated on g‐C3N4 to construct a metal‐free nanozyme with inherent peroxidase mimic functions. The formation of CD/g‐C3N4 was confirmed by different characterization techniques. The CD/g‐C3N4 displays distinct peroxidase mimic activities, as evidenced by the catalyzed oxidation of TMB (3,3’,5,5’, ‐tetramethylbenzidine) in the presence of H2O2, as well as color alteration from transparent to blue. The mechanistic analysis of peroxidase activity indicated that H2O2 was catalyzed by CD/g‐C3N4 to produce reactive oxygen species. In an acidic solution, the presence of Cr (VI) accelerates the breakdown of H2O2 to ⋅OH radicals thereby increasing the rate of TMB oxidation. Hence, a visual colorimetric sensor was developed for the purpose of detecting Cr(VI) with limits of detection (LOD) 0.31 μM, based on the accelerated electron transfer between TMB and H2O2 with the assistance of CD/g‐C3N4.

Light‐Triggered Transformable Ferrous Ion Delivery System for Photothermal Primed Chemodynamic Therapy

Chemodynamic therapy (CDT) involves the catalytic generation of highly toxic hydroxyl radicals (. OH) from hydrogen peroxide (H2 O2 ) through metal-ion-mediated Fenton or Fenton-like reactions. Fe2+ is a classical catalyst ion, however, it suffers easy oxidation and systemic side-effects. Therefore, the development of a controllable Fe2+ delivery system is a challenge to maintain its valence state, reduce toxicity, and improve therapeutic efficacy. Reported here is a near-infrared (NIR) light-triggered Fe2+ delivery agent (LET-6) for fluorescence (FL) and photoacoustic (PA) dual-modality imaging guided, photothermal primed CDT. Thermal expansion caused by 808 nm laser irradiation triggers the transformation of LET-6 to expose Fe2+ from its hydrophobic layer, which primes the catalytic breakdown of endogenous H2 O2 within the tumor microenvironment, thus generating . OH for enhanced CDT. LET-6 shows remarkable therapeutic effects, both in vitro and in vivo, achieving 100 % tumor elimination after just one treatment. This high-performance Fe2+ delivery system provides a sound basis for future synergistic metal-ion-mediated cancer therapy.

Light‐Triggered Transformable Ferrous Ion Delivery System for Photothermal Primed Chemodynamic Therapy

AbstractChemodynamic therapy (CDT) involves the catalytic generation of highly toxic hydroxyl radicals (.OH) from hydrogen peroxide (H2O2) through metal‐ion‐mediated Fenton or Fenton‐like reactions. Fe2+ is a classical catalyst ion, however, it suffers easy oxidation and systemic side‐effects. Therefore, the development of a controllable Fe2+ delivery system is a challenge to maintain its valence state, reduce toxicity, and improve therapeutic efficacy. Reported here is a near‐infrared (NIR) light‐triggered Fe2+ delivery agent (LET‐6) for fluorescence (FL) and photoacoustic (PA) dual‐modality imaging guided, photothermal primed CDT. Thermal expansion caused by 808 nm laser irradiation triggers the transformation of LET‐6 to expose Fe2+ from its hydrophobic layer, which primes the catalytic breakdown of endogenous H2O2 within the tumor microenvironment, thus generating .OH for enhanced CDT. LET‐6 shows remarkable therapeutic effects, both in vitro and in vivo, achieving 100 % tumor elimination after just one treatment. This high‐performance Fe2+ delivery system provides a sound basis for future synergistic metal‐ion‐mediated cancer therapy.

Sensitive Hyaluronidase Biosensor Based on Target-Responsive Hydrogel Using Electronic Balance as Readout.

The development of simple but sensitive methods for hyaluronidase (HAase) detection has been paid a great deal of attention because HAase is a potential cancer marker. In this work, a novel system coupled with a controlled release system has been designed for HAase determination without complex analytical instruments and skilled technicians. Pt@SiO2 nanoparticles (NPs), which can catalyze the breakdown of H2O2 into O2 and H2O, was embedded in the hydrogel constructed by polyethylenimine (PEI) and hyaluronic acid (HA). In the presence of HAase, the hydrogel was broken down as HAase can catalyze the degradation of HA and hence the Pt@SiO2 NPs in the hydrogel was released. The released Pt@SiO2 NPs mixed with H2O2 solution in a drainage device, and then O2 was generated due to the decomposition of H2O2, resulting in an enhancement of pressure in the drainage device because of the low solubility of O2. A certain amount of H2O overflowed from the drainage device because the difference of the pressure between the inner and outer of the drainage device. The overflowed H2O was collected by a tube, and its amount was easily measured by an electronic balance. The weight of the H2O has a linear relationship with the HAase concentration in the range of 1-60 U/mL (120 min enzymatic hydrolysis time) and 0.2-10 U/mL (240 min enzymatic hydrolysis time). The developed system has been applied to detect the activity of HAase in urine samples with satisfied results.

Point-of-Care Testing of Pathogenic Bacteria at the Single-Colony Level via Gas Pressure Readout Using Aptamer-Coated Magnetic CuFe2O4 and Vancomycin-Capped Platinum Nanoparticles.

Pressure measurements are performed everyday with simple devices, and in the field of analytical chemistry the pressure-based signaling strategy offers two important advantages, signal amplification and particular applicability in point-of-care settings. Herein, by using vancomycin (Van)-functionalized platinum nanoparticles (PtNPs@Van) and aptamer-coated magnetic CuFe2O4 nanoprobes dual-recognition units integrated with a catalyzed breakdown of H2O2 for O2 generation, we demonstrated that gas pressure can be used as a readout means for highly sensitive pathogenic bacteria identification and quantification. Using Staphylococcus aureus ( S. aureus) as a test case, integration of the molecular dual-recognition component with the catalyzed gas-generation reaction leads to a significant pressure change (Δ P), and the correlation between the concentration of S. aureus and the Δ P signal was found to be linear from 5.0 to 1.0 × 104 cfu/mL with a detection limit of 1.0 cfu/mL. Other nontarget bacteria show negative results, verifying the high specificity of the present strategy. When employed to assay S. aureus in saliva and milk samples, the approach shows recoveries from 93.3% to 107.1% with relative standard derivation (RSD) less than 8.8%. By the integration of catalyzed gas-generation reaction with the designed molecular recognition event, obviously the pressure-based signaling strategy could facilitate pathogenic bacteria identification and quantification not only in the laboratory but also in point-of-care settings, which could have great potential in the application of food safety and infectious disease diagnosis.

Glutathione‐Activatable and O2/Mn2+‐Evolving Nanocomposite for Highly Efficient and Selective Photodynamic and Gene‐Silencing Dual Therapy

AbstractPhotodynamic therapy (PDT) has been applied in cancer treatment by converting O2 into reactive singlet oxygen (1O2) to kill cancer cells. However, the effectiveness of PDT is limited by the fact that tumor hypoxia causes an inadequate O2 supply, and the overexpressed glutathione (GSH) in cancer cells consumes reactive oxygen species. Herein, a multifunctional hybrid system is developed for selective and highly efficient PDT as well as gene‐silencing therapy using a novel GSH‐activatable and O2/Mn2+‐evolving nanocomposite (GAOME NC). This system consists of honeycomb MnO2 (hMnO2) nanocarrier loaded with catalase, Ce6, and DNAzyme with folate label, which can specifically deliver payloads into cancer cells. Once endocytosed, hMnO2 carriers are reduced by the overexpressed GSH to Mn2+ ions, resulting in the reduction of GSH level and disintegration of GAOME NC. The released catalases then trigger the breakdown of endogenous H2O2 to generate O2, which is converted by the excited Ce6 into 1O2. The self‐sufficiency of O2 and consumption of GSH effectively enhance the PDT efficacy. Moreover, DNAzyme is freed for gene silencing in the presence of self‐generated Mn2+ ions as cofactors. The rational synergy of enhanced PDT and gene‐silencing therapy remarkably improve the in vitro and in vivo therapeutic efficacy of cancers.

A hydrogen peroxide safety valve: The reversible phosphorylation of catalase from the freeze-tolerant North American wood frog, Rana sylvatica

BackgroundThe North American wood frog, Rana sylvatica, endures whole body freezing while wintering on land and has developed multiple biochemical adaptations to elude cell/tissue damage and optimize its freeze tolerance. Blood flow is halted in the frozen state, imparting both ischemic and oxidative stress on cells. A potential build-up of H2O2 may occur due to increased superoxide dismutase activity previously discovered. The effect of freezing on catalase (CAT), which catalyzes the breakdown of H2O2 into molecular oxygen and water, was investigated as a result. MethodsThe present study investigated the purification and kinetic profile of CAT in relation to the phosphorylation state of CAT from the skeletal muscle of control and frozen R. sylvatica. ResultsCatalase from skeletal muscle of frozen wood frogs showed a significantly higher Vmax (1.48 fold) and significantly lower Km for H2O2 (0.64 fold) in comparison to CAT from control frogs (5°C acclimated). CAT from frozen frogs also showed higher overall phosphorylation (1.73 fold) and significantly higher levels of phosphoserine (1.60 fold) and phosphotyrosine (1.27 fold) compared to control animals. Phosphorylation via protein kinase A or the AMP-activated protein kinase significantly decreased the Km for H2O2 of CAT, whereas protein phosphatase 2B or 2C action significantly increased the Km. ConclusionThe physiological consequence of freeze-induced CAT phosphorylation appears to improve CAT function to alleviate H2O2 build-up in freezing frogs. General significanceAugmented CAT activity via reversible phosphorylation may increase the ability of R. sylvatica to overcome oxidative stress associated with ischemia.

Carbon Nanodots-Catalyzed Chemiluminescence of Luminol: A Singlet Oxygen-Induced Mechanism

The catalyzed luminol chemiluminescence (CL) in a strongly alkaline environment has been rarely induced by singlet oxygen (1O2). This paper reports that cetyltrimethyl ammonium bromide passivated carbon nanodots (CTAB-CDs), prepared by the hydrothermal treatment of fullerene in the presence of CTAB, can be used as excellent catalysts to dramatically enhance the CL intensity of the luminol–H2O2 system in NaOH medium owing to their unique surface property. More importantly, this CL enhancement takes place mainly through the intermediate of 1O2, which follows a different mechanism from traditional reports. The CL spectra, UV–vis spectra, electron paramagnetic resonance (EPR) spectra, transmission electron microscopy (TEM) images before and after the CL reaction, and the effects of various free radical scavengers on the CL intensity were conducted to identify the possible 1O2-participating CL enhancement mechanism. It was demonstrated that the CL enhancement by CTAB-CDs originated from the processes of the catalysis of CDs on the electron-transfer and the breakdown of H2O2. Both processes produced a great amount of 1O2 on the surface of CTAB-CDs, and then the reaction of 1O2 with luminol resulted in an unstable endoperoxide, which could rapidly decompose into the excited state 3-aminophthalate anions (3-APA*), leading to the enhanced CL at 440 nm. The important features of this CDs-catalyzed CL will not only enrich traditional luminol CL mechanism in strongly alkaline conditions but also open up a new route to study this novel carbon nanomaterial, which may broaden the applications in a large variety of fields.

Gold Electrode Functionalized with Catalase for Impedimetric Detection of Nitrite

The principle of the developed biosensor includes the following: Catalase catalyzed the breakdown of H2O2 into H2O and O2. Nitrite was selected as an inhibitor of catalase. Faradaic Electrochemical Impedance Spectroscopy (EIS) has been used in our work as a tool for the characterization of a new nitrite biosensor for environmental applications based on the immobilization of catalase on gold electrode. Under optimal conditions, i.e., buffer capacity corresponding to 3 mM phosphate buffer, the catalase enzyme biomembrane shows a high sensitivity to nitrite inhibition. In both cases, the responses of these biosensors based on nitrite additions are good with a detection limit around 8 × 10−11 M.

Peroxisomal Plant 3-Ketoacyl-CoA Thiolase Structure and Activity Are Regulated by a Sensitive Redox Switch

The breakdown of fatty acids, performed by the beta-oxidation cycle, is crucial for plant germination and sustainability. beta-Oxidation involves four enzymatic reactions. The final step, in which a two-carbon unit is cleaved from the fatty acid, is performed by a 3-ketoacyl-CoA thiolase (KAT). The shortened fatty acid may then pass through the cycle again (until reaching acetoacetyl-CoA) or be directed to a different cellular function. Crystal structures of KAT from Arabidopsis thaliana and Helianthus annuus have been solved to 1.5 and 1.8 A resolution, respectively. Their dimeric structures are very similar and exhibit a typical thiolase-like fold; dimer formation and active site conformation appear in an open, active, reduced state. Using an interdisciplinary approach, we confirmed the potential of plant KATs to be regulated by the redox environment in the peroxisome within a physiological range. In addition, co-immunoprecipitation studies suggest an interaction between KAT and the multifunctional protein that is responsible for the preceding two steps in beta-oxidation, which would allow a route for substrate channeling. We suggest a model for this complex based on the bacterial system.

Oxidative stress limits exercise‐ and insulin‐stimulated muscle glucose uptake (MGU) in conscious, chow‐fed C57BL/6J mice

Mitochondrial oxidative stress is associated with exercise‐induced muscular fatigue and insulin resistance. Catalase is an antioxidant enzyme catalyzing the breakdown of H2O2 into H2O and O2. We hypothesized that reducing oxidative stress by mitochondrial catalase overexpression would improve exercise‐ and insulin‐stimulated MGU. Muscle‐specific mitochondrial‐targeted catalase overexpressing mice (mCAT) and WT littermates were chow fed and studied at 16 wks of age. Arterial and venous catheters for sampling and infusion were implanted 5‐7 d prior to study. Rg, an index of MGU, was determined using 2‐deoxy[14C]glucose during 30 min of treadmill exercise or a 2h hyperinsulinemic‐euglycemic clamp. Fasting body weight, glucose, and insulin were the same in WT and mCAT mice. Arterial glucose and insulin were also similar in WT and mCAT mice during both exercise and the clamp. Exercise‐stimulated Rg was increased in soleus, gastrocnemius, and heart in mCAT vs WT mice. Insulin‐stimulated Rg was increased in gastrocnemius and vastus lateralis in mCAT vs WT mice. In conclusion, reduction in oxidative stress by mitochondrial catalase overexpression improved both exercise‐ and insulin‐stimulated MGU. This suggests that oxidative stress is a limitation to MGU under these conditions and mitochondrial antioxidants are potential targets for treatment of muscular fatigue as well as insulin resistance. (NIH DK54902)

Rapid breakdown of exogenous extracellular hydrogen peroxide by lichens

All organisms, even highly stress‐tolerant lichens, produce a variety of reactive oxygen species (ROS) during and after stress. Furthermore, the cell walls of some lichens in Suborder Peltigerineae contain laccases, and therefore can produce quinone radicals that can break down to yield ROS. While the extracellular ROS produced by these enzymes probably play important roles in the biology of these lichens, they may also be potentially harmful and need to be rapidly broken down. To test this, rates of breakdown of exogenously supplied H2O2 were measured in a range of lichen species. Considerable diversity existed in rates of H2O2 breakdown but rates were on average almost double in members of Suborder Peltigerineae. While all lichens tested appeared to lack extracellular peroxidases and catalases, enzymes normally involved in breaking down H2O2, extracellular tyrosinase activity could be readily detected in the Peltigerineae. A role for tyrosinases in H2O2 breakdown was supported by the results from experiments involving inhibitors, and demonstration of the simultaneous release into an incubation solution of tyrosinase activity and the ability to breakdown H2O2. Rates of breakdown were very high, and tyrosinase appeared to break down H2O2 by a catalase‐like mechanism. However, significant rates of breakdown of H2O2 also occurred in species that did not possess cell wall redox enzymes. These species probably took up the exogenously supplied H2O2 intracellularly and then broke it down by the usual catalases and peroxidases. The importance of H2O2 degradation is discussed in terms of its possible role in defence against the harmful effects of ROS.