Urine Hydrogen Peroxide Levels and Their Relation to Outcome in Patients with Sepsis, Septic Shock, and Major Burn Injury

Kidney Transplant Recipients Show Limited Lung Diffusion Capacity but Similar Hydrogen Peroxide Exhalation as Healthy Matched Volunteers: A Pilot Study

Patients with end-stage chronic kidney disease show higher systemic oxidative stress and exhale more hydrogen peroxide (H2O2) than healthy controls. Kidney transplantation reduces oxidative stress and H2O2 production by blood polymorphonuclear leukocytes (PMNs). Kidney transplant recipients (KTRs) may be predisposed to an impairment of lung diffusing capacity due to chronic inflammation. Lung function and H2O2 concentration in the exhaled breath condensate (EBC) were compared in 20 KTRs with stable allograft function to 20 healthy matched controls. Serum interleukin eight (IL-8) and C-reactive protein (CRP), blood cell counts, and spirometry parameters did not differ between groups. However, KTRs showed lower total lung diffusing capacity for carbon monoxide, corrected for hemoglobin concentration (TLCOc), in comparison to healthy controls (92.1 ± 11.5% vs. 102.3 ± 11.9% of predicted, p = 0.009), but similar EBC H2O2 concentration (1.63 ± 0.52 vs. 1.77 ± 0.50 µmol/L, p = 0.30). The modality of pre-transplant renal replacement therapy had no effect on TLCOc and EBC H2O2. TLCOc did not correlate with time after transplantation. In this study, TLCOc was less reduced in KTRs in comparison to previous reports. We suggest this fact and the non-elevated H2O2 exhalation exhibited by KTRs, may result perhaps from the evolution of the immunosuppressive therapy.

A novel enzyme-free long-lasting chemiluminescence system based on a luminol functionalized β-cyclodextrin hydrogel for sensitive detection of H2O2 in urine and cells

A novel long-lasting chemiluminescent (CL) hydrogel (β-CD@luminol-Co²⁺) was synthesized by embedding luminol and cobalt ions (Co²⁺) into β-cyclodextrin (β-CD) through non-covalent interactions. Due to its porous structure and viscosity, the synthesized β-CD@luminol-Co²⁺ hydrogel exhibited long-lasting CL properties and can emit light for 12 h under both alkaline and neutral conditions. In addition, the CL intensities of β-CD@luminol-Co²⁺ were linear with the logarithm of the hydrogen peroxide (H₂O₂) concentration in the range of 1.0 × 10^-11-1.0 × 10^-7 M, and the limit of detection (LOD) was 0.63 × 10^-11 M and 0.85 × 10^-11 M under alkaline and neutral conditions, respectively. On this basis, an enzyme-free CL sensor based on β-CD@luminol-Co²⁺ was fabricated for the sensitive detection of H₂O₂ in human urine samples under alkaline conditions, and showed good accuracy and recovery. Since β-CD@luminol-Co²⁺ showed good CL properties under neutral conditions, it can be applied to detect H₂O₂ in cells. In order to prolong the emission wavelength of β-CD@luminol-Co²⁺ for better cell imaging, β-CD@luminol-FL-Co²⁺ was prepared by adding fluorescein (FL) to β-CD@luminol-Co²⁺. The as-prepared β-CD@luminol-FL-Co²⁺ also displayed long-lasting CL properties and showed a linear relationship with H₂O₂ concentrations. In addition, the maximum emission wavelength of β-CD@luminol-FL-Co²⁺ was 520 nm, which was red-shifted by 95 nm compared with β-CD@luminol-Co²⁺. The methyl thiazolyl tetrazolium (MTT) assay results and confocal microscopy images illustrated that β-CD@luminol-FL-Co²⁺ had low toxicity and can be taken up by A549 cells. Finally, β-CD@luminol-FL-Co²⁺ was successfully applied for CL imaging and detection of intracellular H₂O₂ in A549 cells under neutral conditions. This enzyme-free long-lasting CL system with high sensitivity can also be extended to real-time monitoring of H₂O₂in vivo.

Nanocomposite films as electrochemical sensors for detection of catalase activity

Cross-linked hydrogel substrates have garnered attention as they simultaneously enable oxidoreductase reactions in a control volume extended to adsorption of redox capacitors for amplification of electrochemical signals. In this study, the effect of catalase immobilization in mold-casted alginate-based thin films (1 mm × 6 mm × 10 mm) containing multi walled carbon nanotubes (MWCNT) coated with chitosan has been studied via amperometry. The amperometric response was measured as a function of peroxide concentration, at a fixed potential of −0.4 V vs. SPCE in phosphate-buffered saline (pH = 7.4). Results indicate substrate detection is not diffusion-limited by the 100 μm thick chitosan layer, if the cationic polyelectrolyte is in contact with the sensing carbon electrode, and the linear detection of the enzyme absent in solution is enabled by immobilization (R² = 0.9615). The ferricyanide-mediated biosensor exhibited a sensitivity of 4.55 μA/mM for the optimal formulation at room temperature comparable to other nanomaterial hybrid sensing solution namely amine-functionalized graphene with an average response time of 5 s for the optimal formulation. The suitability of the optimized chitosan-coated alginate slabs nano-environment for co-encapsulation of catalase and carbon nanotubes was confirmed by cyclic voltammetry.

Chemistry of Hydrogen Peroxide Formation and Elimination in Mammalian Cells, and Its Role in Various Pathologies

Hydrogen peroxide (H2O2) is a compound involved in some mammalian reactions and processes. It modulates and signals the redox metabolism of cells by acting as a messenger together with hydrogen sulfide (H2S) and the nitric oxide radical (•NO), activating specific oxidations that determine the metabolic response. The reaction triggered determines cell survival or apoptosis, depending on which downstream metabolic pathways are activated. There are several ways to produce H2O2 in cells, and cellular systems tightly control its concentration. At the cellular level, the accumulation of hydrogen peroxide can trigger inflammation and even apoptosis, and when its concentration in the blood reaches toxic levels, it can lead to bioenergetic failure. This review summarizes existing research from a chemical perspective on the role of H2O2 in various enzymatic pathways and how this biochemistry leads to physiological or pathological responses.