Local Oxygen Pressure Research Articles

Correlation between local instantaneous dose rate and oxygen pressure reduction during proton pencil beam scanning irradiation

Background and purposeOxygen dynamics may be important for the tissue-sparing effect observed at ultra-high dose rates (FLASH sparing effect). This study investigated the correlation between local instantaneous dose rate and radiation-induced oxygen pressure reduction during proton pencil beam scanning (PBS) irradiations of a sample and quantified the oxygen consumption g-value. Materials and methodsA 0.2 ml phosphorescent sample (1 μM PtG4 Oxyphor probe in saline) was irradiated with a 244 MeV proton PBS beam. Four irradiations were performed with variations of a PBS spot pattern with 5 × 7 spots. During irradiation, the partial oxygen pressure (pO2) was measured with 4.5 Hz temporal resolution with a phosphorometer (Oxyled) that optically excited the probe and recorded the subsequently emitted light. A calibration was performed to calculate the pO2 level from the measured phosphorescence lifetime. A fiber-coupled scintillator simultaneously measured the instantaneous dose rate in the sample with 50 kHz sampling rate. The oxygen consumption g-value was determined on a spot-by-spot level and using the total pO2 change for full spot pattern irradiation. ResultsA high correlation was found between the local instantaneous dose rate and pO2 reduction rate, with a correlation coefficient of 0.96–0.99. The g-vales were 0.18 ± 0.01 mmHg/Gy on a spot-by-spot level and 0.17 ± 0.01 mmHg/Gy for full spot pattern irradiation. ConclusionsThe pO2 reduction rate was directly related to the local instantaneous dose rate per delivered spot in PBS deliveries. The methodology presented here can be applied to irradiation at ultra-high dose rates with modifications in the experimental setup.

Isoflurane lowers the cerebral metabolic rate of oxygen and prevents hypoxia during cortical spreading depolarization in vitro: An integrative experimental and modeling study

Cortical spreading depolarization (SD) imposes a massive increase in energy demand and therefore evolves as a target for treatment following acute brain injuries. Anesthetics are empirically used to reduce energy metabolism in critical brain conditions, yet their effect on metabolism during SD remains largely unknown. We investigated oxidative metabolism during SD in brain slices from Wistar rats. Extracellular potassium ([K+]o), local field potential and partial tissue oxygen pressure (ptiO2) were measured simultaneously. The cerebral metabolic rate of oxygen (CMRO2) was calculated using a reaction-diffusion model. By that, we tested the effect of clinically relevant concentrations of isoflurane on CMRO2 during SD and modeled tissue oxygenation for different capillary pO2 values. During SD, CMRO2 increased 2.7-fold, resulting in transient hypoxia in the slice core. Isoflurane decreased CMRO2, reduced peak [K+]o, and prolonged [K+]o clearance, which indicates reduced synaptic transmission and sodium-potassium ATPase inhibition. Modeling tissue oxygenation during SD illustrates the need for increased capillary pO2 levels to prevent hypoxia. In the absence thereof, isoflurane could improve tissue oxygenation by lowering CMRO2. Therefore, isoflurane is a promising candidate for pre-clinical studies on neuronal survival in conditions involving SD.

Memory CD8+ T cells upregulate glycolysis and effector functions under limiting oxygen conditions.

Memory CD8+ T cells are indispensable for maintaining long-term immunity against intracellular pathogens and tumors. Despite their presence at oxygen-deprived infected tissue sites or in tumors, the impact of local oxygen pressure on memory CD8+ T cells remains largely unclear. We sought to elucidate how oxygen pressure impacts memory CD8+ T cells arising after infection with Listeria monocytogenes-OVA. Our data revealed that reduced oxygen pressure during in vitro culture switched CD8+ T cell metabolism from oxidative phosphorylation to a glycolytic phenotype. Quantitative proteomic analysis showed that limiting oxygen conditions increased the expression of glucose transporters and components of the glycolytic pathway, while decreasing TCA cycle and mitochondrial respiratory chain proteins. The altered CD8+ T cell metabolism did not affect the expansion potential, but enhanced the granzyme B and IFN-γ production capacity. In vivo, memory CD8+ T cells cultured under low oxygen pressure provided protection against bacterial rechallenge. Taken together, our study indicates that strategies of cellular immune therapy may benefit from reducing oxygen during culture to develop memory CD8+ T cells with superior effector functions.

Synthesis of dual-stimuli responsive metal organic framework-coated iridium oxide nanocomposite functionalized with tumor targeting albumin-folate for synergistic photodynamic/photothermal cancer therapy

The synergistic effects of photothermal therapy (PTT) and photodynamic therapy (PDT) has attracted considerable attention in the field of cancer therapy because of its excellent anti-tumor effect. This work provides a novel pH/NIR responsive therapeutic nanoplatform, IrO2@ZIF-8/BSA-FA (Ce6), producing a synergistic effect of PTT-PDT in the treatment of osteosarcoma. Iridium dioxide nanoparticles (IrO2 NPs) with exceptional catalase-like activity and PTT effects were synthesized by a hydrolysis method and decorated with zeolitic imidazolate framework-8 (ZIF-8) shell layer to promote the physical absorption of Chlorin e6 (Ce6), and further functionalized with bovine serum albumin-folate acid (BSA-FA) for targeting tumor cells. The IrO2@ZIF-8/BSA-FA nanocomposite indicated an outstanding photothermal heating conversion efficiency of 62.1% upon laser irradiation. In addition, the Ce6 loading endows nanoplatform with the capability to induce cell apoptosis under 660 nm near-infrared (NIR) laser irradiation through a reactive oxygen species (ROS)-mediated mechanism. It was further testified that IrO2@ZIF-8/BSA-FA can function as a catalase and convert the endogenous hydrogen peroxide (H2O2) into oxygen (O2) to improve the local oxygen pressure under the acidic tumor microenvironment (TME), which could subsequently amplified PDT-mediated ROS cell-killing performance via relieving hypoxia microenvironment of tumor. Both in vitro and in vivo experimental results indicated that the nanomaterials were good biocompatibility, and could remarkably achieve tumor-specific and enhanced combination therapy outcomes as compared with the corresponding PTT or PDT monotherapy. Taken together, this work holds great potential to design an intelligent multifunctional therapeutic nanoplatform for cancer therapy.

Avoiding the effects of translocation on the estimates of the metabolic rates across an elevational gradient.

Body maintenance costs are often considered a proxy for performance in fitness traits. Maintenance energy requirements are measured as minimal metabolic rate of inactive, postabsorptive individuals in the laboratory. For mountain-dwelling species, translocation to the laboratory often means that they are also moved to another elevation. Due to physiological adaptations to local oxygen pressure, rapid elevational change can alter metabolic rate and translocation may result in erroneous estimates of body maintenance costs. In this study, we measured resting metabolic rate (RMR) of three populations of the Mesquite lizard (Sceloporus grammicus, Wiegmann 1828) at their native elevations (i.e., 2600, 3200 and 4100m). Our results showed that at native elevations, mass specific RMR of lizards from the high elevation population (4100m) did not differ from the RMR of the other populations (i.e., 2600 and 3200m), whereas the lizards from the low elevation (2600m) had lower RMR than those from the intermediate population. These results differ from a previous study in which the RMR of lizards from the same populations were reported to increase with native elevation when translocated and measured at an intermediate elevation. Hence, our results show that translocation in elevation can affect metabolic measures. We caution researchers that changes in elevation may preclude accurate measures of RMR in some animals and may therefore incorrectly predict performance of fitness-related traits.

Use Co- and Ni-Free Air Electrode in Solid Oxide Cell Manufacturing for Electrolysis and Fuel Cell Applications

The production of durable and high performance Solid Oxide Cells (SOC) units for electrolysis (SOE) and fuel cell (SOFC) applications, using cost efficient raw materials with low recycling cost is one of the main challenges for SOC developers to reach a large scale industrialization. Nickel and cobalt, state-of-the-art compounds in the manufacturing of SOC electrodes, require costly safety management during the manufacturing and recycling processes due to their carcinogenic properties. Cobalt, also recognized since 2017 as Critical Raw Materials (CRM) for the EU community, presents also a high economical risk for European SOC manufacturers, regarding its supply (55% of the world’s cobalt being sourced from Central Africa). Use of Co- and Ni- free electrode materials would provide a significant reduction of use of CRM in European SOC manufacturing and offers cell and stack developers the benefit of a more environmental-friendly and lower cost manufacturing process, and the potential of using recycled materials from previous manufacturing.Within the European project NewSOC, TNO develops Co- and Ni-free air electrode materials based on the (La, Ca, Sr)FeO3 perovskite class of materials for SOE and SOFC applications. The electrochemical performances of different Co-free compounds were measured and compared to the state-of-the-art electrode materials (e.g. La0.6Sr0.4Co0.2Fe0.8O3- d) to achieve the performance targets as defined within the NewSOC project: Area Specific Resistance (ASR) < 0.5 ohm.cm2 for Low-Temperature operations at 650°COperations at high current densities (1 A/cm2) for SOFC and SOE operationsLow degradation rates under SOFC and SOE operations and SOFC/SOE cycles (< 1%/kh)Stability upon thermal cycling (< 0.2 mV%/cycles) and redox stability The removal of nickel and cobalt in the oxygen electrode tends to increase the overpotential of the air electrode, with ASR values = 0.6-0.9 ohm.cm2 and maximum current density < 1 A/cm2 for operation at 650°C. Taking this drawback into account, TNO addresses the performance optimization of the Co- and Ni-free air electrode compounds by developing a novel air electrode architectures based on Co-free air electrode materials. The envisaged electrode architecture aims to enhance the triple phase boundary density at the Co- and Ni- free air electrode/electrolyte interface by creating a gradient composite electrode on top of a patterned porous barrier layer. This novel concept is also envisaged to improve the electrode performance and prevent electrode delamination during SOC operations. A higher triple phase boundary density contributes to lower the local partial oxygen pressure between electrolyte and oxygen electrode, known as critical degradation phenomena of the oxygen electrode at high current density under electrolysis conditions. During the conference, the last development of the novel Co- and Ni- free air electrode design developed at TNO will be presented. Figure 1

A Comparative Study between Indigenous Low Cost Negative Pressure Wound Therapy with Added Local Oxygen versus Conventional Negative Pressure Wound Therapy.

Introduction:The incidence of compound fractures and severe soft tissue loss has increased manifolds due to high speed traffics. Negative Pressure Wound Therapy (NPWT) is a treatment modality for managing soft tissue aspect of such injuries. It reduces the need of flap coverage. However, many patients from developing countries cannot afford a conventional NPWT. We developed an indigenous low cost NPWT for our patients and supplemented it with Topical Pressurised Oxygen Therapy (TPOT). We conducted this study to compare its treatment outcome with the use of conventional NPWT.Materials and Methods:The study was conducted from 2018 to 2020 at a tertiary care teaching hospital. A total of 86 patients were treated with NPWT and their results were assessed for various parameters like reduction in wound size, discharge, infection, etc. We included patients with acute traumatic wounds as well as chronic infected wounds, and placed them in three treatment groups to receive either conventional NPWT, Indigenous NPWT and lastly NPWT with supplement TPOT.Results:We observed a significant reduction of wound size, discharge and infection control in all three groups. The efficacy of indigenous NPWT is at par with conventional NPWT. Only six patients who had several comorbidities required flap coverage while in another four patients we could not achieve desired result due to technical limitations.Conclusion:Indigenous NPWT with added TPOT is a very potent and cost effective method to control infection and rapid management of severe trauma seen in orthopaedic practice. It also decreases the dependency on plastic surgeons for management of such wounds.

Mild Hyperoxia Stimulation Increases Regional Tissue Oxygen Pressure in Rat Hippocampus via Oxygen Radical

Aims: The purpose of this study is to examine a rise of the local tissue oxygen pressure in hippocampus (Hip-pO2) which means neuronal activation by mild hyperoxia through oxygen radical.&#x0D; Study Design: Study was an animal experiment with rat.&#x0D; Place and Duration of Study: Department of Department of Life Science and Applied Chemistry, Nagaya Institute of Technology, between January 2014 and January 2018.&#x0D; Methodology: Rats were exposed to air or mild oxygen gas. At the same time, Local tissue oxygen pressure in hippocampus (Hip-pO2) were measured for 20 min with or without treatment of two type of radical scavengers.&#x0D; Results: The Hip-pO2 levels were significantly increased by mild hyperoxia exposure (50-60% above resting level). The mild hyperoxia-induced enhancement of the Hip-pO2 levels were inhibited by MnTMPyP (radical scavenger), but not by NADPH oxidase (NOX) inhibitor Apocynin.&#x0D; Conclusion: These findings suggested that mild hyperoxia could activate hippocampus through generation of oxygen radicals.

Co-imaging of the tumor oxygenation and metabolism using electron paramagnetic resonance imaging and 13-C hyperpolarized magnetic resonance imaging before and after irradiation.

To examine the relationship between local oxygen partial pressure and energy metabolism in the tumor, electron paramagnetic resonance imaging (EPRI) and magnetic resonance imaging (MRI) with hyperpolarized [1-13C] pyruvate were performed.SCCVII and HT29 solid tumors implanted in the mouse leg were imaged by EPRI using OX063, a paramagnetic probe and 13C-MRI using hyperpolarized [1-13C] pyruvate. Local partial oxygen pressure and pyruvate metabolism in the two tumor implants were examined. The effect of a single dose of 5-Gy irradiation on the pO2 and metabolism was also investigated by sequential imaging of EPRI and 13C-MRI in HT29 tumors.A phantom study using tubes filled with different concentration of [1-13C] pyruvate, [1-13C] lactate, and OX063 at different levels of oxygen confirmed the validity of this sequential imaging of EPRI and hyperpolarized 13C-MRI. In vivo studies revealed SCCVII tumor had a significantly larger hypoxic fraction (pO2 < 8 mmHg) compared to HT29 tumor. The flux of pyruvate-to-lactate conversion was also higher in SCCVII than HT29. The lactate-to-pyruvate ratio in hypoxic regions (pO2 < 8 mmHg) 24 hours after 5-Gy irradiation was significantly higher than those without irradiation (0.76 vs. 0.36) in HT29 tumor. The in vitro study showed an increase in extracellular acidification rate after irradiation.In conclusion, co-imaging of pO2 and pyruvate-to-lactate conversion kinetics successfully showed the local metabolic changes especially in hypoxic area induced by radiation therapy.

Hypoxia is not required for human endometrial breakdown or repair in a xenograft model of menstruation

Menstrual endometrial breakdown induced by estradiol and progesterone withdrawal is regularly attributed to vasospasm of spiral arteries causing ischemia and hypoxia. We investigated whether hypoxia actually occurred in an in vivo model of menstruation. Three complementary approaches were used to look for signs of hypoxia in fragments of human functionalis xenografted to ovariectomized immunodeficient mice bearing pellets-releasing estradiol and progesterone, and then deprived of ovarian steroids. Hormone withdrawal 21 d after grafting induced menstrual breakdown and MMP expression within 4 d. Local partial oxygen pressure (pO2) was measured by electron paramagnetic resonance using implanted lithium phtalocyanine crystals. In mice with hormone maintenance until sacrifice, pO2 was low one week after grafting (14.8±3.4 mmHg) but increased twofold from the second week when tissue was largely revascularized. After 3 wk, pO2 was not modified by hormone withdrawal but was slightly increased on hormone reimpregnation 4 d after removal (34.7±6.1 mmHg) by comparison with hormone maintenance (27.1±8.6 mmHg). These results were confirmed using fluorescence quenching-based OxyLite measurements. In a further search for signs of hypoxia, we did not find significant HIF1-α immunostaining, nor pimonidazole adducts after hormone withdrawal. We conclude that hypoxia is not needed to trigger menstrual-like tissue breakdown or repair in human endometrial xenograft.

Local Cytokine Concentrations and Oxygen Pressure Are Related to Maturation of the Collateral Circulation in Humans

Our aim was to determine cytokine and oxygen gradients over the collateral circulation in humans. The molecular background of the maturation of the collateral circulation in response to coronary narrowing is poorly understood in humans, partly because of difficulties in obtaining local samples from the human collateral circulation. Coronary collateral blood was sampled in 60 patients with nontotal (n = 25) or total coronary occlusions (n = 35) using a special wide-lumen catheter. Coronary collateral flow index (CFI) was assessed by intracoronary pressure measurements. Oxygenation and lactate content was measured as well as 30 cytokines potentially involved in collateral artery growth, using a custom-made multiplex assay. No rise in lactate or change in pH was found in collateral blood. Oxygen gradient between coronary and collateral arterial blood correlated inversely with CFI (r = -0.61, p < 0.001). Locally increased plasma levels were found for basic fibroblast growth factor, eotaxin, macrophage migration inflammatory factor, monocyte chemoattractant protein-1, and transforming growth factor-beta, while stem cell factor and stem cell growth factor-beta were significantly decreased. The highest cytokine gradients were found in patients with the least developed collateral circulation. The majority of cytokines correlated more strongly with the pO(2) gradient across the collateral bed than with CFI. Intravascular ischemia during brief balloon coronary occlusion is absent in human coronary collateral arteries. The oxygen gradient found over the collateral circulation is increased in patients with a less matured collateral circulation and relates to local levels of several known pro-arteriogenic cytokines. In case of a more developed collateral circulation, relatively low levels of cytokines are present, suggesting that growth factor therapy might be beneficial at this stage.

SU‐GG‐I‐127: Multiple Stepped Magnetic Field Technique Applied to Enhance the Resolution of Electron Spin Echo Oxygen Imaging (ESEOI) at 250MHz

Purpose: The knowledge of local partial oxygen pressure (pO2) in malignant tumors is important due to the effect of hypoxia, or low oxygen concentration on tumor aggressiveness and response to radiation therapy. Three dimensional ESEOI is one of the few noninvasive modalities that provide a quantitative, spatially resolved measure of pO2 inside tumor. The spatial resolution is defined by the gradient field magnitude and therefore is limited by the imager frequency bandwidth. By using the multiple magnetic field B0 technique (MB0) we have extended the effective bandwidth of the imager and acquired images with better spatial resolution. Method and Materials: A phantom with the same spin probe (OX063H) used for small animal imaging was also employed in this study. Our pulse imager design allows us to use high microwave power and achieve frequency bandwidth of 20MHz. This bandwidth is sufficient to image a 2cm long sample using 50 mT/m gradient in the single B0 (SB0) technique. In the MB0 technique, the same experiment is repeated at multiple B0 values to increase the efficient acquisition bandwidth. Results: Using SB0 and MB0 methods, we obtained 3D images of our phantom with spatial resolution of 0.5mm. This is a large improvement compared to the 1.4mm resolution for current ESEOI protocol and 1.3mm resolution of continuous wave EPROI, both used in small animal imaging. The measured T2 uncertainty was about 5%. Conclusion: The MB0 method was found to be technically more complicated than the SB0 method but less susceptible to instrumental limitations in applying larger gradient fields. These results pave the way for high resolution ESEOI in small animal imaging. This makes ESEOI a more powerful tool for understanding the tumor physiology based on 3D pO2 imaging.

Relación de la expresión del factor inducido por hipoxia-2α (HIF-2α) y sVEGF-R1/sFlt-1: implicación en la fisiopatología de preeclampsia

Trophoblast invasion is critical for the establishment of uteroplacental circulation. At the early phases of this process, local oxygen pressure in the placenta is lower, which pathologically remains constant in preeclampsia. Consequently, understanding the response of placental cells to these stimuli is important. In the present study, we used primary cultures of trophoblast cells (TCs), fibroblasts from villous cells, and human umbilical endothelial cells isolated from preterm and term placentas (with and without preeclampsia) to explore the effect of oxygen pressure on the expression and synthesis of VEGF, sVEGFR-1/sFlt-1, and HIF-1α and-2α. Our results show that low oxygen pressure led to a significant selective increase in mRNA and the sVEGF-R1 receptor protein in TCs. VEGF expression and synthesis was elevated in three cell types, but free protein (not bound to sVEGF-R1) was decreased in TCs. Expression of HIF-1α or -2α mRNA in cells was similar in all the types of placentas, but the increase in HIF-2α protein was greater in the TCs of preeclamptic placentas. To evaluate the relationship between HIF-2α and the increase in the sVEGFR-1 receptor, we used siRNAHIF2α. In response to inhibition, expression of the sVEGF-R1 receptor diminished dramatically. HIF-2α blockade did not alter VEGF expression. Our data are the first to indicate that the HIF-2α transcription factor protein is one of the molecules involved in the selective expression of the sVEGF-R1 receptor in TCs during hypoxia.

Quantifying the role of oxygen pressure in tissue function

it has been suggested that oxygen had reached significant levels in the earth's oceans as early as 2.5 billion years ago and has rapidly increased to near current levels about 50 million years later ([6][1]). The appearance of oxygen dramatically changed the chemical composition of the oceans and

Co-evaporated YBCO/doped-CeO2/Ni–W coated conductors oxygen improved using a supersonic nozzle

A novel process for the coated conductors (CC) deposition, characterized by a single CeO2 buffer layer architecture, and a new oxygenation device for the YBCO layer has been developed.In CC technology, usually the ceria layer thickness must be less than 100nm to avoid the formation of cracks; in order to ensure an efficient barrier effect, complex and costly multi-buffer layers architectures must be grown. In this work, we describe the way to increase the thickness of crack-free single buffer layer.Single CeO2 buffer layer is grown on biaxially textured Ni–5at.%W substrates (RABiTS) by e-beam evaporation technique, introducing different doping elements at various percentages in pure Ceria targets. Since the crack formation in cerium oxide layers mainly depends on the stresses introduced by the lattice mismatch with Ni alloy substrate and on the arrangement of the oxygen vacancies in the lattice, it is possible to reduce these stresses by optimizing the doping in the Ceria layer, thus obtaining very thick and crack-free CeO2 buffer layers.The texture quality of our samples is tested by XRD, giving a strong in-plane and out-of-plane orientation (FWHM values of about 5°). Optical and electron microscopy shows dense and crack-free thick layers (up to 450nm) and confirms excellent insulating properties.A novel technique has been developed to enhance the oxygen pressure on the YBCO film during the deposition as the oxygen content is known to be critical for the growth of YBCO films with high Tc. A supersonic oxygen nozzle (SNEO) incorporated into the vacuum chamber enables a ×103 increasing of the local oxygen pressure close to the YBCO layer keeping a 10−4mbar background pressure.The work demonstrates that the single thick doped-Ceria buffer layer could be a viable way to reduce CC complexity and production costs and that SNEO apparatus can be used to make the oxygenation process of the YBCO films easier and more reliable.

Charge and charging compensation on oxides and hydroxides in oxygen environmental SEM

Oxygen environment was applied to the scanning electron microscopy (SEM) analysis of insulating samples. In the high vacuum SEM, a local oxygen pressure was provided, and in the environmental SEM, oxygen atmosphere was used instead of water, the commercial mode. The charging effects in the SEM observation and component characterization of samples such as Al 2O 3, Al(OH) 3, Mg(OH) 2 and others can be eliminated or significantly reduced. The oxygen environment does not only provide a new approach to releasing the charging difficulty in the analyses using electron beam as a probe, but also provide an insightful hint to the understanding of the charging processes in general.

Hypoxia enables B19 erythrovirus to yield abundant infectious progeny in a pluripotent erythroid cell line

B19 may cause mild to severe clinical manifestations. Owing to the remarkable tropism of B19 for red blood cell progenitors, there is a lack of satisfactory cell lines fully permissive for B19. Because the local oxygen pressure may influence viral replication, we used hypoxia to improve the sensitivity of our infectivity assay in order to link B19 DNA detected by PCR to the presence of infectious B19 particles in plasma. Plasma samples and the WHO International Standard for B19 DNA detection by PCR were used to infect the pluripotent human erythroid cell line KU812F under different oxygen pressures. Specific human anti-B19 IgG was found to reduce infectivity. Low oxygen pressure led to higher yields of infectious B19 progeny and to a higher level of viral transcription than observed under normoxia. This sensitive infectivity assay is a promising model for studying B19 biology, identifying neutralising antibodies, and evaluating new virus inactivation methods.

Problématique des bacilles persistants

Specific immune responses against Mycobacterium tuberculosis antigens conduct to the formation of inflammatory granulomas. These inflammatory reactions play a key role to control the bacterial growth but also to allow the bacterial transmission by the cavernous lesion formation. The local oxygen pressure is low into the granuloma. An adaptation of bacteria to low oxygen pressure was demonstrated in vitro, in culture. The microbial persistence in vivo, during long lasting periods, could be related to adaptation of Mycobacterium tuberculosis to survival under the anaerobic conditions present in granulomas. Antibiotics able to kill such bacteria with reduced metabolism, could reduce the treatment duration.

Oxygen conformance of cellular respiration. A perspective of mitochondrial physiology.

Oxygen pressure declines from normoxic air-level to the microenvironment of mitochondria where cytochrome c oxidase (COX) reduces oxygen to water at oxygen levels as low as 0.3 kPa (2 Torr; 3 microM; 1.5 % air saturation). Intracellular hypoxia is defined as (1) local oxygen pressure below normoxic reference states, or (2) limitation of mitochondrial respiration by oxygen levels below kinetic saturation, resulting in oxyconformance. High-resolution respirometry provides the methodology to measure mitochondrial and cellular oxygen kinetics in the relevant low oxygen range < 1 kPa (7.5 mmHg; 9-10 microM; 5% air saturation). Respiration of isolated heart mitochondria follows hyperbolic oxygen kinetics with half-saturating oxygen pressure, p50, of 0.04 kPa (0.3 Torr; 0.4 microM) in ADP-stimulated state 3. Thus mitochondrial respiration proceeds at 90% of its hyperbolic maximum at the p50 of myoglobin, suggesting the possibility of a small but significant oxygen limitation even under normoxia in active muscle. Any impairment of oxygen delivery, therefore, induces oxyconformance. In addition, a shift of mitochondrial oxygen kinetics to the right, particularly by competitive inhibition of COX by NO, causes a further depression of respiration and a compensatory increase of local oxygen pressure. Above 1 kPa, mitochondrial oxygen uptake increases above hyperbolic saturation, which is probably due to oxygen radical production rather than the kinetics of COX. In cultured cells, the pronounced oxygen uptake above mitochondrial saturation at air-level oxygen pressure cannot be inhibited by rotenone and antimycin A, amounting to > 20 % of routine respiration in fibroblasts. Biochemical models of oxyconformance of COX are evaluated relative to patterns of intracellular oxygen distribution in the tissue and enzyme turnover in vivo, considering the kinetic effects of COX excess capacity on flux through the mitochondrial electron transport chain.

Reducing hemoglobin oxygen affinity does not increase hydroxyl radicals after acute subdural hematoma in the rat.

Extensive evidence is available to show the importance of ischemia after severe human head injury. We have previously shown that pharmacologically increasing the release of oxygen in brain tissue where the local oxygen pressure is low reduces infarct size in animal models. To study the possible negative effects of this strategy, we tested the effect of an allosteric modifier of hemoglobin (RSR13) on free radical production in the rat acute subdural hematoma (ASDH) model, both under normoxic as well as under hyperoxic, normobaric conditions. When compared to baseline, induction of ASDH resulted in a significant increase (p < 0.05) in 2,3-DHBA (2,3 dihydroxybenzoic acid, produced from salicylate after attack by hydroxyl radicals) at 30 and 60 min postinduction, both for the control group (39% and 91%) as well as the RSR13-treated group (41% and 62%). The 2,5-DHBA also increased significantly (p < 0.05) in the drug-treated animals at the 30- and 60-min time points when compared to baseline (49% and 77%). At all time points, except the 30-min, the increase in 2,3-DHBA was less marked in the RSR13 animals than in the control group. Similarly, the 2,5-DHBA increase after ASDH was lower at all time points except for the 30-min time point in the RSR13-treated group. These results indicate that enhanced tissue oxygen release by the allosteric modifier of hemoglobin RSR13 does not increase hydroxyl radical production after ASDH. Clinical trials are needed to test this compound in humans after severe head injury.