Tissue Oxygen Tension Research Articles

Continuous non-invasive optical monitoring of cerebral blood flow and oxidative metabolism after acute brain injury

Rapid detection of ischemic conditions at the bedside can improve treatment of acute brain injury. In this observational study of 11 critically ill brain-injured adults, we employed a monitoring approach that interleaves time-resolved near-infrared spectroscopy (TR-NIRS) measurements of cerebral oxygen saturation and oxygen extraction fraction (OEF) with diffuse correlation spectroscopy (DCS) measurement of cerebral blood flow (CBF). Using this approach, we demonstrate the clinical promise of non-invasive, continuous optical monitoring of changes in CBF and cerebral metabolic rate of oxygen (CMRO2). In addition, the optical CBF and CMRO2 measures were compared to invasive brain tissue oxygen tension (PbtO2), thermal diffusion flowmetry CBF, and cerebral microdialysis measures obtained concurrently. The optical CBF and CMRO2 information successfully distinguished between ischemic, hypermetabolic, and hyperemic conditions that arose spontaneously during patient care. Moreover, CBF monitoring during pressor-induced changes of mean arterial blood pressure enabled assessment of cerebral autoregulation. In total, the findings suggest that this hybrid non-invasive neurometabolic optical monitor (NNOM) can facilitate clinical detection of adverse physiological changes in brain injured patients that are otherwise difficult to measure with conventional bedside monitoring techniques.

Normobaric hyperoxia ameliorates renal ischemia reperfusion injury in rats

IntroductionAcute kidney injury (AKI) represents an ever‐increasing clinical problem with high morbidity and mortality. The kidney, due to its inhomogeneous blood flow, is particularly susceptible to changes in oxygen delivery. Renal hypoxia constitutes a common hallmark of AKI, and in the progression to chronic kidney disease (CKD). However, the role of hypoxia per se in the acute phase of renal injury remains largely unclear. The present study investigated 1) the role of systemic hypoxia in the acute progression and recovery of AKI, and 2) if normobaric global hyperoxia following AKI improves renal outcome.MethodsAnaesthetized (thiobutabarbital 120mg/kg i.p.) adult male Sprague‐Dawley rats were subjected to unilateral complete warm renal ischemia for 45 minutes followed by 2 hours of reperfusion under normoxic (21% inspired oxygen, n=10), hypoxic (10% inspired oxygen, n=10), and hyperoxic (60% inspired oxygen n=10) conditions. Kidney function, renal hemodynamics, intrarenal tissue oxygen tension (PO2), and renal oxygen consumption were estimated before and after the ischemic insult.ResultsAll investigated parameters were similar between groups at baseline. Animals subjected to 10% inspired oxygen developed intrarenal tissue hypoxia, whereas animals subjected to 60% inspired oxygen presented with increased intrarenal PO2 demonstrating that the approach to manipulate intrarenal tissue oxygen availability was successful. Furthermore, GFR at baseline were independent of renal tissue oxygenation.IR per se caused a steep decline in GFR in all groups (−97 ± 1, −87 ± 3, and −70 ± 11% for hypoxic, normoxic and hyperoxic animals, respectively), although renal blood flow and renal vascular resistance were similar before and after the ischemic insult. However, following IR there was a linear relationship between GFR and cortical PO2 when analysing all animals in all groups (Fig 1, linear regression P<0.05).ConclusionThis study demonstrates that renal function following IR is dependent on intrarenal oxygen availability. Furthermore, normobaric hyperoxia‐treatment initiated at the time of the ischemic insult has the potential to protect kidney function.Support or Funding InformationThis study was supported by the Swedish Research Council Medicine and Health.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

In Silico Model of Critical Cerebral Oxygenation after Traumatic Brain Injury: Implications for Rescuing Hypoxic Tissue.

Cerebral oxygen delivery is central to the modern intensive care of patients with severe traumatic brain injury. Low brain tissue oxygen tension (PbtO2) results from microvascular collapse and diffusion limitation and is associated with adverse outcome. A number of therapies to improve oxygen delivery are known to be effective in improving PbtO2. Their relative effectiveness and microscopic regions of hypoxia, however, may exist/persist even in the presence of normal PbtO2. Unfortunately, there are no methods currently for assessing this quantitatively. We used an in silico (computational) simulation approach to understand the effect of common interventions on the microscopic distribution of brain tissue oxygen tension. We constructed a non-linear mathematical model of cerebral oxygen supply, diffusion, and consumption for a simplified geometry. Model parameters were chosen to agree with clinical parameters. We found that it was possible to create a plausible diffusion-limited scenario with a significant hypoxic fraction by increasing the mean diffusion distance. We found that increasing cerebral blood flow/blood oxygen content or suppressing the cerebral metabolic rate were most effective at improving PbtO2 and reduced the hypoxic fraction. Within the limitations of our modeling assumptions, increasing the arterial oxygen partial pressure was less effective and only improved PbtO2 by creating a region of hyperoxic tissue with no improvement in hypoxic fraction. The in silico simulations can be useful in understanding the likely physiological effect of complex treatments for which measurement techniques do not exist.

Low-Flow Domiciliary Oxygen as a Mechanism of Ongoing Oxidative Stress.

Oxidative stress occurs when imbalances exist between the production of oxygen free radicals and endogenous antioxidants that neutralize their harmful effects, causing irreversible tissue damage. Oxygen free radicals readily interact with DNA, proteins, and lipids, instigating conformational changes to cellular structures and leading to derangement and dysfunction. Oxidative stress is a key feature in the pathology of COPD. As disease progression occurs, supplemental oxygen is often warranted to ameliorate dyspnea. It has been established that supplemental oxygen at > 0.60 FIO2 is an instigator of oxidative stress. We sought to determine whether chronic exposure to low-flow domiciliary oxygen served as a mechanism of ongoing oxidative stress in this patient population. This study serves to inform best practices for low-flow domiciliary oxygen therapy. We utilized prospective data collection for this study. The exhaled-breath condensate (EBC) of 52 subjects with COPD (FEV1 < 70% of predicted normal for age and gender, height, weight, and smoking history) was evaluated for isofuran (IsoF), an oxidative stress biomarker synthesized in response to elevated tissue oxygen tension. The active control group (n = 26) was compared to the active treatment group receiving low-flow domiciliary oxygen for ≥ 6 h/d (n = 26). The active control group generated a mean ± SD EBC IsoF level of 35.81 ± 25.0 pg/mL compared to the active treatment group's level of 51.37 ± 42.2 pg/mL (P = .057). In subjects diagnosed with advanced COPD, chronic exposure to supplemental oxygen therapy at concentrations ≤ 36% did not appear to induce oxidative stress based on EBC IsoF levels. Our findings do not substantiate that chronic exposure to supplemental oxygen at concentrations < 36% instigates oxidative stress, and, therefore, changes to current domiciliary oxygen therapy prescription practices are not warranted.

Management of Intracranial Pressure Part II: Nonpharmacologic Interventions.

Pharmacologic and nonpharmacologic interventions are available to treat patients who experience serious elevations in intracranial pressure (ICP). In some cases, patients may experience ICP that is refractory to treatment. Significant negative effects on cerebral blood flow, tissue oxygenation, and cerebral metabolism occur as a result of intracranial hypertension, leading to secondary brain injury. In part 2 of this series, nonpharmacologic interventions for ICP and ICP refractory to treatment are discussed. Interventions include neurologic monitoring (bedside assessment and multimodal monitoring), ventilatory support, fluid and electrolyte maintenance, targeted temperature management, and surgical intervention. Technology is always evolving, and the focus of multimodal monitoring here includes devices to monitor ICP, brain tissue oxygen tension, and cerebral blood flow and cerebral microdialysis monitors. Nursing care of these patients includes perspicacious assessment and integration of data, monitoring ventilatory and hemodynamic functioning, and appropriate patient positioning. Nurses must collaborate with the interprofessional care team to ensure favorable patient outcomes while utilizing an evidence-based guideline for the management of ICP.

Cerebral metabolism is not affected by moderate hyperventilation in patients with traumatic brain injury

BackgroundHyperventilation-induced hypocapnia (HV) reduces elevated intracranial pressure (ICP), a dangerous and potentially fatal complication of traumatic brain injury (TBI). HV decreases the arteriolar diameter of intracranial vessels, raising the risk of cerebral ischemia. The aim of this study was to characterize the effects of moderate short-term HV in patients with severe TBI by using concomitant monitoring of cerebral metabolism, brain tissue oxygen tension (PbrO2), and cerebral hemodynamics with transcranial color-coded duplex sonography (TCCD).MethodsThis prospective trial was conducted between May 2014 and May 2017 in the surgical intensive care unit (ICU) at the University Hospital of Zurich. Patients with nonpenetrating TBI older than 18 years of age with a Glasgow Coma Scale (GCS) score < 9 at presentation and with ICP monitoring, PbrO2, and/or microdialysis (MD) probes during ICU admission within 36 h after injury were included in our study. Data collection and TCCD measurements were performed at baseline (A), at the beginning of moderate HV (C), after 50 min of moderate HV (D), and after return to baseline (E). Moderate HV was defined as arterial partial pressure of carbon dioxide 4–4.7 kPa. Repeated measures analysis of variance was used to compare variables at the different time points, followed by post hoc analysis with Bonferroni adjustment as appropriate.ResultsEleven patients (64% males, mean age 36 ± 14 years) with an initial median GCS score of 7 (IQR 3–8) were enrolled. During HV, ICP and mean flow velocity (CBFV) in the middle cerebral artery decreased significantly. Glucose, lactate, and pyruvate in the brain extracellular fluid did not change significantly, whereas PbrO2 showed a statistically significant reduction but remained within the normal range.ConclusionModerate short-term hyperventilation has a potent effect on the cerebral blood flow, as shown by TCCD, with a concomitant ICP reduction. Under the specific conditions of this study, this degree of hyperventilation did not induce pathological alterations of brain metabolites and oxygenation.Trial registrationNCT03822026. Registered on 30 January 2019.

Acute intrarenal angiotensin (1-7) infusion decreases diabetes-induced glomerular hyperfiltration but increases kidney oxygen consumption in the rat.

Common kidney alterations early after the onset of insulinopenic diabetes include glomerular hyperfiltration, increased oxygen consumption and tissue hypoxia. Increased activity of the renin-angiotensin-aldosterone system (RAAS) has been implicated in most of these early alterations. The RAAS peptide angiotensin (1-7) has the potential to modulate RAAS-mediated alterations in kidney function. Thus, the aim of the present study was to determine the acute effects of angiotensin (1-7) in the kidney of insulinopenic type 1 diabetic rat and the results compared to that of normoglycaemic controls. Renal haemodynamics and oxygen homeostasis were measured 3 weeks after administration of streptozotocin before and after acute intrarenal infusion of angiotensin (1-7) at a dose of 400ngmin-1 . Arterial pressure and renal blood flow were similar between groups and not affected by exogenous angiotensin (1-7). Diabetics presented with glomerular hyperfiltration, increased urinary sodium excretion and elevated kidney oxygen consumption. Angiotensin (1-7) infusion normalized glomerular filtration, increased urinary sodium excretion, decreased proximal tubular reabsorption, and elevated kidney oxygen consumption even further. The latter resulting in tubular electrolyte transport inefficiency. Angiotensin (1-7) did not affect tissue oxygen tension and had no significant effects in controls on any of the measured parameters. Diabetes results in increased responsiveness to elevated levels of angiotensin (1-7) which is manifested as inhibition of tubular sodium transport and normalization of glomerular filtration. Furthermore, elevated angiotensin (1-7) levels increase kidney oxygen consumption in the diabetic kidney even further which affects tubular electrolyte transport efficiency negatively.

Expression of Hypoxia-Inducible Factor 1α (HIF-1α) and Genes of Related Pathways in Altered Gravity.

Immune system deterioration in space represents a major risk, which has to be mitigated for exploration-class missions into the solar system. Altered gravitational forces have been shown to regulate adaptation processes in cells of the immune system, which are important for appropriate risk management, monitoring and development of countermeasures. T lymphocytes and cells of the monocyte-macrophage system are highly migratory cell types that frequently encounter a wide range of oxygen tensions in human tissues and in hypoxic areas, even under homeostatic conditions. Hypoxia-inducible factor 1 and 2 (HIF’s) might have an important role in activation of T cells and cells of the monocyte-macrophages system. Thus, we investigated the regulation of HIF-dependent and, therefore, hypoxia-signaling systems in both cell types in altered gravity and performed transcript and protein analysis from parabolic flight and suborbital ballistic rocket experiments. We found that HIF-1α and HIF-1-dependent transcripts were differently regulated in altered gravity, whereas HIF-1α-dependent gene expression adapted after 5 min microgravity. Inter-platform comparisons identified PDK1 as highly responsive to gravitational changes in human U937 myelomonocytic cells and in Jurkat T cells. We suggest HIF-1 as a potential pharmacological target for counteracting immune system deterioration during space flight.

P4HA1 is a new regulator of the HIF-1 pathway in breast cancer.

Hypoxia-Inducible Factor (HIF)-1 is a transcription factor that plays the key role in response to low oxygen concentrations, or hypoxia. Activation of the HIF-1 pathway is not only crucial for normal tissue development and function, but also involved in disease progression, such as cancer. Cancer cells proliferate rapidly in solid tumors, and thus, solid tumors consume much more oxygen and nutrients than normal tissue and generate oxygen tension. It is well established that oxygen tension in solid tumor tissue induces the aberrant activation of the HIF-1 pathway, and subsequently promotes angiogenesis and tumor progression. Breast cancer is a heterogeneous disease and can be classified into luminal, Her2 positive, and triple negative (TNBC) subtypes base on ER/PR and Her2 expression in the breast cancer tissue. HIF-1 activation is observed in all breast cancer subtypes; interestingly, the HIF-1 pathway is hyperactivated in TNBCs compared to other subtypes. The differential activation of the HIF-1 pathway in breast cancer subtypes suggests that oxygen-independent pathways may be involved in HIF-1 regulation during TNBC progression. However, these pathways have not been well-characterized. We demonstrate that collagen proly 4 hydroxylase 1 (P4H1) induces HIF-1α expression at the protein level by modulating α-ketoglutarate (α-KG) and succinate levels. These results reveal a novel link between collagen hydroxylation and activation of the HIF-1 pathway and unveil a new HIF-1 regulation mechanism in TNBC.

Decreases in Oral Tissue Blood Flow Induced by Remifentanil Are Not Accompanied by Deterioration of Oral Tissue Oxygen Tension in Rabbits

The purpose of this study was to investigate the effects of remifentanil infusion on tissue blood flow and tissue oxygen tension in the mandibular bone marrow and masseter muscle in rabbits. In addition, changes in tissue oxygen consumption in those tissues during remifentanil infusion were investigated. Sixteen male tracheotomized Japanese White rabbits were anesthetized with sevoflurane under mechanical ventilation. Under oxygen and air inhalation, fraction of inspiratory oxygen was set at 0.4 and remifentanil was infused at a rate of 0.4μg ∙ kg-1 ∙ min-1. Measurements were performed before remifentanil infusion, 20minutes after the start of remifentanil infusion, and 20 and 60minutes after the completion of remifentanil infusion (n=8). The observed variables included heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), mandibular bone marrow tissue blood flow (BBF), masseter muscle tissue blood flow (MBF), mandibular bone marrow tissue oxygen tension (PbO2), and masseter muscle tissue oxygen tension (PmO2). Another 8 rabbits were observed for arterial pH, lactate, base excess (BE), and tissue oxygen consumption in the region from which the retromandibular vein received venous blood. Measurements were performed before remifentanil infusion and 20minutes after the start of remifentanil infusion. HR, SBP, DBP, MAP, BBF, and MBF decreased during remifentanil infusion. PbO2 increased 20minutes after remifentanil infusion and returned to almost the baseline value 60minutes after remifentanil infusion. PmO2 did not change throughout the experiment. The difference between the arterial oxygen content of the femoral artery and the venous oxygen content of the retromandibular vein decreased during remifentanil infusion. Arterial pH, lactate, and BE did not change during remifentanil infusion. Remifentanil decreased BBF and MBF but did not decrease PbO2 and PmO2. It is suggested that tissue oxygen consumption decreased during remifentanil infusion.

Мониторинг изменения содержания кислорода в тканях по кинетике замедленной флуоресценции экзогенных красителей

The dynamics of oxygen consumption during photodynamic processes and its subsequent restoration in malignant tumors and healthy tissues of mice were studied in vitro by kinetics of long-term luminescence of xanthene dyes. It was shown that to estimate changes in tissue oxygen tension, specific type of delayed fluorescence can be used which caused by singlet-triplet annihilation of singlet oxygen and a sensitizer in triplet state. In tumors under pulse excitation of sensitizers, reversible quenching of delayed fluorescence was observed, which is associated with a decrease in the tissue oxygen tension during photodynamic processes. Method for visualizing the restoration of the initial oxygen level in tissues after photodynamic action is proposed.

Application of mathematical modeling methods in the evaluation of severity of ischemic stroke in patients with arterial hypertension

To study the possibility of applying methods of mathematical modeling in assessing the severity of ischemic stroke in patients with arterial hypertension. The study included 80 patients with ischemic stroke. Blood pressure was measured. Transcutaneous polarography was used to measure the oxygen tension in tissues. Measurements of gas composition of the blood and thickness of the intima-media complex were performed. The level of stable metabolites of nitric oxide in the blood was determined. Measurement of endothelin-1 in the blood was performed by enzyme immunoassay. NIHSS scale was administered to assess the neurological status. Patients were divided into 3 groups according to the degree of neurological deficit. The control group consisted of 10 people without signs of vascular pathology. An increase in the neurological deficit was accompanied by an increase in the level of endothelin-1, a decrease in the level of stable metabolites of nitric oxide, and a reduction in tissue oxygenation. Discriminative functions were developed for each group of patients using discriminant analysis based on the data obtained in the study. The most statistically significant were two signs: the level of systolic blood pressure and the content of stable metabolites of nitric oxide in the blood. Thus, the imbalance in the indices of endothelium-dependent mechanisms of vascular tone regulation reflect the severity of the condition in ischemic stroke. The method of discriminant analysis allows the creation of sufficiently reliable mathematical models that can have practical significance, and can be used as a method of clarifying the severity of the condition in the acute period of ischemic stroke.

Oxygenation differs among white matter hyperintensities, intersected fiber tracts and unaffected white matter.

White matter hyperintensities of presumed vascular origin are frequently observed on magnetic resonance imaging in normal aging. They are typically found in cerebral small vessel disease and suspected culprits in the etiology of complex age- and small vessel disease-related conditions, such as late-onset depression. White matter hyperintensities may interfere with surrounding white matter metabolic demands by disrupting fiber tract integrity. Meanwhile, risk factors for small vessel disease are thought to reduce tissue oxygenation, not only by reducing regional blood supply, but also by impairing capillary function. To address white matter oxygen supply–demand balance, we estimated voxel-wise capillary density as an index of resting white matter metabolism, and combined estimates of blood supply and capillary function to calculate white matter oxygen availability. We conducted a cross-sectional study with structural, perfusion- and diffusion-weighted magnetic resonance imaging in 21 patients with late-onset depression and 21 controls. We outlined white matter hyperintensities and used tractography to identify the tracts they intersect. Perfusion data comprised cerebral blood flow, blood volume, mean transit time and relative transit time heterogeneity—the latter a marker of capillary dysfunction. Based on these, white matter oxygenation was calculated as the steady state cerebral metabolic rate of oxygen under the assumption of normal tissue oxygen tension and vice versa. The number, volume and perfusion characteristics of white matter hyperintensities did not differ significantly between groups. Hemodynamic data showed white matter hyperintensities to have lower blood flow and blood volume, but higher relative transit time heterogeneity, than normal-appearing white matter, resulting in either reduced capillary metabolic rate of oxygen or oxygen tension. Intersected tracts showed significantly lower blood flow, blood volume and capillary metabolic rate of oxygen than normal-appearing white matter. Across groups, lower lesion oxygen tension was associated with higher lesion number and volume. Compared with normal-appearing white matter, tissue oxygenation is significantly reduced in white matter hyperintensities as well as the fiber tracts they intersect, independent of parallel late-onset depression. In white matter hyperintensities, reduced microvascular blood volume and concomitant capillary dysfunction indicate a severe oxygen supply–demand imbalance with hypoxic tissue injury. In intersected fiber tracts, parallel reductions in oxygenation and microvascular blood volume are consistent with adaptations to reduced metabolic demands. We speculate, that aging and vascular risk factors impair white matter hyperintensity perfusion and capillary function to create hypoxic tissue injury, which in turn affect the function and metabolic demands of the white matter tracts they disrupt.

Application of transcutaneous oxygen pressure in scar assessment

To review the application and research progress of transcutaneous oxygen pressure (TcPO 2) in scar assessment. The original articles about scar and TcPO 2 were reviewed and analyzed. Hypoxia environment plays an important role in the progression of scar tissue. TcPO 2 can accurately reflect the oxygen tension of scar tissue, which is of great significance in the assessment of scar maturity, the guidance of scar treatment, and the study of correlations between hypoxia and the progression of scar. TcPO 2 measurement is important in the study of scar evaluation, treatment, and correlation between hypoxia and scar formation.

Arterial oxygen content regulates plasma erythropoietin independent of arterial oxygen tension: a blinded crossover study

The production of erythropoietin (Epo) is modulated by renal tissue oxygen tension, which in principle depends on both arterial oxygen content (CaO2) and arterial oxygen tension (PaO2). Uncontrolled observational studies suggest that alterations in CaO2 fundamentally regulate Epo synthesis. We sought to establish whether reduced CaO2 enhances plasma Epo concentration independently of PaO2. In a blinded crossover study, 8 healthy young subjects were exposed to three conditions: room air (normoxia); 11% oxygen balanced in nitrogen, which lowers both CaO2 and PaO2 (hypoxia); and carbon monoxide plus normoxia, which decreases CaO2 to the same degree as hypoxia while preserving PaO2 (hypoxemia). Arterial blood samples were obtained prior to and throughout the 5 hours of exposure to each condition. In the hypoxic conditions, average CaO2 was reduced to similar levels, whereas PaO2 was only decreased with exposure to hypoxia. Plasma Epo concentration was increased in both hypoxic conditions relative to normoxia after 150 min of exposure and was augmented more than two-fold after 300 min, with no difference between hypoxic conditions. Reduced CaO2 induces similar increases in circulating Epo concentration irrespective of PaO2 manipulation, demonstrating that CaO2 is the critical variable regulating Epo production.

The Role of Tissue Oxygen Tension in Dengue Virus Replication.

Low oxygen tension exerts a profound effect on the replication of several DNA and RNA viruses. In vitro propagation of Dengue virus (DENV) has been conventionally studied under atmospheric oxygen levels despite that in vivo, the tissue microenvironment is hypoxic. Here, we compared the efficiency of DENV replication in liver cells, monocytes, and epithelial cells under hypoxic and normoxic conditions, investigated the ability of DENV to induce a hypoxia response and metabolic reprogramming and determined the underlying molecular mechanism. In DENV-infected cells, hypoxia had no effect on virus entry and RNA translation, but enhanced RNA replication. Overexpression and silencing approaches as well as chemical inhibition and energy substrate exchanging experiments showed that hypoxia-mediated enhancement of DENV replication depends on the activation of the key metabolic regulators hypoxia-inducible factors 1α/2α (HIF-1α/2α) and the serine/threonine kinase AKT. Enhanced RNA replication correlates directly with an increase in anaerobic glycolysis producing elevated ATP levels. Additionally, DENV activates HIF and anaerobic glycolysis markers. Finally, reactive oxygen species were shown to contribute, at least in part through HIF, both to the hypoxia-mediated increase of DENV replication and to virus-induced hypoxic reprogramming. These suggest that DENV manipulates hypoxia response and oxygen-dependent metabolic reprogramming for efficient viral replication.

Knockdown of Ant2 Reduces Adipocyte Hypoxia And Improves Insulin Resistance in Obesity.

Decreased adipose tissue oxygen tension and increased HIF-1α expression can trigger adipose tissue inflammation and dysfunction in obesity. Our current understanding of obesity-associated decreased adipose tissue oxygen tension is mainly focused on changes in oxygen supply and angiogenesis. Here, we demonstrate that increased adipocyte O2 demand, mediated by ANT2 activity, is the dominant cause of adipocyte hypoxia. Deletion of adipocyte Ant2 improves obesity-induced intracellular adipocyte hypoxia by decreasing obesity-induced adipocyte oxygen demand, without effects on mitochondrial number or mass, or oligomycin-sensitive respiration. This led to decreased adipose tissue HIF-1α expression and inflammation with improved glucose tolerance and insulin resistance in both a preventative or therapeutic setting. Our results suggest that ANT2 may be a target for the development of insulin sensitizing drugs and that ANT2 inhibition might have clinical utility.

Metformin attenuates renal medullary hypoxia in diabetic nephropathy through inhibition uncoupling protein‐2

The purpose of the study is to examine the effect of metformin on oxygen metabolism and mitochondrial function in the kidney of an animal model of insulinopenic diabetes in order to isolate any renoprotective effect from any concomitant effect on blood glucose homeostasis. Sprague-Dawley rats were injected with streptozotocin (STZ) (50mgkg-1 ) and when stable started on metformin treatment (250mgkg-1 ) in the drinking water. Rats were prepared for in vivo measurements 25 to 30days after STZ injection, where renal function, including glomerular filtration rate and sodium transport, was estimated in anesthetized rats. Intrarenal oxygen tension was measured using oxygen sensors. Furthermore, mitochondrial function was assessed in mitochondria isolated from kidney cortex and medulla analysed by high-resolution respirometry, and superoxide production was evaluated using electron paramagnetic resonance. Insulinopenic rats chronically treated with metformin for 4weeks displayed improved medullary tissue oxygen tension despite of no effect of metformin on blood glucose homeostasis. Metformin reduced UCP2-dependent LEAK and differentially affected medullary mitochondrial superoxide radical production in control and diabetic rats. Metformin attenuates diabetes-induced renal medullary tissue hypoxia in an animal model of insulinopenic type 1 diabetes. The results suggest that the mechanistic pathway to attenuate the diabetes-induced medullary hypoxia is independent of blood glucose homeostasis and includes reduced UCP2-mediated mitochondrial proton LEAK.

Abstract 278: A Randomized, Blinded Trial of 100% Oxygen vs. Room Air During Cardiopulmonary Resuscitation in a Large Animal Model of Pediatric Cardiac Arrest

Introduction: Guidelines recommend CPR with 100% oxygen, but its effect on the pediatric brain is unknown. Hyperoxia during CPR may lead to significant oxidative injury from mitochondrial-derived reactive oxygen species (mtROS). Hypothesis: We hypothesized that swine receiving 100% FiO2 during CPR would have similar survival outcomes and mitochondrial oxidative phosphorylation, but would have cerebral hyperoxia and increased mtROS compared to those resuscitated with room air (21%). Methods: Four-week-old female piglets (n=25) underwent 7 minutes of asphyxia followed by randomization and blinding to CPR with 100% (n=10) or 21% FiO2 (n=10) during CPR through 10 minutes post-ROSC, at which point FiO2 was set to 21% in all animals. Sham n=5. Brain tissue oxygen tension (PbtO2), cerebral blood flow (CBF), and invasive hemodynamics were continuously monitored. Survivors received 4 hours of post-ROSC care, whereupon cortex and hippocampus were obtained for mitochondrial analysis. ROS were measured simultaneously with mitochondrial respirometry measurements, utilizing high resolution respirometry with concomitant fluorometric analysis. Data are described as median [IQR]. Groups were compared using Fisher’s exact test, Kruskal-Wallis test, Wilcoxon rank-sum, and a generalized estimating equation regression model. Results: The two oxygen strategy groups did not differ in 1) systemic, coronary, or pulmonary hemodynamics or 2) cerebral blood flow at baseline, during asphyxia, during CPR, or post-ROSC. Survival was the same in each group (8/10 vs 8/10, p=1.0). PbtO2 was higher with 100% than 21% during CPR (point estimate +54.9±26.7, p=0.04) and during the first ten minutes post-ROSC (point estimate +505±41.4, p&lt;0.001). There were no differences in maximal oxidative phosphorylation in either cerebral cortex or hippocampus between groups. In cortex, mtROS was higher with 100% compared to 21% during maximal oxidative phosphorylation (0.283 [0.275,0.290] vs 0.224 [0.205,0.239] H2O2 pmol/(s*ml), p&lt;0.03). Conclusions: Compared to 21% FiO2, provision of 100% FiO2 during CPR confers no difference in survival and is associated with cerebral hyperoxia and increased mtROS generation.

A swine model of intracellular cerebral edema – Cerebral physiology and intracranial compliance

Cerebral edema leading to elevated intracranial pressure (ICP) is a fundamental concern after severe traumatic brain injury (TBI), stroke, and severe acute hyponatremia. We describe a swine model of water intoxication and its cerebral histological and physiological sequela. We studied female swine weighing 35–45 kg. Four serum sodium intervals were designated: baseline, mild, moderate, and severe hyponatremia attained by infusing hypotonic saline. Intracranial fluid injections were performed to assess intracranial compliance. At baseline and following water intoxication wedge biopsy was obtained for pathological examination and electron microscopy. We studied 8 swine and found an increase in ICP that was strongly related to the decrease in serum sodium level. Mean ICP rose from a baseline of 6 ± 2 to 28 ± 6 mm Hg during severe hyponatremia, while cerebral perfusion pressure (CPP) decreased from 72 ± 10 to 46 ± 11 mm Hg. Brain tissue oxygen tension (PbtO2) decreased from 18.4 ± 8.9 to 5.3 ± 3.0 mm Hg. Electron microscopy demonstrated intracellular edema and astrocytic foot process swelling following water intoxication. With severe hyponatremia, 2 cc intracranial fluid injection resulted in progressively greater ICP dose, indicating a worsening intracranial compliance. Our model leads to graded and sustained elevation of ICP, lower CPP, and decreased PbtO2, all of which cross clinically relevant thresholds. Intracranial compliance worsens with increased cerebral swelling. This model may serve as a platform to study which therapeutic interventions best improve the cerebral physiological profile in the face of severe brain edema.