Changes In Oxygen Tension Research Articles

An observational study to find out changes in arterial oxygen tension during fiberoptic bronchoscopy

Background: Arterial hypoxaemia is the commonest complication, since respiratory depressant drugs are used for premedication, and the airway is also partially occluded by the bronchoscope. The study is therefore designed to find out the changes in arterial oxygen tension during (FOB) along with effect on central hemodynamics, pre and post procedure ECG and PFT. Objectives were to find out the changes in arterial oxygen tension during FOB, to study the effects of FOB on central hemodynamics, electrocardiographically and pulmonary function tests.Methods: One hundred patients aged 20 years undergoing FOB were evaluated for the arterial oxygen tension and cardiac rhythm changes at KNCH, Jodhpur during 12 months study period from 2019 to 2020.Results: All patients developed a fall in PaO2 following FOB but hypoxaemia was noted only in 18 cases. Bronchial washing, punch biopsy and brush biopsy did contribute to hypoxaemia significantly. There was a uniform rise in heart rate in all the patients after FOB which was statistically significant. There was slight sinus tachycardia in most of the cases although ECG indicated no major arrhythmias. The pulmonary functions which include change in VC, FVC, FEV1 and PEFR after FOB, on statistically comparison no statistical difference could be observed. There was no significant change in PaCO2 level and pH level. Mean of SBP and mean of DBP was statistically significant.Conclusions: All patients showed a decline in arterial PaO2 after FOB which was highly significant. There was slight sinus tachycardia in most of cases. FOB itself does not endanger the patients with any significant or serious complications.

Data-driven identification of inherent features of eukaryotic stress-responsive genes.

Living organisms are continuously challenged by changes in their environment that can propagate to stresses at the cellular level, such as rapid changes in osmolarity or oxygen tension. To survive these sudden changes, cells have developed stress-responsive mechanisms that tune cellular processes. The response of Saccharomyces cerevisiae to osmostress includes a massive reprogramming of gene expression. Identifying the inherent features of stress-responsive genes is of significant interest for understanding the basic principles underlying the rewiring of gene expression upon stress. Here, we generated a comprehensive catalog of osmostress-responsive genes from 5 independent RNA-seq experiments. We explored 30 features of yeast genes and found that 25 (83%) were distinct in osmostress-responsive genes. We then identified 13 non-redundant minimal osmostress gene traits and used statistical modeling to rank the most stress-predictive features. Intriguingly, the most relevant features of osmostress-responsive genes are the number of transcription factors targeting them and gene conservation. Using data on HeLa samples, we showed that the same features that define yeast osmostress-responsive genes can predict osmostress-responsive genes in humans, but with changes in the rank-ordering of feature-importance. Our study provides a holistic understanding of the basic principles of the regulation of stress-responsive gene expression across eukaryotes.

Hypoxia-inducible factor (HIF)-1α-induced regulation of lung injury in pulmonary aspiration is mediated through NF-kB.

Aspiration‐induced lung injury is a common grievance encountered in the intensive care unit (ICU). It is a significant risk factor for improving ventilator‐associated pneumonia (VAP) and acute respiratory distress syndrome (ARDS). Hypoxia‐inducible factor (HIF)‐1α is one of the primary transcription factors responsible for regulating the cellular response to changes in oxygen tension. Here, we sought to determine the role of HIF‐1α and specifically the role of type 2 alveolar epithelial cells in generating the acute inflammatory response following acid and particles (CASP) aspiration. Previous studies show HIF‐1 α is involved in regulating the hypoxia‐stimulated expression of MCP‐1 in mice and humans. The CASP was induced in C57BL/6, ODD‐Luc, HIF‐1α (+/+) control, and HIF‐1α conditional knockout (HIF‐1α (−/−) mice). Following an injury in ODD mice, explanted organs were subjected to IVIS imaging to measure the degree of hypoxia. HIF‐1α expression, BAL albumin, cytokines, and histology were measured following CASP. In C57BL/6 mice, the level of HIF‐1α was increased at 1 h after CASP. There were significantly increased levels of albumin and cytokines in C57BL/6 and ODD‐Luc mice lungs following CASP. HIF‐1α (+/+) mice given CASP demonstrated a synergistic increase in albumin leakage, increased pro‐inflammatory cytokines, and worse injury. MCP‐1 antibody neutralized HIF‐1α (+/+) mice showed reduced granuloma formation. The NF‐κB expression was increased substantially in the HIF‐1α (+/+) mice following CASP compared to HIF‐1α (−/−) mice. Our data collectively identify that HIF‐1α upregulation of the acute inflammatory response depends on NF‐κB following CASP.

Effects of Local Anesthetics With Vasoconstrictors on Dental Pulp Blood Flow and Oxygen Tension.

The aim of this study was to investigate the changes in pulpal blood flow (PBF) and pulpal oxygen tension (PpulpO2) after injecting local anesthetics with vasoconstrictors. Under general anesthesia, male Japanese White rabbits were injected with 0.6 mL of 2% lidocaine with 1:80,000 epinephrine (LE) or 3% propitocaine (prilocaine) with 0.03 IU felypressin (PF) at the apical area of the lower incisor. Relative to baseline, PBF and PpulpO2 significantly decreased 5 minutes after LE or PF injection as compared with saline. The decrease in PBF was significantly lower in the LE group than in the PF group. Although the LE group had a larger decrease in PpulpO2 relative to baseline than the PF group did, that difference was not significant. PBF and PpulpO2 recovered to baseline faster in the PF group than in the LE group. The injection of local anesthetic solutions containing vasoconstrictors (LE or PF) transiently caused significant decreases in PBF that resulted in significant decreases in PpulpO2. The recovery of PpulpO2 was faster than PBF regardless of the vasoconstrictor used.

Effects of hyperoxia and hypoxia on the proliferation of C2C12 myoblasts.

Hyperoxic conditions are known to accelerate skeletal muscle regeneration after injuries. In the early phase of regeneration, macrophages invade the injured area and subsequently secrete various growth factors, which regulate myoblast proliferation and differentiation. Although hyperoxic conditions accelerate muscle regeneration, it is unknown whether this effect is indirectly mediated by macrophages. Here, using C2C12 cells, we show that not only hyperoxia but also hypoxia enhance myoblast proliferation directly, without accelerating differentiation into myotubes. Under hyperoxic conditions (95% O2 + 5% CO2), the cell membrane was damaged because of lipid oxidization, and a disrupted cytoskeletal structure, resulting in suppressed cell proliferation. However, a culture medium containing vitamin C (VC), an antioxidant, prevented this lipid oxidization and cytoskeletal disruption, resulting in enhanced proliferation in response to hyperoxia exposure of ≤4 h/day. In contrast, exposure to hypoxic conditions (95% N2 + 5% CO2) for ≤8 h/day enhanced cell proliferation. Hyperoxia did not promote cell differentiation into myotubes, regardless of whether the culture medium contained VC. Similarly, hypoxia did not accelerate cell differentiation. These results suggest that regardless of hyperoxia or hypoxia, changes in oxygen tension can enhance cell proliferation directly, but do not influence differentiation efficiency in C2C12 cells. Moreover, excess oxidative stress abrogated the enhancement of myoblast proliferation induced by hyperoxia. This research will contribute to basic data for applying the effects of hyperoxia or hypoxia to muscle regeneration therapy.

Invasive Multimodal Neuromonitoring in Aneurysmal Subarachnoid Hemorrhage: A Systematic Review.

Aneurysmal subarachnoid hemorrhage is a devastating disease leaving surviving patients often severely disabled. Delayed cerebral ischemia (DCI) has been identified as one of the main contributors to poor clinical outcome after subarachnoid hemorrhage. The objective of this review is to summarize existing clinical evidence assessing the diagnostic value of invasive neuromonitoring (INM) in detecting DCI and provide an update of evidence since the 2014 consensus statement on multimodality monitoring in neurocritical care. Three invasive monitoring techniques were targeted in the data collection process: brain tissue oxygen tension (ptiO2), cerebral microdialysis, and electrocorticography. Prospective and retrospective studies as well as case series (≥10 patients) were included as long as monitoring was used to detect DCI or guide DCI treatment. Forty-seven studies reporting INM in the context of DCI were included (ptiO2: N=21; cerebral microdialysis: N=22; electrocorticography: N=4). Changes in brain oxygen tension are associated with angiographic vasospasm or reduction in regional cerebral blood flow. Metabolic monitoring with trend analysis of the lactate to pyruvate ratio using cerebral microdialysis, identifies patients at risk for DCI. Clusters of cortical spreading depolarizations are associated with clinical neurological worsening and cerebral infarction in selected patients receiving electrocorticography monitoring. Data supports the use of INM for the detection of DCI in selected patients. Generalizability to all subarachnoid hemorrhage patients is limited by design bias of available studies and lack of randomized trials. Continuous data recording with trend analysis and the combination of INM modalities can provide tailored treatment support in patients at high risk for DCI. Future trials should test interventions triggered by INM in relation to cerebral infarctions.

The role of HIF proteins in maintaining the metabolic health of the intervertebral disc.

The physiologically hypoxic intervertebral disc and cartilage rely on the hypoxia-inducible factor (HIF) family of transcription factors to mediate cellular responses to changes in oxygen tension. During homeostatic development, oxygen-dependent prolyl hydroxylases, circadian clock proteins and metabolic intermediates control the activities of HIF1 and HIF2 in these tissues. Mechanistically, HIF1 is the master regulator of glycolytic metabolism and cytosolic lactate levels. In addition, HIF1 regulates mitochondrial metabolism by promoting flux through the tricarboxylic acid cycle, inhibiting downsteam oxidative phosphorylation and controlling mitochondrial health through modulation of the mitophagic pathway. Accumulation of metabolic intermediates from HIF-dependent processes contribute to intracellular pH regulation in the disc and cartilage. Namely, to prevent changes in intracellular pH that could lead to cell death, HIF1 orchestrates a bicarbonate buffering system in the disc, controlled by carbonic anhydrase 9 (CA9) and CA12, sodium bicarbonate cotransporters and an intracellular H+/lactate efflux mechanism. In contrast to HIF1, the role of HIF2 remains elusive; in disorders of the disc and cartilage, its function has been linked to both anabolic and catabolic pathways. The current knowledge of hypoxic cell metabolism and regulation of HIF1 activity provides a strong basis for the development of future therapies designed to repair the degenerative disc.

Hypoxia and viral infectious diseases.

Oxygen-sensing mechanisms allow cells to adapt and respond to changes in cellular oxygen tension, including hypoxic conditions. Hypoxia-inducible factor (HIF) is a central mediator in this fundamental adaptive response, and has critical functions in normal and disease physiology. Viruses have been shown to manipulate HIFs during their life cycle to facilitate replication and invasion. Conversely, HIFs are also implicated in the development of the host immune system and response to viral infections. Here, we highlight the recent revelations of host-pathogen interactions that involve the hypoxic response pathway and the role of HIF in emerging viral infectious diseases, as well as discussing potential antiviral therapeutic strategies targeting the HIF signaling axis.

Implications for preeclampsia: hypoxia-induced Notch promotes trophoblast migration.

In the first trimester of human pregnancy, low oxygen tension or hypoxia is essential for proper placentation and placenta function. Low oxygen levels and activation of signaling pathways have been implicated as critical mediators in the promotion of trophoblast differentiation, migration, and invasion with inappropriate changes in oxygen tension and aberrant Notch signaling both individually reported as causative to abnormal placentation. Despite crosstalk between hypoxia and Notch signaling in multiple cell types, the relationship between hypoxia and Notch in first trimester trophoblast function is not understood. To determine how a low oxygen environment impacts Notch signaling and cellular motility, we utilized the human first trimester trophoblast cell line, HTR-8/SVneo. Gene set enrichment and ontology analyses identified pathways involved in angiogenesis, Notch and cellular migration as upregulated in HTR-8/SVneo cells exposed to hypoxic conditions. DAPT, a γ-secretase inhibitor that inhibits Notch activation, was used to interrogate the crosstalk between Notch and hypoxia pathways in HTR-8/SVneo cells. We found that hypoxia requires Notch activation to mediate HTR-8/SVneo cell migration, but not invasion. To determine if our in vitro findings were associated with preeclampsia, we analyzed the second trimester chorionic villous sampling (CVS) samples and third trimester placentas. We found a significant decrease in expression of migration and invasion genes in CVS from preeclamptic pregnancies and significantly lower levels of JAG1 in placentas from pregnancies with early-onset preeclampsia with severe features. Our data support a role for Notch in mediating hypoxia-induced trophoblast migration, which may contribute to preeclampsia development.

The middle cerebral artery blood velocity response to acute normobaric hypoxia occurs independently of changes in ventilation in humans

What is the central question of this study? Does the ventilatory response to moderate acute hypoxia increase cerebral perfusion independently of changes in arterial oxygen tension in humans? What is the main finding and its importance? The ventilatory response does not increase middle cerebral artery mean blood velocity during moderate isocapnic acute hypoxia beyond that elicited by reduced oxygen saturation. Hypoxia induces ventilatory, cardiovascular and cerebrovascular adjustments to defend against reductions in systemic oxygen delivery. We aimed to determine whether the ventilatory response to moderate acute hypoxia increases cerebral perfusion independently of changes in arterial oxygenation. Eleven young healthy individuals were exposed to four 15min experimental conditions: (1) normoxia (partial pressure of end-tidal oxygen, =100mmHg), (2) hypoxia ( =50mmHg), (3) normoxia with breathing volitionally matched to levels observed during hypoxia (hyperpnoea; =100mmHg) and (4) hypoxia ( =50mmHg) with respiratory frequency and tidal volume volitionally matched to levels observed during normoxia (i.e., restricted breathing (RB)). Isocapnia was maintained in all conditions. Middle cerebral artery mean blood velocity (MCA Vmean ), assessed by transcranial Doppler ultrasound, was increased during hypoxia (58±12cm/s, P=0.04) and hypoxia + RB (61±14cm/s, P<0.001) compared to normoxia (55±11cm/s), while it was unchanged during hyperpnoea (52±13cm/s, P=0.08). MCA Vmean was not different between hypoxia and hypoxia + RB (P>0.05). These findings suggest that the hypoxic ventilatory response does not increase cerebral perfusion, indexed using MCA Vmean , during moderate isocapnic acute hypoxia beyond that elicited by reduced oxygen saturation.

Metabolic adaptation in hypoxia and cancer.

The ability of tumor cells to adapt to changes in oxygen tension is essential for tumor development. Low oxygen concentration influences cellular metabolism and, thus, affects proliferation, migration, and invasion. A focal point of the cell's adaptation to hypoxia is the transcription factor HIF1α (hypoxia-inducible factor 1 alpha), which affects the expression of specific gene networks involved in cellular energetics and metabolism. This review illustrates the mechanisms by which HIF1α-induced metabolic adaptation promotes angiogenesis, participates in the escape from immune recognition, and increases cancer cell antioxidant capacity. In addition to hypoxia, metabolic inhibition of 2-oxoglutarate-dependent dioxygenases regulates HIF1α stability and transcriptional activity. This phenomenon, known as pseudohypoxia, is frequently used by cancer cells to promote glycolytic metabolism to support biomass synthesis for cell growth and proliferation. In this review, we highlight the role of the most important metabolic intermediaries that are at the center of cancer's biology, and in particular, the participation of these metabolites in HIF1α retrograde signaling during the establishment of pseudohypoxia. Finally, we will discuss how these changes affect both the development of cancers and their resistance to treatment.

The Landscape of Interactions between Hypoxia-Inducible Factors and Reactive Oxygen Species in the Gastrointestinal Tract.

The gastrointestinal tract (GT) is the major organ involved in digestion, absorption, and immunity, which is prone to oxidative destruction by high levels of reactive oxygen species (ROS) from luminal oxidants, such as food, drugs, and pathogens. Excessive ROS will lead to oxidative stresses and disrupt essential biomolecules, which also act as cellular signaling molecules in response to growth factors, hormones, and oxygen tension changes. Hypoxia-inducible factors (HIFs) are critical regulators mediating responses to cellular oxygen tension changes, which are also involved in energy metabolism, immunity, renewal, and microbial homeostasis in the GT. This review discusses interactions between HIF (mainly HIF-1α) and ROS and relevant diseases in the GT combined with our lab's work. It might help to develop new therapies for gastrointestinal diseases associated with ROS and HIF-1α.

In vitro assay for single-cell characterization of impaired deformability in red blood cells under recurrent episodes of hypoxia.

Red blood cells (RBCs) are subjected to recurrent changes in shear stress and oxygen tension during blood circulation. The cyclic shear stress has been identified as an important factor that alone can weaken cell mechanical deformability. The effects of cyclic hypoxia on cellular biomechanics have yet to be fully investigated. As the oxygen affinity of hemoglobin plays a key role in the biological function and mechanical performance of RBCs, the repeated transitions of hemoglobin between its R (high oxygen tension) and T (low oxygen tension) states may impact their mechanical behavior. The present study focuses on developing a novel microfluidic-based assay for characterization of the effects of cyclic hypoxia on cell biomechanics. The capability of this assay is demonstrated by a longitudinal study of individual RBCs in health and sickle cell disease subjected to cyclic hypoxia conditions of various durations and levels of low oxygen tension. The viscoelastic properties of cell membranes are extracted from tensile stretching and relaxation processes of RBCs induced by the electrodeformation technique. Results demonstrate that cyclic hypoxia alone can significantly reduce cell deformability, similar to the fatigue damage accumulated through cyclic mechanical loading. RBCs affected by sickle cell disease are less deformable (significantly higher membrane shear modulus and viscosity) than normal RBCs. The fatigue resistance of sickle RBCs to the cyclic hypoxia challenge is significantly inferior to that of normal RBCs, and this trend is more significant in mature erythrocytes of sickle cells. When the oxygen affinity of sickle hemoglobin is enhanced by anti-sickling drug treatment of 5-hydroxymethyl-2-furfural (5-HMF), sickle RBCs show ameliorated resistance to fatigue damage induced by cyclic hypoxia. These results indicate an important biophysical mechanism underlying RBC senescence in which the cyclic hypoxia challenge alone can lead to mechanical degradation of the RBC membrane. We envision that the application of this assay can be further extended to RBCs in other blood diseases and other cell types.

A Rapid Shift from Chronic Hyperoxia to Normoxia Induces Systemic Anaphylaxis via Transient Receptor Potential Ankyrin 1 Channels on Mast Cells.

Extensive activation of mast cells is the major switch that triggers systemic anaphylaxis, resulting in the subsequent release of anaphylactic mediators into circulation. We previously demonstrated that rapid changes in oxygen tension lead to mast cell degranulation, and the released tryptase triggers retinal angiogenesis in a murine oxygen-induced retinopathy model. However, whether a rapid shift from hyperoxia to normoxia (relative hypoxic stress) is a risk factor for systemic anaphylaxis remains unknown. In this study, we demonstrated that the relative hypoxia stress induces systemic mast cell activation via transient receptor potential ankyrin 1 (TRPA1) channels, which immediately leads to hypothermia and increased vascular permeability in adult mice. Although mast cell-deficient or TRPA1-deficient mice did not exhibit anaphylactic symptoms following a rapid sift to normoxia, preinjection with bone marrow-derived cultured mast cells (BMCMCs) derived from wild-type TRPA1-expressing mice restored anaphylactic responses. In addition, we found that the rapid reductions in oxygen tension in a culture atmosphere triggered the degranulation of BMCMCs derived from wild-type TRPA1-expressing mice but not that of BMCMCs derived from TRPA1-deficient mice. In human LAD2 mast cells, the relative hypoxic stress led to the degranulation, which was suppressed by the addition of a TRPA1 inhibitor. Gradual reductions from hyperoxia to normoxia led to no anaphylactic symptoms. Our results demonstrated that TRPA1-triggered mast cell degranulation is a novel pathway that induces anaphylactic shock without Ag-Ab reactions. These findings introduce a potential role for oxygen in inducing mast cell-dependent anaphylaxis and highlight the need to reconsider chronic pure oxygen therapy for anoxic diseases.

Changes in Arterial Blood Pressure and Oxygen Tension as a Result of Hoisting in Isoflurane Anesthetized Healthy Adult Horses.

Background: In anesthetized adult horses, changes in recumbency can influence the cardiovascular system but how arterial blood pressures and oxygen tension change in isoflurane anesthetized animals as a direct result of hoisting has not been investigated.Objective: To evaluate effects of hoisting on hemodynamic function and pulmonary gas exchange in isoflurane-anesthetized horses.Study Design: Prospective, experimental study.Methods: Six adult horses were anesthetized three times using isoflurane in pure oxygen (inspired fraction 0.9–1.0), and allowed breathing spontaneously in lateral recumbency. After 45 min horses were hoisted using a single hoist-hobble system for 5 min and returned into left lateral recumbency. Heart rate (HR), respiratory rate (RR), and systolic (SAP), diastolic (DAP), and mean arterial blood pressures (MAP) were measured every minute starting from 5 min before to 5 min after hoisting. Arterial blood gas samples were collected before, during, and after hoisting.Results: Significant changes in hemodynamic parameters and PaO2 but not PaCO2 were found between baseline recordings and measurements obtained during and early after hoisting. The MAP decreased within the 1st min of hoisting from a mean of 74 ± 17 mmHg at baseline to 57 ± 20 mmHg (p < 0.05). Thereafter, it rapidly recovered to baseline before continuing to rise to higher than baseline values and then remaining elevated for 5 min after horses were returned into lateral recumbency. Simultaneously, the HR increased by 6–9 beats per min during the initial 3 min of hoisting before returning close to baseline values (p < 0.05). The PaO2 decreased significantly from a mean of 324.9 ±137.0 mmHg at baseline to a mean of 141.3 ± 104.2 mmHg during hoisting (p < 0.001) without recovering any more to baseline values.Clinical significance: Hoisting an adult horse during or at the end of isoflurane anesthesia carries the risk of a precipitous, though short-lived (1–2 min), drop in arterial blood pressures and a persistent decrease in arterial oxygenation. While in systemically healthy animals the observed functional impairments were not life-threatening, they may be more severe in systemically compromised horses.Therefore, arterial blood pressures and oxygenation must be carefully monitored when hoisting sick equine patients during or at the end of inhalant anesthesia.

Remifentanil infusion during desflurane anesthesia reduces tissue blood flow while maintaining blood pressure and tissue oxygen tension in the masseter muscle and mandibular bone marrow.

The aim of this study was to compare changes in tissue blood flow and tissue oxygen tension in the masseter muscle and mandibular bone marrow induced by remifentanil under desflurane or sevoflurane anesthesia. Eleven male tracheotomized Japan White rabbits were anesthetized with desflurane or sevoflurane under mechanical ventilation. The order of the inhalation of desflurane or sevoflurane was randomized. Desflurane or sevoflurane was administered at 1.0 minimum alveolar concentration and remifentanil was infused at 0.4 µg/kg/min. Observed variables included heart rate (HR), blood pressure (BP), common carotid artery blood flow (CCBF), 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). Two way repeated measures ANOVA showed no interaction between volatile anesthetics and remifentanil infusion except for MBF. There were significant differences in HR, SBP, DBP, MAP and CCBF between desflurane and sevoflurane groups. There were also significant differences in HR, SBP, DBP, MAP, CCBF, BBF and PbO2 before, during and after remifentanil infusion. Desflurane reduced tissue blood flow in the masseter muscle and mandibular bone marrow while better maintained HR and BP than sevoflurane. Under remifentanil infusion, although both anesthetics reduced tissue blood flow, tissue oxygen tension was maintained in masseter muscle and mandibular bone marrow.

Key Role of Respiratory Quotient to Reduce the Occurrence of Hypoxemia During Extracorporeal Gas Exchange: A Theoretical Analysis.

Extracorporeal respiratory support, including low blood flow systems providing mainly extracorporeal CO2 removal, are increasingly applied in clinical practice. Gas exchange physiology during extracorporeal respiratory support is complex and differs between full extracorporeal membrane oxygenation and extracorporeal CO2 removal. Aim of the present article is to review pathophysiological aspects which are relevant for the understanding of hypoxemia development during extracorporeal CO2 removal. We will describe the mathematical and physiologic background underlying changes in respiratory quotient and alveolar oxygen tension during venovenous extracorporeal gas exchange and highlight the clinical implications. Theoretical analysis of venovenous extracorporeal gas exchange. Italian university research hospital. None. None. While the effect of extracorporeal CO2 removal on the respiratory quotient of the native lung has long been known, the role of extracorporeal oxygenation in dictating changes in the respiratory quotient has been less addressed. Indeed, both extracorporeal CO2 removal and extracorporeal oxygen delivery affect the respiratory quotient of the native lung and thus influence the alveolar PO2. Indeed, for the same amount of extracorporeal CO2 extraction, it is possible to reduce the FIO2, reduce the risk of absorption atelectasis, and maintain the same alveolar PO2, by increasing the extracorporeal oxygen delivery. Worsening of hypoxemia is frequent during low-flow extracorporeal CO2 removal combined with ultraprotective mechanical ventilation. In this context, increasing extracorporeal oxygen delivery, increases the respiratory quotient of the native lung and could reduce both the occurrence of alveolar hypoxia and absorption atelectasis, thus optimizing the residual lung function.

Deletion of von-Hippel Lindau in Dmp1-expressing cells impairs B cell development

Abstract Our objective is to characterize how altered bone homeostasis influences B lymphocyte development. The von-Hippel Lindau protein (VHL) regulates hypoxia-inducible factor degradation and is involved in responses to low oxygen environments. Osteoblasts (OBs) support B cell development and mature into osteocytes (OCYs). We utilized Dmp1-Cre;Vhl conditional knockout mice (cKO), in which Vhl is deleted in OBs and OCYs. The cKO display dysregulated bone growth, high bone density, smaller bone marrow (BM) cavity volume, and an overall decrease in BM cellularity compared to wild-type (WT) mice. B cell progenitors is significantly increased in frequency and numbers whereas Hardy Fractions B, C, D, E and F were significantly decreased in the BM of cKO mice. Analysis of BM B cells 16 weeks after whole BM transplantation, showed a significant reduction in Fractions B-C and later Fractions in the WT→cKO mice, while B cell development was normal in the cKO→WT chimeras, indicating a cell-extrinsic effect of Vhl on B cells within the cKO BM microenvironment. We hypothesize that B cell development is not supported due to reduction of key niche cells and decreased production of IL7, SCF, CXCL12, and Flt3. To define the defective niche cells, we will use in vitro B cell development assays in which WT B cells will be co-cultured with sorted cKO OBs, MSCs, and OCYs. B cell apoptosis, proliferation and turnover rates will be measured. We have begun preliminary studies using intravital and ex vivo imaging of the cKO BM to identify changes in oxygen tension, blood vessel type and structure, the presence and location of stromal cells. These studies have the potential to reveal novel molecular mechanisms by which Vhl in Dmp1 expressing cells may serve as a B cell niche.

Phenotypic and Functional Characterization of human Umbilical Vein Endothelial Cells (hUVEC) Cultures Established under Physiologic vs. Atmospheric Oxygen Tension

Primary cultures of human umbilical vein endothelial cells (hUVEC) have historically been established at atmospheric oxygen (O2) tension (21%) and their surface marker profiles and angiogenic potential in are understood. However, physiologic O2 tension ranges from ~1% in cartilage to ~13% in major arteries, thus 21% O2 represents a supraphysiologic O2 exposure. We conducted experiments to establish and characterize hUVEC at 21% O2 and physiologically relevant oxygen tension (5% O2) from three independent donors.hUVEC were isolated by standard methods with dissociation and culture steps conducted at 21% or 5% O2. Cells were maintained in standard endothelial cell growth media and were cryopreserved at the end of passage 1. Cells were thawed, used to establish live passage 2 cultures, and confirmed to be sterile and free of mycoplasma and endotoxin. hUVEC established at 5% O2 (hUVEC‐LO) were compared to hUVEC established at 21% O2 (hUVEC‐HO) with respect to population doubling time, surface marker expression by flow cytometry, and angiogenic potential by tube formation assay.Both hUVEC‐LO and hUVEC‐HO were immunopositive for CD31, VE‐cadherin, CD146, CD202b, and vEGFR1, and were negative for CD45 and CD90. hUVEC‐LO uniquely expressed a greater percentage of markers associated with an endothelial progenitor phenotype, including CD117, Slug, CD133, and vEGFR2. The calculated population doubling time of hUVEC‐LO was on average 10% faster than the donor‐matched hUVEC‐HO. Angiogenic potential was confirmed by tube formation assay for each lot at the oxygen tension at which they were established. Crossover experiments were conducted to assess tube formation in hUVEC‐LO and hUVEC‐HO under assay conditions of 21% or 5% O2. No statistical differences were noted after 6 hours of assay duration with respect to: number of junctions, segments, meshes, and total length of segments, branches, or extremities. Significant differences were observed beyond 6 hours between hUVEC‐LO and hUVEC‐HO in mean mesh size and number of branches, but the magnitude and pattern of differences varied from donor‐to‐donor. In contrast, the early phase of angiogenesis (0–6 hours) revealed notable differences between hUVEC‐LO and hUVEC‐HO, with hUVEC‐LO generally exhibiting greater variance with respect to number of junctions, mesh area, number of meshes, and number of segments.Taken together, these results suggest that hUVEC‐LO may have a more stem‐like phenotype characterized by the retention of progenitor‐associated surface markers and a faster doubling time compared to hUVEC‐HO from the same donor. While the ultimate capacity for tube formation did not differ between hUVEC‐LO and hUVEC‐HO assayed at 21% or 5% O2, the preliminary data suggest that hUVEC‐LO respond more actively to adapt to changes in oxygen tension, undergoing significant fluctuations in multiple measures at early time points. Further experiments are needed to elucidate the processes and mechanism(s) that lead to differential phenotype and/or performance of hUVEC‐LO and hUVEC‐HO, in particular during the early initiating events of angiogenesis.

Hypoxia-Inducible Factor (HIF)-1α Promotes Inflammation and Injury Following Aspiration-Induced Lung Injury in Mice.

Acid aspiration-induced lung injury is a common disease in the intensive care unit (ICU) and acute respiratory distress syndrome (ARDS). Hypoxia-inducible factor (HIF)-1α is a major transcription factor responsible for regulating the cellular response to changes in oxygen tension. A clear understanding of the function of HIF-1α in lung inflammatory response is currently lacking. Here, we sought to determine the role of HIF-1α in type 2 alveolar epithelial cells (AEC) in the generation of the acute inflammatory response following gastric aspiration (GA). GA led to profound hypoxia at very early time points following GA. This correlated to a robust increase in HIF-1α, tissue albumin and pro-inflammatory mediators following GA in AECs. The extent of lung injury and the release of pro/anti-inflammatory cytokines were significantly reduced in HIF-1α (-/-) mice. Finally, we report that HIF-1α upregulation of the acute inflammatory response is dependent on NF-κB following GA.