Hyperoxia and brain: the link between necessity and injury from a molecular perspective

Oxygen (O2) supplementation is commonly used to treat hypoxia in patients with respiratory failure. However, indiscriminate use can lead to hyperoxia, a condition detrimental to living tissues, particularly the brain. The brain is sensitive to reactive oxygen species (ROS) and inflammation caused by high concentrations of O2, which can result in brain damage and mitochondrial dysfunction, common features of neurodegenerative disorders. Hyperoxia leads to increased production of ROS, causing oxidative stress, an imbalance between oxidants and antioxidants, which can damage tissues. The brain is particularly vulnerable to oxidative stress due to its lipid composition, high O2 consumption rate, and low levels of antioxidant enzymes. Moreover, hyperoxia can cause vasoconstriction and decreased O2 supply to the brain, posing a challenge to redox balance and neurodegenerative processes. Studies have shown that the severity of hyperoxia-induced brain damage varies with inspired O2 concentration and duration of exposure. Therefore, careful evaluation of the balance between benefits and risks of O2 supplementation, especially in clinical settings, is crucial.

Assessing the pulmonary vascular responsiveness to oxygen with proton MRI

Ventilation-perfusion matching occurs passively and is also actively regulated through hypoxic pulmonary vasoconstriction (HPV). The extent of HPV activity in humans, particularly normal subjects, is uncertain. Current evaluation of HPV assesses changes in ventilation-perfusion relationships/pulmonary vascular resistance with hypoxia and is invasive, or unsuitable for patients because of safety concerns. We used a noninvasive imaging-based approach to quantify the pulmonary vascular response to oxygen as a metric of HPV by measuring perfusion changes between breathing 21% and 30%O2 using arterial spin labeling (ASL) MRI. We hypothesized that the differences between 21% and 30%O2 images reflecting HPV release would be 1) significantly greater than the differences without [Formula: see text] changes (e.g., 21-21% and 30-30%O2) and 2) negatively associated with ventilation-perfusion mismatch. Perfusion was quantified in the right lung in normoxia (baseline), after 15 min of 30% O2 breathing (hyperoxia) and 15 min normoxic recovery (recovery) in healthy subjects (7 M, 7 F; age = 41.4 ± 19.6 yr). Normalized, smoothed, and registered pairs of perfusion images were subtracted and the mean square difference (MSD) was calculated. Separately, regional alveolar ventilation and perfusion were quantified from specific ventilation, proton density, and ASL imaging; the spatial variance of ventilation-perfusion (σ2V̇a/Q̇) distributions was calculated. The O2-responsive MSD was reproducible (R2 = 0.94, P < 0.0001) and greater (0.16 ± 0.06, P < 0.0001) than that from subtracted images collected under the same [Formula: see text] (baseline = 0.09 ± 0.04, hyperoxia = 0.08 ± 0.04, recovery = 0.08 ± 0.03), which were not different from one another (P = 0.2). The O2-responsive MSD was correlated with σ2V̇a/Q̇ (R2 = 0.47, P = 0.007). These data suggest that active HPV optimizes ventilation-perfusion matching in normal subjects. This noninvasive approach could be applied to patients with different disease phenotypes to assess HPV and ventilation-perfusion mismatch.NEW & NOTEWORTHY We developed a new proton MRI method to noninvasively quantify the pulmonary vascular response to oxygen. Using a hyperoxic stimulus to release HPV, we quantified the resulting redistribution of perfusion. The differences between normoxic and hyperoxic images were greater than those between images without [Formula: see text] changes and negatively correlated with ventilation-perfusion mismatch. This suggests that active HPV optimizes ventilation-perfusion matching in normal subjects. This approach is suitable for assessing patients with different disease phenotypes.

Effects of hyperventilation on repeated breath-holding while in a fasting state: do risks outweigh the benefits?

Breath-holding preceded by either an overnight fast or hyperventilation has been shown to potentiate the risk of a hypoxic blackout. However, no study has explored the combined effects of fasting and hyperventilation on apneic performance and associated physiological responses. Nine nondivers (8 males) attended the laboratory on two separate occasions (≥48 h apart), both after a 12-h overnight fast. During each visit, a hyperoxic rebreathing trial was performed followed by three repeated maximal static apneas preceded by either normal breathing (NORM) or a 30-s hyperventilation (HYPER). Splenic volume, hematology, cardiovascular, and respiratory variables were monitored. There were no interprotocol differences at rest or during hyperoxic rebreathing for any variable (P ≥ 0.09). On nine occasions (8 in HYPER), the subjects reached our safety threshold (oxygen saturation 65%) and were asked to abort their apneas, with the preponderance of these incidents (6 of 9) occurring during the third repetition. Across the sequential attempts, longer apneas were recorded in HYPER [median(range), 220(123-324) s vs. 185(78-296) s, P ≤ 0.001], with involuntary breathing movements occurring later [134(65-234) s vs. 97(42-200) s, P ≤ 0.001] and end-apneic partial end-tidal pressures of oxygen (P ET O 2 ) being lower (P ≤ 0.02). During the final repetition, partial end-tidal pressure of carbon dioxide [(P ET CO 2 ), 6.53 ± 0.46 kPa vs. 6.01 ± 0.45 kPa, P = 0.005] was lower in HYPER. Over the serial attempts, preapneic tidal volume was gradually elevated [from apnea 1 to 3, by 0.26 ± 0.24 L (HYPER) and 0.28 ± 0.30 L (NORM), P ≤ 0.025], with a correlation noted with preapneic P ET CO 2 (r = -0.57, P < 0.001) and P ET O 2 (r = 0.76, P < 0.001), respectively. In a fasted state, preapnea hyperventilation compared with normal breathing leads to longer apneas but may increase the susceptibility to a hypoxic blackout.NEW & NOTEWORTHY This study shows that breath-holds (apneas) preceded by a 12-h overnight fast coupled with a 30-s hyperventilation as opposed to normal breathing may increase the likelihood of a hypoxic blackout through delaying the excitation of hypercapnic ventilatory sensory chemoreflexes. Evidently, this risk is exacerbated over a series of repeated maximal attempts, possibly due to a shift in preapneic gas tensions facilitated by an unintentional increase in tidal volume breathing.

Placental T2* and BOLD effect in response to hyperoxia in normal and growth-restricted pregnancies: multicenter cohort study

OBJECTIVES

Blood-oxygen-level-dependent (BOLD) magnetic resonance imaging (MRI) facilitates the non-invasive in-vivo evaluation of placental oxygenation. The aims of this study were to identify and quantify a relative BOLD effect in response to hyperoxia in the human placenta and to compare it between pregnancies with and those without fetal growth restriction (FGR).

METHODS

This was a prospective multicenter study (NCT02238301) of 19 pregnancies with FGR (estimated fetal weight (EFW) on ultrasound < 5th centile) and 75 non-FGR pregnancies (controls) recruited at two centers in Paris, France. Using a 1.5-Tesla MRI system, the same multi-echo gradient-recalled echo (GRE) sequences were performed at both centers to obtain placental T2* values at baseline and in hyperoxic conditions. The relative BOLD effect was calculated according to the equation 100 × (hyperoxic T2* - baseline T2*)/baseline T2*. Baseline T2* values and relative BOLD effect were compared according to EFW (FGR vs non-FGR), presence/absence of Doppler anomalies and birth weight (small-for-gestational age (SGA) vs non-SGA).

RESULTS

We observed a relative BOLD effect in response to hyperoxia in the human placenta (median, 33.8% (interquartile range (IQR), 22.5-48.0%)). The relative BOLD effect did not differ significantly between pregnancies with and those without FGR (median, 34.4% (IQR, 24.1-48.5%) vs 33.7% (22.7-47.4%); P = 0.95). Baseline T2* Z-score adjusted for gestational age at MRI was significantly lower in FGR pregnancies compared with non-FGR pregnancies (median, -1.27 (IQR, -4.87 to -0.10) vs 0.33 (IQR, -0.81 to 1.02); P = 0.001). Baseline T2* Z-score was also significantly lower in those pregnancies that subsequently delivered a SGA neonate (n = 23) compared with those that delivered a non-SGA neonate (n = 62) (median, -0.75 (IQR, -3.48 to 0.29) vs 0.35 (IQR, -0.79 to 1.05); P = 0.01).

CONCLUSIONS

Our study confirms a BOLD effect in the human placenta and that baseline T2* values are significantly lower in pregnancies with FGR. Further studies are needed to evaluate whether such parameters may detect placental insufficiency before it has a clinical impact on fetal growth. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Differential splenic responses to hyperoxic breathing at high altitude in Sherpa and lowlanders

The human spleen contracts in response to stress-induced catecholamine secretion, resulting in a temporary rise in haemoglobin concentration ([Hb]). Recent findings highlighted enhanced splenic response to exercise at high altitude in Sherpa, possibly due to a blunted splenic response to hypoxia. To explore the potential blunted splenic contraction in Sherpas at high altitude, we examined changes in spleen volume during hyperoxic breathing, comparing acclimatized Sherpa with acclimatized individuals of lowland ancestry. Our study included 14 non-Sherpa (7 female) residing at altitude for a mean continuous duration of 3 months and 46 Sherpa (24 female) with an average of 4 years altitude exposure. Participants underwent a hyperoxic breathing test at altitude (4300 m; barrometric pressure = ∼430 torr;P O 2 ${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$  = ∼90 torr). Throughout the test, we measured spleen volume using ultrasonography and monitored oxygen saturation (S p O 2 ${S_{{\mathrm{p}}{{\mathrm{O}}_{\mathrm{2}}}}}$ ). During rest, Sherpa exhibited larger spleens (226 ± 70 mL) compared to non-Sherpa (165 ± 34 mL; P < 0.001; effect size (ES) = 0.95, 95% CI: 0.3-1.6). In response to hyperoxia, non-Sherpa demonstrated 22 ± 12% increase in spleen size (35 ± 17 mL, 95% CI: 20.7-48.9; P < 0.001; ES = 1.8, 95% CI: 0.93-2.66), while spleen size remained unchanged in Sherpa (-2 ± 13 mL, 95% CI: -2.4 to 7.3; P = 0.640; ES = 0.18, 95% CI: -0.10 to 0.47). Our findings suggest that Sherpa and non-Sherpas of lowland ancestry exhibit distinct variations in spleen volume during hyperoxia at high altitude, potentially indicating two distinct splenic functions. In Sherpa, this phenomenon may signify a diminished splenic response to altitude-related hypoxia at rest, potentially contributing to enhanced splenic contractions during physical stress. Conversely, non-Sherpa experienced a transient increase in spleen size during hyperoxia, indicating an active tonic contraction, which may influence early altitude acclimatization in lowlanders by raising [Hb].

Oxygenation During Venoarterial Extracorporeal Membrane Oxygenation: Physiology, Current Evidence, and a Pragmatic Approach to Oxygen Titration

OBJECTIVES

This review aims to: 1) identify the key circuit and patient factors affecting systemic oxygenation, 2) summarize the literature reporting the association between hyperoxia and patient outcomes, and 3) provide a pragmatic approach to oxygen titration, in patients undergoing peripheral venoarterial extracorporeal membrane oxygenation (ECMO).

DATA SOURCES

Searches were performed using PubMed, SCOPUS, Medline, and Google Scholar.

STUDY SELECTION

All observational and interventional studies investigating the association between hyperoxia, and clinical outcomes were included, as well as guidelines from the Extracorporeal Life Support Organization.

DATA EXTRACTION

Data from relevant literature was extracted, summarized, and integrated into a concise narrative review. For ease of reference a summary of relevant studies was also produced.

DATA SYNTHESIS

The extracorporeal circuit and the native cardiorespiratory circuit both contribute to systemic oxygenation during venoarterial ECMO. The ECMO circuit's contribution to systemic oxygenation is, in practice, largely determined by the ECMO blood flow, whereas the native component of systemic oxygenation derives from native cardiac output and residual respiratory function. Interactions between ECMO outflow and native cardiac output (as in differential hypoxia), the presence of respiratory support, and physiologic parameters affecting blood oxygen carriage also modulate overall oxygen exposure during venoarterial ECMO. Physiologically those requiring venoarterial ECMO are prone to hyperoxia. Hyperoxia has a variety of definitions, most commonly Pa o2 greater than 150 mm Hg. Severe hypoxia (Pa o2 > 300 mm Hg) is common, seen in 20%. Early severe hyperoxia, as well as cumulative hyperoxia exposure was associated with in-hospital mortality, even after adjustment for disease severity in both venoarterial ECMO and extracorporeal cardiopulmonary resuscitation. A pragmatic approach to oxygenation during peripheral venoarterial ECMO involves targeting a right radial oxygen saturation target of 94-98%, and in selected patients, titration of the fraction of oxygen in the mixture via the air-oxygen blender to target postoxygenator Pa o2 of 150-300 mm Hg.

CONCLUSIONS

Hyperoxia results from a range of ECMO circuit and patient-related factors. It is common during peripheral venoarterial ECMO, and its presence is associated with poor outcome. A pragmatic approach that avoids hyperoxia, while also preventing hypoxia has been described for patients receiving peripheral venoarterial ECMO.

Role of Oxygen and Its Radicals in Peripheral Nerve Regeneration: From Hypoxia to Physoxia to Hyperoxia

Oxygen is compulsory for mitochondrial function and energy supply, but it has numerous more nuanced roles. The different roles of oxygen in peripheral nerve regeneration range from energy supply, inflammation, phagocytosis, and oxidative cell destruction in the context of reperfusion injury to crucial redox signaling cascades that are necessary for effective axonal outgrowth. A fine balance between reactive oxygen species production and antioxidant activity draws the line between physiological and pathological nerve regeneration. There is compelling evidence that redox signaling mediated by the Nox family of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases plays an important role in peripheral nerve regeneration. Further research is needed to better characterize the role of Nox in physiological and pathological circumstances, but the available data suggest that the modulation of Nox activity fosters great therapeutic potential. One of the promising approaches to enhance nerve regeneration by modulating the redox environment is hyperbaric oxygen therapy. In this review, we highlight the influence of various oxygenation states, i.e., hypoxia, physoxia, and hyperoxia, on peripheral nerve repair and regeneration. We summarize the currently available data and knowledge on the effectiveness of using hyperbaric oxygen therapy to treat nerve injuries and discuss future directions.

Effects of hypobaria, hyperoxia, and nitrogen form on the growth and nutritional quality of lettuce

The objectives of this research were to investigate the impact of hypobaria, hyperoxia, and nitrogen form on the growth and nutritional quality of plants. Pre-culture 20-day-old lettuce (Lactuca sativa L. var. Rome) seedlings grew for 25 days under three levels of total atmospheric pressure (101, 54, and 30 kPa), two levels of oxygen partial pressure (21 and 28 kPa), and two forms of nitrogen (NO3N and NH4N). The ratios of NO3N to NH4N included 3: 1, 4: 0, 2: 2, and 0: 4. The nitrogen quantity included two levels, i.e. N1, 0.1 g N kg-1 dry matrix and N2, 0.2 g N kg-1 dry matrix. The growth status of lettuce plants in different treatments differentiated markedly. Regardless of the nitrogen factor, the growth status of lettuce plants treated with total atmospheric pressure/oxygen partial pressure at 54/21 was equivalent to the treatment of 101/21. Under the hypobaric condition (54 kPa), compared with 21 kPa oxygen partial pressure, hyperoxia (28 kPa) significantly inhibited the growth of lettuce plants and the biomass (fresh weight) decreased by 60.9%-69.9% compared with that under 101/21 treatment. At the N1 level, the sequence of the biomass of lettuce plants supplied with different ratios of NO3N to NH4N was 3: 1 > 4: 0 > 2: 2 > 0: 4, and there were higher concentrations of chlorophyll and carotenoid of lettuce plants supplied with the higher ratio of NO3 to NH4. At the N2 level, the effects of different ratios of NO3N to NH4N on lettuce plants were similar to those at the N1 level. The high nitrogen (N2) promoted the growth of lettuce plants such as 54/21/N2 treatments. Both form and nitrogen level did not affect the stress resistance of lettuce plants. Hypobaria (54 kPa) increased the contents of N, P, and K and hyperoxia (28 kPa) decreased the content of organic carbon in lettuce plants. The high nitrogen (N2) improved the content of total N and the N uptake. The ratios of NO3N to NH4N were 4: 0 and 3: 1, lettuce could absorb and utilize N effectively. This study demonstrated that hyperoxia (28 kPa) inhibited the growth of lettuce plants under the hypobaric condition (54 kPa), and high level of nitrogen (0.2 g N kg-1 dry matrix) and NO3N: NH4N at 3: 1 markedly enhanced the growth, the contents of mineral elements and the nutritional quality of lettuce plants.

Hyperoxia prevents the dynamic neonatal increases in lung mesenchymal cell diversity

Rapid expansion of the pulmonary microvasculature through angiogenesis drives alveolarization, the final stage of lung development that occurs postnatally and dramatically increases lung gas-exchange surface area. Disruption of pulmonary angiogenesis induces long-term structural and physiologic lung abnormalities, including bronchopulmonary dysplasia, a disease characterized by compromised alveolarization. Although endothelial cells are primary determinants of pulmonary angiogenesis, mesenchymal cells (MC) play a critical and dual role in angiogenesis and alveolarization. Therefore, we performed single cell transcriptomics and in-situ imaging of the developing lung to profile mesenchymal cells during alveolarization and in the context of lung injury. Specific mesenchymal cell subtypes were present at birth with increasing diversity during alveolarization even while expressing a distinct transcriptomic profile from more mature correlates. Hyperoxia arrested the transcriptomic progression of the MC, revealed differential cell subtype vulnerability with pericytes and myofibroblasts most affected, altered cell to cell communication, and led to the emergence of Acta1 expressing cells. These insights hold the promise of targeted treatment for neonatal lung disease, which remains a major cause of infant morbidity and mortality across the world.

Extracellular Vesicles From Mesenchymal Umbilical Cord Cells Exert Protection Against Oxidative Stress and Fibrosis in a Rat Model of Bronchopulmonary Dysplasia

Oxidative stress and fibrosis are important stress responses that characterize bronchopulmonary dysplasia (BPD), a disease for which only a therapy but not a cure has been developed. In this work, we investigated the effects of mesenchymal stromal cells-derived extracellular vesicles (MSC-EVs) on lung and brain compartment in an animal model of hyperoxia-induced BPD. Rat pups were intratracheally injected with MSC-EVs produced by human umbilical cord-derived MSC, following the Good Manufacturing Practice-grade (GMP-grade). After evaluating biodistribution of labelled MSC-EVs in rat pups left in normoxia and hyperoxia, oxidative stress and fibrosis investigation were performed. Oxidative stress protection by MSC-EVs treatment was proved both in lung and in brain. The lung epithelial compartment ameliorated glycosaminoglycan and surfactant protein expression in MSC-EVs-injected rat pups compared to untreated animals. Pups under hyperoxia exhibited a fibrotic phenotype in lungs shown by increased collagen deposition and also expression of profibrotic genes. Both parameters were reduced by treatment with MSC-EVs. We established an in vitro model of fibrosis and another of oxidative stress, and we proved that MSC-EVs suppressed the induction of αSMA, influencing collagen deposition and protecting from the oxidative stress. In conclusion, intratracheal administration of clinical-grade MSC-EVs protect from oxidative stress, improves pulmonary epithelial function, and counteracts the development of fibrosis. In the future, MSC-EVs could represent a new cure to prevent the development of BPD.

13C-Metabolic flux analysis detected a hyperoxemia-induced reduction of tricarboxylic acid cycle metabolism in granulocytes during two models of porcine acute subdural hematoma and hemorrhagic shock

Introduction

Supplementation with increased inspired oxygen fractions has been suggested to alleviate the harmful effects of tissue hypoxia during hemorrhagic shock (HS) and traumatic brain injury. However, the utility of therapeutic hyperoxia in critical care is disputed to this day as controversial evidence is available regarding its efficacy. Furthermore, in contrast to its hypoxic counterpart, the effect of hyperoxia on the metabolism of circulating immune cells remains ambiguous. Both stimulating and detrimental effects are possible; the former by providing necessary oxygen supply, the latter by generation of excessive amounts of reactive oxygen species (ROS). To uncover the potential impact of increased oxygen fractions on circulating immune cells during intensive care, we have performed a 13C-metabolic flux analysis (MFA) on PBMCs and granulocytes isolated from two long-term, resuscitated models of combined acute subdural hematoma (ASDH) and HS in pigs with and without cardiovascular comorbidity.

Methods

Swine underwent resuscitation after 2 h of ASDH and HS up to a maximum of 48 h after HS. Animals received normoxemia (PaO2 = 80 - 120 mmHg) or targeted hyperoxemia (PaO2 = 200 - 250 mmHg for 24 h after treatment initiation, thereafter PaO2 as in the control group). Blood was drawn at time points T1 = after instrumentation, T2 = 24 h post ASDH and HS, and T3 = 48 h post ASDH and HS. PBMCs and granulocytes were isolated from whole blood to perform electron spin resonance spectroscopy, high resolution respirometry and 13C-MFA. For the latter, we utilized a parallel tracer approach with 1,2-13C2 glucose, U-13C glucose, and U-13C glutamine, which covered essential pathways of glucose and glutamine metabolism and supplied redundant data for robust Bayesian estimation. Gas chromatography-mass spectrometry further provided multiple fragments of metabolites which yielded additional labeling information. We obtained precise estimations of the fluxes, their joint credibility intervals, and their relations, and characterized common metabolic patterns with principal component analysis (PCA).

Results

13C-MFA indicated a hyperoxia-mediated reduction in tricarboxylic acid (TCA) cycle activity in circulating granulocytes which encompassed fluxes of glutamine uptake, TCA cycle, and oxaloacetate/aspartate supply for biosynthetic processes. We further detected elevated superoxide levels in the swine strain characterized by a hypercholesterolemic phenotype. PCA revealed cell type-specific behavioral patterns of metabolic adaptation in response to ASDH and HS that acted irrespective of swine strains or treatment group.

Conclusion

In a model of resuscitated porcine ASDH and HS, we saw that ventilation with increased inspiratory O2 concentrations (PaO2 = 200 - 250 mmHg for 24 h after treatment initiation) did not impact mitochondrial respiration of PBMCs or granulocytes. However, Bayesian 13C-MFA results indicated a reduction in TCA cycle activity in granulocytes compared to cells exposed to normoxemia in the same time period. This change in metabolism did not seem to affect granulocytes' ability to perform phagocytosis or produce superoxide radicals.

IRF4 affects the protective effect of regulatory T cells on the pulmonary vasculature of a bronchopulmonary dysplasia mouse model by regulating FOXP3

BACKGROUND

Bronchopulmonary dysplasia (BPD) is a common chronic lung disease in preterm infants, characterised by compromised alveolar development and pulmonary vascular abnormalities. Emerging evidence suggests that regulatory T cells (Tregs) may confer protective effects on the vasculature. Knockdown of their transcription factor, interferon regulatory factor 4 (IRF4), has been shown to promote vascular endothelial hyperplasia. However, the involvement of Tregs and IRF4 in the BPD pathogenesis remains unclear. This study aimed to investigate the regulation of Tregs by IRF4 and elucidate its potential role in pulmonary vasculature development in a BPD mouse model.

METHODS

The BPD model was established using 85% hyperoxia exposure, with air exposure as the normal control. Lung tissues were collected after 7 or 14 days of air or hyperoxia exposure, respectively. Haematoxylin-eosin staining was performed to assess lung tissue pathology. Immunohistochemistry was used to measure platelet endothelial cell adhesion molecule-1 (PECAM-1) level, flow cytometry to quantify Treg numbers, and Western blot to assess vascular endothelial growth factor (VEGFA), angiopoietin-1 (Ang-1), forkhead box protein P3 (FOXP3), and IRF4 protein levels. We also examined the co-expression of IRF4 and FOXP3 proteins using immunoprecipitation and immunofluorescence double staining. Furthermore, we employed CRISPR/Cas9 technology to knock down the IRF4 gene and observed changes in the aforementioned indicators to validate its effect on pulmonary vasculature development in mice.

RESULTS

Elevated IRF4 levels in BPD model mice led to FOXP3 downregulation, reduced Treg numbers, and impaired pulmonary vascular development. Knockdown of IRF4 resulted in improved pulmonary vascular development and upregulated FOXP3 level.

CONCLUSION

IRF4 may affect the protective role of Tregs in the proliferation of pulmonary vascular endothelial cells and pulmonary vascular development in BPD model mice by inhibiting the FOXP3 level.

Hyperoxia: Effective Mechanism of Hyperbaric Treatment at Mild-Pressure

HBOT increases the proportion of dissolved oxygen in the blood, generating hyperoxia. This increased oxygen diffuses into the mitochondria, which consume the majority of inhaled oxygen and constitute the epicenter of HBOT effects. In this way, the oxygen entering the mitochondria can reverse tissue hypoxia, activating the electron transport chain to generate energy. Furthermore, intermittent HBOT is sensed by the cell as relative hypoxia, inducing cellular responses such as the activation of the HIF-1α pathway, which in turn, activates numerous cellular processes, including angiogenesis and inflammation, among others. These effects are harnessed for the treatment of various pathologies. This review summarizes the evidence indicating that the use of medium-pressure HBOT generates hyperoxia and activates cellular pathways capable of producing the mentioned effects. The possibility of using medium-pressure HBOT as a direct or adjunctive treatment in different pathologies may yield benefits, potentially leading to transformative therapeutic advancements in the future.

[The number of FOXP3+regulatory T cells (Tregs) decreased and transformed into RORγt+FOXP3+Tregs in lung tissues of mice with bronchopulmonary dysplasia]

Objective To explore the phenotypic conversion of regulatory T cells (Tregs) in the lungs of mice with bronchopulmonary dysplasia (BPD)-affected mice. Methods A total of 20 newborn C57BL/6 mice were divided into air group and hyperoxia group, with 10 mice in each group. The BPD model was established by exposing the newborn mice to hyperoxia. Lung tissues from five mice in each group were collected on postnatal days 7 and 14, respectively. Histopathological changes of the lung tissues was detected by HE staining. The expression level of surfactant protein C (SP-C) in the lung tissues was examined by Western blot analysis. Flow cytometry was performed to assess the proportion of FOXP3+ Tregs and RORγt+FOXP3+ Tregs in CD4+ lymphocytes. The concentrations of interleukin-17A (IL-17A) and IL-6 in lung homogenate were measured by using ELISA. Spearman correlation analysis was used to analyze the correlation between FOXP3+Treg and the expression of SP-C and the correlation between RORγt+FOXP3+ Tregs and the content of IL-17A and IL-6. Results The hyperoxia group exhibited significantly decreased levels of SP-C and radical alveolar counts in comparison to the control group. The proportion of FOXP3+Tregs was reduced and that of RORγt+FOXP3+Tregs was increased. IL-17A and IL-6 concentrations were significantly increased. SP-C was positively correlated with the expression level of RORγt+FOXP3+ Tregs. RORγt+FOXP3+ Tregs and IL-17A and IL-6 concentrations were also positively correlated. Conclusion The number of FOXP3+ Tregs in lung tissue of BPD mice is decreased and converted to RORγt+ FOXP3+ Tregs, which may be involved in hyperoxy-induced lung injury.

The reduction in arterial pH with increased temperature is not affected by hyperoxia in toads (Rhinella marina) and pythons (Python molurus)

It is well established that arterial pH decreases with increased temperature in amphibians and reptiles through an elevation of arterial PCO2, but the underlying regulation remains controversial. The alphastat hypothesis ascribes the pH fall to a ventilatory regulation of protein ionisation, but the pH reduction with temperature is lower than predicted by the pKa change of the imidazole group on histidine. We hypothesised that arterial pH decreases at high, but not at low, temperatures when toads (Rhinella marina) and snakes (Python molurus) are exposed to hyperoxia. In toads, hyperoxia caused similar elevations of arterial PCO2 at 20 and 30°C, indicative of a temperature-independent oxygen-mediated drive to breathing, whereas PCO2 was unaffected by hyperoxia in snakes at 25 and 35°C. These findings do not support our hypothesis of an increased oxygen-mediated drive to breathing as body temperature increases.

β3 Adrenoceptor Agonism Prevents Hyperoxia-Induced Colonic Alterations

Oxygen level is a key regulator of organogenesis and its modification in postnatal life alters the maturation process of organs, including the intestine, which do not completely develop in utero. The β3-adrenoreceptor (β3-AR) is expressed in the colon and has an oxygen-dependent regulatory mechanism. This study shows the effects of the β3-AR agonist BRL37344 in a neonatal model of hyperoxia-driven colonic injury. For the first 14 days after birth, Sprague-Dawley rat pups were exposed to ambient oxygen levels (21%) or hyperoxia (85%) and treated daily with BRL37344 at 1, 3, 6 mg/kg or untreated. At the end of day 14, proximal colon samples were collected for analysis. Hyperoxia deeply influences the proximal colon development by reducing β3-AR-expressing cells (27%), colonic length (26%) and mucin production (47%), and altering the neuronal chemical coding in the myenteric plexus without changes in the neuron number. The administration of BRL37344 at 3 mg/kg, but not at 1 mg/kg, significantly prevented these alterations. Conversely, it was ineffective in preventing hyperoxia-induced body weight loss. BRL37344 at 6 mg/kg was toxic. These findings pave the way for β3-AR pharmacological targeting as a therapeutic option for diseases caused by hyperoxia-impaired development, typical prematurity disorders.

Effects of postovipositional hypoxia and hyperoxia on leatherback turtle reproductive success and hatchling performance

Leatherback egg clutches typically experience lower hatching success (~50%) than those of other sea turtle species (>70%). The majority of embryonic death (>50%) occurs at early stages of development, possibly because embryos fail to break preovipositional embryonic arrest after oviposition. The embryonic arrest is maintained by hypoxia in the oviduct and following oviposition increased availability of oxygen is the trigger that breaks arrest in all turtle species studied to date. We conducted an ex situ incubator experiment and an in situ hatchery experiment to examine the influence of oxygen availability on hatching success and hatchling traits in leatherbacks. After oviposition, eggs (n = 1005) were incubated in either normoxia (21% O2 ), hyperoxia (32%-42% O2 ) for 5 days, or hypoxia (1% O2 ) for 3 or 5 days. As with other turtles, hypoxic incubation maintained embryos in arrest, equivalent to the time spent in hypoxia. However, extending arrest for 5 days resulted in greater early-stage death and a significant decrease in hatching success (4% 5-day hypoxia vs. 72% normoxia). Eggs placed in incubators had greater hatching success than those placed into hatchery nests (67% vs. 47%, respectively). We found no impact of hyperoxia on the stage of embryonic death, hatching success, hatchling phenotype, exercise performance, or early dispersal. Our findings indicate that delayed nesting and the subsequent extension of embryonic arrest may negatively impact embryonic development and therefore the reproductive success of leatherbacks. They also indicate that incubation under hyperoxic conditions is unlikely to be a useful method to improve hatching success in this species.

Perioperative monitoring of the oxygen reserve: where do we stand?

The Oxygen Reserve Index (ORi) is an advanced plethysmography-derived variable that may help to quantify the degree of hyperoxia in patients receiving supplemental oxygen administration. ORi is a (relative) indicator of the actual partial pressure of oxygen dissolved in arterial blood (PaO2). As such, it may help in the titration of oxygen administration or it may help to warn the clinician of a deterioration of oxygen status of the patient.In this issue of the journal, Fadel et al. provide a 'classical' clinical validation study by assessing the correlation between ORi and PaO2 in patients about to undergo open-heart surgery. Within the moderate hyperoxic range (100-200 mmHg PaO2), there is a sound correlation between ORi and PaO2. This editorial discusses the clinical implications of this validation study and elaborates on the possible role of ORi monitoring in addition to SpO2 (peripheral arterial oxygen saturation) monitoring alone.

Oxygen Reserve Index and Arterial Partial Pressure of Oxygen: Relationship in Open Heart Surgery

BACKGROUND

Mild to moderate hyperoxia is potentially beneficial to patients undergoing open heart surgery. Oxygen Reserve Index (ORI) is a novel parameter that correlates to arterial oxygen tension (PaO2) in the hyperoxic range. This prospective study aimed to assess whether the relationship between ORI and PaO2 remains intact in the setting of open-heart surgery.

METHODS

This study included patients undergoing valve, aortic arch and coronary artery bypass grafting (CABG) surgeries, on and off pump, between September 1st 2019 and August 31st 2021. Enrolled patients had arterial blood gas samples collected and analyzed after induction of anesthesia and increases in FiO2 in steps of 0.08 with ORI being recorded at the time of sample collection for cross reference and analysis.

RESULTS

ORI values showed a statistically significant correlation with PaO2 values in the 100-200 mmHg range (r = 0.8193, p < 0.001). Additionally, there was a significant correlation between ORI and SpO2 values in the range of 95% and 100% (r = 0.529, p < 0.05).

CONCLUSIONS

The preserved relationship between ORI and PaO2 in the mild and moderate hyperoxic range can allow more precise titration of oxygen therapy to guide therapy targeting normoxia, mildly and moderately hyperoxia. Additionally, it could have a potential use as an early warning system for impeding hypoxia.

COVID-19 during pregnancy could potentially affect placental function

OBJECTIVE

COVID-19 is an ongoing pandemic and has been extensively studied. However, the effects of COVID-19 during pregnancy, particularly on placental function, have not been verified. In this study, we used blood oxygen level-dependent magnetic resonance imaging (BOLD-MRI) to evaluate whether COVID-19 incidence during pregnancy has any lasting effects with respect to placental oxygenation.

METHODS

This is a case-control study, in which eight cases of singleton pregnancies before 30 weeks gestation with COVID-19 mothers were included. Placental oxygenation was evaluated using BOLD-MRI after 32 weeks of gestation. BOLD-MRI was consecutively performed under normoxia (21% O2), hyperoxia (100% O2), and normoxia for 4 min each. Individual placental time-activity curves were evaluated to calculate the peak score (peakΔR2*) and the time from the start of maternal oxygen administration to the time of peakΔR2* (time to peakΔR2*). Eighteen COVID-19-free normal pregnancies from a previous study were used as the control group.

RESULTS

No significant differences were found between the two groups regarding maternal background, number of days of delivery, birth weight, and placental weight. The parameter peakΔR2* was significantly decreased in the COVID-19 group (8 ± 3 vs. 5 ± 1, p < .001); however, there was no significant difference in time to peakΔR2* (458 ± 74 s vs. 471 ± 33 s, p = .644).

CONCLUSIONS

In this study, BOLD-MRI was used to evaluate placental oxygenation during pregnancy in COVID-19-affected patients. COVID-19 during pregnancy decreased placental oxygenation even post-illness, but had no effect on fetal growth; further investigation of the possible effects of COVID-19 on the fetus and mother is warranted.

Determining the effects of elevated partial pressure of oxygen on hypercapnia-induced cerebrovascular reactivity

Evaluation of cerebrovascular reactivity (CVR) to hypo- and hypercapnia is a valuable test for the assessment of vasodilatory reserve. While hypercapnia-induced CVR testing is usually performed at normoxia, mild hyperoxia may increase tolerability of hypercapnia by reducing the ventilatory distress. However, the effects of mild hyperoxia on CVR was unknown. We therefore recruited 21 patients with a range of steno-occlusive diseases and 12 healthy participants who underwent a standardized 13-minute step plus ramp CVR test with a carbon dioxide gas challenge at the subject's resting end-tidal partial pressure of oxygen or at mild hyperoxia (PetO2 = 150 mmHg) depending on to which group they were assigned. In 11 patients, the second CVR test was at normoxia to examine test-retest differences. CVR was defined as % Δ Signal/ΔPetCO2. We found that there was no significant difference between CVR test results conducted at normoxia and at mild hyperoxia for participants in Groups 1 and 2 for the step and ramp portion. We also found no difference between test and retest CVR at normoxia for patients with cerebrovascular pathology (Group 3) for step and ramp portion. We concluded normoxic CVR is repeatable, and that mild hyperoxia does not affect CVR.

Mechanisms of cardiac collapse at high temperature in a marine teleost (Girella nigrians)

Heat-induced mortality in ectotherms may be attributed to impaired cardiac performance, specifically a collapse in maximum heart rate (fHmax), although the physiological mechanisms driving this phenomenon are still unknown. Here, we tested two proposed factors which may restrict cardiac upper thermal limits: noxious venous blood conditions and oxygen limitation. We hypothesized elevated blood [K+] (hyperkalemia) and low oxygen (hypoxia) would reduce cardiac upper thermal limits in a marine teleost (Girella nigricans), while high oxygen (hyperoxia) would increase thermal limits. We also hypothesized higher acclimation temperatures would exacerbate the harmful effects of an oxygen limitation. Using the Arrhenius breakpoint temperature test, we measured fHmax in acutely warmed fish under control (saline injected) and hyperkalemic conditions (elevated plasma [K+]) while exposed to hyperoxia (200% air saturation), normoxia (100% air saturation), or hypoxia (20% air saturation). We also measured ventricle lactate content and venous blood oxygen partial pressure (PO2) to determine if there were universal thresholds in either metric driving cardiac collapse. Elevated [K+] was not significantly correlated with any cardiac thermal tolerance metric. Hypoxia significantly reduced cardiac upper thermal limits (Arrhenius breakpoint temperature [TAB], peak fHmax, temperature of peak heart rate [TPeak], and temperature at arrhythmia [TARR]). Hyperoxia did not alter cardiac thermal limits compared to normoxia. There was no evidence of a species-wide threshold in ventricular [lactate] or venous PO2. Here, we demonstrate that oxygen limits cardiac thermal tolerance only in instances of hypoxia, but that other physiological processes are responsible for causing temperature-induced heart failure when oxygen is not limited.

Effects of hyperoxia during oxygen nanobubble treatment on innate immunity, growth performance, gill histology, and gut microbiome in Nile tilapia, Oreochromis niloticus

Oxygen nanobubble (NB-O2) technology has been introduced to the aquaculture industry in recent years. This treatment usually results in a tremendously high level of dissolved oxygen (DO) in the water. However, little is known about the possible negative effects of hyperoxia due to NB-O2 treatment (hyper-NB-O2) on farmed fish. Here, we investigated i) the effect of short-term hyper-NB-O2 exposure (single treatment) on the innate immunity in Nile tilapia, Oreochromis niloticus, and ii) the effect of long-term hyper-NB-O2 exposure (26-day treatments) on survival, growth performance, gill histology, and gut microbiome in Nile tilapia. A single treatment with NB-O2 for 10 min in 50 L of water resulted in 24.2 ± 0.04 mg/L DO (approximately 2-3 × 107 nanoscale oxygen bubbles/mL). This treatment did not result in differences in expression of several immune-related genes (e.g., TNF-α, LYZ and HPS70) in various tissues (e.g., gill, head kidney, and spleen) compared to the non-treated control. Over a 26-day period of exposure, no significant differences were observed in survival and growth performance of the fish, but minor histological changes were occasionally noted on the gills. Analysis of the gut microbiome revealed a significant increase in the genera Bosea, Exiguobacterium, Hyphomicrobium, and Singulisphaera in the group receiving NB-O2. Moreover, no signs of "gas bubble disease" were observed in the fish throughout the duration of the experiment. Overall, these results suggest that both short- and long-term hyper-NB-O2 exposure appears to be benign and has no obvious adverse effects on fish.

The ventilatory response to modified rebreathing is unchanged by hyperoxic severity: implications for the hyperoxic hyperventilation paradox

Normobaric hyperoxia stimulates ventilation (V̇e) in a time- and dose-dependent manner. Whether this occurs via an oxygen (O2)-specific mechanism or secondary to carbon dioxide (CO2) retention at the central chemoreceptors remains unclear. We measured the ventilatory response to hyperoxic CO2 rebreathing with O2 clamped at increasingly higher pressures. We hypothesized that the V̇e versus Pco2 relationship is fixed and independent of Po2. On four occasions, 20 participants (10 F; mean ± SD age: 24 ± 4 yr) performed three repetitions of modified rebreathing in four, randomized, isoxic-hyperoxic conditions: mild: Po2 = 150 mmHg; moderate: Po2 = 200 mmHg; high: Po2 = 300 mmHg; and extreme: Po2 ≈ 700 mmHg. Breath-by-breath V̇e, end-tidal CO2 ([Formula: see text]), and O2 ([Formula: see text]) were measured by pneumotach and gas analyzer. For each rebreathing trial, the [Formula: see text] at which V̇e rose was identified as the ventilatory recruitment threshold (VRT, mmHg), data before VRT provided baseline V̇e (V̇eBSL, L·min-1) and the slope of the response above VRT gave central chemoreflex sensitivity (V̇eS, L·min-1·mmHg-1). For each condition, VRT, V̇eBSL, and V̇eS from like-trials were averaged, and repeated measures ANOVA assessed between-condition differences. There were no effects of [Formula: see text] on V̇eBSL (mild: 7.4 ± 4.2 L·min-1; moderate: 6.9 ± 4.2 L·min-1; high: 6.5 ± 3.7 L·min-1; extreme: 7.5 ± 2.7 L·min-1; P = 0.24), VRT (mild: 42.8 ± 3.2 mmHg; moderate: 42.5 ± 2.7 mmHg; high: 42.3 ± 2.7 mmHg; extreme: 41.8 ± 2.7 mmHg; P = 0.07), or V̇eS (mild: 4.88 ± 2.6 L·min-1·mmHg-1; moderate: 4.76 ± 2.2 L·min-1·mmHg-1; high: 4.81 ± 2.3 L·min-1·mmHg-1; extreme: 4.39 ± 1.9 L·min-1·mmHg-1; P = 0.41). The V̇e-Pco2 relationship is unaltered across a range of mild to extreme Po2. Brief exposure to normobaric hyperoxia may not independently stimulate breathing nor does it alter central chemoreflex sensitivity.NEW & NOTEWORTHY Normobaric hyperoxia stimulates ventilation (V̇e) in a time- and dose-dependent manner. Whether this occurs directly or indirectly through heightened central carbon dioxide pressure (Pco2) or via central chemoreflex sensitization is unclear. Participants who performed modified rebreathing at high oxygen pressures (Po2) of 150, 200, 300, and ≈700 mmHg exhibited no changes to their ventilatory responses to Pco2. Brief exposure to normobaric hyperoxia may not independently stimulate breathing nor does it alter central chemoreflex sensitivity.

Comparison effects of Ferula gummosa essential oil and Beta-pinene Alginate nanoparticles on human melanoma and breast cancer cells proliferation and apoptotic index in short term normobaric hyperoxic model

BACKGROUND

Breast cancer is the most common cancer among women, and melanoma is the most dreadful type of skin cancer. Due to the side effects of chemotherapy drugs, the development of new herbal nano-medicines has been considered.

METHODS

This study first investigated the chemical composition of Ferula gummosa essential oil using GC-MS analysis; β-pinene, with 61.57%, was the major compound. Next, alginate nanoparticles containing β-pinene and the essential oil with particle sizes of 174 ± 7 and 137 ± 6 nm were prepared. Meanwhile, their zeta potentials were 12.4 ± 0.7 and 28.1 ± 1 mV. Besides, the successful loading of β-pinene and the essential oil in nanoparticles was confirmed using ATR-FTIR analysis. After that, their effects on viability and apoptotic index of human melanoma and breast cancer cells were investigated in normoxia and normobaric hyperoxia (NBO) conditions.

RESULTS

The best efficacy on A-375 and MDA-MB-231 cells was achieved by alginate nanoparticles containing the EO at hyperoxic and normoxia conditions; IC50 76 and 104 µg/mL. Besides, it affected apoptosis-involved genes; as Bax/Bcl-2 ratio was higher than 1, conditions for induction of apoptosis were obtained. Higher sensitivity was observed in the A-375 cell line treated with Alg-EO in the NBO model.

CONCLUSIONS

Alginate nanoparticles containing F. gummosa EO could be considered for further investigation in anticancer studies. Also, it may be expected that NBO can be a new strategy for delaying cancer progression and improving nanotherapy efficacy.

Supplemental oxygen does not improve growth but can enhance reproductive capacity of fish

Fish tend to grow faster as the climate warms but attain a smaller adult body size following an earlier age at sexual maturation. Despite the apparent ubiquity of this phenomenon, termed the temperature-size rule (TSR), heated scientific debates have revealed a poor understanding of the underlying mechanisms. At the centre of these debates are prominent but marginally tested hypotheses which implicate some form of 'oxygen limitation' as the proximate cause. Here, we test the role of oxygen limitation in the TSR by rearing juvenile Galaxias maculatus for a full year in current-day (15°C) and forecasted (20°C) summer temperatures while providing half of each temperature group with supplemental oxygen (hyperoxia). True to the TSR, fish in the warm treatments grew faster and reached sexual maturation earlier than their cooler conspecifics. Yet, despite supplemental oxygen significantly increasing maximum oxygen uptake rate, our findings contradict leading hypotheses by showing that the average size at sexual maturation and the adult body size did not differ between normoxia and hyperoxia groups. We did, however, discover that hyperoxia extended the reproductive window, independent of fish size and temperature. We conclude that the intense resource investment in reproduction could expose a bottleneck where oxygen becomes a limiting factor.

L-citrulline attenuates lipopolysaccharide-induced inflammatory lung injury in neonatal rats

BACKGROUND

Prenatal or postnatal lung inflammation and oxidative stress disrupt alveolo-vascular development leading to bronchopulmonary dysplasia (BPD) with and without pulmonary hypertension. L-citrulline (L-CIT), a nonessential amino acid, alleviates inflammatory and hyperoxic lung injury in preclinical models of BPD. L-CIT modulates signaling pathways mediating inflammation, oxidative stress, and mitochondrial biogenesis-processes operative in the development of BPD. We hypothesize that L-CIT will attenuate lipopolysaccharide (LPS)-induced inflammation and oxidative stress in our rat model of neonatal lung injury.

METHODS

Newborn rats during the saccular stage of lung development were used to investigate the effect of L-CIT on LPS-induced lung histopathology and pathways involved in inflammatory, antioxidative processes, and mitochondrial biogenesis in lungs in vivo, and in primary culture of pulmonary artery smooth muscle cells, in vitro.

RESULTS

L-CIT protected the newborn rat lung from LPS-induced: lung histopathology, ROS production, NFκB nuclear translocation, and upregulation of gene and protein expression of inflammatory cytokines (IL-1β, IL-8, MCP-1α, and TNF-α). L-CIT maintained mitochondrial morphology, increased protein levels of PGC-1α, NRF1, and TFAM (transcription factors involved in mitochondrial biogenesis), and induced SIRT1, SIRT3, and superoxide dismutases protein expression.

CONCLUSION

L-CIT may be efficacious in decreasing early lung inflammation and oxidative stress mitigating progression to BPD.

IMPACT

The nonessential amino acid L-citrulline (L-CIT) mitigated lipopolysaccharide (LPS)-induced lung injury in the early stage of lung development in the newborn rat. This is the first study describing the effect of L-CIT on the signaling pathways operative in bronchopulmonary dysplasia (BPD) in a preclinical inflammatory model of newborn lung injury. If our findings translate to premature infants, L-CIT could decrease inflammation, oxidative stress and preserve mitochondrial health in the lung of premature infants at risk for BPD.

Measuring Oxygenation in Newborn Infants with Targeted Oxygen Ranges (MONITOR): a randomised crossover pilot study

OBJECTIVE

The Neonatal Oxygenation Prospective Meta-analysis (NeOProM) Collaboration showed that high (91-95%) versus low (85-89%) SpO2 targets reduced mortality. Trials of higher targets are needed to determine whether any more survival advantage may be gained. This pilot study explored the achieved oxygenation patterns observed when targeting SpO2 92-97% to facilitate the design of future trials.

DESIGN

Single-centre prospective randomised crossover pilot study. Manual FiO2 adjustment. Study time 12 hours per infant. 6 hours targeting SpO2 90-95% and 6 hours targeting SpO2 92-97%.

PATIENTS

Twenty preterm infants born <29 weeks' gestation, greater than 48 hours old, receiving supplemental oxygen.

OUTCOMES

Primary outcome was percentage time with SpO2 above 97% and below 90%. Pre-defined secondary outcomes included percentage time spent within, above or below transcutaneous PO2 (TcPO2) 6.7-10.7 kPa (50-80 mm Hg). Comparisons were made using paired-samples t-test (2-tailed).

RESULTS

With SpO2 target 92-97% versus 90-95%, the mean (IQR) percentage time above SpO2 97% was 11.3% (2.7-20.9) versus 7.8% (1.7-13.9), p=0.02. Percentage time with SpO2 <90% was 13.1% (6.7-19.1) versus 17.9% (11.1-22.4), p=0.003. Percentage time with SpO2 <80% was 1% (0.1-1.4) versus 1.6% (0.4-2.6), p=0.119. Percentage time with TcPO2 <6.7 kPa (50 mm Hg) was 49.6% (30.2-66.0) versus 55% (34.3-73.5), p=0.63. Percentage time above TcPO2 10.7 kPa (80 mm Hg) was 1.4% (0-1.4) versus 1.8% (0-0), p=0.746.

CONCLUSIONS

Targeting SpO2 92-97% produced a right shift in SpO2 and TcPO2 distribution, with reduced time at SpO2 <90% and increased time at SpO2 >97%, without increasing time with TcPO2 >10.7 kPa (80 mm Hg). Clinical trials targeting this higher SpO2 range could be conducted without significant hyperoxic exposure.

TRIAL REGISTRATION NUMBER

NCT03360292.

High, Low, and Minimal Flow Anaesthesia Management: Effects on Oxygen Reserve Index and Arterial Partial Oxygen Pressure

OBJECTIVE

To determine the oxygen reserve index (ORI) as a supporting parameter to the arterial partial oxygen pressure (PaO2) in blood gases in hypoxia and hyperoxia monitoring with different fresh gas flows (FGF) in patients undergoing abdominal surgery.

STUDY DESIGN

Randomised controlled trial. Place and Duration of the Study: Department of Anaesthesiology and Reanimation, Samsun Education and Research Hospital, Turkey, from January to September 2020.

METHODOLOGY

The study population of ninety patients was divided into three groups. After the high-flow period, the inspired oxygen fraction (FiO2) and flow-guided ventilation (FGF) were set to be 4 L/m and 40% in Group H (high-flow), 1 L/m and 50% in Group L (low-flow), and 0.5 L/m and 68% in Group M (minimal-flow), respectively.

RESULTS

There was a very high statistically positive correlation between PaO2 and ORI in H, L, and M groups. When using a cut-off value of 0.005 for ORI for the detection of PaO2 >100 mmHg, the area under the curve (AUC) was 0.97 (p<0.001) with a sensitivity of 94.4% and specificity of 95.3%. The AUC was detected to be 0.95 in receiver operating characteristic (ROC) analysis when the hyperoxia cut-off value of ORI was used to determine PaO2 >150 mmHg in the estimation of hyperoxia.

CONCLUSION

ORI can be used to complement SpO2 in low-flow anaesthesia in patients undergoing abdominal surgeries, provide guidance for PaO2, give information about tissue oxygen delivery, and contribute to the individualisation of oxygen therapy, and will therefore be included in the standard monitoring in the future.

KEY WORDS

Anaesthesia, Index, Inhalation, Oxygen, Pressure, Surgery.

[Wedelolactone alleviates hyperoxia-induced acute lung injury by regulating ferroptosis]

OBJECTIVE

To study whether wedelolactone can reduce hyperoxia-induced acute lung injury (HALI) by regulating ferroptosis, and provide a basic theoretical basis for the drug treatment of HALI.

METHODS

A total of 24 C57BL/6J mice were randomly divided into normal oxygen control group, HALI model group and wedelolactone pretreatment group, with 8 mice in each group. Mice in wedelolactone pretreatment group were treated with wedelolactone 50 mg/kg intraperitoneally for 6 hours, while the other two groups were not given with wedelolactone. After that, the HALI model was established by maintaining the content of carbon dioxide < 0.5% and oxygen > 90% in the molding chamber for 48 hours, and the normal oxygen control group was placed in indoor air. After modeling, the mice were sacrificed and lung tissues were collected. The lung histopathological changes were observed under light microscope and pathological scores were performed to calculate the ratio of lung wet/dry mass (W/D). The levels of tumor necrosis factor-α (TNF-α), interleukins (IL-6, IL-1β), superoxide dismutase (SOD), malondialdehyde (MDA) and glutathione (GSH) in lung tissues of mice in each group were determined. The protein expression of glutathione peroxidase 4 (GPX4) in lung tissue was detected by Western blotting.

RESULTS

Under light microscope, the alveolar structure of HALI model group was destroyed, and a large number of neutrophils infiltrated the alveolar and interstitial lung, and the interstitial lung was thickened. The pathological score of lung injury (score: 0.75±0.02 vs. 0.11±0.01) and the ratio of lung W/D (6.23±0.34 vs. 3.68±0.23) were significantly higher than those in the normal oxygen control group (both P < 0.05). Wedelolactone pretreated mice had clear alveolar cavity and lower neutrophil infiltration and interstitial thickness than HALI group. Pathological scores (score: 0.43±0.02 vs. 0.75±0.02) and W/D ratio (4.56±0.12 vs. 6.23±0.34) were significantly lower than HALI group (both P < 0.05). Compared with the normal oxygen control group, the levels of SOD (kU/g: 26.41±4.25 vs. 78.64±3.95) and GSH (mol/g: 4.51±0.33 vs. 12.53±1.25) in HALI group were significantly decreased, while the levels of MDA (mmol/g: 54.23±4.58 vs. 9.65±1.96), TNF-α (μg/L: 96.32±3.67 vs. 11.65±2.03), IL-6 (ng/L: 163.35±5.89 vs. 20.56±3.63) and IL-1β (μg/L: 72.34±4.64 vs. 15.64±2.47) were significantly increased, and the protein expression of GPX4 (GPX4/β-actin: 0.44±0.02 vs. 1.00±0.09) was significantly decreased (all P < 0.05). Compared with the HALI group, the levels of SOD (kU/g: 53.28±3.69 vs. 26.41±4.25) and GSH (mol/g: 6.73±0.97 vs. 12.53±1.25) were significantly higher in the wedelolactone pretreatment group, and the levels of MDA (mmol/g: 25.36±1.98 vs. 54.23±4.58), TNF-α (μg/L: 40.25±4.13 vs. 96.32±3.67), IL-6 (ng/L: 78.32±4.65 vs. 163.35±5.89), and IL-1β (μg/L: 30.65±3.65 vs. 72.34±4.64) were significantly lower (all P < 0.05), and protein expression of GPX4 was significantly higher (GPX4/β-actin: 0.68±0.04 vs. 0.44±0.02, P < 0.05).

CONCLUSIONS

Wedelolactone attenuates HALI injury by regulating ferroptosis.

CNS-oxygen toxicity and blood glucose levels in MnSOD enzyme knockdown mice

Many studies have been conducted in the search for the mechanism underlying CNS-oxygen toxicity (OT), which may be fatal when diving with a closed-circuit apparatus. We investigated the influence of hyperbaric oxygen (HBO) on blood glucose level (BGL) in Mn-superoxide dismutase (SOD2) knockdown mice regarding CNS-OT in particular under stress conditions such as hypoglycemia or hyperglycemia. Two groups of mice were used: SOD2 knockdown (Heterozygous, HET) mice and their WT family littermates. Animals were exposed to HBO from 2 up to 5 atmosphere absolute (ATA). Blood samples were drawn before and after each exposure for measurement of BGL. The mice were sacrificed following the final exposure, which was at 5 ATA. We used RT-PCR and Western blot to measure levels of glucose transporter 1 (GLUT1) and hypoxia inducible factor (HIF)1a in the cortex and hippocampus. In the hypoglycemic condition, the HET mice were more sensitive to oxidative stress than the WT. In addition, following exposure to sub-toxic HBO, which does not induce CNS-OT, BGL were higher in the HET mice compared with the WT. The expression of mRNA of GLUT1 and HIF-1a decreased in the hippocampus in the HET mice, while the protein level decreased in the HET and WT following HBO exposure. The results suggest that the higher BGL following HBO exposure especially at SOD2 HET mice is in part due to reduction in GLUT1 as a consequence of lower HIF-1a expression. This may add part to the puzzle of the understanding the mechanism leading to CNS-OT.

Repeated Short-Term Bouts of Hyperoxia Improve Aerobic Performance in Acute Hypoxia

ABSTRACT

Faulhaber, M, Schneider, S, Rausch, LK, Dünnwald, T, Menz, V, Gatterer, H, Kennedy, MD, and Schobersberger, W. Repeated short-term bouts of hyperoxia improve aerobic performance in acute hypoxia. J Strength Cond Res 37(10): 2016-2022, 2023-This study aimed to test the effects of repeated short-term bouts of hyperoxia on maximal 5-minute cycling performance under acute hypoxic conditions (3,200 m). Seventeen healthy and recreationally trained individuals (7 women and 10 men) participated in this randomized placebo-controlled cross-over trial. The procedures included a maximal cycle ergometer test and 3 maximal 5-minute cycling time trials (TTs). TT1 took place in normoxia and served for habituation and reference. TT2 and TT3 were conducted in normobaric hypoxia (15.0% inspiratory fraction of oxygen). During TT2 and TT3, the subjects were breathing through a face mask during five 15-second periods. The face mask was connected through a nonrebreathing T valve to a 300-L bag filled with 100% oxygen (intermittent hyperoxia) or ambient hypoxic air (placebo). The main outcome was the mean power output during the TT. Statistical significance level was set at p < 0.05. The mean power output was higher in the intermittent hyperoxia compared with the placebo condition (255.5 ± 49.6 W vs. 247.4 ± 48.2 W, p = 0.001). Blood lactate concentration and ratings of perceived exertion were significantly lower by about 9.7 and 7.3%, respectively, in the intermittent hyperoxia compared with the placebo condition, whereas heart rate values were unchanged. IH application increased arterial oxygen saturation (82.9 ± 2.6% to 92.4 ± 3.3%, p < 0.001). Repeated 15-second bouts of hyperoxia, applied during high-intensity exercise in hypoxia, are sufficient to increase power output. Future studies should focus on potential dose-response effects and the involved mechanisms.

Efficiency of exogenous surfactant combined with intravenous N-acetylcysteine in two-hit rodent model of ARDS

Accumulation of reactive oxygen species during hyperoxia together with secondary bacteria-induced inflammation leads to lung damage in ventilated critically ill patients. Antioxidant N-acetylcysteine (NAC) in combination with surfactant may improve lung function. We compared the efficacy of NAC combined with surfactant in the double-hit model of lung injury. Bacterial lipopolysaccharide (LPS) instilled intratracheally and hyperoxia were used to induce lung injury in Wistar rats. Animals were mechanically ventilated and treated intravenously with NAC alone or in combination with intratracheal surfactant (poractant alfa; PSUR+NAC). Control received saline. Lung functions, inflammatory markers, oxidative damage, total white blood cell (WBC) count and lung oedema were evaluated during 4 hrs. Administration of NAC increased total antioxidant capacity (TAC) and decreased IL-6. This effect was potentiated by the combined administration of surfactant and NAC. In addition, PSUR+NAC reduced the levels of TNFα, IL-1ß, and TAC compared to NAC only and improved lung injury score. The combination of exogenous surfactant with NAC suppresses lung inflammation and oxidative stress in the experimental double-hit model of lung injury.

Investigation into the effect of hyperbaric hyperoxia on serum cardiac Troponin T levels as a biomarker of cardiac injury

Introduction

There is clinical equipoise as to whether hyperoxia is injurious to the myocardium, both in the setting of acute ischaemic insults and on the stable myocardium. This study examined the effect of extreme hyperoxia - in the form of hyperbaric oxygen treatment - on the myocardium through measurement of high-sensitivity cardiac troponin.

Methods

Forty-eight individuals were enrolled to undergo a series of 30 exposures to hyperbaric oxygen for treatment of non-cardiac pathologies. High-sensitivity troponin T was measured before and after each session.

Results

There was no clinically significant difference in troponin measurements following acute or recurrent sequential exposures to extreme hyperoxia, despite the studied patient population having a high rate of previous ischaemic heart disease or cardiovascular risk factors.

Conclusions

This study demonstrates that profound hyperoxaemia does not induce any measurable cardiac injury at a biochemical level. Neither is there a reduction in cardiac troponin to suggest a cardioprotective effect of hyperbaric hyperoxia. This provides some reassurance as to the cardiac safety of the routine use of hyperbaric oxygen treatment in management of non-cardiac pathology.

Impact of Hypoxia-Hyperoxia Exposures on Cardiometabolic Risk Factors and TMAO Levels in Patients with Metabolic Syndrome

Along with the known risk factors of cardiovascular diseases (CVDs) constituting metabolic syndrome (MS), the gut microbiome and some of its metabolites, in particular trimethylamine-N-oxide (TMAO), are actively discussed. A prolonged stay under natural hypoxic conditions significantly and multi-directionally changes the ratio of gut microbiome strains and their metabolites in feces and blood, which is the basis for using hypoxia preconditioning for targeted effects on potential risk factors of CVD. A prospective randomized study included 65 patients (32 females) with MS and optimal medical therapy. Thirty-three patients underwent a course of 15 intermittent hypoxic-hyperoxic exposures (IHHE group). The other 32 patients underwent sham procedures (placebo group). Before and after the IHHE course, patients underwent liver elastometry, biochemical blood tests, and blood and fecal sampling for TMAO analysis (tandem mass spectrometry). No significant dynamics of TMAO were detected in both the IHHE and sham groups. In the subgroup of IHHE patients with baseline TMAO values above the reference (TMAO ≥ 5 μmol/l), there was a significant reduction in TMAO plasma levels. But the degree of reduction in total cholesterol (TCh), low-density lipoprotein (LDL), and regression of liver steatosis index was more pronounced in patients with initially normal TMAO values. Despite significant interindividual variations, in the subgroup of IHHE patients with MS and high baseline TMAO values, there were more significant reductions in cardiometabolic and hepatic indicators of MS than in controls. More research is needed to objectify the prognostic role of TMAO and the possibilities of its correction using hypoxia adaptation techniques.

HBOT has a better cognitive outcome than NBH for patients with mild traumatic brain injury: A randomized controlled clinical trial

BACKGROUND

Normobaric hyperoxia (NBH) and hyperbaric oxygen therapy (HBOT) are effective treatment plan for traumatic brain injury (TBI). The aim of this study was to compare cognitive outcome after mild TBI between NBH and HBOT so as to provide a more suitable treatment strategy for patients with mild TBI.

METHODS

A prospective research was conducted between October 2017 and March 2023, enrolling patients with mild TBI (Glasgow coma scale score: 13-15 points) within 24 hours of injury in Cangzhou Central Hospital. Patients were randomized into 3 groups: group control (C), group NBH and group HBOT. The patients in HBOT group received hyperbaric oxygen therapy in high pressure oxygen chamber and patients in NBH group received hyperbaric oxygen therapy. at 0 minute before NBH or HBOT (T1), 0 minute after NBH or HBOT (T2) and 30 days after NBH or HBOT (T3), level of S100β, NSE, GFAP, HIF-1α, and MDA were determined by ELISA. At the same time, the detection was performed for MoCA and MMSE scores, along with rSO2.

RESULTS

The results showed both NBH and HBOT could improve the score of MoCA and MMSE, as well as the decrease the level of S100β, NSE, GFAP, HIF-1α, MDA, and rSO2 compared with group C. Furthermore, the patients in group HBOT have higher score of MoCA and MMSE and lower level of S100β, NSE, GFAP, HIF-1α, MDA, and rSO2.

CONCLUSION

Both NBH and HBOT can effectively improve cognitive outcome for patients with mild TBI by improving cerebral hypoxia and alleviating brain injury, while HBOT exert better effect than NBH.

Selective effects of estradiol on human corneal endothelial cells

In Fuchs endothelial corneal dystrophy (FECD), mitochondrial and oxidative stresses in corneal endothelial cells (HCEnCs) contribute to cell demise and disease progression. FECD is more common in women than men, but the basis for this observation is poorly understood. To understand the sex disparity in FECD prevalence, we studied the effects of the sex hormone 17-β estradiol (E2) on growth, oxidative stress, and metabolism in primary cultures of HCEnCs grown under physiologic ([O2]2.5) and hyperoxic ([O2]A) conditions. We hypothesized that E2 would counter the damage of oxidative stress generated at [O2]A. HCEnCs were treated with or without E2 (10 nM) for 7-10 days under both conditions. Treatment with E2 did not significantly alter HCEnC density, viability, ROS levels, oxidative DNA damage, oxygen consumption rates, or extracellular acidification rates in either condition. E2 disrupted mitochondrial morphology in HCEnCs solely from female donors in the [O2]A condition. ATP levels were significantly higher at [O2]2.5 than at [O2]A in HCEnCs from female donors only, but were not affected by E2. Our findings demonstrate the resilience of HCEnCs against hyperoxic stress. The effects of hyperoxia and E2 on HCEnCs from female donors suggest cell sex-specific mechanisms of toxicity and hormonal influences.

A Standardized Botanical Composition Mitigated Acute Inflammatory Lung Injury and Reduced Mortality through Extracellular HMGB1 Reduction

HMGB1 is a key late inflammatory mediator upregulated during air-pollution-induced oxidative stress. Extracellular HMGB1 accumulation in the airways and lungs plays a significant role in the pathogenesis of inflammatory lung injury. Decreasing extracellular HMBG1 levels may restore innate immune cell functions to protect the lungs from harmful injuries. Current therapies for air-pollution-induced respiratory problems are inadequate. Dietary antioxidants from natural sources could serve as a frontline defense against air-pollution-induced oxidative stress and lung damage. Here, a standardized botanical antioxidant composition from Scutellaria baicalensis and Acacia catechu was evaluated for its efficacy in attenuating acute inflammatory lung injury and sepsis. Murine models of disorders, including hyperoxia-exposed, bacterial-challenged acute lung injury, LPS-induced sepsis, and LPS-induced acute inflammatory lung injury models were utilized. The effect of the botanical composition on phagocytic activity and HMGB1 release was assessed using hyperoxia-stressed cultured macrophages. Analyses, such as hematoxylin-eosin (HE) staining for lung tissue damage evaluation, ELISA for inflammatory cytokines and chemokines, Western blot analysis for proteins, including extracellular HMGB1, and bacterial counts in the lungs and airways, were performed. Statistically significant decreases in mortality (50%), proinflammatory cytokines (TNF-α, IL-1β, IL-6) and chemokines (CINC-3) in serum and bronchoalveolar lavage fluid (BALF), and increased bacterial clearance from airways and lungs; reduced airway total protein, and decreased extracellular HMGB1 were observed in in vivo studies. A statistically significant 75.9% reduction in the level of extracellular HMGB1 and an increase in phagocytosis were observed in cultured macrophages. The compilations of data in this report strongly suggest that the botanical composition could be indicated for oxidative-stress-induced lung damage protection, possibly through attenuation of increased extracellular HMGB1 accumulation.

Type 2 innate lymphoid cell-derived amphiregulin regulates type II alveolar epithelial cell transdifferentiation in a mouse model of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a common complication in preterm infants characterized by alveolar growth arrest. Interleukin (IL)-33 and type 2 innate lymphoid cell (ILC2) affect type II alveolar epithelial cell (AECII) differentiation in BPD mice and may cause increased lung epithelial-mesenchymal transition (EMT). Amphiregulin (AREG) can be produced by ILC2 and is associated with tissue repair. However, the action mechanism of AREG produced by ILC2 to alveolar development in BPD is unclear. In this study, we aimed to demonstrate the role and mechanism of AREG in influencing AECII transdifferentiation in the lung tissue of BPD mice. The effects of ILC2-derived AREG on AECII transdifferentiation were verified in vivo and in vitro, and the role of IL-33 on ILC2-derived AREG in AECII transdifferentiation in BPD mice and a preliminary investigation of the role of AREG's receptor-epidermal growth factor receptor (EGFR) on AECII transdifferentiation. The results showed that neonatal mice developed severe lung injury after hyperoxia, and IL-33 induced AREG production via ILC2 affected normal AECII differentiation and promoted EMT. In addition, the blockade of EGFR was found to alleviate the impaired AECII differentiation under hyperoxia in an in vitro study. In summary, our study demonstrates that AREG secreted by ILC2 affects AECII transdifferentiation in BPD mice, which provides a new idea for the clinical treatment of BPD.

[Hyperoxia caused intestinal metabolism disorder in mice]

OBJECTIVE

To investigate the effect of hyperoxia on intestinal metabolomics in mice.

METHODS

Sixteen 8-week-old male C57BL/6 mice were randomly divided into hyperoxia group and control group, with 8 mice in each group. The hyperoxia group was exposed to 80% oxygen for 14 days. Mice were anesthetized and euthanized, and cecal contents were collected for untargeted metabolomics analysis by liquid chromatography-mass spectrometry (LC-MS) combined detection. Orthogonal partial least square discriminant analysis (OPLS-DA), volcano plot analysis, heat map analysis, and Kyoto Encyclopedia of Genes and Genomes (KEGG) were used to analyze the effects of hyperoxia on metabolism.

RESULTS

(1) OPLS-DA analysis showed that R2Y was 0.967 and Q2 was 0.796, indicating that the model was reliable. (2) Volcano plot and heat map analysis showed significant statistical differences in the expression levels of metabolites between the two groups, with 541 up-regulated metabolites, 64 down-regulated metabolites, and 907 no differences, while the elevated 5-hydroxy-L-lysine was the most significant differential metabolite induced by high oxygen. (3) KEGG pathway enrichment analysis showed that porphyrin and chlorophyll metabolism (P = 0.005), lysine degradation (P = 0.047), and aromatic compound degradation (P = 0.024) were the targets affected by hyperoxia. (4) Differential analysis of metabolic products through KEGG enrichment pathway showed that hyperoxia had a significant impact on the metabolism of porphyrin and chlorophyll, lysine, and aromatic compounds such as benzene and o-cresol.

CONCLUSIONS

Hyperoxia significantly induces intestinal metabolic disorders. Hyperoxia enhances the metabolism of porphyrins and chlorophyll, inhibits the degradation of lysine, and delays the degradation of aromatic compounds such as benzene and o-cresol.

Oxygen Variations-Insights into Hypoxia, Hyperoxia and Hyperbaric Hyperoxia-Is the Dose the Clue?

Molecular oxygen (O2) is one of the four most important elements on Earth (alongside carbon, nitrogen and hydrogen); aerobic organisms depend on it to release energy from carbon-based molecules [...].

SLAB51 Multi-Strain Probiotic Formula Increases Oxygenation in Oxygen-Treated Preterm Infants

Preterm infants are at risk of hypoxia and hyperoxia because of the immaturity of their respiratory and antioxidant systems, linked to increased morbidity and mortality. This study aimed to evaluate the efficacy of a single administration of the SLAB51 probiotic formula in improving oxygenation in respiratory distress syndrome (RDS)-affected premature babies, thus reducing their need for oxygen administration. Additionally, the capability of SLAB51 in activating the factor-erythroid 2-related factor (Nrf2) responsible for antioxidant responses was evaluated in vitro. In two groups of oxygen-treated preterm infants with similar SaO2 values, SLAB51 or a placebo was given. After two hours, the SLAB51-treated group showed a significant increase in SaO2 levels and the SaO2/FiO2 ratio, while the control group showed no changes. Significantly increased Nrf2 activation was observed in intestinal epithelial cells (IECs) exposed to SLAB51 lysates. In preterm infants, we confirmed the previously observed SLAB51's "oxygen-sparing effect", permitting an improvement in SaO2 levels. We also provided evidence of SLAB51's potential to enhance antioxidant responses, thus counteracting the detrimental effects of hyperoxia. Although further studies are needed to support our data, SLAB51 represents a promising approach to managing preterm infants requiring oxygen supplementation.

Oxidative Stress Response Kinetics after 60 Minutes at Different (1.4 ATA and 2.5 ATA) Hyperbaric Hyperoxia Exposures

Hyperbaric oxygen therapy (HBOT) is a therapeutical approach based on exposure to pure oxygen in an augmented atmospheric pressure. Although it has been used for years, the exact kinetics of the reactive oxygen species (ROS) between different pressures of hyperbaric oxygen exposure are still not clearly evidenced. In this study, the metabolic responses of hyperbaric hyperoxia exposures for 1 h at 1.4 and 2.5 ATA were investigated. Fourteen healthy non-smoking subjects (2 females and 12 males, age: 37.3 ± 12.7 years old (mean ± SD), height: 176.3 ± 9.9 cm, and weight: 75.8 ± 17.7 kg) volunteered for this study. Blood samples were taken before and at 30 min, 2 h, 24 h, and 48 h after a 1 h hyperbaric hyperoxic exposure. The level of oxidation was evaluated by the rate of ROS production, nitric oxide metabolites (NOx), and the levels of isoprostane. Antioxidant reactions were assessed through measuring superoxide dismutase (SOD), catalase (CAT), cysteinylglycine, and glutathione (GSH). The inflammatory response was measured using interleukine-6, neopterin, and creatinine. A short (60 min) period of mild (1.4 ATA) and high (2.5 ATA) hyperbaric hyperoxia leads to a similar significant increase in the production of ROS and antioxidant reactions. Immunomodulation and inflammatory responses, on the contrary, respond proportionally to the hyperbaric oxygen dose. Further research is warranted on the dose and the inter-dose recovery time to optimize the potential therapeutic benefits of this promising intervention.

MALAT1 binds to miR-188-3p to regulate ALOX5 activity in the lung inflammatory response of neonatal bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) causes high morbidity and mortality in infants, but no effective preventive or therapeutic agents have been developed to combat BPD. In this study, we assessed the expression of MALAT1 and ALOX5 in peripheral blood mononuclear cells from BPD neonates, hyperoxia-induced rat models and lung epithelial cell lines. Interestingly, we found upregulated expression of MALAT1 and ALOX5 in the experimental groups, along with upregulated expression of proinflammatory cytokines. According to bioinformatics prediction, MALAT1 and ALOX5 simultaneously bind to miR-188-3p, which was downregulated in the experimental groups above. Silencing MALAT1 or ALOX5 and overexpressing miR-188-3p inhibited apoptosis and promoted the proliferation of hyperoxia-treated A549 cells. Suppressing MALAT1 or overexpressing miR-188-3p increased the expression levels of miR-188-3p but decreased the expression levels of ALOX5. Moreover, RNA immunoprecipitation (RIP) and luciferase assays showed that MALAT1 directly targeted miR-188-3p to regulate ALOX5 expression in BPD neonates. Collectively, our study demonstrates that MALAT1 regulates ALOX5 expression by binding to miR-188-3p, providing novel insights into potential therapeutics for BPD treatment.

Hyperoxia-induced stepwise reduction in blood flow through intrapulmonary, but not intracardiac, shunt during exercise

Blood flow through intrapulmonary arteriovenous anastomoses (IPAVA) (QIPAVA) increases during exercise breathing air, but it has been proposed that QIPAVA is reduced during exercise while breathing a fraction of inspired oxygen ([Formula: see text]) of 1.00. It has been argued that the reduction in saline contrast bubbles through IPAVA is due to altered in vivo microbubble dynamics with hyperoxia reducing bubble stability, rather than closure of IPAVA. To definitively determine whether breathing hyperoxia decreases saline contrast bubble stability in vivo, the present study included individuals with and without patent foramen ovale (PFO) to determine if hyperoxia also eliminates left heart contrast in people with an intracardiac right-to-left shunt. Thirty-two participants consisted of 16 without a PFO; 8 females, 8 with a PFO; 4 females, and 8 with late-appearing left-sided contrast (4 females) completed five, 4-min bouts of constant-load cycle ergometer exercise (males: 250 W, females: 175 W), breathing an [Formula: see text] = 0.21, 0.40, 0.60, 0.80, and 1.00 in a balanced Latin Squares design. QIPAVA was assessed at rest and 3 min into each exercise bout via transthoracic saline contrast echocardiography and our previously used bubble scoring system. Bubble scores at [Formula: see text]= 0.21, 0.40, and 0.60 were unchanged and significantly greater than at [Formula: see text]= 0.80 and 1.00 in those without a PFO. Participants with a PFO had greater bubble scores at [Formula: see text]= 1.00 than those without a PFO. These data suggest that hyperoxia-induced decreases in QIPAVA during exercise occur when [Formula: see text] ≥ 0.80 and is not a result of altered in vivo microbubble dynamics supporting the idea that hyperoxia closes QIPAVA.

Exposure to Arterial Hyperoxia During Extracorporeal Membrane Oxygenator Support and Mortality in Patients With Cardiogenic Shock

BACKGROUND

Exposure to hyperoxia, a high arterial partial pressure of oxygen (PaO2), may be associated with worse outcomes in patients receiving extracorporeal membrane oxygenator (ECMO) support. We examined hyperoxia in the Extracorporeal Life Support Organization Registry among patients receiving venoarterial ECMO for cardiogenic shock.

METHODS

We included Extracorporeal Life Support Organization Registry patients from 2010 to 2020 who received venoarterial ECMO for cardiogenic shock, excluding extracorporeal CPR. Patients were grouped based on PaO2 after 24 hours of ECMO: normoxia (PaO2 60-150 mmHg), mild hyperoxia (PaO2 151-300 mmHg), and severe hyperoxia (PaO2 >300 mmHg). In-hospital mortality was evaluated using multivariable logistic regression.

RESULTS

Among 9959 patients, 3005 (30.2%) patients had mild hyperoxia and 1972 (19.8%) had severe hyperoxia. In-hospital mortality increased across groups: normoxia, 47.8%; mild hyperoxia, 55.6% (adjusted odds ratio, 1.37 [95% CI, 1.23-1.53]; P<0.001); severe hyperoxia, 65.4% (adjusted odds ratio, 2.20 [95% CI, 1.92-2.52]; P<0.001). A higher PaO2 was incrementally associated with increased in-hospital mortality (adjusted odds ratio, 1.14 per 50 mmHg higher [95% CI, 1.12-1.16]; P<0.001). Patients with a higher PaO2 had increased in-hospital mortality in each subgroup and when stratified by ventilator settings, airway pressures, acid-base status, and other clinical variables. In the random forest model, PaO2 was the second strongest predictor of in-hospital mortality, after older age.

CONCLUSIONS

Exposure to hyperoxia during venoarterial ECMO support for cardiogenic shock is strongly associated with increased in-hospital mortality, independent from hemodynamic and ventilatory status. Until clinical trial data are available, we suggest targeting a normal PaO2 and avoiding hyperoxia in CS patients receiving venoarterial ECMO.

In critically ill patients, anti-anaerobic antibiotics increase risk of adverse clinical outcomes

BACKGROUND

Critically ill patients routinely receive antibiotics with activity against anaerobic gut bacteria. However, in other disease states and animal models, gut anaerobes are protective against pneumonia, organ failure and mortality. We therefore designed a translational series of analyses and experiments to determine the effects of anti-anaerobic antibiotics on the risk of adverse clinical outcomes among critically ill patients.

METHODS

We conducted a retrospective single-centre cohort study of 3032 critically ill patients, comparing patients who did and did not receive early anti-anaerobic antibiotics. We compared intensive care unit outcomes (ventilator-associated pneumonia (VAP)-free survival, infection-free survival and overall survival) in all patients and changes in gut microbiota in a subcohort of 116 patients. In murine models, we studied the effects of anaerobe depletion in infectious (Klebsiella pneumoniae and Staphylococcus aureus pneumonia) and noninfectious (hyperoxia) injury models.

RESULTS

Early administration of anti-anaerobic antibiotics was associated with decreased VAP-free survival (hazard ratio (HR) 1.24, 95% CI 1.06-1.45), infection-free survival (HR 1.22, 95% CI 1.09-1.38) and overall survival (HR 1.14, 95% CI 1.02-1.28). Patients who received anti-anaerobic antibiotics had decreased initial gut bacterial density (p=0.00038), increased microbiome expansion during hospitalisation (p=0.011) and domination by Enterobacteriaceae spp. (p=0.045). Enterobacteriaceae were also enriched among respiratory pathogens in anti-anaerobic-treated patients (p<2.2×10^-16). In murine models, treatment with anti-anaerobic antibiotics increased susceptibility to Enterobacteriaceae pneumonia (p<0.05) and increased the lethality of hyperoxia (p=0.0002).

CONCLUSIONS

In critically ill patients, early treatment with anti-anaerobic antibiotics is associated with increased mortality. Mechanisms may include enrichment of the gut with respiratory pathogens, but increased mortality is incompletely explained by infections alone. Given consistent clinical and experimental evidence of harm, the widespread use of anti-anaerobic antibiotics should be reconsidered.