Effects Of Hyperoxia Research Articles

Intraoperative mild hyperoxia may be associated with improved survival after off-pump coronary artery bypass grafting: a retrospective observational study

BackgroundThe effect of hyperoxia due to supplemental oxygen administration on postoperative outcomes in patients undergoing cardiac surgery remains unclear. This retrospective study aimed to evaluate the relationship between intraoperative oxygen tension and mortality after off-pump coronary artery bypass grafting (OPCAB).MethodsThe study included adult patients who underwent isolated OPCAB between July 2010 and June 2020. Patients were categorised into three groups based on their intraoperative time-weighted average arterial oxygen partial pressure (PaO2): normoxia/near-normoxia (< 150 mmHg), mild hyperoxia (150–250 mmHg), and severe hyperoxia (> 250 mmHg). The risk of in-hospital mortality was compared using weighted logistic regression analysis. Restricted cubic spline analysis was performed to analyse intraoperative PaO2 as a continuous variable. The risk of cumulative all-cause mortality was compared using Cox regression analysis.ResultsThe normoxia/near-normoxia, mild hyperoxia, and severe hyperoxia groups included 229, 991, and 173 patients (n = 1393), respectively. The mild hyperoxia group had a significantly lower risk of in-hospital mortality than the normoxia/near-normoxia (odds ratio [OR], 0.12; 95% confidence interval [CI], 0.06–0.22) and severe hyperoxia groups (OR, 0.06; 95% CI, 0.03–0.14). Intraoperative PaO2 exhibited a U-shaped relationship with in-hospital mortality in the non-hypoxic range. The risk of cumulative all-cause mortality was significantly lower in the mild hyperoxia group (hazard ratio, 0.72; 95% CI, 0.52–0.99) than in the normoxia/near-normoxia group.ConclusionsMaintaining intraoperative PaO2 at 150–250 mmHg was associated with a lower risk of mortality after OPCAB than PaO2 at < 150 mmHg and at > 250 mmHg. Future randomised trials are required to confirm if mildly increasing arterial oxygen tension during OPCAB to 150–250 mmHg improves postoperative outcomes.

P311 knockdown alleviates hyperoxia-induced injury by inactivating the Smad3 signaling pathway in type II alveolar epithelial cells.

P311 is associated with alveolar formation and development. However, the role and possible mechanism of P311 in hyperoxia-induced injury in type II alveolar epithelial cells (AEC II) need to be elucidated. In our study, rat AEC II (RLE-6TN) were exposure to normoxia (21% O2 and 5% CO2) or hyperoxia (95% O2 and 5% CO2) for 24h, followed by determination of P311 expression. After knockdown of P311 and hyperoxic treatment, cell viability, cell cycle progression, apoptosis and the Smad3 signaling pathway were examined. Rat AEC II were pretreated with SIS3 HCl for 4h and then subjected to P311 overexpression plasmid transfection and hyperoxic exposure. Then, cell viability, apoptosis and the Smad3 signaling pathway were determined. The results showed that hyperoxic exposure significantly elevated P311 levels in rat AEC II. P311 knockdown increased cell viability, accelerated cell cycle progression and inhibited apoptosis, as well as suppression of the Smad3 signaling pathway in hyperoxia-exposed AEC II. Additionally, we found that P311 overexpression enhanced the effects of hyperoxia. Interestingly, SIS3 HCl incubation blocked the effects of P311 overexpression on rat AEC II function under hyperoxic condition, as evidenced by an increase in cell viability, and suppressions of apoptosis and the Smad3 signaling pathway. These results indicate that P311 knockdown may ameliorate hyperoxia-induced injury by inhibiting the Smad3 signaling pathway in rat AEC II. P311 may be a novel target for the treatment of hyperoxia-induced lung injury and even bronchopulmonary dysplasia (BPD).

Inspiratory hyperoxia suppresses lung cancer metastasis through a MYC/SLC1A5-dependent metabolic pathway.

The lack of knowledge about the effect of inspiratory hyperoxia on the lung-specific tumour microenvironment and progression of lung cancer has attracted considerable attention. This study proposes that inspiratory hyperoxia has special significance for the malignant phenotype of lung cancer cells. The effects of different oxygenation parameters on the proliferation, apoptosis, invasion and migration of lung cancer cells were systematically evaluated in vitro and in vivo Our results reveal that inspiratory hyperoxia treatment (60% oxygen, 6 h·day-1) not only has no tumour progression-promoting effects, but also suppresses lung cancer metastasis and promotes long-term survival. In addition, we combined transcriptome, proteome and metabolome analysis and found that hyperoxia treatment induced significant intracellular metabolic changes in lung cancer cells. Overall, we established that MYC/SLC1A5-induced metabolic reprogramming and glutamine addiction is a new mechanism that drives lung cancer metastasis, which can be significantly suppressed by inspiratory hyperoxia treatment. These findings are relevant to the debate on the perils, promises and antitumour effect of inspiratory hyperoxia, especially for patients with lung cancer.

Modeling the Effect of Hyperoxia on the Spin-Lattice Relaxation Rate R1 of Tissues.

PurposeInducing hyperoxia in tissues is common practice in several areas of research, including oxygen‐enhanced MRI (OE‐MRI), which attempts to use the resulting signal changes to detect regions of tumor hypoxia or pulmonary disease. The linear relationship between PO2 and R1 has been reproduced in phantom solutions and body fluids such as vitreous fluid; however, in tissue and blood experiments, factors such as changes in deoxyhemoglobin levels can also affect the ΔR1.Theory and MethodsThis manuscript proposes a three‐compartment model for estimating the hyperoxia‐induced changes in R1 of tissues depending on B0, SO2, blood volume, hematocrit, oxygen extraction fraction, and changes in blood and tissue PO2. The model contains two blood compartments (arterial and venous) and a tissue compartment. This model has been designed to be easy for researchers to tailor to their tissue of interest by substituting their preferred model for tissue oxygen diffusion and consumption. A specific application of the model is demonstrated by calculating the resulting ΔR1 expected in healthy, hypoxic and necrotic tumor tissues. In addition, the effect of sex‐based hematocrit differences on ΔR1 is assessed.ResultsThe ΔR1 values predicted by the model are consistent with reported literature OE‐MRI results: with larger positive changes in the vascular periphery than hypoxic and necrotic regions. The observed sex‐based differences in ΔR1 agree with findings by Kindvall et al. suggesting that differences in hematocrit levels may sometimes be a confounding factor in ΔR1.ConclusionThis model can be used to estimate the expected tissue ΔR1 in oxygen‐enhanced MRI experiments.

Hyperoxia combined with the B-cell antagonist rituximab led to intestinal dysbiosis in neonatal mice.

The adverse factors impacting the intestinal microbiota of newborns remain to be elucidated. We put forward a hypothesis that hyperoxia in combination with rituximab exhibits a synergistic effect that interferes with neonatal intestinal microbiota. Six C57BL/6J mice, aged 12 weeks and pregnant 18 days, were purchased. Their pups were breastfed and raised under a 75% oxygen or conventional environment. Low‐ (20 mg/kg) and high‐dose (40 mg/kg) rituximab were intraperitoneally administered. Fecal genomic DNA was extracted and sequenced by a 16S rRNA platform. Severe intestinal dysbiosis in newborns were observed, whereas mild dysbiosis was caused by inducing hyperoxia alone, confirming the synergistic interference of the combination of hyperoxia and B‐cell antagonist (rituximab) in neonatal intestinal microbiota disruption. Slight dysbiosis was observed in the intestinal microbiota of dams, indicating their much robust ability to confront hyperoxic conditions. The abundance of Akkermansia muciniphila was significantly and extensively altered in both pups and dams after being subjecting them to hyperoxic conditions with or without rituximab administration. In conclusion, this work demonstrated that the synergistic effect of hyperoxia and rituximab led to severe intestinal dysbiosis in newborns. More studies are recommended to explore the precise regulatory mode between hyperoxia and rituximab in intestinal microbiota.

Fetal Zone Steroids Show Discrete Effects on Hyperoxia-Induced Attenuation of Migration in Cultured Oligodendrocyte Progenitor Cells.

Cerebral oxygenation disturbances contribute to the pathogenesis of brain lesions in preterm infants with white matter damage. These children are at risk of developing long-term neurodevelopmental disabilities. Preterm birth is associated with sudden hormonal changes along with an untimely increase in oxygen tissue tension. There is a persistent high postnatal production of fetal zone steroids (FZS), which serve in the fetoplacental unit as precursors for placental estrogen synthesis during pregnancy. The role of FZS in events associated with oxygenation differences and their impact on the developing white matter is not well understood. Therefore, we investigated the effect of hyperoxia (80% O2) and subsequent administration of FZS on the protein composition and migration capabilities of immature oligodendrocytes using the OLN93 (rat-derived OPC) cell line as an experimental model. We tested the effect of the FZS, dehydroepiandrosterone (DHEA), 16α-OH-DHEA, and adiol (5-androstene-3β, 17β-diol). After 24-hour exposure to hyperoxia, we monitored the changes in the proteome profile following treatment and observed significant alterations in pathways regulating cytoskeletal remodelling, cell migration, and cell survival. Additionally, hyperoxia leads to impaired migration of the OLN93 cells in culture. Administration of the FZS showed positive effects on the migration process under normoxic conditions in general. However, under hyperoxic conditions, the trend was less prominent. The observed effects could be related to changes in levels of cofilin/LIMK pathway-associated proteins. Adiol had a negative effect when administered together with estradiol, and the proteomic data reveal the activation of ephrin receptor signalling that might be responsible for the attenuation of migration. The results suggest that FZS can differentially regulate pathways involved in the migration of OLN93 cells. A deeper insight into the precise role of endogenous FZS would be an essential prerequisite for developing new treatment strategies including supplementation of estradiol and other steroids in preterm infants.

Effects of Hyperoxia on Coronary Circulation in Patients with Peripheral Artery Diseases (PAD)

It is well‐known that hyperoxia evokes different effects in patients with different dieaseas conditions. Studies from this lab and others have shown that hyperoxia is a potent coronary vasoconstrictor. Recently, we found that hyperoxia exaggerates systolic blood pressure (BP) response in patients with PAD. The aim of this study is to characterize the coronary circulatory effects of hyperoxia in PAD patients and healthy controls. We recruited 20 PAD patients (14M, 6F, 66 ± 6yrs), and 16 age‐matched control subjects (10M, 6F, 65 ± 8yrs). The ankle‐brachial pressure index (ABI) in the most affected limbs of the patients was 0.58 ± 0.15, compared to the controls ABI of 1.04 ± 0.09. For the hyperoxia procedure the subjects breathed room air for three minutes and 100% oxygen for five minutes. BP and heart rate (HR) were monitored during baseline and hyperoxia. The rate pressure product (RPP), an index of myocardial oxygen consumption, was calculated as the product of systolic BP and HR. Transthoracic Coronary Echocardiography was used to record early and late peak coronary blood flow velocities (CBV1 and CBV2) in the left anterior descending artery. Early and late coronary vascular conductances (peak coronary blood velocity/diastolic blood pressure, CVC1 and CVC2) and coronary perfusion time fraction (CPTF, coronary perfusion time/R‐R interval) were calculated. All data was compared across time and between groups using Repeated Measures Analyses of Variance (RMANOVA).ResultsAt the baseline, RPP and coronary parameters (CBV2, CVC1, and CVC2) were higher in the PAD group compared to controls, also the PAD group showed significantly shorter CPTF. During hyperoxia, CBV1, CBV2, CVC1, and CVC2 decreased to varying degrees in both groups. However, no significant interactions were observed for RPP and all coronary parameters during hyperoxia between the groups (Table). Our findings suggest that the effect of hyperoxia on coronary circulation was not significantly different between PAD and healthy controls.

Neuroprotective Role of Hyperoxia During the Critical Period of Retinal Development in Normal Mice and Mice with Retinitis Pigmentosa

BackgroundThe retina utilizes more oxygen than any other tissue in the body. Photoreceptors located in the retina's outer nuclear layer (ONL) are culled during the “critical period” of eye development when the number of photoreceptors exceeds the supply of oxygen. Retinitis Pigmentosa (RP) is a disease that first affects the rod photoreceptors, causing night blindness and reduced peripheral vision. In mice, RP often starts during the critical period. The objective of this study was to assess the effects of hyperoxia during the critical period on visual function and morphology of the retina in normal mice and mice with RP.MethodThirty five male and female wild‐type (C57BL/6J) mice and 15 mice with an rd1 mutation (C3H/HeJ), which causes a rapidly progressing form of retinitis pigmentosa, were exposed to hyperoxia (75% O₂), hypoxia (12% O₂), and normoxia (21% O₂) from postnatal (P) days 7 to 20. At P26, electroretinography (ERG) was used to assess the visual function of the photoreceptors (A‐wave) and the inner retinal cells (B‐wave). At P27, optical coherence tomography (OCT) and histology were used to observe retinal structure and the effects of the different O₂ groups. For histology, eyes were extracted at P10, P12, P16, and P28. Cell death was evaluated using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL).ResultsIn ERGs from C57 mice, both A‐wave and B‐wave amplitudes were significantly lower in the hypoxic condition indicating that hypoxia was detrimental to visual function compared to the normoxic group. OCT data showed that the hyperoxic groups of C57 mice had thicker ONLs compared to the other treatment groups. TUNEL cell counts in the ONL and INL indicated a significant decrease in apoptotic cells during the critical period in the hyperoxic group compared to the hypoxic group. In C3H mice, hyperoxia improved the A and B waves compared to untreated mice.DiscussionThis study suggests that administration of oxygen during the critical period of retinal development reduces the pruning of cells in the retina and increases visual function in both normal mice and mice with an aggressive form of RP. Oxygen treatment during the critical period of retinal development, which occurs from P8 to P16, may slow retinal degeneration in RP. The effects of hyperoxia on the completion of vascular development must be taken into account when considering the use of hyperoxia therapeutically.

Peripheral Chemoreflex Sensitivity is Augmented in Human Type 2 Diabetes

IntroductionThe peripheral chemoreceptors have been implicated in the pathogenesis of type 2 diabetes. Our main objective was to examine peripheral chemosensitivity in individuals with type 2 diabetes, as well as the contribution of the peripheral chemoreceptors to basal cardiovascular control. We hypothesized individuals with type 2 diabetes exhibit exaggerated peripheral chemoreflex sensitivity to hypoxia compared to healthy, non‐diabetic controls. We further hypothesized the peripheral chemoreceptors contribute to cardiovascular dysfunction in type 2 diabetes.MethodsEight adults with diagnosed type 2 diabetes (3M/5F, 54±3 yrs, HbA1c 8.1±0.6%) and nineteen healthy controls (8M/11F, 50±3 yrs, HbA1c 5.3±0.1%) participated (IRB #2010295 and #2018486). Ventilatory and hemodynamic responses to acute hypoxia were assessed to determine peripheral chemosensitivity [i.e., hypoxic ventilatory (HVR), heart rate (HHRR) and blood pressure (HBPR) response]. Separately, heart rate, blood pressure and forearm blood flow (Doppler ultrasound) were measured while breathing normoxic or hyperoxic air (100% O2; Modified Dejours test) to acutely attenuate peripheral chemoreceptor activity. Forearm blood flow was normalized for mean arterial blood pressure for measures of vascular resistance.ResultsPeripheral chemosensitivity was augmented in adults with type 2 diabetes compared to control as assessed via the HVR (‐1.10±0.16 vs ‐0.50±0.10 L/min/%, p&lt;0.01) and HBPR (‐0.92±0.17 vs ‐0.42±0.19 mmHg/%, p=0.06), with no differences in HHRR (‐0.68±0.22 vs ‐0.56±0.12 beats/min/%, p=0.64). Higher HVR and HBPR were associated with higher fasting insulin (R=‐0.58, p&lt;0.01 and R=‐0.38, p=0.06) and HbA1c (R=‐0.60, p&lt;0.01 and R=‐0.39, p=0.05). Attenuation of peripheral chemoreceptor activity with acute hyperoxia decreased heart rate (p&lt;0.01) and blood pressure (p=0.02), with no effect on forearm vascular resistance (p=0.55); any effect of hyperoxia did not differ between adults with type 2 diabetes and controls (p&gt;0.05).ConclusionIndividuals with type 2 diabetes exhibit exaggerated peripheral chemoreflex sensitivity which is associated with disease severity (i.e., HbA1c). In contrast, the contribution of the peripheral chemoreceptors to basal cardiovascular function in type 2 diabetes does not differ from non‐diabetic controls. Results advance our understanding of the pathogenesis of type 2 diabetes and related complications.

Autonomic Responses to Acute Hyperoxia are Impaired in Patients with Peripheral Artery Disease

Prior reports suggest that oxidative stress plays an important role in the development of atherosclerotic diseases such as peripheral artery disease (PAD). The effects of acute hyperoxia, an important acute oxidative stressor, on autonomic function have not been well studied in PAD. We hypothesized that the autonomic responses to acute hyperoxia would be impaired in PAD. We studied 17 patients with PAD (12M, 5F, 67 ± 2 yrs) and 15 healthy controls (10M, 5F, 65 ± 2 yrs). The ankle‐brachial indexes in the patients were 0.57 ± 0.03 in the most affected leg and 0.77 ± 0.04 in the less affected leg, respectively. Beat‐by‐beat heart rate (HR, from ECG) and blood pressure (BP, with Finometer) were recorded for 10 min under normoxic resting conditions and during 5‐min hyperoxia (100% oxygen) as an acute oxidative stress test. HR variability (HRV) was calculated and cardiac baroreflex sensitivity (BRS) was estimated with the sequence technique. Under resting conditions, mean HR and mean arterial pressure (MAP) were not significantly different between the groups. Resting values of the root mean square of successive differences between normal heartbeats (RMSSD, a HRV index for parasympathetic activity; 14.1 ± 1.0 vs. 19.8 ± 2.2 ms, P = 0.032) and cardiac BRS (6.43 ± 0.78 vs. 14.86 ± 2.56 ms/mmHg, P = 0.001) were significantly lower in PAD than in healthy controls. Hyperoxia lowered HR in both groups and raised MAP only in patients with PAD. During hyperoxia both HR and MAP were significantly higher in PAD than in controls. Hyperoxia induced an increase in RMSSD and the high frequency (HF) component of HRV (another index for parasympathetic activity) in healthy subjects. However, during hyperoxia no increase in parasympathetic activity was observed in PAD. Both RMSSD and the HF component of the whole trial (i.e. baseline and hyperoxia) in PAD were lower than those in healthy control subjects. Hyperoxia did not induce changes in cardiac BRS in either group, while cardiac BRS of the whole trial in PAD was lower than that in healthy controls. These data suggest that resting parasympathetic activity and cardiac baroreflex function are impaired in PAD. Moreover, the autonomic response to acute oxidative stress (i.e. an increase in parasympathetic activity) is also impaired in PAD. Further studies are needed to examine if antioxidant agents can improve autonomic function in PAD.

Abstract 377: Neonatal Hyperoxia Contributes To Early Cardio-renal Fibrosis And Systemic Vascular Stiffness In 1 Year Old Rats

Background: There is a knowledge gap in the mechanisms linking neonatal hyperoxia (O 2 ) exposure and its contribution to cardio-renal dysfunction in adults born preterm. TGF-β, a pro-fibrotic cytokine is a key player in cardio-renal fibrosis and vascular stiffness. Here, we test the hypothesis that neonatal hyperoxia induces cardio-renal dysfunction and systemic vascular stiffness in adulthood and this is associated with increased TGF-β levels. Objective: To determine the association between cardio-renal dysfunction, systemic vascular stiffness and TGF-β levels in adult rats exposed to neonatal hyperoxia. Methods: Newborn rats (N=22) randomly assigned to normoxia (RA) or hyperoxia (85% O 2 ) from postnatal day 1 to 14 (P1 to P14), were recovered in normoxic conditions until 1 year of life. At 1 year, left ventricular (LV) function was assessed by echocardiography. Aortic and mesenteric arterial stiffness was assessed by wire myography. RNA-seq of the aorta and kidney was done to assess the transcriptional effects of neonatal hyperoxia at 1 year. TGF-β expression was assessed by multiplex cytokine analysis in heart, aorta and kidney. Data was analyzed by Student’s T test. Results: At 1 year, there was no evidence of LV dysfunction in rats exposed to neonatal hyperoxia. In contrast, wire myography revealed that rats exposed to neonatal O 2 had significantly increased stiffness of mesenteric artery and aorta. Neonatal hyperoxia exposure differentially regulated genes in 1 year old aorta and kidney. Gene set enrichment analysis showed that genes most induced in the aorta by hyperoxia were “connective tissue development”, “extracellular matrix remodeling” and in the kidney were “actin cytoskeleton”, “epithelial cell differentiation”. As compared to the RA group, rats exposed to neonatal hyperoxia had significantly increased TGF-β1 and TGF-β2 expression in LV and increased TGF-β1 and similar TGF-β2 expression in kidney at 1 year of age. Conclusion: Although LV function was normal in hyperoxia-exposed 1 year old rats, these animals had increased systemic vascular stiffness and increased TGF-β expression in LV, aorta and kidney, implying the crucial role of TGF-β signaling in cardio-renal dysfunction in adult rodents exposed to neonatal hyperoxia.

Lower‐limb venous function in hypoxia and hyperoxia: effect of healthy ageing

Oxygen is an important modulator of vascular function, but its influence on the veins is incompletely understood. While age‐related impairments on arterial function have been well‐established, the effects of ageing on the venous circulation have not been examined. The purpose of this study was to determine the effects of hypoxia and hyperoxia on lower limb venous function in healthy young and older humans. We tested the hypothesis that the venomotor response to hypoxia and hyperoxia is attenuated with ageing.In fifteen young (29±8 years, mean±SD) and seven older (age: 66±6 years) healthy individuals, we assessed peripheral oxygen saturation (SpO2) and the cross‐sectional area (CSA) of the great saphenous vein (GSV; Doppler ultrasound) during a standard thigh cuff inflation‐deflation protocol (11 min) while breathing room air, hypoxia (fraction in inspired oxygen [FIO2]: 0.10) or hyperoxia (FIO2: 0.50), in a single‐blinded, randomized manner. The pressure‐CSA relationship was modelled using an established quadratic regression equation and GSV compliance derived.Resting SpO2 was decreased by hypoxia (80.9±5.6%) and increased by hyperoxia (98.8±0.7%) compared to room air (96.3±1.1%, p&lt;0.001) in both young and older groups. In the young group, hypoxia selectively decreased GSV CSA (index of capacity) (13.4±5.7 mm2, p&lt;0.001) compared to room air (17.0±7.9 mm2), while GSV compliance was unchanged (p=1.000). In contrast, hyperoxia did not alter GSV CSA (17.1±8.7 mm2, p=0.883) in the young group, but GSV compliance was increased by 2‐3 fold compared to room air and hypoxia (p=0.007). In room air, GSV capacity was almost double in older participants (+19.6m2, p=0.016), but GSV compliance was not different from the younger group (p=0.423). Neither hypoxia nor hyperoxia affected GSV CSA and compliance in the older group (p&gt;0.05 vs. room air).These preliminary data suggest that in young healthy individuals, hypoxia reduces GSV capacity and hyperoxia increases GSV compliance. However, such manipulations in blood oxygenation do not alter venous function in older healthy individuals. Further investigations are required to determine whether local and/or chemoreflex‐mediated sympathetic mechanisms underpin such alterations in venous function.

In vivo Molecular Imaging Stratifies Rats with Different Susceptibilities to Hyperoxic Acute Lung Injury

ObjectivesAcute Respiratory Distress Syndrome (ARDS) is one of the most frequent causes of admission to medical intensive care units. It carries a mortality rate &gt;30%, due to lack of early detection tools, inability to identify patients at risk for progression, and limited therapies. Previously, we demonstrated the utility of 99mTc‐hexamethylpropyleneamine oxime (HMPAO) and 99mTc‐duramycin in vivo imaging to detect oxidative stress and endothelial cell death in rats exposed to 100% O2 (hyperoxia) as a model of human ARDS. Pre‐exposure to hyperoxia for 48 hrs followed by 24 hr in room air (H‐T) protects against ARDS in that, when subsequently re‐exposed to hyperoxia, rats are tolerant of and survive the otherwise lethal effects of hyperoxia. Thus, the objective of this study was to evaluate the ability of 99mTc ‐HMPAO and ‐duramycin to track the protection of hyperoxia pre‐exposure and to identify mechanisms involved as potential therapeutic targets.MethodsSprague‐Dawley rats were exposed to either room air, hyperoxia (100% O2) for 60 hr, hyperoxia for 48 hr followed by 24 hr of room air (H‐T), or H‐T followed by 60 hr of hyperoxia (H‐T+60). Rats were anesthetized and imaged using either 99mTc‐HMPAO or 99mTc‐duramycin (37‐74 MBq) (n=4‐6 per group). In vivo scintigraphy images were acquired 20 min post i.v. injection and lung uptake was determined from the images as mean lung activity normalized to mean forelimb blood activity. Rat lung endpoints including wet‐to‐dry weight ratio, volume of pleural effusion in the chest cavity, expression of 3‐nitrotyrosine (3NT), and histological H&amp;E and cleaved caspase 3 positive‐cells (apoptosis marker) were also measured as indices of injury/protection.ResultsLung 99mTc‐HMPAO uptake increased by 200% in hyperoxia‐exposed rats, whereas uptake in H‐T+60 rats was 24% less than in H‐T rats. Lung uptake of 99mTc‐duramycin increased by 167% in hyperoxia‐exposed rats, but uptake in H‐T+60 rats was only 17% greater than H‐T rats. Lung wet/dry weight ratio increased by 21% in hyperoxia‐exposed rats, but by only 15% in H‐T+60 versus HT rats. Similarly, pleural effusion was reduced significantly (66%) in the H‐T+60 rats compared to the hyperoxia rats. 3NT expression, as a measure of oxidative stress, was increased ~300% with hyperoxia, but no significant increase was detected in H‐T+60 rats compared to H‐T. Histological analysis indicates that neutrophilic influx, edema, and apoptotic cells were increased with hyperoxia, but this increase was small or not observed with H‐T+60.ConclusionsLung uptake of 99mTc‐HMPAO and 99mTc‐duramycin, reflecting oxidative stress and cell death, respectively, is reduced significantly in rats preconditioned to tolerate hyperoxia compared to those without the preconditioning. This tolerance is also reflected in lung functional and histological endpoints measured independently. Overall these results suggest the potential utility of 99mTc‐HMPAO and 99mTc‐ duramycin imaging as a tool for identifying those hosts that are more or less susceptible to progressing to severe ARDS following mild symptoms of lung injury.

Neonatal ventilatory changes in the control of breathing in a hyperoxia‐induced mouse model of bronchopulmonary dysplasia

While hyperoxia is needed for survival of very premature infants (&lt;28 weeks gestation) due to immature lungs and immature neural control of breathing, it contributes to bronchopulmonary dysplasia (BPD), a chronic lung disease associated with heighted pediatric morbidity and mortality. Given the plasticity of the neural control of breathing, this study seeks to address whether the neural control of breathing adapts to lung disease and the roles of clusters of pulmonary neuroendocrine cells called neuroepithelial bodies (NEBs) in mediating breathing adaptations (or maladaptations). NEBs line the airways, are O2 and CO2 sensitive, are hypertrophied/hyperplastic in human BPD, and are innervated by vagal fibers that inhibit breathing when activated. Herein, we test the hypotheses that chronic neonatal hyperoxia causes age‐dependent changes to cardiorespiratory control and these changes are in part mediated by NEBs. Mice expressing eGFP in all NEBs were exposed to hyperoxia (FIO2: 0.7 from 0‐14 days of life; P0‐14) had reduced alveolar density (P&lt;0.001) and fewer alveoli (P&lt;0.001) compared with normoxic controls (n=4) at P22 (by 2‐tailed t‐Test), consistent with clinical BPD. Whole‐body flow through plethysmography did not reveal baseline breathing differences between normoxic (n=10) and hyperoxic (n=10) mice at any of the ages studied (P14‐22), though there is a trend (n=3/group) for a greater respiratory exchange ratio (RER) measured by respirometry in hyperoxic mice. There was also a significant main effect of hyperoxia (n=7) reducing the hypoxic and hypercapnic ventilatory responses compared to normoxic mice (n=10; two‐way mixed effect model with Sidak post‐hoc test). Ongoing studies aim to lesion NEBs using Saporin toxin conjugated to an NEB specific membrane protein in a subset of mice to address the functional role of NEBs in breathing in normoxic and hyperoxic treated mice.

Local Mucosal CO2 but Not O2 Insufflation Improves Gastric and Oral Microcirculatory Oxygenation in a Canine Model of Mild Hemorrhagic Shock.

IntroductionAcute hemorrhage results in perfusion deficit and regional hypoxia. Since failure of intestinal integrity seem to be the linking element between hemorrhage, delayed multi organ failure, and mortality, it is crucial to maintain intestinal microcirculation in acute hemorrhage. During critical bleeding physicians increase FiO2 to raise total blood oxygen content. Likewise, a systemic hypercapnia was reported to maintain microvascular oxygenation (μHbO2). Both, O2 and CO2, may have adverse effects when applied systemically that might be prevented by local application. Therefore, we investigated the effects of local hyperoxia and hypercapnia on the gastric and oral microcirculation.MethodsSix female foxhounds were anaesthetized, randomized into eight groups and tested in a cross-over design. The dogs received a local CO2-, O2-, or N2-administration to their oral and gastric mucosa. Hemorrhagic shock was induced through a withdrawal of 20% of estimated blood volume followed by retransfusion 60 min later. In control groups no shock was induced. Reflectance spectrophotometry and laser Doppler were performed at the gastric and oral surface. Oral microcirculation was visualized by incident dark field imaging. Systemic hemodynamic parameters were recorded continuously. Statistics were performed using a two-way-ANOVA for repeated measurements and post hoc analysis was conducted by Bonferroni testing (p < 0.05).ResultsThe gastric μHbO2 decreased from 76 ± 3% to 38 ± 4% during hemorrhage in normocapnic animals. Local hypercapnia ameliorated the decrease of μHbO2 from 78 ± 4% to 51 ± 8%. Similarly, the oral μHbO2 decreased from 81 ± 1% to 36 ± 4% under hemorrhagic conditions and was diminished by local hypercapnia (54 ± 4%). The oral microvascular flow quality but not the total microvascular blood flow was significantly improved by local hypercapnia. Local O2-application failed to change microvascular oxygenation, perfusion or flow quality. Neither CO2 nor O2 changed microcirculatory parameters and macrocirculatory hemodynamics under physiological conditions.DiscussionLocal hypercapnia improved microvascular oxygenation and was associated with a continuous blood flow in hypercapnic individuals undergoing hemorrhagic shock. Local O2 application did not change microvascular oxygenation, perfusion and blood flow profiles in hemorrhage. Local gas application and change of microcirculation has no side effects on macrocirculatory parameters.

Resuscitation of very preterm infants with 30% vs. 50% oxygen: a randomized controlled trial

Background Preterm infants are susceptible to the damaging effects of hyperoxia which may lead to bronchopulmonary dysplasia (BPD) and intestinal damage. Hyperoxia also affects intestinal microbiota. The optimal initial FiO2 for the resuscitation of premature infants is unknown.&#x0D; Objective To determine the effect of different initial oxygen concentrations on BPD, oxidative stress markers, damage to the gastrointestinal mucosa, and the intestinal microbiome.&#x0D; Methods We conducted an unblinded, randomized controlled clinical trial in premature infants requiring supplemental oxygen in the first minutes of life. Infants started at an FiO2 of either 30% (low) or 50% (moderate), which was adjusted to achieve target oxygen saturations (SpO2) of 88-92% by 10 minutes of life using pulse oximetry. The primary outcome was incidence of BPD. Secondary outcomes included markers of oxidative stress [oxidized glutathione (GSH)/reduced glutathione (GSSG) ratio and malondialdehyde (MDA)], intestinal integrity indicated by fecal alpha-1 antitrypsin (AAT), and intestinal microbiota on fecal examination.&#x0D; Results Eighty-four infants were recruited. There was no significant difference in rates of BPD between the 30% FiO2 and 50% FiO2 groups (42.8% vs. 40.5%, respectively). Nor were there significant differences in GSH/GSSG ratios, MDA concentrations, fecal AAT levels, or changes in facultative anaerobic and anaerobic microbiota between groups.&#x0D; Conclusion In premature infants resuscitated using low vs. moderate initial FiO2 levels, we find no significant differences in BPD incidence, markers of oxidative stress, intestinal mucosa integrity, or intestinal microbiota.

NRF2 Alters Mitochondrial Gene Expression in Neonate Mice Exposed to Hyperoxia.

Approximately 1 in 10 newborns are born preterm and require supplemental oxygen (O2) in an extrauterine environment following birth. Supplemental O2 can induce oxidative stress that can impair mitochondrial function, resulting in lung injury and increased risk in early life pulmonary diseases. The nuclear factor-erythroid 2 related factor 2 (NRF2) protects the cells from oxidative stress by regulating the expression of genes containing antioxidant response elements and many mitochondrial-associated genes. In this study, we compared Nrf2-deficient (Nrf2−/−) and wild-type (Nrf2+/+) mice to define the role of NRF2 in lung mitochondrial genomic features in late embryonic development in mice (embryonic days, E13.5 and E18.5) versus birth (postnatal day 0, PND0). We also determined whether NRF2 protects lung mitochondrial genome parameters in postnatal mice exposed to a 72 h hyperoxia environment. We found Nrf2−/− embryonic lungs were characterized by decreases in mtDNA copies from E13.5 to E18.5. Interestingly, Nrf2−/− heteroplasmy frequency was significantly higher than Nrf2+/+ at E18.5, though this effect reversed at PND0. In postnatal mice exposed to hyperoxia, we identified three- to four-fold increases in mitochondria-encoded mitochondrial genes, which regulate oxidative phosphorylation. Overall, our findings demonstrate a potentially critical role of NRF2 in mediating long-term effects of hyperoxia on mitochondrial function.

Hyperoxia Induces Ferroptosis and Impairs Lung Development in Neonatal Mice.

Oxygen is often required to treat newborns with respiratory disorders, and prolonged exposure to high oxygen concentrations impairs lung development. Ferroptosis plays a vital role in the development of many diseases and has become the focus of treatment and prognosis improvement for related diseases, such as neurological diseases, infections, cancers, and ischemia-reperfusion injury. Whether ferroptosis participates in the pathogenesis of hyperoxia-induced lung injury remains unknown. The aims of this study are to determine the effects of hyperoxia on lung ferroptosis and development in neonatal mice. Newborn C57BL/6 mice were reared in either room air (RA) or hyperoxia (85% O2) at postnatal days 1–7. On postnatal days 3 and 7, the lungs were harvested for histological and biochemical analysis. The mice reared in hyperoxia exhibited significantly higher Fe2+, malondialdehyde, and iron deposition and significantly lower glutathione, glutathione peroxidase 4, and vascular density than did those reared in RA on postnatal days 3 and 7. The mice reared in hyperoxia exhibited a comparable mean linear intercept on postnatal day 3 and a significantly higher mean linear intercept than the mice reared in RA on postnatal day 7. These findings demonstrate that ferroptosis was induced at a time point preceding impaired lung development, adding credence to the hypothesis that ferroptosis is involved in the pathogenesis of hyperoxia-induced lung injury and suggest that ferroptosis inhibitors might attenuate hyperoxia-induced lung injury.

Effects of hypoxia and hyperoxia on venous capacity and compliance in healthy men and women.

Blood oxygen is an important modulator of arterial function, but its impact on peripheral venous function is incompletely understood. Herein, we sought to determine the effect of hypoxia and hyperoxia on venous capacity and compliance in the lower limb. In 16 healthy individuals (7 women; age: 28.3 ± 7.6 yr, mean ± SD), we assessed peripheral oxygen saturation ([Formula: see text]), the cross-sectional area (CSA) of the great saphenous vein (GSV; Doppler ultrasound), and calf volume (strain-gauge plethysmography) during a standard 60 mmHg thigh cuff inflation-deflation protocol. Separate trials were undertaken during breathing of room air, hypoxia [fraction in inspired oxygen ([Formula: see text]): 0.10], and hyperoxia ([Formula: see text]: 0.50), according to a single-blinded, randomized design. Lower limb pressure-CSA and pressure-volume relationships were modeled using a quadratic regression equation and compliance derived. [Formula: see text] was decreased by hypoxia (83.6 ± 5.6%) and increased by hyperoxia (98.7 ± 0.5%) compared with room air (96.4 ± 1.0%, P < 0.001). Compared with room air (17.0 ± 7.9 mm2), hypoxia decreased GSV CSA (13.4 ± 5.7 mm2, P < 0.001), whereas no change was observed with hyperoxia (17.1 ± 8.7 mm2, P = 0.883). GSV compliance derived from the pressure-CSA relationships was elevated approximately twofold with hyperoxia (-0.0061 ± 0.0046 a.u.) when compared with room air (-0.0029 ± 0.002 a.u., P = 0.027) and hypoxia (-0.0030 ± 0.0032 a.u., P = 0.007). No differences were observed in calf pressure-volume parameters with either hypoxia or hyperoxia (P > 0.05). Our data indicate that GSV capacity is reduced by hypoxia, and that GSV compliance is increased by hyperoxia, thus highlighting the often overlooked role of oxygen in the regulation of venous circulation.

Using a neonatal rat model to explore the therapeutic potential of coenzyme Q10 in prematurity under hyperoxia.

Hyperoxia, is often used in preterm supportive care, leading to high oxygen exposure in neonates. Coenzyme Q10 (CoQ10) is a free radical scavenger that has been studied in older children but never be investigated for its role in preterm care. We hypothesize that the administration of exogenous CoQ10 would raise serum concentrations of CoQ10 and mitigate the adverse effects of hyperoxia on the organs by reducing oxygen-free radicals and inflammation. The aim of this study was to evaluate the effects of oxidative stress, inflammatory response, and survival in neonatal rats after CoQ10 treatment. Neonatal rats delivered from four pregnant Wistar rats were randomly divided into four groups: (a) control, (b) CoQ10, (c) hyperoxia (O2 group), and (d) treatment (CoQ10 + O2 ) groups. The dose of CoQ10 injected was 30 mg/kg. The CoQ9, CoQ10, cytokines, oxidative stress, and antioxidant enzyme activity were measured. Tissue samples were histologically examined and mortality was monitored for 16 days. The level of CoQ9 significantly increased in the liver, kidney, and plasma, while the level of CoQ10 significantly increased in most organ tissues in the CoQ10 + O2 group. Additionally, CoQ10 decrease oxidative stress in the liver, increase antioxidant enzyme activity in the heart, kidney, and brain, and reverse an inclined level of hematopoietic growth factors. However, CoQ10 had no effect on inflammation, organ damage, or mortality. Therefore, the use of CoQ10 in potential adjuvant therapy for neonatal hyperoxia requires further research.