Sex-specific differences in hyperoxic lung injury in mice: role of cytochrome P450 (CYP)1A

Influence of age and sex on physical, cardiac electrical and functional alterations in progressive hyperoxia treatment: A time course study in a murine model

Oxygen supplementation is a widely used treatment for ICU patients. However, it can lead to hyperoxia, which in turn can result in oxidative stress, cardiac remodeling, and even mortality. This paper expands upon previous research conducted by our lab to establish time-dependent cardiac changes under hyperoxia. In this study, both young and aged mice (male and female) underwent 72 h of hyperoxia exposure and were monitored at 24-hour intervals for cardiac electrophysiological and functional parameters using ECG and electrocardiogram data. Our analysis showed that young male mice experienced significant weight loss as well as significant lung edema by 48 h. Although young male mice were highly susceptible to physical changes, they were resistant to early cardiac functional and electrophysiological changes compared to the other groups. Both young and aged female and aged males developed functional impairments by 24 h of hyperoxia exposure. Furthermore, sex and age differences were noted in the onset of electrophysiological changes. While some groups could resist early cardiac remodeling, our data suggests that 72 h of hyperoxia exposure is sufficient to induce significant cardiac remodeling across all age and sex groups. Our data establishes that time-dependent cardiac changes due to oxygen supplementation can have devastating consequences even with short exposure periods. These findings can aid in developing clinical practices for individuals admitted to the ICU by elucidating the impact of aging, sex, and length of stay under mechanical ventilation to limit hyperoxia-induced cardiac remodeling.

The impact of gender medicine on neonatology: the disadvantage of being male: a narrative review

This narrative non-systematic review addresses the sex-specific differences observed both in prenatal period and, subsequently, in early childhood. Indeed, gender influences the type of birth and related complications. The risk of preterm birth, perinatal diseases, and differences on efficacy for pharmacological and non-pharmacological therapies, as well as prevention programs, will be evaluated. Although male newborns get more disadvantages, the physiological changes during growth and factors like social, demographic, and behavioural reverse this prevalence for some diseases. Therefore, given the primary role of genetics in gender differences, further studies specifically targeted neonatal sex-differences will be needed to streamline medical care and improve prevention programs.

Y It Matters—Sex Differences in Fetal Lung Development

Within this review, sex-specific differences in alveolar epithelial functions are discussed with special focus on preterm infants and the respiratory disorders associated with premature birth. First, a short overview about fetal lung development, the challenges the lung faces during perinatal lung transition to air breathing and respiratory distress in preterm infants is given. Next, clinical observations concerning sex-specific differences in pulmonary morbidity of human preterm infants are noted. The second part discusses potential sex-specific causes of pulmonary complications, including pulmonary steroid receptors and local lung steroid metabolism. With regard to pulmonary steroid metabolism, it is important to highlight which steroidogenic enzymes are expressed at which stage during fetal lung development. Thereafter, we review the knowledge concerning sex-specific aspects of lung growth and maturation. Special focus is given to alveolar epithelial Na+ transport as a driver of perinatal lung transition and the sex differences that were noted in this process.

Oxygen Toxicity to the Immature Lung-Part I: Pathomechanistic Understanding and Preclinical Perspectives

In utero, the fetus and its lungs develop in a hypoxic environment, where HIF-1α and VEGFA signaling constitute major determinants of further development. Disruption of this homeostasis after preterm delivery and extrauterine exposure to high fractions of oxygen are among the key events leading to bronchopulmonary dysplasia (BPD). Reactive oxygen species (ROS) production constitutes the initial driver of pulmonary inflammation and cell death, altered gene expression, and vasoconstriction, leading to the distortion of further lung development. From preclinical studies mainly performed on rodents over the past two decades, the deleterious effects of oxygen toxicity and the injurious insults and downstream cascades arising from ROS production are well recognized. This article provides a concise overview of disease drivers and different therapeutic approaches that have been successfully tested within experimental models. Despite current studies, clinical researchers are still faced with an unmet clinical need, and many of these strategies have not proven to be equally effective in clinical trials. In light of this challenge, adapting experimental models to the complexity of the clinical situation and pursuing new directions constitute appropriate actions to overcome this dilemma. Our review intends to stimulate research activities towards the understanding of an important issue of immature lung injury.

Urinary biomarkers of polycyclic aromatic hydrocarbons and their associations with liver function in adolescents

Associations between polycyclic aromatic hydrocarbons (PAHs) and respiratory diseases have been widely studied, but the effects of PAH on liver toxicity in adolescents are unclear. Here, 3194 adolescents with NHANES data from 2003 to 2016 were selected. PAH exposure was assessed by measuring PAH metabolites in urine. The outcome variables were the levels of alanine aminotransferase (ALT), aspartate amino transferase (AST) and gamma-glutamyl transpeptidase (GGT). The association between PAH exposure and liver function was evaluated by the weighted quantile sum (WQS) and logistic regression, and the associations between PAHs and inflammation and blood lipids were evaluated by linear regression. Covariates were adjusted for age, ethnicity, BMI, physical activity, family income, cotinine, and urinary creatinine. The results showed that for females, mixed PAH exposure was related to an increased ALT level (OR = 2.33, 95% CI 1.15, 4.72), and 2-fluorene contributed the most (38.6%). Urinary 2-fluorene was positively associated with an elevated ALT level (OR = 2.19 95% 1.12, 4.27, p for trend = 0.004). Mechanistically, 2-fluorene can cause a 3.56% increase in the white blood cell count, a 6.99% increase in the triglyceride level, and 1.70% increase in the total cholesterol level. PAHs may have toxic effects, possibly mediated by inflammation and blood lipids, on the adolescent female liver. Additional confirmatory studies are needed.

Early extubation to noninvasive respiratory support of former preterm lambs improves long-term respiratory outcomes

Invasive mechanical ventilation (IMV) and exposure to oxygen-rich gas during early postnatal life are contributing factors for long-term pulmonary morbidities faced by survivors of preterm birth and bronchopulmonary dysplasia. The duration of IMV that leads to long-term pulmonary morbidities is unknown. We compared two durations of IMV (3 h vs. 6 days) during the first 6-7 days of postnatal life in preterm lambs to test the hypothesis that minimizing the duration of IMV will improve long-term respiratory system mechanics and structural outcomes later in life. Moderately preterm (∼85% gestation) lambs were supported by IMV for either 3 h or 6 days before weaning from all respiratory support to become former preterm lambs. Respiratory system mechanics and airway reactivity were assessed monthly from 1 to 6 mo of chronological postnatal age by the forced oscillation technique. Quantitative morphological measurements were made for smooth muscle accumulation around terminal bronchioles and indices of alveolar formation. Minimizing IMV to 3 h led to significantly better (P < 0.05) baseline respiratory system mechanics and less reactivity to methacholine in the first 3 mo of chronological age (2 mo corrected age), significantly less (P < 0.05) accumulation of smooth muscle around peripheral resistance airways (terminal bronchioles), and significantly better (P < 0.05) alveolarization at the end of 5 mo corrected age compared with continuous IMV for 6 days. We conclude that limiting the duration of IMV following preterm birth of fetal lambs leads to better respiratory system mechanics and structural outcomes later in life.

Hyperoxia and Lungs: What We Have Learned From Animal Models

Although oxygen (O₂) is essential for aerobic life, it can also be an important source of cellular damage. Supra-physiological levels of O₂ determine toxicity due to exacerbated reactive oxygen species (ROS) production, impairing the homeostatic balance of several cellular processes. Furthermore, injured cells activate inflammation cascades, amplifying the tissue damage. The lung is the first (but not the only) organ affected by this condition. Critically ill patients are often exposed to several insults, such as mechanical ventilation, infections, hypo-perfusion, systemic inflammation, and drug toxicity. In this scenario, it is not easy to dissect the effect of oxygen toxicity. Translational investigations with animal models are essential to explore injuring stimuli in controlled experimental conditions, and are milestones in understanding pathological mechanisms and developing therapeutic strategies. Animal models can resemble what happens in critical care or anesthesia patients under mechanical ventilation and hyperoxia, but are also critical to explore the effect of O₂ on lung development and the role of hyperoxic damage on bronchopulmonary dysplasia. Here, we set out to review the hyperoxia effects on lung pathology, contributing to the field by describing and analyzing animal experimentation's main aspects and its implications on human lung diseases.

Hyperoxia-induced bronchopulmonary dysplasia: better models for better therapies

Bronchopulmonary dysplasia (BPD) is a chronic lung disease caused by exposure to high levels of oxygen (hyperoxia) and is the most common complication that affects preterm newborns. At present, there is no cure for BPD. Infants can recover from BPD; however, they will suffer from significant morbidity into adulthood in the form of neurodevelopmental impairment, asthma and emphysematous changes of the lung. The development of hyperoxia-induced lung injury models in small and large animals to test potential treatments for BPD has shown some success, yet a lack of standardization in approaches and methods makes clinical translation difficult. In vitro models have also been developed to investigate the molecular pathways altered during BPD and to address the pitfalls associated with animal models. Preclinical studies have investigated the efficacy of stem cell-based therapies to improve lung morphology after damage. However, variability regarding the type of animal model and duration of hyperoxia to elicit damage exists in the literature. These models should be further developed and standardized, to cover the degree and duration of hyperoxia, type of animal model, and lung injury endpoint, to improve their translational relevance. The purpose of this Review is to highlight concerns associated with current animal models of hyperoxia-induced BPD and to show the potential of in vitro models to complement in vivo studies in the significant improvement to our understanding of BPD pathogenesis and treatment. The status of current stem cell therapies for treatment of BPD is also discussed. We offer suggestions to optimize models and therapeutic modalities for treatment of hyperoxia-induced lung damage in order to advance the standardization of procedures for clinical translation.

Estradiol resolves pneumonia via ERβ in regulatory T cells

Current treatments for pneumonia (PNA) are focused on the pathogens. Mortality from PNA-induced acute lung injury (PNA-ALI) remains high, underscoring the need for additional therapeutic targets. Clinical and experimental evidence exists for potential sex differences in PNA survival, with males having higher mortality. In a model of severe pneumococcal PNA, when compared with male mice, age-matched female mice exhibited enhanced resolution characterized by decreased alveolar and lung inflammation and increased numbers of Tregs. Recognizing the critical role of Tregs in lung injury resolution, we evaluated whether improved outcomes in female mice were due to estradiol (E2) effects on Treg biology. E2 promoted a Treg-suppressive phenotype in vitro and resolution of PNA in vivo. Systemic rescue administration of E2 promoted resolution of PNA in male mice independent of lung bacterial clearance. E2 augmented Treg expression of Foxp3, CD25, and GATA3, an effect that required ERβ, and not ERα, signaling. Importantly, the in vivo therapeutic effects of E2 were lost in Treg-depleted mice (Foxp3^DTR mice). Adoptive transfer of ex vivo E2-treated Tregs rescued Streptococcuspneumoniae–induce PNA-ALI, a salutary effect that required Treg ERβ expression. E2/ERβ was required for Tregs to control macrophage proinflammatory responses. Our findings support the therapeutic role for E2 in promoting resolution of lung inflammation after PNA via ERβ Tregs.

Oxygen-mediated lung injury in mice lacking the gene for NRF2: Rescue with the cytochrome P4501A-inducer, beta-naphthoflavone (BNF), and differential sex-specific effects

BACKGROUND

Acute respiratory distress syndrome (ARDS) leads to progressive lung injury, which significantly impacts patient morbidity and mortality but may differ clinically between the sexes. Cytochrome P450 (CYP) 1A enzymes are protective against hyperoxic lung injury and may contribute to sex-dependent pathology. NRF2 is a critical transcriptional regulator of antioxidants and loss of NRF2 leads to severe hyperoxic lung injury and mortality in mice. NRF2 deficiencies and polymorphisms have been observed in patients with pulmonary diseases such as chronic obstructive pulmonary disease and severe asthma. No prior studies have evaluated whether there are sex-specific differences in oxygen-mediated lung injury in Nrf2^-/- mice and there are few rescue studies.

OBJECTIVE

To test the hypothesis that hyperoxia induces greater lung injury and inflammation in Nrf2^-/- mice compared to wild type (WT) that differs between sexes, and that this phenotype will be rescued by the administration of the cytochrome P450 (CYP) 1A inducer beta-naphthoflavone (BNF).

DESIGN/METHODS

Male and female 8-10-week-old WT or Nrf2^-/- C57BL/6 mice were pre-treated with BNF (40 mg/kg) or corn oil control and exposed to hyperoxia (95% O₂) for 68 h. Survival, pulmonary edema, neutrophil recruitment, and lung injury scores were evaluated. Gene expression of phase II detoxification enzymes, pulmonary cytokines, and Cyp1a1/2 was quantified. CYP1A1/2 protein expression and catalytic activities were also measured.

RESULTS

Hyperoxia exposure greatly reduced survival in Nrf2^-/- mice, particularly in females. BNF treatment improved survival by 182.8% in Nrf2^-/- females and by 41.4% in Nrf2^-/- males as well as in WT females by 85.7%. Females had greater pulmonary edema as measured by lung weight to body weight ratios but was attenuated in all groups except Nrf2^-/- females by BNF. Neutrophils doubled in Nrf2^-/- lungs compared to WT in hyperoxia but were decreased in BNF-treated females of both genotypes. Pulmonary cytokine gene expression including Il-6 and Tnf-α increased in hyperoxia especially in Nrf2^-/- mice and was unaffected by BNF. Pulmonary and hepatic Nqo1 gene expression w-as decreased in Nrf2^-/- mice and was largely unaffected by BNF; however pulmonary Ho-1 did not vary significantly between the genotypes and was decreased in WT animals treated with BNF. Activities and protein expression of pulmonary and hepatic CYP1A1/2 were induced via BNF across all groups. Although hepatic Cyp1a2 gene expression was higher in Nrf2^-/- males, the catalytic activity was higher in Nrf2^-/- females.

CONCLUSIONS

Hyperoxia augmented lung injury in Nrf2^-/- mice, and pre-treatment with BNF was protective against mortality and injury, eliminating the sex-dependent survival difference in both genotypes. Our results support the hypothesis that NRF2 protects mice against lung injury, and the fact that BNF rescues the lung injury phenotype in Nrf2^-/- mice suggests that augmented CYP1A expression by BNF may contribute to the beneficial effects. Further studies could lead to the development of BNF and other flavonoids for the prevention/treatment of hyperoxic lung injury, particularly in vulnerable patients with relative NRF2 deficiency, regardless of sex.

Preterm birth and neonatal acute kidney injury: implications on adolescent and adult outcomes

As a result of preterm birth, immature kidneys are exposed to interventions in the NICU that promote survival, but are nephrotoxic. Furthermore, the duration of renal development may be truncated in these vulnerable neonates. Immaturity and nephrotoxic exposures predispose preterm newborns to acute kidney injury (AKI), particularly in the low birth weight and extremely preterm gestational age groups. Several studies have associated preterm birth as a risk factor for future chronic kidney disease (CKD). However, only a few publications have investigated the impact of neonatal AKI on CKD development. Here, we will review the evidence linking preterm birth and AKI in the NICU to CKD and highlight the knowledge gaps and opportunities for future research. For neonatal intensive care studies, we propose the inclusion of AKI as an important short-term morbidity outcome and CKD findings such as a reduced glomerular filtration rate in the assessment of long-term outcomes.

Inhibition of CX3C receptor 1-mediated autophagy in macrophages alleviates pulmonary fibrosis in hyperoxic lung injury

AIMS

To investigate the role of CX3CR1 in hyperoxic lung injury induced pulmonary fibrosis.

MATERIALS AND METHODS

Hyperoxic lung injured mice were used as the disease model. Pulmonary fibrosis was determined by H&E and Masson's staining. Autophagy was investigated by western blot, immunofluorescence staining, and transmission electron microscopy.

KEY FINDINGS

We observed that increased CX3CR1 expression corresponded with increased pulmonary fibrosis. Additionally, silencing of CX3CR1 significantly alleviated the fibrosis when compared to the control. We observed that exposure of mouse to hyperoxic environment increased macrophage levels along with an increased CD11b expression in the lung tissues. Subsequently, we also observed an increased expression of LC3-II and decreased p62 expression in hyperoxic mice models, suggesting the potential role of hyperoxia induced autophagy. CD11b and LC3/CX3CR1 were expressed and co-localized in a manner indicating CX3CR1 indeed does regulate macrophage autophagy in the hyperoxic lung injury model. We observed a decrease in hyperoxia-associated fibrosis, along with a decrease in autophagy when we used 3-MA (autophagy inhibitor) in our hyperoxic lung injury model. To elucidate the pathway through which CX3CR1 regulated autophagy, we further analyzed the Akt1 pathway. Our experimental results indicated that the Akt1 inhibitor (A-674563) did significantly decrease macrophage autophagy and fibrosis in hyperoxic mice models.

SIGNIFICANCE

Thus, our data indicates a novel role of CX3CR1 in regulation of macrophage autophagy and promotion of pulmonary fibrosis in hyperoxic lung injured mice.

Molecular role of cytochrome P4501A enzymes inoxidative stress

Cytochrome P4501A (CYP1A) enzymes play important roles in xenobiotic and endobiotic metabolism. Due to uncoupling reactions during the enzymatic cycle, CYP1A enzymes can release reactive oxidative species (ROS) in the form of superoxide radical, hydrogen peroxide, hydroxyl radical etc. An imbalance between production of free radicals and the ability of antioxidants to detoxify the free radicals can lead to accumulation of ROS, which in turn can lead to oxidative stress. Oxidative stress can lead to inflammation and toxicity, which in turn can cause human diseases such as bronchopulmonary disease (BPD), ARDS, renal hypertension, etc. CYP1A enzymes, depending on the organ system, they either contribute or protect against oxidative injury. Thus, they have dual roles in regard to oxidative stress. This review presents an overview of the mechanistic relationship between CYP1A enzymes and oxidative stress in relation to various diseases in different organs (e.g., liver, lungs, heart, kidneys, and reproductive organs).

Mice Lacking the Cytochrome P450 1B1 Gene Are Less Susceptible to Hyperoxic Lung Injury Than Wild Type

Supplemental oxygen is a life-saving intervention administered to individuals suffering from respiratory distress, including adults with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Despite the clinical benefit, supplemental oxygen can create a hyperoxic environment that increases reactive oxygen species, oxidative stress, and lung injury. We have previously shown that cytochrome P450 (CYP)1A enzymes decrease susceptibility to hyperoxia-induced lung injury. In this investigation, we determined the role of CYP1B1 in hyperoxic lung injury in vivo. Eight- to ten-week old C57BL/6 wild type (WT) and Cyp1b1-/- mice were exposed to hyperoxia (>95% O2) for 24-72 h or maintained in room air (21% O2). Lung injury was assessed by histology and lung weight to body weight (LW/BW) ratios. Extent of inflammation was determined by assessing pulmonary neutrophil infiltration and cytokine levels. Lipid peroxidation markers were quantified by gas chromatography mass spectrometry, and oxidative DNA adducts were quantified by 32P-postlabeling as markers of oxidative stress. We found that Cyp1b1-/- mice displayed attenuation of lung weight and pulmonary edema, particularly after 48-72 h of hyperoxia compared with WT controls. Further, Cyp1b1-/- mice displayed decreased levels of pulmonary oxidative DNA adducts and pulmonary isofurans after 24 h of hyperoxia. Cyp1b1-/- mice also showed increased pulmonary CYP1A1 and 1A2 and mRNA expression. In summary, our results support the hypothesis that Cyp1b1-/- mice display decreased hyperoxic lung injury than wild type counterparts and that CYP1B1 may act as a pro-oxidant during hyperoxia exposure, contributing to increases in oxidative DNA damage and accumulation of lipid hydroperoxides.

Former-preterm lambs have persistent alveolar simplification at 2 and 5 months corrected postnatal age

Preterm birth and mechanical ventilation (MV) frequently lead to bronchopulmonary dysplasia, the histopathological hallmark of which is alveolar simplification. How developmental immaturity and ongoing injury, repair, and remodeling impact completion of alveolar formation later in life is not known, in part because of lack of suitable animal models. We report a new model, using former-preterm lambs, to test the hypothesis that they will have persistent alveolar simplification later in life. Moderately preterm lambs (~85% gestation) were supported by MV for ~6 days before being transitioned from all respiratory support to become former-preterm lambs. Results are compared with term control lambs that were not ventilated, and between males (M) and females (F). Alveolar simplification was quantified morphometrically and stereologically at 2 mo (4 M, 4 F) or 5 mo (4 M, 6 F) corrected postnatal age (cPNA) compared with unventilated, age-matched term control lambs (4 M, 4 F per control group). These postnatal ages in sheep are equivalent to human postnatal ages of 1-2 yr and ~6 yr, respectively. Multivariable linear regression results showed that former-preterm lambs at 2 or 5 mo cPNA had significantly thicker distal airspace walls ( P < 0.001 and P < 0.009, respectively), lower volume density of secondary septa ( P < 0.007 and P < 0.001, respectively), and lower radial alveolar count ( P < 0.003 and P < 0.020, respectively) compared with term control lambs. Sex-specific differences were not detected. We conclude that moderate preterm birth and MV for ~6 days impedes completion of alveolarization in former-preterm lambs. This new model provides the opportunity to identify underlying pathogenic mechanisms that may reveal treatment approaches.

Expression of mutant Sftpc in murine alveolar epithelia drives spontaneous lung fibrosis

Epithelial cell dysfunction is postulated as an important component in the pathogenesis of idiopathic pulmonary fibrosis (IPF). Mutations in the surfactant protein C (SP-C) gene (SFTPC), an alveolar type II (AT2) cell-restricted protein, have been found in sporadic and familial IPF. To causally link these events, we developed a knockin mouse model capable of regulated expression of an IPF-associated isoleucine-to-threonine substitution at codon 73 (I73T) in Sftpc (SP-CI73T). Tamoxifen-treated SP-CI73T cohorts developed rapid increases in SftpcI73T mRNA and misprocessed proSP-CI73T protein accompanied by increased early mortality (days 7-14). This acute phase was marked by diffuse parenchymal lung injury, tissue infiltration by monocytes, polycellular alveolitis, and elevations in bronchoalveolar lavage and AT2 mRNA content of select inflammatory cytokines. Resolution of alveolitis (2-4 weeks), commensurate with a rise in TGF-β1, was followed by aberrant remodeling marked by collagen deposition, AT2 cell hyperplasia, α-smooth muscle actin-positive (α-SMA-positive) cells, and restrictive lung physiology. The translational relevance of the model was supported by detection of multiple IPF biomarkers previously reported in human cohorts. These data provide proof of principle that mutant SP-C expression in vivo causes spontaneous lung fibrosis, strengthening the role of AT2 cell dysfunction as a key upstream driver of IPF pathogenesis.

Effect of neonatal hyperoxia followed by concentrated ambient ultrafine particle exposure on cumulative learning in C57Bl/6J mice

Hyperoxia during treatment for prematurity may enhance susceptibility to other risk factors for adverse brain development, such as air pollution exposure, as both of these risk factors have been linked to a variety of adverse neurodevelopmental outcomes. This study investigated the combined effects of neonatal hyperoxia followed by inhalation of concentrated ambient ultrafine particles (CAPS, <100 nm in aerodynamic diameter) on learning. C57BL/6 J mice were birthed into 60% oxygen until postnatal day (PND) 4 and subsequently exposed to filtered air or to CAPS using the Harvard University Concentrated Ambient Particle System (HUCAPS) from PND 4-7 and 10-13. Behavior was assessed on a fixed interval (FI) schedule of reinforcement in which reward is available only after a fixed interval of time elapses, as well as expected reductions in behavior during an extinction procedure when reward was withheld. Both produce highly comparable behavioral performance across species. Performance measures included rate of responding, response accuracy, and temporal control (quarter life). Exposure to hyperoxia or CAPS resulted in lower mean quarter life values, an effect that was further enhanced in males by combined exposure, findings consistent with delayed learning of the FI schedule. Females also initially exhibited greater reductions in quarter life values following the combined exposure to hyperoxia and CAPS and delayed reductions in response rates during extinction. Combined hyperoxia and CAPS produced greater learning deficits than either risk factor alone, consistent with enhanced neurodevelopmental toxicity, findings that could reflect a convergence of both insults on common neurobiological systems. The basis for sex differences in outcome warrants further research. This study highlights the potential for heightened risk of adverse neurodevelopment outcomes in individuals born preterm in regions with higher levels of ultrafine particle (UFP) air pollution, in accord with the multiplicity of risk factors extant in the human environment.

β-Naphthoflavone treatment attenuates neonatal hyperoxic lung injury in wild type and Cyp1a2-knockout mice

Exposure to supraphysiological concentrations of oxygen (hyperoxia) leads to bronchopulmonary dysplasia (BPD), one of the most common pulmonary morbidities in preterm neonates, which is more prevalent in males than females. Beta-naphthoflavone (BNF) is protective against hyperoxic lung injury in adult and neonatal wild type (WT) mice and in and mice lacking Cyp1a1gene. In this investigation, we tested the hypothesis that BNF treatment will attenuate neonatal hyperoxic lung injury in WT and Cyp1a2-/- mice, and elucidated the effect of sex-specific differences. Newborn WT or Cyp1a2-/- mice were treated with BNF (10mg/kg) or the vehicle corn oil (CO) i.p., from postnatal day (PND) 2 to 8 once every other day, while being maintained in room air or hyperoxia (85% O2) for 14days. Hyperoxia exposure lead to alveolar simplification and arrest in angiogenesis in WT as well as Cyp1a2-/- mice No significant differences were seen between WT and Cyp1a2-/- mice. Cyp1a2-/- female mice had better preservation of pulmonary angiogenesis at PND15 compared to similarly exposed males. BNF treatment attenuated lung injury and inflammation in both genotypes, and this was accompanied by a significant induction of hepatic and pulmonary CYP1A1 in WT but not in Cyp1a2-/- mice. BNF treatment increased NADPH quinone oxidoreductase (NQO1) mRNA levels in Cyp1a2-/- mouse livers compared to WT mice. These results suggest that BNF is protective in neonatal mice exposed to hyperoxia independent of CYP1A2 and this may entail the protective effect of phase II enzymes like NQO1.

Acute lung injury induced by intestinal ischemia and reperfusion is altered in obese female mice

RATIONAL

Acute lung injury (ALI) is a common complication after intestinal ischemia and reperfusion (I/R) injury that can lead to acute respiratory distress syndrome (ARDS). We have previously demonstrated that females are protected against lung damage induced by intestinal I/R through an estrogen mediated mechanism.

OBJECTIVES

To investigate the effect of obesity on ALI induced by intestinal I/R in female mice.

METHODS

C57Bl/6 female mice were fed with a standard low-fat diet (SD) or a high-fat diet (HFD) for 9 weeks. Intestinal I/R injury was induced by a 45 min occlusion of the mesenteric artery followed by 2 and 24 h of reperfusion.

RESULTS

Significant increase in lung myeloperoxidase expression (MPO) and neutrophil numbers of SD and HFD mice occurred at 2 h and 24 h of reperfusion. Furthermore, HFD mice presented a significant increase in lung eosinophil peroxidase (EPO) expression and eosinophil numbers compared to SD mice. Lung wet/dry weight ratio was significantly greater in HFD mice at 2 and 24 h of reperfusion, accompanied by a significant increase in the expression of inducible NO in the lung tissue and a significant decrease in arterial oxygen saturation at 24 h of reperfusion relative to SD mice.

CONCLUSION

Obesity predisposes female mice to increased pulmonary oedema and deterioration in gas exchange, which is accompanied by an increase in iNOS expression in the lung.

Role of Cytochrome P450 (CYP)1A in Hyperoxic Lung Injury: Analysis of the Transcriptome and Proteome

Hyperoxia contributes to lung injury in experimental animals and diseases such as acute respiratory distress syndrome in humans. Cytochrome P450 (CYP)1A enzymes are protective against hyperoxic lung injury (HLI). The molecular pathways and differences in gene expression that modulate these protective effects remain largely unknown. Our objective was to characterize genotype specific differences in the transcriptome and proteome of acute hyperoxic lung injury using the omics platforms: microarray and Reverse Phase Proteomic Array. Wild type (WT), Cyp1a1−/− and Cyp1a2−/− (8–10 wk, C57BL/6J background) mice were exposed to hyperoxia (FiO₂ > 0.95) for 48 hours. Comparison of transcriptome changes in hyperoxia-exposed animals (WT versus knock-out) identified 171 genes unique to Cyp1a1−/− and 119 unique to Cyp1a2−/− mice. Gene Set Enrichment Analysis revealed pathways including apoptosis, DNA repair and early estrogen response that were differentially regulated between WT, Cyp1a1−/− and Cyp1a2−/− mice. Candidate genes from these pathways were validated at the mRNA and protein level. Quantification of oxidative DNA adducts with ³²P-postlabeling also revealed genotype specific differences. These findings provide novel insights into mechanisms behind the differences in susceptibility of Cyp1a1−/− and Cyp1a2−/− mice to HLI and suggest novel pathways that need to be investigated as possible therapeutic targets for acute lung injury.

Age- and sex-related changes in rat renal function and pathology following neonatal hyperoxia exposure

Preterm neonates are prematurely exposed to high oxygen levels at birth which may adversely impact ongoing renal development. The aim of this study was to determine the effects of neonatal hyperoxia exposure on renal function and morphology with aging. Sprague Dawley rat pups were raised in a hyperoxic environment (80% oxygen) from P3 to P10 during ongoing postnatal nephrogenesis. Control litters were kept in room air (n = 6–8 litters/group; one male, one female/litter/age). Kidney function (urine and plasma creatinine, sodium, and protein) and morphology (renal corpuscle size, glomerulosclerosis, fibrosis, and glomerular crescents) were assessed at 1, 5, and 11 months of age. Neonatal hyperoxia exposure had no impact on body or kidney weights. Creatinine clearance was significantly reduced following hyperoxia exposure at 5 months; there was no significant effect on renal function at 1 or 11 months. The percentage of crescentic glomeruli (indicative of glomerular injury) was markedly increased in 11 month hyperoxia‐exposed males. Renal corpuscle size, glomerulosclerosis index, and renal fibrosis were not affected. Findings suggest that exposure to high oxygen levels during development may impact renal functional capacity and increase susceptibility to renal disease in adulthood depending on age and sex.

Should we still use vitamin A to prevent bronchopulmonary dysplasia?

Bronchopulmonary dysplasia (BPD) is associated with significant short- and long-term morbidity in preterm infants, and it can be prevented in some infants with vitamin A prophylaxis. Vitamin A, once widely used in neonatal intensive care, was scarce for the last few years, but has become available again at a much higher price, leading to dilemmas about its routine use. In this review we discuss experimental, clinical and socioeconomic evidence related to BPD, and provide a framework for clinicians and policy-makers to evaluate the value of vitamin A treatment and make decisions about its use for prevention of BPD.

Sex-specific differences in neonatal hyperoxic lung injury

Male sex is considered an independent predictor for the development of bronchopulmonary dysplasia (BPD) after adjusting for other confounders. BPD is characterized by an arrest in lung development with marked impairment of alveolar septation and vascular development. The reasons underlying sexually dimorphic outcomes in premature neonates are not known. In this investigation, we tested the hypothesis that male neonatal mice will be more susceptible to hyperoxic lung injury and will display larger arrest in lung alveolarization. Neonatal male and female mice (C57BL/6) were exposed to hyperoxia [95% FiO2, postnatal day (PND) 1-5] and euthanized on PND 7 and 21. Extent of alveolarization, pulmonary vascularization, inflammation, and modulation of the NF-κB pathway were determined and compared with room air controls. Macrophage and neutrophil infiltration was significantly increased in hyperoxia-exposed animals but was increased to a larger extent in males compared with females. Lung morphometry showed a higher mean linear intercept (MLI) and a lower radial alveolar count (RAC) and therefore greater arrest in lung development in male mice. This was accompanied by a significant decrease in the expression of markers of angiogenesis (PECAM1 and VEGFR2) in males after hyperoxia exposure compared with females. Interestingly, female mice showed increased activation of the NF-κB pathway in the lungs compared with males. These results support the hypothesis that sex plays a crucial role in hyperoxia-mediated lung injury in this model. Elucidation of the sex-specific molecular mechanisms may aid in the development of novel individualized therapies to prevent/treat BPD.

Mechanistic role of cytochrome P450 (CYP)1B1 in oxygen-mediated toxicity in pulmonary cells: A novel target for prevention of hyperoxic lung injury

Supplemental oxygen, which is routinely administered to preterm infants with pulmonary insufficiency, contributes to bronchopulmonary dysplasia (BPD) in these infants. Hyperoxia also contributes to the development of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) in adults. The mechanisms of oxygen-mediated pulmonary toxicity are not completely understood. Recent studies have suggested an important role for cytochrome P450 (CYP)1A1/1A2 in the protection against hyperoxic lung injury. The role of CYP1B1 in oxygen-mediated pulmonary toxicity has not been studied. In this investigation, we tested the hypothesis that CYP1B1 plays a mechanistic role in oxygen toxicity in pulmonary cells in vitro. In human bronchial epithelial cell line BEAS-2B, hyperoxic treatment for 1-3 days led to decreased cell viability by about 50-80%. Hyperoxic cytotoxicity was accompanied by an increase in levels of reactive oxygen species (ROS) by up to 110%, and an increase of TUNEL-positive cells by up to 4.8-fold. Western blot analysis showed hyperoxia to significantly down-regulate CYP1B1 protein level. Also, there was a decrease of CYP1B1 mRNA by up to 38% and Cyp1b1 promoter activity by up to 65%. On the other hand, CYP1B1 siRNA appeared to rescue the cell viability under hyperoxia stress, and overexpression of CYP1B1 significantly attenuated hyperoxic cytotoxicity after 48 h of incubation. In immortalized lung endothelial cells derived from Cyp1b1-null and wild-type mice, hyperoxia increased caspase 3/7 activities in a time-dependent manner, but endothelial cells lacking the Cyp1b1 gene showed significantly decreased caspase 3/7 activities after 48 and 72 h of incubation, implying that CYP1B1 might promote apoptosis in wild type lung endothelial cells under hyperoxic stress. In conclusion, our results support the hypothesis that CYP1B1 plays a mechanistic role in pulmonary oxygen toxicity, and CYP1B1-mediated apoptosis could be one of the mechanisms of oxygen toxicity. Thus, CYP1B1 could be a novel target for preventative and/or therapeutic interventions against BPD in infants and ALI/ARDS in adults.