Vitamin A and retinoic acid act synergistically to increase lung retinyl esters during normoxia and reduce hyperoxic lung injury in newborn mice

Advances in the pharmacological management of bronchopulmonary dysplasia: an update of the literature

INTRODUCTION

Bronchopulmonary dysplasia (BPD) is the commonest adverse outcome of extremely prematurely born infants, and its incidence is increasing. Affected infants suffer chronic respiratory morbidity and are at risk of early onset of chronic obstructive pulmonary disease. It is, therefore, important that these infants are appropriately managed, with efficacious pharmacological treatments.

AREAS COVERED

Searches were made on Embase, PubMed, and the Cochrane database for ('treatment' or 'drug therapy/') and ('bronchopulmonary dysplasia' or 'chronic lung disease') and ('neonatology' or 'newborn' or 'prematurity' or 'baby') between 2019 and 2024. Corticosteroids, diuretics, caffeine, anti-asthmatics, nutritional supplements, and medications treating patent ductus arteriosus and pulmonary hypertension are discussed.

EXPERT OPINION

Dexamethasone is associated with adverse neurodevelopmental outcomes and impairment of adult lung function. Inhaled corticosteroids have not resulted in significant effects on BPD. Diuretics only result in short-term improvements in lung function and have side-effects. Evidence suggests it is better to wait and see than aggressively treat PDA; inhaled nitric oxide and sildenafil can improve oxygenation, but whether they improve long-term outcomes remains to be tested. Stem cells are a promising therapy, but further research is required. Appropriately designed trials are required to identify efficacious treatments for infants with BPD.

Abnormal Fetal Lung of Hoxa1-/- Piglets Is Rescued by Maternal Feeding with All-Trans Retinoic Acid

Neonatal Hoxa1-/- piglets were characterized by dyspnea owing to the Hoxa1 mutation, and maternal administration with ATRA alleviated the dyspnea of neonatal Hoxa1-/- piglets. The purpose of this experiment was to explore how maternal ATRA administration rescued the abnormal fetal lungs of Hoxa1-/- piglets. Samples of the lungs were collected from neonatal Hoxa1-/- and non-Hoxa1-/- piglets delivered by sows in the control group, and from neonatal Hoxa1-/- piglets born by sows administered with ATRA at 4 mg/kg body weight on dpc 12, 13, or 14, respectively. These were used for the analysis of ELISA, histological morphology, immunofluorescence staining, immunohistochemistry staining, and quantitative real-time PCR. The results indicate that the Hoxa1 mutation had adverse impacts on the development of the alveoli and pulmonary microvessels of Hoxa1-/- piglets. Maternal administration with ATRA at 4 mg/kg body weight on dpc 14 rescued the abnormal lung development of Hoxa1-/- piglets by increasing the IFN-γ concentration (p < 0.05), airspace area (p < 0.01) and pulmonary microvessel density (p < 0.01); increasing the expression of VEGFD (p < 0.01), PDGFD (p < 0.01), KDR (p < 0.01), ID1 (p < 0.01), and NEDD4 (p < 0.01); and decreasing the septal wall thickness (p < 0.01) and the expression of SFTPC (p < 0.01) and FOXO3 (p < 0.01). Maternal administration with ATRA plays a vital role in rescuing the abnormal development of lung of Hoxa1-/- fetal piglets.

Mitochondrial DNA Variations Modulate Alveolar Epithelial Mitochondrial Function and Oxidative Stress in Newborn Mice Exposed to Hyperoxia

Oxidative stress is an important contributor to bronchopulmonary dysplasia (BPD), a form of chronic lung disease that is the most common morbidity in very preterm infants. Mitochondrial functional differences due to inherited and acquired mutations influence the pathogenesis of disorders in which oxidative stress plays a critical role. We previously showed using mitochondrial-nuclear exchange (MNX) mice that mitochondrial DNA (mtDNA) variations modulate hyperoxia-induced lung injury severity in a model of BPD. In this study, we studied the effects of mtDNA variations on mitochondrial function including mitophagy in alveolar epithelial cells (AT2) from MNX mice. We also investigated oxidant and inflammatory stress as well as transcriptomic profiles in lung tissue in mice and expression of proteins such as PINK1, Parkin and SIRT3 in infants with BPD. Our results indicate that AT2 from mice with C57 mtDNA had decreased mitochondrial bioenergetic function and inner membrane potential, increased mitochondrial membrane permeability and were exposed to higher levels of oxidant stress during hyperoxia compared to AT2 from mice with C3H mtDNA. Lungs from hyperoxia-exposed mice with C57 mtDNA also had higher levels of pro-inflammatory cytokines compared to lungs from mice with C3H mtDNA. We also noted changes in KEGG pathways related to inflammation, PPAR and glutamatergic signaling, and mitophagy in mice with certain mito-nuclear combinations but not others. Mitophagy was decreased by hyperoxia in all mice strains, but to a greater degree in AT2 and neonatal mice lung fibroblasts from hyperoxia-exposed mice with C57 mtDNA compared to C3H mtDNA. Finally, mtDNA haplogroups vary with ethnicity, and Black infants with BPD had lower levels of PINK1, Parkin and SIRT3 expression in HUVEC at birth and tracheal aspirates at 28 days of life when compared to White infants with BPD. These results indicate that predisposition to neonatal lung injury may be modulated by variations in mtDNA and mito-nuclear interactions need to be investigated to discover novel pathogenic mechanisms for BPD.

Thyroid hormone modulates hyperoxic neonatal lung injury and mitochondrial function

Mitochondrial dysfunction at birth predicts bronchopulmonary dysplasia (BPD) in extremely low-birth weight (ELBW) infants. Recently, nebulized thyroid hormone (TH), given as triiodothyronine (T3), was noted to decrease pulmonary fibrosis in adult animals through improved mitochondrial function. In this study, we tested the hypothesis that TH may have similar effects on hyperoxia-induced neonatal lung injury and mitochondrial dysfunction by testing whether i.n. T3 decreases neonatal hyperoxic lung injury in newborn mice; whether T3 improves mitochondrial function in lung homogenates, neonatal murine lung fibroblasts (NMLFs), and umbilical cord-derived mesenchymal stem cells (UC-MSCs) obtained from ELBW infants; and whether neonatal hypothyroxinemia is associated with BPD in ELBW infants. We found that inhaled T3 (given i.n.) attenuated hyperoxia-induced lung injury and mitochondrial dysfunction in newborn mice. T3 also reduced bioenergetic deficits in UC-MSCs obtained from both infants with no or mild BPD and those with moderate to severe BPD. T3 also increased the content of peroxisome proliferator-activated receptor γ coactivator 1α in lung homogenates of mice exposed to hyperoxia as well as mitochondrial potential in both NMLFs and UC-MSCs. ELBW infants who died or developed moderate to severe BPD had lower total T4 (TT4) compared with survivors with no or mild BPD. In conclusion, TH signaling and function may play a critical role in neonatal lung injury, and inhaled T3 supplementation may be useful as a therapeutic strategy for BPD.

Platelet Activating Factor Activity Modulates Hyperoxic Neonatal Lung Injury Severity

Hyperoxia-induced inflammation contributes significantly to developmental lung injury and bronchopulmonary dysplasia (BPD) in preterm infants. Platelet activating factor (PAF) is known to be a major driver of inflammation in lung diseases such as asthma and pulmonary fibrosis, but its role in BPD has not been previously investigated. Therefore, to determine whether PAF signaling independently modulates neonatal hyperoxic lung injury and BPD pathogenesis, lung structure was assessed in 14 day-old C57BL/6 wild-type (WT) and PAF receptor knockout (PTAFR KO) mice that were exposed to 21% (normoxia) or 85% O ₂ (hyperoxia) from postnatal day 4. Lung morphometry showed that PTAFR KO mice had attenuated hyperoxia-induced alveolar simplification when compared to WT mice. Functional analysis of gene expression data from hyperoxia-exposed vs. normoxia-exposed lungs of WT and PTAFR KO showed that the most upregulated pathways were the hypercytokinemia/hyperchemokinemia pathway in WT mice, NAD signaling pathway in PTAFR KO mice, and agranulocyte adhesion and diapedesis as well as other pro-fibrotic pathways such as tumor microenvironment and oncostatin-M signaling in both mice strains, indicating that PAF signaling may contribute to inflammation but may not be a significant mediator of fibrotic processes during hyperoxic neonatal lung injury. Gene expression analysis also indicated increased expression of pro-inflammatory genes such as CXCL1, CCL2 and IL-6 in the lungs of hyperoxia-exposed WT mice and metabolic regulators such as HMGCS2 and SIRT3 in the lungs of PTAFR KO mice, suggesting that PAF signaling may modulate BPD risk through changes in pulmonary inflammation and/or metabolic reprogramming in preterm infants.

Retinoids stored locally in the lung are required to attenuate the severity of acute lung injury in male mice

Retinoids are potent transcriptional regulators that act in regulating cell proliferation, differentiation, and other cellular processes. We carried out studies in male mice to establish the importance of local cellular retinoid stores within the lung alveolus for maintaining its health in the face of an acute inflammatory challenge induced by intranasal instillation of lipopolysaccharide. We also undertook single cell RNA sequencing and bioinformatic analyses to identify roles for different alveolar cell populations involved in mediating these retinoid-dependent responses. Here we show that local retinoid stores and uncompromised metabolism and signaling within the lung are required to lessen the severity of an acute inflammatory challenge. Unexpectedly, our data also establish that alveolar cells other than lipofibroblasts, specifically microvascular endothelial and alveolar epithelial cells, are able to take up lipoprotein-transported retinoid and to accumulate cellular retinoid stores that are directly used to respond to an acute inflammatory challenge.

Oxygen toxicity: cellular mechanisms in normobaric hyperoxia

In clinical settings, oxygen therapy is administered to preterm neonates and to adults with acute and chronic conditions such as COVID-19, pulmonary fibrosis, sepsis, cardiac arrest, carbon monoxide poisoning, and acute heart failure. In non-clinical settings, divers and astronauts may also receive supplemental oxygen. In addition, under current standard cell culture practices, cells are maintained in atmospheric oxygen, which is several times higher than what most cells experience in vivo. In all the above scenarios, the elevated oxygen levels (hyperoxia) can lead to increased production of reactive oxygen species from mitochondria, NADPH oxidases, and other sources. This can cause cell dysfunction or death. Acute hyperoxia injury impairs various cellular functions, manifesting ultimately as physiological deficits. Chronic hyperoxia, particularly in the neonate, can disrupt development, leading to permanent deficiencies. In this review, we discuss the cellular activities and pathways affected by hyperoxia, as well as strategies that have been developed to ameliorate injury.

Prolonged exposure to traffic-related particulate matter and gaseous pollutants implicate distinct molecular mechanisms of lung injury in rats

BACKGROUND

Exposure to air pollution exerts direct effects on respiratory organs; however, molecular alterations underlying air pollution-induced pulmonary injury remain unclear. In this study, we investigated the effect of air pollution on the lung tissues of Sprague-Dawley rats with whole-body exposure to traffic-related PM1 (particulate matter < 1 μm in aerodynamic diameter) pollutants and compared it with that in rats exposed to high-efficiency particulate air-filtered gaseous pollutants and clean air controls for 3 and 6 months. Lung function and histological examinations were performed along with quantitative proteomics analysis and functional validation.

RESULTS

Rats in the 6-month PM1-exposed group exhibited a significant decline in lung function, as determined by decreased FEF25-75% and FEV20/FVC; however, histological analysis revealed earlier lung damage, as evidenced by increased congestion and macrophage infiltration in 3-month PM1-exposed rat lungs. The lung tissue proteomics analysis identified 2673 proteins that highlighted the differential dysregulation of proteins involved in oxidative stress, cellular metabolism, calcium signalling, inflammatory responses, and actin dynamics under exposures to PM1 and gaseous pollutants. The presence of PM1 specifically enhanced oxidative stress and inflammatory reactions under subchronic exposure to traffic-related PM1 and suppressed glucose metabolism and actin cytoskeleton signalling. These factors might lead to repair failure and thus to lung function decline after chronic exposure to traffic-related PM1. A detailed pathogenic mechanism was proposed to depict temporal and dynamic molecular regulations associated with PM1- and gaseous pollutants-induced lung injury.

CONCLUSION

This study explored several potential molecular features associated with early lung damage in response to traffic-related air pollution, which might be used to screen individuals more susceptible to air pollution.

Metabolism of Neonatal Vitamin A Supplementation: A Systematic Review

A systematic review was conducted to summarize the absorption, transport, storage, and metabolism of oral neonatal vitamin A supplementation (NVAS). This review focused specifically on the neonatal period (first 28 d of life for humans) to inform guidance by WHO on recommendations related to NVAS. A systematic search of international and regional databases was conducted. Inclusion criteria were human or animal studies that gave oral vitamin A as a single or limited number of doses to apparently healthy neonates. Studies evaluating fortification or food-based approaches, dosing with retinoic acid, or studies of neonatal models of disease were excluded. The search retrieved 8847 unique records. After screening by title and abstract, 88 were screened using the full text, and 35 records met inclusion criteria: 13 human and 22 animal studies. Studies indicate that high-dose NVAS is absorbed well by neonates, typically mirroring fat absorption. Doses were primarily stored in the liver and transiently increased in the lung, kidney, spleen, adrenal glands, brain, skin, and adipose tissue, generally with a dose-response. Serum retinol and retinyl esters also transiently increased following NVAS. Although minimal acute adverse effects are noted, there is a lack of data supporting NVAS for improving organ maturation or sustained delivery to target organs. Research gaps include the physiological effects of the short-term increase of vitamin A concentrations in extrahepatic tissues, or whether there are unknown adverse effects over time.

Increased Excitability and Heightened Magnitude of Long-Term Potentiation at Hippocampal CA3-CA1 Synapses in a Mouse Model of Neonatal Hyperoxia Exposure

Preterm infants exposed to supraphysiological oxygen (hyperoxia) during the neonatal period have hippocampal atrophy and cognitive dysfunction later in childhood and as adolescents. Previously, we reported that 14-week-old adult mice exposed to hyperoxia as newborns had spatial memory deficits and hippocampal shrinkage, findings that mirror those of human adolescents who were born preterm. The area CA1 region of the hippocampus that is crucial for spatial learning and memory is highly vulnerable to oxidative stress. In this study, we investigated the long-term impact of neonatal hyperoxia exposure on hippocampal CA3-CA1 synaptic function. Male and female C57BL/6J mouse pups were continuously exposed to either 85% normobaric oxygen or air between postnatal days 2-14. Hippocampal slice electrophysiology at CA3-CA1 synapses was then performed at 14 weeks of age. We observed that hyperoxia exposed mice have heightened strength of basal synaptic transmission measured in input-output curves, increased fiber volley amplitude indicating increased axonal excitability, and heightened LTP magnitude at CA3-CA1 synapses, likely a consequence of increased postsynaptic depolarization during tetanus. These data demonstrate that supraphysiological oxygen exposure during the critical neonatal developmental period leads to pathologically heightened CA3-CA1 synaptic function during early adulthood which may contribute to hippocampal shrinkage and learning and memory deficits we previously reported. Furthermore, these results will help shed light on the consequences of hyperoxia exposure on the development of hippocampal synaptic circuit abnormalities that could be contributing to cognitive deficits in children born preterm.

Enteral Vitamin A for Reducing Severity of Bronchopulmonary Dysplasia: A Randomized Trial

BACKGROUND AND OBJECTIVES

Evidence suggests that intramuscular vitamin A reduces the risk of bronchopulmonary dysplasia (BPD) in preterm infants. Our objective was to compare enteral water-soluble vitamin A with placebo supplementation to reduce the severity of BPD in extremely preterm infants.

METHODS

We conducted a double-blind randomized controlled trial in infants <28 weeks' gestation who were to receive either enteral water-soluble vitamin A (5000 IU per day) or a placebo. Supplementation was started within 24 hours of introduction of feeds and continued until 34 weeks' postmenstrual age (PMA). The primary outcome was the severity of BPD, assessed by using the right shift of the pulse oximeter saturation versus the inspired oxygen pressure curve.

RESULTS

A total of 188 infants were randomly assigned. The mean ± SD birth weight (852 ± 201 vs 852 ± 211 g) and gestation (25.8 ± 1.49 vs 26.0 ± 1.39 weeks) were comparable between the vitamin A and placebo groups. There was no difference in the right shift (median [25th-75th percentiles]) of the pulse oximeter saturation versus inspired oxygen pressure curve (in kilopascals) between the vitamin A (11.1 [9.5-13.7]) and placebo groups (10.7 [9.5-13.1]) (P = .73). Enteral vitamin A did not affect diagnosis of BPD or other clinical outcomes. Plasma retinol levels were significantly higher in the vitamin A group versus the placebo group on day 28 and at 34 weeks' PMA.

CONCLUSIONS

Enteral water-soluble vitamin A supplementation improves plasma retinol levels in extremely preterm infants but does not reduce the severity of BPD.

Halogen exposure injury in the developing lung

Owing to a high-volume industrial usage of the halogens chlorine (Cl₂ ) and bromine (Br₂ ), they are stored and transported in abundance, creating a risk for accidental or malicious release to human populations. Despite extensive efforts to understand the mechanisms of toxicity upon halogen exposure and to develop specific treatments that could be used to treat exposed individuals or large populations, until recently, there has been little to no effort to determine whether there are specific features and or the mechanisms of halogen exposure injury in newborns or children. We established a model of neonatal halogen exposure and published our initial findings. In this review, we aim to contrast and compare the findings in neonatal mice exposed to Br₂ with the findings published on adult mice exposed to Br₂ and the neonatal murine models of bronchopulmonary dysplasia. Despite remarkable similarities across these models in overall alveolar architecture, there are distinct functional and apparent mechanistic differences that are characteristic of each model. Understanding the mechanistic and functional features that are characteristic of the injury process in neonatal mice exposed to halogens will allow us to develop countermeasures that are appropriate for, and effective in, this unique population.

Vitamin A supplement after neonatal Streptococcus pneumoniae pneumonia inhibits the progression of experimental asthma by altering CD4+T cell subsets

Studies demonstrated that pneumonia can decrease vitamin A productions and vitamin A reduction/deficiency may promote asthma development. Our previous study showed that neonatal Streptococcus pneumoniae (S. pneumoniae) infection promoted asthma development. Whether neonatal S. pneumoniae pneumonia induced asthma was associated with vitamin A levels remains unclear. The aim of this study was to investigate the effects of neonatal S. pneumoniae pneumonia on vitamin A expressions, to explore the effects of vitamin A supplement after neonatal S. pneumoniae pneumonia on adulthood asthma development. Non-lethal S. pneumoniae pneumonia was established by intranasal inoculation of neonatal (1-week-old) female BALB/c mice with D39. S. pneumoniae pneumonia mice were supplemented with or without all-trans retinoic acid 24 hours after infection. Vitamin A concentrations in lung, serum and liver were measured post pneumonia until early adulthood. Four weeks after pneumonia, mice were sensitized and challenged with OVA to induce allergic airway disease (AAD). Twenty-four hours after the final challenge, the lungs and bronchoalveolar lavage fluid (BALF) were collected to assess AAD. We stated that serum vitamin A levels in neonatal S. pneumoniae pneumonia mice were lower than 0.7µmol/L from day 2-7 post infection, while pulmonary vitamin A productions were significantly lower than those in the control mice from day 7-28 post infection. Vitamin A supplement after neonatal S. pneumoniae pneumonia significantly promoted Foxp3⁺Treg and Th1 productions, decreased Th2 and Th17 cells expressions, alleviated airway hyperresponsiveness (AHR) and inflammatory cells infiltration during AAD. Our data suggest that neonatal S. pneumoniae pneumonia induce serum vitamin A deficiency and long-time lung vitamin A reduction, vitamin A supplement after neonatal S. pneumoniae pneumonia inhibit the progression of asthma by altering CD4⁺T cell subsets.

Mitochondrial DNA variation modulates alveolar development in newborn mice exposed to hyperoxia

Hyperoxia-induced oxidant stress contributes to the pathogenesis of bronchopulmonary dysplasia (BPD) in preterm infants. Mitochondrial functional differences due to mitochondrial DNA (mtDNA) variations are important modifiers of oxidant stress responses. The objective of this study was to determine whether mtDNA variation independently modifies lung development and mechanical dysfunction in newborn mice exposed to hyperoxia. Newborn C57BL6 wild type (C57ⁿ/C57^mt, C57WT) and C3H/HeN wild type (C3Hⁿ/C3H^mt, C3HWT) mice and novel Mitochondrial-nuclear eXchange (MNX) strains with nuclear DNA (nDNA) from their parent strain and mtDNA from the other-C57MNX (C57ⁿ/C3H^mt) and C3HMNX (C3Hⁿ/C57^mt)-were exposed to 21% or 85% O₂ from birth to postnatal day 14 (P14). Lung mechanics and histopathology were examined on P15. Neonatal mouse lung fibroblast (NMLF) bioenergetics and mitochondrial superoxide (O₂^-) generation were measured. Pulmonary resistance and mitochondrial O₂^- generation were increased while alveolarization, compliance, and NMLF basal and maximal oxygen consumption rate were decreased in hyperoxia-exposed C57WT mice (C57ⁿ/C57^mt) versus C57MNX mice (C57ⁿ/C3H^mt) and in hyperoxia-exposed C3HMNX mice (C3Hⁿ/C57^mt) versus C3HWT (C3Hⁿ/C3H^mt) mice. Our study suggests that neonatal C57 mtDNA-carrying strains have increased hyperoxia-induced hypoalveolarization, pulmonary mechanical dysfunction, and mitochondrial bioenergetic and redox dysfunction versus C3H mtDNA strains. Therefore, mtDNA haplogroup variation-induced differences in mitochondrial function could modify neonatal alveolar development and BPD susceptibility.

Exposure of neonatal mice to bromine impairs their alveolar development and lung function

The halogen bromine (Br₂) is used extensively in industry and stored and transported in large quantities. Its accidental or malicious release into the atmosphere has resulted in significant casualties. The pathophysiology of Br₂-induced lung injury has been studied in adult animals, but the consequences of Br₂ exposure to the developing lung are completely unknown. We exposed neonatal mouse littermates on postnatal day 3 (P3) to either Br₂ at 400 ppm for 30 min (400/30), to Br₂ at 600 ppm for 30 min (600/30), or to room air, then returned them to their dams and observed until P14. Mice exposed to Br₂ had decreased survival (S) and had decreased weight (W) at P14 in the 400/30 group (S = 63.5%, W = 6.67 ± 0.08) and in the 600/30 group (S = 36.1%, W = 5.13 ± 0.67) as compared with air breathing mice (S = 100%, W = 7.96 ± 0.30). Alveolar development was impaired, as evidenced by increased mean linear intercept at P14. At P14, Br₂ exposed mice also exhibited a decrease of arterial partial pressure of oxygen, decreased quasi-static lung compliance, as well as increased alpha smooth muscle actin mRNA and protein and increased mRNA for IL-1β, IL-6, CXCL1, and TNFα. Global gene expression, evaluated by RNA sequencing and Ingenuity Pathway Analysis, revealed persistent abnormalities in gene expression profiles at P14 involving pathways of "formation of lung" and "pulmonary development." The data indicate that Br₂ inhalation injury early in life results in severe lung developmental consequences, wherein persistent inflammation and global altered developmental gene expression are likely mechanistic contributors.

Human mesenchymal stem cells attenuate pulmonary hypertension induced by prenatal lipopolysaccharide treatment in rats

Intra-amniotic injection of lipopolysaccharide (LPS) induces pulmonary hypertension in newborn rats. This study was designed to test whether human mesenchymal stem cells (MSCs) reduce pulmonary hypertension and alleviate cardiac hypertrophy in prenatal LPS-treated rats. Pregnant Sprague-Dawley rats were injected intraperitoneally with LPS (0.5 mg/kg per day) or untreated on gestational days 20 and 21. Human MSCs (3×10(5) cells and 1×10(6) cells) in 0.03 mL of normal saline (NS) were transplanted intratracheally on postnatal day 5. Four study groups were considered: normal, LPS+NS, LPS+MSCs (3×10(5) cells), and LPS+MSCs (1×10(6) cells). On postnatal day 14, lung and heart tissues were collected for measuring the arterial medial wall thickness (MWT) and β-myosin heavy chain (β-MHC) level as markers of pulmonary hypertension and cardiac hypertrophy, respectively. The LPS+NS group exhibited a significantly higher right ventricle (RV)/[left ventricle (LV)+ interventricular septum (IVS)] thickness ratio and MWT, a greater cardiomyocyte width, a greater number of cardiomyocyte nuclei per squared millimeter, and higher β-MHC expression than those observed in the normal group. Human MSC transplantation (3×10(5) cells and 1×10(6) cells) in LPS-treated rats reduced MWT and the RV/(LV+IVS) thickness ratio to normal levels. This improvement in right ventricular hypertrophy was accompanied by a decrease in toll-like receptor 4 (TLR4), nuclear factor-κB, and tumor necrosis factor-α expression in the heart. Intratracheal human MSCs transplantation can attenuate pulmonary hypertension and right ventricular hypertrophy in prenatal LPS-treated rats; this attenuation may be associated with suppression of TLR4 expression via paracrine pathways.

[Correction of the oxidant-antioxidant balance in lungs during hyperoxia by liposomal alpha-tocopherol and retinoids in the experiment]

The influence of inhaled liposomes, containing dipalmitoyl phosphatidylcholine and a-tocopherol, and liposomes containing dipalmitoyl phosphatidylcholine, retinol and retinoic acid, on parameters of the oxidantantioxidant system in lungs of newborn guinea pigs exposed to hyperoxia during 3 and 14 days has been studied. Administration of both types of liposomes under conditions of prolonged hyperoxia (14 days) results in normalization of glutathione peroxidase activity and prevents elevation of the levels of lipid and protein peroxidation products in bronchoalveolar lavage fluid. Unlike liposomes with a-tocopherol, administration of liposomes containing retinoids did not cause the normalizing effect on the content of nonprotein SH-compounds in the bronchoalveolar fluid and contributed to significant reduction of the a-tocopherol level in lung tissues.

Retinoid Homeostatic Gene Expression in Liver, Lung and Kidney: Ontogeny and Response to Vitamin A-Retinoic Acid (VARA) Supplementation from Birth to Adult Age

Vitamin A (VA, retinol) metabolism is homeostatically controlled, but little is known of its regulation in the postnatal period. Here, we determined the postnatal trajectory of VA storage and metabolism in major compartments of VA metabolism-plasma, liver, lung, and kidney from postnatal (P) day 1 to adulthood. We also investigated the response to supplementation with VARA, a combination of VA and 10% all-trans-retinoic acid that previously was shown to synergistically increase retinol uptake and storage in lung. Nursling pups of dams fed a VA-marginal diet received an oral dose of oil (placebo) or VARA on each of four neonatal days: P1, P4, P7, and P10; and again as adults. Tissues were collected 6 h after the final dosing on P1, P4, P10, and at adult age. Gene transcripts for Lrat and Rbp4 in liver and Raldh-1 and Raldh-3 in lung, did not differ in the neonatal period but were higher, P<0.05, in adults, while Cyp26B1, Stra6, megalin, and Raldh-2 in lung did not differ from perinatal to adult ages. VARA supplementation increased total retinol in plasma, liver and lung, with a dose-by-dose accumulation in neonatal liver and lung, while transcripts for Lrat in liver, megalin in kidney, Cyp26A1/B1 in liver and lung, respectively, and Stra6 in lung, were all increased, suggesting pathways of VA uptake, storage and RA oxidation were each augmented after VARA. VARA decreased hepatic expression of Rbp4, responsible for VA trafficking from liver to plasma, and, in lung, of Raldh-1 and Raldh-2, which function in RA production. Our results define retinoid homeostatic gene expression from neonatal and adult age and show that while supplementation with VARA acutely alters retinol content and retinoid homeostatic gene expression in neonatal and adult lung, liver and kidney, VARA supplementation of neonates increased adult-age VA content only in the liver.

Effect of Hyperoxia on Retinoid Metabolism and Retinoid Receptor Expression in the Lungs of Newborn Mice

BACKGROUND

Preterm newborns that receive oxygen therapy often develop bronchopulmonary dysplasia (BPD), which is abnormal lung development characterized by impaired alveologenesis. Oxygen-mediated injury is thought to disrupt normal lung growth and development. However, the mechanism of hyperoxia-induced BPD has not been extensively investigated. We established a neonatal mouse model to investigate the effects of normobaric hyperoxia on retinoid metabolism and retinoid receptor expression.

METHODS

Newborn mice were exposed to hyperoxic or normoxic conditions for 15 days. The concentration of retinol and retinyl palmitate in the lung was measured by HPLC to gauge retinoid metabolism. Retinoid receptor mRNA levels were assessed by real-time PCR. Proliferation and retinoid receptor expression in A549 cells were assessed in the presence and absence of exogenous vitamin A.

RESULTS

Hyperoxia significantly reduced the body and lung weight of neonatal mice. Hyperoxia also downregulated expression of RARα, RARγ, and RXRγ in the lungs of neonatal mice. In vitro, hyperoxia inhibited proliferation and expression of retinoid receptors in A549 cells.

CONCLUSION

Hyperoxia disrupted retinoid receptor expression in neonatal mice.

Vitamin A Transport Mechanism of the Multitransmembrane Cell-Surface Receptor STRA6

Vitamin A has biological functions as diverse as sensing light for vision, regulating stem cell differentiation, maintaining epithelial integrity, promoting immune competency, regulating learning and memory, and acting as a key developmental morphogen. Vitamin A derivatives have also been used in treating human diseases. If vitamin A is considered a drug that everyone needs to take to survive, evolution has come up with a natural drug delivery system that combines sustained release with precise and controlled delivery to the cells or tissues that depend on it. This "drug delivery system" is mediated by plasma retinol binding protein (RBP), the principle and specific vitamin A carrier protein in the blood, and STRA6, the cell-surface receptor for RBP that mediates cellular vitamin A uptake. The mechanism by which the RBP receptor absorbs vitamin A from the blood is distinct from other known cellular uptake mechanisms. This review summarizes recent progress in elucidating the fundamental molecular mechanism mediated by the RBP receptor and multiple newly discovered catalytic activities of this receptor, and compares this transport system with retinoid transport independent of RBP/STRA6. How to target this new type of transmembrane receptor using small molecules in treating diseases is also discussed.

Early exposure to hyperoxia or hypoxia adversely impacts cardiopulmonary development

Preterm infants are at high risk for long-term abnormalities in cardiopulmonary function. Our objectives were to determine the long-term effects of hypoxia or hyperoxia on cardiopulmonary development and function in an immature animal model. Newborn C57BL/6 mice were exposed to air, hypoxia (12% oxygen), or hyperoxia (85% oxygen) from Postnatal Day 2-14, and then returned to air for 10 weeks (n = 2 litters per condition; > 10/group). Echocardiography, blood pressure, lung function, and lung development were evaluated at 12-14 weeks of age. Lungs from hyperoxia- or hypoxia-exposed mice were larger and more compliant (compliance: air, 0.034 ± 0.001 ml/cm H2O; hypoxia, 0.049 ± 0.002 ml/cm H2O; hyperoxia, 0.053 ± 0.002 ml/cm H2O; P < 0.001 air versus others). Increased airway reactivity, reduced bronchial M2 receptor staining, and increased bronchial α-smooth muscle actin content were noted in hyperoxia-exposed mice (maximal total lung resistance with methacholine: air, 1.89 ± 0.17 cm H2O ⋅ s/ml; hypoxia, 1.52 ± 0.34 cm H2O ⋅ s/ml; hyperoxia, 4.19 ± 0.77 cm H2O ⋅ s/ml; P < 0.004 air versus hyperoxia). Hyperoxia- or hypoxia-exposed mice had larger and fewer alveoli (mean linear intercept: air, 40.2 ± 0. 0.8 μm; hypoxia, 76.4 ± 2.4 μm; hyperoxia, 95.6 ± 4.6 μm; P < 0.001 air versus others; radial alveolar count [n]: air, 11.1 ± 0.4; hypoxia, 5.7 ± 0.3; hyperoxia, 5.6 ± 0.3; P < 0.001 air versus others). Hyperoxia-exposed adult mice had left ventricular dysfunction without systemic hypertension. In conclusion, exposure of newborn mice to hyperoxia or hypoxia leads to cardiopulmonary abnormalities in adult life, similar to that described in ex-preterm infants. This animal model may help to identify underlying mechanisms and to develop therapeutic strategies for pulmonary morbidity in former preterm infants.

Paradoxical effects of all-trans-retinoic acid on lupus-like disease in the MRL/lpr mouse model

Roles of all-trans-retinoic acid (tRA), a metabolite of vitamin A (VA), in both tolerogenic and immunogenic responses are documented. However, how tRA affects the development of systemic autoimmunity is poorly understood. Here we demonstrate that tRA have paradoxical effects on the development of autoimmune lupus in the MRL/lpr mouse model. We administered, orally, tRA or VA mixed with 10% of tRA (referred to as VARA) to female mice starting from 6 weeks of age. At this age, the mice do not exhibit overt clinical signs of lupus. However, the immunogenic environment preceding disease onset has been established as evidenced by an increase of total IgM/IgG in the plasma and expansion of lymphocytes and dendritic cells in secondary lymphoid organs. After 8 weeks of tRA, but not VARA treatment, significantly higher pathological scores in the skin, brain and lung were observed. These were accompanied by a marked increase in B-cell responses that included autoantibody production and enhanced expression of plasma cell-promoting cytokines. Paradoxically, the number of lymphocytes in the mesenteric lymph node decreased with tRA that led to significantly reduced lymphadenopathy. In addition, tRA differentially affected renal pathology, increasing leukocyte infiltration of renal tubulointerstitium while restoring the size of glomeruli in the kidney cortex. In contrast, minimal induction of inflammation with tRA in the absence of an immunogenic environment in the control mice was observed. Altogether, our results suggest that under a predisposed immunogenic environment in autoimmune lupus, tRA may decrease inflammation in some organs while generating more severe disease in others.

Raman microimaging of murine lungs: insight into the vitamin A content

The composition of mice lung tissue was investigated using Raman confocal microscopy at 532 nm excitation wavelength supported with different experimental staining techniques as well as DFT calculations.

Retinoic acid promotes primary fetal alveolar epithelial type II cell proliferation and differentiation to alveolar epithelial type I cells

Retinoic acid (RA) plays an important role in lung development and maturation. Many stimuli can induce alveolar epithelial cell damage which will result in the injury of lung parenchyma. The aim of this study was to observe the effect of RA on the proliferation and differentiation of primary fetal alveolar epithelial type II cells (fAECIIs). Primary fAECIIs were isolated from fetal rats at 19 d of gestation and purified by a differential centrifugation and adhesion method. The cells were randomly divided into control (dimethyl sulfoxide, DMSO) and RA groups. Cell proliferation, viability, apoptosis, cycle, and expression of target protein were examined at 24, 48, and 72 h. We found that the proliferation and viability of cells in the RA-exposed group significantly increased compared with the DMSO control group. The proportion (%) of cells in the G2 and S phases in the RA group was significantly higher than that in control group cells. The proportion (%) of both early apoptotic cells and late apoptotic cells decreased significantly in cells exposed to RA compared with cells exposed to DMSO. RA significantly enhanced the expression of aquaporin 5 (AQP5). The expression level of pulmonary surfactant C (SPC) was elevated after cells were exposed to RA for 24 and 72 h but was inhibited when cells were exposed to RA for 48 h. These results suggest that RA promotes fAECII proliferation by improving cell viability, promoting S phase entry and inhibiting apoptosis and RA promotes fAECIIs differentiation to alveolar epithelial type I cells (AECIs).

In search of the elusive lipofibroblast in human lungs

Although the pulmonary interstitial lipofibroblast (LF) has been widely recognized in rat and mouse lungs, their presence in human lungs remains controversial. In a recent issue of the Journal, Tahedl and associates (Tahedl D, Wirkes A, Tschanz SA, Ochs M, Mühlfeld C. Am J Physiol Lung Cell Mol Physiol 307: L386-L394, 2014) address this controversy and provide the most detailed stereological analysis of LFs in mammals other than rodents. Strikingly, their observations demonstrate that LFs were only observed in rodents, which contrasts with earlier reports. This editorial reviews the anatomical, physiological, and biochemical characteristics of the LF to better understand the significance of LFs for lung development and disease. Although lipid droplets are a signature of the LF cell type, it remains unclear whether lipid storage is the defining characteristic of LFs, or whether other less overt properties determine the importance of LFs. Are lipid droplets an adaptation to the neonatal environment, or are LFs a surrogate for other properties that promote alveolar development, and do lipid droplets modify physiology or disease in adults?

Retinoic acid induced repair in the lung of adult hyperoxic mice, reducing transforming growth factor-β1 (TGF-β1) mediated abnormal alterations

The aim of the study was to determine the effects of retinoic acid on lung alveolar repair in adult hyperoxic mice and to investigate the relationship between TGF-β1 and retinoic acid during the repair processes. Adult mice were divided into 4 groups. Two groups were given daily intraperitoneal injections of peanut oil/dimethylsulfoxide mixture and retinoic acid (50mg/kg body weight, 50 μl of volume) dissolved in peanut oil/dimethylsulfoxide mixture for 12 days with a 2-day break on days 6 and 7. Following hyperoxia (100% oxygen) for 72 h the remaining two groups were treated in the same manner as already described: peanut oil/dimethylsulfoxide mixture and retinoic acid. Lung structure was investigated by light microscopy. TGF-β1 and Smad protein expressions in the lung were assayed by biochemical methods. Hyperoxic mice exhibited damage to the alveolar walls, increased cell proliferation and induced Smad3/TGF-β1 signaling. Smad2 and phospho-Smad2 protein expressions were unchanged in all groups. Retinoic acid administration improved the degenerative alterations caused by hyperoxia and helped in alveolar repair. This positive effect of retinoic acid resulted from the inhibition of Smad3/TGF-β1 signaling via reduced Smad4 mRNA and increased Smad7 protein expression. Retinoic acid also induced alveolarization and restricted Smad3/TGF-β1 signaling by decreasing Smad4 mRNA in healthy mice. Thus, retinoic acid helped repair Smad3/TGF-β1-induced lung damage in hyperoxic mice.

Retinol kinetics in unsupplemented and vitamin A-retinoic acid supplemented neonatal rats: a preliminary model

Vitamin A (VA) metabolism in neonates is virtually uncharacterized. Our objective was to develop a compartmental model of VA metabolism in unsupplemented and VA-supplemented neonatal rats. On postnatal day 4, pups (n = 3/time) received 11,12-[(3)H]retinol orally, in either oil (control) or VA combined with retinoic acid (VARA) [VA (∼6 mg/kg body weight) + 10% retinoic acid]. Plasma and tissues were collected at 14 time points up to 14 days after dose administration. VARA supplementation rapidly, but transiently, increased total retinol mass in plasma, liver, and lung. It decreased the peak fraction of the dose in plasma. A multi-compartmental model developed to fit plasma [(3)H]retinol data predicted more extensive recycling of retinol between plasma and tissues in neonates compared with that reported in adults (144 vs. 12-13 times). In VARA pups, the recycling number for retinol between plasma and tissues (100 times) and the time that retinol spent in plasma were both lower compared with controls; VARA also stimulated the uptake of plasma VA into extravascular tissues. A VARA perturbation model indicated that the effect of VARA in stimulating VA uptake into tissues in neonates is both dramatic and transient.

Combined effects of maternal inflammation and neonatal hyperoxia on lung fibrosis and RAGE expression in newborn rats

BACKGROUND

Receptors for advanced glycation end products (RAGE) have been implicated in fibrotic processes. We hypothesized that lung fibrosis induced by maternal lipopolysaccharide (LPS)-mediated inflammation and neonatal hyperoxia involves RAGE in newborn rats.

METHODS

Pregnant Sprague-Dawley rats received intraperitoneal injections of LPS or normal saline (NS) on 20 and 21 d of gestation. The pups were reared in room air (RA) or an O2-enrich atmosphere (O2), creating the four study groups, NS + RA, NS + O2, LPS + RA, and LPS + O2. The O2 treatment was >95% O2 for 7 d, followed by 60% O2 for 14 d.

RESULTS

Rat pups born to LPS-injected dams exhibited significantly higher lung interferon-γ and interleukin-1β (IL-1β) on postnatal day 7 than the pups born to NS-injected dams. Rat pups reared in hyperoxia expressed higher lung IL-10 on postnatal day 7, compared with the RA-reared pups. The LPS + O2 group had significantly higher total collagen and transforming growth factor-β1 on postnatal days 7 and 21 than the NS+RA group. RAGE mRNA and sRAGE protein expression were significantly lower in the LPS + O2 group on postnatal day 7 than the NS+RA group.

CONCLUSION

RAGE may be involved in the pathogenesis of lung fibrosis induced by maternal systemic inflammation and postnatal hyperoxia in rat neonates.

Acidic retinoids in small amounts promote retinyl ester formation in neonatal lung, with transient increases in retinoid homeostatic gene expression

BACKGROUND

Mixing a small proportion, 10%, of retinoic acid (RA) into an oral dose of vitamin A (VA) has been shown to markedly increase retinol uptake and retinyl ester (RE) formation in the neonatal lung, as compared to VA given alone. Concomitantly, several retinoid homeostatic genes, lecithin:retinol acyltransferase (LRAT), RA-4-hydroxylase (CYP26B1), and stimulated by retinoic acid gene-6 (STRA6) were upregulated. However, whether multiple doses may act accumulatively and whether less than 10% RA can be used has not been determined.

METHODS

Neonatal rats were treated once on postnatal day (PD) 4 or PD14 with VA alone or VA combined with 10% RA (VARA10%) or a stable analog, Am580 (VAAm10%), or they were treated with multiple doses on PD4, 7, 11, and 14.

RESULTS

RE increased cumulatively with multiple dosing. However, LRAT, CYP26B1 and STRA6 mRNA levels were similar for single and multiple treatments, indicating a transient noncumulative impact on gene expression. Lung RE was elevated with as little as 0.5% RA (P < 0.05) in a single dosing study. Whereas all concentrations of VARA elevated lung RE in single dosing studies, only 10% RA increased lung RE after multiple dosing, suggesting an attenuation of RA action with repeated dosing. In contrast, VAAm10%, 2%, and 1% all significantly increased lung RE after multiple doses (P < 0.05), while also increasing the expression of LRAT and CYP26B1.

CONCLUSIONS

These results indicate that the neonatal lung is very sensitive to acidic retinoid exposure and suggest that a VA combined with a very small fraction of acidic retinoid could be effective in increasing the lung's storage pool of VA.

Differential and isomer-specific modulation of vitamin A transport and the catalytic activities of the RBP receptor by retinoids

Retinoids are vitamin A derivatives with diverse biological functions. Both natural and artificial retinoids have been used as therapeutic reagents to treat human diseases, but not all retinoid actions are understood mechanistically. Plasma retinol binding protein (RBP) is the principal and specific carrier of vitamin A in the blood. STRA6 is the membrane receptor for RBP that mediates cellular vitamin A uptake. The effects of retinoids or related compounds on the receptor's vitamin A uptake activity and its catalytic activities are not well understood. In this study, we dissected the membrane receptor-mediated vitamin A uptake mechanism using various retinoids. We show that a subset of retinoids strongly stimulates STRA6-mediated vitamin A release from holo-RBP. STRA6 also catalyzes the exchange of retinol in RBP with certain retinoids. The effect of retinoids on STRA6 is highly isomer-specific. This study provides unique insights into the RBP receptor's mechanism and reveals that the vitamin A transport machinery can be a target of retinoid-based drugs.

Inflammation induced by lipopolysaccharide does not prevent the vitamin A and retinoic acid-induced increase in retinyl ester formation in neonatal rat lungs

Vitamin A (VA) plays an important role in post-natal lung development and maturation. Previously, we have reported that a supplemental dose of VA combined with 10% of all-trans-retinoic acid (VARA) synergistically increases retinol uptake and retinyl ester (RE) storage in neonatal rat lung, while up-regulating several retinoid homeostatic genes including lecithin:retinol acyltransferase (LRAT) and the retinol-binding protein receptor, stimulated by retinoic acid 6 (STRA6). However, whether inflammation has an impact on the expression of these genes and thus compromises the ability of VARA to increase lung RE content is not clear. Neonatal rats, 7- to 8-d-old, were treated with VARA either concurrently with lipopolysaccharide (LPS; Expt 1) or 12 h after LPS administration (Expt 2); in both studies, lung tissue was collected 6 h after VARA treatment, when RE formation is maximal. Inflammation was confirmed by increased IL-6 and chemokine (C–C motif) ligand 2 (CCL2) gene expression in lung at 6 h and C-reactive protein in plasma at 18 h. In both studies, LPS-induced inflammation only slightly reduced, but did not prevent the VARA-induced increase in lung RE. Quantitative RT-PCR showed that co-administration of LPS with VARA slightly attenuated the VARA-induced increase of LRAT mRNA, but not of STRA6 or cytochrome P450 26B1, the predominant RA hydroxylase in lung. By 18 h post-LPS, expression had subsided and none of these genes differed from the level in the control group. Overall, the present results suggest that retinoid homeostatic gene expression is reduced modestly, if at all, by acute LPS-induced inflammation and that VARA is still effective in increasing lung RE under conditions of moderate inflammation.

A critical regulatory role for macrophage migration inhibitory factor in hyperoxia-induced injury in the developing murine lung

BACKGROUND

The role and mechanism of action of MIF in hyperoxia-induced acute lung injury (HALI) in the newborn lung are not known. We hypothesized that MIF is a critical regulatory molecule in HALI in the developing lung.

METHODOLOGY

We studied newborn wild type (WT), MIF knockout (MIFKO), and MIF lung transgenic (MIFTG) mice in room air and hyperoxia exposure for 7 postnatal (PN) days. Lung morphometry was performed and mRNA and protein expression of vascular mediators were analyzed.

RESULTS

MIF mRNA and protein expression were significantly increased in WT lungs at PN7 of hyperoxia exposure. The pattern of expression of Angiopoietin 2 protein (in MIFKO>WT>MIFTG) was similar to the mortality pattern (MIFKO>WT>MIFTG) in hyperoxia at PN7. In room air, MIFKO and MIFTG had modest but significant increases in chord length, compared to WT. This was associated with decreased expression of Angiopoietin 1 and Tie 2 proteins in the MIFKO and MIFTG, as compared to the WT control lungs in room air. However, on hyperoxia exposure, while the chord length was increased from their respective room air controls, there were no differences between the 3 genotypes.

CONCLUSION

These data point to the potential roles of Angiopoietins 1, 2 and their receptor Tie2 in the MIF-regulated response in room air and upon hyperoxia exposure in the neonatal lung.

VARA attenuates hyperoxia-induced impaired alveolar development and lung function in newborn mice

We have recently shown that a combination of vitamin A (VA) and retinoic acid (RA) in a 10:1 molar ratio (VARA) synergistically increases lung retinoid content in newborn rodents, more than either VA or RA alone in equimolar amounts. We hypothesized that the increase in lung retinoids would reduce oxidative stress and proinflammatory cytokines, resulting in attenuation of alveolar simplification and abnormal lung function in hyperoxia-exposed newborn mice. Newborn C57BL/6 mice were exposed to 85% O₂ (hyperoxia) or air (normoxia) for 7 or 14 days from birth and given vehicle or VARA every other day. Lung retinol content was measured by HPLC, function was assessed by flexiVent, and development was evaluated by radial alveolar counts, mean linear intercept, and secondary septal crest density. Mediators of oxidative stress, inflammation, and alveolar development were evaluated in lung homogenates. We observed that VARA increased lung retinol stores and attenuated hyperoxia-induced alveolar simplification while increasing lung compliance and lowering resistance. VARA attenuated hyperoxia-induced increases in DNA damage and protein oxidation accompanied with a reduction in nuclear factor (erythroid-derived 2)-like 2 protein but did not alter malondialdehyde adducts, nitrotyrosine, or myeloperoxidase concentrations. Interferon-γ and macrophage inflammatory protein-2α mRNA and protein increased with hyperoxia, and this increase was attenuated by VARA. Our study suggests that the VARA combination may be a potential therapeutic strategy in conditions characterized by VA deficiency and hyperoxia-induced lung injury during lung development, such as bronchopulmonary dysplasia in preterm infants.

Neurodevelopmental impairment following neonatal hyperoxia in the mouse

Extremely premature infants are often exposed to supra-physiologic concentrations of oxygen, and frequently have hypoxemic episodes. These preterm infants are at high risk (~40%) for neurodevelopmental impairment (NDI) even in the absence of obvious intracranial pathology such as intraventricular hemorrhage or periventricular leukomalacia. The etiology for NDI has not been determined, and there are no animal models to simulate neurodevelopmental outcomes of prematurity. Our objectives were to develop and characterize a mouse model to determine long-term effects of chronic hypoxia or hyperoxia exposure on neurodevelopment. Newborn C57BL/6 mice were exposed to hypoxia (12% O(2)) or hyperoxia (85% O(2)) from postnatal days 1 to 14 and then returned to air. At 12-14 weeks of age, neurobehavioral assessment (Water Maze test, Novel Object Recognition test, Open Field test, Elevated Plus Maze, and Rotarod test) was performed, followed by MRI and brain histology. Neurobehavioral testing revealed that hyperoxia-exposed mice did poorly on the water maze and novel object recognition tests compared to air-exposed mice. MRI demonstrated smaller hippocampi in hyperoxia- and hypoxia-exposed mice with a greater reduction in hyperoxia-exposed mice, including a smaller cerebellum in hyperoxia-exposed mice. Brain histology showed reduced CA1 and CA3 and increased dentate gyral width in hippocampus. In conclusion, neonatal hyperoxia in mice leads to abnormal neurobehavior, primarily deficits in spatial and recognition memory, associated with smaller hippocampal sizes, similar to findings in ex-preterm infants. This animal model may be useful to determine mechanisms underlying developmental programming of NDI in preterm infants, and for evaluation of therapeutic strategies.

Lung injury in preterm neonates: the role and therapeutic potential of stem cells

Continuous improvements in perinatal care have allowed the survival of ever more premature infants, making the task of protecting the extremely immature lung from injury increasingly challenging. Premature infants at risk of developing chronic lung disease or bronchopulmonary dysplasia (BPD) are now born at the late canalicular stage of lung development, just when the airways become juxtaposed to the lung vasculature and when gas-exchange becomes possible. Readily available strategies, including improved antenatal management (education, regionalization, steroids, and antibiotics), together with exogenous surfactant and exclusive/early noninvasive ventilatory support, will likely decrease the incidence/severity of BPD over the next few years. Nonetheless, because of the extreme immaturity of the developing lung, the extent to which disruption of lung growth after prematurity and neonatal management lead to an earlier or more aggravated decline in respiratory function in later life is a matter of concern. Consequently, much more needs to be learned about the mechanisms of lung development, injury, and repair. Recent insight into stem cell biology has sparked interest for stem cells to repair damaged organs. This review summarizes the exciting potential of stem cell-based therapies for lung diseases in general and BPD in particular.

Prenatal inflammation exacerbates hyperoxia-induced functional and structural changes in adult mice

Maternally derived inflammatory mediators, such as IL-6 and IL-8, contribute to preterm delivery, low birth weight, and respiratory insufficiency, which are routinely treated with oxygen. Premature infants are at risk for developing adult-onset cardiac, metabolic, and pulmonary diseases. Long-term pulmonary consequences of perinatal inflammation are unclear. We tested the hypothesis that a hostile perinatal environment induces profibrotic pathways resulting in pulmonary fibrosis, including persistently altered lung structure and function. Pregnant C3H/HeN mice injected with LPS or saline on embryonic day 16. Offspring were placed in room air (RA) or 85% O(2) for 14 days and then returned to RA. Pulmonary function tests, microCTs, molecular and histological analyses were performed between embryonic day 18 and 8 wk. Alveolarization was most compromised in LPS/O(2)-exposed offspring. Collagen staining and protein levels were increased, and static compliance was decreased only in LPS/O(2)-exposed mice. Three-dimensional microCT reconstruction and quantification revealed increased tissue densities only in LPS/O(2) mice. Diffuse interstitial fibrosis was associated with decreased micro-RNA-29, increased transforming growth factor-β expression, and phosphorylation of Smad2 during embryonic or early fetal lung development. Systemic maternal LPS administration in combination with neonatal hyperoxic exposure induces activation of profibrotic pathways, impaired alveolarization, and diminished lung function that are associated with prenatal and postnatal suppression of miR-29 expression.

In vitro studies on the effect of particle size on macrophage responses to nanodiamond wear debris

Nanostructured diamond coatings improve the smoothness and wear characteristics of the metallic component of total hip replacements and increase the longevity of these implants, but the effect of nanodiamond wear debris on macrophages needs to be determined to estimate the long-term inflammatory effects of wear debris. The objective was to investigate the effect of the size of synthetic nanodiamond particles on macrophage proliferation (BrdU incorporation), apoptosis (Annexin-V flow cytometry), metabolic activity (WST-1 assay) and inflammatory cytokine production (qPCR). RAW 264.7 macrophages were exposed to varying sizes (6, 60, 100, 250 and 500 nm) and concentrations (0, 10, 50, 100 and 200 μg ml(-1)) of synthetic nanodiamonds. We observed that cell proliferation but not metabolic activity was decreased with nanoparticle sizes of 6-100 nm at lower concentrations (50 μg ml(-1)), and both cell proliferation and metabolic activity were significantly reduced with nanodiamond concentrations of 200 μg ml(-1). Flow cytometry indicated a significant reduction in cell viability due to necrosis irrespective of particle size. Nanodiamond exposure significantly reduced gene expression of tumor necrosis factor-α, interleukin-1β, chemokine Ccl2 and platelet-derived growth factor compared to serum-only controls or titanium oxide (anatase 8 nm) nanoparticles, with variable effects on chemokine Cxcl2 and vascular endothelial growth factor. In general, our study demonstrates a size and concentration dependence of macrophage responses in vitro to nanodiamond particles as possible wear debris from diamond-coated orthopedic joint implants.