Altered urinary excretion of elastin cross-links in premature infants who develop bronchopulmonary dysplasia

Urine Desmosine as a Novel Biomarker for Bronchopulmonary Dysplasia and Postprematurity Respiratory Disease in Extremely Preterm or Low Birth Weight Infants

OBJECTIVE

 This study aimed to evaluate whether elevated urine desmosine levels at 3 weeks of age were associated with severe radiological findings, bronchopulmonary dysplasia (BPD), and post-prematurity respiratory disease (PRD) in extremely preterm (EP) or extremely low birth weight (ELBW) infants.

STUDY DESIGN

 This study recruited 37 EP (22-27 completed weeks) or ELBW (<1,000 g) infants. Urine was collected between 21 and 28 postnatal days, and desmosine was measured using an enzyme-linked immunosorbent assay kit; the urine creatinine level was also measured. Bubbly/cystic lungs were characterized by emphysematous chest X-rays on postnatal day 28. Furthermore, provision of supplemental oxygen or positive-pressure respiratory support at 40 weeks' postmenstrual age defined BPD, and increased medical utilization at 18 months of corrected age defined PRD. The desmosine/creatinine threshold was determined by receiver operating characteristic analysis. The adjusted risk and 95% confidence interval (CI) for elevated urine desmosine/creatinine levels were estimated by logistic regression analysis.

RESULTS

 Elevated urine desmosine/creatinine levels higher than the threshold were significantly associated with bubbly/cystic lungs (8/13 [61.5%] vs. 2/24 [8.3%], p = 0.001), BPD (10/13 [76.9%] vs. 8/24 [33.3%], p = 0.02), and PRD (6/13 [46.2%] vs. 2/24 [8.3%], p = 0.01). After adjusting for gestational age, birth weight, and sex, the urine desmosine/creatinine levels were significantly higher in those who were highly at risk of bubbly/cystic lungs (odds ratio [OR], 13.2; 95% CI, 1.67-105) and PRD (OR, 13.8; 95% CI, 1.31-144).

CONCLUSION

 Elevated urine desmosine/creatinine levels on the third postnatal week were associated with bubbly/cystic lungs on day 28 and PRD at 18 months of corrected age in EP or ELBW infants.

KEY POINTS

· Urine desmosine was prospectively measured in 3-week-old EP/ELBW infants.. · Elevated urine desmosine levels were associated with emphysematous radiological findings on day 28, PRD at 18 months of corrected age.. · Urine desmosine may be a promising biomarker indicating lung damage in EP/ELBW infants..

Deficiency of Integrin β4 Results in Increased Lung Tissue Stiffness and Responds to Substrate Stiffness via Modulating RhoA Activity

The interaction between extracellular matrix (ECM) and epithelial cells plays a key role in lung development. Our studies found that mice with conditional integrin β4 (ITGB4) knockout presented lung dysplasia and increased stiffness of lung tissues. In accordance with our previous studies regarding the functions of ITGB4 in bronchial epithelial cells (BECs), we hypothesize that the decreased ITGB4 expression during embryonic stage leads to abnormal ECM remodeling and increased tissue stiffness, thus impairing BECs motility and compromising lung development. In this study, we examined lung tissue stiffness in normal and ITGB4 deficiency mice using Atomic Force Microscopy (AFM), and demonstrated that ITGB4 deficiency resulted in increased lung tissue stiffness. The examination of ECM components collagen, elastin, and lysyl oxidase (LOX) family showed that the expression of type VI collagen, elastin and LOXL4 were significantly elevated in the ITGB4-deficiency mice, compared with those in normal groups. Airway epithelial cell migration and proliferation capacities on normal and stiff substrates were evaluated through video-microscopy and flow cytometry. The morphology of the cytoskeleton was detected by laser confocal microscopy, and RhoA activities were determined by fluorescence resonance energy transfer (FRET) microscopy. The results showed that migration and proliferation of ITGB4 deficiency cells were noticeably inhibited, along decreased cytoskeleton stabilization, and hampered RhoA activity, especially for cells cultured on the stiff substrate. These results suggest that decreased ITGB4 expression results in increased lung tissue stiffness and impairs the adaptation of bronchial epithelial cells to substrate stiffness, which may be related to the occurrence of broncho pulmonary dysplasia.

Lysyl oxidase regulation and protein aldehydes in the injured newborn lung

During newborn lung injury, excessive activity of lysyl oxidases (LOXs) disrupts extracellular matrix (ECM) formation. Previous studies indicate that TGFβ activation in the O₂-injured mouse pup lung increases lysyl oxidase (LOX) expression. But how TGFβ regulates this, and whether the LOXs generate excess pulmonary aldehydes are unknown. First, we determined that O₂-mediated lung injury increases LOX protein expression in TGFβ-stimulated pup lung interstitial fibroblasts. This regulation appeared to be direct; this is because TGFβ treatment also increased LOX protein expression in isolated pup lung fibroblasts. Then using a fibroblast cell line, we determined that TGFβ stimulates LOX expression at a transcriptional level via Smad2/3-dependent signaling. LOX is translated as a pro-protein that requires secretion and extracellular cleavage before assuming amine oxidase activity and, in some cells, reuptake with nuclear localization. We found that pro-LOX is processed in the newborn mouse pup lung. Also, O₂-mediated injury was determined to increase pro-LOX secretion and nuclear LOX immunoreactivity particularly in areas populated with interstitial fibroblasts and exhibiting malformed ECM. Then, using molecular probes, we detected increased aldehyde levels in vivo in O₂-injured pup lungs, which mapped to areas of increased pro-LOX secretion in lung sections. Increased activity of LOXs plays a critical role in the aldehyde generation; an inhibitor of LOXs prevented the elevation of aldehydes in the O₂-injured pup lung. These results reveal new mechanisms of TGFβ and LOX in newborn lung disease and suggest that aldehyde-reactive probes might have utility in sensing the activation of LOXs in vivo during lung injury.

Early Changes and Indicators Characterizing Lung Aging in Neonatal Chronic Lung Disease

Infants suffering from neonatal chronic lung disease, i.e., bronchopulmonary dysplasia, are facing long-term consequences determined by individual genetic background, presence of infections, and postnatal treatment strategies such as mechanical ventilation and oxygen toxicity. The adverse effects provoked by these measures include inflammatory processes, oxidative stress, altered growth factor signaling, and remodeling of the extracellular matrix. Both, acute and long-term consequences are determined by the capacity of the immature lung to respond to the challenges outlined above. The subsequent impairment of lung growth translates into an altered trajectory of lung function later in life. Here, knowledge about second and third hit events provoked through environmental insults are of specific importance when advocating lifestyle recommendations to this patient population. A profound exchange between the different health care professionals involved is urgently needed and needs to consider disease origin while future monitoring and treatment strategies are developed.

Elafin Treatment Rescues EGFR-Klf4 Signaling and Lung Cell Survival in Ventilated Newborn Mice

Mechanical ventilation with O₂-rich gas (MV-O₂) inhibits alveologenesis and lung growth. We previously showed that MV-O₂ increased elastase activity and apoptosis in lungs of newborn mice, whereas elastase inhibition by elafin suppressed apoptosis and enabled lung growth. Pilot studies suggested that MV-O₂ reduces lung expression of prosurvival factors phosphorylated epidermal growth factor receptor (pEGFR) and Krüppel-like factor 4 (Klf4). Here, we sought to determine whether apoptosis and lung growth arrest evoked by MV-O₂ reflect disrupted pEGFR-Klf4 signaling, which elafin treatment preserves, and to assess potential biomarkers of bronchopulmonary dysplasia (BPD). Five-day-old mice underwent MV with air or 40% O₂ for 8-24 hours with or without elafin treatment. Unventilated pups served as controls. Immunoblots were used to assess lung pEGFR and Klf4 proteins. Cultured MLE-12 cells were exposed to AG1478 (EGFR inhibitor), Klf4 siRNA, or vehicle to assess effects on proliferation, apoptosis, and EGFR regulation of Klf4. Plasma elastase and elafin levels were measured in extremely premature infants. In newborn mice, MV with air or 40% O₂ inhibited EGFR phosphorylation and suppressed Klf4 protein content in lungs (vs. unventilated controls), yielding increased apoptosis. Elafin treatment inhibited elastase, preserved lung pEGFR and Klf4, and attenuated the apoptosis observed in lungs of vehicle-treated mice. In MLE-12 studies, pharmacological inhibition of EGFR and siRNA suppression of Klf4 increased apoptosis and reduced proliferation, and EGFR inhibition decreased Klf4. Plasma elastase levels were more than twofold higher, without a compensating increase of plasma elafin, in infants with BPD, compared to infants without BPD. These findings indicate that pEGFR-Klf4 is a novel prosurvival signaling pathway in lung epithelium that MV disrupts. Elafin preserves pEGFR-Klf4 signaling and inhibits apoptosis, thereby enabling lung growth during MV. Together, our animal and human data raise the question: would elastase inhibition prevent BPD in high-risk infants exposed to MV-O₂?

Pathogenesis of bronchopulmonary dysplasia: when inflammation meets organ development

Bronchopulmonary dysplasia is a chronic lung disease of preterm infants. It is caused by the disturbance of physiologic lung development mainly in the saccular stage with lifelong restrictions of pulmonary function and an increased risk of abnormal somatic and psychomotor development. The contributors to this disease’s entity are multifactorial with pre- and postnatal origin. Central to the pathogenesis of bronchopulmonary is the induction of a massive pulmonary inflammatory response due to mechanical ventilation and oxygen toxicity. The extent of the pro-inflammatory reaction and the disturbance of further alveolar growth and vasculogenesis vary largely and can be modified by prenatal infections, antenatal steroids, and surfactant application.

This minireview summarizes the important recent research findings on the pulmonary inflammatory reaction obtained in patient cohorts and in experimental models. Unfortunately, recent changes in clinical practice based on these findings had only limited impact on the incidence of bronchopulmonary dysplasia.

The Extracellular Matrix in Bronchopulmonary Dysplasia: Target and Source

Bronchopulmonary dysplasia (BPD) is a common complication of preterm birth that contributes significantly to morbidity and mortality in neonatal intensive care units. BPD results from life-saving interventions, such as mechanical ventilation and oxygen supplementation used to manage preterm infants with acute respiratory failure, which may be complicated by pulmonary infection. The pathogenic pathways driving BPD are not well-delineated but include disturbances to the coordinated action of gene expression, cell-cell communication, physical forces, and cell interactions with the extracellular matrix (ECM), which together guide normal lung development. Efforts to further delineate these pathways have been assisted by the use of animal models of BPD, which rely on infection, injurious mechanical ventilation, or oxygen supplementation, where histopathological features of BPD can be mimicked. Notable among these are perturbations to ECM structures, namely, the organization of the elastin and collagen networks in the developing lung. Dysregulated collagen deposition and disturbed elastin fiber organization are pathological hallmarks of clinical and experimental BPD. Strides have been made in understanding the disturbances to ECM production in the developing lung, but much still remains to be discovered about how ECM maturation and turnover are dysregulated in aberrantly developing lungs. This review aims to inform the reader about the state-of-the-art concerning the ECM in BPD, to highlight the gaps in our knowledge and current controversies, and to suggest directions for future work in this exciting and complex area of lung development (patho)biology.

Collagen and elastin cross-linking is altered during aberrant late lung development associated with hyperoxia

Maturation of the lung extracellular matrix (ECM) plays an important role in the formation of alveolar gas exchange units. A key step in ECM maturation is cross-linking of collagen and elastin, which imparts stability and functionality to the ECM. During aberrant late lung development in bronchopulmonary dysplasia (BPD) patients and animal models of BPD, alveolarization is blocked, and the function of ECM cross-linking enzymes is deregulated, suggesting that perturbed ECM cross-linking may impact alveolarization. In a hyperoxia (85% O2)-based mouse model of BPD, blunted alveolarization was accompanied by alterations to lung collagen and elastin levels and cross-linking. Total collagen levels were increased (by 63%). The abundance of dihydroxylysinonorleucine collagen cross-links and the dihydroxylysinonorleucine-to-hydroxylysinonorleucine ratio were increased by 11 and 18%, respectively, suggestive of a profibrotic state. In contrast, insoluble elastin levels and the abundance of the elastin cross-links desmosine and isodesmosine in insoluble elastin were decreased by 35, 30, and 21%, respectively. The lung collagen-to-elastin ratio was threefold increased. Treatment of hyperoxia-exposed newborn mice with the lysyl oxidase inhibitor β-aminopropionitrile partially restored normal collagen levels, normalized the dihydroxylysinonorleucine-to-hydroxylysinonorleucine ratio, partially normalized desmosine and isodesmosine cross-links in insoluble elastin, and partially restored elastin foci structure in the developing septa. However, β-aminopropionitrile administration concomitant with hyperoxia exposure did not improve alveolarization, evident from unchanged alveolar surface area and alveoli number, and worsened septal thickening (increased by 12%). These data demonstrate that collagen and elastin cross-linking are perturbed during the arrested alveolarization of developing mouse lungs exposed to hyperoxia.

Bronchopulmonary dysplasia early changes leading to long-term consequences

Neonatal chronic lung disease, i.e., bronchopulmonary dysplasia, is characterized by impaired pulmonary development resulting from the impact of different risk factors including infections, hyperoxia, and mechanical ventilation on the immature lung. Remodeling of the extracellular matrix, apoptosis as well as altered growth factor signaling characterize the disease. The immediate consequences of these early insults have been studied in different animal models supported by results from in vitro approaches leading to the successful application of some findings to the clinical setting in the past. Nonetheless, existing information about long-term consequences of the identified early and most likely sustained changes to the developing lung is limited. Interesting results point towards a tremendous impact of these early injuries on the pulmonary repair capacity as well as aging related processes in the adult lung.

Dynamic expression of chymotrypsin-like elastase 1 over the course of murine lung development

Postnatal lung development requires coordination of three processes (surface area expansion, microvascular growth, and matrix remodeling). Because normal elastin structure is important for lung morphogenesis, because physiological remodeling of lung elastin has never been defined, and because elastin remodeling is angiogenic, we sought to test the hypothesis that, during lung development, elastin is remodeled in a defined temporal-spatial pattern, that a novel protease is associated with this remodeling, and that angiogenesis is associated with elastin remodeling. By elastin in situ zymography, lung elastin remodeling increased 24-fold between embryonic day (E) 15.5 and postnatal day (PND) 14. Remodeling was restricted to major vessels and airways on PND1 with a sevenfold increase in alveolar wall elastin remodeling from PND1 to PND14. By inhibition assays and literature review, we identified chymotrypsin-like elastase 1 (CELA1) as a potential mediator of elastin remodeling. CELA1 mRNA levels increased 12-fold from E15.5 to PND9, and protein levels increased 3.4-fold from E18.5 to PND9. By costaining experiments, the temporal-spatial pattern of CELA1 expression matched that of elastin remodeling, and 58-85% of CELA1(+) cells were <10 μm from an elastase signal. An association between elastin remodeling and angiogenesis was tested by similar methods. At PND7 and PND14, 60-95% of angiogenin(+) cells were associated with elastin remodeling. Both elastase inhibition and CELA1 silencing impaired angiogenesis in vitro. Our data defines the temporal-spatial pattern of elastin remodeling during lung development, demonstrates an association of this remodeling with CELA1, and supports a role for elastin remodeling in regulating angiogenesis.

Chronic lung disease in the preterm infant. Lessons learned from animal models

Neonatal chronic lung disease, also known as bronchopulmonary dysplasia (BPD), is the most common complication of premature birth, affecting up to 30% of very low birth weight infants. Improved medical care has allowed for the survival of the most premature infants and has significantly changed the pathology of BPD from a disease marked by severe lung injury to the "new" form characterized by alveolar hypoplasia and impaired vascular development. However, increased patient survival has led to a paucity of pathologic specimens available from infants with BPD. This, combined with the lack of a system to model alveolarization in vitro, has resulted in a great need for animal models that mimic key features of the disease. To this end, a number of animal models have been created by exposing the immature lung to injuries induced by hyperoxia, mechanical stretch, and inflammation and most recently by the genetic modification of mice. These animal studies have 1) allowed insight into the mechanisms that determine alveolar growth, 2) delineated factors central to the pathogenesis of neonatal chronic lung disease, and 3) informed the development of new therapies. In this review, we summarize the key findings and limitations of the most common animal models of BPD and discuss how knowledge obtained from these studies has informed clinical care. Future studies should aim to provide a more complete understanding of the pathways that preserve and repair alveolar growth during injury, which might be translated into novel strategies to treat lung diseases in infants and adults.

Altered lung development in bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is the main respiratory sequela of extreme prematurity. Its pathophysiology is complex, involving interactions between host and environment, likely to be significantly influenced by genetic factors. Thus, the clinical presentation and histological lesions have evolved over time, along with the reduction in neonatal injuries, and the care of more immature children. Impaired alveolar growth, however, is a lesion consistently observed in BPD, such that it is a key feature in BPD, and is even the dominant characteristic of the so-called "new" forms of BPD. This review describes the key molecular pathways that are believed to be involved in the genesis of BPD. Much of our understanding is based on animal models, but this is increasingly being enriched by genetic approaches, and long-term respiratory functional studies.

The role of desmosines as biomarkers for chronic obstructive pulmonary disease

Since chronic obstructive pulmonary disease (COPD) has a progressive and major impact on health management, many aspects of this disorder, including development of effective and reliable biomarkers to monitor disease progression, are under intensive investigation. A huge amount of data, accumulated over the years, have provided solid evidence that two pyridinium-ring-containing amino acid isoforms, desmosine and isodesmosine (usually referred to as desmosines), unique to mature elastin in humans, are representative of the elastin breakdown occurring in chronic destructive disorders, such as COPD. This paper is aimed at providing a critical review of the methodological steps that have marked the progress in the detection of desmosines in biological fluids in health and disease, as well as the progress in the authors knowledge of desmosines' role in the pathophysiology of COPD. The authors have tried to emphasize that the suitability of desmosine as a biomarker for COPD increased over the years, as the techniques developed for its detection became progressively more sophisticated and precise. The authors conclude that desmosines, although not yet definitely proven, have nevertheless all the requisites to become a critical COPD biomarker.

Elastin turnover in malignant solid tumors

Desmosine, a crosslinking amino acid unique to elastin, was investigated as a possible biomarker for cancer. Twenty-eight normal controls, median age 67 years, had a median value for urine desmosine of 43.5 picomoles desmosine/mg creatinine. The median for 19 untreated cancer subjects of similar age was significantly higher (175 picomoles desmosine/mg creatinine, p < 0.001). Urine desmosine levels in 55 subjects currently receiving chemotherapy, as well as 67 individuals who had survived cancer and were currently clinically disease free, were not significantly different from controls. Our findings indicate that elastin is being turned over in malignant solid tumors, releasing significantly elevated levels of desmosine in the urine.

Neonatal mice genetically modified to express the elastase inhibitor elafin are protected against the adverse effects of mechanical ventilation on lung growth

Mechanical ventilation (MV) with O(2)-rich gas (MV-O(2)) offers life-saving treatment for newborn infants with respiratory failure, but it also can promote lung injury, which in neonates translates to defective alveolar formation and disordered lung elastin, a key determinant of lung growth and repair. Prior studies in preterm sheep and neonatal mice showed that MV-O(2) stimulated lung elastase activity, causing degradation and remodeling of matrix elastin. These changes yielded an inflammatory response, with TGF-β activation, scattered elastic fibers, and increased apoptosis, culminating in defective alveolar septation and arrested lung growth. To see whether sustained inhibition of elastase activity would prevent these adverse pulmonary effects of MV-O(2), we did studies comparing wild-type (WT) and mutant neonatal mice genetically modified to express in their vascular endothelium the human serine elastase inhibitor elafin (Eexp). Five-day-old WT and Eexp mice received MV with 40% O(2) (MV-O(2)) for 24-36 h. WT and Eexp controls breathed 40% O(2) without MV. MV-O(2) increased lung elastase and MMP-9 activity, resulting in elastin degradation (urine desmosine doubled), TGF-β activation (pSmad-2 increased 6-fold), apoptosis (cleaved-caspase-3 increased 10-fold), and inflammation (NF-κB activation, influx of neutrophils and monocytes) in lungs of WT vs. unventilated controls. These changes were blocked or blunted during MV-O(2) of Eexp mice. Scattered lung elastin and emphysematous alveoli observed in WT mice after 36 h of MV-O(2) were attenuated in Eexp mice. Both WT and Eexp mice showed defective VEGF signaling (decreased lung VEGF-R2 protein) and loss of pulmonary microvessels after lengthy MV-O(2), suggesting that elafin's beneficial effects during MV-O(2) derived primarily from preserving matrix elastin and suppressing lung inflammation, thereby enabling alveolar formation during MV-O(2). These results suggest that degradation and remodeling of lung elastin can contribute to defective lung growth in response to MV-O(2) and might be targeted therapeutically to prevent ventilator-induced neonatal lung injury.

Inhibiting lung elastase activity enables lung growth in mechanically ventilated newborn mice

RATIONALE

Mechanical ventilation with O₂-rich gas (MV-O₂) offers life-saving treatment for respiratory failure, but also promotes lung injury. We previously reported that MV-O2 of newborn mice increased lung elastase activity, causing elastin degradation and redistribution of elastic fibers from septal tips to alveolar walls. These changes were associated with transforming growth factor (TGF)-β activation and increased apoptosis leading to defective alveolarization and lung growth arrest, as seen in neonatal chronic lung disease.

OBJECTIVES

To determine if intratracheal treatment of newborn mice with the serine elastase inhibitor elafin would prevent MV-O₂-induced lung elastin degradation and the ensuing cascade of events causing lung growth arrest.

METHODS

Five-day-old mice were treated via tracheotomy with recombinant human elafin or vehicle (lactated-Ringer solution), followed by MV with 40% O₂ for 8-24 hours; control animals breathed 40% O₂ without MV. At study's end, lungs were harvested to assess key variables noted below.

MEASUREMENTS AND MAIN RESULTS

MV-O₂ of vehicle-treated pups increased lung elastase and matrix metalloproteinase-9 activity when compared with unventilated control animals, causing elastin degradation (urine desmosine doubled), TGF-β activation (pSmad-2 tripled), and apoptosis (cleaved-caspase-3 increased 10-fold). Quantitative lung histology showed larger and fewer alveoli, greater inflammation, and scattered elastic fibers. Elafin blocked these MV-O₂-induced changes.

CONCLUSIONS

Intratracheal elafin, by blocking lung protease activity, prevented MV-O₂-induced elastin degradation, TGF-β activation, apoptosis, and dispersion of matrix elastin, and attenuated lung structural abnormalities noted in vehicle-treated mice after 24 hours of MV-O₂. These findings suggest that elastin breakdown contributes to defective lung growth in response to MV-O₂ and might be targeted therapeutically to prevent MV-O₂-induced lung injury.

Prolonged mechanical ventilation with air induces apoptosis and causes failure of alveolar septation and angiogenesis in lungs of newborn mice

Defective lung septation and angiogenesis, quintessential features of neonatal chronic lung disease (CLD), typically result from lengthy exposure of developing lungs to mechanical ventilation (MV) and hyperoxia. Previous studies showed fewer alveoli and microvessels, with reduced VEGF and increased transforming growth factor-beta (TGFbeta) signaling, and excess, scattered elastin in lungs of premature infants and lambs with CLD vs. normal controls. MV of newborn mice with 40% O(2) for 24 h yielded similar lung structural abnormalities linked to impaired VEGF signaling, dysregulated elastin production, and increased apoptosis. These studies could not determine the relative importance of cyclic stretch vs. hyperoxia in causing these lung growth abnormalities. We therefore studied the impact of MV for 24 h with air on alveolar septation (quantitative lung histology), angiogenesis [CD31 quantitative-immunohistochemistry (IHC), immunoblots], apoptosis [TdT-mediated dUTP nick end labeling (TUNEL), active caspase-3 assays], VEGF signaling [VEGF-A, VEGF receptor 1 (VEGF-R1), VEGF-R2 immunoblots], TGFbeta activation [phosphorylated Smad2 (pSmad2) quantitative-IHC], and elastin production (tropoelastin immunoblots, quantitative image analysis of Hart's stained sections) in lungs of 6-day-old mice. Compared with unventilated controls, MV caused a 3-fold increase in alveolar area, approximately 50% reduction in alveolar number and endothelial surface area, >5-fold increase in apoptosis, >50% decrease in lung VEGF-R2 protein, 4-fold increase of pSmad2 protein, and >50% increase in lung elastin, which was distributed throughout alveolar walls rather than at septal tips. This study is the first to show that prolonged MV of developing lungs, without associated hyperoxia, can inhibit alveolar septation and angiogenesis and increase apoptosis and lung elastin, findings that could reflect stretch-induced changes in VEGF and TGFbeta signaling, as reported in CLD.

Lysyl oxidase activity is dysregulated during impaired alveolarization of mouse and human lungs

RATIONALE

Disordered extracellular matrix production is a feature of bronchopulmonary dysplasia (BPD). The basis of this phenomenon is not understood.

OBJECTIVES

To assess lysyl oxidase expression and activity in the injured developing lungs of newborn mice and of prematurely born infants with BPD or at risk for BPD.

METHODS

Pulmonary lysyl oxidase and elastin gene and protein expression were assessed in newborn mice breathing 21 or 85% oxygen, in patients who died with BPD or were at risk for BPD, and in control patients. Signaling by transforming growth factor (TGF-beta) was preemptively blocked in mice exposed to hyperoxia using TGF-beta-neutralizing antibodies. Lysyl oxidase promoter activity was assessed using plasmids containing the lox or loxl1 promoters fused upstream of the firefly luciferase gene.

MEASUREMENTS AND MAIN RESULTS

mRNA and protein levels and activity of lysyl oxidases (Lox, LoxL1, LoxL2) were elevated in the oxygen-injured lungs of newborn mice and infants with BPD or at risk for BPD. In oxygen-injured mouse lungs, increased TGF-beta signaling drove aberrant lox, but not loxl1 or loxl2, expression. Lox expression was also increased in oxygen-injured fibroblasts and pulmonary artery smooth muscle cells.

CONCLUSIONS

Lysyl oxidase expression and activity are dysregulated in BPD in injured developing mouse lungs and in prematurely born infants. In developing mouse lungs, aberrant TGF-beta signaling dysregulated lysyl oxidase expression. These data support the postulate that excessive stabilization of the extracellular matrix by excessive lysyl oxidase activity might impede the normal matrix remodeling that is required for pulmonary alveolarization and thereby contribute to the pathological pulmonary features of BPD.

Inflammatory mediators in the immunobiology of bronchopulmonary dysplasia

Inflammation is important in the development of bronchopulmonary dysplasia (BPD). Polymorphonuclear cells and macrophages and proinflammatory cytokines/chemokines denote early inflammation in clinical scenarios such as in utero inflammation with chorioamnionitis or initial lung injury associated with respiratory distress syndrome or ventilator-induced lung injury. The persistence and non-resolution of lung inflammation contributes greatly to BPD, including altering the lung's ability to repair, contributing to fibrosis, and inhibiting secondary septation, alveolarization, and normal vascular development. Further understanding of the role of inflammation in the pathogenesis of BPD, in particular, during the chronic inflammatory period, offers us the opportunity to develop inflammation-related prevention and treatment strategies of this disease that has long-standing consequences for very premature infants.

Decreased expression of transforming growth factor-beta1 in bronchoalveolar lavage cells of preterm infants with maternal chorioamnionitis

Maternal chorioamnionitis has been associated with abnormal lung development. We examined the effect of maternal chorioamnionitis on the expression of transforming growth factor-beta1 (TGF-beta1) in the lungs of preterm infants. A total of 63 preterm (<or=34 weeks) infants who were intubated in the delivery room were prospectively enrolled. Their placentas were examined for the presence of chorioamnionitis. Bronchoalveolar lavage (BAL) fluid and cells were obtained shortly after birth. TGF-beta1 was measured in BAL fluid and TGF-beta1 mRNA expression was determined by reverse transcription polymerase chain reaction (RT-PCR) in BAL cells. TGF-beta1 mRNA expression in BAL cells showed a positive correlation with gestational age (r=0.414, p=0.002). TGF-beta1 mRNA expression was significantly decreased in the presence of maternal chorioamnionitis (0.70+/-0.12 vs. 0.81+/-0.15, p=0.007). Adjustment for gestational age, birth weight, and delivery mode did not nullify the significance. TGF-beta1 mRNA expression was marginally significantly decreased in preterm infants who developed bronchopulmonary dysplasia (BPD) later (0.75+/-0.11 vs. 0.82+/-0.15, p=0.055). However, adjustment for gestational age, patent ductus arteriosus (PDA), and maternal chorioamnionitis nullified the significance. These results might be an indirect evidence that maternal chorioamnionitis may inhibit normal lung development of fetus.

Regulation of alveologenesis: clinical implications of impaired growth

During its development that begins in intrauterine life, the lung is transformed from a simple epithelial lined sac that emerges from the foregut into a complex arrangement of blood vessels, airways, and alveoli that make up the mature lung structure. This remarkable transformation that continues for several years postnatally, is achieved by the influence of several genes, transcription factors, growth factors and hormones upon the cells and proteins of the lung bud. A seminal event in this process is the formation of the air-blood barrier within the alveolar wall, an evolutionary modification that permits independent air-breathing existence in mammals. Molecular biological techniques have enabled elucidation of the mechanistic pathways contributing to alveologenesis and have provided probable molecular bases for examples of impaired alveologenesis encountered by the paediatric pathologist.

Mechanical ventilation uncouples synthesis and assembly of elastin and increases apoptosis in lungs of newborn mice

Prolonged mechanical ventilation (MV) with O2-rich gas inhibits lung growth and causes excess, disordered accumulation of lung elastin in preterm infants, often resulting in chronic lung disease (CLD). Using newborn mice, in which alveolarization occurs postnatally, we designed studies to determine how MV with either 40% O2or air might lead to dysregulated elastin production and impaired lung septation. MV of newborn mice for 8 h with either 40% O2or air increased lung mRNA for tropoelastin and lysyl oxidase, relative to unventilated controls, without increasing lung expression of genes that regulate elastic fiber assembly (lysyl oxidase-like-1, fibrillin-1, fibrillin-2, fibulin-5, emilin-1). Serine elastase activity in lung increased fourfold after MV with 40% O2, but not with air. We then extended MV with 40% O2to 24 h and found that lung content of tropoelastin protein doubled, whereas lung content of elastin assembly proteins did not change (lysyl oxidases, fibrillins) or decreased (fibulin-5, emilin-1). Quantitative image analysis of lung sections showed that elastic fiber density increased by 50% after MV for 24 h, with elastin distributed throughout the walls of air spaces, rather than at septal tips, as in control lungs. Dysregulation of elastin was associated with a threefold increase in lung cell apoptosis (TUNEL and caspase-3 assays), which might account for the increased air space size previously reported in this model. Our findings of increased elastin synthesis, coupled with increased elastase activity and reduced lung abundance of proteins that regulate elastic fiber assembly, could explain altered lung elastin deposition, increased apoptosis, and defective septation, as observed in CLD.

Cathepsin S deficiency confers protection from neonatal hyperoxia-induced lung injury

RATIONALE

Bronchopulmonary dysplasia (BPD) is a chronic lung disease that adversely affects long-term pulmonary function as well as neurodevelopmental outcomes of preterm infants. Elastolytic proteases have been implicated in the pathogenesis of BPD. Cathepsin S (cat S) is a cysteine protease with potent elastolytic activity. Increased levels and activity of cat S have been detected in a baboon model of BPD.

OBJECTIVES

To investigate whether deficiency of cat S alters the course of hyperoxia-induced neonatal lung injury in mice.

METHODS

Newborn wild-type and cat S-deficient mice were exposed to 80% oxygen for 14 days. Histologic and morphometric analysis were performed and bronchoalveolar lavage protein and cells were analyzed. Lung elastin was assessed by real-time polymerase chain reaction, in situ hybridization, desmosine analysis, and Hart's stain. Distribution of myofibroblasts was analyzed by immunofluorescence. Hydroxyproline content of lung tissues was measured.

MEASUREMENTS AND MAIN RESULTS

Hyperoxia-exposed cat S-deficient mice were protected from growth restriction and had improved alveolarization, decreased septal wall thickness, lower number of macrophages, and lower protein concentration in bronchoalveolar lavage fluid. alpha-Smooth muscle actin-expressing myofibroblasts accounted for at least some of the increased interstitial cellularity in hyperoxia-exposed mouse lungs and were significantly less in cat S-deficient lungs. Lung hydroxyproline content was increased in hyperoxia-exposed wild-type, but not in cat S-deficient lungs. Desmosine content was significantly reduced in both genotypes with hyperoxia.

CONCLUSIONS

Cathepsin S deficiency improves alveolarization, and attenuates macrophage influx and fibroproliferative changes in hyperoxia-induced neonatal mouse lung injury.

Dysregulation of pulmonary elastin synthesis and assembly in preterm lambs with chronic lung disease

Failed alveolar formation and excess, disordered elastin are key features of neonatal chronic lung disease (CLD). We previously found fewer alveoli and more elastin in lungs of preterm compared with term lambs that had mechanical ventilation (MV) with O(2)-rich gas for 3 wk (MV-3 wk). We hypothesized that, in preterm more than in term lambs, MV-3 wk would reduce lung expression of growth factors that regulate alveolarization (VEGF, PDGF-A) and increase lung expression of growth factors [transforming growth factor (TGF)-alpha, TGF-beta(1)] and matrix molecules (tropoelastin, fibrillin-1, fibulin-5, lysyl oxidases) that regulate elastin synthesis and assembly. We measured lung expression of these genes in preterm and term lambs after MV for 1 day, 3 days, or 3 wk, and in fetal controls. Lung mRNA for VEGF, PDGF-A, and their receptors (VEGF-R2, PDGF-Ralpha) decreased in preterm and term lambs after MV-3 wk, with reduced lung content of the relevant proteins in preterm lambs with CLD. TGF-alpha and TGF-beta(1) expression increased only in lungs of preterm lambs. Tropoelastin mRNA increased more with MV of preterm than term lambs, and expression levels remained high in lambs with CLD. In contrast, fibrillin-1 and lysyl oxidase-like-1 mRNA increased transiently, and lung abundance of other elastin-assembly genes/proteins was unchanged (fibulin-5) or reduced (lysyl oxidase) in preterm lambs with CLD. Thus MV-3 wk reduces lung expression of growth factors that regulate alveolarization and differentially alters expression of growth factors and matrix proteins that regulate elastin assembly. These changes, coupled with increased lung elastase activity measured in preterm lambs after MV for 1-3 days, likely contribute to CLD.

Control mechanisms of lung alveolar development and their disorders in bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease that occurs in very premature infants and is characterized by impaired alveologenesis. This ultimate phase of lung development is mostly postnatal and allows growth of gas-exchange surface area to meet the needs of the organism. Alveologenesis is a highly integrated process that implies cooperative interactions between interstitial, epithelial, and vascular compartments of the lung. Understanding of its underlying mechanisms has considerably progressed recently with identification of structural, signaling, or remodeling molecules that are crucial in the process. Thus, the pivotal role of elastin deposition in lung walls has been demonstrated, and many key control-molecules have been identified, including various transcription factors, growth factors such as platelet-derived growth factor, fibroblast growth factors, and vascular endothelial growth factor, matrix-remodeling enzymes, and retinoids. BPD-associated changes in lung expression/content have been evidenced for most of these molecules, especially for signaling pathways, through both clinical investigations in premature infants and the use of animal models, including the premature baboon or lamb, neonatal exposure to hyperoxia in rodents, and maternal-fetal infection. These findings open therapeutic perspectives to correct imbalanced signaling. Unraveling the intimate molecular mechanisms of alveolar building appears as a prerequisite to define new strategies for the prevention and care of BPD.

Bronchopulmonary dysplasia in preterm infants: pathophysiology and management strategies

Bronchopulmonary dysplasia (BPD) has classically been described as including inflammation, architectural disruption, fibrosis, and disordered/delayed development of the infant lung. As infants born at progressively earlier gestations have begun to survive the neonatal period, a 'new' BPD, consisting primarily of disordered/delayed development, has emerged. BPD causes not only significant complications in the newborn period, but is associated with continuing mortality, cardiopulmonary dysfunction, re-hospitalization, growth failure, and poor neurodevelopmental outcome after hospital discharge. Four major risk factors for BPD include premature birth, respiratory failure, oxygen supplementation, and mechanical ventilation, although it is unclear whether any of these factors is absolutely necessary for development of the condition. Genetic susceptibility, infection, and patent ductus arteriosus have also been implicated in the pathogenesis of the disease. The strategies with the strongest evidence for effectiveness in preventing or lessening the severity of BPD include prevention of prematurity and closure of a clinically significant patent ductus arteriosus. Some evidence of effectiveness also exists for single-course therapy with antenatal glucocorticoids in women at risk for delivering premature infants, surfactant replacement therapy in intubated infants with respiratory distress syndrome, retinol (vitamin A) therapy, and modes of respiratory support designed to minimize 'volutrauma' and oxygen toxicity. The most effective treatments for ameliorating symptoms or preventing exacerbation in established BPD include oxygen therapy, inhaled glucocorticoid therapy, and vaccination against respiratory pathogens.Many other strategies for the prevention or treatment of BPD have been proposed, but have weaker or conflicting evidence of effectiveness. In addition, many therapies have significant side effects, including the possibility of worsening the disease despite symptom improvement. For instance, supraphysiologic systemic doses of glucocorticoids lessen the incidence of BPD in infants at risk for the disease, and promote weaning of oxygen and mechanical ventilation in infants with established BPD. However, the side effects of systemic glucocorticoid therapy, most notably the recently recognized adverse effects on neurodevelopment, preclude their routine use for the prevention or treatment of BPD. Future research in BPD will most probably focus on continued incremental improvements in outcome, which are likely to be achieved through the combined effects of many therapeutic modalities.

Transient induction of TGF-α disrupts lung morphogenesis, causing pulmonary disease in adulthood

Clinical studies have associated increased transforming growth factor (TGF)-α and EGF receptor with lung remodeling in diseases including bronchopulmonary dysplasia (BPD). BPD is characterized by disrupted alveolar and vascular morphogenesis, inflammation, and remodeling. To determine whether transient increases in TGF-α are sufficient to disrupt postnatal lung morphogenesis, we utilized neonatal transgenic mice conditionally expressing TGF-α. Expression of TGF-α from postnatal days 3 to 5 disrupted postnatal alveologenesis, causing permanent enlargement of distal air spaces in neonatal and adult mice. Lung volume-to-body weight ratios and lung compliance were increased in adult TGF-α transgenic mice, whereas tissue and airway elastance were reduced. Elastin fibers in the alveolar septae were fragmented and disorganized. Pulmonary vascular morphogenesis was abnormal in TGF-α mice, with attenuated and occasionally tortuous arterial branching. The ratios of right ventricle weight to left ventricle plus septal weight were increased in TGF-α mice, indicating pulmonary hypertension. Electron microscopy showed gaps in the capillary endothelium and extravasation of erythrocytes into the alveolar space of TGF-α mice. Hemorrhage and inflammatory cells were seen in distal air spaces at 1 mo of age. In adult TGF-α mice, alveolar remodeling, nodules, proteinaceous deposits, and inflammatory cells were seen. Immunostaining for pro-surfactant protein C showed that type II cells were abundant in the nodules, as well as neutrophils and macrophages. Trichrome staining showed that pulmonary fibrosis was minimal, apart from areas of nodular remodeling in adult TGF-α mice. Transient induction of TGF-α during early alveologenesis permanently disrupted lung structure and function and caused chronic lung disease.

Low levels of tissue inhibitors of metalloproteinases with a high matrix metalloproteinase-9/tissue inhibitor of metalloproteinase-1 ratio are present in tracheal aspirate fluids of infants who develop chronic lung disease

OBJECTIVE

The pathogenesis of chronic lung disease (CLD) involves inflammation with proteolytic damage to lung extracellular matrix. Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that, acting in concert with their tissue inhibitors, tightly orchestrate extracellular matrix morphogenesis and repair after injury. Imbalances in their levels relative to that of their inhibitors have been implicated in diseases characterized by matrix disruption and remodeling. We investigated the possibility that imbalances in MMP-9 and MMP-2 relative to their tissue inhibitor of metalloproteinase-1 (TIMP-1) and TIMP-2, respectively, in tracheal aspirates of preterm infants may be involved in the development of CLD.

METHODS

Serial tracheal aspirates collected from birth until extubation in 49 ventilated preterm infants (24-32 weeks' gestations) were analyzed for MMP-2, MMP-9, TIMP-1, and TIMP-2. Data normalized by TA values of free secretory component of immunoglobulin A were compared for CLD (n = 22) versus no CLD (n = 27). Also, known clinical predictors of CLD (gestational age, birth weight, and sex) were assessed for both groups. Association of predictors with the outcome CLD was assessed by logistic regression.

RESULTS

Mean gestational age was lower in CLD infants, but birth weight and gender were comparable for both groups. CLD infants had significantly lower TIMP-1 level with higher MMP-9/TIMP-1 ratio during the first 2 weeks of life and low TIMP-2 and MMP-2 levels during the first 3 days of life compared with no-CLD infants. Logistic regression analysis indicated that the findings are predictive of CLD.

CONCLUSIONS

We conclude that low tracheal aspirate levels of TIMPs, with a high MMP-9/TIMP-1 ratio early in life, are associated with subsequent development of CLD.

Infection, neutrophils, and hematopoietic growth factors in the pathogenesis of neonatal chronic lung disease

Continued definition of the biochemical and molecular mechanisms underlying the development of chronic lung disease (CLD) has persuaded investigators that inflammatory cells and mediators are key factors in the pathophysiology of the disease. High numbers of inflammatory cells and their products are present in the airways of ventilated neonates with respiratory distress syndrome and precede the development of CLD. This article reviews the mechanisms underlying neutrophil recruitment in the lungs of ventilated preterm infants with respiratory distress syndrome and the injurious effects that these cells can produce on lung parenchyma with special emphasis on the development of CLD. The role of granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor is stressed as a pivotal mechanism of neutrophil recruitment and activation.

Loss of lung mitochondrial aconitase activity due to hyperoxia in bronchopulmonary dysplasia in primates

The premature primate exposed to hyperoxia provides a useful model of bronchopulmonary dysplasia. A critical target in hyperoxic injury is the mitochondrial matrix enzyme aconitase. We hypothesized that this enzyme's activity would decline in the premature baboon lung during exposure to hyperoxia. Total aconitase activity was significantly decreased in the lungs of premature baboons of 140 days gestation with exposure to 100% oxygen for 6-10 days compared with as needed [pro re nada (PRN)] oxygen exposure and fetal controls (P = 0.0001). In activity gels, lungs from 100% oxygen-exposed animals (6-10 days) showed a nearly complete loss of mitochondrial aconitase activity relative to lungs from animals exposed only to PRN oxygen. Decreased lung aconitase activity was not a nonspecific effect of hyperoxia, causing mitochondrial damage or loss, because the activity of the mitochondrial respiratory enzyme cytochrome oxidase was not different in lungs of 100% oxygen-exposed relative to PRN oxygen-exposed newborns. In 125-day-gestation premature primates (age 6-10 days), lung total aconitase activity was correlated with inspired oxygen tension (r = 0.73 for fraction of inspired oxygen > 0.35), whereas, for animals of 140 days gestation, no such correlation was found. Thus the more premature animal's lung was more susceptible to loss of aconitase.

alpha1-Proteinase inhibitor therapy for the prevention of chronic lung disease of prematurity: a randomized, controlled trial

BACKGROUND

An imbalance between increased neutrophil elastase and a decreased antiprotease shield has been suggested as a factor contributing to the development of chronic lung disease (CLD). We hypothesized that administration of alpha1-proteinase inhibitor (A1PI), also known as alpha1-antitrypsin, to premature neonates would prevent CLD.

DESIGN

A randomized, placebo-controlled, prospective study of A1PI supplementation was performed. Neonates <24 hours of age with birth weights 600-1000 g on respiratory support, and 1001-1250 g with respiratory distress syndrome (RDS) were eligible. Intravenous A1PI (60 mg/kg) or placebo was infused on days 0, 4, 7, and 14. Primary outcome was CLD in survivors, defined as the need for supplemental oxygen on day 28.

RESULTS

A total of 106 patients were recruited. There were no significant differences between groups in birth weight or incidence of RDS. The incidence of CLD in survivors was lower in the treated group, but the difference did not reach statistical significance (relative risk [RR], 0.79; confidence interval [CI], 0.60-1.02). This beneficial trend persisted at 36 weeks corrected gestational age (RR, 0.48; CI, 0.23-1.00). The incidence of pulmonary hemorrhage was lower in the treated group (RR, 0.22; CI, 0.05-0.98). Other complications were not significantly different between groups.

CONCLUSIONS

In this, the first trial of a protease inhibitor for the prevention of CLD in premature infants, the infusions were well-tolerated. A1PI therapy may impede the development of CLD and appears to reduce the incidence of pulmonary hemorrhage in some neonates born prematurely.

Cytokines in chronic lung disease of prematurity

Chronic lung disease of prematurity (CLD) is a common respiratory disorder of preterm infants. At autopsy, fibroblast proliferation, and components of the extracellular matrix, including collagen and fibronectin, are markedly increased in the lungs of infants who die from CLD. Examination of broncho-alveolar fluid suggests that the persistence of neutrophils is associated with the development of CLD. In our studies, the pro-inflammatory cytokines, interleukin-1 beta (IL-1 beta) and interleukin-6, (IL-6) and mediators which reflect neutrophil recruitment and activation, including soluble intercellular adhesion molecule, interleukin-8 (IL-8) and neutrophil elastase, were increased in lavage fluid obtained from infants who developed CLD when compared to infants who did not. Furthermore, semiquantitative reverse transcriptase-polymerase chain reaction of mRNA extracted from lavage cells suggested that luminal cells may be the source of IL-6 detected in lavage fluid but non-luminal cells may be the sources of IL-1 beta and IL-8. Fibrosis is thought to be mediated by the pro-fibrotic cytokines including transforming growth factor-beta1 (TGF-beta 1). Both active and total TGF-beta 1 were increased in lavage fluid from infants who developed CLD. Furthermore, both type I procollagen and TGF-beta were increased qualitatively in lung tissue obtained at autopsy from infants who died from respiratory failure. The increase in inflammatory mediators was maximal at 10 days of age. By contrast, the increase in TGF-beta 1 was maximal at 4 days of age. This suggests that the interaction between inflammation and fibrosis in CLD is complex, and that prenatal factors may be important in the pathogenesis of CLD.

Increase in the concentration of transforming growth factor beta-1 in bronchoalveolar lavage fluid before development of chronic lung disease of prematurity

OBJECTIVE

Pulmonary fibrosis is a prominent feature of chronic lung disease of prematurity (CLD). We sought to determine the influence of the potent profibrotic cytokine transforming growth factor beta-1 (TGF-Beta 1) on the development of CLD.

METHODS

We determined the concentration of active and total TGF-Beta 1 in bronchoalveolar lavage fluid obtained from 18 infants who subsequently had CLD (mean gestation, 25.7 weeks; birth weight, 816 gm) 15 (29.8 weeks, 1493 gm) who recovered from the respiratory distress syndrome, and 7 (35.1 weeks, 2441 gm) control infants.

RESULTS

The concentration of both active and total TGF-Beta 1 was increased in the infants with CLD when compared with the respiratory distress syndrome and control groups. The increase in active and total TGF-Beta 1 was greatest on day 4 of age, when infants who eventually had CLD were compared with those who did not progress to CLD (active TGF-Beta 1, 39.5 vs 4.6 ng/ml; total TGF-Beta 1, 43.8 vs 13.8 ng/ml). In addition, immunocytochemistry studies localized pan-TGF-Beta to alveolar macrophages obtained by bronchoalveolar lavage.

CONCLUSIONS

These observations indicate that TGF-Beta 1 may contribute to the fibrotic response that is observed in the lungs of infants who have CLD.

Activation of circulating polymorphonuclear leukocytes in preterm infants with severe idiopathic respiratory distress syndrome

We have studied activation of circulating polymorphonuclear leukocytes (PMN) in plasma of preterm infants with severe idiopathic respiratory distress syndrome (IRDS group, n = 15) and without IRDS (reference group, n = 15) during the first 5 postnatal days. We have observed lower median PMN counts in the IRDS group than in the reference group from d 2 (1.4 x 10(9)/L versus 4.8 x 10(9)/L in the reference group, p < 0.001) to d 4 to 6 (1.6 x 10(9)/L versus 4.0 x 10(9)/L, p < 0.01). Lower PMN counts in the IRDS infants were accompanied by lower median plasma elastase-alpha1-proteinase inhibitor (PI) concentrations (53.6 ng/mL versus 128.0 ng/mL in the reference group on d 2, p < 0.05). Simultaneously, median elastase-alpha1-PI/PMN ratios of these infants were significantly higher (40.8 ng/10(6) PMN versus 21.8 ng/10(6) PMN on d 2, p < 0.05), indicating activation of circulating PMN. Activation of circulating PMN in the IRDS group is associated with platelet-activating factor (PAF) release and complement activation from within 6 to 12 h of birth but not with release of tumor necrosis factor-alpha. PAF release was represented by significantly reduced inhibiting capacity (58% of normal human plasma, p < 0.01) and complement activation by higher median plasma C3a des-Arg concentrations (1680 ng/mL versus 325 ng/mL in the reference group, p < 0.001). We conclude that circulating PMN are activated in preterm infants with severe IRDS, which might be caused by systemic PAF release and complement activation. This activation process may play a role in the pathogenesis of the IRDS by influx of activated PMN into the lungs.

Outcome measures for clinical trials in cystic fibrosis. Summary of a Cystic Fibrosis Foundation consensus conference

The CFF Consensus Conference concluded with a summary of those outcome measures that would be most useful in studies of patients 6 years of age and older and those measures that would be most useful in studies of the younger population (< 6 years of age) (Table). These measures were further divided into biologic markers most appropriate for initial (phase I and phase II) clinical trials and those especially useful in large, multicenter (phase III) pivotal trials. There is an ongoing need to improve the accuracy and validity of currently available measures of biologic activity and clinical efficacy in CF, especially in the younger population. The conference participants recommended that the following eight issues be addressed as soon as possible: (1) definition of pulmonary exacerbation, (2) broadly applicable methods of testing pulmonary function in small children (ideally a single test for all ages), (3) a comprehensive severity-of-disease score for young children, (4) reliable methods of quantifying chest x-ray and CT scan changes in young patients, (5) simple, inexpensive measures of lung inflammation, (6) a centralized, uniform approach to the establishment of data monitoring committees, (7) a quality of well-being scale for small children, and (8) reliable, reproducible aerosol delivery systems with defined characteristics. In addition, participants recommended that better methods be developed for assessing patients' adherence to research protocols.

Nitrogen dioxide exposure and urinary excretion of hydroxyproline and desmosine

The relationship between average and peak personal exposure to nitrogen dioxide and urinary excretion of hydroxyproline and desmosine was investigated in a population of preschool children and their mothers. Weekly average personal nitrogen dioxide exposures for subjects who resided in homes with one or more potential nitrogen dioxide source (e.g., a kerosene space heater, gas stove, or tobacco smoke) ranged between 16.3 and 50.6 ppb (30.6 and 95.1 micrograms/m3) for children and between 16.9 and 44.1 ppb (12.8 and 82.9 micrograms/m3) for mothers. In these individuals, the hydroxyproline-to-creatinine and desmosine-to-creatinine ratios were unrelated to personal nitrogen dioxide exposure--even though continuous monitoring documented home nitrogen dioxide concentration peaks of 100-475 ppb lasting up to 100 h in duration. Significantly higher hydroxyproline-to-creatinine and desmosine-to-creatinine ratios were observed in children, compared with mothers (p < .001 and .003, respectively).

Risk factors for the degradation of lung elastic fibers in the ventilated neonate. Implications for impaired lung development in bronchopulmonary dysplasia

In order to evaluate the risk for proteolytic destruction of lung parenchymal elastic fibers in ventilated premature infants, the concentrations of elastase were determined in tracheal aspirates of 65 infants from whom we obtained a total of 327 sequential samples. Elastase was detected at least once in 39 of the 65 infants studied. Eleven of these infants were ventilated with greater than 60% oxygen for greater than 5 days. In 19 infants, the presence of elastase was associated with positive bacterial and/or viral cultures and/or elevated ratios (greater than 0.22) of immature neutrophils to total neutrophils. Elastase was not detected in the lung secretions of 26 infants ventilated with greater than 60% oxygen for less than 3 days, suggesting minimal risk for elastic fiber destruction in the intubated infant who neither has pneumonia nor requires prolonged hyperoxic ventilation. The risk for elastic fiber destruction was further evaluated by analyzing sequential urine and tracheal aspirate samples for the presence of an elastolytic degradation product of elastin (desmosine). The biochemical data indicated a potential risk for proteolytic destruction of elastic fibers in association with infection and/or prolonged hyperoxic exposure. In addition, autopsy specimens obtained from three of the infants revealed structurally abnormal lung parenchymal elastic fibers. Because elastic fibers are believed to provide the structural support for alveolar septal development, proteolytic degradation of these fibers may be a significant factor in the impaired lung development that occurs in infants with bronchopulmonary dysplasia.

Elastase activity and surfactant protein concentration in tracheal aspirates from neonates receiving synthetic surfactant

Neutrophil elastase activity and the concentration of surfactant proteins A and B (SP-A, B) were measured in tracheal aspirate fluid from preterm neonates who were treated with the synthetic surfactant Exosurf Neonatal or air placebo in randomized, placebo-controlled, clinical trials. Elastase activity was transiently reduced in surfactant-treated infants on the second day of life, but the reduction was not sustained. In placebo-treated infants with established respiratory distress syndrome, tracheal aspirate SP-A was low on the first day of life and increased with time as respiratory distress syndrome resolved. In infants with respiratory distress syndrome treated with surfactant, significantly higher levels of SP-A were observed by 2 days after treatment and were maintained through at least the sixth day of life. These data suggest that lung inflammation is not increased and that endogenous surfactant secretion may be stimulated, not suppressed, by treatment with synthetic surfactant.

Urinary desmosine excretion as a marker of lung injury in the adult respiratory distress syndrome

Desmosine, the intermolecular and intramolecular cross link between the chains of elastin polypeptide, may be useful as a marker of a lung injury in adult respiratory distress syndrome (ARDS). A radioimmunoassay for rabbit antibody developed against desmosine, conjugated to bovine serum albumin, can detect as little as 100 pg of desmosine in plasma or urine. Desmosine is not metabolically absorbed, reused, or catabolized by the body, but rather eliminated unchanged in the urine as low molecular weight peptides. The lung is relatively rich in elastin, and we reasoned that a timed collection could be used as an index of elastin degradation in vivo. A 2-h collection of urine for desmosine assay was obtained at the time of Swan-Ganz catheter insertion in 41 consecutive patients. On the basis of clinical and initial Swan-Ganz catheter data, the patients were assigned to one of three groups: an ARDS group (n = 12); a cardiogenic pulmonary edema (CPE) group (n = 12); and a critically ill, nonpulmonary edema group (NPE, n = 17). The mean urine desmosine concentration (mg/L) for the ARDS group (0.728 +/- 0.22 SE) differed from the CPE group (0.149 +/- 0.07; p less than 0.001). The total excretion (microgram/2 h) was 64.95 +/- 24.7 in the ARDS group and 24.71 +/- 11.7 in the CPE group (p less than 0.05). Urine desmosine concentration/serum creatinine index for the ARDS group (0.78 +/- 0.28) was greater than in the CPE group (0.07 +/- 0.04; p = 0.019). Desmosine excretion was increased in the NPE group compared with CPE and ARDS groups, possibly reflecting heterogeneity in this group. In the differentiation of ARDS from CPE, we conclude that substantial increases in urinary desmosine excretion favor a diagnosis of ARDS.

Bronchoalveolar lavage desmosine in bleomycin-induced lung injury in marmosets and patients with adult respiratory distress syndrome

Measurement of urinary desmosine in experimental models of emphysema has been used to demonstrate elastin catabolism. In order to evaluate the hypothesis that accelerated elastin degradation also occurs in association with acute lung injury characterized by fibrotic repair, we prepared acid hydrolysates of lung lavage (LL) and used a radioimmunoassay for desmosine to measure concentrations of this elastic-specific cross-link in LL. Lavage desmosine (pmol/100 microliter LL) was measured following bleomycin-induced lung injury in marmosets and was shown to be elevated at 1 week (median 6.0, range 5.1-7.8), 2 weeks (8.4, 6.2-8.7), and 4 weeks (7.6, 4.8-7.8) compared to control levels (1.8, 1.4-3.7). Elevations of lavage desmosine after bleomycin were temporarily associated with remodeling of the lung as indicated by increased total lung collagen, reduced diffusing capacity and lung compliance, and histologic evidence of pulmonary fibrosis. Bronchoalveolar lavage (BAL) desmosine was measured in patients with the Adult Respiratory Distress Syndrome (ARDS) and compared with patients at risk, patients with other interstitial lung diseases, and normal healthy controls. BAL desmosine (pmol/100 microliters) was not significantly different in patients with ARDS (3.2, 2.1-3.0), patients at risk for ARDS (2.8, 2.5-4.4), and those with interstitial lung disease (3.0, 1.7-5.3) compared to normal controls (2.9, 1.9-4.7). There were poor correlations of BAL desmosine with physiologic indices of severity of disease in patients with ARDS and those at risk. Accelerated elastolysis occurred in the lower respiratory tract during the evaluation of bleomycin-induced pulmonary fibrosis in marmosets but was undetectable in BAL of patients studied within the first 3 days of ARDS.

Effects of dexamethasone and indomethacin on elastase, alpha 1-proteinase inhibitor, and fibronectin in bronchoalveolar lavage fluid from neonates

Elastase activity and concentrations of alpha 1-proteinase inhibitor, albumin, and fibronectin were measured in bronchoaleolar lavage (BAL) fluid from ventilated lungs in preterm neonates with lung disease before and after treatment with dexamethasone or indomethacin. Treatment with dexamethasone was associated with a significant decrease in BAL elastase activity but no change in fibronectin, albumin, or alpha 1-proteinase inhibitor concentrations. In contrast, treatment with indomethacin was associated with an increase in BAL elastase activity and fibronectin concentration, with no change in albumin or alpha 1-proteinase inhibitor concentrations. Control groups showed no changes in these BAL fluid biochemical markers during a similar time period. These data indicate that treatment with corticosteroids decreases lung inflammation as measured by BAL elastase activity. Corticosteroid treatment may not inhibit the development of pulmonary fibrosis, because fibronectin concentrations in BAL fluid were unaffected. Indomethacin treatment may augment lung inflammation and fibrosis by increasing BAL elastase activity and fibronectin concentration.

Oxidant-mediated lung disease in newborn infants

High concentrations of oxygen are administered with increased airway pressure to most preterm neonates with respiratory distress syndrome (RDS). Among 20% to 30% of survivors a form of chronic lung disease, bronchopulmonary dysplasia (BPD), develops. Its pathogenesis may include tissue damage caused by the superoxide anion (O2-) and other free oxygen radicals. Animal experiments and other data suggested a rationale for superoxide dismutase (SOD) administration in an effort to prevent or ameliorate BPD. Our preliminary studies in 19 prematures with RDS demonstrated its safety in human newborns and permitted measurement of its plasma levels. No adverse clinical findings occurred, and laboratory parameters were unchanged. Subcutaneous administration (0.25 mg/kg) of bovine SOD led to detectable levels at 1 1/2 h (mean 0.22 microgram/ml), with a slight rise to a higher peak at 2 1/2-4 h and a plateau over the remainder of the 12-h interval. Following doses 2-5, peak levels of 0.64 microgram/ml occurred at 4-8 h. With this background, a prospective double-blind controlled study of 45 neonates (mean gestational age, 29 weeks; birth weight, 1,100 g) showed a statistically significant reduction in prevalence of clinical and X-ray signs of BPD with fewer days of continuous positive airway pressure required. The safety and pharmacokinetics of bovine SOD were confirmed.