Architectural remodelling in acute and chronic interstitial lung disease: fibrosis or fibroelastosis?

Pulmonary fibroelastosis - A review

Elastin is a long-lived fibrous protein that is abundant in the extracellular matrix of the lung. Elastic fibers provide the lung the characteristic elasticity during inhalation with recoil during exhalation thereby ensuring efficient gas exchange. Excessive deposition of elastin and other extracellular matrix proteins reduces lung compliance by impairing ventilation and compromising gas exchange. Notably, the degree of elastosis is associated with the progressive decline in lung function and survival in patients with interstitial lung diseases. Currently there are no proven therapies which effectively reduce the elastin burden in the lung nor prevent dysregulated elastosis. This review describes elastin's role in the healthy lung, summarizes elastosis in pulmonary diseases, and evaluates the current understanding of elastin regulation and dysregulation with the goal of guiding future research efforts to develop novel and effective therapies.

Usual interstitial pneumonia: a review of the pathogenesis and discussion of elastin fibres, type II pneumocytes and proposed roles in the pathogenesis

The pathogenesis of idiopathic pulmonary fibrosis (IPF) and its histological counterpart, usual interstitial pneumonia (UIP) remains debated. IPF/UIP is a disease characterised by respiratory restriction, and while there have been recent advances in treatment, mortality remains high. Genetic and environmental factors predispose to its development and aberrant alveolar repair is thought to be central. Following alveolar injury, the type II pneumocyte (AEC2) replaces the damaged thin type I pneumocytes. Despite the interstitial fibroblast being considered instrumental in formation of the fibrosis, there has been little consideration for a role for AEC2 in the repair of the septal interstitium. Elastin is a complex protein that conveys flexibility and recoil to the lung. The fibroblast is presumed to produce elastin but there is evidence that the AEC2 may have a role in production or deposition. While the lung is an elastic organ, the role of elastin in repair of lung injury and its possible role in UIP has not been explored in depth. In this paper, pathogenetic mechanisms of UIP involving AEC2 and elastin are reviewed and the possible role of AEC2 in elastin generation is proposed.

Acute cylindrospermopsin exposure: Pulmonary and liver harm and mitigation by dexamethasone

Cylindrospermopsin (CYN) is a cyanotoxin of increasing worldwide environmental importance as it can harm human beings. Dexamethasone is a steroidal anti-inflammatory agent. Thus, we aimed at evaluating the pulmonary outcomes of acute CYN intoxication and their putative mitigation by dexamethasone. Male BALB/c mice received intratracheally a single dose of saline or CYN (140 μg/kg). Eighteen hours after exposure, mice instilled with either saline solution (Ctrl) or CYN were intramuscularly treated with saline (Tox) or 2 mg/kg dexamethasone (Tox + dexa) every 6 h for 48 h. Pulmonary mechanics was evaluated 66 h after instillation using the forced oscillation technique (flexiVent) to determine airway resistance (R_N), tissue viscance (G) and elastance (H). After euthanasia, the lungs were removed and separated for quantification of CYN, myeloperoxidase activity and IL-6 and IL-17 levels plus histological analysis. CYN was also measured in the liver. CYN increased G and H, alveolar collapse, PMN cells infiltration, elastic and collagen fibers, activated macrophages, peroxidase activity in lung and hepatic tissues, as well as IL-6 and IL-17 levels in the lung. Tox + Dexa mice presented total or partial reversion of the aforementioned alterations. Briefly, CYN impaired pulmonary and hepatic characteristics that were mitigated by dexamethasone.

Extracellular Matrix Component Remodeling in Respiratory Diseases: What Has Been Found in Clinical and Experimental Studies?

Changes in extracellular matrix (ECM) components in the lungs are associated with the progression of respiratory diseases, such as asthma, chronic obstructive pulmonary disease (COPD), and acute respiratory distress syndrome (ARDS). Experimental and clinical studies have revealed that structural changes in ECM components occur under chronic inflammatory conditions, and these changes are associated with impaired lung function. In bronchial asthma, elastic and collagen fiber remodeling, mostly in the airway walls, is associated with an increase in mucus secretion, leading to airway hyperreactivity. In COPD, changes in collagen subtypes I and III and elastin, interfere with the mechanical properties of the lungs, and are believed to play a pivotal role in decreased lung elasticity, during emphysema progression. In ARDS, interstitial edema is often accompanied by excessive deposition of fibronectin and collagen subtypes I and III, which can lead to respiratory failure in the intensive care unit. This review uses experimental models and human studies to describe how inflammatory conditions and ECM remodeling contribute to the loss of lung function in these respiratory diseases.

Proliferation of elastic fibres in idiopathic pulmonary fibrosis: a whole-slide image analysis and comparison with pleuroparenchymal fibroelastosis

AIMS

We occasionally encounter patients with idiopathic pulmonary fibrosis (IPF) who have similar imaging patterns to those of pleuroparenchymal fibroelastosis (PPFE) in the upper lung fields but are not diagnosed as having PPFE clinically. The aim of this study is to identify the clinicopathological features and intrapulmonary distribution of elastic fibres and collagen fibres in these patients.

METHODS AND RESULTS

We retrospectively reviewed the medical records of patients with a clinical diagnosis of IPF, and selected consecutive patients who underwent autopsy or pneumonectomy for lung transplantation. Patients with histologically confirmed PPFE were also reviewed for comparison. We quantified the collagen fibres and elastic fibres in each lobe as a percentage of the non-aerated lung area (collagen fibre score and elastic fibre score, respectively) in histological specimens by using whole-slide image analysis, and compared these scores between IPF and PPFE patients. In a total of 55 patients (IPF, 48; PPFE, 7), there were no significant differences in the collagen fibre scores between IPF and PPFE patients. The elastic fibre scores in the upper lobe in PPFE patients were significantly higher than those in IPF patients (23.5 versus 10.3, P = 0.005). However, it is of note that, in 12 of 48 IPF patients, the elastic fibre scores of the upper lobes were above the first quartile of those in PPFE patients.

CONCLUSIONS

IPF occasionally shows intense elastosis in the upper lobes, and such cases are histologically indistinguishable from PPFE. There seem to be histologically borderline cases between PPFE and IPF.

Mitochondria dysfunction: A novel therapeutic target in pathological lung remodeling or bystander?

The renascence in mitochondrial research has fueled breakthroughs in our understanding of mitochondrial biology identifying major roles in biological processes ranging from cellular oxygen sensing and regulation of intracellular calcium levels through to initiation of apoptosis or a shift in cell phenotype. Chronic respiratory diseases are no exception to the resurgent interest in mitochondrial biology. Microscopic observations of lungs from patients with chronic respiratory diseases such as pulmonary arterial hypertension, asthma and COPD show accumulation of dysmorphic mitochondria and provide the first evidence of mitochondrial dysfunction in diseased lungs. Recent mechanistic insights have established links between mitochondrial dysfunction or aberrant biogenesis and the pathogenesis of chronic respiratory diseases through playing a causative role in structural remodeling of the lung. The aim here is to discuss the case for a mitochondrial basis of lung remodeling in patients with chronic respiratory diseases. The present article will focus on the question of whether currently available data supports mitochondrial mechanisms as a viable point of therapeutic intervention in respiratory diseases and suggestions for future avenues of research in this rapidly evolving field.

Histological evolution of pleuroparenchymal fibroelastosis

AIMS

To investigate the histological evolution in the development of pleuroparenchymal fibroelastosis (PPFE).

METHODS AND RESULTS

We examined four patients who had undergone surgical lung biopsy twice, or who had undergone surgical lung biopsy and had been autopsied, and in whom the histological diagnosis of the first biopsy was not PPFE, but the diagnosis of the second biopsy or of the autopsy was PPFE. The histological patterns of the first biopsy were cellular and fibrotic interstitial pneumonia, cellular interstitial pneumonia (CIP) with organizing pneumonia, CIP with granulomas and acute lung injury in cases 1, 2, 3, and 4, respectively. Septal elastosis was already present in the non-specific interstitial pneumonia-like histology of case 1, but a few additional years were necessary to reach consolidated subpleural fibroelastosis. In case 3, subpleural fibroelastosis was already present in the first biopsy, but only to a small extent. Twelve years later, it was replaced by a long band of fibroelastosis. The septal inflammation and fibrosis and airspace organization observed in the first biopsies were replaced by less cellular subpleural fibroelastosis within 3-12 years.

CONCLUSIONS

Interstitial inflammation or acute lung injury may be an initial step in the development of PPFE.

Pleuroparenchymal Fibroelastosis: Its Clinical Characteristics

Pleuroparenchymal fibroelastosis (PPFE) is a rare pulmonary fibrosis that is clinically characterized by upperlobe predominant fibrosis. PPFE is a slowly progressive disorder and its first symptom is dyspnea or dry cough. Chest pain because of pneumothorax may be the first symptom in some patients. Patients with PPFE are slender with a flat rib cage or abnormally narrowed anterior-posterior thoracic dimension. Decreases in forced vital capacity, total lung capacity, and diffusing capacity are respiratory-function characteristics of PPFE, similar to those seen in idiopathic pulmonary fibrosis (IPF). The most remarkable difference in clinical features between PPFE and IPF is imaging findings, with upper-lobe-predominant lesions in PPFE and lower-lobe-predominant lesions in IPF.

Imunofenotipagem e remodelamento da matriz extracelular na sarcoidose pulmonar e extrapulmonar

OBJETIVO: Investigar o significado de marcadores de imunidade celular e de componentes elásticos/colágeno da matriz extracelular em estruturas granulomatosas em biópsias de pacientes com sarcoidose pulmonar ou extrapulmonar. MÉTODOS: Determinações qualitativas e quantitativas de células inflamatórias, de fibras de colágeno e de fibras elásticas em estruturas granulomatosas em biópsias cirúrgicas de 40 pacientes com sarcoidose pulmonar e extrapulmonar foram realizadas por histomorfometria, imuno-histoquímica, e técnicas de coloração com picrosirius e resorcina-fucsina de Weigert. RESULTADOS: A densidade de linfócitos, macrófagos e neutrófilos nas biópsias extrapulmonares foi significativamente maior do que nas biópsias pulmonares. Os granulomas pulmonares apresentaram uma quantidade significativamente maior de fibras de colágeno e menor densidade de fibras elásticas que os granulomas extrapulmonares. A quantidade de macrófagos nos granulomas pulmonares correlacionou-se com CVF (p < 0,05), ao passo que as quantidades de linfócitos CD3+, CD4+ e CD8+ correlacionaram-se com a relação VEF1/CVF e com CV. Houve correlações negativas entre CPT e contagem de células CD1a+ (p < 0,05) e entre DLCO e densidade de fibras colágenas/elásticas (r = -0,90; p = 0,04). CONCLUSÕES: A imunofenotipagem e o remodelamento apresentaram características diferentes nas biópsias dos pacientes com sarcoidose pulmonar e extrapulmonar. Essas diferenças correlacionaram-se com os dados clínicos e espirométricos dos pacientes, sugerindo que há duas vias envolvidas no mecanismo de depuração de antígenos, que foi mais eficaz nos pulmões e linfonodos.

Small airway remodeling in acute respiratory distress syndrome: a study in autopsy lung tissue

INTRODUCTION

Airway dysfunction in patients with the Acute Respiratory Distress Syndrome (ARDS) is evidenced by expiratory flow limitation and dynamic hyperinflation. These functional alterations have been attributed to closure/obstruction of small airways. Airway morphological changes have been reported in experimental models of acute lung injury, characterized by epithelial necrosis and denudation in distal airways. To date, however, no study has focused on the morphological airway changes in lungs from human subjects with ARDS. The aim of this study is to evaluate structural and inflammatory changes in distal airways in ARDS patients.

METHODS

We retrospectively studied autopsy lung tissue from subjects who died with ARDS and from control subjects who died of non pulmonary causes. Using image analysis, we quantified the extension of epithelial changes (normal, abnormal and denudated epithelium expressed as percentages of the total epithelium length), bronchiolar inflammation, airway wall thickness, and extracellular matrix (ECM) protein content in distal airways. The Student's t-test or the Mann-Whitney test was used to compare data between the ARDS and control groups. Bonferroni adjustments were used for multiple tests. The association between morphological and clinical data was analyzed by Pearson rank test.

RESULTS

Thirty-one ARDS patients (A: PaO2/FiO2 ≤200, 45 ± 14 years, 16 males) and 11 controls (C: 52 ± 16 years, 7 males) were included in the study. ARDS airways showed a shorter extension of normal epithelium (A:32.9 ± 27.2%, C:76.7 ± 32.7%, P < 0.001), a larger extension of epithelium denudation (A:52.6 ± 35.2%, C:21.8 ± 32.1%, P < 0.01), increased airway inflammation (A:1(3), C:0(1), P = 0.03), higher airway wall thickness (A:138.7 ± 54.3 μm, C:86.4 ± 33.3 μm, P < 0.01), and higher airway content of collagen I, fibronectin, versican and matrix metalloproteinase-9 (MMP-9) compared to controls (P ≤0.03). The extension of normal epithelium showed a positive correlation with PaO2/FiO2 (r2 = 0.34; P = 0.02) and a negative correlation with plateau pressure (r2 = 0.27; P = 0.04). The extension of denuded epithelium showed a negative correlation with PaO2/FiO2 (r2 = 0.27; P = 0.04).

CONCLUSIONS

Structural changes in small airways of patients with ARDS were characterized by epithelial denudation, inflammation and airway wall thickening with ECM remodeling. These changes are likely to contribute to functional airway changes in patients with ARDS.

Lung parenchymal mechanics in health and disease

The mechanical properties of lung tissue are important determinants of lung physiological functions. The connective tissue is composed mainly of cells and extracellular matrix, where collagen and elastic fibers are the main determinants of lung tissue mechanical properties. These fibers have essentially different elastic properties, form a continuous network along the lungs, and are responsible for passive expiration. In the last decade, many studies analyzed the relationship between tissue composition, microstructure, and macrophysiology, showing that the lung physiological behavior reflects both the mechanical properties of tissue individual components and its complex structural organization. Different lung pathologies such as acute respiratory distress syndrome, fibrosis, inflammation, and emphysema can affect the extracellular matrix. This review focuses on the mechanical properties of lung tissue and how the stress-bearing elements of lung parenchyma can influence its behavior.

Asbestosis: demonstration of distinctive interstitial fibroelastosis: a pilot study

Asbestosis has long been defined as a diffuse interstitial "fibrotic" process, in similarity to other chronic interstitial pulmonary diseases. To address the hypothesis (which was based on morphological nuances) that the interstitial connective tissue response in asbestosis may be fibroelastotic rather than fibrotic, a comparative characterization of the connective response in cases of asbestosis and other forms of interstitial lung disease was performed. Archival open lung biopsies or autopsy specimens of pulmonary diseases featuring interstitial connective tissue abnormalities (15 of asbestosis, 21 of organizing pneumonia, 15 usual interstitial pneumonitis/idiopathic pulmonary fibrosis [IPF], 9 organizing diffuse alveolar damage, 9 "nonspecific" interstitial pneumonitis, 4 sarcoidosis, 3 each of desquamative interstitial pneumonia and chronic amiodarone toxicity, 2 cryptogenic organizing pneumonias, and 1 each of chronic hypersensitivity pneumonitis and chronic eosinophilic pneumonitis [85 total]) were stained histochemically with hematoxylin and eosin, Perl's method, Gomori's trichrome procedure, and the Verhoeff-van Gieson technique. Representative subsets of the cases (n = 20) were also studied immunohistologically using an antibody to elastin. Fibroelastosis in each of the samples was assessed for the degree of response and its location using a 3-tiered scale. The degree of fibroelastosis in the 15 cases of asbestosis was variable, with the pattern being peribronchial and perivascular in all instances; at least 2 asbestos bodies were identified in fibroelastotic foci in each of the 15 cases as highlighted with Perl's stain. Forty-seven cases of nonasbestotic lung disease (71%) showed interstitial fibrosis with a variable (usually modest) amount of admixed elastic tissue; when present, elastic fibers were distributed in a diffuse interstitial pattern, with or without perivascular accentuation. All cases of IPF also showed areas of fibroelastosis, but those foci were confined to regions of overt "honeycomb" change. No asbestos bodies were seen in any disease except asbestosis, and a predominantly peribronchial pattern of fibroelastosis was not identified in any nonasbestotic interstitial lung disease in this study. The authors conclude that the types and patterns of pulmonary connective tissue response in interstitial lung diseases may provide additional diagnostic clues to the presence of asbestosis.

Effects of amiodarone on lung tissue mechanics and parenchyma remodeling

We studied the results of chronic oral administration of amiodarone on in vitro lung tissue mechanics, light and electron microscopy. Fifteen Wistar male rats were divided into three groups. In control (CTRL) group animals received saline (0.5 mL/day). In amiodarone (AMIO) groups, amiodarone was administered by gavage at a dose of 175 mg/kg 5 days per week for 6 (6AMIO) or 12 weeks (12AMIO). Lung tissue strips were analyzed 24h after the last drug administration. Tissue resistance and elastance were higher in 6AMIO and 12AMIO than in CTRL, while hysteresivity was similar in all groups. Total amount of collagen fibers in lung parenchyma increased progressively with the time course of the lesion. However, at 6 weeks there was an increase in the amount of type III collagen fibers, while in 12AMIO mainly type I collagen fibers were found. In our study amiodarone increased lung tissue impedance that was accompanied by matrix remodeling and lesion of type II pneumocytes.

The extracellular matrix of the lung and its role in edema formation

The extracellular matrix is composed of a three-dimensional fiber mesh filled with different macromolecules such as: collagen (mainly type I and III), elastin, glycosaminoglycans, and proteoglycans. In the lung, the extracellular matrix has several functions which provide: 1) mechanical tensile and compressive strength and elasticity, 2) low mechanical tissue compliance contributing to the maintenance of normal interstitial fluid dynamics, 3) low resistive pathway for an effective gas exchange, d) control of cell behavior by the binding of growth factors, chemokines, cytokines and the interaction with cell-surface receptors, and e) tissue repair and remodeling. Fragmentation and disorganization of extracellular matrix components comprises the protective role of the extracellular matrix, leading to interstitial and eventually severe lung edema. Thus, once conditions of increased microvascular filtration are established, matrix remodeling proceeds fairly rapidly due to the activation of proteases. Conversely, a massive matrix deposition of collagen fiber decreases interstitial compliance and therefore makes the tissue safety factor stronger. As a result, changes in lung extracellular matrix significantly affect edema formation and distribution in the lung.

Inflammatory related changes in lung tissue mechanics after bleomycin-induced lung injury

The impact of lung remodelling in respiratory mechanics has been widely studied in bleomycin-induced lung injury. However, little is known regarding the relationship between the amount of lung inflammation and pulmonary tissue mechanics. For this purpose, rats were intratracheally instilled with bleomycin (n=29) or saline (n=8) and sacrificed at 3, 7, or 15 days. Forced oscillatory mechanics as well as indices of remodelling (elastic fibre content and hydroxyproline) and inflammation (myeloperoxidase content, total cell count, alveolar wall thickness, and lung water content) were studied in lung tissue strips. Tissue resistance increased significantly at day 15, while hysteresivity was significantly higher in bleomycin group compared to control at all time points. Elastic fibres, hydroxyproline and myeloperoxidase contents augmented after bleomycin at days 7 and 15. Tissue resistance and hysteresivity were significantly correlated with myeloperoxidase, elastic fibre and lung water content. In conclusion, inflammatory structural changes and elastogenesis are the main determinants for hysteretic changes in this 2-week bleomycin-induced lung injury model.

A novel method for quantification of the folding of elastic laminae in elastic arteries

A transgenic mouse overexpressing the human form of semicarbazide-sensitive amine oxidase (SSAO) is known to have an abnormal structure of the elastic laminae and the elastic fibres in the aorta. Compared to the non-transgenic littermates, the elastic laminae are less folded. In order to quantify the undulation of this structure, an image analysis program that identified the elastic laminae was developed. The program measures the area fraction in different sectors from a plane parallel to the aorta wall. Images were taken from unstained aorta specimens where the elastic laminae were visualised with phase contrast microscopy. A contextual operation of the images produced a local orientation estimation for every linear structure. The image was then thresholded in eight sectors from 0 degrees to 180 degrees , with different orientation angles. The results show that the area fraction of the elastic laminae was significantly lower for the transgenic mouse in all sectors measured except for two. At 0-25 degrees , no difference was seen. In the sector at 160-180 degrees , parallel to the aorta wall, the area fraction of elastic laminae was instead significantly higher in the transgenic mouse. A novel method is presented, developed for detection and quantification of pathological changes in the elastic laminae in the aorta wall. The method gave reliable results and is considered to be a useful tool for morphometric studies of aorta with this kind of altered morphology concerning the elastic laminae. When compared with tangent count, the control group had a significantly larger mean curvature.

Abnormal deposition of collagen/elastic vascular fibres and prognostic significance in idiopathic interstitial pneumonias

BACKGROUND

Vascular remodelling has recently been shown to be a promising pathogenetic indicator in idiopathic interstitial pneumonias (IIPs).

AIM

To validate the importance of the collagen/elastic system in vascular remodelling and to study the relationships between the collagen/elastic system, survival and the major histological patterns of IIPs.

METHODS

Collagen/elastic system fibres were studied in 25 patients with acute interstitial pneumonia/diffuse alveolar damage, 22 with non-specific interstitial pneumonia/non-specific interstitial pneumonia and 55 with idiopathic pulmonary fibrosis/usual interstitial pneumonia. The Picrosirius polarisation method and Weigert's resorcin-fuchsin histochemistry and morphometric analysis were used to evaluate the amount of vascular collagen/elastic system fibres and their association with the histological pattern of IIPs. The association between vascular remodelling and the degree of parenchymal fibrosis in usual interstitial pneumonia (UIP) was also considered.

RESULTS

The vascular measurement of collagen/elastic fibres was significantly higher in UIP than in the lungs of controls, and in those with diffuse alveolar damage and those with non-specific interstitial pneumonia. In addition, the increment of collagen/elastic fibres in UIP varied according to the degree and activity of the parenchymal fibrosis. The most important predictors of survival in UIP were vascular remodelling classification and vascular collagen deposition.

CONCLUSION

A progressive vascular fibroelastosis occurs in IIP histological patterns, probably indicating evolutionarily adapted responses to parenchymal injury. The vascular remodelling classification and the increase in vascular collagen were related to survival in IIP and possibly play a role in its pathogenesis. Further studies are needed to determine whether this relationship is causal or consequential.

Morphological and functional determinants of fluoxetine (Prozac)-induced pulmonary disease in an experimental model

Fluoxetine treatment effects were determined by evaluating respiratory mechanics (elastance/resistance) and exhaled nitric oxide, as well as mononuclear and polymorphonuclear cell recruitment into the lungs, in an experimental guinea pig model. Guinea pigs were divided into four groups: Fl (fluoxetine only, n=7); Fl+Sw (fluoxetine and forced swimming, n=7); Ns+Sw (normal saline and forced swimming, n=8); and Ns (normal saline only, n=8). Treated animals received oral fluoxetine (10 mg/(kg day)) for 30 consecutive days. On day 31, all animals were anesthetized and mechanically ventilated so that respiratory system elastance and resistance, as well exhaled nitric oxide, could be determined. The lungs were then excised en bloc for histological and immunohistochemical evaluation. Forced swimming induced bronchodilation in untreated animals and bronchoconstriction in fluoxetine-treated animals. Fluoxetine treatment was also associated with mononuclear infiltration (predominantly into alveolar walls) and neutrophil recruitment. In addition, levels of exhaled nitric oxide, an inflammatory marker, were higher in fluoxetine-treated animals. Swimming-induced stress also amplified mononuclear cell recruitment to the lungs. These results show that, in this experimental model, fluoxetine treatment reproduces the pathology of chronic interstitial pneumonia in humans.

Idiopathic and collagen vascular disease nonspecific interstitial pneumonia: clinical significance of remodeling process

Recently, active remodeling may indicate a good prognosis in idiopathic interstitial pneumonias. In this study we sought to validate the importance of the collagen/elastic system in the extracellular matrix remodeling and to study the relationships between the collagen/elastic system in nonspecific interstitial idiopathic pneumonia (NSIP) and collagen vascular disease associated with nonspecific interstitial idiopathic pneumonia (CVD-NSIP). We examined collagen/elastic system fibers in open lung biopsies of 20 idiopathic NSIP and 21 CVD-NSIP patients. The clinical features were analyzed with respect to age, gender, pulmonary functional tests, chest X-ray and computed tomography, treatment, and survival. We used the picrosirius polarization method and Weigert's resorcin-fuchsin histochemistry and morphometric analysis to evaluate the amount of collagen/elastic system fibers and their association with the NSIP histologic pattern. No differences in clinical features and pulmonary function tests were observed between idiopathic NSIP and CVD-NSIP, but a significantly higher collagen and elastic fiber proliferation was detected in CVD-NSIP lungs and fibrosing NSIP histologic pattern. Multivariate Cox model analysis demonstrated that sex and quantitative elastic fiber staining added important prognostic information (p=0.01) and was indicative of a worse prognosis than collagen staining. A cut point at the mean staining of 1.5% for elastic fibers divided the patients into two groups with distinctive survival times. Those with elastic fibers greater than 1.5% had a median survival time of just 52 months. We concluded that idiopathic NSIP and CVD-NSIP were clinically similar but pathologically different, suggesting that different remodeling profiles in NSIP may represent evolutionary adapted responses to injury grade, which depend, at least in part, on the extent of elastic extracellular matrix deposition. Patients with greater than 1.5% of elastic fibers comprise a subset with a high risk for dying due to NSIP and may be an appropriate target for prospective studies.

Pleurodesis induced by talc or silver nitrate: evaluation of collagen and elastic fibers in pleural remodeling

This study evaluated the extracellular matrix (collagen and elastic fibers) in pleurodesis induced by intrapleural talc (TL) or silver nitrate (SN). Study subjects were 420 rabbits divided into two groups and sacrificed from 15 min to 12 months after the injection of the sclerosing agents at intervals previously defined. Pleural adhesions and fibrosis were graded (0-4), and the collagen and elastin were quantified. The maximum score of the pleural adhesions was observed two months after TL (2.80 +/- 0.99) and 15 days after SN (3.75 +/- 0.25). More intense pleural adhesions were observed in the SN group from day 5 (p < 0.05). Pleural thickness and pleural fibrosis were, in general, significantly higher after SN (p < 0.05). Increased deposition of collagen and elastin was observed in both groups but was more evident in the SN group. In the TL group, a linear correlation was observed between pleural adhesions and fibrosis (r = 0.775), between pleural adhesions and collagen (r = 0.779), and between fibrosis and collagen (r = 0.709). In the SN group, these correlations were acceptable (r = 0.605, 0.665, and 0.663). The elastin presented a correlation of 0.707 (p < 0.001) in the TL group and of 0.564 (p < 0.001) in the SN group. In conclusion, intrapleural 0.5% silver nitrate and talc (400 mg/kg) are effective in the induction of pleurodesis. However, the intensity of adhesions and the richness of collagen after SN, in combination with the early onset of tissue remodeling, demonstrate the local superiority of this agent. Considering the easy availability and instillation, the low cost, and the absence of important side effects, silver nitrate might be considered as a sclerosing agent to induce pleurodesis in humans.

Immune Cell Infiltration and Broncovascular Remodeling After Nitric Acid Nasal Instillation in a Mouse Bronchiolitis Obliterans Model

Immune cell airway infiltration and the bronchovascular remodeling process have shown to be promising in the understanding of bronchiolitis obliterans (BO) pathogenesis. In this study we sought to validate the importance of immune cells, whether diffusely distributed or forming lymphoid follicles, collagen density, and vascular factors. Eight weeks after a single nitric acid (NA) nasal instillation, lung changes were characterized by lumen distortion, epithelial layer folding, reduction or total obliteration of terminal bronchiole (TB) lumen, and wall thickness increase. The morphologic changes in the TB and TA (terminal artery) lumen coincide with the measurement difference in the three groups. The TB diameter and lumen were significantly decreased in BO when compared with non-BO lungs (0.76 +/- 0.05 microm vs. 0.81 +/- 0.05 microm and 12,286.13 +/- 378.83 microm vs. 18,182.27 +/- 5,593.98 microm, p = 0.05 and p = 0.01, respectively). Equally significant was the increase in TB thickness in BO when compared with the non-BO group (201.72 +/- 35.75 microm vs. 149.75 +/- 40.61 microm, p = 0.007). The morphologic changes in immune cells seen in TB, TA, and bronchus-associated lymphoid tissue (BALT) also coincide with the quantification differences observed in the three groups. We concluded that immune cell infiltration and collagen/vascular remodeling are related to the spectrum of histologic changes in a BO nasal-induced model in mice and may be an appropriate target for prospective studies of human bronchiolitis.

Active remodeling in idiopathic interstitial pneumonias: evaluation of collagen types XII and XIV

Fibril-associated collagens with interrupted triple helices (FACITs) XII and XIV act as fibril organizers and assist in the maintenance of uniform fibril size. We investigated the spatial expression patterns of collagens XII and XIV in cryptogenic organizing pneumonia (COP)/organizing pneumonia (OP) and in idiopathic pulmonary fibrosis (IPF)/usual interstitial pneumonia (UIP) and compared them to normal human lung. Study subjects included 10 patients with COP/OP, 10 patients with IPF/UIP, and 8 control subjects. Immunostaining for collagens XII and XIV was carried out in paraffin-embedded human lung tissue sections. Picrosirius red histochemical staining for collagen I expression and electron microcopy to evaluate fibril diameter were also performed. In normal lung, collagens XII and XIV were expressed in perivascular and subpleural connective tissue. In COP/OP, both collagens showed intense staining in perivascular connective tissue, thickened alveolar septae, and subpleural areas. In IPF/UIP, XII and XIV were expressed in perivascular connective tissue, in areas of established fibrosis, and in areas of subpleural thickening. Only collagen XII was expressed in granulation tissue plugs in COP/OP and in fibroblastic foci in IPF/UIP. Collagen type I was overexpressed in fibrotic areas. Electron micrographs revealed obvious fibril diameter alteration and fusion in the same areas. FACITs XII and XIV are expressed in normal and fibrotic lung. Unlike collagen XIV, collagen XII was expressed in granulation tissue plugs in COP/OP and in fibroblast foci in IPF/UIP. This may suggest a possible distinct role for both collagens in the modulation of the extracellular matrix during the onset of fibrotic process.

Measurement of pulmonary edema in patients with acute respiratory distress syndrome*

OBJECTIVE

We measured pulmonary edema by thermal indocyanine green-dye double-dilution technique and quantitative computed tomography (CT) in patients with acute respiratory distress syndrome and compared the two techniques.

DESIGN AND SETTING

Prospective human study in a university hospital.

PATIENTS

Fourteen mechanically ventilated patients with acute respiratory distress syndrome (nine primary; nine with intubation <7 days).

INTERVENTIONS

All patients underwent a spiral CT of the thorax. We measured pulmonary thermal volume (PTV) and its components, extravascular lung water and pulmonary blood volume, with an integrated fiberoptic monitoring system (COLD Z-021).

MEASUREMENTS AND RESULTS

PTV was tightly correlated with lung weight (LW) measured by CT (PTV = 0.6875 * LW(CT) + 292.77; correlation coefficient = 0.91; p < .0001; bias -11 +/- 8 %). Neither etiology of acute respiratory distress syndrome (primary vs. secondary) nor days of intubation affected the accuracy of thermal dye dilution in comparison with CT. There was no correlation between the extravascular lung water (12.3 +/- 3.4 mL/kg) and CT distribution of lung tissue compartments. Extravascular lung water and pulmonary blood volume showed good reproducibility in 32 pairs of thermal dye dilution measurements.

CONCLUSIONS

Measurements of lung edema by thermal indocyanine green-dye double-dilution method show good correlation with those by quantitative computed tomography and good reproducibility in patients with acute respiratory distress syndrome.

Time course of lung parenchyma remodeling in pulmonary and extrapulmonary acute lung injury

The aim of this study is to test the hypothesis that the early changes in lung mechanics and the amount of type III collagen fiber do not predict the evolution of lung parenchyma remodeling in pulmonary and extrapulmonary acute lung injury (ALI). For this purpose, we analyzed the time course of lung parenchyma remodeling in murine models of pulmonary and extrapulmonary ALI with similar degrees of mechanical compromise at the early phase of ALI. Lung histology (light and electron microscopy), the amount of elastic and collagen fibers in the alveolar septa, the expression of matrix metalloproteinase-9, and mechanical parameters (lung-resistive and viscoelastic pressures, and static elastance) were analyzed 24 h, 1, 3, and 8 wk after the induction of lung injury. In control (C) pulmonary (p) and extrapulmonary (exp) groups, saline was intratracheally (it; 0.05 ml) instilled and intraperitoneally (ip; 0.5 ml) injected, respectively. In ALIp and ALIexp groups, mice received Escherichia coli lipopolysaccharide (10 microg it and 125 microg ip, respectively). At 24 h, all mechanical and morphometrical parameters, as well as type III collagen fiber content, increased similarly in ALIp and ALIexp groups. In ALIexp, all mechanical and histological data returned to control values at 1 wk. However, in ALIp, static elastance returned to control values at 3 wk, whereas resistive and viscoelastic pressures, as well as type III collagen fibers and elastin, remained elevated until week 8. ALIp showed higher expression of matrix metalloproteinase-9 than ALIexp. In conclusion, insult in pulmonary epithelium yielded fibroelastogenesis, whereas mice with ALI induced by endothelial lesion developed only fibrosis that was repaired early in the course of lung injury. Furthermore, early functional and morphological changes did not predict lung parenchyma remodeling.

Collagen and elastic system in the remodelling process of major types of idiopathic interstitial pneumonias (IIP)

AIMS

Structural remodelling in acute and chronic idiopathic interstitial pneumonia (IIP) has been extensively investigated, but little attention has been directed to the elastic tissue in these situations. The aim of this study was to determine whether elastic deposition accompanies collagen deposition in the four major histological patterns of IIP: diffuse alveolar damage (DAD), organizing pneumonia (OP), non-specific interstitial pneumonia (NSIP) and usual interstitial pneumonia (UIP).

METHODS AND RESULTS

We measured, by image analysis, the content of fibres of the collagenous and elastic systems of the alveolar septum in histological slides of open lung biopsies, using the picrosirius-polarization method and Weigert's resorcin-fuchsin stain, respectively. Five groups were studied: 10 cases of DAD; nine cases of OP; nine cases of NSIP; and 10 cases of UIP. Four normal lungs were used for comparison. The content of collagen fibres was significantly higher in UIP when compared to DAD, NSIP, OP and normal lung. The content of elastic fibres was increased in comparison with normal lungs but this was not significantly different among the histological patterns.

CONCLUSION

Acute and chronic IIP cause a similar increase in the collagen and elastic contents of the lungs, representing a process of 'fibroelastosis' rather than an exclusive process of fibrosis. A profibrogenic mechanism is responsible for the unparallelled collagen augmentation observed in UIP subjects, the nature of which is yet to be determined.

Endotoxin-induced lung injury in mice: structural, functional, and biochemical responses

Acute lung injury is usually a complication of sepsis, and endotoxin treatment of mice is a frequently used experimental model. To define this model and to clarify pathogenesis of the lung injury, we injected with 1 mg/kg endotoxin ip and measured pulmonary function, pulmonary edema, serum concentrations of cytokines and growth factors, and lung histology over 48 h. During the first 6 h, tidal volume and minute volume increased and respiratory frequency decreased. Serum concentrations of cytokines showed three patterns: 10 cytokines peaked at 2 h and declined rapidly, two peaked at 6 h and declined, and two had biphasic peaks at 2 and 24 h. Growth factors increased later and remained elevated longer. Both collagen and fibronectin were deposited in the lungs beginning within hours of endotoxin and resolving over 48 h. Histologically, lungs showed increased cellularity at 6 h with minimal persistent inflammation at 48 h. Lung water peaked at 6 h and gradually decreased over 48 h. We conclude that intraperitoneal administration of endotoxin to mice causes a transient systemic inflammatory response and transient lung injury and dysfunction. The response is characterized by successive waves of cytokine release into the circulation, early evidence of lung fibrogenesis, and prolonged increases in growth factors that may participate in lung repair.

Vascular remodeling process in reversibility of pulmonary arterial hypertension secondary to congenital heart disease

Pulmonary vascular remodeling process was analyzed using morphometry in lung biopsy specimens taken from 26 children, aged 6 to 160 months, who had congenital heart disease and significant pulmonary arterial hypertension. Reparative surgery was performed in 22 patients and palliative surgery was performed in four patients. One patient expired postoperatively and four others after hospital discharge. Vascular remodeling examination revealed a characteristic pathological picture: pronounced medial thickening with increased collagen content (fibrosis), without significant arterial intimal proliferation. At a mean follow-up of 44 months, 72% of the survivors were asymptomatic with no medication. Diagnosed by echocardiogram, 22% of these patients were shown to have pulmonary arterial hypertension. The characteristic pathological features described above occurred in 38% of the patients who either expired or had pulmonary hypertension postoperatively. These findings were an aid to identifying a high risk group in which the outcome does not meet expectations for the classical grade I and II changes. We concluded that the presence of isolated medial thickening does not ensure either survival or a normal postoperative pulmonary arterial pressure at late follow-up and that the collagen content can be a better reference for good outcome. Early intracardiac repair is recommended before the development of significant medial fibrosis.

Synovial Remodeling Process Induced by Type V Collagen Immunization in Rabbits

The pathogenesis of diffuse connective tissue diseases is still unknown despite studies of the autoimmunity aspects related to extracellular matrix elements, mainly the collagens. Articulations are frequently affected by the synovitis process in these diseases. The objective of the present study was to verify the morphologic aspects of the synovial membrane of rabbits immunized with type V collagen, which has some particular characteristics 75 days after the first antigen inoculation and when compared to control animals. The synovial membrane of the animals sacrificed after 75 days of immunization presented an intense remodeling phenomenon along the connective tissue screen and interlobular septa of the adipose-muscle tissue screen compartment. The remodeling process determined type I and III collagen fiber depositions in the vascular and connective tissue compartments of the synovial membrane. The nutrient vessels of the adipose-muscle compartment showed a similar remodeling process, which resulted in small vessel occlusion. Few residual inflammatory foci consisting of monocytes and eosinophils were observed. Thus, our experimental model reproduces morphologic changes in different tissues, characterized by an extracellular matrix remodeling process similar to those observed in many diffuse connective tissue diseases such as systemic lupus erytematosus and scleroderma. Therefore, this model could be useful in understanding the pathogenesis and the treatment of these diseases.

Acute remodeling of parenchyma in pulmonary and extrapulmonary ARDS. An autopsy study of collagen-elastic system fibers

This study aimed at evaluating acute pulmonary remodeling, focusing on alterations of fibers of the collagenous and elastic systems in ARDS in the exudative phase according to the etiology of the disease. ARDS patients (n = 23), who died in our institution between 1989 and 1997, were retrospectively studied. Ten patients who died in accidents, without any pathological changes in the lung, and ten patients with Congestive Heart Failure (CHF), submitted to mechanical ventilation, were used as control groups. Histological slides were sampled from the autopsied lungs and stained by the Picrosirius and Weigert's resorcin-fuchsin methods. The fiber content of the collagenous and elastic systems of the alveolar septum was measured by image analysis. All patients were in the early ARDS phase (n = 23), 10 pulmonary and 13 extra-pulmonary diseases. Collagen content was greater in pulmonary (1.23+/-0.27) than in extra-pulmonary (0.92+/-0.39) ARDS in the early phase of the disease (p = 0.05). No differences were observed concerning the elastic fibers' content. Extracellular matrix (ECM) remodeling occurs early in the development of acute lung injury and appears to depend on the site of initial insult (pulmonary or extrapulmonary). The present study provides the basis for a prospective, controlled investigation.

Amyloid associated with elastin-staining laminar aggregates in the lungs of patients diagnosed with acute respiratory distress syndrome

BACKGROUND

The heterogeneity of conditions underlying respiratory distress, whether classified clinically as acute lung injury (ALI) or the more severe acute respiratory distress syndrome (ARDS), has hampered efforts to identify and more successfully treat these patients. Examination of postmortem lungs among cases clinically diagnosed as ARDS identified a cohort that showed a consistent morphology at the light and electron microscope levels, and featured pathognomonic structures which we termed elastin-staining laminar structures (ELS).

METHODS

Postmortem tissues were stained using the Verhoeff-Van Gieson procedure for elastic fibers, and with Congo red for examination under a polarizing microscope. Similar samples were examined by transmission EM.

RESULTS

The pathognomonic ELS presented as ordered molecular aggregates when stained using the Verhoeff-van Gieson technique for elastic fibers. In several postmortem lungs, the ELS also displayed apple-green birefringence after staining with Congo red, suggesting the presence of amyloid. Remarkably, most of the postmortem lungs with ELS exhibited no significant acute inflammatory cellular response such as neutrophilic reaction, and little evidence of widespread edema except for focal intra-alveolar hemorrhage.

CONCLUSIONS

Postmortem lungs that exhibit the ELS constitute a morphologically-identifiable subgroup of ARDS cases. The ordered nature of the ELS, as indicated by both elastin and amyloid stains, together with little morphological evidence of inflammation or edema, suggests that this cohort of ARDS may represent another form of conformational disease. If this hypothesis is confirmed, it will require a new approach in the diagnosis and treatment of patients who exhibit this form of acute lung injury.