Lungenfibrose

Many, different diseases can result in pulmonary fibrosis and its prevalence is continuously increasing. Pulmonary fibrosis is defined by a diffuse accumulation of connective tissue in the interstitial space resulting in destruction of lung parenchyma. Older individuals are more often affected by this disease than younger. Approximately one half of all patients with pulmonary fibrosis suffer from rheumatic diseases. The classification of pulmonary fibrosis was revised 1998. Now 6 different types of interstitial pneumonia according to 6 different pathologic patterns are newly defined. Still, there is no efficient treatment known, which resolves fibrotic lung remodeling. However, immunosuppressive treatment strategies are established in pulmonary fibrosis evoked by inflammatory processes.     

Heterogeneous proliferative characteristics of human adult lung fibroblast lines and clonally derived fibroblasts from control and fibrotic tissue

Pulmonary fibrosis results from an altered deposition of collagen within the lung parenchyma. This alteration is likely the result of both increased fibroblast proliferation and abnormalities in fibroblast collagen metabolism. Although the development of pulmonary fibrosis is preceded by inflammatory events in the lung, it is unclear whether altered fibroblast behavior requires continuous exposure to inflammatory mediators or alternatively results from the emergence in the lung of fibroblast populations possessing characteristics such as to explain the abnormalities seen in pulmonary fibrosis. To examine the latter hypothesis, we have established a number of fibroblast cell lines from control (C) lung tissue as well as from tissue from patients with active pulmonary fibrosis (PF), and have examined their in vitro proliferative characteristics. Our data show that PF fibroblasts proliferate significantly faster compared to C fibroblasts under standard culture conditions. We have also examined the in vitro proliferative characteristics of a substantial number of clonally derived fibroblasts. We report that a marked heterogeneity exists in terms of proliferation and also that a small but significant number of fast-growing clones are present in panels of clones derived from fibrotic tissue. These data suggest that there exists in fibrotic tissue, clones of fibroblasts with intrinsic growth characteristics which could in itself explain the increased fibroblast proliferation seen in pulmonary fibrosis. The fibrotic clones may emerge as dominant in the fibrotic lung under conditions of injury and repair likely to favor the expansion of this phenotype.     

The rapamycin analogue SDZ RAD attenuates bleomycin-induced pulmonary fibrosis in rats.

Pulmonary fibrosis is characterized by excessive deposition of extracellular matrix proteins within the pulmonary interstitium. The new macrolide immunosuppressant SDZ RAD, a rapamycin analogue, inhibits growth-factor dependent proliferation of mesenchymal cells and might therefore be of therapeutic interest for the treatment of fibrotic lung disease. In this study the effect of SDZ RAD on lung-collagen accumulation in the bleomycin model of pulmonary fibrosis in rats was investigated. SDZ RAD (2.5 mg x kg(-1) x day(-1)) or drug vehicle were administered orally by daily gavage. Successful dosing was confirmed by measuring splenic weight. Total lung-collagen content was measured by high-performance liquid chromatographic quantitation of hydroxyproline. In animals given bleomycin and drug vehicle, total lung collagen was increased by 182+/-11% (mean+/-SEM) compared with saline controls at 14 days (p<0.001). The increase in lung-collagen accumulation was reduced by 75+/-12% (p<0.01) in animals given SDZ RAD and was accompanied by a concomitant 56+/-6% (p<0.001) reduction in lung weight. SDZ RAD is currently in clinical trials for the prevention of solid organ graft rejection, another condition characterized by excessive extracellular matrix production. The authors propose that SDZ RAD warrants evaluation as a novel therapeutic agent for fibrotic lung disease.     

Integrin alpha4beta1 regulates migration across basement membranes by lung fibroblasts: a role for phosphatase and tensin homologue deleted on chromosome 10

Idiopathic pulmonary fibrosis is a disease that is characterized by fibroblast accumulation and activation in the distal airspaces of the lung. We hypothesized that fibrotic lung fibroblasts migrate/invade across basement membranes by integrin-mediated mechanisms as a means of entering alveoli. We demonstrate that in lung fibroblasts derived from patients with idiopathic pulmonary fibrosis, fibronectin signaling is both necessary and sufficient for basement membrane migration/invasion across basement membranes. This effect is mediated through the alpha5beta1 integrin because blockade of fibronectin-alpha5 integrin ligation attenuated this response. In contrast, ligation of alpha4beta1 integrin inhibits basement membrane invasion by normal lung fibroblasts but not by fibrotic lung fibroblasts. This phenotypic difference is not related to surface expression of the alpha4beta1 integrin, as demonstrated by flow cytometry. In normal lung fibroblasts but not in fibrotic lung fibroblasts, we show that ligation of alpha4beta1 integrin induces a significant increase in phosphatase and tensin homologue deleted on chromosome 10 (PTEN) activity. Fibrotic lung fibroblasts express constitutively less PTEN mRNA and protein as well as phosphatase activity in comparison to normal lung fibroblasts. Together, these data suggest that a loss of alpha4beta1 signaling via PTEN confers a migratory/invasive phenotype to fibrotic lung fibroblasts. Furthermore, this study implicates a loss of PTEN function in the pathophysiology of idiopathic pulmonary fibrosis.     

Lung reflexes and receptor activity in a rabbit model of pulmonary fibrosis

Our objective was to see if activity of individual slowly and rapidly adapting pulmonary receptors was changed by pulmonary fibrosis. Diffuse interstitial lung fibrosis of several weeks’ standing was induced in 8 rabbits. They displayed changes in lung mechanics and patterns of breathing, when compared to control rabbits, similar to those seen in patients who develop pulmonary fibrosis. Lung reflexes in the fibrotic rabbits were more profoundly changed than eupneic breathing in a way that could be interpreted as slowly adapting receptor activity, which was increased, being overpowered by a prepotent input from pulmonary rapidly adapting receptors. An increase in number of active rapidly adapting receptors was found in the fibrotic rabbits during direct vagal recording. We have demonstrated that pulmonary receptor activity is changed by lung fibrosis. It may be that these changes in receptor activity produce conflicting respiratory drives that could result in the sensation of dyspnea.     

Lung reflexes and receptor activity in a rabbit model of pulmonary fibrosis.

Our objective was to see if activity of individual slowly and rapidly adapting pulmonary receptors was changed by pulmonary fibrosis. Diffuse interstitial lung fibrosis of several weeks' standing was induced in 8 rabbits. They displayed changes in lung mechanics and patterns of breathing, when compared to control rabbits, similar to those seen in patients who develop pulmonary fibrosis. Lung reflexes in the fibrotic rabbits were more profoundly changed than eupneic breathing in a way that could be interpreted as slowly adapting receptor activity, which was increased, being overpowered by a prepotent input from pulmonary rapidly adapting receptors. An increase in number of active rapidly adapting receptors was found in the fibrotic rabbits during direct vagal recording. We have demonstrated that pulmonary receptor activity is changed by lung fibrosis. It may be that these changes in receptor activity produce conflicting respiratory drives that could result in the sensation of dyspnea.     

Antifibrotic therapy for the treatment of pulmonary fibrosis.

Fibroproliferative lung disease is prevalent and associated with high mortality. The pathogenesis of fibrotic lung disease involves inflammation, mesenchymal cell proliferation, and deposition of interstitial matrix components, such as collagen and fibronectin. Corticosteroids and other immunosuppressive medications have been routinely employed, but have demonstrated only marginal efficacy. Even though this information has been known for some time, the optimal medical regimen for treating pulmonary fibrosis remains largely undefined. This article addresses the rationale for, and efficacy of, antifibrotic regimens used to treat humans with fibrotic lung diseases.     

Mechanical aspects of lung fibrosis: a spotlight on the myofibroblast

Contractile myofibroblasts are responsible for the irreversible alterations of the lung parenchyma that hallmark pulmonary fibrosis. In response to lung injury, a variety of different precursor cells can become activated to develop myofibroblast features, most notably formation of stress fibers and expression of α-smooth muscle actin. Starting as an acute and beneficial repair process, myofibroblast secretion of collagen and contraction frequently becomes excessive and persists. The result is accumulation of stiff scar tissue that obstructs and ultimately destroys lung function. In addition to being a consequence of myofibroblast activities, the stiffened tissue is also a major promoter of the myofibroblast. The mechanical properties of scarred lung and fibrotic foci promote myofibroblast contraction and differentiation. One essential element in this detrimental feed-forward loop is the mechanical activation of the profibrotic growth factor transforming growth factor-β1 from stores in the extracellular matrix. Interfering with myofibroblast contraction and integrin-mediated force transmission to latent transforming growth factor-β1 and matrix proteins are here presented as possible therapeutic strategies to halt fibrosis.     

Production of collagenase and tissue inhibitor of metalloproteinases by fibroblasts derived from normal and fibrotic human lungs.

Several experiments have demonstrated low collagenolytic activity during the development of pulmonary fibrosis. In order to determine if fibroblasts play a role in this alteration, procollagenase and tissue inhibitor of metalloproteinases (TIMP) were quantified in fibroblasts derived from 12 human lung specimens (normal = 6, idiopathic pulmonary fibrosis [IPF] = 6). Under basal conditions, three cell strains from normal and three from fibrotic lung specimens did not synthesize collagenase and a similar number of normal and IPF-derived fibroblast strains produced the enzyme. However, the rate of enzyme synthesis among normal and fibrotic collagenase producing fibroblasts exhibited significant differences. Thus, whereas normal fibroblasts produced more than 300 ng/ml, fibrotic lung fibroblasts secreted approximately half of this amount (115 +/- 67 ng/ml). Phorbol myristate acetate (PMA) enhanced collagenase production in all of the 12 lung fibroblast lines tested. In four IPF fibroblasts, PMA increased collagenase secretion close to those of normal stimulated lung fibroblasts; however, a lower induction was observed in cell strains from two fibrotic lung specimens. There was a wide variation in TIMP production both in normal and fibrotic lung fibroblasts, and no statistically significant difference was observed. Under basal conditions, TIMP levels ranged from 329 to 16,911 ng/ml in normal lung cells, and from 377 to 17,557 in fibrotic lung fibroblasts. PMA induced a severalfold increase in all cell lines. These results suggest that there are subpopulations of lung fibroblasts with different potential to produce collagenase and TIMP in vitro, and that the predominance of low collagenase-producing subsets may contribute to the development of fibrosis.     

Idiopathic pulmonary fibrosis: prevailing and evolving hypotheses about its pathogenesis and implications for therapy

Idiopathic pulmonary fibrosis is a progressive and usually fatal lung disease characterized by fibroblast proliferation and extracellular matrix remodeling, which result in irreversible distortion of the lung's architecture. Although the pathogenetic mechanisms remain to be determined, the prevailing hypothesis holds that fibrosis is preceded and provoked by a chronic inflammatory process that injures the lung and modulates lung fibrogenesis, leading to the end-stage fibrotic scar. However, there is little evidence that inflammation is prominent in early disease, and it is unclear whether inflammation is relevant to the development of the fibrotic process. Evidence suggests that inflammation does not play a pivotal role. Inflammation is not a prominent histopathologic finding, and epithelial injury in the absence of ongoing inflammation is sufficient to stimulate the development of fibrosis. In addition, the inflammatory response to a lung fibrogenic insult is not necessarily related to the fibrotic response. Clinical measurements of inflammation fail to correlate with stage or outcome, and potent anti-inflammatory therapy does not improve outcome. This review presents a growing body of evidence suggesting that idiopathic pulmonary fibrosis involves abnormal wound healing in response to multiple, microscopic sites of ongoing alveolar epithelial injury and activation associated with the formation of patchy fibroblast-myofibroblast foci, which evolve to fibrosis. Progress in understanding the fibrogenic mechanisms in the lung is likely to yield more effective therapies.     

The vitronectin-binding function of PAI-1 exacerbates lung fibrosis in mice

Plasminogen activator inhibitor-1 (PAI-1) is increased in the lungs of patients with pulmonary fibrosis, and animal studies have shown that experimental manipulations of PAI-1 levels directly influence the extent of scarring that follows lung injury. PAI-1 has 2 known properties that could potentiate fibrosis, namely an antiprotease activity that inhibits the generation of plasmin, and a vitronectin-binding function that interferes with cell adhesion to this extracellular matrix protein. To determine the relative importance of each PAI-1 function in lung fibrogenesis, we administered mutant PAI-1 proteins that possessed either intact antiprotease or vitronectin-binding activity to bleomycin-injured mice genetically deficient in PAI-1. We found that the vitronectin-binding capacity of PAI-1 was the primary determinant required for its ability to exacerbate lung scarring induced by intratracheal bleomycin administration. The critical role of the vitronectin-binding function of PAI-1 in fibrosis was confirmed in the bleomycin model using mice genetically modified to express the mutant PAI-1 proteins. We conclude that the vitronectin-binding function of PAI-1 is necessary and sufficient in its ability to exacerbate fibrotic processes in the lung.     

Association between pulmonary fibrosis and coronary artery disease

BACKGROUND: Pulmonary fibrosis and atherosclerosis have many similarities at the histopathologic level. Moreover, fibrotic lung diseases exhibit systemic effects and have the potential to affect the vasculature beyond the lung. The existence of a relationship between the two, however, has not been studied. METHODS: To investigate whether fibrotic lung disorders may predispose to atherosclerosis, we conducted a cross-sectional study of 630 patients referred for lung transplantation evaluation at a university hospital. We compared the prevalence of angiographic coronary artery disease (CAD) in patients with fibrotic vs nonfibrotic lung diseases. RESULTS: Fibrotic lung diseases were associated with an increased prevalence of CAD compared with nonfibrotic diseases after adjustment for traditional risk factors (odds ratio, 2.18; 95% confidence interval, 1.17-4.06). The magnitude and significance of this association were maintained when only nongranulomatous fibrotic disease or its subset, idiopathic pulmonary fibrosis, was examined. The strength of the relationship between fibrotic disorders and CAD increased when multivessel disease was analyzed (odds ratio, 4.16; 95% confidence interval, 1.46-11.9). No significant association was detected for granulomatous fibrotic disorders (odds ratio, 1.56; 95% confidence interval, 0.47-5.16; P =.47), although this subgroup had fewer cases of CAD for analysis. CONCLUSIONS: These findings support an association between fibrotic lung disorders and CAD. Further research is necessary to confirm this relationship and to explore the pathologic processes underlying, and potentially linking, these 2 conditions.     

Rolipram attenuates bleomycin A5-induced pulmonary fibrosis in rats

Background and objective:   Pulmonary fibrosis has a poor prognosis. The pathogenesis of fibrotic disorders is unclear, but the extent of lung damage due to persistent inflammation is regarded as a critical factor. Rolipram inhibits inflammation induced by various stimuli, as well as the chemotaxis of fibroblasts. In this study rolipram was used to treat pulmonary fibrosis induced by bleomycin A5 in rats, and the possible mechanisms were investigated.
Methods:   Rolipram (0.25 mg/kg) was administered intraperitoneally daily, following intratracheal instillation of bleomycin A5 (5 mg/kg). Animals were killed at 7 or 28 days after bleomycin A5 instillation, and indices of lung damage and fibrosis were evaluated.
Results:   Bleomycin A5 induced pulmonary inflammation and fibrosis, increased the levels of malondialdehyde and tumour necrosis factor-α and enhanced accumulation of collagen in the lungs. Rolipram administration significantly attenuated these effects.
Conclusions:   Rolipram ameliorated pulmonary inflammation and fibrosis induced by bleomycin A5 in rats. The effects of rolipram may be associated with its antioxidant activity and inhibition of tumour necrosis factor-α production.     

Collagen synthesis by normal and fibrotic human lung fibroblasts and the effect of transforming growth factor-beta

Collagen accumulation is a major feature of pulmonary fibrosis and other fibrotic lesions. We have studied the synthesis of collagens in fibroblasts cultured from normal and fibrotic human lung specimens and evaluated how it is affected by transforming growth factor-beta (TGF-beta). Fibroblasts were obtained from normal and fibrotic adult human lungs (n = 11; normal = 6, idiopathic pulmonary fibrosis = 5). They were exposed to TGF-beta and pulse-labeled with [3H]proline and [3H]glycine. Collagen production was measured as bacterial collagenase-susceptible radioactivity, and collagen mRNA levels were determined by a solution hybridization assay using labeled procollagen alpha 1[I] cDNA clone HF677 as probe. Synthesis of collagen types I, III, and V were assessed after separating them by DEAE-cellulose chromatography and SDS-polyacrylamide gel electrophoresis. The results showed that both normal and fibrotic lung fibroblasts synthesized similar amounts of collagen. Type I was the major collagen species synthesized by both normal and fibrotic cell types, and the relative proportion of type I, III, and V collagens was similar in both cell types. TGF-beta caused a two to fourfold increase in stimulation of collagen production and collagen mRNA levels, and no differences were detected in the response of normal and fibrotic lung fibroblasts. All collagen types were stimulated by the TGF-beta. TGF-beta did not increase fibroblast proliferation and the majority of normal and fibrotic lung cells exposed to TGF-beta remained in G1 phase of the cell cycle. We conclude that fibroblasts of normal and fibrotic human synthesize similar amounts of collagens.(ABSTRACT TRUNCATED AT 250 WORDS)     

Idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis is a devastating, age-related lung disease of unknown cause that has few treatment options. This disease was once thought to be a chronic inflammatory process, but current evidence indicates that the fibrotic response is driven by abnormally activated alveolar epithelial cells (AECs). These cells produce mediators that induce the formation of fibroblast and myofibroblast foci through the proliferation of resident mesenchymal cells, attraction of circulating fibrocytes, and stimulation of the epithelial to mesenchymal transition. The fibroblast and myofibroblast foci secrete excessive amounts of extracellular matrix, mainly collagens, resulting in scarring and destruction of the lung architecture. The mechanisms that link idiopathic pulmonary fibrosis with ageing and aberrant epithelial activation are unknown; evidence suggests that the abnormal recapitulation of developmental pathways and epigenetic changes have a role. In this Seminar, we review recent data on the clinical course, therapeutic options, and underlying mechanisms thought to be involved in the pathogenesis of idiopathic pulmonary fibrosis.     

The pulmonary vasculature in haematite lung

A histological study was made of the pulmonary vasculature in two cases of haematite lung. Between fibrotic nodules in the lung the muscular pulmonary arteries showed the development of longitudinal muscle in the intima, a change thought to be associated with stretch and distortion of these vessels. In some arteries this muscular layer in the intima showed secondary fibrosis. No muscularized pulmonary arterioles were seen, indicating an absence of constriction of the terminal portions of the pulmonary arterial tree. Pulmonary arteries in fibrotic areas had become progressively engulfed by the fibrous tissue. The occlusive and obliterative vascular changes in 'haematite lung' are in reality those of silicosis which are brought about by the inhalation of silica particles with the iron sesquioxide. The only feature peculiar to haematite lung is the intense accumulation of iron-containing dust in and around the pulmonary blood vessels.     

Aberrant mural cell recruitment to lymphatic vessels and impaired lymphatic drainage in a murine model of pulmonary fibrosis

Pulmonary fibrosis is a progressive disease with unknown etiology that is characterized by extensive remodeling of the lung parenchyma, ultimately resulting in respiratory failure. Lymphatic vessels have been implicated with the development of pulmonary fibrosis, but the role of the lymphatic vasculature in the pathogenesis of pulmonary fibrosis remains enigmatic. Here we show in a murine model of pulmonary fibrosis that lymphatic vessels exhibit ectopic mural coverage and that this occurs early during the disease. The abnormal lymphatic vascular patterning in fibrotic lungs was driven by expression of platelet-derived growth factor B (PDGF-B) in lymphatic endothelial cells and signaling through platelet-derived growth factor receptor (PDGFR)-β in associated mural cells. Because of impaired lymphatic drainage, aberrant mural cell coverage fostered the accumulation of fibrogenic molecules and the attraction of fibroblasts to the perilymphatic space. Pharmacologic inhibition of the PDGF-B/PDGFR-β signaling axis disrupted the association of mural cells and lymphatic vessels, improved lymphatic drainage of the lung, and prevented the attraction of fibroblasts to the perilymphatic space. Our results implicate aberrant mural cell recruitment to lymphatic vessels in the pathogenesis of pulmonary fibrosis and that the drainage capacity of pulmonary lymphatics is a critical mediator of fibroproliferative changes.     

Chitotriosidase activity in patients with interstitial lung diseases

BACKGROUND: In previous papers, we found significantly higher activity of chitotriosidase, a macrophage derived enzyme, in serum and BAL of patients with sarcoidosis, especially in those with progressing disease and lung involvement, than in controls. Locally and systemically produced chitotriosidase activity was correlated with radiological stage and also with degree of lung infiltration, suggesting that this enzyme may play a role in the pathogenesis of sarcoidosis and may be used as a marker of disease severity. AIM: To analyse chitotriosidase activity in serum and bronchoalveolar lavage of patients with idiopathic pulmonary fibrosis and pulmonary fibrosis associated with systemic sclerosis and to compare it with chitotriosidase activity in controls and sarcoidosis patients. METHODS: Chitotriosidase activity was determined by a fluorometric assay. RESULTS: The results showed that serum chitotriosidase activity was only elevated in sarcoidosis patients; in patients with idiopathic pulmonary fibrosis and pulmonary fibrosis associated with systemic sclerosis it was in the normal range. On the contrary, in BAL of sarcoidosis and idiopathic pulmonary fibrosis patients the activity was significantly higher than in controls. CONCLUSION: Serum chitotriosidase is a potential marker of sarcoidosis severity; it increases in sarcoidosis in relation to radiological stage and degree of lung infiltration. The increase in chitotriosidase activity in BAL of sarcoidosis and idiopathic pulmonary fibrosis patients suggests that the enzyme could be involved in fibrogenesis in diffuse lung diseases. Further research is needed to understand the role of chitotriosidase in the pathogenesis of sarcoidosis and its involvement in fibrotic remodelling in certain diffuse lung diseases.     

Glucose Transporter-1 Distribution in Fibrotic Lung Disease: Association With [18F]-2-Fluoro-2-Deoxyglucose-PET Scan Uptake,Inflammation, and Neovascularization

Background[¹⁸F]-2-fluoro-2-deoxyglucose (FDG)-PET scan uptake is increased in areas of fibrosis and honeycombing in patients with idiopathic pulmonary fibrosis (IPF). Glucose transporter-1 (Glut-1) is known to be the main transporter for FDG. There is a paucity of data regarding the distribution of Glut-1 and the cells responsible for FDG binding in fibrotic lung diseases.MethodsWe applied immunofluorescence to localize Glut-1 in normal, IPF, and Hermansky-Pudlak syndrome (HPS) pulmonary fibrosis lung tissue specimens as well as an array of 19 different lung neoplasms. In addition, we investigated Glut-1 expression in inflammatory cells from BAL fluid (BALF) from healthy volunteers, subjects with IPF, and subjects with HPS pulmonary fibrosis.ResultsIn normal lung tissue, Glut-1 immunoreactivity was seen on the surface of erythrocytes. In tissue sections from fibrotic lung diseases (IPF and HPS pulmonary fibrosis), Glut-1 immunoreactivity was present on the surface of erythrocytes and inflammatory cells. BALF inflammatory cells from healthy control subjects showed no immunoreactivity; BALF cells from subjects with IPF and HPS pulmonary fibrosis showed Glut-1 immunoreactivity associated with neutrophils and alveolar macrophages.ConclusionsGlut-1 transporter expression in normal lung is limited to erythrocytes. In fibrotic lung, erythrocytes and inflammatory cells express Glut-1. Together, these data suggest that FDG-PET scan uptake in IPF could be explained by enhanced inflammatory and erythrocytes uptake due to neovascularization seen in IPF and not an upregulation of metabolic rate in pneumocytes. Thus, FDG-PET scan may detect inflammation and neovascularization in lung fibrosis.