Lung Fibrosis In Rats Research Articles

Differential immunolocalization of VEGF in rat and human adult lung, and in experimental rat lung fibrosis: light, fluorescence, and electron microscopy.

Vascular endothelial growth factor (VEGF) is a cytokine with main angiogenetic functions in embryonic development and tumor-formation. In the adult lung, reports of the localization of VEGF were controversial. A precise cell typing of VEGF-positive pulmonary cells is still lacking. Nothing is known about a potential role in pulmonary fibrosis. Immunohistochemistry (IH), double immunofluorescence microscopy (DIF), and immunoelectron microscopy (IEM) were used to study the differential distribution of VEGF in paraffin-embedded (IH, DIF) and in cryo-substituted, Lowicryl-embedded (IEM) specimens of normal rat and human lungs and fibrotic rat lungs. Fibrosis was induced by intratracheal bleomycin treatment. IH and DIF showed that VEGF was present in surfactant protein (SP) D-positive alveolar type II pneumocytes, bronchiolar Clara cells, smooth muscle (SM) cells, and alpha-SM actin-positive myofibroblasts of normal rat and human lungs. Fibrotic lesions in bleomycin-treated rat lungs were rich in VEGF-positive cells presenting with a heterogeneous phenotype (mainly SP-D-positive type II pneumocytes, alpha-SM actin-positive myofibroblasts). There were no signs of angiogenesis. Post-embedding immunogold labeling using protein A-gold and IgG-gold technique revealed a specific localization of VEGF to mitochondria, Clara cell secretory granules, and capillary interendothelial cell junctions. The predominant localization of VEGF to bronchiolar and alveolar epithelial and alpha-SM actin-positive cells, and the marked increase of VEGF-positive type II pneumocytes and myofibroblasts in fibrotic lung lesions, indicate that in adult lungs VEGF is involved in processes other than angiogenesis.

Biochemical and connective tissue changes in cyclophosphamide-induced lung fibrosis in rats

The present investigation was designed to characterize the biochemical and connective tissue components and to correlate the significance of morphological and biochemical perturbations in cyclophosphamide (CP)-induced lung fibrosis in rats. Lung fibrosis was induced in male Wistar rats by intraperitoneal injection of 20 mg/100 g body weight of CP, and their pneumotoxic derangements were characterized during an early destructive phase followed by a proliferative and synthetic phase. Serum angiotensin-converting enzyme (ACE) activity was higher in CP-treated rats at days 2, 3, 5, 7, and 11, but there was a significant decrease in lung ACE activity during the same time period. Elevated levels of β-glucuronidase activity were observed in the lung lavage fluid of CP-administered rats days 2, 3, 5, and 7. Lung myeloperoxidase activity was higher in CP rats. Of significance was the presence of collagenase and collagenolytic cathepsin in the lavage fluid of CP rats, when compared with the barely detectable levels in controls. A similar increase in these enzyme activities was also noticed in the lung tissue of CP rats during the same experimental period. Lavage fluid hydroxyproline content was higher in CP rats when compared with controls. Similarly, lung protein and DNA levels were elevated significantly after treatment with CP. The pulmonary histamine and serotonin contents were significantly higher in CP rats. The incorporation of [ 3H]thymidine into lung total DNA, [ 3H]proline into lung hydroxyproline, and [ 35S]sulphate into lung glycosaminoglycan, measured as indicators of lung DNA, collagen, and glycosaminoglycan synthesis, respectively, was also higher in CP groups. Increased levels of hydroxyproline, elastin, hexosamine, total hexose, fucose, sialic acid, and uronic acid in the lungs of rats 14, 28, and 42 days after CP insult were characterized as biomarkers of CP-induced interstitial changes. These findings indicate that CP-induced lung fibrosis results in alterations not only in collagen synthesis and accumulation, but also in glycosaminoglycan and glycoprotein content.

Double intratracheal instillation of keratinocyte growth factor prevents bleomycin-induced lung fibrosis in rats.

Alveolar re-epithelialization is necessary in the repair of damaged alveolar epithelium after lung injury. Keratinocyte growth factor (KGF) has been shown to be a potent proliferation and differentiation factor for rat alveolar type II cells. The present study examined whether KGF would prevent bleomycin-induced lung fibrosis. Adult rats were anaesthetized and recombinant human KGF (rhKGF) (150 micrograms/kg) or saline was injected intratracheally at 48 h before and 24 h after bleomycin (Bleo, 5 mg/kg) instillation. Seven and 14 days after the last administration, rat lungs were processed for lung physiology, immunohistochemistry, and in situ hybridization. Double instillation of KGF prevented the loss of body weight and reduction in total lung capacity (TLC) due to Bleo, and markedly attenuated the protein accumulation and mRNA expression of collagen types I and III and the decreased expression of surfactant protein mRNAs in the fibrotic lesions of Bleo-treated rats. KGF may play an important role in maintaining alveolar epithelium and repairing the damaged epithelium after lung injury.

Double intratracheal instillation of keratinocyte growth factor prevents bleomycin‐induced lung fibrosis in rats

Alveolar re-epithelialization is necessary in the repair of damaged alveolar epithelium after lung injury. Keratinocyte growth factor (KGF) has been shown to be a potent proliferation and differentiation factor for rat alveolar type II cells. The present study examined whether KGF would prevent bleomycin-induced lung fibrosis. Adult rats were anaesthetized and recombinant human KGF (rhKGF) (150 μg/kg) or saline was injected intratracheally at 48 h before and 24 h after bleomycin (Bleo, 5 mg/kg) instillation. Seven and 14 days after the last administration, rat lungs were processed for lung physiology, immunohistochemistry, and in situhybridization. Double instillation of KGF prevented the loss of body weight and reduction in total lung capacity (TLC) due to Bleo, and markedly attenuated the protein accumulation and mRNA expression of collagen types I and III and the decreased expression of surfactant protein mRNAs in the fibrotic lesions of Bleo-treated rats. KGF may play an important role in maintaining alveolar epithelium and repairing the damaged epithelium after lung injury. © 1998 John Wiley & Sons, Ltd.

Induction of pulmonary fibrosis in organ-cultured rat lung by cadmium chloride and transforming growth factor- β1

Cadmium chloride (CdCl 2) exposure has been reported to induce pulmonary fibrosis in rats. Accumulating evidence has shown that cytokines play a pivotal role in the excessive production of connective tissue components in pulmonary fibrosis. In this report, rat lung slice cultures were used to study the synergistic involvement of transforming growth factor- β1 (TGF- β1) in CdCl 2-induced alveolar fibrosis. Rat lung slices were maintained at the interphase of air and medium on a polyester mesh stretched on a plastic scaffold. Treatment of lung slices with 2.5, 5 or 10 μM CdCl 2 for 7 days resulted in 85, 40 and 6% respectively for relative survival. Under these culture conditions, CdCl 2 alone did not induce alveolar fibrosis in rat lung slices. However, in the presence of 0.5 ng/ml TGF- β1, CdCl 2 at a dose ranging from 1 to 5 μM increased the thickness of alveolar septa. Furthermore, the thickness of alveolar septa in lung slices treated with CdCl 2 was dose-dependently increased by the presence of TGF- β1. The thickened alveolar septa were apparently due to the deposition of excessive extracellular matrix, as revealed by trichrome stain and ultrastructural examination. Our results also show that fibrogenic activity induced by the combined treatment with CdCl 2 and TGF- β1 can be reduced by co-treatment with 200 μg/ml λ-carrageenan, a TGF- β1 inhibitor. Therefore, the present results indicate that TGF- β1 can synergistically stimulate the fibrogenic activity in lung tissue subsequent to CdCl 2 injury.

Upregulation of the PDGF-alpha receptor precedes asbestos-induced lung fibrosis in rats.

Platelet-derived growth factor-AA (PDGF-AA) and its matching alpha receptor (PDGF-R alpha) are upregulated in rat lung fibroblasts (RLFs) after exposure to chrysotile asbestos fibers in vitro, which results in asbestos-induced RLF proliferation. We now report our in vivo observations, which show an increase in the expression of PDGF-R alpha mRNA, but not PDGF-beta receptor mRNA, in asbestos-exposed rat lungs when compared with RNA from air-exposed (sham) and iron-exposed lungs. Western analysis of membrane preparations confirmed the observations on mRNA expression by demonstrating an increase in PDGF-R alpha peptide expression in the asbestos-exposed rat lungs, compared with that in the air-exposed lungs. Immunohistochemistry for the PDGF-R alpha was performed on air- and asbestos-exposed rat lungs and revealed a clear increase in staining within interstitial and subepithelial compartments in the exposed animals. These observations, along with our previous report demonstrating an increase in the PDGF-AA isoform expression immediately after asbestos-exposure, suggest a scenario in which a potent lung mesenchymal cell mitogen, PDGF-AA, and its alpha-receptor are upregulated prior to the development of a fibroproliferative lung lesion, and thus may play a central role in the pathogenesis of asbestos-induced lung fibrosis.

Adenovector-mediated gene transfer of active transforming growth factor-beta1 induces prolonged severe fibrosis in rat lung.

Transforming growth factor (TGF)-beta1 has been implicated in the pathogenesis of fibrosis based upon its matrix-inducing effects on stromal cells in vitro, and studies demonstrating increased expression of total TGF-beta1 in fibrotic tissues from a variety of organs. The precise role in vivo of this cytokine in both its latent and active forms, however, remains unclear. Using replication-deficient adenovirus vectors to transfer the cDNA of porcine TGF-beta1 to rat lung, we have been able to study the effect of TGF-beta1 protein in the respiratory tract directly. We have demonstrated that transient overexpression of active, but not latent, TGF-beta1 resulted in prolonged and severe interstitial and pleural fibrosis characterized by extensive deposition of the extracellular matrix (ECM) proteins collagen, fibronectin, and elastin, and by emergence of cells with the myofibroblast phenotype. These results illustrate the role of TGF-beta1 and the importance of its activation in the pulmonary fibrotic process, and suggest that targeting active TGF-beta1 and steps involved in TGF-beta1 activation are likely to be valuable antifibrogenic therapeutic strategies. This new and versatile model of pulmonary fibrosis can be used to study such therapies.

Biochemical and morphological characterization of carbon tetrachloride-induced lung fibrosis in rats.

The short-term and long-term lung CCl4 injuries in rats were studied by i.p. CCl4 for 2 or 5 weeks, respectively, and the lung injury in the third progression group receiving i.p. CCl4 for 2 weeks followed by 3 weeks without. Acute haemorrhagic interstitial pneumonia resulted from short-term injury; chronic interstitial pneumonia from long term injury, and residua of injury or advanced chronic interstitial pneumonia in the progression group. All groups also exhibited features for diffuse alveolar damage. Connective tissue stains revealed both interstitial and intra-alveolar fibrosis in short-term injury. Hydroxyproline content and the activities of prolyl hydroxylase and galactosylhydroxylysyl glucosultransferase were elevated. This suggests an early onset of pulmonary fibrosis. Immunohistochemistry revealed the interstitial accumulation of BM proteins. In contrast, increased type III pN-collagen could also be found in the intra-alveolar spaces. The degrees of both interstitial and intra-alveolar fibrosis, BM proteins and type III pN-collagen, and also hydroxyproline content were greater in long-term injury, while the progression group showed on average fewer fibrotic changes than did the long-term injury group, but more than the short-term injury pointing to persistence or progression of the changes. Additionally, intra-alveolar crystallized haemoglobin was found following short-term injury. We conclude that CCl4-induced lung injury is an useful experimental model to study pulmonary fibrosis. The mechanism of CCl4 lung injury is not known but free radical-mediated lipid peroxidation is suggested.

Bronchiolarized Metaplasia and Interstitial Fibrosis in Rat Lungs Chronically Exposed to High Ambient Levels of Ozone

The cellular and tissue changes in the lungs of rats were studied using electron microscopy following 20 months exposure to a range of ozone levels from 0.12 to 1.0 ppm. Male and female Fischer 344 rats were exposed and morphometric methods were used to determine the volume, surface area, and cellular changes observed in bronchiole-alveolar duct regions following chronic ozone exposure. No major gender-related effects were observed in response to chronic inhalation of ozone nor were significant effects of ozone exposure found in either terminal bronchioles or the proximal alveolar regions in animals chronically exposed to 0.12 ppm ozone. The proximal alveolar regions of animals exposed for 20 months to 0.5 and 1.0 ppm ozone were significantly altered with exposure. The high-dose, long-term exposure to ozone resulted in a pronounced increase in volume of both the interstitium and epithelium in the proximal alveolar regions. The thickening of the epithelium was due to a change in tissue type from the normal squamous epithelium to a cuboidal epithelium similar, but not identical, to that found in terminal bronchioles. This bronchiolar epithelial metaplasia of proximal alveolar ducts, which was dose related, was composed of differentiated ciliated and Clara cells similar to those found in terminal bronchioles. In addition, unique cells which contained morphologic features of many different cell types were observed. These cells, which may represent stem cells or differentiated but transformed cells, were found associated with the bronchiolar metaplasia of alveolar ducts. In conjunction with the epithelial changes, cellular and matrix components in the interstitium were increased with chronic exposure to 0.5 and 1.0 ppm ozone. All matrix components were increased including collagen, elastin, and basement membrane, as well as other acellular spaces which did not contain identifiable structures. The total volume of interstitial fibroblasts was also increased in the high-dose exposure group. Alveolar macrophages were increased only in the 1.0 ppm exposed animals. The cell and tissue changes in the terminal bronchioles were less pronounced indicating a relative resistance of this tissue to ozone and mainly consisted of a change in cell type from ciliated to Clara cells in the 1.0 ppm exposed animals. The relative resistance of bronchiolar tissue to high concentration ozone exposure and the extensive bronchiolar epithelial metaplasia seen in the alveolar ducts suggest that bronchiolar metaplasia may be an adaptive mechanism following chronic ozone exposure. The bronchiolar epithelial metaplasia and interstitial fibrosis seen with high-dose chronic ozone exposure are similar to, and may be a model for, the early steps in human fibrotic diseases such as idiopathic pulmonary fibrosis.

Neoformation of blood vessels in association with rat lung fibrosis induced by bleomycin.

We have used intratracheal instillation of bleomycin in rats to study the microanatomical changes of blood vessels associated with lung fibrosis. Bleomycin is a toxic cytostatic drug employed in classical models of lung fibrosis. Wistar rats were submitted to intratracheal injection of 1.5 units of bleomycin and sacrificed 2.5 months later, a timing when marked fibrosis of the lung is observed. We casted the vascular tree of the rat lungs by perfusion with a methacrylate resin. These casts were studied by scanning electron microscopy. Lung tissue was also studied by light microscopy and thin section electron microscopy. The major vascular modifications observed in the bleomycin-treated rats were: (1) neoformation of an elaborate network of vessels located in the peribronchial domains of the lung, and (2) distortion of the architecture of alveolar capillaries. By light microscopy, it was clear that the newly formed vascular network was located in regions of fibrosis (which in the resin casts were digested away). These neoformed vessels appeared to originate from bronchial arteries. Thin section electron microscopy revealed that endothelial cells of the neoformed vessels were plump, presented large nuclei, and showed numerous pinocytotic vesicles that were also observed in subendothelial pericytes. The alveoli of the bleomycin-treated rats were heterogeneous in size and shape in contrast with the homogeneity of alveoli of control animals. The alveolar capillaries of fibrotic lungs appeared to occupy a larger volume of the alveolar wall than alveolar capillaries of control rats. Our findings indicate that lung fibrosis encompasses marked changes of the vascular system, namely, the neoformation of vessels and the rearrangement of alveolar capillaries. These structural changes suggest that fibrotic transformation of the lung is associated with the local generation of angiogenic stimuli.

Radiation-Induced Endothelial Dysfunction and Fibrosis in Rat Lung: Modification by the Angiotensin Converting Enzyme Inhibitor CL242817

The purpose of this study was to evaluate the angiotensin converting enzyme (ACE) inhibitor CL242817 as a modifier of radiation-induced pulmonary endothelial dysfunction and pulmonary fibrosis in rats sacrificed 2 months after a single dose of 60Co gamma rays (0-30 Gy) to the right hemithorax. CL242817 was administered in the feed continuously after irradiation at a regimen of 60 mg/kg/day. Pulmonary endothelial function was monitored by lung ACE activity, plasminogen activator (PLA) activity, and prostacyclin (PGI2) and thromboxane (TXA2) production. Pulmonary fibrosis was evaluated by lung hydroxyproline (HP) content. Lung ACE and PLA activities decreased with increasing radiation dose, and cotreatment with CL242817 significantly ameliorated both responses. CL242817 dose-reduction factors (DRF) were 1.3-1.5 for ACE and PLA activity. Lung PGI2 and TXA2 production increased with increasing radiation dose, and CL242817 almost completely prevented both radiation responses. The slope of the radiation dose-response curves in the CL242817-treated rats was essentially zero, precluding calculation of DRF values for PGI2 and TXA2 production. Lung HP content also increased with increasing radiation dose, and CL242817 significantly attenuated this response (DRF = 1.5). These data suggest that the ability of ACE inhibitors to ameliorate radiation-induced pulmonary endothelial dysfunction is not unique to captopril [Ward et al., Int. J. Radiat. Oncol. Biol. Phys. 15, 135-140 (1988)], rather it is a therapeutic action shared by other members of this class of compounds. These data also provide the first evidence that ACE inhibitors exhibit antifibrotic activity in irradiated rat lung.

The effect of endotoxin on bleomycin-induced lung fibrosis in the rat

Bleomycin is a commonly used antineoplastic agent which produces dose- and time-dependent pneumonitis and fibrosis in humans. The mechanism of bleomycin-induced lung injury is uncertain. However, current data shows that bleomycin can generate reactive oxygen species such as Superoxide and hydroxyl radicals. We therefore investigated whether intraperitoneal (i.p.) injection of endotoxin, a protectant for hyperoxia, could modulate the biochemical and morphological estimates of bleomycininduced lung fibrosis in rats. However, pretreatment with multiple i.p. injections of endotoxin, combined with intratracheal bleomycin instillation, resulted in increased lung collagen content compared to bleomycin treatment alone and controls. Furthermore, morphological estimates of the severity of lung lesions present in the endotoxin-bleomycin treatment group were increased when compared with saline and endotoxin control lung lesions. These data indicate, in the current study design, that endotoxin did not reduce, but instead increased the severity of bleomycin-induced pulmonary fibrosis in rats. The mechanism for this increase in fibrosis may be the result of pre-existing endotoxin-induced cell injury.

The Effect of Colchicine on the Accumulation of Hydroxyproline and on Lung Compliance after Irradiation

The development of late radiation fibrosis in rat lung after a single dose 750, 1000, 1250, or 1500 rad of ..gamma.. radiation was studied. The concentration of hydroxyproline was measured to evaluate collagen deposition in irradiated and control lungs. At 120 days after irradiation a linear dose--response curve can be established. Colchicine, known to modify collagen secretion and deposition, was used to modify lung fibrosis after irradiation. It was found that collagen deposition can be reduced only if colchicine is injected when the lung collagen is being synthesized, namely around 90 days after irradiation with these doses. Lung compliance at intervals up to 150 days after irradiation is reduced mainly as a result of increase in lung weight, not collagen deposition.

Beta-aminopropionitrile as a radiation reaction preventive agent.

Beta-aminopropionitrile (BAPN), an inhibitor of collagen maturation, was tested as a radiation reaction preventive agent (RRPA) using radiation-induced lung fibrosis in rats and mice as a model. Following pulmonary irradiation, treatment with BAPN significantly prevented an increase in collagen content as measured by hydroxyproline analysis. This effect persisted during BAPN maintenance for periods of up to 10 weeks but was lost when the drug was discontinued. BAPN administration did not increase the mouse lung LD50/160 in the drug doses employed in this study. Other possible RRPAs deserving further study include D-penicillamine and beclomethasone dipropionate.