Experimental pulmonary fibrosis induced by paraquat plus oxygen in rats: a morphologic and biochemical sequential study

Relationship between pulmonary surfactant protein and lipid peroxidation in lung injury due to paraquat intoxication in rats

BACKGROUND

Pulmonary damage resulting from lipid peroxidation is a principal effect of paraquat intoxication. The host-defense functions of surfactant are known to be mediated by the surfactant proteins A and D (SP-A and SP-D, respectively). The primary objective of this study was to evaluate the variations over time in levels of surfactant protein and lipid peroxidation (LPO) in lung tissue following free-radical-induced injury.

METHODS

42 adult, male, Sprague-Dawley rats were administered intraperitoneal injections of paraquat (35 mg/kg body weight). SP-A and SP-D levels were determined via Western blot. LPO in the left lung homogenate was measured via analyses of the levels of thiobarbituric acid-reactive substances.

RESULTS

LPO levels peaked at 6 hours, with no associated histological changes. SP-D levels increased until hour 12 and declined until hour 48; SP-D levels subsequently began to increase again, peaking at hour 72. SP-A levels peaked at hour 6, declining thereafter.

CONCLUSIONS

We suggest that in the early phase of paraquat injury, SP-D levels reflect alveolar damage and that de novo synthesis of SP-D takes 72 hours. Levels of SP-A, on the other hand, reflect abnormalities in the surfactant system in the late stage of paraquat intoxication. Surfactant proteins may play a role in protecting the lungs from reactive oxygen injury. A time-dependent variation has been observed in the levels of surfactant proteins A and D following paraquat injury, and it has been suggested that these proteins play a role in the protection of lung tissue against ROS-induced injuries.

The transcription factor NRF2 protects against pulmonary fibrosis

The molecular mechanisms of pulmonary fibrosis are poorly understood, although reactive oxygen species are thought to have an important role. NRF2 is a transcription factor that protects cells and tissues from oxidative stress by activating protective antioxidant and detoxifying enzymes. We hypothesized that NRF2 protects lungs from injury and fibrosis induced by bleomycin, an anti-neoplastic agent that causes pulmonary fibrosis in susceptible patients. To test this hypothesis, mice with targeted deletion of Nrf2 (Nrf2-/-) and wild-type (Nrf2+/+) mice were treated with bleomycin or vehicle, and pulmonary injury and fibrotic responses were compared. Bleomycin-induced increases in lung weight, epithelial cell death, and inflammation were significantly greater in Nrf2-/- mice than in Nrf2+/+ mice. Indices of lung fibrosis (hydroxyproline content, collagen accumulation, fibrotic score, cell proliferation) were significantly greater in bleomycin-treated Nrf2-/- mice, compared with Nrf2+/+ mice. NRF2 expression and activity were elevated in Nrf2+/+ mice by bleomycin. Bleomycin caused greater up-regulation of several NRF2-inducible antioxidant enzyme genes and protein products in Nrf2+/+ mice compared with Nrf2-/- mice. Further, bleomycin-induced transcripts and protein levels of lung injury and fibrosis markers were significantly attenuated in Nrf2+/+ mice compared with Nrf2-/- mice. Results demonstrated that NRF2 has a critical role in protection against pulmonary fibrosis, presumably through enhancement of cellular antioxidant capacity. This study has important implications for the development of intervention strategies against fibrosis.

Inhibitory effect of caffeic acid phenethyl ester on bleomycine-induced lung fibrosis in rats

BACKGROUND

Pulmonary fibrosis (PF) induced by anticancerogenic bleomycin (BLM) is one of the more common side effects encountered during cancer treatment. It has been suggested in the last decades that the main responsible agent in PF is reactive oxygen species which were generated also in normal physiological conditions in the human body. In this experimental study, we investigated the preventive or attenuating effects of caffeic acid phenethyl ester (CAPE) that has been demonstrated to have anti-inflammatory, cytocytatic, anticancerogenic, antiprolipherative and antioxidant effects on BLM-induced PF.

METHODS

Thirty-six Sprague-Dawley rats were divided randomly into four groups as sham operation, BLM, BLM + vitamin E (vit E), and BLM + CAPE groups. BLM (7.5 mg/kg, single dose) was applied intratracheally, and CAPE and vit E intraperitoneally in the appropriate groups. At the end of the fibrosis processes, lung tissues were removed and the levels of tissues hydroxyproline (OH-proline), malondialdehyde (MDA) and NO as well as the activities of superoxide dismutase (SOD), catalase (CAT) and myeloperoxidase (MPO) were determined. Also, the weights of the rats were recorded at 7th and 14th days of the experiments.

RESULTS

BLM application to the rats resulted in a significant increase in the OH-proline level as compared to the controls. Administration of CAPE and vit E led to the remarkable reduction of total lung OH-proline levels compared to the rats treated with BLM alone (p < 0.0001). There were a decreases in antioxidant enzyme (SOD and CAT) activities while an increase in MPO activity in BLM group was found vs. the control group (p < 0.0001). CAPE had a regulator effect on these parameters: the increase in CAT and SOD activities and the decrease in MPO activity were seen after CAPE application. NO, MDA and OH-proline levels were increased in BLM group vs. the control group. CAPE was more effective in decreasing the tissue levels of NO, MDA and OH-proline than vit E. MPO activity, as a good marker of neutrophil sequestration to the tissues, in the BLM group was decreased by CAPE approximately to the control group.

CONCLUSION

We suggest that CAPE is more effective on the prevention of BLM-induced fibrosis via antioxidant and free radical scavenger properties than vit E at the doses used in the present study. CAPE has some attenuating effects on BLM-induced PF affecting both oxidant and antioxidant systems as well as neutrophils sequestration.

Unbalanced collagenases/TIMP-1 expression and epithelial apoptosis in experimental lung fibrosis

In this study, we examined the sequential expression of several matrix metalloproteinases (MMPs), tissue inhibitors of metalloproteinases (TIMPs), and growth factors as well as the presence of apoptosis in a model of pulmonary fibrosis induced in rats with paraquat and hyperoxia. Animals showing neither clinical nor morphological changes with this double aggression were classified as "resistant". Rats were killed at 1, 2, 3, and 6 wk, and lungs were used for collagen content, gene expression by real-time PCR, gelatinolytic activity by zymography, apoptosis by in situ DNA fragmentation, and protein localization by immunohistochemistry. Our results showed a significant decrease of collagenases MMP-8 and MMP-13, with an increase of TIMP-1 and transforming growth factor-beta. Immunoreactive TIMP-1 was increased in experimental rats and primarily localized in alveolar macrophages. Expression of gelatinases MMP-2 and MMP-9 mRNAs was not affected, but lung zymography revealed an increase in progelatinase B, progelatinase A, and its active form. Epithelial apoptosis was evident from the first week, whereas at later periods, interstitial cell apoptosis was also noticed. Resistant animals behave as controls. These findings suggest that an imbalance between collagenases and TIMPs, excessive gelatinolytic activity, and epithelial apoptosis participate in the fibrotic response in this experimental model.

Relationship of jute dust to interstitial fibrosis in rat lung

The relationship between jute dust and lung interstitial fibrosis was studied by instilling groups of rats, via trachea, with jute dust and comparing the results with those for positive (quartz) and negative (saline) controls. The rats were sacrificed at regular intervals and their lungs and hilar lymph nodes were analyzed for collagen content and morphologic changes. The earliest changes consisted of alveolar edema, increased numbers of intraalveolar macrophages, and marked thickening of the interalveolar septa, with mixed cellular infiltrates. Moderate thickening of the alveolar walls and the zones around the peribronchioles was seen in the test groups at 6 mo. After 12 mo, some fibrosis of the alveoli walls and peribronchiole zones occurred. Interstitial cellular nodules were observed occasionally, composed mainly of dust particles, fibroblasts, reticular fibers, and collagen fibers. The collagen content in the lungs of the jute dust groups was significantly higher than for the saline control group for all test periods. The authors conclude that jute dust may induce lung interstitial fibrosis.

Serum SP-D is a marker of lung injury in rats

Pulmonary surfactant protein D (SP-D) is expressed in alveolar type II and bronchiolar epithelial cells and is secreted into alveoli and conducting airways. However, SP-D has also been measured in serum and is increased in patients with acute respiratory distress syndrome, pulmonary fibrosis, and alveolar proteinosis. To demonstrate that SP-D can be measured in rat serum, we instilled rats with keratinocyte growth factor, which produces type II cell hyperplasia and an increase in SP-D in bronchoalveolar lavage fluid (BALF). To evaluate serum SP-D as a biomarker of lung injury, we examined several injury models. In rats treated with 1 unit of bleomycin, serum SP-D was elevated on days 3, 7, 14, and 28 after instillation, and SP-D mRNA was increased in focal areas as detected by in situ hybridization. However, there was no increase in whole lung SP-D mRNA when the expression was normalized to whole lung 18S rRNA. After instillation of 2 units of bleomycin, the serum levels of SP-D were higher, and SP-D was also increased in BALF and lung homogenates. In another model of subacute injury, serum SP-D was increased in rats treated with paraquat plus oxygen. Finally to evaluate acute lung injury, we instilled rats with HCl; SP-D was increased at 4 h after instillation. Our data indicate that serum SP-D may be a useful indicator of lung injury and type II cell hyperplasia in rats.

Attenuation of bleomycin-induced pulmonary fibrosis by a catalytic antioxidant metalloporphyrin

Oxidative stress plays an important role in the development of fibrotic responses in the lung. However, it is not clear whether inhibiting oxidative stress with antioxidants can attenuate fibrotic processes in the lung. The objective of these studies was to test whether the catalytic antioxidant porphyrin manganese (III) tetrakis (4-benzoic acid) porphyrin (MnTBAP) could protect mice against bleomycin-induced lung fibrosis. A 10 mg/kg intraperitoneal dose of MnTBAP was established as safe and had a serum and lung half-life of 9.5 h in mice. Based on this data, four groups of mice were given one dose of bleomycin (3.2 U/kg, intratracheal) or saline and MnTBAP (5 mg/kg, intraperitoneal) or saline twice daily for 14 d. Lung fibrosis was assessed by measuring (1) lung hydroxyproline content as an index of collagen accumulation, (2) airway dysfunction by whole body plethysmography, and (3) histopathology. Bleomycin produced a 20% loss in body weight that was only 10% in the bleomycin/MnTBAP group. Bleomycin produced a twofold increase in hydroxyproline content that was decreased 23% by MnTBAP. Bleomycin produced a twofold increase in airway dysfunction that was also attenuated 30% by MnTBAP. Histopathologic analysis of the lungs of mice treated with bleomycin demonstrated a severe fibrotic response that was attenuated 28% by MnTBAP. Future studies on the oxidant mechanisms that MnTBAP is affecting in this bleomycin model of lung fibrosis may shed light on potential new therapeutic approaches for treating interstitial lung diseases.

TIMP-1, -2, -3, and -4 in idiopathic pulmonary fibrosis. A prevailing nondegradative lung microenvironment?

Fibroblast proliferation and extracellular matrix accumulation characterize idiopathic pulmonary fibrosis (IPF). We evaluated the presence of tissue inhibitor of metalloproteinase (TIMP)-1, -2, -3, and -4; collagenase-1, -2, and -3; gelatinases A and B; and membrane type 1 matrix metalloproteinase (MMP) in 12 IPF and 6 control lungs. TIMP-1 was found in interstitial macrophages and TIMP-2 in fibroblast foci. TIMP-3 revealed an intense staining mainly decorating the elastic lamina in vessels. TIMP-4 was expressed in IPF lungs by epithelial and plasma cells. TIMP-2 colocalized with Ki67 in fibroblasts, whereas TIMP-3 colocalized with p27 in inflammatory and epithelial cells. Collagenase-1 was localized in macrophages and alveolar epithelial cells, collagenase-2 was localized in a few neutrophils, and collagenase-3 was not detected. MMP-9 was found in neutrophils and subepithelial myofibroblasts. Myofibroblast expression of MMP-9 was corroborated in vitro by RT-PCR. MMP-2 was noticed in myofibroblasts, some of them close to areas of basement membrane disruption, and membrane type 1 MMP was noticed in interstitial macrophages. These findings suggest that in IPF there is higher expression of TIMPs compared with collagenases, supporting the hypothesis that a nondegrading fibrillar collagen microenvironment is prevailing.

Alveolar epithelial cell death adjacent to underlying myofibroblasts in advanced fibrotic human lung

Earlier work from this laboratory showed that abnormal fibroblast phenotypes isolated from fibrotic human lung produce factor(s) capable of inducing apoptosis and necrosis of alveolar epithelial cells in vitro [B. D. Uhal, I. Joshi, A. True, S. Mundle, A. Raza, A. Pardo, and M. Selman. Am. J. Physiol. 269 (Lung Cell. Mol. Physiol. 13): L819-L828, 1995]. To determine whether epithelial cell death is associated with proximity to abnormal fibroblasts in vivo, the spatial distribution of epithelial cell loss, DNA fragmentation, and myofibroblasts was examined in the same tissue specimens used previously for fibroblast isolation. Paraffin sections of normal and fibrotic human lung were subjected to in situ end labeling (ISEL) of fragmented DNA and simultaneous immunolabeling of alpha-smooth muscle actin (alpha-SMA); replicate samples were subjected to electron microscopy and detection of collagens by the picrosirius red technique. Normal human lung exhibited very little labeling except for positive alpha-SMA immunoreactivity of smooth muscle surrounding bronchi and vessels. In contrast, fibrotic human lung exhibited moderate to heavy ISEL of interstitial, cuboidal epithelial, and free alveolar cells. ISEL of the alveolar epithelium was not distributed uniformly but was most intense immediately adjacent to underlying foci of alpha-SMA-positive fibroblast-like interstitial cells. Both electron microscopy and picrosirius red confirmed epithelial cell apoptosis, necrosis, and cell loss adjacent to foci of collagen accumulation surrounding fibroblast-like cells. These results demonstrate that the cuboidal epithelium of the fibrotic lung contains dying as well as proliferating cells and support the hypothesis that alveolar epithelial cell death is induced by abnormal lung fibroblasts in vivo as it is in vitro.

Immunocytochemical detection of growth factors (PDGF and TGF beta) in equine chronic pneumonia

The roles played by platelet-derived growth factor (PDGF) and transforming growth factor beta (TGF beta) in the development of pulmonary fibrosis in equine chronic pneumonia varied greatly. Macrophages, epithelial cells and fibroblasts were identified as a source of PDGF, the principal role of which was related to its mitotic effect on epithelial cells, and particularly on fibroblasts in the final phase of the disease. TGF beta was detected in epithelial cells in all three phases of the disease and in fibroblasts in the last phase. However, the role of TGF beta in this pulmonary disease is not clear because its expression in the cytoplasm of fibroblasts in areas of strong collagenation during the last phase was weak. Nonetheless, it was responsible for the production and release of collagen during the stage of total fibrosis.

Hepatic alterations in experimental paraquat intoxication

Results obtained during experiments on rats intoxicated with Gramoxone herbicide containing 25 per cent paraquat are reported using light- and electron microscopic examinations. The development of the liver's lesion may be divided into three phases: in the first phase predominates the destruction of the cytoplasmic organella in the hepatocytes, in the second one the proliferation of the Kupffer cells and in the third one the lesion of the biliary region. The regeneration is slower than in case of a healthy liver: the hepatic parenchyma is recovering at first and only later the epithelium of the bile ducts. The mechanism of action of the paraquat intoxication is discussed.

Comparison between lung parenchyma and bronchoalveolar lavage collagenolytic activity

We have evaluated, in an experimental model of silicosis in guinea pigs, if the presence of collagenolytic activity in bronchoalveolar lavage (BAL) fluid reflects the collagen catabolism in lung parenchyma. We measured simultaneously BAL collagenase activity, using as substrate [3H]type I collagen, and lung collagenolytic activity by the tissue pellet assay. Animals (n = 30) were instilled intratracheally with 50 mg of quartz DQ-12 and sacrificed 15, 30, and 60 days after silica administration. Guinea pigs instilled with saline solution were used as controls. Our results showed that lung parenchymal collagenolytic activity was present in all experimental and normal guinea pigs. There were no statistical differences between silicotic and normal animals at 15 and 30 days. At 60 days, however, a significant decrease in tissue collagenolytic activity was observed in silicotic animals (161 +/- 100 vs. 400 +/- 152 units of collagenase activity; p < 0.001). In contrast, BAL collagenolytic activity was revealed only in 7 of 10 silicotic animals at 15 days and 30 days, and in 4 of 10 at 60 days. Normal guinea pigs did not exhibit BAL collagenase activity. BAL and tissue collagenase activity from each experimental animal were analyzed by straight line regression and no significant relationship was observed (r = 0.082; p = 0.87). This suggests that BAL collagenolytic activity does not reflect lung tissue collagen turnover.

Immunological tolerance to hapten prevents subsequent induction of hapten-immune pulmonary interstitial fibrosis (HIPIF)

Pulmonary interstitial fibrosis (PIF) is a morphological term which in part can be defined as accumulation of collagen in the extracellular matrix. Previously we showed that hamsters sensitized with 2,4,6-trinitro-1-chlorobenzene (TNCB) developed PIF 14 days after an intratracheal challenge with 2,4,6-trinitrobenzene sulfonic acid (TNBS). The participation of delayed-type hypersensitivity (DTH) in lung collagen deposition was clearly demonstrated. In this paper, we use an adaptation of this model to mice and show that the lung collagen deposition observed was related to the genetic ability of the strain to maintain a DTH response to the immunizing hapten (TNP). Specifically, the lung collagen deposition on Day 14 in hapten-sensitized, challenged animals in high responder to TNP (BALB/c, H-2d) was higher than that in low responder mouse (C57BL/6, H-2b). Furthermore, aged C57BL/6 strain (retired breeders) possessed a DTH response to TNP and produced significantly higher accumulation of hydroxyproline than that of TNBS-challenged-only animals. A DTH mechanism for the induction of the fibrosis is consistent with the observation that responder mice that were made tolerant to the antigen were unable to respond to the lung challenge with a specific increase in lung index or collagen deposition. These results suggest that effector T lymphocytes that are important in DTH play a key role in the regulation of lung collagen deposition in hapten-immune pulmonary interstitial fibrosis (HIPIF) in mice.

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.

Collagen synthesis and degradation during the development of asbestos-induced pulmonary fibrosis

Although pulmonary fibrosis results from exposure to a high level of asbestos, the relative contributions of increased synthesis and/or reduced degradation of total collagen and of any specific type of collagen are not clear. To examine collagen turnover, rats were instilled with crocidolite fibers via the trachea and killed at 1, 2, 4, 6, and 8 weeks. The left lobe was used to determine collagen synthesis by incubating lung pieces with [3H]proline and subsequently measuring 3-hydroxyproline (HYP). Collagenolytic activity was estimated from the release of soluble HYP after incubation of lung homogenates for 48 h. Ratios of collagen types I and III were assayed by gel electrophoresis, both on whole lung and on the labeled homogenate. As fibrosis develops, both total HYP and HYP per dry weight increase at 2 weeks and continue to rise over the experimental period with no differences in the ratio of total types I:III collagens. However, newly synthesized collagen showed an increase in type III at 2 weeks and later a higher proportion of type I collagen when compared with the control. Total collagenolytic activity of asbestos-treated lungs was the same as controls when expressed per dry weight, but was reduced when calculated per unit of collagen. However, active collagenolytic activity was lower than control values when expressed by HYP content and per dry weight at all times after asbestos. The results suggest that reduced degradation of collagen contributes to the fibrotic process in addition to the progressive increase in collagen synthesis, particularly the type I form.

Collagenase and collagenase inhibitors in bronchoalveolar lavage fluids

Collagenase, collagenolytic activity and tissue inhibitor of metalloproteinases were evaluated in bronchoalveolar lavage from 25 patients with hypersensitivity pneumonitis and four control subjects. Patients were followed between two and three years, after which they were classified as "healed," "improved," or "worsened." In control samples, immunoreactive collagenase was not detected. The enzyme was present in four of seven patients who healed, six of ten patients who improved, and four of eight patients who worsened. There was no relationship between the presence or absence of BAL collagenase or its concentration and the evolution of the disease. Latent collagenolytic activity was detected only in 5 of the 14 patients who displayed immunoreactive collagenase. Regarding collagenase inhibitor, TIMP was present in BAL fluid from all patients and normal subjects. Although the highest values were found in two cases who healed or improved, there was not a statistically significant difference among the three groups of patients, neither between patients nor control subjects. These findings suggest that at least in HP, the presence of collagenase, collagenolytic activity, or TIMP in BAL fluid is not associated with the prognosis of the disease.

Lung collagenase inhibitors and spontaneous and latent collagenase activity in idiopathic pulmonary fibrosis and hypersensitivity pneumonitis

In order to analyze the mechanisms involved in the decreased collagenolytic activity previously observed in interstitial lung fibrosis, we studied the inhibitory collagenase activity and the latent activable collagenase in lung samples from five patients with IPF, six with HP, and three control subjects. Our results showed that in both diseases, the inhibitor levels were significantly higher than in control subjects. Findings suggest that in IPF low amounts of collagenase plus excessive enzyme-inhibitors may be operating to decrease collagen catabolism. In contrast, HP lungs seem to contain adequate amounts of the enzyme but higher levels of inhibitors play a role in the abnormal degradation observed in some patients.