A new model of diffuse interstitial pulmonary fibrosis in the rat

Novel and extensive aspects of paraquat-induced pulmonary fibrogenesis: comparative and time-course microarray analyses in fibrogenic and non-fibrogenic rats

Although paraquat (PQ) is widely known to induce pulmonary fibrosis, the molecular mechanisms are poorly understood. Therefore, to bring a new dimension to the elucidation of the mechanisms, we conducted microarray experiments to investigate the expression profiles of 1,090 genes in the lungs during the progressive phase of PQ-induced pulmonary fibrosis in rats. After several s.c. injections of PQ, rats were divided into a fibrogenic group and a non-fibrogenic group. Time-course gene expression analysis of the fibrogenic group showed altered gene regulation throughout the experimental period. The expression levels of many cell membrane channel, transporter, and receptor genes were substantially altered. These genes were classified into two categories: polyamine transporter- and electrolyte/fluid balance-related genes. Moreover, comparative analysis of the fibrogenic and the non-fibrogenic group revealed 36 genes with significantly different patterns of expression, including the pro-apoptotic gene Bad. This indicates that Bad is a key factor in apoptosis and that apoptosis provides a major turning point in PQ-induced pulmonary fibrosis. Notably, subtypes of transforming growth factor (TGF)-beta genes that are considered to play a pivotal role in fibrogenesis showed no differences in expression between the two groups, though TGF-beta3 was markedly induced in both groups. These results provide novel and extensive insights into the molecular mechanisms that lead to pulmonary fibrosis after exposure to PQ.

Changes in the fatty acid composition and hydroxyproline content in rat lung in relation to collagen synthesis after paraquat administration

OBJECTIVES

Effect of paraquat on the fatty acid composition (weight percentage) of rat lung was studied with particular reference to the change of hydroxyproline content in the course of paraquat-induced dysfunction and subsequent repair.

METHODS

Eight-week-old male Wistar rats were administered paraquat at 20 mg/kg body weight subcutaneously, and the wet weight, hydroxyproline content and fatty acid composition of lungs of each group rats were analyzed at 2, 7, 14 or 28 days after treatment, respectively.

RESULTS

The percentage of palmitic acid (C16:0), arachidonic acid (C20:4) and docosahexaenoic acid (C22:6) significantly increased, and the percentage of oleic acid (C18:1) and the ratio of monounsaturated fatty acids/saturated fatty acids (M/S) significantly decreased comparing to control on day 28 after paraquat administration. The time-course of each fatty acid was observed for 28 days after paraquat administration. M/S ratio decreased after paraquat administration up to the 28th day, but the polyunsaturated fatty acids/saturated fatty acids (P/S) ratio decreased during the first 7 days, followed by a increase, and then reached higher level than the 0 day control at the 28th day. Hydroxyproline also increased between the 14th and the 28th days. Eicosapentaenoic acid (C20:5) had once increased during the first 2 days and decreased gradually, while C20:4 maintained high level in this period. C22:6 increased after paraquat administration and maintained high level up to the 28th day. This result indicated that desaturation and elongation in n-3 series fatty acids were accelerated after paraquat treatment, and consequently C20:5 was rapidly converted into C22:6 and decreased.

CONCLUSIONS

Paraquat might cause elevation of unsaturated fatty acids, espe- cially C20:4 but not C20:5 by the stimulation of the fatty acid desaturase system, and could consequently stimulate local collagen synthesis by C20:4 metabolites in the healing stage.

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.

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.

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.

Platelet-derived growth factor in idiopathic pulmonary fibrosis

Fibrosis is a complex process involving an inflammatory reaction, fibroblast proliferation, and abnormal accumulation of interstitial collagens. Mononuclear cells are usually present in lung fibrosis. Activated monocytes and macrophages in culture have been shown to produce several growth factors including platelet-derived growth factor (PDGF). PDGF is a potent mitogen and chemoattractant for fibroblasts and smooth muscle cells and a stimulator of collagen synthesis. We have studied the expression of c-sis/PDGF-2 mRNA in lung tissues derived from five patients with idiopathic pulmonary fibrosis (IPF) and from four control individuals without IPF. Northern blot analysis of specimens obtained from four patients with IPF revealed the expression of the c-sis/PDGF-2 protooncogene. A control lung tissue without IPF did not express the c-sis protooncogene. In situ hybridization extended these studies demonstrating the expression of the c-sis mRNA in the five specimens with IPF but not in the four control specimens without IPF. The expression of c-sis mRNA was localized primarily in the epithelial cells. Invading alveolar macrophages also expressed c-sis mRNA. The expression of c-sis mRNA was accompanied by the expression of PDGF-like proteins in lung specimens with IPF but not in control lung specimens. These findings demonstrate the in vivo expression of the c-sis/PDGF-2 protooncogene and the production of PDGF-like proteins in the epithelial cells and macrophages of the fibrotic tissue. This localized and sustained production of PDGF-like mitogen may constitute an important contributing factor in the abnormal fibroblast proliferation and collagen production, events associated with pulmonary fibrosis.

The histopathology of rat lung following exposure to zinc oxide/hexachloroethane smoke or installation with zinc chloride followed by treatment with 70% oxygen

The effects of inhaled zinc oxide/hexachloroethane smoke (11,580 mg x min/m3) and intratracheally instilled zinc chloride (2.5 mg/kg body weight) have been studied in rat lung. The effects of subsequent treatment with 70% oxygen have been studied after both procedures. Both the inhalation of the smoke and instillation of zinc chloride produced similar effects that included pulmonary edema, alveolitis and, at a later stage, some fibrosis. After zinc chloride instillation, the pathological changes largely spared the periphery of the lung, while following smoke inhalation they were more diffuse. Subsequent oxygen administration had little effect on the development or progression of the pathological changes.

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

Changes in lung structure and collagen metabolism were studied at 1, 2, 3, 4, 6, and 8 weeks in a model of pulmonary fibrosis induced in rats with paraquat plus hyperoxia. Morphologic examination of the lungs revealed that the earliest lesions consisted of severe and irreversible endothelial and alveolar epithelial cell damage. Afterward, an inflammatory process took place, initially dominated by polymorphonuclear leukocytes and then by mononuclear cells, but with the constant presence of granulocytes. From the fourth week on there were fibroblast proliferation and a moderate increase of mast cells. In the early stages alveolitis was focal, but from the second week the lungs were diffusely affected with severe distortion of the architecture. Collagen content was moderately increased in the first 2 weeks and then showed a progressive increment until the end of the experiment. Collagen synthesis was significantly elevated from the fourth week, coinciding with interstitial fibroblast proliferation, although there were some animals that showed increased collagen production from the first week. Collagenolytic activity occurred in 3 stages: at 2 weeks there was increased collagen degradation, at 3, 4, and 6 weeks the values showed a trimodal behavior, and at 8 weeks almost all experimental rats presented an important decrease of collagenolysis. Thus, the development of lung fibrosis was associated first with increased rates of collagen synthesis and later with a decrease of collagen degradation.