Published ahead of print on July 3, 2003, doi:10.1164/rccm.200302-256OC
© 2003 American Thoracic Society
Effect of Corticosteroid on Lung Parenchyma Remodeling at an Early Phase of Acute Lung InjuryLaboratory of Respiration Physiology, Carlos Chagas Filho Biophysics Institute, Federal University of Rio de Janeiro, Centro de Ciências da Saúde, Ilha do Fundão, Rio de Janeiro; Laboratory of Cellular Biology (LIM59); and Department of Pathology and Department of Clinical Emergencies, University of São Paulo, São Paulo, Brazil Correspondence and requests for reprints should be addressed to Walter Araujo Zin, M.D., Ph.D., Universidade Federal do Rio de Janeiro, Instituto de Biofísica Carlos Chagas Filho-C.C.S., Laboratório de Fisiologia da Respiração, Ilha do Fundão, 21949-900, Rio de Janeiro, RJ, Brazil. E-mail: wazin{at}biof.ufrj.br
In vivo (lung resistive and viscoelastic pressures and static elastance) and in vitro (tissue resistance, elastance, and hysteresivity) respiratory mechanics were analyzed 1 and 30 days after saline (control) or paraquat (P [10 and 25 mg/kg intraperitoneally]) injection in rats. Additionally, P10 and P25 were treated with methylprednisolone (2 mg/kg intravenously) at 1 or 6 hours after acute lung injury (ALI) induction. Collagen and elastic fibers were quantified. Lung resistive and viscoelastic pressures and static elastance were higher in P10 and P25 than in the control. Tissue elastance and resistance augmented from control to P10 (1 and 30 days) and P25. Hysteresivity increased in only P25. Methylprednisolone at 1 or 6 hours attenuated in vivo and in vitro mechanical changes in P25, whereas P10 parameters were similar to the control. Collagen increment was dose and time dependent. Elastic fibers increased in P25 and at 30 days in P10. Corticosteroid prevented collagen increment and avoided elastogenesis. In conclusion, methylprednisolone led to a complete maintenance of in vivo and in vitro respiratory mechanics in mild lesion, whereas it minimized the changes in tissue impedance and extracellular matrix in severe ALI. The beneficial effects of the early use of steroids in ALI remained unaltered at Day 30.
Key Words: tissue mechanics • acute lung injury • corticosteroid • hysteresivity • elastin The use of corticosteroid in the treatment of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) has been subject of great controversy and debate over the years. Although the exact mechanism of action remains unknown, corticosteroids inhibit a host of potent inflammatory mediators and have been shown to improve morbidity and mortality in animal models of ALI (1–4). Because of the great difficulties in designing and interpreting studies in humans, much of our knowledge about ALI/ARDS pathophysiology comes from animal experimentation. Corticosteroid therapy in ARDS has been studied in three main different situations: (1) prevention in high-risk patients (5); (2) early treatment with high-dose, short-course therapy (6); and (3) prolonged therapy in unresolved cases (7–10). Unfortunately, trials of short-term, high-dose steroid therapy failed to show an improvement in mortality of patients at risk of or with early ARDS (5–6). Despite the unfavorable experience with steroids at the early phase of ALI, there has been a recent resurgence in enthusiasm for their use in late ALI (fibroproliferative phase) (8). The late phase of ALI is characterized by progressive pulmonary fibrosis and lung restriction (11). In addition, pulmonary fibrosis contributes to the unremitting respiratory failure and death in a significant proportion of patients with ALI (12). Several investigators have suggested that the use of corticosteroids in the late phase improved lung function and survival (7–10). Steroids prevent excessive collagen deposition and increase collagen breakdown (9, 13); however, its effect on the elastic system in ALI is much less understood. Some authors have recently observed an increased number of myofibroblasts and cells producing procollagen types I and III in the early course of ALI (14–18), suggesting that the proliferative phase begins much sooner than had been previously appreciated. As a complement to this finding, we observed pronounced mechanical changes at the tissue level and fibroelastogenesis at an early phase of ALI, even in mild abnormal lung parenchyma (19). Thus, in this study, we tested the hypothesis that low-dose corticosteroid when used at an early phase of ALI could modify: (1) in vivo and in vitro respiratory mechanics, (2) lung histology, and (3) the structural remodeling of lung parenchyma in two different degrees of paraquat-induced ALI. These parameters were studied at 1 and 30 days after the induction of lung injury. We also examined whether oscillatory tissue mechanical data were correlated with collagen or elastic system fiber contents. Some of the results of this study have been previously reported in the form of abstract (20, 21).
Animal Preparation A total of 78 Wistar rats (250–300 g) were divided into 13 groups of 6 animals each. In the control group, saline (5 ml/kg body weight) was administered intraperitoneally. In paraquat groups, two different doses of paraquat were injected intraperitoneally (10 [P10] and 25 [P25] mg/kg body weight), 1 or 30 days before the measurements. P10 and P25 groups were treated with methylprednisolone (2 mg/kg, intravenously) at 1 or 6 hours after paraquat administration. Animals were sedated (diazepam 5 mg intraperitoneally), anesthetized (pentobarbital sodium 20 mg/kg intraperitoneally), and a snugly fitting cannula (1.7 mm inside diameter) was introduced into the trachea. Airflow, volume, tracheal, transpulmonary, and esophageal pressures were registered. Respiratory system (rs), lung (L), and chest wall (w) resistive (  P1) and viscoelastic/inhomogeneous pressures (P2), Ptot (P1 + P2), and static elastance (Est) were computed by end-inflation occlusion method (22, 23). Lungs were removed en bloc and placed in a modified Krebs-Henseleith solution (in mM: 118.4 NaCl, 4.7 KCl, 1.2 K3PO4, 25 NaHCO3, 2.5 CaCl2.H2O, 0.6 MgSO4.H2O, and 11.1 glucose) at pH = 7.40 and 6°C (11–13), bubbled with 95% O2–5% CO2. Strips (3 x 3 x 10 mm) were cut from the periphery of the left lung and suspended vertically in a Krebs-Henseleith organ bath maintained at 37°C and continuously bubbled with 95% O2–5% CO2. One clip was attached to a force transducer, whereas the other one was fastened to a vertical rod. This fiberglass stick was connected to a woofer cone, which was driven by a waveform generator. A side arm of the rod was linked to a second force transducer by means of a silver spring of a known Young's modulus value, allowing the measurement of displacement (19, 24). Strips were preconditioned by sinusoidally oscillating the tissue during 30 minutes (frequency = 1 Hz; amplitude large enough to reach a final force of 1 x 10-2 N). Thereafter, the amplitude was adjusted to 5% of the strip's resting length (L0). The strips were unloaded to a force of 8 x 10-3 N, and the oscillation was maintained for another 30 minutes or until a stable length-force loop was reached. The final basal force was approximately 5 x 10-3 N. After stress adaptation, strips were oscillated at a frequency = 1 Hz. Tissue resistance, elastance, and hysteresivity were calculated from the oscillatory recordings according to Fredberg and Stamenovic (25).
Morphometric Analysis
Statistical Analysis
The survival rate in P10 and P25 groups was 85% and 50%, respectively, within the first day after injection. At Day 30, survival was 33% in P10. Steroids led to 100% survival in the P10 group but presented no beneficial effect in rats from the P25 group, which died within 48 hours after ALI induction (Table 1) .
In Vivo Mechanics Respiratory system and lung static elastances (Figure 1) , resistive, viscoelastic/inhomogeneous, and total pressures (Figure 2) increased significantly with the severity of lung injury (from P10 to P25). Respiratory system and lung static elastances and resistive pressures returned to control values at 30 days in P10, whereas respiratory system and lung viscoelastic and total pressure variations remained higher than control. The P10 group treated with steroid presented values of mechanical parameters that were similar to the control group. The beneficial effects of methylprednisolone were similar when given 1 or 6 hours after ALI induction and remained unaltered at Day 30. In P25 group, corticosteroid prevented the modifications in Est,rs; Est,L; P1,rs; and P1,L and attenuated P2,rs; P2,L; Ptot,rs; and Ptot,L changes. Chest wall total and resistive pressures increased in P25 group, and steroids did not modify these changes (Figures 1 and 2).
In Vitro Mechanics Elastance and tissue resistance augmented from the control to P10 and P25. In P10, elastance was higher at 30 days than at the first day after ALI induction, whereas tissue resistance was similar independently of the time course (Figure 3) . The use of methylprednisolone, either 1 or 6 hours after ALI induction, yielded elastance and tissue resistance values similar to control in P10 group and attenuated the changes in P25; hysteresivity increased in only the P25 group (Figure 3).
Lung Histology Typical photomicrographs of lung parenchyma from control, P10 at 1 and 30 days, and P25 groups with and without steroid 6 hours after ALI induction are shown in Figure 4 . Because lung histology was similar in the methylprednisolone at 1 hour group and the methylprednisolone at 6 hours group, we depicted only one treatment (6 hours). Lung histologic changes included atelectasis, interstitial edema, and inflammation with polymorphonuclear cells in P10 group (Figure 4B). Lung parenchyma in P25 presented an increment in all histologic changes described previously here, together with alveolar edema and intraalveolar hemorrhage (Figure 4D). P10 lung parenchyma at Day 30 showed only thickened alveolar membranes and increased cellularity in comparison to the control group (Figure 4F). Both P10 groups treated with steroid presented less interstitial edema and tissue cellularity than P10 independent of the time of analysis (Figures 4C and 4G). In the P25 group, alveolar modifications were prevented by corticosteroid, whereas interstitial edema and inflammatory cells, although lessened, remained increased (Figure 4E). Morphometric examination of the lung demonstrated significant increase in alveolar collapse in all paraquat groups in relationship to the control (Table 2) . Steroid reduced alveolar collapse in the P10 and P25 groups, although they remained higher than control at Day 1 and similar to the control group at Day 30. Alveolar hyperinflation was not present in any group. Total and polymorphonuclear cell contents augmented from control to P10 and P25, but there was no difference in cell count between P10 at Days 1 and 30 (Table 2). Steroid presented antiinflammatory effects on ALI independently its severity. Mononuclear cell content was smaller in P25 and P10 than in the control group. Mononuclear cells increased with the time course of the lesion (Table 1).
Figure 5 shows the amounts of collagen and elastic system fibers in the alveolar septa from lung tissue strips of control and ALI groups (P10 and P25), at Days 1 and 30, and after methylprednisolone (2 mg/kg) injection 1 or 6 hours after ALI induction. Collagen fiber content increased with the severity of lung injury and with the temporal evolution of ALI (Figure 5). Corticosteroid attenuated the increment in collagen content independently of ALI degree. Additionally, its beneficial effects were present until 30 days after steroid injection. The elastic system fiber content increased only at 30 days after ALI induction in P10, augmenting earlier in the more severe lesion (P25). Steroid administration maintained the elastic fiber content equal to control value independently of the dose (severity of the lesion) at Day 1 and time (P10, 30 days) (Figure 5).
Figure 6 shows the ultramicroscopy of lung parenchyma. In the P10 group, inflammatory cells, including lymphocytes, plasma cells, macrophages, fibroblasts, and primitive mesenchymal cell, were seen in the interstitium. The alveolar interstitium was thickened because of both edema and increased amounts of matrix elements, such as collagen fibers. The alveolar spaces had a mixed inflammatory infiltrate consisting of polymorphonuclear and alveolar macrophages. Fibroblasts were frequently found together with types I and III collagen fibers and elastin (Figure 6B). Steroids decreased the number of fibroblasts and type III collagen fiber content. At Day 1, elastic fiber content was normal (Figure 6C). However, in the P10 group 30 days after ALI induction and in P25, there was an increased number of types I and III collagen fibers and elastin, thus characterizing fibroelastosis (Figures 6D and 6F). Steroid treatment inhibited the aggregation process of type III collagen fibers into type I (Figures 6C, 6E, and 6G). In addition, the amount of elastic fibers was also normal (Figures 6E and 6G).
Considering all groups together, tissue elastance and resistance were correlated significantly with total cell count (p = 0.007, r = 0.37, and p = 0.001, r = 0.44, respectively) and with polymorphonuclear cell count (p = 0.002, r = 0.42, and p = 0.002, r = 0.42, respectively). Additionally, tissue elastance and resistance values were correlated significantly with collagen (p < 0.001, r = 0.65, and p < 0.001, r = 0.57, respectively) and elastic fiber content (p = 0.01, r = 0.36, and p = 0.01, r = 0.34, respectively). Hysteresivity was correlated only with elastic fiber content (p = 0.02, r = 0.33).
In this study, low-dose corticosteroid administered at an early phase of ALI kept unaltered in vivo and in vitro mechanical parameters in mildly abnormal lung parenchyma, whereas it minimized the changes in tissue viscoelastic properties in a severe lesion. Paraquat-induced ALI led to a time- and dose-dependent increase in the amount of collagen and elastic fibers. Furthermore, the amount of elastic system fibers augmented later in the course of mild ALI. Corticosteroid treatment acted on the remodeling process, significantly reducing collagen fibers deposition in mild and severe ALI and also preventing elastogenesis. In addition, the use of steroids at the early phase of ALI showed beneficial effects 24 hours after lung injury induction, which lasted until the 30th day after injection in the mild form. It has been previously described that corticosteroids, when given in large doses before or shortly after endotoxin administration in sheep, prevent the subsequent increase in lung vascular permeability but do not reverse the abnormality once established (30). In addition, these abnormalities resolve within 24 hours even if no treatment is given. These results differ from ours, where 50% of the animals with 25 mg/kg paraquat-induced ALI died at the first 24 hours and 100% at 48 hours. At autopsy, these animals presented acute tubular necrosis, esteatosis, carditis, and diffuse alveolar damage. The use of corticosteroid did not change the survival rate in the severe lesion. On the other hand, steroid increased survival in 10 mg/kg of paraquat-induced ALI (Table 1).
Methylprednisolone was chosen as steroid therapy because it is commonly used as an antiinflammatory agent in the treatment of human pulmonary fibrosis and ARDS (7–10). Corticosteroids modulate the host defense response at virtually all levels, protecting the host from immune system overreaction. Corticosteroids inhibit nuclear factor- The initial enthusiasm for the use of corticosteroids to prevent and treat ARDS was based on animal and human studies (13, 34). Several investigators suggested that the use of corticosteroids in the late phase of ARDS improved lung function and survival (7–10), whereas trials of short-term, high-dose steroid therapy failed to show an improvement in mortality in patients at risk of or with early ARDS (5–6). However, the studies on early ARDS showed some potential limitations: the population studied, which varied heterogeneously in terms of case mix and patient management, and the use of high doses of steroids, leading to negative effects due to profound immunosuppression or other side effects counterbalancing positive effects. Corticosteroid therapy could also be ineffective if many of the patients, who were considered to have ARDS based on clinical definitions, did not develop activation of inflammatory cascades in their lungs. Furthermore, the use of steroid at the late phase of ARDS was based on the assumption that the fibroproliferative phase began 7–10 days after the onset of the insult. However, different experiments reported that the proliferative phase begins much sooner than had been previously appreciated (14–19). Thus, inflammatory and repair mechanisms occur simultaneously rather than subsequently. In this study, a controlled model of ALI induced by two different doses of paraquat was used, allowing the analysis of different reproducible degrees of severity. In addition, the ALI model selected was confirmed by light and electronic microscopy, with great potential to induce fibrogenesis (19, 35). The single low dose of methylprednisolone (2 mg/kg) administered early in the course of ALI (1 or 6 hours after lung injury induction) minimized the negative side effects related to immunodepression. This study design could potentially bypass the drawbacks observed in previous reports (5, 6). It is interesting to note that histologic lung changes observed at 24 hours in mild and severe ALI were already present as early as 6 hours after ALI induction, although less intense. Thus, methylprednisolone was used before the beginning of functional changes (1 hour) and after the establishment of the lung injury process (6 hours). Our results showed that corticosteroid treatment at the early phase of ALI improved in vivo and in vitro respiratory mechanics (Figures 1–3). The method used for determination of in vivo respiratory mechanics allows the identification of its elastic, resistive, and viscoelastic and/or inhomogeneous components (22, 23). Respiratory system and lung static elastances, resistive, viscoelastic/inhomogeneous pressures increased significantly with the severity of lung injury at Day 1 (Figures 1 and 2), but only respiratory system and lung viscoelastic pressures remained higher than control values at Day 30 in P10. Prior studies described changes in lung resistance and elastance in ALI, resulting from surfactant dysfunction and/or loss of functional capacity due to alveolar flooding (36, 37). Actually, mechanical dysfunction can result from air–liquid interface and/or tissue changes (38). In this work, the increase in lung resistive pressure probably reflects a reduction in bronchial caliber caused by fluid in the airways, reflex bronchoconstriction, and/or reduced lung volume. The augment in lung viscoelastic and/or inhomogeneous pressure suggests the presence of heterogeneities that can be due to many different factors, for example, alveoli collapse and overdistension, distortion of patent alveoli, edema, inflammation with neutrophil and mononuclear cell infiltration (Table 2 and Figure 4), and changes in collagen and elastic fiber contents (Figure 5). The maintenance of the changes in lung viscoelastic pressure at Day 30 suggests that parenchymal dysfunction dominates the later ALI, as alveolar inhomogeneities and edema were less remarkable in this period (Figure 4F). Lung static elastance in P10 and P25 groups was significantly increased compared with the control, in accordance with previous results (39, 40). Corticosteroid prevented the in vivo mechanical changes in P10 group independently of the time of injection and of the moment of analysis (1 or 30 days after ALI induction), whereas in the P25 group, corticosteroid prevented the modifications in lung static elastance and resistive pressure and attenuated viscoelastic changes (Figures 1 and 2). These modifications could be attributed to the effect of corticosteroid on inflammatory (41–43) and fibroproliferative processes (9, 13, 44, 45), leading to less atelectasis, cellular influx, and fluid transudation in the groups treated with steroids (Figure 4 and Table 2). It has been demonstrated that in experimental ALI corticosteroid treatment is effective in decreasing lung collagen content and edema formation as long as treatment is prolonged, whereas steroid withdrawal rapidly reverses this positive effect (13, 44, 45). However, recent evidence suggests that the inflammatory and fibrotic processes appear to be separately regulated (46), thus offering the possibility for early directed treatments against fibrosis independently of the effects on inflammation. Recently, the beneficial effects of early low-dose steroid treatment was also observed in patients with septic shock, where low-dose hydrocortisone treatment inhibited systemic inflammation and prevented overwhelming compensatory antiinflammatory response (47). Parallel to the in vivo analysis, oscillatory tissue mechanics were also addressed. The importance of alterations in the biophysical properties of the surfactant system in ARDS/ALI pathophysiology (36, 37), as well as the relevant role of tissue inhomogeneities secondary to alveoli collapse/hyperdistension, is well established. The method used to determine lung tissue mechanics avoids the influence of kinetics of surface-active molecule absorption–desorption to the surface film and of recruitment–derecruitment (25, 48, 49). This method specifically allows the analysis of tissue resistance, elastance, and hysteresivity after the induction of ALI in the absence of surfactant and interdependence effects, providing a direct assessment of tissue physiology (38). Additionally, a direct analysis of the role of fiber–fiber network within the connective tissue matrix on tissue mechanical properties is ensured (25, 48, 49). This study is the first analysis of oscillatory tissue mechanical properties of lung parenchyma in animals with ALI treated with corticosteroid. Elastance and resistance of lung parenchyma of paraquat-treated rats were significantly increased in relationship to the control (Figure 3), supporting previous findings that parenchymal mechanical dysfunction plays an important role in ALI pathophysiology (19, 38). Hysteresivity increased only in P25 group. The changes in tissue mechanics were accompanied by deposition of collagen and elastic fibers in the alveolar septa (Figure 5). The kinetics of paraquat-induced fibrogenesis showed a continuous transition among the control, P10 at Day 1, and P10 at Day 30, as previously reported (50). In addition, these results disclosed that collagen content was already elevated 1 day after tissue damage whatever the dose of paraquat used, indicating that the biochemical processes implicated in collagen synthesis are indeed able to react very quickly to the aggression. Conversely, several studies (9, 14–16, 18) have reported that elevated procollagen aminoterminal propeptide levels in the BALF reflect collagen synthesis at the site of disease and may be used as markers of the reparative process. Newly synthesized procollagen is cleaved by specific endopeptidases at the amino and carboxy termini, forming collagen molecules (51). The amino and carboxy propeptides are soluble proteins, sampled relatively ease by BAL, and used as good markers of collagen synthesis without resorting to invasive tissue sampling (52). Thus, these studies (9, 14–16, 18) demonstrate the presence of increased collagen synthesis, with no indication of matrix deposition, which would be possible only through direct histological analysis. In this line, our findings demonstrated that the increased collagen synthesis previously observed (9, 14–16, 18) was actually followed by matrix deposition. Collagen types were identified by electron microscopy (Figure 6). Type I collagen fibrils closely aggregate to form thick fibers of 74 nm, whereas type III collagen fibrils present a mean fibrillary diameter of 45 nm (53). Type III collagen appeared early in mild lesion (P10), whereas type I collagen appeared late in the P10 group (at 30 day) and in the severe lesion (P25). In this context, Armstrong and colleagues (52) hypothesized that an imbalance between synthesis and degradation may contribute to the net accumulation of type I collagen in ARDS and that the profibrotic response occurred early in the course of disease, being associated with the severity of the lung injury and mortality. In our study, steroid treatment was administered before fibroproliferation advanced to end-stage acellular fibrosis when the more resistant type I collagen predominates. Methylprednisolone prevented the increment in tissue elastance and resistance of paraquat-treated rats (Figure 3). The improvement in tissue mechanics could be explained by the effect of steroid preventing excessive collagen deposition, increasing collagen breakdown, or inhibiting the aggregation process of type III collagen fiber into type I (9). Corticosteroid also minimized epithelial and endothelial cell damage, fibroproliferation, and extracellular matrix deposition (Figure 6). The beneficial effects of steroid could be attributed to its inhibitory effects on host defense response, including modulation of macrophage and fibroblast activity (7–10, 43, 54). This study also disclosed the effects of corticosteroid on elastic system. Although there are some studies describing collagen changes after corticosteroid treatment in ALI, the elastic system is scantly dealt with. Mild ALI was followed by a late increase in elastic fiber content, whereas the severe lesion presented early elastogenesis. In bleomycin models of lung fibrosis, elastic fiber content increased at 14 and 30 days (55, 56). However, in severe paraquat-induced lung injury, the amount of elastic fibers was augmented as early as 24 hours after ALI induction. Methylprednisolone modified elastogenesis both in mild and severe ALI (Figure 5). Recently, we quantified the amount of different types of elastic fibers in the alveolar septa (elaunin, oxytalan, and fully developed fibers) and observed that oxytalan fibers were increased in paraquat-induced ALI (19). Oxytalan fibers appear early in the development of the elastic system and consist of microfibrils without elastin, rigid under mechanical stress (28). In our study, the amount of oxytalan fibers in the presence of steroid did not increase, supporting the hypothesis that steroid could probably diminish elastase activity, consequently interfering in the resynthesis of the elastic system fiber. The anatomic elements that potentially determine tissue viscoelastic behavior include the network of stress-bearing collagen and elastic fibers, proteoglycan, and glycosaminoglycans, as well as the contractile elements present in parenchymal tissues (25, 57). Other authors (58, 59) have suggested that the pulmonary parenchyma can be modeled as an interconnected network of elastic elements, presumably composed of collagen and elastic fibers, which determine the mechanical behavior of the system. In our study, tissue Elastance and tissue resistance changes were correlated with collagen and elastic fiber contents, whereas hysteresivity was correlated only with elastic fibers. Similarly, Yuan and colleagues reported (48, 49) that collagen and elastic fibers contribute to tissue elasticity during normal breathing. According to the structural damping hypothesis, induced changes in hysteresivity with ALI must reflect changes in the kinetics of the stress-bearing process, for example, the extracellular fiber matrix, the surface lining layer, and the contractile apparatus (25). In the P25 group, a significant modification of collagen–elastin fiber network was present and was probably the main determinant of the increase in hysteresivity. We hypothesized that the increment in the amount of elastic fibers, primarily oxytalan fibers, could be responsible for a derangement of the tridimensional extracellular matrix organization, which would had a greater impact on tissue mechanics than the effective amount of each fiber component. These findings are supported by the observation that tissue hysteresivity is not determined by collagen and elastic fibers alone, being most likely a network effect (49). It is interesting to observe that in mild ALI the increment in collagen and tissue cellularity was not large enough to affect hysteresivity. In conclusion, single low-dose methylprednisolone led to a complete maintenance of in vivo and in vitro respiratory mechanics in mild ALI and minimized the changes in tissue impedance and extracellular matrix components in a severe lesion. In addition, the beneficial effects of the early use of steroids in ALI were also seen at 30 days after lung injury. We should be extremely cautious in extrapolating these data to the more complex clinical situation, as this is an animal model of ALI induced by paraquat, and thus, the direct extrapolations to the clinical syndrome are unwarranted. Additionally, our animals were not ventilated or treated with fluid management, thwarting the comparison of the animal outcome with the humans. However, this study has an important clinical relevance, that is, the treatment with a single low dose of methylprednisolone at the early phase of ALI may help to prevent fibroelastogenesis, avoiding the side effects related to prolonged and high doses of steroid. Finally, this study may help the design of a clinical trial focused on diminishing clinical lung injury with steroid.
P.R.M.R. has no declared conflict of interest; A.B.S. has no declared conflict of interest; D.S.F. has no declared conflict of interest; C.P.P. has no declared conflict of interest; F.B.S. has no declared conflict of interest; E.M.N. has no declared conflict of interest; J.G.M.L. has no declared conflict of interest; R.S.C. has no declared conflict of interest; V.L.C. has no declared conflict of interest; W.A.Z. has no declared conflict of interest. The authors express their gratitude to Mr. Antonio Carlos de Souza Quaresma and Mrs. Alaine Prudente for their skillful technical assistance and to Dr. Ana Paula B. Barbosa for her help with the initial analysis of tissue mechanics.
Supported by the Centers of Excellence Program (PRONEX-MCT), the Brazilian Council for Scientific and Technological Development (CNPq), the Financing for Studies and Projects (FINEP), the Rio de Janeiro State Research Supporting Foundation (FAPERJ), and the São Paulo State Research Support Foundation (FAPESP). This article has an online supplement, which is accessible from this issue's table of contents online at www.atsjournals.org Received in original form February 21, 2003; accepted in final form June 30, 2003
This article has been cited by other articles:
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
TOP
ABSTRACT
METHODS
= macrophage; PMC = primitive mesenchymal cell.
B and activator protein-1, blocking nuclear factor-
