Halofuginone does not reduce fibrosis in bleomycin-induced lung injury

Halofuginone, a coccidiostatic alkaloid, has anti-fibrotic properties, and may be useful as a therapeutic agent in lung fibrosis. To test this hypothesis we investigated the effect of halofuginone on bleomycin-induced lung fibrosis in Sprague-Dawley rats. Treatment groups included: (1) a single intratracheal (IT) instillation of 1.2U bleomycin, and intraperitoneal (IP) injection of halofuginone (0.5 mg/dose), every other day; (2) IT 1.2U bleomycin and IP distilled water (D.W.), every other day; (3) IT 0.8U bleomycin and daily IP halofuginone (0.5 mg/dose); (4) IT 0.8U bleomycin and daily IP D.W.; (5) IT saline and IP halofuginone, every other day; (6) IT saline and daily IP D.W.; (7) IT 0.625U bleomycin and oral halofuginone (10 mg/kg rodent lab chow); (8) IT 0.625U bleomycin and standard lab chow. Animals were studied 14 days after IT instillation. Lung injury was evaluated by total and differential cell count in bronchoalveolar lavage fluid, by a semi-quantitative morphological index of lung injury, and by biochemical analysis of lung hydroxyproline content. Overt signs of lung injury were apparent in bleomycin-treated rats by all measures. These changes were not affected by treatment with halofuginone, irrespective of the treatment regimen used. This study does not support the use of halofuginone to prevent or ameliorate lung fibrosis.     

Eosinophils and T lymphocytes possess distinct roles in bleomycin-induced lung injury and fibrosis

Leukocyte infiltration is characteristic of lung injury and fibrosis, and its role during tissue repair and fibrosis is incompletely understood. We found that overexpression of IL-5 in transgenic mice (IL-5(TG)) or by adenoviral gene transfer increased bleomycin (blm)-induced lung injury, fibrosis, and eosinophilia. Surprisingly, blm-treated IL-5-deficient (IL-5(-/-)) mice also developed pronounced pulmonary fibrosis but characterized by marked T lymphocyte infiltration and absence of eosinophilia. In both murine strains however, induction of lung TGF-beta expression was evident. Purified lung eosinophils from blm-treated IL-5(TG) mice stimulated alpha-smooth muscle actin and collagen expression in mouse lung fibroblasts, without affecting proliferation. Furthermore instillation of purified eosinophils into murine lungs resulted in extension of blm-induced lung fibrosis, thus confirming a role for eosinophils. However, lung T lymphocytes from blm-treated IL-5(-/-) mice were able to stimulate fibroblast proliferation but not alpha-smooth muscle actin or collagen expression. Blocking T cell influx by anti-CD3 Abs abrogated lung fibrosis, thus also implicating T lymphocytes as a key participant in fibrosis. Pulmonary fibrosis in IL-5(TG) mice was preferentially associated with type 2 cytokines (IL-4 and IL-13), whereas fibrotic lesions in IL-5(-/-) animals were accompanied by proinflammatory cytokine (TNF-alpha, IL-1beta, and IFN-gamma) expression. We suggest that eosinophils and T cells contribute distinctly to the development of blm-induced lung fibrosis potentially via their production of different cytokine components, which ultimately induce TGF-beta expression that is intimately involved with the fibrosis.     

Niacin attenuates bleomycin-induced lung fibrosis in the hamster

Bleomycin (BLM)-induced lung fibrosis has been shown to be accompanied by the activation of poly(ADP-ribose) polymerase and depletion of nicotinamide adenine dinucleotide (NAD) in the lung. Niacin, a precursor of NAD, was used in the present study to investigate its possible ameliorating effect on BLM-induced pulmonary fibrosis in hamsters. Niacin (500 mg/kg IP) or saline (IP) was injected daily for 16 or 23 days. On day 3, hamsters were treated with BLM (7.5 U/5 mL/kg) or an equivalent volume of saline intratracheally. BLM alone significantly increased lung hydroxyproline levels, bron-choalveolar lavage fluid protein concentration, and various inflammatory cell counts in the lavage in both experiments. In addition, BLM alone elevated prolyl hydroxylase and poly(adenosine-5′-diphosphate [ADP]-ribose) polymerase activities in the 3-week study. Niacin treatment significantly decreased BLM-elevated lung hydroxyproline, prolyl hydroxylase, and poly(ADP-ribose) polymerase activities. Histopa-thology revealed that niacin treatment attenuated BLM-induced thickened alveolar septa, foci of fibrotic consolidation, and accumulations of inflammatory cells in the parenchyma and air spaces. The ability of niacin to attenuate BLM-induced lung fibrosis in hamsters suggests that it may have potential as an antifibrotic agent in humans.     

Role of macrophage migration inhibitory factor in bleomycin-induced lung injury and fibrosis in mice

Macrophage migration inhibitory factor (MIF) is a unique cytokine that reportedly overrides the anti-inflammatory effect of endogenous glucocorticoids. MIF has been demonstrated to be involved in a variety of inflammatory diseases. In this study, we examined the role of MIF in bleomycin (BLM)-induced lung injury and fibrosis. The levels of MIF in lung tissues and bronchoalveolar lavage fluids were significantly increased in the period 5-10 days after intratracheal administration of BLM. Treatment with the anti-MIF antibody significantly reduced the mortality at 14 days and the histopathological lung injury score at 10 days. These effects were accompanied with significant suppression of the accumulation of inflammatory cells in the alveolar space and tumor necrosis factor-alpha in the lungs at 7 days. However, the anti-MIF antibody did not affect either the content of lung hydroxyproline or the histopathological lung fibrosis score at 21 days after BLM. These data provide further evidence for the crucial role of MIF in acute lung inflammation but do not support the involvement of MIF in lung fibrosis induced by BLM in mice.     

Altered bleomycin-induced lung fibrosis in osteopontin-deficient mice

Osteopontin is a multifunctional matricellular protein abundantly expressed during inflammation and repair. Osteopontin deficiency is associated with abnormal wound repair characterized by aberrant collagen fibrillogenesis in the heart and skin. Recent gene microarray studies found that osteopontin is abundantly expressed in both human and mouse lung fibrosis. Macrophages and T cells are known to be major sources of osteopontin. During lung fibrosis, however, osteopontin expression continues to increase when inflammation has receded, suggesting alternative sources of ostepontin during this response. In this study, we demonstrate immunoreactivity for osteopontin in lung epithelial and inflammatory cells in human usual interstitial pneumonitis and murine bleomycin-induced lung fibrosis. After treatment with bleomycin, osteopontin-null mice develop lung fibrosis characterized by dilated distal air spaces and reduced type I collagen expression compared with wild-type controls. There is also a significant decrease in levels of active transforming growth factor-beta(1) and matrix metalloproteinase-2 in osteopontin null mice. Type III collagen expression and total collagenase activity are similar in both groups. These results demonstrate that osteopontin expression is associated with important fibrogenic signals in the lung and that the epithelium may be an important source of osteopontin during lung fibrosis.     

Niacin attenuates bleomycin-induced lung fibrosis in the hamster.

Bleomycin (BLM)-induced lung fibrosis has been shown to be accompanied by the activation of poly(ADP-ribose) polymerase and depletion of nicotinamide adenine dinucleotide (NAD) in the lung. Niacin, a precursor of NAD, was used in the present study to investigate its possible ameliorating effect on BLM-induced pulmonary fibrosis in hamsters. Niacin (500 mg/kg IP) or saline (IP) was injected daily for 16 or 23 days. On day 3, hamsters were treated with BLM (7.5 U/5 mL/kg) or an equivalent volume of saline intratracheally. BLM alone significantly increased lung hydroxyproline levels, bronchoalveolar lavage fluid protein concentration, and various inflammatory cell counts in the lavage in both experiments. In addition, BLM alone elevated prolyl hydroxylase and poly(adenosine-5'-diphosphate [ADP]-ribose) polymerase activities in the 3-week study. Niacin treatment significantly decreased BLM-elevated lung hydroxyproline, prolyl hydroxylase, and poly(ADP-ribose) polymerase activities. Histopathology revealed that niacin treatment attenuated BLM-induced thickened alveolar septa, foci of fibrotic consolidation, and accumulations of inflammatory cells in the parenchyma and air spaces. The ability of niacin to attenuate BLM-induced lung fibrosis in hamsters suggests that it may have potential as an antifibrotic agent in humans.     

Modulation of PDGF-C and PDGF-D expression during bleomycin-induced lung fibrosis

PDGF isoforms are a family of polypeptides that bind to cell surface receptors and induce fibroblast proliferation and chemotaxis. The PDGF-A and -B chain isoforms have been implicated in fibroproliferative lung injury in animal models and in human disease. Two recently recognized PDGF polypeptides, PDGF-C and -D, differ from the PDGF-A and -B isoforms in that they require proteolytic cleavage before they can bind and activate the PDGF receptors. Our findings demonstrate that administration of bleomycin to murine lungs leads to a significant increase in PDGF-C mRNA expression and a significant decrease in PDGF-D mRNA expression. PDGF-C expression was localized to areas of lung injury by in situ hybridization, and PDGF-C expression was not upregulated in the lungs of BALB/c mice that are resistant to bleomycin-induced lung fibrosis. Moreover, there is in vivo phosphorylation of the PDGF-receptor that binds PDGF-C in response to bleomycin administration. These observations strongly suggest a role for PDGF-C in bleomycin-induced pulmonary fibrosis.     

Effects of taurine on bleomycin-induced lung fibrosis in hamsters

Four groups of hamsters were assigned as saline + saline, taurine + saline (TS), saline + bleomycin (SB), and taurine + bleomycin (TB). The animals were treated with either saline or taurine (500 mg/kg ip) for 1 week and just prior to intratracheal instillation of bleomycin (7.5 units/kg) or saline on the eighth day. Thereafter, taurine administration was continued ip (250 mg/kg) and in drinking water (1%) for another 14 days. Bleomycin-induced increases in lung collagen were significantly inhibited in TB hamsters. Plasma taurine concentration in the TS group was significantly higher than that of the other groups. Lung lavage (bronchoalveolar lavage fluid) taurine in the SB group was significantly higher than the saline + saline and TS groups. Bronchoalveolar lavage fluid supernatant protein and acid phosphatase levels in the SB and TB groups were significantly increased over the saline + saline and TS groups. Although the total number of cells recovered in bronchoalveolar lavage fluid was not different among the four groups, there were significantly fewer neutrophils in the TB as compared with SB hamsters. Morphometric analysis revealed less than half as much lesion (diffuse mononuclear alveolitis and multifocal fibroplasia) in TB as compared with SB hamsters. Also, consolidated foci were less frequent and smaller in TB as compared with SB hamsters. Taurine may attenuate bleomycin-induced inflammation and fibrosis by scavenging reactive oxygen metabolites.     

Lysyl oxidase promotes bleomycin-induced lung fibrosis through modulating inflammation

Enzymes involved in collagen biosynthesis, including lysyl oxidase （LOX）, have been proposed as potential therapeutic targets for idio- pathic pulmonary fibrosis. LOX expression is significantly upregulated in bleomycin （BLM）-induced lung fibrosis, and knockdown of LOX expression or inhibition of LOX activity alleviates the lung fibrosis. Unexpectedly, treatment of the mice with LOX inhibitor at the inflammatory stage, but not the fibrogenic stage, efficiently reduces collagen deposition and normalizes lung architecture. Inhibition of LOX impairs inflammatory ceU infiltration, TGF-β signaling, and myofibroblast accumulation. Furthermore, ectopic expres- sion of LOX sensitizes the fibrosis-resistant Balb/c mice to BLM-induced inflammation and lung fibrosis. These results suggest that LOX is indispensable for the progression of BLM-induced experimental lung fibrosis by aggravating the inflammatory response and subse- quent fibrosis process after lung injury.     

Rac2 is involved in bleomycin-induced lung inflammation leading to pulmonary fibrosis

Background

Pulmonary fibrotic diseases induce significant morbidity and mortality, for which there are limited therapeutic options available. Rac2, a ras-related guanosine triphosphatase expressed mainly in hematopoietic cells, is a crucial molecule regulating a diversity of mast cell, macrophage, and neutrophil functions. All these cell types have been implicated in the development of pulmonary fibrosis in a variety of animal models. For the studies described here we hypothesized that Rac2 deficiency protects mice from bleomycin-induced pulmonary fibrosis.

Methods

To determine the role of Rac2 in pulmonary fibrosis we used a bleomycin-induced mouse model. Anesthetized C57BL/6 wild type and rac2 ^-/- mice were instilled intratracheally with bleomycin sulphate (1.25 U/Kg) or saline as control. Bronchoalveolar lavage (BAL) samples were collected at days 3 and 7 of treatment and analyzed for matrix metalloproteinases (MMPs). On day 21 after bleomycin treatment, we measured airway resistance and elastance in tracheotomized animals. Lung sections were stained for histological analysis, while homogenates were analyzed for hydroxyproline and total collagen content.

Results

BLM-treated rac2 ^-/- mice had reduced MMP-9 levels in the BAL on day 3 and reduced neutrophilia and TNF and CCL3/MIP-1α levels in the BAL on day 7 compared to BLM-treated WT mice. We also showed that rac2 ^-/- mice had significantly lower mortality (30%) than WT mice (70%) at day 21 of bleomycin treatment. Lung function was diminished in bleomycin-treated WT mice, while it was unaffected in bleomycin-treated rac2 ^-/- mice. Histological analysis of inflammation and fibrosis as well as collagen and hydroxyproline content in the lungs did not show significant differences between BLM-treated rac2 ^-/- and WT and mice that survived to day 21.

Conclusion

Rac2 plays an important role in bleomycin-induced lung injury. It is an important signaling molecule leading to BLM-induced mortality and it also mediates the physiological changes seen in the airways after BLM-induced injury.     

The effect of suramin on bleomycin-induced lung injury

Since transforming growth factor beta (TGF-beta) is presumed to play a role in lung fibrosis, we evaluated the effect of suramin (Sur), a substance with an anti-TGF-beta effect, in vivo on bleomycin (Bleo)-induced pulmonary injury in mice and in vitro on human lung fibroblasts. Four groups of C57BL/6 mice each received one of four treatments: (1) intratracheal (i.t.) instillation of Bleo and intraperitoneal (i.p.) injections of Sur, every other day, starting one day before i.t. instillation of Bleo (Bleo-Sur); (2) i.t. Bleo and i.p. injections of saline (Bleo-Sal); (3) i.t. saline and i.p. Sur (Sal-Sur); and (4) i.t. and i.p. saline (Sal-Sal). Animals were sacrificed 14 days after i.t. treatment. Lung injury was evaluated by analysis of bronchoalveolar lavage (BAL) fluid, histologically by the semiquantitative morphological index, and biochemically by analysis of lung hydroxyproline content. In vitro, Sur did not affect TGF-beta induced increase of alpha1 (I) collagen mRNA in human lung fibroblasts. In vivo treatment of mice with Sur did not affect Bleo-induced lung injury. These results indicate that despite its potential anti TGF-beta and lymphocytotoxic effects, Sur is not a therapeutic candidate drug for rescue of lung fibrosis.     

Impairment of bleomycin-induced lung fibrosis in CD28-deficient mice

Lung fibrosis is an important pulmonary disease with a high mortality rate, but its pathophysiological mechanism has not been fully clarified. Various types of cells have been implicated in the development of lung fibrosis, including T cells. However, the contribution of functional molecules expressed on T cells to the development of lung fibrosis remains largely unknown. In this study, we determined whether costimulation via CD28 on T cells was crucial for the development of lung fibrosis by intratracheally administering bleomycin into CD28-deficient mice. Compared with wild-type mice, the CD28-deficient mice showed markedly impaired lung fibrosis after injection with low doses of bleomycin, as judged by histological changes and hydroxyproline content in the lungs. In addition, bleomycin-induced T cell infiltration into the airways and production of several cytokines and chemokines including IL-5 were also impaired in the CD28-deficient mice. Furthermore, adoptive transfer of CD28-positive T cells from wild-type mice recovered the impaired bleomycin-induced lung fibrosis in CD28-deficient mice. These findings suggest that the CD28-mediated T cell costimulation plays a critical role in the development of lung fibrosis, possibly by regulating the production of cytokines and chemokines in the lung. Thus, manipulation of the CD28-mediated costimulation could be a potential therapeutic strategy for the prevention of lung fibrosis.     

Alterations in lung and skin compositions of rat in bleomycin-induced fibrosis

Male albino rats were given bleomycin subcutaneously (5 mg potency/kg body weight twice a week) for a period of 6 weeks. At this dosage, mortality was found to be nil with marked fibrotic changes. Pulmonary and cutaneous changes at the end of 2, 4, and 6 weeks of treatment were investigated both by light microscopy and analyses of the intra- and extracellular components. Histologically, fibrosis set in as early as 2 weeks of treatment with bleomycin and was pronounced with increasing duration of treatment. Biochemically, total collagen and hexosamine contents of lung and skin increased significantly compared to control toward the end of treatment period. Thus, this animal model can be conveniently used to mimic the human condition and to test effective antifibrotic agents.     

Role of allograft inflammatory factor-1 in bleomycin-induced lung fibrosis

Allograft inflammatory factor-1 (AIF-1) is a protein expressed by macrophages infiltrating the area around the coronary arteries in a rat ectopic cardiac allograft model. We previously reported that AIF-1 is associated with the pathogenesis of rheumatoid arthritis and skin fibrosis in sclerodermatous graft-versus-host disease mice. Here, we used an animal model of bleomycin-induced lung fibrosis to analyze the expression of AIF-1 and examine its function in lung fibrosis. The results showed that AIF-1 was expressed on lung tissues, specifically macrophages, from mice with bleomycin-induced lung fibrosis. Recombinant AIF-1 increased the production of TGF-β which plays crucial roles in the mechanism of fibrosis by mouse macrophage cell line RAW264.7. Recombinant AIF-1 also increased both the proliferation and migration of lung fibroblasts compared with control group. These results suggest that AIF-1 plays an important role in the mechanism underlying lung fibrosis, and may provide an attractive new therapeutic target.     

Induction of arginase I and II in bleomycin-induced fibrosis of mouse lung

Arginase, which hydrolyzes arginine to urea and ornithine, is a precursor for the synthesis of polyamines and proline, which is abundant in collagen. The supply of proline can be a crucial factor in the process of lung fibrosis. We investigated the induction of arginine metabolic enzymes in bleomycin-induced mouse lung fibrosis. Histological studies and quantification of lung hydroxyproline showed that lung fibrosis develops in up to 14 days after bleomycin treatment. Under these conditions, collagen I mRNA was induced gradually in up to 15 days, and the content of hydroxyproline reached a maximum at 10 days. Arginase I mRNA was undetectable before bleomycin treatment but was induced 5-10 days after this treatment. Arginase I protein was induced at 7 days and remained little changed for up to 10 days and decreased at 14 days. On the other hand, arginase II mRNA that was detectable before treatment was increased gradually for up to 10 days and decreased at 14 days. Arginase II protein began to increase at day 5, increased for up to 10 days, and was decreased at day 14. mRNAs for cationic amino acid transporter-2 and ornithine decarboxylase were induced in a manner similar to that seen with collagen I mRNA. Immunohistochemical analysis showed that arginase I is induced in macrophages, whereas arginase II is induced in various cell types, including macrophages and myofibroblasts, and roughly colocalizes with the collagen-specific chaperone heat shock protein 47. Our findings suggest that arginine metabolic enzymes play an important role in the development of lung fibrosis, at least in mice.     

Changes of lung surfactant and pressure-volume curve in bleomycin-induced pulmonary fibrosis.

We investigated whether alveolar surface force increased and participated in the lung pressure-volume relationship in bleomycin-induced pulmonary fibrosis in hamsters and, if so, whether lung surfactant was hampered in the lungs. On the air-filled pressure-volume curve, decreases of lung volume from control level were significantly higher at 3-8 cmH2O pressure on day 10 than on day 30. Because the change of lung tissue elasticity evaluated from the saline-filled pressure-volume curve was equal for the 2 days, the higher decrease of air volume on day 10 was due primarily to contribution of alveolar surface force. Pressure differences between deflation limbs of air-filled and saline-filled pressure-volume curves, which represented net alveolar surface force, were significantly higher at any lung volume between 50 and 90% total lung capacity on day 10, but almost no significance was observed on day 30. Phospholipid concentration in bronchoalveolar lavage fluid significantly decreased on day 10 but had improved by day 30. Analysis of phospholipid species in purified lung surfactant showed decreased fractions of disaturated phosphatidylcholine and phosphatidylglycerol on day 10. Surface-active properties of the surfactant, measured by a modified Wilhelmy balance, were remarkably hampered on day 10, but most of them had improved by day 30. We consider that the quantitative and functional abnormalities of lung surfactant have a part in the aggravation of lung mechanics in the acute phase of pulmonary fibrosis.     

Resistance of fibrogenic responses to glucocorticoid and 2-methoxyestradiol in bleomycin-induced lung fibrosis in mice

Bleomycin-induced lung fibrosis in mice reproduces some key features of pulmonary fibrosis in humans including alveolar inflammation, myofibroblast proliferation, and collagen deposition. Glucocorticoids have been used as first-line therapy for the treatment of lung fibrosis, although their clinical efficacy is equivocal. We examined the effect of the glucocorticoid, methylprednisolone (MP), and the estrogen metabolite, 2-methoxyestradiol (2MEO) on bleomycin-induced bronchoalveolar inflammation, fibrosis, and changes in lung function. The characterization of the time-course of the bleomycin-induced fibrosis indicated that lung dry mass and hydroxyproline content showed less variance than histopathological assessment of fibrosis. The bleomycin-induced increases in bronchoalveolar lavage (BAL) fluid cell number and protein levels were not significantly influenced by treatment with either MP (1 mg.(kg body mass)(-1).day(-1), i.p.) or 2MEO (50 mg.(kg body mass)(-1).day(-1), i.p.). Lung fibrosis, measured histopathologically or by hydroxyproline content, was not significantly influenced by either MP or 2MEO treatment, whereas the latter agent did reduce the increment in lung dry mass. The enlargement of alveolar airspaces and the decline in lung compliance were exacerbated by MP treatment. These data suggest that bleomycin-induced pulmonary fibrosis is resistant to inhibition by concurrent treatment with either glucocorticoids or 2MEO.     

Cigarette smoke exposure potentiates bleomycin-induced lung fibrosis in guinea pigs

The role of tobacco smoking in the development and outcome of pulmonary fibrosis is uncertain. To approach the effects of cigarette smoke on bleomycin-induced lung fibrosis, we studied five groups of guinea pigs: 1) controls, 2) instilled with bleomycin (B), 3) exposed to tobacco smoke for 6 wk (TS), 4) bleomycin instillation plus tobacco smoke exposure for 6 wk (B+TS), and 5) tobacco smoke exposure for 6 wk and bleomycin after smoking (TS/B). Guinea pigs receiving bleomycin and tobacco smoke exposure exhibited higher fibrotic lesions including a significant increase in the number of positive alpha-smooth muscle actin cells compared with bleomycin alone (B+TS, 3.4 +/- 1.2%; TS/B, 3.7 +/- 1.5%; B, 2.3 +/- 1.5%; P < 0.01). However, only the TS/B group reached a significant increase in lung collagen compared with the bleomycin group (TS/B, 3.5 +/- 0.7; B +/- TS, 2.9 +/- 0.4; B, 2.4 +/- 0.2 mg hydroxyproline/lung; P < 0.01). Bronchoalveolar lavage (BAL) from TS/B showed an increased number of eosinophils and higher levels of IL-4 and tissue inhibitor of metalloproteinase-2 (P < 0.01 for all comparisons) and induced a significant increase in fibroblast proliferation (P < 0.05). Importantly, smoke exposure alone induced an increase in BAL neutrophils, matrix metalloproteinase-9, and fibroblast proliferation compared with controls, suggesting that tobacco smoke creates a profibrotic milieu that may contribute to the increased bleomycin-induced fibrosis.     

A micro-CT analysis of murine lung recruitment in bleomycin-induced lung injury.

The effects of lung injury on pulmonary recruitment are incompletely understood. X-ray computed tomography (CT) has been a valuable tool in assessing changes in recruitment during lung injury. With the development of preclinical CT scanners designed for thoracic imaging in rodents, it is possible to acquire high-resolution images during the evolution of a pulmonary injury in living mice. We quantitatively assessed changes in recruitment caused by intratracheal bleomycin at 1 and 3 wk after administration using micro-CT in 129S6/SvEvTac mice. Twenty female mice were administered 2.5 U of bleomycin or saline and imaged with micro-CT at end inspiration and end expiration. Mice were extubated and allowed to recover from anesthesia and then reevaluated in vivo for quasi-static compliance measurements, followed by harvesting of the lungs for collagen analysis and histology. CT images were converted to histograms and analyzed for mean lung attenuation (MLA). MLA was significantly greater for bleomycin-exposed mice at week 1 for both inspiration (P<0.0047) and exhalation (P<0.0377) but was not significantly different for week 3 bleomycin-exposed mice. However, week 3 bleomycin-exposed mice did display significant increases in MLA shift from expiration to inspiration compared with either group of control mice (P<0.005), suggesting increased lung recruitment at this time point. Week 1 bleomycin-exposed mice displayed normal shifts in MLA with inspiration, suggesting normal lung recruitment despite significant radiographic and histological changes. Lung alveolar recruitment is preserved in a mouse model of bleomycin-induced parenchymal injury despite significant changes in radiographic and physiological parameters.