Platelet-derived growth factor in bronchiolitis obliterans-organizing pneumonia

Bronchiolitis Obliterans and Pulmonary Fibrosis after Sulfur Mustard Inhalation in Rats

Inhalation of powerful chemical agents, such as sulfur mustard (SM), can have debilitating pulmonary consequences, such as bronchiolitis obliterans (BO) and parenchymal fibrosis (PF). The underlying pathogenesis of disorders after SM inhalation is not clearly understood, resulting in a paucity of effective therapies. In this study, we evaluated the role of profibrotic pathways involving transforming growth factor-β (TGF-β) and platelet-derived growth factor (PDGF) in the development of BO and PF after SM inhalation injury using a rat model. Adult Sprague-Dawley rats were intubated and exposed to SM (1.0 mg/kg), then monitored daily for respiratory distress, oxygen saturation changes, and weight loss. Rats were killed at 7, 14, 21, or 28 days, and markers of injury were determined by histopathology; pulmonary function testing; and assessment of TGF-β, PDGF, and PAI-1 concentrations. Respiratory distress developed over time after SM inhalation, with progressive hypoxemia, respiratory distress, and weight loss. Histopathology confirmed the presence of both BO and PF, and both gradually worsened with time. Pulmonary function testing demonstrated a time-dependent increase in lung resistance, as well as a decrease in lung compliance. Concentrations of TGF-β, PDGF, and PAI-1 were elevated at 28 days in lung, BAL fluid, and/or plasma. Time-dependent development of BO and PF occurs in lungs of rats exposed to SM inhalation, and the elevated concentrations of TGF-β, PDGF, and PAI-1 suggest involvement of these profibrotic pathways in the aberrant remodeling after injury.

Case of polycythemia vera with unusual organizing pneumonia mimicking the clinical features of military tuberculosis and possibly caused by the involvement of neoplastic megakaryocytes

Polycythemia vera (PV) is a clonal myeloproliferative neoplasm (MPN) of hematopoietic stem cells. Although the management of MPN patients generally focuses on the prevention of thromboembolic events caused by hypercoagulability, it is true that the patients with hematological malignancy often suffer from pulmonary diseases with atypical radiological patterns. We present here a 56-year-old woman with PV harboring a JAK2(V617F) mutation that had a diffuse reticulonodular pattern on chest radiography and was initially suspected of having military tuberculosis. Pathological assessment of a video-assisted thoracoscopic surgery lung biopsy revealed that the lesions were in fact organizing pneumonia (OP). Interestingly, pulmonary extramedullary hematopoiesis with a diffuse plugging of the alveolar blood capillaries by numerous atypical megakaryocytes was also observed around the granulation components. The histological findings of our case of unusual OP suggest that local activated neoplastic megakaryocytes and platelets played an important role in the development of spreading fibrotic lesions. JAK2 mutation or the preleukemic phase of MPN may accelerate the activation of megakaryocytes and result in the proliferative process of fibrosis.

Effect of nilotinib on bleomycin-induced acute lung injury and pulmonary fibrosis in mice

BACKGROUND

The tyrosine kinase inhibitor imatinib mesylate was developed as an inhibitor of the kinase activity of BCR-ABL. However, imatinib also has potent inhibitory activity against the platelet-derived growth factor receptor (PDGFR). Nilotinib is approved for treating patients with chronic myeloid leukemia showing resistance or intolerance to imatinib. Like imatinib, nilotinib selectively inhibits the tyrosine kinase activity of PDGFR.

OBJECTIVES

We examined the effect of imatinib and nilotinib on acute lung injury and pulmonary fibrosis in a mouse model.

METHODS

Mice were treated by intratracheal instillation of bleomycin. Imatinib or nilotinib were administered by oral gavage. To study the early inflammatory and late fibrotic phases of lung injury, mice were sacrificed on days 3, 7, 14 and 21 after bleomycin instillation.

RESULTS

Histopathology showed that imatinib and nilotinib attenuated the extent of lung injury and fibrosis. The numbers of inflammatory cells and levels of IL-6, IL-1β and tumor necrosis factor-α were decreased in the imatinib and nilotinib groups on days 3 and 7. Imatinib and nilotinib therapy significantly reduced the levels of hydroxyproline on days 14 and 21, which was accompanied by decreased expression levels of transforming growth factor (TGF)-β1 and PDGFR-β. Imatinib and nilotinib also significantly reduced the expression levels of the genes for TGF-β1 and platelet-derived growth factor (PDGF). Imatinib and nilotinib treatment also significantly inhibited the PDGF-induced proliferation of lung fibroblasts in vitro. When imatinib or nilotinib was given 7 days after the instillation of bleomycin, only nilotinib attenuated pulmonary fibrosis.

CONCLUSIONS

Imatinib and nilotinib attenuated bleomycin-induced acute lung injury and pulmonary fibrosis in mice. In a therapeutic model, nilotinib showed more potent antifibrotic effects than imatinib.

Contribution of polymeric immunoglobulin receptor to regulation of intestinal inflammation in dextran sulfate sodium-induced colitis

BACKGROUND

Inflammatory bowel disease (IBD) affects approximately 4 million people worldwide and can be caused by dysregulated mucosal immune responses to the intestinal commensal microflora. Immunoglobulin A (IgA) is considered to be the principal antibody in intestinal secretions and functions to prevent commensals and pathogenic organisms from gaining access to epithelial cell surfaces. Immunoglobulin A deficiency in humans has been associated with celiac disease and ulcerative colitis. However, the precise role of IgA in the pathogenesis of these disorders is yet to be fully understood.

METHODS

Mice with a targeted disruption in IgA production (IgA(-/-) mice) and polymeric immunoglobulin receptor (pIgR(-/-) mice) were analyzed for the contribution of secretory immunity in the pathogenesis of dextran sulfate sodium (2.5%)-induced colitis.

RESULTS

It was found that dextran sulfate sodium-treated pIgR(-/-) mice displayed greater loss of bodyweight and had severe clinical illness compared to similarly treated IgA(-/-) mice and wild-type animals. Additionally, colonic tissues from the pIgR(-/-) mice exhibited progressively and significantly greater degrees of mucosal edema, ulceration, crypt abscesses and macrophage infiltration when compared to similarly treated IgA(-/-) mice and wild-type animals.

CONCLUSIONS

The results indicate that secretory immunoglobulins contribute to protection of the colonic mucosa against dextran sulfate sodium-induced epithelial injury, although the isotype of the secretory immunoglobulin (IgA or IgM) may not be a decisive factor in such protection. Collectively, the pIgR and/or the secretory component are important for the maintenance of epithelial integrity and mucosal homeostasis in the colonic epithelium.

Effect of ductus ligation on cardiopulmonary function in premature baboons

RATIONALE

The role of the patent ductus arteriosus in the development of chronic lung disease in surfactant-treated premature newborns remains unclear.

OBJECTIVE

To examine the effects of ductus ligation on cardiopulmonary function and lung histopathology in premature primates.

METHODS

Baboons were delivered at 125 d, (term = 185 d) treated with surfactant, and ventilated for 14 d. Serial echocardiograms and pulmonary function tests were performed. Animals were randomized to ligation (n = 12) or no ligation (controls, n = 13) on Day 6 of life. Necropsy was performed on Day 14.

RESULTS

Compared with nonligated control animals, ligated animals had lower pulmonary-to-systemic flow ratios, higher systemic blood pressures, and improved indices of right and left ventricular performance. The ligated animals tended to have better compliance and ventilation indices for the last 3 d of the study. There were no differences between the groups in proinflammatory tracheal cytokines (interleukin [IL] 6 and IL-8), static lung compliance, or lung histology.

CONCLUSION

Although a persistent patent ductus arteriosus results in diminished cardiac function and increased ventilatory requirements at the end of the second week of life, ligation on Day 6 had no measurable effect on the histologic evolution of chronic lung injury in this 14-d baboon model.

Elevated platelet-derived growth factor-BB concentrations in premature neonates who develop chronic lung disease

BACKGROUND

Chronic lung disease (CLD) in the preterm newborn is associated with inflammation and fibrosis. Platelet-derived growth factor-BB (PDGF-BB), a potent chemotactic growth factor, may mediate the fibrotic component of CLD. The objectives of this study were to determine if tracheal aspirate (TA) concentrations of PDGF-BB increase the first 2 weeks of life in premature neonates undergoing mechanical ventilation for respiratory distress syndrome (RDS), its relationship to the development of CLD, pulmonary hemorrhage (PH) and its relationship to airway colonization with Ureaplasma urealyticum (Uu).

METHODS

Infants with a birth weight less than 1500 grams who required mechanical ventilation for RDS were enrolled into this study with parental consent. Tracheal aspirates were collected daily during clinically indicated suctioning. Uu cultures were performed on TA collected in the first week of life. TA supernatants were assayed for PDGF-BB and secretory component of IgA concentrations using ELISA techniques.

RESULTS

Fifty premature neonates were enrolled into the study. Twenty-eight infants were oxygen dependent at 28 days of life and 16 infants were oxygen dependent at 36 weeks postconceptual age. PDGF-BB concentrations peaked between 4 and 6 days of life. Maximum PDGF-BB concentrations were significantly higher in infants who developed CLD or died from respiratory failure. PH was associated with increased risk of CLD and was associated with higher PDGF-BB concentrations. There was no correlation between maximum PDGF-BB concentrations and Uu isolation from the airway.

CONCLUSIONS

PDGF-BB concentrations increase in TAs of infants who undergo mechanical ventilation for RDS during the first 2 weeks of life and maximal concentrations are greater in those infants who subsequently develop CLD. Elevation in lung PDGF-BB may play a role in the development of CLD.

Treatment of Immature Baboons for 28 Days with Early Nasal Continuous Positive Airway Pressure

Using the 125-day baboon model of long-term bronchopulmonary dysplasia, we hypothesized that early use of nasal continuous positive airway pressure (nCPAP), a noninvasive ventilatory method, combined with prophylactic surfactant therapy would permit continuation of alveolar and vascular development in the lung. Retrospective human studies have shown that infants treated with nCPAP spend less time on mechanical ventilation and thereby sustain less volutrauma. After delivery by cesarean section at 125 days (term, 185 days), the infants received two doses of surfactant (Curosurf) and daily caffeine citrate. Weaning from low-volume positive pressure ventilation to nCPAP was attempted at 24 hours of age. Serial physiological parameters were recorded. Lung histopathology and morphometric measurements of nCPAP animals were done after necropsy at 28 days and data were compared with 125- and 156-day gestational controls. Documented episodes of clinical sepsis and pneumonia at postmortem examination were absent. nCPAP lungs showed enlarged thin-walled air spaces with minimal fibroproliferation and scattered secondary crests. Internal surface area and surface-to-volume ratio dimensions were similar to those of 156-day gestational control lungs, the intrauterine developmental control. nCPAP is an effective noninvasive ventilatory technique that minimizes lung injury in baboons at risk of developing bronchopulmonary dysplasia.

DNA sequence variants of the platelet-derived growth factor A-chain gene

BACKGROUND

Platelet-derived growth factor A-chain (PDGF-A) is a potent connective tissue mitogen implicated in lung growth and development. PDGF-A may have a role in asthma through effects on fibroblasts and bronchial smooth muscle cells.

OBJECTIVE

To test the hypothesis that there exist variations in the PDGF-A gene associated with the asthma phenotype.

METHODS

We screened genomic DNA from normal and asthmatic subjects using single-stranded conformational polymorphism (SSCP) for mutations in the promoter and all seven exons of the gene.

RESULTS

Four transition polymorphisms (three novel) were identified: one each in exons 3 and 4 (overall population allele frequencies 0.18 and 0.02, respectively) which did not alter the protein sequence, one in exon 4 (frequency 0.005) which resulted in a valine to isoleucine substitution, and one in intron 5 (frequency 0.5). The intron 5-sequence variant is close to the 3' end of exon 5 but does not appear to affect alternative splicing of PDGF-A exon 6 RNA. The frequencies of the polymorphisms in exons 3 and intron 5 did not differ between the asthmatic and non-asthmatic subjects, but there was a significant frequency difference between Caucasian and African-American subjects for each of these polymorphisms (P = 0.03 and 0.003, respectively).

CONCLUSION

No association was found between the sequence variants in the PDGF-A gene and the development of asthma. However, the allele frequency of some of the sequence variants differed between the Caucasian and African-American subjects.

Involvement of platelet-derived growth factor in disease: development of specific antagonists

Platelet-derived growth factor (PDGF) is a family of dimeric isoforms that stimulates, e.g., growth, chemotaxis and cell shape changes of various connective tissue cell types and certain other cells. The cellular effects of PDGF isoforms are exerted through binding to two structurally related tyrosine kinase receptors. Ligand binding induces receptor dimerization and autophosphorylation. This enables a number of SH2 domain containing signal transduction molecules to bind to the receptors, thereby initiating various signaling pathways. PDGF isoforms have important roles during the embryonic development, particularly in the formation of connective tissue in various organs. In the adult, PDGF stimulates wound healing. Overactivity of PDGF has been implicated in certain disorders, including fibrotic conditions, atherosclerosis, and malignancies. Different kinds of PDGF antagonists are currently being developed and evaluated in different animal disease models, as well as in clinical trials.

Mechanism of action and in vivo role of platelet-derived growth factor

Platelet-derived growth factor (PDGF) is a major mitogen for connective tissue cells and certain other cell types. It is a dimeric molecule consisting of disulfide-bonded, structurally similar A- and B-polypeptide chains, which combine to homo- and heterodimers. The PDGF isoforms exert their cellular effects by binding to and activating two structurally related protein tyrosine kinase receptors, denoted the alpha-receptor and the beta-receptor. Activation of PDGF receptors leads to stimulation of cell growth, but also to changes in cell shape and motility; PDGF induces reorganization of the actin filament system and stimulates chemotaxis, i.e., a directed cell movement toward a gradient of PDGF. In vivo, PDGF has important roles during the embryonic development as well as during wound healing. Moreover, overactivity of PDGF has been implicated in several pathological conditions. The sis oncogene of simian sarcoma virus (SSV) is related to the B-chain of PDGF, and SSV transformation involves autocrine stimulation by a PDGF-like molecule. Similarly, overproduction of PDGF may be involved in autocrine and paracrine growth stimulation of human tumors. Overactivity of PDGF has, in addition, been implicated in nonmalignant conditions characterized by an increased cell proliferation, such as atherosclerosis and fibrotic conditions. This review discusses structural and functional properties of PDGF and PDGF receptors, the mechanism whereby PDGF exerts its cellular effects, and the role of PDGF in normal and diseased tissues.

Neonatal chronic lung disease in extremely immature baboons

A borderline viability model of bronchopulmonary dysplasia (BPD)/chronic lung disease of infancy (CLD) with pathophysiologic parameters consistent with those in extremely immature humans with BPD/CLD is described. After prenatal steroid treatment of pregnant dams, 12 premature baboons were delivered by cesarean-section at 125 d (term gestation, 185 d), treated with exogenous surfactant, and maintained on appropriate oxygen and positive pressure ventilation for at least 1 to 2 mo. In spite of appropriate oxygenation (median FI(O(2)) at 28 d = 0.32; range, 0.21 to 0.50) and ventilatory strategies to prevent volutrauma, the baboons exhibited pulmonary pathologic lesions known to occur in extremely immature humans of less than 1,000 g: alveolar hypoplasia, variable saccular wall fibrosis, and minimal, if any, airway disease. The CLD baboon lungs showed significantly decreased alveolization and internal surface area measurements when compared with term and term + 2-mo air-breathing controls. A decrease in capillary vasculature was evident by PECAM staining, accompanied by dysmorphic changes. Significant elevations of TNF-alpha, IL-6, IL-8 levels, but not of IL-1beta and IL-10, in tracheal aspirate fluids were present at various times during the period of ventilatory support, supporting a role for mediator-induced autoinflammation. IL-8 levels were elevated in necropsy lavages of animals with significant lung infection. This model demonstrates that impaired alveolization and capillary development occur in immature lungs, even in the absence of marked hyperoxia and high ventilation settings.

Role of platelet-derived growth factor in obliterative bronchiolitis (chronic rejection) in the rat

The role of platelet-derived growth factor (PDGF) in the development of obliterative bronchiolitis (OB) as a manifestation of chronic rejection was investigated in the heterotopic rat tracheal allograft model. An increase in intragraft PDGF-Ralpha and -Rbeta mRNA expression, and in PDGF-AA and -Ralpha immunoreactivity, was demonstrated during the progressive loss of respiratory epithelium and airway occlusion in nontreated allografts compared with syngeneic grafts. Treatment with CGP 53716, a protein-tyrosine kinase inhibitor selective for PDGF receptor, alone and in combination with suboptimal doses of cyclosporin A, significantly reduced myofibroproliferation and the degree of OB by more than 50%. CGP 53716 did not affect airway wall inflammatory cell proliferation, the number of graft-infiltrating CD4(+) or CD8(+) T cells, ED3(+) macrophages, or the level of immune activation determined as IL-2R and MHC class II expression. This study suggests a regulatory role for PDGF, especially for PDGF-AA and -Ralpha, in the development of obliterative bronchiolitis in this model, and demonstrates that inhibition of PDGF receptor protein-tyrosine kinase activation prevents these obliterative changes. Thus, receptor protein-tyrosine kinase inhibitors may provide a novel therapeutic strategy for the prevention of chronic rejection.

The expression of PDGF-B chain mRNA in lung tissue from rats repeatedly infected with mycoplasma pneumoniae

In order to investigate the role played by platelet derived growth factor-BB (PDGF-BB) in the pathogenesis of pulmonary interstitial fibrosis in rats repeatedly infected with mycoplasma pneumoniae (MP), a rat MP infection model was developed by infecting rats with MP for 9 times during a period of 24 weeks with a technique of ultrasonic nebulizing inhalation. Then in situ hybridization was performed with PDGF-B chain cDNA probe and the results were quantitatively analyzed to measure the changes in PDGF-B chain mRNA expression in the lung tissue. The results showed that: (1) MP polymerase chain reaction (PCR) tests showed positive results in the bronchoalveolar lavage fluid (BALF) from all of the MP-infected rats (n = 4) while they were all negative in BALF from the control animals (n = 4, P < 0.05) and in BALF from those rats both infected with MP and, at the same time, treated with erythromycin (n = 4, P < 0.05). Bacterial cultures of the bronchial and lung tissue were negative in all three groups. The observation under a transmission electron microscope indicated that the interalveolar septa were widened with increased amount of collagen in the MP-infected rats while there were no obvious abnormalities in the other two groups. (2) Strong positive expression of PDGF-B chain mRNA was found in the plasma of monocytes and macrophages located in the locally widened interalveolar septa and alveolar spaces in the lung tissue from the MP-infected animals with the integral optical densities being 37.42 +/- 9.05 (n = 4) which was significantly higher than the values of control group (0.42 +/- 0.08, n = 4, P < 0.01) and of the group with MP-infection plus erythromycin treatment (1.62 +/- 0.40, n = 4, P < 0.01). These results suggest that PDGF-BB may be involved in the process of the development of pulmonary interstitial fibrosis caused by the repeated MP-infection. It may be an important growth factor for mediating the roles of monocytes and macrophages to promote the aggregation and proliferation of fibroblasts which can then secrete collagen in large quantity in the pulmonary interstitium.