Bleomycin-induced pulmonary fibrosis in fibrinogen-null mice

A pivotal role of cytosolic phospholipase A(2) in bleomycin-induced pulmonary fibrosis

Pulmonary fibrosis is an interstitial disorder of the lung parenchyma whose mechanism is poorly understood. Potential mechanisms include the infiltration of inflammatory cells to the lungs and the generation of pro-inflammatory mediators. In particular, idiopathic pulmonary fibrosis is a progressive and fatal form of the disorder characterized by alveolar inflammation, fibroblast proliferation and collagen deposition. Here, we investigated the role of cytosolic phospholipase A(2) (cPLA(2)) in pulmonary fibrosis using cPLA(2)-null mutant mice, as cPLA(2) is a key enzyme in the generation of pro-inflammatory eicosanoids. Disruption of the gene encoding cPLA(2) (Pla2g4a) attenuated IPF and inflammation induced by bleomycin administration. Bleomycin-induced overproduction of thromboxanes and leukotrienes in lung was significantly reduced in cPLA(2)-null mice. Our data suggest that cPLA(2) has an important role in the pathogenesis of pulmonary fibrosis. The inhibition of cPLA(2)-initiated pathways might provide a novel therapeutic approach to pulmonary fibrosis, for which no pharmaceutical agents are currently available.

Induction of plasminogen activator inhibitor-1 in endothelial cells by basic fibroblast growth factor and its modulation by fibric acid

Plasminogen activator inhibitor-1 (PAI-1) inhibits fibrinolysis and proteolysis. Basic fibroblast growth factor (bFGF) stimulates angiogenesis, which requires regional proteolysis. Because modulation of vasculopathy requires tight control of proteolysis, effects of bFGF on PAI-1 expression in endothelial cells (ECs) were characterized. bFGF increased PAI-1 mRNA and accumulation of PAI-1 protein in conditioned media in human umbilical vein ECs. The bFGF-mediated increase in PAI-1 mRNA was attenuated by inhibition of extracellular signal-regulated kinase kinase in human ECV304 cells. The rate of decrease in PAI-1 mRNA after actinomycin D treatment was not affected by bFGF. Transient transfection assays of the human PAI-1 promoter-luciferase construct demonstrated that bFGF-induced PAI-1 transcription was dependent on the elements within the -313 to -260 bp relative to the transcription start site. This region contains an E26 transformation specific 1 (Ets-1)-like site. Electrophoretic mobility shift assay showed that bFGF increased nuclear translocation or DNA binding of the Ets-1-like transcription factor to the PAI-1 promoter. Nucleotide substitution to disrupt the Ets-1-like site reduced bFGF-stimulated promoter activity. Fenofibric acid, an agonist ligand for the peroxisome proliferator-activated receptor-alpha, inhibited basal and bFGF-stimulated PAI-1 expression. By inducing PAI-1 expression from ECs, bFGF may control proteolysis and fibrinolysis in vessel walls.

Direct thrombin inhibition reduces lung collagen, accumulation, and connective tissue growth factor mRNA levels in bleomycin-induced pulmonary fibrosis

Dramatic activation of the coagulation cascade has been extensively documented for pulmonary fibrosis associated with acute and chronic lung injury. In addition to its role in hemostasis, thrombin exerts profibrotic effects via activation of the major thrombin receptor, protease-activated receptor-1. In this study, we examined the effect of the direct thrombin inhibitor, UK-156406 on fibroblast responses in vitro and on bleomycin-induced pulmonary fibrosis in rats. UK-156406 significantly inhibited thrombin-induced fibroblast proliferation, procollagen production, and connective tissue growth factor (CTGF) mRNA levels when used at equimolar concentration to the protease. Thrombin levels in bronchoalveolar lavage fluid and expression of thrombin and protease-activated receptor-1 in lung tissue were increased after intratracheal instillation of bleomycin. The characteristic doubling in lung collagen in bleomycin-treated animals (38.4 +/- 2.0 mg versus 17.1 +/- 1.4 mg, P < 0.01) was preceded by significant elevations in alpha1(I) procollagen and CTGF mRNA levels (3.0 +/- 0.4-fold and 6.3 +/- 0.4-fold respectively, (P < 0.01), and total inflammatory cell number. UK-156406, administered at an anticoagulant dose, attenuated lung collagen accumulation in response to bleomycin by 35 +/- 12% (P < 0.05), inhibited alpha1(I) procollagen and CTGF mRNA levels by 50% and 35%, respectively (P < 0.05), but had no effect on inflammatory cell recruitment. This is the first report showing that direct thrombin inhibition abrogates lung collagen accumulation in bleomycin-induced pulmonary fibrosis.

Expression profiling of acetaminophen liver toxicity in mice using microarray technology

Drug-induced hepatotoxicity causes significant morbidity and mortality and is a major concern in drug development. This is due, in large part, to insufficient knowledge of the mechanism(s) of drug-induced liver injury. In order to address this problem, we have evaluated the modulation of gene expression within the livers of mice treated with a hepatotoxic dose of acetaminophen (APAP) using high-density oligonucleotide microarrays capable of determining the expression profile of >11,000 genes and expressed sequence tags (ESTs). Significant alterations in gene expression, both positive and negative, were noted within the livers of APAP-treated mice. APAP-induced toxicity affected numerous aspects of liver physiology causing, for instance, >twofold increased expression of genes that encode for growth arrest and cell cycle regulatory proteins, stress-induced proteins, the transcription factor LRG-21, suppressor of cytokine signaling (SOCS)-2-protein, and plasminogen activator inhibitor-1 (PAI-1). A number of these and other genes and ESTs were detectable within the liver only after APAP treatment suggesting their potential importance in propagating or preventing further toxicity. These data provide new directions for mechanistic studies that may lead to a better understanding of the molecular basis of drug-induced liver injury and, ultimately, to a more rational design of safer drugs.