A controlled trial of sildenafil in advanced idiopathic pulmonary fibrosis.

BACKGROUND: Sildenafil, a phosphodiesterase-5 inhibitor, may preferentially improve blood flow to well-ventilated regions of the lung in patients with advanced idiopathic pulmonary fibrosis, which could result in improvements in gas exchange. We tested the hypothesis that treatment with sildenafil would improve walk distance, dyspnea, and quality of life in patients with advanced idiopathic pulmonary fibrosis, defined as a carbon monoxide diffusion capacity of less than 35% of the predicted value. METHODS: We conducted a double-blind, randomized, placebo-controlled trial of sildenafil in two periods. The first period consisted of 12 weeks of a double-blind comparison between sildenafil and a placebo control. The primary outcome was the proportion of patients with an increase in the 6-minute walk distance of 20% or more. Key secondary outcomes included changes in oxygenation, degree of dyspnea, and quality of life. The second period was a 12-week open-label evaluation involving all patients receiving sildenafil. RESULTS: A total of 180 patients were enrolled in the study. The difference in the primary outcome was not significant, with 9 of 89 patients (10%) in the sildenafil group and 6 of 91 (7%) in the placebo group having an improvement of 20% or more in the 6-minute walk distance (P=0.39). There were small but significant differences in arterial oxygenation, carbon monoxide diffusion capacity, degree of dyspnea, and quality of life favoring the sildenafil group. Serious adverse events were similar in the two study groups. CONCLUSIONS: This study did not show a benefit for sildenafil for the primary outcome. The presence of some positive secondary outcomes creates clinical equipoise for further research. (Funded by the National Heart, Lung, and Blood Institute and others; ClinicalTrials.gov number, NCT00517933.)

Vitamin D decreases respiratory syncytial virus induction of NF-kappaB-linked chemokines and cytokines in airway epithelium while maintaining the antiviral state.

Epidemiological studies suggest that low vitamin D levels may increase the risk or severity of respiratory viral infections. In this study, we examined the effect of vitamin D on respiratory syncytial virus (RSV)-infected human airway epithelial cells. Airway epithelium converts 25-hydroxyvitamin D3 (storage form) to 1,25-dihydroxyvitamin D3 (active form). Active vitamin D, generated locally in tissues, is important for the nonskeletal actions of vitamin D, including its effects on immune responses. We found that vitamin D induces IkappaBalpha, an NF-kappaB inhibitor, in airway epithelium and decreases RSV induction of NF-kappaB-driven genes such as IFN-beta and CXCL10. We also found that exposing airway epithelial cells to vitamin D reduced induction of IFN-stimulated proteins with important antiviral activity (e.g., myxovirus resistance A and IFN-stimulated protein of 15 kDa). In contrast to RSV-induced gene expression, vitamin D had no effect on IFN signaling, and isolated IFN induced gene expression. Inhibiting NF-kappaB with an adenovirus vector that expressed a nondegradable form of IkappaBalpha mimicked the effects of vitamin D. When the vitamin D receptor was silenced with small interfering RNA, the vitamin D effects were abolished. Most importantly we found that, despite inducing IkappaBalpha and dampening chemokines and IFN-beta, there was no increase in viral mRNA or protein or in viral replication. We conclude that vitamin D decreases the inflammatory response to viral infections in airway epithelium without jeopardizing viral clearance. This suggests that adequate vitamin D levels would contribute to reduced inflammation and less severe disease in RSV-infected individuals.

Identification of an autophagy defect in smokers' alveolar macrophages.

Alveolar macrophages are essential for clearing bacteria from the alveolar surface and preventing microbe-induced infections. It is well documented that smokers have an increased incidence of infections, in particular lung infections. Alveolar macrophages accumulate in smokers' lungs, but they have a functional immune deficit. In this study, we identify an autophagy defect in smokers' alveolar macrophages. Smokers' alveolar macrophages accumulate both autophagosomes and p62, a marker of autophagic flux. The decrease in the process of autophagy leads to impaired protein aggregate clearance, dysfunctional mitochondria, and defective delivery of bacteria to lysosomes. This study identifies the autophagy pathway as a potential target for interventions designed to decrease infection rates in smokers and possibly in individuals with high environmental particulate exposure.

Respiratory syncytial virus limits alpha subunit of eukaryotic translation initiation factor 2 (eIF2alpha) phosphorylation to maintain translation and viral replication.

The impact of respiratory syncytial virus (RSV) on morbidity and mortality is significant in that it causes bronchiolitis in infants, exacerbations in patients with obstructive lung disease, and pneumonia in immunocompromised hosts. RSV activates protein kinase R (PKR), a cellular kinase relevant to limiting viral replication (Groskreutz, D. J., Monick, M. M., Powers, L. S., Yarovinsky, T. O., Look, D. C., and Hunninghake, G. W. (2006) J. Immunol. 176, 1733-1740). It is activated by autophosphorylation, likely triggered by a double-stranded RNA intermediate during replication of the virus. In most instances, ph-PKR targets the alpha subunit of eukaryotic translation initiation factor 2 (eIF2alpha) protein via phosphorylation, leading to an inhibition of translation of cellular and viral protein. However, we found that although ph-PKR increases in RSV infection, significant eIF2alpha phosphorylation is not observed, and inhibition of protein translation does not occur. RSV infection attenuates eIF2alpha phosphorylation by favoring phosphatase rather than kinase activity. Although PKR is activated, RSV sequesters PKR away from eIF2alpha by binding of the kinase to the RSV N protein. This occurs in conjunction with an increase in the association of the phosphatase, PP2A, with eIF2alpha following PKR activation. The result is limited phosphorylation of eIF2alpha and continued translation of cellular and viral proteins.

Insulin-like growth factor-1 levels contribute to the development of bacterial translocation in sepsis.

RATIONALE: Many lines of evidence point toward the gastrointestinal (GI) tract in the pathophysiology of organ dysfunction in sepsis. Splanchnic hypoperfusion during sepsis leads to enterocyte apoptosis, diminished barrier function, and release of bacterial products. Sepsis lowers levels of insulin-like growth factor (IGF)-1, a known antiapoptotic factor. We recently demonstrated that treatment with IGF-1 is protective in murine sepsis. OBJECTIVES: We hypothesize that decreased IGF-1 levels in sepsis contributes to the development of bacterial translocation. METHODS: Sepsis was induced in C57BL/6 mice via intratracheal instillation of Pseudomonas aeruginosa. Human subjects with sepsis were enrolled if they had a documented positive blood culture with a nonenteric organism. Bacterial translocation was measured in serum by quantitative real-time polymerase chain reaction with primers specific for enteric bacteria. Serum IGF-1 was measured by ELISA. Apoptosis of the GI epithelium was assessed via immunohistochemistry. MEASUREMENTS AND MAIN RESULTS: We found that mice with severe sepsis had evidence of bacterial translocation by 24 hours. Enteric bacterial load correlated inversely with levels of serum IGF-1. If we treated mice with IGF-1, bacterial translocation was significantly decreased. In addition, we found increased GI epithelial cell apoptosis after sepsis, which was significantly decreased after IGF-1 treatment. Human subjects with nonenteric sepsis developed progressive enteric bacteremia over 3 days. The degree of enteric bacteremia correlated inversely with serum IGF-1 levels. CONCLUSIONS: These data support the hypothesis that sepsis-induced reductions in IGF-1 levels contribute to the development of bacterial translocation in both a murine model and human subjects.

Respiratory epithelial cells convert inactive vitamin D to its active form: potential effects on host defense.

The role of vitamin D in innate immunity is increasingly recognized. Recent work has identified a number of tissues that express the enzyme 1alpha-hydroxylase and are able to activate vitamin D. This locally produced vitamin D is believed to have important immunomodulatory effects. In this paper, we show that primary lung epithelial cells express high baseline levels of activating 1alpha-hydroxylase and low levels of inactivating 24-hydroxylase. The result of this enzyme expression is that airway epithelial cells constitutively convert inactive 25-dihydroxyvitamin D(3) to the active 1,25-dihydroxyvitamin D(3). Active vitamin D that is generated by lung epithelium leads to increased expression of vitamin D-regulated genes with important innate immune functions. These include the cathelicidin antimicrobial peptide gene and the TLR coreceptor CD14. dsRNA increases the expression of 1alpha-hydroxylase, augments the production of active vitamin D, and synergizes with vitamin D to increase expression of cathelicidin. In contrast to induction of the antimicrobial peptide, vitamin D attenuates dsRNA-induced expression of the NF-kappaB-driven gene IL-8. We conclude that primary epithelial cells generate active vitamin D, which then influences the expression of vitamin D-driven genes that play a major role in host defense. Furthermore, the presence of vitamin D alters induction of antimicrobial peptides and inflammatory cytokines in response to viruses. These observations suggest a novel mechanism by which local conversion of inactive to active vitamin D alters immune function in the lung.

Cigarette smoke induces cellular senescence via Werner's syndrome protein down-regulation.

RATIONALE: Werner's syndrome is a genetic disorder that causes premature aging due to loss-of-function mutations in a gene encoding a member of the RecQ helicase family. Both Werner's syndrome and cigarette smoking accelerate aging. No studies have examined the effect of cigarette smoke on Werner's syndrome protein. OBJECTIVES: To investigate the role of Werner's syndrome protein in cigarette smoke-induced cellular senescence. METHODS: Cellular senescence and amounts of Werner's syndrome protein were measured in fibroblasts isolated from patients with emphysema and compared with age-matched nonsmokers. The in vitro effects of cigarette smoke on amounts of Werner's syndrome protein, function, and senescence were also evaluated in primary human lung fibroblasts and epithelial cells. MEASUREMENTS AND MAIN RESULTS: Cultured lung fibroblasts isolated from patients with emphysema exhibited a senescent phenotype accompanied by a decrease in Werner's syndrome protein. Cigarette smoke extract decreased Werner's syndrome protein in cultured fibroblasts and epithelial cells. Werner's syndrome protein-deficient fibroblasts were more susceptible to cigarette smoke-induced cellular senescence and cell migration impairment. In contrast, exogenous overexpression of Werner's syndrome protein attenuated the cigarette smoke effects. CONCLUSIONS: Cigarette smoke induces cellular senescence and cell migration impairment via Werner's syndrome protein down-regulation. Rescue of Werner's syndrome protein down-regulation may represent a potential therapeutic target for smoking-related diseases.

Cigarette smoke alters respiratory syncytial virus-induced apoptosis and replication.

Individuals exposed to cigarette smoke have a greater number and severity of viral infections, including respiratory syncytial virus (RSV) infections, than do nonsmokers, but the cellular mechanism is unknown. Our objective was to determine the mechanism by which cigarette smoke augments viral infection. We hypothesize that cigarette smoke causes necrosis and prevents virus-induced cellular apoptosis, and that this is associated with increased inflammation and viral replication. Primary airway epithelial cells were exposed to cigarette smoke extract for 2 days, followed by 1 day of RSV exposure. Western blot detection of cleaved caspases 3 and 7 showed less apoptosis when cells were treated with cigarette smoke before viral infection. This finding was confirmed with ELISA and TUNEL detection of apoptosis. Measures of cell viability, including propidium iodide staining, ATP assay, and cell counts, indicated that cigarette smoke causes necrosis rather than virus-induced apoptosis. Using plaque assay and fluorescently-labeled RSV, we showed that although there were less live cells in the cigarette smoke-pretreated group, viral load was increased. The effect was inhibited by pretreatment of cells with N-acetylcysteine and aldehyde dehydrogenase, suggesting that the effect was primarily mediated by reactive aldehydes. Cigarette smoke causes necrosis rather than apoptosis in viral infection, resulting in increased inflammation and enhanced viral replication.

Insulin-like growth factor-1 improves survival in sepsis via enhanced hepatic bacterial clearance.

RATIONALE: Both insulin-like growth factor (IGF)-1 and bacterial clearance by Kupffer cells are significantly reduced in severe sepsis. Kupffer cell apoptosis is triggered by tumor necrosis factor (TNF)-alpha and activation of the PI-3 kinase pathway prevents TNF-induced Kupffer cell death. OBJECTIVES: We evaluated if the marked decline in IGF-1 is related to bacterial clearance in sepsis. METHODS: Sepsis was induced in C57BL/6 mice by intratracheal inoculation with Pseudomonas aeruginosa (strain PA103). Some mice received IGF-1 24 mg/kg either before infection or 12 hours after infection. In vitro studies were performed using the clonal Kupffer cell line KC13-2. MEASUREMENTS AND MAIN RESULTS: Sepsis resulted in decreased levels of IGF-1. In vitro studies with KC13-2 cells demonstrated that IGF-1 protected Kupffer cells against TNF-alpha-induced apoptosis by activating the PI-3 kinase pathway and stabilizing the inhibitor of apoptosis protein, XIAP. In the animal model, pretreatment with IGF-1 decreased hepatic TNF-alpha and IL-6, improved hepatic bacterial clearance as demonstrated by real-time polymerase chain reaction with primers specific for P. aeruginosa, and improved survival in severe sepsis. Moreover, we rescued mice from severe sepsis by IGF-1 treatment 12 hours after infection. CONCLUSIONS: These studies show that the decline in IGF-1 levels in sepsis is related to bacterial clearance and that replacement of IGF-1 in a murine model of sepsis improves overall survival.

Interferons increase cell resistance to Staphylococcal alpha-toxin.

Many bacterial pathogens, including Staphylococcus aureus, use a variety of pore-forming toxins as important virulence factors. Staphylococcal alpha-toxin, a prototype beta-barrel pore-forming toxin, triggers the release of proinflammatory mediators and induces primarily necrotic death in susceptible cells. However, whether host factors released in response to staphylococcal infections may increase cell resistance to alpha-toxin is not known. Here we show that prior exposure to interferons (IFNs) prevents alpha-toxin-induced membrane permeabilization, the depletion of ATP, and cell death. Moreover, pretreatment with IFN-alpha decreases alpha-toxin-induced secretion of interleukin 1beta (IL-1beta). IFN-alpha, IFN-beta, and IFN-gamma specifically protect cells from alpha-toxin, whereas tumor necrosis factor alpha (TNF-alpha), IL-6, and IL-4 have no effects. Furthermore, we show that IFN-alpha-induced protection from alpha-toxin is not dependent on caspase-1 or mitogen-activated protein kinases, but requires protein synthesis and fatty acid synthase activity. Our results demonstrate that IFNs may increase cell resistance to staphylococcal alpha-toxin via the regulation of lipid metabolism and suggest that interferons play a protective role during staphylococcal infections.

Important roles for macrophage colony-stimulating factor, CC chemokine ligand 2, and mononuclear phagocytes in the pathogenesis of pulmonary fibrosis.

RATIONALE: An increase in the number of mononuclear phagocytes in lung biopsies from patients with idiopathic pulmonary fibrosis (IPF) worsens prognosis. Chemokines that recruit mononuclear phagocytes, such as CC chemokine ligand 2 (CCL2), are elevated in bronchoalveolar lavage (BAL) fluid (BALF) from patients with IPF. However, little attention is given to the role of the mononuclear phagocyte survival and recruitment factor, macrophage colony-stimulating factor (M-CSF), in pulmonary fibrosis. OBJECTIVES: To investigate the role of mononuclear phagocytes and M-CSF in pulmonary fibrosis. METHODS: Wild-type, M-CSF-/-, or CCL2-/- mice received intraperitoneal bleomycin. Lung inflammation and fibrosis were measured by immunohistochemistry, ELISA, collagen assay, BAL differentials, real-time polymerase chain reaction, and Western blot analysis. Human and mouse macrophages were stimulated with M-CSF for CCL2 expression. BALF from patients with IPF was examined for M-CSF and CCL2. MEASUREMENTS AND MAIN RESULTS: M-CSF-/- and CCL2-/- mice had less lung fibrosis, mononuclear phagocyte recruitment, collagen deposition, and connective tissue growth factor (CTGF) expression after bleomycin administration than wild-type littermates. Human and mouse macrophages stimulated with M-CSF had increased CCL2 production, and intratracheal administration of M-CSF in mice induced CCL2 production in BALF. Finally, BALF from patients with IPF contained significantly more M-CSF and CCL2 than BALF from normal volunteers. Elevated levels of M-CSF were associated with elevated CCL2 in BALF and the diagnosis of IPF. CONCLUSIONS: These data suggest that M-CSF contributes to the pathogenesis of pulmonary fibrosis in mice and in patients with IPF through the involvement of mononuclear phagocytes and CCL2 production.

Noninfectious lung pathology in patients with Crohn's disease.

Lung involvement in Crohn's disease is not well characterized. We reviewed our experience with 11 lung biopsies (seven wedge and four transbronchial) from patients with Crohn's disease to study this association further. Negative cultures, special stains for organisms Gomori-methenamine-silver [GMS], acid fast), and polymerase chain reaction for (four cases) were required for inclusion. The group included five women and six men with a mean age of 47 years (range 13-84 years). A diagnosis of Crohn's disease preceded the lung disease in nine patients. In two patients the diagnosis of Crohn's disease followed the diagnosis of their pulmonary disease 1 and 15 months later. Radiologically, eight patients had diffuse infiltrates, two had bilateral nodular infiltrates, and one had a mass. Chronic bronchiolitis with nonnecrotizing granulomatous inflammation was present in four patients, one of whom was taking mesalamine. Two patients had an acute bronchiolitis associated with a neutrophil-rich bronchopneumonia with suppuration and vague granulomatous features. One patient on mesalamine had cellular interstitial pneumonia with rare giant cells. Four patients demonstrated organizing pneumonia with focal granulomatous features, two of whom were taking mesalamine, and one of these two responded to infliximab (anti-tumor necrosis factor) monoclonal antibody therapy. Noninfectious pulmonary disease in patients with Crohn's disease has variable histologic appearances, including granulomatous inflammation and airway-centered disease resembling that seen in patients with ulcerative colitis. Drugs may contribute to pulmonary disease in some patients.

Radiologic findings are strongly associated with a pathologic diagnosis of usual interstitial pneumonia.

PURPOSE: To determine which clinical and radiologic findings are independently associated with a pathologic diagnosis of usual interstitial pneumonia (UIP). METHODS: We recently reported, using a prospective, multicenter study of patients suspected of having idiopathic interstitial pneumonia (IIP), that a confident diagnosis of UIP made by experienced radiologists was correct in 95% of cases. In the current article, we further analyzed data from this study. Ninety-one patients were entered into the study. Clinical, physiologic, chest radiographic, and CT features were prospectively recorded, and analyzed using univariate and multivariate logistic regression analysis to compare the patients with a histologic diagnosis of UIP with those who received other pathologic diagnoses. RESULTS: Fifty-four of 91 patients (59%) received a pathologic diagnosis of UIP. The following features recorded at the referring clinical centers were associated with a pathologic diagnosis of UIP on multivariate analysis: lower-lobe honeycombing on high-resolution CT (HRCT) [odds ratio, 11.45], radiographic findings consistent with UIP (odds ratio, 5.73), elevated ratio of FEV(1) to FVC (odds ratio, 4.8), and absence of smoking history (odds ratio, 0.19). On multivariate analysis of specific HRCT features recorded by four experienced chest radiologists, lower-lung honeycombing (odds ratio, 5.36) and upper-lung irregular lines (odds ratio, 6.28) were the only independent predictors of UIP. Using only these two factors, a diagnosis of UIP could be established with a sensitivity of 74%, a specificity of 81%, and a positive predictive value of 85%. CONCLUSION: In patients presenting with a clinical syndrome suggestive of IIP, CT findings of lower-lung honeycombing and upper-lung irregular lines are most closely associated with a pathologic diagnosis of UIP.

Smoking inhibits the frequency of bronchovascular bundle thickening in sarcoidosis.

RATIONALE/OBJECTIVES: Smoking has been associated with decreased incidence and prevalence of sarcoidosis, but few studies have evaluated effects of smoking on clinical parameters of the disease. The objectives were to determine the association of smoking with radiographic patterns and to evaluate the associations of these smoking-related radiographic patterns on airflow obstruction in sarcoidosis. MATERIALS AND METHODS: Clinical data and computed tomography (CT) scans of 124 patients with sarcoidosis were reviewed. CT scans were assessed for lymph nodes, nodules, bronchiectasis, bronchovascular bundle thickening, displaced hilum, fibrosis, ground glass, emphysema, pleural changes, and alveolar opacities. CT patterns were compared between patients with and without a history of smoking. The effect of smoking on the associations between radiographic patterns and airflow obstruction was assessed with multivariable analysis. RESULTS: Smokers had less frequency of bronchovascular bundle thickening than nonsmokers (11/38 subjects [29%] vs 50/86 subjects [58%], P = .003) and more emphysema (7/38 subjects [18%] vs 1/86 subjects [1%], P = .001). Patients who had bronchovascular bundle thickening were less likely to have ever smoked (11/61 subjects [18%] vs 27/63 subjects [43%], P = .003) or be current smokers (4/61 subjects [7%] vs 15/63 subjects [24%], P = .008). Age (P = .003) and bronchovascular bundle thickening (P = .02) were independent predictors of airflow obstruction. There were no differences in smoking history between patients with airflow obstruction versus those without (10/37 subjects [27%] vs 28/87 subjects [32%], P = .63). CONCLUSIONS: In patients with sarcoidosis, smoking is associated with decreased frequency of bronchovascular bundle thickening, an important clinical manifestation of the lung disease. Further, bronchovascular bundle thickening and age are the only independent predictors of airflow obstruction, and smoking does not confound these associations.

Effect of segmental bronchoalveolar lavage on quantitative computed tomography of the lung.

RATIONALE AND OBJECTIVES: With employment of both multidetector computed tomography (MDCT) and endobronchial procedures in multicenter studies, effects of timing of endobronchial procedures on quantitative imaging (Q-MDCT) metrics is a question of increasing importance. MATERIALS AND METHODS: Six subjects were studied via MDCT at baseline, immediately following and at 4 hours and 24 hours post-bronchoalveolar lavage (BAL) (right middle lobe and lingula). Through quantitative image analysis, non-air, or "tissue" volume (TV) in each lung and lobe was recorded. Change in TV from baseline was used to infer retention and redistribution of lavage fluid. RESULTS: Bronchoscopist reported unrecovered BAL volume correlated well with Q-MDCT for whole lung measures, but less well with individual lobes indicating redistribution. TV in all lobes except the right lower lobe differed significantly (P < .05) from baseline immediately post lavage. At 24 hours, all lobes except the left lower lobe (small 1% mean difference at 24 hours) returned to baseline. CONCLUSIONS: These findings suggest fluid movement affecting Q-MDCT metrics between lobes and between lungs before eventual resolution, and preclude protocols involving the lavage of one lung and imaging of the other to avoid interactions. We demonstrate that Q-MDCT is sensitive to lavage fluid retention and redistribution, and endobronchial procedures should not precede Q-MDCT imaging by less than 24 hours.

Chronic liver disease impairs bacterial clearance in a human model of induced bacteremia.

Sepsis often causes impaired hepatic function. Patients with liver disease have an increased risk of bacteremia. This is thought to be secondary to impaired reticuloendothelial system function. However, this has not been demonstrated clinically. Since transient bacteremia occurs following toothbrushing, we hypothesized that subjects with cirrhosis would have impaired bacterial clearance following toothbrushing compared with subjects with pulmonary disease and healthy controls. After baseline blood was drawn, the subjects underwent a dental examination to determine plaque index and gingival index. Following toothbrushing, blood was drawn at 30 seconds, 5 minutes, and 15 minutes. Bacteremia was measured using quantitative real-time PCR with primers that amplify all known bacteria. We found greater than 75% incidence of bacteremia following toothbrushing. While control and pulmonary subjects were able to clear this bacteremia, subjects with cirrhosis had prolonged bacteremia. Baseline and peak bacterial load correlated with plaque index, suggesting that dental hygiene predicts the degree of bacteremia. However, only the severity of cirrhosis was predictive of bacterial clearance at 15 minutes, suggesting that liver function is important in clearing bacteremia. In this study, we demonstrate clinically that cirrhosis results in impaired bacterial clearance. This suggests that cirrhotic patients may be more susceptible to sepsis because of ineffective bacterial clearance.

Constitutive ERK MAPK activity regulates macrophage ATP production and mitochondrial integrity.

A unique feature of human alveolar macrophages is their prolonged survival in the face of a stressful environment. We have shown previously that the ERK MAPK is constitutively active in these cells and is important in prolonging cell survival. This study examines the role of the ERK pathway in maintaining mitochondrial energy production. The data demonstrate that ATP levels in alveolar macrophages depend on intact mitochondria and optimal functioning of the electron transport chain. Significant levels of MEK and ERK localize to the mitochondria and inhibition of ERK activity induces an early and profound depletion in cellular ATP coincident with a loss of mitochondrial transmembrane potential. The effect of ERK suppression on ATP levels was specific, since it did not occur with PI3K/Akt, p38, or JNK suppression. ERK inhibition led to cytosolic release of mitochondrial proteins and caspase activation. Both ERK inhibition and mitochondrial blockers induced loss of plasma membrane permeability and cell death. The cell death induced by ERK inhibition had hallmarks of both apoptotic (caspase activation) and necrotic (ATP loss) cell death. By blocking ERK inhibition-induced reactive oxygen species, caspase activation was prevented, although necrotic pathways continued to induce cell death. This suggests that mitochondrial dysfunction caused by ERK inhibition generates both apoptotic and necrotic cell death-inducing pathways. As a composite, these data demonstrate a novel mitochondrial role for ERK in maintaining mitochondrial membrane potential and ATP production in human alveolar macrophages.

Does current knowledge explain the pathogenesis of idiopathic pulmonary fibrosis? A perspective.

The cause of idiopathic pulmonary fibrosis (IPF) remains unknown. Although the observed biologic and biochemical processes associated with the disease are consistent with a fibrotic process, they are not necessarily unique to IPF. Furthermore, the importance of these observations will not be apparent until a directed therapy alters the natural history of the disease. There are essentially no studies that explain the unique histologic features of this disease. As mechanistic data accumulates, it is our opinion that these data should pass the test of explaining the clinical histologic features of the disease before it can be assumed that these features are unique for IPF.