Faculty Bibliography

We compared the diffuse lung uptake of 67Ga-citrate, an index of inflammatory lung activity, with the lung clearance of inhaled 99mTc-labeled diethylenetriamine pentaacetate (DTPA) aerosol, an index of pulmonary epithelial permeability, in a group of 19 West Virginia coal miners whose pulmonary status was compatible with coal worker's pneumoconiosis. 99mTc-DTPA clearance alone and 67Ga-citrate uptake alone were measured in nine and five additional subjects, respectively. The objective of this study was to determine if increased 99mTc-DTPA lung clearance was caused by inflammation at the lung epithelial surfaces. Subjects inhaled approximately 150 microCi (approximately 5.6 MBq) of 99mTc-DTPA aerosol, and quantitative gamma camera images of the lungs were acquired at 1-min increments for 25 min. Regions of interest (ROI) were selected to include (1) both lungs; (2) each individual lung; and (3) the upper, middle, and lower thirds of each lung. 99mTc-DTPA clearance was determined from the slopes of the respective time-activity plots for the different ROI. Each subject was intravenously administered 50 miCroCk (1.9 MBq)/kg 67Ga-citrate 48 to 72 h before imaging the body between neck and pelvis. The extent of 67Ga-citrate lung uptake was expressed as the gallium index (GI). Mean radioaerosol clearance half-time (T1/2) for the six nonsmoking coal miners (60.6 +/- 16.0 min) was significantly shorter (p less than 0.001) than for the nonsmoking control group (123.8 +/- 28.7 min). T1/2 for the 12 smoking miners (18.4 +/- 10.2 min) was shorter than for the smoking control group (33.1 +/- 17.8 min), but the difference did not attain statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)

Asbestosis is characterized by an alveolar macrophage alveolitis with injury and fibrosis of the lower respiratory tract. Alveolar macrophages recovered by bronchoalveolar lavage spontaneously release exaggerated amounts of oxidants including superoxide anion and hydrogen peroxide that may mediate alveolar epithelial cell injury. Dehydroepiandrosterone (DHEA) is a normally occurring adrenal androgen that inhibits glucose-6-phosphate dehydrogenase, the initial enzyme in the pentose phosphate shunt necessary for NADPH generation and superoxide anion formation. In this regard, we hypothesized that DHEA may reduce asbestos-induced oxidant release. DHEA added in vitro to alveolar macrophages lavaged from 11 nonsmoking asbestos workers significantly reduced superoxide anion release. DHEA was measured in bronchoalveolar lavage and found to be similar to serum concentrations. DHEA is an antioxidant and potential anticarcinogenic agent that may have a therapeutic role in reducing the increased oxidant burden in asbestos-induced alveolitis of the lower respiratory tract

The insulin-like growth factor (IGF)-II/mannose-6-phosphate (M6P) receptor, which targets acid hydrolases to lysosomes, is a multifunctional protein with separate binding sites for IGF-II and M6P. The purpose of this study was to determine if alveolar macrophages (AM) and their precursor cells, blood monocytes, expressed this receptor. AM expressed IGF-II/M6P receptors as detected by [125]IGF-II surface binding that was not reduced by recombinant IGF-I or IGF-I receptor monoclonal antibody (alpha IR3). Surface binding was also detected on blood monocytes and could be upregulated approximately 4-fold by incubation with lipopolysaccharide. There were no differences in surface binding by AM lavaged from individuals with asbestos exposure or from normal volunteers. Using the polymerase chain reaction and reverse transcriptase to reverse-transcribe mRNA from mononuclear phagocytes, specific IGF-II/M6P receptor cDNA was amplified and detected by agarose gel electrophoresis from both AM and blood monocytes. The IGF-II/M6P receptor has an intracellular transport role in many cells cycling from the cell surface to the cytoplasm, or binding to phosphorylated acid hydrolases in the Golgi and transporting them to an acidic prelysosomal site where they dissociate and fuse to the lysosomes and IGF-II/M6P recycles to the trans-Golgi. These functions may be particularly important in asbestosis and other interstitial lung diseases where AM are activated, intracellular lysosomes are a prominent morphologic feature, and acid hydrolases are found in recovered lavage fluid

Alveolar macrophages (AM) recovered from the lower respiratory tract of individuals with interstitial lung disease (ILD) proliferate at a 2- to 15-fold increased rate (P.B. Bitterman et al. 1984. J. Clin. Invest. 74:460-469). Normal AM stimulated with immune complexes or asbestos release platelet-derived growth factor and insulin-like growth factor-I (IGF-I), and AM activated in vivo in ILD release these growth factors. We evaluated normal unstimulated and activated AM for the receptor for IGF-I to determine if macrophage IGF-I could be involved in the enhanced macrophage proliferation. Although normal AM did not have specific 125I-labeled recombinant IGF-I binding, AM activated by chrysotile asbestos or lipopolysaccharide in vitro or from individuals with ILD had detectable binding that could be inhibited by an anti-IGF-I receptor monoclonal antibody in a dose-dependent fashion. Autoradiography with 125I-labeled recombinant IGF-I revealed binding to the IGF-I receptor on the surface of activated AM, and the percentage of labeled cells was reduced with anti-IGF-I receptor monoclonal antibody or excess unlabeled recombinant IGF-I. Hybridization of total AM RNA to a 32P-labeled IGF-I receptor riboprobe using solution hybridization demonstrated IGF-I receptor mRNA transcripts in AM from an individual with asbestosis, consistent with active expression of the IGF-I receptor gene. In the context of the known role of IGF-I as a growth factor for many cells, these data are consistent with the concept that IGF-I and its receptor may play an important role in the proliferation of AM in the inflamed lower respiratory tract

Asbestosis is an inflammatory and fibrotic process of the alveolar structures mediated, at least in part, by cytokines released by 'activated' alveolar macrophages. The process of phagocytosis and 'activation' of alveolar macrophages is poorly understood. Are all macrophages activated or only subpopulations? Which cytokines are up-regulated? How does the local milieu modulate profibrotic and antifibrotic mediators? Is protein release accompanied by up-regulation of gene transcription? Is there an ordered sequence of cytokine activity? What roles do neutrophils and lymphocytes play? How can disease progression best be quantified absent further exposure? Answers to these questions are important to direct rational strategies at interdicting the fibrotic process. The question of cancer and asbestos is more vexing. The processes of inflammation, fibrosis, and carcinogenesis appear to be closely intertwined. For example, proto-oncogenes such as c-sis (PDGF B-chain) are up-regulated in activated alveolar macrophages from fibrotic lungs; these and possibly others may play an important role in asbestos carcinogenesis. Second, asbestos can transfect DNA into cells. Furthermore, DNA can adhere to asbestos fibers, and these fibers are capable of direct transmigration into cells. The questions of the mechanisms of cigarette smoke cocarcinogenicity and latency remain. Lastly, if the bronchial epithelium is highly metaplastic throughout from cigarette smoking, what triggers a single (or several) nidus of cells to transform into carcinoma? Malignant mesothelioma poses the most challenging questions because of association with brief asbestos exposure by history. Mesothelial cells are susceptible to minute environmental manipulations, and changes occur after exposure to all fiber types. Yet epidemiologic studies point toward long amphiboles as having greater mesothelioma risk. To test this hypothesis, experimental data must be generated differentiating tumorigenesis risk from short, chrysotile fibers that can migrate to the parietal pleura from the associations of long amphiboles persisting in lung tissue. Despite the future decreasing numbers of clinical cases of asbestos-related disease, solving the important mechanistic questions remaining will contribute significantly to our understanding of fibrosis and cancer

The pneumoconioses due to chronic occupational exposure to asbestos, coal, or silica are characterized by an alveolar macrophage-dominated alveolitis with exaggerated spontaneous release of mediators: oxidants, chemotaxins for neutrophils, and fibroblast growth factors. Bronchoalveolar lavage was performed on 66 non-smoking inorganic dust-exposed individuals with a chest x-ray greater than or equal to 1/0 stratified by presence or absence of restrictive respiratory impairment, and 28 unexposed non-smoking controls. Both dust-exposed groups stratified by presence or not of impairment had increased numbers of total cells recovered by lavage compared to normals, and those with respiratory impairment (n = 40) had a significant increase in percent and number of neutrophils recovered. Similarly, only those with respiratory impairment had macrophages that spontaneously released significant amounts of the oxidants superoxide anion and hydrogen peroxide. There was a significant trend for the release of fibronectin by macrophages from controls to dust-exposed without impairment to those with impairment. Both dust-exposed groups also had increased release of alveolar macrophage-derived progression growth factor, but this was significantly less than macrophages from patients with idiopathic pulmonary fibrosis. Since occupational exposure was virtually identical in inorganic dust-exposed individuals with versus without respiratory impairment, the quantitative differences in the release of macrophage mediators may be due to factors in host susceptibility