Several in vitro studies suggest the involvement of active oxygen metabolites in cell damage caused by asbestos. To determine if lung injury, inflammation, and asbestosis could be inhibited in vivo in a rapid-onset, inhalation model of disease, a novel method of chronic administration of antioxidant enzymes was developed. In brief, Fischer 344 rats were treated with polyethylene glycol-conjugated (PEG-) superoxide dismutase or catalase in osmotic pumps over a 10-day (5 days/wk for 2 wk) or 20-day (5 days/wk for 2 wk) period of exposure to crocidolite asbestos. Control rats included sham-exposed animals and those exposed to asbestos but receiving chemically inactivated enzymes. After 10 days of exposure to asbestos, lactic dehydrogenase (LDH), alkaline phosphatase, and total protein in bronchoalveolar lavage (BAL) were measured in one group of rats. Total and differnetial cell counts in BAL also were assessed. After 20 days of exposure, lungs of an additional group of rats were evaluated by histopathology and by measurement of hydroxyproline. Asbestos-associated elevations in LDH, protein, and total cell numbers in BAL were reduced in rats receiving PEG-catalase. Decreases in numbers of alveolar macrophages, polymorphonuclear leukocytes, and lymphocytes occurred in these animals. Exposure to asbestos for 20 days caused significant increases in both the amount of hydroxyproline in lung and the severity and extent of fibrotic lesions as determined by histopathology. These indicators of asbestosis were inhibited in a dosage-dependent fashion in rats receiving PEG-catalase. Use of inactivated PEG-catalase failed to boost serum levels of catalase and did not inhibit asbestos-induced elevation of hydroxyproline in lung.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of inositol phospholipids and phosphatidylcholine was investigated in tracheobronchial epithelial cells exposed to mitogenic concentrations of crocidolite asbestos. Alterations in levels of diacylglycerol, the endogenous activator of protein kinase C, and inositol polyphosphates, presumed mobilizers of intracellular calcium, were examined. Occupational exposure to asbestos results in development of bronchogenic carcinoma, mesothelioma, and asbestosis (1). The pathogenesis of carcinoma caused by asbestos has been studied experimentally in tracheobronchial epithelial cells and organ cultures. Results suggest that asbestos is a classical tumor promoter in the development of bronchogenic carcinoma. For example, many of the effects reported in mouse skin cells exposed to tumor-promoting phorbol esters (2) occur in tracheobronchial epithelial cells exposed to asbestos (3). Additionally, asbestos acts as a tumor promoter in a "two-stage" model of carcinogenesis. Insertion of chrysotile asbestos into rodent tracheal grafts previously exposed to a chemical initiator results in the development of tumors arising from the tracheal epithelium. In contrast, fibers alone do not induce tumors (4).Many of the morphological and biochemical changes expressed in cells exposed to soluble tumor promoters such as phorbol 12-myristate 13-acetate (PMA) occur after direct interaction of PMA with calcium-and phospholipiddependent protein kinase C (PKC) (5), an enzyme implicated in cellular growth control. For example, dramatic morphological changes have been seen in rat fibroblasts that overproduce a transfected isoform of PKC (6). Recent work from this laboratory implicates PKC in crocidolite asbestosinduced proliferation of hamster tracheal epithelial (HTE) cells, a cell type giving rise to bronchogenic tumors. For example, asbestos-stimulated induction of ornithine decarboxylase is reduced by inhibitors of PKC (7). Because it is unlikely that soluble asbestos fibers bind directly to PKC as do the lipophilic phorbol esters, we sought to investigate other plausible mechanisms whereby asbestos fibers could initiate PKC-mediated proliferation. In this report, we present evidence that diacylglycerol (acyl2Gro), the endogenous activator of PKC, is produced upon hydrolysis of inositol phospholipids in crocidolite-stimulated HTE cells. MATERIALS AND METHODSChemicals. Union Internationale Contre le Cancer reference samples of crocidolite [(Na2Fe2Fe3+(Si8022)(0H)2] asbestos were used in these studies. Riebeckite (a nonfibrous particle) and glass beads (8) were used as negative controls to determine whether fibrous geometry was critical for inducing altered lipid metabolism. Physiochemical characterization and size dimensions of fibers and particles have been pub- (0.5 ,uCi/ml, Ci/mmol; 1 Ci = 37 GBq) for 24 hr and at confluency were incubated briefly (1 hr) with unlabeled medium. Agents (phospholipase C, PMA, or asbestos) then were added in fresh serum-free medium, and exposures were continued for 10-240 min. Next, cultures...

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A short-term inhalation model of asbestosis was developed in rodents to examine possible preventive approaches to lung disease. Fischer 344 (F344) rats were exposed for 10 and 20 days to National Institute of Environmental Health Sciences (NIEHS) crocidolite asbestos while sham controls were exposed to air only. To determine quantitative biochemical indicators of asbestos-induced lung disease, bronchoalveolar lavage (BAL) fluids were analyzed for lactic dehydrogenase (LDH), alkaline phosphatase, angiotensin-converting enzyme (ACE), and protein. Total and differential cell counts were performed on cell pellets from BAL. Lungs from additional rats were processed for histopathology, measurement of hydroxyproline, and autoradiography after injection of rats with 3H-thymidine. Exposure to asbestos for 10 and 20 days caused increases in LDH, alkaline phosphatase, and protein in BAL. In contrast, ACE was undetectable in BAL fluids from sham or asbestos-exposed rats. At both time periods, the percentages of polymorphonuclear leukocytes (PMNs) and lymphocytes in BAL were increased in asbestos-exposed rats. Total cell numbers in BAL were increased significantly at 20 days in animals inhaling asbestos. Exposure to asbestos for 10 and 20 days caused elevated amounts of hydroxyproline in lung and the development of fibrotic lesions. Asbestos-exposed rats exhibited increased numbers of interstitial cells and airspace epithelial cells incorporating 3H-thymidine, whereas labeled bronchiolar epithelial cells were not elevated significantly. The quantitative changes in asbestos-associated enzyme levels, cell types and protein in BAL, as well as increases in hydroxyproline and morphologic evidence of fibrosis, are useful indices of asbestos-related lung injury which enable preventive and therapeutic approaches to disease.