Beth Hart - US grants

Inhalation of cadmium, a known environmental pollutant and a contaminant of cigarette smoke, induces the synthesis of a metallothionein - like protein in the lungs of rodents. The purpose of our research project is to study the synthesis and role of this pulmonary protein in the rat. First we will determine the relationship between cadmium inhalation conditions (i.e., concentration, frequency of exposure, and solubility of Cd compound) and cadmium and metallothionein levels in the lung, kidney, and liver. Then, by means of bronchopulmonary lavage, elutriator centrifugation, and density gradient techniques, we will isolate alveolar macrophages, Type II alveolar cells, and Clara cells from cadmium exposed animals and quantitate cellular levels of metallothionein with a radio-immune assay. To test the hypothesis that pulmonary metallothionein plays a protective role in the lung we will determine whether: 1) multiple Cd exposures lead to the development of pulmonary tolerance to Cd; and 2) pre-treatment of rats with low dose Cd concentrations (a) offers pulmonary protection against a subsequent challenge with a highly toxic dose or (b) increases the ability of the lungs to retain Cd and, as a consequence, spares the kidneys and liver. Cd-induced lung damage will be assessed cytologically by determining the number and type of free alveolar cells, biochemically by assaying for cellular enzymes in lavage fluid, and histologically. To test the hypothesis that metallothionein when present extracellularly has a deleterious effect on pulmonary tissue and cells, we will determine whether: 1) intratracheal instillation of metallothionein has greater cytotoxic effects on the lung than an equivalent amount of cadmium as CdC12 and 2) the viability and/or growth of lung cells (i.e., lung fibroblasts, alveolar macrophages, Type II cells) is more affected by the presence of metallothionein than by an equivalent amount of Cd.

Cadmium is a known environmental and industrial pollutant and a contaminant of cigarette smoke. Prior inhalation to Cd results in pulmonary adaptation which helps protect the lung against an acute inhaled dose. Metallothionein (MT), a metal and sulfur rich protein, is synthesized by the lung in response to Cd inhalation. Type II alveolar cells appear to be a primary site for MT synthesis. The role of MT and type II alveolar cells in pulmonary adaptation/tolerance to Cd will be investigated. The dose and time dependent nature of Cd adaptation/tolerance will be determined and correlated with pulmonary MT levels. Ultrastructural morphometry and quantitative autoradiography will assess type II cell hyperplasia and/or hypertrophy during Cd adaptation. Calculations of the type II cell contribution to total lung MT will be made using morphometric data and biochemical analyses of MT content of lung homogenates and isolated type II cells. Sub-cellular localization of MT in isolated type II cells and in situ in lung will be performed using immunohistochemical techniques to establish whether translocation of MT from the cytoplasm to the nucleus occurs during the Cd adaptive process. The role of glucocorticosteroids in the pulmonary response to Cd will be investigated by: (a) correlating plasma corticosterone levels during repeated or acute Cd exposures with the inflammatory cell response; (b) testing whether adrenalectomy exacerbates the toxic effects of Cd and/or reduces the ability of the lung to adapt to Cd; and (c) determining whether dexamethasone administration induces MT synthesis in the lung and/or reduces Cd-induced lung injury. The hypothesis that MT acts as a scavenger of free radicals in the lung will be tested by determining whether Cd-adapted animals, which have elevated levels of pulmonary MT, are more resistant to lung injury induced by oxygen or bleomycin. Animals made tolerant to oxygen will be tested for induction of pulmonary MT and cross tolerance to Cd. Experiments will be performed to differentiate the protective effect of metallothionein in Cd-adapted animals from that provided by glutathione, glutathione shuttle enzymes, and/or superoxide dismutase. The results of the proposed research will increase our understanding of the effects of cadmium inhalation and the roles that metallothionein and the type II cell play in pulmonary defense.

DESCRIPTION (Adapted from the Investigator's Abstract): Cadmium is an atmospheric pollutant, a tobacco smoke contaminant, and a human lung carcinogen. The investigators have previously demonstrated that chronic cadmium exposure to both cell lines and whole animal studies leads to the emergence of an epithelial cell sub-population with increased resistance to oxidant induced cell death. This new phenotype is hypothesized to be caused by cadmium induced alterations in gene expression, linked mechanistically to cellular glutathione levels and to a common transcription factor. Some of these resistant cells may exhibit increased proliferation (when exposed to tumor promoters) and are resistant to apoptosis. This could ultimately cause clonal expansion and tumor formation. To test these hypotheses, the investigators propose (1) study Cd- induced expression of known cytoprotectins (metallothione, GSH S-transferase, heme oxygenase-1) and enzymes that increase GSH levels (gamma glutamylcysteine synthetase and gaama glutamyl transpeptidase) in rats; (2) immunolocalize these resistance factors in presumptive lung tumor target sites (alveolar type II cells); (3) establish the role of the Ap-1 transcription factor in lung epithelial cell adaptation to cadmium and cross-tolerance to oxidants; (4) determine if malondialdehyde-DNA adducts form in Cd exposed lung epithelial cells; (5) evaluate the potential link between cadmium induced type II cell proliferation and metallothione (MT) expression; and, (6) determine whether Cd-adapted lung epithelial cells are resistant to normal apoptotic processes by oxidants and cytokines and whether phorbal esters increase the proliferative capacity to grow in culture and soft agar (as a marker for tumor promotion).