Naphthalene an 2-methylnaphthalene are priority toxic pollutants to which humans are exposed from several sources. Administration of these compounds to mice results in highly selective injury to nonciliated bronchiolar epithelial cells; lungs of rats are refractory even to LD50 doses. Nasal olfactory epithelium of both rats and mice is sensitive to parenterally administered naphthalene. A similar distribution of toxic effects of naphthalene has been observed in the NTP 2 year chronic bioassay in the mouse; metaplasia of the olfactory epithelium and an increase in alveolar/bronchiolar adenomas were notable findings (NTP-TR-410). The relevance of these data to the human is not established, primarily because there are no reliable methods for determining whether the mouse or the rat is a good surrogate for humans in testing lung toxic chemicals. This application proposes to continue multidisciplinary studies which utilize the differences in species, tissue and cell susceptibility to these agents as tools to explore the underlying basis for cellular injury in the lung. The long term goals are twofold: 1) identify biochemical/metabolic/molecular events controlling susceptibility of cells to cytotoxic agents and 2) refine and use in vitro methods to assess toxicity in animal models and in humans. In this application for renewal, these goals will be pursued by testing the following hypotheses: 1) naphthalene epoxide arylates two proteins (Mr 15-16 kDa) within susceptible cells; arylation of these proteins is critical to the cytotoxicity which ensues after exposure to naphthalene but not 2-methylnaphthalene; 2) S- thiolation of proteins in susceptible cells results from exposure to either naphthalene (mediated by naphthoquinones) or 2-methylnaphthalene; 3) naphthalene oxides diffusing from metabolically active cells are capable of producing cytotoxicity in other cells; and 4) the tolerance which develops after administration of multiple doses of naphthalene is a result of several factors including: a) decreased ability of target cells to catalyze the metabolic activation of naphthalene to epoxides, b) increased protection afforded by increases in epoxide hydrolases or glutathione transferases capable of rapid conversion of the epoxides to diols/conjugates, c) decreased sensitivity due to more rapid turnover of glutathione (GSH) in tolerant cells or d) an alteration in the level of the 15-16 kDa proteins to which reactive naphthalene metabolites specifically bind in the Clara cell. Species, regional and cellular differences in naphthalene and 2- methylnaphthalene induced injury and repair will be defined in vivo. Interaction of naphthalene, 2-methylnaphthalene and metabolites within Clara cells, hepatocytes, and dissected airways in vitro will be examined to identify biochemical/metabolic alterations which correlate with cellular toxicity. Once those factors critical to determining cellular susceptibility to these chemicals are identified, additional work will be performed in lung specimens obtained from Rhesus macaques as surrogates for humans. These studies will provide a better basis for assessing risk of human exposure to naphthalene/2-methylnaphthalene and will result in methods that are applicable for assessing hazards of other pneumotoxic chemicals.
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