Superfund Research Program

Biomarkers of Exposure to Pulmonary Toxicants

Project Leader: Alan R. Buckpitt
Grant Number: P42ES004699
Funding Period: 1995-2010

Project-Specific Links

Final Progress Reports

Year:   2009  2004  1999 

This project focuses on two structurally related compounds-naphthalene and 1-nitronaphthalene.  Both compounds produce injury to airway epithelial cells in rodents and the cytochrome P450 monooxygenases are responsible for generating reactive, cytotoxic metabolites.  Naphthalene is volatile and produces species selective injury to lung of mice but not rats and to nasal epithelium in both species.  In comparison, 1-nitronaphthalene has low vapor pressure, is not species selective and likely reaches the lungs adsorbed to particulate matter.  Recent rodent cancer bioassays on naphthalene demonstrate regional susceptibility that follows the sites injured after acute doses.  Naphthalene has been found in a large number of Superfund sites and concentrations measured in air of a contaminated site undergoing clean up are high.  The overarching goal of this project is to obtain sufficient knowledge about the precise mechanisms by which these chemicals produce cytotoxicity in rodents to make a judgment regarding the susceptibility of humans to these compounds.  Several significant studies have been completed this year.  The project investigators have demonstrated that the underlying basis for the species selective injury associated with naphthalene is the difference in the levels of CYP2F.  The catalytic activities of the mouse and rat isoforms are identical.  Cloning, sequencing and cDNA directed expression of the human and rhesus orthologue in baculovirus infected Ti. ni cells demonstrated the over-expression of protein with no detectable heme incorporation.  This indicates that the human sequence does not incorporate the iron protoporphyrin properly and suggests that this protein might not be functional in vivo.  Continuing work is determining whether other CYP in human lung are capable of metabolizing naphthalene.  A second set of studies focused on the metabolism of naphthalene and 1-nitronaphthalene in rhesus macaque airways.  While the rates of formation of water soluble metabolites were 100 fold lower in airways of rhesus monkeys compared to mice or rats, the rates of reactive metabolite formation differed by only three fold.  This indicates that the formation of metabolites that are thought to be important in the toxicology of these compounds may be nearly as high in non human primates as in susceptible species.  A third series of studies demonstrated excellent correlations between naphthalene metabolism in well defined segments of the rat nasal epithelium with susceptibility to naphthalene toxicity (inhalation and parenteral administration).  Although earlier reports have shown significant P450 levels in the nasal epithelium of rhesus monkeys, the scientists have been unable to replicate this finding in studies using a number of macaques of different ages and genders.  A fourth series of studies has focused on the identification of proteins adducted by reactive naphthalene and 1-nitronaphthalene metabolites in susceptible rodent species and compared these with those adducted in rhesus macaques.  Nearly 50 protein adducts were identified in these studies and substantial overlap was found in those proteins adducted in rodents and rhesus airways.  These findings are being used as the basis for the development of biomarkers which can be applied to human nasal swipes.