Formation of covalently bound protein adducts from the cytotoxicant naphthalene in nasal epithelium: species comparisons.

BACKGROUND

Naphthalene is a volatile hydrocarbon that causes dose-, species-, and cell type-dependent cytotoxicity after acute exposure and hyperplasia/neoplasia after lifetime exposures in rodents. Toxicity depends on metabolic activation, and reactive metabolite binding correlates with tissue and site susceptibility.

OBJECTIVES

We compared proteins adducted in nasal epithelium from rats and rhesus macaques in vitro.

METHODS

Adducted proteins recovered from incubations of nasal epithelium and 14C-naphthalene were separated by two-dimensional (2D) gel electrophoresis and imaged to register radioactive proteins. We identified proteins visualized by silver staining on complementary non-radioactive gels by peptide mass mapping.

RESULTS

The levels of reactive metabolite binding in incubations of rhesus ethmo-turbinates and maxillo-turbinates are similar to those in incubations of target tissues, including rat septal/-olfactory regions and murine dissected airway incubations. We identified 40 adducted spots from 2D gel separations of rat olfactory epithelial proteins; 22 of these were non-redundant. In monkeys, we identified 19 spots by mass spectrometry, yielding three non-redundant identifications. Structural proteins (actin/tubulin) were prominent targets in both species.

CONCLUSIONS

In this study we identified potential target proteins that may serve as markers closely associated with toxicity. The large differences in previously reported rates of naphthalene metabolism to water-soluble metabolites in dissected airways from mice and monkeys are not reflected in similar differences in covalent adduct formation in the nose. This raises concerns that downstream metabolic/biochemical events are very similar between the rat, a known target for naphthalene toxicity and tumorigenicity, and the rhesus macaque, a species similar to the human.