Comparison of respiratory tract effects of inhaled naphthalene in rats with and without co‐exposure to carbon nanoparticles

Abstract

We have previously observed that inhalation co‐exposure of rats to carbon particles resulted in increased deposition of naphthalene in the bronchi and lungs. In order to examine whether these changes in naphthalene deposition might alter the location or severity of naphthalene toxicity within the respiratory tract, male Sprague‐Dawley rats were exposed nose‐only to naphthalene vapor (20 ppm) with or without carbon particles (5mg/m3) for 4 h. Animals exposed to particles only or to filtered room air alone (no naphthalene or particles) served as controls. Respiration was monitored during exposure by plethysmography. Forty‐eight h after exposure, rats were euthanized and brochoalveolar lavage fluid (BALF) was collected. Nasal and lung tissues were removed and prepared for histological assessment. Lymphocyte counts in BALF from animals treated with naphthalene plus particles were significantly higher than in animals treated with naphthalene or particles alone, or in controls. However, there was no increase in pro‐inflammatory cytokines or chemokines in BALF in animals co‐treated with naphthalene and particles compared with other treatment groups. Animals treated with naphthalene, with or without particles, had significant epithelial damage in the nasal cavity characterized by extensive fibrinous membrane and necrosis and loss of epithelium, as well as inflammation characterized by lymphocytes and plasma cells in the submucosa and epithelium. Particle co‐exposure did not appear to influence the severity of lesions. No nasal cavity epithelial lesions were observed in animals treated with particles only or room air alone. No significant pathology was observed in trachea, bronchioles or alveoli in any treatment group. The results of this study suggest that the increased deposition of naphthalene in lungs with particle co‐exposure observed previously is not associated with increased pulmonary toxicity, at least under the conditions of this study.