Subchronic effects of nasally instilled diesel exhaust particulates on the nasal and airway epithelia in mice

Abstract

Diesel exhaust is the major source of ultrafine particles released during traffic-related pollution. Subjects with chronic respiratory diseases are at greater risk for exacerbations during exposure to air pollution. This study evaluated the effects of subchronic exposure to a low-dose of diesel exhaust particles (DEP). Sixty male BALB/c mice were divided into two groups: (a) Saline: nasal instillation of saline (n = 30); and (b) DEP: nasal instillation of 30 µg of DEP/10 µl of saline (n = 30). Nasal instillations were performed 5 days a week, over 30 and 60 days. Animals were anesthetized with pentobarbital sodium (50 mg/kg intraperitoneal [i.p.]) and sacrificed by exsanguination. Bronchoalveolar lavage (BAL) fluid was performed to evaluate the inflammatory cell count and the concentrations of the interleukin (IL)-4, IL-10, and IL-13 by enzyme-linked immunosorbent assay (ELISA). The gene expression of oligomeric mucus/gel-forming (Muc5ac) was evaluated by real-time polymerase chain reaction (PCR). Histological analysis in the nasal septum and bronchioles was used to evaluate the bronchial and nasal epithelium thickness as well as the acidic and neutral nasal mucus content. The saline group (30 and 60 days) did not show any changes in any of the parameters. However, the instillation of DEP over 60 days increased the expression of Muc5ac in the lungs and the acid mucus content in the nose compared with the 30-day treatment, and it increased the total leukocytes in the BAL and the nasal epithelium thickness compared with saline for 60 days. Cytokines concentrations in the BAL were detectable, with no differences among the groups. Our data suggest that a low-dose of DEP over 60 days induces respiratory tract inflammation.

Keywords::

• Air pollution
• diesel exhaust particulate
• nose epithelium
• lung
• interleukins
• Muc5ac
• hyperplasia
• mucus

Acknowledgements

The authors thank the support of Dr. Luís Fernando Ferraz Silva for technical assistance regarding the image analysis software system (Image Pro-plus), Prof. Dr. Roger Chammas for helpful suggestions in RT-PCR (MUC5ac), and Laísa Moreira for the technical support. The authors also thank Dr. Regiani Carvalho de Oliveira for supporting elemental metals determination, Dr. Paulo Afonso de André for particle collection, and Luiz Afonso Pires and the technical staff of the Experimental Air Pollution Laboratory for animal care during the exposure period of this study.

Declaration of interest

This work was supported by CAPES, CNPQ (484819/2007-7), and FAPESP.