Comparative evaluation of the effects of short-term inhalation exposure to diesel engine exhaust on rat lung and brain

Abstract

Combustion-derived nanoparticles, such as diesel engine exhaust particles, have been implicated in the adverse health effects of particulate air pollution. Recent studies suggest that inhaled nanoparticles may also reach and/or affect the brain. The aim of our study was to comparatively evaluate the effects of short-term diesel engine exhaust (DEE) inhalation exposure on rat brain and lung. After 4 or 18 h recovery from a 2 h nose-only exposure to DEE (1.9 mg/m(3)), the mRNA expressions of heme oxygenase-1 (HO-1), inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and cytochrome P450 1A1 (CYP1A1) were investigated in lung as well as in pituitary gland, hypothalamus, olfactory bulb, olfactory tubercles, cerebral cortex, and cerebellum. HO-1 protein expression in brain was investigated by immunohistochemistry and ELISA. In the lung, 4 h post-exposure, CYP1A1 and iNOS mRNA levels were increased, while 18 h post-exposure HO-1 was increased. In the pituitary at 4 h post-exposure, both CYP1A1 and HO-1 were increased; HO-1 was also elevated in the olfactory tuberculum at this time point. At 18 h post-exposure, increased expression of HO-1 and COX-2 was observed in cerebral cortex and cerebellum, respectively. Induction of HO-1 protein was not observed after DEE exposure. Bronchoalveolar lavage analysis of inflammatory cell influx, TNF-alpha, and IL-6 indicated that the mRNA expression changes occurred in the absence of lung inflammation. Our study shows that a single, short-term inhalation exposure to DEE triggers region-specific gene expression changes in rat brain to an extent comparable to those observed in the lung.

Fig. 1

mRNA expression of HO-1, iNOS, COX-2 and CYP1A1 in rat lungs after 4 h (a) or 18 h (b) recovery from diesel engine exhaust (DEE) inhalation exposure. Data represent mean values and standard errors (n = 5) and are expressed as GADPH-adjusted fold-increase mRNA expression compared to controls. * p < 0.05 versus air-exposed group

Fig. 2

mRNA expression of HO-1 (a), iNOS (b), COX-2 (c) and CYP1A1 (d) in specific rat brain regions after 4 h recovery from diesel engine exhaust (DEE) inhalation exposure. Data are shown as mean and SEM (n = 5 per treatment) of the GAPDH adjusted mRNA expression, relative to the mean mRNA expression as measured in the cerebellum of the air-exposed animals for each gene. * p < 0.05 versus air exposure in the same brain region

Fig. 3

mRNA expression of HO-1 (a), iNOS (b), COX-2 (c) and CYP1A1 (d) in specific rat brain regions after 18 h recovery from diesel engine exhaust (DEE) inhalation exposure. Data are mean and SEM (n = 5 per treatment) of GAPDH adjusted mRNA expression, relative to the mean mRNA expression as measured in the cerebellum. * p < 0.05 versus air exposure in the same brain region

Fig. 4

HO-1 protein expression by immunohistochemistry (a, b) and ELISA (c) in rat brain tissue after diesel engine exhaust (DEE) inhalation exposure. Representative HO-1 staining in rat cerebellum after 24 h recovery from a 2 h exposure to filtered air (a) or DEE (b). Original magnification ×25. Panel C shows HO-1 expression presented as pg/mg total protein, in brain section lysates