Inhalation of residual
oil fly ash (ROFA) has been shown to impair lung defense mechanisms in laboratory animals and susceptible populations. Bioavailability of soluble transition metals has been shown to play a key role in
lung injury caused by ROFA exposure. The goal of this study was to evaluate the effect of soluble metals on lung defense and injury in animals preexposed to ROFA followed by pulmonary challenge with a bacterial pathogen. ROFA was suspended in saline (ROFA-TOTAL), incubated overnight at 37 degrees C, and separated by centrifugation into soluble (ROFA-
SOL) and insoluble (ROFA-INSOL) fractions. A portion of the soluble sample was treated with the
metal-binding resin
Chelex for 24 h at 37 degrees C. Sprague-Dawley rats were intratracheally dosed at d 0 with ROFA-TOTAL (1.0 mg/100 g
body weight), ROFA-INSOL, ROFA-
SOL, saline, saline +
Chelex, or ROFA-
SOL +
Chelex. At d 3, 5 x 10(5) Listeria monocytogenes were intratracheally instilled into rats from each treatment group. At d 6, 8, and 10, left lungs were removed, homogenized, and cultured to assess bacterial clearance. Histopathological analysis was performed on the right lungs. Pulmonary exposure of ROFA-TOTAL or ROFA-
SOL before
infection led to a marked increase in
lung injury and
inflammation at all three time points after inoculation, and an increase in morbidity in comparison to saline control rats. Treatment with ROFA-INSOL, saline +
Chelex, or ROFA-
SOL +
Chelex caused no significant increases in lung damage and morbidity when compared to control. By d 10, the ROFA-
SOL and ROFA-TOTAL groups had approximately 200-fold more bacteria in the lung than saline control, indicating the inability of these groups to effectively respond to the
infection. None of the other treatment groups had significant impairments in bacterial clearance when compared to saline. In conclusion, exposure to ROFA-TOTAL and ROFA-
SOL significantly suppressed the lung response to
infection. These results suggest that soluble metals present in ROFA may play a key role in increased susceptibility to pulmonary
infection in exposed populations.