Accumulation of Iron in the Rat Lung after Intratracheal Instillation of Coal Dust

Abstract

Inhalation of coal dust is associated with an accumulation of iron in the human lung. Collagen deposition in the lungs of coal miners can correlate with the concentration of tissue nonheme iron. Associations between the accumulation of this metal and fibrotic injury could result through either (1) catalysis of free radicals by iron associated with the dust and subsequent oxidant dependent mediator release, or (2) metal dependent enzyme activation. To better quantify and characterize the accumulation of the metal in the lung, 60-day old, male Sprague Dawley rats were intratracheally instilled with 1.0 mg coal dust (Dust 1508; Pennsylvania State University repository) twice a week for 6 months. Every 4 weeks, animals were euthanized and the lungs excised. Tissue nonheme iron was measured and lungs, fixed with 10 percent formalin, were stained for iron (Perls' Prussian blue), ferritin using a polyclonal antibody, and collagen (Masson trichrome). Nonheme iron accumulated during the 6 months of study. Stains for iron demonstrated an accumulation of the metal in the area adjacent to the dust but only after 2 months of instillation. However, an increase in stainable ferritin was noted within the first 4 weeks of instillation. Increases in ferritin developed first in the airway epithelial cells and alveolar macrophages and then later in the epithelial lining cells of the alveoli. Collagen deposition was observed in the area adjacent to the dust but, similar to the iron stain, only after 2 months of dust instillation.