Addition of Calcite Reduces Iron’S Bioavailability in the Pennsylvania Coals—Potential Use Of Calcite for the Prevention Of Coal Workers’ Lung Diseases

Abstract

In the present study, a hypothesis was tested that the addition of calcite into the Pennsylvania coals may reduce levels of bioavailable iron (BAI), an important component in the mixed coal dust that may contribute to coal workers’ lung diseases. Predetermined proportions of calcite (0, 1, 2, 5, 10% w/w) were added into three PA coals. After suspending the mixtures in an aqueous phosphate solution (10 mM, pH 4.5), which mimics the phagolysosomal conditions of the cells, levels of pH as well as calcium ions (Ca²⁺) in the coals were increased in a calcite concentration-dependent manner. In contrast, levels of BAI (both Fe²⁺ and Fe³⁺) were decreased. The inhibitory effects of calcite on the bioavailability of iron in human lung epithelial A549 cells and primary rat alveolar macrophages (AMs) were also examined. It was found that levels of low-molecular-weight (LMW) iron were significantly decreased in both A549 cells and AMs treated with the 10% calcite–PA coal mixture compared to those treated with the PA coal alone, while calcite itself had no effect on intracellular LMW iron. Calcite also showed a significant inhibitory effect on PA coal-induced ferritin synthesis in A549 cells. Reverse-transcription polymerase chain reaction (RT-PCR) studies revealed that the iron-containing PA coal downregulated levels of transferrin receptor (TfR) mRNA in A549 cells, which was partially restored by the addition of calcite. Our results indicate that calcite can inhibit the bioavailability of iron in the iron-containing PA coals.

This project was supported by grant OH 03561 from the National Institute for Occupational Safety and Health and in part by the National Institute of Environmental Health and Science Center grant ES00260.

Notes

This project was supported by grant OH 03561 from the National Institute for Occupational Safety and Health and in part by the National Institute of Environmental Health and Science Center grant ES00260.