Student Research: Raymond Bruce Christian
MS, , 1992
Faculty Advisor: Daniel L. Luchtel
Toxicity of Fibers and Particulates as Studied in Rat Lung Organ
Lung organ culture is a method that allows lung tissue to be maintained with normal architecture for 4-6 weeks in vitro. The lungs of rats were infused intratracheally with a warmed 0.5% agarose solution in serum free culture medium. The initial infusion inflates the lung, the agarose solution then solidifies at room temperature, maintaining the lung in an inflated state. The lungs were then cut into 1-2mm transverse slices and the slices placed on surgical gelfoam soaked in culture medium, which exposed each slice to both air and nutrients. This method has been used by others to study the fibrotic responses to asbestos, silica and bleomycin in various animal species. The fibrotic potential of several types of dusts were studied. Advanced composite materials are composed of carbon fibers enbedded in a matrix material. Three types of composite dusts were studied; those composed of carbon fiber only, carbon fiber with an epon 828 coating, and a fully formed composite composed of carbon fibers bound in a matrix containing polyetheretherketone. Three grades of Diatomite filter material composed of diatomaceous earth were also included in this study. Diatomaceous earth contains varying degrees of crystalline silica, and when processed and heated to form different grades of filter material, the percentage of crystalline silica changes. Three types of such amterial with varying silica content were studied. Silica, a known fibrotic agent, was the positive control while a negative control consisted on an agarose infusion without a test dust. Certain test materials were cultured both alone and in the presence of tumor necrosis factor, a cytokine linked to silica induced fibrosis in mice. The response of the tissue to the dusts was assessed at day 0, 1 week, 2 weeks and 4 weeks. A histopathological examination evaluated qualitative changes. Quantitative changes were assessed utilizing two methods: measurement of the percent tissue area with an image analysis system and determination of the amount of collagen with a biochemical assay for hydrocyproline. The results indicated that the tissue maintained itself in culture with minor degenerative changes. Qualitative changes could be observed among the different test materials, although the quantitative changes as measured by image analysis were not sufficiently different to determine the differential fibrotic potential of the test materials. Lungs exposed to dusts did show significantly greater percent tissue area compared to the negative control. The hydroxyproline levels increased slightly from day 0 to week 1 and then remained at approximately the same levels throoughout the experiment. The hydroxyproline changes were similar in both the negative control and lungs exposed to dusts. It was concluded that although rat lung tissue could be maintained successfully in oprgan culture, the method is unsuitable as a model or assay system for testing environmental particulates.