Morphology and Elemental Composition of Inhaled Particles in Human Lungs as Defined by Analytical Scanning Electron Microscopy (SEM) and SEM Energy Dispersive X-ray Microanalysis (SEM/EDX).
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- Life Sciences; Medical Sciences; Oncology
thesis / dissertation description
Worldwide, more men and women die of lung cancer than any other type of cancer. Approximately 85% of all lung cancers are attributed to smoking. The cause of the remaining 15% of lung cancer deaths is unknown. However, during the last year, the National Toxicology Program has designated respirable silicon dioxide particles as a known human carcinogen. Airborne particles are ubiquitous and are heterogeneous with respect to origin, size, morphology, and chemical composition. Many types of particles are inhaled and penetrate deep into the lung where they are often phagocytized by alveolar macrophages. The question arises as to whether airborne particles that are inhaled are causative agents of pulmonary diseases, including cancer. The goal of my research was to determine whether the chemical element composition of inhaled particles in the human lung could be elucidated. This investigation was undertaken to test the hypothesis that the chemical element composition of an individual particle within a given human alveolar macrophage could be defined with an analytical scanning electron microscope (SEM) that had been configured for energy-dispersive X-ray microanalysis (SEM/EDX). Methods have been developed in order to obtain a pure macrophage population for these studies. Fresh, surgically excised lung tissue was obtained from cancer patients who were undergoing a pneumonectomy to remove a malignant lung tumor. Different samples of the lung specimens processed for analysis by SEM/EDX included: (a) lung tissue that had been digested chemically and the residue collected by filtration onto micropore membranes; (b) lung tissue that had been embedded in wax blocks, sectioned, and mounted onto glass microscope slides, and subsequently de-waxed; and(c) glass and polystyrene slides of macrophages present in touch imprints prepared using fresh lung tissues. Single particles were then probed with a Hitachi S-4000 SEM and a Princeton Gamma Tech (PGT) X-ray microanalyzer. Individual particles were viewed simultaneously in the specimen using both the secondary electron image (SEI) and backscattered electron image (BEI) modes. The X-ray spectrum that identifies a particular element is given by the PGT microanalyzer. SEM/EDX analysis of individual inhaled particles present in the residue of chemically digested human lung specimens revealed the presence of sodium (Na), aluminum (Al), silicon (Si), phosphate (P), sulfur (S), iron (Fe) and zinc (Zn). Elemental composition of inhaled particles in thin (~ 5 pm) sections of human lung tissue was also elucidated by SEM/EDX. In subsequent studies, the same technology successfully displayed the chemical element composition of a selected inhaled particle within a single macrophage. Particularly noteworthy is that Fe was found in all specimens examined. The results of these studies have advanced our knowledge of the chemical composition of inhaled particles and will provide the basis for future studies defining the role of macrophages and macrophage-derived factors in the etiology of different malignant and non- neoplastic lung diseases.