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PubMed2004

Tissue distribution of Thorotrast and role of internal irradiation in carcinogenesis.

Carcinogenesis in Thorotrastosis has been assumed due to direct bombardment by alpha-particle with high linear energy transfer during decay of 232Th. To revisit the mechanism of carcinogenesis by Thorotrast (THR), we examined the tissue distribution of THR granules and two-dimensional distribution of radioactivity in the organs of Thorotrastosis patients and studied their spatial relationship to histopathological changes. The high radioactivity in the patients' organ was predominantly derived from decay of Thorium series and showed unique distribution, while the far lower natural radioactivity was mainly from Uranium series decay and fairly evenly distributed. It was found that a large majority of THR granules were phagocytized by macrophages and were embedded in extensive fibrosis. Cancer was rarely in the center of THR deposition but rather at a distance from the deposits. These observations may indicate that the predominant feature of THR deposition is the tissue damage by direct hit of alpha-particles and subsequent fibrosis. The effect of THR resembles action of toxic chemical agents, as several authors have pointed out. We therefore assume that carcinogenesis in Thorotrastosis is a combination of events, such as regeneration of liver tissue after radiation damage, emission of secondary electrons, ionization of the surrounding tissue, and beta- or gamma-ray from daughter nuclei of Thorium (Th). In this context, the role of alpha-particle is important but more intriguing.

Aged↗
PubMed1979

Cytological events in allo-stimulated lymphocytes triggered by exposure to stimulatory alloantigens. III. Changes in the areal density of cytoplasmic vacuoles containing endocytized Thorotrast.

H-2b lymphocytes were sensitized against H-2d alloantigens by a lymphocyte culture reaction (MLR) and incubated with H-2d mastocytoma cells. Thirty minutes before incubation with the mastocytoma cells Thorotrast was added to the lymphocyte culture medium. The interaction between lymphoid cells and mastocytoma cells was stopped by fixation with glutaraldehyde. The areal densities of the cytoplasmic vacuoles were examined by electron microscopy. Two populations of lymphocytes were observed, small lymphocytes with heterochromatic nuclei and larger lymphocytes (lymphoblasts) with euchromatic nuclei. Only the lymphoblasts showed changes following interaction with target cells. The areal density of Thorotrast containing vacuoles in sensitized lymphoblasts increased during the three hour observation period, but the percentage of vacuoles containing Thorotrast in the total area of cytoplasmic vacuoles decreased in the first thirty minutes of interaction with target cells. This observation may indicate greater formation of vacuoles from the Golgi apparatus compared with the formation of vacuoles from the cytoplasmic membrane at the onset of interaction with target cells. In the multivesicular bodies (MVB) the Thorotrast was first observed inside the small vesicles and later on it was also observed in the matrix of the MVB. After three hours of interaction Thorotrast was observed laying "free" in the matrix of phagosomes along with myelin figures.

Animals↗
PubMed1975

Intralysosomal formation of amyloid fibrils.

Unusual inclusions, which occurred in the reticuloendothelial cells intimately associated with fresh amyloid deposits, were analyzed by electron microscopy. The inclusions were located in the areas rich in the primary lysosome type of dense bodies and the cytoplasmic invaginations containing well-oriented amyloid fibrils. They were single-membrane-bounded, measured 0.3 to 0.8 mu in width and 0.5 to several microns in length, and showed considerable variation in the electron density of their contents. The latter consisted of two different ultrastructural elements: fibrillar profiles and a homogeneous or finely granular electron-dense substance. The fibrillar profiles were virtually identical in ulstrastructure to the amyloid fibrils and were well-oriented parallel to the long axis of the inclusion. The homogeneous or finely granular electron-dense substance appeared to be comparable to that composing the dense body matrix. The inclusions were usually acid phosphatase positive, but did not take up intravenously injected Thorotrast particles. These data led us to conclude that these inclusions were transitional forms from the usual dense bodies to the deep cytoplasmic invaginations containing well-oriented amyloid fibrils (which are accepted by most investigators as the sites of amyloid formation) and thus constitute direct evidence for the involvement of lysosomes in amyloid fibril formation.

Acid Phosphatase↗