The locus of pathogenicity of asbestos dust: a theory

Lung response to particulates with emphasis on asbestos and other fibrous dusts

Many theories have been proposed to explain asbestosis and asbestos-related pulmonary disease. However, none of the theories give a completely plausible explanation for the pathogenesis. Recently, attention has been drawn to a theory that the fibrogenicity or carcinogenicity of fibrous dust particles is related to fiber diameter and length rather than to chemical properties. This theory may help partially elucidate the disease process but is still far from solving the enigma of pulmonary fibrosis or carcinogenesis. The theory cannot explain the absence of these pathological effects among fiberglass workers or experimental animals exposed by inhalation (even though mesotheliomas are induced by intrapleural implantation and fiber dimension-related fibrogenicity is demonstrated by intratracheal injection). Little information regarding the pulmonary response to manmade fibrous particles is available in animals following inhalation exposure. Attempts should be made to confirm the absence of adverse effects using animal inhalation experiments even though to this point there is no conclusive evidence that either lung cancer or pulmonary diseases can be produced among employees in manmade fiber industries. A new research trend seems concentrated on testing the durability of asbestos or manmade fibers. This is based on the concept that biological effects of fibrous particles are the result of relative durability and that particles which can be fragmented or shortened may be less pathogenic. In the last two decades, considerable understanding about pulmonary fibrosis and carcinogenesis of asbestos has been achieved by clinical and animal experiments. In vitro tests including cytotoxicity, hemolysis, immunology, and enzyme biochemistry have provided important information on the interrelationships among these various biological effects of asbestos.

Asbestos bodies in a bile duct cancer after occupational exposure

A case of asbestosis after 5 years of occupational asbestos exposure is presented. At the postmortem examination, cholelithiasis and a cancer developing from the cystic duct were found and identified histologically as a squamous cell carcinoma. After digesting the tumor tissue, short asbestos bodies and fragments could be identified having a similar shape as those observed in the lung. The possible role of asbestos in the carcinogenesis of the observed bile duct cancer is proposed. The digestive examination of all malignant tumors of any origin after an asbestos exposure is suggested for the identification of the possible presence of ingested asbestos fibers, and to obtain further comprehensive human pathological data.

Biological effects of ingested amosite asbestos, taconite tailings, diatomaceous earth and Lake Superior water in rats

Because amphibole fibers were found in Lake Superior and in Duluth municipal water, this study was initiated to evaluate the carcinogenicity of ingested asbestos. Groups of 22-30 Sprague-Dawley rats were fed asbestos and related materials during their lifetime and were examined at autopsy after spontaneous death. Test materials were unfiltered Duluth city tap water, municipal water reservoir sediment suspension, taconite plant tailings, amosite asbestos (a "low-dose" group at 20 mg/rat . day an a high-dose group at 300 mg/rat . day) and diatomaceous earth; a control group drank fiber-free well water or filtered city tap water. Autopsy studies revealed no significant increase in the incidence of malignant tumors in any experimental group compared with that in the control group.

Induction of pulmonary carcinoma in rats by chronic inhalation of dust from pulverized asbestos pipe covering

Rats and hamsters were exposed to the dust of pulverized asbestos pipe covering at an average concentration of 85 mg/m(3) for 6 h/d, 5 d/wk, for 7 mo, followed by a lifetime observation period. In rats, the pulmonary responses were alveolar adenomatous proliferation, nonprogressive fibrosis, squamous metaplasia, and a substantial incidence of pulmonary carcinoma formation. A smaller group of hamsters exposed under these conditions experienced an earlier onset of mortality than control hamsters, which were not subjected to the exposure regimen. Although this prevented conclusive evaluation of the pulmonary response in this species, no pulmonary neoplasms were noted in the surviving hamsters.

Asbestos and embryonic development

Chrysotile asbestos was administered to pregnant CD-1 mice in their drinking water and to Day 4 blastocysts during culture. Administration to pregnant mice did not affect embryo survival. In vitro administration of asbestos did not interfere with embryo implantation upon transfer of blastocysts to recipient females but did result in a decrease in postimplantation survival. These studies did not demonstrate asbestos to be teratogenic whether administered to the dam or to the blastocyst in vitro.