Epidemiology of mesothelioma and historical background.

Mesothelioma is a "new" malignant disease strongly associated with exposure to amphibole asbestos exposure (amosite and crocidolite) environmentally and in the work place. Nonetheless, in recent years, we have learned that many cases of mesothelioma are idiopathic, while some are caused by therapeutic irradiation or chronic inflammation in body cavities. This paper reviews the key epidemiological features of the malignancy in the context of the biological and mineralogical factors that influence mesothelioma development. These tumors challenge the diagnostic pathologist's acumen, the epidemiologist's skill in devising meaningful and definitive studies, the industrial hygienist's knowledge of environmental hazards in diverse occupational settings, and the clinician's skill in managing an intrepid and uniformly fatal malignancy.

Cardiac synovial sarcoma with translocation (X;18) associated with asbestos exposure.

A primary cardiac spindle cell tumor with immunoreactivity for keratin proteins is reported. Cytogenetic analysis of the tumor demonstrated a translocation (X;18), an aberration almost exclusively reported in synovial sarcomas. Postmortem examination revealed amphibole asbestos within the lungs and diaphragmatic pleural plaques indicative of asbestos exposure. These findings raise questions about the possible causation of this tumor.

Talc pneumoconiosis: a pathologic and mineralogic study.

Seventeen cases of "talc pneumoconiosis" were examined pathologically and mineralogically to ascertain whether a true talc pneumoconiosis existed and also to compare these results in primary, secondary, and tertiary exposures. Mineralogic analyses were performed on wet tissue or tissue blocks by a variety of techniques, including analytical transmission electron microscopy and x-ray diffraction. Overall, the pathologic appearance of the tissues was similar in primary, secondary, and tertiary exposures, although ferruginous bodies and foreign body giant cells were not always present in cases caused by secondary exposures. Mixed dust fibrotic lesions were found in two cases in which there were substantial quantities of quartz present. There was great variation in the minerals found within the lung tissues. Several cases showed significant quantities of mica and kaolin in addition to talc. One case consisted predominantly of mica and in fact could be regarded as "mica pneumoconiosis"; this diagnosis was correctly attributed because of the mineralogic findings. Tremolite fibers were found in only two cases. Substantial quantities of crocidolite and amosite fibers were found in one case. This study shows that "talcosis" frequently represents disease associated with a variety of minerals and that talc is a common denominator. It shows also the usefulness of lung dust mineral analysis, particularly in secondary industries, for evaluating the cause of a pathologic reaction when exposures are especially complex.

In vivo administration of TNF-alpha prevents EMC-M virus induced viral encephalitis.

EMC-M virus causes a monophasic paralytic syndrome characterized by encephalitic lesions in the brain and patchy demyelinating lesions in the spinal cord and nerve roots of BALB/c mice. Since the replication of EMC virus in vitro is inhibited by tumor necrosis factor (TNF)-alpha we have studied the effect of in vivo administration of this cytokine on the acute disease. Our studies show that periodic administration of TNF-alpha to animals infected with EMC-M reduces viral titers in the brain, and decreases the degree of clinical paralysis and the severity of the inflammatory lesions in the brain.

Bronchiolar inflammation and fibrosis associated with smoking. A morphologic cross-sectional population analysis.

The lungs of 42 smokers and 13 nonsmoking males of various ages who died suddenly and unexpectedly were examined grossly using Gough-Wentworth whole-lung sections and by microscopic planimetry to assess the severity and prevalence of emphysema. The bronchioles in representative histologic sections were evaluated for inflammation and epithelial metaplasia as well as for fibrosis and muscular hypertrophy. Postmortem interviews with next of kin established a history of cigarette smoking and excluded possible occupational exposures to toxic or particulate inhalants. Emphysematous changes were not prominent in members of the study group, but they tended to be more severe in smokers (p = 0.059) and increased in severity with age (p less than 0.001). Inflammatory changes (so-called smoker's bronchiolitis) were evident in smokers of all ages, although they were significantly less prominent in the lungs of older smokers. On the other hand, respiratory and membranous bronchiolar wall fibrosis was increasingly evident in older smokers (p less than 0.05). Muscular hypertrophy in the bronchiolar walls was significantly greater in smokers, but a change with age was not observed. These findings strongly suggest that bronchiolar fibrosis is associated with chronic cigarette use. These lesions occur independently of emphysema and may account for some of the subtle physiologic alterations observed in smokers.

T-lymphocyte effects on murine cytomegalovirus pulmonary infection.

Cytomegalovirus (CMV) infections were induced in male BALB/c mice treated with rat monoclonal antibodies (MAb) to deplete selectively CD8 and CD4 cell populations in vivo. The animals were then inoculated intraperitoneally with murine CMV and the infection was monitored virologically and histologically. High concentrations of virus were found in the lungs of mice depleted of CD4 or both CD4 and CD8 cells. These animals developed pulmonary infections that persisted for at least 49 days after inoculation. In contrast, immunologically intact mice and those administered anti-CD8 MAb experienced only a transient infection of the lungs. Focal interstitial infiltrates of mononuclear cells were demonstrated in pulmonary tissues of CD4 MAb-treated animals, but not in normal mice and those receiving the CD8 MAb. Adoptive transfer of CD4 cells to animals (rendered immune-incompetent by thymectomy and irradiation) protected against pulmonary infection and the development of interstitial pneumonia. Mice treated with CD4 MAb failed to produce specific CMV antibody, whereas the depletion of CD8 cells had no effect on antibody elaboration. Administration of anti-CD4 and CD8 MAb did not affect virus replication in the salivary glands, the preferential site for CMV infection in the mouse. Induction of pulmonary infection and interstitial pneumonia by CMV in BALB/c mice is mediated by CD4 T cells.

Induction of DNA strand breaks in cultured rat embryo cells by crocidolite asbestos as assessed by nick translation.

Asbestos, a proven carcinogen, is reported to have no genotoxic effects. We hypothesized, however, in light of its clastogenic effects that one mechanism by which asbestos induces cell transformation and tumorigenesis involves the induction of DNA strand scission. Cultured rat embryo cells were exposed to low concentrations of International Union Against Cancer crocidolite and examined at intervals ranging from 2 to 48 h. The induction of DNA strand breaks was examined using the technique of nick translation followed by autoradiography or scintillation counting. Our results indicate that cells exposed to crocidolite have a higher incidence of DNA breaks and that this effect becomes apparent within 2-6 hours of exposure. Ball-milled crocidolite as well as riebeckite have a significantly lower effect while glass fibers induce a more pronounced DNA strand damage. These observations support the role fiber length plays in carcinogenesis and suggest that the classification of asbestos as a nongenotoxic carcinogen be reconsidered.

Chromosomal translocations with specific breakpoints in asbestos-induced rat mesotheliomas.

Cytogenetic analysis was conducted on cells of 15 rat mesotheliomas induced in rats by the i.p. inoculation of crocidolite or chrysotile asbestos. These tumor cells were diploid, triploid, or tetraploid. All tumor lines exhibited aneuploidy and marker chromosomes. Loss of at least one copy of the X chromosome was observed in each of the tumors analyzed, and loss of copies of chromosomes 8, 16, 20, or 18 characterized at least six of the tumors. Translocations were observed in 12 tumors, with six chromosome rearrangements present in at least two different tumors. However, the breakpoints were not always identical. On the other hand, translocations involving chromosomes 5, 10, and 13 exhibited repeated breakage at the same loci. Such specific and repetitive translocations may be involved in the process of asbestos-induced tumor development.

1987 H. P. Smith award lecture. Eyes for the epidemiologist: the pathologist's role in shaping our understanding of the asbestos-associated diseases.

Asbestosis was first recognized as an entity at autopsy by a pathologist in 1900. Pathologists also discovered the unique relationship of mesothelioma and bronchogenic carcinoma with exposure to asbestos. The observations of preceding pathologists have provided insights that have served as the basis for epidemiologic studies associating asbestos with disease in humans.

Characteristics of tumors and tumor cells cultured from experimental asbestos-induced mesotheliomas in rats.

Mesotheliomas developed in rats in the abdominal cavity 6-23 months after peritoneal introduction of chrysotile and crocidolite asbestos. The tumors were strikingly similar to those occurring in man both with regard to histologic features and growth patterns. The authors have cultured cells from these tumors and established epithelial lines with a variety of karyologic features and doubling times shorter than those of normal mesothelial cells. Lines of diploid or near-diploid tumor cells required serum in the medium to replicate, whereas most aneuploid cell lines were maintained in a serum-free medium. In serum-free medium, the aneuploid line monolayers produced anchorage-independent excrescent masses of cells which "bud" and float free. These spheroids, which strikingly resemble the papillary structures in human mesotheliomas, are composed of mesothelial-like cells that produce hyaluronic acid and have a rich complement of intermediate filaments, predominantly cytokeratins. Aneuploid cells also replicated in soft agar with high efficiency, whereas the diploid and near-diploid cells did not. All but one cultured cell line, regardless of karyotype, produced tumors after subcutaneous or intraperitoneal inoculation (or both). Aneuploid cells caused lung tumors sporadically when introduced intravenously. Comparative analysis of the nuclear DNA of primary tumors and cultured cells demonstrated a high degree of chromosomal instability and selection among cells during early passage in vitro.

Intermediate filament proteins in asbestos-induced mesotheliomas of the rat.

Abdominal diffuse malignant mesotheliomas develop in rats administered asbestos by the intraperitoneal route. A latency period of 6 to 24 months precedes tumor development; the biological and morphological features of these tumors resemble mesotheliomas in humans. Using one- and two-dimensional gel electrophoresis and immunoblotting, rat mesotheliomas (n = 24) were shown to express two classes of intermediate filament (IF) proteins. The tumors contained both vimentin and at least one of six keratins (p40, Mr 40,000; Dm, Mr 50,000; p53, Mr 53,000; Bm, Mr 53,000; Cm, Mr 54,000; Am, Mr 54,000). Vimentin predominated in 15 of 16 tumors exhibiting either sarcomatous or mixed (epithelial and mesenchymal) appearance. One of eight mixed lesions and six of eight epithelial tumors had a complement of IF proteins in which cytokeratins predominated. A similar pattern has been reported in mesotheliomas in humans (Blobel et al., Am. J. Pathol. 121: 235, 1985). Epithelial tumors often contain comparable amounts of vimentin and low molecular weight cytokeratins, while vimentin is the most actively expressed IF protein in sarcomatous tumors. Thus, tumors induced by asbestos in the rat peritoneum express IF proteins in a manner that resembles human mesotheliomas, supporting the notion that these lesions are appropriate models of human mesothelioma.

Chlorozocin. A diabetogenic analogue of streptozocin with dissimilar mechanisms of action on pancreatic beta cells.

Chlorozotocin (chlorozocin, CLZ), the 2-chloroethyl analogue of streptozocin (STZ), was evaluated in three species of rodents. The drug is currently being used in phase II chemotherapeutic trials in man, and appears to be effective in the treatment of certain tumors. In our studies, hyperglycemia was induced in hamsters as early as 2 days after a single intraperitoneal (i.p.) injection of 30-60 mg/kg and was most striking at 4 days. Greater concentrations of CLZ (greater than or equal to 50 mg/kg) were required to produce hyperglycemia in CD-1 mice. Degranulation and necrosis of beta cells developed in hamsters and mice, whereas alpha and acinar cells of the pancreas revealed no morphologic changes. Hyperglycemia was not induced in rats at any concentration tested; however, animals showed abnormal carbohydrate tolerance after administration of 100 mg/kg CLZ (LD50 dosage). The nature of damage by CLZ to beta cells was investigated both in vivo and in vitro. Pretreatment of hamsters with nicotinamide (500 mg/kg, i.p.) failed to alter the extent of CLZ-induced beta cell injury and associated hyperglycemia, but decreased the amount of beta cell necrosis and hyperglycemia in animals receiving STZ. The nonmetabolizable sugar, 3-O-methylglucose (3-O-MG), and 3-aminobenzamide, an inhibitor of the nuclear enzyme, polyADPribose synthetase, prevented STZ-associated damage to beta cells in islet cell cultures, but only 3-O-MG reduced CLZ-induced toxicity. Thus, in comparison to STZ, CLZ appears to be a diabetogenic agent with different species specificity and alternative mechanisms of cytotoxicity. The glucose moiety of both drugs appears critical in the induction of beta cell damage.

Induction of squamous metaplasia in organ cultures of hamster trachea by naturally occurring and synthetic fibers.

Asbestos exhibits many properties of classical tumor promoters. These characteristics include the ability to stimulate proliferation and inhibit normal differentiation of cells. In organ cultures of trachea, crocidolite and amosite asbestos stimulate squamous metaplasia, a pathological process in which a rapidly proliferating squamous epithelium replaces the normal epithelium. We hypothesized that the induction of metaplasia depends upon the fibrous nature of asbestos. Accordingly, several naturally occurring and synthetic fibrous materials and their nonfibrous analogues were assessed for their ability to induce metaplastic changes in tracheal mucosa of the Syrian hamster. Exposure to both crocidolite asbestos and fiberglass resulted in significant increases (p less than 0.05) in squamous metaplasia over a range of dosages (1.0, 4.0, 16.0 mg/ml). Attapulgite (palygorskite) and both "long-" and "short-" fiber preparations of chrysotile asbestos had similar but less marked effects. Nonfibrous analogues of each material (riebeckite, antigorite, and glass particles) failed to produce metaplasia. Asbestos, and fibrous materials in general, appear to stimulate squamous metaplasia because of their fibrous geometry.

Interaction of asbestos with metaplastic squamous epithelium developing in organ cultures of hamster trachea.

The normal mucociliary epithelium of the respiratory tract in chronic cigarette smokers often is replaced focally by a metaplastic squamous epithelium. Because asbestos workers who smoke have a substantially greater risk of bronchogenic carcinoma than nonsmokers, we hypothesized that interaction of asbestos with squamous epithelium might be a contributing factor. To address this question, an in vitro model was developed to study the interaction of asbestos with both mucociliary and squamous epithelium. Explants of tracheas from hamsters were cultured in either a chemically defined minimal essential medium, which maintains a differentiated epithelium, or a nutritionally complex medium, which encourages the development of squamous metaplasia. Scanning electron microscopy (SEM) was used to measure quantitatively the development of a squamous epithelial surface on the explants. The interaction of chrysotile and crocidolite asbestos with cells of the mucociliary and squamous epithelium was studied using both SEM and transmission electron microscopy (TEM). Long fibers of asbestos were cleared, whereas shorter fibers were phagocytized by cells of the mucociliary epithelium. In contrast, asbestos was phagocytized by superficial squamous cells regardless of fiber length, and fibers penetrated between intercellular junctions in the metaplastic epithelium. The relevance of these interactions to the induction of bronchogenic carcinoma is discussed.