Asbestos exposure stimulates pleural mesothelial cells to secrete the fibroblast chemoattractant, fibronectin

Parietal pleural plaques and visceral pleural fibrosis are well-recognized stigmata of occupational asbestos exposure. However, their pathogenesis is poorly understood. Conceivably, phagocytosis of asbestos fibers by pleural mesothelial cells may stimulate the recruitment of fibroblasts to sites of asbestos-induced pleural injury. To test this hypothesis, rat parietal pleural mesothelial cells were cultured for 6 to 96 h with or without crocidolite or chrysotile asbestos fibers (concentration range, 2 to 100 micrograms/cm2). Asbestos fibers were actively phagocytosed by pleural mesothelial cells and were incorporated within phagosomes. Conditioned medium was assayed for chemotactic activity toward RL-87 rat lung fibroblasts and for fibronectin immunoreactivity. The effects of asbestos were compared with those of alpha-cristobalite (which is strongly fibrogenic), alpha-quartz (a less fibrogenic particulate), and carbonyl iron (a nonfibrogenic agent). Both types of asbestos stimulated the secretion of fibroblast chemoattractant activity by pleural mesothelial cells in a time-dependent manner. This effect peaked at 96 h in cultures containing 4 micrograms/cm2 of asbestos (P < 0.001). alpha-Cristobalite also enhanced the secretion of the mesothelial cell-derived chemoattractant, an effect that was maximal at a concentration of 20 micrograms/cm2 (P < 0.001). Furthermore, crocidolite, chrysotile, and alpha-cristobalite stimulated pleural mesothelial cell fibronectin synthesis. In contrast, alpha-quartz and carbonyl iron particles had no noticeable effect on either immunoreactive fibronectin secretion or chemoattractant release by pleural mesothelial cells. The ability of asbestos fibers and alpha-cristobalite particles to stimulate the secretion of the fibroblast chemoattractant, fibronectin, by pleural mesothelial cells may have relevance to the induction of pleural injury by fibrogenic particulates.

Enhanced release of an alveolar macrophage-derived chemoattractant for fibroblasts in rats after asbestos inhalation

Our studies indicate the effects of in vivo asbestos exposure on the ability of alveolar macrophages (AM) to elaborate a chemoattractant for fibroblast using a rat model of asbestos inhalation. Two groups of rats were exposed by intermittent inhalation (6 hr/day for 5 days/week over a total period of 4 weeks) to either amphibole (crocidolite) or serpentine (chrysotile) asbestos. A group of control rats were sham-exposed to clean air only. The animals were sacrificed 2-5 months after the cessation of exposure. The AM were obtained from the 3 exposure groups in 2 different rat strains by the bronchoalveolar lavage and the cultured in RPMI-1640 medium for 24-96 hr at 37 degrees C. The supernatants from cultured AM were tested for chemotactic activity towards fetal rat skin fibroblasts in a chemotactic assay using 8 microns pore-size filters. The culture supernatants of AM obtained from crocidolite-exposed rats exhibited a significantly greater chemotactic activity towards rat fibroblasts than similar culture supernatants from sham-exposed control animals (p < 0.01) in both rat strains. Significant chemotactic activity was observed after chrysotile exposure (p < 0.05) in ACI rats but not in Fischer-344 rats. Maximal chemoattractant release from AM was noted after 48 hr in culture. Preliminary characterization of the chemoattractant has shown that it is a thermolabile and trypsin sensitive factor whose activity was partially reduced after dialysis. Since AM accumulate at sites of intrapulmonary asbestos deposition, these findings may have relevance to the pathologic accumulation of interstitial lung fibroblasts which occurs during asbestos-mediated lung injury.

Effect of estradiol on accelerated atherosclerosis in rabbit heterotopic aortic allografts

Migration and proliferation of vascular smooth muscle cells are early and major events in the formation of atherosclerotic lesions. We report on an aorta transplant model in rabbits wherein myointimal proliferation is inhibited by 17-beta-estradiol. The abdominal aortas of outbred white New Zealand rabbits were harvested and allografted to the carotid artery of the recipient. The animals, which were fed either a normal or a high-cholesterol (0.5%) diet, were killed 3 weeks later. The degree of myointimal proliferation was measured with a digitized system attached to a light microscope. The myointimal hyperplasia was expressed as the cross section area of the intima/the area of the intima + the area of the media x 100. Transmission electron micrographs were obtained for all vessels. Intimal thickening was shown mainly to consist of proliferating smooth muscle cells. The cholesterol diet resulted in significantly higher serum total cholesterol levels compared to animals on a normal diet (p < 0.0001) but did not affect serum high-density lipoprotein-cholesterol or serum triglyceride levels. The cholesterol diet was also associated with a greater but not significant amount of intimal thickening. Treatment with 17-beta-estradiol significantly decreased both serum triglyceride concentration (p < 0.05) and myointimal thickening (p < 0.01) in cholesterol-fed animals. Transmission electron microscopy showed that the endothelial cells appeared structurally normal in the estradiol-treated animals. Further, estradiol prevented the appearance of vacuolized macrophages. Thus estradiol may decrease myointimal thickening by preserving the endothelium and preventing macrophage appearance in the intima.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of asbestos inhalation on the distribution and enhancement of immunoassociated antigen expression of alveolar macrophage subpopulation

We have studied the effects of in vivo asbestos exposure on the surface immune-associated (Ia) antigen expression and distribution of alveolar macrophage subpopulations defined by continuous iso-osmotic Percoll gradients (density range: 1.006 to 1.123 g/ml) using a rat model of asbestos inhalation. Two groups of rats were exposed by intermittent inhalation (6 hr/day for 5 days/week over 4 weeks) to either amphibole (crocidolite) or serpentine (chrysotile) asbestos. A group of control rats was sham-exposed to clean air only. Alveolar macrophages from rats of three groups were obtained by bronchoalveolar lavage. During exposure, distinct differences appeared within 7 days of asbestos exposure, and some of these findings persisted in the crocidolite-exposed group for as long as 2 to 5 months after the cessation of exposure. Furthermore, relatively greater proportions of Ia-antigen positive cells were detected in several density fractions obtained from both asbestos-exposed groups (especially the crocidolite-exposed group). Multinucleated alveolar macrophages were seen frequently in all Percoll fractions after both types of asbestos inhalation. A significant proportion of multinucleated alveolar macrophages in these fractions expressed surface Ia-antigen positivity. The finding of enriched numbers of higher-density phagocytes in bronchoalveolar lavage cell subpopulations from asbestos-exposed rats may reflect the presence of newly recruited-immature monocytes and/or macrophages at sites of intrapulmonary asbestos deposition. Also, increased proportions of Ia-antigen positive cells suggest that a part of them were functionally activated.

Brief ischemia-reperfusion induces stunning of endothelium in canine coronary artery

BACKGROUND

Brief ischemic episodes that induce stunning of the myocardium may also induce stunning of the coronary endothelium. To test this hypothesis, we examined both in vivo and in vitro responses of canine coronary arteries exposed to brief ischemia.

METHODS AND RESULTS

Functional recovery of the endothelium was examined in vivo during reperfusion after 15 minutes of ischemia. Vasodilatory responses to acetylcholine were severely impaired during the first hour of reperfusion but gradually improved over a 90-minute period after ischemia. The vasoconstrictive response to U46619 was enhanced for the first 30 minutes of reperfusion and returned to normal within 60 minutes. In vitro vasomotor responses to potassium chloride, acetylcholine, bradykinin, and sodium nitroprusside were examined in isolated segments of canine coronary arteries preexposed in vivo to brief ischemia (10-30 minutes) and 20 minutes of reperfusion. The results showed enhanced contractile responses and blunted endothelium-dependent but not endothelium-independent vasodilatory responses of arterial rings subjected to 10 minutes of ischemia. Twenty and 30 minutes of ischemia completely impaired endothelium-dependent vasodilation. When reperfusion was extended to 120 minutes after 15 minutes of ischemia, vasodilatory responses to acetylcholine had recovered by almost 90%. Examination of endothelial integrity by transmission electron microscopy after 10-15 minutes of ischemia revealed no evidence of structural damage. Twenty and 30 minutes of ischemia induced cytoplasmic vacuolation, partial detachment of endothelium, and swelling of cytoplasmic organelles.

CONCLUSIONS

These data support the hypothesis that brief ischemia-reperfusion induces stunning of endothelium in which endothelium-dependent vasodilatory function is impaired temporarily without morphological damage.

A novel biotinylated probe specific for hyaluronate. Its diagnostic value in diffuse malignant mesothelioma

Diffuse malignant mesotheliomas are known to secrete a large amount of hyaluronate, whereas adenocarcinomas produce predominantly neutral mucins. In the present study, we assessed the diagnostic usefulness of a new, highly specific and sensitive hyaluronate binding probe to discriminate between mesotheliomas and adenocarcinomas. We studied 33 mesotheliomas and 37 adenocarcinomas in order to establish specific diagnostic criteria for using the hyaluronate binding probe. Of the adenocarcinomas, only three showed significant positive staining for hyaluronate (8%). By contrast, all the mesotheliomas exhibited positive staining for hyaluronate. Furthermore, the staining reaction was classed as moderate or greater in 26 mesotheliomas (79%), thus suggesting the utility of this probe in the differential diagnosis of malignant mesothelioma versus adenocarcinoma. We conclude that strong cytoplasmic or membranous staining for hyaluronate is highly predictive of malignant mesothelioma. The hyaluronate binding probe should therefore be considered an important adjunct to be used in combination with electron microscopy and immunohistochemistry in the histologic diagnosis of diffuse malignant mesothelioma.

Coronary artery ultrastructural changes in cardiac transplant atherosclerosis in the rabbit

Accelerated coronary atherosclerosis is the limiting factor for long-term survival of cardiac transplant recipients, but its pathogenesis is poorly understood. Morphologic and ultrastructural changes in suitable models may help explain the underlying mechanisms. In this study, early (3, 7, 14, and 21 days) and late (42 days) ultrastructural changes of the coronary artery were characterized in rabbit cardiac allografts. Thirty-four New Zealand white male rabbits (3.0-4.0 kg) served as donors and recipients. All recipients received cyclosporine (10 mg/kg/day i.m.) as immunosuppressant. In order to increase the normally very low cholesterol levels in rabbits, both the donor and recipient animals were fed a 0.5% cholesterol diet. Recipient animals were sacrificed between 3 days and 6 weeks after transplantation. The specimens from both donor and recipient were examined by transmission electron microscopy, immunohistochemistry, and morphometry. Our data indicate that intimal thickening was initiated with smooth muscle cell migration within 1 week after transplantation, and occurrence of macrophage-derived foam cells and vacuolized smooth muscle cells 3 weeks after transplantation. These changes occurred in the presence of an ultrastructurally intact endothelium. Platelets were only seldom seen adhering to the endothelium. In contrast, lymphocytes and monocytes were frequently found adhering to the endothelium at 2 and 3 weeks posttransplantation. From 3 weeks posttransplantation, lymphocytes were seen only occasionally in the intima but not in the media. This study suggests that early events elicit a change in the smooth muscle cells in the media to the secretory phenotype that migrates to the intima and proliferate. Lymphocyte and monocyte adhesion to the endothelium may enhance smooth muscle migration and proliferation. The large macrophage involvement may relate to the high serum cholesterol levels induced by the cholesterol diet. All these changes occurred in the presence of a structurally normal endothelium and without apparent platelet involvement.

Mesothelial cells produce a chemoattractant for lung fibroblasts: role of fibronectin

Pleural fibrosis may complicate several types of non-exudative pleural injury. Although the pathogenesis of such lesions is poorly understood, it is conceivable that mesothelial cells may recruit fibroblasts to sites of pleural damage. In order to test this possibility, conditioned medium from cultured rat mesothelial cells was tested for chemoattractant activity towards RL-87 rat lung fibroblasts. For this purpose, rat pleural or pericardial mesothelial cells were maintained in vitro for 6 to 96 h. Conditioned medium from each source was obtained at defined culture times and tested for chemotactic activity in a 48-well microchemotaxis assembly. A progressive, time-dependent increase in fibroblast chemoattractant activity was detected in both pleural and pericardial mesothelial cell conditioned medium samples. This effect was maximal in 96-h cultures. Checkerboard analysis revealed that the conditioned medium was truly chemotactic for lung fibroblasts. Characterization of the chemoattractant demonstrated that it was a nondialyzable (greater than 16 kD), thermolabile (100 degrees C for 15 min), acid-stable (pH 2.5), trypsin-sensitive, and pepsin-sensitive protein. The chemotaxin was shown to be fibronectin, since activity was abolished, in a dose-dependent manner, by treatment with anti-rat fibronectin antiserum as well as by passage through a gelatin agarose affinity column. This product consisted of two bands on sodium dodecyl sulfate polyacrylamide gel electrophoresis of apparent molecular masses 250 and 220 kD. The secretion of a mesothelial cell-derived fibroblast chemoattractant may play a role in the response of the pleura to injury and in the pathogenesis of pleural fibrosis.

Fatal adenovirus pneumonia in a newborn identified by electron microscopy and in situ hybridization

A male infant born at 25 weeks' gestation died at 2 weeks of age from progressive respiratory insufficiency, metabolic acidosis, and renal failure. Autopsy revealed extensive hemorrhage and necrosis in the lungs, as well as hyaline membrane disease. Alveolar and bronchiolar lining cells contained frequent intranuclear inclusions visible by light microscopy that corresponded to arrays of icosahedral particles suggestive of adenovirus by electron microscopy. Confirmation of overwhelming adenovirus infection was made with in situ DNA hybridization. This case demonstrates the advantage of DNA probe analysis for retrospective diagnosis when no adequate specimen is available for culture or antigen detection. This case is also unusual in that a premature newborn had severe adenovirus infection.

Current issues regarding the pathobiology of asbestosis: a chronologic perspective

Asbestosis is a pneumoconiosis that results from the inhalation of asbestos fibers. There is a body of evidence that implicates the alveolar macrophage in the pathogenesis of asbestosis because of its prominence in asbestos-related histologic lesions. Injury to the alveolar epithelium also may contribute to the pathogenesis of asbestosis. Evidence is presented to suggest that pulmonary fibrosis may result from the persistent release of inflammatory mediators (chemoattractants, lysosomal enzymes, toxic oxygen radicals, arachidonic acid metabolites, interleukins, and fibroblast growth factors) at sites of asbestos deposition. Histologic features of asbestosis can be detected within months after the initial contact with asbestos. In contrast, the stigmata of asbestos-related disease usually are not radiologically detectable, even by the most sensitive imaging techniques, until after a latency period of at least a decade, and often considerably longer. There is, therefore, a long diagnostic delay between the time when asbestosis is histologically detectable and when it is radiographically detectable.

Visceral pleural thickening in asbestos exposure: the occurrence and implications of thickened interlobar fissures

We evaluated fissural (ie, visceral pleural) thickening on radiographs in two asbestos-exposed study populations and a control group. Asbestos workers had an incidence of fissural thickening of 54.5% compared with 16.0% in the unexposed control group, with a strong positive statistical effect due to asbestos exposure beyond that attributable to age. Fissural thickening occurred in 85% of workers with parietal plaques and in 36% without pleural plaques. Fissural thickening occurred in 45% without radiographic evidence of pulmonary fibrosis, but it was very common (85%) in those with pulmonary fibrosis. Data analysis showed that fissural thickening responds more strongly to asbestos exposure than does plaque formation, with 21 years of asbestos exposure needed for a 50% chance of developing fissural thickening, while 31 years of exposure were needed for a 50% chance of forming pleural plaques. From a second group of 57 asbestos workers evaluated clinically, 8 were diagnosed as having asbestosis with radiographically clear lungs and fissural thickening. We conclude that visceral pleural thickening is common in asbestos exposure, that it is related to the years since first asbestos exposure, and that its presence may indicate the presence of pulmonary asbestosis, even with radiographically normal lungs.

Intrapulmonary distribution of inhaled chrysotile and crocidolite asbestos: ultrastructural features

Although all commercial types of asbestos can cause pulmonary fibrosis, little is known about ultrastructural differences in the evolution of pulmonary lesions induced by amphiboles and serpentines. The present study was designed to compare the histological and ultrastructural effects produced by chronic inhalation of either crocidolite (amphibole) or chrysotile (serpentine) asbestos in the rat. Animals, exposed by intermittent inhalation for 3 months, were killed after 2 to 16 months. When inhaled, both types of asbestos caused thickened alveolar duct bifurcations associated with macrophage aggregates. Crocidolite inhalation also produced subpleural collections of alveolar macrophages and lymphocytes. Electron microscopy revealed some similarities, but also distinct differences, in the pulmonary distribution of inhaled chrysotile and crocidolite. Whereas both asbestos varieties were identified within the pulmonary interstitium, only crocidolite was detected inside alveolar macrophages. Chrysotile fibres were seen infrequently within the vascular compartment. Microcalcifications were noted after chrysotile inhalation, but were never observed following crocidolite exposure. Both asbestos types induced slight pulmonary fibrosis. These findings indicate that crocidolite and chrysotile produce different pathogenetic features, although both are fibrogenic.

Enhanced interleukin activity following asbestos inhalation

Asbestos inhalation can cause pulmonary fibrosis and is associated with a variety of immunological abnormalities. The purpose of this study was to evaluate the effects of asbestos inhalation on interleukin-1 (IL-1) and interleukin-2 (IL-2) production in a rodent model. Two groups of rats were exposed, by intermittent inhalation, to either amphibole (crocidolite) or serpentine (chrysotile) asbestos. A third (control) group of rats was sham exposed to clean air. Animals from the three exposure groups were thereafter immunized (or not immunized) with fetal calf serum antigens. In order to assay interleukin activity, supernatants were generated from cultures containing alveolar macrophages and autologous splenic lymphocytes, and from cultures containing alveolar macrophages alone. Using assay systems designed to detect IL-1 and IL-2 functional activity, the supernatants were evaluated for their capacity to stimulate lymphoproliferation and fibroblast DNA synthesis. Macrophage-lymphocyte co-culture supernatants, when obtained from immunized, asbestos exposed rats, contained greater IL-1 and IL-2 activity than identical supernatants from immunized, sham exposed animals. These between group differences were not, however, observed in supernatants from unimmunized rats, or when supernatants were generated in the absence of immune lymphocytes. These observations suggest that asbestos exposure is associated with enhanced activation of lymphocytes by antigens. The possible relevance of these findings to asbestos related fibrogenesis and immunological stimulation is discussed.

The effects of chrysotile and crocidolite asbestos on the lower respiratory tract: analysis of bronchoalveolar lavage constituents

This study was designed to evaluate the effects of amphibole and serpentine asbestos inhalation on the constituents of the lower respiratory tract. Bronchoalveolar lavage (BAL) analyses were performed on three groups of rats: one group was exposed to chrysotile (serpentine) asbestos, another group was exposed to crocidolite amphibole asbestos, while a third group was sham-exposed. Intermittent inhalational exposures lasted three months. The total BAL cell yields and the macrophage content of BAL cells were significantly lower after asbestos exposure, especially in the chrysotile-exposed group. These effects persisted for as long as 1 year after the cessation of exposure. Multinucleated macrophages were seen in BAL cells from both asbestos-exposed groups. Striking ultrastructural alterations of macrophage morphology were noted in BAL cells from both groups of asbestos-exposed rats. Chrysotile fibers were not seen in any BAL cells from chrysotile-exposed animals. However, 15 months after terminating the exposure regimen, a sizeable proportion of BAL macrophages from crocidolite-exposed rats contained phagocytosed asbestos fibers. Significantly higher beta-glucuronidase and lactate dehydrogenase activity was found in BAL fluids from both asbestos-exposed groups and was detected 17-18 months after exposure had ceased. These observations have served as useful correlates of asbestos-mediated injury to the lower respiratory tract. They have also provided evidence of continual pathological sequelae occurring long after withdrawal from asbestos exposure.

Enhanced release of a chemoattractant for alveolar macrophages after asbestos inhalation

Alveolar macrophage supernatants from 2 groups of asbestos-exposed rats and a group of sham-exposed rats were tested for chemoattractant activity towards rat alveolar macrophages. Enhanced chemotaxin release was observed in culture supernatants from both crocidolite and chrysotile asbestos-exposed rats when compared with supernatants from sham-exposed rats. These between-group differences persisted for as long as 15 months after exposure had ceased. Chemotactic factor release was maximal after 24 h of culture in all animal groups. Partial characterization of the chemoattractant from each of the 3 rat groups revealed that it was thermolabile, nondialyzable, and trypsin-sensitive. Separation on SDS-polyacrylamide gel electrophoresis revealed 3 major peaks of activity. The production of the chemotaxin in supernatants from asbestos-exposed rats was partially inhibited by both actinomycin D and puromycin. These agents had no appreciable effect on the production of chemoattractant in cultures from sham-exposed animals. The enhanced release of an alveolar macrophage chemoattractant after asbestos inhalation may explain why macrophages accumulate at sites of asbestos deposition in the lungs.

Lymphoid and plasma cell malignancies: asbestos-related disorders of long latency

We have identified 13 asbestos workers with lymphoplasmacytic neoplasms: six with chronic lymphocytic leukemia, four with IgG myeloma, two with IgA myeloma, and one with histiocytic lymphoma. The subjects' occupations were varied, but all had experienced protracted asbestos exposure (ranging from 3-37 years). Tumor latency periods were similar to other known asbestos-related malignancies and ranged from 16-41 years. Stigmata of asbestos-related pulmonary disease were evident in 12 subjects. Malignant pleural mesotheliomas co-existed with IgG myelomas in two individuals, an association which seems unlikely to be fortuitous. It has been speculated previously that asbestos may be a lymphoid system carcinogen. Our findings strongly support this view and indicate that patients presenting de novo with lymphoproliferative neoplasms should be investigated for previous occupational or environmental exposure to asbestos.

Prophylactic antibiotics in elective colorectal surgery

In an effort to determine whether or not the addition of parenteral antibiotics to orally administered erythromycin and neomycin would diminish postoperative septic complications in elective colorectal operations, a randomized, double-blind, controlled trial was conducted comparing three groups. All patients received vigorous preoperative mechanical bowel preparation, 3 g erythromycin and 3 g neomycin orally, the day prior to operation. Patients in Group O received three doses of saline intravenously as placebo, patients in Group C received cefazolin, 1 g, immediately preoperatively and 1 g every 6 hours postoperatively, intravenously, for two doses, and patients in Group T received a single immediate preoperative dose of 6 g of ticarcillin intravenously and two saline placebo doses intravenously, postoperatively. The patients' progress was followed in the hospital and for one month postoperatively. Septic complications occurred in 35 per cent of patients in Group O, 7 per cent of patients in Group C, and 5 per cent of patients in Group T. Wound infections comprised most of these complications, occurring in 29 per cent of Group O, 4.7 per cent of Group C, and 2.3 per cent of Group T patients. Thus, the addition of either parenteral cefazolin or ticarcillin in this study significantly reduced wound infections in elective colorectal surgery.

Cytotoxicity of a short-fiber chrysotile asbestos for human alveolar macrophages: preliminary observations

Studies were performed to compare the cytotoxicity for human alveolar macrophages of a naturally occurring short-fiber chrysotile asbestos (RG 144) to that of a standard reference mixed-fiber (long and short) chrysotile asbestos (UICC chrysotile A. Rhodesian). Parallel studies were also performed with quartz (Min-U-Sil 15), a known macrophage toxin. On a mass basis, and after 24 hr incubation, RG 144 was more cytotoxic than the UICC standard reference fiber and less toxic than quartz (silica). The cytotoxic potential of RG 144 chrysotile was further enhanced after size reduction by milling. These findings may have important biologic implications with respect to the use of short-fiber asbestos in industry.