Silicotic Nodules Research Articles

Treatment of experimental silicosis with antifibrotic agents

We tested the efficacy of 2 antifibrotic agents, the proline analogue cis-4- hydroxy- l- proline (cHyp) and the lathyrogen β-aminopropionitrile (BAPN), on experimental silicosis in hamsters. Silica (75 mg) was instilled intratracheally, and 3 months later lung hydroxyproline content, the volume density of silicotic nodules in lung parenchyma, fluid-filled lung pressure-volume curves, body weight and survival were measured. Animals were injected with cHyp, 200 mg/kg body weight, or BAPN, 150 mg/kg body weight, twice daily for 3 months. Hydroxyproline contents (mg/lung) at 3 months were: control, 0.8 ± 0.1; silica, 1.4 ± 0.1 ( P<0.05 compared to control); silica-cHyp, 1.2 ± 0.2; silica-BAPN, 1.4 ± 0.1 (both NS compared to silica). The volume density of granuloma (% of surface area) was: silica, 0.7 ± 0.1; silica-cHyp, 5.9 ± 1.0; silica-BAPN, 9.7 ± 1.5 (both P < 0.5 compared to silica). There was no difference among the groups as assessed by lung pressure-volume curves. No toxic effects were produced on the skeletal system as assessed by bone hydroxyproline content and skeletal roentgenograms. Final body weights (g) were: silica, 114 ± 5; silica-BAPN, 108 ± 6; silica-cHyp, 88 ± 7 (the latter P<0.05 compared to silica). Survival (%) was: silica, 62%; silica-BAPN, 34%, silica-cHyp, 28% (both P<0.05 compared to silica). These data show that cHyp and BAPN treatment did not prevent silica-induced pulmonary fibrosis, led to more extensive silicotic nodules, and were toxic. Both cHyp and BAPN have some efficacy in other models of fibrosis, and the observations in the present study could be specific to silicosis in the hamster.

Quartz but not iron oxide causes air-flow obstruction, emphysema, and small airways lesions in the rat.

Recent epidemiologic studies have suggested that some workers exposed to inorganic dusts develop air-flow obstruction independent of or greater than that produced by cigarette smoke; the morphologic basis of this effect is unknown. To investigate this problem, we administered saline alone, 10 mg iron oxide (an inert dust), or 10 or 30 mg of quartz to rats by intratracheal instillation. Animals were killed after 30 days, and pulmonary function and morphologic changes were examined. The iron oxide group was similar to the saline control group in all functional and morphometric parameters. However, both quartz-exposed groups showed evidence of air-flow obstruction, with more severe abnormalities in the high dose group. These findings correlated with morphometric observations of emphysema and thickened airway walls, with changes again more severe in the high dose group. Early silicotic nodules were also present in the latter animals. We conclude that in addition to the classic lesions of nodular silicosis, quartz can produce morphologic and functional changes of air-flow obstruction; no such changes are seen with iron oxide. These observations may explain the air-flow obstruction seen in workers exposed to mineral dusts.

Prevalence and pathogenesis of pneumoconiosis in coal workers.

Dust dose and composition do not appear to account wholly for changes in the prevalence of coal workers' pneumoconiosis in Europe. In certain coal pits high progression evidently occurred with relatively low dust exposure or vice versa, whereas progression in relation to dust levels might be variable. Exceptionally high quartz concentrations occur in coal mine dust when pneumoconiosis may progress with unusual rapidity. Under such circumstances lesions resembling silicotic nodules may be found, but with the customarily lower levels of quartz the pathological features assume the form characteristic of coal workers. Morphological changes in relation to dust content of human and animal lungs, as well as cellular behavior, have not accounted completely for the epidemiological findings. Considering all the pathological evidence helps explain the pathogenesis of pneumoconiosis and vagaries of progression. The origin of progressive massive fibrosis cannot be explained simply in terms of dust burden or immunological features, and the role of an infective factor cannot be dismissed. Moreover, lipid secretion by alveolar epithelium introduces a new element that could affect the development of simple and complicated pneumoconiosis. In vitro, cytotoxicity appeared to be too variable for predictive purposes, though direct assay of fibrogenicity using the macrophage fibrogenic factor suggested that dust dose was more important than dust composition. Assessing individual susceptibility presents serious obstacles.

Prevalence and Pathogenesis of Pneumoconiosis in Coal Workers

Dust dose and composition do not appear to account wholly for changes in the prevalence of coal workers' pneumoconiosis in Europe. In certain coal pits high progression evidently occurred with relatively low dust exposure or vice versa, whereas progression in relation to dust levels might be variable. Exceptionally high quartz concentrations occur in coal mine dust when pneumoconiosis may progress with unusual rapidity. Under such circumstances lesions resembling silicotic nodules may be found, but with the customarily lower levels of quartz the pathological features assume the form characteristic of coal workers. Morphological changes in relation to dust content of human and animal lungs, as well as cellular behavior, have not accounted completely for the epidemiological findings. Considering all the pathological evidence helps explain the pathogenesis of pneumoconiosis and vagaries of progression. The origin of progressive massive fibrosis cannot be explained simply in terms of dust burden or immunological features, and the role of an infective factor cannot be dismissed. Moreover, lipid secretion by alveolar epithelium introduces a new element that could affect the development of simple and complicated pneumoconiosis. In vitro, cytotoxicity appeared to be too variable for predictive purposes, though direct assay of fibrogenicity using the macrophage fibrogenic factor suggested that dust dose was more important than dust composition. Assessing individual susceptibility presents serious obstacles.

Silica earth provoked lung fibrosis with stimulation of lysosomal enzymes and lipid peroxidation in rats.

The dynamics of the biological response of pulmonary tissue to silica dust (silica earth from Piotrowice, Poland, recommended as a domestic reference fibrogenic standard) was studied in rats after single-shot intratracheal instillation of a suspension of 20 mg of the dust for one, three, and seven months. Silica dust provoked pronounced pulmonary fibrosis as inferred from increased collagen content together with pathomorphological alteration (silicotic nodules). The lung burden of silica dust affected the lysosomal subfraction as manifested by an increase in its protein content with concomitant stimulation (release and presumably induction) of beta-glucuronidase and cathepsin D and a transient (up to three months) stimulation of lipid peroxidation. Stimulation of activity of lysosomal enzymes and lipid peroxidation mediated by silica dust may reflect destructive metabolic processes resulting in the development of pulmonary fibrosis as the sign of a pathological repair mechanism. The extent of the effects brought about by silica earth testify that it may be recommended as a reference standard for evaluating the potential health hazard from industrial exposure to dusts containing SiO2.

Late aluminum therapy reduces the cellular activities of simple silicosis in the sheep model.

To evaluate the biological effects of aluminum lactate therapy on nodular silicosis, we exposed the tracheal lobe of three groups of sheep containing eight sheep per group to either 11 mg of Al lactate in 100 ml saline (Al group), 100 mg of Minusil-5 in 100 ml saline (Si group), or 100 mg of Minusil-5 in 100 ml saline followed by 11 mg of Al lactate at monthly intervals 4 months after exposure (Si Al-treated group). The lung biological processes were evaluated by sequential lung lavage analyses of cellularity and biochemistry of supernatant and by autopsy analyses of cellularity and biochemistry of supernatant and by autopsy analyses of lung tissue histopathology and quartz content. Al lactate alone did not have any significant effect. Silica exposure produced the silicotic nodules and significant increases on lung lavage of cellularity, enzyme release, surfactant, and glycosaminoglycan accumulations. Al lactate therapy at month 4 after exposure did not decrease the pathological score of disease, but it significantly reduced all markers of cellular hyperactivity. This therapy was associated with a 65% reduction of the quartz retention in lung tissue and might help to prevent long-term progression of the disease process.

Pathogenesis of silicosis: current concepts and hypotheses.

Silicosis is caused by the inhalation of crystalline silica (silicon dioxide, SiO2) in various forms. This review proposes that the cascade of inflammatory and fibrotic events involved in cell-mediated, and possibly humoral, immune responses also produces silicosis. The hypothesis rests on the central concept that interactions between silica and pulmonary macrophages are the pivotal events in the pathogenesis of silicosis. Resident and recruited pulmonary macrophages demonstrate intimate contact with silica from the moment of deposition, and throughout the time the particles remain in the lung. The silica probably exerts its effects on the macrophages that ingest it by altering their function while they are alive, rather than merely by disrupting them. The macrophage appears to be stimulated to secrete mediator substances, such as interleukin-1 (IL-1), which alter the function and behavior of other cells. Lymphocytes and macrophages appear in close proximity to one another in developing silicotic nodules, and increased proportions of lymphocytes are found in bronchoalveolar lavage specimens from animals and humans with silica dust exposure. Hypothetically, macrophages influence and activate lymphocytes, which then feed back to amplify the response by stimulating the same or other recruited macrophages. An expanded and activated population of lymphocytes under the influence of IL-1 in turn can secrete a variety of lymphokines which profoundly alter monocyte/macrophage function. The macrophage has been implicated as a major cause for the fibrosis that accompanies silicosis. The products of activated T-lymphocytes, particularly interferon-gamma (IF-g), are potent stimulators of secretion from macrophages of a fibroblast growth competence factor, macrophage-derived growth factor (MDGF). IL-1 may have an additional stimulatory effect on fibroblasts. Neutrophils and macrophages also may be important in silicosis because of their potent ability to cause lung tissue injury. Silicosis provides a model of chronic diffuse interstitial immunologic and fibrotic lung disease in which the cause is known, can be applied in defined doses, and tracked in the lung throughout the course of the disease. Further studies should provide better understanding of the mechanisms that goven pulmonary injury, inflammation, repair, and fibrosis.

Collagen Crosslinking in Lungs of Rats with Experimental Silicosis

Rats were intratracheally instilled with 50 mg of size-fractionated crystalline quartz to induce silicosis. Lungs were analyzed 1, 4, 6, and 9 months after instillation for their content of the reduced difunctional collagen crosslinks dihydroxylysinonorleucine (DHLNL) and hydroxylysinonorleucine (HLNL), of the nonreducible trifunctional (mature) crosslink, hydroxypyridinium (OHP), and of hydroxylysine. Ratios of DHLNL : HLNL were elevated in silicotic lung collagen at all times sampled, due both to increased levels of DHLNL and decreased amounts of HLNL. Hydroxylysine content of collagen in the silicotic lungs was also increased as compared with age-matched control rats. Hydroxypyridinium content of silicotic lung collagen was less than control values at 1 month, but was significantly increased to about 120%, 150%, and 175% of the age-matched control values at 4, 6, and 9 months after silica instillation, respectively. The increased levels of OHP in lung collagen were temporally correlated with the appearance of mature silicotic nodules in these lungs. We conclude that the large amounts of excess collagen deposited in silicotic lungs differs biochemically from normal lung collagen despite maintenance of the normal ratio of major collagen types in silicotic lungs.

Extrapulmonary silicosis: A clinical, morphologic, and ultrastructural study

A variety of silicotic lesions derived from thoracic silicosis via lymphohematogenous spread to the liver, spleen, bone marrow, and extrathoracic lymph nodes are described. The morphologic features of these lesions depend on the extent of macrophage aggregation, the occurrence of fibrogenesis, and the development of necrosis and degradative changes in macrophages and adjacent extracellular matrix, presumably caused by lysosomal enzymes released from macrophages. Ultrastructurally, the degenerative alterations of matrix material include longitudinal splitting and breakage of collagen fibrils into segments one and three quarters the length of the original fibrils and deposition of flocculent electron-dense material either focally or diffusely around collagen fibrils. The corresponding changes viewed light microscopically are those of fibrinoid necrosis. The sclerohyaline nodule, the characteristic lesion of silicosis, includes all of these features as it evolves through nodular histiocytic and subsequent fibrohistiocytic phases. Its ultimate morphology appears to be determined by the reassembly of the degraded matrix into non-native, fibrous long-spacing collagen via a spiny collagen intermediary. The sclerohyaline nodule occurs infrequently in the spleen and liver, although less typical lesions caused by silica alone or admixed with other dusts seem to occur more commonly in these organs. These lesions appeared as loose or nodular histiocytic or fibrohistiocytic aggregates. Nonspecific fibrous nodules or more extensive fibrosis, as seen in portal triads, may represent advanced stages of such lesions. Acute or healed focal segmental glomerulonephritis occurred in 40 per cent of the cases, suggesting that it may be an important remote effect of silicosis. Continuous destruction of lymphocytes adjacent to silicotic nodules may be an antigenic source of the high concentration of autoimmune reactants described in silicosis.

Morphology and pathogenesis of pneumoconiosis in dental technicians

The morphology of pneumoconiosis occurring in dental technicians could be studied by systematic light and electron microscopical investigation of 30 lung preparations from such cases. Diffuse streaky fibrosis and, in some cases, nodular fibrosis was observed together with occasional formation of silicotic nodules that may lead to extensive transformation of the alveolar structure. The etiological relationship between occupational dust exposure and pulmonary changes could be documented by element analysis of dust deposits on histologic sections, and of dusts from grinding and polishing instruments collected in the laboratory. The energy-dispersive X-ray microanalysis used in this study helps to differentiate and delimit this form of pneumoconiosis. The pathogenesis is discussed on the basis of light and electron microscopic results and physicochemical analyses.

A further experimental study of the antisilicotic effect of glutamate.

Two groups of rats were exposed to quartz dust for six months and in addition one group was given drinking water containing 1.5% sodium glutamate while the second received only water. In the rats receiving glutamate we observed (a) evidence for a considerably reduced cytotoxic effect of the quartz on cells obtained by bronchopulmonary lavage, (b) a reduction in dust retention in the lungs, especially in the tracheobronchial lymph nodes, (c) a considerable reduction in the weight gain in the lungs and in their hydroxyproline and lipid contents, and (d) the inhibition of the formation of silicotic nodules. Polarographic studies of the oxygen consumption of peritoneal macrophages from rats receiving glutamate showed that glutamate prevents the adverse effects of quartz on mitochondrial oxidative processes.

Silicotic lesions of the bone marrow: histopathology and microanalysis.

Silica deposition and characteristic nodular silicotic lesions of the bone marrow, virtually unknown features of silicosis, are described in a case of severe lung silicosis with silicotic granulomas of the liver and spleen. Scanning electron microscopy and X-ray microanalysis confirmed the presence of quartz and feld-spars. The bone marrow lesions included inconspicuous accumulations of silica-containing macrophages, free silica, slight lymphocyte and plasma cell infiltration, and reticulin fibre formation; and development of slightly larger partly fibrous silicotic nodules, comparable to those of the lung, liver, and spleen. Silicosis must therefore be considered in the differential diagnosis of bone marrow granulomas.

Observation of the effect of tetrandrine on experimental silicosis of rats

It was proved in this experiment that tetrandrine, one of the bisbenzylisoquinoline alkaloids, may inhibit the development of experimental silicosis on rats whether the drug was given to the animal right after dusting or after the formation of silicotic nodules. As compared to the silicotic control rats, lowering of total weight and collagen content of the lungs were shown and some degradation of collagen fibers was also indicated from the histopathological examination.

Physico-chemical aspects in silicosis

Silicosis is a pulmonary disease which afflicts persons who inhale over long periods of time freshly-ground silica-containig dust. Its mechanism of action at the molecular level is not yet understood. The majority of crystalline SiO 2 forms are pathogenic whereas the amorphous silicas are largely inactive. The primary cause of silicosis has thus to be sought in the structural and surface characteristics of the SiO 2 particles. Recent biological work envisages in the engulfment of the SiO 2 particles into a macrophage the first step ending up with the formation of the silicotic nodule in the lung [1–3]. Intermediate stages of the process are illustrated in Fig. 1. Any silica particle ▪ exhibits a membranolytic action on the phagolysosome, probably related to the surface hydroxyls configuration, with consequent release of lytic enzymes into the cytoplasm, death of the macrophage and release of the free SiO 2 particle in the lung tissue where it can be phagocytosed by another macrophage. This does not imply any fibrotic action per se. If the process takes place with fresh ground, crystalline SiO 2 , namely quartz, tridymite and cristobalite, within the phagolysosome a fibrogenic factor is also formed, which, when released in the lung tissue, stimulates fibroblasts to an abnormal production of collagen, and hence the formation of the silicotic nodule. Membranolysis can be reduced or blocked by chemical modification of the surface, however the intimate cause of silicosis relies on the catalytic role of crystalline SiO 2 in the production of the ‘factor’. Virtually any difference in surface properties between amorphous and crystalline silicas may account for their different biological activities. We have investigated, so far, the formation of free radicals at the crushed surface (E.S.R.), the heat of interaction with water molecules (adsorption microcalorimetry) and the kinetics and energy of interaction with some aminoacids (immersion calorimetry) on amorphous and crystalline silicas of comparable size [4]. Free radicals are produced by mechanical grinding of quartz, and readily react with various atmospheric components yielding paramagnetic species such as SiO • 2 and SiCO • 2, possible intermediates in the formation of the fibrogenic factor. Water vapour reacts with silicas in various ways depending on the dehydration degree of the surface. The heat of adsorption on micronized quartz (∼ 5 M 2 g −1), low and high surface area amorphous silicas (porasil ∼ 16 m 2 g −1), (aerosil ∼ 380 m 2 g −1 all out-gassed in vacuo below 423 K (in order to prevent elimination of silanols), are reported in Fig. 2 as a function of water uptake. Micronized quartz exhibits at low coverages an interaction energy (∼ 210 kJ mol −1) which is much higher than corresponding one on the two amorphous silicas (∼ 125 kJ mol −1). ▪ Crystalline structure rather than particle size thus dictates the binding energy of surface sites. Aminoacids are adsorbed at the quartz surface [5] but when the process occurs from aqueous solution their interaction energy is competitive with water itself. In the case of proline, however, a specific interaction with quartz was observed: in that case the heat released upon contact with quartz was 30 times higher than on amorphous silica and the interaction lasted many hours indicating an activated process, possibly the oxidation to hydroxyproline specifically catalyzed by the quartz surface. All these findings may be regarded as a first step in the investigation of the particular reactivity of crystalline SiO 2 within the cells.

Pathologic changes associated with experimental exposure of rats to coal dust

Male Wistar rats were exposed to bituminous coal dust considered to have high potential for induction of coal workers' pneumoconiosis (CWP). They developed lesions similar to simple CWP as described in human subjects. Comparable lesions observed were macules (focal, coal-laden macrophage accumulations associated with increased interstitial reticulin and collagen, with emphysema involving alveoli within the macule), which were of increased size, altered shape, and increased density in animals experiencing chronic exposures. More advanced lesion types, i.e., micronodule, macronodule, silicotic nodule, Caplan's lesion, and infective granuloma, were not observed in the experimental animals. Focal bronchiolization occurred in animals receiving at least 20 months' exposure. In the literature reviewed, this pathologic change is not described as a component of CWP.

Unusual silica granulomas of the skin with massive involvement of axillary lymph nodes

Silica granulomas are rare in the skin. Involvement of the regional lymph nodes seems to be unusual. The case of a 35-year-old man with massive diffuse fibrosis of the axilla with multiple foreign body granulomas and involvement of axillary lymph nodes is presented. The lymph nodes exhibit multiple epithelioid cell granulomas and silicotic nodules which are indistinguishable from similar nodules in mediastinal lymph nodes in pulmonary silicosis. It is assumed that the numerous silica particles which were identified by X-ray microanalysis under the scanning electron microscope and recovered from the mineral ash after incineration were accidentally implanted into the skin at the time of an injury 26 years previously. The long delay between silica exposure and granuloma development is a typical feature of these lesions. The possible mechanisms operative in this process are discussed.

Acute silicoproteinosis.

A case of alveolar lipoproteinosis associated with silicosis is reported. A 58-year-old man had been exposed to silica for seven years and died three years after the onset of symptoms. Light microscopy of biopsy and necropsy material showed small silicotic nodules, silica particles, and alveolar lipoproteinosis, and ultrastructural studies were performed to define changes in alveolar epithelium and macrophages. The case provides a further example of alveolar lipoproteinosis developing as a response of the lung to injury by an external agent.

Effect of quartz dust on the lungs of mice

Intratracheal inoculations of quartz dust (250 mg/kg body weight) of a particle size less than 5 mum were given in mice and pulmonary tissue reactions studied over a period of 210 days. Acute inflammatory reaction in the lung parenchyma was observed at early periods and later the aggregates of dust laden macrophages encountered around bronchi and blood vessels. Towards the termination of the experiment at 210 days the fibrotic reaction comprised chiefly of thick compactly arranged reticulin fibers with few collagen fibers which remained restricted to the peribronchial and perivascular areas. There was no silicotic nodule formation in the parenchyma of the lung. The atypical pulmonary tissue response to quartz dust in mice has been attributed to different tissue reactivity.

Simple Siliceous Pneumoconiosis in Negev Bedouins

The purpose of this retrospective study is to evaluate the siliceous dust content in the lungs of a population for whom the Negev formed permanent habitat. The material consisted of 54 Bedouin autopsy lung specimens. The microscopical study revealed the presence of silica dust particles in the lung tissue distributed in the lymphatic bed in early involvement and in fibrous scars in advanced involvement. No classical collagenous silicotic nodules could be observed. The preponderant involvement of Bedouin women was explained by their habitual higher exposure to siliceous desert dust. It is suggested that the harmlessness of the dust accumulated in Bedouin lungs is due to its being “old dust” particles less than 5μ in diameter that had originated from dunes of the Negev desert. The benignity of this nonclinical entity prompted us to name it simple siliceous pneumoconiosis.

Apical Lung Biopsy

A method for biopsying the apex of the lung through a supraclavicular approach, under local anesthesia and without positive-pressure breathing, is presented together with our experience using the procedure in 19 patients. In 9 patients with unilateral or bilateral infiltrates, the possibility of cancer was investigated. Bronchogenic carcinoma was identified in 4, 4 showed scarring with chronic inflammation, and 1 had a silicotic nodule. A presumptive diagnosis of cancer was confirmed in 6 other patients. An apical empyema was drained, diffuse interstitial fibrosis recognized, granuloma identified, and fibrosis without pneumoconiosis diagnosed. The only complication was in 1 patient who bled and required a thoracotomy. Apical lung biopsy provides a means of accurately identifying lesions arising in the upper portion of the lung.