Effects of silica on the composition of the pulmonary extracellular lining

Alveolar Proteinosis and Phospholipidoses of the Lungs

Three pulmonary disease conditions result from the accumulation of phospholipids in the lung. These conditions are the human lung disease known as pulmonary alveolar proteinosis, the lipoproteinosis that arises in the lungs of rats during acute silicosis, and the phospholipidoses induced by numerous cationic amphiphilic therapeutic agents. In this paper, the status of phospholipid metabolism in the lungs during the process of each of these lung conditions has been reviewed and possible mechanisms for their establishment are discussed. Pulmonary alveolar proteinosis is characterized by the accumulation of tubular myelin-like multilamellated structures in the alveoli and distal airways of patients. These structures appear to be formed by a process of spontaneous assembly involving surfactant protein A and surfactant phospholipids. Structures similar to tubular myelin-like multilamellated structures can be seen in the alveoli of rats during acute silicosis and, as with the human condition, both surfactant protein A and surfactant phospholipids accumulate in the alveoli. Excessive accumulation of surfactant protein A and surfactant phospholipids in the alveoli could arise from their overproduction and hypersecretion by a subpopulation of Type II cells that are activated by silica, and possibly other agents. Phospholipidoses caused by cationic amphiphilic therapeutic agents arise as a result of their inhibition of phospholipid catabolism. Inhibition of phospholipases results in the accumulation of phospholipids in the cytoplasm of alveolar macrophages and other cells. While inhibition of phospholipases by these agents undoubtedly occurs, there are many anomalous features, such as the accumulation of extracellular phospholipids and surfactant protein A, that cannot be accounted for by this simplistic hypothesis.

Effects of 28 days silicon dioxide aerosol exposure on respiratory parameters, blood biochemical variables and lung histopathology in rats

Inhalation toxicity of silicon dioxide aerosol (150, 300 mg/m(3)) daily over a period of 28 days was carried out in rats. The changes in respiratory variables during the period of exposure were monitored using a computer programme that recognizes the modifications of the breathing pattern. Exposure to the aerosol caused a time dependent decrease in tidal volume, with an increase in respiratory frequency compared to the control. Biochemical variables and histopathological observation were noted at 28th day following the start of exposure. Biochemical markers of silica induced lung injury like plasma alkaline phosphatase, lactate dehydrogenase and angiotensine converting enzyme activities increased in a concentration dependent manner compared to control. Increase in the plasma enzymatic activities indicates endothelial lung damage, increased lung membrane permeability. Histopathological observation of the lungs confirmed concentration dependent granulomatous inflammation, fibrosis and proteinacious degeneration. Aggregates of mononuclear cells with entrapped silica particles circumscribed by fibroblast were observed in 300 mg/m(3) silica aerosol exposed group at higher magnification. Decrease in tidal volume and increase in respiratory frequency might be due to the thickening of the alveolar wall leading to a decreased alveolar volume and lowered elasticity of the lung tissue. The trends in histological and biochemical data are in conformity with the respiratory data in the present study. This study reports for the first time, the changes in respiratory variables during silica aerosol exposure over a period of 28 days.

Metabolomics in lung inflammation:a high-resolution (1)h NMR study of mice exposedto silica dust

ABSTRACT Here we report the first (1)H NMR metabolomics studies on excised lungs and bronchoalveolar lavage fluid (BALF) from mice exposed to crystalline silica. High-resolution (1)H NMR metabolic profiling on intact excised lungs was performed using slow magic angle sample spinning (slow-MAS) (1)H PASS (phase-altered spinning sidebands) at a sample spinning rate of 80 Hz. Metabolic profiling on BALF was completed using fast magic angle spinning at 2 kHz. Major findings are that the relative concentrations of choline, phosphocholine (PC), and glycerophosphocholine (GPC) were statistically significantly increased in silica-exposed mice compared to sham controls, indicating an altered membrane choline phospholipids metabolism (MCPM). The relative concentrations of glycogen/glucose, lactate, and creatine were also statistically significantly increased in mice exposed to silica dust, suggesting that cellular energy pathways were affected by silica dust. Elevated levels of glycine, lysine, glutamate, proline, and 4-hydroxyproline were also increased in exposed mice, suggesting the activation of a collagen pathway. Furthermore, metabolic profiles in mice exposed to silica dust were found to be spatially heterogeneous, consistent with regional inflammation revealed by in vivo magnetic resonance imaging (MRI).

Comparison of functional, biochemical, and morphometric alterations in the lungs of 4 rat strains and hamsters following repeated intratracheal instillation of crocidolite asbestos

Four rat strains and hamsters were exposed to 0.7 mg crocidolite asbestos/g lung once/week for 3 weeks by intratracheal instillation (IT). Pulmonary function, biochemistry, and morphometry were evaluated at 3 and 6 months after IT. Each rat strain, but not the hamster, exhibited elevated lung volumes. Quasistatic compliance in rats and hamsters was reduced 15%-40% and 25%-50%, respectively. Diffusing capacity for carbon monoxide was elevated in the rats, but in hamsters, it was reduced at both time points. Hydroxyproline was increased in the rat strains but not in hamsters. Lung protein/dry weight was not altered in most of the rat strains and in hamsters at both time points. The linear mean intercept value was increased in Fischer 344 (F344) rats (3 and 6 months) and Long Evans rats (6 months), whereas in hamsters only at 6 months. Surface area was unchanged in both species. Specific density for parenchymal tissue was reduced for F344 rats at both time points, but alveolar density values did not change overall relative to species and time. The correlated functional and morphological changes in the hamster appeared more consistent with human asbestosis. Divergent lung responses in different species and strains should be considered when selecting laboratory animal models for studies related to asbestos exposure.

Mechanistically identified suitable biomarkers of exposure, effect, and susceptibility for silicosis and coal-worker's pneumoconiosis: a comprehensive review

Clinical detection of silicosis is currently dependent on radiological and lung function abnormalities, both late manifestations of disease. Markers of prediction and early detection of pneumoconiosis are imperative for the implementation of timely intervention strategies. Understanding the underlying mechanisms of the etiology of coal workers pneumoconiosis (CWP) and silicosis was essential in proposing numerous biomarkers that have been evaluated to assess effects following exposure to crystalline silica and/or coal mine dust. Human validation studies have substantiated some of these proposed biomarkers and argued in favor of their use as biomarkers for crystalline silica- and CWP-induced pneumoconiosis. A number of "ideal" biological markers of effect were identified, namely, Clara cell protein-16 (CC16) (serum), tumor necrosis factor-alpha (TNF-alpha) (monocyte release), interleukin-8 (IL-8) (monocyte release), reactive oxygen species (ROS) measurement by chemiluminescence (neutrophil release), 8-isoprostanes (serum), total antioxidant levels measured by total equivalent antioxidant capacity (TEAC), glutathione, glutathione peroxidase activity, glutathione S-transferase activity, and platelet-derived growth factor (PDGF) (serum). TNF-alpha polymorphism (blood cellular DNA) was identified as a biomarker of susceptibility. Further studies are planned to test the validity and feasibility of these biomarkers to detect either high exposure to crystalline silica and early silicosis or susceptibility to silicosis in gold miners in South Africa.

Amino-terminal and midmolecule parathyroid hormone-related protein, phosphatidylcholine, and type II cell proliferation in silica-injured lung

Acute silica lung injury is marked by alveolar phospholipidosis and type II cell proliferation. Parathyroid hormone-related protein (PTHrP) 1-34 could have a regulatory role in this process because it stimulates phosphatidylcholine secretion and inhibits type II cell growth. Other regions of the PTHrP molecule may have biological activity and can also exert pulmonary effects. This study examined the temporal pattern for expression of several regions of PTHrP after silica lung injury and evaluated the effects of changes in expression on cell proliferation and lung phospholipids. Expression of all PTHrP regions fell at 4 days after injury. Reversing the decline in PTHrP 1-34 or PTHrP 67-86 with one intratracheal dose and four daily subcutaneous doses of PTHrP 1-34 or PTHrP 67-86 stimulated bronchoalveolar lavage disaturated phosphatidylcholine (DSPC) levels. Cell culture studies indicate that the peptides exerted direct effects on DSPC secretion by type II cells. Neither peptide affected type II cell proliferation with this dosing regimen, but addition of an additional intratracheal dose resulted in significant inhibition of growth, consistent with previous effects of PTHrP 1-34 in hyperoxic lung injury. These studies establish a regulatory role for PTHrP 1-34 and PTHrP 67-86 in DSPC metabolism and type II cell proliferation in silica injury. Growth inhibitory effects of PTHrP could interact with phospholipid stimulation by affecting type II cell numbers. Further studies are needed to explore the complex interactions of PTHrP-derived peptides and the type II cell response at various stages of silica lung injury.

The ability of mineral dusts and fibres to initiate lipid peroxidation. Part II: relationship to different particle-induced pathological effects

Exposure to pathogenic mineral dusts and fibres is associated with pulmonary changes including fibrosis and cancer. Investigations into aetiological mechanisms of these diseases have identified modifications in specific macromolecules as well as changes in certain early processes, which have preceded fibrosis and cancer. Peroxidation of lipids is one such modification, which is observed following exposure to mineral dusts and fibres. Their ability to initiate lipid peroxidation and the parameters that determine this ability have recently been reviewed. Part II of this review examines the relationship between the capacity of mineral dusts and fibres to initiate lipid peroxidation and a number of pathological changes they produce. The oxidative modification of polyunsaturated fatty acids is a major contributor to membrane damage in cells and has been implicated in a great variety of pathological processes. In most pathological conditions where an induction of lipid peroxidation is observed it is assumed to be the consequence of disease, without further establishing if the induction of lipid peroxidation may have preceded or accompanied the disease. In the great majority of instances, however, despite the difficulty in proving this association, a causal relationship between lipid peroxidation and disease cannot be ruled out.

Silica binds serum proteins resulting in a shift of the dose-response for silica-induced chemokine expression in an alveolar type II cell line

There is a growing concern about whether the myriad of culture conditions, cell lines, and doses of nonfibrous and fibrous particles used in vitro are truly representative of the complex environment of the in vivo particle exposure situation. The use of serum as a supplement to the growth medium of cultured cells is a widely accepted practice. However, little is known about whether the various serum proteins may interact with the surfaces of particles, consequently altering their toxicity, inflammatory properties, or fibrogenicity, etc. observed in vivo. Using a murine alveolar type II cell line, MLE-15, we measured the early changes in various chemokine mRNA species following exposure of the cells to silica (cristobalite) in the presence or absence of serum. Total mRNA was isolated and assayed using an RNase protection assay after 6 h of particle exposure. We observed that the addition of serum to the culture media reduced the in vitro silica-induced chemokine response (i.e., shift in the dose-response curve) in MLE-15 cells. Further, using Western blot analysis and protein sequencing techniques, we have identified a specific serum component, apolipoprotein-A1 (apo-A1), as a protein in serum that binds selectively to silica, thus leading to the altered chemokine response. We also found that apo-A1 not only binds to silica but also binds to other nonfibrous and fibrous particles such as titanium dioxide and asbestos. These results demonstrate the importance of culture conditions for modifying the outcome of an experiment when performing in vitro particle exposure studies.

Immunocytochemical characterization of lung macrophage surface phenotypes and expression of cytokines in acute experimental silicosis in mice

The expression of the surface phenotypical profile and the cytokines TNF-alpha and IL-1beta from murine lung macrophages was studied in parenchymal lung tissue and bronchoalveolar fluid of mice, over a 2-week period, following a single intratracheal instillation of silica. The acute inflammatory reaction, confirmed by a significant augmentation of four times the control values of the number of macrophages recovered by lavage from experimental animals, was followed by organized granulomas in the interstitium. The immunohistochemical analysis of lung tissue sections after silica instillation demonstrated the increased alveolar and interstitial tissue expression of all surface antigens and cytokines studied, mainly Mac-1, F4/80 antigens, TNF-alpha and IL-1beta, which were occasionally observed in normal uninjected and saline-treated mice. These findings show that, after silica instillation, the expression of surface phenotypical markers of lung macrophages increased, and this change was concomitantly associated with an increased expression of the cytokines TNF-alpha and IL-1beta. These changes support the conclusion that an influx of the newly recruited and activated macrophage population, with a different phenotype, is induced by treatment during inflammation. The populational changes involve difference in functional activity and enhance TNF-alpha and IL-1beta expression. These cytokines, produced in the silicosis-induced inflammatory process, are associated with the development of fibrosis and may contribute to disease severity.

Adhesive characteristics of type II pneumocyte subpopulations from saline- and silica-treated rats

Alveolar epithelial cells isolated from silica-treated rat lungs provide a system for the in vitro study of repair mechanisms. In studies of type II cell interactions with the extracellular matrix, we observed that type IIB pneumocytes from silica-treated rats adhered to tissue culture plastic more readily than do normal type II cells. This paper examines the adhesion characteristics of IIA and IIB cells and their modulation by divalent cations. We describe differences in the adhesive behavior of two subpopulations of freshly isolated type II pneumocytes from saline- and silica-treated rats. The observations have implications for repair and tissue remodeling in the lung.

Subchronic pulmonary inflammation and fibrosis induced by silica in rats are attenuated by amiodarone

A previous study demonstrated that the acute phase of silica-induced lung injury in rats can be attenuated by concomitant administration of amiodarone, a cationic amphiphilic drug that inhibits phospholipase activity in the lungs. The purpose of the present study was to determine whether continued amiodarone administration could inhibit subchronic silica-induced lung injury and fibrosis. Male Fischer-344 rats were administered amiodarone (150 mg/kg, p.o., 5 days/week) for 14 days and were then instilled with silica (100 mg/kg) intratracheally. Amiodarone treatment then continued for 60 days. Injury was evaluated by parameters in bronchoalveolar lavage fluid and fibrosis was assessed by lung hydroxyproline content and trichrome staining of collagen. Within the bronchoalveolar lavage fluid, amiodarone treatment resulted in significant decreases in silica-induced elevations in albumin levels, lactate dehydrogenase activity, beta-glucuronidase activity, and neutrophil influx. Amiodarone treatment resulted in significant reductions in silica-induced increases in lung weight and hydroxyproline levels; the diminution of fibrosis due to amiodarone treatment was confirmed histologically. These results indicate that subchronic pulmonary inflammation and fibrosis induced by silica in the rat can be attenuated by the concomitant administration of amiodarone.

N-acetyl-beta-D-glucosaminidase activity within BAL from macaques exposed to generic coal dusts

N-acetyl-beta(beta)-D-glucosaminidase is a lysosomal enzyme secreted by alveolar macrophages in response to phagocytosis of particulate material. Alveolar macrophages participate in the degradation and fibrosis of pulmonary tissue that results in pneumoconiosis. Known quantities of four characterized respirable dusts were bronchoscopically placed into the right caudal lung lobe of macaque monkeys. Bronchoalveolar lavage (BAL) samples were collected from dust-exposed right lung and unexposed left lung of the same individuals at 2-week intervals for 12 weeks after dust instillation. The samples were tested for N-acetyl-beta-D-glucosaminidase activity to determine if the enzyme levels could serve as an indicator of pulmonary injury induced by generic coal dusts when compared to known fibrogenic and nuisance dusts. Installation of generic quartz, anthracite, or TiO2 dusts produced significant elevations of enzyme activity and increased numbers of macrophages in the dust-exposed lobes. Elevations in enzymatic activity and macrophage numbers were greatest in response to generic quartz dust. These results suggest that quantitative levels of N-acetyl-beta-D-glucosaminidase activity may be a useful indicator of acute and chronic lung injury following exposure to fibrogenic and nonfibrogenic dusts.

Alterations in the pulmonary microsomal cytochrome P-450 system after exposure of rats to silica

Because some evidence indicates that there is an increased incidence of lung cancer in silicosis, we studied the effects of exposing rats to silica on the pulmonary microsomal cytochrome P-450 system. Rats were exposed to silica by intratracheal administration, lung microsomes were obtained from untreated and silica-treated animals, and the amount of microsomal tissue, the level of total cytochromes P-450 (all isozymes), the activity of NADPH cytochrome P-450 reductase, the metabolism of two xenobiotics, and the relative amounts of cytochrome P-4502B1 and P-4501A1 were measured. Lungs from silica-treated rats were almost 2-fold heavier and contained more than 10 times more alveolar phospholipids than lungs from untreated animals, indicating that acute silicosis had been produced. In lungs from silica-treated animals, the concentration of microsomal tissue, expressed as milligrams of microsomal protein per gram of lung, was increased by more than 2-fold, and total microsomal protein content was increased by almost 5-fold relative to untreated animals. When expressed as activity or amount per milligram of protein, the microsomal concentrations of NADPH cytochrome P-450 reductase, total cytochromes P-450, 7-ethoxycoumarin (EC)-0-deethylase, and cytochrome P-4502B1 are reduced by approximately 50% in silica-treated rats. However, when expressed as total activity or amount in the lungs, all are increased by approximately 1.5- to 2.5-fold in silica-treated lungs. On the other hand, total lung 7-ethoxyresorufin (ER)-0-deethylase activity and cytochrome P-4501A1 are increased by 4- to 5-fold in silica-treated lungs.(ABSTRACT TRUNCATED AT 250 WORDS)

The surfactant system of the adult lung: physiology and clinical perspectives

Pulmonary surfactant is synthesized and secreted by alveolar type II cells and constitutes an important component of the alveolar lining fluid. It comprises a unique mixture of phospholipids and surfactant-specific proteins. More than 30 years after its first biochemical characterization, knowledge of the composition and functions of the surfactant complex has grown considerably. Its classically known role is to decrease surface tension in alveolar air spaces to a degree that facilitates adequate ventilation of the peripheral lung. More recently, other important surfactant functions have come into view. Probably most notable among these, surfactant has been demonstrated to enhance local pulmonary defense mechanisms and to modulate immune responses in the alveolar milieu. These findings have prompted interest in the role and the possible alterations of the surfactant system in a variety of lung diseases and in environmental impacts on the lung. However, only a limited number of studies investigating surfactant changes in human lung disease have hitherto been published. Preliminary results suggest that surfactant analyses, e.g., from bronchoalveolar lavage fluids, may reveal quantitative and qualitative abnormalities of the surfactant system in human lung disorders. It is hypothesized that in the future, surfactant studies may become one of our clinical tools to evaluate the activity and severity of peripheral lung diseases. In certain disorders they may also gain diagnostic significance. Further clinical studies will be necessary to investigate the potential therapeutic benefits of surfactant substitution and the usefulness of pharmacologic manipulation of the secretory activity of alveolar type II cells in pulmonary medicine.

Ranking toxicity of industrial dusts by bronchoalveolar lavage fluid analysis

Female wistar rats were inoculated intratracheally with 10 mg/ml suspensions of various dusts, viz: quartz, fly ash, mica and corundum in physiological saline. Biochemical markers of bronchoalveolar lavage fluid (BALF) were analysed 8 days after the instillation of the dusts. Elevated levels of proteins, sialic acid and phospholipid contents and the activity of lactate dehydrogenase correlated well with the degree of the known fibrogenic potential of different dusts in the lungs in the following order, quartz greater than fly ash greater than mica greater than corundum. beta-glucuronidase activity, was however, only elevated in the quartz inoculated group of rats. It is suggested that biochemical constituents of BALF analysed shortly after the exposure to different dusts can be useful to mirror alterations in the tissue response to mineral dusts.

Extracellular matrix components in bronchoalveolar lavage fluid in quartz exposed rats

To investigate the long term effects of quartz, bronchoalveolar lavage (BAL) and analysis of lung silica were performed in rats (n = 20) one, four, and 12 months after exposure to intratracheally instilled crystalline silica. Total and relative concentrations of silica in the lungs were highest one month after exposure. At this time BAL fluid concentrations of total cells, macrophages, and lymphocytes increased five to 10-fold compared with saline instilled controls (n = 19). The number of polymorphonuclear cells (PMNs) increased about 200-fold. The increased number of PMNs persisted during the year. Furthermore, albumin and fibronectin concentrations increased continually during the year, about two to fivefold the values of controls. Hyaluronan, by contrast, increased during the four month period (about eightfold) but decreased after one year to the one month concentration. Phospholipids in BAL fluid, raised already after one month, remained high at one year. The findings suggest progressive damage of the alveolar and interstitial tissues. Moreover, the increases in components of the extracellular matrix capable of building fibrotic networks are in agreement with the microscopical findings of fibrosis. Because only total cells, macrophages, and albumin concentrations correlated weakly with the silica contents of the lung, it is unlikely that the relation between quartz burden and the reaction in the lung is simple.

Effect of blood leucocyte depletion on the inflammatory response of the lung to quartz

This study determined the effect of blood leucocyte depletion on the early inflammatory response of the lung to alpha-quartz. F344/N rats were instilled intratracheally with either physiological saline or 2 or 5 mg of alpha-quartz suspended in saline. One day prior to the instillation, half of the rats received an ip injection of rabbit antiserum that had been raised against rat neutrophils. The other half of the rats received an ip injection of normal rabbit serum. One day after the instillation of saline or quartz, the animals were euthanized and observed for changes in blood cell numbers, lung histopathology, and bronchoalveolar lavage fluid (BALF) content of indicators of an inflammatory response and cytotoxicity. The rabbit antiserum depleted the blood of most white blood cells of all types. BALF fluid from saline-instilled animals did not differ between the white blood cell-depleted and the nondepleted animals except for a 20% reduction in numbers of alveolar macrophages in the depleted animals. BALF fluid from the nondepleted, quartz-instilled animals had a dose-dependent increase in content of neutrophils and protein (indicator of an increase in the permeability of the alveolar/capillary barrier) as well as an increase in lactate dehydrogenase and glutathione reductase (cytoplasmic enzymes whose presence extracellularly indicates cytotoxicity), alkaline phosphatase (indicator of type II cell secretory activity), beta-glucuronidase, and acid proteinase (lysosomal enzymes) activities. The higher dose of quartz also elicited an increase in LTB4 and PGE2 content of BALF. GSH content of BALF was decreased by the quartz exposure. The depletion of blood white blood cells prevented the influx of neutrophils into the alveoli of the quartz-exposed rats and decreased the BALF markers of capillary permeability and cytotoxicity (protein content and extracellular cytoplasmic enzymes). The absence of neutrophils in the alveoli had no effect on the lysosomal content of BALF, indicating that the neutrophils were not the source of these enzymes in nondepleted rats exposed to alpha-quartz. The quartz-induced elevation of LTB4 in BALF was not observed in depleted rats, suggesting that neutrophils may be the source of the increase in this leukotriene in the BALF. Both the GSH content and the alkaline phosphatase activity in BALF were enhanced in the absence of alveolar neutrophils. The enhancement of GSH in BALF is consistent with the neutrophils being the source of reactive oxygen species that deplete GSH. The increased alkaline phosphatase activity in the BALF of both the depleted and nondepleted animals is consistent with the type II cell hypertrophy that was induced by quartz instillation and was neutrophil independent.(ABSTRACT TRUNCATED AT 400 WORDS)

Enzyme activities of lung lavage in silicosis

The cytotoxic effect of quartz on lung cells has been well documented by in vitro and animal studies, but the pertinence of these findings to humans has not yet been documented. We measured lactate dehydrogenase (LDH) activities in the lung lavage of 24 long-term workers in the Québec granite industry and 25 control subjects. We found significant increases in LDH activities in the workers' lung lavage, even in the absence of established silicosis (9 subjects). We looked at a similar observation in the sheep model of early silicosis, measured quartz content of lung lavage, and found significant correlation with LDH levels (R = 0.64, p less than 0.001). All of the quartz particles in human and sheep lung lavage were in the alveolar macrophages. To test further the relationship of macrophage damage (cytotoxicity of quartz) we measured the release of LDH by sheep alveolar macrophage in 24 h cell culture under control conditions, exposure to inert dust, titanium, minusil-5 quartz, or aluminum-treated quartz. The LDH release was at control levels during titanium exposure and showed a significantly dose-related increase during quartz exposure. The latter cytotoxic effect was largely attenuated by aluminum treatment of quartz. These in vitro data agreed with previous reports. This study presents evidence of a cytotoxic effect of quartz inhalation in humans. The effect is related to the intensity of quartz retention in the lung macrophages; it is not a nonspecific dust exposure effect and can be attenuated by surface modification of the quartz.

Induction of surfactant protein (SP-A) biosynthesis and SP-A mRNA in activated type II cells during acute silicosis in rats

The synthesis of the major surfactant protein, SP-A, was studied in activated alveolar type II cells isolated from the lungs of rats exposed to silica by intratracheal instillation. Exposure of rats to silica resulted in large increases in the levels of disaturated phosphatidylcholine and SP-A in the extracellular and intracellular surfactant compartments. Isolated type II cells were used to determine if the observed increases in SP-A were associated with increased SP-A synthesis. Type II cells were isolated by a combination of elastase digestion, centrifugal elutriation, and differential adherence on IgG-coated petri dishes. Type II cells from silica-treated lungs were separated into two populations, designated type IIA and type IIB. The type IIB, or activated population, consisted of type II cells that were larger than normal type II cells and, in addition, contained larger and more numerous lamellar bodies than normal type II cells. Type IIB cells contained 4.3-fold higher levels of SP-A compared to normal type II cells. SP-A synthesis was measured by incubating freshly isolated cells with [35S]Translabel (70% [35S]methionine, 15% [35S]cysteine) for up to 4 h in methionine-free medium, followed by immunoprecipitation of newly synthesized protein. The rate of SP-A synthesis was increased approximately 6.7-fold in the activated type II cells. Analysis of the newly synthesized protein by one-dimensional SDS-PAGE indicated three intracellular forms of SP-A with molecular weights of approximately 26,000, 30,000, and 34,000. In type II cells from control rats, the 34-kD protein accounted for approximately 93% of the newly synthesized SP-A after 4 h of incubation; only a small amount of radioactivity was associated with the lower molecular weight species. The increased biosynthesis of SP-A in the activated type II cells was associated with a 7.3-fold increase in the level of SP-A mRNA. These results indicate that the content and synthesis of SP-A are both highly elevated in activated type II cells and that these increases may be due to increased levels of SP-A mRNA.

Regulation of phosphatidylcholine biosynthesis in activated alveolar type II cells

The biosynthesis of phosphatidylcholine was studied in a population of activated Type II cells isolated from the lungs of rats treated with silica. Type II cells were separated by centrifugal elutriation into two populations, designated Type IIA and Type IIB. The Type IIB or activated population consisted of Type II cells that were larger than normal cells; Type IIA cells were morphologically similar to normal Type II cells. Type IIB cells incorporated more [Me-14C]choline into both total phosphatidylcholine and disaturated phosphatidylcholine than did Type IIA or control Type II cells. Measurement of the pool sizes of the choline-containing precursors to phosphatidylcholine indicated that the biosynthesis of phosphatidylcholine was increased 4- to 5-fold in Type IIB cells. Increased conversion of cholinephosphate to CDP-choline was associated with increased phosphatidylcholine biosynthesis in Type IIB cells. Cholinephosphate cytidylyltransferase activity was increased approximately threefold in Type IIB cells. Subcellular fractionation indicated that essentially all of the increase in cytidylyltransferase activity was associated with the particulate fraction (100,000 x g pellet). In Type IIB cells, the particulate fraction contained 83% of the total cellular cytidylyltransferase activity; in control cells, this fraction contained 67% of the total activity. The specific activity of the cytidylyltransferase associated with the particulate fraction was increased twofold in Type IIB cells. The specific activity of the cytosolic enzyme was similar to that in control cells. Cholinephosphotransferase specific activity was increased approximately twofold in the activated Type II cells. The specific activity of choline kinase was the same as that in control Type II cells. These results demonstrate that the increased biosynthesis of phosphatidylcholine in Type IIB cells is a result of stimulation of the CDP-choline pathway. This study indicates that both cholinephosphate cytidylyltransferase and cholinephosphotransferase may be involved in regulating the de novo biosynthesis of phosphatidylcholine in alveolar Type II cells.

Quartz exposure, retention, and early silicosis in sheep

The purposes of this study were (1) to investigate the chronology of events in cellular and biochemical changes thought to be important in the development of silicosis, (2) to relate these to changes in lung function and radiograph, and (3) to evaluate the relation of quartz exposure and retention to individual response leading to early silicosis. Thirty-six sheep were exposed by repeated intratracheal infusion at 10-day intervals to 100 mg Minusil-5 in 100 ml saline (Si group), and 10 sheep were exposed at the same intervals to 100 ml saline (control). All sheep were investigated at 3-month intervals by chest radiograph, lung function, and lung lavage. At month 9, chest radiograph score of parenchymal opacities was significantly increased at 2.8 +/- 0.6 versus 0.4 +/- 0.4 in the Si group (p less than .05), establishing early radiologic silicosis. Lung function was significantly altered with reduction in lung compliance, vital capacity, and diffusion capacity (p less than .05). Lung lavage cellularity revealed significant increase in total cells (X 2.5), macrophages (X3), and neutrophils (X3). Albumin in BAL remained at the control level. Fibronectin production was significantly increased, as was the fibroblast growth activity, without significant change in procollagen 3 at this early stage of disease. Total phospholipids were significantly elevated in the Si-exposed sheep, and the profile demonstrated an increase in all the phospholipid components. Spontaneous release of hydrogen peroxide by alveolar cells was not increased, but in the presence of phorbol myristate acetate (PMA) higher levels of peroxide were found in the quartz-exposed sheep (p less than .05). The cellular and biochemical alterations of lung lavage preceded other changes. At month 12, there were good correlations (r greater than .49, p less than .001) between parameters evaluating related phenomena but poor correlations between measurements evaluating different aspects of the disorder. To investigate the heterogeneity in the individual response of sheep to the same exposure (susceptibility), individual quartz retention levels at month 12 were measured and found to correlate well with individual parameters of disease activity. We concluded that in early silicosis of sheep, cellular and biochemical changes in lung lavage preceded derangements of pulmonary function and radiographic abnormalities. Thereafter, parameters of lung lavage, lung function, and radiograph were significantly interrelated, but for a given exposure the degree of quartz retention appeared to determine the intensity of the silicotic process.

Toxicity of cadmium oxide instilled into the rat lung. I. Metabolism of cadmium oxide in the lung and its effects on essential elements

The metabolism of cadmium oxide (CdO, insoluble form) and cadmium chloride (CdCl2, soluble form) instilled intratracheally into the rat lung was investigated. CdO might be solubilized rapidly in the lung and consequently pulmonary clearance rate of CdO was not so different from that of CdCl2. At a dose of 5 micrograms Cd/rat about 20% of the dose was translocated to the liver within 12 h, whereas gradual and consistent accumulation of Cd was observed in the kidney up to 7 days. Both pulmonary clearance and translocation of Cd to the liver were accelerated with the dose of instilled CdO, however, Cd accumulated in the kidney was proportional to the dose. Lung weight was increased by the instillation of CdO. Lung essential elements such as S, P, Mg, Zn and Mn were not affected in the inflammatory-reparative proliferative process, but Cu content of unit lung weight was slightly decreased.

Kinetics of pulmonary surfactant phosphatidylcholine metabolism in the lungs of silica-treated rats

Exposure of rats to silica by intratracheal injection increased the intra- and extracellular compartments of pulmonary surfactant phospholipid. These changes were dose and time dependent, but both pools were not affected equally. Seven days after the instillation of 10 mg of silica, the intracellular pool increased 13.3-fold, from 1.49 +/- 0.30 to 19.86 +/- 0.77 mg of surfactant phospholipid per pair of lungs, and the extracellular pool increased 7.4-fold, from 1.87 +/- 0.79 to 13.79 +/- 0.72 mg of surfactant phospholipid per pair of lungs. To investigate the physiologic processes responsible for these massive accumulations of surfactant. [14C]choline was injected into the tail veins of control and silica-treated rats and the specific activity of surfactant phospholipids within the intracellular and extracellular pools was determined at various times between 0 and 26 hr after injection. All of the processes measured were increased in response to silica exposure, but not to the same extent. At 1 hr, incorporation of [14C]choline into the intracellular surfactant pool was increased 12.6-fold above controls, from 4.8 +/- 1.1 x 10(3) to 60.6 +/- 26.6 x 10(3) dpm. The flux of [14C]choline-labeled phospholipid from the intracellular to the extracellular pool was increased 7.3-fold, from 102 +/- 10 to 749 +/- 39 micrograms/hr in silica-treated animals, but its disappearance from the extracellular pool was increased only 5.0-fold, from 87 +/- 8 to 434 +/- 21 micrograms/hr. The half-life of [14C]choline-labeled phospholipids in the intracellular pool of surfactant was increased from 10.1 +/- 1.0 to 18.3 +/- 5.3 hr and that in the extracellular surfactant pool from 14.8 +/- 1.4 to 21.9 +/- 4.9 hr. Expansion of the intra- and extracellular pools of surfactant phospholipids may be explained on the basis of a metabolic imbalance in which the intracellular production of surfactant is increased above its secretion rate into the extracellular compartment, and the secretion rate is elevated above the rate at which surfactant phospholipids are cleared from the alveoli.

Relationship of lipid secretion and particle size to diffuse interstitial change in pneumoconiosis: a pathogenetic perspective

Simple pneumoconiosis due to compact particles, notably in coal workers, sometimes departs from its customary focal formations and a more diffuse distribution of dust-impregnated fibrosis is superimposed. To account for this change, which may be reflected in the acquisition of radiologically irregular opacities in addition to rounded ones, attention is directed first toward type II alveolar epithelium. These cells come early into contact with inhaled particles and the lipid secretion provoked prevents their characteristic aggregation, so they remain in a more dispersed state and the consequent fibrotic reaction then tends to become diffuse. Second, submicron particles appear to act not from within the alveolus like the more usual larger ones, but after direct passage through type I epithelium into the interstitium, where lacking focal accumulation they are able to produce diffuse changes. Complexities, however, remain, among which are coalescence of focal lesions as their severity increases and interplay of agents producing interstitial fibrosis in the general population.

Stimulation of surfactant phospholipid biosynthesis in the lungs of rats treated with silica

The effects of intratracheally instilled silica (10 mg/rat) on the biosynthesis of surfactant phospholipids was investigated in the lungs of rats. The sizes of the intracellular and extracellular pools of surfactant phospholipids were measured 7, 14 and 28 days after silica exposure. The ability of lung slices to incorporate [14C]choline and [3H]palmitate into surfactant phosphatidylcholine (PC) and disaturated phosphatidylcholine (DSPC) was also investigated. Both intra- and extra-cellular pools of surfactant phospholipids were increased by silica treatment. The intracellular pool increased linearly over the 28-day time period, ultimately reaching a size 62-fold greater than controls. The extracellular pool also increased, but showed a pattern different from that of the intracellular pool. The extracellular pool increased non-linearly up to 14 days, and then declined. At its maximum, the extracellular pool was increased 16-fold over the control. The ability of lung slices to incorporate phospholipid precursors into surfactant-associated PC and DSPC was elevated at all time periods. The rate of incorporation of [14C]choline into surfactant PC and DSPC was maximal at 14 days and was nearly 3-fold greater than the rate in controls. The rate of incorporation of [3H]palmitate was also maximal at 14 days, approx. 5-fold above controls for PC and 3-fold for DSPC. At this same time point, the microsomal activity of cholinephosphate cytidylyltransferase was increased 4.5-fold above controls, but cytosolic activity was not significantly affected by silica treatment. These data indicate that biosynthesis of surfactant PC is elevated after treatment of lungs with silica and that this increased biosynthesis probably underlies the expansion of the intra- and extra-cellular pools of surfactant phospholipids.

Functional and biochemical effects on rat lung following instillation of crocidolite and chrysotile asbestos

Groups of rats received a single intratracheal instillation of saline (control), 1.6 mg crocidolite, and 1.6 mg chrysotile. At 1, 3, 6, 9, and 12 mo after instillation, respiratory functional tests were performed and the lungs were biochemically analyzed. Throughout 12 mo, obstructive small-airway abnormalities with air trapping were observed in the asbestos-treated rats. The degree of airway obstruction and air trapping was higher in the chrysotile-treated group than in the crocidolite-treated group. Lung weight increased significantly in both asbestos-treated groups. Collagen and elastin content of unit lung weight significantly increased in the chrysotile-treated group compared with the control and crocidolite-treated group throughout the experimental period up to 12 mo. However, the collagen and elastin content of unit lung weight in the crocidolite-treated group was not as different from the control group. These results indicate that chrysotile is more fibrogenic than crocidolite, as has been suggested in histopathological studies.

Effect of intratracheal gallium arsenide administration on delta-aminolevulinic acid dehydratase in rats: relationship to urinary excretion of aminolevulinic acid

Exposure to gallium arsenide (GaAs) is a potential hazard in the semiconductor industry and there is a need for specific biological indicators of exposure/toxicity for this compound. These studies examined effects of GaAs exposure on the heme biosynthetic pathway enzyme delta-aminolevulinic acid dehydratase (ALAD). Male CD rats received GaAs suspensions at doses of 50, 100, or 200 mg/kg via a single intratracheal instillation. Six days after treatment a dose-dependent inhibition of blood ALAD was observed with activity decreasing to 5% of controls at the highest dose, with a concomitant marked increase in the urinary excretion of aminolevulinic acid (ALA). Inhibition of blood ALAD following administration of GaAs was maximal (30% of control) 3 to 6 days postexposure and returned to approximately control values on day 18. Urinary excretion of ALA was maximal 3 to 6 days postexposure and recovered toward control values at 18 days. Inhibition of kidney and liver ALAD following GaAs exposure was also evident. Intratracheal instillation of silica did not alter the activity of ALAD in blood, liver, or kidney. Marked increases in lung wet weight/body weight ratios were evident in lungs of silica- and GaAs-treated rats. Histopathological changes in the lungs were characterized by multifocal granulomas following silica treatment and Type II pneumocyte hyperplasia following GaAs treatment; mild necrosis was evident in both groups. Rats treated with 100 mg/kg GaAs exhibited swelling of kidney proximal tubule mitochondria 6 days following exposure. Silica and GaAs exposure produced marked decreases in cumulative weight gain. The concentration of gallium required to achieve half-maximal inhibition of ALAD in vitro was 200-fold less in blood and 40-fold less in kidney and liver than that required for arsenite and the inhibition was partially prevented by excess zinc. These data suggest that gallium is the primary inhibitor of ALAD following dissolution of GaAs in vivo and that competition for or displacement of zinc from the enzyme active site may be involved in the mechanism of inhibition. The data also demonstrated the utility of including a particulate control group when assessing the chemical-induced toxicity of compounds administered intratracheally as particulate suspensions. Finally, measurement of heme precursors, e.g., ALA, in urine coupled with assay of red blood cell ALAD activity may be of value as an early biological indicator of GaAs exposure and/or toxicity.